&EPA
    •
            United States
            Environmental ProtbCtio:
            Agency
           Industrial Environmental Research
           Laboratory
           Research Tnanvjin >-;rir!< N1.. 2771 1
EPA GOO 9 80 039a
September 1 980
            Research and Dewopment
Second
Symposium on th
Transfer and
Utilization of
Particulate  Control
Technology

Volume I.
Control of Emissions
from Coal Fired Boilers

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                RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology.  Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

      1   Environmental  Health Effects Research
      2.  Environmental  Protection Technology
      3.  Ecological Research
      4.  Environmental  Monitoring
      5.  Socioeconomic Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7  Interagency Energy-Environment Research and Development
      8.  "Special" Reports
      9.  Miscellaneous Reports
 This document is available to the public through the National Technical Informa-
 tion Service, Springfield, Virginia 22161.

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                                              EPA-600/9-80-039a
                                              September 1980
             SECOND SYMPOSIUM ON THE
           TRANSFER AND UTILIZATION OF
         PARTICULATE CONTROL TECHNOLOGY
        VOLUME I. CONTROL OF EMISSIONS FROM
               COAL FIRED BOILERS
                       by

F,P. Venditti, J.A. Armstrong, and Michael Durham

            Denver Research Institute
                  P.O. Box 10127
             Denver, Colorado  80210
              Grant Number: R805725
                 Project Officer

               Dennis C. Drehmel
   Office of Energy, Minerals, and Industry
 Industrial Environmental Research Laboratory
       Research Triangle Park, NC  27711
 INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
      OFFICE OF RESEARCH AND DEVELOPMENT
     U.S. ENVIRONMENTAL PROTECTION AGENCY
        RESEARCH TRIANGLE PARK, .NC 27711

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                                DISCLAIMER
     This report has been reviewed by the Industrial Environmental Research
Laboratory-Research Triangle Park, North Carolina,  Office of Research and
Development, U.S. Environmental Protection Agency,  and approved for publi-
cation.  Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products  constitute endorsement
or recommendation for use.
                                     ii

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                            ABSTRACT
     The  papers  in  these  four  volumes  of  Proceedings were pre-
sented at  the  Second  Symposium  on the Transfer and Utilization  of
Particulate Control Technology held  in  Denver,  Colorado during  23
July through  27 July 1979,  sponsored by the Particulate Technology
Branch of the  Industrial  Environmental  Research Laboratory  of the
Environmental Protection Agency  and hosted by the Denver Research
Institute of the University of Denver.

     The  purpose of the  symposium was  to bring together research-
ers,  manufacturers,  users,  government  agencies,  educators  and
students  to  discuss  new  technology  and to  provide  an  effective
means  for  the  transfer  of this technology out of  the laboratories and
into the hands of the  users.

     The  three  major categories of control technologies - electrostatic
precipitators,  scrubbers,  and fabric  filters -  were the major concern
of  the symposium.   These  technologies  were  discussed from the
perspectives  of  economics; new technical advancements  in  science and
engineering;   and applications.  Several  papers  dealt  with  combina-
tions of devices and technologies, leading to a  concept of  using a
systems  approach to particulate  control  rather than  device  control.
Additional   topic   areas  included   novel  control   devices,   high
temperature/high  pressure  applications,  fugitive  emissions,  and
measurement techniques.

     These proceedings are  divided  into  four volumes,  each volume
containing a  set of related session topics to provide easy access to a
unified technology area.
                                 ill

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                             CONTENTS

                                                                Paqe
VOLUME II CONTENTS	vii
VOLUME III CONTENTS	xi
VOLUME IV CONTENTS	xiv

                  Section A - Electrostatic Precipitators

COST AND PERFORMANCE OF PARTICULATE CONTROL
DEVICES FOR LOW-SULFUR WESTERN COALS	   1
  R.A. Chapman, D.P.  Clements,  L.E.  Sparks and J.H.  Abbott

CRITERIA FOR DESIGNING ELECTROSTATIC PRECIPITATORS  ...   15
  K. Darby

EVALUATION OF THE GEORGE NEAL ELECTROSTATIC
PRECIPITATOR	35
  R.C. Carr

EPA MOBILE ESP HOT-SIDE PERFORMANCE  EVALUATION  ....   56
  S.P. Schliesser, S. Malani, C.L. Stanley and L.  E. Sparks

PRECIPITATOR UPGRADING AND  FUEL CONTROL PROGRAM
FOR PARTICULATE COMPLIANCE  AT PENNSYLVANIA
POWER & LIGHT COMPANY	80
  J.T. Guiffre

MODIFICATION OF EXISTING PRECIPITATORS TO  RESPOND TO
FUEL CHANGES AND CURRENT EMISSION REGULATIONS	100
  D.S. Kelly and R.D.  Frame

PERFORMANCE OF ELECTROSTATIC  PRECIPITATORS WITH
LOAD VARIATION	117
  W.T. Langan, G.  Gogola and E.A.  Samuel

FLY ASH CONDITIONING BY CO-PRECIPITATION WITH
SODIUM CARBONATE	132
  J.P. Gooch, R.E. Bickelhaupt and  L.E. Sparks

PREDICTING FLY ASH  RESISTIVITY  -  AN EVALUATION	154
  R.E. Bickelhaupt  and L.E. Sparks

SO3 CONDITIONING FOR  IMPROVED  ELECTROSTATIC PRECIPITATOR
PERFORMANCE OPERATING ON LOW  SULFUR COAL  ......  170
  J.J. Ferrigan,  III and J. Roehr

DOES SULPHUR IN COAL DOMINATE  FLYASH COLLECTION IN
ELECTROSTATIC PRECIPITATORS?	184
  E.G. Potter and C.A.J.  Paulson

ANALYSIS OF THERMAL DECOMPOSITION PRODUCTS OF FLUE
GAS CONDITIONING AGENTS	202
  R.B. Spafford, H.K. Dillon,  E.B.  Dismukes and  L.E.  Sparks

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                                                             Page

BIOTOXICITY  OF FLY ASH PARTICULATE	224
  A.R.  Kolber, T.J. Wolff, J.  Abbott and L. E. Sparks


                       Section B - Fabric Filters
FABRIC FILTERS VERSUS ELECTROSTATIC PRECIPITATORS  ...  243
  E.W. Stenby, R.W. Scheck, S.D. Severson, F.A. Horney
  and D.P. Teixeira

DESIGN AND CONSTRUCTION OF BAGHOUSES FOR
SHAWNEE STEAM PLANT  	  263
  J.A. Hudson, L.A. Thaxton, H.D. Ferguson,  Jr., and N.  Clay

OPERATING CHARACTERISTICS OF A FABRIC FILTER ON A
PEAKING/CYCLING BOILER WITHOUT AUXILIARY  PREHEAT
OR REHEAT	297
  W.  Smit and K.  Spitzer

OBJECTIVES AND STATUS OF FABRIC FILTER
PERFORMANCE STUDY  	  317
  K.L. Ladd,  R. Chambers,  S. Kunka and D. Harmon

START-UP AND INITIAL OPERATIONAL EXPERIENCE ON A 400,000
ACFM BAGHOUSE  ON CITY OF COLORADO SPRINGS' MARTIN DRAKE
UNIT NO. 6	342
  R.L. Ostop and  J.M.  Urich,  Jr.

DESIGN, OPERATION, AND PERFORMANCE TESTING
OF THE CAMEO NO.  1 UNIT FABRIC FILTER	351
  H.G.  Brines

EXPERIENCE AT COORS WITH  FABRIC FILTERS -  FIRING
PULVERIZED WESTERN  COA1	359
  G.L. Pearson

FABRIC FILTER EXPERIENCE AT WAYNESBORO	372
  W.R. Marcott.e

A NEW TECHNIQUE FOR DRY REMOVAL OF SO2	390
  C.C.  Shale and  G.W.  Stewart

SPRAY DRYER/BAGHOUSE SYSTEM FOR PARTICULATE AND
SULFUR  DIOXIDE  CONTROL, EFFECTS OF DEW  POINT,  COAL
AND PLANT OPERATING CONDITIONS	410
  W.R.  Lane

SELECTION,  PREPARATION AND  DISPOSAL OF  SODIUM COMPOUNDS
FOR DRY SOX SCRUBBERS	425
  D.A.  Furlong, R.L. Ostop and  D.C.  Drehmel
                                VI

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                                                             Page

HIGH VELOCITY FABRIC FILTRATION FOR CONTROL OF
COAL-FIRED BOILERS	432
  J.C. My cock, R.A. Gibson and J.M. Foster

EPA MOBILE FABRIC FILTER - PILOT INVESTIGATION OF
HARRINGTON STATION PRESSURE DROP DIFFICULTIES	453
  W.O. Lipscomb, S.P.  Schliesser and V.S. Malani

PASSIVE  ELECTROSTATIC  EFFECTS IN FABRIC FILTRATION  ...  476
  R.P. Donovan, J.H. Turner and  J.H. Abbott

A WORKING MODEL FOR COAL FLY ASH FILTRATION	494
  R. Dennis  and H.A. Klemm

                         Section C - Scrubbers
PARTICULATE  REMOVAL AND OPACITY USING A WET VENTURI
SCRUBBER - THE MINNESOTA POWER AND LIGHT EXPERIENCE  .   .  513
  D. Nixon and C. Johnson

PERFORMANCE OF ENVIRONMENTALLY APPROVED NLA
SCRUBBER FOR SO2	529
  J.A. Bacchetti

DESIGN GUIDELINES FOR AN OPTIMUM SCRUBBER SYSTEM ....  538
  M.B. Ranade, E.R. Kashdan and D.L. Harmon

TESTS ON UW  ELECTROSTATIC  SCRUBBER FOR PARTICULATE AND
SULFUR DIOXIDE COLLECTION	561
  M.J. Pilat

EPA MOBILE VENTURI SCRUBBER PERF9RMANCE	570
  S. Malani, S.P.  Schliesser and W.O. Lipscomb

THE RESULTS  OF A TWO-STAGE SCRUBBER/CHARGED
PARTICULATE  SEPARATOR PILOT PROGRAM	591
  J.R. Martin,  K.W. Malki and N.  Graves

AUTHOR INDEX	616
                                 vii

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                             VOLUME II

                   ELECTROSTATIC PRECIPITATORS

                       Section A  - Fundamentals

                                                             Page

COLLECTION EFFICIENCY OF ELECTROSTATIC PRECIPITATORS
BY NUMERICAL SIMULATION	    1
  E.A.  Samuel

THE EFFECTS OF CORONA ELECTRODE GEOMETRY ON THE
OPERATIONAL CHARACTERISTICS OF AN ESP	31
  G.  Rinard, D.  Rugg,  W.  Patten and L.E. Sparks

THEORETICAL METHODS FOR PREDICTING ELECTRICAL CONDITIONS
IN WIRE-PLATE ELECTROSTATIC PRECIPITATORS	45
  R.B.  Mosley, J.R. McDonald and L.E. Sparks

LATERAL PROPAGATION OF BACK DISCHARGE	65
  S. Masuda and S.  Obata

THEORETICAL MODELS  OF BACK CORONA AND
LABORATORY OBSERVATIONS	74
  D.W.  VanOsdell, P.A. Lawless and L.E. Sparks

CHARGE MEASUREMENTS ON  INDIVIDUAL PARTICLES
EXITING LABORATORY  PRECIPITATORS	93
  J.R.  McDonald, M.H.  Anderson, R.B. Mosley and L.E. Sparks

OPTIMIZATION OF COLLECTION EFFICIENCY  BY VARYING PLATE
SPACING WITHIN AN ELECTROSTATIC PRECIPITATOR	114
  E.J.  Eschbach  and D.E. Stock

INTERACTION BETWEEN ELECTROSTATICS AND  FLUID DYNAMICS
IN ELECTROSTATIC PRECIPITATORS	125
  S.  Bernstein and C.T. Crowe

PARTICLE  TRANSPORT  IN ELECTROSTATIC PRECIPITATORS ...  146
  G.  Leonard, M. Mitchner and S.A. Self


                  Section B - Operation and Maintenance


THE "HUMAN ELEMENT" - A PROBLEM IN OPERATING
PRECIPITATORS	168
  W.J.  Buchanan

ELECTROSTATIC PRECIPITATORS -  ELECTRICAL PROBLEMS
AND  SOLUTIONS	173
  R.K.  Raymond


                              viii

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VOLUME II CONTENTS (Cont.)
                                                             Page

ELECTRODE CLEANING SYSTEMS:  OPTIMIZING RAPPING
ENERGY AND  RAPPING CONTROL	189
  M. Neundorfer

COMPOSITION OF PARTICIPATES — SOME EFFECTS ON
PRECIPITATOR OPERATION	208
  J.D.  Roehr

INCREASING PRECIPITATOR RELIABILITY  BY PROPER LOGGING
AND INTERPRETATION OF OPERATIONAL PARAMETERS -  AN
OPERATORS GUIDE	219
  P.P.  Bibbo and P. Aa

ELECTROSTATIC PREC1PITATORS  - START-UP,  LOW LOAD,
CYCLING, AND MAINTENANCE  CONSIDERATIONS	242
  F.A. Wybenga and R.J. Bat.yko

ELECTROSTATIC PRECIPITATOR EMISSION AND  OPACITY
PERFORMANCE CONTROL THRU RAPPER STRATEGY  	  256
  W.T. Langan,  J.H. Oscarson  and S. Hassett

RAPPING SYSTEMS FOR COLLECTING SURFACES IN AN
ELECTROSTATIC PRECIPITATOR	279
  H.L. Engelbrecht

LOW POWER ELECTROSTATIC PRECIPITATION -  A LOGICAL
SOLUTION TO COLLECTION PROBLEMS EXPERIENCED WITH
HIGH RESISTIVITY PARTICIPATE	296
  J.H. Umberger


                      S_ect|_°I!  B  - Advanced Design


HIGH INTENSITY IONIZER TECHNOLOGY APPLIED TO
RETROFIT ELECTROSTATIC PRECIPITATORS	314
  C.M. Chang and A.I.  Rimcnsberger

BOXER-CF1ARGER  - A NOVEL CHARGING DEVICE FOR HIGH
RESISTIVITY  DUSTS	334
  S. Masuda and H.  Nakatani

PRECIPITATOR  ENERGIZATION UTILIZING AN ENERGY
CONSERVING  PULSE GENERATOR	352
  H.H. Petersen and P.  Lausen

PRECHARGER COLLECTION SYSTEM  - DESIGN FROM THE
LABORATORY THROUGH FIELD DEMONSTRATION	369
  M. Nunn, D. Pontius, J.H. Abbott and L.E. Sparks
                                  ix

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VOLUME II CONTENTS (Cont.)
                                                             Page
TOWARDS A MICROSCOPIC THEORY OF ELECTROSTATIC
PRECIPITATION	374
  C.G. Noll and T. Yamamoto

ION CURRENT DENSITIES PRODUCED BY  ENERGETIC ELECTRONS
IN ELECTROSTATIC PRECIPITATOR GEOMETRIES	391
  W.C. Finney, L.C.  Thanh and R.H. Davis

EXPERIMENTAL STUDIES IN THE ELECTROSTATIC
PRECIPITATION OF HIGH-RESISTIVITY PARTICULATE	399
  J.C. Modla,  R.H. Leiby,  T.W. Lugar, and K.E. Wolpert

PILOT PLANT  TESTS OF AN ESP PRECEDED BY  THE
EPA-SoRI PRECHARGER	417
  L.E. Sparks, G.H.  Ramsey,  B.E. Daniel and J.H.  Abbott

                   Section C - Industrial Applications


PILOT PLANT/FULL SCALE EP SYSTEM DESIGN AND
PERFORMANCE ON EOF APPLICATION	427
  D. Ruth and D. Shilton

THE SELECTION AND OPERATION OF A NEW PRECIPITATOR
SYSTEM ON AN EXISTING  BASIC OXYGEN FURNACE	441
  D. Ruth and D. Shilton

CONTROL OF  FINE PARTICLE EMISSIONS  WITH WET
ELECTROSTATIC PRECIPITATION	452
  S. A. Jaasund

TUBULAR ELECTROSTATIC PRECIPITATORS OF  TWO
STAGE DESIGN	469
  H. Surati, M.R. Beltran  and I. Raigorodsky

PRESENT STATUS OF WIDE-SPACING TYPE PRECIPITATOR
IN JAPAN	483
  S. Masuda

LOW FREQUENCY SONIC CLEANING APPLIED TO
ELECTROSTATIC PRECIPITATORS	502
  S.B. Smith and J.A.  Schwartz

AUTHOR INDEX	514
                                 x

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                            VOLUME III

                   PARTICULATE CONTROL DEVICES

                        Section A - Scrubbers

                                                            Page

FLUX FORCE/CONDENSATION SCRUBBER DEMONSTRATION
PLANT  IN THE IRON AND STEEL INDUSTRY	    1
  R.  Chmielewski, S. Bhutra, S. Calvert, D.L. Harmon, J.H. Abbott

COLLECTION CHARACTERISTICS OF A DOUBLE STAGE SCRUBBER
TO ELIMINATE THE PAINT MIST FROM A SPRAY BOOTH   ....   16
  T.  Isoda and T.  Azuma

APPLICATION OF SLIPSTREAMED AIR POLLUTION  CONTROL
DEVICES ON WASTE-AS-FUEL PROCESSES	25
  F.D.  Hall,  J.M. Bruck,  D.N.  Albrinck and R.A.  Olexsey

EVALUATION OF THE CEILCOTE IONIZING WET SCRUBBER   ...   39
  D.S.  Ensor and D.L.  Harmon

DEMONSTRATION OF A HIGH FIELD ELECTROSTATICALLY
ENHANCED VENTURI SCRUBBER ON A MAGNESIUM FURNACE
FUME EMISSION	61
  M.T.  Kearns and D.L. Harmon

DROPLET REMOVAL EFFICIENCY AND SPECIFIC CARRYOVER
FOR LIQUID  ENTRAINMENT SEPARATORS	81
  J.H.  Gavin and F.W.  Hoffman

AN EVALUATION OF GRID ROD FAILURE IN A MOBILE
BED  SCRUBBER	95
  J.S.  Kinsey and  S. Rohde

OPERATION AND MAINTENANCE OF A PARTICULATE  SCRUBBER
SYSTEM'S ANCILLARY COMPONENTS	104
  P.A.  Czuchra

LOWERING OPERATING  COSTS WHILE INCREASING THROUGHPUT
AND  EFFICIENCY OF REACTORS AND SCRUBBERS	117
  R.P.  Tennyson, S.F.  Roe, Jr. and R.H. Lace, Sr.

OPTIMIZING VENTURI SCRUBBER PERFORMANCE THROUGH
MODELING	127
  D.W.  Cooper

THE IMPACT OF HUMIDIFICATION CHAMBER PHYSICS ON
WET GAS CLEANUP SYSTEMS	145
  D.P.  Bloomfield,  M.L. Finson, G.A. Simons and K.L. Wray
                               xi

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VOLUME III CONTENTS (Cont.)
                                                             Page

IMPROVING THE EFFICIENCY OF FREE-JET SCRUBBERS	162
  D.A. Mitchell
                       Section B - Fabric Filters


HIGH VELOCITY FIBROUS FILTRATION	171
  M.J.  Ellenbecker, J.M.  Price,  D. Leith and M.W. First

THE EFFECT OF DUST RETENTION ON PRESSURE DROP IN
A HIGH VELOCITY PULSE-JET FABRIC FILTER	190
  M.J.  Ellenbecker and D. Leith

ROLE  OF FILTER STRUCTURE AND ELECTROSTATICS
IN DUST CAKE FORMATION	209
  G.E.R. Lamb and P.A.  Costanza

PRESSURE DROP IN ELECTROSTATIC FABRIC FILTRATION ....  222
  T. Ariman and D.J. Helfritch

EXPERIMENTAL  ADVANCES ON FABRIC FILTRATION TECHNOLOGY
IN JAPAN -  EFFECTS OF CORONA PRECHARGER  AND RELATIVE
HUMIDITY ON FILTER PERFORMANCE	237
  K. linoya and Y. Mori

BAGHOUSE OPERATING EXPERIENCE ON A NO. 6
OIL-FIRED BOILER	251
  D.W.  Rolschau

NEW FABRIC FILTER  CONCEPT  PROVEN MORE FLEXIBLE
IN DESIGN,  EASIER TO MAINTAIN, AND UNSURPASSED
FILTRATION	260
  B. Carlsson and R.J. Labbe

EPRI'S FABRIC  FILTER TEST MODULE PROGRAM: A REVIEW
AND PROGRESS REPORT	270
  R.C.  Carr and J. Ebrey


                       Section C - Granular Beds
 ELECTROSTATIC ENHANCEMENT OF MOVING-BED
 GRANULAR FILTRATION	289
   D.S. Grace, J.L. Guillory  and F.M. Placer

 ELECTRICAL  AUGMENTATION OF GRANULAR BED FILTERS ....  309
   S.A. Self, R.H. Cross and R.H.  Eustis
                                  xii

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VOLUME III CONTENTS (Cont.)
                                                             Page

THEORETICAL AND EXPERIMENTAL FILTRATION EFFICIENCIES
IN ELECTROSTATICALLY AUGMENTED GRANULAR BEDS	344
  G.A. Kallio, P.W. Dietz and C.  Gutfinger

AEROSOL FILTRATION BY A CONCURRENT MOVING
GRANULAR BED:   DESIGN AND PERFORMANCE	363
  T.W. Kalinowski  and D. Leith

DEEP  BED PARTICULATE FILTRATION USING THE
PURITREAT (TM) PROCESS	382
  L. C. Hardison
                       Section D - Novel Devices
PILOT-SCALE FIELD TESTS OF HIGH GRADIENT
MAGNETIC FILTRATION	404
  C.H. Gooding and C.A. Pareja

EXPERIENCES WITH CONTROL SYSTEMS USING A UNIQUE
PATENTED STRUCTURE   	  416
  G.C. Pedersen

ELECTROSTATIC EFFECTS IN VORTICAL FLOWS	429
  P.W. Dietz

CONDENSATIONAL  ENLARGEMENT AS A SUPPLEMENT TO
PARTICLE CONTROL TECHNOLOGIES	439
  J.T. Brown, Jr.


                     Section E - Specific Applications


WELDING FUME AND HEAT RECOVERY - THE PROBLEM,
THE SOLUTION, THE BENEFITS	448
  R.C. Larson

PARTICULATE REMOVAL  CONSIDERATIONS IN SOLVENT
EMISSION CONTROL INSTALLATIONS	472
  E.A. Brackbill and P.W. Kalika

ARSENIC EMISSIONS AND CONTROL TECHNOLOGY - GOLD
ROASTING OPERATIONS	484
  J.O. Burckle, G.H. Marchant and R.L. Meek

CONTROL OF SALT LADEN PARTICULATE EMISSIONS FROM
HOGGED FUEL BOILERS	508
  M.F. Szabo,  R.W. Gerstle and L. Sims

AUTHOR INDEX	526

                                xiii

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                            VOLUME IV

              SPECIAL APPLICATIONS FOR AIR POLLUTION
                    MEASUREMENT AND CONTROL

         Section A - High Temperature High Pressure Applications

                                                            Page

FUNDAMENTAL  PARTICLE COLLECTION AT HIGH
TEMPERATURE  AND PRESSURE	    1
  R.  Parker,  S. Calvert, D.C. Drehmel and J.H.  Abbott

PARTICULATE COLLECTION IN A HIGH TEMPERATURE CYCLONE .   .   14
  K.C.  Tsao, C.O. Jen  and K.T. Yung

EVALUATION OF A CYCLONIC TYPE DUST COLLECTOR FOR HIGH
TEMPERATURE  HIGH PRESSURE PARTICULATE CONTROL  ....   30
  M.  Ernst, R.C. Hoke,  V.J. Siminski, J.D. McCain,
  R.  Parker and D.C. Drehmel

CERAMIC FILTER TESTS AT THE EPA/EXXON PFBC MINIPLANT  .   .   42
  M.  Ernst and M.A. Shackleton

HOT  GAS CLEAN-UP BY GLASS ENTRAINMENT OF
COMBUSTION BY-PRODUCTS	64
  W.  Fedarko, A. Gatti  and L.R. McCreight

THE  A.P.T. PxP DRY SCRUBBER FOR HIGH TEMPERATURE AND
PRESSURE PARTICULATE CONTROL	84
  R.G.  Patterson, S. Calvert and M. Taheri

GAS  CLEANING UNDER  EXTREME CONDITIONS OF
TEMPERATURE  AND PRESSURE	98
  E.  Weber, K. Hu'bner, H.G. Pape and  R. Schulz

PROGRESS ON  ELECTROSTATIC PRECIPITATORS  FOR USE
AT HIGH TEMPERATURE AND HIGH PRESSURE	126
  G.  Rinard, D. Rugg,  R. Gyepes and J.  Armstrong

REDUCTION OF PARTICULATE CARRYOVER FROM A
PRESSURIZED FLUIDIZED BED	        136
  R.W.  Patch

COMPARATIVE  ECONOMIC ANALYSIS OF SELECTED PARTICULATE
CONTROL SYSTEMS FOR ADVANCED COMBINED CYCLE POWER
PLANTS	        154
  J.R.  Bush, F.L. Blum and P.L.  Feldman

CONCLUSIONS  FROM EPA'S HIGH TEMPERATURE/HIGH
PRESSURE CONTROL PROGRAM	     170
  D.C.  Drehmel and J.H. Abbott
                              XIV

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VOLUME IV CONTENTS (Cont.)
                     Section B - Fugitive Emissions
                                                            Page
WATER SPRAY CONTROL OF  FUGITIVE PARTICULATES:  ENERGY
AND UTILITY REQUIREMENTS	182
  D.P. Daugherty, D.W. Coy and D.C. Drehmel

THE CONTROL OF DUST USING CHARGED WATER FOGS	201
  S.A. Hoenig

SPRAY CHARGING AND TRAPPING SCRUBBER FOR FUGITIVE
PARTICLE EMISSION CONTROL	217
  S. Yung, S. Calvert, and D.C. Drehmel

CONTROL OF WINDBLOWN DUST FROM STORAGE PILES	240
  C. Cowherd, Jr.

THE CONTRIBUTION OF OPEN SOURCES TO AMBIENT
TSP LEVELS	252
  J.S. Evans and D.W. Cooper

FUTURE AREAS  OF INVESTIGATION REGARDING THE
PROBLEM OF URBAN ROAD DUST	274
  E.T. Brookman and D.C. Drehmel

STATUS OF  CONNECTICUT'S CONTROL PROGRAM FOR
TRANSPORTATION-RELATED PARTICULATE EMISSIONS	291
  J.H. Gastler and H.L. Chamberlain

NEW CONCEPTS  FOR CONTROL OF FUGITIVE PARTICLE
EMISSIONS FROM UNPAVED ROADS	312
  T.R. Blackwood and D.C. Drehmel

DEVELOPMENT OF A SAMPLING TRAIN FOR THE ASSESSMENT
OF PARTICULATE FUGITIVE  EMISSIONS	321
  R.L. Severance and H.J. Kolnsberg

SECONDARY NEGATIVE ELECTRON BOMBARDMENT FOR
PARTICULATE CONTROL	333
  W.E. Stock
                  Section C - Measurement and Analysis


 HIGH TEMPERATURE AND  HIGH PRESSURE SAMPLING DEVICE
 USED FOR PARTICULATE CHARACTERIZATION  OF A FLUIDIZED
 BED COAL GASIFICATION  PROCESS	338
  S.P. Tendulkar, J.  Pavel and P. Cherish

 ON-STREAM  MEASUREMENT OF PARTICULATE SIZE
 AND LOADING	351
  E.S. VanValkenburg

                                 XV

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VOLUME IV CONTENTS (Cont.)
                                                             Page

ANALYSIS OF SAMPLING REQUIREMENTS FOR CYCLONE
OUTLETS	368
  M.D. Durham and D.A.  Lundgren

ELECTROSTATIC  EFFECTS ON SAMPLING THROUGH
UNGROUNDED PROBES 	  387
  W.B. Giles and  P.W. Dietz

OPTICAL PARTICULATE SIZE MEASUREMENTS USING A
SMALL-ANGLE NEAR-FORWARD SCATTERING TECHNIQUE   ....  396
  J.C.F.  Wang

IN-STACK PLUME OPACITY FROM ELECTROSTATIC
PRECIPITATOR SCRUBBER SYSTEMS	411
  L.E. Sparks, G.H. Ramsey and B.E. Daniel

TI-59 PROGRAMMABLE CALCULATOR PROGRAMS FOR
IN-STACK OPACITY	424
  S.J. Cowen, D.S. Ensor and L.E. Sparks

UTILIZATION OF  THE OMEGA-1 LIDAR IN EPA
ENFORCEMENT MONITORING	443
  A.W. Dybdahl and F.S. Mills

EFFECTS OF PARTICLE-CONTROL DEVICES  ON  ATMOSPHERIC
EMISSIONS OF MINOR AND TRACE ELEMENTS FROM COAL
COMBUSTION	454
  J.M. Ondov and A.H. Biermann

A SOURCE IDENTIFICATION TECHNIQUE FOR AMBIENT
AIR  PARTICULATE	486
  E.J. Fasiska, P.B. Janocko and D.A. Crawford

PARTICLE SIZE MEASUREMENTS OF AUTOMOTIVE
DIESEL EMISSIONS	496
  J.D. McCain, and D. Drehmel

CONTROL STRATEGIES FOR PARTICULATE  EMISSIONS FROM
VEHICULAR DIESEL EXHAUST	508
  M.G. Faulkner, J.P. Gooch, J.R.  McDonald,
  J.H. Abbott and D.C. Drehmel

AN  EVALUATION  OF THE CYTOTOXICITY AND  MUTAGENICITY OF
ENVIRONMENTAL PARTICULATES IN THE CHO/HGPRT SYSTEM  .   .  524
  N.E. Garrett, G.M.  Chescheir, III, N.A. Custer, J.D. Shelburne,
  Catherine R. De Vries,  J.L. Huisingh and M.D. Waters

AUTHOR INDEX	536
                                 XVI

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                               RM-064-EPA-79/RI
            COST AND PERFORMANCE OF PARTICIPATE CONTROL
                  DEVICES FOR LOW-SULFUR WESTERN COALS
                                      By:

                       Richard A. Chapman, Senior Engineer
                                      and
               Donald P. Clements, Ph.D., Senior Computer Scientist
                             Teknekron Research, !nc.
                   2118 Milvia Street, Berkeley, Califomia 94704
                              Leslie E. Sparks, Ph.D.
                                      and
                             James H. Abbott, Chief
                          Participate Technology Branch
                       U.S. Environmental Protection Agency
                   industrial Environmental Research Laboratory
                   Research Triangle Park, North Carolina  27711
                                   ABSTRACT

A computer model is being developed and used to assess  the cost and performance of
hot-side  and  cold-side electrostatic  precipitators (ESPs), fabric  filters, and venturi
scrubbers for particulate control on low-sulfur western coals. The model's performance
module incorporates  simplified  versions of  the EPA/Southern Research  institute ESP
model, the  EPA/Air Pollution Technology, Inc., venturi model, and the EPA/GCA, Inc.,
fabric filter model.  It calculates the control-device size  required to meet a specified
emission  limit for any size of unit burning a specified coal. The cost modules developed
for  each  of the particulate control devices are used to select the  device having the
lowest  levelized cost.  The program is structured to allow the  use of  an ESP  and a
venturi scrubber in series and calculates the least-cost combination of these devices. In
this paper the model is discussed and selected results of the assessment are presented.

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             COST AND PERFORMANCE OF PARTICULATE CONTROL
                  DEVICES FOR LOW-SULFUR WESTERN COALS

 INTRODUCTION

      Teknekron Research, Inc., is developing a Participate Control Performance and
 Cost Model (PC2M) for use in the design and evaluation of particulate control devices
 for  coal-fired boilers  burning low-sulfur coal.   The PC2M uses state-of-the-art EbP,
 venturi, and fabric  filter performance models for the design of particulate contro
 devices and detailed cost models to calculate capital and  operating costs.  This model
 brings together  for the first time simplified versions of the EPA/SoRI ESP model, the
 EPA/APT venturi  model, and the EPA/GCA fabric filter model in a format that allows
 the  design of the particulate control device to  meet a  specified emission  limit at the
 lowest  levelized cost.  In addition, the PC2M is structured  to model the performance of
 a cold-side ESP in  series with a venturi scrubber.

      The  model  is  being developed on  the  CDC 7600  computer at  the Lawrence
 Berkeley Laboratory and is scheduled for completion in August  1979.  The final report
 and  user's guide  will be available by the end of the year.

      In the following sections  the  overall  modeling approach  and  the  individual
 performance and cost  models are discussed.  The last  section presents  a  typical case
 study in which the PC2M was used  to  calculate particulate  control costs for a new
 500-MW boiler.
 OVERALL MODELING APPROACH

      A schematic representation of the PC2M is provided in Figure I.  Inputs to the
 computer model include boiler characteristics, coal properties, environmental regula-
 tions, and  ash characteristics.  If the user chooses not to provide boiler characteristics
 and coal properties, nominal default values are provided for these parameters, while the
 user must input, in a namelist format, values'for the environmental regulations and ash
 characteristics.  From these inputs the model calculates the gas flow rate, uncontrolled
 emissions,  and the  penetration  (I - removal  efficiency) required to meet the stated
 emission limit.  The PC2M then calls the appropriate  performance and cost models to
 design and  cost the various particulate control devices.

      If an  ESP and venturi in series is being evaluated, the PC2M successively calls the
 ESP and venturi models using a binomial  search iteration technique until the least-cost
 combination is found.
DISCUSSION OF CONTROL DEVICE MODELS
Fabric Filter Performance Model

     The fabric filter performance model  is the one developed by GCA for EPA  minus
the graphics capability.  This model uses fabric filter design and operating data along
with data on dust and fabric  properties in the calculation  of dust penetration.  The
PC2M  uses  the GCA  model  in an  iterative fashion  to determine  the  least-cost
combination of pressure  drop  and face velocity to provide  the  required  penetration.

-------
BOILER CHARACTERISTICS
Sin- (MW),-.., 	



Boiler type 	 . 	










I er
1 i \j \j i/
COAL PROPERTIES





ENVIRONMENTAL REGULATIONS
ASH CHARACTERISTICS



\__





Specific resistance coefficient, Kj (N-min/g-m)
Chemical composition 	 -\
(Optional)







GAS FLOW
Calculate gas
quantity to be .
cleaned (m /sec)


EMISSIONS
Calculate
uncontrolled
emissions (ng/J)
t
PENETRATION
Calculate P
to meet limit

)







-

ASH RESISTIVITY









Calculate p as
function of ash
chemical composition









	 **-


FABRIC
FILTFR
Performance
model

Fabric area __
Ash removal rate __
AP
Gas flow ^_

FABRIC
FILTFR
Cost
model

VEN1URI
Perfarmaice
model
Liquid rate
Ash removal rate _

Gas flow _
f
f-cpl p
L:> j ' 1
1
1
^
1
_J

ESP
Performance
model
Plate area
Elec. cond.
Ash removal rate
Temperature
Gas flow
VENTURI
model


ESP
Cost
model

*»-

*
-
Capital cost ___
Fixed
operating cost

Variable
operating cost
Energy penalty

Levelized
annual cost ^^

Figure 1.  Participate control performance model.

-------
     The iterative technique is summarized below:


      I.    Select limiting pressure drop
     2.    Select face velocity
     3.    Use GCA model to calculate penetration
     4.    Perform  steps 2  and 3 until  calculated  penetration equals the
           required penetration within a user-defined margin
     5.    Calculate levelized annual cost
     6,    Perform  steps  I  through  5  until  least-cost combination of
           limiting pressure drop and face velocity is found

Successive values of face velocity are selected using a power curve iteration technique.
This technique assumes that the relationship between penetration and face  velocity can
be represented by an equation of the form:

                                      V = aPtb                                    (I)

             where:      V    =   face velocity

                         P.    =   calculated penetration

                         a&b  =   constants

After each iteration, a and b are recalculated on the basis of the most recent values of
V and Pf.

     Successive values of limiting  pressure drop are selected using a binomial search in
which steps of decreasing size are taken until the lowest cost value of limiting pressure
drop is found.  The model  may also  be used in a noniterative manner to  determine
penetration for a given face velocity and limiting pressure  drop or cleaning  cycle.


Fabric Filter Cost Model

     The fabric  filter  cost model  is based on costs developed by Stearns-Roger, Inc.,
for EPRI.    Costs  are  a  function  of  face velocity,  gas  flow  rate,  number  of
compartments, pressure drop,  and the quantity of ash removed.   There  are 19 user-
defined inputs with default valuess including  bag life, bag cost, labor rate, number of
modules, duty factors, and time required for bag replacement.

     The model  assumes that  bag life  is a function  of face velocity,  with  higher
velocities requiring  more frequent cleaning and  resulting  in  a lower bag  life.  The
relationship between face velocity and bag life is assumed  to be:

                          Bag Life =  Bag L Fac --'    ,                        (2)

-------
where:

             Bag L Fac =  Bag life in years at a face velocity of
                           0.61 meters per minute

                      V =  face velocity in meters per minute

                      b =  user-defined constant with a default
                           value of 0.6

If the user feels that  bag life is independent of face velocity, a value of b = 0 may be
specified.

     The user has  the option of having the model perform a present  worth analysis in
order to provide levelized costs.   User inputs required  by the levelizing  routine  are:
discount rate, fixed charge rate, economic life, and the escalation plus  inflation rate.


ESP Performance Model

     The ESP  performance^model uses the Southern Research Institute (SoR!) model as
simplified by Leslie Sparks.   That simplified model calculates penetration as a function
of ESP size and operating conditions for  particles of various size. Rapping pufi and
small  diameter  migration velocity adjustments from  the original SoR!  model   are
included in the PC2M ESP model.  The PC2M ESP model calculates the penetration of
particles in distinct  size  ranges between 0.01 ym and (d  ) (a ) ym,  where d  is the
geometric mean particle diameter and a  is the geometric"stanatird deviation. "

      The model includes 80 tables of migration velocity as a  function  of particle
diameter for  use in calculating total  penetration.   These tables were developed using
the SoRI ESP  model and are representative of typical hot-side and American cold-side
ESPs.   Temperatures, specific collection  areas, dust loadings,  and current densities
represented by these migration velocities are illustrated  in Table I. Hall's equation  is
used to  select the  maximum current  density  allowed for  a given ash resistivity.  The
model  selects the migration  velocity table  that corresponds most  closely to the design
and operating conditions of the ESP under investigation.

      A  power curve  iteration  technique similar to  the one  used in  the  fabric filter
performance model is used to find the specific collection  area required to produce the
desired penetration.


ESP Cost Model
                                                                                  2
     The ESP  cost model is based on costs developed by Stearns-Roger, Inc., for EPRI.
Costs are a function of ESP type (hot-side or American cold-side), collector area, gas
flow rate, electrical conditions in the  ESP, and the quantity of ash removed. There are
11 user-defined  inputs with default values; included, for example, are duty factors,
capacity factor, load factors, fan and motor efficiencies, contingency costs, and the
cost of electricity.

-------
        TABLE I. ESP DESIGN AND OPERATING CONDITIONS FOR WHICH
                   MIGRATION VELOCITIES ARE AVAILABLE
 Case Number          12345678


 SCA (m2/m3/sec)     49.2   157.4   49.2   157.4   29.1    118.0   29.1    118.0

 Dust load (g/m3)      4.58   4.58    11.44  11.44   3.43   3.43    8.01    8.01

 Temperature (°C)     150    150    150    150    370    370    370    370


Current
L-'CI lil 1 J
(nA/cm2)
70
57
50
42.9
28.7
21.6
17.3
11.6
8.7
5.8
4.4
2.2
1.7
0.9
0.45
Resitivity
(ohm-cm)
I.OEIO xxx
I.5EIO xxx
I.7EIO x x x x
2.0EIO x x x x x x x
3.0EIO xxx
4.0EIO x x x x x x x
5.0EIO x x x x x x x
7.5EIO xxx
I.OEII x x x x x x x
I.5EII xxx
2.0EII x x x x x x x
4.0E II x x x x
5.0E II x x x x
I.OEI2 x x x x
2.0EI2 x x x x
x
X

X
X
X
X
X
X
X
X





-------
      The cost of electricity to energize the ESP is calculated from the collector area,
operating voltage, and current density.

      As with  the  fabric  filter costs,  the user has  the  option of having the costs
reported on a levelized basis.


Venturi Performance Model

      "Die venturi performance  model is the EPA/APT performance model modified by
Sparks  for use on  a programmable calculator.  The model calculates penetration as a
function of particle size for specified operating conditions of throat velocity and liquid-
to-gas ratio.   Particles  in distinct  size ranges between 0.01 ym and (d ) (a  ) ym are
included in the penetration calculations.                               9

      The PC2M uses the venturi  performance model iteratively to find the lowest
pressure drop combination of throat velocity and liquid-to-gas ratio  that achieves the
required penetration. A power curve iteration  technique  is used  to find the required
throat velocity at a given liquid-to-gas ratio, while a binomial search is used to iterate
over  liquid-to-gas-ratio values.  This iterative technique is the same as that used in the
fabric filter performance model, with  venturi throat velocity  replacing  fabric filter
face velocity and liquid-to-gas ratio replacing limiting pressure drop.

      If the user wishes to calculate venturi penetration for a  given set of operating
conditions,  two of the three following operating  parameters must be supplied: pressure
drop, throat velocity, liquid-to-gas ratio.


Venturi Cost Model

      The  venturi  cost  model  is based on cost information contained  in reports  by
Ponder et al.   and Kinkley and Neveril.  Costs are calculated as a  function of gas flow
rate, liquid-to-gas ratio, pressure drop, number of modules, and  whether or not an FGD
system is included  for SO-, control.  If FGD is included, a common  pond is used for ash
and sludge disposal, and the cost of  flue gas reheat is assigned to the FGD system.

      The cost model includes 10 user-defined  inputs with default values.  Typical user-
defined inputs include:  number of spare  modules, water cost,  steam cost, electricity
cost, and fan and pump efficiencies.

      Capital  and operating costs can be reported either on a first-year annual ized basis
or on a level ized basis over the  life of the system.


CASE STUDY

Presented here are the  results of a typical case study comparing  the costs of various
control devices designed to meet a particular emission limit.   Since the fabric filter
performance  model  is not yet fully implemented  in  the  PC2M, curves presented by
Dennis  et al.   were used to find various combinations of the face velocity and limiting

-------
pressure drop needed for the required penetration.  The corresponding average pressure
drop and face velocity were then used in the PC2M  fabric filter cost model to calculate
the fabric filter costs.

      Fabric filter performance was determined for  a system with the  following dust
and fabric properties:
                                                          3
           •    Inlet particulate concentration, Cj  = 6.87 g/m
                                         ,j£
           •    Specific cake resistance, K- = 1.0  N-min/g-m

                                **               3
           •    Effective drags S   = 400 N-min/m
•
                Residual fabric loading, W^ = 50 g/m

           «    Fractional area cleaned, a  = 0.40


      The following model input parameters  were used in the case study:

           Boiler Characteristics

                New 500-MW dry-bottom pulverized coal unit
                Capacity factor = 0.65

           Coal Properties

                23,258 J/g( 10,000 Btu/lb)
                 10% ash

           Environmental Regulations

                Particulate limit =  13 ng/J (0.03 Ib/MBtu)

           Ash Characteristics

                d  = 20 ym
                cr^ = 4ym

           Economic Factors

                January 1979 costs and dollars
                Electricity cost = 40 mills/kWh
                Discount rate =  16.1%
                Fixed charge rate = 19.2%
                Escalation rate = 5.5%/yr
                Economic life = 30  yrs

For  this combination of ash properties and environmental  regulations, a 99.65 percent
collection efficiency  is required  if 85 percent of the coal  ash leaves the boiler as fly
ash.
      at a face velocity of 0.61 m/min and 25°C

**    at 25°C

-------
     Levelized  fabric filter costs are presented in  Figure 2 as a function of average
fabric pressure drop (corresponding to various face velocities) for bag  lives of between
0.5 and  4 years.  In all cases a fabric filter operating at a face velocity of 1.0 meter per
minute  was found to be the design of lowest cost.   The least-cost design point may
indeed be somewhere  between 0.61 and  1.0 meters  per minute.  However, the curves
used for the performance analysis did not allow for the evaluation of devices operating
in this range of face velocities.

Levelized hot-side EPS costs are presented  in Figure 3 as a function of ash resistivity.
The flat portion of the curve reflects the effect of limiting hot-side current densities to
70 nA/cm .

     Figure 4 shows the level ized costs of a cold-side ESP, a venturi scrubber (with and
without  FGD), and  various combinations of these devices.  Cold-side ESP costs are
plotted  on the left-hand  side of the figure  for  various ash resistivities,  while venturi
costs are plotted on the right-hand side.  The curves represent various combinations of
ESPs and venturi  scrubbers plotted as a function of ESP penetration.  For this case, no
combination of ESP  and venturi is less expensive  than an ESP  or venturi alone.  In other
cases, not shown here, a combined ESP/venturi  system may be  the least expensive
choice.

     A summary  of particulate  emission control costs for  the conditions considered in
this case study is presented in Figure 5.  The range of costs for fabric filters represents
a  bag-life  range of between  0.5 and 4 years.  A cold-side ESP  and a fabric filter are
cost competitive for  low-resistivity ash,  while a  fabric  filter  is clearly the  most
economical choice for ashes with higher resistivity.


IMPACT OF THE REVISED NSPS FOR SO2

      The revised New Source Performance Standard (NSPS) for  SO^ promulgated by
EPA in  May  1979 requires 70 percent SO-, removal for low-sulfur  coals containing less
than about 430  ng/J sulfur (I Ib/IO Btu). Teknekron  Research, Inc., has shown that the
use of a spray dryer (dry scrubbing)  for SO^ control is less costly than the use of wet
FGD systems for these low-sulfur coals.   This fact has a number of implications for
the choice of a particulate control strategy:

      •     Particulate control  is downstream  instead of  upstream of the
           FGD system

      •     Gas temperature is lower (65-80 C) and closer to the dew point

      •     Cold-side ash resistivity is lower for most ashes

      •     Gas flow rate  is lower

      •     ESPs are cost  competitive with fabric filters

These implications clearly illustrate the need to evaluate  particulate control and SO^
control  as  an integrated system in order to select the most reliable and cost-effective
control  technologies for a given application.

-------
4.6
              Face Velocity (meters/minute) 1.00
2.6
                      8        10        12       14

                    Average Fabric Pressure Drop (cm of H2O)
   Figure 2.  Cost to achieve 99.65 percent participate removal for
              fabric filters of various designs for a 500-MW boiler.
                                  10

-------
a

5.

a
a
TS

m

m
^

>
c
a
e
o
c
o
o
e

2
"5
•B


I

"3

o
                      1 x 101"             2 x 1010


                              Ash Resistivity at 370° C (ohm-cm)
5 x 1Q10
101
      Figure 3.   Cost to achieve 99.65 percent particulate removal

                 with a hot-side ESP as a function of ash resistivity

                 for a 500-MW boiler.
                                             11

-------
9.0
                                                                                         Venturi Only (No FGD)
      0.35   0.5
1.0
2.0             5.0         100
 Cold-Side ESP Penetration (percent)
                                                                        20.0
                                                                                          Venturi Only (With FGD)
50.0
                                                                         100.0
   Figure 4.   Cost to achieve 99.65 percent particulate removal for
              cold-side ESP. venturi, and ESP/venturi systems
              for a 500-MW boiler.

-------
a
a


0
a
M

£


•a


r-
a

c
a
M


o
10
O
o
c
o
o

2
%
"5




I

•o
e



1
5 x 109
1 x 1010      2 x 1010         5 x 101C       1 x 10"



                   Ash Resistivity (ohm-cm)
                                                               2 x 10"
5 x 1Q11
      Figure 5.  Cost to achieve 99.65 percent particulate removal

                 for various control technologies as a function of

                 ash resistivity for a 500-MW boiler.
                                         13

-------
REFERENCES

 I.   Dennis, R., and H.A.  Klemm.  Fabric  Filter Model Format Change; Volume I.
     Detailed Technical Report.   EPA-600/7-79-043a  (NTIS  No. PB  293551).   U.S.
     Environmental Protection Agency.  Research Triangle Park, N.C., February 1979.

 2.   Steams-Roger, Incorporated.  Economic Evaluation of Fabric Filtration versus
     Precipitation  for  Ultrahigh Particulate  Collection Efficiency.   EPRI  FP-775.
     Electric Power Research Institute.  Palo Alto, Calif., June 1978.

 3.   Sparks, L.E.  SR-52 Programmable Calculator Programs for Venturi Scrubbers and
     Electrostatic  Precipitators.   EPA-600/7-78-026  (NTIS No.  PB  277672).   U.S.
     Environmental Protection Agency.  Research Triangle Park, N.C., March 1978.

 4.   McDonald, J.R.   A Mathematical  Model  of  Electrostatic  Precipitation (Revi-
     sion I): Volume I. Modeling  and Programming.  EPA-600/7-78-I I la (NTIS No.
     PB 284614).   U.S.  Environmental Protection Agency.  Research  Triangle Park,
     N.C., June 1978.

 5.   Hall,  J.H.   Trends in Electrical Energization of Electrostatic Precipitators.
     Presented  at the Electrostatic  Precipitator Symposium.    Birmingham,  Ala.,
     February 23-25, 1971.

 6.   Ponder, T.C., Jr. et al.  Simplified Procedures for  Estimating Flue Gas Desulfuri-
     zation System Costs.  EPA-600/2-76-150 (NTIS No. PB 255978).   U.S. Environ-
     mental Protection  Agency.  Research Triangle Park, June 1976.

 7.   Kinkley, M.L., and R.B. Neveril.  Capital  and Operating Costs of Selected Air
     Pollution  Control  Systems.   EPA-4SO/3-76-OI4  (NTIS No. PB  258484).   U.S.
     Environmental Protection Agency.  Research Triangle Park, May 1976.

 8.   Dennis, R., H.A. Klemm, and W.  Battye.  Fabric Filter Model Sensitivity Analysis.
     EPA-600/7-79-043c  (NTIS  No.  PB  297755).   U.S.  Environmental Protection
     Agency. Research Triangle Park, N.C., April !979.

 9.   Van Horn,  AJ. et al.  Review of New Source Performance Standards  for  Coal-
     Fired Utility Boilers, Phase 3 Final Report:  Sensitivity Studies for the Selection
     of  a Revised  Standard.  Teknekron Research, Inc.  Report  R-OI3-EPA-79/R-2.
     EPA Contract 68-02-3092.   Submitted to Office of Research  and Development,
     U.S. Environmental Protection Agency. Washington, D.C., June 1979.
                                        14

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               CRITERIA FOR DESIGNING ELECTROSTATIC PRECIPITATORS
                                       By

                                    K. Darby

                             Lodge-Cottrell Limited

                     (Subsidiary of Dresser Industries, Inc.)

                           Birmingham B3 1QQ, England

                                    ABSTRACT
     The Paper discusses the concepts of effective migration velocity and
specific collector area as derived from the Deutsch equation.  These two
factors are commonly used as a means of specifying a plant size and comparing
proposals by different suppliers.

     It is demonstrated that effective migration velocity is not a constant
dependent only on the fuel, being subject to large variations according to
various features of the design of the precipitator.  It is also shown that
specific collector area cannot be used without at the same time considering
the contact time of the gases in the electrostatic field.

     The removal of dust by a precipitator is carried out in two stages.  The
dust is first deposited on the collecting electrode, and a layer of significant
thickness must be allowed to form so that when, in the second stage, it is
dislodged by rapping, the layer breaks into agglomerated masses sufficiently
large to fall into the hoppers below the collecting electrodes before being
carried by the moving gas stream into the outlet flue.  This requires that the
frequency of rapping of each field of the precipitator shall be set at the
correct rate according to the concentration of dust entering the field.

     Currently much stress is being placed on the intensity of the rapping
blow and there is a tendency to specify increasing values of this blow.  Due
to the necessity to allow a layer of dust to form, no increase in rapping
intensity can overcome the effect of highly resistive dust.  While the rapping
force must be enough to shear the dust layer, any increase above this level is
likely to result in the breakdown of agglomerates with an increase in dust
emission and may also cause metal fatigue problems.

                                      15

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               CRITERIA FOR DESIGNING ELECTROSTATIC PRECIPITATORS

INTRODUCTION

     When a specification is drawn up for the design of an electrostatic
precipitator for a power station, the information supplied to the designer
usually consists of coal and fly ash analyses, dust concentration expected
at the inlet of the gas cleaning plant, together with some indications of
particle sizing, and the efficiency of gas cleaning required or the guarantee
for residual dust concentration in the clean gas.

     Recently, in addition to this basic information, it has become the
custom to provide additional guides such as the maximum effective migration
velocity or alternatively the minimum specific collecting area which will be
acceptable, thus avoiding the possibility of grossly under-sized plant being
offered.  Even more recently there is an increasing tendency to include
minimum values of the rapping forces for discharge and collecting electrodes.

     It is well known that the fuel and ash composition influence precipitator
performance.  Equally important, but less well known, is the design of the
precipitator which can have a substantial effect on the performance obtained.
Incomplete understanding of the basic mechanics of the operation of the
precipitator as a dust collecting device can further influence its performance.
The object of this paper is to illustrate the effect of the more important
factors involved, but due to time, all factors cannot be included, and effort
is concentrated, therefore, on the lesser known or more controversial areas.

THEORY OF PRECIPITATION

     In Figure 1 is shown the theoretical equation for the calculation of the
velocity of a charged particle suspended in a gas in a uniform electric field.
This equation gives particle migration velocity, but has no practical
application in precipitator design except that it shows that the mobility of
the particle will increase with increasing electric field strength.  Thus
precipitator efficiency could be expected to improve with increasing voltage
between the electrodes.

     Similarly, particle velocity is opposed by the gas viscosity; this means
that particle mobility will decrease as gas viscosity increases, that is with
increasing gas temperature.  Hence, the probability of the particle being caught
would be expected to decrease with increasing gas temperature.  This is in
line with practice.  On the basis of this equation it would also be expected
that fine particles would be very difficult to catch effectively in a
precipitator.  Due to the flow condition of the gas which will be explained
later, this is not so, and fine size particles can be readily removed from the
gas.

     An equation which is commonly used in precipitator design is that derived
by Deutsch, also shown in Figure 1.  This shows that efficiency will increase
with increasing effective migration velocity, and also with increasing value
of the ratio of A/V, this ratio being commonly referred to as specific collector
area, often used as a means of comparison of different plants.


                                       16

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     It must be emphasized that the effective migration velocity  (EMV) bears
no relationship to the theoretical value from the first equation.  EMV is
calculated from the size of the precipitator and test efficiencies obtained
in operation, and to express the number calculated as migration velocity is
misleading.

THE PROPERTIES OF DUST AND GAS

     In this section are discussed briefly the properties of dust and gas.
These will have similar effects on all types and designs of precipitators.
It is often assumed that these properties are the dominant ones in determining
the effective migration velocity obtained.  As will be seen later, this is
not so.

Dust

     The effect of particle sizing of the dust is shown in Figure 2, which
shows the  change  in effective migration velocities calculated from the Deutsch
equation for different particle sizes for typical highly resistive fly ash.
There is some reduction in migration velocity with increasing particle size,
with a minimum occurring between 4 and 5 micron.  While this change is
significant - the ratio being roughly 2  : 1 from the best to the worst
condition  - it is far less than the pure theory would indicate.  The
significance of these curves is that as  the residual dust requirement becomes
lower, or  the efficiency of gas cleaning required becomes higher, so the
design effective migration velocity must be reduced.  Dust in successive
fields will become progressively finer.  The graph shows that the effect of
adding a conditioning agent improves the collection of fine particles
selectively probably in part due to improved agglomerate strength.

     This  graph is for pulverized fuel dust and shows values down to 1 micron.
This was the smallest particle size which could be effectively de-agglomerated
in pulverized fuel ash.  In Figure 3, for interest, is included a similar
curve for  a wet precipitator working on a metallurgical fuel substantially
all below  1 micron in size.  This shows  that the electrostatic precipitator
can collect particles effectively down to the order of 0.01 micron.  In this
case a minimum migration velocity is shown at 1 micron.  The existence of a
minimum value for both dry and wet precipitators has been recorded by a number
of investigators, although the reason is not fully clear.

Dust Concentration

     Dust  concentration is important, since apart from the particle sizing effect
referred to above, there is evidence that with high dust concentrations, the
effective  migration velocity is higher, regardless of particle sizing, probably
due to the electrostatic field causing some agglomeration of the  particles
which can  fall into the hoppers without actually being deposited  on the
electrode  system.  Agglomeration is a very important part of the  complete process
and will be discussed later.
                                       17

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     Figure 4 shows for a sub-bituminous coal the change in migration
velocity actually measured on a precipitator with different numbers of fields
in operation.  It was assumed for the purpose of this exercise that the
de-energized fields retained no dust, although this is difficult to prove.
On the basis of these measurements, t will be seen that with high dust
concentrations of the order of  -05 gm/M3, effective migration velocity was
in excess of 8 cms/sec., falling to 4.5 cms/sec, when the dust concentration
was less than .05 grams/m3  which is the concentration for which this plant
was designed.

     In practice, on this particular plant, the dust emissions measured were
in the range  -01  gm/M3  and lower.  The effect of this low dust concentration
on migration velocity will be referred to under the discussion on the practical
features of operation of a precipitator.
                                                               q
     If the measured dust emission had been higher, .05 grams/m   guaranteed,
the curve would have indicated higher migration velocities for the outlet field
than the graph indicates, and the slope of the curve would be less steep, due
to rapping slip constituting a smaller percentage of the dust.

Dust Resistivity

     Much has been written on the subject of dust resistivity.  It has been
established that  at the temperature at the air heater outlet, usually about
121°C, the resistivity  of the dust is determined by the surface properties of
the dust, and hence the composition of the gas.  The occurrence of trace
quantities of sulphur trioxide and other conditioning agents can materially
affect the efficiency of dust removal.

     It has been  demonstrated that where these natural conditioning agents are
missing, they can be successfully added to the gases to substantially increase
the effective migration velocity.  The effect of sulphur trioxide and other
conditioning agents has been reported by Darby and Whitehead   and by other
investigators.

     Increases in effective migration velocity of more than 2 : 1 have been
obtained on a full scale precipitator plant by the addition of as little as
10 p.p.m. of sulphur trioxide.  This was first commercially applied on large
power plant precipitators by Lodge-Cottrell more than fifteen years ago, and
after a period of uncertain popularity, now seems to be becoming an accepted
system in the United States.

     Other conditioning agents which have been demonstrated with varying
degrees of effectiveness include ammonia, triethylamine and water vapor, but
sulphur trioxide  still  appears to be the most cost-effective additive.

     Considering  the types of coal, in the case of the hard bituminous coals,
there is evidence to support the view that the surface resistivity is largely
determined by an  adsorbed layer of sulphuric acid or a layer of sulphite as in
general effective migration velocity increases with increasing combustible
sulphur content.  There is some scatter of the test points when plotted graphi-
cally, but since  it is  known that other constituents of the ash can also affect
the performance,  it is not unexpected that the relationship should not be precise,

                                         18

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     In the case of the sub-bituminous coals, experience  of which has  occurred
mostly in the American mid West, sulphur content  is generally  low.   In  this
case, the presence of sodium and potassium compounds  in the ash  are  significant
factors.

     Figure 5 shows a typical curve for the effect of  sodium on  effective
migration velocity.  It is of significance that sodium appears to have a more
pronounced effect than potassium, although potassium will also further improve
the effective migration velocity.

     Conditioning agents, either natural or artificial, have the effect  of
giving more stable electrical operation of the precipitator at a higher  field
voltage with the consequent higher efficiency of  dust  removal.   In a paper by
Lederman et alia , chemical conditioning is also  reported to work on a hot
side precipitator.  In this case, the effect is unlikely  to have been  to reduce
resistivity, since before the air heater, the temperatures are generally in
excess of 260°C, at which temperature all dusts exhibit resistivities  well
below the accepted critical level.

     This paper indicates that  the effect of conditioning agents was to  increase
the breakdown voltage, thus counteracting the effect of the increasing
temperature in this respect.  For example, breakdown voltage was said  to be
increased by as much as 50% when using conditioning agents in  the form of
various salts of sodium and potassium.  Apart from the effect on the electric
field, in the opinion of the author, a major additional effect was likely to
be an increase in agglomerate strength and reduction in re-entrainment.
                                                                     3
     The comparison of hot and  cold side units by Darby and Whitehead  shows
that despite the reduction of resistivity, the effective  migration velocity at
the high temperature was not always higher than on the cold side.  Due to
this and the effect of increased volume due to higher  temperature, the hot side
plant could in many cases be larger than for the  cold  side.  It  now seems
proven that the hot side approach has limited application and is not the
panacea which would enable variations in fuel and ash  properties to be ignored.
The consideration of the use of conditioning agents on hot side  units  is
confirmation that this is so.

The Properties of the Gases

     On the standard cold side  approach to the application of  precipitators,
it is difficult to separate the effect of gas composition completely from that
of the dust.  For example, in the case of sulphur conditioning,  the effect is
probably due to an adsorbed layer of acid vapor.  Reduction of the resistivity
of the deposited layer of dust  has the effect of  increasing stability  of
operation and reducing reverse  ionization effects.  It is also known that
increasing the sulphur dioxide  content of the gas also increases the breakdown
voltage, thus giving additional benefit, so that  for example an  increase in
combustible sulphur in the coal has a double effect.

     In addition to the resistivity effect on the dust, more stable operation
and higher voltages often result as an additional effect  from  the presence of
significant quantities of conditioning agents, in particular water vapor.

                                       19

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Brown coal with very high water content, over 60% by weight but containing no  ^
other recognized conditioning agent, has given test values of effective migration
velocity well in excess of 10 cms/sec.

EFFECTS OF PRECIPITATOR DESIGN

The Mechanism of Collection of Dust by Precipitator

     The single stage plate precipitator, the type universally used in
power plants, consists of a horizontal flow gas chamber containing varying
numbers of electric fields in series.  (See Figure 6.)  The gas enters at a
velocity  (V) in the range of 9 - 21 m/sec. and is reduced by gas distribution
devices so that the velocity over the whole cross section of the field is
uniformly of value (v) usually in the range of about .9 - 1.8 m/sec.

     Consider first the effect of the electric field.  In the single stage
precipitator with a non-uniform electric field, flow conditions are in the
turbulent range and increased turbulence is created by the effect of the
electric wind resulting from the corona discharge.  The net effect is that
the turbulent velocity of the gas is high compared with that of the velocity
of the particles through the gas under the influence of the electric field.
The consequence of this turbulence is that dust particles are brought into
close proximity to the collection electrodes, and the probability of being
caught is determined by this proximity, which has the effect of largely
cancelling out the reduction in efficiency of collection of small particles
suggested by the fundamental equation.  Dust is, therefore, deposited for a
wide variety of particle sizing in each successive field with only comparatively
small reduction in the mean particle sizes in the successive fields.

     After the particles have been deposited on the electrode system or in a
small percentage of cases on the discharge system, they cannot at this stage
be regarded as effectively removed from the gas stream.

     The next stage in the precipitation process is to remove the dust so
deposited either by vibrating or rapping mechanically to dislodge the layer
of dust so that it falls into the hopper below the precipitator.  Only then
can the dust be regarded as 'caught'.

     Figure 7 shows free falling velocity of different particle sizings, from
which it will be clear that individual particles of fly ash dislodged from
the collecting electrode would only fall at a very low velocity of less than
.03 m/sec. towards the hopper.  At the same time they are carried forward
through the chamber at the gas velocity (v), so that very few would reach the
hoppers.

     Further considerations of the mechanism of collection shows that the
precipitator can only effectively collect dust when the deposited layer, on
being sheared from the electrodes, stays in the form of agglomerated masses
sufficiently large to give a high velocity sufficient to reach the hoppers
before the gases accelerate again into the outlet flue, at which point the
dust can be regarded as effectively not caught.


                                      20

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     Consideration of the graph shows that the mean size of the aggomerates
needs to be in excess of 1 mm  (1000 micron) in order to have free falling
velocities in excess of 3 m/sec.  It is in fact a vital part of the
precipitation process that a layer of significant thickness is allowed to
build up in order to permit the formation of the necessary size of agglomerate.
In practice, the size of the agglomerates is related to the molecular forces
between the particles and in particular the natural adhesiveness which often
is a contributory effect of a  conditioning agent.

     When any form of rapping  takes place to dislodge the dust, the layer
breaks down into masses of varying sizes.  One of the most important features
of the rapping mechanism is that it must be designed so that the frequency
of rapping permits the necessary layer to accumulate, and the intensity is
sufficient to dislodge the layer with the minimum breakdown of the agglomerates.

     The rate of dust collection in the successive stages as predicted by the
Deutsch equation shows an exponential relationship.  For example, in a three
field precipitator in series designed for 99.9% efficiency, the first field
would retain approximately 90%, the second 9% and the third field 0.9% of the
dust in the gases.

     This is in practice a rough approximation as the effect of particle size,
dust concentration, etc., is ignored, but from this it will be seen that the
rapping frequency in order to  permit the same thickness of layer to build up
must be very much lower on the outlet field, approximately 1/100 of the
frequency of the inlet field.  The rapping of the outlet field is most critical
as there is no further chance  to catch re-entrained dust.

     Figure 8 shows the variation of effective migration velocity for a single
field with intervals between the rapping blows.  A high rate of rapping, i.e.
every 15 seconds, gives an effective migration velocity of 6.3 cms/sec, compared
with 10 cms/sec, when the frequency is reduced to once in 1,000 seconds.  These
data were obtained on an inlet bank with a dust concentration of the order of
23 grams/nP.  At a frequency of 10 rapping blows/hour, the higher migration
velocity was maintained; at longer intervals, a gradual fall-off over several
days was observed.  This frequency was adopted as a general standard for this
dust concentration, and has proved satisfactory for most conditions.  For
successive banks, the optimum  frequency was found to be correspondingly less.
Outlet fields may only need rapping at intervals of several hours, long enough
to permit a layer of significant thickness to build up so that when dislodged
by rapping, the agglomerates reach the hopper quickly-  Consideration of
Figure 8 shows that the frequency is not highly critical, so the same frequency
can be used for a range of different coals without serious effects on performance.

     The other variable in rapping is the intensity.  Currently, high intensity
rapping is being put forward as a cure for many of the problems resulting from
highly resistive dust.  Considered in light of the fact that it is the
presence of a deposited layer  which creates problems, it would appear logical
to increase rapping intensity.  On the other hand, in view of the need to
accumulate a layer of dust which is the essential to the formation of
agglomerates heavy enough to fall to the hopper, it is obvious that achieving
the objective of minimizing the dust layer on the collector to a degree where

                                       21

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high resistivity is no problem will result in a considerable increase^
in re-entrainment of dust due to the smaller agglomerate size which will
result.  This will more than negate the effect of the advantage obtained
in electrical operation.  The layer of highly resistive dust which can be
tolerated without affecting the electric field is reported as less than 1 mm.
This, taken together with Figure 6, illustrates the limitation on improvement
in efficiency which changes in rapping frequency and intensity can be expected
to achieve.

     In the experience of the author, there is no evidence that high intensity
rapping has contributed any significant improvement to efficiency under highly
resistive dust conditions.  In a recent paper by Juricic and Herrmann4 ,
Juricic carried out interesting laboratory experiments on the dislodgment of
dust, and a very interesting film, using high speed photography, showed how
the dislodged layer was broken into agglomerated masses which fell to the
hopper.  Furthermore, increasing displacement of the collector due to higher
intensities resulted in disintegration of some of these agglomerates.

     Their paper was the result of a limited research programme which might add
much to the knowledge of the precipitation process if continued.  In contrast
to what might be expected, high intensity rapping can be disadvantageous for
many types of dust where the agglomerate strength is not high.  Surprisingly,
the benefit is more likely to result with highly conditioned dust resulting
from, for example, high sulphur fuels, where with normal intensity rapping
there can be a progressive build up of significant thickness, i.e. in excess
of one inch, which can influence the operation of the plant by reducing
clearances and modifying the corona discharge.

     Dalmon  in an unpublished report stated "accelerations of the order or
lOg removed most of the dust, but left the surface coated with a layer of dust
so tenacious that they are not dislodged by forces an order higher (lOOg)".

     In a paper presented at a recent Conference, he further concluded that
for U.K. coals, 60g was the rapping force most likely to produce the required
effect on collecting electrodes.  This would not necessarily be true for all
types of coal.  In practice, the forces used should be verified for different
fuel compositions.  Excessive forces can result in breakdown of agglomerates
and also increase the risk of failure from metal fatigue problems.

     In current specifications,  the value of rapping force is tending to
increase and minimum requirements of over lOOg are sometimes specified.  There
is a danger that unless the problem is fully appreciated, these high values
could be expected to increase mechanical problems.

Aspect Ratio

     Aspect ratio is a term which has been used in the last few years as a
means of regulating the ratio of field length to field height, and is in fact
a ratio of these two quantities.  In Figure 6 this would be represented by
(3*1)/H.   The object of specifying a value of Aspect Ratio, although often not
appreciated, is to ensure the maximum possibility of agglomerates having time
to reach the hopper, i.e., if taller collecting electrodes are used then the

                                        22

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field length must correspondingly increase to give comparable conditions  to
shorter collectors.  Using this concept, aspect ratio should also increase as  the
efficiency of dust removal required increases and the residual dust decreases  -
it is not a constant for all conditions.

     Examination of Figure 6 will show that the significant factors determining
whether dust reaches the hopper should include the time that the gas remains
in the chamber.  Wherever the agglomerate is released from any point on
any collecting electrode, it will only be retained effectively by the precipi-
tator when the time interval which elapses from when it is released to when
it leaves the chamber  is equal to or greater than that needed to fall to the
quiescent hopper zone below the collecting electrodes.  This time will obviously
vary according to the position in the field, but the maximum time available is
given by the ratio of L/v where L includes the inter-bank spaces in addition
to the actual length of the electrostatic field.  This is permissible since in
this space the dust is also still falling towards the hopper.

     Dust will be retained effectively by the precipitator only if the dust
reaches the hopper, and this in turn means that the outlet bank is particularly
critical so far as rapping and size of dislodged agglomerate is concerned.
Dust leaving the outlet upper end of the collector, B in the diagram, will
mostly fall on the outlet slope of the flare, but some will be carried into
the outlet flue and become part of the dust emitted from the precipitator.

     The object of Figure 6 is to illustrate that gas velocity must be included
in the consideration of the problem.  In place of the present concept of aspect
ratio, it is suggested that from the point of view of dust collection, the
geometry of the gas chamber is better expressed when comparing different
designs as the ratio t/H where t is the time the gas is in the precipitation
chamber and H is the collecting electrode height.  This ratio shows that
increasing the height of collector is permissible only if contact time of the
gases within the precipitation chamber also increases.  The height of the
precipitator collector in practice is essentially a compromise, designed to
give the lowest re-entrainment slip, together with the most economic
construction.

     Due consideration of the mechanics of dust collection, re-entrainment etc.,
make possible the design of precipitators giving residual dust emissions well
below  .02 grams/m  .  While the correct rapping is important on all fields, the
minimizing of rapping slip on the outlet bank is most critical as this has
least chance of being re-deposited.

     Generally, single blows with an impulse hammer give the least re-entrainment
slip.  Any form of vibrator, since the time of operation is longer than a
single hammer blow, will cause a greater re-entrainment slip.  Similarly, if
in order to maintain a high average rapping force "g" over the whole collector,
a number of hammers are used at different points, this has the effect, so far
as rapping re-entrainment slip is concerned, of increasing the frequency  of
rapping, since it is not possible to precisely synchronise the blows.  In such
a case, while in some areas the rapping intensity may be below the level  needed
to shear the dust layer, re-entrainment of the newly deposited dust on the
surface will still take place.

                                      23

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Gas Distribution

     From Figure 6 and from examination of the Deutsch equation, it is apparent
that the best efficiency, assuming all other factors are optimized, is obtained
when:

1.   The gas distribution is absolutely uniform over the whole cross section
     of the field.

2.   No gas by-passes the electrostatic field either in the roof or hopper
     regions.

     It is not practical to carry out gas flow correction work in the field on
the full scale unit, and the custom is, therefore, to use standard wind tunnel
techniques with large scale models.  These models should preferably be as large
as possible.  Lodge-Cottrell custom is to construct no smaller than one-eight
of the full size, as it is believed that the scale factor for small models
introduces significant errors into the final distribution pattern.

     Figure 9 shows the effect on precipitator efficiency of varying
degrees of gas distribution correction expressed in terms of percentage
deviation from ideal.  Under ideal conditions the precipitator would give 99%
efficiency.  Standards laid down by the I.G.C.I, would give roughly 98.8%
efficiency while poor distribution can give efficiencies well below 97%.  Since
this is due to poor distribution, the efficiency could be brought back to the
desired level by increasing the plate area and the size of the plant.  The
plant would give on test a lower effective migration velocity.

     In practice, a perfectly uniform distribution over the whole field is not
possible, particularly at the upper and lower extremities.  It is very
important that the full height should be utilized and at the same time gas
should not by-pass the electrostatic field.  Figure 10 shows, for varying
precipitator efficiencies, the effect on the calculated effective migration
velocity of a 0.1%, 0.5% and 1% by volume by-pass.

     As would be expected, the effect is small in all cases when the design
efficiency of the precipitator is only 80%, but when efficiencies of 99.9%
for example are required, even the 0.1% condition, with perfect collection of
the dust passing through the field, can only just reach the desired efficiency.
In present day plants, therefore, where high efficiencies are guaranteed, the
permissible by-pass effectively must be considerably less than 0.1%.  This is
achieved by baffling, which prevents the gas completely by-passing the field for
the complete length of casing.  For example, 0.1% of the gas having partial
treatment by looping in and out of successive banks (See Figure 6 - upper and
lower ends of plate) can be reduced in significance to an acceptable level.
In practice, measured efficiency on dry plant in excess of 99.99% have been
obtained, thus verifying that with the correct approach to this problem, the
effect of by-pass can be made insignificant.

Electrical Conditions

     The electrical conditions, i.e., the D.C. voltage and corona current applied
to the electrode system, are determined by the geometry of the precipitator.  It
can be shown that for any plant design, the highest mean voltage which can be
applied to the electrode system will result in the highest efficiency of dust
removal.
                                      24

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Thus if the design in any way limits  this voltage, measured  effective
migration velocity will also be reduced.  The ultimate  aim of  all
precipitator automatic control system, whether  they  operate  by measuring
electrode voltage or by spark counting,  is  to apply  at  all times the highest
possible voltage to the electrode  system.

     Figure 11 shows the variation of effective migration  velocity with
increasing total current applied to the  electrode  system.  Total current  is
the term used, since while  the current is almost entirely  corona discharged at
the lower voltages, ultimately most of the  power is  absorbed in power  arcs
which  contributes nothing to the precipitator efficiency if  the applied
voltage is too high.

     The graph shown was derived by the  Central Electricity  Generating Board
to  test the theory of  the control  system which  in  this  case  operates on high
tension voltage.  It will be seen  that there is a  large variation in effective
migration velocity between  either  under-running or over-running the rectifier
compared with the optimum setting.  This can be a most  significant factor when
a plant efficiency is  measured by  sampling; it  is very  important that  the
rectifier control system is correctly designed  and is also functioning
correctly.

     The conditions  inside  the gas chamber  which determine voltage and current
which  can be carried  safely vary with dust  and  gas loading,  and the nature of
the coal, so that the  control  system cannot operate  at  a pre-set voltage  or
current input.

     A second factor which  has long been recognized  in  the precipitation
industry, but for which no  theoretical explanation exists, is  the effect  of
the bus section  size  energized by  one rectifier set.  Figure 12 shows  the
change in effective migration velocity with increasing  bus section size,
shown  as the size of  collector electrode plate  connected to  a  single rectifier.
The effective migration velocity varies  from over  10 cms to  approximately
6.5 cms for plate areas ranging from 450 m   to 7500 m.   This effect  was
also reported by Ramsdell  .

     The choice  of plate area  and  the number of bus  sections is determined by
the most economic combination, striking  a balance between  the  cost of  the
rectifiers and the cost of  the precipitator and internals.   An important
point  to remember is  that rectifier costs do not decrease  proportionately with
decreasing current output rating.   Also  additional bus  sections require
additional rapping and lead-through insulators  which add to  the cost.

Plate  Spacing

     Plate spacing is  probably one of the most  controversial factors in
precipitation.   Examination of the Deutsch  equation  would  give the impression
that A/V, the specific collector area is, apart from effective migration
velocity, the most significant factor, being directly related  to precipitator
efficiency.

     Taken to its logical conclusion, the implication of this  formula  is  that
for a  particular precipitator  casing size and contact time,  the closer the
plates can be spaced,  the more efficient the precipitator  will be.

                                       25

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     There are obvious practical limitations to this argument because of the
difficulty in manufacturing large collecting plates (up to 15.2 m x 4.6 m) to
the necessary degree of flatness, and hence extremely low spacings are
automatically eliminated.

     Similarly with the discharge electrodes, the same limitations are imposed
although these are less in the case of weighted wire than in the rigid electrode
constructions.  Plate spacings on commercial plant currently in use range from
203 mm  (8") to 610 mm (24") and even higher, but most commonly are in the range
of 203 mm to 305 mm.

     Figure 13 shows the results of tests carried out on a full-scale boiler
plant with the plates spaced at 305 mm and 610 mm.  Due to the fact that the
precipitator casing was designed for 305 mm spacing, the electrical conditions
for the 610 mm space were artificially limited.

     The tests were taken with a wide variety of fuels which explains the
scatter of the test points.  Even so, there is seen to be an increase in
average migration velocity of from 12 to 18 cms when the plate spacing is
increased from 305 mm to 610 mm.

     The tests were carried out on a C.E.G.B. power station a few years ago, and
patent applications were made to cover this wide spacing approach.  A number
of plants have been installed with more than 508 mm spacing for applications
where expensive materials of construction were needed, and this effect was
particularly favorable on cost.  In the case of power stations, since with
increasing plate spacing, the casing must also increase in size, a review of
economics indicated that spacings of the order of 305 mm were an acceptable
compromise.

     It is interesting to note that apart from the work by Lodge-Cottrell, the
effect has also been recorded in papers by Misaka et alia   and Aureille and
Blanchot°.  Both these papers showed a greater increase in effective migration
velocity with spacing than the Lodge-Cottrell tests.  Currently spacings in
excess of .6 m have been mentioned as a standard approach of Nippon Steel in
their publications, and similar spacings are being used by yet another Japanese
manufacturer.

     Considering the implications of this effect, together with the tendency
to quote plant size in terms of specific collector area, which assumes that
migration velocity is constant regardless of plate spacing, then it would seem
that the present methods using either effective migration velocity or specific
collector area do not give a correct comparison of plants of different
designs where the spacing of the plates vary.

     The effective migration velocities measured in all cases quoted were for the
same contact time, the same gas velocity in the field and the same inlet dust
conditions.  Thus there is little doubt that the wider spacing resulted in an
increase in effective migration velocity.  In practice, use of wider spacing with
the same collector area must also at the same time give an equally propor-
tionate increase in contact time.  In view of the importance of time in the
field in collecting agglomerates after they are removed from the collectors,


                                       26

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the wider spacing plant at the same plate area has the double potential advantage
of a higher effective migration velocity and a longer 'contact' time in the
precipitator casing than a smaller spaced plant for similar fuel and gas condi-
tions.

CONCLUSION

     The Deutsch equation is commonly used for electrostatic precipitator size
calculations.  It contains two terms, effective migration velocity and specific
collector area.  The first of these is often considered to be determined only
by the properties of the coal and ash.  In practice, since effective migration
velocity is calculated from the size of the precipitator and measured dust
removal efficiency, it is also strongly influenced by a number of design
features of the precipitator plant.  These include gas distribution, rapping
frequency and intensity, electrical operation, dust concentration and dust
sizing distribution.

     Comparing plant size in terms of specific collector area assumes that
effective migration velocity is constant regardless of spacing.  There is
strong evidence to support the view that effective migration velocity does in
fact increase with plate spacing.  Furthermore, the mechanism of the dust
collection process, which has been shown to depend on agglomerate formation
sufficiently heavy to fall to the hoppers, supports the argument that the time
that the gases are exposed to the electrostatic field must also be taken into
account.  This increases with plate spacing for the same collector area so that
when comparing plant of different design, not only must correction be made
for effective migration velocity for the different plate spacing, but also
with the wider plate spacing there is the added advantage of increased time
in the field which can only result in a further increase in precipitator
efficiency for which additional credit must be given.

     The whole mechanism of the removal of the dust from the collector plate
and the manner in which it is transferred to the hoppers is a subject which
requires a considerable amount of additional study.  While the forces needed
to dislodge the dust layer must be sufficiently large to keep the plant
reasonably free of dust, this should not be so great that the motion induced
in the collector is sufficient to start break-up and reduction in the size of
the agglomerates, and hence increase the re-entrainment slip.  For this reason,
the present trend towards specifying progressively higher acceleration forces
for rapping must be treated with caution.
                                       27

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                                  REFERENCES
1.    Busby, H. G. T. and Darby, K.  Efficiency of Electrostatic Precipitators
      as Affected by the Properties and Combustion of Coal.  Institute of Fuel,
      May 1963.

2.    Lederman, P. B. and Bush, J.  Chemical Conditioning of Fly Ash for Hot
      Side Precipitators.  CSIRO Conference on Electrostatic Precipitators.
      Australia 1978.

3.    Darby, K. and Whitehead, C.  The Use of Electrostatic Precipitators in
      Current Power Station Practice.  Institute of Fuel Symposium on Changing
      Technology of Electrostatic Precipitation, Adelaide, Australia 1974.

4.    Juricic, D. and Herrmann, G.  Modeling and Simulation of Dust Dislodgment
      on Collecting Plates in Electrostatic Precipitators.  EPRI Sponsored
      Project Research Contract RP533-1.

5.    Dalmon, J.  Investigation into Forces Required to Dislodge Precipitated
      Dust from an Electrode.  Unpublished CEGB Report.

6.    Ramsdell, R. G.  Design Criteria for Precipitators for Modern Central
      Station Power Plant.  American Power Conference,  1968.

7.    Misaka, T., Sugitomo, K. and Yamada, H.  Electric Field Strength and
      Collection Efficiency of Electrostatic Precipitator having Wide Collecting
      Plate Pitches.   CSIRO Conference on Electrostatic Precipitators, Australia,
      August 1978.

8.    Aureille, R. and Blanchot, P. - Electricite de France.  Experiments to
      Test the Influence of Different Parameters on Electrofilter Efficiency.
      Staub 31, 1971.
                                       28

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         FIGURE S
ELECTROSTATIC PRECIPITATOR

THEORETICAL MIGRATION VELOCITY

MCmON OF CHARGED PARTICLE IN
ELECTRIC FIELD


              p  VARIES WITH PROPERTIES
                  OF MATERIAL
                  1-5 -3 FOR AVERAGE
                  INSULATING MATERIALS
              E  ELECTRIC FIELDSTRENGTH
              Q  PARTICLE ftflC>l US
              W  PARTICLE MIGRATION
                  VELOCITY
              |J  GASVISCOSFTY

DELJT5CH EQUATION
              S - EFFECTIVE MIGRATION
EFFICIENCY
SPECI
AREA
ooujEcroR
   VELOCITY
I -FIELDLENGTH
V -GASVELOCITY
d -ELECTRODESPACING
A - TOTAL PLATE AREA
V - GAS VOLUME THROUGH
   PREC1PITATOR
                                                   U
                                                   u
                                                   in
                                                   **.
                                                   2
                                                   
-------
    4SUMERATE STRENGTH.
                   *     n

                   V

                FIGURE 3
    TYRCALPARTICLESIZE-EFFiaENCY
    RELATIONSHIP FOR ELECTRO STATIC
    PRECIPITATOR ON FINE DUST AND
    FUME PARTICLES
              OPAwrre» f MIOJON I
           QJ
                  FIGURE 4
CHANGE N EFFECTIVE MIGRATION VELOCITY IN
SUCCESSIVE FIELDS OF PREQP!TATOR DUETQ
REDUCING C)LOTOCMZNTRAT!ON AND1NCREASING
          FINENESS OF RES1DUALDUST
INLET DUST CONCENTRATION

DUST CONCENTRATION LEAVING
FIELD No.6

EFFICIENCY OF DUST COLLECTION
                         2T.S GRAMS/NUT

                         LESS THAN OO5 GRAMS / NM3


                         GREATER THAN 97 8»/e
            Ha.
                   30

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CO
                       FIGURES
        SUB-E'I« JMINOUSC30AL5 AhDUGNTTES
        \ARIAT ;•..)! ^ IN PREQPrTATOR SIZE WITH \ARtATCN
        NTHErODRJM GCIDEOCNFENrOFTHECCALASH
           03
ti •   i
  IN ASH
                                2SS
                                                            RGtJRE 6
                                         IDEALGONDITTON - UNIFORMVELQOTY v OVERFULL
                                                          HE1GHTAND WIDTH OF RECEIVING
                                                          ELECTRODES
                                                      L  - NQMOTIONINROOFORHOPPER
                                                                         CHOPPER /^HOPPER /\HOP«B / N FIELD - 3 l/»

                                                                                               MAXIMUM TIME FOACUtr
                                                                          \T-JT5W  \   I   \    /  TOFAU.TOHOPPB8 - LfV

-------
           FIGURE 7
  FREEBUlM^VELOCrTYOFSR-EFJICAL
  FBRTICLESSPG2iNAlR
  AT2O°CAND76Omm
  HG PRESSURE
        PAHTtd-g OIAMCTEP ( MICROM « lO^MSTRSS J
            )OO
                       K3OO
              RGURE 8
EFFECT QFRECElVINGELECTROCe RAPPING
FREQUENCYON EFFECTIVE MIGRATION
VEUDCITY (INfTENSITYCONSTANT)
   MRKVM. KTWeCN RAPMNO *UHM ( SECONDS )
     SO    tOO          SCO   KXX>
                32

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                           FKSURS
       VARIATIONS t)F EFFICIENCY AGAINSTGAS DISTRIBUTION
       ASSUMING Wo EFFICIENCY UNDER im. CONDITIONS
                  10   is    Jo   is
                   •/• STAN&AnO DCVIATION
                                                  FIGURE 1O
                              EFHCTtVEMlGRATONVEljOaTYANDPREaPrrATOR
                              EFICIENCYFOR VARMNG PERCENTAGESOFGAS
                              ^PASSING ELECTRODES STSTEM.
WOCASBY-WSS
                                                                                   N.B.
                                                                                     EMV FOR ZERO GAS
                                                                                     BY-PASS ASSUMED IO CM/SEC
                                                                                 •ft KFTICIINCV Or PMCII>ITATM
CO
CO
1!
e

»
                                                            FKSUREI)
                                           EFFECT OF POWER INPUT TO ELECTRODE SYSTEM
                                           ON EFFECTIVE MIGRATION VELOCITY
                                               MEANOEVOUAGE48KV
                                           MEANDS
                                           VCUAGE4OW
                         NOTE HIGHEST MIGRATION VELOCITY
                          CORRESPONDS TO HIGHEST MEAty

                          VALUE OF ELECTRODE VOLTAGE
                                                                MEANDE
                                                                VOLTAGE 45 KV
                                                             TtM |tp*jiKovti»RU»eo«eNst
             abs
                                                               ofo
                                                                           OKI
                                                                                       ao

-------
G2
                    FIGURE 12
           VARIATION OF EFFECTIVE MIGRATION
           VELOCITY WITH PREC1P1TATOR PLATE
           AREA ENERGISED BY EACH RECTIFIER
            O REPEAT TESTS FOLUOWIWO
             RKCTiriCAVlOH OF MINOS FAUUS
             IK MECiPITATONS
                      >B«A ( g  »3M8 I
                        4.8
                  FIGURE S3
        EFFECTIVE MIGRATION VELOCITY V
        DISCHARGE ELECTRODE VOLTAGE FOR
        305 MM AND 610 MM SPACING OF
        ELECTRODES IN PRECIPITATQ8

          @ S05»"H U281)  PLATE SPA6IN6
          K €10 MM (24*1 PLATE SPACINS
                                    ,£-•
                                      BC
                3O
                              eo
                                       •o
                        34

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      EVALUATION OF THE GEORGE NEAL ELECTROSTATIC PRECIPITATOR
                           Robert C. Carr
                 Electric Power Research Institute
                   Palo Alto, California  94303
                           David S. Ensor
                      Meteorology Research, Inc.
                     Altadena, California  91001


                              ABSTRACT
     The Electric Power Research Institute  (EPRI) is currently supporting
a major research program characterizing the performance of high efficiency
electrostatic precipitators  (ESP).  One such effort evaluating the George Neal
ESP of Iowa Public Service Company is described in this paper.

     Results show that under well tuned conditions the ESP overall collection
efficiency was 99.7 percent at a specific collecting area of 745 ft2/kacfm
(520 MW) with associated mass concentrations of 0.025 lb/10& btu and stack
opacity of 4.6 percent.  The boiler outlet size distribution was found to be
bimodal with submicron and large particle peaks at 0.2 and 5 microns diameter,
respectively.  Consequently, an apparent bimodal fractional efficiency curve
results with efficiencies of 99.6, 98 and 90 percent measured for 20, 2 and
0.2 micron diameter particles, respectively.  Rapping reentrainment losses
were found to be insignificant except during episodes of high ash hopper
levels resulting from a malfunctioning ash removal system, when large rapping
puffs were observed.  In addition, outlet emissions increased dramatically to
0.08 Ik/10^ btu during these periods, suggesting that an emission level more
representative of daily operation lies somewhere between 0.025-0.08 Ib/io^ btu.
                                      35

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INTRODUCTION
     It has become apparent that regulatory agencies are intent on reducing
permissible particulate emissions from pulverized-coal fired utility boilers.
The most recent example is the 0.03 ^/lO6 btu revised New Source_Performance
Standard promulgated by EPA.  An even more striking example is evident in
California, where the State Air Resources Board has defined Best Available
Control Technology as 0.005 lb/106 btu, or equivalent to 99.9+% control for
new coal-fired boilers.  In addition, increasing attention is being directed
to control of fine particulates (less than 2 micron particle diameter),
trace element emissions and plume opacity.

     In response to these regulatory constraints the utility industry,
through the Electric Power Research Institute (EPRI), is conducting a major
research program to develop and assess the capability of future and current
technologies to cost effectively and reliably address these issues.  The
results reported here are the outcome of the first in a series of evaluations
to quantify the total and fine particulate emission control potential of
modern, high efficiency electrostatic precipitators  (ESPs) under EPRI project
RP780 "Evaluation of High Efficiency Electrostatic Precipitators".   Of parti-
cular interest in the program is characterization of well-maintained ESPs
operating under optimum conditions as well as documenting off-design perfor-
mance induced by normal day-to-day operating and maintenance problems.  In
addition to consideration of the emission control capabilities, these studies
are also evaluating the economic, engineering and operational aspects of the
ESPs.  Although these latter considerations are frequently the governing
factors in achieving acceptable performance, this paper will deal only
with the emissions aspects.  The reader is referred to the individual EPRI
reports for more detailed information  (Ensor, et  al (1979)-*-).

PLANT DESCRIPTION

     The data reported here were obtained at the George Neal Unit 3 ESP
of Iowa Public Service Company, located on the Missouri River, 20 miles south
of Sioux City, Iowa.  The unit tested was a Foster Wheeler pulverized-coal
fired boiler nominally rated at 520 Mw.  Flue gas from the boiler enters a
single economizer, splits into two separate ducting systems, and then enters
an air preheater before passing through the ESP, I.D. fan and stack.  At
design conditions the total flue gas flow is 2,084,000 ACFM  (300 °F and
-20 in. H2O) at the ESP outlet ducts.  A diagram of the gas flow system is
shown in Figure 1.

     The fuel fired was a low-sulfur western subbituminous coal with a heat-
ing value of approximately 10,000 btu/lb and an ash content of 9-12%.  A
complete coal analysis as occured during the test period is given in Table 1.

     The Neal Unit 3 has two precipitators  (sides A and B) of European design
operating in parallel with approximate size of 70 feet wide by 200 feet long.
The ESPs were manufactured by Lodge-Cottrell and designed to achieve a removal
efficiency of 99.7% at a specific collection area (SCA) of 880 ft2/kacfm>
Table 2 outlines the important ESP design features.


                                       36

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EXPERIMENTAL PROCEDURES

     Field testing was performed simultaneously at the inlet and outlet of
the "A" side of the ESP.  Measurements included particulate size distributions
from 0.02 to 10 micron diameter and opacity.  Gas measurements of oxygen, sulfur
dioxide, carbon monoxide and nitric oxide were also performed to monitor
boiler operation.  Description of the gaseous sampling system will be omitted,
since it follows fairly well-established procedures and has no direct bear-
ing on the results presented.  A complete description of the sampling system
is provided in Ensor et  al  (1979)1.

Particulate Size Distribution

     Particulate size distributions were obtained with cascade impactors
and Electrical Aerozol Size Analyzers  (EASA).  The impactors provided size
distribution information from nominally 0.5-20 micron particle diameter, and
the EASA from nominally 0.02-0.8 micron particle diameter.

     The impactor used in this study was a unit designed at Meteorology
Research, Inc.  (MRI) to facilitate sampling of particulate matter in stacks.
The Model 1502 Inertial Cascade Impactor design is based on a simple annular
                                                                    o
arrangment of jets and collectors reported by Cohen and Montan (1967) .  There
are seven stages with backup filter.  Stainless steel foil discs coated with
Apiezon-L grease were used to collect the particles.

     The EASAs used were two model 3030 units manufactured by Thermo Systems,
Inc.  This instrument is currently the only practical commercially available
instrument capable of measuring aerosol particle size distribution in the
0.01-to-l.O micron diameter range.  It was commercially introduced in 1973
and is a greatly improved version of the Model 3000 which was commercially
introduced in 1967.  The EASA is described in detail by Liu, Whitby, and Pui
 (1974)3 and Liu and Pui  (1975)4.

     It should be mentioned that the cross-sensitivity between many of the
EASA particle diameter channels greatly affects interpretation of the data.
A basic assumption behind the channel constants reported in the Thermo
Systems, Inc., manual is that cross-sensitivity may be neglected.  Use of
the constants reported in the manual results in large errors when applied
to narrow size distributions such as those often seen in combustion aerosols.
Accordingly, in this work the EASA data were reduced with a number of different
approaches to correct for cross sensitivity.  The details of the data in-
version method are presented in Ensor, et  al  (1979)!•

Opacity

     Measurement of opacity was conducted with two MRI Plant Process Visio-
meters  (PPV).  The instruments are based on light scattering theory and
provide real-time monitoring of stack opacity as described by Ensor et  al
 (1974)^.  The large differences in inlet and outlet concentrations required
                                     37

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full scale ranges in opacity of 97% and 7% respectively-  In the present
situation, opacity is defined as unity minus the light transmittance through
the plume expressed as a percentage.  The PPV allowed real-time measure-
ment of opacity and recording of real-time events such as boiler upsets and
precipitator rapping.  This instrument was the sole measurement of opacity
since the Neal station was not equipped with stack transmissometers.

RESULTS AND DISCUSSION

Introduction
     To fully characterize the George Neal ESP emission control capabilities,
a number of test conditions were examined.  For example, the basic features
of interest were the particulate matter mass collection efficiency and
associated opacity at full load (520 Mw) under favorable electrical and
mechanical conditions.  The effects of ESP plate area (SCA)  and rapping re-
entrainment on outlet emissions as well as particle size dependent collection
efficiency are presented as a more in-depth examination of the ESP.

ESP Operation
     The George Neal No. 3 ESP emission testing was performed in two distinct
phases roughly five months apart.   Although this approach reflects the
prevailing EPRI philosophy of control device evaluation, several operating
problems occured during the program which made the two test phase approach
mandatory to insure representative data collection.  The Phase I data were
collected with a malfunctioning ash removal system and therefore are indica-
tive of off-design operation.  The Phase II data were collected following a
unit outage for overhaul and are more representative of optimum ESP operation.
Accordingly, the majority of the data presented will reflect the Phase II
results.  However, the Phase I results will be discussed when appropriate to
illustrate the effect of operating problems on ESP performance.

Overall Particulate Mass Collection Efficiency

     Total particulate mass collection efficiency data were collected at
both full and partial loads of 520 and 303 Mw, respectively, as summarized
in Table 3.  The data are presented in several formats including penetration
and collection efficiency.  Penetration (defined as the outlet concentration
ratioed to the inlet) is equivalent to unity minus collection efficiency.
The use of penetration is useful because it is a more sensitive measure for
very efficient collectors.  For example, the difference in collection effi-
ciency between 99.9% and 99% seems fairly small.  In terms of penetration,
however, the difference is 0.1% compared to 1%, or an order of magnitude.

     To determine the effect of ESP plate area on particulate emissions,
artificial variations in SCA were achieved by a combination of load reduction
and deenergizing the last field.  Although this approach does not absolutely
isolate the effect of SCA as would different size ESPs operating at design
conditions (due to effects of velocity distribution, residence time, etc.),
it is believed that the observed trends described below are at least semi-
quantitatively correct.
                                      38

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     As can be seen in Table 3, the overall collection efficiency ranges
from 99.7 percent at a full load SCA of 745 ft2/kacfm to 99.89 percent at a
reduced load SCA of 1270 ft2/kacfm.  This performance exceeds the design
specification of 99.7 percent at an SCA of 880 ft2/kacfm.   (The measured
gas volumetric flow rate was about 10 to 15 percent greater than design).
Also tabulated in Table 3 is the inlet flyash resistivity, which ranged
from 2.5 - 5.0 x 1012 ohm-cm.

     Examination of the full load data reveals total outlet emission levels
of typically less than 0.025 Ik/106 btu.  The stack plume was slightly visible
under these conditions, as suggested by the 4.6 percent stack opacity measured
by the PPV.  By comparison, the emissions are below the New Mexico particulate
standard of 0.05 Ib/lO^ btu total and 0.02 lb/106 Btu for particles less
than 2 microns in diameter.  In addition, these emission levels fall slightly
below the revised New Source Performance Standard of 0.03 lb/106 btu recently
promulgated by EPA.

     There are two other effects of interest included in Table 3.  First,
with the given Neal flyash characteristics, it appears that an SCA in
excess of 750 ft2/]cacfm j_s required to achieve a clear stack (opacity of 2-4
percent).  Second, the fraction of particulate emissions less than 2 micron
particle  diameter ranges from 20-40 percent depending upon the specific
operating condition.  This fraction is larger than expected, as will be
discussed later, and may in part explain the unusually high opacities
observed at relatively large values of SCA.

•     Figure 2 gives a more graphical presentation of the data summarized in
Table 3 and clearly illustrates the importance of SCA on emissions.  It can
be seen that significant improvements in collection efficiency by increasing
plate area  (SCA) may be confined to lower values of SCA.  The "tailing off"
of performance at higher SCAs may result from increasing dominance of non-ideal
effects such as sneakage and velocity maldistribution.  In terms of mass
emissions it is interesting to note from Figure 1 that SCAs in excess
of 700 ft2/kacfm are required to achieve the EPA revised New Source Performance
Standard of 0.03 lb/10^ btu.  Although these data are site-specific to Neal
Unit 3, they do suggest a generic limitation of improving collection efficiency
by increasing SCA alone.  Other approaches such as improved electrics and
sectionalization should be considered as possibly more cost effective options.

     Also shown in Figure 2 is the effect on ESP performance of high ESP
hopper ash levels due to a malfunctioning ash removal system.  Note that
the outlet emissions exibit a significant deterioration in performance during
these episodes to roughly 0.08 Ik/106 btu.  This observed deterioration is
believed to be due to the complex nature of the boiler/ESP/ash removal
system, unavailability of critical monitoring instrumentation for plant
operators, and the inherent difficulties associated with maintaining this
equipment at peak performance.  As a result, an emission level more repre-
sentative of normal daily operation probably lies somewhere between 0.025 -
0.08 lb/106 btu.
                                     39

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     It should be mentioned that problems with ash removal systems such
as those observed at Neal are not uncommon in the utility industry and,
in many cases, can be the "achilles heel" limiting performance of an other-
wise well operating ESP.  To address this issue, EPRI is currently conducting
research project RP1401 "Reliability Assessment of Particulate Control
Systems".  The objectives are to develop a detailed data base documenting
the major factors influencing control device reliability with emphasis on
separating cause and effect and recommending appropriate improvements.

Size Dependent Collection Efficiency

     Particle Size Distribution.  Before the particle size dependent removal
efficiency of the ESP can be determined, a careful measurement and interpreta-
tion of the particle size distribution entering and leaving the ESP is
required.  Previous experience has shown that the most useful method of
presenting particle size distribution data is in terms of differential mass
vs logarithmic particle diameter.  When plotted on semi-logarithmic paper the
area under the curve is proportional to the total mass.  In addition, subtle
features in the data become apparent which are not readily detectable in other
formats such as cumulative mass vs particle size.

     Figure 3 shows a typical ESP inlet differential mass distribution as
a function of particle diameter measured under full-load conditions (520 Mw) .
The data above and below 0.3 microns diameter are EASA and cascade impactor
results, respectively.  The insert scale has been expanded by a factor of five
to illustrate the noise estimation and overlap of data obtained with the two
different instruments.

     Figure 4 shows a typical ESP outlet differential mass distribution as
a function of particle diameter measured simultaneously with the data shown
in Figure 3.   The ESP was operating under normal conditions with an SCA of
745 ft2/kacfm.  The cascade impactor data for diameters less than 1 micron
are shown in both figures as dotted lines.  These lines are the upper concen-
tration limit, since examination by a scanning electron microscope (SEM)
indicated some particle blowoff onto the two lower impactor stages.  The
cascade impactor data are the average of four runs in both figures, and the
error bars indicate the standard deviation of the individual values, not
the averages.  The error bar on the peak of the submicron distribution indi-
cates the variation in the average submicron concentration (assuming a
variation in peak height).  The agreement between the EASA and cascade
impactor in the regions of overlapping data was good.  The apparent differ-
ences although small on absolute basis may be due to blowoff in the impactor
data and noise in the EASA data and inversion programs.  The difference in
the EASA and impactor data near 0.3 microns illustrates the difficulty in
computing size distributions and penetrations in the 0.2 to 1 micron range.
The EASA data were reduced with a number of different approaches to correct
for cross-sensitivity as described in Ensor et al (1979)!.
                                      40

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     Bimodal Character of Distribution.  The aerosol mass distribution has
a distinctly bimodal nature as shown in Figures 3 and 4.  A submicron mode
is very sharp and distinct near 0.15 microns diameter and a second large
particle mode is observed at 2 to 8 microns diameter.

     The larger submicron peak in the outlet size distribution results from
the inlet size distribution and size-selective removal of particulate matter
by the ESP.  The large particle mode is removed with much greater efficiency
than the submicron mode as shown by comparing Figures 3 and 4.

     The relative fraction of the submicron particle mode is typically 2
percent of the inlet total mass as determined by cascade impactors.  The
effect of reduced load is to reduce the relative fraction of submicron mode
particulate matter.  At the outlet of the precipitator, the amount of submicron
particle mode is sensitive to the precipitator operation.  Under normal condi-
tions, the submicron mode is about 20 percent of the total outlet mass
emissions.

     The submicron particle mode was obvious only after the advanced data
reduction techniques described in Ensor et al  (1979)1 had been used.  The
biomodal nature of the particle size distribution has been observed by
the authors at other locations and may be a universal feature of coal combus-
tion.  A review of combustion-generated aerosol literature indicates that
many investigators have not identified the submicron mode.  This may be attri-
buted to a failure to correct their EASA data for cross-channel sensitivity.
The qualitative presence of a bimodal aerosol distribution with a submicron
mode was reported by Ragaini and Ondov  (1974)6 with samples collected with
filters and cascade impactors at the outlet of an electrostatic precipitator
and subjected to SEM analysis.  Schultz et al  (1975)7 observed particles
approximately 0.1 micron in diameter collected on the last stage and final
filter of cascade impactor samples which were  "so uniformly sized"  that they
believed them to be condensed material.  Follow-on research to further
identify the submicron mode with respect to origin and chemical composition
is currently being supported by EPRI.

     Comparison to Aerosol Formation Theory.  The inlet size distribution
data were compared with the theoretical model reported by Flagan and Fried-
lander  (1976)8 as shown in Figure 5.  The peak predicted by the model at
5 x 10-L4 particles/m^ is approximately an order of magnitude larger than
measured.  However, the narrowness of the peak compares very favorably
with the measured data.  The theoretical model is based on a proposed mechanism
in which part of the mineral content of the coal vaporizes and undergoes
homogeneous condensation forming the submicron particle mode.  According
to this model, the submicron size mode may be expected to be enriched with
volatile species.  The remainder of the mineral material forms the fly ash
mode at 2 to 8 microns and has a distribution  shape similar to the initial
pulverized coal size distribution.  The  agreement between the measured and
theoretical number size distribution, though qualitative, is remarkable.
The model was developed using data from the literature for the pulverized
coal distribution and typical conditions of combustion.  Possibly the agree-
ment of theory and data would be better if the model was refined to match
the subject boiler.
                                         41

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     Penetration as a Function of Diameter.   Size-dependent penetration is
the outlet aerosol distribution divided by the inlet distribution, with both
distributions as functions of particle diameter.  Penetration results for the
three SCA conditions tested are shown in Figure 6.  Penetration greater than
0.3 microns is based on cascade impactor data; penetration less than 0.2
microns is based on EASA data.

     It can be seen from Figure 6 that a double peaked (bimodal)  penetration
behavior is prevalent under all test conditions.  Near design (SCA of 745
ft^/jtacfji,) f penetration peaks of 10 and 5 percent are evident at 0.2 and 1.0
micron, respectively.  In addition, the submicron mode penetration is observed
to be about thirty times the overall ESP penetration.  Even at extremely large
values of SCA (1270 ft2/kacfm), the bimodal characteristic  is preserved
despite the high overall collection efficiency of 99.89 percent.

     The large penetration at 0.2 micron can be qualitatively explained by
physical arguments.  Hewitt  (1956)9 reported a fundamental laboratory and
theoretical study of electrostatic precipitation.  His data were recently
reproduced by Smith et al  (1978)1°.  The minimum particle mobility (or
migration velocity) was found at a particle diameter of 0.2 microns.  Thus,
the 0.2 micron particles would be expected to have the lowest collection
efficiency or highest pene.tration of the particles entering the precipitator.
The penetration of particles less than 0.2 microns in diameter decreases with
a reduction in particle diameter, because of the increasing significance
of diffusion charging and Brownian and turbulent migration.  The penetration
of particles greater than 0.2 microns in diameter decreases with increasing
particle diameter because of the increased effect of field charging and
increased migration velocities.  The submicron particle mode was at the point
of minimum mobility or efficiency as reported by Hewitt.   Thus,  the penetration
of the submicron mode was much higher than the total mass penetration.  How-
ever, the submicron mode penetration is much larger than expected by consider-
ation of only particle mobilities.

     It has been assumed in this analysis that a continuous curve joins the
EASA and cascade impactor data as indicated by the dashed lines without
error bounds.  The steep increase of the penetration near 0.13 micron and
the dropping penetration below 1.0 micron forces a sharp peak in penetration
between 0.18 and 0.25 micron.  The peak is sufficiently sharp to cast some
doubt on its reality because a smoother curve was expected as reported by
Hewitt.  The sharp submicron distributions make penetration calculations
very sensitive to error, and the blowoff in the lower cascade impactor stages
may create an anomalous drop below 1.0 micron.  This phenomenon unfortunately
lies in the region in which both the EASA and impactor data are least
reliable.  This uncertainty is due in part simply to the relative scarcity of
aerosol between 0.2 and 1.0 microns in the flue gas.  Accordingly, the "true"
curves may more closely resembly a smooth line joining the squares at 0.13
microns with the cascade impactor data at 1 micron.

     There are several possible  explanations  for the large penetration of
submicron particles and the  double peaked penetration curve as discussed below:
                                      42

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      o  Experimental problems inherent with the measurement techniques.
         Most of the problems have been described above and in Ensor et  al
         (1979) -1-.  However, the use of matched EASAs, extensive data inver-
         sions,   SEM micrographs of  filters and impactor stages, and
         the reproducibility of the data stongly suggest that the results
         are real,

      o  The high resistivity ash caused the ESP to operate in an extreme
         back corona condition.  The effect on particle charging and
         collection under these conditions is not completely understood
         at the present time.

      o  The possibility exists that the high penetration of submicron
         particles is fictitious in the sense that it is influenced by
         agglomeration.  However, the agglomeration would have to take
         place between the 0.13 to 0.3 micron particles because agglomeration
         between 0.13 and larger particles would have reduced penetration
         of the:submicron particle mode.  There is some evidence to support
         the presence of this mechanism.  Comparing Figures 3 and 4
         indicates that the distribution peak increased in mean diameter
         by about 0.05 microns from the inlet to the outlet of the ESP.
         The highly charged aerosol may have grown through coagulation
         during the 25-second residence time in the ESP.  The penetration
         is very sensitive to small changes in the submicron particle mode
         because of the sharpness of the distribution.  The small shift
         in the outlet submicron particle mode was towards the "valley"
         between the inlet size distribution modes.  Thus, the large
         penetration calculated for the 0.15 to 0.3 micron particle range
         may result from a submicron particle growth rather than precipita-
         tion.

      In summary, although the exact mechanisms responsible are not well
understood, the bimodal aerosol inlet distribution and the subsequent double
peaked penetration curve in the fine particle region  (less than 2 microns in
diameter) appears to be real and present under all test conditions.
Rapping Losses

      When an ESP collection plate is rapped to remove the layer of accumulated
ash, some of the ash is reentrained by the gas stream.  These emissions are
called rapping losses.  The loss of particles appears to result from two
mechanisms:  1)  the fracturing of the layer of ash from the plates immediately
after the rap, and 2)  "boilup" of ash from the hoppers as the sheets of
dislodged ash reach the ash in the hoppers.
                                       43

-------
      The primary experimental technique used to investigate rapping
losses were tests conducted with the rappers on and off similar to the techni-
ques described by Gooch and Piulle (1977)10.  The sampling approach was^
to position two sets of two impactor probes at the outlet of the precipitator.
One set was used to sample emission during a half-hour operation with the
rappers on and the other was used during the half-hour when all rappers
were shut off.  The EASA, PPV, inlet impactors, and gas monitors were
operated normally.  The hoppers were all emptied about two hours before the
testing was started to reduce the likelihood of excessive "boilup" emission
because of high hopper levels.

      A limitation of this test approach is the distortion of the operation
of the ESP.  During the rappers-off tests, layers of ash on the plates may
build to an excessive depth, resulting in particle losses due to erosion
by the gas stream.  This excessive buildup may be significant only on the
inlet fields.  The outlet fields performance could then be affected by the
ash losses from the inlet fields.

      Based upon comparison of data from two sets of rappers-on and-off tests,
it is estimated that rapping losses account for roughly six percent of the
outlet emissions.  However, statistical analysis of the results reveals no
significant difference between the rapper-on and -off tests, thus suggesting
that the differences measured may have been obtained by chance.

      The small difference between the rap and no-rap operating conditions
was substantiated by the outlet PPV opacity measurements.  The rapping puffs
in opacity reported by other investigators, given in Gooch et  al   (1975)11,
were not obvious during the test.  However, it should be mentioned that signi-
ficant rapping puffs were observed in the outlet opacity measurements during
times of high ash hopper levels.  This result suggests that ash hopper
level may be a significant parameter affecting the absolute level of rapping
losses, at least for ESPs of European-design. Details of the rappers-on and-off
tests are given in Ensor et  al   (1979)1-

CONCLUSION

      Test results for the Neal ESP indicate that high particulate removal
efficiencies are possible with large ESPs collecting high resistivity flyash.
For example, outlet emissions of 0.025 lk/10^ btu were measured at full load
conditions of 745 ft2/kacfm, below the revised EPA New Source Performance
Standard  (NSPS) of 0.03 :lb/106 btu.  However, these results must be tempered
by the fact that the data were collected from a well tuned ESP shortly after
overhaul.  In contrast, emission levels measured prior to overhaul revealed
a significant deterioration in performance to roughly 0.08 Ik/106.  This
observed deterioration is believed to be due to the complex nature of the
boiler/ESP/ash removal systems, unavailability of critical monitoring instru-
mentation, and the inherent difficulties associated with maintaining this
equipment at peak performance.  Accordingly, an emission level more representa-
tive of normal daily operation probably lies somewhere between 0.025-0.08
 lb/106 btu.
                                      44

-------
      Examination of the particulate size distribution revealed that the
ESP inlet aerosol  has a distinctly bimodal nature, i.e. the particle mass
is concentrated in two distinct size regions: a submicron mode at 0.15 microns
and a large particle mode at 2 to 8 micron diameter.  This bimodal nature
propagates through the ESP resulting in a bimodal penetration behavior not
previously reported.  The submicron aerosol mode penetration averages 10 percent
at full load, or about 30 times the overall ESP penetration.  In terms of
total mass, the sub-2 micron particles account for 20-  40 percent of the total
outlet emission.  The implications of the high submicron penetration are
presently unclear, although it may be responsible for the relatively high
stack opacities observed at correspondingly large values of SCA.

      If it is assumed that emission standards more stringent than those
currently in effect will be promulgated, then it is clear that suffi-
cient cushion must be provided in the ESP design to account for operational
excursions and the seemingly time dependent deterioration in performance.
However, the most cost effective methods to achieve this cushion are not
obvious.  Adding plate area is one option used extensively in the past,
although the results presented here show that the proportional gains in
performance diminish rapidly at large values of SCA.  Therefore, to retain
ESPs  as a viable alternative for the utility industry it appears that
advancements in ESP systems will be required.  Several such alternatives
are currently under development both by EPRI and independent  research
organizations.

ACKNOWLEDGEMENTS

      The permission to test the George Neal Unit No. 3 by Iowa Public Service
is gratefully acknowledged.  The assistance by G. Spooner and J. Hardie
during the test is appreciated.  A special thanks to MRI personnel including
G. Markowski, M. Murphy, S. Muller, R. Hillestad, M. Drehsen and L. Knoll.
The technical support by J. Ebrey and D. Cook of Lodge-Cottrell, Inc. during
the study is appreciated.
                                       45

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 REFERENCES


 1.   Ensor  et  al,"Evaluation of the George  Neal Electrostatic Precipitator".
     EPRI Final Report RP780-1, Volume I

 2.   Cohen, J.J.,  and D.M.  Montan.   "Theoretical  Consideration, Design and
     Evaluation of a Cascade Impactor".   Am.  Ind. Hyg.  Assoc.,  Vol. 28, 1967
     PP. 95-104

 3.   Liu, B.Y.H.,  K.T. Whitby, and D.Y.H. Pui.   "A Portable Electrical Analyzer
     for Size Distribution  Measurement of Submicron Aerosols."
     J. Air Poll.  Cont. Assoc.,  Vol. 24, 1974, p. 1067

 4.   Liu, B.Y.H.,  and D.Y.H. Pui.  "On the Performance  of the Electrical Aerosol
     Analyzer."  J. Aerosol Sci., Vol. 6, 1975, p. 249.

 5.   Ensor, D.S.,  L.D. Bevan, and G.  Markowski.   "Application of Nephelometry to
     the Monitoring of Air  Pollution  Sources".   In Proceedings  of the 67th
     Annual Meeting of the  Air Pollution Control  Association, Denver, June,  1974.
     Paper No. 74-110.

 6.   Ragaini, R.C., and J.M. Ondov.   "Trace Contaminants  from Coal-Fired Power
     Plants."  In  Proceedings of the  International Conference of Environmental
     Sensing and Assessment, Las Vegas,  September 14-19,  1975.

 7.   Schultz, E.J., R.B. Engdahl, and T.T.  Frankenburg.   "Submicron Particles
     from a Pulverized-Coal-Fired Boiler."  J. Atmos. Environ., Vol.  9, 1975, p. 111.

 8.   Flagan R.C.,  and S.K.  Friedlander,  "Particle Formation in  Pulverized Coal
     Combustion -  A Review."  In Proceedings  of the Symposium on Aerosol Science
     and Technology at the  82nd National Meeting  of the American Institute
     of Chemical Engineers, Atlantic  City,  New Jersey,  August 29 - Sept. 1,  1976.

 9.   Hewitt, G.W.  "The Charging of Small Particles for  Electrostatic Precipitation".
     AIEE Paper 56-353, New York, 1956.

10.   Smith, W.B.,  et al.  "Experimental  Investigations  of Fine  Particle Charging
     by Unipolar Ions—A Review."  J. Aerosol Sci., Vol.  9,  1978, pp. 101-124

11.   Gooch, J.P.,  and W. Piulle,  "Studies of Particle  Reentrainment Resulting
     from Electrode Rapping."  Proceedings:  Particulate  Collection Problems
     Using ESPs in the Metallurgical  Industry.  EPA Report No.  600/2-77-208,
     October, 1977, pp. 103-128.

12.   Gooch, J.P.,  and N.L.  Francis.   "A Theoretically Based Mathematical
     Model  for Calculation  of Electrostatic Precipitator Performance."  J. Air
     Poll. Cont. Assoc., Vol. 25, 1975,     pp. 108-113.


                                      46

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                          TABLE I
                     NEAL COAL ANALYSIS
    Coal Proximate Analysis
Moisture
Ash
Volatile Matter
Fixed Carbon
Sulfur
Heat Value*

    Coal Ultimate Analysis
Carbon
Hydrogen
Nitrogen
Chlorine
Oxygen

    Coal Mineral Analysis
A1203
Na20
K20
CaO
MgO
P205
S03
Mean
Percent
12.66
10.62
35.96
40.75
0.61
10,011*
65.76
4.93
1.12
0.00
15.33
44.6
17.4
5.72
0.33
1.13
16.1
2.8
0.78
0.92
8.7
Standard
Deviation
0.905
1.3
1.1
1.03
0.19
181*
1.2
0.17
0.012
0.0
0.39
3.0
0.93
2.5
0.065
0.21
1.7
0.26
0.14
0.14
2.4
Fifteen coal samples from five coal feeders at three different
times
* - Heat Value units are Btu/lb
                            47

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                       Table 2

DESIGN FEATURES, NEAL No. 3 ELECTROSTATIC PRECIPITATORS


                            Design          Range
Gas volume (acfm)

Gas velocity through
 ESP (FPS)

Treatment time (Sec.)
 2,084,000

 2.26


26.5
1,026,000 to 2,084,000
Number of chambers per pre-
 cipitator

Number of cells per pre-
 cipitator

Number of electrical fields
 per precipitator

Bus section per field
 per precipitator
 per boiler

Number of T-R sets per bus
 section
 Number of T-R sets per field
 Number of T-R set per pre-
 cipitator

Collecting Plates

Number of gas passages per
 bus section

Number of plates per field

 a.  Field 1
 b.  Field 2
 c.  Field 3
 d.  Field 4
     Total
    Quantity


    One (two per boiler)


    Eight (sixteen per boiler)


    Four


    Eight
    Thirty-two
    Sixty-four

    1/2

    4

    16

    ASTM A-36, 18 GA.


    24
    196 per ESP
    196 per ESP
    196 per ESP
    196 per ESP
    784 per ESP
   1568 per boiler
Active plate area              921,600 ft2 per ESP
(does not include stiffeners)   1,843,200 ft2 per boiler
                           48

-------
                                                                                 Table 3
                                                               Summary of Collection Efficiencies for "A"
                                                                ESP Under Various Operating Conditions
Tesf
Conditions
Partial load
Full load
Rappers on
Rappers off
Last field
deenergized
Load
(MW)
303
522
520
520
523
SCA
(ft2/kacfm)
[m2/(m3/sec)l
1270 [250]
745 [1 47]
740 [146]
740 [146]
550(108]
Average Inlet
Resistivity
(ohm-cm)
2.5 X 1012
4.0 X 1012
5.0 X 1012
5.0 X 1012
4.0 X 1012
Total
Corona
Power
(kW)
415
330
300
300
215
Average Inlet
Concentration®)
(gr/scf)
[g/m3]
2.35 [5.38]
3.30 [7.56]
2.55 [5.84]
2.55 [5.84]
2.95 [6.76]
Average Outlet
Concentration®)
(gr/scf)
[g/m3]
0.00265 [0.00607]
0.0101 [0.0231]
0.0129 [0.0295]
0.01 22 [0.0279]
0.0305 [0.0698]
Efficiency
(percent)
99.89
99.70
99.49
99.52
98.97
Penetration
0.0011
0.0030
0.0051
0.0048
0.0103
Opacity^
(percent)
1.6
4.6
5.2
5.0
12.7
Total
Emissions
(lb/10BBtu)
0.005
0.019
0.024
0.023
0.057
Less Than
2 MicronsStandard conditions: 21.1°C, 76 cm Hg dry
'^Corrected to 6.9-meter path length corresponding to the top of the stack
(d*Actual diameter with a density of 2.6 g/cm3
(e'Rappers turned off for 30 minutes every hour

-------
                To ash collection
                     system
                                                 Chimney
                To ash collection
                     system
Figure 1.   Gas flow diagram for Neal Unit No. 3.
                      50

-------
c
CD

£
CD
a.

c.
o
+2
C
CD
0.
       80   90

    10 cr-
                         m2/(m3/sec)

             100  120  140  160  180  200  220  240  260
0.5
    0.1
   0.05
   0.01
                                  D
                                D
                                    D
                             -(—Design
         • Average performance data

           with one standard deviation

           limits for Phase II tests

         O Ash removal system mal-

           function for during Phase II

           tests

         D Performance data for

           Phase I tests
                                                           90
                                                               95
                                                               99
         c
         CD

         2
         CD
         Q.
    99.5  o

         CD
         '
                                                                o
                                                                CD
    99.9
    99.95
       400       600       800        1000

                            ft2/(1000ft3/min)

                         Specific Collection Area
                                             1200
1400
0.08

0.07

0.06

0.05


0.04


0.03


0.02



0.01
                                                                                      CD
                                                                                      
-------
        2.8
        2.4
        2.0
        1.6
     CD
     O
        1.2
        0.8
        0.4
                  0.20
                  0.10
                     0
-) 1
/
oi I inl
i > /
•'• /
\/
\ °
° IOI Pi II II
r
                                0.1
    O Noise estimate, one standard
       deviation limits shown
	Fit to EASA data
	Cascade impactor
       520 MW load
       ConcentrationS.30 gr/ft3
       Density 2.6 g/cc
 	Impactor upper bound
  Lower section expanded by
     5 times in magnitude
          0
          0.01
          0.1              1              10
      Geometric Aerosol Diameter (microns)
Figure 3.  Differential mass particle size distribution at the inlet of the ESP.
                                  52

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  35
  30
   25
   20
CT
°  15
   10
        One standard deviation limits shown
 	EASA
 —— Cascade impactor
        520 MW load
        745ft2/1000ft3SCA
        Penetration = 0.003
        Efficiency = 99.7%
        Concentration = 0.0101 gr/ft3
— — — Impactor upper bound
    0.01            0.1              1             10
               Geometric Aerosol Diameter (microns)


  Figure 4.  Differential mass particle size distribution at the
            outlet of the ESP
                            53

-------
    1015
    1014
    1013
en
o   1Q11
    1010
     109
     108
                     /  '\
             /o  o  /  i  v
                    'o  •  \
                         !   \
                                o
 ••—  Theoretical      Q
      condensation mode
— —  Theoretical matrix mode
      (After Flagen and
      Friedlander 1976)
	EASA size distribution
      (Corrected for cross sensitivity)
—— Cascade impactor size distribution
   O Noise estimate EASA
 Full load conditions 520 MW
 ESP normal operation 748 ft2/IOOO ft3/min)
 Particle density =  2.6 g/cm3

     I I III
       0.01
         0.1            1.0            10
       Geometric Aerosol Diameter (microns)
   Figure 5.  Comparison of inlet differential number size distribution
             to the theoretical distribution reported by Flagen and
             Friedlander (1976) for the combustion of pulverized coal.
                              54

-------
    100
     10
  c
  0)
  c
  o
  o>
 Q.
     0.1
                           O Point calculation, EASA

                         	 Distribution EASA

                         •"-— Hypothetical

                           • 550 ft2/1000 acfm (108 m2/m3/sec)

                           D 745 ft2/1000 acfm (147 m2/m3/sec)

                           A 1270 ft2/IOOO acfm (250 m2/m3/sec)

                              Density = 2.6 g/cm3
       I	L
                                            0
                                            90
                                                                    c
                                                                    
-------
                EPA MOBILE  ESP HOT-SIDE  PERFORMANCE EVALUATION
                                      By:

                   S.P.  Schliesser,  S.  Malani,  C.L.  Stanley
                              Acurex Corporation
                    Research Triangle Park,  North Carolina

                                      and

                                  L.E.  Sparks
                        Environmental Protection Agency
                 Research Triangle Park, North  Carolina 27711

                                   ABSTRACT

     This report describes the Environmental Protection Agency mobile
electrostatic precipitator performance evaluation conducted at the Navajo
Generating Station, Page, Arizona.  The objective was  to evaluate discrete
process and control device parameters in order  to effect improved collection
performance of a hot-side electrostatic precipitator applied to a western-
coal-fired utility boiler.  The pilot-scale  electrostatic precipitator was
operated in a hot-side mode, slipstreaming flue gas  upstream of the air
preheater and full-scale hot electrostatic precipitator.  Performance
measurements on the pilot unit were conducted over a 3 month period in order
to study the effects of dust layer characteristics,  temperature/boiler load
conditions, and sodium carbonate conditioning.   A time-dependent degradation
in collection performance was observed in  the pilot  model,  as  evidenced in the
full-scale models.  Sodium conditioning effected a substantial improvement in
collection performance, eliminating the time-dependent degradation pheonomenon.
Use of mathematical performance models provided a reasonable reference for
data interpretation, as well as insight into the hot precipitation problem.

INTRODUCTION AND OBJECTIVE

     This pilot-scale electrostatic precipitator (ESP) is one of three conven-
tional particulate emission control devices  mobilized  by the Utilities and
Industrial Power Division, Industrial Environmental  Research Laboratory,
U.S. Environmental Protection Agency (UIPD/IERL/EPA),  Research Triangle Park,
North Carolina.  The objective is to evaluate and compare the performance
characteristics of a pilot scale electrostatic  precipitator, scrubber, and
baghouse on industrial particulate emission  sources.  The purpose is to provide
characteristic information and insight for appropriate selection of particulate
control devices, in light of operation, performance, and cost considerations.

