Proceedings of the Fifth International Conference on
Volume

Developmental Act
    • : •-.. .    ..-vV;)--:'.

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     The Proceedings of the
Fifth International Conference
 on Fluidized Bed Combustion

               Volume III
       Developmental Activities
            12-14 December 1977
             Washington, D.C.
                Sponsored by

            U.S. Department of Energy
             with the cooperation of
        U.S. Environmental Protection Agency
            and the assistance of the
            Tennessee Valley Authority
                  and the
          Electric Power Research Institute
                Coordinated by
       The Metrek Division of The MITRE Corporation

               Charles Pliss. rditor
           Barbara M. Williams. Associate Editor

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orally presented are nevertheless  included  in  this  volume.   Accordingly,
these papers do not have author introductions  and the transcript  of
the question/answer session afterward.   Introductions and question/
answer dialogue as taken from the  taped  record of the conference  and
edited for the Proceedings, appear for all  papers otherwise.   In  most
cases, the speaker reviewed the record for  his paper and edited it
for clarity and accuracy.

     For convenience in referencing,  an  Appendix contains the  tables
of contents for Volumes I and II.   An index of authors for  all the
papers in the three volumes follows.
                                  iv

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                     Table of Contents
                          Volume III
INTRODUCTION
TEST INSTALLATIONS                                              1

  Atmospheric Fluidized  Bed Component  Test                       4
    and Integration Facility-An Update:
    J. W. Byam and J.  S.  Wilson, Morgantown
    Energy Research Center; Charles C. Space,
    Reynolds, Smith and  Hills, Jacksonville,
    Florida

  B&W/EPRI's 6'  x 6' Fluidized Bed Combustion                   24
    Development  Facility:  An Overview:
    D. L. Bonk and T.  E.  Dowdy, Babcock and
    Wilcox Company, Alliance, Ohio; T. E.
    Lund, Electric Power Research Institute,
    Palo Alto, California

  Industrial Fluidized Bed Program:  A Status                   33
    Review:  William R.  Norcross, Combustion
    Engineering, Inc., Windsor, Connecticut

  Atmospheric Fluidized  Bed Combustion Technol-                 55
    ogy Test Unit for  Industrial Coaeneration
    Plants:  R.  S. Holcomb and Arthur  Fraas,
    Oak Ridge National Laboratory, Oak Ridge,
    Tennessee

  ERCO's Fluid Bed Combu'-Lion Development                       73
    Facility: James H.  Porter, Energy Resources
    Company, Inc., Cambridge, Massachusetts
  Results of Recent Test  Program Related to AFB                 82
    Combustion Efficiency:  R. Reed, C. Aulisio,
    and R. Divilio, Pope, Evens and Robbins, Inc.,
    Alexandria, Virginia

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Table of Contents                                               Page


  Pressurized Fluidized Bed Combustion Compo-                    102
    nent Test and Integration Unit (CTIU):
    Design Status:  W. F. Podolski, Argonne
    National Laboratory, Argonne, Illinois;
    R. W. Crawford, Steams-Roger Engineering
    Company, Denver, Colorado

  Further Experiments on the Pilot-Scale Pres-                  123
    surised Combustor at Leatherhead,
    England:  H. R. Hoy, A. G. Roberts, and P.
    Raven, National Coal Board Coal Utilisation
    Research Laboratory, Leatherhead,
    England

  Solid Tracer Studies in a Tube Filled Fluid-                  135
    ized Bed:  T. Fitzgerald, N. Catipovic,
    and G. Jovanovic, Oregon State University,
    Corvallis, Oregon

  The Effects of Finned Tubing on Fluidized Bed                 156
    Performance:  Gabriel Miller, Victor Zakkay
    and G. Kiviat, New York University, New York,
    New York

  Industrial Application of Fluidized Bed Com-                  184
    bustion - Single Tube Heat Transfer Studies:
    D. C. Cherrington, L. P. Golan, and F. G.
    Hammitt, Exxon Research and Engineering
    Company, Florham Park, New Jersey

  Fluidized-Bed Combustion of Lignite and Lignite               211
    Refuse:  J. S. Mei, U. Grimm, R. L. Rice, and
    J. S. Halow, Morgantown Energy Research
    Center, Morgantown, West Virginia

  Battelle's Multisolid Fluidized-Bed Combustion                223
    Process:  H. Nack, K. T.. Liu, and-G. W.
    Felton, Battelle Columbus Laboratories,
    Columbus, Ohio
                                 vi

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Table of Contents                                               Page


  Pneumatic Solids Injector and Start-Up Burner                  241
    for Battelle's Multisolid Fluidized-Bed
    Combustion (MS-F6C) Process:  G. W. Felton,
    R. D. Giamrnar, H. R. Hazard, and D. R.
    Taylor, Battelle Columbus Laboratories,
    Columbus, Ohio

  Fluidized Combustion of Beds of Large, Dense                   254
    Particles in Reprocessing HTGR Fuel:  D. T.
    Young, General Atomic Company, San Diego,
    California

  Research of Gas Combustion in Fluidized Bed                    268
    Plants:  K. Ye Makhorin and A. M. Glukho-
    manyuk, Institute of Gas of the Ukrainian
    SSR Academy of Science, Kiev, U.S.S.R.

  Combustion Experiments Within a Rotating Fluid-                275
    ized Bed:  C. I. Metcalfe and J. R. Howard,
    University ot Astoi ?r. Birmingham, Birming-
    ham,
  Centrifugal Fluidized Bed Combustion:  E. K.                   288
    Levy, N. W. Martin, and J. C. Chen, Lehigh
    University, Bethlehem, Pennsylvania

  Progress in the Development of the Desul-                      300
    phurizing Gasifier:  G. Moss, Esso Petroleum
    Company, Oxford, England

  A Technical Description of the Plant Design and                310
    Project Progress Report:  David H. Broadbent
    and S. J. Wright, National Coal Board (IEA
    Services) Ltd., London, England.
INSTRUMENTATION                                                  323

  A High-Temperature High-Pressure Isokinetic/                   326
    Isothermal Sampling System for Pressurized
    Fluidized Bed Applications:  James C. F. Wang,
    Carl G. Ringwall, and C. M. Thoennes, General
    Electric Company, Schenectady, New York
                                 vii

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Table of Contents
  Participate Analysis Instrumentation for Advanced
    Combustion Systems:  E. C.  Muly and E. S.  Van
    Valkenburg, Leeds and Northrup Company, North
    Wales, Pennsylvania

  Particle Field Diagnostics Systems for                         362
    Fluidized Bed Combustion Facilities:
    William D. Bachalo, Spectron Develop-
    ment Laboratories, Inc., Costa Mesa,
    California

  A Particulate Sampling System for Pressur-                     379
    ized Fluidized Bed Combustors:  William
    Masters and Robert Larkin,  Acurex Corporation,
    Mountain View, California
MATHEMATICAL MODELING                                            403

  FBC-Modelling and Data Base:   S. E. Tung,                      406
    J. Goldman, and J. F. Louis, Massachusetts
    Institute of Technology, Cambridge,
    Massachusetts

  A Model of Coal Combustion in Fluidized Bed                    437
    Combustors:  J. M. Beer, R. E. Baron, G.
    Borghi, J. Hodges, and A. F. Sarofim,
    Massachusetts Institute of Technology,
    Cambridge, Massachusetts

  Fluid Dynamic Modelling of Fluidized Bed Com-                  458
    bustors:  A. Bar-Cohen, L. Glicksman, and
    R. Hughes, Massachusetts Institute of Tech-
    nology, Cambridge, Massachusetts

  A Mechanistic Model to Explain Ash Agglomeration               475
    in Fluidized Bed Combustors and Gasifiers:  A.
    Rehmat, Institute of Gas Technology, Chicago,
    Illinois; S. C. Saxena, University of Illinois
    at Chicago, Chicago, Illinois

  Dynamic Modeling, Testing, and Control of Fluid-               488
    ized Bed Systems:  D. A. Berkowitz, A. Ray, V.
    Sumaria, and M. Wilson, The MITRE Corporation,
    Bedford, Massachusetts

                                 viii

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Table of Contents                                               Page


PARTICULATES AND REMOVAL                                         501

  Evaluation of a Granular Bed Filter for Partic-                504
    ulate Control in Fluidized Bed Combustion:
    M.  S. Nutkis, R. C. Hoke, M. W. Gregory,
    and R. R. Bertrand, Exxon Research and
    Engineering Company, Linden, New Jersey

  Granular Bed Filters for Farticulate Removal                   516
    at  High Temperature and Pressure:  Richard
    D.  Parker, Shui-Chow Yung, Ronald G. Patterson,
    and S. Calvert, Air Pollution Technology, Inc.,
    San Dieqo, California; Dennis C. Drehmel,
    U.S. Environmental Protection Agency, Research
    Triangle Park, North Carolina

  Particulate Removal From Pressurized Hot                       538
    Gas:  Hiroshi Terada, Babcock Hitachi
    Company, Hiroshima, Japan; R. Yamamura,
    Japan Coal Mining Research Center, Tokyo,
    Japan

  Particulate Removal from Hot Gases Using the                   551
    Fluidized Bed Cross-Flow Filter:  Chaim
    Gutfinger, G. I. Tardos, and David Degani,
    Technion-Israel Institute of Techology,
    Haifa, Israel

  Filtration Performance of a Moving Bed Granu-                  567
    lar Filter:  Experimental Cold Flow Data:
    J.  L. Guillory, Combustion Power Company,
    Inc., Menlo Pack, California

  Mathematical Model of a Cross-Flow Moving Bed                  583
    Granular Filter:  H. F. Wigton, Combustion
    Power Company, Inc., Menlo Park, California

  Multiple Jet Particle Collection in a Cyclone                  607
    by  Reheating Fluidized Bed Combustion Pro-
    ducts:  Ken C. Tsao, Kuang T. Yung, and
    Jeffrey F. Bradley, The University of
    Wisconsin-Milwaukee, Milwaukee, Wisconsin
                                 IX

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Table oi Contents                                               Page


  Feasibility of Barrier Filtration Using Cera-                  620
    mic Fibers:  Michael A. Shackleton, Acurex
    Corporation, Mountain View, California

  High Temperature, High Pressure Electrostatic                  640
    Precipitation:  Paul Feldman, John Bush, and
    Myron Robinson, Research-Cottrel1, Inc.,
    Bound Brook, New Jersey


CORROSION AND EROSION                                            657

  Erosion/CorroGion of Turbine Airfoil Materials                 660
    in the High-Velocity Effluent of a Pres-
    surized Fluidized Coal Combustor:  Glenn R.
    Zellars, Anne P. Rowe, and Carl E. Lowell,
    NASA-Lewis Research Center, Cleveland,
    Ohio

  High-Temperature Corrosion of Metals and Alloys                682
    in Fluidized Bed Combustion Systems:  John
    Stringer, Electric Power Research Institute,
    Palo Alto, California; R. D. LaNauze and E. A.
    Rogers, Coal Research Establishment, National
    Coal Board,  England.

  Thermal Stresses and Fatigue of Heat Transfer                  700
    Tubes Immersed in a Fluidized Bed Combustor:
    L. Glicksman, R. Pelloux, N. Decker, and
    T. Shen, Massachusetts Institute of Technology,
    Cambridge, Massachusetts

  Turbine Materials Corrosion in the Coal-Fired                  714
    Combined Cycle:  R. L. McCarron, A. M.
    Beltran, H.  S. Spacil, and K. L. Luthra,
    General Electric Company, Schenectady,
    New York
SORBENT REGENERATION                                             737

  Thermodynamics of Regenerating Sulfated Lime:                  740
    F. M. Rassiwalla and T. D. Wheelock, Iowa
    State University, Ames, Iowa

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Table of Contents                                               Page
  Pressurized Fluidized Bed Coal Combustion and                 756
    Sorbent Regeneration:  L. A. Ruth, R. C. Hoke,
    M. S. Nutkis, and R. R. Bertrand, Exxon
    Research and Engineering Company, Linden,
    New Jersey

  Development of a Process for Regenerating Par-                776
    tially Sulfated Limestone from FBC Boilers:
    J. C. l.ontagna, F. F. Nunes, G. W. Smith,
    E. B. Smyk, F. G. Teats, G. J. Vogel, and
    A. A. Jonke, Argonne National Laboratory,
    Argonne, Illinois

  Regeneration of Lime-Based Sorbents in a Kiln                 798
    with Solid Reductants:  Ralph T. Yang,
    James M. Chen, Gerald Farber, Ming-Shing
    Shen, and Meyer Steinberg, Brookhaven
    National Laboratory, Upton, New York

  Evaluation of Sorbent Regeneration Processes                  811
    for AFBC and PFBC:  R. A. Newby, S.  Katta,
    and D. L. Keairns, Westinghouse R&D  Center,
    Pittsburgh, Pennsylvania

  An Engineering Study on the Regeneration of                   832
    Sulfated Additive from a Fluidized-Bed Coal-
    Fired Power Plant:  J. H. Bianco, D. A. Huber,
    J. W. Morton, and R. M. Costello, Burns and Roe
    Industrial Services Corporation, Paramus, New
    Jersey

  Economic Feasibility of Regenerating Sulfated                 851
    Limestones:  E. B. Smyk, J. C. Montagna,
    G. J. Vogel, and A. A. Jonke, Argonne
    National Laboratory, Argonne, Illinois


APPENDICES                                                      865

  Appendix A - Table of Contents - Volume I                     A-l

  Appendix B - Table of Contents - Volume II                    B-l

  Appendix C - Author Index                                     C-l
                                 XI

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Test Installations

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                         INTRODUCTION

   .  WAYNE A.  HcCURDY,  CHAIRMAN:  Our first speaker this morning is
John Byam from the  Morgantown  Energy Research Center, who is in charge
of our project for  the  construction of the CTIU component test and
integration unit—the atmospheric unit.  John received his Bachelor
of mechanical  engineering degree from the University of Minnesota in
1966.  He was  fortunate enough, if you want to use the words, as I
was at one time, to serve 4-1/2 years in the Navy.  From 1971 to 1977
he was with the Gas Turbine Division of General  Electric Company.
He is now with the  Morgantown  Energy Center and in charge of the
project being  built on  the West Virginia University Campus.  John?

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                      Atmospheric Fluidized Bed Component Test
                          and Integration Facility-An Update
                                    JohnW  Byam.Jr.
                                     John S. Wilson
                                  Department of Energy
                            Morgantown Energy Research Center
                                    Charles C. Space
                                 Reynolds. Smith and Hills
ABSTRACT
       The recent energy crisis has brought about an awareness of the growing depen-
dence of the United States on foreign energy supplies.   To reduce the nation's
dependence on foreign energy sources, the Department of Energy (DOE) has taken the
lead in promoting and advancing atmospheric fluidized bed combustion projects for
the direct utilization of coal in generating electricity and process heat for industry.

       This paper consists of an update on the design and construction of the Atmos-
pheric Fluiclzed Bed Component Test and Integration Facility (AFBC/CTIU) which will
be sited by DOE on the campus of West Virginia University. 1  The pape*- presents a
brief history of the project, discusses the final facility design pa..meters and
reviews the current procurement/construction progress.   The flexibility for equipment
configuration changes which have been designed into the facility and its systems is
discussed in detail.  Plans for the initial testing program at the facility are
discussed.


INTRODUCTION

       The Atmospheric Fluidized Bed Combustion Component Test and Integration Unit
(AFBC/CTIU) currently under design and construction by the Department of Energy was
first conceived in mid-1975.*  The facility is intended to be used in developing, with
subsequent optimization, the hardware systems required for successful commercialization
of utility and industrial atmospheric pressure fluidized bed combustion units.  The
size of the facility is such thaf. prototype commercial scale components can be utilized,
yet small enough to allow rapid modification of equipment and substitution of compo-
nents without requiring excessive renovations.  Extensive instrumentation is incorpo-
rated so that all aspects of fluidized bed combustion and support system operation can
be analyzed in detail.

       The major objectives of the AFBC/CTIU include the evaluation and testing of
materials, components and instrumentation and their integration into a workable
fluidized bed boiler system.  The specific objectives include:

       •  The testing of mechanical components, subsystems and systems to develop
          optimum configurations.

       •  Investigation of the dynamic behavior and control of an Integrated stacked
          multi-cell fluidized bed boiler.

       •  Evaluation and optimization of boiler internal configuration for emission
          control and stable operation.

       •  Provide rapid data dissemination through "hands-on" access for component
          designers, manufacturers, and research engineers.

       The facility will provide a focal point for hardware development, process
optimization and scale-up analysis in the national atmospheric pressure fluidized bed
combustion program for industrial and utility applications.

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       Within the fluidized bed combustion cells, there are several research areas
that will be addressed.  These areas include:

       •  Air distributor:  type, location with respect to tube bundles, sealing
          methods and expansion tolerance.

       •  Tube bundle material:  spacing, stresses, corrosion and erosion factors.

       •  Solids injection and removal points:  number, type and location.

       •  Sectionalizing of air plenum:  local fluidization for studying startup and
          turndown.

       •  Freeboard height and above-bed convective tube bundle location for
          freeboard disengagement and quench.it.,> of combustion reactions.

       •  System control schemes for operation of the unit to follow load demand
          typical cf a utility installation.

       The control system for the CTIU requires development and analysis of combustion
controls and safeguards.  Analytical instrumentation will be provided to enable adequate
acquisition of data for performance evaluation and system optimization.  An initial
control algorithm will be established for implementation into the hardware of the
electronic analog system.  In addition, a direct digital control system will be
installed in parallel to the hard-wired analog system so that the algorithm may be
modified to test alternative control schemes.  The two control systems will permit
transfer from one system to the other during operation to test and compare the
algorithms contained in each as well as to provide a full backup control system for
the facility.

       The systems external to the steam generator which will be of a developmental
nature include:

       •  A fuel stream splitting system for controlled size and weight distribution
          to multiple feed points.

       •  A hot bed material (up to 200(PF) handling system for removal, classification,
          storage and reirjection into the combustion cells of spent bed material.

       •  A hot fly ash stream transport system for storage, splitting and reinjection
          into either the carbon burnup cell or into the main cells of hot ash
          collected by the cyclones.

       •  Particulate removal systems for entrained ash.

       •  Calcium sulfate regenerator system as a design concern for future installa-
          tion.

       Each of these areas is involved with the development of systems to optimize
commercial application of fluidized bed combustion technology.

       To assist in the development of these auxiliary systems, the facility is
tailored to allow easy access to components so that they may be modified or replaced
with alternative hardware in the course of the test program.  The actual development
work will be stimulated in the private sector by providing access to a well-instrumented
test facility.  The initial system configuration will be based on the state-of-the-art
hardware which has been applied in the DOE-sponsored Rivesville installation as a
result of operating experience.  Beyond the initial configurations, second generation
system prototypes will be sought which can be tested in the CTIU after manufacturer
development.

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SYSTEM FLEXIBILITY

       In order to meet the research goals for the project, the design includes the
allowance for a greater overall flexibility than most facilities.  The steam generator,
support systems and special arrangement are all designed to provide for rapid recon-
figuration of operating modes, system controls, and actual hardware.

Steam Generator

       The steam generator is a vertically stacked, three cell boiler as shown in
Figure 1.  The bottom two 6 ft. x 6 ft. cells are coal burning anJ the 3 ft. x 6 ft.
carbon burnup cell is located at the top of the stack.  Preheated combustion air enters
each cell below a perforated air distributor plate and rises through the fluidized bed.
existing the boiler after gas quenching in the convection section.  The supporting
equipment is capable of obtaining velocities of 4-16 feet per second with expanded bed
height of between 2 and 8 feet.  Gas retention times between the top of bed and the
convection tubes under these modes of operation are in the range of .5 to 3 seconds.

       The basic configuration of the unit allows for removal and replacement of all
tube bundles both in bed and above the bed.  Replacement bundles with different tube
numbers, diameters, and spacing will be tested in the unit.  In addition, Figures 2
and 3 illustrate two operational modes of superheater arrangement which will be tested
for the effect on turn-down control.  Both these modes of operation can be accomplished
by valving alone.

       It is recognized that at higher velocities, with less than 1 second retention
time, it might be desirable to increase the freeboard for certain experiments.  Ar.
increase of some 12 equivalent feet is possible under the alternate configuration shown
in Figure 4.  In this mode, the convection bundles are removed from cell A and rein-
serted in the flue gas duct downstream of the boiler.  Under this operation, the
retention time can he increased to approximately two seconds at maximum velocity.  Since
the cross section of the flue gas duct is reduced, the superficial velocity in the
reconfigured convection system is approximatley doubled, allowing further experiments
in convection section performance.

       Further increases in retent.'on time can be obtained in tho. operational mode
shown in Figure 5.  With the removpl of cell A convection section and removal of the
internals of the lower portions of cell B. the unit can be operated as a single cell
with a freeboard of 44 feet.  This results in the ability to extend retention tioc to
11 seconds at 4 feet per second, or 2.7 seconds at 16 feet per second.  Other experi-
ments at velocities up to 32 feet per second are also possible in this configuration.

       Another goal of the unit is to investigate performance of the submerged tube
bundles.  In addition to the previously state' ability to change tube bundle con-
figurations, it is desirable to investigate .the effect of variable distance between
the air distributor and the submerged tube bundle.  Since the physical relocation of
the bundles at different elevations was considered quite difficult, another method
was developed.  Figure 6 illustrates the movable distributor place concept employed
in this ruit.  The distributor level can be adjusted up to 24 inches between runs to
allow these tests.

       Coal and sorbent feed and its distribution are important design concents.
Figures 7 through 13 illustrate seven separate feed schemes which con be employed
without modification to the steam generator.  Four of these schemes will require
little or no modification iu the piping system for tests.  Feed modes include:

       •  Mixed coal, limestone additives, etc., above bed         4 feed points

       •  Mixed coal, limestone additives, etc., below bed         4 feed points

       •  Coal at distributor level  limestone at higher level     8 feed points

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                         DRUM
FLUE GAS
FLUE GAS
FLUE GAS
        Figura 1. Baue Configuration of AFBC/CTIU Steam Generator Colb

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                  BASIC SUPERHEATER
                  ARRANGEMENT
                  (MODE A)
00
            CONOENSATE
            RETURN	
            SYSTEM
                         AIR COOLED
                         CONDENSER
            WVU STEAM
            DISTRIBUTION,,
            SYSTEM      H
                            PEGGING STEAM
                             TO DEAERATOR
                                                  CECONQMIZER
                                                     CBC
                                                    BOILING
                                                    CELLB
                                                 C BOILING
                                                 C  BOILING
  C BOILING
                                                   CELL A
  (PRI. SUPERHEATER I
                                                  STEAM SYSTEM
                                                   FOR CTIU
                                                 CSEC. SUPER HEADER
                ,   ATTEMPEKATOR
DESUPERHEAT AND
PRESSURE REDUCTION

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                    SPLIT SUPERHEATER
                    CONFIGURATION
                    AS SHOWN
                    (MODE B)
VD
             CONDENSATE
             RETURN
             SYSTEM
                         AIR COOLED
                         CONDENSER
             WVU STEAM
             DISTRIBUTION^
             SYSTEM •*-
                              PEGGING STEAM
                              TO DEAERATOR
                                                     CBC
                                                    BOILING
                                                    CELLB
                                                 C BOILING
                                                  fPRI. SUPERHEATER |     I
    BOILING
                                                    CELL A
    BOILING
                                                             —I
                                                  (SEC. SUPERHEATER^
                                                                  ATTEMPERATOR
                                                                       d
DESUPERHEAT AND
PRESSURE REDUCTION*
              CONDENSATE
              RETURN
              SYSTEM *	
                                                                                                STEAMSYSTtM
                                                                                                   FOR CTIU
                                   FORCED CIRCULATION
                                         PUMPS
       PEGGING
       STEAM
         CONDFNSATE
         RETURN
   _      MAKE-UP
DEAERATOR )*ATER
j	i/
r~\ FEEDWATER
L J HEATER
                                                                                                'BOILEI FEED
                                                                                                 PUMPS
                                                        Figure 3.

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                                           DRUM
                     BUNDLES  REMOVED
                     AND REINSTALLED
                     IN FLUE GAS  DUCT
                           Figure 4. Alternate Configuration Retocat* Convection Section
                                          10
b,

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                      DRUM
CELL  B' BUNDLE
REMOVED

DAMPER
FLANGES
BANKED OFF

CELL 'A* BUNDLE
REMOVED
CELL B DISTRIBUTOR
SECTION REMOVED
           Figure 5. Alternate Configuration Combined Cell Operation
                        11

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                    FIXED TUBE
                    BUNDLE
                        OAL/SORBENT
                       FEED TUBES

                    MOVABLE
                    DISTRIBUTOR

                  ALTERNATE
                  LOCATIONS
                  OF DISTRIBUTOR
                        COMBUSTION
                        AIR
Figur*6. Variable Sub*nergซnce Arrangement
         12

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Figure 7.  Four Feed Tubes Above Combined
   Coal & Limettom Feed
Figure 8.  Four Feed Tubes Below
  Combined Coal & Limestone
       Feed Below Bed
  Figures. Eight Tubes Above Separate
        Coal & Limestone Feed
    Figure 10. Eight Feed Tubes
          4-Coal Below
        4 • Limestone Above
                                       13

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       1. Single Feed Above
Combined Coal & Limestont
Figure 12. Two Feed Tubes Above
   Separate Coal & Limestone
                              Figure 13.  Five Feed Tubes
                             Single Limestone Feed Above
                                Four Coal Feeds Below
                                      14

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       •  Coal below bed. limestone above bed                      8 feed points

       •  Single feed above bed mixed coal and limestone           1 feed point

       •  Separate coal and limestone feeds                        2 feed points

       •  Single limestone above bed. four coal feeds below        S feed points

Support Systetrs

       Coal and limestone feed supplies to the steam generator are designed to be
pneumatic system utilizing dilute phase flows.  These feed systems will be capable of
replacement with other industry designed alternatives for future tests.

       Material preparation and delivery to the above-mentioned equipment are con-
ventional in nature.  Provisions are made for single or double screening feed with or
without fines and all coal is capable of being dried to within 1 to 2 percent surface
moisture.  Coal from fines to 1-lnch size can be used in the unit.

       The hot bed material handling systems are designed to be operated at bed
temperatures of 1SOO F to 2000 F as well as reduced temperatures.  This will allow
component testing under either set of  -onditions. and tests to continue in the cool
state even if higher temperature components fail and must be temporarily replaced with
low temperature units.

       The control system is extensive - a system providing complete analog capability
with full digital redundancy.  Both unit operators and research operators control
panels will be provided with capability for parallel operation, simulation, and
substitution.

       These basic flow diagrams for the CTIU are contained in Figures 14-17.

Spatial Flexibility

       The facility arrangement allows greater working soace than commercial instal-
lations to provide for installation of newer components e-~, developed, and to limit
down time during installation of these components.


ENGINEERING PROGRESS

       The project conceptual design was begun by DOE in the fall of 197S and completed
in spring 1976.  A/E selection was completed in July 1976. followed by orientation and
concept validation.   The Preliminary Design Report was submitted for approval In March
1977 and with DOE scope modifications incorporated, finalized in late 1977.  Design of
the basic structure was completed in August 1977 and bids received in November 1977.
Bids were within the projected funds and WP-C accepted by DOE.  Construction should
begin in spring of 1978.

       The steam generator, along with fuel feed and hot bed material systems, is out
for bid with an opening date of early 1978.

       Preparation of specifications for virtually all advance procurement mechanical
and electrical equipment is complete, with specifications for pre-purchased primary
instrumentation and control systems to be completed in early 1978.  Design of the
balance of pre-purchased instrumentation components should be completed in late 1978.

       Overall facility design will be approximately 60 percent complete by the end of
December 1977.
                                           15

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               RAW MATERIALS    I
                                               PROCESS INC FOR USE
PRODUCT USC
a\
                                                                                                                                     FLUE  CAS
                                                                                                                                     TO LANDFILL
                                                                                                                                     (REUSE l\ FUTUREI
                                                                                                                                —-70 WVU
                                                                                                                                      FROM WVU
                                                              Figure 14. Simplified Flow Diagram

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Figure 15. MaterUh Receiving and Preparation Syttem AFBC/CTIU

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00
                                                                 ;   >uii        i
                                                                 |   WUINO     I
                                                                •^   STATICN     j		

                                                                 I	1



                                                                     Figurt 16. Air *nd Flut Gil Olqnm

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                                                                                     TO 10 FAN
                                                                                     	ป•
                                                                                     AND STACK
                                                                               i—1—I WEIGH
                                                                                     BUNKER
                                          SPENT BED
                                          RECEIVING
                                    V  /  BUNKER
                                      XX     ^ta^_
                                                                               ASH COOLER
COOLER
                                                       ASH AND BED REMOVAL SYSTEMS
                                        Figure 17.

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TESTING PROGRAM

EPA Support and Integration

       The Morgantown Energy Research Center CTIU project team has worked closely with
EPA to incorporate sampling access points into the CTIU equipment and systems design so
that efficient effective sampling may be done.

       In addition to stack gas sampling, the facility has the capability to sample
both feed materials and waste discharges at several selected points.  In addition.
there will be a capability to provide large quantities (up to several tons) of spent
bed material as well as ash from the several cyclones for EPA waste disposal testing
progre -s.

       The facility design will also permit testing of the EPA mobile oarticulate
control devices on a slipstream of the flue gas froc the CTIU steam generator.  The
devices to be tested include a mobile scrubber, baghouse and electrostatic precipitator.

       EPA will likewise provide inputs to the basic 30-month test plan being developed
for the facility.  They will evaluate such items as coal/sorbent selections, the span
of AFBC operating conditions, total operational range of the steam generator and
system configurations with a goal of providing recommendations to enhance sulfur
removal within the FBC.

Optimization of Components

       One of the main areas of intense investigations during initial operations of the
CTIU facility will be optimization of the material feed and hot bed removal systems.
Proper design and operation of these systems on utility fluidized bed boilers will be
highly dependent on successful resolution of those problems.

       Other testing will place emphasis on evaluation of the boiler components and
optimization of a dependable control algorithm for fluidized bed electric power
generation units that will meet the demands of the electric utility and industry with
reliability and dependability.


SCHEDULE STATUS

       The project has moved front the preliminary design phase into detail design and
procurement of components.  The preliminary engineering phase of the project was
completed in early 1977 and detail engineering of equipment and systems is approximately
60 percent complete.  Bid packages have been issued on the steam generator and most long
lead equipment.  The general contractor for the site preparation and building construc-
tion is under contract and the steam generator contract is due to be let in early He:ch
1978.  Site preparation and building construction are exoected to start in March of
1978 with boiler installation expected to begin in mid-1979.  Functional checkout of
all systems should begin in June of 1980 and the facility will be operational by
October 1980.


SUMMARY - LOOKING AHEAD

       This paper has discussed the design refinements and procurement activities of the
Atmospheric Fluidized Bed Component Test and Integration Unit during the last six months.
To summarize, during this time period, modifications to the equipment scope of the
project have been incorporated into the detail design, and procurement packages have
been released for the site preparation equipment and miscellaneous other equipment.  The
b*H package for the electronic Analog-Direct Digital Control and Data Acquisition System
is due to be issued shortly.
                                          20

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       By June of 1978 it is expected that all major items of equipment will be on order
and the steam generator design will be complete.  Construction on site will be underway
and overall design of the facility will be complete except for some details of equipment
location and electrical interfaces.  The test plan is expected to be drafted during this
time period and Morgantown Energy Research Center will be working closely with EPA to
ensure the facility effectively supports the EPA efforts to establish realistic meaning-
ful restrictions for AFBC emissions.

       As construction approaches completion, the final test plan and equipment shake-
down will be coordinated by a contractor who will be selected by DOE to operate the CT1U
facility.
REFERENCES
    Wilson.  J.  S.,  "Design Status of an Atmospheric Pressure Fluidized-Bed Combustion/
    Component Test  and Integration Unit", Fluidized-Bed Combustion Technology Exchange
    Workshop. Volume II.  MITRE Corporation/Metrek Division.  McLean. Virginia. 1977.
    pp.  3-15.
    Wilson.  J.  S.  and Gillmore, D.  W..  "Conceptual Design of an Atmospheric Fluid-Bed
    Component Test  and Integration Facility".  Proceedings of Fourth International
    Conference on  Fluidized-Bed Combustion,  The MITRE Corporation. McLean, Virginia,
    1975. pp. 187-197.


                                          21

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          QUESTIONS/RESPONSES/COMMENTS
    ALBERT JONKE, CHAIRMAN:  Are there any questions, then,  for
Mr.  Byam on the  atmospheric CTIU?  There are two microphones  on the
floor, and please come to the microphones and identify yourselves.
Well, it looks like Mr. Byam did a very good job, and we covered all
the  questions.
                               22

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                          INTRODUCTION
     WAYNE A.  McCllRnY,  CHAIRMAN:  Our next speaker is Ton Howdy, who
is a Research  Engineer  at  the  Rahcock and Hi 1 cox Alliance Center.  He
served as a principal investigator  for the study conducted for EPRI
of atmospheric pressure fluidized bed conhustion applied to electric
utility large  stean generators.  He had responsibility for the
environmental  factors in that  program.  He is currently responsible
for the process design  test  program and data analysis of the 6 foot
by fi foot fluidized bed conbustion  development facility described in
the paper to be presented.  Mr. Dowdy has a  Bachelor of Chemical
Engineering and Master  of  Science in Chemical Engineering degrees
from the Georgia Institute of  Technology.  Tom?
                                 23

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                           B&W/EPRI's6' x6' Fluidized Bed
                           Combustion Development Facility:
                                     An Overview
                            Thomas E. Do vdy and Donald L. Bonk
                              The Babcock & Wilcox Company
                                     Terry E.Lund
                            The Electric Power Research Institute
SUMMARY
       The Babcock & Wilcox Company has built under an Electric Power Research Institute
(EPRI) contract a 6* x 6" atmospheric pressure fluidized bed combustion development
facility.  This unit is designed to be a versatile, we11-instrumented and readily modi-
fiable research tool.  It is large enough to bridge the gap between '.he bench-scale/
pilot-scale test facilities now in operation and the large semi-commercial demonstration
units now being proposed.

       The design of the Fluidized Bed Combustion Development Facility began in Febru-
ary 1976.  The unit's first firing of coal and generation of steam occurred on
October 20, 1977 during the initial shakedown tests.

       Tests are currently being performed to characterize the unit.  The initial test
program is designed to characterize coal combustion performance and to gather the heat
transfer and other data needed for economic and engineering analyses of the process.


INTRODUCTION

       Babcock & Wilcox has studied the fluidized-bcd combustion process since the early
1950's, but the intensity of this involvement has increased during the pasปt few years.
In 1975 b&W conducted a literature survey under an EPRI contract(l) to ascertain the
state of the art for atmospheric fluidized-bed combustion as appliu to utility steam
generators.  During this study B&W examined the overall status of fluidized-bed combus-
tion related to heat transfer.  -
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It was further agreed that the unit should be sized  to represent an  intermediate  scale
between bench-scale test units and the proposed  semi-commercial demonstration units.
with provisions for multiple coal feed points within  the bed.  Other important  d  sign
considerations required that the unit be small enough to be easily r.odified and •  conomi-
cally operated, yet capable of operating over a  wide  range of  test conditions.

       Based on this design philosophy, a 6' x 6' square bed .-rea was selected.   Four
feedpoints were to be placed at the state-of-the-art  spacing of one  feedpoint per 9
square feet of bed area, with design allowances  for  operating  with fewer  feedpoints.
This unit was designed to generate steam, but only the amount  needed to he.-.t the
Alliance Research Center (ARC). B&W's research facility ar Alliance,  Ohio.  Condensing
the steam and recycling treated water Lack to the unit would provide operational  cost
savings.

       Once the overall bed size ซปnd steam producing  capabilities were defined, it was
possible to establish the other basic design parameters listed in Table II.


                    Tablt II.  Design Parameters  (Nominal)
                    Bed Area
                    Superficial Velocity
                    Coal Feed Rate
                    Heat Rate
                    Saturated Steam Production
                    Superheated Stc-v.i Production
                    Bed Operating ?t..lerature
6' x 6*
I fps
1880 Ib/hr
10.000 Ib/hr at 150 psig
2.000 Ib/hr at 1000ฐF
M600ฐF
       An artist's rendition (Figure 1) Identifies the major components of  the  facility.
Coal and limestone are co. veyed to the top oC the ARC Boiler Room where they arc  crushed,
then transported either directly to two separate bunkers or through an intermediate
screening operation.  Coal and limestone from the bunkers are fed through separ.-ite weigh
feeders into a common transport line.   The feed solids are picked up by transport air
and carried to a splitter where they are separated into four equal feed streams.  These
pass up through the windbox and the distributor piatc into the corrbustion zone  of the
fluidUed-bed boiler.

       Forcfd draft air to the fluidized bed is supplied by a Spencer turbine centrif-
ugal blower capable of delivering 6,000 cfra at a 60-inch water ^.luyi- head.  The corr.bus-
tion air supplied by this fan first passes through a steam prehcater and then through a
direct-fired preheatcr before it diverges into the four separate ducts entering the wind-
box.  Each of these ducts has a separate damper and venturi flowmcter for control and
measurement.

       The windbox itself is split into four quadrants.  This division of the windbox
allows us to isolate bed "slumping" to one or more segments of the bed while the  other:;
function normally.  Slumping will be studied as a possible means of turning down  the
boiler.  Startup and shutdown of the unit will also be facilitated by this windbox sep-
aration.

       The distributor plate is currently made of woven Ni-Chrome wire that has been
calendared to obtain a specified pressure drop at a design flow rate per square foot of
bed area (10-inch water pressure drop at 8 feet per second).  The distributor plate and
windbox have been designed as a unit that can be lowered from 20 ir.ches below (initial
position) to 40 inches below the immersed tube bank.

       The main furnace structure of the fluidized bed test facility consists of an
atmospheric pressure water wall with fireside refractory lining.  This tr.ethod of con-
struction will facilitate changes in the configuration of the furnace by inserting
additional penetrations if necessary.   This can be done by simply cutting a hole  through
the external and internal water walls  and the refractory liner,  and seal-welding a pipe
liner into place.
                                          25

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                                                             WATER JACKET VENTS
GAS DISCHARGE
                                                                               '   SAMPLE PORTS
             AIR HEATER
                                                                      RECIRCULATION PUMPS
                          Figure 1. Fluidized Bed Combustion Development Facility
                                               26

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       The immersed tube bank consists of a serpentine arrangement of eleven  1-1/2  inch
tubes on a 3-inch triangular pitch.  A cross section of the tube bank is shown  in
Figure 2.  Two tubes, designated "C" and "E", will be used for heat  transfer  studies.
The tubes are subcooled with high-pressure water taken directly from rhe plant  feedwater
system.  Increases in water temperature are measured by 32 thermocouples.  By measuring
the temperature rise and flow rate through each tube, heat transfer coefficients can be
calculated for various tube lengths.

       The upper portion of the tubes designated "H" and "I" are used as a superheater.
This superheater is also instrumented for heat transfer studies.  The balance of the
tube bank consists of steam generating tubes which will produce 130 psig sati rated  steam.
         COLUMN A
                   Figure 2. Tub* Bjnk A thermocouple Identification North Looking South


       As shown In Figure 1, an 18-foot freeboard Is located between  the  ircroersed  tube
bank and the convective cube bank at the top of the furnace.  This height was chosen  so
that tho larger particles thrown out of the bed would be  recycled onto  the bed;  i.e..
particles with a terminal settling velocity greater than  the fluidizinp velocity would
fall back.  This extended freeboard should also allow us  to determine what reactions
take place in the freeboard and the extent of freeboard combustion.  The tr.axiaun height
of the freeboard was set by existing building limitations.

       The convective tube bank at the top of the furnace serves two purposes.  First, it
cools the flue gas before it exits the furnace and enters the cyclone dust collectors.
Second, it produces additional saturated steam for heating the Alliance Research Center.
Space in the center of this tube bank has been allotted for a sootblover. if one is
found necessary.

       Four cyclone separators are mounted at thi furnace exit to collect particulates
escaping the furnace.  Dampers on each of the cyclones can be closed  to maintain reason-
able entering velocities and. by so doing, improve collection efficiencies.  Material
collected by the cyclones can be recycled to the bed or removed  from  the unit by the
ash-handling system.  Material to be recycled is fed from the cyclone hoppers through a
water-cooled conveyor.  After passing over an in-line impact flowaetcr. tho material
passes through a downcomer to the transport air line in the coal and  limestone  feed
system.
                                           27

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       The flue gas exiting the cyclones passes through a large venturi flowraeter and
then is spray quenched before entering the induced draft fan which carries it out the
stack.

       The boiling water circuit consists of a split steam drum and two recirculation
puxps which feed the immersed and convective tube banks.  Separate makeup and blowdown
systems are also provided.   This split-drum system provides flexibility for an experi-
mental unit and allows the craount of steam produced in each of the boiler circuits to be
measured.

       The bed (ash) removal system consists of five drain pipes which extend from the
bed through the windbox and the distributor plate to the basement.  Each ash pipe has
a separate shutoff valve controlled by an air cylinder.  Initially, only the center pipe
will be used to remove ash from the bed.  During an upset condition all of the pipes
can be opened to rapidly drain the bed of solids.  Presently the rate of bed removal is
controlled by the pressure drop across the bed.  This system can be easily modified so
that the control of solids removal is set either by bed temperature, the Input limestone
and coal feed rates, and/or a time sequence.


CONTROLS AND INSTRUMENTATION

       The controls used on the fluidized-bed combustion facility are similar to those
found in any boiler control room.  Steam and water circuits are controlled through
elcctropneumatic controllers receiving their input signals from flow elements mounted in
each of the lines of the boiler circuit (feed-water, blowdown, and rccirculating loops).
Controls for forced draft and induced draft fans are pneumatic and receive either air
control signals from the venturi flow elements mounted in the air/flue gas ducts or
measurements of furnace pressure.

       The rest of the control panel consists of toggle switches used to operate the
numerous air solenoids which control the air cylinders on the ash, cyclone, and coal
feed dampers.  The control elements for the facility are tied together through 14 inter-
locks.  These interlocks are designed to protect the facility and operating personnel
in the event of upset situations.  For example, flue gas exiting the furnace is monitored
for percentage of carbon monoxide present.  If the level of carbon monoxide exceeds 0.1%,
an alarm annunciates in the control room.  If the condition Is not corrected and the
percentage of carbon monoxide In the flue gas reaches 0.31, the entire coal feed system
automatically shuts down.

       Other instrumentation consists of seven gas and particulate probes used to moni-
tor the composition of gases and solids exiting the unit.  Data gathered from these
probes will be used in the overall effort to understand the mechanics of fluidized-bed
combustion.  All Information gathered by the flow measuring elements in the control
section of the system and the special instrumentation for gas and particulate analysis
is monitored by, or Input into, the data acquisition system.


DATA ACQUISITION SYSTEM

     The data acquisition system samples approximately 400 data channels at a rate that
varies from 50 readings a second (for short-term temperature oscillation tests; to one
channel every 6 minutes for channels on the pressure multiplexer.

       The data channels consist of approximately 200 thermocouples, 15 RTD's, 150 pres-
sure/differential pressures measured through a multiplexer, 20 control signals, three
weigh feeders, and eight gas analyzers.  The analog-to-dlgltal converter provides the
high resolution needed for the thermocouples as well as a high sample rate and random
addressing under computer control.

       Data is stored in a dedicated mini-computer and periodically transmitted Into the
Alliance Research Center's computer network.  It is then available for data reduction
and analysis on any of B&W's computers.  The 6' x 6* computer system does not perform
any control function but does provide a supervisory function by supplying operational
Information on a console.
                                           28

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TEST PROGRAM

       The test program for this 6' x 6' facility has been divided  into two parts:

          •  Base case testing
          •  Main test program

       Base case testing his been designed to characterize the- performance of our unit
at the various operating conditions which are sinilar to  those used on other fluidized-
bed units.  Further, base casi' testing will determine a set of base line parameters
against which future tes^*: can be evaluated.  The range of base case  test conditions  is
summarized in Table III.

                          Table II I. Base Case Tests
                    Coal                          1/4" x 0"
                    Limestone                     1'4" x 0"
                    Fluidizing Velocity           4 to 10  ft/sec
                    Bed Temperature               14^0 to  1600ฐF
                    Excess Air                    5 to 307.
                    Calcium-to-Suifur Xole Ratio  As needed  for KPA  Unit
       These conditions arc similar to test conditions run on B&W's  3' x 3'  fluidi:'.ed
bed and several other test units.  During the 6' x 6' testing, calciuu-to-sulfur -ole
ratios will be adjusted so that S0;> emission is approximately ihc Federal KPA designated
limit.  The bed depth during base case testing will be permitted to  vary as  needed,  to
obtain other conditions such as lower heat rates.  Once all the tubes are irnmers'-d  in
the bed, however, we will test deeper beds until our fan  limits are  reached.

       The initial test program is designed to investigate ways to obtain improved  car-
bon burnout (combustion efficiency) in a fluidized-bed combustor.  The first series  of
tests conducted will examine the elfects of recycle on carbon burnout.  During  this
scries of tests a constant mass flow rate of recycle material will b? returned  10 the
fluidizcd bed.  This flow will be m-ii:;*.ained until cquil   •iutn is reached wit!:in the
unit.  Equilibrium will be assumed when the inlet and r.-jtiet cyclone dust Io3iiin>;s.  bed
particle size, and rmount of cyclone catch material being diverted to d'sposai  have
reached steady state.  At this time, test data will be obtained.  The recycle rate will
then be increased and the test procedure repeated.

       It has been suggested that coal feed size distribution may affect co ibustion
efficiency.  To test this, base lest conditions for 1/8" x 0" coal and 3/S"  x 0" coal
will be compared t.o those run on a 1/4" x 0" coal.  Next, screened top si;:e  coal will
compared with the base case;  for oxrrople. -1/4" x 1/16" nnd -1/4" x  30 r.esh  will he  com-
pared with the base cas
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             QUESTIONS/RESPONSES/COMMENTS
     ALRERT A.  JOflKF,  CHAIRMAN:   Next  is Ton Powdy on the RAW 6' x 6'
conbustor.

     f'R. not.'DY:  Okay.  I  had  a  question fron Mr. Crawford at Stearns
Rogers:  "Have we ever,  during operation, experienced a tube failure
either in the watery/alls or in the coils?"  No, we have not; neither
in our 3* x 3*  facility  nor in the 6*  x 6', although the operational
experience on the 6'  x 6'  is fairly limited.  I don't guess I mentioned
it, hut we are operating the facility  now.  They are bringing it on
line today.  It was operating  last night and we tripped off due to a
materials handling problem, wet  limestone, which is a new one.  Wet
coal we've seen before,  hut not  the limestone.

     Mr. Reynard at Standard Oil  Company of Ohio:  "Would you elabo-
rate on your solids feed splitter?" And then he has several questions:
"How long is the vertical  section?"  It's about 12 to 15 feet long,
vertically upward into the splitter.   "Po you know the pressure
drop?"  Offhand I do not.   "What is the  I.D.?"  He have a 4-inch
schedule 40 pipe going up  into the splitter, and then coming out we
have four 2-inch diameter  schedule 40  pipes.  "What is the superficial
gas velocity?"  Me designed to keep it above RO feet per second.
However, we have run some  essentially  choking tests, and I don't know
offhand what we decided  was the  lowest velocity vie could operate at.
If you need additional information, and  if you could contact me at
the research center, I could get whatever you need on that.  Are
there any other questions?

     MR. HANSON:  Henry  Hanson from Fluidyne Engineering.  A ques-
tion about the lining in your 6'  x 6'. You mentioned the waterwalls,
and I thought I saw in one of the pictures here what looked like a
refractory brick lining.

     MR. POWPY:  Right.  The ambient waterwalls give you something
on the order of 220 degrees, at  the bottom, which we didn't think was
really typical  for the bed to see, so  one of the reasons we put in a
refractory brick lining  was to g-ive us some insulation and give us a
higher surface temperature.

     The other reason was  we tried it  on the 3' x 3' for abrasion
resistance purposes, without giving a  lot of thought to it, and it
works out well  there; and  v/e just designed the fi' x 6' the same way.
Any other questions?

     MR. POWPY:  I had a comment and a question from Derrell Young,
General Atomics:  "Can you easily modify to quickly recycle your
fines hot?  We had very poor burning results with graphite fines,

                                 30

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which are probably easiar to burn than fly ash,  when the fines  were
cooled before recycle, and/or when we tried nixing the fines back
with the feed."  He could modify to recycle hot.  "Easily"  is a
relative word.  It is not as easy to do as it will he to do cold.

     How, our reasons for doing it cold were that we do neter the
recycle feed back in.  We have a way to neter in the recycle lines,
so we can control a constant nass flow rate of recycle back to  the
bed.  To do it hot would require a different piece of equipment if we
tried to follow the sane technique.  The hot recycle method I an
familiar with would be a hot cyclone with a dip leg back into the
bed.  It is very difficult to know what the recycle rate is. We
could do it, however, without tremendous difficulty.

     ALBERT A. JONKE, CHAIRMAN:  Thanks, Tom.
                                 31

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                       INTRODUCTION

     GEORGE  WETH,  CHAIRMAN:  n,,r next speaker, Mr. Bill  Norcross  of
Combustion Engineering, received his degree in Mechanical  Engineering
from the New Jersey  Institute of Techno1ogy, and then proceeded
to join Cc;-bustion Engineering in 1960, where he has had jobs  in
standardization, value engineering, manufacturing and field construc-
tion of steam generators.  Today he is the Product Development
Manager for the  Industrial Fluidized Bed project at Combustion
Engineering, and is  responsible for the contract project management.
Bill, with that your present job, we certainly look forward to your
paper.  Mr.  Bill Norcross of Combustion Engineering.
                                32

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                            Industrial Fluidized Bed Program:
                                    A Status Review

                                    William R. Norcross
                                Combustion Engineering. Inc.

       Combustion l.r.gineer ing is currently developing an  industrial  fluiili zed-bed
boilc-r for the combustion of coal.  The contract,  initiated with the- l:ne;gy Research
anJ l>cvc-lopne;it AJnini strut ion  in July 1'.ป"<>, and now under the jurisd ic t i >n of  the
Department of Lncrgy, is scheduled  for completion  in the  first quarter  of H'Sd.  The
purpose of the program is to develop and commercialize a  shop-assembled,  ra i I -shippahl e,
natural circulation boiler.  Ihero are two distinct phases of the cont-.-ct  -- develop-
ment and demonstration.  The development, which began in  !'.)?(> and is scheduled  to
continue the entire length of the program,  is comprised of cold flow model ing and hot
flow modeling.  I he denionst rat ion phase, which is  scheduled to run  fron  the first quar-
ter of 197S to the fi'st quarter of  I'.'SO, consists of huildini; and demonstrating a
50,000 pounds of ste-..: per hour demons i rat ion unit.

       This paper is .: report on the status of the prog'an to date.  It  reviews the
cold flow nude I i UK and the construction of the hot flow .nodel.

       Cold flow model testing has been conducted    both two- and three-dimensional
flow models to provide design data  for the hot scale unit.  figure  I illustrates the
full-size .VI) cold flow model,   located at C-K's Kre i s i nger Dove lo-ment  i.aboratory (KOI.)
in IVitidsor, (.'onnect ic'it .  Air fron a blower is ducted into the plenum chamber below the
model and passes through the perforated plate and  limestone Jed.  The results of this
activity have been used to determine the conf i gurat ion of the inlet plenum and  distri-
bution plate, the air velocity through the bed, and the effects of sloped bed tubes on
fluid izat ion.

       The idea of defluidi'ing discrete sections  ,;f a fluidized bed for control of
stean generation ;lnj turndown has been discusse.l for years, hut very little operating
data is available.  In addition to the development program, cold flow testing was also
performed to evaluate def lu id i : i ng and ref luiil i z ing a section of a fluidizcd bed.  To
test for "slumped" bed operation, the model w.is modified  (l;ig. -)  by adding a 3 by 3-
ft section to the left of the boiler model.   i'his  section was inactive,  i.e., at the
beginning of the test, all the  limestone was placed in the ri;;ht section and during the
test, air flowed only through the right half of the bcJ.

       The "slumped" area accumulates additional  solids from the neighboring active bed
by lateral flow of fluidized ,-iteri.il and elutriation.  Testing indicated that with no
addition of bed material, the movement of materi.il f;om the active to the "slumped"
section approached equilibrium in approximately one hour  (l-ig. .VI.   The slope of the
material from the active to the "slumped" section  is about 3(1 degrees.   The addition
of a one foot high vertical wall between the active and slumped beds improved the
fluidization of the active section.

       This test work has provided basic design criteria  for the larger demonstration
fluidized-bed boiler.   A final  report on the cold  flow testing is being written and
will he released next  quartei.

       The characteristics of the actual process will be  identified by hot flow testing
in a complete f1uidized-bed steam generating system (l:ig. 41 also located at MIL.  The
design capacity of the installation is 2300 pounds per hour of superheater steam firing
approximately 300 pounds of coal per hour and using ICO poitnds of limestone per hour.
Dry coal will be received, crushed, screened, and  fed into a storage silo.  The crusher
can he bypassed if si:cd coal is supplied.  Limestone will be purchased as 1/8-inch top
size material and fed  via the screencr to the limestone bin.  Separate coal and lime-
stone vibra screw fc^i'.ers discharge into a rotary air lock mixing valve.  The mixed
fuel feed is transported pneumatically to the boiler through a single fuel line.

       Combustion air, supplied by a forced draft  fan, passes through a tubu!ar air
heater prior to entering the boiler.  An inlet d'ict burner will be provided for use
during start-up.   A  portion of the air from the tubular air heater is blended with FD
fan tempering air and  directed  to the bed start-up burner.



                                          33

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I'>- 1.  3D cnM llntv nnxlfl tysvem

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Figure 2.  Modified co*d flow model for slumped bed operation





                          35

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Figure 3. Efed tevel configuration for partial fluidization

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                                                  INDUSTRIAL FlUIOIZED  BED SUB-SCAlf UNIT
U)
                                                          Figure 4. Sub U4lซ unit Jchtmatlc

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       Gas side equipment  includes a mechanical  collector to control c;uhon loss and
improve boiler efficiency,  an air heater,  and a  hag filter.   Alter the collection
cquij::'ent, die gases pass  through an induced draft fan and stack.

       The ash hand! in.n system consists  of an ash cooler, rotary val,-e, and ash
collecting tank.  Calcined  limestone at  1550 I- will he cooled to 200 I' before being
fed to the collecting tank.   A vacuum coiiveyor system rcnoves the disposed solids from
the tank.

       The construction of  the sub-scale unit i.-  nearly completed.  Operation of the
plant is planned for late January 10TS.   Several  . .-cent photographs have been taken of
the fuel, air, and gas side  equipment.   A brief  description  of each illustration has
been included to identify  the system components.

       Figure. 5 is a photograph of the f In id i zeJ-bcd boiler  with the removable wall to
the left of the hoilcr.  In  the interior of the  boiler, horizontal heating surfaces and
the external  water circuits  can be seen.  '!hc evaporative heating surface, nade up of
the five tube circuits in  the removed panel  (Fig. <>). will be ip.mcrseJ in the bed.
Three of the  circuits continue to Co nn the water-cooled wall anJ two circuits arc
designed to allow evaluation of the performance  of the bed surface.  Hgure 7, the
exterior view of the panel,  shows the flanged surfaces which are the inlet and outlet
connections of the bed test  loop circuits.  The  circuit has  beer, arranged to provide a
method to determine heat  transfer and fluid flow  characteristics of this critical
design area.   The data will  be used to confirm natural circulation design parameters
for operation at the lower  operating pressures associated with industrial-type boiler
p 1 a n t s .

       Dust collection equipment has been selected to provide flexibility in testing
the performance of the boiler with respect to re in ject ion of unhurnt carbon particles.
Figure S shows the cyclone's inlet.  Two of the  three cyclone collector tubes can be
closed off, as required,  to  vary the quantity of  recycled material and allow determina-
tion of cyclone efficiency.   Figure 0 is a view  of t lie cyclone re inject ion line to the
ho i1e r.

       The tubular air heater and bag filter equipment are shown in Fig. 10.  The ait
heater is upstream of the  ha;; house to protect the bag fabric from the 3!MI F gas
temperature entering the bag bouse.

       The forced draft fan  is shown in  Fig. II-   The horizontal line from the fan
discharge is the transport  air to the fuel feed  systera.  After the air leaves the
tubular air heater  it enters the plenum Juct beneath the  fluidized-bed boiler.  Figure
IJ shows the  inlet to the  boiler and the in-duct  preheat burner.  'ibis burner is only
used during start-up to raise the air temperature to appro*, ima t el y <>IHI I.  After the
unit is operating, the tubular air heater will perform this  function.  Figure I." is a
view of the bed burner opening.  N'ext to the opening is thr  fuel feed line and above
the opening are the cyclone  re inject ion valves and piping.

       Coal and limestone  preparation occur in a  separate enclosure located immediately
behind the air and gas side  equipment area.  Coal is crushed and then transported in
the vertical  elevator shown  in Fig. 14.   The crusher bypass  line is shown in the fore-
ground.  From the elevator  the coal or limestone  is discharged into the classifier
screen (Fig.   15).  The fully enclosed scrcener bus been selected to allow l/-l-ir.ch size
and smaller particles to pass through the steel  wire cloth.

       Coal and limestone  bins are provided with  live bottom activators.  Figure I (>
shows the bin bottoms and  the extra outlets that  have been provided for removing the
material without disconnecting the continuous weigh belt feeders.  Figure IT is another
view of the bins and feeders.  Also shown is the  rotary air  lock blender valve and the
transport air line to the  fuel feed piping.

       Other construction  activity includes the  installation of wiring and instrumen-
tation.  Wiring between the tnotur control center  and the various motors, pumps and fans
is  currently being completed.  Instrumentation wiring to the control room has begun.
Control room  instrumentation panels arc  assembled anil will he transported to the control
room platform using specially designed lifting rigs.

       The sub-scale facility is an integral part of Combustion Engineering's program


                                           38

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FiguraS. Fluidizod bed boiler
            39

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Figure 6. Removable wall p*nซl - fumaot udซ
                 40

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Figure?. Rwnonbkwallpซปl-titeriorudซ
                  41

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Fiytrt 8. Mซchปnical dint eolttctor - (cyclone) mWt tid*
                          42

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Figurt 9. Cyclone r*tnjซclK>o fyiMm
               43

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Figure 10. Tubular •ป hrat*r and txgfilttr
                44

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                                                        \
Figurall. Forced draft t*i
          45

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Figure 12. Boiler mitt pltnum md air preheat burner
                    46

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Figun13. Bed burner opening
              47

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Coปl crujh*r
      48

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CtaHifiv lawn
49

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Fiqure 16. Coal and linmtocw turn
            50

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Fuel tซedซn and rotary air lock ปu. -.
        51

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to develop and commercialize fluidizcd-bcd  combustion for  the  industrial  market.   This
installation will  provide the necessary  information  to demonstrate  the  near  term  appli-
cation of this technology.
                                           52

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           QUESTIONS/RESPONSES/COMMENTS


     MR. NORCROSS:   I have two questions that were asked of me.  This
Is on the Combustion Engineering work.  One is  from John Boland,
Trane Company:   "Are the in-bed tubes sloped, and at what angle?"

     You will recall in the cold flow test, I mentioned that the
variably inclined tubes were tested to see what their effect was on
fluidization.   Yes, the in-bed tubes are sloped at 7 degrees.

     I might mention Georgetown University—I don't know if there is
a representative here from Georgetown, so I will just hint that they
have sloped tubes also in their fluidized bed demonstration plant,
another industrial application.

     Ken Chipley, Oak Ridge National Laboratory, asks:  "Are the
walls in the bed region of the 3-by-3 unit watercooled or refractory
insulated?"

     The unit is a welded-wall, watercooled construction.  When you
read the paper, you will notice that the bed area has been refractory
lined.  The explanation for that is:  since the scale of the unit is
such that we have an over-abundance of heat transfer surface in that
lower bed area, we are trying to bias (i.e., eliminate) the furnace
cooling effect  in order to give us good data on heat transfer in the
bed tube circuits.  Thank you.

     CHAIRMAN:   Thank you.
                                53

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                          INTRODUCTION
     WAYNE A. McOJRDY,  CHAIRMAN:   Our next  speaker  is Art Fraas who was
engaged in the design and development of advanced energy conversion
systems at the Oak Ridge National  Laboratory from 1950 until his sup-
posed retirement in October 1976.   He proposed  designs and directed
development work on a variety of  systems including  fluidized bed coal
combustion, gas turbine generation units.  He proposed the closed
cycle oas turbine combustion system for cogeneration  in 1973. arid was
Manager of High Temperature Energy Conversion Systems at Oak Ridge at
the time of his retirement.  He was named a Corporate Enginte.ing
fellow of the Union Carbide Corporation which operates ORNL and is a
fellow of the American Society of  Mechanical  Tngineering.  Art?

     MR. FRAAS:  Thanks, Wayne.  I don't know whether I ปecognize
myself or not but I guess I'm not  really fully  retired, working about
80 percent of the tine.  I should  say, first, that  Bob HoleODD has
taken over the work on the Fluidized Bed Closed Cycle Gas Turbine
Project at Oak Ridge; and for reasons that  I  won't  try to explain,
somehow I'm giving the paper today, rather  than Bob.  But he's really
responsible for the project now.
                                 54

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                      Atmospheric Fluidized 3ed Combustion Technology
                           Test Unit For Industrial Cogeneration Plants
                                     A. P. Fraas and R. 5. Holcomb
                                     Oak Ridge National Laboratory
                                        Oak Ridge. Tennessee
ABSTRACT

       The AFST Technology  Test I'nit Program will develop the technology for a fluldlzed bed coal com-
bustion system to provide .1 source of high temperiture air for p.-occss h.-.iting and pover generation
with gas turbines in Industrial plants.  Th.ป gas turbine hns the advantages of * hijป.h*-r r;ปr io of elec-
tric power output to exhaust  heat load and a higher exhaust temperature than do steam turbines In
Cogeneration applications.   This type 01* syst-.'ffi appears tj be attractive for development, particularly
for Installations In tSe range of ^> to 30 MW(e).

       Tlie conceptual design  of thซ- Technology Test I'nit has been cor.pleled.  The 1.8 n (ft ft)-souare
conbustoi  has a bed depth of  0.6 n (2 ft) which has been dcslpned for atmospheric pressure and 900'C
(16iO'F) to produce a heat  output of about 150O kVtt) (5 • 10'- Btu/hr).  A number of furnace design
firms have been invited to  submit their own designs for the conbustor, from which a final selection
wll1 be nade.

       Development and testing- have been conducted in the areas of fluidl^.it Ion. heat transfer, tube
corrosion and coal feeding.  New results on heat transfer, tube corroslitn and coal feeding are pre-
sented In this paper.

       The TTU prigraa was  authorized by F.KDA In June 1977. nnd will require about two years for design.
procurement and Installation  followed by two years of testing.


INTRODUCTION

       Fluldfxed bed combustion represents a very promising method for using a wide r.* botli
electricity and process tn-.it.  Tlie gai turbine Is very well suited for cogenerat Ion systems since i!.t>
ratio of heat to power iif about 3 to 1 fur the gas curnlmf cvclr as compared to a ratio of about 5 to 1
for a back-pressurv steam turbine, and the exhaust heat from the ,:as turbine Is available at a higher
temperature.  A fluldlzed bed coal ccabimtor heating air to a high temperature Inside tubes Immersed in
the bed Is an attractive system for supplying clean air to drive a gas turbine for Industrial cogenera-
tlon plants.

       A prograa for DOC Is underway at ORNL to assess the potential application of f..n firblne cogen-
cratlon systems and to Investigate the technology required for them.  The program, entitled the Coal
Coeibustor for Copvnerat ion  (CCC) Prograa, in directed at the study of systems In the size range from
5 HW(e) to SO MV(e).  Construction and testing of a 0. J W~ was supplied by natural
gas, 211 by orlroleua. \">7.  by coal and 28! by electricity.1  These data Indicate that a considerable
aaount of natural gas and oil can be conserved as the use of coal for Industrial fuel is Increased.  The
amount of electricity used  by industry indicates a very good potential application for cogeneration
•ysteas.
     •Consultant

                                                  55

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       The use of envrgy by Industry Is concentrated in a few industries that are very large users.
The industries tfiat .ire ranked as the six largest ronsiraers of process heat use about 80Z of the total
heat.^  In order of their ranking by process heat use. these categories are (1) chemicals; (?) primary
metals; O) petroleum refining; (i) pulp and paper: (S) stone, clay, glass and cement; and (6) food
products.  In order to have significant Ircpact on industrial fuel use, applications for gas turbine
cogenerat ion systems would need to be found in one or more of th-^se categories of industry.

       Une of the cost Important fncturs in assessing the suitability of the gas turbine cycle for an
industrial application is the 'enperature at which the process heat is used.  From one of the surveys*
on industrial energy use. it is estimated tti.it about 'JO? of the process heat is used at temperatures
below 177ฐC OWK). another 30?. at teaiperaf.ir.-s from I77-W!*C OiO-llOO'F). and the remaining 401 at
temperatures above 49}*C (1100ฐF).  In the lower tesperature range heat can be supplied e;isily from
either steam or p.as turbine systems.  The gas turbine cycle is better suited to provide I.eat with a
coRencratlon system in the middle range of temperatures.  Tht; g->s turbine regeneration system is not
adapted to supplying heat at 'raperaCures above about S93ฐC (!!09*F).  The fluidlzcd bed rombustor will
supply air at about Hlfe'C (1>0;J'K) that could be used directly for process heating at teuoeraturcs near
that  level with no g.is turbine-generator unit included in the system.  In general, the higher tempera-
ture process heat requirements occur in the primary metals and the stone, clay, glass and cement indus-
tries.

       The early results of the survey Indicate that tl>e chemical, petroleum refining, paper and pulp
and food Industries have the most processes that require heat at temperatures no-.t suitable for gas
turbine systems and potentially offer the most promising applications for gas tu:bine cogeneration.

       The flow sheet for a typical industrial application Is shown in Fig. 1.  Air from the compressor
is preheated in a recuperator and then is sent through the economizer and fluidized bed furnace, both
of which are incorporated In the furnace unit.  After being heated to 816ฐC (ISOO'F). the air is admit-
ted to the gas 'urblne which drives the compressor and electric generator.  Kron the turbine exhaust
the air passes through the recuperator to the waste heat exchanger and the process water healer where
it supplies heat to the process heating and hot water systems.  The air is then returned to the Intake
of the compressor in the closed cycle gas turbine system shown here.  Not shown hut included In the flue
g.is system is appropriate dust removal equipment including a cyclone separator between the economizer
and the regenerator .ind a bag house In the exhaust from the regenerator to the Induced-draft fan.  Also,
a forced-draft fan is used on the in!et air to reduce the power for pumping the combustion air.


DESCRIPTION OF THE TEST SYSTKM

       The conceptual design of the technology test unir has been coapleted and in described more fully
in Ref. 4.  A drawing of the 1.8 o (6 ft)-squ.ire reference design furnace in shown in Fig. 2.  Combus-
tion air enters at the top rf the furnace and passes through the outer annulus to the air plenum at the
bottom of the furnace.  The air flows through orifices In a large number of nozzle:< in the distributor
plate, and into the 0.6 m (2 ft) deep fluldi (4 ft)-square cold flow
test model with full- cale diameter .tubes shown in Fig. 3.

       A photograph of the nodel of the air distribution plate is shown in Fig. 4.  The air tuyeres are
pipe stubs with horizontal holes 90* apart to orifice the air.  The tuyeres are spaced on a 7.6 cm (3
in.)-square pitch.  Coal feed nozzles are located in the four quadrants, and a limestone feed nozzle is
located at thซ" center of the plate.



                                                    56

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tfi
                232 C (4JO F)  ป•
               S/.BX (103'F)
PROCESS
HEATING
 SYSTEM
                6i.6'C (ISO'F)
                          PROCESS
                 i;.6"C (60'F)
   MOT
 WATER
                                                                         738 r
                                                                       (1142"F)      TO STACK
                                                                        *•   -•    U9'C (300'F)
                                        FIUI3
                                         an

                                       (USO'F)
                                                                                    .  i INCUCFD
                                                                                    ~)DR&F: FAN
                        i     0
 S'-'C1   |"0'C   ป8'"C    i     ^^
p   |™^.n   :       •      ,

1     *         •LUIJ
                                                               41R  15.6 C (60 F)
                                                                     .  .V.
                                     :""• fCl;'i!i^J;-'i".":  ""''"".
                                     1      cowiESscaJ ,ซ'TUซB:KE :^'I   ซNERปTSIป
                                     :       iJ^JM  J^J-1	1
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                                                         <;i-,iซoi"  r  '     c:;'v-r,v.ia
                                               Fifurซ1. Floซnhsซt lot Imtuitiial AppUotion

-------
                                                   ORNL DWG 7$ 3227
                       COMBUSTION POOOUCTS
                               i

                              ^v
                                           AlR (fro* ftg*fซ*Qtoซ>
                                          /
                                                     — REFRACTOR*
                                                          OOMC
                                                       TUTtRt
                                          •AM OISTRI8UTION PLATE
      FUEL
  (CMl • hf
                                SOCIK OVERFLOW
SCHEMATIC DIAGRAM SHOWING FLUIWttMEO COAL-COMBUSTION SYSTEM
   OESIGNCD TO SERVE AS A HE/ TEH FOR A CLOSED-CYCLE GAS TURBINE
           Figure 2. ORNL R*fซranoซ Onign Combustot
                         58

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FiguraX TutoBuixftitoclJin|4ft)*>uซ™ป*xM
                 59

-------
Fiปiซ4. Air Distributor for UHI (4ft)-tqMr*Modri
                      60

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       Asser.bl v and suS-aus*inbly  drawings of the reference des inn turnace won1 prepared wi tti  suff ic ii-nt
detai1s so that the cost of  (lie  furnace CPU Id he esl invited and  shop f abr icat ion drawings  cmi Id  be  pre-
pared froo th.-a.  A hid p;ukage  including these drawings and  the  sfwrif ical ions was prepared  ;md sent
with *-ป request to hid  to prospective  vendors, and two bids were received.

       A reviev of the prngran vitii er-.ph.isis on the prospects for coianerr ial ir.pU-n^ntal i.in of  the ro-jl-
burnlns gas turbine svsten was held at  ฃRI>A-Fฃ in September  i'*/h.  As .1 result of this review ORNL v.is
directed hv KKDA-Ft not to place  the  order for the furnace on the hasis of  the lov bid th.it h.'id be*ti
rereived. Hut rattier prepare performance sped f icat i-ms and obtain designs  from furnace namitactur in*;
f iras lJi.it they consider suit able for volurse product ion and  t tms  enhance l he curarH-rc ial prospect s  of the
systt-r..  The spe* i t it :it ions  are  nearly  complete, and a request  lor proposal lor f urn. tee des i t;ns will be
S'-nt to furnace o.i:iufaci.urlng firms in  the near future.


PK>y fi>r ind-.islrial  appl i cat ions.  The present  pror.rara
schedule is shown in Fit*. ^  with  the  t ime sea le ht-^inn inr, at  t he  program start In A-i^ust .   1 hi:  insl al-
l.it ion --HI he i-ircpK-tvii  in  about 2 years. :\>lltซw*.*d by a year of  testing with plant air eon I ing t he
cor.hu-* tor, -ind f inal ly a year ซปf  test ing w Jtl\ a pas I urb ine  sub feet to fH)K  concur rt?tu e.

       The flov sheet  lor the lirst ph.iso ซf tlir CCC teihnolot;c test unit t-xpor imi-nl is ซivon In Fig. ft.
It   is sir. t l.i r ti* the )trซ-vf ous f lov d iar*.rar with the except ion t hat t he- t*as  turbine is on It tod.   Con-
prt.-ssซ-d air will hป* supp 1 led from th.- plant ni r syst era fป>r t hป-  ear 1 y phase ot t ho combust or performance
tests .ปnd for the t ube corrosion  anJ  endurance t i-st i up,.  The  latter phase of the test prt.*j*,rani will lie
conducted with t hซ- j;.is t urhini.- inst.'t 1 led in the svsten to obtain  the response character i st ics of the
fnrn.ii-e and K.IS turbine to chanr.es in the i-lecl r ica I load on  the  generator.

       Ttte basic objectives  of the test program arป- to dt'termiiu-  the performance, reliability,  and cor-
rosion HFxt ปTซปsi on life of t he combust or with its heat t ransf er tube bundles, and to de term in**  the
reliability of the c(..i! and  1 inn-slum- handling and feed systems and the paniculate reanv.il and ash
handling, svsten.  These results  will  be evaluated in terms of the suitability of this technology as a
basis for 1 ar;tป-r Industr ia 1  furnaces  to prnv ide h i(-h temporal ure  air for pas t urb ine-generators and
pr*n-fss hir.it itiK-

       ';!ปซ.• re .-.tilts ot  the test pn^ram  will not only be of v;ilue  for 'he information they provide
specifically fซปr this  particular  svsten and its applications, hut they will also be of benefit  for the
Informal i'*n they cont r Unite-  to t he general knowledge of f I uld t zed bed ronbustors.  Th is  inc. I uies such
areas as t ube cor rซปsiซm and  erosion,  heat t ranster, coa 1 f oed Inn  ซind nixing, bod temperature  d ifilr Ibu-
t ion, f In Id \7. In^ character i st Ics, sul f ur dioxide absorpt Ion,  sol ids el ut rial ton, part icu late  rป'nt>va 1
I'ron fluซ* Eases, and coal f<-*.-d system reliability.  The results will provide data on beds utilizing
f .'ii r ly scia 11-si zc'l part 1 c les at  low f luf d i -r. In>; velocity as is very often fo*:nd in f !u Idi/ed bed pasi-
flers and cumhttstcrs burnlnp, coal waste deposits.


SrpPORTISG TF.STS

       Support fnE test work  has  been  conducted on A fluidized bed cold flow model, the coal feed system,
heat transfer and f ireside corrosion.

Cold Flow Mod<-l

       A nuxber of tests were conducted with a 1.3 m (•* ft)-square, 4 o (12 ft)- high Luclte  model of
the  fluidized bed furnace.   The.  areas of testing include flutdizlng velocity, pressure drop,  air dis-
tribution, coal oi xing rate  and  tube  vibr.it ion.  The fluidtztnp; velocity tests indicate that  it should
be possible to operate the furnace at about 1/3 of the full power air flow  rale.  The coal mixing  datj
showed that adequate hor f 7.onta I  mixing  of the coal should be  obtained f ron  t he four coal  feed nozzl es
at   1/3 of the full pnver .ilr flow rate.  Tube vibration was  found having a  frequency range of 20-30 h;,
but  It was of low amplitude.   The natural frequency of a full-length furnace tube was racasured  and
found to he 15 Hz with no support under the horizontal U-bend portion.  The results -if the vibration
test led to the decision to  provide supports at the ends of  tlie horizontal L'-tubes in the ORNL  reference
design furnace.
                                                    61

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ro
                                                                 PR03SA.1 PLAN
                                                          AF3C  TECHNOLOGY TEST UNIT

DESIGN

PROCUREMENT

INSTALLATION

TESTING

DATA ANALYSIS












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Figuf*6. Flow Shtn for Comtuotor Tซt with Want Air

-------
Coal feed System

       Tests have been conducted on €-oraponents nf three different coal feed systems, and endurance
testing has been done on the svs'.em that  vas selected as the reference design.  The vihrator-educlor
unit enploying a vibrating feeder to fee-) coal in four streams tr- air-driven oductors was tested, and
it was found afrer trying several air flow settings that the coal feed rate is not split equally anon;;
the four streams over the range of the vibratory amplitude to Rive the desired range of total coal feed
rate.  After a considerable, amount of effort to obtain equal flow in the four streams without success,
it was decided that the development work on this type of coal feed splitter should be discontinued.

       A coal feed system consisting of a gravity flow splitter feeding four air ejectors for trans-
porting the coal (see Tigs. 7 and H) has been tested and has been found to give four streams that can
be kept within plus or minus 5Z of tlie mean coal flow rate over the entire operating range, and the
results are repeatahlo.  A series of batch-flow tests were run on this system (see Fig. 1) and no
operating problems were encountered over a total running tine of 175 hr.  The svstem was selected as
the reference design roal feed system and was operated continuously for 1000 hr without incident.

Heit Transfer Test

       A heal transfer test was run on an alr-coolcd tube In the FluiDyne Rnglneering Corporation 45
cm (18 in.)-;.')uare fluldlzcd bed furnace at a bed temperature of 900ฐC (1650ฐF) over a r.inge of fluld-
izlng velocity of 0.2V-G.65 m/se.- (0.8-2.2 ft/sec) with a bed mean particle size of -'.60 urn.  As may he
observed in Fig. 10, the heat transfer coefficient iron the bed to the tube was found to vary from
about 227 W/m^-'C (40 Bt u/hr-f t ''-ฐT) at a fluldizing velocity of 0.25 in/sec (O.H ft/sec) to a value of
about 483 U/m?-ฐC (85 Htu/hr-ft•-*F) at a velocity of 0.5 a/sec (1.6 ft/sec) and was essentially con-
stant at higher velocities.''

Fireside Corrosion Test

       A corrosion test on air-cooled tubes made up of sections rtmposed of 304, 31O, '116 stainless
.".tee I, Inconel 600 and Inrolny HOO was run in the FluiDyne f luidlzed bi .1 combiistor for a period of 500
hr.  The tubes were julntalncd at a constant maximum wall temperature of about 870*C (1600'F).  The
tubes were removed from the furnace, and one-fourth of the specimens were sectioned and samples were
prepared for netallographlc examination.

       The results of the examination are encouraging.  So evidence of erosion was found, and a thin
hard scale composed of aHout 60ฃ CaSOi. was present on the tubes.  No measurable loss of wall tnickness
was found.  A nrlal oxide layer about 0.025 to O.018 mm (O.O01 to 0.0015 in.) was observed on e.irh of
the materials.  The Incolo-/ KOf) specimen showed Intergranul.ir oxidation attack for a depth of about
0.03 n (0.0012 in.)  No inter^ranular corrosion was observed In .104 and 110 stainless steel and Inconel
600.

       A second corrosion test of 100O hr exposure was completed In October.  A new specimen tube of
Inconel 600 failed after the test had run only 46 hr.  This failure was Attributed to what Is believed
to be an unevin air distribution across the bed caused by about 25Z of the total air flow through the
bed entering as transport air through the. coal feed line.  Fxaalnat ion of samples from the failed tube
Indicated sulfidatlon attack.  Mlcroprobe scan., of the corrosion product l.iyrr revealed the presence of
nickel sulflde in the corrosion layer, and depletion of nickel in a zone lust below this layer.  The
attack occurred over a length of about 1O cm (A in.) at each end of the tubet and the presence of nickel
sulfide indicates that reducing conditions were present at the regions near the ends of th<- lube.

       The failed tube was replaced with a new tube of Inconel 600. and the test was resumed with a
lower coal feed air flow and a total excess air of 15t Instead of the original IOX.  Two Inconel hOO
tubes failed at a time of 120 hr later.  Those failures occurred at the hot end of the tubes ju.-tt in-
side the refractory lining where the tube passes through a hole In the refractory furnace wall.  It  is
believed that the corrosion occurred here as a result of a low oxygen level lending to attack by calcium
suliate and possibly hydrogen sulflde from Incomplete combustion of coal particle* ih.it may have been
present.  No other evidence of attack was seen on any of the tubes in the bed zone.

       It was decided that Inconel 600 was too susceptible to corrosion attack where reducing conditions
are present, ar.d this material was dropped from the test propraB.  The two tubes were replaced with
tubes of 310 stainless steel, and the 1000 hr test was completed without further incident.

       The. 16 tubes were removed at ti.e end of the 1000 hr test, and visual Inspection revealed that
the surface of the tubes had a somewhat different appearance froo that observed earlier.  The calciua
sulfate deposit was not as hard and shiny as before, but rather it was a rougher surface, and in some
                                                  64

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                       DAY TANK VENT
FROM STORAGE SILO
           OAT TANK
 fUD HtIGM TANK
ROTARI tttttt
Bt-PASS VALปt
                                                                                                COMBUSTION
                                                                                                 PRODUCTS
                                           BALWCฃ WIVฃ
                               ^ - -- ^WTART FtT.ซR
                                                                                                           COMBUSTOR
                                                                                                              AIR
                                                                                                         TRANSPORT AIR
                                                                                                          COMPRESSOR
                                                                                          1.4S kg/on'
                                    Figutซ7. Flow ShMt for Coซl Ffed Syitrm

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FijuraS. Riffta for Splitting Coal Fซd Stream
                    66

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Figure 9.  Cod FMO Syttm Twt Equipment
                  67

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S
                      30
                        0.6
                                                                    1.4         1.6
                                                                    VELOCITY. FT/StC
                                                    Figurt 10. Hwt Transfer CoaMictent w. Fhitdliing Vซlodty

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spots it had scaled off.   Metallograpbic examination has not been performed, but this will be done in
the near future.

       A third test with an exposure of 5000 hr is planned '.or this year.


REFEREKCES

1.  Federal Energy Administration. National Energy Infernal Ion Center. Monthly Energy Review, March,
    1976.
2.  rk.Z>onnel-DouRlas Astronautics Co.. West. Industrial Applications of Solar Energy, Report SAN/1132-1,
    January. 1977.
3.  Intertechnology Corporation, Analysis of the Economic Potential of Solar Thermal Energy to Provide
    InSustrial Process Heat, Volute 1. Final Report, Report CO02S-1, February 1477.
6.  A. P. Fraas. Oak Ridge National Laboratory. Conceptual Design o: a Coal-Fired Gas Turbine for HJIJS
    Applications!  Phase II Suooary P.eport, to be published.
5.  A. P. Fraas. et al..  Oak Ridge National Laboratory, Design Study for a foal-Fueled Closed Cycle Cas
    Turbine Systsa for Hl'JS Applications, IEEE Catalog No. 75 CHO 96J-7TAB.
6.  R. S. Holccmb, Oak Ridge National Laboratory, Heat Transfer Performance of an Air-Cooled Tube in 
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           QUESTIONS/RESPONSES/COMMENTS
     ALBERT A.  JONKE, CHAIRMAN:  Next is Art Fraos.  Do you have any
questions?  If  you  do, come or, up.

     MR.  FRAAS:  I  might be accused of having planted this question.
I didn't.  Mr.  Casapis of United Engineers and Constructors asks two
questions:  First,  "Could you please give an estimated plant down time
to repair burned-out tubes in an FBC commercial-sized plant?"  When-
ever one  shows  evidence of difficulty in a test program, it can be
construed as indicating th?t one is headed for disaster.  I welcome
this question because, first, to answer it, I would say that we would
not expect very much down time, in fact, essentially none, to repair
burned-out tubes. Were it to occur, of course, one would have to do
something about it.

     The  reason why we believe that this would not happen is that,
when trouble occurred in the corrosion tests cited in the paper, we
were deliberately running with a low amount of excess air; we thought
about 10  percent.   There are evidences that because of instrumentation
it was closer to 5  percent; and obviously, with such a small amount
of excess air on the average, one could have local regions that would
be subject to reducing conditions, and clearly were, as evidenced by
the tube  burnout.   One factor which produced this was that the coal
was carried into the bed pneumatically with about 25 percent of the
total air flow, and this led to poor distribution of the air flow
through the bed.

     The  previous speaker was mentioning an 80 ft/sec air conveyance
velocity  for the coal in this 4-inch tube.  That gives a large frac-
tion of the total air flow to the bed.  We deliberately, in develop-
ing our coal metering and conveyance system, have tried to keep
the amount of air used to convey the coal down to a low value like 6
percent,  because, if you want turndown, let's say 10 percent conveyance
air at full flow power will, represent about 30 percent of the total
air flow if you get down to a 25 percent power flow.  This, of course,
is quite  bad and one would like to avoid it.

     The  second question was:  "Please expand, if possible, on the
work mode to do che above."  I won't bother trying to get the slide
back, but you may have noticed that the installation made use of a
bell jar  which  fitted down over the top of the bed.  One can remove
that bell jar by breaking a single flange joint and have access for
detailed  inspection of the tube bundles directly.  If one wishes, any
one of the four bundles can be removed independently of the others
and replaced.  Individual tubes in any given tube bundle can also be
replaced  once the bundle is pulled from the bed.

                                70

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     A good deal of thought was given to this ratter,  and many dif-
ferent layouts were investigated, before the layout which I showed
there was chosen:  The prime reason for the choice of  that layout was
accessibility and ease of maintenance.  Thanks.

     ALBERT A. JONKE, CHAIRMAN:  Are there any other questions for
Art?  Here cones one.

     KR. BUSCEHI:  Vince Buscemi fron Gibbs and Hill.   I  would like
to ask Art what industrial needs you expect to tree* with  this closed-
cycle gas turbine; that is, what steam flows, what electricity require-
ments, perhaps what steam conditions.

     MR. FRAAS:  One is process steam, at temperatures up to 403 or
500'F.  There are applications for which you also night want hot air,
which could be supplied at temperatures up t? 15QQฐF.   One can increase
the size of the plant over a wide range fron our smal 1 test unit having
a projected furnace input 1-1/2 megawatts and about 325 kilowatts of
electric power output fron the closed-cycle gas turbine.   This can be
scaled up to give perhaps 20 MH of electric power output.

     One other point, we are of the opinion that one ought to increase
the excess air to about 20 percent to assure that you  would never havs
reducing conditions in the vicinity of the tubes in the bed under any
combinations of operating conditions including those that might give
fluctuations in the air or fuel flow rates.  I night say  that these
corrosion problems have been paralleled in other combustion systems
such as superheater installations.

     In the experimental program one clearly wants to  find out how
good the fuel and air flow distribution is throughout  the bed in order
to know how much excess air is required to assure that there will be
no local region with reducing conditions.  For example, fluctuation
in the coal feed rate presents an obvious mechanism for giving trans-
ient fuel-rich conditions.  If you have wet coal and you  get cojl
going into the furnace in slugs, this can lead to fluctuation in the
fuel-air ratio, and alternatively oxidizing and reducing  conditions.
Similarly, many other factors will give a poor distribution of the
fuel.  For example, with a small bed you can get bPd .slugging, another
mechanism for fluctuations between oxidizing and reducing conditions.

     KR. FRAAS:  Mr. Waters of CSIRO, Australia, asks: "Has the
effect of the tube Reynolds nunber on the heat transfer coefficient
been examined?  What is the normal or working value of the Reynolds
number?"  The answer is "Yes," and I don't renerier; and  Bob Holconb,
can you answer that?

     MR. HOLCOKB:  Up to ^bout 80,000, inside the tube.

                                 71

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                     INTRODUCTION

     ALBERT A.  JONKE, CHAIRMAN:  Thank you.  The last speaker is
James Porter, who received his Bachelor of Chemical  Engineering
degree in 1955  from Renssalaer Polytechnic Institute and his  Doctor
of Science in Chemical  Engineering from MIT.  Dr. Porter has  had over
20 years' experience as a practicing chemical engineer,  both  in
industry and as a professor of engineering.  He is known for  his
development of  new process concepts and for the application of
computers to advc.  id computer-aided design systems.  Currently he is
vice president  and chief scientist, Energy Systems Division,  EkCO.
Dr. Porter.
                                 72

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                            ERCO's Fluid-Bed Combustion
                                 Development Facility
                                    James H. Porter
                             Energy Resources Company Inc.
ABSTRACT
       Energy Resources Company Inc.  (ERCO)  has developed a 6 MMBtu/hr test  fluid-bed
combustion system.  The system has been in operation for 2-1/2 years during  which time
ERCO has pained a wealth of operating and design experience and data on KBC  operations.
The unique design of the system allows the rapid alteration of boiler tube configura-
tion to study these effects on boiler performance.   As  a result of this experience.
ERCO has announced its offering of commercial fluid-bed combustion units in  sizes from
50 to 250 MMBtu/hr thermal output.  ฃRCO now has under  design and construction its new
50 MMBtu/hr demor.st 'ation boiler,  to be operational  by  June 1978.


INTRODUCTION

       ERCO was founded 4 years ago based on the premise that projected oil  and gas
shortages would increase the need  to consume solid  fuels.   As a result of potential
environmental insult in burning solid fossil fuels,  ERCO made the decision to develop
two processes, fluid-bed combustion and fluid-bed oyrolysis,  both operations conducted
with limestone sorbents present in the fluid bed when required for high sulfur fuels.
I will confine ny remarks to our fluid-bed combustion activities although ERCO is
offering both processes commercially.


DESCRIPTION

       Figure 1 shows the process  flow dlagraz of the facility.   Coal and limestone
arc premixed and fed to the facility in a screw feeder.  Tho hopper is supplied with a
vibrator to prevent bridging.  This was especially  useful when non-coal solids vere
being fired in the boiler.  Tubes  .ire submerged in  the  bed and as will be shown the
tubes can be installed in any number of positions.   Atmospheric steam with up to 90" F
superheat is produced in the boiler.   There was no  need to produce pressurized steam
in the system to get the design data we required.   Tubes have thermocouples  embedded
along the exterior Tor skin temperature measurements.   Steam temperature. pressure and
quality are measured.  Thus heat transfer coefficients  and heat fluxes can be computed
knowing the exposed tube area.  Thermocouples are extended into the bed at various
levels to measure bed temperature.

       A natural gas line is shown which is used to ignite the system.  Natural gas
and air burn in a water-cooled plenum chamber.   The hot gases rise and preheat the bed
of coal and limestone.  Observing  bed temperature,  a sudden rise indicates coal igni-
tion point.  We ha e collected this information for a variety of solid fuels.   These
include:

       1.  coals
       2.  wood waste
       3.  paper
       4.  ground rubber tires
       5.  RDF fuel
       6.  corn cobs
       7.  wheat straw
       8.  rice hulls

Ash and spent sorbcnt in the bed are collected through  an overflow port, stored.
cooled in drums and analyzed.  Overflow ports exist every 3 feet up the bed  so we can
operate at 3, 6 and 9 feet bed depths.  Gas velocities  in the bed can range  from 4 to
16 ft/sec.

       A cyclone is installed at the gas exit port  at the top of the bed to  collect
coarse ash and unburncd carbon. This material is returned to the bed.  Samples of


                                          73

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                                                         Sample
 Blower
                             I	
                 ID.
To
                                    New
                                    Fine
                                    Collretor
                                    l/lb'/S

                                    	I
                                                      I	1
                                                      I          I
                                                      I Condenser
                                             K	-t
                                                    Water
                       ซ	•-
           Figur* 1. ERCO Fluid Bed Combustion Facility.
                                  74

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this material are collected for analysis.   The present system cools the off-gas and
collects fine participates in a water spray scrubber.   The exhaust gas is then drawn
through an induced draft fan and to the stack.  Hot combustion gases are sampled and
analyzed for SO?. NO?, CO and oxygen.  An oxygen probe can also be installed at vari-
ous levels in the bed.

       In January the system will be modified by cooling the gases through an electro-
moving Sed. a new fine particulatc device we ซre developing in partnership with a
company called EFB.   This device has demonstrated removing particul^tcs down to the
12 ..m level at berter than 99 percent collection efficiency.  We will thus have the
capability of collecting and analyzing fine particulates.


BOILER TUBES

       Figure 2 shows the bed section containing the immersed boiler tubes.   Boiler
tubes can be inserted in the bed through various test  ports or the ports irjy be capped
off.  The tubes are connected external to the bed to allow to consider a variety of
series and parallel  flow path options at various tube  spacings in the bed.


DESIGN CONSIDERATIONS

       Although I will not present, any of our data since this information has been
collected entirely in the private sector,  I will present a rather detailed list of
design considerations which will ultimately determine  whether a specific system will
operate successfully.  By the way. not -ill of our attempts were successful.   We have
had distributor plate failure, refractory failing, tube warping, etc.  Thus, the in-
formation I an providing is based on experience and is indicative of the problems we
have solved in the lart 2 years.  Table I  shows this list.  These problems a/e exclu-
sive of coal feeding ind ash removal problems.

       When I consider the list and our experience, some of the proposed concepts I
review cause 
-------
LJ
   o   o   o   o
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           	20"—
                                         I
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FigunZ. Combuaof C*nt>r Croa action.
              76

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                         Table I.   AFBC Design Considerations
Considerat ion
1.  Minimum sized pilot  unit to
    ensure scale-up

2.  Tube height above distributor
    plate

j.  Distributor plate protection

A.  Sulfur retention


5.  Holier tube configuration


6.  Heat transfer


7.  Coal feed distribution

3.  Tube materials
Problems Ic- Be Solved

Bed stability, vo.d (bubble) forn.it ion
and void (bubble) growth

Volatiles combustion kinetics and gas
phase fluid mechanics

Volatiles combustion kinetics

Bed height, bed velocity and effect of
limestone oorphologv on kinetics

Solid and fluid mechanics in the presence
of obstructions

Solid flow rซ?chanics and effect of boiler
tube size and confipuration

Volatiles burn-out ar.d solid flow irechanlci

Heat flux, hc.it transfer coefficient
chemical environment
                                          77

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           QUESTIONS/RESPONSES/COMMENTS
     WAYNE A.  McCURDY,  CHAIRMAN:   Thank you.   I have one question of
my own for Dr. Porter.   Jim,  would you happen  to have any order blanks
with you?

     DR.  PORTER:   I've  got  about  five questions here but two of them,
which are the  same, I'm not at  Iib2rty to divulge.  Those questions
are:  can I expand on the nature  of  the heat shield and chemical
shield over the air distributor.   That information is proprietary at
this point in  time.

     The second question is,  "What is the material of construction
for your dolomite/codl  screw  feeder?"  First of all, I want to men-
tion we use a  screw feeder  In our 20-inch bed.  That's a relatively
small diameter system.   We  would  not propose that anyone use a screw
feeder in any  bed of any significant size.  In fact, one of our
developments,  for which we  have just now applied for a patent, is a
new underfeed  device.  This device allows us to feed coal at a rate
of one feed point, per roughly 70  square feet of bed rather than 9
square feet of bed.  The screw  feeder that we  are using in our
small system is just a  normal stainless steel.

     "How do we effect  its  protection during shutdown?"  It's a
portable system.   That  yreen  box  you saw is the screw feeder mounted
on a pair of casters.  We simply  roll it away  from the bed and put a
cover plate on the feed port  so solids don't run out of the bed.  So
it's very simple.  We just  move it out of the  confines of the bed and
that's how we  protect it.

     Next question is,  "What  magnitude of overall heat transfer
coefficient have you observed?"  This question is highly dependent
upon several things. First of  all,  there's the fluidization velocity
in the system.  First,  we find, the  system has to operate at fluidiza-
tion velocities of about 2-1/2  times the minimum fluidization velocity
in order to get consistent  results on heat transfer.  The heat transfer
coefficient is also dependent on  the size and  density of the bed
material.  For 2-inch tubes with  a reasonable  arangement of tubes, a
heat transfer  coefficient o.  about 40 Btus per hour per square foot
degree F is normally observed.  However, that  number can vary signifi-
cantly, depending on how one  arranges the tubes within the system.
For some arrangements of tubes  you can get that number as low as
about IS.  There are also optimal  arrangements in the ted, and if one
has systems arranged optimally, we have run the heat coefficient as
high as 60 Btu per hour per square foot per degree F within that
system.
                                 78

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     The next question is "What  principle  are you  considering  for
fine participate collection following  the  cyclone  collectors in your
flow diagram?"  This is also a new development  that we've been
working on for a number of years now.   In  conjunction  with  another
group called "EFB," we have formed a joint venture company  to  market
this particular device for its application in fluid bed  combustion.
It's called an "electrified bed."  It  operates  on  the  principles
of filtration by fine particles  as in  a granular bed,  but it also has
the additional feature of electrostatic collection.  But it's  electro-
static collection potential is much different than one would observe
in an electrostatic precipitator, in that  we have  collector particles
in a field through which a dirty gas is flowing.  The  collector
particles are placed under a voltage gradient of about 20,000  volts
per centimeter within that system.

     Now one might think you would have very high  power  requirements
for that kind of voltage gradient, but actually the power requirements
are very low because one is not  discharging throughout the  system.
What one does within the collector particles is polarize these par-
ticles.  Essentially the only criteria is  that  they be nonconductive.
One polarizes collector particles and  then after screening  out fairly
large size particulates through  an additional stage of granular bed
filtration, one then charges the particles, the very fine particles.

     One of the problems we found in developing electrostatic  collec-
tion devices is in fact that if  one applies a corona discharge to a
large mass of particulates of dirty gas, a large fraction of the
charge lands on fairly large size particles.  I'm  talking about
particles, let's say, 30 microns and above. But if you  look at the
charge per unit mass, you'll find that the charge  per  unit  mass for
these Is very low and you don't  really effect very much  in  collection
efficiency.  Therefore, you screen these out by normal filtration
techniques, first through a moving bed filter of granular particles.
Having made this filtration step, you  then apply the corona discharge
across the submlcron particles,  this is from 30 microns  down.  Then
you can pass these particles through the voltage gradient that you
apply to another section of this moving-bed filtration system, and
you can find that you have very high collection efficiencies in this
system.

     To date, we have applied this concept to a very difficult
collection system, and we're jusw getting  ready to install  it  in our
fluid bed.  Fhe collection system has  been operating on  an  asphaltic
mist that was developed in asphalt coating plants  where  they coat
roofing tiles.  In that operation one  gets characteristically  a blue
haze.  The blue haze 1s characteristic of  the very fine  submicron
particles which only reflect the blue  wavelength light.  In this mist
operation, we have collected particles as  small as .2  microns  with
99.9 percent collection efficiency.
                                 79

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     The otheป* unique feature about this system is that,  whereas if
one is looking at systems such as baghouses and so forth, and  you're
limited to about somewhere fron a quarter to 2 feet per minute space
velocity within those systems, we operate this system at  60 feet per
minute space velocity and maintain those filtration efficiencies.
This means you can get away with substantially smaller and less
capital cost devices.

     WAYNE A. McCURDY. CHAIRMAN:  Any other questions for Dr.  Porter?
Okay, Al.  Will you wrap it up?

     ALBERT A. JONKE, CHAIRMAN:  Well, I'd like to thank  all the
speakers again for a very interesting set of presentations and thank
all of you tor a *ery active participation.
                                 80

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                         INTRODUCTION
     ROBERT CHRONOWSKI, CHAIRMAN:  Our next paper has to do with the
results of recent  test programs related to atmospheric fluidized bed
combustion efficiency.  This  is work done by Pope, Evans, and Robbins
in their Alexandria  and, possibly, at Rivesville, units.  The paper
is going to be presented by Mr. Callixtus Aulisio, who earned his
Bachelor's degree  in Chemical Engineering at the University of
Maryland, and he worked for the Navy in a very appropriate area, in
pyrotechnics, for  a  while.  He then joined Pope, Evans and Robbins in
1974, where he has been since tnen.  He has been involved in both
the test programs  at Alexandria on the 9-square-foot unit and as the
startup engineer at  Rivesville.

     MR. AULISIO:  This paper describes work done at the Alexandria
labs, not at Rivesville.
                                 81

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                      Results of Recent Test Program Related to
                            AFB Combustion Efficiency
                           Callixtus Aulisio. Robert DIVI'IO and
                                   Robert H. Reed
                          Pope. Evans and Robbins Incorporated
                                 Alexandria. Virginia
ABSTRACT

       Test programs at the Alexandria. Virginia laboratory have been directed toward
defining and improving the factors affecting combustion efficiency in atmospheric
fluidi zed-bed combustors.  Test programs conducted Included determination of the chem-
ical composition of fly ash as a function of particle size and the effect of ash re-
cycle to a coal burning cell and to a Carbon-Burnup Cell.  The results of these pro-
grams indicate that the overall combustion efficiency of an atmospheric fluidized-bed
combustor can be increased to over 95X with a fly ash recycle system and to over 99Z
with a Carbon-Burnup Cell system.  In addition the dust collection equipment should be
selected to optimize ccmbustlon efficiency for a recycle system.


INTRODUCTION

       In the fluidized-bed combustion process, operating conditions are typically
chosen to optimize the heat release rate and sulfur capture efficiency.  In order to
optimize the heat release rate, a high air input rate Is typically used which results
in a high superficial velocity.  However, the high velocity results In a high solids
clutrlation rate.  In onU-r to maximize the sulfur capture efficiency the operating
temperature is kept relatively low. in the range of 1500 to 1600ฐF.  This low tempera-
ture is not conducive to efficient carbon burnup.  Due to these operating conditions,
10 to 15Z ot the heat Input is usually lost as high carbon content fly ash.  Effi-
cient operation of a FBC demands that a large fraction of this heat loss be recovered.
Two methods of recovering this heat arc by rcinjcctlng the fly ash Into the cell frota
which It was generated, or by feeding the fly ash to 'a cell operated at conditions
which promote more efficient carbon burnup. commonly known as tho Carbon-Burnup Cell.

       During the past yoar, testa were conducted in the Alexandria, Virginia flul
-------
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u.
                                                               5000

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                                                               2000
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                                                                                     LIMESTONE
to     SO   90  40  90  tO  70   M
    PERCENT  LESS THAN STATED SIZE
                                                                                                                      90    95
              Fifur* 1.  AMjundru. V. Flwdmd 8ซd Modgta
Pjrticl* Si/e Dittnbution lor Solid* Into! and Oulkl Stream
lor fly Ash CharKttfuation Tซt 2

-------
Table I.  Operating Conditions for Fly Ash Characterization Tests
Superficial Velocity, ft/sec
Bed Temperature, *F
Bed Depth, static inches
Air/Coal Ratio. Ib/lb
Ca/S Ratio, moles/mole
Fly Ash/Coal Ratio, Ib/lb
Bed Drain/Coal Ratio. Ib/lb
02 in Flue. Vol. I
                                84

-------
       Figure 3 shows a comparison of the fly ash size distribution for the two tests.
As would be cxnectcd. the higher velocity test showed a higher scan particle size CMC
to the elutriation of larger particles.  It can Le seen from the graph, that in t/oth
tests, less than 17. of the fly ash is preater than 600 microns.  All size cuts o!  the
solids sanples were chemically analyzed for carbon, hydrogen, calciun. sulfur and Issa
on ignition.  These analyses are shown in Table II.  In both tests the data shows that
the highest carbon burnouts were obtained in both the largest and smallest fly ash
particles, with the poorest carbon burnout resulting around 150 microns.  Another in-
teresting result is that in the lower velocity test there was a slightly higher carbon
burnout at approximately 500 microns.  The fly ;-sh carbon analysis data becomes r^ore
meaningful when the carbon analysis for each screen cut is r.ultiplted by the weight
fraction of fly as'i in that screen cut.  This gives the distribution of carbon as a
function of fly ash particle size.  The results of rhis data reduction procedure are
contained in Table III and shown graphically in Figure 4.  From Figure 4 tt can be
seen that in both tests ttu major portion of carbon is contained in two particle size
ranges, one being a rather wide range fron 150 to 400 microns and ihe other being a
narrow range fron 50 to 75 microns.  The presence of two peaks in the carbon diitrib-.-
tlon suggest lhat two different mechanisms are responsible for the low carbon burnout
in these two size ranges.  The peak in the lar-i.r size range can he explained by cos-
piring the residence tice of fl- ash particles in the FBM to their burnout times.


^Y ASH BURNOLT MODELING

       As a coal particle burns in the fluidized bed. burning p'cces break off due t ;
thermal cracking and abrasion.  If these particle? are small enough such that their
terminal velocity is less than the superficial velocity, they will be carried out of
til" bed as fly ash.  These particles will continue to burn, out of the bed. until thi-
flue gas has been cooled sufficiently to stop combustion (less than 1000ฐF).  In the
Alexandria FBM this usually takes place in the economizer bundle located above the
steam drum.

       The residence time of the fly ash particles in the combustion zone aHovc the
bed is given by
where II is the height of the freeboard, V is the pas superficial velocity *nd Vt lซ the
terminal velocity of the particle.  Thus the maal'cct particles, vhere terminal veloc-
ity is very low, will have residence times close to the &as residence tlee. Particle*
vith terminal vclociti-s nrar the superficial velocity will rise norc slowly.

       The burnout time of the fly ash particle can be estimated, using a modification
of the calculation net nod described by Casncr and Divilio'.  Assuming a shrink nv, par-
ticle model, the shrinking rate is given by
                                     *c dT • *b                                  <ซ
vherc
      "c
      r
      C
carbon density
particle radius
time
overall reaction constant • (;— * i—)*'
      It
           bulk oxygen concentration
      kg * surface reaction rate coefficient
      kg, • mass transfer coefficient of oxygen to the particle surface

The overall reaction rate constant, ซ. is the sua of the iiass transfer resistance an-J
the surface reaction resistance end is dependent upon the surf.-<<.e  emperaturc of the
burning particle.  The surface temperature will determine whether the reaction is
diffusion limited or kinetics Halted

       The -urface temperature can be estimated from an energy balance around the
burning particle.  Equating the heat generation rate to the heat transfer rate yields


                                          85

-------
CD
TOO
600
500
400
m
I300
X
b;200
N
S)
y
a
S 100
s eo
< TO
S 60
"• 50
40
30

Jt 0*
/ ,'

s .,'
/'*

ฐ/J>'

* y SYMBOL U, FT/SEC
// 0 94
If D 11.2




13
12
5"
5*ฐ

1 8
5
8 7
ฃ 6
AMS CARBON 1
u ซ u>
s z
i
o




/r\ A
• / \ \
/i \ ป •
.9;. \^ \ SYMBOL Ut FT/SEC
M 1 \ \ 0 9.4
1 \ 1 I ^ \ 0 .1.2
'oV' ! ' v \
'V ! \ \
j ?. \ \
t\ \x
\l \\
* fl Ln i 	
                        PERCENT  LESS THAN STATED SIZE
0      100     200    300    400    500    600    TOO    800    900

               FLY ASH MEAN PARTICLE SIZE. MICRONS
              Figure 3.  Comparison of Fly Ath Size Distribution tar Fly Ash
                       Characterization Tests 1 and 7.
         Figure 4. Carbon Distribution in Fly Ash as a Function of
                  Particle Size

-------
Table II.  Chemical Analysis of Solid Samples  for Fly Ash Characterization Tests
                 Height Percent of Component  in Hach Size Cut
                        U.S. Sieve Series  Screen Sizes
Material Size
+4
-4+8
-8+14
-14+18
Bed -18+25
Test 1 -25+40
-40+50
-50+70
-70
-16+30
-30+40
-40+70
Fly Ash -70+100
Test 1 -100+140
-140+200
-200+400
-400
-4+8
-8+14
-14+18
Bed -18+25
Test 2 -25+40
-40+50
-50+70
-70
-16+30
-30+40
-40+70
Fly Ash -70+100
Test 2 -100+140
-140+200
-200+400
-400
C
4.9
2.2
1.1
3.0
1.0
1.4
0.5
4.3
16.1
20.7
29.9
44.9
51.0
53.2
47.1
41.6
24.1
S.32
3.67
0.81
0.48
0.22
0.72
0.71
13.83
5.80
23.10
40.71
42.83
48.41
48.20
44.01
29.6
17.87
H
0.88
0.92
0.57
0.79
0.71
0.57
0.24
0.70
1.07
1.51
1.09
1.20
1.30
3.50
1.6
1.4
.87
0.54
0.51
0.64
0.62
0.47
0.23
0.29
9.84
0.75
0.84
0.59
1.14
0.75
1.62
1.37
1.38
1.15
Ca
19.7
15.6
28.9
35.9
33.1
33.3
30.4
28.8
22.3
20.8
7.1
10.2
11.2
9.0
11.7
8.7
16.2
9.0
14.21
31.05
34.90
33.47
23.73
23.40
24.68
29.05
4.99
15.32
12.14
9.74
9.24
10.25
10.79
16.06
S
1.2
2.5
6.4
8.3
9.6
10.3
9.8
10.1
6.6
5.0
1.5
2.9
2.7
2.6
3.0
3.1
6.6
3.42
2.66
6.05
7.99
10.37
9.20
10.23
5.60
8.48
2.35
2.91
3.56
3.53
3.31
3.73
3.83
4.23
LOI
15.9
5.6
6.3
4.4
5.5
3.4
4.2
7.2
23.4
--
39.4
51.3
58.6
57.0
54.6
49.2
28.4
9.31
5.75
9.31
7.51
5.13
4.94
4.65
24.21
11.39
29.43
45.60
47.80
55.14
53.83
49.95
35.16
21.50
                                      87

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Table III.  Carbon Distribution in  Fly Ash  from Fly Ash Characterization Tests
            U.S. Sieve Scries,  Pound Carbon Per 100 Pounds  of Fly Ash.

-16+30
-30+40
-40+70
-70+100
-100+140
-140+200
-200+400
-400
Composite
Test 1
0.02
0.06
6.7
12.1
7.8
2.3
8.1
5.4
42.48
Test 2
0.08
O.E5
11.5
11.9
0.98
3.7
5.5
3.0
37.51
                                      88

-------
                                  TS ' TB + — h— ' ~

where Tg ป surface temperature
      TB = bed temperature
      h  ซ• overall heat transfer coefficient, = >.t + hR
      :.H = heat of reaction
      hc - convective heat transfer coefficient
      hR = radiative heat transfer coefficient

       Estimates of hc and k;,, were made using Froessling type equations.  These types
of correlations yield the film heat and mass transfer coefficients for a single sphere
in a flowing gas stream, which is lower than the coefficients for a sphere in a fluid-
ized bed.  Therefore, it was necessary to multiply the coefficients by an enhancement
factor to obtain estimates for the actual coefficients.  An estimate of the enchance-
ment factor was obtained as the ratio of the convective heat transfer coefficient in
fluidized bed to the convective heat transfer coefficient in free flowing gas.  This
ratio is usually on the order of 4.0.  The procedure used was to assume an enhance-
ment factor of 4.0. for particles whose terminal velocity is greater than the super-
ficial velocity, and 1.0 for particles whose terminal velocity is less than the
superficial velocity.  The value of hR was estimated from the Boltzman equation using
cmissivities of .75 for both the coal particle and the bed.  The value of ks was cal-
culated using the equation of Parker and Hottel1', given by
where  T  is in ฐK.
                                 i SA v 1ni
                           .   .  5.86 x 10'  e            cm/sec                   (4)
       The calculation procedure involves a trial and error solution where a value of
Ts is chosen to calculate hc ,  (IR,  k_ and ks .   These values are then used to calculate
a new T.  The method converges rapidly to give the desired values.  Graphical integra-
tion of Equation 2 then gives  the  burnout time as a function of particle sizes.  Re-
sults of thfcse calculations are shown in Figure 5 for both tests.  The results in
Figure 5 show that at both velocities there is a range of particles whose residence
tirae in the combustion zone is shorter than the predicted particle burnout tine.
Therefore, incomplete combustion of particles in this size range would be expected.
This size range for the lower  velocity test is from 150 to 320 microns.  A wider range
of from 150 to 400 microns is  predicted for the higher velocity test.  This implies
that in the higher velocity test the fly ash  particles with poor carbon burnout should
be contained in a wider size range.

       When these predicted results are compared to the experimental results shown in
Figure 4, the agreement is seen to be fairly  good.  As predicted, the particles with
the poorest carbon burnout are contained in the 150 to 400 micron size range.  In
addition the size range of particles with poor burnout is wider for the higher veloc-
ity test as was predicted by the burnout model.  An obvious discrepancy exists between
the preducted and the actual burnout in the fly ash particles around 50 microns.  At
this size the model predicts good  carbon burnout which disagrees with the experimental
results.  In both tests a significant portion of the fly ash carbon was found around
the 50 micron particle size.  A possible explanation for this carbon peak is that it
results from large coal particles  (whose Vt>V) which break apart while in the free-
board region.  The fine coal particles which  result will have very short residence
times if they are formed near  the  exit of the combustion zone.  This abbreviated
residence time would cause poor carbon burnout despite the reduced burnout time re-
quired for smaller  particles.


FLY ASH RF.INJECTION TESTS

       A series of tests were  conducted to study the combustion of this fly ash by
reinjection to the coal burning cell from which it was produced3.  Two test methods
were followed during this program.   The first test method consisted of open loop tests
in which both coal and fly ash were fired to  a fluidized bed operating at typical coal

                                         89

-------
VO
o





o
Ul
CO
LJ
2
P


IO
9
8
7
I
6
5


4
3
2
o
PARTICLE ^*j 1
RESIDENCE , 	 M
TIMES IN FBM 1
1
* • 1

; /r
'/ L ** *
i 0i^
ft *
/ '1 1
\ ' /
x^/x/
•rr^r"*^^ .
^^ ---
x^*^^ >v --'""*"
_/ -X*" PARTICLE
^ "< — ^BURNOUT
„" TIMES
^ ^ ^



	 9/ป FT/SEC
	 11.2 FT/SEC
TBซI500CF
I • ' • * ft
                               100     200    300    400     500     600

                                                    PARTICLE SIZE MICRONS
700    800    900    1000
                                          Figure 6. Compviton of Particle Burnout Timt and Residence Time
                                                 As Functions of Particle Size

-------
burning conditions.  The fly ash was fed from a storage silo which was filled from
previous coal burning tests.  The fly ash emitted fron the fluidized bed was collected
for analysis purposes only, and not for reinjection.  This procedure results in a
"pseudo-reinjection" scheme, allowing only one pass for the "reinjปcted" fly ash.

       This allowed monitoring of the fly ash feed rate and fly ash emission rate
which would not be possible during the true recycle tests.  By comparing the results
of these tests with results of coal burning alone, it was determined that approxi-
mately 607. carbon burnup of the fly ash feed was achieved on a one pass basis.   This
indicated that approximately three passes would be required to achieve a 95% overall
combustion efficiency.

       The second test method provided data on the closed loop reinjection of the fly
ash to the coal fired cell from which it was produced.  In this series of tests, all
of the fly ash collected in the cyclone was reinjected to the fluidized bed.  The only
fly ash not reinjected is that which is too fine to be collected by the cyclone.
This fine dust is emitted to the atmosphere with the flue gas.

       The operating conditions and results for these closed loop recycle tests are
contained in Table IV.  This recycle scheme resulted in very high combustion efficien-
cies, greater than 95% in most cases.  One interesting result obtained from these
tests concerned the rate of the fly ash recycle.  Since incrts as well as combustables
were being recycled, it was expected that the amount of fly ash being reinjected
would increase steadily and the carbon content would decrease steadily.  This was not
observed.  Instead, a steady state recycle condition developed and continued through
the tests.  One probable exolanation is that most of the fly ash that was reinjected
stayed in the bed.  This e>planation is supported by theoretical calculations which
show that burning fly ash particles could have surface temperatures above the ash
fusion temperature, and thus they could become sticky and fuse to the cooler bed
particles.

       T?ble V shows the typical carbon analyses for the fly ash which was reinjected
and the finer dust which was carried out with the flud gas for both test methods.  For
comparison purposes, a typical carbon analysis of fly ash and dust which results from
coal combustion alone is included.  During main cell operating conditions with no fly
ash reinjection, the fly ash will typically contain about 46% carbon.  In both the
open loop and the closed loop tests, the carbon ccntent in the fly ash was 417..

       A carbon balance for Test 650-12, one of the closed loop tests, is given in
Table VI.  The purpose of the carbon balance is to demonstrate the validity of the
steady state recycle condition.  This steady state recycle condition was not antici-
pated, and hence an inspection was made to find a place in the system where a signif-
icant amount of fly ash could accumulate.  Since r.o such accumulation was found, and
since the results of this and other carbon balances were reasonable, it was concluded
that some of the fly ash was retained in the bed where it burned.

       Figure 6 shows the effect that fly ash recycle has on the combustion efficiency
of the Alexandria FBM.  The dramatic increase in the combustion efficiency is due to
the combustion of all of the fly ash collected in the cyclone.  The only losses in
this case are due to the carbon monoxide and hydrocarbons emissions and the fine dust
which by-passes the cyclone ar-* if-ves with the flue gas.  These tests showed that
combustion efficiencies as high as 96% are consistently achievable.  This combustion
efficiency with fly ash recycle is satisfactory for industrial scale boilers where a
separate Carbon-Burnup Cell would be impractical.


CARBON-BURNUP CELL TESTS

       For utility size applications, the use of fly ash reinjectio:i would not  be sat-
isfactory due to the need for combustion efficiencies greater than 99%.  In the design
of the 30 MW Multicell Fluidized-Bed toiler, MFB, in Rivesville and more recently in
the design studies for utility size FBC's. the concept of a separate cell for fly ash
combustion has been utilized.  This Carbon-Burnup Cell, or CBC, is operated at  condi-
tions different from the main cells which are more favorable for carbon combustion.
In the case of the Rivesville MFB, the CBC concept resulted in a four cell boiler with
three main cells burning coal and a fourth, smaller cell burning ily ash from the
other cells.  The differences between the main cell and the CBC operating conditions


                                         91

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          Table IV.  Fly Ash Closed Loop Recycle Test Results.

Bed Temperature, ฐF
Bed Depth, inches static
Superficial Velocity, ft/sec
Air/Coal Ratio, Ih/lb
Ca/S Ratio, moles/mole
0? in Flue, Vol 7.
co. voi r.
Hydrocarbons, ppm
Dust Emitted/Coal Ratio, Ib/lb
Bed Drai.i/Coal Ratio, Ib/lb
7.C in Dust
7.C in Bed
7.C in Fly Ash Recycled
Combustion Efficiency, %

1670
13.8
9.8
10.5
2.9
3.0
0.3
1928
0.03
0.13
13.7
0.4
50.0
96.1
650-1
1675
13.6
').7
10.6
2.9
2.6
0.26
1538
0.03
0.23
14.7
1.3
49.2
95.9
2
1680
13.6
0.8
10.6
2.9
2.8
0.27
1448
0.06
0.23
13.7
0.0
41.8
95.8

1630
13.7
9.6
12.0
3.0
4.2
0.08
428
0.06
0.26
15.6
0.3
44.7
97.4
650
1545
12.7
9.4
12.6
3.5
7.2
.14
143
0.05
0.39
22.1
0.9
42.6
96.4
-13
1570
12.6
9.3
12.5
3.4
6.7
.11
63
0.06
0.38
22.7
1.2
38.0
95.8
650-14
1610
18.4
9.3
9.4
2.6
2.5
.34
1350
0.06
0.39
22.1
0.8
44.2
95.2
1615
18.7
9.3
9.4
2.6
1.9
.42
1430
0.06
0.26
23.4
0.3
41.1
95.1
1620
18.5
9.5
10.0
2.8
1.8
.40
2110
0.07
0.27
22.7
1.2
41.2
93.8
Table V.  Typical Carbon Analysis  for Fly Ash  and Dust  Reinjection Tests.
Type of Test
Coal Combustion
Coal and Fly Ash Ooen Loop
Coal and Fly Ash Closed Loop
Fly Ash
467,
417.
517.
Dust
21%
227,
227.
          Table VI.   Carbon Balance  for Test  6SO-12  Period  1.
Inputs
Carbon in
Carbon in
Total
Outputs
Carbon as
Carbon as
Carbon in
Carbon in
Carbon as
Total

Coal
Limestone


COy
CO
Dust
Bed Drain
Hydrocarbons

7. Difference

366.
24.
391.

377.
7.
2.
0.
4.
392.
0.

6
5
1

5
9
2
3
2
1
26

Ib/hr
Ib/hr
Ib/hr

Ib/hr
Ib/hr
Ib/hr
Ib/hr
Ib/nr
Ib/hr

                                    92

-------
100

90
c
•
o
6 80
0.
u
bi
u
It 70
w
o
g
i 60
u
so
•
n ฐ Trrt

L^3m mm
Eg- m


-
ฉ WITH FLY ASH RECYCLE

- GD WITHOUT FLY ASH RECYCLE
i i a i
1500        1550        1600

         BED TEMPERATURE ฐF
1650
                                                1700
    Figure 6.  Improvement in Main Cell Combustion Efficiency
            Due to Fly Ash Recycle
                      93

-------
are summarized in Table VII.  The design conditions for the Carhon-Burnup Cell were
based on a test program conducted in 1972 at the Alexandria. Virginia laboratory1*.
These tests were conducted in a one square foot combustor with a single i'ly ash feud
point installed through the air distributor.  Due to the small size of the combustor,
no evaluation of the number of feed points could be maJo during these early tests.
To assure successful operation of the much larger 6 ft. by 12 ft. cross section CBC
at Rivesville, a test program was conducted to verify the ChC design parameters and
to evaluate the number of feeders necessary for efficient carbon burnup.

       The test program was carried out in the Alexandria laboratory FBM which was
modified to allow high temperature operation.  The waterwalls were covered with one
and one-half inches of a castablc refractory to reduce the heat removal from the bed.
However, not enough refractory could be added in the vertical direction to prevent
cooling of the bed caused by splashing of bed material into the low freeboard area of
the FBtl.  In order to achieve bed temperatures above 2000ฐF, the operating ranges for
bed depth and oxygen had to be reduced.  The fly ash fuel was produced by burning
4.57. sulfur Sewickley coal in a lin.estone bed in the FBM during various test programs.

       Table VIII shows the size distribution and composition of the fly ash fuel used
in the test program.  The carbon content of the fly ash varied considerable due to the
different operating conditions during which the fly ash was produced.  Bed material
for the fly ash combustion tests was 1/8 inch by down limestone fahich had been cal-
cined and sulfatcd while burning coal.  Ho attempt was made to capture sulfur or re-
plenish bed material during the test program.  Bed material was withdravm during
testing to maintain a constant bed level.  Detailed description of the operating pro-
cedures^ and test results'- are contained in the references.

       In Figure 7 the data from this test program has been compared to the results
from the small combuntor test program reported in 1972.  During that test program,  a
statistical correlation of the data was developed to predict the combustion efficien-
cy to within a standard deviation of 2^7..  This is the shaded portion of the graph.
When the data from the recent test program is applied to the correlation, it can be
seen that the observed combustion efficiencies are generally higher than the correla-
tion predicts, particularly for the two and three feeder tests.  The test data shows
that fly ash combustion efficiencies of over 901 are achievable.

       During the test program, four najor operating conditions wrro identified as
having an important effect on the combustion efficiency.  Bed temperature was consid-
ered to be the most critical factor in obtaining a high carbon burnup.  As was experi-
enced in the previous test work, the closer the bed temperature was to the ash fusion
temperature, the better the carbon burnup.  This result is thought to be due to both
the effects of agglomeration of ash to bed particles and to improved fuel reactivity
at the higher bed temperatures.  F.xcess air was considered the next most import int
operating condition and was measured in terns of percent excess oxygen in the flue
F,.is.  Bed depth and superficial velocity are also inportant operating conditions since
they affect the mixing and directly determine the residence tine of the gas and the
fly ash particles in the bed.  Based on the test results, fly ash carbon burnups
greater, than 907, can be achieved with the designed operating conditions of 2000ฐF.  57.
excess oxygen, 2 feet static bed depth r.nd 9 ft/sec superficial velocity.

       A CBC operating at 907. combustion efficiency can bring the overall plant com-
bustion efficiency up to 99% or more, depending on the efficiency of the primary dust
collection equipment.


SUMMARY

       In the fluidizcd-bed combustion processes, 10 to 15% of the heat input is
usually lost as high carbon content fly ash.  The results of these recent test pro-
grams related co combustion efficiency'have demonstrated thac a major portion of the
heat loss in high carbon content fly ash can be recovered.  When fly ash reinjcction
to a main cell is used, combustion efficiencies of over 967. are attainable.  When fly
ash is injected to a Carbon-Burnup Cell, combustion efficiencies over 99% can be ex-
pected.  The fly ash characterization tests show that fly ash which will be used for
reinjection should be selectively collected to minimize inerts reinjection.  Theoreti-
cal calculations show that the carbon distribution in the fly ash will be affected by
Che operating superficial velocity as well a? the combustor geometry.


                                          94

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        Table VII.   Comparison of Typical  AFBC Operating Conditions.


                                       Main Cell          CRC

Bed Temperature.  ฐF                      1550            2000
Superficial Velocity,  ft/sec               12               9
Primary Fuel                             Coal            Fly Ash
In-Bed Heat Transfer Surface             Yes             No
Sorbent                                  Limestone       Sulfated Bed
                                                          (from Main  Cell)
                     Table VTU.   Typical Fly Ash Fuel.
                             Size Distribution

                 US Sieve Series          Mass Fraction

                       +  20                0.001
                 -  20 +  30                0.006
                 -  30 +  40                0.029
                 -  40 +  ',8                0.068
                 -  70 •ป•  80                0.120
                 -  80 + 100                0.101
                 - 100 -I- 140                0.122
                 - KO + 170                0.117
                 - 170 + 200                0.073
                 - 200 + 270                0.036
                 - 270 + 325                0.097
                 - 325 + 400                0.033
                 - 400                      0.156

                               Compos it ton

                       Component
                       Carbon
                       Calcium
                       Sulfur
                       Hydrogen
                       Balance*
    Coal and Limestone Derived Ash.
                                     95

-------
    100
ซ   90
o
u
     80
     70
     GO
     9.0
O Thrซ* Fcod Point*
X Two Fod Point*
Q On*  FMd Point
        BO         6O        7O        80        9O
                   COMBUSTION EFFICIENCY, % (Obsorv.d)
                                                    IOO
         Figure 7. Companion of Small Combuttor Teiti and Current test Program
                                 96

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ACKNOWLEDGEMENTS

       This report presents work conducted under U.S.  ERDA Contract No.  EX-76-C-01-
1237.  Special thanks are given to PSR's Alexandria,  Va.  st^ff for their diligent
effort in performing these experiments and to Ms. L.  Breault for preparing the manu-
script.


REFERENCES

1.  Gasner. Larry L. , and Divilio. Robert .'., "Combustion Efficiency Enhancement  in
    Fluidized-Bed Boilers", 70th Annual Meeting of the American Institute of Chemical
    Engineers, Paper 34d, November 15. 1977.  New York City.

2.  Parker and Hottel. Ind. Eng. Chem.. 28. 1334 (1936)

3.  Pope, Evans -nd Robbins Incorporated, Multicell Fluidized-Bcd Boiler Design.  Con-
    struction and Tjst Program. Quarterly Progress Repott No.10, Aug-Oct.1977.
    United States Energy Research and Development Administration, Contract  EX-76-C-01-
    1237.

4.  Pope. Evans and Robbins Incorporated, Study of Characterization and  Control of
    Air Pollutants from A Fluidized-Bed Combustion Unit.  The Carbon-Hurnup  Cell.  NTIS
    Report No. PB210-828, OTfice of Air Programs, Environmental  Protection  Agency,
    Feb. 1972.

5.  Pope, Evans and Robbins Incorporated, Multtccll Fluidized-Bod Boiler Design,  Con-
    struction and Test Program. Interim Report No.4,  June,1977.United States Energy
    Research and Development Administration,  Contract EX-76-C-01-1237.

6.  Reed, Robert R., and Divilio, Robert J.,  "Fly Ash Combustion in A Fluidized-Bed
    Boiler", 70th Annual Meeting of the American Institute of  Chemical Engineers,
    Paper 80b. November 16, 1977, New Vork City.
                                          97

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            QUESTIONS/RESPONSES/COMMENTS

     SHELTGN EHRLICH,  CHAIRMAN:  Are there any questions?

     MR. STRUMPF:   Hal  Strumpf, AiResearch Manufacturing Conpany.   In
the carbon burnup  cell, what  is the bed material?

     MR. AULISIO:   The bed material used in the carbon burnup cell
test was bed material  from a main cell type of operation,  tohen we
were storing fly ash from main cell tests to be used in CBC tests,  we
were also storing  bed  material for the CBC test program; so the CBC
bed consists of calcined and sulfated limestone.

     MR. STRUMPF:   Well, if we were really going to run this, what
would we use for bed material?

     MR. AUI IS10:   That would be the bed material in an actual
situation.

     MR. STRUMPF:   Well, then, there is no more sulfur capture in  the
CBC.  Is that, right?

     MR. AULISIO:   I don't want to say there is no more sulfur cap-
ture.  There is reduced sulfur capture.  We know that sulfur capture
drops off as temperature increases; however, I ^on't think  that it
goes to zero at 2,000  degrees Fahrenheit.  We h*ave limited  data indi-
cating that there  is some extent of sulfur capture in a CBC.

     MR. STRUMPF:   Could that be a problem, that we will have too
much S02, since we will have  reduced sulfur capture?

     MR. AULISIO:   It  has to be considered in the design and operation
of a unit.  The main cells have to be operated, in order to have $03
emissions for the  total unit below EPA limits.

     SHELTON EHRLICH,  CHAIRMAN:  Are there any other questions?  This
is from Ram Seth,  of Gilbert Associates.  "What kind of bed height
and fluidizing velocities were used for the testing?"  And.the second
question:  "Did you observe any biradal stability as was observed
in older tests?"

     MR. AULISIO:   Let me try to answer the second question first.   I
don't think I am as old as the older tests.  I am not sure  what you
mean by "bimodal stability."  Ram, could you explain that a little
bit?
                                 98

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     SHELTON EHRLICH, CHAIRMAN:   There is a potential  mode of  opera-
tion in which the carbon is heated in the bed instead  of burned,  and
then burns in the freeboard. As  a result, the bed  temperature  starts
to drop, the combustion rate within the bed drops  further and  while
the carbon is still  being fed as well as the air,  the  carbon burns  in
the freeboard.  Under some apparently identical  conditions the carbon
burns in the bed or  it burns in  the freeboard and  that is what Ram
means by "bimodal stability."

     MR. AULISIO:  The CBC at Rivesville, and probably other CBCs in
design studies, are  equipped so  they can have supplemental  coal  feed
if there is a drop in the bed temperature.

     SPEAKER:  Okay.  Let me repeat the first question.  You wanted
to know what heights and fluidizing velocities were used in the tests.
The test I just described was actually three different programs and a
variety of velocities and bed heights were used.  In the fly ash
characterization program, we used two different velocities, not
widely apart, but those are because of our test unit,  and those were
for the purpose of determining the effect of velocity  on fly ash.

     In the fly ash  reinjection  to a main cell, a  wide variety of
velocities--or what  we consider  a wide variety of  velocities—were
used.  This was from about 7 to  12 ft/sec; and in  the  carbon burnup
cell, the same case  holds.  Bed  depths ranged from 18  inches to 24
inches in both the CBC and fly ash reinjection tests.

     SHELTON EHRLICH, CHAIRMAN:   The next question is  from Darrell
Young of General Atomic.  "Your  96 percent approximate combustion
efficiency may be improved if you could recycle the cyclone bypassed
fines, that is, the  material that isn't caught.  Any tests planned
for better recovery on the recycle?"

     MR. AULISIO:  That's a possibility.  The 96 percent could be
improved by recycling all the fines; but as we showed  in the fly  ash
characterization test, the smaller the particle becomes, the lower  the
carbon content becomes, and you  reach a point of diminishing returns,
where you start reinjecting a lot of ash and it sinply tends to cool
the bed down further, which would then require an  increase in  coal
feed.

     To take that a  little bit further, I also want to point out, if
it wasn't clear from the first slide, that we have an  extremely short
freeboard in the FBM, the unit in which these tests were done;
and that probably led, to a great extent, to combustion efficiencies
no higher than 96 percent.  Our  CO losses are fairly high, since  we
have a very short gas residence  time before the gases  are cooled  down
below 1,000ฐF.  By -.-educing the  CO losses, this combustion efficiency
could be increased significantly.
                                  99

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     SHELTON EHRLICH, CHAIRMAN:   Are there any other questions?

     MR. HOLDHUSEN:  Jim Holdhusen of Fluidyne Engineering.   Maybe
the answer is very simple, but I don't understand why 96 percent may
be a high enough efficiency for an industrial  application, and 99
percent is required for utility applications.   It seems to me it's 3
percent in fuel cost.  Is there something else?

     MR. AULISIO:  Well, I'm not a utility man, but from what they
tell me, they burn an awful lot of fuel, and a few percent gets  to be
extremely expensive.

     SHF.LTON EHRLICH, CHAIRMAN:   It can be answered another way.  The
guarantees that the manufacturers of industrial coal-fired boilers
make, using spreader-stokers for example, generally inc.ude a 3  to 5
percent efficiency loss as lost carbon; and, since that was the  target
for the fluidized bed industrial boiler, meeting that efficiency with
FBC was considered acceptable.  Utilities on the other hand demand
near 100 percent combustion efficiency.  But you're right.  You  don't
want to throw away any fuel, if you don't have to.  Any further  ques-
tions?  All right.  Before we go on with the next speaker, I would
like to take a co-chairman's opportunity to give a little lecture for
us, here.

     I remember meeting Kixie Aulisio for the first time about
three years ago, when he came to work for us at Pope, Evans, and
Robbins in Alexandria.  The first assignment I gave him was to take
Levenspiel's book on fluidization and have him experimentally verify
Ergun's correlation using the experimental boiler in cold tests.  We
then went over the data very carefully and compared the results  to
the correlations.  The lesson I wanted to teach was that engineering
development—successful development—follows from a number of steps
that go like this: insight, experiment, data,  and then going back to
new insight, experiment, and then design data. One of the pleasures
for a man who is qrowinq older is to know that he has had an impact
on a younq man who is briaht, aqqressive and doinq a qood job.
                                 100

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                        INTRODUCTION

     WAYNF A.  McCURnV, CHAIRMAN:  Our next speaker is Walter  Podolski,
a chemical engineer  on the CTIU project at Argonne.  Walt got his
degree in chenical engineering from the University of Detroit in
1966, a Master's  degree  fron Northwestern University in 1969  and a
Doctorate in chemical engineering in 1973 fron Northwestern.
He has been actively involved with component test and integration
unit since its inception and is the lead process engineer responsible
for the process and  operations overview for the CTIU.  He is  a member
of American Institute of Chemical Engineers.  Walter?
                                101

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                         Pressurized Fiuidized-Bed Combustion
                          Component Test and Integration Unit
                                     Design Status

                                    Walter F. Podolski,
                                Argonne National Laboratory
                                          and
                                    Rufus W. Crawford.
                               Steams-Roger Engineering Co.

ABSTRACT

       Argonne National Laboratory is providing technical direction to the design of
the Pressurized Fluidized-Bed Combustion/Component Test and  Integration Unit (PFBC/
CTIU) which is now in progress at the Steams-Roper Engineering Co.  This paper
describes the prelininary design of the PFBC/CTIU which is nearly complete at this
tine.  Individual plant systems arc described in relation to  the design criteria
established for the systems.  The major goals and objectives  of the CTIU are:  (1) to
te~t and evaluate components, instrumentation, samplinp. technicues. control concepts
and techniques, and materials of construction proposed for PFBC systems and (2) to
investigate alternative PFBC concepts.  These goals are being inplenented bv
designing a modular facility with inherent flexibility.      .


INTRODUCTION

       A proposal to design and build the Pressurized Fluidis-.C'l-Bed Combustion/
Component Test and Integration Unit (PFBC/CTIU) was prepared  bv Areor.ne National
Laboratory (AXL) and was submitted to ERDA Fossil Enerp.v in  January 1975.  The
proposal was suonlenented in M.iv 1975 by a more detailed conceotual n o<" the
facility develoix-d by AMI..  This conceptual 'lesipn was described in an earlier paper.'1
In Aaril 1976. E"DA authorized the nroiect and in Auo.ust 1976 selected the
Stearns-Pop.er Engineering Co. (S-P) as architect-engineer/construction manaoer.

       Soon after S-R began work  >n the project, thev re-estiraatcd earlier ANI.
estimates of project cost and scnedule and perfomc-d a number of trarfe-oT studies
in order ro enhance the flexibility of the PFBC/CTIU aiid to  incorporate the results
of technical reviews and AI.'L subcontractor recommendations into the arolcct scope.
*11 of the above information was assembled into a Comprehensive Analvsis report
describinp, the reconnended clesien. capabilities, and cost of  the ''F3C/CTIL'.  This
report was presented to EPJ)A Fossil Energy in February 1977.  Title I (or preliminary
engineering) has proceeded since that time on the basis of the Coir.prohcnsive Analysis
and i<= nearly complete.  The fo'loving sections of this caper describe the design and
testing philosophy, major system designs, and schedule for completion of the plant.


DESIGN AND TESTING PROGRAM

Objectives and Design Philosophy

       The objectives of the CTIU are (1) to test and evaluate cot:-.->onents,
instrumentation, sampling  techniques, control concepts and technioues.
and materials of construction proposed for PFBC systems and  (2) to
investigate alternative PFBC concepts, which is possible because of iL3
inherent flexibility.

       The philosophy being employed  to design the CTIU in order to ?ulfill these
objectives can be stated as follows:  (1) the initial facilitv wi11 have as few
desizn corinlexi'-ies as is practicable; (2) provisions will be rcade for future
expansion in size and complexity usins a modular add-on approach, and O) svstem
components will te easily accessible.

       The following schematic of the CTIU. Figure 1. represents th? design
ohilosophy outlined above.  The facility to be initially built is indicated on the
left side of the figure.  The conbustor pressure vessel contains a 3 ft x 3 ft
refractory-lined fluidized bed in which is submerged an array of horizontal tubes


                                          102

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o
CO
                                                     Figure 1. Schematic of PFBC/CTIU Showing Expansion Capability

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wh'ich are cooled by circulating pressurized water.  The unit will be operated at
relatively high excess air levels.   This initial configuration represents a less
demanding set of operating conditions than even the baseline operating conditions
and should provide a high probability of successful operation within a short time
period.  The lines inside the fluidized-bed combustor (Figure 1) represent either
horizontally or vertically oriented cooling tubes, only one version of which can be
tested at a given time.  Similarly, only one of the two indicated hot-gas niping
outlets (the two top outlets) from the combustor pressure vessel will be used at
a given time.

       The right side of Figure 1 illustrates the expansion caoability of the CTIU.
Equipment can be installed in parallel with existing eauipir.ent in order to
accommodate testing at the increased gas and solids flow rates associated with a
4 ft x 4 ft combustor or with two 3 ft x 3 ft combustors* stacked one on top of
the other.  The eauipment additiors are represented by diaRonallv-lined blocks.

Combustor Design Cases

       The key to CTIU flexibility lies in the design of the conbustor svstem.  The
combtistcr pressure containment vessel is tall enough to be able to accommodate all
foreseeable single-bed concepts or a representative stacked-bed design.  Secondly.
the inner combustor is relatively easily replaced ..as a shutdown changeover) with a
combustor of different cross section and/or a combustor containing cooling tubes of
different geometry.  The flow rate of gas through the system remains relatively
constant, but the gas velocity through the combustor can be varied in order to
investigate different sets of operating conditions.

       To ensure the capability of testing alternative combustor designs, several
designs have been developed far enough to investigate interface problems and to
provide assurance that these cases can be fabricated and installed in the future.
These cases are as follows:  Case A, a single, 3 ft x 3 ft refractory-lined
fluidized bed in which is submerged an array or horizontal tubes which are cooled
by circulating pressurized water; Case B, a single 4 ft x 6 ft refractory-lined
combustor in which is submerged an array of horizontal tubes (different from those
in Case A) which are cooled by circulating pressurized w.iter; Case C, two stacked
3 ft x 3 ft combustors enclosed by a common water wall; in each bed is submerged an
array of horizontal tubes which are cooled by circulating pressurized water or
superheated steam; Case D, a single 3 ft x 3 ft refractory-lined combustor in which
is submerged an array of vertical tubes which are cooled by compressed air.

       Case A is further divided into Cases A-l and A-2.  Case A-l hardware will be
installed initially.  Case A-2 has more submerged cooling surface than A-l in order
to operate at 20 percent excess combustion air and is the baseline design case.
Hardware for Case A-2 which is different from that for Case A-l will be fabricated
but will not be installed initially.

Future Expansion Capabilities

       The combustor, supporting systems, and other portions of the facility have
been designed with possible future modification and expansion in mind.  The more
significant areas are as follows:

       (1) The combustor has been designed to accommodate thi testing reauirements of
future Cases B, C. and D, as defined above.  Sufficient nozzles and penetrations will
be included on the pressure containment vessel to allow removal of the initial
fiuidized bed internals and replacement with the other fluidized bed internals
without a need to perform mechanical modifications to the pressure vessel.  The
pressure vessel has been designed with a flanged upper semi-elliptical head; the
head can be removed to improve accessibility to fluidized-bed internals for
maintenance or changeout.  Additionally, other manways are provided for maintenance
access.
*A combustor here refers to a group of modules bolted together and containing
 a fluidized bed.


                                          104

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       A pressure vessel height has been established that meets the requirements of.
all cases; i.e., the height is sufficient to allow the Case A single fluidized bed
internals to be replaced with the other units reouired tor future testing.

       Since the design requirements have been cstabli shec! usinp. selected engineering
criteria for future cases,  any future fluidized-bod configurations to be tested
(other than those established for purposes cf design) will have to be designed and
fabricated to be consistent with the nhvsical constraints presented bv the initial
nressure shell.

       (2) The raw material handling, nrenaration. and feed svst2m has been designed
with room enough for the installation of two additional feeding svstems (one for coal
and one for sorbent) in order to double the feed rate canacitv of the svsten.  Raw
material preparation eouipnent is slip.htlv oversized so that with additional operating
time, increased preparation and feed rates can be maintained.

       (3) The air compression svstcm has been designed to allow snace for future
addition of an identical system in order to double the air flow capacity of the
system when a A ft x 4 ft fluidized bed or two 3 It x 3 ft fluidized beds one
stacked on top of the other are tested.

       (4) The hot gas cleanup system has been designed to allow space for the addition
of a second parallel train of cleanup equipment of the same capacity as the initial
train of equipment.  In addition, there is the capability in the initial design to
extract a stream of up to 1000 acfm downstream from the primary cyclone in order to
test prototypical gas cleanup equipment.  There is also provision in the form of a
space allowance for adding a waste heat recovery boiler.

       (5) The turbine test system has been designed around n stationary array of
turbine blades (test cascade) in the baseline design.  The cascade can he replaced
by a unit with twice the flow capacity.  In addition, space has been allowed for
future Installation of a turbine-comprcssor-ecnerator sct--either a corrmercial ly
available small existinp. machine or a turbine speciallv designed and fabricated
for the CTIU.

       (6) The heat removal svstem has hoen desip.ned to expand from the baseline
(Tase A-"?) pressurized water svsten with 17.S **>< Btu/hr dutv (1) to a pressurized
water svstem with double the capacitv (15.6 f*M Btu/hr) ror rase B or (2) to a
nressurized water/superheated steam cooling svsten for Case C with a dutv OF
20.3 MM Btu/hr.  Expansion would be bv the addition of extra nutnns.  stea-n generators.
and associated equipment.

       (7) The space allowances for the utility systems within the CTIU building have
been established to allow additional compressors, coolers,  pumps, and other utility
system hardware items to be incorporated that will be reouired to support future
expanded operations.

       (8) The CTIU building has been designed to allow a future extension to be built
that will be Iccatcd on the east side of the initial facility.   This bay will house
the utility, water, and steam generation equipment that will be required for operation
of the future cases.

       (9) The spent solids handling systems can be expanded by adding parallel
vessels, coolers, feeders,  and conveyors to handle the increased material flow rate
requirements for future testing.

Test Program

       Experiments in the CTIU can conveniently be categorized as component testing.
main process variable testing, and materials testing, all of which mav be under wav
during a particular experimental run.  After initial shakedown and startup testing is
complete, intermediate-duration experiments of several hundred hour's leneth are
planned for CTIU operation.

       Table I indicates the tvne of experimental proeram nlanned for the CTIU.  The
main process conditions for each test run are prinarilv determined bv the combustor
configuration.  Component testing and evaluation wiil be done under differing and

                                         105

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                      Table I.  CTIU Experimental Program Outline.
    Component Testing

  • Solids Feed
    Equipment
  • Solids Handling
    Valves
  • Hot Gas Cleanup
    Equipment
  9 Hot Gas Piping
  • Control Valves
  • Spent Solids
    Handling Equipment
  • Instrumentation
  Main Process Testing

• Process Conditions
   Case A-l
   Case A-2
   Case B
   Case C
   Case D
   Future:  Unspecified
• Research
   Heat Transfer
   Sampling of Solids
   and Cases
   Material Balance
   Determination
   Supervisory Control
   Development
     Materials Program

• Materials of Construction
   Review

   Specification
• Materials Research
   Testing of coolerl and
   uncooled materials in
   combustor
   Testing of turbine
   blade materials in
   cascade
changing conditions in order to fully evaluate oerformancc characteristics.  As the
materials testing program is nore fully developed, materials for testing and
conditions of exposure will be selected and these materials and conditions will be
integrated into the overall test program.

       After Case A-l has be-in subject to initial shakedown and testing, combustor
assemblies for any of the ot'nev cases .r an as-yet-unspecified combustor configuration
could be fabricated and installed for testing.

Quality Assurance

       The design, procurement, construction management and construction activities
associated with the CTIU will be carried out in accordance with the QA program
established for the CTIU Project.  Three levels of quality assurance have been
identified for CTIU systems.'  Those systems whose failure or malfunction would
jeopardize personnel safety or ANL Heating Plant operation or whose unioue design or
developmental nature require design verification are classified as Level I.  Those
systems whose failure or malfunction is not serious enough to warrant their inclusion
in Level I but would result in the CTIU being inoperative for one year or lor.gcr, or
whose malfunction could result in a subseauent hazard in another system, are
classified as Level II.  All other systems are classified as Level III.

       Although a system is classified in a certain level, subsystems or components
within that system can carry either a higher or lower classification level.  These
systems will be identified during the detailed engineering design.  Level I
classification indicates that design verifications are reouired and that procurement
will be from venders having previously aooroved OA programs.  Level II classification
systems will be designed, procured, and inspected according to predetermined OA
reouirements.  Design verification  is not mandatory.  Table II indicates the OA
level assignments for the major CTIU systems and the principal hazards associated
with these systems.


SYSTEM DESIGNS

       The following sections contain a more detailed description of the more
important systems and their capability.  Only the hardware associated with Case A
is described since that is the only equipment to be installed initially.  The designs
of the combustor and supporting CTIU process equipment for Cases A-l and A-2 are
based upon the design criteria listed in Table III.
                                         106

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                            Table II.  OA Level Assignments
     Raw Material Receiving.
     Storage, Preparation
     and Handling
     Feed Injection
     Spent Solids Handling
     and Cooling
     Combustor
     Pressurized Spent Solids
     Hot fias Cleanup
     Process Air Compression
     Turbine Test Cascade
     Pressurized water and
     Steam Generation
     Utility Systems
      Nine Subsystems

     Instrumentation and
     Control
      Plant Protection
      Process Control

      Supervisory Control

      Data Acquisition
                             Level                   Principal Hazard
                               I               Coal dust fire or explosion

                               II              Mechanical failure/rupture

                               II              Internal fire
                               I               Pressure vessel rupture
                               I               Mechanical failure/rupture
                               I             '  Mechanical failure/rupture
                               II              Lube oil fire
                               I               'ressure vessel ruoture

                               I               Pressure vessel ruoture
                             I,II, or III      Varies depending on hazard
                                               of subsystem
                               I               Personnel safety
                               II              Loss of full performance
                                               design capability
                               II              Loss of full performance
                                               design capability
                               II              Loss of full performance
                                               design capability
                  Table III.  CTIU Baseline Combustor Design Criteria
Operating pressure
Bed operating temperature
Bed height
Freeboard height

Fluidizing air (dry)
Feed transport air
Excess combustion air
Superficial gas velocity
Ca/S mole ratio
Target sulfur removal (min)
Combustion efficiency
   Reference
10 atra (147 psia)
X650ฐF
* ft. 5 in
23 ft

10 Ib/sec
0.8 Ib/sec
207.
7 ft/sec
2
90%
                                                                   3-12 atm
                                                                   1350-1850ฐF
                                                                   Variable onlv
                                                                   during shutdown
                                                                   20-100"
For purposes of analysis and design, the various functional areas of the CTIU facility
have been categorized.  These are discussed in the following sections.
Facility Description
       The CTIU will be constructed on the site of the Argonne National Laboratory,
which is located in Argonne, Illinois.  The CTIU location (adjacent to the existing
Argonne Heating Plant) was selected due to its proximity to existing railroad spurs.
                                         107

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electrical service,  building utilities,  process utilities,  and existing facilities.
This location will  allow the use o? many existing Areonne facilities associated with
the Heating Plant operation,  including portions of the coal  receiving and handling
facilities and cho  ash storage system.

       Existing railroad spurs and roadways located .iust to the west and south of
the CTIU will allow raw coal and prepared dolomite or limestone to be brought in by
railroad cars or trucks.  Facility utilities,  including steam, domestic water, and
sanitary sewers are in close proximity and will be extended to serve the CTIU
operation.  Figure  2 is an artis''s sketch of  the facility  that is based on che
results of Title I  Engineering.

       The plant equipment and supporting items will be housed in a rigid-frame steel
structure, enclosed with insulated metal siding.  The building will be approximately
110 ft by 125 ft and approximately 145 ft high.  As planned, the structure will be
heated and fully ventilated and will have six  floors, with  an industrial elevator
serving the five lower floors.  The major equipment items that will be inside the
building are the combustor,  the hot gas cleanup system, the pressurized-water heat-
removal system, spent solids handling,  and the combustor feed and injection sytems.
The raw materials receiving, preparation, and  handling system will be installed
outdoors in an area adjacent to the CTIU structure.  Other  eouipment items that do
not require enclosed weather protection will be installed outdoors at grade or on
the roof of the structure.

       The layout of the building has been influenced bv the reouirenents for room
for additional hardware items associated with  the selected  nlant operational cases.
Conceotual equipment arrangements for the future ol.int configurations were made oart
of the Title I F.ngineering to ensure that the  buf.lding layouts will allow incorpora-
tion of the future  cases.

       The coab'istor will be located in a central elevated  position within the
building and will be supported by the interior frame strucf.ire.  A traveling overhead
crane will be installed to allow maintenance,  removal, and  replacement of heavy
combustor components and other process equipment.  The 'ayours and arrangements for
the combustor supporting equipment allow easy  access to >_-ฃf_••- : maintenance, repairs,
replacement, or inspections.  As designed, the combustor internals will he
disassembled by being lifted upward from within the shell by the overhead crane.
Laydown areas are included that allow repairs  and inspections.

       There will be an office arc-a for the plant operations and engineering staffs.
A central control room will also be provided.

Combustor System

       The fluidized-bed combustor is located  inside a 12-ft-ID pressure containment
vessel carrying a rating of 200 psig.  The contain-ncnt vessel is 49 ft long, seam-to-
sca.n.  The pressure containment vessel surrounds an internal fluiiiized bed module
section which has been designed for ease oC replacement or  modification.  Most
disassembly of the  conbustor is through the top of the vessel, although the air
distributor plate and some instrumentation can be removed through the bottom of
the vessel.

       A  fluidized  bed combustor is constructed of a stack  of flanee-connected.
refractory-lined modules.  The module shells are circular in cross section although
the refractory linings for several of the cases have souare cross sections.  The
f !'iidized-bed nodules for Cases A-l and A-2, referred to as 3 ft x 3 ft. are
actually  33 in. x 33 in. internal dimension.  The bottom module is a feed and air
distribution codule through which air and solids feed materials enter the bed.  Above
this are  several modules containing bed cooling tube bundles and specialized test
probes.  Above these modules are several blank or freeboard modules, which may have
various heights so  that the desired freeboard  height is achieved.  Figure 3 shows the
combustor concept and indicates flows to and from the combustor; Table IV is a
simplified material balance around the combustcr.

       Many features have been designed into the combustor  to enhance its usefulness
as an experimental  facility.  They are as follows:



                                          108

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Figure 2. PFBC/CTIU Architectural Drawi >j

-------
Figura 3. Comburtor and Heat Removal Syitom

-------
                         Table IV.   Combustor Material Balance
In
Coal
Sorbent
Wet Transport Air
Fluidizing Air
Total In
Out
Combustor Off-Gas
Solids and Partlculate
Total Out
Case A-l.
Ib/hr
2.194
999
1.681
14.562
39,436

38.292
1.144
39.436
Case A-2.
Ib/hr
3.656
1.665
2.800
33.438
41.559

39.654
1.905
41.559
       (1) Solid feed materials can be  ntroduced into the combustor, through five
feed nozzles located in the sidewall just above the air distributor or through five
nozzles projecting upward through the air distributor.  Two additional,  sorhent feed
nozzles are placed at higher locations in the bed sidevall.  It is intended to feed
coal and sorbent through only one or two feed nozzles, respectively,  with the
remainder used as spares or to test mixing patterns in the fluidized bed.

       (2) Fluidizing air sweeps down through the annulus between the nodules and
pressure vessel and then is ducted out of the pressure containment "essel (as an aid
to measuring air flow and inlcakage to the fluidized bed and to allow future addition
of compressor discharge bypass valves); then the fluidizvng air flows into the modules
through the air distributor.

       (3) The main cooling tube bundle is split into two sections in a  sir.gle nodule.
Between the sections is a U-shaoed organic linuld-cooled heat transfer ore-be.  In
addition, on either side of this probe are located bavonet-tvre probes (cooled or
uncooled) for testing of various tubtr.-. r.^terials.   These orobes arc so  located that
a uniform geometric pattern of tubes immersed in the bed is maintained.

       (4) Above and below the main cooling bundle are two steam-cooled  test coils.
These, too, maintain a uniform tubing geometry and are mainly useful for evaluating
corrosion behavior of various tube materials.  Steam for these coils (200 psie.
saturated) is obtained froni the ANL Heating Plant;  the exit temperature  from the
steam-corled coils can range up to 1000 F.

       (5) In the module just above the flu-dlzed bed. an array of uncooled baffle
tubes can be inserted to study their effect on material elutriatlon.

       (6) Quench nozzles are located in a module high in the freeboard.  They may be
used to reduce temperature excursions due to afterburning of carbon-containing
materials in the freeboard by injecting a water mist.

       (7) The combustor internal fluidized-bed module is flanged allowing the
replacement of assemblies to change the freeboard section height.

       (8) A pulse feeder located near the bottom of the fluidized bed can recvcle
primary cyclone underflow material into the bed in order to investigate  how this
affects combustion efficiency.

       (9) Bed material either overflows from the bed at a fixed location at the top
of the bed or exits through a solids discharge line located ne^r the bottom of the
bed.  A range of bed levels mav be achieved in orrier to wholly or partly expose the
tube b:mdle in simulating part-load operation.
                                         Ill

-------
       (10) The design of the lover modules permits the distance from the air
distribution plate to the heat-removal  coils to be changed.

Combustor Heat-Removal System

       The heat-removal system flow is  depicted in Figure 3.   It is essentially a
closed system,  requiring a small amount of boiler feed water  (BFW)  from ANL as
makeup.  Pressurized water at about 1000 psip is circulated at a sufficient flow
rate, velocity and pressure to orevent  vaporization in the tubes or in the circuitry
between the fluidized bed combiis tor and the kettle-tvpe steam generator.  The steam
generated (200 psig. saturated) can be  routed to either a steam condenser or the ANL
Heating Plant.  depending on the constancv of operation anH the tine of vear.
Eouinment has been sized for the hicher Case A-2 heซt duties.

       The Case A-l tube bundle, which  will be the first one  installed, will be
"loosely" packed, with a relatively larp.e diagonal clearance  between the tubes to
permit testing at high (}00 7,) excess conbustion air levels.   The Case A-2 tube
bundle will be more "tightly" packed for operation at lover (-v.20%)  excess combustion
air rates.  Table V is a heat balance around rhc cbmbustor for Cases A-l and A-2.

                           Table V.  Combustor Heat B'-ance
In
Heat of combustion of coal
Sensible heat of coal
Sensible heat of sorhent
Sensible heat of dry conveying air
Sensible and latent heat of water
in conveying ait
Sensible heat of dry fluidizing air
Sensible and latent heat of water
in fluidizine air
Heat of sulfation reaction
Total In
Out
Sensible heat of spent sorbent
Sensible heat of char
Sensible heat of ash
Sensible heat of dry air
Sensible and latent heat of water
vapor in off-gas
Heat of calcination of MpC03
Heat losses
Tube bundle duty
Total Out
Case A-l,
KBtu/hr

21.926.6
3.5
1.1
20.1
5.6
1.524.0
269.9
108.4
24,039.2

343.5
60.1
106.5
15.392.3
2.574.3
257.5
100.0
5.225.0
?4. 050,. 2
Case A-2.
MBtu/hr

36.544.2
5.9
1.9
33.2
9.4
1.474.4
261.0
514.1
38.844.1

572.5
100.?
177.5
15.734.7
3,977.5
429.2
100.0
17.752.6
38.844.1
Solids Feed Materials Handling. Preparation, and Feeding Systems

       Coal and sorbent are handled by a common solids preparation svstem that
permits crushing and drying of either feed material.  It is anticipated that the
sorbent received will meet moisture and size specifications.  In any event,  conplete
flexibility is provided in the solids preparation system in that both or either of
the crushing and/or drying steps can be bypassed when either coal or sorbent feed is
                                         112

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processed.  Intermediate storage is provided for drv, prepared coal and sorbent feeds.

       The solids preparations plant is designed assuming that operation will be
one shift per-dav. six-days per week when preparing 1/4-in. coal product, plus an
extra two shifts per week for storage of prepared limestone.  The preparation of
coal products of minus 1/8 in. or minus 1/16 in. or sorbent products of 3 x 28 mesh
for alternative operating conditions would require extra shifts.

       The coal feed system is a commercially available Petrocarb solids pneumatic
injection system, while the limestone injection system is a lockhopper rotary valve
type system.   A blended coal and limestone stream can be fed to the coiibustor through
either feeder.  Figure 4 indicates the flow of material in the raw material
preparation system, and Figure 5 indicates the flow of material in the feed systems.

Hot Gas Cleanup System

       The hot gas cleanup system comprises three stages of particulate removal.
Flows through the system are shown in Figure 6.  The primary or roughing cyclone will
be of moderate efficiency (i847.) and will allow operation of the plant both with and
without recycling of underflow solids materials to the combustor.  If solids are not
recycled to the combustor, they will be discharged through two parallel lockhoppers
to the solids coolers.

       Off-gas from the primary cyclone will flow to the secondary cyclone (of about
907. overall efficiency).  The specifications currently being prepared for this
cyclone will lead to procurement of an improved inertial separator such as those
offered by Aerodyne and Shell.  Responses to bid reauests mav be used to modify
the final specification.  The unit will be chosen on the basis of the most recent
test information available at th*ป time the procurement order must be placed.

       Flow sheet development has been based on the Aerodyne unit.  Two solids streams
issue from the Aerodyne unit; the larger will be directed to a parallel lockhopper
system similar to the one for the primary cyclone.  The smaller streani will be
discharged thorugh a single lockhopper and disposal bin.

       The third-stage particulate cleanup device is specified to be a granular-bed
filter, such as that offered by Ducon. of 957, overall efficiency; the pressure
containment shell will be somewhat oversized to accept alternative internals (as
yet unspecified).  The piping designs will allow the filter to be bypassed if
desired.  Solids from this device are discharged through a single lockhopper into
a disposal bin.

       The hot gas cleanup system has a provision for extraction of a slipstream of
up to 1000 acfm downstream from thfป primary cyclone and for returning this stream
to the main gas flow upstream from the tertiary cleanup device.  This slipstream may
be used to test prototype gas cleanup devices.  There are also provisions for both
extractive sampling and in situ monitoring of gas streams both upstream and
downstream from each cleanup device in order to determine particulate loadings and
size distributions in evaluating the performance of each device.

Spent-Solids Removal and Storage Systems

       The solids that are at pressure flow from the combustor and from the hot gas
cleanup system through water-jacketed lines for preliminary cooling, then into
lockhoppers that lower the pressure to atmospheric, then into the atmospheric scent-
solids handling system.  The water-jacketed lines cool the solids to some extent;
this may permit valves to be tested for solids handling service at temperatures
somewhat below 1600 F.  The valves specified for initial installation will have a
design temperature rating of 1650 F although the solids mav be somewhat cooler than
that as a result of water-jacketing.  Pressurized solids-handling systems are shown
in Figures 3 and 6.

       The atmospheric spent-solids-handling downstream from the pressurized equipment
system cools the solids, keeping the combustor solids separate from cyclone solids,
then transports cooled solids to one of several storage bins for intermediate storage
or for disposal.  Also, spent material from the combustor and from the hot gas
cleanup system may be stored in separate bins in order to facilitate experimentation;


                                        113

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Figure 4. Solids Ftod Materidi Handling and Preparation

-------
Flflurt 6. Coal and Sorbent Feod Syltem

-------
Figurt 6. Hot Gaป Cttanup Syttsm

-------
for instance, spent cyclone underflow can be stored in a bin.  then transported to
the feed system for testing of the cotnbustor as a carbon burnup cell;  alternatively,
combustor spent solids can be stored for subsequent testing in landfills.

Turbine Cascade Systems

       Hot gas from the tertiary cleanup device flows through a stationary turbine
test cascade operated as either a choked or unchoked orifice depending on the unit's
final design.  When the cascade is operated in an unchokeri con^'rion,  system pressure
is controlled by the choked orifice downstream fr.-m -ve casca*  •  as shown on Figure 6.
If the cascade is operated in a choked condition, ty.   m pressure is controlled by
the flow through the bypass line cooler and control valve.  Gases from the turbine
test system flow up the short exit pipe- and into the atmosphere.  Several sizes of
flow orifices are available in order to operate the system at pressures and mass
flow rates other from those in the initial test series.

CTIU Instrumentation and Control

       The CTIU instrumentation and control system Is designed to accommodate the
experimental and expected changing nature of the facility.  A digital data acquisition
system will gather and analyze data from many instruments and also be adaptable to
a changing complement of instruments as programmatic and equipment changes are made.
Similarly, the CTIU control system will be able to control the CTIU in a variety of
configurations and operating modes.  In addition to the capability for total system
monitoring, analysis, and control, individual subsystems will also be capable of
manual control in order (1) to permit checkout and functional testing of equipment
without interaction with a central controller and (2) to permit emergency manual
control of portions of the system when required.

       The CTIU instrumentation and conrrol system comprises the centralized process
control system (CPC), supervisory control and data acquisition system (SCADA), plant
protection system (PPS), instruments, and control elements.  A block diagram of the
system is shown as Figure 7.  The CPC, SCADA, and PPS systems control and monitor
individual controllers and instruments directly and also via some local process
control (LPC) panels that may be a part of delivered CTIU subsystems.

       Control of the CTIU will normally be from a single CPC control console in
the central control room, but control of individual subsections of the CTIU can also
be maintained by manual use of the dedicated controllers.  The controllers also have
provisions for supervisory input signals.  The CPC will be a stand-alone
microprocessor-based system with one or more keyboards and cathode ray tubes (CRT)
the primary interfaces with the operator; e.g., Honeywell TDC 2000, Taylor MOD III.
All subsystem controllers and the SCADA will also be located in the central control
room.  The SCADA is a real-time digital central processor, e.g., Honeywell 4500,
Taylor 1010.  The SCADA will perform data recording, supervisory control, data
reduction, batch processing, and graphic display support functions.  The SCADA
will eventually be used for direct digital control functions.

       The CPC, LPC, and SCADA systems will have a backup plant protection system
(PPS) that will set back or shut down the CTIU if the normal systems fail to do so
when required.  The PPS uses both hardwired logic control schemes and dedicated
digital computer-based logic systems with nonvolatile memories and uninfierruptable
power sources.  The PPS control console and the peripherals supporting the SCADA
will be located in the central control room.

       The CPC operating console in the control room will be arranged for convenient
operation by a seated operator.  The operator interfaces will feature at least one
graphic and two colored CRT data displays and two keyboards.  The operator will
also be able to observe other indicators located on oanels facing the console,
including.video monitors for observing critical portions of the CTIU.


SCHEDULE

       Figure 8 shows the CTIU major schedule milestones, beginning with the
engineering evaluations that were undertaken late last year to develop governing
criteria for the combustor design.  Additional effort was expended early in the


                                         117

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                                                           Figura 7. Block Diagram of Overall Control Syttem Confijurttlon

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-------
project to establish the Quality Assurance Plan that will be followed to project
completion.  The project critical path follows the development of process flow
diagrams for the major systems, including the combustor.   The path then follows
through the preparation of the combustor specification, DOE approval for purchase,
and extends to delivery of the combustor in mid-1979.

       Since the procurement of the combustor body flanges has been determined to be
an additional critical path activity, the specifications for these items have been
completed and a fabrication order has been recently let to t. domestic supplier.  An
early start in Title I on the design, fabrication, and delivery of the body flanges
was required to prevent unnecessary extension of project completion.

       The entire engineering effort by Stearns-Roger to date has been directed to
completing the assigned Title I engineering scope.  The Title I Report will be
issued to DOE shortly after the first of the year.  The report will present
preliminary plant arrangement drawings, process specifications for major PFBC/CTIU
hardware items, including the combustor, a safet> analysis, a su-nmary of
environmental considerations, and a projected proj ~t cost estimate.  CTIU system
descriptions will be included.

       The project schedule included is undergoing additional evaluations as the
Title I work has firmed up the design requirements in greater detail.  The final
schedule, based upon the completion of Title I engineering, will be included in
the Title I Report.


ACKNOWLEDGMENT

       The authors wish to acknowledge the contributions of the members of the CTIU
project team, from Argonne, from Stearns-Roger, and from DOE who have contributed
their skills and efforts toward the realization of the CTIU facility.


REFERENCE

1.     E. L. Carls and W. .odolski. Conceptual Design of a Pressurized Component
       Test and Integration Facility, Fourth International Conference on
       Fluidized-Bed Combustion, McLean, Virginia, December 9-11, 1975.
                                         120

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          QUESTIONS/RESPONSES/COMMENTS

     ALBERT  A.  JONKE, CHAIRMAN:  All right.   Let's go on, then, to
Walt Podolski on  the pressurized CTIU.

     MR.  PODOLSKI:   I had one question from  Larry Naultz from Morrison-
Knudson,  Incorporated.  The question is:   "Please give the rationale
in some detail, pros and cons, for the pressurized containment
shell in  your PFBC/CTIU."

     The  main reason for having a pressure shell in this system is
that flexibility  is enhanced particularly with  regard to changing
modules.   Modules can also be designed for a lesser differential
pressure.  We do  also envision that at least part of what I called
the "Case-C  design11 was a waterwall design,  which would not be able
to withstand 150  psi ot differential pressure.

     The  "cons" of the argument are pretty valid.  A pressure vessel
costs more money, and it is a harder design  to  get all the piping
inside the vessel.  We feel the design problems can and have been
overcome  and that is the way that the system ought to be designed.
In addition, the  CTIU may be required to  investigate as yet unspeci-
fied combustor  designs in the future.
                                121

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                        INTRODUCTION
     MR.  MARKOWSKY, Chairman:  The next paper Is on "Further  Experiments
on the Pilot-Scale Pressurized Combustor at Leatherhead."   Mr. Hoy
is the director of the Coal Utilization Research Laboratory,  formerly
called BCURA,  Ltd., at Leatherhead, England.  He has been  involved  in
energy research for many years, heading teams which have investigated
and are investigating cyclone combustion, coal gasification,  MHD, and
fluidized bed  combustion.  He is a graduate in gas engineering from
Leeds University.  Mr. Hoy.
                                122

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                              Further Experiments on the Pilot-Scale
                             Pressurised Ccmbustorat Leatherhead
                                            Raymond Hoy
                                             Alan Roberts
                                             Philip Raven
                                  National Coal Board Coal Utilisation
                                     Research Laboratory, England
ABSTRACT
       Recent work en the 3 ft x 2 ft pressurised combustor at Leatherhead has been concerned with
operation over a range of fluidising velocities   (2S  and  7ft/s), deep beds (8 ft) and a tall tube bank
 (7 ft).   Operation was satisfactory at all  conditions, but performance at 7 ft/s as regards corbustion
efficiency, sulphur retention and elutriation was not as  good as at 2V ft/s.  Details of these measure-
ments are presented and compared with earlier results.


INTRODUCTION

       The pressurised combustor at Leatherhead began operation in 1969.  Work has been sponsored by
the United States  Department of Energy (and its  predecessors) and others, and has been reported from
time to tune (References 1 to 4).   Withii. the past twelve months the facility has been modified to
allow operation with a deeper bed (and correspondingly deeper tube bmk) and at higher f luidisiiig
velocities.   In particular two tests, totalling  25O  hours duration, have been carried out under
contract to the Department of Energy, with an 8 ft deep  bed and at velocities of 2S and 7 ft/s.  Some
of the results from these two ttsts are reported  here and ccrpared, where appropriate, with earlier
work utilising a <: ft deep bed at 2S ft/s.


TIE ril/OT PWOT

The Combustor

       The conbustor (Fig. 1) in its present form has a plan cross-section of 3 ft by 2 ft and is
suspended within a 6 ft diameter pressure vessel.   Most  of the services enter the pressure vessel
through a thick steel ring clamped between the dome and the top casing flanges.  The main air flow
enters the done and provides sore cooling of the  conbustor casirgs as it descends to the air distrib-
utor.

       The tube bank begins about 17 inches  above the distributor level and extends upwards for about
7 ft.   The bod cooling tubes (Fig. 2),  designed  and  manufactured by Foster Wheeler, arc IS inch
diameter and arc formed in staggered horizontal layers each comprising ten passes across the bed.
Details of the tube bank are given in Table I, together with details of the tube bank used in the
previous Investigations.   The tube bank geometry (dioneter, pitch, depth) is similar to that which
would be required in a cairnercial unit operating  at,  say, 1O atmospheres pressure.

       Three probes formed from four lengths of IS inch diameter tubing are installed in the bed
(see Fig. 1) for assessing corrosion behaviour of airheater tube materials.  The two probes installed
about 5 ft above the distributor are airoooled to 147CTT  and the third, at a lower level in the bod,
is unccoled.

       Two water cocled tube assemblies  are  installed in one of the end walls of the combustor
(Fig. 3).   These simulate membrane wall construction.    The tubes are l\ inch outside diameter.
The ir-ner assembly is considered to be the most reler \nt  as regards providing heat transfer data.

       Air enters the oombustor through 185  heat  resisting steel "bubble" caps with horizontal holes
about 1  inch above the upper of the two carbon steel  plates into which they are welded.  The static
 layer of bed material below the holes is sufficient  to prevent the  metal surface toiperature from
exceeding 48OT1.   The main outlet for bed material  is a  IS inch diameter passage through the
distributor plate.
                                                 123

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                                                            !7   13
                                                             14
1. Cooling witar inlets
3. Main tuba bank
4. Start-up burner
6. Distributor plat*
& Bad offtake
7. Intel
                              Figun 1. Afranoamant of Fluid Bad Combujtor Mk III
       •tarvcydo
14. Oust sampling and
                                                                          1&BiDMdownfn
 9. fttaun ซhซJI                 gai tampling probai    19. Coal intea
10. f^yy** and targat rods     15. Exhaust gaaa to       20. Corrosion probH
11. Sampta for SO2. NO.          pranura tat-dowi      ZI.Bafflatubn
   aarotob                  18. By-pan exhaust       22. CooOng tubas
12. "Mambrana wtlf section    17. Venturi
13. Water spray*
                                                                    eye
                                               124

-------
                    iVj'od x !Og
                    A I SI 3IO St St
    Figure 2. Plan view of bed cooling coil
 fc
 Bte.-—-
      :oooo
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Figure 3. Arrangament of Cooling Tube* in Combuttor Wall
             125

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                         Table I.  Details of Tube Banks used en the Orixistor

Tube dianeter incbซ
Nurcber of rows
liorizcntal pitch incbป
Vertical pitch infixes
Total surface area ft"
Total depth of
tube bank inches
Surface area 'c~f
Bed volume* 'ft
Proportion of bod
occupied by tubes* 'ป
Ratio Velocity between TLEKS
Superficial velocity
Tests 6
and 7
1.5
28
1.5
1
209

82.5
5


17
1.75

Earlier
Tests
1.0
25
6.0
1.5
79

37
4.3


9
1.5

                        *The bid volune is that -.Such encloses tie tube bank and
                         ignores free space above end below the bank.
       Pre-crushod and dried coal (either 1/16 inch - O or 1/8 inch - 0) is f>3d fran a Petrocarb
feeder to any or all of four nozzles that enter the ccrobustor S inches above the distributor plate.
            The number of coal nozzles used is an experimental variable.  In the two trusts reported
here only two nozzles were normally in use, whereas in previous aork four nozzles y.re used.  The
nozzles are water-cooled as a precauticci against fciodcaqe by caking, should highly caking coals be
used.  This trouble has yet to bo experienced however.
                                                                         •
       SO, acceptor is fed fran a separate lock hcccer system through an uncjoled nozzle which can
also be used for feeding the initial bed material during stait—jp.

       Heating of the bod (initially about 24 inches deep* to about ST'T is accorplished by two gas
burners with an aggregate lieat input of O.8 x 1O  Siu/h which inject ocrfcustion gases at about
1GOO deg F through two 4 inch diancter liolcs sited 7 indies abo>.^ t'ซe distributor.  The bed is then
brought up to about 145OT"  by burning propane fed i^to tl-ie bubble caps fran a ccrpartmented plenum
chamber foircd between the trfo plates of the distributor.   Det^xls of the distributor, coal nozzleo,
and start-mj burners arc shown in Table II.
                             T/ihl,. 11.  oistributicn of Coal arid Air

Air Distributor
No. of nozzles .,
Area of holes Inches"
Co.il/doliiraiU' norzli's
Number Coal
Do 1 no i t e
Insiue diameter
oi nozzles Izcbes
Co,il/jir ratio
Velocity of stri-ao ft/s
1
2lft/s
185
9

2*
I

o.*r
i
30
JJt/S
18,
18

2*
1

0.82
2
30
                     *"Ihis was Che nuaber of coal
                                                          normally in us?.
                                                 126

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                         Figure 4. Arrangement ol Gas Off-take*
1. Gas off-tike to cascade
2i Gas off-take (by-pan)
3. Protective cooling coil
4. Expamkm txilows
6. Insulating refractory sleev*
6. Cooling air supply (forms part of the
  tluxJiiing air supply)
 7. Dust tamping probes (4 probes at V
   radius positions)
 8. tias sampling probe
 9. Q;iench vr> ter sprays
10. Exit >? verturi scrubber and pressure
   let-down
      ฃ "
      o>
     ฐ5
     I98
      g  Q7

     i    .
                                                       .._ 25ft/.
    ป/> 8ft  deep bed
    o 4ft  deep bed
c16OOฐF  bed temperature

c6 atm. abs. pressure
           O     2O    4O     6O    8O     1OO   12O

                              Excess  air  ฐ/o


           Figure 5. Effect of Some Operating Parameters on Combustion Efficiency
                                       128

-------
       Baffle tubes are installed 21 inches above the noidnal top of the bed which is maintained just
above the top of the main tube bank.   The two rows of  1 inch diameter uncooled tubes on staggered
pitches contribute to reducing loss of bed material by  splashing.

       freeboard coolinq, for use only if unsatisfactory combustion in the bed leads to freeboard
combustion and excessive gas temperatures, ... provided  by six rows of 1 inch diameter tubes on
staggered pitches.

Dust Ronoval and Exhaust Gas System

       There are two offtakes, at the top of tlie cotfcustor  (Fig. -5;.   The gases from one  (about
1.6 Ib/s) pass successively through two 1O inch diameter cyclcne dust collectors in series, a cascade
of turbine blades, a sampling section and a venturi scrubber system before passing through a pressure
let-down valve en-route to the exhaust stack.

       The gases fron the second offtake (about 3 Ib/s wtv n Uir> fluidising velocity is 7 ft/s) only
pass through a sampling section and then to a venturi scrubbป.-.~ -/stem before pressiire let-down.  The
layout of the duct work has however been designed so that gas cleaning cyclones, a hot gas filter, and
a second cascade of turbine blades can be installed at  a later date.

       The cyclone dust collectors in the present main  stream have inlet velocities of 1OO *  120 ft/s
respectively and an overall pressure loss of 5 psi.   The dusi- frcm Ux! cyclones is "blown-down" in
about 2 percent of the gas flow into a disposal and sampling system.  The turbine blade cascade
(X.4O alloy) is a sector of the first row of stator blades  for a Proteus marine aas turbine.  Tin-
combustion gases are accelerated from about 75O ft/s at the inlet to about 180O ft/s at the outlet
and then pass at about 16OO ft/s over pin specimens (1/8 inch and 1/4 inch diameter), of different
a.Uoys.


RESULTS

       The operating conditions for the two most recent tc-..ts are sumnarised in Table III.  The first
test in wiuch the fluiOi3ing velocity was maintained at 2^  ft/s but the bed depth was increased to 8 ft
was a logical extension of previous work.   However, as in  most expensive pilot-scale work, other
changes were made which would have had an effect on some of the results.  The most important of Uieoc
changes werc:-
(l)
only two coal nozzles were ^;ed, compared with four previously.
adverse effect en combustion efficiency.
                                                                       This may have had a slight
(ii)  the tube bank, apart from being deeper, was of closer pitch.
In the second test the main variable was the fluidising velocity.   In both tests the additive  rate
was varied; excess air was v-iried by changing the number of tubes in the tube bank which were cooled
by water.

       Corrosion specimens were exposed in the bed and in the exhaust g.->ses (turbine blade material) .
These specimens are currently being examined and no commits can be made here.


                                   Table III.  Operating Conditions
Test No.
Fluidising velocity, ft/s
Excess air %
Bod temperature 'f
Bed height ft
Pressure atm abs.
Coal size
Coal
Dolomite
6
2\
25 and 10O
1600
8
6
1/16" x 0
7
7
95 and 65
1650
8
5.5
1/8" X 0
Illinois No. 6
Ref. 1337
                                                  127

-------
Combustion Efficiency

       Results arc sumnarised in Fig. 5.  At a fluidising velocity of 2\ ft/s, combustion efficiency
was better than 99%.   No effect of bed depth was apparent, although this could have boon masked, as
indicated earlier, by the change in the number of coal feed points between the two series of tests.

       Operation at 7 ft/s led to a small but significant drop of about 1% in corbustion efficiency.
Not enough data are available to be able to assess the effect of excess air at 7 ft/s.

Sulphur Detention

       The sulphur dioxide concentration in the exhaust gas downstream of the cascade was ncrmally
measured by two techniques: (i) conventional "wet" chemical metnods and (ii) infra-red analysis.  A
third method using a ffeloy FSA 19O flame photometric analyser was also used occasion/illy.  All three
methods were in reasonable agreement.

       Results are given in Fig. 6.   Sulphur retention at 2\ ft/s varied from about 7O% at a Ca/S
ratio of l.O to over 95% at a Ca/S ratio of 2.O.   Previous experience suggested that sulphur
retention should increase with bed depth, but this was not the case.  Reasons for this are not clear,
but may have been due to the closer tube packing which may have restricted mixing.

       Retentions at 7 ft/s were significantly lower, as would be expected, varying front 5OI at a
Ca/5 ratio of 1.1 to 8O% at a Ca/S ratio of 2.O.

NO  Emissions
       NO  was measured using a Thermr -Electron Corporation "Cherai lumines- -once" monitor, the sanple
being taken from the line that supplied the SO2 analyser.   Results are sumnarised in Table IV.
Increasing the bed depth at 2^ ft/s appeared to cause a slight reducti ซi in N'OV emissions whilst
Increasing the velocity increased,the emissions.  At all conditions, the concentrations were well
within the EPA limit of O.7 Ib/lO  Bin.


                                   Table IV.    NO  R?.issicns
Bed
depth
ft

4
4
8
8
Velocity
ft/s

2S
2S
2<5
7
Excess
air

2O
100
100
100

S0x
ppm Ib/lO^tu
150 0.2
120 0.3
9O 0.25
ISO 0.5
Heat Transfer and Temperature Distribution

       Bedside heat transfer coefficients, calculated from measured heat fluxes are plotted as a
function of bed height in Fig. 7.  It will be seen that at 2\ ft/s there is a substantial increase
in heat transfer up the height of the tube bank.   This feature had not been noticed in 4 ft deep beds
although more critical examination of earlier data shows that there may have been a trend in this
direction.  Tais variation in heat transfer did not arise from the temperature distribution in the
bed, which cohered a range of + 6OฐF from the average, but without any discernible vertical or
lateral bias.   No explanation for this phenomenon can be offered at this stage.

       At 7 ft/s the heat transfer coefficients were lower, as expectjd, and the effect of tube bank
height was not as clearer marked.  The temperature distribution in the bed within the tube bank
covered a range of + 7O F, but there were indications that the distribution in the region below the
tube bank was becoming less uniform with appreciably higher temperatures possibly occuring near the
coal nozzles.   However, at none of the conditions examined in the two tests were there any signs of
sintering in the bed or accumulations on the tubes.
                                                 129

-------
  1OO

   90

,0*0
o~
 e
 I  7O

 8
 ..  60
 a.
 5  SO

    4O
      T
                                                          	7ft/s
                                                ^-^'       A
                                          AA8ft deep bed
                                          o 4ft deep bed
                                          c 16OOฐF bed temperature
                                          c 6 atm. abs. pressure
                                          1337 dolomite
          O-8   1O   1-2     14    t6    18    2O   2-2   34
                              Ca/S mol. ratio

             Figure 6. Effect of Some Operating Parameter! on Sulphur Retention
    SO
*•'
*  70
1  60
:    50
1
w  4O
ฃ
m
n  3O
    2O
                                                                   7 f t/s
                  Tube Bank
             1O    2O   3O   4O   SO    6O    7O    8O   9O   1OO
                    Height  above distributor               inches

                Figure 7. Heat Transfer Coefficients to Tubes in the Tube Bank
                                   130

-------
      At g ft/s the bod temperature about 3 inches abovt t^hc plar>c at which the air was admitted  was
about 300 F below the bulk bed temperature.  These were the lowest temperatures ever observed at this
point on this plant, and indicate that as the mass flow rate of air increases, a significant tine
interval (or spaoo) is required to neat up the air to bed temperature.   This factor will need to be
borne in m ind in designing commercial units to operate at high pressure, particularly for part load
 peration where the tendency to def luidise is greatest.   At 2\ ft/s the temperature at the 3 inch
plane was 100 F  lower than the bulk bed temperature.

Elutriatlor.

      At 2% ft/s fluidising velocity, approximately 50^ of the input coal ash and dolomite was
elutriated.  This increased to about 95s at 7 ft/s.

      Fig. 8 summarises the size distributions of the coal and  iolomito feeds.  Marked on the diagram
are the particle sizes which vjuld be elutriated theoretically at 2\ and 7 ft/s (A and B, respectively).
If it is assumed that the coal ash was the same size distribution as the coal (this is usually a
reasonable approximation), then it will be seen that the quantity of input material which was
immediately elutriable was considerably less than the measured quantities of 5Os and 951.  This was
partiejlarly so at 7 ft/s.   Ths difference is due to degradation of particles in the bed which
would be more severe at thr? higher velocity conditions.   It was also likely that the dolomite was
fully calcined in the bed at these test conditions.   This would reduce the strength of the particles.

      The size distributions of the product materials (bed and elutriated dust)  are shown in Fig. 9.
The appropriate theoretical elutriable particle sizes are marked as A and B.   Only a small percentage
of particles greater than the theoretical elutriable size were, in fact, elutriated, and the size
distributions of the dust at both 2^ and 7 ft/s were similar.   The bed at 2^ ft/s contained no
elutriable material, but the bod at ~> ft-/s contained a surprising ijuantity of fines.   This may have
been because both the proportion and the actual quantities of fines produced at 7 ft/s was so great
that inmodiate elutriatinn did not occur.


COMCIJUSia-B

      Operation with an 8 ft deep bed at both 2"j ft/s and 7 ft./s is feasible.  Performance at 7 ft/s
as regards combustion efficiency, sulphur retention and elutriation is not as good as at 2^ ft/s.


ACKNCWIฃnoซtKIS

      The work described in this paper was carried out as part of a proqramne of rcscarJi under
contract to the Department of Energy, U.S.A.   Any views expressed are those of the authors and not
necessarily those of the Department of Energy or of the National Coal Board.


REFERENCES

1.  II.R. Hoy and A.G.  Roberts, Fluidised Combustion of Coal at High Pressures, A.I.Ch.E
    Symposium Series,  Vol.68, 197.2, No. 126, p. 225.

i..  U.S. Office of Coal Research, Pressurized Fluidized Bed Combustion, R & D Report No.  85,
    Interim No. 1.

3.  A.G. Roberts, H.R. Hoy, H.G. Lurm and II.B. locke, Fluidised Conbustion of Fossil Fuels,
    Coal Processing Technology, Vol.  2, 1975, p. 34.

4.  A.G. Roberts, J.E. Stantan, D.M.  Wilkins, fl. Beacham and H.R. Hoy, Fluidised Combustion
    of Coal and Oil under Pressure, Institute of Fuel Symposium Series No. 1, 1975, p.  D-l-1.
                                                 131

-------
10OO


 i
 v
 E
 s
CO
 1OO
                                  7ft
                                                      •"•"  Dolomite

                                                      —  Coal
                                                 -ป-
O1
                            1O          SO          9O
                             Smaller than stated size
99     994
                        Figure 8. Size Distributions of Feed Materials
                                       132

-------
KXX>
I
-B


-A
  KX>
                                                                            B-
                                       2ift/8
                                                                            A-
                                                                         XX)
   a
   5
   E
   8
   0)
10
                                                           Bed material
                                                           Elutriated dust
   10
                            10          SO          9O
                         ฐ/o Smaller than stated size
                                                          99    99-9
                              Figure 9. Size Distribution* of Dust and Bad
                                       133

-------
                      INTRODUCTION
     ROBERT BROOKS, CHAIRMAN:  Our first paper this afternoon  is
"Solid Tracer Studies  in a Tube-FiMed Fluidized Bed," by Fitzgerald,
Catipovic,  and Jovanovic.  Tom Fitzgerald will present the paper.

     He received  his BS and Ph.D. in Chemical Engineering from
Illinois Institute of  Technology.  He then taught at the ITT and then
subsequently moved to  Oregon State University where he is Professor
of Chemical  Engineering.  These fluidization studies at Oregon State
are funded  by the Electric Power Research Institute and B&W.
                                134

-------
                          Solid Tracer Studies in a Tube-Filled
                                     Fluidized Bed
                          T. Fitzgerald, N. Catipovic and G. Jovanovic
                             Department of Chemical Engineering
                                  Oregon State University
                                    Co rvallis. Oregon
ABSTRACT
     Coarse sand was fluidized in a one-meter square bed containing an array of
horizontal two-inch diameter heat exchange tubes.  While the bed was* fluidized,
feirite tracer with physical (,roperties similar to coal was injected, and monitored
by 64 inductance probes located in a four by four by four array inside the bed.  The
measured '.racer movement varied from run to run indicating that the solids flow
r.attern in the bed changed continuously.  The speed with which the tracer spread
indicates the effect of gas velocity on solids mixing.


INTRODUCTION

     The rapid mixing of solids in a fluidized bed gives rise to its nearly iso-
thermal performance.  In most applications of fluidized beds in which solids react,
they do so slowly enough (compared to nixing) to be considered well mixed.  Such is
not the case for large scale fluicizod bed coal combustors.  Coal particles burn to
completion in a few minutes, and evolve large quantities of combustible gases  in the
first few sections after they are introduced.  Unless a very large number of feed
points are used to introduce the coal, it cannot be considered well mixed.

     In order to desiijr. a largr> fluidized bed combustor it is important to know just
how fast solids move through the bed.  It is this problem which motivates this study.
The bod ir.ii-.rial, the bed geometry (with heat transfer tubes) and the range of air
velocities are representative of fluidized bed combustors.


r.XPrjRIMENTAL. METHOD

     It is not necessary that the experiments on solids movement be conducted  in a
hot bed; the movement of solids depends on bubble size and bubble frequency and can
be modelled quite well at room temperature.  In fact, high temperatures arc * dis-
advantage since they make tracer monitoring much more difficult.

     Various techniques have been used to study solids movement in fluidized beds.
One method uses colored or otherwise tagged particles injected into the bed, after
which th~.ฃluidization is abruptly stopped and the bed material is removed layer by
layer to find how far the tagged particles have migrated  (see for instance, the
studies by Rowe, et al., 1965 and Babu, ct al., 1972).  Besides being time consunino
and laborious, large uncertainties arc introduced in the slumping process:  the bed
requires a few seconds to defluidize and in that time, particles can move a signi-
ficant distance.  Furthermore, segregation of particles by size can and does occur
while the bed is being slumped (see Donlevy, 1977).

     Collecting simultaneous so!ids samples from multiple points in the bed while it
is running is also a difficult task.  This method was used by I'.iohley and Merrick
(1971).  It is disruptive of the flow patterns which exist in the bed just before
sampling  (although this effect can be minimal if the samples arc small enough).  For
a large number of collection sites and collection at regular time intervals after
injection, it is necessary to use automatic sampling techniques, and it is difficult
tc collect more than a few samples at a given point during the time the tracer is
spreading throughout the bed.

     In situ detection of radiactive particles can bo used to follow solids movement
in the bed.  The disadvantage of this technique involves all the hazards of handling
radioactive material.  In addition, the radioactive tracer method can be expected to
give more "noisy" data than that which would be obtained with ferrite tracer-irduc-
tance probe techniques.  This follows from the fact that radiation jctectors will



                                          135

-------
only detect particles which are not shielded by bed material.  In order for the
detector to respond to radioactive particles which are 5 millimeters distant from the
detector, it would be necessary to use high energy gamma radiation.  This would not
only require massive shielding around the entire bed, but would also give rise to
interaction between the multiple detectors, since a particle would be detected by
more than one probป.  Thus it is likely that a lower energy radiation with a shorter
effective penetrating distance would be used.  In fact, the detector would probably
only detect radiation from the layer of particles closest to the probe.  The stat-
istical fluctuations in the number of particles in this layer would contribute signi-
ficantly to the noise.  For instance, with a probe surface of 200 square centimeters,
a tracer particle size of one-half centimeter, and a one percent tracer concentration,
the average number of particles detected by the probe would be only 8 and the stan-
dard deviation of the number of particles would be nearly 3.  Thus even at steady
state, the tracer signal would fluctate by at least an order of magnitude.

     The ferrite tracer technique is to be preferred over all these other tracer
methods.  The ferrite can be detected over a large nearly spherical volume, approxi-
mately throe  times the diameter of the coil, but the sensitivity falls off sharply
outside that volume.  The ferrite tracer can be readily removed by magnetic separation
after a tracer run has been conducted.  The tracer can be incorporated in a polyester
casting resin, thus providing tracer material in any size desired (with a density
comparable to coal), wnich has the soft magnetic properties necessary to allow it to
change the inductance of a nearby coil as well as to be collected by magnetic separ-
ating techniques.

     In this study we used approximately 40 pounds of ferrite material (1% of '..he brd
weight) to trace the movement of the solids.  The inductor probe itself consisted oฃ
a coil approximately tv.o inches in diameter and two inches in length which is inserted
inside a "dummy" hoat transfer tube (see Figure 1). The coil is connected to a sensi-
tive bridge circuit which has been developed at Oregon State University.   The sensi-
tivity is high enough and the stability is gooJ enough to allow the use of tracer
concentration as low as one volume  percent.  The response of the device to tracer
concentration is very nearly linear, with a one percent tracer concentration in the
vicinity of the probe producing a one volt signal.  The response time is less thfin
one one-hundredth of a second, thus making it possible to capture transients which
could not be detected by sampling techniques.


EXPERIMENTAL CONDITIONS

     Ten runs were made using ferrite tracer to study the movement of solids in the
large fluidized bed.  The table below gives the conditions at which the runs were
made.


                           Table I.  Experimental Conditions
Run
1
2
3
4
5
6
7
8
9
1C
Superficial Velocity
12
12
12
12
12
12
7
7
7
3
ft/3
ft/s •
ft/s
ft/s
ft/s
ft/s
ft/s
ft/s
ft/s
ft/s
Type of Tracer
ferrite rings
•
"
imitation coal
•
•
ซ
ซ
•
*
For all of the runs, the tracer was introduced above the bed in a single slug.   Only
one tube spacing was used for these runs:   triangular pitch with six-inch spacing
between adjacent tubes.  The spacing tes-ween the bottom row of tubes and the distri-
butor plate was ten inches.   The bed material was sand (EI16)  with a size distribu-
ibution tabulated below.
                                          136

-------
                                                         ^•Fiberglass
                                                     ^/ dummy
                                                           heat transfer
                                                           tube
                                                               wire
Figur* 1. Inductor Coil for Senting Ferrit* Tracer in th* Fluidind Bod

-------

Tyler
-60
+ 60
+ 35
+ 23
+ 2C
+ 14
+ 12
+ 10
+ 8
Table II.
Mesh

-35
-28
-20
-14
-12
-10
- 8
- 6
Sand Size Distribution
Cumulative %
0.33
0.98
4.54
34.6
81.60
90.75
94.8
99.8
100.00
The weight of bed material was 2000 pounds (a height of 30 inches when the bed is
slumped).  The surface mean particle size is 1.04 nun; and the minimum fluidization
velocity is 0.59 m/s (1.95 ft/s).

    Sixty-four inductance probes within the bed were used to measure the concentration
of the ferrito material as it spread through the bed.  The arrangement of the tubes
and the location of the fcrrite inductor coils is shown in Figure 2.  In each tube
marked by an X there are four inductor coils spaced at eight inch intervals with a
space of approximately four inches on either end.  Each inductor coil monitors a
concentration of ferrite in.a volume whose radius is approximately 10 en, centered
around the coil.  The tracer was introduced through a chute which terminates 74 cm
(29 inches) above the top row of tubes (see Figure 3).

     The inductance probe signals were sampled 40 times per second by an analog-to-
digital converter.  Data was collected on all 64 channels for approximately 10 seconds
before any tracer was introduced in order to determine accurately the background or
zero level for each of the inductor coils.  The tracer was then introduced in a nlu7
(30 pounds of ferrite ring'.,  or 40 pounds of fcrritc-containing resin).  Data was
then logged for another thirty seconds.  At the end of each ten-second interval, a
gap in data taking occurred because of the necessity of transferring accumulated data
in the computer's core memory to disc storage.  After a run was completed, the ferritc
was removed from the bed material by magnetic separation as both were discharged  fron
the bottom of the bed.  The bed material was then returned and the tracer was used
again for the next run.

     Two typos oi fetr.'tc tracer were used.  Ferrite rings were used for runs 1,2
and ^.  The ri,:gs have an outside diameter of 4 mm and an inside diameter of 2 ran and
consist of ferrite material with a specific gravity of 4.6.  The bulk density of
ferrite rings is 2.0 gx-m-*.  A different type of fcrrite tracer naterial wa3 used for
the remaining runs.  This material was m*rte of ferrite powder incorporated in a
polyester casting resin to produce a tracer with a specific gravity of approximately
1.6 (within the specific gravity range found for coal).  This ferrito-fillcd resin
was used to simulate the behavior of coal in the fluidized bed.  It was in the form of
5 mm cubes and held up very well throughout the fluidization; there was no evidence
of particles breaking into smaller pieces.  The magnetic permeability of the material,
however, was not as good as that of the ferrite rings.  As a result, it was necessary
to use a larger slug of for rite-containing resin for the tracer runs.


RESULTS

     The collected data was digitally smoothed in an attempt to get rid of the
effe-t of bubbles passing the probes.  When a bubble comes close to a probe, the
ferrive material is separated from the tube, causing a drop in the apparent concentra-
tion oi ferrite.  when the bubble moves away from the prcbe, the ferrite material
comes back in close contact with the inductor coil and the inductance goes back up.
A simple non-linear follower  circuit was used to smooth the data in an attempt to get
rid of these dropouf-.s.  The follower responds very quickly to an increasing signal,
but it has a damped response to a decreasing signal.  The smoothing of actual data
was done using the digital computer according to the following relation:



                                          138

-------
5"
,--
5"
            o
       a       o
T
 6
     
-------
                                         Solid
                                         Tracer
                                         Injection
                                         Port
                                         (6" Pipe)
                                    Heat Trans for
                                    Tube Bundle
                                       Distributor
                                          Plate
Figure 3. Sobds Injection Port in tfw 3* • 3* B*L



                140

-------
                         Yt -
                         Yt =



                              if "t - Vl


     Values of x , the raw data, were collected at intervals of 1/40 second, but the
smoothed output,  Y. , was well represented at intervals of  1/5 een that the
tracer tends to remain in a clump for as long as 20 seconds.  Even after 30
seconds, very little of it has made its way to the bottom left side of the bed.

     In future experiments we plan to study the effects of different tube spacings
and bed material sizes.  Tracer particles of various sizes  will be injected both
above the bed and near the bo t ton.


                                         141

-------
                              10 20 3D 40 sec.
                                /ISM
                                W-n
                   in
                                 INS
Figure 4. Ron 1 12 ft/s ferrrt* rin^




        142

-------
             Ann
                        10 23 30 <0 sec
                        VTv-1
 /inn
             hnn
FiguraC. Rjn212ft/sfarrrt*ringt



      143

-------
wrVS
                                       II 1 V I




                                       Ivy^
                                       ./vv^
                                            40 sec
w-n
                                        inn
            Figura& Run3 12ftAfwritปfinfli




                   144

-------
 i
                                          10  20 30 40  sec
Figura 7. Run 4 12 ft/t inuu6on oat



           145

-------
                                             I'-V/'-^V—^V
/V.	^
A	_^
                                                                 10 20  30 40  sec
                                         I   ll/X^ซ^>y->ป
                     FigureS. Run 5 12 ft/s imitation coal



                                 146

-------
                                       10 2o 30 40 sec
                                         /V~V-'\
Figure9. Run612ft/fimititioneod



           147

-------
            11	i  L
            I   ^_      L
                          I  L—
               fU	
Figure 10. Run 7 7 ft/ป ImJtation owl




       148

-------
 JL
lLv/>w/
                      JWปV^
                                         10 20  30  40 sec
Figure 12. Run 9 7 ft/i imitation coal



           150

-------

   A^ - !
W-MU'
                  IL
                  JWw-\
                                  Sv~>v~\
                                 1C 20 30 40 sec
Figure 11. Run 8 7 ft/t imitation coal



         149

-------
                   1
                       /V.
                                        2& 30 40 sac
Figure 13. Run 10 3 ftA imitation coal



           151

-------
P.r.FKP.F/.TE.'.

3.   Kabu,  S.  r.,  S. U-ipiiccr,  3.  H. Loc a.-.c:  S.  A. Veil. /.TChF.  Synp. Scries,  fi9(l23),
     49  (J973).

2.   Ccnlevy,  B.  T. , "measuring  Solids rtovoiv.ent in a l^cgc Particle Air Fiuidizo-J
     Rod:   Two :."ow Methods,* M.  S.  Thesis, Oregon State L'nivorsi f/. J977.

3.   Highley,  .!.  -ir-.d D. Itorric'c,  ATOhi; ?yr^p. serins, 67(1H),  ?19  (1971).

4.   Rove,  !'.  :;.,  B. A. !'artrii!'jo,  A. C. Chcnoy,  C. A. iicnv.ood and E. Lyall.  Trans.
     Instn.  Chen,  [.'nnrs. , 43, T271  (195S).
                                            152

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             QUESTIONS/RESPONSES/COMMENTS


     ROBERT BROOKS,  CHAIRMAN:   Thank you, Tom.  Are there questions
from the floor?  Would you  please  identify yourself, and then provide
us with a written copy of your  question?

     MR. GELDART:  My name  is Derek Geldart fr^m the University of
Bradford.  I would like  to  ask  Dr. Fitzgerald if he is familiar
with the work by White-head  in Australia where a clump of material
was dropped into a much  finer particle bed and an attempt was nade to
follow how it was dispersed by  a much nc -e tedious rethod.  They
found that in fact if they  dropped the mat-.rial near the wall, it
indeed tended to go down to the botton; and it wasn't until it got
into a violently bubbling region that it dispersed.  I wonder if you
are familiar with that.

     DR. FITZGERALD: No, I am  not.  Dp they use a method like Highly
and Merrick did, with radioactive  particles?

     MR. GELDART:  No;  it was very tedious, indeed.  They had a large
bed.  I think it was four feet, or maybe six feet square.  They had
technicians go in and vacuum off the solids and draw patterns of
where the tracer had got to. But  Ihe work showed quite clearly thjt
if you drop tracer irto  certain regions where there is a downflow of
solids, you don't get dispersion.  If you drop it into a bubbling
region, you do.

     DR. FITZGERALD:  I  must look  at that.  I'm not faniliar with it.

     These are a questions  for  Dr. Fit2gera1d fro™ William C. Howe of
the Radian Corporation.  The questions are:  1) "Was there any evidence
of improved solids radial dispersion with varying bundle geonetries
or varying grid plate to tube bundle distances?"  The answer is that
other tube arrangements  haven't been tested yet.  2) "Would such data
be used to determine optimum grid-to-tube relationships to reduce
feed points per square  foot requirements on large-scale conbustors?"
The answer is yes; that's one re the goals of the research to find
the best type of a tube  geometry co enhance motion of particles; and
to find whether one can  get enhanced circulation, by using unsystem-
metric tube bundles, and the like.

     SPEAKER (not identified):  Is there any data yet relating to
feed point requirements?

     DR. FITZGERALD: No data yet, but we should be getting data in
at an accelerated rate,  very soon.
                                153

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     ROBERT BROOKS, CHAIRMAN:   I  would  remind you that  Tom Fitzgerald
from Oregon State does have some  sanples  of  his instrumentation  here
for those who would like to come  forward  and see them during  the
coffee break.
                                 154

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                       INTRODUCTION
     ROBERT BROOKS,  CHAIRMAN:  Our  second  paper this afternoon
reports on the work  being conducted at  NYU on "The Effects of Finned
Tubing on Fluidized  Bed  Performance."   The paper will be presented by
Dr. Victor Zakkay, who received his Bachelor's, Master's, and Ph.D.
degrees from Brooklyn Polytechnic  Institute, and upon completing that
work, joined the  faculty there.  He was one of the contributors
to the organization  of the Aerodynamics Laboratory at the Polytechnic
Institute of Brooklyn, and then in  1964 he moved with Dr. Antonio
Ferri to NYU, where  he was involved in  the design of a new hypersonic
facility.  He also joined the faculty there, and in September of 1977
became Chairman of the Department of Applied Science.  He is presently
involved in the designing of a fluidized bed boiler for ERDA.
Dr. Zakkay.
                                155

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                                The Effects of Finned Tubing on
                                   Fluidized Bed Performance
                                  G. Miller. V. Zakkay. and G. Kiviat
                                        Mew York University
ABSTRACT
       UndtT ERDA Contract EF-76-C-01-2?^>6. rc-sts have been conducted in the New York University pilot
(one fooc diarieter) fluidi/od hod to ascertain the effects of finned tiiing on heat transfer.  The
results nrf> presented as n function "jf hod pressure . superficial velocity, and air injection pattern.
A vertical firmed U tube (similar to Che one envi s i sr.idy, under realistic ooerar'rv, conditions, the details of
circulation patterns, heat transfer, velocity distributions, voidor.e. ter^ieraturc and pressure profiles
as a function of particl.- si;:e, heat exch;oi)',er p fluidixed bods: (1) a pilot bed one-foot in dianeter; and (2) a three-foot
diameter bed.  These beds have been designed as versatile structures so that detailed in-bed measure-
ments can be taken.  In addition, a specially ilcsi>T>ed grid allows the e:d Enj-ineerinj', Corpany of Linden, New Jersey. The
purpose of this joint effort is to inject into the research the constraints of system requira.tntsv.Mch
exist in practical applications.

       The present paper presents results obtained in the one-foot diameter bed to determine how the
following parameters affect heat transfer performance:

            (a)  Bed depth.

            (b)  Tube length (with vertical tube configurations).

            (c)  Bed pressure and Injection pattern at '_ne grid.

            (d)  Vertical fins.


II  PREVIOUS MHK

       In [1] heat transfer results were presented in the one-foot oianeter bed for shallow bed condi-
tions.  A schematic of the one-foot bed is presented in Fig. 1, and a detailed description of the fa-
cility can be found in [1]. The results of the previous investigation indicated that a parabolic gas
distribution at the grid can, under some conditions, improve the heat transfer coefficient by 257. over
that of a uniform distribution.  These results were obtained for a 27" settled bed height, and for a


                                                  156

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Exhaust Valve
Blow up Patch
Valve
Ex hat, it Screen   •	
Windows
Fluidi/ed Bed
Chamber
Fuel Lines

Air Lines
                                                                                      12- 5"
                   Figure 1. Schematic of Pilot Scale (1* Diameter) Fruidized fled.
                                            157

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hear exchanger heipht of 18".  The bottom of the coil was placed six Inches above the grid in both the
horizontal and vertical heat exchanger arrangements (the horizontal arrangtrsnt -.sis sizilar to the "ope,
Evans and Bobbins design used at Rivesville, West Virginia; the vertical arrangement is similar to the
Exxon design utilized in Linden, New Jersey).  A sunrnary of the overa'". heat transfer coefficients is
presented in Fig. 2.  It is clear from Fig. 2, that the maximum overall heat transfer coefficient is
obtained for the parabolic velocity distribution with the vertical tube arrangement in the lower veloci-
ty range.  In addition to the above results, the effect of operating the bed at 7 atmospheres resulted
in an overall heat transfer coefficient 757. higher than die one obtained at 1 atmosphere.  A summary of
these results is presented in Fig. 3 for the vertical bundle.  All of the above results were obtained
with bed particles whose diameters were in the 1/16" to 1/8" range, and utilizing methane or propane as
the heat source (eliminating the complexities of coal handling and high temperatures).


Ill PRESENT INVESTIGATION

       The main objective of the present investigation was to determine the overall heat transfer co-
efficient for a vertical heat exchanger, with and without fins.  In addition, an assessment of the
overall heat transfer for vertical heat exchanger configurations, as a function of bed depth and flow
parameters, is also presented.  The heat exchanger configurations examined here are shown in Firs. 4a
and 4b.  The short tube bundle (18" in extent) of Fig. 4a is the heat exchanger whose performance was
analyzed  [1] previously.   The new heat exchanger is 6'2" long and utilizes  a 2" diameter U shaped
pipe with a 6" distance between the centers of the two legs.  The surface areas of the two designs in
Fig. 4a are approximately the same.  Figure 4b presents a schematic of the finned U tube; each leg has
12 fins 1/2" high and A'6" long, resulting in a total surface fin area of 9 ft2.

       Figure 5 shows the U tube mounted in the bed.  In-bed instrumentation includes pressure trans-
ducers, thermocouples, and fast response heat transfer probes (the configuration of these probes were
described in [1]).

       The overall heat transfer coefficient presented in the figures is calculated by assuming that
while the cooling fluid is circulating, the temperature of the bed remains constant.  Therefore, the
local heat balance

                       dQ1  *  h (Tb - TV,) dS = nvi Cซ dTw

can be integrated to give:

                       hav - r^ C^S In   |(Tb - Tw.)/(Th -

where n^ is the water flow rate, S ts the tube surface area, C^ the specific heat of water, Tb the bed
temperature, and Twi and TWo are the inlet and outlet water temperatures.  The confutation of hgv there-
fore requires the determination of i\, (given by a floumeter) and the temperatures Tb, Twi and TWO.  The
water inlet and outlet temperatures Tuj and Ty,, are measured by two thermocouples whereas the bed
temperature Tfe is defined as the average of the readings yielded by six thermocouples radially position-
ed in the fluidized bed placed 15". 36". and 66" above the grid.

A.  Results With the Unftimcd Tube

       Three settled bed depths (27", U,", and 55") were tested with the long unfinned U tube in place
for a variety of conditions.  The heat transfer results for the 27" rettled bed arc presented in Fig. 6.
The results are presented for uniform and parabolic velocity distributions at die grid, and for 1, 3,
5, and 7 atmospheres utilizing 1/16" particles.  It is clear from these figures that the parabolic
distribution yields a higher heat transfer coefficient than the uniform distribution for all conditions.
This is consistent with the results obtained previously in [1] for the 18" vertical tube bundle (the
Exxon configuration).  There is a substantial increase in the heat transfer coefficient from one to
three atmospheres; however, a maximum is reached at approximately 7 atmospheres.  The value of the
heat transfer coefficient at 7 atmospheres is as much as 757. higher than the coefficient at 1 atmosphere
for the same superficial velocity.  This phenomenon of increasing heat transfer at elevated pressures
has been explained previously in [1], and is mainly due to bubble or slug breakup within the bed result-
ing in an increase of the resilience time of contact of particles and heat exchanger.  This was shown
utilizing the transient probes.

       Figu-e 7 presents the re.vilts for the heat transfer coefficient in the W deep becd with the
sane unfirtned heat exchanger configuration and for the sore flew conditions.   The results indicate a
moderate increase in the heat transfer coefficient over that of the 27" bed at atmospheric conditions.
but at the sane tune, a substantial increase docs result  at  7  atnosphercs.  A inr.xinum
value of 36 Btu/hr ft2 ฐF (add approximately 157. for radiation heat transfer to determine the value


                                                 158

-------




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Pressure: Atmospheric
COIL INJECTION
""" "* tj™ฐ"" Vertical Parabolic
^*™O^^ " Uniform
•••*O~"** Horr Parabolic
••=^^"^" " Uniform
4 8 12 16 20
VSUPI't.sec)
Figure 2. Overall Heal Transfer Coefficient For Horizontal and Vertical
Tube Bubbles For Parabolic and Uniform Infection (Bottom of Coil • 6"
      Above Grid. Coil Length  18". Settled Bed Height • 27").
                        159

-------
40
30
20
 10

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        	•	228-O.D.
Figure 4*. Schematic of Lou Unfinned U-Tube *nd Short Bundle
          (Wetted Areas An ApproximstBry Equal).
                          161

-------
()
(
//
//




0
 "2"
        1/8"
                                       6' 3"
                                       V 6"
  •XX'
               \
                23/8"
Weld Spot

Fin Lengths Are Between AA' Shown in Drawing
Length of Fin: 4'6"
Surface Area of Bare Tub?: 7 ft?
Surface Area of Fins: 9 ft?
                                                                             A'-
                                   Fiqur*4b. Sdwmatic of Finned U Tube.
                                                  162

-------
Height (in)

132
126
120
114
108
102
96
90
84
78
72
66
60
54
48
42
36

30
24
18
12
6
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	 T/C ป 18. G29
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T/C Rakes s13. 15
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T/Cซ16. G30


             Figure 5. Schematic of Unfinned U Tube Mounted in Bed Indicating
                        Thermocouple and Transducer Placemenb.
                                       163

-------
14
                                               VSUP. 't'sec


                     Figure 6. Variation of Overall Heat Transfer Coefficient With
                Picture ttr a  2" Unfinned U Tube in 2T' Sen led Bed (Shaded Symtioh
                IH&-.M Pifibolic Injection. Open Symbols Indicate Uniform Injection).
                                                164

-------
               7 ATM
                          VSUP. 't/sec

 Figure 7. Variation of Overall Heat Transfer Coefficient With Pressure
for 6' 2" Unfirmed U Tuba in 44" Settled Bed (Shaded Symbols Indicate
    Parabolic Injection. Open SymooJ* Indicate Uniform Injection).
                              165

-------
utilizing coal) was obtained for the 27" IH.-U, while a value of  >0 Stu/Vy ft 2 of -^35 obtained for the
W bed.

       Figure 8 presents the results for tJio 35" deep bed.  A slight tTjro-jertTit  is obtaircc over the
44" deep bed.  Figure 9 presents a surnary of the results for the- naxinrs heat transfer coefficient  as
a function of bed pressure  for the various bed hti.f.ts.  It nrr \*: " or less  tr<;'ethcr with lar>;er particles of the
order of .1" in equal percentages.  The small particles would be  able to penetrate throuj*i the dense
bed, carried by the ft'ises,  and therefore the circulation would  ir-rro-je.  Ihe lar?.e panicles wnuld theri
nerve to distribute the heat evenly throughout the bed.  This sci-xsu: couid result  in subsMitially
hijher heat transfer coefficients.  Tils effect will be exaninrx!  at the facility  at A later date to-
gether with the novel desijTi  presented below.

       In order to determine the local heat transfer coefficients  shown in Fip,. 10.  as well as particle
and shy, velocities, fast response instruncntaticm has been ust-d.   This instrunentat ion has been de-
scribed in detail [t].  For the ncasurenmi; of the instantaneous  heat tr3ซfer coefficient, a fiUr,
probe was used and the temperature tine hi.--.tcry -was recorded.   T!-e prcfce has an internal cooling systes
whereby the tenporaturc can be decreased to essentially anhlent conciticrs.  The  coolant flcv is rain-
talned prior to taking the  local heat transfer reading.  At the time the instantaneo-s coefficient Is
to be read, the coolant flow is suddenly terminated, and the tcrK-rature tiiK history is recorded.
Figure 11 presents a typcinl result of such mcasurecent.  The tejrperatxrc has been nondiaoBionalized
with respect to the local bed temperature and the initial tempcTafjrc of the probe.   TTrjs. the parameter
which reflects the local teat transfer is (T(j - Ti,,)/^- Tlocal). where Tg is the- I real bed teqpera-
turc In the vicinity of the probe, Tjn is the initial tenpcrature of the filri at  the instant the cool-
ing is terminated, Tlocal is the terperature as a function of tisc.  The lcvปl of this parxx'er de-
termines the local he-it transfer coefficient within the bed. and  therefore the instar.taneoxs coefficient
could be calculated frcn the tcnpcrature tine history shown in  Fi?. 11.  In addition to enabliro', the
investipator to measure the instantaneous coefficients, the probe is capable of neas'jrins', the erulsion
and slug (or bubble) residence times at all sections in the bed.   the local slug  and particle veloci-
ties may be obtained b" placing two such probes a known srnll diitzice  apart.  In the cases ;>!r}fcn
here, two probes were placed at heights of 32" and &i" above the  Krid.   "2*e nondiraensionalized traces
of both probes are sh/vn in Fig. 11 for pressures of 15, 65, and  75 psia. Sue inyortant results and
conclusions could be deduced from  this
            a.  TV  local heat  transfer my be obtained by measuring the slope of the
                temperature  tura  trace at each instant.

            b.  The  local porosity  is also proportional to the slope of the tisperat^re tire
                history and  therefore slug and emulsion distributions can be derived from the
                curve.

            c.  An explanation  for  the subsume Lai  increase ir. the heat Udi&fer  coefficient, at
                a function of pressure can also be  derived.  By observing the length of duration


                                                  166

-------
CD
O
              Figure 8.  Variation of Overall Heat Tranter Coefficient With Pretun* For
                   6* 2" UnlinrMd U Tub* 55" Settled Bed (Uniform Inrctionl.
                                              167

-------
       18" Packed Vert.cal
       Configuration (Welted
       Area - 54 <|2|
                    I
                      6'2" loivjUr,finr.ed
                      U Tube (Welted AtC-a
                   40            60

                        Bed Prersune. PSIA

Figure 9.  Comparison of Maximum Heซt Trjrafer Coefficient of Unf inned
      U Tub* (At 3 Stttted Bed Depths) ซnd Snort Padwd Vertical
                   Configuntion in Shellow Bed.
                              168

-------
     6'8
"   T
•ปht  I
Coil
Height
Expanded
Bed
                                                           SetUed
                                                           Bed
                                                           Helaht
                                                           44"
                                                            6"
                           1.0   .5  0  Oh    SO   100
                              Porosity       Local
                                                                               -N
                                                                             ft
S
                                                                                           P
                                                                                           I
                                   1

                                   I
                                   1
                                                                                                            I
                                      .50  0  Oh    SO    100
                                  Poiosily         Local
                                   (lObl
                        Figure 10. Companion ol Local Poroiity and Heat Tramler Coatlictenti For
                                   • Long Unlmned U Tub* in • Shallow and Deep Bed.

-------
TB_T|mt_

    T Local
 Figure 11. Local ProtMRnporaani Function of Prob* Petition and
       Prawn tot 6rr Unlinrwd U Tub* in 44" Setttad B*d.
                            170

-------
              of the lew heat transfer periods (vihieh represents a very high porosity stream
              or a slug or bubble) for the various pressures one can conclude that the local
              average porosity decreases substantially with pressure, and the length of the
              bubbles or slugs also diminishes considerably with pressure.  This result in-
              dicates that the effect of pressure is to break up bubbles (or inhibit their
              formation).  Since the heat transfer coefficient is much higher when particles
              are in contact with the ttbes. the suppression of bubbles or slugs is of primary
              importance.

          d.  Tie local lengths of bubbles or slugs, as well as their velocities, can be cal-
              culated frcra the tire delays obtained between two probes placed in close
              proximity.

B.  Results with the Finned Tube

       Overall heat transfer film coefficients were obtained utilizing the configuration shown in Fig.
4b, and the results can be compared to the unflnned configuration.  All such comparisons have been
made frota expert-nits with limestone particles in the l/16"-l/32" range.  The results for the 27" deep
bed at pressures of 1, 3. 5. and 7 atmospheres art presented in Fig.12.  The tests were conducted for
both uniform and parabolic injection at the distributor plate.  It tuiy be observed fma Fig. 12 that
the parabolic velocity distribution had little effect on increasing heat transfer.  It - tnc sane, away from the surface of the tubes.  This result leads
us to concluue that the reason one ootains a lower film coefficient with finned tubing Is entirely due
to the effect of the fins on local flow patterns.  Additional information with local neasursnents be-
tween the fins yielded the result that a cxrpletel> different pattern of fluidization is occurring in
the proxisd'.y of the tubes.  One can infer for these results that channelling of air bubbles, and cool-
Ing of particles within these c!-.rmelซ are the main causes for the degradation of the overall heat
transfer film coefficient.  Thus, at pressure, whereas large slugs are supressed utilizing either
finned or unfinned tubes, the effect of fins is to keep local bubble development possible and thus
the effect of fins reduces the increase in overall heat transfer at pressure.

       The results which have been obtained above are for particles  In the 1/16" to 1/32" ranpe.
It is doubtful that additional inprovtment could be obtained utilizing finned tubing with smaller par-
ticles (as opposed to unfinned tubir.j).  The effect of fin height and the number of fins for each tube
would, of course, influence the overall film coefficient; however, under no condition^ would we expect
that fii.ied tubing would yield a higher film coefficient than unfinned tubing-


IV.  SUfAJW OF RESULTS

       The following list summarizes the results obtained to date for the comparison of dense and
shillow beds and the comparison of finned and unfinned  cubing-


                                                  171

-------
   28
   24
   20
D 16
m
6
   12
Sett led BซJ-Htfi<>h!              27"
Finned TUปJซ II? Fmjl          6'2" Hi-jh
Coil Bottom Height Above Grid  4"
Total Wetted Area             16lt2
   Air Velocity Distribution:

                Uniform
                                                            8

                                                   Vstji>. K/sec
                                                                         10
                                                                                      12
                                                                                                   14
                                                                                                                16
                               ftftn 12. Variation of O
-------
38
34
30
               Settled Bed Height              44"
               Finned Tube* < 12 FITO)          6'2" High
               Coi! Bottom Height Above Grid  4"
               Bare Tube Wetted Area          7 ft2
               Fim Wetted Area               9 f|2
               Total Wetted Area             16 ft?
                    Air Velocity Distribution • Parabolic:

                                           •    1 ATM

                                           •    3 ATM

                                           A    5 ATM

                                           A    7 ATM
26
r>
18
14
_,_*

/*  A'
                  /A
                                                                        10
                                                                                      12
                                      VSUP. 't'sec

                Figure 13. Variation of Overall Heat Tramfar With Prwture For
                          6' 2" Finrwd U Tube in 44" SinW Bed.
                                         173

-------
   275
   250
   225
™  200
<
   175
   150
   125
Settled Bed Height 27~
Solid Line: Finned Tub*
Dorid Line: Unfimed Tube

1 ATM: Shacfed Sy.ntxjl
7 ATM: Open Symbo*
Bare Tube Wetted Are*   7 ft2
F.m Wetted Area        9 f t2
Total Wetted Are*      16 It 2
                                                A • Surface Area
                                     VSUP ft/see

               Figum14. Conparton or Tottl Hm Tnmfarrad to Wortiaig Ffaid
                  Utjfciing Fin ซd end Unfinrxd TBDBM 1 
-------
   450
   400
   350
2 300
   250
   200
    150



















.
A /
/
ฃ/ A

/ Q/*
A/
/ /
4
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"*—
Settled Bed Height 44"
Solid Line: Finned Tube A
Dotted Line: Untinned Tube O
1 ATM Shaded Symbol
.' ATM Open Symbol
Bat Tube Wetted Area 7 It2
Fins Wetted Area 9 ft? [
Total Wetted Area
For Finned Tube 16 It?
A • Surface Area




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^•-""^







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	 -•-
                     246            8             10
                                        VSUP 
-------
Tfl -Tlniiial
                                                                      44" Bed Depth
                                                                      Probe Position • 32"
                                                                      ALove Grid
              1.6
              t.4
              1.2
              1.0
                                                      Time (sec)

                        Figur* 16. Co .ipcraon of T*mpcr*turซ-Time Trcon M • Position
                              32" Above Grid For Fmnod ซnd Unlmnwi Tuba in •
                                 44" Settled Bed at 1.3. and 5 Atmospheres.
                                                 176

-------
         a.  For a bed height of 27". the 18" heat exchanger bundle yielded signifi.:antly
             higher heat transfer coefficients than the 6'2" unfimed U tube for approxi-
             mately the sane wetted surface area.

         b.  To recover the sane heat transfer coefficient, the long unfirmed tube re-
             quired twice the bed material at pressurized conditions.

         c.  For all conditions, the heat transfer coefficient wss substantially hi;-her
             for 7 atmospheres than the value obtained at 1 atmosphere.

         d.  Figures 10a and lOb indicate sore of the neasurenents made with local
             instantaneous heat transfer probes.  These important results substantiate
             che overall results obtained by showing the local coefficient distribution
             as a function of height within the bed.  For the 27" bed  (Fig. 10a> the
             maxima heat transfer coefficient is obtained near the bottom of the bed.
             This indicates the reason for the higher heat transfer coefficient obtained
             for the 18" bundle in (!].  For the W bed (see Fig. lOb) the heat transfer
             coefficient is quite low on the bottoo of the bed (due to poor circulation)
             and a maxima is reached at almost 27" above the distributor, follrits of lav. an^ short heat
crs and finned and unfimed tubes.  The following mmarizcs our conclusions:

         a.  The effect of pressurizb*; a fluidi^ed bed frcn 1 to 7 atrmphvrvK can in-
             crease the heat tr.insfer coi-fficicnt jy as nuch as 73". both lor s:ปrt anu
             long heat exchanger configurations.

         b.  Results obtained previously fir shallow bed.--, whereby the ovt-r.ill !ic.it trans-
             fer coefficient was increased by 25T1. by a nonuniforra gas velocity .it the
             distribution plate, do not apply for deep beds.  The parabolic velocity
             distribution seers to lose its effectiveness in deep beds with respect to that
             of a uniform pas distribution due to the large pressure gradients associated
             wilhin deep beds which dorp initial profile distributions.

         c.  Heat exchanger configurations in deep beds experience a highly nomffiiform
             local heat '.ransfer coefficient, as a function 01 bed height.  A leu- heat
             transfer coefficient nt the bottoa section of the bed. resulting from a poor
             circulation of particles, is followed by an optiian heat transfer coefficient
             in the middle of the bed (which corresponds to vnlues cbtainabli- in a slullcv:
             bed) which is then followed by a region of ;ow heat transfer at tic top of Uu-
             bed (which corresponds to a region of high jorosity).

         d.  For the conditions tested here, firmed tubing did not contribute to an increase
             in heat extraction frin pressurized fluidizid beds compared to unfimed tuhinj-..
             It is believed that this will probably also be true for other finned tubing
             configurations, and for different sized oarticles.  Kmn Uie present results
             it appears that on both technical and ei.ona.iic croundj.. firmrd cubing should
             not be utilized in the expanded bed region of a fluldi;xd facility.



                                                 177

-------
Settled
                                   Grid
Settled
Bed Hetql
o>
Settled
eป
Settled
2
~
It
rs

"'_.
.
r*
ซ 17. Schematre R^irtunution of Oacp Bed With Long Vtrtiol
                    Hot Exchanger Configuration and • Suit* of Shallow Bซdi
                  (Hut Eachanga Surface Ann and Partidi Volume* An Equal).
                                          178

-------
         e.  For a given long unfinned cube bundle configuration, and with a deep settled
             bed (say of 57' in our facility) an optirun heat extraction probably  would
             be obtained by havir,g three separate tube bundles connected in series, each
             having its own grid and each having a shallow bed one-third the height of the
             deep bed.  Such a configuration is shown in Fig. 17.  It is felt that the
             second schene depicted will yield heat transfer coefficients significantly
             higher than the long tube hurdle with a deep bed.  Such a scheme does not re-
             quire an increase in the mct>er of coal feed points.  All the coal could still
             be burnt at the bottom, the only additional requirement is that of additional
             grids in the U-d to facilitate particle circulation and to keep the local
             porosity everywhere near the value which optimizes the  heat transfer coefficient
             (an •: on the order of .6)

         f.  Other heat exchanger arrangements such as those discussed in [2]vherehori-
             zontal finned tubing is placed in the upper portion of the bed (v*iere the
             oorosity is very high) as an econonizer rany also yield additional heat
             extraction.
VI.  RETERQJCES
       1.  Zakkay, V.. Miller. C..  and Brentan, A., "Hc.it Transfer Characteristics in a Kluidized
           Bed Packed with lie.it Exchangers." paper presented at Combustion Institute Uestem States
           Section 1977 Fall Meeting on Catalytic Ccrfcustion/Fluidized Bed Conbustion. 17-18 October
           1977. Stanford. California.

       2.  ZakXay. V.. Miller. G..  and Panunzio. S., "The Use of Fluidi:'.ed Beds for Heating Air
           for Wind Tunnels," paper presented at the Wth Semiannual t-t-eting of the Supersonic
           Tumel Assocl/'ion. SeptenbcT 14-15, 1977. Toulouse, Franco.
                                                  179

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            QUESTIONS/RESPONSES/COMMENTS


     ROBERT BROOKS,  CHAIRMAN:  Are there questions?

     MR. CATIPOVIC:   My  name  is Nick Catipovic from Oregon State
University, and we are doing  some similar heat transfer studies.  I
would have a question regarding the transient heat transfer measure-
ments which you showed,  with  the instantaneous heat transfer coeffi-
cient oscillating between zero and 100.  What were the particle
sizes?

     DR. ZAKKAY:  The particle size was l/16th inch.

     MR. CATIPOVIC:   1/16?

     DR. ZAKKAY:  Between 1/16 and 1/8, actually.

     MR. CATIPOVIC:   And what was the minimum fluidization velocity?

     DR. ZAKKAY:  I  think it was about 2-1/2 to three feet per second.

     MR. CATIPOVIC:   Okay. 2-1/2 to 3 ft/sec.  And when the bubble
engulfs your probe,  you  get a coefficient of zero.

     DR. ZAKKAY:  You don't get exactly zero.  You get the heat
transfer from the gas.   That's all.  Thus heat transfer is much lowe1*
than the heat transfer from the emulsion.  It's about an order of
magnitude lower.    /

     MR. CATIPOVIC:   Yes.  But the air is going at a velccUy of
maybe six feet per second or more.

     DR. ZAKKAY:  Yes.   But if I expand the scale, you know, then  you
would be able to see the heat transfer from the bubble as it passes
the probe.  You don't get zero; you never get zero.  But, in comparison
to the heat transfer particles, you can consider it practically insigni-
ficant..

     MR. CATIPOVIC:   Okay.  The reason I am asking you is because  we
have some very similar results, and for 4-millimeter limestone or
dolomite, our coefficients oscillate from say, 20 to 50 Btu's.

     DR. ZAKKAY:  20 to  50.  Yes.  Is this atniospheric pressure?

     MR. CATIPOVIC:   Atmospheric.

     DR. ZAKKAY:  Well,  we seem to see values considerably below 20.

                                 180

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     SPEAKER (not Identified):  Could ycu tell rce what is the differ-
ence between a shallow and a deep bed?  You have a 27-inch bed which
you call shallow, and a 5[-i ci bed which you call deep.

     DR. ZAKKAY:  i.'el 1, I think this is actually a characteristic of
the bed itself, of the diameter of the bed.  The proper parameters
bed height to bed di^neier, I believe.

     SPEAKER:  Do you have any such statement, that this ratio is
smaller, then this is shallow, and —

     DR. ZAKKAY:  I woild say not right now; but I would guess that a
H/D of 1 to 2, I would call a shallow bed; for H/D ป1, this would
probably be a deep bed.

     DR. BAR-COHEN:  Bar-Cohen from HIT.  Could you comment on the
size and frequency of the bubbles observed and the impact on the
heat transfer rate at the ti-be wall?

     SPEAKER (not identified):  Well, I think you nay well be right;
but I think there is another feature which perhaps ougltt to be taken
into account.  There has been some work published recently about the
effect of higher pressure on the convective component, when you have
large particles.

     DR. ZAKKAY:  The convective component of the gas or the particles?

     SPEAKER:  Of the heat transfer in the gas between the particles;
as you get larger particles, of course, that becomes more important,
and it becomes mor.ป important when you get hiy.ier pressures.

     DR. ZAKKAY:  I see.

     SPEAKER:  So I don't think one could explain your results on
that alone; I think you may well be right about the reduced bubble
size.

     DR. ZAKKAY:  Well, we are trying to improve our in-bed diagnos-
tics to determine exac*ly wnat is happening. And I know the BCURA
results of the effects of heat transfer due to pressure do not agree
with ours.  They did not find this enhancement effect.  Of course,
they had a very packed bed with horizontal tubes; and probably the
horizontal tubes suppress the bi.bble formation considerably.  There-
fore, when they worked at higher pressure, there were no bubbles to
suppress and thus the heat transfer was unchanged.
                                 181

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     SPEAKER:  I have another comment,  really, by which perhaps you
might be able to explain some of your other results about the bottom
section of the bed not giving high heat transfer.  We have noticed
that, particularly with large particles, when you get a fairly deep
bed, you get a phenomenon which has been described as "solid slugging",
where you get horizontal voids across the whole of the cross-section.
Now these break down further up into the bed into wall slugs, which
give you very good particle circulation; and it may be that's what's
happening.

     DR. ZAKKAY:  But I didn't get any slugging at the bottom of the
bed.  In fact, our observations indicate that the bottom of the bed
was only percolating, the air was just going through a porous media.
Finally at a certain height, the bed acts like a fluidized bed.  But
at the bottom, there was very little movement.

     SPEAKER:  Yes.  We agree, I think.  Okay; thank you.

     ROBERT BROOKS, CHAIRMAN:  Yes, next?

     MR. WEBB:  Ralph Webb, Penn State University.  "Did you account
for fin efficiency, in your heat transfer coefficient?"

     DR. ZAKKAY:  The fin efficiency?

     MR. WEBB:  You are transferring heat in this fin, so there must
be a temperature drop due to conduction in the fin material?

     DR. ZAKKAY:  I'm measuring the Q-dot, actually.  I am measuring
how much heat I am extracting and comparing one condition to the other
with the same temperature distribution in the bed.  But I am supplying
more heat, actually, at the bottom in order to account for that, so
the bed distribution of temperature is the same for the unfinned as
the finned.

     MR. WEBB:  All right.  If you had a fin of infinite thermal
conductivity, would you get a higher Q-dot.

     DR. ZAKKAY:  We should, yes; in a gas media but perhaps not in  a
fluidized media.
                                 182

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                       INTRODUCTION
     GEORGE WETH,  CHAIRMAN:  Our next speaker will be Lawrence Golan.
Lawrence got his Bachelor's and his Master's in Mechanical  Engineer-
ing at West Virginia  University and his Ph.D. at Lehigh University.
He is the Senior Project  Engineer at Exxon Research and Engineering
Company.  At Exxon, his present responsibilities include technical
supervision of the flow visualization, coking, and heat flux studies
on the FBC task force; so with that, we'll have Dr. Golan.
                                183

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                       Industrial Application of Fluidized Bed
                          Combustion - Single Tube Heat
                                Transfer Studies
                       D. C. Cherrington, L. P. Golan, F. G. Hammitt
                       Exxon Research and Engineering Company
                              Florham Park, New Jersey
ABST ACT
          The purposes of this paper are (1)  to review the objectives and status of
the DOE supported program on FBC process heaters underway at Exxon and (2) to present
some preliminary data from the program on heat transfer coefficients tor large
horizontal tubes immersed in a fluidized bed  of large limestone particles.

          The goal of the Exxon/DOE FBC program is to make a thorough technical and
economic assessment of the FBC concept for refinery and chemical plant fired process
heaters.  The underlying philosophy of the program is to build on the developments
of the boiler oriented programs, concentrating on areas of difference between boilers
and process heaters.  Two significant areas are being investigated - effects of tube
size and hydrocarbon coking.  The R&D work in progress includes ambient air fluidiza-
tion studies on tube bundles containing tubes from two to six inches in diameter,
coking studies of a hydrocarbon process stream, and peripheral heat flux measurements
on tubes immersed in a fluidized bed.

          An experimental study where the heat transfer coefficient for large, single
horizontal tubes immersed in a fluidized bed  was measured has been completed.  The
heat transfer experiments were conducted on 2 inch diameter tubes with 390 L*, 1000 u
spherical glass beads, and 2, 4. and 6 inch diameter tubes with a blend of limestone
particles ranging in size from 200-4000 ป.  The measured heat transfer coefficients
displayed a dependence on particle diameter,  tube diameter, and fluidization velocity.
The heat transfer coefficient for the limestone blend exhibited less dependence on
the fluidixatior: velocity than the glass beads.  Visual observation of the solids
movement around the tube circumference and the peripherally measured heat transfer
coefficients indicate at least three different heat transfer zones on the tube wall.


PART I:  PROGRAM OBJECTIVES AND SUMMARY OF PROGRESS TO DATE

          During the past decade. r..any agencies have been evaluating the use of
fluidized bed combustors as a Eeans of achieving more efficient fuel consumption and
for utilizing coal and other lover quality fuels in a more environmentally acceptable
manner.  These investigations have had as their end application electric power
generation.  The industrial sector where nearly 1/3 of the total United States energy
is consumed was not receiving attention.  Primarily for this reason, the Energy
Research and Development Administration (now the Department of Energy) has awarded
contracts for developing Fluidized Bed Combustion (FBC) for Industrial Applications.
The goal of the Exxon FBC program is to make a complete technical and economic assess-
ment of the FBC concept for refinery and chemical plant fired process heaters.  This
portion of the paper contains an outline of the overall Exxon program, including a
status report of the ongoing R&D activity.


Objectives and Scope of Work

          The purpose of this program is to extend the state-of-the-art of fluidized
bed coal combustion, which at present, addresses the generation of steam to applica-
tions where oil passing through immersed tubes in the bed will receive heat and be
heated to a required condition.  This purpose will be achieved by the successful
completion of the following program objectives:

  a.  To conduct an R&D program necessary to provide the engineering data and know-
      how for designing a fluidized bed process heater.
                                        184

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  b.  To conduct an economic analysis necessary to evaluate the economic attractiveness
      of fluidized bed combustion for indirect fired process heater applications.

  c.  To demonstrate the operation of a coal fired fluidized bed heater in an actual
      refinery environment for an extended period of time.

  d.  To prepare a complete Design Specification and Control Cost Estimate for a
      commercial sized fluidized bed coal fired process heater.

          The basic approach to be followed in pursuing the objectives of this program
will be to build on the fluidized bed technology that is now available and under
development by others in the related area of fluidized bed boiler applications.  Effort
in this program will be concentrated on doing the incremental work necessary to extra-
polate the boiler oriented technology to refinery and petrochemical plant type indirect
fired process heaters.  The areas of technology common to both steam generating boilers
and process heaters will not intentionally be advanced by this program.  However, the
state-of-the-art and the results of complimentary programs in the boiler area will be
used in the overall technical and economic assessment of potential fluidized bed process
heater applications.

          The two principle areas of technology that have been identified as being
peculiar to process heater applications and which are not being addressed in the on-
going boiler oriented programs concern the effects of tube size and hydrocarbon coking.
These two areas will be investigates in this program.

          Indirect fired process heater tubes are conventinally two to five times
larger in diameter than boiler tubes.  A typical crude oil heater, for example, may
have a multitude of 4" to 8" diameter tubes in the heat pick-up zones, as contrasted
to the 1" to 2" diameter tubes normally used in steam boilers.   The effect that these
larger tubes will have on fluidization characteristics and definition of the optimum
or acceptable configuration of a tube bundle immersed within a fluidized bed must be
investigated.

          Similarly, the parameters affecting hydrocarbon coking must be investigated.
When heating a hydrocarbon to 600"F+ (as required for separation by distillation or
other typical processes),  some degradation ot the oil and coke laydown on the inside
tube wall is unavoidable.   The rate of coke laydowr. is affected primarily by the
temperature of the hydrocarbon film on th
-------
Summary of Progress to Date

          The program got underway July 1. 1976.  The program effort to date has been
devoted to the design and construction of the three major laboratory units that will
be used to generate most of the Phase 1 program data.  The first of these units is
the Two-Dimensional Flow Visualization Unit.   This is an atmospheric pressure, trans-
parent test chamber where fluidization and mixing characteristics of a fluidized bed
containing immersed tubes can be visually observed and quantitatively measured.  A
schematic of the facility is shown in Figure  1.  (This unit is described in Part II
of this paper.)  The unit construction was completed and testing comr/'.nced in June,
1977.  To date, five different bundle configurations have been rested and evaluated.
The first consisted of 2-inch diamter tubes on 3-diameter ceuter-to-cซnter spacing.
This configuration was identical to the bundle array installed in the Rivesville
demonstration boiler and was intended to establish a baseline of performance against
which comparisons could be made with data as  it becomes available from that unit.

          These tests were followed in cum by bundle configurations which were
designed to evaluate the effects on fluidization performance of varying tube size
and spacing.  The additional bundles tested to date were all 6-inch diameter tubes
but arranged on 2-diameter, 3-diameter and 4-diameter cencer-to-center spacing using
a scaleup of the Rivesville vertical and diagonal proportional spacing.  One tube
bundle on 2-diameter equilateral triangle pitch was also tested.

          In conjunction with the fluidization performance testing,  some conductive/
convective heat transfer data were obtained on each of the bundle configurations.
Variations in heat transfer coefficients as a function of peripheral tube surface
orientation and tube location in the bundle have been determined.  In addition, heat
transfer data on single isolated tuhes immersed in a fluidized bed have been measured
using a range of tube sizes and bed materials to determine what affects the presence
of adjacent tubes and varying bed materials (particularly bed particle size) have on
heat transfer characteristics.  These data are particularly useful in comparing the
program results with data reported by other investigators who predominantly used
single tubes and/or relatively fine bed materials.  These single tube data are
reported in Part II of this paper.  It is expected that, all aspects of the Flow
Visualization portion of this program will be completed during December, 1977.

          The second laboratory unit is the Process Stream Coking Unit (a simplified
flow plan is shown on Figure 2).  The goal of the testing conducted in this unit will
be to determine what effect the high fluidized bed heat flux levels will have on the
coking rate of a hydrocarbon process stream.

          The major pieces of equipment in the Coking Unit are:  pump (1000 B/D,
650 psig), four single tube heat exchangers (0.6 inch I.D., 9 ft. long), four 50 kW
electric heaters, a 2.8 M Btu/hr gas fired crude preheater, and necessary instrumenta-
tion.  The coking tests must be carried out in a refinery location because of the
crude handling facilities required and the volume of crude involved (1000 B/D).
The unit is now completely assembled at the test site, Exxon's Bayway Refinery,
Linden, New Jersey.  Final pre-startup checkout of the unit is now underway with
testing expected to begin in December, 1977.

          The hydrocarbon feed to the coking unit will be a slip stream from a
refinery pipestill process stream.  During a  test, the hydrocarbon feed to the four
exchangers will come from a sinrle point so that all exchangers receive a feed common
in inlet bulk temperature and composition. The coking tests on these four exchangers
will proceed simultaneously.  The need to run multiple coking tests concurrently is
dictated by the fact that the crude feed to a pipestill heater changes with time.
By running multiple exchangers in one test, a direct comparison of the influence of
film temperature on coking rate will be observed and the influence of feed type
eliminated.  The ability to cross-correlate data between tests will depend on the
number of crude slate changes during a given test.

          The test conditions are designed to simulate conventional pipestill heater
operations and those expected for a FB heater.  The start of test tubeside mass
velocities expected to be run in the four exchangers are 150,  300,  450,  and
600 Ibm/sec ft^.  These mass velocities correspond to nominal pipestill operation
                                         186

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                                     DUST COLLECTOR
VENT
  AIR SUPPLY



     AIR  METERING RUN
              TUBE  BUNDLE
                      GRID
                   Figure 1.2-D Flow Visualization Unit
                             187

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-------
(300 Ibm/sec f t2) .  pipestill turndown (150 Ibm/sec f t2) ,  an? two increased mass
velocities possibly needed in a FB combustor to limit the process film temperatures.
The selected feed temperatures represent nominal pipestill heater outlet conditions
(650ฐF), heater inlet conditions (450ฐF),  and nominal crude temperature at the
desalter (250ฐF).  The start of run heat flux levels on the hot crude cases (650ฐF,
450ฐF) have been selected as 15.000.  30.000  45.000. and  60.000 Btu/hr ft2.  Higher
flux levels of 80,000 and 100.000 Btu/hr ft2 are planned  for the cold crude tests.
Hot crude tests at the 15.000 3tu/hr ft2 flux level represents the average heat flux
in a conventional pipestill heater, while a 30,000 heat flux represents a peak flux.
Operation at these heat flux levels will permit tie-in with conventional heater coking
rate experience.  The higher heat flux levels for both hot and cold crude represent
the heat flux conditions possible in a fluidized bed
          The heat exchanger unit will be placed in operation at the designed test
conditions and run until the pressure drop and energy balance data indicate that
coking has progressed to a significant extent.  The individual coked exchangers will
be phut down and removed for visual inspection.  A test will continue until all
exchangers are coked or until the test period has expired.  The entire unit will
then be phut down, all exchangers replaced,  and another run begun.

          The third laboratory unit will be the High Temperature Heat Flux Unit (see
Figure 3) .  This fluidized bed will be operated :.n the temperature range of 1000-
1600 F.  The purpose of the studies to be conducted in this unit are to determine
the local heat transfer coefficients (including radiation) and variations in heat
flux at significant positions in the tube bundle submerged in the bed.  The tube
bundle to be tested will be the arrangement determined in tne Two Dimensional
Studies to be of potential commercial interest for the design of process heaters.

          The heat flux studies will first be conducted without fuel combustion in
the bed.  The hot fluidizatrion gas will be produced by combustion of fuel in a
combustor and ducting the gas to the test facility.  In this way, fuel distribution
variables will be eliminated as an element of concern in these studies.  At a later
stage in the program, solid fuel will be burned directly in the bed.

          The fluidized bed will be capable of firing 12 M B';u/hr.  The design of
the unit has been completed and approved by DOE.  Vendor proposals have been received
for all major equipment components and orders should be released in the near future.


PART II:  SINGLE TUBE HEAT TRANSFER STUDIES

          Several heat transfer studies have been conducted where measurements o'
heat transfer coefficients from a horizontal tube or to a horizontal tube immerst^
a fluidized bed have been made.  A number of correlations have been proposed as pre-
dictive tools, but the results of different correlations give conflicting trends.
References (l."?_- 3-4)1 review these correlations.  Reference (1_) points out that there
is very little agreement between the various correlations or between correlations and
data.  An uncertainty band of 100% is found between correlations.  It is also
suggested that the wide range of results may have been influenced by the scale of
the experimental equipment.  These previous studies have limited applicability to
many industrial applications (2_) in that fine or narrow particle ranee bed material
and/or small tube diameters (1 and 2 inch) have been used.  In many industrial
applications, large tubes ranging up to 6 inch diameter can be conveniently used.
In addition,  large particle bed material with a wide particle size distribution appear
likely.  This is especially true for fluidized bed combustors where attrition of the
limestone will naturally cause a wide particle size distrubution to exist in the bed.

          For this reason, this study was initiated to experimentally measure tube to
bed heat transfer coefficients in an atmospheric pressure/temperature bed where large
tubes would be exposed to a bed of large particles in test equipment of relatively
large scale.   The experimental variables consisted of fluidization velocity (ranging
up to 16 fps) , bed particle siiie (390 u, 1000 u, spherical glass beads and limestone
with a wide size distribution ranging from 200-4000 u), and tube size (2-4-6 inch
diameter) .  The limestone particles tended to be quite angular with the large particles
being rectangular in cross section.  The volume average particle size of the limestone
was 1000 u .
1.  Underlined numbers in parenthesis refer to the references.

                                         189

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                                                I
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                  Flow Visualization Studies
                                                                    Process
                                                                     Fluid
                                                                    (Water)
                                                                    Cooling
                                                                    System








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Air Meter
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                                                                                                            Flue Gas
                                                                                                            Discharge
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                                                       Figure 3. High Temperature Heat Flux Unit Flow Plan

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Fluldization Facilities

          The heat transfer measurements were made by inserting a specially designed
tube (described in the next section) into one of two fluidization units.  The larger
fluidization unit was approximately 1 ft. in depth by 7.5 ft. wide by 12 ft. high
(Fig. 1) .   The 1 ft. horizontal dimension was selected to minimize wall effects.
The large walls of the unit were constructed of plexiglass so tnat bed behavior could
be visualized.  Fluidization air to this unit was provided by an electric motor
driven compressor which supplied up to 10,000 SCFM of air at 10 psig discharge pres-
sure.  Air from the compressor v;as directed to the plenum located at the bottom of
the flow visualization unit.  The grid used was that recommended for and installed
in the Rivesville FBC (6) boiler.  The grid consisted of 1/10 inch diameter holes
located on a triangular~pitch for an open area of approximately 4%.  Downstream of
the flow visualization section the fluidization air was cleaned of entrained parti-
cles before being discharged to the atmosphere.  Two 29 inch diameter cyclones
designed for a maximum of 100 fps inlet velocity at 10,000 SCFM total air flow rate
operated in parallel with the solids remc/ved in the cyclones returned to the bed.

          The second and smaller of the two facilities was an 8 inch circular, column
constructed of plexiglass.  A Riversville grid was also installed in the small unit.
Fluidization air to this unit was supplied by a separate blower and metering system.
Heat transfer experiments with glass beads were conducted in the smaller column
while limestone tests were conducted in both units.  The grid to tube centerline
was maintained at 7 inches for all glass bead and limestone data collected in the
circular column.  The packed bed height was above tube level.  In the large unit,
the tube centerline to grid spacing was maintained at 18 inches.  The size range
distribution for the limestone as charged to the unit is shown on Figure 4.

Heat Transfer Probe

          The heat transfer data was gathered from a specially designed probe
inserted in the fluidized bed zone.  Heat transfer measurements in the small fluid-
ization unit were made on the 2 inch diameter tube while 2, 4(2).  and 6(2) inch
diameter tubes were tested in the large unit.

          The heat transfer probes consisted of specially instrumented plexiglas
tubes which were installed in the fluidized bed zone of the test unit.  Each tube
had a 1/4" x 6" x .005'' thick Nichrome strip imbedded flush with the outside tube
surface.  One or two 40 BWG iron-constanran loop junction thermocouples were attached
to the under surface of the strip to monitor strip temperature.  (See Figure 5 for
assembly detailed.)

          The Nichrome strip which had a resistance of approximately 0.2 ohms was
electric resistance heated to a temperature of 30* to 60s above the ambient bed
temperature.  The power input required to maintain this differential temperature
between the strip and the bed was monitored and is a direct function of che mean
conductive/convective heat transfer coefficient over the area of the strip.  By com-
paring the relative power required to maintain the temperature of the strip at
various locations around the circumference of the tube and from one tube location
to another.  A pattern of maldistribution as a function of tube location and surface
orientation was obtained.

          The instrumentation for the heater element consisted on a D.C. power source
with a built-in volt and ammeter and a digital temperature indicator.  The Nichrome
strips were resistance heated to a temperature of 30 to 60ฐF above the ambient bed
temperature.  The heat transferred was therefore from the strip to the cooler bed.
After the system reached equilibrium, the strip temperature was monitored for one
minute with maximum aud minimum temperatures during this time period noted.  The
average of the maximum and minimum temperature level was used in evaluating the
average heat transfer coefficients, so that:

                                      3.14 I2 R
                                               S
                              ave     As "save
   ~4 inch and 6 inch nearest plexiglas equivalent to nominal pipe size or 4.5 inch
    and 6.5 inch O.D. respectively.

                                         191

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I-*
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ro
                 5000



                 6000
                               0.1
                                                          5     10                    50



                                                                   Cumulative Wt."  Less Than
                                                                                                                                         99.9
                                         Figure 4. Particle Size Distribution of Limestone Bed For "Rivetville Configuration" Tests

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                                                                       Figure 5. Ambient Temperature Test Probe

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                                    P = I2RS - El

to assure that .the voltage, amperage, and resistance of the circuit all balanced.

          Each heat transfer tube could be indexed or rotated on its axis so that
local heat transfer data could be collected around the circumference of the tube.
Data for all tubes at all velocities was gathered at 45" degree intervals of tube
rotation.


Probe Calibration

          In order to compensate for the thei-rcal losses other than those directly
from the strip surface, each heater assembly was calibrated prior to testing.  The
calibration war performed by placing the heated probe in a metered air stream and/or
water where the heat transfer coefficient could be calculated with a reasonable
degree of accuracy.  By comparing this coefficient with that back calculated from
the measured power input, a correction factor for each strip was generated.  Fox
imposed heat transfer coefficients greater than 30 Btu/hr ft2 ฐF, the calibration
experiments including computer modeling of the probe design indicated a probe error
not greater than 157,.  The higher the imposed heat transfer coefficient, the greater
the probe accuracy.  At an imposed coefficient of 100 Btu/hr ft2 ฐF. probe error was
much less than 57..  Probe to probe correction factors varied only by 2-37=.  In all
calibration runs, the measured coefficients were higher than that predicted.  All
heat transfer coefficients presented are as measured with no corrections applied
since the coefficients generally are in the 30 Btu/hr ft2 ฐF and higher ranges where
probe accuracy is within other experimental variables.


Single Tub? Tests Run

          The following single tube tests were run in either the 8-inch diameter
column or the Two-Dimensional Flow Visualization Unit.

          Tests run in 8-inch column:

          Test No. 1 - Two-inch diameter tube: 390 u spherical glass bead bed
                       material.  Kluidization velocities u = .34 to 1.6 ft/see.

               No. 2 - Two-inch diameter tube; 1000 u spherical glas?; beads: u = 1.8
                       to 4.0 ft/sec.

               No. 3 - Two-inch diameter tube: 200 u - 4000 u limestone (1000 u wt.
                       avg. size); u = 2.1 to 8.4 ft/sec.

               No. 4 - Two-inch diameter tube: 200 u - 1800 u "fertilizer filler"
                       graded limestone (650 ป wt. avg. size); u= 2.2 to 3.5 fiz/sec.

               No. 5 - Two-inch diameter tube; 1000 u - 4000 u "moon mountain grit"
                       graded limestone (2500 u wt.  avg. size); u" 6.3 to 8.0 ft/sec.

          Test runs in Two-Dimensional Flow Visualization Unit:

               No. 6 - Two-inch diameter tube; 200 u - 4000 u limestone (1000 u wt.
                       avg. size); u ป 11 to 15.8 ft/sec.

               No. 7 - Four-inch diameter tub>; 2CO u - 4000 u limestone; u = 10.5 to
                       14.6 ft/sec.

               No. 8 - Six-inch diameter tube; 200 u - 4000 u limestcne; u = 11.9 to
                       15.0 ft/sec.
                                         194

-------
               No. 9 - Six-inch diameter tube;  200 u - AOOO u limestone (1000 u wt.
                       avg.  size).   Bed depths of 15-inch and 21-inch above grid
                       level,   u =  11.4 ft sec.

          By analyzing the results  from tests in the above matrix,  various conclusions
and observations can be made concerning the effects of fluidization velocity,  bed
particle size, tube diameter and bed depth.  Each of these parameters will be discussed
separately in the following paragraphs.


System Limitations

          All single tube tests were run over a range of fluidization velocities -
the range for each test varying depending on the bed particle size  and the physical
limitations of the test facilities  being used.   For example,  in tne B-inch
tests with glass beads, maximum fluidization velocity was limited only to the entrain-
ment velocity of the particles being used.  With limestone, on the  other hand,  a
system pressure head limitation restricted the region of investigation to a maximum
of 8 ft/sec or about 3 times u r.

          When testing single tubes in rhe Two-Dimensional Flow Visualization Unit,
it was not possible to operate the  unit at low fluidization velocities in the range
from 2.4 ft/sec (umj) up to about 8 ft/sec.  In this operating range,  the entire bed
tended to alternately lift and collapse as a single mass, putting very high oscil-
latary forces on the plexigias walls of the unit.  Operating in this mode was judged
tj be inappropriate for the safety  of this equipment.

          It is interesting to note that when the unit is operated  under the same
conditions but with a tube bundle immersed in the bed, the same phenomena is not
observed.


Visual Observations

          During the course of running these test? in both the 8-inch column and the
larger Two-Dimensional Flow Visualization Unit,  some visual observations were noted
which may help to explain or interpret the data.  These observations will therefore
be described before discussing the  test results.

          Three distinct zones of Folids flow or solids-to-tube contacting were
observed around the periphery of the horizontal  iranersed tubes.  Since there is
general agreement among investigators that the relatively high heat transfer coef-
ficients in a fluidized bed are a result of the scrubbing action or contacting of
the solids particles on the tube wall, it would  follow th.it these different patterns
or zones of flow could be significant to our understanding of the heat transfer
mechanism.

          The first zone occurred on the lower portion of the tube  - that is.  the side
of the tube facing toward the direction of oncoming fluidization gas (identified as
180* position on all accompanying figures).  This area has been described by others
as a bubble shrouded zone; however, in this study, it did not appear as a complete
gas pocket.  The zone appeared to be lighter than normal bed density with very rapid
density variation occurring.  This  zone can be contrasted to the second zone located
on top of the tube (0*).  in this second zone,  the tube was covered by a dense "cap"
of particles.  The cap was not stagnant as oscillations of the cap  occurred in a
regular side to side sliding motion.  In addition to the sliding,  frequent bubbles
crossed the upper surface causing solids replacement.  This bubbling behavior
regularly occurred only over the center two thirds of the tube, indicating a possible
wall effect.  This wall effect was  also noted in the size of the cap.   When the bed
was defluidized and solids drained  from the bed, the cap of material remaining on the
heat transfer tube was observed to  be saddle surfaced, the peak of  the cap being two
to three times higher near the wall than tube center.  In the fluidized condition,
it VAS not possible to measure the  cap at the tube center.   However, a qualitative
judgement was made as to cap size by brightly back lighting the cap area and comparing
light transmitted to the height of  the cap at the wall.  Again, the wall cap appeared



                                        195

-------
taller than at the tube center.   The location of the third zone varied with fluidiza-
tion velocity, but was normally locateo at approximately the 45-90ฐ position.   This
zone alternated between the dense cap and dilute phase, much like that of the
advancing and retreating of ocean surf.  As will be seen later, this "surf" con-
sistenly coincided with the area of highest heat transfer.


Average Heat Transfer vs. Fluidization Velocity and Particle Size

          The heat transfer data as a function of fluidizacion velocity and particle
size were analyzed on the basis of both overall average coefficients and the effects
on peripherial maldistribution patterns.  The overall average coefficients will be
discussed first.

          The average overall coefficients measured for the 390 uand 1000 v spherical
glass beads and the 200-4000 u limestone blend are displayed on Figure 6.  The data
are plotted against a velocity parameter of

                                          u
                                         umf

which tends to normalize the data for the differences in fluidization characteristics
imposed by differences in particle size.  The umf used for the glass beads were
calculated by the Leva method while a nominal Ujnf of 2.4 ft/sec was used for the
limestone blend.

          At the higher end of the velocity ranges tested, the limestone data com-
pared very closely with the 1000 u glass bead data.  It is interesting to note that
the weight average particle size for the limestone blend was nearly 1000 u (see
Figure 4 for the particle size history of the limestone bed material used in all
tests).

          At lower fluidization velocities, the resultant limestone heat transfer
coefficients deviated substantially fron the 1000 u line.  At the lowest fluidization
velocity at which data were collected, the limestone and 390 u glass beads had nearly
identical measured heat transfer coefficients.  Based on Leva's correlation for
minimum fluidization velocity, much of the larger sized limestone would have senre-
gated out of these low velocities with only particles of about 600 u or smaller
still in a well fluidized state.  Under these conditions, this aveiage size t'luidized
particle would have been 340 ป.   It is probable that multi-layer fluidization had
occurred as described by Wen.^Z.'  Wen's discussions center on a two-particle system;
however, the same general trend should occur in multi-particle systems.  Wen's theory
predicts distinctly separated layers of fluidization when

Dp
K——  >1.3.  In these tests, the particle size range was significantly greater
UP2         than 1.3.

          It was observed that both the 390 u and 1000 u glass bead heat transfer
coefficients increased rapidly with fluidization velocity while the limestone blend
displayed much less sensitivity to fluidization velocity.

          The coefficients measured for the glass spheres followed the inverse
relationship with particle size of
                                       ..  . 0.36
                                have
fr)
This relationship has also been reported by Zabrosky. -'

          A few tests with 106 u glass spheres were also run which further confirmed
this inverse relationship over the entire 10:1 particle size range.
                                        196

-------
vo
                          ฃ 90
                          o

                          CM



                          ^ 80
                           5  70
                            8
                            ra
                              60
t  50
u
o
o


ฃ  40
u.
(/>
z
<

H  30
                             20
                          UJ
                          o
                             "
                                                                                                Glass Beads
                                                                                               Limestone Blend

                                                                                               (50/50)
                                  Note: Slumoed Bed Height Above Tube;

                                       Tube Diameter  2" O.D.
                                                                       I
                                                                                 I
                                                   1.0      1.5
                                           2.0     2.5


                                               U/Umf
3.0      3.5      4.0     4.5
                                                   Figure 6. Heat Transfer Coefficient vs. Bed Particle Size

-------
Local Heat Transfer vs.  Fluidization Velocity and Particle Size

          The effect of fluidization velocity and bed partible size on local peri-
pheral hefit transfer can be seen from an examination of Figures 7a, 7b,  and 7c.
Figures 7a and 7b are polar plots of peripheral heat transfer patterns for the 390 u
and 1000 u glass beads respectively with velocity parameters of  u  in the range of
1.0 to 4.                                                        umf

          An inspection of the data indicate that at relatively low fluidization
velocities the highest rate of heat transfer occurred ar  the 90ฐ/270ฐ  positions
on the tube where particle aggitation was the most vigorous.  The coefficient  at the
upper surface (0ฐ) increased rapidly with an increase in fluidization  velocity.   This
corresponds to the observed increase in mobility of the particles located in this
"cap" region.  As the fluidization velocity was increased,  the heat transfer profile
became more circular and the cusps or flatness in the "cap" zone disappear.  Very
little change in heat transfer coefficient occurred at the bottom (180ฐ)  of the  tube
since this position was consistently contacted by dilute emulsion phase solids.   The
highest heat transfer rates at the intermediate and higher velocities  were found
approximately at the 45ฐ/315" position with the exact maximum position depending on
velocity.   These high coefficients are consistent with the visual observation  of the
rapidly oscillating solids layer at the location of the previously described <:surf
line" and "cap".  Rotation of the test probe into and out of the surfe line region
caused substantial and very rapid strip temperature variations at constant power
input.

          The local heat transfer data shown on Figure 7c were obtained in the same
8-inch column but using the limestone blend bed material.  In this case,  runs  were
made at  u   ranging from .9 to 3.0.   While the data are not conclusive,  it would

        umf

appear that at  u  „ ,  the maldistribution patterns are less sensitive to fluidiza-

               ^w-1
tion velocity for the limestone.  This performance would be consistent with data
discussed earlier for overall average coefficients and summarized on Figure 6.

          Two additional brief tests were run in the 8-inch column to  evaluate the
effects of varying the particle size distribution of the limestone bed material.  One
test used a quarry graded "fertilizer filler" limestone with a size distribution of
200 u to 1800 u with a weight average size of 650 u.  The second test  used a "moon
mountain grit" with a size distribution of 1000 ;: to 4000 u and a weight  average size
of 2500 ;i.  (It is a 50-50 blend of these two grades of material that  is  used  as the
charge material for all tests run in the Two-Dimensional Flow Visualization Unit for
both single tubes and bundle configuration tests).

          The results of these two rests are compared on Figure 8 with the previously
noted data on the limestone blend.  i'he data appear to follow the same general pattern
observed in the glass bead tests - namely, that heat transfer coefficients increase
with a decrease in weight average psrticle size.  No more definitive conclusions are
drawn from these limited data.


Heat Transfer Coefficients vs. Tube Diameter

          The effects of tube diameter on overall heat transfer performance was  also
investigated.  Since the 8-inch test column obviously could not accocmodate tubes
larger than 2-inch diameter, these tests were carried out in the Two-Dimensional Flow
Visualization Bed.  Tests were run on single 2-inch. 4-inch, and 6-inch diameter
tubes.  As can be seen on Figure 9. the 2-inch diameter tube data blended very well
with the single overlapping data point obtained on the 8-inch column during the  lime-
stone bed tests on that unit.

          In these tests, heat transfer coefficients were measured at  15ฐ increments
around the tube circumference and averaged to obtain overall heat transfer data  for
each tube at each velocity.
                                         198

-------
LOCAL HEAT TRANSFER COEFFICIENT VS. FLUIDIZATION VELOCITY
          390/x GLASS BEADS - 2" TUBE  DIAMETER
        315
                            ieoฐ
                  = 4.4
        	   a

              Umf
= 2.5
                  = 1.2
                           Figure 7a.
                            199

-------
LOCAL HEAT TRANSFER COEFFICIENT VS. FLUIDIZATION VELOCITY
         lOOOpt GLASS  BEADS - 2" TUBE DIAMETER
        315
                                               45ฐ
                                                       ocal
                                                      ave
        225
                  *-ซ.!
                   Umf
                   Ua
                   Umf
                   Ua
= 3.1


= 1.9
                          Figure 7b.
                            200

-------
                LOCAL HEAT TRANSFER COEFFICIENT VS. FLUIDIZATION VELOCITY
                           BLENDED LIMESTONE - 2"  TUUE DIAMZTER
 a
•   ;

 mf
 a  _
Uซf"
= 1.6
                        315".
                                                                         'local
                     225"
                                                                 135ฐ
          Characterization 01  The Blended Limestone Bed As A Function Of Fluidization Velocity
                     U
                    _Umf-

                     1.3

                     1.6

                     2.5


                     3.8
                                  . Bed  Material
                                  Fluldized

                                       70

                                       95

                                     100


                                     100


                                   Figure 7c.
Largest Particle Fluidized'50 ,
	Particle	

     2000 /i /800/i

     3000 fj. /lOOO/i

Exceeds Max. Particle  In Bed/
       1100/i

Exceeds Max. Panicle  In Bed/
       1100 M
                                         201

-------
vu
IT
f$ 80
u.
DC
* 70
= u
^_
CO

> 60
h-
Z
G 50
CZ
g "
8 ฐ 4o
a:
UJ
ii
S? 30
<
a:
K
< 20
UJ
LJ
< 10
oc
<
Q
i ! 1 1 1 1 1 1

—

Limestone
50/50 Wt
1 1 1 1 ••

'~

Blend
. Moon Mountain
Grit And Fertilizer Filler

Fertilizer
Filler

,
i
4,^^.-** Moon Mountain
S''"'
-^x^
Grit ;
1 	 	
' Limestone Particle Size Distribution

Wt. Ave. Size
~ Fertilizer Filler 650 M

Moon Mountain Grit 2500 n
50/50 Blend 1000 M


Size Range
200 - 2500

1800 - 4000
200 - 4000

Note: Slumped Bed Height Above Tube
u-

1 1 1 II 1 1 1
0123 4567 8


1 1 1 1 1 •
9 10 11 1? 13 14 If
    ACTUAL FLUIDIZATION VELOCITY,  U. (fns)
Figure 8. Heat Transfer Coefficient Limestone vi. Particle Size

-------
90
oJ 80
i—
LL.
(g
ง70
5
cj
_•ป
-
5 50
0
n.
JNป IL
O uj
t*> o 40
0
a:
UJ
| 30
a;
i-
K 20
UJ
X
UJ
o 10
a
UJ
2
I 1 1 1 1 1 1 1 1 1 1 1 !
6" Nominal
Pipe
4" Nominal /
Pipe /
L..~Lr"~~~
-.*•"""" """"—-
' t
•* s \
	 * •
f'" ,2" O.D. Tube
+ '
8" Column Tests
_ 2" Tube: Slumped
Bed Heiyht Above Tube
Data Collected In 20 Bed; 50/50 Wt. Limestone
Blend; Bed Height Equal To Upper Tube Tangent
- In Slumped Condition

-
1 1 1 ! 1 1 1 1 1 1 1 1 1
3 ซJ 5 6 7 8 9 10 11 12 13 14 15 1
                                                                             17
 ACTUAL FLUIDIZATfON VELOCITY, fps
Figure 9. Heat Transfer Coefficient vs. Tube Siza

-------
          The data show an increase in heat transfer coefficient with ar. ir-cr^ase it-
tube diameter.  Dependence at constant fluidization velocity followed the relationship.

                                       h    o (D-.'i '
                                        ave     T

These results are in general agreement with results reported by McLaren f.t al —  and
Kuruchkin^^ but are not consistent with results reported by several other investigators.


Heat Transfer Coefficient vs. Bed Depth

          One experiment was conducted to test the sensitivity of the heat transfer
coefficient to bed depth.  In this experiment, a 6-inch diameter tube was positioned
18 inches above the grid, while the defluidized bed depth was 15 inches in one run
and 21 inches in the other.  In other words, in the first case, the slumped bed was
even with the bottom tangent of the tube and in the second with the top tangent
line.  In both cases, the tube was well inundated in the bed wnen fully fluidized.

          The results of the heat transfer measurements are shown on Figure 10.  The
measured overall average coefficient was about 77. higher for the deeper bed.  Also,
there was a rather significant change in the profile or pattern of heat transfer.
The coefficient at the 45ฐ/315" "surf line" positions was measurably higher for the
shallower bed.  With the increase in bed depth, the region of highest heat transfer
shifted to the top of the tube, indicating an increase of particle activity in the
"cap" area.


Summary Observation and Conclusions

          The following summary observations and conclusions can be made from an
analysis of the single tube heat transfer tests reported here.

  (1)  Three distinct zones of particle activity or particle-to-tube contacting
       can be observed when a tube is immersed in a fluidized bed.  These zones
       appear to bear a relationship to the heat transfer coefficient measured at
       each respective zone.

  (2)  The overall average heat transfer coefficient to a tube immersed in a
       fluidized bed appears to follow a relationship with particle size of

                                                 .36
                                     have

  (3)  For a bed containing a wide particle size distribution, the heat transfer
       coefficient is approximately governed by the weight average particle size of
       the portion of the bed that is in a well fluidized state.

  (4)  The hear transfer pattern in a bed composed of a range of particle sizes is
       less sensitive to fluidization velocity than a narrow graded size bed
       material.

  (5)  Patterns of peripheral heat transfer to an immersed tube become more symmetrical
       with an increase in fluidization velocity.  The local coefficient at the
       bottom or 180ฐ position on the tube is affected very little by changes in
       fluidization velocity.
                                                 2
  (6)  These experiments indicated a h    
-------
           LOCAL MEAT TRANSFER  COEFFICIENT  VS. BED DEPTH
          BLENDED LIMESTONE  - 6" NOMINAL  PIPE SIZE ~ = 4.4
                                                          - Curve 1
"local
 ave
     270"
                                                                 •-   Curve 2
                                    180ฐ
    Explanatory Notes:
                      _loc
                      ave
I,       Curve 1 - Slumped Bed Depth 21 Indies
                                  r Ft2 ฐF
                                       have = 68.9  Bm/Hr
                             Curve 2 - Slumped Bed Depth 15 Inches
                                       have =64.4  Bln/Hr Ft2 ฐF
    Curve 1 And 2 - Tube Center  Line 18" From Grid

                                 Figure 10.
                                   205

-------
REFERENCES

1.  Zabrodsky. S. S.,  Hydrodynamics and Heat Transfer in Fluidized Bed. M.I.T. Press,
    Cambridge, MA. (1966).

2.  Bottcrall, J. S. M.,  Fluid Bed Heat Transfer, Academic Press, New York, 1975.

3.  Saxena, S. C., etal,  "Modeling of the Fluidized Bed Combustor with Ismersed
    Tubes," ERDA Quarterly Report No. FE-1787-6. December 1976.

4.  Chen, J. C., "Heat Transfer to Tubes in Fluidized Beds," ASME 76-H5-75, National
    Heat Transfer Conference, St. Louis (1976).

5.  Cherrington, D. C., Golan, L. P., Halow, J. S., Hammitt, F. G., "Fluidized Bed
    Combustion for Industrial Applications - Process Heaters," AIChE Paper No. 1,
    17th National Heat Transfer Conference, Salt Lake City. Utah, August 1977.

6.  "Multi-Cell Fluidized Bed Boiler Design Construction and Test Program," OCR
    Contract No. 14-32-001-1237, Quarterly Report No. 1, July/Sept. 1974.

7.  Wen, C. Y., Yu, Y. H., "Mechanics of Fluidization," Chemical Engineering Symposium
    Series Vo. 62, 1966.

8.  McLaren, J., Williams, D. F., J. Institute of Fuel, Vol. 42, p. 303 (1969).

9.  Kuruchkin  (as reported in "Modeling of a Fluidized Bed Combustor with Immersed
    Tubes," ERDA Quarterly Report FE-1787-6, Sept.-Nov. 1976, Department of Energy
    Engineering, Illinois University.)
NOMENCLATURE

  A - heat transfer area
  D - diameter
  E - volts
  h - heat transfer coefficient
  I - amps
  P - power
  R - nichrome resistance
  T - temperature
  u - velocity
ft*
ft
volts
Btu/hr ft41
amps
watts
ohms
"F
fps
SUBSCRIPT

  a   - actual
  ave - average value
  bed - denotes bed condition
  P   - particle
  S   - nichrome strip
  T   - tube
  mf  - minimum fluidization
                                         206

-------
            QUESTIONS/RESPONSES/COMMENTS


     MR. GOLAN:   The first  question is from Mr. W. L. James, Fennel 1
Corporation.  He asks,  "Your  fluid bed slide showing the equipment
schematic indicated  a gaseous fuel using a orecombustor.  You also
showed cyclones  and  ash disposal equipment, and it's an obvious ques-
tion, where does the ash come from?"

     During the  time we were  discussing that slide, I said the heat
flux unit would  be used in  two applications.  Initially we would burn
only a gaseous fuel, and obviously we wouldn't have any ash at that
time.  The cyclones  are however required to recycle the entrained
limestone bed material.  Then, in a later stage of the program, we
would be adding  the  coal  feeding facilities, and at that time we
would need both  the  cyclones  and the ash disposal equipment.

     His second  question is:   "Is the limestone particle size inter-
mixed?"  I don't know exactly what he means by that, but our stone
has a rather wide size  distribution of 100 to 560ฐ .  We buy two
different blends of  limestones.  One is the Moon Mountain grit
and the other one is the fertilizer filler.  The limestones arrive
separately and are loaded into different drums.  At t!ie time we
start a test, we determine  how many barrels of each limestone we
are going to put into our 2-D unit; normally a barrel of each, which
gives us about 1,000 pounds limestone in the bed.  We then fluidize
the bed and the  limestone particles intermix.

     The next question  is frora Dr. Rao of MITRE:  "Why does the heat
transfer coefficient increase with the tube diameter?"  That is a
very good question,  and I don't have the explanation at this time.
As I said, I really  don't know if our work's been conclusive, but for
the set of 16 measurements  that we've made, the four-inch tubes
always had higher coefficients than the two-inch, and the six-inch
tubes had higher heat transfer coefficients than the four-inch tubes.
We have tested over  a limited velocity range.  To confuse the issue
a little more, when  we  did  the experimental work with a bundle of
tubes, the two-inch  bundle  give us higher heat transfer coefficients
than the six-inch bundle.  So far we have no explanation for this
phenomena.

     MR. Newby from  Westinghouse:  "How is the heat transfer coeffi-
cient distributed around  the  tube circumference?"  It's difficult to
describe without using  a  chalk board, but if we were to visuali.:e the
gas stream coming onto  a  tube which is facing the gas stream—and
label that the 180-degree position—we'd find at this loca  on the
                                207

-------
coefficient is very insensitive to fluidization velocity.   A 30
coefficient at three feet per second would still  be 30 at  6, 10,
and 12 fps.

     The coefficient on the top surface of the tube (that  is, at  the
0-degree position), however, was relatively sensitive to the fluidi-
zation velocity.  At rather low fluidization velocities, those around
one, 1 to 1-1/2 umf, the particles become defluidized at the zero degree
position and the coefficients are rather low.  As the velocity is
increased, that coefficient would increase due to particle activity
at the zero position, and in some cases it became equal to the tube
averaae coefficient.

     The coefficients along the sides (the 90-desree positions)
are, at the minimum fluidization condition (2-1/2 feet a second),
very high and the "surf line" is located right at that position.
As fluidization velocity was increased, the surf line would move
up along the tube circumference, and the coefficient, then, would
look, as we affectionately call them, like "bunny ears" at that surf
line.  The surf line coefficients could be twice that of the 180
degree coefficients.

     Mr. Howell asks:  "Is there any indication that a different,  grid-
plate-to-tube-bundle distance, other than the 18 inches that you  have
been using, would be more advantageous?"  That's difficult to say,
because we haven't tested anything besides 18 inches.  However, our
test plan includes investigations with varying grid to tube spacing.
Right now we've got the four-inch tube bundle on two-diameter equi-
lateral triangular pitch arrangement at the IP-inch level, with the
50-50 blend of limestone.  We will be dropping the tube bundle to
nine inches above the grid to investigate just the question that's
been asked.  Lowering this distance should reduce the size of the
bubbles that enter into the tube bundle, and that may be helpful.  I
really shouldn't anticipate the results at this time.

     Mr. Howell*s second question is:  "How do the cold model studies
compare to those run by Foster-Wheeler two years ago?  Is  there as
much channeling and stagnant locations in the bed?"

     When we ran the two-inch-diameter bundle, with a duplicate of
at the 3-D Rivesville spacing, we saw that the bed tended  to operate
in what I call an oscillatory type mode.  The fluidization gases
would swish to this side of the unit, and then swish back  to the
other side, so there would be channels of almost pure gas  existing
through the bed.  As we increased the velocities to approximately 12
                                 208

-------
foot per second, the tendency was to evacuate the tube bundle of
particles and stack the particles up in the upper tube.  This appears
to be a very undesirable mode, because all the heat transfer particles
would be sitting on "••to of the tube bundle.  In all cases, the bed
appeared to be very   Mve and there didn't appear to be any stagnant
zones in the bed.

     When we went to our six-inch diameter tubes, this oscillatory
motion or side-to-side n;oMcn didn't exist.  The packing of par-
ticles on top of the tube appears to depend upon the horizontal
tube spacing, particle size and fluidization velocity.

     Are there any other questions?

     CHAIRMAN:  Thank you very much.
                                 209

-------
                         INTRODUCTION

     ALRFRT A.  JOMKF,  CHAIRMAN:  The next speaker is Joseph Mei,  who
received his bachelor  of  science in mechanical engineering from  Chu
Hi College in Hong Kong in  1962, and his MS in engineering science
from West Virginia University  in 1967.  He received his Ph.n.  in
Aerospace Engineering  from  West Virginia University in 1973.  He
joined the Morgantown  Fnergy Research Center in 1975, and was  involved
in the development of  advanced coal gasification processes.  Currently
he is engaged in research and  development in fluidized bed combustion.
Mr. Mei.
                                210

-------
                         Fluidized-Bed Combustion of Lignite and
                                     Lignite Refuse

                               J. S. Mei, U. Grimm. R. L. Rice.
                                     andJ.S. Halow
                                   Department of Energy
ABSTRACT                    Morgantown Energy Research Center

       Lignites comprise about 29  percent of the Nation's solid  fuel  reserves and
constitute a major potential source  for  future' energy needs.  Samples of Texas  lignite
from the Wilccx formation have boon  investigated at  the Morgantown Energy  Research
Center, V.S. Department of Energy, to assess this fuel as a potential feed stock  for
fluidized-bed combuslors.  Combustion tests wen- performed over  a wide  range of
operating conditions to develop  fluidized-bed combustion ( FBC) engineering and  emissions
data on this low-quality fuel.  Desirable combust ion characteristics observed include:
no clinker formation at bod temperature  as high us 2OOO"F. high  sulfur  retention  capa-
bility of the mineral  from lignite at bed temperature below lt>OOฐF. and  freeboard
burning of carryover less than expected.  Results of these tests indicate  that  lignite
may be a particularly  attractive solid fuel  for industrial KliC applications.  One
potential problem with the use of  this fuel  is formation of very line ash  particles
which are difficult to retain in tho bed.  Use of an attrition resistant bed material
was required to maintain bed inventory.

INTRODUCTION

       The Morgantown  Energy Research Center of the U.S. Department of Energy began a
program in Juno 1976 to examine  the application of atcospher i-_""l 1 uidi nod-bed combustion
(AFI1C) technology to low-qua 1 i t y fuels.  The purpose of this program  is  to evaluate the
feasibility oi' burning low-quality fuels in AFBCs.  Conbust ion character ist ics  of
various low-quality fuels such as  anthracite culm, sub-hiluminous coal,  and  lignite coal
have bi.-t.-n examined in  an 18-inch diameter f luidi iv'-b'-d combustor.  This paper  presents
the results of recent  tests of Texas lignite and  lignite refuse.

       I,ignites comprise approximately 29 percent of iln.- Nation's coal reservesi  and
constituto a major potential replacement for oil and natural gas in industrial  applica-
tions for steam raisins: and process  heating.  Lignite reserves,  however, have been
virtually untouched due to their relatively  low-quality.  Ti.-xas. which  is  the largest
lignite producing state-, still generates almost 90 percent of its electricity from
natural gas in spite of the state's  rich lignite deposits.  Identifii.u coal resources in
Texas have been assessed^ to be about one percent  ปf tho Nation's total.   It is esti-
mated that more than half of the Texas coal resources are lignite occurring in  three
formations in the lower Tertiary of  the  Gulf Coastal Plain (Figure I).  Tho wilcox
formation contains approximately 80 percent of the  licnite resources, while smaller
lignite deposits are IOUIHI in the  Yegua  and Jackson  format ions.  Two samples of Texas
lignite from the Wilcox formation  were examined to assess this fuel as a potential feed
stock for fluidized-bed comhustors.  One sample was  from a commercially-mined deposit
termed the "Big Brown" lignite.  The second sample.  "Bon-hole -6". was obtained fron
large boreholes owned  by Dow Chemical a  few miles fron  the "Big  Brown" commercial
operation.  Both of these samples  came from an area  near FairfieJd. Texas,  located in
Freestone County.

EXPERIMENTAL FACILITY  AND PROCEDURE

       The experimeTtal facility at  the  Morgantown Energy Research Center  for fluidized-
bed combustion fuel feasibility studies  is shown schenatica1ly in Figure 2.  It is
basica*"y a ref ractory-1 ined cycl indric.al combustor  having an internal diameter of IS
inchos an the 45-inch  high bed region and a 27-inch high expanded freeboard section of
24 inch diameter.  The combustor contains a set  >f hair-pin-type water cooled bed heat
exchanger tubes located in the bed region and a single pass water cooled heat exchanger
In the expanded freeboard.  Coal is metered  fr<
-------
                                                                              Ill Hut
                                                                       II1C01 IIGNIK

                                                                   ;:SJฅ:3 eillMlMOUS COIl

                                                                           CISON name
                                Figure 1. Coal Resources of Texas


additional carbon burnup.  Flue gas leaving  the combustor  was continuously sampled and
analyzed.  CO and COg aro determined by non-dispersive  infra-red analyzers.  A chemi-
lurainescence analyzer was used to determine  NO ai.d  N'OX.  SO2 and total hydrocarbon
analyses are nude by a flame photometric analyzer  and a flame lonization analyzer,
respectively, and O2 by a paramagnetic analyzer.

       Start-up of the unit is accomplished  by preheating  the lower part of the con-
bustor to 1500ฐF.with premixed natural gas and air.  When  the desired temperature level
( 1500ฐF) is reached, sfpproximately 50 pounds of bed material is added at a slow rate
until it is also up to a temperature of about 1500ฐF.   When  this occurs, fuel feed is
started and continued until the desired bed  level  is attained.   At this point, the
natural gas is shut off and the fire is self-sustaining.

Chemical Analyses of Texas Lignite and Lignite Refuse

       The chemical analyses of Texas lignite and  lignite  refuse on an as-received basis
are given in Table I.  A portion of the Borehole #6 lignite  was subjected to a water
washing, coal cleaning process and separated into  two sizes:  lumps which .sere 1 x J-
                                           212

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                                                                  LIMESTONE f	-\
                                                                  , HOPPER  ;     ''"EL HOPPER
                                                                                  !GH HOPPER
                                                                                 SCREA FEEDtR
                                                       ASH
                                                   LOCK HOPPER
                                  Fip-..-.e2. Fluidized-Bed Combustor
                Table f.  Analyses of As-Received Ligr.ite for Fiuidizcd-Bcd Conbustion

Constituent ,
pet .
Total carbon
Hydrogen
Oxygon
Nitrogen
Sul fur
Moisture
Ash
Heating value,
Btu/lb (as
recc i ved )

Texas
"Big, Brown"
55.21
5.00
1-1.98
0.94
1.03
10.65
12.19
9.170


Ma t •
Borehole *6
•19. 13
•1.66
13.88
1.09
1.30
16.42
13.52
8.237


•rials Used
ป6 Washed
Lumps
51 . 15
5.83
11 .69
0.94
0.88
21.26
8.25
8,920



=6 Washed
-~=-Jฃirn.US5, ^- -*-.
56.09
5.80
11 .53
1 .08
1.00
15.26
9.24
9,375



=C V.'a.shery
	 Ref use _
4 1 . 33
4.14
9.75
0.72
2.34
11.13
30.59
6,805

1
inch, and  a  fines fraction -J  x 0 inch.   The washery refuse had a  size range of 1x0
inch.  All  fuels were crushed  to a -i inch before  injection into the FBC.   The Borehole
#6 washed  fines had the highest heating value, 9400 Btu/lb, while  the? lignite refuse
had the  lowest  heating value of 6800 Btu/lb.  Ash  content ranged from a high of 31
                                             213

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percent in the refuse- to a low of 8 percent  in  the washed lumps.  Moisture  content
varied from approximately 11  percent in the  Big Brown  to 21  percent  in  the  washed
lumps.  Tin- sulfur  content,  as seen from this  table,  ranged from a  low  of 0.88 percent
in the borehole t*G  washed lumps to a high of 2.3'1  percent in the Borehole -6  washery
refuse.

Operating Conditions

       Fluid)xed-bed combustion tests of lignite and lignite refuse  were carried out
over a fairly wide  range of operating conditions.   Those; are given  in Table II bolow.


         TabJ
-------
rates up to 15 percent.  Carbon combustion ef fie iencies also increase with bed  tempera-
tures up to I600ฐF.  Increasing excess air rate beyond 15 percent or raising bed  tem-
perature above 1600ฐF has little effect on carbon combustion efficiency.  The effects
of excess air rate, and bed temperature on carbon combustion efficiency are reflected
in decreases in carryover of paniculate carbon and in the carbon monoxid" concentration
in the flue gas at higher excess air rates and bed temperatures.  Table  III illustrates
these effects at bed temperature of 1-1701' to 1750ฐF and excess air  rates of from  3.7
to 7.0 percent.
          Table III.  Effects of Bed Temperature and Oxygen  in Fine GAS on Carbon Monoxide
                             and Part-iculate Carryover of Unturned Carbon
Run ! Bed Temp. ,
N.ป.-- 1, - .ฐ.r— _.
7/3 | 1600
8/7 i 1GOO
7/2 | 1-170
8/8 j 175O
Sup. Vol. .
ft/sec
3
1
3
•1
Oxvgen in
Flue Gas,
... .J>v-t = ^ . _
7.00
'1.00
4.50
:\ . 70
Carbon in
2nd Cyclone
Ash, pet.
1 .5
8.82
1C. 20
0.32
Carbun in
Bag Filter
Ashj p,-t.
2.7
2.^2
10.81
1 .41
CO in
Flue Gas
	 pot......
O.OG
0.17
0.40
0. 16
Sii'l fur Dioxide.' Emissions

       Sulfur dioxide emissions in the flue- gas are plotted against  the Ca/'S mole  ratio
in Figure -1.  The mineral constituents of these lignites and  lignite refuse materials
contain significant amounts of calcium which is effective  in  sulfur  capture.  The  cal-
cium tc sulfur iu>le ratio was therefore defined as the calcium  in  the fuel pi us  the
calcium content of the fresh stone divided by the sulfur content of  the coal.  The test
data of lignite and lignite refuse over a bed temperature  range  from 1450" to IGOOฐF
were correlated fairly well by a single curve despite variation  in superficial gas
velocities, bed depths, bed materials, sorbents and sulfur contents  in the fuel  feeds.
The results indicate that current EPA sulfur dioxide emission limits can be net  with
relatively  low sorbent addition rates and in some; cases without  sorbent addition.  Cal-
cium oxide  in the lignite ash reduces or eliminates the need  for sorbent -addition.  At
bed temperature above 1GOO'>F, no consistent effect of Ca/S mole  ratio on sulfur  dioxide
(.•missions is evident.   The sullur retention data is plotted as a function of the Ca/S
mole r::tio  in Figure 5.  As seen, a 90 percent sulfur retention  can  often he achieved
at Ca/S mole ratio greater than 1.0 and at operating bed temperatures at or below  1600ฐF.
Again, a single curve was used to correlate the tost data.

       It has been previously reported'' that sulfur is retained  in tho ash material
while burning western lignites.  To confirm the hypothesis that  ash  participated in
sulfur capture;, a portion of the as-received lignite was tested  for  its sulfur capture
capability by ashing the coal in a temperature range which characterix.es the normal
f 1 uidizcd-bcd combustor.  X-ray fluorescence analysis of the  ashes showed that SO;j
content of  the ashes decrease's from 15.45 percent at 1600ฐF ashing temperature to'0.36
percent at  1850"F ashing temperature confirmin. the FDC results  that  the ca'cium in the
ash participates in sulfur capture.  Tin.- resul.s also indicate  that  there rr.ay be a
temperature range where tho lignite can be burned without added  sorbents for sulfur
emission control.

       During the combustion tests with a pure quartz sand bed material, sulfur  dioxide
emissions increased in spite of the addition of sorbent.  Observation of lignite ash by
x-ray diffraction and SKM testing indicate an increase of calcium-aluminum-silicate
parallel to the disappearance of the sulfur in the ash.  These preliminary results
suggest that quart?, sand bed material may affect the sulfur capture  capability of  a
composite bed of lignite mineral, sorbent, and inert material.  These results, however.
are net conclusive.

Nitrogen Oxide Emissions

       Nitrogen oxide emission in the flue gas measured during the combustion tests was
low over the entire range of operating conditions.  Values of NOX concentration  in the
flue gas ranging from 50 ppm to 600 ppm were observed depending on operating conditions
as well as nitrogen content in the fuel.  The fluidized-bcd combustor was operated at a
bed temperature between 1450ฐ to 1750ฐF which is well below the  temperature level  at
                                          215

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4.0



g
2 3.0
CD
^
CM
s

1 2-ฐ
8
5


i , ?
— 1 . C
o
ce I.C
3




0
1




—
—



Ca/S
— THE F
-
e
9
- 8 *

•
- •• • g

a

_• *


9
i

1






•

N
JEL
9
o







v,
X
j
•


11111



• WITHOUT LIMESTONE ADDITION
OWITH LIMESTONE ADDITION
—




O



~

O
	 EPA EMISSION STANDARD 	

-

ฐ ฐ o
^- 	 0 ฐ ฐฐ
0
1 ฐ 1 I 1 1
2 3 4561
                                       Ca/S MOLE RATIO
                       Figure 4. Effect of Ca/S Mole Ratio on Sulfur Dioxide Emissions
                              (Ca derived from ash and limestone- addition)


which oxidation of atmospheric nitrogen occurs-.*'   The only significant -source of
nitrogen oxide was fuund to bo nitric oxide.   In  Figure 6, nitric oxide emissions are
plotted versus oxygen in flue gas.  With SiOo and AloO-^ beds, the nitric oxide level
in the flue gas increases with oxygen.  Thป*  spread of the data suggests that bed
material may affect the nitric oxide emission.  The nitric oxide concentration measure-
ments shown in Table IV indicate  that in the bed  temperature range of 1450ฐ to 1650ฐF,
NO omission is only slightly dependent upon  bed  temperature.  Above 1650ฐF, however,
nitric oxide decreases with increasing bซ.'d temperature.  The reduction in NO concentra-
tion observed at higher temperatures is in contrast to the results obtained by Pope,
Evans and Bobbins5 and Sheffield6 which indicated that the nitric oxide emission
increases with bed temperature.  The most  likely  explanation for the NO results in  this
study is an interaction of  NO and 50%  ln  tne bed.  As mentioned earlier, sulfur reten-
tion capability of the composite  fluidizcd bed decreases as bed temperature  increases
above 1600ฐF.  The nitric oxide concentration,  in turn, likely decreases due  to the
effect of sulfur dioxide concentration  on  the NO reduction reaction.**
                                           216

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                                  C WITH  LIUESTONE  ADDITION
                                  O WITHOUT LIMESTONE ADDITION
                           3         4

                         Co/S HOLE RATIO
        Figure 5. Effect of Ca/S Mole Ratio on Sulfur Retention
             (Ca derived from ash and limestone addition)
Table IV.  Effect of Bed Temperature on Nitric Oxide
Run
No.
T-Z_ฑi =;ฃ_-=
871
P/2
8/9
8/10
8/3
8/5
8/11
8/13
Bed Temp. .
	 QF ^ 	 ^.
1450
1600
1500
1650
1700
1550
1700
1650
O-2 in Flue
GaSj_j)ct.
"""5.50'
5.00
8.50
7.10
3.75
3.00
3.50
3.75
Sup. Vel . .
ft /sec
"-4 -
4
6
6
4
4
4
4.5
X2 in Coal
_pct .
1.01
1.01
1.08
1.08
1.01
1 .01
0.72
0.72
NO in Fluo
	 .Gas^ jJEm _
180
210
125
150
190
210
100
240
                             217

-------
 Q.
 Z
 I-
 00
10
 o
      0.8
      0.7
 S   0.6
 CD
tO
i
iii
UJ
Q
X
O
O
a:
 0.5

 0.4

0.3


0.2


0.1 h
          3N_0]_CORRESPONDING TO
          EPA EMISSION  STANDARD
                         OVD
             1   1   1   1    1
                                I   I   i
^X. BED
BED\MAT'L
TEMP 'FX^
1450
1500
1550
1600
1650
1700
1750
Si02
D
O
O
A
O
9
Q
AI203
a


A


i
AI203
USED
a


&


-------
CONCLUSIONS

       Based on the test data, several conclusions can be drawn from the present
feasibility studies on combustion of Texas lignite and lignite refuse:

       1.  With the recycling of primary cyclone ash,  95 percent or better carbon com-
bustion efficiency is attainable.
       2.  Current EPA sulfur dioxide emission standards can be mot with little and in
some cases no sorbent addition provided that the fluidized-bed combustor operates al
bed temperatures at or below 1600ฐF.
       3.  A 90 percent sulfur retention is attainable with Ca/S mole ratio equal to
or greater than 1.0 at operating bed temperature below or at 1600ฐF.
       4.  Nitrogen oxide concentration in the flue gas is low and is dependent upon
the excess oxygen.
       5.  The high volumetric heat release rates comparable with rates obtained in
burning higher quality coal were found.
       6.  Based on the combustion test data,  the atmospheric fluidtzed-bed combustion
technology offers a promising way to utilize Texas lignite and lignite  refuse.

ACKNOWLEDGEMENT

       The authors wish to thank Dow Chemical, Texas Division, for providing the lignite
samples.

REFERENCES

1.  Hammond.  A. L. , Hetz, W. D. ,  and Maugh II, T. 11.,  Energy and the Future. American
    Association for the Advancement of Science, 1973.-
2.  Evan, T.  J. and Kaiser. W. R. .  "Texas," 1976 Keystone Coal Industry Manual, p.  638.
3.  Levone, II. D. . and Hand, J. W. ,  "Sulfur Stays in the Ash When Lignite Burns," Coal
    Mining and Processing. February 1975,  pp.  46-48.
4.  Westinghouse Research Laboratories, "Evaluation of the Fluid)zed-bed Combustion
    Process Summary Report-Envi ronmontal Protection Agency," Archer, D. II., et  al,
    Pittsburgh, PA. November 1971.
5.  Ehrlich.  S..  "A Coal Fired Fluidized-Bed Boiler,"  Institute of Fuel Symposium
    Series No. 1:   Fluidised Combustion, Internaliona'l Conference, London,  UK,
    September 1975, pp. C4-1-C4-10.
6.  Gibbs, B. M.,  et al, "Coal Combustion and NO Formation in an Experimental Fluidizcd-
    Bed," Institute of Fuel Symposium Series No.  1:   Fluidised Combustion,  International
    Conference, London, UK, September 1975, pp. D6-1-D6-13.
7.  Burke. D. P.,  "FBC May be a Better Way to Burn Coal," Chemical Week, September 22,
    1976.
                                          219

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          QUESTIONS/RESPONSES/COMMENTS

     WAYNE A. McCURDY:   1 believe that Mr. Mei has a question or so.

     MR.  MEI:  I  have quite a few questions here as a matter of fact.
The first ons is  from Dr. Porter from Energy Resources Company.
"What precaution  do you  take in fuel (lignite) storage and handling
to prevent auto-ignition?"

     Some lignite material I have observed will burn spontaneously if
left in a pile for as short a period as two hours.  The lignite we
received  from Low Chemical is in drums.  We have a cold storage
plant, which is maintained at a certain temperature.  The lignite was
stored in the storage plant.  We did not observe any auto-ignition.

     The  second question is from Mr. Shelton Ehrlich, EPRI.  The
question  has three parts; the first one is, "What is lignite refuse
and give  analysis."  The lignite washe'ry refuse is the residue after
the coal  cleaning process, i.e., the residue coming from the washing
process.   Actually most  of it is ash.  I believe I did show the
chemical  analysis of lignite washery refuse.   It is about 40 percent
of carbon and approximately 31 percent ash.

     The second part is, "Your data did not seem to show 90 percent
of sulfur retention at  a calcium to sulfur mole ratio equal to one.
Could you review  this?"   I recall in rny slides that it did show
a calcium to sulfur mole ratio equal to one or greater than one.  We
have several runs which  show a 90 or better sulfur retention.

     The last part of the question  is, the NOX data show a very
high variation with a coal ash bed.  "What result was found with
limestone?"  Hell, as you recall on the NOX emission plot versus the
excess oxygen, in the flue gas, there is one data point which is the
last test for the lignite refuse using ash as bed material.  We found
that the NOX emission is rather high.  That's why I mentioned in my
talk that the scatter of the data suggests that the bed material may
effect the NOX emission. And the reason for that is not quite
clear at the present.  During the lignite and  lignite refuse tests we
did not use limestone as bed material.

     I have a question  from R.G. Seth, Gilbert Associates, "What kind
of particle size  is used in the 18-inch combustor, and what is total
pressure drop across the bed?"  The size of the coal particle is
quarter inch by zero.  The total pressure drop across the bed is
somewhere around  30 to  35 inches of water.

     Another question,  frcn C. C. Gentry, Phillips Petroleum Company.
"Was the immersed tube  plain or finned?"  We use just a plain tube.

                                220

-------
     "What were the tube dimensions and material  types?"  The diameter
for the bed heat exchange tube is 1/2 inch,  schedule 160,  type 316
stainless steel.  And for the freeboard heat exchanger,  the tube
diameter is 3/4 inch.

     "What was tube layout spacing?"  Well,  the tubes were arranged
in a triangular pitch.  The horizontal  distance between  tube centers
is 3 inches, and the vertical distance between tube centers is 2
inches.

     "What range of heat transfer coefficient was produced in the
immersed tube?  Has a dimensionless correlation been developed?  If
so, please indicate from your correlation."

     Well, during the lignite run, we did not use the bed  heat
exchange tube in order to maintain the bed at certain temperature
levels.  But we did use the freeboard heat exchange tube.   The
average overall heat transfer coefficient for the freeboard heat
exchange tube is somewhere around 10 Btu per hour per square foot per
degree F.  So, we did not have any correlation for the heat transfer
coefficients.

     "When will an ERDA (DOE now as of October 1, 1977)  report be
issued, title arid report number?"  Well, we have not finished the
entire report, but v/e expect to finish it by the end of  January.  At
the present time, we do not know the number of the report.

     The last question is from Mr. M. H. Schwartz, Shell Development
Company.  "The extremely high moisture and ash content which charac-
terize coals of the Yequa and Jackson formations suggest thdt fluid
bed combustor may be an appropriate utilization technology.  Do you
plan to test such coals?"  At the present time, we do not  have
such plans to test other types of lignites.   He also asks, "Since
the fusion temperatures and softening points for these lignites are
extremely low, did you observe any significant fouling,  refractory
attack, or slagging when you ran your combustor at extremely elevated
temperatures near 2000ฐF?"

     MR. ME I:  We ran the combustor at a bed temperature of 2000ฐF
for only several hours.  For the rest of the tests, bed  temperature
was ranged from 1450ฐF to 1700ฐF.  Are there any more questions?
Thank you.
                                 221

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                       INTRODUCTION

     OFORC.F HFTH, CHAIRMAN:   Our  next presentation will he by
Mr. Heman Mack with the Rattelle Coltnbus Lahoratories.  He received
his deqree in chenical engineering from Cooper Union, and is currently
the  program nanager of fluidized bed technology at Battelle.  So,
Heman?
                                222

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                                Battelle's Multisolid Fluidized-Bed
                                        Combustion Process

                                         H. Nack. K.T.Liu, and
                                             G. W. Felton

                                    Battelle Columbus Laboratories
ABSTRACT

       A novel fluidlzed-bed combustion  process has been developed and called Xultisolid Huidized-Bed
Combustion (MS-1 EC).   Studies in a  6-inch-diaceter cocbustor have demonstrated feasibility of operation
at superficial gas velocities exceeding  30  feet per second with good linestone utilization and con-
bust ion efficiency.  Scale-up studies on a  400 pounds of coal  per hour cc^bustor/boiler are in progress.
Successful results will lead to a demonstration steam-generator plant of 25,000 pound per hour capacity.
A description of the  concept and results of studies in the 6-inch-diaceter bench-scale unit are pre-
sented in this paper.


BACKCKOIAU

       About 4 years  ago,  Battelle  initiated a program aimed at advancing the state of the art of
fluidlzcd-bed combustion.   A technique was  conceived and developed that is called the Multisolid
Fluldized-bed Combustion (.VS-FBC) process.  The initial experimental development was done in a 6-incli-
diancter conbustor.  Presently, we  are studying the process in a rectangular 2-square-foot cross section
subscale experimental combustor/boiler under a L.S. DOE Industrial Applications Demonstration Program.
This program is aiL-_-d toward construction and operation of a 25,000 Ib/hr steam plant at Battelle which
will be our lead boiler.

       In this paper, we describe the Multisolid  Fluldized-Bed Ccr.bustlun process and present some
results of our work in the 6-inch unit.   Shakedown of the subscale unit has been completed and vc are
into the test program.  However, definitive results are not yet available.


DESCKIH-IO.N OF Hit KS-FBC  PROCESS

       Multisolid Fluidized-Bed Combustion  cay be viewed as a  process in vhlch an entrained fluidizcd
bed is superimposed on a conventional dense fluldized-bed combustion process.  The dense flu'dizcd-bcd
process (Figure 1), as related to the MS-FBC, has the following characteristics:

       •  Air is used for  bed fluidizatlon  and coal combustion; the air velocity is high —
          30 to 40 ft/sec.

       •  The bed consists of high-specific-gravity material.

       •  Crushed coal is  the fuel.

       •  Finely ground limestone is fed into the bed to capture the sulfur.

       •  Sulfated limestone and ash are blown out of the dense bed and are collected downstream.

       The entrained  fluidlzed bed  (Figure  2) consists of inert material that:

       •  Is sculler  in size than the dense flul^lzed-bed material

       •  Is separated from the exhaust  gases and recycled to  the dense bed (in the combustor).

       Combining these two fluldized beds yields  BatteUc's Multisolid Fluidlzed Bed, shown In Fig-
ure 3.

       During operation, the MS-FBC has  two distinct zones in  the cocbustor column.  The bottom zone
is the dense bed region, where the  heavy bed material is fluldized and retained.  Immediately above the
dense bed region is an entrained bed zone,  Consisting of relatively fine particles cf the same or
another bed material.  The entrained bed material, which is fed into the dense bed region in the cor.-
bustor, is carried upward  by the air stream in the burner column an*i into a gas-solid separator; froo
there, the material is recycled into the coabustor.
                                                 223

-------
tCUANIU
IlUt CAS
                                       ASH AND
                                       SUIFATED
                                       LIMfSTONE
DISTRIBUTOR
PLATE
                                                          DENSE
                                                          BED
                                                          MATERIAL
                                                          CRUSHED
                                                          COAl
                                                           HNHV
                                                          GROUND
                                                           HMtSIONE
                        Figure 1. Dens* Fluidited Bad
                                 224

-------
ACUANIO
'nut CAS
                                                       STEAM
                                                       WAIt*
                                                   BURNtR
DISTRIBUTOR
PIAII
                                                         CrUSHID
                                                         COAl
                                                       r- IINHY
                                                          GROUND
                                                          IIMISIONE
                                                     AIR
                     Figur* 2. Entrained Fluidized Bed
                                225

-------
                                         ป SHAM
             DISTRIBUTOR
             PLATE
Figure 3. Battelle Multisolid Fluidized Bed
                 226

-------
       Crushed coal and finely ground limestone are also fed into the dense bed region where the con-
bust ion of coal and reaction between the linestone and liberated sulfur dioxide occur, both at the
same tine.  Like the entrained bed particles, the coal ash and sulfated limestone particles are blown
upward into the separator.  Because the ash and sulfated limestone particles are lighter and smaller
th&R the entrained bed material, nose of these particles remain in the flue-gas stream and are col-
lected in one or more high-efficiency cyclone separators.  The flue gas emitted to the air is environ-
mentally acceptable.  Tne dry ash plus sulfur-bearing limestone mixture is disposed of o- used for
some non-process purpose.

       A few operating features of the MS-FBC should be emphasized:

       •  The combustor contains entrained bed material as well as dense fluidlzed-bed material,
          coal, and limestone.

       •  The dense fluidlzed-bed material serves to trap or slow down the escape of other mate-
          rials that are blown out of the dense bed at the high (30 to 40 ft/sec) air velocities
          of operation.

       •  The heat released in the burner is transferred to the entrained fluidized-bed material
          and iaises its temperature to 1600 to 1750 V.

       •  The entrained bed material acts as a heat carrier, giving up it? heat to the stean
          tubes located outside of the dense bed.

       •  The entrained bed material is separated from the exhaust stream and returned, at a
          controlled rate, to the conbustor.

       One method of providing for the use of the heat produced in the burner is to immerse the boiler
tubes in the entrained fluidized-bed region (just above the dense fluidized bed) ar illustrated in
Figure 3.  This process is called the "Multisolid Fluidized Bed With integral Boiler".

       Here, as the hot entrained bed material and exhaust gases move upward iron the dense bed, they
transfer heat to the boiler tubes, thus converting the incoming water to steam.  At the same time, the
entrained bed material and exhaust gases cool to about 650 F -- the stack gas temperature for some
industrial butlers.

       An important variation of this process involves the use of an external boiler, as Illustrated
in Figure <••  The process, called the "Multisolid Fluidized Bed With External Boiler", has the follow-
ing characteristics:

       •  The steam tubes are Immersed in a separate fluidized bed within the external boiler,
          not in the conbustor column.

       •  The hot entrained fluidized-bed material (at 1600 to 1750 F) is separated from the
          exhaust gases and drops into the external boiler.

       •  The external boiler is, a conventional fluidized bed operated at low velocities of 1 to
          2 ft/sec (compared to 30 to 40 ft/sec in the conbustor).  Little or no conbustion occurs
          in the external boiler.  Erosion/corrosion of the boiler tubes is minimized under these
          working conditions.

       •  The external boiler Is operated to maximize the heat transfer coefficients, thus
          minimizing the tube requirements and size of boiler.

       •  The hot gases leaving the separator (and the external boiler) are cleaned via the ash
          and sulfated limestone collector, and move to a separate convective heat exchanger
          or economizer where the gas temperature is reduced to a reasonable stack temperature.
          About one-third of the steam is produced in the economizer, and the remainder in the
          external boiler.


OPERATIONAL AM) PERFORMANCE CHARACTERISTICS

       Technical feasibility of the MS-FBC has been successfully demonstrated in a bench-scale 6-inch-
diaoeter x 20-foot-high combustion unit at Battelle.  Crushed coal of less than 1/4-lnch size and
limestone of less than 100-mlcron size were used.  The combustor temperature was maintained at 1600 to
1750 F under atmospheric pressure.


                                                  227

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HUE CAS TO
KONOMIZH
            SHAM
            WAHI

 DISTRIBUTOR PLAIE

              AIR
30TOซ
RET/SEC
              Figure 4. Btttelle Multisolid Fhritizad Bซd
                          External Boiler
                               228

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       Three types of high-sulfur coal — coal  fron Ohio,  from Illinois,  and from Pennsylvania -- were
tested.  The process operated similarly with all.   The  limestones evaluated to date were obtained from
Flqua, Ohio, and Grove, Virginia.

       Specullte, a brand of hematite (iron ore}, was used as the high-specific-gravity material in the
dense fluidized bed.  Speculite is relatively inexpensive. Is chemically  stable in this application,
and demonstrates a low attrition rate.

       Fine Speculite, 1icestone, and a rounded sand vere  tried as the entrained fluidized-bed mate-
rial.  Sand is currently used because it  is low in  cost and attrition rate, and shows satisfactory
or superior performance in other respects.

       As described earlier. In the MS-FBC with either  integral boiler or external boiler, the
entrained fluidized-bed material serves as a heat carrier  that absorbs combustion heat in the dense
fluldlzed-bed region (the burner) and transfers the heat to heat-exchange surfaces located outside
the dense bed region.  In the feasibility assessment of the XS-FBC, the 6-lnch bench-scale unit was
run to simulate operations of the process with an integral boiler.  Demonstrated characteristics .ire
discussed below.  A comparison of operating characteristics of conventional FBC and MS-FBC is shoun
in Table 1.  A dlagrao of the 6-inch unit Is given  in Figure 5.

Superficial Air Velocities

       The MS-FBC has been operated at superficial  air  velocities up to 35 ft/sec.  This is between
3 and 4 times the velocities used in conventional FBC boilers (8 to 10 ft/sec).  There have been no
indications that 35 ft/sec is an upper licit for the process.  It should  be mentioned that the system
throughput is directly proportional to the air velocity; thus, increased  velocity Implies a more
compact boiler design.  The MS-FBC boiler would have a  cor.bust ion rate of 200 or more Ib of coal
per hr per ft? of bed area.

Sulfur Sorbent Requirement

       EPA sulfur oxide enlsslon standards (1.2 Ib  S02  per nil lion Btu) have been met consistently
with a limestone requirement equivalent to l.S to 2.2 while burning 4 percent sulfur coal.  Figure 6
shows the effect of limestone size on sulfur capture.   The effect of bed  temperature is shown in
Figures 7 and 8.

       It should be emphasized that MS-FBC can eiploy almost any :ypc of  limestone or dolomite regard-
less nf its physical characteristics (pore size, attrition resistance, etc.) because the process uses
finely ground sorbents.  In conventional  FBC, the particle size of sorbent is generally an order of
magnitude larger than that for MS-FBC; therefore, suitable selection of a sorbent for the conventional
process can become restrictive.

Combustion Efficiency

       Up to 96 percent coal combustion efficiency  has  been obtained in the 6-in. experimental
HS-FBC unit.

Erosion/Corrosion of Steat. Tubes

       Erosion/corrosion of vertical steaa tubes has been  ceasured in a SO-hr test run.  In the en-
trained fluidized bed, metal wastage rates of vertical  specimens was 0.0054 mil/hr for carbon steel
(A109) at 485 F, 0.00018 mll/hr for 9 percent chromium  steel (P9) at 525  F. and 0.00019 mil/hr for
Type 347 stainless steel at 570 F.  These cetal wastage rates do not appear to be excessive.   The
maximum allowable rate is about 0.0015 mil/hr.

       In the dense fluldlzed-bed. erosion/corrosion rates were approximately an order of magnitude
higher.  However, heat-exchanger tubes are not subjected to the dense bed in the KS-FBC process.

Part Load Operation

       The fluidizatlon characteristics of the dense fluidized bed of high-specific-gravity material
are such that fluidlzation can be maintained over a wide range of superficial air velocities  and,
hence, combustion rates.  Because the dense-bed temperature is controlled by the reclrculatlon of
entrained bed material rather than by Icsersed heat-exchanger tubes, the  range of loads is not
restricted by the decreasing bed temperature, as is the case in conventional FBC.
                                                  229

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Table I.  Comparison of Operating Characteristics of Conventional FBC and KS-FBC
                                               FBC
                                                                       MS-FBC
Superficial Gas Velocity

Densu Bed Material
  Type

  Typical Size
  Particle Density

Entrained Bed Material
  Type
  Typical Size
  Particle Density

Sulfur Sorbent
  Type

  Typical Size

Method of Heat Recovery
  Steam Tubes In Dense Bed
  Steam Tubes in Free Boar-1
  Steam Tubes in Entrained ^ed

Method of Controlling Dense Bed
  Temperature
12 ft/sec, max
Limestone or
  Dolomite
8 x 30 mesh
2.6 g/cc
Not used
Limestone or
  Dolomite
8 x 30
    Yes
    Yes
By Immersed
  nteam tubes
30-40 ft/sec
Iron ore, etc.

6 x 12 mesh
5.2 g/cc
                         Sand
                         20-100 oesh
                         2.6 g/cc
Limestone or
  Dolomite
Minus 325 mesh
    Ho

    Yes

By adjusting
  recirculation
  rate of en-
  trained bed
  solid
                                       230

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To 4th
cyclone
ond stock
                                                                          Deflector plote
                                                                             Flue gos
                                                                             sompling
                                                                             port
                                                                               Combustor
                                                                                        l ond
                                                                                    limestone
                                                    Distributor
                                                    (dote
                                                                           t=— A,r
                            Figure 5. Schematic of 6-lnch-Diar 
-------
100
 90
80
c 7ฐ
QJ
U


I 60
ง
'•ฃ  50

o>
 30




 20




 10
         .Federal S02 Emission
         Standard
       -325 mesh
                                 -200 mesh
                      Coal: Illinois No. 6

                      Limestone:  Piqua Limestone
          O.5     1.0      1.5     2.O

                 Ca/S Molar Ratio


         Figure 6. Effect of Limestone on Sulfur Retention
                                            2.5
                      232

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o>
   IOO


   90



   80


   70
tt>
Q. 60
o
'•   50
I 4ฐ
 30



   20


    10


    O
          1550-1700 F         1850 F
                1760 F  '800 F
Federal
Emission
Standard <<
              Coal:  Illinois No. 6
              Limestone:  Pi qua Limestone  _
                         (-325 mesh)
              Data Taken  From Run 1013
                1234

                      Ca/S Molar Ratio

          Figure 7. Effect of Combustion Temperature on Sulfur Retention
                          233

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o
I4
h.
o
o
 o>
 E
 o>
fa
O)
o
o>
                    Coal: Illinois No. 6
                    Limestone: Piqua  Limestone
                               (-325 mesh)
I40O  I5OO    I60O   1700   1300    1900
       Combustor Bed Temperature,  F
              Figure 8. Effect o i Combustion Temperatw* on
                    Limestone Requirement
                                               2000
                         234

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       The 6-in. experimental unit has been operated at loads ranging from the nominal 100 percent
(corresponding to a superficial velocity of 32 ft/sec) to about 20 percent,  l-o difficulty .as en-
countered at any of the loads.

Shut-Down and Standby

       The absence of heat-exchanger tubes in the dense fluidized bed of MS-FEC permits the process to
be shut down rapidly by simply stopping the flow of air, coal, and limestone.  Ko deliberate cooling
of the bed material is required.  Further, the bed material can be retained at high temperatures for
considerable periojs, permitting rapid restarts following an ext< iced shut-down.


IMPLICATIONS AND ADVANTAGES OF THE PROCESS

       The MS-FBC process has many implications and advantages.  These are presented below as cate-
gorized in four areas of interest:

       1.  Environmental

              •  Effective SOj emission control, even when more stringent emission standards
                 are imposed
              •  Low KOX emissions, due to low c-abustion temperature

              •  Small amount of dry-solid wastes to be disposed of, due to low sulfur-sorbent
                 requl i i-'Cfcnt

       2.  Operational

              •  Excellent turn-down capability

              •  Fast load-following
              •  Immediate restart and shut-down

              •  Adaptability to a variety of fuels
              •  Ability -.o use any type of limestone sorbent

       3.  Engineering/Developmental
              •  I ewer ,cale-up problecs, so faster rate of development to a coccerciol
                 scale plant is likely

              •  Natural circulation of water, because heat-exchanger tubes are vertical

              •  Applicability to retrofitting existing boilers
              •  Greatly reduced or virtually eliainated corrosion/erosion of steam tubes,
                 because steam is generated in a low-velocity 1luidized-bed external boiler

       It,  Economic

              •  Low capital cost, because the boiler (a) is compact with a high throughput.
                 (b) can be shop fabricated and rail shipped — even in the case of talrly
                 high capacity boilers, and (c) requires a smaller Investment in solid-waste
                 handling and disposal facilities or activities
              •  Low operating cost, due to low capital cost, low requirement for sulfur
                 sorbent, and small amount of solid waste.

       Large-capacity packaged boilers (of the order of 150,000 Ib of steam per hr) are expected to be
feasible for the H',-rEC process.  These will provide reduced boiler cost, increased reliability of
construction, and enhanced ease of installation.


TIMETABLE OF CURRENT DOE MS-FBC PROJECT

       The Kultlsolid Fluidized-Bed Combustion process was developed under the Battelle Energy Program,
which invested some $600,000 In the development over a three-year period.  The feasibility of this
concept has been successfully demonstrated in a 6-in.-diameter (0.22-ft2 bed area) coal-co-bustIon
unit.  The L.S. DUE contract with Battslie calls for a two-phasr scaling-up of this process over
six years (Including .'hree years of ope)ating the demonstration plant).  The Sub-Scale Experimental
Unit System (SSELS), vl.iro represents a 10-fold scaleup of the 6-in. bench-scale unit, is now in


                                                  235

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operation.  This pilot-scale unit Is designed to produce about 6,000 Ib of stean per hr  from 400 Ib of
coal per hr.  The coehustor/boller Is sketched In Figure 9.  The full-scale deaonstratios plant, which
will be built adjacent to BattelIt's present steam plant, will represent a further scale-up of about
t> ti-es; it will produce 25.000 Ib o! steao per hr irom 2,500 Ib of coal per hr.  Data obtained Iron
this deoonstration unit will be used to design and build coccercial boilers.

                                        STEAM
                                        4000LB/HR
                        STEAM DRUM
                                                        IS STEAM
                                                        TUBES, r IMA.
                                                                   HUE CAS
                                                                   TO CLEAN UT
                                                                   CYCLONES AND
                                                                   STACK
                                                                           SAND RECYCLE
                                                                         SOLIDS
                                                                         DISENCAGEMlNf
                                                                         ZONE
                  COAl AMD
                  UMESIONE fill)
                                                                 RECYCLED ENTRAINED
                                                                 MATERIAL
                                                                       RECYCLED ASM.
                                                                       SORCENT.ASAND

                                                                     MAIN
                                                                     UUIOIZING AIR
                              DENSE BED ZONE
                            Figure 9. Battelto Sub-Scale Experimental Unit Fhjidued-Bed
                                             Stsam GMM/ator
                                                   236

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            QUESTIONS/RESPONSES/COMMENTS

     MR. N'ACK:  Fron J.  S.  Cordon,  TRH Energy Systems:  "Some infor-
ration on pressure drops in your  system?"  Typically  in the 6-inch
unit, we neasure a pressure drop  of about  35 inches of water across
the dense bed.  He note  very little pressure drop, possibly as nuch
as 2 inches of water, due to drop in the entrained zone.

     Fugene 5-nyk, Arqonne National  Laboratory, asks three questions:
1.  "Pcesn't your use of the entrained bed as the heat transfer
neditm result in ni/ch lower heat  transfer  coefficients, thereby
partially nullifying one of the biggest advantages of FBC?"  The
transfer coefficients in our system in the entrained zone have been
measured at about in to  20 Rtu per  hour per square foot per degree
Fahrenheit, against about 40 to 50  in conventional systems, and so
it is lower. However, in the integral boiler node, we are using the
freeboard space, essentially, and the spacing of the tubes is not
critical; that is, they  can he relatively close together, so that
on a volume basis, we feel  that the heat transfer space required is
aboi:t the same.

     2.  "Poes the limestone recycle7 'f  not, how do you keep it in
the bed lorn; enouoh for  nood sulfur retention?"   Since K^ use a very
finely divided limestone, tiv mechanism of reaction  is diffusion
limited, rather than reacti  -limited; so  reaction time has very
little effect.

     3.  "Poos unburned  carbon recycle?  If not, how do you keep the
coal in the bed long enough for good  combustion efficiency?"  Yes;
we do collect and reinject  carbon in  t-.oth  the 6-inch unit and our
pilot plant unit, and we feel that  this increases combustion effi-
ciency by about 6 percent.

     A question asked by farl Oliver  of SRI.  "Have you measured
attrition of the iron ore?   How fast  is it?"  The attrition rate of
the iron ore is about .on?  pounds of  ore per pound of coal.   As  I
mentioned, this corresponds to probably less than 2 cents per* million
Ptu's.

     Pick Heldhart, University of Bradford, U.K.  1.   "How much
attrition of the sand occurs, and does the attrition occur princi-
pally in the cyclone or  in  the bed?"  Sand attrition rate is about
.02 pounds per pound of  coal.  Vie don't know where it occurs.   We
think it occurs in the dense bed, primarily, although certainly
there is some attrition  in  the cyclone; 2.   "Hhat are the bed  den-
sities in the iron ore section and  in the dilute phase?"  The bed
density in the iron ore  section is  about 50 pounds per cubic foot.
We do not know what the  bed density in the dilute phase is.   We  have
no good way of measuring that at  this time.
                                237

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     A. l/omser, Homser Engineering:  "Hhat combustion efficiencies
and NOX enissions have you observed?"  Our conhustion efficiencies
in the fi-inch unit have been in the range of 87 to 9fi percent.   Using
Illinois No. 6 coal, i/e have observed f!0x emission concentrations of
300 to 400. ppn.

     Fron Henry Kwon, Porr-Oliver:  "Fron the process point of view,
high gas velocity seens to offer a possible alternative, but what
about mechanical aspects?  Pue to high gas velocity, the unit nay be
relatively very tall, which would cause a lot of mechanical  problems
in construction of a commercial size."

     As I mentioned, the tubes can be closely spaced, so that the
height of the unit will not be considered to he excessive.   Our pilot
plant unit combustor is 21 foet high, which is not unusual  for a
large comhustor.  'cale-up would be primarily by length and width,
rather than height, and so consequently, we don't see this  as becom-
ing the najor problem.

     From Ken Chipley, Union Carbide-Oak Ridge National Laboratory:
"Ho you have any idea as to the heat transfer coefficient on the
vertical tubes?"  I mentioned that it is about 10 to 20 Rtu/hr per
square foot per degree Fahrenheit.  It is a function of the recycle
rate, and varies to some extent with that rate, going up as the
recycle rate goes up.

     Another question from Ken Chipley:  "What is the wall  construc-
tion of the pilot plant unit?"  The pilot plant unit is constructed
of stainless steel, hot wall construction.  It was designed so that
it could be rapidly started up and operated easily and changes made
easily.

     From Masayuki Horio, fJagoya University:  "Hhat do you  expect or
have you experienced with deposit of fine limestone sticking on the
wall duct, which was seen in the dry limestone stack gas desulfuri-
zation?"  My answer is, as 1 mentioned, to date we have had over 300
hours of operation on the pilot plant unit, and we don't see any
problem in terms of the ducts clogging up with dry limestone.  We
don't anticipate any in view of the high velocities and the presence
of other materials in the flue gases that will scour the limestone.

     From A. Saha, Burns and Roe Industrial Services:  "!t  seems
that you need a high calcium-sulfur mole ratio for meeting  EPA
limits, as in simole fluidized bed combustion systems.  So, are
you substituting a smaller but more complex system for a bigger and
simpler fluidized bed combustion system?"  I think we have  demon-
strated, for the most part, that our calcium-sulfur ratios  are con-
siderably lower than in the conventional system; aliout 2 to 2.5

                                 238

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seens like a fairly good number that we have routinely experienced.
In addition, we can use almost any type of limestone.  The fact  that
it night attrite is a benefit in our system so that it gives us  a
lot nore flexibility in terms of the source of limestone.

     Secondly, Mr. Saha asks:  "Hhat percent of carbon loss are  you
having?"  I mentioned that we have experienced combustion  efficien-
cies between 87 and ifi percent.  These are not optimized values, by
any neans, as they were obtained in a small unit.  He hope that
possibly we can exceed that as we continue in our test program on
our pilot plant.

     CHAIRMAN:  Thank you very much, Mr. Mack.
                                 239

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                         INTRODUCTION
     ROBERT BROOKS,  CHAIRMAN:  Our r.ext paper is a report of work at
Battelle on a pneumatic  solids injector and startup burner for their
muHisolid fluidized bed combustion process.  The paper, by G. W.
Felton and R. D.  Giamma., will be presented in parts by both G.W.
Felton and R. D.  Giammar.  Mr. Giammar received his MS degree in
Mechanical Engineering and  has been a research scientist at Battelle
since 1967.  His  fields  of  interest include heat transfer, fluid flow,
and thermodynamics,  and  he  has worked on the firing of pulverized and
stoker coal as well  as conventional fuels.
                                 240

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                         Pneumatic Solids Injector and Start-Up
                            Burner for Battelle's Multisolid
                     Fluidized-Bed Combustion (MS-FBC) Process

                          G. W. Felton. R. O. Giammar, H. R. Hazard.
                                      D. R. Taylor
                              Battelle Columbus Laboratories
                                    Columbus, Ohio
ABSTRACT

       Two important and innovative  components have contributed to the successful
operation of Battelle's Multisolid Fluidized-Bed Combustion Process:  a pneumatic
solids injector ar I a start-up burner.  This paper, appropriately in two parts,
describes each equipment's development,  dcsiqn, and test.

       In Part I, we describe how Battello has developed and successfully combustor-
tested a novel pneumatic injector for feeding solids ir.to the bottom of a fluidized-
bed against back pressures of up to  four  PSI.  The injector was sized to feed 600
pounds por hour of 1/8 x 0 material  using 1/2 oound ot  air per pound of solids fed.
In the process downstream air from the iniector is bypassed back throuqh a control
valve into the injector solids entrance stream to reduce the solids inlet vacuum to
any desired low level.

       Part II describes how Battello selected the qas turbine can-type burner because
it operates stably over a wide range of firing rates (50 to 1). air/fuel ratios  (100
to 1) and pressures (up to 15 atm).   Due  to its high heat-release rate, (8.5 x 106
Btu/hr-ft^ atm), it is extremely compact  and provides uniform nas-outlot temperatures.


PART I.  A PNEUMATIC SOLIDS INJECTOR FOR  BATTELLF'S MULTISOLID FLUIDIZF.D-BF.D
         COMBUSTION PROCF.SS

Introduction

       The injection of solids into  rrorc-traditional fluidizcd beds has already boon
successfully accomplished by a variety of techniques, but the problem of solids injec-
tion becomes more difficult for flattelle's  Multisolid Flujdizcd-Bed Combustor (MS-FBC)
when crushed coal d/8" x 0)  is fed  along with -325 mesh limestone.  The necessity to
keep dry the powdered limestone is evident.  However, coal with a high surface moisture
will cloq feed mechanisms and injectors for cbvious reasons.

       A quick review of somo of the technioues used to feed solids into a fluidizcd
bed include:

       •  Angled needle tubes (used  at Rivcsville)
       •  Coal slirjger feeder used for stoker boilers being evaluated for top
          feeding of laroe coal fractions (used by Foster-Wheeler)
       •  Pneumatic injection systems of  various types.

       Potential problem areas for coal-feed mechanisms include:

       •  Coal is allowed to heat up to the plastic state where agglomeration will
          plug tubes if coal  is not  sufficiently cooled
       •  Excessive fluidized-bed velocity  that will entrain fine coal if it is top
          fed
       •  Mechanical feeders that have a  lower reliability factor where more moving
          parts and several coal streims  exist, especially when feeding coal with
          greater than 31 moisture
       •  The type of feed system can be  solids size dependent.  For example, some
          injectors may require finer crushed coal than a slinaer type of system
          which will not work well for fine coal
       •  Mechanical solids feed system reliability weighed against initial and
          operating costs for a pneumatic injector system
       •  Air requirements for injector systems evaluated with attention to potential
          scale-up problems including amount of air used for injection of solids.



                                         241

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       A  ypical coal injection system will use 1/2 pound of air per r^ound of solids
fed.  Horizontal velocities roust be hich enouqh tc prevent saltinq out of solids.  To
accomplish this, a velocity of 80 feet per second is generally in a safe region to
prevent solids dropout.

       Battclle's MS-FBC requires greater than 600 pounds per hour of solids per
injector.  Coal is dryed to 9'' moisture crushed and screened to 1/8" x 0 at Battelle's
West Joffcrson coal preparation plant for use with iniectors.  We were aware that nany
mechanical problems were encountered in soli-1-feed systems with rotary valves and
conveyors.  To us, a more simplified pneumatic solid-feed system seemed desirable for
tho MS-FEC, especially with the use of -325 mesh limestone along with 1/8' x 0 coal.
We believed that properly designed injectors prevented coal frcr. becoming heated to
the plastic region due to a rapid discharge into the combustor.

       To begin with, Battelle wanted a solids injector that met the following
specifications:

       •  Work against a four pound per squara inch back pressure of the fluidized bcrf
       •  Introduce no additional air that was not measured along with solids being
          fed
       •  Life time of one year between inspections
       •  Solids throughput of 1/2 pound of air per pound of solids with outlet
          velocity of 80 foot per second
       •  Feed 1/8" x 0 coal and -325 mesh limestone.

       To meet these specifications, we tested several commercially-available
injectors at Battclle's West Jefferson site, using feeders for a conventional 24-inch
diameter FBC and feeding 260 pounds per hour of crus/-fx} coal with 70 pounds per hour
of limestone (;-cc Figure 1).  This testing resulted in nozzle failures after approxi-
mately SO hours of operating time because of erosion of the inside of the nozzle where
feed jir exited and because of erosion of the nozzle bore by discharging solids  (see
Figure 2) .

       Since most nozzles are designed to evacua;-o a vessel with steam or air flow
through the nozzle, we know very little about material flow rotes versus particle size.
We tested several Penberthy nozzles  (designed for steasi operation) for solid flow
rates but were not able to meet Battelle's specifications.  We modified these nozzles
by enlarging the body bore and trimming .060 off the nozzle inlet, and this proved to
be a very satisfactory solution as tested in a bench-scale test rig.

Testing

       We used a small test set-up to investigate soli;s flow through nozzles into a
tank against varying back pressures.  (See Figures 3 and 4).  This apparatus consists
of a rotometcr to measure external bleed air to the iniectors.  This design proved
unsatisfactory because so much air was required {over 600 SCFH) to control the inlet
vacuum to a desired level.  We then developed another arrangement where downstream air
from the nozzle was bled back through a control valve to reduce the vacuum at the
solids inlet to any desired low value.  In this process some solids are recycled back
through the bleed valve used to reduce suction pressure, but this did not have any
detrimental effect on the operation of the system and did not require any air that had
not been previously measured.  A very low vacuum is maintained easily by controlling
the amount of air recycled.

       To increase the operating life tine of the injector nozzle, the body was
fabricated from 4340 steel hardened to Rockwell C 50.  This prevented excessive wear
such as was noted on the inside of the test nozzle where exit air had eroded the brass.


RESULTS

       Two finished nozzles of the modified Penberthy design, manufactured from 4340
hardened steel, were tested in Battelle's MS-FBC.   With over 250 hours of operating
time, they-have performed satisfactcrily.  One nozzle injects 1/8" x 0 coal with -325
mesh limestone and the other rcinjects ซ-he flyash to inprove combustion efficiency.
These nozzles should have near 50 pounds per square inch operating pressure and
require an auxiliary air compressor in addition to the main fluidizing air blower.


                                         242

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Figure 1. Coal Injector Nozzte Tot Site
               243

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Figure 2.  Commercial Noitle Failure at 50 Hours Run Tirm at 260 Pounds/Hour Solids Feed
                                      244

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I
 I
 *
 3
                                      Figure 3. Injector Test Apparatus
                                                  245

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~ -  •**      J-. ~ <      - I  _;
*<-      2?-      55^
                                                Z  i


     Figure 4. Injector Test Apparatus
                  246

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The advantages arc obvious: they arc sinple to construct, they work well and they are
reliable.  Larger nozzles could be fabricated to feed 1/4" x 0 coal in larger systems
if desired.

       A picture of the actual injector nozzle used for both coal/limestone and ash
injection into Battelle's MS-FBC is shown in Figure 5.

       This nozzle will feed 600 pounds per hour of solids with 11/16 inch bore at 60
pounds per square inch pressure and 561 pounds per hour at 50 pounds per square inch
with  two-inch Hg suction or less at the solids feed point.


PART  II.  A START-UP BURNER FOR BATTELLE'S MULTISOLID FLUIDIZED-BED COMBUSTION PROCESS

Introduction

       An auxiliary start-up burner is used initially to heat the bed to some temper-
ature  (generally above 1000 F) so that when coal is injected into the bed, ignition
occurs and combustion is maintained.  This start-up burner also generates a stable
flame and a uniform outlet gas temperature over a wide range of air/fuel ratios and
firing rates.  Most importantly, it operates against the pressure of the fluidized bed
system.  Most "off-the-shelf" commercial oil/gas burners meet these requirements,
except for the last — the capabilit/ of firing at elevated pressures.  The "off-the-
shelf" burner is generally designed to operate noar atmospheric pressures and specially
designed housings are required for pressures much above 2 psig.  The standard burner
accessories such as pilots, controls, and regulators, usually are not designed for
elevated pressures.  These burners, with the possible exception of the high excess
burners, also cannot provide a uniform outlet temperature of 1000 F over a wide turn-
down  range (although dilution air can be mixed into the gas stream downstream of the
burner).

       Accordingly, the start-up burner for Battelle's V.ultisolid Fluidizod-Bed System
requires a specially designed burner or a modification of a commercial burner.  Because
of the constraint of a relatively short delivery tine, we, at Battelle's Columbus
Laboratories, decided to design and build the start-up bjrner.  We selected a burner
design similar to that of a gas turbine can-type ooaibustor.

       This paper provides the background to the desian of this start-up burner.
(For a more detailed discussion, the reader is referred to the Gas Turbine Engineering
Handbook.!)

Start-up Burner Design

       The burner design, based on the gas turbine combustor, was selected because it
met all the specifications of stable flame and uniform qas temperatures,  over a range
or air/fuel ratios (up to 100/1), turndown ratio (up to 40:1), and pressures (up to
15 atmospheres).  In addition, because of its high heat release rates (up to 8,500,000
Btu/hr-ft3 atm), the gas turbine combustor is relatively compact in comparison to an
industrial burner.

       We knew that the design of qas turbine ror.bustors had been advanced through
experimental development with qualitative assistance fron theory.   We also know that
in any practical combustion system the large number of variables and their complex
interrelations make designs from fundamental principles difficult.  Although gas
turbine combustor design and development is still an empirical air, we were prepared
to meet the difficulties.

Gas Turbine Start-up Burner Design

       Although gas-turbine start-up burners vary widely in design, all similarly
perform the basic functions.  Fuel, either gas or distillate oil,  is injected into a
region whore ignition and flame stabilization are provided by a recirculating flow
pattern within the burning flame.  Combustion continues in a region in which near
stoichiometric air/fuel ratios are maintained.  The hot combustion products are then
mixed with the remaining air in a dilution region to provide a uniform and suitable
temperature profile at the outlet of the combustor.



                                          247

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Figure 5. Modified Penberthy Tyv Injector Nozzle Used to Inject Solids Into BatttNe't MS-FBC
                                       248

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        Figure 6 shovs  the tubular  -rorJoustor that  Eattello -ised  for  -ho start--.p
burner  for its Mu!tisoliO F'luidized-Eod Systeri.   This start-up  burner con.bines i..->sr  of
the oenc-ral features  in  coir.bustor  de-si in   Th.-;- corbustion air passes throu.;h a perfor-
ated plat' to improve  flow distribution and is distributed around  tho co-irjstor  lir.c-r.
The air then enters the  annular space  b"tween the- liner and casin.i  (6-inch pir,e)  .3--;
is admitted ar3dually  into the space within the  liner through nunurous holes :::,2  s!  ts.
The cicsiun of these holes and slots provides for  distinct rones  for Mane stabiliza-
tion, co-bust ion,  and  dilution, and also provides film coolino  of  tho liner.  i'-;--l  :s
admit tc-d through a  nozzle that distributes wit.hin an  included amile of 60 to 90 decrees
A spar'i plug is used  for linht-off only.

        In Fiqure 6, the  combustion zone is surrounded by .; cyl in-iric-.il shro'jd that
provides a good ci rcun-.f crential flow distribution.  This shroud  !ui = a soco.idjry eff'--rt
of roc:::cinc: radiation  to the outer cj~i:n:, thus  ziini^izinq casino  ten:.c-raturcs.   In
the dilution zone,  rows  of holes arc arranqea for thorough ict  mixi.no and on tra inner.*
to provide nearly  uniform outlot tcnperatures.

        The coiT.bustor  linor is const rur:tc •:'. of air-roolod s^r-f-r. ri.nal.   The outsid'-
surface is cooled  by  flow of air in the annular  r-r,;ic" around i  , and tr.c- insi-io
surface is cooled  by  a filn of air odnitt": throuuh slurs .-.rr.-inj..-'  to blanket the
surface.  This filn is trie feature t h^t rak.es 1 iซhtw-i>:h^ netal  c-^nst ruct ion :-ossi;jle
as all  the heat received by the linor  is only that radiated from the :'ia~<.-.

        Conbustion  air  is admitted  through tn'- rjius o:  r.'idial iets.  These iets are
deni'jnc-u so their  anole  one r-enetr.jt ior: t.ruvid'-s  an  ir-T.-in-i'-r.-'nt  at  the cerbustor  axis.
This results in an  uปst rcuri flow ••:hicr. ni abi 1 i z<:-r, • h" flanr-.   i.ach  lot entrains air
and b.irnir.j fuel.  A  reci rculat;ion pattern it. formed  th-'it provit.'es  intensive turbu-
lence- and nixinn throtrihoct tho conb-js'or.  rnrierJ to Jj.iv> ,1 cold flew  i rossuro <:r-p  of
9" I!2O  et desi'in condition of one  nilli^n litu/nr  j:j['Jt  with -in  outlet t'>r.pซ.-r.if-.r-.- of
1200!-'.   This burr.er ,  h-ns the following  ad.'anta<:fs ปhat  iran not  b..' n.itrhod by any  o'.h- r
conb'jst ion O'tuipnc-nt:

        •  It will  opi-rate equally  well  at any air prt-bsure within  th<- rjr.ซ.iu' of
           pressures available, f/rr: 1 r>  to 100 f.si-i.
        •  It can be operated with  .-sr.y  desired Jas cut !c-'. t•-•::•:.•• -raturo. frcr. a!:o:;t
           200F ^o  about  1ROOP.  Gnrr- the air flow is  vstabl ishc-d th-.'  st3rt--.::J b'jrr...-r
           outlet tonpet aturc ran 'if changed within this ran'-i" by .-Jijn.Jir.w fuo!  flew.
        •  It will  lit:ht  off innocli-itely -ind t,or. it ively with .jn  .-K-i-trio F-..-ar'-: at  any
           fuel rate above the niriir.-irti  required for  ior.ition.  which  rorros: cr.J^ to a
           rather low  outlet tr-npcrature.
        •  With ?hซ' burner operatino. it  ran he oxp-osc-J to lar*:ซ--  i:xctirsปor.s i:i ->ir
           flow, in pressure, and in fuel rate with no danrror of  b'owo-.it.  Thv cnly
           way of blowinc; out the fla.-nc is to redur-e : h'- fuel  rlow  rate b.-!"w ti:'-
           nininun. which corresponds to a burn'--r-fvn lot t c."r^p--r.it in e of -00 to -5CGF.

        Tho cas turbine burner is uniu-j^ in that ovr  r.ost of tho operating rin.---, th"
overall  fuel/air ratio is too loan to  i-inite. explode,  or b'..rn.   This is nado possible
by carrying out cor.bustion with a  stoichio.-ietrir  nixtures in thi- buincr r-nii of th--
combustcr. followed by suo-ossive  dilution by air iets thai- thoroughly nix the com-
bustion  •pro.-iuct s to a  lean. lcw-tcor,erature Dixt-jre.   In case of an jntorrur.t icri  of
fuel rlow that would  put the flame out.  or if there w--ro a failure  to inniti-, th<-
mixture at the burner  outlet, and  throughout tho  qasifior vessel or rorrbustor, would
be too  lean to iqnite, burn, or explode.  Thus,  the burn'-r is bJ si ••ally r.-.ich safer
than conventional burners.  As a r-onscq-jcnce, only a  thermocouple  located in exhaust


                                             249

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CO
a
c
•o
39

Z
I.I
                                                             O   >

                                                                 5
                                 Figun&
                                         250

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stream was used to cut off the fuel  supply  in  the event that the aas temperature
deviated above or below the desired  set  point.


RESULTS

       The start-up burner was checked out  prior to installation in Battelle's
Multisolid Fluidized-fled Systen.   At the desian firing rate, ionition occurred at air/
fuel ratios of about 50 to 1.   Once  the  flaire  was established this burner was operated
at air/fuel ratios of over 500 to 1.

       After check out. we installed burner in our fluid-bed system.  Ignition occurs
readily.  Upon establishing the desired  air and fuel rates,  the burner maintained a
gas outlet temperature to within  a degree.


REFERENCES

1.  Hazard, Herbert R., 'Combustors'. Chapter  5 of the Gas Turbine Engineering
    Handbook, First Edition. Editor, John W. Sawyer. Gas Turbine Publications, Inc.,
    Stamford, Connecticut, 1966.
                                         251

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            QUESTIONS/RESPONSES/COMMENTS
     P.DRFPT RPnnr.S, CHAIRMAN':  Are there questions?  Could you
identify yourself, please?

     MR. W1RKSFR:  Al Womser of Womser Engineering.  What oil
nozzle did you  use, and was that running on oil or gas, then?

     MP. filAHMAR:  For oil , and we have used a standard air-atonized
nozzle that you would use  in a conriercial burner.  We have also  fired
the burner with a  sonic-core nozzle with very fine atorvization,  which
perfomed equally  as well  as a Delavan Swell-Air Nozzles operating  at
An pounds pressure with air atonization—nothing really specific or
special  with this  nozzle.

     FIR. FFLTflfl:   That rccirculating air stream just serves to kill
the vacuun that you would  nomally yet with an injector, an eductor.
And all  we are  doinq there is recirculatinq air hack to eliminate
that vacuun, because we don't want a larye volume of unncasured  air
coning hack in  with the solid naterial.  This enables us to get  a
fjood neasure of conhustion air in our unit.

     PORFRT RP.nOKS, CHAIRMAN:  Are there other questions?  Are there
any questions on any of the four papers we have heard this afternoon?
If not,  I want  to  thank the authors for bringing to us information  on
this very important subject this afternoon.
                                252

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                        INTRODUCTION
     ROBERT CHRUNOWSKI,  CHAIRMAN:   The  first  paper  on the agenda
will be "Fluidized Combustion of  Beds of  Large, Dense Particles in
Reprocessing HTGP Fuel"  by Derrell  Young  of the General Atomic
Company.  Darrell graduated fron  Lamarr University  in Beaumont,
Texas, in 1970 with an MS  in chemical engineering.  He's worked for
a couple of years with Texaco. Since 1973, he's been a process
development engineer for General  Atomic and is  now  a senior engineer.
I'd like to get this started right  away,  and  get right  into the
session.  Oarrell?

     MR. YOUNG:  First of  all, ny thanks  to the Conference coordinators
for inviting our paper.  It is on cjraphite burning.  We'll depart a
little bit from coal burning and  !  d also like  to thank you for
your attention at the outset, especially  those  who  might have heard
this paper at the AICHE  meeting just last month. I'll try to throw
in some different stuff  especially  for  you, and hopefully make
it interesting for everyone.  May I have  the  slides on please?
                                253

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                               Fluidized Combustion of Beds of
                                   Large, Dense Particles in
                                   Reprocessing HTGR Fuel
                                         DerrellT. Young
                                     General Atomic Company
ABSTRACT
       Fijldized  bed  combustion of graphite fuel elements and carbon  external  to fuel particles Is
required in reprocessing high-temperature gas-cooled reactor (HTGR) cores  for  recovery of uranium.
This burning process  requires combustion of beds containing both  large particles and vjry dense car-
tides as  well  as combustion of fine graphite particles which elutriate from the bed.  Equipment must
be designed for optimum simplicity and reliability as ultimate operation will  occur in a limited
access 'hot cell1 environment.

       Results  reported in  this paper indicate that successful long-term operation of fuel element
burning with complete combustion of all graphite fines leading to a fuel particle product containing
< 1: external carbon  can be performed on equipment developed in this  program.


INTRODUCTION

Objective

       The High-Temperature Gas-Cooled Reactor (HTGR) Is a thermal reactor concept which uses helium
as the coolant  and graphite as the moderator and core structural  material.  The HTGR fuel cycle employs
an additional energy  source by the use of thorium as the fertile  material.  The U-233 bred material is
recovered  for recycle to the reactor with U-235 as the makeup fissile material.

       The fuel In an HTGR  consists of fissile mlcrosphere particles  containing e1.her U-235 for fresh
fuel or U-233 for recycle fuel, and thorium fertile particles. The fissile partu ie? are coated with
a multi-layer pyrolytic carbon-silicon carbide ('TRISO') coating  and  the fertile particles are coated
with a two-layer  pyrolytic  carbon ('BISO') coating.  These particles  are bonded into fuel rods and
are contained in  a hexagonal graphite fuel element. 'The fuel element and  the  fuel particles are
shown in Figs.  1  and  2.
                       196 18 • 89 KG GRAPMITI
                       7ปI8 • 116 KG IOIปl
                       711 IB 96KG I01AI CปOBO%
                                                         CROiSSiClON
                                       Figure 1. HTGR Fuel Element
                                                254

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                                                  fyHOLปIlC CARBON
                                                                       TRISOHSSILl
                                    Figure 2.  HTGR Coated Fuel Particles


       The recovery of bred U-233 'in HTGRs for recycle requires reprocessing of the spent graphite-
base fuel.  This reprocessing involves removal of the graphite, separation of fissile and fertile
particles, dissolution and solvent extraction to separate uranium, thorium and fission products.  The
reference method of removing the graphite is by combustion, which is most readily achieved in flui-
dized-bed burners.

       Two types of fluidized-bed burners are bein-) used:  the crushed fuel element, or 'primary
burner,1 and the crushed particle, or 'secondary burner.'  The secondary burner i. discusbฐd briefly
by Young (l) and in rare detail by Rlctaan (;).  This paper presents details of the primary burner
development as its relatively large and widely rancing size and density distribution bed material
presents interesting fluidization and fines recycle problems which are unique in the varied jses of
large particle fluidized-bed combustion.

The Problem

       The primary crushed fuel element burner receives a feed stream of intact fuel particles and
crushed graphite produced by a three-stage crushing system.  Average properties of the burner feed,
nominally minus 5000 -_m, are shown in Table I.  The prinary burner must ignite and burn the fuel
element graphite, the fuel rod pitch, and the fuel  particle pyrolytic carbon at 900ฐC producing a
product of discretely separable silicon carbide coated fissile oarticles and fertile fuel  kernel
particles containing less than 1 wt. * exposed burnable carbon (Table II).  Adequate fluidization of
the largest burning graphite and the large, dense fuel particles requires superficial velocities of
1.01 to 1.37 m/sec and a carefully designed gas distribution device.   Graphite fines (-425 ..m)
generated both in the crushing process and in the fluidized-bed burning, elutriate before they are
burned.  This carryover of fines is significant, amounting to over 301 of the carbon fed.   This large
mass of fines presents an expensive nuclear waste disposal problem: hence, combustion of the fines
within the burner system is necessary.
                    Table I.  Average Properties of Primary Burner Feed & Startup Bed









Tap Density:
Bulk Density:



Angle of Repose:






Avg. Burnable
Avq. Particle

1.25
1.08
35*

g/cm3
g/cn3





Carbon: 817
Size:
1378
urn

1 Burnable




Ut 5
Size Total
-6350
-4760
.
.
-
.
"
869
550
420
375
250
m
m
m
Fl
m
n
m
* 4760 m
* 869 m
+ 550 m
+ 420 m
+ 375 m
+ 250 n

5
60
20
5
4
3
3
of
Sample







Carbon
in
Fraction
100
100
21
78
97
98
98







                                                 255

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                 Table  II.  Average Properties of Prirary Burner Fuel Particle Product
                                  Bulk Density:             2-6 gr/cc
                                  Size:                     200 - 870 -_
                                  Exposed Burnable Garten:  < 17
       Tie primary burner operates in semi-continuous batch cycles.  Operating guidelines ere sumnar-
 i;ed  below in Table  III.  This operating mode processes an incoming lot of fu-.-l elements in a series
 of burner runs which are separated by brief fresh feed interruptions for unl-.ddii.g a partial batch of
 the fuel particle product.  The burner temperature is raintained by t>e theial inertia of the par-
 tial  bed retained and by external  induction heating.  The burner is completely emptied only after the
 specified lot of fuel elements is processed.  The burner is then restartec by using the induction
 system to heat the initial crushed fuel element loading from the next customer lot to ignition tem-
 perature.  Thus, the bed composition ranges from one ric'i in burnable ca-bon to one rich in burned-
 back  fuel particles.  Bed bulk density and. hence, bed Height, varies by a factor > 5.


                     Table III.  Operating Guides - Prirary Fluidize-l-Sf-d Baner
                                                                        Fuel
                                                                       p.urner
                        a.  operating mode 	 semi-continuous batch
                        b.  startup	induction heater
                        c.  gas distributor  	 perforated cone
                        d.  feed system	gravity/rotaซ-y valire
                        e.  product removal	gravity/pne'jnatic
                        f.  feed/product control .... s*tered feed/batched product
                        g.  heat removal	air cooling *ia awtular shroud
                        h.  fines recycle  	 gravity external recycle to
                                                         burner via external cyclone/
                                                         filter sysfan
                        i.  temperature	900 + 50=C
                        j.  pressure 	 less"than 15 psiq at all
                                                         vessel locations
                        k.  materials
                               - vessel 	 Hastelloy x*
                        	-auxiliaries	304 L SST	

                        * Product of Cabot Corporation
The major design problems have included:  the requirenent for a specialized t'on of the exces-
sive irass of fine particles elutriated from the bed; and development of a vife. reliable neans of
operation using automatic controllers.

Scope

       The development work described has been done prircipally in a turner of 0.20 n internal diame-
ter (Fig. 3) and proceeds from development documented by Stula, et alt-) arrt Young  (0.   A 0.4 m
burner (Fig. 4) has also been recently activated and is being operated in conjunction with the O.Z m
burner test work.

       These bi-rr.ers are engineering-scale systems for a planned larr-e-scale demonstration facility.
The work is funded by DOE'S Division of Waste Management. Production and Recycle.

Significance

       The direct importance of this work is the verification of a difficult process which is vital
to the recycle/recovery of uranium in the HTGR fuel cycle.
                                                 256

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       Burner showing induction coiK
       viewed through safety glass window
Full scale burner
    drawing
Local instrumentation
panel
          ,  .
..X
                                           Figure 3. 020 m Bufrm Cabinet
                                                       257

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     OH GJS f>Hf Cyclone
                Fttrl S/sttm
B?   r-urSiSHK-jr"
R  '  , -H^PJife
  t    '  /""""nsf        --'•,?>
        p/            •*- -i.^
       Figure 4. 0.40 m Burner • Upper Section
             258

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        An indirect significance 07" this work involves the nuch wider applications  of fluidized-bec:
combustion and/or gasificv.ion of coal  in po;/er plants.  The  techniques of process control,  fines
recycle,  removal  of ash, avoiding particle fusion and the results of heat transfer,  scale-up,  and
autcration studies apply readily to such uses of atrospheric  and pressurized  fluidized-bed combustion
of  large  particles.


SUMMARY Of RESULTS

Cas Pis tributor Design

        The gas distributor design {shown at the botton of the burner in F~'q.  1} was  a  product  of de-
velopment experience with flat perforated plates and single gas inlet  cones.   It consists of a per-
forated cone and  vertex line.   The cone orifice size and an'ile were experinenta'ly optimized to
yield  even gas distribution through all perforations, limit plenum drainage,  maximize  solids nixing
at  the plato surface, and rrini^ize plate surface temperature,  'lie vertex line was sized for levita-
tion of bed cdterial during normal operation and for free flowing product discharge.   Design calcu-
lations for perforated cones have developed fro<-' scale-up information.
                    leed hopixr —
                      heating susceptoi &
                       cooling i*cket  -

                             induction     "*•
                            healing coil	•
                               cold ait in —ป. -
                    perforated cone	ซ
                    93$ d'S'nhutor           J
                              oซvg*n COp —S
    	 rotary valve
    ... . - _  .  .— __— insulation
finci
   secondary
                                                            pneumatic product tiansport
                                     Figure 5. Primary Burner Configuration


       The general gas distributor  functions  considered in design were:  to support the bed and pre-
vent excessive solid naterial  fron  flowing  down in to the pleriun charbcr; to distribute the nas uni-
fomly over the bed cross  section by designing sufficient pressure drop across the plate while main-
taining a naxinuri pressure drop  to  lir;it  the  bacr-Dressure on the gas Supply system; to propote rapid
particle rovenent throughout  th<" bed and  at the plate and minimize solid; stannation on plate.  Des'cn
problens specific to the prirarv burner  included the cyclic burner operation expected (rultiplc start-
ups and shutdowns).  TMs  required  a distributor v.hich functioned well over extreme ranges of gas
flow.  Avoiding stagnation areas of the burning solids and resultant hot spots in Mich varied opera-
tion was further conplicated  by  the wide  rar.-:e of particle sizes and densitir'. in the nixed heavy
metal-carbon beds.  The distributor design  also had to be within the constraints of burner confiqura-
tion dictated by the mechanics cf rerote  hardware, r.inimization of high raterial stress and wear areas,
and safety.
                                                  259

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       Conventional flat perforated plates were tested on the primary burner.  Although relatively
simple in their design and fabrication, a disadvantage of flat distribution devices was that solids
stagnation zones were liable to form between the distributor holes and at the wall-plate juncture.
The bed stagnation and resultant fusion of bed solids into defluidized clinkers, or agglomerates,
caused flat distributor plate inal-distribution and hot spots in pri:r.ary burning(-;.  Theie problems
with flat distributor plates were a result of the horizontal geometry of the device and the resul-
tant potential for stagnation of solids.

       The subsequent distributor designs tested departed from the flat configuration to circumvent
the distributor stagnation failures.  These designs utilized sloping surfaces to avoid burning solids
stagnation.  A 50" included angle cone with a single vertex inlet gas opening was tested initially.
The device worked adequately with feed containing material '; 4760 \m.  However, when a nominal crusher
product containing •ป. 5 wt. 1. > 4760 \-.m was fed, intermittent spikeo fluctuations of the bed pre*  ire
drop (;.P) occurred.  These fluctuations were more than twice the magnitude of the recorded slugg. i
bed ;.P and occurred on •• 1 min. cycles.  The bed ;.P cycles were followed by excursions in bed temp, •*-
lure and off-qas compositions and resulted in formation of agglomerated fuel particles which adherec
to portions of the sloping v.all of the cone.  It was concluded that these operating problems were
due to cyclic internal gas spouting caused by the intermittent accumulation of the largest feed ma-
terial in the cone distritutor('-).  The bed material was apparently in continual transition between
spoutable and unspoutable conditions as described by Hathur(^) and Ge1dart(7).  This spouting con-
dition could not be allowed in the combustion process due to the local stagnation of burning solids
at the cone surface radial to the internal spout.

       The merits of the flat perforated plate and the single gas inlet cone were then combined to
overcome the problems inherent to the separate devices.  The resultant device was a perforated cone
with a gas inlet through the cone vertex opening.  The vertex gas inlet opening was sized to levitate
the largest bed material with -. 25 vol. 1, of ป.he total inlet gas flow.  The remaining 75 vol. 1 of
the total qas flow was allotted to flow to the plenum chamber and through the cone perforations.  The
device worked well with the largest nominal feed^-'.

       An experimental program was then undertaken to determine the optimum included angle for the
cone.  Included angle cones of W, 90", and 120" were used in ccr.bustion runs at similar conditions.
The 90ฐ cone was selected as the steeper 50' cone surface temperature ran 100ฐ to 150ฐ hotter than
the 90" and 120ฐ cones, and the shalV^.-ir 120ฐ cone produced solids agglomerates which fused to the
cone surface around the periphery of several orifices^).

       A 90" perforated cone has proven effective in hundreds of hours of combustion operation on the
0.2 m burner, including many start-ups and shutdowns.  A scaled-up version has been operated in ini-
tial shakedown of the 0.4 m burner and has also given good performance. Distributor design from (10).

Fines Recycle System Design and Testing

       Disposal of the large mass of elutriated fines ('•. 30 wt. X of the carbon fed) Kas been accom-
plished by returning the fines to the burner for combustion in nultiple recycle pasces.  Three types
of fines transport systems have been used:  1) a dual-parallel pressurized hopper rtense phase system;
2) a tri-series pressurized hopper donse phase system; and 3) a single gravity hooper-rotary air-
lock system.  The fines transport systems are shown in Fig. 6.  Parametric analysis has indicated
the main effects of each system on the process and has shown that the gravity system is the best al-
ternative.

       Equivalent fines burning capacity was noted with the fines recycle injected through the bed
via the cone vertex gas inlet and with the recycling fines injected above the static bed into the
bed solids disengaging height.  However, in-bed fines recycle drastically increased fuel particle
carryover  into the recycle loop, thereby breaking more particles and increasing non-combustible
heavy netal oxide buildup in the fines.  Agglomeration of fuel particles also increased with in-bed
fines recycle.  In addition to these negative a^jt-cts, final bed carbon was highest with in-bed
recycle, indicating poorer bed burnout,  ffi neat transfer showed an apparent increase with above-
bed recycle as minimum radial and axi>'1. temperature differences were found in the runs using above-
bed recycle.

       'oOth the dual-rv.i-dllel and the tri-series pressurized hopper systems were capable of trans-
porting fines o^iinst the back-pressure of in-bed recycle, with the tri-series system having the
potential o; being smoother in mass flow properties.  In-bed recycle of the fines aggravated the bed
sl'-'jing, however, causing the deleterious effects mentioned above.  Both of the pressurized fines
transport  systems were studied in injection of fines above the bed perpindicular to rising slugs.
This injection seemed to destabilize slugs and, hence, was beneficial in its effects on the burning


                                                  260

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  gravity
  single-
  hopper
  system
             recycling fines from
               cyclone-filter
- gas in

 rotary valve
                      fines
                                                              presurized
                                                              dual-parallel
                                                              hopper system
                                to above-bed
                                or to in bed
                                                   recycling fines from
                                                      cyclone filter

                                                          i
pressurized
-gas in
                                                                       fines
                                            recycling fines from
                                              cyclone-filter
                           pressurized
                           tri series
                           hopper system
                         to above bed ••
                                                            gas m
                                                                       pressurized
                                 Figure 6. Three Fines Recycle Systems Tasted


bed.  As fines burning  efficiencies  were equivalent with above-bed or in-bed pressurized  recycle,  the
possibility of a simpler gravity  above-bed recycle loop was investigated.

       Gravity above-bed fines  recycle  resulted in the least final fines inventory; fuel  particle
elutriation, breakage,  and  agglomeration; oxide build-up in fines; and final bed carbon of  any  of
the recycle systems  tested.   The  gravity system was the simplest to operate and its single  moving
part (the rotary valve) increased the reliability of the system.   This system was capable of  feeding
fines with large quantities  of  fuel  particles or fresh feed material.  (The pressurized systems were
known to plug with such large materJai.)  The fabrication cost of the gravity system was  less than
half the cost of either of  the  pressurised transport systems.  On this basis, the gravity system
was chosen as the optimum fines recycle technique for further long-term testing (see Fig. 5).
These results are discussed  in  detail elsewhere(:l).

Statistical Analysis

       A series of tests was made on the 0.2 m burner without fines recycle and then with fines re-
cycle using the varied  recycle  systems  described above.  These tests were devised and analyzed  based
on a statistical design of experiments  utilizing a 'fractional factorial' analysis technique  as
described by Hunterl'2).  The series of runs has been used to quantify the weighted effects of  basic
independent process variables such as superficial velocity, particle size, etc., upon burner  heat-up
times, fines elutriation, particle breakage and agglomeration, burner axial and radial temperature
profiles, and off-gas compositions.

       The most useful  information obtained were recommended operating levels for:  the induction-
heated start-up phase;  the  'equilibrium'  phase of burning with gravity above-bed recycle; and the
final product bed 'tailburning' phase immediately prior to shutdown.  These results are summarized
in the following text and given in detail  in (") and (n).
                                                  261

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       For the 0.2 m burner induction heated start-up:  velocities us?d were 1.10 and 1.22 m/s;
bed weights were 32 and 36 kg; ignition 0^ levels were 100 and 150 SLFK; 02 ramp rates to full burn
rate levels were 2 to 8 SLPM/min; feed sires used either had an '- 980 or -. 1300 :.m average particle
size.  The results showed that:  minimum total velocity and bed weight yielded the fastest heating
to ignition temperature; using minimum f<2 f'ow rate fฐr ignition and ninir-un 02 ramp rates reduced
fuel particle breakage and agglomeration; relatively large feed size, although not a directly con-
trolled variable, was beneficial in reducing both heat-up time and particle breakage-agglorreration.

       For the 'equilibrium' phase of burning with above-bed gravity recycle:  velocity was either
1.00 or 1.10 m/sec; above-bed or 'secondary' 0? used was either > 40 or > 80 SLPH; fines recycle
either started immediately after the full in-bed 02 (burn rate) was reached or 30 minutes after-
wards; in-bed Oj levels were either 300 or 350 SLPH.  The combined results indicate that for opti-
nura operation with above-bed gravity fines recycle, the fines recycle should be started irmediately
after the oxygen ramp is convicted and total in-bed oxygen, above-bed oxygen, and in-bed velocity
should be matched (i.e., at high burn rate, use higS above-bed oxygen flow and high in-bed velocity).

       The phase of operation just before shutdown in which the final bed carbon is reduced to < 1
wt. ">. was referred to as 'tailburning.' This phase was not. statistically analyzed but its essential
parameters were varied and the results compared.  The parameters were:  induction heated assist
versus unassisted tailburn; allowing either 5 or 10 \ol. -  02 in the off-cas during tai'buming; and
either continuing or discontinuing (Fines recycle during the tailburn.  The results indicated that
using induction, continuing fines recycle, and allowing raximum off-gas 02 until off-gas CO was no
longer detectable, minimized final system carbon at shutdown.

       Other interesting results included:  1) Much lower fuel particle agglomeration (0.001 to
0.015 wt. ? of final bed) was found in fines recycle runs compared to runs without fines recycle
(0.02 to 0.2 wt. ?.).  The apparent explanation was that fines recycle (whether in-bed or above-bed)
improved bed mixing, and thus avoided any local or temporal stagnation which can allow fuel par-
ticles to be fused by eutectic compounds.  2)  Use of additional 0^ flow through the vertex gas
inlet (the major 02 flow was through the cone perforations) was beneficial to all stuaied dependent
•/arables except the desired decrease in the axial bed terperature profile (.-T).

Sys tern^ Automa t i on

       The details of the primary burner automatic control  system are discussed hy Rode^:^.  A brief
sumary of that discussion is given below.

       The burner automatic control incorporates a digital  process controller with an all analog
input/output interface.  The advantages of sur.h a control system to a pilot plant operation can be
su-TTvarfzerf as follows:  1) control loop functions and configurations can be changed easily; 2) con-
trol constants, alarm limits, output limitc, and scaling constants can be changed easily; 3) calcu-
lation of data and/or interface with a computerized information retrieval system during operation
are available; 4) diagnosis of process control problems is facilitated; arv) 5) control  panel/room
space is saved.