     Hot-side precipitation has recently evolved as  a  cost- and technology-
effective means for particulate control from low sulfur coal-fired utility


                                     56

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boilers.  Several low sulfur coals produce high  resistivity  fly ash, causing
dramatic increases in costs for cold-side ESP  control.  The  hot-side approach
utilizes thermal conditioning of the fly ash to  reduce resistivity.  By posi-
tioning the ESP to the hot-side of the air preheater, the resultant increase
in gas temperature from  170°C to 370°C typically reduces fly ash resistivity
by 2 to 3 orders of magnitude.  However, certain hot-sided ESP's have demon-
strated a time-dependent performance degradation, with evidence of electrical
breakdown of the collected fly ash.  Such characteristics have been observed
at the Navajo Station, prompting a cooperative effort to investigate this
phenomenon between the Salt River Project and  IERL/EPA.  An  evaluation of the
full-scale ESP performance was conducted by Southern Research Institute (SRI).1
Further investigation has been conducted by Acurex with the  EPA pilot-scale
ESP.

     This report summarizes the results of the EPA mobile ESP performance
evaluation at the Navajo Station during the summer of 1978.  The mobile ESP
treated an isokinetically removed slipstream over a temperature range of 230°C
to 330°C.  Particulate concentration and size  distribution measurements were
conducted daily on the influent and effluent streams of the  pilot unit.
Boiler  and ESP operating data were collected,  along with fly ash samples.  Dry
sodium  carbonate was injected to evaluate conditioning effects.  Performance
levels  and trends are included in this report, along with analytical discus-
sions on operating and particulate data, fly ash composition, and means of
data reduction and interpretation.

CONCLUSIONS

     The following conclusions result from this  study:

          •    Several ESP behavior characteristics indicate breakdown of the
               collected fly ash during normal operation

          •    Electrical breakdown severely limits collection performance

          •    Sodium conditioning alleviates  breakdown and  performance
               limitations by favorably reducing base/sodium ratio

          •    Sodium conditioning reduces emission levels by an order of
               magnitude—from -V300 to 30 ng/J for SCA of ^90 m2/m3/sec (from
               M).7  to 0.07 Ib/million Btu for SCA of ^450 ft2/kcfm)

          •    Substandard pressure conditions adversely affect hot precipita-
               tion  of low alkali, low sulfur  western coals.

DESCRIPTION  OF FACILITIES

Test Site

     Navajo  Generating Station is owned and operated by the  Salt River Project.
It consists  of three 800 MWe pulverized coal-fired boilers.  They were completed
from 1974-1976 and represent  current design and  operating methodology.  Emis-
sions are controlled by  hot-side electrostatic precipitators,  located upstream

                                      57

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of the air preheaters (340-380°C) instead of in the conventional downstream
location (150-180°C).  The flue gas characteristics at the ESP location were:

               Temperature Range:            290-370°C
               Particulate Concentration:    9.3 gm/DSCM
               Specific Resistivity:         4 x 109 ohm-cm & 350°C

                         • C02    14.5-15.0% v/v
                         •  02     4.5- 5.0% v/v
                         • H20  -  9-0-10.0% v/v
                         • S02    450-500 ppm

Pilot ESP

     The EPA mobile ESP consists of two separate units mounted on 12.2 m
freight trailers.  One unit is the process trailer, which houses a
five-section electrostatic precipitator and the following auxiliary equipment:

          •    Flow rectification devices (vaned turning elbows and diffusers)

          •    An induced-draft fan with cooling system for 540°C service

          •    A screw conveyor and rotary airlock for fly ash removal

          •    Electromagnetic plate vibrators and pneumatic corona frame rappers

          •    Five transformer rectifier units (each rated at 50 kV, 15mA DC)

The system is designed to handle 28-85 m3/min at 540°C maximum.

     The other unit is a control/laboratory trailer containing all process
instrumentation and controls, analytical laboratory equipment, and spare
equipment storage.  A more complete description of the EPA mobile ESP is
presented in Reference 2.

     A comparison of pilot- and full-scale ESP design and operating specifica-
tions is shown in Table 1.

PROGRAM METHODOLOGY

Installation

     The mobile ESP trailers were placed on the north side of Unit No. 1.  The
slipstream probe was installed in the ductwork between the boiler and the air
preheater at a point of sufficiently isokinetic velocity.  The duct ran 14 m
horizontally and 35 m vertically to the mobile ESP.  The vertical section was
supported by a spring hanger to allow for thermal expansion.  The duct was
electrically heat traced and insulated.  Heat losses in the slipsteam limited
the temperature range of this evaluation.
                                      58

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Operation

     The tests were conducted in increments of 4 to 5 days, with the mobile
ESP operating continuously during those periods.  Precipitator performance as
a function of operating time could thus be observed.  All internal precipitator
components were cleaned of fly ash before the initial operating period.  In
order to observe the cumulative effects of dust layer buildup, normal wire and
plate cleaning patterns were employed for collected ash removal.  Corona wire
and plate rapping cycles were not interrupted during sampling in order that
rapping losses be included in the precipitator performance evaluation.

Test Conditions

     The mobile ESP tests were performed in phases as described below:

     Phase I

     The first 11 tests were conducted between June 7 and June 23.  Opera-
     tional problems with the duct heaters resulted in an average inlet gas
     temperature of 260°C, well below the 340-370°C range of the full-scale
     ESP.

     Phase II

     After a 2-week shutdown period for heater repairs, 15 more tests were
     conducted between July 11 and August 3.  Average operating temperature
     was 295°C.

     Phase III A

     Five tests were conducted between August 8 and August 14.  Sodium carbonate
     was injected upstream from the pilot ESP as a conditioning agent.  The
     average concentration injected was 8.16 percent as Na20, expressed as a
     mass fraction of fly ash.  Average operating temperature was 295°C.

     Phase III B

     The boiler output dropped to half-load and remained there from
     August 22 to 25.  Four tests were conducted.  Average sodium carbonate
     injection was 2.33 percent as Na20, and the operating temperature dropped
     to 245°C due to reduced boiler load.

Table 2 summarizes the test conditions and analytical results.

Data Acquisition

     The following pilot ESP data were recorded semihourly throughout the
program:
                                      59

-------
          «    Inlet and outlet gas temperature

          «    Slipstream interface temperature

          «    Individual secondary voltages

          •    Individual secondary currents

     Corona current as a function of voltage were recorded daily and plotted
(corona discharge curves).   Dust layer thickness measurements were made periodi-
cally at the beginning of the program but were discontinued due to the long
off-line and reheat time requirements.

     Pertinent boiler operating data were recorded hourly in the control room.
Copies of the logs were made available for all test days.   Operating points of
selected plant ESP cells were also recorded.

     Flue gas composition and velocity data were recorded daily as a part of
particulate sampling preparation.  Filter and impactor stage weight data were
obtained in the field using the mobile laboratory, and were usually available
within 2 days of a given test.

Particulate Measurements

     Particulate loading and particle size distribution were determined with a
Brink impactor at the pilot ESP inlet and with a University of Washington Mark
III impactor at the outlet.  Each impactor train was operated in conjunction
with a modified EPA Method 5 train using a 47 mm glass fiber filter as a
comparison and quality control check.  All filters and impactor substrates
were made of Reeve Angel 934AH glass fiber.  Filter preconditioning was not
performed due to the low sulfur content of the flue gas.

Data Reduction

     Several analytical tools were employed in the reduction and analysis of
particulate concentration and size distribution data.   The large number of
particulate tests (concentration: 130;  size distribution:  120) taken over a
variety of conditions for 35 test days required a substantial analytical
effort.

     A computer program was used to calculate impactor stage cut-points and
dust loadings.  Fractional penetrations were calculated using a program that
performs the following:3

          e    Log-normal transformation of inlet and outlet cumulative size
               distributions

          ®    Linear, quadratic, and spline fits to the transformed data
          »    Analytical differentiation of the fitted curve

          •    Calculation of fractional penetrations from differential inlet
               and outlet size distributions
                                     60

-------
     Performance of the ESP was evaluated using  the performance model developed
by SRI.4  In view of the fact that the model overpredicts penetration to a
large extent and that V-I data do not conform to the predictions, only a
moderate modeling effort was made.

     The pilot ESP tests were conducted at different SCAs to evaluate the
effect of specific collection area (SCA) on particulate emissions.  However,
performance results require adjustment to a common SCA to evaluate the effects
on a common design basis.  This was accomplished by the use of two ESP perfor-
mance equations:

           1.  Deutsch-Anderson (D-A) Equation

               This equation relates efficiency  (n) to SCA and particle migra-
               tion velocity (w) by the equation

                             ,    -(SCA • w)
                         n = I - e ^       J

               Using measured efficiency and SCA for a given test, w can be
               calculated with the above equation.  Assuming w to be constant
               for small variations in SCA, efficiency can then be calculated
               for the desired common SCA by applying the above equation.

           2.  Matts-Ohnfeldt (M-0) Equation

               Matts and Ohnfeldt have determined empirically that the following
               relationship describes the ESP performance better than the
               Deutsch-Anderson equation:5

                                             -(w • SCA)°-5
                                    n = 1 - e

               This equation can similarly be used to adjust efficiency data
               to a common SCA.

     Australian  experience with electrostatic precipitation technology has
 shown that ESP performance can be described by extending the Deutsch-Anderson
 equation as shown:6

               In (1-n) = In (1-n ) + C(SCA • V2)

 Where n  is the  mechanical efficiency, V is the applied voltage, and C is a
 constant.  The first term accounts for mechanical settling, and the second one
 restates the Deutsch-Anderson equation by relating voltage and migration
 velocity.  Theoretically a semilog plot of penetration (1-n) vs. SCA-V2 gives
 a straight line  relationship.  In actuality the ESP performance plots a line
 as shown in Figure 1.  Leveling-off of the performance line at high values of
 SCA.V2 is due to reentrainment losses.  In similar fashion, the M-0 equation
 can be extended.  The abscissa in this case is (SCA'V2)6'5 instead of SCA'V2.

 RESULTS AND DISCUSSION

     This program was directed to study hot ESP performance limitations at the
Navajo Power Station and to assess alternate means for improved performance.

                                     61

-------
The tundamental cause of the limitation appears to be excessive resistivity
due to relatively low sodium levels.  Use of an in situ resistivity probe
would have documented real-time and possible time-dependent resistivity levels.
Nonetheless, test results with laboratory resistivity values have provided
additional understanding into the character of hot precipitation.  A discus-
sion of the results follows, describing and relating pilot precipitator behavior
characteristics under a variety of conditions.

Summary of Pilot ESP Performance

     Analytical and graphic accounting for the 35 days of pilot ESP perfor-
mance is detailed and depicted in Table 2 and Figure 2, respectively.  Collec-
tion performance trends are observed in Figure 2 as the series of test days
are segregated in week-to-week increments.  Outlet loadings increase as the
pilot ESP operation and performance levels degrade with elapsed on-line time
(0-4 days) for the first 7 test weeks.  During this period (Phase I and II),
the pilot precipitator was treating a representative slipstream at half-load
temperature levels.  The last two data series in Figure 2 show a trend of
performance enhancement.  During this period (Phase III), sodium conditioning
by dry injection into the slipstream effected a dramatic improvement in collec-
tion performance.  Virtual restoration of clean-plate performance was effected
by sodium conditioning, as the performance levels on the first and last test
days approach the same value of 0.07 gm/DNCM.  Results of chemical analyses of
30 samples support the conclusion that performance improvements were directly
associated with sodium content levels.

     The extent of hot-side performance improvement associated with sodium
conditioning is more appropriate and dramatic as steady-state conditions are
described (Figure 3).  An approximation of steady-state performance was formed
by extrapolation of transient profiles to depict a more respresentative compari-
son.  A 80-90 percent reduction in emission level is supported by the improvement
levels resultant from sodium conditioning at the Commanche Station of Public
Service Company of Colorado.7

Summary of Precipitator Operation Characteristics

     Operating corona points and the associated corona discharge relationships
(V-I data) were taken regularly during the program.  Manual control of the
transformer-rectifier was conducted, since the pilot facility was not equipped
with automatic controllers customarily included in full-sized precipitators.
Operating points were set 2-3 kV lower than the maximum to prevent frequent
high-voltage cable breakdown.

     Average operating data for each three test phases are presented in Table 3.
Specific trends in the individual field voltage and current levels are not
clearly recognizable, although the averaged operating levels show a slight
correspondence with temperature and collection performance levels.  The cause
of the apparent scatter is twofold:  1) the indicated dust breakdown phenomenon
causes fluctuating electrical characteristics, as evidenced in the full-scale
ESP;1 and 2) temperature and flow fluctuations experienced by the pilot ESP.
                                      62

-------
     Typically, the relationship of the voltage applied and the resultant
current for each precipitation field may be analyzed to gain insight into
precipitator operation and performance.  These corona discharge curves usually
show a characteristic profile for the volt-amp relationships from each field
for a given set of conditions.  Compilation of corona discharge curves taken
on the pilot- and full-scale ESP at Navajo reveal an exception to this approach.1
Volt-amp relationships taken on the pilot- and full-scale system are presented
in Figures 4 and 5, respectively, indicating that a broad range of operating
profiles are experienced.  Such variation in precipitator operation has riot
been explained in detail, but has been generally described as precipitator
fouling or breakdown.

     The operating temperature levels for each test day are shown in Figure 6.
Temperature fluctuations were more pronounced in Phase I than Phases II and
III.  However, the time-dependent performance deterioration effect superseded
any noticeable effect of temperature.  Although the pilot ESP treated the flue
steam over a partial temperature range (230°-330°C) compared to the full-scale
ESP  (270°-370°C), the operation and performance characteristics were reasonably
similar.  The breakdown phenomenon at Navajo does not appear to be temperature
sensitive in the range of 250°-370°C.

Effect of Fly Ash Composition

     Laboratory  assay and resistivity determinations were performed on 32 ash
samples by SRI.  The individual and collective results are presented in Table 4.
Ash  samples were collected regularly from separate fields in the pilot ESP,
with occasional  samples collected directly from the plates and wires.

     Sodium content was the principal compositional variant between the base
ash  and sodium-conditioning ash.  The base ash contained an average 3.0 per-
cent sodium, compared to 4.5 percent sodium content during conditioning.  The
sodium mass balance showed that 20-55 percent of the injected sodium was
recoverable from the precipitator fields.  Sulfur content had a corresponding
increase from 0.5 percent to 1.9 percent for the base and conditioned ashes,
respectively.  These sulfur level results support claims that sodium ash
conditioning will collect and reduce SO  emissions.

     Inspection  of compositional values across the precipitator produced the
following observations:

          •    Sodium levels varied slightly across the precipitator, showing
               a peak in the third and fourth fields

          •    Phosphorus concentrations were progressively higher from the
               first through the last fields
          •    Iron concentrations were progressively higher from the first
               through the last fields

     The ratio of base material to sodium content is reported to be a signifi-
cant indicator for hot precipitation fouling conditions.8  The base material
is composed of the oxides of calcium, potassium, sodium, iron, and magnesium.
For  the Navajo fly ash case of 21 percent base material, the base/sodium ratio


                                      63

-------
was 4.7 and 7.0 for the conditioned and unconditioned ashes, respectively.
Evidence from the pilot precipitator behavior at the reduced barometric pres-
sures at the Navajo site (75-85 percent standard pressure) indicates the
limiting base/sodium value to be 5 to 6, compared to a generalized value of 10
for standard pressure conditions.  Similar reductions in precipitator stability
factors are being documented for substandard pressure conditions in current
research.9

     Results of laboratory resistivity measurements are also given in Table 4.
The log mean resistivity values for the base and conditioned ashes were 2 x 1010
and 5 x 108 ohm-cm at 318°C, respectively.  This 40-fold reduction in resistivity
for a 1.5 percent increase in sodium content correlates with the indicated
resistivity/sodium level changes from the Commanche Power Station conditioning
results.7

COLLECTION PERFORMANCE RESULTS

     The control device characteristic of practical importance is that of
overall collection performance.  This performance can be described and measured
by the emission level which penetrates the device and passes into the atmos-
phere.  Emission levels for each test day are grouped in chronological series
in Figure 2, and are included with SCA, efficiency percentages, and averaged
inlet concentrations in Table 2.  Note that several emission levels have been
adjusted to a common SCA value for reference.

     Two methods were attempted to standardize operating SCA levels to a
common value--Matts-Ohnfeldt (M-0) and Deutsch-Anderson (D-A) methods.  Figures 7
and 8 show the results of the M-0 and D-A methods, respectively.  The transient
emission levels were not grouped chronologically for averaging, but were
categorized according to startup and near steady-state conditions.  For Figure 7
line  'a1 corresponds to startup day performance in Phase II, and lines 'b1 and
'c' represent near steady-state performance with and without conditioning,
respectively.  For Figure 8, line 'a1 corresponds to start-up and conditioning
performance levels, and lines  'b' and 'c1 represent Phase II and I performance
levels, respectively.  The data scatter under this grouping basis shows a
better correspondence for the M-0 than the D-A method.  The more traditional
D-A relationship appears to overestimate the sensitivity of SCA with collection
performance from this and other data bases.

     The performance model being developed by SRI was used to evaluate ESP
performance.4  A summary of this evaluation is presented in Table 5.  The
model predictions were computed for one ideal and two nonideal cases.  The
last column in Table 5 gives the ratio of actual penetration to model-predicted
penetration.  The model underpredicts penetration for Phase I, but overpredicts
penetration for all other phases.

Fractional Data and Performance Results

     Analysis of particle size data offers support and insight into collection
performance.  As technological advances are being made, it is becoming common
knowledge that particulate control device performance is sensitive to particle
size, and that size distribution data serve a principal role in performance
characterization.

                                      64

-------
     Results from 50 inlet irapactor tests showed reasonably consistent size
distribution levels for full-load boiler operation (800 MWe).  A distinct
distribution curve for half-load operation (350 MWe) is shown along with
full-load in Figure 9.  It is noteworthy that half-load boiler operation
results in 37 percent higher overall loading because of a higher concentration
of large particles (above 5 microns).  Figure 9 shows a greater inlet concentra-
tion in the ESP-vulnerable size range of 0.3 to 1.5 microns at full-load than
at half load.  The differential concentration in this size range could explain
the superior performance of Phase III B (half-load) to Phase III A (full load)
despite the lower temperature of Phase III B.

     Comparison of fractional penetrations for Phase II and III A are shown in
Figure 10.  Sodium conditioning enhanced performance across the particle size
range, but enhancement decreased with smaller particle sizes.  Figure 10 also
includes comparison of the SRI model predictions for the respective conditions
of Phases II and III A.

              RECOMMENDATIONS FOR FUTURE HOT-SIDE EVALUATIONS

          •    Extend temperature range of evaluation up to 380°C

          •    Conduct evaluation with in-situ resistivity probe to determine
               real time and possible timedependent resistivity and breakdown
               levels

          #    Evaluate another hot-side case at standard pressure levels

          •    Evaluate sensitivity of hot-side performance on fly ash composition

                                  REFERENCES


1.   Marchant, G.H., Jr., and L.E. Sparks.  A Performance of a Hot-Side Electro-
     static Precipitator.  Symposium on the Transfer and Utilization of Particulate
     Control Technology:  Volume I, Denver, Colorado, 1978.  EPA-600/7-79-044a.
     pp. 39-56.

2.   Nichols, G.B. and D.L. Harmon.  Preliminary Design and Initial Testing of
     a Mobile Electrostatic Precipitator.  EPA-600/7-78-096, U.S. Environmental
     Protection Agency, Research Triangle Park, NC, June 1978.

3.   Lawless, P.A.  Analysis of Cascade Impactor Data for Calculating Particle
     Penetration.  EPA-600/7-78-189, U.S. Environmental Protection Agency,
     Washington, DC, September 1978.  39 p.

4.   McDonald, J.R. and L.E. Sparks.  A Mathematical Model of Electrostatic
     Precipitation (Revision I):  Volumes I and II, EPA-600/7-78-llla.  U.S.
     Environmental Protection Agency, Research Triangle Park, NC  June 1978.

5.   Maartman, S. and A.B.S. Filaktfabriken.  Experience with Cold-Side Precipi-
     tators on Low Sulfur Coals.  Symposium (Ref.  1).  EPA-600/7-79-044a.
     p. 26.


                                       65

-------
6.   Electrostatic Precipitation Technology:   A Different Viewpoint.   Journal
     of Air Pollution Control Association.   January 1978.

7.   Lederman, P.B., P.B.  Bibbo and J.  Bush.   Chemical Conditioning of Fly Ash
     for Hot-Side Precipitation.  Symposium on the Transfer and Utilization of
     Particulate Control Technology:  Volume I, Denver, Colorado, 1978.
     EPA-600/7-79-044a. pp.  79-98.

8.   Atkins, S. and D. V.  Bubenick.  Keeping Fly Ash Out of the Stack.  Environ-
     mental Science and Technology, 12:6,  1978.

9-   Bush, J.R., et al.  Development of a  High-Temperature/High-Pressure
     Electrostatic Precipitator.  EPA-600/7-77-132, U.S. Environmental Protec-
     tion Agency, Research Triangle Park,  NC, November 1977.   69 p.

Mailing Address:  Acurex Corporation, Route 1, Box 423, Morrisville,  NC 27560.
                                      66

-------
         TABLE 1   COMPARISON OF PILOT- AND FULL-SCALE ESP DESIGN AND
                   OPERATING SPECIFICATIONS
DESIGN

Discharge wire diameter, cm

Wire-wire spacing, cm

Wire-plate spacing, cm

Collection area/T-R set, m2

Aspect ratio

Gas Velocity, m/sec

No. of fields in series
FULL SCALE3
PILOT ESP
0.27
22.9
11.4
2340
0.2
0.8-1.6
6
0.25
18
12.7
9
0.67
0.7-1.3
5
OPERATION

Secondary voltage, kV

Secondary current density, nA/cm2

Specific collection area, m2/m3/sec

Inlet gas temperature range, °C

Inlet particulate concentration, g/dsm3

Measured efficiency range, %
22
40
65
300-370
5.4
98.5
29.7
14
60-100
230-330
9.0
95-99.8
                                      67

-------
                                                                        TABLE 2    SUMMARY OF ESP TEST DATA
CTt
CO


TEST
NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

TEST
DATE
1978
6/7
6/8
6/9
6/12
6/13
6/14
6/15
6/20
6/21
6/22
6/23
7/11
7/12
7/13
7/14
7/18
7/19
7/20
7/25
7/26
7/27
7/28
7/31
8/1
8/2
8/3
8/8
8/9
8/10
8/11
8/14
8/22
8/23
8/24
8/25

SEQUENTIAL
OPERATING
DAY
1
2
3
0
1
2
3
0
1
2
3
1
2
3
4
1
2
3
0
1
2
3
0
1
2
3
0
1
2
3
0
0
1
2
3


SCA
m2/ma/sec
102.6
104.8
102.6
102.6
104.8
63.0
104.8
83.9
104.8
104.0
0
118.1
99.4
88.9
65.9
70.2
65.5
82.4
82.4
85.7
83.9
98.3
104.8
98.3
82.1
0
81.7
88.9
98.6
98.6
103.7
58.0
58.0
58.0
64.8

SERIES AVERAGE p™^'jJN
INLET LOADING ' rpyv-f
gin/DNCH gm/DNCf|
0.508
0.059
0.145
0.0476
9.31 0.054
0.764
PHASE I 0.823
0.0412
0.019
0.332
3.751
0.084
0.154
0.236
0.357
0.062
9.31 0.111
0.087
PHASE II 0.077
0.058
0.087
0.136
-
0.063
0.135
3.169
0.148
8.851 0.094
PHASE II I A 0.055
0.077
0.026
0.116
12.58 0.171
PHASE 1IIB 0.167
0.140


EFFICIENCY
PERCENT
99.45
99.37
98.44
99.49
99.42
91.8
91.2
99.56
99.8
99.44
59.7
99.1
98.3
97.47
96.17
99.33
98.82
99.07
99.17
99.38
99.06
98.52
-
99.32
98.55
66.0
98.41
99.00
99 . 4 1
99.17
99.71
98.75
98.17
98.20
98.49

D-A EFFICIENCY
FOR
SCA=B8.6 mz/m3/sec
98.88
98.61
97.25
98.94
98.71
97.63
87.1
99.67
99.47
94.2
-
97.08
97.35
97.44
98.77
99.82
99.75
99.34
99.42
99.47
99.27
97-74
-
98.88
98.96
-
98.87
99.00
99 . 00
98.64
99.31
99.88
99.79
99.80
99.68
1
D-A OUTLET
LOADING
gm/DNCM
0.104
0. 129
0.256
0.098
0.120
0.277
1.20
0.031
0.049
0.542
-
0.272
0.247
0.238
0. 114
0.017
0.023
0.661
0.054
0.049
0.068
0.210
-
0.104
0.097
~
0.105
0.094
0.094
0.126
0.063
0.015
0.027
0.026
0.041

M-0 EFFICIENCY
FOR
SCA=88,6 m2/m3/sec
99.2
99. 1
97.9
99.26
99.12
96.04
89.22
99-62
99.67
95.40
*
98.3
97.86
97.47
97.73
99.63
99.43
99.21
99.3
99.43
99.17
98.16
-
99.12
98.77
-
98.65
99.0
99.22
98.93
99.55
99 . 56
99 . 30
99 . 32
99.26

M-0 OUTLET
LOADING
gm/DNCM
0.074
0.084
0.195
0.069
0.082
0.368
1.003
0.0354
0.031
0.428
-
0.0692
0.087
0.103
0.0924
0.015
0.023
0.032
0.0285
0.0232
0.0338
0.0749
-
0.0358
0.050
-
0.126
0.093
0.072
0.099
0.042
0.041
0.065
0.063
0.069

-------
TABLE 3   AVERAGE OPERATING LEVELS FOR PILOT ESP

FIELD
WTIMRFR

1
2
3
4
5
AVERAGE
PHASE I
V
37.4
26.6
30.8
26.0
27.8
29.7
I
4.3
1.13
11.6
29.9
14.8
12.3
PHASE II
V
30.5
24.7
29.3
26.0
25.9
27.3
I
3.63
1.29
4.83
13.1
11.5
6.9
PHASE
V
30.8
24.8
28.8
25.4
24.8
26.9
IIIA
I
4.64
1.68
5.34
15.3
8.63
7.1
PHASE
V
36.0
26.5
32.0
27.8
27.5
30.0
IIIB
I
6.33
0.7
8.01
11.8
8.6
7.1
             V = Kilovolts, kV




             I = Current Density, nA/cra2
                        69

-------
                                                          TABLE 4   RESULTS OF FI.Y ASH ANALYSIS
PHASE
  IIIA
  TUB

TEST
NUMBER
1
3
3
3
5
5
5
7
7
7

21
21
21
22
22

27
27
27
29
30
30
31
31

32
32
32
32
32
32
33
34
35
35
35


DATE
6/7
6/9
6/9
6/9
6/13
6/13
6/13
6/15
6/15
6/15

7/27
7/27
7/27
7/28
7/28

8/8
8/8
8/8
8/10
8/11
8/11
8/14
8/14

8/22
8/22
8/22
8/22
8/22
8/22
8/23
8/24
8/24
8/25
8/25




FIELD Na20 S03
NUMBER PERCENT PERCENT
1
1
3
4
1
3
5
1
4
5

1
3
5
1
3

1
3
5
3
1
5
W-l
W-2

,
5
W-3
W-5
P-3
P-5
3
1
5
1
5

2.
2.
3.
2
6
2
K20
PERCEN1



P205
r PERCENT



Fez03
PERCENT


BASE
PERCENT


BASE/
Na20


RESISTIVITY
AT SKV/CM
318°C, 9% H20
Ohm • cm

3.4
2.
4.
3.
3.
3.
3.
AVG: 3.
2.
3.
3.
2.
3.
AVG: 2.
3.
3.
3.
-
7.
5.
4.
5.
AVG: 4.
5.
4.
4.
4.
3,
4.
-
3.
3.
4.
4.
AVG: 4.
7 0.57
5
8
1
5
4
M
4
0
0
6 0.45
2
84
0
6
6

1
0
3
4
6
6
7
7
7 1.3
7 2.0
0 2.3

4
3
2
6
3
.1
.4
.3
.4
.4
.4




1.7
1.9

1.3
1.3
1.1

1.3
1.3





1.5
1.5
1.4
1.4






0
0
0
0
13
34
46
18
0.26
0




0
0

0
0
0

0
0





0
0
0
33




18
21

14
26
27

22
56





37
41
47
0.49












4.7
5.7
7.4
5.4
6.5
6.6




6.1
6.5

6.3
7.3
7.2

5.2
7.5





5.0
7.0
6.8
6.9






15.4
25.7
23.2
22.0
21.7
21.4




17.2
19.2

20.1
22.7
22.7

20.6
25.0





18.3
18.8
22.2
22.4






5.7
5.7
6.1
7.1
6.2
6.3




6.6
6.0

6.7
6.3
6.3

2.9
5.0





3.9
4.0
6.0
5.6











2.0 x 10'°










6.2 x 107
1.4 x 108




1.4 x 108

6.5 x 10*



8.3 x 10s
3.5 x 109

6.0 x 10s



-------
         TABLE 5   COMPARISON OF DATA WITH MODEL PREDICTED PERFORMANCE
                               APPROXIMATE     MODEL     ACTUAL PENETRATION/
         AVERAGE     SODIUM   STEADY-STATE   PREDICTED        PREDICTED
PHASE  TEMPERATURE, INJECTED   PENETRATION  PENETRATION      PENETRATION
           °C        PERCENT     PERCENT      PERCENT
I


II


IIIA


IIIB


*
a.
b.
c.


260 NIL


294 NIL


294 8.16


246 2.33



ASNUCK =0.0 AZIGGY = 0
ASNUCK =0.1 AZIGGY = 0
ASNUCK =0.1 AZIGGY = 0
ASNUCK = cell bypass fraction
AZIGGY = normalized standard
4.66


1.82


0.74


1.6



.00
.25
.50

deviation
*a.
*b.
*c.
a.
b.
c.
a.
b.
c.
a.
b.
c.





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                                      71

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                                  72

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           Figure 2    Matts-Ohnfeldt common  SCA adjusted emission
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                                           73

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                                                    SCA -   88.6 m2m3/sec

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                                              STEADY STATE PERFORMANCE RANGE -
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                                     74

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                     75

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                                        78

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                                        79

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                   PRECIPITATOR UPGRADING AND FUEL CONTROL
                     PROGRAM FOR PARTICULATE COMPLIANCE
                   AT PENNSYLVANIA POWER AND LIGHT COMPANY
                               John T. Guiffre

                    Pennsylvania Power and Light Company

                       Allentown, Pennsylvania  18101
ABSTRACT

Two cold side electrostatic precipitators handling low sulfur Eastern
bituminous 'coal flyash were upgraded from 94% to 99.4% efficiency in
order to meet a particulate compliance limit of 0.1 Ib/MMBTU.

The comprehensive upgrading was the result of a two year research and
testing 'program during which various aspects of flue gas conditioning,
electrical energization, rapping, coal quality control and gas distri-
bution were independently tested on three similar precipitators.  The
ensuing upgrading program included the installation of hardware designed
for maximum performance and reliability as well as flue gas conditioning
and a fuel ash control program.

A cost and reliability analysis of the upgrading program as compared
with the installation of an additional series precipitator is included.
                                      80

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INTRODUCTION

     In 1974, Pennsylvania Power and Light Company (PP&L) was faced with
the problem of having several generating units which did not comply with
the particulate emissions regulations of the Pennsylvania Department of
Environmental Resources.  This paper deals with the approach taken to
analyze and solve the emissions problems on three similar units.

     The three units are Montour Units 1 and 2, located in
Washingtonville, Pennsylvania, and Brunner Island Unit 3, York-Haven,
Pennsylvania.  Each unit is nominally rated at 750 MW and is equipped
with a Combustion Engineering tangentially fired boiler burning Eastern
bituminous coal pulverized to 70% through 200 mesh consistency.  Each
boiler is equipped with a Western Precipitation electrostatic precip-
itator (ESP) in a chevron arrangement with a total specific collecting
area (SCA) of 40m2/(m3/sec) (204 ft2/1000 cfm) at design flow of 1062
m3/sec (2,250,000 acfm) at 149°C (300°F).  Under actual boiler operating
conditions, an SCA of only 35 m2/(m3/sec) (180 ft2/1000 cfm) is achieved.

     Although these ESP's had a guaranteed design efficiency of 99.5%,
this level of performance was never achieved under actual operating
conditions.  In fact, due to degrading fuel quality, changes in boiler
operation to prevent slagging and the small size of the ESP's, effi-
ciencies of only about 94% were achieved with low sulfur coal (1.0%S).

     In late 1974, a project team was established to study the ESP
problems on these units as well as one smaller unit (Brunner Island 1).
This Air Quality Project (AQP) team consisted of seven full time engineers.
The basic objective of the AQP was to assure that compliance was achieved,
but also to minimize the compliance cost by placing primary emphasis on
upgrading the existing collectors rather than installing new ones.

     From March 1975 until March 1977, a variety of parameters which
affect ESP performance were investigated by the AQP team.  The areas of
investigation included:

                         o Fuel Quality
                         o Flue Gas Conditioning
                         o ESP Sectionalization
                         o Rappers
                         o High Voltage Controllers
                         o Flue Gas Distribution
                         o Reliability Items
                                       81

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     Each of the above areas was independently investigated by a member
of the AQP.  When the investigations indicated that a change in a par-
ticular area could improve ESP performance or reliability, the change
was implemented on one single unit on a trial basis.  To fully evaluate
the change, ESP efficiency tests were run after each trial change and
the results were compared with baseline data.  A total of 47 full efficiency
tests were run on the four units during the two year investigation.  In
addition, continuous opacity monitor data was used for comparative
purposes whenever it was impractical or inconvenient to run an efficiency
test.

     As a result of the AQP investigation, the Montour ESP's were upgraded
to achieve particulate compliance instead of building additional collectors.
Although Brunner Island Unit 3 is similar to Montour Units 1 and 2, this
unit could not achieve compliance through upgrading due to dissimilar
boiler operation and an inability to control long range coal quality at
the Brunner Island station.  Due to these differences a series ESP was
installed on Brunner Island Unit 3.

     With the exception of a cost and performance comparison between the
upgrading modes selected for Brunner Island 3 and Montour, the remainder
of this paper deals with the Montour upgrading investigation and implementa-
tion phases.
                                     82

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                     RESULTS OF THE INVESTIGATION PHASE
FUEL CONTROL

     Bituminous coal burned on the PP&L system is obtained both from
company affiliated mines and from numerous open market sources.  The
quality of the coal is highly variable with sulfur content ranging from
0.8% to 2.5% and ash content ranging from 11% to 25%.  The fuels investiga-
tion that was performed by the AQP team sought to quantify the effect of
sulfur content and ash content on ESP efficiency and to determine if
fuel quality could realistically be controlled to improve ESP performance.

     A high sulfur (2.4% S) low ash (12% Ash) coal supplied by
Benjamin Coal Company was used for benchmark data since it was con-
sidered to be one of the best collecting coals (as measured by the
achieved ESP efficiency) burned on the system.  The ESP efficiencies
measured while burning Benjamin coal were compared with efficiencies of
lower sulfur coals of various ash content.  Several important conclusions
which were applicable to all four of the tested units were drawn from
these tests.

          - A coal sulfur content of 2.2% or greater was required
            to obtain optimum ESP efficiency.

          - Given a constant sulfur content, ESP efficiency did not
            change as the ash content was varied in the 11% to 25%
            range.

          - As the ash content of the coal increased, the percentage
            of ash that found its way into the ESP's in the
            form of fly ash decreased.  Prior to this investigation, it
            was assumed that 80% of the ash in the coal "carried over"
            into the ESP's in the form of flyash.  As can be seen in
            Figure 1, the percentage of flyash carryover was found to
            be inversely proportional to the ash content.

          - Due to the lower percentage of fly ash carryover in the
            higher ash coals, the ESP efficiency which is required
            to meet the 0.1 Ib/MMBTU compliance limit does not have
            a linear relationship with the ash content of the fuel
            (Figure 2).  It is apparent from Figure 2 that an ESP
            efficiency of 99.3% would be sufficient to meet the par-
            ticulate compliance limit of 0.1 Ib/MMBTU with any of the
            tested coals.
                                      83

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     The conclusions drawn from the Fuels Investigation provided the
basis for the decision to upgrade the existing Montour ESP's rather than
adding new collectors.  While testing with the Benjamin coal at Montour,
an ESP efficiency of 99.4% was achieved, thus indicating that compliance
could in fact be attained under controlled conditions.

     Unfortunately, under low (1.0%) sulfur coal conditions, ESP efficiency
would degrade to below 94%.  Due to the fact that the major supplier of
coal for the Montour station is Greenwich Collieries, a PP&L affiliated
mine which produces a coal with a low average sulfur content (1.2% S) it
was not feasible to establish a fuel procurement plan which would
eliminate low sulfur coal.

FLUE GAS CONDITIONING

     Due to the observed detrimental effect of low sulfur coal on ESP
performance, the use of 803 flue gas conditioning as a resistivity
modifier was investigated by the AQP.

     After a careful evaluation of industry experience with SO^ con-
ditioning, a trial 803 injection system was installed on Brunner Island
Unit 1 (BI-1).  BI-1 was selected for the trial because it was the
smallest unit under investigation and therefore the installation costs
of the system could be kept to a minimum.

     To evaluate the effect of S03 conditioning, our benchmark coal
(Benjamin) was tested without S03 injection to establish a "maximum" ESP
efficiency for BI-1.  A second coal with low sulfur content (1.0% S)
from Greenwich Collieries  (the major coal supplier for Montour) was then
tested both with and without 803 conditioning.  The tests run without
the 803 conditioning indicated that the Greenwich coal was one of the
poorest collecting coals normally burned.  However, with the addition of
25 ppm of 803, the ESP efficiency with Greenwich coal improved to a
level slightly better than that measured with Benjamin.  The tests
results are summarized in Figure 3.

     Supplemental testing using opacity monitors and flyash resistivity
probes as performance indicators revealed that 803 conditioning was
capable of offsetting the effects of burning low sulfur coal to the
degree of maintaining optimum ESP efficiency with virtually any coal
normally burned at either Montour or Brunner Island.

     Since the use of 803 as a flue gas conditioning agent had demon-
strated repeatable and predictable results, the AQP concluded that 803
conditioning was a viable alternative for improving ESP performance
under conditions of high resistivity flyash resulting from burning low
sulfur coal.
                                     84

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     It should also be noted that another flue gas  conditioning  trial
was conducted at Montour using proprietary  chemicals.  Although  some
improvements in stack opacity had been  achieved, no significant  improve-
ments in ESP efficiency were measured during  the trial period.

ESP ELECTRICAL ENERGIZATION

     Electrical energization was investigated in two primary areas; a)
Automatic high voltage control systems  and  b) Transformer - Rectifier
(TR) set capacity.

     A.   Automatic High Voltage Controls

               At  the time that the AQP investigation began, almost all
          of PP&L's precipitators were  equipped with high voltage control-
          lers which used saturable core reactors  (SCR) and outdated
          control  logic.  The investigation therefore focused on modern
          thyristor controllers with compatible high speed control
          logic.   A series of full scale trials using thyristor  control-
          lers was subsequently conducted.

               The ability of a modern  control to greatly improve ESP
          efficiency was not demonstrated during this study.  Power
          levels  (V and I) were increased in  some units but the  ESP
          efficiencies did not noticeably change from the values measured
          before  installation of the new controls.  Operational  experience
          indicated, however, that the  frequency of wire failures was
          greatly  reduced after the new controllers were installed.
          Heavy sparking and wire burning were almost completely eliminated.
          It was  concluded that the new controls would improve reliability
          while maintaining voltage and current levels.

     B.  TR Set Capacity

               During the SO-^ conditioning  trial at Brunner Island, it
          was noted that most TR sets operated at the current limit when
          503 conditioning was utilized.  Further investigation  and
          trial operation revealed that for optimum ESP efficiency with
          S03 conditioning, the TR sets should be sized large enough to
          provide  a current density of  at least 54  na/cm^- (50 ma/1000
          ft^), particularly in the outlet  sections.

GAS DISTRIBUTION

     Due to the unusual chevron shaped  inlet  duct on the Montour ESP's
(Figure 4), an investigation into the possibility of poor gas distribution
within the  ESP's was undertaken.
                                      85

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     Motivated by what later proved to be an erroneous air load velocity
test performed by a subcontractor, the AQP contracted to have an ESP
model constructed and a model study performed.

     The results of both the model study and subsequent field tests
revealed that the ESP's were operating with an RMS velocity deviation of
about 12.5% which is well within the standards of the Industrial Gas
Cleaning Institute (I.G.C.I.).

     Further model studies were conducted to determine whether the
velocity distribution could be further improved.  An additional 50% open
perforated plate was subsequently installed on one-half of one ESP for
evaluation.  Since ESP efficiency testing did not indicate that the
additional perforated plate had resulted in a performance improvement,
no additional modifications were made to the remaining chevron ESP's.

RAPPERS

     The Montour ESP's were initially equipped with vibrating rappers
and electromechanical (cam type,) rapper controls.  The need for better
rapping was evident from the heavy plate deposits which were routinely
observed during internal ESP inspections.

     As part of the rapper evaluation study, 96 electric impact collecting
plate rappers, were installed on one-half of the Montour 2 ESP, replacing
the existing vibrating rappers.  In addition, an electronic matrix type
rapper controller with the ability to quickly change rapper timing,
intensity and programming, was installed to control the new rappers.

     Tests results indicated that the impact rappers did a significantly
better job of cleaning the collecting plates than did the vibrating
rappers, and that the clean plates resulted in an improvement in ESP
performance.  The testing also indicated the need for a programmable
rapper control which was capable of minimizing rapping intensity and
frequency on the outlet sections in order to minimize rapping reentrainment,

     Additionally, it was concluded that the existing configuration of
one rapper for every seven plates did not provide sufficient cleaning of
the plates which were farthest from the rapper.  An improved arrangement
of one rapper for every three plates was suggested.
                                     86

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                        THE MONTOUR UPGRADING PROJECT
CAPITAL IMPROVEMENTS

     The results obtained from the individual investigations which were
performed by the AQP team were utilized to formulate a comprehensive
upgrading program for Montour.  A key aspect of the upgrading was to
achieve an ESP efficiency of 99.4% (as previously seen while burning
Benjamin coal) and to maintain this level of performance, as much as
possible, for the wide variety of coals and operating conditions encountered
at Montour.  To accomplish this objective, the following improvements
were incorporated:

     o    An S03 flue gas conditioning system was installed on each unit
          to offset the effects of low sulfur coals which account for
          two-thirds of the station's fuel supply.  The sulfur burner
          type system was equipped with sufficient redundant equipment
          (including spare boilers, air heaters and sulfur pumps) to
          ensure 95+% reliability of the system.  The 803 system feed
          rate is varied according to the unit load and the sulfur
          content of the coal being burned in order to maintain a total
          803 concentration of 19 ppm at the inlet to the ESP (including
          that portion of 803 produced by the coal being burned).
          This corresponds to a fly ash resistivity of about 5 X 10
          ohm-cm.

     o    The existing rappers and rapper controls were replaced with
          electric impact rappers and matrix type rapper controls with
          considerable programming flexibility.  The number of rappers
          used for plate rapping was approximately doubled in number so
          that each impact rapper would clean either three or four
          plates.  Impact rappers were also installed on the high voltage
          discharge system.

     o    All automatic high voltage electrode controls were replaced
          with thyristor type controls.  In addition, secondary  (d-c)
          metering (voltage, current and spark rate) was installed for
          each TR set in order to provide better information for operating
          personnel.
                                      87

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     o    The number of TR sets utilized on each half of the ESP chevron
          was increased from 8 to 14.  The original ESP design utilized
          one TR set to power two sections.  This arrangement was changed
          on all but the inlet sections to allow one TR set per section,
          thus increasing the available current density on the outlet
          sections to 97na/cm2 (90ma/1000 ft2).  The original and final
          arrangements are shown in Figure 4.

     o    Each ESP was refitted with new discharge wires as part of the
          upgrading.  Additionally, each unit originally had a double
          wire per weight high voltage framework design which was modi-
          fied to a single wire per weight framework.

     o    Each hopper was equipped with nuclear type hopper level detectors
          and electric hopper heaters in order to minimize the possiblity
          of hopper overfill.  This improvement was made because the AQP
          had identified hopper overfilling as a leading cause of ESP
          section outages.

     o    In order to implement the various phases of the Montour upgrading
          project,one full-time engineer was added to the plant staff.
          In addition, the position of ash equipment operator (one per
          shift) was established at the plant.  The ash equipment
          operator is responsible for ESP operation, ash removal equipment
          operation and SO^ system operation.

FUEL CONTROL PLAN

     A unique aspect of the Montour upgrading program is the inclusion
of a fuel ash control plan.

     As previously outlined and Illustrated in Figure 2, an ESP efficiency
of 99-3% is sufficient to handle coals of ash contents of up to 25%.  In
order to incorporate additional operating margin and reliability into
the upgrading plan, the ash content of coals shipped to Montour has been
restricted to less than 17% (d.b.).  As can be seen from Figure 2, an
ESP efficiency of about 99.1% would be sufficient for coals of this
quality.

     Approximately 60% of the coal burned at Montour is supplied by
Greenwich Collieries, which ships 100% of its produced coal to Montour.
The mine is equipped with a modern coal cleaning plant capable of producing
coal as low as 8% ash.  As a compromise between mine economics and
Montour ESP reliability, the average ash content shipped from Greenwich
is about 14% with virtually all of the coal being less than 17% ash.
                                     88

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     Most of the remainder of Montour's coal supply is purchased on the
open market.  The vendors which ship to Montour are presently restricted
to a 14% ash content and are selected by the PP&L Fuels Department based
on their history of quality control.  Vendors which ship a single
trainload (13,000 tons) of coal to Montour which is in excess of 17% ash
are subjected to a field investigation by the Fuels Department.  If the
shipment is in excess of 19% ash, all future shipments from that vendor
are suspended until quality assurance is reestablished.

     An "early warning" system has been established which allows the
Montour plant to know the ash content of all coal shipped to the plant
before it arrives.  All of the coal burned at Montour is shipped to the
plant in PP&L owned fleet trains.  An independent coal analysis firm has
been hired  to sample coal from each car in the fleet train at the time
that it is  loaded at the mine.  The analysis firm then performs a "quick
ash analysis" which takes about three hours and has proven to be fairly
accurate.   The results of the quick ash analysis are teletyped to Montour
in less than 12 hours from the time the sample is taken. (Train transit
time is 12  - 24 hours.)

     In the event that a high ash shipment of coal arrives at Montour,
the early warning system allows the plant to take appropriate action.

     The plant's coal yard is equipped with a stacker reclaimer with
capacity to hold 5 trainloads of coal.  Sufficient area is reserved on
the stacker reclaimer at all times for the storage of at least one
trainload of high ash coal (greater than 17% ash).  If the early warning
system reveals that a trainload of high ash coal will arrive at the
station, the coal is unloaded into the reserved storage area.  From this
area, the coal is reclaimed on a controlled basis and mixed with coal of
lower ash content.  Since the Montour plant has three raw coal silos per
unit, the mixing is usually accomplished by loading high ash coal in one
silo and low ash coal in the other two silos.  In this manner, a 13,000
ton trainload of high ash coal can be safely disposed of in about one
week.  A schematic layout of the Montour high ash coal handling system
is shown in Figure 5.

RELIABILITY ANALYSIS

     Before the decision was made to upgrade the Montour ESP's, a compre-
hensive reliability analysis of all components that would be a part of
the upgrading was undertaken.  Essentially, the objective was to determine
the percentage of time that the Montour units could be expected to
remain in compliance, given the known fallibility of some aspects of the
compliance  plan.  This was an important consideration in light of the
fact that the units would probably have to drop load (at substantial
cost) to maintain compliance if the installed collection equipment
failed.
                                     89

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     The histogram which is shown in Figure 6 illustrates the predicted
day-to-day emissions at Montour after ESP upgrading.  The stack emissions
are affected by five variables.  The histogram includes the overlapping
probability of multiple component failure.  The variables, the ranges
and the probabilities of occurence are listed below.

     1.   Boiler loading (historical)

               750 MW              50%
               700 MW              20%
               650 MW              20%
               400-500 MW          10%

     2.   ESP sections out of service

               0 sections          90%
               1 section            6%
               2 sections           3%
               3 sections           1%

     3.   Fuel ash content (dry basis)

               Greater than  17% ash          5%
                       14% - 17% ash         50%
                  Less than  14% ash         45%

     4.   Fuel sulfur content

               Less than   1% S         20%
               Less than 1.5% S         60%
               Less than 2.0% S         20%

     5.   SO,, injection system

               95% reliability  (based on  Commonwealth Edison experience)

     The combined effect of the performance variables listed above re-
sults  in a predicted compliance level of  96.5%.  During the remaining
3.5% of the time, the units would have to operate at a reduced load to
maintain compliance.
                                      90

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COST COMPARISON - MONTOUR UPGRADING VS. BRUNNER ISLAND 3 SERIES ESP

                          MONTOUR S.E.S.  - 750 MW

Design criteria:                   99.4% efficiency with 1.0% S coal
                                   with all equipment operating.

                                   Compliance limit of 0.1 Ib/MMBTU
                                   to be met 96.5% of time without
                                   forced load reductions.
Costs:   (per unit)

          Upgrading hardware  (includes SO-
                    system)                       $ 4,000,000.

          Annual 0 & M                            $   500,000

          Annual forced load  reductions           $ 1,000,000
                       BRUNNER ISLAND UNIT 3 - 750 MW

Design criteria:                   Series ESP designed for 90% effi-
                                   ciency with 1.5% S coal.  Existing
                                   ESP to operate at 95% efficiency for
                                   combined efficiency of 99.5%.  803
                                   flue gas conditioning to be utilized
                                   with coals of less than 1.5% sulfur.

                                   Compliance limit of 0.1 Ib/MMBTU to
                                   be met 99+% of time without forced
                                   load reductions.

Costs:

          ESP and auxiliaries
          (includes booster fans, 863
           system, auxiliary transformer
           and site preparation)                  $ 38,000,000

          Annual 0 & M                            $  1,500,000

     Approximately two-thirds of the annual 0 & M cost for the Brunner
Island ESP is for electrical power for the new ESP and booster fans.  It
is interesting to note that the annual cost of power which will be used
to operate the new collection equipment on Brunner Island Unit 3 is
equal to the annual cost of the anticipated forced "compliance" load
reductions at each Montour Unit.
                                       91

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RESULTS AND CONCLUSIONS

     Since the upgrading at Montour was completed, the opacity on both
units has been continually maintained in the 6% to 8% range even when as
many as three ESP sections have been taken out of service.  Figure 7
shows a comparison of opacity monitor charts during three phases of the
Montour program.  Note that the addition of TR sets and rappers in
November, 1978 not only reduced the overall opacity but also greatly
reduced the rapping spikes which were previously observed.

     As of July 1, 1979, only Montour Unit 2 had been tested for par-
ticulate compliance.  Preliminary results of the three emissions tests
performed by the Pennsylvania Department of Environmental Resources
indicated an average emission rate of 0.057 Ib/MMBTU which is substantially
below the allowable limit of 0.1 Ib/MMBTU. (ESP efficiency is estimated
at 99.6%).  These tests are a positive indication that the Montour
upgrading program has been successful in effecting a reliable, low cost
solution to a problem which otherwise would have been resolved by the
addition of expensive retrofit collectors.
                                       92

-------
                          Fly Ash Carryover
OJ
        10
14
16     18     20    22



    %Ash In Coal As Received
24
26
28
                                   Figure 1

-------
        Required ESP  Efficiency For Compliance
                         Chevron Units
O
c
05

O
UJ
•a
CD
CD
DC
   99.4
   99.2 -
99.0 -
98.8 ~
   98.6 -
   98.4 -
   98.2
                 14
                   16     18    20    22

                     %Ash In Coal As Received
24     26
28
                              Figure 2

-------
          SUMMARY  OF EFFICIENCY TEST DATA
                BRUNNER ISLAND UNIT
crv
DATE
7/28/76
7/29/ 76
9/14/76
9/15/76
9/2 1 /76
9/22/76
COAL TYPE SULFUR %
BENJAMIN | 2.2
BENJAMIN 1 "
GREENWICH ! 1 .0
GREENWICH \ "
GREENWICH ! 1.0
GREENWICH \ "
ASH%
14.2
12.1
11.5
WAHLCO
IN
SERVICE
NO
NO
YES -25 PPM
YES -25 PPM
NO
NO
PRECiPITATOR EFFICIENCY
BUELL
92.8
92.1
93.3
92.7
70.9
71.9
R.C.
94.7
94.7
96.1
97.0
86.8
89.9
TOTAL
93.6
93.2
94.5
94.8
78.0
79.7
                         Figure 3

-------
           Montqur
     TR Set Modification
Original
TR Sets
Modified
               Figure 4

-------
                          Montour S.E.S. Coal  Control
                                                                                 Car Dumper
                                Dead Storage Area
                                                                            Coal
            I	
	I
                                                                           Conveyor x
            i_.
            r
                                  Low Ash Coal
                  Stacker-Reclaimer
                                  High Ash Coal
                                                                      ... J
             Unit No. 2
              Boiler
              Unit No. 1
               Boiler
Low Ash Coal f Low Ash Coal High Ash Coal
 Low Ash Coal I Low Ash Coal I High Ash Coal
                                            Figure 5

-------
                           Compliance  Histogram
        30
OD
     CD
     E
     c
     O
        20
        10
         0
0>
_l
(U
o
c
.2
"5.
E
o
o
                                                     —i—
            .01 .02  .03 .04 .05 .06 .07  .08  .09 .10 .11 .12  .13 .14 .15  .16  .17 .18 .19

                                 Emission Level Ib./MMBTU
                                       Figure 6

-------
Before Upgrading
    6/78
            Opacity  Comparison
    With
    Injection
      4/79
After TR Sets and Rappers
       11/78
                      Figure 7

-------
MODIFICATION OF EXISTING PRECIPITATORS
      TO RESPOND TO FUEL CHANGES
   AND CURRENT EMISSION REGULATIONS
                  By:
            D. Scott Kelly
              R.D. Frame
   Air Correction Division, UOP Inc.
      Darien, Connecticut  06820
               ABSTRACT

 Practical improvements are presented for
 modifying existing precipitators to improve
 collection efficiency for high resistivity
 ashes from burning low sulfur coals.  These
 modifications are also recommended as a
 foundation for other improvement programs
 such as temperature or ash conditioning.
                    100

-------
     The drive to reduce sulfur dioxide emissions has often been
satisfied by burning coals with low sulfur content. The reduction
in sulfur has in turn caused a marked reduction in the collection
efficiency of electrostatic precipitators.  Sulfur oxidizes upon
combustion of the coal and forms S03, an  important ash conditioning
agent.  Without it, efficiency deteriorates causing operators to
turn to electrostatic precipitator vendors for recommendations.

     There is no generally preferred solution.  Replacement of the
precipitator, ash conditioning, temperature conditioning and pro-
cess modifications have all been successful.  Each, however, involves
a major commitment and has its drawbacks.  It is felt that an al-
ternative first step in responding to the need for improved perfor-
mance of existing precipitators consists  of modifying the precipitator
to come closer to, if not to meet or exceed today's performance stan-
dards .

POSSIBLE SOLUTIONS

     To demonstrate this approach. Figure 1 depicts typical trends in
ash resistivity over a range of collection temperatures for coals of
different sulfur contents.  Although reduction in sulfur is generally
detrimental to collection efficiency, the effect is most significant
when  the reduction is to a level of less  than 1 percent sulfur.  For
example, a unit collecting 1.5 to 2.0 percent sulfur coal ash at
about 150° C  (point A) could show a ten-fold increase in resistivity
if the coal sulfur content were decreased to below one percent (point
B).   Such a shift in resistivity is generally accompanied by a sig-
nificant reduction in collection efficiency.

      More common approaches attempt to reduce resistivity to a more
manageable level by decreasing collection temperatures (point C),
increasing collection temperatures  (point D), or by fuel or flue gas
conditioning  (point E).

LOWERING RESISTIVITY

      Operating the precipitator at decreased temperatures has been
successful, however, this approach may require operating close to
the dew point.  This greatly increases the chances of condensation,
corrosion, and fouling in the precipitator, air heaters, and ash
removal system.  When operating in this mode, particular attention
must be paid  to small changes in coal sulfur content which affects
the acid dew  point, and dictates how low  one can drop the temperature.
 (1)

     An alternative remedy that has been widely used to decrease
resistivity is to operate the precipitator at the higher temperatures
that  are commonly found upstream of the air heaters.  (2)  It should,
however, be a well studied decision to retire an existing "cold" side
precipitator  and install a new "hot" side unit.


                                 101

-------
    Another approach that has shown success is the lowering
of resistivity by fuel or fly ash conditioning.  Operating
costs should be compared to other alternatives as a possible
deciding factor.  Conditioning should not be categorically
discounted.  Work is continuing in the field and technically
successful and cost-effective applications on difficult fuels
have been demonstrated.

DEALING WITH HIGH RESISTIVITY

    In addition to the three foregoing remedies which might
decrease resistivity to a low or moderate level, an alternative
may be to deal directly with the higher resistivities.  This is
not a popular approach because its application is limited and
success is difficult to predict.

    Despite this, circumstances exist where collecting a high
resistivity dust is possible by upgrading existing hardware that
was designed for a low resistivity ash.  By reviewing precipi-
tator design fundamentals, specific operating parameters can be
picked out that are important in the collection of high resis-
tivity ash.(4)

    An example can be made of a small boiler that switched from
2.0% to 0.8% sulfur coal.  The collection efficiency of its
precipitator in turn dropped from 88 percent to below 60 percent
(Figure 2).  The corresponding precipitator power levels dropped
from 60 to 30 watts/1000 acfm.  After a modification program
consisting of several of the changes discussed, power levels
increased to 85 watts/1000 acfm and collection efficiencies are
expected to be above the 90 percent level.

    The following review of precipitator design theory shows how
modifications can be chosen and how their individual contribution
can lend to an overall improvement in precipitator performance.

SELECTING AREAS FOR MODIFICATIONS

    Whether designed by analogy or by methods based on theory,
the precipitator operation will generally follow the relationship
given by the Deutch equation:

                n - 1 - e

        where:  r\ = probability of particle collection
                A = collecting electrode surface area (ft^)
                V = gas flow rate (ACFS)
                oj = migration velocity  (ft/sec)

    By increasing collecting electrode area A, by decreasing gas
flow rate V, or by increasing migration velocity w, collection
efficiency ri can be increased.


                                102

-------
    The first two options, increasing plate area and decreasing
gas volume, involve major commitments that should only be
contemplated after less severe options have been exhausted.
Unless a spare precipitator bay already exists for additional
plate area, or derating of the boiler is acceptable, these
alternatives are not the most desireable.

    The remaining variable w, or migration velocity, thus,
becomes the prime target for improvement.  Migration velocity
is synonymous with precipitation rate for ideal uniform condi-
tions of particle size, gas velocity, etc.  Because these ideal
conditions do not necessarily exist in actual operation, an
effective precipitation rate parameter we is used instead.(5)
The most important variables that affect ^e are:

              1.  Fly ash resistivity
              2.  Particle size distribution
              3.  Gas velocity distribution
              4.  Reentrainment
              5.  Gas sneakage
              6.  Rapping conditions
              7.  Electrical conditions

    Resistivity and particle size distribution are given condi-
tions whose range of values should be reasonably well established
for actual or anticipated boiler operating conditions.  Each is
measurable if a test burn of low sulfur coal is planned as part of
a modification program.  This is strongly recommended, since source
test data collected during a preliminary burn will help identify
potential problem areas and form a basis for modifications.
Improvement of the five remaining variables that affect <% can be
addressed from the standpoint of precipitator modifications.

Gas Velocity Distribution

    Precipitators that are 15 or more years old may not have been
engineered to meet specific gas velocity distribution criteria
such as provided by the IGCI.  With increasingly higher levels of
required efficiency over the past years, more importance has been
placed on obtaining flow patterns that are as uniform and ideal
as feasible.  Beginning v/ith a cursory review of the installed
flue work and gas distribution system, an evaluation of the need
for improvement can be made.  Some units, for example, have poten-
tially more collection plate area available if gas distribution
were improved.(6)

    A reliable method of determining the need for improvement is
to measure the velocity distribution at the inlet and outlet of
the precipitator as well as in the gas passages between collecting
electrodes.  When this information is compiled, it is often
combined with a model study program, in which a 1/16 scale model
is built representing the precipitator and its related ductwork.
By installing various baffles, turning vanes, etc., numerous

                               103

-------
configurations for improving the flow profile can be tested at
a fraction of the full-scale cost.

    Whether from model or from field data, enough information
can be evaluated to determine if modifications to gas distribution
will improve toe anc^ hence precipitator performance.

Reentrainment

    Among the problems addressed by a gas distribution study
is reentrainment.  Reentrainment is generally referred to as
dust that returns to the gas stream after collection rather than
leaving via the ash removal system.  It occurs mainly as a
function of four things:  gas flow, particle characteristics,
electrical energization, and rapping.  Reentrainment due to gas
flow should be corrected by modifications to the existing duct-
work as specified by the model study or distribution study.

    Dust properties are a function of upstream conditions, so
precipitator modifications should not affect dust properties
beyond altering the pattern of selective collection as the dust
moves through the unit.  The remaining variables that affect toe
are then rapping and electrical energization.

Rapper System Modifications

    Resequencing of individual raps, and varying rapping intensities
and time cycles can minimize reentrainment.  Of equal importance
is the necessity to keep collecting electrodes as clean as possible.
It has long been established that the non-conductive properties of
high resistivity dusts impair precipitator current flow and are
readily suspect in causing back corona once resistivities are 1010
ohm-cm or more. ^  Rather than reiterate the principles involved,
it is sufficient to note that back corona and reduced performance
often occur when too much high resistivity dust has accumulated on
the collecting electrodes.  The important point is to keep dust
accumulations to a minimum so that current flow will not be impaired
and the breakdown voltage of the dust layer will not be met.
Although back corona can occur for a lower resistivity dust, substan-
tially more ash must be accumulated before the phenomenon is
encountered.  This is evident from the Ohm's law relation:

                   AV - Jpt                              (2)

           where:  AV = sparkover voltage  (volts)
                    J = corona current density through the ash
                        layer (A/cm2)
                    P = resistivity  (ohm-cm)
                    t = thickness of the layer  (cm)

    Breakdown voltages for most dust are on the order of 10 to
20 kV/cm. (5)  In Figure 3, Ohm's lav? has been used to show
graphically how substantial accumulations of high resistivity
                              104

-------
dust on the collecting electrode could produce a voltage drop
across the layer that exceeds the usual range of breakdown voltages
if the current is hypothetically unsupressed by sparking and assumed
to be constant.  If such currents were feasible, a 0.5 cm accumu-
lation of 10° ohm-cm dust should show a voltage drop of less than
5 kV.  When 0.5 cm of lQl° ohm-cm dust is accumulated, however,
the voltage drop should be well in excess of the breakdown field
of 10 to 20 kV, and back corona will likely ensue.  It should be
apparent that collecting electrodes need to be cleaner than on
moderate or high sulfur coal applications, and because of the
strong dipolar attachment of the dust, effective rapping is
needed for high resistivity dust, otherwise current density will be
lower than is already necessary to avoid back corona.

     Rapper systems designed for high sulfur coals were adequate
for the job required.  Collecting electrodes were often rapped only
on their leading edges at nominal intensities and at rather lengthy
time intervals.  To meet the increased demand associated with high
resistivity dust, operators have often resorted to more intense and
more frequent rapping cycles.  As might well be expected, this can
substantially reduce the operating life of the rapping system. (7)

     Proper modification of the existing rapping system can greatly
improve reliability and effectiveness.  Areas to consider are the
rapper, the transmission hardware, and the rapper controls.

Rapper Assembly - The rapper assembly should be reliable for its
new duty cycle.  Because numerous types and models are available,
it is difficult to pinpoint specific required modifications.  Another
concern is useful rapper energy.  Many rappers installed over the past
decade are capable of delivering the required higher energies.  The
question is whether or not operation at the high end of their capabili-
ties under more frequent time cycles can be reliably sustained.  All
available modifications should therefore be considered to build in
required rapping power and reasonable reliability.

Transmission Hardware - The increased demand on the; rapps:r itself
can be substantially reduced by modifying the rapper transmission
hardware.  By the time energy from a single rap is delivered to its
applied area of collecting electrode, it will often have traveled
through a tortuous path with substantial energy losses.  Through
proper modification, the losses can be reduced and more energy
delivered to the plates.  A typical rapping transmission system that
can be upgraded is shown in Figure 4.  The rapper impact is trans-
mitted via a rapper rod through the penthouse roof and floor to a
striker assembly attached to the collecting electrode support member.

     To reduce failures under demanding low sulfur coal operation,
the quality of the striker block connection can be improved.
                               105

-------
Typical connections used are butt welds to anvil beams or welded
cup assemblies (Figure 5).  In either case, the amount of available
weld surface between the rapper rod and the anvil system is minimal,
with multiple welds required for assembly.  An improvement is the
gusset joint which requires little field welding and can remain
functional even if the critical weld between the rapper rod and
striker block fails.  An added advantage to the gusset joint is
the more uniform distribution of rapping energy along the electrode
support member.  This permits outboard electrodes a better chance
receiving their share of the rapping energy.

    Replacement of older seals with newer designs can reduce the
possibility of binding.  Newer seals can be chosen that do not
need periodic repacking.  Others have been designed to reduce
seizure in the seals due to corrosion.  To reduce further energy
loss and promulgate even distribution, the electrode support
system can be reinforced  (Figure 6).  The rapper impact is
delivered to the collecting electrode through a tube support
that rests upon the electrode support beam.  By reinforcing the
plate support tubes with a stiffening member, more even distri-
bution is achieved across the top of the collecting electrode.

    To complete transmission modifications, the trailing edge of
the collecting electrodes should also be supplied with a rapper
and the same modifications as shown for the leading edge.  As
mentioned earlier, the tube member rests upon the electrode
support member, and in some cases only one edge of the plate was
secured to the support member.  By securely welding both edges
one can improve the transmission of rapped energy without impairing
precipitator reliability. (8)

Rapper Control - A rapper control sequences rapper timing and
energizes individual rappers.  A breakdown in either area v?ill
eventually disrupt precipitator performance, especially on a low
sulfur coal operation.  Particularly vulnerable to this type of
malfunction are those controls which incorporate mechanical
switching and sequencing.  Where these are used, malfunctions
will occur primarily in contact assemblies because of arcing or
mechanical wear.   Arcing and wear of both sequencing and switching
contacts is enhanced by poor contact closure, poor timing, and
rapper ground fault conditions.

    The use of more reliable solid-state devices is recommended
for substitution of the above mechanical system where operating
voltages permit.   In addition to increased reliability, solid-state
controls permit continuous on-line monitoring of system operations.
Where a faulty rapper used to cause control damage, the newer
systems will test individual rappers before energization and by-
pass them if they are defective.  The defective units will be
displayed on the control panel, thereby permitting ea-sy location
during maintenance periods.

                                 106

-------
Electrical Conditions

     Thus far most of the areas that affect coe: and precipitator
performance have been covered.  The remaining area of electrical
energization is dealt with last because of its complexity and
importance.  In Equation  (1) it was shown that an increase in
drift velocity or its operating equivalent, we/ would result
in an increase in precipitator efficiency.  Precipitation rate
coe may be related to the corona power by the relation

                         coe = K-L Pc/A                     (3)

where K^ is a parameter characteristic of the given ESP in its
application and Pc/A is the corona power density in watts/ft^ of
collection surface.  It follows that if modifications can
increase corona power, efficiency will benefit.  Improvements
in electrical energization can be obtained by modifying several
areas.

High-Tension Sectionalization - In theory, as well as in practice,
optimum collection is achieved by applying maximum peak and
average voltages while losing as little power as possible to
sparkover conditions.  It is therefore important to match tha
corona level of each relatively small corona section to the
dust characteristics in that section.  This is most commonly
achieved by minimizing the number of discharge wires associated
with individual voltage supplies and their controls.   Adequate
high-tension sectionalization is also important from the
standpoint of sparkover.  The more often sparkover occurs in
a particular high tension section, the more power will be lost
and not be used for collection.  By increasing sectionalization,
the detrimental effects of individual sparkovers can be contained
in relatively small sections of the precipitator, thereby
increasing peak voltages.  This is especially important when
dealing with high resistivity dusts because of the greater
tendency toward sparking and difficult charging characteristics.
Sectionalization should, therefore, be carried out not only in
the direction of gas flow to compensate for changing dust
properties, but also across the gas flow, to minimize the
problems of sparkover.  In Figure 7, examples of increased section-
alization in series and parallel to gas flow are shown.

Voltage Wave Shape - The faster a voltage supply control can
respond to a sparking condition, quench the spark, and restore
power to the precipitator, the better are the chances of increased
power usage and increased collection efficiency.  As with rapper
controls, solid-state logic systems have found a natural home in
the electrostatic precipitator.  Accurate, fast responding systems
are available with power recovery times of only one or two cycles
                              107

-------
after quench.  Modifications in this area often include use of
state-of-the-art rectifiers and controls, linear inductors for
improved waveform control, and fast acting feedback networks that
trigger the automatic voltage control systems.

SUMMARY

    There are numerous areas for potential improvement of the
performance of existing precipitators.   It is well recognized
that the modifications described are not applicable or
feasible in all cases of existing units, however, the
discussion points out that given certain conditions, the
modifications may improve performance on high resistivity ash
to an acceptable level.  In addition, they should be considered
first to improve overall performance, regardless of any other
plans for increasing performance via process changes or condi-
tioning systems.
                                108

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                          REFERENCES
1.  Oglesby, S., and Nichols, G.B. "Electrostatic Precipi-
    tation."  Marcell Dekker, Inc., N.Y., N.Y., 1978 p. 134.

2.  Walker, A.B. "Hot-Side Precipitators."  APCA Journal,
    Vol. 25, No. 2:144, February, 1975."

3.  Brennan, J.H. and Reveley, R.L. "Flue Gas Conditioning
    with 663 to Improve Precipitator Performance."
    Proceedings of the American Power Conference, 1977.

4.  Panev, S.N. et al. "The Problem of Collecting Dusts that
    Cause Reverse Corona Formations in ESP's."  Proceedings
    of Second US/USSR Symposium on Particulate Control.
    EPA, March, 1978.

5.  White, H.J. "Electrostatic Precipitation of Fly Ash."
    APCA Reprint Series, July, 1977. p. 17, 48.

6.  Bump, R.L. "Electrostatic Precipitators in Industry."
    Chemical Engineering, January 17, 1977, p. 133.

7.  Lynch, J.L. and Kelly, D.S., "A Review of Rappei  System
    Problems Associated with Industrial Electrostatic
    Precipitators."  Proceedings of Operation and Maintenance
    of ESP's, APCA, April, 1978, p. 48.

8.  Unpublished information from authors files.
                                109

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        FIGURE  1   OPERATION  DEPENDENT  RESISTIVITIES
   101°n
   10
     9.
5
o
 I
2
I
o
CO
CO
UJ
DC
   10'
             A-ORIGINAL OPERATION
             B-LOW SULFUR OPERATION
             C-LOW SULFUR COLD OPERATION
             D-LOW SULFUR HOT OPERATION
             E- CONDITIONING OPERATION

200

300

°F

400
	 	 1
500

600
                  100
150   C   200
   TEMPERATURE
     no
                                               250
300

-------
    FIGURE 2   ESP  COLLECTION  EFFICIENCY VS.

           CORONA POWER  DENSITY  (Pc/V)
99
   98




   97



#  96


>  95
O
Z
III
7t  93
U-
U.
UJ

Z
g
H-
o
UJ
_i
_i
O
O
90
80





70



60



50



30
    LOW SUL W/MODIFICATIONS TO ESP,
                                       K, = 0.55
                                 TEST DATA


                                 SAMPLE PRECIPITATOR

                                 (REF- 8)

                                 HISTORICAL DATA

                                 (REF.5)
           25
                   50
                              75
                                   100
                                           125
                                                       150
         CORONA POWER, WATTS/1000 acfm (Pc/V)
                           111

-------
    FIGURE 3   EFFECT OF  ASH  THICKNESS ON


 VOLTAGE DROP FOR  VARIOUS ASH RESISTIVITIES
a.
o
oc
o

UJ
o
      5 •
       0.0
      0.5


ASH THICKNESS (cm)
1.0
                        112

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    FIGURE 4.  TYPICAL  COLLECTION  ELECTRODE
    RAPPING  SYSTEM  ON  OLDER  PRECIPITATOR
               RAPPER
 PENTHOUSE ROOF
 PENTHOUSE FLOOR
TRUSS
RAPPER ROD
 STRIKER ASSEMBLY
ELECTRODE SUPPORT MEMBER
           COLLECTION ELECTRODES
                          113

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FIGURE 5   RAPPER  BAR CONNECTIONS
   BUTT JOINT
                GUSSET JOINT
                   114

-------
    FIGURE  6   MODIFIED  COLLECTION ELECTRODE

    RAPPING  SYSTEM   ON  OLDER  PRECIPITATOR.
  IMPROVED SEAL
SECURE LEADING AND
  TRAILING EDGES
    STIFFENER
   GUSSET JOINT
 STRONGER SUPPORT MEMBER
                           115

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       FIGURE  7.   EXAMPLES  OF  MODIFICATIONS

            TO  INCREASE  SECTIONALIZATION
                  BEFORE
  AFTER
    IN

 SERIES
                   (9, 9, 6)
(4 x 4'/2, 6)
   IN

PARALLEL
                   (9,9)
i
4
i
I
  (9,9)
                            116

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                     PERFORMANCE OF ELECTROSTATIC PRECIPITATORS
                                 WITH LOAD VARIATION
                                         By:

                                 William T. Langan
                                 Gordon S. Gogola
                                 Eric A. Samuel
                          Buell Emission Control Division
                              Envirotech Corporation
                          Lebanon, Pennsylvania     17042
                                      ABSTRACT

     The load variation performance of electrostatic precipitators has been
characterized through a field test program.  The test program results indi-
cate significant differences between cold-side and hot-side electrostatic
precipitators.

     Hot-side precipitators have been found not to follow the expected
Deutsch-Anderson relationship with load variations.  Various mechanisms are
postulated and are validated or rejected, based upon the results from the
test program.

     The test program included measurement of chemical analysis of the coal
source, the inlet and outlet particulate loading,  resistivity of the dust,
participate size distribution and chemical analysis of the dust samples.
                                      117

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                       PERFORMANCE OF ELECTROSTATIC PRECIPITATORS
                                   WITH LOAD VARIATION
INTRODUCTION

     The performance of electrostatic precipitators has  been traditionally
described by the modified Deutsch-Anderson relationship (Reference 1).
                             -(co.SCA)
                      n =
                           -e
                      where e = natural logarithm
                            k = non-dimensional constant
                          SCA = specific collection area
                            f| = precipitator collection efficiency
                            to = migration velocity

     The K value in the classic Deutsch equation has a value of one; whereas,
recent analysis has K values between 0.5 and 0.75, Reference 2.  This formu-
lation has been made to reflect the decreasingly effective migration velocities
at the higher collection efficiencies because of the decreased ability of the
precipitator to collect the increasingly finer particulates.

     The Deutsch-Anderson formula predicts the precipitator performance to
increase with decreasing load conditions due to the reduced gas volume.  This
expected behavior has been typically experienced with cold-side electrostatic
precipitators.  For instance, the precipitator performance with load variation
is presented in Figure 1, see Reference  3.
PERFORMANCE OF HOT-SIDE ELECTROSTATIC PRECIPITATOR WITH LOAD VARIATION

     The performance of two hot-side electrostatic precipitator units with load
variation is shown in Figure 2.  These data clearly demonstrate that the precip-
itator performance can decrease with load reduction.  This relationship of
decreased precipitator performance with reduced load is inconsistent with the
performance expectations from the Deutsch-Anderson equation.

Plant A, depicted in Figure 2, is a 99.1% efficiency precipitator burning
South African coal; whereas, Plant B is a 99.0% efficiency precipitator using
primarily Hazard, East Kentucky coal.  The analysis of the coal from these two
plants is shown in the following table:

                                   COAL SOURCE
Parameter
Moisture
Ash
Total Carbon
Sulfur
BTU/Paund
Plant A
5.95
13.93
68.47
0.71
11,500
Plant B
2.69
10.49
74.23
0.72
12,600
                                       118

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     The operating conditions for the precipitator at the two plants are
presented in the following table:
Operating Conditions
Megawatt Production
at Full Load
Flow Rate
at Full Load (ACFM)
Flow Rate
at Half Load (ACFM)
Temperature
at Full Load (°F)
Temperature
at Half Load (°F)
Plant A
195
1,021,000
762,500
700
575
Plant B
— 450
2,537,000
1,395,000
643
529
     Thus, although these units are burning considerably different coal, as
well as having different operating conditions, these units clearly indicate
decreased precipitator performance at reduced loads.

     The following mechanisms were postulated-as potential explanations for the
degraded precipitator performance with decreasing load:

- High resistivity problem at the lower load condition due to decreased temper-
  ature.

- Particle-size distribution change at the lower load boiler operation.

— Flue gas properties change at the lower load boiler operation.

- Dust dropout at low load which is picked up with increasing load; thereby,
  overloading the precipitator.

- Increase in precipitator inlet loading during low load boiler operation.

- Poor gas flow distribution at low load condition.

     Tests were conducted to determine which of the hypothesized mechanisms
were responsible for the degraded performance at reduced load.  A test program
included measurement of the inlet and outlet particulate loading, resistivity
of  the dust, particulate size distribution and chemical analysis of the dust
samples at different load conditions.

     Four tests were conducted at Plant A under reduced load conditions.  Two
were conducted at stable three-quarter load conditions and two were performed
during transient condition from low to full load conditions.
                                      119

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     The efficiencies obtained from these tests are compared with the corres-
ponding values for full load condition in the following table:
Condition
3/4 Load
Transient
Full Load
Efficiency
%
99.0
94.5
99.5
Volume ,
ACFM
1,000,000
920,000
1,030,000
     The efficiency for both the 3/4 load and transient load condition are
lower than at the full load condition.  The performance at the transient
condition is dramatically below the full load performance.

     The inlet loading and corresponding emissions for these conditions, along
with the design values, are the following:
Condition
3/4 Load
Transient
Full Load
Design
Inlet Loading
Grains /SCF
6.47
13.1
6.5
4.98
Emissions
Grains /SCF
.06
.7
.02
.04
     The inlet loading for the transient load condition is much higher (greater
than factor of two) than the corresponding design value.  The inlet loading's
full load and 3/4 load are nearly identical and are slightly higher than the
design value.

     The inlet median particle size and resistivity for the conditions are the
following:
Condition
3/4 Load
Transient
Full Load
Inlet Median
Particle Size, Microns
11
16
11
Resistivity
Ohm/ CM
2 x 10'9
8 x 109
1 x 109
     The inlet median particle size measured during transient condition is
larger than either the 3/4 load or full load condition.  This could result from
either a change in boiler operation or dust being swept up from the ductwork
when the load is increased.  The measured increased inlet dust loading under
transient conditions would also support these hypotheses.  The performance
degradation during decreasing load conditions would be caused by different
mechanisms.

     The resistivities presented in the previous table are at the temperature
corresponding to the load condition.  The temperature at the 3/4 load is well
characterized and does not have a large spread: 617°F to 646°F.  The tempera-
                                      120

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ture spread during the transient load condition is quite large: 569° F to
679° F.  The resistivities were measured in the laboratory.  Previous studies
on other precipitators have indicated that resistivities determined by in-situ
and laboratory measurements are in reasonable agreement at high temperatures.
The resistivity-temperature dependence for the transient and 3/4 load condi-
tions are shown in Figure 3.  These data demonstrate that the resistivities do
increase at the lower temperatures associated with the low loads.  The resis-
tivities at low load would not be expected to cause precipitator problems.
The critical resistivity for back corona initiation associated with hot-side
precipitators is suspected about the order of magnitude lower than for the
cold-side unit.

     The comparison between the resistivity for the transient load condition
appears to be higher than corresponding resistivity at 3/4 load condition for
a given temperatures.

     This suggests there could be a difference in flyash characteristics between
transient and 3/4 stable load.  In order to assess this effect, a comparison of
the chemical properties of the inlet flyash for the transient load and 3/4 load
conditions was made and is presented in the following table:
Condition
Transient
3/4 Load
LOI
11.22
12.34
Si02
37.13
36.49
Fe203
3.77
3.01
A1203
28.85
26.81
CaO
5.63
5.05
MgO
2.26
2.17
Condition
Transient
3/4 Load
so3
2.25
2.17
Ti02
3.93
3.54
K20
0.30
0.29
P20
0.75
0.83
Na20
0.35
0.30
Li20
0.06
0.06
     A comparison of this data does not indicate a significant difference in
the flyash properties due to boiler operation.

     The hypothesized mechanisms are reviewed with the findings from the test
program in the following table:
                                     121

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              MECHANISM
              FINDINGS
 Dust Dropout
•  Extremely high inlet loading
   measured during transient
   condition.

•  Particle size data for transient
   condition higher than stable load.

•  Mechanism could not be cause of
   performance degradation from high
   load to low load transient.
 Particle Size Distribution of Flue
 Gas Properties Change at Lower
j Boiler Operation
•  Present data does not support this
   hypothesized mechanism.

I  Little data available at low load
   to totally disqualify this mechanism
 High Resistivity Problem at Partial j
 Load                                j
t  Transient resistivity appears higher
   than 3/4 load.

•  However, 3/4 load resistivities
   lower than previous full load data.
 Plate Dust Buildup
0  Additional plate buildup probable
   during transient loads due to high
   inlet loadings.
 Poor Gas Flow at Low Load Condition i   •  No data on this unit.
                                        t  Model study data on other units do
                                           not support this hypothesized mech-
                                           anism.
 Power Loss Due to Inability of Con-
 trols to Respond to Transient
 Conditions
t  Controls have adequately responded
   to transient load conditions.
Based on these results, the main contributions due to the degraded performance
at low load are:

                           •  High inlet particulate loading

                           I  High resistivity problem at partial load

                           t  Aging of dust material on collecting plates.

     The aging of dust material on collecting plates is described in the next
section.                              122

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HOT-SIDE ELECTROSTATIC PRECIPITATOR LONG-TERM PERFORMANCE DETERIORATION

     Several hot-side electrostatic precipitator units have experienced a
performance deterioration after several months of operation.  This has been
most pronounced with units operating with low sulfur fuel, such as Western
coal.

     The precipitator unit at Plant A, described in the previous section,
exhibited this type of long-term performance deterioration.  After several
months of operation, the unit's collection efficiency of 99.5% and corona
power level of 204 kilowatts decreased to a collection efficiency of less than
99% and a corona power level of 110 kilowatts.

     A detailed internal inspection of the unit indicated that ash buildup on
the collecting plates consisted of two distinct layers:  an outer layer of
gray, fluffy material, and an inner layer (adjacent to the plate) of white
crusty material.  The thickness of the inner layer was approximately 1/16 inch;
whereas, the outer layer thickness was approximately 1/8 inch.

     The inner layer, presumably, is older residue ash not removed by rapping;
whereas, the outer layer is collected transient ash, rapped free, and replaced
by newly-collected ash.

     The precipitator performance degrades after several months operation;
presumably, from change in the inner layer properties.   The residue dust layer
not removed by rapping undergoes alteration in properties with age.

     It was postulated that the inner layer significantly increases in resis-
tivity with time.  This change could be induced by thermochemical or electro-
chemical reaction.

     Analysis was performed with the inner and outer layer dust samples to
discern the differences between the inner and outer layer properties, as well
as to determine if the change was primarily a result of thermochemical or
electrochemical reaction.

Flyash Analysis

     Samples of each layer, as well as dust samples from the emitting wires,
were obtained during the internal inspection for chemical analysis.  These
samples were obtained from two similar precipitator units operating on similar
boilers with the same fuel source.  The results of the chemical analysis of
these dust samples are presented in the following table:
                                     123

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                           CHEMICAL/ANALYSIS  OF FLYASH
Sample Description
Inner Plate Layer
Plant A, Unit #1
Outer Plata Layer
Plant A, Unit #1
Inner Plate Layer
Plant A, Unit #2
Outer Plate Layer
Plant A, Unit #2
Wire Sample
Plant A, Unit #1
Wire Sample
Plant A, Unit #2
Si02
35.5
39.2
34.1
39.2
42.1
42.1
AT 203
28.8
33.3
28.3
33.9
33.4
34.3
Ti02
1.42
1.64
1.35
1.61
2.41
2.26
Fe2C>3
6.76
4.02
8.00
3.57
4.08
3.73
MgO
2.08
2.40
2.16
2.41
2.45
2.48
CaO
7.34
7.32
7.00
6.98
5.50
5.57
MnO
0.11
0.11
0.11
0.08


Na20
0.42
0.37
0.36
0.43
0.46
0.39
K20
0.73
0.51
0.48
0.55
0.36
0.36
Li20
0.050
0.067
0.045
0.067
0.08
0.07
P2°5
2.52
2.58
2.34
2.64
1.23
1.10
S03
9.1
4.2
11.1
4.1
3.6
2.55
     The inner and outer layer differ most significantly in their Fe and S
content.  Identical samples of the inner and outer layer were analyzed by two
independent analysts.  The results from both analyses show the significant
difference in the Fe and S content between the inner and outer layer.  It is
likely that the inner layer is formed by a chemical reaction among the S02,
503 in the flue gas and the plate:
S02 + 1/2 02
                                            S0
                                     flyash
                                     catalyst

                             |o2 + X S03 X Y H20 + Fe ->

                                         Fe

     X-ray diffraction patterns from the inner and outer plate layers were
         to discern differences between the layers.  Analysis of the X-ray
diffraction patterns shows a distinct difference in the relative intensities
of the X-ray peaks between the inner and outer layer.  These differences are
attributable to the iron-sulfur compound, referred to previously.

Resistivity

     The resistivities from the inner and outer layers were measured in the
laboratory, using a parallel plate arrangement in atmospheric air with relative
humidity control.   Figure 4 shows the temperature dependence of the resistivi-
ties of the inner and outer layers at 8% moisture.  The inner layer shows a
somewhat higher resistivity, principally at the lower temperature, than the
outer layer.
                                     124

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     In order to ascertain the extent of electrochemical effects upon  flyash,
a sample of hopper flyash mixture was maintained in the resistivity apparatus
with a potential of 2KV applied at the condition of 700°F and 8% moisture.
To discover the effect of temperature only, another hopper flyash sample was
maintained at 700°F and 8% moisture.  The resistivity for these two samples
was obtained over an extended time period.  The flyash resistivity measure-
ments from the experiment are presented in the following table:

                              FLYASH RESISTIVITY
Time
(Hrs.)
3
6
9
62
Heated Sample
1.97 x 109 ohm-cm
1.96 x ICr ohm-cm
1.96 x 109 ohm-cm
1.67 x 1010 ohm-cm
Sample Heat Plus
Electrical Current
2.45 x 109 ohm-cm
3.25 x 109 ohm-cm
4.2 x 109 ohm-cm
9 x 10 9 ohm-cm
     These resistivity experiments show that the effect of electrical current,
 in addiiton to heat  does not significantly alter the flyash resistivity.  This
 suggests that the ash layer change is thermochemical.  It need not be electro-
 chemical reaction.

 Power-Off Rapping

     The use of power-off rapping was attempted in the field in order to stop
 the power deterioration.  Results of the electrical readings for Plant A, with
 one side having normal rapping and the other half of the unit employing power-
 off rapping, are shown in the following table.  Results after 8 weeks of oper-
 ation  indicate the improvement was due to .power-off rapping technique.
FOR Side
TR Set
A
C
E
G
J
L
Secondary
KV
20
19
FOR
21
21
33
Secondary
AMP
.86
.44

1.30
1.38
1.31
Non-POR Side
TR Set
B
D
F
K
H
M
Secondary
KV
Off
26
24
25
24
22
Secondary
AMP

.58
.39
.40
.20
.19
                                       125

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SUMMARY

     The load variation performance of hot-side electrostatic precipitators
has  been found to differ from cold-side electrostatic precipitators.

     The governing condition for the proper design of precipitators can be
partial boiler load condition, rather than full boiler load condition.   The
partial load condition can require the precipitator to adequately collect a
higher loading of higher resistivity particulates than would be present at
the full boiler load condition.

     The hot-side precipitator can adequately perform through boiler load
variations by the following approach:  Precipitator design should reflect the
governing condition, as well as use an intelligent rapper system, advanced
electronic control system, and power-off rapping with a high degree of
sectionalization.
                                     126

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References

1.  White, H. J., Electrostatic Precipitation/Fly Ash, Journal of the Air
    Pollution Control Association, Volume 27, No. 1, January 1977.

2.  Lane, W. R., Factors Detrimental to Electrostatic Precipitator Performance
    ASME  '77, WA/APC-7, 1977.

3.  Tassicker, 0. J., Performance of Cold-Side and Hot-Side Electrostatic
    Precipitators Treating High Resistivity Fly Ash
                                      127

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   99.5
   99
   98
O
   97

M-  96
O
LLJ
O
O
95


93


90

80


70

60


40
                                                TEMP. 240°F
                                          LOWSULFURNEWCOMASH
      100    150    200    250    300   350    400    450    500    550   600
                   SPECIFIC COLLECTING AREA, SQ. FT./1,000 CFM
       Fig. 1 — COLLECTION EFFICIENCY AS A FUNCTION OF SCA
                                 128

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99.9
      DEUTSCH-ANDERSON
            PREDICTIONS
                        PLANT A

                          PLANTB
          PLANT A MEASURED
                   PLANTS MEASURED
98.5
PLANT A
PLANTS
135     145      155     165
300     325      350     375
   MEGAWATT PRODUCTION
    Fig. 2 — HOT SIDE PRECIPITATOR PERFORMANCE WITH LOAD
                              129

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 1010
                                    TRANSIENT
o
  109
CO

CO
UJ
DC
         STABLE 3/4 LOAD
  108
             550
750
     Fig. 3 -
                 650
           TEMPERATURE, °F

RESISTIVITY VS. TEMPERATURE AT PLANT A
                             130

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    1011
o
X
o
co

CO
LU
DC
    1010
                                           INNER LAYER
                      OUTER LAYER
    109
       Fig. 4
  600               700

              TEMPERATURE, °F

— RESISTIVITY VS. TEMPERATURE

                 131
                                                  800

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                          FLY ASH CONDITIONING BY
                   COPRECIPITATION WITH SODIUM CARBONATE
                                    by

                               John P. Gooch
                            Roy E. Bickelhaupt
                        Southern Research Institute
                         Birmingham, Alabama 35205

                                    and

                             Leslie E. Sparks
               Industrial Environmental Research Laboratory
                   U.S. Environmental Protection Agency
               Research Triangle Park, North Carolina 27711
                                 ABSTRACT
     A temporary solids handling system has been installed at a 55 MW coal-
fired utility power boiler to inject sodium carbonate powder into the flue
gas stream entering an electrostatic precipitator.   The coal used in the
boiler produces a high resistivity fly ash under normal operating conditions
at 160°C.  Field measurements and supporting laboratory studies are underway
to evaluate the concept of attenuating resistivity  by coprecipitation of
sodium carbonate powder with fly ash on the collecting electrodes of the
precipitator.  This paper gives a progress report on results obtained thus
far.
                                     132

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                         FLY ASH CONDITIONING BY
                  COPRECIPITATION WITH SODIUM CARBONATE
INTRODUCTION

     This paper presents the results obtained to date on a field trial of
sodium carbonate conditioning of fly ash conducted by Southern Research
Institute under contract with the Environmental Protection Agency.  The con-
tract includes as major tasks:  1) the selection of a suitable boiler for the
use of sodium conditioning in a cold-side precipitator collecting ash from a
low-sulfur, low-sodium western coal; 2) the design of a dry, cold-side sodium
carbonate injection system; 3) an evaluation of the precipitator performance
with and without conditioning; and 4) a comparison of sodium conditioning and
sulfur trioxide conditioning.

     The project, with the cooperation of the Department of Public Utilities
of the City of Colorado Springs, Colorado, involved the Martin Drake Power
Station Unit 5 boiler.  This installation provided suitable circumstances for
the conditioning evaluation, including a sulfur trioxide injection system for
the electrostatic precipitator which could be used for direct comparison of
the two conditioning processes.
BACKGROUND

     In 1971 research involving fly ash resistivity was conducted under the
sponsorship of Calgary Power Limited of Calgary, Alberta,  Canada.  Later this
research was formally presented by Bickelhaupt.1  This work ultimately led to
the unequivocal evidence that, in the absence of significant concentrations of
sulfuric acid vapor, the conduction process in fly ash is  principally controlled
by the ionic migration of sodium ions.

     As a consequence of this work, an attempt was made to attenuate the
resistivity of fly ash on a commercial scale by  conditioning with sodium com-
pounds.  Laboratory experiments showed that resistivity could be markedly
decreased a predictable amount by simply mixing  a compound such as sodium
carbonate with the fly ash.  However, since the  time involved required a quick
decision, it was suggested that the commercial conditioning experiment should
involve adding the sodium compounds to the coal feed.  Since Calgary Power
normally burns coal that produces ashes containing 2 to A percent "sodium
oxide," management accepted this suggestion.  Three compounds were used as a
                                     133

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sodium source.  In each case, the in situ resistivity of the ash was reduced
from ^IxlO12 ohm cm to ^1-5x1010 ohm cm when the sodium "oxide" content of the
ash was increased to ^2.5 percent from the inherent 0.3 percent.  Parts of
this research and the results of the sodium conditioning field tests were later
recorded by White2 in a review of resistivity problems.

     Subsequently a report by Bickelhaupt3 was issued outlining the rudimentary
principles for conditioning by adding sodium compounds to the coal feed.  This
technique has not been widely used because of potential slagging, fouling, or
corrosion problems related to boiler operation.  Southern Research Institute
has participated in two additional short-term field studies involving the
addition of sodium carbonate to the coal feed.  In one case, the results were
marginally successful; in the other, they were uninterpretable.  (No serious
attempt was made to define the reasons for the degree of success.)  Considerable
effort is sometimes required to determine the reason for an unsuccessful demon-
stration or execution of a process that is theoretically and technically valid.
Recently, the authors have been advised that successful sodium conditioning
has been conducted in which sodium carbonate was added to the coal feed.

     Unsophisticated laboratory experiments have been conducted to illustrate
the effectiveness of ammonium ions and alkali metal ions for increasing the
electrical conduction of fly ash.  Experiments have also been run to examine
the conduction mechanism related to sodium at high and low temperatures.
However, no laboratory experiments regarding the techniques or procedures for
fly ash conditioning have been conducted by Southern Research Institute.

     The first observations of the influence of sodium concentration of fly ash
resistivity were made at the Grand Forks, North Dakota, Energy Research Center
during studies of fouling potentials for lignites and other western coals.
After simple laboratory experiments, more sophisticated evidence was obtained
regarding sodium conditioning.  The possible use, as conditioning agents, of
fly ashes having very large concentrations of sodium and other high sodium ores
and minerals was reported by Selle, et al.1* and Selle and Hess.5  By reentrain-
ing premixed, -100 mesh blends of high resistivity ash and sodium compounds
into an environmentally controlled cold-side pilot precipitator, the effective-
ness of sodium conditioning was evidenced by increased migration velocity and
decreased in situ resistivity.  This effect was similar to the coprecipitation
of fly ash with sodium compounds formed j.ri situ by reaction between volatilized
sodium and other gaseous species.  The investigators acknowledged that problems
concerning agent delivery and optimum particle size could develop in translating
these experiments to a commercial venture.  These papers represent the first
reported effort to examine sodium conditioning in which the agent was not added
to the coal feed.

     The first commercial utilization of sodium conditioning on a continuous
basis involved a hot-side precipitator.6  Observing that low-sulfur, low-
sodium western ashes can have high resistivity at hot-side temperatures and
that dielectric breakdown strength is lower, sodium conditioning was attempted.
To avoid the boiler, the sodium compound was added as an aqueous solution
atomized into the gas stream between the economizer and the precipitator,

                                     134

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     No information was given about the fly ash-sodium compound homogeneity
or the concentration of sodium with or without conditioning.  However, the
reported precipitator efficiency data, the current-voltage relationships,
and the in situ resistivity data indicate that the conditioning procedure was
highly successful.

     Schliesser attempted to demonstrate the effectiveness of sodium carbonate
as a conditioning agent using a pilot precipitator and the cold^side slipstream
from a commercial boiler.7  This test used a dry injection system that deliv-
ered a controlled amount of sodium carbonate powder (8 ym mmd, Banco) to the
slipstream.  The fly ash was produced from a low-sodium, low-sulfur western
coal.

     Although there are certain ambiguities in the results and procedures,
the general conclusion was that the conditioning effect was significant.
In situ resistivity data showed considerable scatter and contained values much
too high for the stated concentration of sodium carbonate.  Unfortunately
sodium concentrations from the resistivity probe samples and pilot precipitator
collection plates were not available.  In spite of the minor effect on
resistivity, efficiency determinations and allowable current density values
indicated that a desirable conditioning effect had occurred.

     Laboratory, pilot precipitator, and commercial results involving sodium
conditioning have recently been reported for hot-side installations by
Lederman et al.8  Laboratory tests utilized a wire-pipe precipitator and re-
entrained ashes that were coated with conditioning compounds by dry mixing or
spraying with solutions.  All compounds containing alkali metal ions gave
favorable results.  Later an aqueous solution of sodium carbonate was sprayed
into the duct work prior to extraction of a slipstream to a wire-pipe pilot
precipitator.  Current-voltage data and efficiency measurements indicated that
favorable conditioning had been achieved.

     Based on these data, sodium conditioning (sodium carbonate)  for hot-side
units has been put into commercial service utilizing both aqueous solutions
and dry powder injections.  Efficiency and current density measurements  were
given in evidence of their success.

     In summary, data have been accumulated showing the technical feasibility
of sodium conditioning both in the laboratory and commercially with respect
to additions of sodium compounds to the coal feed and either dry  or as aqueous
solutions preceding a hot-side precipitator.  Data from pilot precipitator
tests have shown the effectiveness of sodium compounds injected dry as condi-
tioning agents when used in conjunction with cold-side precipitation.  From the
available information, a commercial evaluation of sodium conditioning by dry
injection of sodium carbonate into the gas stream between the air preheater and
the precipitator seemed in order.

PLANT AND PROCESS DESCRIPTION

     Unit 5 at the Martin Drake Power Plant is owned and operated by the
City of Colorado Springs, Colorado.  The unit is rated at 44 MW,  and includes
a Riley Stoker Pulverized Coal Boiler which is a front wall fired, balanced

                                     135

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draft furnace.  Unit 5 is normally operated at a 54 MW generating rate and
fires approximately 22,680 kg (25 tons) of coal per hour.  The typical coal
burned at Martin Drake is a low-sulfur, low-sodium coal obtained from mines
near Craig, Colorado.

     The electrostatic precipitator installed on Unit 5 was manufactured by
American Standard, Inc., and was designed to operate downstream of a mechani-
cal collector with a collection efficiency of 96.0 percent at a design specific
collection area (SCA) of 77.2 m2/(m3/sec) (392 ft2/1000 acfm).   There are four
electrical fields in the direction of gas flow, and each field is powered by
one transformer rectifier (TR), which is connected to two electrical bus
sections each of which is operated in a half-wave mode.  Each field consists
of 46 gas passages spaced 22.9 cm (9 in.) apart.  The collecting electrodes
are 2.29 m (7.5 ft.) deep and 9.14 m (30 ft.) high which results in 1932 m2
(20,700 ft2) of collecting surface per field.  The discharge electrodes are
straight 2.7 mm (0.106 in.) diameter wires spaced 17.8 cm (7 in.) apart in
the direction of gas flow.  Each field is equipped with 12 electric impulse
rappers for the collection electrodes and 4 electric vibrators  for the dis-
charge electrodes.  A sulfur trioxide injection system enables  the precipita-
tor to maintain plume opacity below 20 percent.

     The soda ash injection system consisted of a vessel for storing sodium
carbonate powder, a flexible screw feeder for unloading barrels of sodium
carbonate into the storage hopper, two parallel metering feeders followed by
rotary air locks, and two blowers to convey the powder from each feeder into
the duct.  The conveying lines discharged the sodium carbonate  powder onto
two dispersion cones to improve the distribution of the powder  across the
inlet duct.  Figure 1 is a schematic side view showing the location of the
injection nozzles and dispersion cones in the inlet duct work.

     Sodium carbonate powder for the conditioning experiment was obtained from
Stauffer Chemical Company from the dust collection system normally used to
collect the "fines" which are not suitable for standard applications.  Obtain-
ing the proper size distribution of sodium carbonate for the experiments was
an important consideration, since the size distribution of the  injected powder
will influence the uniformity with which the fly ash and conditioning agent
are coprecipitated.  It was considered impractical to install a pulverizer and
the necessary auxiliary equipment for an experimental program,  and it was
therefore decided to use the powder collected from the dust collection equipment
at Stauffer.  The variability of the size distribution from the source presented
a problem, as illustrated by Figure 2.  The material originally supplied from
the dust collection equipment gave a reasonable match with the  fly ash distribu-
tion at the precipitator inlet.  However, this parameter was not a controllable
variable, and the material later supplied in bulk was deficient in small C<2 ym)
diameter particle concentrations.  This problem was overcome by blending sodium
carbonate collected in the precipitator with that collected in the cyclone from
the dust collection system of the sodium carbonate plant.  The  symbol in Figure
2 indicating "20% fines" means that the mixture consisted of 20 percent by
weight of the sodium carbonate with the small size distribution from the

                                     136

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precipitator and 80 percent by weight of the coarser material from the cyclone.
Note that, below about 8 ym diameter, this mixture compares favorably with
material obtained from another sodium carbonate injection system which included
a pulverizer and a baghouse to crush and collect the material prior to injec-
tion.  Because of the indicated deficiency of sodium carbonate particles with
sizes of 8 ym and smaller compared to the fly ash, an injection rate was
selected which would provide approximately a 5 percent equivalent increment of
sodium oxide, approximately twice the intended dosage level.  This was done to
increase the mass of sodium carbonate that is collected in the outlet field'7
of the precipitator.

FIELD TEST PROCEDURES AND RESULTS

     The field work at the Martin Drake Unit 5 installation included the
following major  tasks:

     (1)  a limited performance evaluation of the precipitator
          with the sulfur trioxide conditioning system in
          operation;

     (2)  a detailed performance test of the precipitator with
          no conditioning of the fly ash;

     (3)  an evaluation of the performance of the sodium
          carbonate injection system;

     (4)  preliminary sodium carbonate conditioning trials
          with electrodes in a relatively unclean condition;
          and

     (5)  a detailed performance test of the precipitator
          with sodium carbonate injection used as condition-
          ing technique.

     The performance tests on the precipitator included size distribution
measurements at  the precipitator inlet and outlet with impactors, total
particle mass concentration and gas flow measurements using EPA Method 17 at
the  same location, resistivity measurements with an in situ point-plane probe
at the inlet sampling location, voltage-current measurements on the precipitator
power supplies,  and collection of coal and fly ash samples for chemical analysis.
Appropriate data from the control room instruments were also recorded during the
test program, including plume opacity from an in-stack transmissometer.  A
five-stage series cyclone was employed to collect size-fractionated samples of
fly  ash at the precipitator inlet for the determination of soluble sodium
content.

     Preliminary sodium  carbonate  injection  experiments were begun on
November  6,  1978 by  discontinuing  sulfur  trioxide  injection, starting the
sodium carbonate injection, and performing a power-off rapping procedure on
fields 1, 2, and 3 of  the precipitator.   The objective was  to  remove  as  much
                                     137

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of the residual dust layers from the plates as possible.  A similar procedure
was carried out during each of the following 24-hour periods, except that the
fourth field also received power-off rapping.  The precipitator input power
decreased, and opacity increased to well above 20 percent.  Since the opacity
meter and the TR meters suggested that the precipitator performance was
limited by dust resistivity, a plant outage was requested for November 11 and
12 to allow samples to be obtained from the precipitator electrodes for
chemical analysis.  The unit was brought off line on Friday evening,
November 10, and a plan was devised for collecting samples and determining
the effectiveness of the injection equipment in distributing sodium carbonate
throughout the precipitator.

     Table 1 gives the soluble sodium oxide concentrations obtained from
traverses at the inlet sampling plane with a five-stage cyclone and a mass
train with an in-stack filter during the preliminary injection trials.   These
data indicate that the injection equipment was delivering approximately the
intended dosage of sodium carbonate (equivalent to 5 percent sodium oxide),
and that the mixture of "coarse" and "fine" soda ash was providing sufficient
fine particle concentrations to result in a 1.5 to 3.3 percent sodium oxide
concentration increment in the finer size fractions.

     After the unit was shut down for the electrode sampling task, samples of
fly ash were obtained from the top of every third lane at the inlet and exit
of each field.  Similarly, samples were obtained approximately 1.5 meters from
the bottom of the precipitator plates where access to this region was  possible.
Selected discharge wires were also chosen for sample procurement.   The  precipi-
tator was not rapped after the TR sets and the soda ash feeding system was de-
energized so that the ash layers on the plates would represent the composition
existing during the operation of the unit.

     The samples of fly ash obtained from the electrodes were analyzed for
soluble sodium content, and the results are displayed in Figures 3 and  4 as  the
percentage of equivalent sodium oxide.  Previous analytical work with this fly
ash indicated that an insignificant portion of the naturally occurring  sodium
in the fly ash is water soluble.  Therefore, determination of the water solu-
ble sodium content indicates the amount of sodium contributed by the condition-
ing system.  The data in Figures 3 and 4 indicate that, after 4 days of opera-
tion, the conditioning system had distributed the sodium carbonate with
reasonable uniformity across the width of the precipitator.   The outlet fields
contain lower concentrations as would be expected.  However, the data from the
leading edge of the last field indicates an incremental sodium concentration
which, when combined with the naturally occurring sodium, should give a useful
resistivity reduction if the sodium compound is properly distributed.

     Data from the top of the precipitator plates indicate uniformly low
concentrations of soluble sodium.  The dust layers in the region near the top
were thin (^ 1 to 2 mm), and it is hypothesized that the dust collection rates
in this region are low and that the relatively thinner layers at the top
resulted in a higher ratio of residual ash to recently collected ash than is
present at lower plate elevations.  Since residual unconditioned ash layers on
the plates would form a high resistance in series with recently collected ash,
an effort was made to obtain layered samples which would provide data on sodium

                                    138

-------
concentration as a function of distance from the plate.  These data are dis-
played in Table 2 and indicate the expected decrease in soluble sodium oxide
concentrations with decreasing distance to the plate surface.  These data
could only be obtained at lower plate elevations due to the previously mentioned
thin dust layers near the top of the plates.  However, it is apparent from the
data obtained on samples from the top elevation that residual dust layers
adjacent to the plate will be deficient in added sodium.

     The relatively poor precipitator performance experienced during this
injection trial was consistent with laboratory data obtained using a series
arrangement of high and low resistivity dust.  Therefore, it was decided that
it would be necessary to wash the precipitator and initiate the sodium carbonate
injection simultaneously with the firing of coal in the boiler in order to ob-
tain a proper evaluation of the coprecipitation conditioning method under cold-
side precipitator operating conditions.

     The precipitator was thoroughly washed during a regularly scheduled outage
in April 1979, and the unit was brought on line May 2 with the sodium carbonate
injection system in operation.  A performance test of the precipitator was
conducted during the week of May 14, and the injection trial was continued
through May 25, 1979.  At full load operation (54 MW), the plume opacity
exiting the precipitator varied from 12 to 44 percent during the time that
sodium carbonate was injected.  Since it was demonstrated that the plume
opacity could not be continuously maintained below 20 percent and since the
electrical operating parameters did not indicate that effective resistivity
attenuation had been accomplished, the field trials were terminated on May 25,
1979.  As of this report, data from the test series are still undergoing
analysis.  However, sufficient information is available to allow conclusions
to be drawn regarding the use of the dry powder coprecipitation technique as  a
means of accomplishing sodium conditioning of fly ash under cold-side operating
conditions.

     Secondary voltage and current data from the precipitator power supplies
for the three performance tests are given in Table 3 and Figure 5.  The
voltage-current relationships in Figure 5 have been selected from a large
number of V-I curves which were obtained on each power supply during each day
of the three test series and are representative of electrical conditions
existing at the precipitator inlet and outlet during the measurement programs.
The sensitivity adjustments on the TR set control panels were adjusted manually
by the plant electrician to obtain the maximum voltage possible in the absence
of excessive sparking during each test series.  It is obvious that, during the
sulfur trioxide injection test sequence, the precipitator exhibited more
favorable electrical operating conditions than were indicated during the base-
line or the sodium carbonate test series.  Both the baseline and sodium carbon-
ate test series V-I curves indicate that the operating points are severely
limited by dust resistivity.  This indication is consistent with resistivity
measurements obtained in the field which is discussed below.

     The interpretation of field resistivity data was complicated by the
variability of the inherent sodium content of the ash.  This variability is
illustrated in Figure 6 by the sodium oxide concentrations of fly ash collected
in the resistivity probe during the sulfur trioxide conditioning test series.

                                     139

-------
Also shown are sodium oxide concentrations of ashes obtained from the economizer
hopper and from filters which collected test samples at the precipitator inlet
and the mechanical collector inlet.  The following general conclusions could
be drawn from the in situ resistivity data obtained during the three test
series:

     9 The sulfur trioxide injection system reduced resistivity
       from an average of SxlO11 to 6xl010 ohm cm at ^153°C
       during the sulfur trioxide test series.  The sulfur tri-
       oxide concentration at the precipitator inlet averaged
       8 ppm.

     • The in situ resistivity of typical Martin Drake ash
       without conditioning was ^1x1012 ohm cm at ^160°C.

     • The resistivity of fly ash collected in the probe was
       not effectively reduced by coprecipitation with sodium
       carbonate, even when the sample on the probe collection
       plate contained as much as 7.9 percent soluble sodium as
       sodium oxide.  This is illustrated by the data contained
       in Table 4.

     The averaged collection efficiencies of the precipitator during each of
the three test series are given in Table 5.  It is obvious from these data that
the sodium carbonate coprecipitation process was relatively ineffective as a
conditioning technique compared to the sulfur trioxide injection.   The perfor-
mance data suggest that the sodium carbonate injection resulted in improvement
of the collection efficiency compared to the baseline test series, but the
improvement was not sufficient to allow the 20 percent plume opacity limit to
be maintained as Figure 7 illustrates.  Figure 8 displays the size dependent
efficiency data obtained with impactors during the three test series.  These
data consistently show the same order of performance as the mass train data
given in Table 5.

     The analysis, of the precipitator performance during the three test series
is still in progress.  Chemical analyses for the sodium carbonate test series
are also still in progress, but sufficient work has been completed to indicate
that the injection system was delivering the sodium carbonate to the precipita-
tor at a rate no less than the intended dosage increment of 5 percent sodium
oxide equivalent.  Soluble sodium concentration in fly ash samples obtained
from mass train filters which had traversed the inlet sampling location are
given in Table 6, along with similar data obtained from precipitator hopper
samples.  Typical fly ash and coal composition data from the baseline test
series are displayed in Tables 7 and 8, respectively.

SUPPORTING LABORATORY STUDIES

     In the preceding section the ineffectiveness of sodium conditioning was
documented for the process in which the sodium compound is injected as a dry
powder into the flue gas between the air preheater and the precipitator inlet.
This occurred even though every conceivable precaution was taken to ensure that
the conditioning results would not be masked by the condition of the precipita-

                                     140

-------
tor, inferior conditioning agent injection system, etc.

     It has been shown that the injection system delivered the intended concen-
trations of a dry sodium carbonate powder selected to have a particle size
distribution similar to that of the ash to be conditioned.  Furthermore, chemi-
cal analyses have shown that the injected agent was present in the collected
fly ash to a degree that should have registered a significant influence on
the precipitation characteristics.  The failure to achieve expected results is
not uncommon with respect to conditioning agent trials.  Usually one does not
have the opportunity to determine the reason for a given end result.  In this
instance, a strong effort was made both in the field and in the laboratory to
explain our results.

     Resistivity data expressed as a function of sodium concentration  show
that an inherent fly ash sodium concentration of about 2 to 3 percent expressed
as oxide will produce a resistivity of 1 to 5xl010 ohm cm at 145°C.  Although
the inherent sodium "oxide" concentration at Martin Drake was found to be as
high as 3.0 percent on occasion, the usual concentration is 0.4 to 0.6 percent.
Therefore, the standard laboratory addition for "conditioning" was 3.5 percent
sodium carbonate.  This addition would yield a combined inherent and added
sodium "oxide" concentration of about 2.5 percent.

The Effect of Sodium Carbonate Concentration Added

     Several blends of a typical Martin Drake fly ash with various concentra-
tions of sodium carbonate were prepared.  A dry sodium carbonate having a
Bahco mmd of 8 ym was used.  In conducting this type of experiment, one must
select a procedure to blend the fly ash and the conditioning agent.  The fly ash
was placed in a mortar, and the required amount of brilliantly white soda ash
was placed on top.  The two components were stirred together with a pestle with
no intentional grinding until the two colors were not visually discernible.
This procedure was used previously at various times and is herein identified as
Severity of Mixing No. 2 (SM2).

     Using blends of this description, laboratory resistivity determinations
were made to illustrate the effect of the amount of sodium carbonate added.
The environment for the resistivity test10 contained no sulfur oxides.  The data
from three tests are shown in Figure 9 for sodium carbonate additions of 0.0,
3.5, and 30.0 percent by weight to a typical Martin Drake fly ash.  The 3.5
percent addition produced the expected attenuation of resistivity.  The 30.0
percent addition shows the effect of establishing a continuous matrix of
sodium carbonate throughout the resistivity specimen.  This resistivity curve
is almost identical to the data produced for a resistivity specimen consisting
of 100 percent sodium carbonate.

     These data point out the severe discrepancy between the laboratory results
and the performance of the conditioning agent in the field.  In both cases, fly
ash has been treated with a concentration of sodium carbonate capable of
producing a significant degree of resistivity attenuation; however, this is
manifested only in the laboratory test.

                                       141

-------
The Effect of Fly Ash-Soda Ash Homogeneity

     The degree of intimacy or homogeneity between fly ash particles and
sodium carbonate particles was considered as a possible explanation for the
observed results.  Resistivity experiments similar to those described above
were conducted to evaluate the effects of the severity of mixing for a given
amount of added sodium carbonate, 3.5 percent.  In this series of tests
sodium carbonate having a Bahco mmd of ^ 30 ]Jm was used.

     In one case a laboratory resistivity cell was loaded by alternately adding
fly ash and then sprinkling on a portion of the pre-weighed, required amount
of sodium carbonate until a layered mixture filled the cell.  This was
designated Severity of Mixing No. 1 (SMI).  A mixture was also prepared using
the previously described procedure SM2.  A third blend of fly ash and sodium
carbonate was prepared in a manner similar to that described as SM2 except the
simple stirring action was replaced by vigorous grinding  action.  The later
blend was labeled Severity of Mixing No. 3 (SM3).

     Figure 10 shows the results of these tests.  When the soda ash was layered
into the fly ash (SMI), only a minor attenuation of resistivity occurred.
Mixing procedure SM2 caused a decrease in resistivity equivalent to that which
would be anticipated for a comparable change in Inherent  sodium "oxide"
concentration.  The most severe mixing (SM3)  caused a reduction in resistivity
much greater than one would predict based on the effect of inherent sodium
concentration.

     These data suggest several interesting points.  First,  it would seem quite
possible that the degree of homogeneity between the fly ash  and sodium carbonate
produced by SMI is similar to that produced during coprecipitation of the fly
ash and the sodium carbonate in the full scale precipitator.  If this is true,
the ineffectiveness of the conditioning trials can be understood.   It is hoped
that, in the concluding effort of this program,  samples of ash retrieved during
conditioning tests will be examined in the laboratory to  determine resistivity
and degree of homogeneity.  The degree of homogeneity could  be evaluated by
determining the smallest random sample that can be taken  from a large sample
and still contain the average concentration of sodium oxide.  A comparison of
this type for field samples and samples prepared in the laboratory should be
informative.

     The second point of note is with regard to SM2 producing an attenuation
of resistivity equal to the amount of decrease one would  expect from an
equivalent change in inherent sodium concentration.  This degree of mixing or
homogeneity produces this effect simply by chance.  In retrospect, this was an
unfortunate occurrence because it equated the effect of added sodium to that
of inherent sodium.  Intuitively one would expect  the added  sodium to be more
effective on a weight basis.

     The third point is that these data suggest that a much  lower concentration
of sodium is required to attenuate resistivity a specific amount than is
predicted from data based on inherent sodium concentrations.  The key to the
conditioning technique is the efficient transfer of the agent to the fly ash
to produce a reasonably homogeneous mixture.   This point  is  emphasized by the
data shown in Figure 11.  In this series, SM3 was  used with an extremely fine
                                     142

-------
sodium carbonate.  The combined vigorous grinding and ultra fine soda ash
produced a significant attenuation of resistivity with only a 0.5 percent
addition of agent.

Laboratory Evaluation of Series and Parallel Circuits Created from Uncondi-
tioned and Conditioned Ash

     In the discussion of field test results, it was pointed out that the
effect of a solid conditioning agent used to attenuate resistivity would be
negated if a layer of unconditioned ash prevailed on the collection plates.
This apparently obvious statement was demonstrated with a laboratory experi-
ment.

     A quantity of conditioned ash was prepared using 3.5 percent sodium
carbonate blended with a typical Martin Drake fly ash employing SM2.  Using
a 5 mm deep, ASME, PTC-28 resistivity cell, a test specimen was prepared by
filling the cup with 2.5 mm of unconditioned ash topped by 2.5 mm of condi-
tioned ash to illustrate the series effect.  Another cell was prepared so that
50 percent of the current measuring electrode area superimposed a 5 mm deep
layer of conditioned ash while the other 50 percent of the electrode covered
a 5 mm deep layer of unconditioned ash to develop a parallel circuit.

     The results of these experiments are shown in Figure 12.  As anticipated,
overlaying a layer of high resistivity dust with a properly conditioned layer
of dust has little effect.  The result is essentially equivalent to halving
the thickness of the high resistivity layer.  The parallel circuit experiment
demonstrates that if a significant collection plate area is clear of high
resistivity ash, a homogeneously conditioned ash will show an improved
precipitator performance.

CONCLUSIONS AND RECOMMENDATIONS

     • This research indicates that conditioning to attenuate
       resistivity for cold-side precipitation using a process
       involving the coprecipitation of fly ash and an
       injected dry powder can be ineffective.  In the specific
       case, anhydrous, 30 urn mmd, sodium carbonate was
       injected at ^ 150°C.

     • The above conclusion is opposed to the results mentioned
       in the background section with respect to similar experi-
       ments utilizing a pilot precipitator and a commercial
       flue gas slipstream.

     • In no way do these results imply that sodium condition-
       ing is ineffective when the additive is injected either
       as a fine dry powder or in an aqueous solution to either
       the coal feed or the flue gas stream at a temperature
       equal to or exceeding hot-side operation.

     • This research emphasizes the need for caution when
       quantitatively interpreting the results of laboratory

                                     143

-------
       tests including pilot precipitators that demonstrate
       conditioning effects using premixed fly ash/condi-
       tioning agent blends.

     • Assuming a high degree of homogeneity between fly
       ash and sodium additive, the sodium addition required
       for a given resistivity attenuation is apparently
       less than would be predicted from resistivity/
       sodium concentration relationships based on inherent
       sodium.

     » Methods of achieving the required degree of homogeneity
       for sodium conditioning with practical injection
       methods should be explored,

ACKNOWLEDGMENTS

     The cooperation and assistance of Ronald L.  Ostop,  Senior Environmental
Engineer of the Department of Public Utilities of the City of  Colorado  Springs,
is greatly appreciated.  The assistance of plant  personnel at  the Martin Drake
Power Station is also greatly appreciated.

REFERENCES

1.   Bickelhaupt, R. E.  Electrical Volume Conduction in Fly Ash.   APCA
     Journal.  24 (3) 251-255.  March 1974.

2.   White, H. J.  Resistivity Problems in Electrostatic Precipitation.
     APCA Journal.  24 (4) 314-338.  April 1974.

3.   Bickelhaupt, R. E.  Sodium Conditioning to Reduce Fly Ash Resistivity.
     EPA-650/2-74-092^ NTIS No. PB236-922.  U. S. Environmental Protection
     Agency, Research Triangle Park, North Carolina 27711.   October 1974.

4.   Selle, S. J., L. L. Hess, and E. A. Sondreal.   Western Fly Ash Composition
     as an Indicator of Resistivity and Pilot ESP Removal Efficiency.   Paper
     75-02.5 presented at:  68th Annual Meeting of the Air Pollution Control
     Association, Boston, Massachusetts.  1975.

5.   Selle, S. J., and L. L. Hess.  Factors Affecting ESP Performance on
     Western Coals and Experience with North Dakota Lignites.   In:   Symposium
     on Particulate Control in Energy Processes.   EPA-600/7-76-010, NTIS No.
     PB260-499,  1976.  p. 105-125.

6.   Walker, A. B.  Operating Experience with Hot Precipitators on Western Low
     Sulfur Coals.  Presented at:  American Power Conference,  April 18-20,
     1977.  Palmer House, Chicago, Illinois.

7.   Schliesser, S.  P.  Sodium Conditioning Test  with EPA.Mobile  ESP.   In:
     Symposium on the Transfer and Utilization of Particulate  Control Tech-
     nology:  Volume 1.  Electrostatic Precipitators.  EPA-600/7-79-044a,
     NTIS no. PB295-226,   1979.  p. 205-240.

                                      144

-------
 8.    Lederman,  P.  B.,  P.  B.  Bibbo,  and J.  Bush.   Chemical Conditioning of Fly
      Ash for Hot Side  Precipitation.  In:   Symposium on the Transfer and
      Utilization of  Particulate  Control  Technology:  Volume 1.  Electrostatic
      Precipitators.  EPA-600/7-79~044a,  NTIS No,  PB295-226,  1979.  p. 79-98.

 9.    Bickelhaupt,  R. E.   A Technique  for Predicting Fly Ash Resistivity.  In:
      Symposium on the  Transfer and  Utilization of Particulate Control Tech-
      nology:  Volume 1.   Electrostatic Precipitators.  EPA-600/7-79-044a,
      NTIS No. PB295-226,   1979.   p. 395-407.

10.   Bickelhaupt, R.  E. Measurement of Fly Ash Resistivity Using Simulated
     Flue Gas Environments.  EPA-600/7-78-035, NTIS No. PB278-758.  U. S.
     Environmental Protection Agency,  Research Triangle Park, North Carolina
     27711.  1978.
                                      145

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   Table  7.   Soluble  A/a  from Na^CO^  test series.
                                         Table 2.
                                             contents in  layered samples.