       There are five principal functions (and a host of less significant ones) to be performed or
supervised by the primary burner control system.  These functions are suncarized in Table IV.

       The control system selected to perform these functions is a centralized digital  process con-
troller called DTO'lK'.'F.Xt manufactured by Rosemount, Inc. of Minneapolis.  The .'.'.'W.v;y system is a
hard-wired real-time dedicated process controller designed to control up to 100 loops by neans of
a continuous one-second scan of the lo>ps.  A 20-loop configuration with capacity for expansion to
50 loops was purchased for the reprocessing cold pilot plant, as shown in Fig. 7.

       Each loop accepts a 4-20 ma dc analog signal from the process and provides a continuous <-20
na dc analog output signal back to tt-e process.  The analog (A) input signals are converted to digi-
tal (D) form for interfacing with the computer-based central controller, and the digital feedback
instructions from the central controller are reconverted to analog ojtput signals.  The A/D and
D/A conversion is performed by process interface modules (PIHs); one PIK is required for each
P/''7T.Vฃ7 channel that has an analog input and/or an analog output.

       The configuration of the control loops is set up by the operator beforehand with pins and wire
links on a functionally diagrammed diode pinboard called the channel function matrix (CFK).  The
various control schemes which may be implemented include cascade, ratio, feed forward,  calculating,
and multi-variable types.  The actual operating parameters  for these functions are alterable values



                                                 262

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Profess Interface
 Modules (PIMs)
 Central
Controller
OIOGE VfS Operator's
     Console
Chjnne' Function
  MJIIH i
                           Figure 7. Pilot Plant Control Instrument Panels

                                               263

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                           Table IV.  Primary Burner Hajor Control Functions
Function
Fluidized-Bed
Heaf'ng

Post-Ignition
Bed Temperature
Control
Oxygen Flow
Fluidiztng Gas
(CO?) Flow
Vessel Cooling

ง
Method of Control
Induction heater cascaded to
bed/vessel/susceptor tempera-
ture

Adjust oxygen flow
Fqual -percentage control
valve
Equal -percentage control
valve; adjust CO? flow set
point based on ted tempera-
ture to maintain a constant
total gas flow velocity
Adjust coolino air flow and
maintain proper coaling air
blower discharge pressure


Type of Sensor
I.S.A. Type K (Chrotnel-P/
alunel )-Thermocouples

Type K Thermocouples
Precision gas flow-
meter (SWIRLKTTER)
Precision gas flow-
meter (SUIRIKETER)
Type-K Thermocouples/
Flow averaging (A.'iNU-
BAR) Pilot Tubes


Control Criteria
(1) Heat fresh feed or
particle beds to ig-
nition temperatures
(700ฐC) in < 2 hours;
(2) Maintain clanp to
hub :.T < 112ฐC for
vessel flanges.
Control tw<>eratures
within ป 10CC of set
points (-• * U).
Flow within * 3T of
set point.
Flow within ป 3" of
set point
(1) Maintain full bed
at SOO'C ซnile bum-
ing at 800 ga carbon
per minute;
(2) Air flow within ป
3: of set point;
(3) Maintain tempera-
tures within ป 101 of
set point (-- ฃ i:).
 entered  through an operator's control console and stored in an internal ccrory.  Restructuring of the
 control  schemes is sirply a ratter of altering the pin and link arrangements on the CFM.

       All  loops nay be controlled digitally by the central controller under the automatic one-second'
 scan  arrangement.  This is the normal node of operation, called the 'central' control rode.  A varia-
 tion  of  this modo is the 'central eanual' which allows a loop to be controlled manually thrcugh  he
 operator's  console.  In addition, there is a corcletely seoarate ar.d independent analog 'Nicl'w' con-
 trol  node,  which is effective even if the ccntr*! controller breads down.

       There are currently 23 out of SO available channels (CFM) and 13 out of 20 available control
 loops (PIHs) assigned to the priryjry burner during the period of initial development work.  Possible
 later changes  tn the nethod of control to provide greater versatility and more automation will con-
 sune  up  to  39  channels and 16 loops for the prtca'y burner.

       The  .'•''•'rT'.rr system has been in operation since March. 1976. and has been satisfactory in
 control  of  the primary burner.  Minor malfunctions have been Quickly traced and corrected by the
 manufacturer.  The controller and the control philosophy have been very beneficial in simplifying
 the burner  operator's duties and in providing s.ifer, more constant operating conditions.

 Empirical Scale-up and Heat Transfer Studies

       Initial operation of the 0.4 n burner has shown significant bed nixing irprovements over the
0.2 m burner.  These results may be interpreted in light of decreased bubble bypassfno at the vessel
wall  as  the vessel diameter increases, as shown by yertherP').  Internal hปat transfer coefficients
during 0.4 ra induction heating have ranged fron 351  to 602  watts/erOR  fn the 5^ An(j 47.7  t0 M2.2
watts/mJฐK  In  the slugging *one(!').  The highest in-bed Internal heat transfer coefficient was ob-
tained with the shallower beds tested 
-------
 from the increased slugging of deeper beds (L/D ' 4.5).  The coefficient  increased with increasing
 temperature as velocities  were fceld constant. An optinun velocity was  found at each  constant  tem-
 perature which gave a naxirxm in-bed coefficient.   The optinun velocity was dependent  on bed  weight
 and particle size, with deeper beds and  larger particles requiring higher velocities for good mixing
 and heat transfer.


 FUTURE WORK

        Both the 0.2 n and  the 0.4 n prinary burners will be operated in concurrent tests which will
 include studies of scale-up differences, effects of varied feed sizes, hybrid cone distributor de-
 signs, extended automatic  control, and equipment wear.


 ACKNOWLEDGEMENTS

        The work described  in this report was supported by the U.S. Departnent of  Energy, under con-
 tract EY-76-C-03-OI67.   The results precede from investigations acco'-'plished by technical contribu-
 tors over a span of several yea'-s.  The contributors include:  D. H.  Stallings.  N.  B.  Jacavkh.
 N.  C. H.irvaez, R.  M.  Earle, T. 0. Wri-jht and U. S.  Ricknan in the fabrication and operation of the
 0.2 and 0.4 m primary burner equiprcfit; 8. T. Stula in the subsystem design, burner  operation and
 data evaluation; H. H.  Yip in heat transfer an>J related analysis and design work  on  botn burner, sys-
 tens; 0. S. Rode in design of eปperi-ซ?nts. burner operation, and data  evaluation; antf  J. W. Allen
 and R. 0. Zitrrernan in the leadership of the burner development program.

        NOTE:  Thป parallel sressurizซ?d fines recycle hows were scaled-up from  hoppers originally
 tested by H. B. Paltrier of  Allied Cheoical Corporation. Idaho Falls, Idaho.  Discussions with  W. B.
 Palmer also contributed to the development of the series pressurized hopper system.


 REFERENCES

 1.   D. T. Young. "The Use  of Fluidized 6*d Combustion in HTGR Fuel Reprocessing." Proc.  Fourth Intl.
     Fluidized-Bed Combustion Conf.. McLean. 1975, pp. 657-659.
 2.   W.  S.  Rickrcan. "Interin Development  Report  for  Secondary Burning." GA-A13540.  Dec.  1975.

 3.   R.  T.  StuU.et al. "Interim Development Report  for Prirary Burning." GA-A13546.  Jan.  1976,
     pp.  6-1, 6-2.

 4.   "HTGR  Base Program Quarterly Progress Report  for  t^e Period Ending Feb. ?S.  1973. W-A1251S.
     March  30, 1973. pp.  J6--9.

 5.   "Thoriun Utilization Proorar. Quarterly Progress Report for the Period Endi
-------
13.   "Thorium Utilization Proqran Quarterly Progress Report for the Period Ending Aug. 31, 1976.
     GA-A14083.  Sept.  30. 1976. pp. 4-3 to 4-11.

14.   J.  S.  Rode. "Process Control of an HT&R Fuel Reprocessing Cold Pilot Plant." GA-A14101.
     Oct.  1976.

15.   Joachim Herther.  "Influence of the Bed Diameter on the Hydrodynamics of Gas Fluidized Ceds.
     A1CHE Symposium Series on Fluidization. 70. 1S74. pp. 53-62.
                                                266

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           QUESTIONS/RESPONSES/COMMENTS

     SHELTON EHRLICH,  CHAIRMAN:  Can we have the lights?  Okay, are
there any questions?  Any written questions?  Any oral questions?
Come on over to the microphone.  Identify yourself and the company
you're with.

     MR. MARGARITIS:  Paul  Margaritis with Westinghouse Electric.
You said something about...when your bed spouted that you got agglo-
meration on the wall.   Did  I  hear you right?  Could you tell me
a little bit about what the mechanism is that causes the agglomeration
on the wall.  Do you think  there's  hot particles in a bubble that are
getting thrown 'jp against the wall  or do you think that just raising
the oxygen content on the wall or what.

     MR. YOUNG:  It's simply  stagnation.  All the gas is going up in
the central spout.  It's not  distributing itself among those solids,
and it is stagnant at the wall.  The hot solids--of course, a lot of
us might suspect that solids  temperature in a fluid bed is a good
deal hotter than the overall  bulk temperature—stagnate, become a
packed bed and really get hot.   It  simply fuses everything where
the gas isn't distributed.   So it's gas maldistribution which results
in stagnation outside that  spout, all annular to the spout.

     MR. MARGARITIS:  Thank you.

     SHELTON EHRLICH, CHAIRMAN:  Any more questions?  I feel kind of
a special relationship with the work that was just described.  A
little historical note:  About ten  years ago when I was working in
Alexandria, Virginia on fluidized bed combustion, one of my associates,
John Bishop, got a telephone  call from the General Atomic people
asking for all of the information we had on fluidized bed combus-
tion.  So very quickly we wrote  them a letter proposal, and never
heard from them until  today!
                                267

-------
                                 Rosoarr.h of Gas Combustion in
                                              od Bod Plants
                               K /<: Math^rm JififJ A F/ Gliji'fi

                                   IriMitut': O' G'j'. ol UK.- Uf r^i
                                                U lo,?i R
        H uit.'i .•.••.  tin.- \-.ti\\. t h.ir.K ' i r i ••• ic "I  the::,
        •  (.u::i!<*,i-. I i'!" .1  tiปj::.ซij i-neo-j1. ,'•>:. -:nnl-;i i r trix.lure  in jccli-'i  liirou; :i .1

        •  i ซ.::.!.u:;l inn '.;.i r irn :il.i i  sy.le:::. iiii" ::  ::.
l.il.m'.il "iry -Hid i i:   *"
                            Air
       .
0 ,0 0. 0 O
              r,.,'..




•':*-*?&
'•::'ฃ•ฃ*'
•** :'/>.'. •'-•?.•'
t ill
u
                         t   L
                                                                     Air
           Figure 1.  Deiigrn ol Air and Gat (nation into the Fluidind
                    Bed. a • Homogeneout Gn and Air Mmture: b< •
                    Partial Mixture ol Gas and Air ounide (he Fluidi/ed
                    Bed: d e • Separate Jell ol Gas and Air.
Comh'i slion  ซ'f Homogeneous  G.is-ond-Air Mixtures

        Tlic  process  of con;bust.ion  of hoHior.cncJus R.is-nnd-alr  mixtures was  studied  usin;-.
100  and 160 trm dia  laboratory  furnaces  with an  air  consumption ratio equaling 0.7-  '• • 2 . 0 .
and  pressure of  1  to lt>  aim.

        Corundum  balls, htf,hly-aliminifcrous ch.iraottc  and quart^y  sand were used as
pscudof luiai.-.ed  heat-carrying  agents.

        The  most  favorable  conditions  for pas  combustion arc  crc-itcd during the injection
of a previously  prepared j;as-and-air r-.ixture  into the fluidized bed.  Keeping up  .1
constant  source  >/f  flame over  the fluidi.~-.ed bed of  monodisperscd  natcri.il, rhe natural
gas  is observed  to  i>;nilc  over  the fluidized  bed surface burning  out with a bright blue
                                                268

-------
 : I "IT t-  ". :*. '. r.c  e<.•.. .1:..-;:./ :• j: :-11 .s  .i:*.c  ~; r.iy s .
          : r  t T.c  :.*•%;.   .-.,.u"  vr.v  t i-r-j-c-r.**.'.ii'i  ป:K-
                                                        s tr.e te::;-ซ. r :iure  -. :  the up:-er p.irticles
                                                        I.IM-S  t r.  1 ;<.i.il'C tht- i::>:: has I ;<.-:< process
                                                        n,-  r.ipidlv  i.vr.ti'.iv.-'L.eU insi>:e  trie  i!ui>:i.:i
                                : i.-i-.-.'i-r.i*.
                                              v:.:^!-.  is ••;.•  i-.i- j.j j*'C  l..--.ซ-r  '. h.in  ihi.-  i.-niii--:-.
                                             vii  r.i"!i>uis;>crsni  p.irt ic it-s .   KIT  i-x.i: .;>!ซ•.  na:ur.i'
.  .IK is  ii'ni'.i/ii a:  : i.i-^i n:  o.j'j-'J.j  ;ir.>:  i - .! rrr. spin-r ic.ii corur.dum
\i;tf. it !i -s .  vi-iU-  in ..  :mi <>:" O.'io-'i.b :'.::. fr.n.-; iop.  ^-i:.-, ::.<•: iซ-  p.irl icli-s .  .'..IN  ซ.-n::itiuat. ion
iii.'in:>  .v_  7'JO"C.   7::is IN .iccoui.'-t-o  f>>r  L.V t hi- I.icl til. it  iluriii)'  jisi-tiilof luiui.:.iLiปr.  ol
;'i-:yซii s;n-r>.i-is ::-ili-ri.'i! -••.ซ-ri- is  .t r.ir>-:ii->: .-...•in- of i.c.iic-ii ;>..i:icit-s  lio.itin-,' <>v>.-r thL-
:-*-•!-. -'i'.ich  ser'.'t-'-s  -is  i i'.c- . •*•.".ป.•  *.-'.  /.ir.  \.'tj:'.i".ij! inr..
         r'i/uri- .'  ;.h"V
v.-r.-,us  'hi;  -Ii-;.: h <.f
                                            Oi ,
                                                    ..  '•.<>. :: i .  Cii.-, i -tini-ent r.n. ion and  the  ten.per.i
                                                   ':.-  the *_•ซ>;. iii:st ion  of .1  hoiM>;-ei!i-.n:s i-as-and-a
:• •':-:'-;.ire  i:: .1  'l.-'i-\.'j  "::. bet: of  >.-or;::i>!.::-..    i-.  i :• .•;-:owii  Th.it  the  >-.'is hi,-ins  to lปurn  or.
' :.i-  ,-r.itt- *..i-:i the- -i i r  cor-.stt".p: ior. r.it. iu  -   '  i . ! .   "."ne  v.-or.ci-p. tr.'it ion  of  :-.!>-t iiane  .'ind TJX
<:> cri-.i^-e  r.ipidiy  ••:'. r.  the i.i-i.-ht  of  tin-  :'! \t i t; i .-.<-,: !n-tj.  while those of c.'irhon ilioxitit-
ir.i-Te.'i.se.  Tin- c'.r.pos: t io;i  o:   the n>:-.l.'J:.t icr,  pr-uiuc: :  :-i-i-o:-.i .-. st.iiu 1 i.'.i-ti -it.  .1 tlist.-ir.ce
of  1'J r.::  fn-:-. ::.ซ.- ,-r.iTi.-.   !'  i :,  i.i-n-  th.t.  thi-  t_o::.h-..M inn .:<>.;e end:;.   The ilepth  t>f t!u
.iciivi- .:oiie  is •'.  r.r... h.ere.  •">'i  of the ,  i s  !>-.irr.s  o-.il .   iit-.it  r.iiti.it iun  in  this :irt.-.i is J
;ij.-h .1.-.  i ''il>. -)';'i. 'iii') kc.il/r.' per  I'.our .   'li'.t-  p.-.e'nii'f 1 uitli .u-ti  p.-iriicles  h:ivi.- no li::.-.- to
fon.jui't  ; he r.u:i:it id hc.r. ,  wiiivii  re-.-.ilt.-i  ::i  -i  J'jO-'j'J()"<-  t er.j.i-r.iiure ;-r.nl icr.l .-ij>pi-.ir in.-
on  the deptl.  of the co:-.:>u.-.t i on .:i.i:e.   '.-.'i'ii  the  -iir  i-or.:.ur. pt. i on r.it it:  of   • -  l.b.  the ;•
:M-,-in:. tu !mr:i o'j'.  in  '.i-.e h-ihhli-. .iiul in  the  rarefied .-.one  of the  fluidi:-.ed  l.*
                                                                              3
                                                                           DISTAKCi
                                                                                         16       24
                                                                                          X CRATE
         Figure 2.  Changt of Temperature (a) and Composition of
                  Combustion Product! (b) venut th* Fhiidi/ed Bed
                  D*pth with the Air Contumption Ratio Equaling
                  a . 1.1 .1  H2. 2 • CO: 3  CH4; 4 - Oj. 5 CO2-
         The  temperatures
the particles.   The it--
equalize os  a result of
honwgencous  mixtures in
because of  bad exchange
fact that accounts for
fluidizcd bet' when the
dynamically  no nitrogen
                                ••vn dy  ir.c  thurr-.ocouple  do not  always correspond  tป> those  of
                            pcratures  of the gas and the  "packets" are  seen  to quickly
                             intense  interphasc  heat exchange.   During  the coi7.bustion of
                             the  bubbles the temperature  in  them  reaches very hif.h values
                             between  the bubbles and the  particles (Figure 3).   It is this
                            the }-.esence of nitric  oxide  in  the cor.bustion products at the
                            thermocouple shows  1300-1400ฐC and at  such  temperatures thertr,o-
                            -oxygcn reactions are possible (Figure 4).
                                                   269

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       Combustion of  a  preliminarily prepared gas-and-air mixture  can be organized
both in experimental  systems  and in szali-size industrial furnaces used for fluicized-
bed heating of inecal  to tenperaturts of 900-130GฐC.

Combustion of Gas Partially Mixed with Air
                                                                             %
       It is possible to organize fluidizod-bed combustion of gas  partially mixed with
air by injecting the  gas-and-air mixture into the  ted through the  tuyeres (Figure Ib) .
or through the grate  (Figure  lc>-

       Studies of fluidized-bed combustion of gas  partially mixed  with air were conducted
with the use of 300 ind iOO trim dia experimental furnaces where 0.1-0.5 m fraction
river-sand acted as the,heat-carryin th*
           Air Coraumption Ratio Equaling a' 1.1.
           1 • bubbto; 2 • bubble trace; 3-4 • gas;
           0 • 0 • experimental data
                                              Figur.4.
                                     oncentration in Natural Gas
                           ranafMuiun Product*.
                            -'• - 1 atm; 0-0 - 5 atm; • - • - 8 atm-
                            ซ-ซ-tta?m; a . Q . tSairo
                                           270

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       The burning ouc of '.he combustible components is not always completed in the
zones of circulation, this process depends on the bed temperature, primary air consump-
tion rate and the nature of pseudofluiuized material; that is why there is always a
snail amount of methane and carbon oxide present in the combustion products over the
bed (Table I).


             Table i.  Data on Gas Combustion in 500 rat 
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gas conbustion in the bed sets  in when  the-  temperature of  the  fluidized bed is as hi^.h
as 650-870&C.  At this temperature there  is  no  hydrogen, carbon oxide or no thane- in the
combustion products if the air  conburr.ption  ratio  of  gas con.bustion is 1.3-1.7 and primary
nir consumption on the tuyeres  is 35-50/i  of  the steichiometric value.  With the increa.se
of secondary air temperature  from 100 to  50GฐC  co-plete fluidizcd.-bc.-d combustion of gas
is obtained with o = 1.1-1.2.   With  the tuyeres method of  t'luidizcd-bed cor.buction of
gas. a l:iG-2000C thermal gradient is observed  to  develop 'uctwcen the combustion /.one and
the fluidizcd bed core-.

Gas Combustion with Separate  Injection of Gas and Air into the Kluidized Bed

       The technique of  fluidized-bed conbustion  of  natural gas with separate injection
of gas and air was developed  in experimental and  operating industrial furnaces.
                  dia furnace the process  proceeded in the  following way.  -The air was
1.J-1..I.  v i :ปuii L uu:>ervui.iu[i:>  :iiiuwi u  i-iiciL  \>m n.>u i c i ugg ir>u ,
stretched tongues of bright yellow flarae vere  jumping,  through the lluidizcd bed. their
form being quite different from that  or the  ,:as  bubble.   The  flame moved both in the
vertical and horizontal planes.  The  natural gas  was  burning  out above Che bed.

       In a 2.75 m dia industrial furnace,  the natural gas was injected into a fiuidi/.ed
bed of 3-10 nan limestone particles under a  pressure of i atiri  and at a rate of 1700 m-Vhour
(Figure Id) through 20 no;:z!es of 7 ran diar.ซ.tcr.   I'he  nozzles were accommodated on the
periphery of the furnace shaft 200 mm above  tin-  grate.  The air for pscudofluidization
of the particles and gas combustion was injected  through the  ('.as-lining grate.

       The results of '.he test showed that  the li:ngth  of the  jet was 0.5 "'.  In the
circular space around the wall a surplus of  j-.-in  wa.% developed which burned ou'. above
the bed, leaving the center of the furnace without any g ••!.•ป.  The substitution of the
cylindrical nozzles for Lavalle nozzles did  not  improve  the completeness of gas ,_ mbuslion.
       The failure to obtain  fluid i.-.-il-bed  combustion of the i
through the peripheral tuyeres  is  n.-!_ropซ.
the air.  The air injected  into  the  bed  through  the gas-tiir.in,
between the particles in the  "packets" and  comes to the surfac.
as when it is injected
r mixture of the gas with
 grate undergoes filtering
  in thซ form of bubbles.
the movement both of the ซ:as and  the air  bubbles  coinciding, neither in time nor in space.
Tlie process of gas and air mixing in the  fluidi^ed  bed can be improved by injecting, the
gas into the grate zone in the  form of  thin  je^s  striking each other.   This technique
was used In a 3.8 m dia furnace for roasting antlmonic ore tails.

       The gas was injected into  the bed  through  56 gas caps uniformly fit'.i-d on the
sole of the furnace (Figure le) with a  rate  of  900-1000 m-Vhour.   tvory gas cap was
equipped with 9 air caps situated on a  3^0 mm dia concentric circle around It (Figure 5;
Figure le).  The rate of air consumption  through  each cap was 18.5 la-Vhour.  Altogether.
504 caps were installed on the  gas-timing sole.

       The gas and air jets were  directed toward  each other,  the  difference in their
heiphc being 80 ran.  Such an arrangement  prevented  gas combustion  in the space between
the caps.  During the two months  of the furnace's continuous operation the process of
fluldized-bed combustion of the gas was stable, no  lumping of the  particles or burning
of the caps was observed.  The  temperature ranr.c  of the bed 500 rai above the prate and
at a 200 ran distance fron the wall was  maintained at a level of 1000-1020 C.


CONCLUSIONS

       An analysis of the work  of industrial systems shows that gas combustion in large-
size furnaces can be organized  by using the  technique of injecting tha gas, ,>artially
mixed with the air outside the  fluidizcd  bed. through the tuyeres or by injecting t'.it
gas and the air into the bed by separate  jets.  Such furnaces are  of simple structure
and warrant reliable operation.
                                          272

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1 '
8 OPKHIKO.: 03 ป
9 CAPo
I
1
•o
1

• .'
/' '
T. *
•••*•
'ol

i

f •
i
3
040/25

t

.'-',-,'

>•





t •

- ^
0| 3 OP5iKlM3

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'

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oi

i
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              AliV
t All,
Figure 5.  Structure of Gat-Timing Grate with Separate
          Infection ot Gas and Air into the Fluiili/ed Bed
                                    273

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                        INTRODUCTION
     ROBERT CHRONOWSKI, CHAIRMAN:   We've  got  to continue our tribute
to the late Professor Elliott  here.  Our  next  speaker  is Dr. J. R.
Howard fron Aston University.   I  v/ant to  read  a little bit from
his own biographical sketch.

     Dr. Howard's interest in  fluidized bed combustion and heat
transfer was first stirred by  his talented colleague, the late
Professor Douglas Elliott. Dr. Howard continues to teach at Aston
University and is involved in  fluidized combustion and heat transfer
•esearch.  He has a long history  of research  and work with industry
and combustion activities, power  plant design, temperature control,
and production engineering.  The  paper deals with combustion experi-
ments within a rotating fluidized bed. The coauthor is Mr. C.
Metcalfe, who is sitting for his  Ph.D. at the  University now under
Dr. Howard.  Dr. Howard?
                                274

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                           Combustion Experiments within a
                                Rotating Fluidized Bed
                              C. I. Metcalte and J. R. Howard
                           Department of Mechanical Engineering.
                             University of Aston in Birmingham.
                            Gosta Green. Birmingham. England
ABSTRACT

       Rotating fluidized bed combustors offer the exciting prospects of raising tl-o
rate of heat release per unit volume of bed to dramatically high  levels and extending
the range of 'turn down' significantly.  1'esults obtained with a  gas-fired fluidized
bed coinbustor are discussed briefly and followed by an account of experience obtained
when burning coal, (anthracite).  The latter work exposed some of tho problems to t^e
ox'ercome before the lull potential of this combustion system can  be realised.  Start-
up, control and segregation problems are described and the direction which future
work should take is discussed.
NOMENCLATURE

c     Specific heat of sand particles

(CV)  Calorific value

H     Geometric mean particle diaroeter

g     Gravitational acceleration

B'    Ng

Ga'   Modified Oalilco number
                                           Q     Thermal output power

                                           Ko  ,  Reynolds number at minimum  fluid!?.-
                                             mf  ation

                                           t     Time

                                           T     Bed temperature

                                           V     Fluidty.jp •* velocity

            .,       .  ,-[.3                 t' ป   Minimum fluidization velocity

          ~~~~     2                       c     Particle density
                  u                         p

mc    Mass flow rate of anthracite         ฐf    Fluldlzing air density

n.p    Mass of sand particles in the bed    "     Viscosity of  fluidizing air

N     Integer


INTRODUCTION

       Because the particles in a rotating fluidized bed have  a high centripetal
acceleration imposed on them due to rotation of the entire bed about an axis parallel
to its free surface, as shown in Figure 1, high fluidization velocities are  possible
without nlutriation of particles from the bed.  The resulting  increased mass flow of
air allows a greater mass flow of fuel to be burnt, hence a greater rate of  heat
release within the bed.  For a given thermal output, a rotating fluldizeii bed cotabust-
or will be much smaller than a stationary type.

       In stationary fluidized beds, combustion can be controlled by altering the
fuel feed rate and fluidizing velocity.  The operable range of fluidizing velocity is
limited on the one hand by the mininun velocity at which the bed is properly fluid-
ized and on the other by particle elulriation.  With the rotiting fluidized  bed. the
operable range of fluidizing velocity can be extended by increasing the rotational
speed to prevent particle clutriation and reducing the speed to lower the minimum
fluidizing velocity.
                                        275

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                       Pneumatic Solids
                       Transporter

                        Air Feed
                        Fluidi/ed
                        Particles

                       Plenum
                       Chamber

                        Air & Propane
                        flotameler
                       Propane
                       Supply
Coal Hopper
Coal Feed
{



\



                                         *ir Supply
                                         Fan
Pressure
Tapcmg
HoikM Drive
Shaft

Rotary Seal
                     Figure 1. Schematic Layout of Rotating Fluidiicd Bed Conu-
triation.  This limit was then raised by increasing the rotational speed  so that the
fluidiซ:ing velocity  could be increased.  This method  of increasing the fluidizing
velocity was  eventually limited ty the residence tinve of the propane/air  cixture
within the bed  becoming too small for the necessary pre-heatinK to ignition temp-
crc'uro. so that the combustion reaction could  tako place within the bed.  This
condition will  be referred to as 'flame out*.
                                          276

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       The  r. i r. i - urn  thermal output  of the corsbuslor '.vas  1 imitr-d . conceptually., by:

       (a)   The largest  air:propane ratio r.t  which conbustion could bo  sustained.

       (b)   Th<- i^ininun  i luidiz.at ion velocity at  the lowest  rotational  speed aซ -.i
a reasonably ur.ilors  radial thickness of bซ"l  would occur.   (The shape of  the I rซ-e
surface  of  the betl  -xas parabolic  at low rotational speeds.)
        (c)   Fla=ซ-- preparation velocity exceodinK the ' luirli/ai ior. •.•••loci tj .  res
in burning  upst.-eae  of  the distributor.

        (d)   Vass.  flex of mixture  through tin-  distributor  iioinj; insufficient  to kr-.-p
the distributor cool.

        In j-ractice,  the f luidi ?.at inn velocity v.-as not alloyed to  fall  below 1 i vr-
tir.es  that  rซ-q-ired  for incipient,  f luidi zat ion of the !>• -I .   Thus  < <• ) and (d) dictated
the t-inir.uri practical  operatinc  the ma I out pi.. .   Xซ-vซ-ri nป- !<-ss .  the rorr.bi n"  'turn down' rat:-i to
5:1. co.-pared v.-jth about 2:1 ntit ainab !•• lith  sir. pie stationary l.i-ds . ( ^ • •' )   A t;.p:val
oporatine envelope is shov:n in i'ip;ure 2.
       The  experir.enta 1  work en  burning propanerair -ixiur'-s in rotating
bซ-d cor.bustors r.as  also  der.onstrat<-'J tin- capacity of this  >-.ystซ-m >o burn mixtures
which are si p.n : : icant ly  weaker than the publ isheil' f la.Tjr.ab i 1 i t y ii^.it  ' •>) .  thus 'jr,-.-rii ni:
up the possibility  c! burning w.vak  inilustrip)  fur."-.s wi.. h  a  IOV.IT ccnsur.pt ion "I .v.:x.l-
'ary jas. <">
                               80


                               70

                             I 60


                             1 50
                             u.

                             < 40
                             ง 30
                               20.
                               10
Loss of Fluidi/od
Bed Combustion
      Maximum
      Tempe'dJuie
      Limit
                             _
                             Data
                                  0   1.0  20  30  4.0  SO  60
                                     Hot Air Velocity (nv'sl
                                 Acceleration
                                 Particle Type
                                 Site Range
                                 Mass
                                 Distributor
   : - 30xg
   : • Silicon Sand
   :  180 250m
   :  600g
   : • Conidur No 10
                                Figure 2. Typical Operating Envelope
                                            277

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COAI. COMBUSTION

Te^t Equipment

       The rotating fluidized bod comhustor used for experiments described above v:as
u.s---d without modification apart from including a coal feeder.  A schematic arrangement
of the tost facility is shown in Figure 1.  Thr- distributor was raade of perforated
stainless stnel sheet rolled into the shape of a hollow cylinder 200 mm diameter and
67 mm axial length.  Tho lower plate carried the hollow drive shaft through which
fluidizing air was passed to the plenum chamber surrounding the distributor as des-
cribed in Reference 1.

       A water-cooled probe was located in the exhaust gas duct through which gas
samples were drawn for analysis.  A paramagnetic oxygen analyser and an infra-re'i
CO/CO,, analyser were used to determine concentrations and, for corroboration of these
analyses, a gas chromat.ograph calibrated with gas samples of certified composition
was used.

       The coal feeder was of the vibrating platform type, fed from a hopper bolted
to the platform, the coal feed rate being varied by altering the amplitude of the
vibration.  The coal particles dropped into the throat of a pneumatic particle trans-
port duct arranged to blow the coal particles through a nozzle on to the free surface--
of the rotating fluidizr-:! bed.  The position of the point of coal injection on to the
fluidized bed free surface wan adjustable so as to be able to find the most suitable
point at which to inject the coal.

       Initially, GOO g of silica sand particles of size range 180-250 urn were used
in the rotating fluidized bed.  The type of coal used was anthracite, crushed and
sieved to a size range GOO - 1000 urn  and of proximate analysis, moisture IT., ash -1.5%,
volatile matter 10%, fixed carbon 84.57..  The choice of the latter size range arose
because this produced excellent combustion in stationary shallow fluidized beds and
the anthracite could be crushed to this size economically.

Initial Start-Up Experiments

       The combustor was started from cold in the normal way, being fuelled by pro-
pane and allowed to reach a steady state with the bed temperature 950 C.  The super-
ficial fluidizing velocity was 1.1 m/s and centripetal acceleration of the bed part-
icles 10 x gravity.  When anthracite was fed ปo the bed at the ra'.e of 50 g/min.
(sufficient to give a thermal output of 25 kW), excessive elutriation of fine anthra-
cite particles occurred.  Clearly, the rotational speed hart to be increased, hut even
when the centripetal acceleration was 15 x gravity, the reduction in elutriation rate
of the fines was not very substantial.  However, the major part of the anthracite
particles reached the bed.

       The propane flow was t..en gradually reduced in an attempt to maintain the bed
temperature constant.  But even when the propane was shut off completely, the bed
temperature continued to rise, reaching 1140 C, at which point the anthracite feed
was stopped.  A non-uniform distribution of anthracite particles could be seen on the
free surface of the bed burning with a yellow flame.  More uniform anthracite dist-
ribution was achieved by movinc t!:e coal injection nozzle from the lower end of the
rotating fluidized bed to the upper end.  It was also noted that if the exit velocity
of the anthracite particles from the feed nozzle wei-.j increased sufficiently, local
breakdown of fluidization of the rotating bed occurred, and as Figure 3 shows, anthra-
cite became centrifuged towards the distributor where local fusion of particulate
matter had taken place.

       These difficulties demonstrated that operation of the above start-up procedure
which has hitherto been found adequate for stationary shallow fluidized bed coal
combustoi-s, is decidedly inadequate for rotating fluidized bed combustors.  Two other
manual start-up procedures were also investigated but neither gave satisfactory trans-
ition from propane fuelling to self-sustaining anthracite combustion.  However, for
the sake of c ,:tipleteness, the results are reported briefly below.  Commencing from
steady state combustion of propane, the procedures and results were:-
                                          278

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       lllljllll llllllllllllll
         M/H  ป
ir
                 •i
                        figure 3. Fused Paniculate Matter from Near the Distributor
       (a)  Feeding of anthracite  commenced  at  the  rate of 50  g/min for one minute.
The propan*? supply was then shut off quickly.   This  resulted in  rapid reduction in
bed temperature and cessation of combustion.  During the period  of simultaneous
supply of propane and anthracite,  local  fusion  of sand  and some  clinkering occurred,
disturbing the mixing of particles in  the  bed.

       (b)  Simultaneous commencement  of anthracite  feed at SO g/min and cut off of
propane supply resulted in quenching of  combustion  alone.

       In order to make progress and explore  the mechanism of  transition from propane
to anthracite combustion further,  some ancillary tests  to examine particle mixing and
bed cooling characteristics were carried out.

Ancillary Tests
       With the bed operating on propane  at  950ฐC,  superficial  fluidizing velocity
1.1 m/s and centripetal acceleration  15 x gravity,  the  propane  flow was shut off
suddenly and the mass  flow  rate of  fluidizing  air held  constant.   The exhaust gas
temperature was recorded continuously  for about  10  minutes.   The  average rate of
                                         279

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cooling during the first 30 seconds was used to estimate the mass flow rate of anthra-
cite required to maintain the bed temperature at. 950 C fron equation (1).


                             rapCp 
0-30s - *c (CV) (1) This simple relationship however ignores the heat input required to the anthra- cite particles from the hot bed to raise their temperature to ignition point. It also says nothing about the ma.ss of anthracite u-hich, at any desired thermal output from the combustor, must reside in the beci. Despite the lack of these data, it was decided to c:irry out brief start-up trials at anthracite flow rates estimated from equation (1), to obtain further insight into their effect on the transition process. The results of these trials are discussed under "Further Start-Up Trials" later in the text. Mixing Anthracite and Sand Particles A half-scale perspex model of the cotnbustor which was capable of imposing accelera- tions of up to 30 x Gravity on the particles was used to investigate particle mixing patterns visually with the aid of stroboscopic illumination. The independent vari- ables were: (a) Sand particle size (b) Fluidizing velocity (c) Anthracite particle si*e Anthracite and silica sand particles v.ere selected so that each would have similar minimum fluidizing velocities. The correlation formula used was equation (2) below, which is due to Wen and Yu.<7> Remf = (33.72 + O.0408 Ga']S - 33.7 (2) Equation (2) predicted the final particle size ran^e choices as:- Silica sand 250 - 355 urn Anthracite 300 - 500 um mixed in the proportions 20 grams of anthracite to 200 grams of silica sand in the bed. Figures 4a, 4b and 4c are stroboscopic photographs obtained with the perspex model of the rotating fluidlzed bed combustor with the above particle mixtures at various fluidizing velocities >vhen the centripetal acceleration on the particles was 10 x gravity. It will be seen, Figure 4c. that at a fluidization Index, U/U ... of about 2.85, the mixing of sand and anthracite particles is very uniform and there Is no elutriation. Conclusions from Initial Start-L'p Experiments and Ancillary Tests 1. Anthracite feed rates calculated from equation (3) below: Q = Ac (CV) (3) used for the initial start-up experiments are too large to effect transition from propane fuelling to self-sustaining anthracite combustion. 2. Selection of both sand and anthracite particle sizes can be critical because uniform mixing of anthracite and sand is essential for the avoidance of local hot zones and fusion of particulate matter. 280

-------
                          Fijdre 4a. Slroboscopic Photograph of Free Surface
                                   U/Umf • 0.9      Umf • 0.4 m/i
           More generally, differences  In  density,  size  and shape of particles tends
to promote segregation.  Radial segregation  seems  to be  accentuated In  high gravlta-
lonal fields, while axial segregation is affected  by the positioning of the anthracite
feed point.  Where possible,  the  former differences should be kept as small as practic-
able because good mixing is desired.

       3.  In the above tests, the  radial  thickness of the bod was almost  uniform to
promote uniform fluidization  and  only about  10  mm  thick  in order to maintain a low-
pressure drop, (<150 mm water across the bed at 15  x gravity).  However,  it has been
shown in rotating bed experiments at ambieiit temperature by Demtrcan and  Swithenbank(s
that very good particle mixing can  also be obtained when operating the  bed in a tumbl-
ing mode.

       4.  When running continuously on solid fuels, ash removal becomes  an important
requirement and further experimentation is required to establish a satisfactory compro-
mise between good mixing of fuel  and sand, segregation of ash and the possibility of
excessive air by-pass and non-uniform fluidization.
                                          281

-------
Figure 4b.  Stroboscopic Photograph of Free Surface
             U/Umf • 1.97      Umf - 0.4 m/t

-------
U)
                                                       Figure 4c.  Stroboscopic Hhotograph of Free Surface
                                                                   U/Umf" 2.85      Umf • 0.4 m/$

-------
Further Start.-fp Trials

       New experiments enabled start-up to be performed using  the  sand  and  anthracite
particle sizes found to give satisiactory mixing by  the ancillary  tests.  The  new
start-up procedure from full propane  firing at 950 C with an acceleration on the
particles of 15 x gravity was:

        (1)  Shut off propane completely and simultaneously commence  feeding anthra-
cite ;t the rate of 50 g/min for the  first 30 seconds.

       .Mi)  Thereafter, reduce the anthracite feed  rate to 30 g/min.

Results

       Sclf-suf>tait ing anthracite combustion was achieved, but the combustion  quality
was not always satisfactory.  However, the best dry  exhaust gas analysis obtained was
0.1% CO, 0.14* II,,, 8.7% C0_, 9t Op.   Localised overheating caused  some  sintering of
the silica sand,  see photograph  in  Figure 5, but there was no evidence of general
migration of anthracite particles towards the distributor as occurred with  the initial
start-up  xperiments on burning anthracite.
                                                      3
       The nominal intensity of combustion was 35 MK/m  of fluldized bed.
                                FigunS. Fined Silica Sand
                                         284

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GENERAL CONCLUSIONS

       1.  Although it was possible to obtain self-sustaining cor.bustion of anthra-
cite by manual control of transition Iron steady combustion of propane, some form of
automatic control of the transition process is desirable, particularly if no heat
transfer surfaces are located in the bed for control of its temperature and the
thermal capacity of the bod is small.

       2.  There is at present insufficient data for design of a control system for
effecting satisfactory transition from propane fuelling to self-sustaining combustion
of anthracite.  The data required are the times required for pre-heating the anthra-
cite particles to ignition temperature and to burn to extinction together with the
bed heating and cooling time constants under rotating fluidized bed conditions.

       3.  When compared with stationary fluidized bed combustors, the rotating type
has a very low thermal capacity for its thermal output, air and fuel flows.  This
gives it the characteristics that rapid changes of bed temperature occur with changes
in fuel flow when burning gaseous fuels which ignite and burn rapidly.  When operating
on solid fuels, however, heating to ignition temperature and burning of the fuel part-
icles takes a longer time, so that the temperature response of the bed to a chango in
fuel feed rate is not immediate.  After this dflay, the bed temperature can then
change in a rapid and uncontrolled manner.  This points to the need for an antici-
ptttory control system.

       4.  Increasing the thermal capacity of the bed will help alleviate the above
problems but the extent to v.-hich this can be done and the best way of doing so is a
matter for further investigation.


ACKNOWLEDGEMENTS

       The work described hero is part of a programme supported by the National
Research Development Corporation.

       This paper could never be complete without, the authors expressing the debt
they owe to their inspiring colleague, the late Professor Douglas Elliott, for the
encouragement and invaluable advice he gave.  His sad death in June 197G deprived the
engineering profession of one of its most imaginative, creative an~ truly courageous
spirits.


REFERENCES

1.  r. I. Metcalfe and J. R. Howard, "Fluidization and Gas Combustion in a Rotating
    Kluidized lied".  Applied Energy (3), (1977), pp 65-74.

2.  C. I. Metcalfe and J. R. Howard, "Towards Higher Intensity Combustion:- Rotating
    Fluidized Beds".  To be published at Engineering Foundation Conference on
    Fluidization, Cambridge, April 1978.

3.  C. R. Westwood, (1975), PhD Thesis, University of Aston in Birmingham.

4.  K. K. Pillai, (1976), PhD Thesis, University of Aston in Birmingham.

5.  H. M. Spiers, "Technical Data on Fuel"  The Hritish National Committee World
    Power Conference, Lor.don, 1961, p 260.

6.  British Patent 1 471 598 (27 April 1977).

7.  C. Y. Wen and Y. H. Yu, "ft Generalised Method of Predicting Minimum Fluidization
    Velocity".  A.I.Chem.E. Journal 12 (3), May 1966.

8.  N. Demircan, B. M. Gibbs, J. Swithenbank and D. S. Taylor, "Rotating Fluidized
    Bed Combustion", to be published at Engineering Foundation Conference on Fluidiz-
    ation, Cambridge, April 1978.



                                        285

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           QUESTIONS/RESPONSES/COMMENTS
     SHELTON EHRLIfH, CHAIRMAN:  Do we have any questions?  Last
call.  This is from Frank  Hill of Brookhaven National Labs and the
question is addressed to Dr. Howard and Dr. Levy, who is going to be
the next speaker and who is going to describe something not unlike
what we have just heard.   "Have you been able to make any observations
on bubble behavior in the  rotating system?  How might bubble dynamics
in the rotating system  differ from bubble behavior in the stationary
system?"

     DR. HOWARD:  Well, I  think I won't answer for Professor Levy.
He will also be able to answer for himself, but I will say that our
experience at Aston is  that we certainly observed the bubbling in the
bed when it was taking  place—when the bed was rotating.  There were
earlier papers that implied that bubbles would not form; but in fact,
there is a bubbling motion that takes place, certainly, and I
can show photographs of this to prove it.

     The other aspect of it, namely, how might bubble dynamics in a
rotating system differ  from bubble behavior in stationary systems—or
how might the process be modelled—I don't really know the answer to
that one.  I would say  that bubbles certainly form (and with the beds
that I was playing with, whose radial thickness was quite thin, 10
millimeters or so) the  bubbles were fairly small and well-distributed,
and what you might reasonably expect out of a shallow fluidized bed
(a stationary fluidized bed, of course).  That is work that remains to
be done.

     SPEAKER (not identified):  We have made pictures of the surface
of our bed, and we can  see bubbling occurring.  We don't have any
quantitative information on the rate at which they grow, or the
relationship between fluidizing velocity and bed depth and bubble
size.

     SHELTON EHRLICH, CHAIRMAN:  Thank you.  We are going to have a
coffee break now, if there are no further questions.
                                286

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                     INTRODUCTION
     SHELTON EHRLICH, CHAIRMAN:  Ed Levy?  Come on up.  If you are
here to listen to  the second portion of the second session on tech-
nology test installations, you're in the right place.  All right.
Can we all  get ourselves  seated now?

     The next speaker, who will talk on "Centrifugal  Fluidized Bed
Combustion," is Ed Levy of Lehigh University.  He has a degree in
Mechanical  Engineering and I think it is a delight to see a mechanical
engineer amongst all these chemical engineers once in a while.  He's
been at Lehigh for the last 10 years.  He works in heat transfer,
fluid mechanics, and energy conversion.  Come on up,  Ed.
                                287

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                          Centrifugal Ftuidized Bed Combustion
                            Er'-vird K. Levy, Norman W. Martin and
                                       JohnC. Chen
                                      Lehigh University
ABSTRACT
       Centrifugal  fluidizcd bed combustion  is  a  relatively new concept  for coal  com-
bustion, where  the  bed rotates about  its vortical  axis of symmetry and the  fluidizing
air  flows  radially  inward through the porous cylindrical  surface of the  distributor.
l.chigh University has been involved  in analysis and  experiments with centrifugal  beds
since l'.'~4  and  is presently performing room  temperature fluidization experiments.  Oata
arc  presented on the effects of particle size,  bed mass,  angular velocity, distributor
taper angle and distributor pressure drop on minimum fluidization and bed pressure
drop.  Analyses which predict bed shape,  niiniraum  jfluidi z;it ion and bed pressure drop are
described and compared with the data.
I \TROIitlCTION

       Centrifugal  Huidiznt ion is a relatively new  ftiiiilizeil bed concept, where  the
bed rotates abou.  it's  axis  of  symmetry and the fluidizing  air flows radially  inward
through the porous  cylindrical  surface of the distributor  (l-igure 1).   The inward drag
force of the  fltiidizing  air on  the bed material is balanced by the large radial accel-
erations caused  by  the rotational  notion, permitting  much  larger air flow rates per
unit volume than arc possible  with a conventional  fluidizcd bed cr crating vertically
against gravity.
                                                        ROTATIONAL POWER
                                                 ID"
                         HOT GASES
                               ,-PLENUM
                              / VESSEL
                                 AIR
                                 DISTRIBUTOR
                                              S
                                                 10"
                         V SOL I OS REMOVAL

                         BEARINGS AND SEALS
       50      100     ISO     200

       ANGULAR VELOCITY, ct/0 (f/mcn)
                                                                                      250
  Figure 1. Conceptual Drawing of Centrifugal Flurdirad
         Bad Comfauttor
Figure 2. Electrical Capacity of a Combined Cycle
       Power Plant
                                          288

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       The rotational motion of the system gives it a number of distinct operating ad-
vantages, which make this device interesting for coal combustion applications.  The
high fluidi:ing velocities provide for a compact system with relatively easy startup
and fewer problems with solids feed and bed mixing.  In addition, !>;. varying the ซpeed
of rotation of the bed, the bed temperature, and the fluidi:ing velocity, the thermal
power output of the device can be varied over an extremely wide raime.  Some of these
advantages arc illustrated in Figure 2, which shows the theoretical electrical output
of a large utility combined cycle power plant utiliii*;! a centrifugal fluidized bed
coal combustor.1  The combustor operates at 10 atrosphcrcs and 8"(lฐC and has a distri-
butor which is 3.04 m in diameter and 2.28 a high.  With a nornal operating point on
curve 5 and an angular velocity of ISO rpm, the system would produce approximately
500 Mh'c.  By decreasing the speed of rotation to 75 rpn and the velocity of the fluid-
i:ing air to minimum fluidi:ation conditions, the power output would be reduced to
50 MlVc.

       Past re earch on centrifugal f luidizat ion includes experiments on minimum fluiJ-
1^.2.' ion and bed pressure drop performed at I'.rookhavcn National Laboratory and the Air
Force Acrosnacc Research Laboratory,-"'" cxpcr'.nicnt s by Ccl'pcrin in Russia on bed be-
havior,''"6 anu experiments by Farkas and his colleagues of the II. S. Pepartncnt of
Agriculture for food drying applications.7  At present, research is underway at
Brookhavc!> National Laboratory on the use of centrifugal fluidiied beds for flue gas
dcsul fur izat ion,h by Metcalfe and Howard in Crcat liritain on fluidination phenomena
and gas combustion,' and by Swithcnbank ct al. in (Irejt Britain on coal combustion.10

       I.ehigh University has been involved actively in analysis and experiments witli
centrifugal iluidized beds since 1!>74.  This includes parametric analyses of centrifu-
gal fluidizcd bed combustors,'•'' studies of fluniiicd bed cycles for combustion appli-
cations,12 and theoretical and experimental studies of minimum fluidi:ation. particle
clutriation, bed pressure drop, and bed startup. l 3 • ' "*

       This paper describes recent experiments performed at room tcmpeiature and at-
mospheric pressure on f1uidi:ation.  A theoretical analysis which predicts the onset
of minimum fluidi:ation and bed pressure drop is described and compared witli experi-
mental data.


RF.VIF.IV OF Till; TIIHORY

       The experimental results described in this paper were obtained with tancred
distributors, having the larger diameter at the top.  From other experiments,^1 it was
found that the presence of a slight distributor taper angle is very useful in achiev-
ing distribution of bed material over the entire distributor surface.

       For given bed dimensions and particle and gas densities, the important varia-
bles effecting minir.um fluid i ;at ion and bed pressure drop arc distributor angle T,
total weight of bed material, distributor pressure drop, angular velocity of the bed,
and particle diameter.  Because of the influence of gravity and the coniril shape of
the distributor, the bed thickness varies in the vertical direction.  An analytical
model, described in more detail in Reference 15, was developed which accounts for
vertical variations in bed thickness and air velocity by treating the system as a
scries of "n" elements, each of height l\z (sec Figure 31.  The total pressure drop
across the grid and bed for each clement is given as


                                tPT "  Pr>RII) * APBF.n                                (1 *

If the bed is packed locally, the bed pressure drop is equal to


                     *PBED

                               1.75(1-^1 „ ,.. , , * |_i_ . _i_|                        (2)
If the bed is fluidizcd locally, the voidage c is independent of radius, and the bed
material is in rigid body motion, the expression for bed pressure drop is


                                         289

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                                                                                     (3)
Tor thin beds, the radial velocity at minimum fluidizat ion, calculated at  the outer
raJius of the bed, reduces to
                          Ca = [150(l-c)/c
1 1 . 7S/ Jc 3 IRe2
                                                                                     (4)
The calculation procedure assumes a value for APr and uses equation  (1J  to compute
        for each of the n elements.  The total mass flow rate through  the distributor
                             m(APT)
                                                                                     (5)

EXPLRIMUNTAL APPARATUS

       The test section consists of a 0.3 m diameter, 0.15 in high distributor  contained
in a square air plenum.  The distributor is fabricated  froin reinforced  fine  mesh screen
and the top end wall is transparent for visualisation of  flow.  A variable speed motor
is used to rotate the distributor by means of a shaft connected to  the  bottom  end wall
of the test section.  Room temperature air is supplied  to the plenum  fiom a  compressor.

       In all experiments the apparatus was b;itch operated, where a Riven charge of
     atcrial was loaded into the test section and the distributor was accelerated tr<>m
bed material
rest to the desired angular velocity.  The experiments were  performed  with  glass
having narrow particle size distributions with mean diameters  of  121,  351 and 475
                              beads
                               urn.
TIIUORF.TICAL AND LXPURIMF.NTAL RI-SULTS

       Theoretical results were obtained on the effects of  distributor  shape and oper-
ating conditions on bed thickness.  Typical results of the  analysis  arc given in l:ig-
ures 4, 5, and 6 as a function of distributor angle anJ angular  velocity.   The  graphs
indicate the  large non'jni formi t ies  in bed thickness which can  occur,  particularly with
small bed masses and low angular velocities.  An  extreme situation  is presented in
Figure 5 for  a 2ฐ taper angle and 1.5 kg of bed material, where  the  bed docs not cover
the top of the distributor at low angular velocities.  The  opposite  trend  is shown in
Figure 6 with a bฐ taper angle, where the bed thickness  increases  in the vertical di-
rection.  Measurcir.-nts of hcd thickness made at the top  transparent  end wail of the
test section  are in good agreement  with theoretical results.   l-'igurc 7  shows bed thick-
ness as a function of air flow rate for.a 3.47ฐ grid with 1.5  and  4.5 kg of bed ma-
terial.  Once the bed is fluiJi:cd  (at m^f) bubbles erupt from vi.^ bed  surface, cuus-
inc an apparent increase in bed thickness.

        Ihe vertical variations in bed thickness lead  to  a nonuniformity of fluiJiia-
tion at transition from a packed to a fluidi.'.od slate.   Th'-,  is  illustrated in  I-i cure
8, showing the variation of bed pressure drop with  lir  flow rate,  and l:igurc :>, showing
                              r, (ป)-
                          Fijure 3. Mo0el of Bed (or Analysis of Fluidiutien

                                          290

-------
    O.IS
u  0.10
u
z

in
                 6*   10'      2' 4ซ 6' 8*  10*      2ซ  4'  6ซ
                     5*8
                                        4.5kg
        0                    0.02                  0.04                 0.06
                                 BED THICKNESS (m)


       Figure 4. Predicted Bed Thickness for Sev ;al Bed Masses at 26.2 rad/s




   0.15  •
   0.10  •
in
a
   0.05
x
4
                             -4.5kg
7.5 kg
        0         0.01        0.02        0.03       0.04       0.05        0.06

                                 BED THICKNESS (m)



       Figure 5.  Predicted Bed Thickness for Several Bed Masses with 2ฐ Grid Angle
   0.15
                                                            7.5kg
                 0.01
                            0.02       0.03       0.04

                                BED THICKNESS (m)
                                                              0.05
                                                                         0.06
      Figure 6. Predicted Bed Thickness for Several Bed Masses with & Grid Angle
                                  291

-------
G
en
Ul
z
U
I
o
tu
00


0.04



O.02

O
O
C
(rt
UJ
z
1C
ซJ
X
1-
o
UJ
Ok
2

.



1
r1
'j

I.5.,O SURFACE
dp ป 4 75 > 10 n* " ^-/
<-. 36.7 rod/, 4.5 k,Q SURFACE
™ * J.^ f
Deป0.l02m 4.5hg\79U8BLE PEAK
GRID * 1

•
V

V
El
•61
i 	 TT™ IS— g-1-
r 	 ^x^.0..
T , ! . "^
                                                         3.0
                  O.I     02     0.3     0.4
                   AIR FLOW RATE  (ms/$)

     Figure 7. Comparison of Theoretical and (Experimental
             Results on Bed Thickness
                                                     3
                                                     S
                                                     S  1.0
                                                     o
                                                        O.3
    ua> 36.7 rod/*
    ซp -SSOllO"*!!!
    a • 3.5ป
    1.9 kg BED MASS
0      O.09     O.IO     O.IS     O.ZO

      VERTICAL DISTANCE. Z (m)


Figure 9. Axial Variation of Radial Velocity
   2,500
                                 Ctป0ซ 36.7 rod/ป
                                 dp ซ350ปIO'6m
                                 a ซ3.5*
                                 I.S kg 8EO MASS
                        •0.38
                         O.4I
                         O.45
                                                      4.000
                                            -  3.000
                                            o.
                                            o
                                            
-------
       Theoretical and experimental  results  showing the effects of angular velocity
and bed mass on fluidization are given  in  Figures  10 and 11.  For these conditions, a
4.5 kg bed mass corresponds to an approximate  bed  thickness of 2.5 cm.

       The analysis and experiments  both show  a  strong effect of grid pressure drop on
fluidization.  Several different grid resistances, with the measured grid pressure drop
characteristics shcvn in Figure '2,  were used  in the experiments.  Figure 13 shows the
effect of grid resistance on bed pressure  drop as  predicted by the theoretical analy-
sis.  Generally, the influence of grid  resistance  is felt only during transition  from
a packed to a completely fluidized state.  The smaller the grid pressure drop, the
longer the re?ulting transition.  In the case  of a very low grid pressure drop, transi-
tion from minimum fluidization to complete fluidization may require such a large  in-
crease in air flow rate that particle clutriation  occurs before complete fluidization.
Figure 14 shows the theoretical axial variation  of radial velocity at minimum  fluidi-
zation for different grid  resistances.  A  small  flow resistance leads to extremely
large axial variations  in  velocity and  as  the  grid flow resistance approaches  zero,
the velocity nonunifornity can be large enough to permit clutriation to occur  immedi-
ately after the first ring of bed material is  fluidized.

       These effects were  observed in the  experiments shown in Figure IS.  Using  a
1.5 kg bed mass, the bed pressure drop  data  and  theory for grids 1 and 2 both  exhibit
a well-defined transition  between the packed and the fully fluidized states.   Once
fluidized, the bed pressure drop  is  relatively insensitive to air flow rate.   The low
grid pressure drop case, grid 0,  gives  radically different bed pressure drop behavior.
Transition to a fluidized  state begins  at  a  lower air flow rate and continues  to  very
high values of flow rate.  This very long  transition region is marked by a bed pres-
sure drop which increases  continuously  with  flow rate after the initiation of  fluidi-
zation.  bimilar results are shown in Figure 16  for a thicker bed where particle  elu-
triation occurs before  minimum  fluidization  when grid 0 is used.

       Through analysis of these  results and others, it is concluded by the authors
that the ratio of grid  to  bed pressure  drop  at minimum fluidization should be  greater
than 0.2 if the bed is to  fluidizc with a  narrow well-defined transition region.
     7.0 OO
     6.000
  ~.  5.000
  a
  o
  e
  o
4.000
     3.000
  O
  kJ
  O
     2.000
     I.OOC
       Oe- 0.1524m
       3P ซ475ซIO~6m
       wซ36.7rod/s
       GRID- 2
       o .3.47*
                                                 7.000
                                                 6.OOO
                                           5.000
                                         oT 4.0OO
                                         o
                                         cc
                                         o
                                         U
                                         oc
                                         2 3.000
                                  1.5kg
                                  CซO.4I
                                                 1,000
                                                           BED MASS • 0
                                                           c~>' 36.7rod/ป
                                                                 GRID 3
                                                                 ซ• 5.19*
                                                                              GRID 0
                                                                              aซ 3.47ป
          0     O.I     0.2     0.3    0.4

                 AIR FLOW RATE  (mS/t)

         Figure 11. Effect of Bed Mats on Bed Pressure Drop
                                                0     O.I     0.2     0.3     0.4

                                                       AIR FLOW RATE  Im5/f)

                                            Figure 12. Measured Grid Pressure Drop Characteristics
                                         293

-------
   s.ooo
ฃ  4.000
u  3.000
   2,000
    I.OOO
                 BED MASS-3.Okg
                 De •O.IS24m
                  aซ4ซ
                  C -0.42
                 dpซ35lซIO"6m
                            GRID 0
                      -GRID I
                O.I      0.2      O.3      0.4-
                 AIR FLOW RATE (ms/ป)
                                                       4.000
                                                       3.000
                                                    u  2.000
                                                        1.000
    -— MEASURED APC
    	 THEORETICAL  APe
    BED MASS' 1.5kg
    3p-475ซIO"6m
    W36.7:od/ป
     •ป• 3.47*
     DATA | CRIP
           0
            I
           2
                                                                                             AP6. GRID 2
                                                                                                     GRID 0

                 AIR  FLOW RATE (m3/ป)

Figure 15. Effect of Grid Resistance on Transition;
         Thin Bed
   Figure 13.  Theoretical Effect of Grid Resistance on
             Bed Pressure Drop
        10
            &J-20.9 rod/*
            dpซ35lปIO"6m
            a .4*
            6 -0.42
            BED MASS* 3.0 kg
                                   GRID 0
                                   GRID 2
                                     UMF
          0      0.05    0.10     0.15
              VERTICAL DISTANCE. Z (m)

    Figure 14. Theoretical Axial Variation of Radial
             Velocity; Low Angular Velocity
                                                        7.000
                                                        6.000
            AIR FLOW RATE
 Figure ia  Effect of Grid Resistance on Transition•
           Thick Bed
                                                 294

-------
     6.000
      5.000
   - 4.000
   a.
   o
   cr
   o
     3,000
     2.000
1,000

A
0
a
3P |MF
I2IXIO"6
351 ป IO'6
475xlO~6
TMEO
0.027
O.IO8
0.230
                         BCD MASS > 3.0 kg
                            36.7rod /ซ
                         GRID I
                         aซ 3.47*
                                               4.000
                                               3,000
                                             o
                                             DC
                                             O
                                             ir  2.OOO
                                          I.OOO
          O.I     0.2     0.3    O.4
           AIR FLOW RATE tm3/j)

      Figur. 17. Effect on Particle Size
                                                                 AIR FLOW RATE ds  and
large particles.  Low grid  pressure drop and particle noisturo arc believed  to  nc re-
sponsible for the anomalous fluid i :at ion behavior observed with the snail  particles.

       The flow resistance  of the  grid is an important factor in determining  the  qual-
ity of fluidii.it ion.   As with conventional  fluidizcd beds operating vertically  against
gravity, sufficient Rii
-------
RUFP.RP.XCnS

 1.  E.  K. Levy and .J. C. Chen, Proceedings 01' the International Powder and  Bulk
     Solids Hand 1 ins a"d Processing Conference, Rosemont,  Illinois,  1977, p. 452.
 2.  Brookhaven National Laboratory, "Rotating Pluidi:ed Bed Reactor  for Space
     Nuclear Propulsion," Upton, New York, Reports BNL 50321, August  1971; and
     BNL 50362, September 1972.
 3.  L.  Anderson,  ct al., .>. Spacecraft, Vol. 9, Xo. 5, May 1972: p.  311.
 4.  .J.  Howard, Air Force Aerospace Research Laboratories, "An l:xper incntal  Investi-
     gation of Heat Transfer in a Rotating Fluidiicd Bed," ARL 75-0115, IVright
     Patterson Air Porce Base, Ohio, May 1975.
 S.  N.  Get'pcrin, V.  C. Ainshtein and 1. U. Ooikhman, Khimichcskoc  i Xoftyanoc
     Mashinostro-;nic (translated from Russian), No. 5, 1964, p. 18.
 6.  X.  Gel'pcrin, P.  D. l.cbedcv, V. C. Ainshtein and C".. N. Napalkov, Kh imichcskoc
     i Ncftyanoc Mashinost rocnic (translated froir Russian), Xo. 5, 1966, p.  5.
 7.  I).  l:. Parkas, ct  al., Pood~ Technology, Vol. 25, November 1969, p.  125.
 8.  P.  Hill, Brookhavcn Xational Laboratory, personal communication, August 1977.
 9.  C.  I. Metcalfc and .1. R. Howard, Applied Energy (3),  1977, p. 65.
10.  X.  Demircan,  G. Gibbs, .1. Swithcnbank aniT~l). S." Taylor, Fl'ii dilation,
     Cambridge University Press, 1978.
11.  E.  Levy, ct al.,  "Parametric Analysis of a Centrifugal Fluidized Bed Combustor,'
     ASML Paper 76IIT68, 1976.
12.  IV.  Shakespeare, P.. K. Levy, .J. C. Chen and V. Kadambi, Proceedings of the 1977
     Intersociety  F.nergy Conversion Engineering Conference, Washington, D.C.,
     August 1977,  p. 751.
13.  I;.  Levy, N. Martin and .1. Chen, Fluidizat ion, Cambridge University Press, 1978.
14.  K.  Levy and J. Chen, Lchigh University, "Centrifugal  Pluidizcd Combustion of
     Coal," Quarterly  Reports PP.-2S16-1, .January 1978; PE-2516-2, April 1978;
     PP.-2S16-3, July 1978.
                                          296

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            QUESTIONS/RESPONSES/COMMENTS
     SHELTON EHRLICH,  CHAIRMAN:  Do we have any questions?

     WILLIAM REID,  EPRI:  What  is 1000 pascals in terms of inches of
water?

     MR. LEVY:   1000 pascals  is approximately 4 inches of water.

     SPEAKER (not identified):  A rather obvious question is whether
you think that  this rotating  system could be built to work in an
industrial or some  sort of  practical application eventually.  But
what I would really like  to ask is whether you know of any precedent
of a moving system  in  an  application where it has to work under
severe conditions for  a long  period of time and so forth.  Is there
anything analogous  to  this  that has been successful?

     MR. LEVY:   IV sorry.  Would you repeat that question?

     SPEAKER:  Well, the  elementary question is:  Is it really
practical to think  of  such  a  system working in—you showed it as an
application for a combined  cycle.  Can you really imagine such a
system, with a  rotating member, operating year after year that you
could maintain, and so on?  But supplementing that, I wonder whether
there is any precedent for  something like this—whether you can think
of some other application where, you know, something of this sort did
operate successfully?  Maybe  that's too involved a question?

     MR. LEVY:   I don't know  of any other precedent.  The gas turbine
is a system that has very high  temperatures and a relatively, perhaps
not as dirty an environment as  this, and that operates at very high
speeds of rotation. I am not sure I can cite any precedents for
this system.  We do believe that it has very good potential for the
kinds of applications  that  I  described.  Jack Howard has described
others, and there are  other people working here in the States and in
Britain who are convinced that  the thing has merit.  I don't know
what else to tell you  at  this point.  It is in a very early stage of
development, and we certainly can't point to a "Rivesville" yet.  You
would have to give  us  time  to ao that.

     SHELTON EHRLICH,  CHAIRMAN:  Any other questions?  Okay.  Thank
you, Ed.  Bill  Reid's  question, "How many inches is 1,000 pascals?"
reminds me of a thing  that  happened to us at EPRI two weeks ago.
We were sent a  stack of reports from the Environmental Protection
Agency about that (indicating)  high for us to review and comment on
                                297

-------
today, regarding the justification  for revised  new source performance
standards.  I  was given one of  these  reports  to review, and it wos
all in the SI  units.  And if anyone can tell  me what  a heat rate is
in 2340 kilojoules per kilowatt/second, when  you can  come to work for
us.  (Laughter).
                                298

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                       INTRODUCTION
     JOHN WILSON,  CHAIRMAN:  Our third speaker, is going to discuss
the chemically active  fluid bed.  Dr. Gerald Moss is with us this
evening.  He is an Engineering Associate at the Esso Research Center
in Abingdon, Oxfordshire, United Kingdom.  He is the inventor of the
chemically active  fluidized bed system for regenerative desulfuriza-
tion of fuels during either full or partial combustion in a fluid-
ized bed of line.   He  is also the author of some 25 issued patents.

     Dr. Moss is currently developing a range of new projects in the
field of fuel processing and energy conservation, some of which were
derived from the chemically active fluidized bed principle.  This
evening he is going to discuss with us the Progress in the Development
of the Desulfurizing Gasifier.  Dr. Moss?
                               299

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                          Progress in the Development of the
                                Desulphurising Gasifier
                                     Gerald Moss
                             Esso Petroleum Company Limited
ABSTRACT

       The development of the E.P.A.  sponsored Chemically Active Fluidised Bed de-
sulphurising gasifier has now reached the demonstration phase and a 20 MWe unit is
under construction at the La Palma plant of Central Power and Light at San Benito in
Texas.

       Although the gasifier was originally designed to burn residual fuel oil, it has
been established that solid fuels can also be gasified and desulphurised.  The paper
deals with the operation of the Abingdon pilot plant on coal and also describes what
appears to be a feasible and attractive technique for the reduction of SO2 to ele-
mental  sulphur within the regenerator of the gasifier.


INTRODUCTION

       The C.A.F.B. principle for regenerative desulphurisation during combustion was
disclosed at the First International  Conference on Fluidised Bed Combustion and is
described in more detail in a paper given to the Institute of Fuel Fluidised Combustion
Conference in 1975 (1).  It is somotimes described at the one-stt-p regeneration process
and is the subject of patents held by Exxon Research and Engineering Company.

       The pilot plant which was built with the support of E.P.A. at the Esso Research
Centre at Abingdon has also been described previously (2), (3).  The gasifier is a two
reactor unit, both reactors containing beds of lime fluidiscd with air.  Bed material
is exchanged in a controlled manner between the two reactors which are of the same-
height but differ considerably in tiiameter.  The large reactor is the gasifier.  It
operates at about 900ฐC and fuel introduced below the surface of the fluidised bed is
partially combusted.  Normally about  80*. of the sulphur in the fuel is retained by the
bed material as calcium sulphide.  The bed material also retains metals which tho fuel
may contain.  The regenerator is operated at about 1050 C being held at a higher temp-
erature than the gasifier by the exothermic oxidation of CaS to lime and SO0.  The
regulated flow of ted Material between the reactors controls the regenerator^ temper-
ature and at 1050ฐC sulphur dioxide is formed in the regenerator at a concentration in
the region of 7-8" by volume.  Diagrammatic cross sectional •. jrvป of the first unit
are shown in Figure 1.


THE C.A.F.B. GV5IFICATION OF COAL

       Under the comparatively mild opex-ating conditions which favour sulphur retention
a substantial proportion of the fuel  is merely cracked to produce appreciable concen-
trations of condensible hydrocarbons  in the fuel gas.  When the fuel is oil, the carbon
rejected by cracking is laid down on  the surfaces of the lime particles and is subse-
quently gasified.  When coal is substituted for oil the following factors modify the
operating conditions:

       •   Less hydrogen is available in the fuel for the formation of tars

       •   The char tends to remain as discrete particles instead of being
           spread over the surfaces of the lime particles

       •   Small char particles arc elutriated from the bed and pass through
           the cyclones to the burner

       •   Appreciable amounts of water and ash enter the system
                                          300

-------
                    Outer metal casing-
                    Insulating refractory

                    Castable refractory\
Cyclone for
  gasifier

    /
u>
o
                                                                         Connection between cyclones
•Expansion bellows to
 absorb vertical expansion
 on gas outlets
                                                                         Removable lid
                                                           Gas pulse
                                                            Regenerator
                                                            Cyclone fines
                                                            fed into bed
                                                            transfer pipes
                                             Cos pulse
                                                                                                                      Bed return
                                                                                                                      from
                                                                                                                      regenerator
                                                              ED.
                       Bed
                       drain
                                                                                                                  Regenerator
                                                                                                                     drain
                                                                                          Air  Supply
                                                                                                     Air Supply
                                                      Figure 1. Layout of Continuous Gasilier Unit

-------
The fine char v.-hich is elutriated docs not have to be gasified but is burned directly,
whilst the water in the coal  acts as an oxidant.  Consequently, despite the less
favourable hydrogen to carbon ratio of coal, the proportion of stoichiometric air
which is required to operate  the unit on coal is not very much greater than when oil
is used.  The presence of ash and ปater in the fuel also tend to hold down the oper-
ating temperature.

       The initial  coal gasification tests were made using a small batch reactor and
it was I'ound ihat four quite  di ffert-nt coals could be "gasified" at temperatures in the
region ol 900 c and fluidising velocities in the region of 1.4 metres/sec., in a bed 0.4
wires deep.  The decree of desulphurisation appeared to somewhat exc'.-od the degree
to which the coal had he-en truly gasi f i'.-d, the best figure, bast-d on the sulphur
content of the bed material,  being ihout 641.  A large proportion of the coal ash *as
elutriated from the bed and cyclic regenerations, made by simply turning off the fuel
supply showed that  continuous operation uas feasible.

       Before continuous operation could be demonstrated it was first necessary to
solve two practical problems.  We had to provide the pilot plant with suitable coal
handling faci 1 i tic:;, and ปe also had to modify the cyclone drainage system to c'.able
it to cope with the larger flow of solids resulting from the presence of the coal ash.
The coal handling system ปas  specific to the pilot sc.ilc of the operation and of
limited general interest, t>ut the cyclone drainage system could have wider appli-
cations in situations where head roon is limited.

       The system was devised to meet the following criteria:

       •     No valves handling hot solids

       •     A capability for removing largo chunks of carbon from the
             system

       •     Provision for fines re-inject ion near the bottom of the
             gasi fier bed

       •     Provision for discarding very fine material for fines
             i-.iventory control

The rejection of systems incorporating hot solids handling valves was based on
previous exfxrienre with a variety of such systems, one of the problems being the
presence of largo chunks of carbon following cyclone burn-outs.  It was considered
desirable to re-inject the fines near the bottom of the gasifier bed in order to
ensure a reasonable retention time, ปhi1st discarding very fine material would reduce
the amount of material escaping through the gasifier cyclones into the burner.

       A line diagram of the  fines handling system which was devised to meet these
criteria is shown in Figure 2.  The pilot gasifier is fitted with two cyclones in
parallel and as shown in the  top left hand corner of Figure 2 the solids drains from
these two cyclones were joined to a common diplcg which drained into a small hopper
containing a fluidisable bed. The term fluidisabie is used,  because the flow of
fluidising gas to this bed is intermittent, being controlled by the level of solids
•ithin the dipleg.   When the  hopper is fluidiscd, bed material can flow out of the
dipleg into the hopper, displacing material which drains over the weir, but when the
hopper bed is slumped no such flow can occur.  The hopper dipleg svstem Is, therefore,
a gas flow restrictor which enables the or ssure within the hopper to be maintained at
a higher level than that within the cyclor.es.  Any lumps of carbon which emerge from
the dipleg sink to the bottom of the hopper when the bed Is flnidised and can be
removed through the large drain valve.  Uaterial flowing out of the hopper and over
the weir is entrained by an eductor and is delivered at a still higher pressure to a
low efficiency cyclone, of very small dimensions.  The solids draining from this
cyclone enter a second eductor and are re-injected into the gasifier.  The gas
leaving the low efficiency cyclone passes through a higher efficiency cyclone, then
through a cooler and finally  through a blower which recycles it through the eductor
nozzle, cyclone circuit.
                                         302

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to
o
to
                           "Level  Control
Hopper with
fluidised  bed-)-'
            Nitrogen
                                   Eductor
                                                   Low
                                                   Ef'iciency
                                                   Cyclone
High
Effici
Cycle;;.
                                                                    Hopper
                                                                     -Air
                                                          —Gasifier
                                              Figure 2. Flow Diagram for Fines Return System

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       Thfs system gave good results during our first runs using coal and is still in
use.  Though those runs were of shc-rl duration, they showed that as much as 897 of the
lignite could be combusted without taking stops to rccove* the carbon discarded with
the cyclone fines,and that desulphurisation efficiencies exceeding SOT. are obtainable.
Between coal tests the gasifier was operated on fuel oil, since it v.as found to be a
simple natter to switch from one fuel to the other.  This provided some insight into
the ash retaining capacity of the gasifier bed, because it wad found that coal ash
particles continued to drain from the cyclones during the periods when oil was gasified,
indicating that the ash held in the gasifier bed was not on the whole permanently
hound to the bed particles.  During one such period when no limestone was added to the
bed.it was found that over 007 of the loss in  lime inventory was accounted for by
material removed from the- cyclone drainage system.  L'nder comparable conditions prior
to the installation of this system, stone losses from the gasifier into the boiler
amounted to about 2.7 Kg/hour, most of which was retained either within the boiler or
by a flue gas cyclone- fitted between the boiler and the stack.  L'sing the new system
the loss amounted to 1.K Kg/hour and only a tenth of this entered the boiler.  The
lower loss 1.8 Kg/hour versus 2.7 Kg/hour presumably reflected the improved operation
of the gasifier cyclones with a reduced fines burden due to the extraction of the
finer material Irom the fines recycle stream.  Unfortunately, it turned out that a
large proportion of the lignite ash was too fine to '•ซ• retained not or.ly by the
gasilier cyclones but also by the flue gas cycloro system, and it would appear that
be'.ueon 257 and 557. of the fly ash went up the stack.  Further details of these test
results art- given in Reference 4.

       A prob!ซ-m common to all C.A.F.H. i-i-geni-rativo systems is the disposal of the
concentrated SO,, stream from tin; regenerator.   Flemontal sulphur may be obtained by
reacting SL>2   ~  with carbon to produce sulphur and vas i.oped that the SO0 formed
in the lime bed would be reduced to elemental sulphur in the char layer floating on
top, thus eliminating the need for the Kesox plant and reducing the cost of the process.

       So far only one test has been made using a batch gasifier but the results have
been encouraging and the technique appears to be feasible.  Obtaining a mass balance
during a batch regeneration is extremely difficult, sulphur in particular is difficult
to measure accurately.  An aspirator was used to sample the tail gas at a steady rate
throughout the regeneration and whilst this enabled the presence of sulphur to be
verified, it did not allow instantaneous conversion efficiencies to be measured.

       A normal batch regeneration was run at a fluidising velocity in the region of
O.C met res/second and when the SOo content of the tail gas had risen to about 67 the
bed was slumped and the char was introduced.  The effect of this char on the subse-
quent composition of tht tail gas following refluidisation, is shown in Figure 3,
though it should be pointed out that the lines Joining the points prior and subsequent
to the introduction of the char are somewhat questionable and it is likely that sharp
discontinuities occurred.  The suppression of SO2 and the production of C02 do not of
themselves necessarily indicate the production    of elemental sulphur, since carbon is
oxidised much more rapidly than CaS and unduซj mixing of the char with the bed would
simply put the regenerator out of action.  However, although the char layer was
initially only about 4 cms. deep, the indications were that between 30 and 60% of the
missing SOo was converted to elemental sulphur during the period when the SOo  con-
centration*~was less than 6*.  Whilst encouraging,  this result is not by any   means



                                         304

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GAS  COMPOSITION DURING FLOATING CHAR

             REGENERATION
    2    4   6    8   10  12   14   16   18   20  22
 TIME MINS  FROM  INTRODUCTION OF  CHAR
   Figure 3. Tail Gas Composition During Floating Char Regeneration

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conclusive,  but it is perhaps worth pointing out that in completely combusting systems
the degree of segregation required will be less stringent,  since,  in this case,  the
regenerator must in any event operate under overall  reducing conditions.   The technique
is, therefore, recommended to those proposing to operate desulphurising fluidised bed
boilers in the regenerative mode.


CONCLUSIONS

       It has been established that coal can be treated by  the C.A.F.B. process to
produce a hot desulphurised fuel gas.

       A reliable cyclone drainage system has been demonstrated which allows the
height of the disengagement sections of fluidised bed reactors to  be drastically
reduced.

       What appears to be a promising technique for the direct production of elemental
sulphur within C.A.F.B. regenerators has been proven to be  feasible.


ACKNOWLEDGEMENTS

       The author wishes to thank  the Knvironmental  Protection Agency for the financial
support which enabled this work to be done, and to acknowledge the  valuable contri-
butions made by all the members of the C.A.F.B. project at  Abingdon. In particular
he would like to thank those who worked under the leadership of Dr. D.  Lyon on the
conversion of the continuous gasifier to coal firing.


KEFEREXCES

1.     C. Uoss, "The Mechanisms of Sulphur Absorption in Fluidised Beds of Lime"
       Institute of Fuel Symposium Series No. 1:  Fluidised Combustion, London
       September 1975.

2.     G. Uoss, "The Fluidised Bed Desulphurising Gasifier" Proceedings of the
       Second international Conference on Fluidised Bed Combustion, Houston Woods,
       Ohio. 1970.

3.     G. Moss and D.E. Tisdall "The Design, Construction and Operation of the
       Abingdon Fluidised Bed Gasifier" Proceedings of the  Third International
       Conference on Fluidised Bed Combustion, E.P.A.- C50/2-73-053, 1973.

4.     D. Lyon, "First Trials of C.A.F.B. Pilot Plant on Coal", E.P.A.- GOO/7-77-027,
       1977.

5.     Kirk-Othmer Encyclopedia of Chemical Technology. 2nd Edition, Vol.19 p.410.
                                         306

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            QUESTIONS/RESPONSES/COMMENTS


     JOHN WILSON, CHAIRMAN:   Dr.  Moss,  I  believe, has a few questions
as wel1.

     DR. MOSS:  Mr. Wormser,  of Wormser Engineering, wants to know:
"What is the spacing of fuel  injectors  when you operate on oil?"  The
point is" that we've only got  quite  a  small unit, and it only has
one injector.  The largest version  we built had a bed area of 5
square feet, and that is the  sort of  spacing which  is being used by
Foster Wheeler in Texas.  "Would  it be  the same if  we operated the
CFB as a burner?"  Well, we do operate  it as a burner, of course, on
startup and sometimes on hot  standby; but we don't  normally operate
in the fully combusting mode  and  try  to trap sulfur in that way.
Probably the National Coal Board  people,  who have done this sort of
thing in conjunction with BP, are in  a  better position to answer that
particular question.

     "How high above the distributor  do we inject the oil?"  Well,
basically you get it as near  to the distributor as  you can, without
squirting it into the nozzles; 2  or 3 inches above  the air nozzles.
The distributor itself isn't  flat.  I think I pointed out at the last
conference that in order to get the fuel  distributed over a large
area, as in the case of the Texas plant,  we have used a number of
pits in the distributor, so that  the  oil  ducts can  be covered with
refractory and not exposed to the environment of the fluidized
bed until  they reach the point at which you want the oil introduced.

     I've got a whole range of questions  here from  Joe Yerushalmi.
First, "What is the gas velocity  in the gasifier?"  We normally work
in a range of 4 to 6 feet a second, going back to our original units,
and it is difficult to say what the maximum velocity would be.  You
can only work a fluidized bed, as probably most of you realize, over
a fairly narrow range of velocities because otherwise you run into
pressure drop problems with your  distributor, which is designed for
a specific velocity.  Now if  you  blow a bit harder, you're probably
all right until you reach the situation where you spout.  What we
have found is that the reaction between H2$ and the stone is
extremely rapid.  The material which comes out--'he sulfur which
leaves the bed—is present in the form  of organic compounds, and you
have to break down these compounds  in order to desulfurize them.  If
the bed spouts, you can get a situation where you squirt the stuff
through.   And that, I think,  is probably the limitation.

     "What is the mean particle size of the lime?"  Well, we operate
with about 1200 microns, but  just for convenience. Tne external  surface
of lime isn't the controlling factor.   Size isn't ail  that important,


                                 307

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we've found.  It's the internal  surface which seems to do the work.
Increasing the amount of fines in our bed material  has not,  of itself,
improved its reactivity appreciably.

     "What is the quality of the fuel gas?"  The answer to that is
"highly combustible."  It depends, of course, on the stoichiometric
ratio which we are operating at.  We normally "turn down" by varying
our stoichiometric ratio which may be anything between, maybe 30
percent stoichiometric to maybe 15 percent, with oil; so naturally,
you're going to get variations in the quality of the gas, different
amounts of tar in it, and so on.  There is, of course, a variation  in
temperature when you vary the stoichiometric ratio, which you can
compensate for by using a bit of flue gas recycle,  but we're not
really strapped on the question of operating temperature.  It doesn't
make all that much difference to the desulfurization efficiency over
a reasonable range.  A range of say 870ฐC to about  970ฐC, I  suppose,
gives you reasonable results.

     "What is a typical carbon utilization?" was another question.
Well, the only carbon you would lose in the case of oil firing would
be that which came out of your regenerator as ฃ03.   All of the fuel
is burned. It's just a two-stage combustor, basically.  The  efficiency,
if you like to put it that way, of fuel utilization in a large unit,
allowing for heat losses through the wall and for calcining  stone and
so on, may be in the region of 98 percent on a thermal basis.  But, of
course, there is a power requirement, wh--:h would knock the  overall
efficiency down maybe to about 95 percent.

     And there is another question here, "What are the proportions of
lime and char in the gasifier?"  Well, this relates to the case where
we were using coal, and we have worked with carbon  contents  in the
range of 1 to 10 percent by weight.  The problem is basically that  if
you get too much carbon in your bed, then you'll put your regenerator
out of business, because the carbon reacts much more rapidly with
oxygen than does calcium sulfide.  So, if you have  too much  carbon  in
the material entering your regenerator, you cease to regenerate. Okay?

     JOHN WILSON, CHAIRMAN:  Okay.  Are there any other questions?
                                 308

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                          INTRODUCTION


     DR. FREEDMAN, CHAIRMAN:  We v^ll  return  to the technical  proqram
now.  The next paper,  which  is not  printed in your  progan, will be by
Dr. Steve Wright,  who  is  the Deputy Program Manager of  IEA Services,
which is building  the  pressurized flcidized bed plane *  urimethorpe,
England, and with  that,  I will turn it over to   .eve.

     MR. BROADBENT:  Hello.   Actually, Steve  is going to talk to you
in a few minutes.   I just wanted to say a few words first.

     I spoke to you  generally on Monday about the NCB, the National
Coal Board, IEA Services  Limited; about its constitution and aims, and
we welcome this opportunity  of talking to you now and extending the
discussion of the  more technical aspects of the plant at Grimethorpe.
Since most of the  design  work is not complete,  it is possible to
technically describe it  in some detail, and we  are  going to concen-
trate on the combustor and the exhaust gas cleanup  system.  Time
permitting, we will  go on to other  things, but  I think those two are
the most important parts.

     Before handing  you over to Steve Wright, who is the project
manager of the Grimethorpe job,  I would like to emphasize that this
project is designed  to cover a very large span  of pressures.  It's
designed from 6 to 12  atmospheres;  therefore, it is a rather large
span, and a very experimental facility.  Dr. Steve  Wright.
                                309

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                         A Technical Description of the Plant
                         Design and Project Progress Report
                                  David H. Broadbent
                                         and
                                     S.J.Wright
                          National Coal Board (IEA Services) Ltd.
HISTORY OF THE GRIMETHORPE PROJECT

       The history leading up to the agreement to build a fluidised-bed facility at
Griroethorpe.  near Barnsley, Yorkshire in England is lengthy and has been given in the
paper tr the  Fluidised-Bed Combustion Technology Exchange- Workshop here in Washington
earlier this  year.   In summary the scheme for the present programme of building a pres-
surised tluidised-bed research facility stems from the setting up in 1974 ot the Inter-
national Energ> Agency,  for which the NCB was invited to establish the Coal Working
Group under che chairmanship of Mr.  Leslie Grainger.  NCB's then Member for Science.
Five priority agreements emerged from the working group, one of which is the building
of the experimental Fluidised-Bed Combustion Plant.  In order to formally manage the
five projects. NCB (IEA Services) Ltd.. a wholly owned subsidiary of the NCB was set
up. and from the signing in 1975 of the implementing agreement, a tripartite agreement
was reached between the United Kingdom, United States, and the Federal German Republic
to build the experimental facility,  having commenced in November 1975 and due for com-
pletion in early 1979 w'th the subsequent experimentation for an additional four years.


OBJECTIVES AND SCOPE OF THC PROJECT

       The agreement provides for four principal stages in the programme over the period
of seven years Curing which the experimental 3tage provides the most important objective.

       The stages are as follows:

       Stage I  Procurement of the design study with accompanying documents.

       Stage 2  Tendering for the construction of plant and appraisal of tenders.

       Stage 3  Construction and acceptance of plant.

       Stage 4  Operation of the plant.

       The major part of the work is now in stage 3 of the programme, whilst soms minor
sections are still  in stage 3.  Details of these will be described later.

       Broadly the objectives of the programme are threefold:

       Objective 1  To build the experimental facility to study combustion, heat transfer.
                    gas clean up, corrosion and energy recovery in a pressurised fluidised-
                    bed combustion system.

       Objective 2  To carry out tests over a wide range of operating conditions and to
                    make measurements in greater detail than would be either economic
                    or possible in an intergrated unit.

       Objective 3  To provide data for the analytical modelling of design data for
                    larger commercial plant by empirical data extrapolation.

       The experimental facility provides the means to conduct research into a number
of aspects of large commercial plant, and in the immediate future, the following studies
are sought:
                                         310

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        (i)    Combustion performance using high ash coal.

        (ii)   Effects of dolomite additives on sulphur retention.

        (iii)  Study of heat transfer co-effecients, heat transfer element
               materials, and geometry.

        (iv)   Gas clean up and dust removal prior to atmospheric discharge.

        (v)    Flue Gas corrosion and particulate erosion effects upon gas turbine
               blade material,  leading to the optimisation of a flue gas driven
               gas turbine design.


THE GRIMETHORPE EXPERIMENTAL FACILITY

        The facility evolved from the design study will be built adjacent to the
National Coal Board's Grimethorpe power  station near Barnsley in Yorkshire. England.
The major components of the facility will be workshop fabricated and transported to
site for erection and interconnection ready for start up in late 1978 early 1979.
Whilst it is not a condition of the agreement, it is interesting to note that plant
and equipment is coming from each of the countries party to the agreement.  In round
figures, of the  10m construction cost about  2m has gone to Germany,  1m has gone to
the U.S.A.  and remainder to the U.K.


GENERAL DESCRIPTION OF TTE EXPERIMENTAL FACILITY

        The facility (Figures 1 and 2) consists principally of the combustor  which is
coal rue led trom a coal/dolomite crushing and blending plant.   The combustor's  own
steam generation powers a turbo compressor pressuring the combustion system.   The  steair
is condensed, the condensate being processed to the required water quality before  return
to the steam water circuit.

        Off-gas from the combustor is cleaned of entrained particulate matter by passage
through two cyclone stages, before cooling, pressure let down and discharge to at-
mosphere through a silencer and stack.

        Ash disposal from the combustor and gas cleaning system is provided by suitable
batch hold and dumping facilities.

        The whole facility is to be housed in a building some 30m high, 15m wide by 51m
long, attached and adjacent to the existing Grimethorpe Power Station.  Construction of
the building is already underway and on schedule.  Lifting of heavy equipment necessary
during construction and maintenance is facilitated by a 40 ton capacity remotely con-
trolled gantry crane.


TECHNICAL DESCRIPTION OF THE PLANT

        Since rost of the design work is complete, it is now possible  to technically
describe the plant in the following order:  i) fuel preparation and injection, ii) the
combustor, iii) ash handling and disposal, iv) exhaust gas clean up system.  Finally.
mention is made of auxiliary items such as the turbo-compressor.


FUEL PREPARATION EQUIPMENT

        The contract for the fuel preparation equipment (Figure 3) was let to Head
Wrightson Process Engineering Ltd. early in August with the next step being the
finalization of detail plant design with NCB (IEA Services) Ltd. prior to the commence-
ment of fabrication.  This contract is currently on schedule.

        The Fuel Preparation equipment provides an installation to accept raw coal from
a 10,000 tonnes stockpile into a 30 tonne capacity surge bin supplied by an armoured
faced conveyor (AFC).  Screening facilities for -25mm coal size, conveyor fed from


                                           311

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CO
I—•
ro
                                                                                            MofcSregUrt Ftmon


                                                                                 Vntd    Cduitic/Adtf.—
                                          Figure 1. NCB (IEA Services) Ltd. Grimetiiorpe Experimental Facility Plant Layout-Elevation

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                  A
                  U
                               Y
                             .  T
           a-r    -
              v_-f
(.•Cf.S.'l    _(J

                        01
                        (I*
                  rt    <-r
                  ป•    ซป
                  cซ    cป
                                     t •ป'
                                                     '•
             n,
                   N
-"V;     'VvJ   OT
ป:.*•.   . J(-        I  / •
.,...„  . ซ ^        !__/_,
              Figure 2. NCB (IEA Services) Ltd. Grimethorpe Experimental Facility Gn/Solidi Flow Sheet

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              P*€ CGNVC1OA
 Figure 3. NCSIIEAServicn) Ltd.
 Gcimethorpe Experimental Facility
Schematic of Fuel Preparation Plant
             314

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the raw coal surge bin, are provided to permit +25mm only feed to a primary 30t/h
Hammer Mill Crusher.  All -25ram coal is conveyed to a 16t/h -30t/h fluidised bed
drier acheiving an output of coal at -17. moisture c.f.  normal air dried value.

        Secondary crushing of the dried coal is provided by two lOt/h Hammer Mills
capable of comminution to -6.4mm or 1.6mm as required,  the product being conveyed
to a 370 tonnes Coal Silo.  The internals of these mills can be adjusted, as can the
speed of rotation allowing a wide variation in the size spectrum of the product coal.

        A 640 tonnes capacity Dolomite Storage Silo will be supplied with pro-prepared
material delivered by road ".cnkcrs.  Space has been left in the layout for a 20 tonnes
Additive Silo which will be similarly supplied with pre-prcpared material.

        A blending system, integral with and supplied by the avove storage system.
functions to permit batch mixing of coal, dolomite, and additives to any proportion
required by the experimental facility.  The blender is equipped with weighing hoppers
sensed by strain gauges, delivery control valves, and the necessary control system co-
ordinated by a micro-processor unit.  The blend will be system delivered to the fuel
injection assembly.


FUEL/BED MATERIAL INJECTION SYSTEM

        The contract for the fuel injection system was let to Petrocarb Inc.,  in the
early part of this year and is well into the detail design stage.  Problem.0 have existed
with the juxtapositions of the Ash Screw Conveyor which is to be supplied by Head
Wrightson Process Engineering as part of the ash removal system.   The Petrocarb fuel
feed lines must have a straight run to the corabustor before a single vertical  rise into
the pressure shell to ensure proper pneumatic transport.   However,  these  problems now
appear to be resolved.


THE COMBUSTOR

        The contract for the combustor (Figure 4) was let to Vereinlgte Kesselwerke AC
(VKW) early this year, and the detail design work is nearly complete.   A  number of design
changes have come about motivated by realizations of cost saving, and principally affect
the construction of the pressure shell and resulting logistics of handling the combustor
intervals during shutdown.  The testing procedures to be used for the pressure shell
construction will satisfy the statutory T.U.V. authority in Geroany.  and  have  been
accepted by the U.K. Insurance Company.

        The combustor has a datum capacity of 80MW operating under pressures in the
range 6-12 bar with the off-gas in the temperature range 600-950 C with the maximum
design temperature of 1100 C.  The combustor structurally consists of four principle
elements, namely:  i) the pressure shell, ii) furnace water wails, iii) distributor
plate, iv) heat transfer tube bundles.  The combustor pressure shell is cylindrical
in shape, 4m in diameter by 14m in height to the gas outlet flange, and will weigh sone
100 tons erected.


PRESSURE SHELL

        The pressure shell, designed to operate at a maximum pressure of IS bar. and
fabricated from 17Mn/4 shaped steel plates, butt welded together, has been sub-contracted
by VKW to Borsig in Berlin.  The cylindrical shell is terminated by domed ends, of which
the upper is welded to the shell, and the lover is flange fitted permitting removal and
ready interior access for inspection, adjustment and removal cf the combustor internals
during shutdown.  The upper pressure shell dome is integral and a refractory lined hood
removing flue gas from the combustor.  The pressurised fluidising air intake is to
the annulus between the hood and the main pressure shell.  At the lower end the hood
is connected to the upper end of the furnace water-wall.  The lower pressure-shell done.
carries the pipework penetrations for the fluidised bed services such as fuel  feed.
bed material and ash disposal.  The combustor is supported in a vertical  position on
anchorages designed to accomodate thermal expansion and vibration.
                                          315

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COM. MLEfS
         Figur* 4. NCB (IEA Servien) Ltd.
         Grimethorpe Experimental Facility
            Combustor/Preiiur* Vessel
                      316

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FURNACE


        The furnace contained within the pressure shell is of square cross section 2m
x 2m. the walls of which are constructed as water '-alls consisting of spiral tubes
(38mm od x 4.5mm wall) fabricated in st 35.3 steel filleted together with 6mm steel
plate regularly perforated to accomodate thermocouples as demanded by the experimental
programme.  The water walls, in addition to heat absorption duties, contain the flui-
dised bed and the resulting hot gas stream.  The upper connection is to the insulated
hood and gas outlet as previously described.


PROBE FACILITIES

        75mm diameter perforations are provided in the furnace u^ter walls in a specific
location pattern,  permitting the installation of measurement probes within the in-bed
tube bank as required by the experimental programme.   The water walls are deflected about
these probe perforations.   To facilitate installation. iC.-noval, and servicing of probes,
tr.anholes are provided in the pressure shell service by both internal and external gal-
leries.


DISTRIBUTOR PLATE

        The distributor plate provides the floor of the f'uidised bed and accomodates the
fuel injection nozzles, the fluidising air distribution system, ปsh removal, and bed
material supply.  To date two distributor plates, designated DPI and DP2. have been
designed and provide for differing numbers of fuel feed points.  The distributor plates
are capable of positioning at three specific levels relative LO the tube bank.  DPI
1.32m x 1.96m in size, !•• constructed as double plate sandwiching a pattern of vertical
baffles so dividing the space into the nine even size compartments.  Propane feed to
these compartments provides the means of bed ingition to any required pattern.  DPI,
supports nine fuel feed nozzles perforating the plate, designed to render an even across
bed supply without risk of plugging during operation.  The nozzles are designed as
obliquely truncated short horizontal pipes.  Bubble caps al.;o perforate DPI and are so
designed and arranged to ensure complete fluidisation of '    bed without risk of partial
collapse or non fluidiscd zones, being fed from the primary pressuring air supply to the
corabustor.  Distributor plate DP.' is constructed in essentially the same manner as DPI
but provides for four coal feed nozzles.  Thus, both DPI and DP2 provide for a range of
coal feed rates and supply patterns requiring study during the experimental prograrone.
The associated pipework between the lower pressure shell dome and the distributor plate
is so designed that all necessary dismantling, adjustment,  and assembly require the mini-
mum of worktime.


HEAT TRANSFER TUBE BUNDLES

        Heat transfer from both rhe combustion zone and the off-gas is -.indertaken by j
number of horizontally orientated tube bundles so designed as to present the necessary
surface area for required duty with the minimum disturbance of the in-bcd flow patterns
necessary for efficient operation.  All of the heat transfer tube bundles installed in
the combustor, heat exchanger, ,?nd auxiliary heat exchanger are connected to complete
the steam water circuit, which provides steam to drive the turbo-compressor and. under
most test conditions, will also export steam to tv-! power station range  (Figure 5).


ASH DISCHARGE

        Problematical ash discharging from the combustor. whilst ensuring an efficient
seal has envoked an inclined screw conveyor proposal operating at variable speed to ac-
commodate proper ash discharge rates as demanded by combustor operation.  Maintaining
full discharge chutes from the combustor would effect the seal.  A precise layout of the
proposed screw conveyor arrangement in consideration of the Petrocarb fuel injection
system ir. in preparation,  possibly requiring modification should an incline screw con-
veyor bfe inoperable.
                                          317

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U)
t—•
00
                                            I    MOT

                                            LFr
                             ,- ^  -tป^  •  , •   >>
                             I    .    I  - ปTซI,0ซ.
                                                                                                   CC*S€ •>ซ'!_
                                                                                                   • I'IซN  (
                                       Figur* 5. NCB (IEA Strvica) Ltd. Grimtthorp* Exporimental Facility
                                                   Stesm/Woter Circuit. Tube Bank A

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GAS CLEANING EQUIPMENT

        The Exhaust Gas Cleaning Equipment contract was  let  to Head Wrightson Process
Engineering Ltd. early this year and is still  in the detail  design stage with a number
of technical matters at present remaining unresolved.

        The overall design provides for gas cleaning equipment serving  to remove par-
ticulate matter that will be elutriated from the fluidised bed, and is  interposed between
the combustor and the primary heat exchanger.  Flue gas  leaving the combustor is divided
between the four primary cyclones arranged circumferentially about the  top of the pres-
sure shell.

        Refractory lined ducting will connect  each primary cyclone individually to a
secondary cyclone of which there are four arranged in a  line.  The secondary cyclone
outlets terminate in a gas manifold connected  to the principle heat exchanger.  A
second refractory duct from the secondary cyclone manifold is provided  for connection
to the test cascade loop.

        Ash disposal from each primary, and each secondary cyclone is provided by
quenching at pressure using a controlled water supply.   The  resultant slurry is passed
to a pressurised holding and pressure let down vessel prior  to discharge to the water
recovery and ash disposal system.  Ancillary items include low pressure (L.P.) and high
pressure (H.P.) slurry pumps for the ash handling system, and a silencer in the main gas
path before final exhaust gas delivery to the  chimney stack.

        The water to be used for the ash quenching is to be  re-cycled and requires
chemical processing to maintain it at a specified quality.   Plant is to be installed
in the facility to settle particulate matter from the water.  Cooling and pH adjustment
of the supernatant water takes place before laggon storage,  with intcrmittant biocide
dosing to maintain a freedom from algal growth in the cooling tower.


TURBO-COMPRESSOR

        The remaining item of m;. 'or pl.-.nt is 'he Turbo-Compressor, the contract for
which was let to Compair Industrial '.-c. in October 1976.  Fabrication of the main
castings is now well in hand am': or. schedule al'.hough some minor delciys have occured
with some of the detail design.

        The Turbo-Compressor consists of a low pressure  (L.P.) multistage centrigugal
compressor coupled to a high pressure (H.P.) centr ifu)-.:l compressor both driven by a
steam turbine powered by the • team fctnerated during norcal combustor operation, although
as previously described the turbine wil.i :;u powered fro-n tf.c ;.iปwer station's own steam
supply during start up.

        The Turbo-Compressor has a design delivr-ry of 31kg srr~  dry air mass at a dis-
charge pressure of 12 bar absolute, used to r>ressurlse the corob'-.-itor and supply the
fluidising air flow demanded by the combustc-r operating cond: t ;..ms.


CONCLUSIONS

        In conclusion there are three points I wish •••> :-.ike:

        1.  The co-opeiation of all concerned with l!-.e project has been excellent.  The
sponsor's input--that is government departments ot three nations, the technical input.
the design input, and the contractors have all integrated so effectively "-hat we are
still on schedule for both cost and time.  And here I feel that particular mention
should be made of the efforts of the three contractors concerned with the heart of the
plant, namely, Petrocarb of New York, U.S.A., V.K.W. of Dusseldorf, Germany and Heat
Wrightson of Stockton on Tees, Great Britain.

        2.  The planning of an experiment?! programme for the 4 year period following
commissioning of the plant is now the most important aspect of the Grimethorpe exercise.
This planning is about to commence in detail at the first meeting of the Technical Com-
mittee on Thursday here in Washington and the ultimate objectives must be, in my opinion,
to produce a test programme which will enable the design parameters for say, 200 MW
d-Tuonstration plant.

                                           319

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        3.  The Operating Agent,  the !!CB (IEA Services) Limited, has assembled and in-
tegrated a unique and experienced tcara--A Task Force--of technical people, design people,
consultants and contractors who are capable of extending their activities to achieve
such an objective and I would like to see them charged with the function of carrying
out such an objective so that the "nO MW design parameters could then be translated
into a demonstration plant ns soon as the Grimcthorpe Experimental Facility has proved
the points on the extrapolation curve.  This is surely the sensible way of keeping up
the momentum and speeding development of P.F.B.C.
                                          320

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             QUESTIONS/RESPONSES/COMMENTS


     DR. FREEDMAN,  CHAIRMAN:  Mr. Broadbent is here now,  and he has
to leave in a few minutes.  Are there any questions on the  IEA pro-
ject and the mechanical design of the equipment and systems?

     SPEAKER (from  the  floor):  Can you give the size of  the unit?
The dimensions?

     MR. BROADBENT:  The  bed  is six feet square in dimension,  in  plan
area; ai>d it is about 24  feet in height.  'hat'ซ the comhustor withi-i
the pressure vessel.

     SPEAKER (from  the  floor):  What is the size of the pressure
vessel?

     MR. BROADBENT:  The  pressure vessel is about a little over  12  feet
in diameter, and about  42 feet, fran dome to dor.ie.

     DR. FREEDMAN:  The pressure vessel  weight is about 100 tons, Mr.
Broadbent says.  Since  it's an IEA project, Isn't it two  meters by two
meters, and not six feet.

     MR. BROADBENT:   Yes.  Yes; two meters  by two meters.

     SPEAKER (from  the  floor):  Could Mr. Broadbent tell  us a little
bit about the particle  cleanup aspect of his work?

     MR. BROAPBEMT:   Well, we have two sets of cyclones in  series.  There
are, in fact, four  cyclones, primary cyclones, arranged around the
pressure vessel;  and  then behind that there is another set  of cyc-
lones.   These are what  in England is called the "Steerman High-
Efficiency Cyclone,"  which is, you know, we U .nk the  best  inertial
system there is around.

     DR. FREEDMAN:  Well, then, thank you David, and thank .you, Steve.
                                321

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Instrumentation
     323

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                       INTRODUCTION
     FREDERICK HANZALEK, CHAIRMAN:  Our first paper this morning is
entitled, "A High-Temperature, High-Pressure Isokinetic/Isothermal
Sampling System for Pressurized Fluidized Bed Applications."  This  is
a paper produced by the General Electric Company, and will be pre-
sented by Dr. James Wang, who received his Bachelor's degree from
National Taiwan University, and subsequently his MS and Sc.D. from
MIT.  He did post-doctoral research at the 'Jniversity of Michigan,
and joined the General Electric Corporate RaD Center in 1972.  He has
had multidisciplinary projects and activities including such things
as laser vilisymmetry development, jet noise suppression, gas turbine
exhaust flow studies, and nuclear core flow hydraulic studies.  Dr.
Wang?
                                325

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                          A High-Temperature High-Pressure
                      IsokineXc/lsothermal Sampling System for
                        Pressurized Fluidized Bed Applications

                        w    J.C.F. Wang.C.G. Bingwall
                        *W         c.M. Thoenr js
                               General Electric Company
ABSTRACT                         Schenectady, New York

       A program has been  str^-'g^-ed to characterize the efflux from a Pressurized
Fluidized Bed (PFB) Reactor-.   i,
-------
SAMPLING SYSTEM

       A schematic of the high-temperature high-pressure (HTHP) isokinetic/isothernal
sampling system is sKjwn in Figure 1.  It consists of three major components:

       1. Isokinetio sampling probe and controller
       2. Isothermal environment controller

       3. Particulate and vapor sampler

       Each of these categories is described in detail in the following sections.  I'.ost
parts of this HTHP sampling systwn are made of Kastelloy-X which has been confirmed**?)
to provide minimal surface corrosion under a PFB effluent environment.


ISOKIHETIC SAMPLING PROBE AND CONTROLLER

       This component group consists of (1) a sampling probe, (2) two static pressure
sensors, (3) a S-type probe, CO a high-temperature shut-off valve, (5) an isokinetic
sampling controller, (6) a control valve, and (7) a flow meter.

       Two types of sampling probe were designed and fabricated.  The first one is sim-
ilar to that use-* in Reference 1 and is shown in Figure 2.  The free jtrean static pres-
sure taps at O.Gi-inch -iiameter are on the 0.125-inch O.D. tubing above the sampling
nozzle.  The sampled flow sensor is the second 0.125-inch O.D. tubing on the same axis
of the sampling nozzle with the static pressure taps near the entrance of the nozzle.
The sampling nozzle is made of 0.25-inch O.D. and 0.025-inch thick wall Hastelloy-X
tubing.  A picture of this sampling probe assembly is shown in Figure 3-  The perfor-
mance of this configuration wan tested in a room temperature wind tunnel.  Free stream
air velocity was measured by a pitot-static probe.  The sampling flow was established
via a vacuum pump and measu"ed by a Brooks 10 CFM flow meter.  The differential static
pressure signal from the free stream sensor and that from the sensor at the sampling
nozzle entrance were zeroed through the throttling adju.-*ment on th< vacuum pump.  The
mean sampling velocity was compared to the free stream air velocity and is shown in
Figure iJ.  In the air velocity range from 20 to 100 ft/sec, 'he mean sar.pling velocity
was about 8$ higher than the free stream air velocity.  This constant bias character-
istic can be corrected by the electrical control circuit.  We can preset the sampling
velocity to be BJ higher than the free stream velocity for all the velocity conditions
or adjust the biased value according to the calibration curve at each velocity condi-
tion.  Eased on the bench test results, we are able to maintain isokinetic sampling
conditions in the velocity range from 20 to 100 ft/sec to within ป 5$ accuracy.  The
effect of blockage of the vertical portion of the sampling tube was found to be only
2% of the mean velocity measured and can also be corrected easily.

       Because of a concern for potential plugging of the sampling nozzle and sensors
in the high dust loading PFB effluence, a second sampling head was designed (Figure 5)
The static tap holes on the nozzles inside wall can be made to O.OUO-inch diameter in-
stead of 0.02-inch en the first sensor tube.  The center-body type sensor tube on the
axis of the nozzle entrance in the first design (Figure 2) does not exist in this sec-
ond sampling head design.  This difference is expected to minimize the possibility of
sampling nozzle plugging in the latter arrangement.  Room temperature wind tunnel test
on this sampling nozzle arrangement is presently in progress.

       The S-type pilot probe (Figure 3) is used to measure the actual velocity of the
sampled gas stream.  The performance of this probi was tested in the rcon temperature
windtunnel and compared against a pitot-static probe measurement.  The calibration data
is shewn in Figure 6 and agrees closely with our prediction.
       The high-temperature shutoff valve is made of stainless steel 3'0 body with_S
      te #6 ball.  The center body gasket, seals, a    "
operating temperature and pressure ratings are 1750
urc 7 shows a picture of the assembled valve.
a 9-inch O.D., 2-kW electrical furnace is built
Stellite #6 ball.  The center body gasket, seals, and gland packing are grafoil.  The
                                                750 F and 220 psi, respectively.  Fig-
ure 7 shows a picture of the assembled valve.  Due to the physical size cf the valve,
                                                to maintain the valve at 1750 F.
       The block diagram of the isokinetic sampling controller and peripheral equipment
is shown in Figure 8.  The differential pressure between the two static ports of the
velocity sensor (Figure 2) is monitored with a sensitive pressure to an elect! ! • trans-
ducer located in a pressurized cold gas environment.  The differential pressuie is

                                          327

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                  KV2ปi    VWPLIWi
                             wtcee
         ^—-,i--ซ            ^O

                                                    CONTROLUJ FLOW L.. EXHMIST
       (TCIMTC
       .* AK R

        (iBK'.VI
Figure 1. Schematic at the HTHP liokinetic/liothcrmat Sampling Syrtem
                              328

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FREE STREAM
STATIC PRESSURE SENSOR
    KOZZLE INLET
    STATIC PRESSURE
    SENSOR
              SAMPLING NOZZLE
                          SAMPLED GAS
                                     TO PRESSURE
                                     TRANSDUCERS
            Figure 2. Original lioki.ietic Sampling Probe Design
                           329

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Figure 3.  Isokinetic Sampling Probe Assembly
                  330

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    1.2


    1.1


*s  1.0


    0.9


    0.8
                 BASED ON PITOT  TUBE
  .1.03
CORRECTED  FOR BLOCKAGE
                                        VN =  SA.rPl.KiG NOZZLE VELC-CITY
                                        Vs =  FREE AIR STREAM VELOCITY
                      20             40            60             80

                               FREE AIR STREAM VELOCITY  -  FT/SEC
                          Figure 4. liokinetic Sampler Teปt Results 0.319" I.U. Nouto

                 FREE  STREAM
                 STATIC  PRESSURE SENSOR
       SAMPLING
       NOZZLE
          NOZZLE INLET
          STATIC PRESSURE
          SENSOR
                                      TO PRESSURE
                                      TRANSDUCERS
           Figure 5. liokinetic Sampling Probe Back-Up Design
                                                                100
                           331

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  OUTPUT -
INCHES  H20
                     TEMPERATURE  658F
                        PRESSURE  14.7 PSIA
                         20             40            60
                                    AIR VELOCITY - FT/SEC
80
JOO
                                    Figure 6. S Probe Calibration

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-'=  or  ST.  tf.rl    :,t:ซ OT f'l. M,-:!1;ปH ,C'f: ป'ป, ซ'ป|rit 11!ซ ui'tl
                              Tigur* 7.  High-Tempซratur* Shutofl Valvo

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to
SAMPLING
NOZZLES
t SENSORS
I
1

I

P/E
7RANSD.



I
N
PUR
                                             I	
7RANSD.


?"
SURE
SEL



PURGE

1

ELECTRONIC
CONTROLLER


(
SAMPLE
i HOLD




POKER
AMP
                                                            Figurt 8. Block Diagram of Sampler System

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related to the difference in the free stream gas  velocity and the gas velocity at the
sampling nozzle inlet.   A differential pressure of  zero corresponds to isokinetic flow
in the sampling nozzle.   The output  from the pressure transducer is integrated (to pro-
vide high steady state  gain) and differentiated (to provide dynamic stability to the
control system) by an electronic controller.  The resultant signal is then amplified
in a power amplifier coupled to the  torque motor  of a flow throttling valve.   The inte-
gration in the controller maintains  the output of the pressure transducer at  a steady
state value of essentially zero which corresponds to isokinetic sampling.

       The velocity sensing ports are periodically  backflushed with dry nitrogen to pre-
vent blockage of the ports.  The backflush cycle  is controlled by an electric mechani-
cal program with a five (5) minute cycle time. The duration of the backflush can be
varied between 10 to 90 percent of the total cycle  time.  During the backflush, the gas
flow in the sensing line may produce an erroneous signal from the pressure transducer.
Consequently, during this period the automatic control is interrupted by an electronic
"sample and hold" circuit.  This circuit continuously monitors the error signal at the
input of a power amplifier driving the flow control valve.  Several seconds prior to
the backflush flow, the error signal is stored and  held in the "sample and hold" cir-
cuit.  The control valve area is held at the value  corresponding to the isokinetic flow
just prior to the installation of backflush for the duration of the backflush cycle.

       The periodic backflush sequence can be overridden by the operator at any time.
This allows a continuous backflush mode of operation.  When operating in this mode, the
flow must be reduced to levels which do not produce erroneous signals in the  velocity
sensor line.

       The pressure transducers and  electrically  operated valves associated with back-
flushing ore located in a cold gas pressurized vessel (shown in Figure 9).  The static
pressure in the vessel  is maintained just slightly  higher than the static pressure in
the fluidized bed reactor.  This equalizes the pressure across val^e seals, tube con-
nectors, and the pressure transducers, thus minimizing problems due to leakage in seals
and connectors.  The pressure in the vessel is maintained by a tube connecting the ves-
sel interior to the vessel from a check valve connected to a nitrogen supply  10 to 20
psi higher than the sampled gas pressure.  The vessel pressure will then be higher than
the sampled static pressure by the line pressure  drop required to support the input
flow.

       The flow through the sampler  is monitored  with a commercially available mass
flow meter.  The meter  measures the  true mass flow  ind requires no calibration for gas
temperature or gas pressure.  The output of the flow meter is an analog electrical sig-
nal which can be stored in the data  logger.  The  flow meter and the flow control valve
assembly are shown in Figure 10.

       This automatic isokinetic sampling controller is also desipned to be operated
manually.  For u Specific sampling nozzle area, the mass flow corresponding to isokin-
etic condition can be computed fron  the measured  pressu.-e, temperature, and velocity
of the PFB exhaust at the sampling location.  The sampled gas flow can be manually ad-
Justed via the control  valve driver  to match the  computed isokinetic mass flow.  This
manual operation provides an independent backup system for the isokinetic controller.


ISOTHERMAL ENVIRONMENT  CONTROLLER

       To keep the sampling gas at the temperature  of the PFB exhaust, the entire sam-
pling system from the sampling nozzle to the entrance of the vapor condenser  is heated
via electrical furnaces.  The sampling nozzle and sensors inside the sampling "tee"
section are insulated with Johns-Hanville Min-K material.  The sampling tube  and the
high-temperature shutoff valve between the "tee"  flange and the flange on the pressure
vessel are enclosed inside a 9-inch  O.D. electrical furnace.  This electrical furnace
employs 208-volt 10-amp single phase power.  This electrical furnace and shutoff valve
configuration was tested in the laboratory and successfully maintained at 1750 F  +5ฐF
after 30 minutes from room temperature conditions.                       .          ~

       Tne entire cyclone train for  particulate sampling is enclosed in a Inconel 601
pressure vessel (Figure II).  Pure nitrogen is maintained inside the vessel at the
pressure of the PFB exhaust to minimize the pressure differential across the cyclone



                                          335

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Figura9. Inkmrtc Sapling Contralto
             336

-------
                                                      FLOW M
CONTROL VALVE

                      Figur* 10. Control Vllv* ปnd Flow Meter Aoembly

-------
                                                                           H
                                                                                           •?   t?   xi
u>
U>
                                                                                                .	j	
                                                                    --------- ,
                                                                                    .t .
                                                                                                                   jxj
                                                                                                                        ,5
                                                                                                                        V.
                                                   FigurtH. Schematic of Cyclona ind Pmsura Veuel

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train.  The pressure vessel is heated by a 36-inch long and 1U-inch O.D. electrical
furnace which is designed to input t^O-volt, 36-arap single phase power.  During the
checkout t'.st, it took 145 minutes to heat the pressure vessel and the cyclor.e train
assembly to 1750 F from room temperature.  Temperature variat on at 175GฐF was found
less than ฑ5 F.  Figure 12 shows a picture of this pressure vessel and furnace assembly.
The cuter case of the furnace is designed to provide weatherproofing and electrically
safe protection.


PARTICIPATE AND VAPOR SAMPLER

       The dust loading at the PFB exhaust is expected to be high, e.p  10 grain/SCF.
In addition to their inherent shortcomings such as particle rebounce, •' 3'etc., commer-
cially available impactors would also require dilution in fluid application.  A multi-
ple-stage cyclone train appears to be the best choice in this high dust loading high-
tetrperature application.  A multi-stage cyclone train designed and built by Southern
Research Institute (SRI) for the Environmental Protection Agency, has been selected as
the particulate sampler and collector.  This cyclone train has five stages, each with
a different cut-size ranging from 0.3 i"" to 7 urn.  Beyond the f.'.'th stage, a 0.14-inch
thick Astroquartz mat acts as a positive filter element to collect particulates of less
than 0.3um diameter.  The entire cyclone train and the positive filter holder assembly
is made of Hastelloy-X and is shown in Figure 13.  Results of SRI performance testing
of these five cyclones at room temp'rature is shown in Figure 1U. >^J

       At. the inlet of the cyclone train, a 0.02-inch diameter orifice is installed on
the side port of a "tee" connector (Figure 15).  This orifice provides a connection be-
tween the pressure vessel and the cyclone train.  At the beginning of each sampling
test, dry nitrogen can be passed through this orifice to the cyclone train and the rest
of the sampling line.  At the end of each test, the hot dry nitrogen inside the pres-
sure vessel will again be flushed through the cyclone train and the sampling line.
This nitrogen purge is an important operation to ensure the last sampled gas just be-
fore the close of the shutoff valve to be pushed through the sampling line.

       After the cyclone train and filter assembly, the sampled gas is fed into a vapor
condenser which is made of a 2t-inch long and 2-inch diameter Hastelloy-X tubing sur-
rounded by ice and water.  The gas temperature at the exit of this condenser was about
200 F during the bench tests at 1750 F upstream temperature.  Most of the alkali and
water vapors are expected to be condensed inside the condenser.  The condensed vapor
is then analyzed by the atomic absorption technique to identify the alkali setal con-
centrations.


PFB EFFLUX TESTING AND ANALYSIS

       The objective of this HTHP isokinetic/isothermal sampling system development is
to employ it to characterize the particulate and vapor constituents at the PFB exhaust
and various points in the cleanup train.  Thus, a comprehensive model of the efflux fron
a PFB Combustor and the transfer furstion of the cleanup equipment can ce established
to assess the utilization of the Coai-firec? Combined Cycle (CFCC) Systes as described
in a related paper by Bekofske, et al.  An this conference measurements using this de-
veloped HTHP sampling system will be accomplished as part of the existing United States
ERDA-funded CFCC development test series at f.'CB/CURL, Leatherhead, England in early 1973.

       Two HTHP sampling systems have been fabricated and assembled to be used at HCB/
CURL.  One system will be installed between the PFB exhaust and inlet to hot gas cleanup
equipment.  The second system will be installed at the exit of the cleanup device.  The
measurements from these two sampling systems will be used to characterize the efflux
from the NCB/CURL PFB and the equipment transfer function of the Aerodyne Cyclone.

       The collected particulate and vapor in the HTHP constituents sampling system will
be analyzed to obtain information on the size distribution, constituents, dust loading,
stickiness, and other mechanical characteristics.  The following five types of analysis
on the sampled particulate and condensed vapor are the basic information to be deter-
mined.
                                          339

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                               .     ;,,-
                                         .   •
Figure 12. Cyclone Train Ho'ising and Furnace

-------
Figure 13. Five Stag* Cyclone Sampling Turn and Pontivi Filter

-------
e
t>
o
14

&
    100,
      8(
S
8
     60 —
     4C
     20
O C/clone I
A Cyclone II
O Cyclone III
V Cyclone IV
O Cyclone V
                                   ,	I
      0.1                            1.0

                     PARTICLE DIAMETER, micrometers

               Figure 14. Five-Stage Cydona Train Room Temperature
                       Calibration Data (Courtesy of SRI)
                                                                   10
                 SAHPLED GAS I
                 tHLET      ป
                                                OUTLET
        CYCLOHE TRAIN
               Figure 15. Cydona Train Nitrogan Purge Arrangement

                                  342

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          Quantity of participate matter (or dust loading)
          •  Cyclone train and microbalance
          Paniculate size distribution
          •  Cyclone train and microbalance
          •  Coulter counter
          •  Banco -ounter
          Chemical Composition (Ca,  S, C, Cl, :-;6, K, N'a, ..=h, etc.)
          •  Atomic absorption
          •  X-ray fluorescence
          Stickiness of the particulate
          •  Scanning electron microscope
          Mechanical characteristics of the particulate
          •  Scanning electron microscope
SUMMARY
       Two HTHP isokinetic/isothermal sampling systems are developed and huilt at Gen-
eral Electric to te employed at t.'CB/CURL in conjunction with the CFCC Development test
series in early 1978.   Each component of the sampling system was tested at CF.-CRD with
satisfactory results.   The isokinetic and isothermal features of the system were con-
firmed based en our bench test results.  The backflushing and automatic velocity track-
ing capabilities for high dust loading environments are uniquely useful in the PFB ap-
plication.  The checkout test for the assembly is underway at elevated temperature and
pressure conditions.


ACKNOWLEDGMENT

       The authors wish to thank Mr. R. Tourin of Hew York State ERDA for his consis-
tent support of this work and Messrs. P. Niclas, E. Wheeler, and P. Viscosl for their
help in oesign, assembly, and checkout.


REFERENCES

1.   Rlnpwall, C.G., "Compact Sampling System for Collection of Particulates from Sta-
     tionary Sources," EPA-65D/2-7I4-0/9, Contract Ho. 68-02-0516, April,  197^.
2.   Cray, B. and KcCarron, R.L., General Electric, personal ccmnunication, April, 1977.
3.   McCain, J.D., "Impactors:  Theory, Practical Operating Problems, and Interferences,"
     Proceedings of the Workshop on Sampling, Analysis, and Monitoring of Stack Enis-
     sicns, FB-2527i48, April, 1976.
it.   Smith, W.B. and Wilson, R.R., Jr., "The Development and Laboratory Evaluation of
     a Five-Stage Cyclone," EPA Contract Ho. 08-02-2131, (Final Report is in preparation).

-------
             QUESTIONS/RESPONSES/COMMENTS
     FREDERICK HANZALEK,  CHAIRMAN:  Are then, any questions for Dr.
Wang?  Dr. Wang,  have you accumulated some?

     DK. WANG:  Yes.   I have  a  question here from Sam Wolosin, excuse
my pronunciation,  from Curtiss  Wright Company.  There are two ques-
tions.  One:   "Does the baffle  for gas mixing remain in the system at
all times?  It seems  it would be  subject to erosion of active particu-
lates in the  gas  stream."

     We intend to have the baffle in the system all the time.  It can
be removed.  Actually, the first  test we are goinq to run will be a
75-hour test, so  by the end of  the test we should know what damage
erosion would do  on the baffle.   Actually, there is one time that we
are thinking  of using the baffle  plate as the erosion-test material.

     The system will  be hot during i:he- test, so I don't think there
io much more  corrosion.   By the way, the baffle is not a flat baffle.
It's a curbed, plumb-body type  of baffle; it's a spherical surface,
so it should  have minimum disturbance to the flow and cause less
deposition on the surface.

     So at this stage we  don't  know yet.  The baffle plate itself is
made of Hastelloy X material; and we have some previous experience
with it.  It  gave us  minimum  erosion in that PFB environment.  That's
the reason the whole  system we're using, you know, from the baffle
plate to the  nozzle,  the  sampling sensors, the five-stage cycling
trains, the positive  filtered supports, even the condensers, are all
made of Hastelloy X.

     The second question  is,  "Have any bench tests been made introduc-
ing a known amount of particulates and alkaline metal contaminations
into the system and collecting  for calibration of the system?  What
were the results?"

     We are in the process of running a bench test in the laboratory
with the clean gas to start with, and using the same pressure and
temperature.   And then we were  planning, actually, m?ybe this week or
next, putting aluminum oxide  powders of different sizes into the
system and do a hot calibration.

     The calibration  curve I  showed you on the slides is the cold gas
under room temperature gas calibration made by SRI, before they
delivered the system to us.  So we do need a hot gas calibration,
because when  the  gas  is getting into higher temperatures and pres-
sures, the characteristic changes and the cut size will be changed too.


                               344

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The resulcs haven't come out yet.  We will be going that before we do
tfiซi tests on PFB.

     By the way, I wanted to riake one comment.  I think this is really
the first of this kind of sampling probe dealing wi*.h truly PFR
exhaust studies, because it keeps all the conditions the same as the
sampled i'FR exhaust: the temperature, the pressure and everything; and
there are no condensations, there are no dilutions and so forth, and
it reasures the aerodynamic size.  Besides, it also provides an
opportunity to take a look at the particulates, or alkali vapors
collected, and correlate with any other method you want to use after-
wards.  So I think this is really the first of this kind.
                                 345

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                      INTRODUCTION

     FREDERICK HANZALEK,  CHAIRMAN:   The second paper this morning is
entitled "Participate  Analysis  Instrumentation for Advanced Combus-
tion Systems."  It  is  authored  by  Drs. Muly and Van Valkenburg of
the Leeds and Northrup Company.  The paper will be presented by Dr.
Huly, who is a graduate of  Johns Hop!:ins University, and from there
went to Northwestern University, where he received both his MS and
Ph.D. degrees in Electrical  Engineering.

     Dr. Muly joined Leeds  and  Northrup in 1971 as Program Manager
for Environmental  and  Industrial Instrumentation.  He is presently
Program Manager for Particulate Analysis Products in the Advanced
Business Development Department.   Dr. Muly.
                                346

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                          Paniculate Analysis Instrumentation
                           for Advanced Combustion Systems

                          Emit C. Muly and Ernest S. VanVa'kenburg
                                Leeds* Northrup Company



ABSTRACT

       An on-line paniculate- analvsis  inv.r'jmt-nt  h.is bee"  developed  bv Ix-e-ds  and
J.'orthrup Conpany under EKDA sponsorship for ronitorinf.  the  concentration and  size  dis-
tribution cf particles in the cas  .-lean ur> siape of advanced  eonbu.st ion systems.   This
instrunent utilizes Iou-.inr.le forward scatter In,": of laser  illuminated oarticli-s  bv
across-the-duct cx-asurements.  A prototype instrument has been  tested or a  fluidized-
bed combustion system at the Arp.onne National  Laboratorv.   This r>ar>er Dresent.fi a brief
description of this instrument and discusses  the results obtained  frora the  Arj'.onne
tests.


I.'.TRODl'CTIO:;

       An on-line particulate analvsis  instrument  h/is been  developed  bv \j- -i!s  i,  "orth-
rup Company under EKDA sponsorship for  jn-situ measurement  of particle !o;.jinp and si::e
in the product pas sire.ims of advanc-.-d  combustion  svsters.  A nrototvpe in".trurซ.-n'. has
been aesir.ned and constructed co evaluate this means of measuring  particles on fluidl-
zed bed combustion systems and field tests have been completed  on  this unit at the
Arp.onne National Laboratory.

       This particulate instrumental ion is based on Leeds f< Northrun's orior  research
in low-an^le forward scattcrim; of llrht by r.icron si/-:- particles  pusnendcd in fluid
streams.  When such particles are optically  lllunrnated. the  scattered li;-ht  Intensity
at any civen an?,le is a function r-f  the size,  siiape and index of refraction of the
particles.  In the case vhere the wavelength  is snail in comparison  to the  size  of the
particles, the spatial distribution of  the scattered iiy.rit  in the  far field !s domi-
nated by the volume and size characteristics of the r<.-irt ic les.   The  desipn  of  the  KRDA
instrument is based on utilization of sirole diffraction theory to cor.vert  measurements
of the ccr.oosite Fraunhofer diffraction pattern for a l.irre number of narticlert  into
meaningful particle data which characterizes  the size distribution and concentration.

       This type of instrumentation  is  needed  to evaluate the performance of seconJarv
particle clean up and to measure the size distribution  and  concentration of n.irticles
at the inlet to pas turbines  in direct  combustion  croal-fired  svstens.   The  latter
application requires instrumentation amenable  to measurement  of n.irticles in  hir-h
temperature (liOO-2000F) pressurized (up to  iO atrxjsphercs) cas streams and be adjpt-
able to rather larp.c diameter pas cucts.  The pr-'totypc instrunent reets these require-
ments and accommodates p,as ducts up  to  one foot infernal diaxeter.


iNSTRL-MEirr DESCRIPTIO:;

       A schematic diapram of the onticat train of the  ^RDA instrument Is shovn  in
Fip.urc 1.  Inis instrunent consists of  ottlc.il elements mounted to an optical  bench
which extends under a horizontal run of the combustion  system duct.   (The duct is  not
shown in the schematic, only  its vertical center linn.) The  illumination source is a
helium cadmiun laser counted  to the underside- of the oDtlcal  bench.   Koldinr. optics.
attached to the left erd of the optical bench, i.reel the laser bean  across the  duct
where particles in the r.as stream, vhich arc  illuminated by the bean,  scatter  the
li^.hr.  The scattered flux Ib collected bv a  lens  and focused on a set of function
masks.  The portions of flux, which are transmitted throur.h the f. cticn masks,  avc
focused by a second lens on to the photosultiplicr detector.

       The output pover of the laser Is ceasurcd bv a silicon photo
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                                                Stationary Kar.k
                                                                              Rotator Hask

                                                                                    flotfltor Lens
     ,—Folding  Prism
•Folding Mirror
t—Interference
\        Filter
                                       Figure 1. ParticulMa Instrument Schematic

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       A photograph of the prototype instrument is shown in Figure 2.  This instrument
consists of the optical subsystem assembly, in electronics package. laser pover supply,
a .d a digital line r"'nter.  All units, except the printer, are contained in NEMA-12
class enclosures to ceet industrial environmental requirements.  The laser and recei-
ving optics units contain thermostat controlled heaters so that the ootical subsystem
may be installed on gas ducts which are either indoors or exposed to the weather out-
of-doors.

       The electronics package includes a microcomputer, visual display and all the
operating controls.  This unit can be located up to 200 feet from the optical subsys-
tem.  The digital data printer is used to log the output measurements and can be loca-
ted remotely from the electronics package, if desired.

       The opening on the optical subassembly from the folding optics on the left to the
collection lens bezel is 30 inches.  The vertical clearance above the optical bench to
the Laser beam center line is 9%= inches.  These dimensions were chosen to accommodate
a 12-inch I.D. duct with a tee section viewing port extending on each side of the duct.

       Mechanical adjustments are provided on the folding optics for alignment of the
optical train to the duct windows after the instrument is installed.  The instrument
can be mechanically mounted to the duct through the load carrying base structure.

       All particles illuminated by the collinated laser beam as it traverses across
the gas duct scatter flux off the beam axis.  For particles in the size range 1-100
microns most of the scattered flux is in the near forward direction.  He collect that
flux, and through an optical process, convert that data into information concerning the
particle size distribution and the particle loading.   The particle loading output is
calibrated to be direct reading in parts per million by volume, i.e.. ratio of total
volume of particles per unit volume of gas.

       A common means of presenting size distribution is to plot the population of par-
ticles as a function of their size as shown in figure 3A.  In order to obtain data more
useful for control purposes, it is possible to describe size distributions in ways
other than number density.  Three means of presenting the same particle distribution
arc shown in Figure 3.  the area disbribution DA
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CO
en
o
                                                                   Figure?  Ptototyiw IMrl'

                                                                            liut'umenl

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             ':i r: :rl<- K.u! i ir..  .1
Figute 3. Three Methods of Defining Particle Sue Oittnbution
                         351

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Fiqufeb  ClnwupVKwol
    ANL

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353

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       The average cean volume -jiameters. 37.  for  the  iirpactor samples were calculated
 from  truncated  lop, r.omai distributions obtained via the Anderson Ir.pactor.  Since the
 MICROTRAC has a  linear size  response for particles one micron in diameter and larger.
 and an attenuated  response to submicron size-  particles, the  lowest channel (submicron
 region) data points  from the irrsactor were not  used.  This  nrovides directly comparable-
 data  over the size ranp.e I-'.") cicrons.  The  average ncan area diameters.  MA. were
 similarly calculated fron the- Anderson Impactor data.  The  differences between the
 direct reading, on-line observations via XICROTRAC and the  impactor data  arc tabulated.

       The meeiian diarieter,  V) t h pc rccn t i I e  for lop, norm.nl  distributions  can be ex-
 pressed as Median Diameter * .•??/ x MA. The results of  this  computation are shown in  the
 bottom three rows of Table I.

       These results indicate pood agreement  between optical  scattering and cascade
 tmpactor methods  for particle sizing.  In all  but one case,  the difference is less than
 one micron.

       Two interesting characteristics arc observed, however. The MICROTRAC size mea-
 surement tends  to indicate slirhtly smaller  size for the median diameter  and the
 MICROTRAC shows  the average  size of particles  coninp. out of the final filter to be
 larf.er than at  the input.  In one of the three  tests,  the  inpactor data also shows the
 output particle  size to be greater than  the  input.  This anomaly will be  explained
 later in discussion of test  chronology.

       The loading, data as functions of  time  are shown in  Figures 6-7 for two opera-
 tional tests.   Th. in-situ volurttric loadings, as outnutted  by the MICROTRAC instru-
 ment, are converted  to standard pressure/tenr.erature conditions by the following equa-
 tion:

                           I (Graras/ra1)  - D(l  * 0.003fe7T)dV                         (2)
                                                 p

 where D - density of paniculate (p.m/cc)
       T ป c.as temperature, nominally 160C
       P = Ras pressure, nominallv 'i atms.
      dV • instrument output  in ppa.

 The  density of  the material  samples in these  tests was 1.2  ;^n/cc.

       The data  from MICROTRAC are shown ns  dots for unit  intervals of time.  The
 loadinp. is always hieh at the b<-s>,inninp, of each run due  to  material loosened in set tine.
 the  duct valves   It takes about 15 to 20 minutes  for  this  Lo be ourp.cd out of the c.as
 strcara.

       The MICROTRAC loading da'a show sl^w  oscillator-/  variations.  Initially, wo
 thought that this raisht be instrumental error caused by  chanpc in laser beam intensllv.
 However, observations of particle size as a  function of  tine  show similar variations
 and  these data  arc,  independent cf laser intensity.  Therefore. --o conclude that these
 oscillations are characteristic of the Ar^onne/Coabustor process.

       Sncoth lines  are drawn through the MICKOTRAC data points to show the loadinn
' trends.  In addition, the loading values obtained  by the cascade iirpactor and the nen-
 brane filter samples are shown.  The horizontal location and  lonc.th of lines for the
 extracted sample  loadings indicate approximate tice and  duration for collection of
 each of these samples.  The  vertical  locations  of  these  lines dcs'.p.nate the sample
 loading measurements for those intervals.

       A sip.nificant part of the variance between  MICROTRAC and the extracted samolos
 may  be due to non-uniformity of loading  across  ..he duct or.  nrobably more likelv, due
 to problems of  achieving isokcnetic sampling with  the  extractive probe.  A oarticular
 advantage of the MICROTRAC type of instrument is that  it measures all oarticlcs passinp
 through the  laser beam and t'-.e gas flow  is not  influenced  in  any way by this method  of
 measurement.
                                           354

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                    He-Irian Filti-r S.-imnlc
                                                   Outnut  of Cvclones
                                                 Output  nf "tt.nl  Kilter
                    II
                     Figure 6.  Experiment L&N-4
                                     Outr>ut of Cvcloncs
                               '.i-lrnn  F\ Itcr
Amlcrson  !~.".ictor  S.'iirplc
                                 iclnan  Filter Sample

                   *  ป  •

                                 Oi:tnut  of 'lot.il  Filter


         Andc-rsnn  Inn.ictor S.innlc

         1     I     I    I     I     I     ป     I     I     I
   10
              :o         30
                 >!  I  N U T E  S
                                               50
                                                          60
                     Figure 7. Experiment L&N-6
                             355

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       Figures 8-9 show the tine variations of the mean area dianeter (MA) superimposed
en the loading functions.   It is noted that the size variations tend to follow closely
the loading variations.  Thus, it is concluded that the size of particles is a major
contributor to the total loadings in thij process.

       Furthermore, the amplitude of variation in MA is consistently largest at. the
beginning of the metal filter output reasureirsents and the mean size tcnos to decrease
with time.  This is characteristic of the performance of the AM. metal filter.  The
efficiency cf filtration improves as particulate builds up in the filter media.

       It is also observed in these data, that the MA variations at the input to the
final filter are less than ac the output.  The test sequence at ANT. soecificd first
measurement of the particulatc at the output of the netal filter, then at the input.
For all three combustion tests, the output measurements were made in the morning, a
few hours after start-up,  and the input measurements occurred in the afternoon.  One
can now only hypothesize that this combustion system requires a long time to stabilize
and that the netal filter output variations would have been smaller had the test se-
quence been reversed.  This also explains why the average size over the total measure-
ment time was larger at the output than the input.  For example, at the end of the
IA"J-5 metal filter output run, the average MA was 1.73 microns and the input average
particle diameter, measured two to three hours later, was 2.26 microns,  these results
Indicate the desirability of having two MICROTRAC instruments to enable simultaneous
measurements at thซ input and output of the final filter in order to obtain complete
characterization of a coiabustor/f iltration process.

       After completion of the tests at ANL. the prototype instrument was returned to
L&N where the calibration of the particulate loading output was rechecked.  For a cali-
brated sample of 10.0 ppm diamond dust of nominal 3 microns diameter, the instrument
read 10.11 ppm, while the standard deviation of this calibration procedure is 0.18 ppm.
Thus, the calibration constant for dV did not change in a measurable degree during two
months of operation.


CONCLUSIONS AND FUTURE WORK

       The results of those tests on the AJIL fluidized-bed combustion system indicate
that the MICROTRAC data output compares reasonably well with Anderson impact"- measured
samples.  Furthermore, differences observed for these two types of measuremc..i.j nay be
attributed to the means of extracting the particulate sample for the cascade impactor.

       Three problems were observed with the MICROTRAC instrument and all three pro-
blems seem related to the laser:

       (1)  The laser output power slowly decreased with time,
       (2)  The loading sensitivity (0. 1" graii.j/scf on a 1 inch i.u. duct) is
             marginal for after final filtration measurements, and
       (3)  A significant part of the particulate loading is contributed by
             submicron size particles which sre not measurable by the prototype
             instrument.

       The latter problem was anticipated since the instrument response falls rapidly
as the particle size  (diameter) approaches the wavelength of the laser emission
(0.442 ;:m).  Improvements in submicron response can be achieved in future in.-truments
by use of a highly stable ultraviolet laser which is now commercially available.

       The loading sensitivity observed at ANL was about three tines less sensitive
than predicted from our laboratory measurements.  This is directly relatable to the
instabilities of the  laser output oowcr in th.-.t instrument.  Loading sensitivity of
0.001 grains/sr.f should be achievable on a 10 inch i.d. duct at 10 atns. with an
Improved  laser which now exists.

       The Argonne tests demonstrate the applicability of forward scattering for on-
line in situ measurements of particulate size and concentration in fluidized-bed com-
bustion processes.  Current research, which Leeds & t.'orthrup is conducting for the U.S.
Environmental Protection Agency, indicates that use of combined forward and 90ฐ scat-
tering will enable measurement of submicron and larger size particles at lower concen-
trations, in the ppb rather than ppm range.  Thus, optical scattering type instruments


                                           356

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                                                               -13.0
MA AndersSTr* —•
   Innactor
                           Input """••MA MICRnTKAC
                           Inrut IVICROTRAC
    HA  Aruil'f .*ion  Inr'.TC tor
                                 Outnut I MICROTRAC


                                     I     I     I      I
I      I     I     I     I      I
                         30
                    •t i t: v  T F. s

                     Figure 8.  Experiment L&N-S
                                                                 1.0
                                                               -i3.0
                        30         40
                    MINUTES
                                                                  1.0
                     Figure 9.  Experiment L&N-6
                              357

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offer pronisc of net-tin;1, the increased requirements of p,as turbine instrumentation as
advanced fluidized-foed systems evolve.

       The prototype forward scattering instrument is ready to bo delivered  to Curtiss
Wrif.ht Corporation where it will be installed between the final filter and the turbine-
inlet on the Small t'.ns Turbine System.  The f,as duct at that location is a 4-inch i.d.
refractory lines spool niece.   With this size 
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           QUESTIONS/RESPONSES/COMMENTS


     MR. HANZALEK:   Thank  you.  Dr. Muly.  We are a couple of minutes
ahead of schedule,  so if there  are any direct questions, preliminarily
at least, that anyone would like  to  address to Dr. Muly, we can handle
one or two at this  time.  Does  anyone have a question on the top of
his head?  Tnerr is one.  Would you  go to the microphone, please?

     SPEAKER (not identified):   I would like to know at what particle
loading rates your  instrument ceases to function?

     DR. MULY:  The detection limit  is about .1 grains per standard
cubic foot for the  one inch duct  reported on here.  The detection
limit is reduced as the ID of the duct or gas pressure increases.
This should result  in a detection limit of .001 grains per standard
cubic foot for a 10 inch duct operating at 10 atmospheres pressure.
By increasing either the path length, operating pressure or the power
of the laser the detection limit will be proportionally reduced.

     SPEAKER (not identified):  What is the maximum sensitivity of
your instrument?

     DR. MULY:  That again depends on the dianeter of the duct.  For
an instrument with  aim  path  length, concentrations as high as 1
thousand parts per  million can  be measured accurately.  The upper
limit of loading measurement also depends upon the particle size
distribution.  Particle streams with large particles can be measu :d
at higher concentrations.

     DR. RAO, MITRE Corporation:  Is the difference between your
instrument readings and the conventional methods due to possible
condensation?

     DR. MULY:  We  did not collect the samples for either the Gellman
filter analysis nor the Anderson  impactor analysis.  Both the collec-
tion and data analysis were carried  out by Argonne personnel.  Every
effort was made to  keep the temperature at the filter above the dew
point.  However, when particulate samples are collected on a filter,
some condensation of the gas phase components may take place.  This
could result in erroneously high readings for the solid phase con-
stituents.  This might explain  the observed higher readings for the
Gellman filter. No  effort  was expended to determine if this was the
cause for the observed higher loadings given by the filter method.

     DR. RAO, MITRE Corporation:  How significant is the impact of
condensation on the conventional methods?
                                359

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     DR. MULY:  We have no experience in evaluating the effects of
condensation on the conventional  methods used  in this study.

     SPEAKER (not identified):   What will be the influence of radiant
particles on the measurement?

     DR. MULY:  The instrument  has been designed using a narrow band
pass interference filter (50A at 442 rm).  The signal levels  there-
fore produced by thermal radiation aro insignificant in the  tenoera-
ture ranges of interest between 1500-2000ฐF.

     DR. WANG, General  Electric Company:  Can  you explain the reason
why your measurements agree with impactor results?  Is there  a the-
oretical analysis explaining this agreement?

     DR. MULY:  The optical  method is not responsive to particles
less than 1 micron in diameter.  The intercomparison between  the two
techniques was, there ."ore, performed by first  truncating the  impactor
data at 1 micron and then renormalizing the data.  The resulting
agreement is therefore, to some extent, expected.  No analysis exists
concerning the actual response  factor of the impactor device; i.e.,
its shape factor dependancy and therefore no theoretically derived
prediction of the inter-comparison was performed.
                                360

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                         INTRODUCTION
     FREDERICK HA'JZALEK,  CHAIRMAN:   We  will  now proceed to the third
paper, entitled "Particle Field Diagnostics  Systems  for Fluidized Eed
Combustion Facilities."   This  paper is  offered by '-!r. William
Bachalo of Spectron Development Laboratories,  Inc.

     Dr. Bachalc received his  Ph.D. fron the University of California
at Berkeley, and his degree was in  fluid dynamics.   He previously
worked at the fJASA Ames  Research Center, investigating the phenomenon
of transonic turbulent boundary layer separation, using laser veloci-
metry.  While at Anes, he developed holographic  interferorcetry for
use in the- transonic flow studies.   He  is currently  in charge of the
particle field diagnostics program  at Spectron Development Laborator-
ies in California.  Dr.  Bachalo?
                                361

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                            Particle Field Diagnostics System
                         for Fluidized Bed Combustion Facilities
                                    William D. Bachalo
                           Spectron Development Laboratories. Inc.
                                  Costa Mesa. California
ABSTRACT

       Particle diagnostics instrumentation that have been developed for application
in  fluidized bed combustion plants will be described.  The devices have been designed
to  make simultaneous on-line measurement;; of particle diameter over two decades of
size range and of the particle velocity for the determination of particle flux or con-
centration.  These ruggedized laser-based light scatter detection instruments make use
of  angular scattering intensity ratios for sizing particles in the range O.b - lOjm in
diameter and particle sizing interfcrometry (visibility) in the range 2 - lOOura in
diameter.  A brief description of the physics involved will be given together with a
discussion of other available techniques.


INTRODUCTION

       Particle diagnostics instruments that are to be i-tilized in the hostile environ-
ments of the fluidized bed combustion power plants face a serious challenge.  The in-
struments must mako in situ measurements in a flow field environment with temperatures
as  high as 1000 to 2000'F and pressure of 1 to 10 atm.  A broad range of particulatc
loading and size will occur in these fields.  The system flowrate will also vary de-
pending on the facility output conditions making measurements of velocity necessary if
paniculate rate measurement are to be meaningful.  At present, no single instrument
exists that can make in situ particle- size measurements over the entire sli:c range of
interest (i.e.. 0.05 to 20nm).
       Hone'iiclesr. particle field size measurements are essential in all areas of the
design, development, and operation of the fluidizod bed combustion facilities.  For
example, to understand anj mathematically model the combustion processes, including
the formation of soot and fly-ash, an accumulation of data both on the species and
size of the particulates generated must be available.  The optimization of particulatc
removal equipment requires upstream and downstream particle content analysis.  Par-
ticle impact ton studies on turbines to determine corrosion and erosion rates as a func-
tion of the incident r.ns particulatc content are also dependent on accurate particu-
late size and velocity measurements.
       In the operating plant, constant monitoring of the facility will be required.
Real time in situ sizing equipment will be needed to act as early warning sysccms of
unusually high particle concentrations entering the gas turbine or for water droplets
in  the steam turbine.  Effluents from the operating plant will demand careful assess-
ment of the particle cmmissions.  Detrimental effects of particulates '.s. to a large
extent, dependent on the size distribution.  Particles in the size range of .Olum to
lOuni are not easily removed from the effluents.  It is particles in this size range
that arc effectively deposited in the pulmonary region of the human respiratory sys-
tem, d)
       The sizing techniques that are available fall Into categories based on sampling
and optical methods.  Sampling requires extraction of a sample from the flow and this
sample Is then analyzed externally with Instrumentation including microscopy, scanning
electron microscopy, weighing, or a combination of these methods.   The sampling inher-
ently disturbs the flow field and hence the particle distribution even If the sample
is  withdrawn isckinetleally.  Furthermore, agglomeration, impaction and deposition
occur in the sampling process.  Sample preparation and analysis frequently requires
several hours.  Optical methods based on light scatter detection have several advan-
tages over sampling techniques.  These include the fact that they produce near real
time analysis, they are non-instrusive. and measurements can be made with high spatial
resolution at exceedingly high rates.  A brief review of other techniques can be found
In  Reference 2.
       Spectron Development Laboratories, Inc. has developed particle sizing systems
based on the scattering of light from highly focused laser beams to make single par-
ticle measurements of both size and velocity at sample rates as high as I0*/sec.  With


                                          362

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the proper definition of the sample volume, the measured accumulation rate and the
velocity, a measurement of the particle concentration is available.  The systems spe-
cifically dcs'gncd for application to particle field diagnostics in fluidizcd bed com-
bustion plants will be described in this paper.


SCATTERING OF LIGHT BY SMALL PARTICLES

       Because the instruments to be described are based on the scattering of light
from small particles, a very brief discussion of the pertinent scattering mechanisns
will be given here.  The formal description of the scattering of electromagnetic radi-
ation by homogeneous spheres requires a solution of Maxwell's equations with the ap-
propriate boundary conditions.  Such solutions were derived for spheres of arbitrary
size by Mie in 1908.  Tins theory, described fully in References 3 and A. is exact for
incident light that is composed of linearly polarized plane parallel waves and that is
constant over the particle.  The scattering radiant flux is given as
                              ..n) sin" :   +  i, (;..,n) cos' M sin -dvd;         (1)
where '  is the scatter angle measured from the beam propagation direction. :  is the
angle between the plane ci observation and the E-electronagnetic vector. I0 is the in-
cident intensity of wavelength '•. ,  ij and i-> are the Mie coefficients for perpendicular
and parallel polarization components.  In the arguments of the Mie coefficients, n is
the index of refraction and  < is the non-dimensional size parameter defined as ("d)/>,
the particle circumference divided by the wavelength.
       Mie scattering coefficients can be readily generated with the appropriate com-
puter code for spherical particles in the size range of interest.  Polar plots of
intensity with respect to the .ingle o . measured from the plane of incidence,  called
scattering diagrams arc computed.   The scattering diagnms for several particle sizes
shown in Figure 1 serve to show the significant characteristics of the scattering
function.  A logarithmic scale is  u?ed with each ring representing an order of magni-
tude and tht; dots nark each 5 degrees of angle.  These polar scattering diagrams ..re
then used in all phases of instrument design.  For example, an instrument designed to
collect forward scattered light would require a knowledge of the variation of scatter
intensity with particle size, collection nngle. collection F/number. index of refrac-
tion. incident polarization and an evaluation of the relative effects of these param-
eters .
       Several scatter detection techniques have evolved from a knowledge of the scat-
tering diagrams.  Any number uj." scattering angle collection arrangements and incident
sources could be devised as optical counti-rs.  Of che techniques available, those
making use of highly focused high  intensity beams of light are superior in most appli-
cations.  Focusing the light source has the advantage of prouacing a very small sample
volume.   Good spatial resolution is available with the high incident intensity on the
particle providing a good signal-to-noiso ratio.  Su-h devices sample a single particlo
at a time to produce a measure of  the optical scattering diameter.  Other considera-
tions of the particle's scattering properties need to he made in order to relate :his
quantity to the actual particle diameter.
       Careful consideration of what constitutes a probe volume must he made in all
laser-based scatter detection instruments if a meaningful particle flux is to bo deter-
mined .   When using a laser light source operating in the common TCMOO mode, the bea:<
intensity distribution has a Gaussian shape.  The incident intensity on the particle
is then dependent on where it passes through the beam.  Because there is always a back-
ground noise level due to other particles in the field scattering from outside of the
focal volume, scatter from the access ports, photomultiplicr r.oiue. .inJ other sources.
a minimum detectable signal level  exists.  Large particles passing through the focal
vuluuc will scatter light above the minimum or  threshold level over a larger region
than will smaller particles, as shown in the rough sketch in Figure 2.  Dependence of
the effective probe volume on particle properties was recognized by Farmer*') and by
Hirlctran ct al. who analyzed the effect in his dissertation^-.  Kith the Gaussian
intensity distribution of the laser illumination, the effective pr^-be dia-.ctcr will in-
crease with increasing particle scatter cross section resulting in concentration mea-
surements that are biased.



                                          363

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Diameter -- 10.0 pm
MAX = 10'
          \
                     Figure 1. Polar Ploti Showing the Magnitudes of tf<ซ Miซ Scattering Functions
                           lot Typical Soot like Particle) (n - 1.57-056 and X - O5145pm)
                                                  364

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         II If
             1/C2'
                                       -c  -
        Voltage
                                                      Partic'g S.22S
                                                         n larqc
                                                          -. small
                                                        Gaussian  Beam
                                                        Intensity Distribution
!     Signal  Output

        Threshold
                                                           Li'V'71
                            Figure 2. Dependence of the sample volume on
                                   Scattering Cross Section
        To correct t'or the variation in measuring cross section,  the effective probe
 volume. V(J.pj)  where il is the particle diameter and p[ are the  relevant particle prop-
 pert, ics.  must be defined.  Because Mle scattering theory assumes the particle to he
 uniforrily illuminated,  the focal volume must  first  be formed at  typically an order of
 maftp.i tude larger in dian-.eter  -ban the largest  particle to be measured. ;this diameter
 is defined to be the rec.ion within which the  intensity is above  the l/e- of the peak
 intensity.  Achieving the sufficiently snail  focal  volume required often makes bca.T.
.expansion necessary.  Kocusin,: of the Gaussian beams is treated  in detail by Korei-
 nik (').   This ai .lysis will  ensure that the maximum intensity is incident on the par-
 ticle  in the probe  rcr,ion and that the waves  there  are plane,  satisfying the .'lie
 theory assumptions.
        Once the  focal volume  intensity distribution is defined a relationship can be
 df-rived to evaluate the effective probe volum^.   A  sensitive probe tarpit area.
 A_(d.n) i * established  that is a function of  the particle scalte-'ir.g cross section
 (uepcndf r.t o^. particle  diameter and index of  refraction for nor.-absorbing spheres).
 In the present case where the particles are primarily soot or other carb naceous mate-
 rial,  the bcattcrinr, has only a very weak dependence on the index of refraction.  To
 determine the particle  flux a histogram is formed of the particle counts for each
 small  size interval over a r.iven time period.   The  sensitive area. A.,(d) is then deter-
 mined  for each size interval  and is used to properly weight the  histogram to correct
 for the statistical bia.  in dctcrrslnin?, particle flux.  This phenomenon is a hidden
 blcssinr, since there is typically a p.rcater nun-.bcr  of particles  in the small sizes.
 The s:r.all Affective probe arej for the smaller sizes reduces the possibility of mul-
 tiple  particles  existing in the probe volu-.e  simultaneously.
        Because the  refractive index of nost particle fields is unknown, the scattering
 instruments should  be dcsir.sied to minimize the effects of this parameter.  It i:> knov-i
 from  comparisons to Mie scattering theory and  through asymptotic approximations -_o the
 theory that the  scattering in the near forward direction can be  approximated very well
 by Fraunhofer diffraction theory.   Diffractive scattering is Independent of the^index
 of refraction and has been shown to have only  a weak dependence  on the particle's
 shape*-3'.   The size measurements of irregular  shaped isometric particles (i.e.. par-
 ticles that do not  have a ^reat difference in  their respective dimensions) do not
 differ much from spheres of equal projected area.
                                           365

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       Availability of  f hi-  .sc-'i' tor in;-  inti.-nsi'y a-: .1 we] 1 -'K-f ::.<••: func'. :' on ป:" par'.icle
si/.e h;i:.  lซ-:n;'. :<•  j.ar'. i c ! e- coun'er.s  based eiri  the
s.casuron.fnf •; of absolu'e scattering intensity.  .'-:ซ.- vi-ral  d: f f it -jl '. :<-s  i~.ป.-d:.-i' el v  :.-o-
corxo apparent in i h i :. approach.   i'erhaps  '.If r..n::< trou:. i <-:;o.~e is li'jt-  • o  •_:.ซ_• 'j.-rj.s.sian
intensity ili ;, t r i but ion  of the  !a:.<-r boan.   In a :i-i\ yd i sper.-.e par'icli-  field : •  i .".
po:;sibi(-  10 ;•<•!  si:..i!ar  sea', t c-r in;; i nt err; i t i <••; . dependin;;  on 'ho particle : r.'i j< c r. ory
• hrou;;h tljo probe. for  p.'irticles vi-ry  different  in size.   Several techni-;';es h.-sv.- been
devised in el forts to (.vซ-n-(.:::t- t ho uncc-r ; ;ii ru y in p.'irticlo • ra jc-c'.ory .   K'ir t-x.irr.plc-.
.it-roijyn.'i::iic fotusiri;; h;is hcon  ur.til lo  forco  '. hi- p.'ir"- i cits  ihrn-iy.'n iht  con'i-r ซ!" t he
j/rohi-  volurao whi-ro the  inltn:> i t •/ i :; .-ipproxirnt •-! y co:is-. /ml .   This is  nor.  iK-fir.'iblo nor
ovi-n po::sibli- if in sinj nif.-i.surcTiont r:  ;irc  rซ-'j-ii rt.-'i .  'j'hi-r aftt-rip's h.-jvซ-  l>ot-n r:.;jdt- i'j
ri-jt-ct .ill tT>issin;;s oiilsido  of  I he ct-ntr-'il  port ion  of The foc.'i! '/olimt-.   7::e cri ; ic-il
.'il i i;n:n<-nt required render:;  these t <.-chrปi'|uos  less th-'in  ties i r.'ihle outsidt-  of the J.-ปbซir.i-
lory cnvi ronmcnl .   In .-'.d
  • ;hl by other ;>.-irt iclcs in the p;ith .'ind by acctrr.-.!.-it ion of ;.;ir- ticul.iie m.-it cr i:i I on the :icce.-;s wint (he panic1'; velocity. The techniques will be describ.-d in the following .sections. ('ARTICLE SlX.n.'c; IN I'article si/.in;; by the measurenienl of the laser doppler ;if,nal visibility was orif.inally invest ij-.at ed by rVimii-r C) jjy that t ice laser velocinetry was oecor-.inf. well-established as a viable fluid flow measurenenl technique. Analysis of f he scat- tering phenomena associated with the dual beam laser velocimeter were bein;; investi- gated in an effort to improve the signal- t o-noise ratio of the instrument. This led to the real i/.at ion that there was a dependence of the sir.nal modulation on the size of the scattering particle relative lo the interference frinc.e spacing. Relationships were derived and analy/.ed to correlate the particle si/.e and properties to tie signal visibility. A schom.it Ic drawing of a typical optical arrangement for particle sizinR inter- feronietry is shown in Figure 3-a. An Arp,on-ion laser (blue, '• - O.&SSura) prcvidcs the necessary coherent lip.ht source for tliis technique. The laser beam is split Into two equal intensity beams with a beam splitter and focused with a lens to a crossover point. Careful optical design is required to ensure that the beani crossover ;:nd the foci of the beams coincide. At the crossover, the beams interfere to forra a station- ary set of frinr.es (Figure 3-b) . The spacing; of these fringes can be determined very accurately either ~y direct measure or from the optical geometry and the following expression: 2 sin 0/2 where A is the wavelength of the incident beam and u is the bean intersection angle. 366 (2)

  • -------
                            Pa-ticie-LaCcn
                              Gas Flow
                                                Samc*2 Volume
                                                                    -PM.T.
                            Figure 3ซ. Sdwmatiol Diagram of the Pvticle Si* ing
                                      lnttft*romct*f Optra
       GAUSSIAN RADIAL
    INTENSITY DISTRIBUTION
    
      * -  >
                                                          BRIGHT  FRINGES
    1/c2  RELATIVE  BEAM
          INTENSITY
                     sin (0/2)
                               Figun3-b. Entar^ad View ol ttw ftote Region
                                           367
    

    -------
            t'.ir •. i c i ซ•-. ::.ovi •-.;•  vi'h ' :.<• fl'jw  and ;,ass:ti;'  rhr-.-j;':i '.h<-  f'jca!  •:•> ;•:.-.<.- <•: c a'. •. e r
    1
    .,
    
    r
    j
    '.". '
    
    r i
    el
    la
    : c.'i
    .11 1.
    ri;- (-
    at l
    -,t. •
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    1
    
    VI •
    • •r )
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    V.-i r i a • :
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    • •'.eLted !.y ' .'.<-• ;>:.,.•
    • 'i(- • i ••' 'I 1 M(_(. '!•••
    '.:i i n • he lien' h of
    r i :::•ซ• s;.ac in;- ( i e
    A heuristic '•>::>! anat ion
    
    
    • :.e r.oij'ii.v :' or. is a :"•]:>-..••
    . a f;i:ii:t itin <;f '''u.-. w.-'.e
    <•:" vhv t he- vi •;:!<: 1 : • v var
    ::-.jre '.. -.::.-
    
    " . *
    ',:: r>:" • i.t.- ;,.-ir '
    o -J is * : t- :i-ir"
    
    ; c : t- .li ;H-
    * : c 1 1-
    
    1:: as  !oi]o-*-:;.  i'ai t i c 1 ซ-s rrj-u.-h st-.a 1 ! ซ-r  ' fi.'in '.he fri:';;-!- Mia^in;-, tros-.i.-.;1 * he pro:/*- vul-
    '.:~ie will  sca-'er li/h'  'o 'rare n-i'. the sinusoidal  fringe in'ir.-.i'y i- i s • r i I,'.;; i :m  :n-
    <-ident  MI.on it.  l:icri-.-r.: :;;• i ho p.ir'iclc-  -,: .-.e with  res;u-ct. to • : .•  :'r:r.,c spacitij'  vi !'.
    result  in 'he nar'ii'ie  s; .it i er i r.;-  iii-.h'  fr';ni the  fr:n;-e i'_ is en-<-r i r:;-  -i-: -_-e 1 !  as • i:e
    or.e it  is li-avin/..   'i'.'n-  vi ::* hi J i ' v . a-.  siu:h. i s the-  ra*io rif • he ii-'n*  sea'. * i.-f'. ;i  v:!-.-:>
    tin- |i.-iri icii- i:: i:t-nt cn-il  over a Ijri;1::.  fringe in when  i'
    ! riiii-t-  .'imi is ;• iven l,y
                                 re.i
    vliere  I  is  the jilui' ซ>c;it hfilt- current..
    ซj! the multiple IM.-.IRI :;c.-it. I rrin;' |irnci.-s
    useful  in vi si.ial i .: int'  the  phennrien.i .
           The  tht.ir1/ !ป*-iiiiul  tin- pheniin'.cti-i
           .i::u;t r i i- in-h.iviur n!  th
    A! t Jj'i'Jrr.  I tie r i j'/iro'js  r.:it hcr:.'it ic.* I  *!esc
    :> i :.  rather i_i>ra;ilex.  'iiis simple Je ;cr i
                                                                                       r i pt. :or.
                                                                                       :n i on  is
                                                    /df
    wlu-ri- Jj  is the Ilessel's  function of  the  first kind.   In addition,  it  vas concluded
    that  in  'lie case of p.iraxial  lii-.lu col led i on, the  visibility  is  independent of  tin-
    Mil' scat, l.erin;' amplitudes,  the particle  shape, anil  index of re! ra.; t iปn.
           Subsequent 1 y, Robinson and Chu('")  derived the  functional  re Lit ionsh i p usiniป,  a
    Pore rigorous approach  hase'J  en scal.ir diffraction  (henry.  biffrjctimi  theory does
    not. include index of refraction effects  and Is valid unly for  sc.it teri n;'. centers  that.
    are several diameters (-.renter than the w.ivelenป'.lh of  lii-.lit..  The  analysis cor.c luded
    that the  visibility is  a  function of  the  lir.ht collection aperture as  woll as the  par-
    ticle diameter.  With p.iraxial forvarc! scatter observations the thecrv vas  in i-.ood
    agreement with Farmer's resu.ts.   More  important is the fact that  their  experimental
    data and  Farrier's agreed  very well with  the theory  usins; the above arsunpt ions.   The
    theory was also able, to predict experimental results  for particle si::cs  down to only
    a few microns in diameter.
           Evaluation of the  possible effects  of refractive index,  were ~ade  in a more  re-
    cent paper by Chi. anJ KobinsonO 1 hisinc,  a  di-tailcd  analysis of scat.terin?, from par-
    ticles in two cr-ssed coherent lii-ht  beams.    In this study the exact  solutions of
    Hflswell's equations (Hie  cheery) were employed.  For optics confirurations wherein
    the scalar diffraction  theory applied,  the analysis was in ar.reer.ent with Krju.it ion 4.
    The analysis showed reasonable agreement with the diffraction  theory  for scatterers
    that aro  absorptive.  The scalar theory  did, however,  i;ive consistently  hic.her values
    of visibility than did  the  !lie calculations.  For transparent  spheres  havin;; little  or
    no absorption significant oscillations of  the visibility function iccurs for frinrc
    spacing  less than  10.; of
    light passing through the sphere with the  diffractive  scattering.  The lobes seen  on
    the scattering diagrams in  Figure 1 arc  in parr due to this phc-r.or.ป?non.   For compari-
    son. Figure 5 shows the Mic scattering diagrams for a  particle with  and  without
                                                 363
    

    -------
                                       (b)   V - U.-W
    F190*ป 4. Otcillotcopt Tracm of S>rปH ''ซ" "ป Pvttcto d/mซ
           lnt
    -------
    absorption.  It is clear that the  small  lobes  arc-  due  to  inter ference with the li;;ht
    transmitted thro'jr.h the particle.   For  Lire, or  p.irticlc-s  the  diffractive scatter is
    dominant about the near- forward direction  and  the  main forward scatter lobe is sev-
    eral orders of magnitude ;-reater than the  off-axis secondary lobes.   Thus, in the dual
    beam scatlerinc, the interference between the  forward lobe and the secondary lobes is
    diminished.  It is believed that the oscillation  in the  visibility function is tlut- to
    the secondary lobe interference.
           Robt-rds( ' ^' examined some further aspects  of the  desipn of the optical c,eometry.
    In particular, the size of the collection  aperture and bean  stop, with respect to the
    beam spacing at. the collection len:;. were  shown  to affect the visioility.  This re-
    sult is not surprising, in th.it the entire  forward  scattered  lobes should be collected
    if the result is to aj-.ree with the analysis.   The  dependence was shown to be minimized
    with an adequately larc.e collection F/nuraber.  His data  also showed excellent agree-
    ment with the theory.
           From these observations and the  experimental results, it is clear that the mea-
    surement of visibility can dole-mine particle  size reliably  if the instrument is prop-
    erly designed.  Instruments based  on this  concent  will produce the size and velocity
    of the particle sinul laneous 1 y .  We have developed the electronics for processing the
    sic.nals to reduce the signals to particle  sixe and velocity  distributions in near-real
    tine.  Sophisticated noise discrimination  loc.ic  has been  introduced to reject undesir-
    able sic.nals and spurious noise.   The p.resent  systems  can make measurements in parti-
    cle field concentrations as hif.h as 105/cc(for  s:r.a 1 1  particles) at  rates as hii-h as
    !0"*/sec anil in flows of very hii'h  velocities  (•  600 n/sec).   A: present, we limit the
    lower si/.e ranc.e of this instrument to  approximately 'ซ_ra to  safely satisfy the afore-
    mentioned scattering criteria.  However, ri-liable  measurements r>i spherical water
    droplets as larc.e as *> mr  have been made.  To  extend our  measurement capabilities down
    I <> approximately O.Oum, scattering intensity  rat.ioinc,  has been integrated into our
    system.
    
    
    SCATTKKKIG INTENSITY KATIQl.'X:
    
           This '.<.-ch:i t'l'Je. based on the collection of  scattered  lii'ht at two angles in the
    near-forward direction (f-ic.ure ft) .  also makes  use  of a hic.hly focused lic.ht source
    allowing, for very hic.h spatial resolution.  The  .-•hsoltitv  scattering intensity docs
    not enter  into the size determinat ion and  bซ-cause  of the  near- forward lic.ht collec-
    tion. there is sufficient independence  of  particle shape  and index if "-efraclion (for
    absorbing part iclos) .
           Figure 7 is a schematic diagram  of  (he  optical  c.come I r v required for this sys-
    tem.  An Arc.on-Ion laser is used to provide  lic.ht  of wavelength U . <145;ji?..  To obtain
    the desired probe volume, beam expansion is used  before  the  he. in is focused by the
    transmitting lens to a spot of approximately  50um  in diameter.  The scattered lic.ht
    Is detected by the collection lens and  separated  by a  pair of annular masks into two
    anr.lcs of scatter; 2.5* and 'j' In  this  case.   Ratios of  tin-  sii-.nals from the photo-
    multiplier tubes arc taken in the  electronics  processor  for  conversion to particle
    size.
           Reduction of the measured ratios requires  the use  of  the polar scattering in-
    tensity distributions computed from the Hie theorv.  It  is important to note that the
    ratios of radiant flux. F. scattered by .1  particle of  diamo'.i-r d is independent of
    the incident intensity.  That is the ratio
                         F(f'j)    M,C"1(i.n>  +  i,('.,. i.r:)|  sin  rtj
                         FT77;! "  H, <•<-,.. ,n)  t  i2(-2...n)|  sin  ••,
    for two finite collection angles  "j  and  "j.  has  !„ cancel  from the expression.   This
    is of course the reason for  taking  the ratios.   The incident  intensity on the particle
    Is unknown as a result of intensity  variation vltli trajcctorv through the focal volume
    and benra attenuation.  The plots  of  the  normalized scattering intensity ratios versus
    particle diameter for three  pairs of collection  angles are shown in Figure 8-a   Com-
    plex index of refraction eivcn  by n  • 1.57  - 0.561 typical of soot was used in .he
    calculation of these curves.
           Dependence on the index  of refraction can become troublesome for non-absorbing
    spheres (e.g.. pure water droplctn with  n  -  1.33 - 01).  For  such tutorials, the
    
    
                                              370
    

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          Figure 6. Expanded Forward Scatter Lobe* Showing Collection
                     Anglei lot Intensity Ration^
              Particle-Laden
                Gas Flow
                                  Sample Volume
    
                                       /—Annular Mask Pair
    Beam E xpanaa" / Coiiimator —,
                                                   Zf Scatter
                                                  .2,5"   /LJ
                                                   Scatter
                                                          PM.T.
                                             L_J
                                         Argon-ion Laser
           Figure 7. Schซmซtic Oitgnm ol thซ Rttiotnq Optia Sytt*m
                            371
    

    -------
    intensity ratio is not nonotonic with p-jrticle si/.e but  shows  sone  oscillation  lead-
    ing, to multivaluedness (Kif.urc H-b) .   This effect  is due to  the  interference  of the
    electromagnetic wave scattered by diffraction with the scattered light  transmitted
    through the sphere and hence, that is shifted in phase.   Fortunately,  the  oscillations
    are damped for absorbing particles.  In the case of soot,  n  =  1.57  -  0.56i. or  other
    carbonaceous material, the relationship is a well-behaved nonotonic function  of  'xe.
           Another difficulty occurs when the instrument is  used to  measure in pop/dis-
    perse particle fields.  r'or example,  with the 10"/5" .scattering  anj^le combination.
    particles i.,;i;ei  than approximately 'J..m in diameter will show  similar ratios  to
    smaller particle:; (figure 8-a) .   This is due to the larger angle detector  bei'inning
    to collect light  fron the secondary scattering lobe (r.ce figure  I).   Hirlesan^ J
    suggested using a third collection angle to form two ratios  as a means  of  overcoming
    this problem.  In our integrated system, the visibility  processor will  have a size
    range overlap with the intensity ratioing system.  If the ratioing  sixer samples  a
    particle larger than its design range, the visibility processor  will  also  sample  that
    particle .simultaneously and will cause the ratioing electronics  to  reject  the sar.ple.
           Hirleraan performed a thorough analysis of the intensity ratioing technique and
    rr.ade estimates of the instrument accuracy.  He quotes estimates  as  hij'.h as 507,  uncer-
    tainty for combust ion aerosols with very little absorption.  The uncertainty  is re-
    duced significantly to approximately '/.Q7-. for absorbing particles.   Our  ratioing system
    is expected to operate at a sample rate as high as  IG'/scc,  in  particle concentra-
    tions as high as  lO'/cc.
    Ml'LTII'LE I'ROBK {'ARTICLE DIAGNOSTICS KISTKliMKN'T
    
           It is clear that an in situ particle sixing  instrument will  be  required  to  op-
    erate over a sixe range greater than one decade.  The achievement of  this  is  no triv-
    ial matter since the scatter intensity goes approximately  as  the diameter  to  the
    fourth power.  For two decades of si;:e range, the scattering  intensity would  range
    over roui-.hlv eight orders of magnitude on the forward lobe.   Because of this  intensity
    range and the fact that, there are typically a larger number of  particles  in  the small-
    er end of the sine range, two probe volume si/.es are used.
           Tlie Argon-Ion laser can produce both a blue  (0.488;.m)  and a  green  f.31'ป5..n)
    wavelength of light s Imul l.-.neously.   Figure <> is a  schematic  drawing of this  systen.
    The wavelength's .ire separated with a dispersion prism and  directed  throu/.h the  respec-
    tive optical elements previously described.  Since  the  rat ioing technique  is  sensitive
    to the smaller si;-.e range, that beam is expanded to achieve a focal volume that is an
    order of magnitude smaller than the visibility probe volume.  The incident intensity
    (energy flux per unit area) is thus increased by 10' in  the smaller probe.   Particles
    in the focal volume scatter light simil f aneous ly fron both wavelengths.  The  collect-
    ing optics separate tile signals by wavelength and direct them to the appropriate de-
    tectors .
           Tills concept n. t only extends the si;:e ranf.e without any need  for adjustments
    by the operator hut also provides a check for the sizing ambiguity of  the  ratioini;
    system.  Our desii;n has been directed toward development of a working  system  that  will
    function in the harsh environments without requiring; attention  by trained  specialists
    in optics or electronics.
           The entire optics package is compactly mounted on a single chassis  to  ensure
    instrument a 1 is;nraent .  A sealed rupgedi.:ed enclosure Is  used  to prevent fouling of the
    optics elements and to protect the components from  the environment.  Flexible connec-
    tions between the instrument ,?nd the facility access windows  are used  to keep these
    elements clean while allowing the probe to be traversed  across  the  test field.   In
    very hlr.h temperature applications,  an additional insulated housing can be provided
    and outfitted with cooling by either air or water.
    
    
    CO:;CUJSIONS
    
           The concepts incorporated Into our particle  si/ing  instrument have  been  shown
    to offer a reliable ceons of maklni- real t irae in situ particle  size measurements.
    Both particle sizing interfcrometry and scattering  intensity  ratiolng  have been tested
    in real measurement situations and have produced reliable  data.  Because of  the rela-
    tive complexities involved in these systems, great  care  is needed in their design  and
    applications.  Our goal has been to develop a field-ready  instrument that  will  produce
    reliable results without requiring operators sophisticated in the physics.   To  realise
    this goal, we have integrated our optics systems such that measurements ovซ;r  a
    
    
                                              372
    

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                            3     4     *i    ft      7
                        Diamater  m Microns
            Figure 8 a. Seafaring Intensity Ratio Venus Particle Size
                  (or Rtpxsentativa Cclfcct on Angle Pairs
    CC
       1O
      Ofe-
      C.2-
                                   nr1.57-0i
    
                                           = 1.57-0.57.
             4ฐ/2ฐ  Scattering
          O123456
                  Diamztcr  tn Microns(M)
         Figure 8-b. Comptnon of Absorptive end Non-ebsorptive
                        Scancring Ratio*
                              373
    

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    \
                                                                              'i
                                     X
                                   /  .
                                         • * .' .fi-'.s. >f r  t-* ',* rj?r *;* r*'V    i-' i. .*f . f j *J> •ป'
                                                                             64
                        Figure 9. Integrated Particle Siiinq Syitem Combminq P. rtide Sumq
                               Inlctftrometry and Scntei.nq Inttmity RซtK>n 9
    realistic  p.iriiclc' sixo r.iny.e can  he nwide without  .inv nan ipul.il ions  by  the- opc-r.:itor.
    We h.'ivc  found  in p.isl cxperivict- that the requirement for such tvmi pul.it ions ii'.id to
    instrument  failure or unrol i.iblc djt.'i.
           Relali*;:i data rates.  The instruments al?o
    have the capability of beinp interfaced to the power plant to warn the  systcn,  for
    example, of excessive particle  loading.
           In  the  future, we plan to extend the nininum size defection ranr.c  down to O.lyra
    particles.  A  candidate method  th.jt  'las produced accurate results is  based on ralioinr,
    the forward and backseattcred li;-,ht.   Such -i technique could be incorporated into our
    present  system.
                                                374
    

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    REFERENCES
    
    1.  D. orvce-Sr.i'.h. i'hysics Bulletin.  Vol.  25.  197'..  p. 173
    
    ?.  J. D. Trolinf.cr and W. D. Bachalo.  Spcctron Develonnent Labor.V-.nr ies .  Ir.c..
        "Particle field Diagnostic Systems  for  Hirh Tempera turo/Pre:. sure  Kr.vironr-c-nts".
        presented at "KPA/EKOA Sv^iposiuni on Hir,h Temperature/Pressure Paniculate Control".
        Washington. D. C.. JO ar.J. Jl September  1977
    
    'j.  H. van cl<> Hulst. Light Scattering  by Snail  Part icles . John Wilev  a.id Sons. New
        York. 1957       "
    4.  M. Kerker. The Seal tor ing of Light  and  Other Elect ror^i^nct ic R.-nliat ion. Academic
        Press. New York. 1V67
    
    "3.  V. M. rarr.er, "Sample Space for  Particle Si/.e- and Velocity Measuring  Interferom-
        eters". Appi ied Opt ics . Vol. 15.  No.  8.  August 1976
    
    6.  '.. D. Hirlenan. "Optical Technique  for  Paniculate Character ix.at inn in Combustion
         >.vironir.ents:  The Multiple Ratio Single ['article Counter", 1'h.D. Thesis.  Purdue
        L'niversi t v. August 1977
    7.  H. Kn^elnilc. "ImaRinR of Optical  Modes  -  Resona'ors wit!: Internal Lenses".  Be 1 1
        Systems Technical Journal. Vol. 44.  No.  1-6.  1965
    
    8.  C. N. Davies. Aerosol Science. Academic  Press.  London. 1966
    
    9.  W. M. Fanr.er. "TI.e Interieronietric Obse:vation  of Dynamic Particle Sir.e.  Velocity.
        and Number Density". !'h . .'  Thesis. University of Tennessee. 1973
    
    10. D. M. Robinson ar.d W. P. Chu. "Diffraction Analysis of Poppler Signal Character-
        istics :"or a Cross-hearn Laser Uoppler Velocimeter" . Appl icd Opt ics , Vol.  14, No.  9,
        September 1975
    
    11. W. P. Chu and D. M. Robinson. "Scattering from  a Movim- Spherical Particle  by  Two
        Crossed Coherent PI ne Waves". Apj; ' ' _'_ Optics.  Vol. 16. No. 3. March  1977
    
    12. D. W. Roberds . "Particle Siting Usinp, Laser Inter ferometry". Appl ied Opt ics .
        Vol. 16. No. 7. July 1977
                                               375
    

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                QUESTIONS/RESPONSES/COMMENTS
         FREDERICK HANZALEK, CHAIRMAN:  Thank you, Dr. Bachalo.  We have
    a minute or two since we are ahead of schedule.  Is there anyone who
    would like to ask  an  immediate question?  Would you identify yourself,
    please?
    
         MR. KWON:  I  am Henry Kwon from Dorr Oliver, Inc.  Suppose two
    particles, side by side, not quite put together, happen to enter that
    crossover point.   How would your  instrument respond to that situation?
    That is the first  question.
    
         The second one is what is the maximum and minimum range of
    particle concentrations your instrument could be applied to?
    
         DR. BACHALO:   My answer to the first question is if two parti-
    cles pass through  the probe volume at the same time, one slightly
    behind the other,  they will undoubtedly produce a signal that is out
    of phase.  The electronics processor tests the periodicity of each
    signal by comparing the period ratio measured over 5 cycles and 8
    cycles to the ratio 5/8 to within a preset acceptable difference.
    Aperiodic signals  would be rejected.
    
         The second question:  If you have a long enough time to wait,
    there really is no minimum particle rate.  Both of the techniques
    described are single-particle counters; they are sampling an indivi-
    dual particle at a time.  The upper limit is determined by the
    requirement of having a high probability of having one particle in
    the probe volume at any time.  Knowing the size of the probe volumes,
    you can determine  the loading that will give a sufficiently high
    probability of having one particle in the probe volume at one time.
    If the number- of multiple particle occurrences is too great, the
    distribution will  be biased since multiple occurrences are rejected
    by the electronics.
    
         To work in flows of high concentration every effort must be
    taken to reduce the measurement cross-section.  The probe volumes can
    be made as small as 10"' cubic centimeters for scattering intensity
    ratioing and 10~4  cubic centimeters for the particle sizing inter-
    ferometry.  This would correspond to measurable concentrations of
    106 and 103 particles per cubic centimeter, respectively.
    
         FREDERICK HANZALEK, CHAIRMAN:  Dr. Bachalo, I think you had at
    least one.
                                    376
    

    -------
         DR. BACHALO:  Yes; I have two questions.   One is *rom Dr. Janes
    Wang.  His question is:  "Can you explain why your neasurenent
    disagrees with Coulter counter results?  Is there a theoretical
    analysis?"
    
         For those of you who don't know, we also had an instrument at
    Argonne National Laboratories doing tests at a similar time that Dr.
    Muly's instrument was there.  Some of these results were presented
    last niaht by Mr. Swift.
    
         Our instrument measured particles that were somewhat larger
    than the Coulter counter.  There are two possible reasons for this.
    The Coulter counter is obviously not an on-1 ine device.  To make a
    measurement, a sample of particle laden fluid must he extracted from
    the flow.  This sample is then placed into an electrolytic solution
    and the impedance of the current flow through an orifice is measured
    as particle* moving with the electrolytic solution through the
    orifice obstruct the current flow.  An electric volume (E.V.)  is
    measured and related to the actual particle size.
    
         If particles measured in situ by our instrument were composed
    of agglomerated sub-particles, these agglomerates could have been
    redispersed in the electrolytic solution.
    
         The other  Tssihility can be related to a difficulty with
    our electronic processor.  The system was picking up noise and some
    of the size distribution indicate that this was the case.  Unexplain-
    able himodal distributions occurred during the measurements.  Trouble
    with the processor was discovered later and corrected.
    
         The other questions were from Jerry Whitfield from the United
    Kingdom.  The first question is:  "What are the fringe spacings in
    the green and blue probe volumes?"  I may not  have made myself
    clear.  There are two techniques that we have introduced into our
    system.  One makes use of particle sizing interferometry, in which we
    spl. c the beam into two and interfere them; that causes the fringes.
    
         That technique was used for the larger size range.  We were
    sensitive to sizes from about 5 to 40 microns  for this particular
    instrument, so the fringe spacing was set at about 45 microns.
    
         In the green, we are using scattering intensity ratio.  A single
    beam is focused down to a very small point (approximately 80//m in
    diameter) and we then look at the scattering at two angles.  By
    ratioing the two intensities we can get an indication of the particle
    size, using the scattering diagrams to relate  the collected scatter
    intensity ratio to the particle size.
                                    377
    

    -------
         Ti.e second question is:   "Can you describe the influence of
    turbulence in the particulate flow stream on the output  signal  and  on
    the estimate of particle size?"
    
         You nay remember from the introduction that I  have  measured
    transonic and supersonic flows with a laser velocimeter  and thus have
    addressed that difficulty.  We have made accurate measurements in
    sunersonic turbulent boundary layer separation wherein the turbulence
    levels are very high.
    
         If a turbulent cell passes  through one beam and not the other
    (or through the other later), a  phase shift in the  interference can
    occur which will  cause the fringes to move and can  also  change the
    fringe spacing by changing the beam intersection angle.   However, the
    beams are entering the flow very close together and as long as the
    turbulent cells are large enough the time in which  this  error might
    occur is an extremely small percentage of the total  time.  This is
    especially true in the low speed flow found in the  fluidized bed
    combustion facilities.
    
         As to the size measurement, the effect of the  slight variation
    in fringe spacing will manifest  itself as a proportionate error in
    size measurement.
                                    378
    

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                                 A Particulate Sampling System
                            for Pressurized Fluidized Bed Combustors
                                  William Masters and Robert Larkin
                                       Acurex Corporation
    ABSTRACT
    
           A particulate sampler for high-temperature,  high-pressure processes has been
    developed and successfully demonstrated.  The system uses an extractive approach, re--
    moving samples from the process stream for complete analysis of particulate size dis-
    tribution, morphology, and chemical composition.  System capabilities have been demon-
    strated by sampling a pressurized fluidized bed combustor.  This paper describes the
    extractive sampling approach, the HTHP sampler design, and the data obtained from
    sampling operations.
    
    
    INTRODUCTION
    
           Advanced coal conversion processes present new problems in particulate sampling,
    including severe environments beyond the capabilities of conventional equipment.  This
    paper describes a newly developed sampling system,  specifically designed for the high
    temperatures and pressures found in pressurized fluidized bed combustors.  The system
    uses an extractive sampling approach, withdrawing sampler, from the process stream for
    complete analysis of particulate concentration, shape, size, and chemical composition.
    The capabilities of the new system have been demonstrated in two phases of sampling
    operations at a pilot-scale fluidized bed combustor owned and operated by Exxon Corpo-
    ration.  The first phase of testing was performed with the sample probe in its basic
    configuration.  The second test phase utilized modified probe internals designed to
    investigate possible condensation of alkali metals.  The system performed successfully
    in a variety of operating modes, producing sample data from both test series.
    
           Acurex Corporation has developed the HTHP sampler for the Industrial Environ-
    mental Research Laboratory of the Environmental Protection Agency.  The work is part of
    a broad program investigating new sampling technology for advanced coal conversion
    processes (Contrcct 68-02-2153).  The EPA Project Officer for the contract is William
    Kuykendal.
    
           The following sections of this paper discuss the extractive sampling concept,
    the HTII" sampler design, and sampling operations that have been performed with the new
    system.
    
    Extractive Sampling
    
           In extractive sampling, a quantity of particle-laden product gas is drawn out of
    the process for analysis.  Once extracted, the sample can be thoroughly examined by
    conventional methods.  If proper care is taken to obtain and maintain a representative
    sample, the extractive approach will provide complete, accurate information on proc^-?
    constituents.
    
           The sample is typically extracted through a probe inserted into the process
    duct.  The sample withdrawal rate at the probe nozzle must be matched to the duct velo-
    city to avoid biasing particle size distribution measurements (isokinetic sampling).
    The error in measured particle content as a function of an isokinetic velocity mismatch
    can be estimated analytically (see Figure 1).  For fine particles at low velocities the
    error is negligible, but for larger particles or high velocities, serious errors re-
    sult.
    
           Sample temperature is also a consideration in the extractive approach.  Ideally,
    the temperature would be maintained at process conditions during particulate separation
    and analysis.  In practice, however, the sample is usually cooled to temperatures com-
    patible with analysis equipment.
    
           The major advantage of the extractive method is that the sample can be analyzed
    by conventional techniques.  For example, particulate removal and size classification
    
                                              379
    

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       2.0
        1.8
    
    O
    O
    
    ง1.6
    c
    O
    111
    5  12
    Z
    O  1.0
    
    
    (C
    O  0.8
    
    8
    O
    u<
    c  0.6
    O
    O
    u.
    O  0.4
    I
        0.2
              k = 1.0
                    0.1        0.3         1         3
    
                               VELOCITY RATIO (R)
                                                             10
                  Figure 1. Probe Inlet Bias (from Reference 1)
                                       380
    

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    devices, trace element collectors, and chemical analysis techniques are all highly
    developed  (References 1 to 5).   Extractive sampling is commonly used in emissions
    measurement and combustion studies.       . .
    
           Access to the pressurized duct is  the main difficulty in extending extractive
    sampling technology to hign-pressure, high-temperature processes.  The hardware re-
    quirements for entering a pressurized process are much more complex than for ambient
    pressure applications.  The selected design Cor the HTHP sampler is described in the
    following sc-ction.
    
    
    HTHP SAMPLER DESIGN
    
           The new sampler design adapts conventional sampling technology to high-
    temperature, high-pressure environments.  Key system components are:
    
           •  A traversing sample probe that  can be inserted or withdrawn during process
              operation
    
           •  A probe housing that contains process pressure during sampling
    
           •  A cascade impactor to both collect and size particulate — interchangeable
              with a bulk filter (Phase I tests)
    
           •  An in-stack scalping cyclone and backup filter followed by a "cold" final
              filter (Phase II tests)
    
           •  Conventional trace element collectors (organics trap and impingers)
    
           •  Measurement and control instrumentation to assure isokinctic conditions
    
    A schematic diagram of the Phase I sampler is shown in Figure 2.  The samp'e prcje is
    mounted within a pressure-containment housing.  The probe can be inserted into the
    stream through valves that connect the housing assembly to the process duct.  Sample
    flow in the probe pacse-j through a cooler and particulate collector (cascade impactor).
    Flowrate is controlled by a throttle valve at the piobe exit.  After leaving the probe,
    sample gases are conducted through the trace element collectors, and vented.
    
           The sampling system is shown in Figure 3.  In addition to the probe and housing
    assembly, controls, and sample collectors, the system includes a portable hydraulic
    pump.
    
           One of the basic decisions in designing the sampler was the choice between fixed
    and translating probe configurations.  A  translating probe (one that is insertable and
    removable during process operation) is more complex than a stationary probe, but offers
    several operating advantages:
    
           •  Particulate deposition losses in the probe can be recovered
    
           •  Nozzles can be changed to maintain isokinetic conditions
    
           •  The probe can traverse the duct to measure flow variations
    
           •  Probe exposure to erosive/corrosive conditions is minimized
    
           •  Inspection and maintenance are possible during process operations
    
    Based on these advantages, the translating probe design v.-as selected for the HTHP sam-
    pler.  The sample probe and particle collector are shown in Figure 4.
    
           Selecting the particulate collection temperature was a second major design deci-
    sion.  A number of well-characterized device^ are available for use below 500ฐF, but,
    high-temperature particulate collectors are in an early stage of development.  Based on
    this practical limitation, a collection temperature of 450ฐF was selected with the
    awareness that possible changes in particulate composition would have to be considered.
    Major changes in composition are not likely above the sulfuric acid dewpoint.  However,
    changes in trace element concentration are a potential concern.  The HTHP sampler has
    
    
                                              381
    

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       ft'
    Flow
                    Process Duct
                   Access Valves
                                        Enclosure
                                       ' (Pressure Boundary)
           JKNV^NLy
    
             Cooler'	Impacto
                                                          Control Valves
                                                                 Flexible Line
                                                                 Heat Tracing
    t ..n,
    
    
    
    
    
    
    
    
    Flow Organic
    ontrols Collector
    
    
    1 1 	 .^.
    Vent
    Trace
    Metals
    Implngers
                                   Figure 2. System Schematic
         Probe Drive
         Hydraulic Cylinder
                       Microswitches For
                       Transverse Control
                                  Inner Tubular Housing
                                                     Dowtherm Coolant
                                                    Systems And  Controls
                                                          •i	
    Outer Tubular'  Control Umbilical-7!
    Housing                      ซ^
                                                           Dowtherm Coolant
                                                           Supply And Return
                                                       Sample Line
    
                                    '•-T-tff-r       Control Valve
                                   u'-r-:r       And Operator
                _  . -  _     .      Hydraulic
                Control Console     Supply System
    
                       Figure 3. High-Temperature. High-Pressure Sampling System
    
                                          382
    

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    Figure 4. Exploded View of HTHP Probe
    
    
    
    
    
    
                   383
    

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    been used in an experiment investigating the effect of collection temperature on par-
    ticulatc composition, as described in a later section of this paper.  The impactor used
    with the HTHP sampler is a Mark III, University of Washington Source Test Cascade Im-
    pactor, Model D.
    
           The cascade impactor has several advantages over other particle collectors.  The
    device provides many stages of size classification in a small volume.  Also, impactors
    classify particlo size based on incrtial and aerodynamic properties that relate di-
    rectly to the performance of particulate removal devices.  Impactor performance is well
    characterized for moderate temperature, ambient pressure operation.  The effect of high-
    pressure on sizing performance can be estimated using theoretical correction factors.
    For fine particles at moderate temperatures, even large pressure increases have little
    effect on impactor performance.  Collection temperature, however, can affect measure-
    ments more significantly.  Variations in cut size with temperatures have been calcu-
    lated by the impactor supplier for temperatures up to 500ฐF.
    
           In the selected sampler design, the sample probe enters the pressurized process
    through 4-inch diameter full-opening valves while process pressure is contained by a
    surrounding housing assembly.  The housing, shown in Figure 5, consists of two tele-
    scoping cylinders which move the probe into and out of the process.  Hydraulic cylin-
    ders ccnnect the two parts of the housing.  Their function is to accurately position
    the prooe, and withstand the large forces from process pressure.  Scaling at the joint
    between the housing cylinders is critical, so redundant seals are used.  The tele-
    scoping housing is the most complex part of the sampling system and consequently re-
    quired the most design and development effort.
    
           The HTHP sampling system also includes the instruments and controls necessary
    for accurate sampling.  Sample flowrate is one of the important parameters that is
    monitored and controlled.  Flow nust oe both isokinetic at the probe nozzle and within
    the operating limits of the particle collector.  For proper control, flow conditions
    in both the process stream and sample probe must be measured.  A pitot tube and thermo-
    couple are mounted on the probe to measure process stream conditions, and a calibrated
    orifice and thermocouple check the sample flow.  The flowrate is adjusted to particle
    collector requirements by a valve near the probe exit.  Nozzle entrance velocity is
    varied by selecting larger or smaller nozzles.  The sampling system includes other con-
    trols for sample temperature, probe traverse, trace element collector flow, and other
    key operating parameters.  System controls are housed in two portable enclosures, shown
    in Figure 6.
    
           The trace element collection equipment included in the sampling system consists
    of an organics module and impinger train  (see Figure 7).  Both units are identical to
    those used in the Source Assessment Sampling System that is commercially available from
    Acurex.  The organic module cools the sample gas to 70ฐF and traps organic vapors in a
    potous polymer granular bed.  The polyjier used in this test series is Rohm & Haas XAD-2
    gas chromatographic packing material.  The impinger train has four high-volume glass
    impingers, three filled with oxidizing solutions and one with silica gel moisture
    absorbant.  The oxidizing reagents in the impingers collect volatile trace elements by
    oxidative dissolution.  The reagents are:
    
                          Impinger               Solution
    
                            No. 1      6M H/Ox
    
                            No. 2      0.2M (NH4)2S2O8 + 0.02M AgNO3
    
                            No. 3      0.2M (N!l4>2S2^i + 0.02M AgNOj
    
                            No. 4      Silica gel
    
    The peroxide solution in Impinger No. 1 collects reducing gase1" such as sulfur dioxide
    which would lessen the oxidative capability of Impingers Nos. ซ  nd 3.  The ammonium
    sulfate and silver nitrate solutions serve as the trace element collectors in the
    impinger train (Reference 3).
    
    PFBC Facility
    
           The new HTHP sampler has been demonstrated in operations at the Exxon Miniplant
    PFBC.  The PFBC facility is described in this*section.
    
    
                                              384
    

    -------
    Figure 5. Aarotherm HTHP Sampling Probe and Duct Interface Valve
                               38b
    

    -------
    Figure 6. Control Console!
            386
    

    -------
                                                     Impingers   j/. -J'
     Flow
    Control
     Ovsn
                                             -^E^iP
                            Figure 7. Flow Control Oven and Gas Train
                                       387
    

    -------
           The- V.iniplant  is .-ป pilot-scale- pre-ssuri ze-d  fluidize-d  bod coir.bustor operated  for
    t h<- Kf'A by the  Kxxon  pes'-arch "m'i Kr.'fi no'.-r i n-( Conpany  in  I. indc-n, :.'e-w Je-rsey.  The- I-FIiC
    procr-KSt shown  in  Ki'jure H,  i:'; a ceiir.bine-d-cycle- coal combustion process.  Combustion
    occur;; under  pressure- in a lime-stone- bed that is fluidiz'-d by incoming air.  Fluidiza-
    t. ion ijivr-s -food mixinq for efficient combustion, and the-  lime-stone- bod ronovos ri'jch of
    the- :;ul!'ur role-.'ise-d durin-j the- combustion proce-r.s.  Added useful e-ner'r/ con be produced
    by e-xpandini]  hi'|h-pres:;ure- flue- q.ise-:; in a 'jas turbine-,  if particulato loadinq can  bo
    roduce-d to the-  leve-ls (0.0002 t.o O.OOi -jr/scf) ro'iu i re-d  to protect turbinr- bla-Je-s.  The-
    Kxxon Minipl.mt facility in be-in') use-'l to invest i'jat'--  fluirlize-d bod combustion, 'jas
    cl'.-.inup devices, and  part icul ate- 
    -------
     Gas turbine
                          Boiler
                                                       R*generator
    Figure 8.  Pressurized Fluidized Bed Coal Combustor System
                              389
    

    -------
    Figure9. Minipiant PFBC
    
    
    
    
            390
    

    -------
    Figure 10. HTHP Probe Assembly (rotated at Exxon Mimplant
                         391
    

    -------
        :OO
    
        SO
    
    
        60
                                  PERCENTAGE UNDERSIZE (BY WEIGHT)
    
                          10       20     3C    40   50   60    70    80      90
                                                                                         98
    J)
    N
        4C
        10
    
         8
    UJ
    
    
    5
    UJ
    d    2
       10
    
       08
    
    
       06
    
    
    
       0.4
       02
        0.1
                         90      80    70    60   SO   40   30
    
                                      PERCENTAGE OVERSIZE
    
    
                                Figure 11. Partids Size Distribution
                                                                          10
                                             392
    

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                                                         i;l?>''v --vVf-V- •  '.  '
                                                                                      -•
       • ., , '*'  rf-f," ,'i "• • j>- i  ;          '•••A'-""-  .' •' •""' *>^'-*<.  '*: .*  •" " *•••"••-
         <*!;'v  '•'ซ\. •-*•• ''•••" •"•••   •-••• '••"*'•'•'•       •   j-       •       '
                .  .   \\ ,-. , ->-;.  , ,    .         , ..  -
              .'•••ป••;.-'•;-•-
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    Figura 12. Imptctor Subflratw
                393
    

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    STAGE 5
                                                                                   FILTER
                                   Figure 12. Concluded
                                         394
    

    -------
    several plugged jets.   The substrates from Run 2 are lightly loaded.  Those from Run 3
    show heavier, three-dimensional deposits.
    
           Examples of particulate photomicrographs, showing particle size and shape, are
    shown in Figures 13 and 14.  These plots were made by a scanning electron microscope.
    The irregular appearance is typical of flyash from lower temperature combustion pro-
    cesses (Reference 8).   The photos show the trend of decreasing physical size from
    Stage 1 to Stage 6, although irr&gular shape and possible agglomeration make visual
    interpretation of particle size very difficult.
    
           The chemical composition of the collected particulate was analyzed by dispersive
    X-ray fluorescence.  Spectra of X-ray emissions from impactor Stage 1 and Stage 6 are
    shown in Figure 15.  The peaks in the spectra correspond to the number of emissions
    detected at characteristic wavelengths of various elements.  Results show the presence
    of aluminum, silicon,  sulfur, potassium, calcium, titanium, iron and copper.
    
           Comparing the relative height of the peaks in two spectra can give a rough indi-
    cation of the relative quantities of elements present in two samples.  The comparison
    of Stoge 1 and Stage 6 spectra shows no apparent difference in bulk composition between
    the coarse particles collected (DSQ of about 30 microns) and the finer particles (050
    of about 0.6 micron).
    
           Data from the system demonstration tests are discussed more extensively in a
    test report submitted to i-PA IERL  (Reference 9).
    
    Phase II — Condensation Tests
    
           Following the system demonstration tests, a second series of sampling operations
    was conducted at the Exxon Hiniplant.  The purpose of these tests was to investigate
    the effect of sample cooling on measured particulate mass and composition.  We were
    specifically concerned that trace elements might condense between process temperature
    and conventional particulate collection temperature  (about 450''F) .  Of particular
    interest were the alkali metals, primarily sodium and potassium.  For these tests, the
    sampler was set up to collect particulate at process temperature, so trace element con-
    densation could be investigated in two ways.  First, the trace element content of
    particulate collected at 450ฐF (from the demonstration test series) could bo compared
    with the content of particulate collected at duct temperature to see if any significant
    differences result.  Second, after the particulate was removed at process temperature,
    the sample gasses could be cooled and filtered to collect condensation products.
    
           The probe configuration for the condensation tests is shown in Figure 16.  A
    scalping cyclone and a high-temperature filter are mounted on the front of the probe to
    remove particulate at process conditions.  After a series of chokod orifices, used to
    gradually reduce sample gas pressure, a final filter removes condensed material as well
    as breakthrough particulate.  The cyclone is a Southern Research Institute model,
    designed for much loss severe operating temperatures.  This cyclone was readily avail-
    able, was small enough for insertion into the duct, and had a very efficient C.6-micron
    cut-point.  During the tests, however, the cyclone's protective gold plating blistered
    and fell off, leaving titanium surfaces exposed to heavy oxidation.  Chemical analysis
    of the particulate samples showed significant gold contamination in the cyclone and
    front filters but none in the rear filter.  Titanium contamination was not evident in
    any of the samples.
    
           The high-temperat.ure filter following the scalping cyclone is made of saffil
    alumina, a material that Acurex is currently testing for high-temperature baahouse
    filters.  This material c-eems to offer excellent temperature resistance and effective
    filtration, but its performance hasn't yet been fully characterized. .Its porfor-ar.co
    .'.i the condensation tests was quite good, particularly with a two-filter "sandwich."
    The estimated filter efficiency was well over 90 percent of the fine particulate passed
    by the scalping cyclone.
    
           The final filter at the sample probe exit is a standard Gel-!an "microquartz"
    type with high efficiency and low trace element content.  It is possible to use con-
    ventional filter materials at this location because sample gas temperatur"> are sub-
    stantially reduced by  the probe cooler section and by sonic throttling in tho orifice
    section. •
                                              395
    

    -------
    Figure 13.  Particle Photomicrograph! Impactor Stage 1
                         396
    

    -------
    Figure 14. Particle Photomicrographs Impactor Stag* 6
                            397
    

    -------
    Figure 15. Particle Chemical Composition-Demonstration Tests
                             398
    

    -------
    CO
    VO
                    Normal
                                        Cooler
       4 \ Process Flow
    
    
    Condensation Test
                           Process Flow
                                        Impactor
                                                                           Sample Flow
                                                        (Or Filter)  Throttling
                                                                     Valve
    Scalping
    Cyclone
    r"br
    1350ฐF
    Filter
    HT
    
    Choked
    Orifices
    Cooler I 	 1- I 	
    i
    H)0ฐF
    Filter
    I
    3^7.
    Sample
    Flow
    — ปป
                                               Figure 16. Probe Configuration
    

    -------
           Four sampling runs were completed in the condensation test series.  Conclusions
    have fcoen drawn on the available data regarding condensation of trace notals, parti-
    cularly the more common alkali metals, sodium and potassium.
    
           The original intention of the Phase II tests was to compare- the elemental con-
    centrations found in the filtered natcrial of the in-stack scalping cyclone and backup
    filter with the material caught on the rear filter.  If the oysten worked ideally, one
    could assume all the material on the rear filter was in a gaseous state at stream con-
    ditions and would thereby pass through the hot cyclone filter combination and thus be
    indicative of condensation products produced within the probe.  Unfortunately, the rear
    (or cold) filter could not be reliably analyzed.  Carryover of glass fiber filter
    material during sample preparation, the snail amount of the sample available on the
    cold filter and additional contaminations, yielded poor detection limits with the spark
    source mass spectrometer  (SSMS) .  .Moreover, the values reported ฃor tnia iiltcr W(Tซ> '' n
    mass units rather than concentration units because a r.et filter collection weight was
    not determined.  This made any direct comparisons of cold and hot catches from Phase II
    results alone difficult.
    
           Samples of the probe wash were analyzed by Arthur D. Little, Inc., to determine
    the source of the suspected contamination of the rear filter.  A sample from each test
    was analyzed by thermal gravimetric analysis (TGA), infrared analysis (IR), X-ray
    fluorescence (XRF) , and low resolution mass spectra (LH.XS) .  Results indicated there
    were three sources of contanination.  They were: (1) approximately 30 percent particu-
    late -- attributed to hot, in-stack filter ijreakthrouch, (2) approximately 25 percent
    sulfuric acid and sulfatc condensate — attributed to localized cold spots (measured
    at 200ฐF) below the HjSC^ condensation temperature, arxi (3) approximately 40 percent
    organics — attributed to the disintegration of packir.g material from a valve located
    just upstream of the roar filter.  The evidence of breakthrough particulate contami-
    nation was supported by photomicrographs, which showed similar appearance between
    material on the front and roar filters, and by dispersive fluorescent X-ray spectrum
    which shows a similarity in chemical composition.  The sulfur content did, however,
    increase on the rear filter, apparently as a result of sulfate condensation.
    
           An alternate approach was taken to resolve the question of trace netal conden-
    sablcs.  During the Phase I demonstration tests at Exxon, a test run was made at essen-
    tially the same operating and scream conditions as the Phase II tests.  A total mass
    filter was used in place of the cascade inuactor and was maintained near 400ฐF.  North-
    rop Services, Inc. performed a SSMS analysis of the bulk filter catch, as they did with
    the Phase II cyclone and backup filter supples.  Table i presents the results for these
    analyses.  The measured elcr.ental content is similar to common flyash.  A partial,
    nondimensionalized comparison of these two sets of results. Phase I and Phase II, is
    presented in Table II.  Reference quantities Fe and Kc, have been chosen to nondimen-
    sionalizc the results because they exist in significant concentrations in each sample
    and are not likely to be present as a result of contamination.  ''ondimensionalizir.q
    was done because there appeared to be a diluent in the Phase I filter catch.  The Si
    concentrations indicate that the filter material itself nay be the diluent in the
    samolc.  In fact, the sample analyst acknowledged some difficulty in separating the
    sample from the filtering media.
    
           Aside from the Si results, comparison of the other quantities shown indicates
    that there was no detectable change in the concentration of Ha or K fros the hot to
    cold particulate catches.  This limited data would indicate that particulate collection
    at low-pressure and 400ฐF yields accurate results for particu'.ates.
    
    
    CONCLUSIONS
    
           The sampling system described in this paper der^..strates that extractive sam-
    pling is a feasible approach for sampling high-temperature, high-pressure processes.
    Furthermore, the Phase II condensation test data indicates that sample filtration at
    reduced pressure and low temperature (400ฐF) yields accurate results for particulates.
    Technology for sampling pressurized fluidized bed combustors is now developed and
    available.  Future development also will be required, however, to make useful appli-
    cation of this technology and extend it to other advanced coal conversion processes.
    
           One of the remaining issues for FBC high-temperature, high-pressure sampling,
    is system cost/performance trade-offs.  Process developers seem to be interested in
    both upgraded and downgraded versions of the sampling system.  Upgraded versions offer
    
    
                                             400
    

    -------
          Table I.  Concentration of Elements in Flyash SSMS Analysis  (Partial)
    
    Element
    
    K
    Ila
    Rb
    Cs
    Al
    Si
    Fe
    Ca
    Mg
    Ti
    Sr
    Ba
    Au
    P
    Cu
    Zr
    Ni
    Cr
    Pb
    
    Cyclone
    (ppm)
    8,200
    1,310
    <70
    6.7
    164,000
    94,000
    30,000
    20,000
    11,400
    2,430
    810
    710
    650
    276
    248
    160
    120
    <90
    85
    Test No.
    Front
    (ppm)
    8,850
    2,500
    :68
    0.23
    94,000
    82,600
    13,400
    19,000
    17,800
    1,950
    555
    694
    118
    223
    165
    140
    100
    <140
    75
    3 — Phase II
    Rear
    (ppm)
    15.1
    <135.0 *
    <0.43*
    <0.62
    64.2
    <2510.0
    60.0
    <6.6 *
    38.0
    7.1
    0.6
    <5.0 *
    <1.4
    <224.0 *
    <1.5 *
    <2.1 *
    5.8
    <13.1
    <4.0 *
    
    Rear Blank
    (ppm)
    5.4
    91.0
    0.13
    --
    6.4
    1210
    2.36
    7.3
    5.9
    3.1
    1.15
    1.5
    —
    68.0
    0.91
    0.64
    0.29
    6.4
    1.2
    Phase I
    Bulk Filter
    (ppm)
    16,260
    3,560
    866
    8.8
    Major
    310, OO"1
    36,300
    44,700
    28,600
    10,600
    1,320
    1,080
    13
    1,880
    142
    334
    348
    366
    86
          Notes:   <   - Natural  background  limited  detection limit.
                  <*  - Blank  limited detection  limit.
    longer sampling durations, quicker turnaround and better operating convenience.   Down-
    graded versions, such as fixed-probe designs, arc cheaper, but give  less  information.
    gasi
        The next objective for extractive sc.-npling is to develop technology for coal
    ififjrs.  Particulatc measurement is also important for developing these processes,
    ^ ซ-i i 1. * *_ L *? •  IC1lt.lv.uJU\.L IIH_ M ^ u I *_ lllrjll l_ JO U J ฃ31^  Itlll-'Ul.l.ClIll.  i UI tit: VU i Ul.- i il
    
    and environmental difficulties are even more sovere than  for FPBC's
    REFERENCFK
    
    1.  Lundgrcn and Calvert, "Aerosol Sampling with a Side Per: Probe," Amor.  Ird.  Hvo
        Ass. J. , 28:213 (1967) .                                                        ' '.
    
    I.  Calvert and Parker, "Collection Mechanisms at High Temperature and  Pressure,"
        Symposium on Particulato Control in Energy Process, EPA-600/7-76-010, Sept.  1976.
    
    3.  Homersma, et al., 1ERL-RTP Procedures Manual:  Level  1 Environmental Assessment,
        EPA-600/2-76-106a, June 1976.
    
    4.  Blake, D. E. , Operating ar.d Service Manual -- Source  Assessment Sampling Svsten,
        Aerothorm Report UM-77-80, March 1977.                                   ~
    
    5.  Gooding, C. 11., Wind Tunnel Evaluation of Particle Sizing Instruments,  EPA-600/2-
        76-073, March 1976T
    
    6.  Operation Manual,  Mark III University of Washington Source Test Cascade Inpactor
        (Model D), Pollution Control Systems Corporation, Renten Washington, March  1974.
    
    7.  Hoke, R. C., "FBC Particulatc Control Practice and Future Needs:  Exxon V.iniplant,"
        Symposium on Particulatc Control in Energy Processes, EPA-600/7-7G-010, Sept.  1976.
    
    8.  Hoke, R. C., Exxon Research and Engineering Company,  Linden, New ?  rsey, Personal
        Communication.
    
    9.  Masters, W. Z., "Field Testing of a Sampling System for High-Tenperature/High-
        Pressure Processes," Annual Report, Measurements of High-Temperaturc/High-i'rossure
        Processes, Aerotherm Report TR-77-55, July 1977.
    
                                              401
    

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    II.  Partial  Comparison  of Front and Rear Particulate Catches
         from Exxon Test  Series  I and II
    
    K
    Fc
    Na
    Fe
    Si
    Fc
    Ca
    Fe
    Mq
    Fe
    Sr
    Fc
    Ba
    Fe
    K
    Mg
    Ha
    Mg
    Si
    Mg
    Fe
    Mg
    Ca
    Mg
    Sr
    Mg
    Ba
    M?
    Phase I Tests
    Bulk Filter
    0.45
    0.10
    8.54
    1.23
    0.79
    0.04
    0.03
    0.57
    0.12
    10.84
    1.27
    1.56
    0.05
    0.04
    Cyclone
    0.26
    0.04
    3.13
    0.67
    0.38
    0.03
    0.02
    0.72
    0.11
    8.25
    2.63
    1.75
    0.07
    0.06
    Phase II Tests
    Front Filter
    3.66
    0.19
    6.16
    1.42
    1.33
    0.04
    0.05
    0.50
    0.14
    4.64
    0.75
    1.07
    0.03
    0.04
    Avg.
    0.47
    0.12
    4.65
    1.05
    0.86
    0.04
    0.04
    0.61
    0.13
    6.45
    1.69
    1.41
    0.05
    0.05
    Ratio
    0.96
    0.83
    1.84
    1.17
    0.92
    1.00
    0.75
    0.93
    0.92
    1.68
    0.75
    1.11
    1.00
    0.80
                              402
    

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    Mathematical Modelling
             403
    

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                          INTRODUCTION
         FREDERICK  HANZALEK, CHAIRMAN  Our next paper was originally
    scheduled for presentation at 10:40.  As I mentioned before, we are
    interchanging those.   So, we are going to go now to the paper on FBC
    modeling and data  base.  This paper was authored by Messrs. Tung,
    Goldman, and Louis of  Massachusetts Institute of Technology.
    
         The paper  will  he presented by Dr. Tung, who is a graduate of
    MIT.  After work at Continental Oil Corporation on natural gas
    liquefaction, and  where he also set up a catalysis and catalytic
    process research laboratory, he joined the MIT energy laboratory
    approximately three years ago.  His work there has been primarily in
    the areas of fluidized bed combustion, energy-to-energy conversion,
    fuel-to-fuel conversion, and catalysis.  Dr. Tung.
                                     405
    

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                                 FBC-Modelling and Data Base
                                   Shao E. Tung. Jay Goldman,
                                       and Jean F. Louis
                               Massachusetts Institute of Technology
    I.  INTRODUCTION
           One of the most attractive, near-term advanced technologies for the environment-
    ally compatible use of coal is fluidized bed combustion.  For that reason, significant
    commitment has Laen made by DOE to bring this technology to commercial application.  As
    a part of this overall effort, MIT .has organized a broad-based multi-disciplinary group
    working toward the establishment of a systen model for the technology.  The overall
    objectives of the project are:
    
           (1)  To establish a comprehensive system model that is sufficiently
                precise to be suitable for process and engineering design
                optimization.
    
           (2)  To establish a data base system that will reposit all relevant data
                on coal based FBC (fluidized bed combustor) in a single site and
                can be used to answer various queries from remote sites.
    
           It is proposed to achieve these broad objectives in several phases.  The initial
    phase, which is currently being conducted, has the following more limited qoals:
    
           Modelling:  To develop an initial system model using mainly the
                       state-of-the-art information
    
           Data Base System:  To select and implement a data base management system
                              suitable- for FBC.
    
    
    II.  FIRST GENERATION SYSTF.M MODEL DEVELOPMENT
    
           In this initial phase of nxxlelling, a portion of effort has been devoted to
    develop adequat.; pro.-ess representation.  In this regard,  a major finding of our study
    is that the behtvior of an FRC in which relatively large particles (e.g., 1mm) are being
    fluidized differ; significantly from the behavior of a more traditional fluidized bed
    reactor such as i-n FB catalytic cracking un> c where relatively small particles
    (e.g., 60u) aie being fluidized.  Furthermore, the differences seem to permeate through
    all phases of bed behavior'^'^).
    
           When uncertainties regarding process representation and our commitment to put
    togother a system model utilizing the available information in the best way possible
    were considered together, we decided to proceed with the structure of an initial model
    comprised of four component models.  Four existing models were selected.
    
                                               Existing Models Selected
           Component Models                    for Initial Application
    
           fluid dynamics                      fast bubble model
           combustion                          modified Davidson Model<3>
           heat transfer  (horizontal tubes)    modified Vreedenberg Model!'')
           d^sulfurization                     Borgwardt Model(5), (6),  (7)
    
           Along with the Ken and Leva   model for vertical tube heat transfer, the Merrick
    and Highley'8! models for attrition and elutriation are also being used.
    
           Not all existing models can be used directly.  Some need considerable modifi-
    cations while some others need incremental development19ป10ปHซ12) .   it is also
    apparent that all the submodels adopted for the system model use must be compatible and
    consistent so that thi;y may be linked together for continuous operation.  When the
    modifications and link-ups are properly executed, the system raodel has demonstrated to
    be capable of approximately computing the following grous bed parameters:
    
    
    
                                              406
    

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           o Carbon Loading
           o Combustion Efficiency
           o Carbon Particle Size Distribution
           o SC>2 Emissions
           o Stone Utiliz-tion
           o Heat Transfer Coefficients of
             Horizontal/Vertical Immersed Tubes
           o Bed Temperature
           o NOx Emission
    
           A sketch of this initial model is shown ir. Figure 1 .  ""•ป facili - c- the use of
    this model, a standard set of values concerning bed proportit   operating conditions,
    acceptor properties, coal properties, cyclone properties are p.ovidea.  This will allow
    the users to compute any particular output parameters of interest to him j.n relation to
    any input parameter.  A segment of the computer output is shown in Appendix I.  In this
    segment, the combustion efficiency is computed to be 99.lt. for a superficial velocity
    (U0) of 1.5 meters/sec, operating under the conditions set forth by the standard values
    furnished.  Kith a number of such calculations, a sensitivity analysis can be carried
    out to investigate the influence of Uo on the combustion efficiency.  Other sensitivity
    analyses can be carried out in a similar manner.
    
           In one respect, our modelling experience has been particularly encouraging.
    After having recognized that the fast bubble is perhaps inadequate to represent the
    fluid dynamic behavior of an entire bed, we have discovered an important need to modu-
    larize our component models so that a capability ey'.sts to replace each unit individually
    at a later time.  Yet, due to the complex interactions between the various component
    models, we were previously uncertain as to whether modularization would DC successful.
    It now appears that the four selected component models are linked together only by
    relatively weak interactions.  Hence, they can be necoupled.and to that extent modular-
    ization is feasible.
    
           Despite the fact that the computed output parameters appear to be reasonable in
    magnitude and their trends of variation witn relevant input parameters also appear
    reasonable, the simplistic nature of this initial model must be fully recognized.  As
    such, the model is more suitable to serve as a framework for further refinement, rather
    than as a functional model.  The present model is still useful for parametric studies.
    Nevertheless, introduction of better physical description developed as the key feature
    of the process w: 11 upgrade the present model to a powerful predictive tool.
    
    
    III.  FIRST ROUND SYSTEM MODEL UPGRADING
    
           Even though our essential commitment during this first phase is to the application
    of state-of-the-art models, our effort has not been bound by the formality of this
    commitment.  Since the beginning, a part of our effort has been devoted to the develop-
    ment of twenty key feature models.  These key feature models, together with nine
    additional key feature models of which the development will be initiated soon, are
    listed in Table 1.
    All of these key feature models are beyond state-of-the-art models, and their develop-
    ment has provided a broad base for the upgrading of our system model.
    
           In many key areas, our analytical inquiries have already improved our under-
    standing in the process representation a great deal.  These newly acquired insights,
    which are being targeted for our first round model improvement, are briefly discussed
    below.
    
    (1)  Slow Bubble Region (Fluid Dynamics)
    
           It was recognized at the outset that the fast bubble model probably does not
    adequately represent the fluid dynamics of the entire bed.  The oxygen profile data
    obtained by Pereira and Beฃrd3)at Shefield suggest that a large fraction of combustion
    occurs in a region near the distributor plate.  In this region, bubbles are either small
    or not as yet formed.   If fast bubble is assumed for this section, the computed oxygen
    delivery to the carbon surface will be unduly small because,  for fast bubbles, there is
    a significant diffusional resistance for the oxygen to transfer from the bubble phase to
    the emulsion phase.  Such resistance is extremely small for the slow bubbles ard r.cn-
    existant prior to the  bubble formation.  Hence, the fast bubble model tends to under-
    estimate combustion efficiency.
                                               407
    

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    -
    8
                   User's Input
                     (e.g. U0>
                    User's Input
                   (e.g. Combus-
                  tion efficiency)
                                        Fluids Dynamics
                                       Fast Bubble Model
                                Standard Set of Input
                                                                                     Temperature
                 Combustion
              Modified Davidson
                    Model
    Desulfurization
      Borgwardt
        Model
                                                                                          Material Balances
                                                                                                 +
                                                                                           Concentration
                                                                                               Profile
    Heat Transfer
      Modified
    Vreedenberg's
       Model
                                                                   Physical
                                                                Thormodynamic
                                                                   Properties
    Output
                                                                  Figure 1.  First Generation System Model
    

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                                              Table I.  Key Feature Models
    o
    VO
    lindcr Development
    (1) Coal Dcvolatilization  (Combustion)
    (2) Char Combustion  Kinetics  (Combustion)
    (3) CO  Burnout  (Combustion)
    (4) NOX Emission  (Combustion)
    (5) Flow Regimes  (Fluid  Dynamics)
    (6) Slow Bubble Model  (Fluid  Dynamics)
    (7) Bubble  Size  (Fluid Dynamics)
     (8) Mass Transfer  Coefficient
         (Fluid  Dynamics)
     (9) Mass Heat Transfer to  Single
        Particle  (Fluid  Dynamics)
    (10) Pore Plugging  (Desulfurization)
    (11) Expanding Grain  (Desulfurization)
    (12) Horizontal  Tube  Correlation
         (Heat  Transfer)
    (13)  Influence of  Large Particle in
        Heat Transfer (Heat  Transfer)
    (14) Honuniform  Heat  Flow to Tubes
         (Heat  Transfer)
    (15)  Force  on Tubes  (Heat Transfer
         and Fluid Dynamics)
    (10) Thermal and Mechanical Stresses  (Ma.nrials)
    (17) Creep Deforraantion and Creep Rupture
         (Materials)
    (13) Fatigue Mode of Failure  (Materials)
    (la) Corrosion Mode of Failure  (Materials)
    (20) Transient Behavior
    
    To Bo Initiated
    (21) Flow behavior with/with<>ut Tubes
         (Fluid Dynamics)
    (22) Coal Combustion (Combustion)
    (23) CO Emission and Reducing Zone  (Combustion)
    (24) NO Emission Refinement  (Combustion)
    (25) Desulfurization Under Varying SO,
         Concentration Zone Environment  (Desulfurization)
    (26) Local Temperature Profiles and Hot Spots
         (Combustion and Heat Transfer)
    (2V) (Bed Bcnavior of Free Board  (Fluid Dynamics)
    (2d) Acceptor Calcination (Desulfurization)
    (29) u.iat Transfer to Tubes and Bounding Wall
         (Heat Transfer)
    

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           Significant improvement can be achieved if the bed is divided into two sections:
    a pre-bubble/sJow bubble region (where U[jr < t!mfA ^f) followed by a fast bubble region
    (where Ugr > Umf/emf).  The transition occurs when UBr = Umf/--mf.  However, if this
    computed transition point is less than 5cm from the distributor plate, we will use 5cm
    as the transition height because below that height bubble is assumed to be not yet
    formed,and in that pre-bubble region, the bed behaves closely to a slow hubble bed with
    respect to oxygen delivery to the carbon particle.  Oxygen delivery is important to
    combustion efficiency calculation.  Such a two-region bed model has already been
    implemented, and the improvement achieved in the combustion efficiency prediction is
    given in Figure 2.
    
    (2)  Devolatilization
           Devolatilization and combustion of volatile matter from coal are important
    because they exert influence on the oxygen and temperature profiles of the bed and on
    the formation of hot spots.  The stability range of FB operation is also extended to
    lower te-.peratures because of the volatile matter's lower ignition temperature.
    
           The traditional approach to FBC modeling has been either to ignore the volatiles
    altogether or to assume that the devolati1ization is instantaneous.  Our analysis shows
    that devolatilization is a time-dependent process<2ป9ป14>.  For a 1mm particle with 2%
    oxygen in the surrounding gas and 1173ฐK (1650ฐF), Figure 3 indicates that the
    devolatilization is complete after 2 seconds, while the final burning time is 308
    seconds.  Thus, the devolatilization time is commensurate with the mixing times for
    particles in an FD which is typically on the order of 1 second.
    
           This analytical finding is important when feeding from above the bed is con-
    sidered.  It also implies that both NOX and S02 are more probably being released all
    over the bed rather than all at once near the feed point.
    
    (3)  Combustion Kinetics (Combustion)
    
           Whether the combustion in an FBC is a diffusion controlled process depends both
    on particle size of carbon as well as on the temperature of combustion.  The combustion
    may be mainly diffusion controlled if temperature is high and the particle size is
    large; but will be mainly kinetically controlled if the conditions are reversed.  For
    1mm diameter carbon particle at 1173ฐK (1650ฐF), the diffusion and the chemical
    kinetics roucjhly offer equal nsistance to combustion.  In Figure 4, the oxygen con-
    centration at the surface over the oxygen concentration at infinity at the time of 50%
    burnout in taken as the average fractional kinetic resistance.  If the chemical kinetics
    are not taken into account, the burning rate for small particles such as elutriated
    carbon particles could be too high, and the combustion efficiency will be overestimated.
    
           ft simple version of chemical kinetics (not taking pore diffusion into account)
    has already been incorporated into the system model.
    
    (4)  KOy and CO emissions
    
           A NOX generation model for a two-region bed has been developed assuming that the
    evolution and burning of coal volatiles take place uniformly throughout fie bed and the
    NOX produced can be reduced to N2, either by char or by any reducing gases.  The model
    has already been incorporated into the system model.
    
           A CO burnout model is being developed.  Our preliminary results show that there
    is a kinetic limitation on CO burnout below 1050ฐK  (1430ฐF).  However, if the CO
    concentration leaving the bed is higher than 1%, the heat release due to combustion may
    be sufficient to overcome this limitation.  Nevertheless, if the cooling rate is in
    excess of a few thousand degrees per second, CO may quench regardless of it-j initial
    values.  The average experimental evidence supports the kinetic limitation, but does
    not show t'.e same extent of burnout.  This may be due to, among other things, the overly
    simplistic free-board fluid dynamics model employee'.
    
    (5)  Pore Plugging and Stone Evaluation
    
           Figure 5 shows our model calculations on the variation of SO2 emissions as a
    function of the calcium-sulfur ratio.   The lowest curve shows that same variation using
    an empirical model developed from the available data sets.  It appears that the model
    
    
                                              410
    

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                         100
                          90
                   G      80
                   '&
                          70
                          60
                          SO
                                                           Superficial Velocity - ?.5 m/s (7.5 (t'jecl
                                                           eซceoAir-20%
                                                           Bed Temperature - 1200 K 1170O Fl
                                            800          900         1000          1100         1200
    
    
                                     Figure 2.  Effect of Two Region Bed on Carbon Efficiency
    i.o
           c   ฃ
           5   u-
                                                                                                     \
                                                                                                      Volatile mjtttr
                                                                                                      *nd rniduAf
                                                                                                      carbon burr*
    T. i
    Particle diamrtvf 1m.r>
    V • Amount of Volatile Released
    Vo • Total Amount of Volatile*
    W • Amourn of Total Cartxm Burned
    WQ * Total Amount of Carbon
                                * y Volatile matten
                                    bumai
                                    detactied vlame
                                    t.0
                                                                  10
    
                                                             Time (
    -------
                   1.0
              I     .
    t\>
                             ISO
                                                                       1000
                                                                                               3000
                                                                                                                  100
                                                                                                                   90
                                                                                                                   70
                                                                                                                   60
                                                                                                                   SO
                                                                                                                   40
                                                                                                                                                System Model Stone No 6
                                                                                                                                                         Temperature- tt!6e
                                                                                                                                                         Tempers .re- 11I6'K I1S50ฐF>
                                                                                                                                                         Exploded Bed Height • 1M (3 ft.)
                                                                                                                                                         FluiUi/ing velocity • Uf *
                                                                                                                                                         233M<ซclMl'wc.l
                                                                                                                                  1.5
                                                                                                                                               2.0
                                                                                                                                              C./S
                                                                                                                                                             2.5
                                                                                                                                                                          3.0
                                                                                                                                                                                       3.5
                                                    Particle Diameter (ป ml
    ซ 5 stone is a medium grained, granular arid porous, gray reef type of
    dolomite. ซ6 Hone contains 81% dolomites some clay and fine ouari;
    silica impurities, medium grained, gramular and microporous.
                             Figure 4. Dependence of Kinetic Resistance to Combustion on
                                         Particle Size With Ignition of Volatile!.
                Figure 5. % Sulfur Removal vs. Ca/S Rafio
    

    -------
    calculation yields higher SC>2 removal.  This might be attributed to:
    
           o The Borgwardt model does not account for the pore plugging
             due to solid volume expansion  when CaO is converted to CaSC>4.
    
           o The Borgwardt model applies only to the precalcined stone,
             while the empirical model applies to uncalcined stone.
    
    This figure illustrates the importance of incorporating both pore plugging and stone
    colcii.ation features into the system model.
    
           Two models, namely a "pore plugging model" and an "expanding grain model" are
    being simultaneously developed.  Analytical solutions have been attained for both
    cases.  Figure 6 illustrates the variation of percent conversion versus initial porosity
    according to the expanding grain model both for calcine and for dolomite.
    
           The maximum conversion values in Figure 6 are obtained with the assumption that
    the radius of the grains (which are assumed uniform) are the sanie for all grains in the
    pellet.  This is equivalent to assuming uniform reacting gas concentration inside the
    pellet; i.e., no pore diffusion.  In actuality, pore diffusion is operative and pores
    are only plugged at the mouth.  This will result in a conversion lower than the maximum
    level predicted.  Hence, it is not surprising that the experimental data in Figure 6
    are less than the model predicted values.  Improvement of the model can be attained if
    a size distribution is assumed for the grains.
    
           The development of a stone calcination model will be initiated soon.
    
    (6)  Heat Transfer Correlations (Heat Transfer)
    
           Heat transfer coefficient data from Pope, Evans and Robbins'16', General
    Electric(17)( an<} McLaren and Williamsd2) have been compared with the modified
    Vreedenberg correlation used in our system model.  The data are not in good agreement
    (see Example B of DBMS Applications) with model predictions.  It should be noted that
    most of these newly acquired data are from beds with high superficial velocities
    operating in slugging or turbulent regimes, whereas the original correlation was based
    on freely bubbling beds.  Additionally, each of the present sets of data were insuf-
    ficient in some way for complete comparison with the correlation.  Some information is
    assigned to fill the information gaps, thus leave considerable possibility of error.
    Nevertheless, the comparison appears to suggest that a high velocity fluidized bed
    operating in the slugging or turbulent regimes may require a different correlation.
    
           A new correlation comprising a gas conduction model and a parallel convective
    heat transfer model has been developed by our heat transfer group.  As is shown
    Figure 7, agreement with the experimental data is good and appears to have the
    potential of developing into a physical correlation for large particle FBC heat
    transfer.
    
    (7)  Thermal Stresses (Materials - Heat Transfer)
    
           We previously reportedH' that we would have yielding with the 304 stainless
    steel tubes immersed in a fluidizcd bed, and would consequently face a low cycle
    fatigue problem due to startup-shutdown eye-lie operations.
    
           Subsequently, thermal stresses induced by two-phase flow (water and steam)
    within a horizontal tube have been analyzed.  From the temperature profiles
    calculated 111),  it appears that signficant thermal stress might set up in the inside
    wall of the tube.
    
    
    IV.  FBC DATA BASE MANAGEMENT SYSTEM (DBMS) DEVELOPMENT
    
           Data should be regarded as vital resources which must be organized to maximize
    their value.  This is especially true for KBC where tho rate of technical development
    is so high that  the data file will soon grow at a large rate.  Furthermore, it is
    believed that the value of data is enhanced when data are assembled together in a data
    base setting.
    
    
    
                                             413
    

    -------
    I
           100
            80
                                                                0.511
                                                                              0.676
            40
            20
               0.0      0.1
             60
    
             40
            20
                                 0.2
                                                                0.5
                                                                          O.G
                                           0.3        0.4
                                             Initial Porosity
                             Figure 6. Effect of Initial Porositv on Conversion
                                 as Predicted by Expanding Grain Model
                                     (Points Are Experimental Data)
                                                                                   0.7
                                                          BCE
                                                          DGE
                                                          ^Mclaren 8, Williams
                                                          ฃ Pef
                                                          A Bartel & Genetti
                                                          CNYL1 HSpsia
                                                          9 NYU 40 psia
                                                          ONYU ISpsia
                                                          9 NYU 75 psia
                                                          	I     l   i
    3175vm
                         10
                                  20
                                           40
                                                     Re
                                                        100       200
                                                         Oo
    -------
           In this initial phase, a portion of our effort has been devoted to the selection
    of a JEMS.  Our early study suggested that the selection of a correct data uase system
    would be a critical step in our overall task of establishing a DBMS, due to  the fact
    that most of the available data base systems were developed for administrative purposes.
    A large body of available well-used systems were found to be unsuitable for  our appli-
    cation because of constraints in data type, limitations in physical storage  structure,
    and/or lack of broad capability in user-system interactions, etc.
    
           Our selection criteria were:
    
           1.  flexible data base structure
           2.  concurrent use capaoility
           3.  on-line query capability
           4.  data accessible from Fortran programs
           5.  well developed and well supported
    
           Starting with nine commercial systems,  Computer Corporation of America's
    Model 204& was finlly selected.  A major advantage of Model 204-- over the other
    s/tems investigated is its flexibility.  Any number of files with almost any structure
    (hierarchy, network or even relational) can bo used with equal ease and efficiency.
    While Model 204's creation procedure is fairly involved, fine tuning of the data base
    in relation to its user's pattern is better facilitated, with a resultant net savings
    in cost and increase in performance.  Although some other data base systems nay have
    slightly simpler (i.e., non-procedural) user's language, our experience has been that
    these languages are less able to cope with the kind of users we feel the FUC data base
    must support.   On the other hand. Model 204'K uses a semi-procedural language whici. can
    support airaost any kind of processing ^hile still remaining relatively easy to use.
    Thus, ou- conclusion is that Model 204'K best fits the needs of the FBC appl icatioi'.
    
           As soon as we realized that the selection of a FU'table data base system would
    be prolonged,  we decjded to establish a prototype data base system based upon an MIT
    developed KDMS (relational data management system).  The establishment of a prototype
    system has allowed other tasks such as data input,  file design, system-user interface
    development to proceed 
    -------
    L'xample A.  Getting tho Relevant Information
    
           A user wants to know soxc information that rcicht be of interest to hi- in the
    area of Ucsm f urization.  'ihe information is not specified at the beginning: he may
    proceed to use DBMS in the following nannor:
    
           First, he may ask DBMS to print out what papers are available in the data
    base by typimj in three input lines (underscored):
    
             "cc  list_area"
             "dcsulfurization"
             "yes"
    
    The HUMS will produce Table A-l.
    
           After examininq Table A-l, the user decides that he wants to examine or.e paper,
    i.e., "Isothermal Reactivity of Selected Calcined Limestone with SO,", more closely.
    He can type in the following two statements:
    
              ec  list_figures
              name of tne paper - "Isothermal Reactivity of Selected Calcined
                                   Limestone with SO2"
    
    The DBMS then produces Table A-2.
    
           If the user now wants to know more about Figure 1,  he can type in the following
    3 lines of statements:
    
              oc  tab_figure
              name of the paper - "Isothermal Reactivity of Selected Calcined
                                   Limestone with SO,"
              Figure I
    
    The OHMS will produce Figure 1 in the tabular form. . (Table A-3).
    
           If he wants tho figure plotted, he can type in
    
              ec gr.tuh figui^
              name of the paper - "Isothernal Reactivity of Selected Calcined
                                   Limestone with SO2"
              Figure 1
              Other relevant information DBMS r.ocds
    
    The DBMS will tnen present the plot.  (Table A-4).
    
    
    L'xample b.   Check Modi tied Vrccdonborg Correlation with GE Data, ftR  Data, etc.
    
           Tnis example shows the utility of a general purpose macro facility which can
    either plot a graph or print a list of values of the left  hand side and the right hand
    side of a correlation.  To use the macro, type
    
             "cc  check_correlation"
    
           As is shown in Table B-l, the macro wil'. then ask cq_vbl  = variable: e.<:..
    Uf = fluidizing velocity.  The macro will report the above query until you type a
    pcriout.).
    
           The macro will next ask for the left hand side and  the right hand side of the
    correlation.  After obtaining the answers, the macro will  compute the left and the
    right sides for any set of data and plot out as the left side vs. the right sice.
    
           The  macro also allows the user to obtain a list of  data sources and the user can
    restrict the set of data points to those of a particular paper or even to a particular
    table/figure, if desired.
                                              416
    

    -------
                                    Table  A-l
    ec list_arca
    
    For which area?   desulphurization
    
    include paper titles with author names?   yes
    Listing of papers for area desulphurization:
    TITLE
       AUTHOR (S)
    
    Charachterization and Control of Caseous Emission from Coal Fired Flui
    \cdized Bad Boilers
       Robison E. B.
    
    Fluidized Bed Combustion: A status report
       Jonko A. A.
    
    Isothermal Reactivity of Selected Calcined Limestones with SO2
       Borgwardt, R. H.
    
    Kinetics of the Reaction of SO2 with Calcined .Limestone
       Borgwacdt, R. H.
    
    Properties of Carbonate Rocks to S02 Reactivity
       Borgwardt, R. H.   Harvey, R. D.
    
    Reduction of Atmospheric Pollution by the Application of Fluidized Bed
    \c Combustion
       Jonko A.A.
    
    Supplementary Borgwardt Data
       Borgwardt. R. H.
                                      417
    

    -------
                                   Table A-2
    ec list_fiqures
    
    For which paper?   Isothermal Reactivity of Selected Calcined  Limestones  \
    with S02           	
    List of 16 Fiqures (and Tablesi for dosulplrjrizacion paper
          Isothermal Reactivity of Selected Calcined Limestones with  SO2':
      Figure 1   -- Comparison of Reactivity of Calcines with SO2  at  980C
      Figure 2   — Sorption of SO2 by Different Particle Sizes of Type  4
    \cCalcine at 980C
      Figure 3   — Estimation of Initial Rate (r3) and Effectiveness  Fact
    \cor (eta)  for the Sorption of SO2 by Type 4 Calcine
      Figure 4   — Comparison of Reactivity with B.E.T. Surface Area
      Figure 5   -- Reaction rate at Constant Sulfation as a Function  of P
    \carticle Diameter
      Figure 6   — Reaction Rate vs Surface Area of 150/170 mesh  Particle
    \cs
      Figure 7   — Effect of Mode of Calcination on Reactivity of  Michiga
    \cn Marl
      Figure 8   — Relation between Effectiveness Factor and Pore  Size  Co
    \cr 42/65 mesh Particles at 988C
      Table 1    — Kinetic Parameters for SO2 Sorption by Calcines
      Table 2    — Parameters for S02 Sorption by Calcines as a function
    \cof Particle Size
      Table 3    — Summary of Physical Properties of Calcines
      Table 3a    — Effect of Calcination Temperature on Physical  Properti
    \ces of Type 2 Calcite Spar,  12/16 mesh
      Table 4    — Comparison of Reactivates of  150/170 mesh stones at 98
    \cOC
      Table 5    -- Maximum Percent CaO conversion to which equation 4 app
    \clies
      Table 6    — Physical properties of Raw Limestone, 10/28 mesh
      Table 7    — Chemical Analysis Of Michigan Marl
                                        418
    

    -------
                                        Table A-3
    ec tab figure
    
    Which paper?   Isothermal Re-ictivity of Selected Calcined  Limestones \
    with 502      	
    
    Whicn .figure?   F i g j:o 1
    Table of 66 data pomes from
    Figure 1 of • Isother-nal Reactivity of Selected Calcined  Limestones with  S02'
    
      fixed     Temperature * 980
      fixed     lower roesh = 150
      fixed     upper mesn = 173
         Bed
         5.
         5.
         5.
         5.
         S.
         5.
         5.
         6.
         6.
         6.
         6.
         6.
         8.
         8.
         8.
         8.
         8.
         8.
         8.
          16.
          16.
          16.
          16.
          16.
          16.
          16.
    Material
              S03 absorbed
              0
              .6
              1.1
              1.6
              2.
              2.3
              2.7
              0
              6.5
              11. 2
              15.2
              18.3
              0
              4.
              5.3
              6.3
              7.
              7.7
              8  2
               0
               5.
               8.1
               10.7
               12.8
               14.6
               14.6
    Time
    0
    20
    40
    60
    80
    100
    120
    0
    20
    40
    60
    80
    0
    20
    40
    60
    80
    100
    12?
     0
     20
     40
     60
     80
     100
     120
                                        419
    

    -------
                                    Table A-4
    oc graph figure
    
    Which paper?    Isothermal  Reactivity of Selected Calcined Limestones  \
    with SO2       '	
    Which figure?    Figure  1
    
    for what x variable?    Time
    for what y variable   SO3  absorbed
    
    constrained variable   Bed Material
    
    value for Bed Material:    B
    
    how tr.jny coo--.tca ints niust  be  satisfied:    1
    
    with interpolation?   yes
    
    
              12.+
                 I                '-data point
                 • .                ^Interpolated point
                  :
                 r
                 i
              10.4
                 i
                 t
               9.+
                 I
                 I
               8.*
                 I
                 I                                +
               7.+
                 I                        +
                 I
               6.+                  ซ•
                 I                +
                 I
               4.*
    
                 I     +
               3.+
                 |    +
                 I
               2.*   *
                 I  +
                 I
               1.* +
                 I
                 1 +
               g.t ----- + ----- + ----- + ----- +. ----- + ----- 4. ----- +
                 e.    17.1  34.3  51.5  68.6  85.7  102.8 120.
                                         420
    

    -------
                             Table B-l
    ec  :?v;c
    
    •rfiicM  ar?i?   hoat t r ansfor
    
    •?•}  vbl  = 7iri39lo:    n _; _ oytsiJo .T? itr.tf.an sf or  .ooff ic i ?f>t
    
    oj  vol  ป vJriillo:    Dt ป  tab?
    31  /bl  =  ^arii^lo:   k ป  TJ-; t.lornjl con j_ujtj.yity_
    
    ?T  v'jl  =  variiolc:   Pr  ซ  gil Pran-ltl nuibJr
    
    OT  vbl  ป  vjriiblc:   -Tosilon = h^i norosity
    
    on  vbl  ป  vjrii'jlc:   TI -j  *  1 3 o •/ i s :_o s i t y
    
    C-)  vbl  ป  vjriiblc:   Do  ป__ ? j r t i - 1 j s 1 7?
    
    •JT  vbl  =  v.iriiblo:   r'na  r. = pirticlo ionsity
    
    C-T  ^01  *  vjti-ablo:   Uf  ฐ  fluiMsim /clocity
    
    o-j  /1>1  ซ  viciiolo:   i ซ  ir.T/itJtiTi.-il cansunt
    typ?  loft  hinl si.'Jc of on'Jition:
           ( ('i*Dt/Kl /( (Pf •*. i) * ( I -on- i Ion) ) )
    tyn?  ri-jht  nnl nil? of i
        l:>ir>JJ*( (  Uf*Dtซ^g| /( ( (Oo.MUJ)**i)*rno  *g) ) *ซ. 325)
    
    '3o  yu wis'i i  list of -Jjta  sources?   y-?3
    •Jot.i  fcoti  Ui?  fol lowing J o.joors .Jn3 figures  :
             Eloctric Ot)i qjjrt?rly  rooort
            ; i
    
    H?it tro.nsf-or  in pilot pljnt  fluiJizoJ bc.l conbastor
           lo 1
    PER rooort  FE123 ?-5/b-2
       Tiblo  1
    V.iic'.i oioor    al 1
    
    ch?ck cortclation:  J7 djta points  have boon correlated.
    
    do yoj *is:i  to plot tin correlation?    yes
    
    •Jo you wish  to tabulate tho correlation?   no
                                  421
    

    -------
                          Table B-l  (Cont'd.)
    of relation CORRECTION  on 12/05/77  Pa-jo  1
    
    
                                          126) J
    X = lojf ilon) ))
    Y = l3i(jJUซ((('Jf*Ot*aiu)/(((Do/10il)**3)*ch3_s*q) )•*
           C X \XtT V\LU?:  loft
              3 plottsJ  33  points:
              i J;ntifier           nine
                  *                riiht
           J.OOJf
                I
                I
           2. J4J +
                 I
           2.J5U
                 lซ
                 I
           2.dUJป
                 I
                 I
           2. 7r>Jf
           2.652+
                 I
                 I
           2.6UU
                 I
                 I
                )f
                 I
                 I
           2. 402 + -----*	ซ.__.__ป_--.-ป_-	ซ.	*	>
                2.425  2.527  2.632 2.714 2.839 2.941 3.042  1.143
                                  422
    

    -------
           Two more examples; i.e., Example C and Example D are given in Appendix II.
    
    
    VI.  PLAN FOR THE ATTAINMENT OF A "SECOND GENERATION" SYSTEM MODEL
    
           The approach to attain a secoiid generation model sufficiently precise for FBC
    design optimization is summarized in Figure d.  Referring to that figure, the first
    step is to develop a simplistic first generation system model using essentially
    state-of-the-art models.  This development is now coirplete, as is described in the
    previous section.  Simultaneously, a number of key feature models which go beyond the
    current state-of-tho-art are being developed (Table I;.  The introduction of such key
    feature models in the initial system model leads to a refined and more comprehensive
    first generation system model, as is described under another previous section.  Doth
    tiie key feature models and they system model are being validated against data found in
    the developing data base.
    
           In the meanwhile, using the data assembled in the data base, empirical models are
    being developed for such bed parameters as combustion efficiency and emission charac-
    teristics.  When the two sets of models (i.e., analytical set and empirical set) merge,
    the combined model will be considered as our "second generation" system model.
    
    
    VII.  SUMMARY
    
           To summarize, our accomplishments during the current phase are:
    
           o Completed a "first generation system model", which o.in approximately
             compute a number of FBC parameters.
    
           o Incorporated a slow bubble mojol and a combustion kinetic model into
             the initial first generation system model to upgrade the model
             performance.
    
           o Developing additional key feature mode-Is to gain an improved
             understanding in the physical representation of FBC, and to
             establish a broad base for further model upgrading and refinement.
    
           o Evaluated a number of available data base management systems (DBMS)
             and selected one most appropriate for FBC system use.
    
           o Implemented a prototype data base system.
    
           o Developed a number of macros for several sample applications
             of the DBMS.
    
    
    ACKNOWLEDGMENT
    
           The desulfurization empirical model was developed outside of this project by
    Dr. James Gruhl, to whom we are grateful.
    
    
    REFERENCES
    
    1.  Tung, S.E., A.F. Sarofim, L.R. Glicksman and J.F. Louis, "The Fluidized Bod
        Combustor Modeling", Conference on Mathematical Modeling of Coal Conversion
        Processes, Washsington, D.C., November 16, 1976.
    2.  Tung, S.E., A.F. Sarofim, L.R. Glicksman and J.F. Louis, "System Model  and Data
        Base System for FBC, FBC Technology Exchange Workshop, Rcston, Va.,
        April 13-15, 1977.
    3.  Avedisian, M.M. and J.F. Davidson, "Combustion of Carbon Particles in a Fluidized
        Bed", Trans. Institute of Chemical Engineering, 51_; 121, 1973.
    4.  fl.I.T. Energy Lab Report, "Heat Rejection from Horizontal Tubes to Shallow
        Fluidized Beds", rt.I.T. E.L. 74-007, Andeen, B.R., L.R. Glicksman and W.M. Rohsenow,
        H.I.T., Cambridge, Mass., 1974.
    
    
                                              423
    

    -------
      Key
    Feature
    Models
       First
    Generation
      System
      Model
                                                       _\/aijdatipn__ __
                  Refined
              First Generation
                  System
                   Model
                                        Second Generation
                                         System Model
    Data
    Base
                                                Empirical
                                                 Models
                                  Figures. Modelling Approach
                                           424
    

    -------
     5.  Borgwardc,  "Kinetics of Reaction of SC>2 with Calcined  Limestone",  Environmental
        Science and Technology, 4_ & ^: January 1970, pp.  59-63.
     6.  Borywardt,  "Properties of Carbonate Rocks Relatea to S02 Activity",  Environmental
        Science and Technology 6 & 4_, April 1972, pp.  350-360.
     7.  Borgwardt,  R.H.,  "Isothermal Reactivity of Selected Calcined  Limestone  with  SO,1',
        presented at  International Dry Lir.estone Injection Process  Symposium, Paducah,  Ky.,
        June 22-26, 1970.
     8.  Merrick, D.,  and  J. Highley, "Particle Size Reduction  and Elutriation in  a
        Fluidizcd Bed Process, AIChE Symposium Series, V. 70,  N.  137,  1974.
     9.  M.I.T., "Modeling of Fluidized Bed Combustion  of  Coal", Quarterly  Technical  Progress
        Report  (No. 2), November 1976.
     10. M.I.T., "Modeling of Fluidized Bed Combustion  of  Coal", Quarterly  Technical  Progress
        Report  (No. 3), tebruary 1977.
     11. M.I.T., "Modeling of Fluidized Bed Combustion  of  Coal", Quarterly  Technical  Progress
        Report  (No. 4), May 1977.
     12. M.I.T., "Modeling of Fluidized Bed Combustion  of  Coal", Quarterly  Technical  Progress
        Report  (Nol 5), August 1977.
     13. Gibbs, B.M.,  F.J. Pereira and J.M. Beer, "Coal Combustion and  NO Formation in an
        Experimental  Fluidized Bed", Institute of Fuel Symposium, Series No. 1, Fluidi/.cd
        Bed Combustion, Longdon, Sept. 1975.
    
    
                                          APPENDIX I
    
    
    A SEGMF.NT OF MODEL COMPUTATION
    
           A segment  of model computation is shown in  Table II.
    
           Referring  to that table, the user's objective  is to compute combustion efficiency
    at Up = 1.5.  TPS Ithcrmal power syste-) is a subsystem we use  to  facilitate  the
    writing modelling program under TSO environment.   As  presently  structured,  the model
     first lists a series of subroutines that are executed.  It then asks whether  the user
    would like to print out (1) coal particle size distribution and (2) :;OX  profile  in  the
    bed.  Alternatively,  the display of these stops can be suppressed.  The  final result of
     interest is printed out in the last statement.  In this manner, the effect  of Uo on
    combustion efficiency can be attained with a number of such calculations usinq different
    Uo input.  Effect of other output parameters by any relevant input parameters can bo
    similarly computed.
    
    
                                         APPENDIX II
    
    DATA EASE SAMPLE  APPLICATION EXAMPLES
    
    Example C.  Chock Pigford Model with Borgwardt's Data
    
           An algebraic form of the Pigford model nas been developed by our dcsulfurization
    group usinu single point collocation method U2>.   the equation  is given as:
                   •(f = 4/3.55  (60 + 0.5775 0.5 -f^.2-0.17-.-1 • 5 + 0.3335 )               (1)
    
            where
    
                    F = fractional conversion of CaO
                      — ' t
                    t = time  (sec)
                    F,t and y arc dimensionloss physical panv^ters which are derived
                    from the model, and are unique characteristics of each calcined
                    stone type.
    
           In this example, we wish to compare the derived values of time dependent con-
    version with actual experimental values.  The DBMS contains Borywardt's experimental
    data.  By use of the macro check_conversion_correl-;Lion, the experimental data is
    converted to the comparible form of conversion vs. time.  The experimental and derived
    points for conversion vs. tine are then superimposed in separate plots for each of
    several stones.  One such plot is given,  (See Table C-l)
    
    
                                             425
    

    -------
                                        TABLE II.
                      XODEL COMPUTATION OF COMBUSTION EFFICIENCY
                      WHEN U  =1.5
                            o
    select uo comef
    TPS READY
    set uo 1.5
    TPS READY
    run select
                                    CALL INPUT
                                    OUTER LOOP
                                    CALL PRECAL
                                    MIDDLE LOOP
                                    CALL FLUIDM
                     FLUIDM:  TRANSITION POINT BELOW 5 CM - SET TO 5 CM
                                    CALL HASSEX
                                    INNER LOOP
                                    CALL COMB
                                    CALL DESULF
                                    CALL MATBAL
                                    CALL ENERGY
                                    CALL NOX
                                    CALL OUT
    
                    IF THE USER WANTS THE PARTICLE SI7.E DISTRIBUTION
                    OF CARBON IN THE BED AND ASSOCIATED STREAMS
                    HUNTED AT THE TERMINAL
                    TYPE 1.  AMD PUSH RETURN
                    —OTHERWISE TYPE 0.  AND PUSH RETURN
                    IF THE USER WAOTS THE NO PROFILE IN THE BED
                    PRINTED AT THE TERMINAL
                    TYPE 1.  AND i-USH RETURN
                    — OTHERWISE TYPE 0.  AND PUSH RETURN
                    UO •- +1.50000E+OO
                    COMEF - +9.91220E-01
                    TPS READY
                                        426
    

    -------
                              Table  C-l
    
    
            Jc ck condor sicncorrol ")t ion
    
     wnich "jol aatoriil   i \
    
     esti.notod /aluo fot jan.-na?   52. 65
    
     sstiaat?J //iluo for bot-a?   6.167
    
     Jo  you visi 3 list of data sources?    yos
     data  fro.ii tho fallowini 7 oaoors nd  fi^uccss:
    
    
     Isotnifnul  R-ปa:ti/ity of 3-jloctoJ  CilcinDl  Liaostonis vitrt "02
        Pijuro 1    Figure 2    Figure  1
    
     Proaorties  of Cicbonat? Rocks to >02  R-o-ictivitv
        Fijur.? IU    Fi-jurซ J    Fi7uri 4
    
     Saoolo-nsnt-ity 3orirfacrlt Data
        Fijuro Jr]
    
    
     •Viiich  o-ioer    Supol ?n?nt.iry B
    .*riic;i  fi-juro    Fiiuro 3d
    
    ck_con/crsi3n_corrcl.ation:  16 dat-i points have  bco.n correlated.
    
    do /ou wia'i to  plot  th? ;orrelition?   y/?s
    
    do /ou wis^i to  t-ioul-ate th3 correlation?    yog
    
    Jo /ou wisn the Jati brokon down by source?   no
             Graol of rotation  C^RaEL^TI^^J on 12/UO//;   Pa:? I
    
        1 is reporteJ Jat.a
        F is co.np'jtod /aluo.
        GM1A=i2.65, 9ET\=6. 167
        For n-itirial 11. author is "Jor^wardt, R. H.. author's id is 4
    
    •1JMERIC X \XIS V\LUE: X
    
             s plotted 35 points:
             ilentificr           n.an3
                 •                Y
                                  P
                                      427
    

    -------
                        Table  C-l  (Cont'd.)
    d4.
    42. ป
       I
       I
    15. *
       I
       I
    2d. ป
       I
       I
    21.+
       I
       I
    14. +'
    
       *
           Uorqwardt':;
              Data
                               Compared values
                               from Pigford  Model
       I
     0.+-
             96.
                          2/4.
                               . f- -— ,
    
                                J6J.
                                           . f-.--.
                                            452.
                                            541.  630.
    Tabulation of  3'53 Con/crsiDn Correlation  for
    For natorial 11, .luthoc  is Bor-jwirdt, R.  H. ,
         9jnna =   52.65
         beta ซ  6. 167
                                 CoTioute.1 Con/or sion
                                 8.26JJ24
                                 9.dd422ป
                                 10.d3331
                                 14. 00304
                                 17. 16352
                                 19. ซ2792
                                 22. 17531
                                 24.29751
                                 26.24907
                                 28.06554
                                 29.77161
                                 31.33525
                                 32.92002
                                 34.33349
                                 51.60946
                                 7d.86511
                                            •luthor ' s  i'J  is  4
    TIME
    7.
    IU
    12.
    20
    3d
    40
    50
    bJ
    70
    dO
    90
    10 J
    110
    120
    270
    630
    Convor s
    3. 734672
    4. 7)05d4
    7.469)43
    11. 70197
    16. 1335d
    Id. 92234
    19.42029
    24. 39J35
    2b.dU964
    30. 37533
    32. 36715
    32. 11313
    34.dba94
    36.84376
    53.77927
    62.49351
                              428
    

    -------
    Example D.   Check Desul f urization Empirical Model with ANL Data
    
           The following empirical equation has been developed from a group of  data  to show
    sulfur removal in the KBC.
           i sulfur removal =
           100-
                           ฐ'25
                                - 0.30!
                                            0.420  (fe----
    where
    
           C- = parameter for effect of coal source = 1.13  for this application
           Ca = Ca/S ratio, valid in ramie from 1.0 to 5.0
           lif - fluidizinq velocity, ft/sec, valid from 2.0 to .-1.0
           1'jj = bed temperature, ฐF, valid from 1380T to 1650ฐF
           Bj = static bed depth, in., valid from 10.0 in.  to 70.0 in.
                   (expanded bed depth = 1.3 y. H(;J
           Rs = parameter for number of times sbrbcnt used,
                   1 + number of times recycle = 1 for this application
    
           This sample application is actually another example of tho use of  the
    check_corrclat ion mac re .   In this case, us is shown in Table D-l, the left side  is
    simply the neasured quantity of S(j-> while the other side is the equation  which
    represents the empirical  nouol .
                                              429
    

    -------
                                Table  D-l
    cc cJiocfc correlation
    
    rfhic!i aroi?    dcsulpliur izjtion_
    
    ?q vbl * variaolc:    c^ซ*Ci to S note ratio
    
    si vbl • variible:    Uf_     .
    
    oq vbl ซ vari-Vjlo:    TปTe.nperature_
    
    eq vbl ป variable:   .">l'_s?..tSlel. b.^i fcoi
    
    oq vbl ซ yariiblo:    so2 ป 'iOZ rqjipyป?j
    
    cq vbl ป viti-iblo:
    
    typo loft rti.Ti  silo of oquition:
    typo tiiht *ปjr>1  side  af  oqj.it ion:
       '.J--LV- U*< IJ.b/CT>*lUt**.2j-.
                ''     '
        .-
    \c(2. I a -= i) l'7i'2 ? /] ) *'• 2 . 0 1 * ( 2 . 24 • n 1* •- . 2i
    
    do  /3J wisi  i  li-Jt  of Jati siur;i>3?
          ftoi  th?  follorftni  i  aa>;rc mi fiiurcss:
    
    
      ir j:ht?t irition ml Control  of Gmoua Cniziion  fron Coal Fired Flul
        izod ซc-J  Boilers
        Tiolc I
    
           i^J  DoJ  Conbust ion:  \  statua report
        Fable 1
    
    R?.luw-tion  of Ataosph;ri= Pollution by  tnc  ^ppli;atio.t of KluidizoJ Bo.i
    \c  Cinbustion
        Tible 1
      ic:i paoer    Fluidiz-jl  B.?d Conbuation^^ Jitatuj  rcpor_t
    
          fiiurc   .Tcble.l^.
    
    ch;ck correlation:  20  data points '10 /" been correlated.
    
    do you wis^ to olot  thป  correlation?   yoa
    
    do you wis>t to tabulate  th-; correlation?
    
    should dita bo identified  uy source??
    P\PER
                          3IOG  • RIGMT H^SO 51DE
                                       430
    

    -------
                           Table D-l (Jont'd.)
              3raovi af r?l3tion COaRSlATIO*  on 12/06/77
    
    X • S3 2
    f • lOU-O. U'(JJ.6/ca)ป('Jfซ*.25-.3)  (l + . 429* ((11. 
    -------
    Tdblc n-1  (Contr'd.)
    Flu- HZJ 1 I'll C
    Table- 1
    445
    i'M
    441
    443
    4 J4
    446
    45)
    4s2
    447
    yl2
    4iu
    450
    4i I
    44 d
    41 J
    9) V
    iJu
    44 4
    454
    444
    o.-oj-.ti
    
    j
    d
    j
    2'ป.
    42.
    51.
    52.
    SJ.
    60
    61.
    6V.
    jt.
    01.
    72.
    /4.
    74.
    7i.
    Jo.
    ai .
    41.
    •>n: \ ititu-, tcojrt
    
    1UJ
    luu
    luo
    )5. 25779
    24. 1-44-i)
    5i. 7)7)1
    64. 22471
    67. 7577
    C.5. 67244
    55. 4J152
    7J. 45244
    56. 345dl
    36. J45SI
    65.42575
    08.4)446
    70. J=iiH
    57. 420J5
    11. 215S/
    64. 24454
    /I. 124U5
             432
    

    -------
                QUESTIONS/RESPONSES/COMMENTS
         FREDERICK HANZALEK,  CHAIRMAN:  Are there questions on the FBC
    modeling and data base for Dr.  Tung?   I will ask Dr. Tung to come up
    to defend his paper.
    
         DR. TUNG:  The one question  is by Dr. Saxena:  "Could you tell
    me something about the inappropriateness of the Vreedenberg Correla-
    tion and the direction in which you are working to  improve it?"
    
         I shall answer you as I  see  it,  and perhaps Professor
    Glicksman, if he is present,  would  like to make comments afterwards.
    
         The Vreedenberg Correlation  was  developed for  small particles
    operating at relatively low superficial fluidizing  velocities.  In
    the present application,  we are extrapolating the correlation to cover
    the large particle fluidization at much higher fluidizing velocities.
    In addition, the Vreedenberg  Correlation was developed to correlate
    data of a single tube and not for that of tube banks.  Hence, if it
    does not work, there are  plenty of reasons for it.
    
         We are at present developing a new correlation to replace the
    Vreedenberg Correlation.   The new correlation utilizss a characteris-
    tic of a large particle system.  As you know, for large particles,
    the temperature of the particles  does not substantially change during
    the heat transfer process. In  other  words, the bed may be approxi-
    mated as an isothermal bed.  The  conduction component of the new
    equation was developed with this  assumption.  In addition, the new
    equation also has a gas convection component.  As was shown in one of
    my Vugraphs, the new equation correlates the experimental data quite
    well.
    
         The second question  asked  by Dr. Saxena is:  "How can your data
    base be used by outsiders?"
    
         DR. TUNG:  The data  base can be  used in Chicago as easily in
    Boston.  The next question, by  Dr. Rao of the MITRE Corporation:
    "From the mathematical model  effort,  could you now  give some comments
    on the scale-up factors that  could be employed with confidence?"
    
         With confidence, no.  You  see, the scale factor is essentially a
    matter of fluid dynamics  and  fluid dynamics is one  area about which
    we do not feel very comfortable.  The physics in fluid dynamics is
    not as yet well defined.   For instance, the flow regimes under which
    a FBC is operating are not well defined.  They might be different in
    different sections of the bed.  All in all, it will be some time
    before our model can predict  scale factor with confidence.
    
                                     433
    

    -------
         Tne second portion of Dr.  Rao's question is:   "Does the mathema-
    tical model handle pressurized  fluidized bed combustors at this time?"
    
         No, not at this time.  We  intend to do one thing at a time.
    After the AFBC is wel1-modeled, we will  then extend our model  appli-
    cation to the PKBC.  This v.ill  require some modification in the
    fluid dynamic aspects of the model, but  the kinetic portion of the
    model should remain essentially the same.
    
         Mr. McNeese of Oak Ridge National  Laboratory  asks:  "Will you
    conduct experiments to oheck your correlation?  If so, what type of
    experiments?"
    
         The scope of our contract  with DOE  does not include conduction
    experiments, but we are gathering some small-scale experimental data
    on NOX emission under an EPA contract.   We are also building a 21 x
    2* experimental FBC.  We realize, of course, that  the role of experi-
    mentation is paramount and are  hoping that we shall have the oppor-
    tunity to do more experiments in the future when the 2' x 2' combustor
    is built.
    
         A question from Dr. Bastress:  "Does the MIT  model predict
    a particulate emission?  Does an information base  exist to develop
    particulate emission?"
    
         We have a cyclone model, and the cyclone model will treat some
    of the particulate problems. We are also working  on an empirical
    model.  The data available are  very scanty.  The empirical model
    attempts to utilize whatever data there are to predict emissions.
    Eventually, we shall have good  particulate models.
    
         The next question, by Dr.  Seth of Gilbert Associates, was in
    three parts.  The first part of the question is:  "What is the
    rationale of separating the bed between the fast and slow bubble
    regimes?"
    
         The rate at which the oxygen is delivered to  the carbon surface
    depends upon whether you are operating in a fast bubble regime or in
    a slow bubble regime, since with fast bubbles there is a resistance
    for oxygen to diffuse from the  bubble to the emulsion phase; but witli
    slow bubbles the resistance is  very small or nonexistant.  Of course,
    before the bubbles are formed,  there is  no such bubble-to-emulsion
    phase diffusional resistance.  Now the rate of combustion very much
    depends upon the rate of oxygen delivery to the carbon surface.
    Hence, it is important to calculate the rate of oxygen delivery
    correctly.  It, in turn, means  that you  have to know whether you are
    in a slow bubble/pre-bubble regime or in a fast bubble regime.
                                    434
    

    -------
         In a FBC, the bubbles form near the Distributor plate.   After
    they are formed, they are initially small  in size and travel  slowly.
    For a certain distance, they could be travelling in a slow bubble
    regime.  After a certain point, because the bubbles grow bigger and
    travel  faster, they may be travelling in a fast  bubble regime.   This
    transition point can be calculated.  We have found that by separating
    the model into two regimes, the predictive capability of the  model
    for combustion efficiency has much improved.
    
         The second part of Dr. Seth's question or comment was:   "The
    applicability of the Vreedenberg equation to a fluidized bed  with
    external heat source in the bed is doubtful."
    
         Yes.  In uct, for a fluiaized bed in which relatively larger
    particles are fluidizing and in which heat is transferred to  the tube
    banks, its applicability is doubtful  even without considering
    external heat source in the bed.
    
         The third portion of his question or comment was:  "The  conven-
    tional  modeling techniques are not applicable due to the presence of
    the heat source in the bed, burning coal  particles".
    
         It can be modeled, I believe, but you have  to be careful.
    Professor Sarofim's calculation has shown  that when coal  burns,  the
    temperature will shoot up and then cool  down. It has been estimated
    that the temperature of a burning coal  particle  is about  200ฐF  higher
    than the bed material.  All this has  to be taken into consideration
    if you wish to model the combustion precisely.
    
         FREDERICK HANZALEK, CHAIRMAN:  Thank  you very much.
                                    435
    

    -------
                         INTRODUCTION
         FREDERICK HANZALEK,  CHAIRMAN:  Our first paper of the second
    session is the one which  was  originally scheduled as the last of the
    first session.  This is entitled,  "A Model of Coal Combustion in
    Fluidized Bed Combustors."  This paper is authored by Messrs. Beer,
    Baron, Borqhi, Hodges, and  Sarofim of MIT and the paper will be
    presented by Dr. Sarotim, who received his initial degree from Oxford
    University in England, but  then subsequently took his SM and Sc.D.
    degrees at MIT.  He is currently there as a Professor of chemical
    engineering.  Addo?
                                    436
    

    -------
                               A Model of Coal Combustion in
                                 Fluidized Bed Combustors
                                R.E. Baron. J.M. Beer. G. Borghi.
                                 J.L. Hodges, and A.F. Sarofim
                               Department ot Chemical Engineering
                              Massachusetts institute of Technology
    ABSTRACT
          This paper describes the development of a model to predict the carbon combustion
    efficiency in a fluid bed combustor (FBC).   The model is part of a larger program
    aimed at producing a comprehensive model of total system performance.
    
          In order to predict carbon combustion efficiency,  it is necessary to be able to
    predict burning times of individual particles.  Therefore, a detailed model for single
    coal particle combustion has been developed.  This detailed model has been used to
    develop kinetic parameters which can be utilized in the system model and provides an
    approximate procedure for accounting for the differences in coal reactivity, as
    manifested by differences in B.E.T. surface and effective pore diameter.
    
          System codel predictions of carbon combustion efficiency arc in reasonable
    agreement with limited experimental data.  The nodel currently proviaes a means for
    evaluating the effects on carbon combustion efficiency of mean bed temperature, coal
    and acceptor particle sizes and physical properties, superficial velocity, excess air,
    and bed height.  A nimber of approximations are incoroorated into the systen model
    and there is a need for a continuous critical evaluation and refinement of the model
    as data becomes available from pilot plant and demonstration units.
    
    
    INTRODUCTION
    
          Fluid bed combustion (FEC) is a promising technology for burning coal in
    industrial and utility boilers in an environmentally acceptable manner (1).  One of
    the problems with fluid bed combustion Is that the carbon entrainment from t!-.e bed is
    high, amounting to as much as 20 percent of the carbon feed (2,3).   The carbon
    combustion efficiency can be increased by recycling carbon fines, and by such means
    efficiencies comparable to those attained in stoker furnaces can be achieved.  Higher
    carbon combustion efficiencies c.in be attained by use of a carbon burnout cell.
    
          The focus of this paper is on a modeling effort undertaken to predict the carbon
    combustion efficiency in order ro assist in the scale up. optimization, and design of
    fluid bed cosbustors.
    
          The factors that influence carbon combustion efficiency are shown In Figure 1.
    The two major sources of combustible loss are the elutriatlon of solid carbon
    (governed by carbon loaning,  particle size distribution, and pas velocity) and carbon
    overflow (which is determined by rhe carbon loading and accentor withdrawal rate).
    Clearly, a model for carbon combustion requires a good description of the carbon
    loading in the bed.   The carbon loading can be calculated by equating the carbon feed
    rate to the sun of the carbon burning and loss rates.   The ^olloving section Is devoted
    to a description of the carbon combustion rate, since this is a critical input to the
    overall systen model.
    
    
    SINGLE PARTICLE COMBUSTION
    
          The important factors that have to be correctly predicted by a particle
    combustion model include the effects of particle size, bed tcnncrnture, oxidant
    concentration, and coal-rype on the burnlne times.   In the present model the rate of
    weight loss of a particle is determined by the rate of evolution of volatile •naceri.il
    and by the rate of consumption of the residue.  Separate models have been develope:!
    for these two contributions,  but in reco.^nition of the fact that the two processes arc
    not necessarily independent of each other,  but can occur simultaneously, provision has
    been made to allow for a dynamic interaction between the two.
    
    
                                              437
    

    -------
    ^
    Acceptor
    Stone Feed
    Rate
    
    
    
    
    
    _ Carbon
    *^ Overflow
    ^.
    Attrition
    Rate
    t
    Feed Particle
    Size Distribution
    
    Bed Fluid \^^
    Mechanics |
    •*
    V
    -
    
    
    ,-ป
    ^^
    \
    ^-*
    Combustion
    Efficiency ป-ซ^
    
    _— —
    Carbon
    Loading
    
    
    
    -^— - ~~
    Supi
    * Ve
    
    Bed Carbon Particle
    Size Distribution
    
    H
    
    
    
    Paitide Combustion
    Model
    
    
    
    Excess
    Air
    
    
    ^~~^ Elutriation/
    • — "* Carbon Recycle
    / f
    erficial I/ /
    tocity f /
    /
    
    ^^^^
    Particle
    Fluid
    Mechanics
    
    Figure 1.  Factors Affecting Combustion Efficiency.
                        438
    

    -------
          The devolatilization model employed is based on the work of Anthony et al (4).
    Simultaneous thermal decomposition reactions are assumed to occur, which are first
    order in the amount of volatiles present in the coal and wi.'.ch are described by
    Arrhenius-type rate expressions having the -same preexponent:il factor ko but different
    activation energies.  The large number of reactions occurring justifies the intro-
    duction of a continuous spectrum of activation energies.  Assuming a Gaussian
    activation energy distribution with mean EO and standard deviation a ths amount of
    volatiles released up to any time is obtained by integration over the range of
    activation energies.  The result is:
        VR- VR
                     00
    
              -L-Texp
              nsrt J
                                     exp(-E/RT) dt -
                                                      E -
                                dE
    where Vp is the amount of volatiles evolved up to time t (grams volatiles/grams
    original coal), V-> is the asymptotic value of Vjj for large times, T is the particle
    temperature,  and  R  the Heal gas constant.  Equation (1) describes the devolatiliza-
    tion history of particles :..: an inert atmosphere.  When interest is in devolatilization
    in an oxidizing nediun, as in the case of fluidized bed combustion, the oxidant attsc!;s
    the residue and any as yet unreleased volatiles, so that the value of VR must be
    modified to allow for the heterogeneous combustion processes.
    
          The model of residue combustion developed considers a spherical particle wit'.i
    cylindrical pores of length equal to the particle radius.  For the purpose of
    performing mass and energy balances on the particle, values of the Sherwood and
    Nussclt numbers are obtained from the Ranz and Marshall (5) corrolation for heat and
    mass transfer to a sphere.  An oxygen balance on the particle is made by equating the
    flux to the particle as expressed by use of the Sherwood number and the total oxygon
    consumption due to combustion, given by the sum of the oxygen flux into the pores,
    the oxygen reaching the external surface of the particle, and the oxygen needed to
    combust the volatiles evolved.  For an nc" order reaction at the surface (n ^ 1) the
    balance takes the form:                            	
    2 DGSh(C.
                   -Cs>
               2R
                            4TtR2(l-a)knCsn
                 ATiR2a 2
                                                    h(n-H)
                                                                   OoVOL
    where:
                        h
    
                        kn
    
                     32VOL
    
                        a
    
    
                       Sh
    radius of particle.
    
    oxygen concentration in bulk phase.
    
    oxygen concentration at the surface.
    
    molecular diffusivity of oxygen.
    
    pore diffusion coefficient for oxypcn.
    
    pore radius.
    intrinsic reaction rate for heterogeneous reaction.
    
    oxygen required for combustion of volatiles.
                                  void surface fraction of particle, taken to be
                                  equal to the porosity of the particle.
    
                                  Sherwood number for the burning particle.
    The term M^VOL 1s calculated from equation (1) with the assumption that the elemental
    composition  of the volatiles is the same as that of the pnrent  coal and that thev
    undergo complete combustion.  After an initial short heat-up period, this term exceeds
    in magnitude the term on the left-hand side of the equation.  In this case the
    volatiles evolved shield the particle from the oxygen diffusing towards it and no
    combustion of the residue occurs.  With increasing time volatile evolution decreases
                                              439
    

    -------
    according to equation (1) and oxygen can then reach the surface, as is the case during
    the initial transient heating, when the particle temperature is low.  Equation (2) can
    then be solved for the surface oxygen concentration and the oxygen fluxes can be
    evaluated.  A one-h ilf order reaction at the surface is assumed and the reaction rate
    expression used is a modification of that obtained by Snith and Tyler (6) in their
    studies with brown coal.
    
                        Rn 5 =  96.66 exp(-32.600/RT) C^0'5  ^'^s C                    (3)
                                                        2     cm"sec
    
    This is an intrinsic reaction rate expression which is based on the true surface area
    of the coal.  The particles are assumed to shrink due to the reaction occurring on the
    external surface and to increase in porosity due to reactions occurring in the pores.
    In recognition of the fact th*c for short penetration depths of t!ie  -xidant into the
    pores the par-.icles may appear to burn as shrinking suheres of constant density, a
    fraction of oxygen flux into the pores given by (1 - 6) . where P is the depth of
    penetration and R the radius of the particle, was also assumed to contribute to the
    shrinkage of the particle rather than to a change in porosity.  The radius of the oores
    is allowed ~o grow due to internal combustion but the cylindrical geometry is main-
    tained to simplify the mathematical treatment.
    
          The energy balance on the particle considers raoiation between the particle
    and the bed, heat generation due to the heterogeneous combustion reaction, and
    convection heat transfer from the particle:
    
    
          3"R3pCp dTp - 4ปR2aB(TB4 - Tp4) + 4*R2h(TB - Tp) + F^C-AH^)                 (4)
                   dt
    
    where Tp, R, o. and Cp are the temperature, radius, density, and heat capacity of the
    particle, respectively,   f/j, is the molar flux of oxygen with its associated heat of
    reaction AHp>. Tg is  the  bod temperature, Og is Boltzmann's constant, and h the ho.it
    transfer coefficient to the particle, estimated from the Ranz and Marshall correlation.
    When the volatiles shield the particle from the oxygen there is no heat generation d-je
    to reaction and the volatiles are assumed to burn in a diffusion Flarae which surrounds
    the particle, so that a term for heat conduction from the flane to the particle is
    substituted for the convection term.  In consideration of the fact that for the case
    of high coal feed rates or low excess air values the fast evolution of the volatiles
    •aay cause a local depletion of the oxygen concentration and thus quench the flame,
    an alternative energy balance which assumes that volatiles burn in a premix.ed mode far
    away from the particles has also been formulated.  The heat of reaction used in t'lis
    energy balance corresponds to reaction oฃ rarbon and oxygen to vicld CO. since it is
    known from experiment.il evidence available in the literature (6) that at the
    temperatures of interest for fluidizcd bed combustion this is the nain product of the
    carbon-oxygen reaction.   It is postulated that the burnout of CO occurs far enough
    from the particle surface to cause the effect of this exothermic reaction on the
    particle temperature to be negligible.  This assumption will be tested in the future
    by implementing a 'rinetic model for the boundary layer reactions of CO.  The solution
    to equation (4) describes the transient heat-up of the particles upon immersion into
    the bed and their tenperature history during devolatilization and combustion.
    
          The model of coal combustion described stresses the simultaneous occurance of
    devolatilization and combustion.  Figure 2 shows a schematic representation of thr
    Interactions which the model considers.  The rate of combustion of the particle is
    computed from the rate of devolatilization and residue consumption.  The rate of
    themal decomposition depends according to equation (1) on the instantaneous volatile
    content of the coal,  the temperature of the particle, arjd on the specific coal tyne
    and composition, sine", the parameters i, ko, Eo, and VR  can vary between different
    coals.  In turn, it influences the temperature of the particle, since the form of ths
    energy balance (equation (4)) depends on the magnitude of F02VOL- the oxygen flux to
    the particle by equation (2). and obviously the volatile content of the residue bv
    equation (1).  The rate of combustion of the residue depends on the oxygen flux that
    reaches the particle and tJ-" coal composition and affects the anoint of volatiles
    present in the residue.   The oxygen flux to the particle depends in turn, as shown
    by equation (2), on the rate of volatile evolution through   02VOL. on tne physical
    properties of the coal through a and h, on the Sherwood number, on the oxygen
    
    
                                              440
    

    -------
    
    
    x*
    f
    Particle Combustion
    Rate "^^_
    
    	 -/ 	 _! - — .^
    1 J Volatile Evolution
    J[L - „ Rate 	 	
    1 Volatile
    | Content
    
    
    
    Residue Combustion
    Rate
    	 T J 	 1
    Particle
    Temperature
    
    \
    
    \
    
    Coal
    Properties
    -j 	 i
    Oxygen f\ai
    To Particle
    i *
    
    Intrinsic
    Reaction
    Rate
    
    Nusselt
    Number
    
    •*
    
    
    ^-^
    i ซ i
    Sherw
    Num
    i
    
    ood
    aer
    
    - Coal
    Physical C
    Prop.
    i /
    	
    Fluid
    Mechanics
    ^
    
    
    1
    0:
    "Mruxn-
    tration
    r
    Figurt 2. Factors Affecting Particle Burning Rat*.
                         441
    

    -------
    concentration in the bulk, and on the particle temperature by virtue of equation (4).
    While the initial physical properties of the coal are generally known, the oxygen
    concentration in the bulk and the Sherwood and Husselt numbers depend on the fluid
    mechanical characteristics of the fluidization, so that the oxygen profile and
    fluidization velocities must be determined before the combustioi model can be applied.
    In practice the fluid mechanics routine incorporated In the systems model provides
    the combustion routine with the necessary inputs.  The predictive capabilities of
    this model are shown in the following figures.  Figure 3 shows the weight loss and
    devolatilization histories obtained for particles 3 nrn. in diameter for an ฐ7, oxygen
    concentration in the dense phase at two different temperatures.  At 102VK the model
    predicts that after a heat-up period of the order of 1 second, volatile evolution
    takes place over a time-span of about 18 seconds.  Combustion of the residue occurs
    over a much larger period of time, 810 seconds, the rate of combustion increasing
    due to the effect of pore widening.  At the higher temperatures the same character-
    istics are visible although the time scale is reduced due to the exponential
    dependence of the rates of devolatilization and combustion on temperature.  Burning
    times obtained with the use of this model were found to agree to within a factor of
    two with experimental data.
    
         The devolatilization times shown are commensurable with particle mixing times,
    which are of the order of seconds for typical fluidization conditions.  This implies
    that the assumption of 'nstantaneous devolatilization at the distributor plate
    commonly made in connection with coal combustion cannot be considered to be valid
    for the large particle sizes and low temperatures characteristic of fluidized bed
    operations.  Although the kinetics of devolatilization must be considered in
    calculating local hot spots and other parameters sensitive to the local fuel/air
    ratio, the devolatilization times are a small enough fraction of the total burning
    times that they can be neglected when the objective is the limited one of this paper,
    notably the calculation of carbon combustion efficiency.
    
         Figures A and 5 pertain to the two cases shown in Figure 3 and illustrate the
    detailed information that the model can provide.  In Figure A, the porosity, density,
    and temperature of the particle as well as the ratio of surface concentration to free
    strean concentration of oxygen during the combustion process are shown for the higher
    bed temperature, 1323ฐK.  The ratio of oxygen concentration is a measure of the
    extent of pore diffusion and kinetic limitations in the overall combustion process.
    Also shown are the radius of the volatile diffusion flame and a ratio of the reaction
    rate calculated assuming reaction to occur on the outer surface of the particle  down  .
    to the true reaction rate.  The value if this ratio is a measure of the importance
    of pore diffusion in the process.
    
         Following the particle from the time of immersion into the bed one notes a
    transient he?.t-up period during which little combustion or devolatilization occurs,
    so that the density and the porosity of the particle remain constant.  As the particle
    heats up, volatile evolution -ets in and a volatile flame ignites.  Conduction of heat
    from the flame causes a further steep increase in temperature which in turn enhances
    the devolatilifc-irion rate.  As the volatile content of the coal drops, the flame
    eventually receeds and attaches to the surface.  As the radius of the volatile shell
    decreases, the temperature of the particle reaches a sharp peak due to the proximity
    of the flame.  The density of the particle drops quickly during the devolatilization
    and the oxygen ratio, initially having a value close to one due to the low tempera-
    tures and slow surface kinetics, drops to zero while the particle is enveloped by the
    volatile flame and then rises to a steady value during combustion of the residue.  It
    can be seen that the residue combustion is mainly controlled by external diffusion,
    the oxygen ratio being low, so that the particle burns in a "shrinking core" fashion
    at constant density and porosity.  Only towards the end of its life-time, when the
    particle has shrunk to a small size, is there an upturn of the porosity and surface
    oxygen ratio and a slight decrease in density.  For small particles these trends are
    nuch more evident.  It is however interesting to note that even for the 3 mm. particle
    reaction in the pores accounts for most of the combustion occurring, as can be seen
    from the low value of the reaction rate ratio.  The penetration depth, however, is
    apparently too shore to cause significant changes in the particle porosity.
    
         It must be pointed out that the values obtained for the radius of the volatile
    shell are too large to be considered realistic.  This is due to the fact that the
    volatile evolution is an intrinsically transient phenomenon which does not lend itself
    well to the quasi-steady analysis of the combustion process that has been used in
    
    
                                              442
    

    -------
                                                 CASE I :  T •  1 323'K
                                                    KLAME  FORMATION  t-O.S:scc.
                                                   ^FI.AMF. ATTACHMENT C-6.91.sec.
    
                                                         E  2:  T  " 1023*K
                                                            Ayr KORM.t-  J.-9 sec.
                                                             LAME ATT. f]fv)0sec.
                                 II  II.)
                                                                          IUO'>.f)
                                   Figure 3. Bumout and DevolatilUation Histories
                             of Pwttcla* with Ignition VoUtiles. Particle Radius H = 0.15 cm.
       i.c-5r
    K.
    
    ฐ>
    >• H
    C W
    tea
    o
         .70
    
                                              (a)
                         POROSITY
          01	L.
            0.1    1.0
                            1O7D
                                     1CO.O 300.0
        6.0
      fa.  0
             0.1   1.0
                          TIME  (SECi
                              10*J  X TCK)   (b)
             0.]    10       10.0   100.0   300.0
                              TIME  (SEC)
                                              (c)
    
                               VOLATILE FLAME
                                 RADIUS  (cm)
                             10.0    100.0 300.0
                              TIME  
    -------
    developing the model .   A more exzict treatment of the volatile flane is currently
    being iaplesented.   Figure 5 exhibits the same trends evident in Figure 4. Due to the
    lower tenperature.  however,  it can be seen that the burning of the residue is
    controlled to a larger extent by the surface kinetics and pore diffusion resistances.
    the oxygen ratio averaging about 0.5 during that time.   The nodel predicts that.
    depending on operating conditions and particle sizes, the ccnbustion rate nay be
    limited by external rr.ass transfer or by pore diffusion and chemical kinetics. Figure 6
    shows the ratio of oxygen concentration at the surface to oxyp.en concentration in the
    bulk, which is a oeasure of the importance of pore diffusion and reaction kinetics in
    the overall process.   Since the surface oxygen concentration varies during combustion,
    the value selected for che purpose of this graph is that at the half-life of the
    particles, when the oxygen concentration has in fact reached a steady value.  It
    appears that decreasing the particle size and lowering the temperature has a narked
    effect of shifting the conbustion process from an external dif fusionally contrclle-f
    to a kinetically limited repine.  For the temperature and particle ranees of interest
    for fluidized combustion, the kinetic resistance is by no means negligible, so that
    allowance for kinetics at the surface clearly must be made in predicting burning rates.
    carbon loading, and combustion efficiencies.
    
         It is unclear at  the present time whether the building of an ash layer on the
    burning particle is an important factor that should be considered in modeling the co.il
    burning process.  Allowance for diffusion through the ash layer will be made in f'irurc
    refinements of tho single particle model, and the sensitivity of the results to this
    aJded resistance will  deterninc whether it kill be considered in an improved version
    ot the systems nodel.
    
         The physical implications of the results shown on Figure 6 are evidenced in
    Figure 7. where the different behavior of particles burning in different regimes is
    dexonstratcd.  It can  be seen that large particles at high temperatures bum at
    almost constant density in a "shrinking core" fashion,  while snail particles at lov
    temperatures burr, in depth.   The size of these particles changes little during
    combustion while their density 
    -------
             1.0--
    
    
             0.9  '
    
    
             0.8  .
    
    
             0.7. .
            j
            i
    
            <0.6-
           = 0.5.
           o
           t-
           Ui
           ?0.4.
           gO.3
           gO.2'
             0.1-
                   —h-
               100   ISO
                      JOCO
    PARTICLE DIAMETER (pm(
                                    3000
                    Figure 6. Dependence of Kinetic Resistance to
                Combustion on Particte Sim with Ignition of Votatitev
                       02
                                    0.4           0.6
                                  TiVE/BURNOUT TIME
                                                                           1.0
    Figure 1. Density Chang* of Ptrtictes with Combustion. Co* of Ignition of Vounites.
    
                                     445
    

    -------
                                 ks - " K;
    
    When reacrion is fast, it can be shown (7) that definition of a Thiele modulus:
    
                                      k C n'1
                                      kC
                                       De/R2                                           (8)
    
    where De is an effective diffusion coefficient for oxygen in the particle, leads to
    the result:
    
                             n ,  J_  or  n *  -5 --- * ---                           (9)
                                  3ซ           3R
    
    so that n is inversely proportional to particle radius.  Since AT is porportional to
    particle volume and As to the particle R2 ,  it follows that:
    
                                n A^VA,, rป  f(R)                                       (10)
    
    
    and thus ks is independent of particle radius, as is the case when using the
    unmodified first order rate expression.  When reaction is slow n approaches one and
    thus ks is proportional to R:
    
                                     kgaR
    
    The detailed combustion model for a single particle can provide values of n which can
    be used in equation (7) to obtain a value of ks that will be compatible with a first
    order rate expression hut will now depend on the particle radius of interest and will
    therefore allow more accurate predictions.   Since the different reactivities of coals
    depend mainly on variations in the value of their specific surface area and not on
    a difference in their intrinsic reaction rate, this procedure in essence enables one
    to introduce coal type as one of the important model parameters.
    
         Due to the dependence of the effectiveness factor on the particle size .
    -------
          5.0
          4.0
       23JO
    in
    rป
         .1.0
      o<
      o
                     I
                            I
                                    I
                                           I
                    O2     0.4     0.6    0.8     1.0
    
    
                    FRACTIONAL  WEIGHT LOSS
        Figure 8. Variation of Nomuliied Effectiveness Factor
    
                      During Combustion.
                            447
    

    -------
         A second order approximation is to treat the volatile evolution
         as uniform throughout the bed since it has been shown that the
         devolatilization tines are comparable in magnitude with the
         tines of particle reoirculation in the bed.
    
         2)  The temperature differential between particle and bed is
         small enough (see Figures 4 and 5), other thrn for the short
         initial period of strong volatile evolution, •-''at they can
         be neglected In the system model
    
         3)  The density of the particle can be treated as a constant
         over most of the burnout period.
    
         4)  The chemical resistance is important but can be acco-jnted
         for by use of a simple kinetic model accounting for resistances
         in series of diffusion and chemical kinetics:
                                    kdif?     kocxp(E/RT)
    
         for a first order reaction, vhore the difference in reactivity of
         different coals can be inserted if kinetic data are available on
         tiieir oxidation rates.  In the absence of such date the variability
         which is due to differences in pore structure and surface area can
         be obtained by substitution in equation (71.  For example, for a
         coal particle of radius 0.15 cm. and 250 m-/p. speciftc,,surf3ce area
         with a porosity of 3U percent and a pore-radius of 2*> A burning in
         the presence of a 2 percent oxygen concentration, use of equation (7)
         in conjnction with the results of the single particle model predicts
         the following rate constant:                  ,
    
              Ks - ^.96 x 105cxp(-22.7SO/RT) gatoms C  Am
    
                                               cm-*   /
    
    This relation can be compared with the expression given by Field et al (5).
    
    
              Kc - 1 38 x lO7' x T c-xp(-35.700/RT) gatomsC
                                                   lee—
    
    
    At 1323ฐK the rate constant derived for the Smith and Tyler intrinsic kinetics is a
    factor of 2.2 larger than that of Field et al (8).  This difference may well be
    attributable to differences in surface area and pore diameter, in addition to
    possible variations in intrinsic carbon reactivity.  It should be noted,  however,
    that the difference in effective activation energy is large.  This has a profound
    significance for purposes of modeling the temperature dependence of combustion
    efficiency as will be shown later.
    
    
    S/STE.M MODEL
    
         There are four main components in the system model: fluid r.ec'-nnics, combustion,
    desulfurization, and heat transfer.  The model, receiving information on stone and
    coal feed particle size and density, bed weight,  temperature, superficial velocity.
    etc.. will predict carbon combustion efficiency,  steam generation rate, heat transfer
    coefficient, flue gas emission levels (SO?. NOX), stone utilization. ,ed expansion.
    and the particle size distribution of the'carbbn  in the bed, in the recycle leg and
    in the elutriant.
    
         A brief description of tr.odel components appears below.   This paper will be
    particularly concerned with the structure of the  combustion conponent.   The other
    components are treated in a more comprehensive fashion elsewhere (9).
    
    
                                             448
    

    -------
    Fluid Mechanics
    
         The Cranfield and Geldart bubble frequency correlation (10) is used,  along wivh
    the necessary gas mass balances,  to predict bubble growth throughout the bod.   The
    distributor plate/slow bubble region (i.n the lower section of the bed) is treated
    as one phase plug flow.  The upper section, if in the fast bubble repine,  is treated
    classically; two ohases are assumed with the emulsion gas well-stirred and the bubble
    gas in plug flow.  The Davidson-Harrison correlation (11) is used to calculate bubble/
    emulsion phase gas interchange races in the fast bubble regime.
    
    Combustion
    
         As mentioned previously, a valid first approximation for single particle
    combustion in fluid bed boilers can be based on instantaneous devolatilization,
    constant density of the burning carbon particle, and the Field correlation for first
    order surface kinetics.  The oxygen mass transfer rate to the particle was estimated
    using the single particle correlation for Sherwood number.
    
         A modified form of the population balance suggested by Kunii and Levenspic-1 (12)
    has been used to calculate the bed particle size distribution.  The modifications
    were necessary to account for the attrition and elutriation rates.
    
    
    COMPARISONS OF SYSTEM MODEL PREDICTIONS FOR COMBUSTION EFFICIENCY WITH SELECTED PILOT
    PLANT DATA.
    
         In order to test the validity of the systems model, three experimental programs
    were considered:  the Pope. Evans, and Robbins (PER) fluid bed colum (?). the six
    inch National Coal Board (SCB) atmospheric combustor (14). and the experiments of
    Gibbs . Periera, and Beer (15).  These experiments were selecred because they were
    simple, with no peripherals such as carbon recycle or burnup cell to complicate
    interpretation of the data.  They were also selected in order to evalu.-ite the  model
    over as wide a range of operating conditions as possible.  The PER studies were
    performed with comparatively large particles and high superficial velocities,  arid the
    NCS data with small particles and low velocities.  The Cibbs. Periera. and Beer
    experiments were in the intermediate range.
    
         Figure 9 illustrates data of Pope. Evans, and Robbins. along with system  model
    predictions for combustion efficiency.  The data were obtained over seven hour runs
    and the range of data are shown.   Average values, when reported, have also been
    included.  For the two highest bed temperatures the agreement between theory and
    experiment is reasonable.  However, for the cwo lovest temperatures the model  appears
    to underestimate bed combustion efficiency.  The temperature effect (calculated using
    the rate constant of Fields) seems to suggest that the activation enerpy used  is too
    high.  This is consistent with the findings of the detailed model of particle  burning.
    
         Figure 10 illustrates the data of Gibbs. et al, alone with  system model predic-
    tions for combustion efficiency as a function of temperature.  The predictions
    obtained using the Field's rate constant compare reasonably well with the data.
    However, the predictions show a stronger temperature dependence  than was observ:d
    experimentally.  The model underestimates combustion efficiency  for the lower  bed
    temperature.  This is another indication that the activation enerpy used in the Field's
    constant is too high.  This activation enerpy (35.700 cal/pmole) represents an average
    value obtained by fitting a first order model to a large number  of data.  These data
    were taken with many different types of carbon, ranging from electrode carbon  to coal
    char.  The single particle burning model previously discussed in this paper supeests
    that a much lower activation energy might be appropriate for the bitursinous and
    lignite coal used in fluid bed combustors.  For this reason, a modified first  order
    correlation was generated with an activation enerpy equal to one-half Field's  value.
    The modified correlation was developed by setting the two constants equal at a
    temperature midway between the two data points.  It can be seen  that the modified
    constant does a much better job of predicting the temperature dependence of the
    combustion efficiency than dees the Field's constant.  This emphasizes the need for a
    single particle burning model which can take account of differences in the reactivitv
    of various coal types.
                                             449
    

    -------
    Run Number C-321
    EXCESS AIRU)
    UQ (M/S)
    BED TEMP (ฐK)
    nc 
    -------
         Model predictions are compared with NCB data in Figure 11.  Efficiency is plotted
    as a function of excess air.   Predicted trends appear to be correct, and the predicted
    values appear to compare reasonably with experimental data.  The relative importance
    of chemical kinetics are emphasized with small particles as well as at low bed
    temperatures.  Since the system model underestimated corhustion efficiency for lower
    bed temperatures, it would be expected that the model will also underpredict
    combustion efficiency for small particles.   This does appear to be the case.
    Correlation appears to be Rood.  However,  it should be recognized that large errors
    in carbon loss estimates will be less evident for high combustion efficiency than
    for low efficiency.  For example,  an agreement between theory and experiment of one
    percentage point in combustion efficiency would amcunt to an error of about 5 percent
    in carbon loss for an efficiency of 80 percent.  For an efficiency of 99 percent.
    however, this would amount to a 100 percent error in the carbon loss estimate.  The
    apparent agreement between theory and experiment for the smaller particle sizes
    should be considered within this context.
    
         In summary, system model predictions appear reasonable for conditions expected
    at full load bed operation.  However, for part load (low temperature) operation,  it
    appears that the first order rate constant of Fields, et al. overemphasizes the rolo
    of chemical kinetics.  A modified version of the Field's constant, using a lower
    activation energy, provides a realistic estimate of the temperature dependence of the
    bed combustion efficiency.
    
    
    CONCLUDING REMARKS
    
         Elutriation of solid carbon represents the major combustible loss in fluid bed
    furnaces under normal operating conditions.   Carbon loss in the fluid bed combustor
    is high.  It may, in certain cases, exceed 20 percent of the coal feed (this may be
    compared with a combustion efficiency in a stoUer furnace of over 95 percent and in
    a pulverized coal furnace of over 99.5 percent).  The high carbon carryover results
    from .a desire to minimize furnace size by increasing the volumetric he.it release rate
    in the bed.  This is usually accomplished by running with large sized ccal feed and a
    high superficial velocity.  Unfortunately,  this results in a rapid elutriation of t'.ic
    carbon fines generated oy attrition and combustion.  Carbon combustion efficiency can
    be Increased by recycling these elutriated fines, or by use of a high temperature
    carbon burn-up cell.  Carbon recycle loops and burn-up cells introduce capital
    expenditures which must be considered within the conttxt of an overall optimization
    program.  The expense of a carbon burn-up cell (CBC) is probably justified in a
    large utility furnace, where capital costs are amortized over a comparatively lonp.
    time period and there is a great need to reduce operating costs.  The CBC would be
    less useful in a small industrial boiler,  where there is a greater emphasis on
    minimizing the initial cost of the boiler.
    
         The system model can play a useful role in performing the cited trade-off
    analyses.  The model also has a potential use in the design and scale-up of fluii'
    bed combustors.  The model has the capability to predict the dependence of bed
    combustion efficiency on temperature, coal particle size, superficial velocity, and
    carbon reactivity.  The agreement of the theoretical predictions for combustion
    efficiency with limited pilot plant data is gratifying, but there is a need to
    incorporate a more refined model for char combustion in the system model which can
    take account of the varying reactivity of different types of coal.
    
    
    ACKNOWLEDGEMENTS
    
         The research work presented in this paper has been supported by the Department
    of Energy under contract number E(49-18)-2295.  The financial support and the
    assistance given by DOE in the course of ihis study are gratefully acknowledged.
                                             451
    

    -------
       ] . OII
      0 . 9 8
    u
    So
    o
    ป-t
    b.
    b.
    U U
    7.
    O
    9f,
    94
      0 . 9 2
    O 0.
    o
         r.XCKSS  A1K   1  •   (t-xp)~|  nc
    
              12. f     I"  9•>.<>
         	 9.8     1"  fi.it   "|    94.7
                                  6"  DIAMKTF.K
                                  ATM  FLUID  BED
                                  OF  NCB-CRE
                             REF.:I'ii-Ma ป>;•>
                             KUNS ป  1.2  I,  1.5
                          •>             10
                             EXCKSS  AIK
    Figure 11.  ompariwn of Experimental Data with System
         Model Predictions for Combuition Efficiency.
                          452
    

    -------
     1. Comparative Evaluation of Phase 1 Results frora the Energy Conversion Alternative
        Study. NASA TMX-71855. February,  1976.
    
     2. Waters. P.L..  "Factors Influencing the  Fluidizrd Combustion of Low Grade  Solid
        and Liquid Fuels",  Institute of Fuel Symposium,  Series No. 1,  Fluidized Combustion,
        London. September.  1975.
    
     3. Cordon, J., et al,  "Study of the  Characterization and Control  of Air Pollutants
        from a Fluidized Bed Boiler- The  S02 Acceptor Process". PB-229 242.  July,  1977.
    
     It. Anthony, D.B. , J.B.  Howard,  H.C.  Hottel,  and H.P. Keissner. "Rapid De-volatilization
        of Pulverised Coal", Fifteenth Symposium (Int.)  on Combustion. The Combustion
        Institute. Pittsburgh. 1975, p. 1303.
    
     5. Ran^. W.E. and W.R.  Marshall, Jr., Chemical Engineering Progres 48.  1952,  p.  141-
        146 and 173-180.                                                ~
    
     6. Smith, I.W. and R.J. Tyler.  "Receptivitv of a Porous Brown Coal Char to Oxygen
        Between 630 and 1812ฐK".  Combustion Science and Technology. 9. 87. 1974.
    
     7. Carberry.  J.J., "Chemical and Catalytic Reaction Engineering", McGraw Hill
        Chemical Engineering Series, 1976.
    
     8. Field. M.A..  D.W. Gill. B.B. Morgan and P.G.W.  Hawksley,  "Combustion of Pulverized
        Coal". BCURA,  LEATHERHEAD. 1967.
    
     9. Louis, J., et al. "Modelling of Fluidized Bed Combustion of Coal", Quarterly
        Technical Progress Reports I through 5.
    
    10. Cranfield, R.  and D. Geldart. "Large Particle Fluidization". Chemical Engineering
        Science. Vol.  29. 1974.
    
    11. Davidson,  J.  and D.  Harrison. "Fluidization", Academic Press,  1971.
    
    12. Kunii. D.  and 0. Levcnspiei. "Fluidization Engineering",  John  Wiley and Sons.  1969.
    
    13. Merrick, D. and J.  Highley,  "Particle Size Reduction and Elutriation in a Fluidized
        Bed Process".  AIChE Symposium Series. No. 137.  Vol. 70, 1974.
    
    14. Reduction of Atmospheric Pollution, Appendices 1-3. National Coal Board.  PB-21067A.
    
    15. Gibbs. B.  and J. Beer. "Concentration and Temperature Distribution in a Fluidized
        Bed Coal Combustor", Presented at the Combustion Institute Europeon Symposium.
        University of Sheffield.  England. 1973.
                                              453
    

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                QUESTIONS/RESPONSES/COMMENTS
         FREDERICK HANZALEK,  CHAIRMAN:   We are now ready for the question
    and answer period.   I  think  that  a  number of questio.... have *>een
    passed now to each,  of  the authors;  perhaps not to Dr. Saxena, *>ut
    please furnish him  with them while  I go more or less in time ore -.
    Dr. Sarofim has had the most time to prepare, and also most people
    have had more time  to  prepare questions for him.  You have a few,
    presumably.  Would  you please read  from whom the question comes
    before you answer it?
    
         DR. SAROFIM:  In  view of the time limitations for the presenta-
    tion, we did not present  the details of the model, and the questions
    that I have received relate  to those.  We also didn't have time to
    acknowledge prior work in this area, and  I would like to comment that
    two of the questions come from two  individuals who have done pioneer-
    ing studies in the  modeling  of fluidized combustion.
    
         Professor Saxena  has a  three-part question.  The first part
    says:  "Your external  diffusion resistance refers to gas film and/or
    ash film diffusion  resistances.  From where do you get your values?"
    
         We do not allow for  an  ash film diffusion resistance.  We used
    for the external gas film resistance the correlation of Rentz and
    Marshall.  We are aware of correlations that have been presented
    for fluidized bed operation  showing much lower heat transfer correla-
    tions, but we are reasonably convinced and have evidence to support
    that the correlations  such as the ones presented by Sikali and
    Reischenden for fluidized beds are  not valid and that Rentz and
    Marshall is a much  more appropriate one.
    
         The second question  says:  "Do you account for bubbles in the
    bed?"  And the third one  is  related:  "How are gas and solids flow
    approximated in the model?"
    
         We have relied heavily  on the  inputs from Professor Glicksman
    and his work in modeling  fluid dynamics.  We allow for the fact that
    bubbles are born small, and  grow; and as they grow, they eventually
    reach a size where  their  velocity is less than the mean velocity of
    the gases in the bubble,  or  they move into the slow bubble regime.
    
         So we account  in  our model for a fast bubble regime up to the
    point of transition to the low bubble, and allow for the Grandfield
    and Gc-lgard correlation for  bubble  growth, and the Davidson and
    Harrison coefficient for  exchange between the bubbles and the emulsion
    phase.  For the circulation  of solids in  the bed, we assume the
    solids to be well mixed.
    
                                     454
    

    -------
         Professor Wen, West Virginia University, also has a three-part
    question.   He comments first that "combustion efficiency is roughly
    equal to the coal feed less the eleutriation rate."  He then goes on
    to ask:  "Have we compared carbon loadings in the bed with experi-
    mental data?"  Of course, he is referring to the fact that the
    eleutriation is proportional to the carbon loading in the bed, and we
    have worried about carbon loadings in the bed.  The numbers we get
    are in the range of 0.1 to 1 percent, and we have compared them with
    the very limited data that are available in the literature.  We find
    good agreement whenever data, such as the British, with small par-
    ticle sizes, low carbon loadings are on the lower end of the scale.
    The data with larger particle sizes have carbon loadings closer to 1
    percent, and again, we predict the right magnitudes.  The data are
    sufficiently imprecise, though, that we really cannot say that this
    is a great check.  We do need more information in this area.
    
         He asks a second question:  "Did you take into account the
    swelling of the particle?"  And the answer is, "No."  The evidence, I
    think, is slight; I would like to hear the data which support very
    significant swelling.  But at this stage, we do not allow for swelling.
    And the third question I have already answered.  It relates to solids
    mixing.
    
         Dr. Rao of MITRE has a four-part question.  I only have three
    cards, but 10 questions.  "How does the ratio of devolatilization
    time to the particle burning time vary with such variables as pressure,
    temperature, and particle diameter?"
    
         The devolatilization times really are kinetically limited; and
    so we say that the time required for devolatilization is entirely a
    function of temperature, and it's only a function of particle size
    to the extent that particle size, in fact, also determines temperature.
    
         The burning time follows in the diffusion-limiting regime a
    square power dependence on particle size; and as you would expect, as
    you get to smaller diameters where chemical  kinetics becomes more
    important, then dependence on particle size decreases.
    
         The effect on pressure; there we have a first-order dependence
    on the chemical rate constant which can vary down to a  half-order
    rate on the chemical  rate constant.  On the mass transfer coeffi-
    cient, of course, you have the canceling effects between the effect
    of pressure on concentration and the effect of pressure on diffusivity.
    
         The second part of the question:   "Does the model  currently
    account for the discrete feed points in real  systems?"   We do not at
    this stage have a solid diffusion model, which is what  is required
                                    455
    

    -------
    in order to account for the discrete feed points.   We anticipate that
    in future work that we will, as we get into the details of solid
    mixing into the bed, then address this very important practical
    problem.
    
         I don't think I should comment on the third one.  He says,
    "Could I comment on the numbe1* of feed points required for a given
    AFB combustor."  Well, the rule of thumb is one feed point for nine
    square feet.  The only comment to be made is that  it is a function of
    circulation rates, too; the interesting questions  are, can you people
    have proposed parting beds for overfeed, and I think this is something
    that I should leave to -he practical sessions to answer.
    
         "Does the model incorporate feed size distribution and determine
    the particle size distribution in the bed and in the off-gas?"  We
    certainly allow for the feed particle size distribution and use  the
    population balance mechanics to follow the particle size distribution
    within the bed, with allowance for the effects of  eleutriation and
    attrition.  In the off-gases, we do not allow for  a freeboard combus-
    tion model at this stage, but it is important, and we have plans to
    do so in future work.
                                     456
    

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                           INTRODUCTION
         FREDERICK HANZALEK, CHAIRMAN:  We will proceed innediately to
    our third oaper of the  second half of the session, which is entitled
    "Fluid Dynamic Modeling of  Fluidized Bed Conbustors."  This is
    authored jointly by Messrs.  Bar-Cohen, Glicksman, and Hughes of KIT.
    The paper will be presented  by Dr. Clicks-nan, who received his
    initial training and BS degree at MIT, wandered all the way out to
    Stanford to get his MS, but  then came back to MIT for his Ph.D.,
    where he is currently on the faculty in the Mechanical Engineering
    department.  Dr. Glicksman?
                                    457
    

    -------
                                         Fluid Dynamic Modelling of
                                         Fluidized Bed Combustors
                                          A. bar-Cohen, L. Glicksman.
                                                   R. Hughes
                                     Department of Mechanical Engineering
          CT                         Massachusetts Institute ot Technology
    
           The dvnaalcs of ^.v bubbles  rising  and  growing  vlthin the sollds/gaa enulslon are today known to
    define the operating characteristics of  rvtny practical fluidized beds and* in snal l-part tele svstens,
    l...ve be.-n sliown to follow the tw>.-phase  theory.  The present effort focuses on the fluid cv.hanics of
    larw particle fiulJization. as  Is  anticipated for  fluldlzed bed co;ahustors. nnd extends the Iwo-ph.ise
    the.try to this iapctriant flufdization category.  The results sugp*~Kt that tvo-phase theory, when com-
    bined with an appropriate bubhle-f requer.cv relation, can prov* !e an accurate prediction uf bubble size
    and bubble fraction and their variation  with height  in the  bed.   Furthermore. examination of these re-
    I. it ions in Hunt of the particle sizes .ind air flow rates proposed for prototype fluidi'ed bed eonbus-
    lors suggests that an ippreciahle part of  bed  operation will be  in the slow-bubble regime where ouch
    <>t  the erajlsion gas f K>wป through tlte bubble void.   In this regime, gas flow through the bed can be
    noJelled as plug fli-c and thus provides  substantially  less  resistance to nass transfer than is encount-
    ered In the conventional, fast-bubble reside.
           I".,.- operating characteristics of  t lulrilzcd  bed  toabustors. Including:  coabustlon efflcU-ncv.
    t'vd txpanslon and he.tt - rets-tva !  tate. are largely deterained by the f lu id-dvnamlc merbanlsBM active  in
    the ! iii ii' irt.-d oedlun.  In  bubhleii  rlsinK throtich the enulslon are viewed as the Second
    ph. ire.  Kvtfnilve i>tvซ-]it I ป-ai lป-ns bv I)aviJs\>n and co-workers |1| have shovn that the dynamics of a single
    nan biiohli- la  : lluldlz>d Bed Inn are Ind l-t in,;u Ishable fro^ Iho-:e of a i;as bubble In a hoaogeneous
    liquid and that potenllal t li*w  the rv as first developed bv tMvles and Tavlor [2| can be used tci estab-
    lish the velite.lt v tieldi In  tlie sur r.'.iml I n>; eeulslon aป \Jvl'. as In the rising bubble.
    
           In flutdlrod b4 ! i-i>nhustซrs, I lie  coal p.irtlclei ore  anticipated to constitute onlv a verv sT.all
    fra.iloa (Ivplcallv ir> ot t !„•  p.ir t I. een obtained In  InveBt Igat Ions of relatively snail particles
    (tvplc.illv HXM) and  l.n.- tluldlrlng veliซc 1 1 lvป.  II  Is thus Inportant to Identify and quantify the diff-
    erence betveen the tluld dvn.iaic
    -------
                                CMUktlON
    Figui* 1. SMtch Of Gซ Flow For A Slow Bubfalt.
         At S*cn In Bubbte't Rctenno* firm*
                      459
    

    -------
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    IwihMcs to  IM-  nrr. I i .- ilป I v  ;.n.-i 1 1 , -is  sui^.-st o*l hv  r* : .-r.-n.-*-  I •* | .  <>r  -i-;  ^.in s.-  i^pl l.-.l  t r>T. t hป-  .-.-i-.  ! li-w
    .ir.xiivl  .1  •:!••*  h.iM.I. .   U'.tli thin  .i-;su-;pt Ion  .in.1  vuh^i 1 1ซ: ;..n  fr->3  l!q.  I  ,mปl  .'  fur  I !>c '.MiMil.-  rise
    vt-I.H-itv.  K.|.  'i .-.in  h.' rx-dlflfJ t.'  r.-.nl
    l"he  rnnllnnity  of  s lnv-hiibHIe  c.iซ!  fl
    -------
     .Ict.iture.   ..•-••.eve r ป  ; :i
     ut..  :u..Mv  lr.-iiu-n.-y  ..:..:
    
    
    **J "• * * . * ti * r itt .ri
    
    ; j ป..lo:4 , ^-- .1 i tul *:i.' I I . . 1:1 t'.** v.' 1 .*r*. tiic t uLM*.- f !••'- ft 1 .il inn , I •; . ?
    LuLi- !ป• t f ..t 1 iun i r. ii'U.'td to ."J't.tl
    
    
    
    
    -1:1 J i no lu- in;- t •; . M ป t :u*
    ior  sj'vcifivd nr ซ-i >;.jr i r.i 1 1 / J--tป-r:.m.-J v.il-i.-s  nl  ป.   ..:u! t   , t;^- buILU- Ji.ir.etfr  auj hui.Ulo  (r. action
    at v-ir ion-. ucii>tt-t c.iit  .i i *iu i ;•!••ป ->i-  •!elซ-ri-Tnf.l  f . ปr 'ป .tcl.  input  v.i 1 w nt  i.t'perf lci.il  f't*ป   vปr 1-
    i-c il /  Ly  -.it^ul tanvi'u ป 1 y -.oi vir... i.'\.  J .itiJ '>.  ttu^ovttr , I i^.-  rnn;ปlrx ป!ป'pซ'n*Jrnre -i!  i   on bub U It*  J i,ttu-tป*r
    t.-ir.t--. ซ.-x;i 1 .ci t '.oiut 111:1 f -if t .tesซ'  p.t r ur-'l crs  all tjut  injtussiblt.* .ปnJ  .in  t to rat ivc  nuncr teal  li-clmi-jut* ,
    uซ."ปcr i UvJ ii. Ootat 1  in  ri-f ซ-rctici*  1 1 1 * *••••* upy 1 IcO.
    
            W!ปi 1*  .'.ever at t .I'tt - '..u!>blซ'  cor re l-*t tuns arซ'  av *I 1 a!> li*  in the t ltซr,tture and a recent  "no due to
    I'.trtcn. et al. \'t\ .ป;'pc-.ir.-ป to .irhievc *.i mil tc Jnt ^ccur.icy,  none of t!ies-.~  furo-jl.tf.lonb at tetr.pt ii to
    *ati.,ty K.IS (low  continuity via t:ปป- two-piiu**** •••motion::.   TIw ! re'iu*-ncv/two-piirtปe fomul^tion  'lt'.cu:.*od
    -itovc ro-*ซ'nt el furl  focuses prlewri ly on  * low buLblc
    J/n.ป^icj, it is oi interest to  extend t.'ic nodcl  into  t!i*'  fast-buMilc  rcp.loe by appropriate  nod I f ic.it ion
    .,* i,,.  ;.
    
            liubLtc ~** flow  ia 'itis  rซ'>>,ia4> Invulvcs  r.as rcclrcula^ Ion  in  tl.e bubble cluud and walco  as well
    .1, tue  i;ปป vulunu rl-,lnr. i i tin- but. Me, liut  In  cuntr.v.t  tป  tlic ilow  lni'ublc  (low.  there 1ป no throupii-
    f!uw In .in l:.                                 c  :
    
    ป>sปunint;  once again  tltat tiic isolated-bubble  results  can  be  used  to  characterize  Che behavior  o( bubble
    bwarns  and coaoininj; bubble (law  with r.ai (low  in  the emulsion pnuie. ซ;aป-(lov continuity (or  this
    rcKinu  can bo cxpfcsscJ as,
            Solution tut  the (a>t-hubblc  dianetcr and bubble  (ractlon can now follow the  procedure  discussed
    (or tite uluv-bubblc  rcr, Ine by use.  of Cranficld  and Celdart's I?) (requrncy correlation.  As w.is  noted
    earlier,  while this  correlation wai  developed  (roe slow. bubble d.ita obtained wltli  larRe-part Icle
    (iuldlied buds. 11 agreed <(uile kvll with Culdart's ! -1 1  s=al 1-part Iclc/ (ast- oubb-lซ  results ind could.
    thui, >crv.-> as a starting point (or a cocpietc 'jujble oodol.
    
            Tlio relations presented above have been  baaed exclusively on the  potent lal-(lov codcl for   an
    isolated  l-ubbla.  Ycl,  Ja t!>c relative bubble  rise velocity  approaches  the interstitial Ra> velocity,
    L.   • L(, the transition (roa slow to (.i^t bubbles, Ujvldion and Harrison's aodcl.  as veil as  later
    rcilnencnta, predicts a rapid increase towards  infinity  In tile olzc of  tiic rcclrculat Ion zone.   ซ~illc
    this conditlcn nay be approxiutvd ' y a single  bubl le  in a l.ir,-c flui.Ii^cJ red, t'.c  size of the  recir-
    culatlon  zone around in individual bu'-ulc In -i  uuULlo :i.-.i;n  -rut c'.'.irly j;-p.'c.ic'.i x  finll>- llnli  .1.4 live
    
    
    
                                                          461
    

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    bubble r Ise  ve I'M- it v approach*--; t hซ-  f nr erst 1 1 Jal >•;ป*•  v*-lซป i f v.  The  f lปj Jd-nechanl'- 'li-ta I i s  ป;f  this nซ're
    ซ ormnrilv I'll* nuntered ซ out J ;'.urat i-- such .'* solut ion  verv unwield 1 v .
    
           Alternately,  In  tin- pre<..-nt model,  the  tvn-phase  e*;u.it inns b.isซ-d tin an  isol.-(t**d buhble  vtrซ- .'i1.-
    Mj&4t! lo a[.;ปly as  Ion;-,  a-, t tt.- ••ป|ซj i va |t-nl  sp!n-rf'.il vulun.- '.!  I (M- h-*hM*-, Its vn\rv and  Its rlnud ftปr
    rซ-f i r< i: I at i<ปn /on*-) d Id iml  ovt- r lap  t hซ-  -i'l jaซ-c-nt hu(ปl>lซ /w.^t-/ซ l*.nfl vซปl urac.  Consi-^urnt 1 y, < a Irulat iซm
    til r l:i- fjfซ'< I.,e t*uttMt--s I /ซ• var I at  inns nป .ir t tiซ- s lov/f .isi t ran1. It ion  rvjst /tw.t i t  a nor*.*  ret Jr*-d  rป>d*.- 1 and
    .ili'l.r-.I.  lnt*-rpi*Ial I'.a t>*-tw<->n i In*  fast  aiwl slow !ปuhhlซ* rt.'1.il Inns ausl suffl'o fซ>r the  pri-sซ-nl t Irw,-.
    
    VAI.IIiAII'iN OK KI'HHI.K **/)[]ป,!,
    
           IKJC to tin- v-huhMซ-  d-ita In t h*-  I i tซ-ratur*-. <..r.plt-tซ- validation of the  Iwo-phas**/
    I ri-qtifitrv hn'ibU* K'"V* li wซlซ-l d.-rlv.-d  in MM- |ir.-vlซ-us section Is r*ปซil dilflrult.  There ar*.-. n*-verthe-
    less, several  central fjin-st Ions vhle answered hy cneijiarlnR the prซ-JIซti'ปn of various f!ov
    parameters with put>Ush*-d • xp.-r f m-nl a I  results.
            In  the O.infield  ;irirl  fu-ldart study (?) tmth huhhle f rt-^iiency and huhhle d|.-imt-l*T w^-re measured
    hy  Independent  neans.  The re Int Ivc (*rc-dic| I ve cap.ibi I i t v of i he  present h;iti!ปle growth mode 1 and
    Ikirtun's l.isl-liuhMr fnrnnlnc inn | ** | * .m  I hus hi- ex.idfned hv mnp.'ir I son with Cr.mf Iซ- 1 d and C*-lUart*s
    1 7 t ex per (men I a I  d  va lues.   'I he exrel 1 1 -ill  at'.rceoent  h*-t wป-ป-n t he  f r*"?' i*-ncv/t wo- phase t heorv  and dat .1
    .,hi>vii  in Figure ^,  --rovltlos  •'ป initial iont Irnwition of  t!w v.ilidjlv <ปf the  two-phase thi'ory  In t :te slow
    huhhle  regime.   A 1 1 crn.il ป• 1 y . the failure  of  the- Unt'-n  taodel to anuralely  predict the Cranffeld arttl
    Celdart results h 1 i-h I U-.ht s the limited applicability  of  this rorrel.'it ion to slow-hubb lc- data
            In addition to  huhhle t-rn-t Ion dfataeler. McCrath and St re.it f I e Id f 1O|  reintrtrd visual  r;thvUes
    of t he  nuciher of Imhltle  erupt Ions, N, visible .it .1 *;! ven instant.   S ince  this  nur.ber I s  appro:'.Inat ely
    .•qu.il  lซป I he number of bubbles present  In a control  volume orrupvInK tปซ'  tซ'd  <-ross*serC Ion  and oqual
    In hc-lKhl to a bubble  diameter. Hie enpirL -; bubble fraction was  ra leu lated  arrordinp l
    
    and Inserted In the two-phase i^uat Ions to vie Id a bubble K Ize.  As  c.m be  seen In Fl >',.  3,  this ••rovlded
    euch  Inprovrd a^reem-nt  with the McCrath and St rc.it field | 101 data.   Furthermore,  the resul t InR ^'allies
    of bubt>le diameter are ;i(;.'ilii seen to suggest  that a  132 reduction  In the experimental * effective bubble
    Nlze  a;iy be appropriate.  With Much a corf* l.'it Ion, tbe r^^xilfled  frequencv/two-ph^se model  (Including the
    ftpec I f If, empl r Ira I Iv  der Ived bubble f r.ict ion) wi*uld yield cxrel lent  resul Is.
    
            The validity of the present  frequency/two-phase approach  Is  ronflnaed,  as well, bv examination
    of Verifier's data obtained with typical  ooan particle diameters  of  103U fill.   Ttie Investigation w.:s
    alraonc  exclusively In  the fast-bubble refine, but Is one of the  few in the  literature that  provide* an
    explIcit bubble-frequency corre Iat Ion.   Tit Is eopirleal expression,  shown  in Kq.  13 below
    
                                               fฃ - (0.039H + 0.57)"3                                    (13)
    
    la Bubstantlal1v different frnai the Cranfleld and Celdart relation and was  Inserted In the  frequency/
    two-phase model for this particular calculation*  The dramatic Improvement  In  the  predictive  accur.ic /
    of the  present txxicl resulting frott the use of f** Is clearly shown  In Kip. 4 where the  locus  of the
    bubblc-dtaocter prediction using f** In  cnnpared wfth that bated  on Cranfleld and f^eldart's  frequency
    (Eq.  8)  as well as with  the Dartnnw(9)  hubble-Rrซwth oodel.
                                                          462
    

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    -  10
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    3    2
             sirrscis:
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    BUBBLE DUKETER < MEASURED). d   (ea)
                                                              20
          Figur* 2.  Infhjtnce Of Frequency On Bubble Sin Prediction—
    
                       Oau ol ConlnkJ 4 CeUart 1 7 1
                                463
    

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                                                                             i
                                      464
    

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           j;.*j  k.:  L.--- iuuuo.--.mtal difficulties in .i:tdl/2iur  uluv-Lubble Urliaviur  i i the need to determine
    aad account for t.*e t.troug.if low  and  rocirculatiou of emulsion r.-*s-  CK-aily,  at very K>k bubble  ri^e
    velocities  it  ii tiie fon^r  taut  dor.inates, Lmt as t.*e slow/ fast transition is  appro ached. the cross-
    M:*:t.lonal **rca for tiirouK.if low decreases and rocirculation  involves pror.rt--jsivcly nore of ti>* bubble
    v,.lmปc.  IM.-VVT t.Mflcss, it :u> Leon ^uw.t'Stctl tiiat for tu-.t ซ'f tlie ujov-bul'ble  re*:*,ino, it oay be possi-
    ble t-ป cx^r^aj i;a:ป flow continuity for a sinp.lr Luablc in  sic^lificd forn [I'*}  a;> below
                                                                                                       04)
    i-tar.ia.it ion  of L'\. 14 in  light  of  the rare rlgoroui r.as-fl
    t.ut t:te  lainii and Leซens;iiel  fornulation c
           A norc JotjllcJ L-iunination of  tlic effective tiirou-.lifIbu coefficient  for  Crjiiflrld anj CelUarc's
    invvi>tirซ*tion 17) i*ป Uisplayod  in  Fii%  6 vtitrre a rvlati0)
    [1J a;ปuo^r^ to a^ply over nuc'i  of  tite  tปlov-|jubblc  ranp.e.
            inu  vx,>etirซ.ntiii variation  of '.,  olitalnud t>y Cranflcld  and (^.-Idart (7)  in  two different run* of
    a larr,ซ.--. 'article fluldijcd ued operating in t.ic blow l>ubolc  regime, witli t.  /L. ran^inK froo 0.4 to
    >>.0? and  'J. itf to iJ.'^A, rcb;H:ct ively, is  u!tovn in Fl^(. 7.   T>*e  Intllc.itcd data pointa were obtained by
    •M>lvin>; O\.  14 at *}>cclficd bed  lป.-Ii;!it •-., v!>erc bul.bic tlze vaa c-xpor Inrntally  dctvrnined and reported.
    'i.te solid line represent :ป a icni-c-npir ic.il  e-juation for  c  obtained froa the bubble  frequency and size
    coi relations ;iri:ซenteJ b/ Cranficld  and  c seen in Fir,. 7 loth tl'O calculated
    value j a. id  tite locu? of tlic  t correlation bliov tiic anticipated trend wltli bed  Itviglit and vliile tlio cal-
    culated value* arc -e:ierally uelow tiic correlation, t'.ie dlfforencc Ij typically less than II".
    
    Subtle Si/.e I're.l ict iun^
                           -..UKKv&t!i  that  tiic tvo-pltase theory of  fluidlzed bed behavior  can be
           Ituc  perforaancc of fluidlzed  beds  1* closely linked  to  the flow reglnc prevailing in tlie fluld-
    izcd nudlua and varies substantially as the WJ passes Iran Incipient fluldlzation  through bubbling
    and on to slugging.   Lxanination  of  tiic governing relations suggests that in an open bed of specified
    geooctry. particle and gas density, and pxrtlele shaoe  tlic superficial velocity at vhlch the transitions
    between various flov regincs occur  is dependent exclusively on particle size.  In  succeeding paragraphs
    tne approximate loci of cinlaua fluldlzation, slvw to fait  bubble transition, slugging, turbulent flow
    ซnd particle teroinal velocity will  be discussed.  The resulting flow-rcgloc naps  for two typical bad
    configurations are displayed In Figs. 8 and 9.
                                                        465
    

    -------
           80
        [;  T>
    
        n
        w
        (r
        -  70
    
        ฃ
        n  60
    
        a
        in  ซ
                 HAi.^-'rr-fri.fcs I^'ATF. AVK^A-KS
                     | >j  ^At.1:11! ATRO  ••sir'
                 ERROR PARS: 1  1  STS.  DEV.
                 DATA  OP CHAV?IELD A?;0
                    CEU5AST : V "
    e   '
               DOTS:   VALtrES CAL^LATED PRO" DATA
    
                    OP C8AKPIELO ANT) 1ELOAHT  71
                                                                      O.?0
                'ERPHIAL VELOCITY  (^PESlrENTAL J, u  (e?./a j     *
    
                                                                  g
           Figure 5. Comparhon Of Superficial Veloeitiei Calculated     f;
           With And Without Recirculation. thing Eqnป. (8) and (14).     J  0.10
                 Respectnety-Data of Crcnf ield & Geldart 171          ^
                                                                     c.or.
                                                                     0.00
                                                                           srr.sct
    
                                                                             o
                                                                             o
                                                                             o
                                                                                          V8.ซ
                                                                                      10         10         10
    
                                                                                          HEIOHT.  f! (c*i
                                                                                                                      ซ0
                                                                         Figure 7. Variation Of Bubble Fraction With Height
                                                                               Above Distributor-Data of Cranfield
                                                                                         & Geldart (71
    0.0       0.2        04        0.6
    
                             ut,r/ur
                                                    0.8
    1.0
                Figura 6.  Throughftow Coefficient At A Function
                    With Height Above Diitributor-Oatl of
                          Cranfield and Geldart |7|
                                                           466
    

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                         467
    

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    :!lnlpun riutdlzatloo Velocity
    
           ^ille several correlations are available for predicting the superficial  velocity required to
    achieve particle t luidization. aost, if not all, seem to be based on  a  force balance between the v>.*ielit
    of liic particles and the bed pressure drop, calculated from Ergon's correlation [12].
    
           Tiic graphical display in Figs. & and t reveals tlic anticipated trend of  Increasing t'cf vlth
    particle size.  Comparison of the run! nun fluidizatlon velocities for 2UOu and  2000'j particles accentu-
    ates the significant difference in superficial gas velocities encountered in flolnp. fron snail to large
    particle fluid! zed beds.
    
           It oust be noted, of course, that aggregative f luidization is  not  generally achieved at alni-;ua
    fluldlzatlon, but ratiier requires sone further increase In superficial  gas velocity.  Soae early --or*
    by bavldson and Harrison |1| suggests that the transition from particulate to aggregative fluldization
    iccurs wlien the ratio of predicted bubble diameter to particle dlanseter is in the range of 1*10, but a
    precise correlation of this fluidlzed bed .transition is not yet available.  In Its absence  Cranfield
    and Ccldait's [7] Bea->ur>.-d bubbling Incipience excess velocity, UQJ, - U , - 5 en/sec,  nay serve as a
    point r-f reference for beds operating with relatively large particles.
    
    Transition Between Fast and 1.1 ox Bubbles
    
           As discussed in the previous section, the flow of gas In an aggregatlvely fluldized ooJlum gives
    rise to two distinct bubble rugiacs, depending on the ratio of the bubble  rise velocity to the Ras
    velocity between the fluldized particles. I.e. the Interstitial velocity.  The  <. -nmonly encountered
    fast-bubble regime Is associated wit a velocity ratios greater than one. while for •.-•-ios l"ss than one
    the bed is a.- id to operate in the slov-luublc regime.  Tor a given particle size, the  superficial  velo-
    city at vhlch tlie slow/fast transition. I.e. L'ur - t'Qf/cDf, occurs can  be determined by use of the
    f requency/two-pliase bubble raoucl    previously discussed, with t'^ equal to
    la i.q. '*•  The ainic~a fluidization velocity relation previously discussed  can  then  be used to relate*
    tlic transition velocity directly to the particle lilancter.
    
           examination of Figures 
    -------
    nay not  Lซc  applicable to larr.e-?art icle,  sn.il l-ป!iarx.'tt-r beds, where  the slur, rise velocitv nay fall
    lปvlo-  t.ie  Interst i t 1 jl c.iu velocity a:ij thereby  p.ive rise- to .1 slov-;;lmป vliicli lias 7ns throur.'.f lo'*'
    -ปi::ilar  to  a slow bubble.
    
    J i iicnnt iuuous  i.eglne
    
            l.i-cenl  c::.'C*r iijcntal o: servat io::;. Ji'ป,  lj.  '.'•] '.'irj'.est that nt  appruxir.itel y or.o-half  t;te  particle
    terrinal velocity tiic slui'j'.inr. b.-havior ceases and is replaced Sv a  ttir'iilent, c'l.iotic flni:  durlnf,
    wliicii  erratic  voids and snail flow channels as veil  a-j vigorous ..- ircul.it Inn of Mu- .-ol Ids In fin !><•'!
    tซoco;ic a:>narunt.   .'Jut to the linited nun!ปซ^r of tur'-nlfnt flow cxporinent^ i*crforr^-d thus far,  tiie
    Ijoundary of this  post-sluf.^inj; flow rt-rlnc r.ust  at this tine tnป viewed  as tentative.
    
    Turninal V<-locity
    
           Tlio  uppc'-Lound on t'te fluidlzatlnn velocitv  for a solids/etas  <.*rtilston is attained when the
    superficial (;as velocity is equal to t!ie  t-rr.ilnal  volocltv of the particles and thry are elutriated
    froa t!ie bed.   In a fluldlzod radius wltli a sicnlficant particle size Jlst r li.ut Ion, tlie >-lut ri.it'nn
    process occurs over a ram**.* ปif superficial velocities, hut t!io terminal velocitv of the nean particle
    size can l>c used  tf> characterize this  final fluidized bed transition.  Following Kunii and t.evensnlel
    j!>)t the particle terninal velocity can he found  !w  iteration nsinr  a different rซ*l.ition for each of
    t'aree  r anr.es of particle i'^ynolds nunher  and  :lio  locu* of this final  flov-rerlr:e l.oundary Is shown In
    UPS.  a and 'i.
    
           These flow regime naps reveal that vlth ir.crnaslnp partic-le size, the oncratinr. ranpe of  tlic
    fluidized l>ed ,  i.e. the region between ninintun f luid i ?.at ion and terminal velocitv, decreases and is
    occupied by a  progressively  larger slow-t>uht*1c rซ'r.irin.
    
    Tim Influence  of  I'art iclc Size
    
           Lxanlnat ion of two typical Kluldized Red  Conbtistor f low-repime naps rcvo.ila the Innortant role
    played by particle size In dctcrninlnp the !>cd im-r.it I IIP. n-i''"'1.  Aป  particle size Increases,  the
    operating ran|-e of fast bubbles Is found  to docrca-ie and the s).>w-bubMe rer.inc bccoirci progressively
    r^>re inportant,  Furthernore, in relatively larrc-nart icle, :ir..l 1-dlar.eter bods, the slue rise velocity
    nay fall uelow tin- interstitial velocity  and  give  rise to a "slow-slui;" rer.lr.e.  Alternately,  since
    riobl expertnent.il fluidized teds to-datc  'i.we been designed to operate  with reldtlvclv snail  particles,
    the f lov- repine nap can be u*cd to explain the prevalence of fast-buhblc models and the relative
    scarcity of :*lov-Lubblc formulations.
           The  results of the present work yurc.eat  the following conclusions:
    
           Uirr.e-partlclc fluidized beds linv  flow  regimes radlrally different  fror snail-particle  beds.
           The  slow-bubble flow rer.lnc and the  transition fron sloซ to fast 1-ubMe flov rerlraa are  very
    inportant  for larr.e particle svstctn.  The  two-Dlia.sc hyvo thesis appears tc  be valid for larrc-nart Ic le
    beds.
    
           Tlic  classical bubble oodels used  In  the  two-phase theory have  llnlt.it Ions in large-part Iclc
    aystcns due to overlapping clouds near flow transition and the inapplicability of U'Arcy's law.
    
           The  bubble size can t-e approximated  by the  use of exnerlocnt.il  frequency correlations.
           The  effort  reported heroin is part of a  comprehensive FDC modelling study being conducted  at
    JUT under UU)A Construct :lo. E(19-l 8)- 2290.
    A    -   bed  crots-scctlonal area, co
    
    D    -   bed  dlanctcr, ca
    
    d    -   particle dlasietcr, en
                                                       469
    

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    d       -  vuluoetric iM-an  Uootle diaoeicr,  cm
    
    
    
    f       -  level  frequency,  s
    
    
    
    f       -  Cranfleld & Ccldari's point - freiuซicy correlation, s
    
    
    
    f"      -  '.Jurtlier' :* correlation for frequency per unit area^ c=i    s
    
    
    
    ;;       —  gravitational  acceleration,  'JซJQ.*>^3 en/s~
    
    
    
    ii       -  level  above distributor, cm
    
    
    
    II,      -  Halting bed lielp.i.t used In  !iacye*s & Celdart's sluฃzฃar. criterion,  CD
    
    
    
    u       -  throughflow coefficient
    
    
    
    N       -  number of bubbles la sooe specified volioae
    
    
    
    iu.1      -  particle Keynolds fza&et
    
    
    
    f       -  superficial fluidizuig velocity.ca.'s
    
    
    
    L       -  bubble rise velocity ftr a  freely uubbliag bed, cm/s
    
    
    
    Li       '  relative bubble  rise velocity, cn/i
    
    
    
    t. fy(.  -  bubble rise velocity at the  slow/fast bub-ble transition, CB/ ;
    
    
    
    b' _      -  interstitial gas velocity, absolute velocity of p.as in tiie eaulsion  phase, era/*
    
    
    
    L'       -  absolute velocity of teas in  the eon;!Bion s*uue at aininoo lluidlzatIon,  L  ,/c .. ca/i
      I                                                                                   *J   KX
    
    
    L ,     -  superficial (;as  velocity at  wliicii brjbbliij; begins, ca/t
    
    
    
    L,     -  superficial f.al  velocity at  mint cum fluidiution, cn/ป
    
    
    
    L       -  velocity of solids  ta the en-ulslon phjse (defined positive for upward  not 1cm). c*/*
    
    
    
    1.      -  terminal velocity of particles, co/ซ
    
    
    
    V       -  bubble volume, CD
    
    
    
    V       -  cloud  volun:,  CD
    
    
    
    V       *  uako voluDc, en
    
    
    
    ft       -  bubble wake fractloa V^/V
    
    
    
    ii       -  bubble cloud fractioa V /V,
                                      c  b
    
    
    f       -  voluoctrlc fractioa of Internal reetrculaiioa reeion
     n
    
    
    i       -  volunctrlc fraction of external recirculatioo region
    
    
    
    t       -  bubble fraction
    
    
    
    c ,     -  bed voldagc at niniasa Huidlzatiaa
     ml
    
    
    
    
    REFERLIJCtS
    
    
    
    1.  J.f. Davidson and D.  llarrlton. fluldlzed Particles. Caabrldge University Press, Cc&brldge. 1963.
    
    2.  K.H. Uavles and C. Taylor. Pruc- Roy. Soc. A. 20u. 375 (1930).
    
    1.  X. Ilughci, S.M. Thesis, Uc^artaent  of Mechanical Eagloeerlng. KT, Cttfcrldge, Mass,  (in preparation).
    
    4.  U. Zuber ซnd  J.A. Flndlay, Trans. ASIIE - J.  of Heat Tr.nnfer. vol. 37C. fr.  453
    
    S.  D. kunil and  O. Uvcnsplel, floidtiatlon E;:jtneซrtag. Wiley and Soas. Sev York
    
    
    
    
    
                                                       470
    

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     6.    :.. Olciart  and '...?..  CranfielJ ,  C'.ien.  r.n.-.rtun, K.U.  La.iiiizo. .1.1. N.iviJson,  nr.J  :>.  !!arrl:;on. Tr.i^.s.  I.  r:ier..  !.. .  Veil.  3j, p.  37
           (I.-77).
    l.i.    :..  JtUrat'i  and K.I!.  '.trc.it field, Tr.ins. •.:"  I"-.t.  c.f Ciiva. Tn.-.. •'.".  7"  ('.  7:;
    II,   J.  .*.rt:ur,  in I luiui^jati- T 1.'c'.r.;>It>.-'-'  (.-tJitft!  i.v  ;>.'..  :\-.ii r*i-. ; , '.'••!.  I,  r.  2K>  ^]'17').
    11.   .1. !Ucyc-.-.:, and 1>.  ^•-•Id.trt. i:'ion.  !"n-.  :cl.,  2~>,  2'jj (l''7i).
    14.   J. "jtrai-is,  :;.:!.  Tit*.'Si5.  Ik-p.irtr.i-nt  of .%-c':ianic.il  !'.nr Ineer inr , "IT (in ''r^^'ir.ic ie-i ).
    li.   c.ir.ad.1. ';.:;., ::.;:.  "cLju-.'.ii:.  .m..1 !.•..'. :iau!>, r:inซr :•'.>.  I'UJ.  (.'•::.  .•.;f.:  :...-, -tim-. c'i:c.n-o,  in.
          1^76.
    l'"j.   Ver-A^':ialni , J. , :i.I'. "urnur, .trv!  A..'l.  fi^ulros. In. I. fnr.  C'IPL . , Pr^^os :*ei.  I.'ov. .  1>.  A7  (!'>7^i
    17.   ฃit?t>;lu<-Y,  Veil.  1. 1>'.7.  n. '.I.
                                                               471
    

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             QUESTIONS/RESPONSES/COMMENTS
         FREDERICK HANZALEK, CHAIRMAN:  Dr. Glicksrnan.
    
         DR. GLICKSMAN:   First of  all, I would like to acknowledge the
    efforts of my colleague, Professor Bar-Cohen, who has been working
    with me for the last  year on this particular program and is sitting
    in the back of the room.  That is called "sharing the guilt," if I
    can't answer some of  the questions.
    
         The first question is from Ralph Wood of General Electric, and
    the question is:   "Have you tried other coordinates to describe the
    flow regime map?"  I  presume that what he is referring to is a way we
    can use a non-dimensional coordinate systen which will generalize the
    flow regime map?   We  have looked at that, and there is no general
    coordinate system one can use  for different phenomena which are being
    controlled by different physical variables.  For minimum fluidi-
    zation and for the transition  to this turbulent flow or diffuse flow,
    we are concerned  about the drag on individual particles.  When v/e are
    talking about transition from  slew to fast bubbles, we are concerned
    here about bubble frequencies, and the partition between flow between
    the bubbling phase and the dense phase.
    
         We chose this particular  set of dimensional coordinates just to
    give people a physical "feel"  for what flow regime they would expect
    to encounter for the  particular particle size and velocity.
    
         Now there are a  couple of other parameters hidden in the flow
    regime map.  One is the height above the distributor plate, which has
    a modest effect on flow regimes, and also, of course, the density of
    the particle.  This nap is constructed for standard atmospheric
    conditions; for a heated bed with calcined limestone, the flow
    boundaries are going  to shift.
    
         His second question was:   "How do you reconcile the poor predic-
    tion of combustion efficiency  that you presented with the good
    predictions shov/n in  the preceding MIT report?"
    
         The point I  was  making is that when we used just the one-region
    bed model , the one where we assurae fast bubbles from the bottom of
    the bed to the top, you get lousy predictions.  That is confirmed by
    the earlier work  that Professor Sarofim and his colleagues got.  In
    some cases when we have gone to this two regime nap with a slow
    bubble at the bottom  of the bed and fast bubbles at the top as
    Sarofim nas done, you start getting much better predictions of the
    combustion efficiencies.  So this paper should have been before
    Sarofim's, to set the stage for vdiat he was then going to present,
    using that same two-regime flow raodel.
                                    472
    

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         Finally, a question by Dr.  Rao of MITRE:   "Can a small  error in
    temperature measurement result in the lower predicted efficiency
    shown?"  Temperature has some effect on the combustion kinetics, as
    you saw from the results of Professor Sarofim.   The slope is rela-
    tively modest, so one would not  expect that that is the problem.  I
    think the problem is, and I would like to reemphasize this,  a fast
    bubble model for a bed containing large particles doesn't work.   And
    the reason it doesn't work is it's not modeling the correct  physics
    within the bed.  Certainly we haven't modeled  the entire physics.  We
    must include the area near the distributor, where the jets from  the
    distributors are penetrating a certain distance, giving higher
    particle Sherwood numbers because of the higher agitation around the
    distributor.  That is an area that we hope to  model  in the future.
    
         FREDERICK HANZALEK:  Dr. Saxena?
    
         DR. SAXENA:  Can I make a comment about this?
    
         MR. HANZALEK:  Surely.  You're the cleanup speaker; you have
    every privilege.
    
         DR. SAXENA:  Now, there is  no hassle here.  Probably there  is a
    difference in the terminology and I want to make sure that I under-
    stand things correctly.
    
         You know, in the slow and fast regime models, what we are
    talking about is essentially the thickness of  the cloud around the
    bubble; and that thickness also  depends upon the bubble size, so you
    don't have to have two compartments.  What you  have to have, actually,
    you build in, and when the bubble is small, the cloud is thin.  As the
    bubble grows, the thickness of the cloud increases,  and therefore the
    diffusion resistance builds up,  and you've got  to account for that and
    the same computer program can do it.  In fact,  we did this type  of
    report in my own modeling work.   I'm sure most  of you are familiar;
    it was out in the Fuel Journal only a couple of months back.
    
         DR. GLICKSHAN:   This is not entirely correct.  Both slow and
    fast bubbles can have clouds. The key distinction is that fast
    bubbles produce a significant mass transfer resistance between the
    bubbles gas and dense phase while slow bubbles  allow the gas to
    freely flow from the dense phase to the bubble, eliminating  any
    bubble to dense phase mass transfer resistance.
                                    473
    

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                             INTRODUCTION
         FREDERICK HANZALEK, CHAIRMAN:  We proceed immediately to the
    last paper of the  session, which then will be followed by the
    question and answer  period.  This paper is entitled, "A Mechanistic
    Model  to Explain Ash Agglomeration in Fluidized Bed Combustors."
    It is coauthored by  Drs. Rehmat and Saxena of the Institute of Gas
    Technology and the University of Illinois.  It will be presented by
    Dr. Selena, who received his initial degrees, bachelor's and
    master's, from Lucknow  University in India.  He then went on to his
    Ph.D. at Calcutta  University in India.  For several years he was
    a research associate, and became research officer of the Bhabha
    Atomic Research Center  in Bombay, India.  Coming to the United
    States and serving at Purdue University, he assumed his present
    position at the University of Illinois at Chicago as a full
    professor in 1968.  Dr. Saxena?
                                     474
    

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                                     A Mechanistic Model To Explain Ash
                                        Agglomeration in Fluidized Bed
                                           Combustorsand Gasifiers
    
                                                S. C. Saxena
                                        Department of Energy Engineering
                                               University of Illinois
                                                 Chicago. Illinois
                                                 A. Rehmat
                                         Institute of Gas Technology
                                               Chicago. Illinois
    ABSTRACT
           A mechanistic model  for ash agglomeration has been proposed In which the higher Internal temper-
    ature "f a reacting part'cle  for  a given UeJ temperature under certain favorable conditions will  celt
    the Inorganic ash and which in view of  its high surface tension will ooze out of the particle and will
    Ber^e with similar ash beads  to torn agglomerates.  The frame work of matliematical equations describing
    ..nls model are derived and  have been solved for a range of operating and system variables.  The experi-
    mental data generated at 1CT  have been  discussed in detail and explained on the basis of proposed
    theory.
    
    
    INTRODUCTION
    
           During coal combustion or  gasification an Improved carbon conversion efficiency can be achieved
    if the loss of carbon in the  MSh  is minimized.  One way of .ichievlng tilts is to separate ash and  carbon
    from the coal particle, segregate coal  and ash particles within the reactor and remove such segregated
    ash particles from the reactor.   The combustion or gasific.it inn process itself separates the carbon
    and ash from coal.  However,  segregation and the selective removal of ash from the combustor or gasl-
    fier still remains a major  industrial problem.  Using a fluidized bed reactor and agglomerating ash to
    the extent that the agglomerated  ash  Is made heavier than the rest of the bed material offers as  one
    of the solutions to the above mentioned problen.  The agglomeration of ash generally requires that at
    least part of the total ash produced during combustion or gasification acquires the ash melting temper-
    ature which is generally in the range of 1150'C to 1400SC.  However, operating the reactor at such
    high temperatures may result  in the  formation of a massive clinker.  A much desired method of agglo-
    merating ash at relatively  low bed temperature is proposed here.
    
           Since the carbon-oxygen reaction is exothermic. It is possible to achiev.- higher than average
    bed temperature within the  coal particles by appropriately selecting the operating parameters.  When
    the temperature in the range  of 1150'C  to 1400':C are attained within the particle, the inorganic  ash
    melts and some ash beads ooze out of  the cracks.  The molten ash has a high surface tension and does
    not wet the coke particles  readily.  Thus, the ash beads that ooze out of the coal particles separate
    from them and merge with similar  ash beads from the nearby coal particles.  The molten ash beads  also
    wet and trap the solid ash  particles present within the bed.  An ash agglomerate grows by collecting
    inore and more of such liquidous ash beads.  It Is prevented to grow too lurge by the quenching effect
    of relatively lower bed temperatures and by limited collisions with other hot ash particles due to
    turbulence present in the Huidized bed.  After the ash agglomerates grow sufficiently large, they
    drop to the bottom of the reactor from  where they c.m be withdrawn selectively.
    
           The ish fusion temperature depends sensitively on the composition of the inorganic ash, and
    may vary considerably froa  one coal to  the other.  In order to be able to agglomerate asli from a  given
    coal feed, its fusion temperature must  be known to establish the conditions in the reactor to achieve
    these temperatures within the particles.  The internal temperature of the coal particle is generally
    a function of the average bed temperature, the initial size of the particle, the oxidant concentration
    In the reactant gases, and  the atjount of ash produced during reaction.  The latter is Incorporated In
    the size factor Z, which Is defined as  the ratio of the volume of ash produced to the volunsu of coal
    reacted.  For most of the coals,  this volume ratio varies between 0.07 to 0.2.  The ash agglomeration
    can proceed at bed temperature much below the ash fusion'temperature, if the factors affecting ปw
    Internal temperature of the partible are optimized.  With a view to adequately understand •'
    menon of ash agglomeration, the effect  of each of the above factors has been investl"
    paper to determine the favorable  conditions to produce'ash fusion temperatures w1
    to initiate ash agglomeration.
    
    
    
                                                   475
    

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    a^glozierat ion model which nay be applicable to all the processes in various forns to enable correlation
    of the data obtained 510 far and also predict  the conditions necessary to obtain ash agglomerates under
    a wide variety of operation conditions.
    
           In the following section, a mechanistic model has been presented to enable the determination of
     >f the core temperature :>f a coke particle which would determine the plausibility of ash aKf.loraer.it icn
     mder the given condit fairs of size, partial pressure of oxygen, the ash content of the Riven feed stock
     md the average bed temperature.
    und
    THEORY
    
           In the derivation of equations which mr.y enable the evaluation of the internal temperature uf
    the particle, we r.hall assune that  the bed is composed of raany individual feed particles suspended In
    the fluldi~cd bed maintained at a constant temperature Tc>.  The bed is fluidl/.ed by a gas havinj; an
    oxidnnt concentration of Co.  Since our interest is confined mainly li\ establishing the maximum tempera-
    ture attainable within the particles, we shall focus our attention to a single particle being exposed
    ti> the fluidlzing ftas. of oxldant concentration of C0.  Thus, tlie problen reduces to that nf a single
    particle of arbitrary radius Rn and hence use can be made of the heat and mass balance equations for
    the single pellet of changing size derived by Rehmat and Saxena\  These equations have been normalized
    with respect to the initial particle size R0, the bed temperature T(), and the partial  pressure of I he
    oxidant, P0, present  In the reacting gases.  The quasi-steady state approximation will be employed for
    the nass transfer equations, and the unsteady state heat transfer equations will he used to obtain a
    more accurate estiiute nf the temperatures that develop within a particle.
    
           The temperature within the particle is assumed to he sufficiently high so that the rea'-tlun
    
                                                 C + J ฐ2 • cf)                                          (1>
    
    predominates.  For simplicity it has been assumed that rhe feed is In the form of char.  The rate
    expression, the effectIve dlffuslvity, cas film diffusion coefficient and the activation energy have been
    used b-ised on the work of Dutta and Wen''.
    
           The reaction of equation (1) is primarily diffusion controlled at tbe temperatures of present
    Interest.  The char particles are assumed to be spherical and the p.as-solid reaction takes place
    following the shrinking core model.  The reaction Is confined to a thin layer at the Interface of coke
    and ash.  A detailed description of shrinking core model is given elsewhere^.  According to Dutta and
    Wen*", the rate of reaction Is given by
    
                                               S - *,v
    
    Here, S    Is the specific external surface area of the particle and k  is the rate constant based on
           Reic                                                            B
    external surface area of the reacting solid.
    
           Based on the above rate equation and under the assumption of quaslsteady state, the material
    balance for oxygen Is given by the following expression:
                                                      476
    

    -------
    with  the  following  boundary conditions
                                        el-.,
    and
    ^f = S   (1 - .- ) at •; =  •-,
    d .    Sho      s          s
                                             cxp
                                                   R T
                                                                                                         (4)
                                                                                                        (5)
           Equation  (3)  in conjunction with  tin- boundary  conditions of equations (4) ;ind (5) can be solved
    to yield  the expression  for  the concentration of oxygen at  the reaction surface.  Thus
                                  — =  1 + -^   (1  - ~)  uxp
                         tj
    
                        R T
                                            ; exp  )—'- (1  - -V-)
                                                  /R  T        Lc
                                                                                                        (h)
                                                ' Sho's 'c
           Similarly,  the heat balance equation with  transient  term Include') in the analysis is given by
                                             A  .
                                                                                                         (7)
    witli Lin: following boundary riinUitlous
    and
    The initial condition  is given by
                                                R T
                                            !,' ซ U   =1   at  ••  =  0
                                                                                                         (8)
                                                                                                         (9)
                                                                                                        (10)
           In the above equations, the core  is assumeu  to maintain  a  uniform temperature, and the walls of
    the reactor are maintained at  the. bed temperature T .   The  pressure  is maintained constant throughout
    tiie reactcr.  The ideal gas law  is assumed and  the  effective, diffusivlty of trie oxidaiu through the
    ash layer as well as the effective heat  conductivity of  the ash layer arc assumed to be proportional
    to the temperature.
    
           The rate of conversion, X, of the solid  recctant  is  already >:iven by equation (J).  Since for
    spherical particle, the conversion is related to the system parameter /.^, as
    
                                                 X  - 1  - •-.'                                            (11)
    
    The expression for the rate of change of •'.  follows directly from equation (2).  Thus,
                                       •,    •:      u
                                             	X^  vป i	?	 /1    1  i
                                                i exp i       11 -    j
                                             4 ,-.      / R  T        c
    with the following boundary condition:
                                                   1  at 0 • 0
                                                                                                       (13)
                                                    477
    

    -------
           Equations (12) and (13) in conjunction with equations (6) to (10) arc to be solved simultan-
    eously to Ret the conversion-tine relationship as well as the interior temperature of the particle.
    Obviously, Because of turbulence in the fluidiztd bed, none of the feed particles are going to remain
    in contact with the incominK Rases and get completely reacted at one stretch.  Each particle may get
    only a fraction of the total tine required for complete reaction, to remain in contact with the in-
    coming gases.  Therefore, it is essential to solve the above equations for the core temperature us a
    function of time.
    
           The following relations are also required for the solution of the problem:
    
                                               Volume; of ash formed                                    /1 A \
                                           ' * Volume of coke consumed
    
    
                                              f.* - Z + (1 - Z)C*                                       (15)
    
    
           In the fluidized bed, the solid particles are mostly in the emulsion phase where the gas flow
    is generally laminar.  Therefore we ran approximate the heat and mass transfer crefiicients for the
    single pellet to correspond to the laminar regime and employ the following simple expressions for Nc
    and S.. „:                                                                                          " 10
         NuO
    
                                              K:   K:(N  )1/3(sB fl)1/r
                                       H-.   - 71 +  2  hc  ... ROฐ	                                 (16)
                                        Sho   !.           f 1/2
                                                          ''a
    and
                                       "NuO   f, T        fl/2                                          Vi"
    
    
    vliere N_ , N   and N    are evaluated at the constant bed temperature T  and initial particle size  R .
    
           Since the bed temperature in the present case is ma intalned constant, equal icns  (l*ป) and  (17)
    can be further simplified as
    
    
                                               N    - 3- * —3-                                         (18)
    
                                                            s
    and
    
                                                      K'    K
                                                       1     4
                                               NNuO * Z^ * fl/2                                         <19)
                                                            's
    where
    
    
    
    and
    
    
    
    
           The following notations are used in t.he above equations for simplification:
    
    
    
    
    
                                                  NNu - 2hR/k                                           (23)
    
    
                                                Nu „ " OR T3/k                                          (24)
                                                 NuR     oo
                                                     T0ke(To)P8
    
                                                     478
    
    

    -------
                                                  2 p (-'.H) D (T )
                                                    ro       eo
                                                           T E,
                                                            o 1
                                                                                                        (26)
                                                     4 C  M T
                                                        pc s o
                                                        (-.-.H)
    (27)
                                                   R T R k (T }
                                                      o o s  o
                                                    2 D (T ) M
    (28)
    and
                                                       i. R
                                                        s o
                                                    4k (T )p
                                                       s  oo
                                                                                                        (29)
                                                        t/i
                                                                                                        (30)
    DISCUSSION
    
           The above heat and mass balance equations have been solved by numerical method for  the  range, of
    values of the various parameters of practical Interest.  The rate data of C-0  reaction reported by
    Dutta and Wen6 have been utilized In the solution of these equations.  The size oฃ coke particles
    rarising from 2.5 cm to 0.006 <-m has been used.  The ash content of the coke  is varied from If)  percent
    to 20 percent which corresponds to the values of Z from 0.1 to 0.2.  The partial pressure  of oxyp.cn
    Is varied from 21 percent as it occurs in the air upto oxygen enrichment of  42 percent.  The average
    temperature of the fluidized bed is varied from 900'C to 1000'C.  Tho value  of K.  is taken as  unity.
    The other parameters viz., K^, K^, ;, C, A, .-.and N%.   vary with the change in transport p.-opertles due
    to temperature and with the change in the size of If lie particle.  K  and K  vary very little when
    temperature is changed from 900-'C to 1000{'C and hence constant values h,we been used for both  of these
    parameters at these temperatures.  In Tables 1 through IV,  only those values of conversions are listed
    which yield core temperatures close to ash fusion temperature of approximately 1200JC.  The calcula-
    tions have been found to be Insensitive to the value of dlDenslonlesu parameter A, which depends upon
    the values of the various physical properties of the reacting system.
                    Table I.
                              Internal Core Temperature for an Initial 2.5 cm Coke Particle.
                                (K. • 1.0, K, - 2.0, K  ซ 0.57 and N.. u ป 5.0)
    T p Z
    0 *0
    ฐC atm
    1000 0.21 0.1
    
    
    
    1000 0.21 0.2
    
    
    
    900 0.21 0.1
    
    
    900 0.42 0.1
    
    
    
    900 0.21 0.2
    
    
    4 i. A G t
    - sec
    315 0.024 40 0.86 2000
    3300
    5500
    6900
    315 0.024 40 0.86 2000
    3600
    5400
    7600
    102 0.02 43 0.79 3400
    5600
    7000
    102 0.04 86 0.79 990
    1070
    2700
    3450
    102 0.02 43 0.79 5500
    7600
    9000
    X
    percent
    70
    80
    90
    95
    60
    70
    63
    90
    80
    90
    95
    70
    80
    90
    95
    80
    90
    95
    T
    "C
    1020
    1130
    1300
    1420
    1100
    1175
    1275
    1410
    1000
    1160
    1285
    920
    1090
    1400
    1600
    1130
    1260
    1350
                                                     479
    

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    Table !I.   Internal  Con-  Temperature  for an Initial  0.62 en Coke Particle.
                  (Kj  =  1.0,  K3 =  1.0,  K4 - 0.3 .ind N.,uf. = 1.25)
    T p Z : .-.AC l
    0 ro
    ^C atm - - - - - sec
    1000 0.21 0.1 79 0.024 40 0.86 225
    300
    480
    600
    900 0.21 O.I 25.5 0.02 43 0.79 230
    325
    490
    610
    1
    Table III. Internal Corn Temperature lor an Initial O.Ofc rm Coke
    (K, * 1.0. K, = 0.3, K. =0.1 .ind Nu _ =• 0.125)
    1 3 ** ."iiln
    T p 7. :• .'• A C t
    o o
    'JC aim - - - sec
    1000 0.21 0.1 7.9 0.024 40 0.86 5.0
    7.3
    8./
    900 0.21 0.1 2.55 0.02 43 0.79 4.0
    5.9
    8.4
    Table IV. Internal Core Temperature for an Initial 0.006 c:ra Coki
    (Kj = 1.0, K3 ป 0.1. K/( * O.O3 and NN(|R = 0.013)
    T p 7. : .1 A C t
    0 0
    ';C aim - - - - ser
    1000 0.21 0.1 0.79 0.024 40 0.86 0.113
    0.14
    0.15
    1000 0.42 0.1 0.79 0.04ป 80 0.8f> 0.038
    0.050
    O.U67
    0.078
    1000 0.21 0.2 0.79 0.024 40 0.86 0.107
    0.128
    0.160
    0.177
    900 0.21 0.1 0.255 0.02 43 0.79 0.22
    0.256
    0.266
    900 0.42 0.1 0.255 0.04 86 0.79 0.118
    0.130
    0.141
    900 0.21 0.2 0.255 0.02 43 0.79 0.207
    0.23t>
    0.276
    X
    percent
    70
    80
    90
    95
    70
    80
    90
    95
    
    Particle.
    
    X
    
    percent
    80
    90
    95
    70
    80
    90
    Particle.
    
    X
    
    percent
    80
    90
    95
    70
    80
    90
    95
    70
    80
    90
    9r>
    80
    90
    95
    80
    90
    95
    70
    80
    90
    Tc
    rjc
    1050
    1100
    1250
    li/0
    920
    985
    1105
    1190
    
    
    
    T
    C
    'C
    1090
    1215
    1310
    901
    970
    1060
    
    
    T
    C
    'T.
    1070
    1160
    1230
    1005
    1115
    1275
    1430
    1085
    mo
    1240
    1290
    3iO
    1030
    1120
    980
    1100
    1150
    960
    1000
    1055
                                       480
    

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            Some of  the qualitative  trends  that  follow  fron  the  analysis  of  data  presented  In Tables  I
     through IV and  which  favor  the  creation of  high core  temperature  and thereby proMotu agglomeration
     are:   the large size  of  the coke particle,  the high ash content of  the  coke, the high  partial  pressure
     of oxidantt or  the high  average bed  temperature.   It  therefore  follows  that  depending  upon  the
     properties of the given  coke  feed stock, different conditions may be necessary  in order to  agglomerate
     the ash.  For example, If the feed contains  large  particles, the  ash a/glo:rerat<-ซ; ran  be produced at
     relatively lower bed  temperatures.   When fines are fed  to the reactor,  it  requires higher bed  tempera-
     tures  and or higher oxidant concentrations  to promote, the formation  of  ash agglomerates.  Based  on  the
     results contalmJ in  Tables I through  IV, the following rvcomraendations are  offered for the operation
     of ash .iggloDfr.it ing  oor.bustor  or gasifler.
    