DAT
W1S/
5/19-
b/21.'
G/22/
5/24;
5/2S/
5/19/





9 iViA
9 MA
9 MA
9 MA
9 MA
9 MA
9 HO




SOURC
S TRAIN
S TRAIN
S TRAIN
S TRAIN
5 TRAIN
S TRAIN
PER. ROV





TER
TES
TER
'£R
TER
TER
3 1ELD 1
FIELD 2
FIELD 3
FIELD 4
SOLUBLE Na ai
NsoO. %
6.0
6.6
11.3
7.5
6.2
5.1
90
12.2
2.5
2.4
                                                                                                  LANE 16, BOTTOM
                                                                                    LOCATION 	 PLATE MIDDLE OUTER
                                                                                 FIELD 1. NORTH SIDE,  15   2.1    4,6 -«	 Sclubla
                                                                                    BACK PLANE
                                                                                 FIELD 2, WORTH SIDE,
                                                                                    FRONT PLANE
                                       LANE 19, BOTTOM
                                       0.99  2.4   3.2 -«

                                       1.3   2.8   4.3 -«
                                                                  LANE 4, BOTTOM
                                                                 PLATE MIOPLEOUTEH
                                                                -»- 2.4   Z.6    6.1
                                                                                                                            - 2.9    29   5.3

                                                                                                                             LANE 4, BOTTOM
                                                                         - Soiublu

                                                                         - Total
                                                                                                                            -2.8
                                                                                                                            - 3.2
          40    4.1

          4.6    4.4
                                                                                         Table 4.    Resistivity probe data.
  Table 3.   Average operating points for TR sets.
                                                     CURRENT
                                                     DENSITY
                                                                                         SAMPLE DESCRIPTION

                                                                                   DATE  RUN NO.    LOCATION
                                                	 SOLUBLE Na  TEMP.  RESISTIVITY BREAKDOWN
                                                    as Na2O, %   °C    ohm-cm      kV/cm
TEST NO    CONDITION
  1
  2
                                  DATES    VOLTAGE, kV  nA/Cf
                   SO3 INJECTION    4/25-29/7b
                   BASELINE       10/10 ~ 14'7
                   NapCO-. INJECTION 5/1b-19,'7S
                        5/16/79
                        5/16/79
                        S/16/79
                                                        ROSE TOTAL CATCH
                                                        ROBE GUARD RING
                                                        ROBE COLL. PLATE

                                                        ROBE GUARD RING
                                                        ROBE COLL. PLATE
17S
Ml
177
2.7 x

2.5 x
Table 5,   Averaged precipitator performance comparison.
     DATE
               CONDI riON
                                      MASS CONCENTRATION
                          INLET GAS-FLOW 	mp/'DNCM	 PENETRATION OPACITY
                             DNCM/iai
   4/28-4/29/78  SOs INJECTION       62.2
   10/13-10/14/78 BASELINE           56.7
   5/18-5/25/79  Na2C03 INJECTION     57.2
INLET
2395
2229
2525
0.91
12.5
6.46
ib/e 6.
DATE
11/7/78




11/8/78




Soluble A/a2'
°50
RUN ym
MOICY10 6.79
3.45
1.39
1.09
056
MOI-CY11 5.51
2.81
1.62 «
0.89
0.45
0 contents.
Ma2O
i5.2
6.6
3.3
3.3
2.8
12.1
4.8
2.0
1.7
1.5
                                                                                          11/S/7B - Mass train sample from inlet

                                                                                          11/10/78 - Mass train sample from inlet
                                                                      146

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Table 7.   Fly ash composition - baseline test series.
                                                        Soluble
Date Field Row
10/10/78 1 3
2
3
4
10/11/78 1 2
2
3
4
10/12/78 1 3
2
3
4
10/13/78 1 3
2
3
4
10/14/78 1 3
2
3
4

Date 10/10/78
Time 10:00 AM
As -Received
Proximate , Wt . %
Moisture 11.07
Volatile Matter 35.91
Fixed Carbon 42.71
Ash 10.31
Sulfur 0.63
As-Received
Ultimate, Wt.%
Carbon 61.36
Hydrogen 4 . 07
Oxygen 11.15
Nitrogen 1.34
Sulfur 0.63
Moisture 11.07
Ash 10.31
LizO Na20
0.02 1.0
1.2
1.1
0.9
0.02 1.3
1.2
1.4
1.2
0.02 0.5
0.6
0.9
1.0
0.02 0.5
0.5
0.5
0.8
0.02 1.9
1 .7
1.0
1.1
Table 8.
K20 MgO CaO FejOa A12O3 SiO2 TiO2 P20s SO; SOi. LOI
1.1 1.4 4.9 5.0 27.1 55.7 1.0 1.5 0.3 0.5 4.1
4.5
3.0
3.0
1.0 1.6 5.8 5.5 26.6 52.8 1.1 1.5 0.3 0.6 5.2
3.5
2.7
2.7
0.9 2.2 7.1 4.3 29.5 51.8 1.0 1.4 0.4 0.6 3.8
4.3
3.5
4.5
1.5 1.6 4.8 4.6 25.6 57.6 1.0 0.9 0.3 0.5 3.6
3.8
3.6
3.3
1.1 1.7 5.8 4.8 25.3 56.2 1.1 1.0 0.5 0.6 1.9
1.7
3.5
2.5
Coal analyses from baseline test.
10/10/78 10/11/78 10/11/78 10/12/78 10/12/78 10/13/78 10/13/78 10/14/78 10/14/78
3:45 PM 10:
12.63 12.
37.45 38.
42.02 42.
7.90 1.
0.59 0.
61.83 62.
4.12 4.
11.76 11.
1.14 1.
0.59 0.
12.63 12.
7.90 7.
00 AM 4:00 PM 11:00 AM 3:00 PM 10:40 AM 3:30 PM 10:50 AM 1:10 PM
06 16.47 14.34 15.76 14.01 13.69 13.77 13.78
19 35.82 34.66 32.71 35.87 36.02 36.26 36.10
15 39.11 39.99 37.48 39.67 44.04 44.31 39.17
60 8.60 11.01 14.05 10.45 6.25 5.66 10.95
52 0.50 0.50 0.55 0.55 0.44 0.43 0.47
91 57.08 58.18 53.04 58.17 62.27 62.61 58.36
06 3.79 3.67 3.38 3.49 4.24 4.40 3.65
55 12.29 11.00 12.01 11.94 11.78 11.85 11.57
25 1.22 1.25 1.15 1.37 1.20 1.22 1.17
52 0.50 0.50 0.55 0.55 0.44 0.43 0.47
06 16.47 14.34 15.76 14.01 13.69 13.77 11.78
60 8.60 11.01 14.05 10.45 6.25 5.66 10.95
                     147

-------
          DISPERSION CONE




         INJECTION NOZZLE •*
                            BYPASS DUCT >
^
                                            INLET SAMPLING PORTS
                                                            TO ESP
                             GAS FLOW
Figure 1.  Schematic elevation view of sodium carbonate injection system.
         VI
         C/)
         LU
         O
90
80
60
40
20
10
5
2
1
n t.
I
AES
1
3 INLET • IMPACTORS

D ESP INLET • BAHCO
O ORIGINAL Na2CO^ - BAHCO
<
_ 1
•-
-


A


iMa
• Na




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    Figure 2. Particle size distributions of Martin Drake fly ash and

             sodium carbonate.
                                148

-------
                        SOLUBLE Na2O CONCENTRATIONS, wt %
                                  TOP ELEVATION
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                   22 19 16 13 10  7   4  1 22 19 16 13 10 7  4  1
                                                                                        SOLUBLE Na2O CONCENTRATIONS, wt %
        Figure 3.  Distribution of sodium after 4 days of injection,
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                                                                                              BOTTOM ELEVATION
                                                                                                               NORTH
                                                                                22  19 16 13 10  7   4  1 22 19 16 13 10  7   4  1
                            GAS FLOW


Figure 4. Distribution of sodium after 4 days of injection,

         bottom of precipitator.

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                                       150

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                                                                                                                     TEMPERATURE
                                      TEMPERATURE
        Figure 9.  Effect of the amount of sodium carbonate added
                    on  the resistivity  of a fly ash.
                                                                Figure 10.   Effect of the intensity of mixing fly ash and a given
                                                                              concentration of sodium  carbonate  on resistivity.

-------
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Figure 11.   Effect of sodium carbonate particle size and intensity
              of mixing on the resistivity of a fly ash.
                                                                                                                TEMPERATURE
Figure 12.   Effect on resistivity of unconditioned and sodium-
              conditioned ash forming series  and parallel circuits.

-------
                 PREDICTING  FLY  ASH  RESISTIVITY - AN EVALUATION
                                      by

                               Roy E.  Bickelhaupt
                          Southern Research Institute
                           Birmingham, Alabama 35205

                                      and

                                  L.E. Sparks
                  Industrial Environmental Research Laboratory
                      U.S. Environmental Protection Agency
                  Research Triangle Park, North Carolina 27711
                                    ABSTRACT
     Recently a technique for predicting fly ash resistivity from an as-re-
ceived, ultimate coal analysis and the chemical composition of the coal ash
produced by simple laboratory ignition was published.  This paper evaluates
this technique by comparing predicted resistivity data with laboratory mea-
sured values, in situ resistivity data, and precipitator performance informa-
tion acquired from 12 field test programs.  Considering the precision of
measurement generally encountered in precipitator technology and the limited
amount of certain laboratory data available, the results are encouraging and
the evaluation is favorable.
                                      154

-------
                 PREDICTING FLY ASH RESISTIVITY - AN EVALUATION
INTRODUCTION

     Electrical resistivity is an important property in the design of an elec-
trostatic precipitator for the dry collection of fly ash.  For a given col-
lection efficiency, high resistivity necessitates large precipitators requir-
ing greater capital investment and operating expense.  Although resistivity
data serve many purposes, the principal use of these data is for sizing precip-
itators with respect to design coals.

     If the given design coal is relatively uniform in character and the precip-
itator manufacturer has had experience with the coal, the design problem is
minimal.  This desirable situation is not available in many instances.  How-
ever, there are several ways in which the required resistivity data can be
obtained.  In situ resistivity measurements can be made if the coal is being
commercially burned.  When the design coal is not being burned in a full scale
boiler, small samples of the coal can be fired in laboratory scale boilers
to produce a fly ash.  The resistivity of ash produced in this manner can
be measured in situ or after removal from the flue system.  A third alter-
native is to predict the resistivity of the fly ash using the chemical composi-
tions of the ash and the flue gas.

     The subject of this paper is an evaluation of a method for predicting
fly ash resistivity.  Predicted resistivity values are compared with resis-
tivity data acquired in situ and in the laboratory.  To help interpret the
quality of the predicted data, precipitator efficiency and outlet-field cur-
rent density values are also considered.
BACKGROUND

     Recently a technique for predicting resistivity has been published.l  The
predictive technique is dependent on a series of correlations between labora-
tory-measured resistivity and the factors that influence this property.
Factors included are fly ash composition, flue gas analysis, and the field
strength in the ash layer.  A large number of fly ash specimens were used to
develop the correlations with the intention of minimizing the effect of  ash
layer porosity and specific surface.  Utilizing the chemical composition of a
coal ash and the flue gas composition calculated from the stoichiometric
                                      155

-------
combustion of  the  coal,  the  correlations  are used to predict fly ash resistiv-
ity.  The method is applicable to the most fundamental case; that is,  the
prediction of fly ash resistivity from a core bore sample of coal.

     Obviously the quality of the predicted  resistivity data depends on:
1) the relatively good agreement between the  true value of resistivity and
the value determined in  the  laboratory, 2) the ability to produce coal ash
having a chemical composition similar to fly  ash, and 3) the ability to predict
the flue gas analysis, in particular the amount of sulfur trioxide.  This
paper attempts to assess the quality of the  resistivity predictions.

     Table 1 illustrates the printout of data from the computer program based
on the subject predictive technique.  The first page of the table shows the
input of the as-received, ultimate coal analysis  from which the stoichiometri-
cally calculated flue gas composition is acquired using  30 percent  excess  air.
The data critical  to the calculation of resistivity  are gathered at the bottom
of the page:  water concentration in volume  percent, sulfur trioxide in ppm
on a dry volume basis, and ash layer field strength, E.  The field strength
unless otherwise noted is always taken as 10  kV/cm.  The value of sulfur tri-
oxide is computed as 0.4 percent of the stoichiometrically calculated  sulfur
dioxide value.  On the second page of Table 1, the chemical composition of the
coal ash is the input data.  The technique for producing the coal ash  is shown
at the bottom of the page.   Chemical elements of  importance to the prediction
of resistivity are shown immediately below the ash composition.  The output
data are resistivity values  as a function of  temperature.  The columns headed
RHO (VS) and RHO (VSA) are the predicted resistivity values without and with
the effect of sulfuric acid  vapor taken into  account respectively.

     Figure 1 shows this type of data plotted as a function of reciprocal
absolute temperature.  The pronounced influence on resistivity of sulfuric
acid vapor in the  flue gas is shown.  In situ and laboratory measured  resis-
tivity data are superimposed on the curve of  predicted data.  Table 1  and
Figure 1 illustrate the  source of the data used in the evaluation that fol-
lows .
EVALUATION OF THE TECHNIQUE FOR PREDICTING RESISTIVITY

     Concurrently with the research effort to produce the resistivity predic-
tive technique, field tests2'3 were conducted to evaluate various aspects of
precipitator performance and operation.  While power stations were operating
under normal full-load conditions, the following data and samples were
obtained within the shortest possible time:  isokinetic fly ash sample, repre-
sentative coal sample, in situ resistivity data, flue gas analysis, outlet-
field current density-voltage relationship, and mass train efficiency measure-
ment.

     The coal samples were ashed according to the method defined  in Table
1, and the resulting chemical analysis was compared with the concomitant fly
ash analysis.  The coal ash chemical analysis also served as input data for
the resistivity prediction.

                                      156

-------
     The fly ash samples were chemically  analyzed  and  used  for  laboratory
resistivity determinations.  When resistivity  was  determined  using  these speci-
mens, the environment was air containing  the water  and sulfur  trioxide  con-
centrations reported for the field  test flue gas.   The temperature  used was
the same as that recorded during the _in. situ resistivity  measurement.   The
last current reading prior to dielectric  breakdown  was used to  calculate labo-
ratory resistivity.

     The data and samples from  tests at 12  power  stations are used  in
this evaluation.  Table 2 presents  general  information about  the  stations
involved and the analysis of the coal  being burned  during the  field test
period.  The ultimate coal analyses shown were used to determine  the predicted
flue gas analyses.  These predicted values  were compared  with  the measured
flue gas analyses and were used in  the resistivity  prediction.  The W or E
following the power station number  indicates that  coal from the western or
eastern part of the country was being  burned.

Coal Ash - Fly Ash Comparison

     Table 3 shows the comparison of fly  ash and coal  ash chemical  composi-
tions and the comparison of ir±  situ and predicted  flue gas  analyses.  The
subject technique for predicting resistivity utilizes  the concentrations in
atomic percent of lithium plus  sodium, magnesium plus calcium,  and  iron.  The
only obvious difference between the fly ash and coal ash  analyses with  respect
to  the elements of interest concerned  the iron concentration  for  stations
3 and 5.  These deviations would only  affect high  temperature  resistivity.
At  350°C, predicted resistivity based  on  the coal  ash  analysis  was  nearly a
factor of two greater than the  predicted  value using the  fly  ash  analysis.

In  Situ - Predicted Flue Gas Comparison

     Considering  the comparison of  iri  situ  and predicted  flue  gas analyses,
the water concentration and sulfur  trioxide concentration are  most  important.
The largest deviation between jm situ  (8.1%) and predicted  (10.5%)  water con-
centrations occurred at station 5.  In this case under typical  cold-side
precipitator conditions, the predicted resistivity  would  be about a factor
of  1.5 lower than a predicted value based on the  in situ  water  concentration.
In  general, the predicted and in situ  water concentrations  showed excellent
agreement.  The average values  for  the predicted and measured  water concentra-
tions for the 12 stations were  identical.   Six times the  predicted  value
was greater than and six times  it was  less  than the respective  measured value.

     The comparison between the predicted values  for the  sulfur trioxide con-
centration and values measured  jm situ is more difficult  to assess.  It was
mentioned above that the predicted  sulfur trioxide  value  was  obtained by
multiplying the sulfur dioxide  value calculated from the  stoichiometric com-
bustion of the coal by 4 x 10~3.  This multiplier  was  selected after reviewing
the information from 17 field test  programs conducted  by  Southern Research
Institute prior to this paper.   In  this method of  predicting  resistivity, it
is  assumed that at the precipitator inlet the  fly  ash  is  in equilibrium with

                                       157

-------
the sulfur trioxide concentration measured  in  situ  and  that  in  the  laboratory
the volume of fly ash under  test is  in  equilibrium  with this  same concentra-
tion of sulfur  trioxide  at the  time  that  the resistivity data are taken.

     For five of the six stations burning eastern coal  and having an  ir± situ
sulfur trioxide concentration greater than  1 ppm, a range of  values  is given.
In each case, the predicted  value for sulfur trioxide was within the  range
established by  in situ   measurement.  Only  in  the case  of station 12,  burning
a coal of very  low sulfur content, was  the  predicted value significantly
different from  the i.n situ value.  Awareness of the problems  encountered in
making in situ  sulfur trioxide  determinations  leads one to speculate  that this
value could very well have been greater than the recorded 0.5 ppm.

     The average sulfur  concentration for the  six stations burning western
coal was 0.5 percent, and the predicted average sulfur  trioxide concentration
was approximately 2 ppm.  In all cases, the measured concentration was < 1 ppm.
A possible explanation for this difference  is  related to the  difficulty in
making precise  in situ   sulfur  trioxide determinations  especially at very low
concentrations  combined with the greater affinity of the more alkaline west-
ern ash for the sulfuric  acid vapor.  Although this deviation is small, it
can have a significant effect because the sulfuric acid vapor has a very
pronounced effect on resistivity.

Comparison of Predicted,  Laboratory, and  In Situ Resistivities

     Before comparing the predicted  resistivity values  with measured  resis-
tivity data and precipitator performance  information, several important points
should be noted.  First,  the predicted  resistivity  is based on the water and
sulfur trioxide concentrations  calculated from the  stoichiometric combustion
of the coal, while the laboratory measurement of resistivity  was conducted
in an environment in which an attempt was made to duplicate the in situ con-
centrations of  these agents.  When the  in situ value for sulfur trioxide was
< 1 ppm, the laboratory  environment  contained approximately 1 ppm.   Because of
the inability to precisely duplicate environments, it is noted that small
differences existed in the environments used for predicted,  in situ, and labor-
atory-measured  resistivities.   Second, one should recall that resistivity
determinations  are not extremely precise.   Although no statistical interpre-
tation is available, repetitive laboratory determinations of  identical speci-
mens will yield an average value with a data spread of ±30 percent.   The
in situ data are usually  averages for several determinations made during the
test period of  interest.  Although atypical, the range of in situ values for
a series of determinations can  cover an order of magnitude.

     To avoid repetitive  explanation for certain observations, the data shown
in Table 4 are  best discussed in three groups:   data pertaining to hot-side
precipitators,  cold-side  precipitators burning western  coal, and cold-side
precipitators burning eastern coal.
                                       158

-------
     The field test data were  available  for  hot-side precipitators from two
power stations, 4E and  6W-13W.   The  data for  stations labeled 6W and 13W
represent two sets of data  from  the  same installation.   For  each of three
sets of data, the laboratory-measured  resistivity value was  in good agreement
with the predicted value.   In  one  instance,  station 13W, the _iri situ resis-
tivity measurement was  identical to  the  value obtained  in the laboratory,
while at the other, station 4E,  the  ir± situ  value was one order of magnitude
greater than the predicted  and laboratory-measured values.   It should be noted
that only one resistivity data point was obtained at station 4E before the
high-temperature resistivity probe degraded  due  to mechanical and thermal
abuse.  The precipitator performance data for station 4E cannot suggest which
resistivity data are more likely to  be correct.   The low current density and the
evidence of back-corona for the  13W  and  6W stations, respectively, were judged
not  related to the inherent resistivity  of the fly ash.

     Data are available from four  stations burning western coal and operating
cold-side precipitators.  These  stations are designated:  1W, 5W, 10W,and
11W.  Laboratory-measured resistivity  data were  greater than the respective
predicted data by a factor  of  2  to 4.  Since in  each case the water and sulfur
trioxide concentrations used in  the  resistivity  prediction were slightly
greater than the concentrations  used in  the  laboratory  test  environment, the
agreement between laboratory results and predicted data is outstanding.  How-
ever , only  the in situ  data for  station  1W agreed with  the laboratory and
predicted information.   The ir± situ  resistivity  data taken at stations 5W,
10Wrand 11  were nominally 1.5  to 2.5 orders  of magnitude greater than the
predicted resistivity.   If  these iri  situ data were correct,  an untenable situ-
ation would prevail.   Since factors  other than resistivity affect precipitator
characteristics,  the  efficiency  data and, in particular, the outlet-field
current density values  suggest that  the  correct  resistivity  values are signif-
icantly lower  than  the  in situ  data indicate.  The correlation among outlet-
field  current  density,  laboratory-measured resistivity, and  predicted resist-
 ivity  is  encouraging.

     The observation  regarding these in  situ resistivity data is not unusual.
When surface resistivity dominates and conduction is principally dependent
on charge carrying  ions of  limited concentration, in situ resistivity data
are  often unrealistically high.  No  serious  effort to clarify this situation
has  been made-  One can suggest  several  potential explanations for this occur-
rence.  The point-plane,  in situ,resistivity probe can  collect a particle
size distribution that  is biased toward  the  coarse fraction.  This reduces
the  surface area available  for conduction, and if charge carrying ions such
as sodium are disproportionately distributed among the  finer sizes, current
carrying ability  is further lessened.  Often a rather long time period occurs
in depositing the ash in the probe under high current density.  If conduc-
tion is dependent on  sodium ions of  finite concentration, the long-term, high-
current-density deposition  technique can distort the resistivity by developing
a high resistivity  layer depleted  of sodium  ions.  Finally,  if by some unusual
circumstance the collected  ash is  wetted by  condensed water  which is subse-
quently evaporated, the measured resistivity will be incorrectly high.  Clearly,
this position regarding point-plane  data deserves attention.


                                       159

-------
     The data for Stations 2E,  3E, 7E, 12E, and  14E were  obtained  from cold-
side precipitator operations collecting ash from eastern  coals.  Considering
the precision of the measurements made and the slight deviations between  labor-
atory and in situ environments, the data for stations 2E,  3E,  7E,  and  12E
stand reasonably free of criticism.

     No laboratory resistivity  data were available for the Station 14E review.
The in situ resistivity value is an order of magnitude less than the predicted
result.  Although a desirable resistivity level  was predicted, the outlet-
field current density suggests  that the _in situ  resistivity data are more
nearly correct.  The poor efficiency recorded was related  to other circum-
stances.

     The evaluation of the resistivity comparison can be  summarized as fol-
lows :

     • All of the laboratory resistivity measurements made under conditions
       simulating the in situ water and sulfur trioxide concentrations were
       in reasonable agreement  with the predicted resistivity  value.

     • Although circumstances allow only qualitative interpretation, no fla-
       grant disagreement occurred between outlet-field current density data
       and predicted resistivity.

     • Resistivity determined in situ was in reasonable agreement  with pre-
       dicted resistivity in 6  out of 11 tests (55%).  Several aspects  of
       this undesirable situation were elaborated upon above.
CONCLUSIONS AND RECOMMENDATIONS

     A bold step was taken  in attempting to predict fly ash resistivity from
input data consisting of the as-received, ultimate coal analysis and the chemi-
cal composition of the coal ash.  Considering the imperfections in the mea-
surements used in precipitator technology and the limited amount of laboratory
data available with respect to environments containing sulfur trioxide, the
subject evaluation of an initial  resistivity prediction technique of this
type is very favorable.  However, serious discrepancies have been pointed
out.  These points and an awareness  that some critical correlations used in
the predictive method are based on limited information suggest the need for
the following additional effort.

     • A point-plane, ir± situ,resistivity probe and a laboratory resistivity
       test cell should be  simultaneously evaluated in an environmental cham-
       ber with electrification techniques, temperature, fly ash composition,
       and water and sulfur trioxide concentrations as variables.
                                      160

-------
      With  special attention to measurement precision, additional sulfur
      dioxide  and sulfur trioxide data taken at the hot and cold sides of
      the air  preheater are needed.  These data are required to substantiate
      or alter the present method of determining the sulfur trioxide concen-
      tration  used in the resistivity prediction and to justify the sulfur
      trioxide concentrations used in developing the laboratory data.

      The predictive technique should be evaluated using coals having high
      ash and/or moisture contents.  These coals produce environments con-
      taining  disproportionately high sulfur trioxide concentrations for
      a given  sulfur content.

      Although the fly ash - coal ash compositional correlation has been
      good, it would be desirable to develop an objective method for estab-
       lishing  the ignition temperature for the crucible ashing of each coal.

       A broader laboratory resistivity data base must be established for
       the  relationships among the variables: fly ash composition, temperature,
       and  the  environmental factors.
REFERENCES

1.  Bickelhaupt, R.E.  A Technique For Predicting Fly Ash Resistivity.
    EPA-600/7-79-204, U.S. Environmental Protection Agency, Research Triangle
    Park, North Carolina, August 1979-

2.  Gooch, J.P. and Marchant, G.H., Jr.  Electrostatic Precipitator Rapping
    Reentrainment and Computer Model Studies^  EPRI FP-792 Volume 3, Electric
    Power Research Institute, Palo Alto, California, 1978.

3.  Unpublished reports pertaining to field tests conducted by Southern Re-
    search Institute.
                                       161

-------
Table 1.
 Computer Printout of Resistivity Prediction
             Station 3E
                                   FOR COMBUSTION
                            MOLTS' 100  IB FUEL



c
M?
ri C-
02
M2
s
H20
ASH
SUM




AS RECEIVED
ULTIMATE COAL
ANALYSTS
6?, 44
3.95
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fl.27
1.25
?.02
10,84
11.23
joo.oo




02 AND AIR * 130/100
EXCE
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ss o?
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4 ft A IQ
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5,199
1,955
0.258
0.045
0.06?
0.602
0,000
8.122
RFQ FOR
MOLES/
»30X
02
TOTAL 7.777

1,795
AT 100% TOT

02
5.199
0.978
*0,25B
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0.063
0,000
0,000
5.9*2
COMBUSTION
100 l.R FUFL
EXCESS AIR
DRY AIR
37,014
8.542

'At AJR

PRY AIR
24.747
4.653
-1.228
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0.300
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28.47?







PRODUCTS OF COMBUSTION



C02
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TOTAL
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13,104
8.399
0.159
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10
               162

-------
                      Table 1.   (Cont'd.)
LI 20
NA?0
K20
MGO
CAO
FF.203
At. 20 3
si02
TI02
P205
            ASH
         ANALYSIS

            0.03
            0.63
            2.10
            1,00
            a.7o
            9.00
           2S.ao
           53.30
            1 .60
            f.?!
            0.77

           OH.74
                     CORRECTED
                        ASH
                      ANALYSIS

                         0.03
                         o.t>a
                         2.13
                         1.01
                         a.7fe
                         9.U
                        25,7?
                        53.98
                         1.6?
                         0.21
                         0.7fl

                       100.00
                                       ATOMIC
                                   CONCENTRATION
 1.
 0,908
 7.297
 Q.4P9
 o'.nsi
 0. J 76

36.901
    OF LITHIUM AND SODIUM ATOMIC CONCENTRATIONS        0,55
    OF MAGNESIUM AMD CALCIUM  ATOMIC  CONCENTRATIONS      4,0
     ATOMIC CONCENTRATION                               1.7
POTASSIUM ATOMIC CONCENTRATION                         1,09
TEMP *n0o/T(Ki
                    K  PP:G c  DEC
                                                 RHOCVSAJ
l.tt
1.6
t.fl
?.o
2.2
2.«
2.6
2.8
7ia
625
S56
50Q
4S5
ai?
3fl5
3S7
441
352
2R3
227
182
i«a
U?
sa
826
666
sai
aat
3*i9
291
233
1R3
?.3F+Oft
) .7F+09
1.2P*10
8.3F. + 10
3.3E+11
3.6F-H1
1.5E+11
1 , at 4- 10
2.3F+08
l.7E*n<»
1.2F+10
8,3F*10
2.9E + U
J.9E+JO
**
**
**  FXT5T1NR FXPFRIHFNTAL DATA
    AT TFMPf-RATHRES LOWER THAN
                               DO NOT JUSTIFY  COMPUTATIONS
                               lfl« DFGPEFS  C'.
NOTF! HECAU8F THF PRFDICTED
SFNSITTVE TO SFVFRAL Fl UE GA
ONf MUST FXfRcISF RRFAT CARf
OF COAl  AND ASH SAMPLES.
QUANTITATIVE CHEMICAL
IN ESTABLISHING THIS
ANALYSES WERE OBTATNFD USING
COAL ASH WAS PRODUCED USING
A StCOND JGWITIOM AT 1050 DF
STTLI. AIR FOR 10 TO  1? HOURS
                            RESISTIVITY VALUFS ARE VERY
                            S AND ASH COMPOSITIONAL FACTORS,
                             IN THE SELECTION AND PREPARATION
                            THFRMORE, THF QUALITY OF  THE
                            IS WORK IS OF GPFAT  IMPORTANCE,
                            . THF AS-RFfFlVED. ULTIMATE COAL
                             ASTM D3176 PROCFDLIRF, AND THE
                            ASTM 0271 PROCFDURE  FOLLOWED  BY
                            GRFES C + OP . 10 DEGREFS r' IN
                           163

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                         Table 2.   Evaluation of Predicted Resistivity
               General Information and Coal Analyses for Several Power Stations
STATION NUMBER              1W        2E        3E        4E        5W       6W
TEST DATE                7 AUG 75    15 JAN 76   2 MAR 76   27 APR 76  5 OCT 76   1 FEE 77
UNIT SIZE, MW              135       160       122       271       508       800
SCA of ESP, m2/m3/sec
          ft2/ft3/min
COAL ANALYSIS
AS RECEIVED
  PROXIMATE, wt. %
  Moisture
  Volatile Matter
  Fixed Carbon
  Ash
  Sulfur

  ULTIMATE, wt. %
  Carbon
  Hydrogen
  Oxygen
  Nitrogen
  Sulfur
  Moisture
  Ash
98.8
504
13.94
37.78
43.07
5.21
0.41
59.41
4.24
15.33
1.46
0.41
13.94
5.21
49.8
254
2.07
39.05
47.91
11.00
3.28
71.26
5.01
5.87
1.54
3.28
2.04
11.00
50.2
256
10.84
33.99
43.94
11.23
2.05
62.44
3.95
8.27
1.25
2.02
10.84
11.23
76.4
390
6.22
30.73
50.20
12.85
0.95
64.75
4.11
9.42
1.69
0.96
6.22
12.85
117.2
598
19.91
26.48
42.16
11.45
0.43
52.01
3.53
11.55
1.02
0.53
19.91
11.45
60.2
307
8.26
38.90
43.56
9.28
0.45
65.23
4.25
11.52
1.01
0.45
8.26
9.28

-------
                                                Table 2.   (Cont'd.)
O-p
on
STATION NUMBER
TEST DATE
UNIT SIZE, MW
SCA of ESP, m2/m3/sec
          ft2/ft3/min
COAL ANALYSIS
AS RECEIVED
  PROXIMATE, wt%
  Moisture
  Volatile Matter
  Fixed Carbon
  Ash
  Sulfur
            ULTIMATE,  wt %
            Carbon
            Hydrogen
            Oxygen
            Nitrogen
            Sulfur
            Moisture
            Ash
                                      7E
10W
11W
12E
13W
                                                                                       14E
                                  17 SEPT 76  29 SEPT 77 19 OCT 77   18 DEC 77  21 JULY 77 15 SEPT 77
350
500
500
250
800
                                                                                       400
33.3
170
11.68
31.06
46.36
10.90
0.81
65.22
3.87
6.21
1.21
0.91
11.68
10.90
172.9
882
13.44
31.69
43.55
11.32
0.61
56.77
4.09
12.48
1.29
0.61
13.44
11.32
96.0
490
18.67
38.14
30.62
12.57
0.58
53.31
4.36
9.44
1.07
0.58
18.67
12.57
158.0
806
8.41
16.90
48.88
25.80
0.79
57.21
3.74
3.03
1.02
0.79
8.41
25.80
60.2
307
12.34
37.81
40.59
9.27
0.48
60.58
4.16
11.78
1.39
0.48
12.34
9.27
34.7
177
4.71
33.64
47.20
14.45
2.15
62.89
4.47
9.89
1.44
2.15
4.71
14.45

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                                              Table 3.   Evaluation of Predicted Resistivity
                                 Fly Ash,- Coal Ash, and Flue Gas Compositions for Several Power Stations
STATION NUMBER
                          1W
                                               2E
                                                                     3E
                                                                                          4E
                                                                                                               5W
                                                                                                                                     6W
ASH COMPOSITION
WEIGHT PERCENT
Li20
Na20
K20
MgO
CaO
Fe203
A1203
Si02
Ti02
P205
SO 3
TOTAL
LOI
SOLUBLE SULFATE
FLUE GAS
COMPOSITION
C02, vol %
02, V01 %
H20, vol %
S02 ppm
SO 3 ppm
FLY
ASH
0.02
0.29
1.8
3.6
8.6
5.9
23.7
51.9
1.3
0.39
1.2
98.7
0.8
0.7
IN SITU
13
7
8.3
262
<1
COAL
ASH
0.01
0.27
1.0
2.8
7.5
6.0
15.2
65.3
1.2
0.35
0.58
100.2


PREDICTED
13
5
9.6
440
1.8
FLY
ASH
0.02
0.55
2.5
0.9
5.6
24.4
18.3
45.1
1.3
0.30
1.9
100.9
4.0
0.9
IN SITU
15
5
8.3
3000
9-12
COAL
ASH
0.02
0.49
2.1
0.8
5.5
24.1
19.2
41.6
1.6
0.29
4.7
100.4


PREDICTED
13
5
7.6
2380
9.5
FLY
ASH
0.03
0.67
2.1
1.0
5.0
13.1
21.8
50.2
2.0
0.78
2.3
99.0
10.9
1.6
IN SITU
13
5
8.2
2440
6-9
COAL
ASH
0.03
0.63
2.1
1.0
4.7
9.0
25.4
53.3
1.6
0.21
0.77
98.6


PREDICTED
13
5
8.4
1730
6.9
FLY
ASH
0.04
0.43
3.5
1.3
1.1
7.2
28.4
53.8
1.8
0.23
0.50
98.3
3.5
0.3
IN SITU
15
5
8.5
755
2-3
COAL
ASH
0.04
0.44
3.2
1.2 '
1.0
7.4
28.4
53.3
1.9
0.24
0.15
97.3


PREDICTED
13
5
7.8
800
3.2
FLY
ASHS
0.02
1.38
0.54
1.1
5.8
6.1
13.2
70.8
0.9
0.05
0.50
100.4
1.0
0.5
IN SITU
13
6
8.1
480
0.18 mm (+80 mesh)  and mostly carbon.   It was removed prior to testing.

-------
                                                            Table  3.  (Cont'd.)
STATION NUMBER
                          7E
                                              10W
                                                                    11W
                                                                                          12E
                                                                                                               13W
                                                                                                                                    14E
ASH COMPOSITION
WEIGHT PERCENT
Li20
Na20
K20
MgO
CaO
Fe203
A1203
Si02
Ti02
P205
SO 3
T.OTAL
LOI
SOLUBLE SULFATE
FLUE GAS
COMPOSITION
C02, vol %
02, vol %
H20, volZ
SO 2 ppm
SO 3 ppm
FLY
ASH
0.05
0.27
2.1
0.9
3.7
7.1
29.3
53.5
1.8
0.20
0.7
99.6
7.5
0.7
IN SITU
ND
ND
9.0
600
3-4
COAL
ASH
0.05
0.31
2.2
0.9
3.2
6.8
29.4
54.4
1.6
0.33
1.6
100.8
	
	
PREDICTED
13
5
8.2
740
3.0
FLY
ASH
0.02
0.39
1.7
2.6
15.0
7.4
18.6
50.8
1.0
0.8
0.7
99.0
0.8
0.4
IN SITU
14
6
9.5
510

-------
cr>
oo
                                           Table 4.   Evaluation of  Predicted Resistivity

                              Temperature,  Resistivity, and  Performance Data for Several Power Stations
STATION NUMBER
TEMPERATURE, °C
RESISTIVITY, ohm. cm
In situ, @ Spark
Laboratory, @ Spark
Predicted, @ 10 kV/cm
ESP EFFICIENCY, %
CURRENT DENSITY 2
OUTLET FIELD, nA/cm
STATION NUMBER
TEMPERATURE, °C
RESISTIVITY, ohm-cm
In situ, @ Spark
Laboratory, @ Spark
Predicted, @ 10 kV/cm
ESP EFFICIENCY, %
CURRENT DENSITY
1W 2E
145 158

3.0 x 1011 1.0 x 1010
5.0 x 1011 1.2 x 101D
1.2 x 10n 2.0 x 1010
99.92 99.55
15 24
7E 10W
163 138

2.7 x 1011 6.9 x 1012
2.2 x 1011 2.0 x 1011
5.0 x 1011 6.0 x 1010
e (99.6)d
e 15
3E
158

2.1 x 1010
2.3 x 1010
7.0 x 10 10
99.87
45
11W
134

7.0 x 1012
2.2 x 1010
1.4 x 1010
(99.8)d
16
4E
332

3.0 x 1010
4.0 x 109
2.3 x 109
99.65
37
12E
143

3.0 x 1011
5.0 x 1011
2.3 x 1011
(99.8)d
46
5W 6W
1053 350

5.0 x 10 u b
5.0 x 1010 1.1 x 109
1.6 x 1010 8.5 x 108
99.85 99.47
23 50°
13W 14E
350 154

1.8 x 109 3.0 x 109
2.0 x 109 b
1.4 x 109 4.0 x 1011
99.22 89
13 90
                 OUTLET FIELD, nA/cm
                   a) Test temperature below that of acquired laboratory data involving sulfur trioxide,
                   b) Not determined.
                   c) j-V curves indicate back-corona.
                   d) Typical only.
                   e) Not available.

-------
SYM STATION NAME
D
O
A
O
2
2
2
2
PREDICTED
PREDICTED
IN SITU
LABORATORY
H2O
7.6
7.6
8.3
9.1
°2
5
5
5
AIR
co2
13
13
15

so2
2380
0
3000
0
S03
9.5
0
(9-12!
11.4
E. kV/cm
10
10
SPARK
SPARK
          10
            12
          10
             11
      O
      s
      I
      O
      in
      LLI
      cc
          10
            10
           109
           108
1000/T(°K)—- 3.0
                      I
        °C
        °F
60
141
2.8
84
183
               I
                I
                              I
                                             I
Z6
112
233
2.4
144
291
2.2
182
359
2.0
227
441
1.8
283
541
1.6
352
666
1.4
441
826
1.2
560
1041
                                     TEMPERATURE
                  Figure  1. Predicted, injsitu, and laboratory measured resistivity.
                                          169

-------
                                SO3 CONDITIONING
                                      FOR
                IMPROVED ELECTROSTATIC PRECIPITATOR PERFORMANCE
                          OPERATING ON LOW SULFUR COAL
                                       BY:

                               J.  J. FERRIGAN III
                                  J. D. ROEHR
                                  WAHLCO INC.
                          SANTA ANA, CALIFORNIA  92704
     This presentation deals with a case study of a particular utility's dilemma
of having to choose an efficient and reliable air pollution control device to
lower stack emissions on an existing unit.  The paper traces the study from the
time when excessive emissions required MW load deratings into the decision mak-
ing process, the testing stage, and finally into the installation of 503 flue
gas conditioning.

     It points out why, in this particular case, 803 flue gas conditioning is a
more reasonable choice than the installation of a new cold side precipitator or
fabric filter baghouse.  It clearly shows via test results supplied by a utili-
ty based in upstate New York that 803 flue gas conditioning enables units at
their power plant to operate well within the legal standards enforced by the
New York State Department of Environmental Conservation (NYSDEC).
                                        170

-------
SO  CONDITIONING FOR IMPROVED ELECTROSTATIC PRECIPITATOR PERFORMANCE OPERATING
ON LOW SULFUR COAL
INTRODUCTION

     This presentation deals with a case history concerning the upgrading of a
two chamber, two field, twenty-six year old electrostatic precipitator.  The
utilities Unit 3 (boilers 4 and 5) is a s.team electric generating unit rated at
57.7 MW.  It has two steam boilers and until 1971 was equipped with only me-
chanical dust collectors.  The existing #4 & #5 precipitator at the station is
the original #6 precipitator (see Figure 1) and has been in operation since 1953.
In 1971, this precipitator was optimized by increasing the TR capacity and con-
verted to serve #4 & #5 boilers with a total gas volume of 270,000 ACFM at 330°F
and an efficiency of 97.5% following mechanical collectors.

     In 1976 the utility installed an opacity monitor on Unit 3 stack and from
this addition came the realization that Unit 3 emissions were often higher than
the 20% opacity limit.  It was significant that the only time Unit 3 was in vio-
lation of the 20% opacity limit was when low sulfur, high ash coal was being
burned.  When high sulfur, low ash coal was introduced into the system the opac-
ity would eventually drop significantly.  These results pointed to one possible
problem; high resistivity fly ash.

SOLUTIONS

     The utility prepared a list of possible solutions to alleviate the emission
problems when firing low sulfur coal on Unit 3.  The list included:   (1) a new
electrostatic precipitator; (2) a new fabric filter baghouse; or  (3) upgrading
the existing mechanical and electrostatic precipitators along with the addition
of flue gas conditioning.

     1.  The installation of a new cold side electrostatic precipitator on
boilers #4 and #5 would have had to be designed to meet today's present coal and
ash qualities and the precipitator would have to contend with collecting the low
sulfur coal, high resistivity fly ash while meeting both EPA particulate and
SOX emission regulations.  One of the most important factors in precipitator
design and operation is the fuel analysis with sulfur being the most critical.
One to three percent of the sulfur content of the coal is converted to 803 in
the economizer portion of the boiler.  The SO3 generated is accepted as the
prime element controlling resistivity for most coals.  The fact that the EPA con-
siders sulfur emissions to the atmosphere undesirable sets up an  opposition of
interests.  On one side the EPA requires low sulfur emissions and on the other
the industry needs sulfur in the fuel to condition the fly ash so that it can
be precipitated.  When low sulfur fuels are fired, high resistivity fly ash is
often the result, and very large precipitators are required to efficiently remove
the fly ash.

     The utility has had some very unsatisfactory experiences with  cold side

                                         171

-------
electrostatic precipitators ostensibly designed for low sulfur coal  (600 square
feet of surface collecting area per 1000 ACFM) in the past because of high resis-
tivity problems.  This was the major reason that they did not pursue the instal-
lation of a cold side precipitator.  In addition, the total estimated cost for
the installation of an electrostatic precipitator to handle 270,000 ACFM of flue
gas at 330°F was approximately $5,400,000 with a lead time of 24-36 months.

     2.  The installation of a fabric filter baghouse on boilers #4 and #5
appeared to be a more viable solution than an electrostatic precipitator in this
particular application with low sulfur coal.  A baghouse is totally unaffected
by the high resistivity fly ash.  Changing of fuels on a daily basis will not
affect the operation of the baghouse.  The baghouse also has the advantage of
99.9+% collection efficiency.  Should the EPA in the future require even stricter
standards, the baghouse would be in compliance without modification.  Two major
drawbacks of the fabric filter baghouse are the life of the collecting bags and
the increased pressure drop across the system.

         The major reasons for excluding the fabric filter baghouse from the possi-
ble solution list were the cost which was $3,200,000, the 16-18 months delivery,
and the fact that new I.D. fans would have to be purchased.  The total cost of
replacing the I.D. fans was approximately' $1,100,000.

     3.  The third and final solution was to upgrade the existing mechanical
collector and electrostatic precipitator and install flue gas conditioning.  The
mechanical collecting cones and vanes had been in service for 30 years without
a  changeout.  The cones and vanes were in poor condition and were in need of im-
mediate replacement.  As  far as the electrostatic precipitator was concerned, it
was in good operating condition except that it needed new discharge electrodes.

         So far, so good,  except for flue gas conditioning.  The utility expe-
rienced extensive testing at another station with a liquid additive conditioning
agent which required injection upstream of the air heater to vaporize the con-
ditioning agent.  The results of the conditioning agent tests proved to be nega-
tive and extremely costly in terms of downtime and material cost.  The air heater
was plugged after two weeks of operation and the emissions were not reduced while
injecting the additive.   Needless to say, the utility's view of flue gas con-
ditioning was not very optimistic after this episode, but they continued to in-
vestigate other methods.

         From correspondence with other major utilities it was discovered that
they were using, quite successfully, SO., flue gas conditioning to help maintain
particulate  collection efficiency and opacity requirements.  After consulting
these major  electric utilities, field trips were conducted to observe the sys-
tems  in operation.  The utility was quite impressed with the results they saw.
The major point that was  made clear by the other operating utilities was that
S03 injection will only allow the precipitator to perform as well as they would
with high sulfur coal, and not better than the design efficiency which for #4
and #5 precipitator, was  97.5%.

         After  evaluating the above solutions, it was decided to conduct effi-
ciency tests on Unit 3 to determine if #4 and #5 precipitator with 803 con-
ditioning could consistantly stay under the 20% opacity limit.
                                        172

-------
TEST RESULTS PRIOR TO GAS CONDITIONING

     The testing procedure was set up into two basic categories, high and low
sulfur coal tests.  The first series of tests were conducted in January 1978
on boiler #5 while burning low sulfur coal prior to the changeout of the mechan-
ical dust collectors.  (See Table 1.)  The efficiency averaged 73% for these
tests with the outlet emission rate at 619 Ib/hr.  The maximum allowable emission
rate for boiler #5 set forth by the New York State Department of Environmental
Conservation was 84 Ib/hr.  The inlet dust loading of 2,523 Ib/hr indicated that
the mechanical collectors would have to be replaced to help lower the inlet
grain loading.

     During the annual #5 boiler outage all 297 collecting cones and vanes were
replaced with new ones and efficiency tests were conducted while burning high
sulfur coal in May 1978.  (See Figure 2.)  These tests highlighted two impor-
tant facts.  The mechanical dust collectors significantly lowered the inlet dust
loading by 841 Ib/hr and the high sulfur coal enabled the precipitator to per-
form higher than the design efficiency of 97.5%.   (See Table 2.)

FLUE GAS CONDITIONING

     Based on the test results it was decided to rent an SO2 source flue gas con-
ditioning system and install a test  set up on #5 boiler precipitator.  The cost
of the rental system was $20,000/month with 50% of the rental cost applied to
the purchase of a new system.

     The equipment which was shipped to the station was a liquid SO2 source
system consisting of a liquid S02 vaporizer, air filter, fan, SCR controlled
electric heaters, S02-SO3 catalytic  converter and  injection probes.  The system
was designed to inject 40 ppm of SO3 into 135,000  ACFM of flue gas at 330°F.  A
40 ton S02 tank was rented as temporary storage for the liquid SO2.  (See Figure
3.)  Process instrumentation provided fail-safe operation and automatic adjust-
ment of 303 production in response to boiler load.

TEST RESULTS WITH SO3 GAS CONDITIONING

     The rental S02  source flue gas  conditioning system was delivered to the
station in early October 1978 and placed in service November 1, 1978.  However,
prior to the start-up some efficiency tests were conducted while burning low
sulfur coal in boiler #5.  All these efficiency tests were necessary as the
stack mounted opacity monitor recorded both #4 and #5 precipitator readings.
The test results  indicated that the  mechanical collectors were definitely help-
ing to lower the grain loading to the electrostatic precipitator.  However, the
outlet dust loadings were far worse  than any other test results recorded to
date.   (See Table 3.)

     The same quality low sulfur coal was used in  the tests when the 303 system
was placed in operation.  The utility waited 12 days to completely condition
the fly ash.  Improved electrical readings on the  precipitator were observed
during this time.   (See Table 4.)  At this point  (14) efficiency tests were con-
ducted to determine  the effectiveness of 503 injection  at different  injection
rates.   (See Table 5.)  Looking at tests one through  four, the  average efficiency
                                       173

-------
equalled the average of all of the high sulfur coal tests which was 97.7%.  It
was quite clear from looking at the remaining tests on Table 4 that as the 803
injection rate decreased, so did the efficiency of the precipitator.

     The utility was so impressed by the results of the SO2 source test unit
that they contracted to rent the unit for a five month period to permit increase
of the MW load generation.

CONCLUSION

     The final decision to install a permanent SO2 source flue gas conditioning
system was based solely on the performance of the five month rental system at
the test station.  The rental system was revised to inject 803 into #4 precipi-
tator which also shares Unit 3 stack.  This enabled the station to obtain accu-
rate opacity readings while 803 was being injected.  The opacity readings rarely
ever exceeded  20% and when it did it occurred due to insufficient liquid SO2
supply.

     The permanent flue gas conditioning system had one major change over the
rental  system; the converter and air heaters were not mounted on the motor
control skid,  but were mounted on their own skid.   (See Figure 4.)  The conver-
ter and air heater skids  are to be located at the point of 803 injection to al-
low for less hot gas piping and less temperature loss of the SO^/air mixture.
The permanent  system is  to be in operation by July  1, 1979.  The cost of the
total  installed  system was approximately $460,000.

     After evaluating cold precipitators and baghouses, the utility was con-
vinced that a  small 296 SCA precipitator which had been upgraded combined with
803 flue gas conditioning, would be a reliable and cost efficient solution to
meeting federal particulate emissions while burning low sulfur pulverized coal.
                                       174

-------
Table 1   SUMMARY OF PRECIPITATOR TEST RESULTS WHILE BURNING LOW  SULFUR COAL
          PRIOR TO CHANGEOUT OF MECHANICAL DUST COLLECTORS
          (TEST CONDUCTED BY THE UTILITY)
TEST
1
2
3
AVG
INLET
GR/SCF
3.99
2.48
2.02
2.83
LB/HR
2,881
2,583
2,104
2,523
LBS/106BTU
8.12
5.05
4.11
5.76
OUTLET
GR/SCF
1.09
.63
.58
.77
LB/HR
714
595
548
619
LBS/10&BTU
2.22
1.28
1.18
1.56
EFFICIENCY
%
72.7
74.6
71.3
72.9
                            TYPICAL COAL ANALYSIS

                        PROXIMATE ANALYSIS AS  RECEIVED
                        MOISTURE, %              8.26
                        VOLATILE, %              19.21
                        FIXED CARBON,  %          52.06
                        ASH, %                   20.47
                        SULFUR,  %                1.31
                        HEATING  VALUE, BTU '     10,366
                                        175

-------
Table 2   SUMMARY OF TEST RESULTS  WHILE BURNING HIGH SULFUR COAL AFTER CHANGE
          OUT OF MECHANICAL DUST COLLECTORS
          (TESTS CONDUCTED BY  AN INDEPENDENT CONSULTANT)
TEST

1
2
3
4
5
6
7
8
9
10
AVG
INLET OUTLET
GR/SCF
1.37
1.84
1.86
2.11
1.91
2.81
2.42
2.33
2.56
2.36
2.16
LB/HR
1063
1387
1439
1661
1453
2212
1988
1880
1927
1807
1682
LBS/106BTU
2.85
3.88
3.82
4.51
4.34
6.05
5.07
4.84
5.36
4.94
4.57
GR/SCF
.078
.048
.042
.037
.041
.046
.050
.049
.044
.035
.047
LB/HR
58.7
34.4
31.3
30.5
30.8
36.3
41.3
39.3
32.1
27.4
36.2
LBS/106BTU
.162
.101
-090
-083
.092
.099
.102
.106
.093
.076
.100
EFFICIENCY
%
94.5
97.5
97.8
98.2
97.9
98.4
97.9
97.9
98.3
98.5
97.7
                              TYPICAL COAL ANALYSIS

                          PROXIMATE ANALYSIS AS RECEIVED
                          MOISTURE, %              7.11
                          VOLATILE, %             26.31
                          FIXED CARBON, %         53.40
                          ASH, %                  13.18
                          SULFUR, %                2.56
                          HEATING VALUE, BTU     12,136
                                          176

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Table 3   SUMMARY OF TEST  RESULTS WHILE BURNING  LOW SULFUR COAL WITH NO S03
          INJECTION AFTER  CHANGE OUT OF MECHANICAL DUST COLLECTORS
          (TESTS CONDUCTED BY AN INDEPENDENT CONSULTANT)
TEST
1
2
3
4
5
AVG
INLET OUTLET
GR/SCF
1.90
2.16
2.03
2.42
2.40
2.18
LB/HR
1397
1589
1490
1905
1891
1654
LBS/106BTU
3.77
4.72
4.42
5.46
5.33
4.74
GR/SCF
.747
.624
1.521
1.225
.518
.927
LB/HR
529
474
1158
974
419
711
LBS/106BTU
1.53
1.34
3.30
2.76
1.07
2.01
EFFICIENCY
%
60.64
71.13
25.04
49.40
78.44
56.93
so3
PPM
0
0
0
0
0
0
                              TYPICAL COAL ANALYSIS

                          PROXIMATE ANALYSIS AS  RECEIVED
                          MOISTURE, %               9.63
                          VOLATILE, %              18.89
                          FIXED CARBON, %          52.67
                          ASH, %                   18.81
                          SULFUR, %                 1.38
                          HEATING VALUE, BTU      10,568
                                         177

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Table 4   ELECTRICAL READINGS OF #5  PRECIPITATOR WITH AND WITHOUT SO  INJECTION
          1.   WITHOUT SO   INJECTION,  10/23/78

                                   INLET     OUTLET
               AC AMPS               20        30
               DC MA                100       100
               PRIMARY VOLTAGE      190       190
           2.   WITH  SO   INJECTION,  11/12/78

                                   INLET     OUTLET
               AC  AMPS               80       135
               DC  MA               500       800
               PRIMARY  VOLTAGE      270       310
                                        178

-------
Table 5   SUMMARY OF PRECIPITATOR TEST RESULTS WHILE BURNING  LOW SULFUR COAL
          WITH S03 GAS CONDITIONING AFTER CHANGE OUT OF MECHANICAL DUST COL-
          LECTORS
           (TESTS CONDUCTED  BY AN INDEPENDENT CONSULTANT)

TEST

1
2
3
4
5
6
7
8
9
10
11
12
13
14
AVG
INLET OUTLET


GR/SCF
2.74
2.07
1.18
2.23
1.91
1.95
2.09
2.07
1.94
1.96
2.00
1.93
1.94
2.48
2.04

LB/HR
2195
1740
1050
1887
1623
1676
1727
1774
1674
1635
1640
1608
1541
2121
1707

LBS/106BTU
6.06
4.89
2.56
4.94
3.94
3.84
4.11
4.16
3.86
3.93
3.89
3.87
3.69
5.33
4.22

GR/SCF
.045
.031
.047
.050
.051
,051
.078
.097
.100
.111
.127
.133
.103
.059
.077


LB/HR
33.7
24.5
38.2
38.8
38.7
40.2
60.5
71.2
79.4
85.1
87.7
98.3
78.0
49.5
58.8

LBS/106BTU
.117
.070
.015
.111
.111
.108
.172
.206
.199
.252
.264
.247
.192
.136
.157

EFFICIENCY
%
98.4
98.5
96.1
97.8
97.3
97.4
96.3
95.3
94.8
94.3
93.7
93.1
94.7
97-6
96.1

so3
PPM
24
24
24
24
16
16
16
12
12
12
12
8
8
8
—
                              TYPICAL COAL ANALYSIS
                          PROXIMATE ANALYSIS AS RECEIVED
                          MOISTURE, %             12.63
                          VOLATILE, %             24.19
                          FIXED CARBON, %         48.57
                          ASH, %                  14.61
                          SULFUR, %                 1,
                          HEATING VALUE, BTU
   .37
10,345
                                         179

-------
 \\\\\\\\
\\\\\\\\\\\\\\\\\\
       FLUE GAS FROM
       #6 BOILER
   #6 PRECIPITATOR,
         (1953)
                                     ,FLUE  GAS FROM
                                      #4  &  #5 BOILERS
                       ORIGINAL LAYOUT
                            (1953)
\\\\\\\
                FLUE GAS FROM
                46 BOILER

                #6 PRECIPITATOR
                      (1971)
 \\\\\\\\\\\\\\
     #5
                                    FLUE GAS FROM #4 & $5 BOILERS

                                  #4 & #5  PRECIPITATOR
                                  (ORIGINALLY  #6 1953)
                        PRESENT LAYOUT
                            (1979)
             Figure 1   SCHEMATIC  OF UNITS 3 & 4
                (PRESENT AND ORIGINAL LAYOUTS)
                             180

-------
          BOILER
CO
 MECHANICAL
   DUST
 COLLECTOR

\x\/
                             Figure 2   SCHEMATIC OF BOILER #5 GAS FLOW

-------
oo
ro
                      SO2 STORAGE
                      (TEMPORARY)
         MAIN AIR BLOWER
                                                 VAPORIZED SO-
                                  AIR HEATERS
                                                                      I	AIR-S02
                                                                         800°F-825°F
                                                             CONVERTER-
  825°F-1100°F
                       BOILER
                      FLUE  GAS
                                                                                                 INJECTION
                                                                                                  PROBES
    Figure  3    SCHEMATIC OF SO2 SOURCE FLUE GAS CONDITIONING  SYSTEM
CONDITIONED FLUE  GAS
         TO
    PRECIPITATOR
                                                                                                     T

-------
co
OJ
                     Figure 4.   PERMANENT GAS CONDITIONING EQUIPMENT FOR #4 & #5  PRECIPITATORS

-------
                      DOES SULPHUR IN COAL DOMINATE

           FLYASH COLLECTION IN ELECTROSTATIC PRECIPITATORS?
                                   by

                     E.G. Potter and C.A.J. Paulson
        Commonwealth Scientific and Industrial Research Organization
                     Division of Process Technology
                     North Ryde, Sydney, Australia.
It is commonly believed that the sulphur content of a coal has a profound
influence on the efficiency with which its flyash is collected in an
electrostatic precipitator.   This question is discussed from theoretical
and practical viewpoints and the evidence for and against examined.    The
discussion necessarily ranges over such topics as the surface chemistry of
flyash, forms of sulphur in coal, correlation and causation, the measurement
and interpretation of electrical resistivity, precipitation temperature,
and the role of competing variables such as particle size and voltage.
Precipitation data obtained in the authors' laboratory are used to show
the extent to which low-sulphur coals can be accused of generating difficult
flyashes.   It is concluded that sulphur in coal is a misleading indicator
of flyash behaviour and is unreliable for estimating precipitator size for
a specified performance.   At cold-side temperatures even low sulphur coal
produces flyash carrying a conducting film of sulphuric acid, but this
mechanism is not available at hot-side temperatures where volume conduction
must be relied upon to avoid electrical difficulties in the precipitator.
Such volume conduction may be impeded by the normal coatings of lime or
alumina on flyash particles.
                                     184

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DOES SULPHUR IN COAL DOMINATE FLYASH COLLECTION  IN ELECTROSTATIC  PRECIPITATORS?

1.  INTRODUCTION

     There must be few engineers and scientists  acquainted w±th the
technology of electrostatic precipitation who do not accept  that  the
collection of flyash is adversely affected by a  low sulphur  level in  the
parent coal.   This belief has been expressed in countless publications in
recent years, usually without support - as if there were no  longer a  need
for any.   The enquiring newcomer to this aspect of precipitation technology
may well be dismayed with the scarcity of consistent information,  which is
disappointing in  a matter of such economic importance as the proper sizing
of precipitators, given that the use of low-sulphur coals is nowadays being
enforced or encouraged.

     In North America one may suspect that design engineers  have  placed
reliance on the set of curves published by Ramsdell (1973)1  relating  required
precipitator size and collecting efficiency  at selected coal sulphur  levels.
The curves, which are claimed to reflect extensive full-scale data, imply
clearly and quantitatively that the lower sulphur levels incur a  considerable
penalty in precipitator size for a given performance.   Although  probably
hundreds of precipitators have been built and tested since the curves were
made public, there seems to be no attempt to compare measured performances
with those predicted, an omission which may  give reassurance to the convinced
but could seem suspicious to the sceptic.    In Britain, Barrett (1971)^ drew
on the results of 109 collection efficiency  tests from. 23 power plants and
analysed their multiple correlations to show that coal sulphur was positively
correlated to effective migration velocity.   Although it is uncertain
whether the tests selected for examination were  all independent of each other
and representative of the whole situation (see later), the analysis stands
as evidence that  coal sulphur has a significant  association  with  precipitator
efficiency - at least under British conditions.   Unlike the Ramsdell curves
the. Barrett study did not reveal an overriding influence of  coal  sulphur,
which  simply emerged as one of several factors in precipitator performance.

     Australian electric utilities have been fuelled for decades  by pulverized
coals  low in sulphur, largely because there  is little else.   While this
means  tha.t Australia has accumulated almost  no experience with controlling
sulphur oxides emissions, the opposite is the case with flyash precipitation.
So far as the present authors are aware, there never has been a well-founded
body of Australian evidence or opinion that  flyash from low  sulphur coals
is invariably difficult to collect in precipitators.   Rather have precipitation
engineers observed repeatedly that coals with the same low-sulphur level
(say 0.5%) can generate flyashes of widely differing precipitabilities,
from faultless in some cases to feeble in others.

     For several  years it has been pass£ among devotees in Australia  to
blame, low-sulphur coals for difficult flyash, with the result that
precipitation research and development have  acquired an emphasis  and  a
progression quite different from any seen elsewhere.   It is the  purpose
of this paper to  examine the circumstances of flyash precipitation in the
particular context of coal sulphur levels and to put the entire question
into perspective.

                                     185

-------
2.  WHY SHOULD COAL SULPHUR AFFECT FLYASH COLLECTION?

     The authors do not know of a closely-argued answer to the above
question in the literature, and they offer the folloxd.ng rationale in
descriptive language as a base for subsequent development.   A number of
the steps in the argument should be familiar to the combustion chemist
but they have not appeared before in this particular context.

     For the most part the sulphur in coal is present as heavy metal
sulphide (e.g. pyrite) or bound organically (in macromolecules of vegetable
and animal origin).   Some sulphur may be present as inorganic sulphate
(e.g. gypsum).   When the coal is burned in the usual excess of oxygen
(i.e. of air), the sulphide and the organic sulphur are oxidized to sulphur
dioxide, and inorganic sulphate will be decomposed at least partially to
sulphur trioxide and sulphur dioxide.   As the flue gas (containing sulphur
oxides) cools on passing from the flame through the passages of the combustion
chamber and the other equipment, opportunity arises to convert a small
proportion (often considered about 1%) of the sulphur dioxide to trioxide.
While there is probably ample catalytic surface in the plant to secure the
formation of sulphur trioxide, the flyash itself may share in the process
and indeed may take the full burden if no other effective area is available.
In any event at some, elevated temperature below the normal boiling point
of sulphuric acid (338°C) the sulphur trioxide and water vapour (the latter
typically 5 - 10% of the flue gas) combine and sulphuric acid begins to
condense on the electrically-insulating nuclei provided by the suspended
flyash.   In this way the flyash surface has the opportunity to become
conducting by the time it reaches the entrance to the precipitator at
110  - 250 C (note that this temperature range is too high to support a
liquid film of sulphurous acid, so that sulphur dioxide is itself useless
for conferring any surface electrical conductivity on the flyash).   It
should be noted that above the evaporation temperature of sulphuric acid
(say at > 300 C) the flyash has no opportunity to receive surface conduction
from coal sulphur and therefore this coal property has no relevance to so-
called hot-side precipitation.

     Confining attention to cold-side precipitation, the next step requires
the assumption that the amount of sulphur trioxide available to make the
flyash conducting passes from adequate to inadequate as the coal sulphur
level is decreased from, typical higher values to low values (say from
2-2 - 5% to below 1%).   If the flyash has too low a conductivity (i.e. too
high  a resistivity)s this constitutes an impediment to electrostatic
precipitation by mechanisms that are known (Goard and Potter (1974)3) and
collection efficiency must fall accordingly.   Thus, if the above assumption
holds (and provided sulphur trioxide is the only origin of flyash conduction),
then low-sulphur coals should cause poor precipitation and the flyash should
exhibit a resistivity above that which causes an impediment to precipitation
(popularly supposed to be 10 " ohm-m, following White (1963)4, but 1Q9-5 ohm-m
is also supportable (Potter (1978)5).   A corollary to this argument states
that the low-sulphur impediment should be. removed by the addition of sulphur
trioxide (or of its equivalents, sulphuric acid or oleum) to the flue gas.
                                     186

-------
3. TO WHAT EXTENT SHOULD COAL SULPHUR AFFECT FLYASH COLLECTION?

     To answer this question we observe that modification of flyash
resistivity is the sole suggested mechanism by which coal sulphur  influences
precipitator performance and then only at cold-side temperatures
(approximately 110 - 250°C).   The significance of this observation is that
once a resistivity impediment is removed (say by sulphur trioxide) further
improvement of collection efficiency cannot be expected.   Thus, based on
the mechanism described above, and assuming a dominant role for coal sulphur
(or of sulphur trioxide added to the flue gas), its anticipated effect is
an initial progressive rise in collection efficiency as sulphur level
increases, followed by a diminishing effect as a constant upper value of
efficiency is reached above a certain sulphur level.   Above this  the
resistivity continues to be decreased below the impediment limit (10°«3 -
10"-5 ohm~m, see above), and at some higher sulphur level the possibility
arises of lowering the flyash resistivity too much, that is to below about
10  ohie-in where the collection efficiency falls on account of the
electrodispersion effect encountered under these conditions  (Paulson
et al (1978)6).

     There could also be a  dependence of the expected sulphur effect on
the amount and particle size of the ash generated by the coal, and two
situations may be discerned.   First, if the ash surface has little or
no power to catalyse the formation of sulphur trioxide in the time available
before the precipitator is  reached, then an increase in ash content or a
lessening of particle size  (on passing from one coal to another at constant
sulphur level) will result  in the available sulphur trioxide being spread
more thinly over the total  ash area and a reduced benefit may be expected
from coal sulphur.   Thus,  in this situation coals high in fine ash may have
nothing to gain from sulphur at any realistic level, and there nay be little
precipitation contrast between low and high sulphur coals.   On the other
hand a good catalytic flyash may succeed in satisfying all its sulphur
trioxide requirements no matter how great an area, of incombustible residue
the coal may produce, in which case the sulphur content of the coal would
be of minor concern and even the lowest levels may not impede precipitation.

     It is relevant to compare these expectations with the corresponding
indications from the Ramsdell and the Barrett approaches described above.
In the Ramsdell data the precipitation efficiency at l50°C is shown steadily
increasing with coal sulphur level up to 3.0% sulphur where the data cease.
It is not clear, however, by what mechanism the precipitation improves above 2%
sulphur, since supporting graphs show that above this level,,the flyash
resistivity lies in the "ideal precipitation zone" below 10  ohm-m.   The
Barrett data are presented  in terms of migration velocity rather than
collection efficiency and show that the penalty to precipitator performance
diminishes as the coal sulphur increases.   The data cease at 3% sulphur,
but were they to continue beyond this it seems that the performance would
have no impediment from coal sulphur above approximately 5%.   To  this extent
the Barrett data reflect the expectation deduced above, but the author
himself warns of extrapolating his data.   Neither Pvamsdell nor Barrett
indicates any dependence of the sulphur effect on ash yield or flyash size.
Ramsdell alone suggests that the sulphur effect is temperature-dependent and
asserts that it should have disappeared at hot-side temperatures (315°-425°C)
as explained above.
                                     187

-------
An interesting aspect of the Barrett data arises from the suggestion that
the results originated from precipitator acceptance tests.   Such tests
have a habit of giving efficiency results conforming to the design value,
so that, if the sizes of the precipitators were originally computed by the
manufacturer with some allowance for coal sulphur level, then this allowance
will tend to persist as a partial correlation to be found in the acceptance
data.

4.  WHAT IS THE PRACTICAL EVIDENCE ON COAL SULPHUR AND FLYASH COLLECTION?

     Previously published work on precipitation efficiency and coal sulphur
has already been reviewed, and much of it was found inconsistent or
inadequate (Potter (1978)*).   Fore evidence has accumulated since, particularly
an extension of the authors' studies and another set of observations from
English electric utilities.   In this latter work  (Sochaczewski (1978) ),
which to the authors' knowledge offers the only practical data definitely
following the expected pattern described in Section 3 above, twenty four
experimental points cover the sulphur range 0.6 - 5.1% and the effective
migration velocity rises linearly from 6.4 to 14.7 cm s"1   with only minor
scatter, there being no further rise above 2.5% sulphur.   Private communi-
cation with the author has disclosed that the four points at and below 1.0%
sulphur originated from two power plants, and that the twenty remaining
points  (covering sulphur levels at and above 1.1% and collection efficiencies
from 93.3 to 98.8%) were obtained at a third plant "during routine performance
checks  carried out under day-to-day operating conditions".   All the tests
were done at 130 - 150 C at gas flow rates within +_ 10% of design and at the
optimum voltages and currents of the precipitators (at least three in number).
Presumably no flue gas additives were used.   Particle size information was
not available, but it would be remarkable if there were no significant
differences.   It is also not clear how many unrelated coals were tested, but
the four points for coal below 1.0% sulphur suggest two unrelated coals, and
the remaining data (20 points) are consistent with three unrelated coals being
tested  (one having 5%S, and the others 1.1% S and 2.8% S plus accidental
blends  of these last two).   It is possible, therefore, that the English data
were obtained from tests on five unrelated coals.   The significance of this
number  of coals and of studies on coal blends emerges from later discussion,
but it  appears that the English information requires more detail and
amplification before its meaning becomes clear.

     In an earlier publication reference was made to the authors' fully
comparative work at 120 C on 23 unrelated Australian coals using a pilot-scale
combustion and precipitation rig with a record of concordance with full-scale
results (Paulson (1974)8).   This work has now been extended to include
43 unrelated coals, combining the results from two different pilot-scale
rigs known to yield results in agreement.   The experimental data were
sufficiently comprehensive to allow efficiencies and migration velocities at
constant voltage or current or at maximum voltage to be plotted against
measured levels of any of the forms of coal sulphur.   The precipitator
performance could also be expressed as precipitator size (i.e. specific
collecting area) for a selected flyash emission at maximum voltage with
adjustment to 15% ash, and these figures were also plotted against coal
sulphur parameters (Figure 1).

                                      188

-------




-
1
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"c
o
u
f—
^^
CL
1


6
5
4
3

2

1
0-8
0-6
0-5
0-4
0-3
0-2
n.]
X
x Australian coals
0 USA coal
-
x
-
X
X
-XX
x
x" *
x x x x
X X y X X
v. Y. v* u
/\ J\
$ X
XA
1 >« X<
~ x x
XX
X
1 1 1 1 1 1 1 1 1
      0    20    40
         SCA  at
60    80   100  120
and 15% ash  content
 140   160   180
m2/m3 s"1)
        FIGURE  1.  PLOT  OF TOTAL COAL  SULPHUR  AGAINST
SPECIFIC COLLECTING AREA  AT 1201  FOR  A FLY-ASH  EMISSION OF
        0-23 gm'3 STP FOR  43  UNRELATED  AUSTRALIAN  COALS
  (Data obtained  at  maximum  voltage and normalized to 15% ash)
                              189

-------
     In addition an attempt was made (Figure 2) to allow for any scatter
attributable to variations in flyash surface area among the coals by
plotting precipitator performance against a modified coal sulphur parameter,
namely, "(total coal sulphur x mass median diameter)/ash content."  (See
Appendix 1.)   In no case was any semblance of a reasonable correlation
found, and our former conclusion is strengthened that in Australia at least,
no reliance can be placed on an association between any coal sulphur
parameter and any measure of precipitator performance.

     Since the 40 Australian coals have appeared in random array in all
attempts to correlate precipitator performance with any coal sulphur
paraineter (see for example Figure 1), it follows that arbitrary selections
of the coals can be made displaying a wide variety of relationships between
these variables.   For example, 22 of the 40 points conform well to a
linear relation between precipitator size (at optimum voltage and 15% ash)
and log total coal sulphur, the relation being in the popular direction,
i.e. low sulphur means larger precipitators (Figure 3a).    However, another
selection of 18 of the 40 points conforms even better to the opposite
relation, i.e. low sulphur means smaller precipitators (Figure 3b).   In
contrast, a third selection of 20 points forms a narrow horizontal band,
meaning that coals with 0.3 - 0.5% sulphur may require a precipitator size
anywhere in a range of 4 to 1, i.e. from unusually large to rather small
(Figure 3c).   On the other hand, 19 points form a narrow vertical band,
meaning that the same medium-sized precipitator suffices for all sulphur
levels from. 0.2 to 2.5% (Figure 3d).   It is only xvhen the full assembly
of points is used that the futility of seeking a coal sulphur effect stands
out (Figure 1).

     Because information is not available, the possibility arises that the
English, data referred to earlier consist essentially of only 5 rather than
24 unrelated coals  (blends not being admissible, see Section 6).   Clearly,
if the true picture is that which prevails in Australia (i.e. no correlation),
then there is a chance of a properly-designed experiment being carried out
with five chosen coals that happen to conform with a coal sulphur effect.
The next section assesses the magnitude of this chance.

5.  THE CHANCES OF FINDING A CORRELATION THAT IS NON-EXISTENT

     In experimental science there is always a chance of  discerning an
apparent relation between two variables when none in fact exists.   A
simulated experiment can show that this chance is not always as remote as
intuition would suggest.   Consider the following such experiment.

     Imagine a practical investigation being undertaken for which five
unrelated coals have been selected with sulphur contents  at intervals
equally-spaced over an acceptably-wide range (for example 0.2 - 4.2%).
In the investigation the coals are burned separately in successive trials,
each producing a characteristic flyash that is electrostatically precipitated
under typical conditions  (the exact conditions being irrelevant so long
as they are agreed equivalent for all the coals).   The five efficiencies  of
ash collection are then imagined to be measured reliably, the intention being
to plot the efficiencies against the corresponding coal sulphur contents
and look for a relation betxreen the two.

                                      190

-------
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V
X ^ X
—
	 II
- (b)
—
—
X
_ X
- v
*x*x
x*
ir
—
1 1 1 1 1 I 1
(d)
X
—
X
E x x
- ^x
_ XX
—
-
1 1 1 1 1 1 1
20  40  60  80  100 120 140     0  20  40  60  80 100 120  140

    SCA at Vmax  and 15%  ash content  (n^/iT^s'1)

  FIGURE 3.  ARBITRARY  SELECTIONS  OF  POINTS FROM
         FIG. 1 SHOWING  FALSE CORRELATIONS
                      192

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     Intuitively, most scientists would probably agree that an assembly of
five well-spaced points on a graph should suffice to show up a monotonic
relation between two variables, although many would prefer to have more
than five points to fix such a relation with satisfying precision.
Suppose, however, that there is, in fact, no monotonic relation to be
found between the two variables;  what chance is there of meeting a
disposition of the points that leads the observer to conclude (falsely)
that the relation does exist?

     To answer this question it was supposed that the five efficiencies
would be dependent on unspecified variables (not coal sulphur) with levels
outside the control of the experimentalist (in precipitation work particle
size is one such variable, but the occurrence of uncontrolled variables
is common in applied scientific work).   These variables would be
responsible for such diversity as was observed in the percentage efficiencies,
within a range that all would agree reasonable but otherwise unnecessary
to specify  (say 80.0 - 99.8%, possibly in one hundred equal 0.2% steps).
With these imposed (but realistic) conditions, one might as well create
the "measured" efficiencies by a random selection process, such as tables
of random numbers or picking them out of a hat.

     Thus in the simulated experiment a hand calculator was used to select
at random the five efficiencies from within a range covering 100 equal steps,
and each efficiency was coupled as it was generated to the next sulphur
content in order on a repeating list of the five of them compiled beforehand.
This procedure was repeated until 96 sets of five points had been assembled,
yielding 96 separate graphs.   A panel of thirteen post-graduate scientists,
active and skilled in experimental research, were then asked to select
independently which of the 96 graphs revealed in their judgement a monotonic
relation.   As might be expected most of the graphs displayed such a wide
scatter of the five points that no monotonic relation could be seen by anyone,
but seme graphs gave more than a hint of a straight line or gentle curve
through the points, and a few left the observers in no doubt.   Since the
scientists' assessments were a matter of personal judgement based on individual
experience, unanimity was the exception, but average results of adequate
precision were readily obtained.   The exercise yielded the following main
conclusions :

1.  the probability that a monotonic relation in a chosen direction occurred
    by chance was estimated to be 1 in 11, this estimate being based only on
    instances where the observer was certain of a relation;

2.  if instances were included where the observer suspected but was unsure
    of a relation, then the probability that a monotonic relation in a
    chosen direction occurred by chance became 1 in 4.

     Paraphrasing the findings of this desktop study, we may say that, in
a given 5-point experiment of the kind envisaged, the chance that a competent
scientist hopeful of a rising monotonic relation will be happy to see this
when there is none at all is 1 in 4;  and the chance that an open-minded
scientist will be quite sure of it is 1 in 11.


                                      193

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     Obviously, when two variables are not cause and effect, something
more searching than a 5-point experiment is required to avoid a disturbingly
high chance of reporting the opposite of the truth.   Indeed to show
convincingly that coal sulphur and flyash collection efficiency are unrelated
when this is the fact requires much more evidence than to demonstrate they
are related when that is the case.   This is not the only pitfall for the
unwary experimentalist, as the following contrasting example shows.

6.  CORRELATIONS TO ORDER FROM GENUINE RESULTS

     Figure 4 illustrates a plot of total coal sulphur against the size of
precipitator required to achieve the same typical flyash emission.   The
size has been normalized to 15% ash for each coal in order to eliminate
one uncontrolled variable.   Each of the four points on the graph is fully
experimental, having been obtained from separate combustion and precipitation
trials on the technical-scale plant at the authors' laboratory.   The
results are quite comparable, being obtained at the same temperature and
at maximum voltage in every case.   Each point is an average based on a
number of efficiency tests, and it may be assumed that no additional amount
of replication could alter the obvious relation to any significant degree.
Although there are only four points (albeit precise ones), the reader may
take it that, had any further trials been carried out between the extremes
of coal sulphur shown, the additional points would only have confirmed the
relation that is there.

     Thus, with the reliability of the information in Figure 4 taken for
granted, it is indisputable that it shows a quadrupling of the required size
of precipitator on passing from 5.6% coal sulphur down to 0.6%;  and this
behaviour would undoubtedly be reproduced on another occasion if attempted.
The authors stress at this point, however, that the results are totally
unable to support the popular view that low coal sulphur causes poor flyash
precipitation.   The reason is important,yet subtle.

     The extreme points of Figure 4 (top left and bottom right) originate
from two unrelated coals, but the two intermediate points are from separate
blends of these two coals.   Thus the four coals burnt were related.   It is
our practical experience that a blend of two coals produces a composite
(or mixed) flyash with precipitating properties intermediate between those
for the two flyashes separately and pro rata on the proportions of each in
the blend.   Clearly, the pulverized fragments of each coal burn separately
and the flyash particles from each coal solidify too quickly for collisions
to merge them into hybrids of different identity.   Since precipitation is
the sum total of at least as many individual acts of migration as there are
flyash particles to collect, the collection efficiency is pro rata on the
composition of the coal blend.   A graph, therefore, of precipitation
properties (observed under comparable conditions) against composition of
coal blend is bound to show a smooth monotonic progression between the extremes.
Furthermore, any property of the coals or of their flyashes that is also
pro rata on the blend will likewise be associated with precipitation properties
in the same monotonic fashion.
                                       194

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0-7
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             10    20    30   40   50    60   70

       SCA at  Vmax and 15%  ash  content (morn's"1)

    FIGURE 4.  PLOT  OF  TOTAL  COAL SULPHUR  AGAINST
PRECIPITATOR  SIZE  AT  120 °C  SHOWING FALSE  CORRELATION
            DUE  TO BLENDING OF TWO  COALS
                        195

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     In this category is the sulphur content of the coal blend, and thus
Figure 4 shows an inevitable relationship that depends solely on the
relative positions of the extreme points of the graph.   It is merely a
matter of selection of coals in the first place to produce any desired
direction of the line displayed in Figure 4 vertical, horizontal, or
diagonal with any direction and slope (hence the heading for this section
of the paper).   Figure 4 is thus quite valueless to show a causal general
correlation of coal sulphur with flyash precipitation and it is possible
that some published work (including the Ramsdell data and the recent English
work) has rather restricted validity because it may be dependent, largely
or wholly, on results from coal blends.   Certainly, in view of the expense
and complex logistics of dust-collection tests in electric utilities, the
use of coal blends is a most attractive and economic experimental plan to
adopt.   It is, however, illusory in the coal sulphur context, as the
above example demonstrates.

7.  WHY THERE IS NO OVERRIDING EFFECT OF COAL SULPHUR ON FLYASH COLLECTION

     There are several reasons why an overriding effect of coal sulphur on
flyash collection is not to be expected.   The chief reasons requiring
comment are (a) the unique surface chemistry of flyash, (b) the existence
of alternative sources of surface conduction for flyash, and (c) the masking
effect of other variables.   In discussing these features it will be seen
that some limitations of hot-side precipitation emerge.

     The surface chemistry of flyash has recently received considerable
clarification through work at the authors' laboratory (Collin (1974)9).
Most of Collin1s work has been carried out on flyash from coals with below
1% sulphur.   No exception has yet been found to the rule that the surface
of fresh flyash consists essentially of a multimolecular but extremely thin
film of aqueous sulphuric acid.   Beneath this invisible fil-i is found a
layer of calcium sulphate (or exceptionally aluminum sulphate) which separates
the acid film from a thin sublayer of calcium hydroxide (or exceptionally
alumina).   Beneath the sublayer is the glassy aluminosilicate core of the
flyash bead.   Storage of fresh flyash in air or at elevated temperature
promptly removes the outermost acid layer by neutralization and volatilization,
and thus the surface properties of the flyash are radically changed.   For
this reason recovery of accumulated flyash from precipitator hoppers for further
collection tests or for later analysis is an unreliable procedure yielding
doubtful results.   Furthermore, water washing of flyash removes all three
layers, exposing the underlying glassy surface, which has quite different
electrical properties from those of the fresh product.   Hence flyash from
lagoons or otherwise washed material is valueless for assessing electrostatic
collection if relevance to electric utility application is required.

     The meaning of this surface structure of fresh flyash to its
electrostatic precipitation is that even low-sulphur coals have a good
chance of producing flyash with ample surface electrical conduction at
so-called cold-side precipitation temperatures (approximately 110  - 250°C) .
                                      196

-------
Thus, the question whether the particles will receive an adequate sulphuric
acid film does not rely in practice on the amount of coal sulphur available,
but is more a matter of how long the dispersed flyash has to scavenge
sulphur trioxide from a supply in the flue gas that is continually replenished
catalytically before the precipitator is reached.   That the flyash normally
takes up sulphur trioxide rapidly from a sufficient supply is demonstrated
by the fact that the flyash is recovered with an acid film present, in spite
of a reactive coating of lime (or alumina) and an elevated temperature.
If the sulphur trioxide supply were poor or were not being scavenged
quickly by the flyash, its surface would not carry any free acid because
this would be converted to calcium or aluminium, sulphates as soon as it
reached the surface.

     If, on occasion, at cold-side temperatures, the sulphuric acid film
is spread too thinly to be continuous (perhaps as a consequence of poor
catalysis or unusually high flyash area), the flyash still need not display
excessive resistivity since water absorption by the sublayers (lime/calcium
sulphate or alumina/aluminium sulphate) can ensure a complete surface
conduction path.   At hot-side temperatures (approximately 300 - 450 C)
neither sulphuric acid nor water appears on the flyash surface, and conduction
must depend on the normal thermal diminution of the resistivity of the glassy
core of the flyash particles to acceptable levels.   While this so-called
volume conduction can be relied upon in many cases at hot-side temperatures,
it is dependent on there being no electrically-obstructive coating on the
flyash surface.   This possibility seems to have been ignored by proponents
of hot-side precipitation, since the obstructive film may be provided in the
relevant temperature interval by the normal lime (or alumina) coatings on
the particles.   Instances of back ionization and associated poor precipitation
of flyash at hot-side temperatures may find their explanation in such
insulating coatings, and this could apply irrespective of the level of
sulphur in the coal.

     There are numerous variables that influence the precipitation efficiency
of flyash at constant temperature and at fixed specific collecting area,
including applied voltage, particle size, carrier gas velocity, particle
re-entrainment and gas distribution.   None of these variables would appear
to have any connection with coal sulphur level, and hence if important enough
they could mask a presumed effect of coal sulphur.   Consider, therefore,
the effect on collection efficiency of particle size (expressed as mass median
diameter with a mixture of sizes as in flyash).   The theoretical effect of
particle size is established and enjoys reasonable practical verification
(Paulson et al (1976)10).   With voltage, specific collecting area, and
temperature all fixed, the observed migration velocity is directly proportional
to the particle size, ignoring mechanical collection efficiency for
simplicity.   This means, for example, that if a given mean size of particle
is associated with a collection efficiency of 90% at a typical operating
condition, then doubling the size elevates the efficiency to 99% and tripling
the size raises it to 99.9%.
                                     197

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Since it is practical experience (Paulson et al (1976)  ) to encounter
flyashes from different coals that cover nearly a threefold range of
mean particle sizes, any specific effect of coal sulphur has to be discerned
against an efficiency variation that may range from 90% to over 99% for
size reasons alone.   In these circumstances it is not realistic to expect
to see an overriding effect of coal sulphur on precipitation efficiency
of any plausible magnitude.   The introduction of the other variables into
the argument only serves to strengthen this conclusion.

     Bearing in mind that precipitation experts have long recognized the
considerable effects on collection efficiency of the several variables
listed above, it may well be asked why an overriding influence of coal
sulphur has found such wide and prolonged acceptance at cold-side
precipitator temperatures.   The answer to this question appears to be
that low coal sulphur has been considered to render the flyash critically
more resistive, so much so that the resulting back ionization is reckoned
to neutralize the electrostatic precipitation process itself, thus overriding
all other variables.   This particular sequence of events now appears to be
more of a fear than a fact for the following reasons:

     a)  there is normally enough sulphur in low-sulphur coal to produce a
         conducting film of sulphuric acid on flyash at cold-side
         precipitator temperatures;  and discontinuities in the film can
         be bridged by water interaction with the sublayers of lime or
         alumina that are present;

     b)  the effect of applied electric field in reducing the resistivity
         of highly insulating flyash layers at all practical precipitator
         temperatures allays losses of collection efficiency that would
                   occur;
     c)  if back, ionization does take place, it is unlikely to neutralize
         all collecting areas completely and simultaneously, provided the
         phasing and intensity of plate rapping are properly selected.


8.  CONCLUSION


1.   This paper addressed itself to the question:   does sulphur in coal
     dominate flyash collection in electrostatic precipitators?   To this
     we answer:  in theory coal sulphur should rot be dominant at any
     typical temperature, and. in practice the weight of the evidence
     confirms it is not.

2.   The combined influence of well-established variables produces such
     large variations in flyash collection efficiency among different
     coals that any plausible effect of coal sulphur could not be dominating
     and at most is probably minor.
                                      198

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3.   Some coal sulphur is probably vital to efficient precipitation
     at cold-side temperatures, but sufficient is present in low-sulphur
     coals to furnish the flyash particles with a conducting film of
     sulphuric acid, and this alone is normally adequate to prevent
     resistive impediments to precipitation.

4.   When poor flyash collection occurs in hot-side precipitation it
     is attributable to electrical obstruction by the normal lime or
     alumina coatings on flyash particles.   This situation has no
     potential for being avoided through the intervention of coal sulphur,
     as in the case in cold-side precipitation.

5.   Experimental tests of whether coal sulphur influences flyash
     precipitation may give false results either by chance or if coal
     blends are relied upon.
                                      199

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 REFERENCES


 1.    Ramsdell,  R.G.   Practical  Design Parameters  for Hot  and Cold
      Electrostatic Precipitators.    Combustion.   45  : 40-43,  October 1973.

 2.    Barrett, A.A.   Electrostatic  Precipitators  - Guidance  for Designers
      and Purchasers.    Filtration and Separation.  67-73,  Jan/Feb.  1971.

 3.    Goard,  P.R.C.,and E.G.  Potter.  Resistivity  in  Electrostatic
      Precipitation -  a Re-appraisal.      In:Proc. Symp. on "The Changing
      Technology of Electrostatic Precipitation",  Adelaide, South Australia,
      Nov. 8, 1974. Inst.  Fuel  (Australian  Membership), 1974.

 4.    White,  H.J.   Industrial Electrostatic Precipitation.   Reading,  MA,
      Addison-Wesley Publishing  Co.  Inc.,  1963, p.297.

 5.    Potter, E.G.   Electrostatic Precipitation Technology :  A Different
      Viewpoint, JAPCA.  28 : 40-46, January 1978.

 6.    Paulson, C.A.J., E.G. Potter,  and K. Ramus.  Pilot-Scale  Electrostatic
      Precipitator  Tests on Copper Converter Flue  Gas. In-.Proc.  Internat.
      Clean Air  Conf., Brisbane, Australia,  May 15-19, 1978.
      Ann. Arbor, Mich., Ann  Arbor Science Publishers Inc., 1978,  p.499

 7.    Sochaczewski, Z.W.   The Relevance of  New and Stricter  Standards for
      Particulate Emission  and Plant Modifications Necessary  to Meet  Them.
      CSIRO Conference on Electrostatic Precipitation, Leura, New South Wales,
      Australia, August 23-24, 1978.

 8.    Paulson, C.A.J.    In: discussion at  Symposium on "The Changing  Technology
      of Electrostatic Precipitation",  Adelaide, South South  Australia, November  8,
      1974;   separate  discussion booklet published by Inst. Fuel (Australian
      Membership),  see pp.  47-48 and diagrams 20-22.

 9.    Collin, P.J.   Some Aspects of the Chemistry of Flyash  Surfaces.  In :
      Proc. Symp. on "The Changing Technology of Electrostatic  Precipitation",
      Adelaide,  South  Australia, November  8, 1974.    Inst.  Fuel (Australian
      Membership),  1974.

10.    Paulson, C.A.J., R.B. Kahane,  and E.G. Potter.    Electrostatic
      Precipitation of Flyash from a Range of Australian Coals.    1976
      Conference of the Institute of Fuel  (Australian Membership), November 3-5,
      1976, Sydney, Australia.
                                      200

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APPENDIX 1
                     A MODIFIED COAL SULPHUR PARAMETER
Assume all particles of a  selected flyash are solid spheres of uniform
size, equal to the mass median diameter D.
                                  3
The weight of each particle  is  irD p/6 when p is the density of flyash
(assumed constant) .

Therefore the number of particles per unit weight of the flyash is
6/rrD3p.
                                             2
Since the surface area of  each  particle  is irD  the total area per
unit weight of  flyash  is  SffD^/TD^p ,  i.e. K/D where K is a constant.

If  the weight fraction of ash  in  the coal  is A  then the area of the
flyash per unit weight of coal is KA/D.

If  the weight fraction of sulphur in the coal is S then coal sulphur
per unit  surface  area  of  flyash is  SD/KA.

Under circumstances where the  available sulphur in coal must be shared
equally by all  the flyash area, it  is preferable to seek a relation between
precipitator performance  and the  parameter SD/A.
                                     201

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                  ANALYSIS OF THERMAL DECOMPOSITION PRODUCTS
                        OF FLUE GAS CONDITIONING AGENTS
                                      by

                               Ralph B. Spafford
                               H. Kenneth Dillon
                              Edward B. Dismukes
                          Southern Research Institute
                           Birmingham, Alabama 35205

                                      and

                               Leslie E. Sparks
                 Industrial Environmental Research Laboratory
                     U. S. Environmental Protection Agency
                 Research Triangle Park, North Carolina 27711
ABSTRACT

     The reactions of two proprietary flue gas conditioning agents used in high
temperature applications have been investigated in the laboratory under condi-
tions simulating those in the flue gas train of a coal-burning power plant.
The two agents investigated were Apollo Chemical Corporation's Coaltrol LPA-40
and LPA-445.  LPA-40 was found to be primarily an aqueous ammonium sulfate
solution and LPA-445 an aqueous solution of diammonium hydrogen phosphate.
The two predominant types of reactions observed in the study were thermal
decomposition and recombination reactions.  The primary thermal degradation
products of LPA-40 at 650 °C were ammonia and sulfur trioxide.  At 160 and
90 °C the decomposition fragments recombined into ammonium sulfate salts.
Extensive decomposition of LPA-445 into ammonia and phosphate species was
observed at 650 °C, with recombination into ammonium phosphate salts occurring
at lower temperatures.


INTRODUCTION

     Most of the older electrostatic precipitators used in coal-burning power
plants operate at temperatures around 150 °C (300 °F).  The recent widespread
use of low-sulfur coals in electric power production in order to comply with
sulfur dioxide emission regulations has led to difficulty in achieving

                                       202

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efficient collection of fly ash in these precipitators.  This difficulty  is
primarily attributable to an increase in the electrical resistivity of  the ash,
which limits the useful voltage and current that can be maintained in a precip-
itator.

     A common approach that has been taken to  improve  the  collection efficien-
cies of these precipitators is the injection of chemical additives into the
gas stream before  it enters the precipitator in order  to modify  the electrical
resistivity of  fly ash or to obtain some other beneficial  effects on precipita-
tor performance.   While chemical  conditioning  agents have  substantially
improved precipitator efficiencies in many instances,  however, it is conceiv-
able that the injection of chemicals into flue gas may result in the release
to the environment of undesirable compounds consisting of  the agents, their
thermal decomposition products, or their reaction products with  components of
the flue gas.

     We have recently completed a laboratory investigation of the chemical
reactions of several flue gas  conditioning agents under conditions simulating
those  in the flue  gas train of a  coal-burning  electric power plant.  The  pri-
mary purposes of the study were to characterize the chemical species resulting
from the addition  of conditioning agents to the flue gas of a coal-fired  power
plant  and to identify hazardous chemical species originating from the agents
that can potentially undergo stack discharge to the environment.

     This paper presents the results of our investigations of two proprietary
conditioning formulations marketed by the Apollo Chemical  Corporation,  Coaltrol
LPA-40 and Coaltrol LPA-445.   The work was funded under EPA Contract 68-02-2200
and was monitored  by Dr. Leslie E. Sparks of the Industrial Environmental
Research Laboratory at Research Triangle Park, North Carolina.


DESCRIPTION OF  THE LABORATORY  APPARATUS

     For the investigation of  the reactions of flue gas conditioning agents, a
laboratory bench-scale facility was constructed to simulate the  flue gas  train
in a full-scale coal-burning power plant.  The basic flue  gas mixture consisted
by volume of approximately 76% nitrogen, 12% carbon dioxide, 8%  water vapor,
and 4% oxygen.  This synthetic flue gas was prepared by mixing charcoal-
filtered compressed air with nitrogen and carbon dioxide from regulated,  com-
pressed gas  cylinders and then electrically heating the mixture  to a tempera-
ture of approximately 650 °C.  Water vapor was added to the hot  gas mixture by
the flash evaporation of metered, gravity-fed  liquid water in the heated  gas
stream.  Trace  amounts of gaseous sulfur dioxide, nitric oxide,  and nitrogen
dioxide could be added individually or in various combinations to the hot gas
mixture.  Typical  concentrations  of these oxides in the gas stream were,  on
the volume basis,  approximately 600 ppm sulfur dioxide, 1000 ppm nitric oxide,
and 100 ppm nitrogen dioxide.  The total volume flow rate  of the gas mixture
was usually maintained at approximately 35 1/min (expressed for  25 °C).

     We had originally planned to suspend fly  ash in the gas stream to  simulate
the particulate produced from  the combustion of coal.  However,  the anticipa-
tion of technical  difficulties associated with resuspending fly  ash in  the flue
gas stream and  with interpreting  the results of reaction studies in a hetero-
geneous system  led to abandoning  the inclusion of fly  ash  in the system.

                                      203

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     The synthetic flue gas mixture was introduced into a series of heated
cylinders of quartz, Pyrex, or stainless steel that represented various parts
of the flue gas train of a coal-fired power plant extending from a point
upstream from the economizer to the outlet of the stack.  The principal compo-
nents of the laboratory train are schematically illustrated in Fig. 1 and are
itemized and described briefly below:

     • A heated quartz cylinder maintaining a portion of the gas stream
       at 650 °C, a representative gas temperature in the duct upstream
       from the economizer.

     « A Pyrex heat exchanger representing the economizer.

     • A heated Pyrex cylinder maintaining a portion of the gas stream
       at about 370 °C, a representative gas temperature in the duct
       between the economizer and the air preheater.

     • A Pyrex heat exchanger representing the air preheater.

     • A heated Pyrex cylinder maintaining a portion of the gas stream
       at about 160 °C, representing the temperature in the duct
       between the air preheater and the electrostatic precipitator.

     • A small wire-and-pipe electrostatic precipitator (ESP)  main-
       tained at a temperature of about 160 °C.

     • A Pyrex heat exchanger simulating cooling near the stack exit.

     • A heated Pyrex cylinder maintaining a portion of the gas stream
       at about 90 °C, a conceivable temperature of the gas stream near
       the top of the stack.

     The dimensions of the cylinders were chosen to provide gas residence
times of 2 sec within each cylinder except in the heat exchangers and the ESP.
The gas residence time within each of the heat exchangers was a fraction of a
second.  The gas residence time within the ESP was about 7 sec.  Each cylinder
enclosing a constant temperature zone was provided with an injection port near
its inlet and a sampling port near its outlet.

     The ESP was activated in some of the earlier experiments with nonproprie-
tary conditioning agents, but it was not activated in any of the experiments
reported in this paper.


CHEMICAL ANALYSIS "OF LPA-40 AND LPA-445

     Samples of Coaltrol LPA-40 and Coaltrol LPA-445 for use in this investiga
tion were supplied by Apollo Chemical Corporation.  Both of these formulations
were chemically analyzed so that possible thermal decomposition products of
the agents could be postulated.  The flue gas stream would be sampled and
analyzed for the appropriate chemical species.
                                       204

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HEAT
EXCHANGER
        r~\\
           HEAT
           EXCHANGER

           (AIR
           PREHEATER)
             370 °C
             ZONE
                                   S02  NC>2  NO
                                   IN   IN
                                   N2   N2
              HEAT
              EXCHANGER
              (ECONOMIZER)
                                650
                                     ZONE
ELECTRIC
HEATER
                 Figure 1.   Schematic diagram of flue gas train.
                                        205

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     The sample of LPA-40 supplied by Apollo was a light brown solution with a
density of 1.27 g/ml and a pH of 3.9.  The qualitative identification of  the
primary components of the formulation was performed by infrared spectroscopy
and ion chromatography.l  The solid material resulting from the evaporation
of the solvent from the formulation possessed an infrared spectrum that was
identical to that of ammonium sulfate, (NHi»)2SOi,.  Analysis of the formula-
tion by ion chromatography revealed that sulfate ion was the only anion that
was present in significant amounts.

     The LPA-40 formulation was quantitatively analyzed for ammonium ion by
the indophenol method2 and by acid-base titration with sodium hydroxide solu-
tion.  The sulfate concentration was determined by titration with barium per-
chlorate solution using Thorin as an indicator.3  The results of these
analyses showed that the LPA-40 formulation consisted of about 40% w/w
ammonium sulfate in water.

     The brown coloration of our sample of LPA-40 was believed to be due to
the presence of ferric ion in the formulation.  The LPA-40 solution was
analyzed by atomic absorption spectroscopy and was found to contain approxi-
mately 0.2% w/w iron.  The nature of the iron compound in the formulation was
not characterized; but the compound is speculated to be ferric hydroxide, pres-
ent in the formulation as an impurity in the ammonium sulfate used to prepare
the agent.

     The  sample of LPA-445 was a clear, colorless liquid with a distinct
ammoniacal odor.  Its  density was 1.14 g/ml and its pH approximately 8.2.
Mass spectrometrie analysis of the solid residue remaining after evaporation
of the formulation to dryness indicated that the solid residue was an ammonium
phosphate salt.

     LPA-445 was identified as an aqueous solution of diammonium hydrogen phos-
phate, (NHit) zHPOit, and the concentration of the solution was determined by
analyzing the formulation for ammonium ion by the indophenol method and for
orthophosphate ion by ion chromatography and by the vanadomolybdophosphoric
acid colorimetric method.1*  The LPA-445 formulation was found to  consist of a
solution of approximately 24% w/w diammonium hydrogen phosphate in water.
Analysis of the formulation by ion chromatography also revealed the presence
of trace amounts of sulfate ion (approximately 7.30 ymol/g or 0.08% w/w).

     Two separate samples of LPA-445 were used during the investigation of
this conditioning agent.  Each of the samples was analyzed individually, and
the two samples were found to be identical within the experimental limits of
error of the chemical methods used in the analyses.


POSTULATED REACTION MECHANISMS

     The predominant reaction types expected in the study of both LPA-40 and
LPA-445 were thermal decomposition reactions at high temperatures and recombi-
nation of the degradation fragments at lower temperatures.  At 650 °C the
probable decomposition of ammonium sulfate, the major component of LPA-40, was
expected to proceed via the following equation:

                  (NHit)2SOil(s) —> 2NH3(g) + H20(g) + S03(g)                (1)

                                      206

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 The  occurrence of this reaction is consistent with the thermodynamic data of
 Kelley  et  al.5 and Scott and Cattell.6  In addition, based on the findings of
 Halstead,7 nitrogen,  nitrogen oxides, and sulfur dioxide were expected as
 relatively minor products from the thermal decomposition of ammonium sulfate.
 The  recombination of  the major thermal decomposition products was expected to
 proceed by the stepwise reversal of equation 1 with decreasing temperature:

                         S03(g) + H20(g) ~> H2SOi,(g)                      (2)

                     NH3(g) + H2S(Mg) — * NH^HSCKd or g)                 (3)

                   NH3(g) -f mUHSCMl or g) — >  (NHj,)2SOl((s)               (4)
     We initially expected the major component of LPA-455, diammonium hydrogen
phosphate, to dissociate at 650 °C into gaseous ammonia and phosphoric acid.
The resultant phosphoric acid was then expected to decompose completely into
phosphorus pentoxide (P20s) and water or to polymerize into condensed phosphate
species (linear polyphosphates such as pyrophosphate, cyclic metaphosphates,
or "infinite chain" metaphosphates) .

      The thermal decomposition of diammonium hydrogen phosphate was studied by
 Erdey, Gal, and Liptay8 by means of thermal gravimetry and differential thermal
 analysis.  This study indicated that diammonium hydrogen phosphate thermally
 decomposes in a stepwise fashion with several decomposition processes proceed-
 ing sequentially as the temperature is raised.  These processes are:


                                                       NH3(g)              (5)


                                                      )                    (6)


                2NH«lH2POif(l) -i—   (NH^)2H2P207(s) + H20(g)             (7)


               n(NHO2H2P207(s) ^°-°-^> 2 (NH4P03)n(s) + nH20(g)           (8)

            2(NHlfP03)n(s) SOOzSOO^ 2nNH3(g) + nP205(g) + nH20(g)        (9)

Thus, on the basis of this study, at 650 °C diammonium hydrogen phosphate was
expected to thermally decompose into ammonia, phosphorus pentoxide (which
would be analyzed as orthophosphate ion in gas samples removed at 650 °C) , and
water.  As the flue gas stream was cooled from 650 to 90 °C the reaction
sequence given in equations 5 through 9 was expected to be reversed.  Thus,
near the exit of the gas train, the probable recombination products were
expected to be diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

      The decomposition reactions of both LPA-40 and LPA-445 discussed above
 were expected to be identical whether or not reactive sulfur and nitrogen
 oxides were present in the flue gas.  However, significant amounts of the
 ammonia formed during the thermal decomposition of injected LPA-40 and LPA-445
 were expected to possibly be destroyed in the 650 °C zone in the presence of
 added nitrogen oxides in the gas stream due to the reaction of ammonia with
 nitrogen oxides.

                                        207

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     No unusual or highly toxic decomposition or reaction products of measur-
able concentration were expected to be formed in the gas stream when LPA-40 or
LPA-445 were injected.  The only highly toxic compound that we could envision
possibly being formed in the gas stream was phosphine (PH3) from the highly
unlikely reduction of some phosphorus-containing species during the injection
of LPA-445.
INJECTION OF LPA-40 AND LPA-445 INTO THE FLUE GAS

     Both of the formulations were introduced into the flue gas stream as aero-
sols.  Dilute, filtered aqueous solutions of LPA-40 and LPA-445 were nebulized
at a rate of 0.2 ml/min with a Retec X70/N nebulizer assembly (Burton Division,
Cavitron Corporation, Van Nuys, California).  The nebulizer was activated with
dry nitrogen gas, and the aerosol resulting from the nebulization process was
introduced into the 650 °C constant temperature zone through a quartz tube
that extended from the outlet of the nebulizer to the center of the flue gas
stream.  Since Apollo's LPA series of additives are normally used for high tem-
perature application (gas stream temperatures of 590 to 900 °C), both LPA-40
and LPA-445 were injected into the hottest constant temperature zone in our
laboratory flue gas train, the 650 °C zone.  The rate of injection of LPA-40
was chosen so that the concentration of ammonium sulfate in the flue gas at
650 °C did not exceed the upper limit specified by Apollo,  41 yg/1.9'10   The
measured concentrations of ammonium sulfate injected into the flue gas stream
over the course of the study ranged from 9 to 41 yg/1 at 650 °C.   No informa-
tion was found on the concentration of diammonium hydrogen phosphate in  the
flue gas recommended by Apollo.  The rate of injection of LPA-445 was thus
somewhat arbitrary and ranged from approximately 14 to 67 yg/1 at 650 °C
during the first half of the study of LPA-445.   During the second half of the
study, however, the nebulizer began malfunctioning, and the injection rates
ranged from only 4 to 26 yg/1.

     The average injection rates of ammonium sulfate and diammonium hydrogen
phosphate were determined by chemically analyzing the solutions in the nebu-
lizer before and after a series of experiments.  The solutions of LPA-40 were
analyzed for ammonium ion and sulfate ion, and the LPA-445 solutions were
analyzed for ammonium ion and phosphate ion.  The injection rates were calcu-
lated from the differences in the amounts of ammonium ion and sulfate or phos-
phate ion in the nebulizer before and after the nebulization period.  These
analyses indicated that in many experiments with LPA-40 as much as 25% more
ammonium ion was injected into the gas stream than was sulfate (based on the
ratio of equivalents lost from the nebulizer).   In the experiments with
LPA-445, a 25% excess of ammonium ion relative to phosphate ion (again on an
equivalent basis) was apparently nebulized into the gas stream when the  nebu-
lizer was functioning properly.  During the later experiments, when the
nebulizer was not functioning properly, the average excess of ammonia over
phosphate averaged 90%.  The apparent origin of the excess ammonia during the
nebulization of LPA-40 was the decomposition of a residue of ammonium sulfate
that collected in the quartz tube of the nebulizer at high injection rates.
The excess ammonia, apparently injected during the nebulization of LPA-445,
can be partially explained by the appreciable vapor pressure of ammonia  that
is present over solutions of diammonium hydrogen phosphate, even at room
temperature, and by the decomposition of solid ammonium dihydrogen phosphate

                                       208

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that collected in the quartz tube of the nebulizer.  However, these cannot
completely accout for the large excess of injected ammonia during the period
of malfunctioning of the nebulizer, and no satisfactory explanation could be
found.
SAMPLING AND ANALYTICAL METHODS

     During the  investigations of LPA-40  and  LPA-445,  the  flue  gas was  sampled
and analyzed for a variety  of substances.   In both  studies  the  gas stream was
analyzed for background sulfur dioxide, sulfur trioxide, nitric oxide,  and
nitrogen dioxide.  In  the investigation of  LPA-40,  the gas  stream was specifi-
cally analyzed  for ammonia,  ammonium ion, sulfate ion,  sulfite  ion, nitrate
ion, nitrite ion, and  iron.  In  the  investigation of LPA-445, the gas stream
was specifically analyzed for ammonia, ammonium ion, orthophosphate ion, con-
densed  phosphate species  (pyrophosphates, metaphosphates,  etc.), and phosphine.
The selection of these compounds for analysis was based on  the  anticipated
thermal decomposition  reactions  of  the conditioning agents  and  the expected
chemical reactions of  the agents or  their degradation  products  with various
components  of the flue gas  stream.

     Sulfur trioxide was determined  by sampling  the flue gas through a con-
trolled condensation coil11'12 and by subsequently measuring the collected
sulfate by  the barium  perchlorate-Thorin  titration method or by ion chromatog-
raphy.  Sulfur dioxide was  collected downstream  from the coil in a bubbler
containing  3% hydrogen peroxide, and the  resulting  sulfate was determined by
titration of the bubbler solution with 0.1 N  sodium hydroxide to the bromphenol
blue endpoint or by analyzing the solution  for sulfate by ion chromatography.

     In the absence of added nitrogen oxides  to  the gas stream,  nitrogen diox-
ide was determined by  the Greiss-Saltzman procedure;13 nitric oxide was first
oxidized to nitrogen dioxide on  firebrick impregnated with chromium trioxide
and then analyzed by the Greiss-Saltzman method.  In the presence of added
nitrogen oxides,  the phenoldisulfonic acid method11* was used to determine the
sum of  nitric oxide and nitrogen dioxide  concentrations (as nitrate ion), and
the Greiss-Saltzman method was used  to determine the nitrogen dioxide concen-
tration.  The concentration of nitric oxide was  determined by difference.

     In the investigation of LPA-40,  ammonia  was absorbed from  the flue gas in
bubblers containing 0.1 N sulfuric acid;  the  resulting  ammonium ion was then
determined by the indophenol colorimetric procedure.  Particulate material
from the flue gas was  collected  ahead of  the  bubblers  on heated quartz wool
plugs at 650 °C  and on heated Teflon filters  at  160 and 90  °C.  Exposed fil-
ters and plugs were usually washed with distilled,  deionized water.  The
washes  were analyzed for ammonium ion by  the  indophenol method  and for sulfate,
sulfite, nitrate, and  nitrite by ion chromatography.   In some experiments,
exposed filters  were washed with tetrachloromercurate solution, and sulfite
was determined by the  West-Gaeke method.15  In other experiments, iron was
determined by atomic absorption  spectroscopy  in  either water washes or hot
hydrochloric acid washes of the  quartz wool plugs.
                                       209

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     In the investigation of LPA-445, the gas stream was usually sampled
through a particulate filter (either a quartz wool plug at 650 or 370 °C or a
fine porosity Teflon disc at 160 or 90 °C) and then through a bubbler of 0.1 N
sulfuric acid.  The material collected on a filter or in the bubbler was
analyzed for ammonium ion, orthophosphate ion, and condensed phosphate species.
In a few experiments the gas stream was sampled into a bubbler of sodium
bicarbonate-sodium carbonate buffer solution, and the solution was subsequently
analyzed by ion chromatography.  Ammonium ion was determined by the indophenol
method.  Orthophosphate and condensed phosphate ions were determined colori-
metrically, either by the vanadomolybdophosphoric acid method or by the stan-
nous chloride method.16  In both methods, orthophosphate ion was determined
directly, whereas condensed phosphate ions were first hydrolyzed by boiling
in a dilute acid solution and then determined colorimetrically as ortho-
phosphate ion.

     In one set of experiments with LPA-445 the gas stream was sampled through
a bubbler containing silver diethyldithiocarbamate reagent and analyzed colori-
metrically for phosphine.17


VARIATION OF EXPERIMENTAL PARAMETERS

     The experimental parameters that were varied in these investigations
included the composition of the flue gas into which LPA-40 and LPA-445 were
added  and the temperature of removal of gas samples to be analyzed.  The speci-
fic combinations of experimental conditions that were employed are shown in
Table  1.  In the investigation of each agent, the first series of experiments
was conducted with a simplified flue gas mixture containing no added oxides of
sulfur or nitrogen.  In the later series of experiments, the reactive oxides
of sulfur and nitrogen were added.


                 Table 1.  EXPERIMENTAL CONDITIONS USED IN THE
                     INVESTIGATIONS OF LPA-40 AND LPA-445

                               Injection
         Gas composition    temperature, °C   Sampling temperature, °C
       No  added  SOX  or  NOx        650        650, 370 (LPA-445 only),
                                               160, and 90

       600 ppm S02 added          650        650  (LPA-445 only)

       600 ppm S02,               650        650, 160, and 90  (LPA-40);
         1000 ppm NO, and                      160 and 90 (LPA-445)
         100 ppm N02 added


     As previously discussed, both LPA-40 and LPA-445 were added to the gas
 stream at  650 °C in  all of  the  experiments.  In the investigation of LPA-40,
 the  flue gas was usually removed near the outlet of the 650 °C zone into a
 sampling manifold.   In  some experiments the sampling manifold was maintained
 as hot as  possible  (approximately 500 °C) in order to study the thermal


                                       210

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degradation of the conditioning agent, and in other experiments the  flue gas
was allowed to cool rapidly to 160 or 90  °C in the sampling train in order  to
study the recombination reactions of the decomposed conditioning agent.  The
purpose of this sampling procedure was to minimize the wall losses that would
have occurred in the flue gas train if the gas stream had been sampled at the
outlets of the 160 and 90 °C constant temperature zones.  In the investigation
of LPA-445, the sampling manifold was not used due to gas flow metering prob-
lems encountered in the use of the manifold in the investigation of LPA-40.
Rather, the flue gas was sampled directly from the outlet of the 650 °C zone
in the thermal decomposition studies and  from the outlets of the 370, 160, or
90 °C zones in the recombination studies.
EXPERIMENTAL  RESULTS  OF  THE  INVESTIGATION OF LPA-40

Thermal  Decomposition Studies

      Typical  results  of  the  thermal  decomposition studies of LPA-40 are given
in Table 2.   The primary thermal degradation products of LPA-40, at 650 °C in
flue  gas containing no added sulfur  or nitrogen oxides, were sulfur trioxide,
sulfur dioxide, and ammonia.   The  sulfur oxides recovered were approximately
90% sulfur  trioxide and  10%  sulfur dioxide.  Microgram quantities of a solid
iron  compound were also  found, but the iron compound was not further character-
ized.  Nitrogen or nitrogen  oxides should also have been produced along with
sulfur dioxide from the  oxidation  of ammonia by sulfur trioxide.  Because of
the large background  levels  of nitrogen in the flue gas, however, measurement
of the trace  amounts  of  nitrogen produced by this reaction was not possible.
Nitrogen oxides were  found at  levels no higher than the background concentra-
tions of approximately 10  ppb.

      In  one set of experiments, instead of injecting LPA-40, an aqueous solu-
tion  of  ordinary ammonium  sulfate was injected into flue gas containing no
added sulfur  or nitrons a oxides.   The primary thermal degradation products of
ammonium sulfate found were the same as those of LPA-40 at 650 °C—ammonia,
sulfur trioxide, and  sulfur dioxide.   The sulfur oxides recovered consisted of
about 95% sulfur trioxide  and 5% sulfur dioxide.   There was no indication that
the relative  amount of sulfur dioxide changed significantly as the result of
the absence of the iron  compound found in LPA-40.

      The primary thermal decomposition products of LPA-40 in flue gas contain-
ing added sulfur and  nitrogen oxides were sulfur trioxide and ammonia,  the
same principal degradation products  that were found in the absence of reactive
gases in the  flue gas stream.  Because of the large background concentrations
of sulfur dioxide that were added  to the gas stream in these experiments, how-
ever, the small amounts  of sulfur dioxide produced during the thermal degrada-
tion of  LPA-40 that were observed  in the absence of reactive gases could not
be detected.

Recombination Studies

     No  Oxides of Sulfur or Nitrogen Added to Flue Gas.   The averaged results
of the recombination  studies of LPA-40 in the absence of added reactive oxides
in the flue gas are given  in Table 3.  When the gas stream was sampled at

                                        211

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          Table  2.  DETERMINATION  OF  THERMAL  DECOMPOSITION PRODUCTS
                              OF  LPA-40 AT  650 °C

                                      Concentration, meq/1 x  10.000*
                                   	Observed	    Injected
                                               Total
             Gas  composition        SO3   S02    SOX    NH3  SOiT2    NHi,+

        Without added  S02  or NOX    4.97   0.56   5.53  4.44  6.11   6.lit

        Without added  S02  or NO^  5.54   0.22   5.76  5.01  7.81   7.53

        With 600  ppm S02  and       3.43   -     -     3.21  7.85   7.85t
          1100 ppm NOX added
        * Expressed for 25 °C.   To convert the concentrations  to  parts
          per million (gas by volume) multiply the SOs  and  S02  concentra-
          tions by 1.22 and the NH3 and NHi/4" concentrations by 2.44.

        t Not determined independently.  Based on S0ij~2 lost from the
          nebulizer.

        t An ammonium sulfate solution was injected instead of LPA-40  in
          this experiment.


160 °C, the primary product  found on the particle filters appeared to  be ammo-
nium bisulfate, NHijHSOi,.  Evidence of  lesser amounts of ammonium sulfate was
also found by analysis  of the  filters, but the predominance of the bisulfate
salt was indicated by the low  ratios of ammonium ion concentration to  the
anion concentration.  These  ratios are listed in Table 4.  Expressed in equiva-
lents, the average ratio was 0.59.  This corresponded to mole fractions of 0.83
for ammonium bisulfate  and 0.17 for ammonium sulfate in the filter catch.   An
average of about 4% of  the total sulfur species recovered was sulfur trioxide
(or sulfuric acid vapor), and  about 4% was recovered as sulfur dioxide.
Ammonia was the only nitrogen  compound found at significant concentrations.
Nitrogen oxides were not above the background levels.

     When the gas stream was sampled at 90 °C, the primary recombination pro-
duct found appeared to  be ammonium sulfate.  The average ratio of ammonium ion
concentration to anion  concentration expressed in terms of equivalents was
0.89.  This corresponded to mole fractions of 0.76 for ammonium sulfate and
0.24 for ammonium bisulfate  in the filter catch.  Sulfur trioxide (or sulfuric
acid vapor) was found to be present at concentrations representing 0.5 to 0.8%
of the sulfur compounds, while sulfur  dioxide represented from 4 to 6%.  Since
no sulfuric acid should exist as vapor at 90 °C, the sulfuric acid found must
have occurred as fine particles of condensed liquid that slipped through the
filter.  As above, ammonia was the only nitrogen compound found in significant
concentrations.

     When ordinary ammonium sulfate was injected into the flue gas instead of
LPA-40, the predominant recombination product found at 160 °C was apparently
ammonium bisulfate; at  90 °C the main product appeared to be ammonium sulfate,

                                       212

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Cable 3.   RESULTS OF THE RECOMBINATION STUDIES OF LPA-40 AND AMMONIUM  SULFATE
        IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
      Agent
     injected

    LPA-40
Sampling
 temp.,
   °C
    Concentration, meq/1  x  10,000*
 Observed  (averaged values)
HSOi,"                Total
                     sulfur
 or
   160     7.31  0.29  0.31
    90    14.80  0.11  0.73
                    species  injected
                      7.91
                     15.64
                        13.81
                        19-08
                                Recovery ,
                                                 57
                                                 82
160     5.29
 90     5.35
                                0.06  0.14
                                0.06  0.14
                                5.49
                                5.55
                                7.45
                                7.45
                                   74
                                   74
    LPA-40
    (NHi»)2SOi,
   160
    90

   160
    90
 4.28
13.07
5.89
5.52
 3.06
 4.53
                                              Total
                                            nitrogen    NHi,
                                             species  injected
                            10.17
                            18.59
13.63
19.30

 8.01
 8.01
75
96
    * Expressed for 25 °C.  To convert the concentrations to parts per
      million on a hypothetical volume basis, multiply the concentrations
      of the sulfur species by 1.22 and the concentrations of NHit  and
      NH3 by 2.44.
   Table 4.  ANALYSIS OF THE RECOMBINATION PRODUCTS OF LPA--40 AND AMMONIUM
    SULFATE IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN
        Agent
       injected

      LPA-40
   Sampling
    temp.,
      °C
      160
       90
            [HSOiTl or  [SOiTz]
             found on  filter

                  0.59
                  0.89
                            Mole
                          fraction
                            0.83
                            0.24
                                Mole
                              fraction
                             (NHlt)2SOi)

                                0.17
                                0.76
                    160
                     90
                      0.58
                      0.85
                            0.84
                            0.30
                                0.16
                                0.70
                                      213

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as during the injection of LPA-40.  The predominance of one sulfate salt over
the other was indicated by the ratios of ammonium ion concentrations to the
sulfate and bisulfate concentrations (Table 4).  At 160 °C the average ratio
expressed in terms of equivalents was 0.58, which corresponds to mole  frac-
tions of 0.84 for ammonium bisulfate and 0.16  for ammonium sulfate.  At 90 °C
the average was 0.85, which corresponds to mole  fractions of 0.70  for  ammonium
sulfate and 0.30 for ammonium bisulfate.

     Sulfur and Nitrogen Oxides Added to Flue  Gas.   The averaged  results of
the recombination studies of LPA-40 in flue gas  containing added oxides of
sulfur and nitrogen are given in Table 5.  The predominant recombination pro-
ducts found at 160 and 90 °C were ammonium sulfate salts.  However, uncertain-
ties in the data did not permit a definite conclusion to be drawn about the
distribution of the recombination products between ammonium sulfate and ammo-
nium bisulfate.  The data obtained in these experiments were based on only a
few determinations, had a large scatter, and gave poor mass balances.   At
160 °C the ratio of ammonium ion concentration to anion concentration  (each
expressed in meq/1) was found to range from 0.85 in one experiment (which
would indicate a predominance of ammonium sulfate) to 0.21 in another  (which
could indicate the occurrence of ammonium bisulfate in an excess of sulfuric
acid).  At 90 °C the ratio ranged from 0.51 to 0.06.  With the exception of
one value of 0.41, which corresponds to mole fractions of 0.98 for ammonium
bisulfate and 0.02 for ammonium sulfate, these low ratios indicate an excess
of sulfuric acid over any ammonium salt present.  Any sulfate salt initially
formed would have been converted to the bisulfate salt by the excess acid.


          Table 5.  RESULTS OF THE RECOMBINATION STUDIES OF LPA-40 IN
            FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN

                  	Concentration, meq/1 x 10,000*	
        Sampling    Observed  (averaged values)
         temp.,    HSOrt"           Total sulfur     SOi,"2    Recovery,
        	^C	  or SOi,"2    S03     species      injectedt      %

           160      2.08    0.41       2.49         5.12        49
            90      6.80    0.37       7.17         9.62        75
                                  Total nitrogen
                             NHs     species      injectedt
160
90
2.02
1.93
0.22
0.23
2.24
2.16
                                                    5.12        44
                                                    9.62        22
        * Expressed for 25 °C.  To convert the concentrations to parts
          per million on a hypothetical volume basis, multiply the con-
          centrations of the sulfur species by 1.22 and the concentra-
          tions of NHn+ and NH3 by 2.44.

        t Based on S0i|~2 lost from nebulizer.
                                      214

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     The only chemical species  found at significant  levels  in any of  the
experiments with added sulfur and nitrogen oxides  in the gas stream were ammo-
nium and sulfate ions, sulfur trioxide, and ammonia.  Only  negligible amounts
of nitrite, nitrate, and sulfite ions could be detected in  any of the filter
washes analyzed by ion chromatography.  And because  of the  high background
levels of nitric oxide, nitrogen dioxide, and sulfur  dioxide, the small quan-
tities of these oxides that  could possibly be formed  in these experiments
could not be determined.

     In most of the experiments with added nitrogen oxides present in the gas
mixture, the concentrations  of  ammonia and ammonium ion recovered from the gas
stream were significantly less  than the injected concentrations of ammonium
ion into the flue gas.  This observation is consistent with the finding
obtained in earlier studies with ammonia during these investigations that
extensive reaction occurs between nitrogen oxides  and ammonia in the flue gas
train at 650 °C.


EXPERIMENTAL RESULTS OF THE INVESTIGATION OF LPA-445

Injection of LPA-445 into Flue Gas Containing No Added Oxides of Sulfur  or
Nitrogen

     The experimental results of the study of LPA-445 in flue gas  containing
no added oxides of sulfur or nitrogen are given in Tables  6 and  7.   Table 6
compares the total amounts of ammonium and phosphate ions  that were  collected
with the amounts injected.  Table 7 gives the quantities  of ammonium,  ortho-
phosphate, and condensed phosphate ions found on the particulate filters  and
in the bubbler solutions.

     Thermal Decomposition Studies.   The thermal degradation products of
LPA-445 found at 650 °C on the filters and in the bubblers  in flue gas contain-
ing no added sulfur or nitrogen oxides were ammonium ion,  orthophosphate  ion,
and condensed phosphate ions.  Table 6 shows that, on the average,  88% of  the
injected ammonium ion was recovered at 650 °C whereas only  52% of  the  injected
phosphate ion was recovered.  This difference in recoveries strongly suggests
that when LPA-445 was injected into the gas stream at 650  °C diammonium hydro-
gen phosphate decomposed extensively into gaseous ammonia  and particulate
phosphate species.  The low recovery of the phosphate species can  be attrib-
uted chiefly to wall losses of phosphate particles due to  either impingement
and adsorption or to settling out of the particles.

     From Table 7 it can be seen that about 90% of the recovered ammonium ions
was collected in the bubbler, a result also indicating that extensive  decompo-
sition of the diammonium phosphate to ammonia gas occurred.  For phosphate
ions, roughly 50% was found either on the filter or in the  bubbler.  This
result suggests that extensive volatilization of phosphate, perhaps  to phos-
phorus pentoxide, also occurred.  On the other hand, the presence  of a signif-
icant fraction of the phosphate on the filter suggests that part of  the  phos-
phate remained as particulate.   The mole ratio of ammonium  ion to  total
phosphate on the filter was approximately 0.9.  This ratio  suggests  that  the
filter may have collected an ammonium phosphate solid with  a mole  ratio  of
ammonium ion to phosphate of 1:1.   The thermal stabilities  of ammonium


                                       215

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  Table 6.  RECOVERY OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
        IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN

                          Concentration, pmol/1*
                                                      Recovery, %
                                                             Total
Sampling
temp . ,
°C
650
370
160
90
Injectedt

NH4+
1.666
2.838
1.949
2.271
Total
POiT3
0.660
1.363
0.706
0.879
Observed

NH4+
1.462
2.173
1.131
0.921
Total
PO.T3
0.344
0.772
0.111
0.119
                                                       88     52
                                                       77     57
                                                       58     16
                                                       41     14
           * Expressed for 25 °C.  To convert to parts per million
             on a hypothetical volume basis, multiply by 24.4.

           t Based on NHit  and P0i»~3 lost from nebulizer.
Table 7.  DISTRIBUTION OF DECOMPOSITION AND RECOMBINATION PRODUCTS  OF  LPA-445
        IN FLUE GAS CONTAINING NO ADDED OXIDES OF SULFUR OR NITROGEN

                                 Concentration, ymol/1*
Sampling
temp. ,
°C
650
370
160
90
Collected on

NHtt+
0.124
0.267
0.102
0.127
Ortho-
P04-3
0.123
0.393
0.068
0.087
filter
Condensed
P04-3
0.041
0.148
0.029
0.013
Collected in

NHi,"1"
1.338
1.906
1.028
0.794
Ortho-
POiT3
0.156
0.188
0.002
0.004
bubbler
Condensed
POi+~3
0.025
0.042
0.011
0.016
     * Expressed for 25 °C.  To convert to parts per million on a hypo-
       thetical volume basis, multiply by 24.4.
                                      216

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orthophosphates, however, make the existence of  an ammonium phosphate  solid
appear improbable at 650  °C.  Perhaps gaseous  compounds were merely adsorbed
on the quartz wool in a ratio suggesting a  stoichiometric compound.

     The decomposition studies at 650 °C also  led to  the  following observa-
tions :

     • Approximately 25%  of  the  original orthophosphate was converted
       to condensed phosphate  (see Table 7).

     • Negligible quantities of  ammonia were oxidized to nitrogen
       oxides.  The total concentration of  nitrogen oxides was about 1%
       of the concentration  of ammonium ion collected on the filter and
       in the bubbler.