            The contact time  of  the  coke  particle with  the oxldant Is  an  Important factor in ob:.lining
     sufficient conversion and bunco suf f ic lont ly high  core  temperatures  to  fuse  the ar.lt.   Generally
     In the fluidized bed  combustor, the  oxidation zone is confined  to a  very narrow band above  tile vrld
     due to very high rat-.- of carbon-oxygen reaction.   If  the ratio of the superficial velocity  In  the
     reactor to the  minimum fluidization  velocity of the given feed stock Is low,  t!iซ" segreeat ion yf  the
     particles occurs, Saxena a- i Vofe,.;'.  The large particles settle  down at the bottป,-n and henre  tin-
     smaller particles get a  very  little  chance  to react with oxygen.  Therefore,  in order  to agglonerate
     a feed stock of mixed particles of a wide size distribution, caution oust  be exercised Iti maintaining
     3 good solids mixing  in  the bed so that all size particles  get an equal  chance to re.let with oxvgen.
     Good solids circulation  also helps In controlling  and limiting  the overall size of the agglomerates
     produced.  If the agglomerates  grow  too large, they are not easily removed from the bed and cause
     local  defluidlzatIon  of  the bed resulting in hot spots  and  eventual  clinkering of the entire bed.
    
            Although the time required for complete reaction of  0.06 cm particle  is small,   it is not
     always possible for such a  particle  to renain in contact with the react.inl gases even  for such snail
     periods because of either segregation or elutriatifjn.   This would imply that  the presence of large
     particles would promote  ash agglomerat ion.  Ash forsk.-d  on small particles  can stick to the  fused ash
     formed from larger particles and thus sustain ash agglomeration.  When  the elutriated  flues are
     recycled, these should be injected where the oxygen concentration is maximum and the rate of injection
     should nlhii be  sufficiently low In order to allow maximum contact time  between the fines and the
     oxvgen.
    
            In many  gasification processes, the steam is added to Inprovo the quality of gas being  produced.
     Since  the carbon-steam reaction is endothermic, it may  have considerable effect on the core 'emperature,
     In such cases it may  be  necessary to attain ash fusion  temperatures  either bv raising  the average bed
     temperature or  by Increasing the partial pressure of  oxidant In the  react.inl gases.
    
    
     COMIY.RISON WITH K;T DATA
    
            Some of  the data  obtained on  the IOT ash agglomerating gasifler  are presented in Table V.   The
     average  particle size of the feed, the pattljl pressure  of  oxygen in the <:as feed,  and  the  fluidized
     bed temperature  are important paraneters and are recorded in Table V.   It has generally been observed
     that when the average size of the feed is Increased,   It   requires  lower  bed terrer.-.ture  to agglomerate
     ash If  the other parameters such as partial  pressure of oxygen and the  ash content  of  the feed stock
     are maintained  constant.  Also  when  the fines are recycled  Into the  bed, thereby decreasing the
     average  feed sl/.e,  the agglomerates could only be produced  by increasing the bed temperature by about
     60'JC and almost doubling the partial  pressure of oxygen  In  the agglomeration zone.   With  FMC char,
     which  contained  particles smaller than 40 mesh (0.042 cm),  no ash agglomerates could be produced
     either at the bed temperature of 10?S"C or the oxygen partial pressure of O.4 atmosphere  because  it
     Is not  possible  to achieve  the ash fusion temperature within these particles.  Further* because of
     turbulence In the bed .ind the sire of the particles,  none of these partlclos stayed within the  oxida-
     tion zone long  enough to attain ash fusion.   The result* suggest  that as the size of  the  feed  particles
     approaches zero, the  bed temperature should  approach  the ash softening  temperature  In order to
     agglomerate the  resultant ash.  All these observations are  completely consistent  with  the  predictions
     of the- analytical model  proposed here and the conclusions drawn on its basis as discussed  in the  pre-
     vious section.
    
    
    CONCLUSIONS
    
           The mechanistic model proposed here for the agglomcratli n  of  ash  In a fluidized  bed  combustor
    or gasifier suggests  that it Is possible to  agglomerate  ash at bed temperatures much below the  ash
     fusion  temperatures-   The factors that control the agglomeration  process are the size of  the coal,
    oxidant concentration in the reactant gas,  the average bed  temperature and the ash  content  of  the
     feed.   The presence of endothermic reactions such as  carbon-stean reaction nay inhibit  the  ash
    
    
                                                    481
    

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                        Table V.   Lxper irae-.ital Data from ICT Ash Agglomerating Gasifler.
                                       (u  = 5 cro/sc-c. Tr  ,   =1183 "O
                                                        fusion
    Feed Avg. Size
    — cm
    Coke 0.170
    Breeze
    Coke 0.085
    freeze
    Coke 0.085
    Breeze
    FNC 0.022
    Char
    T* p
    C aim
    1000 0.21
    
    1040 0.21
    lOftO 0.40
    1070 0.44
    
    Fines Remarks
    —
    retboved ••tgxlomerales were
    
    removed agglomerates were
    increased T
    o
    increased p
    
    
    torm-d
    
    forced with
    
    
    removed no agglomerates were formed
    
    
           •Minimum bed le. pcralure for agglomeration.
    
    agglomerate: formation by retarding the temperatures developed within the coal particles during
    combustion.  The proper design of the reactor Is crucial to segregate agglomerates from the rest
    of the bed material so that these can be selectively removed.  Enough turbulent  .• should be provided
    not only to control the size of the agglomerates but also to provide opportunity to the jnaller coal
    particles to react and participate in the agglomeration process.  When the fines are recycled into
    the reactor, enough residence time should be provided within the reaction zone  to consume them.
    
    ACKSO'.n.EDCEMKIJT
           This work is supported by the United States National Science Foundation. Grant So. KSC 77-01780,
    under a  joint USA-USSR research program.
    
    NOMENCLATURE
    A       - Dlmensicnless quantity defined by equation (25)
    C       ** Specific lieat of bulk gas at constant pressure
    C       • Specific heat of coke
     DC        '
    C       • Specific heat of ash
    D       • Molecular diffusivity of oxvgen in the bulk gas phasi>
    D       • Effective diffusivity of oxygen In Che ash layer
    E.      • Activation energy
    C       - Dlmcnsionless quantity defined by equation (27)
    h       • Convectlve heat transfer coefficient
    •111      • Heat of reaction per mole of the reactant and is negative for exothermic reactions
    k       • Thermal conductivity .'f the bulk f.as
    k       ซ Effective thermal conductivity of the ash layer
    kn      • Mass transfer coefficient for oxygen across the gas film
    ks      - Rate constant b.'iHed on the external surface area of the reacting solid
    Kj      • A nuffierical constant which occurs in the correlation of Shrrwood and Nusselt numbers
    K,      - K,/2
    K.      ป A numerical constant which occurs In the correlation of Sherwood and Nusselt numbers
    
    
                                                     482
    

    -------
    K-      - K2/2
    K..      ซ Dinensionless quantity defined  by equation (20)
    K,      3 Dimensionless quantity defined  by equation (21)
    M       ป Molecular weight of coke
    S.,      • N'usselt nunber • 2Rli/k
     Nu
    N  o    " DIocnsionKss quantity defined  by equation (22)
    X       •ป Dinenslonlcss quantity defined  by equation (24)
     NuK
    N       * Prandtl number ซ C (../k
    N_      a Reynolds number ซ* 2uR, /;.
    NR!O    ' N>RO(RO/R)
    NS<;     ป Schmidt •  sber •= '../. D
    N .      ป Sherwood nunber - 2Kk /D
     Sn                             ci
    NSho    -NSh(V2R>(D(V/DefToป
    p       * Partial pressure of oxygon
    p       * Value of p at the unre.'irlcd  trore S'irface
    p       a Vnluv of p in the bulk jt.'is
    p,      ป Value of p at the outer surface of tlie partlclv
    r       = Kadi.il distance fron  tlic  center of the spherical particle
    r       ซ Rndius of the unreacted core
     c
    R       ป Particle r.idius
    R(      ป Initial particle r-.dius
    R       ฐ Gas Constant
    S       ป Spc-clfit: external surtace area  of tlit- particle
     *cx
    t       • Time
    T       • Ti-mper.riture
    T.      - Temperature of tlie unre.u-ted i-ore
    T       * Average bed temperature
    T       • Particle surface tenperature
    u       ซ Flow velocity of bulk g.-is
    U       • Reduced temperature • T/T(>
    U       ป Reduced core temperature  ซ T /T
     c                                     c  o
    U       - Reduced particle siirfaru  tenperature, T./T
    X       * Conversion of solids  defined by equation (11)
    Z       " A parameter to characterize  Rrowth or shrinkage pf the particle,  defined by equation (14)
    Creek Letters
    r.       B Dimcnsionless quantity defined  by equation (26)
    '!       - Reduced time defined  by equation (30)
    11       • Viscosity of bulk gas
    t.       * Reduced distance ซ r/R
    f.       ป Reduced core radius of the particle = r ,/R
            • Reduced size of the particle •  K/R0
    v       * Density of the bulk gas
    i1       • Density of the solid  react.int
                                                      4C3
    

    -------
              • C'l.ir.ictorlst ir tin.-  m (2'tt
    
    •,         - Dlni-nsl'inlrss "Mantlf/ dellni-1 by ซ"j.:/it Inn  '2>i)
    
              ป ki-durfd valui- of ;>  ป (p/p  >
    
              • Ri-d.in-d valui- r,f p_  . fiV/P0>
    
              ป Ri-duot-d value* nf p   a (p _/p  >
    
     :         - R.idl.ilivr  li.-.it tr.insfi-r < o,:t I i< |.-i.t
    
    
    KKH-IRKNCKS
    
    I.   I.,  .li-qulcr. I., l.onj-t-Ik-irnhnn  nnd (J. V;m Ih- Putn-, .1.  Insi.  Fui-1 TJ.  No.  12.  19'>0,  584.
    /.   W.  A. S.-ind'tlrtin.  A.  Rftira.-it  .-m:l W. f;.  li.ilr.  "Tin- C:isi f Ic.lt Inn of Oi.il Cluirs In .-i  Fluid I iri-d-Rc-d
         Af.li-AKr.ltimiT.it Inn ^;isifi*rt" I'.'ipor pr<-sซ*ntefl /it tin-  *>9th Annual Hcfllnf; of  the A.I.Ch.K.,
         Cl.li-.is'..   UvstinKhoiiHi.- KliTtrli: Corporation.  "Adv.mrcd Coal Casl f Irat Ion Systi-m  fnr  EK-ctrlr Power
         r,.wrat Ion." Monthly l'roi>ri-iis Rซ'port  fnr Si-ptcmbi-r  1977.  prfp.-ired  for U.S. EntTKy Ri-si-artli
         and OfVirlopncnt Administration, tindi'r contrart No.  KF-77-C-01*! *il4.
    •>.   A.  Rt-hn.it and  S.  C.  Saxi-na. Ind.  Knป;. (;h.-n.. Pron-ss l>-s.  I)ซ-v..  IS.  197'i.  Tซl.
    h.   S.  Dulta  and r  Y. Ui-n,  Ind. Kn^. Clii-ra. Pr-n-i-ss l)t-s. l>vv., 16. 1977, 11.
    7.   S.  C. Saxfiia .. d  (i.  .1. VnKr 1 . Chfra.  Knc.. J.  I''. 1977. 'j9.
                                                           484
    

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                QUESTIONS/RESPONSES/COMMENTS
         FREDERICK HANZALEK, CHAIRMAN:   Dr. Saxena?
    
         DR. SAXENA:  Okay; I will now try to answer the question  that
    has been asked me by Dr. Haldipur from Westinghouse Electric.   If
    I have pronounced your name wrong,  please excuse me.  He  asks:   "Does
    your model neglect fluid dynamics effects in the reactor?"   In  the
    Westinghouse agglomerator, we have  tested fully agglomerated FMC
    chars which were identical feedstock to the ones used by  IGT.   A
    very good question.
    
         No, we have not neglected the  fluid dynamics,  but we have  taken
    its simplest form for our present illustrative purpose. It  is assumed
    that the particles are suspended in the fluid which flows around it in
    a laminar regime.  As a result, the correlations developed  by Ranz and
    Marshall for gas film mass transfer and convective  heat transfer
    coefficients have been employed in  the calculations.   It  is also
    implied that the particle stays continuously in contact with the gas
    which maintains as constant oxygen  concentration equal to its initial
    value.  This ideal  requirement will  not be met in a real  fluidized bed
    and, therefore, the calculated core temperatures may differ from the
    actual temperatures developed in the particle while in the fluidized
    bed.  However, in order to agglomerate ash from coal, all the efforts
    should be made to achieve gas-solid contact conditions as close to the
    ideal us possible.
    
         The Westinghouse agglomerating gasifier, unlike the  Institute
    cf Gas Technology gasifier, operates at a relatively higher oxygen
    pressure.  Consequently, the amount of oxygen available per unit
    carbon in the Westinghouse gasifier is considerably larger than the
    Institute of Gas Technology gasifier.   As a result,  the Westinghouse
    gasifier is capable of generating higher temperatures within the
    particles than the Institute of Gas Technology gasifier.  These
    temperatures will also depend upon  the scheme of introducing steam in
    the gasifier, an aspect we have not considered at all in  this work.
    We propose to undertake such calculations and will  report our findings
    at some later date.
    
         Then, there is a second question:   "Could you  comment on the
    effect of the agglomeration of the  insoluble iron content in the
    ash?"  Only in general  terms.   The  composition and  nature of ash
    present in the coal influences the  calculations in  a  sensitive fash-
    ion.  The intraparticle diffusion coefficient  which controls the rate
    of oxygen transport to the surface  of  the reacting  coal particle will
    depend upon the physical  properties  of the ash through porosity.  The
    thermal  conductivity of the ash also appears  in the calculation and
    all  of these properties will  be controlled by ash decomposition.
    
                                     485
    

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         So to the best, what we have done, actually, is provided material
    for thought.
    
         KARL BASTRESS, CHAIRMAN:  Thank you.  Is there anyone who
    submitted a question that did not get answered, or does anyone have a
    single burning question of general interest? (Laughter)  Please
    introduce yourself and make your question brief, please.
    
         MR. YERUSHALMI:  The gentleman from Westinghouse made me inter-
    ested.  Oh, I am Joseph Yerushalnii from the City College.  Could the
    gentleman from Westinghouse describe the shape and the othet physical
    characteristics of the ash agglomerate they made from FBC cfur?  And
    number two, does he agree with Professor Saxena that the surf.-ce
    temperature of the char does not exceed the temperature of the bed,
    the surrounding bed?
    
         MR. HANZALEK:  1 am afraid I may have let this get out of control.
    Go ahead.  Please introduce yourself.
    
         MR. HALDIPUR:  Golan Haldipur from Westinghouse Energy Systems
    Operations.  I will answer the last question first, because I remember
    it.  We don't have any means of measuring radial temperature distribu-
    tions in the particles in the fluidized bed agglomerator.  We have
    attempted to measure actual  temperature gradients in our reactor,
    but we haven't as yet got a thermocouple which could penetrate our
    agglomerator and determine the hottest zone in the reactor.  And
    regarding particle temperature distributions, it's virtually impos-
    sible in our reactor to measure it.  The diameter of the reactor
    is 20 inches, and we have a high-pressure reactor, 15 atmospheres,
    which is different from the IGT reactor.  I don't think there is any
    more to add on this, unless you have a question.
    
         MR. YERUSHAMI:  What was the shape--
    
         MR. HALDIPUR:  Oh, the shape.  Okay.  We ran three feedstocks
    from the FMC coal, the Western Kentucky, and the Utah; and we also
    ran coke breeze.  When we ran a combination of FMC and coke breeze.
    we got sub-angular particles, and when we ran the FMC-Utah char, we
    got well rounded particles.   The size was approximately about 500
    microns, and the angular particles were about 800 to 1,000 microns.
    
         MR. BASTRESS:  I think  the speakers will be here for a few
    minutes if you have specific questions, and we will devote the rest
    of the time to extending the lunch hour.  Fred and I would like to
    thank the speakers in particular, as well as the projectionist, for
    helping us close this session on time.  Thank you very much for your
    interest.
                                     486
    

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                            INTRODUCTION
         FREDERICK HAN7ALFK,  CHAIRMAN:  Our next paper will be presented by
    Dr. David Berkowitz of The MITRF Corporation.  It is entitled, "Dynanic
    Modeling, Testing, and Control of Fluidized Bed Systens."  Dr. Berkowitz
    received his Ph.n. in physics from MIT.  He brings impressive creden-
    tials in that he organized the Seminar in Boiler Modeling, held in
    November of 1074 and v/as  subsequently editor of its Proceedings.   He
    first joined the MITRF Corporation in 1%1, and is now the firoup  Leader
    o^ Power Plant Dynamics and Control.  Dr. Rerkowitz.
                                    487
    

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                                 Dynamic Modeling, Testing, and
                                Control ot Fluidized Bed Systems
    
                                 D. A. Berkowitz, A. Ray,'/. Sumaria,
                                          and M.Wilson
    
                                      The MITRE Corporation
                                      Bedford, Massachusetts
    ABSTRACT
    
           A nonlinear dynamic modeling technique for fluidized bed combustion (FBC) sys-
    tems has been adapted to the Alexandria Process Development Unit and validated in a
    steady state and transient response test program.  Datr. from all signal channels were
    sampled every few seconds, and are available on magnetic  tape.  The modeling technique
    can be adapted to other FBC plants to evaluate their design and operation, and to ana-
    lytical design of their control systems.  Several frequency and tine domain methods are
    discussed, including classical single-input single-output control, optimal regulators
    incorporating a performance index, and decoupled multivariable control using state
    feedback.
    
    
    INTRODUCTION
    
           The purpose of this paner is to suggest initial control development guidelines
    for fluidized bed combustion systems.   Control system development requires a detailed
    understanding of the process, p.-jrticularlv its transient response characteristics as a
    function of operating load level.  If one's understanding of the process is embodied in
    an analytical process description, or sr.-callcd process model, then control systems can
    be developed analytically.  The methods considered here involve development of a vali-
    dated process model as a critical first step, followed by its subsequent use for con-
    troller design.   This technique - modeling,  validation, controller design - has been
    successfully applied to solving performance problems of existing conventional electric
    generating units.   It has been used in specification of new units and simulation of
    their performance.   Ard it has also been applied to fluidized bed combustion, although
    control design in that case is far from complete.
    
           The paper is divided into three parts.  Part I (Modeling) discusses purposes for
    modeling and the type of modeling method selected for fluidized bed systems.   Part II
    (Testing) describes data acquisition requirements for model validation and an experi-
    mental program at the Alexandria Process Development Unit, in which measured data is
    compared with predictions of the Alexandria process model.  Part III (Control)  deals
    with the manner in which the model is used to explore process characteristics and to
    develop control system strategies.
    
    
    PART I:  MODELING
    
    Why Model?
    
           In the case of a large steam-elecrric generating unit, design and integration of
    its many subsystems is a complex process involving several organizations:   the owner-
    utility, architect-engineer, boiler manufacturer, turbine manufacturer,  control system
    manufacturer, and other major component suppliers.  To increase productivity, greater
    attention must be focussed on systems design and integration to insure that major com-
    ponents function together, within specifications, under normal steadv state and tran-
    sient operating conditions.  This nned has been recognized for conventional nuclear and
    fossil fueled generating units [l,2] .   There is no less a need in the case of fluidized
    bed power plants - perhaps a greater need, because the technology is less mature; the
    process less understood.
    
           The work described in this paper deals with extension to fluidized bed combus-
    tion systems of what a utility company calls "Design/Operation Evaluation Models" [2].
    These models permit:
    
           (1)  Increased understanding of the process, including subsystem interaction and
                integration;
           (2)  Improved design and analysis capability for plant control systems to ensure
                that major components arc maintained within design limits during normal
    
    
                                              488
    

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               steady  state and transient operating conditions-.
          (3)  Verification of desired performance capabilities  for  different modes  of
               plant operation: and
          (ft)  Pre-start-up simulation capability for development  of operational  procedures
               ,->nd resolution of operational problems.
    
          Models are not new.  Modeling ond analytical capabilitv  does  exist in  the  indus-
    try and is customarily used (1) as part of the basic plant de-sign function,  (2)  for
    nuclear plant safety, and (3) for operator training.  Various  models which have  been
    developed differ in their objectives, the extent to which they include different plant
    r.ystems. and the level of mathematical detail required to neet the  objectives.   A de-
    sign code developed to predict performance details \.-hich influence  pipe sizing,  mate-
    rial selection, etc.. requires a high level of mathematical  detail, but it's  limited
    to the boundaries  of only one component.  A safety related design code requires  signi-
    ficant mathematical detail in those systems which influence  plant safety; other  systems
    are not included,  or only included superficiai.lv.  A training,  model disnlays  to  the
    operator hov the plant will perform under specified transient  conditions, which  re-
    quires the least mathematical detail, but covers the greatest  number of plant systems.
    
          A Design/Operation Evaluation Model is intended to represent  plant operation
    (particularly under automatic control) during normal plant operating conditions  when
    safetv is not an issue.  This model includes more sv;tems than a safetv code  and less
    than a training simulator; but it's: more detailed than a training simulator and  less
    detailed than a safetv code.
    
          TraditionalIv. nower plant development has occurred bv trvins things out,  then
    fixing them latr.-  [2].  This process has resulted ir. generating  units that perform ade-
    quately, rather than ontimally. and utility personnel end un accenting numerous  operat-
    ing peculiarities  as inherent performance 1 imi t.-itiors.  Kxisr.ir.g design approaches need
    to be supplemented with systems oriented analysis techniques,  such  as Design/Operation
    Evaluation Models, to assure higher plant availability and .performance.
    
    .Modeling
    
          The method most suitable for Design/Operation Evaluation Models is deductive
    (sometimes called  .? first principles method), based on fundamental  phvsical laws for
    energy,  mass, and momentum conscrvat ion. and well kr.own empirical correlations for
    material properties, heat transfer and flow coefficients.  Models of this tvpe have
    these advantages:
    
          (1)  All model parameters can be determined from available design and steadv
               state data;
          (2)  Model structure is independent of available data:
          (3)  The model provides insight into the nature of the process that is  so  vital
               in design of new systems, particularly when scale up  from pilot systems is
               required; and
          (4)  It establishes a rational basis for increasing or decreasing model complex-
               ity.
    
          Mathematically, a deductive process model is:  r.on-1 ine.ir.  tine-invariant,  de-
    terministic,  continuous-tirn .  and in state-snace forr..  The  actual process generally
    consists of distributed parameter dvnamic elements mathematically represented bv  non-
    linear partial differential equations with snace anci time as independent variables.
    To obtain numerical solutions of these equations bv digital  computer,  the partial dif-
    ferential equations are apprximated hv a finite set of ordinarv  nonlinear differential
    equations with time as independent variable.   Thus, the fundamental modeling  assumption
    is that a distributed parameter process can be approximated  by a  lur.ipcd parameter mod-
    el.  This approach has been shown to be adequate in the simulation of fossil  and nu-
    clear power generating units at Philadelphia Electric Companv  (Cromhv Station I'nit No.
    2) [3]',  Boston Edison Company (New Boston Station irr.it No.  2)  [4], and Public Service
    Conipony of Colorado (Fort St.  Vrain Unit Nc.  1) (>) . and has also been shown  to  be
    adequate for fluidized bed combustion at the Alexandria Process  Development Unit  [6] .
    Additional applications of the approach by Philadelphia Electric  Company include  tddy-
    stonc Station furnace implosion studies. Peach Bottom Reactor  feedpump start-up  analy-
    sis,  and plant dynamic simulation for the proposed Fulton Station HTCR unit,  and those
    bv Ontario Hydro include Nanticoke Station pulveriser control  and deaerator control at
    CANDU nuclear power plants [2] .
    
    
                                             489
    

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          It is not sufficient to create a large computer program simulating the deductive
    model of a thermofluid process:  the model must be validated.  For a plant in the plan-
    ning and design stage, validation is with respect to plant heat balance and other
    steady state design calci.  ."ions made by the manufacturer, which represent the most
    that is known about the ' • ..it prior to actual start-up.  For an operating plant, vali-
    dation can be with mear ^rec> data from steady state and transient response tests, as
    well as heat balance  esign cita.  The process of reconciling model predictions with
    actual measurements .an proviae deep insight into less well understood portions of the
    process.  Performar-e of the er.tire system becomes an important diagnostic in under-
    standing process retails.
    
    
    PART ii:  TEST:NG
    
    Data Requirei. V - for Model Validation
    
          Experimer. .  /allelation of a dynamic process model suggests the need for large
    amounts of data,   •••rded as a function of time, preferably available in machine acces-
    sible form.
    
          An important i'eafire of the data is its completeness.  That is, the measured var-
    iables must constitu:e :• set of process outputs that permit an accurate, complete de-
    scription of what went on.  For example, there is little value in recording tempera-
    tures every five seconds if air, water, steam, and solid flow rates are only recorded
    manually every 15 or 30 minutes.  There is little value in sampling gas analyzers con-
    tinuously, if fuel and air flows are not known continuously, as well.
    
          Frequency of observation is also important during start-up and transient opera-
    tions, whether planned or unplanrซ?d.  All measured variables should be sampled at a
    rate several times faster than the fastest natural response time of the process during
    the transient periods.
    
          The type of data acquisition 
    -------
                          Figure 1. Block Diagram of the Data Acquisition System (DAS)
    each channel.
           The scan list for a typical run ar. Alexandria includes 76 process variables  (36
    temperature*.  10 flows, 13 pressures. 1 level. 3 control signals. 8 gas analysis  sig-
    nals, and 5 wtight signals), plus 18 channels for calibration and electrical check-out.
    Data Reporting Tapes for nineteen test runs at Alexandria are now stored and can  be
    readily copied for anyone who is interested.
    
    Alexandria PDU Results
    
           Model predictions and test results were compared at different steady state load
    levels, and for several transient conditions.  Table 1 shows the comparison for two
    load levels, corresponding to different values of bed level and coal firing rate.
           In transient response tests, the plant is allowed to stabilize while maintaining
    constant controlled input values.  Then, a single input is shifted to a new value, and
    data is recorded as a function of time until a new steady state has been reached.
    Tests are repeated at different load levels for each controlled input.  In this manner,
    the ability of the model to predict the complex natural dynamic response of the process
    is evaluated.   Figures 2, 3, and 4 show the agreement between predicted model responses
    and measured values of bed temperature, drum steam pressure, and steam flow, respec-
    tively, for an 18-minute interval following an 8.22% step decrease in coal feed rate.
    Bed temperature results (Figure 2) agree closelv with experimental data.  For drum
    steam pressure (Figure 3). model predictions appear faster than test data.  This  may be
    due to inaccuracy in drum water level (that is, drum water thermal capacitance).  Steam
    flow data (Figure 4) fluctuates due to instrumentation noise, but the average profile
    agrees closely with model predictions.
    
           Figures 5,  6, and 7 compare model responses and measured data for bed tempera-
    ture, drum steam pressure, and steam flow following a 6.757. step increase in main air
    flow.  For bed temperature (Figure 5),  model results and test data are initially  in
    close agreement.   About ten minutes after the disturbance, test results show an upward
                                              491
    

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    ro
                          8.22 Z STEP IN COAL  FLOM
                                ป MCCEL RESULTS
                                O MEASURED VALUES
               Figure 2. Bed Temperature Transient Response
               Following 8.22% Step Decrease in Coal Feed
               Ran
                .22 Z STEP IN COAL FLOM
                     ซ MODEL RESULTS
                     O MEASURED VALUES
                                                                              4   6  e   10  12  ii  iซ  is
                                                                               Tine  IN MINUTES
     Figure 3.  Drum Steam Procure Transient Re-
     iponse Following Step Decrease in Coal Feed
     Rate
               -8.22 X STEP IN COAL FLOM
                      * MODEL RESULTS
                      
    -------
              TABLE I   Comparison of  Steady-state Model Results with  Test Data
                                               Bed depth 0.508 m  (20  in)
      Process  Variables
                                  Model results
                                                                           Test data
    Bed Temperature
    Drum steam pressure
    Main steam flow
    Coal feed rate*
    Limestone feed rate*
    FD fan air flow
    Carrier air flow*
    884.4 C(1624 F)
    0.7623 x 106 N/m2 (110.7 psia)
    0.3404 kg/cec (0.7504 Ibn/sec)
    0.0857 kg/sec (0.189 Ibm/sec)
    0.0367 kg/sec (0.0809 lbm/~ec)
    0.5770 kg/sec (1.272 Ibm/sec)
    0.0506 kg/sec (0.1114 Ibm/sec)
    882.2 C(1620 F)
    0.7653 x 106 N/ri? (111 psia)
    0.3402 kg/sec  (0.75 Ibn/sec)
    0.0857 kg/sec  (0.139 Ibm/sec)
    0.0367 kg/sec  (0.0809 Ibm/sec)
    0.5783 kg/sec  (1.275 Ibm/sec)
    0.0506 kg/sec  (0.1114 Ibm/sec)
      Process  Variables
                        Bed depth 0.304 m (12 in)
            Model results
                    Test data
     Fed Temperature
     Drum  steam pressure
     Main  steam flow
     Coal  feed rate*
     Limestone feed rate*
     FD Fan  air flow
     Carrier air flow*
    920.56 C(1689 F)
    0.7543 x 106 N/m2 (109.4 osia)
    0.3329 kg/sec (0.7339 Ibm/sec)
    0.0844 kg/sec (0.186 Ibn/sec)
    0.0367 kg/sec (0.0809 Ibm/sec)
    0.516 kg/sec (1.238 Ibm/sec)
    0.0506 kg/sec (0.1114 Ibm/sec)
    918.33 CU685  F)
    0.7584 N/m2  (1110 psia)
    0.3311 kg/sec  (0.73  Ibm/sec)
    0.0844 kg/sec  (0.186  Ibm/sec)
    0.0367 kg/sec  (0.0809  Ibm/sec)
    0.5171 kg/sec  (1.240  Ibm/sec)
    0.0506 kg/sec  (0.1114  Ibm/sec)
     -Given  input to the model
    
    drift due to a small, inadvertent increase in coal feed rate, which was confirmed by a
    decrease in flue gas oxygen concentration.  This drift is obvious in drum steam pres-
    sure response (Figure 6), but cannot be identified in steam flow response (Figure 7)
    because of noise.  Following the main air flow increase, both model results and test
    data show an initial increase in steam pressure (Figure 6) which then relaxes to a low-
    er value.   The increase occurs because of an increase in convective heat transfer co-
    efficient in the freeboard region.  Later on, as bed temperature decreases, flue gas
    temperature drops reducing heat transfer.  Test data show a larger increase than the
    model which is probably associated with some inaccuracy in formulating model equations
    for overbed combustion.
    
    PART III:  CONTROL
    Analyzing the Model
           The nonlinear process model in state-space form can be analyzed by sceci.il pur-
    pose codes to find steady state operating conditions, to derive linearized nodels at
    any load condition,  to deteimine system eigenvalues of the linearized models and fre-
    quency response plots for any input-cutout pair. etc.  For example. Table II shows
    system eigenvalues of the linearized Alexandria PDU model at steady state conditions
    before and after the 8.227ป decrease in coal  feed rate.  The eigenvalue magnitudes de-
    crease with reduction in coal feed rate indicating that, at  lower firing rate, the
    process slows down.  The smallest eigenvalue is strongly associated with thermal re-
    laxation of the fluidized bed and corresponds to a tine constant of approximately 220
    seconds before the change and 235 seconds after the change, which illustrates the ef-
    fect of process nonlinearity.  The -0.100 eigenvalue corresponds to an assumed 10-sec-
    ond time constant, which is'related to average coal residence time in the bed during
    combustion.  The largest eigenvalues, corresponding to time constants of approximately
    1.9 and 1.3 seconds  are strongly associated with waterwall metal temperatures in the
    freeboard region and in the fluidized bed, respectively.  These states are fast be-
                                              493
    

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    cause of the very high rate of heat transfer through the metal walls.
    
           Frequency response plots of bed temperature, drum steam pressure, and steam
    flow rate with respect to coal feed rate are shown in Figures 8, 9. and 10, respective-
    ly, for the plant conditions existing before the coal feed rate disturbance.  Figure 8
    shows that the transfer function of bed temperature versus coal feed rate can be ap-
    proximated by a simple structure of two finite poles and one finite zero.  The plot of
    magnitude versus frequency shows that process gain attenuates rapidly with increasing
    frequency.  Thus, a proportional-integral-derivative (P-I-D) controller would result
    in fast response, closed-loop action.  The transfer function inferred from Figure 8 is
    useful for single-input sinj?' e-output controller design.  Though the fluidized bed sys-
    tem is interactive and multivariable, single-input single-output controller design
    methods may be useful as a first step.
    
           Figure 9 shows that the drum pressure versus coal feed rate transfer function
    can be approximated with 3 finite poles and 1 finite zero, and Figure 10 shows that
    the steam flow versus coal feed rate transfer function could be represented by two fi-
    nite poles and 1 finite zero.   In these two cases, also, single-input single-output
    controllers (possibly P-I controllers) can be designed with the aid of standard algo-
    rithms.  Frequency response plots provide some insight into the fluidized bed process
    dynamics.
    
    Alternative Controller Design Methods
    
           One major objective of state-space modeling is analytical controller design and
    its evaluation by digital simulation.  The plant model allows determination of a con-
    trol law with respect to certain specified performance criteria, as well as input and
    state constraints.  Various controller design methods are available.  Four of them are
    reviewed briefly in this section with some technical depth, with respect to commerical
    scale fluidized bed power plant applications.  These methods can be classified as fol-
    lows :
    
           (1)  Design based directly on the nonlinear model;
           (2)  Time domain design using a family of linearized models;
           (3)  Frequency domain design using a family of linearized models; and
           (4)  Design on the basis of reduced order models.
    
           Method 1:  Design based on nonlinear model
    
           Exact optimal controller design solutions for nonlinear systems with a quadrat-
    ic cost functional is very complex and extremely difficult to implement  [7] .  It in-
    volves 2-point boundary value problems.  One powerful solution method that has been
    employed for low order nonlinear models is "continuation" or "imbedding"  [8] .  In this
    method, a parameter or a set of parameters is introduced in the original problem such
    that a class of similar problems is obtained with the property thar the solution to
    one of them is known.  By successive variation of the imbedding parameter(s), the de-
    sired solution can be obtained from the known solution.  Jamshidi applied an imbedding
    approach to control system design for a 6th order power system model' where solutions
    of 2n(n + 1) = 84 differential equations were necessary  [8].  For larger order system?.
    this approach is too expensive for practical application.
    
                     TABLE II.  r.igenvalues of linearized model before and
                                after -8.227. change in coal feed rate
    
                                Before                     After
    -.00451 sec"
    -.00642
    -.0103
    -.0168
    -.100
    -.535
    -.780
    -.00426
    -.00641
    -.0103
    -.0162
    -.100
    -.524
    -.764
    sec"1
    
    
    
    
    
    
                                              494
    

    -------
    Wl
                 100
                  so
                 -so
                -too
                -ISO
                 -so
                -no
                           J0-l    JO'1
    10'    10*
                                       IN nno/scc
                           JO''    JO'1    10'     JO*     10*
                                                                u  *7
                                                                S
                                                                   -ISO
                                                                    -Z25
                                                                   -300
                                                                g  -•ซ
                                                                    -180
                                                                    -J60
                                                                              to-'    io-'\  to1     toป     to1     2
                                                                                                                       eo
                                                                     a    jo
                                                                                                                      -30
                                                                                                                      -60
                                                                                                                                10"
                                    rncoucNcr IN RBO/SCC
                                  io-ซ    ID-'    ID'    toป     to*
      FREQUENCY  IN RRO/UC
    
    10'*    10"'    101     JO*     10*
              Figure 8. Frequency Retponse of Bed Temperature       Figure 9.  Frequency Reiponje of Drum Steam Prei-    Figure 10. Frequency Retponte of Steam Flow with
              with Rotpect to Coal Feed Rite                        turt with  Rnpect to Coal Feed Ron.                 Roipoct to Coal Feed Rate
    

    -------
           Lccper and Mulholland presented a method for optimal control of  nonlinear  sin-
    gle-input systems where no 2-point. boundary value problems need be solved, and closed
    form solutions for optimal control can be obtained  [y] .  However, an  extension of  this
    method has apparently nor. been achieved for multivariable systems.
    
           It is felt thar controller de-sign for a cocmerci.i 1 scale fluidized bed power
    plant by direct use of the nonlinear model is not a feasible alternative.
    
           Method 2:   Time donain with linearized node Is
    
           The linearized model of a nonlinear process represents  its local  characteristics
    around the operating point of linearization; a family  cf 1 ir.car: ::eH -^Hpls at a number
    of operating points approximates global characteristics of the nonlinear process o.er
    the operating range.
    
           McDonald and Kwatny designed a fossil fueled drum boiler plant controller  fro:?
    a nonlinear 1'tth order plant model linearized .it several operating points  [10] .  The
    design algorithm was based o.. optimal linear regulator theury  using a standard quadrat-
    ic cost functional perfomanco index.  To compensate  for model inaccuracies, -i random
    noise bias vector, whose derivative is white noise with ^ero mean, was  introouced; the
    a priori unknown bias became constant as the derivative noise  approached zero.  Linear
    stochastic theory was applied to svnthesi.-.e a deternin: si ic optimal controller such
    that the plant output tracks a constant desired value  wi
    -------
    tton cime requirements, for example).   During the last ten years. significant prepress
    has been made in identifying low order models of large time-invariant systems  [22-27] .
    Yu and Siggprs demonstrated application of a reduced order linear deterministic model
    to approximate a nonlinear, single generating uni-. infinite-bus power system model
     (28) .   A control system designed with the low order model was : hen shewn to be ade-
    quate for the original high order model.
    
           A deterministic high order nonlinear process can be adequately represented by a
    family of low order linear stochastic models  [29-32] .   Tn a survey paper, Astrom and
    Eykhoff have discussed various ways of choosing model  structure  in simple linear forms
    and subsequent identification of model parameters  [2?] .   Moore and Schwenne formulated
    a stochastic model of !:he nuclear reactor in a pressurised water reactor (PWR) power
    plant  [42] .   A detailed high order analog simulation of the plant *:hat included n&n-
    linear effects, disturbances, and measurement noise,  was developed.  Frcm data >ener-
    ated by the analog plant simulation, a priori unknown parameters of a li-w order linear
    stochastic model were identified by the maximum likelihood criterion.  The reduced or-
    der model was used for reactor controller design.  This method is worthy of additional
    exploration.
    
    
    SIT-C'-ARY
    
           The method of process modeling • nd model validation loading to analytical con-
    trol system design, which is finding increased application in conventional fossil and
    nuclear generating units, can advantageously be applied to fluidized bed combustion
    systems.  The modeling and testing program at Alexandria has demonstrated that the
    modeling method adequately represents process dynamic interactions, and information
    useful for analytical control system design, such as input and output matrices of th-'
    linearized system at several load levels and frequency dependent input-output transfer
    functions,  can be derived readily from the validated nonlinear prcccss model.  In gen-
    eral,  fluidized bed systems are nonlinear, multivariahle. and interactive.  Although
    classical controllers based on individual single-input single-output control loops mav
    he specified for such systems as a first step in formulating the controller structure.
    alternate analytical control design methods seem more promising.  Time domain dc-ign
    using a family of linearized models and a quadratic cost functicnal performance index
    has already been applied to gene-rat ing unit controller problems.  Krequencv <'.onain de-
    sign usir.g a family of linearized models and state feedback to achieve decoupling of
    output variables seeT.s very appropriate,  and offers a way to apply conventional single-
    input single-output frequency response irethods more effectively.
    
    
    ACKNOWLEDGEMENT
    
           This work was supported by the U.  S. Energy He-search and  Development Adminis-
    tration (Department of Energy). Coal Conversion and !_'t i 1 i ;:at ion  Division, under Con-
    tract No. EX-76-C01-24S3.  The authors express their appreciation to R. Reed and the
    Pope.  Evans and Robbins staff for their pp'ience and help during the experimental pro-
    gran at Alexandria.
    
    
    REFERENCES
    
    1.  Electric Power Research Instutute, Request for Proposal - Project Description. RFP
        6021 "Power Plant Performance Modeling". 17 October 1977.
    
    2.  J. P. McDonald and L. M. Smith (Philadelphia Electric Company). DC f in i nr. r>ocu~en t
        for a Design/Operation F.valuatton Model for BUT Power Plants, Electric Power "Re-
        search Institute.Research Project 606-1 Final Report(June, '977).
    
    3.  H. C. Kwatny. J. P. McDonald, and J.  II. Spare. "A Nonlinear Model for Reheat B< 11-
        er-Turbine-Generator Systems:  Part II - Model Development". Proceedings of the
        12th Joint Automatic Control Conference. 227-236 (1971)
    
    ft.  Y. Lin.  R. S. Nielsen, and A. Ray, "Fuel Controller Desig;. :'.i. a Once-through Sub-
        critical Steam Generator System", Trans. ASME. Journal of F.;iginccrinp, for Power
        (in publication'.
    
    
    
                                              497
    

    -------
     5.   R.  W.  McNamara,  M.  R.  Ringham.  G.  C.  Bramblett,  and L.  C.  Souchworth,  "Practical
         Simulation of an Industrial  Fluid  System with Controls  - The Ciruclator Auxilia-
         ries for the Fort St.  Vrain  Nuclear Generating Station". Proceedings of the 18th
         Joint  Automatic  Control  Conference. 345-350 (1977).
    
     6.   D..  A.  Bcrkowitz. A.  Ray.  and V.  Sumaria, "Dynamic Modeling of Fluidized-Bed Boil-
         ers for Control  System Design".  Proceedings of the 12th Intersociety Energy Con-
         version Engineering Conference.  28 August-2 Sentember(1977) .
    
     7.   A.  Wernli. and G. Cook.  "Suboptimal Control for the Nonlinear Quadratic Regulator
         P.-oblem".  Automatica U.  75-84   (1975).
    
     8.   M.  Jamshidi, "Optimal  Control of Nonlinear  Power Systems by an Imbedding Method",
         Automatica 11,. 633-636  (1975).
    
     9.   J..  L.  Leeper. and R. J.  Mulholland, "Optimal Control of Nonlinear Single-Input
         Systems".  IEEE Trans.  Automatic Control  (Correspondence).  AC-17. 401-402 (1972).
    
    10.   .1.  P.  McDonald,  and H.  G.  Kwatny.  ''Design and Analysis  of Boiler-Turbine-Cenera-
         tor Controls Using Optimal Linear  Regulator Theory". IEEE Trans. Automatic Con-
         trol.  AC-18. 202-209  (1573).
    
    11.   H.  G.  Kwatny, "Optimal Linear Control Theory and a Class of PI  Controllers for
         Process Control", Proceedings of the 13th Joint Automatic Control Conference,
         274-281 (1972).              	
    
    12.   H.  G.  Kuatny and L.  H.  Fink. "Acoustics, Stability, and Compensation in Boiling
         Water  Reactor Pressure Control  Systems", IEEE Trans. Automatic  Control. AC-20.
         727-739  (1975).                         	
    
    13.   I.  M.  H. Horowitz,  and U.  Shakcd.  "Superiority of Transfer Function over State-
         Variable Methods in Linear Tirae-Invariant Feedback System Design". IEEE Trans.
         AutomaUc Control.  AC-20,  84-97  (1975).
    
    14.   A.  G.  J. MacFarlane,  "A Survey  of  Some Recent Results in Linear Multivariable
         Feedback Theory". Automatica 8.  455-492   (1972).
    
    15.   A.  G.  J. MacFarlane,  "Return-Difference  and Return-Ratio Matrices and their use
         in Analysis and  Design of Multivariable  Feedback Control Systems", Proceedings
         of the ZEE 117.  2037-2049  (1970).
    
    16.   J.  .'.  Belletruttl,  and A.  G. J.  MacFarlane, "Characteristic Loci Techniques in
         Multivariable-Control  System Design", Proceedings of the IEE 118, 1291-1297
         (1971).	
    
    17.   P.  L.  Falb, and  W.  A.  Wolovich.  "Decoupling in the Design and Synthesis of Multi-
         variable Control Systems", IEEE Trans. Automatic Control.  AC-12. 651-659  (1967).
    
    18.   E.  G.  Gilbert, "The Decoupling  of  Multivariable Systems by State Variable Feed-
         back", SIAH J. Control 7.  50-63  (1969).
    
    19.   E.  G.  Gilbert, and J.  R.  Pivnichny, "A Computer Program for the Synthesis of De-
         coupled Multivariable  Feedback  Systems", IEEE Trans. Automatic  Control. AC-14,
         652-659  (1969).
    
    20.   E.  E.  Yore, "Optimal Decoupling Control", Proceedings of the 9th Joint Automatic
         Control Conference,  327-336  (1968).
    
    21.   C.  R.  Slivinsky. and D.  G. Schultz, "State  Variable Feedback Decoupling and De-
         sign of Multivariable  Systems",  Proceedings of the 10th Joint Automatic Control
         Conference, 869-876  (1969).
    
    22.   E.  J.  Davison, "A Method for Simplifying Linear Dynamic Systems", IEEE Trans.  Au-
         tomatic Control. AC-11.  93-101  (1966).
                                             498
    

    -------
    23.   M.  R.  Chidambara,  and E.  J.  Davison.  "On a Method for Simplifying Linear Dynamic
         Systems", IEEE Trans.  Automatic Control (Correspondence), AC-12. 119-121  (1967).
    
    24.   M.  Aoki. "Control  of Large Scale Dynamic Systems by Aggregation", IEEE Trans.
         Automatic Control.  AC-13.  246-253 "(1968).'
    
    25.   M.  R.  Chid.imbara,  ana R.  B.  Schainker,  "Lower Order Generalized Aggregated Model
         and Suboptimal Control".  IEEE Trans.  Automatic Control, AC-16. 175-180  (1971).
    
    26.   A.  Kuppurajulu, and S. Elangovan, "System Analysis by Simplified Models", IEEE
         Trans. Automatic Control,  AC-15, 234-237  (1970).
    
    27.   T.  C.  Hsia, "On the Simplification of Linear Systems". IEEE Trans.  Automatic
         Control. (Correspondence), AC-17. 372-374 (1972).
    
    28.   Y.  N.  Yu. and C. Si&gers,  "Stabilization and Optimal Control Signals for a Power
         System". IEEE Trans. Power Apparatus and Systems PAS-90. 1469-1481  (1971).
    
    29.   K.  J.  Astrom, and P. Eykhoff, "System Identification - A Survey". Autcmatica ]_.
         123-16?-  (1971).
    
    30.   F.  C'.  Schweppe. Uncertain Dynamic Systems. Prentice-Hall (1972)
    
    31.   R.  L.  Kashyap, "Maximum Likelihood Identification of Stochastic Linear Systems",
         IEEE Trans'. Automatic Control. AC-15. 25-34  (1970).
    
    32.   R.  L.  Moore, and F. C. Schweppe, "Model Identification of Adaptive Control of
         Nuclear Power Plants". Automatica 9.  309-318  (1973).
                                             499
    

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                QUESTIONS/RESPONSES/COMMENTS
                 K HAMZALFK, CHAIRMAN;  Pr.  Rerkowitz.
    
         np. RFRKWIT7:  Thank  you.   I've  qot one card and two questions
    fron Ralph Wood of General  Flectric.   "What numerical methods do you
    use for solving your nodel?"  is the first question.  (ซir model equa-
    tions are written in CSMP;  we qenerate an ordered Fortran load nodule
    to simulate systen response as a  function of tine.  He give the node!
    a set of initial values for the state  variables, go down through all
    the equations evaluating the  process variables as well as rates of
    change of the state variables, and then, integrate to the next tine
    step.  The systems are rather stiff, so  we use variable tine step and
    Fowler-Marten integration.  To find steady-state solutions, we operate
    on the Fortran load module  with various  analytical codes that we de-
    veloped or that are available, that use  Newton-Raphson or Steepest
    descent techniques.  Typically, that costs about one dollar for the
    Alexandria or CTIll nodels.  TO simulate  a thousand seconds of CTIH
    operation (the Model is 36th-order model), it takes typically about a
    minute of CPU time, which costs approximately $?n.
    
         The second question:  "Is there any physical significance to the
    oscillations that are superimposed on  some of the data which you showed?"
    It is difficult to control  coal feed rate to a fluidized bed boiler,
    and there is noise associated with the lack of uniformity of the coal
    feed.  I assume that these  probably are mostly concerned about steam
    flow, which was the one that  oscillated  quite a bit.  There were also
    oscillations in steam flow.  Steam passes through an orifice with RP
    cell, control valve, and a  long pipe connected to the drum.  Oscilla-
    tions might very well occur in that line.  There might also he some
    transducer noise.  Typically, on  one day, steam flow signals are
    noisier than on other days, so I  suspect that the signal oscillations
    do have some physical significance.
    
         FRFPFRICK HAMZALFK, CHAIRMAN:  Thank you.
                                    500
    

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    Participates and Removal
              501
    

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                                        Evaluation of a Granular Bed
                                       Filter for Particulate Control in
                                         Fluidized Bed Combustion
                                       Melvyn S. Nutkis. Ronald C. Hoke,
                                   Michael W. Gregory, and Rene R. Br.-rtrand
                                   Exxon Research and Engineering Company
    ABSTRACT
           In a pressurized fluldized bed coal  combustion  system where  the  due gas Is expanded through a
    gas turbine to achieve greater cycle efficiency,  it  is Important  that the particulate emissions be at
    a level satisfying both turbine and environmental requirements.   A  program in progress using the EPA-
    Exxon Research pressurized fluidized bed  coal  combustor is evaluating the effectiveness of a granular
    bed filler to remove particulars from the  high pressure, high temperature flue gas.  A 24-hour shake-
    down run was accomplished in August 1977.   Main problems are with filter cleaning at system conditions,
    filter plugging and loss of filter media.
    
    
    INTRODUCTION
    
           The successful development of the  pressurized fluidized bed  coal combustion process is depen-
    dent on the ability of particulate control  devices to  remove particulates from the hot combustor flue
    gas to very low levels.  This must be done  to  assure that the expansion of the flue gas through a gas
    turbine doos not cause damage to the turbine '^y erosion, corrosion, or deposition of solids on the
    turbine blades.  Current estimates of the allowable  particulate concentration in the flue gas entering
    the turbine range from 0.04 to 0.001 g/m3  (0.02 to 0.Of 104 grains/SCF)l.  To meet these estimated
    requirements, the flue gas leaving a pressurized  combustor must first be prccleaned in a two stage
    cyclone and then sent to a third stage high efficiency device for final cleaning.  The efficiency of
    the third stage device must be in the range of 93 to 99.72: to be  within the currently estimated parti-
    culate loading target range.
    
           In addition to the gas turbine inlet requirements, the U.S.  Environmental Protection Agency has
    Imposed limits on the emission of particulates from  coal fired installations of 0.1 Ib/M BTU coal
    fired.  This translates to a particulate  concentration in the flue  gas of about 0.1 g/m3 (0.03 gr/SCF),
    somewhat higher than the limit set by turbine  requirements,  li.^reforc, at the present time, removal
    efficiencies are dictated by the turbine  requirements.   However,  the environmental standards are
    currently being reviewed and may be tightened  in  the future.
    
           The present particulate removal program at Exxon Research  and Engineering Company, which is
    sponsored by the U.S. Environmental Protection Agency  (Contract 68-02-1312), will tc.ปt two particulate
    removal devices.  The first device is a granular  bed filter of a  design developed by the Uucon
    Company,  ihe choice of the second device has  not yet  been made,  but will probably be a high tempera-
    ture bag filter or electrostatic precipitator.
    
           The Ducon-type granular bed filter consists of  a number of small beds packed with suitable
    granular filter media such as alumina, quartz, etc.  A stack of the filter beds form a single filter
    element.  A number of filter elements can be used depending on the  volume of gas to be filtered.  A
    photograph of a filter element purchased  from  the Uucon Company for this program, is shewn In Figure 1.
    This element consists of a total of twelve  individual  filter beds.  Dirty gas passes through the
    screen sections down into the filter beds immediately  below the screen sections.  Clean gas from the
    beds is collected in a manifold in the interior of the element and  then passes to the clean gas outlet
    system.  As the filtration step proceeds, the  pressure crop across  the element increases and eventually
    the element muot be cleaned by the reverse  flow of clean gas.  This "blow back" occurs by flowing
    clean gas in reverse direction through the  outlet gas  manifold, up  through each filter bed and out
    through the screens.  The function of the screens is to retain the  filter media during the blow back
    step, keeping it inside the filter beds, while allowing the fine  particulates removed from the filter
    media by the blow back gas tc pass through. The  fine  particulate then settles outside the filter ele-
    ments and is collected at the bottom of the vessel containing the filter elements.
    
           This type of granular bed filter was chosen to  be tested in  the EPA/Exxon Hinlplant since it
    was considered to possess certain advantages over other high temperature particulate removal systems,
    and development of granular bed filters as  a class was believed to  be further along than the develop-
    ment of other high temperature particulate  removal systems.  Of the granular bed filters under
                                                     504
    

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    01
    o
    01
              Figure 1.  Ouoon Granular Bed Filter and Shroud
    Figure 2. View of Miniplant Showing Filter Prenura Vessel
    

    -------
    development, the Ducon filter had been previously tested at relatively high temperatures and pressures
    and shaved some promise in meeting the high particulate removal efficiencies required by the gas
    turbines3.  The Ducon design also had  the desirable feature of retaining che granular filter media
    in the filter vessel during tie cleaning step.  In all other high pressure granular bed filters, the
    filter oedia is removed, cleaned externally and recycled b&ck to the filter vessel.
    
           The objectives of the granular  bed filter test program at Exxon Research were to measure the
    outlet loading from the granular bed filter, determine if the removal efficiency was maintained with
    use, measure operational stability of  the filter e.g., can low pressure drop across the filter be
    maintained, does the filter plug, is the aaount of blow back gas needed to maintain steady operation
    within reason, etc. and linally, to measure the long term life of the filter hardware.  The primary
    operating parameters were the filtered gas flow rate, usually measured as the gas velocity entering
    each filter bed. the blow back gas flow rate, the duration and the frequency of the blow back step,
    and the type of filter media used i.e., particle size, shape, density.
    
    
    DESCRIPTION OF EQUIPMENT
    
           The granular bed filter was Installed in a pressure vessel tied into the flue gas exit system
    from the EPA/Exxon Hlnlplant pressurized fluidlzed bed combustion unit.  The Hiniplant was described
    in detail in a previous report2.  Briefly, it consists of a comhustor, 33 en (15 in) inside dlaaef!?
    and 10 n (32 ft) high, capable of operating at pressures up to 1000 kPa (10 atm abs), temperatures
    up to 980ฐC (1800ฐF), superficial gas  velocities up to 3 m/s (10 ft/sec) with coal feed rates up to
    (1200 SCFM).  At a typical fluidization velocity now anticipated for a PFBC boiler (about 6 ft/sec),
    the flue gas rate is 18Sm3/nin (650 SCFM).  The partiiulate loading in the flue gas entering the filter
    is about 2.3 g/c>3 (1.0 gr/SCF).  The mass median particle size Is 5 to 7 nlcrons.
    
    
           The pressure vesr I housing the filter cle&ents consists of a refractory lined vessel
    approximately 2.4 m (8 fw) in diaseter by 3.A (11 ft) high.  Figure 2 is a photograph of the Mini-
    plant showing the pressure vessel. Access to the interior of the pressure vessel can be made through
    a 70 era (27 in) manhole.  The vessel can hold up to four filter elements installed through four flanges
    at the top of the vessel.  Each filter element is contained within a shroud, as shown In Figure 1, in
    the inside of the pressure vessel. Inlet gas is piped to each shroud, passing through a measuring
    orifice which determines the flow rate to each filter element.  The gas then enters through the flanged
    openings shown in Figure 1.  Clean gas exits from each shroud through openings at the top (Figure 1)
    and fills the interior of the pressure shell.  Blow back air enters each filter element through the
    top flanges of the pressure vessel and flows in reverse direction through each filter element.   Parti-
    culates removed from the filter element during blow back impinge on the inside surface of the shrojd,
    fall to the bottom and are collected in lock hoppers.  The blow back gas leaving a filter element flows
    in reverse direction through the inlet gas system into the filter elements which are in Che filtration
    step.
    
           A natural gas preheat burner was Installed to heat the interior of the pressure vessel to a
    temperature above the dew point of the combustor flue gas before starting a filtration test.   The
    burner fires into the vessel through a side port for an 8 to 12 hour period prior to the start  of a
    run.  The filter vessel is at atmospheric pressure during this period.  The burner was Installed
    after Initial operation of the filter  resulted in condensation of moisture on the filter elements
    during heat up with flue gas from the  coal combustor.  Condensation in the presence of flue gas parti-
    culates caused plugglrg of the filter  and particulate removal lines.
    
           A number of filter element designs and blow back methods were tested during the filter shake-
    down tests.  Each design and the results of the tests are described in the following Section.
    
    
    RESULTS
    
    CBF Model 1
    
           Initially, three filter elements were purchased from the Ducon Company.  Each element  was 20 cm
    (8 in) in diameter ty 1.8 m (6 ft) long and contained twelve beds.  The Inlet screen size was 50 mesh.
    The nominal flow capacity of each element was 8.5Sa^/min (300 SCFM).  One of the Ducon elements was
    designed to be blown back by short pulses of high pressure air.  The pulse duration was approximately
    0.5s.  This blow back method was cot tested.  The other two Ducon elements were blown back with a
    larger volume of air for longer durations.  The Intent was to fluidize the filter beds rather than
    shocking them with a shore pulse of high pressure air.  The volume of blow back air was sufficient to
    
    
                                                     506
    

    -------
     fluidize  the filter media.  The duration was designed to be less than 10s.   Blow back was accomplished
     by  Isolating one end of a filter element by a blow back nozzle and seal plate and blowing back with air
     at  a pressure slightly higher than filtration pressure.
    
           After Installation of the filters, shakedown began with ambient temperature testing of the
     system.
    
           The objectives of these preliminary tests were to (1) check combustor pressure control with
     the filter on line, (2) pressure test the system, (3) check the alignment of the blow back nozzles,
     (4) check out the operation of the blow back flow system, and (5) measure the distribution of flow
     to  each one of the filter elements.  A number of mechanical problems were discovered (leaks,  mis-
     alignments, etc.) and had to be corrected before further testing could be resumed.
    
           A number of high temperature runs were then attempted but the pressure drops across the filter
     were extremely high and all attempts at blow back were unsuccessful.  Inspection of the filter ele-
     ments after each of these runs showed that a hard filter cake had formed on the inlet retaining
     screens.  This Is shown in Figure 3.  The filter medium was usually participate free indicating very
     little penetration through the screens.  It was originally thought that the plugging occurred during
     startup when moisture was present.  The preheat burner was later installed and a run was made to
     re-evaluate the Ducon filter.  The same screen plugging problems occurred and the original Ducon
     filter was deemed to be unacceptable for our application.
    
     CBF Model 2
    
           Discussions with the Ducon Company led to the design and fabrication of a second filter system.
     Ducon Indicated that they had encountered the same screen plugging problem with flyash and bypassed
     it  by removing the screens and designing the individual beds with more freeboard to prevent entraln-
     nent of the filter media during blow back.  It was also recommended that a fluldizlng grid be used
     at  the bottom of the beds to assure good distribution of the blow back air.  The use of an ejector
     to  replace the sometimes troublesome plunger type blow back nozzles was also suggested.  Filter
     elements incorporating these suggestions were fabricated by Exxon Research and shakedown continued
     using two of these elements each of which contained five filter beds.  A photograph of one of these
     elements Is shown In Figure 4.
    
           Dirty gas enters the beds through the openings below the top flanges and passes downward through
     the filter beds and out into the clean gas outlet tube in the center of the decent.  During blow
     back, the blow back air passes up through the fluldlzing grids supporting each bed, fluidizes the
     beds and blows the fine partlculates out through the inlet slots.  A 18 cm (7 in) freeboard above the
     the filter beds acts as a disengaging section for the filter media and prevents its entralnment
     through the outlet slot.
    
           Operability of the modified filter system has been demonstrated.  The end of the initial shake-
     down phase was signified by the successful completion of a 24 hour demonstration run.  This run was
     preceded by a number of shorter duration runs used to establish suitable operating conditions for the
     demonstration run.  The successful use of an ejector was also demonstrated during one of these runs.
     These runs were successful in that filtration, ability to blow back, ability to calntain low pres-
     sure drops and collection of particulates after bior back were demonstrated.  Collection efficiencies
     of  90 to 9SZ were measured for the first few hours of the runs based on outlet particulate concen-
     trations of about 0.1 g/m3 (0.05 gr/SCF).  Operation for up to 24 hours was also demonstrated with no
     significant increase in baseline pressure drop across the filter.  Blow back was usually required
     every 10-20 minutes during which time the filter pressure drop had increased 14 kPa (2 psl) above its
     baseline value.  A range of blov back conditions were used to restore the baseline pressure drop.
     Blow back durations ranged between 2 and 30 seconds and superficial velocity between 0.15 and 0.75
     m/s (0.5 and 2.5 ft/s).  Filtration velocities generally ranged between 20 and 24 m/min (60 and 80
     ft/nin).  Filter media consisting of 300 to 600 micron quartz particles and 840 to 1400 micron alumina
     particles were tested.  The quantity of blow back air used ranged from 1 to 5! of the filtered gas
     rate.
    
           The particulates passing the filter had a cass median eizr of about  3 microns with about 101
    larger than 10 microns.
    
    Problem Areas
    
           A number of problems were defined during the shakedown and operation of the filter.  Demonstra-
    ted particulate outlet concentrations are still higher than the tentative gas turbine inlet require-
    ments.  However,  firm turbine requirements have not been set as yet and it  may be too early to reach
    
    
                                                     507
    

    -------
    Figure 3.  Filter with Plugged Inlet Retaining Screens
                                                                                                Figure 4.  Modified Filter Element
    

    -------
    any ccr.clusior.5  regardir.g the suitability  cf the filler  to  protect a nas turbine.   The lover out! ••.
    particulate  loadings .->f 0.1 ฃ/r.i  (0.05  ฃr/Si,i )  r.eet the  curre-t  Ll'A eirission  standards,   h'.-.wever,  ir.
    all runs,  :t  was observed liiat the outlet  loading increased  -'it:: tir.e.  Inis is  =.howr. in Figure-  r>
    for two  recent  rur.s usir.t: the alnrina filter r.edifi.  in  these recent rur.i"   the increase  has been  less
    than tl:at  observed in earlier runs due  to  -ore  frequent  blow  backs at higher  velocities.  It has  r.ot
    as yet been  uer.onb'rated that the tPA emission  standard  can be set for r.cre thai:  a few hours of
    operation.
    '.nsfad of  forcing a layer or. the  top of  the beds as had been  expected
                                   f  line part ic'jla
    process explains  tin-
                                                     es ฐ. Mri.u/houl the  1 liter b
    .'t also ;-cปs:bly
                                                                               .
                                                      the increase  :n  outlet particui.ite  cor.v'er.trat i
           Ar.t'tlier  factor vhic!. kir-jlii be  resj.or sil.i*.- !(-r ti:ซ.- retention ct  par t .ci'latet;  in the filter bco:.
    is the rec.>cl in,:  uf  part :cu! jit,3 : rc-r. bed  tu l.d ซ'urii:,- the  bK;-.  Lacf.  step.  lhe  ;-hrouJs ui:ich surrour.
    e.'icl. ilt.Tviil  r.a>  :r.^e'ie the ;;et!.iir.;-  ol  t::t- ;'.irt u uiatos bleuT:  fro-, the cle:.ป-r.'s.   Uiib co-jj-: result  i
    hifih ir.len.'il rec ircuiat iun rales Let'-eer.  ป• it.-r.er.ts, or. :.:::ฃ  t!.e ;>ar t ii:ulutes to buiid up it", "lie t%ec.ป
    anJ thereby  c.'iu.sir.^  a~, ir.creji.e  :i.  t:ie  outlet  ;ป;ปri icu'.ate cuncentiat ior. .  II. is viji  be examined it:  t:ie
    future.
    
           Anttt.er  r--turri::K probler, vas  t::e los.-> .if filter r.edia Jurin, bl'-'v rack.   This occurred ever.
    vhen blov i-ack  velocities ve:e relatively  In:-.  .:old r.odei testa  indicated that the  iot>& vas prouuoly
    caused by instantaneouslv hii.ii velocities  at the becinninj; o! the bluv back  step.   i::e use o: sicwer
    cper.in^ b lev back valves ar.d sufiic.er.t  sur^-e volur.e between the  vilves ard  the I liter beds prevented
    the loss of  the filter r.edia.  L'ecruasini;  tr.e sire  ol tiu.- inie1. ^as slt-t at  the top  o!  ti.e liltei beds
    also decreased  t i:e exte:.t ol the filter  neuia loss.
    
           Another  pctentiai proyle". vltii the  curre'it uesipn is  its vjl t-.er.ib '. i itv to  uj'sets.  If upsets
    occur, such  as  bed pluฃฃir.g cr loss of  lilter -edia, the operatiiuj problems caused  by sue:: upsets
    usually require shutdevn of t!:e syf.ieE.   it is usually not pcssible tc take corrective action vr.ich
    restores gocd operation.  Another probler.  which -ay be unique '.o  the >!ini;-:ant was  the interaction
    of thy ^ror.ui.ir bed  filter witn the rest of the r EC syster. during blow rac< cycle.   .*>n increase in
    sysler, presaure was  noted during blow back resultir.i; ir. probier:*  with  the .:.;al • i  oi  syster. vliic!: Is
    cor.trullcd bv tin- differential pressure  between tnc coal feed vessel ar.d cc-bustcr.   Vhiป required
    codifications to  the coal feea control  systes. to r.ini=.i;e ti;e effects.
    
    
    Ci'KKtNT l'KO(-KA.V
            In addition to the tl'A sponsored  progra" to evaluate  hot  i:as cleanup systers,  LXX-JII Research
    is also under  coi.tract to the Depaitr^nt  of  tner^-y to carry  out  extended >-as tur'rir.e  and boiler tube
    tuterlals tests.   Preparations are now  In progress for a 100 hcur shakedown test  in whic'r. the current
    granular bed  lilter systec will be used  to clean the flue gas before it is expanded through a static:,
    ary turbine test  section.  The test section was provided by  the  General Liectric  Cesp.ir.y.  Boiler
    tube spcci-cns for this te-^t were provided by Westir.ghouse Research Laboratory.   Fallowing the 100
    hour test, additional tests will be carried out ur.der KHA sponsorship alr.cd at  i-provinn the filter
    efficiency and efficiency nair.tenar.ee.   These tests will primarily concentrate  on i:.provinc the
                                                        509
    

    -------
    C   0.12
    u
         0.08
    I
         0.04
                   O H1N1PLANT  RUN 63
    
                   O MIN1PLANT  RUN 65
                                                 EPA EMISSION STANDARD
                                                                            0.3
                                                                            0.2
                                                                            0.1
                                                                                 u
    
    
                                                                                 cj
                                            I
                                     4            6
    
    
                                   TIME INTO RUN (HRS)
                                                                          10
                             Figure 5. Time History of GBF Performanea
                                            510
    

    -------
    cleaning of the filter during the blow back step.  The effect of  the  shrouds which surround each
    filter element on the settling of the particles will also  be examined.  The couple don of  the DOE
    sponsored materials test program, consisting of a 1000 hour exposure  test, will await the  outcome
    of the above programs.
    
           In addition to the CBF evaluation program, Exxon Research  will also evaluate alternate parti-
    cjlute removal devices for the EPA.   Current plans are to  carry out small scale tests on a flue gas
    side stream using two devices being  studied under EPA sponsorship.  The devices are a high temperature
    bag filter studied by Acurex and a high temperature electrostatic precipitator studied by  Fesearch-
    Cottrell.  After the small scale tests are completed, one  of the  devices will be  tested in larger
    scale on the Hiniplant.
    
    
    REFERENCES
    
    1.  0. L. Realms, et al. Westinghouse Research Laboratory, "Fluidlzed Bed Combustion Process
        Evaluation," EPA-650/2-75-027-C, September 1975.
    
    2.  R. C. Hoke, et al, Exxon Research and Engineering Company, "Studies of the Pressurized
        Fluldlzed-Bed Coal Combustion Process," EPA-600/7-76-O11, September 1976.
    
    3.  AlChE Symposium Series No. 137 Vol. 70 pp. 388-396 (1974).
                                                    511
    

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                QUESTIONS/RESPONSES/COMMENTS
    
         MR.  7ESORIERO:   Al  Tesoriero of  the Ducon Company.  As you are
    aware, the element that  has  been shown on the slide is not, in fact,
    the current Ducon design.  The  freeboard height, which could explain
    the loss  of media in  the testing, appears to be approximately six
    inches.  Secondly, the media that has been used, I think you said
    800 or 1400 microns,  and a space velocity of 66 to 100 ft/min; and,
    of course, you realize that  both of those variables will affect
    performance.   Those are  the  two comments that I have.  The question
    that I would like to  address to you -is what you are going to use
    that 250  to 600 micron filter media which is needed to get good
    filtration that the face velocity is  a problem and the freeboard
    height is a problem.
    
         MR.  HOKE:  The question was by Al Tesoriero who is associated
    with the  Ducon Company.   The first question was concerned with the filter
    bed freeboard.  The units that  we use have a freeboard of six
    inches.  Al mentioned that Ducon1s design now specifies 10 inches.
    We have looked at the question  of filter media loss in some cold
    model Plexiglas units.   We think that the problem is not the free-
    board, but rather the fact that during the initial part of the blowback
    step, unless you're very careful, a flow surge occurs which lifts
    the bed and Mows some media out.  If we can control the flow surge,
    there is  no problem with loss of filter media.
    
         This is the approach that  we are taking now.  We are putting
    in slower acting valves, and we are trying to locate the valves some
    distance  from the filter in  order to  get some surge capacity in the
    inlet lines.   We think that  if  this is done, we can run without
    losing the filter media.
    
         As far as the filter media particle size is concerned, from a
    purely theoretical standpoint,  you would like to use finer filter
    media.  However, we feel that the problem at the present time is not
    in getting good filtration,  but rather in cleaning the particulate
    from the filter media.   To balance the situation, we are trying to
    get a filter media which isn't  lost during the blowback.
    
         We have run with smaller granules in the filter bed.  We
    haven't really seen any  difference in filtration efficiency; and
    the reason for that,  I think, is that we are seeing penetration
    by the dust caused by mixing in the bed which is independent of the
    particle  size of the  filter  media.
    
         If we once get to the point where the beds are being adequately
    cleaned during the blowback  step, we  will then use smaller filter
    media particle sizes.
    
                                    512
    

    -------
         DR. ZENZ:   I  might point out  that  you  realize that if you make
    the filter media particles  smaller, you clean  the  bed  easier.
    
         MR. HOKE:  Well, again, we have tried  to balance two considera-
    tions.  We had a considerable loss of filter media during our first
    runs with the quartz because it was a smaller particle and it had
    lower density; so we've gone in the direction of using larger particles
    and higher density in order to minimize that problen.
    
         DR. ZENZ:  What is your support screen like?  Is it just a  plain
    screen?
    
         MR. HOKE:  The screen at the bottom of the bed?
    
         DR. ZENZ:  The bottom of the bed,  yes.
    
         MR. HOKE:  No, it's a screen backed up with a fluidization  grid.
    
         DR. ZENZ:  What's the fluidization grid like?
    
         MR. HOKE:  It's a perforated plate.
    
         DR. ZENZ:  You don't know the percentage of open area,  do you?
    
         MR. HOKE:  I  don't recall exactly, but it's designed to give a
    pressure drop which I think is about 30 percent of the pressure  drop
    through the bed.  It's conventional  design  practice.
    
         SPEAKER (from the floor):  Just vo ask Dr. Zenz a question.
    When you say "optimizing the particle size  to 250 to 600 microns,"
    do you mean that you have to go to that size to prevent re-entrainment.
    of fines after you have completed the blowback?
    
         DR. ZENZ:  If the particle size is too big, we don't fluidize.
    We could use so much gas on the fluidization to clean it that it
    becomes impractical and yet we are not  cleaning the filter media as
    we'll.  If we go down too fine, then it  gets kind of ridiculous;  the
    pressure drop gets too high.  So w& more or less optimize out at 250
    to 600 iiiicrons.
                                     513
    

    -------
         MR. HOKE:   We have looked at the effect of velocity during
    blowback.  In ambient temperature tests in Plexiglas units.
    Again, the problem appears to us to be the adhesive nature of the
    particulate.   Enough of it sticks to the outside of the filter media
    so that it is mixed back in the bed, and eventually, we get a uniform
    distribution of the particulate from top to bottom.
    
         We've looked at the beds after an extended run, and the filter
    beds are loaded with the particulate.   Sometimes as much as 30
    percent of the weight of the filter media is the particulate, and it
    is a uniform distribution from top to bottom.   We think the reason
    for this is the fact that the dust is very adhesive, and it doesn't
    get completely cleared off of the bed during blowback.
    
         CHAIRMAN:   Are there other questions?  Yes.
    
         SPEAKER:  Just out of curiosity,  who supplied the  filter and
    the media?
    
         MR. HOKE:   The initial  filter was purchased from Ducon.   The
    second filter was designed by Exxon after consulting with Ducon,  and
    we constructed it and tested both systems.
    
         CHAIRMAN:   Are there any other comments or questions?  Thank
    you very much,  Ron.
                                     514
    

    -------
                            INTRODUCTION
         DALE KEAIRNS,  CHAIRMAN:  The next paper will address Granular
    Bed Filters for Participate Removal at High Temperature and Pressure.
    This paper is by personnel at Air Pollution Technology, R.D. Parker,
    S-C Yung, R.G. Patterson,  and S. Calvert; and it is also coauthored by
    Dennis Drehmel of EPA.  Dr. Parker will present the paper.
    
         Dr. Parker received his Ph.D. in mechanical engineering from
    Duke University, and  he has been with Air Pollution Technology since
    that time.  He has  been carrying out work in terms of developing and
    understanding high-temperature, high-pressure particulate control
    equipment.  Dr. Parker.
                                    515
    

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                                     Granular Bed Filters for
                                   Paniculate Removal at High
                                   Temperature and Pressure
    
                                S.C. Yung. R.D. Parker, R.G. Patterson,
                                             S.Calvert
    
                                            A.P.T.Jnc.
    
                                          D. C. Drehmel
    
    AHSTRACT                                 US EPA
    
           The technological status of granular bed filtration  for particulatc control
    at high temperature and pressure (H'l'l')  is critically examined with  regard to appli-
    cations for fluidizcd bed combust ion (I;KC) processes.  A performance model for
    granular hod filtration is presented and  compared with experimental data  fron lab-
    oratory and industrial scale filters.  The potential of granular  bed filters for
    I IT I* particulatc control is evaluated with re>,:rd to the cleanup requirements based
    on turbine limitations, emissions regulations inr current  information on  the size
    and mass loading of particulatc emitted  from  l:!iC processes.
    
    
    INTRODUCTION:
    
           Cranular bed filters have been proposed  for the removal of particulatc matter
    from high temperature and pressure pases.  One  such application would be  as the
    tertiary collection device in a pressurised fluidiied bed  boiler  power  plant as
    illustrated schematically in l-'ic.ure 1.   The gas leaves the  boiler at a  temperature
    of approximately '.>!MIฐ(; and a pressure of  about  II) atm.  l;irst it  passes through a
    primary cyclone which removes larger particles  (including  unburnt carbon) and recy-
    cles these particles to the comhustor.   The pas leaves the  primary  cyclone and
    passes through a secondary cyclone or mil tic lone separator.  This removes nore
    large particles and reduces the mass loading  of particulatc to the  order  of 1 gr/SCF.
    
           A tcrtiaiy cleanup device is necessary to reduce the part iculate loadini;
    sufficiently to protect the gas turbine  from  exc-.-ssivc erosion and  corrosion damage.
    It is also desirable fur the )'.as at this  stage  to he sufficiently clean to satisfy
    all emissions regulations.  However, if  necessary,  it is possible to satisfy the
    emissions regulations by cleaning the gas downstream of the turbine using convc-n-
    tional control technology.
    
           An idea of the size of equipment  required for a fnll-scr.le power plant can
    be obtained from the Phase II I'.lIAS study.  In the h'est i nghousc report (Reedier et al.
    I'.lTfi)1 a design for a (>K(l "!KO power plant was presented.   Four pressurized fluidizcd
    hod boilers fed gas to two gas turbines.  liach  gas turbine  handled  7M)  Ih/s of gas.
    llach boiler had four granular bed filters associated with  it.  The  granular bed
    filters each handled HH.75 Ib/s or approximately 30,000 CI-'M at 1,77<)ฐF  and 10 atn.
    
    
    CI.F.AMIP KF.QIIIRBIF.XTS
    
           It is generally supposed that the  paniculate removal requirements imposed by
    the gas turbine tolerance will be more stringent than the  emissions regulations.
    This may or may not he the case depending on  what turbine  tolerances arc  specified.
    It has been suggested (West inghousc7) that a  mass  loading  of 0.15 gr/SCF  for par-
    ticles smaller than 2 um would allow a satisfactory turbine life.   If there were a
    sufficient loading of particulatc smaller than  2 urn  it would be possible  for the gas
    to be cleaned sufficiently to protect the turbine while still exceeding the emissions
    regulation of 0.1 Ib/lO'-RTII  (approximately 0.06 gr/SCF).
    
           The best available information concerning the size  and mass  loading of par-
    ticulatc entering the tertiary collection stage of a pressurized  fliiidizcd bed pro-
    cess has been reported by lloke et al.'   The mass loading has been found to be
    typically about I gr/SCF.  The size of this part iculate  is  represented  in Figure 2.
    Approximately .iO', of the mass is smaller than 2 um so that  about  H.5 j.r/SCF can be
    expected in this size range.  It may he  possible to protect the turbine with 50'.
    collection of these fine particles, but  the current emissions regulations require
                                            516
    

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                          AIR
                           I
    COMPRESSOR
                                                                  6AS  TURBINE
                                                                                              >STACK
                                                                        TERTIARY     HEAT
                                                                        COLLECTOR   RECOVERY
                                                             CYCLONE
    en
                                     BOILER
                                                      •STEAM
                                  FEED
                                                        WATER
                                                       Figure 1. Pretturized fluiditad bed boiler
    

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         50
    I    10
    i     s
         1.0
         0.5
         10           30      50       70
                 Wt % undersize
    Figure 2. Particle tile distribution from Exxon miniplant
                                                                         90
                                     518
    

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    at least 80** collection.  If the emissions regulations were reduced to 0.05 lb/106
    BTIJ at least 90ป collection would be required.  This assumes effectively 100ฐ  collec-
    tion of particles larger than 2 urn.
    
           f.ccently Svcrdrup and Archer* proposed that a mass loading of 0.002 gr/SCF
    (for all particle si:es) is required to protect the turbine.  If this criterion were
    ado.-tcd, clearly the emissions regulations would be satisfied.  However, a tertiary
    collection efficiency of at least 99.8ฐ would be required to reduce the loading
    observed at the lixxon miniplant to this level.
    
           Increasing the efficiency of n tertiary collection device from about 80 to
    90' (emissions regulations) to 99.8', (turbine limitations) is a very significant
    increase affecting both the cost and the availability of technology for high tem-
    perature and pressure (IITP) ^articulate control.  A firmer understanding of the
    degree of collection required to protect turbines would greatly facilitate the
    development of 1ITI1 particle collection technology.
    
    
    C.RA.NULAR BI:D I-UTKRS
    
           l-'or our purposes, granular bed filters arc -Icfined as any filtration system
    comprised of a stationary or slowly moving bed of sc|.:'ratc  relatively close-
    packed granules as the filtration ni-dium.  There arc three basic approaches to
    granular bed filtration currently being developed.  The filter being tested at the
    lixxon miniplaiit is in the class referred to as "fixed bed" filters.  The bed of
    granules is kept stationary during filtration.  It is cleaned by a reverse flow
    of gas which fluidizcs the bed and entrains the collected paniculate.  The Uucon
    and Rexnord granular bed filters are examples of fixed bed filters.  The principal
    advantage of the fixed iicd approach is that the granules do not have to he recir-
    culatcd and thus can he used for many filtration cycles.  I'or this reason, fixed
    beds have potentially lower operating costs.
    
           In a second type of granular bed filter, referred to as the "moving bed"
    filter, the gas flows through a slowly moving bed of granules.  Ttie collected
    dust particles arc carried with the bed and later removed from the granules before
    the granules are recirculatcd.  The Combustion Power Company's "dry scrubber"  is
    an example of a moving bed filter.  Moving beds have the advantage that the granules
    and dust arc separated externally and arc free from the problem of particle buildup
    and bed plugging.  An inexpensive but effective means of rccirculating the granules
    could significantly lower operating costs.
    
           The third type of filter is the "intermittently moving" filter.  This filter
    uses stationary granules for filtration and causes the granules to move through the
    system intermittently during the cleaning cycle.  The panel-bed filter developed at
    the City College of the City University of New York (Squires and Pfeffer"1) is  an
    example of an intermittently moving bed filter.
    
           The major problems with each approach arc summarised in Table I.  Many  of
    these problems can be resolved through further research and development.  Granular
    bed filters are used successfully to control emissions from clinker coolers in the
    cement industry and on hog-fuel boilers in the forest products industry.  They
    operate in the range of 100-200ฐC and near atmospheric pressure.  However appli-
    cations for controlling fine particulatc at elevated temperatures and pressures are
    very scarce.  Granular bed filters are attractive for these applications because
    they can be made to withstand high temperature and pressure environments relatively
    easily.  However more work is needed to determine whether granular bed filters are
    satisfactory from the point of view of primary collection efficiency, cost, and
    reliability.
    
    Granular Bed filter Model
    
           In order to help evaluate the potential of granular bed filters for IITP
    particulatc control we have developed a performance model which has been used  to
    predict collection efficiency for lab-scale and full-scale filters.  The model is
    based on the collection of particles in a clean granular bed.  The collection
                                            519
    

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                           Table I.  Granular Bed Filter Problems
            FIXED PF.D
    
        Plugging of retaining
        grids and possible par-
        ticle buildup in bed.
    
    2.  Particle seepage through
        bed during cleaning
        cycles.
        l-'luidization redisperses
        fine dust during clean-
        ing.
    
    4.  IITP valving required
        for reverse air
        clcanirg.
    
    S.  Temperature losses
        proportional to vol-
        ume of cleaning air.
              MOVING BHI1
    
    1.  Particle re-entrainment
        in moving bed.
    2.  Granule rccirculat ion
        may cause high opera-
        ting cost.
    
    
    3.  Difficult to form a
        cake in moving bed.
                                    4.  Rrosion of retaining
                                        grids and transport
                                        systems.
    
                                    5.  Temperature losses
                                        proportional to heat
                                        capacity of recircu-
                                        lated granules and
                                        rccirculation rate.
      l.\'Ti:RMITTi;\T BED
    
    1.  Low gas capacity
        can cause high
        capital cost.
    
    2.  Granule rccircu-
        lation may cause
        high operating
        cost.
    
    3.  Need •   form sur-
        face cake to avoid
        plugging problems.
    
    4.  Erosion of retain-
        ing grids and
        transport system.
    
    5.  Temperature losses
        proportional to
        heat capacity of
        recirctilatcd
        granules and re-
        circulation rate.
                                             520
    

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    efficiency would be affected if there were a significant filter cake on the bed sur-
    face and within the bed.   The presence of a surface cake, however, has not been
    noticed by many investigators working with large-scale filters,  h'e feel the clean
    bed nodel predicts a conservative estimate of the efficiency attainable by granular
    filtration and is a satisfactory model for filters which operate primarily without
    the presence of a filter cake.
    
           The granular bed can be envisioned as a great number of impa:tion stages
    connected in series as illustrated in I-'igurc 3.   Particle collection is by
    inerttal impaction and is similar to collection  in a cascade impactor.  The jet
    openings arc the pores in each layer of granules.  It is assumed that the jet diam-
    eters in the granular bed arc of uniform si:e  and are equal to the hydraulic diam-
    eter of the void space.  The gas velocity in the jet is the average superstitial
    gas velocity.
    
           If ' TI' is the collection efficiency of one inpaction stage, the particle
           la  i|  *^< llll- vvfl*l-l,llYJII Vltlt-lvlt
    penetration for the granular bed will be
                                    Pt, = (1-nV
                                                                           (1)
    where  Pt
                 penetration for particles with diameter d ,  fraction
    
                 single stage collection efficiency,  fraction
    
                 number of impact icn stages
           As in some cascade impactors, each layer of granules serves both as the jet
    plate and as the collection plate.   Therefore,  each lay -r is an impact ion stage
    and "X" is equal to the number of granular layers in a bed.  l:or a randomly packed
    bed
                                    X
                                        3 Z
    where   Z = bed depth, cm
           AC = granule diameter, cm
    
    and
                                    Pt
                                                                           (31
           The impaction collection efficiency,  n,  is .1 function of, K ,  the Lnertial
    impaction parameter.  The impaction parameter is defined as       '
    where  C'
    since
                                           9 v.
                Cunningham slip factor,  dimcnsionlcss
    
                particle density, g/cm3
                particle diameter, cm
    *
    u. = jet velocity, cm/s
    u_ = gas viscosity, poise
    
    dJ
                jet diameter, cm
                                         "r.i
                                                                           (5)
                                           521
    

    -------
    
         969
           TAR6ET
    Figure3. Impaction model
        522
    

    -------
    and                          dj ป 4rH = | (^J dc                     (6)
    
    
    where  u^.j ซ average interstitial gas velocity, cm/s
             c •> bed porosity, fraction
    
            TJJ ฐ hydraulic radius, cm
    
            dc = granule diameter, cm
    
    
                                      ,  ,.  .  C' p  d ' ur
    we have                      K  • J  (—1 —*-2—I}	                (7)
                                  p   2  \  e' /   9 ur d
    
           The relationship between, r,, and, Kp, can be evaluated once the flow field
    is defined.  Flow fields reported in the literature; e.g., Ranz and Konp.' and
    Marple7 are adequate for Kp>0.15.  For Kp<0.15, there is no suitable flow field
    reported in the literature.  Therefore, the relationship between, n, and, K ,
    cannot be calculated analytically from the available literature.           p
    
           The single stage collection efficiency has been calculated as a function of
    Kp from equation 3 and experimental data.  Figure 4 shows the results.  There is
    scatter in the lower end of the curve.   For Kp<10"r, n is very sensitive to experi-
    mental data.  A few percent scatter in  data will cause, n, to fluctuate greatly.
    Figure 5 compares the experimentally determined, n, versus, K'p, curve with those
    reported by Ran: and h'ong*. Stern et al.',  and Mercer and StuVford.'  All reported
    curves arc for Kp>0.15.  As can he seen, the present study is consistent with other
    researchers's results and is a continuation of their curves into the raiiฃe most
    likely to he important for high temperature and pressure filtration.
    
           P?.ป.tsky ct al.10 and Kncttig and Bceckmans1' studied the collection of
    monodispcrscd aerosol particles in granular bed filters.  Their data were trans-
    formed into, Kp, versus, n, plots as shown in Figure 5.
    
           Knettig and Bceckmans11 used 42S urn glass beads as granular material.  Bed
    porosity was 0.38.  Aerosol particles were 0.8, 1.6, and 2.9 ;im in diameter.  As
    can be seen from Figure S, their data are in close agreement with the results of
    the present study.
    
           Parctsky ct al.10 investigated the filtration of 1.1 urn diameter polystyrene
    latex aerosols b/ beds of sand.  They used a bed of 10-14 mesh (1,200-1,700 urn)
    angular sand and a bed of 20-30 mesh (500-850 urn) sand at superficial gas velocities
    between 0.3 and 80 cn/s.  Bed porosities were 0.41 and 0.43, respectively,  h'e have
    calculated single stage collection efficiencies from their data.  In the calcula-
    tion, the granule diameters were assumed to be the arithmetical mean of the smallest
    and the largest granule size in the bed.  The results are plotted in Figure 5.  For
    a given incrtial parameter, Paretsky ct al.'s10 data give a higher collection effi-
    ciency than reported in this study.  Their data would be close to that of the pre-
    sent study if the smallest granule dianeter were used instead of the arithmetic
    mean.
    
           The design model is based on particle collection by a clean bed.   If there
    is no filter cake formed on the surface and the collected particles are  uniformly
    distributed in the bed, the model should be applicable.  The design model has
    been used to predict the performance of a Rexnord gravel bed filter and of Combus-
    tion Power Company "dry scrubber."  The predictions are compared with field samp-
    ling data taken from the literature.
    
    Rexnord Gravel Bod Filter
    
           McCain" conducted a performance test on a Rexnord gravel bed filter.  The
    gravel bed filter was installed to clean emissions from a clinker cooler in a
    Portland cement plant.
                                           523
    

    -------
         O.lc—i   i  i   i <  ui
        0.01
     o>
    "5
     BB
     CO
    J2 0.001
                   O  1.09ft
                   A  0.76ft
                   O  0.5/t
      0.0001
                                      _l	I   I  I  I  I  I I I
           0.002
    0.01
    0.1     0.2
                             Figure 4. Experimental data
                                       524
    

    -------
         1.0
    
    
         0.5
         1.0
    
    
    ฃ  0.05
    tป
    o
        0.01
    
    
        .005
       0.001
                                 20-
                           PAHETS8Y
                              DATA   X
                     10-14 (11ESH
                                                    STEBW
    IMERCER
     STAFFORD
                I   I   I  I I
                                                        KUETTI6  and
           0.002
                           0.01                       0.1
    
                               Impaetion parameter
    
                             Figure 5. Compcriton with pravious wortc
               0.5
                                    525
    

    -------
           Saraples were taken simultaneously at the fi!ter inlet and outlet with cascade
    inpactors.  The operating conditions of the gravel beJ were:
    
                              Crave! diameter * 4 nm
                              Face velocity   = 73 cn/s
                              Gas temperature ป 175ฐt:
                              Pressure drop   ซ 25.4 cm K.C.
    It was assumed that there was no surface cake ami that the pressure drop across the
    bed was 80* of the overall pressure drop.  Mrgun's equation fHrgun'1) was used to
    estimate a porosity of 0.25.  Kith this be.' porosity, the r.rade penetration curve
    was calculated for the operating conditions listed above.
    
           Figure 6 is the predicted Rrade penetration curve along with that neasurcd
    by McCain17.  The prediction is in good agreement with the data.
    
    Combustion Power Company Moving Crave! Red
    
           Hood1* reported the evaluation of the Combustion Power Company (CI'C) moving
    gravel bed filter on the control of participate emissions from a hog-fuel fired
    boiler.  The gravel bed filter was a prototype unit with suggested capacity of
    1,133 Am Vein (40,000 ACFM).  The bed was packed with an intermediate-size gravel
    which was retained on a 3.2 mm 11/8") wire mesh and passed at b.4 ma (1/4") nesh
    screen.  The bed was a single down-flowing annulus 2.6 m (8.5 ft) O.I), and 1.8 n
    (6 ft) I.D.
    
           During sampling the unit was operated at a How rate of 1,558 nVmin (55,000
    ACFM).  The gas temperature was 177"C (350ฐl-).  Figure 7 shows the penetration
    curves for three sampling runs.
    
           The avciage granule diameter was assumed to be 4.6 mm and the bed porosity
    was calculated to he 0.25.  The predicted grade penetration curve is shown in
    Figure 7.  The predicted penetration is higher than that  measured.  Recent data
    obtained by A.I'.T. on the CI'C moving bed filter is shown in Figure 8.  These data
    agree well wit!, the model's prediction.
    PERFORMANCE PREDICTION FOR IH T APPLICATION
    
           Exxon Research and Engineering Company installed a Ducon granular bed filter
    at their fluidized bed coal combust or miniplant.  The bed is packed with Agsco no.
    2 quart: (400 um mean diameter) to a depth of 3.8 cm (J.S in.).  The temperature
    of the flue gas from the combustor is 870ฐC (1,600ฐF) and the pressure is 10 atm.
    
           According to lloke1*, there is no surface cake formed and the fly ash is
    uniformly distributed in the bed.  lor this condition, the clean bed model  can
    be used to predict the performance of the Ducon granular bed in the miniplant.
    
           From the pressure drop data reported by Exxon, the bed porosity was  esti•
    Dated to be 0.24.  Figure 9 shows the predicted performance of the miniplar.t
    granular bed filter at high temperature and high pressure and at ambient condi-
    tions.  A particle density of 1.5 g/cm' was used in the calculation.
    
           If the particle si:c distribution is known. Figure 0 can be used to  estimate
    the overall collection efficiency of the Ducon granular bed filter.  The equation
    relating the efficiency for collecting one particle diameter to the overall
    efficiency is:
                            E
                                1-Ft ป 1- I Pt
    id f
    -------
        1.0
    ฃ  0.1
       0.01
                  MCCAIN'S
                      DATA
    as      UD                 s
              Particle dia.
                                               10
           Figura& Compvison with d*ta for Raxnord fitter
                         527
    

    -------
      1.0
    
      0.5
     0.1
    0.05
    PREDICTIiH
                H000S   \  ^^
       0.1              0.5       1
                   Particle  dia.pm
          Figure?. Comparison with d*t* for CPC moving ted fitter
                          528
    

    -------
     0.5
    0.05
    0.011  I M . I 1
        0.4          1                   5
              Particle dia./imft
    
      Figure 8. Comparison vrith CPC moving bed fitter
                  529
    

    -------
     1.0
    
    
     0.5
     0.1
    
    
    0.05
                                          I  i i  i i
    0.01
                  20UC
                            Graoale  tiiaaeter:400/A
                            Bed  Bepth:3.8caj     :
                                 .
                            p = 1.5 g/eซ3
                            c = 0.25
                               lOatn
                               870ฐC
                            latra
                            870ฐC
        0.1            .5    1.0             5
    
                PARTICLE DIAMETER, pn
    
    
              FigunS. PrtaSctwJ C8F Pwfeปmaneป
                                                 10
                         530
    

    -------
           Hokc' reported data on the particle sire distribution leaving the secondary
    cyclone (Figure -).  The mass median diameter is 5.5 urn and the geometric standard
    deviation is 2.9.  The mass loading is approximately 1  gr/SCF.   The overall collec-
    tion efficiency for this size distribution was calculated graphically to be 95.11
    (4.9* penetration!.  The emission, therefore, is predicted to be about O.ns gr/SCF
    which is satisfactory to meet current emissions regulations, and is within thi
    measured range reported by iloke'1.
    
           As can be seen from Figure •>  '.he granular bed filter should be very effi-
    cient for all particles larger than 1 to 2 urn in diameter.  Whether or not this
    filter is efficiency enough to protect the gas turbine  will depend strongly on the
    turbine's tolerance for submicron particles.
    
    
    CONCLUSIONS
    
           Granular bed filter technology has the potential for resolving the 1ITP
    paniculate control problem.  Collection efficiencies should be sufficient to meet
    the current emissions regulations for particulates.  Performance may be satisfac-
    tory for protecting gas turbines, however, this will depend strongly on the amount
    of subnicron particles a turbine can tolerate.
    
           There arc many operational problems and uncertainties which need to he
    resolved before HTP granular bed filters can  be considered sufficiently reliable
    and economical for commercial application. These problems include:
    
           how to prevent particle seepage through the bed  (during  cleaning or
           fill rat ion).
           how to reduce temperature losses (especially during cleaning).
    
           how to improve the efficiency and reduce the cost  of granule regeneration
           and recirculation.
           how to reduce pressure drop across the bed.
    
           how to prevent attrition of granules causing particle re-entrainment.
           how to prevent sintering of granules.
    
           how to prevent plugging of retaining grids.
    
           Resolving these problems will not only provide a solution to the HTP par-
    ticle collection problem, but will improve granular bed filter  technology for many
    other applications, especially where hot, corrosive gases arc encountered.
    
    ACKNOKLI-DCMIINT
           This work is supported by the U.S. F.nvi ronmental Protection Agency.
    
    LIST OF SYMBOLS
    
    
              C1 ป Cunningham slip factor, dimensionless
             d  = granule diameter, cm
    
             d. • jet diameter, cm
             dp * particle diameter, cm
            d   ป aerodynamic 'iiaroeter ซ d  (p C1)', uraA
             pa                           P   P
              E ป overall collection efficiency,  fraction
    
          f(d ) • particle size frequency distribution
             K  ป incrtial impaction parameter, dimensionless
    
              X ซ number of impaction stages
             Ft" ป overall penetration, fraction
    
            Pt , • penetration for particles with  diameter,  d  , fraction
    
    
    
                                           531
    

    -------
              r.. = hydraulic radius, cm
    
             u_. = average interstitial gas velocity, cm/s
    
              u, = jet velocity, cra/s
    
               Z ป bed depth, cm
    
               r = bed porosity, fraction
    
               n = single stage collection efficiency, fraction
    
              PP ป gas viscosity, poise
    
              P  = particle density, g/cm'
    
    
    
    LIST OF REFERENCES
    
    
     1.  Bccchcr, O.T. et al. Energy Conversion Alternatives Study fECAS), h'cst in-house
         Phase II Final Report, Vol. Ill, "Summary and Advanced Steam Plant with Pres-
         surized Fluidizcd Bed Boilers", Report NSF/RA-760S90. NTIS PB 268-558,
         November 1976.
    
     2.  Westinghouse Electric Corporation, "Clean Power Generation from Coal", O.C.R.
         84, NTIS PB 234-188, April 1974.
    
     3.  Moke, R.C.  et al., "A 'rtegcncrativc Limestone Process for Fluidizcd Bed Coal
         Combustion and Desulfurization", Monthly Report 87, 1977.
    
     4.  Svcrdrup, E.F. and I).II. Archer, "The Tolerance of Large Gas Turbines to Rocks,
         Dusts, and Chemical Corrodants", presented at EPA/ERDA Symposium on High
         Temperature and Pressure Paniculate Control, Kashington, DC, September 1977.
    
     5.  Squires, A.M. and R. Pfoffor, "Pane! Bed Filters for Sinultaneous Removal  of
         Fly Ash and Sulfur Dioxide", -I. APCA 2_0: 534-538, 1970.
    
     6.  Ranz, N.i;.  and .I.B. h'onp, "Inpaction of Dust and Smoke Particles", Ind. Eng.
         Chcm. 4ฃ: 1371-1381, 1952.
    
     7.  Marple, V.   The Fundamental Study of Incrtial Inapctors.  Ph.D. Thesis,
         University of Minnesota, 1970.
    
     8.  Stern, A.C. , U.K. Zcllcr, and A.I. Schckman, "Collection Efficiency of .let
         Impactors at Reduced Pressures", Ind. and ling. Fundamentals, _[: 273, 1962.
    
     9.  Mercer, T.T. and R. G. Stafford, "Impact ion forn Round Jets", Ann. Occupational
         llygicncc, ^2: 41-48, 1969.
    
    10.  I'aretsky, I.., L. Theodore, R. Pfeffcr, and A.M. Squires, "Panel Hed Filters
         for Simultaneous Removal of Fly Ash and Sulfur Dioxide: II Filtration of
         Diluted Aerosol by Sand ซcds",'j. APCA, 2ฑ: 204-209, 1971.
    
    11.  Knettig, P. and J.M. Becckmans, "Capture of Monodispcrscd Aerosol Particles
         in a F'ixed and in a Fluidizcd Bed", Canadian J. of Chcm. ling., 52: 703-706,1974.
    
    12.  McCain, .T.D., "Evaluation of Rexnord Gravel Bed Filter", EPA 600/2-76-;64,
         NTIS PB 225-095, June 1976.
    
    13.  Ergun, S. "Fluid Flow Through Packed Columns", Chcm. Eng. Prog., 48: 89-94,1952.
    
    14.  Hood, K.T.  "Evaluation of the Combustion Power Company Moving Gravel Bed Dry
         Scrubber on the Control of Paniculate Emissions from a Hog-Fired Boiler",
         NCASI Special Report, September 1976.
    
    15.  llokc, R.C., "Ducon Gravel Bed Filter Testing", presented at EPA/ERDA Symposium
         on High Temperature and Pressure Particulate Control, Washington, DC,
         September 1977.
    
    
    
                                           532
    

    -------
                 QUESTIONS/RESPONSES/COMMENTS
    
         SPEAKER (from the floor):   I  guess  I an developing some objec-
    tions to both DOE's and EPA's continued,  I'll call it, plowing the
    sane ground, relative to granular  bed  filters.   I think the state of
    the art in the technology really hasn't been advanced at al1 in the
    last three years.  As I said, I  keep hearing the same conclusions,
    the same problems, meeting after meeting.
    
         Now relative to some of the fundamental issues here, when you
    are talking about the pressurized  fluidizcti bed, I think that one of
    the underlying issues relative to  the  entire cleanup system is,
    indeed, what can the gas turbine tolerate?  I know I have heard at
    least three papers today saying, "Here is the range of estimates."  I
    think considerably more work should be put into determining just what
    a reasonable tolerance limit is  for a  gas turbine.  That is something
    that's been lacking right from the beginning of the whole effort.  I
    think when you are talking about meeting the EPA emission standards,
    if you meet them while you are protecting the turbine, fine, but we
    certainly don't need high-pressure or  high-temperature cleanup systems
    to meet EPA standards when you can always do it downstream of the
    turbine.
    
         I also think relative to the  loading specs that it's very
    obvious that the loading is a function of the size of the particles;
    and the gross range per standard cubic foot of the tolerances are just
    not applicable.  It's very dependent upon the size of the particulate.
    So again, that gets back to the  issue  tnat someone better, at some
    point, start taking a good h.ird  look at establishing some tolerances.
    If one does know what the gas cleanup  has got to do, then I would like
    to see both DOE and EPA take a more mature look at this background and
    stop really supporting a lot of  surveys that have gone on and on.  I
    want to see some firm new ideas  and new concepts developed for parti-
    culate control.  Thank you for the soap box.
    
         CHAIRMAN:   Other comments?  Yes.
    
         SPEAKER (from the floor):   We have been trying to build a turbine
    which would eject particulate material for 40 years.  The permissible
    limits for particulates in the gas stream from the standpoint of tur-
    bine bucket erosion, I think, are  very soundly based on that experi-
    ence.  I don't  think there is any  point in going into the details here.
    But let's not kid ourselves:  we are not going to be able to eject
    large particulates from the gas  turbines, no matter how you dislike
    it.  Unfortunately sandblasting  is a very effective way of removing
    material from the turbine and the  effects of particulates on gas
    turbine buckets.
                                    533
    

    -------
         CHAIRMAN:   Thank you.   Other questions?  Go ahead.
    
         MR. SCHWARTZ:  Michael  Schwartz from Shell Development.  This
    is essentially a general  question.  What consideration has been
    given to generalizing this  technology to additional  applications?
    What I am thinking of in particular are high-temperature, highly-
    fouling particulate streams which arise from incineration.
    
         CHAIRMAN:   Are there people that would like to comment to that?
    
         SPEAKER (from the floor):   I guess not very much consideration.
    
         CHAIRMAN:   I think there was another comment or question here.
    
         SPEAKER (from the floor):   I will ask a simple question. Dr.
    Parker mentioned several  times in his talk that he does  not think
    that at high temperature and high pressure filtration is by filter
    cake.  Could he elaborate on what basis does he expect this.  Just to
    look at it or what?
    
         DR. PARKER:  The  question was, what was my basis for saying
    that I did not think there was any filter cake formed in these appli-
    cations at high temperature and pressure.  I did not mean to imply
    that there never could be a filter cake formed.  But in  what has
    been reported on the experiments at Exxon, the tests of  a Squires
    granular bed filter at Morgantown, and the tests of Combustion Power
    Company, is that there has  been no evidence that there was a cake
    formed.  And we are using that as the basis for justifying, using a
    clean bed model for these predictions.
    
         SPEAKER (from the floor):   Then how did they arrive at that,
    that no filter cake was formed.  By looking at the bed,  or what?
    How do they see it?
         DR. PARKER:  Well, all they say is there is no evidence that
    there was a cake formed.  What does that mean?  They did not see any
    cake; any evidence of a cake.  That is, they don't see large clumps
    of ash in the hopper after cleaning.  They don't see any cake, I
    guess, if they stop a test in the middle, they don't see a cake
    formed before cleaning the bed.
    
         SPEAKER (from the floor): Did you see a cake of fine particles
    or big particles?
    
         DR. PARKER:  Well, a filter cake would be a cake like the cake
    that Ron Hoke showed on his screen, on the Dueon filter.  It will be
    on the surface of the bed, and it will be separate from the bed
    material; there will be a cake of granules.
    
                                     534
    

    -------
         SPEAKER (from the floor):   Doesn't cleaning  cause  the  pressure
    drop to go down?
    
         DR. PARKER:  Uell, the pressure drop will  go up as the bed  loads
    up anyway, no matter where the  particles are collecting.
    
         SPEAKER (from the floor):   Can I comment on  that?
    
         CHAIRMAN:  Sure.
    
         SPEAKER (from the floor):   Well, we have taken clean sand  in  the
    Ducon filter, and we have put in dust.  We look at the  surface;  and
    let's take an ordinary kerosene flame, where we sucked  the  smoke right
    through the bed, we get the surface black.  Now,  I don't know whether
    you want to call that "cake7  or not.  Let's put it this way.  We see
    penetration into the bed about  a half-inch, and it's a  gradient  in
    color; so the surface is much,  much blacker than  anything else.  So
    you look at the bed, and at the top the surface is black, you say,
    "Oh, well, it's all there."  But if you want to call  that a layer,
    it's a hell of a thin layer.   It's so thin that—well,  it's hardly a
    cake.  Now, we only horse around with pressure  drops on the order  of
    six inches at most.  If we let  the pressure drop  build  up to  several
    pounds maybe you would see a  layer that would be  a more significant
    layer.  But just taking the ordinary fixed bed  pressure drop correla-
    tions, and assume a particle  that has collected—a dust of  a  few
    microns diameter—and you will  see that the layer has to be almost out
    of sight, and you've already  got a tremendous pressure  drop.
    
         So I don't know whether  I  am answering the question; but the
    layer that you would see, if  you had a layer, would be  hellishly
    thick, put it that way; and I suppose that's really what Dr.  Parker
    is saying.  He got away with  this correlation on  the basis  that  it
    is more impaction than layer.
    
         DR. PARKER:  Right.  Well, a lot of people have proposed that
    granular bed filtration would be similar to fabric filtration,  but
    this seems to be a basic difference between the two.  It is a lot
    more difficult to build up a  discrete cake on the surface of  a  bed
    of granules.
    
         CHAIRMAN:  Yes.
    
         MR. GOREN:   Simon Goren  from the National  Science  Foundation.
    With regard to your bench-scale experiments, would you  tell me what
    the aerosol test particle was,  the gradient velocities, the grain
    size, and to what extent were your beds loaded, or cleaned  very
    frequently.
                                     535
    

    -------
         DR. PARKER:  We used polystyrene particles ranging fron 1/2  to
    two microns, and in very low concentrations,  so that the total
    amount of participate collected was small  enough to assume that the
    bed was clean.  We did not take the granules  out and wa'.h them after
    each test, but there were very low concentrations of polystyrene
    particles.  Superficial  space velocities were around 40 centimeters
    per second, probably ranging from about 25 to 65, but I'm not certain
    about that.  We tested various types of bed materials.   We looked at
    glass beads about 1 millimeter in diameter.  We looked  at iron shot
    ranging fron 500 microns to 1 millimeter.   We looked at sand, which
    was an average of about  400 microns; coarse sand, and there may be
    others.  I can't think of any now.
    
         CHAIRMAN:  Thank you very much.  Were there other  consents or
    questions?  I thought I  saw one more hand  over here. Okay.  Let's
    see.  Maybe just a couple of comments.
    
         I think certainly the need for experimental data,  as it has
    been made in several comments, is very critical  and very important
    in terms of understanding and developing an effective particulate
    control system that is going to be required for pressurized fluidized
    bed combustors.  I think the other point that was raised over here is
    certainly something that we would agree with, and I think most other
    people would concur with, in terms of the  need to have  more work  to
    extend our understanding of what the tolerances are for particulates
    and for deposition from fluidized bed combustion systems, building
    upon the broad base of knowledge which does exist, but  has not really
    been fully understood for systems where you have limestone beds with
    char and ash coming off the beds, an area  which certainly requires
    more definitive work if we are really to expeditiously  move forward
    and develop commercial systems.
                                    536
    

    -------
                             INTRODUCTION
         DALฃ KEAIRNS, CHAIRMAN:   We will  now have three papers on noving
    beds and finish up with a paper on  participate control for fluid bed
    combustion processes.   The first paper which we will have on moving
    beds is entitled "Particulate Renoval  from Pressurized Hot Gas."
    It will be presented by Hiroshi Teradu of the Babcock Hitachi Company.
    He graduated fron the N'agoya  Institute of Technology and entered
    Hitachi Research Laboratory in 196n.   He is mainly engaged in research
    on conbustion oscillation, nitric oxide emission fron combustion pro-
    cesses, and fluidized bed combustion.  He is now the chief researcher
    for the coal gasification program contracted with the Resources and
    Energy Agencv.
                                    537
    

    -------
                              Paniculate Removal from Pressurized
                                            Hot Gas
    
                                        Reijiro Yamamura
    
                                 Japan Coal Mining Research Centre
                                          Tokyo.Japan
    
                                         HiroshiTerada
                                     Babcock Hitachi Company
                                        Hiroshima, Japan
    
    
    
    ABSTRACT
    
           This paper describes cold and hoc  test programs for developing a new parciculate
    removal system which contains moving bed  filters  and fludiized bed regeneration of
    alumina balls.  Based on cold modelling ttscs studying si ch problems as movement of
    ball, in the bed. control of ball discharge- rate  and dust removal efficiency, we have
    concluded that this system should be very feasible.   Hot gas programs have been carried
    out in the use- of a one-sragc test filter set for the raw gas line of a 5 T/D pressurized
    coal gasifier in Vubari City.  We confirmed that  we  could attain high removal efficiency
    of about 90 to 97%.  This indicates that  a two or three-stage parffculate removal system
    will satisfy the inlet condition of a gas turbine.
    
           As you know, high temperature dust removal systems are required for fluidized
    bed combustion or for gasification in combined cycle power generation as well as for
    hij^h temperature desulfurization.  Dust removal systems will require rapid development
    as electrostatic precipitators and other  conventional techniques will not be enough.
    In the United States many projects are under study  as is demonstrated by the attendance
    here today.  In our project, we are studying and  developing a filtration system usinp
    a moving bed consisting of ceramic balls.  Although, in Japan, no pressurized FBC
    projects have been started yet, gasification projects have been undertaken since 197"ป.
    We are focussing much attention on the development  of high temperature dust removal
    equipment as one of the important elements of the gasification project.  1 will explain
    the outline of our program here.
    
           By the way, we at Babcock Hitachi  and Coal Mining Research Centre in Japan have
    been assigned to this research by the Resources and Energy Agency of the Japanese
    Government.
    
           Figure 1 shows the concept of our  system.   Dirty gas will be cleaned after passing
    through the moving bed filled with alumina balls.  Dust containing alumina balls will
    enter into a separator beine controlled at a suitable flow rate.  In this separator the
    dust is removed from the balls, and the balls are heated up if necessary.  They will
    then enter the moving bed filter again.  The important technical points of this system
    are mentioned on the figure.
    
           Figure 2 shows our research and development  schedule of a moving bed filter to
    realize the concept mentioned in Figure 1.   Our schedule has been set up to keep the
    pace with the development of a coal gasifier.  Starting from a feasibility study and a
    conceptual design in 1975, we launched tests using  cold model equipment in 1976.  In
    this period, we tested the dust removal performance using simulated dusts.  In 1977, we
    ran a recirculation test in the system which included dust separation.  In parallel with
    this, we are carrying out a hot gas test  with a test rig connected to a 5 T/D gasifier.
    The plan is underway to construct an 8,000 normal cubic meter pilot plant for a 40 T/D
    coal gasifier.
    
           Today's report is focused on the cold test and hot gas test results (see Figure 3).
    In the cold model tests, we tried to have a smooth  flow of alumina balls with a satis-
    factory flow rate control, and also measured dust removal performance.  The main parts
    of equipment are made of clear plastic.  Alumina balls supplied from the feed hopper will
    move through the moving bed filter with a moderate  speed, and the dust will be separated
    in the fluidized bed separator.  After that,  the  balls return to the moving bed filter.
    The simulated dust supplied from a constant dust  feeder will be suspended in the air
    stream.
    
                                              538
    

    -------
     HEAT
     EXCHANGER,
    ATMOSPHERIC |
     SEPARATOR
                  [SEPARATOR
                     AND
                  [ BALL HEATER
    T
     I
            (5) DUST SEPARATION
            1(6) HEATING OF ALUMINA BALL
        A ALUMINA BALL
    
    -At-,  'N
               GAS OUT
                                                  (1) STRUCTURE OF
                                                     MOVING BED
                                                  (2) C'JST REMOVAL
              FLOW RATE
              CONTROLLER
                   | ALUMINA BALL
                   a      OUT
                  Figure 1. Contact of Dim Removal System* end Its Problems
    
    FEASIBILITY STUDY
    CONCEPTUAL DESIGN
    COLD MODEL TEST
    PRESSURIZED HOT
    GAS TEST
    PILOT PLANT
    8,000 Nm 3/h
    GASIFICATION
    COMBINED CYCLE
    POWER SYSTEMS
    '75
    T
    >
    i
    t
    OESI
    CON
    '76
    t
    \
    >
    t
    F
    '77
    
    rousT
    k
    Y.
    '78
    
    '79
    
    REMOVAL
    FRECIRCULA
    STSTEMS
    1
    WTfซ:f RIO
    iCONSTRUC
    1 T
    ION
    f
    MOT CAS TEST
    ON AN
    STRUC
    0
    TIONj
    RUN
    51/0 GASiriER
    i
    301
    
    k
    NINC 1
    T
    ซOI/oGASlVlCATIC
    c
    I* PO
    KERF
    LANT/
    1
    rEST/
    '80
    
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    >
    k
    >N PliNT 1
    
    ป
    
    
    REMARKS
    
    
    5 t/e GASIFIER
    (YUBARI CITY)
    40 t/o GASIFIER
    (YUBARI CITY)
    RESOURCES AND
    • ENERGY AGENCY
    COAL MINING
    RESEARCH CENTER
                      Figured R & D Schedule ol Moving Bed Filter for
                              Presuirind Hot Ga Cloning
                                    539
    

    -------
                         OUST MONITOR
                                              FEED HOPPER
               FABRIC
               FILTER
    MOVING BED FILTER
    
    
       DUST MONITOR
                                                                  CUST FEEDER
                  CYCLONE
                   FLUIDIZEO BF.O /
                   SEPARATOR
                                                                     COMPRESSOR
                             Figure 3. Schematic Diagram of the Cold Model Test Rig
    
    
           Figure U shows an outside view of the cold  test  rig.   In this case,  beU depth is
    500 mm.  The partition plate is one of the  important  elements  of the iroving bed filter
    as the movement of alumina balls near  it will tiiifer  significantly depending on the
    type of partition plate.  In this case it is a  louver type.
    
           In Figure 5 you can see the pneumatic recirculation  line for system rccirculation
    tests.  The fiuiJizcd bed separator is located  above  this line.
    
           In the cold model tests the selection and supply method for the simulated dust, is
    very important, because the simulation of their physical properties affects the success
    of this test.
    
           In Figure 6. a sample of char  collected  from the test gasificr is shown (Column A).
    We also used the simulated dust as shown in Columns B and C.   We are going to mention
    the results of our cold model test with several figures now;  but,  we would like to say
    beforehand that our tests results can't be assumed to be quantitatively a true simulation
    of dust removal from actual gases.  Our test was only for setting up a qualitative con-
    cept for a design.  Therefore, the quantitative study should be made from the results
    of operations with actual dust-lader  gases.
    
           Figure 7 shows the effect of bed depth and  alumina ball diameter on outlet dust
    concentration.  Three different ball  diameters  were investigated,  namely 0.5, 1, and
    2 mm, untjer the condition of a gas velocity of  0.5 n/sec, and the  inlet dust concentration
    of lgm/mj have been used.  As you can  see,  the  outlet dust  concentration decreases
    logarithmically as the bed depth increases.  It is very interesting here that the outlet
    dust concentration increases in the smallest diameter of 0.5 mm compared with 2 mm.
    
           The crussplotted graph of outlet dust concentration  against alumina ball diameter
    directly shows this tendency.  In short, the outlet dust concentration is the least for
    the ball diameter of 2 mm in this case.  Consequently,  the  highest dust removal efficiency
    can be obtained in the 2 mm ball diameter.  This tendency can be seen as the type of
    dust varies; therefore, ic can be considered that  an  optimum ball  diameter must exist.
                                                540
    

    -------
         Fijurt 4. Phosoflrtph of tht Cold MocM Tซt Rifl
    FigurcS. Ptiotogriph of th* Moving Bซd FilMr of Cold MocM
    
    
    
    
    
                            541
    

    -------
                                      to
             05
       BWTIOE
     Figured Pfoptfty of Sซnutat*d Dun for CoU Model Tut
                                00.1
    100     30O     500
       BED DEPTH (ren>)
       12345
    ALUMINA BALL OIA. (mm)
      Figure?. Effect ol Bซd Depth & BaO Du.  Outtat Out Cone.
                           542
    

    -------
    OUTLET DUST CONCENTRATION (g/Nmป)
    P P - w o
    •ป v •* wo o O
    MOVING RATE OF BALL
    6 Cm/min
    INLET OUST CONG.
    1 g/Nm'
    _jf -~8~"
    ^r
    BALL DIA. 1mm
    BED DEPTH 100mm
    
    A 	 a~"
    A^HT
    X-5T
    BALL OIA. 2
    BED DEPTH 30Omm
                                 0.5
                          6AS VELOCITY (m/ซ)
                                            1.0
                                                   ^
                                                   z
                                                   o
                                                   til
                                                   o
                                                   o
                                                   o
                                                     50
                                                   o
                                                   ujO.1
    GAS VELOCITY: 0.5m/*
    • INLET DUST CONC.1g/Nm>
    ^ 	 -g
    BALL DIA.
    HFn OFPTH
    
    	 9
    1mm
    
    Jf^* 	 *"
    BALL DIA.
    BED DEPTH
    1 1 1
    Zfflffl
    300mm
    0    2   4   6    8  10
    MOVIN3 RATE OF BALL(cm/min)
                    Figurซ 8. Effect of Gas Velocity and Moving Rate of Ball on Outlet Dust Concentiation
          Figure 8 shows the effect of gas vclocit/ .tnd moving rate  of  balls  on the outlet
    dust concentration.  We can sec from this figure that ns  the gas velocity becomes
    low, the outlet dust concentration decreases; and as the  moving  rate  of the ball in-
    creases, the outlet dust concentration will increase to some extent also.   This increase
    seems to be larger with the increase of the ball diameter.  But  as  the moving rate of
    the balls continues to climb, its ultimate effects seen to be minor.
    
          The dust accumulation on alumina balls of a unit volume in the  moving bed varies
    with the conditions of the moving bed and inlet gas.  In  other words,  when the inlet
    dust concentration is high or the moving rate of the ball is low, accumulation will be
    high.  As can be seen from Figure 9, the dust removal efficiency increases with the
    increase of an average dust accumulation in the early stage; but, it  reaches a peak at
    some point and afterwards it decreases with the increase  of average dust  accumulation.
    Therefore, we can see that there is a critical point in the relationship  between
    average dust accumulation and dust removal efficiency.  For this reason,  we consider it
    totter to think carefully on these critical points.
    
          When connecting with a gas turbine, small diameter  and good quality are required
    for dust at the turbine inlet, as well as for the amount  of dust.   Aside  from the
    quality of dust, the diameters of dusts collected from the moving bed filter outlet
    were compared with those at the inlet (see Figure 10).  As you can  see,  the average
    dust diameter decreased at the outlet compared with that  at the  inlet.  And therefore,
    this moving bed filter can be considered to be effective  for the dusts smaller than
    10 microns.
    
          Figure 11 shows the pressure drop through the filter for varying conditions of
    ball diameter and distance from gas inlet.
    
          In the following several figures, we will mention hot gas  tests connecting our
    moving bed filter with a gas line of 5 T/D gasifier under investigation at Yubari City
    in Japan.
                                               543
    

    -------
           0          5           10         15          20
              AVERAGE  OUST  ACCUMULATCN  (Q/L   BAa)
    
    
          ttyan 9. Oust Removal Efficancy vs. Atmagt U- 
    -------
                        f
                           too
    
                           ao
    
                           60
    
                           40
    
                           20
    
                            0
        INLET OUST CONC.
                   0 ex
    GAS
                             GAS VEL.
                             MOVING RATE
                                          20   40   60   60   100  120
                                        DISTANCE FROM GAS INLET (--)
                                Figure 11. Prcuun Drop in Moving Bed Filter
    
    
    
          Figure  12 shows a  flowsheet of the hot gas test equipment.  The design condition
    of  gas  flow rate is 200  KnjJ/hr. the pressure is 10 Kg/craZ, and the temperature is 700ฐC.
    The main parts of equipment will be pressurized.  The flowing rate of alumina balls was
    controlled by a rotary valve, and dust concentration was measured with a cylindrical
    filter  paper at botn the inlet and outlet of the moving bed filter.  As the Oow of the
    alumina balls was run through, the running time was only 1 to 3 hours.
    
          Figure 13 shows an outside view of the hot gas test equipment.  Here we can see
    the moving bed filter and feed hopper.   The gas-supply sectional area in the moving
    bed filter is 1 foot by  1.5 feet,  and the bed depth is 8 inches.
    
          Figure 14 shows an outside view of the rotary valve used to control the flow rate
    of  alumina balls.  We can see a spent ball hopper under the rotary valve.
    
          Figure 15 shows the dust removal  performance in a hot pas test.  We can see. just
    as  in the cold test, that the outlet dust concentration increases with the gas velocity
    in  the  range of 0.2 to 0.6 m/sec in the moving bed filter.   The curve of the dust
    removal efficiency shows a high rate of 90 to 97 percent.  The figure on the right
    side shows the effect of the moving rate of alumina balls.   The efficiency decreased
    with the increase of moving rate of the balls,  but it eventually becomes asymptotic.
    
          As you can see here,  these tests  were carried out  under the condition of pretty
    high dust accumulation,  so it will be expected that the  removal efficiency must be
    raised  further.   Anyway, these values cannot meet the demand of the gas turbine.   In a
    commercial operation,  it will be necessary to provide for 2 to 3 stages of novinz KcJ
    filtration.
    
          Figure 16 shows micrographs  of dusts sampled at both inlet and outlet of the
    moving bed filter in the hot gas tests.   These  are char  consisting of about 50X fixed
    carbon,  as already mentioned.
    
          After completion of the test,  the alumina  balls were  taken out through the
    fluidized bed separator.  In this  case,  the char is very flaky,  and it easily separates
    from the balls.   During  the present  tests,  the gas  temperature is about 500ฐC.   There
    is not ouch adhesion of  tar to the balls.
                                              545
    

    -------
    RAW GAS LINE
                                                     PRESSURE
                                                     CONTROL VALVE
          FLUIOIZEO BED
          SEPARATOR
    GAS FLOW RATE :  200 Ntn 3/h
    PRESSURE     :   10 Kg/cm*
    TEMPERATURE  :  700 ฐC
                  Figure 12. Simplified Equipment Flomhett of Hot C i Tett
                Figure 13. Photograph of Moving Bed Filter of Hot Gซ Ten Rig
    
                                      546
    

    -------
                F.jure 14. Photograph of Rotwy Valw of Hot CM Tซ Rig
    1
    BED DEPTH   300—
    BALL DIA.      2-
    INLET OUST CONC
                                  X
      BED DEPTH    300"
      BALL DIA.       2"
      INLET  DUST CQNC.
            0.2   OA   OS   OJB
          GAS VELOaTY (V.)
    02468
    MOVING RATE OF BALLfX.)
                Figun 15. Effect of CM Velocity and Moving Ratป of Ball on
                            Outlet Dint Concentration
                                   547
    

    -------
    M.B.FILTER INLET
    ME AN PARTICLE DIA.9.MI
    M.B.FILTER OUTLET
    MEAN PARTICLE DHL
    

    -------
                         AiUM.'NA BALL
                 MCVltC BEU
                 FILTER VESST.I
              RA.V
    ^•v
       AI.UMIMA BAIL
    FUJIL>2LD  BED
    BALI  RtGOCRATOR
              LIFT GAS
                                                               :  710  *C
    •  COLD MOOEL TEST
         IT  V
    -------
                             INTRODUCTION
         MR. KEAIRNS:   This is  the  session on Emission Control and
    Participate Removal.   I am  Dale Keairr.s with Westinghouse R&D Center,
    and I'm co-chairman of this session with Dennis Drehmel, who is with
    the Particulate Technology  branch of  EPA.   It  is a pleasure to have
    the opportunity to chair this session, which I think covers a very
    important aspect of the problem of fluidized bed combustion, and a
    very challenging problem in the sense that  one has a variety of
    moving targets.  Depending  on how you design the bed and what beds
    you are talking about, the  particulate control people don't know what
    they have to deal  with coming in, and the turbine tolerance require-
    ments are somewhat of a moving  target, depending on the design, and
    as we increase our understanding of what the tolerances are.  Then
    there are the environmental  aspects,  in terms of what tolerances will
    be required from an environmental point of  view, both from dust
    loading and particle size distribution.  So I think the boundary
    conditions on this problem  present a  very interesting and a dynamic
    problem.
    
         I would also then like to  mention, and hopefully it is being
    announced in the other parallel  sessions this afternoon, that the
    first paper will not be presented.  Professor Gut finger will not be
    here this afternoon, and so that paper will not be held, although it
    will be included in the proceedings of the  conference.
                                    550
    

    -------
                               Particulate Removal from Hot Gases
                               Using the Fluidized Bed Cross-Flow
                                                Filter
                                   Chain Gutfinger, G.I. Tardos and
                                             David Oegani
                                Department of Mechanical Engineering
                                Technion - Israel Institute of Technology
                                             Haifa. Israel
    ABSTRACT
    
           This work describes a granular  filter  for separation of particulars from a hot gas.
    The **rtvice operates in a steady state  mode by means of continuous introduction of clean filter
    granu.es from the top and removal  of dirty granules fron the bottom.  The qas flows trans-
    versely across the moving active filter material.  A bench scale sand filter of 100 cm; cross-
    section was constructed and tested during this work and its filtration and hvdrodynamic charac-
    teristics are reported.  A theoretical model  for the computation of filtration efficiencies is
    also presented.
    
    
    IirTRODUCTION
    
            This paper deals with filtration of hot gases containing particulatcs in the size
    range of 0.01 to 10 urn  by cleans of a  moving, continuously regenerating cross-flow filter.  The
    existing methods for rcraov.il of particles in  this size ranqo are electrostatic precipitation
    (0.01 - ID urn);  packed beds (0.01 - 100);  high efficiency-cyclones (0.1 - 3.0);  cloth collec-
    tors (0.1 - 60);  and liquid scrubbers (0.3 - 100).  Unfortunately, these methods do not lend
    themselves to continuous operation at  elevated temperatures either due to their very high cost
    (electrostatics), filter clogging  (packed beds), high erosion rates or material limitations
    (cyclones, bag filters, etc.).
    
           During the past several  years the fluidizcd bed filter has been extensively investigated
    by different authors [l,  2,  3,  4,  5, 6].   The reported results ir.di.atc clearly that fiuidizcd
    t*d filters collect efficiently particles in  the size range O.01 - 1O urn and have the advantage
    of regeneration by continuous withdrawal and  replenishment of bed material.  The disadvantage of the
    fluidized bed as a dust collecting filter is  in its limitation to low qas velocities.  These in
    turn require high filter areas  for flowrates common to industrial systems.  Thus, even thnuqh it
    was clearly demonstrated that a particle-bod  is a useful means for cleaning dirty gases, it was
    necessary to expand further effort toward the investigation of a regenerative granular bed filter
    J.ble to operate at high gas velocities and elevated temperatures encountered in power plants,
    cement factories, fluidizcd bed combustion systems and/or gas turbine cycles.
    
           The present work evaluates  the  cross-flow filter as a continuous separating device of
    small particulatcs from a gas stream.   Experiments performed with du~ty gases at 30 C and TOO C
    indicate that the cross-flow filter features good separation characteristics, low pressure drop
    and high gas flowrate capacity.  The experiments and theory reported in this paper can serve as
    a basis for the design of -. dustrial granular filters.
    
    
    FILTRATION EXPERIMENTS
    
           The laboratory scale cross-flow filter device used in this work is presented schematically
    in Figs. 1 and 2.  It is essentially a moving sand bed.  The filter operates in a steady state
    node by cieans of continuous introduction of clean granules from the top and removal of dirty gra-
    nules from tho bottoa.  The gas stream flews transversely across the moving active filter material.
    Fluidization of the granules is used in order to allow the removal of dirty filter elements froa
    the bed.  The sand bed is held  in  position by two 45 mesh brass screens on the gas inlet and out-
    let sides.  Thซ active filter thickness is about 10 cm and the surface area normal to the gas
    flow is about 100 cm*.  The device is  operated with quartz sand in the size range 2O - 40 mesh
    (40O -  810 u).  This sand is capable  of continuously withstanding operating tcnperatures up to
    1200ฐC.
    
                                               551
    

    -------
                              FILTER ELEMENTS
                              INLET
    FLUIDIZATION
    AIR
     GAS
     OUTLET
     ...._.  /30MESH
     SANฐ  140 MESH
    FILTER ELEMENTS
    OUTLET
             Figure 1. The fluidizad bed croo flow filter
                     552
    

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    Figure 2. View of the f luidued bed cross-flow filtration system
                         553
    

    -------
           The device is used to clean the exhaust gases coning from a 2.5 HP "Peter' Diesel engine.
    These gases were chosen in order to test the filter with industrial pollutants and to reveal
    specific difficulties which nay arise during industrial use of the system.  The test lovp is
    given schematically in r'ig. 3.  The exhaust gases pass through a cooler and a cyclone before they
    enter the filter.  This precaution is necussary in order to renove coarse oil and water drops
    from the gases before they reach the inlet screen of the filter.  For high temperature  .ests the
    cooler is disconnected.  A gas dilution system with compressed air is also connected to the gas
    inlet in order to increase the gas velocity in the bed.  The dirty gas nay be passed either
    through the filter or through a by-pasr.  The gas is sampled isokinetically from a point downstream
    the filter.  A pressure tap upstrean the filter is connected to a differential manometer.
    
           The pressure drop through the filter was measured as a function of the superficial gas
    velocity.  These experiments were carried out with compressed air.  The results are presented in
    Fig. 4, for differei.*ii sand sizes.  The total pressure loss through the device varied between
    8 - 21 en HO for all gas vel'.'.-ities between IS - 60 cra/.~?c.  The "smoke* produced by the Diesel
    engine was characterized usir • a TSI and a Royco particle size and concentration tr/mitcrs [?].
    A typical smoke characteristic is reproduced in Fig. 5 in terns of the number of dust (carbon)
    particles per cm- ot ga:; vs. cho particle size* for the specific case of 1 IIP load o.  tl.i engine
    and JOOO rpm*  Au seen, the maximum numh'.r of carbon particles in the smoke is in the diameter
    rai.gซ of 0.1 - O.iy, while particles coarser than lu are almost absent,  from this figure the
    weight concentration of particulatcs was calculated as 1.4 g/n .  These data arc subjf.- *. to appre-
    ciable changes depending on the engine Ic**!, amount of dilution-air and particle con*:nt.
    
           Kig. 6 presents dust separation characteristics of the fluidized bed cross-flow filter
    obtained at roon temperature (JOฐC).  The filter was tested with dust naturally present ir. a com-
    pressed air stream and with smoko produced by the engine.  The difference between particles from
    these twn sources is in their sticking properties.  The compressed air dust is dryer ar.d therefore
    less sticky.  This is the reason why carbon particles are separated with somewhat higher efficiency
    than atmospheric ttust.  The filter was o|>cratcd in the packed and fluidized bod mode with gas velo-
    cities between 18 - SO cm/sec, for about 50 hours without a sensible pressure drop increi-e in
    time.  Approximately 30 kg of sand was continuously circulated through the system during this
    period.  No efficiency decrease was observed in time throughout the experiment.  As seen in the
    figure, tho efficiency of the packed bed decreases from about 70\ to OO\ as the cas velocity
    increases while the efficiency of the fluidized bed decreases from about un\ to 71* for similar
    conditions.  The ouch higher efficiency of the fluidized bed is due to electrostatic charges
    produced on tho bed granules during fluidization [&].
    
           Thcie experiments show that the cross-ilOK filter has the good properties of the
    fluidizeti bed filter such as high efficiency* low pressure drop and continuous operation and
    in addition allow-, high gas velocities through the bed.  Another good feature of the filter is
    its vertical configuration which requires less floor si>ace as compared to tho fluidized bod filter.
    Tho active filter area may be increased by increasing the height of the bed.  The filler material
    (sand) consumption between two consecutive cleanings proved to be very small.
    
           Fig. 7 nresents total efficiencies, n, of the cross-flow filter as a function of dust parti-
    cle diameter, with -.he gas temperature as a parameter.  The experiment was carried out with snoV.e
    from the Oi> jel engine, diluted with hot compressed air.  The gas velocity was U =87cm/sec.  The
    results were obtained at mean gas temperatures of 30, 195 and 205ฐC.  The influence of elevated gas
    temperature on the total efficiency may be observed:  efficiency increased for fine dust particles
    (2r <0.5u), whereas the efficiency of coarser particles, (0.5<2r 
    -------
                                               rn.TOป
    n
    MTUKTUt
              -04-
            CTOOK
                                                         tXBTT riLTOI
                                                         O.CMMT  *CMOWU.
                           •THUS
          MWTKUS
    VC MDMU. VATCM
    fllCT
    1'
    ,
    HTia co
    -------
                                               Sot*
                                               SOmttk-
                                               40lMih-42O-StOu
                         Got  moeity to H* bed.
    
       Fig/an 4. Relationship between pretsure drop *nd vปtoerty in the Ihjidind
                             bed cross flow filler
           	..
          aoi   aoz       o-os    o-i     0-2
    
                       Owl porlicto •)<• 2rp [/*]
    
    
    Figura 5. Oust parlid* conesntrttion n pvtid* til*. Sonka produced by
                          a 2.5 hp diซel engtn*.      	
                            — POUMT: 1 hp Rotations: 3000 rpjit.
                                  556
    

    -------
    IUU
    90
    80
    T 70
    u
    1 60
    *:
    S I 50
    il
    40
    0
    i iii iii
    a
    o
    0 A A o o -
    • A oA o oo
    x ' X
    f . •
    X X
    A A -
    A A A
    -
    Eiporiitwital
    ro-u0- IB cm/tec \cซ>mPซซ8ซd (L-l5cm)
    Packed K.v.nsm/MC ฐ"
    . . „ 'ปmoke (LซIOcm)
    Fluidizedf A-U0ซ 60 cm/we
    69(1 \a-Uo'87cm/*ec J
    I III III
    01 002 005 01 02 05 1-0 2 5
    Dust particle  diameter  2rp [p]
        Figure 6. EKiciencv of the crou llo* filter
              2040 ireth sand d -=04)
    

    -------
           100
            80
    S
        I  "
            20
                    ---  30C
                    Sar.d 20-40 oe*h  (t-0.4)
                    CAS velocity  U -87  cn/iec
                    Filter thickness L-10 cm
               0.01
                           0.02
                                             0.05
                                                          0.1
                                                                       0.2
                                             DUST PARTICLE DIAMETER  2r (u)
                                                                       P
                                                                                      X
                                                                                         0.5
                                                                                                     1.0
                                 Flgur*?. EHiciซncy of aoo-flow filtar at aWvstad ga tempoituto
    

    -------
    where, c, is the porosity of the filter bed and a, is the filter element (granule) radius.
    Typical values of granular-filter porosity, c, are in the range O.4 - O.S,  hence, the total
    efficiency n, depends mainly on three paraaeters:  filter height, filter element dianeter and
    single filter element efficiency, E.   Of these only the latter is know a priori and has to be
    either computed or measured experimentally.  We suamarize now the basic steps of the filtration
    theory leading to the computation of, E.  A more detailed exposition on this topic is given in
    the literature [?, 8].
    
           The analysis considers a single dust particle approaching a spherical filter element.  It
    is assumed that any dust particle hitting a filter element is retained by the filter.  The mecha-
    nism of separation nay be inertial, interceptional, diffusional, electrical, etc., depending on
    the combination of forces which act on the dust particles.  Trajectories of these particles in the
    vicinity of the filter element nay be calculated.  Out of all trajectories one is interested in
    the "limit trajectory," i.e., the trajectory which just misses the collector, (filter elenent).
    Due to the axisynaetrical nature of the problem, any trajectory contained within a streaatub*
    generated by the limit trajectories will meet the collector resulting in particle separation.
    Hence, for a filter element of diameter 2a and limit trajectory streamtube of diameter 2b. the
    single element efficiency is defined as:
    
                             E - (|,2                                                    ,2)
    
           The equation of the trajectory of a dust particle approaching a filter element, was presen-
    ted by different authors, [l. 3. 8, 12]:
    where x is the position vector, i    ,
    and u is the gas velocity.  Eq. (3)  may be put in non-dimensional fora by using
    
                             U • u>Uo. x - x/(a * r ), T • U0t/(a +r )
    
    which yield
    
                             ..2?   1 * *..  -   ^    ?__a(l * "J
                                                                                         (4)
    
    
    Here, U is the dioer. .ionloss gas velocity, St * 2Cp UQr 2/(9ua) is the so-called Stokes number and
    R  • r /a is the Interception parameter.  The equation of motion as written above is general enough
     P    P
    to incorporate any effect that influences the notion of the dust particle.  This is accomplished by
    introducing the proper effect through the external force F   .  If several effects coexist, they
    may be Added together at this point.
    
           Equation (4) Bay be written for the particular case where only the effects of inertia,
    interception and diffusion is considered as [7. s]:
                                                                                         (5)
    where the diffusion velocity Vn can be computed as follows [l3]i
                                  D
                             U        Pe N dR
                              o
    
    As seen, V  depends on the Peclet number, Pe. the dust particle concentration, N, and the concen-
              ts
    tration gradient, dN/dR.  The latter two quantities are calculated fron the diffusion equation and
    substituted bock through Eq. (6) into Eq. (i>.  CT. (S) nay be integrated numerically.  This integ-
    ration leada to the limit trajectory froti which the singlo filter element efficiency, E, follows
    directly froa Eq. (2).
    
    
                                                 559
    

    -------
           rig. 11, presents confuted values of  E as  a  function of the S'_c>:es nunbcr. St, with Peclot
          , Pe, as art  better than the predicted efficiencies.  This
     ifference it: due to electrical charging of  the filter granules by friction effect, which improves
     erration ef ficiei.cy.  Fig.  10, reproduced  fron  a previous work on fluidized bed filters L^J*
     how:ป the effect of electrical chare on filtration  efficienc.
    show:, the effect of electrical charge on  filtration efficiency
    
           It can bซ clearly seen that the  theory  predicts reasonably well efficiencirs in uncharged
    filtration systems.  It is known that charging due  to friction is reduced at elevated tempera-
    tures and/or high gas humidities, hence,  the theoretical  results are to ix: preferred for a con-
    servative design of such systems.
    
    Use of Present IXita to Predict Filter Pertoi.-n.vico
    
           Fig. 11 is a design nomograph based on  experimental data given tr. Fig. f>, together with the
    measured pressure drop data.  The designer first selects  a qas velocity and a filter thickness,
    A horizontal line at constant value ol  L  will  yield n as  a function of dust pjrticl'i diameter as
    will as the pressure drop through the filter.   Alternatively, givon the minimum ace. ptablo
    efficiency for a certain dust diameter, the designer car  look >ip directly tho fil'.ci  depth, L,
    arid the corresponding pressure drop.  A similar noirogr-iph  nay bo obtained for the caปe of high qas
    ti'ioiH-ratu.';3 from Fig. 7 or by using theoretically  predicted data.
    
    CONCLUSIONS
    
          The cross-flow granular filter rpovcd to separate snail p->rticulates from n eoi.tomirated gas
    stream with reasonable efficiency.  Hy ซi  corresponding increase of  tho filter thickness this effi-
    ciency may be dramatically improved.  Tho device can bo used at low as well  as at higii gas tempera-
    tures in places where dirty gases arn produced.
    
          A full sire filter may be designed  using the  experimental or  theoretical data rc.*x>rt:ed in
    this |Hii>er.  Tho design should be carried out  using Fig.  11  for the case of  low gas tei-jซraturcs
    and using theoretical data from rig. h for tiio case of high  qas temperatures.
    
    
    ACKNOWLEDGEMENT
    
           Tho sponsors of this research. KFA JOli-h and tiCRD. Israel arc gratefully acknow;edged.
    
    NOMENCLATURE
    
           a           -  filter clement  (granule) radius
           L           -  distance of limit trajectory  froc* OX.  axis
           C           -  Tunninqhan correction  factor
           il           -  particle diffusion  coefficient
           f>(b/a)     -  sinqle sphcr*> efficiency
    
           E ป4 (~—•) PC    -  pure diffu3ic:ial deposition efficiency.
    
           F           -  external force acting on particle
    
           L           -  filter thickness
           m           -  rasa of dust particle
    
                       -  dust particle concentration
                       -  dust particle concentration,  dinensionlcss
                                                  560
    

    -------
    0-002
     0001
          OOOJ
    0-01
          0-1
    
    Stokm  Numbtr  St
    10
                  Figum 8. Theoretical fJngta fitter element oHicfency varan ttckn nuntbtr coraktering
                         intfliti and diffinkxvB) dปpoซtion n coraunt twd porotity. c • 0.4
                                           561
    

    -------
       2
        Ul
         u
         ฃ
         u
         V
    
    Ul   ?
    rs>
        a.
        w
        oป
        to
      50
    
    
      20
    
      10
    
      05
    
      02
    
      0-1
    
    005
    
    
    002
    
       001
                    Theory (C'O 4)
                    •          • Uo "18 cm/Me
                    — — — - Uo • 33 cm/we
                    	—.—- Uo*60cm/stc
                       I	i     i      I
        x -U0* 33 cm/sec
        A-u0ซ60cm/ปซc
    1   I • - U0ซ 87 cmAec
    I _ i       _
                        > smoke
                     002   005  0-1    02     0-5    1-0   20     50
    
                                          Oust  particle diameter 2rp
    
                                    Figure 9. Co(np*iion of •xpcrimental dau with theory
          10
    

    -------
        I
      05
      g  02
     bl
         0-1
     U
    ^005
     >ป
     U
     '5
      0-5
      0-1
    005
    002
                                              Theory  Eซ0-4, Uo" 18 cm/sec
                            Experimental
    Uoฐ 18 cm/sec
    Aerosol
    Lotex oorosols
    Carbon powder
    Atmospheric dust
    Zinc powder
    Neutralized
    bed
    •
    ซ
    a
    e
    Charged
    bed
    •
    
    •
    *
                                      Chorqcd  Bed
         001      005   0-1   0-20-51      235
                     2rp[/i]  Dust particle diameter
           Figun 10. ExpVBiwntsI ซnd tti*cw*ticซl vn<$* tphaซ eHicitncici in • ntutnlind ซnd •
                   ctaryd and bซd of 660n diamtttr grtnulcs (porosity c - 0.4)
                                   563
    

    -------
                                  Prusure drop. Ap(em
         O    10   ?O    3O   4O    50	60   TO   8O   9O   tOO   I!Q   120   130
       80
    
       70
    
    
    
    I  50
    o
    ฃ  40
    
    ฃ  30
    
       20
    
       10
    ^•999%
    FhjidiMd_bjd
    Cos vtlocify
    —— Uoซ60 cmAtc
    	Uoซ PT em/ปc      X
    
                        / ^J^.%
                      /
        001    OO2      005   01     02       05     10
                                 Oml pwlid* dnmtlcr 2fp [M]
                                                                                  10
                                  Prtuurc  drop. Ap[cm H,0)
                                   -y   y   ?
         0
    

    -------
                            -   dust. jซirticle  cor.cer.tratio:. at ir.fir.ity
    
                e-.'au /.    -   Svdot r.'jnbcr
                     o            .
                            -   ra'iius
                            -   dinur.sior.loas  radius
                            -   at.-r'iiol  Ciiust  particle) radius
    
                            -   lr.turci.-1-tio.'i
                               Strike.-; r.'jnfccr
                               t ine
                            -   dirw;nsior.lซ-:;s  tictu
    
                            -   1*0-; it ion w:tor
    
                            -   i*>sitiQi. vector,  ciiner.sionless
    
                            -   fluid velociv/ vector
    
                            -   fluid vป_-l\  por
                           -   t'jt.al flltt.-r  ••( f i
                               Mui'l vi>.c*j';it.y
     1.  1..  l-arutaky. L. T(iซ-xl-r.-. K. l-f<:{(ur .ind A.M.  :;<|uir<:s. .t. Air  Pol Int.. r.mtrol  A-.a.. ฃ1^,  I't71.
         f.  204.
     i.  II. !•.  M^i^sivur ar.'l  U.S.  Micklcy,  "Kv.il of Mists and Dusts  f roo Air hy hods of Kluidiipd
         Solids," Ir.-). Ji.ii  l.i.-j:.. 12 IX.
     I.  '"..  Tardon, C. <;uป f iri'(i-r ar.--|K)aition of Du-it Particlts in a  I'luidircd Bod Ciltor,"
         Ir.rjซ;l  .1. Toc-h.. !_.'.  1(74, |..  1H4.
     4.  •"..  Tarilos, !.'. Al.-i.il  and C. ^ut f ir.-icr. "tiif f u::iorul ril'.ratlon  of Dust in  a  Fluidiiod Bed Filter,"
     S.  t-.  Kr.ซ-ttinT and J.M.  b'-ci'jwri-j,  "Capture of •v.modinpor'-.pd A<-ro3ol  I'articlos  In  a Fixed and  in a
         fluidUcd tuyt.~ Oinadian .1 . _ of  Ch<:n.  Kn'j. ^2,  1174,  p. 701.
     fc.  D.  XcCarthy, A. .7." Vo"i.kr-l, K.ซ.  l-at'turr.on and H.L.  J.icknon, "Multistaifn Fluidizcd Bed Collection
         of  Aerosols."  Ind.  fn-j.  rtn.-n. ,  rr-x-'-.-r-.s ;>?s. r—v  ,  IS. i', ri70,  |>.  2t>n.
     7.  ^,1.  Tardos, ":".ranulor Hซ?.
    11.  I.b.  Stcchkina and II. A.  Fucho.  Ar.n. Occup. Hy  and
    12.  H.J.  l>ilat and A.  Prea,  "Calculated  Particle Collection r.f f icienclcs of Sinqlo  Droplets  Including
         Inortial  lapaction,  Brownian Diffusion, Dif fusiophoresls and Thernophoresis." Ata.  r.r.v.,  10,
         l'>7fc,  p.  13.
    13.  B.B.  Bird. W.E. Stewart and E.H.  Leightfoot, Transport rhcnoaena,  J. Wilny  I Son*.  Now York,
         London,  1960.
                                                       565
    

    -------
                              INTRODUCTION
    
          DALE KEAIRNS,  CHAIRMAN:   Thank you.  Our next presentation will
    be "Filtration Performance of  a Moving Bed Granular Filter:  Experimental
    Cold-Flow Data."   It will  be presented by John Guillory of Combustion
    Power Company, Inc.
    
         Pr. r.inllory received his RS frori the  University of  Southwestern
    Louisiana in  1ฐK? and t'S in nochanical  onqinoorinq fron Louisiana
    State, and a  Ph.D.  in nochanical  onqineerinq fron DHahona State.   Ho
    is a roqistored profossional  enqineor  and  holonqs to  tho  Anerican
    Society of npchanicol Fnqinoors.   His  specialty  is combustion  and  air
    pollution control.  Or. fiuillory is a  part-tine  instructor at  the?
    nivision of Fnqinoorinq, San Francisco State University.  Hn  is
    currently tho supervisor of thomal and  filter sciences at the
    Conbustion Power f.onpany, Menlo Part,  Talifi
                                     566
    

    -------
                                     Filtration Performance of a
                                    Moving Bed Granular Filter:
                                   Experimental Cold Flow Data
                                            J.L.Guillory
                                     Combustion Power Company
    ABSTRACT
    
           Data  fron jn KKDA- sponsored  c-xporimt-nt.il st.jdy  rel.itinq certain mechanical  .in  j 1 I untrjted in Fi-jure  1.
    
           iv r t i c 1 !•  collection i :; uccon[>l i shed l.y c.'iusinซ| the  part icu l,,t <•- laden  <|.is to
    .-ove r.t'ii.illy '.-jtvjr'l in cror.Mflow through an .intiulur, of ijranular collecting material
    (nedial.  Th" dovr.ward flow rate of the <;ranular bed is  so lee tod such that the
    deposition rate  of  part iculat e onto the irntiia and  its removal  rate from the  active
    filtr.itir.fi zone  r'-sult in r.teaily-.Ttate operation which  is  --| excessive deiosition  of [xirticulate  ITI the gas
    p,-i;;.".,i'l<:S.  The outer screen is r.ized  for complete retention  of media.
    
           In older  to 
    -------
    Figural.
               568
    

    -------
              corrosion associated with certain na^eous  pollutants can t>c nil. in: zed  through
              nainter.ance of olo/atcd temperatures.
    
              Relatively Flat Collection Efficiency/Particle Size Curve.
    
              The  geor.etry of tho GBF is such that  the various capture nui-cham s:ns  (e.g.,
              iripaction requiring high gas velocity arid  di: fusion r<->:uirir:g r.orc1 modest
              velocity)  can be made effective wi;.nin the Sjrr.e unit.  This characteristic
              allovs capture of a given size particle L/v '. :ie riost r-ffici'iit Mechanism
              thereby r.inir.i zitui utility eonsuniit ion.
    
              Favorable Secondary Pollution characteristics.
    
              Soluble [^articulate is not reintroduced to the i-nviron.Tcnt through use of
              liquid scrubbing r.edia.  Furthermore,  since cuf.tured paniculate  is  concen-
              trated into a small gas stream, it  is t/rซซ'?l ie.il to use very sophist ic.iteU
              (and ix-jssibly high specific utility consumption) final filtration  to limit
              atnospheric pollution as:  'Ciated with mofli.i cl'-aiiin-i.
    TKST P
    
           The objective of the tost proijran was  to  quantify the- Affect ซ,f n-rtiin design
    and process  variables on the particulate rol lection  pซ.-r t'Tr.anc-'- of a ORF.  The testing
    effoit w,is divided  into "subexper imento" represent ing specific curb mot ions of Jesign
    i!iid '.perat lonal  para-m.-ters.  The following  subexper iments will be considered  in
    detai 1 : 'J
    
           •  ThicK  Hซ'd Suhexper incnt
    
                 t  •  1 ', . J in
                 II  -  51  in
                 •;rr> =  t.'i inai (122 lป>/tt3 bulk density)
    
           •  NoTij tiaj _ Bed Sub-  (peritnent
    
                 t  =  ' .'.- in
                 If  =  ^)  in
                 "P. •-  1. 'I rjn (132 Ib/ft3 bulk density)
    
           •  :'.ri a 1 1  •1cซlij Sulicjxyer imcnt
    
                 t  =•  7.f, in
                 II  =  51  in
                 '•n -  0.8 iwii (100 lb/ftj bulk density)
    
           i:ach  oubexpor ir.ent consinted of a series  •>{  tests in which the ir.let part icul jtc
    concentration  (Li), approach velocity  (V) ,  and m -dia rate (ft) wore varied independently.
    Selection of  independent variable combinations to be tested within a given subexperi-
    mcnt were hosed  on  a Latin Square cxpf.-r incntal design.
    
    
    FACILITY DCSCPIPTIOK
    
           The system constructed for this test proaram  ia  trhcrvit ical ly illustrated  in
    Figure 2.  A positive-displacement blower capable of continuous operation at  about
     Tt". totin  tost  proarari consisted  >'. nine  subexperincnts representing  Iu4  test  points.
     Conplctc res ilts of  _ach test arc av.-ilable  in  reference 121.
                                                569
    

    -------
    r-
    -------
    5 psig and 4000 scftn supplied air to the GBF and auxiliary systems including dust
    injection air, media circulation air and fluid bed air but excluding instrusent air.
    System pressure was controlled by an automatically-positioned bypass valve.  The-
    fraction of air which flows through the main duct to the GBF was controlled by a
    pneumatically-actuated damper.  An integrating pitot-static flow sensing element
    located in the main flow branch provided both flow indication and input to the main air
    flow control system.
    
           One of the principal functions of the auxiliary air system was to provide air to
    the dust injection station.   The purpose of the dual-venturi dust injection system
    was to provide a means of feeding dust into the main air line (which was u^der positive
    pressure during operation), deagglomerate the dust from its packed condition and remove
    large foreign or agglomerated particles from the feed.
    
           This was accomplished by setting the flow through the dust injection system to
    about 350 scfm by means of a manual valve and flow sensing element (which also pro-
    vided input to the main air valve control loop).  This flow passed through a venturi
    which caused a subatmospheric throat pressure  (about - 70IK at 5 psig blower pressure).
    A hopper threaded to the throat of this venturi allowed dust to be introduced into the
    air stream with a variable-speed vibratory feeder.4  The dust so introduced was
    subjected to very high velocity (about Mach 0.6) which deagglomerated most of the
    compacted caterial.
    
           The dust-air mixture flowed from the feed venturi into a cyclone containing
    three baffles in the annulus.  This cyclone served both to complete the deagqlom-
    erating process and separate any remaining large particles.  The underflow from the
    cyclone was captured in a sealed container at the bottom of the conical section which
    was emptied periodically.  The venturi in the main air line produce j a depression to
    help overcome losses in the feed venturi and the cyclone as well as provided a high-
    velocity region in which to disperse the dust-air mixture prior to deceleration into
    the main duct.
    
           The remainder of the auxiliary air was used in the media transport and cleaning
    system.  Both injector and transport air flow to the "L-Valve" below the G3F were
    automatically and independently controlled.  Calibration of this system for a given
    media size and density allowed continuous monitoring of media flow.  A manually-
    controlled air stream to the bottom of the fluid bed provided final media cleaning
    and uniform distribution of the clean media into the GBF.  These air flows and the
    entrained particulate removed from the media were then routed to a conventional bag
    filter for final collection and disposal.
    
           Dual sample stations were positioned at the inlet and outlet cf the GBF ir
    accordance with EPA recommendations.  An opacity indicator on the outlet duct aidud in
    identifying steady-state operation.
    
           An automatic data acquisition system scanned 40 instrument signals (seven of
    which are shown in Figure 2) every minute.  These signals were processed by a
    Tektronix 4051 computer, converted to engineering units and recorded on macnetic tape.
    In addition, a cathode ray tube display of certain parameters (e.g., GBF pressure drop,
    opacity, superficial velocity) was. updated every minute to assist in the operation of
    the unit.  Plots of the parameters with respect to elapsed time (similar to those
    shown in Figure 3) could be displayed upon demand by the operator.
    4
     A mixture of two grades of hydrated alumina (Al203'3H20) was used to achieve the
     desired particle size distribution.
                                              571
    

    -------
    TEST: CI6S5          D*TE: 8  3i  ?r
    OUTLET  OPACITY • ';>
                                              TIME:  1526
    13.0
    12.0
    II. 0
    10.0
    !>.0
    6.0
    7.0
    ฃ.0
    4.0
    3.0
    0
    
    
    
    
    
    
    
    
    
    A
    Vv
    
    
    
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    \A
    \
    
    
    
    
    20 40 eo
    
    
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    ft.
    ^Wl
    K
    
    
    
    
    
    
    
    
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    1
    
    
    
    
    
    
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    60 100 lid 140 KO
    ET -nir,.
    
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    "VulN
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    1 0 200 2.
     FILTER PFESiUPE C'RijP  -1H
    a. a
    ?.o
    e.o
    4.0
    3.0
    2.0
    1.6
    0.6
    
    \n
    "V
    
    
    
    
    
    
    
    
    "^^
    
    
    
    
    
    
    
    
    	 	 ,
    
    
    
    
    
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    |
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    V
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    0 20 48 eo ฃ0 100 120 140 ItO ISO 200 2<
    ET -nit,.
    MEM* CIRCULATION P~TE' Ib-'MIt,,.
    200.0
    180.0
    tcO.O
    140.0
    120.0
    100.0
    80.0
    60.0
    40.0
    20.0
    0.0
    
    
    h~
    
    
    
    
    
    
    
    
    
    f^KfJ
    
    
    
    
    
    
    
    
    
    **ปA^v-
    
    
    
    
    
    
    
    
    
    ^ป-^~
    
    
    
    
    
    
    
    o 20 40 eo
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    ^
    
    
    
    
    
    
    
    
    
    %0 10'J
    ET
    EPA
    — IIILET
    ~liilET
    EPA
    1
    • HI
    ป
    
    
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    20 14
    r. '
    " OUItEI
    
    
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    ฃ
           Figure 3. Typical data acquisition system record
                              572
    

    -------
    TEST MEASUREMENTS
    
           The process variables recorded by the data acquisition system were all measured
    by conventional techniques requiring minimum operator attention.   Particulate loading
    and size distribution were measured by the discrete sanple techniques listed below:
    
           •  Particulate Concentation. - A conventional EPA Method 5 isokinecic filtration
              sampling system was used to measure loading at the inlet and outlet of the
              GBF.  In the absence of condensible material in the sample, the impingers
              were replaced with a desiccant cartridge.  Three MIETO Model ~,2QO control
              stations were available to withdraw samples.  In accordance with EPA recom-
              mendations, each sample consisted of two 90ฐ traverses.
    
           •  Particulate Size Distribution. - Size distribution was measured with
              Anuersen 2000 Hark III impaction classifiers.  All samples were taken iso-
              kinetically at the duct centerline.
    
    
    DATA REDUCTION AND PRESENTATION TECHNIQUES
    
           Two important aspects of the performance of a particulate control system are:
    
           •  The relation of overall particulate capture to utility consumption, usually
              expressed in terms of gas-side pressure loss ar.c
    
           •  The efficiency attainable in controlling specific particle sizes (fractional
              efficiency).
    
           Since a relatively large number of variables was involved in these tests,
    linear regression analysis was used to correlate the data.  It was shown by analysis
    of variance that a good and relatively simple correlation between collection efficiency
    and pressure drop IP
                                                         A.
                                             A0  [if "l '  1
    
    
    where Ao and AI are the "best" coefficients determined from linear regression.  The
    numerical value of these coefficients will be listed for each subexperiment.
    
           Fractional efficiency performance for each subex?eriment configuration will be
    illustrated by plotting the capture efficiency for five size ranges corresponding  (in
    terms of fractional efficiency) to the most favorable ara. least favorable combinations
    observed during each subexperiment.5  since each subexperiment addressed roughly the
    same variable combinations, the position of the envelope formed by these extreme
    observations is a measure of the effectiveness of a particular configuration.  The
    variable combinations corresponding to these extreme observations are listed.
    
    
    TEST RESULTS
    
           Table I lists the results of the Oata correlation for the three subexperiments
    previously described.  Table II lists the best observed collection performance of
    particulate associated with erosion/deposition.
    5
     This is a  somewhat subjective choice since different combinations sonetines resulted
     in the same efficiency.  The points selected were, however, always representative of
     the category of combinations associated with "most favorable" and "least favorable*
     performance.
                                              573
    

    -------
                              TABLE I.  DATA CORRELATION
    SU3EXPERIMENT
    FIGURE NUMBER
    AVERAGE MEDIAN
    DUST DIAMETER (pm)
    (0 —
    M EH
    6. g A
    O U
    U —
    O CJ v
    2 W 2 V
    M J u
    
    ป-3 rf O
    03 O IK Li
    U > b
    (u
    2 J m
    O f* < "
    M CO 2
    MEM
    ง20 AP
    U.
    gซt; v
    M _3 2
    M m cj
    |J < M
    o 2 o
    CO O M L;
    
    O H >4 H
    M CO <
    H ซ•• 3
    M U O
    a a M
    2 H AP
    O 2 0
    Thick Bed
    4
    
    2.6
    0.00303
    -0.7
    
    
    151
    
    
    
    0.92
    
    
    0.74
    
    
    23
    
    80
    
    
    0.18
    
    1.20
    
    
    
    2
    
    Nomiaaj Bed
    ^
    
    3.2
    0.0170
    -0.5
    
    
    120
    
    
    
    1.23
    
    
    0.62
    
    
    15
    
    59
    
    
    0.25
    
    1.08
    
    
    
    4
    
    Small Media
    6
    
    7.0*
    0.00589
    -0.6
    
    
    157
    
    
    
    0.40
    
    
    0.90
    
    
    34
    
    41
    
    
    0.37
    
    5.01
    
    
    
    9
    
    * Correlation was not materially  influenced  by deletion of  four  data  points
      resulting in an average median  diameter of 2.Sum.
                                          574
    

    -------
    o
    
    K
    <
    cr
    UJ
    ?
    ^^
    
    
    >-
    ซt
    z
    o
     _
    -
                                                                                         o
    
                                                                                         t-
                                                                                         u
                                                                                                 -I
                                                                                                 o
                                                                                                 o
                                                                                0.995    g!
                                                                                         o
                                                 575
    

    -------
         10
           -1
    UJ
    z
    ee.
    UJ
    
    g
         10
           -2
            10-3
                                         o
                                    10-
                                                                   o
                                                        O
                                                            1C
                                                         -1
                                                                                 O
                                                                                        0.9
                                                                                           ฃ>
    
                                                                                           >-
                                                                                  0.95     ^
                                                                                                z
                                                                                                o
                                                                                  0.99     S
    
                                                                                           _i
                                                                                           _i
    
                                                                                  0.995    2j
    
                                                                                           >
                                                                                           o
                                                                                      I
                                                                                lO1'
                Figure 5(a). Overall particb collection performance, nominal bed tubexperiment
    >•
    u
    z
    u.
    u.
    UJ
    
    _i
    <
    
    o
    ซx
    ce
          l.O
          B.9
    0.8
         0.7
                                5                  10                 15
    
    
    
                                AERODYNAMIC PARTICLE  DIAMETER (>ปM)
    
    
                 Figure 5(b).  Fractional particle collection performance, nominal bed subexperiment
                                               576
    

    -------
    r
    z
    o
         10-
    >
    o
         10
           -2
                                                                 O
                                     I
    I
                                                                                      0.90
                                                                                    -10.95
                                                                                      0.99
                                                                                      0.995
           10-3                    ID'2  ฃp  Li             10'1
    
                                         TW
    
                Figura 6(a). Overall particle collection performance, small media lubexperiment
                                       LU
    
                                       z
                                       o
                                       o
                                       o
                                       u.
                                       UJ
    tu
    z
    LJ
    Q.
          1.0
          0.9
          0.8
                 i    i    i
                                I
                                5                 10                 15
    
                               AERODYNAMIC PARTICLE  DIAMETER  (PM)
    
    
               Figure 6(b). Fractional particle collection performance, small media lubexperiment
    
    
    
                                             577
    

    -------
                          TABLE II.   CONDITIONS RESULTING IN MAXIMUM
                                     REMOVAL EFFICIENCY OF 2-5lim PARTIO'LATE
    Subexper iir.cn t
    Small
    Media
    
    Thick
    Bed
    
    Nominal
    Bed
    
    Velocity
    (ft/min)
    41
    95
    41
    157
    121
    82
    61
    74
    61
    Inlet
    Loading
    (gr/sdcf)
    1.2
    0.7
    0.3
    o.y
    0.4
    0.4
    1.6
    2.3
    1.6
    Media
    Rate
    ()b/lb)
    0.6
    2.4
    0.9
    9.7
    0.7
    0.3
    0.6
    0.9
    0.7
    Median Dia.
    of Distri-
    bution (urn)
    1.8
    2.0
    1.5
    3.3
    2.7
    1.8
    1.6
    2.9
    4.0
    Reriova 1
    Efficiency,
    2-5vm
    0.999
    0.991
    0.990
    0.995
    0.994
    0.993
    0.986
    0.985
    0.984
    Outlet
    Loading
    2jjm +
    (PPMW)
    6
    7
    5
    4
    3
    1
    39
    40
    16
    Pressure
    Drop
    (IKd)
    15.9
    23.5
    9.1
    23.1
    15.5
    14.8
    17.4
    4.3
    11.3
    DISCUSSION OF RESULTS
    
           Figure 7 shows the penetration/pressure drop correlation for both the thick bed
    and nominal bed subexperimcnts plotted on the same axes.  The relative position of the
    two curves is explained by noting that the product (VM) is, for a given superficial
    flow area and gas density, only a function of the media circulation (in, for example,
    Ib/hr) and not gas velocity.   Therefore, for a fixed inlet dust load and media circu-
    lation, a given pressure drop w:'.ll result in higher removal efficiency for the t.iicker
    bed.  This behavior was anticipated in view of the fact that the t/dm ratio for the
    thicker bed was greater (i.e., a greater number of collector sites present in the
    principal flow path).  The thinner bed had a more favorable t/11 (smaller values pre-
    sumably resulting in less bypass flow around the top of the bed) but this effect was
    overfiiidowed by the influence of the increased collector sites.  It is also observed
    that the negative slope of the thick bed data is greater than the thinner bed data so,
    at larger values of |"Ap Li "1   (i.e., higher allowable pressure drops), the relative
                        LV  TTJ
    advantage of the thicker bad increases.
    
           The importance of t/dm compared with t/H can be further illustrated by con-
    sidering the small media subexperiment.  Figure 8 repeats the thick bed and small
    media data points.  However,  the media rate measured in the small media subexperiment
    was multiplied by 1.3 to produce equivaler1  volumetric- media rates.6  It is noted that
    the data thus transformed is very nearly coincident.  Although the t/H ratio differs
    by a factor of 2, the t/dm ratio differs only by about 13*..  As in the comparison of
    the thick and nominal beds, the influence of t/H appears marginal with respect tot/dn,.
     The ratio of the bulk density of the alumina media used  in the  thick bed subexperiment
     to the bulk density of the silica media used in the small media subexperiment  is
     about 1.3.
                                              578
    

    -------
    z
    U.I
    Q_
    >
    O
           10
             -1
           10
             -2
                                                                                                *—^
    
    
                                                                                        0.90    o
    
                                                                                                tu
    
                                                                                                o
                                                                                        0.95    ฃ
                                                                                                u.
                                                                                                UJ
    
                                                                                                z
                                                                                                o
    
                                                                                                I—
                                                                                                o
                                                                                        0.99
                                                                                        0.995
                                                                                                o
    
                                                                                                -J
                                                                                                o
             10
               -3
                                      10-2
                                             ft Li
                                             T7T
    10-1
                            Figure 7. Influence of configuration of GBF performance
    o
    I—
    <
    z
    UJ
    Q.
    >
    o
          10
            ,-1
            -2
           10
             10-3
                                             O 15.3" BED,  1.9 MM MBDIA
    
                                             Q 7.6" BED, 0.8 MM MEDIA
                                      I
                                                              I
                                    ID
                                      "2
                                              .
                                           LP M
                                           TT
    
                              Figure 8. Influence of media size on GBF performance
                                                                                       0.9
                                                                                       0.95     t
                                                                                       0.99     3
                                                                                       0.995
                                                                                                o
                                                579
    

    -------
           The fractional, efficiency curves show that very high (90*,+) efficiency is
    attainable in the submicron size range for all configurations.  These conditions tend
    to be identified with high velocities, high inlet loadings and low media rates.7  It
    is though- that tho annular configuration improves small particulate capture by pro-
    viding lower velocities (and hence favorable diffusion collection) near the outer
    radius of the bed,  even when high velocities (associated with good impaction collect-
    ion)  are present near the inner radius of the bed.
    
           The less favorable conditions  (which are strongly identified with high media
    rates and low inlet dust loadings) also have a detrimental effect on large particulate
    capture.  This apparently results from reentrainment of previously collected material.
    It is observed that the "best" performance of the thinner bed still resulted in a small
    amount of large particulate escaping the bed whereas the beds with greater t/dm were
    capable of capturing essentially all particulate Oibo~ ? 3um.
    
           Table II addresses collection performance on particulate above 2pm which is
    normally identified with erosion and deposition problems in energy recovery equipment.
    It is again observed that performance is superior (and, on the average, nearly
    identical) in tho larger t/dm subexperiments.
    
    
    CONCLUSIONS
    
           The moving bed granular filter was found to be consistently capable of particu-
    late removal efficiencies in excess of 981 for dust loadings  (0.2 to 2.0 grains/sdcf)
    and size distributions (1 to lOiim median) associated with many combustion operations.
    Submicron coJlcctiori above 90?. was associated with high inlet velocities, high inlet
    loadings and low media rates.  The beds with larger t/dm ratios were most effective in
    capture and retention of large particulate.
    
    
    ACKNOWLEDGEMENT
    
           This work was funded by the U.S. Energy Research and Development Administration
    (Department of Energy) under Contract No. EF-77-C-01-2579.
    NOMENCLATURE
    "m
    II
    Li
    M
    t
    V
    AP
    n
    REFERENCES
                 Representative- diameter of media (mm)
                 Height of perforated inlet screen normal to gas flow (inches)
                 Inlet dust concentration (Grains/std dry cu ft)
                 Media rate (Ib media/lb gas)
                 Radial thickness of granular bed measured parallel to gas flow  (inches)
                 Superficial gas velocity at inlet screen (ft/min)
                 Gas pressure drop across granular bed  (inches of water)
                 Particulate collection efficiency (dimensionless)
    1.  J.H. P^rry, Chemical Engineers Handbook, 4th Edition; McGraw-Hill (New York), 19bj.
    2.  Cold Flow Test Program, Data Analysis and Observations, Special Task Report
        FE-2579-15 prepared for the U.S. Department of Energy by Combustion. Power Company
        (Menlo Park, California) under Contract No. EF-77-C-01-2579.
    7
     Loading and media rate are of greater importance in the smaller t/dm case.
                                              580
    

    -------
               QUESTIONS/RESPONSES/COMMENTS
         DALE KFAIRNS,  CHAIRMAN:  Do we have any questions?  Would you
    uce the microphone, please?
    
         SPFAKFR (from  the floor):  Could you give us sor^e nurbers for
    face velocities,  pressure drops, grain loadings, those kinds of
    numbers, please?
    
         PR. r.lJILLORY.   All  right.  Before we started the test, we picked
    a common group of parameters to keep throughout all the configuration
    changes.  The face  velocities we were looking at ranged from 40 feet
    per minute to 160 feet per minute.  This represented a maximum flew
    rate of about 3,000 CFM.
    
         The gain loadings:  the lowest was around 1/10 grain per stan-
    dard dry cubic foot.  The maximum, if I recall correctly, was about
    2-1/4 grains per  standard dry cubic foot.  Realize we are running at
    relatively low temperatures, so using grains per standard dry cubic
    foot really doesn't mean that much in this case.  Presentation in
    terms of "actual" cubic  feet would have been just as meaningful.
    
         The particle size distributions, the ones that we are showing
    here, were around 2 to 3 micron median diameter.  The pressure drops
    that we observed, of course, being dependently variable, were all
    over the map.  Of course our better performance tended to be identi-
    fied with the higher pressure drops, which I would say, depending on
    the configuration,  were  anyv/here from about 15 or 20 inches of v/ater
    in the case of the  thick bed subexperiment up to as high as 35, in
    the case of the smaller media; at the low end, two or three inches.
    
         SPrAKFR (from  the floor):  Are these steady-state?      :
    
         DR. GUILLORY:   Yes, this v/as.  In fact, that was quite an opera-
    tion in some of the cases, v/here we were dealing with, say, the thick
    bed case.  We had 16,000 pounds of media, and it took quite a while
    to come to steady state.  This is one of the reasons that we did use
    an opacity meter.  We used a Lear-Sigler opacity meter on the outlet,
    and this was, of  course, one of our important parameters that we were
    continually watching to  see when v/e finally did pull into steady
    state, not only in  terms of such things as pressure drop, but also in
    terms of apparent outlet loading.  We didn't use the opacity as an
    absolute number,  but it was an indication that we were no longer
    changing.  Did that take care of all the questions?
                                    581
    

    -------
                           INTRODUCTION
    
         DALE KEAIRNS,  CHAIRMAN:  Our next paper is "Mathematical  Model
    of a Cross-Flow Moving  Bed C-ranular Filter."  It will be given by
    Henry Wigton of Combustion Power Company.  Dr. Wigton received his
    Ph.n. from the University of  Colorado in chemical engineering.  He
    also has a master's in  chemical engineering from Oklahoma State
    University, and a RS in chemical engineering from Texas Tech.   Dr.
    Wigton is chief scientist at  the Combustion Power Company.
                                   532
    

    -------
                             Mathematical Model of a Cross-Flow
                                 Moving Bed Granular Filter
                                         H.F.Wigton
                                  Combustion Power Company
    ABSTRACT
    
           As part of an ERDA-sponsored program,  the theoretical performance of a granular
    bed filter was modeled.  Tho magnitudes of individual filter media grain collection
    coefficients for the mechanisms of impaction,  interception,  diffusion,  and sedimenta-
    tion are estimated from published theory and  data.   Recent work by Dr.  S. Goren is
    used to revise these coefficients for clean media grains.   The effects  of captured
    particulate on thec.a filter coefficients and  frictional pressure drop are estimated.
    Governing differential equations for gas and  solids flow patterns, and  of media-borne
    and gas-borne particulate matter throughou'  the filter are derived.  Computer solutions
    to these equations are used to correlate actual experimental data.
    
    
    INTRODUCTION
    
           The objectives of this task were to:
    
           •   Understand and model the mechanisms by which particulatn matter (aerosols)
               are removed from a qas by collector grains (spheres).
           •   Model the gas and media flow patterns within the filter as a function of
               operational parameters.
           •   Relate the operational factors and the capture equations through coupling
               equations which incorporate the effects of captured particulates on flow
               patterns and collection rate equations.
    
           This task ontailed:
    
           •   Formulation of ijovernir:j equations.
           •   Estimation of numerical coefficients.
           •   Updating of numerical coefficients to incorporate the best values from
               experimental data.
    
    Discussion
    
           The capture of aerosols by spheres is  a subject which is treated by many
    authors, such as llerne (3) and Paretsky (4) .   Basically, a particle is  captured by a
    sphere if it contacts the- sphere.  Surface forces will then hold the particle on the
    sphere, since these forces arc relatively large for small (micron range) particles.
    
           Neglecting electrostatic and thermophoric effects,  individual spheres collect
    aerosol particles by at least four mechanisms:
    
           •   Inertial impaction.
           •   Interception.
           •   Diffusion.
           •   Sedimentation.
                                             583
    

    -------
            The capture efficiency of an individual  sphere is conventionally assessed by
     determining that fraction of gas approaching the sphere which is cleaned by particu-
     lates.   For example,  referring to Figure 1,  the volume flow rate of gas sweeping by
     each sphere is equal  to TI .  2   whereas the  volume flow rate of  gas which is cleaned is
                 ,           4 dc "'
     equal to uyc U,  with  yc  being dependent on  particle gas properties.  For each particle
     size (dp), an efficiency equal to 4y 2 may be calculated for either interception or
     impaction by determining the limiting trajectories of each particle size.
    
     Impaction
    
            Collection by  impaction occurs when the  inertia of a particle causes it to de-
     part the gas streamline and  collide with or  graze the sphere (Figure 2).  The theore-
     tical models indicate that a partijle flow parameter, called the Stokes number,  is a
     satisfactory correlating dimensionless group for these analyses.  Numerical analysis of
     the streamlines and particle trajectories which are calculated by Fuks (2), and
     Herne (3) and confirmed by Paretsky (4) indicated that no impaction of particulates
     would occur on isolated spheres below a critical Stokes number of 1.212.  These calcu-
     lations were based on the viscous flow pattern  shown in Figure 1.  Using the potential
     flow model (Figure la), Herne (3)  predicts better collection efficiency and a lower
     critical Stokes number, because the gas streamlines are c- vded  closer to the spheres.
     This impaction parameter is  defined by Paretsky to be:
                              Stk = -ฃง--—*—                                          (1)
                                       c
    
     where: C = Cunningham slip factor expressed as:
    
                                        21 t           ~A3d-  \
                                c = : + a^ (VA2 exp —ฃ   I
                                         P
    
    
     and   A. = 1.257
           A, = 0.400
           A^ = 0.55
           ฃ  = mean free path of gas molecules ~0.065 micro meters at 25 C and ambient
                pressure
    
            This coefficient is important when the particle size approaches the same magni-
     tude as the mean free path of gas molecules.  Paretsky, using the free-flow model
     proposed by Happol (5), showed mathematically that the confinement of gas flow near the
     spherical surface to a volume which is equivalent to the void fraction of the packed
     spheres** would decrease the critical impaction  parameter to less than 0.1.   The theo-
     retical curves arc shown in Figure 3 for several values of packing void fraction.  How-
     ever, his experimental data taken on packed sand grains indicated:
    
            •  There was no evidence of a critical value of this parameter even three orders
               of magnitude below the theoretical critical value for ah isolated sphere.
               (Collection was observed for values as low as St=0.001).
            •  Collection efficiencies attributable to individual media grains were essen-
               tially proportional to the Stokes number and inversely proportional to the
               void fraction of the packed array at the values which he investigated.
      The Stokes number as used by Paretsky,  Herne,  Goren (6),  and Friedlander (7),  is twice
      the similar impaction number of inertial separation number used  by Jackson (8)  and
      Perry's Handbook, respectively.
    **In Happel's model, the volume of voids  associated with each sphere is represented by
      the volume between the two spheres having radii r^ and r  , respectively (see  Figure 2) .
                                               584
    

    -------
    UC   0
                  Figure 1. Flow Line* Around a Sphere
                          (Taken from Fuks)
                   Figure 2. Free Surface Model Applied
                          to Inenial Impaction
                         (Taken from Paretsky)
                                585
    

    -------
             Jackson  (5)  found  that  the  extrapolated  values of Parctsky were still con-
             servative (i.e.,  higher  experimental  values were obtained than could be pre-
             dicted).   Among the reasons  for  higher than theoretical behaviors are:
    
             1)   The existence of a wake  downstream of a sphere at finite values of the
                 Reynolds  number. Baird  (9)  has shown this to be an important factor
                 when falling raindrops were  -ised  as collectors.
             2)   The channeling  effect of the preceding "row" of spheres which tends to
                 increase  the number  of streamlines which are initially directed toward
                 the center of the target sphere.   This results in a greater net direct-
                 tional change of gas streamlines  and  increases the probability of a p:^' -
                 icle's impacting the sphere  rather than following the streamline.  The
                 effects of this important factor  are  best determined experimentally,
                 since the actual computations are too complex for rigorous determinations.
    
             Impact ion Efficiency. -  If the Stokes number is modified by dividing it by
    the void fraction, the single particle collection  efficiencies reported by Paretsky
    are obtained directly  over the range'  of his data (see Figure 3) .
    This expression is used as the value for clean media in the initial calculations.
    Interception
    
          Interception of a particle occurs when the particle, oven though following the
    gas streamline, comes to within one half a particle diameter and grazes the sphere.
    Particle inertia is not required for this mechanism of capture (Figure 2).
    
             Interception Efficiency. - The theoretical interception efficiency has also
    been treated by llerne and Paretsky.  The estimated efficiency is a function of whether
    the potential or viscous gas flow models (Figure 1) are used.  For potential flow, a
    vnlue of n.  equal to approximately
                                    3d
                                                                                     (3)
    was suggested by Ranz and Wong (10)  and also Jackson, whereas the value of
                             ""--HdfJ                                            ปป
    
    is recommended by Paretsky (4)  and Goren (6) when using Happcl's (5) viscous flow
    model.  The variation in collection efficiency is again due to how closely the stream-
    lines approach the collector surface.  The gas velocity near the surface of a sphere
    is proportional ซ-.o the square of the distance from the surface in potential flow and
    varies linearly with the distance in viscous flow.  This capture mechanism plays a
    more significaiit "ole when captured particles themselves can act as collectors.
    Jackson (8) foL-Vd .-quation (3)  to be a better indicator of actual data.  This equation
    will be used in "iht initial estimation of capture coefficients for individual spheres.
    
    Diffusion
    
          Brownian diffusion caused by random motions of small particles being bombarded
    by gas molecules enhances the possibility of a particle's being collected.  Even though
    the particle may be generally following a gas streamline, random motion may occasion-
    ally allow the particle to approach a collector surface and could cause it to contact
    that surface and be captured.  Kriedlander  (11) recommends that collection efficiency
    for a single isolated sphere by diffusion can be expressed as
                               Dlf .
                                             586
    

    -------
    10
      -3
                      1             1
                            THEORETICAL
                            •"•''
                          >   =  0.43
    
          _EXPERIMEtJTAL  .  = 0.49
    
             //*  ' 0.43
            /'  20.30  MESH
          * t  - r\ A \
              = 0.41
           10-14 MESH
                          INERTiAL PARAMETER
                   Figure 3. Companion of the Theroetical
                     and Experimental Efficiency due to
                            Inertial Impaction
                          (Taken from Pareuky)
                                                           10
                             587
    

    -------
    where: Pe = Peclet number defined as —=•
                                 d_U
                            d as
    
    D = gas diffusivity = ~
                                        — 16
    Ic = Boltzraann's constant = 1.38 x 10
    
    T = absolute temperature, Kelvin degrees
        3nd^ g
            C = Cunningham slip factor
    
    Sedimentation
    
           Particles, under the influence of gravity, will tend to settle from the gas
    stream onto solid surfaces.  This mechanism contributes primarily at low gas veloci-
    ties.
    