      Recombination Studies.  At  370, 160, and  90 °C,  ammonium  ion, ortho-
phosphate  ion,  condensed  phosphate  ion, and traces of nitrogen oxides  were
found  in the gas  stream.   These  were the same  species found in the flue  gas
sampled at  650  °C.  As shown in  Table 6, the recovery of  ammonium ion  was
greater than the  recovery of total phosphate ion at each of the three  collec-
tion  temperatures.  The recovery of ammonium ion averaged 77,  58, and  41%,
respectively, at  370, 160, and 90 °C.  The  recovery of total phosphate species
averaged 57,  16,  and 14%  at  the  same temperatures.  The greater recovery of
ammonium ion relative to  phosphate ion at all  collection temperatures  (see
Table 6) seems  to indicate,  as discussed previously, that the  collected ammo-
nium ion originated from  a gaseous species  (ammonia) in the flue gas stream
and that the collected phosphate ions originated from particulate phosphate
species.  However, the data  in Table 6 also show a general decrease in the
recoveries  of both ammonium  ion  and phosphate  ion, as the physical location of
the sampling point was further removed from the  conditioning agent injection
po'int.  The decreasing recoveries of phosphate ions can be attributed  to wall
losses of particulate phosphate  species, but wall losses alone would be inade-
quate to explain  decreasing  recoveries of gaseous ammonia.  Rather, the trend
of decreasing recoveries  of  ammonium ion indicates that recombination  of
ammonia with particulate  phosphate species  occurred in the gas stream  at the
lower temperatures.  The  decreasing recoveries of ammonium ion at the  lower
temperatures can  thus be  partially attributed  to wall losses of particulate
ammonium phosphate salts.

     On the average nearly 90% of the ammonium ion collected at each tempera-
ture was found  in the bubbler solution.  This  indicates that the source of the
ammonium ion collected in the bubbler was gaseous ammonia.  This ammonia gas
presumably  originated from two separate sources:  (1) the original decomposi-
tion of diammonium hydrogen  phosphate, or (2)  the injection of excess  ammonia
from the nebulizer.

     At 370 °C, approximately 70% of the total collected phosphate was found
on the particle filter.   This percentage increased to approximately 85% at 160
and 90 °C.   These results indicate that as  the temperature was lowered the
extent of recombination of the original decomposition products into solid ammo-
nium phosphate  salts increased significantly.  At all of the sampling  tempera-
tures, approximately 75%  of  the  phosphate ions collected on the particle
filters were orthophosphate  ions.

                                       217

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     The mole ratios of ammonium ion to orthophosphate ion and ammonium ion to
total phosphate ion collected on the Teflon filters were approximately the
same at both 90 and 160 °C, 1.0:1.0 and 1.0:1.5, respectively.  This indicated
that the same recombination product was present at both temperatures.  Thermo-
dynamically, ammonium dihydrogen phosphate appeared to be the most probable
recombination product at both 90 and 160 °C.  However, based on the amounts of
phosphate ion found at 90 and 160 °C and the equilibrium dissociation pres-
sures of monoammonium and diammonium phosphate at these temperatures, the only
species that would be expected to be found on the particulate filter at either
of these temperatures would be monoammonium phosphate at 90 °C — i.e.,
     The assertion that the only stable ammonium phosphate species at either
160 or 90 °C should be monoammonium dihydrogen phosphate at 90 °C is explained
as follows.  The weight of phosphate ion collected on the particulate filter
at 90 °C corresponded to an average gas stream concentration of 3.0 ppm of
phosphate as a hypothetical vapor.  At 160 °C the weight collected corresponded
to an average of 4.0 ppm of phosphate.  The dissociation pressures of diammo-
nium hydrogen phosphate at 90 and 160 °C are 4.57 and 257 mmHg, respectively.18
These dissociation pressures correspond to 6,000 and 340,000 ppm of NHs at 90
and 160 °C, respectively.  Thus, the amounts of phosphate collected at 90 and
160 °C were totally insufficient to produce the ammonia concentrations that
would be in equilibrium with diammonium hydrogen phosphate.

     The dissociation pressure of monoammonium dihydrogen phosphate is
0.05 mmHg (66 ppm) at 125 °C.19  The value is not known at 90 °C, but it is
probably low enough to be consistent with the occurrence of the monoammonium
salt at 90 °C.  The dissociation pressure at 160 °C is also unknown, but it is
certainly too high to be consistent with the occurrence of the monoammonium
salt at 160 °C.  But since the experimental data indicate that the same recom-
bination product was present at both 90 and 160 °C, perhaps the monoammonium
phosphate salt was stabilized at 160 °C by some process such as adsorption on
the particulate filter.

Injection of LPA-445 into Flue Gas Containing Added Oxides of Sulfur and
Nitrogen

     The experimental results of the study of LPA-445 in flue gas containing
only added sulfur dioxide or both sulfur dioxide and nitrogen oxides are given
in Tables 8 and 9.  These tables are analogous to Tables 6 and 7.  Table 8 com-
pares the total amounts of ammonium and phosphate ions that were collected with
the amounts injected.  Table 9 shows the quantities of ammonium, orthophos-
phate, and condensed phosphate ions found on the filters and in the bubblers.

     Thermal Decomposition Studies.  When approximately 600 ppm of sulfur
dioxide was added to the flue gas, ammonium ion, orthophosphate ion, and con-
densed phosphate ion were again collected on filters and in bubblers at
650 °C.  Table 8 shows that, on the average, approximately 63% of the injected
ammonium ion and 55% of the injected phosphate ion were recovered at 650 °C,
the remainder of the injected ions presumably being lost on the walls of the
650 °C reaction zone and sampling port.  Table 9 shows that about 86% of the
ammonium ions was collected in the bubbler, whereas 75% of the total phosphate
ions was found on the filter and 25% in the bubbler.  These results indicate
                                      218

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  Table  8.   RECOVERY OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
         IN FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN

                              Concentration, ymol/1*
                                                          Recovery,  %
                                                                 Total
                                                          NHi*+   i"v~3
Sampling
temp. ,
°C
650
160
160
90
(S02
(S02
(S02
(S02
only)
only)
and NOX)
and NOx)
Injectedt
NHit"1"
0.
0.
1.
1.
625
893
096
231
Total
POiT3
0
0
0
0
,231
.133
.230
.392
Observed
NH,,"1"
0.
0.
0.
0.
397
297
140
078
Total
POiT3
0.
0.
0.
0.
127
020
017
025
                                                           63     55
                                                           34     15
                                                           13      8
                                                            7      6
      * Expressed for 25 °C.   To convert to parts per million on a
        hypothetical volume basis,  multiply by 24.4.

      t Based on NHit+ and P0n~3 lost from nebulizer.
Table 9.  DISTRIBUTION OF DECOMPOSITION AND RECOMBINATION PRODUCTS OF LPA-445
         IN FLUE GAS CONTAINING ADDED OXIDES OF SULFUR AND NITROGEN

                                      Concentration, ymol/1*



650
160
160
90
Sampling
temp . ,
°C
(S02 only)
(S02 only)
(SO 2 and NOX)
(S02 and NOX)
Collected on

NIU+
0.057
0.153
0.032
0.027
Ortho-
PO^T3
0.065
0.011
0.010
0.018
filter
Condensed
PO^"3
0.030
0.003
-
0.001
Collected in

NH^"1"
" 0.340
0.143
0.108
0.051
Ortho-
POiT3
0.028
0.002
0.004
0.004
bubbler
Condensed
POiT3
0.004
0.004
0.004
0.002
 * Expressed for 25 °C.  To convert to parts per million on a hypothetical
   volume basis, multiply by 24.4.
                                      219

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that at 650 °C the diammonium hydrogen phosphate in LPA-445 decomposed pri-
marily into gaseous ammonia and particulate phosphate species, with some vola-
tilization of phosphate, probably to phosphorus pentoxide, also occurring.

     Although these results were qualitatively very similar to the results
obtained in the absence of added reactive gases, there were, however, some
quantitative differences.  Much larger recoveries of ammonium ion were found
in the absence of reactive gases (approximately 88%) than in the presence of
added sulfur dioxide, and a larger fraction of the phosphate species was found
in the bubblers (approximately 50%).  These results indicate that more exten-
sive thermal decomposition of diammonium hydrogen phosphate and more extensive
volatilization of phosphate ion occurred in the absence of reactive gases than
with sulfur dioxide added to the gas stream.  No satisfactory explanation for
this observation, however, can be offered.

     Recombination Studies.   With both sulfur oxides and nitrogen oxides
added to the flue gas stream, the same general trends in the recovery and dis-
tribution of ammonium ion and phosphate species at 160 and 90 °C (Tables 8 and
9) were observed as those trends observed in the absence of added reactive
gases to the flue gas stream.  These results indicate that gaseous ammonia and
particulate phosphate species in the flue gas stream recombined into ammonium
phosphate salts at 160 and 90 °C, with the extent of recombination increasing
as the temperature was lowered.  From the thermodynamic considerations dis-
cussed earlier, the most probable recombination product at 160 and 90 °C is
monoammonium dihydrogen phosphate,
     From the ion chromatographic analyses of the filter washes,  sulfate ion
and nitrate ion were found to be present at concentrations comparable to or
greater than the concentrations of orthophosphate.  Thus, in the  presence of
added oxides of sulfur and nitrogen, there appears to be a competition for the
available ammonia in the gas stream during recombination reactions at 160 and
90 °C among orthophosphate, sulfate, and nitrate ions.  The background level
of sulfur trioxide in the gas stream was the source of the sulfate species in
these experiments.  The background concentration of sulfur trioxide was mea-
sured and found to average approximately 2 ppm (0.1 ymol/1, expressed for
25 °C) with an average concentration of 600 ppm sulfur dioxide in the gas
stream.  The concentration of nitrate ion in the gas stream, on the other hand,
was expected to be on the trace level.  The source of the nitrate ion is
assumed to be the oxidation of ammonia by the nitrogen oxides added to the gas
stream.  However, as was pointed out earlier, the average input concentration
of phosphate ion into the gas stream at 650 °C in these experiments was so
small (0.25 pinol/l, only two-and-a-half times greater than the average sulfur
trioxide background level) and the apparent wall losses were so great that
there is little significance to the observed competition between  the phosphate
ion and the sulfate and nitrate ions for the available ammonia in the gas
stream.  In the presence of a large excess of phosphate ion relative to sulfate
and nitrate ions, the competition might be negligible.

     Reaction of Ammonia with Nitrogen Oxides.    Table 8 shows that when
nitrogen oxides were present in the gas stream during the injection of LPA-445,
the ammonia recoveries at 160 and 90 °C were significantly less than those in
the absence of added nitrogen oxides.   The average recovery of ammonium ion
was 34% at 160 °C with sulfur dioxide as the only reactive oxide  added to the

                                      220

-------
gas stream.  With both sulfur dioxide and nitrogen oxides added to the gas
stream, the recovery of ammonium ion averaged only 13%, less than one-half the
recovery found at 160 °C witn no nitrogen oxides present.  This observation is
consistent with the gas stream reaction of nitrogen oxides with ammonia at
650 °C observed during the investigations of ammonia and ammonium sulfate.

Phosphine Determination

     No measurable concentrations of phosphine could be found in flue gas sam-
ples taken from the outlet of the electrostatic precipitator (160 °C) or the
outlet of the 90 °C zone in the absence of added reactive gases or in flue
gas samples from the 650 °C reaction zone during the injection of LPA-445 into
flue gas containing added oxides of sulfur and nitrogen.


CONCLUSIONS

Coaltrol LPA-40

     Apollo Chemical Corporation's Coaltrol LPA-40 was found to consist of an
aqueous solution of ammonium sulfate.  The formulation was injected into a
simulated  flue gas at 650 °C, and the gas stream was sampled downstream from
the point of injection at flue gas temperatures of 650, 160, and 90 °C.  The
high injection temperature was selected because of Apollo's practice of inject-
ing LPA-40 ahead of the economizer in a full-scale power plant.

     At 650 °C, ammonium sulfate decomposed primarily into its constitutent
compounds:  ammonia, sulfur trioxide, and water.  Upon cooling of the flue gas
to 160 or  90 °C, recombination of the molecular fragments occurred.   Ammonium
bisulfate  appeared to be the principal recombination product at 160 °C, and
ammonium sulfate seemed to be predominant at 90 °C.

     The implications of these results with respect to stack emissions are
that some  ammonia may be present in the stack emissions, and ammonium salts
may also be present if these solids are not effectively removed in the electro-
static precipitator.  Ammonia stack emissions appear to be less likely when
the flue gas contains large concentrations of nitrogen oxides due to the appar-
ent chemical reaction of ammonia with nitrogen oxides at high flue gas tempera-
tures .

Coaltrol LPA-445

     Coaltrol LPA-445 was found to consist of an aqueous solution of diammo-
nium hydrogen phosphate.  The formulation was injected at 650i °C, inasmuch as
Apollo recommends high temperature injection to produce thermal decomposition
of the ammonium phosphate.

     Decomposition of diammonium hydrogen phosphate to ammonia and unidenti-
fied phosphate species appeared to occur at 650 °C.  Recombination of the high
temperature fragmentation products was observed at 160 to 90 °C.  The most
logical explanation for the mechanism of recombination was that ammonia and
phosphate species recombined principally as ammonium dihydrogen phosphate
                                       221

-------
(with the mole ratio of ammonium ion to phosphate ion being 1:1 rather  than
2:1 as at the beginning).  A considerable excess of ammonia vapor remained in
the gas stream after the solid phosphate was removed by filtration.

     It thus appears that some ammonia will be emitted from the stack of a
power plant when LPA-445 is used for conditioning, although the amount  emitted
may be decreased when large concentrations of nitrogen oxides are present in
the flue gas.  If not removed by electrostatic precipitation, ammonium
dihydrogen phosphate particles will also be emitted.
REFERENCES

1.   Small, H., T. S. Stevens, and W. C. Bauman.  Novel Ion Exchange Chromato-
     graphic Method Using Conductimetric Detection.  Anal. Chem., 47:1801-1809,
     1975.

2.   Harwood,  J. E., and A. L. Kuhn.  A Colorimetric Method for Ammonia in
     Natural Waters.  Water Res., 4:805-811, 1970.

3.   Fritz, J. S., and S. S. Yamamura.  Rapid Microtitration of Sulfate.  Anal.
     Chem., 27:1461-1464, 1955.                                           ~~

4.   Kitson, R. E., and M. G. Mellon.  Colorimetric Determination of Phosphorus
     as Molybdivanodophosphoric Acid.  Ind. Eng. Chem., 16:379-383, 1944.

5.   Kelley, K. K., C. H. Shomate, F. E. Young, B. F. Naylor, A. E. Salo, and
     E. H. Huffman.  Thermodynamic Properties of Ammonium and Potassium Alums
     and Related Substances with Reference to Extraction of Alumina from Clay
     and Alunite.  Technical Paper 688.  U. S. Bureau of Mines, Washington,
     D. C., 1946.  pp 66-69.

6.   Scott, W. D., and F. C. R. Cattell.  Vapor Pressure of Ammonium Sulfates.
     Atmos. Environ., 13:307-317, 1979-

7.   Halstead, W.  D.  Thermal Decomposition of Ammonium Sulphate.   J.  Appl.
     Chem., 20:129-132, 1970.
8.   Erdey, L., S. Gal, and G. Liptay.  Thermoanalytical Properties of Analyti-
     cal-Grade Reagents—Ammonium Salts.  Talanta, 11:913-940, 1964.

9.   Bennett,  R. P., and M. J. O'Connor.  Method of Conditioning Flue Gas to
     Electrostatic Precipitator.  U. S. Patent 4 043 768, August 23, 1977.
     Assigned  to Apollo Chemical Corporation, Whippany, New Jersey.

10.  Bennett,  R. P., M. J. O'Connor, A. E. Kober, and I. Kukin.  Method of
     Conditioning Flue Gas to Electrostatic Precipitator.  U. S. Patent
     4 042  348, August 16, 1977.  Assigned to Apollo Chemical Corporation,
     Whippany, New Jersey.

11.  Goks^yr,  H., and K. Ross.  The Determination of Sulfur Trioxide in Flue
     Gases.  J. Inst. Fuel, 35:177-179, 1962.


                                       222

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12.  Maddalone, R. L.  Guidelines for Combustion  Source  Sulfuric Acid Emission
     Measurements.  TRW Document No. 28055-6005-RU-OO.   TRW Defense  and  Space
     Systems Group, Redondo Beach, California,  1977.  14 pp.

13.  Recommended Method of Analysis for Nitrogen  Dioxide Content of  the  Atmo-
     sphere (Greiss-Saltzman Reaction).  In:  Methods of Air Sampling and
     Analysis^ M. Katz, Ed.  American Public Health Association, Washington,
     D. C., 1977.  pp 527-534.

14.  Tentative Method of Analysis for Total Nitrogen Oxides as Nitrate
     (Phenoldisulfonic Acid Method).  In:  Methods of Air Sampling and Analy-
     sis, M. Katz, Ed.  American Public Health  Association, Washington,  D. C.,
     TT77.  pp 534-538.

15.  West, P. W., and G. C. Gaeke.  Fixation of Sulfur Dioxide as Sulfito-
     mercurate III and Subsequent Colorimetric  Determination.  Anal. Chem.,
     28:1816-1818, 1956.                                               ~~

16.  Phosphate/Stannous Chloride Method.  In:   Standard  Methods for  the  Exam-
     ination of Water and Wastewater, 14th ed. , M. C. Rand, A. E~] Greenberg,
     and M. J. Taras, Eds.  American Public Health Association, Washington,
     D. C., 1975-  pp 479-480.

17.  Dechant, R., G. Sanders,  and R. Graul.  Determination of Phosphine  in Air.
     Am. Ind. Hyg. Assoc. J.,  27:57-79, 1966.

18.  Passille, A.  Dissociation of Ammonium Phosphates.  Comptes rendus, 199:
     356-358, 1934.

19.  Warren, T.  E.   Dissociation Pressures of Ammonium Orthophosphates.
     J. Am. Chem.  Soc., 49:1904-1908, 1927.
                                       223

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                  BIOTOXICITY OF FLY ASH PARTICULATE

                                  By:

                  Alan R. Kolber and Thomas J. Wolff
                      Research Triangle Institute

                                  and

                        J. Abbott and L. Sparks
         Industrial Environmental Research Laboratory (E.P.A.)
                  Research Triangle Park, N.C.  27709
                               Abstract

     Fly ash samples were collected as part of field tests of electro-
static precipitators on boilers fired with coal of varying sulfur
content, and from hopper and stack plumes.  The filter samples were
obtained by isokinetically sampling flue gas.  Collection temperatures
ranged from ambient to 350°C.  A known weakly mutagenic fly ash was
supplied by Battelle (Columbus).
     The mutagenic potential of fifteen fly ash samples from five coal-
fired power plants was evaluated.  Mutagenicity was assessed utilizing
the Salmonella/Mammalian microsome assay, employing bacterial strains
TA1535, TA100, TA1537, TA1538, and TA98.  Fourteen samples were negative
for mutagenicity; although some of these materials exhibited varying
cytotoxicity to Chinese Hamster Ovary cells as measured by a number of
parameters.  One previously tested fly ash (Battelle Columbus Labora-
tories) generated a positive mutagenic response.  The effect of solvent
extraction on the apparent mutagenicity of the Battelle Fly Ash was
investigated.  The effect of sampling temperature, extraction procedure,
and particulate size on the determination of apparent mutagenicity is
discussed.
                                  224

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                  BIOTOXICITY OF FLY ASH PARTICULATE

INTRODUCTION
     Western nations and Japan, faced with the eventual shortage of
commonly used fossil fuels, must now develop technologies to exploit
more abundant less-efficient alternative fuel sources.  A greater world
population density resulting from increased net population growth in
this century must now be considered when planning new energy programs,
because of the possible attendant human health risk resulting from
pollutant streams generated by new energy producing industries, and from
production industries planning to utilize low-efficiency, low grade
fuels.
     The enormous number of xenobiotic (synthetic, non-biological) sub-
stances being presented to the environment each year has inumdated the
capacity for assessing their insult to human health and to the environ-
ment.  Until very recently, classical toxicological methodology was
nearly completely restricted to studies with whole animals.  Table 1
illustrates the large investment in time and cost required to test the
toxicity of single substances using whole-animal protocols.  The end-
points measured here were carcinogenicity, and general toxicity determin-
ed by acute (death-producing) protocols, and are compared to the much
smaller investment required to determine the same endpoints using recent-
ly-developed in vitro bioassay techniques.
     Toxicity from substances present in synthetic fuels production
effluents and other industrial pollutants is not restricted to cancer
risk; there is a possibility of organ-specific toxicity as well (lung,
nervous system, liver, reproductive organs, etc.).  In this respect,
teratological effects and disorders of development must also be consid-
ered. Although this report will be concerned only with the mutagenic/
carcinogenic and general cytotoxic potential of energy production byprod-
ucts and effluents, other attendent health risk possibilities must not
be forgotten;  especially in the case of the neonate or infant, where
developing organ-systems are often more susceptible to the effects of
environmental agents than the adult (Press, 1978) .
                                 225

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DESCRIPTION OF TEST SAMPLES AND BIOASSAY
Sampling Procedure
     The fly ash samples used in this study were collected during exten-
sive field tests of electrostatic precipitators (ESP), collecting fly
ash from combustion of coal.  The samples were collected at five different
plants by two different EPA contractors (Southern Research Institute and
Air Pollution Technology, Inc.)-  Brief information on the different
plants is given in Table 2.
     Except for plants 1 and 5, where only hopper samples were obtained,
filter samples were obtained by isokinetic sampling of the flue gas.
The filter was maintained at the flue gas temperature, which was essential-
ly the same as the ESP operating temperature.  At the end of the sampling
period the filters were cooled and placed in sealed containers, which
were shipped to EPA's Industrial Environmental Research Laboratories/
Research Triangle Park, and given to Research Triangle Institute.   The
samples from plants 3 and 4 were stored at EPA's Industrial Environmental
Research Laboratories/Research Triangle Park for some time prior to Ames
testing.   The plant samples were tested shortly after they were received
from the field.
     Inorganic flue gas conditioning agents were used at plants 2,3, and
4 to improve the performance of the ESP's at these plants.  Sulfur
trioxide (S0_), was used at plants 2 and 3 while a proprietary agent was
used at plant 4.  This agent is believed to be an ammonium phosphate
salt.  Particulate samples were obtained for these 3 plants,  both with
and without flue gas conditioning.  In all cases,  samples at the outlet
or the ESP were obtained.  Both inlet and outlet samples were obtained
at Plant 2.
Extraction Procedure
     Two extraction procedures were employed with the E.P.A.  particulate
fly ash samples.  Samples A1Q01 were added directly to dimethylsulfoxide
(spec, grade) and exposed to sonic disruption.  A1010 through A1014 fly
ash particulates were extracted using 20 ml cyclohexane-methanol
(50% by volume) and sonication.  The solvent extract was then
                                 226

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evaporated to dryness under nitrogen and the solute transferred to
dimethylsulfoxide.
     Four solvents were employed to extract the Battelle samples:  horse
serum, water, cyclohexane-methanol, and methylene chloride.  Horse serum
was selected for its chemical and physiological similarity to lung
alveolar fluid; the serum protein forms soluble complexes with some
                                          2
carcinogenic heavy metals (Chrisp, et al.) .  Water was used by Battelle.
Cyclohexane-methanol, a nonpolar nonmutagenie solvent, was utilized for
extraction of polar organics while methylene chloride was employed for
extraction of nonpolar organics.  Both horse serum and deionized water
were incubated with ash for 48 hrs at 37°C prior to bioassay.  The
cyclohexane-methanol and methylene chloride extracts were separated from
the particulate by filtration and the solute evaporated to dryness under
nitrogen and suspended in dimethylsulfoxide.  EPA fly ash particulates
remained in suspension in vehicle, while the Battelle sample was filtered
prior to bioassay.
Ames/Salmonella Mutagenesis Bioassay
     The Ames/Salmonella bioassay provides a rapid, sensitive screening
procedure for determining the mutagenic potential of a given chemical
substance or complex mixture in a genetically well-defined system (Ames,
1979)3.  The specific Salmonella strains employed (TA98, TA100,  TA1538,
TA1535, TA1537>! allow determination of the class of mutagen (base substi-
                                                      3
tution, frame shift etc.) being evaluated (Ames, 1979) .  The Salmonella
strains utilized carry mutations in the histidine genes; such that the
normally prototrophic bacteria now requires histidine in the growth
medium due to their inability to synthesize histidine, de novo.   When a
substance interacts with the DNA at or very near the site of the original
point mutation, the reading frame may be corrected by the second muta-
tion, reverting the bacterium to protorophy - or enabling the bacterium
to once again grow in minimal medium void of histidine supplement.   This
is termed a reverse mutational event.  Different mutational events (base
pair substitution and frameshift mutations) are detected by the  bacterial
strains employed:  TA98, TA1538, and TA1537 detect frame-shift mutations
                                  227

-------
while TA100 and TA1535 are utilized to detect base-pair substitutions
(non-sense, or mis-sense mutations).
     As many as 10 -10  bacteria can be plated on a 100 mm diameter
culture dish in minimal medium.  The fraction of revertant bacteria
which have acquired mutations in the histidine gene can be scored by
couting the number of colonies  (arising from individual revertants)
growing on minimal medium void  of histidine.
     Many substances are metabolically transformed in mammalian tissue
to mutagenic/carcinogenic intermediates;  these substances would exhibit
no mutagenicity in the Ames assay without prior metabolic activation.
Therefore, microsomal preparations (with increased enzyme activity) from
Aroclor-induced rat livers, which metabolize procarcinogens to their
proximate carcinogens, are incorporated into the bioassay (Ames, et.al.,
     4
1975) .  Thus, the resultant assay can detect different classes of
mutagens/carcinogens (requiring, or not requiring metabolic activation),
as well as different mutational events (frame-shift, substitutions,
etc).
Mammalian Cell Cytotoxicy Assays
     Mammalian cells grown in tissue culture might serve as a substitute
for the whole animal as a screening tool for assessing the cellular
toxicity of xenobiotics to mammals.  In this assay, a stable tissue-
culture cell line with well known growth characteristics and biochemistry
would serve as the test system.  The putative toxins would challenge the
cells by addition to the growth medium when the cells are growing as a
monolayer, attached to a plastic substrate (plastic culture dish).   The
cell type chosen for this study is the Chinese Hamster Ovary (CHO)  cell
line introduced in 1967 as a parent diploid cell for the production of
mutant cells (Kao and Puck, 1967) .  The cell line is available from the
American Type Culture Association, and although no longer diploid,
posesses a constant chromosome number (ploidy), is fairly resistant to
infections, is relatively easy  to maintain in culture on defined medium,
and divides rather rapidly (12-14 hr doubling-time) for a mammalian
cell.  The CHO cells grow in a uniform population and the levels of
various key metabolites involved in their metabolism can readily be
                                 228

-------
measured.  The CHO cell exhibits consistent growth kinetics when  cultured
under standard conditions of pCO~ and pCL, temperature and humidity, and
when provided with a standard nutrient culture medium containing  serum,
salts and essential amino acids.  When exposed to a known cytotoxin  (we
have chosen Cadmium; Ozawa, et al., 1976)  the growth and metabolism of
the CHO cell is affected (Winiger et al., 1978)7.
     Inhibition of cell growth is determined in this study by two assay
methods.  In the first, cells are explanted onto a growth substrate by
seeding 10  cells into a 35 mm diameter plastic culture dish, allowing
24 hrs. for cell attachment, and incubating with the compound to be
studied for 24 hrs.  The medium is then replaced with fresh medium, and
the dishes incubated for about one week, with cell counts of control and
treated cultures performed at 24 hr. intervals.  A control growth curve,
exhibiting the lag, logarithmic, and stationary phases of growth is
depicted in Figure 1.  The effect of Cadmium is also shown.
     The second method quantitates the ability of a single CHO cell to
give rise to a viable colony (or clone) of cells.  This cloning efficiency
assay  is performed by seeding a small number of cells (200-1000) in a 60
mm culture dish, allowing 24 hrs. for attachment, adding test substance,
incubating for 24 hrs., replacing medium, and incubating about 10 days,
or until colonies of cells grow large enough to count.  These two cell-
growth studies provide an overall screening assay to quantitate general
cytotoxicity, where the parameters measured are the ability of cells to
grow and divide as members of a large population, and the ability of a
single cell to survive the toxic insult, and give rise to progeny.
MATERIALS AND METHODS
Ames Mutagenesis Bioassay
     Chemicals.   NADPH (tetrasodium salt, Type 1) and known positive
mutagens (highest purity available) were obtained from Sigma Chemical
Company.  Dimethylsulfoxide (spectrophotometric grade) and sucrose were
                                                                  ®
obtained from the Fisher Chemical Company.  Agar (Difco Bacto-Agar ) was
obtained from Difco Laboratories.
                                 229

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     Bacterial Strains.   Tests were conducted with Salmonella typhimurium
strains TA100, TA1535, (utilized to detect base-pair substitution mutagens),
and strains TA1537, TA1538 and TA98 (employed for detection of frameshift
mutagens).  All histidine auxotrophic strains were obtained directly from
Bruce Ames (Biochemistry Department, University of California, Berkeley).
CHO Cytotoxicity
     Tissue culture medium was obtained from KC Biologicals (Lanexa, Kansas)
and from Grand Island Biologicals  (N.Y.).  Cells were obtained from the
American Type Culture Association.  Disposable tissue culture dishes, flasks
and pipettes were obtained from Corning Corp.  All water used in preparing
medium was triple distilled after passing through ion-exchange resins.
Standard Protocols
     Ames Mutagenesis Assay.  The procedures for handling the strains and
                                                           4
preparing media components were those of Ames et al.,  1975) ,  with the
following exceptions:  (a) Craig-Dawley male rat livers were used as the
source for metabolic activation (S-9) {activation potentials were very
similar to Sprague-Dawley male rats (data not shown)],  (b) NADPH was added
directly to the plate (per plate, 0.10 ml containing  0.32 mg NADPH), (c) use
of a 2.5 ml agar overlay rather than a 2.0 ml overlay;  (d) S-9 microsomal
preparation was diluted in 0.25 M sucrose at a concentration of 30 mg protein/ml
and added at protein concentrations of 3.0mg/ plate for initial testing; (e)
bacterial strains are centrifuged and concentrated in  normal saline at 10
cell/ml.  The S-9 microsomal preparation was obtained  from rats injected
with Aroclor 1254.  Protein was measured by the method  of Lowry et al. ,
(1951)8.
     All test components were added at 100 yl per plate.   All  dose levels
were performed in triplicate and duplicate experiments  were performed on
separate days if sample was available.
                                        230

-------
     For quality assurance, the test is divided into five parts:
     Toxicity Testing. Plate Incorporation Method.   200-300 cells per petri
dish are plated on histidine containing medium (histidine positive). Toxicity
tests were done with and without induced S-9.  Test compound was added at
0.1 ml/plate in all tests.  The viability ratio was calculated as the ratio
of surviving colonies with sample to colonies without sample.  The schematic
of the test procedure is illustrated in Figure 2.
     Mutagenesis Testing, Plate Incorporation Method.   With S-9—To a tube
containing 2.5 ml of agar void of histiding (histidine negative) was added
0.1 ml of S-9 microsomal preparation, 0.1 ml of NADPH, 0.1 ml of a solution
of test material or positive control compound in dimethylsulfoxide, and 0.1
ml of bacterial suspension.  Without S-9—Prepared as above, 0.1 ml of test
material or positive control, 0.1 ml of bacterial suspension and 0.1 ml of
sucrose and deionized water.
     Sterility Testing, Plate Incorporation Method.    Sterility tests are
conducted with histidine-positive overlay plates, using the amounts of
components employed in the tests.  Components tested were:   sample, positive
controls, solvent, water, 0.25M sucrose solution, saline,  microsomal prepar-
ation (S-9), and NADPH solution.
     Negative Control, Plate Incorporation Method.   Solvent control was
taken through the bioassay, and tested for toxicity, mutagenicity and
effect on the metabolic activation S-9 microsome system.
     Positive Mutagen Control Testing, Plate Incorporation Method.    Using
histidine-negative overlay, 10  cells were plated in each  dish.   Known
mutagens were tested to assure that the strains were active and the microsomal
preparation was activating promutagens to the desired levels.   If known
positive controls do not show proper mutagenic activity, the test components
(cultures and/or microsomes) are rejected.   Control  compounds  currently in
use are:
                                         231

-------
          Strain         Without S-9              With S-9

          TA 1535        Sodium azide             2-Anthramine
                         200, 20, 2 Mg/plate      100, 10, 1 pg/plate

          TA 1537        Quinacrine HC1           2-Anthramine
                         250, 25, 2.5 pg/plate    100, 10, 1 pg/plate

          TA 1538        2-Nitrofluorene          2-Anthramine
          TA 98          100, 10, 1 (Jg/plate      100, 10, 1 \Jg/plate

          TA 100         Sodium azide             2-Anthramine
                         200, 20, 2 Mg/Plate      100, 10, 1 [Jig/plate

     Mutagenesis Data.   No test is considered positive unless all four
sections of the assay are performed, and the spontaneous reversion rate
determined.  The experiment is discarded if the spontaneous background
exceeds normally observed values, if positive controls are not accept-
able, or if the sterility test indicates contamination.  Mutagenic
ratios of 3 or greater, determined on the linear portion of the dose-
response curve are considered positive.
Cytotoxicity Testing:  Growth Kinetics
     Chinese Hamster Ovary cells were obtained from the American Type
Culture Association, explanted in Ham's F12 tissue culture medium supple-
mented with 10% fetal calf serum.  The cells are explanted and grown to
confluence, the monolayer dispersed, cells diluted with medium containing
10% DMSO and frozen at -80°C in 1 ml aliquots for storage, and are
subsequently thawed and cultured for experiments.  No antibiotics were
used in the following experimental protocol.  Cells were seeded at 10
cells/35 mm culture dish in 2 ml medium, and incubated at 37°C in a 5%
C09 atmosphere.  Three dishes were used for each time point of 6 points
measured (24 hours apart) after 24 hours incubation with a sample added
in not more than 25 Ml DMSO vehicle.  After incubation with sample, the
                                 232

-------
medium is discarded and replaced with 2 |Jl fresh medium.  The  cell
monolayer is dispersed with 0.05% trypsin and the cells  counted using  a
Fisher automated cell counter.
     Cloning efficiency.   Chinese Hamster Ovary cells,  obtained from
the source described above, and cultured as described above, are explanted
in 60 mm dishes at 200 and 1,000 cells per dish in 5 ml  F12 medium with
10% calf serum and no antibiotics.  The cells are incubated for 24 hours
to attach, the test substance added in 10 and 25 pi DMSO, incubated 24
hours, the medium replaced with fresh medium, and the cells incubated
until visible colonies arise  (about 6-10 days).  At this time, the
medium was removed, the colonies washed with methanol, stained with
methylene blue, and counted with an automatic colony counter.  Control
colony formation was done with 25 pi DMSO added to the medium.
Quality Control and Assurance Procedures:  Ames Mutagenesis Bioassay
     Sample Receipt and Dilution Procedures.   Extracted samples are
immediately stored at 4°C.  Dilution with spectral grade DMSO  (N~
bubbled) is done under an operating fume hood (yellow lights are used to
avoid photodeactivation).
     Salmonella Strain and S-9 Activation Validations.   Quality control
and assurance procedures were undertaken to insure proper functioning of
bacterial  strains and microsomal preparations.  In general, our quality
assurance  and control requirements are in agreement with those suggested
by DeSerres and Shelby  (1979)9.
RESULTS
Ames Mutagenesis Bioassay Results
     Table 2  illustrates the  fly ash particulate results from  the Ames/
Salmonella assay.  Results were negative for mutagenicity under all
conditions tested.  Toxicity  to the bacterial strains was apparent for
several  samples, as shown in  Table 2.
     The Battelle Laboratory  fly ash data is given in Table 3.  Battelle
Laboratories  found a water-extract of this sample to be  weakly mutagenic
for TA98;  a mutagenic ratio of 3.5 was obtained.  This response required
S-9 activation.  We determined a mutagenic ratio of 3.4  for TA98 requiring
S-9 activation, but only the  methylene chloride extract  was active.
                                  233

-------
Toxicity determinations are as follows:  Both the cyclohexane/methanol
and methylene chloride extracts were toxic for bacterial strains TA98
and TA100 (without S-9 addition).  Water and dialized horse serum ex-
tracts were nontoxic to both strains with and without S-9 addition.
Table 3 illustrates that while toxicity decreased with metabolic activa-
tion, mutagenic activity increased.
Chinese Hamster Ovary Cell Cytotoxicity Results
     Fourteen fly ash samples were tested for toxicity by the growth
inhibition and clonal toxicity methods using 50 and 125 |Jg samples.
The method was validated using CdCl_ at various concentrations from
  8
10  M.  The validation results are shown in Figure 1.  At concentra-
tions as low as 10" M, CdCl inhibits growth of CHO cells, and as the Cd
concentration is increased, the effect becomes more pronounced.  Figure
3 illustrates the effect of 50 and 125 |Jg of fly ash particulate added
to the cells in 10 and 25 (JL DMSO as described above.  A marginal affect
was noted.  Sample A1008, a hopper sample from a high sulfur Eastern
coal-fired power plant, exhibited medium toxicity measured by the growth
kinetic method.  This sample was also toxic to the Salmonella (Table 2).
None of the remaining 13 samples exhibited really significant toxicity
at the concentrations tested, agreeing with the mutagenicity findings.
DISCUSSION
     Several investigations of the mutagenicity of fly ash have been
reported.  Natush and Torakins (1978)   predicted that temperatures near
100° are critical for adsorption of polynuclear aromatics onto fly ash
particulate.  Fisher et al., (1979)   have shown that heating coal fly
ash to 350°C, eliminates mutagenicity, consistent with the hypothesis
that the bulk of the mutagenicity originates from organic constitutents
which volatilize at 350°C.  Natusch et al.., (1979)   and Fisher et £l. ,
(1979)   have reported the mutagenicity of fly ash to be greatest in the
finest (submicron sized) particles, which have the greatest surface area
per unit mass.  These submicron particles have the longest atmospheric
residence time, are the most efficiently deposited in the lung, and are
                                                     2
the least efficiently removed.  Chrisp et al., (1978)  Fisher et al.,
(1979)   also reported the E.S.P. collected particulates (whether size
                                 234

-------
classified or not) were not mutagenic, while stack-collected respirable
particulates were mutagenic.  It was presumed by these authors that
failure to control mutagens was due to E.S.P. collection temperatures
in excess of 100°, resulting in volatilization of organic mutagens which
were thus not collected by the E.S.P.
     Failure to detect mutagenicity in the 14 fly ash samples tested in
this study may have been due to inefficient extraction procedures.  Weak
mutagenicity detected for the Battelle sample may be a result of the
very low organic content (<0.1%) of most fly ash samples.  Failure to
remove the inorganic matrix permits readsorption of organics onto the
particulate during solvent evaporation, inhibiting mutagenic potential.
Concerning possible control technology, it is suggested that volatilized
mutagenic organics may condense onto cooled inorganic particulate down-
wind of a stack where ambient temperatures are realized.
                                 235

-------
                            References
 1.   Press,  M.F.,  Lead Encephalopathy in Neonate Long Evans Rat:   Morpho-
     logic Studies.   J. Neuropath.  Exp.  Neurol.  36:   169-193,  1977.
 2.   Crisp,  C.E.,  G.L. Fisher,  J.E.  Lammert.   Mutagenicity of  Filtrates
     from Respirable Coal Fly Ash.   Science Vol.  199 January 6,  1978
     pp 73-75.
 3.   Ames, B.  N.,  Identifying Environmental Chemicals Causing  Mutations
     and Cancer.   Science, 204:  587-593, 1979.
 4.   Ames, B.N.,  J.  McCann, and E.  Yamasaki.   Methods for Detecting  Car-
     cinogens  and Mutagens with the Salmonella Mammalian Microsome
     Mutagenicity Test.  Mutat. Res., 31:  347-364,  1975.
 5.   Kao, F. and  T.  Puck.  Genetics of Somatic Mannalian Cells.  IX.
     Properties  of Chinese Hamster  Cell  Mutants  with Respect to  the
     Requirements for Proline.   Genetics, 55:  513-524,  1967.
 6.   Ozawa,  K.,  A. Sato, and H. Okada, Differential  Susceptibility of
     L Cells in  the Experimental and Stationary  Phases to Cadmium
     Chloride.   Japan J. Phannacol.   26:   347-351, 1976.
 7.   Winiger,  H., F. Kukik, and W.  Rois,  In Vitro Clonal Cylotoxicity
     Assay Using Chinese Hamster Ovary Cells  (CHO-K1) for Testing
     Environmental Chemicals.  In Vitro  14: Abstract no.  193, 1978.
 8.   Lowry,  O.K., N.J. Rosebrough,  A.L.  Farr,  and R.J. Randall, Protein
     Measurement with the Folin Phenal Reagent.   L.  Biol.  Chem.  193:
     265-275 (1951).
 9-   DeSerres, F., and M. Shelby.  The Salmonella Mutagenicity Assay:
     Recommendations.  Science, 203:  563-565, 1979.
10.   Natusch,  D.F.S., and B.A.  Tomkins,  Polynuclear  Aromatic Hydro-
     carbons,  Carcinogenesis 3, P.W. Jones and A.I.  Freudenthal, eds.,
     Raven Press, pp 145-153 (1978).
11.   Fisher, G.L., C.E. Crisp,  O.G.  Raabe.  Physical Factors Effecting
     the Mutagenicity of Fly Ash from a  Coal-Fired Power Plant.  Science,
     Vol. 204, May 25, 1979, pp 879-881.
12.   Natusch,  D.F.S., J.R. Wallace,  C.A.  Evans,  Jr.,  Science 183,  202
     (1974).
                                 236

-------
                                 72      96
                                 TIME (HOURS)
                                                            168
Figure 1.   The Effect of Cadmium on the Growth of Chinese Hamster
            Ovary Cells.

     BHK1 Chinese Hamster Ovary cells  (10s cells/plate) were explanted
in 35 mm diameter dishes in 2 ml F12 (Harris) culture medium, incubated
24 hr at 37°C with 5% C02.  Cadmium was added in 25 pi DMSO at a  final
concentration of 10~8 M  (A), 10~7 M  (A), 10 6M (0).  Control  cells
were grown in the presence of 25 pi DMSO ( © , Q)-  After 24 hrs.,  the
medium was discarded, replaced with 2 ml fresh medium, and the cells of
3 plates counted at 24 hour intervals, as described in the text.
                                   237

-------
    INDUCED
   ACTIVATION
   FRACTION
    SAMPLE
      IN
    VEHICLE
BACTERIA
                                           '77777777117777771
Figure  2.    Scheme  of Ames/Salmonella Test  Procedure.
                                   238

-------
              10
                       24
                                       72

                                    TIME (HOURS)
       Figure 3.   The Effect of  Selected  Fly Ash  Particulate Samples
                   on the Growth  of  Chinese  Hamster  Ovary Cells.

       Fly ash particulate in 25  yl  DMSO  (from  Plant A.A1008; 300 yg Q ;
150 yg H ) was biotested as described  in the text  and in the legend to
Figure 1.  Control cells were grown  in 30  yl DMSO  (  •), and with no
added DMSO ( Q )•
                                   239

-------
         Table  1.  RELATIVE EFFICIENCY OF IN VIVO AND IN VITRO
                  BIOTESTING FOR ENVIRONMENTAL  BIOTOXICITY
                                               Per Substance
                                      Time Required
                                          (Yrs.)
              Cost (Dollars)
NCI Whole Animal Carcinogenesis

NCTR Whole Animal Toxicity

Level  1 Biotest (in Vitro Biotesting)
3.5

1.2

0.01 - 0.2
2.5 X 105

1.5X 105

  6X 103
                                  240

-------
ro
                            Table 2.   SUMMARY OF BIOTESTING RESULTS OF FLY ASH
                                      SAMPLES FROM COAL-FIRED POWER PLANTS
LABORATORY EXTRACTION PLANT COLLECTION TYPE OK COAL REMARKS AMES /SALMONELLA (Strain) CHINESE HAMSTER OVARY CELLS
CODE NUMBER PROCEDURE NUMBER TEMPERATURE UTILIZED IN COMBUSTION MUTACENICITY
AOOJ
A1002
A1U03
A1004
A1005
A 1006
A1007
A1009
A1008
A1010
A1011
A1C13
A1012
AlOli
*Extrac
A:
B:
A 3
A 3
A 3
A 3
A 3
A 3
A 3
A 3
A I*
B 5
B 2
B 2
8 1
8 1
tlon Procedure
Addition of Dimethyls
The particulace mater
dimettiylsulfoxlde.

115'C
115"C
115"C
115'C
115'C
150"C
1508C
STACK SAMPLE NONMUTACENIC
NONMUTACENIC
NONMUTACENIC
f NONMUTAGENIC
, NONMUTACENIC
Hoppi-r Sample NONMUTACENIC
Hopper Sample NONMUTAGENIC
hopper samp le
hot side E.S.P.
high unburne
176eC
176eC
176'C
1 carbon hopper samp le
NONMUTACENIC
No conditioning NONMUTAGENIC
hopper aample
j NONMUTACENIC

ulfoxide to partlculate with subsequent sonic disruption for 2 minutes.
ials are extracted from filters using cyclohexane methanoi (502 by volume)

TOXICITY
NONTOXIC
TOXIC (37,98)
TOXIC (37,98)
NONTOXIC
NONTOXIC
NONTOXIC
TOXIC (37,98)
TOXIC ALL
STRAINS
TOXIC (37)
TOXIC (98)
TOXIC (98)
NONTOXIC
NONTQX I C
NONTOXIC



KINETICS
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC
NONTUX1C
TOXIC (I-)
NONTQXIC
NONTOXIC
TOXIC (H)
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC
NONTOXIC



CLONAL EFF.
NONTOXIC
NONTOXIC
TOXIC (M)
TOXIC (M)
TOXIC (M)
TOXIC (L)
NONTOXIC
NONTOXIC
NONTOXIC
_




-------
                           Table  3.   MUTAGENTCITY OF FLY ASH FROM BATTELLE LABORATORY
1N3
MutigiriK Kilio
Solwnt Vihicli
Cyclohnane Mtthanol DMSO
60S by volume



Mithylint Chloridi DMSO




Diioniiad H;0 H20
37°,48hrt



Horn Strum dulued Hunt
37°, 48 hri Serum



Ponlivt Control DMSO
Solvint Control
Dou
5000
1000
SOO
250
100
5000
1000
500
250
100
5000
1000
500
250
100
5000
1000
500
250
100


TA
-MA
.65
.79
.93
.96
.99
.68
.85
.95
.88
.96
1.03
1.13
1.02
1.01
1.00
.88
.95
.97
1.08
1.03
11.98
1.00
100
1-MA
1.09
1.01
1.01
.95
.90
1.06
1.12
1.01
1.05
.87
1.17
1.19
1.07
.98
.98
.90
.98
.93
1.02
.98
17.05
1.00
TA98
-MA
1.17
1.45
.78
.88
.97
.71
1.06
.89
.82
1.10
1.35
1.68
1.60
1.27
1.19
.86
.88
.67
.83
.84
59.19
1.00
+MA
1.70
1.08
.90
1.34
.94
3.41-*-
1.22
1.09
.95
1.39
1.83
1.59
1.63
1.07
1.60
1.38
1.00
1.27
1.19
1.28
53.25
1.00
TA
-MA
.16
.66
.88
.91
1.22
.22
.75
.73
.90
1.02
.95
.89
.84
.99
.76
.94
.95
.86
.86
.77

1.00
Vubility FUlio
100
•HHA
1.15
1.17
1.08
1.09
.99
1.15
.92
1.01
1.00
.90
1.11
1.13
.93
.96
1.04
.99
1.08
1.08
1.10
.90

1.00
TA96
-MA
.54
.69
.78
.67
.96
.06
.13
.52
.58
.86
1.12
1.30
1.29
1.10
.89
.95
1.02
.98
1.07
.86

1.00
+MA
1.20
1.12
1.09
1.16
.97
1.21
1.23
1.35
.30
.14
.15
.14
.14
.04
.06
.99
1.01
1.05
1.10
1.00

1.00

-------
               FABRIC FILTERS VERSUS ELECTROSTATIC PRECIPITATORS

                                       By

                      Edward W. Stenby, Robert W. Scheck,
                     Stephen D. Severson and Fay A. Horney

                                       of

                     Steams-Roger Engineering Corporation

                                      and

                               Donald P. Teixeira

                                      of

                       Electric Power Research Institute


Presented at the Second Symposium on the Transfer and Utilization of
Particulate Control Technology.  Sponsored by the U. S. Environmental
Protection Agency and the Denver Research Institute.  July 23-27, 1979;
Denver, Colorado.

                                    ABSTRACT

Control of particulate emissions from pulverized coal fired steam generators
is becoming a significant factor in the siting and public acceptability of
large coal burning power plants.  The particulate emission limit established
by the EPA for new coal fired boilers is 0.03 lb/106 Btu (13 ng/J).
Possibly more restrictive than this is the State of New Mexico's particulate
regulation which calls for no more than 0.05 lb/106 Btu (22 ng/J) total, and
no more than 0.02 lb/106 Btu (9 ng/J) less than 2 microns in diameter.  This
paper will evaluate the effect of these stringent limitations on the technical
feasibility and economics of dry particulate removal.  Electrostatic
precipitators have been the dominant particulate collection device in the
electric utility industry for many years because of their low capital and
operating cost.  However, increasingly stringent emission standards have led
to substantially higher costs for precipitators.  These costs have increased
sufficiently for fabric filtration to become a competitive alternative in
achieving cost effective control.  This paper will compare the economics and
performance of fabric filtration with respect to conventional electrostatic
precipitators.  The paper will also address the preliminary evaluation
procedures that should be followed in order to select the appropriate device
for new or existing coal-fired boilers.
                                     243

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           FABRIC FILTERS VERSUS ELECTROSTATIC PRECIPITATORS
INTRODUCTION

    The particulate emission limit initially set by the EPA under
provisions of the Clean Air Act of 1970 for large, new coal fired
boilers was 0.1 lb/106 Btu (43 ng/J).  Under the Clean Air Act of
1977, EPA promulgated on June 11, 1979, (Federal Register, Vol. 44,
Page 33581) a New Source Performance Standard for particulates of 0.03
lb/106 Btu (13 ng/J).  Possibly more restrictive (because of the
limit on fine particulate)  than this are the State of New Mexico's
limits for new plants of 0.05 lb/106 Btu (22 ng/J) for total
particulates and 0.02 lb/106 Btu (9 ng/J for particulates less than
2 microns in diameter.  These more stringent particulate emission
limitations will have a definite impact on the economics of power
production for new coal fired boilers.

    Electrostatic precipitators have been the dominate particulate
collection device in the electric utility industry for many years,
because of their relatively low capital and operating costs.  However,
increasingly stringent emission standards have led to substantially
higher costs for precipitators.  These costs have increased
sufficiently for fabric filters to become a competitive alternative in
achieving cost effective control.  This paper presents comparative
data on the economics and performance of fabric filters and
conventional electrostatic precipitators.  The data presented are
based on investigations sponsored by the Electric Power Research
Institute.1

SUMMARY OF EPRI STUDY

    The economic findings from the EPRI study are presented in
Figure 1.  These are 1978 levelized costs of all capital and operating
expenses evaluated for the plant's 35-year life.  For particulate
collection at the 0.03 lb/106 Btu emission limit, these costs may
represent 3 to 5 percent of the total cost of power production.

    The levelized costs are made up of capital investment costs and
operating and maintenance costs, combined by application of
appropriate economic factors (plant life, finance charges, etc.) to
establish present worth and equivalent revenue requirements.  The
levelized costs (or revenue requirements) allow the direct comparison
of the various cases as shown in Figure 1.  The significant components
of levelized cost are shown graphically in Figure 2 and tabulated
below in Table 1.

    "Capital Charges" are based on a fixed charge rate of 16% per year
applied to the capital investment.  This category includes
depreciation, minimum acceptable return on investment, income tax on
return, property taxes and insurance.  It is the most significant of
the factors considered, averaging about 60% to 80% of the total cost.
The fixed charge rate varies considerably with the tax situation of

                               244

-------
the utility, the basic cost of money  and  the  life  of  the  facility.   A
municipal or REA utility may use figures  as low  as  11 or  12%  per  year,
whereas a private utility may use  18% per year or  more.   A lower  fixed
charge rate narrows the cost difference between  the precipitators and
the fabric filter, but not sufficiently to change  the general
conclusions.

    "T-R Power" refers to the power consumed  by  the transformer-
rectifier sets of the electrostatic precipitator (ESP).   The  amount
includes both energy and demand charges.  Power  consumption for T-R
Sets averages about 10% of the levelized  cost.   The "Bags" catagory
covers maintenance material, labor, overhead  and bag  replacements both
scheduled and unscheduled.  For a  2 year  replacement  schedule, the
"Bags" category represents about 17%  of the total  cost.

    The "Fan Power" category represents cost  for incremental  induced
draft fan power associated with the collector and  associated
ductwork.  The reverse air fans are also  included  in  the  category for
the fabric filter.  For ESP's a total  pressure drop of 3  inches W.C.
represented about 4% of total cost.   For  fabric  filters a 7 inch  W.C.
drop represented about 15% of the  total cost.

    Finally, the "Miscelleneous" category contains  all other operating
and maintenance costs plus power for  the  hopper  heater, purge air
blowers, ash system blowers and other  necessary  equipment.

                                TABLE  1
                     COMPONENTS OF COLLECTOR  COST*
                           	Levelized  Cost,  mills/kwh	
 Coal
 Source

 Wyoming
 N.  Dakota
 Lignite

 Alabama
 Eastern
 High Sulfur
        Collector
          Type**

         HS-ESP
         ECS-ESP
         FF-20/2
         FF-20/4
         FF-40/2

         ACS-ESP
         FF-20/2

         HS-ESP
         ACS-ESP
         ECS-ESP
         FF-20/2

         ACS-ESP
         FF-20/2
Capital
Charges

  1.52
  1.43
  0.75
  0.75
  0.88

  1.12
  0.90

  1.15
                              13
                              27
  0.78

  1.10
  0.82
 TR Power
or Bag Repl

    0.23
    0.18
    0.23
    0.12
    0.24

    0.26
    0.29

    0.18
    0.16
    0.17
    0.24

    0.35
    0.36
 Fan
Power

 0.08
 0.05
 0.16
 0.16
 0.15

 0.09
 0.23

 0.08
 0.07
 0.07'
 0.18

 0.10
 0.25
Misc   TOTAL
0.26
0.25
0.12
0.12
0.13

0.23
0.15

0.20
0.28
0.23
0.13

0.32
0.16
2.09
1.91
1.26
1.15
1.40

1.70
1.57
  61
  64
  74
  33
1.87
1.49
**
At NSPS emission level of 0.03 lb/106 Btu.
See Figure 2 for explanation of collector type designation,
                                 245

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    As shown in Figure 1 the cost of participate collection  by
electrostatic precipitation increases significantly as emission  limits
become more restrictive.  For example, decreasing the outlet
particulate emission from 0.1 lb/106 Btu to 0.03 lb/106 Btu,
increases the cost to own and operate a precipitator by about 30%.
This percentage varies somewhat depending on the type of coal and
properties of the fly ash.  Costs for the fabric filter do not change
over the range of emission limitations considered, since the high
efficiency of a fabric filter would enable compliance with limitations
from 0.01 to 0.1 lb/106 Btu.  For the new federal limit of 0.03
lb/106 Btu, the economics favors the fabric filter over the
precipitator for all of the coals investigated.  In general, it was
found that the economic comparison of precipitators and fabric filters
was dependent on the particulate emission limitation, the ash content
and heating value of the coal, the electrical properties of the fly
ash, the bag replacement schedule of the fabric filter, and site
specific aspects.

    Each collector's ability to collect fine particulate matter was
also studied.  For the four coals considered, it was predicted that if
the New Mexico limit on total emissions of 0.05 lb/10° Btu were met,
then the limit on emissions of particles less than two microns in size
also would be met.  For equal outlet loadings, the fabric filter
collects submicron particulate more effectively than the precipitator,
and so produces correspondingly lower opacities than the
precipitator.  Opacity is of more concern for precipitators whereas a
fabric filter normally will produce a clear plume.  Computer models
indicate that an opacity of 5 percent (essentially a clear stack) can
be obtained with a design limit of 0.014 lb/10° Btu.  Based on the
limited experience to date, fabric filters will have a significant
economic advantage in almost all cases if the design is based on
obtaining a clear plume.

    It should be noted that, although fabric filters have some clear
advantages over precipitators, experience with these devices on large
coal fired power plants and with high sulfur coal is minimal.  The
largest fabric filter installation to date is at the Monticello
Station of Texas Utilities (equivalent to 500 MW unit).  As further
experience is gained with fabric filters, valuable information on
reliability and cost will allow more accurate comparisons of the two
particulate collectors.

CASE STUDIES

    Four coals were selected for a hypothetical 500 Megawatt (MW)
pulverized coal fired boiler as shown in Table 2.  The collectors
considered appropriate for each of these coals are also shown in
Table 2.  The estimated collection areas required to produce various
emission levels are shown in Figure 3.
                                 246

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                                TABLE 2
                    SUITABILITY OF COLLECTOR SYSTEMS

  Type  of Coal                         Suitable Collectors

                                      Hot Side Precipitator
  Wyoming Sub-bituminous,             European Cold Side Precipitator
  Hanna,  Wyo.  Region (0.5656S)         Fabric Filter

  North Dakota Lignite                American Cold Side Precipitator
  High  Sodium Ash (0.68JJS)            Fabric Filter

                                      Hot Side Precipitator
  Alabama Bituminous                  American Cold Side Precipitator
  Warrior River Area of               European Cold Side Precipitator
  Alabama (1.9%S)                     Fabric Filter

  Eastern Bituminous                  American Cold Side Precipitator
  Ohio  Region (4.3%S)                 Fabric Filter
    Selection of the specific collection area (usually referred to as
SCA, expressed in terms of square feet of collecting plate area per
1,000 actual cubic feet of gas per minute) is probably the most
difficult and controversial procedure.  The method used in the EPRI
study for establishing the SCA was based on a modified form of the
Deutsch Equation:
             n = 1 - exp -
    °r       SCA »


    where   n = particulate removal efficiency
            w = precipitation rate, fpm
            k = dimensionless parameter, used to
                modify the original Deutsch equation.

    The value for k can vary from 0.4 to 0.6.  The EPRI study used a
value of 0.5.  The value for w depends on the characteristics of the
fly ash, primarily resistivity and mineral composition.  Empirical
data from existing installations were used in assigning the
appropriate values in each case.  The collecting plate areas shown in
Figure 3 for precipitators are for specific coals from the
geographical regions and can vary considerably with  small changes  in
coal analysis.  The curves shown in Figure 3 should  not be construed
to apply to all coals in general.  Cloth area for the fabric filter
changes only with gas volume to be filtered.  The gross air to  cloth
ratio was selected at 1.81 acfm/ft2 (1.93 net) for all cases over
the range of emission limits considered.


                                247

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CAPITAL COSTS

    Installed costs, presented in Figure 4 for the range of  outlet
emission levels, are based on 20 different designs and estimates
prepared for the study.  Included in the estimates are materials  and
labor for installation of the collectors, hoppers, support steel,
ducts, nozzles, dampers, fans, expansion joints, ash-handling
equipment, insulation, and other miscellaneous items.  Added to these
are differential and indirect field costs, engineering and fee at 3
percent, and contingency and miscellaneous costs at 10 percent.1

    Note that the capital investment for precipitators increases  as
the outlet emission is reduced.  Since fabric filters operate at  high
particulate removal efficiencies with relatively constant outlet
loading, the capital cost is essentially constant for the range of
emission limits.  The fabric filter capital cost is different for each
of the four coals, since the cloth area depends on the gas volume.
Options such as air-heater temperature control and preheat,  for
controlling the inlet flue gas temperature were not included.  Some
plants such as peaking or cycling units, incorporate these elements to
minimize excursions through the acid dew point and to prevent
corrosion to metal components or damage to the filter bags.

    Detailed estimates were made for three plant sizes (or gas flow
rates) and for three different precipitator collection areas.  For
example, the hot side precipitator was evaluated for 250, 500, and
1000 MW at SCA's 200, 400, and 800 ft2/103 acfm.  The fabric
filter was estimated for these plant sizes at air-to-cloth ratios of
1.6, 2.0, and 3.0 acfm/ft2.

    Graphical representations of how capital costs were found to  vary
with plant size, collection area, and number of compartments (for
fabric filters) are shown in Figures 5, 6, and 7.  The discontinuity
in cost versus gas flow for precipitators is due to layout
considerations.  For smaller boilers space for the precipitator is not
a problem.  For the larger boilers, longer (deeper) precipitators must
be turned sideways (parallel or chevron arrangement) to fit  in the 300
feet space allowed between the boiler house and the chimney.  Thus,
ducting is more extensive.  Generalized relations were developed  for
expressing the costs as functions of design parameters, such as
collection area and gas flow rate.  The relations listed below allow
the extrapolation of costs for collector systems of different plant
size and gas flow rates.

For electrostatic precipitators (ESP):


         CIESP    =   CI'ESP x  (  TT )   x
                                 248

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For fabric filters (FF):

                                                        M
Where CI = capital investment; F = inlet gas flow,  acfm;  SCA  =  ESP
specific collecting area, ft2/ 1000 acfm; A/C = gross  air-to-cloth
ratio of the fabric filter, acfm/ft2; M = number of compartments; f
= flow exponent; s = SCA exponent; a = air-to-cloth exponent; m  =
module exponent; and primed variables are those of  the  base case.
Cost-scale exponents for the four types of collectors  for the base
case conditions were determined from the various estimates.   These are
given in Table 3.

                                TABLE 3
                        EXPONENTS FOR ESTIMATING
                              CAPITAL COST

    Collector               f          s        a        m

    Hot-Side ESP          0.97       0.58      N.A.     N.A.

    Cold-Side ESP  (Am.)   0.93       0.60      N.A.     N.A.

    Cold-Side ESP  (Eur.)  0.89       0.74      N.A.     N.A.

    Fabric Filter         0.72       N.A.     -0.52     0.24

The base costs and design parameters are listed below  in  Table 4.

                                TABLE 4
                     BASE CASE PARAMETERS AND COST

                   A/C or    Gas Flow      No. of   Capital Investment
Collector System    SCA    JIO6 acfm)    Modules      ($106, 1977)


Hot-Side ESP         400       2.64         N.A.            23.9

Cold-Side ESP (Am.)  350       1.97         N.A.            14.8

Cold-Side ESP (Eur.) 550       1.97         N.A.            20.7

Fabric Filter        1.81      1.97         16              14.6
                                249

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OPERATION AND MAINTENANCE COSTS
    Operation and maintenance costs were estimated for  collectors  and
ash-removal systems based on information obtained from  existing
installations.  As shown in Table 5, operation of the collector  was
assumed to be constant at $20,000 per year for all collectors  and
$60,000 per year for ash handling.

                                TABLE 5

                       COST AND UNIT FACTORS FOR
                       OPERATION AND MAINTENANCE
                    FOR THE 500 MW BASE CASE SYSTEMS
               COLLECTOR  EQUIPMENT

                          Maintenance
Collector  Operation     ($/yr/106ft2)
System       ($/yr)     Material   Labor
                                    ASH REMOVAL EQUIPMENT

                                              Maintenance
                               Operation     ($/yr/106ft2)
                                ($/yr)   Material     Labor
Hot-Side
   ESP
20,000
Cold-Side    20,000
ESP  (Am.)

Cold-Side    20,000
ESP  (Eur.)
 Fabric
 Filter
20,000
  25,000


  25,000


  15,000


*280,000
25,000    60,000     30,000     30,000
                      25,000    60,000     10,000     10,000
                      15,000    60,000     10,000     10,000
35,000    60,000    **8,000    **8,000
     *This  figure,  estimated  for  two  year  bag  replacement  cycles,  is
     approximately  halved  for four  year  bag  replacement  cycles.

     **These  figures  increase to  $15,000 per year  per  106ft2  for
     the  40 comparment  system.

     Maintenance  figures were based on  cost  per  10^  ft2  of
 collection area  per  year.   For fabric  filters,  maintenance costs  were
 derived  from costs due to scheduled  and unscheduled bag replacements
 and  additional maintenance.   Bags  were  estimated  at 90  ft2 per bag
 and  $40  per  bag.   Labor was  based  on $14  per  hour for unscheduled
 replacements and $4  per hour for scheduled  replacement.  Unscheduled
 bag  replacements were  estimated  to be  5 percent of  total  inventory per
 year,  with labor based on one hour per  bag  replacement.  Other
                                 250

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maintenance was assumed to require 350 hours per year, with  the  cost
of materials at the same rate as the cost of labor.  These costs  are
summarized in Table 6.

                                TABLE 6

                          DETAILS OF BASE CASE
               FABRIC FILTER COLLECTOR MAINTENANCE COSTS
                                    Maintenance Costs  ($/yr/106ft2)
Type of Maintenance

Scheduled bag replacement*
Unscheduled bag replacement
Additional Maintenance
Materials
Labor
Total
250,000
25,000
5,000
20,000
10,000
5,000
270,000
35,000
10,000
Total
  280,000
35,000    315,000
    *Costs presented are for a two-year bag replacement cycle.   If a
    four-year bag replacement cycle is assumed, costs decrease
    approximately 50%.
    Power requirements were determined for each case.  These include
induced-draft and reverse-air fans, transformer-rectifier sets, hopper
heaters, accessories (rappers, valves, compartment dampers, and ash
removal equipment.  Power requirement factors are shown in Table 7.

                                TABLE 7

                      BASE CASE POWER REQUIREMENTS

                                            Connected Power

Collector
Hot Side ESP
Cold Side ESP
Cold Side ESP
Fabric Filter
Collection
Area
(lQ6ft2)
1.056
(Am.) 0.691
(Eur.) 1.086
1.091
Reverse
Air-Fans
(kW)
0
0
0
780
Hopper
Heaters
(kW per
hopper)
0
10
10
15
Accessories
(kW per
10W)
300
300
300
200
Ash
Removal
System
(kW)
500
500
500
500
                                251

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    The power requirements for the transformer-rectifier  sets were
determined separately for each case from estimates of the  current and
voltage needed for each precipitator.  A factor of 0.60 was  used  in
the conversion of alternating to direct current.  It was  assumed that
power connected to the sets would be double  the maximum  demand for
power.  For further details on the factors used to develop the
estimated power requirements, see the detailed EPRI report.!

    Annual operation and maintenance costs are presented  in  Figure 8.
The trends are similar to the capital cost, but the fabric filters
incur higher costs than the precipitators.  Operating and maintenance
costs were included for both the collectors and the ash removal
equipment.  The major operating cost was the consumption  of  electrical
power.  As expected, the frequency of bag replacement had  a
substantial effect on the maintenance costs for the fabric filters.

LEVELIZED COSTS

    To compare the collectors, capital investment, operation and
maintenance costs, and power requirements were combined and  levelized
over the 35-year life of the plant.  For the economic analysis, the
following factors were used:

         Minimum acceptable return (MAR):          11%

         Fixed charge rate (MAR, depreciation,
         insurance, and income on MAR):            16%

         Interest during construction:             8.5%

         Base year (Time zero):                    1977

         Escalation (fuel, operation and
         for materials and labor):                 7%

         Plant Capacity Factor:                    0.70

    The levelized costs for a 500 MW system, shown previously in
Figure 1, represent the added or differential cost of power, in mills
per kilowatt-hour, for particulate collection.

FINE PARTICLE EMISSIONS AND OPACITY

    The outlet emission of particulates less than two microns in size
were estimated by applying inlet size distributions of fly ash to
fractional efficiencies for each particular case.  Typical fractional
efficiencies, shown in Figure 9, were tailored for collectors of
different size through the use of a modified Deutsch relation.2  By
dividing both the inlet distribution and the fractional efficiency
into particle size increments, an outlet size distribution was
                                252

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calculated for each case.  This calculation is essentially a
prediction of emissions less than two microns in aerodynamic
diameter—the amount limited to 0.02 lb/10^ Btu by New Mexico.  For
all cases, it was found that when emissions total less than 0.05
lb/106 Btu (the New Mexico limit for total particulate) the State's
limit on sub-2-micron emissions was also met.

    The observed opacity of a plume emitted from a power plant stack
depends on a great number of variables, including the angle of the
sun, wind direction, atmospheric conditions, and the qualifications of
the observer.  The measurement of opacity by an in-stack instrument
reduces the variables to:  grain loading; size distribution, shape,
density, refractive index, and reflectance of the particle; stack
diameter; and NOX concentration.3  Mathematical correlations based
on these variables may be used to predict opacity, but the two most
important parameters are grain loading and particle size
distribution.  Outlet particle size distributions were developed for
each collector based on typical fractional efficiencies, rather than
actual size measurements.  The calculated opacities for precipitators
were judged, on the basis of past experience, to be somewhat high.
Upon investigation, it was found that the prediction of high opacity
resulted from larger than expected concentration of fine particles.
The high percentage of fines was a direct result of applying
fractional efficiencies that were adjusted for each precipitator using
the modified Deutsch relation.  Based on considerable experience with
existing installations, it was found that precipitators designed for
the limit of 0.1 lb/10° Btu and meeting corresponding guarantees
produced opacities of less than 20 percent.  Combining this with the
trends in the calculated opacities yielded Figure 10.  The average
curve shown in Figure 10 corresponds closely to good design emission
limits—that is, precipitators designed for these limits will yield,
during operation, approximately the opacities shown.  For a design
limit of 0.03 lb/10° Btu, opacities from 5 to 15 percent would be
expected.

EQUIPMENT SELECTION PROCEDURE

    The source of coal and the fly ash produced from burning that coal
will have a major impact on the selection of particulate removal
equipment.  Within recent years, trends have developed that make the
sizing of precipitators and fabric filters for continuous high
performance more difficult.  The four coals selected for the detailed
EPRI study was an attempt to cover the major variation of coal and ash
characteristics in the United States.  But with new mines opening,
both east and west, there are coals that are both better and worse for
precipitators and fabric filters.

    The Appalachian region production of high, medium, and low sulfur
coals will make the decision extremely difficult between precipitators
and fabric filters.  Variation in precipitability of all coals from
this region are well known.  In general, precipitability is not
                                 253

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strongly related to sulfur content as would normally be expected.
Washing of the higher sulfur coals to remove sulfur (mainly as  iron
pyrite) will probably reduce the precipitability more than would  be
indicated by the percent of sulfur removed.  The low precipitability
of the low sulfur coals from this region  is well known.  Hot side
precipitators have been used with varying success, depending mainly on
the sodium content in the ash.  Fabric filters need to be proven  on
the higher sulfur coals, but they should  be considered on most medium
and low sulfur Appalachian coals.

    The East Central coal region (Illinois, Indiana, Iowa, Missouri,
etc.)  is a medium to high sulfur coal region, with very little  low
sulfur coal.  These coals produce an ash  that, in general, has  a  high
precipitability, leading to reduced precipitator size and cost.
Because of this fact, this region will probably see a higher
percentage of precipitator installations  than any other region  in the
United States.

    The Northern Great Plains region (comprising North Dakota,  South
Dakota, Eastern Montana, and the Powder River Basin of Wyoming)
contains a variety of coals, for which fly ash precipitability ranges
from the highest to the lowest of any in  the country.  The high
sodium, high moisture, and medium-low sufur North Dakota lignites are
very easy to precipitate.  The low sodium, low sulfur, and the medium
moisture coals in the Powder River Basin may present major problems to
precipitators because of the high restivity and high concentration of
fine particulate.  Fabric filters may have high pressure drop problems
when handling the same Powder River Basin coal.  However, additional
experience is needed to accurately characterize the impact of these
coals.

    The low sulfur, low sodium coals in the Rocky Mountain region are
difficult to precipitate, but the high sodium, low sulfur coals in
this region will precipitate quite well.  Existing fabric filters are
performing very well with medium to low gas-side pressure drops and
fabric filters will probably see extensive application on Rocky
Mountain coals.

    In order to determine what the appropriate device is for a
specific application, the following plan might be considered:

    1.   Establish the coal to be burned over the life of the plant,
         if at all possible.

    2.   Define particulate characteristics (concentration, particle
         size, resistivity, etc.)

    3.   Determine efficiency required to meet all applicable
         regulations.

    4.   Size precipitator, selecting the appropriate SCA for
         guarantee performance, including redundancy for deterioration
         and other contingencies.

                                254

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    5.    Size fabric filter in a similar manner.

    6.    Establish economics (capital cost, operating cost,
         maintenance cost, present worth or levelized annual costs).

    7.    Select the appropriate device (considering technical
         feasibility as outlined in Table 1, as well as bottom-line
         economics as developed in steps 1 through 6).

    In  developing comparative capital costs for the precipitator
versus  the fabric filter, it is extremely important to define all the
components of the particulate removal system.  Each device must be
evaluated on a complete and comparable basis.  In addition to the
basic device itself, the additional costs that should be developed are
for inlet and outlet ductwork, structural supports, duct insulation,
dampers, expansion joints, turning vanes, foundations, ash handling
equipment (up to a common transfer point), electrical power supply,
hopper  heaters, hopper ash level detectors, differential I.D. fan
costs,  fabric filter preheat and purge system if appropriate and
erection costs.  In the case of a hot side precipitator, the cost
impact  of air heater location and longer combustion air duct runs
should  be considered.

    Careful attention must be paid to development of comparative
operating and maintenance costs.  Estimates of electrical power demand
must be developed for the I.D. fan, transformer-rectifier sets,
reverse air fans, hopper heaters, ash removal system and accessories,
such as rappers, damper operators, purge and preheat systems, etc.
The determination of precipitator transformer-rectifier (T-R) set
power consumption can be a difficult number to establish.  T-R set
power consumption for high efficiency large SCA precipitators can be a
significant value, almost exceeding the power difference in flue gas
pressure drop between a precipitator and a fabric filter.  Fabric
filter  bag life is another difficult area.  Although the EPRI study
used 2  year or 4 year bag lives, it is apparent from the fabric filter
operating experience to date that bag lives of 3 to 4 years are
common.  In other words, the 2 year bag life may be too conservative.

    Comprehensive and accurate maintenance data are difficult to
obtain.  The best sources for these data are the users; however, only
a few utilities have kept accurate maintenance records.  Typically,
annual  maintenance costs have been estimated as a small percentage
(from 2 to 5%) of the original installed cost of the equipment.

DESIGN  FOR RELIABILITY

    The fact that no system can be expected to produce optimal results
100 percent of the time must be addressed in the design of a
particulate collection system.  For precipitators, clogged ash hoppers
and broken wires are the biggest detriments to optimal performance.
                                255

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For the fabric filter, the main difficulty is the premature failure of
bags.  As previously pointed out, operating experience with fabric
filters has been much less than with precipitators, particularly for
large coal-fired units and applications with high sulfur coal.  Fabric
filters now in operation on large low sulfur coal burning units will
help to determine additional factors affecting reliability and
operability.

    For precipitators, since on-stream maintenance is not considered
practical, additional bus sections are desireable to enable
satisfactory performance until disabled sections can be repaired.
Generally, utilities schedule a seven to ten day outage each year for
minor maintenance.  Major outages are scheduled every two or three
years and can last 30 to 40 days.  Since activity during unscheduled
outages is very intense, only very high priority items are likely to
receive attention.  Thus, a well-designed precipitator should operate
reliably at or above the efficiency corresponding to the emission
limit for periods of a least one year without internal maintenance.

    Degradation of precipitator performance can be minimized by
increased electrical sectionalization.  In recent installations,
precipitators having as many as 100 independent electrical sections
(bus sections) are not uncommon.  In order to minimize the effect of
an ash valve failure or plugged hopper, the trend is toward locating a
hopper under each bus section.  The reliability of a bus section
depends on the design of the precipitator (e.g., rigid vs.
weighted-wire electrode design), the ash-handling system, the
abrasiveness of the dust, the degree of sparking encountered, and the
temperature.  Failure of weighted wire electrodes are usually
concentrated in the inlet field where higher dust loadings cause more
sparking and more abrasion.  The use of the rigid electrodes has
increased significantly because of this characteristic of the weighted
wire electrode.  Ash system failures can occur when a clinker of
semi-fused fly ash falls into a hopper.  The net result is that even a
well designed precipitator may have 5 to 25 percent of the bus
sections out of service by the end of a year.  The loss in efficiency
must be offset by additional collection area beyond the plate area
added for performance efficiency contingencies.  Commonly, this extra
area is expressed in terms of extra fields.  For instance, a
precipitator that could meet guarantees with four fields may have a
fifth field installed to account for normal deterioration and
contingency.  Occassionally, optimal contingencies are incorporated
into the design, such as the addition of a sixth empty field.  The
plates and wires are installed in the sixth field only if performance
proves to be unacceptable.

    The reliability of a fabric filter system in meeting performance
requirements is dependent mainly on the frequency of bag breakage, the
time taken to isolate the broken bags, the leakage of bypass dampers,
and sometimes the air-to-cloth ratio.  Conservative design and proper
                                256

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operation can generally minimize the frequency of broken  bags.   Also,
periodic replacement of all bags in a compartment will reduce the
average age of the bags and the frequency of breakage.  Minimizing
excursions below the acid dew point also tends to extend  bag  life.
The time to isolate a broken bag can be drastically reduced if
detectors are placed on the outlet of each compartment.   These
detectors indicate the opacity of the gas stream at the individual
compartment outlet, therby allowing the operators to quickly  isolate
the faulty compartment for repair.  Leaks through bypass  dampers also
affect performance.  The design used in the EPRI study incorporated
two louvered dampers in series with a purge of clean reverse  air to
block uncleaned flue gas.  High air-to-cloth ratios experienced  during
cleaning or maintenance can reduce performance.  However, fabric
filter efficiency generally is high enough that requirements  can be
met even during these periods.  The air-to-cloth ratio influences
reliability more strongly than performance because it affects bag life.

    In contrast to a precipitator, dampers on the compartments of a
fabric filter pose a possible restriction to the flow of  gas from the
boiler.  As a result, controls must be designed so that it is
essentially impossible for all compartment valves to close at once.
As a back-up measure, the fabric filter bypass damper should  be  set to
open automatically at high furnace pressure.

CONCLUSION

    Stricter particulate emission standards have increased the costs
for electrostatic precipitation, so that fabric filters have  become
cost competitive.  Fabric filters remove submicron particles more
thoroughly than do precipitators.  However, there is much less
operating experience with fabric filters than precipitators,
particularly on large coal-fired units or applications with high
sulfur coal.  In general, the relative economic feasibility of well
designed fabric filters and precipitators is dependent on the emission
limitation, the ash and heating content of the coal, the  properties of
the ash, the bag replacement schedule for fabric filter,  and  site
specific constraints.  As a result of these considerations, the
utility industry is comparing these two particulate collectors very
carefully to determine the optimum choice.

                               REFERENCES

1.  R.W. Scheck, S. D. Severson, et. al., "Economics of Fabric Filters
    Versus Precipitators," EPRI FP-775, June 1978.

2.  S. Matts and P.Q. Ohnfeldt, "Efficient Gas Cleaning with  S.F.
    Electrostatic Precipitators," SF Review, 1964.

3.  D. S. Ensor, R. W. Scheck, et. al., "Fabric Filter Fractional
    Efficiency," EPRI FP-297, November 1976.

4.  S. D. Severson, R. W. Scheck, et. al.,  "Economics of  Fabric
    Filters Versus Precipitators," presented at the 86th  National
    Meeting of the AICHE, Houston, Texas  (April, 1979).

                                257

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                                     WYOMING
                                       COAL
                       -EUROPEAN COLD-SIDE ESP
                               HOT-SIDE'ESP
                                              AMERICAN COLD-
                                                             SIDE ESP
 LEVELIZED

  COSTS,

MILLS/kWH
                                                       NORTH DAKOTA
                                                          LIGNITE
NO. OF COMP.: A & B = 20, C = 40~\
BAG LIFE, YRS.: A&C = 2, B = 4   J
FABRIC FILTER
                                                                           EASTERN
                                                                         HIGH SULFUR
                                                                            COAL
                        AMERICAN COLD-SIDE ESP
                                    i   i  i   i I
                                   HOT-SIDE ESP
                                PARTICULATE EMISSION LIMIT, LB/10  BTU
                                     FIGURE 1
              LEVELIZED COSTS FOR 500 MW COLLECTORS (1978)
LEVELI
MILLS/K
2.0 —
1.5-
1.0 —
0.5-
?E[
Wl-



)
< HS
ESP
MISC
FAN
TR
PWR

ECS
ESP
MISC
FAN
TR
PWR
CAP
CHAF
FF
MISC
FAN
BAGS
TAL
?GES
FF
20/4
MISC
FAN
BAGS
FF
40/2
MISC
FAN
BAGS



ACS
ESP
MISC
FAN
TR
PWR
CAP
CHA
FF
20/2
MISC
FAN
BAGS
TAL
1GES


HS
ESP
MISC
FAN
PWR,
ACS
ESP
MISC
FAN-
TR
PWR
CAP
CHA
ECS
ESP
MISC
FAN
TR
TAL
1GES
FF
MISC
FAN
BAGS


ACS
ESP
MISC
FAN
PWR
CAP
CHA
FF
MISC
FAN
BAGS
TAL
iGES
\ 	 WYOMING 	 / NORTH DAKOTA \ 	 ALABAMA 	 / EASTERN HIGH
LIGNITE SULFUR
                    FIGURE 2

          COMPONENTS OF COLLECTOR COST
       AT THE 0.03 IB/106 BTU EMISSION LEVEL
                                                 KEY
                                 fcfP
                                 ECS     EUROPEAN STYLE ESP
                                 FF      FABRIC FILTER
                                 20/2     20 COMPARTMENTS, 2 YEAR BAG LIFE
                                            258

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                      •1500
         SPECIFIC
       COLLECTION
       AREA (SCA)
      FT2/103 ACFM
                                        EASTERN HIGH SULFUR/COLD-SIDE
                                        NORTH DAKOTA
                                        LIGNITE/COLD'-SIDE
                           0.01         0.02    0.03     0.05        0.10
                           \	 PARTICULATE EMISSION LIMIT, LB/106 BTU -
                                          FIGURE 3
                              COLLECTING AREA REQUIREMENTS
                             FOR ELECTROSTATIC PREC1PITATORS
                                                                        0.15
ESTIMATED CAPITAL  20

INVESTMENT, $/kW
                                    PARTICULATE EMISSION LIMIT, LB/10 ° BTU •
                                      FIGURE 4
                 CAPITAL INVESTMENT FOR 500 MW COLLECTORS (1978)
                                          259

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01
O
                150   200     300       500    700
                                    SCA
                                          FIGURE  5
                                                      1000
1.5    2.0
      A/C
                      ESTIMATED CAPITAL INVESTMENT FOR  COLLECTORS
                                                    0.5           1.0
                                                          SCA RATIO TO BASE
2.0  0.5            1.0           2.0
        GAS FLOW RATIO TO BASE
                                                                                                                                         FIGURE  6

                                                                                                                COST CORRECTION FACTORS FOR ELECTROSTATIC PRECIPITATORS

                                                                                                            COST CORRECTION FACTORS ARE APPLIED TO THE CAPITAL INVESTMENT (CD OF THE BASE
                                                                                                            CASE ESP SYSTEMS TO ARRIVE AT THE Cl FOR THE CASE WITH A DIFFERENT DESIGN PARA-
                                                                                                            METER. FOR EXAMPLE, DOUBLING BOTH SCA AND GAS VOLUME ON A HOT SIDE ESP YIELDS
                                                                                                            A COST CORRECTION FACTOR OF 1.57 x 1.96 = 3.08. THIS FACTOR IS APPLIED TO THE Cl OF
                                                                                                            THE BASE CASE HOT SIDE ESP SYSTEM  ($23.9 X 10B| TO ARRIVE AT THE Cl OF THE NEW SYS-
                                                                                                            TEM- DUAL LINES ON GRAPHS ON RIGHT RESULT FROM ORIENTATION CHANGES.

-------
ro
CTl
                                                                OPERATION AND   100

                                                                  MAINTENANCE,

                                                                        $103/YR
 (A, B & 0 SEE FIG. 1)
                                                                                  100
                                                                                                  "****r.
                                                                                          EUROPEAN    X*"
                                                                                          01 n cine ccp/
                                                                                         COLD-SIDE ESP
                                                                                      0.01
                                                                                       \
                        *»ir,
                       0.5
                          0.5          1.0      "   2.0
                       NO. OF COMPARTMENTS RATIO TO BASE

                                 FIGURE 7

                  COST CORRECTION FACTORS FOR  FABRIC FILTER

        COST CORRECTION FACTORS ARE APPLIED TO THE CAPITAL INVESTMENT (Cl| OF THE BASE
        CASE FABRIC FILTER SYSTEM TO ARRIVE AT THE Cl FOR CASES WITH DIFFERENT DESIGN
        PARAMETERS. EXAMPLE: DOUBLING AlFi TO CLOTH RATIO, GAS FLOW AND NUMBER OF
        COMPARTMENTS WILL YIELD A COST CORRECTION FACTOR OF 0.70 x 1.65 -  1.36. THIS
        FACTOR IS APPLIED TO THE Cl OF THE BASE CASE FF SYSTEM ($14.59 x 106> TO ARRIVE AT
        THE Cl OF THE NEW SYSTEM.
      0.02  0.03   0.05       0.1    0.01
	PARTICULATE EMISSION  LIMIT,
                  FIGURE  8
 OPERATION AND MAINTENANCE COSTS
     FOR 500  MW COLLECTORS (1978)
0.02  0.03    0.05

     BTU 	

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PENETRATION
 (100-EFF)%   10
                    TYPICAL EUROPEAN
                      COLD-SIDE ESP
                                                                      EFFICIENCY
          01 0.2  0.5  1
          \	
                             2    5  10  20  0.1  0.2  0.5  1   2
                            ACTUAL PARTICLE DIAMETER, MICRONS

                                        FIGURE 9
                                                          5  10  20
        TYPICAL FRACTIONAL EFFICIENCIES FOR  EXISTING COLLECTORS
PERCENT OPACITY
                    APPROXIMATE AVERAGED
                                           1 lb/10" BTU=
                                        0.31 gr/acf (AVERAGE)
                                                                EPA AND NM LIMIT
                                                                CLEAR PLUME
                  .005
                                .02 .03  .05      0.1     0.2  0.3
                       PARTICULATE EMISSION LIMIT, LB/tO6 BTU
                                  FIGURE 10
                PREDICTED OPACITY VS. DESIGN EMISSION LIMIT
                             FOR PRECIPITATORS
                                      262

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                     DESIGN AND CONSTRUCTION OF BAGHOUSES

                            FOR SHAWNEE STEAM PLANT
                  J.  A.  Hudson, Head Mechanical Engineer
                  Fossil Fuel and Air Pollution Equipment
                  Division of Engineering Design
                  Tennessee Valley Authority
                  Knoxville, Tennessee
                  L. A. Thaxton, Vice President Agency Sales
                  Envirotech Corporation
                  Pittsburgh, Pennsylvania
                  H. D. Ferguson, Jr., Mechanical Engineer
                  Fossil Fuel and Air Pollution Equipment
                  Division of Engineering Design
                  Tennessee Valley Authority
                  Rnoxville, Tennessee
                  Neil Clay, Mechanical Engineer
                  Envirotech Corporation
                  Lebanon, Pennsylvania
                                   ABSTRACT
This paper is a sequel to "Precipitators?  Scrubbers?  or Baghouses?  for
Shawnee" given at the first EPA symposium in 1978, which explained the basic
reasons and philosophy for TVA's selection of baghouses for Shawnee.

In this Dresentation, the authors deal with the basic considerations of the
specifications, detail design, and construction of the baghouse system for the
10-unit Shawnee Steam Plant.  Special attention is given to a unique preheating
and reheating system for each baghouse prior to boiler startup or for cycling
operation, criteria for varying number of compartments online against flow
(ACFM) to minimize dewpoint consideration, criteria of air-to-cloth ratio as
well as filter material and coating, selection of materials, and construction
of a unique raft foundation system—all within a total construction period of
42 months.
                                       263

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                     DESIGN AND CONSTRUCTION OF BAGHOUSES
                            FOR SHAWNEE STEAM PLANT
INTRODUCTION AND GENERAL BACKGROUND

     The Shawnee Steam Plant is located on the south bank of the Ohio
River about 13 miles downstream from the mouth of the Tennessee River at
Paducah, Kentucky.  Construction of the ten 175-MW units was authorized
in January 1951.  Unit No. 1 was placed in commercial operation 27 months
later in April 1953 and the last unit, No. 10, went into operation in
October 1956, providing a total plant generating capacity of 1,750,000 kW
at the total cost of $216,500,000 or $124 per kW.

                (Based on today's costs for fossil plants, that
                sounds like a fairy tale, doesn't it!??)

     The plant was first equipped with mechanical dust collectors primarily
for induced-draft fan protection.  Then in 1968, shortly after issuance of
a Federal Executive Order in 1966, mandating increased pollution control
TVA initiated a retrofit program for design and construction of electro-
static precipitators in order to comply with this order.  This program of
retrofitting ten units with 90 percent efficient electrostatic precipitators
was completed in 1973 at a cost of $9,161,000.  At that time, the flue gas
was exiting into the ten stacks as seen here in this aerial photograph.  (Show
slide 1.)  Then in 1974, in an effort to improve the ambient air quality and
reduce local ground level concentrations of SO-, a program of building two
large 800-foot-high stacks was begun.  These stacks were located 187 feet
to the rear of the old stacks with long runs of ductwork connecting into
a common breeching each one serving five units, as can be seen here in the
photograph.

     Since there was room for argument regarding our tall stack approach for
control of SO-, we also left room in the ductwork between the old stacks and
new breeching for additional pollution abatement equipment if we lost our
argument.  In April of 1976, the Supreme Court ruled against tall stack
control of S0?, so we now had a chance to fill up this space of some 187 feet
with something.

     If we recap the chronology of air pollution project work at Shawnee,
it shows up something like the illustration on slide 2.
                                     264

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     Chronology of Air Pollution Projects

                        Program                             Cost

     1st Retrofit - Ten electrostatic precipitators
     at 90 percent efficiency - 1968-1973               $  9,161,000

     2nd Retrofit - Two 800-foot stacks,  ductwork
     and breeching - 1974-1977                            25,600,000

     3rd and (Final)(?) Retrofit - Ten structural
     baghouses and all auxiliaries - 1978-1981            80,000,000

                                             Total      $114,761,000

                                  Total Plant Cost      $216,500,000

                                                              or

                                                         53 percent

     Last year at this symposium, I presented a paper explaining the
philosophy and economic advantages of why TVA chose a baghouse and low-
sulfur coal in lieu of scrubbers as the solution.  Today, we will try to
explain the basic design criteria we have used in this baghouse installation.

TYPE OF CONTRACT AND SCOPE OF WORK

     In considering the workload of our design and construction forces,
it was decided that the Shawnee project should be done on a turnkey basis.
Within this concept we would write specifications and take bids on the
complete job of engineering, furnishing,  and erection of equipment for the
project.  And so it was that on March 14, 1978, TVA awarded a contract to
Buell Division of Envirotech Corporation in the amount of $53,218,000 for
engineering, furnishing, and erecting ten baghouses and all auxiliaries as
listed in the scope of work shown on slide 3.

Specification Outline

      1.  Structural Baghouse Fly Ash Collectors

      2.  Ductwork, Distribution Devices, Expansion Joints, and Louver Dampers
      3.  Insulation and Lagging

      4.  Fly Ash Handling Systems and Ash Sluice Water Piping

      5.  Washdown Pad Sump Pumps, Valves, Pipe, Hangers, Sewerage, and Freeze
          Protection

      6.  Induced-Draft Fans

      7.  Elevator and Hoists

      8.  Control Houses

      9.  Instruments and Control

     10.  Electrical Work
                                      265

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     11.   Structural Steel Supports and Miscellaneous Steel Access Platforms
          and Stairs

     12.   Concrete Foundations

     13.   Washdown Pads, Drains, and Sumps

     14.   Site Improvement, Parking Facilities, and Access Roads
     15.   Painting

     16.   Fire Protection

     The next five slides  (show slides 4, 5, 6, 7, and 8 of plans and
elevations, pointing out various features) show the basic equipment layout
and relationship to existing equipment.  Significant man-hours have gone into
the scheduling, design, procurement, and construction of the project to date.
Last year little actual work had progressed at the project site; this year
construction is well underway and the first unit is scheduled for tie-in in
late fall.  As can be seen from the slides there just is not ample room to
spread out; equipment, laydown area, and workmen all are confined to the
same general area.  Scheduling the activities has been a difficult task.

SCHEDULE

     The overall schedule, we believe, is very ambitious, and calls for
completion of all ten units 42 months after award of contract.  However,
the industry did respond in a favorable manner; no one claimed the time
was too short.  Some of the major milestones for the schedule are shown
on the bar chart here in slide 9.

Schedule

     Program Schedule

         TVA start specification                June 29, 1977
         Purchasing issue  invitation to bid     September 22, 1977
         Bid opening                            December 13, 1977
         Award of contract                      March 14, 1978
         Start construction                     April 24, 1978

     Construction and Tie-in Schedule

          Unit           Start Tie-in             Complete Tie-in

            5          November 1, 1979          December 1, 1979
            6          January 15, 1980          February 15, 1980
            4          March 15, 1980            April 15, 1980
            3          June 1, 1980              July 1, 1980
            7          August 15, 1980           September 15, 1980
            8          October 15, 1980          November 15, 1980
            9          January 1, 1981           February 1, 1981
           10          March 15, 1981            April 15, 1981
            2          May 15, 1981              June 15, 1981
            1          August 1, 1981            September 1, 1981


                                       266

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     The contract provides for a bonus-penalty for early or late completion
of the project.  Since it is impossible as well as impractical to identify
a precise cutoff date, we identified a 30-day dead band on each side of the
complete construction date before bonus-penalty would be applied.  On the
31st day, the bonus-penalty would accrue and continue until a maximum value
of $500,000 was reached.  The Contractor has recognized the potential for
the bonus and from the very start has proceeded with the organization,
design, schedule, and construction to capitalize on receiving the maximum
bonus.  All schedules and actions to date indicate they will complete the
tie-in of the final unit early and earn a bonus.

SPECIFICATION REQUIREMENTS

     In the spring of 1977 very few baghouses had been installed in utility
plants and it certainly behooved us to take advantage of standing experience
at that time.  Therefore, in writing the specifications we had four
objectives.  They were:

     1.  Build on industry experience in adapting baghouses to utility
         boilers.
     2.  Specify a very conservative design (low differential pressure and
         air-to-cloth ratio [A/C]).
     3.  Stretch the industry's practice regarding bag life guarantees.
     4.  Incorporate and redefine TVA's broad precipitator experience into
         their first baghouse.

     In short it was our intent to obtain equipment that would perform to
the best available technology while providing ease of maintenance and at a
competitive cost.

     One major area of concern was the selection of the method of cleaning.
Early in the project, we selected reverse air cleaning as the only type of
cleaning method acceptable.  This was not an accident or casual selection.
As best could be determined, from the industry itself, it was the only
method that had proven itself in utility operation.  More experience had
been collected on this cleaning method than any other and we felt that
the Shawnee units should be given every opportunity to become a model design,
not an experiment.

     In slide 10 we see a summary of some detailed design criteria.  (Show
slide 10.)

Design Criteria

     1.  Coal - Either separately or blended eastern or western low-sulfur
         coal.  Sulfur 0.33 percent.  Moisture 30.2 percent.  Ash 7.44 percent
         Heating value 8075 Btu/pound.

     2.  ACFM - Test block 650,000 with normal operation 585,000.

     3.  A/C - All compartments online at test block 2:1 (this will be
         explored later in the paper in great detail).

     4.  Bag - 11-7/8-inch diameter by 34-foot-7-3/4-inch 14-ounce fiberglass
         bag coated with teflon B finish, 9 percent by weight.

                                      267

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     5.  Cor-Ten for casing, hoppers, ductwork, and all gas contact surfaces.

     6.  Stainless steel bag hardware and poppet valve shafts and seals.

     7.  Dry fly ash handling system to pond and then wetted.

     8.  Fans, dampers, expansion joints, control houses, and related
         equipment necessary for the operation of the baghouse.

     9-  Each baghouse has ten compartments with 324 bags per compartment.
         Bags are arranged on 14-inch centers with 2-bag reach providing a
         grid of 12 by 27 (three walkways).

     Well-designed equipment must be capable of being easily maintained.  It
was our intention, particularly since this was our first baghouse, to pay
special attention to the ease of maintenance and especially to replacement
of bags.  I am well aware of the arguments regarding 2-bag versus 3-bag
reach, but am not prepared to argue all the details and merits of one versus
the other.  We all know that Murphy's Law says "If something can go wrong it
will."  We could paraphrase that and say "If it is hard to maintain it won't
be" or not often enough.  Conversely, if you make it easy to fix or replace,
chances are a lot better care will be taken of that particular feature.  Pure
and simple, this was the reason behind °ur decision to use a 2-bag reach in
the design of the Shawnee baghouse.  We believe that with ten units,
100 compartments, and  33,000 bags to watch after that anything to make
maintenance or replacement easier is money well spent.  One might ask "How
much extra real estate or space does your 2-bag reach design take over the
3-bag  reach?"  The next slide indicates the difference in space.  (Show
slide  11.)  There is only a 7 percent differential in the plan area and this
only occurs in one direction.  In our view this is "small potatoes" compared
with the overall space required and of very little significance in extra
money  spent for 2-bag versus 3-bag reach.  As a result of this, our 2-bag
reach  decision was really an easy one.

AIR-TO-CLOTH RATIO CRITERIA

     As most of you know who have tried to size dust collectors, obtaining
a consistent story of how much cloth area is in a bag is not an easy task.
To keep all bidders on an equal footing, we were very specific on how to
determine active cloth area.  The calculating of active cloth area is no
art; it is just important that all bidders understand and calculate the
active cloth area in the same manner.  As a guide, I have included how we
calculated active cloth area.  (Show slide 12.)  On the left you will see
a typical bag configuration and just to the right of it is a flat cloth layout
of the same bag.  Our approach was to use the overall cloth area and deduct
the top cuff, vertical seam, anticollapse ring seams, and bottom cuff seam
areas.  The overall cloth area is 107.71 square feet and with the deductions
this reduces to 102.47 square feet.  On the extreme right-hand side of the
slide  is a summary of  the cloth area per bag, per compartment, and per
collector.  There is only 5.24 square feet differential area per bag, but
this equates to 16,977 square feet per collector.  Significant advantages
or disadvantages could be given to a potential bidder if all bidders were
not calculating cloth area in the same manner.  This is by no means the only
approach, and I do not intend to pretend other approaches are not acceptable.
It is  our method and we believe indicates a conservative approach.

                                      268

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     As  a  followup  to  calculating cloth area,  we think the definition and
 calculation of  air-to-cloth ratios is equally  important.   (Show slide 13.)

                               AIR-TO-CLQTH RATIO

              BASED ON ACTIVE CLOTH AREA (102.47 SQUARE FEET/BAG)
 All compartments
 online (10)

 One compartment
 down for
 cleaning (9)

 One compartment
 down for cleaning
 and one down for
 maintenance (8)
                        Test Block
                        (Excluding
                       Reverse Air)
                       650,000 ACFM
1.96
2.18
           Test Block
           (Including
          Reverse Air)
          708,000 ACFM
2.37
            Normal
           Operation
          (Excluding
          Reverse Air)
          585,000 ACFM
              1.76
1.96
            Normal
           Operation
          (Including
          Reverse Air)
          643,000 ACFM
2.15
2.45
2.67
2.20
2.42
*Reverse air is not on when ten compartments are filtering.
      As can be seen in the slide,  it is easy to get  confused when talking
 A/C ratios, and it is important to know the basis  when you talk A/C ratios.
 You can see that while a 2 to 1 ratio is referred  to,  it is more or less
 nominal and the real operating condition which the baghouse uses is a more
 conservative 1.76 to 1.

      The arrows indicate the normal conditions of  service that the baghouse
 will see.  The air-to-cloth ratio  changes from 1.76  to 2.15 (for cleaning)
 to 2.42 (for cleaning and maintenance).  We feel this  is consistent with our
 conservative approach of providing low maintenance by  designing for longevity
 of bag life due to low differential pressure.   The additional capital cost for
 a larger dust collector is easily  written off  when compared to the subsequent
 capitol and maintenance cost of high-pressure  drop and more frequent bag
 maintenance.  The increase in incremental capitol  cost for lower air-to-cloth
 ratios is relatively insignificant compared to the cost of replacement power.

      Our philosophy of conservative air-to-cloth ratio and resultant low-
 pressure drop paid off in a suprising bonus.  The  successful bidder offered
 a 3-year bag life guarantee rather than the 2-year as  specified.  This extra
 year of guarantee we feel is the type response that  the pollution abatement
 equipment suppliers must extend to the utility industry.  Last year I
 challenged the industry itself that "its success depends upon the industry's
 response to new applications of an old technology."  We at TVA were glad to
 see that not only Envirotech but the industry  took steps in a responsive
 direction.   The extra year of bag  life guarantee equates directly to savings
 in loss of power generation.  Shawnee is a base load station and as such must
 run relatively loaded all the time.   The utilization rate for Shawnee is the
                                       269

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highest in the system and runs around 90 percent.  Anything that can be
done to reduce maintenance will result in savings over the long haul and help
hold the cost of electricity as low as possible.

GUARANTEES

     The next slide highlights a few of the performance and guarantee data that
was required by the specifications and offered by Envirotech.   (Show slide 14.)
Performance and Guarantee Data
     Maximum allowable outlet
       grain loading  (grain/ACF)

     Maximum allowable pressure drop
        (inches  of water)

     Fabric filter bag life  (years)
                                         Specification
                                          Requirement
0.005
6-3/4
             Envirotech
              Offered
0.005
5-7/8
     As  can be  seen,  Envirotech offered the same outlet grain loading while
improving  on  pressure drop  and bag life guarantees as defined in the invitation.

     I said earlier that  one of our objectives was to stretch the industry's
practice regarding bag life guarantees.  We did not expect that a Contractor
would go us one better by offering 1 extra year bag life than we specified
and  7/8-inch  less pressure  drop.  Needless to say we were pleased with this
response,  particularly since it was in the two most difficult and important
areas of the  specification  requirements.  These guarantees offered by the
contractor represent  hundreds of  thousands of dollars if not attained and we
know they  were  not taken  lightly  by the contractor.

     Again we feel that this type of response on the part of the industry is a
necessary  step  for baghouse supplier's to take in order to participate in
particulate control for utility applications.

DESIGN SCHEMATIC

     The fabric filter baghouse system, as furnished by the contractor,
receives a total of 6,500,000 ACFM of flue gases from twenty air preheaters
 (two for each boiler)  at  325° F,  processes this volume of flue gases through
ten  fabric filters and exits at 0.005 grain/ACF.  Each of the ten fabric
filters  serve one pulverized coal-fired reheat unit of radiant type, natural
circulation.  Each fabric filter  will be placed downstream of an existing
deenergized precipitator.   The fabric filters, as furnished by the contractor,
are  capable of  being  operated immediately upon startup of each boiler, without
adversely  affecting operation of  the baghouse through the employment of a
uniquely designed warm air  preheat system.

     Immediately upon leaving the two deenergized precipitators, the flue
gases travel  through  air  preheater pressure equalizing louver-type dampers.
These dampers are interlocked with the boiler logic and they also act to
balance  the load on the boiler.   The damper blades are of airfoil design,

                                       270

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stiffened as necessary, have no external ribs, and have built-in provisions
to accommodate the thermal expansion between the blades and the damper  frame
proper.

     At the inlet area of each of the ten fabric filters are six poppet-type
bypass dampers.  (Show slide 15.)  The filter bypass poppet valves  (three of
which are shown) are activated automatically due to overpressure, excessive
temperature, and low temperature; and manually for the maintenance of an
entire unit.  With the bypass dampers in the bypass mode or position, the
differential pressure across the system is not allowed to vary by more
than 2 inches from normal, with fabric filter online, in order to prevent
boiler unbalances associated with significant changes in flue gas pressures.
During normal filtering mode all six bypass poppet valves are closed.

     As the flue gases leave the bypass area, they begin their travel to
the fabric filter through the inlet manifold fabricated of 1/4-inch-thick
Cor-Ten A steel plate.  It should be noted that all ducts are designed  to
support a 1-foot depth of 75 pounds per cubic foot of fly ash.  Quick-opening
access and inspection doors, as well as appropriate turning vanes, are  provided
throughout the ductwork system.

     (Show slide 16.)  To enter each of the ten fabric filter compartments, the
flue gases must pass through inlet poppet dampers of a metal-to-metal positive
seal design.  There are twenty of these dampers for each fabric filter, and
they normally remain in the open position, except when a compartment is down
for maintenance or inspection and bypass, in which case the inlet poppet dampers
(two per compartment) are closed for complete isolation of flue gases.  When a
boiler is operating on reduced load, there will be a lower flue gas volume and
a lower gas temperature.  During these periods (especially when a boiler is
in a cycling mode) baghouse compartments can be isolated to reduce the  total
cloth area  (that is, to keep the A/C ratio close to 2:1) and exposed steel
surfaces to the flue gas.  This will accomplish two key objectives:  (1) It
will reduce loading and unloading of the filter cloth and should extend over
all bag life and (2) it will reduce the heat sink (large amount of metal surfaces
in contact with gas) that would decrease even further the gas temperature and
help to maintain temperature above the dewpoint.  If all ten compartments are
offline for any reason, all twenty inlet poppet dampers would be placed in the
closed position.  The dampers are heavy duty air-cylinder driven, and are
designed such that the normal flow of the flue gas aids in establishing a seal.
In addition to the twenty poppet-type inlet dampers, there are twenty similar
design outlet and reverse air dampers.  (Show slide 17.)  The outlet and reverse
air dampers are continuously used in the continual process of sequentially
operating and cleaning the fabric filter compartments.  When a compartment is
down for maintenance all inlet, outlet, and reverse air poppet dampers  providing
flue gas to that compartment are in tight closed, sealed position. (Show
slide 18.)

     A purge air system is also incorporated in the fabric filter design
to assist in the rapid cooling down of any compartment which is brought offline
for maintenance, while the adjacent compartments remain online.  To accomplish
this task, the contractor has included one vaneaxial fan per fabric filter.

     The exact design of the ductwork and fabric filter equipment distribution
devices were identified and incorporated as a result of an extensive model

                                       271

-------
study of the total system conducted by the contractor.  The contractor con-
structed a 1/4-inch 3-dimensional scale model of the fabric filters and of
that portion of ductwork that was necessary to perform tests to minimize fly ash
fallout and provide uniform flue gas and temperature distribution through the
fabric filters and associated ductwork.  (Show slides 19, 20, and 21.)

     These photographs of the model show turning vanes and gas distribution
devices that were added to aid in the reduction of pressure losses.  Good
gasflow distribution in some places was only obtainable through the use of
gas distribution devices.  An example of this is obtaining even gasflow across
the grid sheet.  (Show slide 22.)  The flue gas entering the individual hoppers
from the two inlets passes across a baffle or deflector plate, which has the
effect of equally distributing the flue gases to all bags within the individual
compartments.  The hopper flow deflector will aid in the evening of particulate
concentrations across all the cloth in the compartment and this should result
in reducing localized bag failure.  Without this deflector plate the flue gas
tended to turn immediately upwards through the tube sheet and not flow across
to the far side as indicated in this slide.

     It may be the opinion of some that good gasflow distribution is necessary
only for precipitators.  This was basically our "gut feel" at the start but
since this was our first baghouse we felt we would go ahead and model test—"it
couldn't hurt anything."  Now we are glad we did.  Based on the improvements in
gasflow, reduction of pressure drop, and all we learned from this model test, we
would have to say "it is just as important and beneficial to model test a bag-
house as it is a precipitator."

     In order to provide delivery power for the flue gases from the air preheater
through the base of the two 800-foot stacks, two induced-draft fans per fabric
filter are provided.  Each of the induced-draft fans are double inlet, double
width units.  The two fans per boiler will normally be started and run together.
The test block requirements for each induced-draft fan is 354,000 ACFM at 325° F,
with a fan static pressure of 31.5 inches wg at the inlet, and 0 inch wg static
pressure at the outlet of the fan.  The blades of the induced-draft fans are
of the airfoil type.  The fans have direct connected 2000-hp motors, operate at
900 rpm, and have inlet louver dampers for isolation.  The fans also have
conical variable inlet vanes for inlet volume control and to provide pressure
balancing for the fabric filter and boiler operation.

     (Show slide 23.)  The most unique feature of the entire baghouse installa-
tion is the reverse air cleaning and prewarming system.

     The induced-draft fans are the principal mode of fabric filter reverse
air cleaning with the reverse air fans being provided for backup cleaning
during periods of excessive pressure drop or other unusual conditions.  As
such, the induced-draft fans can be subjected to variations in pressure of up
to +1 inch wg every 5 minutes and having a duration of some 30 seconds.  The
induced-draft fans, dampers, actuators, and controls have been selected for this
duty.  There is a total of ten reverse air fans (one for each fabric filter).
The compartment warming system utilizes the reverse air system to preheat
offstream compartments or an entire baghouse with cleaned, heated flue gas from
the outlet breeching.

     Referring to the slide and as noted before there are five baghouses
connected to each breeching and stack.  Thus, there is always a constant source

                                      272

-------
of clean, heated flue gas to be used for reverse air cleaning or prewarming a
compartment or baghouse.  Here is how it works:  The pressure in the stack
breeching is approximately 0 to +1 inch tLO and the pressure at the inlet to
the baghouse is approximately -20 inches HO.  To initiate cleaning, all that
is required is to open the appropriate damper, bypassing the reverse air
fan, and clean hot gas will flow to the desired compartment.  As long as an
induced-draft fan is running, it may never be necessary to use the reverse
air fan.  The reverse air fans will be used if pressure upset conditions should
occur or to preheat offstream compartments when the induced-draft fans are out
of service  (an example would be on cold startup).  To ensure that the bags are
not subjected to violent pressure changes during cleaning or warming, a
modulating reverse air damper will control and maintain a constant flow, thus
providing a constant A/C ratio when cleaning.  We believe the real advantage of
this system is the ability to prewarm any baghouse prior to its receiving gas
from the boiler.  We can avoid shocking a cold baghouse with 325° F dust-laden
gas without a costly steam or other type preheating system.

QUALITY ASSURANCE PROGRAM FOR BAGS

     The quality control program which the contractor established in cooperation
with the bag vendor for the manufacture of the TVA filter bags is necessary to
ensure the bags are manufactured to the customer specifications.  (Show
slide 24.)

Fabric Filter Quality Assurance Program

     1.  Bag hardware:  Inspected at 10 percent random sample minimum, includes
         weld strength tests on anticollapse rings.
     2.  Fabric:  In-house fiberglass rolls are inspected 100 percent for roll
         numbers, lot numbers, and test certifications.
     3.  Thread:  Tested for strength, plies, and compliance to specifications.
     4.  Equipment:  Machines are inspected for proper operation and function,
         including layout table marks.

     5.  Fabrication:  Workmanship is checked at all work stations:   layout,
         seaming, ringing, cuffing, packaging.  Cloth condition is inspected
         at each work station.

     The program provides the bag vendor with the ability to trace all raw
materials used during manufacture back to the original supplier, and due to
various inspections and certifications also ensures that these raw materials
meet the specifications as required by TVA.

     The quality assurance program provides methods of inspection whereby all
hardware and fabric items are checked for proper sizing, as well as material
type specifications.  The program stipulates work in process quality control
checks be made at the different manufacturing stations for cutting,  seaming,
cuffing, and ringing.  (Show slide 25.)
                                       273

-------
Filter Cloth Test Certifications

                     Test                     Method

                Weight                  ASTM D 1910
                Thickness               ASTM D 1777
                Count*                  ASTM D 1910
                Permeability            ASTM D 737  '
                Tensile strength"       ASTM 1682, Method IR-T
                Mullen burst            ASTM D 231
                Mit flex
                Organic content         ASTM D 578
                Water repellancy        ASTM D 2721
                Yarn weight             ASTM D 578
                Yarn twist*             ASTM D 578
                Microscopic exam*

               *Warp and fill

     After manufacture, each individual bag is then checked for size and any
defects before being individually packaged.

     The contractor as well as the bag vendor believes in quality; the quality
assurance program is the tool used to enable them to purchase the raw materials
and produce some 35,000 quality filter bags.

     This quality control program, coupled with the conservative air-to-cloth
ratio and low pressure drop and the specification requirement of 14-ounce-per-
square-yard cloth, was the main consideration in the contractor's decision
to offer a 3-year bag life guarantee.

INSTRUMENTATION AND CONTROLS

     The Shawnee baghouse has been equipped with a full complement of alarms,
annunicators, monitors, and strip chart recorders in order that the control
room operator can monitor and operate the baghouses.  Dual monitoring controls
are provided in the unit control room and baghouse control room.  Depending
on the type of maintenance and/or operation, the appropriate control panels can
be selected to perform the activity.

     Display boards, mimic panels, lights, and status indicators add much
needed useful information to the operators.  The approach for design has been
to make available to the main control room operator controls of the level
and type necessary for the operation of the baghouse in conjunction with the
boiler.  At a glance the control room operator can determine the mode of
cleaning operation, baghouse pressure differential, inlet and outlet flue
gas temperatures, reverse air temperature, status of compartments (whether
filtering, cleaning, or maintenance) system draft, various system failures,
or other key operational inputs.  Envirotech and TVA have worked closely to
identify and provide the instrumentation, controls, and boiler interlocks
necessary for the operation of the boiler, turbine generator, and baghouse
as an integrated system.
                                       274

-------
CONSTRUCTION

     There were two schemes considered for constructing the ten baghouses.  One
was to start at one end and work towards the other end in progression.  However,
after completing the schedule for this scheme it was decided we should try to
find a way to complete the job in a shorter time frame.  As a result we struck
upon the scheme now being used of starting at the center on units 5 by 6
simultaneously and working out towards each end at the same time.  This scheme
permitted the use of two cranes simultaneously and more efficient scheduling
and use of manpower.  (Show slide 26.)

     One of the most unusual construction features of this project is the
foundation.  Because of the high water table and soil characteristics, it
was necessary to design and build a raft or bathtub type foundation which
would float.  The floor of this bathtub foundation for all ten units is
100 feet wide, 825 feet long, and 3 feet thick.  The walls are 13-1/2 feet
high and 1-1/2 feet thick around the entire perimeter.  A grid work of steel
support columns is erected inside this bathtub to support decking, over which
is poured a washdown slab as a roof over the bathtub at grade level.  (Show
slide 27.)  The baghouses are then erected above this grade level roof over
the bathtub foundation starting in the center and working outwards to both
ends simultaneously.  At the present, construction is proceeding ahead of
schedule and from all indication it appears the contractor will be ready for
an earlier tie-in than called for in the schedule.  (Show slides 28, 29, 30,
31, 32, 33, and 34.)

SUMMARY

     When we announced our decision to install ten baghouses at Shawnee
two years ago, we were certainly aware of the pioneering nature of the magnitude
of this decision.  I shall never forget the question put to me by Ed Stenby
of Stearns Rogers when he asked incredulously "Al, you are putting in ten
baghouses?  You're not going to put in one and try it out"?  I have explained
before that we did not have the luxury of that option, sensible as it is.  We
had to commit all ten units to particulate control, but believe me that
question had its impact on our thinking.  If we made a mistake, it would
happen ten times in whatever area of design we were in!I

     As a result our goal has been to design a conservative baghouse system.
There has been no attempt at any stage of design to cut corners or economize
at the expense of quality.  TVA and the contractor, Envirotech, have recognized
the importance of conservatism and quality in design from the beginning of
this project.  The spirit of cooperation could not be better, and the turnkey
concept has proven to be a satisfactory one.

     Late this year at Shawnee No. 5, TVA will start up the first baghouse
ever in its system to be followed at approximately 2-month intervals by
nine more.  We do not expect that this startup will be trouble-free—nothing
ever is.  However, because of conservatism in design, special attention paid
to all details and desire to do a good job on the part of the contractor, we
believe after initial shakedown that the Shawnee plant will be living testimony
to the fact that baghouses can be a viable alternative to successfully collect
particulates in large, multiunit central electric generating stations.


                                       275

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                                      CHRONOLOGY OF_AIR POLLUTION PROJECTS
                                                  UNITS  1-10
                                               SHAWNEE STEAM PLANT
                 PROGRAM

       1ST RETROFIT -  10  ELECTROSTATIC  PRECIPITATORS AT 90-5
         EFFICIENCY -  1968-1973
     COST

$  9,161,000
       2ND RETROFIT  -  TWO  800-FOOT  STACKS,  DUCTOWRK, AND
         BREECHING - 1974-1977
  25,600,000
01
3RD AND (FINAL)(?) RETROFIT - 10 STRUCTURAL BAGHOUSES
  AND ALL AUXILIARIES - 1978-1981
                                                               TOTAL
                                                    TOTAL  PLANT COST
  80,000,000


$114,761,000 --53% TOTAL PLANT COST

$216,500,000
SLIDE NO. 2

-------
                                                     STRUCTURAL BAGHOUSE
                                                     SHAWNEE STEAM PLANT
                                                    SPECIFICATION OUTLINE
             1.  STRUCTURAL BAGHOUSE FLY ASH COLLECTORS
             2.  DUCTWORK, DISTRIBUTION DEVICES, EXPANSION JOINTS, AND LOUVER DAMPERS
             3.  INSULATION AND LAGGING
             4.  FLY ASH HANDLING SYSTEMS AND ASH SLUICE WATER PIPING
             5.  WASHDOWN PAD SUMP PUMPS, VALVES, PIPE, HANGERS, SEWERAGE, AND FREEZE PROTECTION
             6.  INDUCED-DRAFT FANS
             7.  ELEVATOR AND HOISTS
             8.  CONTROL HOUSES
             9.  INSTRUMENTS AND CONTROL
            10.  ELECTRICAL WORK
            11.  STRUCTURAL STEEL SUPPORTS AND MISCELLANEOUS STEEL ACCESS PLATFORMS AND STAIRS
            12.  CONCRETE FOUNDATIONS
            13.  WASHDOWN PADS, DRAINS, AND SUMPS
            14.  SITE IMPROVEMENT, PARKING FACILITIES, AND ACCESS ROADS
            15.  PAINTING
            16.  FIRE PROTECTION
SLIDE NO. 3

-------
                                                                      ELEVATOR UNITS
                                                                        3$8 ONLY
                                                 /T\
                                         BYPASS POPPET
                                        REMOVAL MONORAILS
                                                              BAG HOIST AND
                                                                MONORAIL
                                      BAGHOUSE
                                     PLAN VIEW
SLIDE NO. 4

-------
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--J
                 REVERSE AIR DUCT
             TRUNK DUCT
             REVERSE AIR

             BOOSTER FAN
                                         0 D  DID D  DID D  DiD D  D
                                         D"D""D ! 0 D  D ! D  D  0 : D D  D
                                                        BAGHOUSE

                                               WEST  WALL ELEVATION
              SLIDE NO. 5

-------
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                                        MANUALLY OPERATED
                                        BUTTERFLY DAMPER
                                   REVERSE AIR DAMPER
      OUTLET POPPET
      REMOVAL MONORAIL


       PENTHOUSE
                                                                                             REVERSE AIR DUCT
                                                   POPPET DAMPERS IN
                                                   CLEANING MODE
POPPET DAMPERS IN
FILTERING MODE
QUICK OPENING
COMPARTMENT
ACCESS DOOR
                                                                                                 HOPPER
                                                                 BAGHOUSE
                                                             SECTIONAL  VIEW
                       SLIDE NO. 6

-------
                                                                                          - ELEVATOR
PO
CO

V
/ \
INLE
T DUCT
V
/ \
                                                           -SUMP UNITS
                                                            3(8 ONLY
                                                                                               T.O.G. EL. 4IS'-l'/j
                                                                                               ra^El-. 407'-l'/s
                                                                                              ELEVATOR LANDING
                                                                                              T.O.G. EL. 375'-!^*
                                                                                              ELEVATOR LANDING
                                                                                              -NOMINAL GRADE
                                                                                                EL. 345'-0*
              SLIDE NO._Z
         BAGHOUSE
SOUTH V/ALL  ELEVATION

-------
                                            PENTHOU3E
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                   I.S. ROOF EL. 415 - 0
                   T. 0. G. EL. 407 -
                  HOPPER ENCLOSURE
                                                                                 REVERSE  AIR DUCT
                                                                                           T.O.G. EL. 375'-l'j
                                                                                          rNOMINAL GRADE

                                                                                          \  EL. 345'-0"
                                                             1.0. FANS-
                SLIDE NO. 8
         BAGHOUSE
NORTH WALL ELEVATION

-------
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                                                                               SCHEDULE
                                                                     SHAWNEE  STEAM PLANT "UNITS I-10
                                                                 STRUCTURAL BAGHOUSE  FLY  ASH COLLECTORS
                                                                           TVA - ENVIROTECH
PROGRAM SCHEDULE
TVA START SPECIFICATION
PURCHASING ISSUE INVITATION TO BID
BID OPENING
AWARD OF CONTRACT
START CONSTRUCTION
CONSTRUCTION AND TIE-IN SCHEDULE
UNIT START TIE-IN
5 NOVEMBER 1, 1979
6 JANUARY 15,1980
4 MARCH 15, 1980
3 JUNE 1, 1980
7 AUGUST 15, I960
8 OCTOBER 15,1980
9 JANUARY 1, 1981
10 MARCH 15,1981
2 MAY 15, 1981
1 AUGUST 1, 1981
cc
SS I BO ASC ST CT
JUNE £9, 1977
SEPTEMBER 22,1977
DECEMBER 13,1977
MARCH 14, 1978
APRIL 24,1978
COMPLETE TIE-IN CC
SC ST CT
Di-ctMHhw i, ly.'y !\\\\\\\v\\\\ v\\ v\\\ via



JULY 1, 1980 1 V\ W\ VV\\\\V\'v\ \V\\\B1


NOVR MH^PV is, iw> I\\\\\\\\\\\\\\\\^\\\M

FEBRUARY !. 1981 !\\\\\\ \V\V\\\ V\ \\V\\IH

APRIL (5.1981 i\\\\\\\\V\'\lv\\'\\\\\\»
JUKJF 15 1981 ( V\ \ K \-T\' \ \ \ \ \ \ \~\ \ S \"V \ N R^
SEPTEMBER ! 1981 1 \ \ v^Ws \\\'\'\VVV'\vvv\^p

II 2-3 41 234 1234 1234 1234
1 	 1077. 	 1 	 IQ70 	 . 	 1 	 I07n_ . 1 	 ino^ ... .no, 1
                                                                                                        LEGEND
                                                                                    E3  - CONSTRUCTION       A  - AWARD
                                                                                    a  -TIE-IN              SC - START CONSTRUCTION
                                                                                    SS  - START SPECIFICATION   CC - COMPLETE CONSTRUCTION
                                                                                    I   - ISSUE INVITATION      ST - START TIE-IN
                                                                                    BO.  -- BID OPENING         CT - COMPLETE TIE-IN
   SLIDE NO.  9

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                                          STRUCTURAL BAGHOUSE FLY ASH COLLECTORS
                                                        UNITS 1-10
                                                    SHAVINEE STEAM PLANT
                                                      DESIGN CRITERIA


             1.   COAL  -  EITHER SEPARATELY OR BLENDED EASTERN OR WESTERN LOW-SULFUR COAL.  SULFUR .33 PERCENT.
                   MOISTURE  30.2  PERCENT.  ASH 7.44 PERCENT.  HEATING VALUE 8075 BTU/POUND.

             2.   ACFM  -  TEST BLOCK 650,000 WITH NORMAL OPERATION 585,000.

             3.   A/C - ALL COMPARTMENTS ONLINE AT TEST BLOCK 2.0 (THIS WILL BE EXPLORED LATER IN THE PAPER
                  IN GREAT DETAIL).

             4.   BAG - 11-7/8" DIAMETER BY 34'-7-3/4" FIBERGLASS BAG COATED WITH TEFLON B FINISH; 9% BY WEIGHT.

^            5.   CORTEN  CASING, HOPPERS, DUCTWORK, AND ALL GAS CONTACT SURFACES.
oo
"^            6.   STAINLESS STEEL  BAG HARDWARE AND POPPET VALVE SHAFTS AND SEALS.

             7.   DRY FLY ASH HANDLING SYSTEM TO POND AND THEN WETTED.

             8.   FANS, DAMPERS, EXPANSION JOINTS, CONTROL HOUSES, AND RELATED EQUIPMENT NECESSARY FOR THE
                   OPERATION OF THE BAGHOUSE.