           Collection efficiencies attributable to individual spheres, as recommended by
    Friedlander (11) can be defined as:
    
                                                /U \ ฐ'77
                                   nsed = ^lM(0i)                                 C6)
    
    where: U  = terminal settling velocity of the particle calculated according to:
                                     Ut
                                      C    18M
    
            U = superficial gas velocity
            g = gravitational constant
    
           The fraction of particles which bypass the sphere (1- n o) will be reduced by
    each mechanism acting on the remainder according to:
    
                          (1- noTj - (1- nimp) (1- n inc) (1-ndif;   (1-nsedi
    
    Since these individual mechanisms arc small,  the equation reduces to:
    
                               "o  =n imp +  n inc  +  n dif  +   r' sed
    
    and the equation will be expressed as:
    
    
                      no = C1(St)n + C2 (^E) + C3(Pe)"2/3 + C4(Grv)3/4               (7)
    
    
    As an initial approximation, values for clean media will be:
    
          no = totil collection efficiency (fraction)  of a single,  clean, media sphere
          C. = 1/r. n=l
    The rate at which particles are captured will be calculated from equation (8) which is
    readily derived from previously defined terms.
    
           The efficiency of an individual media grain (sphere) is defin-d as that fraction
    of gas approaching a sphere which is completely cleaned of particulate natter.  The
    area of the sphere normal to gas flow is nd 2 .  If the area swept clean is denoted
                                               4
    as "c", the efficiency for a single sphere could be expressed as:
                                             588
    

    -------
                           4c   _  g approaching -  g leaving
                          ltd             g approaching           ""g  "c
    
    The number cf spheres in a differential volume of packed spheres will be
    
                                           dV
    and the total reduction in concentration in a differential volume would equal the
    capture by a single sphere times the number of spheres per unit volume
    substituting for "c"
    results in the capture equation
    
                                                    dL
    
                                    g    t g        d
    which is the governing rate equation to be integrated along gas streamlines.
    
    where: dV = volume of differential filter element (cm )
            ซ = 1-e fraction of spatial volume occupied by solid spheres
           Sc = cross-sectional area normal to gas flow (cm2)
          dL  = differential distance measured along a gas streamline (cm)
           d^ = diameter of media collector (cm)
           C  = the concentration of particulate in the gas in gms per cubic centimeter
          dCg = differential change in particulate concentration in the gas stream in
            "   gms/ci.i3
    
           An improved approximation of the values  of C^,  ^ ,  Co,  and C^ for clean static
    packed aluminous spheres may be made  by fitting the  experimental  data obtained by
    Goren  with curves as shown in Figure 4.
    
           Reentrainment of particles can occur when media particles  move.  This movement
    has been observed to be by individual media grains falling or rolling into a void and
    decelerating within a finite distance,  shedding a fraction of the particles which are
    on the surface of the sphere.  The rate at which particles are reentrained will be
    proportional to the gas velocity, the solids  concentration and a  power function of the
    solids velocity.  The net removal of  particles  from the  gas stream will be those
    captured minus those reentrained, according to  equations (3),(9), and (10)  listed
    below.  Equation (11) couples/"t and  Cs.   Equation (11)  may be integrated along any
    gas streamline.
    
                                                    Capture
                                I     •• •ป   -c
    
                             dC_
                                                    r=reentrainment coefficient      (9)
    
    
    
                                              .&)0-n*oi;
    
    Net removal from gas (along a gas streamline)
    
                                            U u nC  )  22_                             (ID
    
    
    
                                             589
    

    -------
    I
    1  Eff.
              .01
             .005 —
             .002
                                         10         20
                                                U. It/min
                                    Figure 4.  Gas Velocity in ft. per minute
                                                                             100       200
                                            590
    

    -------
           The three-dimensional global model, Figure 5, as simplified in Figure 6, may be
    represented as a rectangular cross-section (ABCD) rotated around the vertical axis of
    symmetry.  Individual volumetric elements are represented by areas (such as 1,2,3,4).
    
           Similarly  if an isoparametric element such as 1234  in Figure  7  is used  to
    make material balances, equation (12)
                                                  - rU.U.
                                       us
    may be integrated along a solids streamline (between gas streamlines) to determine the
    net change of particulate matter associated with the media.  The use of isoparametric
    elements simplifies the material balances since only one inlet and outlet component
    for each phase need be considered with the particulate concentration in the gas,
    specified at the gas inlet face and the concentration of particulate in the media
    specified at the solids inlet boundry.  Integration along the upper gas streamline can
    proceed, yielding simultaneous values of Cs and Cg along the gas streamline  (and at
    each solid streamline where it is intersected by the gas streamline) . The complete
    solution can be found in this inarching mode.
    
           New values of gas velocity (streamline location) can then be calculated and the
    process repeated until convergence is obtained.  At each iteration, the problem can
    be solved as a linear system of equations.
    
           An alternate method of solving the gas flow equations as nonlinear sets is
    discussed in detail under computer implementation.
    
    
    OPERATIONAL PARAMETERS
    
           Gas Flow. - Gas flow depends on geometry, boundary conditions, and governing
    equations. While the average gas velocity through the filter is the primary variable
    which is fixed by design requirements, the actual velocity at any point in the filter
    is a complex function of geometry and other operating variables.
    
           The end effects in the cold flow model apparatus are accentuated because the
    ratio of outer to inner diameter is greater than one and the ratio of filter thick-
    ness to filter height is significant.  The actual gas velocity at any point  in the
    filter is required to calculate the prevailing capture coefficients and to establish
    the gas streamlines which are needed to make integrated (path dependent) material
    balances.
    
           For normal operation  at ambient  or higher pressure  and ambient and higher temp-
    eratures,  the gas may he  considered  as  an incompressible,  viscous,  Netwonian  fluid.
    Derivation of equations  representative  of key  variables in the model are as  follows.
    
           Flow of a viscous incompressible, Newtonian fluid through packed beds or
    through porous materials will obey:
    
           Darcy's Law              VP = RU
    
           Continuity Equation     7-U = 0
    
    so that in Cartesian coordinates, the simplified equation:
    
    
                                "Pi) = ป
    is the overall governing equation
    
    where: 7P = pressure gradient
            R = specific resistivity to flow
          V-U = divergence of velocity
                                             591
    

    -------
           MEDIA INLETS (4)
              SOLIDS  FLOW
    Figure 5. Moving Bed GBF Geometry
                  592
    

    -------
     GLOBAL HODFL (ABCD)
    VOLUMETRIC ELEMENT  (1234)
                  Figures. Control Vc'ymes
                             593
    

    -------
     ซปz
       X
       /    I   I   I   I   I
    
      till   '   '
         I   /   /  '   '
    fill
    "S3
                          I   t  I
    
                          f   I  I
             /   /  /   ,'~M
         •• x
                       /    f
                       I   I
                       I   I
                      f   I
                      I   I
    
                     -M-
        A'
    1
    *
    1
    1
    1
    1
    1
    1
    f
    1
    f
    1
    1
    f
    1
    1
    f
    1
    
    
    
    
    
    
                           "s8
    -ปV
    — v
    
    — V
    
    -~ v
    
    
    
    
    — "96
    
    
    
    — v
    
    
    ~~ "98
                              "slO
         Figure 7. Solids Streซnlines vs. Gas Streamlines
                      594
    

    -------
           To quantify this relationship, this equation may be compared to Ergun's  (1)
    correlation of one-dimensional flow through parked media.
    
           Ergun Correlation             jp
                                        ^TT—  = (a+bU) U                              (14)
                                         dL
                                                         2
    where:                                    _ 150  (1-c) y                           ....
                                            a — 	~—~	                           liJj
    
    
                                            b = j^75  (1-r.) g                          (16)
                                                     3
                                                 ฃd  c g
    
           —jj- = pressure drop per unit length
             U = superificial velocity of the gas  (based on an empty  filter)  in  the
                 direction of the pressure drop in cm/sec.
    
    By using both a viscous term "a" and a kinetic term "b", Ergun resolved many apparent
    discrepancies in the literature as well as correlating his own extensive  d,-ปca.  The
    viscous  term dominates at lower Reynolds numbers and the kinetic  term  is  mDro  import-
    ant at higher Reynolds numbers.  (The granular filter operates at Reynolds numbers in
    which "a" and "bU" are the same order of magnitude so tnat both terms ~^st be  con-
    sidered when determining flow distribution and pressure drop).  When Ergun's correla-
    tion is  resolved in two-dimensional Cartesian coordinates, the following  equations
    result:
                                                      ' ) U
                                          ay           '   y
    
    where: U  = component of velocity in the y direction
           Uy = component cf v.-locity in the x direction
                                       /2   2
           |u| = total vector velocity \UX +Uy   (cm/sec)
           dc = diameter of media grains (cm)
            i. = void fraction  (fraction of the total volume not occupied  by media)
            I •= sphericity of media grain, defined as equal to the  ratio  of surface  area
                of hypothetical perfect sphere of equal volume to the actual  surface area
                of the media grain        ,
           pg = density of the gas  (gms/cm )
            n - viscosity of gas in consistent units  (i.e., gm/cm sec!
            g - gravitational constant
    
           Forchcimer's Law for steady-state flow as discussed by Irmay  i'ij)  rnciy  be  COM-
    binc-d with the continuity equation and written as:
    
                                  ? /  VP__\  = Q                                     (17)
    
    A triple identity will result if
    
                                     R = a+bU = a'+b'q
    
    so that for Cartesian coordinates
    
                                                                                      (18)
                                       '•"(^) - ฐ
    may be evaluated by using the coefficients of the Ergun correlation
    
                                            R = a+bU
    
    When written for cylindrical coordinates, with no angular dependence  (axisymetrical),
    the governing equation for pressure distribution throughout the bed is:
    
                                    _ ^ I  + ^1 - '^-\  ,-   o                           <19)
                                      or /  '  :>z \ R
    
                                             595
    

    -------
           The stream function (ijr) which is the value of a streamline is defined according
    to the equations
    
    
    
    The equation for the stream functions may bo solved directly as
                               j,r.-^J+^r(-^l=   0                            (20)
    
    Inasmuch as R is a function of if/, this equation is nonlinear and must be solved
    numerically, subject to the following boundry conditions:
    
           ifi = 1 along top barrier (D'-D-C-C'J; See Figure 7
           if" = 0 along bottom barrier (A'-A-B-B'j
    
          UJ: = 0 at gas inlet  (D'-A'J
    
          |i = 0 at gas outlet (C'-B1)
    
    a similar set of boundry conditions
    
           P = 1 along inlet (D'-A')j See Figure 9
           P = 0 along outlet  (C'-B')
    
          || = 0 along barriers CA'-A), (b'-B),  (C'-C) &  (D'-D)
    
          3P
          yr = 0 along media inlet and outlet  (A-B)& (D-C)
    
    allow a solution for the normalized pressure distribution if desired.  Either of  these
    equations may be solved numerically by relaxation or direct methods.  Since the
    equations arc nonlinear (R is dependent on P and 0)  iterative methods are required
    for precise solution.  With no front face spillage, and smoothe walls movement of
    media within the filter annulus has been observed to  follow a "mass  flow" pattern in
    which the velocity of the  solids  is everywhere constant.  Front face spillage for
    clean media has been found to be  proportional to the vertical velocity of media in
    the filter and indirectly  proportional to the inlet gas velocity.
    
    
           This flow pattern can Be described by an equation similar to the governing gas
    flow equation,  with the solid stream function designated as "S"
    
                                      3SX   J_
                                      Tt,   Jz
    with boundary conditions
    
           S = 1 along outer cylinder radius C-C'-B'-B ;  See Figure 7
           S = 0 along inner radius upper boundary (D-D*)
           S = Sfc constant - a function of geometry solids velocity and gas velocity
               -long (A1-A)
           S = a function of Z and Sb along gas inlet (D'-A1)
    
          •37 = 0 along both top (D-C) and bottom (A-B)
                                             596
    

    -------
    A solution of this equation for Rs = 1 and Sb = 0.4 is shown as the vertically oriented
    dotted lines in Figure 7.  These solid streamlines, when superimposed on the gas
    streamlines, form isoparametric volume elements such as represented by area 1234  in
    Figure 7 and simplify the material balance equations which are discussed next.
    
    
    MATERIAL BALANCES
    
           The material balance r>qnปซ- -. ..is (Table I) state simply that at steady state (no
    accumulation) the input to any volume within the filter must equal the output from
    that volume.  Equation (21) is applied to each individual particulate size classifi-
    cation as well as the overall particrlate balance and states that any change in parti-
    cle concentration in the gas stream  ('~g) must appear as a proportional change in  the
    solids concentration (Cs).  The particular form of this equation is advantageous  in
    implementing numerical computations.
    
    
                                Table I.  Material Balance
           I         'p^c^u^ * ^C.-0,.)    dn = 0       dn = vector norm.
           /surface   9 g g    s s s
           1
          •'
                   Vซ(P C U  + pcco^o^  dv = 0       Divergence theorem true for any
           volume
    ggg
                                  vo lume .
           and            0=7ซu =7ซC                 p  and p  are constants.
           L1  = gas velocity in cm/sec
           Ug = solids velocity in,cm/sec
           P^ = gas density, gm/cm   ,
           p" = solids density, gm/cm
           C  = concentration of particles in the gas, gm/gm
           Cg = concentration of particles in the gas, gm/gm
                                                                                      (21)
    COUPLING GAS FLOW AND CAPTURED PARTICULATE
    
           The flow equation and capture efficiency equation can be solved individually
    for the clean media case, but coupling relationships are required to account  for the
    effects of captured particulate material.
    
           First, a correction is made on the resistivity of media to gas flow.   The
    presence of particulate matter alters both the effective void fraction of the packed
    media spheres and the surface characteristics of the spheres.  As can be observed from
    the relationships in the Ergun equation coefficients, for the flow resistivity
    
                                         R = (a+bU)
    
                                         =, -  150  (1-c)2 ป
                                         a ~~       O 1
                                              (yd ) G Q
    
                                         b =  1.75 (l-c)Pg
    
    
    
    an agglomerate of micron-size particles will offer sevoral orders of magnitude more
    resistance to flow than an array of media spheres so that the effective void  fraction
    between large collector spheres will be reduced by the bulk volume of small particles
    deposited within the interstices.
    
    
                                              597
    

    -------
           The net effective void fraction can be estimated by considering a unit volume
    of filter bed
    
           V. .  , = 1 = V  +r.       when clean
            total        c    o
    
           V_   , = 1 = V  +c+V
            Total        c       a
    
    The mass of collector particles in a unit volume is Mc = Vt x pbc = pbc-  Tne rcass  of
    ash particles in the same volume is Ma = Va x ()Da.   Tne mass or weight ratio of ash
    to media
    
    
                                           Ma   Vba
    
                                      s  = ^ = ~^T
    
    substituting JT™ x C  or V  (the volume of ash per unit volume) and 1-ฃ  for V  (the
    
    volume of collector grains per unit volume. Equation (22) becomes
    
    
                                            E ' ^ ฃ Cs
    
    where: p.  = bulk density of the media in grams per cubic centimeters
           pP0 = bulk density of the ash in grams per cubic centimeters
            Del
            C  = ash concentration in weight of ash per unit weight of media
    
             o
    cs = void fraction of  clean media
           The sphericity (
    The mass ratio of particles to collectors (C )  equals the total mass of particles (N)
                                        '
                            (!i!-ป)
                            V-6    P'
    times the mass of each particle [   p  p  I divided by the mass of the single media
    sphere under consideration (  c  p  1.  Substituting  C      c c  for N results in:
                               V—  c/                  s   ^T-
                                                                p P
    where: N = number or particles of diameter d  on the collector surface
           d = diameter of the ash particle     p
           pp= densitv of the ash ^article
           PP= density of the media grain
    
           Since the effective volume of a large spherical particle is essentially un-
    changed by coating it with a monolayer of micron-size particles, only the surface area
    changes will be considered in adjusting the sphericity according to:
    
                   $'  _ effective sphericity _  original area
                   $   ~ original sphericity  ~  effective area
    
    
    
                                             598
    

    -------
                                                 . w
    
    Equation  (23) could possibly yield a sphericity less than would be obtained with each
    media  sphere completely coated with particulate spheres.  This complete coverage would
    
    effectively double the surface area by replacing circles of area     p   with hemi-
                    TI   2                                                4
    spheres of area •= d   .  The mathematical equivalent to  this physical limit is obtained
    
    by using  the value of $ or ^o  whichever is greater as the actual  sphericity of dirty
    media  calculations.
    
           Figure 8 shows how the specific resistivity to flow varies throughout the filter.
    The field above and to the right of the dotted line R = 1 remain" as essentially
    clean media while the region below and to the left of the line R = 3.0 represents
    the highest concentration of collected materials.
    
           Usin-i values of C  (ash concentration) specified  at each grid  point and impres-
    sing boundary conditions, a grid  of velocity (stream  functions) and  pressure vectors
    can then  be calculated using either relaxation methods  or direct  methods.  Once  the
    velocity,  pressures,  and  the stream functions are  known, the  flow net  of streamlines
    and isobars can be plotted as in  Figure 9.   Such a flew net is required to establish
    the path  of the gas so that a material balance of  the gas can be  made  as it flows
    through the filter. The material  balance and rate  equations can  then be used to  calcu-
    late flow resistivity profiles  as shown in Figure  8 by  a method such as is outlined
    in Figure 10.
    
    
    COUPLING  MATERIAL  BALANCES WITH  RATE EQUATIONS
    
           As particulate matter is  collected, the particle themselves now function  as
    small  collectors! operating with  the same basic mechanisms of collection as the  larger
    media  collectors.
    
           These particles are effective insofar as they protrude into  the gas flow
    streams.   It is important to note that the theoretical  models such as  proposed  by
    Gorcn  and Paretsky show that the  increase in efficiency should be proportional  to the
    same factors as the  increase in  flow resistivity.  Those relationships are also  com-
    patible with the frequently observed relationships between the friction factor  (f) and
    the mass  transfer  factor  (j) in diffusional  processes.  The equation used to estimate
    the coupling of capture efficiency with solids concentration  will be
    
                                                                                      (24)
    where:  " =  collection coefficient  for an  individual dirty media  sphere
            n =  collection coefficient  for an  individual clean media  sphere
            a =  viscous  Ergun  coefficient for  clean media
            bฐ=  kinetic  Ergun  coefficient for  clean media
            U =  loc-il  superficial gas velocity
            a =  viscous  Ergun  coefficient corrected for changes  in void  fraction  and
                sphericity
            b =  kinetic  Ergun  coefficient corrected for changes  in void  fraction  and
                sphericity
    
    
    CONCLUSIONS
    
            The  effective particle capture efficiencies of  an array of packed  spheres  is
    greater than can  be predicted fi.m theories applicable to single spheres.  This
    synergism is futher enhanced at the Reynolds numbers prevailing  in  the  normal opera-
    tional  ranges of  commercial filters.
    
            The  effects  of captured particulate material on the  pressure drop  and overall
    filter  efficiency are greater than car. be explained by the  reduction of interstitial
    voids.   An  additional correction of media grain sphericity  as it is applied  in the
    Ergun flow  correlation appears to  predict these effects.
    
    
    
                                              599
    

    -------
    FILTER r*\
    
    INLET LV
                                        GAS
    
                                        STREAMLINES
             !\ \
              \
              \  \
    A\\\\\
              -*—\
                ป\vป
           \ \
                 \ \ \ \ \ \
               \ v \\\"ฐ-
                \  \ \ \ \
                V \ \ ^
            \\>
                   \x^
            • \ \  \
            \ \ \ \
                 \ \
                  \  %  \ \
                  \  t \ \
                  \  \  \ i
    
    
    
    
                    \  \
          ปป-\\\\
    N
                \\
                          B'
                                      B
            Inlet
         '3.0
                                    routlet
              Figure 8. Solids Loading Factor ซ. Gas Streamltnas
                          600
    

    -------
                              MEDIA
                                                   P=3
             P=10
        INLET
        SCREEN
    GAS FLOW
                                                                OUTLET
                                                                SCREEN
                                Gas Flow Model
                                                          'out
                           Figures. Gas Flow Model
                                     601
    

    -------
                     MEDIA SOLIDS IfiUT
      GAS INLET
     PARTICIPATE
       SOLIDS   ~
    CONCENTRATION
    GAS
    CONCENTRATION
    PROFILE
    MEDIA
    CONCENTRATION
    PROFILE
    A GAS 1
    | "1 STREAMLINES 1
    I PRESSURE 1
    | DROP ง
    	 1 _ .._._
    1 fc| SOLIDS 1
    1 STREAMLINES |
    1 " 	
    1
    i
    MATERIAL ^ COLLECTION
    BALAKCE MECHANISM
    1
    t
    
    <
    'ARTICULATE NEU SOLIDS CONCENTRATION PROFILE
    MCENTRATION
      GAS OUTLET
     CONCENTRATION
    ป
     /  FILTER  \
     VEFFICIENCY/
                                    Figure 10. Filter Efficiency Calculation Method
                                                          602
    

    -------
    Summary of Equations
    
           Material Balance  (Isoparametric Volume) :
         3C
    Vg 3L* dLg
                                         3C
                                         3IT dLs
                                           s
           Rate Equation:
           Gas Flow:
                            dC
                      _i  /I 1Z\ +   _i /I  IP
                      3r  |R 3rJ    3z IR  3z
    
    
                      _i  I ^ ill +   -JL /^.  III "
                      3r  Ir 3r/    3Z |r  3z/
           Solids Flow:
                      .ป  fe- ปd +  i.  /R-  is
                      3r  \r  3ry    3z  IF"  Sz
           Capture:
           Coupling:
                                           C2(St)n + C3(Pe)~2/3  +  C4(Grv)3/4
                              R  =  (a+bU)
                                                 fa+bV
                                        Mba  '1
    ACKNOWLEDGEMENT
    
           This work was done as part of ERDA Contract No.  EF-77-C-01-2579.   The consult-
    ing services of Dr. S. Goren  (University of California,  Berkeley),  Dr.  S.K. Friedlander
    (UCLA) and advice of Dr. M.L. Jackson are gratefully  acknowledged.   Special thanks are
    extended to L.B. Wiaton  (University of California, Berkeley)  for his help in the field
    of applied mathematics.
                                             603
    

    -------
    NOMENCLATURE
           A,, A-, A,  = coefficients to evaluate Cunningham slip factor
    
           A  = total effective area of a sphere when partially covered with small
                spheres (cm2)
           a, a  = coefficients to evaluate the viscous term of the Ergun flow resistivity
               0   (gms SP.c/cm4) . (a0 applies  specifically to clean media case).
           Li, b  = coefficients to evaluate the kinetic term of the Ergun flow resistivity
                   (gm sec^/cm5).  (b  applies specifically to clean media case).
           c = fractional volumetric flow approaching a sphere which is cleaned by a
               single sphere.
           C = Cunningham slip factor (dimensionless).
           C,, C_, C,, C. = coefficients to evaluate  ...   .      ,.,     .  (dimensionless)
            1234                             int,  imp,  dir,  sea
           C  = concentration of particles in the gas,  gm/gm
           C' = concentration of particles in the solids, gm/gm
           d  = diameter of media grains (cm)
           d  = diameter of aerosol particle (cm)
           D" = gas diffusivity (cm/sec2)
           f  = 3nd u
    
                 C
           g  = gravitational constant - 980(gms mass)  (cm)
                                            (gms force)(sec2)
           Grv = gravitational number  /U.\ (dimensionless)
           k = Boltzmann's constant = 1.38 x 10    ergs/degree
           I = mean free path of gas molecules (cm)
           L  = distance measured along a gas streamline (cm)
           Lg = distance measured along a solid streamline (cm)
           N = number of captured particles associated with collector sphere
           N   = number of collector spheres in a unit volume
    
           P = pressure in gms force/cm
           Pe = Peclet number dcU (dimensionless)
                               D
           R = resistivity to gas flow = (a+bU)
           RS = normalized resistivity to solids flow
           S = solids stream function
           Sc = cross-sectional area of a sphere normal to gas flow
           St = Stokes number
           T = temperature in absolute Celsius (Kelvin)
           0 = superficial velocity of the gas (based on an empty filter) in the direction
               of the pressure drop (cm/sec)
           U  = component of velocity in the y direction
           Ujj = component of velocity in the x direction
    
           |U|= total vector velocity ^U 2+U 2   (cm/sec)
           U  = gas velocity in cm/sec  x   ^
           V9= volume (cm3)
           V  = volume of media grains (cm )
           V  = total spatial volume (cm^)
           V  = total volume occupied by collected particulates (cm )
           "  = fraction of volume occupied by media grain
           c  = fraction of volume not occupied by either media grains or collected
            M   particulate. c  applies to clean media only.
           /  = total capture efficiency of an individual sphere
           /*?   = particle capture efficiency of an individual sphere by interception
    
           /jLp = particle capture efficiency of an individual sphere by impaction
    
           /^ij = particle capture efficiency of an individual sphere by diffusion
    
           /*sed = Part*cle capture efficiency of an individual sphere by sedimentation
    
            /*  = total capture efficiency of an individual sphere of a clean sphere
    
    
    
                                             604
    

    -------
             Ut  = terminal settling velocity of particle
    
            P   =  bulk density of collected particulate gms/cm
             ba
            p   =  bulk density of collected media grains gms/cm
             DC
            p = absolute density of media grains gms/cm
    
            p = absolute density of particles
    
            p = gas density, c—./cm
    
            p = bulk solids density, gin/cm  = ph
    
            V =  gas viscosity in gms mass/cm sec
            Us = velocity of media solids
    
     REFERENCES
    
     1.   S. Ergun,  Chem. Eng. Prog., 48, No. 2, 1952.
    
     2.   N.A. Fuks, The Mechanics of Aerosols, CWL Special Publication 4-12, USDC
         59-21069,  1955.
     3.   H. Herne,  Aerodynamic Capture of Particles, edited by E.G. Richardson,
         Pergamon  Press, 1960.
     4.   L. Paretsky, L. Theodore, R. Pfcffer, A.M. Squires, J. Air Poll. Control Assoc.,
         2_1, 204 (1971).
    
     5.   J. Happel, AIChE J., 4,  197, j'>58.
     6.   S.L. Goren, Consulting Report to CPC to be published as an addendum to Final
         Report  for Contract EF-77-C-Oi -2579.
     7.   S.K. Friedlander, Smoke, Dust and Hazo;  Fundamentals of Aerosol Behavior,
         Wiley-tnterscience, N.Y., 1977.
     8.   M.L. Jackson and R.G. Patterson, Shallow Multistage Fluidizcd Beds for Particle
         Collection, paper presented at AIChE, 68th Annual Meeting, Los Angeles, CA,
         November  1975.
     9.   K.V. Baird, Journal of the Atmospheric Sciences, 31, September 1974.
    10.   W.E. Ranz, j'.B. Wong, ln~d. Eng. Chom.. 4j4, 1371  — (1952).
    11.   S.K. Friedlander, S.K. , personal commuTTtcation.
    12.   A.C. Pajfltrtkes. AIChE J., 2^, November 1977.
    13.   S. Irmay,  T., Ancr. Gco. UnT, 39, No. 4, 1958.
                                              605
    

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                              INTRODUCTION
         DALE KEAIRNS,  CHAIRMAN:   The  three  papers  that we will hear prior
    to the break address the problems  of  high-temperature, high-pressure
    particulate control  as it would  apply to pressurized fluidized bed
    combustion concepts.  The first  paper this  afternoon will analyze a
    new particulate control  technique;  in the second  paper we will hear
    some experimental  results on  a high-temperature,  high-pressure
    granular bed filter operation; and then  the third paper this morning
    will provide some  input  into  an  overview in terms of the technical
    status of granular bed filtration  and the potential for that technology.
    So I think we have an opportunity  to  increase our understanding of
    these areas here this afternoon.
    
         The first speaker is Dr. Ken  Tsao.   Dr. Tsao is a professor
    in the Energetics  Department  at  the University  of Wisconsin in
    Milwaukee.  He obtained  a Ph.D.  in Mechanical Engineering at the
    University of Wisconsin  in Madison.  He  has an  interesting background
    and one that is applicable to the  fluid  bed combustion development in
    that as part of his background he  served as a power plant supervisor
    with a petroleum corporation, among other activities.  The title of
    his paper is "Multiple Jet Particle Collection  in a Cyclone by
    Reheating Fluidized Bed  Combustion Products."   Dr. Tsao.
                                     606
    

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                                  Multiple Jet Particle Collection in a
                                 Cyclone by Reheating Fluidized Bed
                                        Combustion Products
    
                                       Ken C. Tsao, Kuang T. Yung
                                         and Jeffrey F. Bradley
    
                                  The University of Wisconsin—Milwaukee
    ABSTRACT                             Milwaukee, Wisconsin
    
           A new particle collection technique is analyzed and presented for its potential
    application in high temperature and high pressure gas cleaning systens.  The new tech-
    nique is based on the probability of particle collision and agglomeration phenomena by
    reheating fluidized bed combustion products near coal-osh fusion temperature.  The en-
    trapped solids after impactions will agglomerate and adhere together to form into
    larger sizes for effective separation linger centrifugal action.  A mathematical model
    is constructed leading to the design of an experimental high temperature cyclone.  Ef-
    fect of particle jet geometry and velocity distribution is discussed for the highest
    rate of generation of new particles.
    
    
    INTRODUCTION
    
           Effective use of fluidized bed combustion products in a combined gas-steam tur-
    bine cycle depends upon the ability of cleaning particulatc concentration in the high-
    temperature, hiqh-pressure flue gas to an acceptable degree for the safe operation of
    gas turbines.  Presently, there are numerous research and development projects involving
    cyclones, granular bed filters, molten salt scrubbers,  and other hybrid processes such
    as charged filters in modified electrostatic precipitators dซ2).  However, some spec-
    ific problems such as the effect of sticking on adherent particles in the efficiency of
    clean-up apparatus result in making hot gas clean-up a major technical challenge.  It
    was proposed that a new approach^3' utilizing the self-agglomerating phenomena of car-
    bon ash particle near its fusion temperature to a modified multi-inlet, multi-pass cy-
    clone with insitu combuo'-.ion be investigated.  Collection efficiency of submicron par-
    ticles could be increased further in such an apparatus with additional collection mech-
    anism of impaction of solid particles.
    
           The combustion products from the fluidized bed boiler when passing a region of
    high temperature zone in the cyclone such that coal/ash particles would enter momentar-
    ily a partial moltun state.  The particles will coagulate, agglomerate and stick to-
    gether after impaction to form into a greater size but subsequently will be separated
    out under centrifugal action.
    
           The goal of this paper attempts: 1)  to establish a mathematical model to simu-
    iute the particle collision and agglomeration phenomena occurred in the proposed
    multi-jet cyclone, and 2) to estimate the concentration of agglomerated new particles
    by taking the effect of particle size and the jet velocity of  incoming fluidized bed
    combustion products.
    
    
    FORMULATION OF COLLISION EO.UATIONS
    
           The formulation of mathematical model is based on, firstly, the collision of an
    elastic collision and then modified with a term called "probability factor" for inelas-
    tic impaction.  The particles are considered to be removed from the main dust stream
    after the first collision process.  Consider a particle with a diameter DO moving at a
    velocity v into a group of particles of the same size,  DO and concentration ng-  The
    number of elastic collision between a single incident particle and the group of par-
    ticles, as shown in Figure 1,  is
    
                                         A = n0  r,OQ v                                 (1)
    
    where n0 is the particle number concentration per unit volume; v, the velocity of
    
    moving particles; and o.^ = ^~ (Da+Db) , the total cross-section of hard spheres of
    
    diameters, Da and DD-  The subscripts, 00 or ab refer to two groups of particles of
    a chosen reference size or particles with diameters D.  and D-, respectively.  To extend
    
    
    
    
                                              607
    

    -------
    
    
    JL
    nflCJ *
    T
    -4ฎ O
    Tn ฐ o
    ifi . a"
    o
    O *
    O^o
    o
    
    x 	 PARTICLE
    DIAMETER. Dfa
    	 PARTICLE
    CONS., nb
    COLLISION  RATE
          Figure 1. Single Particte Collision
                   608
    

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    the single particle collision into a system of collisions between two  groups of par-
    ticles where each group contains no particles  of  uniform size DO, the number of colli-
    sions per unit time becomes
                                          oo
                                               ฐoo no 3oo
    where  Qgo   is  the  "probability factor" to account for the effect of  inelastic colli-
    sion.  Since the particles after striking each other are considered to be removed  from
    the main dust stream, no secondary collision would occur.  Thus, the  number of colli-
    sions is greatly reduced depending on the probably striking chance, QOQป among the
    particles.   Extension of Equation  (2) to two groups of dissimilar particles of dia-
    and  D. ,  and their respective number density
    meters
    equation of collision is,
                                                              n  and n^,
                                                                          a general rate
                                            (k  + k.
    
                                             a  b
    where  kg  and  ku  are the ratios of diameters of particles  a  and  b with respect
    to that of the reference size  On.  Equation (Z) reduces to Equation  (2)  for  ka = kv>
    = 1.  And the new particle formed will have a diameter of  (k-} + kฃ) */3 DQ-
    RATE OF GENERATION OF NEW PARTICLES
    
           Intuitively, the rate of generation OL new particles of greater  size would de-
    pend on many  factors such as the collision rate, the thickness of molten  layer enclo-
    sing the coal-ash particle, the activation energy of molecules, etc.  The rate of gen-
    eration of new particles is further governed by perhaps, the operating  parameters such
    as temperature, velocity of dust ladden gas stream, and the incident  angle, etc. in  the
    proposed multi-jet cyclone.  It is postulated that the rate of generation of new par-
    ticles after  collision between particles a and b is,
                                         G
                                          ab
                                               fab Aab
    where fab is referrod to as an "adhesive ability factor," 0 <_ fat,  <_  1, and   fajj  =  f^a-
    In the case of a system composed of two groups of particles with number concentration
    particles is
    where Pa, Pb  (
                                in each group; Figure 2, the rate of generation of  new
    
                                                         ,+k.
             ^ab
                   If
                                 aa
                                             2ฃab papb
                                                                       .,
                                                                  fbb pb
                                                                               oo
                                       * a             ™a *b            *b
    
                                    are the percentages of the number of particles
                                                                                       i-nd
    b with respect to the total number of particles in the gas stream.  Generalization of
    Equation  (5) will lead to Equation (6) that for a system of groups containing particle
    concentrations of nj, n2,..., nN with particle sizes of U\, D2,..-> DM  and number
    percentages of PI, P2, --- , PNป Figure 3,         2
    EFFECT OF JET VELOCITY PROFILE ON A NEW PARTICLE GENERATION
           One of the most controllable operating parameters in a multi-jet cyclone with
    reheating is the dust ladden gas stream velocity.  The offeet of jet exit geometry on
    the new particle generation is of particular interest to the experimental design, set-
    up and testing of the proposed new gas clean-up technique.  Two ca..cs of jet velocity
    profile (4) were incorporated for a case study.  The profiles are:
    
           (1) for a plane jet.
                       "n        x
                       -S =2.48  (ฃ +
    
                       50
                                                 0.6)
                                                     "1/2 "0 1/2
                                                         {— )
                                   ^- = exp 1-75
                                                                                        (7)
                                              609
    

    -------
    DO, "a
    Db.Hb
    V
    D0fn0
    *.S
                                                                             WHERE      Dj •  kjDซ
    Gob
                                                                                               Pi   •   I
            Figure 2.   Rate of Generation of New Particle*
    Figure 3. Rate ol Generation of New Particles with Sin Variation
    

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            (2) and for a round jet
    
    
                                   J!= 6.3 (ฃซ)    &)
    
                                   5o
    
                                   — = exp [-96 (ฃ) 1                                  (3)
    
                                   ปm
    
    where  UQ, u_, u are the mean gas exit velocity, the mean axial velocity, and the
    local jet velocity; r-Q, • aป  • • ^nc densities of dust lodden gas stream at nozzle exit,
    of the entrained air and of the cor,l-ash particles: h, do. tlr  nozzle height of a
    plane jet and the diameter of a round jet, respectively.
    
           In cooperation of the jet velocity profile and the incoming coal-ash particle
    mass concentration, the number of particles at a given section along the jet axis is
    calculated.  Hence, the rate of collision at any location of (x, y) in a plane jet  is,
                                            2
                                  357.12 G-C    .   3/2                       2
                      A00(x,y) = ( - - !-2)  (-ฐ)    <  + 0.6) exp 1-148 (^) |Q        (9)
        fur a round jot,
                                    •:D0
                      A00(x,r) = <— ~> (-)   (-•)  exp i-211 <) 1 Q               (10)
    
    
    Substituting Equations (9) and (10) into Equation (6), the rate of generation of new
    particles is obtained.
    
    
    DISCUSSTO:; OF RESULTS
    
           For a given mass density of coal ash particles in the gas stream. Figure 4 shows
    the effect of particle size upon the collision rate.  The smaller the size  of the in-
    cident particles, the greater will be the collision rate.  This is of interest to  the-
    partical application of the proposed multi-jet cyclone, since its intended purpose is
    to clean up the submicron particles.
    
           Figure 5 shows the effect of particle size with constant adhesive ability fac-
    tor on the rate of generation of new particles.  There appears that the values of  f
    is not sensitive to the rate of generation when the particle size exceeds the reference
    particle of  2.. .  On the other hand, the rate of generation would differ by approxi-
    mately one magnitude of order when the particle sizes are varied fvom 1;;  to  2...
    It can be viewed that the proposed hot gas cleaning process is favorable toward
    the smaller particles.  The effect of non-uniform adhesive ability factor is shown
    on the same figure by the dashed line.
    
           With a given sot of  f  values (fn = f^2 = ^22 ~,0.5), the effect of percent
    of particles containing two different sizes of particles in each group is shown in
    Figure 6.  The trend is f>"i:?cnt that the greater the percentage of the smaller size
    particle.-; contained in a gas stream, the greater wTIT~'be th'o generation rate of new
    particles.
    
           Figure 7 presents the plot of AQO with respect to a plane jet stream profile.
    AOO decreases as the jet travels Lurthcr down its axis.  The graph can be utilized to
    calculate the number of new particles produced at any given section of jet stream.
    This will be beneficial for selecting an optimum geometry regarding the effectiveness
    cf the proposed cyclone design.
                                                                                     — 8
           As a practical example,  let us take the probability factor  Ogo = 0.5 x 10
    and a plane jet velocity profile to estimate the actual rate of generation of new
    particles.  The  QOO vai_e was calculated and based on the probability of that among
    7500 possible choices, there are 75 red balls for which any random draw of 75 balls
    from the 7500 total containing 10 red balls in one draw is 0.5 x 10"8. Assume also
    ^11 = fl2 = f22 = ฐ-5ป PI = ?2 = 0.5 and kj = 2, kj = 1:  we find from Figures 6 or 7,
    that II t* 0.27 at  y_ _ x = 5.0.  Further using  Figure 7,  AQQ is found to be 5.2 x  10~2.
                      x ~ h
    
                                             611
    

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    0.1       0.ซ        1.0        L4        1.0
               RATIO OF DIAMETERS.    k,=
                                                  D.
                 Figure 4. Ratio of Collision Rate for Single Component
                              612
    

    -------
    4H
    
       30
      10
    
    
    
      50
    
    
    
      3.0
      I.O
      05
       0.25
                   WHERE Ps - PERCENTAOE OF MASS
                          ,   CONCENTRATION
                          fs-ADHESIVE ABILITY
                          k's-PARTICLE  SIZE  RATIO
    1.0            2.0            3.0
    
       PARTICLE SIZE  RATIO, k=-Sป
    
      Figure S. H Value* Versus Particle Sin
                             613
    

    -------
    BO
                 as                    i.o                    1.0
                         PARTICLE  SIZE RATIO , k,
    
                       Figure 6. Effect of Particle Mass Percent on '1 Values
                                        614
    

    -------
     .6'
    .52
    io3
                                            D.-DIA. OF REFERENCE
                                               PART1CLE.2/4
                      s-V/x)x,62lฐ
                     Figure 7. Dimemionlesi Rata of Collision. A0
    15
                               615
    

    -------
    Hence the rate of generation of new oarticl.es is
    
                                     _,      357.2 G0 Cjj     p  3/2
                        G = (5.2 x 10 Z) [(	4  ฐ  ฐ  )  (-2)   J 0QO
                                              n Dj  p2       ('a
    
    For un =  33 m/s,  Cn = 0.001 ltom/ft3,  o = 454 lbm/ft3, Dn = 2 u  , G becomes  (i.78 x
      14                                    ft                    6
    10  ) Qnn.  Further take Qn. = 0.5 x 10  , then G = 0.89 x 10  particles/sec.  In the
           UU                 UU                                                  j i
    above calculation, tho incoming total number of particles of  2 u  is 1.86 x 10   and
    
    that of 4 p  is 2.32 x 1010.
    
    
    ACKNOWLEDGEMENT
    
           This research was sponsored by the U.S. Energy Research and Development Admin-
    istration under Starter Grants—University Projects in Coal Research.  Use of the
    computing facility through a grant from the Graduate School, The University of Wis-
    consin at Milwaukee is sincerely acknowledged.
    
    
    REFERENCES
    
    1.  EPA/ERDA Symposium on High Temperature/Pressure Particulate Control, September,
        1977, Washington, D.C.
    
    2.  Wade, G.L., "Particulate Removal from Hot Combustion Gases,* Proc. of 4th Inter-
        national Conference on FBC, Washington, D.C., 1975.
    
    3.  Tsao, K.C., "Particulate Removal at High Temperature/High Pros., re by Self-
        Agylomeration Process in a Cyclone," Coal Research Starter Grant with ERDA,
        September, 1977.
    
    4.  Field, M.A., et.nl., "Combustion of Pulverized Coal," The British Coul Utilization
        Rescrach Association, 1967.
                                             616
    

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                 QUESTIONS/RESPONSES/COMMENTS
         MR. SMITH:   Ken  Smith, Exxon Research.  I've got two questions.
    The first one is:  have you considered the relative velocity difference
    between the different size particles?
    
         DR. TSAO:   At  this moment, we are talking of one velocity para-
    meter only, "V". Certainly, the model can be incorporated into two
    different velocities, in essence the relative values between the
    particles.  Yes, it can be done.
                                              \
         SPEAKER (from  the floor):  But if the relative velocity is small,
    that means that  the particles won't collide.
    
         DR. TSAO:   Yes.   I follow your question.  If the two particles
    are one in front of the other, and suppose they are moving at the
    same velocity, certainly they won't have any chance of colliding at
    all.  In order to incorporate this condition, if you are trying to
    see that, the particles, the greater the size, the greater the
    surface drag; therefore, we do not expecc that the various sizes
    will move at the same velocity at all.  In e.>sence, I am saying that
    the model, to assume  one uniform velocity, perhaps may not be realis-
    tic.  However, this has to be verified in performance under the
    experimental conditions.
    
         SPEAKER (from  tha floor):  The smaller particle will have more
    drag.
    
         DR. TSAO:   Yes,  under the condition of equal momentum achieved
    for different size  of particles in the cyclone.
    
         SPEAKER (from  the floor):  One other question is:  are you
    worried about refragmentation of the particles after you have agglom-
    erated them, at  the high velocities in the cooling section of the
    cyclone?
    
         DR. TSAO:   There is such a possibility.  I think I agree with
    you.  I wish to  enter this factor, our "F" factor, if you recall.
    The "F" factor could  be varied between zero and one.  In essence, the
    worst case would be F equals zero:  no colliding, no collision at
    all, which would be the worst case.  I hope I have answered you.
    
         MR. KEAIRNS:  Let's see.  I think we have another question over
    here, and could  you repeat the question into the microphone so that
    all could hear?   I  don't think there are microphones around.  Yes,
    Professor Beer.
                                    617
    

    -------
         PROFESSOR BEER:  I would like to ask a question about the
    super-imposition of rotating flow in the cyclone and the temperature
    gradient introduced as you have mentioned it.  Now, it is known that
    if one had a positive density gradient, radial density gradient, in
    the rotating flow field, that this can cause a density-stratified
    emission, because the low-density gas in the middle cannot get out
    and therefore the flow is laminarized, thence the turbulence is less.
    Conversely, if you are introducing the high-temperature region
    outside, you get highly unstable situations.  Now, do you believe
    that either of these, that is, a laminarized core in the cyclone or a
    highly turbulent situation with the high-temperature zone outside,
    might help you in reaching your objectives?
    
         DR. TSAO:  If I may repeat the question, if I can repeat it
    correctly—
    
         MR. KEAIRNS:  I gave you a tough assignment to begin with.
    
         DR. TSAO:  I am here and happy to learn, in essence; and Professor
    Beer raised the question about density stratification as well as the
    distribution of the temperature across the cyclone; and also because
    you do have a swirling effect, swirling velocity, in the cyclone,
    therefore what would it be?  Should we have a laminar flow in the
    central core, or will we have turbulent flov: in the outer core, or how
    the penetration of the particle is from one region to another, if this
    is the question.  If I may answer your question, based upon my specu-
    lation:  In the experimental cyclone which we propose, we do have
    auxiliary jets on the sides   We will hope introducing the auxiliary
    jets around the peripheral section will help to stabilize the tempera-
    ture distribution in the center core, which we intend to maintain the
    uniform temperature.  By introducing the additional peripheral jets,
    hopefully the jets will have enough pressure gradient which would
    penetrate into the center core of the cyclone.  This is something wa
    hope.  We still have no experimental data.  We have no verification;
    but it's based upon my intelligent conjecture.
    
         CHAIRMAN:  Let's see.  There was a question submitted for Dr.
    Tsao.  Perhaps he could comment on that.
    
         DR. TSAO:  Thank you.  I have two questions that were submitted
    by Mr. Henry Kwon from Dorr Oliver, Inc.  The first question is:   "At
    the temperature range you have shown, some elements of ashes can be
    softened, which may cause scale buildup on the wall.  If so, your
    scheme may not work as you hope.  Did you look at the problem from
    this direction?"
    
         I was anticipating this question to be raised.  I  believe the
    boiler manufacturer may be able to answer this question better than  I
    
                                     613
    

    -------
    can.  However, based upon ny experience with the boilers, we do have
    the wet-bottom, also called cyclone burners, and with that type of a
    boiler you night be plugging the "ashtray," or should I say the
    discharge duct of the wet-bottom with ash.   But it didn't happen.
    However, I cannot assure you in the case of this cyclone, whether  it
    will happen or will not happen.  There is no experimental evidence
    yet; so my answer to that question would be "yes or no."  I hope that
    it v/il 1 not happen.
    
         The second question is:  "At the turn-down rate of flue gas
    flow, do you foresee a significant reduction in cracking efficiency?"
    The question here depends upon how you control  your temperature zone.
    The heating and the residence time of the particulate, the size of
    particles traveling level in the high-temperature zone will have
    tremendous effect upon the cracking efficiency.  Therefore, I would
    inject, if the design of the cyclone itself can be met at the high
    temperature zone, some type of path is available.  It depends upon
    your loading conditions.  Therefore, under that condition, I would
    hope the cracking efficiency will remain at its design point.
    
         MR. KEAIRNS:  Okay.  Thank you very much,  Dr. Tsao.
                                     619
    

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                                 Feasibility of Barrier Filtration
                                     Using Ceramic Fibers
                                      Michael A. Shackieton
                                       Acurex Corporation
                                       Mountain View. Calif.
    ABSTRACT
           Barrier filtration using ceramic fiber filters offers a promising solution to
    the problem of controlling particles in the high-temperature, high-pressure environment.
    Industrial experience has proven this technique is capable of high efficiency particle
    control, including fine particles, in near ambient temperatures and pressures.  Exam-
    ining those particle removal mechanisms which apply to barrier filtration indicates
    that adverse effects caused by increased gas viscosity at high temperatures can be
    compensated for in the design of the filter medium and in the design of the filter
    system.  Ceramic fibers are available which have smaller diameters  (3..m) than conven-
    tional fibers used for filters (10 to 20 ..m) .  Analysis indicates that using these fine
    diameter fibers should make it possible to produce filter media having weights less
    than or, at most, equal to conventional media.
    
           This paper reports on work being performed under EPA Contract 68-02-2169 to dem-
    onstrate the feasibility of high-temperature, high-pressure particle control by filtra-
    tion.  Tests at room ambient have shown the filtration capability of ceraraic fiber
    beds.  Tests at high temperature and pressure have demonstrated several ceramic media
    configurations capable of withstanding in excess of SO,000 cleaning pulse cyclos.  To
    solve the high temperature gas cleaning problem for TDC application rapid development
    of this technology is clearly needed.
                    FEASIBILITY OF BARRIER FILTRATION USING CERAMIC FIBERS
    INTRODUCTION
           Many advanced technology processes currently being developed require removing
    particles from high-temperature and pressure gas streams.  An objective of developing
    these processes is to increase coal use by making it economically efficient and environ-
    mentally safe.  These processes, such as pressurized fluidizcd-bcd coal combustion,
    involve expanding the high-temperature and pressure gases across a turbine to generate
    power to produce electricity.  Such applications require removing particulate flyash
    from the gas streams before expansion across the turbine.  Techniques to accomplish
    the required particle control have not yet been demonstrated.
    
           Under normal environmental conditions, barrier filtration is an effective method
    of achieving the required '^vel of particle control.  However, at high temperature
    (815ฐC)  and pressure (10 atm), barrier filtration and other conventional particle control
    methods arc limited by materials capable of surviving in the environment and by effects
    of changes in gas properties.
    
           Under EPA Contract 68-02-216y, Acurex Corporation is investigating the suitabil-
    ity of commercially-available ceramic fiber filters for high-temperature filtration.
    This work is sponsored by the Particulate Technology Brunei: of the Industrial Environ-
    mental Research Laboratory at Research Triangle Park, North Carolina.
    
    Major goals of this program are to:
    
           •  Design and build a filter media test facility capable of operating at 815'C
              and 10 atm pressure
           •  Test available ceramic fiber forms (woven cloths, felted mats) to determine
              if any can survive mechanical displacements and accelerations likely to be
              encountered in online cleaning of high-temperature filter applications
                                              620
    

    -------
              Develop preliminary performance data for those configurations which
              appear most promising for high-temperature filter applications
    
              Make recommendations based on the experience and data collected
           Barrier filtration with available ceramic fibers is likely to be a good tech-
    nique for particle control at high temperature and pressure.  To illustrate why this
    is true, a short review and discussion of barrier filtration theory is helpful.
    
           Figure 1 is taken from a report titled "rffects of Temperature and Pressure on
    Particle Collection Mechanisms:  Theoretical Review" by Seymour Calvert and Richard
    Parker (EPA-600/7-77-002), January 1977.*  This figure shows a calculated fractional
    efficiency curve for a fiber bed.  Minimum efficiency is indicated for a particle size
    of about 0.5 vm.  The dip in the curve occurs because of the interaction of the three
    collection mechanisms which apply to barrier filtration.  These mechanisms are direct
    interception, diffusion, and inerti.il impaction.  For particle size less than about 0.5
    um, collection by diffusion is increased, improving the efficiency of the filter bed.
    For particle size larger than about 0.5 -fm, collection by inertial impaction is improved,
    increasing the collection efficiency of the filter bed.  It should be remembered that
    this curve applies only to initial performance of a clean fiber bed.  That is, it does
    not include the increased collection efficiency that results from the filtration of the
    accumulating dust cake.  Note also that the Ho. 3 curve indicates that the inertial
    impaction parameter for high-temperature and pressure conditions .should show a small
    decrease in performance.  To understand the magnitude of this effect we can compare the
    performance of standard filter media when tested with Dioctylphthalate smoke (D.O.P.) to
    its performance when tested after a stabilized dust cake has been developed.  A D.O.P.
    smoke penetration test is a standard test to measure the efficiency of high performance
    filters such as those used to filter "Clean Room" air or to collect biological contami-
    nants.  This test measures how efficiently a filter ro>nov3s a 0.3 um diamcte' D.O.P.
    smoke particle.  Woven or felt filter media of the type corr.r-.only used for industrial
    filters will collect only 10 or 20 percent of 0.3 urn D.O.P. smoke.  Yet, after develop-
    ing a dust cake, these same filter media will collect submicrometer particulate at an
    efficiency of greater than 90 percent.  Thus, compared to the c-'.ianges in performance
    which take place in a filter media during the conditioning process, the changes pre-
    dicted as a result of high-temperature operation are small.
    
           Available ceramic fibers offer unique advantages for filtration, since many of
    these fibers have finer diameters than conventional filter fibers.  Conventional fibers
    are usually 10 or 20 yin in diameter, while ceramic fibers are available with average
    diameters of only 3.0 ym.
    
           Collection efficiency can be improved simply by making a filter bed thicker, thus
    increasing the basis weight of the filter (its weight per unit area).  However, to
    achieve high collection efficiency in this way can lead to high operating pressure drops.
    Collection efficiency can also be increased by reducing the fiber diameter, which can
    result in decreased basis weight and filter bed thickness.  The importance of fiber
    diameter is illustrated in the following equations which describe the three primary par-
    ticle collection mechanisms applicable to barrier filtration.
    
                                                        dp
                            Interception parameter K- = -r—                              (1)
    
    
                                                        c.r- d 2b
                               Impaction parameter K  =   9P ?—•*                       <2'
    
    
                                                           f * kT
                               Diffusion parameter K. = •=— . „  ,                       (3)
                                                    a   3 ~ j cl u ci,-
                                                           g p g f
    
    
    These equations describe the collection mechanisms, but are not collection efficiency
    equations.  However, when expressed as above, an increase in any of the mechanism pa-
    rameters (K , K , Kd)  will result in an increase in efficiency.
    
    
    
                                              621
    

    -------
       100
    
    
        90
    
    
        80
    U  60
    iu
    O
    t  50
    UJ
    
    
    I  40
        20
    
    
        10
    
    
         0
                CONSTANT FACE VELOCITY
    NO.    CONDITIONS
     1     20ฐC. 1 atm
     2     1.100ฐC. 1 aim
     3     I.IOO-C. 15 atm
           0.1
                                         0.5          1.0
                                     PARTICLE DIAMETER — urn
                                                                                     50
                       Figure 1. The effects of high temperature and pressure on the
                                   collection efficiency of a fiber bed
                                               622
    

    -------
           The interception parameter is not a function of temperature and pressure, but
    it is a function of fiber diameter.   Changing from a 20-vm fiber to a 3.0-^m fiber will
    increase the interception parameter  by a factor of 6.67 times.
    
           The impaction parameter is a  function of temperature and pressure, essentially
    through changes in the gas viscosity (ug).  For air, increasing temperature froTi 20 to
    815ฐC increases viscosity by about 2.5 times.  This reduces the impaction parameter by
    a factor of 1/2.5 or 0.4.  But, che  change in fiber diameter from 20 urn to 3.0 ;.m in-
    creases the impaction parameter by 6.67 times.  The net effoct of the two changes is
    to increase the impaction parameter  by 2.7 times.
    
           The diffusion parameter is a  function of temperature and pressure through changes
    in the ratio of (C'T/ug) .  When operating at 815ฐC and 10 a>Ti pressure, this ratio tends
    to remain unchanged or to increase slightly.  But, the diffusion parameter is also a
    function of fiber diameter and a change in fiber diameter from 20 um to 3.0 urn will
    increase the diffusion parameter by  6.67 times.
    
           From the above discussion it  is evident that if we make a filter using 3.0-ym
    diameter ceramic fiber (which is commercially ivailable), it is reasonable to expect
    that even at high temperature and pressure this filter will have high collection effi-
    ciency without excessive filter bed  thicknesses or basis weights.  Using the method
    developed by Torgeson, .-t- is possible 1-3 calculate collection efficiency for a given
    particle size and fiber t^ed parameters.  This calculation was performed for a 0.5-..ni
    diameter particle with a density of  1.5 g/cm3 (as measured at the Exxon Miniplant),
    for gas temperature of 815ฐC, and pressure of 10 atm.  A fiber bed composed of alumina
    fibers with 3.0-um diameter and fiber density of 2.8 g/cn3 was assumed.  Results of
    this analysj : for two filtration velocities and two solidities (a - the volume frac-
    tion of the Tiber bed which is solid) are plotted in Figure 2.   This analysis indicates
    that a 3.0-um diameter ceramic fiber filter bed with a basis weight of 500 to 600 g/m2
    will collect submicrometer particulate with an initial (clean)  efficiency of about
    90 percent at high temperature and pressure.  Recall that a typical industrial filter
    media (20-um fibers) would collect such particles at only 20 percent efficiency for
    the same basis weight.  Another way  to look at this is to note that to achieve col-
    lection efficiency comparable to commercial industrial media will require a ceramic
    fiber filter media with weights only one-tenth that of the commercial media.  Another
    interesting feature of the analysis  is that efficiency decreases for increasing veloc-
    ity.  However, by adding fibers, the given efficiency can be maintained as velocity is
    increased.  The quantity of additional fiber required is relatively small, especially
    if only 20-percent initial efficiency is adequate for a 0.5-um particle.
    
           Most commercially-available ceramic fiber structures are produced for insulation
    applications.   Consequently, these materials are generally characterized by in open
    fibrous structure.  That is, they have low solidity, with perhaps only 2 percent of
    the volume occupied by fibers (a = 0.02).  A solidity of a - 0.10 is more typical of a
    structure designed for filtration.  Figure 3 shows the effect on fiber bed thickness
    for changes in solidity and air-to-cloth ratio.  For solidity typical of insulation
    materials (i = 0.02), a fiber bed about 1 cm thick should achieve high initial collec-
    tion efficiency of submic^oiieter particulate, while a more compressed media with
    o — 0.10 would achieve this efficiency with a bed thickness of  only 2 ran.  If effi-
    ciency typical of industrial filters is adequate, very thin layers of the 3.0-^m
    diameter fibers will suffice.  Note  also that filter media thickness is not a strong
    function of air-to-cloth ratio, indicating that high filtration velocity should be
    possible.  Of course, higher filtration velocity will result in increased pressure drop,
    but this may be acceptable in a PFBC application.
    
    Room Ambient Filter Media Tests
    
           Available ceramic fiber configurations can be classified into the following three
    groups of materials:
    
           •  Woven structures - cloth woven from long-filament yarns of ceramic fibers
           •  Papers - Ceramic structures produced from short lengths of fibers, generally
              held together with binders.
           •  Felts - Structures produced to form mats of relatively long fibers.  These
              materials are known as blan.':ets in the insulation industry.  They tend to be
              less tightly packed than conventional felt materials.
    
                                              623
    

    -------
                                                     3.0* m DIA FIBERS
                                                     2.8 g/cm> FIBER DENSITY
                                                         05* m OIA PARTICLE
                                                          1.5 9/em'
                                                         815'C
                                                          10 ATM
                                            90
    oป
    j
     I   60
    5
    
    y
    D   70
    i
    
    uj   60
    
        50
    
        40
    
    
        20
    
         0
                                                      (i FT/MIN) *\
                                                      2.54 cm/tec)J
                                                                                          (25 FT/MIN)
                                                                                        1 12.7 cm/Me
                                                                                 c
                                                     I	I      I	I	I  I	I
                                                                                     IB ox/yd'
                                                    100   20>)    300    400    500   GOO    700   SCO    900   1000   1100   1200
    
                                                                           BASIS WEIGHT ~g/M>
                                                       Fijure 2. CtlcuUted ptrformanet 3.0 pm alumina fibtf tad
    

    -------
        1.4
    
    
        ra
    
    
        1.2
    
    
        1.1
    
    
        ro
    
    
    O 09
     I
    
    8 08
    w
    2
    O 0.7
    z
    
    g 06
    a
    
    ฃ O.S
    Q
       as
    
       02
    
       01
    
         o
    0.5 Km PARTICLE
    81S*C
    10 ATM
                             4         6         8         10
    
                              AIR-TO-CLOTH RATIO - CM/SEC
                                                                              14
                                Fi8urป3.  Fiber bad thidcrwa
                                         625
    

    -------
           A larqo number of ceramic fiber filter r.edia candidates  have been subjected  to
    a scries of filtration tests at room ambient conditions.  These tests  included  some
    examples of conventional filter r.edia for co~.parison.  Included among  the  tests were:
    
           •  Diootylphtalatc ssoke (D.O.P)  penetration as a function of air flow velocity
           •  LX?termination of maxir.um poro size !in micrometers)
    
           o  Measurement of j>ermeabil i ty
           •  Flat-sheet dust loadini tests using A.C. Fine test dust.  Over-all  collection
              efficiency and dust loading roquirca to develop 3.7 KFa  {15  in l^O) pressure
              drop are detcrnined froci this test which is operated  at  10 cm/sec  (20 ft/min)
              air-to-cloth ratio.
    
    Data collected fron these tests are summarised on Table I.
    
           Penetration tests using D.O.P. smoke measure the ability of the clean  fiber  bod
    to stop fine particles.  The- D.O.P. smoke generator is adjusted to provide a  noninal
    particle size of 0.3 .,m diameter which is a "roost penetrati.-.g"  particle Fizc  because
    of the minimal effect of diffusion and inertial impaction at this j.aiticle size.  The
    D.O.I-. tost results should correlate well to the results prc-dicted by  analysis  since
    particle collection is provided only by the fibers and not hy the dust cake.  Figure 4
    provides a plot of the D.O.P. efficiency as a function of air flew velocity  for all the
    media tested.  Ceraraic media el^ta arc plotted in solid lines and conventional rac-iia in
    dotted lines.  Numbers on the curves refer to *bose on Table I. Several interesting
    observations cass be ir-adc eoncernir.q this data:
    
           •  Several of the ceramic natorials, especially the ceramic papers  and felts,
              are capable of higher efficiency collection of fir.e particles than  are media
              normally used successively in commercial filter units.
    
           •  Many of the woven ccraaic materials, had zero D.O.P. efficiency at  low velocity
              and hiqher D.O.P. efficiency at highc-r velocity.
              This is contrary to what theory suggests and to tho Lc-hjvior normally seen
              in tests of conventional filter mati-r ials.  A likely  explanation for  this
              performance is that it is caused by t.>c presence o: man-/ large pores  in the
              r.edia.  {examination of the pore size 'Jata in Table I  shows that  the woven
              ceramic materials as a group are charicterized by larger pore size  than are
              conventional filter materials.  Thus, at low airflc/w  velocity, most of the
              flow passes through the larqo |>ores ar.u little filtration takes  place.  As
              velocity is increased, flow through the large pores, becomes  restricted ^nd
              some of the flow is caused to pass through smaller pores where more filtra-
              tion can take place.
           •  The D.O.P. data also supports the theoretical analysis.  Efficiency as J
              function of basis weight for selected ceramic materials  is plotted  in Figure
              5.  The materials selected arc ceramic uapcrs and felts.  These  materials
              provide a fiber bed sirailar to that for which the analysis summarized in
              Figure 2 was based.  Figure 5 shows that the nominally J -n  fibers do indeed
              provide higher collection efficiency on a woight-per-unit area basis  than
              conventional media produced with larger diameter fibers.
    
           Maximum pore size data shows that many of the woven ceramic materials  had pores
    larger than those characteristic of commercial filter materials. Also, many of the
    felt and paper materials had pore sizes similar to those of conventional filter
    materials.
    
           Permeability is measured as the flow per unit area at a  co-rtant pressure drop.
    Thar, a material with low permeability offers a high restriction to gas flow and one
    with high permeability allows more gas to pcnetrste for a given pressure drop.  Table
    I shews that some ceramic materials arc available which have low permeability,  while
    othe;s have high perceability.  Socc of the woven materials have low permeability and
    large port size, while others have high permeability and larce  pore size.  Most of  the
    paper and felt materials have permeability similar to that of commonly used filter
    materials.
                                              626
    

    -------
    TAHLE I.  SUMMARY  ROOM AMBTEN'T TEST DATA
                        627
    

    -------
                                                              TABLE   I     (ConcJudcd)
        ...,(,„'.-.I.,*  * Mt-ltt .ป         '-(.4        "I •. rป
        I ,|*-i  'viin  i,iMtfi>  •#/>ป!
    r>-i  <-it (, i	!••• t                          •' I'.t.iii
    
    .•I. <-~it.,ป-.t. I.M  KiU-i I r.i>          I'-/        -I't.ft             '                            I/.41*.
    li| i-ij-t fr. . l.l.^Utl  l/'i  Alt                                   '   '".'•.                    1/4. ป4.
            tปil '>:'*w.*v-;i lfjM.ni*     I/'.
                                                                              628
    

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       100
        90
        80
        70
        60
     |  60
    n
    d
     g
    .B
     S  40
        30
         20
         10
                                     5                        10
    
                                         Airflow Velocity cm sec
                             Figure 4. D.Ot. effideney in air-flow velocity
                                               629
    

    -------
                                                 1200       -ป00
    Figure 5. D.O.P. e ficiencv'n basis weight.
                    630
    

    -------
           Flat sheet dust loading tests were performed as follows:  A 7.62 cm (3 inch)
    diameter disc of media is suspended across an air stream which is maintained at 10.16
    cm/sec (20 ft/min) velocity through the filter media.  In this test the media supports
    itself against the pressure drop (no screen is used) .  Standard A.C. Fine test dust
    (0-80 yn silica) was fed to the media at a nominal rate- of 0.883 g/m3 (0.025 g/ft?)
    until a pressure drop of 3.73S KPa (15 in H20) is reached.  Pressure drop as a function
    of time is monitored during the test.  This data is presented in Figures 6, 7, and 8
    for selected materials.  From the aata collected, dust loading (g/m2) necessary to
    cause a given pressure drop 3.735 KPa (15 in f^O) is determined.  Examination of this
    data in Table I shows that so.v.e of the woven materials reached high pressure drops
    while collecting only a small weight per unit area of dust.  This is true also of the
    commercial woven materials (items 31 and 32).  Other woven ceramics were penetrated so
    severely that they would not develop a oressure drop of 3.735 KPa (15 in HjO).
    
           Two of the non-woven samples (which were unsupported)  fractured as a result of
    the pressure drop across them.  Several of the ceramic paper and felt materials
    exhibited dust loading, similar to that which is expected from conventional filter
    papers and felts.
    
           The flat sheet leading tests also provided overall collection efficiency (mass
    basis) data for the tested materials.  Dust penetrating the mcuia was collected in an
    absolute filter downstream of the test media.  Table I reveals that most of the woven
    ceramic materials did not achieve high collection efficiency in this test.  On the
    other hand, woven commercial materials were only moderately efficient.  Several of the
    ceramic paper and felt materials, however, did provide collection efficiency of 99
    percent or better.  The two materials which fractured would have provided higher effi-
    ciency performance had they not fractured.  The test was stopped as soon as the fracture
    was detected.
    
    General Conclusions from Room Ambient Tests
    
           •  Several of the ceramic paper and felt materials are capable of removing fine
              particles at high efficiency without excessive filter basis weights.
           •  The ceramic paper and felt materials have filtration characteristics and
              performed similar to paper and felt commercial filter media in a scries of
              filter media tests.
    
           •  The ceramic woven materials in general were characterized by large pores and
              poor collection efficiency in the dust loading tests.  The range of parameters
              exhibited by the various materials, however, indicate that an acceptable
              woven ceramic filter media can proiably be fabricated, b.it such a filter
              media would have the sarcc limitations as currently available woven filters.
              That is, acceptable performance is only probable at low air-to-cloth ratios.
    
           •  "Blanket" ceramic fiber materials (felts) consisting of small diameter fibers
              (3.0 urn) appear to be the most promising materials for high temperature and
              pressure tests because of their combination •>*. good filtration performance
              and relatively high strength.
    
    High Temperature/Pressure Tests
    
           Two major questions concerning the suitability ot ceramic fibers for filtration
    need to be answered.  These are:
    
           (1)  How durable are ceramic fiber structures when subjected to environmental
                conditions associated with filtration applications.
           (2)  How well do ceramic fibers perform as filters in the HTHP environment.
    
    Some preliminary answers are available concerning the first of these questions.
    
           Three ceramic filter media configurations have survived a test during which the
    filter elements were subjected to 50,000 cleaning pulses.  The objective of the tests
    was to simulate approximately one year of operation of mechanical loads on the media
    at high temperature and pressure.  Test conditions were as follows:
                                             631
    

    -------
    oo
    ro
                                          10
    20
                                                              n  *
                                                                               I
    30          40
     Time ~ Minutes
                                                                                          50
                                                                                                   A.C. FineTซtOuปt
                                                                                                   0883gM3
                                                                                                   A C 10 16cm sec
    
                                                                                                   ป33 • Conventional Fe'l Filter
    60
    70
                                                              Figure 0. Dun loading of wramlo ftto.
    

    -------
                            A.C. Fine Test Oust
                            0883g/M3
                            A/C 10.16 cm/see
    Figure?. Dint loading of ceramic paper.
                  633
    

    -------
    U)
                                                                                                                   AC F mt Tm Dint
                                                                                                                   ORlUfi.'
                                                                                                                   A.CIOI6.TOป<-
    
                                                                                                                   • 31. 1? Ciw>vnliซn
    -------
                          Temper a t'J re - 815 *C
                          Pressure - 930 KPa
                          Air-to-cloth-ratio - five to one  (2.54 cm/sec)
                          Cleaning pulse pressure - 1100 KPa
                          Cleaning pulse interval - ~ 10 seconds
                          Cleaning pulse duration - 100 a second
                          Dust - recirculated fly ash
    
           The three filter media configurations tested were:
    
           •  Saffil Alumina Mat contained between an inside and an outside  layer of  304
              stainless steel knit wire screen.   Figure 9 shows how easily the  residual
              dust cake was removed from this media after the  test.
    
           •  Woven Fiberfrax cloth with nichrome wire scrim    insert.  Figure 10 shows the
              dust cake following the 50,000 pulse test.
           •  Fiberfrax blanket contained between an  inside and an outside cylinder of 304
              stainless steel square oesh screen similar to common window screen.  The
              ceramic fiber blanket was held in position txitweon the screen  with 302  SS
              wire sewn between the screens.  This resulted in <-
    -------
    Figure9.  SaHil aluminป-pon ttft dust ata
       (Cliarnd strip using vacuum cleaner)
                    636
    

    -------
    Figure 10. Woven (iberfrax-post test dun cakt
                      637
    

    -------
    v'^-ff^iL^fjr^Wj
     ••^V'^^7ฃ55l
    //••^t-^iซgg5jig!tg
               Fibปflf
                  633
    

    -------
    639
    

    -------
                              High Temperature, High Pressure
                                  Electrostatic Precipitation
    
                                        Paul Feldman
                                          John Bush
                                       Myron Robinson
                                     Research-Coitrell. Inc.
                                   Bound Brook. New Jersey
    
    
    ABSTRACT
    
           This paper presents results of worr. conducted by "osearch-Cottrel 1 under FPA
    Contract 68-02-2104.  Tho purpose of the work completed to date was to demonstrate
    tho ability to qenorate stable corona a*. temi>oratures to 2000ฐF and oressures to 500
    psiq, thus establishing the feasibility of electrostatic precipitation as a means of
    particulate removal from the effluent of fluidized hod combustors or coal nasifiers
    at hiqh temperature and pressure.  Tho work was quite successful in demor.strat inq
    stable corona qeneration and in dcfininn ranges of temperature and pressure over
    which the stable discharge can be maintained.
    
           Oases investigated were air, flue nas, and simulated  (noncombustible) fuol
    las in coaxial wire-pipo electrodes.  Pino diameter was ^ixed at 3 inches; wire
    diameter varied from 0.062 to 0.125 inches.  Results are reported for both tx>larities
    in terms of curront-vol ta'te characteristics, corona onset and sparkovcr voltanes,
    and critical siq.  By
    technical feasibility  is meant the ability to qenerate stable corona over the ranao
    of temperature and urossuro indicated.  This was accomplished in a laboratory scale
    tubular precipitator in no-flow,  particle-free oocration.  ^hiT method of oocration
    was chosen because it allowed a we 11-control led, economical  evaluation o' the
    electrical characteristics of the system over the total ranoe of the variables.  A
    second uhase uroqram is needed to carry the work further into evaluation of narticulate
    collection characteristics.
    
           The primary variables studied were tonoeraturc, oressure, 
    -------
           There is a fundamental problem encountered in desionino a precioitator for a
    given hiah temperature/pressure service,  "his is our incomplete knowle'lqe of i) the
    ranqe of variables (pressure, temperature, electrode aoometry, qas composition.
    polarity) over which a stable corona discharge can be maintained, and ii) the current-
    voltace characteristics in that ranoe.  In particular, there exists for the oosik.ive
    discharae a critical pressure above which soarkover alone, without antecedent corona,
    prevails.  When the discharqe polarity is neoative, the critical ohenomenon is not
    so precisely defined, and a postcritical discharae (often unstable) may be found at
    pressures extending beyond the critical value.
    
           Two opposinq effects are responsible for the phenomenon of the critical
    pressure.  First, shorter mean-free oaths at elevated oressures imoede ionization *w
    collision and so tend to raise the sparkover level.  Second, the doriser oackinq o?
    aas molecules renders photoionization more likely and reduces ion diffusion.  Thus,
    pressure facilitates strcaxer proportion from the Anode across the qap and, at the
    critical pressure, sparkover results.
    
           The likely explanation of the relatively low value attained by the positive
    sparkover voltaqe and its concomitant lower critical density is as follows:'  Intense
    ionization of the qas is produced in the hiah-field renion in the vicinity of the
    discharge wire which attracts and removes the hiahly nobile electrons.  The heavy
    positive ions are repelled from the wire and move rlowly toward the collectinq
    electrodes.  However, on the far side o.r the i
    -------
    rXPF.RIMKNTAl, APPARATUS
    
           Fi'iure 1 shows t.hc- configuration of the tost orccipitator  used  in  this  nrooran.
    It is a wire-pipe d.?siqn (inclosed in a pressure vessel.  ^ho  nressure  vessel was
    desiqned for pressures to VJO psi'i and was assembled  in  three sections, each servina
    a specific purpose.  The top section contains the feedthrouah hushini  for aonlyinq
    hiqh voltaqo to the discharge electrode and a pressure relief line  to  protect  from
    over pressurization.  The bottom section has a sitie access openinn  for adiustments
    and observ.it ions, a bottom support insulator to center the discharoe electrode, and
    the Mas inlet.  The center section of the vessel holds the urecioitator tube surrounded
    by a three-zone heater used to reach the desired ouoratinq temperature.   A layer  of
    Kaowool insulation separates the heater and the pressure vessel wall.
    
           The collection tube electrode is a 7.26 cm internal diameter,  Inconol 00ฐF to 2000ฐF  for all  oas
    compositions,  and, with air, ambient temperature data were also taken.
    
           Pressure was varied in 50 psi intervals from ami ,ent to 500  osiq.   In novin
    -------
    E?:t>
                                             m
                                             LU
                                                          Tor  :::si;LA7jF BCSHIN
     DISC1SASGE  ELECTRODE
    
    
    
    
    
    
    •TUDE ELECTF.O^E
    
    
    
    
    
    
    
    
    
    • HEA7EP
                                                         •ACCESS POPT
                                                         • 3O7TO.". SuPFORT
                                                         • GAS  INLET
               Figure 1. Laboratory Precipitttor and Pressun Vessel for Test Program
                                        643
    

    -------
                                  Table II.   fias Composition
    
                                          (Volume %)
    Component
    co2
    He
    ฐ2
    N2
    "2ฐ
    Substitute Fuel fias
    23.0
    18.5
    —
    53.5
    5.0
    'Cfombustion f,as
    9.2
    —
    2.8
    83.0
    5.0
           Data were t^ken for three discharge electrode sizes as shown in Table I with
    air.  For the combustion gas and substitute fuel gas mixtures, only the 2.34 mm wire
    was used.
    
           The primary data taken were current-voltaqe curves for each of the experimental
    conditions.  The current-voltaqe curves were obtained on an X-Y recorder by recording
    the curves for both increasing and decreasing voltaqe levels and repeating each
    trace.  Sparking voltage was determined as the final voltaae attained after being
    held at sparking for two minutes.   Corona starting voltages were determined by (1)
    observation of voltaqe at which corona pips disapp, ircd on the oscilliscope with
    decreasing applied voltage and (2) extrapolation or the current-voltage curves to
    zero.
    
    
    RESULTS
    
           The raw experimental data,  consisting of curves of linear current density
    (mA/m) vs impressed voltage (kV)  ire reproduced in Figures 2 throuah 5 for air,
    Fioure 6 for simulated combustion gas and Fiqure 7 for substitute (i.e., noncom-
    bustiblc) fuel gas.  Corona-starting and sparkover voltaaes, derived from these
    curves and independent measurements, are shown as functions of relative gas density,
    <•*, in Figures 8 to 10 for air. Figure 11 for combustion oas, and Fiaure 12 for
    substitute fuel gas.
    
           The first and most important objective is to examine th™ data for the puroosc
    of establishing temperature or pressure limits to a stable corona discharoe.  Such
    limits may be caused by:  i)  excessive currents at low voltages resultina from
    thermal ionization (where "excessive" and "low" are taken from the point of view of
    practical prccipitator operation)  and ii) the disappearance of (stable) corona due
    to the manifestation of the critical pressure.
    
           Examination of the data shows that catastrophic high-temperature currents are
    not observed in this study under any conditions.  This significant point is evident
    over the full range of experimental pressures and temperatures and both polarities.
    
    
    
    •The relative gas density 6 is taken with respect to atmosoheric oressure and room
     tenperature (294ฐK)
                                             644
    

    -------
    Figure 2. Current-Voltage Curva Taken in Dry Air at Temperatures ol 294 K. 533 K.
                     end 950 K for • 2344 mm Wire Electrode.
                                      645
    

    -------
    Figure 3.  Current-Voltage Curves Taken in Air at a Temperature of 811 K for
             Wire Electrode! of 1.575mm. 2.344mm. and 3.17Sm.n.
                                  646
    

    -------
    Figure 4. Current-Voltage Curves Taken in Air at • Temperature of 1089 K for
              Wire Electrodes of 1575mm. 2344mm. and 3.175mm.
                                   647
    

    -------
    Figure 5. Currant-Voltage Curvm Taken in Air it a Temperature of 1386 K for Win
                  Electrodes of 1.575mm, 2344mm. and 3.175mm.
                                    648
    

    -------
    o\
    f*
    VO
                                                 Figure 6.  Current-Voltage Curves Taken in • Simulated Combustion Gas Mixture for
    
                                                Temperatures of 533 K, 811 Kt 1089 K, and 1366 K Using a 2.344mm Wire Electrode.
    

    -------
    at
    vn
    o
    
    • *
    i.
    c
    r
    
    ' a
    ปuttt<*l
    1. JLU^>
    11 ซU M M MM 'f
    •ซt !•ซ•.*•
    *
    S%
    Ij
    a
    — -f r - .
    •uป'ปi
    'b
    i.
    —
    I
    c
    di
    <•
    1.
    j;
    - , , ,
    
                                                                                         "f
    \
                                                  Figur* 7. Current-VolUge Curvซi Taken With a Substitute Fuel Get Mixture at
    
                                                   TemperaturM of 533 K. 811 K. and 1366 K for • ?.344mm Wira Eloctrodt.
    

    -------
                                        • I
                                     a   i
             Figure 8. Sparking and Corona Starting Voltage in Air at a Function oป
                         Relative Air Density at 294 K and 533 K.
                      B   v'
    
                                                i  3  JTrl.
                                                I S ..
    j ~r" g **
    1
    -, -.*
    '! • • • • * 5 "*'
    > o
    j . .-•••; •-
    >/• 	 I ';
    rr_ f
    
    
    [••'-. :::'....
       Figure 9.  Sparkwig and Corona Starting Voltages in Air as a Function of the Relative
    Air Density at 811 K and 950 K for Wire Electrodes ot 3.175mm, 2344mm. and 1.575mm.
    
    
                                         651
    

    -------
    H
     •1
      13    :•"
        Hi*
                                             '.ir
                                                •
    
                                                                    iv—  • • a*
              --.-I   *
                    J   i
                         I  —        f
    
                            *""
    
                                                                 W. -
    13
        --• .  .,_
    ,   . . i ~— -
    •   •. ..
    
    
        '
                                             .
          Figure 10. Sper*ing and Corona Starting Voltage* in Air a • Function of Rctetitt
    
    Air C*nuTf it 1089 K and 1366 K end for Win Ekjctrodnof 3.17Smm.2.3C4mm. and 1.575mm.
                                        652
    

    -------
                                                      '!,-::::'.':: I   l,-:
                              7f:._'.-_.
    ^T '•~"'-;-
             -  h :
                                                       q      .
                                                      T ซl     •
                                                       5.•:.•:::...i     *.'
          Ftgufป11. Spsrkcng and Coron* Suning Vohagn fora Simulated Combustion Gaj Miปturซ ttป
       Function of Rclnivt Gn Ocmtty ซ 533 K. 811 K. 1083 K. tod 1366 K fof • 2.344mm Wtiป Elwtrode.
    :,; ITI::':"
    •••i
    ..j
    i
    ] •
    L:.;.-:.-.:.-.:.::
    d fTCl'" b
    fZ,
    iป. .
    'I ••'.:" . "
    3u.u:-:"ej -
    •3~" ..! 5?
    
    'i?:::' f:-:
    •/T-il"' d !
    :
    1
    
    ,.."::...!
     .
    5-1
                                                         "^r:
         Figure 12. Spwfcng •ซ) Coran* Stirling Voluget in a Stdatitut* Fud Oซ Mixtur* M • Ftmctiofl
           of Rซl*tnป On Ownity M 633 K. 8J1 K. 1089 K. end 1366 K lor • 2.344mm Wnป EtoetrwJfc
                                             653
    

    -------
            ;• -:•::;>  :..- ••x:..!-:ซ •••>.  •.':•.ป  r ;.--..iw.iy  T'jrr'T^s  ^t. low  volt i-if? ..re  ~',s'.  lik-lv to
    oco-;r  at  tj.i-  I'^v-'-'vT  ':.!-• '!e:isi* iซ-"    II''V.-'-"ซ-r   for  t * <• r'-'iu* -•-*•-  '"iror.a ซj*  '  l*-ss  ?ha*:
    .il.'jj1  -inity,  t :;•• r-Y-T-.e i::  •:ซ.-rซ.-r.i 1 iy '..••;••.  i.e..  •.'.'• :>r'-r.'.,irk'ivซ-r c'jr r'-nป::  .ir'.- ruch
    lซ.-sr.  • h,i:. at.  iii':!.--i  •:••.•.:; i ป.!ซ••;.   !'•..'  i.'jsitiv t.ol.ir i •.-/.  • r.ซ- low-'  :.r.-r-.:,.ir i-.ov.-r
    
    sifJ'-ri.'i'i  the  posit i ve ti i ::r7n.ir':--,  the data show '.ha*,  c'jr.b'i::'-ior
    |e:;sซ-r  extent ,  l',vซ •;*. d.-rv.ir ie:;.   (-.'it ,  in .ir:y eve.-.t, -i  :-r'.ซk,lep
    as*:->c > .it ed with low  'ier.-. i t. jes d'>e;;  r:f>t  -irir.e.
    
    
    l.-ant  .it  lower  tซ-ri<-r.i'.'jr<-:.,  ซ>..it  Mi-- or i t ir7,i 1-:,rer.-:'jr<- :ik!"p.o.-?er.oii woul'! set an
    iif.i>'-r-:.ri-:;:;-ir<-  lir>it  t-j th<-  i-'initiv- cur rent -•/•> 1 t.i-ป" t:urv-s an-i  t h'- .T.;so':iซiป.o'l
    vol t jซit —tlej.;; i ty ป-.irv<-!: --  uiv,n '-or-v.-rt i r;'i density  to :-::  !->r e.ich  (xilarity, i!  i r.  clear • li.it  'he r.e'T.it i vซ-  -7rttic.il
    iปri-s-:urt-  .ilw.iyr. exrt-edr: t !iซ'-  i.oritive.    It  is furt'i'.-r .iptj.irent  t h.i'- • he ne-iative
    critic.il  iire;;sui.-,  like '!:••  |>o-.it.ive,  i nere,-ir:<.-s with tennซ-r.'iป.!jre.   ! r\  other virds,
    'he tiiuln'-r the  r--r.:--i at i;r<.-,  the >ire.it.er  the  r.iti'ie  ri! :,rซ.-:;r.urer.  for r.t.ahle r:ซ.-M.it i v>*
    corona.
    
          Oinn.ir i son ol t t.e sn.irkover-vol t ,i'ie  vs  ;' ricr.jres  H- 1 0 r-'Vals
    a t"t,.|i-n':y t<:r  tre s,-)-;itive  r.i-.irkover volt.i'ir to exceed the :i."iative .it  t emiier.jf ure-,
    of  ri ! I  r  and  li inner  and tor  low air  densities (.  lc;;:; t.han 1 or 2).  "}•.ซ• data  .ire
    not une'iui vi<:a I on tin:; •.•.<•• if in  each c.isr ,  hut  'he  trend sirens clear,  u.irl icular 1 v
    
    in-native  than jiositivo ป:urrป-nt.n pn-vailinn at a nivi.-n voltane  at  ปhe hi'iher  tt-mner.it'irci
    are,  howevei1,  unrii :.t akahle.
    
            r.omewhat  hinder in-nalive than Kosit.ive current:;  that m.'iv he ol>served  at  ปho
    lower  ten|ป-rat uro-; are, in  part,  to  |,e  at.t r I b.Jted  to the  s inn i f i cant rree-e Icot ro.i
    comf*onซ-nt of  t he cjrrent presertt  ?-ir ri-lat i velv  lonn mean ''r'-i'-  uat hs (low : ) and
    narruw  in'erelect r<ปle sn.icinn.
    
            AM.11 n,  it  rs-iy hi: nen- :allv  (thounh not inv.iriahly)  :;eer.  rror\ Kiitur'"ป  H-10
    that,  above  an  air d'-n:;ity  of 1 or  2,  the nena' iv  soar ko-.-er volt.Ki*.- i :•  hinhiT  * han
    •_he ixDGi'ivi.-.   f-inre i noro.ir.ed density  reduces tho  mean f roe oath", and nobilities of
    the charne carriers,  enhanced oloct ron  attachment  and increase.! neuat.i ve-ion snace-
    charne  itensity  ninht  ho ex|x-cted  to  li.-ad  to  hi'iher  nenativr r.narkover  voltam-a.
    That  in,  hinh pressure in  combination with hinh  temperature restores,  in a r.enso,
    tho low-tempi-raturo  situation.
    
            In tho c.tso of substitute  fuel nas (Kinurt;  12) the iปositi\o suarkovor voltace
    excoof1:! tho  noaatjvo, over  tho full  temperature  ran'io shown, 1111 to .1 density of 6 or
    7.  For combustion aas (Finurc 11)  th-:  transition  occurs  at about a density of  4 for
    temperatures  of,  or  nroator  than,  loa9  K.
    
            As temperature and  pressure arc  increased  toq<;thor,  'or  all of  tho oxoor ipen'.il
    situations,  it  is  clear from the  data that precipitation  is i:or.siblo at  sinni f Scant ly
    hinhcr  voltanes than at normal conditions.   This  is  a most important fact whon
    assessing tho viability of  electrostatic  urecipitat ion  'or hiah tenuorature, hioh
    pressure particulato removal  applications, esoecially in  comnarison to other collection
    devices.   Tho reason for this is  that the rate of  particle collection  in a orocioitator
    is  rounhly proportional to the square of  the electric field stronath in  tho orecinita-
    tor.   The field strennth in  turn  increases with  npolii.-d volta-:o.   Tho  not effect of
    an  increase  in  particle collection efficiency, or  a  decrease  in :>r.--cioi t.'tv.: size.
    Thus  precipitation becomes  noro efficient as temoorature  and urossuro  increase
    together.
                                                    654
    

    -------
           Other  particle- c >1 lect ion i!o>vicfs such  -is filters of  various tyuos, cyolor.es,
    otc. -Jo  not bonofi". fro->.  increasing temperature and orossuro.   In fact, -oerforr.anco
    deteriorates  in th^so -ovicos  becauso of i r.crea.s ir.q iias viscosity ar.J dorreasi r.!'• thซ.- na -or  conclusions  dt-rivcd fron this work:
    
            1.   Thoro arซ- r.o torir.cr.it uri.- or pressure linitations to cl>-ct ror.tat ic  ure
     ipitation  cvor tho ran'ic stu-iiod.
    
            2.   Precipitation boccr^s  noro ot'ficicnt with increasing tor.uซ.-rat ure ami
     .ross'jre.   This is in diri-cf  contrast to the  trend of other ocrticl-- collection
     ir;V ic<:^.
    
            1.   Critical pressure  increases with tonpcrature.
    
            4.   !.''"'iat ivซ- critical  pressure is hi'ihor than nositive.
    
            rj.   ;.'cซi.ปli •.•<•• currents  arc  hit>i r.so.-.,  M.,  "I'.lectrontat ic I recipitat ion" in Air ''ol lulipji_Contฃol , K,  Strauss,
        • -I.,  Voi.  1,  V.'i ley-Interr>c-ii'nce, New York,  lrป71, "in/." 227- US"     ~
    
    2.  Cooperrvjn,  I'., "Stxintaneous lonization of  f,ar,es at Hioh Tonijoraturo, Tonforonco
        tMper C1-17J.  .••--n-r.  IMS'.  i:lec. Knurs.,  1*165
    
    1.  H row: >.  f.  r .  .inii w.ilK^r,  A. h., Teasifoi 1 i ty IV'nonat rat ion  of Klectros-.atic
        I'recipitat ion jt 1700ฐK"  •) . Air Pollution  Control Ansoc. ?1 , 617-620 (1971)
    
    4.  roopeman,  I1., "Stjont.'inซrous lonJ7..ปtion of  Oasos at Hiqh Temperature," Paper l"S-
    MO:J-6,   Ir.st..  I'.'octron.  Kn.iru., l'ป71
    
    r>.  hnliinson.  M. ,  'Critical  Pressure.-, of "he  Positive Corona Between Concentric
    Cylinders  in  Air,' .1. Aniil.  !'hys.  40. 5107-5112 (1969)
    
    6.  H'jwoll.  A.  H. , "Breakdown Studies in Compressed r.asos," Trans.  Am. Inst.  Klec.
        Knars..  S?, 153-204  (I9J9)
                                                 655
    

    -------
    Corrosion and Erosion
              657
    

    -------
                           INTRODUCTION
         STAMT.Y DAPK'mAS, CHAIRMAN:  Our next speaker will  bo Anne Rowe
    of NASA-Lewis.   The title of her paper will  he "Corrosion/Frosion of
    Turhine Blade Materials  in the Hiqh-Velocity Effluent  of a Pres-
    surized Fluidized  foal Conhustor."  Coauthors on this  are Zellars and
    Lowell, also of  f.'A.SA.
                                    659
    

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                                  Erosion/Corrosion of Turbine Airfoil
                                Materials in the High-Velocity Effluent of
                                A Pressurized Fluidized Coal Combustor
                                     Glenn R. Zellars. Anne P. Rowe. and
                                                Carl E. Lowell
                                           Lewis Research Center
                                National Aeronautics and Space Administration
                                              Cleveland. Ohio
     , ,;  /_..-.->  •,.-,:•••'•  • .  . • vi  •••••• ..••••.-••••• f •• • .	•.	,.   •/••'•
     • '  '  •-  •'.ป  I.. I..*	    /.!.•*!     ..   ...  > .  - ..,	,  /  .
    
                                      in K'l'.  ', tr." I'.r.t rr'. r^'>n  !::  ! •>••••!•.•.• i  !n • :.••  '. • :>  !*<••:•••-
    •ro it.cl.
    ^orpriri'^r^t.r;, rtr.  "o^n  In  r'it*.  P.   K',*jrl*_-  -j  I:; :i  .*.?}. '-.".Tt I '• -ir'-.w! :;ป• :;h"iv;Inr vri" :'ซ%1';" \'•_, LT,
     o  03 en  (9 In.  to ^1  !n.)  '.r.  ^0?  rn (6-1/2 ft).  ":;•?  ti".i •.lonJrinfrs  rrojoclca *.h.-jt t.:.c
                                                    660
    

    -------
    Figurtl. Lewi* PFB Tot Facility.
                661
    

    -------
                                FUTURE
                    CARROUSEL  CYCLONE
                    WEDGE      AND
                    TESTUNIT-v  FILTERH
    
                    TV        ViCTj
                    CAMERA
    
                          ^
                 SOLIDS
                 REMOVAL
                 SCREW
    Oi
    ro
                                                          FILTER
                                                                                                                             "r
                       Figure 2. High Bay Ten Area.
    Figure 3. Schematic Drawing o< Corrlnntoi and Aumli.iry Coi
    

    -------
    
         ..  •     .'  ' -.-  :..•••,-    .:'  • :.••  >.•• :  •.:. :    . -.  -,••.:••••  I':.'-.  ;•• /.;...;)  :,-  • !;..-  •.-:   of  • •:••
    
    *:.::••   ':.•:•.: :.-:-.••.•  -:.-sr:   ':-.:•:.••:•.:  •ป•.-;  •  :.••::.    r.;--".--:.: -i i  •.::•;  x-:--iy  :! :':':• , ••':':.  ••.:.•<";.-.-1
    :•'. v -i i • •:   .'•..   .,   i-:.-::--  •':•-.  K--;'--.,  '•:.'!  -::.or  '.r^';:.'2  :,:'  •"
    
                  -.;  -.:'.' \i.:."    :'  :;.•;  '.'•.;:•  ••. '. r •:•••.:'••.   i"i".  :..:•''.,'.•..••   -.\\',;-.:;  -.-.•'.-•r'.•••>.  L-.---,-:n--
                                     _
                                                                     663
    

    -------
    Figurt4. CVYT AftซTซt.
    
    
    
    
            664
    

    -------
                          COMBUSTOR EFFLUENT
    o
    
    OS
     Qฃ
     JLJ
     Q_
    1100
                     10
                               20   30    40
                                  TIME, hr
                                                 TOTAL
                                               AIR FLOW
                                               Ib/hr kg/hr
                                               650-1300
                                               600 J 275
    50   60
          Figure 5. Representative Temperature and Flow Variation!
           During the Second Week of the 150 m/iee 745 C Test.
                      TABLE!
        COAL AND  LIMESTONE  ANALYSES
    COAL
    CONSTITUENT wt %
    FIXED CARBON
    VOLATILES (INCLUDING 1.86%
    ASH
    
    SILICA
    ALUMINA
    FERRIC OXIDE
    LIME
    PHOS PENTOXIDE
    TITANIA
    POTASSIUM OXIDE
    SODIUM OXIDE
    SULFUR TRIOXIDE
    MAGNESIA
    UNDETERMINED
    SULFUR
    JOULES
    Btu
    53.92
    SULFUR) 38.07
    
    
    3.74
    2.04
    1.37
    .32
    .03
    .06
    .10
    .03
    .14
    .06
    .14
    1.86
    3.157xl07/kg
    13586/lb
    LIMESTONE
    CONSTITUENT wt %
    SULFUR 0.02
    SILICA 1.28
    ALUMINA <. 10
    CALCIUM CARBONATE 96.32
    MAGNESIA .51
    UNDETERMINED 1.77
    
    
    
    
    
    
    
    
    
    
    
    
                           665
    

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                TABLE II
    SUMMARY OF  TEST  CONDITIONS
    TEST
    NO.
    
    
    
    I
    II
    III
    IV
    GAS
    VELOCITY,
    m/sec
    
    
    150
    270
    150
    270
    SPECIMN
    TEMP.
    c
    
    
    745
    720
    800
    790
    AVC
    SOLIDS
    LOADING,
    g/scm
    
    3.9
    4.4
    2.3
    3.7
    AVG GAS COMPOSITION
    
    
    
    ฐ2-
    %
    7.7
    7.6
    11.7
    6.6
    
    
    co2.
    %
    9.5
    10.6
    7.5
    11.1
    
    
    CO.
    ppm
    20
    14
    9
    4
    
    
    NOX,
    ppm
    122
    110
    231
    239
    
    
    so2.
    ppm
    450
    420
    258
    365
    
    
    THC.
    ppm
    2
    2
    2
    1
                                     CS-77-2681
           Fiซura6. Effluent Pvticta from PFB.
                    666
    

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                TABLE III
    
    MASTER HEAT ALLOY COMPOSITIONS
                  wt%
    
    Ni
    Co
    Cr
    At
    Ti
    Ta
    Id
    A/In
    nfJ
    •jf
    L\
    ft
    et
    >l
    c
    B
    S
    Uf
    MI
    IN-100
    HAL
    14.90
    9.30
    5 ?S
    4.90
    
    ? sn
    C. ou
    08
    . Uo
    a 21
    on
    .07
    ff,
    . U5
    a i?
    .014
    .C92
    
    U-700
    BAL
    15.50
    14.20
    4 on
    3.25
    
    A A(\
    
    
    
    a 10
    
    
    a 06
    .016
    .004
    
    IN-792
    BAL
    9.20
    1Z70
    a cjt
    j. Jt
    3.90
    4nc
    . (fj
    1 OA
    1. VO
    4 in
    . 1U
    nA
    . UD
    a is
    
    
    a 10
    .015
    .005
    on
    . CU
    MM-509
    9.90
    BAL
    S. 4
    
    a 28
    i in
    3. /U
    
    A QC
    O.'O
    JIH
    .*u>
    a 32
    
    
    a 59
    .006
    .007
    
                                      CS-77-2475
                  667
    

    -------
    and MX-509 as an e/.a.r.ple of a Co-base vane alloy.   These par-t Icular alloys were
    selected because they have boon used ox tons I vely  !n corrosion  studies lr. our labora-
    tories and thus offer possi bl 1 it ier of data correlation.
    
           Figure 7 is a sketch of the wedge  :;p.ec I men.   The  fc.-jse Is held in the carrousel
    by a set screw, while the top end Is free.  The narrow e*i ;••ป•; or. the left !c designated
    the leading ed;;e; the curved surface opposite  In  the trail'm:  od^e.  L-x-.'/iInr. alori,", the
    leading '--dee from the free end, the side  In view  is sailed the left face and the one
    behind Is the rl;;ht face.
    
    
    RECULT:; AJ;D Di"cu::r.io:!
    
           Specimens exposed In the CWT to the high-velocity coal  combustion products of
    the PFii suffered damar.e fron both erosion and corros:lon, the extent depending prinar-
    ily on the velocity of the n/'H stream, the solids  loading In the ,~as, the specimen
    ter.perature, and to a lesser extent the alloy properties.
    
           As a result of the r.eometry of the test section and entry nor.zle, Inpait of t.he
    f;as strenn on the rotating specimens produced unevenly distributed d.-:r.na>;e.  I'r.!r.ary
    r.aterlal removal occurred at the center section of  ee.ch  specimen,  which was directly
    above the noz/.le and thus received the maximum impact  of the gas stream and the
    erc-sive particles.  As can be seen In Fl^. 8, a photograph of  specimens fron the
    second test run, the leading cdt;c shows the greatest material  loss.  :'.oth face:; are
    eroded, and the trailing edge also loses  some material although It is exposed to '.ho
    direct path of the stream only a third as much time a:> the leading edr.e.  Kvldence
    tliat the direct partt'ilo paths aro diverted by the  rotating specimens is seen in the
    fact that the two faces experience slightly different  damage patterns:   the rljfht- face
    suffers somewhat more damage than the left.
    
           Stronf; dependence of erosive damage on geometrical factors err,phasl;:f.-. the
    necessity of testing turbine materials for PKB applications in a turbine confli'uratioa.
    
           At the end of each test the wedge  specimens  were  removed fron the carrousel,
    rinsed in cold water, wiped dry, wcir.hed, measured, ptioto;;raphed,  and then aee tinned
    for notallographlc examination.  Loose du.st war, removed  by this procedure but there
    remained particles of KepOj, r;iOp, and CaoO/i  firmly embedded in the specimen surfaces
    after exposure at both velocities.  I-Mgure 9  shew::  scanning; electron mlcroivypiis; (.':!•::•!)
    and energy dispersive spectra (KD.S) of the elements present on the surfaces of two
    typical eroded leading; edr.es.  ."EM portrays raised  areas, in this  case  the embedded
    particles, as lighter than the background alloy.  The  KD.'; scans Indicate Ca and ;; from
    CaSOlj, Fo from FejO^, and oi and Al from  aluminum silicates and SlOp, aloni; with Ti,
    Cr, Co and i.'l fron the alloy3.  Oxyi;en docs not appeal- on the  EDS scans because it is
    out of ranr;e of this analysis technique.
    
           Figure 10 Is a cross-sec' tonal view of an  lil-100  specimen from the high-velocity
    h'Eh-temperature run In which the particles,  SiOj  In this case, have deformed the usual
    cubic Y-Y' morphology of this alloy, by the force of the Impact.  The Au peak Identi-
    fied In this and subsequent EDS seine arises  from the  coating  applied to make the
    specimens conductive for SEil analysis.
    
           The leading edge to trailing edge  distance,  t,  at the center of  each specimen
    was measured by micrometer before and after exposure.   Since Initial examination of
    the specimens had shown that erosion wis  the  primary mechanism of danage, the center
    section At data were divided by the average solids  loading for the run  In order to
    assist In evaluating temperature and velocity effects.
    
           The resulting data are listed In Table IV, grouped by velocity to show the
    relatively small influence of the temperature differences a;id  the  much  larger Influ-
    ence of the gas velocity differences.  Duplicate alloy specimens gave results that
    agreed within i 0.3 cm/yr :• g/scm.  Thus  differences between alloys under the same
    test conditions are In some cases below the level of significance.  Minor differences
    are really insignificant anyway since the smallest  loss  rate in the table represents
    a loss of over 2 cm In 10,000 hrs, totally unacceptable  for power turbine application.
    This result was of course not unexpected:  these tests were run in order to establish
    a base for comparison with results after  various  levels  of gas clean-up.
    
    
                                              668
    

    -------
                        1.27cm
    ESTIMATED EFFECTIVE
    ATTACK AREA-13.5 cm? \
            ZONE OF HOT
            GAS STREAM <
            IMPINGEMENT
             1.27cmDlAM
        CS-77-2682
          Figure?. Carrotoel Wedge Test (CWT) Specimen.
    7.62cm
            Figure 8. Test Specimens After Exposure.
    
    
                        669
                                                          C-77-2880
    

    -------
    

    -------
       VfVfl
    SPFCIViFf,
    
    

    -------
           Although differences between loss rates  for different alloys and u.: f ferer.t
    temperatures are snail,  '.he v-;ocl:.y "ffe::t  Is  -jioar,  as seen In .-'ฐ evidence
    of reaction products.   If  i:;-]i)9 reacted, as would be  expected from the previous  test
    results, both  reaction  product:: and depleted son-- have  been eroded away.
    
           In the  third  t-st,  at. 1^0 ryr..,-; ;lnd 80"  C  for 91 hours, all four alloy:-,  devel-
    oped continuous layers  of  react Inri products  and depl"t!on -/.ones, a:; seen In  Fig.  1 •'',
    on both faces  and  trail Ing  ..-dgos.  These lay.-:; had  been larger, oi-oded away f:-.-:m thv
    leading edge:;, a portion of wnlch can be seen In  the il-700 nir-rograph.  Th^  'i -p:ot ion
    zone on :-!M-C09 '-'annot be seen !r; this 1'1,-ur--.' t.-ecause It Iri'/olves fine  :;tr:i':ture wh !'-•::
    Is not resolved by light microscopy; It appears In .".KM  mlcroj-raphs.
    
           .'IKK examination  of  the reaction product  arid depletion layers,  exar-.p :••:; of  which
    are seen In Fig. l.:i, revealed small particles dm-p In  the depletion ::'.n-.-:!  '>'.' all  f;•,•:••..
    In some cases  the  scans suggest that the su! fides are  I.'!", It: snmo Crp."o,  in S''"'- botn.
    The uutrr layer1 of reaction products appears to be a mixture of corrosion  produc:'...; ••.::;!
    effluent particles.
    
           The presence  of  sulfides on thes-: alloys rr.ay  have arl:;ซ-n fr"".m  "ondensat Jr.t: of
    "aj.SOjj or >o.T)|| on the  r.[)eclmens, although ^00  C  Is  near '.he lower thr'-.-.hcl'J reported
    for that su7fldatlon nechanlr.tn. '  Neither of those compound.' war. ••':<:'• ••••' •••!  !:i the
    solids analyses, including a sample collected on  the test sect. Ion cold  f'.s:."er and
    analyzed by atomic absorption, but only a trace amount  is needed : :: ' nit late th?  reac-
    tion arid the possibility cannot be ruled out.   The coal analyses do Include  .",  '^i an-i
    K, and the !!a  did  not show up downstream; but the 1 lr:.estone contains  a iur.Ir.u:-. sili-
    cates, which it has  been suggested might be  effective  in tying up the  ulk.-il! :.vtals
    an.,1 thus preventing  sulfate formation.
    
           An altersiatlve mechanism for sul f i'iatlor; Is reaction with gaseous :;0-.  A  trial
    calculation on the basis of equilibrium gas  compositions yielded values for-  '.h1"1 ."•?.
    0;j, and SO, pressures such that sulftdation  should not  occur, according to  the  therrr.c;-
    chemical diagrams.  However, the molecular gas  transport mechanism, for example,  which
    carries SO^ into the oxygen-poor Interior of the  alloy, has been reported-  to cause
    sulfidatlon with an  SOj pressure as low as the  average  calculated for  these  ru:?s.
    Also, that average value ma; well have been  exceeded substantially for short periods.
    
           In the  final  test,  at 270 m/sec and 790  C  for 36 hours, the s-ime types of  corro-
    sion products  were presumably formed as In the  previous run, but the  reaction r.ro-ijcts
    were removed more  rapidly  at the higher velocity.  Figure 17 shows an  example of  .'!!-
    rich oxides underlaid by a Cr-rich region and then a depleted son? cont.a Snir.~ '•I?-
    particles.  How-'/er, as seen in Fig. 18, most of  the reaction products and  depleted
    zones have been eroded  away.  Examination of crocr sections near the  free  ends  of the
    specimens Instead  of at the centers, where the  temperature was perhaps  lower than at
    the center but the erosive force was certainly  less, revealed both reaction  products
    and depleted zones as shown in i-'lg. 19.
                                               672
    

    -------
    HI IN-100
    O U-700
    ^ IN-792
    Q MM509
    20
    ^S 18
    >J "*
    Elk 16
    u? 14
    1 12
    i 10
    8
    S 6
    
    •? 4
    2
    n
    AT 730ฐ C
    —
    —
    —
    
    —
    _
    
    — P*1
    H hi
    lei ^ i
    •;;
    ;;
    /'
    1
    '•
    ';
    •;
    '
    .
    :-'
    •
    
    
    
    
    
    
    
    
    
    
    
    I
    
    \x
    ^
    1
    0
    
    is
    
    
    •
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    AT 795ฐ C
    —
    	
    —
    
    —
    -.
    
    —
    _
    B
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    il
    ILI
    tm
    :
    •
    x
    '.
    '•
    .
    i
    ^.
    -
    
    -•
    
    ซ>
    
    
    
    
    
    
    
    
    
    1 "
    |
    
    |
    v
    '..
    V ,
    V
    ง
    \'
    s
    
       150        270               150
              GAS VELOCITY, m/sec
    Figure 11.  Specimen Ccntar Section MซUI Lou.
                                                                         270
              :^f.,
              : >n  '><•ป•? .
      C'VS
    DIRECTION     v->V/<
                    IN-100
              20 urn
            U-700
    IN-792
    MM-509
                        Figure 12. Face$ of Alloys Exposed it 150 m/ปc; 745 C. 100 houra.
    
                                             673
    

    -------
        RFACTION PRODUCTS
    OUTSIDE EDGE
                                                                                    Al\\  %>.:Cr
                                                                                      Si  Au ti   CO'
         AI :   ,   '.   \ Ni
           Au Ti   Cr  Co
                                Figure 13.  IN-100 Exposed at 150 m/sec; 745 C. 100 hours.
       GAS
    DIRECTION
                20 Mm
                           Figure 14. Left Facet of Alloys Exposed at 150 m/sec; 800 C. 91 hours.
    
    
                                                    674
    

    -------
       GAS
    JRFCTIOfv  ?
                                                    TRAILING EDGE
                         DEPLETED
                         ZONE WITH
                         PARTICLES
                                                                                CAS
                                                                              DIRECTION
                                                                              AREA WITH
                                                                              PARTICLES
    Au   S '   '.   '  Ni
          fi  C'r  Co
                                                         Au  S  fi \  \ \i
                                                                  C'r Co
             Figure 15. Sulfide Part:clot in Depleted Zone on U 700 Exposed it
                            1 SO in/MC; 800 C, 91 hours.
         Figure 16. Microprobe Confirmation of Sulfidaticn on IN-100 Expond at
                            ISO m/sec; 800 C. 91 hourj
                                     675
    

    -------
               .-.'  •. ;'' ••  *•;•'•• "ivi1*'
                    '                  '
                          Figure 17.  Resrfon Production Left Face of IN-100 Expowd at
                                          270 m'sec. 790 C. 36hours.
    i
          11)
                      Figure 18. Right F
    -------
    ;!ป•"(, 1111',
    
        ป
                       I'.KM'
    '.'"•'•: ••'-••
     l.i 700
                                                                        -••v  '
    IN-792
                      Figure 19  Right Facn Near Emh ot Alloys Exposed at 270 m/sec: 790 C. 36 hours.
                                                      677
    

    -------
    
                !'o;;r-  alloy:;  r,t  !.•:<: :.:;
                r,r.iv  :-c:;;:t. Jo:.  oi:::<.-.—/'.-'
        (3)   I.'..-|.o:::l::  o!'  boi' '.!iซ-  Tour  alloy::  •.••.:•.••']
               wvr'.1  :;lif,li'-  undo:-  ;.:!e::o  :-.--vo:-'-  ••-•onfjlt Ions.
    1 .  .!.   Ct:-!:iC/:r  .'iiri  ::.  Krl !•;•:,  -ti::i-h  "'•.•r>r,'-r':i<.'j:-'-  Cor-r-oslor!  ! r.  Kl-j: ri I::•_••{  ':••':•'.  S-.r.:i ::::.--i-:;
        A".:-::-:  wintor  ;-:t.,;.,  :;•-••.•:  Y.,:*,  i^.r.,   !?y-:.
                                                                 678
    

    -------
               QUESTIONS/RESPONSES/COMMENTS
    
    
         STANLEY  DAPKUNAS, CHAIRMAN:  We have time for a couple of
    questions,  if whoever has a question will please go to the microphone
    and identify  themselves and submit their question ir, writinq.
    
         MR.  OILS:   Ray Oils, National Bureau of Standards.   What  was  the
    particle  velocity?
    
         MS.  ROWE:   We did not make that calculation.  We calculated the
    gas velocity, a  d we realized that the particles a>-e slightly  silver,
    but we have not  done that analysis.
    
         MR.  OILS:   Well, yes.  It could be markedly slower depending  on
    the configuration of the duct in which you place the specimen.  How
    long did  you  accelerate the particles, before you impinged then on
    the specimens?
    
         MS.  ROWE:   The entry nozzle  is perhaps two inches high.  It's
    decreasing  from  80 psig  In the bed.
    
         MR.  OILS:   Yes.  The problem, of course, is the drag on the
    particles.   You  may not have accelerated them long enough.  In two
    inches, in  that  type of gas stream, they will be entrained only to a
    small friction of the entraining  velocity; a half or a third or
    something of  this nature.
    
         MS.  ROWE:   I don't know what those numbers are.  I  thoroughly
    agree with  you,  but I don't know what you mean by "enough."  It was
    enough to chew up the specimens; and what we're trying to do--
    
         MR.  OILS:   Yes.  But not /50 ft/sec, or--
    
         MS.  ROWE:   That's the gas velocity; yes.
    
         MR.  OILS:   What was the actual temperature variation during the
    test?
    
         MS.  ROWE:   The lower temperatures were 720 and 745 Centigrade,
    the higher  790 and 800.
    
         MR.  OILS:   No; I mean during an individual test.
    
         MS.  ROWE:   Oh, the plot that I showed?  About 20 degrees  up and
    down.
    
         MR.  OILS:   This is metal temperature?
    
                                    679
    

    -------
         MS. ROWE:  The metal  tenperatures were within five degrees of it
    and, yes, followed it up and down.
    
         MR. DILS:  All right; thank you.
    
         STANLEY DAPKUNAS, CHAIRMAN:  We have one here from Sheldon Lee
    of Argonne Lab directed to Anne Rowe.   The question is, "Did you
    detect any alkaline metals on your testing specimens?"
    
         MS. ROWE:  No, we did not.  But let me remind you that the first
    thing that I did when I got them out of the bed  was to rinse them  off
    in cold water.  We frankly didn't expect to find sulfidation at
    that low a temperature; 80D was our top temperature, which is pretty
    well at the bottom of the temperature range for  the usual  sulfidation
    mechanisms.  The next tine, I'll use the hot water rinse,  and analyze
    for tra^j metals; but we didn't do it  in this case.
    
         STANLEY DAPKUNAS, CHAIRMAN:  Thank you.
                                     680
    

    -------
                             INTRODUCTION
    
    
         STANLEY PAPKIINAS,  CHAIRMAN:  Our next paper is entitled "High-
    Tenperature Corrosion of Metals and Alloys in Fluidized Red Combustion
    Systems," by John Stringer  of  EPRI.  John graduated from the University
    of Liverpool in 1955 with his  bachelor's.  His Ph.n. was received in
    '58; and in '75, he was awarded the degree of Doctor of Engineering
    by the University.
    
         He has been at Liverpool  except for the period of '63 to '66,
    when he was at Rattelle Columbus, and since sometime in 1977, he has
    been at EPRI.
    
         Dr. Stringer asks  that Robert LaNouze and Eddie Rogers of the
    Coal Research Establishment at the National Coal Board be credited
    for coauthorship of his paper.
                                    631
    

    -------
                             High-Temperature Corrosion of Metals
                                  and Alloys in Fluidized Bed
                                     Combustion Systems
                                          John Stringer
                                  Electric Power Research Institute
                                  R. D. La Nauze and E. A. Rogers
                                   Coal Research Establishment
                                       National Coal Board
    ABSTRACT
           A series of tests has  boon conducted to examine  the corrosion of metals  and
    alloys in various locations in atmospheric pressure  fluidized bed  combustors.  These
    tests l.ave revealed that under certain circumstances severe sulfidation/oxidation  cor-
    rosion of in-bed comisonents can occur.  A compact deposit  formed on  tho surface  of the
    in-bed components which was rich in calcium sulphate when  a limestone acceptor was used,
    but the presence of the deposit alone did not  seem sufficient for  corrosion  to occur.
    An additional factor is probably the presence  of local low oxyqen  a<  vity renions
    associated with relatively static parts of the bed.  The various factors are discussed,
    and possible remedies suqqested.
    
    
    INTRODUCTION
    
           Fireside corrosion of superheaters in conventional  pulverized coal-fired  boilers
    is due to the formation on the metal of a deposit of ash containinq  alkali sulfates.
    The detailed mechanism of attack is still a matter of some controversy, but  tho  forma-
    tion of the ash deposit is caused by the partial meltinq of the ash  particles  in tho
    hot combustion oases.  The alkalis are released from the minerals  in the coal, and
    react with sulfur .ind oxyqen to form sul fates:  it appears possible  th.it complex sul-
    fatcsf perhaps rontaininq iron, are formed.  These require the presence of hiqh  local
    partial pressures of KO-, which may develop beneath  the  ash deposits.  The sulfatcs are
    molten at least in some parts of the deposits.
    
           The relatively low combustion temperature in a t'luidizoi! bed  combustor  (fb'.'l
    should:-
           (a)  prevent ash fusion
           (b)  limit tho release of alkalis
    
           In addition, if there is a sulfur sorbent present ?.n the .bed, the formation of
    hiqh local SO  activities would appear to be unlikely.
    
           For these reasons fireside corrosion is less of a problem in  an fbc than  in
    conventional coal-fired boilers.  A literature survey (1), however,  showed that  very
    occasionally severe corrosion ot in-bed components at hiqh metal temperatures was
    encountered.  As a result a uroqram was initiated at the Coal Research F.stabl ishmcnt
    (CRE) of the National Coal Board (VCB) under the sponsorship of the  Electric Power
    "osearch Institute (EPRI) to study the corrosion of a range of alloys in different
       nations in a fluidized bod combustor.  This  proqram referred to  as the KPRI tests was
    managed by Combustion Systems Ltd., l!K.  Tests wore carried out at CRK.  Metallooraphic
    examination of duplicate sets of specimens wore undertaken by CRE  and in America by
    General Electric Co.  and Foster Wheeler Development Corp.
    
           Subsequently a joint Ncn/EPRI scries of tests have  been undertaken as a follow
    up to the EPRI tests.
    
           This paper discusses both series of tests.  It attempts to  outline the important
    conclusions that can be drawn from the data, to elucidate  what materials problem areas
    exist and what steps can or should be undertaken to eliminate them.  More detailed
    metallographic results on the EPRI proqram appear elsewhere (2).
                                              682
    

    -------
    THE EPRI TESTS
    
           This program used the 0.3n (12 in) square atmosoheric pressure combustor at CRH.
    Turbine materials were tested  for possib'c pressurized fbc applications, and  for  this
    reason the nomine1 bed temperature of 900 C (1650 F) was 50 c  (90 F) higher than  used
    previously (3) (4).  The other bed operating conditions were:-
              Fluidizing velocity                0.9 m/s (3 ft/s)
              Excess air                         10-20?
              Coal                               Illinois No. 6
              Acceptor                           Penrith (UK) limestone
              Ca:S i  tio                         3:1
              SO  cc  :ent of exhaust gas         300-400 ppm
    
           Two j  '";" h tests wcro conducted under nominally identical conditions.
    
           Specimens of different  alloys (Table I) were tested as:-
              (i)  In-bed air-cooled ' -.ibes
             (ii)  Above bed (freobo-Ti  ) air-cooled tubes
            (iii)  In-bed uncooleo Trjpons
             (iv)  Freeboard uncoo" d coupons
              (v)  Pins in the ex'iaust gases after the secondary cyclone.
    
           The last group of specimens was included to test possible turbine materials.
    Three test sections were installed .nftcr the secondary cyclone, the first and second
    sections wore designed to operate at the scimc nominal gas temperature, but at nominal
    gas velocities of 30.5 m/s (100 ft/s) and 61 m/s (200 ft/s), respectively.  The third
    section was Designed to operate at -i gas velocity of 30.5 m/s  (100 ft/s) and at a lower
    temperature.   in practice, because of heat losses through the walls of the system, it
    proved extremely difficult 'o  attain the required temperatures in the turbine test sec-
    tion.  Some natural gas was burned in the freeboard to raise the exit gas temperature,
    but the amount of this was limited by the need to i:void sintering of the dust and to
    minimize the change in exit gas composition.  For the tests, the nominal temperature
    .';i the first and second test sections was 800 C (1470 F) with 720 C (1330 F)  in the
    third section.  It seems likely that tho temperatures were tco low and the times  too
    short to aive a realistic estimate of the likelihood of hot corrosion in a gas turbine.
    Similarly,  tho velocities were almost certainly too low to give an estimate of possible
    erosion in the turbine.  Because of this, the primary node of attack in the turbine
    naterials was difficult to ascertain.  Oxidation was felt to be the r.ajor form of
    attiick although sulfidation was detected *n several specimens.  C,~ 25-J1 demonstrated
    the best resistance to attach, while r,TD-lll, i:;-713 LC ar.d i;;-738 also performed well.
    Inconel C71 exhibited very severe local corrosion.
    
    
    RESULTS
    
    Tn-Bod Air Cooled Tubes
    
    Specimen temperatures
    
           There were four in-bed  specimen tubes, each compiled of rino scaments 19—.n (0.75
    in) long:  50rni (2 in)  OD and approximately 42mm (1.65 in) ID.  The nominal temperatures
    of these fcjr tubes were 540,  650,  760 and 840 C (1000, 1200, 1400 and 1550 F)'.  The
    two lower temperature tubes were chosen to study conditions appropriate to steam supor-
    heater tubvs, th<_- upper two to simulate conditions Appropriate to air cycle applica-
    tions.
    
           The tube temperatures were measured with thermocouples in vel's drilled in the
    rinos, and thus wore a measure of the mid-wall temperature.  The maximum surface
    temperatures  for  cacn  tube were higher',  as indicated below.
    
    
           During the experimental runs the temperatures were measured with four thornxi-
    couples along the length of  .ich tube at the 3 or 9 o'clock positions.  For an initial
    proving run,  two rings on a i 'be carried four thermocouples; one at the top, one at the
    bottom, and two at opposite si.'es in the 3 and 9 o'cป  k positions.  These revealed a
    circumferential temperature varidtion which increased as the temperature of the tube
    decreased.   The two rings showed different raaanitudss of the effect, suggesting that it
    
    
                                              683
    

    -------
    Table I.  Typical vJomposition of Alloys Tested
    
    Ferri t ic
    Steels
    Cor- Ten B
    2V Cr-1 Mo
    9 Cr-1 Mo
    Type 405 SS
    E-Brito 26-1
    GE 2541
    Austenit ic
    Steels
    (Cr-Ni-Fe)
    Nitronic 50
    Type 321 SS
    Type 310 SS
    Type 347 II SS
    
    Type 329 SS
    
    21-6-9
    Incoloy 800
    .'•'anauritc 36X
    liK-40
    Nickel-Base
    Alloys
    Inconel 690
    Inconel 601
    Inconel 617
    Inconel 671
    Hastclloy X
    
    RA 333
    
    U-500
    
    U-700
    IN-738
    GTD-111
    
    
    IN 713 LC
    
    Cobalt Base
    Alloys
    HA 188
    X-40
    XSX-414
    
    C
    
    
    0.
    0.
    0.
    0.
    0.
    0.
    
    
    
    0.
    0.
    0.
    0.
    
    0.
    
    0.
    0.
    0.
    0.
    
    
    0.
    0.
    0.
    0.
    0.
    
    0.
    
    0.
    
    0.
    0.
    0.
    
    
    0.
    
    
    
    
    
    
    2
    1
    1
    05
    001
    C2
    
    
    
    05
    06
    04
    06
    
    05
    
    03
    04
    4
    4
    
    
    05
    04
    07
    05
    1
    
    04
    
    08
    
    07
    1
    1
    
    
    1
    
    
    
    0.08
    0.
    0.
    
    5
    2
    
    Cr
    
    
    0.
    2.
    9
    12
    26
    25
    
    
    
    22
    18
    25
    18
    
    28
    
    20
    19
    25
    25
    
    
    27
    22
    22
    48
    21.
    
    25
    
    19
    
    14
    15
    14
    
    
    13
    
    
    
    22
    25
    30
    
    Ni
    
    
    5
    2
    -
    0.3
    0.1
    -
    
    
    
    12
    11.6
    17.2
    9.5
    
    4.2
    
    7.2
    31.5
    34
    20
    
    
    64.6
    61
    56
    51
    5 bal
    
    45
    
    bal
    
    .6 bal
    .7 bal
    bal
    
    
    .6 bal
    
    
    
    .2 22.3
    .8 10.6
    10.8
    
    Fe Co Mo
    
    
    bal
    bal - 1
    bal - 1
    bal
    bal 0.01 1
    69.5
    
    
    
    bal - 2
    bal - 0.3
    bal - 0.4
    bal 0.24 0.4
    
    bal 0.2 1.5
    
    ba 1 - 0.1
    46.5
    bal
    bal
    
    
    8 - -
    15.1
    0.2 12.2 8.7
    0.4 -
    18.5 2.1 9
    
    18 33
    
    0.3 19 4
    
    0.1 15 4.2
    0.2 8 1.7
    0.1 9.7 1.5
    
    
    0.2 0.5 4.6
    
    
    
    1.8 bal
    0.2 bal
    1.2 bal
    
    K M Ti
    
    
    -
    - - - 0
    0
    -0.1-0
    - - - 0
    4.76 - 0
    
    
    
    _
    - 0.4 1
    - - - 1
    - - - 1
    
    - - - 0
    
    -
    0.4 0.4 0
    - - - 1
    1
    
    
    0
    1.5 0.4 0
    -1-0
    0.2 0
    0.7 0
    
    - - - 1
    
    3.0 3.0 <0
    
    4.4 3.5 '0
    2.7 3.5 3.5 0
    3.0 5 '0
    
    
    6.0 '0.9 
    -------
    varied along the tube, but both showed the same general form of the temperature distri-
    bution.
    
           From this information the outside skin temperatures have been calculated to
    exceed the nominal tube temperatures by a maximum of 86, 73, fiO and 50 C (155, 132, 108,
    90 F) on the 540, 650, 760 and 840 C (1000, 1200. 1400 and 1550 F) tubes respectively.
    
           Generally, the hottest part of the tube was towards the top, and this may at
    first sight appear surprising.  As only four point temperature measurements were made,
    it is only clear that the tubes were hotter towards the top.  This may be consistent
    with measured circumferential variations of heat transfer coefficients, see for example
    Noack (5) which shows high heat transfer rates from the 10 o'clock to the 2 o'clock
    positions.  Clearly, a circumferential temperature variation of this magnitude is
    worrying, and from the point of view of materials selection it is important to estab-
    lish whether this is a general characteristic of tubes in fluidized beds.
    
    Tube Deposits
    
    At the end of each test period the tubes were found to be covered with a fairly thick
    polished deposit (Figure 1).  This was reddish brown on the upper two tubes and darker
    on the lower two tubes.  This color difference was a function of bed position not of
    tube temperature, because the position of the 650 C (1200 F) and 760 C (3400 F) tubes
    were exchanged for the second run.  The deposit consisted largely of calcium sulfate;
    there appeared to be some calcium oxide present together with other components derived
    from the coal ash.  There was a very small amount of cnrbon detectable.  No systematic
    variation in composition could be associated with the color difference.
    
           The deformation temperature of the deposit WPS found to be 1220 C (2230 F) which
    is well above the bed temperature suggesting that no significant part was molten at
    temperature.  However, this measurement was done under oxidizing and neutral conditions,
    and as will appear loter, reducing conditions might have been more appropriate.  It is
    common for the deformation temperature of coal ashes to be lower in reducing atmos-
    pheres than in oxidizing, although the difference is not usually greater than 100 C.
    CRE have been attempting to measure the sintering temperature of fine ash particles as
    distinct from the standard deformation temperature.  Although this work is still in the
    development stage, indications are that fine Illinois No. 6 ash particles sinter in a
    mildly reducing atmosphere at a temperature close to that of the bed.
    
           Under the scanning electron microscope, the deposits appeared remarkably compact
    and pore-free (Figure 2). composed of particles whose size appeared to be in the range
    l-5:-m.  This was very similar indeed to the particle size in the limestone used (Figure
    3).  High pressure mercury porosimetry on a deposit sample showed that there was less
    than 1% porosity for pore entrances with diameters in the range 58 - 0.014um, support-
    ing the scanning electron microscope observati ns.
    
           The severity of attack of the metal di'l not seem to be influenced by variations
    in the deposit thickness.
    
    Corrosion
    
           The most obvious feature of the corrosion of the in-bed tubes was the presence
    of sulfides beneath the surface of the metal in all the alloys.  The stainless steels
    exhibited a fairly uniform band containing discrete, more-or-less spherical sulfides.
    A typical example is shown in Figure 4, a specimen exposed during the NCB/EPRI tests.
    lor the three hotter tubes, the more sophisticated alloys such as Inconel 617, incoloy
    800 and Haynes 188 showed considerable grain-boundary penetration of sulfides  (Figure
    5).  These alloys also showed local breakdown of protective behavior, with thick oxide
    scales forming beneath the deposit and very considerable sulfi.de formation boneath the
    oxide.  Often -voids appeared to be present in the metal, which could have been due to
    loss of particles, e.g. sulfides or oxides, during specimen'preparation.  Between the
    oxide and the deposit there was frequently a bright white phase which electron probe
    raicroanalysis showed to be a sulfide of the base metals iron, nickel and cobalt, (Fig-
    ure 6).   Since these sulfides are not very stable, it demonstrates that the sulfur
    activity at this point must have been high.
    
           Figure 7 shows typical data for the scale thickness and internal penetration.
    The temperature dependence of the corrosion did not appear to be very great.  Incoloy
    
    
                                               685
    \
    

    -------
                        Figure 1. The General Appearance of tin- Tubes
                        Alter Withdrawal from the Combustor After the
                        First 1000 lu 1 f,t. Showmq the Polished Deposit
                                              tffl  -•
                                  *.:
    Figure 2. The Appearance of a Fracture
        Cross Section of the Deposit
    (scanning electron micrograph: x 2000)
    Figure3. The Surf ace of a Fragment of
      Pennth Limestone (SEM: x 2000).
                                       686
    

    -------
    Fiqi*rปป4. A Cross Section of a Sp^umen of Type
    347M s \ ( ซ|iriซM lot 1".() hr ,il a Met ll T.", J>.M.,
             !..!•• til 760C (1400r-i ป BOO
                                                                 figured.  A S|>**cimen of Hayrw& 188 ฃ
                                                                   lot 1000 hr at a MeTal Teni|>etdtuie ot 180C
                                                                (1550FI The D.irk Upp>-r Section r. the [>|>nsit
                                                                 Pnnciprilly Sulphate. The Liqht Colored Ph iw
                                                                   InitneilMtely Below the Deposit is a Cobalt
                                                                 Nickle Sulphide, the Uiqlit Grey Beneath Thii
                                                                is the Oxide  The Metal. With Internal Penetration
                                                                        ol Guide and Sulphide !ป 300)
        Figures. Specimen UR4|  Inconel 617 Enposed for 250 h in NCB/EPRI Test 2.  Metal Temperature
             843 C (1650 F).  fcr.oi.jY Dispersive Analysis ot Liqhi Globular Phase on Outside ot Suie.
                                                    687
    

    -------
    HASTEUOV X
    
    INCONEl 617
    
    INCONEL 601
    
    INCONEl 671
                      MAXIMUM   MAXIMUM
                     CORROSIVE     SCALE
                     PENETRATION
          Figure 7. Typical Data for the Maximum Corrosion of
                    the Alloys (second 1000 h test).
                                688
    

    -------
    800 was more severely corroded on the tube with a nominal temperature of 760 C (1400 F)
    than on the tubes at 6SO C (1200 F)  and 840 C (1550 F).  but the difference lay within
    what might be expected to be normal  scatter.
    
           The extent of attack en the 540 C (1000 F) tube was less than that observed on
    the higher temperature tubes.  This  may be partially due to the use on that tube of
    alloys somewhat less sensitive to sulfidation attack.
    
           There was a marked variation  in the attack around the circumference of the tubes,
    some regions appearing quite free of accelerated corrosion, while others exhibited
    severe sulfidation.  There was a tendency for the attack to be greater at the top of
    tubes, particularly for the sensitive alloys such as Incoloy 800 and Inconel 617.  It
    seems probable that this could not be attributed to the temperature variations alonซ,
    since:-
           (a)  the temperature dependence- of the corrosion appeared to be snail,
           (b)  the circumferential variation of attack was also present on the nominal
                840 C (1550 F) tube, on  which the circumferential variations of temperature
                were small.
    
           It was particularly interesting that Inconel 671, an alloy well-known for its
    resistance to aggressive oxidizing environments, suffered catastrophic corrosion.  This
    was the worst of the alloys investigated (Figure 8).
    
           The low-alloy feiritic steels, Corten B and 2V Cr-lMo oxidized rapidly.  However,
    in this range the oxidation of these stools is markedly dependent on temperature, and
    the considerable temperature variations on tho nominal 540 C (1000 F) tube nakes it
    difficult to pass judgement on the behaviour of these materials within che fluidized
    bc-1.
    
    Effect of Exposure Time
    
           It. had originally been the intention to expose most of the rings for 2000 h,
    removing a small number at 1000 h and replacing them with duplicates.  In the event,
    the rings were sufficiently disturbed during cooling at the end of the first test to
    fail a leak tost, so only 4 rings on tho 650 C  (1200 F)  tubes wore resubmitted foi the
    second tost.  Those showed much less than twice the attack of those exposed for 1000 h
    implying that the rate of attack was diminishing with time.
    
    Corrosion Criterion
    
           The Central Electricity Generating Board in the UK use a corrosion criterion
    which is equivalent to the loss of 7 mm of metal in 200,000 h, corresponding to the
    total loss of tho tube wall in tho lifetime of a boiler.  Since generally corrosion
    rates fall with time, this gives a reasonably conservative criterion for the extrapola-
    tion of tests of around 10.000 h length.  For a 1000 h test, 'his would he equivalent
    to a maximum loss of structural notal (metal lost by scaling plus the metal affected
    by internal sulfidation or oxidation) of 35:.m assuming a linear rate of loss.  This is
    almost certainly an excessively severe criterion.  For example, if it is assumed that
    the rate of metal loss varies with the square root of time (parabolic oxidation)  and
    that an acceptable loss after 200,000 h is 10% of the wall thickness, 700_m, then the
    acceptable loss at 1000 h would be 50;.m.  Both criteria  would give 70um at 2000 h.
    
           Very few of the alloys tested match these criteria.  At 650 C (1200 F) it scons
    likely that several alloys, includina the austcni!-.ic stainless stools, arc reasonably
    close, but at the higher metal temperatures no alloy meets those criteria.  Some alloys
    may be acceptable for use at the higher temperatures if a less stringent corrosion cri-
    terion can be tolerated.
    
    Above-Bod Air-Coolcd Tubes
    
           The two above-bed tubes had nominal metal temperatures of 650 C (1200 F) and
    760 C (1400 F) .  The deposit which forr.ed on these tubes was relatively loose and
    friable.   The tubes did not show appreciable corrosion,  and several alloys appear cap-
    able of meeting performance criteria (2).
                                              689
    

    -------
    Figur* 8. A Corrosion Pit on an Incond 671 Specimen
        Exposed for 250 h it • Metal TwnfMriture of
                 840C(1550F)
    -------
    The Uncooled Coupons
    
           As might be expected from the results of the cooled <;Decimens, several of the
    coupon materials exhibited severe sulfidation/oxidation attack in the bed, notably
    Inconel 671, '2).  This alloy also underwent severe corrosion in the freeboard.
    Several other alloys had sulfidation attack in the freeboard.  This may be due to the
    accumulation of deposit on the coupons,  or to the proximity of the natural gas flame.
    However, the attack in the freeboard was generally oxidation.  Within the bed, several
    alloys appeared to be corroding slowly enough to be acceptable as uncooled structural
    component materials, notably a G.E. alloy, GE 2541 which resembles Kanthal, and Haynes
    Alloy 188.  Two cast austenitics, UK 40 and Manaurito 36X were also marginally accept-
    able.
    
    
    DISCUSSION OF THE EPRI TESTS
    
           Clearly the most serious aspect of the EPRI tests was the sulfidation/oxidation
    of the in-bed tubes.  This contrasts with an earlier series of tests under the sponsor-
    ship cf EPA using the same combustor and similar nominal conditions which revealed
    little sulfidjtion  (3) (4).  The earlier test used a lower bod temperature 850 C
    (1560 F) and the significance of this is discussed later.
    
           Calcium sulfate can decompose to release sulfur, by a process such as
    
                               CaSO.   	ป   CaO + ปs S, + 3/2 O,
                                   4                  22
    and it is obvious that the lower the oxygen partial pressure (activity),  the higher the
    sulfur partial pressure (activity) and vice versa.  The normal excess oxygen levels
    would correspond to an oxygen partial pressure of 10   atm and at the bed temperature
    this would be equivalent to a sulfur partial pressure of 10~   atm or less.  This is
    insufficient to sulfidizc any of the components of the alloys.
    
           However, it is well known that fluidizod beds consist of two phases, a bubble
    phase and a dense or emulsion phase which is like the bed at incipient tluidization.
    The greater proportion of the fluidizing gas passes through the bed as bubbles.  Since
    the burning carbon particles reside in the dense phase, the oxygen concentration in
    this phase depends amongst other things on the rate of interchange of gas between the
    bubble and ciense phases.   Fluctuating oxygen concentrations in a fluidizcd bed com-
    bustor have been demonstrated by Gibbs et al (6) using a fast response mass spectro-
    meter.  The oxygen concentration in the dense phase was found to be significantly
    lower than that of the bubble phase.
    
           Experiments with a stabilized zirconia probe (7) have suggested that oxygen par-
    tial pressures of 10    atm may be present locally in the bed which corresponds to a
    sulfur partial pressure of around 10~  atm.  This is sufficient to sulfidize almost any
    alloy and certainly high enough for nickel sulf Ide to be stable.  The fact that iron
    and nickel-containing sulfides arc found between the oxid? scale and the  deposit proves
    that in this location the sulfur partial pressure does indeed reach values close to
    those calculated.  Figure 9, the Ca-O-S thermodynamic stability diagram,  and Figure 10,
    the stability diagrams for the major alloy elc icnts (8) , show that this condition
    produces an environment which is close to the oxide/sulfide/sulfate boundary.
    
           Low local oxygen partial pressures may be attained in several ways.
    
           (i)  High concentration of coal,  due for example to the proximity  of a coal feed
                port.
    
          (ii)  A relatively stagnant region of bed material which becomes oxygen starved.
    
         (iii)  Non-uniform flow of air through the bed, with air channelling through
                certain paths.
    
          (iv)  Uneven coal feeding:  if the coal feed increases markedly for a short time
                the oxygen partial pressure can drop abruptly-
    
           (v)  Cn the injection of coal, the vclatiles are released quite rapidly and can
                pass upward through the bed largely uncombusted; they burn in the freeboard
    
    
                                              691
    

    -------
    -60
            Figure 9.  Phasa Stability Diagram for the Ca-O-S System at 1000
                           andZOOOK (1310 and 1670F).
    IV
    s
    
    0
    -5
    
    ซx 10
    &
    S .,,
    
    -20
    -25
    
    -30
    -35
    -4O
    
    — Cf
    Suil.de / *'// '
    — / /^Sฎฐ
    
    ~ ** / •
    / s
    Fe. N. / /
    Cr
    	
    Mn
    -
    -
    Meul
    
    -
    1 1 1 1 1
    /
    
    
    
    
    
    
    //
    /
    
    
    
    
    
    
    \ \
    J
    
    
    
    
    
    
    
    
    
    
    |
    '//
    
    
    
    
    
    
    
    
    
    
    
    S
    
    
    M-O-S
    114< K()600;F)
    
    
    Onxit
    
    
    
    1 1 | 1 1
     -55   -50   -45  -40   -35   -30   -25   -20   -15   -10-5
                                                                      5    10   20
    Figure 10. Flute Stability in Fe. Ni. Co, Cr. Mn-S-O System et 1144ฐK (1600ฐ F).
    
    
                                      692
    

    -------
                immediately above the bed.  Clearly this is equivalent to a low oxygen
                activity zone passing through the bed.
    
          (vi)  Defluidization of parts of the bed can produce local regions starved of
                oxygen.
    
         (vii)  The dense phase, as discussed above, is itself relatively oxygen deficient.
    
        (viii)  Beneath an adherent deposit the oxygen activity may drop if oxygen removal
                by the oxidation reaction is relatively rapid in comparison to the influx
                of oxygen through the deposit layer.  This will clrarly be favored by
                thick, compact, deposits with low levels of porosity.
    
           In the present case, the deposit alono seems insufficient to produce the low
    oxygen partial pressures because some areas of the specimens wore covered witn thick
    deposits but showed no signs of corrosion.  It. is of course possible that the deposits
    had different porosity in different regions, but this was not apparent under the
    microscope.  The deposit, consisting largely of calcium sulfate, is however obviously
    of great importance as a source of sulfur.
    
           The 'stagnant region" hypothesis would imply that only the tops of the tubes
    would be attacked.  As mentioned before, thc-re was indeed a tendency for the top of
    the tube to be rather more corroded, but s-ilfidation was not confined to trioso regions.
    This therefore appears to be a factor in p. Jducing a corrosive environment, but is not
    in itself sufficient to explain the results.
    
           Thore was no obvious tendency for the attack to bo more severe near the coal
    port;  that is the 650 C (1200 F) and 760 C (1400 F) tubes were not obviously more
    corroded when they were in the lower row as opposed to the upper row.  Neither were
    the center rings on the tubes more corroded than those towards the ends.  These con-
    clusions may be altered when the experimental data are subjected to more detailed
    analysis.
    
           There was no evidence of uneven coal feeding or dcfluidization in the tests.
    Non-uniform air flow should be reflected in a non-uniform pattern of attack.  While the
    tests were not dosijnod to reveal such non uniformity, it would probably have been
    detected.
    
           On balance, therefore, it seemed likely thit the major factors contributing tc
    low oxygon activity, in order of importance, werc:-
    
           1.  Relatively stagnant regions of bed material on top of the tubes.
    
           2.  The presence of thick, compact deposits.
    
           It follows that possible solutions to the corrosion problem include:-
    
           (a)  Prevent the build up of a calcium sulfato-higli layer on the tubes.
    
           (b)  Prevent the establishment of stagnant regisns Above the tubes by adjustir.j:-
    
                  (i)   Fluidizing velocity
                 (ii)   Tube dimensions
                (iii)   Geometry of the tube array
    
           (c)  Try to ensure good gas and solids mixing in the bed to reduce reqions of
                low oxygen activity.  At the moment there appears to be little information
                on the level of oxygen activity in the bed, nor arc there combustion models
                of sufficient complexity from which the effects of operatini variables on
                the oxygen level can be estimated with confidence.  Factors which might be
                of importance include:-
    
                  (i)   Excess air
                 (ii)   Fluidizing velocity
                (iii)   Distributor dcsinn
                 (iv)   Method of coal feeding
                  (v)   Form and location of coal feed port
    
    
                                              693
    

    -------
                                                                                     f-.
               (vi)   Macro solids flow patterns
    
    
    THE NCB/EPRI TESTS
    
           A joint NCB/EPRT program has commenced to determine the important factors con-
    tributing to the corrosion observed in the EPRI tests.  A run time of 250 h was
    selected, because it was believed that now the pattern of corrosion had been recognized,
    a shorter time could be tolerated.  Attention was focussed en the in-bed tubes, with a
    rather more restricted range of alloys but including more stainless steels of the 18/10
    type.  The first three tests had the following conditions:-
    
           Tost 1 was essentially a duplicate of the EPRI conditions, to be sure that sul-
           fidation/oxidation could indeed be detected after 250 h.
    
           Test 2 used a bed temperature of 850 C (1560 F), so that the conditions were
           nominally the same as those in the earlier EPA supported tests, (3) which had
           produced only slight sulfidation/oxidation corrosion.  This was to test the
           view that the reason for the severe corrosion  in the EPRI tests was the higher
           bed temperature.
    
           Test 3 used a bed temperature of 900 C (1650 F) without limestone addition.
           The bed consisted entirely of coal ash.
    
    
    PRELIMINARY RESULTS OF THE NCB/EPRI TESTS
    
           The data from those three tests have not yet been fully analyzed, and the
    results presented here must be regarded as preliminary.  However, the major points are
    unlikely to bn altered by more detailed study.
    
           The first test produced corrosion essentially similar in character to that
    reported for the EPRI tests, with sensitive alloys such as Inconel 671, Inconel 617
    and Incoloy 800 showing significant sulf idation/ox'idation corrosion.
    
           The second tost showed a very similar degree of attack, suggesting that bed
    temperature in this instance is not a major variable in determining the extent of
    corrosion.  In detail, it appears that whereas the relatively resistant materials, such
    as Type 347 s.s., and the very sensitive material Inconel 671 seemed to behave in the
    same way in both tests, both Inconel 617 and Incoloy 800 showed reduced corrosion in
    the second test, though this reduction was not great.  This suggests that the latter
    two alloys may be sensitive indicators of corrosive potential in fluidizcd beds.
    
           The third test resulted in very little corrosion indeed.  For most specimens,
    the outer surface of the tube appeared less oxidized than the bore.  Even Inconel 671
    showed no attack.  No specimens showed any evidence of sulfidation.  This demonstrates
    the importance of the CaSO./CaO equilibrium in producing the sulfidation attack.  A
    deposit did form on the tuBcs, and it was of a similar thickness to that formed in the
    other tests; the grain size nlso seemed much the same under the nicroscope.  However,
    electron probe microanalysis showed it to contain largely aluminum and silicon, with a
    smaller amount of iron and no calcium or sulfur.  This is consistent with its being
    coal ash.
    
           It is clearly important to determine the difference between the second of these
    tests, which produced significant corrosion, and the EPA tests, which did rot.  The
    test conditions were the same, but the coals and limestones used were different.  The
    iimestone used in the EPA tests was U.S. limestone No. 18, which contained 15% quartz
    (SiO^; as relatively large crystals (around 200 urn)  intimately mixed with the 1-2 urn
    calcfte crystals.  The limestone used in the tests described in this paper was o U.K.
    Penrith limestone containing 99.8% calcite.  The coal used in the EPA tests was Pitts-
    burgh Humphrey No. 7, whereas that used in the present tests was Illinois No. 6; the
    differences in the compositions of these two coals do not seem great.  The effect of
    the limestone and the coal on the corrosion will be examined in future tests.  The
    lower sintering temperature of Illinois No. 6 as reported earlier also requires further
    consideration.
                                              694
    

    -------
    CONCLUSIONS
    
           It is clear from the experiments described above and from other experience
    reported in the literature that while fluidized bed cornbustors can operate with no
    corrosion at all, there is a risk of sulf idation/oxidation corrosion of high tempera
    ture metal components.  Once initiated, this form of attack can produce very rapid
    local degradation of alloys sensitive to this type of corrosion.  The conditions1
    are likely to lead to this tvpe of attack are:-
    
           1.  The presence of calcium sulfatc as a deposit on the metal surface.
    
           2.  The existence of a local region of low oxygen activity near the metal.
    
           3.  The presence of a sensitive alloy in the low oxygen activity region.
    
           4.  Metal temperatures above 650ฐC.
    
           At th<_- moment, the factors that determine whether cr not a calcium sulfate layer
    forms on the tubes are not understood.  Some of the factors likely to affect the exist-
    once of low oxygen activity regions have been listed earlier, and it may be possible to
    optimize bed operation to eliminate the corrosion risk.  The most important contribu-
    tion of the present investigation has been to establish that alloys such as Inconel 671,
    Incoloy 800, Inconel 617 and perhaps Haynes Alloy 188 arc sensitive to corrosion in the
    bed; but the stainless stools such as Types 304, 329 and ?47 are relatively insensitive;
    they do sulfidizc but the morphology of the sulfidation does not appear to load to
    catastrophic attack.
    
           Further work is clearly required on these aspects.  Experiments should be con-
    ducted to determine the local oxyqen activities within the bed, and the effect of
    operating variables on the oxygen distribution.  The testing of the nore resistant
    materials should be extended to longer times to ensure that the sulf idation/oxidation
    attack does not eventually become catastrophic.  The possibility of using coatings to
    resist attack should also bo investigated.
    
           It docs not seem that in-bed corrosion is an insuperable problem limiting the
    technology; solutions are almost certainly available.  But a note of caution has been
    expressed which can be overcome if the development of a proper understanding of the
    corrosion problem is undertaken.
    
    
    ACKNOWLEDGEMENT
    
           The experimental work was supported by the Electric Power Research Institute
    under contract numbers RP 388 and RP 979-1; and by the National Coal Board.  The con-
    tributions of Mr. A. J. Minchcner, Mr. J. C. Holder and Mr. A. J. Page of the Coal
    Research Establishment and Dr. D. P. Whittle of the University of Liverpool were of
    great value.  The views expressed are those of the authors and not necessarily those of
    the Electric Power Research Institute or the National Coal Board.
    REFERENCES
    
    1.  J. Stringer and S. Ehrlich. ASME paper 76-WA/CD-4 (1976)  pp 11.
    2.  J. C. Holder, R. D. La Nauze,  E. A.  Rogers and G. G. Thurlow.   Paper to Eng.  Found.
        Conf. on Ash Deposits and Corrosion.  Henniker,  New Hampshire,  26 June - 1 July
        1977.
    3.  Fluidized Combustion Control Group,  NCB 'Reduction in Atmospheric Pollution'  Final
        Report of the National Caol Board to EPA,  Reference No. DUB 060971 (Sept.  1971) .
    4.  M. J. Cooke and E. A. Rogers.   Paper No.  B6 Inst. of Fuel Syrap.  Set. No. 1. Sept.
        1975.
    5.  R. Noack.  Chemio Ing Technk 1970,  42, 371.
    6.  B. M. Gibbs, F. J. Pcrcira, J.  H. Beer.  Paper D6, Inst of Fuel.  Symp. Ser.  No.  1.
        Sept. 1975.
    7.  M. J. Cooke, A. J. B. Cutler and E.  Raask. J.  Inst.  Fuel, 45 (1972) 153.
    8.  P. L. Hemmings and R. A.  Perkins.  Report No.  LMSC-D558238 on  EPRI Project No.
        RP716-1 (March, 1977).
                                              695
    

    -------
                 QUESTIONS/RESPONSES/COMMENTS
         STANLFY PAPKUNAS, CHAIRMAN:  Thank you very much, John.  Are
    there any questions?  Pon't  run away. Please go to the nicrophone.
    
         PROF. PEER :  .1.  Reer, MIT.  A couple of years ago, at Sheffield
    University, they carried  out and reported sone experimental data on a
    one square foot fluidized conhustor, in which detailed species
    concentration and distribution, tine-resolved and spatially-resolved
    distribution, were measured  in a fluidized bed.
    
         We found that at about  18 inches above the distributor plate,
    there were strongly fluctuating conditions when the time-average
    oxygen concentration  was  around 3 percent; the fluctuation ran
    between 4 to 4-1/2 percent and reducing conditions.   It seemed to us
    that these are extremely  unfavorable conditions for any metal, and
    they are very favorable for  sulfate formation.  I wonder if Dr.
    Stringer agrees.
    
         Ry the way, I would  like to mention that this work was spon-
    sored by the National Coal Roard, but somehow they didn't very much
    look at the results which they have received.
    
         PR. STRINGER: Thanks for the piece of information.  It's very
    useful.  I was aware  of one  measurement, the measurement I mentioned
    using a zirconia probe, which was done by the National Coal Board
    with some help from CEGR; and that was published about 1972, which
    again showed exactly  the  thing you say, short-term fluctuations.  And
    yes; I agree entirely.  That would he very bad.
    
         PROF. REER:  It's with  one cycle per sec.  So fluctuations
    between 4 percent and zero,  or reducing at one cycle  per second, at
    18 inches above the distributor plate.
    
         PR. STRINGER:  I think  that would be consistent  with the single
    zirconia probe.
    
         PROF. REER:  And with 20 percent excess air overall in the bed.
    
         PR. STRINGER: Yes.  Thank you very much.  That  emphasizes what
    difficult conditions  one  can have under circumstances where one
    wouldn't dream they would occur.
    
         STANLEY PAPKUNAS, CHAIRMAN:  We have a written question here
    for you to answer while the  gentleman is going to the microphone.
                                    696
    

    -------
         PR. STRINGER:  Okay.  This is fron J. Mogul of Curtiss Wright,
    who wants to know what results we had on the iron-chroniun-aluminum-
    yttrium alloy in the test.  That was the GE 2541 alloy, which is
    basically a kanthal containing yttrium to hold the alunina scale on.
    This was just used as an in-hed component of the test for support
    pieces, and it looked good.  It was far and av/ay the best of the
    in-bed materials that we had, and would certainly be acceptable as an
    in-bed supportive material.
    
         MR. YF.3USHALMI:  Joe Yerushalni, The City College.  We have
    heard in the past day and a half that the partial slumping of the bed
    night prove a means of achieving turndown.  Now, John, are you
    suggesting that that will cause disaster at the same time?
    
         OR. STRINGER:  I have been trying to find out from a number of
    my more expert colleages what precisely happens to the metal when you
    slump the bed on it.  My initial reaction would be that the temperature
    would go up fairly sharply, but I don't know how long it lasts for,
    Joe.  And yes, indeed, as the last speaker said, once you start
    sulfidation, it will propagate by itself.  So a little spike can be a
    bad thing for this particular type of attack.  So you know, we have
    to look, I think.
    
         STANLEY DAPKIINAS, CHAIRMAN:  One more question.
    
         MR. LEON:  Okay.  A.l Leon, Dorr Oliver.  I have two questions.
    Based on your corrosion mechanism, would you comment on the effect of
    corrosion rates in an AFB versus a PFB, where a PFB would have higher
    oxygen partial pressures?
    
         DR. STRINGER:  Yes.  We very much hope to get some data on a
    PFB, because there are two things about that.  The higher oxygen
    would look to be good for you.  That would be a first guess.  However,
    don't forget that in that case we are just raising the oxygen pressure
    by a factor of 4 or 5 overall, whereas the oxygen potential differ-
    ence between the oxidizing and reducing regions is enormous.  It is
    several orders of magnitude, from say 10~12 atm going up to one
    atmosphere.  So it may not be as much of a help as one would hope,
    but it's certainly going to be in the right direction.
    
         However, in a pressurized fluidized bed, there are two other
    things different.  You don't use a limestone acceptor.  You use a
    dolomite acceptor, of necessity; and that is going to change the
    chemistry a bit, in a way that I would not like to anticipate.  And
    secondly, the general distribution of the bubble and the emulsion
    phases, I am told, are different; and that would introduce a further
    factor which might change things.
    
    
                                     697
    

    -------
         MR. LEON:  Okay.  The last question was on the effect nf verti-
    cal  tubes as against horizontal tubes.  Horizontal  tubes,  you mention
    a cap on top of the tubes.  You wouldn't have this  with vertical
    tubes.
    
         PR. STRINGER:  Absolutely.  You would hot have it with vertical
    tubes, so long as the tube was continuing straight  up to infinity.
    If you have to bend the tube over at any point, then the position of
    the bend might well be an excellent location for forming something
    nasty.
    
         STANLEY F1APKUNAS, CHAIRMAN:  Thank you very much, John.
                                     698
    

    -------
                                                                                           1
                         INTRODUCTION
         STANELY  DAPKUNAS, CHAIRMAN:   Our next speaker will  be Leon
    Glicksman of  MIT, who will  present a paper on Thermal  Stresses and
    Fatigue of Heat Transfer Tubes Immersed in a Fluidizert Pซvj Combt  jr.
    Dr. Glicksman received his  Bachelor's from MIT in '59, r.   Master's
    from Stanford in  '60 and his Ph.D. from MIT in '64.  He  is on the MIT
    faculty in the Mechanical Engineering Department.
                                   699
    

    -------
                                  Thermal Stresses and Fatigue of Heat
                                 Transfer Tubes immersed in a Fluidized
                                              Bed Combustor
                                  N. Decker. L. Glicksman, R. Pe !oux. T. Shen
                                    Department of Mechanical Engineering
                                    Massachusetts Institute of Technology
    ABSTRACT
           Thermal  stress  conditions are investigated for horizontal tubes In a fluldized bed cocbustor.
    Circumfcrcntially non-uniform temperatures and high frequency cyclic temperature distributions are pro-
    jected from observed licat  transfer variations on tubes immersed In fluldized beds.   The thernal  stress
    produced by the external heat transfer variations arc shown to be less important than that caused by
    Internal variations due to the boiling two-phase flow within the tube.  High cycle fatigue due to ex-
    ternal heat transfer fluctuations is sliovn to be unlikely.
    
           Low cycle fatigue due to cyclic micro-yielding during each start-stop cycle of the bed was also
    Investigated.   Lains fatigue data for 304 stainless steel, it can be concluded that low cycle fatigue
    failure will not occur.
    
    INTRODUCTION
    
           Fluldized bed combustors cormonly use a horizontal tubular Ucat exchanger imersed within the
    Led for generating stcau.   With this arrangement the gas side heat transfer coefficient la strongly
    influenced by the motion of solid particles and, compared ultl. tubes in conventional boilers, there
    will be differences in tiierm.il behavior which will be important to the selection of tube materials and
    dimensions.  Tubes within  the *>cd nay be subject to corrosion and dynamic forces set up by tlte inter-
    action with the bed •   THUS, i.i some designs of fluidizcd bed combustors the tube vails will be thicker
    than a corresponding tube  in a  .•mvcntior.al boiler operating at the same pressure.   The thicker  vails
    will experience more severe thernal stress during operation.
    
           In the particular case of horizontal tubes, the particle motion is not uniform around the cir-
    cumference of the tu'jc.  The tube experience* a spatially non-uniform heat transfer coefficient  whicu
    produces a tioc-averagu tncrmal .stress field which varies Circumfcrcntially .truuad the tube.  The
    particle notion is unsteady causing the local film coefficient cf heat transfer to fluctuate with : 'TC.
    The alternating thcrrul transients induce a time varying thermal stress field in the tube wall.
    
           In addition to  these external effects, the two phase flow within the horizontal tube can  becoae
    stratified with the vapor  occupying the upper portion o'. the lube or a vavc-like liquid flow can exist
    in the tube alternately wetting and drying out the upper portion of the tube.  The internal flow
    conditions can  adversely affect both Instantaneous and time-averaged thermal stress in the tube.  A
    schematic figure ot all of ch?se effects along witli a graph showing a typical external heat transfer
    coefficient distribution  [1), are shown in Figure 1.
    
           Two conceivable tube failure modes arc investigated here.  The therail stress caused by a large
    uniform gas-side film  coefficient is evaluated along with its influence upon possible low cycle  fatigue
    of thick walled tubes  due  to startup and shutdown cycles.  The additional effect of spatial variations
    in the time-averaged thermal stress field is considered with regard to the low cycle fat'gue problca.
    Higher frequency fluctuations in the temperature and stress distribution for both internal and external
    variation-, in the heat transfer coefficient are estimated to determine the likelihood of high cycle
    fatigue.
    
    
    Therm-.t Stress  With Steady Uniform Heat Transfer
    
           To form  a basis of comparison for the non-steady and non-uniform cases, consider first a heat
    exchanger tube  with steady heat transfer coefficients which are uniform over both the inner and outer
    tube surfaces.   In addition, the bed temperature and the bulk temperature of the fluid within the tube
    will be considered constant.  For these conditions analytical expressions exist fcr both the temperature
    distribution in the tube metal and the corresponding thermal stress.  Both :re fractions of radius
    alone.  The temperature distribution, assuming a constant value of thermal conductivity Is given as:
                                                      700
    

    -------
                                   Defluidized particle cap
                                       Possible separated
                                        two phase flow
    
                                        Intermittent contact
                                        h fluctuates ~ 1 Hz
                                    Defluidized gas pocket
                                 Typical circumferential
                                      variation of h
       Figure 1. Conditions at Tube Walls (or a
    Horizontal Tube in a Fluidized Bed Combustor
                    701
    

    -------
      TCr)
                                                             In  r/r.
                                                            jj-j-yi-
    where
    T    1    TBED-*STn          If""^
     s™                     "n ro/ri        k
          11/r ho + 1/^h, +	p—-\ I         |
    and
                                Ti ' TSTM
                                                 TBCD "  TSTM
                                                              tn  ro/rt
                                                              (1)
                                                                                                     (2)
                                                                    (3)
    Manson (2) provides expressions for the  stress within  a cylinder of  linear elastic material In plane
    strain.
          60   tt-vlr'
                          2 ^   2
    (T(r) -
                                   2   _ 2     .r
                                                                    (T(r) - T;rdr -  (T(r) -
                                                                rl
                                 1_^L_  f
                                  ^  - 'i2 7 r
                       - Trc{)rdr - /    (T(r)  - Tref)rdr
                                                  ฐrr>  -  QE(T(r)  -  Tref>
                                                                      (4)
                                                                 (5)
                                                                      (6)
    Integrating the stress equations us inc. the steady state  temperature distribution, the stress Is found
    to be:
                                i    ฐE "TCBE  ['.'<'' * rJ2)     l *  ln  r/ri]
                               "08 '    l-v     ^2^^  . r2}  -  2 ln ro/r1 J
    
    
    
    
                                T    ฐc "TTJBL  fr.2<'2 " rt2>     tn r"i    ]
                               ฐ" '    l~v     [2r2(ro2  - rt2)  "  2 tn ro/rlj
                                                                      (7)
                                                              tn  r/r
         ฐrr> - ฐE   "TUBE
                                                                        Ti ' Tref
                                                                                  1/2
                                                                                                      (10)
    The thermal stress for two tube sizes and two materials  is  given  in Table I for the tube ends uncon-
    strained. T.ie stainless steel can uc seen to experience a greater tticrrul stress  due  to its poor  tlicr-
                                                      702
    

    -------
    T.iMv 1.  Calculated  Siresica - CtrciUufcrcntialiy luifora iซ--at Flux
    .laterlal Sire (ut/ 10) .'.F(*F) c "(?sl) o '"*T(;>st)
    
    1 1/4 cr-Ulo
    304 SS
    2 1/4 Cr-Ulo
    304 ib
    
    2.
    I.
    2.
    2.
    
    50/1
    5J/1
    O'J/1
    oa/i
    
    75
    75
    64
    64
    
    42
    8S
    19
    41
    i:;
    6770
    18510
    2950
    8230
    on
    -5340
    -14600
    -2580
    -725d
    IS
    9680
    21420
    ao40
    13300
    OUT
    -3430
    -U700
    1500
    -3160
           Condlciorts:  t^m -  50')*F          l>n -  3350  DTl7hr-f t"F
                        Tltli> "  lSuo*r         ''EXT ' 30   CTV/hr-ft2*F
                                    P  -  1000 psia
                                     703
    

    -------
        conductivity.  Vac cori'jiiied thermal anil mechanical  stress exceeds  its yield  stress of 21,000 psi in
        larger, tuicker walled tube.
    
           i ij'ure 2 illustrates iiou these stress quantities vary with  nouition In  c'tc  tube  wall.   It  is
         iAnt to note titat the :>tress at tiie inside surface i:;  tensile and chat  at the external  surface is
    co^vruasivc.  it should also be noted that for a given  inside ur cutsld*:  diancter  and  fixed  bod and
    stean Lcuperaturcs a thinner tui-e vail will have smaller thermal stress,  but larger raeclianic.il stress
    due to t.te internal pressure.
    
    
    T.iernal Stress with Circunfercntlally Varying Heat Transfer
    
           Die idealized axisyunetric situation analyzed  in ttie last section  serves  as a standard to  which
    the results for non-uniform itcat fluxes may be compared. Analytical  solutions are net  available  fur
    cite general non-uniforo case, theicforc. the temperature distributions were  determined  using finite
    difference computer programs for specific cases.
    
           The external heat transfer coefficient varies  around the circumference  of a horizontal tube due
    Co Che varying degree of local particle mocion.Thc he;it tr.insfer-ttt Inroerscd  surfaces in fl-:idized beds
    can be related to gas and solid properties, and particle replacement  frequency.  I [any  investigators
    iiave reported frequent exchange of particles at tltc sides of horizontal tubes, but long residence times
    for particles in a stagnant wake region or cap on  Che top of tubes and a  long  residence time of voids
    at Cue lower surface of Che tuh'fs.  Thus, as expected,  the  upper and  lover portions of  the tube surface
    have been observed Co liavc lower local film coefflcicncs 11].
    
           A sketch of r.othcrmal lines within the Cube wall is shown  in  Figure  J  for  an extnoc case in
    wulch Cue cxteiual film coefficient was taken as zero (adlabaclc)  over Che upper region of the cube.
    Lvcn with this abrupt change in  the film coefficient no  incense thermal gradient  is established.  The
    naximun thermal gradient is seen Co be well away from Che adiabatic zone  and has as its eoper bound
    Cite thermal gradient of the ail.pier axisyonptrlc case with  a uniform  heat transfer coefficient equal to
    the local coefficient ac Che side of Che Cube.
    
           Tiie effccc of a non-uniform excernal film coefficient, Chen, is Co produce  stresses no greaccr
    titan those of a uniform film coefficient, Che stresses  for  which can  be obtained from  Che analytical
    onu-dicvnsional relations.
    
           Tiic horizontal orientation of the tubes may produce  anochcr effccc IndependenC of Che fluldized
    bed -jeiuvior.  Alchough horizontal Cubes are not usually used in conventional  boilers,  lltilte.! dac.i
    indicates tiiat severe problems oay occur if a sufficiently  hl^li quality,  low flov  rate  two-phase  mix-
    Cure of water and steam flews within the Cube  (1).   Under  these flow conditions gravitational scpara-
    Ciun of cite phases can keep liquid from vcccinf* Che upper portions of  the tube wall, leaving vapor with
    its low thermal conductivity In contact wlch Che wall.   If  this vcrc  to occur  in a steady fashion, a
    tuiaperacure distribution similar to that shown in  Kip.urc 4  would result.   Here substantial circumfer-
    ential tu.-rnal gradiencs are established at the three pltase InCcrfacc.  In realicy the  position of this
    interface would fluctuate wi .h tine causing large  lcu-.il temperature excursions which  will  be discus-
    sed in another section.
    
           7i>c corresponding thermal stress in cite Cube cross section  was  found  by a finite element numeri-
    cal solution technique [4] assuming Che material was  Isotroplc and llnc.irly  clastic.  Figure 5 shows
    Che clicrmal stress pattern associaced with the temperature  distribution of 1'lgurc  4.  Gi.ovn  hero  It the
    equivalent seres:; as calculated by e-jualiou 10.  The  largest equivalent stress occurs  in the region of
    greatest Ceuperacure.  A large conprcsslve scress  in  the axial direction  is  the  primary contributor to
    Cite cquivalenc scress in Chis region.  The equivalent stress throughout Che  rcsc of the tul/e is consid-
    erably sculler and suggests that Che upper region of  the Cube experiences the  most crucial conditions.
    The use of equivalent stress, however, disguises Che local stress components.  As .in example,  tin:
    stresses in the viclnicy of Che liquld-vapor-wall  Interface are o.Q -  12.10U psi.  o   - 730  psl,
    oz< - -6OIM psi while cite equivalent stress is only -10.QUO psl.
    
           1C must be recognized that this situation has  been greatly  simplified,  but  that  magnitudes of
    these stresses clearly indicate che severity of the problem.  The  problems creatjd by  flow stratifica-
    tion are not likely Co be solved by material selection  alone.  Rather, measure*  will have Co be taken
    Co avoid operation in this particular two-phase flow  regime.  1C should be no;ed in addicion tliac tliu
    presence of 1HO* "ILairpln" bends, especially in the vertical plane, has been observed  15] co intensify
    Che problem by causing Che Cube wall co dry ouC near  Che exit of the  bend.
                                                      704
    

    -------
    3000
              	 Tangential
              	 Radial
              	Axial
              —-— Equivalent
    -3000
         0.82   0.85      0.90      0.9S      1.00
                        Radius (IN)
    
     Figure 2.  Thermal Stress Distribution Within
      a Tube Wall for Axi-symmetric Conditions
                                                                                             ID = 1.64
                                                                                             OD=2.00
                                                                     AdiabJtic
       Figure 3.  Temperature Distribution due to
    Non-uniform External Heat Transfer Coefficient
           ID-1.75 IN    OD-2.50 IN
    
                              TBED = 1500ฐF
    
                                 hป80
          hIN
               HRFT2ฐF
      Figure 4. Steady Temperature Distribution
     within Tube Wall due to Stratified Two-Phase
                 Flow Inside Tub*
    Figures. Equivalent Stress for Tube due to
         Thermal Conditions of Figure 4
                (Stresses in KS1)
                                                   705
    

    -------
    High Cycle Fatigue
    
           The possibility of high cycle fatigue due to the fluctuating nature of the heat transfer coef-
    ficient oust be considered.  The local coefficient at the side of a tube  in a fluidized bed has been
    observed to alternate bctwccr. high and lov values at a frequency of about 1 Hi.  This is caused by the
    frequent passage of a bubble over the tube surface;   .Beeping away solid particles, leaving the region
    temporarily bare and then replenishing the surface with hot particles.  Large particle-: vhich will be
    used in fluidized bed conhustors tend to produce fairly constant local heat fluxes during the period
    of contact.  The flln coefficient is reduced to nearly zero when gas alcne contacts the tube and thus
    if gas and packet residence tines are roughly equal, the instantaneous film coefficients during eaul-
    slon contact nay be roug!il\ tvice the time average flln coefficients at these locations.  When radi-
    ation if included, the rininun and avcrar.o coefficients will both increase.
    
           The upper and lower Units of instantaneous tcnpcrature distributions are shown in Figure 6
    where a regular cyclic variation of t'.c file coefficient occurs with equal gas and emulsion residence
    periods.  It can be seen that temperature only varies over a sm.i!l r.ingc.  The amplitude of the fluctu-
    ations Is greatest at tlic external tube surface and tlic amplitude decreases rapidly <•itii penetration
    into the tul>c Jail.  Coupling this with the earlier observation that the  inner surface is (n ten-ion
    while tlic outer surface is in compression, it becooes clc.ir that the temperature fluctuations are
    greatest where they arc lease likely to assist in Che propagation of a crack.  The actual Instantaneous
    temperature distributions within the tube wall fall within the envelopes  shown in Figure 6 and have a
    sinusoidal appearance with one quarter to three quarters of a wave within the oaterial.  Instantaneous
    thermal stress distributions (the circumferential component only) are shown in Figure 7 for four in-
    stants at equal intervals within a 1 !lz cycle.  The theroal stress fluctuations are not confined to the
    externil surface, but they are small.  Thus, high cycle fatigue caused by fluctuations of heat flux
    on the outside of the tube does not appear to be a likely node of failure.
    
           High frequency thermal fluctuations are also possible at the inner surface of the tube due to
    alternate contact with liquid and vapor at  a given location as was suggested earlier.  A rough esti-
    mate was made of the temperature fluctuations at inner and outer surfaces If the wetting and drying
    occur within the range of periods observed by Lls and Strickland (5).  Conditions and results are given
    in Table II, and the limits of temperature excursions are shown In Figure 8.  It can be seen that in
    this case the temperature changes arc relatively large and located at a surface under tensile stress
    where a crack is likely to r.row.  Figure 9 shows the circumferential stress distribution across the tube
    wall (or the thermal conditions of Figure 8.  The tensile stress is seen  to cycle over an appreciable-
    range.  Figure 'J is based on an internal coefficient which flu,-tunics between 230 and 2000  BTV/hr-ft *F.
    For these conditions the Inside tube wall teenerature fluctuates a maxima, of 22*T; whereas, for the
    conditions of Figure 8 the maximum temperature fluctuation ii }2ฐF.  The  results should only be vleved
    as approxlnatc since the correct values of the cyclic heat transfer coefficient and frequency are a
    function of the particular steam quality and flow rate and the tube size.
    
    Low Cycle Fatigue
    
           If the steady state operating conditions generate combined thermal and nechanlcal stresses which
    locally exceed the elastic Mrolt of the material, micruvicldlng will occur on each start-etop cycle.
    The cyclic mlcroyieldlng in the plastic strain range will ultimately lead to fatigue failure.  The low
    cycle fatigue behavior of type 304 stainless steel under fully reversed,  axial strain-controlled con-
    dition was Investigated by Cheng ct al 16). and the data arc reproduced in Figure 10.  Though the tube
    temperature normally does not exceed 700*F, fatigue data at 1000'F which  are available can be used to
    predict a lower bound of the tube lite.  For the thick walled stainless Cube  given In Table I the ther-
    mal and mechanical stresses will produce a total strain amplitude of the  order of 0.1X.  As a conserva-
    tive approximation, a total strain range equal to twice the total strain  amplitude, i.e. 0.2". will be
    assumed because there may be fully reversed yielding In some part of the  fluidixed bed tubes.  In Fig-
    ure 10, It can be seen that at a total strain amplitude of 0.2Z, Nf approaclies iafinlty.  Tims we can
    safely conclude that Type 304 stainless steel will not crack by low cycle fatigue due to a start-stop
    operation for the conditions given above.  If a steep local teaperaturo gradient exists, such as that
    shown in Figure ft, where substantial clrcucferentt.il thcr:jl gradients exist near the two-phase Inter-
    face, the thenna.' stresses could possibly produce a large total strain range which could cause crack
    Initiation during the life of tho tube.
    
    CONCLUSION
    
           Horizontal steam generating tubes In fluidized beds oay be subject to fluctuating and non-unl-
    fortaly varying iioat transfer coefficients around their circumference.  JJon-unlfcreitles on the exterior
    of the tube do not contribute to increased steady state t her ml itrcss nor do they cause fatigue damage
    since the outside tube surface Is in compression.  The external fluctuations nay contribute to cpalling
    
    
                                                      706
    

    -------
       560
       550
    u7 540
       530
       520
       510
       500
              Effect of fluctuating
                   external h
               hMAX=8ฐ
                   ID  = 1.64
                   OD=2.00
                                 	1  CPS
                                          2  CPS
         0.82    0.85
       0.90       0.95
    Radius (IN)
                                                   1.00
             Figure 6.  Temperature Variation within Tube
             Wall due to Fluctuating Exterior Heat Transfer
                            Coefficient
            6
    
            5
    
            4
    
            3
    
            2
    
             1
    
         _  0
         5
             .82   .85
      .90       .95
      Radius (IN)
                                                1.00
            Figure 7. Circumferential Stress Dijiribution
            for Conditiom Similar to Those of Figure 6.
                             707
    

    -------
    Table II.  :Uxlnum TenperatBTe Chinees  i.'ue to Fluctuating  Internal  Flln Coefficient
           lntem.il,h
         (BTWhr-ft'T)
        MAX         HIM
                                 External. h
       3300
    
       3500
    
       3500
    
       3500
    200
    
    200
    
    200
    
    200
    (STWhr-ft
    
    
          60
    
          60
    
          80
    
          80
                        .
                         '
    Frequency
    
    
    
        .2
    
        .5
    
        .5
    Wall Thickness       AT
         (IN)           <*F)
                    IH       OUT
         .375
    
         .375
    
         .18
    
         .18
    54.6     13.3
    
    33.0      2.9
    
    31.0      6.6
    
    23.0      1.8
                                             708
    

    -------
       620
    
    
       GOO
    
    
    ฃ 560
       560
       540
       620
    Effect of fluctuating
         internal h
    
    NlAX'3500    BTVJ
    
    SlIN •  20ฐ '
                  10 - 1.64
                  00-2.00
           	0.5 CPS  .
           	1  CPS
           	 2  CPS
          0.82 O.K.
      0.90      0.95
    Radius (IN)
                           1.00
         FignreS. Temperature, Variation within Tube
            Wan dua to Fluctuating Heat Transfer
              Caaff ieient on Inner Tuba Surface.
                                                  .82   .85      .90      .95     1.00
    
                                                               Radius (IN)
    
                                               Figure 9. Circumferential Stress Distribution
                                               for Conditions Similar to Those of Figure 8.
                       10'
                       10ฐ
       ~  i  TIMIHI   i  i T Finn   i  iiiiiiiT  r i niiin   i Tiiin:
    
                             O (ANU   * (BMI)	1000ฐF  -
                 A           & (ANL            	1050ฐF  I
                             DIANL)   • (BMI)	1202ฐF_
                           SR
                    ^c
                    a10"1
                         *i**^i   C
                            ป      *•••*>
                              i  i i Mini   i  i i mill   i I i Mini  i STTfTtil  i i
                                                              102
    10'  ?
                                                                                  10ฐ 's
      102       103        104        10s
                        Cycles to failure (Nj)
                                                          106
                                                                                  10"
                                                                                107
                                    Figure 10. Low Cycle Fatigue Behavior of Type
                                       304 Stainless Steel, from Reference (6).
                                                    709
    

    -------
    ot brittle  films 0:1  the  surface.
           At certain flow conditions  the  two phase  flcv within horizontal tubes will  stratify with vapor
    at the top of the tube.  This will cause  severe thermal stresses along the Inside of  the  tube.   If  the
    wall Is alternately  vapor blanketed  anu then revet, fatigue failure may ensue.  Uxact  quantitative
    determination of the  tube stress and fatigue life is dependent on a detailed knowledge of the  flow
    behavior within this  regime which  has  not been tlioroup.iily investigated to date.  To avoid such  problens,
    the designer should  be sure the internal  flew Is outside the troublesome flow regime.
           Low cycle fatigue failure Is  unlikely to occur due to start-stop operations  even for thick wall
    stainless tubes which, of the tubes  investi.-.ated, h.is ;i mxinmn stress r)o.:..-st to the  yielding  point.
    JJUiiUiCLATUiii:
    
    L     -  Young's modulus psl
    h     -  film coefficient of heat  transfer   BTU/hr-fc *F
    k     -  thermal conductivity   inu/iir-ft*F
    :i,    -  numLer of cycles to failure
    r     -  radius  in
    T     -  temperature  *F
    TULD  -  temperature if fluldlzed  bed   *F
    T     -  saturation temperature of steam *l
    AT    -  temperature difference across  tube wall   ฐ1ฐ
    T ....  -  reference temperature at  which thermal strcj: js are zero  ฐF
     M.r
    
    a     -  linear coefficient of  tiirrn->l  expansion  1/*F
    c     -  strain   in/in
    t.t    •  plastic strain range    in/in
    v     -  Pois,son's ratio
    0     -  I lt*>n:M 1 strc-SK  psl
    ~^r
    o     -  equivalent ttn-rni.-il sir*-ss psl
    Subscripts
    00    '  circumferential direction
    rr    *  radial direction
    zz    -  axial direction
    i     -  inside surface
    o     -  outsi.-ie surface
    KEFEREJICLS
     1.   Cclperin, N.  1., and Einstein, V. C. in FluldlzJtIon, ed.  Davidson and Harrison, Academic Press,
         Hew York, 1971,  p.  510.
     2.   Hanson,  S.  S.,  Thermal Stress and Low Cycle Fatigue. McGraw-Hill  Co.,  New York,  1966, pp. 27-33.
     3.   Styrikovich,  M.  A.  and Iliropol'skii, Z. L.. llydrodynamlc and Heat Transfer During Boiling in High
         Pressure Boilers, AEC-tr-44'JO, June 1961,  pp. 244-272.
    
                                                       710
    

    -------
    4.  Uathc, K..AUINA. Import 82448-1, Acoustics  and  Vibration Laboratory, rieciianlcal Lnginccrlng Depr.rt-
        uent, :ilT, Caooridge, ::A, :uy,  1976.
    j.  Lis, J. and Strickland. J. S.,  1Q70  International  llcat Transfer Conference, Paris. August 1970.
    6.  Cheng, C. F., et al. , Low-Cycle Fatigue  Eeh.-ivior of Type 3u4 and 316 Stainless Steel at LMFBK
        Operating Tcc-peraturc, AST.I STP 520.  1973,  pp.  35S-J64.
                                                      711
    

    -------
                QUESTIONS/RESPONSES/COMMENTS
         STANLEY OAFKIINAS, CHAIRMAN:  We have one more question that has
    been submitted by Al Leon of norr Oliver for Dr. Glicksman, and his
    question  is:  "What tube life do you predict?"  Do you want to step
    to a nicrophone in the rear of the roon?
    
         OR.  OLICK.SMAN:  f'n going to have to pass on that one, and ask
    that you  go hack and talk to our metallurgist friends about what type
    of tube life one would predict.  In the thermal stress problems with
    which we  have concerned ourselves, the najor problem is, as I said,
    what's going on inside the tube.  And this depends on a little bit
    better clarification on the flow regimes in there.  We just don't
    know, at  this stage of the game, what kind of problems one will
    have.
                                   712
    

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                         INTRODUCTION
         STANFLY  DAPKUNAS, CHAIRMAN:  Russ  McCarron  is going to present a
    paper on Turbine Materials Corrosion in the Coal-Fired Combined
    Cycle.  Russ  received his BS from Penn  State  and his MS and Ph.D.
    fron the University of Pennsylvania, and he is presently manager of
    fossil energy material for the Energy System  Program Department of
    the General Flectric Company.
                                   713
    

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                               Turbine Materials Corrosion in the
                                   Coal-Fired Combined Cycle
                                    R.L. McCarron, A.M. Beltran,
                                     H.S. Spacil and K.L. Luthra
                                     General Electric Company
                                      S:henectady. New York
    ABSTRACT
           The alkali (tla + K) in the vapcr from a Pressurized Fluidized  Bed Combusto-  (PFBC)
    may be up to two orders of magnitude greater- than the acceptable  limit  based  upon present
    gas turbine liquid fuel experience.  The corrosion conditions developed  in  the  PFBC and
    gas turbine are analyzed and compared to classic hot corrosion  produced  by  petroleum
    fuel combustion.  Available literature regarding materials performance  in PFBC  environ-
    ments is also reviowtd, and the prolable magnitude of the corrosion problem assessed.
    Cladding of superal loys with new hot corrosion-resistant materials  is a  key elc-ment in
    the solution to the corrosion problec which could result if conventional turbine alloys
    and/or coatings were exposed to this environment.  The development  of new cladding  alloy
    compositions to resist corrosion fro-s the direct combustion of  coal and  preliminary re-
    sults of corrosion evaluations of these alloys will be reviewed.
    
    INTRODUCTION
    
           The General Electric concept of the Coal-Fired Combined  Cycle  (CFCC) includes
    a Pressurized Fluidizod Bed Combustor (PFBC) which is cooled through  the use  of steam
    tubes in the bed which supply a stean turbine generator.  Limestone or  dolomite is    ;d
    to reduce sulfur emissions.  The partially cooled combustion pases  exiting  from the com-
    bustor drive a gr>s turbine after pas; ir.g through a hot-gas cleanup  train.   The  low  steam
    tube temperatures in the bed 'about  1000 F) will significantly  reduce the potential cor-
    rosion problem for ht-at transfer tubes located in the bed.  The major materials problem
    to be overcome is the potential for corrosion/orosion of the hot  section parts  in the
    gas turbine duo to carryover of contoninants in the combustion  products  from  the F'FBC.
    Thir. ;.:-oblem will be common -.o any concept which ii.eludes a gas turbine  in  line with
    a i Kb".
    
           A key part of the General Electric (GE) CFCC Development Program  funded  by the
    Department of Energy (DOE) is alloy and process development for tr.e cladding  of turbine
    blades.  In the clad approach, a thin sheet (10 mils) of a corrosion-resistant  alloy
    is bonded to the airfoil surface of a strong superalloy blade.  This  is  tl-.o only work
    of its kind devoted exclusively to th<  development of turbine materials  for application
    in the PFBC gas environment.  Blade ceding alone cannot be counted upon to solve the
    potential corrosion problem because ti'e contaminants in goal can  produce condensed  specie;
    which can cause corrosion at temporaljres as low as 1100 F, and even  after  cleanup  the
    gas may contain enough particulatc matter to plug film cooling  holes.
    
           An important part of the clad alloy development is corrosion t?st;r.g and evalua-
    tion of candidate alloys.  General Electric is conducting corrosion tests of  advanced
    clad alloys in small burner corrosion rig.> using a synthesized  environment  and  is pre-
    paring to test the same materials as airfoil specimens in cascades  in the Exxon Kiniplant
    PFBC and in the Coal Utilization Research Laboratory (CURL) ?. foot  x  3  foot PFBC at
    Leatherhead, England.  The emphasis at the present stage of the program  has been en corro-
    sion evaluation of the illoys.  Some erosion data may be forthcoming  from the cascade
    tests mentioned above, but future tests of rotating hardware in the effluent  from a PFBC
    are required to assess erosion resistance properly.
    
    
    ALKALI CARRYOVER AND IT3 EFFECTS OH GAS TURBINE HOT SECTION PARTS
    
    Cas Turbine Experience with Al kal i-Cor.tami nated Petroleum Fuels
    
           In a gas turbine the heart of the machine is the turbine section, especially the
    first stage buckets.  Its integrity has more influence on machine output, efficiency,
    •This work is sponsored by The Department of Energy under Contract No.  EX-76-C-01-2357.
    
    
                                              714
    

    -------
    and the capability to burn a range of fuels than any other component.  The  integrity
    of the first-stage bucket is largely dictated by mechanical and corrosion limitations.
    Corrosion limitations are determined by sulfur and the trace metal contaminants  in tlie
    combustion products.  These come from the fuel or the environment in which  the machine
    operates.
    
           In petroleum-fired gas turbines the trace metals of most concern are sodium (Ma),
    potassium (K), vanadium (V), lead (Pb), and calcium (Ca).  If they are present in the
    combustion products in significant amounts, the first four can cause turbine tlading
    corrosion while all five can cause fouling due to deposits.
    
           Although all five eler.ents are critical, sodium and vanadium generally are the
    two most frequently found in petroleum fuels.  In coal fuels the two critical elements
    will be the alkalis, sodium and potassium.  A necessary condition for the catastrophic
    attack known as "hot corrosion" to occur is that the combustion products are super-sat-
    urated with alkali chloride, hydroxide, and/or sulfate at the temperature which  prevails
    in the vicinity of the first-stage buckets.  If this condition is fulfilled then conden-
    sation of the alkali salt and reaction with SO-, and 0_ will cause liquid alkali  sulfate
    to form on the metal surfaces.  Following condlr.sation and formation of the alkali sulfate,
    the subsequent steps in the corrosion process are as follows (for the case  of 113,30^).
    
           1.  The con-lensed KapSO-j reacts with the protective oxide film on hot gas path
               parts to form a fiouble oxide such aj Ka,CrO..
           2.  Some of the NapSO.. is reduced to a sulffde, so that the chemical potential
               of S is dramatically increased.
           3.  Sulfur in the forr. of sulfide then penetrates into the metal forming  metal
               sulfides, particularly Cr S .
           <*.  The depletion of the allojf Xf Cr by Three above interferes with  formation
               of a new protective oxide film.
           5.  Continuing dissolution of the protective oxide allows the entire hot  corrosion
               process to accelerate.
           6.  Lead and vanadium in hot gas streams cause an analogous type of  attack.  They
               dissolve (or flux) the protective oxides to a greater extent than :;a,SOy alone.
    
           Cennr.il Electric has conducted a significant amount of research into the  relation-
    ship between trace netal contaminants and bucket life.  The result of this  research has
    been the formulation of a proprietary system capable of predicting the effect of trace
    metal contaminants on hot-gas-path parts lives.
    
           The basis of this corrosion lives system is a correlation between measurements
    on installed gas turbines and data from long-time, laboratory corrosion tests.   The
    correlation involved measurements on over 100 commercial machines, some of  which had
    service times of about 100,000 hours.  The laboratory tests were conducted  ir. a  srr.all
    burner rig facility which has logged millions of specimen hours since the late 19^0s.
    
           Although the correlation itself is proprietary, an exair.ple of its use is  shown
    for the GE HS-5001 Heavy Duty Gas Turbine in Figure 1.  Here, the effect of cr.e  cont.im-
    inant (sodium) on first-stage bucket corrosion life is shown.  The contaminant is ex-
    pressed in terms of equivalent sodium in the fuel, even though it cculd come from fuel,
    inlet air, or water/steam injection.
    
           The results in Figure 1 show that for 25,000 hours life, the specification limit
    for total equivalent (la in the fuel is 1.2 ppm.  The 1.2 ppm sodium in the  f-jel  translates
    to 0.02*4 ppm Ka in the va^or phase at an air/fuel ratio of 50.
    
           Two major points to be observed from Figure 1 are:
    
           1.  Tne strong effect that I.'a in the range 0.5 to 1.0 ppm ir. the fuel has upon
               bucket corrosion life for the petroleum-fired gas turbine.
           2.  The significant effect that materials selection can have upon bucxet  corrc-
               sion life.  At a value of 1 ppm sodium in the fuel, for example, it is expected
               that 111-738 will provide five times the corrosion life of U-700.
                                              715
    

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            100
    
             80
    LIFE
             40
    
             20
    
              0
                                                738
                                                          SPEC  LIMIT
     0.5              1,0             1,5
       EQUIVALENT SODIUM IN FUEL,  PPM
    Figure 1. Sodium Effect on Bucket Life
                                                                                 2,0
                                          716
    

    -------
    Alkali Efflux from the PFBC
    
           Trace elements in the coal which will cause corrosion of hot section parts include
    sodium, potassium,, sulfur, and chlorine.  Sulfur in a PFBC cannot be reduced to levels
    low enough to inhibit alkali sulfate formation even though EPA standards on sulfur emis-
    sions can be met.  The sulfate is the means by which sulfur is transferred to the turbine
    alloys.  Chloride,which will be present in the corbustior. products of coal and resultant
    deposits, accelerates the corrosive attack of the alkali sulfates.
    
           Alkali metals which are introduced into the tied with the coal and dolomite will
    be transported through the system in fine particulate ash and as vapor species which
    are in equilibrium with solid alkali metal-containing compounds in the ced or in the
    hot-gas particulate cleanup equipment.  Because of the gas/solid equilibria which will
    be established in the system, it may not be possible to prevent unacceptably high levels
    of alkali metals from entering the gas turbine even if all the particulate matter is
    removed from the gas stream.
    
           A model has been proposed by two of us (H.S.S. and K.L.L.) which gives a first ap-
    proximation of the level of alkali metal present in the efflux (vapor phase) from a fluid
    bed combustor.  Available thermodynamic data on the relevant compounds were used for
    the necessary calculations.  The coal ash is arsuned to be siiica with about 2% sodium
    plus potassium in the ash.  Typical hydrogen, sulfur, and chlorine contents are assumed
    for the coal, with appropriate sulfur removal by a sorbent.  At the bed temperature,
    sodium plus potassium (Ha + K = M) is present in the system either as a liquid K-O-nSiO,,-
    Si02 solution which coexists with solid SiO,, or as a liquid M-SO^-CaSO^ nolutiofi.  Small
    amounts of alkali metal can volatilize from either type of solution, however, according
    to the reactions
    
                      M20-n?i02(t.)  * HCKg)  <  MCl(g)  + MOH(g)  * nSi02(s)               (1)
    
    or
    
                          r^SOjjU)  ป HCKg)  <  MCl(g)  ป MOH(g)  * SO^g)                  (2)
    
    followed by the reaction
    
                               MOH(g) * HCKg) * KCKg) * H20(g)
    
    which converts almost all of the XOH to MCI.  Equilibria of this sort are represented
    in Figure 2.  Here a correction has been made to account for the increased stability
    of alkali metal aluminosilicates relative to silicates, even though the presence of
    alunina .is such was not considered specifically.
    
           The two curves in Figure 2 represent equilibrium saturation of the vapor phase
    with sodium and potassium for combustion of coals with 0.015 Cl and 0.1* Cl.  Many United
    States coals have chlorine contents of O.if or greater, ar.d the chlorine tends to drive
    the alkali metals into the vapor phase.  Temperature and the chlorine content of the
    coal are the most important factors in determining the level of alkali retals in the
    combustion products.  For example, at a combustor operating temperature of 1750 F and
    with chlorine in the feedstock at 0.IS, the sodium and potassium in the combustor products
    will approach 10 ppm.  Data from the CURL Pressurized Fluidized Bed at Leatherhead, England
    confirm this magnitude of vapor phase alkali content as shown in Table I.  These data
    were obtained by passing an isokinetically drawn sample of the flue gas through a high-
    efficiency cyclone and extracting the positively ionized alkali metal vapors species
    on a collecting electrode in an electric field.  The dashed vertical line in Figure 2
    specifies the regions of stability for sulfate alone and sulfate plus silicate together.
    Below about 1715 F the aluminosi1icate solutions are not stable for ccnditicns given
    In Figure 2, and one would not expect effective gettering of the alkali metals in such
    soluti ~ins.
    
           As the hot combustion products from the PFBC pass into the turbine, the gas temper-
    ature decreases, and the gas comes in contact with cooled octal parts (nozzles and buckets).
    Cooling of the gas which is saturated with alkali chloride causes the alkali chlorides
    to condense and react with S02 and 02 to form f^SO^.
                                              717
    

    -------
                     10
                              700    750    300   350    900    950    CC
                     .1
       ALKALI VAPOR
       CONCENTRATION
           (PPM)
                    .01
                   .001  -
                                            0.1  ZCI
    
    
    0001
    /
    /
    f i 1
    1200 WOO
    
    
    i 1
    1600
    1
    1
    1
    1
    ii l
    180
                                       GAS TEMPERATURE
    
                    Figuc* 2. Alkali Vapor Concentration 
    -------
                 2MC1  (g)  * S0?  (g) *  1/2 0?  (g)* H?0(g);H2SOl4  (1)  *  2  HC1  (g)         (3)
    
    
    The condensed M2^l4 '3 underlined since in this case it may exist in a liquid solution
    with calcium sulfate.
    
           Calculations have been carried out to estimate the flux of alkali netal sulfate
    condensate to the surface of a first-stage turbine bucket for a turbine burning petroleum
    fuel and for a turbine in line with a PFEC.  It was assumed for the petrcleum-fired tur-
    bine that the sodiua level in the fuel was 1.5 ppm (slightly greater than the maximum
    1.2 ppm allowed according to the present liquid fuel specification), and the metal teซ-
    perature was 1600 F.  Fcp the Coal-Fired Gas Turbine it was assumed that the bed operat-
    ing temperature was 1750'F,  and the chlorine content of the coal was between 0.01 and
    0.1%.  A comparison of the results r.t these calculations shows that the f'.ux of alkali
    metal sulfate condensate to the bucket of the Coal-Fired Turbine is 30 to 300 tines
    greater (corresponding to 0.01 and 0.1J CD than for the Petroleum-Fired Turbine.  If
    the PFBC operating temperature is reduced from 1750 to 1650 F, then the alkali metal
    sulfate flux is approximately 10 to 100 times greater than the Petroleum-Fired Turbine
    with 1.5 ppm IIa in the fuel.
    
           From these results it is proposed that for the PFBC/Gas Turbine the net flux of
    alkali sulfate (proportlens! to Ha + K in the combustion products) will saturate the
    nozzle and bucket surfaces such that the overall hot corrosion attack is reaction-rate
    limited, while for a conventional Petroleum-Fired Gas Turbine the flux of alxali metal
    sulfate is limited by present fuel specifications such that overall hot-corrosion attack
    is flux limited.  Qualitative plots of part-life versus alkali metal sulfate flux are
    shown in Figure 3 for two temperatures.  Conventional gss turbine experience includes
    the oxidation and flux-limited regimes as illustrated in Figure 3.  Note there is a
    reversal in the temperature effect on corrosion at low alkali metal contaminant levels.
    This is caused by the increased condensate flux at the lower temperature and has been
    documented by field observations.  As the alkali metal level in the combustion products
    increases, the corrosion reaction is limited by the inherent reaction kinetics between
    condensate and the alloy (i.e., further Increases in the alkali netal sulfate flux will
    not cause a corresponding increase in the corrosion rate), and the predicted part-life
    for an allowable metal loss appi caches a minimum.  As shown In Figure 3. the PFEC/Cas
    Turbine combination is expected to operate in the reaction rate-limited regime.  The
    bucket surface will be completely covered with a iayer of condensate and can be described
    a^ "saturated."  As will te described in a later section, this situation will result
    in unacceptably short lives for conventional gas turbine nozzle and bucket alloys.
    
           The presence of high levels of potassium and chlorine In the combustion products
    from a PFBC creates the potential for further acceleration of corrosion on gas turbine
    parts over and above that due to the high-alkali flux.  Recent small burner rig tests
    conducted by the General Electric Gas Turbine Division have shown that for up to at
    least^^O mole % K-SCK in Ha^SO^ there Is a synergistic effect of Na and K on corrosion
    rate.  That is, K does not Simply substitute for tla in the corrosion phenomena, but sig-
    nificantly increases the rate of corrosion as It is substituted for Na in the deposit.
    Potassium has not been a real problem for gas turbines burning liquid fuels because the
    alkali comes in with the fuel or air mainly as sea salt which is primarily NaCl with
    only a small fraction of KC1.  The potassium level in coal, however, will for the most
    part be as great ->r greater than sodium so that increased corrosion rates may be antici-
    pated from the combined effect of sodium and potassium when compared to sodium alone.
    
           One of the important corrosive contaminants in coal is chlorine.  Unlike a con-
    ventional gas turbine where any chloride salts in a condensate are completely converted
    to sulfates the high chlorine/alkali metal ratio of the PFBC will cause the alkali netal
    chlorides to be incorporated partially into the deposit.  Chlorides have been identified
    in deposits from a PFBC.  Alkali chlorides are important in hot corrosion in that not
    only do 'hey increase the corrosion rate in combination with sulfates as demonstrated
    by crucible ti:^ts, but they hawe oeen reported to attack cobalt base alloys more vigor-
    ously than nickel base alleys.   In conventional gas turbines where condensed chlorides
    are generally not present in deposits, the cobalt base alloys are the most resistant
    materials to corrosion attack.
                                              719
    

    -------
       OXIDATIO'l T
                  1
               '     ELIJX-LIHUED
               !     (FIELD DATA)
       OXIDATION
    LIFE
               REVERSAL
           ^CaWEHTKXIAL GT GAS
              AND OIL EXPERIENCE
    REACTION RATE  LIHITED
      (LABORATORY  DATA)
                                                   PFB/GAS TURBINE
                       MA,  K CONCENTRATION III COMBUSTION  PRODUCTS
                   Figure 3. Life Vป Afluli Conctntietioa for • Hovy Duty
                              Gซs Tufttin* (Schematic)
                                      720
    

    -------
    PRIOR EXPERIENCE
    
           During the last several years tests have  been  run  in  which gas turtir.o hot-section
    alloys have teen exposed to the products of co-bustion  of a  PFBC or Atr-ospr.-rr ic .- lvii
    -------
            ,*OOA)
    722
    

    -------
             of three rones and was fabricated fron AI3I 310SS tube which was n3r.ir.3lly 3  inches
             I.D.   Turtir.e rr.nterials specimens were 3-inch by 1/1-ir.cc diameter pins which
             were  inserted through the wall of the test section at 90  to the gas flow.
             Flow  through the section war atout 100 feet per second.  The list cf materials
             is givf:r. :n Table I!.  Two tests totaling 2000 hours of operation were completed.
             Test  ecr;Jit:?.ns for- both tests were nominally the same.  The bed temperature
             was 1fir.OwC, coal was Illinois S6, and scrbent was limestone.  The temperature
             in Zone j of the turbine lest section was K80WF, and the temperature in Zone 3
             was 1320 F.  All cf tl.o alloys were exposed continuously for 2000 hours.  Most
             cf the alleys wer- exposed in all three zones of the test section.  Duplicate
             samples of three of the nlloys, IN-73S, X-^O, and IN-713C, were rer.oved after
             the first  10CO h^urs and replaced with new samples for the second 1000-hour
             test.
    
           After both 1000-hour tests, there was a soft deposit on the tube wal"  and lead-
    ing, and trailing edge deposits on the specimen pins.  Dust buildup w^s a maximum of 15 mm
    in some locations.  The deposit was light and fluffy and easily removed.  The alkali
    content cf the  c;as was measured downstream of the second ?yclone and before the turbine
    test section.   The ccasurement technique was similar to that used in the PFBC tests at
    Leatherhead.  The technique is not well-developed, and there could be some error.  The
    codiura content  of '_ht f.as was 1.W ppm by weight, and the K level was 0.5 pptr..  These
    levels are comparable to the alkali content measured in the earlier tests at Leatherhead
    (Table I).
    
           The turbine alloy specimens were returned to the Gas Turbine Division of General
    Electric for post-f • • :..• tallurgical evaluation.  The significant results are ar, fol-
    lows:5
    
           1.  Maximum ccrrcsior, attack on most materials in all three zones was  1 to 2 mils
               in  2010 hcurs.
           2.  The  test conditions in the turbine lest section, primarily temperature, were
               not  severe enough to permit a clear-cut distinction between the oxid.it ion/cor-
               rosion be'avior of r.o:jt alloys.
           3.  GE  25ซ1  (FeCrAlY) showed the least attack.  The moat extensive attack was
               on  I'i 671 (Hi-50Cr) which showed oeep localized sulfidation pitting.
           i).  The  oxidation/corrosion attack of about 9 mils in 2000 hours on the above-
               bud  coupons (^ alloy.-i) was core extensive thgn on similar pin specir.er.s.
               This was due to the higher temperature (1650 F) and different environment
               above the ted.
    
    CPC Investigations
    
           For the  past three years, Combustion Power Company (CPC) has been carrying cut
    a progran of testing in a Four-Atmosphere Fluidized Bed Combustor coupled to a Direct-
    Fired Turbine,  and a smaller 2.2 square foot atmospheric model Fluid Bed Corbustor; since
    March 1975 this testing has been directed tcwa d the accumulation of data with regard
    to hot corrosion in the ccal-combustion process and the development of methods for dealing
    with it.
    
           Materials evaluations have been carried out In the One-Atcosphere Model Combustor.
    The Four-Atmosphere Combustor has accumulated about 600 hours burning coal; prior to
    this, garbage  and wood waste were burnt.  Materials evaluations in the PFBC were about
    to begin when  the granular bed filter in the system failed in December 1975.   The inlet
    temperature of  the turbine, however, is limited to 1^50 F, so that materials evaluations
    in the turbine  would be of marginal value.
    
           Material specimens are hung in the freeboard of the Atmospheric Combustor.  Exposure
    temperatures have varied between 1600 and 1700 F, but included some excursions to tenpera-
    tures as high  as 1760 F.  Testing to date has teen conducted with Illinois ป6 coal and
    Kaiser dolomite.  Alloys tested are listed in Table III.  Crude attempts at measuring
    the alkali content of the gas have yielded an estimate of 2 oprn Na in the gas in the
    freeboard.
                                              723
    

    -------
    Table II.
    Turbine Alloys Tested in the BCURA AFBC in
    Stoke Orchard, England
                    Nickel Base
                    U-500
                    U-700
                    IN-738
                    CTD-111
                    IHCO 713C
                    Hast X
                    Inconnel 617
                    Cobalt Base
                    X-UO
                    FSX-41H
                    HS-188
                    Protective Coatings
                    IN-738/Pt-Al
                    IN-738/BC-29E
                    FSX-im/Pt-Al
                    IN-738/BC-21P
                    GE 2541  Clad
                    Inconel  671 Clad
                            724
    

    -------
                                 Table III.  Alloys Tests in AFBC at CPC, Kcnlo  Park, California
    Alloy
    SS 301)
    SS 309
    SS 310
    SS 316
    SS 310
    SS 333
    SS UU6
    Inconel 600
    Inconel 601
    Inconel 706
    NI55
    I.ncoloy 800
    Incoloy 825
    Nimonlc 80A
    Rene 77
    tnco 713C
    U-700
    IN-738
    HS 31
    FS 14 11
    M 509
    PWA 68
    Probable
    Use
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Nonturbine
    Stator
    Nonturbine
    Nonturbine
    Stator
    Rotor
    Rotor
    Stator
    Turbine
    Turbine
    Turbine
    Turbine
    Coating
    Ni
    10
    114
    20
    ID
    35
    148
    0.7
    76
    61
    12
    20
    32.5
    1414
    76
    59
    7U
    55
    6 'I
    10
    10
    10
    --
    Co
    --
    3-1
    — —
    20
    --
    15.0
    17.0
    8.5
    56
    55
    58
    Bal
    Cr
    20.0
    23.0
    25.0
    18.0
    19.0
    25.0
    25.0
    15.5
    23.0
    16.0
    21.0
    21.0
    21.5
    19.5
    11). 0
    12.5
    15.0
    16.0
    25.0
    29.0
    23.5
    19-25
    Fe
    Bal
    Bal
    Bal
    Bal
    Bal
    18.0
    714.0
    8.0
    114. 1
    uo.o
    33.0
    145.0
    30.0
    --
    .-
    i.O
    --
    Composition
    Al Ti
    —
    --
    1.35
    0.20
    --
    0.38
    0. 10
    1.30
    14.30
    6. 10
    14.00
    3. no
    --
    12-15
    —
    —
    1.75
    --
    0.38
    0.90
    2.50
    3-35
    0.80
    3.50
    3.nc
    0.2
    --
    Ko
    —
    2.5
    3.0
    —
    3.0
    3.0
    14.?
    n. 1
    5.0
    1.8
    --
    --
    W Cb
    —
    3.0
    —
    2.5
    —
    2.0
    2.~6 II
    7.5 1.0
    7.5
    7.0
    ..
    Zr C
    0.05
    0.05
    0.05
    0.05
    0.05
    0.05
    0.10
    0.08
    0.05
    0.03
    0.15
    o.or.
    0.03
    0.06
    O.OH 0.07
    0.10 0.12
    0.06
    0.17
    0.50
    0.25
    0.5
    ..
    ro
    VI
    

    -------
           After 3bout. JrOOO r.r.urs of materials  testir.g in the One-Atmosphere Ccr.tiusf.or very
    little corrosion has Lion ob-erved.6   Th-j  results dc net distinguish between JO'iSj and
    111-736 or I1I-713C 'lorro.- ion resistance  of  IK-7-S is vastly superior to 30U3S or It.'-713C
    in conventional ho'.-ccrres i or. tests).  A series of preliminary snort-duration tests showed
    that significant, hot-corrosion attack  aid  occur if the temperature in the freeboard ex-
    ceeded &Lout  :70r;"r.  The CPC tests show S'..r.e ovidr-rce that the addition of an aiunino-
    silioate additive- to the  bod suppresses  the relea.-.o of alkali  sulfate with a redaction
    in the potential for hot  corrosion.   Krosicn of material specimens was not observed i r.
    the freeboard of ปr.e AMnoah^ric i:cmbustor  .low gas velocity).
    
           The main conclusion from the CPC  work to dato in that, tonperaturo i.-. the ?ingiซ
    no"t important factc" in  -Jetern; ininf;  whethoi- or not hotr corrosion will occur in an Atr.o-
    r.pher ic Coa 1-Cor.Lur.tor Cystc-K.  At temperature- o-f 'fjOO'F hot  corrosion did not occur,
    while temperature excursions above  1700JF  produced significant corrosion attack.
    
    Summary of Prior Experience
    
           The most rr.eaninpful data obtained so fa>- aro from the PFEC t^sts at Leatherhead,
    England.  The rea.-on ic that conditions  of  tr-p'-rature, pressure, and Ras velocity were
    the closest to what  :s expected in a  real  r^stem although there were several c^-rrperature
    excursions due to coal feed problems,  and  these excursions could have contribu'.ed to
    the observed attack.  As  previously indicated, hot corrosion was observed in these tests
    after only ?00 hours.  Also the level  of alkali analyzed in the gas was in the ranp.e
    of what is expected based upon thermodynamic estimates.
    
    MATERIALS DEVEI.OrKF.IJT FOR THE COAL-FIRED COUBTI.'hD CYCLE
    
           The current state-of-the-art for  particulate removal and alkali vapor inhibition
    or removal is such that major breakthroughs will be required to achieve acceptably low
    levels of alkali netal contamination.  Therefore, the achievement of acceptable turbin'.
    blade parts liver, in the  expected  alkali environment will require at a minimum, substantial
    improvem-jiit in corros i on-res i -.tant alloys  and hot gas cleanup technology.  Because of
    the advanced  devel opr.eiit  cha'ienpe  in .ill  possible solution."! to the ccrros-ior. problem,
    it  is likely  that a  combination of advancements in each technology will be required to
    achieve an acceptable system.  In  this section present work on a materials development
    approach will bo reviewrrl as n solution  to  the corrosion problem.
    
           Materials development in the present DOi-I sponsored General Electric CFCC Develop-
    ment Program  i:-. directed  towards development of sheet claddings for use on gas turbine
    buckets anu nozzles  that  will operate in the environment generated by a Pressurized Fluid-
    I zed Bed Combustor.  A schematic of the  cladding process is shotin in Fipure 5.  The overall
    philosophy of the technical approach  involves a systematic combined study of cladding
    chemistry, procers variables, and  resultant properties which will lead to a significant
    improvement ovซ>r existing surface  protection schemes for use in PFBC-type environments.
    This program, which  is an extension of previous cladding studies at General Electric
    is divided into tasks as  shown below:
    
             • Task 3.1  - Cladding Alloy  Development
             • Task 3.2  - Cladding Process Developaent
    
    Cladding Alloy Development
    
           Th? primary objectives of this task  are to:
    
            1.  Select and characterize clad  alloy coirpositions with expected superior corro-
               sion resistance  in the  fluidized bed combustion environment;
           2.  Assess the corrosion capability of the best candidate claddings;
           3.  Characterize  the clad substrate interactions as a function of exposure con-
               ditions.
                                               726
    

    -------
    CORROSION • RESISTANT
    SHEET ENVELOPE
    CREEP-RESISTANT
    AIRFOIL  BODY
    CREEP AND CORROSION RESISTANT
    CLAD TURBINE  BUCKET
                   Figure 5. Sketch Illustrating Cladding Concept for Corrosion-Resistant
                                    Gas Turbine Bucket
                                         727
    

    -------
           Three reference cladding alloys have been -jred as controls to form the basis for
    the development of new alloys.   The composition of these alloys are listed fcelow:
    
                                         Weight J
    
              Alloy          Fe      m_     Co     Cr      A_l_       Y       Other
    
              OE-2511        Bal      -       -     25.0    U.O     1.0
    
              Inconel 671     -     Bal      -     50.0     -
    
              S-57            -     10.0    Bal    25.0    3.0    0.15    5.0 Ta
    
           Modifications of these alloys were selected with Cr an-i Al contents as m^jor
    variables since these elements control the type of protective oxide which will form.
    Rare earth element additions  were made to selected compositions to improve scale adhesion.
    
           Some of the alloys were formulated for sheet fabrication by conventional cast
    and wrought metalwcrking practices and, due to anticipated processing probless some of
    t!ie alloys, were fabricated from more readily processed pre-alloyed power.  Initially
    about 15 clad alloy compositions were identified.  In an attempt to increase the Al con-
    centration of certain of the  clad alloys, without reducing fabricability, they were
    aluminided by the standard pack cementation process.  Finally 11 of the 15 original
    alloys were processed to 10-mil sheet which was suitable for the cladding of corrosion
    specimens.  Compositions of nine of these alloys are shown in Table IV.  The two alloys
    which are not shown are presently under review Tor possible patent action.
    
           IN-738 (Hi-base) and FSX-114 (Co-base) have been utilized as substrate materials
    since these alloys are current gas turbine bucket and nozzle alloys.  Prisary emphasis
    has been placed on IN-738.  Small burner rig corrosion disks of these alloys have been
    machined and fully clad with  the candidate sheet clad alloys.  The specimens were pre-
    pared by diffusion-bonding the cladding to the corroson disk using the reference glass
    Hot Isostatic Pressure (HIP)  process.  This process utilizes eolten glass as the pres-
    sure transfer media while in  an evacuated, sealed container.  Hot Isostatic Pressure
    Diffusion Bonding conditions  were 2100 F,  15,000 psi gas pressure for a one r.our hold
    time.  Figure 6 is a Schematic of the Hot Isostatic Pressure Autoclave. . Selected alloys
    were pack aluminided by established techniques.  This does not show in Table IV.  The
    small burner rig test is being used to screen the elaa opecicens.  A schernau-.- of the
    small burner rig is shown in  Figure 7.  Test conditions are givon in Table V.  To date.
    Test Number One shown in TaMe V has been used.  This test environment includes the
    alkali contaminants expected  from coal, sodium, and potassium at levels which will cause
    a saturated layer of alkali sulfate condensate at one atmosphere on the specisen sur-
    face.  As discussed earlier,  this is the expected condition for the PFBC/Gas Turbine
    combination.  Test Number Two shown in Table V is still under development.  This test
    will include levels of chlorine which closely simulate those expected from th<ป combus-
    tion of coal.  An .nitial 1500-hour test has been completed in the small burner rigs,
    and a long-time tes\. to develop data as a function of exposure to approximately 5000
    hours is now under woy.  Following exposure in the small burner rig, the disc-shaped
    specimens are metallographically prepared and measured for maximum depth of penetration
    as illustrated in Figure 8.
    
           Based upon the  1500-hour Small Burner Rig Corrosion Teat, five claddings have
    been selected for testing in the EXXON Hiniplant PFBC facility.  A test section which
    is a series of four stationary cascades designed to simulate gas turbine conditions
    has been  fabricated by General Electric and installed in the Exxon Miniplant as part
    of the DOE Fireside Corrosion Task II Program.  A schematic diagram of the test section
    is shown  in Figure 9.  A summary of the Miniplant test conditions is given in Table VI.
    Airfoil-shaped specimens of impulse and reaction design have been procured for the test-
    Ing.  The  impulse-type simulate the gas turbine bucket, and the reaction-type simulate
    the gas turbine nozzle (Figure 10).  The airfoil specimens are now being clad with the
    selected  claddings.  A similar test section is being built for installation in the CURL,
    ?.  foot by  3 foot PFBC  in Leatherhead, England.  Clod airfoil specimens will aiso be ex-
    posed in  this facility.  It is anticipated that exposure of the airfoil specimens in
    the Exxon Klniplant and the CURL PFBC at Leatherhead, in addition to corrosion data,
    will provide an assessment of the potential erosion problem.
                                              728
    

    -------
                                   YOKE FRAME)
                                    MOVEMENT
    FURNACE WNNN6S
      MOSMCERS
      HYPR&UUC
      CYL1MK8S
                   Figure 6. Schematic of Hot bostatie Pressure Autocta*
                                    729
    

    -------
          Table IV.  CFCC  - Clad Alloy  Developaent
    Alloy
    CE-2541
    GE-25
    -------
                       CROSS
          	0	f- SECTION
                        LINE
           EXPOSED
        TEST SPECIMEN
          AFTER TEST
                                              MET ALLOGRAPH ICALLY
                                               MOUNTED SPECIMEN
                                                  AFTER TEST
                       IMACE OF MOUNTED SPECIMEN
                          IN OPTICAL COMPARATOR
          READ
    WtTAL PENETRATION
     *CR SIDE (MILS)
                                                        METALLOGRAPHIC
                                                          MOUNTING
                                                          MATERIAL
                                                        SET CURSOR IN
                                                    THICKNESS BEFORE TEST
                                                          BO MILS
                  FiguraS. Schematic of Small Burnt* Tซt Specimen! and
                 Mซanxl of Meultographially Measuring Depth of Common
                                    731
    

    -------
           Table V.  Small Burner Rig Corrosion Screening Test
    Temperature   -  1600ฐF
    Pressure      -  Atmosphere
    Velocity      -  70 fps
    Fuel          -  ป2 Distillate
    Cor.taninants  -  1ปS, Na, K Added to Fuel —HC1 Added to Mr
    Deration      -  1500 Hours for Selection of Materials To Be
                       Tested in the Exxon Kiniplant
                     7000 Hours Long Time Test of Selected Materials
    Test ป1       -79 ppm Na, 112 ppm K in Fuel
    Test 12       -  79 ppm Na, 112 ppm K in Fuel Plus 15 ppm
                       HC1 in Air
               18 IMPULSE AIRFOILS
                5 ATM.
                I550ฐF
                955 fps
                0.83 Lbs/SEC.
                                                     REACTION AIRFOILS
                                                             EXIT
    2.9 ATM.
    J550ฐF
    1910 f pi
                        Figured. Turbine Ten Section
                                  732
    

    -------
       Table VI.   Test Conditions  Exxon Miniplant
     Pressure:  8.7 -  9.1  Atmospheres Absolute
    
     Temperature - In  Combus'-or:  1700ฐF -  17bOฐF
    
     Temperature - At  Turbine Test Section  Inlet:
                      155CTF - 1570ฐF
     Gas Mass Flow Rate:   0.7? I/sec - 0.92 */sec
    
                              / be Hec
                               Section
    Combust ion of  Methane may be Hecos.sary  to  Assure
      1S50JF at Turbine Teat ฃ
     Up to 8 Clad Alloys
    
     Time - 1000 Hours
    Figur* 10. Airfoil Corrosion Specitnmi (or Turbine Tot Section
                          733
    

    -------
    Cladding Pro •.•ess  Devi-1 oprr,er;t
    
           The cladding  process ceveiopr.ent effort is ar.  if>tซ-gral part  of  the overall effort
    to develop advanced  ciaddir.?  r.ateria;s for protection of "*-.:; 7-jrbi:'.- Hot-^ect i en par'.s.
    Th-.-r.e studies  recognize  the  ir.r.-.-rer.t physi'.--jl and -^-hani-:%j pr>.perty  o-'.aricter i st ics
    of the individual  cladding alloys  -jr.-o- tne ir.portanc';  of  opt Jr.; z ing  tr.o total  clad/sus-
    strate system  for  turbine bucket appj icatior.r-.
    
           Presentiy,  thtrr.  are  five key activities under cisl'ir.-g process development.
    These are:
    
           1.  Clad sheet  forming
           ?.  ourface preparation  technj^L :s
           "J.  Optimization  of diffusion -ondir.p parameters
           'J.  Total  bucket  cladding (tip. platforn, airfoil)
    
    
           Since an adequate treatment  of the cladding prooens  •Jevelopr.ent effort  is legiti-
    mately the subject of  another complete paper, it will not be discussed further  here.
    
    Corrosion Results
    
           Corrosion  test  results to -.'ate for the cladding alloys consist  of  those  from  the
    1500-hour test at  IfcOO'F in the ssalj burner rig.  Trteso are ::r;own  in  7aL!e VII for  r.o.T.e
    but. not all of tho cladding alloys.   At the bottorr. of Table VII  i.-.  a result for hare
    111-73*} in the  same test.  It  is otviojs fron ti-.eso- preljsiisry results that several  of
    the cladding alloys  offer the prczi.o-^ of a significant decree of protection for the
    present first-stage  bucket alloy,  IM 738.  "ho corros ior. rate of GiC?^-1  ir the  cast  and
    wrought form was  1.1 mi Is/1000  hours and ir. trie powd'-r r.eta, i urgy forr: was 0.ซ  milr./loOU
    hour:;.  Those  w<-re clearly the  mo::t  resistant nater i a Is  in  this  first  test.  Since trie
    small burner rip.  is  being operated  uncer cone!", t i on:; whicr. saturate  thซ- specimen surface
    with condensate  (corrcsponoinf;  to  trie reaction rate-1 ir.: ten regime  in  rigur*-  3 •', small
    burner rig data i:an  be use?:  directly to estir.ate the  life of f < rst-stage  tickets for
    the I'FEC/Oas Turbine.  Presently the cladding process is b<-;;:g developed  to arply 10
    mil thick claddings  to first  r,t;jge  buckets.  'Jsing the re.:u.ts in Table  VII,  a  10 mil
    cladding or GKZOII PM  would provide  25.000 hours of protection at ItOO^F  while  GE 2v'li
    would provide  9000 hours of protection.  On the other hand, th>-  corrosion of  t:are III-
    738 would exceed  10  mils in  j>;.-s than 1000 hour:;.  f!JJ-7'*  is one of tne  r.ost corrosion-
    resistant alloys  in  a  conventional  Oil-Fired -"as Turbine).  "hซ.  above  estimates for  cla-i-
    dings suggest  that there is a pood  chance that thick  corrosion-resistant  claddings will
    offer the corrosion  protection  required in the PFI'-C envi ronK.ent.  hesults from  or." test,
    however, can be misleading.   8e-ults of the add] t i or: jl corrosion tests planned  for the
    program described  here,  together vith additional long-time  tests of at least  10.000  hours
    duration in a  real PFRC  cnvi ronsent, arc re-quired before the life of the  corrosion-re-
    sistant cladding  materials can  be  predicted with confidence.
    
    SUMMARY AND CONCLUSIONS
    
           • There  is  the  potential for  vapor phase alkali tr.etal in  the cor.bustion  products
             from  the  PFBC which  is several orders of n-'.gnituae greater th^n  present limits
             for petroleum-fired  gas turoines.
           • Preliminary test results  suggest that several of the cladding compositions may
             have  excellent  corrosion  rr -stance to the PFEC environment.
           • Long-time corrosion  tests  of at least 10,000 hours in the  coal environment are
             required  to confirm  the corrosion resistance of candidate  materials.
           • Erosion  testing of cladding alloys i: also critical.
           • The overall solution to the problems identified here will  require a  combination
             of improved hot section materials to resist c-rrosicn/erosion and significant
             advances  in hot gas  clean-up technology.
    
    
    ACKNOWLEDGMENT
    
           This study  i.s supported  by  the US Department of Energy under Contract  Ho.  EX-76-
    C-01-2357 issued  by  the  Fossil  Energy Progras.  George C. We'.h of DOE/FE  is gratefully
    acknowledged as  the  Program Manager.  The authors are particularly  ind'bted to  Mr. H. von
    E. Door ing. Gas Turbine  Products Division (GE), Cor many useful discussions.
    
    
                                              734
    

    -------
       Table VII.  Cladding Corrosion Data
                   from 1600 F Sea 11 Burner
                   Rig Test with 79 Pt-E !.'a
                   and 112 pps K in the Fuel
    
    Cladding on IN-738     Hi Is per 1000 hr
    
       CE-25
    -------
    REFERENCES
        A.I-.  Foster. H. f.oering, J.W. Hickey, "Fuel Flexibility in Heavy Duty Gas Turbines,"
        Gas Turbine Products Division State of the Art Paper Ho. GER-2222L,  1977.
        General Electric Cocpany, Gas Turbine Products Division, "High Tenperature Gas Tur-
        tine Engine Corponent  Materials Test Program - Task I, Quarterly Technical Progress
        Report No. 5, EHDA Contract Ho. E( 148- 18}- 1765.
        J.W.  Schultz and W.R.  Hulsizer, "Corrosion Resistant Nickel-Base Alloy  for Gas Tur-
        r-ines," "etals Engineering Quarterly, p.  15, August 1976.
        National Research Development Corporation, "Pressurized Fluidized Bed Combustion,"
        OCH Contract lu-32-001-1511,  Finil Report, November 1973.
        L.3.  '.bsak and H. von E. Doerir.g, "Host-Test Evaluation of Gas Turbine  Alloys in
        Fluidized Bed Combustion Gases at CRE," Gas Turbine Division Report  77  GTD-3, Jan-
        uary}  1977.
        Combustion Power Corporation, "Hot Corros.'on in the Direct-Coal-Fired Gas T.jrbir.e"
        (A Supplemental Heport} ERDA Contract E(^9-18)-1536, September 1976.
                                              736
    

    -------
    Sorbent Regeneration
            737
    

    -------
                             INTRODUCTION
         f'P. rปAMAN,  rHAIPMAfi:   Our next  paper is  entitled  Themodynanics
    of Peqeneratinq  Sulfated Lino to he  qiven hy  Or.  Ton '-'heelock.  
    -------
    

    -------
                       Thermodynamics of Regenerating Sulfated Lime
                            Firoz M. Rassiwalla and Thomas O. Wheelock
                                Chemical Engineering and Nuclear
                                    Engineering Department
                                  Engineering Research Institute
                                      Iowa State University
    ABSTRACT
           The thercodynamics of a high temperature reductive decomposition process for
    regenerating the lime sorbent which has become sulfated in a fluidized bed combustor
    arc analyzed to reveal the process characteristics and to show the effects of various
    operating conditions on process performance.  For this analysis it is assumed that
    the reaction system is in thersodynamic equilibrium.  The effects of temperature,
    pressure, and reducing state on the extent of desulfurization, sulfur dioxide con-
    centration, and the fuel and enerpy requirements are shown.  Also the effects of using
    different types of fuel including coal and cethane for regeneration are indicated.
    
    
    INTRODUCTION
    
           The future application of fluidized bed combustion systems for coal may depend
    on the successful development of a process for regenerating the lime used to absorb
    sulfur oxides in these systems.  Otherwise the problem of supplying these systems
    with lime and disposing the sulfated sorbent may be horrendous.
    
           One of the nost pronising regeneration processes under development involves
    decomposing the sulfated lime at high tentperature in a reducing atmosphere produced
    by the partial combustion of coal or other carbonaceous or hydrocarbon fuel.  This
    process is based to a considerable degree on earlier work at Iowa State University
    which was directed toward the development of a process for decomposi .g gypsum and
    anhydrite, the naturally occurring minerals of calcium sulfate^-*'.  .'he reductive
    decomposition process was demonstrated with a scall pilot plant supplied with anhyd-
    rite and natural ?,as at Kent Feeds Inc.8.  The anhydrite was treated in a fluidizcd
    bed reactor in which natural pas was also partially combusted to supply both heat
    energy and carbon monoxide and hydrogen for reaction with calcium sulfate.  A major
    improvement in the process resulted with the discovery at Iowa State University that
    calcium sulfate can be decomposed advantageously in a two-zone fluidized bed reactor
    in which the material is alternately exposed to reducing conditions and oxidir.ing
    conditions'.  By this procedure the reaction driving force can be kept large without
    resulting in the production of an excessive amount of undesirable calcium sulfide
    by-product.
    
           The application of the reductive decomposition process co the sulfated lime
    produced in fluidized bed combustion systems has been underway for sometime.  Signifi-
    cant process development prograns have been carried out at both Exxon Research and
    Engineering Co.10"1-' and Argonne National Laboratory 14-13.  At Exxon this effort has
    reached the stage of trial runs with a continuous flow "miniplant" regenerator fueled
    with natural gas and coupled to a pressurized fluidized bed coal combustor!3.  At
    Argonne the prograa has advanced to operation of a smaller continuous flow regenerator
    fueled alternatively with isethane or powdered coal!6.18.  The Exxon unit has operated
    under pressures up to about 10 atn. while the Argonne unit has operated at lower pres-
    sures (1.1-1.5 ata.).  Continuous regeneration of sorbent lime has also been demon-
    strated in an atmospheric pressure unit operated in tandem with one of the first
    experimental fluidized bed combustion systems for coal which was built and operated
    by the firm of Pope. Evans and Bobbins Inc.IS.  This unit was fueled with coal and
    operated continuously for several days during a trial run.
    
           Although these developments have been most encouraging, more information is
    needed for process analysis and design.  More specifically, the performance char-
    acteristics of the process are needed.  While these may be determined experimentally,
    the amount of experimental wcrk entailed is so great that use of theoretical models
    of the reaction system to predict these characteristics should also be considered.
    For the work reported here, a nodel of the system based on thormodynamic equilibrium
    was analyzed to predict the effects of temperature, pressure, and reducing state of
    
    
                                             740
    

    -------
    the system on the extent of desulfurization, sulfur dioxide concentration,  and the
    fuel and energy requirements.   Also the effects of using different types of fuel
    including coal and methane were investigated.   The present study relied heavily on
    previous studies of the process thermodynamics made by Wheelock and Boylan3,  Skopp
    eฃ aj.,10. Vogel tฃ ซa.l<>. and  Engel20.
    
    
    REACTION SYSTEM
    
           The most successful demonstrations of the reductive decomposition process
    have been made with fluidized  bed reactors supplied with calcium sulfate. fuel and
    air. with the amount of air being less than that required for complete combustion
    of the fuel and the whole system operated under steady-state conditions.  Under these
    conditions the fuel has been converted to a mixture of carbon monoxide, hydrogen.
    carbon dioxide, and water vapor with a corresponding release of heat.   Thus gaseous
    reducing agents have been available to react with the calciun sulfate at high tempera-
    ture and the following endothermic reactions have probably occurred:
    
                                   CaSO^ + CO = CaO + C02 + S02                       (1)
    
    
                                   CaSOA + H2 • CaO + H-20 + S02                       (2)
    
    
    In addition to these reactions some of the calcium sulfate has been reduced to calciun
    sulfide by exothermic reactions such as these
    
                                   CaSOA + 4 CO = CaS + 4 C02                         (3)
    
    
                                   CaSO^ + A H2 = CaS + 4 H20                         (4)
    
    
    Under these reaction conditions the solids have been well mixed and in intimate
    contact with the gas phase.
    
           If the components of the preceding reactions are in thermodynamic equilibrium,
    it can be shown that the intensive state of the reaction system at 1 atrr. can be
    represented by the phase diagram of Figure 1.   The diagram was constructed of values
    which were calculated from basic thermodynamic properties under the assumptions of
    ideal gas behavior, unit activity of each solid component, and both isothermal and
    isobaric conditions.  It shows that the intensive state of the system depends on fix-
    ing three parameters such as temperature, pressure, and the ratio of carbon monoxide
    to carbon dioxide.  This ratio is a measure of the reducing potential of the system
    since the gas phase becomes more highly reducing as the ratio increases.  Alterna-
    tively the ratio of hydrogen to water vapor could have been used since the two ratios
    are related by the expression
    
    
    
                                                                                      (5)
    where Kg is the equilibrium constant for the water gas shift reaction shown below.
    
                                   CO + H20 - H2 + C02                                (6)
    
           Figure 1 also shows that the number of solid components which are present
    depends on the temperature, pressure and reducing potential.  Each sclid component
    occupies a separate phase.  Thus in the region represented by area 1 of the diagram
    only calcium oxide is present, in the region represented by area 2 both calcium sul-
    fate and calcium oxide are present, and in the region represented by area 3 both cal-
    cium sulfide and calcium oxide are present.   All three components can coexist only
    along the boundary separating area 2 and area 3 so this can be regarded as a co-
    existence line.  Along this boundary the partial pressure of sulfur dioxide is deter-
    mined completely by the following reaction:
    
                                   5 CaS04 + 5 CaS ฐ CaO + S02                        (7)
    
    
    
                                             741
    

    -------
       2400
       2200
    UJ
    a:
    UJ
    a.
       2000
       1800.-
       1600r
                                                      SO,
    .7
    
    .3
    
    
    .1
    .05
    .02
    .01
    
    .005
    
    .003
    
    .001
    
    .0005
    .0001
    .00001
    
    .000003
    .000001
                                         0.04  0.05
                      Figur* 1. Equilibrium phn* diagram
                          of the system rt 1 Mm.
                              742
    

    -------
    Since the equilibrium constant  for  this reaction is
    
                                   V  = P                                             fO\
                                   K7    PS02                                          (8)
    
    
    it follows that the partial pressure of sulfur dioxide is  dependent only on tempera-
    ture when all three solid components are present.  On the  other hand,  in area 2,  the
    partial pressure of sulfur dioxide  is determined by  reaction 1  and the partial pres-
    sure of sulfur dioxide depends  on both temperature and the reducing potential as
    shown by the expression below defining the equilibrium constant K^.
    
    
                                                                                      (9)
    
    
    
    Moreover in area 3 the partial  pressure of sulfur dioxide  is determined by reaction
    10.
    
                                   CaS  -f 3 C02 ป CaO + 3 CO +  S02                     (10)
    
    
    and therefore
    where K\Q is the equilibrium constant for this reaction.   From equations 9 and 11 it
    can be seen that for a given temperature the sulfur dioxide  partial  pressure varies
    directly with the reducing potential in area 2 and inversely with the reducing
    potential in area 3.   Moreover from Figure 1 it can be  seen  that  for a given tempera-
    ture the maximum sulfur dioxide partial pressure is obtained along the three solid
    component coexistence line.
    
           A phase diagram similar to Figure 1 was presented  by  Vogel et al. '•^ for a
    total system pressure of 10 attn.   At the higher pressure  the region  represented by
    area 1 is not present while two other regions corresponding  to mixtures of calcium
    carbonate with calcium sulfatc or calcium sulfidc respectively are present.   The
    calcium carbonate containing regions are present at temperatures  below 1950ฐF.  If an
    inert gas is present, the calcium carbonate containing  regions are limited to lower
    temperatures than this.
    
    
    THEORETICAL MODEL
    
           A specific type of reaction system was assumed to  provide  a basis for analysis
    and prediction of the process characteristics.   Thus it was  assumed  that  calcium
    sulfate, fuel, and air would be fed continuously into a steady state,  isotherr-al and
    isobaric fluidized bed reactor where the solids would be  well-mixed  and all  of the
    products leaving the reactor would be in equilibrium.   It was assumed that the react-
    ants would enter the system at 77ฐF and the products would leave  the system at the
    reaction temperature.  Also it was assumed that the reactancs would  be fed in such
    proportions that essentially all of the calcium sulfate except for a trace would be
    converted to either calcium oxide or calcium sulfide.   In addition it  was assur.ed
    that the gas phase would exhibit ideal gas behavior and that the  activity of each
    solid component would be unity.
    
           The effect of various types of hydrocarbon fuels was  investigated.  It was
    assumed that each fuel would react with oxygen in the fluidized bed  to provide a
    mixture of carbon monoxide, carbon dioxide, hydrogen and  water vapor.   It was further
    assumed in the case of bituminous coal that this material could be represented by the
    formula CHn.8 and that its heat of formation would be negligible.
    
           Although the system was not limited initially to the  components involved in
    reactions 1-4. it became apparent subsequently that those components plus nitrogen
    were the only ones likely to be present in significant  amounts.   Analysis of the
    system by the Cibbs free energy minimization techniquc21  showed that under highly
    
    
                                             743
    

    -------
    reducing conditions produced  by feeding methane, none of the following components
    were present in significant amounts:   methane,  carbonyl sulfide, hydrogen sulfide,
    elemental sulfur,  or sulfur trioxide.
    
           As long as  the preceding assumptions apply, the same model can be used to
    analyze eitr.?r the one-zone or two-zone fluidized bed reactors.   Thus it should not
    pake any difference whether the bed is divided  into various oxidizing and reducing
    zones as long as the solids are well  mixed and  all of the products leaving the reac-
    tion system are in equilibrium.
    
    
    COMPUTATION METHODS
    
           The performance characteristics of the model system defined above were deter-
    mined by analyzing a series of equations representing the equilibrium state of the
    system and the material and energy balances.  In doing this the independent para-
    meters which were  usually specified to fix the  state of the system included tempera-
    ture, pressure, type cf fuel,  and percent air.
    
           The percent air is the  percentage of the stoichiomeiric amount of air required
    for complete combustion of the specified fuel to carbon dioxide and water vapor.
    Hence, it is another measure of the reducing potential of thซป system and it is a more
    convenient independent parameter than the Pco/Pco-> ratio because the percent air can
    be controlled directly by a plant operator.
    
           The performance characteristics which were calculated included the composition
    of the gas leaving the system  and particularly  the sulfur dioxide concentration of
    the gas, the percent desulfurization  of the solids, the fuel requirement of the pro-
    cess, and the thermal energy requirement.  The  thermal energy requirement is that heat
    added to the system beyond that supplied by the fuel which is fed to the reaction
    system.
    
           The performance characteristics were determined for two operating regions A
    and B.  Region A corresponds to area  2 of Figure 1 while region B corresponds to the
    boundary between area 2 and area 3 of this figure.  Thus operation in region A would
    lead to essentially complete desulfurization of the solids while operation in region
    B would lead to incomplete desulfurization because of significant conversion to cal-
    cium sulfide.  However, in both regions the solidi* were assumed to contain a trace of
    unreactcd calcium sulfatc.  Operation in a region corresponding to area 3 of Figure 1
    was net considered because it  would lead to large conversions of calcium sulfate to
    calcium sulfide as well as waste fuel.
    
           For the equilibrium analysis in region A, the series reactor technique22 was
    used.  In applying this technique it  was assumed that reactions 1 and 6 take place
    sequentially with the system first coming to equilibrium with respect to one reartion
    and then the other.  The process is repeated until no significant change in the state
    of the system is observed.  Since this is an iterative technique, the calculations
    were performed by a digital computer.
    
           For the equilibrium analysis in region B, an explicit solution of the algebraic
    equations was obtained.  This  involved solving  the equilibrium defining equations for
    reactions 1, 3 and A together  with the appropriate material balances.
    
           After the equilibrium state of the system was determined and the material
    balances were solved in either region, an energy balance was used next to find the
    additional thermal energy requirement of the process.  The expression for the energy
    balance is shown below.
    
                                   Q -  r n^K. - r  m.H.                               (12)
                                        p  i i   R   J J
    
    This expression indicates that the heat requirement Q is equal to the difference
    between the enthalpy cf the produces  and the enthalpy of the reactants.
                                             744
    

    -------
    PERFOR>JA:;CE CHARACTERISTICS
    
           The calculated performance characteristics of the model reaction system are
    presented in Figures 2 to 10.   The first of these diagrams shows the two selected
    operating regions A and B for the case where methane is the fuel and the total
    operating pressure is 1 atn.  From this diagram it can be seen that in region A the
    partial pressure of sulfur dioxide in the product gas is virtually independent of
    temperature and therefore almost entirely dependent on the percent air supplied to the
    system while in region B the partial pressure of this component is entirely dependent
    on temperature.  In region B the sulfur dioxide partial pressure is determined by
    equation 8 and in region A by equation 9.  Equation 8 shows wh • the partial pressure
    depends only on temperature.  On the other hand, equation 9 indicates that the partial
    pressure of sulfur dioxide should also depend on temperature in region A because of
    the effect of temperature on K.\.  However, the partial pressure of sulfur dioxide is
    also dependent on the PCO/PCUT ratio in region A and from Figure 2 it can be seen
    that this ratio decreases as the temperature increases.  Hence. the effects of temper-
    ature through KI and PCO/PCOT largely cancel out.
    
           Figure 2 also shows that in region A the Pro/Pco- ratio depends on both temper-
    ature and the percent air whereas in region B this ratio depends only on temperature.
    In region A for a given temperature the Hcn/1'cfi•• ratio increases as the percent air
    decreases wh<"h is not surprising since these quantities are both measures of the re-
    ducing potential.  However, in region B for a specified temperature the Pco/Pcoj ratio
    does not change with the percent air because in this region the PCO/PCO- ratio is
    determined by equation 13 below which is based on reaction 3.
    
                                   PCO/PC02 • l/K31/4                                 <13>
    
    Hence, as the percent air is reduced the Pco/Pco.. ratio does noc increase but instead
    more calcium sulfate is converted to calcium sulfiJe in place of calcium oxide.
    
           Although Figure 2 applies specifically to the case where methane is the fuel. ..
    the relationships portrayed by this diagram are not much different for other fuels.
    On the other hand, changes in total system pressure have a marked effect on the loca-
    tion of the boundary separating regions A and B as can be seen from Figure 3.  Even
    though this figure was developed for the case where coal is the fuel, the location of
    the line separating regions A and B at 1 atm. is not far from the location of the
    corresponding line in Figure 2 for methane.  However, increases in system pressure
    nove the boundary separating  regions  A and B to higher and higher temperatures thus
    Increasing region B at the expense of region A.  Therefore at higher pressures there
    is less opportunity to operate in region A than at lower pressures.
    
           The concentration of sulfur dioxide in the product gas where coal is the fuel
    is shown by Figures 4 and i for different operating conditions.  For a total pressure
    of 1 atn.. Figure U again indicates that the concentration of sulfur dioxide depends
    almost entirely on the percent -ilr in region A and on temperature in repion B.   Al-
    though very high sulfur dioxide concentrations arc theoretically attainable in reelon
    A at low percent air. the thermal energy requirement for these conditions is imprac-
    ticably high.  The constant heat input lines or isocalorlc lines plotted in Figure ซ
    represent a reasonable range of heat input.  For an adiabatlc reactor at 1 atm.  the
    maximum attainable sulfur dioxide concentration is about 9.5% and this would be
    obtained with a temperature of 1850ฐF and 777, air.  By supplying 40 kcal./m.  CaSOi
    additional heat, the maximum sulfur dioxide concentration could be increased to about
    lAx while the temperature would have to be raised to 1S70ฐF and the percent air re-
    duced to bo'!..  Or. the other hand, for a heat loss of 20 kcal./m.  CaSOi from the
    system, the maximum attainable sulfur dioxide concentration would be about 3',.   For
    any specified heat input, the maximum sulfur dioxide concentration is obtained along
    the boundary separating regions A and B.
    
           The effect of total system pressure on the theoretically attainable sulfur
    dioxide concentration Is shown in Figure 5 for two different temperatures. 1900 and
    2100ฐF.  In this diagram the Isobars are drawn as solid lines in region A and dashed
    lines In region B.  It can be seen that in region A the total pressure has relatively
    little effect on the sulfur dioxide concentration while in region B It has a major
    effect with the concentration falling off as the pressure Is raised.
    
    
    
                                             745
    

    -------
    2400
    2200-
    o
     jg
    
     i
    2000
    1800-
    1600-
         i        20        40         60
                              AIR. '-
         Figure 2. Sulfur dioxide partial pressures resulting
           from the reaction of CH4-air-CaSO4 at 1 atm.
                                                80
      2300
      2200
      2100
    
      2000
      1900
      1800
      1700
                                                  COAL
    
                              -PRESSURE =  10  atm
              _    CaO-CaC03
                  COEXISTANCE LINE
              	[__  _  ^
            30            50              70
                                AIR,  2
                  Figure 3. Effect of pressure on
              the boundary ceparcting reojora A and B.
                                                           90
                            746
    

    -------
                                          COAl
    
                                      PWSSURl -  1 atm
      Figure 4. Sulfur dioxide eonetnUMions retutting
       from the reaction of coal-air-CaSO4 •ซ 1 atm.
    '.PRESSURE  ซJL atm
                   . kcal/ro CaSO^
    
                               40
    50        70
       AIR. I
                             40
    
    
    
                             32
    
    
    
                             24
    
    
    
                             16
    
    
    
                              8
           TEMPERATURE  ซ 2100 QF
    
    
                 ESSURE • 1 atm
                      kcal/m CaSO.
                               o
                         O O
    30
                                                   SO        70       90
                                                     AIR. :
     FigurtS. Sulfur dioxid* eonccntratiom for vartout
                 prcoum baitd on coal.
                       747
    

    -------
           COAi.
    
       PttSSWE • 1 
    -------
    11
          cow.
    PRtSSL'RE ป 1 au>
    
                FigurtB. Fuel requmnwtt* ol lhซ proom brad on out
                                                 SO        70
                                                   AIR. '.
              Figun9. FoH requirvntnti it ปซnouป pnourtt bnx) on coat
                                                                   90
                                     749
    

    -------
        65
    ปซ
    
    J- 50
    
    
        35
    
    
    ,ซ  20
    
    o~
    W  10
    
    
    ..  20
     ป
    o
    x*-
        10
    
    
      0.1 r
      0.15
     0.05
          30           50            70
                            AIR. I
            Figure 10. Product gป competition bซsea
            on cod or rnttham el 2000'F and 1 (tin.
    90
                           750
    

    -------
           The percentage desulfurization of the solids where coal is the fuel is shown
    in Figures 6 and 7 for different process conditions.   In region A the solids are shown
    to be completely desulfurized because this was one of the underlying assumptions on
    which the analysis is based.   In region B the solids are incompletely desulfurired
    because they are partially converted to calcium sulfide.  From Figure 6 it can be seen
    that lower temperatures and lower values of percent air lower the percentage desul-
    furization and favor the production of calcium sulfide.  Thus at 1500ฐF and 307, air
    almost all of the calcium sulfate would be converted to calcium sulfide.   Figure 7
    shows that higher pressures also inhibit desulfurization and favor the production of
    calcium sulfide.  In this diagram the isobars are again represented by solid lines
    in region A and dashed lines in region B.  Figure 5 and 7 show that for a system at
    10 atm. total pressure it is not very practical to operate at a temperature as low as
    1900ฐF because it would only lead to very incomplete desulfurization and very low
    concentrations of sulfur dioxide.  However, at 2100ฐF it would be theoretically
    possible to operate at 10 atm. total pressure in region A with coraplece desulfuriza-
    tion of the solids and product: a product gas with about 1\ sulfur dioxide.
    
           The fuel requirements of the process in the case of coal are shown in Figures
    8 and 9 for various process conditions.  The fuel requirements are lower in region A
    than in region B because the desulfurization reactions (1 and 2) consume less fuel
    than the calcium julfidc forming reactions (3 and 4).  Also the fuel requirements are
    lower for lower values of percent air in region A than for higher values because less
    of the fuel is converted to heat energy and more heat is supplied to the system from
    an external source.  Figure 9 shows that pressure has only a slight effect on the fuel
    requirements in region A h.it a major effect in region B because of the increased pro-
    duction of calcium sulfide which pressure favors.
    
           It has been noted above that the use of various hydrocarbon fuels does not
    greatly affect the relationships indicated by Figure 2.  In other words,  for a given
    temperature, pressure, and percent air, the equilibrium concentration of sulfur
    dioxide in the product gas changes only slightly as the hydrogen-to-carbon ratio of
    the fuel changes.  Thus as this ratio increases, there is a tendency for the sulfur
    dioxide concentration to decrease with the change being more pronounced at low percent
    air than at high percent air.  For example, at 2000ฐF. 1 atm.. and 80?. air the con-
    centration of sulfur dioxide in the product gas would be 8.57. if coal were used and
    8.0% if methane were used.  Similarly with 607. air the concentration of sulfur dioxide
    would be 18.8% with coal and 17.27. witl, methane.
    
           The concentrations of other components in the product gas are affected more
    than the concentration of sulfur dioxide is affected by the hydrogen-to-carbon ratio
    of the fuel (Figure 10).  As night be expected the gas would contain higher concentra-
    tions of hydrogen and water vapor and lower concentrations of carbon dioxide and car-
    bon monoxide if methane were used than if coal were used under similar conditions.
    
           Although the nature of the fuel would not affect the percentage desulfurization
    of the solids in region A. it would have some effect on this parameter in region B
    with the percentage desulfurization increasing as the hvdrogen-to-carbon ratio of the
    fuel Increases.  For example, at 1900ฐF. 1 atm.. and 55/i air the solids would be 96'.
    desulfurized if coal were used and 997. desulfurized if methane were used.
    
           The fuel requirements of the process would also be affected to some extent by
    the nature of the luel.  In general, the moles of fuel per mole of calcium sulfate
    treated would decline as the hydrogen-to-carbon ratio of the fuel rises.   This effect
    would be due to the Increasing amount of hydrogen present per r.ole of fuel.
    
    
    SELECTED CASES
    
           The anticipated performance of the equilibrium desulfurl.-.atlon system for se-
    lected process conditions is presented in Table I.  A comparison is provided between
    operations with different types of fuel, temperatures, pressures, and heat inputs
    (or losses).  Also a comparison is provided between systems with no heat recovery and
    systems with maximum heat recovery.  The latter would Involve recovering sensible
    heat from the products to preheat the feed.  Although both calcium sulfate and air
    would be preheated, the fuel would not be preheated because It eight undergo decom-
    position and It would be small In amount compared to '.-he other materials.   The maxi-
    mum heat recovery would take place when one of the following conditions is achieved:
    
    
                                             751
    

    -------
     Table I.  Performance of Dt-siil fijri ?..-it ion Sys!ซ:n L'ndtr Different Process f.'onJi i ions
    Fue 1
    Type
    
    Coa 1
    cn/t
    CH,]
    CH,.
    CH^
    Cil,
    
    Coa 1
    cn4
    Cil;
    CH,]
    C"/,
    CH,;
    Ter.p. .
    "K
    
    2000
    2000
    2000
    2000
    2300
    230')
    
    2000
    2000
    2000
    2000
    2300
    2300
    Tress. .
    a i ^ .
    
    1
    1
    1
    10
    1
    10
    
    1
    1
    1
    10
    1
    10
    g"
    kcal ./m.
    .-;.) lie.
    0
    0
    -10
    0
    0
    0
    Ma xi muni
    0
    0
    -10
    0
    0
    0
    Ai
    it
    1
    r .
    S0^
    IKS ul
    f . .
    rr.
    CaSOT
    ::. A i r
    Recovery
    .0
    .5
    .5
    .0
    .0
    . 5
    at
    .5
    .
    . 70
    .(If,
    .>,')
    .66
    'i. 3V
    '.'J.46
    11 .63
    :o. c.6
    1 3 . 36
    16.60
    
    3.21
    3.7-S
    4.27
    2 . OS
    3. 76
    3.67
      heal input, kcal./m. CaMC^
    
    
    
    (l^ the calcium sulfate and air .ire preheat ft! to the reactor temperature or  (2)  the
    products arc cooleii ti> ambient temperature.
    
           A comparison of the: anticipated results with and withoijt heat  recovery  shows
    the importance of the lat'.er.  Hy recovering the maximum possible amount of  heat,  the
    sulfur dioxide concent "ation would he more than doubled and the fuel  requirenents  more
    than halved. In addition the air requirements would be reduced by about two-thirds.
    The smaller air rate would permit usini' a smal ler diameter fluidized  bed reactor.
    
           Most of the cases listed in Table I are based on adiabatic operation.   However.
    it can be seen that a heat  loss of 10 kcal./m. CaSOA treated would  increase  the  fuel
    and air requirements and reduce the sulfur dioxide concentration sij'.nificantly.
    Therefore heat losses should be minimised through adequate insulation.
    
           Operation with coal would be somewhat more attractive than operation  with
    methane because it would require less air and provide ป Mr.hcr concentration of  sul-
    fur dioxide.  It would be impractical to operate at 10 atm. total pressure usinR a
    temperature oป 2000ฐF because of Incomplete desul furi;-.aLlon.  Satisfactory operation
    at this pressure would require a higher temperature such as 2300T.   On the  other
    hand, at 1 atm. votal pressure it would be more efficient to operate  at 2000ฐF than
    at 2300ฐF.
    
           In regenerating material which is only partially sulfated. the unsulfated lime
    would behave like an inert component and it would affect the energy balance.   For
    example, if adolomitic lime were sulfated to the extent that half of  the calcium
    oxide portion were sulfated but none of the magnesium oxide portion and the  material
    was at 77ฐF when supplied to the regenerator, ihc overall effect would be  similar  to
    supplying the system with completely sulfared lime at 77ฐF but with a heat loss  of
    37 kcal./m. CaSO^.  On the other hand, if '..iis partially sulfated material was at
    1700ฐF when supplied to the regenerator, the overall effect wo-ild be  similar to
    supplying completely sulfatc-i lime at 77ฐF but with a heat ^air. of about 25  kcal./m.
    CaSOtf.  In either case the fuel requirement would be based on the actual quantity of
    calcium sulfate supplied.
                                              752
    

    -------
    DISCUSSION AND CONCLUSIONS
    
           The theoretical performance characteristics of  a  reaction svster. for re;
    in;- sulfated lime have been described.  These characteristics  are based on an i
    brium model which m;?;.- or may not truly represent an actual  syste
    evidence presented by various j-.roups is cotif 1 ict in;-, so it  is not
    whether or not the assumption of equilibrium is  valid.   In  some
    tory experiments conducted by the Esso >'.roupl' it was  reported t
    cent rat ions of sulfur dioxide were obtained while re.'enerat inr, s
    ever, more recent operation of the Exxon "miniplant" has produce
    cc-r.t rat ions which are only about half of the calculated  equilibrium
    therm.ore the Exxon j;roup-J has questioned the accuracy of  the  >-er.cr
    published free energy data for the solid components of the  react
    the work of Curran e^ al.-l.  The latter t:roup experimentally  me
    partial pressure of sulTur dioxide provided by reaction  7 and  fo
    ably lower than the value predicted by the generally accepted  tr
    resolve this dilemma, more basic research on the t hermodynaniic r>
    ci.um sulfale svsten needs to be carried out.
                                                                                    'enerat-
                                                                                     quili-
                                                                     m.  ".he  experimental
                                                                       possible  to judt;e
                                                                     o:  the e.'irly labora-
                                                                     hat equilibrium con-
                                                                     ulf.lted  lime.   '!iow-
                                                                     d sulfur dioxide con-
                                                                     ium values'1.   Fur-
                                                                         llv  accepted
                                                                     ion system because of
                                                                     asurt'd the equilibrium
                                                                     ur.d it to  be consider-
                                                                     ee  ener-'v  data.   To
                                                                     roper!ies  of the cal-
            Althou,'h the accuracy of the results may he open  to question,  the  results  can
     still provide some useful insi.-ht for process development and  system  design.   Thus
     the results surest that the sulfur dioxide concentration may  be  limited  as much  by
     •he availability of thermal energy as bv equilibrium because   the equilibrium con-
     centration of this component can be increased by employing less air and  increasing.
     the reducing, potential of the system.   However, increasing the reducing potential
     also requires supplying more heat to the system.  Recovering heat from the reaction
     products and usinr, it to preheat the reactants not only  conserves er.erry  but  also
     serves the same purpose as supplying heat froni another source.  The results also  S'-IK-
     t;est tii.it for an adiabatic system or for some specified  level  of hv.it input the maxi-
     mum sulfur dioxide concentration ar.d most efficient oper.it ion  will result  from oper-
     ating ai  the boundary between the A and B regions.  Since hii'her pressures force  this
     boundary to higher temperature levels, operation at higher pressures  requires operat-
     inj; at higher temperature's.  Operating at temperature lewis and reducing potentials
     which place the system in rvy,i< n H will only lead to wasteful  conversion  of calcium
     sulfatc to calcium sulfiUe.  Finally the results suc.r.est that  the hydror.en-lo-carbon
     ratio of the fuel supplied to the process is not very critical, but a fuel such as
     coal has an edy.e over a fuel such as methane.
    
    
     ACKNOWLEDGE: IE:.T
    
            This work was supported by the Knj;inecring Research Institute, leva State
     University. Ames. Iowa.
     REFERENCES
     I.
     2.
    10.
    11.
               p. 87.
               Wheclock and D. R
               Whcclock and D. R
               Wheclock and D. R
               Hanson. G. F
                              k. Boylan, Ind. Enป;. Chen..  3^. Ara. Chen. Soc. . Washington.
    
                                         Ind. Chemist.  36. Tothill  Press. London.  Dec.
    
                              X. Boylan. Chr". Eng. Pro^r.. 6^. AIChE. New York. Nov.
    W. M. Bollen. Ph.D. Thesis. Iowa State University. Arses.  Iowa.  1954.
    T. U. Wheelock and D.
    D.C., March  1960, p. 21i.
    T. D. Wheelock and i). R. Boylan.
    1960, p. 590.
    T. D. Wheelock and D.
    1968.
    T. D.
    T. D.
    T. D.
    A. M.
    National Meeting of Aa. Cher.. Soc.
    W. M. Swift and'T. D. Wheelock. Ind. Eng. Chcra. .  Process  DCS.  Dev..  lt>.  Am.  Chen.
    Soc.. '..'ashin^ton. D.C., July 1975. p. 323.
    Esso Research and Engineering Co.. "Fluid-Bed Studies of  the Limestone  Sased Flue-
    Cas Desulfurlzatlon Process." Heport No. CR-9-FCS-69. Final Report Kay  15.  1967-
    Aug. 27. 1969. A. Skopp. J. T. Sears, and R, R. Bertrand.  Linden. S..'..  1969.
    Esso Research and Engineering Co.. "A Regenerative Limestone Process for Fluldized
    Bed Coal Combustion ar.d Dcsulfurizat ion," Final Report. C. A.  Mammons and
    A. Skopp. Linden. N.J.. Feb. 26. 1971.
                                 Boylan. U.S. Patent 3.037.790. April  30.  1963.
                                 Boylan. U.S. Patent 3.260.031. July 12.  1966.
                                 Boylan. U.S. Patent 3.607.0i5. Sept.  -!1 .  1971.
                            Rotter. W. R. Brade. and T. D. Wheelock. Fri-print.  158th
                                            :c-.. York. Sept. 7-12.  1969.
                                              753
    

    -------
    II'.   !..  A   R'Uh.  I'r.-ijriri! .  f'i'ir'.h  In'.<:rn:i! i'u<;t ir,n iT'.ces!,."  hep-iri No.  Ki'A-'.OV 7 - 77 - i 07 .  k. f;   iio><-. K   R .
          hi-rt rand.  M  S.  N'I'IMS.   I).  '}.  Kin/.ier.  I..  A.  H'i''i.  '.'..  '<•.  'Iris'ory. .'inli /.ซ.-tl-hซ.-rrr>'js* I'm .'ind  H<-;'<--ii'-r.'i' io.i  of S'.il f •:r-C'):T. :t inini-  A'idi! i vc-s.
          ซi.-;ii.rt :.'o.  A:;i./i:s-f:ป;::-ioo> .••:!7:-.f-:m-  '•ซ;,-.
          C.  .1   Vo;-cl.  K.  I..  ซ:.-irl.s.  .) .  Ai-f-i-r:-!.-i:i. .".  li.i.'is.  J.  Ki-:.'. .  C.  B.  Schnf f s'.oi 1 .
          J .  lii-;i:n-r 1 v.  .-inซl A  A  Joi^t.-.  Ar,-o:iru-.  111.
    
    I'j .   Arj-"nn<- N.it inn.'i I  !..ilior.'ii orv.  "A Dcv<-lป:>r:ซTi'   I'rซป;-r.-im on  Pr<.-ss'.ir i xt-il K! uidi x.t-d-P.i'il
          Conixis? ion."  Hi-por' .'In.   A::i./KS-CK::-1011 .  A:u:':.-,l  St-purt.  Julv  1.  1 '* 74-J-jni.-  10.  1'> T
          (;.  .1.  "iii'i-l .  1'.  C>!tinin;-l,.i;:i. .1.  Kishi.-r.  .1.  H-i!i!ปlซ-.  S. I.i-e. J.  I.t-nc . J.  Mont ;u-n.-|.
          A.  I'.-itu-k.  T.  Sclmf t :.r ol  I .  S.  Sii-i-i-1 .  <;.  Sniith.  S.  Srci'.h,  .'..  Snydi-r. S.  S.ixt-n.i,
          .1.  St (ii.-kii.-ir.  W.  Swi i t . (;.  Ti-.its. I.  Wilson,   .irui  A.  A.  JonV-.i-.  Arj-onnt-.  111.,
          July  \'U',.
    
    !'ป.   .1.  C.  r!.ปi>t .ii-.n.'i.  .1.  I'.  I.CMI.-, C.  .1.  Vo-.'t-l.  fj.   Thoijos. .-miJ A. A.  JonV-i-. Fri-prinf .
          K'i'irih Int i-rn.-il ton-il  Oinfซ-n-iii-ซ- on  I'l uiili xi-d-Hc-d Oimbustinn.  Xcl.f.an. V;i.  . IK-C .
          1-11.  \->r>.
    
    17.   Ar;;oiitK- r.'.ition.il  I..il>or.'iiorv.  "IK-con;iosi t ion  of C.'ilcisim Sujf.-itt':   A Ri-v'li-w of t hi-
          !.: ti-r.ituri-." Ki-'mrt ::.ป.   AM.-1><- 1 J'}.  W. M.  Swift.  A. K.  I'.'ini-k.  G.  W  Srith.
          C.  .1.  Voci-l .  ,-ind A. A.  .lonK-.  Arj-onni-.  111..  Uc-c.  l'<76.
    
    Irt.   .1.  C.  :-liinl.-if.n:i. W.  M.  Swift,  f,'. W.  Smith.  C,.  .1.  Voi-c-1 .  .'ind A.  A.  .Joni'.c.'. Prt-or in: .
          ti'tih Annu.-il  Mi-i-t in;-. AlCliK,  Chic.ij'o,  111..  Nov.  2 it-Dec.  .'-. I'i7d.
    
    \'l.   I'ojii-,  Kv/ins .-ind Koliliins,  Inc.,  "Stud;- of the  Ch/ir.ic K-r Ix.-it ion of Conti'il  of Air
          I'ol 1 ut.-nil s from .1  l-'lnidi::fil-Kfซl Hoili-r  --  The SO/  Acceptor I'rocess." I'.S.
          Knvi ro(v-.ซ-rt.'i 1 l'r< -. KI'A-K.'-/.'-O^l . J.  S.  (Jonlon.'R.  D.
          CU-nn. S.  Khrlich.  K.  Kden-r,  J. ซ.  Itishnp.   -IIK!  A.  K.  Scott.  Atex;iiidr i.i.  V;i. .
          r>7.'.
    
    .'0.   R.  K.  Kin-el.  M.S.   Thesis.  lowi  St.ite  fni v.-rs i t y,  Ar.cs.  lov.i.  t'*7f>.
    
    21.   B.  Ce.irc.e. L. I1.  Krown.   C.  II.  F.-irmer,  I',  ilutliod.  and F. S. M.-innin;>, Ind.  Knr..
          Chem.  I'rocess Dt-c.  Uev..  I'>.  A:n. Chcm.  Soc.  ,  V.';ishinj-,ton.  D.C.,  July 1976. p.  M2.
    
    ii .   M  Hodell  ,-ind R.  C. Reid.  Thi-rmiulvn.'tmics and  11 s  Appl icat iuns .  Trent ice-Ha 11 .
          Inc..  Kn^.U-wood Cliffs.   N.J.:  \W.' ~[~RW.    ""'
    
    23.   C.  !'.  Curran. C.  E.  Fink,  and  K. Corln.  in KUP]_  O;isJ fi c^tj on.  F.  C. Schora.  Jr.
          (editor).  Advances  in Chemistry Series  69. An.' Chora .~~5oc.. Washington,  D.C..
          1967.  p.  141.
                                                     754
    

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                             INTRODUCTION
         MR. DAMAN, CHAIRMAN:   Our next paper this norning is concerned
    with the pressurized  fluidized bed coal combustion and sorbent
    regeneration.  This is  some of the work that is coming out of the
    Exxon activity.  The  paper  will be given by Dr. Ruth, who is a
    graduate of the City  University of fiew York where, among other
    things, he studied under Arthur Squires, who many of you know and
    who's been very active  in this fluidized bed development program.
    Dr. Ruth has been with  Exxon since 1972 and he's been very, very
    active in the work that's going on there in fluidized bod combustion.
    So, Larry.
                                    755
    

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    collected  in  t:.o  second cyclone are rcr/,ved  thrcuj-h a lock i.c^er.   The flu* y.as Is analyzed -..or.tir.-
    uously  lor  :;oj , LO,  COj , *'OXi UI-^ |JJ usln^ or.-lir.e ir.sirurxr.t^.   i't-rloijic samples art- ta^er*  icr
    ;.ar t Kulate cor.t* ntrat lor. u-ji:.x **ri iso*.ir.et it  pr-.^t a;...4 4 total  t i Iter .
    
            Coi^ijst ion studies '-ere r-ade witi.  tv<> Loal:.. ot. Eastern bilur.ir.oui Ml tsi*%:r>;i> Sean  coal ccr.-
    taininft J.U wt . * sulfur and an Illinois  r.o. tt bitur.Ir.ous coal cor.tair.iry. 4.ป' vt . '1 sullur.   i:.e
    Luslt ?n to;*!  was  screened to a size- ra:.?,e of 200 to ปCOO ..r..  The I * i ir.cii toai vas sireeix d ;o  a  si *
    rar.Ku ol 700  to J4MO ซ.c.  iuu :*orLents were  used, a Virginia  linestor.e ('.rove. ป'.> .'•'>.  IV/jj  anlh  were scn.tned to  a siz*.-  rar.ye of feiO to J^GO _^.
    
            ihe  rc>;e iterator vas r.ol operated at the tl=.ซ the coz^ustion  Mudies vert: carried out.
    
    iJbJecl ives
           'Uie  objซcl*ves of tl.c conbustloo studies vere to as^esu  the  e^ls&ซonfป fro^ a pressurized
    f luidized Led  coal  cotXust ton system And  provide add i I ional er.i* Ineer ln^ data tor U.e de-.i*T.  ol  larป er
    units*,   huns vc*re ruซde in vtticii the sorbent  to coal rซiio  'expressed as i.a/S =jol-ir ratio;, ctrLu>t'-r
    tt'C.peralure , ^tes Jure, super! icial velocity^ expanded ted  height ,  so r bent part it: !e si/e,  ar.d ซ.-vi.e'.s
    air  level vere v.irit-d u-iir.t; llic two cc.als and sorbenla described  in ll:e previous section.  A seties ui
    runs vas alsu  r^idซr  vith tt.e i_alcir.ed tore of  the licestcr.e sorbeiit.  llut- ^as composition u.is re.isureซJ
    and  the  emissions uf  So t> , buj, ::0X and CO vere detvrcined.  Carbon  cor_tuttion e! i ic ier.i: y  anu •-•.t-rall
    heat tratisler  coel t ic ier.ls Lelveeti tlie ted and the cooling coils vere also measured.
    
    Keaujjb  an^ Uiscussiyn
    
           ^ t M  te. i s^s i o i i a .  So^ cr;is!iiotis results cbtafr.t-d wilt* the  Lasteri; and Mlir.uis cuals arid t'ti/ci
    tlolucite !>orbvM  are  .-.Uovn in * i,;urc 3.   In  thi:. IJ/.ur*.-. the perci-rt reduction in ^'>j c^Uoicr.t. ia
    plot led  against it it ur i bent to coal t ecd  rat lo expressed as the ฃjolei> oi  calcium t ed in thv  sur Lent to
    the  c-oleb *ปt  sulfur led in ihv coal.  lite btoichlowet r ic Ca/S ruolar ratio for the iJcsul f ur i zat ion
    react ion Is 1.0.  AJ  seen in I iป;ure 3, the* resu i ป tป tor all the  runs are correlated 1 a i r 1 y vi-1 !  * •• a
    :. iM^U-  lliu* dct-^ite a variation in tec[>eralure Iron ซ4O to (>^tJ*C  (IVO to l?>Ofcl>. .1 varialior.  ir; ;-a'.
    l>ha-.e resldenrf tint*  1 roE O.M lo J.O se.:, a  variation in pressure  Iron COO to V JO kt'.t ',*j  to  > ^tc. a!;:*),
    a  two'lold  v.irialloa  in Morbvnt part ic le  si /c and a v-ir lat ion in coal source and sulfur lO'teut.   1 for.
    t'i;;ure  J,  it -;an  be cone ludcd that the Ca/S  cellar ratio is I lie  pr ls-iปry variable at tec t in** the SOj cr i^-
    sionu and the  other variable* play a secondary role.  It can also be concluded lti.*t t hi- ratt* o! tl;v-
    rcac t ion between  :>> ป  ซmd thv so i bent 1 ป approx ic^ite ly f ir^t order  in !*O->  conccr.t rat loi;  ^inn; t hซ: t'J^
    retention  is  independent ot the *>ul f ur content ol the coal .  'ih i s  i ir.d IIIK lids been reported  pr evioi;- 1 y
    by others.   t U',urc>  j  aluo indicate:* that  very M^it SUj reduction  levels can be reached with  -JuJo-ili-
    sorbcntu at fairly  low i.a/S ratiub.  for  c>xae.ple, a VOT reduction  in VJ-v  wo*ild reiufru a ta/S r^tio
    of about ป .0.
    
           1l:c  effect ot  tc&pcralurv on SOj vrUftttionn wai* dctvrnlned usiny; the above data arid additional
    data obtained  at  tt-'C|ปeralurvป as low AH 6^0*C  retention dropped Iron &j+ at a Ca/S  ratio  of 1.^
    to under 301 aa the te&pcrature decreased froo 9OO to */yU*(, .  It.c effect  of r.-ปป pnase residence tir.c
    on Suป cDti;3lons  vaป  also cva^urcd with Jolo<e sorbunt.  It Is known, b-v..ซfd on earlier vor>.  that
    the  detful f urizat ion react ion rate decrease*  an the uu If at ion levr 1  of the so r bent increases.
    therefore,  any reaction rate expression oust include not only the usual react ml concentration  tvrฃ-s,
    but  Dust alปo  account (or the vtfvct of the  sorbent aulfalion level on the rate.  The eiicct  of the
    doloaitc sulfalion  level on the reaction  rate can be determined by  calculating first order rat*- con-
    vtantu und  plotting thvo a^Jlnst the caiciua sulfatlon (or utilization) level,  '.his was  done not only
    for  data obtained in  the Dinlplant but for data published  by Ar^onne National Laboratory  and the
    National Corl  Board Coal Utilisation Research Laboratory.  The  results arc shown In I lt;ure ซ.  Aซ ivcn,
    a Kood correlation  reปultet desalte wide  varl.itions in the geottetry ot the lluidized bed  cocbusloro,
    coal and liorbcnt  source, and operating conditions.  With this information, the effect of  reiปidence
    tine on  SO ^ retention can be calculated.   This was Cone and compared to ceasured effects  in  tixuru  3.
    Aป shown in figure  I/f reasonably good a^reecer.t was obtained between the measured and predicted effects
    of gas phase  residence tlcซ on iปUi enibsions.  Die ca^nltjde of the residence tlcc cifeit la  such that
    a six (old  decrease tn the residence tioซ fron 3 to 0.5 s will cause a decrease in the  SO; retention
    fron 90  to  about  bbl  at a Ca/S ratio of 1.3.   Or, at a 90Z SO2  retention level, decreasing the
    residence tlce froa 3 to 0.3 tป would require doubling the Ca/S  ratio Iroc. 1.5 to About  3.0.
    
           SO;  caisfiions  were also measured using Grove No. 1359 1 item I one as the sorbent.  The  results are
    shown in Figure 6.   Contrary to the result*  seen with do loci to  sorbent, a narked effect ot temperature
    occurs with increasing tc&pcrature giving higher SO, rccoval levels.  Also, the degree of data  s;attcr
    

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    Figure 3. SO, Retention Uting Dolomite
                  Sorbent
                                                                             \
                                                                               V ' :
                                                                                '.
                                                                                  TM i/MK>%  I
      Figun 4. Vootiofi of Rปtป Comtant with
    dtctum Utiluamn (or Sulldton of Dolomit*
    Ftgurt 5.  Etfteซ of Rcudcnoi Titn* on SOj
          Retmlion-Ootomiu Sortxnt
                  SOj RctmtiOfl Using
                                               759
    

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    Is mere pronounced and S02 retention levels are lover compared to results measured with dolomite sor-
    bent.  ihese effects are due to the inability of the limestone to calcine completely, i.e. for the
    carbonate to decompose to the oxide, under pressurized combustion conditions.  Calcination greatly
    increases the )>urcslty of the limvstone mar.ini; the Interior surface of the stone more accessible to the
    SOv rractanl.  At the higher temperature conditions, the limestone undergoes extensive calcination,
    ai.d although tiie sorbenl is not as active as doloslte, it Is considerably core active than at tre
    lc>er t *.'~per;iturcs where the stone is largely In the carbonate fore.
    
           i'cl loving the tests with Grove lines tone, a series of runs was cade in vhlch the limestone vas
    calcined outside the combustor and fed to the cocbustor in the calcined fore along ulth the coal.
    l!:e activity of the precalclned limestone vas found to be significantly higher than that of limestone,
    even w:.cn the ccmbustor vas operated at th.; lover temperatures vhlch •*'. not protect In-sltu calclr.a-
    lion.  li.cse results are shovn in figure 7, vhlch cocpares the 50^ retention meas'-rew vlth precalcined
    limestone will, the results shown previously in figure 6 for limestone and Figure 3 for dolomite.  As
    seen in figure 7, the precalclned limestone is as active, at an equivalent Ca/S cx>lar ratio, as
    dolomite.
    
           Although a Uuldlled bed utility boiler vould noraally be expected to operate In the tempera-
    ture rani'f of about 8iO to 9iU*C (1550 to 1750*F), operation at cuch iDver t*cperature, i.e. dovn to
    ibout 7iO*C (KGO'r), vould be required to turn dovn the boiler output to Batch a decrease in the
    electrical power dcnand.  A series of runs vas made uelng doloelte, limestone and prccalclr.eC lice-
    btone at titperalure* near 7iO*t to determine the behavior of the HiC system at thc&e lover tenpซra*
    lured, in particular to deturnine the effect on SO> removal.  Soae runs vere also made at tenpcratures
    as lov as b90*C to deteralnv the lowest licit of operabillty.  Ihe effect of operating at these low
    temperatures on SOj retention iH shown in figure 8.  In this figure, the curves for higher temperature
    operation vlth doloeite and limestone are Known fur comparison.  As seen, the activity of dolomite and
    calcined lieestone arc cooparablv but loซrer than the activity ceasured in the normal cocbustlon tts-
    peraturv ranf.e.  llu; dashed line la figure t) represents doloelte and precalcloed Ilex-stone results in
    the bVO*7bO*C tecperature rany.e.  However, the results with limestone indicate that it I* coepletely
    inactive at the "turndown" letperalures.
    
           The effecllver.es* -if calcined lieestone Is believed due to the formation of very larKe pores
    during ttie calcinalluo procedure used in this study.  Calcination took place at high temperature (870*C)
    and pressure C*(X> H'J) and at a hl^h LOj partial pressure (~110 U*<).  According to result* reported
    ty WestIngliousv Research Laboratory, these conditions, especially high CO> partial pressure, produces
    a favorable porv structure vhicti alni&izes diffusional effects.  Itte porem are apparently large
    enough that they are not constricted by the lubucquunt furcation ol CaMJ^ and CaLUj to the extent that
    the sorbent becoaeM less activu.
    
           Ihe olnlBua teepcrature at vhlch cosbustlun wus stable va* 6VO*C (l.'/O'l).  At tcepcraturca
    bซlow 690*C, CO concentration In the flu. '.*ป increased and te&pcralurei in the fluldlied bad bccaae
    mutable.
    
           Other variables exanlned In thla studv had no oiRnlflcant effect on SO^ ซnls>lon>.  Thli
    Included total preciure Jtilch ranged froซ 60O to 940 kfa (6 to V ato aba), excel* air vhlch ranged
    froa & to 1101, and Borbent particle slle vhlch vaa varied by a factor of 2 froo on* batch screened
    to a size range of UOO to 240O i-e to a second batch screened to • size range of 79O to 1400 -,D.
    
           Aa a result of the above studies, the sorbsnt requlreoents needed to satisfy the current CPA
    new source pcrforoance standards for SO; eelsslons froa • coal fired boiler (1.2 Ib SOWM BTL' coat
    fired) can be esticated.  The estliute is shown in Table I.  The estimate was based on • rซ phrse
    residence lice of 2 s and • boiler temperature of 9)0*C (1700'F).  As seen in Table 1, doloslte and
    calcined lloeslone are oore effective than lloestone on a molar basis.  However, on a weight basis
    llcesione Is slightly acre effective than doloalte vlth a coal containing 2! sulfur.  Llccstone and
    dolomite are equivalent tor a 3! sulfur coal.  For coals containing core than -K sulfur, doloelte is
    a>re affective than liaestane even on • weight basis.  Uovever, calcined llccstone is core effective
    than dolonlte for all sulfur levels.  Doloalte sorbent requirement can be estimated for other g'ป
    phase residence tiers using data given In Figure 5.  Vlth this information, a process design basis
    can be set for a pressurized fluidized bed boiler in which the relationship between the dolomite
    requirements, fluidization velocity and expanded bed depth can be determined.
    
           KOi Emissions.  SO, calisIons were also ceasured and were found to vary from 10 to 200 ppa or
    0.0* to ".17 g (as :O:)/XJ (0.1 to 0.4 Ib/H BTV).  The data *i- shown in Figure 9 where NO, eclssioat
    are plotted against percent excess a
    -------
    Table I.  Sorhent Kปquire:*r.ts for Once-through
         Pressurized Fluidlzet! Bซd Combustion
    
    Coal SUi
    S (':) Kซrttr.t .<-) Li^-stoi-.i:
    2 b'i 1.3
    3 73 2.1
    4 7* 2.8
    j 84 3.2
    Kv%1diT.ee lie*- 'i !•
    iur-ptrature '930*C
    iolor.ltt? Liru-stonc Lircstir.c Uolo^itc
    0.8 0.8 8.2 i.O 1C
    1.0 J.O 20 V.4 20
    1.2 1.2 34 15 2V
    1.3 1.3 SI 20 40
    
    
    
               i
    
               i
    
              •X-
               C
                 Figun 7. SO2 Retention thing
                         761
    

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                   Figure 8. Effect of Low Temperature
                 Turndown" Conditions on SO2 Retention
                                    K> IWSVDW
       O.I
       O.J
       0.4
    5  ฐ-5
    
    i"
    B* ฐ"'
       O.I
       0.
                              60      CO
                              IJTCISS Ai*. X
           Figui e 9. Cor^btion of NO, Emiaiom with Exoen Air
                               762
    

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    of excess air.  The temperature effect in t:.e 670 to 940'C (1250 to 1750ฐF) rar.ce was secondary ard
    caused only a 251 increase in the emission level.  The emissions are well below the Li'A r.ew source
    performance standard of 0.3 g (a* NOi)/XJ {0.7 Ib/M 31',.) and have an average value of only O.C9 g/.H.1
    (0.2 ib/X Bit) at 151 excess air. the level cost liki.y to be used in a commercial size boiler.
    
           Other Emissions.  SOj emissions in the flue gas were fou-.d to vary wiceiy, usually over a r  is reduced to Cau and Sui in a fluidized
    bed by reaction with a reducing gas at about 1100'C (2000'*F) and rCO-1000 ซPa (7-lO~atn abs) pressure.
    Our objective is to determine if regeneration Is technically viable by studying a continuous com-
    bustion-regeneration system-.  Preliminary work involved batchwise recent, rat ion of sulfated limestone
    in a fluidized bed vessel of eight cm diaccter^.  This paper gives the results of batchwise rซ^ซ--.etj-
    tlvn in the 22 cm diameter Diniplant regenerator and of continuous regeneration in a systen cor.nist ir.g
    of the ciniplanl regenerator coupled to the 33 cc .ilnlplinl combustcr.  Operabillty of this 4ystec was
    demonstrated in a run lasting over 100 hours during which sorbcnt was continuously rcclrculated
    between the cocbustor *nd regenerator.
    
    Regeneration Theory
    
           The principal reaction;  involved in the one-step regeneration of '.'.iSO^ are:
    
                                        CaS04 * CO  •  CaO * CO, + SO,                                 (1)
    
                                          CaSO  4- 4CO  •  CaS * 4CO,                                   (2)
                                              *t                    •.
                                         JCaSO4 * CaS  •  4CnO + 4SO.                                  (3)
    
    Reactions (1) and (2) are written with CO as the reductant but other reducing a^or.ts (e.g.,  H_.. C) can
    be used with r.lnilar effect.  Reaction (1), the desired reaction. '.ป endothercic and is favored by
    high temperature.  Reaction (2) is undesirable and it best avoided by high temperature and low CO
    concentration.  Reaction between CaSO^ *nd CaS can alco occur, although reaction (3) is not  independent
    since it can be written by combining reactions (1) and (2).
    
           The caxlcun partial pressure of SO) is produced in an equilibrium syttrs containing all thre
    -------
           In our fluidlzed bed regenerator, fuel Is Introduced at the bottom of the bed,  creating a
    reducing zone.  To minimize the amount of CaS present, a stream of secondary air is added about half-
    way up the bed, producing an oxidizing zone in the upper portion of the bed.  In the oxidizing zone,
    the following reactions can teke place:
                                              CaS + 202  -  CaS04                                      (4)
    
                                           CaS + 3/202  <•  CaO -t- S(>2                                   (5)
    
    Particles containing CaS are alternately exposed to oxidizing and reducing environments.   In this way,
    the amount of CaS is kept small.
    
    Experimental Equipment and Procedures
    
           The regenerator vessel, shown in Figure 10, is constructed from 46 cm (18 in) Schedule 40 steel
    pipe, refractory lined to an Inside diameter of 22 cm (8.5 in).  The fluidizing grid is a water-cooled
    stainless steel plate containing 89 holes of 3.6 mm (9/64 in) diameter.  The height from fluidizing
    grid to gas exit is 5.8 m (19 ft).  Air and fuel (natural gas) are supplied to a burner located beneath
    the fluidizing grid.  Supplementary air is added higher in the column through a 1.3 cm (1/2 in) tube.
    Flow rates of supplementary fuel and sir are typically about twenty percent of the respective fuel and
    air flows supplied to the burner, but this can vary considerably depending on the air/fuel ratios
    desired in the oxidizing and reducing zones.  Gas leaving the regenerator is passed through a cyclone
    to remove particulates and a single pass double pipe heat exchanger to cool the gas.  Pressure is then
    reduced across a control valve and the gas is then piped to a scrubber for cleanup before venting to
    the atmosphere.
    
           During a typical run with the regenerator alone, a batch of sulfated sorbent is charged and
    heated, under oxidizing conditions, to the temperature desired.  Rc.Jucing conditions are then esta-
    blished by increasing the flow rate of supplementary fuel.  Air and fuel flow rates are adjusted
    during the run to maintain nearly constant fluidized bed temperature.  The concentration of SO, in
    the regenerator off-gas Is recorded, with the shape of the SC>2 vs. time curve appearing similar to
    what is shown In Figure 11.  After the run, the solids are removed fron the regenerator and analyzed
    for Ca, 504-2, s~2 and total sulfur.
    
           Combined operation of the combustor and regenerator required development of a transfer syster
    to circulate sorbent between the two vessels.  The system, which can be seen in Figure 2,  was designed
    to accomplish this by utilizing high bulk density (stick-slip) flow of sorbent in transfer lines.
    Pressure in the regenerator is maintained slightly higher than that in the combustor.  Solids in the
    regencrator-to-combustor transfer line move into the combustor when a pulse of nitrogen is applied
    to the lower end of the transfer line.  The solids' flow rate is controlled by adjusting the frequency,
    duration, and intensity of the pulse.  Two slide valves are used in the combustor-to-regenerator
    transfer line in order to prevent backflow of regenerator gas up the line.  These automatic valves
    trap solids in the piping between them.  Solids are discharged into the regenerator when the bottom
    valve is opened.  The manual slide valve In the regenerator-to-combustor line is used in the event of
    upsets in order to isolate the combustor fiom the regenerator.
    
    Results and Discussion
    
           Batch Operation.  Eleven runs were made in which batch charges of either sulfated limestone or
    dolomite, prepared in the fluidized bed coal combustor, were regenerated.  Pressure was about 910 kPa
    (9 atm) and average bed temperature normally ranged from 1027-1120ฐC (1880-2050ฐF).  Fluidized bed
    height was 1-1.5 m (3.3-4.9 ft) and gas contact time 1-2 seconds.  The objective of these rms was
    to determine the extent of bed agglomeration, if any, the concentration of SC>2 produced In the off-gas
    from the regenerator, and the degree of reduction of CaSO^ to CaO.
    
           Bed agglomeration was invariably associated with excessively high temperatures (above 1150ฐC);
    when temperature was well controlled agglomeration did not occur.  One should appreciate that control-
    ling bed temperature is more difficult in batch than continuous operation because in batch operation
    the rate of regeneration, and hence the heat requirements for the endo thermic regeneration reaction
    (1300 kJ/kg or 560 BTU/lb of CaSO^ converted) varies during the run.  Hence, fuel and air flow rates
    had to be continuously adjusted to compensate for the variation in heat load as the charge of CaSO/,
    was regenerated.  In runs made at average bed temperatures of up to 1100ฐC, the extent of agglomera-
    tion was insignificant.
                                                     764
    

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                                         WY FUEL
    
    
                                 FLJU1D1ZING GRID
                  ^f-	  BtKfCR
    
         1 4|0	Jl	 BXHSK FUCL
        Figure 10. Miniplant Regenerator Fuel
                       and Air Inputs
    Figure 11. Typical SO2 Emission for Batch
               Regeneration Run
                      765
    

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           SC>2 levels measured during batch operation reached 3.0 cole percent (3.7 percent on a dry
    basis), or about half of the calculated equili'-riuii. value.  However, some tice ago, Curran^ determined
    equilibrium SO^, levels for reaction (3) experimentally.  I'slng Curran's levels, which are lower than
    the calculated levels, the SO2 concentrations which we treasured averaged about 80 percent of equilib-
    riun.  In fact, equilibrium was reached in several runs, using Curran's data.
    
           After each run the fractional conversion of CaSO$ to CaO and CaS was calculated from analyticil
    res'-'ts for calcium, total sulfur, sulfate, and sulfide.  An average of 94 percent of the sulfate was
    reduced to oxide.  The acount of CaS present was negligible.
    
           Deaonstration of a Fluldized Bed Combustion System with Continuous Sorbent Regeneration.  After
    operating the regenerator batchwlse we linked the cocbustor and regenerator vessels and made a run to
    deixM.etrate continuous operation.  Operating conditions are given in Table II.  Conditions (especially
    regenerator temper., ;ure) were conservative so as 13 provide the best chance of reaching our goal of
    100 houis continuous operation.  All variables were kept constant except that makeup limestone sorbent
    was added to the combustor at the rate necessary to make up for losses caused by attrition and entrain-
    ment from the fluidized beds.
    
           SC>2 emissions from the combustor are given in Figure 12.  To establish baseline operation, the
    regenerator was operated under oxidizing conditions for the first 24 hours with scrbent recirculating
    between combust or and regenerator.  Emissions gradually increased to about 5.SO ppm (1.1 Ibs S02/106
    Bit).  Since the S02 ecissions would have been about 1330 ppm at zero retention, SSO ppm corresponds
    to about 60 percent retention.  This is a much lower level of S02 emissions than would have been
    expected had the combustor been operated at the same conditions, but without sorbent recirculating to
    the regenerator.  The low combustor emissions can be explained because, even though no regeneration
    was occurring during this period, the regenerator was acting as a calc'ner and supplying freshly
    calcined sorbent to the combustor.
    
           The concentration of S02 in the regenerator off-gas was nearly steady throughout the run and
    averaged 0.53 mole percent (dry basis).  This is very close to the concentration predicted by a sulfur
    mass balance based on the feed rate and sulfur content of the coal entering the coobustor.  The cal-
    culated equilibrium concentration at the operating conditions of the regenerator was 2.9 percent;
    hence, higher SOj ,'evels would probably have been achieved by burning in the combustor more coal of a
    higher sulfur content.
    
           Samples of bed were taken from the combustor and regenerator after the run and analyzed.  The
    combustor bed contained 35.8 mole percent CaO, 18.5 percent CaCO-,, and 45.7 percent CaS04.  The
    regenerator bed was 80.5 percent CaO, 2.3 percent CaC03- and 17.3 percent CaS04.  Because air was
    blown through the hot regenerator bed during shutdown, the composition of these solids may have
    changed.  Any CaS, if present would have been converted to CaSOA, and possibly CaO.
    
           A sulfur mass balance for the demonstration run Is given in Table III.  Recovery of sulfur was
    103.5 percent.  The sulfur balance is very sensitive to the sulfur content of the coal, which would
    have needed to be only 0.07 percent higher to obtain a sulfur recovery of exactly 100 percent.
    
    
    SYNTHETIC RECENERABLE SORBENTS
    
           The conventional sorbents which have been used In fluidized bed combustion are limestone and
    dolomite.  There are many problems with these natural materials.  Only a small fraction of the calcium
    contained in limestone or dolomite is utilized (converted tc sulfate), attrition rates are high,
    regeneration requires high temperatures and deactivation begins after only a few cycles of sulfur
    sorption and regeneration, and different stones vary greatly In their reactivity with S02 and in
    attrition resistance.  Improved sorbents are needed which arc superior to Huestone and dolomite
    in all of these respects.
    
           For nearly two years we have been conducting an experimental program to Identify and develop
    regenerable sorbents that are superior to limestone and dolomite.  The Impetus for this work was
    several paper studies in which the thermodynamics of a large number of compounds were screened In
    order to identify those compounds which could absorb sulfur at the conditions of temperature, pres-
    sure, and gas composition that prevail in a fluidized bed coal combustor and be easily regenerated
    (5,6,7).  About thirty such compounds were identified but experimental results to confirm the thermo-
    dynanlc predictions were lacking.  Also, there was 10 Information available on sulfation and regen-
    eration rates, or on activity maintenance.  Thermogravimetric analysis was chosen as the basic
    screening tool used to determine which of these materials warranted further study.
    
    
    
                                                     766
    

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                               500
    
                               400
                                 0 1.1 ?0 30 40 ^0 60 70 10 'JO   110   130
                                             HOURS INTO RUN
                               Figure 12. Combustor SO2 Emissions During
                                  Combustion-Regeneration Demo Run
                     Table  11.   Operating Conditions During Demonstration Run
    
    Pressure, kPa
    Bed Temperature, Average, ฐC
    Bed Height, Expanded, Avg., m
    Superficial Gas Velocity, m/s
    Combustor
    760
    900
    3.4
    1.5
    Regenerator
    770
    1010
    2.3
    0.6
    Solids Recirculation Kate,  kg/hr
    Residence Tlae of Solids, Avg., hr
    Makeup Acceptor Addition Rate,
      Equiv. Ca/S, Average
      Range
    Cor.bustor Coal Feed Rate, kg/hr
    Coal Type
    Stone Type
    79
                    0.55
                    0-1.3
                                         1-1/2
       Champion (Pittsburgh Seam),  2.07. S
       Grove Limestone, BCR No.  1359
                                                 767
    

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                            Table III.  Sulfur Balance for
                       Combustion-Regeneration Demonstration Run
                                                               of Sulfur Entering
    •  Sulfur Entering System
    
         Coal                                                        100
                                                                     100
    
    •  Sulfur Leaving System
    
         Regenerator off gas                                          47.1
         Combustor flue gas                                           20.3
         Combustor bed reject                                          9.0
         Combustor overhead solids (flyash)                           11.6
         Regenerator overhead solids                                   1.0
                                                                      89.0
    
    •  Sulfur Accumulated (ฃ Inventory)
    
         Regenerator bed
         Combustor bed
    •  Z S .lecovery                                                  103.5
           Table IV.  SOj Pickup Per Unit Mass of BaTiOj, CAC, and Limestone
                        No.                     Mass SO-j Sorbed Per Unit
     Sorbent           Cycles          Mass of Sorbent After t.'o. Cycles Indicated
    BaTi03               50                               0.22
    
    
    CAC                  25                               0.09
    
    Lioestone             5                               0.04
                                         768
    

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           Over thirty materials were screened using TGA equipment.   The compounds and materials tested
    included:
    
              oxiues
              aluminates
              carbonates
              cements
              titanatea
              composites containing CaO, Al-0,, and SiO-
    
           Screening of potential sorbents was accomplished by subjecting each sample to reaction condi-
    tions representative of those in a fluidized bed coal combustor:   900ฐC, 0.1-0.252 S02>  52 02, balance
    N2-  Regeneration of sulfated sorbents was accomplished in an environment of 1100ฐC, 5*  CO,  balance
    N2.  Positive identification of sorberts, sulfated sorbents and  regenerated sorbents was accomplished
    using x-ray diffraction.  Initially, sorbents were tested in the form of fine powders.   Subsequently,
    the powdered sorbents which performed best were fabricated into  pellets and evaluated.
    
           The best sorbents were the titanates of barium and calcium and calcium aluminate  cement.
    These sorbents have constituted the dual development centers of  our program.
    
           Barium titanate, EaUOj, was the most reactive sorbent tested.  It reacted more rapidly with
    SC>2 than all other sorbents and along with CaTiOj was found to be fully regenerable, maintaining its
    activity for any number of cycles.  Calclun aluminate cement (CAr:) is a structural material  thut is
    widely used in high temperature applications.  We found that pellsts with high attrition resistance
    and good activity could be made from CAC.
    
           The clear superiority of BaTi03 and CAC to the conventional sorbent limestone Is  shown in
    Figure 13.  Pellets of all three materials were cycled between Identical sulfation and regeneration
    conditions.  The time period for sulfation was arbitrarily selected as 75 minutes.  Each material
    regenerated completely after several minutes.  The utilization during sulfation for limestone
    declines to less than 5 percent aiter only five cycles, however,  the utilization of CAC  !•. still
    about 16 percent after 25 cycles.  Moreover, CAC declines only slightly in activity whereas  the
    activity of limestone declines sharply.  On the other hand, 63X103 actually increases la activity
    and, after fifty cycles, the utilization is still over 60 percent.
    
           Rather than comparing these sorbents on the basis of percent utilization, a comparison can
    also be made based on the mass pickup of SOj per unit mass of sorbent.  Table IV gives this
    comparison at the number of cycles indicated for each sorrฐnt.  On this basis also, BaTIOj and CAC
    are both clearly superior to limestone.
    
           Several techniques, including pressing, extrusion, and granulation, have been utilized to pre-
    pare pellets from the titanates and CAC.  In a s=all attrition rig designed to simulate  fluidized bed
    operation at room temperature, scne CAC pellets have proven to be core attrition resistant than  natural
    sorbents.  However, the methods used to prepare pellets were only first attempts.   We believe that
    substantial improvement in the strength properties of pellets are ye- to be realized.
    
           Evaluation of CAC in the TGA has shown that CAC pellets prepared without any additives
    to increase activity are already acre activa sorbents than limestone.  Indeed, the CAC pellet of
    Figure 13 contained no additives.  However, the pore volume of CAC can be increased by using core water
    to mix the cement or by using burcables such as carbon black when formulating the  cement.  During the
    heating process the carbon burns out leaving pores.  In one test  of a CAC pellet,  we found that  adding
    one or two percent carbon black increased the utilization about  40 percent compared to a pellet  pro-
    pared without carbon black.
    
           Sorbent pellets have also been prepared from mixtures of  CAC and fly ash, with the expectation
    that the fly ash might act both as a burnable powder to increase porosity and activity and as an
    aggregate which would make the pellet stronger.  However, the magnitude of the effect of fly ash on
    the activity of CAC was unexpected.  After four cycles, the utilization of a pressed pellet  prepared
    from equal volumes of CAC and fly ash was over three t jes the utilization of CAC  prepared without
    fly ash.
    
           Because of the surprisingly large ioprovement in utilization when fly ash was added to CAC,
    we investigated the possibility that fly ash might be chemically  promoting or catalyzing the sulfation
    reaction.  An experiment was performed in which a pressed CAC pellet was rolled in fly ash so that
    the surface of the pellet was covered.  The pellet was then cycled In the TGA.  The result was that
    
    
    
                                                     769
    

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    BARIUM  T I TANAU
    
    CALCIUM  ALUHINAU CEMENT
    
    CONVENTIONAL  SO.''.BENT  (GROVE  LIMESTONE)
                    5   6   7   8
    
                      CYCLE  NUMBER
                                                SO
                                                    AFTER
                                                    SULFAIION
                                                    AFTER
                                                    REGENERATION
    Figure 13. Comparison of Utilization of Limestone and Pellets of
             BaTiO3 and Calcium Aluminate Cement
                            770
    

    -------
    the presence of the snail quantity of fly ash increased the utilization of the CAC by  60-80  percent.
    This suggests that the action of fly ash on the sulfation of CAC is not due to pore formation but
    may be a chemical effect, and is perhaps cataiyt.1-.  A further implication is that the performance
    of CAC as a sortent may be considerably better in a real coal combustor, where fly ash is  present,
    than in the "sterile" environment of a TCA.
    
    
    CONCLUSIONS
    
           The primary variable affecting $03 emissions from a pressurized fluidized Jad coal  combustor
    is the Ca/S molar ratio in the incoming feed streams.  Gas phase residence time axd! temperature  also
    affect SOj emissions but to lesser degrees.  Residence tine effects can be correlated  using  a first
    order reaction rate expression which satisfactorily described data from a number of laboratories,
    using a number of coals with varying sulfur contents.  The effectiveness of dolocite,  limestone  and
    calcined limestone' for SC>2 retention was determined.  Dolomite and calcined limestone  are  equally
    effective at the same Ca/S molar feed ratio basis.  However, at the same Ca/S wel^t feed  ratio,
    calcined limestone is much more effective.  Limestone is less effective than either dolomite or
    calcined limestone due to the inability of the limestone to calcine extensively uufer  pressurized
    FBC conditions.  Dolcmite and calcined limestone are also effective at very low cecbustor  tempera-
    tures whereas lir.estone is completely inactive.  The effectiveness of the calcined limestone is
    believed due to the formation of very large pores which occurs when the stone is calcined  under
    high CC>2 partial pressure conditions.
    
           The data presented in this paper permits the estimation of the sorbent requirements and gas
    phase residence time requirements needed to control 502 emissions to any desired level.
    
           Other emissions from the combustor are fairly low.  NO* emissions vary froa 50  to 200 ppm,
    increasing somewhat with excess air and temperature.  The emissions are well wlthฃn the EPA  emis-
    sion standard.
    
           Pressurized regeneration was studied Initially by reacting batches of sulTzted  limestone  and
    dolomite with a reducing gas at 9 atm pressure and about 1100ฐC in the 22 ex dia-^-ter  miniplant
    regenerator.  The gaseous effluent from the regenerator contained up to 3.7 mole jercent S02 (dry
    basis) and conversion of CaSO^ to CaO was nearly complete.  Formation of CaS was avoided using the
    technique of adjacent oxidizing and reducing zones.
    
           Subsequent to the batch studies, the regenerator vessel was coupled to the combustor  and  the
    system was run with sorbent recirculatlng between the two vessels.  An important question  is what
    reduction in sorbent requirements can be realized by adding regeneration to a once-through system.
    This question cannot yet be answered precisely but results of the continuous run provides  a  clue
    to the answer.  The average SC2 emission from the combustor was 310 ppm, corresponding to  a  retention
    of 11 percent, at an average Ca/S makeup ratio of 0.55.  Figure 6, which gives S
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    REFERENCES
    
    1.  M. S. :.'utkis, et al,  "Evaluation of  a  Granular  Bed Filter for Particulate Control In Fluidlzed Bed
        Combustion," presentation to Fifth international Conference on Fluidized Eed Combustion,  December
        1977, Washington, D.C.
    
    2.  M. S. Nutkis, Proc.  Fourth Intl. Conf.  on  Fluidized Bed Comb., publ.  The Mitre Corp., McLean,
        Virginia, 1975.
    
    3.  L. A. Ruth, Proc. Fourth Intl.  Conf. on Fluidized bed Comb., publ.  The Mitre Corp.,  McLean,
        Virginia, 1975,  425-38.
    
    ft.  C. P. Curran, et al,  Fuv>.l Gasification, Advances in Chemistry Series, 69, Aeerican Chemical
        Society, 1967, 141-65.
    
    5.  E. P. O'Neill, et al, Westlnghouse Research  Laboratory, "Experimental and Engineering Support  of
        the Fluidized Bed Combustion Program,  Task 2, Environmental Control L'slnp Alternate  Sorbents,"
        monthly reports prepared under  EPA contract  68-02-2132, Feb.-April  1976.
    
    6.  P. S. Lowell and T.  B.  Parsons, Radian Corp., "Identification of  Regenerable Metal Oxide  Sorbents
        for Fluidized Bed Coal  Combustion,"  EPA-650/2-75-065, 1975.
    
    7.  J. A. Cusunano and R. B. Levy,  Catalytlca  Associates, "Evaluation of  Reactive Solids for  S02
        Removal During Fluidized Bed Coal Conbustion,"  EPRI project TPS75-603, 1975.
                                                     772
    

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                QUESTIONS/RESPONSES/COMMENTS
    
    
         MR. DAMAN:   Thank  you,  Larry.
    
         MR. DAMAN:   Dr.  Ruth,  I  think you have some questions, right?
    
         DR. RUTH:   I have  a  question from Dr. Macek of DOE.  "According
    to your results, the  gas  residence time is very important in S02
    sorption.  Yet  I understand  that recent CURL results in pressurized
    fluidized bedcombustion shov; no Increased absorption with increased
    bed depth."
    
         I have not  yet seen  this data but I v-nll try to give some possible
    explanations for the  apparent difference in the results.  The most
    significant effect of gas phase residence time that we observed was
    at lower residence times, about one half to one second.  Beyond one
    second, the effect seems  to  decline.  I don't know what range of resi-
    dence times CURL's data represents.  Secondly, we varied the residence
    time by a factor of six.   I'm not sure what range of variation there
    was in the CURL  data.
    
         DR. MACEK:   About  two and a half.
    
         DR. RUTH:   And was the  CURL data with dolomite or limestoi.e?
    There is a lot more data  scatter with limestone because of calcination
    effects, so that it might be difficult to pick up an effect of resi-
    dence time with  limestone.
    
         DR. MACEK:   I would  assume dolomite but I don't know.
    
         DR. RUTH:   I have  three questions from Dave Henzel of Dravo.  The
    first one, "Do you have a cost comparison for the barium titanate
    versus calcium aluminate  cements?  What would be the source of calcium
    aluminate cement?"
    
         All I can give you at  the present time are the costs of preparing
    the synthetic sorbents.  The overall cost picture would also have to
    take into account differences in regeneration costs and sulfur re-
    covery costs. We would expect that there would be large differences
    in those costs as well.  For calcium aluminate cement we would esti-
    mate, and cement makers confirm this, that the cement would cost about
    $150 per ton in  the form  of  pellets suitable for the combustor.  The
    barium titanate  is more expensive, of course.  There we've estimated
    costs between 600 and 1500 dollars per ton.  Some barium titanate
    makers believe they can make it for less than 600 dollars per ton.
    As for the source of  calcium aluminate cement, it's made by fusing a
    mixture of limestone  and  bauxite.
    
                                    773
    

    -------
         The second question from Mr. Henzel.  "Is the precalcination of
    limestone done external  to the FBC unit and under what conditions?"
    
         We actually carried out the precalcination in our combustor
    vessel after we had removed most of the cooling tubes.  The fuel used
    v/as natural gas, and conditions were about 8 or 9 atmospheres pressure
    and somewhere around 1700 or 1750 degrees F.
    
         His third question is, "Would you repeat your contract numbers?"
    Well, here goes again.  The EPA contract was 68-02-1312 and the
    National Science Foundation Grant number is AER75-16194.
    
         I have another from Ray Costello, Burns and Roe Industrial
    Services Corporation.  "Concerning the effect of gas residence
    times on S02 capture your slide only went to three seconds.  Would
    you expect a significant increase in capture at longer residence
    times."
    
         As you can see from Figure 5 of the paper, as the residence
    time increased, the incremental increase in sulfur retention became
    smaller and smaller; our model which relates gas phase residence time
    to sulfur retention (see Figure 4 of paper) also predicts this effect.
    
         MR. DAMAN:  Thanks.
                                     774
    

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                             INTRODUCTION
         MR.  DAMAN,  CHAIRMAN:  All right, o :r next  paper,  also on regen-
    eration of limestone by John Vogel.  John is a  prominent member of
    the Argonne team working on fluidized bed combustion problems.  He
    started off in life messing arcurH with nuclear energy and then
    apparently saw the light and switched to coal.   He's been at Argonne
    since 1956.  John, why don't you go right ahead?
                                    775
    

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                            Development of a Process for Regenerating
                           Partially Sulfated Limestone from FBC Boilers
                          John C. Montanga, Franklin F. Nunes. Gregory W. Smith
                              Eugene B. Smyk, F. Gale Teats, G. John Vegel,
                                         and Albert A. Jonke
                                     Argonne National Laboratory
     ABSTRACT
            In fluidized-bed combustion of high-sulfur coal, a natural calcium-containing
     stone such as a limestone or dolomite is used as the bed material and acts as the
     sulfur-accepting agent, forming CaSO,, .   A means of significantly reducing waste volume
     froir. the combustor is regeneration of the CaSO., to CaO and reuse of the regenerated
     stone in the combustor.  A fluid-bed, reductive decomposition regeneration process has
     been developed in which the sensible heat, the heat of reaction, and the reducing gases
     are supplied by partial combustion of coal in the bed at 1IOOฐC.  The developmental
     stages are reported for-.  (1) selection of the process, (2) evaluating the regenerator
     performance with limestone,  (j) performing cyclic (sulfation-regeneration) liir.estone
     and dolomite life studies, and (<4) incorporating the experimental results in a process
     flowsheet for a 200-MWe KBC boiler-regenerator system.
    
    
    'INTRODUCTION
    
            Kluidized-bed combustion of coal is currently being developed for electric power
     and/or steam generation since the current national goal, to become less dependent on
     foreign energy resources, is heavily dependent on increased utilization of domestic
     high-sulfur coal.  In the fluidized-bed coal combustion process, the coal is combusted
     in a fluidized bi.d of a sulfur-accepting sorbent such as limestone or dolomite.   The
     sulfur released during Combustion reacts with calcium in Che stone to form CaSO,. .  The
     primary reasons for using natural calcium-based stones are thoir acceptable reactivity,
     low costs, anc1 bountiful supply throughout the United States.
    
            In the fluidized-bed process, approximately 500 pounds of limestone is required
     per ton of combusted coal (37., sulfur) to maintain the SO? concentration in the flue gas
     below the EPA emission standard.   The sulfated limestone product (which is mixed with
     coal ash) rnay have commercial uses tor cement block manufacture, landfill, or agri-
     cultural lime.  Even so, methods  for reducing the amount of limestone used in the
     process would have the advantages that less stone would have to be quarried and less
     waste discarded from the process.  Less stone would be used if (1) laboratory-scale
     tests could identify the more reactive stones so that these may be used,  (2) the reac-
     tivity of nonrcactivc stones could be increased by physical or cheni-al modification of
     the stone, or (3) the stone could be regenerated for reuse in the combustor.
    
            A fluid-bed reductive-decomposition limestone-regeneration process has been
     developed in rDU-scale equipment.  In th:.s process,  both the heat and reductants are
     supplied by partial combustion of coal in the bed at 1100"C.  The developmental  stages
     are reported for:  (1) selecting  the process, (2) optimizing the process, O) performing
     cyclic (i.e., sulfation/regeneration) life studies on the sorbent, and (4) incorporating
     the experimental results in a process flowsheet for a 200-MWe FBC boiler-regenerator
     system.
    
    
     SELECTION OF THE REGENERATION PROCESS
    
            Thermodynamic and kinetic  information were obtained from the literature on
     processes for converting calcium  sulfa;e to calcium oxide.'-2  Of the more feasible
     processes examined, thermal decomposit-'.on or calcium sulfate was not considered  to be
     a viable process because of the high temperature, >1200eC.  needed to obtain a high con-
     centration of SO, in the off-gas.  At thif, temperature, ash and sulfated  stone would
     fuse to form unusable clinkers.
    
            Another process (studied in laboratory-scale equipment) consists of two steps.
     CaS that has been produced in the first step by reacting CaSOi, vith a reducing gas at
     •v-870'C is reacted with steam/CO,  at v560ฐC to produce CaC03 and H2S.  Cyclic processing
    
    
                                               776
    

    -------
    by alternate  sulfation and regeneration showed  that  the extent of regeneration  of the
    CaSO_ decreased significantly in succeeding cycles.'   Attempts to understand  the
    mechanism and to develop the process fu'.'ther were  abandoned when it became necessary
    to select a process for larger-scale development.
    
           Selected for further development was the  reductive decomposition process in
    which CaSO., is  heated in a fluidizcd bed to --IIOO'C in  the  presence of reductant gases.
    Two solid-gas reactions by which regeneration occurs  are:
                                  CaSO/, + CO  • CaO +  C02  + SOj
                                          H2  • CaO +  HoO  + S02
    (1)
    (2)
    At lower temperatures and under more highly reducing  conditions, the  formation  of  CaS
    is favored:
                                    CaoO.; + 4CO - CaS +  4CC2
                                    CaSO/, + U\\2 •• CaS +  4H20
    (3)
    The products are CaO.  which is reused in the combustici step,  and a SO.--containing
    off-gas, which  can  be  processed for its sulfur content.   The calcium sulfide concentra-
    tion in the product is maintained below 0.17a by circulating particles into an oxidizing
    zone where CaS  is converted to C".iO. .
    EQl'IPMLNT
    
           Figures  1  and  2  illustrate the Process Development Unit (PDU) combustion  and
    regeneration  systems  used in this investigation.  The  combustor has a 15-cra  ID and  is
    approximately 3.'* m high.  The regenerator consists  of a  nominal 20-cm-dia pipe,
    refractory-lined  to an  ID of 10.o cm.  Bubble-type gas distributor plates are flanged
    to the bottom of  each reactor and accommodate fluidining-air inlets, solids  feed and
    removal lines,  and  thcrnucouples for monitoring the  bed temperatures.  In each system,
    the coal and  sorbent  are metcred separately to a  single pneumatic transport  line which
    discharges these  solids into the fluidizcd bed above the  gas distributor plate.
    Expanded-bed  heights  of -.90 cm in the combustor and  -.46 cm in the regenerator are main-
    tained with overflow  pipes.
                                                            To Gas Analysis
                                                               System
                                                        Test Filter
                                                       Stainless Steel
                      Screw
                     /Compressor
    
                "-^fl
                                                                      Pressure
                                                                      Control
                                                                      Vjlve
                                                                       .?_ Ventilation
                                                            TJ
                                                           Steel
                                                           Filter
                                                                           Exhd'ist
                                                      Secondary
                                                      Cyclone
                                                   Primary
                                                   Cyclone
                      Figure 1. Simplified Equipment Flowsheet of Fluidiied-Bed Combustion Process
                             Development Unit
                                               777
    

    -------
       To Gas
       Analy/ers
                                         ,
                                         I"
                                                      Filter
                                    Sample          >/ |^_ rL^JPres
                                 Gas Conditioner crrzpCyclones   l-T  pon
                                  Sulfated-Sorbent
                      Cou< Hopper 5—7 Hopper
    Rotary Valve
    Feed
       Air -,—
                                                          -
                                                        Filter
                                          I Pressure
                                          Control
                                          Valve
                                                                   xhaust
                                                I Regenerator
                                                ! (10.8cm 10)
                                                             Surge
                                                i v.LinjJ
                                           "Product   -r-
                                            Collector
                               Figure 2. Experimental Sorbent Regeneration System
    
    
           Other  components of the experimental systems  are  an  electrically heated heat
    exchanger  for preheating the fluidizing gas and a solids-cleanup system for the off-gas
    consisting of cyclones  and porous metal filters.  Most constituents (SO? .  Q2 , CO, H>,
    CH,, , and NO)  in  the  off-gas  are  continuously analyzed.
    
           In  the regeneration system,  the solids transport  air constitutes "-407. of the
    total  fluidizing gas in the  reactor.  The remaining  fluidizing  gas is a mixture of pure
    nitrogen and  oxygen.  Oxygen and nitrogen are metered separately and are mixed to pro-
    duce the required oxygen environment in the reactor.  Thus  the  oxygen requirement at
    different  experimental  conditions can be satisfied without  changing the fluidizing-gas
    velocity.
    
    
    MATERIALS
    
           The two sorbents tested in these studies were Tynochtee  dolomite and Greer lime-
    stone.  The dolomite contained DO wt 7, CaCO,, 39 wt % MgCOj,  and 2.1 wt 7. Si as
    received.   The limestone contained 41.2 wt '/„ CaO, 32 wt  7. COj ,  and 4.27 wt 7, Si.   The
    nominal size  distribution of each limestone was -14 +30  U.S.  mesh.
    
           The coal  used in the  sulfation of Tymochtee dolomite was a Pittsburgh seam coal
    which  (as  received)  contained ^-2.3 wt 7, S. -v-7.7 wt % ash, and -ป-2.9 wt 7, moisture  and
    had a  heating value  of  7,600 kcal/kg and an average particle  size of 320 urn.  In  the
    regeneration  steps with Tymochtee dolomite. Triangle coal was combusted under reducing
    conditions.   It  is a high-volatile bituminous coal with  a high  ash-fusion  temperature
    (1390ฐC under reducing  conditions).
    
           Sewickley  coal was used in both the combustion and the  regeneration  stepc of the
    Greer  limestone  study.   As received, it contained 1.4.3 wt % S,  12.7 wt "L ash,  and 1.1
    wt 'I. moisture and had a heating  value of 7,200 kcal/kg.  The  Sewickley coal has a
    relatively low ash-fusion temperature (•v.H20ฐC under reducing conditions) .
    
    
    REGENERATION  EXPERIMENTS USING GREER LIMESTONE
    
           The dependence of (1) CaO regeneration and (2) SO? concentration in the regen-
    erator off-gas on key variables  such as regeneration temperature and solids residence
    time in the fluid-bed reactor was studied for once-sulfated Greer limestone to aid in
    optimizing the regeneration  process conditions for this  limestone.  Regeneration  of
    sulfated Tymochtee dolomite  had  been studied earlier.3   The experimental conditions and
    results for these experiments are given in Table I.  Regeneration of CaO,  calculated
    from chemical analyses  of the steady-state materials, was based on the calcium to sul-
    fur ratios in (1)  the sulfated limestone feed and (2) the regenerated product. These
    calculated regeneration values are compared in Table I with the values based on the
                                               778
    

    -------
    ratio of  the  sulfur contained in the off-gas no that in the sulfated  limestone feed.
    
    
        Table I.   Experimental  Conditions and Results for the Regeneration  of  Greer Lime-
                   stone by the  Incomplete Combustion of Sewickley coal  in a Fluidized Bed
    
                   Nominal  fluidized-bed height:   "-46 cm
                   Reactor  ID:   10.3 en;
                   Pressure:   129  kPa
                   Coal: Sewickley (4.3 wt 7. S) ; ash fusion temperature (initial
                         deformation)  under reducing conditions:  1119  C
                   Scrbent:   -14 +30 mesh sulfated limestone (7.7 wt 7ปS)
    Exp.
    No.
    RGL-1A
    RGL-1B
    RGL-1C
    RGL-1D
    RGL-1K
    RGL-1F
    ?Based
    "Based
    Bed
    Temp,
    "C
    1050
    1050
    1050
    1100
    1100
    1100
    Fluidizing-
    Gas Feed
    Velocity. Rate,
    m/s kg/hr
    1.23 8.2
    1.21 15.4
    1.21 26.3
    1.23 9.1
    1.23 15.9
    1.29 25.3
    Reducing
    Solids Gas Cone.
    Residence in CaO
    Time, Effluent, Regener. ,
    rain 7. 7.* / *,ฐ
    22.54
    11.93
    6.99
    20.23
    11.59
    7.12
    on flue-gas analyses.
    on chemical anlayses of limestone
    3
    2
    3
    3
    3
    2
    sai.iples .
    .2
    .9
    .4
    2
    !5
    .9
    
    72
    43
    28
    79
    72
    66
    
    2/83.0
    1/53.3
    3/27.3
    5/92.0
    3/82.8
    9/70.9
    
    Major Sulfur
    Compounds in Dry
    Off -Gas. 7.,
    S02
    3.3
    3.7
    4.3
    3.9
    6.0
    8.4
    
    I'-2S
    0.09
    0.09
    0.05
    0.2
    0.1
    0.06
    
    COS
    0.07
    0.08
    0.1
    0.1
    0.1
    0.09
    
    CS2
    0.06
    0.05
    0.05
    0.05
    0.03
    0.02
    
    Effects of Solids Residence  Time  and 3ed Temperature on Exter-.t of CaO  Regeneration
    
           Lxtent of regeneration  values are plotted in Fig. 3 as a function  of  solids
    residence time  for  two  temperatures, 1050ฐC and 1100ฐC.  When the solids  residence time
    was decreased,  the  extent  of regeneration decreased.  At 1100ฐC, the regeneration rate
    is higher and therefore the  conversion ratio of CaSO,. to CaO is less affected by a de-
    crease in reactor particle residence time.   With a residence time as low  as  7 min, the
    extent of regeneration  is  considerable.  ->-707o.
                                     Figure 3. Regeneration of CaO in Greer
                                           Limestone as a Function of
                                           Solids Residence Time and
                                           Regeneration Temperature
           A "best  fit"  equation  has  been  obtained by   gression analysis  for  the  experi-
    mental extent of CaO regeneration as a function of .egeneracion temperature  and  solids
    residence time:
                                               779
    

    -------
                                    In (1 - R) = A-  -t- B- :                                (5)
    
    where
    
                R = extent of CaO regeneration (R = 1 for complete regeneration)
                i  = solids residence time (reactor particle contact time)
          A x 102 = -12.4T - 3.98                                                        (6)
          B x 103 = 3.25T - 1.24
                T = (t - 1050)/50
                t = regeneration temperature, "C
    
    The values calculated tv the model equation (Eq. 5) compare favorably with the experi-
    mental results.  A correlation coefficient of '-0.97 -..-as obtained for the experimental
    data and the results predicted from the model equation.  These best fit results for
    Greer limestone are compared with results for similar experiments with Tymochtee
    dolomite in Fig. 3.  The regeneration rates for these two sorbents compare very favor-
    ably.  This relationship for the rate of CaO regeneration is used in the model for the
    regeneration process to optimize the design process conditions and to scale up sorbent
    regeneration systems (described in a later section).
    
    Effects of Solids Residence Time and Temporaturc on SO. Concentration in the Off-Gas
    
           In the fluidized-bed regeneration process, the SO-, concentration in the off-gas
    is determined by (1) the feed rate of CaSO., to the regenerator reactor (solids residence
    time and sulfur content of sulfated sorbent),  (2) the extent of regeneration of CaO,
    and (3) the gas flow rate through the reactor.
    
           In this series of regeneration experiments, sulfated limestone (containing
    7.7 wt 7, uulfur) was used.   The fiuidizing-gas velocity varied from 1.21 to 1.29 m/s.
    a small variation.  The gas flow rate through the reactor was not affected greatly by
    the fluidizing gas velocity in these experiments.  Therefore, the variation of SO, con-
    centration in the dry flue gas was due to the mass rate of CaO regeneration.
    
           The experimentally obtained SO, concentrations in the dry off-gas are plotted in
    Fig. 4.  At 1050"C. the SO-, concentration increased from 3.3% to A. 37. as the solids
    residence time decreased from 22.5 min to 7.0 min (i.e., as the sulfatcd-sorbcnt feed
    rate increased).  At 1100"C. the SO.  concentration in the dry off-gas increased from
    3.9 to 8.47. as the solids residence time decreased from 20.3 min to 7.1 rin.  At the
    longest solids residence time (-20 min), the SO  concentration was found to be only
    slightly higher at the higher termerature.  With this long reaction time, most of the
    CaO was regenerated at both temperature levels and hence the SO- concentracion in the
    off-gas was dependent on the CaSO,, feed rate.   For the shorter reaction timo (7 min),
    the SO. concentration was much higher at the hipher temperature (IIOO'C) due to the
    higher rate of CaO regeneration.
    
    Effect of Regenerating Limestone at a Temperature of 1150">J
    
           One experiment was performed at a temperature of 1150ฐC, the highest temperature
    at which a regeneration experiment has been performed.   The extent of CaO regeneration
    based on solids analysis at the higher temperature did not increase significantly in
    comparison with data for 1100ฐC.  In contrast,  there was a significant increase in CaO
    regeneration observed with an increase in temperature from 1050ฐC to 1100ฐC.  This
    suggests that regeneration at temperatures greater than 1100ฐC would not significantly
    improve the performance of the regeneration step.  Possibly, higher temperatures accel-
    erate the sintering process and render the sorbent less reactive in subsequent sul-
    fation steps.
    
    Effect of Bed Temperature.  Particle Size, and Reducing Gas Concentration on Bed
    Oetluidization Velocity
    
           Bed defluidization velocity, i.e., minimum velocity required to prevent particle
    agglomeration, was studied in a statistical experiment  performed with Greer limestone
    and Sewickley coal.  Details of the study were reported earlier.''  The effects on de-
    fluidization"velocity of bed temperature (1050 and 1100ฐC).  total reducing gas concen-
    tration (2.5 and 5.07=). and feed sorbent particle size  range (-10 +30 mesh and -14 +30
    mesh) were determined.   Defluidization velocities in this study ranged from 0.9 to 1.6
    m/s.  Defluidization velocity as a function of temperature and reducing gas concentra-
    tion is shown in Fig. 5, along with minimum fluidization velocities.   Bed temperature
    
                                              780
    

    -------
                S.-IU* •••I4ป* Tlซ*. *:n
    
    
    Figure 4. Experimental S02 Concentration for the
           Regeneration of Greer Limestone as a
           Function of Solids Residence Time and
           Temperature. Pressure: 129 kPa; Fluid-
           izing-Gas velocity: 1.21-1.29 m/s;
           Limestone sulfur content: 7.7 wt %
                                                                 O  CRCUX CORRELATION
                                                                    (BASED OH ROOM TEMP EXP)
                                                                 O  0%  REDUCING GAS
                                                               -O  1%  REDUCING GAS
                                                                 0 2 S>.  BEOuCISO GAS
                                                                 050%  REIMCIKG GAS
                                                                     MINIUUV rlUIOliATlON VELOCITY
    
                                                                  I  • .I-..-!. ......	I	,	J	
                                                                 BOO     900     1000      1100
    
                                                                        TEMPERATURE.*C
                                                     Figure 5. Oefluidization Velocity and Minimum Fluidization
                                                            Velocity vs. Temperature
    and reducing gas concentration arc important  in  fixing the minimum  fluidization veloc-
    ity.  The  effect of particle  size is minimal.  A least-squares  fit  of the results  is
    the basis  for the following equation:
    
                           Vrl = A.05 - (3.61 \ 10-3T)  -  2.6R + (2.54
                                x  10-3TR) + (5.26  x 10-^F)                                  (8)
    
    where V,] = defluidization velocity,  m/s
           T = operating ternperat ure, ฐC
           R = reducing gas concentration in off-gas, "I,
           F = mean particle size  of sorbent. ;im
    
    
    CYCLIC SORBENT LIFE STUDY WITH TYMOCHTEE DOLOMITE
    
           The general procedure  in the  first combustion half-cycle of  each series of
    cyclic experiments was to 3ulfatc a  batch of  fresh  unsulfated sorbent.   The sorbent was
    then alternately processed in  the regenerator and the  combustor without makeup sorbent
    for a total of ten combustion  and ten regeneration  half-cycles.  Steady-state gas and
    solid samples from each half-cycle were analyzed  to assess changes  in reactivity (sul-
    fur acceptance during combustion), changes in rcgenerability (sulfur  release during
    regeneration), the extent of decrepitation, and  the extent of coal  ash buildup as a
    function of utilization cycle.
    
           The nominal conditions  for the combustion experiments in each  cycle were a 900ฐC
    bed temperature, a aiO-UPa system pressure, a 1. '. CaO/S mole ratio  (ratio of unsulfated
    calcium in sorbent to sulfur in coal), --I?/', excess  combustion air,  a  0.9 m/s fluidizing
    gas velocity, and a 0.9 n bed  height.  Changes in reactivity of the sorbent from cycle
    to cycle were reflected in changes in the SO; levels in the flue gas  from the corabustor.
    
           The regeneration step of each cycle was performed at a system,  pressure of 15&
    kPa, a bed temperature of 1100ฐC,  and a fluidized bed  height of "-46 cm.
    
    Sulfur Acceptance during Combustion
    
           The level of sulfur dioxide in the flue gas  and the corresponding sulfur reten-
    tion based on the flue-gas analyses  for the ten  combustion cycles are presented in
    Fig. 6.
                                                781
    

    -------
                                I'M
    
                                r/K-
                               two-
                               s'
                                400-
                                 0!
                                  o
                            Figure 6. Sulfur Retention in Bed and S02 Concentration in
                                   Flue-Gas as a Function of Cycle Number
           Sulfur dioxide  levels  in  the gas  incrca-.-.ed from --300 ppm in cycle 1 to --950 ppm
    in cycle 10.  This represents a  decrease in  sulfur retention from --88Z in cycle 1 to
    •o57. in cycle 10.  Although there  is some  scatter in the data,  it appears that the
    reactivity of the sorbent for sulfur retention  decreased linearly with increasing com-
    bustion cycle over the  10-cycle  experiment.   The loss in reactivity for sulfur retention
    is in good agreement with results  reported by Zielke et al.'' in a similar cyclic com-
    l>ust ion-regeneration study in which Tymochtee dolomite was used at 155 kPa.
    
           Samples of the  sorbent from each  regeneration half-cycle were also tested for
    reactivity in a TCA apparatus at 900ฐC.  using a reactant gas of 0.3% S0> , 57= 0; , and
    the balance N;>.  The rate of  conversion  (sulfation)  decreased with increasing sulfation
    cycle.  After the eighth sulfation cycle,  however,  the loss in  reactivity with succeed-
    ing sulfation cycles was quite small.  This  potential leveling-off oi reactivity was
    not detected in the cyclic combustion-regeneration experiments  performed in the PDU.
    
    Sulfur Release during  Regeneration
    
           The experimental conditions and results  for a representative segment of each
    regeneration step are  given in Table II.   In the ten regeneration half-cycles, solids
    residence times ranged  from 6.8  to 8 1 rain.   The extent of CaO  regeneration based on
    solids analysis varied  from 67 to  30/1.   There was r.o apparent loss in regenerability
    during the ten utilization cycles.
    
           The S02 concentration  in  the dry  off-gas from the regenerator  ranged fron tt.87.
    to 6.1%.  In the first  cyclic regeneration experiment (CCS-l) ,  the SO_-> concentration
    was diluted by gas usi;-l t.r obtain  the f luidizing-gas velocity of 1.43 m/s (other
    experiments were done  at -.1.26 m/s).  In the three final cyclic regeneration experi-
    ments, the lower S(>2 cf "entrations in the regenerator reactor  off-gas were a result
    of the lower sulfur cr v^entrations in the  sulfated sorbent (7.1-7.9 wt % S instead of
    1.10% SI.  Although t^.   combustion  steps  of these cyclic experiments were performed with
    a constant CaO/S moli-  ratio of ->-1.5 with no  virgin-sorbent makeup, the total sulfur
    content of the 3uivat-ed sorbent  decreased  with  each cycle due to lowered sulfation
    reactivity of the sorbent.
    
    Estimate of Tymochtee  Sorbent Makeup Requirements to Meet EPA Sulfur Emission Limit
    
           To estimate the  relationship between  sorbent makeup (ratio of makeup CaO to total
    CaO) and the total CaO/S mole ratio which  would be required in  a continuous recycle
    operation to meet the  EPA sulfur emission  limit, an analysis was made using the results
    of the cyclic combustion/regeneration experiments along with some previously obtained
    data.  The greater the makeup, the higher  the reactivity of the sorbent for sulfur
    retention and the lower the CaO/S  ratio  required.  Sorbent utilization data (fraction
    of CaO converted to CaSO..) from  selected combustion experiments were used with an
    adaptation of a procedure developed by Nagiev6  for describing cyclic processes to obtain
    the relationship presented in Fig. 7.  The curves in Fig.  7 were developed for a
    
    
                                               782
    

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    Table  II.   Experimental Conditions and Results for  the Regeneration
                Step of the Ten Utilization Cycles with  Tymochtee  Dolomite
    
                Nominal fluidized-bed height:   46 cm
                Reactor ID:  10.3  cm
                Pressure:  153 kPa
                Temperature:  11001>C
                Coal:   Triangle (0.98 wt 7. S) ,  ash fusion temperature
                        (initial deformation under reducing conditions):  1390ฐC
                Sorbent:   -14 +30  mesh sulfaced Tvmochtee dolomite
    Fluid.- Solids 02 Cone.
    Gas Res. in Feed
    Cycle Expt. Veloc., Time, Gas,
    No. No. m/s min %
    1 CCS-1 1.43 7
    2 CCS-2 1.26 7.5
    3 CCS-3 1.22 7.2
    4 CCS-4 1.17 7.3
    .5 CCS-5 1.17 7.4
    6 CCS-6 1.18 7.8
    7 CCS-7 1.16 7.3
    8 CCS-8 1.18 8.1
    9 CCS-9 1.09 7.3
    10 CCS-10 1.24 6.8
    ?Based on off-gas analysis.
    Based on chemical analysis
    Analysis not performed.
    26
    27
    36
    36
    36
    41
    33
    25
    36
    7
    7
    5
    1
    a
    i
    9
    4
    0
    of dolomite
    Red.
    Gas
    Cone. Sulfur
    in Cone . in
    Off- Sulfated
    Gas, Sorbent.
    % 7.
    2.8
    3.0
    3.4
    2.9
    3.0
    2.6
    2.9
    3.0
    3.0
    3.0
    samples
    9.05
    10.7
    10.3
    9.9
    9.5
    9.3
    8.5
    7.8
    7.9
    7.1
    
    CaO
    Major Sulfur
    Compounds in Dry
    Off -Gas. %
    >o / /tt oO<) H-jU
    L ฃ.
    73/71
    67/67
    63/76
    67/69
    69/75
    66/75
    69/77
    64/80
    53/67
    63/69
    
    6
    d
    8
    8
    3
    8
    8
    6
    6
    6
    
    .5
    .6
    .4
    .1
    .8
    .7
    .2
    .3
    .1
    .7
    
    0.04
    0.02
    0.07
    0.04
    --C
    0.03
    0.07
    0.06
    0.1
    0.05
    
    COS
    0
    0
    0
    0
    0
    0
    0
    0
    0
    
    .06
    .1
    .1
    .1
    --C
    .2
    .01
    .07
    .1
    .08
    
    CS2
    0.04
    0.1
    0.1
    0.1
    --C
    0.1
    0.1
    0.07
    0.1
    0.09
    
                                  0   02   0ซ  06   03   10"
                                    MAKEUP CoO/TOTAl CoO. RATIO
                            Figure 7. Calculated Makeup and Total CaO/S
                                    Ratios Required to Achieve 75%
                                    Sulfur Retention as a Function of
                                    the Makeup CaO to Total CaO Ratio.
                                    Sulfation Conditions: Temp, 871ฐC;
                                    Pressure, 810 kPa; Sorbent, Tymochtee
                                    Dolomite.
                                         783
    

    -------
    constant sulfur retention of 757<> as compared with ''70% required to meet the EPA emission
    limit for the Arkwright coal used in the combustion experiments.
    
           As an example of using Fig. 7, operating at a total CaO/S ratio of 1.5 indicates
    that a sorbcnt makeup, -i,  of 0.18 and, hence, a makeup CaO/S mole ratio of '-0.27 are
    required for a sulfur retention of 75%.  Decreasing •, to 0.1 (107. makeup) reduces the
    makeup CaO/S mole ratio to -0.20 (a reduction of 25%) but increases the total CaO/S
    ratio required to 2.0 (an increase of 33%).  In comparison to the once-through CaO/S
    ratio of "-1 for 75% sulfur retention, the makeup CaO/S mole ratio of 0.2 for a cyclic
    process corresponds to an estimated savings of 80% of the fresh limestone requirements.
    
           It should be emphasized, however, that -i cannot be chosen arbitrarily.  The
    value of .1 will affect and will be determined ultimately by both the process flow sheet
    and che system economics.
    
    Porosity of Dolomite as a Function of Utilization Cycle
    
           The porosity of -25 +30 mesh particles was measured by the mercury penetration
    method.  The cumulative pore volumes for pores ^0.4 wm and also for pores ^0.04 um in
    sulfated and regenerated Tymochtee dolomite are given in Table III.  It has been re-
    ported by Hartman and Coughlin7 that most sulfation takes place in larger pores (-0.4
    ;.m) and that pores smaller than 0.4 i,m are relatively easy to plug.  During sulfation
    of CaO, the pores shrink as a result of molecular volume changes.
    
                    Table III.  Porosity (cm;/g) of Tymochtee Dolomite as
                                a Function of Utilization Cycle
    Cycle
    No.
    1
    2
    3
    4
    5
    6
    aPores
    Pores
    Change in
    Porosity on
    Sulfated
    0
    0
    0
    0
    0
    0
    •0
    >0
    120
    120
    120
    156
    144
    132
    4 i,
    04
    a/0
    /O
    /O
    /O
    /O
    /O
    m
    um.
    164b
    212
    140
    164
    Ijo
    140
    
    
    Regenerated
    0
    0
    0
    0
    0
    0
    
    
    269a
    2&U
    252
    244
    238
    204
    
    
    /O
    /O
    /O
    /O
    /O
    /O
    
    
    340b
    308
    276
    258
    260
    220
    
    
    Re-generation (,-.)
    0
    0
    0
    0
    0
    0
    
    
    14J'
    168
    n?.
    OSI8
    094
    072
    
    
    Vo.l76b
    70.096
    /0.136
    / 0.094
    /0.104
    /0.080
    
    
           The porosity of sulfated dolomite was relatively unaffected by utilization cycle,
    although the sulfur content decreased from -.10 wt 7. to -"7 wt "L.  However, the porosity
    of the regenerated dolomite consistently decreased with utilization as did the sulfur
    content in the regenerated stones.  The difference in porosity of the sulfated and
    regenerated samples decreased from 1.0.15 cmj/g (pores ^0.4 ;im) after the first cycle
    to ->-0.07 cm:/g after the tenth cycle.  The porosity of regenerated dolomite decreased
    with cyclic use, and thus its effectiveness as an SOj acceptor decreased.
    
    Coal Ash Buildup during Dolomite Utilization Cycles
    
           The extent of coal ash buildup during repeated utilization cycles was evaluated
    for its effect on the SO.;-accepting capability of the sorbent in the combustion step.
    Based o.. silicon enrichment determined by bulk analysis, coal ash buildups were calcu-
    lated for all ten sulfation and regeneration steps.  The results are illustrated in
    Fig. 8.  After ten utilization cycles, it was found that for every 100 g of starting
    dolomite, %13 g of coal ash had accumulated in the sorbent.
    
           Several analyses were performed confirming "he buildup of an ash layer on the
    surface of the dolomite particles during repeated u/ilization cycles.  Sulfated and
    regenerated particles from the first, fifth, and ten;h utilization cycles were examined
    for macrofeatures under a low-magnification microscope.  The photomicrographs clearly
    reveal that coating of even the once-sulfated stones with a crust-like layer was
    beginning.
                                              784
    

    -------
                                16
    a*
    •  0
    
    o  6
    i—
    
    z
    
    
    8  o
         • - 9 ojh/IOOg VIRGIN DOLOMITE
           COMBUSTION STEP OF CYCLE
         0-gosh/IOOg UTILIZED DOLOMITE
           COMBUSTION STEP OF CYCLE
         • -gosh/IOOq VIRGIN DOLOLOMITE
           REGENERATION STEP OF CYCLE
         0-gcsh/IOOg UTILI/ED DOLOMITE
           REGENERATION STEP OF CYCLE
                           8
                           i ป
                           r  ป
    o
    n
    M
    11
    i i
                                           R
                                  A-COMBUSTION STEP OF CYCLE
                                  ,0-REGENERATION STEP OF CYCLE
                                 02468
                                    TYMOCHTEE DOLOMITE UTILIZATION CYCLE
                                                                   10
                            Figure 8. Coal Ash Buildup as a Function oi Utilization Cycle
           A petrographic  examination of unreacted dolomite  and  of samples from the  first
    and tenth cycles  revealed  the buildup of a vitreous  crust  containing magnetite (Fe;O.)
    and hematite  (Fez03) surrounding irost of the particles.  X-rav diffraction analyses  or
    the crust revealed  the presence and accumulation of  Ca(Al-.7Fe;. ;);0: with increasing
    utilization cycles.
    
           Electron microprobe analyses performed on crosi sections  of sulfated and  regen-
    erated dolomite samples from the tenth utilization cycle confirmed the existence of
    the coal ash  shell  and measured its approximate composition.   The racial component
    concentration profiles for a typical regenerated particle  after  ten cycles is riven
    in Fig  9   Peak  concentrations of -.12 wt % Si. --25  wt 7, Fe.  and  -/ -ปc  , Al were four.a
    in the crust.  The  concentrations of these components in Arkwright coal ash.^which was
    used during the combustion step of the experiments,  are:  12 wt ป Si. 14 wt /. te. ar.c
    12 wt 7. Al    The  above-measured concentrations of  relatively major components in tne
    particle crust were not in Che same proportion as  in the coal ash; re/Si was --2  in  t.-.e
    crust and -.0.7 in the  coal ash.
    
           The sulfur concentration profile shows that  this  particle haJ not completely
    rcEenera'ed and that very  little sulfur was present  in the particle crust.  Scar.s oi
    other reeenerated particles had sulfur profiles which indicated nearly complete  regen-
    eration.  Therefore, the presence of a coal ash shell does not prevent sulfur tron
    escaping during regeneration.
    
           Sulfated particles  from the tenth cycle were  also analyzed with the electror.
    microprobe    The  analysis  for a typical partially sulfated particle is given in  .- ig
    10   In all particles  analyzed, the formation of an  ash  crust was again verifiea.   As
    in'regenerated particles,  the ash crust was enriched in  calcium, suggesting the  poss.-
    bility that calcium diffused from the particle  interiors to the ash crust.
                                                785
    

    -------
    
                            *  3ฐ~ A
                            .-20 -A
                               io -y
                                    Ash           Particle
                                Figure 9. Electron Microprobe Analysis of a Typical
                                      Regenerated Dolomite Particle from the
                                      Tenth Cycle
    
    
    
           For the particle whose analysis  is given in  Fiฃ. JO, the sulfur concentration
    below the ash crust is highest near the crust  and decreases with penetration towards
    the center of the particle.  If diffusion through the ash crust or sulfated shell con-
    trolled the sulfation reaction, the calcium adjacent  to the crust would be expected to
    be more fully sulfated (^.10 wt %) in a  partially reacted particle.  Also, a sharper
    radial sulfur concentration gradient would  be  expected at. the reaction front.  The
    electron microprobe analysis of sulfur  concentration  in tenth cycle partially sulfated
    dolomite suggests a diffusion resistance at the reaction front.  Thus, the loss of
    reactivity could be due to a loss of local  or  microporosity caused by sintering within
    the dolomite particle.
    
    Attrition and Elutriation Losses during Combustion  and Regeneration
    
           The extent of sorbent losses during  the combustion and regeneration steps of
    the ten utilization cycles was determined.   Sorbent losses for each cycle and from
    each stage were calculated on the basis of  the amount of calcium in particulates re-
    moved in the off-gas sys* *ms and the amount of calcium in the sorbent fed to the
    reactor.  The results are given in Table IV.
    
           Although the first combustion half-cycle loss  was quite large, losses during
    the remaining sulfation half-cycles were reasonably small, averaging about 8% per
    cycle.  The lower losses during regeneration can probably be attributed to the very
    brief solids residence time (-v.7.5 rain)  in the  reactor,  as compared with the much longer
    
                                              786
    

    -------
                     10-
                 85
                 o>
    12- 	 ! 	
    
    ^ Q 	 	 .;.......
    w 4- 7\: :.:':.:.:'i-:'
    	 i 	
    
    	 i .......
    -..::• • : ! ; : :ys
    10
     8-
     4-
                                 Figure 10. Electron Microprobe Analysis of a Typical
                                         Partially Sulfated Dolomite Panicle
                                         (PS-3) from the Tenth Cycle
    solids residence  time (-.5 h) for sulfacion in  the  combustor reactor.
    CYCLIC SORBENT  LIFE  STUDY WITH GREER LIMESTONE
    
           The nominal conditions of the combustion experiments were a 308-kPa system
    pressure, 855ฐC bed  temperature, -.177. excess combustion  air, a 1.0 m/s fluidizing-gas
    velocity, a 0.9 n bed height, and a constant sulfur  retention of T-84% by the  sorbent.
    The lov.'er pressure was used to simulate the atmospheric-pressure Cluidized-bed  com-
    bustion concept.  In this study, in which sulfur retention was held constant  (in the
    Tymochtee cyclic study,  the CaO/S ratio was held constant), changes in sorbent  reac-
    tivity were reflected in changes in the CaO/S ratio  required to achieve constant
    retention (retention was the dependent variable of reactivity in the first cycle
    study).
    
                                               787
    

    -------
                 Table IV.  Attrition and Klutriation  Losses  for Tymochtee
                            Dolomite during Combustion and  Regeneration  in
                            the Cyclic Utilization  Study
    Cycle
    No.
    1
    2
    3
    A
    5
    6
    7
    8
    9
    10
    Loss During
    Combustion,
    wt 7.
    16
    A
    5
    3
    3
    6
    4
    7
    6
    A
    Lobs During
    Regeneration.
    wt %
    1.9
    1.7
    3.0
    1.2
    3.5
    3.7
    2.0
    2.6
    0.9
    1.3
           The nominal operating conditions during  the  regeneration  steps for each  half-
    cycle were a system pressure of 129 kPa, a bed  temperature of  1100'C, a  fluidizing-gas
    velocity of -,1.2 m/s, a total reducing gas concentration of -.3.07. in the dry  off-gas,
    and a fluiuized-bed height of i.A6 cm.  The residence  time of the sorbent in the regen-
    eration reactor was nominally -*-7 min.
    
    Sulfur Acceptance during Combustion
    
           The cyclic calcium utilization (i.e., the percent of unsulfated CaO that vis
    sulfated during each combustion half cycle) and the percent of the calcium present as
    CaSO,, in the sulfated sorbent product for each  combustion half-cycle are shown  in Fig.
    11.  The cyclic calcium utilizaticn decreased from  --30% during the first cycle  to --9Z
    in the tenth cycle.  Thus, in order to maintain a constant sulfur retention of  8A*.. it
    was necessary  co increase the CaO/S ratio, which was  --2.97. during the first combustion
    cycle, by a factor of r>-3 over the ten utilization cycles.  This  loss of  reactivity
    agrees closely with the loss of reactivity observed for the experiments with  Tymochtee
    dolomite.
    
           TGA sulfation experiments were also performed  on regenerated samples frcr. this
    cyclic experiment.  The results, also shown in  Fig. 11, were obtained at a reaction
    temperature of 855ฐC and atmospheric pressure,  using  a simulated flue gas of  0.37. S0;.,
    3% 02, and the balance N2.  Agreement of the TGA data with the PDJ combustion results
    was very good.
    
    Sulfur Release during Regeneration
    
           Results for the regeneration step of the ten cycles were  similar to those for
    the Tymochtee  experiments.  The S02 concentration in  the dry off-gas varied from 6.1
    to 8.6%, and the extent of CaO regeneration varied  from A9 to  737. during the  ten cycles.
    The regenerability of the limestone remained acceptable for all  ten cycles.
    
    Porosity of Limestone as a Function of Utilization  Cycles
    
           Porosity effects, as would be expected, were essentially  the same as those
    observed during the Tymochtee series of experiments.
    
           The porosity of sulfated lime'-tcne was relatively unaffected by utilization
    cycle, although the sulfur content decreased from 1,8.9 vt % to tA.l wt 7..  The porosity
    and sulfur content of the regenerated stones decreased with utilization cycle.   Most
    of the porosity loss was experienced in the first six cycles.   This loss can  be  attri-
    buted to the high-temperature (1100ฐC) exposure of  limestone in  the reducing  environ-
    ment of the regenerator.  As a result of the loss of beneficial  porosity, internal
    particle diffusion and reaction with S02 were limited.
                                              788
    

    -------
                                                PERCENT Of CALCIUM AS CeSO4
                                                IN SULFATEO MATERIAL
    
                                                D 6 in COMBUSTOR DATA
                                                •TGA DATA
                                      CYCLIC CALCIUM UTILIZATION
    
                                      O 6 in COMBUSTOR DATA
                                   —  • TGA DATA
                                              466
                                              COMBUSTION CYCLE
                              Figure 11. Cyclic Calcium Utilization for Greer Limestone.
                                      Sulfur retention maintained at 84%.
    Coal Ash Buildup  during Limestone Utilization Cycles
    
           The extent of  coal  ash buildup was again calculated on  the basis of silicon
    enrichment in the sorbent  particles.   It was found that every  100 g  of  starting virgin
    limestone accumulated -<25  g of coal ash in ten cycles.  In the Tymochtce dolomite
    cyclic experiment,  in comparison, -.13 g of coal ash was accumulated  for every 100 g
    of starting virgin dolomite.   Arkwright coal, which was used in  the  cctr.justibn (sui-
    fation) steps of  that cyclic experiment, contains considerably less  ash. 7.7 wt ?„.
    than does Sewickley coal,  12.7 wt 7,.   In both cyclic experiments, most  of the ash was
    probably accumulated  during the combustion steps (where the sorbent  is  exposed to much
    more coal), rather than in the regeneration steps.
    
           Sulfated and regenerated limestone particles from the first and  tenth utilisation
    cycles were examined  with  a low-magnification microscope for riacrofeatures.   Particles
    from the tenth-uti.lization-cycle sample appeared to contain m.ore ash than did the
    first-cycle particles.   However, not  all particles were encapsulated with coal ash, as
    was the case with particles from the  cyclic dolomite experiments.  Many or the tenth-
    cycle Greer limestone particles were  visually identical to first-cycle  particles, which
    would indicate that the ash layer thickness was not increasing and that much of the
    coal ash was present  as individual particles in the bulk utilized limestone.   The
    results suggest that  the maximum ash  buildup to be expected when using  Gteer limestone
    and Sewickley coal is ^20  wt 7ป (-v.25 g ash per 100 g of virgin  limestone) in the utilized
    stone.
    
    Attrition and Elutriation  cf Limestone Particles during Regeneration and b.'.fatior.
    
           The sorbenr  losses  from attrition and elutriation of the  limestone particles
    have been determined  for the sulfation and regeneration steps, and the  data are given
    in Table V.  The  limestone losses caused by attrition averaged "-2.07. in each regener-
    ation step.  During sulfation,  the loss was '.20% in the first  cycle  and steadily
    decreased to *•ฅ/,  in the final cycles.  The greater attrition loss in the first sulfation
                                               789
    

    -------
                   Table V.  Losses of Grcer Limestone Caused by Attrition
                             and Elutriation during Sulfacion and Regener-
                             ation Steps in the Cyclic Utilization Study
    
                             Loss = 100 ฃ
    
                             A = Ca in feed limestone (sulfated or regen-
                                 erated) .  kg/h
                             B = Ca in particles collected froa off-gas.
                                 kg/h
    Cycle No.
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    
    Limestone
    Sultation
    20.0
    12.0
    9.2
    7.4
    8 6
    3.6
    4.3
    3.8
    2.6
    4.9
    Avg. 8.2
    Loss. %
    .-^generation
    2.9
    0.6
    _
    1.3
    .
    2.9
    2.0
    1.6
    2.4
    1.5
    1.9
    step can be attributed to calcination.   In subsequent cycles, the resistance of the
    particles to attrition increased because of (1)  sulfite hardening and (2) the partial
    sintering which occurs at the regeneration teaperatuie.
    
           The losses during sulfation were slightly hight-r in the Greer licjestone
    cyclic experiment than in the Tymochtee dolcaite exj;eriaent.  However, combustion
    conditions differed in these experiments.  The Greer li_-.estcae was fully calcined at a
    system pressure of 308 kPa and a bed temperature of 853*". whereas the Tymochtee
    dolomite was not fully calcined at 810 kPa and 900ฐC.
    
           The combined losses for Greer limestone caused by attrition and elutriation per
    cycle averaged ->-107..  Therefore, a fresh Greer limestone makeup rate of at least '-107.
    will be needed to replenish losses.  A higher nakeup rate cay be required to maintain
    the S02-sorption reactivity in the fluidized bed of the boiler.
    
    Estimate of Crccr Sorbent Makeup Requirements to Meet EPA Sulfur Emission Linit
    
           Figure 12 shows the effect of varying the fresh-to-tocal CaO combustor feed ratio
    on the amount of fresh and total Greer sorbent feed nee-ded to capture 757. of the S02
    formed.  The derivation for this figure is tne same for the Tymochtee dolomite cyclic
    study reported here.6  For comparison,  data from a cyclic experiment with Tysochtee
    dolomite, Arkwright coal, and a combustion system pressure of 8 atm are also presented.
    Although the curves for Tymochtee dolomite and Greer limestone have sicilar shapes,
    the Creer limestone curves are higher by a factor of three ซ-n a molar basis, because
    of the lower reactivity of Greer.  On a mass basis, the difference is not as great, but
    more Greer limestone than Tymochtee dolomite is  still required. The reactivity data
    for Tymochtee dolomite was obtained during sulfacion experiments at 8 ac=i instead of
    1 atm.  ..Hence, the sulfation reactivity data predicted for Tycochtee dolomite for an
    atmospheric boiler may be high.  Also,  the reactivity data for Greer licฃstone was
    obtained using Sewickley coal (4.3 wt 7. S) instead of Arkwright (2.7 wt % S) coal, and
    thus the required sulfur retention was 837. instead of 75%.  Thus, the difference
    between theoe two sorbcnts is not as great suggested by the curves in Fig. 12.
    REGENERATION PROCESS FLOWSHEET DEVELOPMENT
    
    Process Flowsheet for a 200-MW FBC Process
    
           A pr"cess flowsheet for a 203-MWe FBC process with sorbent regeneration has been
    developed based on the performance of Greer licestone in the ten-cycle experiment.  The
    
                                               790
    

    -------
                                         0.2   0.4   O.6   O.B
                                         MAKE-UP CflO/TOTAL CflO
                                                              1.0
                              Figure 12. Effect of Makeup-to-Total CaO/S Mole Ratio
                                     Required for 75% Sulfur Retention. Greer
                                     Limestone and Tymochtee Dolomite.
    following base conditions are assumed  for  the boiler:   242 m2 (2600 ft2) distributor
    plate area, 3.05 m/s (10 ft/sec)  fluidizing-gas  velocity,  3% oxygen in the flue gas,
    and combustion of 1620 !1g/day (loOO  tons/day) of Sewickley coal,  which contains 4.3 we
    7, sulfur and has a heating value  of  28,500 kJ/kg (122aO Btu/lb).
    
           A process flowsheet for the above boiler  conditions and a  fresh -orbent feed
    CaO/S ratio of 1.14 is given in Fig. 13 and Table VI.   The combined (virgin plus regen-
    erated) limestone CaO/S feed ratio is  --5.69.  In the  absence of regeneration, a CaO/S
    feed ratio of '-3.78 would be required  for  Greer  limestone  based or. the previously
    described reactivity data.
    
           Sulfated limestone (1152 Mg/D or 1311 I/D) is  assumed to be introduced into the
    regenerator at lla.6 K (1550T) . the  temperature  in  the  fluid bed  of the boiler.  The
    fluidizing gas velocity in the regenerator of 1.4 m/s  is T.12% greater than the predicted
    velocity required to prevenf agglomeration of sorbent with a mean size of 1500 -_m
    (-1/8 in.) when it is regenerated at 1100ฐC with 27. total  reducing gas in the regener-
    ator off-gas.  The fluidizing gas to the regenerator  is assumed to be heated to 400ฐC
    by waste heat recovered from the  regenerator off-gas.
    
           The coal consumption by the regenerator reactor  with 843ฐC solid and 400ฐC gas
    feed streams was estimated to be  60  Mg/D (66 T/D).  The fuel consumption by the entire
    regeneration process is obtained  by  adding the coal fed to the regenerator, 77 Mg/D
    (85 T/D), to the sulfur recovery  step, 23  Mg/D (25  T/D). and subtracting the fuel
    credits for the regenerator flue  gas cyclone product,  15 Mg/D (17 T/D), and the sensi-
    ble heats of the regenerated sorbent,  13 Mg/D (14 T/D),  and tail  gas stream from the
    sulfur recovery step, 12 Mg/D (13 T/D) that will be routed to the boiler.  The SO;
    concentration in the regenerator  off-gas is predicted  to be 9.7%  (dry), and the gas
    Distributor area for the regenerator is predicted to be 14.0 m2 (150 ft2).
    
    Effect of Makeup CaO/S Feed Rates
    
           Flow diagrams containing mass and energy  flow  streams have been obtained for
    different process conditions.  These calculations are  intended to evaluate the effect
    
                                               791
    

    -------
           MRTICULATE
            REMOVAL
                     TO ATMOSPHERE
                                           AIR 295ฐK .
                    95 Mg/D SULFATED"
                     SORBENT
               18 Mg/0 UN8URNED CARBON
               136 Mg/D ASH
                                 OFF-GAS
                                 653 Mg/D
                                          AIR
                                        HEATER
                                                      -MRTICUi_ATE
                                                        REMOVAL
    
    
                                                        23 Mg/D COAL
                                                        >3Mg,
          a
          0
    
    
          R
              REGENERATED
                SORBENT 1025 Mg/D
      THERMAL CREDIT-
       13 Mg/D COAL
    
     SULFATED SORBENT
    1324 Mq/D  1152 Mq/p
           I36OO Mg/D AIR
                                                _
                                       ffi— HT
                                        675 ฐK    V
                                    435 Mo/D
                                      AIR
    
    
    SULFUR
    RECOVERY
    (90%EFF)
    
    50 Mg
                                                              920ฐK
                                                         ELEMENTAL
                                                          SULFUR
                                                       29 M'/0
                                                    REGEN. SORBENT
                                                       18 Mg/D
                                                   UNBWED CARBON
                                                    THERMAL CREDIT
                                                     (RECYCLED TO
                                                      COMBUSTOR)
                       DRAW OFF
                       I72 Mg/0  145 Mg/D SULFATED STONE
                            ^  27 Mg/0 ASH
      — COAL 1630 Mg/D
    
    	FRESH SORBENT 3IO Mg/D Co/S • I.I
    
    
                 Figure 13. Process Flowsheet for a 200-MW FBC Process
         Table VI.  Base  Conditions  for  Flowsheet  (Fig.  13)
                                    Greer limestone
                                    307.  C=CO,
                                    20%  Inert
    Coal
    
      Sewickley coal
      2B500  kJ/kg (12250 Btu/lb)
      4.3% S
     ' 10.0%  Ash
    
    AFBC Boiler
    
      200 MW @  37% conversion  efficiency  (9200 Btu/kWh)
      Bed temperature. 1120 K  (1550ฐF)
       Pressure.  100 kPa (1 atm)
       Bed area.  242 m2 (2600  ft2)
      Combustion  efficiency, 99%
      Sulfur removal, 837.
    
    Regenerator
    
      BeJ temperature. 1375 K  (2000ฐF)
      Pressure,  100 kPa (1 atm)
      Bed area,  14 m2 (130 ft')
      bed height.  0.55 m (1.8  ft)
      Gas velocity, 1.4 nt/s (4.5  ft/sec)
      Solids residence time, 7 min;  extent of regeneration. 657.
      Total  regeneration system  fuel burden  = 60 Mg/D (66 T/D)
        (i3.6 of  coal fed to the  combustor)
    
    Composition of Regenerator Flue  Gas
    
       8.9%  S02
       2.0%  CO
      19.6%  CO2
       8.7%  H20
      60.7%  N2
                                 792
    

    -------
    of makeup CaO/S feed rates  (feed race of virgin  limestone into the system) to the
    boiler on the size of the regeneration system, on  the  S02 concentration in the regen-
    erator off-gas, and on the  fuel burden of sorbent  regeneration on the boiler or power
    plant.
    
           Figure 14 shows the  effect of the fresh-to-total  CaO combustor feed ratio on
    SOj concentration in the regenerator off-gas and on  the  total  regeneration system fuel
    burden.  The S02 concentration increases quite quickly but  levels  out;  the fuel burden
    decreases quite steadily.   At high fresh limestone maKeup rates,  the size of the regen-
    eration system decreases and the amounts of fresh  limestone feed  and waste sulfated
    limestone increases.  Consequently, the fuel required  for the  regeneration and sulfur
    recovery steps decreases.   Therefore, a decision on  optimum operating conditions must
    be made on the basis of economics.
    
           The effect of makeup (fresh sorbent) CaO/S  mole feed rate  to the boiler on the
    operating conditions and size of the regeneration  system was evaluated ana is shown
    in Table VII.  As the makeup CaO/S feed ratio was  varied from  0.81 (107. of the total
    CaO/S feed) to 1.47 (30% of totoal CaO/S feed),  the  mass rate  of  sulfated stone that
    has to be regenerated decreased from 1881 Mg/D (2074 T/D) to 1076 Mg/D (1186 T/D),
    the sorbent waste stream (combined elutriated and  draw-off soibenn) increased from
    204 Mg/D (225 T/D) to 371 Mg/D (409 T/D), and the  size of the  regeneration system
    decreased by a factor of about two.  The coal required for the regeneration step de-
    creased from 85 Mg/D (92 T/D) to 53 Mg/D (58 T/D).   (The boiler coai. consumption is
    1630 Mg/D (1800 T/D)].  The S02 concentration in the regenerator  off-gas increased
    fi.om 9.0% to 10.087. over the same range of CaO/S makeup  ratios (0.81 to 1.47).  Reducing
    the power plant's fresh sorbent requirements (and  its  spent sorbent waste stream) in-
    creases the size of the regeneration and sulfur  recovery system,  decreases the SO;
    concentration of the regenerator off-gas (which  increases "the  cost of sulfur recovery) ,
    and increases the fuel burden of the regeneration  step on the  boiler,  A sorbent make-
    up rate can only be chosen  on the basis of an economic evaluation.
                                   Figure 14. Effect of Fresh CaO to Total CaO
                                          Feed Ratio to Combustor on S02
                                          Concentration in Off-Gas and Total
                                          Fuel Burden of Regeneration System
                                               793
    

    -------
                 Table VII.  Predicted Effect of Makeup CaO/S Mole Feed Ratio
                             Using Greer Limestone,  on Regeneration System
                             (200-MW FBC Boiler)
                             Regeneration Conditions
                               T = 137i K (2000ฐF)Kxtent of regeneration = 65%
                               P = 100 kPa (2 atm)  Solids Residence Time = 7 min
    Cou'.bustor
    Mole
    CaO/S Feed
    Ratio
    Mass"
    Makeup Total
    0.81 8
    1.14 5
    1.47 4
    *kg feed
    "includes
    Includes
    .06
    .69
    .89
    Makeup
    3.13
    4.42
    5.70
    Total
    26.89
    18.99
    16.42
    Sorbent
    Feed to
    Regen. .
    Mg/D
    1881
    1190
    1076
    Draw-
    Off to
    Waste.
    Mg/D
    204
    290
    371
    limestone/kg S in coal.
    elutriated and draw-off sorbent.
    thermal credit for hot regenerated
    Coal
    Used
    in
    b Regen. ,c
    Mg/D
    83
    65
    53
    sorbent.
    Regen.
    Bed
    Area,
    m2
    19
    14
    11
    
    Regen .
    Bed ht,
    m
    0
    0
    0
    
    .64
    .55
    .52
    
    S02
    Regen.
    Off-Gas
    (dry) ,
    7.
    9
    9
    10
    
    .00
    .74
    .08
    
    CONCLUSIONS
    
           Reductive decomposition of CaSOt, at 1100ฐC in a fluidized bed is a technically
    viable process for regenerating CaO for reuse in the combustion process.  Sutticient
    regeneration is obtained in a short time (a few minutes)  that the regeneration reactor
    can be relatively small.  The S02 concentration in the off-gas is sufficiently high
    that the sulfur can be recovered using commercially available processes.  Data from
    the cyclic studies and flowsheet studies have demonstrated that the quantity of stone
    required per ton of coal processed is significantly less  (-v.1/5) when the stone is
    regenerated than when the stone is used only once and then discarded.  Costs of the
    regeneration process and the once-through processes must  be compared to determine
    economic viability.
    
    
    ACKNOWLEDGMENTS
    
           We gratefully acknowledge support cf this program  by the Department of Energy
    and the Environmental Protection Agency.
    
    
    REFERENCES
    
    1.  G. J. Vogel et al.. "Reduction of Atmospheric Pollution by the Application of
        Fluidized-Bee Combustion and Regeneration of Sulfur Containing Additives," Argonne
        National Laboratory. Annual Report. July 1972-June 1972. ANL/ES-CEN-1005 Q973).
    2.  W. Swift. A. Panek, A. Smith. G. Vogel, and A. Jonke, "Decomposition of Calcium
        Sulfate:  A Review of the Literature," Argonne National Laboratory. ANL-76-122
        (19V6).
    3.  J. C. Montagna et al.. "Fluidized-Bed Regeneration of Sulfated Dolomite by
        Reductive Decomposition with Coal," 69th Annual AIChE Meeting, Chicago, Nov.  28-
        Dec. 2. 1976.
    4.  J. Montagna, F. Nunes. G. Smith, G. Vogel, and A. Jonke. "High Temperature
        Fluidization and Agglomeration Characteristics of Limestones and Coal Ash Particle
        Systems." American Institute of Chemical Engineers Meeting, New York City, November.
        1977.
    5.  W. Zielke et al. , "Sulfur Removal .during Combustion of Solid Fuels in a Fluidized
        Bed of Dolomite," J. Air Pollution Control Assoc. 20(3), 164-169 (Ir70).
    6.  N. F. Nagiev, "The Theory of Recycle Processing in Chemical Engineering," Vol. 3,
        International Series of Monographs on Chemical Engineering, McMillan, New York
        (1964).
    7.  M. Hartman and R. W. Coughlin, "Reaction of Sulfur Dioxide with Limestone and the
        Influence of Pore Structure," Ind. Eng. Chem. 13(3),  248 (1974).
                                              794
    

    -------
                 QUESTIONS/RESPONSES/COMMENTS
    
    
         VR. DAMAN:  Don't kill  yourself.  Thank you, John.  I think
    you have some questions here.
    
         DR. VOGEL:  Our contract  number  is W-31-lOS-ENu-.  .  I h*ve one
    question here from Dr. Hill, Brookhaven National Lab.   "In your
    future work, what equipment  other  than a  fluidized bed  ao you plan to
    investigate?  And please discuss reasons  for the choices."
    
         We plan to investigate  the use of an externally  fired, rotary
    kiln.  And the reason for that is, v/el 1,  we actually  have a couple of
    reasons.  In our fluidized bed unit, we lose heat through the walls
    which means that we have to  add more coal to make up  this heat loss.
    This effectively reduces our S02 concentration  in the off gas.  If
    we use an externally-fired,  rotary kiln,  we think we  can increase the
    S02 concentration in the off gas to 16 or 17 percent.   The other
    reason for working with the  kiln is that  we want to study solid-solid
    reactions.  The calcium sulfate and the calcium sulfide reaction and
    the calcium sulfate and carbon reaction lend themselves to a kiln
    operation.
    
         The other question is from Dr. Steinberg, also from Brookhaven.
    "What is the effect of limestone sulfation and regeneration on the
    coal utilization efficiency  for power production i:i the process you
    describe?"
    
         Well, I can't give you  a  simple answer.  It's true you can pick
    how far you want to sulfate  the particle  and how far you want to
    regenerate the particle later  and these do affect the amount
    of coal  that you use.  I showed you a schematic of a  flow sheet, and
    that was just one case.  There are any number of cases  that are being
    looked at and I can just give  you a broad range of coal utilization
    efficiency.  In the case that  you saw there, if you have a coal  pile
    sitting by the utility plant,  approximately 3 percent of that coal
    is going to be used in the regeneration process while 97 percent is
    going to be used for power production.  Now, you can  change conditions
    in the regenerator, larger regenerator or sraller, and you can affect
    this coal utilization.  You  can use as little as one  or one and
    a half percent coal in the regeneration step and have approximately
    99 percent for power production.  And there are cases where 5 or 6
    percent coal is used in the  regeneration  step and only 95 percent
    in production.   It comes down  finally to  an economic choice.  You've
    got to go through all the cases and find  out which one  is the most
    economic.
    