             9.   EACH  BAGHOUSE HAS 10 COMPARTMENTS WITH 324 BAGS PER COMPARTMENT.  BAGS ARE ARRANGED ON 14-INCH
                   CENTERS WITH TWO BAG REACH PROVIDING A GRID OF 12 BY 27 (3 WALKWAYS).
   SLIDE  NO.  10

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           STRUCTURAL BAGHOUSE FLY-ASH COLLECTORS
           SHAWfCE STEAM PLANT UNITS I-10
           TWO VS. THREE SAG REACH
           GRID ARRANGEMENT
                                   STRUCTURAL BAGHOUSE FLY-ASH COLLECTORS
                                   SHAWNEE STEAM PLANT UNITS HO
                                   TWO VS. THREE BAG REACH
                                   BAGHOUSE ARRANGEMENT
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                  RATO OF PLAN AREA OF 3 BAG VS 2 BAG REACH =  -f?H- =
                                                                            2.06?.
                                                                            7630
    SLIDE NO.  11

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          <£BAG
               VERTICAL SEAM
                                                              V/^
                                                1 CUFF BAND
                   GROSS OVERALL LENGTH
                          3"'-7}"
                                 ANTICOLLAPSE
                                 RING SPACING
                            7SPACES "7V7V^,^ \
, , Kl
"^KT—J" VERTICAL SEAM
""l^
7V y 7-7-7 y~7" / •^7r~7'Nj /

ACTIVE CLOTH
AREA DETERMINATION

i.
?
3.
4.
5

LOCATION
OVERALL CLOTH AREA
TOP CUFF SEAM AREA
VERTICAL SEAM AREA
ANTICOLLAPSE RING SEAM AREA
30TTOM CUFF SEAM AREA
TOTAL ACTIVE CLOTH AREA/BAG
SQFT
107.71
-.51
-1.80
-1.91
-1.02
102.47

CLOTH AREA SUMMARY
CLOTH AREA
PER BAG
PER COMPARTMENT
(!2< BAGS)
PER COLLECTOR
BAG SIZE (SQ.FT.)
107.71
31,898
308,930
102.17
33,200
332,003
A CLOTH AREA
(SQ. FT.)
5.24
I698
16,977

                                              FLAT..CLOTH LAYOJJJ_
FABRIC FILTER
ACTIVE CLOTH AREA
STRUCTURAL BAGHOUSE
SHAWNEE STEAM PLANT
UNITS i-IO
SLIDE  NO.  12

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                                                 AIR TO CLOTH RATIO
                                 BASED ON ACTIVE  CLOTH AREA~(TQ2T4T SQUARE FEET/BAG)
                                          STRUCTURAL  BAGHOUSE - UNITS 1-10
                            TEST BLOCK
                            (EXCLUDING
                             REVERSE AIR)

                            650,000 ACFM
SHAWNEE STEAM PLANT

 TEST BLOCK
 (INCLUDING
  REVERSE AIR)

 708,000 ACFM
NORMAL OPERATION
  (EXCLUDING
   REVERSE AIR)

   585,000 ACFM
NORMAL OPERATION
   (INCLUDING
    REVERSE AIR)

    643.000 ACFM
co
   ALL COMPARTMENTS
   ON LINE (10)                  1.96
   ONE COMPARTMENT
   DOWN FOR CLEANING (9)         2.18
   ONE COMPARTMENT DOWN
   FOR CLEANING AND ONE
   DOWN FOR MAINTENANCE (8)      2.45
      2.37
      2.67
                              1.76
       2.20
                               2.15
       ^2.42
         *REVERSE AIR  IS NOT ON WHEN 10 COMPARTMENTS ARE FILTERING.
   SLIDE NO. 13

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00
00
                                               STRUCTURAL 3AGKOUSE  FLY  ASH  COLLECTOR
                                                  SHAWNEE STEAM  PLANT UNITS 1-10
                                                  PERFORMANCE  AND GUARANTEE DATA
                                                        TVA  AND  ENVIROTECH


                                                            SPECIFICATION                       ENVIROTECH
                                                            REQUIREMENT                          OFFERED

                MAXIMUM ALLOWABLE OUTLET
                  GRAIN LOADING (GRAIN/ACF)                      .005                                .005

                MAXIMUM ALLOWABLE PRESSURE DROP
                  (INCHES OF WATER)                              6-3/4                               5-7/8

                FABRIC FILTER BAG LIFE (YEARS)                     2                                  3
      SLIDE NO. 14

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no
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INLET DUCT
FROM BOILER
                                                                                                              OUTLET MANiFOLD

                                                                                                               TO I D  FANS
                                                                                                     INLET MANIFOLD
                                                                   i*.  3  L, s
       SLIDE NO.  15

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                                FILTER BAGS



                                TUBE SHEET
ro
                                                                                                         OUTLET MANIFOLD
                                                                                                         TO I.D. FANS
                                                                                                         INLET IWANfFOLD
                                                                                                         FROM BOILER
            SLIDE  NO. 16

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                                                                              REVERSE AIR  MANIFOLD
                                                                              FROM  CLEAN AIR  TRUNK DUCT
ro
                                                                                                     OUTLET  MANIFOLD
                                                                                                     TO  I D FANS
                                                                                                     INLET MANIFOLD
                                                                                                     FROM BOILER
             SLIDE NO.  17

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                                                                                        PURGE  DUCT
                                                                                        TO PURGE  FAN
                             ACCESS  DOORS Typ
ro
MD
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                                                                                                    OUTLET  MANIFOLD
                                                                                                    TO  I D  FANS
                                                                                                     INLET  MANIFOLD
                                                                                                     FROM BOILER
          SLIDE  NO. 18

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OO

         SLIDE  NO.  22

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  UNIT 1-5
 SYMMETRICAL
   ABOUT-
             REVERSE AIR/COMPARTMENT WARMING
               FLOW
                              TVA SHAWf^EE STEAM PLANT
                                         mns 1-10
                                BAGHOUSE  FLOW
SLIDE NO.  23

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      FABRIC FILTER QUALITY ASSURANCE PROGRAM

  I,  BAG HARDWARE:  INSPECTED AT 10% RANDOM SAMPLE,
      MINIMUM,  INCLUDES WELD STRENGTH TESTS ON ANTI-
      COLLAPSE RINGS,

 II.  FABRIC:  IN-HOUSE FIBERGLASS ROLLS ARE INSPECTED
      100% FOR ROLL NUMBERS, LOT NUMBERS, AND TEST
      CERTIFICATIONS,

 III,  THREAD:  TESTED FOR STRENGTH, PLIES AND COMPLIANCE
      TO SPECIFICATIONS,

 IV,  EQUIPMENT:  MACHINES ARE INSPECTED FOR PROPER
      OPERATION AND FUNCTION, INCLUDING LAYOUT TABLE MARKS,

  V,  FABRICATION:  WORKMANSHIP IS CHECKED AT ALL WORK
      STATIONS; LAYOUT, SEAMING, RINGING, CUFFING, PACKAGING,
      CLOTH CONDITION IS INSPECTED AT EACH WORK STATION,
                            295

NO. 24

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                   FILTER CLOTH TEST CERTIFICATIONS






        TEST                                  METHOD





        WEIGHT                              ASTM D1910




        THICKNESS                           ASTM D1777



        COUNT *                             ASTM D1910



        PERMEABILITY                        ASTM D737



        TENSILE STRENGTH *                  ASTM 1682 - METHOD IR-T



        MULLEN BURST                        ASTM D231



        MIT FLEX



        ORGANIC CONTENT                     ASTM D578



        WATER REPELLANCY                    ASTM D2721



        YARN WEIGHT                         ASTM D578



        YARN TWIST *                        ASTM D578



        MICROSCOPIC EXAM *
        *  WARP AND FILL
                                296




SLIDE No. 25

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          OPERATING CHARACTERISTICS OF A FABRIC FILTER ON A
              PEAKING/CYCLING BOILER WITHOUT AUXILIARY
                          PREHEAT OR REHEAT

                                 By:

          Walter Smit - Engineer, Power Production Department
                        United Power Association
                       Elk River, Minnesota  55330


          Kirk Spitzer - Product Manager, Fabric Filter Systems
                   Research-Cottrell, Utility Division
                      Somerville, New Jersey  08876
     A fabric filter system has been on-line for one year on a
coal-fired boiler that is primarily a peaking unit within the power
schedule.  For the first six months, Eastern Kentucky coal with
2.5 percent sulfur was the fuel source for 30 percent of the time,
with low-sulfur Montana coal constituting the remaining fuel during
the operation period.

     Bag life has been excellent with no bag failures reported to
date, and pressure drops have been low.  There has never been an
auxiliary heat source to preheat the fabric filter for start-up,
nor to reheat the fabric filter when operating at reduced load
with associated low back-end temperatures.

     Conclusions are that the filter cake formed does' protect the
bags from blinding at low load conditions, and a special acid-
resistant finish applied to the glass fibers protects the bags when
high-sulfur coal is burned at low temperatures.  Overall, this
installation provides an excellent data base for cycling service
and high-sulfur coal usage with a fabric filter.
                                   297

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OPERATING CHARACTERISTICS OF A FABRIC FILTER ON A PEAKING/CYCLING
             BOILER WITHOUT AUXILIARY PREHEAT OR REHEAT
THE HISTORY OF ELK RIVER POWER PLANT

     In 1951, United Power Association began coal-fired electrical
generation utilizing two stoker-fired units at the Elk River
Station.  In 1959, Unit 3 went on-line with a generating capacity
of 25 MW.  In 1964, this unit was one of the first turbine generators
in the country to have steam supplied from a nuclear reactor.  The
nuclear program proved quite successful but was discontinued in
1968 and the reactor was dismantled in 1971 due to the lack of
economics for such a small unit.

     All three units have the capability to burn coal, oil, or
natural gas.  From mid-1975, the plant operated on oil or natural
gas in order to meet State and Federal particulate emission limita-
tions.  With the impact of rising oil costs in the mid-1970's,
the decision was made in 1976 to switch the plant back to coal-burning
operation.  In order to do this, it was necessary to satisfy the
particulate emission limits of the state of Minnesota.  After care-
ful evaluation, a fabric filter was selected to be the control
device.  Since the station is not a base load plant, it is not
feasible to secure long-term coal commitments.  The stoker-fired
units have test-burned refuse, wood chips, sawdust, and tire chips
in combination with coal.  Therefore, fuel variations can be quite
broad, and the fabric filter's inherent ability to meet rigid air
pollution standards on a wide variety of fuels was the determining
factor.

     In January, 1977, under a specification prepared by Black &
Veatch consulting engineers of Kansas City, Missouri, a contract
was awarded to Research-Cottrell to supply, fabricate, and erect
the baghouse.  Research-Cottrell's portion of the contract was
completed in November, 1977, and the resultant general construction
work was completed in May, '1978.  On June 2, 1978, the baghouse
facility began operation with the Elk River units burning coal.

GENERAL DESIGN APPROACH

     Prior to 1978, the boilers dispersed flue gases into the
atmosphere through three separate stacks; however, a decision was
made to cap the three stacks with a by-pass damper in each stack
and run flue work across the top of the power plant to the rear
of the plant where the baghouse would be installed.  Black & Veatch
engineers analyzed the alternatives and determined that a sub-
stantial savings could be gained by installing one baghouse for
the entire plant rather than three smaller units.  This system has
indeed been effective and has not caused any particular boiler
problems.  The fabric filter was installed and two half-capacity
booster fans purchased to accommodate the additional pressure drop


                               298

-------
that would be created by the baghouse.  A new metal stack was
erected at the rear of the plant to disperse the clean flue gases
into the atmosphere.

     The primary fuel source of the plant is low-sulfur, Montana
coal from Colstrip, Montana.  However, a 20,000 ton stockpile of
low-sulfur, Kentucky coal will be used as necessary when mine
service or rail deliveries do not meet the requirements.  Also,
the plant is derated by approximately 10 MW when burning Montana
coal.  Kentucky coal will be burned when the extra generation
needed justifies the premium cost of this coal.  Approximately
10,000 tons of Montana coal are retained as inactive reserve.

     A listing of the fuels which have been burned to date and
the fuel characteristics are as follows:

     1.  Montana Coal

         Sulfur - 0.90 percent
         Moisture - 25.36 percent
         Ash - 9.17 percent
         Heating value - 8,447 BTU/lb.

     2.  Eastern Kentucky Coal

         Sulfur - 1 to 3 percent
         Moisture - 10 percent
         Ash - 10 percent
         Heating value - 12,500 BTU/lb.

     3.  Rubber Tire Chips

         A test burn of five  percent and ten percent tire chips
         in combination with coal was conducted in June, 1979.
         A complete report will be made available from United
         Power Association or the Minnesota Pollution Control
         Agency.  Preliminary results indicate no problems in
         burning tire chips in combination with coal in a stoker-
         fired unit.  The AP across the baghouse increased
         slightly when burning tire chips, which indicates extra
         fly ash, or more likely, extra carbon particles from the
         tires.  The test analysis of the ash will define any
         changes in carbon content or size distribution.

     It was decided that reverse air cleaning with fiberglass bags
would be utilized.  The gas-to-cloth ratios, as presented in Table
1, might seem aggressive if this were a base-load plant.  It is
important to point out that the design volumes are at full load,
and since the baghouse operates on a wide range of boiler loads,
it was not required to be overly conservative in the design approach,
                                   299

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In reality, the average gas-to-cloth ratios in the gross and net
mode are substantially less than the design numbers as presented.

     The construction technique employed for the eight compartment
unit is a modified modular method to increase work in the fabrica-
ting shop and decrease field labor hours.  This system approach
proved very economical and even allowed Research-Cottrell to do a
portion of the final field assembly at grade when the support
steel construction was behind schedule.  The added benefit of this
approach on this size unit is the additional quality control that
is gained by greater shop fabrication.

     The fiberglass bags were supplied by Globe-Albany Filtration
and are their Q78 design. A breakdown of the bag characteristics
are as follows:

     Type:  Fiberglass with acid-resistant finish.

     Specification:  Weight - 14 oz./yd.2
                     Permeability - 35-50
                     Count - 44 x 24
                     Weave -3x1 twill
                     Size - 8" diameter x 264" long

     Components supplied with each bag:

            Research-Cottrell snap ring to facilitate installation/
            replacement.

            Banded top with disposable cap.

            Four anti-collapse rings.

     Advantages:  Resistant to acid attack.
                  Encapsulated fibers.
                  Superior lubricity for flexing ability.

     The precoating of the bags was accomplished by bringing all
three units to full power with the by-pass dampers open and the
flue gases dispersed directly into the atmosphere.  The baghouse
damper was opened and one module of the baghouse was then slowly
placed on-line.  As each module was coated with fly ash, another
module inlet damper was opened.  After all modules were coated,
the by-pass dampers were closed and the flue gases entered the
baghouse.

     Subsequent plant operation has required that the pulverized
coal unit be started on oil and then switched to coal.  Initially,
the by-pass dampers were opened when operating on oil; however,
this created an emission of black smoke.  Therefore, it is necessary
to utilize the baghouse 100 percent of the time.  In this case,
                               300

-------
the ail smoke passes through the filter bags, which have been
cleaned subsequent to the previous shut-down.  There has been no
indication of blinding of the bags.

EXPERIENCE TO DATE

     Baghouse operation has been extremely satisfactory and reliable
to date.  Bag failures have been non-existant.  The on-line reli-
ability has been excellent with no unscheduled outages of the boiler
load due to problems with the fabric filter.  Since the plant is
subject to frequent cycling and peaking demand loads, the number
of cold starts in the past 13 months has been extensive.  Pressure
drop across the unit has been within the design parameters; Figure
1 indicates the drop across the cloth at various boiler loads.
When operating at full design load, the gas volumes have even
exceeded the original design volume and the baghouse is in the
constant cleaning mode.  The pressure drop on the flange-to-flange
unit in no case exceeds 8".  A Dynatrol opacity monitor is installed
in the stack for a continuous readout.  The opacity since start-
up has been essentially zero.  During warm weather it is extremely
difficult to ascertain whether the plant is even on the line.  In
colder weather there is a slight vapor plume but it dissipates
quite readily and has no visible trail.  This has turned out to be
an advantage that we didn't anticipate and affords good community
relations between United Power Association and the local popula-
tion.

     Baghouse performance tests were conducted on July 25, 1978,
and the results are shown in Table 2.  Since these tests were
conducted very close to the start-up of the unit, and during the
weeks preceeding the tests the unit had not been on-line, we would
expect better results today with a more adequate filter cake on the
bag surface.

     During the test, problems were encountered which resulted in
increased air volume across the baghouse.  We could only attribute
this to leakage around the module doors, and subsequent discovery
of corrosion on the inside of the door seals proved this to be
correct.  We feel the problem has now been corrected.  There were
also minor problems with the seals on the poppet damper operators
located on top of the baghouse.  This has also been corrected and
is not recurring.

     Located just inside the boiler housing adjacent to the baghouse
site is a dryer for the compressed air supply.  This proved quite
reliable during the very cold winter months and no freezing problems
of compressed air were experienced in the pneumatic operators
supplied.  The piping to the pneumatic operators is not insulated.
                               301

-------
     Subsequent tests have also indicated incomplete combustion of
the stoker-fired units and a rather high carbon carryover to the
baghouse.  To date this has not caused any noticeable problems
either due to high pressure drop across the fabric or fires in the
baghouse hoppers.  The ash is pulled every eight hours during full
load operation.  A breakdown of the ash analysis from the stoker
and pulverized coal units is shown in Table 3 for your review.

FABRIC CONSIDERATIONS AND FABRIC TESTING PROGRAM

     Experience with fabric collectors on both industrial and
utility coal-fired units had not been conclusive as to the need
for auxiliary preheat.  The specification and fuel variations
contained sulfur as low as 0.3 percent and as high as 2.0 percent.

      Figure  2 depicts a preheat system utilizing  steam coils  and
 the reverse  air fan system to  raise  the temperature  from ambient
 to at least  250°-30Q°F.  The cost per year,  based upon a 30%  load
 factor, would be $11,880 pet year for 200 cold starts.

      More costly would be a separate reheat  system to  raise  the
 temperature  at low load conditions from 190°-220°F.  to 250°-300°F.
 This system  as shown in the figure could cost $27,878  per year.

      Therefore, the operating  cost for both  the preheat and  reheat
 would be $.83/KW.   These figures reflect only the cost 'for the
 necessary steam consumption,  and do  not include additional main-
 tenance or capital costs.

      The ability to operate the system without any auxiliary  heat
 source offers a substantial savings  to us, and simplifies the
 operation of the unit.

      Research-Cottrell, upon addressing the  fuel  specification,
 proposed and recommended the acid-resistant  finish as  developed
 by Burlington Industries.

      Tables  4 and 5 reflect the merits of this finish,  as well  as
 the justification of utilizing 14 oz.  fabrics instead  of 9 or  10
 oz.  The following steps explain the tests for the acid cycle:

      A.   Heat age fabric for specified time  at 500°F.
      B.   Soak fabric in 5.0% Sulfuric Acid at 175°F.  for 5 minutes,
      C.   Place samples (dripping wet)  in oven at  450°F.  for  5
          minutes.
      D.   Repeat "B" and "C"  for a total of 4  cycles.
      E.   Heat for one hour at  500°F.  in oven.
                                 302

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     The results to date are extremely encouraging.  Figure 1
depicts the severity of the operation when partially burning 2
percent sulfur Eastern Kentucky coal.  Particularly note that the
system operates at a temperature as low as 190°F. to 220°F. for
sustained periods of time.

     Since the bags have the potential for requiring high mainten-
ance, we were concerned about bag life and the ability to operate
the baghouse on such cycling/peaking service.  The plant averages
about four  (4) cold starts a week for two  (2) months in the summer
and four (4) months in the winter.  Therefore, in a year's time the
bags have been through the dew point at least 200 times.  Upon
the recommendation of Research-Cottrell,  the hopper heaters were
left on during all shutdowns.  After two or three months of opera-
tion, United Power Association approached Research-Cottrell and
questioned the necessity for continuous operation of the hopper
heaters.  Inasmuch as the bag testing program is ongoing,  we
agreed to observe the results monthly for undue degradation.
Since October 1978, the heaters have been left on only during
low load conditions and shut down after the plant is taken off the
line and baghouse flyash pulled.  No detrimental effects have been
observed to date.  The load of the hopper heaters is 112 KW.

     For the bag testing program, every few months a bag is re-
moved and sent to a testing laboratory.  The major areas to
review are as follows:

     Mullen burst

       The pressure necessary to rupture a secured fabric
       specimen - #/in.2.

     Permeability

       The ability of gas to pass through the fabric, expressed
       in cubic feet of gas per minute per square foot of fabric
       with an 0.5" H20 pressure differential.

     Count

       The number of warp yarns and filling yarns per inch.

     Tensile strength

       The ability of yarns or fabric to resist breaking by
       direct tension.  Ultimate breaking strength is expressed
       in pounds per inch.   (Increase in fabric weight means
       increased strength due to greater bulk density which can
       be expected to yield longer service life.)
                               303

-------
    Loss of  ignition  (L.O.I.)

       Heat cleaning the  fabric  to  remove  the  finish,  starches,
       collected  particles,  etc., and comparing initial weight
       to final weight.

    MIT  (fold flex endurance  test)

       Using  a Tinius  Olsen  Folding Endurance  Tester,  interpal
       abrasion is  tested by folding a sample  through  270°,  180
       times  per  minute.   The  samples are  5  inches  long and  1/2"
       wide with  a  four-pound  weight attached  to one end.  Tests
       are performed at  room temperature.

     A summary of the  test report is shown in  Table 6.

     There  has been no significant  decrease in the  mullen burst
strength.   It is  important to note  that the permeability after
12 months is  unchanged.   This verifies that the interstices  of
the weave have not blinded due to condensation or acid attack.
The tensile strength degradation levels out as expected.  (See
Figure 4)

     Loss of ignition  measurements  indicate that the finish  is
stable.  Since the acid-resistant finish is applied at a minimum
of 4% by weight of the greige goods, the results clearly indicate
its stability.

     Probably the most important measurement is flex-to-failure
tests that indicate individual fiber breakdown and  fiber-to-fiber
abrasion.

     Figures 5 and 6 present curves which clearly show that  the
flex cycles have  leveled out after  one year of service, and  bag
life should exceed the two  (2) years as predicted by Research-
Cottrell and Globe-Albany.

SUMMARY

     After one year of operation, the fabric collector has met and
exceeded design expectations for the Elk River Station.  The
ability to bring the boiler on-line, operate at the low load, and
shut down completely on a random schedule is a  necessity of this
plant within our power grid.  The baghouse's response  and reli-
ability for this  type of service has been proven, and certainly
gives us confidence to consider the fabric filter for future
requirements.  The acid-resistant bags have alleviated our greatest
fear—could the fabric withstand such vigorous service?  For  fuel
variations with less than 2% sulfur content,, we can speak with con-
fidence that a fabric filter can be applied without the need  or
costly maintenance of a preheat system or a reheat system.
                                304

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Table 1.
BOILER AND FABRIC FILTER DESIGN DATA
  Unit #    Steam Rating

     1      135,000 Ib./hr.

     2      135,000 lb./hr.

     3      235,000 lb./hr.
                  Boiler Data


                    Type

                    Stoker

                    Stoker

                    Pulverized Coal
Manufacturer

Springfield

Springfield

Riley
                      Fabric Filter Design Data


  Flue gas volume	255,800 acfm  @  330°F

  Inlet dust loading	1.0  to 1.5 grains/ACF

  Gas-to-cloth ratio	2.15:1 Gross
                                      2.45:1 Net

  Number of bags  per  compartment	324

  Number of compartments	8

  Cloth area per  compartment	14,904 sq.ft.  (actual)

  Bag size	8" diameter x 22'  long
                                    305

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Table 2.   PERFORMANCE TEST RESULTS, JULY 25, 1978, BAGHOUSE EMISSION
           RATE AND EFFICIENCY
                                Inlet
Test
Test
Test
1
2
3
Temperature
in OF
330
Flow Rate
in ACFM
262,027
Particulate
Concentration
in grains/ACF
0.9833
                                                        Particulate
                                                        Emissions
                                                        in #/MM 3TU

                                                           4.125
 Test 1

 Test 2*

 Test 3
Temp.
in OF.

 300

 293

 290
                               Outlet

                               Particulate    Particulate
                    Flow Rate  Concentration  Emissions    Percent
                    in ACFM    in grains/ACF  in #/MM BTU  Efficiency
274,019

265,038

268,457
0.0039

0.0094

0.0038
0.017

0.040

0.017
99.59

99.03

99.56
 *The probe wash contained numerous particles larger in size than one
  would expect downstream of a baghouse.  Probable cause  — particles
  collected from the surface of the sampling port or were reintrained
  from the duct walls.
                                    306

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Table 3.   MONTANA COAL - UPA/ELK RIVER STATION










                  Ash Analysis of February 16, 1979




                  (at air heater settling hoppers)








    1.  Unit 2, Stoker-fired




        Sample           1        11       Average



        Sulfur, %       0.95     0.88    1.02       0.95



        Carbon, %      57.33    45.33   50.24      50.97
    2.  Unit 3, Pulverized coal-fired
        Sample



        Sulfur, %



        Carbon, %
0.49
0.47
0.52
Average



  0.49
                                    307

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Table 4.   COMPARISON OF 9 OZ. VERSUS 14 OZ. GLASS FABRICS
  Tensile Strength
    Original

  MIT Flex
    Original

  MIT Flex-Acid Cycle
    Original
    4 hours @ 500°F

  Mullen Burst

  Yarn
        9 oz.                 14 oz.
Acid Resistant Finish  Acid Resistant Finish
    E^LEE    Filling        Warp    Filling

                              668 x 360


                            30,598 x 18,846


                            30,598 x 18,846
                            10,428 x  3,072

                                  625

                             37-1/10 x 75-1/3
  325 x 185
20,310 x 5,890
20,310 x 5,890
 8,012 x 2,456
      500

 150% x
                                   308

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Table 5,
Test

Tensile

 Original
 7 days
 21 days
FINISHES TESTED AT VARIOUS TEMPERATURE  LEVELS
YARNS ONLY)
         325QF

  Acid       Teflon B
  Resistant  @ 10%
      360
      331
      331
267
281
263
                                           4250F
                             (FILLING
                                 500°F
      Acid
      Resistant
360
292
223
       Teflon B  Acid      Teflon B
       @ 10%     Resistant @ 10%
267
253
161
360
267
201
267
121
109
MIT Flex
Original
7 days
21 days
18,846
10,600
10,600
9,826
7,200
3,200
18,846
6,000
7,600
9,826
3,700
1,300
18,846
6,546
4,346
9,826
625
114
MIT Flex
 Acid Cycle
Original
4 hours
7 days
21 days
18,846
5,500
7,700
4,600
9,826
6
9
9
18,846
5,600
6,200
1,200
9,826
1
1
2
18,846
3,072
2,243
1,114
9,826
1
1
1
                                    309

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Table 6.
UPA TEST REPORT
  Weight
   Top*
   Center*
   Bottom*
                    New
         13.5 + .7
                        Sept., 1978
                            20.3
                            21.6
                            19.7
           Jan.,  1979  May, 1979
               16.9
               18.6
               18.1
   19.6
   18.8
   21.2
  Permeability
   Top
   Center
   Bottom
         40-55
                            46.0
                            42.0
                            44.5
              50.75
              60.25
              62.25
   51.0
   55.0
   56.5
  Strength
  .. (Warp/Fill)

   Top
   Center
   Bottom
         668/360
                        558/283
                        562/272
                        581/281
           433/235
           432/213
           423/240
480/195
465/205
455/213
  Mullen Burst

   Top
   Center
   Bottom
         540-600
                            525
                            538
                            518
               645
               620
               605
    520
    520
    580
  M.I.T.
    (Warp/Fill)

   Top
   Center
   Bottom
         30,598/18,846
                        4500/1700
           2502/1106
           3517/880
           2779/898
3593/1099
3161/1367
3543/996
  PH
   Top/Bottom
         7 -
4.3
  LOI

   Top
   Center
   Bottom
         4% minimum
                            3.7
                            4.0
                            3.8
                4.5
                4.8
                4.7
    4.8
    4.6
    4.6
  *As reviewed
                                   310

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"I
H-


1
01
                                   A P ACROSS CLOTH COMPARING LOW SULFUR WESTERN

                                  COAL TO HIGH SULFUR  EASTERN KENTUCKY COAL  -

                                  DATA OBTAINED FROM R-C  BAGHOUSE INSTALLATION

                                  AT UNITED POWER ASSOCIATION,  ELK RIVER,

                                  MINNESOTA.
(D
Ul
(A
         5".
a
h
o
•a

fa
O
l-t
O
Ul
M

rr
tr
IT)
P)
H
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O
cr
0
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n>
n
O
PI
a
Ul
a
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O

O

Ul

o

o


0.

<3
         3" .
         2" •
         1"
                                                             Temperature Range
                                                             300° to 310°F
                      Temperature Range
                      190° to, 290°F
                                                                            t _ t  f	A P across
                                                                        cloth - Eastern  Kentucky Coal
                                                                        with sulfur >  2%.
                                                                                           A P across
                                                                        cloth - Western Fuel,  operating
                                                                        temperature  =  295  to  320 F.
                  25
                          50
                                  75
                                           100
                                                  125
                                                          150
                                                                  175
                                                                          200
                                                                             —I—
                                                                             225
250
                                                     Volume
                                                    1,000  acfm
           Note:
             Data points reflect the average

              A P of  eight compartments operating

             at  a specific time.

-------
                           PRE MEAT FLOW DIAGRAM
                       ouitcr MANIFOLD
ro
                     	f^.	—,—-

                     IZIlt
f-





,J
t
1
1
1
t
1
no










/
/
t
t
i

          INLt

          MANlKUtU
           7*7=V^
          I
          !
          !
          t

          S5^
                      inrjor]
                         FiiTi.. Fifty
                           /
                           /
                           t
                           i
|i  C7  i TT^^r
*- I'tlClieAf tlOPPtll DAMI*tH V-l'nE HEAT MANIFOLD
   W   I  \V     W
                                              *-lQ i.o FAN
           Figure 2. Preheat systam.

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                           REHEAT  FLOW  DIAGRAM
CO



CO
-4
« Eoooiee
A





f
f

I
4

A
I
             Figure 3.    Reheat system.

-------
o

H

S-l
Hi
eu

en
TI

3
o
3.
       700.
       600
       500
       400
300
        200
        100
                                 (Warp Yarns)
                                 (Filling Yarns)
           CD
           Z
                           3
                                 a
                                 a)
                              -o    >
                              o    O
                              O    Z
o
0)
a
>•
a
    Figure 4.   Tensile strength.
                                         Months
                                      314

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   30,000
   20,000--
o
>1
u
   10,000 •-
                              a
                              0)
                              w
O
o
     >
     o
                                       Months
a:
Cu
01
S
  Figure  5.    M.I.T.  flex-to-failure results  (warp yarns).
                                   315

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    18,000
    15,000

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                            OBJECTIVES AND STATUS
                                     OF
                     FABRIC FILTER PERFORMANCE STUDY
                                     By:

                            Kenneth L.  Ladd,  Jr.
                              Richard Chambers
                                Sherry Kunka
                    Southwestern Public Service Company
                                  Box 1261
                           Amarillo, Texas  79170

                                Dale Harmon
               Industrial Environmental Research  Laboratory
                     Environmental Protection Agency
               Research Triangle Park,  North Carolina 27711
                                 ABSTRACT


     In October 1977, Southwestern Public Service Company executed a con-
tract with the U. S.  Environmental Protection Agency that called for a
study to assess the performance of a fabric filter system installed on a
large utility boiler that utilizes low sulfur Western coal.   The project
is now into its second year and the objectives of this paper are to de-
scribe the scope and intent of the study, as well as to report progress to
date.  In addition, some of the difficulties that we have encountered are
discussed.  Although some of these problems have resulted in procedural
changes, the intent of the study has not been altered.

     This paper describes work being done in specific areas  that both the
EPA and Southwestern are connected with.  These include fabric assessment,
data collection, selection and installation of instrumentation, and overall
fabric filter system performance.   Results of the first performance test
are also reviewed and the installation of a pilot baghouse is discussed.

     This study is being performed under EPA Contract 68-02-2659-
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                            OBJECTIVES AND STATUS
                                     OF
                       FABRIC FILTER PERFORMANCE STUDY
I.    INTRODUCTION

     Southwestern Public Service Company is an electric utility headquartered
in Amarillo, Texas.  The Company has a generating capacity of 2,921,000 kW
and supplies customers in a service area that stretches from the southwest cor-
ner of Kansas through the Oklahoma Panhandle, Texas Panhandle,  South Plains of
Texas, and the Pecos Valley region of Eastern New Mexico.

     Southwestern Public Service Company is unique as a utility because it
does all architectural and engineering design of its power plants. Through-
out the planning, engineering, and construction of a generating facility,
the structural,  electrical,  mechanical, and control engineering groups of the
Plant Design Department interact to design efficient power plants.  The de-
sign and construction of all Southwestern's transmission and distribution
facilities is also the responsibility of in-house engineers.

     Background

     Harrington Station, Southwestern Public Service Company's  (Southwestern)
first coal-fired plant, went into operation in July 1976,  with  one 350 MW unit
on line.  Plans for the conversion to coal as a primary boiler  fuel were begun
in 1970 when Southwestern's management realized that future natural gas sup-
plies could be affected by increasing prices, limited availability, and im-
pending regulations.  The search for alternative fuel focused on low sulfur
Western coal.  By 1971 the decision to convert to coal as  a fuel base had been
made and construction of Harrington Station began in 1974.

     Harrington Station is located approximately 3.1 km (5 miles) northeast of
Amarillo, Texas.  A second 350 MW unit went on line in 1978, and Unit 3 is
scheduled for completion in 1980.

     The basic problem in designing Harrington's second coal-fired unit was
the selection of a particulate emission control system which would satisfy
the Environmental Protection Agency's (EPA) New Source Performance Standards
(NSPS).  Southwestern studied the existing alternatives for controlling coal-
fired boiler emissions which would not require scrubbing for particulate removal.
After comparing all parameters (design, operating, maintenance, costs) South-
western wrote a set of specifications and then negotiated  a contract for a
fabric filter system (FFS) to be supplied by Wheelabrator-Frye, Inc. (WFI).

     Objective of Study

     Only a small amount of information on the performance of fabric filters
at other utility installations was available when Southwestern was making  its
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evaluation; therefore, when the EPA indicated its need for utility input on a
comprehensive study of FFS, Southwestern agreed to participate, hoping other
utilities might some day utilize the data to be collected.  When the 2-year
study has been completed, the following objectives will have been met:

     1.  full characterization of the fabric filter system applied at Har-
         rington Station, Unit 2;

     2.  assessment of the technical and economic feasibility of the system;

     3.  determination of the system's optimum operating condition.

     Following the testing phase of the program, operation and maintenance
data will continue to be recorded until 1982 to determine the long-term re-
liability of the system.  Special tests will be conducted through the use of
an on-site pilot baghouse.

II.  FIRST YEAR EXPERIENCE

     Installation of Support System

     Prior to start-up of the FFS it was necessary to install certain support
systems for the collection of reliable data.  The following systems were
installed.

     1.  Instrumentation.  Instrumentatdon was located so that the best pos-
sible monitoring of the gases entering and leaving the east and west baghouses
could be used to evaluate the performance of these baghouses.  Continuous moni-
tors were placed on the stack so that trends could be established by composite
sampling of flue gas conditions coming from both baghouses.  It is to be under-
stood that the location of the continuous monitoring devices is far from ideal,
because of the short runs of flue gas duct prior to turns and transitions.  The
monitoring devices were located so that the best samples could be obtained
without impeding access to the monitoring equipment.

     Specifications for monitoring equipment needed to meet the study's re-
quirements were submitted to bidders in October 1977.  A review and evaluation
of bids was completed in November 1977 and Lear Siegler and IKOR were the two
major.vendors selected.  The following equipment was purchased:

     5  Lear Siegler SM800, S02/N0 Monitors,  ,
     5  Lear Siegler CM50, Oxygen Analyzer Control Monitors,
     1  Lear Siegler Opacity Monitor,
     4  IKOR Continuous Particulate Monitors,
     2  Ellison Instruments Annubar,
    20  Leeds & Northrup Recorders.

     In addition, miscellaneous support equipment, thermocouples, and flow
transmitters were purchased and a software program was developed.

     Delivery of the equipment began in February 1978 and continued through
April.  Mounting, piping, and wiring of the instruments took place in May and


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June; during July and August 1978, the Lear Siegler monitors were checked out,
started up, and calibrated.

     By September 1978 the Lear Siegler equipment was functional and most of
the initial installation problems had been resolved.  The equipment (with the
exception of the IKOR particulate monitors) seems to be performing in an ac-
ceptable manner.  With proper maintenance the Lear Siegler equipment is expec-
ted to continue to perform with a reasonable degree of reliability and accuracy.
Calibration factors for the IKOR particulate monitors continue to be erratic.
At this time it appears the IKOR particulate instruments may not produce any
meaningful, quantitative data, although they will be left in place for the
purpose of locating bag failures.

     A record of each problem is maintained at the plant which indicates the
date and time it occurred, how it was resolved, and when an instrument went
back into  service.  Strip charts are also filed at the plant after they have
been changed.

     2.  Datalogging System.   One of the objectives of the FFS is to corre-
late manual sampling results with operating data to define the performance of
the FFS; therefore, the parameters listed below are being continuously moni-
tored at five points in the flue gas stream:  S02, NOX, 02> particulate, flue
gas flow,  temperature, and duct pressure.  Additional operating parameters
being measured  or calculated on a continuous basis are pressure drop across
the  system, power consumption, load on the unit, fuel flow, cleaning mode and
cleaning frequency.  This data will not be as specialized as the manual sam-
pling information; its purpose is to represent everyday operation of the FFS.

     The FFS programs are executed under the sublevel processor of the Unit 2
computer.  The  plant computer is a Westinghouse Model W2500, 16 bit, real time
computer with a one million word disc, and 64 k words of core.  All contact
and analog inputs from the five sampling stations are recorded by the computer,
which also has  access to other performance parameters concerning the plant.

     3.  EPA Trailer.   In order to accommodate the extra equipment and per-
sonnel required for special testing, it was felt a mobile laboratory facility
should be  made  available for use during the testing phase of the project. The
EPA had a  9.1 m (30-foot) trailer available for the project work and upon
completion of the necessary paper work the trailer was delivered to Harring-
ton  Station on  May 12, 1978.

    After  necessary repairs had been made, the mobile lab was parked under-
neath the  FFS,  north of the control room.  This position offers natural pro-
tection from the elements and is also easily accessible from the different
sample locations.  The trailer will remain at  this location for the duration
of the project.

     4.  Manual Stack Sampling Equipment and Sampling Sites.   A part of the
study is to perform manual sampling of the flue gas materials entering  and
leaving the east and west baghouses as well as the composite of the gases
leaving the stack.

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     To accomplish this manual flue gas sampling, ports were designed and in-
stalled in the inlet and outlet of each baghouse.  These four sampling points
do not meet the ideal characteristics of static flow for sampling in a duct.
The sampling platform which is on the stack does meet the criteria of stable
flow and also has provided the most consistent results.

     As indicated in this paper, efforts to confirm the actual volume of gas
flow through the baghouses, by performing pitot tube traverses on the inlet
to the baghouse, have indicated a wide distribution of flow patterns within the
inlet ducts and these flow patterns vary with changes of load on the unit.  It
was important to make the best possible effort to determine inlet and outlet
loadings of the different  flue gas constituents.  Also, because of the special
sampling problems of both the inlet and outlet ducts, particular consideration
has been given to design and re-design of equipment used to sample these ducts.
Southwestern1s staff at its System Lab designed and built its own manual stack
sampling equipment; for example, the probes for sampling the duct are designed
for vertical sampling instead of horizontal.  Because of the velocities in the
duct these probes are designed to prevent whipping and bending.
     One effort to prevent breakage of the sampling tube was to utilize an In-
conel liner instead of glass.  Problems with the probe heater and condensation
within the Inconel liners indicated this was a bad decision.  The old probe
heaters are being replaced with ones of greater dependability and capacity.

     Results of the manual stack sampling are included in III A(l).

     j^tart-up Experience

     Before a start-up plan was formulated for Harrington Station baghouse,
Southwestern felt it was important to seek the advice of start-up personnel
at other utilities which have baghouses in operation.  Individuals known to
have experience in the start-up of these systems were consulted.  Addition-
ally, a literature survey x^as made and the recommendations of various manu-
facturers were studied and discussed with WFI and EPA representatives.

     The following procedures were felt to be necessary to minimize difficul-
ties during start-up:
     1.  orient operators;

     2.  check out equipment;
     3.  avoid dew point and acid point conditions;

     4.  preheat compartments;
     5.  condition and precoat the fabric;

     6.  start up with natural gas through the boiler;
     7.  change from natural gas to coal with flue gas going through the
         baghouse as quickly as possible;
     8.  designate specific sequence for compartments to be brought on
         line;
     9.  add compartments as load increases;


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    10.  monitor required operating parameters during start-up and the
         first cleaning sequence, such as inlet and outlet temperatures,
         pressure drop, and opacity.

     Because Harrington Station Unit 2 was capable of start-up on natural
gas, the FFS was bypassed for several weeks before it was started.  With all
compartments isolated from the flue gas, all hopper heaters were energized
for 2 or 3 days prior to start-up in order to help preheat the compartments.

     During the start-up, boiler load was maintained at 200 MW with coal as
the primary fuel; only the igniter natural gas was in service.  Compartments
1 and 3 were initially brought into service and the first bypass damper on
the west side was closed.  Compartments 16 and 18 (east) were then brought
into service and the first bypass damper on the east side was closed.   The
elapsed time between the first compartment being brought into service and
the last bypass damper closed was 3 hours and 50 minutes.  The effect of
the FFS on opacity can be seen in Figure 1, which shows a significant de-
crease in opacity after the last bypass damper on each side was closed. At
this point the baghouse was completely in service with the fabric being
conditioned.

     Approximately 3 weeks after the FFS was initially started, Southwestern
was able to operate Harrington Station Unit 2 at full load with only coal in
service.  The unit has operated at loads consistently above 200 MW and during
the peak periods it has handled 350 MW. Figure 2 shows a history of the time
spent at various loads.

     Very high APs were observed shortly after start-up; the AP climbed
quickly to 23 cm (9 inches) w.g. at full load.  During subsequent months
the full load AP steadily increased until it was in the 25-30 cm (10-12 inches)
w.g. range.  Judging from past performance it appears that the AP tends to
level off a month or so after start-up.  In the next few weeks, Southwestern
will know what kind of AP will be present following rebagging of the baghouse
(see discussion under B - Fabric Assessment).

     Figure 3 is the plot of AP versus air-to-cloth ratio representative of
the performance of both the east and west baghouses until February 1979,
when plugging began in the west baghouse.

     Testing

     1.  Air Flow Tests.   The only comprehensive testing to be performed on
the FFS during the first year of operation was an air flow test which was
conducted by Southwestern personnel in October 1978.  The primary reason for
measuring the air flow was to see if the high AP across the baghouse was due
to over-design air flow.

     During the preliminary testing a large volume of turbulence was encoun-
tered on the inlet, causing the test results to disagree with the air flow
measurements from stoichiometric combustion calculation.  This discrepancy
between calculated and measured values prompted a velocity traverse of the
                                      322

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START-UP OPACITY RECORD
       Figure  1.
            323

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       5000 -
       2^00 -
       2OOO -
HOURS
  ON
 LIME
        1500-
        IOOO-
        500-
              2855 HK.
              35.66%
     60UTHWESTERM PUBLIC 5EEVICE Co.

          HARRINGTON - UMIT 2
7.91%
       1222 HR.
       15.37 %
                                     1090
                       2175 HK
                       27.36%
                     251-275 27^-300 501-525   >325

                       LOAC?  CMWH")

                    LOAD vs. TOTAL TIME
                        As OF  7-4-79

                           Figure 2.
                              324

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                60UTHWESTERW PU5LIC SEKVICf. Co.

                                           2
       IO.O1
        8.0 H
  AP
in. H20
Cm
        6.0-
        4.0H
        2.0-
                                                s  .97695
                                                -  .95443
                    .0       2.0      3.0      4.0
                            AP vs.Vc
                         OCT. '78 - MAY '79

                               Figure  3-
                                 325

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stack.  The stack was selected because it met criteria specified in EPA Refer-
ence Method 2 ("eight stack diameters downstream from the disturbance").  The
October air flow tests are summarized in Table 1.

     2.  Corrosion Testing. Southwestern, in its effort to assess the corro-
siveness of the flue gases passing through the FFS at Harrington Station, placed
low carbon steel coupons in the baghouse structure.  Each of the 28 compartments
had a coupon just inside the entrance door on the clean air side 2.1 m (7 feet)
from the floor.  Inlet and outlet ducts also had a coupon each.  All coupons
were insulated from any baghouse structural metal.
     The coupons were thoroughly cleaned and weighed before installation. They
were cleaned and weighed when removed in order to determine weight loss, if any.
During the first year of operation, every other coupon was removed after 120
days for corrosion analyses.  The remaining coupons were removed after one
year's exposure (including those in the inlet and outlet ducts).

     Analyses performed in Southwestern's System Lab revealed only a minor de-
gree of corrosion after one year's exposure.  The average corrosion rate was
0.006 mpy.  Test results are still preliminary but Southwestern feels corrosion
will not be a serious problem in this particular emission control installation.

     3.  The First Fabric Assessment Program.  One of the goals of the FFS is
to evaluate the performance of different types of fabric filters.  This phase
of the study was begun in June 1978, when 34 Acid Flex and 34 Tri-Treat bags
from Fabric Filters were installed in compartment 22.  In addition, the fol-
lowing bags were placed in compartment 7 in September 1978:

     1   Nomex All-Spun
     2   Nomex Combination
     5   Crissoflex Style 446
     4   Crissoflex Style 449

     These bags were supplied to Southwestern by bag manufacturers for evalu-
ation purposes.

     The test bags will remain in the compartments for the duration of the
study and periodically some will be removed for testing.

     In addition to installation of small groups of test bags within a compart-
ment to evaluate their endurance to the atmosphere and environment, a cleaning
cycle, and potential chemical attack, it was decided that three full compart-
ments should be fitted with test fabrics for evaluation.   This decision fol-
lowed after it was determined that there would be a requirement to replace the
bags in the baghouse.  The decision as to which bags should be used for replace-
ment would be a matter of evaluation of a number of fabrics.

     In January 1979, compartment 21 was filled with W.  W. Criswell 0.28 kg  (10
ounce) Style 442 Teflon-coated material; compartment 23 was filled with Fabric
Filters' 0.38 kg (13.5 ounce) Style 502, Tri-Treat coated fabric.  As the evalu-
ation proceeded it was determined that a change in the shaker mechanism to clean

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                                                           TABLE 1.
                                                     AIR FLOW TEST RESULTS
                                                 Stack                                      Flue Gas Flow Rate
                               0                 Press.     Avg,  AP  Velocity
             02    C02   H20    C    Mol.  wt.     em %     cm  H20    m/a      mz      m*/h        jn3/h          w3/h
   Traverse  %     %     %    (°P )   Ib/lb mole (in. HK)   (in.  H'2Q), (ft/sec) (ag.ft)  (ACFM*)     (ACFM»*)      (ACFH***)

   SPS
                               16fl                67.23     2,852   238,0      31,6    2,750,960  2,746.882      2,679.198
w Tube      4.8   14    9.5  (335)   29.05      (26.47)    (1,123)   (77,99)   (339,8)   (1,618,212) (1.615,813)   (1.575,999)
IN5

   WI'I
   pjcoc                       168               67-23     2.274   237.0      31.6    2,768,232      -         2,696,020
   Tube      4.8   14    9.5  (335)   29.05      (26.47)    (0.895)   (77.79)   (339.8)   (1,628.372)     -         (1,5.85,894)


    *  Corrected to Baghouse inlet conditions 65.18  cm (25.66 inches)  Hg ami 174° C  (345° F)  and 4.55?.:Qk.
   **  Stoichiometric calculation.
  ***  Measured at Stack Conditions

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the bags, increasing the frequency 50 percent, resulted in noticeable improvement
in fabric performance.

     Another compartment of test fabrics was installed in March 1979 (compartment
20) utilizing an experimental all-filament Teflon-coated material.  It was hoped
that this type of fabric would have good efficiency and clean readily.

     A third part of the fabric filter assessment program for selection of re-
placement fabric and investigation of cleaning mechanism was to review a mobile
baghouse study which had been performed at Harrington Station in 1978,  Over and
above a number of difficulties which had to be overcome in operating this mobile
unit, and maintaining general operating procedures, the study provided some inter-
esting information.  The general conclusion which could be made from the data col-
lected indicated that Teflon-coated fabrics had a superior performance to the
silicone-graphite coated fabrics in the pilot test compartment.  Another inter-
esting note resulting from the first mobile unit operation was that bags operating
in the test compartment in the reverse air mode could not be successfully cleaned.

     A second mobile baghouse study was initiated in the spring of 1979 to assist
with the evaluation and selection of alternate fabrics to replace those in the bag-
house which were experiencing accelerated failures.  The following types of fabric
were evaluated:

     1.  Fabric Filters 504-1 Acid Flex.

     2.  W. W. Criswell 445-04.
     3.  Menardi-Southern 601-Tuflex Teflon B.
     4.  Menardi-Southern 601-Tuflex with rings.

     5.  Fabric Filter 0.38 kg (10 ounce) All-Filament Teflon.

     Although the final evaluation report from this second mobile baghouse testing
is not complete, preliminary results indicate that fabric 1 has a better overall
performance, with fabric 5 producing the least desirable results, and all of the
other fabrics tested would be rated in a close middle group.

     It is understood that the performance of the first mobile unit study and the
second mobile unit study should be evaluated in the light of operating conditions
and procedures under which the testing was performed.  The results of these unit
studies were used by the Company to assess fabric requirements.

     A full-scale compartmental fabric testing program was initiated in an effort
to determine overall performance of both durability in the baghouse environment
and efficiency of particulate removal.  Details of this fabric assessment are
covered in III B - Fabric Assessment.

III. SECOND YEAR EXPERIENCE

     A.  Special Testing

     A major objective of the Southwestern/EPA contract is to characterize gaseous
and particulate emissions from the FFS.  To do this a series of special tests was

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scheduled for the second year of the system's operation.  Even though it was
Southwestern's intent to accomplish the objectives of the tasks set forth in the
contract, several problems were experienced during the operation of the baghouse
which kept it from being classified as a typical or standard type of air quality
control device.

     These problems centered around the control of the cleaning cycle, control
of the deflation pressure during the cleaning cycle, proper tension on the bags
when they were initially installed, a higher than normal bag failure rate, and
some indications that Harrington Station's fly ash had some unique characteris-
tics which made predicting proper design difficult, if not impossible.  Programs
were developed to investigate these problem areas and attempt to come up with
solutions.

     During the period of investigation, limited testing of flue gas in and out
of the baghouse was performed because the original intent of the research pro-
gram (to investigate performance of the baghouse) was to characterize a typi-
cal operating system; therefore, many of the flue gas test plans and monitoring
of gases in and out of the fabric filter have been delayed until a more typical
type of operation can occur.  It is felt at this time that since the rebagging
of the baghouse and adjustment of cleaning cycle (finalized in July 1979) typi-
cal operation should begin in late September or early October.

     With this in mind the description below indicates the performance tests
accomplished by Southwestern and GCA to provide useful information.

     The time and expense for performing these tests should have value to those
installations experiencing the same difficulties.  A review of the measures
taken by Southwestern to correct the situation might be of benefit and assistance.

     1.  Southwestern's Performance Test.  In December 1978 Southwestern per-
formed the first series of tests to measure mass emissions of particulate, sul-
fur dioxides, and oxides of nitrogen.  It was originally planned to sample simul-
taneously at five locations; however, procurement problems with equipment pro-
hibited completion of the outlet sampling trains, and Southwestern"s personnel's
first-time effort in flue gas sampling of so many points at the same time, proved
an adverse factor in sampling at all five locations.  For particulate and S02
samples it was believed the test would result in better quality data if only
three stations (both inlets and the stack) were sampled.  The sampling procedure
for oxides of nitrogen required less manpower and equipment than sampling for SC>2
and particulate; therefore, sampling for NOX was performed at all five locations
(two inlet, two outlet, one stack).

     A crew of test personnel from Southwestern's power plants was assembled at
Harrington Station for the first week-long series of tests.  Approximately 26
stack sampling team members participated in the test program.  By taking samples
at three locations, rather than five, experienced personnel were able to work
with the less experienced ones.  As a result, personnel at all the sampling loca-
tions will have some degree of experience during future tests.

     The final analyses of Southwestern's particulate, sulfur dioxide, and oxides

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of nitrogen samples are presented in Table 2.

     The results of the inlet testing compare favorably with the theoretical in-
let grain loading (the theoretical inlet grain loading is estimated and based
upon generation of 80 percent fly ash).   The percent fly ash has never been ac-
curately determined but has been estimated to be between 70 percent and 80
percent.

     Because of the use of an unheated probe and Inconel liner, additional de-
posits on the filter media gave indication of the suspected high stack grain
loading.  As previously mentioned, these conditions have been recognized and
correction is being applied.  The stack concentrations should be accurately de-
termined during the next set of tests.  The results of the NOx testing tend to
be very consistent across the baghouse.   Results of the sulfur dioxide tests
on the stack compare favorably with the stoichiometric calculation for sulfur
dioxide.  The reason for the erratic inlet results has been determined and will
be corrected before the second round of special testing.

     2.  First GCA Special Test.  More specialized tests were conducted by GCA
Corporation under subcontract with Southwestern in February 1979.  The gas
stream was sampled at five locations (two inlet, two outlet, and one stack)
for particulate, Cy-Cjy organic compounds, Ci-Cg organic compounds, C02, 02j
CO, S02, 203, NOX, and particulate particle size distribution.   Baghouse hop-
per ash samples were also collected.

     Only preliminary results from the GCA special test are available at this
time.  These preliminary results are reviewed in Table 3.  At a later time,
when the complete report is received from GCA, the results can be better
addressed.  Examination of the information in Table 3 indicates that even
under the best operating conditions at the time of the test, performance of
the baghouse looks favorable, but it cannot consistently fulfill the new EPA
proposed 13 ng/J (0.03 lb/106 Btu) particulate standard.  Further examination
and study will be necessary to evaluate the differences and inconsistencies
in the S02 testing Method 6 and 803 Method 8.  It is apparent at this time
from the monitoring instruments and the flue gas test that the fabric filter
has no effect on increasing or reducing NOX flue gas stream.

     3.  j?lans for Future Special Testing.  The second series of special tests
to be performed by Southwestern and GCA was initially scheduled for May 1979.
Due to the decision to rebag the FFS (this decision is discussed under Selec-
tion of Replacement Bags), special testing has been tentatively rescheduled
for October 1979.  The experience gained in the first series of tests is
expected to enable stack sampling personnel to conduct tests at all five
sample locations as originally specified in the EPA contract.
     B.  Fabric Assessment

     In September 1978 the Harrington Station baghouse began to experience a
higher than normal failure of bags.  Examination of the problem indicated that
two items needed immediate attention: (1) the control of the deflation pressure
during the cleaning cycle  which, it was believed, contributed to the high


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                                  Table 2.

                       Southwestern Public Service Company
                       Flue Gas Tests        December 1978
RESULTS  OF  PARTICULATE TESTING
Run
(Number
* 1

* 2

** 3

East Inlet
g/m3
(gr/Scf)
5.22
(2.28)
4.67
(2.04)
3.82
(1.67)
West Inlet
g/m3
(gr/scf)
6.27
(2.74)
5.86
(2.26)
3.73
(1.63)
Theoretical
Inlet + Stack ***
g/m3
(gr/scf)
5.47
(2.39)
5.13
(2.24)
5.93
(2.59)
g/m3
(gr/scf)
0.121
(0.053)
0.115
(0.050)
0.075
(0.033)
ng/J
(lb/106 Btu)
45.2
(0.106)
41.7
(0.097
26.3
(0.061)
*   sootblowing continuously
**  not sootblowing
*** the concentrations of particulate obtained from the stack are biased high be-
    cause of a reaction that took place in the unheated Inconel probe liner.
+   assumes 80 percent fly ash, no consideration for sootblowing
RESULTS OF NOX TESTING

            East Inlet
            Method 7
Run         ng/J
Number      (lb/106 Btu)
East Outlet   West Inlet   West Outlet  Stack
Method 7      Method 7     Method 7     Method 7
ng/J          ng/J         ng/J         ng/J
(lb/106 Btu)  (lb/106 Btu) (lb/106 Btu) (lb/106 Btu)
1
2
3
290
(0.68)
310
(0.71)
290
(0.67)
280
(0.64)
290
(0.68)
310
(0.71)
260
(0.61)
250
(0.59)
270
(0.62)
270
(0.62)
270
(0.62)
270
(0.62)
270
(0.63)
280
(0.66)
280
(0.64)
                                                                   (more)
                                      331

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                                  Table 2.
                                 (continued)


                        Southwestern Public Service Company

                        Flue Gas Tests        December 1978
RESULTS OF S02 TESTING


Run
Number
1

2

3

East Inlet*
Method 6
ng/J
(lb/106 Btu)
230
(0.53)
250
(0.59)
270
(0.62)
West Inlet*
Method 6
ng/J
(lb/106 Btu)
150
(0.36)
140
(0.32)
86
(0.20)
Stoichio-
metric **
ng/J
(lb/106 Btu)
330
(0.76)
360
(0.84)
380
(0.88)
Stack
Method 6
ng/J
(lb/106 Btu)
310
(0.73)
340
(0.78)
360
(0.84)
     These concentrations are suspected of being low because of the high
     negative pressure pulling the absorbing solutions forward, with the
     absorbed S02 not analyzed.

     Assumes all sulfur is converted to S02.
                                      332

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RESULTS
Run
Number
1
2
3
4
5
6


Table 3
G C A
OF PARTICULATE TESTING EPA METHOD
East
Inlet
g/m3
(gr/scf)
2.36
(1.03)
2.27
(0.99
3.07
(1.34)
5.06
(2.21)
3.50
(1.53)
3.11
(1,36)
West
Inlet
g/m3
(gr/scf)
3.60
(1.57)
3.85
(1.68)
2.75
(1.20)
3.11
(1-36)
2.34
(1.02)
5.40
(2.36)
East
Outlet
g/m3
(f-r/scf)
0.025
(0.011)
OJ016
(0.007)
0.009
(0.004)
0.009
(0.004)
0.002
(0.001)
0.011
(0.005)

5
West
Outlet
g/m3
(gr/scf)
0.044
(0.019)
0.011
(0.005)
0.018
(0.008)
0.016
(0.007)
0.005
(0.002)
0.096
(0.042)


Stack
g/m3
(gr/scf)
ft
*
0.021
(0.009)
0.018
(0.008)
0.027
(0.012)
0.009
(0.004)
0.039
(0.017)


Stack
ng/J
(lb/106Btu)
ft
ft
7.7
( 0.018)
6.9
(0.016)
10.3
(0.024)
3.0
(0.007)
14.6
(0.034)

RESULTS
Run
Number
2
4
6
OF S02 TESTING EPA METHOD
6
East Inlet West Inlet
ng/J ng/J
(lb/106 Btu) (lb/106Btu)
*
*
420
(0.98)
470
(1-10)
350
(0.82)
400
(0.94)
290
(0.68)




East Outlet
ng/J
(lb/106 Btu)
390
(0.91)
340
(0.80)
260
(0.61)

West Outlet
ng/J
(lb/106Btu)
410
(0.95)
*
A
280
(0.64)

Stack
ng/J
(lb/106Btu)
ft
ft
ft
ft
320
(0.74)

*  No data this run.
                                                                    (more)
                                      333

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Table 3.
(continued)

RESULTS
Run
Number
2
4
6

OF NOX TESTING
East Inlet
ng/J
(lb/106Btu)
ft
*
240
(0.55)
270
(0.63)
G
EPA METHOD 7
West Inlet
ng/J
(lb/106Btu)
260
(0.60)**
220
(0.52)
210
(0.48)
C A

East Outlet
ng/J
(lb/106Btu)
ft
ft
220
(0.50)
230
(0.53)


West Outlet
ng/J
(lb/106Btu)
300
(0.69)
230
(0.53)
240
(0.55)


Stack
ng/J
(lb/106Btu)
ft
ft
220
(0.51)
200
(0.47)

RESULTS
Run
Number
2
4
6
OF SO 3 TESTING
East Inlet
ppm
0.27
2.07
2.56
EPA METHOD 8
West Inlet
ppm
0.99
0.60
1.81

East Outlet
ppm
0.79
0.67
1.96

West Outlet
ppm
0.72
0.82
1.67

Stack
ppm
1.10
ft
1.86

*  No data this run
** Average based on three runs only
                                     334

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pressure drop; and (2) tension on the bag.

     By October 1978 a program was begun  to redesign  the deflation pressure
control system and bags had to be re-tensioned.

     By January 1979 Southwestern was becoming concerned at  the accelerated
rate of bag failures.  These failures were of two types; small pinhole type
failures near the bottom cuff, and a few  failures described  as "blowouts"
where a whole section of the bag would burst and fray "like  a flag whipping
in the wind."

     To develop an estimation of the bag  failure rate to be  expected during
the summer the total number of failures found during  outages was plotted
versus service time  (see Figure 4) and a  simple polynomial curve performed.
At this point two approaches were taken to obtain an  estimate of total bag
failures expected in six months of service.  The first approach was to simply
extrapolate the curve fit polynomial for  6  additional months of service
(see Point II on Figure 4).  This approach predicted  = 3200  failures.  The
second approach was  to assume bag failure rate would  remain  constant at the
present level (after   9  months of service).  The curve fit equation was
differentiated and the slope evaluated at  9  months' service.  Point I
(see Figure 4) was calculated to be - 2200 failures,  using this slope.  Based
on this information  Southwestern accelerated a second fabric selection pro-
gram to obtain replacement bags and have  them ordered and installed by
July 1979.  Figure 4 indicates the extrapolated curve of bag failures which
caused Southwestern's major concern.

     The first bag assessment program initiated by Southwestern was used as
a guideline to develop the second fabric  assessment program.   During the
first assessment program bags had been removed periodically  from compartments
and laboratory tested (by a consultant).  These tests corroborated Southwes-
tern' s concern about an accelerated bag failure rate which would create a
problem during the 1979 summer peak.

     After the decision was made to rebag the entire  baghouse with new fab-
rics as quickly as possible, additional fabrics were  obtained and installed
in certain compartments for short-term testing.  As mentioned previously,
the EPA's mobile baghouse unit was rushed to the site and used to make an
accelerated evaluation of available fabrics.  Southwestern was restrained
by the availability  or delivery of new bags; therefore, selection was
limited.  Types of materials used to rebag the baghouse can be noted in
Figure 5 (shown by compartments).

     One of the interesting developments  of the second EPA mobile baghouse
study was that by adjusting the cleaning  cycle and increasing the frequency
of shake, a greater  positive effect was noted (more positive than the dif-
ferences between the fabric treatments tested).  As a result of this South-
western began to review, again, the theoretical modeling work of Dr. Richard
Dennis.l

     As a result of  these two things, the decision was made  to increase the

                                    335

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Total
Bag
Failures

4000.
3000
2000  -
1000  _
                            5                    10


                             MONTHS OF OPERATION

             Extrapolated Estimate  of  Bag Failure, April 1979.
15
                                  Figure 4.
                                      336

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      WEST   BAGHOUSE
 7  1 Nomex
 All-Spun;
2Nomex Comb.
5Crisoflex
446;4Criso-
flex449
              Menardi-
              Southern
                Teflon

              Test  Bags
 8
  (Warp In)
 11
 13
                       10
12
14
EAST BAGHOUSE
15
Vc*
17
**
19 Original
bags equipped
with special
shaker
mechanism
21 Criswell
442 Teflon
B Test Bags
23 Fabric
Filters 502
Tri-Treat
Test Bags
25
Criswell 449
Teflon B
Test Bags
27
**
16
J-.JU
S\ S\
18
**
Fabric 20
Filters
All-filament
Teflon
34 Acid 22
Flex; 34
Tri-Treat
Balance:
Original
Bags
24
Globe-
Albany
Nomex
26
**
28
**
*    Criswell 442 Teflon B, 0.30  kg  (10.5 oz.)  (rebagging complete).
**   Criswell 449 Tri-Treat;  0.40 kg (14 oz)  (rebagging complete).
***  Balance of Compartment 7:  Criswell 442 Teflon B, 0.30 kg  (10.5 oz.)

                Fabric Installation, July 1979.

                          Figure 5.

                            337

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frequency of the shake in compartments 21 and 23.  The adjustment in fre-
quency of shake was accomplished simply by changing the size of the shaker's
drive mechanism pulley.  Data collected on these two compartments, as a re-
sult of increased shake frequency, exhibited lower pressure drop by as much
as 8.9 cm (3.5 in. w.g.) compared to other compartments at full flow on the
baghouse.

     At the time of preparation of this paper the increase in frequency of
shake has not resulted in any bag failures.  One problem has developed, how-
ever, on those compartments with a high frequency shake and that is the pil-
low blocks holding the shaker mechanism have begun to fail.  An engineering
redesign of these pillow blocks has already been initiated and installation
of the reinforced and strengthened pillow blocks will begin soon.

     Another item which should be noted about fabric assessment is that in
November 1978 three Nomex bags were installed to determine if this material
could survive the environment of Harrington Station conditions; i.e., low
sulfur fuel and low moisture and acid dew point.  After eight months of
operation, examination of the Nomex bags indicates that they are still in
fine condition, though slightly discolored (turning a shade of tan). Based
on this experience, Southwestern has worked with the supplier and ordered
and installed one compartment of treated Nomex as an additional study in
the program of fabric assessment.

     In addition, manometer taps were located across the outlet damper on
each of the compartments to record the flow trends as well as the AP of
each test compartment to be measured and monitored. Bags will be removed
at a given interval and sent to an independent laboratory for testing.  Ac-
curate records will be maintained on bag failure  rates so that at the end
of the 2-year study both performance and bag life data on these fabrics will
have been obtained.  Certain special fabrics will also be tested in a full-
scale pilot unit.

     The decision to rebag the entire baghouse before July 1979 resulted in
the need for developing a second start-up procedure for the baghouse and to
recondition the newly installed bags.  Summer peak loading conditions were
becoming apparent during the period of rebagging (mid-June 1979) and the
availability of bags, on short notice, required that half the baghouse be
rebagged at a time.

     To remain within the emission limitations required by the regulatory
agency, the load on Harrington Station Unit 2 was reduced to 150 MW while
one side  of the baghouse was being rebagged.  Because the west baghouse
exhibited a higher pressure drop problem, it was rebagged first.

     The start-up procedure was amended in the belief that the best way to
condition a fabric is not at design air flow but at a lower flow.  It was
felt that lower air flows would allow a more porous, permanent matrix to
establish itself over the pores in the fabric than would be possible at  the
very high flows Harrington Station's baghouse was designed for (air-to-cloth
ratio = 3:4).
                                     338

-------
     Start-up on the new fabric was accomplished by  simply putting  the  re-
bagged unit on line at 150 MW and holding  the  load until  the baghouse had
gone through the cleaning cycle several  times. Cleaning at a AP of  12.7 cm
(5 in.) w.g. required in excess of 36 hours  to accomplish.  The load was then
increased by 50 MW a day until full load (350  MW) operation was achieved.

     The west baghouse was rebagged June 16, 1979 and  the east on June  20,
1979.  At the present time the AP is between 15.2 cm (6.0 in.) and  17.8 cm
(7.0 in.) w.g. at full flow.

IV.  SPECIAL CONSIDERATIONS

     A.  Air Flow

     One of the most difficult assessment  problems encountered on Unit  2 FSS
is the measurement of gas flow through an  individual compartment.   As a. re-
sult, operating data on the amount of gas  passing through the bags  is limited
thereby prohibiting an analysis of potential bag life.  As was mentioned
earlier, in an effort to resolve this problem  test compartments 19-24 were
instrumented with manometer taps across  the  outlet damper.  During  the recent
rebagging outage, four additional manometer  taps were  placed in the west bag-
house  (compartments 5, 6, 7, and 8) across the outlet  damper.  When the east
baghouse was brought off the line for rebagging, three additional manometer
taps were installed in compartments 25,  26,  and 27.  These were located ex-
actly like  those in the west baghouse.

     The purpose of this instrumentation is  to get an  indication of the flow
rate through the outlet damper.  Complicating  the problem is the fact that
so far AP readings across the outlet have  been in a  very  low range; i.e.,
1.3 to 2.5  cm  (0.5 to 1.0 in.) w.g.; however,  it is  felt  that by continuously
collecting  the manometer readings a relative idea of flow through the test
compartments can be ascertained and correlated to filter  performance.

     B.  Pilot Baghouse

     The EPA contract included a provision to  exercise an option for a  pilot
baghouse.   The EPA has elected to exercise this option and Southwestern has
agreed to operate and maintain a pilot unit  at Harrington Station.  The ob-
jectives of this option are (1) to operate the slipstream unit under the same
operating parameters as the full-scale unit, and  (2) to determine if perfor-
mance of the slipstream can be scaled and  still represent the large operation.
Additionally, optimization of the operating  techniques will be determined on
the pilot baghouse and applied to the full-scale unit.  Future activities will
include air-to-cloth ratio studies.  These study areas have a high  priority at
EPA's research facility.  Air-to-cloth ranges, in general, will be  from 0.5:1
up to 3:1.

     Another activity for the test facility  will be  to investigate  the  physi-
cal dynamics of fabric filtering for the purpose of  determining GCA's mathe-
matical models for the performance and operation of  fabric filtering.   Later
other studies may examine baghouse operation at dew  point, high temperature

                                     339

-------
flue gas operation, and fabric cleaning techniques.  Consideration may also
be given to the effect of chemical injection and moisture injection.

     The pilot unit is presently being installed at Harrington Station and
start-up is tentatively scheduled for the first of August 1979.  The facil-
ity is a WFI Model 366, Series 11.5RS DUSTUBE Dust Collector.  It has two
compartments and initially will be fitted with 12 Criswell Style 442 Teflon
fabric filters.  The bags will be 29.2 cm (11.5 in.) diameter by 930 cm
(366 in.) long, complete with caps, clamps, and hardware necessary for
installation.  Cloth area per compartment will be 51 m2 (549 sq  ft ).


V.   CONCLUSIONS

     One of the most apparent things found over the last year of operating
experience is that there is a great deal yet to be learned about the design,
selection, installation, and operation of fabric filters on large coal-fired
facilities.  In addition to the most common specification of air-to-cloth
ratio and type of cleaning mechanism, information should be collected on
physical and chemical ash properties.  Pilot studies are needed on  the re-
lease of fly ash cake from the fabric, and investigations should be initiated
in the area of re-entrainment of fly ash back into the gas stream.

     The concept that fabric filtration is an easy application and can be
simply applied to any size boiler, with any type of inlet load, with any
type of coal and ash products simply by scaling the units to meet the air
flow requirements, is not correct according to Southwestern's experience.

     Southwestern feels that fabric filtration is a developing technology
and in time many of these design and operating problems will be resolved.
Fabric filtration will be a demonstrated alternative for particulate con-
trol but until that time there is not justification for using fabric fil-
tration as a control technology for all coal-fired facilities.  Those in
the industry and suppliers of such equipment may wish to select filtra-
tion as an alternative, but the exercise of this option should be with
caution.

     During the next couple of years Southwestern will continue its pro-
grams to characterize filters at Harrington Station, arid will continue
programs in the assessment and cleaning of fabrics.  As this information
is documented, it can be shared with industry, with vendors, and with regu-
latory groups.
                                     340

-------
                            References
"Filtration Model for Coal Fly Ash with Glass Fabrics," by  Richard  Dennis
R. W. Cass, D. W. Cooper, R. R. Hall, Vladimir Hatnpl, H. A. Klemm,   J.  E.
Langley, and R. W. Stern, GCA Corporation, EPA-600/7-77-084 (NTIS No. PB
276  489),  August  1977.
                                 341

-------
            START-UP AND INITIAL OPERATIONAL EXPERIENCE
                    ON A 400,000 ACFM BAGHOUSE
       ON CITY OF COLORADO SPRINGS'  MARTIN DRAKE UNIT NO.
                                 By:

                           Ronald L,  Ostop
                   Department of Public Utilities
                  Colorado Springs, Colorado 80947


                           John M. Urich, Jr.
                   Buell  Emission  Control  Division
                     Lebonan,  Pennsylvania  17042
                             ABSTRACT
A fabric filter baghouse was installed on an 85 MW unit at the City
of Colorado Springs' Martin Drake Power Plant,   This baghouse retrofit
was placed on line  in September 1978.   During the initial  operation,
some minor design and operational problems arose.  Minor modifications
were made to the baghouse system which eliminated these problems.  The
baghouse is experiencing a relatively low operating pressure drop and
continues to maintain zero visible emissions.
                                  34?

-------
                 START-UP AND INITIAL OPERATIONAL EXPERIENCE
                         ON A JtOO,000 ACFM BAGHOUSE
             ON CITY OF COLORADO SPRINGS' MARTIN DRAKE UNIT NO.
INTRODUCTION

     As a result of dwindling natural gas supplies as a source of fuel for
electric generating plants, each successive boiler installation after the late
1950's was designed to burn western, low-sulfur coal.  With this switch from a
relatively clean fuel (natural gas) to coal, and with frequent changes in
environmental regulations, the installation of air pollution control equipment
was a necessity.

     The Colorado Springs Department of Public Utilities' experience with air
pollution control equipment is associated with installation of a first gener-
ation, cold-side precipitator with a retrofitted, sulfuric acid gas conditioner;
a second generation, retrofitted, oversized, cold-side electrostatic precipi-
tator with a sulfur dioxide gas conditioner; and a hot-side electrostatic pre-
cipitator.  Each successive installation incorporated the latest technological
changes dealing with the problem of collecting high resistivity fly ash at a
high altitude and with semi-arid conditions.  But, due to changing regulatory
requirements, these units are marginal performers.

     Forecasted energy growth demands and replacement of retired generating
units make it a necessity to  install additional generating units.  Because
the City of Colorado Springs  is located in a valley with the Rocky Mountains
in the background, visible emissions are accentuated; therefore, the par-
ticulate control equipment for these new units must not only meet air pollu-
tion regulatory requirements, but must also result in nearly zero visible
em i s s i on s.

     As a result of an extensive study to review the status and long-term per-
formance of the "state-of-the-art" of particulate control technology, a deci-
sion was made to purchase and install a fabric filter baghouse collection
system for the new 200 MW, Ray D. Nixon Unit No. 1, which will go on line in
the last quarter of  1979.

     Shortly after this decision was made, the Department of Public Utilities
was sited for a violation of  Colorado's opacity regulation on  its existing
Martin Drake Unit No. 6.  Martin Drake Unit No. 6 was equipped with a cold-side
precipitator of 1968 vintage  with a sulfuric acid gas conditioner retrofitted
in 1972.  Because of the passage of more stringent air pollution control
requirements and the advancement of the "state-of-the-art" in  particulate
control for western, low-sulfur coal-fired power plants since  1968, the
decision was made to retrofit Martin Drake Unit No. 6 with a fabric filter
baghouse similar in design to that of Ray D. Nixon Unit No. 1.
                                       343

-------
     In March 1977, the Department of Public Utilities entered into a coopera-
tive contractural agreement with Buell Emission Control Division, Envirotech
Corporation, to perform a research and development product optimization program
to evaluate the design and various materials and operational parameters on a
full-scale, fabric filter baghouse for Martin Drake Unit No. 6.  Martin Drake
Unit No. 6  is an 85 megawatt, pulverized-coal utility boiler with a flue gas
volume of ^00,000 ACFM at full load.

     The purpose of the research and development program is to develop a cost
effective method of design and operation of a fabric filter collection system
for pulverized-coal utility boilers not only to reduce particulate emissions
to achieve a clear stack, but also to find an alternative to wet scrubbing
techniques for the reduction of sulfur dioxide by injecting calcium and sodium
compounds into the baghouse system.  The overall goal  is to advance the "state-
of-the-art" of fabric filtration for particulate and gaseous control.  The
four major objectives to approach this goal are to:  (l)  investigate and eval-
uate the theoretical collection mechanisms of fabric filtration; (2)  perform
optimization tests on fabric filter systems; (3)  investigate the effectiveness
and impacts of sulfur dioxide control in a fabric filter baghouse by first in-
jecting sodium compounds and then injecting calcium and sodium compounds in a
two-stage spray drying process; and   (4)  develop a performance prediction model
to simulate the fabric filtration process.  It is felt that, in order to obtain
maximum benefit from the data to be obtained, the research and development
testing should be done on a full-scale basis.  However, since there is a need
to test the most extreme operating conditions which may irreversibly damage
the full-scale unit, a pilot unit will be run in parallel.   This pilot unit
will allow for gathering information under the most extreme operating conditions
without compromising the integrity of the entire system to function as an air
pollution control device.

     Although the primary objective of this baghouse installation is to conduct
research and development experimentation on fabric filtration systems, the
remainder of this paper will address only the start-up and initial  operation of
the particulate collection system.

DESCRIPTION OF THE FABRIC FILTER SYSTEM

     Under the scope of responsibilities of this research and development
project, Buell furnished the full-size fabric filter equipment; provided tech-
pical erection supervision, start-up supervision and initial operation advisory
services; and conducted performance testing and research and development program
activities.  The City of Colorado Springs' responsibilities were to furnish the
foundations, ash handling system, induced draft fan, hopper enclosures, piping
and wiring, insulation, and auxiliary equipment; erect the fabric filter system;
and operate the unit during testing.
                                       344

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     Figure 1  briefly describes the fabric filter  installation.  Bascially,
the baghouse was designed to handle 400,000 ACFM of flue gas at 315F with a
particulate inlet grain loading of 5-55 GR/ACF.  The Department of Public
Utilities required a design ai r-to'-cloth ratio of  2.0:1 with one compartment
out for cleaning and one compartment out of service for maintenance.  The
Utilities also specified the cleaning method to be reverse-air only, thus
requiring anti-col lapse rings in the bags.  Buell  responded by providing a
twelve-compartment baghouse with 198 bags per compartment for a total of
2376 bags.  The bags in each compartment are arranged so as to provide a
three-bag reach with two walkways on the compartment floor and two in the
upper part of the compartment for easy access to the bags.  Each bag is
thirty feet, six inches (30'6") in length and twelve inches (12") in dia-
meter with an effective cloth area of 91 ft,  per  bag.  This cloth area does
not include the cuffs at the top and bottom of the seven anti-col lapse rings.

     The reverse-air system was designed to provide up to 36,000 ACFM of flow
at a pressure drop of two inches (2") water gauge.  A redundant reverse-air
fan was provided as a backup.  The reverse-air flow Is controlled by an inlet
louvered damper.

     The nominal average pressure drop across the  bags, as estimated by Buell,
was determined to be four inches (4") of water gauge,  The maximum pressure
drop across the flange-to-flange baghouse was estimated to be six inches (6n)
of water gauge.  The guaranteed maximum pressure drop across the system, in-
cluding the breeching to and from the baghouse, is eight inches (8r) of water
gauge.  Because Unit No, 6 is a pressurized-boiler unit, an induced draft fan
was installed only to act as a booster fan for the additional  pressure drop
resulting from the baghouse operation.  This Induced draft fan was designed to
provide 400,000 ACFM of flow, at 315F, at a pressure drop of eight inches (8n)
of water gauge.  The induced draft fan is controlled by an inlet louvered
damper.

     Each compartment can be  individually isolated for inspection or mainten-
ance purposes while the unit  is still on line.  Each compartment has its own
hopper, inlet poppet valve, outlet poppet valve, reinflation poppet valve, and
reverse-air poppet valve,  To isolate a compartment, all valves can be com-
pletely closed by removing the selected compartment from the automatic operating
mode.  This electrically isolates the valve actuators from the automatic clean-
ing cycle and closes all poppet valves.  A key interlock system is incorporated
into the system so that manual valve blocks must be put into position, which
physically prohibits any poppet valve from opening before a key is made avail-
able to unlock the compartment doors.  The two upper doors and two lower doors
are then opened to cool down a compartment before  entering,

     All  inlet, outlet, reverse^air, and reinflation poppet valves and the by
pass damper are pneumatically operated.  Each  individual poppet valve can be
operated manually at the main control cabinet  in the boiler, turbine^generator
control room or at local control stations in the baghouse  itself.  For any com-
partment to be manually operated, the master compartment control switch must  be
put into the manual mode.  This will allow operations at either the  local
                                       345

-------
control station or the main control panel.  In normal operation, all master
compartment control switches will be placed in the automatic mode.  This
places the operation of all compartment poppet valves under the control of
a solid-state programmable, microprocessor control system.  The primary pur-
pose of this control system is to initiate and sequence each compartment
through a cleaning cycle, which  is initiated through a flange-to-flange
pressure drop signal.  This preset pressure drop  is 4.5 inches of water gauge.
Therefore, when the pressure drop across the baghouse reaches 4.5 inches of
water gauge, a cleaning cycle is triggered.  Each compartment is reversed-air
cleaned for about 20 seconds at  a flow rate of 22,000 ACFM (A/C equals 1.22:1)
in sequence from compartment No. 1 through compartment No. 12.  The entire
cycle takes approximately fifty-five minutes.  The microprocessor will also
trigger a trip-to-bypass if it receives a preset  flange-to-flange pressure drop
which has been determined to be  too high to maintain the  integrity of the
baghouse system.  Other safety features include trip-to-bypass functions which
will protect against high or low operating temperatures.  The baghouse controls
are also interconnected with the boiler permissive system to provide for safety
under emergency boiler trip conditions.

START-UP OF THE FABRIC FILTER BAGHOUSE SYSTEM

     The start-up fuel for Martin Drake Unit No.  6 is natural gas.  Because
natural gas is free of particulate and sulfur, and because there is a bypass
on the baghouse system, the decision was made not to pre-coat the fiberglass
bags before initial operation.

     The flue gas was allowed to go through the bypass until  a stable boiler
operation was established with the flue gas temperature well  above the moisture
dew point.  Once this stable operating condition was achieved, this warm dry
flue gas was allowed to pass through the compartments by opening certain com-
partment inlet and outlet poppet valves arid closing of the bypass dampers.  As
the flue gas flow rate was  increased, more compartments were put on line to
maintain a maximum air-to-cloth  ratio of 2.0:1.   Once all compartments were
put on line, natural gas firing  was allowed until the entire baghouse was fully
expanded and allowed to grow to  its fullest extent.

     On September  15, 1978, one  coal mill was put into operation and the first
fly ash laden flue gas entered the baghouse.  At  that moment, the opacity
surged to approximately 60%.  The opacity rapidly decreased so that after
approximately ten minutes,  the opacity was down to 20% and after thirty minutes,
the opacity was 10%.  After the  first twenty-four hours of operation, there
were practically zero visible emissions being emitted from the stack.  The
pressure drop during the initial operating stages across  the flange-to-flange
was undetectable.

     The first cleaning cycle was  triggered approximately twenty-four hours
after start-up.  A momentary opacity excursion was detected up to apnroxiirately
40% when the first compartment came on  line after completing  its reverse-air
cleaning.  When the succeeding compartments went  through  this initial cleaning
                                       346

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cycle, momentary opacity excursions also resulted, but declining  in  intensity
with compartment No. 2 at approximately 10% to compartment No.  12 at  \%.  Sub-
sequent cleaning cycles show momentary opacity excursions of  10% after the first
week of operation, 5% after the second week of operation, 2%  after the third
week of operation, and zero visible emissions after the first month.   It should
be noted that these momentary excursions only occurred during that part of the
cleaning cycle when the first two compartments were put back  into service after
reverse-air cleaning.  At all other times during  its operation, there were zero
visible emissions being emitted from the stack.

     There was no  detectable pressure drop for the first few days of operation.
After three days, the flange-to-flange pressure drop was approximately 1.0 inch
of water gauge following a cleaning cycle.  This  pressure drop  following a
cleaning cycle is presently 3-0 inches of water gauge.  The time period from the
end of one cleaning cycle to the beginning of another is approximately two
hours.  This  is at full load operation with all twelve compartments  in service.

INITIAL OPERATIONAL PROBLEMS

     The major operational difficulty with the baghouse was associated with the
pneumatic system that operates all the poppet valves.  The original  system in-
cluded a 10 CFM dryer and the piping served as the compressed air reservoir.
This proved to be too small and too restrictive for the proper  operation of the
baghouse.  Also, last winter Colorado Springs experienced its coldest season in
decades.  As  a result, there were many icing problems encountered which in-
hibited proper operation of the baghouse, especially during the cleaning cycle.
To  remedy these situations, the air drying system was enlarged  to 100 CFM with
added air receiver to maintain a constant pressure of 82 PSI.   Also, filters,
lubricators and regulators were installed at every one of the 49 actuators to
insure that clean,  lubricated air at a constant pressure would  be provided.
Since the installation of this additional equipment, the problems with the
pneumatic system have ceased to occur.

OPERATIONAL COSTS

     Since the baghouse has only been on line ten months, it  is difficult to
arrive at any annual operational and maintenance  costs that will be  indicative
of  this system.  Since start-up, there have been  only two bag failures.  This
is  about 0.084% of the total bags installed.  The first bag failure  was caused
by  a sharp object that cut the bag fibers.  This  most likely  occurred during
an  inspection of the baghouse during the annual boiler outage.  The  second
failure resulted from fly ash escaping from the first bag leak  and impinging
on  a nearby bag and causing another leak.

     The average operating cost seen to date  is approximately 0.03 mills/KWH.

CONCLUSION

      In conclusion, the Martin Drake Unit No. 6 fabric filter baghouse  is a
very successful particulate control system.  There are no visible emissions
detectable during any phase of normal operation.  Actual test results  indicate

                                       347

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collection efficiency in the range of 99.89% to 99-95?, but the emission rates
were constant at about 0.0013 GR/ACF and 0.00^6 pounds per million Btu.  The
cause for the different efficiencies is due to the variations in the inlet
grain loadings during the different tests ranging from 1.2 GR/ACF to
2.6 GR/ACF.

     Finally, the pressure drop across the baghouse is averaging about 3-75
inches of water gauge.  The baghouse will initiate a cleaning cycle at A.5
inches of water gauge and clean down to 3.0 inches of water gauge.  The time
*rom the end of one clearing cycle to the beginning of the next cleaning cycle
is approximately two hours.

     As a result, the City of Colorado Springs' Department of Public Utilities
feels it has a highly efficient fabric filter system operating at a relatively
low pressure drop.
                                       348

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ENVIROTECH
BUELL:
FABRIC  FILTERS
                           Fly Ash Application
                           At City of Colorado Springs
                                                           Buell structural baghouse (or an 85
                                                           megawatt pulverlzed-coal-flred power
                                                           boiler at the City of Colorado Springs
                                                           Martin Drake Power Plant. Operational
                                                           September 1978.
   Buell Project Scope
   Research and development program.
   Complete process and system design engineering
   responsibility.
   Material supply includes all material from inlet
   flange of baghouse to outlet flange of baghouse
   with all related operational instruments and
   controls.
 (Reproduced with permission.)
                                                           Design Criteria

                                                           Gas volume	400,000 ACFM
                                                           Normal gas temp	315°F
                                                           Max. allow, temp	550°F
                                                           Min. allow temp	250°F
                                                           Coalfired,lb/hr	93,400

                                                           Coal Analysis
                                                             Moisture	13.4%
                                                             Ash	15.6%
                                                             Sulfur	0.3%
                                                             Volatile matter	29.5%
                                                             Fixed carbon	40.9%
                                                             BTUperlb	9,300

                                                           Performance

                                                           Inlet Gr/ACF	1.84
                                                           Outlet Gr/ACF . .  . 0.002(99.89%)
                    Equipment Specifications

                    Overall dimensions	174' x38' x84' high
                    No. of compartments (ea. with hopper)	12
                    Hoppers, outlet manifold	1/4" A-36 steel
                    Casing, inlet manifold	3/16" A-36 steel
                    Bag cleaning method	reverse air
                    Bag material	glass fiber with Teflon coating
                    Bag diameter	12" nominal
                    Bag length	30'-6"
                    Air-to-cloth ratios: Gross	1.85:1
                                   Net	2.01:1
                    Total no. of bags	2,376 (198/compartment)
                    Electronic controls	solid state design
 Copyright © 1979 by Envirotech Corporation
                                           349

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REFERENCES

 Ronald L. Ostop and Larry A. Thaxton, "Optimization of Material, Design and
Operational Parameters Associated with a Full-Scale 400,000 ACFM Fabric
Filter Baghouse on the City of Colorado Springs'  Martin Drake Generating
Unit No. 6," presented before the 40th Annaul Meeting of the American Power
Conference, April 26, 1978, sponsored by the Illinois Institute of Technology.
Chicago, 1978.
                                      350

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           DESIGN,  OPERATION,  AND PERFORMANCE TESTING OF
                   CAMEO WO.  1 UNIT FABRIC FILTER
                                By:
                        H.  G.  "Bill" Brines
                 Public Service Company of Colorado
                      Denver,  Colorado, 80201
                              ABSTRACT

     A Carborundum fabric filter was retrofitted to the Cameo No.  1
unit in 1978.  Cameo Station, owned and operated by Public Service
Company of Colorado, is near Grand Junction, Colorado, and No.  1
unit (22 MW) was first placed in service in 1958.   The purchase
contract for the fabric filter was written on July 2,  1976, but
due to problems in obtaining an 'emission permit from the State of
Colorado, actual construction did not begin until February, 1978.
The fabric filter, designed with 1.92 gross air to cloth ratio and
reverse air, was placed in service December 18, 1978.   This paper
covers the design aspects, construction features, startup
procedures, and acceptance testing.
                                 351

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               DESIGN, OPERATION, AND PERFORMANCE TESTING OF
                       CAMEO NO. 1 UNIT FABRIC FILTER
INTRODUCTION

     Public Service Company of Colorado's (PSCC) Cameo Station is located lU
miles east of Grand Junction on the Colorado River.  The No. 1 unit (22 MW)
was placed in service in 1958, and the No. 2 unit (UU MW") was placed in
service in 1963.  The No. 1 unit consists of a Babcock & Wilcox integral
boiler, front fired, with 215,000-pounds-per-hour capacity.   Steam conditions
are 890 psig and 910° F.  The design flue gas flow is 110,500 acfm at 310° F.
The unit was originally designed for either coal or natural gas firing, and
the only air pollution control device was a mechanical dust collector.

     In April 1970, the No. 1 unit was committed to gas firing only as  a
pollution control measure.  Coal was to be used as the fuel only if a system
electrical emergency existed and natural gas was not available.  As gas
supplies dwindled and the unit was required to fire coal more and more  fre-
quently, it became apparent that either the unit would have to be retired or
a particulate control device would have to be installed to clean the boiler
flue gas.

     Coal contracts for Cameo Station were in a state of flux in 197^ and
1975; and, therefore, the long-term coal supply was unknown.  The selection
and engineering design of an electrostatic precipitator under this condition
would be very difficult.  Also, economic evaluations indicated the cost of a
fabric filter to be nearly equal to the cost of an electrostatic precipitator.

     Field trips to Colorado-Ute's Nucla Station in Nucla, Colorado, and to
Pennsylvania Power & Light's Sunbury Station convinced PSCC's operating and
engineering personnel that fabric filters were a viable pollution control
technology, especially when burning low-sulfur western coals.  The performance
of each fabric filter installation visited indicated that a clear-stack status
was possible with fabric filter technology.

DESIGN

     In mid-1975, a specification for a fabric filter was prepared and was
issued in November 1975-  The basic design criteria for the fabric filter as
specified is included in the following table:
                                      352

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                   Table  1.    FABRIC FILTER SPECIFICATION

     Gas  Volume/Baghouse  - acfxn                       170,000
     Temperature  - °F.                                     290
     Approximate  Inlet  Loading - gr/acf               0 - H (2-79 calculated)
     Outlet Loading - gr/scfd                           0.007
     AP  across Baghouse  (2 Compartments Out) (Max.)    7-0
     Bag  Spacing  (Between Bags)                         2"
     Abrasion Protection                               Thimbles Above & Below
                                                        Tube Sheet
     Rings per Bag                                      5
     Bag  Reach (to Center of Farthest Bag)             36"
     Air/Cloth Gross                   ) Without Reverse  2.0/1
     Air/Cloth Wet Two Compartments Out;   Air            2.3/1

     The  fabric filter cleaning was specified to be by reverse air only.   The
above design criteria were to be met while burning coal from three suppliers:
Energy Fuels Corporation, P & M Coal Company, and Cambridge Mining
Corporation.  The origin of the coal, therefore, would be either Routt County
or Mesa County, Colorado.  The specification did not give analyses from the
various coal suppliers but specified minimum and maximum values.  The proxi-
mate analyses were shown in the specification as follows:

                          Table 2.   COAL ANALYSES

                                      Minimum (%)   Maximum (%}

               a.  Moisture                 k            17
               b.  Ash                      U            18
               c.  Volatile matter         31            36
               d.  Fixed carbon            ^3            51

The ultimate analyses of the above coals were also given as:

               a.  Hydrogen                 U             6
               b.  Carbon                  58            68
               c.  Nitrogen                 1             2
               d.  Oxygen                   9            21
               e.  Sulfur                   0.3           0.7
               f.  Ash                      U            18

The heating value  (as received) was 9»200 Btu minimum; 12,000 Btu maximum.
The specification also listed ash composition and again was on a minimum-
maximum basis.

     A new coal supplier has been added since the specification was issued.
The Bear Coal Company is now supplying more than 80 percent of the coal for
Cameo Station.  This coal falls within the minimum and maximum values as
listed in the specification.
                                      353

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     A particle-size distribution test was performed, on Cameo No. 1 at the
inlet to the mechanical collector for the specification.  The results are
listed in the table below.
                   Table 3.   PARTICLE SIZE DISTRIBUTION
                  Particle Size
                    (microns)

                       l.U
                       2.35
                       >K7
                       7.6
                      10.5
                      17.2
                      20.9
                      23.3
Percent (%} by Weight Finer Than
	Particle Size Shown	

               3.88
               9-06
              22.01
              33.37
              Hli. 62
              65.3U
              73-80
              77-39
FABRIC FILTER SELECTION
     The specification was issued to seven bidders.  The evaluation of the
five proposals received was based not only on the bid documents but also on
the total evaluated cost, including the estimated annual operating and
maintenance expense.  Carborundum was the successful bidder and a purchase  ,
contract was issued to them July 2, 1976 to design, supply and erect the
fabric filter on Cameo No. 1 Unit.

     The table below lists the actual design parameters of the fabric filter
as supplied by Carborundum:

                 Table \.   FABRIC FILTER DESIGN PARAMETERS
          Gas vblume/Baghouse - acfm
          Temperature - °F.
          Approximate Inlet Loading - gr/acf
          Outlet Loading - gr/scfd
          &P Across Baghouse (2 Compartments Out)
          Compartments - Number
          Bags per Compartment
          Bag Material
          Bag Dimensions
          Bag Spacing (Between Bags)
          Abrasion Protection
          Rings per Bag
          Bag Reach (to Center of Farthest Bag)
          Tension  (pounds)
          Air/Cloth Gross                   ^ Without
          Air/Cloth Net One Compartment Out r Reverse
          Air/Cloth Net Two Compartments OutJ   Air
          Fabric Filter Size
               Length
               Height
               width                  354
                170,000
                    290
                   2.79 calculated
                   0.007
                   6.2"
                      8
                    2UO
                Teflon Coated Fiberglass
                8" x 22'6"
                      2"
                Thimbles Above & Below
                  Tube Sheet
                      5
                     36"
                  1*0-60
                    1.92/1
                    2.20/1
                    2.57/1
                    69'
33'
                        8"
                        It"

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     A schematic of the general arrangement of the Cameo No. 1 fabric filter
is shown in Figure 1.

     The filter "bags as supplied by Carborundum have the following
specification:

                           Table 5.   FILTER BAGS

               Manufacturer         Carborundum
               Fabric               Fiberglass
               Treatment            10$ DuPont Teflon B
               Weave                Twill
               Count                5U x 30
               Yarn
                   Warp             150 - 1/2
                   Fill             150 - 2/2
                   Weight           9-1/2 oz/sq. yd
                   Permeability     65 - 80 cfm/sq ft
               Textured Surface     Inside

     The fabric filter as supplied by Carborundum has two reverse air fans.
The reverse air fans have a gas-flow capability of 22,000 acfm with a static-
pressure capability of 12 inches of water.  The unit is provided with two
bypass poppet-type dampers.  All dampers (including inlet, reverse air,
6utlet, and bypass valves)  are  installed with electric-motor-driven
operators.  The control system located at the base of the fabric filter is an
electro-mechanical relay-type control system with complete controls for each
compartment.  The cleaning cycle can be initiated by (a) time of day,
(b) total pressure drop across the fabric filter, (c) lapsed time from last
cleaning cycle, and  (d) manually.  One compartment has an observation port
installed at the lower and upper walkway levels.  Although this port helped
to determine the bag movement when the reverse air fan was taken out of
service, PSCC would not install observation ports on other fabric filters.
The fabric filter was not insulated between compartments nor between the
compartments and the inlet and outlet ductwork.

     The I.D. fan was tested and found to be sufficient in both flow and
static pressure characteristics; therefore, no fan modifications were
required.

     The Company encountered problems when attempting to obtain a permit to
construct.  Therefore, the engineering and procurement of the fabric filter
were put on "hold" October lU, 1976.  Following eleven (ll) months of
negotiations, a permit to construct was obtained September l6, 1977-  On this
same day, Carborundum was authorized to resume engineering on the project.
In February 1978, the engineering was completed and construction of the fabric
filter commenced with the pouring of the foundations.  Carborundum moved on
site and started construction in July 1978, and the fabric filter was com-
pleted and placed in operation December 18, 1978.
                                       355

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CO
en
CTl
                                    MECHANICAL COLLECTOR
                                           (GUTTED)
                                                              FIGURE 1

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     The condenser cooling water for Cameo Station comes from the Grand Canal.
The canal is taken out of service in March and October for maintenance and
inspection.  During the canal outage the plant condenser cooling water- is
provided by a spray pond.  During the October 1978 outage the Ho. 1 unit was
taken out of service for 27 days to make the required inlet and outlet duct
connections.  Blanking plates were installed in the inlet and outlet duct
and the No. 1 unit returned to service on the bypass.  The unit was then
taken, off the line for five days to remove the blanking plates prior to the
December 18 start-up date.

     The start-up procedure used to place the fabric filter in service was
accomplished as follows:  The No. 1 unit was started up on natural gas and
raised to full load capabilities with the bypass poppet valves in the open
position.  After attaining an air-heater-outlet temperature of 270° F. , the
bypass poppet valves were closed, and, while still operating on natural gas,
the fabric filter was heated to within 10° of the boiler outlet temperature.
After attaining the desired fabric-filter temperature throughout, which took
approximately six hours, coal was added to the boiler through one of the coal
mills.  This mill was then fully loaded, and the natural gas equivalent to
that mill was removed from the boiler.  The second mill was then placed in
operation, and the natural gas was completely removed from the boiler.  The
differential pressure from the dust loading took approximately 12 hours to
increase to the desired four inches of water pressure.  At this time, the
reverse-air fan was started, and the first cleaning cycle was initiated.
After being cleaned the first time, the fabric filter indicated a differential
pressure of approximately one inch.  The differential pressure was again
allowed to build up before the next cleaning cycle was initiated, and this
procedure  continued, cleaning only as the differential pressure built to
U-l/2 inches of water.

     At the end of each cleaning cycle, it was noted that a visible plume
appeared at the stack.  It was apparent that the bags were being "overcleaned"
to the extent that dust was penetrating through the fabric.  As a result of
this penetration, the decision was made to try cleaning without the reverse-
air fan.  All cleaning since the first week of operation has been without the
reverse-air fan in operation.  The cleaning cycle presently is based on the
H.5 inches  differential, during which a cleaning cycle is initiated, and each
compartment is sequenced through its cleaning cycle.  At the end of the
cleaning cycle, the differential pressure is 1-1/2 to 2 inches of water.  This
is allowed to build over a period of eight to 10 hours back to U-l/2 inches,
of water, when another cleaning cycle is initiated.  The reverse-air fans,
therefore, have not been used since the first week of operation.

     The initial two weeks of operation with the fabric filter were followed
by a routine two-month annual outage of the No. 1 unit.  During this outage,
a thorough examination of the fabric filter indicated minor leaks through the
retaining  clamps that hold the bags on the thimbles.  These were tightened  as
needed and the compartments vacuum cleaned.  After the unit was put back in
service March ^-, 1979, the operating personnel removed one compartment from
service during each graveyard shift to allow for an inspection during the day
shift.  The major problem encountered was loose clamps around the cuff of the
bag where  it attaches to the thimble.  As leaks were found, the clamps were
tightened; and the compartment was vacuumed in order to make the next visual

                                      357

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inspection easier.  The removal of one compartment each night continued for
two months.  How, however, this inspection cycle has been increased to once a
month.

     Each compartment has two lower access doors and two upper access doors.
Air leakage at the door seals was noted by rust indications on the inside of
the door facings.  An ultrasonic leak detector was used to determine exactly
where the leaks were, and hinge adjustments were made until these leaks were
eliminated.  Wo other noticeable maintenance problems or leaks have been
encountered in the four months since the return to service.

PERFORMANCE CRITERIA AND ACCEPTANCE TESTING

     The guaranteed performance stipulated in the specification states that
the fabric filter shall remove the particulate emission from the Company's
steam generator to a maximum of seven-thousandths grain per standard cubic
foot (0.007 gr/scf) of flue gas measured at the fabric filter outlet on a dry
basis under the following simultaneous conditions:  (a) handling actual gas
volumes over the entire range of the steam generator operation, (b) burning
coal with a maximum of 18 percent ash, (c) handling ash in the ash hoppers,
(.d) isolating any one compartment of the baghouse in a cleaning cycle,
(e) isolating any other compartment for maintenance, and (f) blowing soot in
the boiler or air heater.

     The conformance test (EPA Method 5) was used to determine the actual
acceptance of the fabric filter.  This test was conducted within 180 days
after completion of the fabric filter.  Conformance testing was done, but,
since one test was more than 0.007 gr/scf, the conformance testing was
repeated.  Carborundum was asked to optimize the operation of the fabric
filter and to check for any bypass leakage or other problems that might cause
nonconformance.  Welding beads were found on the bypass poppet valve, and
minor leakage was occurring.  An unwelded seam separating the inlet from the
outlet duct also was found and repaired.  The second set of conformance tests
was completed June 5 and 6.  The average outlet grain loading of these tests
was  0.0053 gr/scfd.  The fabric filter has now been accepted by PSCC as
having met the performance criteria of the purchase contract.

     An Environmental Data Corporation performance monitor is installed in
the stack on Cameo No. 1 unit.  This instrument which monitors opacity, NOX,
SOX, and percent excess oxygen, was transferred to Cameo from PSCC's Comanc'he
Station near Pueblo.  The opacity presently is reading 2 to k percent.  Only
the opacity monitor is required by regulation; however, PSCC and EPRI
presently are engineering a dry alkali injection system.  The Company will
conduct a series of tests to evaluate the capability of nahcolite, trona,
and/or sodium bicarbonate in this system as a sulfur dioxide removal
mechanism.  The tests are to be conducted the latter part of this year.

     Public Service Company of Colorado is to date very pleased with the
operation of the Carborundum fabric filter on the Cameo No. 1 unit.  The unit
has been operating with a clear stack since the fabric filter went into
operation.  Because of this, PSCC has installed a fabric filter at its
Arapahoe Station in Denver and is engineering such filters at two other coal-
fired stations.
                                      358

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           EXPERIENCE AT COOR3 WITH FABRIC FILTERS

                FIRING PULVERIZED WESTERN GOAL
                              By:

                       Galen L, Pearson
                     Aciolph COOPS Company
                    Golden, Colorado 80l[.01
                          JIBSTRAGT


     Coors has been using a fabric filter unit since December,
1976, to control emissions from the Boiler No. ii pulverized coal
fired unit, rated at 250,000 Ibs./hr. steam.

     Pressure drop, bag life, etc,, on this shake-deflate 8 module
filter is presented.  Data from emission tests is reviewed and
discussed.

     The low pressure pulse-jet type fabric filter being installed
on the new Boiler No. 5 is discussed briefly.  This 12 module
unit is designed for 320,000 ACFM and an air to cloth ratio of
5.5 to 1.
                               359

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           EXPERIENCE AT COORS WITH FABRIC FILTERS -

                FIRING PULVERIZED WESTERN COAL
INTRODUCTION

     Based on energy availability and on cost projections,  Coors
made the decision in 197^ to install coal firing capability on
the Boiler No. h. unit which was under construction  at that  time.
Electrostatic precipitators, scrubbers, and fabric  filters  were
evaluated carefully for emission control devices.   The fabric
filter approach was ultimately selected because it  was felt that
it would do the best on a continuous basis of removing particu-
late and achieving a low opacity stack.  The fabric filter  unit
selected went into service in December, 1976, and has been  opera-
ting successfully for the last 2 1/2 years.


EQUIPMENT DESCRIPTION

Boiler No. i|.

     The 2pO,000 Ib./hr. steam generator is a tangentially  fired
pulverized Combustion Engineering, Inc. VU-lj.0 unit.  Pulverization
of the coal is accomplished by two Raymond RB-573 bowl mills.  At
the rear of the boiler, flue gas is cooled to approximately 3^4-0  F
by a fin tube boiler feedwater economizer.  'There is no combustion
air preheater in the normal sense on this unit.

     The basic arrangement of the baghouse, boiler, baghouse by-
pass, I.D. fan, etc., is illustrated by the schematic of Figure 1.

Fabric Filter

     The fabric filter or baghouse on the Boiler No. Lj. unit is a
VJheelabrator-Frye, Inc. shake-deflate cleaning type unit and
operates at a typical flue gas volume of 170,000 ACFM at 3i|0° F
when the boiler is at rated load.  The baghouse has 8 compartments
with ISO bags per compartment for a total of l,ijlj.O  bags.  The bags
are 8 inches in diameter and 22 feet long and do not have rings.
(The total filter area is 66,2l<-0 square feet.)  The fabric
description is as follows:
                                360

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FIGURE 1

BAGHOUSE -

BOILER

SCHEMATIC
                            REVERSE
                            AIR FAN
     180 BAGS PER
         COMPARTMENT

     1440 BAGS TOTAL
     66,240 SQ. FT.
            FILTER AREA
           TO  STACK
CONTROLLER
      BOILER NO.  4
      250,000 LB/HR STEAM
      PULVERIZED
      TANGENTIALLY
      FIRED
                                                    ECONOMIZER

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          Material                    Woven Glass
          Finish                      Silicon Graphite
          Weave                       3x1 KMT
          Thread Count                66 x 30
          Permeability  (new)          h$ - 65
          Weight                      10.5 oz./sq. yd.

     Initially, one compartment of W. H. Criswell's Teflon B
finished bags and one compartment of Cris~0-Flex finished bags
were installed.  These were removed after a few months of opera-
tion when it was discovered that the inservice permeability was
much lower than with the silicon graphite finished bags.

     Each compartment has a 36" diameter manually operated butter-
fly valve at the inlet, a \\2" diameter cylinder operated poppet
valve at the outlet, and a 20" diameter cylinder operated butter-
fly valve for reverse air.  The single reverse air fan has a paral-
lel blade damper (20" x 21}.") with an automatic controller on it
set to accomplish a reverse AP across the bags of at least 0.5
inches  W.G. but not more than 1.0 inches W.G. during the reverse
air mode of the cleaning cycle.  The automatic controller was not
added to the damper until July, 1977.

     Bags are located on 9" centers with a three bag reach from
the one foot wide internal walkways.  The access door to the bot-
tom elevation is 21}." x 60" and the access door to the up-oer eleva-
tion is 20" x ij.8".

     The wall between compartments is insulated as well as all
external areas of compartments, hoppers, and ducts.  Bach bottom
hopper has a series of plate type thermostat controlled heaters
1.5.6 KW per hopper).

     The cleaning cycle used on this unit is shown graphicall:/ by
Figure 2.  The baghouse is cleaned only as necessary when the AP
rises to the designated setpoint for cleaning.  When a clean mode
is initiated, all eight compartments are cleaned one at a time in
the sequence of 1, 2, 3, h., 5, 6, 7, and 8.  It takes 3 minutes
per compartment, or 2lj. minutes total, to get through all eight
compartments.


PRESSURE DROP CHARACTERISTIC
     The pressure drop across the baghouse has been found to be
dependent upon  the boiler  steaming rate, type of coal being burned,
quality of boiler operation, and quality of baghouse operation.
In general, experience has  shown that the typical operating pres-
sure drop for this unit is  as illustrated bj the shaded  area of
Figure 3.  Roughly one inch of  this total baghouse pressure drop
can probably be attributed  to inlet valve, outlet valve, and duct
                                362

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              Figure  2
       BAG CLEAN CYCLE SEQUENCE
        BOILER NO. 4 BAG HOUSE
(8 MODULES TOTAL CLEAN TIME = 24 MIN.)
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OUTLET CLOSE (5 SEC)
SETTLE (10 SEC)
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SETTLE (20 SEC) I
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SHAKE (10 SEC)
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SETTLE (65 SEC) 1
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BAG REINFLATION (10 SEC) i
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PAUSE TO NEXT MODULE (30 SEC) &
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                       363

-------
                                  FIGURE  3   BOILER  NO.  4   BAGHOUSE
                                                                            CHARACTERISTIC
00    .
01    }
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          7


          6
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                                                             OPERATION  ABOVE  THIS  LINE  IS  GENERALLY
                                                             THE  RESULT OF  INADEQUATE CLEANING
                                                      OPERATION  BELOW  THIS  LINE  (ALTHOUGH  POSSIBLE)
                                                      GENERALLY  INCREASES EMISSIONS AND  CAN  DECREASE
                                                      BAG LIFE THROUGH EXCESSIVE  CLEANING
                                       1	r
                                        000
                            BOILER  STEAM OUTPUT
                                                       (\B/HR)

-------
losses at the rated boiler load condition.   Operation below the
lower line of Figure 3, although possible,  generally causes in-
creased emissions and can- possibly decrease bag  life through
excessive cleaning.  Operation above  the upper line  in Figure  3
is not very desirable from a power consumption standpoint.   In
addition, if the filter cake is built up fairly  heavy,  a  condi-
tion develops where bag cleaning can  not be accomplished  adequately
without reducing boiler load.

     Several different types of western coal have  been used to
fire Boiler !To. i|.  Four of these coals and their  basic properties
are listed in Figure [;.  In general,  the low BTU,  high moisture
coals tend to increase baghouse pressure drop.   Also,  the higher
the ash content in the coal, the higher the baghouse pressure
drop.  VJhen the high BTTJ, low ash coals  (like Coal C)  are burned,
there is considerable time when the baghouse is  not  in a  clean
mode of operation.


BAG REPLACEMENT INFORMATION

     The recorded data on the number  of bags replaced per month
for each compartment is illustrated in Figure 5  £or  the time period
from February, 19?8, through June, 1979.  Unfortunately,  no data
was recorded by operating personnel concerning the bags replaced
due to failure prior to February, 1978.  Personnel involved in
replacing bags during the llj. month period from December 1,  1976,
through January, 1978, estimate from  memory that somewhere  in  the
range of 200 to 300 bags x^ere replaced during this period due  to
failure for one cause or another.

     Originally, compartment #6 had Gris-0-Flex  bags and  compart-
ment -ffl had Teflon B finish bags, both manufactured  by W. W.
Griswell.  Due to pressure drop considerations,  these bags  were
replaced with Silicon G-raphite finish bags  in July,  1977, and
longer J support hooks were installed in these two compartments.
These longer J hooks developed a top  of bag total  horizontal
throw of 3.2inches during shake instead of the original 1.9^i
shake throw which is still used on compartments  #1,  ;,-2, #3,
~5, and ;f8.  The bags installed in compartments  -j',-6 and -^7
July, 1977, were too long and were cuffed over.  It  is suspected
that this cuff slipped, eliminating bag tension.  The loss  of
tension, combined with longer than necessary bag shaking  during
certain tests, probably caused the high bag failure  rate  in May
and June of 197&.

     New bags of the proper length for the  longer  J  hooks were
installed in compartments ri-'6 and ;/7 in August, 1978.  To  develop
comparative data between long and short J hooks, the bags in the
adjacent (mirror image) compartments  ;^2 and ^3 were  replaced at
the same time.  Since _August, ;1978, there have been  no bag  fail-
ures in compartments £6, ir7> Jr2, or  ;~3.

                                365

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                 FIGURE 4
VARIOUS WESTERN COALS WHICH HAVE BEEN USED

Heating Value (BTU per LB)
Moisture Content (%)
Sulfur Content (%)
Ash Content (%)
I
Ash (Lb Per Million BTU)
& P Baghouse (inches W.G.)
(at 250,000 Ib/hr steam)
COAL A
8,600
26
.5
9
10.5
9.0
COAL B
10,700
9
.9
11
10.3
7.3
COAL C
12,500
7
.5
7
5.6
5.3
COAL D
11,100
8
.5
10
9.0
6.0
                      366

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                     Figure  5
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   BAG FAILURE RATE PER mm - SINCE FEB.  1978
BOILER NO, *J BAGHOUSE - START UP DATE DEC, L 1976

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              MOTES:   1)   NO BAG FAILURE RECORDS WERE KEPT PRIOR TO FEB., 1978
                      2)   LONGER J  HOOKS WERE  INSTALJfD  IN COMPS, #6 AND #7 IN JULY 1977,  THESE COMPARTMENTS
                          STILL HAVE THE LONG  J HOOKS,

-------
     The original bags in compartments .v'h.  and  7-8 were  replaced  in
March, 1979, after approximately  26 months  of  service.   The  bags
in compartment ;/^ were replaced on April 30, 1979,  after approxi-
mately 27 months in  service.

     In summary, it  is felt  that  a major portion of the  bag  fail-
ures were caused over a period of time by  a combination  of high
flue gas flow rates, excessive bag shaking at  times, and improper
operation of the reverse air fan  control damper.

     .•Jith these items corrected and proper operation in  the
future, it  is felt that it is reasonable to expect  between 2 and
3 years of  bag life  and possibly  more.


EMISSION TESTS
      Emission  tests measuring  the  amount  of  particulate  in the
 stack gas were conducted June  7, 8,  and 9 of 1977,  and the results
 are presented  in Figures 6  and 7.   One  set of test  data  (Figure  6)
 was obtained by the Coors Spectro-Chemical Laboratory (Ref.  1)
 using EPA Reference Method  No.  5.   The  second set of  test  data
 (Figure  7)  was gathered on  the same days  at  about the same time
 by York  Research Corporation (Ref.  2) under  an EPA  contract using
 a modified  form of EPA Reference Method No.  17.

      The results tend to vary  somewhat  between tests  7!, ,r2,  and
 -,r3 in both  data tables.  However,  the composite average  of the
 three tests compare closely between the Coors Sprectro-Chemical
 Laboratory  data and the EPA-York Research data if only the
 G-rains/SCFD, G-rains/ACP, and LB./MR. data is compared.   It appears
 that  an  unrealistically high BTU input  number x/as used in  calcu-
 lating the  Ib./million BTU  ratio in the EPA-York Research  Corpora-
 tion  Report (Ref. 2).

      It  is  of  importance to note,  however, that all data points
 were  less than the Federal  and Colorado limit of 0.1  Ib./million
 BTU.

      During these tests the air to cloth  ratio was  2.7 when all
 eight compartments were on  line and 3.1 when one compartment was
 in a  clean  mode.  Baghouse  pressure drop  outlet plenum to  inlet
 plenum was  9 inches V/.G., typically at  the 3.1 air  to cloth ratio.
 Coal  A,  defined earlier, was used  during  these tests.

      A continuous opacity monitor  has been installed in  the stack
 flue  gas stream (Lear Siegler  RM-kl).   Opacity ranges between 2>
 and 5/3 but  it  is less than  J>%  most of  the time. Generally speak-
 ing,  there  is  no visible plume from the stack on this unit and we
 are pleased that the  fabric filter has  performed very well.
                                368

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                              FIGURE 6
                   EMISSION TESTS - BOILER NO.  4
              DATA BY COORS SPECTRO-CHEMICAL LABORATORY
(Using EPA Reference Method No.  5)
Participate
Emissions
Grains/SCFD
Grains/ACF
LB/HR
IB/Million BTU
Test #1
6/7/77
0.03465
0.01654
25.00
0.0714
Test #2
6/8/77
0.01883
0.00902
14.02
0.0401
Test #3 •
6/9/77
0.01085
0.00521
7.90
0.0226
Average
3 Tests
!
0.02144
i
0.01025
15.64
0.0447
NOTE:  40 Sample points of 3 minute duration each were taken for each
       test.
                              FIGURE 7
                   EMISSION TESTS - BOILER NO. 4
              DATA BY EPA AND YORK RESEARCH CORPORATION

(Using the total of in-stack + out of stack by a modified EPA Reference
 Method No. 17)
Particulate
Emissions
Grains/SCFD
Grains/ACF
!
LB/HR
LB/Million BTU
Test #1
6/7/77
0.01931
0.00918
14.21
0.0336
Test #2
6/8/77
0.01774
0.00852
13.21
0.0316
Test #3
6/9/77
0.02470
0.01178
20.60
0.0428
Average
3 Tests
0.0206
0.00983
16.01
0.0360
NOTE:  32 Sample points of 4 minute duration each were taken for each
       test.
                                 369

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FUTURE PLANS - BOILER HO. 5

     A new pulverized coal fired boiler with  a  generating  capacity
of 11-50,000 Ib./hr. is currently under  construction  and  scheduled
for start-up in November or December of 1979.   Careful  considera-
tion was given to the alternatives  of  purchasing  a  reverse air
unit, purchasing a shake-deflate unit, designing  and  building a
reverse air unit, and purchasing a  low pressure pulse-jet  type
unit.  The low pressure pulse-jet type unit offered by  CSA Carter-
Day of Minneapolis, Minnesota was selected based  on considerations
of overall lower initial capital cost  and system  simplicity and
reliability.

     The 12 modules for this fabric filter system have  been
delivered and field installation is progressing on  schedule.

     Figure 8 lists the significant information concerning this
fabric filter system  and Boiler No. 5.
REFERENCES

1.   Coors Spectro-Chemical  Laboratory Report  ITo.  91353.
     Compliance  Tests  Report for  Adolph Coors  Company Power
     Plant,  Boiler  No.  Lj.~.  Coors  Spectro-Chemical  Laboratory,
     P.O. Box 500,  Golden, Colorado 80li01.   July 7,  1977.

2.   Emission Tests at Adolph Coors- Company No.  Ij.  Coal-Fired
     Steam Generator.   Report No. 77-SPP-17.   Prepared by  York
     Research Corporation for U.S.  Ifoviromaental Protection
     Agency  under" Contract No. 68-02-lliOl.   Task No.  33. "KIC No,
     7-8/J.79-33.   July  26,  1977.
                                 370

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                               FIGURE 8

            BOILER NO. 5 BAGHOUSE UNIT - UNDER CONSTRUCTION

A.   Baghouse Information
     Manufacture:  CEA-Carter Day
     Model No.:  376RF10 (High Temperature)
     Number of Modules:  12 circular configuration
     Number of Bags:   376 per module
                      4512 bags total
     Design Flue Gas Flow:  320,000 ACFM at boiler M.C.R.
     Total Filter Area:  57,600 Sq. Ft. (4800 Sq. Ft. per module)
     Air to Cloth Ratio:  5.5 (with 12 modules)
                          6.0 (with 11 modules)
     Bag Size:  Oval pattern 15.3 inch perimeter by 10 feet long
     Bag Material:  22 ounce felted "Daytex" (a Carter-Day felted media)
     Cleaning Method:  Periodic on-line reverse air pulses from a storage tank
                       charged at 7.5 PSI6.  Each module  has  its own self-
                       contained compressor-blower to charge  this tank.
     System Dampers:   Any module can  be  isolated for maintenance while the
                       boiler and other modules are  in service.  All modules
                       can be bypassed via  two 60 inch diameter poppet bypass
                       valves during  start-up or boiler oil firing.
     Anticipated Pressure Drop:  3 to 6 inches W.G.
     Scheduled Start-Up:  November or December,  1979

 B.   Boiler Information
     Manufacture:  Combustion Engineering
     Type:  Model VU-40 tangentially pulverized coal fired with three coal
            levels being fed by three Raymond RB-613 pulverizers.  Unit will
            be operated balanced draft at a  minus 1/2 inch W.G.
     Economizer:  Unit has a boiler feedwater economizer  which will lower the
                  flue gas temperature to less than  360°F.
     Steam Rating:  450,000 Ib/hr at 825  PSIG and 850°F
     Back Up  Fuel:  No. 2 fuel oil
     Steam Use:   Steam produced from this  and other units at the plant is or
                  will be used for process  heat requirements, electrical power
                  generation, and numerous  steam turbine  mechanical drives.
                                     371

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                   FABRIC FILTER EXPERIENCE AT WAYNESBORO


                                     BY:

                               W. R. Marcotte

                 E.I. du Pont de Nemours & Company, Inc.
                         Waynesboro, Virginia   22980
ABSTRACT

     The paper describes a reverse flow fabric filter installed to
i^aridle the flue gases from four pulverized coal and oil fired boilers.
The unit contains many unique design features which assist with full
time operation.  Start up was by procedures designed to minimize gas
condensation and other undesirable occurrences.

     The unit has been on the line for 18 months.  Operation has been
good with pressure drop varying between 3" and 6" and cleaning frequency
varying between 12 hours and continuous.  Some few bags have been damaged
due to sulfuric acid condensation resulting from maloperation and water
leaks.  Several operating incidents will be discussed.  #6 fuel oil is
sometimes burned with the coal.
                                       372

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     When the Clean Air Act Admendents were passed in 1970, all Waynesboro
boilers were fired with coal.  Since No. 6 fuel oil was plentiful and
reasonably priced, investment monies necessary to equip Waynesboro to burn
oil were authorized.  The compliance plan accepted by the State was to be
100% oil fired by the end of 1974.  In 1973 the Federal Energy Allocation
Act restricted the use of oil as a power generation fuel.  A review of the
situation considering the quadrupled price of oil and our dependence on it
for chemical feed stocks caused us to evaluate available technology to per-
mit burning coal and still meet the Virginia State Implementation Plan of
0.18# particulate/MM BTU input for our plant.  Electrostatic precipitators
were ruled out due to:

  •  Modular design not being available.

  •  Unacceptable roof loading requiring a cold end location.

  •  The low sulphur content in the coal we use.

     The baghouse route was selected and while basic concept designs and
project strategy were being developed we evaluated the two alternates -
pulse jet and reverse air cleaning.  The reverse air cleaning type was
selected and authorization to proceed obtained.  Rowan Perkins has pre-
sented a paper on the considerations used in selecting our baghouse.

     The full size Waynesboro installation is shown as a single filter in
Slide ^//l manifolded to handle gases supplied by four boilers.  Each boiler
has a bypass directly to the stack.  Under normal operation the individual
boiler induced draft fans pull the gases from each boiler and discharge them
to  the baghouse inlet breeching.  The booster fans maintain the 2" suction
at  the filter inlet and overcome the resistance of the filter, discharging
gases to the stack breeching.  Although we were reluctant to try rapid by-
passing of a boiler unnecessarily, circumstances have caused such bypasses
and the system has worked very successfully - several times.  There were no
disturbances of individual boiler controls.

     Slide #2 is a "before" picture of the Waynesboro Powerhouse.  The left
hand stack is handling the coal burning boilers.  The baghouse is under con-
struction on the right.  Neil Zittere was the Design Project Engineer and
deserves a great deal of credit for the nice looking and nice operating
unit.  Slide #3 is a picture of the completed installation in operation.
The same stack is still operating but you can see nothing.  This unit was
started up September 30, 1977.

     The elimination of the smoke is a result of a program which took 3
years to Define, Construct and Start up this baghouse and its auxiliaries.

SPECIFICATIONS

     The filter is 50' wide, 100' long and 70' high.  The system was de-
signed to handle 340,000 acfm of flue gas to clean the fly ash remaining
in the flue gas after individual high efficiency mechanical collectors

                                     373

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Specifications are as follows:
                                     2
  •  air to cloth ratio is 2:1 cfm/ft  of filter surface with 2 modules out
     of service.

  i  operating temperature is normally 340 QF with 415°F max.

  9  16 modules with 256 bags per module for a total of 4096 bags.

  *  bags are 8" diameter by 22" long with 5 anit-collapse rings.

  f  9.5 oz fiberglass material with a Teflon® B filter fabric finish
     (Slide #4)

  •  filter to operate under suction.

     The flue gas to be cleaned comes from 4 water tube pulverized coal
fired boilers with a total capacity around 600M/hr of steam.  The coal
we are burning is approximately 15% ash.  At rated load this is 66 tons
per day.  At present steam loads, the new baghouse collects 7 tons/day
while the remainder is split between furnace ash and that removed by our
mechanical separators.

     At Waynesboro we added extra instrumentation to find out more about
fabric filter operation.  Normal installations have manometers for measuring
pressure drop across each module.  We have added a pitot tube fixed in the
outlet of each module to indicate relative flow.  (Slide #5)  We wanted to
check the assumptions made on module performance as a result of differential
pressure only.  Already we have seen some indications that previous
assumptions are not 100% valid.  However, the individual single pitot
measurement is not as accurate as desired.  Further study will provide
better means to analyze fabric filter performance.  We are also equipped
to test outlet dust loading of each module.  All modules are equipped with
sight ports to inspect for ash from loose or damaged bags and to observe
bag cleaning.  (Slide #6)

START-UP SEQUENCE

     Having selected the type of baghouse with extreme care and evaluation,
we recognized that our goal consisted of 3 major items.

  *  A good smooth start up.

  •  Continuous operation firing coal, oil or a combination.

  •  Low maintenance and long bag life.

     We spent considerable time in the development of a start up pro-
cedure under the guidance of Rowan  Perkins , Niel Zittere and both
vendors, Western Precipitation (Baghouse) and Minardi Southern (bags) .
Preliminary check out of individual pieces of equipment and systems took
about 2 weeks.  (See Appendix 1 for problems.)

                                      374

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START-UP WEEK

     The first day was a final meeting within Du Pont among Operations,
Engineering Design and Power specialist group.  This included a step by
step review of our start up sequence and final modifications to adjust
for the actual operating configuration of the Powerhouse, physical
verification of actual conditions throughout the system and final adjust-
ments of controls.

     The second day finished the verification of baghouse conditions and
included a meeting with the baghouse and bag vendors to review their con-
cerns.  One of them was the looseness of the bags which indicated a need
to retension the bags in the entire unit.  All items were corrected and
by the end of the 3rd day we were ready to commit to start up on the 4th
day and ready to work long hours.

START-UP

     Our philosophy was that this would be the only start-up as the baghouse
was scheduled to be on line continuously.  Subsequent operations were to
consist of cutting modules in and out of service for maintenance.  Our
start-up procedure was very detailed and is contained in Appendix 2.

     Briefly, we assumed four boilers would be operating through their by-
passes with a total steam load of 300,000 Ibs/hr equivalent to flue gas
flow of 170,000 acfm (actual feet per minute).  While this requires only 8
modules we planned to use 12.

     We selected modules 6 and 8 to remain down.  The selection was dictated
as 2 and 4 were unbagged and we wanted to minimize outside wall exposure.

     We did not precoat the bags, but in order to minimize flue gas conden-
sation on the bags; the baghouse and breeching temperatures were brought up
using gases from one operating boiler through the 2 empty (unbagged) modules
number 2 and 4.  All other modules were closed off.

     Modules with bags were then brought on line using flue gas at normal
temperatures and with fly ash having normal characteristics.  Boiler loads
and baghouse parameters were used as criteria for selecting the number of
modules required as each additional boiler was put into the system.  We
continue to use these parameters.

     Start-up was smoothly accomplished (with no long hours) during the
week of 9/26/77, three months ahead of schedule and yielded a savings of
$120M by burning 100% coal instead of 80% during  4Q77.  Performance was
and is extremely satisfactory with no plume.  Optical instrumentation
monitoring the stack reads 2% when the baghouse is used as designed.