         MR. DAMAN:  Thank you,  John.
    
                                    795
    

    -------
                             INTRODUCTION
         MR. HARVEY:  There are  three streams  of waste material that pro-
    ceed from the fluidized bed  combustor.   One is feed material, one is
    intermediate fly-ash and the other of course, is final fly-ash.  Now
    we really haven't considered that intermediate fly-ash, have we?
    We said we've got to put that back in the  bed because  it's unburned
    carbon.  But unburned carbon to us is activated carbon to others and
    that has a market value.  So I don't think we're ready at this stage
    to say what the final outcome of all these waste materials is or will
    be.
    
         Generally, we say there are three  things we can do with this
    waste material.  We say we can dump it  discreetly.  We can utilize it.
    Or we can regenerate it.  The only reason  in tfee world we regenerate
    it is because we say that this means we won't use as much of it.  If
    we regenerate eventually we  have to throw  something, away, and that
    takes us back to the other two.  I think it's interesting this after-
    noon, of the eight papers, the score is four for regeneration, two for
    dumping and two for utilization.
    
         I'm extremely pleased to be able to introduce to  you the cochair-
    man of the afternoon.  When  it comes to v.aste utilization, the man who
    will now introduce the speakers is as qualified to chair or speak
    during this session as anyone I know.  The man is John Faber and he is
    Executive Secretary of the Notional Ash Association here in Washington,
    D.C.  John?
    
         MR. FABER:  I think this ii like a Las Vegas show.  Bill and I
    are the warmup for the dog and pony show that comes a  little later.
    You've already screwed up.  It's "utilization and disposal" not "util-
    ization and regeneration."  I've got to get that in there to get my joke
    in.  Of course, when you talk about disposal, you want the highway
    engineer to take care of it  and you want the Department of Natural
    Resources to take care of it and three  or  four other people you want
    to take care of it as you produce this  gold plated material.  And it's
    kind of reminiscent of a football game  we  had a couple of years ago up
    in West Virginia with Pitt.   Pitt came  down to Morgantown and we had
    things going pretty good. We had a little boy by the  name of Tommy
    Jones.  He was just tearing  them up. Every three or four plays, why,
    he'd make five or six yards  and then they'd pass or something and the
    crowd got the bit on this thing and they'd say give the ball to Tommy
    Jones, like we want to give  this material  to the highway man.
    
         So this went on in the  first half  and we have done pretty good
    but Tommy Jones was getting  a little tired.  Cone back the second half
                                     796
    

    -------
    and the same thing started.  A couple of pass plays and the crowd
    started up.  Give the ball to Tommy Jones.  Well, they came back to
    the huddle and all at once Tommy Jones came out and called time with
    the Ref and ran over to the side and got hold of the public address
    system and said "Tommy Jones don't want the damn ball."
    
         So that's where we're at now with some of these materials we're
    trying to give the highway engineer.  Perhaps this afternoon we'll
    find some information that will make him more receptive to carry the
    ball for us.
    
         Our first speaker this afternoon is Dr. Ralph Yang.  He is
    presently with Brookhaven National Laboratories.  And he is a moder-
    ator's dream because his biological sketch is half a line long.  Ralph
    T. Yang, Ph.D, 1971, from Yale University.  Worked at NYU, Argonne
    National Laboratories and Alcoa before joining Brookhaven.  That tells
    you all about him.  He's a young man and when you get my age you hate
    all of them so there's not much else you can say for them.  There is a
    correction ' would like to make.  If you'll turn to page 16 in the  sum-
    mation of Dr. Yang's presentation on your program.  The last sentence
    in the program reads "five percent S0ฃ was obtained from the regen-
    erator at 1100ฐC kiln temperature."  That should be 1000ฐC kiln temper-
    ature.  Dr. Yang's presentation this afternoon will be Regeneration
    of Lime-Based Sorbents in a Kiln with Solid Reductants.  Dr. Yang.
                                     797
    

    -------
                                  Regeneration of Lime-Based Sorbents
                                       in a Kiln with Solid Reductants
                                  Ralph T. Yang, James M. Chen. Gerald Farber,
                                     Ming-Shing Shen, and Meyer Steinberg
                                     Department of Energy and Environment
                                         Brookhaven National Laboratory
                                                  Upton, N.Y.
    ABSTRACT
    
           1'rocesses based on apparent  solid-solid  reactions  In a kiln-type reactor for regenerating the
    lime-based sorbents are being developed  at our  laboratory.  The specific process investigated is to
    react the sulfatcd lime with fly ash,  both from the  f luldlzed-bed combustor (FBC).  The unburr.t carbon
    In the fly ash Is used aซ the reductant.
    
           Eight-cycle sulfation-reqencratlon based on this scheme has been experimented using Greer lime
    and fly ash from Argorne's 6-lnch FBC  as the starting materials.  The apparatus Included a rotary-kiln
    regenerator and a fluidlzed-bed sulfator, both  with  a i:a.  10-gram capacity and made of quartz.  The
    kiln temperature was 1000rO in the  cyclic experiments.  The SC^ concentration reached the thermodynamlr
    equilibrium values at slow gas flow rates.  The reactivity of the regenerated sorbent did not cecay
    appreciably after eight cycles; it  actually tended to increase due to the impurities absorbed in the
    kiln.  Completion of the regeneration  of the 30^-sulfated stone from FBC CGuld be reached in an hour
    with a time-averaged SO, concentration of 52 from the kiln.  Attrition in the kiln is much less than
    in a FB regenerator.  More results  on  the kiln  regeneration are presented in this paper.
    
    
    INTRODUCTION
    
           A major advantage of the f lu idlzed-hcd combust lor with lime additives is Its ability ti> burn 1:0.1!
    cleanly and to produce economically a  desulfurized hot gas.  Recognition of the potential of this tech-
    nology has accelerated extensive efforts In research and development In this area.  For environmental
    and economical reasons, however, the regeneration of the  lime additive.*; from the spent stone must bu
    considered.  The state of the art.  Including the major problems involved, has been recently reviewed.
    
           The only major process which Is currently under serious consideration Is the reductive decomposi-
    tion scheme based on the Wheelock-Kent Feed?; Process.*•  This process is being modified and developed
    further for application in fluldlzed-bed combustion  by Argonne National Laboratory' and Exxon Research
    and Engineering Company.^  Briefly, the  process consists of fluidizlng the partially sulfated particles
    with reducing gases at a relatively high temperature to produce lime and sulfur dioxide.
    
           In the regeneration processes,  two Important  factors are:  (1) rates of regeneration and (2)
    SC>2 concentration In the pas ph.ise. Because of the  high gas velocity required for fluidlzatlon In the
    Argonne-Exxon process, the SO^ concentration is kinetlcally controlled, and It is substantially lower
    than the thermodynamlc equilibrium  values.$  For example,  to produce an economically sulfur recoverable
    gas, e.g., greater than 52, fInidlzatloii regeneration requires an operating temperature of 1100ฐC, and
    the temperature has to be even higher  for the pressurized systems.  At such high temperatures, the
    problems of sorbent deactlvation, bed  agglomeration, attrition, etc. all become serious.
    
           The specific process that is being Investigated at Brookhaven is to react the partially sulfated
    lime with the fly ash from the f luldlzed-bed combustor in a kiln-type reactor.  The fly ash contains
    significant amounts of unburnt carbon  which is  used  as the reducr.ant for regeneration.  The basic chem-
    istry of this process is:
    
                                     CaS04 + 1/2C  •* CaO +• 1/2C02 -t- S02                               (1)
    
           This reaction has been the basis  for manufacturing sulfuric acid snd cement from anhydrite in the
    European countries.   Recent studies by Turkdogan and Vlncers7 and by Yang et al.8 have shown that the
    amount of carbon is the controlling factor for  determining the reaction product, i.e., CaS vs. CaO, and
    that the reaction proceeds in two consequent steps:
    
                                            CaS04  + 2C  -ป CaS + 2C02                                  (2)
    
    
    
                                                      798
    

    -------
                                          CaS + 3CaS04 - 4CaO + 4S02                                (3)
    
    with reaction (3) as the rate-controlling step.
    
           The equilibrium partial pressure of SO-, PSQ,< based on equation  (3), as a function of tempera-
    ture  Is given In Figure 1.  This equilibrium partial pressure limits the maximum SO, concentration in
    the regeneration process as well as In some other regeneration schemes.^  Cyclic sulfation-regeneration
    using coconut charcoal as the carbon reductant In Reaction (1) for the regeneration step has been stud-
    lei with a TCA system.   After ten sulfatIon/regeneration cycles, the reactivity of the material re-
    mained the same as that of the raw lime.  Also, the kinetic and mechanistic studies showed that the
    rates of reaction (3) is strongly dependent upon temperature, and both steam and sodium chloride catalyze
    the lime regeneration process.  The catalytic effects on lime sulfation by sndlura chloride  anc] by
    steam'" are well known.
    
           This paper will present our results on the 8-cycle sulfation-rei;en
    -------
                                    T.ฐC
    
             1150         1030            950
     1.0 c~
    Iff1
    Iff-*
    1ff3
              0.7
    0.8
    
    
    1/T(oK)x 103
                                                                09
               Figure 1. Equilibrium Partial Pressure of SO2 for Lime Regeneration;
                       1/4CaS+3/4CaSO4   CaO + SO2
                                      800
    

    -------
       oo-
                                        Preheater
       S02
                                                                         FB Sulfator
              Flow Meter
                             Figure 2a. Schematic Diagram of Fluidized-Bed Sulfator
                                                                 Vacuum
                Purifier
                                                                      Sampling Bulbs
                                                                  H	•• To Scrubber and Flue
    Rotameter
                                        Furnace
                        Figure 2b. Schematic Diagram of Rotary Kiln Regenerator
                                              801
    

    -------
    wet chenical and thermal decomposition methods.  It was found that the weight loss of the solid samples
    In N- flow In the temperature range of 1100ฐC ro 1200ฐC was correspondent (within 3/0 to the SO^ con-
    tent (of CaSO.) determined by the ASTM method.  In this study, the thermal decomposition method was
    therefore adopted for the purpose of time saving.  A high temperature TfiA system was used accordingly
    to measure both the contents of CaS and CaSO, In the solid samples.  About 60 mgs sample was used for
    each analysis.
    
    
    RESULTS AMD DISCUSSION
    
           Regeneration experiments at temperatures ranging from 950ฐC to 1050ฐC and with flow rates (Ar)
    ranging fron 10 SCCM (9.5 cm/mln) to 150 SCCM (142 cra/mln) have been made.  In all these experiments
    four grams of the sulfatcd stone were used.  The off gases were found to be predominantly SO,,, CO., and
    Ar.  The temperature effect on the SO- concentration was measured using low carrier gas velocity TlO
    SCCM).  Results of the SO. fraction and C02 fraction at various times are Riven In Figures 3 and 4,
    respectively.  These figures clearly indicate that reaction (1) is a two-step reaction, and reaction
    (3) Is the slower rate step, and this phenomenon Is more obvious at lower temperatures; e.g. 1 = 950ฐC.
    
           As mentioned, the "kiln temperature" Indicated in this report was measured at the center line
    of the kiln near the head of the regeneration zone.  After elaborate temperature measurements, with
    both thermocouples and an optical pyrometer, temperature gradients were detected In both the axial and
    the radial directions of the kiln.  The temperature Increased by 15 to 20ฐC alone the c-.encer line in
    the gas passage direction and the temperature of the quartz wall was about 15ฐC higher than that at
    the center line.  Results on the SO7 concentrations should be, therefore, studied with the understand-
    ing of the non-uniformity of the temperature distribution.
    
           Figure 3 gives the history of the SO- concentration of the off gas at three kiln temperatures.
    The results clearly indicate that the thermodynamic equilibrium partial pressures of SO- (cf. Figure 1)
    were reached at the gys velocity of about 9.5 cm/mln.
    
           The dependence 01 the SO  concentration on the carrier gas velocity was measured at 1000ฐC.
    Figure 5 shows that Increasing carrier ฃas flow rate decreases the SO., concentration.  Froa the data
    shown in Figure 5, the approximate curves of the overall extent of regeneration as a function of time
    ;it different flow rates were calculated.  These results are compared with the limiting regeneration
    rates measured in the TCA system (wt.: 100 mg, flow rate: 500 SCCM) in Figure 6.  It Is clear that the
    regeneration rate is suppressed by the SO, concentration in the gas phai.e.  By increasing the carrier
    gas flew rate, the regeneration rate is increased.  From these figures, one can see that high regener-
    ablllty with short solid residence time and with high S02 concentration In the off gas c^n be obtained
    from this regeneration process.  However, the operating conditions would have to be opt Ini-:..-.! with
    consideration of the trade-off between the higher SOn concentration and a shorter solid residence time.
    
           To tent the reactivity of the regenerated ma'crlal, eight cyclic sulfatIon/regeneration reactions
    have been made.  Sulfatlon rctes were measured In tne 30 mm fluldlzed-bed sulfator.  The reactivity was
    determined based on the fractional uptake of SO., after 5 hours of sulfation time.  Also, in order to
    compare with the reactivity of the raw sorbcnt, Greer lime was used as the starting material.  The
    experimental conditions for both sulfation and regeneration arc shown In the following.
    
           Sulfation
                Temperature:  850ฐC
                Starting material:  Creer lime (prccalcincd at 900ฐC)
                         weight:    10 grams
                         size:      16/20 mesh
                Superficial velocity:  5 ft/sec
                Gas composition:  SO?: 0.252, 0-: 5%, N- balance
                Time:  5 hrs
    
           Regeneration
                Temperature:  1000ฐC
                Material:  Sulfated Creer -I- coal ash (size 200/270 mesh)
                Time:  2 hours    Flow rate (\r): 100 SCCM
    
           After each sulfation/regeneration run, a small portion (about 60 mg) of the sample with size
    16/20 mesh was taken out for analysis of the contents of CaSO, and CaS.  Also, to assure having high
    extent of regeneration, the regeneration period was kept for two hours.  The results of the SOj content
    In the solid sample for the eight cycles are given in Figure 7.
    
    
    
                                                       802
    

    -------
         0.3
         0.2
    s
         0.1
                               10
                                       15      20
                                        Time, min.
                                                      25
                                                              30
                                                                      35
                                                                             40
           Figure 3. Temperature Effect on the Partis) Pressure of SO2 in the Kiln
                    Regenerator; Gas Flow Hate (Ar), 10 SCCM. Tc = 1050-1070" C (D).
                    Tc = 1000 1020 C (D). Tc = 950 970 C (0). Tc was measured along
                    the center of the reactor tube. 4 grams of suHated Greer lime
                    (16/20 meih) from Argonne'c FBC were used.
    5
    <
     CM
    o
               •J.I
               0.6
              0.5
              0.4
              0.3
              0.2
              0.1
                                    10
                                            15      20
    
                                         Time, Min.
                                                            25
                                                                   30
                                                                           35
               Figure 4. Partial Pressure of CO2 from the Kiln Regenerator. Gas Flow
                       Rate (Ar): 10 SCCM. Tc • 1050-1070^C (G). Tc -1000 1020'C
                       (A). Tc = 950-970'C (0). 4 grams of sulfated Greer lime
                       (16/20 mesh) from Argonne's FBC were used.
                                           803
    

    -------
             i      r
    I       r
                           >0    15     ?O     ?b
    Figure 5. Gas Flow en the SO2 Concentration at Tc * 1000-1020ฐC from
            the Kiln Regenerator, Flow Rates (Ar): 10 SCCM (A). SO SCCM
            
    -------
       30%
        20%
    5
    8
         10%
                                                                                   I
               IS     'R   2s   2R   ••ป;>  3R   4S  4j}   5s    5R  65    6R   7S  7R   85
    
                                                  Number cf Cycle*
    
    
                       Figurr 7. Extents of Sutfation and Regeneration of Greer Lime from the
                                Cyclic Sulfator (S) and Regenerator (hi  ConditioftS are Shown
                                in Text.
                                                      805
    

    -------
           This figure shows that for all the regeneration cycles, very high extent of regeneration can be
    reached (88-1007,).  It was also found that the regenerated stone did not contain any CaS.  This indi-
    cated that the regeneration reaction was completed in all the cycles.  This high extent regeneration
    is very encouraging for this regeneration process.
    
           It should be emphasized here that the 2-hr regeneration time used was only to ensure complete
    regeneration of lime so we could study the sulfation char.icteristics in a more meaningful way.  In
    practice, however, the regeneration time can be substantially shortened.  Kor example, based on the
    Integrated .mounts of SO  evolved, over 802 regeneration was accomplished in 1/2 hr at n fiow of 50 SCCM.
                                            o
           The regeneration results at 950"C  perform^u In TCA Indicated the existence of CaS in the solid
    absorbent after 4 hours of regeneration.  The difference in the solid content, compared with the re-
    sults obtained in this study, is very likely due to the difference in reaction temperatures.  Since
    reaction (3) was found to be strongly temperature dependent with about 62 Kcal/mole activation energy,
    by Increasing temperature from 9501 C to 1000ฐC, the reaction rates become 2.7 times higher.  Thus, the
    ซccontl step reaction could be completed in a shorter time.  Other factors such as the extent of sulfa-
    tion of the sorbent and the sources of carbon material may also nffect the reaction rates.'  Snyder ct
    a!.11 have found that by using H, is the rcductant at .:bove 1100ฐC, the only product was CaO whereas
    below 900ฐC. the product was alPCaS.  These results are in line with the above discussion and the
    fact that reaction (2) has a lower temperature dependence, as observed by Turkdogan and Vlntcrs.
    
           Figure 7 also shows a slight decrease In SO, absorption ability of the regenerated lime in eight
    cycles.  To further test the reactivity of the regenerated sorbent, portions of the regenerated samples
    were sulfated la a TCA system.  These results are shown in Figure B indicating approximately 102 de-
    crease in reactivity.  The detrimental eifect of this temperature on the reactivity of the lime sorbent
    Is believed to be lower than the temperature at IIOO"C.  For example, the dolomite regenerated at 1100"C
    was found to he 'MX. lower than the material at 900ฐC.
    
           Attrition experiments were performed to compare the strength of the regenerative  lime with that
    of the fresh lime.  The samples compared were the regenerated lime after eight cycles, which contained
    3 wt Z of SO.j, and the fresh lime precalclned at 900"C, both 16/20 Tvler mesh in particle size.  They
    were fluldizcd with nitrogen gas In a fluidIzed-bed for 5 hours at 850"C with 5 ft/sec superficial gas
    velocity.  Results of the size distribution of the attrituted samples are shk>wn in Table  I.  It Is seen
    that the regenerated lime had a much higher strength than the calcined lime.  Tils is because the re-
    generated lime contained SO,  and some silicates as will he shown later; both would Increase the strength
    of the material.  Also, the regenerated material had been treated at higher temperatures  (iOOOฐC) than
    the fresh lime (at 900ฐC).  The strength of the regenerated material would tnus he higher.  Mere direct
    comparisons on the attrition characteristics arc being made.
    
           Besides the regeneration reactions, many other reactions did indeed also take place In the kiln
    regenerator.  The reactions between CaO and the various minerals in the coal ash are well known to the
    material scientists.  For example, silicates, ferrites, ferrates, aluminates, ferro-si1icatcs, etc. can
    all be formed at below 1000ฐC.  We have found earlier that Ke-iO- catalyzes the sulfation reaction of
    CaO, because it catalyzes the oxidation of SO., to SO .    These reactions arc under investigation in
    the authors' laboratory.  Only some preliminary results will he presented hero.
    
           The sulfaclon rates were compared of a raw Creer line and a kiln-regenerated lime (1000ฐC kiln
    temperature) from the partially sulfatcd Crccr lime from Argonne's KBC.  The kiln regenerated lime
    showed higher reactivity and which absorbed about 30i more SO, at 150 minutes than the raw lime.
    
           X-ray diffraction analysis and atomic absorption methods were used to determine the concentra-
    tions of fhe major Impurities (SI, Fe, and Al) In the limestone particles.  For these analyses, samples
    of Greer limestone particles 06/20 mesh) were screened after each sulfatIon/regeneration experiment and
    the free coal ash and finer particles were sieved out.  X-ray diffraction showed that calcium silicates
    In Creer limestone are present as B-dicalcium silicate form.  It has been reported In our laboratory
    that B-dlcalclum silicate Is a reactive form towards SO-.^  The B-dicalclua silicate was not present
    in Argonne's once sulfatcd Greer limestone while It was present In an appreciable amount as detected by
    x-ray after regeneration of this .sample In our kiln.  Also found in all the Creer limestone samples was
    alpha quartz.  From the x-ray diffraction Intensities, the amount of alpha quartz also Increased In the
    kiln regenerated sample.  Results of the atomic absorption analyses showed that SI, Fe, and Al  all
    increased in the kiln regem-ratIon.   The concentrations were Increased from: 14.502 Si; 0.8*7, Fo,  and
    1.90% Al In the Argonnc sulfatcd stone to:  14.92 SI; 1.162 Fe,  and 2.142 Al In the kiln regenerated
    Argonne stone.  Although these analyses were preliminary In nature and may not be representative because
    only 100 mg sample was used for an analysis,  possible catalytic effects due to the minerals may be the
    cause of the observed Increase In the sulfation reactivity of the kiln regenerated stone.
    
    
    
                                                      806
    

    -------
     0.4
     0.3
    0.2
    0.1
                20
                         40
                                   60
                                            80
                                                      100        120
                                                        Time. min.
    140
                                                                                  160
                       Figure 8. Comparison of the Sulfation Rates between Fresh Lime and
                               Regenerated Lime at T = 900 C. SO2- 0.5%. 02: 5%. N2- bal.
                               Sample: Precalcined Lime (Q). 2nJ Cycle Regenerated Lime
                               (A). 4th Cy-ie Regenerated Lime (0). 8th Cycle Regenerated
                               Lime (VI.
                       180
                                200
                      Table I.  Size Distributions of the  8th Cycle Regenerated Lino
                                nnJ  Fresh Line  after 5 Hours,  of" Fluldlzat Ion at 850ฐC
    Size
    (Tvlcr Mesh)
    16/20
    20/24
    24/f>0
    60-
    Wclsht Pcrcent.-iBe
    Regcnera'.'d lime
    86.1
    13.1
    0.3
    O.S
    
    fresh lime
    30
    20.8
    14.7
    34.5
                                                 807
    

    -------
    CONCLUSION
    
           Results oT regeneration of the sulfdted lime in a kiln using fly ash as the reductants have been
    presented In this paper.   Because of the low gas flow required In this process, high SO. concentration
    ran be obtained at relatively low temperatures In comparison with the fluid tz.it Ion regeneration process.
    The high rrgcnerabilIty In a reasonably short solid residence time, the less detrimental effect of
    temperature on the reactivity of the regenerate*! sorbent and potentially less solid attrition make the
    kiln regeneration process look promts In,;.  The kiln regenerator may also serve the function of the
    c.irhon burn-up cell and thus replaces It.
    
    
    ACK.NQซLEIX;Mfc:.VTS
    
           Discussions and guidance provided by Or. Andfej Macek of the US Department of Ener<;y are ap-
    preciated.  Argonne National Laboratory kindly supplied the materials for our experiments.  The able
    and skillful assistance from Messrs. Frank B. Kalnz and Jacob Pruzansky Is gratefully acknowledged.
    
    
    REFERENCES
    
    1.  A. A. Jonke and U. A. McCurdy, paper No. 62a. AIChE 70th Ann. Mtg., N. Y.. November 16, 1977  (1977).
    
    2.  T. D. Wheelock and I). R. Hoy I an, "Sulfurlc Acid from Calcium Sulfate", In "Sulfur and SO- Develop-
        ments". Chen. Er.:;. Prog. Tech. Manual, AIChE, N. Y. (1971).
    
    1.  G. J. Vogcl et al., "A Development Program on Pressured Fluldlzed-Bed Combustion", Annual Report,
        Argonne National laboratory, Argonne, 111.. ANr./ES-CF.N-1016 (1976).
    
    4.  R. C. Hokc. ct al.. "Studies of the Fl'iidlzcd-Bed Coal Combustion Process", Annual Report, Kxxon
        RMป. Linden. N. J., EPA-hOO/7-76-01I (1976).
    
    5.  L. A. Ruth, Proc. 4th Intern. Conf. KBC, Mitre, McLean, Va., Der. 1975 (1975).
    
    6.  W. Q. Hull, F. Sr.hon, and H. /irngibl. Ind. Eng. Chem.. 4ฃ. 1204 (1951).
    
    7.  E. T. TiTkdogen and J. V. Vlnters, Trans. In-.t. Mining & Metallurgy, In press (1977).
    
    8.  R. T. Yang, M. S. Shcn, and M. Steinberg, "A Regenerative Process for Fluldizcd-Bed Combustion of
        Coal with Lime Additives". BNL Report 22782, Brookhavcn National Laboratory. Upton, Now York  (1977).
    
    9.  S. Ehrllch. patent disclosure to Office of Coal Research. Pope, Evans and Robblns, Inc. (1968).
    
    10. R. T. Yang, P. T. Cunningham. W. I. Wilson, and S. A. Johnson, Advances In Chemistry. U7, 149 (1974).
    
    11. R. B. Snyder. W. I. Wilson, C. J. Vogcl, and H. \. Jonke, Proc. 4th Intern. Conf. FBC, Mitre. McLean,
        Va., Dec. 1975.
    
    12. R. T. Yang, et al., "Regenerative DesulfurtzatIon of Hot Combustion and Fuel Cases", Quarterly
        Reports Nos. 5 and 6, Brookhaven National Laboratory, I'pton, New York, April 1-September 30,  1977.
    
    13. R. T. Yang, M. S. Shen, and M. Steinberg, Env. Sc. Tech.. in press.
                                                       808
    

    -------
               QUESTIONS/RESPONSES/COMMENTS
         •'R.  FABER:  Thank you, Dr. Yang.  We do have time for one  or two
    quick questions  if somebody has one.  Yes, right there.
    
         MR.  HUBBLE:  Bill Hubble, Argonne.  Ralph, did you measure the
    concentration  of carbon in your ash?
    
         DR.  YANG:  Oh, yes.  I'm sorry.  I didn't mention that.  The fly-
    ash was supplied by Argonne.  It was  from Argonne's six-inch  fluidized
    bed combustor.  And the carbon was 13 percent in the fly-ash.
    
         MR.  HUBBLE:  Did you put enough  fly-ash in there that ;'ou  had
    enough carbon  to reduce the sulfur?
    
         DR.  YANG:  We used a molar ratio of two calcium sulfate  ":o one
    carbon in the  feed mixture.
    
         MR.  FABER:  Thank you, Dr. Yang.
                                    809
    

    -------
                         INTRODUCTION
         MR.  FABER, CHAIRMAN:  Our second  speaker this afternoon  is
    Dr. R.  A.  Newby.  Dr. Newby spoke this morning and you heard  his
    credentials  then.  Dr. Newby is with the Westinghouse Research and
    Development  Center in Pittsburgh.  The title of his afternoon presen-
    tation  is The  Evaluation of Sorbent Regeneration Processes for AFBC
    and PFBC.
                                   810
    

    -------
                         Evaluation of Sorbent Regeneration Processes
                                      forAFBCandPFBC
                                 R. A. Newby, S. Katta, D. L. Keairns
                                     Westinghouse R&O Center
    ABSTRACT
           Projections of the economics of regenerative fluidized-bed combustion power
    plants (atmospheric-pressure and pressurized boilers) have been developed on the basis
    of current estimates of regeneration system performance.   Economic comparisons with
    fluidized-bed combustion power plants operated with once-through sorbent systems and
    with conventional coal-fired pover plants using limestone vet-scrubbing are presented.
    Regenerative FBC performance requirements for economic feasibility are projected and
    critical development needs are discussed.
    
    
    INTRODUCTION
    
           Developmental facilities for fluidized-bcd combustion power generation are
    presently based on once-through sorbent operation.   Although research facilities are
    .iddressing the area of sorbent regeneration, the technical and economic feasibility of
    regeneration is not yet known.  Regeneration of sorbent for the purpose of reducing
    the rate of spent sorbent production faces trade-offs in  the areas of economics,
    environmental impact, plant complexity and reliability, and general technical
    performance.
           An assessment of the economic potential, the technical feasibility, the problem
    areas, and the development requirements of the one-step regeneration ..rocess (reductive
    decomposition) as applied to AFBC and PFBC is presented.   Capital and energy costs of
    once-through and regenerative AFEC as a function of the process sulfur load are
    projected.
           The economics and performance of two regeneration  processes that function to
    regenerate sorbent produced in PFBC have been previously  reported.1  These are a one-
    seep process (reductive decomposition) operated at  1000 kPa pressure and the same one-
    step process operated at 1000 kPa pressure.  An update of that work is presented in
    this report.  The projections reflect current performance expectations and revised
    component cost data.
           Details of these studies are presented in an EPA contract report, March 1975
    (EPA 600/7-78-039).
    
    
    CONCLUSIONS
    
           The following conclusions have been drawn from a technical and economic evalua-
    tion of sorbent regeneration processes for AFBC and HFBC:
           •  An integrated regeneration system for AFBC or PFBC has yet to be demon-
              strated.  Information on critical performance factors for commercial oper-
              ation is not yet available.
           •  The sulfur recovery system is the dominant subsystem in the regenerative
              process.  The pressurized regeneration (reductive decomposition) results
              in low SO? concentrations (1-2 v/o) requiring significant amounts of coal
              for reductant. complex energy reco" and hence has a substan-
              tial advantage over the ptessurizcd regeneration^
           •  In the case of atmospheric-pressure regeneration applied to PFBC, the major
              uncertainty lies in the solids transport  system.
    Presented at the 5th International Conference on Fluidized-Bed  Combustion,  December 12-
    14. 1977.
    
                                              811
    

    -------
    •  Assuming 2 and 12 v/o of SO? for pressurized (PR) and atmospheric regenera-
       tion (AR), respectively. Ca/S makeup ratio of 1.0,  a process sulfur load
       of 0.003. and sulfur recovery in the forra of elemental sulfur, the following
       capital .?osts for regeneration (635 MK'e plant)  in terms of $/kW have been
       projected :
    AR for
    AFBC
    32.2
    PR for
    PFBC
    66.8
    AR for
    PFBC
    57.2
    •  Using the same bases as above, the following energy costs in terms of
       mills/kWh have been projected:
    AR for
    AKBC:
    2.9
    PR for
    PKBC
    4.9
    AR for
    PFBC
    3.55
       For atmospheric regeneration applied to AFBC,  the following energy costs in
       terms of mills/kWh for a process sulfur load of 0.025 have been projected
       for three different C;i/S ratios, in the case of regeneration,  and for a
       Ca/S ratio of 2.2, in the case of once-through option:
                     Regenerative Option
                         Ca/S Ratio
                  0.2        0.6        1.0
    Once-through
      Option
                  1.9
                             2.2
                                        2.5
       1.92
       If sulfur is recovered as sulfuric acid rather than as elemental sulfur,  the
       capital cost of the regeneration process can be reduced to the following
       extent:
    AR for
    AFBC
    97,
    PR for
    PFBC
    247,
    AR for
    PFKC
    117,
       If a sulfur recovery process is developed specifically for regeneration,
       the regeneration potential may be considerably improved.   The scope and the
       need for process innovations in sulfur recovery are evident.
       The only regenerative PFBC power plant that is economically attractive,  as
       compared with a conventional power plant with limestone wet-scrubbing,  is
       based on the low-pressure reductive decomposition.
       The overall environmental performance of the low-pressure reductive decom-
       position is superior to the other regeneration processes.
       The once-through sorbent operation is superior to the regenerative opera-
       tions in all environmental aspects except for the quantity of spent sorbent
       produced.
                                       812
    

    -------
    RECOMMENDATIONS
    
           The following recommendations are made after reviewing the present technology
    applicable to regeneration and the development effort that has been carried out so far:
           •  Studies should be continued on particle attrition, sorbent deactivation due
              to the presence of fly ash or due to sintering, particle aggloir.eratic.i due
              to eutectic formation and gas-particle contacting i;i fluidized beds.
           •  Studies should be continued on the change in activity and the regenerability
              of the sorbent with repeated cycling, and the separation of sorbent and ash
              in the regenerator.
           •  The raxiir.u'. percent of S02 in the regenerator effluents that c.-n be achieved
              in a continuous operation of the combustor-vegenerator system at commercial
              operating conditions needs to be demonstrated.
           •  Development of sulfur recovery processes suitable for different regeneration
              schemes under consideration should be initiated.
           •  Exploratory work should be conducted on new schemes, such as the production
              of sulfur vapor rather than sulfur dioxide in the regenerator.
           •  The low-pressure reductive decomposition for PFBC appears to have greater
              potential than pressurized regeneration.  The sorbent circulation system
              for the low-pressure regeneration for PFBC, the area of greatest uncertainty,
              should be evaluated in greater detail.
           •  The present developmental effort on regeneration should be directed to
              correspond to the operating conditions envisaged for commercial operation.
              Much of the past effort ,on regeneration appears to have no relevance to
              industrial practice.
           •  A regeneration system modeling study is needed to assess the regeneration
              technology and process economics in greater detail and to permit the assess-
              ment of the experimental data that is being accumulated.
           •  Development of optimum methods for disposal/utilization of the s.icnt sorbent
              that meet environmental constraints is necessary.
    
    
    REGENERATIVE AFBC
    
           The one-step reductive decomposition of calcium sulfate is the most attractive
    regeneration process proposed for AFBC.  An evaluation was completed to develop per-
    formance projections, cost estimates, and critical development rcquircnents.
    
    Regeneration Concept
    
           The following reaction takes place in the one-step reductive decomposition of
    CaS04:
    
                                     •H,l	       fH-,01
                                       oh	CaO+\clj+S02                       (I)
    
    
    The undesirable competing reaction involving the formation of CaS al.io occurs:
    
    
                               CaS04 + ^Sl^^CaS + 6tcOฐ}                         <2)
    
    An oxidizing zone may Uu provided in the regeneration vessel to convert CaS to CaSO^:
    
                                     CaS + 20, v   ^ CaS04                              (3)
    
    Process De-script ion
    
           In ;:he regeneration process coal is introduced into a fluidi.-ed-beti rcpcr.erator
    for in_ situ partial combust icn to provide the reducing gas and the heat necessary for
    the reducTTon of CaSO^ to CaO (Figure 1).  The regenerated sorbent is returned to the
    fluid-bed boiler, where fresh sorbent will be introduced to make up for reduced activity
    and losses of the sorbent by attrition and elutriation.   Part of the sulfated sorbent
    is discarded for disposal or utilization.  The regenerator off-gas (containing about
                                              813
    

    -------
                                                                                                Pig.  I68JB!>2
    00
               Utilized
               Sorbent
               From
               Boiler
                                                                                                     Air
                                                                                     Steam
                                                                   Sulfur Recovery Plant
                                                                   Resox and Beavon Processes
                    C.W.
    AMAM
                         Spent Stone
                      Cooler/Conveyor
                                       S. S. D.
                                          C.F. -Coal Feeding System
                                          C.W. -Cooling Water
                                                    S. S. D. - Spent Stone Disposal
                                                    U.S. -Utilized Sorbent
                                                    R. S. - Regenerated Sorbent
                                   Figure 1. Atmospheric One-Step Regeneration Schematic Flow Diagram of One Module
    

    -------
    12 percent S02 at a temperature  of 1100CC)  passes  through primary and  secondary  cyclones
    and then exchanges heae  with the incoming air  to  the  regenerator  before being processed
    in a sulfur recovery plant  for the production  of  elemental sulfur.
    
    Performance Projections
    
           Design specifications are listed  in  Table  I.   Material  and energy balances  are
    given in Table II and Figure 2.   The single most  important variable  of the  process is
    the concentration of S02 in the  regenerator effluent, which depends  on the  type  of fuel
    used in the regenerator, temperature.  pressure, heat  losses, and  the change in the
    utilization of calcium across the regenerator.  The concentration of S02 in the  regen-
    erator effluent was estimated to be about 12 percent.   The effect of various factors
    on the maximum concentration of  SO? that can be achieved  has been studied with mate-
    rial and energy balance  considerations in mind.
    
    
                   Table I.   Design  Specifications and Assumptions for AFBC
         Design Conditions:
    
              Boiler coal rate                          240.408  kg/hr  (635  MW)
    
              Basis for boiler design                    Previous Wcstinghouse Study^  '
    
              Sorbcnt type                              Dolomite
    
              Process sulfur load                       0.026
    
              Sorbent disposal                          Before regeneration
    
              Plant capacity factor                     707,
    
              Sulfur recovery                           Elemental sulfur  by the  RESOX
                                                        Process  (Foster Wheeler)
    
              Number of regenerator modules              4
    
              Operating pressure and temperature  of      101 kPa  and  870ฐC
              AFBB
    
              In situ partial combustion  of  coal  in
              tHe regenerator
    
         Design Assumptions:
    
              Regenerator temperature                    1100ฐC
    
              Dolomite makeup rate                       1 mole Ca/1  mole  S
    
              Dolomite utilization  after                 10%
              regenerator
    
              Percent S02 in  the regenerator            1P%
              effluent
    
              No CaS is formed
                                             815
    

    -------
                                         Table  II.   Heat  and Material Balances for AFBC
    Stream
    Ho.
    1 Coal to regenerator
    2 Air to regenerator
    3 Utilized sorbenc
    4 Regenerated sorbent
    5 Regenerator off-gas
    6 Air to heat exchanger
    7 Regenerated off-gas
    to SRP
    8 Coal to SRP
    9 Sulfur (807. recovery)
    10 Tail -gas from SRP
    11 Waste stone to cooler
    12 Waste stone for
    disposal
    13 Sulfur M00%
    recovery)
    Temp. (ฐC) /Pressure
    (k?a)
    93.3/137.8
    704.4/158.5
    871/103.4
    1093.3/103.4
    1093.3/137.8
    121/165.4
    537.8/130.9
    93.3/137.8
    121/103.4
    148.9/110.2
    871/103.4
    93.3/103.4
    148.9/110.2
    Flowratc ; Enthalpy !
    (kg tnoles/hr) i (kJ/kg molo) ! Comments
    5602 kg/hr 86.5 kJ/kg .
    1
    1207 21.074
    -,-,, ke moles of Ca , ,„ 00/ i MgO - 50%, CaSO/ - 17.5%
    //J * Kr uu.oa* Ca0 . 32 5% "
    ,,, kg moles of Ca •,,„ ,,„ | MgO - 50%. CaSO, - 5%
    //J hr ^ILI,ซI i | Ca0 . 457<
    155C i 39.890 i CO, - 18.6%. H?0 - 7.87,
    I SO; - 12.47., Nj - 61.2%
    l.?07 2,888 '
    1553 18,319 j
    3549 kg/hr ; 86.5 kJ/kg i
    155 j j
    1636 : i
    3,, kg moles of Ca . nQ &s, ''
    ,,, kg noles of Ca ;
    hr i '
    33.7
    '
    00
    (—ป
    en
    

    -------
    00
                                      To Stack
                                                                                          Own.  6392A28
                                                     S7R.
                                                    Beavon
                                                   Process
                                 To Stack	* Sulfur	j
                                                    S.R.
                                                    Resox
                                                   Process
    Sulfur
                      Coal
                      Air
                    Make-Upti
                    Sorbent
    Fluid-Bed
       Boiler
      870ฐC
     101 kPa
                                                                                     Coal
                                                     S.R.
                                         Spent Stone
                                         Disposal/Utilization
                             - Sulfur Recovery
                                           Figure 2. Atmospheric One-Step Regenerative Process Flow Diagram
    

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           The required calcium/sulfur nol.ir feed rario depends en the activity of the
    sorbcnt in the boiler a-.ci the regenerator and ihe rate of circulation of solids
    between the two processing steps.  For atnospheric-pressurc operation in on::e-through
    systems. Ca/S makeup ratios of 2.8/1 and 2.2/1 have beer, projected for calcined  lime-
    stone and dolomite, respectively, for a temperature of 616*C.2  Pope, Evans and
    Robbins^ estimated a ratio of 1/1. while from recent ber.ch-scale experimental data
    Argonne^ projected a ratio of about 0.35.
           The combustion efficiencv in AFBC can be expecteii to be about 90 percent  wi'h-
    oul a carbon burn-up celt, the inefficiency result ine mainly from the carry-over or
    carbon fines.  6   In an atmospheric regenerator higher carbon losses can be expected
    because of (a) the reducing atmosphere, (b) the absence of any internals ant! (c) Che
    reaction of carbon with Ci>> .  resulting in the f oroat ion of CO near the top portion of
    the bcJs and its subsequent loss through the regenerator off-pas.  The cor.pensat ins
    factors in favor of regeneration are the highest operating temperature and lower
    fluidixation velocity.   The heat losses of the regenerator have been estimated 10 he
    in the ranye of 0.5 to 1 percent .  Tlie energy requirerx-iit cf the reeenerator for a
    635 MW plant has been estimated  to be approximately i percent of the energy requirement
    of the holler.  Assuming the carbon loss in the regenerator is about 15 percent, tnis
    represents about 1/2 percent  of  the fuel input to the boiler.
    
    Cost	F.st imate
    
           The process investment cost .-,nd the- energy cost as a function of the process
    sulfur load are shown in Figures 3 .-ind 4. respectively,  for the following basis:
           •  Cost corresponds to the er.J of 1976-
           •  Capital charges plus operation and maintenance at 20 percent of the total
              cost.
           •  Contingency at 20 percent and contractor fees at 3 percent of the base
              cost.
           •  No interest during the construction period is incluaed.
           •  Co.il at S20.00 per Mg  and dolomite at S5.00 pc-r Mp.
           •  Waste stone disposal cost at. S3.00 per ^g
           e  Klect.ricit y at 23 mills/kWh
           •  Process water at SO. 10 for 3.8 m1                        •ป
           •  No credit for recovered sulfur
           •  70 percent capacity factor (6132 hours of operation in a v-ar).
           The sulfur recovery element is by far the nost expensive system   For a process
    sulfur load cf 0.025. its cost forms more than 60 percc-n: of the total investment cost.
    The sorhent  circulation element:  is the least expensive o:~ the three elements.  The
    effect of I'SI. on the cost  of the sulfur recovery clciscnt is subst ant ia 1 ly higher thar;
    on the cost of the regeneration  v It-mem or the sorbent circulation ..lenient.  Hence, it
    is desirable to have us 'ow a load as possible on the sis! fur recovery element.
    Assessment
              The tost: of the rcRcnt-r.it ive process is ba^cii on the assumption that a con-
              centration oi' SO? of about 12 percent can be obtained.  This has yet to be
              demonstrated experimentally.
              The sulfur recovery system is the dominant subsystem in the regenentive
              process.
              Comparison of the oncc-thrrxigh option with the rop.enerativc option shows
              that the process investment cost is about 20 percent higher and the energy
              cost, about 4 percent higher for the latter option.  This comparison is
              based on the assumption that the spent stone does not need further
              process ing.
              If sulfur is recovered as sulfuric acid rather than as elemental sulfur,
              the capital cost of Lhc regenerative option can he reduced by aboui
              10 percent.
              The regenerative option might become competitive with the once-t.hrouah
              option  if the makeup ratio of Ca/S can be reduced to about 0.2 for a sorbent
              cost (fresh stone plus disposal) of about S8 per Me.
              For a makeup rate (Ca/S) of 1.0. regeneration is liV.ely to break even at a
              sorbent cost (fresh stone plus disposal) of S12-16 per ton.
                                              818
    

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                                                          Cu'.f 6871li-t
                             4?
                             36
                         ^  30
                               .  635 MW Plant
                                  cone. oป S0-=ai2
                                  FSL - Ib of s handled by Regenerator
                                      per ID of coa! to comnuslor
                              0.01    a 02
     0.03     0.04
    Process Sulfur Load
    0.05
    0.06
                           Figure 3. Capital Cost of Regenerative Process as a Function of PSL
    REGENERATIVE  PFI'.C
           The  economics and performance of two reductive  decomposition  schemes,  one oper-
    ated at about  :'• : •,-•:.  (10 .ii-osphcrcs) and one at  about  100 to 200 kl'a  (1  to  2 atmos-
    phc-res) were  t-st irvit oil.   The tlcsir.ns are conceptual  in r.al;:re anJ were  not  based on
    sensitivity analysis or optimisation.
    
    Bjปs_l_s_ of _Evalu."t ion
    
           The  power plant basis listed  in Table III has boon applied  in the assessment.
    The process sulfur load, reflecting  in part the sulfur content of  the coal, is varied
    from 0.01 to  0.06.  Important process characteristics  are yxivcn in Table IV as a func-
    tion of the process sulfur  load.
           The  specific process options  were selected  on the basis of  result*  of previous
    engineering assessments and are presented in Table V.  Selected regeneration process
    opcrat ini; conditions and projected perfornance levels  arc sunsnnri::cd in Table VI.
    Sulfur dioxide concentrations of  1 and 2 v/o frora  the  regenerator  are ex.-.-ined for the
                                                819
    

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                                                          Curve 687042-A
                    E
    
                    I  3
                    o
                                                              I
                              635 MW Plant
    Cone,
                                    of SCL = 0. 12
                              PSL - Ib of S Handled by Regenerator per
                               Ib of Coal to Combust or
                        0.01    0.02
               0.03      0.04
              Process Sulfur Load
    0.05
    0.06
                          Figure 4. Energy Cost of Regenerative Process as • Function of PSL
    
    
    1000 kPa reductive decomposition process  because the  achievable level for this critic.il
    performance factor has nut  been demonstrated.   A level  of 10 v/o is assumed for the
    low-pressure reductive decomposition  process.   The combustor operating conditions are
    assumed to result in calcination of  the dolomite.   A dolomite makeup rate (Ca/S ratio)
    of 0.5 to 1.0 moles of calcium per mole of  sulfur fed to the combustor is assumed.
    
    Process Performa-.ce Projections
           Some key performance characteristics  of the PFBC regeneration systems evaluated
    are summarized in Table VII as a  function  of the process sulfur load.  Auxiliary power
    requirenents  (for the sulfur recovery  pror-ess,  for the compression of air and stack
    gas and for sorbent circulation),  the  rate of coal consumption for regenerator reduc-
    cant.  the rate of methane consumption  for  sulfur recovery, and the rate of steam consump-
    tion are estimated.  The regeneration  processes are large power and fuel consumers, -ir.ci
    the process designs must be concerned  with maximum energy recovery.  The energy content
    of the regenerator product gas is  used to  provide the regeneration process auxiliary
    power requirements.  No energy is  exported from the regeneration process to the plant
    power cycle in this evaluation, although this may be called for in an optimized power
    plant.
                                              820
    

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                                Table III.   Power Plant Basis
    Plant Capacity - 635 ^e (based on once-through sorbent power plant performance)
    
    Plant Heat Rate - 9040 kJ/kWh (8570 Btu/kWh) (based on once-through sorbent
         performance).
    
    Combustor Excess Air - 17.5%
    
    Conbustor Pressure - 1000 kPa (10 atmospheres)
    
    Process Sulfur Load - 0.01 to 0.06
    
    S02 Control - Meets EPA standard of 0.5 kg S02/GJ (1.2 Ib S02/106 Btu).
    
    Sorbent Type - Dolomite
    
    Layout - Four pressurized boiler modules, four parallel regeneration trains, single
             sulfur recovery plant.
    
    Spent Sorbent Processing - None; sorbent is disposed of following regeneration
    
    Sorbent Circulation System - Dilute pneumatic transport
    
    Sulfur recovery tail-gas - Incinerated and exhausted
                                Table IV.  Process Sulfur Load
    
    Coal Sulfur.
    w/ob
    Combustor Sulfur Removal
    Efficiency, ^c
    Sulfur Production Rate. Kg/hr
    Sorbent Circulation Rate, Mg/hre
    Process Sul fur Load3
    0.06 | 0.03 j
    7.2 4.0
    93 85
    282 141
    150 85
    0.
    1
    65
    42
    30
    01
    .8
    
    
    
     Defined as Ws (:i-mXpX where Ws is the sulfur content of the coal (weight fraction).
     n is the boiler sulfur removal efficiency (fraction), m is the boiler Ca/S makeup
     ratio,and Xs is the fractional utilization of the sorbent material following
    .regeneration.
    "Based on values of m ป 1.0 and Xs = 0.1.
    cfiased on satisfying SC^, emission standard of 0.5 kg/GJ and a recovery efficiency
     for the sulfur recovery process of 90"",.
    "Based on coal heating value of 3,000 kJ/kg (13.000 Btu/lb).
    eBased on a dolomite. 30 percent utilization before regeneration and 10 percent after
     regeneration.
                                              821
    

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                              Table V.   Selected Process Options
    Reductive Decomposition Processes
    
         Kcducl.'ini K-''s f.enerat. ion  -  in  situ  wit.h
    
         Fuel for rcduc'nuL - coal
    
         Sulfur recovery form - L-lcnvcni.il  sulfur  and sulfuric acid evaluated.
    
         Sulfur recovery process  - Allied  Cher.icnl  process with methane reductant  (sec
         Section 4)
                 Table VI.  Operating  Conditions and Performance Projections
    Reductive Decomposition |
    , i i
    Regenerator Pressure. kPa
    Regenerator Temperature. ฐC
    SO., Mole Percent a^.o Produced
    Sulfur Recovery Kfficiency, ~
    Dolomite Utilisation in Boiler. 7,
    Dolomile Utilisation ai'ter
    Rej-enerat ion . 7.
    Dolomite Makeup Rate. Ca/S
    KIuidix.it ion Velocity, m/sec
    Boiler Conditions
    Calcium Sulfide in Sorhcnt . 7,
    Pressur i/ed
    1000
    1100
    1-2
    90
    30
    10
    0.5-1 .0
    1.5
    Calcining.
    0
    i Atmospheric Pressure
    150
    1050
    10
    90
    30
    10
    0.5-1 .0
    1.5
    Calclninc,
    0
                             Table  VII.   Perforisance Projections
    Process Sulfur Load
    Auxiliary Power, MWc
    Coal Consumption. Percent
    of Boiler Coal Input
    Methane Consumption, GJ/hr
    Technical Uncertainties
    Reductive Decomposition
    17, S02
    0.06 0.03 0.01
    70 37 15
    69 35 12
    272 136 il
    Energy recovery,
    sulfur recovery
    27. S02
    0.06 0.03 0.01
    41 22 10
    34 17 6
    272 136 41
    Energy recovery.
    sulfur recovery
    107, S02
    0.06 0.03 0.01
    21 12 6
    6 3 1
    260 130 40
    Temperature con-
    trol . sol ids
    circulation sys-
    tem opcrability
                                               822
    

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           Several Technical unceft aim les exist for each of the  recent-ration schemes.
    The high-pressure reductive- decomposition processes  (I and 2  percent  SOj) require very
    larp,e coal inputs xml a-ixiliar;' power consumption.   The efficiency  and  operabi 1 ity of
    t-nev^y recovery is a technical uncertainty .lion); wi:h r he operability and controllabil-
    ity of sulfur recovery with such low SO-> concentrations.  The  low-pressure reductive
    decomposition process consumes power and coal at a lower rate, but  it:;  oper.ibil ity and
    reliability is in question because of the complexity of the solids  circulation  system.
    
    Capital Investment
    
           Estimates of capita! investment for the  regeneration processes have been
    developed on the following basis:
           • ' Mid-1977 costs
           •  6") 5 MWe power plant
           •  Interest Jui inj; construction, general items, and engineer in);  are .iot
              included.
           •  All other direct and indirect cost items are included.
    The est inated investments are presented as a function of :he  process  sulfur load  in
    Tables VIII t hrous-h X.
           The most  expens ve process sec'ion for the pressurised  reductive decomposition
    process is the sulfur recovery or sulfuric acid recovery section.   The  soiljt-nt  circu-
    lation section is the -ic>st expensive section for the low-pressure reductive decomposi-
    tion process, requirit. • complex lockhoppers with water-cooled  valves.
    
    
                Table VIII.   Investnent for Pressurized  Reductive-  Decomposition
                                   Process - 1 Percent S02, $/kW
    Process Section r
    Ki-k;enerat ion
    Sorbent Circulation
    Sulfur Recovery
    (Sulfuric Acid Recovery)
    Total
    
    0.06
    15.6
    16.9
    92.3
    (55.3)
    124.8 (87 8)
    Process Sulfur Load
    ! ฐ ฐ3 T
    10.6
    16.1
    60.8
    (36.5)
    87.5 (63.2)
    
    0.01
    4.8
    15.1
    29.5
    (17.6)
    49.4 (37.5)
                Table IX.  Investment for Pressurized Reductive Decomposition
                                   Process - 2 Percent S02 . $/kW
    i
    Process Section |
    Rcsenerat ion
    Sorbent Circulation
    Sulfur Recovery
    (Sulfuric Acid Recovery)
    Total
    Process Sulfur Load
    0.06 | 0.03
    10.5 -
    16.9
    68.2
    (44.2)
    95.6 (71.6)
    5.7
    16.1
    45.0
    (29.2)
    66.8 (51.0)
    0.01
    3.2
    15.1
    21.8
    (14.2)
    40.1 (32.5)
                                              823
    

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                Table X.   Investment  for Low-Pressure Reductive Drconposit ion
                                   Process - 10 Percent  S02,
    Process Section
    Re Ktrni;rat ion
    Sorbent Circulation
    Sulfur Recovery
    (Sulfuric Acid Recovery)
    Total
    Process Sulfur Load
    0.06
    11.4
    31.9
    27.7
    (16.4)
    71.0 (61.7)
    1 ฐ-
    7
    31
    18
    (12
    57 .2
    03
    .8
    .1
    .3
    .2)
    (51.1)
    | 0.01
    3.'
    30.1
    8.8
    (5.9)
    42.0 (39. I)
    Energy Costs
    
           Energy costs associated with each of the regeneration processes have been
    projected using the following basis:
           •  Interest during construction included at  7-1/27,/yr.  3-1/2 yr construction
              t ime
              Mid-1977
              Capital charges of 157,/yr
              Operating and maintenance cost of 57, of investment per year
              707, plant capacity factor
              Sulfuric acid recovery not considered
              Mo credit for sulfur produced
              Coal at SO.80 per GJ
              Methane at Sl.O per GJ
              Dolomite at  $10.0 per MR (purchase plus disposal)
              Sorbent Ca/S ratio of 1.0 for all three process sulfur loads.
    For a once-through sorbent operation with dolomite, the required Ca/S ratios as a
    function of the process sulfur load are given as follows, based on a once-through
    sorbent utilization of 50 percent:
    
                Process Sulfur Load                         Once-Through Ca/S
    
                       0.06                                        1.7
                       0.03                                        1.5
                       0.01                                        1.2
    
           Tables XI through XIII give the projected energy costs  for the regeneration
    processes and compare  them to the once-through operation energy cost.
           The energy costs of the regeneration processes are co isiderably greater than
    the energy costs of once-through sorbent operation  on the oasis applied in this study.
    For the optimistic assumption that the regenerative processes  ma/ be operated with a
    Ca/S ratio of C.5, the cost to which dolomite must  rise in order to result in a once-
    through energy cost identical with the regenerative energy cost is shown in Table XIV.
    
    Economic Comparison with Limestone V.'e'-Scrubbing
    
           The pressurized f luidized-bed combustion po.-er plant with regenerative sorbent
    operation must compete economically with commercial power generation systems such as a
    conventional coal-fired power plant with limestone  vet-scrubbing of the plant stack
    gases.  The investment costs and energy costs ot regenerative pressurized fluidized-bed
    combustion (with elemental sulfur recovery) are cocpared with a conventional power
    plant in Tcble XV based on a process sulfur load of 0.03 (4.0 w/o sulfur coal).
           The only regenerative PFBC power generation  system that compares favorably with
    Che conventional power plant with limestone wet-scruobing if the system based on the
    low-pressure reductive decomposition.
                                              824
    

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                       Table XI.  Energy Cost for Pressurized Reductive
                                Deconposition - 1 Percent S02 ,  mills/kWh
    1
    i
    Capital Charges
    Operating and Maintenance
    Coal
    Methane
    Dolomite
    Total
    Cost Relative to Once-through
    Oreration
    Process Sulfur Load
    0
    :i
    I
    5
    0
    I
    11
    
    9
    06
    57
    19
    14
    45
    64
    99
    
    20
    i 0.
    j
    2.
    0.
    2.
    0.
    0.
    7.
    
    5.
    01
    50
    83
    57
    23
    90
    03
    
    68
    j 0
    1
    0
    0
    0
    0
    3
    
    2
    01
    42
    47
    77
    07
    35
    07
    
    65
                       Tsble XII.  Energy Cost for Pressurised Reductive
                                 Decomposition - 2 Percent S02 ,  mills/kWh
    
    Capital Charges
    Opcrat inf.; and Maintenance
    Coal
    Methane
    Do 1 om i t e
    Total
    Cost Relative to Once-through
    Operation
    i
    i
    i 0.06
    2.74
    0.91
    2.54
    0.45
    1.64
    8.28
    5.49
    Process Sulfur Load
    I 0.03 j
    1.91
    0.63
    1.27
    0.23
    0.90
    4.94
    3.59
    
    0.01
    1.15
    0.39
    0.38
    0.07
    0.35
    2.34
    1.92
    Environmental Comparison
    
           The environmental performance of the regeneration processes for PFBC is com-
    pared with once-through PFBC and conventional coal-fired power plants with lines tone
    wet-scrubbing in Table XVI.  All of the power generation systems are assumed to satisfy
    the E'.'A emissions standards (SO2. NOX ,  part iculat es) for coal-fired plants.
           The low-pressure reductive decomposition process is the most environment ally
    satisfactory of the regeneration processes.  The once-throuph PKBC operation is
    environmentally superior to the regeneration processes in all aspects except that of
    spent sorbent production.   The environmental impact of the regenerative spent sorbent.
    versus the once-through spent  sorbent due to differences in chemical nature is not
    known.  The conventional power plant with limestone wet-scrubbing requires coal con-
    sumption at a greater rate than do al'.  of the PTSC power plants except for the pres-
    surized reductive decomposition with 1  v/o S02.
                                              825
    

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                    Table XIII.   Energy  Cost  for Low-Pressure Reductive
                               Decomposi-. ion  - 10 Percent  S(>2 , mills/kUh
    I Process Sulfur Load
    
    Capit.il Charges
    Operating and Maintenance
    Coal
    Methane
    Dolomite
    Total
    Cost Relative to Once-through
    Ope rat ion
    ! 0.06
    2.04
    0.68
    0.47
    0.45
    1.64
    5.28
    2.49
    ] 0.03
    1.64
    0.55
    0.23
    0.23
    0.90
    3.55
    2.20
    i 0.01
    1.21
    0.40
    0.07
    0.07
    0.35
    2.10
    1.68
                    Table XIV.   Cost  of Dolomite Required to Givซ> Eoual
                             Once-through and Regenerative Costs. S/Mg
    Regeneration Process
    Reduce ive
    17. S02
    Reductive
    27. SO,
    Reduct. ivซ.-
    107. S02
    Decomposition with
    
    Decomposition with
    
    Decomposition with
    
    
    0.06
    57
    
    38
    
    23
    
    Process Sulfur Load
    i 0.03 I
    i i
    73
    
    50
    
    34
    
    
    0.01
    118
    
    88
    
    79
    
    Basis:   Regenerative Ca/S =0.5
    
    
            Table XV.   Comparison of Regenerative Pressurized Fluid-Bed Combustion
                       with Conventional Coal-Fired Power Generation
    
    Conventional Plant
    Once-through PFBC
    Regenerative PFBC
    Reductive decomposition with 17. S00
    Reductive decomposition with 27. S02
    Reductive decomposition with
    107. S02
    Capital Investment.
    $/kW
    570
    424
    
    526
    502
    491
    Energy Cost.
    mills/kWh
    23.7
    19.8
    
    25.4
    23.3
    22.0
                                             826
    

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                                 Table XVI,  Comparison of Environmental Impacts for PFBC*3
    Pressurised
    Decompo
    17. S02
    Plane Heat Rate,c KJ/kWh 12.100
    Raw Materials
    Coal input ,d Mg/hr 263
    Sorbcnt input,6 Mg/day 588-1175
    Methane input . 10
    kJ/hr 136
    Plant Exports fe,
    Spent sorbont, Mg/day 435-870
    AshE, Mg/day 631
    Sulfur. h Mg/day 141
    Reduce ive
    sit ion Low-Pressure
    27. S02 107, S02
    10.800 9.600
    
    228 201
    588-1175 588-1175
    136 130
    
    435-870 435-870
    547 482
    141 141
    Once-through
    Operation
    9.040
    
    195
    1,763
    0
    
    1,900
    468
    0
    Conventional
    Power Plant"
    >.11.000
    
    237
    840
    0
    
    1.850
    569
    0
    00
    ro
          Basis:  635 MWe power plant capacity. 4 w/o sulfur coal, emission standards for SOy, NOX and particulates
          satisfied.
         ฐNow plant with limestone wet-scrubbing.
         '•Includes auxiliary coal and methane inpuf .
         dlncludcs coal for regeneration reductant.
         ฐCa/S  (dolomite) of 0.5-1.0 for reductive decomposition, 1.0-2.0 for two-step regeneration, 1.5 for once-
         pthrough PFBC and 1.2 (limestone) for limestone wet-scrubber.
         -Dry,  granular for PFBC. limestone sludge for wot-scrubber.
         RlO w/o ash in coal.
         "Sulfur in auxiliary coal is neglected.
    

    -------
    Assessment of Scgcnerative PFHC
    
           An integrated PKBC regeneration system has yet to be denonstrated.  Most per-
    formance data have he-en generated on small-scale. batch, and serai -continuous apparatus.
    and reliable information concerning the critical performance factors for commercial
    operation is not available.
           The technical performance ol the two PFBC sorSenn regeneration schemes evaluated
    is uncertain.  The pressurised reductive decomposition will result in such low S02
    concentrations (1-2 v/o) that huge amounts of coal for reductant will be required, and
    complex energy recovery and sulfur recovery systems will be necessary.  The low-
    pressure reductive decon;posir ion appears technically favorable except for major
    uncertainties in the solids transport system.  All the regeneration processes are com-
    plex, and th- ir operability and reliability are major concerns.
           The overall environmental performance of the low-pressure reductive decomposi-
    tion is superior to the other regeneration processes.  Both the pressurized and the
    low-prossure redactive decomposition processes require the consumption of clean fuels
    such as ne'.hano.  The once-through sorbent operation is superior to the regenerative
    operations in all environmental aspects except the quantity of spent sorbenr produced.
           Th: only regenerative 1'FBC power plant t.h'at is ocononically attractive when
    compared to a conventional power plant with limestone wet-scrubbing is basi.-d on the
    low-pres.iure reductive decomposition.  The once-through PFRC power plant has a con-
    siderably lower energy cost than iio any of the regenerative power plants, based on a
    dolonite cost of SlO/Mg.
    
    
    ACKNO\;LEDCME:.TS
    
           This work was performed under Contract No. 68-02-2132 for the Industrial
    Environmental Research Laboratory of the Environmental Protection Agency.  We
    acknowledge Mr. D. B. Henschel of EPA for his contribution to this study as project
    officer.
    
    
    REFERENCES
    
     1.  Realms, D. L.. et al.,  Evaluation o^ the Fluidized-Bed Combustion Process
         Vol. II, Office of Research and Development, EPA Westinnhouse Research Labora-
         tories. Pi'tsburgh. Pa.   15235. December 1973. EPA-650/2-73-048b. NTIS number
         PB231-163.
     2.  Kcairns. D. L., et al.,  "Fluidized Bed Combustion Process Evaluation - Phase II-
         Pressurized Fluidized Bed Coal Combustion Development," Westinghouse Research
         Laboratories contract report to EPA - 650/2-75-027c. September, 1975, NTIS
         PB 246-116.
     3.  D. H. Archer, et al.. "Evaluation of the Fluidized-Bed Combustion Process."
         Vol. II. submitted to the Office of Air Program, EPA by Westinghouse Research
         and Development Center,  Pittsburgh. PA, Nov. 1971. Contract 70-9. NTIS
         Number PB 212-916.
     4.  Pope. Evans and Rot/bins R&D Program. Proceedings of a workshop on Regeneration
         of Sulfated Limestone/Dolomite for Fluidized Bed Combustion, ERDA. Washington,
         DC, March 1975.
     5.  Monthly Progress Reports - A Development Program on Pressurized, Fluidized-Bed
         Coal Combustion, EPA, Argonne National Laboratory. Argonne, Illinois, August and
         October 1976.
     6.  J. Y. Shang and R. A. Chronowski, Comparison of AFBC with PFBC, Proceedings of
         the Fourth Intern. Conf. on Fluidized-Bed Combustion. December. 1975.
                                              828
    

    -------
                 QUESTIONS/RESPONSES/COMMENTS
         MR. FABER:  Thank you,  Dr.  Newby.   Are there any quick questions.
    
         MR. SMYK:  Gene Smyk, Argonne.   I'd like to ask you what calcium
    to sulfur mole ratio you used  for AFBC  and the once-through?
    
         DR. NEWBY:  I think it  was  about three and a half.
    
         MR. FABER:  Is there another question?
    
         DR. NEWBY:  This is fron  David  Henzel from Dravo Corporation.
    He had two questions.  "What effect  on  calcium utilization and
    overall cost increase would  an appreciable calcium sulfate formation
    in the regeneration step cost?"   The important parameter here is the
    ratio of the number of moles of  calcium sulfide generated divided by
    the number of moles of S02 generated in the regenerator.  As this
    ratio increases, you're consuming more  reductant from the coal to
    generate calcium sulfide so  you're not  utilizing this for the SO?
    generation.  Therefore, you're reducing the SC>2 concentration,
    increasing the rate of coal  consumption in the regenerator and
    depending on how high that parameter would get could have a very
    significant impact on the cost of the process.  I'm not sure what
    effect it would have on the  utilization of calcium, since it's
    normally assumed any calcium sulfide generated would be oxidized back
    to calcium oxide in the combustor.
    
         The second question is, "Is there  any idea of the savings in
    cost between once-through and  regenerative waste disposal for AFBC?"
    It seems to me that those materials  could potentially be so much
    different in particle size distribution,  in calcium sulfide content,
    calcium oxide content, in the  ratio  of  fly-ash to coarse sorbent
    material, that handling systems  may  have to be largely different for
    those.  We haven't really looked at  the details.  We normally assume
    something like 3 to 5 dollars  a  ton  for an offsite disposal.
    
         MR. HARVEY:  All right.  Did you have a question?  Oh.
    
         DR. SMYKE:  Dr. Smyk from Argonne  National Laboratory asks,
    "How would you propose to control  the feed of fly-ash to the kiln if
    the carbon content were variable, and it  probably would be i.i a real
    life situation?"
    
        DR. NEWBY:  Well, that's a very  good  question.  I've oeen asking
    that myself.  For one mole to  regender  one mole of calcium sulfate,
    you need half a mole of carbon.   But this reactor is e:x!othennic.
    You need .7 moles of carbon  to supply the heat, if you want to burn
    
    
                                    829
    

    -------
    Cdrbon to supply the heat.  Now, this is a control  problem.   I  don't
    know how much the carbon content in the tly-ash varies fron  a fluid-
    ized bed combustor.  If it varies from 2 percent to 60 percent  in  the
    next minute, then we're in trouble.  If it varies from 15 percent  to
    20 percent on an hourly basis,  it's not bad at all.  We're talking
    about time average basis.  So ideally you would like to know the
    carbon content from the fly-ash.  Say you sample the content twice a
    day or three times a day.  That would be the ideal  case.  So again
    it, is a control problem.
                                    830
    

    -------
                             INTRODUCTION
         MP. FARFR, CHAIRWI:   r>ur third  speaker  this  afternoon  is
    Mr. Jerome V. Morton.   '!r.  "orton is  with  Rurns  and  Roe  Industrial
    Services Corporation.   He  has been manager for the past  three years
    of the process enq^neerinq  and previously  held project nanaqer  and
    supervising mechanical  engineer.   Receiving his  r'F degree, Rf'F  rieqree
    fron City College of New York and heing  licensed in  several  states,
    he has been employed with  Purns and Roe  for something like five years.
    Previous employment include ?5 years  of  diversified  experience  in  in-
    dustry and consulting engineering, fir.  Morton.
                                     831
    

    -------
    s
                                                  An Engineering Study on the Regeneration of
                                                     Sulfated Additive from a FluMzed-Bed
                                                             Coal-Fired Power Plant
                                                        J. H. Bianco. D. A. Huber. J. WLMorton.
                                                                and R. M Costeiio
                                                     Burns and Roe Industrial ServicesCbrporation
                                                               Paramus. New Jersey
                            ABSTRACT
                                   I'r.Jer  DOE sponsorship (Contract No. EX-76-C-ra-2371) ,  an engineering study of
                            the regeneration o:  sulfated additives from a coal-lired fluidized-bed power plani was
                            performed.
    
                                   The-  work involved a review of the literature, selection  of a viable process
                            to be  .:sc^, preparation of conceptual flow Jiaorar.s, identification of required eciuip-
                            -t-nt ar.J  order-of-rsaqni tude cost estimates for the complete  sul fated sorbent pro-
                            Cfssir.:: ar.j hand; inn system.  The system was si?ed tar service a 600 megawatt power
                            plant.
    
                            ซ       Several alternative arrangements of the or.c-.ss.cp re7eneration process were
                            studied and compared to a once-throu<-h sorbent systerv
    
    
                            REGENERATION  Or ADDITIVE
    
                                   When coal is  burned in a fluidized bed contaising an  additive such as lire-
                            stone  or  dolomite,  r-O,  fron the conbustion of sulfur in the  crjal reacts with the bed
                            material  and  forms  Ca?O^ which is retained in the bei..
    
                                   The  additive  ruterial nay bo osthor reqeneraizd to a  form suitable for rouse
                            in the fluid  bed system, or disposed of in its partuilly utilized form in a once-
                            throuqh systen.
    
                                   rwo  reaeneration processes were selected for study.  Both consisted of heaiina
                            the spor.t additi' -  in the presence of reducinci oases at relatively high temperatures
                            to produce  caseous  sulfur conji-ounds and either calcizn oxide  or calciur. carbonate.
                            One-Step Regeneration Process
    
                                   The one-step dolomite or limestone regeneration process consists of a sinale
                            f luidi.-.od bed reactor in which spent additive contaiaina CaSO. from the coal-fired
                            fluid-bed system is reacted with a rea-cing <;as, suiii as H, aSd/or CO, to produce
                            CaO and SO,.   The cndothcrmic reaction at. 2000  F  (125>3ฐt:) and 1 atmosphere
                            pressure i~s:
    c.-.so. *
                                              cf
                                              CO
    CaO + SO,
    K,0
    of
    CO,
                                                           (U
                                   The rate cf reaction between Ca.^O. and either H,  or CO is quite high at 2000 F.
                            It  is  desirable to produce hioh concentrations (10 ta> 15%  by Kt.)  of SO,.  The SO,
                            equilibria concentration is favored by reduced pressure,  being inversely proper-"
                            tional to the  total pressure.  The reductian of CafE., to CaO is favored by hich
                            temperatures arid mildly reducina conditions (one no^5 of either H, or CO for every
                            mole of CoS04).
    
                                   At lower temperatures,,1650ฐF (699ฐC) and nore highly reducing conditions, the
                            following reaction is favored :
                                                                     832
    

    -------
         CaSO,
    CO
    or •
    H,
                            CaS + 4
                                       CO,
                                       H20
                                                              (2)
           The formation of large amounts of CaS is undesirable since  it prevents the
    reductive decomposition of CaSO^ to CaO.  This will require careful control of pro-
    cess conditions.  If some CaS is formed along the way, it would eventually be
    eliminated (to some extent) by the following reaction at 2000ฐF  (1093ฐC):
         CaS -t-JCaSO.
                            4 CaO + 4 SO,
                                              (3)
           To limit the forr-.ation of CaS, the concentration of reducing gases must be
    carefully controlled.  Also, advantage can be tukon from the fact that CO, and H,0
    and high temperatures suppress the formation of CaS.                     '
    Two-step Process Regeneration
           The two-step dolomite or limestone regeneration process  involves, first, the
    reduction of CaSO, to CaS, and second, the Reaction of the CaS with CO, and H,O to
    form CaCO, and !i,S.  The first step at 1650 F (699 C)  and 1 atmosphere "pressure
                      CO
           CaSO. ป 4  or
                      H,
               CaS + 4
      co2
      or
      II2O
                                              (4)
    The second step at 1COO F (538 C) and 1C atmosphere pressure is:
           Cap + !!,O
        CO,
    CaCO, + H,S
                                                           (S)
           In the first step, the reaction starts out reasonably fast, but then slews
    down quickly due to the tendency of the CaS to cover the pores of the remaining
    crystals of CaSO,, thereby decreasing the available contact surface.
    
           The regenerated additive from this two-step process must be recalcined tc CaO.
    Furthermore, four times as much reducing gas must be used for the two-step ?roc> :s
    compared witn the one-step process.
    
    Process Variables
    
           For cither of the two processes discussed, the most important rrocoss variables
    from the standpoint of regeneration performance are temperature, partial press-re
    of the reducing gases, and space velocity or contact time of the Ca?0. particle;
    and gases   .  An appropriate system for carrying out the additive regeneration pro-
    cess is a fluidized-bed reactor which will provide the necessary temperature unifor-
    mity as well as efficient contact between the oases and solids involved.
    
           When operating in the range of 2000ฐF (1093ฐC) deactivation of the CaSO^
    particles by sintering or deadburning occurs, especially when the solicis r.ust under-
    go repeated cycles of sulfur absorption and regeneration.  In addition, a decree of
    solids attrition can be expected in the regeneration step.  Additive rccirculation
    rate through the reoenerator and fresh additive make-up rates to the ccr.bustor arc
    determined by the amounts of deactivation and attrition that occur in the overall
    process.  Therefore, the overall economics of regeneration will be greatly depen-
    dent upon the additives resistance to these parameters.
                                             833
    

    -------
             "••;<•  ':on|.o:;iMor: of  •.ป.•: ..:::. ':O.T.:.O:.ซT.*.  • .-.  t :..  :::..•:.•  .,•)••: tiv.- will
    
    of  t!.<-  p.i -t I'.-l--:;  in  t h--  f i .ii •! j •/.••<*. !.•••!.
    
             With hi'ih'.-r r--'i--r.- r.it ion  '••:-;. --r.iM.ir--:: ,  *h--r'.- :>•.
    •.ow.irds !.i'|h'-r  :;o;> -:o:i-:-Tii r-itior::; i :i t h" r<-'!":."r-i '.or
    v--r:;ior. to  '.'.iO.
                      mol" f r .i--t . lor.  of TXr.  i r,  t.h*-  r"-;ซTiซ-r.iป.or  off-').i:;  i :.fr<-.is<-.-. ,   ! •!' 1  co::?.::
    f>,r  rซ"jซ-n<'r.iป-.ion  rซ':;surซ-B  l,'-c.iijr.'.- th"  nol"  f r-i'M ion  nl  .'"/>^  .-it  •••) MI ! ;.-t  th"  •.•'jM.-ict tim" -•  - x:. ••••••-1
    throii-ihout  1 1'." l.ซ.-'j, with  si :ni I I'.-.mt |-ro;iort lor.-;  'if  C-i.r-'>  I." in'!  fornn.-fj in::t".i'i  of
    C'jO.   Thi:; [iroi>l--rp e-.in ljซ-  sh-irf'ly r---lu-_-"ii  l"'l'.   Tin::  ''r--.it-':; .nl j.ir:ซ-nt  rซ-'l-j':i r.-| .i:i'i  oxi:. iriitin.it"  yi- I'i-'-
    hyilro.|.-n  Kulfiil--  lor  r'-c-.v-ry .   T.il.l--  I li::t::  |,ro':- ss  t-or.tl i t ions .ir.-.l .-ml  j-rociu-.-t .
    
             The- 1'illowiri'l  t.. ilml.it. ion  li:;t::  t h"  .,'ivjnt .i'lซ-r;  .ind -ii  -I'lv.int-i-l'-::  to  th"  t wซj
    r--li-niT.it ion  |iroc<-::::"::' :
    
             a.   l-'or th" t.i-;<-  \-T'J'-> ••.;•.;
                                     -  l:x|"T IRI"!lt*jl 'l.lt.'l  IS  lV.lllll.1"
                                     -  C.i')  is  fornn.-d  dir--';tly
    
                  Di s.idvant-'i'l'.'S .irr:
                                     -  H--*f.TJtiirt.-s, 2000 K  (10'n"C),
                                        uro  required to ..ivoid  CjS  for —
                                        mition  .'ind d---.ictiv.it > on of the
                                        .idditivc.   Also.clor.c  t"ni'.-.-r,-iturc
                                        control   is needed to  avoid aq<)lo:ner-
                                        ation of the cool  ash  i :i  the bed.
                                     -  At equilibrium, SO-, concentration
                                        decreases  with pressure.
    
             b.   For the  two-stop  regeneration process:
                  Advnntaies are  -  Thermodynamics favored by  low
                                        temperature 1600ฐF  (871ฐC)
                                     -  No  thermodynamic  disadvantage
                                        due  to  pressure
                                     -  Low  temperature avoids solid
                                        sinter ing
                                     -  Pressure favors HjS production
    
                  Disadvantages arc
                                     -  Two  stages required to form  CaCOj
                                     -  Second  stop requires  high  pressure
                                        CO2  and HjO
    
    
    
                                                         834
    

    -------
              TAB!-!: I.  kKCKNKRATION PKGCKSS  CONDITIONS
    Ono-Stop  bo-j'-Tn:- rat i on
    
        Condition:;:      2uOOฐI',  ono Ate1.,  press..
                          Ono  [Milt: reducing qascs
    
        Knd Products:    CaO  for  ritcyclo to coribustoi.
                          SC>2  for  sulfur recovery
    Tv.o-5t'-p  fro.-iofu.-r.'
        i i r r;t  Sf.-p -  Conditions:     lbOOฐF,  or.o Atn. press..
                                        Four n>oles reducing ;jascs
                                        I f.-qu i r c-d
    
                       Knd  Products:   CaS lor  use in second  step
    
        S'.-cond Stf.-p - Conditions:     1100 F,  ton At*., press.
                                        CO2 and  f^O ijascs required
    
                       End  Products:   CaCO^ for  recycle to
                                        comlnistor
                                        II2S for  sulfur recovery
                                  835
    

    -------
                              - Little experimental data available
                                or publicized
                              - Competing reactions reduce sulfate
                                to yield SO,
                              - Produces carbonate- rather than oxide
                                that must be recalcined for recycle
                              - Reaction rate of CaS conversion slows
                                down drastically.
    
           While it is recognized that no firm conclusion can be drawn from an evaluation
    of the above, the one-step process was selected for economic evaluation in this study.
    
    
    SELECTION OF REGENERATION SYSTEM ALTERNATIVES
    
    Regeneration Systems With Claus Sulfur Recovery Plant
    
           After having selected the process to bo used for regeneratinq the spent addi-
    tive, the support processes required to achieve a conplete integrated system were
    then selected.   The philosophy adopted to guide the system design was to utilize com-
    mercially proven processes where available in order to limit the time and cost re-
    quired to commercial i/.e the plant.  This criteria led to the initial selection of a
    Claus plant for the separation and recovery of elemental sulfur.
    
           Prelimi.--ry calculations indicated that it would not be economical to pur-
    chase H,S for the Claus plant.  In order to produce H-S in-piant, the amount of
    reducing gas required would be four times that required for additive regeneration.
    This factor led to the decision to use a separate reducing gas plant to provide the
    raw qas needs for both a II2 producing plant and for the sorbent regeneratiors.  It
    was further decided that. In the interest of completeness, an estimate would still
    be prepared for the case of purchased II2S.  However, to facilitate design and cost
    estimating efforts, the production of reducing gas for the regeneration process was
    still accomplished in a separate process rather than directly in the regenerator
    vessel itself.   While probably not the most economical approach .or this case, the
    incremental costs involved would not significantly affect the conclusion regarding
    overall economics between Case I (Purchased HjS) and Case II (In-plant II,S manufacture),
    
           Figures 1 and 2 show block diagrams of processes selected for Cases I and II
    respectively.  Reducing gases are separately generated in a Koppers-Totzok Coal
    Casifier Package Unit.  A standard Claus sulfur recovery unit and tail-gas treat-
    ment plant arc also shown.  It should be noted that the Claus tai:-gas clean-up
    plant would only be required if the recycle of tail gas  to the fluid bed ccra-
    bustors proved technically or economically impractical.  While this is considered un-
    likely, the clean-up system is included here as a conservative measure.  Again, the
    cost of this plant does not significantly affect the final conclusions.  Other pro-
    cesses used in Case II include a conventional water-gas shift reaction for production
    of II2 and the catalytic reaction of \\2 and sulfur vapors to produce ll^S gas.
    
           The regenerator itself would be operated as a fluidizcd bed reactor designed
    for the following conditions:
    
                             Temperature
                             Pressure                 - 1-2 Atre.
                             Regeneration Efficiency  - 65%
                             Residence Time           - 5 to 7 Minutes
                             Fluidiiing Velocity      - 4 to 7 Feet per Second
                             Reactivity               - 72%
    
           On the b?sis of the block diagrams shown in Figures 1 and 2, a conceptual flow
    diagram and approximate heat and material balances were prepared for each case.
    Figure 3 shows the flow diagram for both cases, with Case II the more complex of the
    two cases.  Approximate sizes for the equipment and piping indicated on the flow
    diagrams were then established for both cases.
                                             836
    

    -------
    CtMnhotgoM
    Wttoon ptoal
                                                                                             lnซrtป to otmeซpปiซrป
    1
    ^M. llall |
    COMB
    Co* OR
    1 — ,
    \
    Sport *orปMl —
    Rt*i
    r
    
    ^•""....K* TOT7FK
    GAS1FIER
    Cool PLANT
    
    UST-f< -l REGEN-
    S ERATOH
    r
    i * i
    J-Rtgviorot*
    idafloo***
    
    J 1
    ' 1
    STO. IT AIL- CAS ,
    CLAUS 'CLEANUP!
    UNIT t UNIT I
    Tl— 	 L J
    To Mlot or
    ซMXbOBt MeHontulfur *ipoปol
    
    PURCHASE!
    M2S
                        Figure 1. Sorbent Regeneration with Claui Plant and Purchand H2S
                                                   Casel
                                                                                            iMrti to otmotalwr*
                       Figure 2. Sorbent Regeneration with Claut Plant and Manufactured H.S
                                                    One II
                                                       837
    

    -------
    00
    IO
    00
         ?^^irv^^
     ra i—i
     i -'" Li r~7l ^ V •-• •  r-^-il |r—\
    •ฃp  t T'i'irp"]^^r\y^ i
      I        '      *•*    I ,-.f.i  r-.ta-
                                                  rfj  r>
                                                  •N-1  h*-
    ^/vnww**/
    
    "" Mte/f
                                    '**ซ*.'
                                         Cf
              "i-'-'-'i
               \*^*'
    "Vr
    l4i
                               Figur* 3. Sorbent Rejsneration with Clauj Plant
                                       Cam I & II
    

    -------
    Regeneration System With RF.SOX '  Plant
    
           When it became apparent that the costs associated with the Claus Sulfur  re-
    covery system represented a major portion of the total ann'jal operation costs for
    Cases I and II, a decision war- made to investigate Foster h^eolcr's RE3OX process
    for this application.  To our knowledge, there  is no RKSOX   process  in corrjr.ercial
    operation as yet, and there is very little technical information available  for  study
    and evaluation.  However, it appeared that overall system costs with  a RKSOX unit
    could be lower than for an equivalent Claus hased system.  Therefore, it was de-
    cided that for comparison purposes, a third case incorporating a RESG.: system should
    be studied on the same basis as Cases I and II.  The block diagram on Figure 4  and
    the conceptual flow diagram on Figure 5 wore prepared based on our interpretation of
    the  sparse information available on RESOX systems.
    
           Case III also differs from Cases I and II in that the RESOX tail-gas is  re-
    cycled back to the AFBC boiler and no tail-gas  clean-up system is unc
    -------
                Owtotoom
                lo
                                                              RttOl toii QCT
                Coal
                              COMBUST-
    r
    
    t
    
    SORBENT
    REGEN-
    ERATOR
    
    1 RE SOX
    REACTORS
    
    
    
    SOL
    COND
    El
                                                                                                         Antnracin coal
                 Sewt HrbMt ood aid
                                                       •naaanซro1ป< tarittat
                                                                                         IMOHM wlfar ta Mlnar
                                Figure 4. Sorbent Regeneration with Retox Sulfur Recovery Plant
                                                          Can III
    I
    *.
      1U
                  r
                                          •u-     r
                           -.v=i-ii-
                                                                       ? „ •
    _^
     z. \
                                                                                         J
                                   Figura S. Sorbent Regeneration with Reiox Sulfur Recovery
                                                          Gate III
                                                          840
    

    -------
               TABLE II. BASIS FOR ECONOMIC EVALUATION
    Materials
    Coal
    Labor
              12,450 BTU/lb. HHV
              4.5% S
              $19.50 per ton del'd  (Bituminous Coal)
              S25.30 per ton dcl'd  (Anthracite Coal)
              Limestone fc Dolomite SV/ton delivered
    
              H-S       S240/ton
              0,        S40/ton
              Amines    S0.77/lb.
              Electri-
                city    S0.0225/KKH
              Water     S.15/1000 gal avg. for all types
              Waste Dis-
                posal   S3/tcn (spent stone & sulfur)
              Sulfur    S50/ton fob plant (sales)
              Operating labor at $20.000/man yr. incl. fringes
              Operating superv. at $2S,000/man yr. incl. fringes
              Chemist, engineer, etc.
    
    Maintenance
    
              Including labor, supervision, supplies, materials and
              parts at 5% of capital cost.
    
    Capital Charges
    
              At 181 of capital cost
    
    Admin, t Overhead
    
              At 40% of labor and maintenance
    
    Cases Studied
    
    Base Case - Once-through Sorbent System
    
    Case I    - One-Step Sorbent Pegeneration System Buying H,S
                'Over the Fence"
    
    Case II   - One-Step Sorbent Regeneration System Making H,S
                In-Plant
    
    Case III  - One-Step Sorbent Regeneration with Resox Sulfur
                Recovery System
                                 841
    

    -------
    TA.-,L=: in.  CO;;T rac-Aaison FOH 600 we
               COMBINED i-ov.'ER J-LAOT
    Capital Cost
    orieratin/> Cost: -f/yr.
    Direct Costs:
    (a) Haw Materials -
    Additive
    Bituminous Coal
    Anthracite Coal
    Oxyr.en
    Liquid I!?S
    (•Use. Chemicals
    Subtota I :
    (b) Utilities -
    Electricity
    Water
    Subtotal:
    (c) Stone >, Ash Disposal
    (d) Maintenance, Etc.
    (e) Operating Later
    TOTAL DIRECT COSTS:
    Indirect Costs
    (a) Capitol Cfian;es
    (b) Admin. '/ Overhead
    TOTAL DiDIKKCT COCTS:
    TOTAL ALL COSTS:
    Without Sulfur Disposal
    Credit for Sulfur Sales
    Net Cost With Sulfur Sales
    ;!et Cost Without Sulfur Sales
    SO2 Renoval Cost Per KWH:
    With Sulfur Sales
    Without Sulfur Sales
    Once
    Through
    SO, 500,000
    $1ป, 1*61,000
    $1.
    $
    $
    $2
    $
    $7
    $1
    $8
    $
    $8
    ฃ8
    ,1*61,
    31*,
    '•3,
    73,
    ,633,
    275,
    i?a,
    ,625,
    990,
    181,
    ,171,
    ,796,
    ปV?6,
    ,796,
    000
    500
    000
    000
    000
    000
    ooo
    000
    000
    ooo
    000
    000
    0
    000
    ooo
    $ 2.3 ail.
    Regeneration
    Case
    $26,0}0
    $ 953
    1,258
    28,912
    53
    $31,177
    * 1,671
    221
    $ 1,392
    ' $ 901*
    $ 1,302
    t Ull
    S5.686
    $ "*,665
    685
    $ 5,370
    $1*1,056
    $ 7,390
    $33,658
    $1*1,500
    $ 8.9
    $ 11.0
    I
    ,000
    ,000
    ,000
    ,000
    ,600
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    ,uoo
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    mil.
    mil.
    
    $51
    $
    2
    3
    $ 7
    $ 1
    $ 2
    $
    $ 2
    •f
    $13
    $ 9
    $10
    $21*
    $ 2
    $21
    $21*
    $
    $
    Ci^e
    ."•/stems
    ฃ r
    ,310,000
    953,000
    ,606,000
    ,522,000
    160,000
    ,21*1
    ,911
    376
    ,288
    901*
    ,6ir,
    57')
    ,628
    J278
    ,69"*
    ,322
    ,1*57
    ,865
    ,1*69
    5.8
    6.5
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    ,000
    looo
    ,000
    ,000
    ,000
    ,000
    ,000
    mil.
    nil.
    Case
    $1^,200
    $ 1,%6
    1,307
    805
    $ 3
    t.
    $
    $ 1
    t
    $ 7
    t 3
    $ 3
    $10
    $ 2
    $ 8
    $11
    $
    $
    VT'
    III
    ,000
    ,000
    ,000
    .000
    6J5.000
    ,096,000
    510,000
    ,11'*
    ,276
    ,810
    ,92-*
    ,158
    ,766
    ,051*
    2.3
    2.9
    ,000
    ,000
    ,000
    ,000
    ,oco
    ,000
    ,000
    nil.
    nil.
                       842
    

    -------
       17 T
    s
    x
    >s
    CO
    _1
    
    x
    to
    o
    u
    5
    o
    2
    1U
    K
    
    
    O
    CO
                                       	WITHOUT SULFUR SALES
    
    
                                       ———WITH SULFUR SALES
         0   5   10   15  20  25  30  35  40  45   50  55  60   65  70
    
                             CAPITAL COST  $ ป I06
                              Figure 6. Capital Cott Sensitivity
                               843
    

    -------
           In comparing direct operating cost, Figure 7  indicates  that  oven  if  the-  actual
    value wore 40V. less than the estimated value on Table  III,  Cases  I  and II would bo
    uneconomical compared with the- once-through cose.  However,  within  tho accuracy of
    this estimate. Case III cost when credited with sulfur  sales is comparable  to costs
    for a once-throu-jh system.
    
           Fiqure 8 shows tho affect of total opera-ting  cost  on  SO, removal  costs for
    the various cases.
    
           Figure 9 shows tho additive- cost that would be  required in order  for the var-
    ious sorbent regeneration cases to be equivalent economically  to  the  once-through
    operation case.  When taking credit for sulfur sales,  those  breakeven sorbent costs
    are as follows:  Case I - S^B/ton;  Case  II - 534/ton;  and  Case III - S7/ton.
    
    ADDITIONAL REGENERATION I'I MIT DATA
    
           Table IV details tho chomi-.il complex manning requirements for the various
    cases studied.  With proper training all  personnel listed are  considered interchange-
    able with power complex personnel.
    
           Table V show:; a summary of overall material flows  for the  various cases  ;n  tons
    per day.
    
    CONCLUSIONS
    
           The results of this study  indicate tho following:
    
           1 - From a technical viewpoint, sorbent regeneration  appears feasible  if f-
               <|uirod to reduce the environmental impact of  fluid  bed solid  v.iste dis-
               posal and utilization.  .More oxper imenta 1 data is required if a  commercial
               ;.•!••"!* is to be designed with significant  confidence levels.
           2 - Sorbent regeneration utilizing sulfur recovery processes with commerci-.il
               operating  experience, such as the Claus  system,  cannot  bo economically
               justifii-d unless sorbent costs approach S"50  per  ton.
           3 - Additional development efforts are required  in order to  achieve  an
               economical ;:dditive reqenoration nystvn.  These  efforts  must  be  focused
               on the development of an economical sulfur  recovery system, such as
               KKSOX, as well as on tho regenerator  itself.   Development  of  o.iซ- with-
               out the other will be of no use economically.
           4 - If the currently projected costs of a RKSOX  system  provo realistic,  sorlx-nt
               regeneration  jtilining this system for sulfur  recovery may be more econom-
               ical than a once-through sorbent system based  r.n  a  sorbent cost  of over
               $7 per ton.  However, to our knowledge, there  is  no RKSOX  system in  com-
               mercial operation today.
    
    ACKNOWLEDGEMENT
    
           This study was carried out on Contract EX-76-C-01-2371  for the U.S.Department
    of Kneny.  The authors grcatfully acknowledge the assistance  of  Mr.  George Weth of
    D.O.E. in tho publication of this paper.  We wish to acknowledge  tho  assistance and
    cooperation of Argonne National Laboratory  in developing  the input  information  for
    Case III.
    
    REFERENCES
    
    1.  Evaluation of the Fluidized-Bed Ccubustion Process, Volume 1, Pressurized-Bed
        Combustion Process Development and Evaluation, Kestinghouse Research Labora-
        tories, Prepared for EPA, December, 1973. P. 165-167. 149.
    2.  Iloke, R.C., et.al.,  "Combustion and Desulfurization of  Coal in  a  FluicJized
        Bed of Limestone", Combustion, January, 1975, P. 6-11.
    3.  Montagna, J.C., ct. al., "Bench Scalp Regeneration of Sulfated  Dolomite and
        Limestone by Reductive Decomposition", Presented at the  Fourth  International
        Conference on Fluidized-Bcd Combustion, December,  1975,  P.393-423.
    4.  K.M. Guthric, W.R. Grice s Co., "Data and Techniques  for Preliminary Capital
        Cost Estimating", Chemical Engineering Magazine, March  24, 1969.   P. 114-142.
                                              844
    

    -------
                                                                                                            /    /
         ^   ซ.  '\   f.  I*  ซ.   •*    ซ   -.  ft
                                            Figure 9. Additive Coit Sensitivity
                                                          845
    

    -------
    TABLE IV.  REGENERATION PLANT OVERALL MANNirJG REQUIREMENTS
    1
    Basis: 7 Days/Me.
    Once Regeneration Systems
    Through Case I Case II
    Overall Supv.
    
    Operation
    Operation Supv.
    Shirt Supv.
    Operators
    Helpers
    Chemists
    Clerks
    Total
    Maintenance
    Maintenance Supv.
    Electricians
    Holoors
    Millwrights
    Helpers
    Pipe Fitters
    Helpers
    Machinists
    Instrument Tech.
    Engineers
    Laborers
    Total
    Overall Total:
    _ _
    
    
    S l
    5
    3 6
    3 6
    2
    - 1
    6S 21
    
    S I
    1
    1
    1
    1 1
    1 1
    1 1
    1
    1
    1
    	 2
    _ii iL.
    II 33
    Note: It is our considered opinion that
    personnel listed
    plex personnel.
    —
    
    
    2
    6
    t
    e
    2
    2
    28
    
    1
    2
    2
    2
    2
    2
    2
    2
    2
    2
    3.
    22
    50
    after proper
    above are interchangeable with
    
    
    Case III Remarks
    From Power
    Complex
    
    1
    5
    5
    5
    2
    1
    19
    
    1
    1
    1
    1
    1
    1
    1
    1
    1
    1
    2
    12
    31 ,
    training all
    power com-
    
                                  846
    

    -------
              TABLE V.   SUMMARY OT OVERALL MATERIAL FLOWS
                          FOR 600 MWe COMBINED POWER PLANT
      Basis:  Tons/Day
                                Once
                               Through
        Regeneration Systems
    
    Case I   Case II   Case III
    Entering;
      Coal:  For Power          5,000
             For Regeneration
             For Sulfur Recovery   -
    
      Oxygen
    
      Liquid H2S
    
      Misc. Chemicals:
             Nitrogen
             Amines
    
      Additwc                   2425
    
    Leavingซ
    
      Spent Additive t Ash       3340
    
    Recovered Sulfur                o
    5.000
      245
      458
       10
      0.1
    
      518
     1147
    
     563(1)
    5.000
      509(2)
               335
       20
      0.1
    
      518
     1147
    
      167(2)
    5.390
      255
      121
    1025(5)
    
    
    
    1390
    
     164(4)
    Notes:   (1)  High sulfur recovery due to purchase of H-.S
             (2)  Includes sulfur in coal to regenerator an3 qasifior
             (3)  Total coal used for regenerator and qasificr for
                  hydrogen generation
             (4)  Stoichiomctric recovery at 901
             (5)  As optimized by Argonnc National Laboratory.  How-
                  ever, according to Argonnc data the total costs arc
                  quite insensitive to additive feed rate over the
                  range of these studies.
                                  847
    

    -------
                QUESTIONS/RESPONSES/COMMENTS
         MR. FAPFP, CHAIP^AN:   Yes,  do we have  a  question or two'  <-'ould
    you qo to the r.ike, so we  don't  lose our  speaker off the end of tho
    honch here.
    
         MP. COrilPAN:  Mank Cochran, Oak Pidqe.   Would  it he possible to
    provide the hydrogen sulfide requirenents of  the Klaus  (?) plant by
    qasifyinq tho hiqh sulfur  fraction fron the coal heneficiation, and
    providinq the hydrogen sulfide in that way'
    
         rซT. MORTON:  '-'ell, that's a very interestinq Question.  It
    sounds like a good idea hut obviously  without  thinking about  it and
    studying it a little hit I really couldn't  answer it.   It would have
    to he looked into.
    
         fp. STFINRFRf-:  Steinberg fron Rrookhaven  "ational Laboratory.
    When comparing your reqenerativo FPC with once-through, have you
    tried to nake any estimates on tho cost,  including  the  cost of
    disposal, of the once-through system, as  you  mentioned  possibly a
    landfill or sone other means and what are the results?
    
         MP. MORTON:  Yes.  Actually, we -1id  include the cost of disposal
    in all of these estimates.  l*e used the value of 3  dollars per ton
    for the landfill costs.  In the  case of the baseline system v/hich was
    the once-through system, the total amount of  limestone  ash was being
    disposed of at that cost and in  the other systems,  some percentage,  I
    think it came out to approximately ?o percent,  which was our makeup
    rate, was charged at thdt  3 dollars a ton.  So, we  did  include dis-
    posal costs.
    
         HP. STFINRFPfi:  Put there may be a break-even  cost going up in
    land disposal in certain areas where the  cost of land disposal comes
    pretty high.
    
         MR. MORTON:  Yes.  ^e use three dollars  a  ton  and, obviously, if
    that ninher got much higher, it  could change  all the economics.
    
         f9>. POPTFR:  .Hn Porter, Fnergy Resources. In you calculation
    of the break-even prices of limestone, what did you assume for the
    number of times the limestone could be regenerated  before it spent
    itself out?
    
         MR. MORTON:  Okay, here we  used the  data that  Argonne has de-
    veloped.  And using some of their data it appeared  that by replacing
    the limestone that was lost by attrition  and  by sizing  our regenerator
                                     848
    

    -------
    large enouqh to get an adeouate anount cf reci reflation, we could got
    hy with approximately twenty....! think the exact nunher cane out at
    ?? percent nakeup rate.  Approximately that.
    
         This, hy the way, is sonewhat of a tradeoff between the size of
    the regenerator and the anount of naterial you want to nake up.  YOU
    have sone leeway there.
    
         MR. McnAM|_Fv:  'ty nane's Mc^auley, Pope, Tvans and Pobhins.  I'n
    particularly interested in whether these sulfur plants you're examining
    have turn-down.  That is, can they follow the power plant.  Or not.
    Or what does it cost to put the turn-down on?
    
         MR. WPTW':  Okay.  We actually didn't get into that stage of
    detail to worry ahout that sort o^ thing,  odiously, it's a question
    that would have to he exanined if this were carried further.  Rut we
    didn't do it.
    
         MR. HAPVEY:  All right, are there any further questions here?  I
    apologize for naking this rather disjointed in ny anxiety to hear fron
    peon's e like Hick Miller.  I overlooked tha fact that there were two
    questions left fron the first session and to when were they addressed?
    
         SPEAKER:  Mr. Morton.
    
         MP. MAP"Fv:  Allright.  You have. ..where is he?  You going to
    answer?  V'ould you use that nicrophone, please?
         MP. WPTOP:  Mr. nijk Newhy asks the followir.g question of Terry
    Morton of Burns and Roe.  Hhat SO? fraction was assuned to he pro-
    duced fron the regenerator?  In all three cases.. .or nay I say that
    1n case one and two the volume fraction was 7.ฐ.  In case three it was
    &.<>.  The next question was "What pressure was the regenerator oper-
    ated at?"  Essentially atnospheric.  Third question vas, "What was the
    source of your Pesox cost data7"  Fron a nodular cost estinating of
    each conponent in the envisioned systen and sone general infomation
    we ohtained fron conversations with Argonne National  Lahoratories.
    That's how we arrived at the estinated capital cost.
                                    349
    

    -------
                           INTRODUCTION
         MR. FABER, CHAIRMAN:   Our  next,  lecture  is on the subject of
    economic feasibility of regenerating sulfated limestones, presented
    by Eugene B. Snyk   He's with the  Chemical Engineering Division of
    Argonne National  Laboratory,  receiving  his BS in chemical engineering
    from Notre Dane,  his ML from  the University  of Florida.  He was
    employed by the Commonwealth  Edison  Company  as a process engineer in
    charge of operating a wet  SOp scrubbing facility from '71 to '75.
    That in itself would get him  all the credentials he needs to get into
    heaven, I'm sure.  From '75 through  '76, he  was employed by Air
    Correction Division of UOP Incorporated as a project engineer.  He
    joined Argonne National Laboratory in April  of 1976 and has worked on
    pressurized fluidized bed  combustion and, more recently, in bench
    scale fluidized bed regeneration.  Eugene.
                                    350
    

    -------
                       Economic   Feasibility  of   Regenerating   Sulfated
                                           Limestones
                          E. B. Smyk. J. C. Montagna. G. J. Vogel. and A. A. Jonke
                                     Argonne National Laboratory
    ABSTRACT
           Rop.encr.it ior. of  t hi-  C.iSO.  in  the  spent  sorbc-nt  of a f lui ili xod-hed cor.huslor ami
    re-cycle of the-  rcsuit in:' CaO  offers  a  roans of reducing the waste disnosal burden of
    this t echr.oloi".-.  A f luidi::c-d-bed  reductive decomposition limestone re-.-enerat ion pro-
    cess has been developed in  PDl'-scalo equipment..   Predict ions fron a model based on
    these experiments combined  vith cost data  developed by Vest inp.house allows not costs
    to be determined  for  various  opor.it in" and economic parameters.  Economic feasibility
    will denend on  the values selected for these factors   A framework is provided for
    analy;-. in;- specific cases.
    
    
    i::~RODrcTio::
    
           Fluidi:'ed-hซ-d  combustion  is beini* developed as  an environmentally acceptable
    ir.ethod of utili::ir.p our nation's  vast  resources  of coal to rent-rate electricity anil/or
    steam.  In addition to  fly  ash waste,  vhich is also produced hy conventional  boilers.
    f luidi/ed-bc-d cor.bustors produce  significant amounts of spent sorbent vhich mist be
    disposed of,  Reri-nerat ion  of C.isO.  in the spi nt sorbent followed by recycle  of the
    sorbent to the  comhtistor (boiler)  offers a means of substantially reducing this addi-
    t ional waste disposal burden.
    
           A fluidi7.ed-bi.-d  reductive-decomposition 1 iniestone-rei'er->rat ion process (in
    which both the  heat of  '••••iction and  '.he  reducinr. >hr>iisc:  nerforned a  cost  st udv on a sorbent rcp.cnerat ton system  for a
    6 "J 'j • .'-!W AFBC coT^bustor.   The system considered  was an atmospher ic-oresst'.re , fluidixcd-
    bed reduct i ve-Oecompnsit iop. process, followed  by a RKSOX Sulfur Recovery System with
    tail ras incineration.   Capital costs  were presented for x-arious process sulfur load-
    ings (i'SL. pounds of  sulfur to the rcc.enerator versus  pounds of con I to the conbustor)
    ami for different rei*onor.'itor off-pas  SO.  concentrations.   In addition, data on
    capital cost versus solids  ciruclafion rate between the combustor and the rcpenerator
    was presented for the sorbent recirculation system.
    
           However,  in their cost analysis.  MostInr.houso did not specifically include
    different regenerator off-pas SO   concentrations and fresh sorbent feed mole ratios
    but instead used  fixed  values.   (The fresh sorbent feed mole ratio,  hereinafter refer-
    red to as FR. is  the cole fraction  of CaO as  fresh feed to the corabustor. compared
    with the total  CaO feed to  the combustor including regenerated sncnt sorbent.)  ANL
    cyclic experiments with Creer limestone  and Tymochtee  dolomite- •"'•u  show that the sor-
    bent. feed rate, recirculat ion rate,  off-p.as SO;,  concentration,  and regenerator coal
    feed rate can all be predicted for specific operating  conditions.""  The ANL results
    also demonstrate  that an economic  analysis is  necessary to determine the most favor-
    able value of Fh.
    
    
    RESULTS AND DISCUSSIONS                                               •
    
           The A"L  model  and the  PDU-data  were used  to relate the values of various para-
    meters f.o FR.   For example, a low  FR (C.R.,  0.05-0.10) would translate to low sorbent
    consumption, hir.h, coal  consumption (in the rer.cnerator). a larp.e rcp.encrator. lower
    SO.- concentration in  t*H> regenerator off-p.as,  and hip,h solids recirculat ion.   A hip.h
    FR (C.R.,  0.30-0.&0) woulu  translate to  medium sorbcnt consumption,  lower ccal con-
    suription in the regenerator,  a smaller regenerator, hip.hcr SO.  concentration  in the
    -,\l\ results froT these  AM. experiments  were not available to Westinp.house when they
     made their economic  study
    
    
                                             851
    

    -------
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    no  :"jl!'ui'  crr-ii'.t.,  ari'i  a  •.•'1:1 i  |I:MI:--  f>!'  J.'^/tori  vX':< |.t. W:M. r-.-  otti'.-:'w I :T-  n'.ivj.
    
             :•".,-,'; I--.-:; •, ttir-j'ic.f:  :-  l"::.or.:;t I'ut'.-  t >,.•  .-rr'-f:'. '>f v:(r!-it lo-n: •.:' C'lj'.-.ii! co::t ,
    (-•;j;..-|'.-!ty .'"actlu:-, :;',rt,--!.t.  ::-;i;..-,  r.uM'ur  crซ-l Iป. ,  ci.;il  i-rl'.-f,  .'ill 1 rr.  .n  tr."  !;<•.  f-iy.MT-
    ;iLi ,ii  uy=tt.-Ei:;  ci>::t..
    
             Fl.-.ur-i-  Si r.how::  tปiซ> t.-lT-.-'.-t  of capital 'itT.t  IrsrrcT.-o on t!if  n"t  .:y^t"n  cjr.t.
    Ki|-.J"<- V :-.liou:: tin-  '.rrvct of  plant.  c-apa.:!ty fact. )i-  nn  rift systv.-a  .-c:>*>..   r I.Vir-.-  8  r.Sown
    ttif >.•!•'."•••:I-  c.f  cti?i I  i.rSco  oil iu.-v  r,y:;t<-n  co:;t..   Kl^ur'.- *> rr.owj tr."  vlTvct.  cf r.ulrui-
    credit on  net  :;yct'-m  O'jr.t.
    
             At  a KR sil'  i . 0  ' corre:;::'jriUI ru* to  a  o:ici'-thr'C.u>;h sys'-oiTi  wit,;.  t  It  art.- fairly  fl'it !n  the rr region  L^tween  rj. '<.'  ari'l  O.;i.
    Th'i:;,  t->ie  •.•conoralcs oT a  cyuti.-Ri  Juct hf-aklns  t"/en  (i.e., a  net coct  tT  ^ero)  iio  i:ct
    ilfpcnsi str'jnj^ly on  trio vaiuซt  ol"  KH  chocen  for  o:?-rrat Ion wri^n r'H 1^  between '".'.ซ".'  ar-d
    O.-'i.   liOBCV'-T, a:;  the  net i—r,ein.-rat Ion  system  c-j;-,t  cie-j;-ซ2Ees furt.'.'-r, t r.e  cftir.u.-n  FR
    'i'.'ercasns  until at  atout  -l.o nlll/kWh,  thf O|.tinum r'R CCC-JTS  at  0.10 to  0.1'.j.   Mlnl-
    muD breakeven  sorbent  price  (Kii:>P) — Including  disposal—  K.IG chOoen as the variable  In
    whicr.  to express all  recultr.  and  was aeflnecl as the  nlniaua  total r.orbent  price  Tor
    which  a ฃlven  nystem  Ic  economically feasible.   Since  a regeneration  system  conserves
    sorb^nt , a  high UP  :;orbent i;rlce  tenas to nalce  the systen core  viable, while  a  decrease
    In  sorci.-nt  price nakes It less viable.   Therefore,  a total  sorbent  price  greater  than
    K3SP makes  the system  economically  viable.
                                                        852
    

    -------
        25
    d  15
    
    
    in
    O
    u
        10
        05
                              50%
          00
                     0 10
    020       03O
    
      FEED RAT!0
                                                        040
                                                                   050
           Figure 1.  Plant Coil (Including Operating. Maintenance. Contingency.
                    Contractor Fee. and Capital Chargt) ซ. Feed Ratio at
                    Variout Capacity Factor*
                                     853
    

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          0 40 '	
          0 30 I—
                 Figure 2. Utility COM w Feed Ratio
         10
        0 8
        06
    Z
    i~*
    O
        04
        02
                      010
                                 O 20       0.30
    
                                   FEED RATIO
    040
               050
                   Figure 3. Net Coal Coit n. Feed Ratio at Various
                           Cod Pricet (S/Ton)
                                   854
    

    -------
    00
    en
    en
                 80
                 7.0
                 60  —
                 3.0
    *
    M
    ^
    in
             en
             O
             u
                 4.0
                 30
                 20
                  10
                                010
                                  0 20       0 30
    
    
                                    FEED RATIO
                                                                   040
    050
                                                                                          0          010         020
    
                                                                                                            FI.CO HAHO
    
    
    
                                                                               Figure 5. Net Sulfur Credit vs. Feed Ratio at Various Sulfur Prices (S/Ton)
                   Figure 4. Net Sorbenl Savings vt. Faed Ratio at Variout Sorbent Prices
    
                            (S/Ton. including disposal)
    

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              0.10
                        O.20      0.30      O.40
                          FEED  RATIO
    Figur* & Nซt Cod of Regeneration Syrttm v*. Feed Ratio for Varioui
            Sorfaent Prica ond Capital Coil Escalations. Capacity Factor
            70K • Coal Prica S25/Ton. No Sulfur Credit
                               856
    

    -------
    -0.5
                                              0.4
                       FEED RATIO
    Fioir* 7. Net Colt of Regeneration System vs. Feed Ratio for Various
            Sorbent Prices and Capacity Factor*. Coal Price $2S/ton. No
            Sulfur Credit
                                                                           25
                                                                           20
                                                                           10
                                                                       o
                                                                       o
                                                                           05
                                                                          •05
                                                                          •10
                                                                                                                       SORBENT
                                                                                                                           5/TON
                                                                                                                       SORBENT
                                                                                                                       AT MO/TON
                                                ISORBENT
                                                / AT MS/TON
                                                J
                                                                                                                    I
         0        01       02       03      0.4
    
                              FEED RATIO
    
    Figure 8. Net Cost of Regeneration System vs. Feed Ratio for Various
            Sorbent and Coal Prices. Capacity Factor • 70%. No Sulfur
            Credit
    

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                 O.I
                                    0.3
                             FEED RATIO
                                              0.4
    Figure 9. Net Cent o! Regeneration Syitem w Feed Ratio for Various
            Sorbent Prices and Sulfur Credits. Capacity Factor • 70%.
            Coal Price S2S/Ton
                              858
    

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    859
    

    -------
      25
      20
    a.
    in
    m
       10
               I
    I
    I
    I
                         COST    CAPACITY SULFUR
                      ESCALATION FACTOR  CREDIT
                          %        %    $/TON
                          50        50       0
                                    50
                                    50
    
                                    70
                                    50
                                    70
                                    50
                                    70
                                    50
                                    70
                                      25
                                      50_
    
                                      0
                                      0
                                      25
                                      25
                                      50.
                                      50
                                      0
                                                      70       25
    
                                                      70       50_
               10     20     30     4O
                COAL PRICE.  $/TON
                                          50
           Figure 10. MBSP vi. Coal Prica at Various Capacity Factors. Cost
                   Escalations, and Sulfur Credits
                              860
    

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           The  second computer program can predict the effects of the following variables
    cr. net plant  cost:
    
             1.  Capital  cost
             2.  Capital  cost  escalation
             3.  Plant size dXVJ)
             ^.  Plant efficiency (heat rate)
            .5.  Coal  heating  value (iiHV)
             6.  Coal  sulfur content
             7.  Sorbent  calcium content
             3.  CaO/S feed ratio
             9.  Regenerator off-gas S02 concentration
           10.  Contingency
           11.  Contractor's  fee
           12.  Capital  charge
           13.  Operating and maintenance charge
           IH.  Utility  cost
           15.  Coal  price
           16.  Sulfur credit
           17.  Sorbent  Price
           13.  Feed  ratio (FFO
    
    
    REFERENCES
    
      1.   Fluldized Bed Combustion Development, Volune II,—Calcium Based Sorbent
          Regeneration, VIestingtiouso Research and Development Center, Contract  ilo.  68-02-
          213Jr,  USKi'A, February lyYY.
      2.   G.  J.  Vogel  ct  al. ,  "Supportive Studies in Flu;-.11 zed-bed Combustion," Argonne
          liatlonal" LAboratory, July-Septcriber 1976, A.'JL/hlS-CEN-lOl? and FE-1780-5.
      3.   S.  J.  Vo?;el   ':t al., "Supportive Studies In Fluidi7.ed-Bed Combustion," Argonne
          National Laboratory, January-Xiarch 1977, A!IL/K::-CK!;-1019 and FK-1780-7.
      U.   r,.  J.  Vogel  et  al.,  "Supportive  Studies in Fluidized-Bed Combustion," Argonne
          I;atloi;al Laboratory, October-Uecenber 1976, ANL/ES-CiCN-lOlS and FE-1730-6.
    
    
    ACKNOVfLEDGMENTS
    
           This work was performed  under  the auspices  of  the  U.S.  Energy  Research atid
    Development Administration  and  Environmental  Protection Agency.   We  thank D.  Webster
    and Les Burris for their  support and  guidance.   We also thank J.  Simmons the  technical
    editor.
                                              861
    

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                 QUESTIONS/RESPONSES/COMMENTS
         MR. FABLR:  Would you pass your written questions  to  the center
    aisle, please.  Bill will pick them up.
    
         SPEAKER:  I guess I  have some misunderstanding.   I  think you
    said the fresh feed to recycle ratio is  determined  by economics  and
    if one has to have a bed  with fixed reactivity,  given a  coal through-
    put and there sulfur throughput through  that bed, then  I think the
    fresh feed to recycle ratio in the bed is fixed  by  the  loss of
    reactivity of the stone as it goes through the bed. There's a direct
    correlation between the two.  Maybe I misunderstood what you said.
    
         MR. SMYK:  Let me r,o through our experimental  technique first.
    Correct tne if I'm wrong on this, John (Vogel).  We  ran  cycle
    combustion-regeneration experiments (i.e., with  no  fresh make-up
    sorbent) with both Tymochtee dolomite and Greer  limestone  results
    only.  Since the combustion experiments  were run with Sewickley  coal
    (containing 4.3 percent S), 83 percent S0ฃ retention was necessary
    to comply with EPA emission regulations.  In combustion  cycle #1, a
    Cal/S mole ratio necessary to obtain 83  percent  SC>2 retention was
    utilized.  In combustion  cycle #2 (i.e., the stone  had  been regener-
    ated once), the same CaO/S mole ratio was used as before and the
    S02 retention was measured.  The S0ฃ retention in subsequent
    cycles was measured and used to correlate the loss  of reactivity of
    the stone as a function of combust-regeneration  cycle.
    
         Our mathematical model allows us to predict the age distribution
    of the bed sorbent material as a function of the ratio  of  fresh
    sorbent feed to the bed versus the recycled sorbent feed from the
    regenerator.  For example, at a low fresh feed to regenerated feed
    ratio one would have an "old" and fairly low reactivity  bed.  Conver-
    sely, at a high fresh feed to regenerated feed ratio one would have a
    "young" and highly reactive bed.
         Now, if a bed is highly reactive it  can attain  83  percent
    retention at a fairly low total  CaO/S mole ratio;  but  if  it  has a
    fairly low reactivity, a higher  total CaO/S mole  ratio  must  be util-
    ized to attain 83 percent S02 retention in either case; the  trade-
    off is this:  At a low fresh feed to total  feed (including regenerated
    feed) ratio one uses less fresh  sorbent but must  recycle  large amounts
    of regenerated stone therby necessitating a large  regenerator and
    transport system.  At a high fresh feed to total  feed  ratio  one used
    more fresh sorbent but does not  have to recycle as much regenerated
    sorbent therby requiring a small  regenerator and  transport system.
    Thus, the decision is a balance  between operating  and capital costs -
    a question which can only be answerod by  an economic evaluation which
    is what we have attempted to do.
    
                                     862
    

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         MR. FABER:  Before we take a break,  if you've got any more
    questions written down, pass them to the  center.   Bill Harvey
    and I have a little announcement to make.  Most of you are not
    aware that our light man is one of the most intellectual  and  educated
    and highest paid light men in the world,  Dr. John Minnick, a  friend
    of ours.  And we think that since he's done such  a good job in  the
    first half, that we will be cble to go on through the whole session
    without retraining him this afternoon.
                                     863
    

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    Appendices
         365
    

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                                Appendix A
                             Table of Contents
                                 Volume I
    PREFACE                                                       1-il
    
      Welcoming Remarks:  Richard S.  Greeley,                         3
        The MITRE Corporation/Metrek  Division
        McLean, Virginia
    
    KEYNOTE ADDRESS                                                  5
    
      Introduction:  George Fumich, U.S.  Department  of               7
        Energy, Washington, D. C.
    
      Keynote Address:  S. David Freeman, Tennessee  Valley           8
        Authority, Knoxville, Tennessee
    
      Questions/Responses/Comments                                 ^
    DINNER ADDRESS                                                  17
    
      Introduction:  Charles A.  Zraket,  The MITRE                   18
        Corporation, Bedford, Massachusetts
    
      Dinner Address:   John A. Bel ding,  U.S.  Department              19
        of Energy, Washington, D.  C.
    
      Questions/Responses/Comments                                  23
    OVERVIEW OF U.S. AND INTERNATIONAL PROGRAMS                     31
    
      Introduction of Plenary Session Chairman:                      33
        V. Ovcharenko, United Nations Center for
        Natural Resources,  Energy and Transport,
        United Nations, New York
    
      An Overview of the Progress in Fit.id Bed                       35
        Combustion in the United Kingdom:   W. G.
        Kaye, National Coal  Board, Coal Research
        Establishment, Stoke Orchard, England
                                    A-l
    

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                                                                    Paye
      The International Energy Agency Program:                        43
        David H. Broadbent, NCB (IEA Services)
        Limited, London, England
    
      Fluidized-Bed Combustion - Overview of the                      47
        Program of the Federal Republic of
        Germany:  Rolf Holiqhaus, Kernforschunqs-
        anlaqe ("FA), Juelich, Federal Republic
        of Germany
    
      The U. S. Department of Energy Program:                         57
        Steven I. Freedman, U. S. Department
        of Energy, Washington, D. C.
    
      The EPA Fluidized-Bed Combustion Program -                      62
        An Update-  D. Bruce Henschel, Industrial
        Environmental Research Laboratory, U. S.
        Environmental Protection Agency, Research
        Triangle Park, North Carolina
    
      The Ohio Energy and Resource Development                        77
        Authority Program:  Eric K. Johnson,
        Ohio State Department of Energy, Columbus,
        Ohio
    
      Overview of New York State's Fluidized Bed                      81
        Combustion Program:  Richard H. Tourin,
        Energy ".esearch an* Development Authority,
        New York, New York
    
      The Fluidized-Bed Combustion Proqram of the                     87
        Tennessee Valley Authority:  Harold L. Folken-
        berry, Tennessee Valley Authority,
        Chattanooga, Tennessee
    
      Overview of EPRI FBC Program:  Terry E. Lund,                   94
        Electric Power Research Institute, Palo
        Alto, California
    
    
    COMMENT by James J.  Markowsky                                    100
      American Electric Power Service Corporation,
      New York, New York
                                     A-2
    

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                                                                    Page
    APPENDICES                                                       101
      Appendix A - Conference Program                                A-l
      Appendix B - Table of Contents - Volume II                     B-l
      Appendix C - Table of Contents - Volume III                    C-l
      Appendix D - Attendees - Alphabetical Listing                  D-l
      Appendix E - Attendees - Alphabetical Organizational           E-l
                   Affiliation
      Appendix F - Author Index                                      F-l
                                     A-3
    

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                                Appendix B
    
                            Table of Contents
                                 Volume II
    
                                                                   Page
    
    
    INTRODUCTION
    
    
    OVERVIEW OF COMMERCIALIZATION ACTIVITIES                            1
    
      A State of the Art  Resume:   Alan  A. Smith,                        4
        Babcock and Wilcox,  Ltd., England
    
      The Practical and Commercial Application of                      14
        Fluid Bed Combustion for Use  in Industrial
        Boiler Plants:  P.  B.  Caplin, The Energy
        Equipment Company,  Limited, Energy  House,
        Olney, Buckinghamshire,  England
    
      Status of Fluidized Bed  Combustion in Norway                     20
        and Sweden:  Frode  Pedersen, 0. Mustad and
        Sons A/S, Gjovik, Norway
    
      Industrial Coal  Fired Fluidized Bed Boilers                      22
        and Waste Heat Boilers:   Michael  J. Virr,
        Stone-Platt Fluidfire  Limited,  Netherton,
        West Midlands,  England
    
    
    INDUSTRIAL APPLICATIONS                                           41
    
      A Comparison of Industrial  and Utility  Fluidized                 44
        Bed Combustion Boiler  Design Considerations:
        J. William Smith, The  Babcock & Wilcox
        Company, Barberton,  Ohio
    
      Industrial Application - Fluidized  Bed  Combus-                   61
        tion - Georgetown University:   Robert Tracey,
        Fluidized Combustion Company; Frederick
        Wachtler, Foster  Wheeler Energy Corporation,
        Livingston, New Jersey;  Victor  Buck,  Pope,
        Evans and Robbins,  Inc., New York,  New York
                                    B-l
    

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                                                                    Page
    
    
      Fluidized Bed Combustor For Small Industrial                     91
        Applications:  H. A. Hanson, D. G. DeCoursin,
        and D. D. Kinzler FluiDyne Enqineerinq C^rpora-
        tion, Minneapolis, Minnesota
    
      The Anthracite Culm/Anthracite Combustion Pro-                 107
        ijram:  John Geffken, U.S. Department of Energy,
        Washington, 0. C.
    
      A Comparison of Conventional Oil-Fired and                     ll"/
        Fluidized Bed Coal-Fired Petroleum Refinery
        Atmospheric Crude Furnaces:  Charles Bliss,
        The MITRE Corporation, METREK Division,
        McLean, Virginia
    
      A Fluidized Bed Mot Gas Generator for Conversion               145
        of Oil-Fired Boilers into Coal-Firing:  Prabir
        Basu, K. L. Das, and M. K. Chanda, Central
        Mechanical Engineering Research Institute,
        Durgapur, India
    UTILITY APPLICATIONS - Atmospheric Mode                          157
    
      The Department of Energy Atmospheric Fluidized                 160
        Bed Combustion Utility Demonstration Program:
        Edward Trexler, U.S.  Department of Energy,
        Washington, D. C.
    
      Technological Development Priorities of Atmos-                 169
        pheric Fluidized-Bed  Combustion:   John E.
        Mesko, Pope, Evans and Robbins, Inc., New
        York, New York
    
      The Rivesville Installation from the View of  the               187
        Monongahela Power Company:   Homer T. McCarthy,
        Allegheny Power Service Corporation, Greens-
        burg, Pennsylvania
    
      First Performance Results from the Rivesvillo                  191
        Multi-Cell Fluidized  Bed Boiler:   G. Claypoole,
        D. Hill, and R. Mineo, Pope, Evans and Robbins,
        Inc., Rivesville, West Virginia
                                    B-2
    

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                                                                  Page
    
    
    Startup and Initial  Operation of the Rives-                    203
      ville 30 MWe Fluid Bed Boiler:  Thomas E.
      Stringfellow, Pope, Evans and Robbins, Inc.,
      Rivesville, West Virginia; John G. Branam,
      The MITRE Corporation, toetrek Division, McLean,
      Virginia
    
    Lightoff ^ '• Multicell Fluidized Bed Boilers by                 221
      Hot Bed Transfer:   L. Gasner, 9. Turek, Uni-
      versity of Maryland, College Park, Maryland;
      C. Aulisio and Ouane Mill, Pope, Evans and
      Robbins, Inc., Alexandria, Virginia
    
    Material Handling Systems For FBC'S - Extrapo-                 239
      lating Rivesville to 600 Megawatts:  James J.
      Murphy, Allen-Shennan-Hoff Company, Malvern,
      Pennsylvania
    
    An Investigation of Alternative Feed Systems For               248
      Utility-Scale Fluidized-Bed Steam Generators/
      Combustors (200 MWe or Larger Units):  B. K. Bis-
      was, Foster Wheeier Development Corporation;
      J. U. Baley, Foster Wheeler Energy Corporation,
      Livingston, New Jersey
    
    The Application of Atmospheric Fluidized Bed Combus-            267
      tion for Electrical Power Generation:  Thomas  W.
      Becker, Babcock and Wilcox Company, Barberton,
      Ohio
    
    Conceptual Design of a Foster Wheeler Energy                   285
      Corporation Atmospheric Fluidized T-ed Steam
      Generator for Stone and Webster Engineering
      Corporation and Tennessee Valley Authority:
      Kenneth A. Reed and George Cervenka, Foster
      Wheeler Energy Corporation, Livingston, New
      Jersey
    
    Conceptual Design and Preliminary Evaluation of  a               313
      570 MW Electric Power Generating Plant Using a
      Babcock & Wilcox Company or a Foster Wheeler
      Energy Corporation Atmospheric Fluidized-Bed
      Boiler:  P. F. Lipari  am1 T.  C. Wells, Jr.,
      Stone & Webster Engineering Corporation, Boston,
      Massachusetts
    
                                   B-3
    

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      Conceptual  Design  of a  570-MW Combustion Engi-                 326
        neering,  Inc.  Atmospheric  Fluidized-Bed Steam
        Generator:   Russell B.  Covell,  Combustion
        Engineering,  Inc., Windsor, Connecticut
    
      The Conceptual  Design of  an  AFBC  Electric Power                343
        Generating  Plant:   William J. Bradley, Burns
        and Roe,  Inc., Woodbury, New York
    
      A Comparison  of Selected  Design Aspects of Three               355
        Atmospheric Fluidized Bed  Combustion Conceptual
        Power Plant Designs:  D. N. Garner, W. C. Howe,
        and P. S. Dzierlenga, Radian Corporation, McLean,
        Virginia
    
      Experiences of Fluidized-Bed Combustion of Peat                375
        in Finland:  A.  Jahkola, Helsinki University of
        Technology, Helsinki, Finland
    
    
    UTILITY APPLICATIONS - Pressurized   Mode                         385
    
      Design of a Gas Turbine Plant with a Pressuri-                 388
        zed Fluidized Bed  Combustor: H. D. Schilling and
        H. Schreckenberg,  Bergbau-Forschung GmbH, Essen
        Wied, Vereinigte Kesselwerke A. G., Dussel-
        dorf. Federal  Republic  of  Germany
    
      The Curtiss-Wright Pressurized Fluidized Bed                   401
        Pilot Electric Plant:  Seymour  Moskowitz, Cur-
        tiss-Wright Corporation, Wood-Ridge, New Jersey
    
      General Electric Pressurized Fluidized Bed Power               413
        Plant Status:   R.  D.  Brooks and J. R. Peterson,
        General Electric Company,  Schenectady, New York
    
      Conceptual  Design of a  Coal  Fueled, Fluid Bed                  434
        Combined  Cycle Power  Plant:  D. A. Huber and
        R. M. Costello,  Burns and  Roe  Industrial Services
        Corporation, Paramus, New  Jersey; J. J. Morgan and
        A. J. Giramonti, United Technologies Research Center,
        Hartford, Connecticut;  J.  W. Smith, Babcock and
        Wilcox Company,  Barberton, Ohio
                                     B-4
    

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    ENVIRONMENTAL ASPECTS
    
      Monitoring                                                     459
    
      Development of Environmental  Objectives Based                  462
        on Health and Ecological  Effects:   B. W.
        Cornaby, K. S. Murthy, D.A. Savitz, and
        L. Pomerantz, Battelle Columbus Laboratories,
        Columbus, Ohio
    
      Design of Ambient Monitoring  Programs For Pro-                  478
        totype Fluidized-Bed Combustion Facilities:
        J. M. Allen, D. Ambrose,  R. Clark,  and P.  R.
        Sticksel, Battelle Columbus Laboratories,
        Columbus, Ohio
    
      Plans and Studies on Flue Gas Cleaning and                      493
        Particulate Monitoring in PFBC: W. M.
        Swift, S. Lee, J. C. Montagna,  G. W. Smith,
        I. Johnson, G. J., Vogel, and A. A. Jonke,
        Argonne National Laboratory, Argonne, Illinois
    
    
      Emission Characterization and Control                          523
    
      Thermodynamic Projections of  Trace Element                      526
        Release in Fluidized-Bed  Combustion Systems:
        M. A. Alvin, E. P. O'Neill, and D.  L.
        Keairns, Westinghouse R&D Center, Pittsburgh,
        Pennsylvania
    
      Multimedia Pollutant Emissions Data for Fluid-                  544
        ized Bed Combustion of Coal: K. S. Kurthy,
        D. A. Sharp, K. M. Duke,  and J. M.  Allen,
        Battelle Columbus Laboratories, Columbus,  Ohio
    
      Effluent Characterization from a  Conical  Pres-                  560
        surized Fluid Bed:  R. J. Priem, R. J.  Rollbuhler,
        and R. W. Patch, NASA-Lewis Research Center,
        Cleveland, Ohio
    
      NO Reduction by Char in Fluidized Combustion:                   577
        Janos M. Beer, Adel  F. Sarofim, Lisa K. Chan,
        and Alice M. Sprouse, Massachusetts Institute
        of Technology, Cambridge, Massachusetts
    
                                     B-5
    

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                                                                  Page
    Control of Nitric Oxide and Carbon Monoxide                    594
      Emissions in Fluidized Bed Combustion:
      Koya Sakamota, Babcock Hitachi Company,
      Hiroshima, Japan
    
    A Model Study for the Development of Low Nox                   605
      Fluidized-Bed Coal  Combustors:  Masayuki  Horio,
      and Iwao Muchi, Nagoya University, Nagoya,
      Japan; Shigekatsu Mori, Nagoya Institute
      of Technology, Nagoya, Japan
    
    Particulate Control for Pressurized Fluidized-                 626
      Bed Combustion Processes:  D. F. Ciliberti,
      D. H. Archer and D. L. Keairns, Westinghouse
      R&D Center, Pittsburgh, Pennsylvania
    
    Particle Size in Pressurised Combustors:  K. K.                642
      Pallai and W. V. Battcock, (Speaker, H. R. Hoy),
      National Coal Board Utilisation Research
      Laboratory, Leatherhead, England
    
    Characterization of Efflux from a Pressurized                   655
      Fluidized Bed Combustor:  K.  L. Bekofske,
      C. M. Thoennes, and W. G. Giles, General
      Electric Company, Schenectady, New York
    SOX Sorbent - Selection                                        677
    
    Initial Assessment of Alternative S0ฃ Sorbents                  btfO
      for Fluidized-Bed Combustion Power Plants:
      R. A. Newby and D.L. Keairns, Westinghouse
      R&D Center, Pittsburgh, Pennsylvania
    
    Regenerative Iron Bearing Sorbents for Use in                  701
      Fluidized Bed Combustion:   P. J. hcGauley,
      Pope, Evans and Robbins, Inc., New York,
      New York; A. A. Dor and F.  A. Bumje, The
      Hanna Mining Company, Cleveland, Ohio
                                   B-6
    

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                                                                  Page
    
    
    Effects of Coal Composition and Ash Reinjection                729
      on Sulfur Retention Burning Lignite and Wes-
      tern Subbituminous Coals:  Gerald M. Goblirsch,
      Richard W. Fehr, and Everett A. Sondreal,
      Grand Forks Energy Research Center, Grand Forks,
      North Dakota
    
    SOX Sorbent - Utilization                                      745
    
    The Prediction of Limestone Requirements for                   748
      SC>2 Emission Control in Atmospheric Pres-
      sure Fluidized-Bed Combustion:  Robert B.
      Snyder, W. Ira Wilson, and Irving Johnson,
      Argonne National Laboratory, Argonne, Illinois
    
    Limestone Utilization Optimization in Fluidized                763
      Bed Boilers:  Larry L. Gasner and Scott E.
      Setesak, University of Maryland, College Park,
      Maryland
    
    The Mechanism of the Salt Additive Effect on the               776
      S02 Reactivity of Limestone:  J. Shearer,
      Irving Johnson, and C. Turner, Argonne
      National  Laboratory, Argonne, Illinois
    
    Modelling Desulfurization Reactions in Fluidized               787
      Bed Combustors:  C. Georgakis, J. Szekely,
      C. W. Chang, J. W. Chrostowski, and T. Trinh,
      Massachusetts Institute of Technology,
      Cambridge, Massachusetts
    
    SOX Sorbent - Disposal                                         797
    
    Potential Uses for the Residue from the Fluidized              800
      Bed Combustion Process:  Richard H. Miller, Sr.,
      Valley Forge Laboratories, Inc., and Villanova
      University, Devon, Pennsylvania
    
    Leaching Experiments on Soil and Mine Spoil                     821
      Treated vปith Fluidized Bed Combustion Waste:
      R. C. Sidie, W. L. Stout, J. L. Hern, and
      0. L. Bennett, U.S. Department of Agriculture,
      Morgantown, West Virginia
                                  B-7
    

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                                                                    Page
    
    
      Characterization of Fluidized Bed Combustion                   833
        Waste Composition and Variability as they
        Relate to Disposal  on Agricultural Lands:
        J. L. Hern, W. L. Stout, R. C.  Sidle, and
        0. L. Bennett, U.S.  Department  of Agriculture,
        Morgantown, West Virginia
    
      Impact                                                         843
    
      Environmental Impact  of the Disposal of Pro-                   846
        cessed and Unprocessed FBC Bed  Material and
        Carry-Over:  C.  C.  Sun, C. H.  Peterson, and
        D. L. Keairns, Westinghouse R&D Center,
        Pittsburgh, Pennsylvania
    
      Assessment of the Impact of S02,  NOX, and                      875
        Particulate Emission Standards  on Fluidized-Bed
        Combustion System Design and Energy Costs:
        R. A. Newby, N.  Ulerich, E. P.  O'Neill, D. F.
        Ciliberti, and D. L. Keairns,  Westinghouse
        R&D Center, Pittsburgh, Pennsylvania
    
      Relative Environmental Impact of  Two 570 MW                    892
        Atmospheric Flซ:idized-Bed Electric Power
        Generating Plants Compared to  a Pulverized
        Coal Fired Plant Equipped with  a Wet Limestone
        Flue Gas Desulfurization System:  R. C. Stone,
        Stone & Webster Engineering Corporation,  Boston,
        Massachusetts
    
      Environmental Analysis of the General Electric PFB             898
        Combined Cycle Power Plant Design:  V. H. Lucke
        and K. R. Murphy, General Electric Company,
        Schenectady, New York
    
    
    APPENDICES                                                       915
    
      Appendix A - Table of Contents -  Volume I                      A-l
    
      Appendix B - Table of Contents -  Volume III                    B-l
    
      Appendix C - Author Index                                      C-l
                                     B-8
    

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                                Appendix  C
                                Author Index
    ALLEN, J. M.
    Design of Ambient Monitoring Pro-
    grams for Prototype FTuidized-
    Bed Combustion Facilities,
    Vol. II, p. 478
    
    Multimedia Pollutant Emissions
    Data for Fluidized-Bed Com-
    bustion of Coal, Vol. II, p.544
    
    ALVIN, M. A.
    Thermodynamic Projections of
    Trace Element Release in Fluid-
    ized-Bed Combustion Systems,
    Vol. II, p. 526
    
    AMBROSE, D.
    Design of Ambient Monitoring Pro-
    grams for Prototype Fluidized-
    Bed Combustion Facilities,
    Vol. II, p. 478
    
    ARCHER, D. H.
    Particulate Control for Pres-
    surized Fluidized-Bed Combus-
    tion Processes, Vol. II, p. 626
    
    AULISIO, C.
    Lightoff of Multicell
    Fluidized Bed Boilers by Hot Bed
    Transfer, Vol. II, p. 223
    
    Results of Recent Test Pro-
    gram Related to AKB Combustion
    Efficiency, Vol. Ill, p. 82
    
    BACHALO, WILLIAM D.
    Particle Field Diagnostics
    Systems for Fluidized Bed Com-
    bustion Facilities, Vol. Ill,
    p. 362
    BALEY, 0. U.
    An Investigation of Alternative
    Feed Systems for Utility-Scale
    Fluiciized-Bed Steam Generators/
    Combustors (*GG Mw'e or Larger
    units), vol. li, p. 246
    
    BAft-LUritN, A.
    Fluid Dynamic Modelling ot
    Huidized bed Combustors,
    Vol. Ill, p. 45B
    
    BARON, K. E.
    A Model of Coal Combustion
    in Fluidized Bed Combustors,
    Vol. Ill, p. 437
    
    BASU, PRABIR
    A Fluidized Bed Hot Gas Generator
    for Conversion of Oil-Fired Boilers
    into Coal-Firing, Vol. II, p. 145
    
    BATTCOCK, WHALLEY V.
    Particle Size in Pressurized
    Combustors, Vol. II, p. 642
    
    BECKER, THOMAS W.
    The Application of Atmospheric
    Huidized Bed Combustion for
    Electrical Power Generation,
    Vol. II, p. 267
    
    BEER, JANOS, M.
    A Model of Coal Combustion in
    Fluidized Bed Conbustors, Vol. Ill,
    p. 437
    
    NO Reduction by Char in Fluid-
    ized Combustion, Vol. II, p. B77
    
    BEKOFSKE, K. L.
    Characterization of Efflux from
    A Pressurized Fluidized Bed Com-
    bustor, Vol. II, p. 655
                                     C-l
    

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    BELTRAN, A. M.
    Turbine Materials Corrosion in
    the Coal-Fired Combined Cycle,
    Vol. Ill, p. 714
    
    BENNETT, 0. L.
    Leaching Experiments on Soil and
    Mine Spoil Treated with Fluidized
    Bed Combustion Waste, Vol. II,
    p. 821
    
    Characterization of Fluidized Bed
    Combustion Waste Composition and
    Variability as they Relate to Dis-
    posal on Agricultural Lands,
    Vol. II, p. 833
    
    BERKOWITZ, DAVID A.
    Dynamic Modelling, Testing, and
    Control of Fluidized Bed Systems,
    Vol. Ill, p. 488
    
    BERTRAND, R. R.
    Evaluation of a Granular Bed
    Filter for Particulate Control
    in Fluidized Bed Combustion,
    Vol. Ill, p. 504
    
    Pressurized Huidized Bed Coal
    Combustion and Sorbent Regen-
    eration, Vol. Ill, p. 756
    
    BIANCO, J. H.
    An Engineering Study on the Re-
    generation of .culfated Additive
    from a Fluid-i.ed-Bed Coal-Fired
    Power Plant, Vol. Ill, p. 832
    
    BISWAS, D. K.
    An Investigation of Alternative
    Feed Systems for Utility-Scale
    Fluidized-Bed Steam Generators/
    Combustors (200 MWe or Larger
    Units), Vol. II, p. 248
    BLISS, CHARLES
    A Comparison of Conventional  Oil-
    Fired and Fluidized Bed Coal-
    Fired Petroleum Refinery
    Atmospheric Crude Furnaces,
    Vol. II, p. 117
    
    BONK, D. L.
    B&W/EPRI's 6' x 6' Fluidized
    Bed Combustion Development
    Facility:  An Overview, Vol.  Ill,
    p. 24
    
    BORGHI, G.
    A Model of Coal Combustion in
    Fluidized Bed Combustors, Vol.  Ill,
    p. 437
    
    BRADLEY, JEFFREY F.
    Multiple Jet Particle Collec-
    tion in a Cyclone by Reheating
    Fluidized Bed Combustion Products,
    Vol. Ill, p. 607
    
    BRADLEY, WILLIAM J.
    The Conceptual Design of an AFBC
    Electric Power Generating Plant,
    Vol. II, p. 343
    
    BRANAM, JOHN G.
    Startup and Initial Operation of
    the Rivesville 30 MWe Fluid Bed
    Boiler, Vol. II, p. 203
    BROADBENT, DAVID H.
    The International Energy
    Agency Program, Vol. I, p.
    43
    A Technical Description of
    the Plant Design and Project
    Progress Report, Vol. Ill, p.
       310
    BROOKS, R. D.
    General Electric Pressurized
    Fluidized Bed Power Plant Status,
    Vol. II, p. 413
                                    C-2
    

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    BUCK, VICTOR
    Industrial Application - Fluidi/ed
    Bed Combustion - Georgetown
    University, Vol. II, p. 61
    
    BUNGE, F. H.
    Regenerative Iron Bearing Sorbents
    for Use in Flnidi zed Bed Combus-
    tion, Vol. II, p. 701
    
    BUSH, JOHN
    High Temperature, High Pressure
    Electrostatic Precipitation,
    Vol. Ill, p. 640
    
    BYAM, J. W.
    Atmospheric Fluidized Bed Com-
    ponent Test and  Integration
    Facility - An Update, Vol. Ill,
    P. 4
    CALVERT, S.
    Granular Bed Filters for Particu-
    late Removal at High Temperature
    and Pressure, Vol. Ill, p. 516
    
    CAPLIN,  P. B.
    The  Practical ana Commercial
    Application of  Fluid Bed  Combus-
    tion for Us?  in  Industrial
    Boiler Plants,  Vol. II, p . 14
    
    CATIPOVIC N.
    Solid Tracer  Studies in a Tube-
    Filled Fluidized Bed, Vol. Ill,
    p. 135
    
    CERVENKA, GEORGE G.
    Conceptual Design of a Foster
    Wheeler  Energy  Corporation Atmos-
    pheric Fluidizsd Bed Steam Gen-
    erator for Stone and Webster
    Engineering Corporation and
    Tennessee Valley Authority,
    Vol.  II, p. 285
    
    CHAN, LISA K.
    NO Reduction  by Char in Fluidized
    Bed  Combustion, Vol. II,  p. 577
    CHANDA, M. K.
    A  Fluidized Bed Hot Gas Generator
    for  Conversion of Oil -Fired Boil-
    ers  into  Coal-Firing,  Vol. II,
    p. 145
    CHANG, C.  VI.
    Modelling Oesulf urization Reac-
    tions in Fluidized Bed Combustors,
    Vol.  II, p. 787
    
    CHEN, ,). C.
    Centrifugal Fluidized Bed
    Combustion, Vol. Ill, p.  288
    
    CHEN, JAMES M.
    Regeneration of Lime-Based Sor-
    bents in a Kiln with Solid
    Reductants, Vol. Ill, p.  798
    
    CHERRINGTON, 0. C.
    Industrial Application of Fluid-
    ized Bed Combustion - Single Tube
    Heat Transfer Studies, Vol. Ill,
    p. 184
    
    CHROSTOWSKI, J. W.
    Modelling Desulfurization Reac-
    tions in Fluidized Bed Combus-
    tors, Vol. II, p.  787
    
    CILIBERTI, D.  F.
    Particulate Control  for Pressur-
    ized Fluidized-Bed Combustion
    Processes, Vol. II,  p. 626
    Assessment of the Impact of
    NOX, and Particulate Emission
    Standards on Fluidized-Bed Comlus-
    tion System Desiqn and Energy
    Costs, Vol. II, p. 875
    
    CLARK, R.
    Design of Ambient Monitoring Pro-
    grams for Prototype Fluidized-Bed
    Combustion Facilities, Vol. II,
    p. 478
    
    CLAYPOOLE, GEORGE
    First Performance Results from
    the Ri.vesville Multi-Cell
    Fluidized Bed Boiler, Vol. II, p. 191
                                     C-3
    

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    CORNABY, B. W.
    Development of Environmental
    Objectives Based on Health and
    Ecological Effects, Vol. II,
    p. 462
    
    COSTELLO, R. M.
    Conceptual Design of a Coal
    Fueled, Fluid Bed Combined
    Cycle Power Plant, Vol. II,
    p. 434
    
    An Engineering Study on the
    Regeneration of Sulfated Addi-
    tive from a Fluidized-Bed Coal-
    Fired Power Plant, Vol. Ill,
    p. 832
    
    COVELL, RUSSELL B.
    Conceptual Design of a 570-MW
    Combustion Engineering, Inc.
    Atmospheric Fluidized-Bed Steam
    Generator, Vol. II, p. 326
    
    CRAWFORD, R. W.
    Pressurized Fluidized-Bed Combus-
    tion Component Test and Integra-
    tion Unit Design Status, Vol. Ill,
    p. 102
    
    DAS, K. L.
    A Fluidized Bed Hot Gas Generator
    for Conversion of Oil-Fired Boil-
    ers into Coal-Firina, Vol. II,
    p. 145
    
    DECKER, N.
    Thermal Stresses and Fatigue of
    Heat Transfer Tubes Immersed in
    a Fluidized Bed Combustor,
    Vol. Ill, p. 700
    
    DECOURSIN, D. G.
    Fluidized Bed Combustor for Small
    Industrial Applications, Vol. II,
    p. 91
    DEGANI, DAVID.
    Particulate Removal from Hot
    Gases Using the Fluidized Bed
    Cross-Flow Filter, Vol. Ill,
    P. 551
    
    DIVILIO, R.
    Results of Recent Test Program
    Related to AFB Combustion
    Efficiency, Vol. Ill, p. 82
    
    DOR, A. A.
    Regenerative Iron Bearing Sor-
    bents for Use in Fluidized Bed
    Combustion, Vol. II, p. 701
    
    DOWDY, T. E.
    B&W/EPRI's 6' x 6' Fluidized Bed
    Combustion Development Facility:
    An Overview, Vol. Ill, p. 24
    
    DREHMEL, T. t.
    Granular Bed Filters for Particu-
    late Removal at High Temperature
    and I ressure,. Vol. Ill, p. 516
    
    DUKE, K. M.
    Multimedia Pollutant Emissions
    Data for Fluidized-Bed Combustior
    of Coal, Vol. El, p. 544
    
    DZIERLEN'GA, P'. STANLEY
    A Comparison of Selected Design
    Aspects of Three Atmospheric
    Fluidized Bed Combustion Con-
    ceptual Power Plant Designs,
    Vol. II, p. 355
    
    FALKENBERRY, HAROLD L.
    The Fluidized-Bed Combustion
    Program of the Tennessee Valley
    Authority, Vol. I, p. 87
    
    FARBER, GERALD
    Regeneration of Lime-Based
    Sorbents in s. Kiln with Solid
    Reductants, ฅol. Ill, p. 798
                                     C-4
    

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    FEHR, RICHARD W.
    Effects of Coal Composition
    and Ash Reinjection on Sulfur
    Retention Burning Lignite and
    Western Subbituminous Coals,
    Vol. II, p. 729
    
    FELDMAN, PAUL
    High Temperature, High Pressure
    Electrostatic Precipitation,
    Vol. Ill, p. 640
    
    FELTON, G. W.
    Pneumatic Solids Injector and
    Start-Up Burner for Battelle's
    Multisolid Fluidized-Bed Com-
    bustion (MS-FBC) Process,
    Vol. Ill, p. 241
    
    Battelle's Multisolid Fluidized-
    Bed Combustion Process, Vol. Ill,
    p. 223
    
    FITZGERALD, T.
    Solid Tracer Studies in a Tube-
    Filled Fluidized Bed, Vol. Ill,
    p. 135
    
    FRAAS, ARTHUR
    Atmospheric Fluidized Bed Combus-
    tion Technology Test Unit for
    Industrial Cogeneration Plants,
    Vol. Ill, p. 55
    
    FREEDMAN, STEVEN I.
    The U.S. Department of Energy
    Program, Vol. I, p. 57
    
    GARNER, DONALD N.
    A Comparison of Selected Design
    Aspects of Three Atmospheric
    Fluidized Bed Combustion Con-
    ceptual Power Plant Designs,
    Vol. II, p. 355
    
    GASNER, L.
    Lightoff of Multicell Fluidized
    Bed Boilers by Hot Bed Transfer,
    Vol. II, p. 223
    Limestone Utilization Optimiza-
    tion in Fluidized Bed Boilers,
    Vol. II, p. 763
    
    GEFFKEN, JOHN
    The Anthracite Culm/Anthracite
    Combustion Program, Vol. II,
    p. 107
    
    GEORGAKIS, C.
    Modelling Desulfurization Reac-
    tions in Fluidized Bed Combustors,
    Vol. II, p. 787
    
    GIAMMAR, R. D.
    Pneumatic Solids Injector and
    Start-Up Burner for Battelle's
    Multisolid Fluidized-Bed Com-
    bustion (MS-FBC) Process, Vol III,
    p. 241
    
    GILES, W.
    Characterization of Efflux from
    a Pressurized Fluidized Bed
    Combustor, Vol. II, p. 655
    
    GIRAMONTI, A. J.
    Conceptual Design of a Coal
    Fueled, Fluid Bed Combined Cycle
    Power Plant, Vol. II, p. 434
    
    GLICKSMAN, L.
    Thermal Stresses and Fatigue cf
    Heat Transfer Tubes Immersed in
    a Fluidized Bed Conbustor.
    Vol. Ill, p. 700
    
    Fluid Dynamic Modelliuq of
    Fluidized Bed Combustors.
    Vol. Ill, D. 458
    
    GLUKHOMANYUK. A. M.
    Research of Gas Combustion in
    Fluidized Bed Plants. Vol. III.
    n. 268
                                     C-5
    

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    GOBLIRSCH, GERALD M.
    Effects of Coal Composition
    and Ash Reinjection on Sulfur
    Retention Burning Lignite and
    Western Subbituminous Coal,
    Vol. II, p. 729
    
    GOLDMAN, J.
    FBC-Modelling and Data Base,
    Vol. Ill, p. 406
    
    GOLAN, L. P.
    Industrial Application of Fluid-
    ized Bed Combustion-Single Tube
    Heat Transfer Studies, Vol. Ill,
    p. 184
    
    GREGORY, M. W.
    Evaluation of a Granular Bed
    Filter for Particulate Control
    in Fluidized Bed Combustion,
    Vol. Ill, p. 504
    
    GRIMM, U.
    Fluidized-Bed Combustion of
    Lignite and Lignite Refuse,
    Vol. Ill, p. 211
    
    GUILLORY, J. L.
    Filtration Performance of a
    Moving Bed Granular Filter:
    Experimental Cold Flow Data,
    Vol. Ill, p. 567
    
    GUTFINGER, CHAIM
    Particulate Removal from Hot
    Gases Using the Fluiriized Bed
    Cross-Flow Filter, Vol. Ill,
    p. 551
    
    HALOW, J. S.
    Fluidized-Bed Combustion of
    Lignite and Lignite Refuse,
    Vol. Ill, p. 211
    
    HAMMITT, F. G.
    Industrial Application of Fluid-
    ized Bed Combustion-Sinole Tube
    Heat Transfer Studies, Vol. Ill,
    p. 184
    HANSON, H. A.
    Fluidized Bed Combustor for Small
    Industrial Applications, Vol. II,
    p. 91
    
    HAZARD, H. R.
    Pneumatic Soliils Injector and
    Start-Up Burner for Battelle's
    Multisolid Fluidized-Bed Com-
    bustion (MS-FBC) Process, Vol. Ill,
    p. 241
    
    HENSCHEL, D. BRUCE
    The EPA Fluidized-Bed Combustion
    Program - An Update, Vol. I, p. 62
    
    HERN, J. L.
    Characterization of Fluidized Bed
    Combustion Waste Composition and
    Variability as They Relate to
    Disposal on Agricultural Lands,
    Vol. II, p. 833
    
    Leaching Experin -nts on Soil and
    Mine Spoil Trea'.ad with Fluidized
    Bed Combustion Waste, Vol. II,
    p. 821
    
    HILL, DUANE
    First Performance Results From
    the Rivesville Multi-Cell
    Fluidized Bed Boiler, Vol. II,
    p. 191
    
    Lightoff of Multicell Fluidized
    Bed Boilers by Hot Bed Transfer,
    Vol. II, p. 223
    
    HODGES, J.
    A Model of Coal Combustion in
    Fluidized Bed Combustors, Vol. Ill,
    p. 437
    
    HOKE, R. C.
    Evaluation of a Granular Bed
    Filter for Particulate Control
    in Fluidized Bed Combustion,
    Vol. Ill, p. 504
                                     C-6
    

    -------
     HOKE,  RONALD C.
     Pressurized  Fluidized Bed Coal
     Co:nbustion and Sorbent Regenera-
     tion,  Vol. Ill, p. 756
    
     HOLCOMB, R.  S.
     Atmospheric  Fluidized Bed Com-
     bustion Technology Test Unit for
     Industrial Cogeneration Plants,
     Vol. Ill, p.  55
    
     HOLIGHAUS, ROLF
     Fluidized-Bed Combustion -
     Overview of  the Program of the
     Federal Republic of Germany,
     Vol. I, p. 47
    
     MORGAN, J. J.
     Conceptual Design of a Coal
     Fueled, Fluid Bed Combined Cycle
     Power  Plant,  Vol. II, p. 434
    
     HORIO, MASAYUKI
     A Model Study for the Develop-
     ment of Low  NOX Fluidized-Bed
     Coal Combustors, Vol. II, p. 605
    
     HOWARD, J. R.
     Combustion Experiments Within a
     Rotating Fluidized Bed, Vol. Ill,
     p. 275
    
     HOWE,  WILLIAM C.
     A Comparison of Selected Design
     Aspects of Three Atmospheric
     Fluidized Bed Combustion Concei. •
     tual Power Plant Designs,
     Vol. II, p.  355
    
    HOY, H. R.
    Further Experiments on the Pilot-
    Scale Pressurized Combustor at
    Leatherhead,  Vol.  Ill, p.  123
    HUBER, D. A.
    Conceptual Design of a Coal
    Fueled, Fluid Bed Combined
    Cycle Power Plant, Vol. il,
    p. 434
    HUBER, D. A.
    An Engineering Study on the
    Regeneration of Sulfated Additive
    from a Fluidized-Bed Coal-Fired
    Power Plant, Vol. Ill, p. 832
    
    HUGHES, R.
    Fluid Dynamic Modelling of
    Fluidized Bed Combustors, Vol. Ill,
    p. 458
    
    JAHKOLA, ANTERO
    Experiences of Fluidized-Bed
    Combustion of Peat in Finland,
    Vol. II, p. 375
    
    JOHNSON, ERIC K.
    The Ohio Energy and Resource
    Development Authority Program,
    Vol. I, p. 77
    
    JOHNSON, IRVING
    Plans and Studies on Flue Gas
    Cleaning and Particulate Monitor-
    ing in PFBC, Vol. II, p. 493
    
    The Prediction of Limestone
    Requirements for S02 Emission
    Control in Atmospheric Pressure
    Fluidized-Bed Combustion, Vol. II,
    p. 748
    
    The Mechanism of the Salt Additive
    Effect on the $03 Reactivity of
    Limestone, Vol. II, p. 776
    
    JONKE, A.A.
    Plans and Studies on Flue Gas
    Cleaning and Particulate Moni-
    toring in PFBC, Vol. II, p. 493
    
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, p. 776
    
    Economic Feasibility of Regen-
    erating Sulfated Limestones,
    Vol. Ill, p. 851
                                     C-7
    

    -------
    JOVANOVIC, G.
    Solid Tracer Studies in a Tube-
    Filled Fluidized Bed, Vol. Ill,
    p. 135
    
    KATTA, S.
    Evaluation of Sorbent Regenera-
    tion Processes for AFBC and
    PFBC, Vol. Ill, p. 811
    
    KAYE, W. G.
    An Overview of the Progress in
    Fluid Bed Combustion in the
    United Kingdom, Vol. I, p. 35
    
    KEAIRNS, D. L.
    Particulate Control for Pressur-
    ized Fluidized-Bed Combustion
    Processes, Vol. II, p. 626
    
    Initial Assessment of Alterna-
    tive S(>2 Scrbents for  Fluid-
     ized-Bed  Combustion Po^er
    Plants, Vol. II, p. 680
    
    Environmental Impact of the
    Disposal of Processed and Unpro-
    cessed F3C Bed Material and
    Carry-over, Vol. II, p. 846
    
    Assessment of the Impact of S02,
    NOX, and Particulate Emission
    Standards on Fluidized-Bed Com-
    bustion System Design and Energy
    Costs, Vol. II, p. 875
    
    Thermodynamic Projections of
    Trace Element Release in
    Fluidized-Bed Combustion Systems,
    Vol. II, p. 526
    
    Evaluation of Sorbent Regenera-
    tion Processes for AFBC and
    PFBC, Vol. Ill, p. 811
    
    KINZLER, D. D.
    Fluidized Bed Combustor for
    Small Industrial Applications,
    Vol. II, p. 91
    KIVIAT, G.
    The Effects of Finned Tubing
    on Fluidized Bed Performance,
    Vol. Ill, p. 156
    
    LaNAUZE, R. D.
    High Temperature Corrosion of
    Metals and Alloys in Fluidized
    Bed Combustion Systems, Vol. Ill,
    p. 682
    
    LARKIN, ROBERT
    A Particulate Sampling System
    for Pressurized Fluidized Bed
    Combustors, Vol. Ill, p. 379
    
    LEE, S. H. D.
    Plans and Studies on Flue Gas
    Cleaning and Particulate Monitor-
    ing in PFBC, Vol. II, p. 493
    
    LEVY, E. K.
    Centrifugal Fluidized Bed
    Combustion, Vol. Ill, p. 288
    
    LIPARI, P. F.
    Conceptual Design and Preliminary
    Evaluation of a 570 MW Electric
    Power Generating Plant Using a
    Babcock & Wilcox Company or a
    Foster Wheeler Energy Corporation
    Atmospheric Fluidized-Bed Boiler,
    Vol. II, p. 313
    
    LIU, K. T.
    Battelle's Multisolid Fluidized-
    Bed Combustion Process, Vol. Ill,
    p. 223
    
    LOUIS, J. F.
    FBC-Modelling and Data Base,
    Vol. Ill, p. 406
    
    LOWELL, CARL E.
    Erosion/Corrosion of Turbine
    Airfoil Materials in the High-
    Velocity Effluent of a Pres-
    surized Fluidized Coal
    Combustor, Vol. Ill, p. 660
                                     C-8
    

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    LUCKE, V. H.
    Environmental Analysis of the
    General Electric PFB Combined
    Cycle Power Plant Design,
    Vol. II, p. 898
    
    LUND, TERRY E.
    B&W/EPRI's 6' x 6' Fluidized Bed
    Combustion Development Facility:
    An Overview, Vol. Ill, p. 24
    
    Overview of EPRI FBC Program,
    Vol. I, p. 94
    
    LUTHRA, K. L.
    Turbine Materials Corrosion in
    the Coal-Fired Combined Cycle,
    Vol. Ill, p. 714
    
    MAKHORIH, K. YE
    Research of Gas Combustion in
    Fluidized Bed Plants, Vol. Ill,
    p. 268
    
    MARTIN, N. W.
    Centrifugal Fluidized Bed
    Combustion, Vol. Ill, p. 288
    
    MASTERS, WILLIAM
    A Particulate Sampling System
    for Pressurized Fluidized Bed
    Combustors. Vol. III. p. 379
    
    MCCARRON. R. L.
    Turbine Materials Corrosion in
    the Coal-Fired Combined Cycle.
    Vol. Ill, p. 714
    
    MCCARTHY, HOMES
    The Rivesville Installation
    from the View of the Mnnonnahelป
    Power Company. Vol. II. p. 187
    
    MCGAULEY, P. J.
    Regenerative Iron Bearing Sorbents
    for Use in Fluidized Bed Combus-
    tion, Vol. II, p. 701
    MEI, J. S.
    Fluidiied-Bed Combustion of
    Lignite and Lignite Refuse,
    Vol. Ill, p. 211
    
    MESKO, JOHN E.
    Technological Development Priori-
    ties of Atmospheric Fluidized-
    ~"ed Combustion, Vol. II, p. 169
    
    METCALFE, C. I.
    Combustion Experiments Within a
    Rotating Fluidized Bed, Vol. Ill,
    p. 275
    
    MILLER, GABRIEL
    The Effects of Finned Tubing on
    Fluidized Bed Performance,
    Vol. Ill, p. 156
    
    MILLER, KICHAHD H.
    Potential Uses for the Residue
    from the Fluidized Bed
    Combustion Process, Vol. II,
    p. 800
    
    MINEU, RONALD
    First Performance Results from
    the Rivesville Multi-Cell
    Fluidized Bed Boiler, Vol. II,
    p. 191
    
    MONTAGNA, J. C.
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, P. 776
    
    Plans and Studies on F^ue Gas
    Cleaning and Particulate Monitoring
    in PFBC, Vol. II, p. 493
    
    Economic Feasibility of ฐegen-
    erating Sulfated Limestones,
         III, p.
                                     C-9
    

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    MORI, SHIGEKATSU
    A Model Study for the Develop-
    ment of Low NOX Fluidized-Bed
    Coal Conibustors, Vol. II, p. 605
    
    MORTON, J. W.
    An Engineering Study on the Re-
    generation of Sulfated Additive
    from a Fluidized-Bed Coal-Fired
    Power Plant, Vol. Ill, p. 832
    
    MOSKOWITZ, SEYMOUR
    The Curtiss-Wright Pressurized
    Fluidized-Bed Pilot Electric
    Plant, Vol. II, p. 401
    
    MOSS, G.
    Progress in the Development of
    the Desulfurizing Gasifier,
    Vol. Ill, p. 300
    
    MUCH I, Iwao
    A Model Study for the Develop-
    ment of Low NOX Fluidized-Bed
    Coal Combustors, Vol. II, p. 605
    
    MULY, E. C.
    Particulate Analysis Instrumenta-
    tion for Advanced Combustion
    Systems, Vol. Ill, p. 347
    
    MURPHY, JAMES J.
    Material  Handling Systems for
    FBC'S - Extrapolating Rivesville
    to 600 Megawatts, Vol. II, p. 239
    
    MURPHY, K. R.
    Environmental Analysis of the
    General Electric PFB Combined
    Cycle Power Plant Design,
    Vol. II, p. 898
              ^
    
    MURTHY, K. S.
    Multimedia Pollutant Emissions
    Data for Fluidized-Bed Combus-
    tion of Coal, Vol. II, p. 544
    Development of Environmental
    Objectives Based on Healtii and
    Ecological Effects, Vol. II,
    p. 462
    
    MACK, H.
    Battelle's Multisolid Fluidized-
    Bed Combustion Process, Vol. Ill,
    p. 223
    
    NEWBY, R. A.
    Assessment of the Impact of SO? ,
    NOX, and Particulate Emission
    Standards on Fluidized-Bed Combus-
    tion System Design and Energy
    Costs, Vol. II, p. 875
    
    Initial Assessment of Alternative
    S0ฃ Sorbents for Fluidized-Bed
    Combustion Power Plants,
    Vol. II, p. 680
    
    Evaluation of Sorbent Regeneration
    Processes for AFBC and PFBC,
    Vol. Ill, p. 811
    
    NORCROSS, WILLIAM R.
    Industrial Fluidized-Bed Program:
    A Status Review, Vol. Ill, p. 33
    
    NUNES, F. F.
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, p. 776
    
    NUTKIS, M. S.
    Evaluation of a Granular Bed Fil-
    ter for Particulate Control in
    Fluidized Bed Combustion, Vol. Ill,
    p. 504
    
    Pressurized Fluidized Bed Coal
    Combustion and Sorbent Regenera-
    tion, Vol. Ill, p. 756
                                     C-10
    

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    O'NEILL, E. P.
    Assessment of the Impact of SC>2,
    NOX, and Particulate Emission
    Standards on Fluidized-Eod Com-
    bustion System Design ana Energy
    Costs, Vol. II, p. 875.
    
    Thermodynamic Projections of
    Trace Element Release ir. Fluid-
    ized-Bed Combustion, Vol. II,
    p. 526
    
    PALLAI, K. K.
    Particle Size in Pressurized
    Combustors, Vol. II, p. 642
    
    PARKER, RICHARD D.
    Granular Bed Filters for Partic-
    ulate  Removal at High Tempera-
    ture and Pressure, Vol. Ill,
    p. 516
    
    PATCH, R. W.
    Effluent Characterization from
    a Conical Pressurized Fluid Bed,
    Vol. II, p. 560
    
    PATTERSON, RONALD G.
    Granular Bed Filters for Partic-
    ulate  Removal at High Tempera-
    ture and Pressure, Vol. Ill,
    p. 516
    
    PEDERSEN, FRODE
    Status of Fluidized Bed Combus-
    tion in Norway and Sweden,
    Vol. II, p. 20
    
    PELLOUX, R.
    Thermal Stresses and Fatigue of
    Heat Transfer Tubes Immersed in
    a Fluidized Bed Combustor,
    Vol. Ill, p. 700
    
    PETERSON, C. H.
    Environmental Impact of the Dis-
    posal of Processed and Unpro-
    cessed FBC Bed Material and
    Carry-over, Vol. II, p. 846
    PETERSON,  J. R.
    General Electric Pressurized
    Fluidized Bed Power Plant
    Status, Vol. II, p. 413
    
    PODOLSKI, W. F.
    Pressurized Fluidized Bed Combus-
    tion Component Test and Integra-
    tion Unit (CTIU):  Design Status,
    Vol. Ill, p. 102
    
    POMERANTZ, L.
    Development of Environmental
    Objectives Based on Health and
    Ecological Effects, Vol. II, p. 462
    
    PORTER, JAMES H.
    ERCO's Fluid-Bed Combustion
    Development Facility, Vol. Ill,
    p. 73
    
    PRIEM, R. J.
    Effluent Characterization from a
    Conical Pressurized Fluid Bed,
    Vol. II, p. 560
    
    RASSIWALLA, F. M.
    Thermodynamics of Regenerating
    Sulfated Lime, Vol. Ill, p. 740
    
    RAVEN,  P.
    Further Experiments on the Pilot-
    Scale Pressurized Combustor at
    Leatherhead, Vol. Ill, p.  123
    RAY, ASOK
    Dynamic Modeling, Testing, and
    Control of Fluidized Bed Systems,
    Vol. Ill, p. 488
    
    REED, KENNETH A.
    Conceptual Design of a Foster
    Wheeler Energy Corporation Atmos-
    pheric Fluidized Bed Steam Gener-
    ator for Stone and Webster Engi-
    neering Corporation and Tennessee
    Valley Authority, Vol. II, p. 285
                                    C-ll
    

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    REtD, R.
    Results of Recent Test Program
    Related to AFB Combustion
    Efficiency, Vol. Ill, p. 82
    
    REHMAT, A
    A Mechanistic Model to Explain
    Ash Agglomeration in Fluidized
    Bed Combustors and Gasifiers,
    Vol. Ill, p. 475
    
    RICE, R. L.
    Fluidized-Bed Combustion of
    Lignite and Lignite Refuse,
    Vol. Ill, p. 475
    
    RINGWALL, CARL G.
    A High-Temperature High-Pres-
    sure Isokinetic/Isothermal
    Sampling System for Pressur-
    ized Fluidized Bed Applications,
    Vol. Ill, p. 326
    
    ROBERTS, A. G.
    Further Experiments on the
    Pilot-Scale Pressurized Com-
    bustor at Leatherhead, Vol. Ill,
    p.  123
    
    ROB INSCN, MYRON
    High Temperature, High Pressure
    Electrostatic Precipitation,
    Vol. Ill, p. 640
    
    ROGERS, E.A.
    High Temperature Corrosion of
    Metals and Alloys in Fluidized
    Bed Combustion Systems,
    Vol. Ill, p. 682
    
    ROLLBUHLER, R. J.
    Effluent Characterization from
    a Conical Pressurized Fluid Bed,
    Vol. II, p. 560
    
    ROME, ANNE P.
    Erosion/Corrosion of Turbine
    Airfoil Materials in the High-
    Velocity Effluent of a Pres-
    surized Fluidized Coal
    Combustor, Vol. Ill, p. 660
    RUTH, L. A.
    Pressurized Fluidized Bed Coal
    Combustion and Sorbent
    Regeneration, Vol. Ill,  p.  756
    
    SAKAMOTO, KOYA
    Control of Nitric Oxide  and
    Carbon Monoxide Emissions in
    Fluidized Bed Combustion,
    Vol. II, p. 594
    
    SAROFIM, ADEL F.
    NO Reduction by Char in  Fluid-
    ized Combustion, Vol. II, p. 577
    
    A Model of Coal  Combustion  in
    Fluidized Bed Combustnrs,
    Vol. Ill, p. 437
    
    SAVITZ, D. A.
    Development of Environmental
    Objectives Based on Health  and
    Ecological Effects, Vol. II,
    p. 462
    
    SAXENA, S. C.
    A Mechanistic Model to Explain
    Ash Agglomeration in Fluidized
    Bed Combustors and Gasifiers,
    Vol. Ill, p. 475
    
    SCHILLING, H. D.
    Design of a Gas Turbine  Plant
    with a Pressurized Fluidized Bed
    Conbustor, Vol. II, p. 388
    
    SCHRECKENBERG, HEINZ
    Design of a Gas Turbine  Plant
    with a Pressurized Fluidized
    Bed Combustor, Vol. II,  p.  338
    
    SETESAK, SCOTT E.
    Limestone Utilization Optimization
    in Fluidized Bed Boilers, Vol. II,
    p. 763
    
    SHACKLETON, MICHAEL A.
    Feasibility of Barrier Filtration
    Using Ceramic Fibers, Vol.  Ill,
    p. 620
                                     C-12
    

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    SHARP, D.  A.
    Multimedia Pollutant emissions
    Data for Fluidized-Bed Combus-
    tion of Coal, Vol. II, p. 544
    
    SHEARER, J.
    The Mechanism of the Salt Addi-
    tive Effect on the S02 Reac-
    tivity of Limestone, Vol. II,
    p. 776
    
    SHEN, T.
    Thermal Stresses and Fatigue of
    Heat Transfer Tubes Immersed
    in a Fluidized Bed Combustor,
    Vol III, p. 700
    
    SHEN, MING-SHING
    Regeneration of Lime-Based
    Sorbent in a Kiln with Solid
    Reductants, Vol. Ill, p. 798
    
    SIDLE, R.  C.
    Leaching Experiments on Soil
    and Mine Spoil Treated with
    Fluidized Bed Combustion Waste,
    Vol. II, p. 821
    
    Characterization of Fluidized
    Bed Combustion Waste Composition
    and Variability as They Relate
    to Disposal on Agricultural
    Lands, Vol. II, p 833
    
    SMITH, ALAN A.
    A State of the Art Resume,
    Vol. II, p. 4
    
    SMITH, G.  W.
    Plans and Studies on Flue Gas
    Cleaning and Particulate Moni-
    toring in PFBC, Vol. II, p. 493
    
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill,  p.  776
    SMITH, J. WILLIAM
    A Comparison of Industrial  and
    Utility Fluidized Bed Combustion
    Boiler Design Considerations,
    Vol. II, p. 44
    
    Conceptual Design of a Coal
    Fueled, Fluid Bed combined
    Cycle Power Plant, Vol. II,
    p. 434
    
    SMYK, E. B.
    Economic Feasibility of Regen-
    erating Sulfated Limestones,
    Vol. Ill, p. 851
    
    Development of a Process
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, p. 776
    
    SNYDER, ROBERT B.
    Th? Prediction of Limestone
    Requirements for SO? Emission
    Control in Atmospheric Pressure
    Fluidized-Bed Combustion, Vol. II,
    p. 748
    
    SONDREAL, EVERETT A.
    Effects of Coal Composition and
    Ash Reinjection on Sulfur Retention
    Burning Lignite and Western Sub-
    bituminous Coals, Vol. II,  p. 729
    
    SPACE, C. C.
    Atmospheric Fluidized Bed Com-
    ponent Test and Integration
    Facility - An ipdate, Vol.  Ill,
    P. 4
    
    SPACIL, H. S.
    T-irbine Materials Corrosion in
    the Coal-Fired Combined Cycle,
    Vol. Ill, p. 714
    
    SPROUSE, ALICE M.
    NO Reduction by Char in Fluidized
    Combustion, Vol. II, p. 577
                                     C-13
    

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    STEINBERG, MEYER
    Regeneration of Lime-Based
    Sorbents in a Kiln With Solid
    Reductants, Vol. Ill,  p.  798
    
    STICKSEL,  P.
    Design of Ambient Monitoring
    Programs for Prototype for
    Fluidized-Bed Combustion Facil-
    ities, Vol. II, p. 478
    
    STONE, R. C.
    Relative Environmental Impact of
    Two 570 MW Atmospheric Fluidized-
    Bed Electric Power Generating
    Plants Compared to a Pulverized
    Coal Fired Plant Equipped with a
    Wet Limestone Flue Gas Desulfuri-
    zation System, Vol. II, p. 892
    
    STOUT, W. L.
    Leaching Experiments on Soil and
    Mine Spoil Treated with Fluidized
    Bed Combustion Waste,  Vol. II,
    p. 821
    
    Characterization of Fluidized
    Bed Combustion Waste Composition
    and Variability as they Relate
    to Disposal on Agricultural
    Lands, Vol. II, p. 833
    
    STRINGER, JOHN
    High Temperature Corrosion of
    Metals and Alloys in Fluidized
    Bed Combustion Systems, Vol. Ill,
    p. 682
    
    STRINGFELLOW, THOMAS E.
    Startup and Initial Operation
    of the Rivesville 30 MWe Fluid
    Bed Boiler, Vol. II, p. 203
    
    SUMARIA, V.
    Dynamic Modelling, Testing, and
    Control of Fluidized Bed Systems,
    Vol. Ill, p. 488
    SUN, C. C.
    Environmental Impact of the
    Disposal of Processed and Unpro-
    cessed FBC Bed Material and
    Carry-over, Vol. !I, p. 846
    
    SWIFT, W. M.
    Plans and Studies on Flue Gas
    Cleaning and Particulate Moni-
    toring in PFBC, Vol. II, p. 493
    
    SZEKELY, J.
    Modelling Desulfurization Reac-
    tions in Fluidized Bed Combustors,
    Vol. II, p. 787
    
    TARDOS, G. I.
    Particulate Removal from Hot
    Gases Using the Fluidized Bed
    Cross-Flow Filter, Vol. Ill, p. 551
    
    TAYLOR, D. F.
    Pneumatic Solids Injector and
    Start-up Burner for Battelle's
    Multisolid Fluidized-Bed Com-
    bustion (MS-FBC) Process, Vol. Ill,
    p. 241
    
    TEATS, F. G.
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, p. 776
    
    TERADA, HIROSHI
    Particulate Removal from Pressur-
    ized Hot Gas, Vol. Ill, p. 538
    
    THOENNES, C.
    Characterization of Efflux from a
    Pressurized Fluidized Bed
    Combustor, Vol. II, p. 655
    
    A High-Temperature High-Pressure
    Isokinetic/Isothermal Sampling
    for Pressurized Fluidized Bed
    Applications, Vol. Ill, p. 326
                                     C-14
    

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    TOUR IN, RICHARD H.
    Overview of New York State's
    Fluidized Bed Combustion
    Program, Vol. I, p. 81
    TRACEY, ROBERT
    Industrial Application-
    Fluidized Bed Combustion -
    Georgetown University, Vol.  II,
    p. 61
    
    TREXLER, EDWARD
    The Department of Energy Atmos-
    pheric Fluidized Bed Combustion
    Utility Demonstration Program,
    Vol. II, p. 160
    
    TRINH, T.
    Modelling Desulfurization Reac-
    tions in Fluidized Bed Com-
    bustors. Vol. II, p. 787
    
    TSAO, KEH C.
    Multiple Jet Particle Collection
    in a Cyclone by Reheating Fluid-
    ized Bed Combustion Products,
    Vol. Ill, p. 607
    
    TUNG, S. E.
    FBC-Kodelling and Data Base,
    Vol. Ill, p. 406
    
    TUREK, DAVID
    Lightoff of Multicell Fluidized
    Bed Boilers by Hot Bed Transfer,
    Vol. II, p. 223
    
    TURNER, C.
    The Mechanism of the Salt Addi-
    tive Effect on the S02 Reac-
    tivity of Limestone, Vol. II,
    p. 776
    
    ULERICH, N.
    Assessment of the Impact of  S02,
    NOX, and Particulate Emission
    Standards on Fluidized-Bed Com-
    bustion System Design and Energy
    Costs, Vol. II, p. 875
    VAN VALKEN8URG, E. S.
    Particulate Analysis Instrumenta-
    tion for Advanced Combustion
    Systems, Vol. Ill, p. 347
    
    VIRR, MICHAtL
    Industrial Coal Fired Fl'jidized
    Bed Bo-Uers and W*ne Hea1
    Boilers, Vol. II, . . 22
    
    VOGEL, G. J.
    Plans and Studies on Flue Gas
    Cleaning and Particulate
    Monitoring in PFBC, Vol. II,
    p. 493
    
    Development of a Process for
    Regenerating Partially Sulfated
    Limestone from FBC Boilers,
    Vol. Ill, p. 776
    
    Economic Feasibility of Re-
    gener^ting Sulfated Limestones,
    Vol. Ill, p. 851
    
    WACHTLER, FREDERICK
    Industrial Application -
    Fluidized Bed Combustion -
    Georgetown University, Vol. II,
    p. 61
    
    WANG, JAMES C. F.
    A High-Temperature High-Pres-
    sure Isokinetic/Isothermal
    Sampling System for Pressurized
    Fluidized Bed Applications,
    Vol. Ill, p. 326
    
    WELLS, T. G.
    Conceptual Design and Preliminary
    Evaluation of a 570 MM Electric
    Power Generating Plant Using a
    Babcock & Wilcox Company or a
    Foster Wheeler Energy Corporation
    Atmospheric Fluidized-Bed Boiler,
    Vol. II, p. 313
    
    WHEELOCK, T. D.
    Thermodynamics of Regenerating
    Sulfated Lime, Vol. Ill, p. 740
                                    C-15
    

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    WIED, ERWIN
    Design of a Gas Turbine Plant
    with a Pressurized Fluidized
    Bed Coinbustor, Vol. II, p. 388
    
    WIGTON, H. F.
    Mathematical Model cf a Cross-
    Flow Moving Bed Granular Filter,
    Vol. Ill, P. 583
    
    WILSON, J. S.
    Atmospheric Fluidized Bed Com-
    ponent Test and Integration
    Facility - An Update, Vol. Ill,
    P. 4
    
    WILSON, M.
    Dynamic Modelling, Testing, and
    Control of Fluidized Bed Systems,
    Vol. Ill, p. 438
    
    WILSON, W. IRA
    The Prediction of Limestone
    Requirements for SO^ Emission
    Control in Atmospheric Pressure
    Fluidized-Bed Combustion,
    Vol. II, p. 748
    
    WRIGHT, S. J.
    A Technical Description of the
    Plant Design and Project Progress
    Report, Vol. Ill, p. 310
    
    YAMAMURA, R.
    Particulate Removal From Pres-
    surized Hot Gas, Vol. Ill,
    p. 538
    
    YANG, RALPH T.
    Regeneration of Lime-Based
    Sorbents in a Kiln with Solid
    Reductants, Vol. Ill, p. 798
    
    YOUNG, D. T.
    Fluidized Combustion of Beds of
    Large, Dense Particles in Re-
    processing HTGR Fuel, Vol. Ill,
    p. 254
    YUNG, KUANG T.
    Multiple Jet Particle Collection  in
    a Cyclone by Reheating Fluidized
    Bed Combustion Products,  Vol.  Ill,
    p. 607
    
    YUNG, SHUI-CHOW
    Granular Bed Filters for  Particu-
    late Removal at High Temperature
    and Pressure, Vol.  Ill, p.  516
    
    ZAKKAY, VICTOR
    The Effects of Finned Tubing on
    Fluidized Bed Performance,
    Vol. Ill, p. 156
    
    ZELLARS, GLENN R.
    Erosion/Corrosion  of Turbine
    Airfoil Materials  in the  High-
    Velocity Effluent  of a Pressurized
    Fluidized Coal Combustor, Vol. Ill,
    p. 660
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