OPERATIONS

  •  This was the smoothest start-up Western Precipitation had witnessed
     due to advance preparations which included:

                                       375

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   -  one year studying start-up and operation of other installations

      2 man months writing start-up and operating procedures involving
      a total of 6 people at various times.

      Construction follow-up by operating supervisors and engineers
      with documentation of tests and checks.

i  We eliminated changes in the booster fan loading due to reverse-air
   cycling by taking the reverse air suction off after the booster fan
   discharge.  Now the cleaning cycle does not disturb booster fans or
   boilers and controls operate satisfactorily.

•  Mechanically we have had by-pass damper problems associated with
   both design and construction.  Lack of rigidity in design and some
   welding not done during fabrication.

•  We have proven the booster fan control concept.  Boilers can be by-
   passed without upsetting the boilers.   This is a first in control
   design.  No changes were made in boiler controls.

*  A performance test was run 8/29/78.  The delay was required to
   correct the leakage between the thimbles and the tube sheet at the
   entrance to bags.  Slide #7 and #8 show the sealing compound used
   to accomplish sealing.  The average emission was 0.0036 gr/A ft ,
   which is 0.011 #/MM BTU and well below the State required 0.18#/MM
   BTU and less than .01 grains per actual ft3 air, our contractor
   guarantee.

f  Normal AP is maintained between 3" and 6" across the baghouse or 2"
   to 3" across the bags themselves.  Reverse-air cleaning is varied to
   accomplish this and varies from once every 12 hours to continuous,
   depending on boiler loads and ash content.

•  Bags have been successful and operate well with an estimated average
   life of 5 plus years.  One module is equipped with bags of woven
   Teflon® fibers as a test for Company fabrics.

•  Tests also indicate that there is the same relative particulate size
   distribution on inlet and outlet.  (Electrostatic units do not filter
   the smaller particles.)

•  We are selling fly ash from the baghouse for light-weight concrete
   products.

t  We had an increase of /A P across the baghouse to 6" which required
   putting the 13th module in operation.   Our plan is to individually
   clean the bags in each module that has been on line.  Cleaning will
   be done by removing modules from service but leaving the bags in
   place while they are air blown from top to bottom.

                                    376

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  •  The filter is automatically bypassed if inlet gas temperature exceeds
     450°F,  or if inlet suction drops below 0.5 in.  An automatic atmospheric
     damper  prevents implosion of the filter house in case of sudden bypass.

  •  Individual boilers are bypassed if furnace draft remains above 0.1"
     for 10  seconds.

MAINTENANCE

     There have been a total of 35 bags replaced since January 1, 1978.
Twenty-nine  (29) of the defective bags have been in either Module No.
10 or No. 12.   These modules were included in the initial start-up but
were removed from service after one or two weeks of service in an attempt
to raise the gas temperature on the baghouse.  They were left closed and
it appears that there was flue gas leaking into these modules that set
up an acid condition, loss of bag material strength due to acid attack.
Procedure for removing modules has since been changed to having doors open
on idle modules, thereby maintaining a slight in-flow of air through
dampers so as to prevent leakage of flue gas into the idle units.  There
have been two bags replaced in No. 1 Module which has the "Teflon" bags
and these bags appeared to have been installed improperly.  One bag has
been replaced in No. 16 Module which was caused by a bent thimble that
may have torn the bag on initial installation.  Recently, three bags had
to be replaced in Module No. 9 due to small holes.  We feel this must have
been unnoted installation damage as no other causes are apparent.

     Module entry has been a question in some minds with the reverse air
type baghouse.  The modules are removed from service by closing the inlet
and outlet dampers.  Installing a fan in the valve access door located on
top of the module and opening the lower access door provides a purging flow
of air.  Heat flow from adjacent modules is reduced by insulation between
modules.  After a few hours of module cooling with purge fan in operation,
bag replacement can be accomplished by the mechanic in cool air.  Dust
masks are worn because there is some dust on the clean side.

     Safety is maintained by following these safety steps:

  •  Isolating the module, locking it out, obtaining an air analysis
     inside the module.

  •  Defective bags must be located and then dust cleaned from floor
     to prevent entrainment when returned to service.

  •  Bag replacement requires 3 mechanics:  one top, one bottom and a
     standby exterior to the module.

     Our major maintenance efforts have been associated with the fly ash
removal system including the bag filter connected to the ash removal
system.  Most of the problems are the results of the ash being damp and
causing line and equipment pluggage.  These problems seem to have been
greatly reduced due to enclosing the equipment on top of ash silo and
insulating the electrically traced module hopper discharge valves.

                                      377

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     This brings us up-to-date.  We are continuing to learn the fine points
of operating and maintaining our $6MM vacuum cleaner and anticipate finding
out more of its capabilities as time goes on.

GENERAL EXPERIENCES

1.  Tests were run of mixed coal and #6 fuel oil firing in early 1977
    using a reverse-air type pilot baghouse.  Using flue gas from coal and
    #6  oil at a 50-50 ratio, tests indicated that the pressure drop build
    up while filtering and regain after cleaning was better than straight
    coal firing.  No adverse effects were noted even at low gas gemperatures.
    We have passed the flue gas from our large boilers at various ratios of
    coal and both #2 and #6 flue gas oil firing up to 50-50 ratio through
    the baghouse without seeing any detrimental effect on filtering pressure
    drop or regain after cleaning.  No bag failures or "smearing" have re-
    sulted.

2.  There is still some water leakage in and around the valve boxes.  We
    have located a sealing material which expands to fill a void and plan
    to evaluate its ability to seal the leaking joints.

     This baghouse is now an integral piece of operating equipment that
will stay efficient.  We have 3 other RA fabric filters in the Company which
are giving comparably good performance.
                                         378

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                                                     APPENDIX 1
                            CHECK OUT - PROBLEMS


     This phase was continuous through out the construction and even then
we found problems at the end.  The main problems were:

  •  The isolation of individual cells to assure good filtering, bag
     cleaning during continuous operation, and satisfactory isolation
     for maintenance.  This involved checking of actual clearance be-
     tween each valve disk and its elastomeric seat over the entire
     mating surface.  In-place grinding and minute final adjustments
     took days.

  i  Bag installation and tension, 38#/bag, to assure support that
     permits normal ballooning and collapsing during operation,  Since
     the bags had been installed several months previous to start up,
     retensioning was required throughout the unit.

  •  Control sequencing - including the coordination of all the automatic
     valves from the panel board used in reverse-air cleaning as well as
     the controls for the booster fans.

  i  Ash removal system was designed to handle hot, dry, free-flowing ash
     and did not operate well initially.  Line and separation gate pluggage
     was severe until we corrected deficiencies such as leaking gates and
     insufficient insulation.  Initial startup residue had to be cleaned
     off hopper slope sheets.  Knife edge gates were used finally.

  •  Internal leakage - This last problem was solved 9 months after start-
     up.  It involved the loss of the seal where the lower bag thimble goes
     through the tube sheet.  With our assistance the vendor sealed the
     leak between thimble and tube sheet with a hardening liquid called
     Pelmor®.  This is a liquid suspension of Vitron® elastomeric material.
        Registered trademark Pelmor Laboratories
                                      379

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                                                     APPENDIX 2
                          BAGHOUSE START-UP DETAILS
POWERHOUSE OPERATING CONDITIONS

  «  Boilers 2, 3 and 4 - 200,000 stm/hr total.

  •  Boiler 1 - 100,000 Ib stm/hr.

START-UP PROCEDURES

1.  Check Modules 1, 3, 5, 6, 9, 19, 11, 12, 13, 14, 15 and to to assure
    that the inlet and outlet isolation dampers are closed.  Flapper
    valve box should be open to the outlet, closed to reverse-flow duct.
    Inlet and outlet dampers to Modules 6 and 8 are to be locked shut.
    No booster fan on standby.

2.  Inlet and outlet isolation dampers of Modules 2 and 4 should be wide
    open.  Flapper valve in the module valve box should be open to the
    outlet and closed to the reverse-flow duct.

3.  Open inlet and outlet isolation dampers of south and middle (Nos. 3
    and 2) booster fans.  Close inlet control dampers on the control panel.
    (They will be automatically closed when the fans are down, put will
    open rapidly when the fan starts.)

4.  Set the No. 1 bypass damper to the location (open) to give the desired
    start-up condition.

5.  Set atmospheric vacuum relief valve open.

6.  Start the south (No. 3) booster fan.  With the baghouse suction  con-
    trol (fan inlet damper control) on manual and closed, start the  fan.
    Adjust vacuum relief valve and fan inlet damper to obtain 2" suction
    at the baghouse inlet.

7.  Place No. 1 Boiler on manual  control.  Assure personnel are out  of  #4
    Boiler while damper is switched.

8.  Gradually close the No.  1 Boiler bypass manually  (highest temperature)
    (Gas will flow through Modules 2 and 4, which have no bags, to permit
    full warm-up of the inlet and outlet breeching.)  Gradually close
    vacuum relief valve to maintain 2" suction.  Open booster fan inlet
    damper as necessary.
                                       380

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 9.   Carefully observe No. 1 furnace suction and baghouse inlet suction
     as the bypass transfer is gradually completed.  Adjust baghouse
     suction control (booster fan inlet dampers) and vacuum relief valve
     to maintain -2".

10.   Close vacuum relief valve if not already closed.

11.   When fan inlet control damper is maintaining 2" suction at the bag-
     house inlet, place suction control on automatic.  Observe its
     operation to assure even control.  Adjust control sensitivity as
     necessary.  By this time the bypass damper on No- 1 should be closed.

12.   Carefully observe the warm-up and expansion of the breeching and
     Modules 2 and 4.   Reference indicators have been installed at many
     points.  Particular attention should be paid to the compression of
     expansion joints.  Note the temperature rise at the baghouse outlet
     using the boiler  control board temperature recorder.

13.   When (1) the booster fan controls are operating properly to maintain
     2" suction at the baghouse inlet, (2) the proper furnace suction is
     maintained in the No. 1 Boiler, and (3) the baghouse outlet temperature
     has leveled off (should be 10-25°F belox
-------
     b.   Reactivate the baghouse by following Steps 8 and 9.

             After approval by W. R. Denney (Powerhouse Supervisor)

     c.   Trip the bypass to place the gases to the stack to determine
         all responses.  Be careful to observe all furnace fluctuations
         in No. 1 Boiler and be prepared to kill the fires if necessary.
         Relighting and retrials can be made to determine responses  and
         best procedures.

     d.   Close bypass gradually without closing vacuum breaker to check
         booster fan pick up.

             When satisfied that the booster fan and all controls operate
satisfactorily, proceed to to add more boilers to the baghouse.

19.  Open the inlet and outlet dampers to Module 9 and 10-  This may
     cause a change in baghouse differential (l\ P) , so be sure  the
     suction control damper is holding proper suction.  (Check the
     flow indicators.  Modules 3, 5 and 7 will probably be less  flow
     than Modules 9 and 10.  If there is more than a 2:1 difference
     in flow, open the inlet and outlet isolation valve to Module 11.)

20.  Observe the warm-up of the additional modules.  Observe both the
     expansion clearances and the temperature increase.

21.  Gradually close the bypass damper of Boiler No. 3 while watching
     the baghouse suction (maintain -2") and the furnace suction.  (If
     long delay, reverse Step 19.)

22.  When the bypass damper is closed, observe the temperature rise  of
     the baghouse outlet.  (It should have dropped when the new  modules
     were added but should return to normal, 10-20°F lower than  the  inlet
     temperature.)  Continue to observe the flow indicators to Modules  3,
     5,  7, 9 and 10.  They should tend to equalize.

23.  Be sure the inlet control damper and automatic/manual control station
     on the middle (No. 2) booster fan are closed.  (The inlet and outlet
     isolation slide gates were opened in Step 3).

24.  Start the No. 2 booster fan, observing the effect on the suction of
     the No. 3 fan.  Inlet dampers may close somewhat to maintain 2"
     suction in the baghouse inlet.

25.  Gradually open the inlet control damper on the No. 2 fan.  The auto-
     matic control on the No. 3 fan should gradually close to maintain
     suction at 2".
                                      382

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26.  When the control positions for both fans are the same, place No. 2
     fan on automatic and observe automatic control of the baghouse
     suction.

27.  By this time the differential of the operating modules may have in-
     creased to the point where cleaning is desirable, say 1-2".  If not,
     continue to Step 27.

     a.  If so, add another module (11 or 12) per Step 19.

     b.  Adjust the timers and controls to clean Modules 3, 5, 7, 9, 10
         and 11 for settling periods of 40 sec. and one cleaning period
         of 40 sec.  Do not clean modules with lower A P.

     c.  Start one reverse-flow fan.  (The inlet should be throttled to
         use a minimum flow and pressure.  Several trials may be necessary.
         The pressure and flow should be no more than necessary to effect
         the desired cleaning.)

     d.  Operate the fly ash removal system on hoppers of cleaned modules.
         Check ash suction to be sure all are emptied.

             Conduct step * only on request of W. R. Denney (Powerhouse
Supervisor).

*    At this time, various other items can be tried - switching between
     fans (removing the No. 2 booster fan from service and cutting it
     back in) and both gradual and sudden bypass damper operation.  With
     both fans in operation, proceed.

28.  Open the inlet and outlet dampers of the next two modules (11 and
     12, or 12 and 13).  Closely observe the baghouse suction controls
     to assure maintenance of the 2" baghouse suction.

29-  Gradually close the bypass damper of boiler No. 2,   Check bypass
     damper operation.

30.  When the bypass damper is closed, observe the baghouse outlet
     temperature.  (It should have dropped when the new modules were
     added but should return to normal 10-20°F lower than the inlet
     temperature.)

Continue to add modules

31.  Open the inlet and outlet dampers to the next two modules (12 and
     13 or 13 and 14).  Observe that the controls to the fans maintain
     the 2" suction.
                                       383

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32.   Gradually close the bypass damper of No.  1 Boiler.   Observe the
     baghouse suction controls.  Check bypass damper operation and travel.

33.   When the bypass damper is closed, observe the baghouse outlet
     temperature.  (It will have dropped when the additional modules
     were opened but should level out 10-20°F below the  inlet temperature.)

34.   Open the inlet and outlet dampers to the remaining  modules (14 through
     16).  Observe the suction controls.

             After baghouse is operating successfully with all boilers:

35.   Shut down #4 Boiler.

36.   Observe the baghouse outlet temperature.   It should level out 10-20°F
     lower than the inlet.

37.   Set the cleaning for all modules at one cycle with  40 sec. settle
     and 40 sec. clean.  Operate single cycle at 40 sec. to maintain
        P between 3" and 4".

38.   Operate fly ash hopper cleaning system.  Check for  proper pulling
     of all hopper.
                                       384

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                                 REFERENCES
 "Case for Fabric Filters or  Boilers" by R.  P.  Perkins.   Presented  at
  Massachusetts-APCP,  Philadelphia 1976.

2
 "Consideration in the Start-Up of Baghouse  in  Coal Fired Boilers"  by
  R.  P. Perkins,  presented at Second Annual  Filter Fabric Alternatives
  Conference,  Denver 1977.
                                      385

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  L_

     f. 0. FANS
99
                                  »y PASS
                       23*5
"SLIDE 1"   WAYNESBORO  BAG  FILTER SCHEMATIC
 "SLIDE 2"   WAYNESBORO POWER COMPLEX BEFORE
                       386

-------
 "SLIDE 3"   WAYNESBORO POWER COMPLEX AFTER
FIBERGLASS  WITH  TEFLON ^COATING
       "SLIDE 4"   BAG MATERIAL SAMPLE
                 387

-------
   MODULE  PITOT TUBES
   "SLIDE 5"  ADDITIONAL INSTRUMENTATION
I
       "SLIDE 6"  MODULE SIGHTGLASS




                388

-------
"SLIDE 7"   SEALING WITH PELMOR®
"SLIDE 8"   SEALING WITH PELMOR®
            389

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A NEW TECHNIQUE FOR DRY REMOVAL OF
                  By







      C.C. Shale and G.W- Stewart




  United States Department of Energy




  Morgantown Energy Technology Center




    Morgantown, West Virginia 26505
              August 1979
                 390

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                                  ABSTRACT
    Experimental studies are reported on a technique for SO  flue gas control
                                                           X
using a dry limestone sorbent and humidification control of the flue gas.
Kinetic studies of this "modified dry" limestone process (MDLP) show reaction
rates equivalent to high temperature fluid bed processes. SO  removal
                                                            X
efficiency is shown to increase as the water saturation temperature of the
"conditioned" gas increases. At a saturation temperature of 150 F one can
obtain >90% SO  removal from a flue gas stream containing 1600 ppm S09.
              X                                                      £-
Results of economic analysis based on both a moving bed and a counterflow
design are presented.
                                     391

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                   A NEW TECHNIQUE FOR DRY REMOVAL OF SO

                                INTRODUCTION

    Lime/limestone scrubbing is presently considered the best available control
technology (BACT) for flue gas desulfurization, but most wet methods have
characteristic problems of high cost and low reliability. Dry alkali injection
has "been proposed as a potentially viable alternative to wet scrubbing for flue
gas desulfurization (FGD). The concept of dry alkali injection is simple and
involves two basic operations: 1) injection of reactant, and 2) removal of
solid reaction products. The reactant may be injected as a dry powder, a
solution of a soluble alkali, or possibly as a slurry of a relatively insoluble
alkaline earth compound. If introduced as a solution or slurry, the liquid
evaporates almost immediately and leaves a suspension of finely-divided solids
in the gas phase, which is very similar to that created by the dry injection
technique. Subsequent reaction of the suspended solid particles with sulfur
dioxide produces solid sulfite and sulfate particles that are admixed with
fly ash and unreacted alkali. Removal of these dry solids is effected by a
filter (moving-bed/baghouse) or an electrostatic precipitator.

    Independent studies (Dickerman et al., 1978)   have demonstrated that dry
sodium compounds, such as soda ash, trona, or nahcolite, are the preferred
reactant(s) for this mode of FGD because of their high chemical reactivity.
Results of tests using lignite as a fuel show that sodium salts can absorb
approximately 80 percent of the sulfur dioxide from a gas wherein the solids
have a short resident time (~3 sec.). Product solids are then removed in an
electrostatic precipitator. If these solids are removed in a bag filter,
however, additional contact time between the gas and solids is provided and
can result in higher removal efficiencies. The combination of the two processes
(dry injection and filtration) has been used to provide up to 99 percent removal
                       2
for S0? (Dustin, 1977) .  Use of powdered lime/limestone in this mode of treat-
ment normally results in ineffective removal of SO , i.e.,<50 percent (Bechtel
             3
Corp., 1976).

    By-products from reaction with sodium salts consist of sulfur-bearing
particles  that are water soluble and can result in contamination of ground
                                      392

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water unless special precautions are taken. One way to avoid water contamination
is to treat the sulfur-bearing sodium particles with a lime/limestone slurry.
This converts the soluble sulfur compounds to relatively insoluble calcium
sulfate (gypsum), thus producing a solution of sodium salts which is available
for recycle. This combined treatment increases process costs. Further develop-
ment of this dry method for FGD, however, could possibly result in a decrease
in overall processing costs and may improve equipment reliability when compared
to existing BACT.

    Studies conducted at the Morgantown Energy Technology Center (METC)
indicate  that  a new approach, using water vapor to "condition" the flue gas,
may be effective in removing S0_ from a cooled gas stream. The patented technique
                       4                                                 o
(Shale and Cross, 1976)  involves adding water vapor to hot flue gas (300 F) to
increase  the saturation temperature of the gas above a critical minimum and
then cooling the mixture to a predetermined temperature near the adjusted dew
point. Under the conditions studied, it has been shown that greater than 90
percent of the SO. can be removed using small pellets (up to 1/2-inch) of
crushed limestone in a dry bed. The process is called the modified dry lime-
stone process, or MDLP. Through direct use of limestone, a dry, relatively
inert sulfur product (gypsum) can be produced without the need for secondary
processing of soluble salt solutions. This process has the potential of
providing several economic benefits.

                          EXPERIMENTAL PROCEDURES

    Both  laboratory scale and bulk evaluation studies have been conducted on
MDLP. The laboratory studies were performed using a Mettler DTA-TGA instrument
in which  kinetic parameters were obtained by observing the change in weight
of limestone as a function of time. The apparatus and experimental procedures
have been described in an earlier publication (Nesbitt et.al,  1978).  The
gas stream consisted of 2.5-7.0 percent SO-, 2.0 percent  02> and the balance
nitrogen. Limestone pellets ranged in weight from 590 mg.  to 810 mg. The

                                         393

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porosity and surface area of the pellets were monitored and held constant
such that observed changes were the result of a chemical interaction, not
changes in physical properties. The stream humidity was determined by a wet
bulb thermometer and held at the saturation level. Chemical analyses of the
solid product was performed by IR, SEM, X-ray flourescence, and ESCA. All
analyses were consistent in that 1) calcium sulfate was the major product,  and
2) reaction occurred on the pellet surface.

    Bulk absorption studies were performed on limestone beds 1-inch diameter
x 9- inch deep and 1/2-inch diameter x 4-inch deep, using 1/16 x 1/2-inch
pellets. Gas flow rates were controlled between 1 and 3 scfh and were monitored
by a gas flowmeter. The pressure drop across the beds varied between two inches
of water at the beginning and up to eight inches of water at the end of
individual tests. Pressure loss increased because of water deposition on the
limestone and the physical particle enlargement resulting from chemical reac-
tion. For all studies the gas mixture was 14 percent CO., 4 percent 0 , 0.15
to 0.3 percent SCL and the balance N_. Analysis of the S0_ removal was deter-
mined by commercial gas detector tubes. The tubes were sensitive to water,
and the reliability was ±25 percent of the indicated value. Any SO- level
below 1 ppm was below the detection limit of the detector.

    The bulk investigative tests for this system were conducted in equipment
depicted in Figure 1. Simulated flue gas containing up to 3000 ppm sulfur
dioxide flowed at a controlled rate through a heater, a heated saturator, and
a fixed bed of selectively-sized limestone and was exhausted into a hood. In
the experimental program, the gas  flow rate, temperature, moisture content,
and sulfur dioxide concentration were controlled as process variables. Two
limestones and two dolomites of variable particle  (lump) size were tested in
beds of different diameters and depths to allow for a range in space velocity.

    After having established steady state thermal  conditions using a selected
flow rate of dry gas through the system, a controlled flow rate of water was
                                        394

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added continually  to  the saturator  to  establish a controlled level of moisture
in the "conditioned"  gas for  each absorption  test.  Heat  added  to  the saturator
insured complete evaporation  of  all water.  The dry  gas was heated to 280°F and
passed through  the saturator  prior  to  entry into the bed of crushed stone. The
gas cooled during  saturation  and flowed  through the limestone  bed at a temper-
ature of  150  to 160°F  and  a  space  velocity of 500  vol/vol/hr.
                           RESULTS AND DISCUSSION
   Thermogravimetric studies  on  single  limestone pellets indicate that S02
 removal  efficiencies would be a maximum for  a saturated stream temperature
 of 110-120°F.  This  can be correlated to the  sorption of S0_ in H20 as a
 function of  temperature.  The sorption  of SO- in H-0 has been shown to decrease
 rapidly  as the temperature increases.  In addition, thermogravimetric studies
 show no  observable  weight. gain  in the  temperature range of interest unless
 water is present. Therefore, it is fortuitus that the optimum conditions for
 MDLP coincide  with  actual gas stream conditions.
    A representative weight gain curve for water and S09 absorption is shown
in Figure 2. Kinetic  parameters were obtained using the initial rate method.
For this study the following stoichiometric equation was assumed for the
rate controlling step:

    a A (gas) + s S  (solid)^-a A (gas) + s S  (solid)             (1)
     rr         rr           pp         pp
where a and s are the stoichiometric coefficients for gases and solids, and
r and p represent reactant and product. It was assumed that both diffusional
and mass transfer resistance were negligible such that the initial reaction
rate can be represented as:

                     R  = a  k  C   Cn                             (2)
                      o    r  s  s   a
                                  o   o
where R  is the initial molar rate of reaction of the gas per unit surface
       o
area of the solid, k  is the rate constant per unit area, C   is the initial
                    s                                      So
                                       395

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molar concentration of the solid, C   is the molar concentration of the gas
                                   3
                                    o
and n is the reaction order with respect to the gas.

   - It can be shown that the initial reaction rate can be calculated from
the weight gain curve by using the following equation (Westmoreland, 1977)
          (ar/sr)   (dw/dt)o                            (3)
R°=   ^
                              +  (a' /a )M 1
                           r       p  r ' pJ
where  (dw/dt)  is the initial slope, m  is the initial mass of the solid
reactant, a  is the specific surface area of the solid and M  and M  are
           o                                                p      r
molecular weights of the solid product and reactant.

    The reaction rate, as determined by equation (3), is used to determine
the order of reaction with respect to the concentration of the reactant gas
and the reaction rate constant as specified in equation (2). The reaction
was found to be first order in S02 concentration and to obey the classical
Arrhenius relationship
                            k  = A exp (-E /RT)                    (4)
                             S            3.
where  A is the Arrhenius factor, E  is the activation energy, R is the gas
                                  3.
law constant and T is the absolute temperature. Thus, by plotting In k
                                                                      S
versus 1/T it is possible to determine both A and E  .
                                                   3

    The calculated intrinsic rate of reaction (R ) and the initial rate of
                                                o
change (dw/dt)  are given in Table I. From these data the  intrinsic rate
constant can be calculated using the initial limestone concentration
         -2         3
(2.7 x 10   moles/cm ) and the water concentration at the  gas stream
temperature. The intrinsic rate constants evaluated by equation (2) with
n = 1  were found to obey the classical Arrhenius relationship under the
observed conditions where mass transfer resistance was negligible.
                                        396

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    To obtain the reaction order with respect to the concentration of
sulfur dioxide, experiments were performed in which the SO  concentrat
was varied from 2.5 to 7%. A plot of the initial rate of weight gain of SO
concentration at different temperatures is shown in Figure 3 . The linear
dependence indicates that the reaction is first order in SO- concentration.

    A mechanism consistant with the experimental kinetic parameters is
as follows:

               S02 + H20(ad) •+ IH2S03] j H* •* HS03~ •* 2E* + S03=
               HS03~- + -%02 j HS04"
               CaC03 + HS04~ £ CaS04 + BC03~
               EC03~ + H* •* H20 + C02

    This mechanism involves an acid-base reaction in which sulfur dioxide
is dissolved in an adsorbed water layer. The pH conditions in the stream
                           _                           _                   -j
favors the formation of HSO  and are unfavorable for SO  }  (Schroeder, 1966) ,
               8                —
(Roberts, 1979) . Therefore, HSO,. is considered the dominate species. It is
proposed that  the HSO  is oxidized to HSO, by dissolved oxygen present in  the
adsorbed water. This reaction has been shown to be governed by a free radical
mechanism and  thus occurs rapidly in solution (Schroeder,  1966)  . Small
impurities of iron and/or copper present in the limestone have also been shown
                                       9
to catalyze this oxidation (Rand, 1965) . The calcium carbonate subsequently
reacts with HSO, to form calciun sulfate and bicarbonate ion. The bicarbonate
               4
ion reacts with a proton to form C0~ and water.  This mechanism predicts first
order kinetics which has been verified experimentally. The product proposed
by this mechanism is CaSO, which has been verified experimentally by IR and
ESCA analysis.

    For practical considerations it is interesting to compare the kinetic
parameters obtained for the modified dry limestone process with the kinetic

                                        397

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parameters obtained in the reaction of calcined limestone with S09
                 10
(Borgwardt, 1970)  . As seen in Table II, the activation energies and
rate constants are very similar for the two processes.  This similarity is
fortuitious since the processes occur at greatly different temperatures and
the Arrhenius plots are not continuous. However, since the calcined lime-
stone process is economically viable with other techniques, it seems reasonable
that MDLP may also be economically viable with other FGD processes.

    Bulk studies were performed using conditions similar to those used for
the thermogravimetric studies. The effect of saturation temperature on S07
removal efficiency is shown in Figure 4. At a space velocity of 500 v/v/hr,
an S0_ concentration of 1600 ppm, a gas temperature of 150 F, and a saturation
temperature of 100 F the S09 removal efficiency is ~90% for approximately
30 min. and then drops off rapidly with an increase in exposure time.  These
conditions simulate a stack gas from a conventional coal-fired combustion
source burning a 2% sulfur coal and having an exit gas temperature of 150 F.
At the higher removal efficiencies the uncertainty in data is considered to
be ±5%. As the saturation temperature increases from 100 F to 150 F the
maximum removal efficiency is maintained for longer periods of time. Note
on curve 2 that after ~2.5 hours, the moisture content of the gas was increased
from a level corresponding to a saturation temperature of 110 F to that of
120 F. The subsequent increase in SCL removal efficiency is consistent with
the overall variation of removal efficiency with moisture content. At a sat-
uration temperature of 150 F a removal efficiency of ^90% was maintained for
at least 3.5 hours using a bed of Greer limestone. Tests with other lime-
      11              12
stones   and dolomites   show a similar high level of induced chemical activity
upon additions of water vapor to the simulated gas stream.  The effects of
moisture on increasing the S0~ removal efficiency have also been observed by
                                     13
workers at Battelle (Rosenberg, 1979)

    Experiments at higher space velocities (4,000 v/v/hr) have shown that
SCL removal efficiencies of >90% can be achieved when the gas is at complete

                                         398

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saturation, that is, the water vapor saturation temperature is no more than
30 F below the actual gas temperature as it flows through the fixed bed. For
these studies the SO. concentration in the test gas was 1400 ppm.
    Examination of the limestone at the completion of each test showed that
the pellets were covered with a relatively thick, soft shell of reaction
products. After partial drying of the pellets the product layer could be
removed by mild agitation leaving the harder unreacted core of limestone.
Analysis of the initial limestone reaction product and the unreacted core
are given in Table III. From these results it is apparent that the shell is
composed of calcium sulfate plus some unreacted calcium carbonate. Earlier
                               4
reports  (Shale and Cross, 1976)  estimated that ~90% of the limestone was
utilized in the reaction. However, a more recent reevaluation of the original
data suggest that the actual utilization of the limestone is somewhat lower.

                                                              14
    A preliminary analysis by the Cost Evaluation Group (1971)   of the
U.S. Bureau of Mines, using only the data obtained from the bulk studies,
indicated that capital and operating costs for MDLP could be as much as
40 percent less than  corresponding costs for removal of SCL by lime/limestone
wet scrubbing systems when a cross-flow moving-bed concept is utilized for
the dry absorber. The conceptual design used for this study is shown in
Figure 5. A more recent cost analysis has been conducted by TRW (Rao, 1978)
which is based on both the bulk studies and the thermogravimetric studies.
This latter study, however, uses a concept based upon a counterflow moving-
bed which characteristically consumes an excess of energy in pressure loss
through the absorber. This study shows capital and operating costs for MDLP
in excess of those for lime/limestone scrubbing.  The use of dry sorbents and
fabric filtration in FGD systems has been evaluated in a report by TRW for EPA
(Lutz et. al, 1979)  . The capital cost for a dry solvent system utilizing
nahcolite was found to be approximately 40% of that for a lime/limestone
scrubber system while the operating costs were estimated to be approximately
equal.  Adaptations of MDLP to a dry injection technique might offer similarly
induced capital costs.
                                        399

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                                  CONCLUSIONS
    Kinetic studies indicate that limestone is an effective sorbent for SO
in moisture laden flue gas streams. Rate data indicate that the reaction
process is first order in SO  concentration and is reaction rate limited. The
prodjucts from this reaction are gaseous C09 and solid calcium sulfate. The
rate of SO,, removed by MDLP is comparable to the higher temperature fluid
bed processes and unlike the low temperature lime/limestone scrubbers, MDLP
produces a solid waste product. It is also evident from the experimental
studies that the duration of enhanced removal efficiency increases as the water
saturation temperature of the "conditioned" gas approaches the actual gas
temperature of 150 F. At substantially complete saturation, removal
efficiencies of~90% are achieved over an extended period of time.
    Whereas the saturation temperature of combustion gas from coal is about
95  to 100 F (depending on the age of the coal), combustion gas from oil firing
is saturated at about 110°F, while the product from gas firing is saturated at
about 130 F. The high moisture content of combustion gases from a natural gas-
fired source would appear to make this gas ideally suited to cleanup of sulfur
dioxide by dry limestone, without modification, as indicated by the data
given previously in Figure 4. The saturation temperature of gases from oil-
and coal-fired sources, however, is below the established critical minimum
(120 F), so the dew point of these gases must be adjusted to a higher level
for effective application of this sorption technique. Through addition of
adequate moisture and through adequate control of temperature, as specified for
MDLP, a properly "conditioned" gas can in principle be produced from any fuel,
thus yielding the maximum removal efficiency for sulfur dioxide.

    Preliminary economic evaluations have been made on the modified dry lime-
stone process. Early evaluations made before the kinetic data were available and
using a moving bed design were quite favorable. However, a later evaluation
which included the kinetic data and a counter flow design indicated a negative
energy incentive. Favorable capital and  operating costs have  been  found for
nahcolite by dry injection techniques. The possible  use of a  dry  injection/MDLP
                                     4QQ

-------
technique might offer similar advantages and thus needs to be evaluated.
Since each assessment is extremely dependent on the engineering design used,
a detailed systems analysis must be performed before any final conclusions
as to possible economic advantages or disadvantages can be made.
    Additional experimentation is needed to assess the efficiency of a limestone
bed on particulate removal and as a combined NO /SO  removal device. Numerous
                                               X   X
studies have been reported in which calcium salts and sulfite/bisulfite ions
were responsible for the catalytic decomposition of nitric oxides  .  Evidence
for combined NO /SO  removal would greatly  enhance the interest  in MBLP.
               A
                                        401

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                                 REFERENCES

 1.   Dickerman,  J.C.  et al.   Evaluation of Dry Alkali for FGD Systems.  Prepared
     for Pacific Power and Light Company and Public Service Company of Colorado by
     Radian Corporation, Austin, TX.  March 1978.

 2.   Dustin, D.  F.  Report of Coyote Pilot Plant Test Program.  Test Report,  Canoga
     Park,  CA, Rockwell International, Atomics International Div. November 1977.

 3.   Bechtel Corporation.  Evaluation of Dry Al*kalis for Removing Sulfur Dioxide
     from Boiler Flue Gases.  Electric Power Research Institute, Palo Alto,  CA,
     EPRI FP-207.  October 1976.  Pages 18 and 19.

 4.   Shale, C.C., and W.G. Cross.  Modified Dry Limestone Process for Control of
     Sulfur Dioxide Emissions.  U.S. Pat. 3,976,747.  August 24, 1976.

 5.   Nesbitt, F.L.  Kinetic Study of Flue Gas Desulfurization by Limestone.   Thesis,
     Graduate School, West Virginia University, Morgantown, WV.  1978.

 6.   Westmoreland,  P.R. et_ _al_.  Comparative Kinetics of High-Temperature Reaction
     Between H S and Selected Metal Oxides.  Environ. Sci. Technol. 11:488 (1977).

 7.   Schroeder, L.C. Sulfur Dioxide.  New York, Permagon Press, Inc., 1966.  p. 63.

 8.   Roberts, D.L.  Sulfur Dioxide Transport Through Aqueous Solutions.  Ph.D Thesis,
     California Institute of Technology, Pasadena, CA.  January 1979- p. 165.

 9.   Rand, M.C. Principles of Applied Water Chemistry.  In: Proc. Rudolfs Res. Conf.
     4th, Rutgers State Univ., 1965.  p. 380.

10.   Borgwardt, R.H.  Kinetics of the Reaction of SO  with Calcined Limestone.
     Environ. Sci.  Technol. 4:59 (1970).

11.   (a) Greer Limestone Ca., Morgantown, WV.  (b) Limestone No. 1359, Grove Limestone
     Co., Stephens City, VA.

12.   (a) Dolomite No. 1341.  Environmental Protection Agency, Department of  Health,
     Education and Welfare, Cincinnati, OH  45227.
     (b) Charles Pfizer and Co., Inc., Minerals, Pigments, and Metals Division, Gib-
     sonburg, OH.

13.   Rosenberg, H.S. Chemical Process Development Section, Battelle Columbus
     Laboratories, Columbus, OH.  Personal communication.

14.   Process  Evaluation Group.  Modified Dry Limestone Process for Removal of  SO.
     from Powerplant Flue Gases, An Economic Evaluation.  Report  No.  71-26,  U.S.
     Department of the  Interior, Bureau of Mines.   February 1971.
                                       402

-------
15.   Rao, A. K. Modified Dry Limestone Process  Engineering Assessment, Morgantown
     Energy Technology Center, Department of  Energy.   Prepared by TRW Energy Systems
     Planning Division, Morgantown, WV.  September 1978.

16.   Lutz, S.J. et_ a^.  Evaluation of Dry Sorbents and Fabric Filtration for FGD.
     EPA-600/7-79-005, Prepared by TRW,  Inc., Durham,  NC for Industrial Environmental
     Research Lab. Research Triangle Park,  NC,  Jan.  1979.

17.   For example, see English Patent No. 1,134,881.  November 27, 1968.
                                    TABLE  1
                     KINETIC PARAMETERS  FOR THE ABSORPTION

                             OF H20+S02  ON  LIMESTONE
                         E   =13.0 kcal/mole
                         3.
  Temp ( c)         (dw/dt)Q            R   (mole/mg min)         kg (cm /mole min)


     35               .140               2.4xlO~9                      113

     38               .181               2.8xlO~9                      133

     43               .309               3.8xlO~9                      212
                                       403

-------
                             TABLE II




            COMPAIRSON OF CALCINED LIMESTONE WITH MDLP
                       MDLP                Calcined*
E            13+1 kcal/mole            8-18 kcal/molet
 a
R            3 x 10 ° g-mole/g sec       2 x 10   g-mole/g sec



A            4.1 x 10^ g-mole/g sec      2.07 x 10^ g-mole/g sec



AS           -7.86 cal/mole deg



AH           16.2 kcal/mole




* For calcined data Rwas 1 x 10~8 g-mole/cm3 S02 at 870°C,

                     O   _Q

  whereas MDLP was 1 x 10   g-mole/cm3 S02 at 38°C.




 Activation energies vary as to the type of limestone.
                             TABLE III




             ANALYSIS OF VIRGINIA LIMESTONE FRACTIONS
Sample
No.
1
2

3
Description
Original limestone
Surface material
removed
Recovered limestone
CaC03
97.5

5.6
97.5
Composition,
CaS04-l/2 H20
0.0

90.0
0.0
wt . -pet .
SiO Other
2.5 0.0

2.5 1.9
2.5 0.0
                                  404

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o
en
                           V
                                    GAS
                                   SAMPLE
                                              GAS
                                            HEATER
                                    FLOWMETER
                                                                                     GAS
                                                                                   SAMPLE
   WATER
 RESERVOIR
                                                                                           HOOD
                                                                              LIMESTONE
                                                                               REACTOR
   GAS
SATURATOR
                                                             HEATER
                             FIGURE 1 - Flowsheet for Modified Dry Limestone Process

-------
O
Ol
                                    8
                                    6
                                    0
1   I   I   1
                                                             I   I
                                                  o
                                                 o
o
o
                                               o
                                               o
                                                             S0
    I  I
                                     0    20    40    60    80   100

                                               TIME (MIN.)

                   FIGURE 2 - MEASURED WEIGHT CHANGES DURING THE REACTION OF H20 AND H20 + S02
                                    WITH LIMESTONE AT 100°F AND 5% S02
                                         (PELLET WEIGHT = 749.8 MG.)

-------
       o

       'o
         o
        ce
                       T = 42°C
                          1
                                          = 38°C
                            r
                            Cso  *
2         3


~R  ,moles.
                               J2        cm"


FIGURE 3 - ANALYSIS OF REACTION ORDER AS A FUNCTION OF SO 7 CONCENTRATION
                                  407

-------
O
CO
              C
              0)
              O
              0>
              a
              O
              z
              UJ
              O
              uu
              u_
              UJ
             O
             s
             LU
             cc
              CM
             O
             CO
100

 90

 80

 70

 60

 50

 40

 30

 20

 10
SOz concentration, 1,600 ppm
Crushed Greer Limestone, 1/16" x 1/4
Space velocity, 500 v/v/hr
Gas temperature, 150° F
 « Saturated 100° F
 A Saturated (a) 110° F, (b) 120° F
 O Saturated 150° F
                                         34567
                                               TIME, hours
                                                        8
               FIGURE 4 - EFFECT OF MOISTURE ON S02  REMOVAL BY CRUSHED LIMESTONE

-------






(0


• ;"':::-


: 	 ;!:i::; 	 ;;:T;
CONVEYOR, LIMESTONE RECYCLE //
LIMESTONE BIN V3i£/
CRUSHED LIMESTONE '
1/1 6"x 1/2"
                                                                       STACK
                                                                       150° F
WATER SPRAY
                                     LIMESTONE MOVING BED
                                     CROSS-FLOW ABSORBER
        100.0% (Dry Basis)
        plus RESIDUAL FLY ASH
                                       CaSO4
                                     (Disposal)
 FIGURE 5 - CONCEPTUAL APPLICATION FOR THE MODIFIED DRY LIMESTONE PROCESS

-------
                 SPRAY DRYER/BAGHOUSE SYSTEM
          FOR PARTICULATE & SULFUR DIOXIDE CONTROL,
               EFFECTS OF DEW POINT,  COAL AND
                 PLANT OPERATING CONDITIONS
                             By:
                       William R. Lane
                     Bechtel Power Corp.
                        P.O. Box 3965
                  San Francisco, CA  94119
                           ABSTRACT

     This paper discusses the use of a combination spray dryer
and baghouse or spray dryer and electrostatic precipitator for
particulate and  sulfur dioxide control.  Reactant  compounds
are injected  into the  spray  dryer  in a solution or slurry.
The dry reaction  products  and coal  fly ash are  removed  in  a
downstream baghouse or precipitator.

     Several factors influence the system performance including
coal moisture  and sulfur content,  plant altitude,  dew point
temperature approach and boiler design.  A TI-59 computer pro-
gram was  developed to perform combustion calculations and to
calculate  dew  point,  spray dryer operating temperature  drop
and chemical spray rates.  Operating limits of coal sulfur con-
tent and  sulfur  dioxide removal were determined.  Graphs are
presented which can be  used to  study a wide variety of appli-
cation conditions.

     It is concluded that applicability of the spray dryer/bag-
house concept is  limited by flue gas temperature, startup con-
ditions and required sulfur removal.  Boiler design changes  or
extending the averaging period for sulfur dioxide removal  could
alleviate the limitations.
                               410

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                 SPRAY DRYER/BAGHOUSE SYSTEM
          FOR PARTICULATE & SULFUR DIOXIDE CONTROL,
                EFFECT OF DEW POINT,  COAL AND
                 PLANT OPERATING CONDITIONS
INTRODUCTION         ,

     Interest has increased rapidly in the concept of a combina-
tion spray dryer/baghouse or spray  dryer/electrostatic precipi-
tator for  removal  of sulfur dioxide and particulate  from coal
burning plants.  Several such systems are now on order and one
will soon  be  in  operation.   The objective of this paper is to
provide information regarding  the  limits  of applicability of
this system.   The  limit is  determined by  system temperature
drop and the need to stay above the flue gas adiabatic satura-
tion temperature.

     The limits  are summarized by  the graphs which can be used
to study a wide range of conditions.

SPRAY DRYER SYSTEM DESCRIPTION

     The spray dryer for sulfur dioxide removal is located up-
stream of  a  fabric filter or electrostatic  precipitator.  The
flue gas passes  through the  dryer vessel and chemical solution
or slurry  is sprayed into the dryer. The absorbent reacts with
sulfur dioxide while in the  liquid  solution or slurry.

The liquid droplets dry before leaving the vessel and the dry
reaction products and fly ash are  removed from the flue gas by
the downstream baghouse  or precipitator.   Some sulfur removal
also occurs  in  the dry  phase  if a baghouse is  used.  Spray
dryer systems  presently  on  order will use sodium carbonate or
calcium oxide  (calcium hydroxide  after  mixing with  water) as
the' absorbent.

     The spray dryer system reduces the flue  gas temperature
to a level near the adiabatic saturation level (near  the moist-
ure dew point for typical spray dryer conditions).  The system
must be  operated above the  saturation temperature  to assure
that the droplets dry before reaching the vessel walls or enter-
ing the downstream particulate  collector.
                               411

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     Creation of  a  fine spray is achieved by  several  methods
being offered by various system suppliers.  These include high
speed rotary atomizers, steam atomizers and high pressure noz-
zles .

     A  key  to  efficient utilization of chemical  is  to spray
enough  liquid into  the system to bring the flue  gas close to
the saturation temperature.  This increases the droplet drying
time which  increases chemical  utilization  (reduces chemical
consumption) because the reaction is more efficient in the wet
phase.  Utilization is defined as the percent of the absorbent
reacting with sulfur dioxide.   Thus,  higher utilization rates
are desirable.

     Sodium carbonate  solutions must be  limited to  concentra-
tions under 30% due to  solubility limits.  A calcium hydroxide
slurry  is also  limited to  approximately  30%*(based on  calcium
oxide)  due  to  heat generation when slaked with water  and by
grit removal requirements.  Thus the amount of absorbent which
can be  sprayed  into  the system  is limited because of the con-
centration limits and the need  to stay above saturation tempe-
rature.  This limits the amount of sulfur dioxide which can be
removed from the  flue gas.  Thus there is a coal sulfur content
limit for a given required percent sulfur dioxide removal.

     The  coal  sulfur limit is  dependent on many  factors  in-
cluding coal hydrogen and moisture content, boiler excess air,
plant altitude, duct pressure and boiler exit gas temperature.
An objective of this paper  is to show the relative importance
of each of these  variables  and  to establish sulfur limits.  To
do this,  a computer  program  was developed and curves were
drawn for typical lignite,  sub-bituminous and bituminous coals.

THE COMPUTER PROGRAMS

     The computer programs were  developed for the Texas Instru-
ments TI-59 calculator/computer with magnetic card recording
capability.  The  programs  fit onto  three magnetic cards  (each
approximately 0.6" by 2.7").  Two computer programs were devel-
oped.   The first  is a combustion calculation program to deter-
mine gas flow rates  and flue gas analysis.  The second program
uses the output of the  first for spray dryer calculations.

     The 418 step combustion  program input and ouput consists
of:

Input:

1.   Fuel analysis
2.   Percent excess air
3.   Barometric pressure
4.   Duct pressure

 *Concentrations of about  40%  have been piloted by recycling  unused
  absorbent  and  fly ash.

-------
5.   Boiler heat input rate
6.   Gas temperature

Output:

1.   Gas flow rate,  weight
2.   Gas flow rate,  volume
3.   Gas molecular weight and density
4.   Flue gas analysis

     The 547 step spray dryer program input and output consists
of:

Input:

1.   Gas flow rate
2.   Sulfur dioxide flow rate
3.   Flue gas analysis
4.   Plant altitude
5.   Duct pressure
6.   Required sulfur dioxide removal, %
7.   Percent weight absorbent in solution or  slurry
8.   Absorbent molecular weight
9.   Absorbent percent utilization
10.  Flue gas temperature

Output:

1.   Absorbent flow rate
2 .   Water flow rate
3.   Final flue gas temperature
4.   Flue gas specific heat
5.   Flue gas moisture dew point
6.   Temperature margin above dew point
7.   Flue gas molecular weight
8.   Flue gas moisture content
9.   Flue gas vapor pressure.

     The  method of  spray dryer calculations  is  as follows.
Moisture due point temperature is approximated by:

Dew point (°F) = e(In P +  14.562 )/3 .3
where P =  (29.92*-  altitude in feet/1000) x(% vol.  moisture/100)

        This formula is sufficiently  accurate  over the range  of
conditions  of interest here.   Dew point temperature is very
close  to the  adiabatic  saturation  temperature  for typical
spray dryer conditions.

     Flue gas specific heat is calculated for each  gas  consti-
tuent and an  overall  specific heat is calculated based on the
percentage of each  gas constitutent  in the flue  gas. 2The  form
of the  specific heat  equations is:   Cp =  a +  b T  -  CT   - d/T

  * +0.0735 x ("WG duct pressure)

                                413

-------
where coefficients a, b, c and d are given for each gas consti-
tuent in several references including "Manual  for Process Engi-
neering Calculations" by Clarke  and Davidson.

     The heat given  up by  the flue gas to  evaporate the  spray
water consists  of the energy to raise the  water and absorbent
to dew point, latent heat  of evaporation and  the heat to raise
the evaporated  liquid and  absorbent  to the final  temperature.
The latet heat  of evaporation is calculated by a  linear  equa-
tion approximation based on steam  table data  over  the range of
interest.

     The forgoing was combined to  estimate  flue gas final tem-
perature and moisture dew point.

PERFORMANCE GRAPHS

     Figures 1  through  7 show flue  gas data  and  spray  dryer
performance  limits  for  three  classes of coal:  lignite, sub-
bituminous  and bituminous.  Typical coal  analyses used  for
this study are as follows:

                         Lignite        Sub-Bitum.     Bitum.

Carbon                     37.48            53.56         72.0
Hydrogen                   3.36            3.80          4.40
Nitrogen                   0.64            1.08          1.40
Oxygen                     8.90            10.40          3.60
Water                      40.00            20.15          8.00
Sulfur                     0.86            0.84          2.00
Ash                        8.76            10.17          8.60
Btu/lb                     6,500            9,400        12,800

As sulfur content was varied for study, other constituents were
adjusted proportionally.   The above  analyses  were selected  as
typical for each coal class.

     The attached  figures  were  developed for  the  above coals.
Figure  1 shows  the  effect  of moisture content, duct pressure,
plant altitude  and percent excess  air on flue gas moisture dew
point.  Figure  1 is  for conditions prior to spray dryer opera-
tion.   Figure 2 shows flue gas  temperature drop with spraying
of a 30% sodium carbonate  solution or a 20% calcium hydroxide
slurry.  Calcium hydroxide concentration  is expressed  as per-
cent calcium oxide.  Data are shown  for a range of sub-bitumi-
nous coal sulfur contents, percent sulfur  dioxide removals and
chemical utilization rates.  Figure  3 shows coal sulfur limits
for a  sodium carbonate  solution spray dryer.  This figure  is
for a 30% solution.  Usually the solution would be more diluted
to obtain temperatures near the dew  point.  A concentration of
30% is  shown to indicate the limit  of tolerable  coal  sulfur
content.  Figures 4, 5  and 6 show sulfur  limits  for  calcium
hydroxide slurry dryers. These  figures are arranged different-
ly from Figure  3 because three different slurry concentrations
are shown.                                                   '
                               414

-------
     Figures 3 through 6 are for a dryer exit temperature 40°F
(4-4 C) above the  flue gas moisture dew point.   Some  believe
that much  closer approaches can be  used  without substantial
risk of baghouse  or precipitator fouling.   An example  will  be
presented  to  show the effect of decreasing the  margin above
dew point.

WHAT THE FIGURES SHOW

     Figures  1  through 7  include  a large  number of curves.
This is  necessary because the number of variables  is  large.
Curves  are drawn for  two  absorbents,  three flue gas  inlet
temperatures and three classes of coal.  Among the information
shown are:

1.   Flue  gas moisture content  upstream  of the  spray dryer
varies  from  7-17% for the three coals selected.  This  signi-
ficantly affects  the flue gas moisture dew point (Figure 1).
Lignites would have  a  higher moisture dew point and thus lower
spray  dryer  sulfur removal capability.  Fortunately, lignite
often  has  less  sulfur than bituminous coal.  Bituminous coal
often  has  the highest  sulfur content but a  lower  moisture con-
tent.   Thus  more heat would be  available  above  the moisture
dew point and more absorbent could be added.

2.   Significant  differences  in  sulfur removal  capability for
the  three  classes of coal are shown on Figures  3 through  6.
Percent  chemical utilization is  a  key factor.   For a given
chemical concentration,  increased absorbent flow will  require
increased  water  flow.  Dew point approach limits  the amount of
chemical  and water  that  can  be sprayed into the system.   A
higher percent utilization will  result in an ability to handle
higher coal sulfur contents.

     It is not the purpose of this paper to establish absorbent
utilization  percentages.   These  are  determined  by the system
suppliers  and vary with operating conditions and system design.
Values of  70  to  95% are typical.  Recycle of fly ash and unused
reactant can improve utilization.

3.   Duct  pressure  (spray dryer  inlet pressure) influences  dew
point  slightly whereas plant altitude and  boiler excess  air
have  a significant  effect  (Figure  1). Lower duct pressure,
higher plant  altitutde and increased excess air are beneficial
to  spray dryer system capability because of larger available
temperature drop.

4.   The  curves can be used in  conjunction with each  other.
For  example,  Figure 3  shows data for sub-bituminous coal for  a
plant  at sea  level  and operation of  the spray dryer at an exit
temperature  40°F above dew point.   For 90% sulfur dioxide re-
moval,  if  90% absorbent utilization  is assumed with 250°F flue
gas, the figure  indicates that 2.9%  coal sulfur content is  the
maximum that can be used.

                               415

-------
What is the  limit if the design  is  for 20°F above dew point
rather than  40  F?  Figure  2 shows a 20°F  drop  in  temperature
can handle about  0.7% sulfur.  This, added to 2.9%, would give
a capability to handle 3.6% sulfur coal.  What if the plant is
at 6,000 ft altitude rather than  at  sea level?  Figure 1 indi-
cates that the dew point would be reduced by about 8 F. Figure
2 indicates  a  capability to handle  0.3% more  sulfur  or 3.9%
total.

     The above  are  approximations however, the more accurate
computer program gives a sulfur limit within 0.1% of the above.
It should be noted that  flue gas  temperature drops for lignite
and bituminous  coals would not be exactly the  same  as those
shown on Figure 2 because of flue gas composition differences.

5.   Figures 3 through 6 indicate  maximum tolerable sulfur con-
tents for a variety  of conditions.  For example if  80% utiliza-
tion of a 20% calcium oxide slurry is achieved for a case re-
quiring 90% sulfur dioxide  removal from 300 F flue gas;  lignite
could have up to  3.1% sulfur  (Figure 4), sub-bituminous up to
4.4% sulfur  (Figure  5) and bituminous coal in excess of 6% sul-
fur  (Figure  6).   It should be noted that  there  has not been
pilot plant demonstation with high sulfur coal.*

6.   Figure  7  shows the  effect on maximum  sulfur content with
closer  approach to dew point for lignite  and sub-bituminous
coals.  Closer  approach  would also  increase  absorbent  percent
utilization  and thus further increase maximum tolerable sulfur
content.  The absorbent  percent  utilizations shown are illus-
trative and are not meant to imply that they would occur.

7.   The figures  are not affected by any additional sulfur di-
oxide removal  in a  downstream baghouse.   The  baghouse would
increase absorbent percent utilization.  The higher utilization
would be used on the figures to determine the  maximum tolerable
sulfur content.

BOILER INFLUENCE ON SYSTEM CAPABILITY

     Figures 3 through 6 indicate a  limited sulfur dioxide re-
moval capability when flue  gas is at a  low temperature  (200 F
for example).  The lower temperature  limits the amount of water
and absorbent which  can be  sprayed into the system.  Operating
limits  are more  likely  to  occur during  each boiler startup or
during  low  load operation because of probable  lower  flue gas
temperature during these conditions.

     Methods of alleviating this problem include the following:

1.   Reducing the amount of boiler  economizer surface.  This
would increase the  spray dryer inlet temperature but would de-
crease  boiler  efficiency.   This  cost penalty could be  severe
because it would apply at high loads  as well as at low loads.

*There have been some tests where  flue  gas  was spiked  with  SC>2 •

                               416

-------
2.   Install steam coil heaters to increase primary air and/or
secondary air  temperature.   The steam heaters  would  only be
used when operating at low loads.

3.   Install steam  coil  heaters upstream of the spray  dryer.
Potential for heater fouling should be evaluated.

4-   Bypass  some  of the flue gas  around  the  air preheaters.
This may  not be acceptable  for  some  installations  because the
air  preheater  cold end temperature  must  be maintained  above
the minimum  recommended level to prevent  corrosion.  Also, the
primary air  temperature  could be too low to  dry the  coal in
the pulverizers.

5.   Operate the  spray dryer closer to dew point  and reheat
the dryer discharge to protect the baghouse or precipitator.

6.   Each of the above would increase the  plant heat rate (coal
consumption).  As  an  alternate to the  above,  sulfur  dioxide
removal philosophy could be  altered.  Lower  spray rates  and
sulfur dioxide removal during startup may  be allowable.  Appli-
cable laws should be  considered for  each case.  The new federal
emission  limit allows thirty day averaging of  sulfur dioxide
emissions.   Local  regulations should also be considered.  If
higher  emissions  during startups can be  averaged  with  lower
emissions during the  remainder  of the averaging period, boiler
desing changes or a plant heat rate penalty may not be  required.

OTHER COMMENTS

     Again,  it is  not in the  scope of this paper to establish
what absorbent utilization  can  be  expected.   This  is  a  key in
determining  sulfur  limit capability.  Much pilot plant testing
has  been  done  and much more is  going to be done by  several sup-
pliers.

     The  spray dryer  will have  an  influence on  the baghouse  or
precipitator.  Gas volume and temperature  will decrease,  moist-
ure  content  will  increase,  inlet grain  loading will increase,
particle  size  distribution  and  ash electrical resistivity will
change.   Thus  far,  system suppliers  report no detrimental ef-
fect on  pilot baghouse operation.  The  effect on precipitator
operation may  be  beneficial in some cases and  detrimental in
others.   Further pilot testing  is  warranted and will be  con-
ducted this  year.

     At this time,  the future of this method  of sulfur  dioxide
control looks  promising.  It is hoped that operational experi-
ence with the  first units will  justify the high level of  opti-
mism prevalent at this time.
                               417

-------
c
"o
03
Q
o
   150
   130
    90







/~



-------
 *  4
 I
 •+-*

 I'
  5  2
                                                      100% Utilization    75% Utilization
                                                        ^^^^^^^^s^^^^^^^      .^^^^^^^""^^^^^^^^
                                                      % S02 Removal   % S02 Removal

                                                      70    80    90  70     80     90
                                 -Sodium Carbonate, 30% Solution -Sub-Bituminous Coal-

                                                  Based on Coal Analysis and Conditions
                                                  Shown in this Paper
             20
40
60
  80     100      120      140
Temperature Drop (°F)

             100% Utilization
                                                                   160
                                                      180
                                                      200
                                                                 75% Utilization
                                                % SOo Removal
                                                 70    80    90  70
                                                        .30-
                                   Calcium Oxide, 20% Slurry - Sub-Bituminous Coal
                                                     i        I        I        l
                                                Based on Coal Analysis and Conditions
                                                Shown in this Paper
                                     80     100     120

                                   Temperature Drop (°F)
                                                              200
Figure 2.  Spray dryer temperature  drop related to coal sulfur content for sodium carbonate and
          calcium oxide absorbents.          419

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      200°F Gas   250°F Gas
100!	J
       1       2       34       5
             Coal % Sulfur Limit'1'
                                                          200° F Gas
                         250° F Gas     300° F Gas
                                                           .90 70 % S02  90 80^70	90	80—
                                                             ' '  'I Remova.l /  '
                                                                        r
                                                                        Sub-Bitu,
                                                                               V
                               ninous Coal
                                                                                               70
0       12      3       4       5       6
             Coal % Sulfur Limit'1)
200°F Gas
,908070"
                                                                                                                                      250°F Gas
                                                                          Removal
                                                                                 l	90^80

                                                                                       I/
                                                                                 Bituminous Coal
                                                                                                                   234
                                                                                                                  Coal % Sulfur Limit*1)
                                                                                                Removal
NOTES
(1) To stay 40° F (4.4°C) above moisture dew point
(2) Based on sea level ambient pressure —16" WG duct
   pressure and 35% excess air
(3) Sodium carbonate solution is 30% concentration
(4) Based on coal analysis shown in this paper
               Figure 3.  Coal sulfur  content  limit related  to sodium carbonate utilization  for three types of coal.

-------
         20% Slurry 30% Slurry
      100
      90
      80
      70
   O
    E
   '_o
   3
ro
60
      50
      40
      30
              90 70 90 70
                         '% S02i
                         Remova
                    Lignite
                    200°F (93°C) Flue Gas
 234
Coal % Sulfur Limit'1)
                                                        10% Slurry   20% Slurry    30% Slurry
                                                                 90 70
                                                                           90   70
                                                                                        90  80  70
                                                                                              S0
                                                                                                2
                                                                                          Removal
                                                                      Lignite
                                                                      250°F (121°C)'Flue Gas
                                                                         234
                                                                        Coal % Sulfur Limit (1)
                                                                                               10% Slurry

                                                                                                 90  70
20% Slurry

90  80  70
                                                                                                                                SO2
                                                                                                                             Removal
                                                                                                                                                   30%
                                                                                                                                                   Slurry
                                                                                                              3Q00F(149°C) Flue Gas'
                                                                                                                                                           90
                                                                                                                                                           80
                                                                                                                                                           70
                                                                                                                    234
                                                                                                                   Coal % Sulfur Limit*1)
         Notes
         (1)  To stay 40°F (4.4°C) above moisture dew point.
         (2)  Based on sea level ambient pressure, —16" WG duct
            pressure and 35% excess air.
         (31  Based on coal analysis shown in this paper
                     Figure 4.  Coal  sulfur  content  limit  for lignite  using  calcium  oxide  absorbent for three flue gas
                                 temperatures.

-------
       100-
        90
     I 80
     ==
     5
        70
      CD
     ;g
     'x
     O
        60
     O
        50
ro      40
        30
10% Slurry 20% Slurry  30% Slurry
     1 70   90 70    90 80 70  % SOo
                  III
                                        lemoval
                              Sub-Bituminous
                              200°F (93°C) Flue Gas
 234

Coal % Sulfur Limit'11
                                                      6   0
10% Slurry
  1)0 ~7Q
                                                                                    20% Slurry
                                                                                                 S02
                                    70
                   Sub-Bitummous
                  250°F (121°C) Flue Gas
                                                                         234

                                                                        Coal % Sulfur Limit'1
                                   6   0
                                                                                                   10% Slurry

                                                                                                    90 80'70 % SO?
                                                                                                                                    Removal
                                                                                                                                       /
                                                                                                      //I  /
                                                                                                  Sub-Bituminous
                                                                                                  300°F (149°C) Flue Gas
                                                      234

                                                     Coal % Sulfur Limit'1'
                                                                                                                                                          lo
                                                                                                                                                       /70
                                                                                     30

                                                                                   i]

                                                                                   7-70
          Notes
          (1) To stay 40°F (4.4°C) above moisture dew point
          (2) Based on seal level ambient pressure, —16" WG duct
             pressure and 35% excess air
          (3) Based on coal analysis shown in this paper
                        Figure 5.  Coal sulfur content limit for sub-bituminous coal using calcium oxide absorbent for three
                                    flue gas temperatures.

-------
  100
   90
c  80
o
   70
0)
;o
'x
Q  60
E
   50
   40
   30
           10% Slurry
             90 70
                  >S02
                /Removal
20% Slurry
90 80 70
                     J_L
  30% Slurry
90	80    70
         >   ..
        .Removal
                                       /
                           Bituminous
                           200°F (3SFC) Flue
                    234

                  Coal % Sulfur Limit (1)
                                           Gas
10% Slurry

 90~80700/c
                                                       S02_
                                                     Removal
                                              .  / /I /
                                             Bituminous
                                             25q°F (121°C) Flue Gas
20% Slurry

90   80
                                    1234

                                          Coal % Sulfur Limit*1)
                                                                                                  70
                                                                                                  70
                                                                                                 6   0
 10% Slurry

_90 80  70 % S02
                                                                                                                                       Removal
                                                 Bituminous /
                                                 300°F (149°C> Flue Gas
                                              Coal % Sulfur Limit'1'
                                                                                                                                                  90
                                                                                                                                                   80
                                                                                                                          70
     NOTES
     (1) To stay 40°F (4.4°C) above moisture dew point
     (2) Based on sea level ambient pressure — 16" WG duct
        pressure and 35% excess air
     (3) Based on coal analysis shown in this paper
                     Figure 6.   Coal  sulfur  content  limit for  bituminous  coal  using calcium oxide absorbent for  three
                                 flue gas temperatures.

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                                                               30% CaO Slurry
                                                               & 85% Utilization
                                   20% CaO Slurry
                                   & 70% Utilization
                                 1              2

                                    Coal % Sulfur Limit.
Figure 7.  Coal sulfur content limit related to dew point approach for 250° flue gas and 90% SO?
          removal.
                                             424

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                     SELECTION,  PREPARATION AND DISPOSAL
                             OF  SODIUM COMPOUNDS
                            FOR DRY SOV SCRUBBERS
                                     By:

                               Dale A. Furlong
                       Buell Emission Control Division
                           Envirotech Corporation
                              Lebanon, PA 17042

                               Ronald L. Ostop
                       Department of Public Utilities
                          City of Colorado Springs
                         Colorado Springs, CO 80903

                              Dennis C. Drehmel
                Industrial Environmental Research Laboratory
                United States Environmental Protection Agency
                      Research Triangle Park, NC 27711
                                  ABSTRACT

     A program has been initiated to assess an S02 removal method wherein
dry powdered sodium compounds are injected into the gas stream ahead of the
baghouse filter.   The compounds are collected on the surface of the filter
bags for reaction with the gaseous S02-   Initial program efforts include a
survey of suitable and available sodium compounds, methods of preparing
the compounds for injection, and an investigation of environmentally
acceptable methods of disposal.
                                      425

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                     SELECTION, PREPARATION AND DISPOSAL
                             OF SODIUM COMPOUNDS
                            FOR DRY SOx SCRUBBERS
INTRODUCTION

     The increasing use of high-performance fabric filters for removing
fly ash from coal^-fired boilers instigated the investigation of dry alkalis
for removing SO2 from flue gas.  The possibilities of such a process were
suggested by the aluminum industry's success with a dry additive fabric
filter collector system for the control of gaseous and particulate fluorides
in the aluminum potline effluent.  Subsequently there have been a number of
investigations of ways to remove SO2 with solid sorbents.

     The sorbents have been various limestones or dolomites, quicklime,
hydrated lime, manganese dioxide, sodium bicarbonate, sodium carbonate, and
potassium permanganate.  Investigations have confirmed that only sodium car-
bonate and sodium bicarbonate have shown good capability for reducing SO2-
Figure 1 schematically presents the key features of a system that would
inject sodium compounds into the flue gas after the preheaters.

     Considerable economic incentive exists for developing a dry sodium
SO2 scrubbing system in view of current costs of wet SO2 scrubbing systems.
Using data from a recent study by Genco, et al (1975)1 (with escalation to
1979) indicates an installed capital cost of about $6 per kilowatt for the
dry sodium crushing, grinding and injection system compared to current costs
of at least $70 per kilowatt for a wet scrubbing system.  The baghouse cost
was not included in the dry sodium system since all current wet scrubbing
systems also require a comparable, separate fly ash collection device.
Escalated operating costs for the dry S02 scrubber (again without baghouse)
are 1.5 mills/KWH compared to an estimated, and escalated, 2.2 mills/KWH
for a wet limestone scrubbing system.

     To assure utility acceptance of a dry SOX removal system by injecting
dry sorbents upstream of a baghouse filter, it is essential to identify a
near-term and long-term supply of sorbents.  Previous testing has shown
the apparent superiority of sodium bicarbonate in the form of nahcolite
for reaction with SOX/NOX in the dry form.  Other candidate sorbents were
evaluated as alternates considering the current availability of nahcolite.

     To prepare the sodium compounds for use in the dry SOX removal systems,
they must be reduced to fine powders for injection and to increase the
                                      426

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       SODIUM
         CARBONATE
COAL
                                            COMMINUTE [GRIND]
                                            SODIUM  +  SODIUM  + FLYASH
                                             SULFATE  NITRATE
                                  FIGURE 1
                    "DRY  SCRUBBING"  WITH SODIUM SALTS

-------
surface area for improved chemical resistivity.  Currently, tests are under
way to evaluate mechnical grinding and thermal comminution.

     Several methods of disposal for the spent sodium compounds from dry SO2
removal systems are being considered, including clay isolation land fill and
insolubilization by chemical methods and by sintering.

POTENTIAL SOURCES OF SODIUM COMPOUNDS

Nahcolite

     Nahcolite ore is a naturally occurring mineral containing 70 to 90%
sodium bicarbonate.  it is found almost exclusively associated with oil
shale.  Vast resources of oil shale and associated nahcolite exist in the
Eocene Green River formation in the Piceance Creek basin of northwest
Colorado.  According to the United States Bureau of Mines, this area is
conservatively estimated to contain 32 billion short tons of nahcolite.
In 1976, the Bureau launched a multi-year oil shale research and testing
program to identify and resolve environmental problems associated with the
development and mining of the deep deposits of oil shale and associated
saline materials.  A ten-foot diameter pilot mine shaft was completed in
1978 at the Bureau's research facilities in Horse Draw, Rio Blanco County,
Colorado.

     Vast resources of the sodium minerals, nahcolite  (NaHCOs) and dawsonite
(NaAl(OH)2CO3)i exist in the rich oil shale of the Green River Formation.
The significant quantities of the sodium minerals are restricted to the lower
portion of a geologic unit called the Parachute Creek Member.  The nahcolite-
bearing oil shale reaches a maximum thickness of about 1130 feet at the chemi-
cal depositional center for the nahcolite, dawsonite, and the associated halite
(NaCl).  The top of the sodium mineral-bearing section ranges in depth from
approximately 1400 to 2000 feet below the ground surface.  Nahcolite occurs
in four distinctive forms:

     1.   Brown microcrystalline beds

     2.   White coarse-grained beds

     3.   Laterally continuous units of fine-grained crystals disseminated
          in oil shale

     4.   Disseminated  rionbedded crystalline aggregates

     In coreholes analyzed by the United States Geological Survey, the nahcolite
resource ranges from a low of 174 million short tons to a maximum value of 489
million short tons per square mile.  About 257 square miles are underlain by
nahcolite-bearing oil shale with thicknesses in excess of 100 feet.  According
to the United States Bureau of Mines, this area is conservatively estimated to
contain 32 billion short tons of nahcolite.
                                       428

-------
Trona

     Trona contains about 50% sodium carbonates.  Major trona deposits  are
in the Green River formation in southwestern Wyoming.  The total reserves
in this area are estimated at 85 billion short tons.  The Green River trona
is currently a major source of ore for commercial production of soda ash.
Unfortunately, tax considerations  (depletion allowances) do not favor the
use of small quantities of trona as a raw ore.

     The Owens Lake in California is a source of sodium compounds available
for immediate use.  The relatively small current production could be readily
expanded.  Depletion allowance taxes are not a problem.  However, the limited
quantity of sodium available means that the source is only of interim interest
assuming  widespread acceptance of dry SC>2 removal.

     The evaporite deposit at Owens Lake is a complex mixture of sodium
carbonate, sodium bicarbonate, sodium sulfate and sodium chloride including
double salts, hydrates and saturated brine, all resulting from the dessication
of a large saline lake that existed until about 60 years ago.

     In 1917 the City of Los Angeles completed construction of  an  aqueduct
which draws water from the Owens River.  The Owens River was the principal
source of water feeding the then 100-square-mile lake.  Its diversion allowed
the lake level to decline due to evaporation.  As a consequence, its dissolved
salts became concentrated until they began to precipitate onto the lake bed.
When the lake finally reached a new state of equilibrium, it had shrunk to
less than 40 percent of its original size, forming a solid deposit of mixed
salts wet with interstitial brine.

     The Owens Lake evaporite deposit covers an area of approximately 35
square miles at the lower end of the Owens Valley in Inyo County, California.
The nearest town is Lone Pine which lies about 10 miles north.  The elevation
of the surface of the lake is about 3500 feet above sea level.  The lofty
Sierra Nevada range (including Mt. Whitney) rises abruptly to the West while
the eastern side of the valley is formed by the lower and more arid Inyo
Mountains.  Precipitation averages only 4 to 5 inches per year and the net
evaporation rate is about 66 inches.

     The area is served by a branch line of the Southern Pacific Railroad
which passes along the western edge of the lake, providing a direct rail
linkage with the harbors of Los Angeles and Long Beach, a distance of roughly
240 miles.  Also the U.S. Highway 395 between Los Angeles and Reno passes
immediately alongside the lake.

     The raw ore from Owens Lake, upgraded only by mining methods, appears
attractive for use as a sorbent in the SOp removal system.  However, it also
appears attractive to upgrade the raw ore to relatively pure sodium bicarbonate.
It has been estimated that 92% pure sodium bicarbonate could be produced at
the Owens Lake for approximately $50 per ton compared to estimates of $17
per ton for the raw ore.  This appears quite attractive assuming improved
performance and lower handling and shipping costs.
                                      429

-------
Supply Prospect

     Primarily because the oil shale program is still in its exploratory phase,
immediate supply of nahcolite in quantity at reasonable cost is questionable.
Assuming that full-scale dry SOx/NOx removal systems were successfully demon-
strated both technically and economically, commitments from utilities on
nahcolite consumption still would be needed to start the commerical mining
of nahcolite.

     To resolve sodium compound supply problems for immediate implementation
of dry SOx/NOx removal systems, it is possible to use crude trona and/or high
purity sodium bicarbonate upgraded from the crude dry lake ore.  Production
of 1.5 million short tons per year of sodium bicarbonate for 35 years is a
possibility from Owens Lake.

Potential Demands

     The estimated 32 billion tons of nahcolite could be used to desulfur
610 billion tons of 0.7% sulfur coal assuming the requirement of 7.5 pounds
of nahcolite per pound of sulfur removed.  This indicates the adequacy of
the nahcolite resource since the entire reserve of western bituminous and
sub-bituminous coal is estimated at 430 billion tons.

DISPOSAL OF SPENT SORBENTS

Land Fill

     Possibly the simplest method for disposal of spent sorbents is the land
filling technique.  In this technique a combined trench and area land fill
method is used.  The basic building block for the land fill is the isolation
cell concept, such as has been used for sanitary fill.  The spent product
for one working day is transported to the site, emplaced, and compacted,
The day's production constitutes the basic volume for one cell.  This com-
pacted cell is completely covered with a layer of claylike material, which
in turn is also compacted at the end of each working day.  Therefore, the
soluble spent sorbent is encapsulated in an essentially impermeable shell
of silty clay or similar material.  It is important that the landfill be
constructed on a base of material that has low permeability so that leaching
is minimized.

Chemical Fixation

     The Envirotech Chemical Sludge Fixation Process is based on the patents,
research, and commercial operations of the Chemfix Process.  This process
involves the reaction of two or more chemical additives with the waste material
to form a chemically and mechanically stable solid.  This inorganic chemical
system has proven stability when in contact with all of the usual environ-
mental elements of change:  soil, water, air, sunlight and micro-organisms.
The quantity of chemicals added to the waste usually does not increase the
final volume of the solidified material by more than 10 percent; in most
cases, the increase is less than 5 percent.


                                      430

-------
     The particular choice, ratio, and quantities of chemicals used for any
given waste treatment application depend upon three factors:

     1.   The waste

     2.   The speed of reaction require

     3.   The end use of the solidified material

Since the reaction process involves a gelatin stage followed by a hardening
period, gelationtime is an important factor in designing the chemical para-
meters of the system.  Desired gelation time may depend, for example, on
whether the material is to be pumped for some distance after mixing and
on the method of disposal.    End use of the solidified waste is important
because the end product can be either hard of quite soft and can be made to
have varying textures.  If it is to be in contact with a high water table,
or even be under water, the nature of the contacting water will also determine
chemical design.

     The system, as it is normally used, reacts with all polyvalent metal
ions producing stable, insoluble, inorganic compounds.  It is also reactive
with acids, certain nonmetallic ions, and some organic compounds.  Nonreactive
materials are physically entrapped in the matrix structure resulting from the
reaction process.  Because of this variety of entrapment and reaction possi-
bilities, each system must be custom designed for the particular chemical
problem presented by the waste material to be processed.

Sintering

     Laboratory experiments have also demonstrated that spent sorbent can be
insolubilized by mixing it with, fly ash and/or bottom ash, forming an agglomerate,
and sintering at about 1800°F.  The sintered material may be disposed of by
known  landfill techniques or used as an aggregate for road beds, concrete, etc.
REFERENCES

1.  Genco, Rosenberg, Anastas, Rosar and Dulin, "The Use of Nahcolite Ore
    and Bag Filters for Sulfur Dioxide Emission Control", APCA Journal,
    Vol. 25 No. 12, December 1975, p. 1244
                            METRIC CONVERSION TABLE

                                1 inch = 2.54 centimeters
                                1 foot = 0.3048 meters
                                1 mile = 1.6093 kilometers
                          1  square mile = 2.590 square kilometers
                     1 ton/square mile = 2.855 kilograms/square meter
                            1 short ton = 907.2 kilograms
                          1 dollar/ton = 0.1103 cents/kilogram

                                     431

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       HIGH VELOCITY FABRIC FILTRATION FOR CONTROL OF COAL-FIRED BOILERS


                                       By
                                 John C. Mycock
                         Enviro-Systems & Research, Inc.
                                Roanoke, Virginia
                                 Rodney A. Gibson
                                 Joyce M. Foster
                       Environmental Testing Services, Inc.
                                 Roanoke, Virginia
ABSTRACT

     As a follow-up to a pilot plant study, a full scale investigation of
applying high velocity fabric filtration to coal-fired boiler fly ash control
was conducted.  Two filter systems were separately applied to two 60,000
Ib./hr. coal-fired boilers.  Performance evaluations conducted over the.
course of a year included total mass removal efficiency and fractional effi-
ciencies.  One filtration system employed Teflon felt as the filter medium
while the second system employed Gore-Tex, a PTFE laminate on PTFE woven
backing.  During the course of the year, a limited number of glass, felt;and
woven glass bags were introduced into the house containing Gore-Tex.

    As a separate option, the second system was outfitted entirely with woven
glass bags.  Preliminary results indicate acceptable performance at an air-to-
cloth ratio of 6 to 1.  Future plans call for utilizing one of the baghouse
systems for S02 removal.


INTRODUCTION

    For the past six years Enviro-Systems & Research, Inc. has been involved
in an EPA project to determine the techno-economic feasibility of applying
high velocity fabric filtration to control the fly ash emissions of an indus-
trial coal-fired stoker boilerJ

                                      432

-------
    The program started on a small scale in 1973 and financial participation
was divided equally among EPA, Kerr Finishing Division of FabricsAmerica and
Enviro-Systems & Research, Inc.  The Kerr plant, located in Concord, North
Carolina, served as the host site for the program while Enviro-Systems &
Research designed, fabricated and installed the pilot baghouse (Figure 1).
The pilot program provided a short-term screening of a number of filter media
and the data gathered along with preliminary economic analysis indicated that
long-term bag life and performance studies were warranted.2  EPA at this point
decided to award a contract for the full scale demonstration unit for this
approach to fly ash control.  The demonstration contract was awarded Fabrics-
America, with Enviro-Systems & Research as the major subcontractor responsible
for the design, fabrication, installation and operation of the full scale
fabric filter system (Figure 2).

    The purpose of the demonstration program is the testing of a full scale
fabric filter system installed on an industrial coal-fired stoker boiler and
data generated by the program include general operating parameters, media
changes and life data and particle size removal efficiencies as a function of
on-stream time.

    Contract options called for the long term testing of other promising filter
media and to evaluate the fabric filter system as a vehicle for the removal of
sulfur dioxide
 KERR - THE HOST SITE

    The Kerr Finishing Division of FabricsAmerica is a textile dye and finish-
 ing plant located in the textile belt of central North Carolina.

    Kerr's normal production schedule is three shifts per day, five days per
 week with 450-500 employees.  Plant capabilities include processes to bleach,
 mercerize, dye, nap, finish and sanforize both cotton and synthetic fabrics,
 as well as cutting and preparing corduroy.

    Two Babcock & Wilcox steam boilers are in operation at the Kerr facilities.
 Each has a design capacity of sixty thousand pounds of steam per hour and both
 are equipped with spreader stokers.  Each boiler has a two-hour  peaking
 capacity of seventy thousand pounds per hour.  The design efficiency of these
 units is 82 percent.  Based on the above parameters, the heat input for these
 units is 73.2 million BTU/hour each.  Both boilers are equipped with fans for
 supplying draft and unit number two, the unit tapped for the pilot plant
 stream, has overfire steam injection for better combustion control.  In Jan-
 uary, 1973, emission tests were conducted on these boilers.  The particulate
 emission rates were found to be approximately 130 pounds/hour versus an
 allowable rate of about 25 pounds/hour.  Gas volumes were determined to be
 about 35,000 ACFM at a temperature of about 355°.  Thus the grain loading
 measured was about 0.4 grains per ACFM.  Orsat analysis indicated 9.5%, C02,
 10% 03, 0% CO and 80.5% N2-  Coal analysis indicated the sulfur content to be
 about 0.6%.3
                                      433

-------
    Figure 1



Kerr Pilot Plant
      434

-------
                       Figure 2
EPA  DEMONSTRATION OF THE ENVIRO-SYSTEMS FABRIC FILTER SYSTEM
AT KERR FINISHING DIV  FAERICSAMERICA,CONCORD,NORTH CAROLINA

-------
HARDWARE DESCRIPTION

    Each boiler is serviced by its own fabric filter system.  The heart of
each system is the baghouse which is identical in terms of basic hardware.
Each baghouse is designed to contain a total of 7,440 square feet of cloth.
The house is subdivided into eighteen (18) cells, each cell containing thirty-
six (36) bags giving a total house capacity of 648 bags.  The bags are 8' - 8"
long and 5" in diameter, giving 11.5 square feet of cloth per bag.  The bags
are hung from the tube sheet, locked in place by two snap rings which are sewn
into the bags.  The bags are secured to a metal grid at the bottom.  A metal
cage is set inside the bags to prevent collapse.  The baghouses are constructed
of 10 gauge mild steel while the hoppers are of 3/16" mild steel plate con-
struction.  Both house and hopper are insulated with two (2) inches of fiber
board covered with a mild steel skin (Figure 3).


BAGHOUSE OPERATION

    The system is brought on line by closing the boiler stack damper and
opening the system inlet damper.  An auxiliary heater can be employed to pre-
heat the house prior to start-up and it can also be used to purge the house
prior to shutdown.  The vortex damper is employed to maintain a predetermined
pressure at the boiler stack, independent of pressure drop fluctuations
through the baghouse system (Figure 4).  The operation of the baghouse is as
follows:  The dirty gases enter one end of the house, pass through the tapered
duct.into a classifier, then through the bags.  The classifier forces the
dirty gases to change direction abruptly, forcing the heavier particles
directly into the hopper.  Dirty gases enter the classifier through a central
tapered duct to feed the same quantity of gas into each cell.

    The gases are now forced through the fabric, the particulate is deposited
on the outside of the bag while the clean gas passes through the center of
the bag and into a center exit plenum via an open damper above the tube sheet.
The bags are cleaned one cell at a time by closing the cell damper and at the
same time introducing clean gas in the reverse direction.  The in-rush of
cleaning gas expands the bag with a shock causing the "cake" to crack and the
particulate falls off the bag into the hopper.

    Now that the shock has broken off the outer crust, the flow of clean gas
continues pushing and pulling the dust particles away from the fabric in an
operation called "drag".  This phase of the cleaning has proven significant
in minimizing the re-entrainment of fine particles during the cleaning cycle
(Figure 5).

    The entire operation is monitored and controlled by a console located in
the control house.  The control panel (Figure 6) is arranged in three sections,
with test instrumentation located in the center and baghouse controls at left
and right.
                                       436

-------
                           General  Arrangement  5D-IO
   "Not For Construction Purposes
CO
                                       Pyramid Hopper
                                             Figure 3



                                 SD General Arrangement with Pyramid Hoppers

-------
                                                                                                                TO ATMOSPHERE.
                                                                                                                  (EXHAUST)
CO
CO
                                                                  PiSCHAK&E. VALVES

                                                               Figure 4
                                                                                                                          EXHAUST
                                                                                                                             fSHuT OFF)
                                                        Fabric Filter  Schematic

-------
                                                            STEP 2
                                                                                        THE FABRIC FILT
     Otrty
     the  Ctaealfler at  one
     wOWWwIWO Hi 10 IfMI ftOf^JDMW.
                 mvvran cMf*c*
               TMs  quick change In
     lifa^illiiii jkj Until **MU«M*« lh_a '
     OTWHvff v* ROW fwffwVn tnw

                           Step 1

        Baghouse  Pictorial Shov;ing  Gas  Flow
                          The g«M« now p**t Ihrouflh th«
                          fibrtc. depoiltlng Hi* remaining
                          p*rticul*t* on the oul«t turfict ol
                          th» bag*. Thl* dvpotll I* periodi-
                          cally rcmovad from th«  laoric
                          aurfac*  by th« unlqu* SHOCK-
                          DRAG Cleaning Sytl»m. deilgn-
                          ed  to prolong bag life by mini-
                          mizing dltlortton of the fiber*.
                   Step  2

Baghouse Pictorial  Showing Gas  Flow
       FEP 3
   STEP 4
                                       SHOCK
                              A* *oHd matter collect* on the
                              outtkte of the filter bag, a cake or
                              cruet to formed which begin* to
                              rtMrfct the flow of ga*. When the
                             . pressure drop aero** the fabric
                              rtache* a predetermined level, a
                              damper I* actuated which teolate*
                              Hie cell from the main gat stream
                              and  rimuftaneoutly Introduce*
                              cleaning ga* flowing In the re-
                              v*r»e  direction. The biruah of
                              cleaning ga* rapidly clittend* the
                              finer bags, cracking  the dust cake
                              and permitting the  large agglo-
                              merated piece* to  fall into the
                              hopper.
                                       DRAG

                              Now lhat the SHOCK ha* broken
                              off In* outer crutl, lite flow of
                              clean ga* continue*, pushing and
                              pulling  (he du*t  particle*  away
                              from  the fabric In an operation
                              called DRAG. The*e finer  parti-
                              cle* are forced from the bag and
                              propelled  Into the hopper  The
                              Envlro-Clean SO I* unique In that
                              It provide*  both  SHOCK  and
                              DRAG In Independently control-
                              lable amount*. The Drag cleaning
                              pha*e ha* proven significant In
                              minimizing re-*ntralnment of the
                              fine particulate during the clean-
                              Ing cycle.
                      Step  3                                                       Step 4

Baghouse Pictorial  Showing  Gas  Flow -  Shock  Baghouse Pictorial  Showing Gas  Flow  -  Drag
                                                      Figure
                                                           439

-------
 Figure 6
Control Panel
     440

-------
    Since the 1976 start-up, several  modifications have been made to the system,
both to solve unanswered questions as well  as to create optimum operating con-
ditions.  In order to obtain   more effective cleaning of the bags, two differ-
ent measures were undertaken.  On Baghouse  No.  2, the original  flapper dampers
at the top of each cell  were replaced by poppet valves.  Six months operation
indicates that the dampers now seal better  and have increased cleaning pres-
sure.  In Baghouse No. 1, a pulse-jet system was added to the existing reverse-
flush cleaning systems.   The combination cleaning system (shock-drag with
pulse assist) has proven extremely effective and indications are that the
system can clean down even under the most severe conditions.

    One other major modification was made to System No. 1.   In  1978, a multi-
cyclone was installed after the pre-heater  but prior to the baghouse system
inlet damper.  Particle size data, obtained both before and after installation,
show  some reduction, after installation, in the concentration  of larger
particles.
FILTER MEDIA

    The fabrics screened in the original  pilot program were:   Teflon Felt Style
2663 (21-29 oz./yd.2), a tetrafluoroethylene fluorocarbon;  Gore-Tex (4-5 oz./
yd.2), a microporous Polytetrafluoroethylene (PTFE)  membrane  on a woven  PTFE
fabric backing; Dralon-T felt (12-15 oz./yd.2),  an Acrylonitrile homopolymer;
and Nomex felt, a high temperature resistant nylon fiber (polyamide).   Of these
media, Teflon felt and Gore-Tex PTFE laminate proved the most promising  and
were selected as the first to be employed in the demonstration project.

    Baghouse No. 1 was outfitted entirely with Teflon felt and in the  ensuing
twenty-four (24) months of operation has  yielded an average replacement  rate
of 5% per year with no recorded failures  during  the first year.  During  this
time the house was on-stream five or six  days per week with the only signifi-
cant maintenance being industrial vacuuming of the bags which occurred twice
during the first year's operation.

    Baghouse No. 2 was started up in 1976 with a complete complement of Gore-
Tex bags.  One cell (36 bags) was replaced with  Huyck glass felt bags  in March
of 1977 while another cell was outfitted  with Globe Albany 22% oz. woven glass
bags in May of 1977.  Neither of these last cells has shown failure to date.

    Gore-Tex, which had shown a 10% replacement rate after the first year's
operation, was completly replaced with 22.5 oz.  woven glass bags during the
summer of 1978.  It is felt that a large  number of the Gore-Tex failures can
be attributed to manual cleaning and movement of the bags.

    Nomex felt and a 15 oz. woven glass bag were also tested in Baghouse No. 2
during 1978.  Both were found to be lacking in endurance.
                                      441

-------
DATA

     A profile of the flue gas at the inlet of each baghouse is shown in Table
1.

     Characterization of the outlet particle size distribution shows that each
of the media tested thus far (Teflon felt, Globe Albany 22.5 oz./yd/ woven
glass and Gore-Tex), emits essentially the same range of particle sizes (Table
2 and Figure 7).  All comparisons are made at a 6/1 A/C ratio which has  been
the predominant level of operation at Kerr.

     All media tested performed well within the emission boundries set for the
Kerr boilers by the State of North Carolina, with the woven glass showing the
lowest outlet emissions and Teflon felt the highest (Figure 8).


ECONOMICS

     The economics of applying the three media tested to the Kerr boilers were
evaluated and compared with those of an electrostatic precipitator.

     Installed costs were developed for a fabric filter collector sized to
handle 70,000 ACFM at 350° F   at  air-to-cloth ratios of 3, 6 and 9 to 1.
Table 3 shows the influence that the cost of the bags exerts on total installed
costs.

     Figure 9 shows a comparison of the installed costs for the three bag
materials versus the installed costs for an ESP handling the same volume of
flue gas but at efficiencies of 95% and 99%.  The ESP costs were developed by
summing flange-to-flange costs (supplied by an ESP manufacturer) and 70% of
the purchase price for erection costs.  (This same 70% was used in developing
fabric filter erection costs.)

     Operating costs were developed for the fabric filters with two, four and
six year bag lives and compared with those of the electrostatic precipitator.
Fabric filter operating costs were based on actual pressure drops observed at
the 6 to 1 air-to-cloth ratio.  Precipitator pressure drops were assumed to
be 0.5" W.G.  Electrical rates are actuals obtained from Kerr.  These costs
presented in Figure 10 illustrate the importance of achieving longer bag life.

     Annualized costs were calculated using the straight line method of depre-
ciation, 6 2/3% per year over 15 years.  Other costs called capital charges,
which include interest, taxes and insurance, are assumed equal to the amount
of depreciation or 6 2/3% of the initial installed costs.  Therefore, depre-
ciation plus these other annual charges amount to 13 1/3% of the installed
costs.  As illustrated in Figure 11, the baghouse employing any of the fabric
systems is favorable once a four-year bag life is achieved.

     Development of annualized costs employed the formulae published by
Edminsten and Bunyard.H)

                                      442

-------
                                   Table 1

                          Inlet Gas Stream Profile
                                    Inlet to Teflon
                                      Felt House
Inlet to Gore-Tex
(1977), Then Woven
Glass (1978) House
Flue Gas Composition

   CO? (%)
   CO  (%}

   02  (X)
   H20 (%}


Temperature (° F)


Gas Volume (ACFM)


Grain Loading (Grains/dscf)


Inlet Flow Rate (Ft./Sec.)


Inlet Opacity (%}
4.5
0
15.2
5.1
322
37,700
0.5356
76.7

4.4
0
14.6
3.1
317
35,300
0.4272
61.1
40
                                      443

-------
                                                 Table  2
Outlet Characterization by Andersen Irrpactor
(Particle Sizing)
G/C Ratio 6/1
Teflon Felt
Stage
1
2
3
.P> ^
"5
6
7
8
Back-Up
Filter
Diameterf
Microns
>11.40
8.00
4.93
3.47
2.2.6
1.04
.63
.46
<.46
Total
Loading-
Grains/
dscf
.01503
. 00348
.00326
.00271
.00266
. 00230
.00174
.00101
.00174
.03393
Cumulative^
7,
55.70
45.45
35.84
27.85
20.01
13.23
8.10
5.13
-
Woven Glass
Diameter,
Microns
>10.89
7.64
4.70
3.31
2.15
.99
.59
.43
<.43
Total
Loading,
Grains/
dscf
.00319
. 00062
.00057
. 00041
.00043
.00044
.00035
.00036
. 00027
.00664
Cumulative
51.96
42.62
34.04
27.86
21.39
14.76
9.49
4.07
-
Diameter ,
Microns
>10.43
7.32
4.51
3.17
2.06
.95
.57
.41
Total
Gore-Tex*
Loading,
Grains
dscf
.00304
.00102
.00116
.00063
.00075
.00085
.00069
. 00035
.00056
.00905
Cumulative
70
66.41
55.14
42.32
35.36
27.07
17.68
10.06
6.19
-
"Wan Effective Cut Diameter
 rfean Loading Per Stage
~Vfean Cumulative 70 Less Than Size Indicated
    Probe and Nozzle Washes Were Collected

-------
co
Pi
o
^
o
•H
(1)
J-J

•H
4-1
a
cu
w
     10


    8.0


    6.0




    4.0
    2.0
1.0


 .8


 .6
O  Teflon  Felt

                           !•

&  Woven Glass,  22.5 oz/yd"
                                       Gore-Tex
       2    5   10    20      40     60     80   90

          Cumulative  % Le,ss  Than Size Stated



                       Figure 7


        Outlet Particle  Size Distribution for Each  of
                      Three Filter Media
                        (G/C  Ratio 6/1)
                             445

-------
   30 -
   20
•I-l
M
CO
•P
CU
§  10
    0
         State of North CarolinaLimt  25Lb./Hr_J_
              4->
              i-l

              (^
              M-J
                              I
                              CJ
                                             §
                                             o
                        G/C Ratio 6/1


                          Figure 8


      Performance of Three Filter Media in Controlling
             Emissions from a Coal-Fired Boiler"~
     probe and nozzle washes were collected.
                             446

-------
                               Table 3
              Bag Cost as  a Percentage of Installed Cost
Filter Media
Installed Cost
Bag Cost
Bag Cost as % of
 Installed Cost
Teflon Felt
A/C:  3/1
      6/1
      9/1
  $285,080
   153,700
   120,570
$114,480
  57,240
  38,160
     40.2%
     37.2
     31.6
Woven Glass
A/C:  3/1
      6/1
      9/1
   210,884
   116,602
    95,838
  40,284
  20,142
  13,428
     19.1
     17.3
     14.0
Gore-Tex
A/C:  3/1
      6/1
      9/1
   267,800
   145,060
   114,810
97,200
48,600
32,400
36.3
33.5
28.2
                                   447

-------
    400 _
    300
 co
 I-l

 a

on
 o
 i-i

 X

 CO
 -u
 en
13
4-1

CO
    200
    100
     50

           O  Teflon Felt


           A  Globe Albany Woven Glass


           D  Gore-Tex/Gore-Tex


           	• ESP (At 2 Efficiencies)
                   2/1
                                4/1
     6/1


G/C Ratio
3/1
10/1
                                  Figure 9



              Comparison of  installed Costs for Three Filter

                  Media and  Electrostatic Precipitators
                                   448

-------
    60 r
    50
 §  40
 i—i
 r-j
 a
CO
 O
     30
 a
 <§•
    20
    10
o  Teflon Felt


A  Globe Albany

    Woven Glass

n  Gore-Tex/Gore-Tex

—- ESP  (At 2 Efficiencies)


          6A

                   24             6

                   Filter *fedia Life, Years



                             Figure 10


        Comparison of Operating Costs for Three Filter Media

                  and Electrostatic Precioitators
                               449

-------
    90 r
 w
 cd
 r-4
 rH
 a
ro
 o

 X
 1-1
 8
 •U
4-1
U3
to
    80
    70
    60
    50
    40
    30
                                                         99%
 O   Teflon Felt
 ^   Globe Albany
     Woven Glass
 Q   Gore-Tex/Gore-Tex
	 ESP (At 2 Efficiencies)

 G/C Ratio 6/1
                           	95%
                   246
                   Filter Media Life, Years


                          Figure 11

       Comparison of Annualized Cost of Control for Three
           Filter Media and Electrostatic Precipitatdrs'
                             450

-------
CONCLUSIONS

     During the first two years of the full-scale demonstration project, three
filter media (Teflon Felt Style 2663, Woven Glass 22.5 Oz./Yd.2 and Gore-Tex
PTFE Laminate) were evaluated for performance and economy in controlling the
fly ash emissions from a stoker boiler.   The media all performed well within
the particulate emission limits set by the State of North Carolina and each of
the media tested  emits  essentially the same range of particle sizes.

     Teflon felt has been operating for better than twenty-four (24) months
and appears the most likely candidate to achieve a four-year (and possibly
more) bag life.

     All of the media studied appear favorable in terms of annualized costs
when compared with an electrostatic precipitator at 99% efficiency, once a
two-year bag life is achieved.

     In January of 1979 a fire of major proportions destroyed the operating
facilities at Kerr.  The boilers and baghouses, although unharmed, have not
operated since.  Present plans call for the relocation of the baghouses to a
recently acquired Kerr facility in Travelers Rest, South Carolina.

     It is anticipated that the test program will start again in the fall  of
1979 at its new location.
                                      451

-------
REFERENCES

^cKenna, 0. D., "Applying Fabric Filtration to Coal-Fired Industrial  Boilers:
 A Preliminary Pilot Scale Investigation".  EPA 650/2-74-058, July, 1974.

2McKenna, J. D., Mycock, J. C. and Lipscomb, W. 0., "Applying Fabric Filtration
 to Coal-Fired Industrial Boilers:  A Pilot Scale Investigation".   NTIS PB-245-
 186, August, 1975.

3McKenna, J. D. and Brandt, K. D., "Demonstration of a High Velocity Fabric
 Filtration System Used to Control Fly Ash Emissions".  Presented  at the Third
 Symposium of Fabric Filters for Particle Collection, Tucson, Arizona,
 December 5-6, 1977.

4Edminsten, N. G. and Bunyard, F. L., "A Systematic Procedure for  Determining
 the Cost of Controlling Particulate Emissions from Industrial  Sources".
 Journal of the Air Pollution Control Association, V20, N7, p.  446 (1970).
ACKNOWLEDGEMENTS

     This program was sponsored by the Federal  Environmental  Protection Agency
with participation by Kerr Industries and Enviro-Systems & Research,  Inc.
                                      452

-------
               EPA MOBILE FABRIC FILTER - PILOT INVESTIGATION OF
                 HARRINGTON STATION PRESSURE DROP DIFFICULTIES

                                      by

                 W.O. Lipscomb, S.P. Schliesser, and S. Malani
                              Acurex Corporation
                    Research Triangle Park, North Carolina

                                   ABSTRACT

     This report describes the Environmental Protection Agency mobile fabric
filtration performance evaluation at Harrington Station, Amarillo, Texas.  The
primary objective was to evaluate several bag candidates for new and retrofit
application for the full-scale baghouse systems.  A secondary objective was to
evaluate operating and cleaning parameters.  The purpose was to assess alter-
nate means for reducing high pressure drop levels currently being experienced
at Harrington Station.  The mobile facility was operated in a representative
manner with the full-scale baghouse for candidate bag evaluation.  Appropriate
changes in cleaning parameters showed reduction in pressure drop levels, as
did alternate bag types.  Results from electrostatic measurements indicated
that significant charging levels exist.  Performance results from the mobile
baghouse are discussed and related to the full-scale system.

INTRODUCTION AND OBJECTIVE

     This pilot-scale fabric filter is one of three conventional particulate
emission control devices mobilized by the Particulate Technology Branch,
Utilities and Industrial Power Division, Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency (PATB/UIPD/IERL/EPA), Research
Triangle Park, North Carolina.  The objective is to evaluate and compare the
performance characteristics of a pilot-scale baghouse, electrostatic precipitator
(ESP), and scrubber on industrial particulate emission sources.  The purpose
is to provide characteristic information and insight for appropriate selection
of particulate control devices, in light of operation, performance, and cost
considerations.

     The Harrington Station Unit No. 2 fabric filter system, belonging to
Southwestern Public Service Company (SPS Co.), was of interest to IERL/EPA
prior to its startup in June 1978.  Among other evaluations, IERL had directed
a performance evaluation to be conducted with its mobile baghouse system on
Unit No. 1 during the spring of 1977.*  One of the bag/cleaning cases studied
during this evaluation was representative of the Unit No. 2 baghouse system.
Data from this representative case were integrated into the baghouse perfor-
mance model by GCA Corporation.2  The model predicted that operating pressure
drop levels would be significantly higher than the design levels.  As pre-
dicted, the operating pressure drop level currently being experienced is
significantly higher than the design level.  In light of these circumstances,
SPS Co. and IERL have cooperatively entered into an investigation to be

                                     453

-------
conducted with the EPA mobile baghouse to assess pressure drop remedies.
Acurex performed and conducted this investigation by evaluating several bag
candidates and other pertinent pressure drop parameters.

     This report summarizes the results of the second EPA mobile baghouse
performance evaluation at Harrington Station during the spring of 1979-  The
mobile baghouse treated a slipstream from Unit No. 1 educted upstream from the
pollution control system.  The conditions of the slipstream and the pilot
baghouse were representative of the Unit No. 2 flue stream and baghouse sys-
tem, respectively.  Boiler and pilot baghouse operating data were collected on
a regular basis.  Particulate concentration and size distribution measurements
were conducted on the influent and effluent streams.  Several glass fiber bag
types were methodically evaluated, with emphasis on pressure drop performance
and characterization.  Performance levels and trends are included in this
report, along with analytical discussions on operating and particulate data,
coal type, and means of data reduction and interpretation.

CONCLUSIONS

     •    Acid-Flex fabric had the best operating performance characteristics
          of the candidate bags evaluated.

     •    The Teflon B fabrics and the silicone-graphite fabric had comparable
          performance characteristics.

     •    Increasing shake frequency resulted in dramatic improvements in
          cleandown for all fabric types.

     •    Increasing deflation pressure resulted in significant improvement in
          cleandown for all fabrics.

     •    Silicone-graphite bags had slightly higher emission levels than the
          other bag types.

     •    Cage voltage measurements indicated that sufficient electrostatic
          levels are present to have a potential effect on cleandown and
          porosity.

     •    The Wyoming/New Mexico coal blend appeared to generate a dust cake
          with slightly better cleandown characteristics.

DESCRIPTION OF FACILITIES

Test Site

     Harrington Station is owned and operated by Southwestern Public Service
Company.  It consists of two 350 MWe pulverized coal (PC)-fired boilers.  The
identical boilers were completed from 1976 to 1978 and represent current
design and operating methodology.  Emissions are controlled by a series com-
bination ESP/marble-bed wet scrubber on Unit No. 1, and by a baghouse with

                                      454

-------
silicone-graphite coated glass bags on Unit No. 2.  A third unit, now under
construction, will employ a baghouse.  Bag selection for Unit 3 has not been
finalized.

     Harrington Station generally burns a low sulfur coal from Gillette,
Wyoming.  Due to limited availability of Wyoming coal, a New Mexico type was
fired to supplement coal reserves.  Site characterization data for the
Harrington Station boiler, flue gas and coals are presented in Tables 1 and 2.

Full-Scale Baghouse

     The emissions from Unit No. 2 are controlled by a fabric filter, consis-
ting of two houses designated East and West, each with 14 compartments.
Detailed design and operating specifications are given in Table 3.3  In
March 1979, after 6 to 8 months of on-stream time, the operating pressure drop
ranged from 9 to 11 inches W.C. at full load and SPS Co. projected additional
bag life to be a maximum of 6 months.

Pilot Baghouse

     The EPA mobile baghouse consists of a single compartment containing three
14.1 cm (5 9/16 in.) diameter by 1.83 m (6 ft.) long bags.  Designed for the
purpose of determining the effects of dust properties, fabric media, cleaning
parameters and other operating parameters on fabric filter performance, the
system has the following capabilities:

     •    Filtration at cloth velocities as high as 6 m/min with a pres-
          sure differential up to 50 cm of water and at gas temperatures
          up to 260°C.

     •    Adaptability of mobile system to cleaning by mechanical shake,
          pulse jet, or low pressure reverse flow with cleaning param-
          eters varying over a wide range.

     •    Continuous 24-hour operation with use of automatic instruments
          and controls.

     The mobile fabric filter is housed in a 2.4 m by 12 m tandem-axle
trailer.  A more complete description of the EPA mobile baghouse is
presented in Reference 4.

PROGRAM METHODOLOGY

Installation

     The mobile baghouse was located adjacent to and then slipstreamed
from Unit 1.  The slipstream probe was installed in the ductwork down-
stream of the air preheater and upstream of the pollution control de-
vices.  The slipstream was withdrawn and isothermally transported to the
pilot unit at velocities somewhat less than plant conditions.  A return
line from the pilot baghouse back to the site inlet duct was employed due

                                     455

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                            TABLE  1.  HARRINGTON  STATION
                               COAL ANALYSIS* SUMMARY
         Slack Thunder Mine
       Campbell County, Wyoming

Moisture
Ash
Volatile
Fixed Carbon

MJ/kg
Sulfur Content
Typical
28.4
4.8
31.9
35.0
100%
20.0
0.33
Rant
24.2 -
3.3 -
27.4 -
31.0 -

13.3 -
0.09 -
je_
34.4
5.7
38.0
40.0

21.3
0.51
*all  analyses as received
                  McKinley Mine
               Gallup, New Mexico
                                                                             Range
                                                                          14.0 - 15.5
                                                                          11.5 - 13.5
                                                                          23.2 - 24.8
                                                                           .33 - .40
                    TABLE  2.   BOILER AND  FLUE  GAS  CHARACTERISTICS7
           Boiler  Type
           Generation Capacity
           Coal  Type
           Flue Gas  Flow  Rate
           Gas Velocity
           Temperature
           Particulate Loading
           C02
          H20
Pulverized Coal (PC)
350 MW
Low Sulfur Low Ash Wyoming
Low Sulfur High Ash New Mexico/
Wyoming Blend
34000 acm/min
24 - 30 m/sec (78.7 - 98.4 ft/sec)
125 - 185°C (257 - 365°F)
2.4 - 3.4 gm/DNCM (1.05 - 1.5 gn/OSCF)
12.3%
5.0%
77.0%
5.7%
                                             456

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                    TABLE 3.  DESIGN AND OPERATING SPECIFICATIONS
                       FOR HARRINGTON UNIT NO. 2, SAGHOUSE 3'8
       Desian
       Metric
Gas temperature
Gas Flow Rate
A/C Ratio
Sag type

Compartments
Sags/Compartments
Sag Design
Bag Dimensions
Number of Sags
Total Cloth Area
Cleaning Mode
156°C
4.67 x 10  aonn
1 m/sec
Sill cone/Graphite
coated glass fiber
28
204
Caps with Eye Bolts
0.29 x 9.3-m
5712
4.78 x 104m2
Deflate/Shake
313°F
1.65 x 105 acfm
3.27 ft/sec
11.5" x 30.5'
5,14 x 105 ft2
Cleaning Parameters

Acceleration
Amp!itude
Frequency
Duration
Reverse Air £P W. C.
1.56 g (15.3 m/sec2)
3.8 cm
3.2 cps/sec
23 sec
0 - 0.5  in.
1.56 g (50.2 ft/sec2)
1.5 in.


0 - 1.27 cm
Operating

Bag Pressure Drop
Gas Temperature
Gas Flow Rate
A/C Ratio
15 - 28 on.
127 - 188°C
2.8 - 4.0 x  10  acmn
0.9 - 1.2 m/sec
5-11 in.
250 - 370°F
1.0 - 1.4 x 10s acfm
3.0 - 4.0 ft/sec
                                         457

-------
to high negative static pressure in the plant duct and limited blower capacity in
the pilot baghouse.  The slipstream was heated arid insulated while the
return line was insulated only.  Inspection of the ducting after testing
indicated marginal dropout of particulate, due to either gravitational or
centrifugal forces.

Operation

     The pilot baghouse was operated and tested continuously in weekly
increments of 4 to 5 days.  Normal baghouse startup and operating pro-
cedures were employed and included a preheat procedure to avoid the acid
dew point.  Candidate bags were installed in a methodical manner and were
conditioned for 24 hours prior to any performance testing.  Bag test
periods ranged from 1 to 8 days, depending on performance and interest
levels.

Candidate Bags

     The candidate bags for this program included the following:

     *    W-W, Criswell silicone-graphite coated fiber glass, style
          445-04  (same bag installed in Harrington Unit 2 baghouse).

     •    W.W. Criswell Teflon B coated fiber glass, style 442-570C2.

     •    Menardi-Southern Teflon B coated fiber glass, style MS-601.

     •    Fabric Filter Acid-Flex fiber glass, style 504-1.

     •    Fabric Filter all filament fiber glass, style 50G-ITC.

     •    Fabric Filter Goretex laminate fiber glass.

     •    Menardi-Southern Teflon B coated fiber glass, reverse-air bags
          with spreader rings.

Due to performance and/or interest level, the last three bags were not
tested for a sufficient length of time to generate meaningful data and
are not included  in further discussions.  A summary of bag specifications
for the other four candidate bags is given in Table 4.

Test. Conditions                                .

     The mobile baghouse was operated at relatively constant temperature
and air/cloth levels.  Cleaning conditions for each bag type were initi-
ally set to be consistent with cleaning conditions for the full-scale
unit.  Discretionary modifications of pertinent cleaning parameters were
made to assess alternate means of pressure drop reduction other than and
in relation to bag type.  Further clarification of bag cleaning rationale
will be discussed  later.  A summary of the operating conditions, cleaning
parameters and cleaning modes  is presented in Table 5.

                                     458

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TADLE 4.  COMPARISON OF BAG SPECIFICATIONS

Fabric
Weight
Oi./yd2
Weave
Thread Count
4=.
c_n
10 Permeability
cfm/ft'e.S in. H20
Finish




Warp Yarn
Fill Yarn

Fabric Filter
Acid Flex
Style 504-1

woven glass
9.8

3x1 twill (left hand)
54x30


45-60

4.0 - 4.5%
mill ti -component
proprietary finish
graphite/si) Icone/teflon/x
base ^ teflon B coating
75 1/0
50 1/0 text., 9 .
150 1/0 ' * P'y
W. W. Crlswell
Teflon B
Style 442-57IIC2

woven glass
10.5

3x1 twill (right hand)
54x30


60-80

Teflon B
10Z by wt.



150 1/2
150 1/4 all textured

W. W. Crlswell
Silicone/Graphite
Style 445-04

woven glass
11.0

3x1 twill (right hand)
65x33


45-65

silicone 1 graphite
1% by wt. total



150 1/2
37/S textured

Menardl -Southern
Teflon B
Style MS-601

woven glass
9.5

3x1 twill
54x30


75

Teflon B
10% by wt.



150 1/2
150 1/4 all textured
(turned inside)

-------
         TABLE 5.  SUMMARY OF OPERATING CONDITIONS FOR PILOT 3AGHOUSE
Flue Gas Flow Rate

Temperature

Bag Terminal Pressure Drop

Air/Cloth Ratio
 2.3 - 2.5 aon/min (80 - 90 acfm)

 130 - 190°C (266 - 374°F)

 15, 20, 25, cm W. C. (6, 8, 10, in. W. C.

 0.95 - 1.07 m/min (3.1 - 3.5 ft/min)
                          CLEANING CHARACTERISTICS
Shake Parameters

            Amplitude

            Frequency

            First Delay

            Shake Duration

            Final Delay

            Acceleration



            Bag Tension

Deflation Parameter

            Reverse AP
0.95 cm (.375 in.)"

3.2 and 6.4 cycles per second

30 seconds

10 seconds

60 seconds

0.39 g (3.8 m/sec2} at 3.2 cps

1.56g  (15.2m/sec2) at 5.4 cps

13.5 kg (30 IDS)



1.2, 12 cm (0.5, 5.0 in.)
                       CLEANING MOOES                       SYMBOL

        aLow Deflation - Low Shake  Frequency  (LO-LSF)          A

        bHigh Deflation - Low Shake Frequency  (HO-LSF)         B

        Low Deflation - High Shake  Frequency  (LO-HSF)          C

        High Deflation - High Shake Frequency  (HD-HSF)         0

a.  Low Deflation  :  1.2 cm reverse  air pressure drop  (corresponds  to  reverse
    flow air-to-cloth ratio of approximately  1.7

b.  High Deflation  : 12 cm reverse  air pressure drop  (corrssoonds  to  reverse
    flow 3 to 4  times that for low 'deflation     "      '!
                                     460

-------
     Two coal types were fired in Unit No. 1 during the evaluation period
with a two- to threefold difference in ash content between the coal
types.  Previous experience with the high-ash New Mexico coal showed
higher concentration and bag pressure drop on the full-scale baghouse.
Despite the known performance sensitivity to coal type, accountability of
coal type usage was indefinite during segments of this study.

Data Acquisition

     The following pilot baghouse data were recorded continuously through-
out the program:

     •    Pressure drop across the bags

     •    Gas flow rate pressure drop across a Stairmand disc

Other pilot baghouse data were manually recorded semihourly:

     •    Temperature profile across the system

     •    Static pressure profile across the sytem

     •    Slipstream interface temperature

     •    Cleaning cycle data (APR> APT, flow AP, shakes/cycle, etc.)

     Pertinent boiler operating data were recorded hourly in the control
room, and copies of the logs were made available for the test period.
Coal samples were taken 3 times a day, and results of coal analyses were
also made available.

     Flue gas composition and velocity data were taken at least once per
shift for methodology-assurance and particulate sampling preparation.

Particulate Measurements

     Total mass and impactor measurements at the inlet and outlet loca-
tions were conducted at isokinetic conditions.  Brink and Andersen impact-
ors measured the inlet and outlet size distributions, respectively.  All
filters and substrates were made of Reeve Angel 934 AH material because
of low  sulfur dioxide (802) absorptivity.  All substrates were precondi-
tioned  for 6 hours.  Samples were obtained with extractive probes fitted
with interchangeable nozzles at average velocity locations.  Sampling
trains  similar to that described in Method 5 of the FEDERAL REGISTER were
used.

Data Reduction

     Several analytical tools were employed in the reduction and analysis
of bag pressure drop, particulate concentration and size distribution

                                     461

-------
data.  The large number of tests taken over a variety of conditions for
the program duration required a substantial analytical effort.

     A computer program was used to calculate impactor stage cut-points
and dust loadings.  Fractional penetrations were calculated using a
program that performs the following:5

     •    Log-normal transformation of inlet and outlet cumulative size
          distributi ons

     •    Linear, quadratic, and spline fits to the transformed data

     •    Analytical differentiation of the fitted curve

     •    Calculation of fractional penetrations from differential inlet
          and outlet size distributions

     Operating performance was evaluated primarily with respect to fabric/
cake drag and cleandown levels.  Fabric/cake drag, known as specific cake
resistance coefficient (K2), was estimated by a methodical approach.
Cleandown levels were determined by records of residual drag.   The funda-
mentals of baghouse performance modeling were utilized to eliminate
fluctuations in particulate concentration and filtration velocity.

     Since it was impractical to measure cake mass for all the candidate
bags, values of Kg were determined on the basis of dust concentration
instead.  Values of estimated K2 were calculated by the following rela-
tionship:
                              K  =
                                       V2Ct
where:
               TT 	


               c =
Terminal Drag

Residual Drag

Filtration velocity

Dust concentration
               t =  Filtration time
N/m2

N/m2

m/min

g/m3

min
Prior to averaging K2 values, they were arranged in chronological order
and the transient values (corresponding to bag conditioning) were elimin-
ated.  Since the pressure drop-time profiles showed a linear relation-
ship, the mean pressure drop is the average of residual and terminal
values.  This approach provided a fundamental basis for comparing bag
types and cleaning conditions.
                                     462

-------
RESULTS AND DISCUSSION

     This program was directed to assess alternate means for reducing
high pressure drop levels that were being experienced at Harrington
Station.  Factors contributing to high pressure drop levels were bag type,
cleaning parameters, and air-to-cloth ratio.  Available means of reduc-
tion were appropriate selection of bag type and cleaning conditions.
Optimization of these means is recommended, since their synergistic
effects can be substantial.

SUMMARY OF OPERATING PERFORMANCE

     A summary-level accounting for this evaluation is presented and
displayed in Table 6 and Figure 1, respectively.  The residual bag pres-
sure drop values in Table 6 and the curves for average pressure drop vs.
filtration time allow a ranking of candidate bags and an assessment of
cleaning conditions.  The results from the analytical and graphic treat-
ment clearly show the Acid-Flex bags to exhibit the lowest pressure drop
performance.  The Acid-Flex bags achieved both the lowest residual pres-
sure drop and lowest specific cake resistance coefficient values con-
sistently for all cleaning conditions.  The other three bag types per-
formed to a lesser degree with essentially comparable operating charac-
teristics.

     Results from bag cleaning characterization show that higher cleaning
energy also reduces operating pressure drop levels.  Enhancement of
deflation and/or shake cleaning levels consistently achieved lower resi-
dual and mean pressure drops.  Increasing shake frequency is a more
effective and available means for pressure drop reduction.

Estimated K2 Results

     Specific cake resistance is the effective porosity indicator re-
lating fabric cake drag to operating conditions.  By the straightforward
approach discussed earlier, a realistic porosity or drag indicator can be
derived directly from the operating data.  The estimated K2 values rep-
resent the effective fabric/cake porosity.

     Compilation of estimated K2 values is presented in Table 6 for each
bag and cleaning mode.  The first column of estimated K2 values repre-
sents the test conditions, while the values in the second column are for
standard conditions as defined in the GCA performance model.  These
results consistently demonstrate that the effective porosity of the dust
cake on the Acid-Flex bags was significantly lower than that for the
other candidate bags.
                                     463

-------
         TABLE  6.   PILOT  3AGHOUSE  RESIDUAL  PRESSURE  DROPS  AND

                     SPECIFIC  CAKE  RESISTANCE  CO-EFFTCIENTS
Bag Type
Acid Flex
Minardi Southern
Teflon 3
Cri swell Teflon 3
Cri swell Graph i ta/Si 1 icone
APT
CM
15
20
25
IS
20
25
15
20
25
15
20
25
AP, CM
Cleaning Mode
Af
3.9
9.7
10.2
10.7
12.9
-
12.7
14.0
-
11.4
14.0
-
3f
4.3
5.1
5.5
7.6
3.5
3.4
3.9
cf
3.6
4.1
-
9.7
-
-
-
10. Z\ -
-
*5.5 | -
*6.S
•7.1
-
-
0 +
-
-
-
5.1
6.1
-
-
-
-

-
-
KZ
l*-Wn
Actual
1603C
Im/min
10.4
20.4
15.7
13.0
11. S
5ta.
ie v*»
25 u
O.olm/mini
5.2
12.2
9.4
7.3
7.0
Wyoming :  iNew Mexico Coal  1:1 Blend
 All  others Wyoming Coal
t
 See  Table  5 for  key.
                                        464

-------
Q-
o
ce
Q
   25  -
                     O
   20
                           BAG TYPE

               O     FABRIC FILTER ACID-FLEX
               A     MENARDI  SOUTHERN TEFLON  B
               D  H*CRISWELL GRAPHITE-SILICONE
               O     CRISWELL TEFLON B
               O     FULL SCALE BAGHOUSE,
                      CRtSWELL GRAPHITE-SILICONE  BAG

                  • *DENOTES USE OF NEW MEXICOIWYOMING COAL III
                     ALL OTHERS, WYOMING COAL
CC
Q-
 O
 X
    15
    10
                                                          KEY
                                              SHAKE MODE
                                               LD-LSF
                                               HD-LSF
                                               LD-HSF
                                               HD-HSF
                                            I
                   25
             50           75           100

             FILTRATION CYCLE TIME, MINUTES
                                                                    125
     Figure  1.
    25
 Q_
 O
 ce
    20
Baghouse  operating  pressure drop versus
filtration cycle time.
                      O
                          BAG TYPE
               O    FABRIC FILTER ACID-FLEX
               A    MENARDI SOUTHERN TEFLON B
               Q • CRISWELL GRAPHITE-SILICONE
               O    CRISWELL TEFLON B
               <>    FULL  SCALE BAGHOUSE,
                     CRISWELL GRAPHITE-SILICONE BAG
                 • 'DENOTES USE OF NEW  MEXICOIWYOMING  COAL  in
                    ALL OTHERS, WYOMING COAL
 i-
 <
 a.
 o
 O
 I
 IS
    15
    10
                                                              SHAKE MODE
                                                                HD-LSF
                                            _L
                   25
              50           75          100

              FILTRATION CYCLE TIME, MINUTES
                                                                    125
    Figure 2.   Comparison of  performance characteristics
                 of  candidate bags.
                                   465

-------
Effect of Cleaning Conditions

     The factors which ultimately define the degree of cleandown are
those which determine the type and degree of cleaning energy delivered to
the bags for dislodgement of the dust cake.  The fabric must be flexed in
some manner and to a degree sufficient to break the dust cake.  This
flexure overcomes the adhesive forces between particles within the dust
cake and/or those between the particles and the fabric.

     Discussions with representatives of the utility and baghouse vendor
led to the conclusion that the shake cleaning cycle in the pilot
baghouse could not duplicate that in the full-scale house. This con-
clusion was based on differences in amplitude and harmonic shaker motion
and bag size (e.g., aspect ratio). Consequently, the cleaning parameters
were varied with respect to deflation pressure, shake frequency, and
shake duration to determine if any one of the bag candidates would perform
in a superior.fashion over the range of cleaning modes.  Cleaning was
initiated at the terminal levels of 15, 20, and 25 cm W.C.
     The difference in the cleandown characteristics for the four fabrics
is shown in Table 6.  In mode A, when cleaning was initiated at a termi-
nal pressure drop, AP™, of 15 cm W.C., the resulting residual pressure
drop, AP , is lowest for the Acid-Flex fabric.  This differential becomes
even more significant as the AP™ increases.  At a AP™ of 25 cm W.C., the
Acid-Flex still had a lower APD than the other three fabrics at a AP™ of
-.I-                            K                                     J
i5 cm.

     The greatest differential in APR levels was realized between low and
high shake frequency (modes A and C).  The Acid-Flex responded to a
higher degree, 140-150 percent improved cleandown, than did the silicone/
graphite bag, 100-115 percent, while the Teflon B fabric showed minimal
improvement in the range of only 10 percent.

     Significant improvement in cleandown was also realized when going
from low to high deflation pressure  (modes A and B).   However, this would
not be a practical change in the Harrington cleaning cycle since experi-
ence has already shown that operation at design deflation pressure of 1.3
cm (0.5 in W.C.) causes the bags to pancake and prevents dust cake re-
moval during the shake cycle.  However, it does focus interest on a
combination reverse air/shake cleaning cycle with ring bags.

     The curves displayed in Figures 2 and 3, which are the average pilot
baghouse AP vs. filtration time for modes A and B, again show Acid-Flex
to be the most attractive fabric, with the other three fabrics exhibiting
essentially comparable levels of performance.  These curves reflect the
effect of the K2 values for each bag type since they determine the filtra-
tion time required to reach a predetermined AP™.


                                      466

-------
  25 _
                   O
Q.
O
g 20

UJ
                                         BAG TYPE
                              O    FABRIC FILTER ACID-FLEX
                              A    MENARDI SOUTHERN TEFLON B
                              D  B*CRISWELL GRAPHITE-SI LICONE
                              O    CRISWELL TEFLON B
                              O    FULL SCALE BAGHOUSE,
                                    CRISWELL GRAPHITE-SILICONE
                                                              JAG
                                   *DENOTES USE OF NEW MEXICO:KYOMING COAL  1:1
                                   ALL OTHERS, WYOMING COAL
2  15
o
UJ
a
x
   10
                                                   KEY
                                                    A
                                                          SHAKE MODE
                                                           LD-LSF
                                          J_
                                                      _L
                 25
                             50           75          100

                             FILTRATION CYCLE  TIME, MINUTES
                                                                  125
  Figure 3.   Comparison  of performance characteristics
               of candidate bags.
   25
                                                BAG TYPE

                                        O FABRIC FILTER ACID-FLEX
 Li
 QT20
 O
 a:
 Q

 UJ
 o:
   15
   10
                                                         SHAKE MODE

                                                           LD-LSF
                                                           HD-LSF
                                                           LD-HSF
                 _L
                             _L
      0           25          50           75          100
                      FILTRATION  CYCLE TIME,  MINUTES

   Figure 4.   Comparison of  acid-flex  performance  for
                cleaning  modes A, B  & C.

                                   467
                                                                  125

-------
     The curves displayed in Figure 4 demonstrate the improvement in
Acid-Flex bag performance as the degree of cleaning energy is increased.
The curves for modes A and C depict the improved operating levels ob-
tained with the high shake frequency, while curves A and B depict
improvement related to the higher deflation pressure drop across the
bags.

     The normal 10 sec. shake duration was extended to 30 sec. within
several cleaning modes and for several bag types.  Results indicated no
appreciable improvements in cleandown; thus, use of an extended shake
duration was discontinued.

     Selection of the optimum cleaning mode must be based not only on
performance characteristics, but also on the degree of physical wear due
to fabric flexing with each cleaning cycle.  Economics dictate achieving
a minimum bag life before attempting to improve operating pressure drop
levels and the resultant annual operating costs.

Effect of Coal Type

     Two coal types were fired at Harrington Station during this study.
The 50:50 blend of Wyoming and New Mexico coals was fired for the first 2
test weeks and corresponded to 2 of 3 weeks testing for the silicone/
graphite bags.

     A comparison of the performance characteristics for the silicone/
graphite (S/G) bags in Figures 4 and 1 would appear to indicate dif-
ferences related to coal type.  In Figure 4, the S/G bags are closely
grouped with the two Teflon B bags for cleaning mode A.   _;,dse data were
generated when only Wyoming coal was being fired.  The same curves for
cleaning mode B in Figure 1 find the S/G bags demonstrating an appre-
ciably higher level of performance.  The S/G curve in Figure 1, however,
was generated during Wyoming/New Mexico blend firing while the other
curves of Figure 1 relate to Wyoming coal only.  It would appear from
this single case that the Wyoming/New Mexico coal blend resulted in
better performance levels for the S/G bags than those observed for Wyoming
coal only.  This observation illustrates the sensitivity and specificity
of the fabric/cake interface, evidenced in this and other studies on
fabric/cake characterization.

Collection Performance Measurements

     The control device characteristic of practical importance is that of
overall collection performance.  This performance can be described and
measured by the emissions which penetrate the device and pass into the
atmosphere.  Collection performance and fractional efficiency are a
function of inlet particle size distribution, as well as other variables.
                                     468

-------
     Cumulative and differential inlet particle size distribution curves
are shown in Figures 5 and 6, respectively, for Amarillo and three other
utility PC boilers.  As illustrated, the size distribution at Harrington
Station falls in the same general range as the other sites.

     Since fabric filters with glass bags typically deliver efficiencies
in the range of 99.8 percent or higher, only a moderate effort was made
to document collection performance for the four bag types.  A summary of
the inlet and outlet loadings, efficiency, and emission levels in ng/J
are presented in Table 7.  All four bag types performed at a level which
yields emissions an order of magnitude less than the New Source Performance
Standard (NSPS) of 13 ng/J (0.03 Ib/MBtu).  Figure 7 shows fractional penetra-
tion for the Acid-Flex and Criswell Teflon B bags.

Electrostatic Effects

     It has been speculated that electrostatic effects may be a contri-
buting factor to the bag cleaning problems at Harrington Station.  A
cursory attempt was made to measure the electrostatic voltage levels
present on the silicone/graphite bags in the pilot baghouse.  The metho-
dology was the same as that employed by Bob Donovan, Research Triangle
Institute, on the Harrington baghouse.6

     A cage voltage measurement was made by attaching a Type 430 stain-
less steel screen  (0.0075-inch wire, 24 mesh) cage to the bottom of the
middle bag in the pilot baghouse.  The cage was attached to the bag by
sewing it to the bag cuff at the cage top, middle, and bottom points in
such a way that no penetration of the filtering surface of the bag was
required.  The cage was 25.4 cm high and was constructed such that the
diameter was only  slightly larger than that of the bag.  A Teflon-shielded
cable from the cage was passed through the adjacent glass window jamb and
coupled to an electrometer immediately adjacent to the baghouse compartment.

     The profile of cage voltage measurements over two typical cleaning/
filtration cycles  is shown in Figure 8.  A detailed analysis or hypo-
thesis of the resultant, effect on bag pressure drop is beyond the scope
of this report.  However, it appears that sufficient charge levels were
shown to exist to be a potential contributing factor to pressure drop
problems and to indicate the need for further definition, clarification
and evaluations.

RECOMMENDATIONS

     Reduction of operating pressure drop at Harrington Station:

     •    Evaluate higher shake frequencies and monitor bag at quarterly
          intervals via diagnostic tests (i.e., Muller Burst Strength,
          Tensile Strength, MIT Flex Fold tester, etc.).
                                     469

-------
   90  _
   70
t-
§  50
   30
1  10
u
    Ol
    0.01
      0.1
O  AMARILLO, TEXAS            7-4
O  PAGE, ARIZONA             9-6
O  COLSTRIP, MONTANA         20-°
£1  MICHIGAN STATE UNIVERSITY   9-0
                                   GEOMETRIC
                            U50      STANDARD
                          MICRONS   DEVIATION
fi. 2
                                                        10
                     PARTICIPATE DIAMETER/ MICRONS
   Figure 5.   Boiler effluent cumulative  particle  size
                distributions  at four power plants.
    10*
 -z.
 a
 o
 -I
 o
    10
    10
                 O PAGE, ARIZONA
                   COLSTRIP, MONTANA
                   MICHIGAN STATE UNIVERSITY
                               I
      0.1              1              10
              PARTICIPATE DIAMETER/ MICRONS
                                        100
    Figure 6.   Comparison of boiler  effluent fractional
                size  distribution at  four  power plants.
                            470

-------
                       TABLE  7.    SUMMARY  OF PARTICIPATE CONCENTRATION MEASUREMENTS
Bag Type
**Criswell Graph He-Si Itcone
Fabric Filter
Acid Flex
Menardi Southern
Teflon B
Criswell Teflon B
Average Inlet
Loading
gin/DNCM
3.2
2.4
2.4
2.4
Average Outlet
Loading
(jm/ONCM
0.0038
0.0018
0,0007
0,0006
Efficiency
Percent
99.88
99.92
99.97
99.575
*Einiss1on
Level
ng/J
0.71
0.34
0.13
0.11
 *  'Current NSPS  13 ng/J



k*  1:1  blend of Wyoming and  New Mexico  coals.   All  others Wyoming coal.

-------
1.0 ,_
0.1
0.01
   0.1
                            A  FABRIC  FILTER ACID-FLEX

                            O  CRI SWELL TEFLON  B
            1                     10

PARTICIPATE  DIAMETERi MICRONS
 Figure 7.   Fractional  penetration  characteristics
              for two  bag types.
                          472

-------
   ELECTROSTATIC
CAGE VOLTAGE,  KV
                       0315
                   25     30     35      40     45
                      FILTRATION  TIME,  MINUTES
      BAG AP,CM
15
12
 9
 6
 3
 0
                       0315    20
                   25     30     35      40     45
                      FILTRATION  TIME,  MINUTES
50    55
       Figure 8.  Electrostatic  cage voltage profile for two typical cleaning cycles.

-------
     •    Evaluate performance characteristics of Acid-Flex or an equi-
          valent fabric.

     •    Evaluate performance characteristics of higher deflation pres-
          sures with ring bags.

Suggested future studies:

     •    Extend characterization of electrostatics at Harrington and
          other coal-fired boiler/baghouse sites.

     ®    Develop improved hardware and methodology for experimental
          pilot-scale determination of specific cake resistance coef-
          ficients (1(2) -

REFERENCES

1.   Lipscomb, W.O.  Environmental Protection Agency Fabric Filter Program -
     A Comparison Study of Utility Boilers Firing Eastern and Western
     Coal.  In:  Symposium on the Transfer and Utilization of Particulate
     Control Technology:   Volume 2.  Fabric Filters and Current Trends in
     Control Equipment, Venditti, F.P., J.A. Armstrong, and M. Durham
     (eels,)-  Research Triangle Park, N.C., U.S.  Environmental Protection
     Agency, February 1979.  Publication No. EPA-600/7-79-044b. p. 53-74.

2.   Dennis, R., and H. A. Klemm.  Fabric Filter Model Format Change:
     Volume 1.  Detailed Technical Report.  GCA Corporation, GCA/Technology
     Division.  Bedford,  Massachusetts.  Publication No.  GCA-TR-78-51-G(l).
     January 1979. I69p.

3.   Faulkner, G., and K.L. Ladd.  Startup, Operation and Performance
     Testing of Fabric Filter System - Harrington Station, Unit No.  2.
     In: Symposium on the Transfer and Utilization of Particulate Control
     Technology:  Volume 2.  Fabric Filters and Current Trends in Control
     Equipment, Venditti, F.P., J.A. Armstrong, and M. Durham (eds.).
     Research Triangle Park, N.C., U.S. Environmental Protection Agency,
     February 1979. Publication No. EPA-600/7-79-044b. p. 219-232.

4.   Hall, R.R.  Mobile Fabric Filter System: Design Report.  GCA Cor-
     poration, GCA/Technology Division.  Bedford, Massachusetts.  October
     1974.  73p. NTIS No. PB246-287/7BA.

5.   Lawless, P.A.  Analysis of Cascade Impactor Data for Calculating
     Particle Penetration.  U.S. Environmental Protection Agency, Indus-
     trial Environmental Research Laboratory.  Research Triangle Park,
     N.C.  Publication No. EPA-600/7-78-189.  September 1978.  39p.
                                      474

-------
6.    Donovan, R.P.  Passive Electrostatic Effects in Flyash Fabric
     Filtration.  Presented at the Second Symposium on the Transfer and
     Utilization of Particulate Control Technology.   Hosted by the
     U.S. Environmental Protection Agency, Research Triangle Park, N.C.,
     and the Denver Research Institute, University of Denver.  Denver,
     Colorado, July 25, 1979.

7.    Emission Test Results: Harrington No. 1.  C-E Power Systems, Combustion
     Engineering, Inc.  Windsor, Connecticut.  June 1977.   24p.

8.    Chambers, R. Personal Communication.  Southwestern Public Service
     Company, Harrington Station.  Amarillo, Texas.   March 6, 1979.

ACKNOWLEDGEMENTS

     The authors wish to express their appreciation to Southwestern
Public Service Company personnel for their assistance and cordial coopera-
tion, and to Dale Harmon and Jim Turner, EPA, Technical Project Officers.
                                     475

-------
             PASSIVE ELECTROSTATIC EFFECTS IN FABRIC FILTRATION

                                     by

                                R.P.  Donovan
                         Research Triangle Institute
                     Research Triangle Park, N.C.  27709

                                     and
                         J.H. Turner and J.H.  Abbott
                Industrial Environmental Research Laboratory
                    U.S. Environmental Protection Agency
                     Research Triangle Park, N.C.  27711
                                  ABSTRACT

     Electrical charge transport accompanies the flow of dust and flyash
through particulate control equipment.  In a fabric filter these charges can
accumulate on the fabric and other electrically isolated regions.  The magni-
tude of the charge buildup depends upon the electrical properties of both the
dust and the fabric and especially the relative humidity of the gas stream.
This paper presents laboratory measurements of fabric charge accumulation in
both pulse jet and shaker-cleaned baghouses.  Brief field measurements show
similar charging patterns.  No effect on baghouse performance can yet be
unambiguously attributed to these charges.
                                     476

-------
           PASSIVE ELECTROSTATIC EFFECTS IN FLYASH FABRIC FILTRATION


     That electrical charges exist on flyash and other aerosol particles is
well known.1  Such charges arise:  1) because of charge exchange between
neutral materials in contact and their subsequent separation, or 2) because of
ion capture by the particles and the resultant Boltzmann charge equilibrium.
Particle deposition or collection is necessarily accompanied by charge deposi-
tion and collection; and particle flow is to some degree a charge flow, as
evident by the pipe charging effects brought about by particle flow through that
pipe.2

     It is these charging effects that make up the passive electrostatic effects
to be discussed in this paper.  These effects are passive because no overt
charging action is required to create the charges; the charges are an inherent
property of virtually all flowing dust systems.  The questions to be considered
include:

     1.   What is the magnitude of these passive charges in a baghouse and on
          what does the magnitude of these charges depend?
     2.   What influence, if any, do these charges have upon baghouse perfor-
          mance?

BACKGROUND

     Measurements of voltage buildup on the support cages of a pulse jet fabric
filter have previously been reported.3'4  This measurement, shown schematically
in Figure 1, consists simply of connecting an electrometer to the support cage
of a bag and recording current or voltage during operation.

     For voltage measurements the electrical resistance of the fabric determines
the "load" resistance across which the electrostatic voltage is measured.
Physically, this load resistance is the electrical resistance of the fabric
separating the cage collar from the venturi shoulder.  When the resistive
coupling to electrical ground dominates the cage voltage, the magnitude of the
cage voltage is directly proportional to the fabric resistance.  For conductive
fabrics an insulating sleeve must be added between the fabric and the venturi
in order to support a significant cage voltage.

     For current measurements the electrical resistance between the cage and
the collar should exceed the input resistance of the electrometer by several
orders of magnitude.  Again, for electrically conducting fabrics, an insulating
sleeve is necessary in'order to make a meaningful measurement.

     Previous publications summarized the initial observations of such measure-
ments3 and noted a correlation between high cage voltage and dust penetration
through the bag.4  This correlation has been explored further using different
fabrics as described in the first part of this paper.  A second measuring
configuration, appropriate for inside-out filtration, was subsequently developed
and used to make measurements on both a field installation and a laboratory
shaker baghouse.  These experiments are also described in this paper.
                                      477

-------
LABORATORY PULSE JET EXPERIMENTS

     As an extension to the measurements reported in Reference 4,  a fresh set
of fabrics was obtained through the courtesy of E. de Garbolewski of W.L. Gore
Associates.  Table 1 lists these fabrics, their Run Identifiers,  and some
properties.  The set of four different fabric types was prepared so that each
differed from another only in its electrical properties or in the addition of
a specific compositional change—the Gore Tex* layer.  The number contained in
the Run Identifier gives the sequence in which the runs were carried out.

     When all cages of the nine bag array are tied together electrically, a
typical composite cage voltage appears as sketched in Figure 2.   Three quanti-
ties are defined in Figure 2:  1) V  is the value of cage voltage immediately
prior to the reverse pulse cleaning spike; 2) AV  is the height  of the voltage
spike induced by the cleaning pulse; and 3) T is the time required for the
cage voltage to recover to 1/e of its value prior to cleaning.

     V  and AV  correlate with dust penetration through the fabric as shown in
Figure 3.  Each datum point in Figure 3 represents the average of two sequential
measurements of dust penetration, both values being determined by a 20 minute
sampling of the outlet.  The cage voltage for each datum is the  arithmetic
average of 20 measurements.  The standard deviation of the cage  voltage is
about 5% of the mean when, as is true here, all cages are tied together
electrically.

     Cage voltage and dust penetration both correlate with relative humidity.
Because of this dependence, relative humidity was used as an independent control
of cage voltage over a limited range.

     With fixed inlet dust loading and constant air-to-cloth ratio, the buildup
of bag pressure drop between cleaning pulses was lower at 70% relative humidity
than at either 50% or 30% relative humidity.  The absolute pressure drop was
also lower at the high relative humidities.  No dependence of these pressure
drops upon cage voltage was apparent.

     The relationship between flyash penetration and relative humidity is
emphasized by replotting the V  data of Figure 3 in Figure 4.  The shaded
regions represent the data envelope of each fabric.  All data in Figure 4
were measured after 6 hours of operation at the desired set point on the
humidity control unit.  Operation at each relative humidity was  repeated with
sequencing in the opposite directions; for example, 50%-30%-70%-70%-30%-50%.
Sequence effects do exist in that the data collected at a given  relative
humidity depend on the relative humidity of the immediately preceding datum
point.  For example, the dust penetration measured at 70% relative humidity
depended on whether the preceding test point was at 30% or 70% relative
humidity.  This observation implies that the 6 hour equilibrating time
allowed was inadequate and that a major source of error in collecting the data
was failure to reach a steady state at each value of relative humidity.

     Even so the trend toward reduced flyash penetration at high relative
humidity is clear for all these fabrics.  That relative humidity also correlates
*
 Registered Trademark of W.L. Gore £/ Associates, Inc.
                                     478

-------
with cage voltage for a given fabric raises the possibility that the relative
humidity dependence portrayed in Figure 4 originates from electrostatic forces.
Indeed one major reason for including epitropic blends in the fabric test group
was to explore this possibility.

     The preliminary observation of these evaluations is to refute this electro-
static force hypothesis as an explanation of the dependence of flyash penetration
upon relative humidity.  In Figure 4 flyash penetration through the epitropic
polyester fabric (PJ53) is comparable to that through the standard polyester
(PJ50) in spite of the essentially negligible cage voltage measured during
epitropic polyester operation.  While the Gore Tex/polyester fabric differs
from the Gore Tex/epitropic polyester fabric in absolute dust penetration, both
fabrics exhibit the same general relative humidity dependence and it is this
property rather than the absolute values of flyash penetration that is crucial
for the electrostatic hypothesis.  If the relative humidity dependence is elec-
trostatic in origin, a conductive fabric should remove the charge and eliminate
the relative humidity dependence.  The epitropic blend failed to eliminate the
relative humidity dependence in either of the two samples, although it effectively
eliminated the cage voltage of the straight epitropic fiber blended polyester and
greatly reduced it for the Gore Tex/epitropic polyester fabric.

     These experiments still leave room for doubt, however, because of the
composition of the epitropic blended fabrics.  The epitropic fibers with which
the epitropic polyester fabrics are blended consist of polyester fibers impreg-
nated with carbon black particles.  One technique is to draw a bicomponent
fiber whose outer layer has a lower softening point than its core.  When the
outer layer is subsequently softened, carbon black particles can be incorporated
into the surface shell but the fiber retains most of its original dimensions
because of its unaffected core component.  The resulting fiber is one with a
highly electrically conductive surface.

     In the preparation of epitropic fabrics a small percentage of these epi-
tropic fibers blended with conventional polyester staple fibers (5% is typical,
although 3.5% was the blend percentage in our samples) produces a fabric of
greatly reduced surface resistivity which is useful for eliminating static
charge buildup in textile products.5  The presence of these epitropic fibers
in  the test fabrics was to reduce the electrical resistance between the cage
and the venturi shoulder  (electrical ground) to 104 to 106 ohms, preventing the
buildup of any significant charges on the cage.

     At the fiber level, however, most of the fibers are not coupled to the
cage by a conductive fiber—96.5% of the fibers are still the relatively non-
conductive polyester.  The fabric surface seen by the incoming dust could still
be much the same as for the 100% polyester fabric, even though the cage is well
coupled to electrical ground.

     Plans are underway to extend these measurements to 100% stainless steel
felt fabrics.  Here all fibers should be closely tied to electrical ground and
no charge accumulation should occur initially.  As the dust cake builds up, the
electrical properties of the dust will impede charge transfer to the conductive
fabric but this interference requires some minimum operating time before becoming
significant.


                                       479

-------
BAG DUST LOAD

     A second independent hypothesis seeking to explain the relationship between
relative humidity and flyash penetration also invokes electrostatic forces.  In
this model the role of charges building up on the fabric surface is to intro-
duce an electrostatic force which binds the dust to the fabric and hence
creates a larger dust load on the bag than would exist in the absence of such
electrical forces.  Increased dust load on the bag in turn is then postulated
to cause increased dust penetration and higher pressure drop.6'7

     To investigate this hypothesis total bag weights following operation at
various relative humidities were measured.  The technique was to stop the
filtration cycle immediately after the Row 3 cleaning pulse had fired.  The
baghouse was opened gingerly and a large plastic bag slipped over the dusty bag,
including its cage, before demounting.  Once the plastic cover was in place so
as to catch dust inadvertently shaken loose during removal, the bag was demounted
and weighed—plastic bag, dusty fabric, and cage together.  Each of the nine
bags were weighed one after the other and then remounted at the same location
in the baghouse for the next run.

     These admittedly crude weighings uniformly confirmed a dependence of bag
dust load upon relative humidity, the lowest dust loads on the bag occurring at
the highest values of relative humidity.

     Table 2 summarizes a recent data set showing this relationship.  The run
identifier is PJ54.  The bags used in this run were the same polyester bags
removed after completing Run PJ50.  Nine months after the last PJ50 run each
used bag was remounted on a cage, weighed, and inserted in the baghouse for
the PJ54 series.  Table 2 lists the average weight change in the three bags
making up a row after operating for 6 hours at the indicated relative humidity.
Inlet loading for all these data was 9 g/m3 (4 grains/ft3).  Total gas flow
was 7 m3/iain (250 ft3/min), yielding an air-to-cloth ratio of 3 cm/sec (6 fpm).

     Table 2 and the curves constructed from the data (Figure 5) show a dust
load dependence in accordance with the qualitative predictions of the electro-
static model—at high relative humidity, less charge exists on the fabric and
also less dust.  However this confirmation by no means proves an electrostatic
interaction.  Other nonelectrostatic mechanisms could also produce the same
effect.  What is shown is that at high relative humidity (> 60%) less dust
ends up on the bag and less dust penetrates the bag.  The data do not distin-
guish between the postulated reduced electrostatic binding forces at the bag
surface and some other humidity dependent phenomenon, such as enhanced agglom-
eration and fallout, which reduces the dust that reaches the bag at high
relative humidity even though that quantity fed into the baghouse remains
constant for all test humidities.
                                      480

-------
FIELD MEASUREMENTS

     The data reported so far have been collected with a laboratory-sized
pulse jet baghouse filtering redispersed flyash and operating at room tempera-
ture.  Because these conditions are sufficiently different from typical boiler
operations, some pause seemed warrented before embarking on a detailed study
in order to confirm that the charge buildups detected in the laboratory also
occurred in operating field installations.

     Measurements were therefore carried out at two field sites:

     1.   A stoker fed boiler at Kerr Finishing Plant, Concord, NC.

     2.   Harrington No. 2 unit of Southwestern Public Service, Amarillo, TX.

The baghouse installation at Kerr consists of two parallel modules.  At the time
of the electrostatic measurements one module operated in a reverse air cleaning
mode with woven fiberglass bags; the second module used 100% teflon felt bags
cleaned by reverse air with a pulse jet assist.  Both modules are outside-in
filters and employ steel cages electrically isolated from ground by the fabric.
Cage voltage measurement technique therefore was identical to that used in the
laboratory.

     The flyash from the Kerr boiler appears carbon rich and had coated both
fabrics with a black deposit which proved relatively conductive.  The electri-
cal  resistance between the cage and ground was on the order of 10^ ohms when
measured during the weekend before the Monday startup.  Cage voltages at oper-
ating  temperature and flue gas flow were less than 0.1 volts for both fabrics,
as the low values of "load" resistance would anticipate.  Only one bag from
each module was monitored and each of these had been in service for over a
year.  The conclusion was that only negligible charge accumulation on the bags
could be detected; no measurement of charge on the inlet flyash was made.

     Harrington Unit No. 2 includes a pulverized coal boiler fired with low
sulfur western coal from Black Thunder Mine in Wyoming.  The baghouse is a
Wheelabrator Frye unit, cleaned by reverse-deflate air and shake.  The fabric
in service in the compartment monitored for electrostatic effects was silicone-
graphite coated fiberglass.  This utility boiler baghouse, as  most utility
baghouses, is an inside-out filter and hence has no cage with which to monitor
voltage or current.  To gather data comparable to that measured with the cage
electrodes of the outside-in baghouses aim (40 in.)  section of  stainless  steel
screen was wrapped around the bottom of one of the 29.2 cm (11.5  in.)  diameter
bags.  This bag was adjacent to the compartment door so that an insulated lead
could be easily fed through to an outside electrometer.  Electrical resistance
between this outside screen "cage" and ground was about 5xl08 ohms at ambient
temperature and no flue gas flow.

     The flyash entering the baghouse on Harrington is negatively  charged.
Brief  sampling of current and mass yielded an average charge/mass value of
1.7  uC/g, a value perhaps typical of a low efficiency stage of an  electrostatic
precipitator.

     Immediately upon admission of this charged flue gas to the monitored com-
partment a large negative voltage appeared on the screen cage.  This signal

                                       481

-------
settled down to a steady state value of -100 to -300 V during the filtering
cycle, although excursions beyond this range in both directions also occurred.

     During the cleaning cycle as gas flow stops, a voltage spike appeared! in
the trace of cage voltage and the sign of the voltage changed—much like  the
laboratory observations of pulse jet cleaning except that the transition  was
slower.  During the reverse air, pause, and shake periods the cage voltage was
small and usually positive.  Upon resumption of flue gas flow the large nega-
tive signal reappeared and relaxed to its previous steady state range,
typically -100 to -300 volts.

     This type of behavior generally conforms with the prediction of a simple
RC equivalent circuit as sketched in Figure 6.  This circuit is identical to
that previously postulated for the pulse jet cage voltage.  Flue gas flow is
assumed to produce a square wave voltage source, Vp, that is coupled through ,
an effective R? and C? to the detecting screen cage, V    .  The cage itself,
                                                      CciSG        ' -•     •  ' *
is coupled to ground by an effective RI and Cj.  Under sach assumptions V.
responds to a square wave input V  as shown in Figure 7.  The key qualitative
point being made is that the gas on/gas off voltage spikes and sign changes
observed in both the lab and the field can be explained in terms of simple RC
couplings and a forcing function V^ associated with the gas flow.
                                  sL

     The overriding significance of the observations at Harrington is that
charge buildup of magnitude and behavior similar to what has previouslv been
observed in laboratory pulse jet equipment,  operating with redispersed flyash
and at room temperature, is observed in the field with full-scale equipment,
reverse air cleaning, and typical flue gas composition and temperature.   No
unambigu^"': orfect of electrostatic charges upon baghouse performance has been
uncoverf-1  > >  the need to further Investigate the existence of such an effect
is reinf<» fti
        LrUWKAi'ORY  SHAKER BAGHOUSE  EXPERIMENTS
     To extend the fabric charge detection measurements  to the  laboratory shaker
baghouse a modified screen cage was added plus  a center-line probe within the
bag as sketched in Figure 8.   The external cage is  similar to that employed at
Harrington except that it is supported by insulating  phenolic hangers  rather
than tied to the bag itself.

     The center-line probe on the inside of  the bag also hangs  from  a  top support.
Gas flows from inside to outside in this unit and enters at the top  of  the bag  so
that the center-line probe is in the entry way  of the dusty gas.   It detects
charges on the incoming dust and the adjacent dust  cake  that builds  up  on the
inside of the bag.

     The external cage is outside the bag on the clean air side of thetfabric.
It was sized to allow 1.3 cm (% In.)  clearance  between the outside of  the bag and
the screen.   However, the fabric loosens and stretches under pressure  so that
in operation the bag usually makes direct contact with the cage,  much  like'the
support cage of the outside-in flowing pulse jet baghouse.
                             •            •                                (.
     The external cage construction is .analogous to the  internal cage  of  the
pulse jet; the center-line probe is a new feature in the measurement schemes
Figure 9 shows various views of these electrodes with and without the  bag in
I'l.K-e   Th<= shaker mechanism (not shown) moves  the  bottom of the 1.5 m bag-, at
i  i r^qu^ncy of 4 cycles/sec and a p -ak-to-peaK  displacement of  2.5 cm.

-------
     Various operating cycles using redispersed flyash originally collected
from the baghouse hopper at Harrington and a custom sewn silicone-graphite
fiberglass bag are now underway with these electrodes in place.  Typical
electrode voltage traces are sketched in Figures 10 and 11.  Figure 10 shows
an early current and voltage plot measured with the center-line probe.  While
not recorded simultaneously, these curves were recorded within 10 minutes of
each other and during the first 10 hours of new bag operation.  The baghouse
operation cycle for these data was 5 minutes filtration - 30 seconds pause -
30 seconds shake - 30 seconds pause - 5 minutes filtration and so on.   This
rapid cycling mode allows frequent observation of the current and voltage
behavior during the regeneration stage but suppresses dust accumulation below
that normally expected in field operations.

     For all shaker data collected so far, the dust inlet loading has  been 6.9
g/m3 (3 grains/ft3); total gas flow, 0.91 m3/min (32 cfm) for an air-to-cloth
ratio of 2 cm/sec (4 fpm).   These conditions are the standard operating condi-
tions for this EPA shaker baghouse, the same conditions at which the majority
of all previous shaker evaluations and experiments have been carried out.

     Preliminary observations from these shaker baghouse electrostatic measure-
ments are:

     1.   the center-line probe detects larger currents and voltages than the
          cage at low relative humidity (<50% R.H.);

     2.   the center-line probe current tracks with gas flow—when gas flow
          stops, the probe current drops to zero;
     3.   the center-line probe voltage lags the gas flow behaving like a
          charging and discharging capacitor with respect to a charged gas flow;
     4.   an inductive coupling may also exist between a charge sheet  on the
          inside of the fabric and the probe, causing probe current during the
          shake cl^  r. and preventing probe discharge by grounding during the pause
          period (other explanations are possible—the probe current may come
          from dust reentrained during the shake and the probe voltage may be
          controlled by charge on the probe that is isolated from the  probe by
          the resistivity of the flyash);  and
     5.   the cage currents and voltages exhibit the sign changes during gas
          stop and start that would be predicted from the equivalent circuit of
          Figure 6 and as illustrated in Figure 7.

     The cage voltage and current depicted in Figure 11 generally approximates
that seen at Harrington except that the signs are reversed!  Since the dust and
the fabric are identical in the two experiments, the changing charge sign on
the dust and on the cage presumably reflects the different charging properties
of the dust feed lines and the gas induction system.  The Harrington ducts are
steel; the laboratory feed lines are rubber.

     A second general conclusion of the experiments is that the charge appearing
on the bags is dominated by the charge on the incoming dust rather than any
triboelectric interaction between the dust and the fabric as previously postu-
lated. 3>Lt  The crucial triboelectric interactions seem to occur upstream of
the baghouse.

                                       483

-------
     The double electrode configuration in the shake baghouse has now been
switched to a longer filtration period, more representative of field operation
(and previous laboratory work).  This cycle consists of the following sequence:
                            18 minute filtration
1
minute
pause
1
minute
pause
2
minute
shake
     About 100 hours operation have now been logged under these conditions.
Probe currents decrease with increasing relative humidity,  resulting in reduced
probe voltage and cage voltage at high relative humidity.  This dependence on
relative humidity is similar to that previously noted in the pulse jet experi-
ments .

STATUS SUMMARY

     What has been shown is that electrical charges do accumulate in standard
baghouse operation.  The magnitude of these charges depends on the electrical
properties of the dust and the fabric as well as the relative humidity of  the
gas stream.  No unambiguous influence of these charges upon baghouse performance
has yet been identified and such an influence is deemed necessary before more
detailed modeling of the charging/discharging process.  Such a relationship
seems highly likely in view of reported observations of electrostatically
assisted fabric filtration.8  The next phase of this EPA work is to measure  and
control inlet dust charge as this variable appears to be the chief source  of
passive charges.  These experiments will bridge the gap between passive and
active electrostatic effects in fabric filtration.

ACKNOWLEDGMENTS

     It is a pleasure to acknowledge the contributions of:   E.  de Garbolewski,
W.L. Gore Associates, who donated four sets of fabrics for  the pulse jet meas-
urements and critiqued the pulse jet experimental plans and results; J. McKenna,
J. Mycock, and R.  Gibson, Environmental Testing Services, who hosted the Kerr
field measurements; K. Ladd and R. Chambers, Southwestern Public Service,  who
hosted the field measurements at Harrington; and A. Ranade  and P. Lawless,
Research Triangle Institute, who participated in and contributed to all phases
of the work.
                                     484

-------
REFERENCES

1.   Whitby, K.T. and B.Y.H. Liu.  "The Electrical Behavior of Aerosols."
     Chap. 3, pp.59-86 in Aerosol Science, edited by C.N. Davies, Academic
     Press, New York, 1966.

2.   Masuda, H., T. Komatsu, N. Mitsui, and K. linoya.  "Electrification of
     Gas-Solid Suspensions Flowing in Steel and Insulating-Coated Pipes."
     J. of Electrostatics 2, 1976/1977, pp.341-350.

3.   Donovan, R.P., R.L. Ogan, and J.H. Turner.  "Electrostatic Effects in Pulse-
     jet Fabric Filtration of Room Temperature Flyash."  Proceedings of the
     Engineering Foundation Conference, "Theory, Practice and Process Principles
     for Physical  Separations," Asilomar, 1977.

4.   Donovan, R.P., R.L. Ogan, and J.H. Turner.  "The Influence of Electrostati-
     cally-Induced Cage Voltage Upon Bag  Collection Efficiency during the Pulse-
     jet Fabric Filtration of Room Temperature Flyash."  pp.289-327 in Proceedings
     of the Third  Symposium on Fabric Filters for Particle Collection, EPA-600/
     7-78-087, NTIS No. PB 284-969, June  1978.

5.   Ellis, V.S.   "Epitropics—Third Generation Conductive Fibres."  Textile
     Manufacturer  and Knitting World 101, July 1974, pp.19-23.

6.   Leith, D., M.W. First, M. Ellenbecker, and D.D. Gibson.  "Performance of a
     Pulse-jet Filter at High Filtration  Velocities."  pp.11-25, in Symposium
     on the Transfer and Utilization of Particulate Control Technology:  Vol. 2
     Fabric Filters  and Current Trends in Control Equipment, EPA-600/7-79-044b,
     NTIS  No. PB  295-227, Feb. 1979.

7.   Dennis, R., R.W. Cass, and R.R. Hall.  "Dust Dislodgement from Woven Fabrics
     Versus Filter Performance."  J. Air  Pollut. Control Assn. 28, Jan. 1978,
     pp.  47-52.

8.   Lamb, G.E.R., and P.A. Costanza.  "Role  of Filter Structure and Electro-
     statics in  Dust Cake Formation."  Presentation at the Second Symposium on
     the  Transfer  and Utilization of Particulate Control Technology, Denver, CO.,
     July 1979.
                              Table 1. Pulse Jet Fabrics

Run No.
PJ50
PJ49
PJ53
PJ51

PJ52

Fabric Description
Polyester Felt
Polyester Felt + Gore Tex Layer
Polyester Felt with Epitropic Fibers
Polyester Felt with Epitropic Fibers +
Gore Tex Layer
Teflon Felt
Sample Bag Weight (g)
(1 bag, nominally 1.2 m long,
11.4 cm dia) [4 ft; 4^ inches]
220
190
236

212
415
Nominal Collar
Resistance at
50% R.H. (ohms)
5xl09

AxlO14

5xlOs
2xl012
                                      485

-------
                                    Table 2.   Bag Weighing Summary,  PJ54
co
— . — „__ 	 , — , — , 	 , 	 _ 	 	 	 .... — -. . ... 	 •
Bag Weight Change*
Run R.H. (grams)
No. (%) Row 1 Row 2 Row 3
A 51 79.7 48.7 6.0
B 38 84.3 53.0 8.0
C 64 67.9 38.7 -2.7
D 66 52.0 26.7 -5.3
E 34 89.7 52.3 6.7
F 48 83.3 46.7 1.3
2
Pressure Drops, N/m
(in. of H20)
398
(1.60)
460
(1.85)
323
(1.30)
323
(1.30)
386
(1.55)
398
(1.60)
348
(1.40)
400
(1.61)
311
(1.25)
311
(1.25)
336
(1.35)
361
(1.45)
50
(0.20)
60
(0.24)
12
(0.05)
12
(0.05)
50
(0.20)
37
(0.15)
C0, g/m3
grains/103ft3)
0.46
(201)
0.48
(210)
0.22
(94.7)
0.14
(60.4)
0.55
(239.4)
0.44
(190.4)
E (%)
95.5
95.3
97.7
98.6
94.6
95.7

JU
'Actual bag weight after each run less the
Used Bag + Cage
Row 1
Left 1490
Center 1473
Right 1500
following
+ 60 gram
Row 2
1490
1495
1485
initial wei§
plastic ba£
Row 3
1500
1483
1481
jhts
7 '
•J *














-------
   CAGE

    BAG
VENTURI
  PLENUM FLOOR

VENTUR! SHOULDER
  HOSE CLAMP

  BANANA JACK
            Figure 1.  Cage electrical contact, pulse jet baghouse.
   Figure 2,  Cage voltage during pulse-jet fabric filtration
                           487

-------
oo
CO
            10
            0.1
                    X Vc (VOLTS)
                    O AVR (VOLTS)
                                0.1
1                  10
  CAGE VOLTAGE (V)
                                                                                      100
                                                                                                         H 99.99
                 Figure 3.  Correlation of  cage voltages  with outlet  concentration.

-------
                                                                                  -i 0
            PJ52°
  10J r-
o
o
o
  10
cc
o
         x  PJ50

            and

         0  PJ53
  0.1
            PJ49
PJ 51
                30
                           40
                                      50         60


                                     RELATIVE  HUMIDITY
                                                   TEFLON
                                                   POLYESTER AND

                                                 0 EPITROPIC POLYESTER
                                                             0 GORE TEX/POLYESTER
                                                             *( )
                                                               GORE TEX/EPITROPIC

                                                                   POLYESTER
                                                             x( ) = hi stress test
                                                                                    75
                                                                                    90
                                                                                    97.5
                                                                                    99.0
                                                                                    99.75 3
                                                                                    99.9
                                                                                    99.97
                                                                                    99.99
                                                            70
Figure  4.   Dependence of dust  outlet concentration  upon relative humidity.
                                           489

-------
                            5    2
                                          6  1
                                                         3 4
                                                                     RUN ORDER
            500
            400
            300 —
         _  100 —
         LU

         C3
         I
         o
         ca
             80
             60
             40
             20
             10
                                          O
                                  40        50

                              RELATIVE HUMIDITY (%)
                                                          X  X
                                                          e> Q
                                                          o e
                                                                    x APF


                                                                    O APE
60
          70
                                                                      APn
                                                                      ROW 1
                 ROW 2
                                                                       ROW 3
Figure  5.   Relative humidity dependence  of  bag weight  changes and  pressure

            drops.

                                       490

-------
     VE<
-O vc
                    C2
                                    -I- C1
          C2
         7Vc-2^-
                                1
                                                                        Rl
                              1 =	 (C^ + C2I
                                R, + R2
Figure 6.   Simple equivalent circuit.      Figure 7,  Circuit response.
                                            INLET
                                            GAS

                               TO ELECTROMETER  [ / RG-58 CABLE



                                                 INSULATORS
                                                 BAG
                       Figure 8.  Shaker  baghouse electrode

                                   configuration.
                                         491

-------
a.  front view.
b.  front view, bag in place,
                          c.  bottom view.
             Figure 9.  Electrodes for r*haker baghouse-
                                 492

-------
                                      ZU.
<0  , ,"* , ,--
"' ''" "•""•-'"'^''•M/Y SHAKE |*"'--"'^>r: '
1 MINUTE' " x ;
i 	 1 	 1 	 i 	 \ 	 ' i '•' — • 	
UJ —
D0<
Oco
IT I
3£°
Z1^— •

£m
1 2°=
00
                         TIME
      1 MINUTE
                                                     -
                                                     °
                                                   arm
                                                   OO
                       TIME
Figure 10i  Centerline probe current and voltage.
§2
2o
I
I

*' -~i- • •** i- '' '&
,Kf >»*»• ^ ' ^*"* ^ir " ^.- »'»*'"*
I !•
j 	 1 	 	 »

Zu.
»•-,, .t,^'v _


I !
, 	 --

1 MINUTE
	 	 TIME
3

2
1


0

-1
-2
CD
I
0

I-
UJ
oc
CC
o
UJ
0
<
o
                                     Zu.
             1 MINUTE
                         TIME
   Figure 11.   Shaker cage  current  and voltage.
                         493

-------
                 A WORKING MODEL FOR COAL FLY ASH FILTRATION
                                     By:

                      Richard Dennis and Hans A. Klemm
                           GCA/Technology Division
                        Bedford, Massachusetts 01730
                                  ABSTRACT
     A compact mathematical model Ls described for use by enforcement, design
or user personnel to determine whether a fabric filter system can comply with
particulate emission regulations.  All calculations have been incorporated in
the computer program to facilitate model application by control agency and
other concerned groups.  Given the correct combustion, design and operating
parameters, the model will predict emission and pressure loss characteristics.
The model user has the option of requesting a summary printout of key
performance data or highly detailed results for research purposes.  Several
built in error checks prevent the generation of useless data.  The model
considers dust properties and concentration, face velocity, compartmentized
operation and cleaning procedures.  The model function depends upon the unique
fabric cleaning and dust penetration properties observed for coal fly ash and
woven glass bags.  Examples of model applications are presented including
typical data inputs and outputs.
                                     494

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                 A WORKING MODEL FOR COAL FLY ASH FILTRATION
INTRODUCTION

     Fabric filter systems represent an effective and often the only prac-
tical means for controlling fly ash emissions from coal-fired industrial or
utility boilers.  In the latter case, the physical size and cost of large
baghouses (often filtering more than 30,000 m3/min at temperature) demands
that the design and operation of the system be undertaken with a priori
assurances that compliance with emission regulations can be attained at an
acceptable energy expenditure.

     To avoid risky extrapolation of design parameters for existing but not
necessarily replicate systems to new designs and to reduce dependence on
"engineering judgement" as a basis for designing a new filter system, the
U.S. Environmental Protection Agency has sponsored the development of a
mathematical model for predicting the performance of filter systems (Contract
No. 68-02-1438, Tasks 5, 6, and 7).  Detailed results of these studies from
the inception of the fundamental modeling concepts to the recent publication
of a working model for use by agencies responsible for enforcement of
emission regulations have been described in the literature.O~6)

     The purpose of this paper is to describe how enforcement personnel can
use the filtration model as a diagnostic tool to determine whether a
proposed or existing filter system design affords a reasonable chance of
successful field performance.  The qualification "reasonable" is emphasized
because the model output depends not only upon the proper physical descrip-
tion of the filtration process (which we believe to be essentially correct)
but also upon accurate definition of key variables necessary to the modeling
process.

Model Role

     The present model is designed for use with woven fabrics that are
cleaned by (a) collapse and reverse flow, (b) mechanical shaking, or
(c) some combination of the above.  Although not restricted to fly ash
filtration, the model is not intended for use with pulse jet cleaned, felt
fabrics.  A new model based upon GCA studies^7*8) and recent Harvard
research^9'10) has been proposed by Dennis and Klemm for predicting
performance of pulse jet filters with fly ash and other dusts.O1)  Although
the present paper deals mainly with the diagnostic applications of the
model, it should also be noted that the model may be applied equally well by
system designers and equipment users as a predictive device and/or in support
of whatever historical or experience backlog is available.

     The model discussed in this paper describes the overall performance of
real field systems in terms of the variables considered to exert a significant
impact on filter performance.  Past use of the term "mathematical model"
has often referred to specific mathematical relationships between dust,
fabric and gas properties and filter performance.  Although such correlations


                                    495

-------
have in many cases correctly defined certain aspects of the filtration
process, they cannot, taken singly, be used to predict overall filter
system performance.

Modeling Approach and Requirements

     The new model takes into account that air flow, pressure loss and dust
penetration through the many compartments and bags of a sequentially cleaned
system will vary from point to point in accordance with the local fabric
dust loadings.  Because these flow interrelationships are highly complex it
is only by means of iteration techniques and a computer that the model can
be adapted to the solution of practical problems.  Therefore, it was very
important to exercise extreme care in designing the model so that it can
be used by experienced environmental engineers who are not necessarily
specialists in filtration and/or computer technology.

     The pollution control engineer wants a relatively uncomplicated
prodedure whereby he can input specific values for the controlling filtration
and process variables into a predictive model and receive as output a summary
of the probable system performance.  He is concerned not only with average
and maximum particulate emissions but also with the probable ranges in
fabric pressure loss and predicted cleaning frequency, the latter information
for comparison with design specifications.

PRE-MODELING PROCEDURES

     It is emphasized again that the reliability of the filtration model
output is only as good as the quality of the data inputs available for the
modeling process.  Additionally, the degree to which the model user under-
stands the operation of the boiler of interest and the rationale for the
design parameters for the existing or proposed fabric filter system will
play an important role in model utilization.  Again, it must be stressed
that the model is normally intended to augment the available data base and
not to replace it unless the information quality is suspect.

     Before undertaking any modeling operations, a thorough inspection of the
filtration plant should be made, preferably by both enforcement and user
personnel.  This procedure will help to identify specific problem areas
that may or have contributed to unsatisfactory performance, e.g., missing or
defective bags, lack of thermal insulation, defective gauges, overflowing
hoppers, leaking gasketing and signs of corrosion.  The above defects should
be corrected before comparisons are made with the results of detailed
modeling efforts.

BASIS FOR MODEL DESIGN

Working Equations

     The developmental aspects for the filtration model have been discussed
at length in recent publications.1"5  It suffices here to point out that the
model embraces several well recognized filtration principles that have been


                                     496

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reviewed extensively by Billings and Wilder.8  A listing of the basic equations
used to estimate individual filtration parameters and/or to establish their
roles within the filtration model is given in Table 1.

     Many of these relationships appear in the open literature5'8 such as the
equations used to calculate filter drag, S, or resistance, P,  (Equations la,
Ib, and 4); specific resistance coefficient, K2 (Equation 7) and specific
surface parameter, So, (Equation 9).  Certain of the  equations were developed,
however, in conjunction with recent modeling studies. ^ '1+' '   These include
the expression describing nonlinear drag curves (Equation 2),  the effect of
filtration velocity and dust surface properties on K2  (Equations 5 and 6),
the relationship between the degree of cleaning, ac,  the method and intensity
of cleaning (Equation 11-12, 14-16); and finally, the  general  expressions
used to estimate overall filter system drag and penetration (Equations 4 and 20)

New Filtration Concepts

     The introduction of three new concepts, however,  has made it possible to
estimate the performance of a multicompartment filter  system in much more
realistic fashion than previously possible.  The first  describes dust
separation from woven fabrics as a spalling-off process wherein the application
of cleaning energy causes dust separation to occur at  the dust layer-fabric
interface.1'2  The above phenomenon permits the use of  Equation 4, Table 1,
for computation of resultant filter system drag.  The  second concept is based
upon a  straightforward description of the fabric cleaning process1>^,^
that relates the amount of dust removed to the method  of cleaning and the
prior dust loading on the fabric.  Equations 10 through 14, Table 1,
depict  the types of calculations carried out within the program to estimate
the fraction of cleaned fabric area, ac, by reverse flow cleaning.  If
mechanical shaking is used, Equations 10, 15, and 16  are employed to compute
penetration behavior exhibited by many fabrics woven  from multifilament and
bulked  yarns.  Temporarily or permanently unblocked pores or pinholes
contribute to extensive penetration of the upstream aerosol such that
up- and downstream particle size properties are very  similar.  Because of this
phenomenon, the model treats filter emissions on a mass basis  only
(Equations 17 through 20).

MODEL FIELD APPLICATIONS

     In this section, the actual application of the model is described as
intended for use by field engineers to determine whether a proposed or existing
fabric  filter system is able to reduce fly ash emissions to required levels.
The following material represents an abridgement of model operating
instructions appearing in a recent EPA report.^

Input Variables

     For immediate reference, a listing of the input  variables used with the
filtration model is presented in Table 2.  Data inputs are grouped in four
                                     497

-------
              TABLE 1.   SUMMARY OF MATHEMATICAL RELATIONSHIPS USED TO MODEL FABRIC FILTER PERFORMANCE
CC
Squat i on
number Equation
(la} S = P/V = Sr + K:H
- I IT ' - ' ' D " 3

(2) S = SR + K: W + (KR - K;) W*(l-exp
W = '.' - W
(3) W* = (S - S + K;, W )/K - K?
S = P/V =1 > -J2 + — ^ + T~
\4~f c sUl V /
(T) K^ = 1. 8 V'
(6> r 2
CK2)f -  "u m3
A = dimens ion less = 1.0
See Figures 1 and 2.
MMD = cm"1
o = dimensionless
T = °C
S S cnT1
°c 0
f , n
V = poise
£ = dimensionless
Cc = dimensionless

-------
                                                      TABLE  1.     (continued).
Equation
number
(9)



(10)

(11)

(12)




(13)

(14)
Equation
„ _ Jio'-i" Log%\
o ' MMD /


P. - S V C. V It
u' i U i -1
WP K2V ' HR 2

ac - 1.51 x 10~8 Wp2-52

ac = (6.00 x 10~3) (V C tc)°-715

tc = It + t£


Wp = 166.4 (C± V Zt)0-28"

a = (6.00 x 10-3) (V C. Zt)°-715
Comments
Equation (9) computes distribution specific surface parameter, So>
from cascade impactor data for a logarithmic normal mass distribution.
Reverse Flow with Bag Collapse
Intermittent, pressure controlled cleaning. Substitution of W' from
Equation (10) in Equation (11) gives area fraction cleaned, a ,
as function of limiting pressure loss, PL, and previously cited system
parameters. Wp accounts for the fact that the average Wp value over
the cleaning cycle will exceed the initial values.
Intermittent, time controlled cleaning. Equation (12) applies when
total cycle time, tc, is given. Note that t is the sum of time re-
quired to clean all compartments, £t, plus the time between compart-
ment cleaning, t^. Face velocity, V, and inlet concentration, C^,
must be nearly constant for safe use of time control.
Continuously cleaned system. Equation (13), which shows dust loading
on compartment ready for cleaning, applies when Wp ilO times WR.
Equation (14) computes ac for a continuously cleaned system where £t
Terms and units
S = cm"1


a = dimensionless
c



t , It, t,, = min
c f

C = 8/m3

V = m/min
n = number of compartments


                                                    is the  time  to  clean  all  compartments.

                                                    Mechanical Shaking

(15)     ac = 2.23 x 10~12 (f2 Ag wp2-52            Intermittent, pressure  controlled cleaning system.  Substitution of    ac = dimensionless
                                                    Wp from Equation  (10) in  Equation (15) in conjunction with shaking        _  ,  ,  .             _
                                                    parameters f and  As determines ac.  Wp accounts for the fact that       * ~ shaking frequency - Hz
                                                    the average W  value over the cleaning cycle will exceed  the initial   A  = shaking frequency = cm
                                                    values.

(16)     ac = 4.9 * 10~3 (f2 AS Ci Vlt)0-715          Continuously cleaned  system.  Equation (16) computes ac in terms of    It = time to clean all
                                                    cleaning parameters f and Ag and the dust accumulation over the time     compartments = min
                                                    required to  clean all compartments (C, VSt).

(17)     C  = [pn  + (0 1 - Pn )  e~aW~| C  + C        Equations (17)  through  (19) are empirical relationships used to com-   Cis Co,  CR - g/m3
         o   L   s     "      s      J  i    R       pute  outlet  concentrations, Co, in terms of incremental increase in    rj  _  /  2
,.g.         = 1 5 x IQ-7     fi2 7(1-   1.03V-J    fabric  loading  (W = W  -  WR); inlet dust concentration C.; and local      ~ g
          s                  [                 J    face  velocity,  V.  The  term CR is a constant, low level outlet con-    V  = m/min
, Irt,         , , v ,M_3 T_u ,  _ nn,                   centration that is characteristic of the dust fabric combination.      ^           ,     .
(19)     a = 3.6 x 10   V-" +0.094                  Pns and  a are curve fitting constants for specific systems.            PV P"t = dimensionless

                      I     J                                                                                             3  =m2/g
,„„,         _   I    ^^   V "•                      Equation (20) depicts basic iterative structure for defining system    I = No.  compartments
         "t   V  IJ  f  j   f J   "-"-Jf  ^           penetration  at  any time,  Pnt as a function of parallel flow through
                     i=l   j=l                      "I" compartments  (each  subdivided into "j" individual areas) where       ~     areas per
                                                    local face velocities and fabric loadings are variable with respect        compartment
                                                    to time  and  location.                                                  t = time

-------
TABLE 2.    SUMMARY LISTING OF INPUT DATA  FOR FILTRATION MODEL
Item Symbol Units Card Valid range Default Note
0 Title
1 Number of compartments n
2 Compartment cleaning time At
$ 3 Cleaning cycle time £t
Q 4 Time between cleaning cycles tf
M 5 Limiting pressure drop PL
§ 6 Reverse flow velocity VR
7 Shaking frequency f
8 Shaking amplitude A
o 9 Average face velocity V
H< 10 Gas temperature T
w3 11 Inlet dust concentration C;
fr<
12 measured at temperature of T
13 Specific resistance coefficient KZ
14 measured at temperature of T
15 measured at velocity of V
16 measured at mass median diameter of MMDi
17 measured at geometric standard ogj
u deviation of
H
oj 18 Mass median diameter of inlet dust HMD?
H
O 19 Geometric standard deviation of inlet dust 0£2
20 Discrete particle density of inlet dust p
a 21 Bulk density of inlet dust p
9
h 22 Effective residual drag Sg
S 23 measured at temperature of T
EH 24 Residual fabric loading WR
o 25 Residual drag SR
26 measured at temperature of T
27 Initial slope KR
28 measured at temperature of T
29 Maximum number of cycles modeled nc
30 Accuracy code 0 or
2 w 31 Type of tabular results -
OB:
at M 32 Type of plotted results
^ tj
^ g 33 Fractional area cleaned ac
o en 34 x axis length
S M
to 35 y axis length
*
These values are used when no entry has been made for the
Used only when K2 is to be estimated from size properties
Notes: a. Enter item 4 or 5, but not both.
b. Enter item 6 or 7 and 8, but not both.
c. Enter items 13 through 15 when K2 measurement
d. Enter items 13 through 19 when Kj measurement
-
-
min
min
min
N/tn2
m/min
cps
cm
m/min
°C
g/m3
°C
N-min/g-ra
°C
m/min
ym
_

ym
-
g/cm3
g/cm3
N-min/m3
°C
g/m2
N-min/m3
°C
N-min/g-m
°C
-
1
-
-
-
inches

inches

parameter.



is available.
1
2
2
2
2
2
2
2
2
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
6
6
6
6
6
7

7






must be corrected

1 to 30
O.Sdtem 3/Item 1) s

a
a
0 b
b
b
0.3 to 3.0
>0

25
0.25 to 10 c,d
>0 25
0.6L
2 to 50 d
2 to 4 d

2 to 50 d,e
2 to 4 d,e
e
e
350 f,g
>0 25
50+ f,g
f
>0 25
f
>0 25
h
0 or 1 0
Average i
i
>0 to 1 j
6 k

5






for size properties.
e. Enter items 18 through 21 when Ka is to be estimated from dust size and density parameters.
f. Enter items 22 through 28 for nonlinear drag model.
g. Enter items 22 through 24 for linear drag model.
h. Generally 20 cycles are sufficient.



 i.   For tabular results specify DETAILED, SUMMARY or AVERAGE;  for graphical results specify
      PLOT or leave blank.

 j.   Enter only in special case when ac measurement is available.

 k.   Card can be left out if default values are sufficient or if no plotted output is desired.
                                     500

-------
                                        FABRIC  FILTER  MODEL - DATA  INPUT  FORM
11 OK THE SAME CARD, ENTER OIK OH
blTHE OTHER. BUT HOT BOTH
•-REQUIRED IF Kj IS KKOWI
4 -REOmRED IF I] IS TO BE COMtECTEC
  FOB  SUE PROPERTIES
• -REouoreo  F KJ a TO u ESTMATEO
I- REOUREO  FOR  HOM-UMEAJ) MUC H09CL
1- REQUIRED  FOR LIRCAB MAS HOOEL
                                                                                                  UUE Of FCRSM
                                                                                                  COWUTIM  FORV

1 2

3

4

S

6

T

>


9


«


1


B


13

TITLE
M

a

e

J7

18

19

20

M

77

n

M



a

ji

a

a

»

31

S

















«l

































M

•

EO

61

2

Ea

M


a

a

s?

n

mxj

         CLEAMBS TIMES
1234967* 9 KNI C IS 14 O I61J7 18 19M it
 2 3 4 5 K 7 ) 9l«|» C 13 H OIfel 17 18 19
  22    ,. 23        24       25      26
   34 S 67 IS 9 10 I S 13 H Blie J7 18 W
1234 5 l« 7 I 9 W I
            35
                                  DCUMAL POMT
                         ALL OTHER EMTHIES MUST BE RTOHT JUSTIFIED  EXCEPT  FOB ITEMS 0. 31 AND 52.
                      Figure  1.     Fabric  filter  model  -  data  input  form.
                                                        501

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categories:  Design Data, Operating Data, Dust and Fabric Properties and
Special Program Instructions.  Table 2 also shows the correct units for each
data input as well as the Card and Item number for entry on the Data Input
Form, Figure 1.  Additionally, the valid ranges; i.e., the range of numerical
values that will allow the program to run, are indicated for key variables.
Table 2 also indicates Default Values which are automatically assigned by
the program when no data inputs are available or when the model user forgets
to make an entry.  In the Table 2 footnotes, those conditions defining
specific or mutally exclusive data inputs are summarized.  A more detailed
treatment of user instructions is given in the User's Guide.4

Data Input Forms

     The specific data inputs to be entered on each of the seven cards are
listed below:

          1 - Heading or Title Card
          2 - Design Data
          3 - Operating Data
          4 - Specific Resistance Coefficient/Gas and Dust Properties
          5 - Fabric and Dust Properties
          6 - Special Program Instructions
          7 - Plot (Graph) Dimensions

     To facilitate data entry and subsequent card punching, a "FABRIC FILTER
MODEL-DATA INPUT FORM" has been prepared, Figure 1, with the data entry
locations labeled to correspond to their respective code numbers on Table 2.
In those blocks where no decimal point indicator is shown, right justification
of the entry is required.  Some items requiring special consideration are dis-
cussed in this section.  If more than one compartment is cleaned simultaneously
(Item 1, Card 2) the revised or effective value for number of compartments is
the total compartment number divided by the number undergoing simultaneous
cleaning.  Failure to enter a value for compartment cleaning time (Item 2,
Card 2) will result in a DEFAULT entry.  However, the program will not
function if the cleaning cycle time (Item 3, Card 2) is omitted.  In the
case of back-to-back or continuous cleaning, Items 4 and 5, Card 2, may be
left blank although a "zero" entry avoids confusion.  It should also be
noted that the program will function when no value or a zero value is entered
for reverse flow velocity (Item 6, Card 2).  The average face velocity
(Item 9, Card 3) as computed from the total volume flow through the
baghouse and the total available filtration area must always be entered at
the actual gas stream temperature (Item 10, Card 3).  In the case of K£
estimation, DEFAULT values for temperature and velocity (Items 14 and 15,
Card 4) are automatically entered.  Note that if no value for K2 is entered,
the program will not function unless specific size and density parameters
(Item 18 through 21, Card 4) are entered.  Except for those cases where data
inputs are available for the terms S-g, W^, S-^, and K^ (Items 22, 24, 25,
27, Card 5) the program will always select the linear modeling approach.
In most cases, it is advisable to select 20 operating cycles (Item 29,
Card 6).  With respect to accuracy code, (Item 30, Card 6) "0" and "1"
entries, respectively, define -convergence limits within 1 and 0.3 percent
of the estimated limiting values for the key performance variables.  The

                                    502

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selection of "DETAILED" for Item 31, Card 7 provides highly specialized
outputs that are only necessary for research applications.  Specification
of SUMMARY will furnish information on the changes in overall system effluent
concentration, penetration and fabric pressure loss with time as well as
average, maximum and minimum values for the above performance characteristics
(the AVERAGE output).  For many practical situations, selection of AVERAGE
parameters is sufficient to assess compliance potential.  Although the
graphing capability is an extra feature, the curves produced when PLOT is
specified may elimiante considerable hand plotting.

Error Messages

     In accordance with good programming procedures, an attempt has been made
to anticipate the major causes of computer program malfunctions, most of which
relate to improper data entries.  Thus, when the program fails an error mes-
sage(s) will appear on a separate print-out sheet captioned DIAGNOSTIC
MESSAGES.  A listing of typical error messages and their probable causes and
means of correction is given in Table 3.  Note also that this same print-
out also signifies a "go ahead" by the statement "THERE ARE NO ERRORS IN
THE INPUT DATA."

EXAMPLE OF MODEL APPLICATION

     The following example illustrates how the filtration model may be used
by enforcement personnel to help solve a typical field problem.  An electric
utility operates two, coal-burning steam-electric plants, the first of
which now uses a pressure-controlled baghouse to maintain particulate
(fly ash) emissions at or below compliance levels.  It has been proposed
that a continuously cleaned fabric filter system be installed at the second
plant.  Both the utility operator and the local emission enforcement groups
would like to determine whether operation of the new filter system in
accordance with the input data shown in Table 4 will satisfy local emission
requirements while maintaining average system pressure drop levels within
the exhaust capacity range of the induced draft fans.  For present purposes,
it is assumed that operation at an efficiency of 99.5 percent (equivalent
to 0.5 percent penetration) and an average pressure drop of, < 1750 N/m2
(7 in. water) indicates acceptable performance.  Although a lower operating
pressure loss is usually preferred, limited physical space and a desire to
make use of the existing draft fans has led to the utilities acceptance
of the indicated pressure drop characteristics ( <1750 N/m2).

     Design and operating data appearing in Table 4 for the proposed
"second" plant baghouse represent a composite of information received from
both utility personnel and the dust collector manufacturer.  It is also
assumed that previous measurements of uncontrolled mass emission rates and
fly ash size distributions at both plants are available as well as estimates
for the terms K2, SE and WR based upon special tests performed at the first
plant.  It should be noted that the above terms might have been estimated
from strip chart records from the first plant showing the pressure loss
versus time traces.  There is the important constraint, however, that the
time intervals between cleaning be long enough (^2 hours) to develop a uniform
density dust deposit on the fabric surface.

                                     503

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       TABLE  3.   SUMMARY  OF  DIAGNOSTIC MESSAGES  AND THEIR INTERPRETATION
                       Message
                                                               Probable cause/corrective measures
-  ILLEGAL REQUEST FOR TYPE OF RESULTS


-  THE NUMBER OF COMPARTMENTS MUST HOT EXCEED 30


-  THE NUMBER OF COMPARTMENTS TIMES THE COMPARTMENT
   CLEANING TIME MUST BE LESS THAN THE CLEANING
   CYCLE TIME
-  THE COMPARTMENT CLEANING TIME MUST BE LESS THAN
   THE TOTAL CYCLE TIME


-  TIME INCREMENT TOO SMALL, I.E., < 0.01 MINUTES
-  AVERAGE FACE VELOCITY OUT OF RANGE,  0.3 TO 3.0

-  A GAS TEMPERATURE HAS NOT BEEN ENTERED

-  INVALID FREQUENCY OR AMPLITUDE FOR SHAKER


-  INVALID ACCURACY CODE
-  BOTH TIMED AND PRESSURE CONTROLLED CLEANING
   SPECIFIED - ONLY ONE IS VALID
-  PARTICLE SIZE DATA FOR K2 ARE INCOMPLETE
-  MASS MEDIAN DIAMETER OF MEASUREMENT OUT OF
   RANGE 2 TO 50

-  THE PROGRAM HAS BEEN TERMINATED BECAUSE OF
   ERRORS IN THE INPUT DATA

-  THERE ARE NO ERRORS IN THE INPUT DATA
Incorrecc spelling of DETAILED, SUMMARY,  AVERAGE or
PLOT for Items 31 and 32, Card 6.

Too many compartments were entered for Item 1,
Card 2.

Too many compartments, too large a compartment
cleaning time or too small a cleaning cycle time
were specified - Items 1, 2, and 3,  Card  2.

Too large a compartment cleaning time, Item 2,
Card 2, or too small a cleaning cycle time, Item 3,
Card 2, were specified.
The time increment calculated by the program is too
small.  Too many compartments (Item 1, Card 2)  or
too small a cleaning cycle time, Item 3,  Card 2,
will cause this problem.
Too large or too small an average face velocity was
entered for Item 9,  Card 3.
A value less than or equal to 0°C was entered for
Item 10, Card 3.
A > 0 value entered for either frequency,  Item  7,
Card 2 or amplitude, Item 8, Card 2.  Both must be
entered or left blank for program to operate.
Only 0 and 1 are valid codes.  Make certain the
number is right justified when entered for Item 30,
Card 6.

On Card 2, values for both Items 4 and 5  were
entered.  Only one item may be entered per test.
A value for K2, Item 13, Card 4, was entered along
with data to be used in correcting K2 for dust
size properties, Items 16 through 19, Card 4.
However, an omission from Items 16 through 19 has
led to any of the following error messages.
The MMD of the reference dust, Item 16, Card 4,  is
out of the valid range.

Since one  or more of the above errors has  occurred,
program execution is stopped.  Correct the error(s)
and rerun  the program.
No errors  were detected.   The simulation  will be
performed.
 Out of order and missing cards  (with  the  exception of Card 7) will cause many of the above errors to
 occur.   Check card  order before running program.
                                               504

-------
        TABLE 4.   AVAILABLE INPUT DATA FOR MODELING BAGHOUSE PERFORMANCE
                  AT ELECTRIC UTILITY, PLANT 2
Inlet dust geometric standard
  deviation
Dust specific resistance, K2
  Measured @
  Measured @
Effective residual drag
  Measured @
Residual fabric loading
                                    Existing Plant A
                          Proposed Plant B
Number of compartments
Cleaning cycle duration
Time to clean one compartment
Cleaning type
Reverse flow volume
Cleaning cycle initiation
Volume flow into baghouse
Total filtration area
Temperature of flue gas
Inlet concentration
Inlet dust mass median diameter
10 ym (Reference)
3.0   (Reference)

10.2 in.W.C.-ft-min/lb
500°F
2 ft/min
0.636 in.W.C.-min/ft
500°F
0.015 lb/ft2
30
30 minutes
        A
1 minute
Collapse/reverse air
30,000 acfm
Continuous cleaning
600,000 acfm
200,000 ft2
350°F
5 grains/scf
7 ym
2.5
Note:  All English units must be converted to their metric equivalents,
 Usually 2 to 3 minutes are allowed for cleaning.
                                     505

-------
     The data summarized in Table 4 are sufficient to carry out the predictive
modeling operation.  Following transcription of the information from Table 4
into the units and format shown in Figure 2, the data inputs are ready for
punch-carding.

     Card 1 contains the title which will appear with the results.  Note that
on Card 2 the time between cleaning cycles, Item 4, and the limiting pressure,
Item 5, have been left blank because a continuous cleaning system has been
chosen.  The reverse flow velocity, Item 6, Card 2, is calculated from the
total reverse flow rate (30,000 acfm) and the cloth area per compartment
(200,000 ft2/30) as 4.5 ft/min or 1.37 m/min.  The average face velocity,
Item 9, Card 3, is computed from the indicated value for the total gas
flow (600,000 acfm) and the total fabric area (200,000 ft2) as 3.0 ft/min
(0.915)m/min).  Inlet concentration is reported at ambient temperature,
^25°C, the value entered for Item 12, Card 3.

     The data available for K2 are sufficient to allow for correction of the
measured K2 at the first plant to the size properties of the dust at the
second plant.  Thus K2, the temperature and face velocity at which it was
measured and the size properties of the two dusts are entered as shown on
Card 4.  The model user should note that much of the raw field data may
appear in English units, necessitating their conversion to the metric units
used in the model.  See Table 5

     Twenty cycles are considered sufficient to complete the simulation and
achieve steady state conditions (see Card 6).  Similarly, an accuracy level
of zero is considered acceptable for the first trial.  Because the utility
personnel and the enforcement agency are concerned mainly with average emis-
sion rates and average pressure drop, AVERAGE results are requested.  Since
no plotting is desired, Item 32, Card 7 has been left blank.

     If the results of the simulation had indicated emission levels close to,
but greater than, the allowable level, the simulation could bave been rerun
with an accuracy level of 1.  If convergence had not been reached within
20 cycles, a value of 40, for example, might have been entered provided that
the costs for added computer time were acceptable.

     In Table 6, the actual computer printout provided for the input data and
instructions of Figure 2 have been arranged in a convenient tabulation showing
each of four separate printout sheets.  Printout No. 1 shows the actual sum-
marized input data as entered into the program so that the user can check the
data for errors or omissions.  Printout No. 2 instructs the user via the
statement "There are no errors in the input data" that the modeling program
will be executed as requested.  Printout No. 3 provides a listing of those
parameters whose values were computed or corrected by the program such as ac
and K2.  Again, inspection of these data by the model user allows him to
determine the reasonableness of the indicated values.  Finally, the AVERAGE
data shown in Printout No. 4 indicate that both the pressure drop and penetra-
tion expectations for the filter system (< 1750 N/m2 and 0.5 percent) should
be realized.  In addition, Printout No. 4 also indicates that 10 cycles rather
than the 20 requested on the data input form, were sufficient to define steady
state operating conditions.
                                     506

-------
a Ion T
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 OTHW.BUT NOT BOTH
C -REWIRED If Kj IS
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  FOR SIZE H1WERT1ES
C -REWIRED IT KZ IS TO tf ESTIMATED
 f-KOWRID rtm WOU-LIHCAR
                                                                                          10
                                                                                           NAME Of PERSON
                                                                                           COMP1.CTIHS  FORU
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         CLEAMIMC  TIMtS
  2345671 9 10 I B 13 H O «J7 18 19
                   Figure 2.    Fabric filter model  -  data  input form.
                                                     507

-------
TABLE 5.  ENGLISH/METRIC CONVERSION FACTORS

Quantity
Filter resistance
Filter drag
Velocity
Volume flew
Fabric area
Areal density
Specific resistance coefficient
Dust concentration
Density
To convert from
in. H20
in. H20-min/ft
f t/min
ft3/min
ft2
lb/ft2
in.W.C.-rain-ft/lb
grains/ft3
lb/ft3
To
N/m2
N-min/m
m/min
m /min
m2
g/m2
N-min/g-m
g/m3
g/cm3
Multiply by
249
817
0.305
0.0283
0.093
4882
0.167
2.29
0.0160
                    508

-------
  TABLE 6.   SAMPLES OF  TABULAR  PRINTOUT  FOR  EXAMPLE OF MODEL APPLICATION
                                 PRINTOUT  NO.  1
SUM"A«Y  Of  INPUT CATA FOR BAGHOUSE  ANALYSIS
AN ELECTRIC  UTILITY / PLANT  8 BAGHOUSE
HASIC DESIGN  DATA
     NUVBE« OF" COMPARTMENTS         30
     CQwPAHTMt-jT CLEANING TI"E         1,0
       (OFF LINE TIVE)
     CLEANING CYCLE TI M E             JO.n
     CONTIGUOUSLY CLEANED SYSTE"
     REVERSE  FLHrt VELOCITY          1.3725
OPfWATING  DATA
     AVEPAGE  FACE VELOCITY
     GAS  TEWPERATUPE
     INLET  DUST CCNCEMTKATIQN
          "•EASUREC AT

FABRIC  AND  OUST PROPEHTItS

     SPECIFIC RESISTANCE,  KE
          MEASURED AT
     CORRECTED TO   w"D2

EFFECTIVE  RESIDUAL DRAG, SE

RESIDUAL LOADING, rtH
 0.9150
 177.
 1 1 ,«5
  1 .70
 ?feO,
 O.blOO
10.0
 7.0

 520.
 260.
  73.2
DEGREES  CENTIGRADE
G/M3
DEGREES  CENTIGRADE
                                                DEGREES CENTIGRADE
MICRONS
DICKONS
                                                              -STANDARD  DEVIATION 3.00
                                                              -STANDARD  DEVIATION 2.50
                                                DEGREES CENTIGRADE
SPECIAL  PROGRAM INSTRUCTIONS
     WAX  MUMHER OF CYCLES  MODELED   20
     ACCURACY LEVEL                0
     TYPE OF RESULTS REQUESTED      AVERAGE /
                                 PRINTOUT  NO.  2
 DIAGNOSTIC  -FSSAGES
       ARE  NO ERRORS IN THE INPUT  DATA
                                    (continued)
                                        509

-------
                                  TABLE  6.   (continued)
                              PRINTOUT  NO.  3
CALCULATED VALOfS
I'-LET OUST CONCENTRATION
      TED TO OPERATING TEl'PERATORE
                                     7.58
FCHMC "NO DUST CA»F PROPERTIES CORRECTED FriR f, t, s VISCOSITY

     SPECIFIC CAKE RESISTANCE, K?    2.i«         N-WIN/G-*

     EFFECTIVE CRAG, St              b J 0 .          \ . w ; /g / M j
           «NEa CLEANED,
TI»E
     " C i INSTANT A'*
                                     0.0
                              PRINTOUT  NO.  4
                RESl'LTS OF BAGrinijSE  ANALYSIS
                   tLFCIHIC  UTILITY  /  PLANT B BA&HOUSE
FQR
        30.00
                                  CYCLF
                                                        PtNETWAlJON=
                                                AVERAGE  PRESSURE  DROP*
                                                AVERAGE  SYSTEU  K0rt =
                                                        PRESSURE
                                                                              3. J1E-01
                                                                                1SS6.78
FOR     30.00 "IMlTtS OPERATION,   CYCLE  MJWHER    <)
                                                AVERAGE  PENE TRATION =
                                                AVERAGE  PRESSURE DROP=
                                                AVERAGE  SYSTEM  FLO*=
                                                wftxl«'jw  PENETRATION:
                                                VAXIUUW  PRESSURE DROP:
                                                                              u.7u£-0i
FOR
        30,00 MINUTES OpERAT !
                                  CYCLE  NUMBER   10
                                                svERAGE  PENETRATIfJK =
                                                AvERAGF  PRESSURE D«CP=
                                                AVERAGE  SYSTEM  FLOA:
                                                ««AXIMUW  PENETRATION^
                                                WAXIWU"  PRESSURE DWOP=
                                                                              3.33E-03
                                                                                 O.P607 "/WIN
                                                                              U.7UE-03
                                                                                1S74.50 N/M?
                                             510

-------
SUMMARY

     The primary purpose of this paper has been to highlight the develop-
mental aspects of the filtration model that have been described in detail  in
precursor studies and to show precisely how the model can be used to estimate
the performance of a new filter system while design and operating parameters
are still open to change.  The example chosen to illustrate the model
application indicates that a basic understanding of filtration concepts with
concurrent definition of key input parameters enables the model user to
obtain a simple answer as to the probable success of the filter system
design undergoing evaluation.

ACKNOWLEDGMENTS

     The authors express their appreciation to Dr. James H. Turner, EPA
Project Officer, for his continued technical  support throughout the
programs under which the present filtration model has been developed.

     This project has been funded at least in part with Federal funds from
the Environmental Protection Agency under contract number 68-02-1438, Task
Order Nos. 5, 6 and 7, and contract number 68-02-2607, Task Order Nos. 7
and 8.  The contents of this publication do not necessarily reflect the
views or policies of the U.S. Environmental Protection Agency, nor does
mention of trade names, commercial products, or organizations imply
endorsement by the U.S. Government.

REFERENCES

1.   Dennis, R., et. al.  Filtration Model for Coal Fly Ash with Glass
     Fabrics.  U.S. Environmental Protection Agency, Industrial Environmental
     Research Laboratory, Research Triangle Park, North Carolina.
     EPA-600/7-77-084.  August 1977.

2.   Dennis, R., R. W. Cass, and R. R. Hall.  Dust Dislodgement From Woven
     Fabrics Versus Filter Performance.  J Air Pollut Control Assoc.
     4_8 No. 1, 47-52, 1978.

3.   Dennis, R., and N. F. Surprenant.  Particulate Control Highlights:  Re-
     search on Fabric Filtration Technology.  U.S. Environmental Protection
     Agency, Industrial Environmental Research Laboratory, Research Triangle
     Park, North Carolina.  EPA-600/8-78-005d.  June 1978.

4.   Dennis, R. and H. A. Klemm.  Fabric Filter Model Format Change.  Vol. I
     Detailed Technical Report, Vol. II User's Guide. U.S. Enivronmental Pro-
     tection Agency, Industrial Environmental Research Laboratory, Research
     Triangle Park, North Carolina.  EPA-600/7-79-043a, EPA-600/7-79-043b.
     February 1979.

5.   Dennis, R. and H. A. Klemm.  A Model for Coal Fly Ash Filtration.  J  Air
     Pollut Control Assoc. 49 No. 3,230-234, 1979.
                                     511

-------
6.   Dennis, R., H. A. Klemm and W. Battye.  Fabric Filter Sensitivity
     Analysis.  U.S. Enivronmental Protection Agency, Industrial Environmental
     Research Laboratory, Research Triangle Park, North Carolina.  EPA-600/
     7-79-043c.  April 1979.

7.   Dennis, R., and J. E. Wilder.  Fabric Filter Cleaning Studies.  U.S. En-
     vironmental Protection Agency, Control Systems Laboratory, Research
     Triangle Park, North Carolina.  EPA-650/2-75-009 (NTIS No. PB-240-372-3G1)
     January 1975.

8.   Billings, C. E., and J. E. Wilder.  Handbook of Fabric Filter Technology,
     Volume I, Fabric Filter Systems Study, 1970.  U.S. Environmental Protec-
     tion Agency, Control Systems Laboratory, Research Triangle Park, North
     Carolina.  EPA-APTD 0690  (NTIS No. PB-200-648).  December 1970.

9.   Leith, D. H. , M. W. First and H. Feldman.  Performance of a Pulse-Jet
     Filter at High Filtration Velocity - II.  Filter Cake Redeposition,
     J. Air Pollut Control Assoc.  27_ No. 7, 636-640, 1977.

10.  Ellenbecker, M. J., and D. Leith.  Effect of Dust Cake Redeposition on
     Pressure Drop in Pulse-Jet Fabric Filters.  Paper Presented at 3rd
     International Powder & Bulk Solids Handling & Processing Conference,
     Rosemont, 111., May 1978.

11.  Dennis, R. and H. A. Klemm.  A System Model for Pulse-Jet Filtration.
     Publication pending editorial review.  1979-
                                     512

-------
PARTICULATE  REMOVAL AND OPACITY USING A WET  VENTURI
SCRUBBER - THE MINNESOTA  POWER. AND LIGHT EXPERIENCE

                         By:

                    David  Nixon
             Plant Mechanical  Engineer
         Minnesota Power  &  Light Company
             Duluth, Minnesota  55802

                        and

                  Carlton  Johnson
           Manager of Process  Engineering
            Peabody Process  Systems, Inc.
            Stamford, Connecticut  07907
Minnesota  Power and Light  is  installing a wet  venturi
particulate scrubber and a spray tower S02  absorber as
the  Air  Quality Control  System for their 500MW Unit #4,
Clay  Boswell Station,  Cohasset,  Minnesota.   The System is
being designed and installed  by  Peabody Process Systems,
Inc.,  Stamford, Connecticut.

Prior to start-up the  full scale unit, a 1MW pilot plant
was  installed and tested to evaluate  the performance of
the  system.  Estensive data was  collected for  two differ-
ent  western coals with regard to venturi particulate re-
moval characteristics  and  its effect  on opacity.   Corre-
lations  were also developed using pilot plant  opacity
data  to  predict full seale opacity results.

This  paper summarizes  the  test results obtained and
conclusions reached.
                           513

-------
PARTICULATE  REMOVAL AND_OPACITY USING  A  WET  VENTURI SCRUBBER-
THE MINNESOTA  POWER AND LIGHT EXPERIENCE
1.  INTRODUCTION

    Minnesota  Power & Light is  currently expanding its power
    generating capacity at its  Clay-Boswell  station, Cohasset,
    Minnesota  by the addition of  Unit  #4 with a capacity of 500
    MW.   The Air Quality Control  System  this unit was designed
    and  installed by Peabody Process  Systems, Stamford, Conn.,
    and  consisit of an integral venturi  particulate scrubber
    and  a spray tower S02 absorber...   The system is designed
    for  99.7%  particulate removal  and  90% S02 removal based
    upon burning a sub-bituminous  coal from the "Big Sky" mine
    at  Colstrip, Montana where  the  Rosebud and McKay seams vary
    In  sulfur  content from 0.4% to  2.8%  with about 10% ash con-
    tent .

    The  initial design of the plant  called for a hot-side or
    coId-side  electrostatic precipitator followed by a spray
    tower S02  absorber.   However,  when  Minnesota Power &
    Light solicited bids on this  basis,  the quoted costs ap-
    peared to  be very high.  In addition, Minnesota Power &
    Light had  some doubts that  the  precipitator could meet the
    stringent  performance required  for their system.  Likewise,
    It  was also known that  the  alkali  contained in the flyash
    could offer economic benefits  in  S02 remova 1.These
    factors led Minnesota Power & Light to explore the concept
    of  using a wet venturi  for  particulate removal and
    integrating it with  the S02 spray  tower absorber.

 2 •  E CONQMI C^^E V ALUAT ION

    Three alternate systems were  evaluated by Minnesota Power  &
    Light.  They were:

    System #1:  Hot-side electrostatic precipitator followed by
                 an  S02 absorber.   Reheat by means of a 5% hot
                 flue gas bypass which  is treated for particu-
                 late removal  via  a small hot-side electrostatic
                 precipitator.

    System #2:  CoId-side electrostatic precipitator followed
                 by  an  SO2 absorber.  Reheat by means of  a  5%
                 flue gas bypass which  is treated for particu-
                 late  removal  via  a small hot-side electrostatic
                 precipitator.

     System #3:  Venturi  scrubber  followed by an S02 absorber.
                 Reheat  by  means of a 5%  flue  gas bypass  which
                               514

-------
                is treated  for  particulate  removal via a small
                hot-side electrostatic  precipitator.

    The economic evaluation, based  upon actual  bids received,
    included investment, operating  and  maintenance costs for
    the three systems.  Special emphasis  was  placed on de-
    termining the availability  of  these systems and the risk
    factors associated with each.

    The total investment for each  system, including necessary
    sub-systems (e.g. , waste disposal  for ash and scrubber
    sludge;  induced  fans;  and air  preheaters),  is tabulated
    below in thousands of dollars:
System 1
73,939
20,660
System 2
81 ,091
27,812
System 3
53,279
BASE
INVESTMENT

DIFFERENTIAL
    The following  table  summarizes  annual  owning  and  operating
costs in thousands of dollars:
FIXED CHARGES

CAPABILITY CHARGE

REAGENT & UTILITIES

OPERATING & MAINTENANCE



TOTAL ANNUAL CHARGES

DIFFERENTIAL

PRESENT WORTH - 30 YEARS

DIFFERENTIAL
Sy s tern 1
1



2

9
2
1
4
5
3
3
3
,57
,33
,12
0
5
9
,096
,130
,07
9
,000
Sys
13,
1,
3,
51
24,
4,
203,
7
5
7
5
tern 2 System 3
8
6
8
7
30
2
0
5
1
5
3
1
7
6
3
4
9
1
3
6
20
,05
7
,606
,30
7
,083
,05
3
BASE
167
,50
5
25,696
35,509
BASE
    The conclusions of the economic analysis  are  self-evident.
    System 3	is a great deal  lower  in  installed cost,  but
    operating and maintenance costs are  only  slightly  greater
    than -the ESP/spray tower systems.  The  net  result  is that
                             515

-------
the integral venturi/spray tower absorber system  is  the
most economical method  of  achieving Minnesota Power  &
Light's air quality  control requirements.

DESCRIPTION OF  PILOT PLANT AND TEST OBJECTIVES

In November 1977,  Minnesota Power & Light awarded a  con-
tract to Peabody  Process  Systems, Inc., Stamford, Conn, for
the design and  installation of an Air Quality Control  Sys-
tem (AQCS) based  upon  using the venturi for particulate re-
moval and a spray tower absorber for SC>2 removal.  As
part of its contractual commitment, Peabody offered
guarantees with regard to  both particulate and S02 re-
moval.  To confirm these  guarantees and to further Min-
nesota Power &  Light's  understanding of the operating
characteristics  of the  system which they purchased,  Peabody
was authorized  to design,  install and supervise a pilot
plant test program for  the evaluation of the system.   This
test program covered an 18 month period and involved a cost
of approximately  two million dollars.  The objectives  of
this pilot plant  included  the following:

1.  Confirm the pressure  drop in the venturi required  to
    meet particulate and  opacity emission standards.

2.  Confirm that  the system can remove 90% SO? when  burn-
    ing coals  containing  up to 2.8% sulfur.

3.  Demonstrate that the  system can operate on a  closed
    loop water  balance.

4.  Determine  the alkali  utilization of the flyash.

5.  Evaluate alternative  alkalis.

6.  Define waste  solids characteristics such as settling
    rates, percent moisture and settled solids, etc.

The pilot plant installed  to achieve the above objectives
was installed  at  the Clay-Boswell station taking  the flue
gas from Unit  #3.   Unit #3 has the same boiler design  and
is burning the  same  coals  which are to be burned  in  Unit
#4.  Thus, the  results obtained from the pilot plant could
be considered  representative of the results to be expected
for Unit #4.
                          516

-------
                       Minnesota Power and Light
                        Pilot Plant Installation
                      Clay Boswell Station-Unit no. 3
The pilot plant  system was identical  in concept  to  proposed
full scale  unit  with some modifications based on practical
considerations.   The lime slakers  system was not  installed.
An in line  electric reheater  was  used in lieu of the hot
gas bypass  system.   A thickener and  vacuum filter  was used
in lieu  of  a  waste solids pond  system.

The pilot  plant  was designed  to  treat 3200 ACFM  of gas.
The flue gas  is  taken from Unit #3 ahead of an existing
particulate scrubbing system  and  contacted  in  the venturi
with slurry for  removal  of the  particulate matter.   This
slurry  is  the same material  used  for  absorbtion  of S02.
The gas  and slurry leaving the  venturi  flows  to  the base of
the spray  tower absorber where  the gas  and  slurry separate.
The slurry  drains to  the recycle  tank,  the  gas  flows upward
through the spray tower  absorber  where  it  is  further con
tacted  with recirculated slurry which  is pumped  through
multiple spray headers  to achieve the  desired degree of
S02 removal.   The clean  gas  prior to  leaving  the absorber
flows  through a mist  eliminator section consisting  of  an
interface  tray and  chevron mist eliminator.   After  leaving
the absorber, the  gas is reheated by  an in-line electric
heater.  The reheated gas then  goes  through an I.D.  fan^and
is reintroduced  into  the suction  of  the I.D.  fan for Unit
#3.   The pilot plant  also contains an alkali  feed  tank  from
which  alkali is  fed to  maintain the  desired slurry  pll ,  a
supplemental flyash feeding  system and  a  thickener  and
vacuum filter for  treatment  of waste solids.   Particular
attention was given to  the  quality of instrumentation  to
 insure reliability  of the pilot plant operation  and test
results.   Inlet  and outlet  S02 concentrations were  con-
 tinuously  monitored by  means of  S02  analyzers.   A  nuclear
                           517

-------
    d e n s i t y  device was maintaining the slurry  c o n c e n t r at i o n.
    Automatic  pH control and  an  optical opacity meter  were also
    provided with the system.
                  —i
                AI.KAU j  lr
                l-Ll-.b TANM	f*3
                	J >~ •
Ven t ur i
    The  vcnturi  selected  for  pa rticulate removal  is  based  upon
    the  radial  flow design concept.   The design of a venturi
    must  contend with the problems  of abrasion and also  solids
    build  up  due to hot gas contacting the slurry used for
    parti c. ul ate  removal.  To  avoid  solids build up,  the  venturi
    is designed  using a "dentist  bowl" concept.   The upper  sec-
    tion  of  the  venturi consists  of  a conical  section  in which
    slurry is  introduced  tangentially.  The quantity of  slurry
    used  is  several times greater than the potential evapora-
    tive  capacity of: the  hot  flue gas.  The excess quantity of
    the  tangentiable flows of  the slurry insures  that  the  con-
    ical  section is completely wetted.  The hot flue gas enters
    the  venturi  through an insulated thimble section which
    introduces  the gas below  the  slurry injection point  and
    this  keeps  the gas slurry  contact point below the  wet-dry
    line  and  avoids solid build up.
                              518

-------
Abrasion can  occur  in three distinct areas  of  the  venturi.
The first is  where  the  gas makes a 90° turn to  flow
through the cylindrical orifice.  Abrasion  in  this  area is
avoided by having  the gas  impinge on a pan  filled with
slurry, which absorbs the  impact of the gas.   This  pan  is
maintained full  by  the  flow of slurry from  the  "dentist
bowl" and supplemental  slurry added via a bull  nozzle.

The slurry overflow from the pan and the gas are  then
mixed intimately  in the cylindrical orifice around  the  pan.
It is at this point that particulate removal is  achieved.
Abrasion is also  a  factor  at the orifice which  cannot be
eliminated.   However, the  wear surface in the  orifice area
is fabricated from  disposible angle iron sections which
provided for  simplified maintenance.

The gas and. slurry  mixtur-e leaving the orifice  area  has a
high velocity which if  allowed to impact on a  surface,
could also cause  severe abrasion problems.  This  situation
is avoided by maintaining  a sufficient distance  between the
orifice area  and  the wall  of the venturi.   This  allows  the
gas to expand and  slow  down sufficiently to be  nonabrasive.
As an added precaution  the wall is rubber lined  to  with-
stand any residual  abrasive impact.

Thus of the three  intended abrasive cases,  two  have  been
eliminated and the  third one minimized by providing  a de-
sign for simplified replacement.  The radial flow  venturi
design is a balance force  system since the  gas  velocity is
equal in the  360°  lateral  plane circumference  of  the ori-
fice.  The force  exerted on the mechanical  operator  due to
the venturi pressure drop  therefore becomes zero.   This
balanced design  will minimize maintenance problems  and  is a
                          519

-------
    key design feature  in  the  reliable operation of the
    v e n t u r. i .

    The design concepts  discussed  above are those used for  the
    full scale system as well  as  the pilot plant test program.

    All of the objectives  of  the  test program were achieved.
    However, only the results  pertinent to particulate removal
    and opacity will be  discussed  in this paper.

4.  CHARACTERIZATION OF  FLYASH PARTICLE SIZE

    The flue gas  duct to the  pilot plant had a 14" diameter.
    The Unit #3 duct from  which the  flue gas was to be sampled
    has a dimension  of  approximately 10 feet high x 146 feet
    wide.  From previous testing  that the Minnesota Power &
    Light performed  it  was known  that some segregation of the
    flyash occured in the  section  of ductwork where the flue
    gas was  to be sampled.  As a  result, there was a concern
    that the flue gas to the  pilot plant would not be re-
    presentative  with regard  to both total grain loading and
    particle size distribution.  Prior to locating the pilot
    plant test port  connection in the Unit #3 duct, extensive
    work was done to characterize  the particulates in the cross
    section  of the Unit  #3 duct.   Based upon this data, a test
    port was selected with two alternates provided should later
    results  dictate  changing  the  test port.  After the instal-
    lation of the pilot  plant, repeated particulate a n—
    alyses were made of  the flue  gas flowing to the pilot plant
    and simultaneously  the flue gas  from Unit #3.  The com-
    parison  showed that  a  proper  sampling port had been
    selected and  the flue  gas  to  the pilot plant was re-
    presentative  of  that obtained from the full scale unit.

    For particle  size distribution data, EPA method 5 was used.
    However, the  method  was modified by the use of an Anderson
    Impactor.  This  device allows measurement of both total
    grain loading and particle size  distribution down to 0.3
    microns.  The standard EPA method 5 was also used as a
    check against the modified method.  There was good agree-
    ment between  the two methods.

    At  the start  of  the  project there was some question as  to
    how the  size  distribution  varied with total grain loading.
    Some theories were  expounded  that the absolute quantity  of
    fines would be a constant  and  that higher grain loadings
    • would-be the  .result  of greater quantities of larger
   , particles.  The work done  in  characterizing both Rosebud
    • and McKay coals  demonstrated  that the size distribution  re-
    mains approximately  constant  under varying total grain
    loadings.  When-the  absolute  quantity of submicron:material
                              520

-------
    was  plotted  against the  total  grain  loading  in  the  raw flue
    gas  a  linear  relationship  existed  for  both Rosebud  and
    McKay  coals.   However,  the McKay coals  had a  greater
    percentage  of submicron  material.
                         Absolute Amount Less Than One Micron

                            Tolal Inlet Grain Loading
                         Total Inlet Gram Loading. Gram/SCFD
                        Total Inlet Grain Loading. Grain/SCFD
5.   PART1CULATE REMOVAL

    Having characterized the  size  distribution of  the two  coals
    tested,  the effect-of venturi  pressure  drop was  evaluated
    withregard to  percent  particulate removal.   For a  given
    test  condition,  simultaneous particulate  measurements  were
    made  of  the inlet  and outlet flue gasses.  Again the  An-
                                 521

-------
derson Impactor was used  to  that  the removal efficiency as
a function  of  particle size  could  be determined.   Data for
the Rosebud and McKay coals  were  established for  venturi
pressure  drops ranging from  6"  to  31" w.c.

The percent removal of various  particle sizes  for  different
venturi  pressure drop was  plotted  for both coals.   The
curves all  follow the s-ame trend  for both different  pres-
sure  drops  and different  coals.  A typical'set  of  curves is
shown below.
           I	
                       Panicle Diameter. Midoris
For  particle sizes of L'. 3  microns -or larger,  the  percent
removed  is  essentially 100%,  regardless of venturi  pressure
drop.   The  percent removed  drops off slightly  as  particle
size decrease.^  from 2.5 microns  to  0.8 microns.  It  is  in
the  less than 0.8 micron  size that  the venturi  pressure
drop has the greatest significance.

For  a  given venturi pressure  drop,  a comparison  of  the  two
coals  showed that a greater  percentage removal  of  submicron
particles  for MeKay coal  was  achieved as compared  to  the
Rosebud  coal.  This higher  removal  efficiency  partically
offsets  the higher quantity  of  submicron particles  1n  the
McKay  coal.                                         ,

D,a t a was also plotted showing the. total .outlet  gra.in loa-
ding, a.s  a.function of venturi pressure drop.   The  curves
for  both coals, are shown.   The  economics the  venturi system
had  been based,.upon achieving a  0.03 gr./SCFD  .(0.06 Ibs/MM
BTU) u s i n..g  a 12 "w.c. pressure  drop.  The curye,s_ show that
with Rosebud coal the 0.03  gr/SCFD  could be achieved  with a
6" w.c.  drop pressure, whereas  the  McKay coal  required  a 8"
w.c. pressure drop.  Both  curves appear to indicate that re-
gardless of pressure drop,  outlet grain loadings
                           522

-------
   significantly  less than 0.01 gr./SCFD  (0.02  Ibs/MM BTU) is
   not achievable.
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10 12 14 16 1B 20 22
Pressure Drop, Inches W.C.

                         Venturi Pressure Drop, Inches W.C.
6.   OPACITY

    In addition to meeting  particulate emission standards
    flue gas stack opacity  of  20%
    performance criteria.   It  was
    burned significantly effected
was also established  as  a
known  that  the  type  of coal
opacity results.   Therefore,
    Minnesota Power  & Light  wanted a means of predicting  stack
                              523

-------
opacity as a  function  of  both venturi performance  and  type
of coal being burned.   To  achieve this objective,  tech-
niques were devised  for measuring opacity in the pilot
plant tn'd then extrapolating  the  data to the full  scale
system.

To obtain pilot'plant  opacity data a Lear Siegler  RM41  op-
acity instrument was used.   The  opacity instrument was
located down  stream  of the venturi and absorber system  and
thus, reflected total  system  performance.  Initially the
unit was installed with the light beam traversing  the  dia-
meter of the  12" gas duct.   After limited experience with
this ins talla'tion  it became apparent that the margin for
error with this small  a path  length was too great.  Con-
sequently, a  second  installation was made in which the  path
length was increased to 6'6". To  achieve this path length
the  unit was  installed between two elbows in which the
larger path was parallel  to the  gas flow.  The installation
is shown below.
                     Opacity Meter Installation

                          n Reflector
                      Path
                      Length •
Venturi performance  was  varied to allow various outlet
grain  loadings  to  exist  and thus permit measuring  opacity
over a range  of  grain  loadings.  Data was collected  for
both Rosebud  and McKay coals.  A semi-log plot of  percent
opacity vs. grain  loading resulted in a straight line.
When comparing  opacity data forthe two different  coals  it
can be seen that the slope of the lines are different.
                          524

-------
                        Outlel Grain Loading, Grsin/SCFD
For  a  grain loading  of  0.03 g r ./. SCF,  the Rosebud  coal would
produce  the higher percent opacity.   For grain loading of
0.01 gr/SCF or less  the McKay  coal  would produce  the..higher
opacityvalue

Opacity  as  a function of  venturi pressure drop was  also
correlated  for each  coal.   As  night  he expected,  the curves
which  result are consistent with the  particulate  removal
curves.   As the pressure  drop  increases, the  opacity
achieved  approaches  a limiting value.   Consistent  with the
other  opacity curves, at  the expected venturi  pressure drop
of 12" w.c. which was required to meet particualate emis-
sion  standards Rosehu.
o a I  h ;
 525
he. lower  percent opacity.

-------
                            e Drop, Inches W.C
Having  m.  - vired  opacity in  the  pilot plar-",  the question
still r e v, •. •• n e d as  to  how to  scale up the  * ,^ta  for  Unit #4
to  the  sicick tip  diameter of 35 feet.   A  correlation  be-
tween particulate  grain loadings  and opacity has been shown
to  be as follows:
1.    W=KPlnLl/J_°l. Formula from  paper by  D.S.  Ensor  and
      _  _,_MN.J.  Pilot  - U.  of  Washington  APCA
                     Journal,
                     Vol. 21,  No. 8, August 1971.

      W= Total  Particulate Mass  Concentration in  Effluent
      K= Specific  Particulate  Constant
      p= Density  of Particulate
      1= Intensity of Transmitted Light
     Io= Intensity of Incident Light
      D= Illumination Path Length of  Diameter of  Plume
   I/Io= Light.  Transmittance
                            526

-------
^n the. assumption,  that  the particulate characteristics in
the. pilot plant are  identical to those in the  full  scale
system the  following relations were developed:
   log (100-0S)  =  log (100 Ops
where:  ^  - percent  opacity measured in the pilot
                  plant.

        0 s = predicted percent Opacity in  the  Unit  #4
                  stack.

        D  = pilot  plant  optical path length.

        D s = optical  path length in the Unit #4  stack.

Using this relationship  , a .04.1% opacity reading  in  the
pilot plant  would be  equal to a 20% opacity  in the  stack.
This opacity relationship when plotted is  shown  below:
This  curve, highlights the significance  of  stack  geometry in
determining  the  measured opacity.  The  conclusion  that  can
be  reached  is  that as stack diameter  is  increased,  the  flue
gas particulate  loading would have to be significantly  d e -
creasedto  achieve desired opacity value.
                          527

-------
    At the required design  particulate  emissions level of 0.03
    gr/SCF (0.06 Ibs/MM BTU),  the  opacity  for Rosebud coal
    would be 75% as opposed  to  64% for  McKay coal.   The lowest
    measured pilot plant opacity  reading  obtained was 6% for
    either coal burned.  To  achieve this  minimum opacity value,
    particulate emissions of  0.01  gr/SCF  (0.02 Ibs/MM BTU) or
    lower were required.  When  scaled  up  to Unit # 4 ,  this 6%
    pilot plant opacity value  is  equivalent to a 28%  stack op-
    acity.  Thus is appears  that  for Minnesota Power  ft Light's
    situation, a 20% stack  opacity is not  achievable.

7.   CONCLUSION

    The Minnesota Power & Light experience has shown  that:

    a.  A venturi for particulate  removal  can offer significant
        economic savings.

    b.  The pilot plant data  confirmed  that the required
        particulate emission  standards  can be met.

    c.  The pilot plant data  indicated  that for Clay  Boswell
        Station Unit #4 particulate emission standards and op-
        acity requirements  are  not consistent.  Even  when
        particulate emission  standards  are far exceeded, a 20%
        stack opacity is not  achievable.
                              528

-------
             "PERFORMANCE OF ENVIROMENTALLY
              APPROVED NLA SCRUBBER FOR S02"
                          By:

                    J.A. Bacchetti
                    Pfizer, Inc.
                    East St. Louis, Illinois  62201
                      ABSTRACT
     This paper describes the commercial development and operation
of the NLA - Lewis scrubber for flue gas.  The scrubber was installed
on three coal fired boilers at Pfizer1s chemical plant in East St.
Louis, Illinois.  Total operating cost, including depreciation,
is budgeted at $0.90/MM BTU.  Further improvements have reduced
this to $0.60.  On stream time averaged 94% the first year of full
operation.  Both S02 and particulates are within legal limits.
                               529

-------
INTRODUCTION

     The subject of this paper is the technical success of a gas absorption
unit with impingement and condensation particulate collection.

     But more importantly it is a success story of our present regulated
technostructure.

     This is a young nation.  We have a strong spirit of economic progress.
As a result, we have produced a record of major contributions to the health
and welfare of this country and the world.  Classical economics has produced
much human progress and well-being.

     Yet, as a nation, we have a limited sense of history and future; of
tradition and culture.  We depend on classical economic motivations to pro-
vide our direction.

     However, classical economics alone cannot provide motivations for controll-
ing the aggregate, long-term or probabalistic side effects of economic progress.

     Therefore, we have asked our government to place constraints on the
side effects of this progress.

     One major side effect is aggregate air pollution.  My car, my stack, by
itself, has no effect on my well being or that of the community.   But our
cars - our stacks, together, do1.

     This paper is a case study of a chemical plant which installed a stack
gas scrubber for purely classical economic reasons - we wanted to stay in
business - legally.  And, we wished to do so at the least expenditure of
resources - both present and future.

     Therefore, what will be presented today is primarily development history
and final results, with a limited amount of technical data.

     Most of the papers of this conference are research oriented.  This paper
is user oriented.

     The net result is this:  A 140,000 Ib/hr. steam boiler system firing 3.5%
sulfur coal that meets SO2 and particulate standards while burning high sulfur
coal, for a total add'l cost, including depreciation of less than 90C/MM BTU.
                                      530

-------
THE PROBLEM

     Pfizer's plant in East St. Louis,  111., produces  iron oxide pigments for
end use products such as colorants and  magnetic  tape.   It is  the largest plant
in the MPM division.  This plant has  three  coal  fired  boilers,  (see table 1),
with a total rated output of 140,000  Ib/hr. of steam.   All three boilers were
designed to burn high sulfur coal  (4%)  from the  local  Illinois  #6 seam.

                                TABLE 1
                             BOILERS
HEAT INPUT
MM BTU/HR
STEAM PRODUCED
M LBS/HR
  TYPE
MANUFACTURER
   150
    50
    20
   100
    30
    10
SPREADER
TRAVELING GRATE
TRAVELING GRATE
  ERIE CITY
  B&W
  O'BRIEN
     The Illinois high sulfur  coal  (table  2) is purchased  from any  of four or
more mines  (both strip and underground) within 75 miles  of the plant.   Both
price and availability are extremely  favorable when  compared  to alternate
fuels.

                                TABLE 2
                          COAL   TYPE
              SULFUR
              ASH
              HEAT CONTENT
              WASHED SIZE
                                 3.5%
                                10.0%
                                11,000 BTU/LB.
                                1 1/4 X 0
     However, when burning this fuel the boilers did not meet  the  allowable
emission standards for either S02 or particulates.  (tables  3&4)

                                TABLE 3
                        SO2 EMISSIONS
              NATURAL
              ALLOWED
              REMOVAL EFFECIENCY REQUIRED
                                1408
                                 396
                                  72%
                                TABLE 4
              PARTICULATE  EMISSIONS
              NATURAL
              ALLOWED
              REMOVAL EFFECIENCY REQUIRED
                                 145
                                  49
                                  66%
SOLUTIONS

     We therefore had three alternates:  Switch  fuels,  stack  gas  treatment or
do nothing.
                                      531

-------
     In a country based on law, we cannot pick and choose those we wish to obey
so that rules out alternate three, unless we cease operation.

     The remaining alternates are strictly an economic choice.  We chose the
stack gas treatment route as being inherently more economical and, long term,
more reliable than dependence on oil and gas.  Yet, we wished to minimize the
commitment of technical resources.

     We wish to concentrate our technical resources on iron oxide, not pollu-
tion control.  We needed a device that had the following characteristics:

     Reliability - Higher than the boilers
     Reasonable Cost - Low enough to still be more economical than alternate
                       fuels.
     Enviromentally sound - Not create new problems
     Compatible with boiler operation - Should not require more complexity.

     There are many types of FGD systems presently in some phase of development
or operation.  Due to political and economic considerations, the relative re-
liabilities and costs are difficult to obtain on a comparable basis.   However,
the following qualitative evaluation is accepted.

     1.)  Throw away systems (those that produce a sulfate or sulfite solid
          waste) are presently the most satisfactory.

     2.)  Calcium based systems, such as lime, are inherently simple and use
          inexpensive raw materials.  However, the plugging characteristic
          of lime requires more complex systems and reduces reliability.

     3.)  Sodium based systems, such as double aklali, seem to be impractical
          for large facilities.  For smaller facilities, they are in use, but
          add the operational and maintainance complexity of a major chemical
          plant; also, chemical costs can be quite high.

     Of course, all the systems must have sludge separation and disposal systems,
Some of these can be quite massive due to the large quantity of water required
for the scrubber to prevent plugging.

THE SELECTION
     We believe the scrubber we are about to describe is a reasonable answer
to many of these difficulties.

        It inherently resists plugging
        It is simple to operate
        It uses very little water, so no water recycle is required
        And, of course, it uses an inexpensive reagent - Lime

     The simplicity is the most important feature for us at East St. Louis,
111.  It can be operated by existing boiler house personnel with very little
additional training.  It can be maintained with existing shop personnel with
no additional training.  The flow chart is simple.

                                     532

-------
     So, what is this magic device?

     Very simple - a kiln.

     In 1974, through Mr. Wayne McCoy's membership on the Clean Air Committee
of the Nat'l. Lime Assn., Pfizer at East St. Louis became aware of the develop-
ment of Mr. Clifford Lewis.  Mr. Lewis is a consultant to the National Lime
Association and, as such, had developed a stack gas scrubber that,

     a.)  Used lime/limestone manufacturing technology and
     b.)  Used lime as the scrubbing reagent.  Pfizer, through its membership
          in the Nat'l. Lime Association, had access to Mr. Lewis's work and
          rights to the ultimate patent as well.

     The basic concept of Mr. Lewis's device is similar to most scrubbing
systems.  The flue gas is contacted with an aqueous aklaline material to remove
SC>2 by  absorption and subsequent precipitation,- particulates are captured by
impingment and condensation agglomeration.  In the NLA - Lewis scrubber, (see
figure  1) flue gases pass through a rotating kiln - a cylindrical shell
sloped  about 1/8"/ft. to provide gravity flow of the lime slurry scrubbing
liquid.  The apparatus contains rings of lifter boxes and great quantities of
loosely hung chain.  A circular dam confines a lime slurry pool through which
the lifter boxes pass as the shell rotates.  In this way, lime slurry is lifted
and poured over the chains, providing wetted chain surface for contact with the
flue gas.  Internal pumping rate in our particular unit is about 5000 GPM.   The
loosely hung chain also scours the internal scrubber surfaces to prevent plugging.

                                FIGURE 1
                    SCRUBBER  CONCEPT
                  U.S. Patent   NOV. 29,1977
4,060,587
     We will now review the developmental history of this device at the East
St. Louis plant.

PFIZER'S SCRUBBER

     In 1975 Pfizer installed at 87-foot kiln, 11-foot diameter and fitted it
with a modified NLA - Lewis chain system.   (figure 2&3)  In addition, Pfizer
Incorporated our own design concept of a drying zone contiguous to and down
stream of the wet scrubber section to dewater the waste sludge by contacting
it with the incoming hot flue gases.  This offers a dry waste product suitable
for landfill with reduced disposal costs.  It was installed as shown to handle
flue gas from the large boiler only. r,"

-------
                                                                          To Stack
            PFIZER  SCRUBBER-1975   ORIGINAL
Boiler
                        ^7 Spent Lime, Particulates
                                       FIGURE  3
                                                             o
              ORIGINAL  SCRUBBER  CONFIGURATION
                                 30-
SCRUBBING
	40'	
          The  gas  exit  section  of  the  rotating kiln contained eight lifter box cages
     and 15  tons of chain.   The center drying section had about five tons of chain in
     a "garland" arrangement.   Except  for  a  few test chains, all scrubber and scrubbed
     gas handling  equipment  was of mild  steel.

          From the start, tests on this  first configuration indicated excellent SO?
     removal,  but  inadequate particulate capture.  Particulate emissions were still
     twice the allowable  limit.

          We felt  that, with our type  of boilers and coal, we should be able to
     meet particulate as  well as SO2   requirements with this scrubber.  Therefore,
     we shifted the scrubbing section  to the center of the kiln, using heavier
     chains,  (figure 4)   We  also eliminated  the drier chains, added a de-mister
     section and a dropout,  or  disengaging section.
                                         534

-------
                                        FIGURE 4
          SECOND   SCRUBBER  CONFIGURATION
                                                   -   1977
1977
^
f

\Z"
BARE
28"






SC
f~\j -


RU
35








BBING


f , -
[

DROP-
OUT
»• -tr^.
DEMISTER3' ID
          Wiih -his design, S02 collection  further improved.   The particulate
         t->;:t i in i was doubled - to  about  only 20% more than allowable, (see table 5)

                                     TABLE  5
              1977   SCRUBBER  PERFORMANCE
   S02
   PART.
NATURAL

  960
  115
ALLOWED

   270
    21
ACHIEVED

   30
   26
        We now felt quite sure that, with only minor modifications,  the  scrubber
   would handle the load of all 3 boilers.  This would be a substantial  break-
   through since it eliminated the need for additional scrubbing devices for the
   other boilers.   This offered significant savings in investment  and  operating costs.

        Therefore,  in early 1978, we tied in both small boilers to the scrubber,
   added a mist eliminator at the stack, enlarged the ID fan and added 30 tons
   more chain upstream of the scrubber section - back to the concept of  drying.
   So we now have  this configuration, (see figure 5 & 6)
                                         FIGURE 5
                         FINAL  CONFIGURATION
                                                                            To Stack
Boilers
       ]Irx'                 Lime Slurry

       •^7 Spent Lime, Participates
                                                               o
                                                                           Demister
                                        535

-------
                                   FIGURE 6
                   FINAL   CONFIGURATION
                                                   DEMISTER
     In August of last year, we achieved the SO  and particulate  limits  on all
3 boilers and, shortly thereafter, obtained the final signed permit from the
State of Illinois Environmental Protection Agency.   (see table 6)
                FINAL  EMI
              TABLE 6
             S S I 0 N
TESTS
                  UNABATED
                    ALLOWABLE
                                                              ACTUAL
so2
PARTICULATE
1408
 145
396
 49
42
37
     Here are some operating characteristics of the scrubber.

     The lime utilization is excellent (table 7).   The water flow is low and
we have operated with dry discharge.  Our data and experience  with dry discharge
is limited, since our primary concern has been to  meet emission limits and
generate steam for pigment manufacturing.  Also,  recently an improved plant
wide solid waste disposal system provides minimal  economic incentive for adding
the complexity of dry discharge.

                                  TABLE 7
                       SCRUBBER  FLOWS
                 LIME

                 WATER IN
                 SLURRY OUT
                 pH
                            1000 Ibs/hr.
                         (90 + % Utilization)
                            50 GPM
                            30 GPM
                            6.0
                                       536

-------
     The energy use is quite low  (table 8).  Our total energy penalty  is  less
than 3%.  Many FGD's require from 3 to as much as 8% of the output.

                                TABLE 8
                         ENERGY  USE

              KILN                            100 H.P.
              I.D. FAN                        400 H.P.
              PUMPS                            43 H.P.
              TOTAL P                          15" H2O

     Our actual costs are shown in table 9.  Though we did invest  $1,800,000
we modified the scrubber several times.  We would anticipate that  this system
could be duplicated for less than $1,000,000. (in 1976 dollars)

                                TABLE 9
     ANNUAL  COSTS  -  BUDGETED  FOR  1979

              LIME PURCHASE                    $170,000
              WASTE DISPOSAL                    120,000
              POWER                              50,000
              DEPRECIATION                      150,000 ($1,800,000 Investment)
              MAINTENACE                        200,000
                                               $690,000

    A comparison of costs with other fuels shows that we can still use coal
at lower cost than any other competitive fuel.

     Since last fall we have had some other noteable successes.  Monthly  on
stream time has never been below 90% and has averaged over 94%.

     Recently we have experimented with lower cost raw materials and have been
successful.  We have found that lime kiln dust can be used as effectively as
quicklime.  Lime kiln dust is a by-product from Pfizer lime plants and all
other lime plants.  This has further reduced operating costs.

     Also, actual maintenance for 1979 is well below what we had anticipated.
These economic improvements have reduced our total operating cost  to about
60C/MM BTU - including depreciation'.

     Let me review what we have here - a stack gas scrubber that works.   It
is simple to operate, has demonstrated on-stream times in excess of 90% its
first year, costs less than $0.60/MM BTU, and perhaps its most unique  feature
is, it was developed, designed and commissioned without public funds.  This
device was created entirely within the private sector'.  Classical  economics
wins again.
                                     537

-------
              DESIGN GUIDELINES FOR AN OPTIMUM SCRUBBER SYSTEM

                                     by
                   Madhav B.  Ranade and Edward R.  Kashdan
                         Research Triangle Institute
                     Research Triangle Park,  N.C.   27709

                                     and

                               Dale L.  Harmon
                Industrial Environmental Research  Laboratory
                    U.S.  Environmental Protection  Agency
                     Research Triangle Park,  N.C.   27711
                                  ABSTRACT

     The revised New Source Performance Standards  (NSPS)  for  the  utility
industry mandates reduced particulate matter and sulfur dioxide emissions  from
new utility boilers.  A wet scrubber system can be an advantage in  controlling
both of these emissions.  Existing wet scrubber systems may meet  the  new
standards with significant increase in power consumption.   A  careful  design  of
the entire scrubber system, based on the-experience gained  at the existing
installations, is necessary to ensure cost effectiveness.

     The experience with existing wet scrubber systems used on coal-fired
utility boilers is reviewed and their performance  is correlated with  power
consumptions.  Based on a correlation of scrubber  pressure  drop against outlet
concentration, conventional scrubber-systems would be able  to meet  the revised
NSPS with a theoretical scrubber pressure drop of  17±2 in.  W.G.   Overall system
pressure drop, however, could easily run as high as 30 in.  W.G. ;  Novel scrubber
systems such as the electrostatically augmented scrubber  may  provide  the
necessary collection performance at lower pressure drops.

     The performance of the various scrubber components  such  as mist  eliminators
and reheaters is reviewed.  Operating problems are also  discussed.
                                      538

-------
                         CONVERSION TABLE
To Convert From
To
Multiply By
Btu/lb
scfm (60°F)
cfm
°F
ft
gal/mcf
gpm
gr/scf
hp
in.
in. W.G-
Ib
psia
1 ton (short)
nm3/hr (0°C)
m /hr
m /hr
°C
m
1/m3
1/min
gm/m
kW
cm
mm Hg
gm
kilopascal
metric ton
2.324
1.61
1.70
<°F-3:
0.305
0.134
3.79
2.29
0.746
2.54
1.87
454
6.895
0.907
                               539

-------
              DESIGN GUIDELINES FOR AN OPTIMUM SCRUBBER SYSTEM

INTRODUCTION

     The U.S. Environmental Protection Agency has lowered its New Source
Performance Standard for particulate emissions from coal-fired boilers to
0.03 Ibs of particulate/million Btu.l   In the case of power plants which
require a scrubber system to meet S02  emission standards, it is economically
advantageous to also collect the particulate matter with the scrubber system.
But existing utility scrubber systems  either would require relatively large
power consumptions to meet the standard,  or would be incapable of meeting it at
all.  Hence it is desirable to design  an optimum wet scrubber system which would
have a high and acceptable collection  efficiency at low energy requirements.

     The performance data and operating experiences of existing scrubber systems
were summarized in an EPA report by Kashdan and Ranade (1979) .   This information
is essential for the design of an optimum wet scrubber system for coal-fired
utility boilers.

     The particulate emissions from power plants exhibit tremendous variability
in flyash particle size distribution,  composition, and the flue gas composition.
For given emission properties the scrubber components need to be chosen so that
acceptable performance is obtained at  the lowest cost.  The past operating
experience from the scrubber systems used with power plants will provide guid-
ance in selecting various components of the scrubber system.  However, the
technology of the scrubber system components has not advanced far enough to
prevent problems arising after construction.  Flexibility of the design to
allow easy replacements of various components is desirable to accomodate devel-
opments in the scrubber technology. Highlights of the review of operating
experiences are presented in the next  few pages.

PROCESS DESCRIPTION

     For a complete understanding of the problem, the source of pollutant
emissions must be considered as well as the collection device.   A brief descrip-
tion of a coal-fired electric generating plant and its effluents follows with
emphasis on aspects relevant to a scrubber system.

     Modern coal-fired, electric generating plants consist of boilers, genera-
tors, condensers, coal handling equipment, dust collection and disposal equip-
ment, water handling and treatment facilities, heat recovery systems (such as
economizers and air heaters), and possibly flue gas desulfurization systems.

     Boiler types in use include cyclone, pulverized, and stoker units, but
nearly 90 percent are pulverized coal  boilers (Sitig, 1977).  Pulverized coal
boilers are commonly classified as either wet bottom or dry bottom depending
on whether the slag in the furnace is  molten.
 See Conversion Table, pg.2.
                                     540

-------
     Two condensing cooling systems are used by the electric utility industry:
the once-through system and the recirculatory system.  In the once-through
system, all the cooling water is discharged to a heat sink, such as a river or
lake.  In recirculating systems, cooling devices, such as cooling towers or
spray ponds, permit the use of recirculated water.

     Wet scrubbing systems in coal-fired electric generating plants may be
used to collect particulate matter and/or to scrub 862 from the flue gas.  In
any case, a wet scrubbing system increases both the solid and wastewater
disposal problems of the plant.

     Combustion of coal in the furnace produces both flyash (airborne) and
bottom ash (settled).  Both bottom ash and collected flyash along with sludge
from a throwaway flue gas desulfurization system (where used) are the major
sources of solid waste from coal-fired utilities.  These solid wastes, which
are in a slurry form, are usually sluiced to a solid-liquid separator; the
solids settle out and clarified water is returned to the system or discharged.
Ultimate disposal of the wastes may be either in an onsite settling pond or,
after further dewatering and treatment, in a landfill.

CHARACTERIZATION OF EMISSIONS FROM COAL-FIRED UTILITY BOILERS

     The successful design of a wet scrubber system on a particular coal-fired
boiler requires careful consideration of the flue gas characteristics of that
boiler.

Physical and Chemical Properties of Flue Gas

     In designing a wet scrubber system, the volume of gas handled, inlet and
outlet temperatures, humidity, and S02 concentration are all important consid-
erations.  Typical power plant flue gas volumes range from 3000 to 4000 acfm/MW
depending on coal composition, boiler heat rate, gas temperature, 'and amount of
excess air.  Because of economies of scale, the utility industry has tended
toward larger and larger power stations implying that scrubber systems must be
capable of handling volumes of gas as large as 4,000,000 acfm.

     The temperature of the gas entering the scrubber is determined by the
efficiency of the air heater.  Most steam power plants operate in the range of
250-300°F downstream of the air heater.  Exit temperatures from the scrubber
vary with sulfur content and range from 150°F for coals with less than 1 percent
sulfur to 180°F for coals containing above 3 percent sulfur (Mcllvaine, 1974).
Because exit temperatures are low, most scrubbing systems incorporate reheat
systems which provide greater plume buoyancy and prevent corrosive condensation.

     Flue gas contains from 5 to 15 percent moisture depending on the amount of
volatile matter and on the moisture content of the coal.  The concentration of
sulfur dioxide in the flue gas depends on the sulfur content of the coal:  for
an average sulfur content of 2.5 percent, there will be approximately 1500 ,.ppm
of SOg in the flue gas (Mcllvaine, 1974).  On the average, 1-3 percent of the
S02 will be converted to SOs-  Sulfur oxides in the flue gas make for a corrosive
environment; special alloys, coatings, and linings must be used on scrubber
internals.


                                      541

-------
     Of particular concern to the designer of a wet scrubber system is the
chlorine content of the coal.  The chlorine content of coal (in the form of
sodium and potassium chlorides) may vary from a trace amount to as high as
0.5 percent.  During combustion, some of the chlorine is converted to
hydrogen chloride or other volatile chlorides.   Most of the hydrogen chloride
will be absorbed in scrubbing liquor, thereby increasing the potential for
chloride stress-corrosion.

Characterization of Flyash

     The characteristics of flyash (concentration, size distribution,  and
chemical composition) affect both the performance and maintenance of the
scrubber.

     Particulate Emission Quantity—The concentration of flyash in utility flue
gas depends primarily on the following variables:  (1) amount of ash in the coal,
(2) method of burning the coal, and (3) rate at which coal is burned (Sitig,
1977).  Pulverized coal units produce greater quantities of dust than  stoker
or cyclone units.  Furthermore, for a given furnace type,  the flyash emission
quantity will be approximately proportional to the ash content of the  coal.
Inlet dust loadings in utility flue gas may vary from 2 to 12 gr/dscf,  but 4  or
5 gr/dscf is fairly typical.

     In general, the size distribution of the flyash and not the emission quanti-
ty determines the collection efficiency of a particular scrubber.   However,  the
dust concentration does affect the abrasiveness of the flue gas, and hence,  the
potential for eroding a scrubber system.  In cases where the inlet dust loading
is very heavy, some scrubbing systems use mechanical collectors before the
scrubber.

     Flyash Size Distribution—The particle collection efficiency of a scrubber
is lowest for the fine particles (<3.0 microns, aerodynamic).   Hence,  the
collection efficiency of a particular scrubber will depend on the amount of fine
particles in the inlet dust.

     Figure 1 shows flyash size distributions from four utility boilers.   The
fine fraction varies widely, ranging from roughly 4 percent to 45 percent of
the inlet dust loading,  and representing about 0.05 gr/dscf to 0.5 gr/dscf.
This variation is accounted for in part by the coal and furnace type.   Lignite,
for example, appears to produce a very fine distribution.   Because of  the lim-
ited amount of data, however, generalizations are difficult to make.   Further,
the effect of process variables on the size distribution is not known.   Suffice
it to say that if the design of the optimum wet scrubber system is to  be based
on impactor measurements of the inlet flyash size distribution, then careful
measurements in sufficient number must be made to accurately determine the fine
particle fraction.

     (Figure 1 shows that the flyash size distribution from the stoker unit had
a large fraction of fine particles,  contrary to what one would expect  from this
method of firing.  The distribution was indeed  biased toward the smaller sizes
by the scrubbing system sampling duct which acted like a mechanical collector
(Hesketh, 1975).  Nevertheless,  the sampled flue gas did contain approximately
0.1 gr/dscf below 3.0 microns.)

                                      542

-------
  40
  20
   10
    8
93

O
i   2
Q
    1.0
    0.8

    0.6


    0.4
    0.2
    0.1
                                                            D
        LEGEND

PC:  Bituminous (1.3 gr/dscf)
Lee et al. (1975)

PC:  Subbituminous (2.0 gr/dscf)
Accort et at. (1974)

Stoker (0.4 gr/dscf)
Hesketh (1975)

Lignite (1.0 gr/dscf)
Fox  (1978)
           0.05     0.5 1   2    5   10   20    40    60     80   90  95      99

                               Cumulative % by Weight Less Than Dp


            Figure 1.   Flyash  size distributions  from four utility boilers.
                                            543

-------
     Chemical Composition of Flyash—Flyash is composed primarily of silicates,
oxides, sulfates, and unburned carbon.  For purposes of designing a particulate
scrubber system, the calcium oxide content of the flyash is an important consid-
eration:  the calcium oxide will scrub a certain amount of S02 thereby forming
calcium sulfate and increasing scaling potential.  In cases where the flyash
was extremely alkaline, the design of a combined particulate-SOp scrubbing
system encorporated the collected flyash as the scrubbing reagent (Grimm
et al., 1978).

SUMMARY OF EXISTING SCRUBBER SYSTEMS IN THE U.S.

     Table 1 is a summary of the design and operating parameters of the various
particulate and particulate-S02 scrubber systems in use at coal-fired power
plants across the U.S.  Gas-atomized scrubbers, and particularly, Venturis, are
the most widely used scrubber design for particulate removal.

     The newer installations generally have better particulate removal capabili-
ties, greater availabilities (defined as the fraction of a year that the scrubber
appeared to be in operable condition), and treat larger volumes of flue gas.
Landfill and ponding are the predominant methods of waste disposal.   Few of the
existing scrubber systems are now meeting the New Source Performance Standard
for particulates, 0.03 Ib of particulate/million Btu, or about 0.017 gr/dscf.
As shown in Table 1, the particulate scrubber at the Four Corners Station
(Arizona Public Service) operates with an overall system pressure drop of 28 in.
W.G. and is capable of just meeting the standard.

ESTIMATING POWER REQUIREMENTS

     Estimating the power requirements of a particulate wet scrubber is a two-
step process:  first a determination of the size distribution of the dust is
made; and second, an estimate is made of the power requirements for the scrubber
which are necessary to meet emission standards.  Two approaches, the contact-
power rule and the cut-power rule, have been developed and are discussed below.

Contacting-Power Rule

     The contacting-power rule, developed by Semrau (1977), represents a
completely empirical approach to the design of particulate scrubbers.  The
fundamental assumption is that, for a given dust, scrubber performance depends
only on the power consumed in gas-liquid contacting, regardless of scrubber size
or geometry.

     Power consumed in gas-liquid contacting depends on the manner in which the
energy is introduced.  For gas-atomized scrubbers, where the energy comes from
the gas stream, theoretical power consumption is given by

                         Pr = 0.158 AP, hp/1000 acfm                       (1)
                          Lr

where AP = pressure loss across unit in inches W.G.

For preformed spray scrubbers, where the energy comes from the liquid stream,
theoretical power consumption is given by

                                      544

-------
TABLE 1. CONDENSED SUMMARY OF PARTICULATE AMD PARTICULATE-S02 SCRUBBERS IN THE U.S.
                           PARTICULATE-S02 SCRUBBERS

Utility
Stat.on

Design and Operating Parameters
Start-up date
Reagent
Vendor
Design

Number of equipped boilers
Number of scrubber modules
Installed scrubber capacity, MW
Collector preceding scrubber
Reheat7
Bypass'
Annual cost, mills/kWh
Coal heating value, Btu Ib
Sulfur m coal, pet
Ash in coal, pel.
Calcium oxide in ash, pet
L/C, gal/1000 acf

P partieolate scrubbet, in W.G
P system, m W.G
Inlet dust loading, gr/rlscf
Inlet SC12. PPm
Outlet dust loading, yr/dscf
S02 removal, pet.
Waste disposal
Availability
Reference
Pennsylvania
Power Co.
Bruce Mansfield
No 1, 2

4 76
line
Chemico
Vpnturi

2
12
1650

Yes
No
4.25
11,900
4 7
125
NA
20

20
NA
5-65
2,200-2,600
0.007 0 017
92%ldesign)
Landfill
974
38, 10, 21
Kentucky
Utilities
Green River
Station

9 75
ime
AAF
Ventur
Moving Bed
3
1
180
Mech
Yes
Yes
2.0
10.800
3 /
13.4
NA
39 5

7
NA
2.2
2,200
99%ldesign)
90
Pond
854
21,22
Montana
Power Co.
Colslrip
No 1. 2

9 75
flyash 'lime
CEA
Ventur
Wasti Tray
2
6
720

Yes
No
0.26
8.840
08
9
22
15 lor venturi
18 for spray
17
25.5
27
800
0.018
80
Pond
90*
21, 16, 27
Tennessee
Valley Authority
Shawnee
IDA
[Test lacility)
4 72
lime'limestone
UOP
Moving Bed

1
1
10

Yes
No

lO.SOOIave i
coal type variable


37

8 16

3.5 8.5
2.500 4,000
0.035-0.090
60 99
Pond

31, 2, 39
Tennessee
Valley Authority
Shawnee
10B
(Test facility)
472
lime-limestone
Chemico
Ventori-1
Spray Tower
1
1
10

Yes
No

10,500lave.)
coal type variable


21 for venturi
9 4 far tower
3 16

3.5-8,5
2,500-4,000
0.003 0050
60 99
Pond

31, 2, 39
Arizona Public
Service Co.
Cholla Station


12/73
limestone
R-C
Venturi
Spray Tower
1
2
115

Yes
Yes
2 2
10,400
0,5
13.5
35
10 for ventur
49 far towP'
15
235
20
420
0.016
59
Pond
95
21, 23, 20
Northern
States Power
Sherburne
No 1, 2

3 76
limestone
CE
Venturi
Moving Bed
2
24
1400

Yes
No
04
8,300
08
9
NA
17 lor venturi
10 for bed
11
22
2040
400-800
0.035 0044
50 55
Pond
90
10, 21, 19
Kansas City
Power & Light
La Cygne
No 1

2'7j
hmestone
B&W
Venturi,
Sieve Tray
1
8
870

Yes
No
1 4
9.000 9.700
5 6
20 30
69
12 loi vfnturi
26 5 for tower
7
22
56
4,500
0074
80
Pour!
NA
10, 21, 24
Kansas
Power & Light
Lawrence
No 4

1 77
limestone
CE
Rod Scrubber
Spray Tower
1
2
125

Yes
Yes
NA
10,000
05
9.8
132
20 fur sc'iibbe'
30 for tower
9
24
43
425
004
90
Pond
NA
10,21, IS
Nevada
Power Co.
Reid Gardner
No 1.2.3

3 74
soda asfi
CEA
Venturi
Wash Tray
2
2
330
Mech
Yes
Yes
MA
11.800
00
9 4
18
12 5

15
20
0306
300
0.02
85
Pond
90
20

-------
                            TABLE 1 (cont.) CONDENSED SUMMARY OF PARTICULATE ARID PARTICULATE-S02 SCRUBBERS IN THE U.S.

                                                           PARTICULATE    SCRUBBERS
en
-l^
01
Utility
Station
design and Operating Parameters:
Start-up date
Vendor
Design
Number of equipped boilers
Number of scrubber modules
Installed scrubber capacity, MW
Collector preceding scrubber
Reheat'
Bypass?
Annual cost, mills/kWti
Coal heating value, Btu/lh
Sulfur in coal, pet.
Ash in coal, pet.
Calcium oxide in ash, pet. ,
L/G, gal/1,000 acf
^ P paniculate scrubber, in. W.G.
i P system, in. W.G.
Inlet dust loading, gr/dscf
Inlet S02, ppn>
Outlet dust loading, gr/dscf
S02 removal, pet.
Waste disposal
Availability
Reference
Arizona
Public Service
Four Corners

12/71
Chemico
Venturi
3
6
575

Yes
No
NA
9,200
0.75
22
S.3
8.5
18
28
12
650
0.01-0.02
30-40
Mine
100
38, 20
Picific Power
& Light
Dave Johnston

4/72
Chemico
Ventur
1
3
330

No
No
NA
7,430
0.5
12
20
13.3
10
15
4
500
0.04
40
Landfill
NA
20

Valmont

11/71
UOP
TCA
1
2
118
Mech
Yes
Yes
NA
10,800
0.8
9.0
10
50
10-15
NA
0.8
500
0.02(min.)a
40
Landfill
75
20, 29
Public Service
Company of Colorado
Cherokee

11/72-7/74
UOP
TCA
3
9
660
Mech/ESP
Yes
Yes
NA
10,100
0.6
12
4
50
10 15
NA
0.4 - 0.8
500
0.02(min.)a
20
Landfill
70-90
20, 29

Arapahoe

9/73
UOP
TCA
1
1
112
Mech/ESP
Yes
Yes
NA
10,100
0.6
12
4
50
10 15
NA
0.8
500
0.02(min.)a
20
Landfill
40-70
20, 29
Minnesota
Power & Light
Clay Boswell

5/73
Krebs
Preformed Spray
1
1
350

No
No
NA
8,400
0.9
9
11
8
2.5
4
1.25
1,125
0.03
40
Pond
100
20, 36

Syl Laskin

6/71
Krebs
Preformed Spray
2
2
116

No
No
NA
8,400
0.9
9
11
8
2.5
4
2
1,125
0.04-0.046
40
Pond
100
20, 36
Montana-Dakota
Utilities
Lewis and Clark

12/75-
R-C
Venturi
1
1
55
Mech
No
No
NA
6,450
0.5
8.5
NA
11
13
14.5
1
520
0.03
50
Pond
NA
20, 33, 32
               aBest performance of scrubber at highest pressure drop (29).

-------
                     PL = 0,583 APL QL/QG, hp/1000 acfm                    (2)
where AP  = pressure loss in liquid, lb/in2

       Q  = liquid flow rate, gal/min
        Li
       Q  = gas flow rate, ft3/min
When scrubber overall particle collection efficiency for a constant inlet dust
is measured over a range of power consumptions, it is often found that the
"scrubber performance curve" plots as a straight line on log-log paper, implying
a power relationship given by
where N  is the dimensionless number of transfer unit related to efficiency (n)
by N  = In (l/(l-n)), and P  is given by
                                  P  = P  + P
                                   T    G    L
The empirical constants, a and y> depend only on the characteristics of the
particulate, but are little affected by scrubber size or geometry.

     The contacting-power rule implies that scrubbers operated at higher power
consumptions will be more 'efficient particulate collectors—provided the increased
energy results in better gas-liquid contact.  Figure 2,  derived from the above
Table 1, is a log-log plot of operating points, outlet dust loading at a given
power consumption for various power plant scrubber systems.  (Theoretical
power consumption was determined by Equations 1 and 2.  Plotting outlet dust
loading against power consumption is essentially equivalent to the procedure used
in the contacting-power rule, assuming that flyash size distributions are the
same for various utility boilers.)  As shown, the operating points can be
readily fitted to a straight line, implying a power-function relationship be-
tween scrubber overall collection efficiency and power consumption.  The
least-squares correlation was Y = 0.068X i"^1 and r2 = 0.86.  The good fit is
quite remarkable given the variety of coals, furnaces, process variables, and
inlet particle size distributions among the plants.  Based on this correlation,
to achieve the New Source Performance Standard for particulates of  about 0.017
gr/dscf, approximately 2.7±0.3 hp/1000 acfm (95 percent  confidence limits)
theoretical power consumption, or eqUivalently, 17±2 in. W.G.  pressure drop is
required.  Although this value is only approximate, it does underscore the fact
that conventional scrubbers require a large power consumption to meet the New
                                     547

-------
   0.08

   0.07

   0.06


   0.05

U
C/9
1  0.04
ts
   0.03
co
=3
a
0  0.02
KCPL
   Cr
  MPL C\ O
  (SL)KPL\PL  NSP
    O
   MPL
   (CB)
 ON
MDU"
   KCPL - KANSAS CITY POWER AND LIGHT
   MPL - MINNESOTA POWER  AND LIGHT
      SL - SYL LASKIN
      CB - CLAY  BOSWELL
   KPL - KANSAS POWER AND LIGHT
   PPL - PACIFIC POWER AND LIGHT
   NSP - NORTHERN STATES POWER
   MDU - MONTANA-DAKOTA  UTILITIES
   NPC - NEVADA  POWER COMPANY
   PSCC - PUBLIC SERVICE  COMPANY OF COLORADO
   APS - ARIZONA PUBLIC SERVICE
      FC - FOUR  CORNERS
      CH - CHOLLA
   PPC - PENNSYLVANIA POWER COMPANY
   MPC-MONTANA POWER COMPANY

Y = 0.068X"1'41
   (r2  = 0.86)
                          PSCC. NPC
                                        MPC
                                 O
                                APS
                                (CH)   Aps
                                      (FC)
                                   PPC
                                                                          j	I
       I                     2            3         456789   10
                        THEORETICAL POWER  CONSUMPTION, hp/1,000 acfm

        Figure 2.   Correlation of  scrubber  outlet  dust  loading with
                   theoretical power consumption.
                                      548

-------
Source Performance Standard.  Further, this figure represents only the
theoretical power consumption across the particulate scrubber.  The actual
system pressure drop will include fan losses, losses across the absorber, mist
eliminator, and ductwork.

Cut-Power Rule

     Whereas the contacting power rule provides an empirical approach to the
design of particulate scrubbers, it lacks generality because it is specific to
a particular dust.  A more general and theoretical approach was taken by
Calvert (1972, 1977) who related scrubber fractional efficiency to power
consumption.

     The cut-power rule uses the quantity called the "cut diameter," the diameter
at which the collection efficiency of the scrubber is 50 percent.  Most scrubbers
that collect particles by inertial impaction perform in accordance with the
following equation:


                               P = exp(-A d B)                             (3)


where P = particle penetration
    A,B = constants
     d  = aerodynamic particle diameter

Assuming a log-normal distribution, Equation 3 can be integrated, yielding a
plot of overall penetration against the ratio of required cut diameter to mass
median diameter.  Hence, by knowing the inlet particle size distribution and
the efficiency needed to meet emission standards, one can determine the required
cut diameter.  For example, for a "typical" flyash particle size distribution of
d  = 17 ym, a  = 4, to achieve 99% collection efficiency would require a cut
diameter of approximately 0.6 ym.  To determine which scrubber types can meet
this cut diameter, Calvert developed theoretical impaction models of scrubber
performance (cut diameter) versus power consumption for various scrubber types.
To achieve a cut diameter of 0.6 ym, a venturi scrubber would require a
theoretical pressure drop of 15 in. W.G., which agrees with the figure of
17±2 in. W.G. determined from the empirical correlation above.

     Figure 3 is a plot of theoretical venturi scrubber performance curves and
actual performance points for scrubbers operating on coal-fired boilers (based
on published data).  The performance of the actual scrubbers suggests that, as
expected, lower cut diameters (higher collection efficiencies) are achieved at
the expense of greater power consumption.  Further, the performance of the
venturi scrubbers agrees well with the theoretically predicted performance for
wettable particles.  The venturi scrubber performance model is evaluated for
different values of the dimensionless factor f.  The value f = 0.50 corresponds
to wettable particles, whereas f = 0.25 corresponds to nonwettable particles
(Calvert, 1977).

     The case of the moving-bed scrubber at Cherokee Station deserves special
mention.  As shown in Figure 3, independent measurements at similar pressure
drops resulted in radically different values for the cut diameter.  In this

                                        549

-------
   5.0
   4.0

   3.0

   2.0
 E
ST.
UJ
§ '( 0
5 fl.8
o
o 0.6
   0.4
o
ec
   0.2
                                                        I
                  JL
                                                       t.O          2.0     3.0
                                                         POWER, hp/1,000 acfm
                       4.0  5.0  6.07.0
                                              JL
      10      15   20  25 30     40
 PRESSURE DROP, in. W.G.
__J	L_	L	I   i
                                              10           20          40
                                                PRESSURE DROP, cm. W.G.
                     60    80  100
                                        VENTURI SCRUBBERS
                                        (f = 0.25, f = 0.50)
                                        TCA [CHEROKEE, 1975,1974]
                                        CHEMICO VENTURi
                                        CEAVENTURI[COLSTRIP]
                                        VENTURI
                                        TCA
                                        TCA [MOHAVE]
        [TVA]
200
                             Figure 3.   Theoretical and  experimental cut diameters.

-------
regard, Ensor et al.,  (1975) reported highly variable outlet particle concen-
trations which did not correlate with pressure drop suggesting the presence of
reentrained solids from the mist eliminator.  The authors concluded that the
"evidence...weighs against one considering the agreement between predicted and
experimental cut diameters to be anything more than coincidence."

     In general, the limitations of the techniques for measuring flyash size
distributions undermine the usefulness of the cut-power approach.

NOVEL SCRUBBERS

     Conventional scrubbers collect particles primarily by inertial impaction.
However,  the collection efficiency of conventional scrubbers decreases signifi-
cantly for fine particles, resulting in the need for relatively large power
consumptions to remove the fine particles.  As has been shown, flyash contains
a substantial fraction of fine particles, with the result that scrubber systems
operating on utility boilers may require overall system pressure drops as high
as 30  in. W.G.  This pressure drop represents a large power loss to a utility.

     In 1973, EPA initiated a novel device evaluation program.  The purpose of
the program was to identify, evaluate, and where necessary, develop devices
which would have better collection efficiencies for fine particles.  The results
of this program indicate that the most efficient novel scrubbers are those that
utilize additional collection mechanisms other than just inertial impaction.

     The most promising of these novel devices are electrostatically augmented
scrubbers and condensation scrubbers.  The former increases particle collection
by increasing the electrostatic attraction between particles and droplets.   The
latter increases particle collection by growing particles into a size range
which  is  easier to collect and, also, by increasing diffusiophoretic forces.
Other  novel scrubbers, which either consume large amounts of power or require
the use of waste heat, are deemed inappropriate for use on utility boilers and
are not discussed below.

     Condensation Scrubbers—The use of condensing water to improve scrubber
particle  collection efficiency is not a new idea, but until EPA sponsored
research  on the subject, only small-scale laboratory studies had been done.
Calvert (1973, 1974, 1975, 1977) developed models for particle collection in
condensation scrubbers and attempted to verify those models in bench- and
pilot-scale studies.  His studies indicate that collection of fine particles in
a condensation scrubber depends strongly on the inlet dust concentration and the
flue gas  enthalpy.  In assessing the possible uses of condensation scrubbing,
Calvert (1975) gives an approximate minimum enthalpy of 100 kcal/kg (about 180
Btu/lb) which would be necessary for high efficiency particle removal in a con-
densation scrubber.  Flue gas from utility boilers typically contain 5 to 15 per-
cent moisture.  Even at 15 percent moisture, the enthalpy would only be about
180 Btu/lb, indicating that condensation scrubbers would have only marginal
application to power plants.  Furthermore, the collection efficiency of
condensation scrubbers decreases with increasing dust concentration because
there  is  less water available to condense on'each particle.  Theoretical
calculations by Calvert (1974) have shown, for example, that for a three-plate


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condensation scrubber operating at a condensation ratio of 0.1 g vapor condensed/
g dry air, particle collection efficiency for 0.75 ym (aerodynamic) particles
decreased from 100 percent at a concentration of 2xl05 particles/cm3 (about
0.01 gr/scf, assuming a density of 2.0 gm/cm3) to about 60 percent at a
concentration of 107 particles/cm3 (about 0.6 gr/scf).  Insofar as utility flue
gas may contain dust loadings as high as 8 gr/scf, condensation scrubbing does
not seem very feasible.

     In short, whereas it may be possible to incorporate some condensation
effects in scrubbers operating on utility flue gas, a condensation scrubber
per se would not be recommended.

     Electrostatically Augmented Scrubbers—A number of novel devices have
been developed recently which use electrostatic forces to enhance particle
collection.  The scrubber types using electrostatic augmentation vary consider-
ably in design, but can be classified according to whether the particles and/or
the water is charged, and whether an external electric field is applied.

     Two of the most tested electrostatically augmented scrubbers are the TRW
Charged Droplet Scrubber and the UW Electrostatic Scrubber.   The TRW scrubber
uses charged droplets and an externally applied electric field to collect parti-
cles.  It has been used successfully on emissions from a coke oven battery.
The UW scrubber charges both the water droplets and the particles (charged to
opposite polarity); a pilot-scale unit has been successfully used on emissions
from a power plant.  Both of these devices have shown high efficiencies (over
90 percent) for submicron particles at substantially less power consumption
than would be required for a conventional venturi.

     Whereas the performance of these small-scale units has  been encouraging,
several points must be taken into consideration before a full-scale unit is
planned for use on a power plant.  First, utility flue gas contains a heavy
dust loading, as large as 8 gr/dscf, and even greater.  (The UW scrubber,
although showing good collection efficiency of flyash from a power plant,  because
of the sampling arrangement, had extremely low inlet dust loadings of 0.5 gr/dscf
or less (Pilat and Raemhild, 1978).  Heavy dust loading, for example, would
probably necessitate greater charging in a UW-type scrubber.  Secondly, most
utilities handle large volumes of gas compared to the volumes handled by these
small units.  The same cost savings may not be realized in a scaled-up version
of these smaller units; the economics would have to be worked out on an
individual basis.

MIST ELIMINATORS

     Mist elimination is a requisite for every scrubber system.  Mist elimina-
tors remove scrubber-liquid droplets that are entrained in the flue gas and
return the liquid to the scrubber.  Poor mist elimination, an all too common
problem, can have serious consequences, including corrosion downstream, an
increase in particle outlet loading, an increase in power requirements for
reheat, and an increase in water consumption.
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     In a system study for EPA,  Calvert,  Yung, and Leung (1975)  evaluated  the
performance of various mist eliminators.   The results of this study that are
relevant to a utility scrubber system are as follows:

    •Overall droplet collection efficiency of a mist eliminator  depends on
     primary collection and reentrainment.   Both overall and primary collection
     increase with increasing gas velocity,,  But at high gas velocities
     (nominally, 5 m/sec and over), reentrainment occurs, decreasing the over-
     all collection even though primary collection remains high.

    •Higher reentrainment velocities (greater mist eliminator capacity) are
     obtained with mist eliminators which have good drainage.  Thus, horizonal
     gas flow mist eliminators have greater capacities than vertical gas flow
     types.  Similarly, vertical gas flow mist eliminators with  45° baffles had
     larger capacities than those with baffles inclined at 30° or 0°.

    •Pressure drop across a baffle mist eliminator is reasonably well predicted
     by a model based on the drag coefficient for a single plate held at an
     angle to the gas flow.

    •Solids deposition is greater on inclined baffles than on vertical ones
     because of the increase in settling rate of suspended solids.   Deposition
     rate decreases as the slurry flux on the surface increases.

     A review of commercial mist eliminator designs in use in the utility  indus-
try revealed the following practices (Ellison, 1978) :

    •Vertical gas flow mist eliminators are used almost exclusively.  The  chev-
     ron multipass (continuous vane) construction and the baffle construction
     (noncontinuous slats) are common.
    •Vane spacing is generally 1.5 to 30 inches except in the second stage of
     two-stage designs which generally use 7/8 to 1 inch spacing.

    •Plastic is the most common material of construction due to  reduced weight,
     cost, and corrosion potential.
    •Precollection and prewashing stages are commonly used to improve demister
     operation.
    •Demister wash systems typically operate intermittently using a mixture of
     clear scrubber liquid and fresh makeup water.

     Horizontal gas flow mist eliminators have only recently been used in this
country, although they are common in Japan and Germany.  This type of mist
eliminator has better drainage than vertical flow types, but space requirements
are greater.

REHEATERS

General Considerations

     Although reheating of scrubbed flue gas is not required by  law, reheaters
are often incorporated into flue gas wet scrubber systems.  Usually, little
                                      553

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attention is given to the design of reheaters, yet failure of the reheater can
cause severe operational problems.

     There are four major reasons for providing reheat in flue gas wet scrubber
systems:

    •avoid downstream condensation

    •avoid a visible plume
    eenhance plume rise and pollutant dispersion

    •protection of the induced-draft fan.

Reheat may also prevent acid rain and stack icing as well as reduce plume
opacity.

     There are three types of reheaters commonly used at utilities.  These are
in-line reheaters, direct combustion reheaters, and indirect hot air reheaters.
In-line reheaters are heat exchangers placed within the gas stream.  Steam or
water is used as the source of heat.  Direct combustion reheaters burn either
oil or gas, mixing the combustion gas with the flue gas.  Combustion chambers
can be located either in-line or external to the duct.  Indirect hot air re-
heaters inject heated ambient air into the flue gas stream.  The air is heated
either in an external heat exchanger or in the boiler preheater.  Alternatively,
some utilities have chosen not to use any reheat system, operating the stack
under wet conditions.

     Experience gained with reheaters has produced some useful caveats.  In-line
reheaters are subject to plugging, corrosion, and vibration.  Plugging can be
minimized by good mist elimination and by soot blowing done at frequent inter-
vals.  Corrosion is a difficult problem since carbon steel, 304SS, 316SS, and
Corten do not appear to be able to withstand combined acid and chloride-
stress corrosion..  More exotic and expensive materials, such as Inconel 6z5 and
Hastealloy G, have been used successfully at Colstrip.  Design against vibration
can readily be done by using frequency analysis.  Direct combustion reheaters
are best designed with an external combustion chamber, preventing the problems
encountered with in-line reheaters.  Both direct combustion reheaters and
indirect hot air reheaters require interlocks to prevent the heated gas from
damaging ductwork when the cold flue gas is not present.  At the Dave Johnston
Plant, where reheat is not used, the induced draft fan is periodically washed
with water to prevent solid deposits and an acid-resistant lining is used on
the stack.

SCALING AND OTHER.. OPERATING PROBLEMS

     Scaling is the single greatest operational problem in wet scrubbers and
one that is most difficult to control.  In scrubbers used for particulate
removal only, the calcium and other alkalis present in the flyash react with
SC>2 causing scale deposits (calcium sulfate) .  In lime and limestone systems,
calcium sulfite (from the reaction of absorbed SC>2 and slurry alkali) and
calcium sulfate (from the reaction of dissolved sulfite and oxygen) tend to
precipitate out and form scale.  In lime systems, calcium carbonate may also be
precipitated when CC>2 from the flue gas reacts with the lime  (pH is high) .

                                      554

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     Various techniques for controlling scale include:

    > Control of pH — If a limestone system is operated at pH's above 5.8 to
     6.0 or if a lime system is operated above 8.0 to 9.0, there is a danger of
     sulfite scaling (Leivo, 1978),  The pH is controlled by adjusting the
     feed stoichiometry.  On-line pH sensors have been successful in controlling
     the feed in lime systems but not in limestone systems because the pH is
     fairly insensitive to the limestone feed rate in the normal pH range.
     However in the limestone system, the feed can be controlled by varying the
     flue gas flow rate.  In particulate control systems, the pH is generally
     low, hold time in the retention tank is short, and suspended solids con-
     centration is low.  All these contribute to the formation of calcium
     sulfate scale.  Hence, it is desirable to increase the scrubber liquor
     pH by addition of supplementary alkali.

    •Hold Tank Residence Time — By providing greater residence times in the
     scrubber hold tank, the supersaturation of the liquor can be decreased
     before recycle to the scrubber.  Typical retention times of 5 to 15 minutes
     are used.

    •Control of Suspended Solids Concentration — Supersaturation can be mini-
     mized by maintaining a supply of seed crystals in the scrubber slurry.
     Typical concentrations range from Z to 15 percent suspended solids.   Solids
     are generally controlled by regulating slurry bleed rate.
    •Regulating Oxygen Concentration — Since calcium sulfate scaling depends
     on the presence of dissolved oxygen, control techniques center on regula-
     ting the oxygen concentration.  In the forced oxidation method,  air is
     bubbled into the reaction tanks to encourage sulfate crystal formation.
     These crystals have better settling characteristics than sulfite crystals.
     In the co-precipitation method, magnesium sulfite is used to depress the
     sulfate saturation level.  Precipitation of sulfate in the holding tank is
     achieved by co-precipitation of'sulfate with sulfite in a mixed crystal.
    >Liquid-to-Gas Ratio — High liquid-to-gas ratios reduce scaling potential
     since the scrubber outlet is more dilute with respect to absorbed S02-
     Unfortunately, increasing the liquid-to-gas ratio also increases operating
     costs and sludge disposal.

    •Additives — Two additives, Calnox 214DN and Calgon CL-14, when used
     together, have been found to effectively reduce sulfate scaling in lime-
     stone systems (Federal Power Commission, 1977) .

    •Alkali Utilization — Experience at the TVA test facility at Shawnee
     indicated that certain mud-type solid deposits,  which tended to form
     particularly in the mist eliminators, could be reduced by improving alkali
     utilization.  Above about 85 percent alkali utilization, these solids
     could be removed easily with infrequent (once per 8 hours) washings.  Con-
     trol of calcium sulfate scaling at TVA was effected by varying the operating
     parameters listed above (Williams, 1977).

CONCLUSIONS AND RECOMMENDATIONS

     Design of the optimum wet scrubber system for use on coal-fired utility
boilers is a two-step process consisting of characterizing the inlet gas stream,
and then choosing the best designs for the various scrubber components based on
operating experiences and research studies.
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     Characterization of the inlet flue gas stream is essential,  but too fre-
quently, neglected.  The following properties should be determined.

     Flyash Size Distribution — Flyash size distributions vary greatly among
power plants, depending on boiler and coal types.  For a particular  scrubber,
particle collection efficiency is determined by the inlet size distribution.

     Flyash Composition — The chemical composition of the flyash is important.
If the flyash contains substantial quantities of alkalis, calcium and magnesium
oxides, it will scrub some SC>2 from the flue gas leading to scale formation.
Flyash may also contain chlorides which can cause stress corrosion in stainless
steels.
     Flue Gas Composition — The concentration of S03 (or I^SO^)  should be
determined because of its corrosiveness.  Flue gas may also contain hydrogen
chloride which poses another corrosion problem.

     Once the inlet gas stream has been characterized, it is necessary to
select the best scrubber components to obtain maximum performance.   The choice
of components should be based on past operating experiences and research studies.
Unfortunately, operating experiences do not always present a consistent picture,
making it difficult to formulate hard-and-fast rules.  It should also be borne
in mind, that scrubber design technology has not advanced far enough to prevent
problems from arising after construction.  Hence the best overall designs are
those that are flexible enough to permit easy replacement of damaged parts.

     This study recommends the following for the various scrubber components.

     Particulate Scrubber and S02 Absorber — Current practice suggests the
use of simpler designs for both the particulate scrubber and SC-2 absorber.
Hence, of the conventional particulate scrubber types, a gas-atomized scrubber,
such as a venturi or rod scrubber, is recommended.  Other types are less effi-
cient or have more operating problems.  Also, spray towers are preferable for
use as the S02 absorber.

     Based on a correlation of scrubber performance against energy requirements,
a theoretical pressure drop of 17+2 in. W.G. would be necessary to meet the
New Source Performance Standard of 0.03 Ibs particulate/million Btu in a con-
ventional scrubber.  When fan losses and pressure drops across the absorber,
ductwork, and mist eliminator are taken into account, total system pressure  drop
may run as high as 30 in. W.G.  If this energy requirement is considered too
high, a novel particulate scrubber should be chosen.  Of the novel scrubbers
tested by EPA to date, the electrostatically augmented scrubbers appear to be
the most suitable for use on coal-fired utility boilers.  Pilot units have shown
good collection efficiency for flyash, coke oven battery emissions, and steel
mill electric arc furnace emissions.

     Mist Eliminator — Horizontal mist eliminators have greater capacities   than
vertical types, but space requirements are also greater.  Vertical mist elimina-
tors are best designed with sharp angled baffles to promote good drainage.
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     Reheaters — Operating experience with reheaters militates against the use
of in-line reheaters because of combined acid and chloride stress corrosion.
The two other types of commonly used reheaters, direct combustion and indirect
hot air reheaters, are recommended and should be designed with interlocks to
prevent heated gas from damaging ductwork when flue gas is not present.  Adequate
mixing is sometimes a problem with these types of reheaters.

     Materials of Construction — The most common construction material for
scrubbers is 316 stainless steel.  At points of high abrasion, wear plates,
brick linings, or high grade nickel alloys are recommended.   The higher grade
alloys are also recommended in areas subject to chloride attack.

     The best material for in-line reheaters appears to be the higher grade
alloys—Inconel and Hastelloy have worked well at Colstrip (Montanta Power).
Carbon steel and lower grade stainless steels have worked at  some plants but
have failed at others.

     Plastic is the best material for mist eliminators because of low cost,
light weight, and reduced corrosion potential.

     Waste Disposal — Disposal of collected flyash from a particulate scrubber
is easily controlled, typically it is disposed of along with  bottom ash.  With
a dual-function particulate-S02 scrubber system, waste disposal is problematic
because of the thixotropic nature of the sludge.  Ponding is  the most common
and least expensive method of disposal, but creates a large unreclaimable
area.  Landfill is a better method of disposal, but the sludge requires greater
dewatering as well as stabilization.  In some site-specific cases, it may be
possible to use less common places, such as a dry lake (arid  regions) or a
mine.

REFERENCES

1.   Accortt, J.L., A.L. Plumley, and J.R. Martin.  "Fine Particulate Matter
     Removal and S02 Absorption with a Two-State Wet Scrubber," EPA-APT Fine
     Particle Scrubber Symposium, San Diego, May 1974.

2.   Bechtel Progress Report, "EPA Alkali Scrubbing Test Facility TVA Shawnee
     Power Plant," June 1977.

3.   Calvert, S., J. Goldshmid, D. Leith, and D. Methta.  Scrubber Handbook,
     NTIS No. PB 213-016, July 1972.

4.   Calvert, S., J. Goldshmid, D. Leith, and N. Jhaveri.  Feasibility of Flux
     Force/Condensation Scrubbing for Fine Particulate Collection, EPA-650/2-
     73-036, NTIS No. PB 227-307, October 1973.

5.   Calvert, S., and N. Jhaveri.  "Flux-Force Condensation Scrubbing," in
     EPA Fine Particle Scrubber Symposium, EPA-650/2-74-112,.  NTIS No. PB 239-
     335, October 1974.  .
                                      557

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6.    Calvert, S. ,  N.  Jhaveri, and T. Huisking.  Study of Flux Force Condensation
     Scrubbing of  Fine Particles, EPA-600/2-75-018, NTIS No.  PB 249-297,  August
     1975.

7.    Calvert, S. ,  S.  Yung, and J. Leung.  Entrainment Separators for Scrubbers-
     Final Report, NTIS No. PB 248-050, August 1975.

8.    Calvert, S.   "How to Choose a Particulate Scrubber," Chemical Engineering,
     Vol. 18, No.  84, August 29, 1977, pp.54-68.

9.    Calvert, S. ,  and S. Gandhi.  Fine Particle Collection by a Flux-Force
     Condensation Scrubber:  Pilot Demonstration,  EPA-600/2-77-238,  NTIS  No.
     PB 277-075,  December 1977.

10.  Devitt, T.,  R. Gerstle, L. Gibbs, S. Hartman, and N. Klier.   Flue Gas
     Desulfurization System Capabilities for Coal-Fired Steam Generators.
     Volume II Technical'Report,"^PA=600/7-78-032b7"NTIS No.  FB 279-417,  March
     1978.

11.  Ellison, W.   "Scrubber Demister Technology for Control of Solids Emissions
     from SC>2 Absorbers," in Symposium on the Transfer and Utilization of
     Particulate Control_Technoiogy, EPA-600/7-79-044c, February 1979.

12.  Ensor, D. et al.  Evaluation of a Particulate Scrubber on a Coal-Fired
     Utility BoTle7,~NTls~No. PB 249-562, November I975~.

13.  Federal Power Commission.  The Status of Flue Gas Desulfurization Applica-
     tions in the United States:  A Technological  Assessment,  July 1977.

14.  Fox, Harvey.   Personal communication, Research-Cottrell,  Bound  Brook, New
     Jersey, July 1978.

15.  Green, K., and J. Martin.  "Conversion of the Lawrence No. 4 Flue Gas
     Desulfurization System," in Proceedings:  Symposium on Flue Gas Desulfuri-
     zation - Hollywood, Florida, NTIS No. PB 282-091, November 1977.

16.  Grimm, C., J.Z. Abrams, W.W. Leffman, I.A. Raben, and C.  LaMantia.   "The
     Colstrip Flue Gas Cleaning System," Chemical  Engineering Progress, Vol.
     74, No. 2, February 1978, pp.51-57.

17.  Hesketh, H.E.  "Pilot Plant S02 and Particulate Removal Study,  Report of
     Fiscal Year 1974-1975 Operations," Sponsored  by Illinois Institute for
     Environmental Quality and Southern'Illinois University,  Project No.  10.027,
     August 1975.

18.  Kashdan, E.R. and M.B. Ranade.  Design Guidelines for an Optimum Scrubber
     System, EPA-600/7-79-018, NTIS No. PB 292-327, January 1979.

19.  Kruger, R.,  and M. Dinville.  "Northern States Power Company Sherburne  County
     Generating Plant Limestone Scrubber Experience," Presented at the Utilities
     Representative Conference on Wet Scrubbing, Las Vegas, Nevada,  February 1977.
                                      558

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20.  LaMantia, C.  et_ al.   Application of Scrubbing Systems to Low Sulfur/Alkaline
     Ash Coals,  EPRI FP-595, December 1977.

21.  Laseke, B.   EPA Utility Flue Gas Desulfurization Survey:  December 1977-
     January 1978, EPA-600/7-78-051a, NTIS No. PB 279-011, March 1978.

22.  Laseke, B.   Survey of Flue Gas Desulfurization Systems:  Green River Sta-
     tion, Kentucky Utilities, EPA-600/7-78-048e, NTIS No. PB 279-543, March 1978.

23.  Laseke, B.   Survey of Flue Gas Desulfurization Systems:  Cholla Station;
     Arizona Public Service Company, EPA-600/7-78-048a, NTIS No. PB 281-104,
     March 1978.

24.  Laseke, B.   Survey of Flue Gas Desulfurization Systems:  LaCygne Station,
     Kansas City Power and Light Company, EPA-600/7-78-048d, NTIS No. PB 281-107,
     March 1978.

25.  Lee, R.E.,  H.L. Crist, A.E. Riley, and K.E. MacLeod.  "Concentration and
     Size of Trace Metal Emissions from a Power Plant, a Steel Plant, and a Cotton
     Gin," Environmental Science & Technology, Vol. 9, No. 7, July 1975, pp.643-647,

26.  Leivo, C.C.  Flue Gas Desulfurization Systems:  Design and Operation Con-
     siderations, Volume II, Technical Report, EPA-600/7-78-030b, NTIS No.  PB 280-
     254, March 1978.

27.  McCain, J.D.  CEA Variable-Throat Venturi Scrubber Evaluation, EPA-600/7-78-
     094, NTIS No. PB 285-723, June 1978.

28.  Mclllvaine, R.W.  The Mclllvaine Scrubber Manual, Volume II, The Mclllvaine
     Company, 1974.

29.  Pearson, B., Private communication, Public Service Company of Colorado.

30.  Pilat, M., and G. Raemhild.  "University of Washington Electrostatic
     Scrubber Evaluation at Coal-Fired Power Plant," EPA-600/7-78-177b, NTIS No.
     PB 292-646, December 1978.

31.  Rhudy, R., and H. Head.  "Results of EPA Flue Gas Characterization Testing
     at the EPA Alkali Wet-Scrubbing Test Facility," Presented at the 2nd EPA
     Fine Particles Scrubber Symposium, EPA-600/2-77-193, NTIS No. PB 273-828,
     September 1977.

32.  Richmond, M. and H. Fox, Private communication, Research-Cottrell, Inc.

33.  Sadowsky, D., Private communication, Montana-Dakota Utilities.

34.  Semarau, K.  "Practical Process Design of Particulate Scrubbers," Chemical
     Engineering, Vol. 84, No. 20, September 26, 1977.

35.  Sitig, M.  Particulates and Fine Dust Removal, Processess and Equipment,
     Noyes Data Corporation,,Park Ridge, New Jersey, 1977.
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36.  VanTassel, D.,  Private communication,  Minnesota  Power  and Light.

37.  Williams, J.E.   "Mist Eliminator Testing  at  the  Shawnee Prototype Lime/
     Limestone Test FAcility," 2nd US/USSR  Symposium  on Particulate Control,
     EPA-600/7-78-037, NTIS No.  PB 279-628,  March 1978.

38.  Winkler, P.,  Private communication,  Chemico  Air  Pollution Control Company.

39.  Dallabetta, G., Private communication,  Bechtel Corporation.
                                      560

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                   TESTS  ON  UW ELECTROSTATIC SCRUBBER FOR

                  PARTICIPATE AND SULFUR DIOXIDE COLLECTION
                                      by
                                Michael  J.  Pllat
                        Department of Civil  Engineering
                           University of Washington
                           Seattle, Washington 98~!95
                                  Abstract


The University of Washington Electrostatic Scrubber pilot plant was  tested  for
participate and sulfur dioxide collection at the unit no. 2 coal-fired  boiler
at the Centralia Power Plant.   The UW Electrostatic Scrubber involves  the use  of
electrostatically charged water (or alkaline absorbing liquor)  to collect a^r
pollutant particles  charged to the polarity opposite from the droplets  and  to
absorb gaseous  a'ir  pollutants.  The portable UW electrostatic Scrubber pilot
plant (located inside a 40 ft. trailer)  is designed for 1,000 acfm gas  flow at
the inlet to the scrubber; however, at Centralia inlet flows as high as 1,600
acfm were used.  Simultaneous  inlet-outlet source tests using the UW Source
Test Cascade Impactors (Mark 10 model at the inlet to the scrubber and  Mark 20
model at the outlet} and 'in-stack filters showed the overall particle  cc/! lection
efficiency ranged from 99.30 to 99.992 (depending on the scrubber operating
conditions) and the  outlet particle concentration ranging from .00013  to .00116
grains/sdcf.  Using  a sodium carbonate scrubbing liquor, the sulfur dioxide
collection efficiency ranged from 36.2 to 98.8% depending on the operating
parameters such as the liquor  to gas flow rate ratio, liquor pH, inlet S00
concentration, etc., and spray voltage.   The test results illustrate that^the
addition of electrostatic charging of the aerosol particles and the spray liquor
droplets can enhance the collection efficiency for both particulates and sulfur
dioxide.
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               Tests on UW Electrostatic Scrubber for Participate
                         and Sulfur Dioxide Collection

                                      by
                               Michael  J.  Pilat
I.  INTRODUCTION


A.  Objectives of Research Project

         The objectives of this on-going research project are to demonstrate
    the effectiveness of the UW Electrostatic Scrubber for controlling
    emissions of fine particulates and gaseous air pollutants from various
    industrial sources.  The test data obtained is to be used to improve
    scrubber performance and to develop preliminary designs and economic
    information of full-scale electrostatic scrubber systems.

B.  Review of Previous Work

         Penney (1944) patented an electrified liquid spray test precipitator
    involving particle charging by corona discharge and droplet charging by
    either ion impaction or induction.  Penney's system consisted of a spray
    scrubber with electrostatically charged water droplets collecting aerosol
    particles charged to the opposite polarity.  Kraemer and Johnstone (1955)
    reported theoretically calculated single droplet (50 micron diameter
    droplet charged negatively to 5,000 volts) collection efficiencies of
    332,000% for 0.05 micron diameter particles (4 electron unit positive
    charges per particle).  Pilat, Jaasund, and Sparks (1974) reported on
    theoretical calculation results and laboratory tests with an electrostatic
    spray scrubber apparatus.  Pilat (1975) reported on field testing during
    1973-1974 with a 1,000 acfm UW Electrostatic Scrubber (Mark IP model)
    funded by the Northwest Pulp and Paper Association.  Pilat and Meyer
    (1976) reported on the design and testing of a newer 1,000 acfm UW
    Electrostatic Scrubber (Mark 2P model) portable pilot plant funded by the
    EPA,  Pilat, Raemhild, and Harmon (1977) reported on tests of the UW
    Electrostatic Scrubber pilot plant (Mark 2P model) on collecting laboratory
    generated DOP aerosols and emissions from a coal-fired boiler and an
    electric arc steel furnace.  Pilat, Raemhild, and Gault (1978) reported
    on some of the results of SO^ and particulate collection efficiency tests
    performed on the UW Electrostatic Scrubber at the Centralia Coal-Fired
    Power Plant.  Pilat, Raemhild, and Prem (1978) reported on the tests at
                                    562

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     a steel  plant (Bethlehem Steel Co., Seattle).  The UW Electrostatic  Scrubber
     (patent  pending)  has been licensed to the Pollution Control Systems
     Corporation (of Renton and Seattle, Washington) for production  and sales.


II.   Description of UW Electrostatic Spray Scrubber

          The UW Electrostatic Scrubber involves the use of electrostatically
     charged  water droplets to collect air pollutant particles  electrostatically
     charged  to a polarity opposite from the droplets.  A schematic  illustration
     of the UW Electrostatic Scrubber system is presented in  Figure  1.
                                                                     s&s OUTLET
                   CORONA
                (ARTICLE CHARGING)
 CHARGED WATER SPRAYS          MIST ELIMINATOR
(COLLECTION OF CHARGED PARTICLES
 BY OPPOSITELY CHARGED WATER DROPLETS)
                       Figure  1,  UW  Electrostatic  Scrubber
          The particles are electrostatically charged  (negative polarity) in
     the corona section.  From  the  corona  section the  gases and charged
     particles flow into a scrubber chamber  into  which electrostatically
     charged water droplets (positive  polarity)  are sprayed.  The gases and
     some entrained water droplets  flow out  of the spray chamber into a mist
     eliminator consisting of a positively charged corona section in which
     the positively charged water droplets are removed from the gaseous stream.

          The general layout of the UW Electrostatic Scrubber pilot plant
     CMark 2P model) which was  used during the tests at the Centralia Power
     Plant is shown in Figure 2,  The  system (in  the direction of gas flow)
     includes a gas cooling tower,  an  iniet  test  duct with sampling port, a
     particle charging corona section  (corona #1, not used for these tests),

                                        563

-------
    a charged water spray tower (tower #1, not used for these tests), a
    a particle charging corona section (corona #2), a charged water spray
    tower (tower #2). a positively charged corona section to collect the
    positively charged water droplets, an outlet test duct with sampling
    port, and a fan.
                                                                 TUT
      \P
                                       OWSS KCTiO**'. Vltw C*
                                      TMKtt mSS HCft-iONTA* ICCTKX
                  mot TEJT ewer
] S*IUT TOwCH MO X
i
B-P^1

j
E
CORONA MO 1


»**«,


K1ST



twurr TDWEA «1 i



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         Figure 2,  General Layout of Electrostatic Scrubber Pilot Plant
                    (Model Mark 2P)
         The model Mark 2P has a scrubbing liquor recycle system.  This system
    utilizes an electrically isolated pump, insulated hosing, and a current
    limiting spray system for current containment and safety.


III.  Experimental Procedure

         The particle size distributions were measured simultaneously at the
    inlet and outlet of the elctrostatic scrubber using UW Source Test Cascade
    Impactors.  The inlet test port is located downstream of a spray cooling
    tower (as shown in Figure 2) and hence, the measured particle collection
    efficiencies are for the electrostatic scrubber portion of the system,
    The 27 stage Mark 10 model (sampling at about 0.2 acfm) was used at the
    inlet where the particle concentration is higher.  The 14 stage Mark 20
    model (sampling at about 2.0 acfm) was used at the scrubber outlet where
    the particle concentration is typically low.  Both the Mark 10 and Mark
    20 models utilize reduced absolute gas pressure in the outlet  jet stages
    in order to provide stage aerodynamic cut diameters (dj-n) down to about
    Q.02 microns.                                         bu
                                      564

-------
          Thermo Electron Model 40 Fluorescent S02 Analyzer was used to
    measure S0~ levels in the gas stream at the inlet and outlet of the pilot
    plant.  The principle of operation of this monitor is based upon the
    measurement of the fluorescence of S02 produced by its absorption of
    ultraviolet radiation.  The analyzer was connected to a strip chart
    recorder so that 5-minute averages of the inlet and outlet S02
    concentrations were used to calculate the scrubber's S02 collection
    efficiencies.
IV.  Results of Particulate Tests

         In October 1977, the UW Electrostatic Scrubber pilot plant (Mark 2P
    model) was transported to the Centralia Steam-Electric Project (two
    655-megawatt pulverized coal-fired boilers) operated by Pacific Power
    and Light Company.  A sample gas stream was tapped from the outlet of
    PP & L no. 2 and transported via ducting to the Electrostatic Scrubber
    pilot plant.  The UW Electrostatic Scrubber pilot plant system was
    modified prior to testing by:  (1) the installation of a larger booster
    fan at the inlet to the scrubber in order to accomodate the large
    negative pressure (around -14 inches water) in the main duct and to allow
    a higher gas flow rate through the scrubber pilot plant; and (2) the
    connection of a newly constructed liquor recycle system in a 40 ft. trailer
    to the spray scrubber tower which enabled operation with either an
    open-loop or a closed-loop liquor recycle system.

         The results of the particle collection efficiency tests over the
    O.Q75 to 15 micron aerodynamic diameter size range are presented in
    Figure 3.  These efficiency curves are based on log-normal approximations
    of the inlet and outlet particle size distributions, and hence  the minimum
    in the collection efficiency at about 0.5 microns diameter is smoothed out.
    The tests were run in an open-loop liquor recycle mode with the water used
    as the scrubbing liquor.  The outlet particle mass concentration for these
    tests ranged from .00065 to .00459 grains/sdcf.


V,  Results of Sulfur Dioxide Tests

         Sulfur dioxide collection efficiency tests were conducted at the
    Centralia Power Plant with an open-loop liquor system using scrubber
    liquor of water and of sodium carbonate solution.  The measured S0?
    collection efficiencies were found to be a function of the liquor/gas
    flow rate ratio (L/G), the S02 inlet concentration, the stoichrometric
    ratio (moles of alkaline liquor sprayed/moles of inlet S02), and the
    liquor spray voltage,  Figure 4 shows that the S02 collection efficiency
    increases with incoming stoichrometric ratio, witn increasing spray
    voltage, and with increasing liquor/gas flow rate ratios.
                                      565

-------
  ioa
         UW Electrostatic  Scrubber
           Centralia Power Plant
              March-May 1979
                                       Test Series #3-N
                                              Liquor
                                       502 I" * 552 ppm
                                         = 0.87
                    Test Series #2-N
                           Liquor
                      * 0.96 £/akm3
                           = 545 ppm (average)
                    TF6FCN Fog Nozzle
                    Pressure = .79 MPa
                       .5                 1.0
                         Stoichiometric Ratio
1.5
Figure 4.   SCL Collection Efficiency as a Function  of Stoichrometrie Ratio
                                566

-------
8
CJ
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u_
UJ
CJ
UJ
UJ
d
   89.0
g| 10.0
   0.0
UW Electrostatic  Scrubber
  Centralia Power Plant
     March-May  1979
          Units
  Overall Efficiency (%)
  Overall Penetration (%)
  SCA (m2/(sm3/min))
  L/G
Test
No.
1
2
3
4
7
8
Symbol
s>
©
A
4-
US
H
Overall
Eff.
98.99
99.55
99.58
99.48
99.79
99.80
Pen.
1.01
0.45
0.42
0.52
0.21
0.20
SCA
.091
.091
.087
.095
.095
.101
L/G
1.14
1.12
1.05 j
1.02
1.13
1.18
                                                                    6
                                                                    8
                                                                    Orl
                                                           4  UJ
                                                             O
                                                           8  £
                                                             Q_
                                                           8  ~
                                                           oog
                                                             (X
                                                             ce
                                                             UJ
                                                             UJ
                                                             Q-
     B4JO  10"1     2         S      10°      2        5      101
             PflRHCLE flERODYNRMIC  DIRMETER.  DSDtMICRONS)
  Figure 3.  Particle Collection Efficiency versus Particle Size
                                   567

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 VI. Conclusions

          The  test results on  the UW Electrostatic Scrubber on the emissions
     from the  Centralia  coal-fired power boiler demonstrates the system's
     effectiveness for collecting particulates and sulfur oxides.  The outlet
     concentrations from the UW  Electrostatic Scrubber system were .00065 to
     .00459 grains/sdcf  particulates and 10 to 510 ppm SC2 depending on the
     inlet concentrations, operating parameters, and liquor alkalinity.  With
     sodium carbonate liquor the S09 collection efficiency ranged from 41.1
     to  97.4%.                     *•


VII. Acknowledgements

          This  research  was supported by the US EPA (IERL) Research Grant
     (EPA Grant Nos.  R-8-4393  and R-06035).  The assistance, advice, and
     cooperation  of our  EPA Project officer, Dale A. Harmon is gratefully
     acknowledged.  The  assistance of University of Washington students and
     staff, Terrell Gault (whose MSE thesis research was on the effects of
     electrostatics on the sulfur dioxide collection efficiency), Tracey Steig,
     and, Gary  Raemhild is acknowledged.  The cooperation and assistance of
     Pacific Power and Light Company personnel including Tom White, Ted
     Phillips,  Bob Werner, Gary  Slanina, Steve Lambert, Don Sakata, Al
     Seekamp,  John Angelovich, and Pete Steinbrenner is greatly appreciated.
                                        568

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                                 References


 1.   Kraemer, H. F. and H. F. Johnstone  (1955).  Collection of Aerosol Particles
     in  the  Presence of Electric fields.   Ind. Engr. Chem.  47:2426.

 2.   Penney, G. W.  (1944).   Electrified  Liquid Spray Dust Precipitator.  U.S.
     Patent  No. 2,357,354.

 3.   Pilat,  M. J.,  Jaasund,  S.  A.,  and L. E. Sparks (1974).  Collection of
     Aerosol Particles by Electrostatic  Droplet Spray Scrubbers,  Envir. Sci.
     & Tech.  8:340-348.

 4.   Pilat,  M. J.  (1975).  Collection of Aerosol Particles by Electrostatic
     Droplet Spray Scrubbers.   APCA Journal.  25:176-178.

 5.   Pilat,  M. J.  and D. F.  Meyer  (1976).  University of Washington Electrostatic
     Spray Scrubber Evaluation.  Final Report on Grant No. R-803278, EPA Report
     No. EPA-600/2-76-100  (NTIS No. PB 252653/AS).

 6.   Pilat,  M. J.,  Raemhild, G. A., and  D. L. Harmon (1977).  Fine Particle
     Control with  UW Electrostatic  Scrubber.  Presented at Second Fine Particle
     Scrubber Symposium, May 2-3,  1977,  New Orleans.

 7.   Pilat,  M. J.,  Raemhild, G. A., and  D. L. Harmon (1977).  Tests  of
     University of Washington Electrostatic Scrubber at an Electric Arc Steel
     Furnace.  Presented at  Conference on Particle Collection Problems in the
     Use of  Electrostatic Precipitators  in the Metallurgical Industry,
     June 1-3, 1977, Denver.

 8.   Pilat,  M. J.  and G. A.  Raemhild  (1978).  Control of Particulate Emissions
     with UW Electrostatic Spray Scrubber.  Presented at EPA Symposium on the
     Transfer and  Utilization of Particulate Control Technology, July 24-28,
     1978, Denver.

 9,   Pilat,  M. J.,  Raemhild, G. A., and  A. Prem (1978).  University of Washington
     Electrostatic Scrubber  Tests  at  a Steel Plant.  EPA Report No. EPA-
     600/7-78-177a, September 1978.

10,   Ptlat,  M. J.  and G. A,  Raemhild  (1978).  University of Washington
     Electrostatic Scrubber  Tests  at  a Coal-Fired Power Plant.  EPA Report
     No. EPA-600/7-78/177b,  December  1978.

11,   Pilat,  M, J,,  Raemhild, G. A., and  T. W. Gault 0978).  Tests on  UW
     Electrostatic  Scrubber  for Particulate and Sulfur Dioxide Collection.
     Presented at  Pacific Northwest International Section of Air Pollution
     Control Association meeting,  November 9-10, 1978, Portland.
                                      569

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                 EPA MOBILE VENTURI SCRUBBER PERFORMANCE
Environmental Protection Agency Mobile Venturi Scrubber Performance - An
empirical and modeling study of New Source Performance Standard-level venturi
performance on pulverized coal boiler characteristics


                                       By:

                 S. Malani, S.P. Schliesser, and W.O. Lipscomb
                              Acurex Corporation
                    Research Triangle Park, North Carolina
                                 ABSTRACT

     This report describes the Environmental Protection Agency's mobile venturi
scrubber performance evaluation conducted at the power plants of Michigan
State University, East Lansing, Michigan, and the City of Ames,  Ames,  Iowa.
The effects of pulverized coal emission characteristics on venturi scrubber
collectability are reported.  Controlled variables were boiler operation, fuel
type, and scrubber pressure drop.  Use of a mathematical performance model
provides support and insight into scrubber performance and measurement metho-
dologies.  Cost modeling data are shown for different boiler and scrubber
characteristics for performance in the range of current and projected New
Source Performance Standards.

     The following highlights emerge from this study of conventional venturi
scrubber performance on coal-fired boilers:

          •    Conventional venturi scrubber performance is cost-sensitive in
               the New Source Performance Standards' range of interest.

          •    Scrubber operation and performance characteristics are
               predictable with complete characterization and an improved
               computerized model.

          «    Scrubber operation, performance and cost levels are strongly
               dependent on influent fine particle concentration levels.

          •    Fuel type and/or boiler design are the primary factors for
               generation of fine particle concentration levels.

          •    Cofiring coal with refuse fuel increases fine particulate
               generation, causing dramatic increases in scrubber costs.

                                     570

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INTRODUCTION AND OBJECTIVE

     This pilot scale venturi scrubber is one of three conventional particu-
late emission control devices mobilized by the Utilities and Industrial Power
Division, Industrial Environmental Research Laboratory, U.S. Environmental
Protection Agency (UIPD/IERL/EPA), Research Triangle Park, North Carolina.
The objective is to evaluate and compare the performance characteristics of a
scrubber, baghouse and electrostatic precipitator (ESP) on industrial parti-
culate emission sources.  The purpose is to provide characteristic information
and insight for appropriate selection of particulate control devices, in light
of operation, performance, and cost considerations.

     This report summarizes the results of mobile scrubber tests conducted at
the power plants of Michigan State University, East Lansing, Michigan and City
of Ames, Ames, Iowa over a 4-month period beginning July 1978.  The particu-
late emission source at each site was a pulverized coal (PC) boiler; the Ames
utility had refuse cofiring capability.  The particulate-laden flue gas was
slipstreamed and sampled at inlet and outlet locations of the scrubber by
total mass measurements and Brink and Andersen cascade impactors.  The test
matrix was designed to study the effects of scrubber pressure drop and
liquid-to-gas (L/G) ratio for different boiler/fuel cases.  Scrubber perform-
ance and cost modeling generated the following:

     •    Comparison of empirical overall and fractional collection effi-
          ciencies with model predictions

     *    Comparison of experimental pressure drops with model predictions

     •    Scrubbing costs for tested boiler/fuel cases in New Source Performance
          Standards' (NSPS) range of interest (43 to 13 ng/J)

CONCLUSIONS

     The following conclusions result from this study:

     •    Scrubbing costs become very sensitive to required performance levels;
          cost factors can range as much as 100-200 percent across the NSPS
          range of 43 to 13 ng/J (0.1 to 0.03 Ib/million Btu).

     •    Boiler effluent characteristics are strongly dependent on fuel type
          and/or boiler design; differences in generated fine particle concen-
          trations can impact scrubbing costs as much as 25-300 percent,
          dependent on required performance level.

     •    Cofiring coal with refuse fuel increases fine particle concentration;
          economic gains in fuel cost savings are offset by 10-80 percent cost
          penalties for scrubbing costs.

     •    The EPA/Calvert scrubber model was modified to incorporate two
          improvements:
                                      571

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               1)    The log-normal size distribution format was changed to
                    accommodate a more realistic particle size-histogram
                    format.

               2)    The effect of flue gas quenching in the venturi throat was
                    mathematically defined, affording a more reasonable
                    description of droplet formation, pressure loss and
                    particulate collection.

     «    The model predicts venturi scrubber operation and performance with
          fair accuracy and precision; the model's accuracy is better for a
          6 cm (2.3 in.) throat than a 3.5 cm (1.4 in.) throat, indicating
          appreciable wall effects for throat sizes less than 6 cm.

     •    For a given set of scrubber conditions, the model tends to:  under-
          predict overall collection performance; underpredict the collection
          of fine particles (less than 2 (Jm); overpredict the collection of
          large particles (greater than 4 (Jm) .

     •    The discrepancy between the model predictions and data can be attri-
          buted partly to measurement methodology, since the existing methodology
          does not account for differences in aerodynamic characteristics
          between the influent (dry) and effluent (wet) particles.

DESCRIPTION OF FACILITIES

Power Plants

     Michigan State University (MSU) Power Plant 65.   This power plant consists
of three boilers designated as Units I, 2 and 3.  The pilot scrubber was
tested on Unit 2 which is a 113,600 kg/hr (250,000 Ib/hr) 30-35 MW boiler.
The boiler fires pulverized Eastern Kentucky Coal (6 to 7 percent moisture,
8 percent ash, 0-75 percent sulfur, 29 million J/kg (12,500 Btu/lb)).

     Ames Power Plant.  Owned and operated by the city of Ames, this power
plant consists of three boilers designated Units 5, 6 and 7.  Scrubber tests
were done on Unit 7 which is a 33 MW PC-fired boiler capable of firing up to
20 percent refuse-derived fuel (RDF).  The plant uses a blend of 55 percent
Iowa coal at 3 to 5 percent sulfur and 45 percent Colorado low-sulfur western
coal.  The heating value for the coal blend is 24.1 million J/kg (10,400 Btu/lb),
compared to 13.9 million J/kg (6,000 Btu/lb) for the RDF.

Scrubber

     The mobile scrubber facility is contained inside a standard freight
trailer (12.2m x 2.4m, or 40 ft. x 8 ft.).  It is equipped with three available
venturi throats (3.5, 6.0, and 8.5 cm), a presaturator, a cyclone separator,
and a baffled mist eliminator.  Each venturi has a throat length of 30.5 cm
and a radial water dumping nozzle 5.1 cm below the throat entrance.  Appropriate
auxiliaries and instrumentation are provided inside the trailer.
                                      572

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PROGRAM METHODOLOGY

Installation

     Care was taken to ensure that a representative stream was withdrawn and
delivered to the pilot scrubber.  The slipstream was extracted isokinetically
and transported isothermally to the pilot unit through heated ducting at
velocities comparable to plant conditions.  Inspection of the ducting after
each test series revealed marginal dropout of particulate, due to either
gravitational or centrifugal forces.  At each test site, the slipstream was
educted downstream of the air preheater and upstream of the pollution control
device.  For the Ames site, a second ducting was installed downstream of the
full scale ESP.

Operation

     The pilot scrubber was operated and tested on a daily start-up/shutdown
basis.  Equipment startup and system equilibrium were carried out in the
morning, and performance measurements were conducted in the afternoon.  There
were indications of scaling at the wet/dry interface, a condition which
warranted scale removal daily.  Each set of inlet and outlet mass and impactor
measurements were conducted concurrently.  Sampling periods required 2-3 hour
tests, enabling two sets of tests to be conducted daily.  The scrubber liquor
pH was maintained between four and six by adding a lime solution.  The filtrate
recycle-to-purge ratio was maintained at approximately 1:1 to restrict sulfate/
sulfite accumulation.

Test Conditions

     Table 1 summarizes scrubber test conditions and operating parameters.
Pressure drops were varied from ~25 to 125 cm H^O (~10 to 50 in. I^O).  Gas
flowrates ranged from 7 to 16 am3/min. (250 to 560 acfm).  The liquid/gas
(L/G)  ratio was evaluated at 2 and 4 1/m3 (15 and 30 gal/kcfm).

Data Acquisition

     After setting the prescribed test conditions, the important operating
parameters were recorded on a semihourly basis and included:

          •    Scrubber pressure drop

          •    Gas flowrate

          •    Scrubber liquor flowrate

          •    Gas temperature (before and after scrubber)

          •    Makeup water flowrate

          •    Scrubber liquor pH
                                      573

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     On-site analyses of performance measurements were conducted to provide
feedback on performance data and data quality.

Particulate Measurements

     Total mass and impactor measurements at the inlet and outlet points were
conducted at isokinetic conditions.  Brink and Andersen impactors measured the
inlet and outlet size distributions, respectively.  Gelman glass fiber sub-
strates were used at MSU, whereas Reeve Angel 934 AH material was preferred at
Ames because of low S02 absorptivity.  All substrates were preconditioned for
6 hours.  Samples were obtained with extractive probes fitted with inter-
changeable nozzles at average velocity locations.  Sampling trains similar to
that described in Method 5 of the Federal Register were used.

Data Reduction

     A  computer program was used to calculate impactor stage cutpoints, parti-
cle size distributions and overall particulate loading.  Fractional penetra-
tions were calculated by a program that performs linear least square, quadra-
tic least square and spline fits to log normal transformed inlet and outlet
cumulative size distribution data.1  This program was supplemented by manual
graphical procedures whenever data showed excessive scatter.

     The computer program for the scrubber model was applied to predict and
compare scrubber operation and performance levels.2  The original program was
modified to accept inlet size distribution histograms and account for gas
cooling in the venturi throat, assuming instantaneous quenching.  The program's
inlet requirements include seven parameters to define scrubber conditions and
several descriptors for the influent particulate stream.  The model then
determines the fractional penetration relationship from the specified conditions
to--

               1)   relate the influent size distribution for the prediction
                    of the effluent size distribution, and

               2)   integrate the influent size distribution to predict the
                    effluent particulate concentration.


                         RESULTS AND DISCUSSION

Overall Collection Performance

     The control device characteristic of practical importance is that of
overall collection performance.  This performance can be described and measured
by the  emission level which penetrates the device and passes into the atmosphere.
Emission levels are used by the regulatory agency to stipulate NSPS.  The
scope of this report entails venturi scrubber performance and costs in the
range of current and projected NSPS for coal-fired utility boilers.  Analyses
were made for NSPS levels of 43 and 13 ng/J, and for an intermediate emission
level of 21.5 ng/J, respectively.
                                      574

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     Scrubber performance levels as a function of pressure drop are shown in
Figure 1 for the three fuel types studied.  Two performance curves for each
fuel case are included, comparing results from the empirical data and comput-
erized model.  The three model curves methodically reflect distinct performance
requirements for the three fuel cases.  The fuel-specific performance relation-
ships should be considered realistic since they account for measured differences
in influent size distributions.  These performance relationships are presented
over the range of current and projected NSPS.

     A correspondence between the model and data curves is observed (Table 2),
although the model results are consistently overpredictive to the data.  The
spread between the data curves is more apparent than between the model curves
due to appreciable wall effects in pilot scale Venturis discussed below.
Considering that better data/model correlations have been shown by others,
scrubber performance can be described or bracketed by the paired curves in
Figure 1.

Particle Size Collection Performance

     Analysis of particle size collection performance (i.e., fractional efficiency
or fractional penetration) offers support of and insight into overall collection
performance.  As technological advances are being made, it is becoming appropriate
to evaluate performance in terms of penetration, rather than collection.  In
this text, fractional penetration is used to describe particle size collection
performance.

     This study was conducted on three different fly ash species with two
venturi throat sizes.  Figures 2 through 6 compare fractional penetration
curves predicted by the model with the data for various pressure drops and L/G
ratios.  Most of the data are for the 6 cm throat; the results for the 3.5 cm
throat are noted in Figures 5 and 6.  The graphs show a fair comparison between
the model predictions and the empirical data.  The following peculiarities are
worth noting:

     •    The data are skewed with respect to the model with recurring simi-
          larity.

     •    In general the model overpredicts penetration for particles below
          2 microns aerodynamic diameter.

     •    The model generally underpredicts penetration for particles above
          4 microns aerodynamic diameter.

     •    In the middle of the particle size range, model and data curves
          intersect, showing better correlation.

     •    The degree of correlation is higher in the case of the 6.0 cm venturi
          as compared to the 3.5 cm venturi.

     These discrepancies/peculiarities are somewhat accountable in that there
are several difficulties in measuring scrubber effluent size distribution,
                                      575

-------
including:

     •    Concentration of particulate is reduced,

     •    most of the penetrated material is composed of fine particulate,

     •    saturation conditions occur with the presence of penetrated and
          re-entrained droplets, and

     •    the particle species measured as the effluent is distinct from the
          dry species measured as the influent.

For the first three difficulties listed, procedural improvements can be made
to resolve or minimize the complications.  However, the problem of comparing
dry fly ash size concentrations to wet fly ash size concentrations requires
further analysis.  Demonstration of the anomalous effects attributable to this
dry/wet phenomenon are shown by the hypothetical diagrams in Figure 7.

Pressure Drop

     Figures 8 and 9 compare experimental and predicted pressure drops for the
6 cm venturi.  MSU data show excellent correlation, whereas Ames data show the
model slightly overpredicts the pressure drop.  However, the model overpredicts
pressure drop by about 100 percent for the 3.5 cm venturi (Table 3).  This
reiterates the need to completely account for scrubber geometry, throat size
and wall effects in pilot scale Venturis.

     The above predictions for fractional collection efficiency and pressure
drop assume instantaneous quenching of flue gas to outlet1 conditions upon
contact with scrubber water.  The predictions by quench-corrected modeling
give higher penetration in small particle range and lower penetration in large
particle range (the difference being less than 10 percent for each particle
size, and about 30 percent less pressure drop for tested scrubber conditions).

Scrubber Influent Characteristics

     The fractional collection in a venturi scrubber is a function of particle
diameter, and hence overall penetration is a strong function of inlet particle
size distribution.  The average inlet particle size distributions are>plotted
in Figure 10 with fuel type and slipstream location as parameters.  The overall
particle concentration for each case is also tabulated.

     Particular attention should be drawn to the comparison of these size
curves in the fine particle range.  The apparently small divergence of the
three size curves below 2 (Jm corresponds with substantial differences in
outlet loading.  The Ames case in which coal plus 20 percent RDF were fired
shows the highest concentration of fine particulate, whereas the MSU case
offers the lowest concentration.

     Effluent concentrations with operating pressure, drop for the three fuel
cases are presented in Figure 1.  Comparison of .the two extreme cases in fine
particle concentration show that pressure drop requirements can vary from


                                      576

-------
     •    25 to 35 cm at the NSPS level of 43 ng/J, and

     •    40 to 140 cm at the NSPS level of 13 ng/J

These dramatic differences in pressure drop were generated by the model, and
were supported by the empirical particle size and concentration results.  The
cost impact of these results will be discussed later.

Effect of L/G Ratio

     At MSU, scrubber tests were conducted for two L/G ratios (2 and 4 1/m3)
to study their effect.  Figure 11 presents the data and model predictions.
The model shows that a L/G ratio of 4 1/m3 gives inferior scrubber performance.
The data do not show an equally dramatic difference, but they do show qualitative
agreement.  Calvert, et al. have shown that the optimum L/G range is 1-2 1/m3,
which supports these results.5

Scrubber Performance as a Secondary Device

      In Ames, the scrubber was also tested as a secondary device slipstreaming
downstream of a full scale ESP.  Figure 12 shows data and model predictions.
The results are fairly similar to the case in which the scrubber operates
upstream of the ESP.  These results, along with Reference 4, indicate that
particle collection by a venturi scrubber is not affected by an upstream ESP.

Cost  Analysis

      The cost analysis objective was to obtain an estimate of scrubbing costs
in the NSPS range.  The analysis is based on the following factors:

      The analysis is based on the following factors:

      1.   Emission source is 350 MW PC boiler.

      2.   Flue gas flow rate is 130 acm/min per MW at 177°C.

      3.   Flue gas is treated in three parallel modular venturi scrubbers.

      4.   Sludge  treatment involves clarification, filtration and land-filling.

      Capital, operating and maintenance costs for three scrubber systems
designed to operate at 25.4, 76.2, and 127 cm (10, 30, 50 in.) pressure drop,
respectively, are summarized in Table 4.  The capital costs have been annual-
ized, assuming an equipment life of 10 years and an annual discount rate of
8 percent.  Annualized capital costs are added to annual 0 & M costs to obtain
scrubbing cost per kW-h energy.  Scrubbing costs in mils/kW-h are plotted
against scrubber pressure drop in Figure 13.  This figure in conjunction with
Figure 1 gives scrubbing costs as a function of emission level for each fuel
type, as plotted  in Figure 14.

      Scrubber costs for various emission levels are  shown in Figure  14.  This
figure shows that for NSPS, 43 ng/J (0.1 Ib/million  Btu) scrubbing costs are

                                     577

-------
between 2.6 to 3.1 mils/kW-h.  The costs increase slightly to 3.1 to
4.1 mils/kW-h for emission level 21.5 ng/J (0.05 Ib/million Btu).  Between
21.5 and 13 ng/J 0.03 Ib/million Btu) costs increase exponentially, resulting
in a 6.4 to 9.2 mils/kW-h cost estimate for the 13 ng/J NSPS level.

     The range of costs associated with the above emission levels reflect the
cost impact of the range of fly ash characteristics encountered  in this study.
The cost range for the three levels increases for decreasing levels because of
the exponential nature of the cost/performance relationship.  As evidenced by
this cost range, scrubber performance and cost become specific and sensitive
to boiler/fuel types.

     From this performance/cost analysis, the following conclusions can be
drawn:

     •    Venturi scrubbing can be considered a competitive control option for
          an emission level range of 21.5 to 43 ng/J for particulate and
          gaseous control.

     •    For the emission range below 21.5 ng/J, venturi scrubbing costs rise
          dramatically, indicating scrubbing becomes less cost-attractive in
          this range.

     ®    As NSPS levels become stricter, selections of coal/boiler types
          become increasingly cost sensitive considerations for venturi scrubbing.

                                  REFERENCES

1.   Lawless, Phil A.  Analysis of Cascade Impactor Data for Calculating
     Particle Penetration.  EPA - 600/7-78-189, U. S. Environmental Protection
     Agency, Washington, DC, September 1978.  39 p.

2.   Yung, S. C. ,  S. Calvert, and H. F. Barbarika.  Venturi Scrubber Performance
     Model.  EPA - 600/2-77-172, Research Triangle Park, NC, August 1977.  197
     P-

3.   Ramsey, G. H., L. E. Sparks, and B. E. Daniel.  Experimental Study of
     Particle Collection by a Venturi Scrubber Downstream from an Electro-
     static Precipitator.  In:  Symposium on the Transfer and Utilization of
     Particulate Control Technology:  Volume 3.  Scrubbers, Advanced Technology,
     and HTP Applications.  EPA - 600/7-79-044c, U. S. Environmental Protection
     Agency, Washington, DC, February 1979.  p. 161-177.

4.   McCain, Joseph D.  CEA Variable - Throat Venturi Scrubber Evaluation.
     EPA - 600/7-78-094, U. S. Environmental Protection Agency, Washington,
     DC, June 1978.  75 p.

5.   Yung, S., H. Barbarika, S. Calvert, and L. Sparks.  Venturi Scrubber
     Design Model.  In:  Symposium on the Transfer and Utilization of Particulate
     Control Technology:  Volume 3.  Scrubbers, Advanced Technology, and HTP
     Applications.  EPA - 600/7-79-044c, U. S. Environmental Protection Agency,
     Washington, DC, February 1979.  p. 149-159.


                                     578

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                               Acknowledgements

     This program was sponsored by the Utilities and Industrial Power Division,
Industrial Environmental Research Laboratory, U.S. Environmental Protection
Agency (UIPD/IERL/EPA),  Research Triangle Park, North Carolina.

     The authors express sincere appreciation to the following individuals
for their involvement with and contributions toward this program:

          •    Dale Harmon, Les Sparks, and James Turner of IERL/EPA, Research
               Triangle Park, North Carolina.

          •    Robert Olexsey of IERL/EPA, Cincinnati, Ohio.

          •    Joe Kavanaugh of Michigan State University Power Plant, East
               Lansing,  Michigan.

          •    Merlin Hove of Ames Power Plant, Ames, Iowa.

          •    Fred Hall, John Bruck, and Diane Albrinck of PEDCo  Environmental,
               Inc., Cincinnati, Ohio.

Mailing address:  Route 1, Box 423, Morrisville, North Carolina  27560
                                      579

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Table 1   SCRUBBER TEST CONDITIONS AND OPERATING PARAMETERS

1.
2.
3.
4.
5.



6.
7.
8.
9-
10.
Parameter
Fuels Tested
Mode
Venturis Tested
L/G Ratio
Pressure Drops
3.5 cm Throat
(L/G = 2 1/m3)
6.0 cm Throat
(L/G = 4 1/m3)
6.0 cm Throat
(L/G = 2 1/m3)
Gas Flow Rate
Acm/m (acfm)
Water Flow Rate
1/m (GPM)
Throat Velocity
m/sec (ft/sec)
Temperature before
venturi (Inlet) °C
Temperature before
Mist - Eliminator
(Outlet) °C
MSU
Coal
As primary device
3.5 and 6 cm
2 and 4 1/m3
(15 to 30 gal/1,000 ft3)
cm of W.C. (in. of W.C.)
101.6, 127
(40, 50)
25.4 to 127
(10 - 50)
20.3 to 76.2
(8 - 30)
8.5 - 10.8
(301 - 380)
15.9 - 30.2
(4.2 - 8.0)
43.8 - 157.2
(144 - 516.0)
131° - 182°
90° - 139°
Ames
Coal only and coal +
20 percent RDF
As primary and
secondary device
6 cm
2 1/m3
(15 gal/1,000 ft3)
cm of W.C. (in. of W.C.)


25.4 to 76.2
(10 - 30)
7.22 - 15.9
(255 - 560)
12.5 - 30.2
(3.3 - 8.0)
42.6 - 93.6
(140 - 307.0)
149° - 168°
103° - 156°
                               580

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C71
CO
                              Table 2   SCRUBBER PRESSURE DROP  AND COST REQUIREMENTS
                                            AT THREE PERFORMANCE  LEVELS
Performance
Level
SNO
1.
2.
3.
4.
5.
6
43 nanograms/ joule
Scrubber AP Scrubbing Cost
Parameter cm W.C. mils/kW-h
Ames-RDF-Data
Ames-RDF-Model
Ames -Coal-Data
Ames -Coal-Model
MSU-Coal-Data
MSU-Coai -Model
20.3
35.6
7.62
25.4
5.08
15.?
2.76
3.12
2.52
2.88
2.50
2.64
21 5 nanograms/ joule
k. ibbet AP Scrubbing Cost
cm W.C. .. mils/kW-h
35.0
67.0
20.0
50.0
18.0
37.0
3.1
4.06
2.7
3.48
2.7
3.16
13 nanograms/ joule
Scrubber AP Scrubbing Cost
cm W.C. mils/kW-h
114.3
152.4
53.3
135.0
30.48
109.2
6.7
9.2
3.58
8.16
3.04
6.4

-------
Table 3   COMPARISON OF EXPERIMENTAL AND PREDICTED
          PRESSURE DROP (MSU)

                   3.5 cm Throat

Test ID
Al
A2
A3
A4
A5
Bl
B2
B3
B4
AP - Experimental cm W.C.
101.6
101.6
101.6
101.6
101.6
127.0
127.0
127.0
127.0
AP - Predicted cm W.C.
173
185
185
226
225
253
253
243
249
                        582

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                           Table 4   SUMMARY  OF  COSTS

                        All Costs in December 1979  dollars

SNO
1.
2.

Scrubber
Scrubber
Parameter
pressure drop
and auxiliary

cm W.C.
equip-
Case A
25.4
$
Case B
76.2
$
Case C
127
$
      ment  capital  cost  on  turnkey
      basis.   (excluding sludge
      treatment plant)                    6,738,800     12,355,500     18,579,100

 3.    Operating and maintenance
      costs.   (per  annum)                 2,081,800      3,453,800      5,352,700

 4.    Capital  cost  of  sludge
      disposal system.                    6,443,000      6,443,000      6,443,000

 5.    Operating cost of  sludge
      disposal system,  (per annum)        4,145,000      4,145,000      4,145,000

 6.    Total capital costs  (2  + 4)        13,182,000     18,799,000     25,022,000

 7.    Total operating  and maintenance
      costs,  (per annum) (3 + 5)          6,227,000      7,599,000      9,497,700

 8.    Uniform  annual equivalent  of
      capital  cost  at  8  percent  dis-
      count and 10  years equipment
      life  (Ref. 4, page 4-89 and
      Table A-8)                          1,965,000      2,801,000      3,729,000

 9.    Uniform  annual equivalent  of
      capital  cost. (mils/kW-h)             0.67           0.95            1.27

10.    0  & M costs  (mils/kW-h)              2.11           2.58            3.23

11.    Scrubbing costs  (mils/kW-h)
      (9 +  10)                             2.88           3.53            4.5

      percent  of 4  C/kW-h energy
      cost                                  7.2           8.8           11.25
                                        583

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1000 i—
                     	 MODEL
                     	DATA
                    	MODEL
                    	DATA

                    	MODEL
                    •—	DATA
                   COAL + 20Z RDF,  AMES


                   COAL, AMFS


                   COAL, MSU
                              6.0 cm THROAT
           11
                                                           10
  ~JO      75100      115      ISO      I7i l°
  SCRUBOER PRESSURE DROP, cm W.C.

Figure 1
Comparison of  predicted  scrubber effluent
particulate  concentration with  data.
                                                                                                                   o
                                                                                                                   o
                                                                                                                   o
                       	DATA  dP 25'4 CI"

                                  P 76.2 on
                                                                                                6.0 cm THROAT   ,
                                                                                                L/G = 2 liters/mj
                                                                                                COAL, AMES
                                                                                                    _L
 4      a  10     1      4      •  10     3      4      •  10*
 PARTICLE AERODYNAMIC DIAMETER,  MICRONS
Figure  2
Comparison of predicted fractional  pene-
trations with data for pulverized  coal
at Ames.

-------
    10
1O
 •
  tj
  oc
o,£
OOUJ
01°-
    2 -
    10'
     10*
         J	L.
                                --- DATA

                                --- MODEL
                                .......... DATA
                                                 * n  o c A
                                                 AP  25.4 cm

                                                 A0  7, , „„,
                                                 AP  76"2 cm
                                    6.0 cm VENTURI  .,
                                        = 2 Hters/mJ
                                    COAL + 20% RDF. AMES
                            J	L.
                                                J	L
                                           • 10*
                       	 MODEL
                       	DATA
                       	 MODEL
                       	DATA

                          6.0 cm VENTURI  ,
                          L/G » 2 Uters/m
                          COAL, AMES
                          SECONDARY DEVICE
                                                                                                                    Lf)
                                                                                                                    o
                                                                                                                    o
                                                                                                                    o
                                                                                                                25.4 cm

                                                                                                                76.2 cm
                                                                10
              4     • 10     1      4
               PARTICLE AERODYNAMIC DIAMATER, MICRONS
               F i g u re 3
               Lui,1(jdr-iiOn of  predicted fractional pene-
               trations with  data for pulverized coal
               plus  20% RDF at Ames.
                                                               no
!     4     * 10"    2     4      (10*     2      4
      PARTICLE AERODYNAMIC  DIAMETER, MICRONS
 Figure  4
 comparison of predicted  fractional  pene-
 trations  with data for pulverized coal
 at Ames,  scrubber operating as  secondary
 device  downstream of full  scale ESP.
                                                                                                                            »icr

-------
                                                                                                      o
                                                                                                      o
                                                                                                      o
                                                                                                      I
                                                                            6.0 cm VENTURI  m


                                                                            6.0 cm VENTURI


                                                                               cm VENTURI  '
                                                                                           COAL, HSU
                                                                                           L/G = 2 liters/m
                                            17.8 cm


                                            76.2 cm


                                           127.0 cm

                                             3
6.0 cm VENTURI


3.5 cm VENTURI
2     4     » W     2     4     • 10*    2
      PARTICLE  AERODYNAMIC DIAMETER,  MICRONS
    Figjre 5
    Comparison of  predicted  fractional  pene-
    trations with  data for pulverized  coal at
    Michigan State University.
     4      8 10"    2     4     » 10*     2
      PARTICLE AERODYNAMIC DIAMETER, MICRONS
Figure 6
Comparison of  predicted  fractional  pene-
trations with  data for pulverized coal at
Michigan State University.

-------
                                                                               r-.
                                                                               O
                                                                               o
                                                                               O
                                                                                I
                                                                               
-------
                                                                                                                      00
                                                                                                                      o
                                                                                                                      o
                                                                                                                      o
                                                                                                                       I
Figure 9
            25    SO     75     WO    125    150
             EXPERIMENTAL PRESSURE DROP, cm W.C.
                                                          5
                                                          -^
                                                          f
                                                          13
                                                          o
                                                             10
                                                                                                         OVERALL INLET LOADINGS
                                                                                                                nm/DNCM
                                                                                      PRIMARY DEVICE
                                                                                      	COAL + 20t  RDF. AMES     8.38
                                                                                      	COAL. AMES              6.11
                                                                                      	COAL. MSU              4,65

                                                                                      SECONDARY DEVICE
                                                                                      	COAL + 20%  RDF. AMES     0.46
                                                                                      	COAL. AMES              0.318
                                                                                                            _L
                                                   10
                   • 10     3     «     •  10     »
                  PARTICLE  AERODYNAMIC DIAMETER. MICRONS
                                                                                                            *  10
Comparison  of predicted and  experimental
scrubber pressure  drop at  Ames.
Figure 10    Average  inlet  particle  size  distributions
              and overall loadings.

-------
   too

    •
    JO
  0  •
CJT—
             -rir
             	DATA
                                                L/G - 4 liters/,


                                                L/G =2 liters/.3

                                                6.0 cm THROAT
                                                COAL, HSU
-is-
          75
                       SCRUBBER PRESSURE  DROP, cm M.C.
  Figure  11    Effect of L/G  ratio on  scrubber  per-
                 formance.
                                                                       too

                                                                         •
                                                                     £
                                                                     g
                                                5  10
                                                                      l/J
                                                                      a:
                                                                                                           cr>
                                                                                                           0
                                                                                                           O
                                                                                                           O
                                                                                   -MODEL
                                                                                   -DATA
                                                                      COAL  * 201 RDF. AMES
                                                                                  AVERAGE INLET CONCENTRATION
                                                                                          
-------
                                                           10
    10
                                 _L
                                                 25
                                                20
                                                   -E

                                                   3:
                                                 15
                                                   o

                                                   ta
                                                 10
Figure  13
       50            100            150
   SCRUBBER PRESSURE DROP, cm W.C.


Scrubbing  cost per kW-h  as  a function
of pressure drop.
                                                            8
                                                        t/i
o


CD
*T
h—t
02 4
cc
=>
ct:
                                                                         	DATA
                       •MODELCOAL   AMES
                       DATA
                       DATAL
                                                                                     COAL,  MSU
          13 NG/J   21.5  NG/J

          —U	J	L_
                                                                                           43 NG/J

                                                                                             i  I
                                                                    10      20      30     40      50

                                                                            NSPS NANOGRAMS/JOULE
                                                     25
                                                                                                               o
                                                                                                               o
                                                                                                               o
                                                                                                20
                                                                                                    CD

                                                                                                    LU
                                                                                                    z:
                                                                                                    LiJ

                                                                                                15  U_
                                                                                                    o

                                                                                                    H;
                                                                                                    ^1_
                                                                                                    LU

                                                                                                    OL
                                                                                                    UJ
                                                                                                    Q-

                                                                                                     f\
                                                                                                    (—

                                                                                                10  o


                                                                                                    o
                                                                                                                CO
                                                                                                                cc
                                                                                                                a:
                                                   60
 Figure  14   Scrubbing  cost per kW-h  as  a function
              of NSPS.

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                        THE RESULTS  OF A TWO-STAGE SCRUBBER/
                            CHARGED  PARTICULATE SEPARATOR
                                    PILOT PROGRAM

                                         By:

                                    J. R. Martin
                                    K. W. Malki
                                    N. Graves

                            Combustion Engineering,  Inc.
                              Birmingham, Alabama 35223
                                      ABSTRACT

     Until recently,  the two-stage wet scrubbing system (a venturi followed by
an S02 absorber)  has  been successful in meeting the old EPA particulate matter
and S02 emission levels.  However, the two-stage scrubber may have limited
application because of the power required to meet the new EPA particulate emis-
sion standards.

     With this in mind,  Combustion Engineering developed a new wet scrubbing
concept:   a two-stage scrubber that incorporates a charged.particulate separator
(wet precipitator).

     To demonstrate performance and obtain design data, a test program was con-
ducted at a Midwestern utility.

     This paper presents the test results, a conceptual design for a full-size
unit, and an economic evaluation that will show the potential for this unique
system to meet the new EPA requirements.
                                       591

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                           THE RESULTS OF A TWO-STAGE SCRUBBER/
                               CHARGED PARTICULATE SEPA.RATOR
                                       PILOT PROGRAM
INTRODUCTION
     In the past decade, the EPA standards for emissions from stationary sources
have gradually become more stringent.  To meet today's standards, Combustion
Engineering, Inc. developed an improved scrubbing concept, the Two Stage Plus.
The Two Stage Plus, which is a low pressure drop rod scrubber (venturi), follow-
ed by a spray tower absorber and a charged particulate separator, is capable of
meeting the new EPA requirements without restriction on the quality of coal.

     Additionally, the Two Stage Plus is economically attractive compared to a
conventional dry collector followed by a wet 862 absorber.  Its attractiveness
is demonstrated by its low capital and operating costs over a wide range of
sulfur and ash contents in the coal.

     Compared to the dry scrubbing concept, the "Two Stage Plus" is economically
favorable with Western coals (which produce alkaline flyash), even with sulfur
content in the coal as low as 0.7%.
BACKGROUND

     Prior to June 1979, the EPA emission standards for power plants were 0.1 lb/
106 Btu for particulate and 1.2 lb/106 Btu for SC^.^1)  To meet these standards,
Combustion Engineering offered two concepts for particulate and S02 removal:  a
two-stage scrubber system and an electrostatic precipitator followed by an S02
absorber.  The two stage system is comprised of a rod scrubber (venturi) followed
by a spray tower absorber with an integral mist eliminator and reheater.  The rod
scrubber is designed to remove mostly particulate and a fraction of S02> whereas
the spray tower is designed to remove mostly SOo and a small fraction of partic-
ulate.

     For most coals, particulate emission from the two stage scrubbing and the
ESP/S02 absorber has generally been below the EPA requirement.  The particulate
emission level achieved was less than 0.08 lb/10" Btu at Northern States Power's
Sherburne County Units  1 and 2 (two-stage system), less than 0.04 Ib/lO^ Btu at
The Kansas Power and Light Company's Lawrence 4 (two-stage system), and less
than 0.04 lb/10^ Btu at Louisville Gas and Electric Company's Cane Run 5 (ESP
followed by an S02 absorber).  See Kruger (1977),2 Green and Martin (1977),3
Green et. al. (1978),4 and Van Ness et. al.  (1979).5

     In June 1979, EPA issued new emission standards.  The proposed stand-
ards will limit the emission of particulate matter from steam generators that
fire more than 250 x 10^ Btu/hr (73 megawatts) of fossil fuel.  The partic-
ulate emissions are limited to 13 nanograms/joule heat input (0.03 Ib/lO^ Btu)
and must be reduced 99% from uncontrolled emission levels.  In the case of S02»
the following three conditions must be satisfied:
                                       592

-------
a)  SCL emission must not exceed 520 ng/J (1.2 lb/10  Btu).

b)  SO  must be reduced 90% from uncontrolled emission levels, unless

c)  tbe emission level is 250 ng/J (0.6 lb/10  Btu) or less, in which case a,
    sliding scale of removal efficiency applies down to a level of 0.2 lb/10
    Btu, at which level and below a 70% minimum removal is required.

     Presently, C-E offers several design concepts that have the capability of
achieving the new EPA S0_ and particulate emission requirements.  These con-
cepts are:

The Two Stage Wet Scrubbing

     This concept can achieve EPA's new particulate requirements; however, it
requires a relatively high pressure drop depending on the flyash characteristics
and, therefore, its effectiveness is limited to certain coals.

ESP/Single Stage Wet Scrubber

     With proper design of the ESP, this system can meet the EPA particulate
emission requirements.  This system may be costly, depending on the flyash
characteristics, especially if requiring a precipitator SCA of greater than
500 to  600.

Dry Absorber Particulate Collector

     This concept can achieve the EPA particulate requirement, but has not
been demonstrated in full size and may not be practical with high sulfur coals.
THE TWO STAGE PLUS CONCEPT

     In an effort to meet the EPA emission requirement without restriction on
the quality of coal, C-E has developed a modified two-stage scrubber, Two
Stage Plus.  The Two Stage Plus is comprised of a low pressure drop rod scrub-
ber (venturi) followed by a spray tower and a "Charged Particulate Separator"
(CFS) based on the concept of wet precipitation.  The offering of this con-
cept is predicated on C-E's long and successful experience with two-stage
scrubbing and wet precipitators.  Two-stage scrubbing using the rod design has
demonstrated success in terms of performance and availability.  The rod scrub-
ber has been used in AQCS installations totalling over 2000 megawatts of gener-
ating capacity.  The two-stage  system at i\TSP's Sherburne County Units 1 and 2,
representing  1520 MW, has been  in operation  for 3%  years.   Component  development
and material  evaluation during  this  period has  resulted  in  design  improvements
to the  rod scrubber.

     The charged particulate separator (GPS) has been designed as a wet
electrostatic precipitator, which was demonstrated  on a  full  size unit in
Bressoux, Belgium over 16 years ago.  The wet ESP was installed behind a wet
filter.  The wet filter is similar to C-E's rod scrubber except that  the flow is
horizontal.  The design fuel for this application was as follows:

                                       593

-------
                              Sulfur       0.85%
                              Moisture     14.0
                              Ash          29.0
                              Volatiles    13.0
                              Carbon       44.0

     Tests conducted in June, 1976 (13 years after start-up) by an independent
Belgium laboratory showed that the particulate collection efficiency of the
wet precipitator was 90%.  The design gas volume for the wet precipitator is
100 cubic meters per second  (211, 765 ACFM).   The water spray system is designed
for two level application.  Below the precipitator, water is sprayed against
the gas flow at a rate of 20 cubic meters per hour (80 GPM).  Above the precip-
itator the spray was intermittent at the rate of 60 cubic meters per hour (264
GPM).   During cleaning, the precipitator voltage level is reduced to avoid heavy
sparking and power arcing.

     The shell and ductwork are rubber-coated mild steel and internal parts are
stainless steel.  There has been no significant corrosion of the precipitator
during 16 years of operation.

     The use of the wet electrostatic precipitator preceded by an S0« absorber
for particulate removal, as opposed to a conventional dry ESP was necessitated
at that time by the stringent Belgium emission requirements.  These require-
ments limited particulate and SO,., emission to very low levels.  Since then,
however, the European SO,, emission limits have been relaxed precluding the need
for the SO,., absorber.  As a result, the S0« absorber/wet ESP became economic-
ally less attractive than a dry ESP for particulate removal only and is no
longer a practical design in Europe.
TWO STAGE PLUS BENEFITS

     To demonstrate the benefits of the Two Stage Plus, it will be compared
to several other flue gas desulfurization techniques.  These techniques include:
the two-stage scrubber (venturi for particulate collection followed by an SO
absorber), a cold ESP for particulate collection followed by an S0» absorber,
and finally the dry SO  absorber followed by a particulate collector.

     The charged particulate separator in the Two Stage Plus is much smaller
that a conventional cold ESP because:

1)  To meet the EPA limits the CPS requires a low particulate removal effic-
    iency compared with the ESP.  This is due to precollection in the rod scrub-
    ber, which causes the particulate at the CPS inlet to become small compared
    with the ESP inlet, 0.10 vs. 7 lb/lQ6 Btu.

2)  The gas treated in the CPS is saturated and is relatively cold (130 F) ,
    thereby resulting in conditions favorable for particulate collection.  The
    gas treated in the ESP on the other hand is drier and hotter (300 F).  Both
    conditions tend to increase the resistivity of the ash reducing the ability
    of the ESP to collect ash.
                                     594

-------
3)   Because of the lower gas temperature, the volumetric flow through the CPS
     is smaller than flow through the ESP.

4)  Re-entrainment of the ash deposit is usually a major consideration in
    choosing the right gas velocity for an electrostatic precipitator.  Since
    the charged particulate separator (CPS) operates in a wet environment, the
    deposit on the collecting electrodes is wet, and therefore, more difficult
    to re-entrain.  As a result, it is usually safe to operate the CPS at
    gas velocities higher than usually required in a conventional ESP.

     Calcium compounds are commonly present in varying concentrations and
degrees of alkalinity in the flyash.  If an ESP is used ahead of an 862
absorber, the flyash with its calcium is collected and sent to disposal.  If
allowed in the scrubber, these calcium compounds can be very useful in absorb-
ing SC>2'  In the Two Stage Plus, all the ash generated by the furnace can be
used in absorbing S02-  Thus the addition of supplementary limestone is mini-
mized, resulting in significant operating cost savings.

     In a conventional two-stage scrubber, the pressure loss across the venturi,
is usually set at high levels (15-20 in. w.g.) to achieve high particulate re-
moval efficiency.  In the Two Stage Plus, where the venturi acts only as a
precollecting device, the pressure loss Is much lower  (3-5 in. w.g.).  As a
result, the operating cost of the Two Stage Plus will be reduced significantly.

     The charged particulate separator has been successfully used in various
applications as a high efficiency mist eliminator.  The mechanism for removing
mist in the CPS is similar to that for dust in an electrostatic precipitator.
With its mist removal capability, the CPS precludes the need for a fine mist
eliminator, which is usually required in conventional S02 scrubbers.

     The Two Stage Plus collects particulate and SC^ in one system.  This is
because the particulate collection stage and the SC^ absorber stage both dis-
charge into a common disposal system.  In contrast, systems that require dry
precollectors such as an ESP followed by a wet scrubber require two waste
disposal systems.  The single disposal system is simpler than the double
disposal system since it includes fewer components to operate and ruaintain.

     Unlike some concepts, such as dry scrubbing, where SC>2 removal is
limited at high sulfur levels, the two stage plus is capable of removing SCU
to any required emission level for any sulfur level in the coal.  More impor-
tantly, the additive consumption is only slightly above the theoretical require-
ment.  The additive consumption for the dry absorber on the other hand is
significantly higher than the theoretical requirement, especially with high
sulfur conditions.

PILOT PLANT TEST PROGRAM

Pilot Plant Description

     To demonstrate the capability of the Two Stage Plus, a pilot plant was
installed at Northern States Power Company, Sherburne County Plant.  The purpose
of the pilot program is:

                                       595

-------
1)  To demonstrate that a particulate emission level of (13 ng/J) 0.03 lb/10°
    Btu can be achieved.

2)  To determine a method of maintaining the CPS in a clean state that will not
    hinder performance.

3)  To develop design criteria for a full-size system.

     The 10,000 cfm pilot plant was installed at the 730-MW NSP's Sherburne
County Unit 1.  The fuel fired was Sarpy Creek coal.  The coal and ash analyses
are shown in Tables 1 and 2.  The air quality control system at Unit 1 consists
of 11 (+1 spare) scrubber modules.  Each module consists of a rod scrubber
(venturi) and a marble bed, a mist eliminator and a reheater.


                       TABLE  1  TWO-STAGE PLUS PILOT PLANT
                             COAL PROXIMATE ANALYSIS
                                                 Mean
                   Moisture                      23.9%
                   Ash                           10.3%
                   Volatile Matter               27.7%
                   Carbon                        37.6%
                   Sulfur                         1.0%
                   Heating value                 8300 Btu/lb.
                       TABLE 2  TWO-STAGE PLUS PILOT PLANT
                                 FLYASH ANALYSIS
                                              Mean % by wt
                   P205                           OT'5
                   Si02                          35.2
                   Fe203                          6.9
                   A1203                         17.2
                   Ti02                           0.7
                   CaO                           17.4
                   MgO                            4.3
                   Na20                           1.50
                   K20                            0.4
                   S03                           15.3
                   Undetermined                   0.6
                   Total                        100.0


                                      596

-------
     The marble bed of one module was converted to a spray tower several years
ago for test purposes.  The Two Stage Plus pilot plant was installed on the
module with the spray tower (Figure 1).   Flue gas was extracted from the outlet
of the two stage scrubber via a duct, and treated in two horizontal CPS's in
series.  To insure that the slip stream was representative of the gas in the
scrubber, the duct extended about 6 ft.  into the 18 x 26 ft. scrubber, and
pointed in a direction opposite to the gas flow.  Additionally, to prevent
condensation in the CPS, the inlet and outlet ducts were insulated.  The amount
of gas treated varied between 4800 to 8000 ACFM.  Initially the gas was extract-
ed downstream of the mist eliminator.  Later tests were conducted with the gas
extracted from a point ahead of the demister.

     Phase 1 tests were conducted on a two field CPS that contained five gas
lanes on eleven-inch centers.  The collecting plate height was four feet and
each field has 38 inches of treatment length.  The CPS was equipped with a
flat bottom and has a spray system for removing collected particles from the
discharge and collecting electrode surfaces.  The location of the seven banks
of spray nozzles is shown in Figure 2.

     Each electrical  field was served by a separate transformer-rectifier set
with automatic voltage  controls.  The spray system was operated manually with
the effluent being drained back into the spray tower.  Figures 3 and 4 show
equipment layout for  the two-field CPS.
                            Figure 1   NSP Sherco 1

                                        597

-------
                                                                   SPRAY NOZZLE
                   Figure 2  Spray nozzle arrangement in CPS pilot
     Phd j ? tests were conducted on a five field CPS.   The field height,
number of gas lanes, and plate spacing were as described earlier.  Treatment
length and total collecting surface were 2.5 times the values used for the two
field unit.

     Upon leaving the CPS, the treated gas was exhausted back to the scrubber at
a location downstream of the mist eliminator.
Pilot Plant Results

     A total of 35 tests were conducted as part of the test program.   These tests
were designed to determine the particulate and S02 removal capability of Two Stage
Plus.  Immediately following these tests, several extended tests were conducted to
determine the cleaning requirements of the CP'S and its performance as a function
of time.

     Tables 3 and 4 summarize the test results of the program.  The data reveals
that the Two Stage scrubber is capable of removing 96% of the particulate leav-
ing the boiler air heater outlet.  This was achieved with a rod scrubber pressure
drop of 5 to 6 inches w.g., a total spray liquid-to-gas ratio of 27 gallons/1000
cfm, and an average inlet ^articulate loading of 2.5 gr/DSCF.  To be successful
the CPS had to produce an emission level of 0.03 lb/10  Btu or less.

     The phase 1 two-field CPS tests were performed in accordance with EPA
method 5 and were each three hours long.  Test  runs were made at these oper-
ating conditions:

                                        598

-------
                                         CPS
                                                                t
                                                                     'FAN
                              Figure 3   CPS  pilot  plant

                         (1)   CPS  velocity:   4,  5  &  6.5  FPS

                         (2)   Electrical Current Density:   100%  and  50%

                         (3)   With and  without On-line washing.

     The results of phase 1 are shown in Table 3.   During Phase 1 the scrubber
aas extracted after the mist eliminator was varied.   The results indicate that
the CPS was capable of achieving the 0.03 lb/106 Btu  (0.013 gr/DSCF) at a velo-
city of up to 4.5 ft/sec.

     The results of these tests also indicated no  difference in performance
with or without washing.  Inspection of the CPS upon completion of a three-
hour test run revealed expected wetness of collecting plates and a measurable
quantity of water and dust in the hopper.  The majority of tests were there-
fore conducted without use of washing.

     During the second phase of the program,  the  extraction point was relocated
upstream of the mist eliminator, thus resulting in a  higher particular loading
due to increased mist (slurry) carryover, and a five  -  instead  of two - field
CPS was used.  The results of changing  the  extraction point reveals  that  the mist

                                        599

-------
           CHARGED
           PARTICULATE
           SEPARATOR
                                  A   A    A    A
                                      A      A      A
                              Figure 4  CPS pilot plant
eliminator is capable of removing about 60% of the solids leaving the spray
tower (0.095 versus 0.035 gr/DSCF).

     The phase 2 tests were conducted on a five-field CPS and the results are
listed in Table 3.  The data is very consistent and the 0.013 gr/DSCF (0.03
lb/106 Btu) desired emission was achieved at velocities in excess of 6.5 ft/sec,
Detailed results of 20 short-term test with five fields are listed in Table 4.

     The emission particulate loadings were plotted as a function of treatment
time in the CPS.  The graph is shown in Figure 5.  The results show that 2.4
seconds of treatment time is required to meet the desired .013 gr/DSCF.
1.
2.
 The following conclusions can be made from the pilot results:

On-line washing made marginal improvement on the CPS performance, when
compared with no washing.

The effect of current density in the five-field CPS using high velo-
cities was marginal in the 50 to 100% range.
                                       600

-------
                           TABLE 3   TWO STAGE PLUS CHARGED PARTICULATE  SEPARATOR  TEST  RESULTS
CTi
O
Scrubber
Extraction
Location

Downstream B.E.S.
Downstream B.E.S.
Downstream B.E.S.

Upstream B.E.S.
Upstream B.E.S.
Upstream B.E.S.
Upstream B.E.S.

Rod P Treatment Velocity
(in. w.g.) Time (sec) (EPS)

6" 1.7 3.9
6" 1.3 5.4
6" 1.1 6.15

6" 1.1 6.10
6" 3.2 5.5
6" 2.7 6.5
6" 2.7 6.4

# of Current
Fields Density %
Phase I
2 100
2 100
2 100
Phase II
2 100
5 100
5 100
5 100

Wash
On/Off

Off
Off
Off

Off
Off
Off
On

Inlet Interim
(qr/DSCF) (qr/DSCF)

2.5 .03
2.5 .026
2.5 .045

2.5 .093
2.5 .089
2.5 .100
2.5 . 07 9

Outlet
(gr/DSCF)

.007
.012
.012

.027
.008
.009
.009

-------
TABLE 4   ?[LOT TESTS RESULTS FOR TWO  STAGE  PLUS  CHARGED PARTLCULATE SEPARATOR



                        jummary ofJ5_Fie_ld__Test Results
Velocity
FPS
6.42
6.40
6.50
6.50
6.36
6.27
6.4
6.34
6.13
6.01
6.63
6.62
6.33
6.37
6.38*
5.33
5.37
5.50
5.45
5.32
5.30
5.38*
* Average Values
Dust
Inlet to CPS
.0550
.0972
.0834
.1213
.0908
.1389
.1565
.1048
.1032
.0554
.0610
.1443
.1026
.0686
.0998*
.1036
.0571
.0830
.1117
.2622
.0273
.1075*

Load-GR/DSCF
Outlet from CPS
.0061
.0069
.0088
.0075
.0088
.0064
.0061
.0110
.0100
.0084
.0130
.0104
.0085
.0107
.0088*
.0061
.0075
.0077
.0116
.0067
.0063
.0077*

                                     602

-------
           0.03  -
           0.02
           0.01
                  	I	I	i
                        1                    2                    3

                                   TREATMENT TIME-SECONDS

             Figure  5   Pilot  tests  on GPS  performance vs.  treatment time

3.  The required  CPS treatment  time to achieve 0.013 gr/DSCF (0.03 lb/106 Btu)
    is 2.4 seconds.

4.  During the test  program S02  levels were measured entering and leaving the
    Two Stage Plus.  The  results show a removal of 75% with an inlet concen-
    tration of 700 ppm.   This is comparable with two stage scrubbing,  indicat-
    ing the CPS has  no  significant  effect  on S02 removal.

     To determine any degradation in performance,  a 140-hour test run on the
five-field pilot  CPS was  conducted.   Emission  was  checked  periodically during
the week using EPA method 5.  A  portable opacity monitor was installed down-
stream of the CPS to yield a continuous surveillance of the operation.  Figure 6
is a bar chart indicating test and  cleaning cycles for this long-term perform-
ance test.  Four  tests  conducted during this period showed consistent  CPS per-
formance.  The outlet particulate loading  did  not  exceed 0.01 gr/DSCF.  A
minimal amount of washing (six)  was  required during this period with each cycle
lasting 10 minutes only.
                                  FLUSH PERIODS
    5:00 PM  8:00 AM
                       11:00 AM
                                                 4:30 PM
                                                            4:30 PM
                                                                   6:00 AM
     TUES
                WED
                           THURS
                                      FRI
                                                  SAT
                                                             SUN
                 Figure 6  CPS pilot long-term performance test
                                     603

-------
CONCEPTUAL DESIGN

Design Criteria

     The full size unit selected for the conceptual design application is a
500-MW unit.  The fuel fired is a Western coal with about 8000 Btu/lb heating
value, and two levels of sulfur, 0.54 and 2.3%.  The design requires 70 and
90% S02 removal for respective sulfur levels and an outlet particulate emission
of 0.03 lb/106 Btu (0.013 gr/DSCF).

     The rod scrubber/spray tower design selected for this application requires
a liquid-to-gas ratio of 85 gpm/1000 cfm.  The pressure drop across the rod
scrubber has been set at 4 in. w.g.   The CPS gas treatment time used in this
design assumes 3.13 seconds, which is 30% higher than the pilot value of 2.4
seconds.

     An intermittent wash system to operate off or on-line is required to keep
the CPS clean.  The wash system frequency of operation will be in the order of
once per day.

     The material selection for the Two Stage Plus is based on C-E's experience
with two stage scrubbers, charged particulate separators, and the pilot plant
at Sherburne County.  Material evaluation over the years has led to improve-
ments, especially in the high wear components, such as rod scrubbers, piping,
and pumps.  In addition, the CPS experience in Belgium provided telling testimony
on the use of Type 316L stainless steel, where it has shown little wear in the
last 15 years.  Type 316L ss Is the material for the scrubber shell and elec-
trodes, refractory the material for the rods, fiberglass for the piping,  and
rubber lining for the pumps.  For C-E experience with 316L ss in flue gas
scrubbers, see Lewis et. al. (1978).°

Description

     The conceptual design is shown isometrically in Figure 7.  The Two Stage
Plus consists of 5 modules including a spare.  The gas flow entering each module
is approximately 450,000 cfm.

     In the rod section, the vertical spacing between the rods is automatically
controlled to maintain 4 inches w.g. of pressure drop.  The rod scrubber, not
only removes most of the particulate matter from the flue gas, but also a portion
of the S02 in the flue gas.  A steam soot blower located in the inlet duct pre-
vents deposit from building on the wet/dry interface.  The spray slurry in the
rod scrubber discharges into the reaction tank.  Figure 8 shows a flow schematic
of the Two Stage Plus.

     From the rod scrubber, the flue gas turns 180 degrees and enters the second
stage consisting of a spray tower.  The spray tower is a low pressure drop SOo
absorber.  In the spray tower the spray slurry is sprayed counter-current to the
gas.  The spent spray tower slurry is also discharged into the reaction tank.

     The flue gas then passes through a bulk entrainment separator  (BES).  The
BES consists of vanes mounted at 45-degree angles on 3-inch parallel spacing.
The BES is maintained in a clean state by intermittent washing with a fixed grid
arrangement.

-------
TWO STAGE
    PLUS
        Figure 7  Isometric cutaway of Two Stage Plus
                     605

-------
                                        TO STACK
en
o
CTl
                            REHEATER::
                                                 CHARGED
                                                 PARTICIPATE
                                                 SEPARATOR
                                                   SEPARATOR WASH
          0-E
    ROD SPRAY

      PUMP
REAC
TlOf
M
TANK

O
*

MIXER
«
i

c
— , L
                                                   ABSORBER

                                                   SPRAY PUMPS
TO POND
                                     ABSORBER BLEED PUMPS
                                           D
                                             MIXER
ADDITIVE STORAGE

     TANK
                                                                             *- MAKE-UP WATER
                                       Figure 8  Two Stage  Plus  flow schematic

-------
     Upon leaving the BBS, the gas enters the charged particulate separator,
where liquid entrainment and particulate matter are further reduced.  The GPS
is a vertical compartment containing a grid of electrical cells.  These cells
are comprised of 316L stainless steel discharge and collecting electrodes.
To facilitate the particulate removal, the gas is allowed to travel at a reduced
velocity through the GPS.  The collector plates will be cleaned periodically
using a fixed grid flush system.

     The GPS is divided into two cells powered with a transformer rectifier.
Insulator compartments external to the CPS shell span two opposite sides of
the shell.  The discharge electrode wire frames extend below the collecting
plates and are connected to give greater stability to the high voltage system.

     Upon leaving the CPS, the gas temperature is increased by 30 F to
eliminate the plume and to bring the gas above its dewpoint.

     The auxiliary equipment, which includes the reaction tank, bleed,
additive feed, and makeup water, will not be described in this paper.  Instead,
the reader is referred to a paper presented by Martin (1977).6

Economic Evaluation

     The capital and operating costs for the full scale Two Stage Plus are shown
in Table 5.  Four cases were evaluated for two sulfur levels, 2.3 and 0.54%, with
and without taking credit for the alkalinity in the ash.  These specific variables
were selected in order to facilitate comparison with competing concepts.

     The capital costs were based on 1981 dollars (present worth)  for 35 years.
The installed capital cost includes,  the scrubbing system, steel,  building,
electrical, controls, etc.  The Two Stage Plus installed cost for  a 500-MW unit
increases by 10% as the sulfur in the coal increases from 0.54% to 2.3%.   This
is primarily due to the increase in pumping capacity.   The presence of calcium
in the ash reduces the installed cost slightly primarily due to a  reduction in
the additive subsystem.

     The operating cost has been evaluated based on a 35 year life,  load factor
of 75%, and present worth dollars.   Unlike the installation cost the operating
cost is significantly higher for the higher sulfur coal.  The cost is further
increased when the alkalinity in the ash is ignored.

     The economic data for the Two Stage Plus design is of even more interest
when compared against other FGD concepts.  Table 5 also shows a comparison of
the costs for four FGD concepts, 3 wet scrubbing and 1 dry scrubbing.  The wet
scrubbers include the Two Stage Plus, the Two Stage, and the ESP/Spray Tower.
The dry scrubbing data is based on information presented by Basin Electric at
the EPA Scrubber Symposium in March 1979.  For the high sulfur condition the
stoichiometric lime feed rate was assumed to be 160% based on S02 removal.  The
manpower requirement was also adjusted to allow for the dry system.

     In evaluating the four concepts, the following assumptions were made:


                                       607

-------
                     TABLE  5   ECONOMIC EVALUATION  WITH  CREDIT FOR ALKALINITY IN FLYASH
                                                 BASIS:  500 MW UNIT
                                                        2.3% SULFUR IN COAL
TWO-STAGE
Cost*/Basis
$
Capital 39.0 X 106/Actual
Additive 24.7 x 106/95,200 tons/yr.
CaC03
cr, Power 51.3 X 106/22,000 KW
o
CO
Reheat 20.0 X 105/71.4 mm BTU/hr
Manpower 32.8 X 106/j° ^
Replacement 26.8 X 106/Actual
TWO-STAGE PLUS
Cost*/Basis
$
43.0 X 105/Actual
24.7 X 105/95,200 tons/yr.
CaC03
39.0 X 106/16,500 KW
20.0 X 106/71.4 mm BTU/hr
34 2 X 106/10 oper"
w.d. A lu /13 maint_
29.8 X 106/Actual
ESP/SPRAY TOWER DRY SCRUBBER/BAG FILTER
Cost*/Basis Cost*/Basis
60.0 X 106/Actual 50.0 X 106/Actual
47.0 X 106/181,000 tons/yr. 196.8 X 106/147,000 tons/hr
CaC03 CaO
44.0 X 106/19,000 KW 21.0 X 106/9,100 KW
20.0 X 106/71.4 rim BTU/hr O/-
•u ? x in6/10 oper- ?fi R x in6/10 °Per-
34'2 X 10 713 maint. 26'8 X 10 78 maint.
29.8 X 106/Actual 18.0 X 106/bag filter, atom-
                                                                                                           bearings, etc.
Total
194.6  X 10U
196.7  X 10U
                                                                      235.0 X 10
                                                                                   312.0 X 10
*  Cost is based on 35 year life, 75%  load factor, and  1981 worth, with commercial date set at 1981.

-------
                TABLE  5 CONT'D    ECONOMIC  EVALUATION  WITH  NO CREDIT  FOR ALKALINITY  IN FLYASH
                                                BASIS:  500 MW UNIT
                                                       2.3% SULFUR IN COAL

TWO
Cost*
Capital 40.0 X
Additive 47.0 X
Power 51.3 X
o Reheat 20.0 X
UD
Manpower 32.8 X
Replacement 26.8 X
10
10
10
70
10
10
STAGE
/Basi
$
TWO
STAGE PLUS
ESP/SPRAY TOWER
s Cost/Basis
J
6/Actual
6/18T
CaCO
6/22,
6/71.
6,10
712
,000 tons/yr.
3
000 KW
4 mm BTU/hr
rS.
6/Actual
44.0
47 X
39 X
20.0
34.2
29.8
X 106/Actual
106/181 ,000 tons/yr
CaC03
106/16,800 KW
X 106/71 .4 mm BTU/hr
v ,,,6,10 oper.
1 3 rnaint.
X 106/Actual
60
47
44
20.
34.
29.
DRY
Cost/Basis
X
X
X
0
2
8
10
10
10
X
X
X
5/Actual
6/181,000 tons/yr
CaC03
6/19,000 KW
106/71.4 mm BTU/hr
,~6,10 oper.
13 maint.
106/Actual
50 X
196. f
21.0
O/-
26.8
18.0
SCRUBBER/BAG FILTER
Cost/ Actual
S
106/ Actual
3 X 106/147,000 tons/yr
CaO
X 106/9,100 KW

X Io6/8°rna°in[:
X 106/bag filters, star
                                                                                                         bearings, etc.
Total
217.9 X 10U
214.0 X 10C
235.0 X 10°
                                                                                                312.0 X  10
   Cost is  based on 35 year life,  751 load factor, and 1981 worth, with  commercial date set at  1981.

-------
                             TABLE  5 CONT'I>    ECONOMIC  EVALUATION  WITH CREDIT FOR ALKALINITY  IN  FLYASH
                                                         BASIS:   500  MW UNIT
                                                                 0.54% SULFUR IN COAL
en
O
Capital


Additive



Power


Reheat


Manpower



Replacement



Total
                           TWO-STAGE
                         CostVBasis
                      34. OX 10/Actual
                     O/-
                     45.0 X 106/19,300 KW
                      20.0 X 10V71 .4 mm BTU/hr
                     32.8 X 10 /
                              &,10  oper.
                                12 maint.
                     26.8 X 10 /Actual
                     158.6  X 10
   TWO-STAGE PLUS

    CostVBasis
         $

39.0 X 106/Actual
O/-



32.8 X  106/14,000 KW


20.0 X  106/71.4 mm BTU/hr


34.2 X  106/!°°P?!V
29.8 X 10°/Actual
155.8  X 10
                                ESP/SPRAY TOWER

                                 CostVBasis
                                     $

                             54.0 X 106/Actual
                               8.5 X 10"/42,500  tons/yr.
                                       CaC00
                              37.8 X 10/16,200  KW
                             29.8 X  10u/Actual
                             184.3  X  10
                                                          DRY SCRUBBER/BAG FILTER

                                                                CostVBasts
                                                           50.0 X  10/Actual
                                                            5.8 X 10/25,800 tons/yr
                                                                    CaO
                                                          20.0 X TOYS,700 KW
                              20.OX 10D/71.4 mm BTU/hr      O/-
                                                           26.8 X
                                                           18.0 X 10 /bag filters,  atomizers
                                                                     bearings,  etc.
                                                           141.9 X 10
         Cost  is based on 35 years  life, 75% load  factor, and 1981 worth,  with commercial  date  set at 1981,

-------
                    TABLE 5  CONT'D    ECONOMIC  EVALUATION WITH  NO  CREDIT  FOR ALKALINITY  IN FLYASH
                                                      BASIS:   500 MW UNIT
                                                              .54% SULFUR IN COAL
Capital


Additive



Power


Reheat


Manpower


Replacement



Total
                       TWO-STAGE
                     Cost*/Basis

                         fi$
                 35.0  X  10 /Actual
                 8.50  X  10D/42,500 tons/yr
                          CaCO,
                 45  x  10°/19,300 KW
     TWO-STAGE PLUS

      CostVgasis

 40.0 X 106/Actual
  8.5  x  106/42,50Q tons/yr.
           CaCO,,
 32.8 X 10D/14,OOX) KW
   ESP/SPRAY  TOMER

    CostVBasis

54.0 X 105/Actual


 8.5 x 106/42,500 tons/yr
                                                                                     CaCO
                                                                                         3
37.8 X  10°/16,000
                      y  m6/10 °Per-
                      X  10 712 maint.
                 26.8 X 10D/Actual
                 168.T X 10"
 34.2 X  106/™ °P?r:
           13 ma int.
 29.8  X  10°/Actual
T65.3   X  10°
34.2 X  10°/10 oper.
          13 maint.

29.8 X  105/Actual
184.3 X  TOD
DRY SCRUBBER/BAG  FILTER

     Cost*/&asis
         ,-  $
50.0 X 10 /Actual


26.8 X ](f/25,&CiO tons/yr.
         CaO
20.0 X 10D/8,700 KW
                 20.0  X  10D/71.4 mm BTU/hr      20.0 X 10b/71.4 mm BTU/hr      20.0  X  T0b/71,4 mm BTU/hr      O/-
26.8 X
                                                                                                                          +
                                                                                                                    8 maint.
18.0 X 10D/bag filters, atomizers,
           bearings, etc.


14T.9 x 106
*   Cost is based on 35 year Tife,  75%  load factor, and'1981  worth, with commercial  date at 1981.

-------
1)  Limestone stoichiometry for the wet scrubbers of  110% based on  the  SC^
    removal.

2)  Credit for calcium in the ash was taken only .for  the wet concepts.

3)  75% load factor.

4)  35 year  plant .life with 8% escalation and 9% discount rates.   Start-up date
    set at 1981.

5)  Limestone cost as of 1981:  $8.7/ton.  Lime cost  as of 1981:  $45/ton.

6)  Steam cost set at $2.0/106 Btu in 1981.

7)  Power cost set at $-013/kWh (1981).

8)  Operator cost/year = $50,000

     The cost breakdown shows that additive feed, power and reheat  are  the
determining factors in evaluating the four concepts.  As the sulfur in  the coal
increases, the differential in power and reheat costs between the dry and the wet
concepts remains relatively constant, but the additive cost differential becomes
extremely high.

     A plot of evaluated cost versus the % sulfur in  the coal is shown  in Figures
9 and 10.  The graph shows that among the wet concepts the Two Stage Plus has
the least evaluated cost.  When compared with dry scrubbing the Two Stage Plus is
slightly more costly at the 0.54% sulfur level, but at the 2.3% sulfur  level,
the Two Stage Plus is significantly less.  The Two Stage Plus appears to be
economical above 0.7% sulfur in the coal if credit for the alkalinity in the
flyash is considered, and above 0.8% if the ash alkalinity is ignored.

CONCLUSION

     The Two Stage Plus is technically and economically viable as an SOo and
particulate control system.  Its ability to meet the  new EPA requirements can
be predicted safely.

     In terms of cost,  Two Stage Plus is the most economical of the majority
of the wet scrubbing concepts.  When compared with the dry system, Two Stage
Plus is economical if the sulfur in the coal exceeds  0.8%.  When the coal's ash
has high alkaline quantities,  as do many western subituminous and lignite coals,
the breakpoint is even lower,  i.e. (0.7% Sulfur).

     For Western fuel-fired plants, with highly alkaline flyash that is
difficult to collect in precipitators, Two Stage Plus looks very promising.

ACKNOWLEDGMENT

     Special appreciation is given for the assistance provided by Northern
States Power Company's management and plant personnel during the test program.


                                    612

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   300x 106
35 YEAR
EVALUATED
COST
   200x10°  -
   140 x 10'
         6
                      TWO STAGE PLUS

                    O ESP/SPRAY TOWER

                    ED DRY SCRUBBER/BAG HOUSE

                      TWO STAGE SCRUBBING
                                      1.0

                                     % SULFUR IN COAL
     Figure 9  35-year  evaluated cost as a function  of  sulfur in coal
               with credit  for alkalinity in flyash
                                      613

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  300x 106
35 YEAR
EVALUATED
COST
  200x1P6
  140x 10°
                   A  TWO STAGE PLUS

                   O  ESP/SPRAY TOWER

                   D  DRY SCRUBBER/BAG HOUSE

                   •  TWO STAGE SCRUBBING
                       0,54
 1.0

% SULFUR INCOAL
2.0
                                                                     2.3
       Figure  10  35-year evaluated  cost as a function  of  sulfur in coal
                   with no credit  for flyash alkalinity
                                     614

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REFERENCES

1.  36 Federal Register, page 24876, December 23,  1971.

2.  Kruger, R. J.  Experience with Limestone Scrubbing At Sherburne County
    Generating Plant, Northern States Power Co.,  (Presented at EPA Symposium
    on Flue Gas Desulfurization, Hollywood, Florida, November 1977).

3.  Green, K.  and Martin, J. R., Conversion of the Lawrence #4 Flue Gas
    Desulfurization Systems.  (Presented at EPA Symposium on Flue Gas Desulfur-
    ization, Hollywood, Florida, November  1977).

4.  Green, K., Conrad, L., Martin, J. R.,  and Kingston, W. H.  Commitment to
    Air Quality Control.  In:  Proceedings of the  American Power Conference,
    Haigh, B.  (ed).  Chicago, American Power Conference, 1978.  p. 632-645

5.  Van Ness, R. P., Kingston, W. H., and  Borsare, D, C.  Operation of C-E
    Flue Gas Desulfurization System  for High Sulfur Coal at Louisville Gas
    & Electric Company, Cane Run #5.  (Presented at American Power Conference,
    Chicago,  Illinois, April 23-25,  1979).

6.  Kettner, D. C., Hickok, W. W., Martin, J. R.,  and Dutton, R. W.  Design of
    a Spray Tower  Scrubber For Coal  Creek  Station.  (Paper presented at PACHEC
    '77 -  The  Second Pacific Area Chemical Engineering Conference, Denver, Col.,
    August 28-31,  1977).

7.  Lewis, E.  C.,  Stengel, M. P., and Maurin, P. Gr  Performance of Type 316L
    Stainless  Steel and other Materials  in Electric Utility Flue Gas Wet Scrubbers
    (Paper presented at APCA, IGCI and NACE Seminar on Corrosion In Air
    Pollution  Control Equipment, Atlanta,  GA, January 17-19, 1978).  Combustion
    Engineering Publication TIS-5366.
                                     615

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                              AUTHOR INDEX



AUTHOR NAME                                                         PAGE



Ariman, T.                                                        111-222



Bacchetti, J.  A.                                                     1-529



Bernstein, S.                                                      11-125



Bibbo, P.  P.                                                       11-219



Bickelhaupt, R.  E.                                                   1-154



Blackwood, T.  R.                                                   IV-312



Bloomfield, D. P.                                                 III-145



Brackbill, E.  A.                                                  III-472



Brines, H.  G.                                                        1-351



Brookman, E. T.                                                    IV-274



Brown, J.  T.  (Jr. )                                                III-439



Buchanan, W. J.                                                    11-168



Burckle, J. 0.                                                   III-484



Bush, J. R.                                                        IV-154



Carlsson, B.                                                     III-260



Carr, R. C.                                                 1-35, III-270



Chang, C.  M.                                                       11-314



Chapman, R. A.                                                       1-1



Chmielewski, R.                                                      III-l



Cooper, D.  W.                                                     III-127



Cowen, S.  J.                                                       IV-424



Cowherd, C. (Jr.)                                                 IV-240



Czuchra, P. A.                                                   III-104



Darby, K.                                                             1-15



Daugherty, D.  P.                                                   IV-182
                                 616

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AUTHOR NAME                                                         PAGE



Dennis, R.                                                           1-494



Dietz, P.  W.                                                       III-429



Donovan, R. P.                                                       1-476



Drehmel, D. C.                                                      IV-170



Durham, M. D.                                                       IV-368



Dybdahl, A. W.                                                      IV-443



Ellenbecker, M. J.                                      III-171, III-190



Engelbrecht, H. L.                                                 11-279



Ensor, D.S.                                                        111-39



Ernst, M.                                                   IV-30,  IV-42



Eschbach,  E. J.                                                    11-114



Evans, J.  S.                                                       IV-252



Fasiska,  E. J.                                                     IV-486



Faulkner,  M. G.                                                    IV-508



Fedarko, W.                                                         IV-64



Ferrigan,  J. J.                                                     1-170



Finney, W. C.                                                      11-391



Furlong,  D. A.                                                      1-425



Garrett,  N. E.                                                     IV-524



Gastler,  J. H.                                                     IV-291



Gavin, J.  H.                                                       111-81



Giles, W.  B.                                                       IV-387



Gooch, J.  P.                                                        1-132



Gooding,  C. H.                                                    III-404



Grace, D.  S.                                                      III-289



Guiffre,  J. T.                                                       1-80
                                  617

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AUTHOR NAME
Hall, F.  D.                                                       .  HI-25
Hardi son, L. C.                                                    III-382
Hoenig, S.  A.                                                    •   IV-201
Hudson, J.  A.                                                        I" 263
linoya, K.                                                         III-237
Isodas T.                                                          I-H-16
Jaasund, S. A.                                                     H-452
Kalinowski, T. W.                                                ,111-363
Kallio, G.  A.                                                      III-344
Kearns, M.  T.                                                       111-61
Kelly, D. S.                                                        1-100
Kinsey, J. S.                                                       111-95
Kolber, A. R.                                                        1-22^
Ladd, K. L.                                                         1-317
Lamb', G. E.R.                                                      III-209
Lane, W. R.                                                         1-410
Langan, W. T.                                                1-117,  11-256
Larson,  R. C.                                                     I I 1-448
Leonard, G.                                                        11-146
Lipscomb,  W.  0.                                                     1-453
Malani,  S.'                                                         1-570
Marcotte,  W.  R.                                                     I-.372
Martin,  J.  R.                                                       1-591
Masuda,  S,                                          11-65,  11-334,  11-483
McCain,  J.  D.                                                       1V-496
McDonald,  J.  R.                                                     11-93
                                  618

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AUTHOR NAME                                                         PAGE
Mitchell, D.  A.                                                   III-162
Media, 0. C.                                                       11-399
Mosley, R. B.                                                        11-45
Mycock, Jr C.                                                        1-432
Neundorfer, M.                                                    11-189
Nixon, 0.                                                           1-513
Noll, q, G.                                                        11-374
Nunn, M.                                                          11-369
Ondov, J. M.                                                       IV-454
Ostop, R. L                                                         1-342
Parker,  R.                                                          IV-1
Patch, R. W.                                                       IV-136
Patterson, R. G.                                                    IV-84
Pearson, G, L.                                                      1-359
feders,en} G.  Q.                                                   III-416
Petersen, H.  H.                                                    11-352
Pilat, M. J.                                                         1-561
Pptter,  E. C.                                                       1-184
Ranade,  M. B,                                                       1-538
Raymond, R. K.                                                    11-173
Rinard,  G.                                                 11-31, IV-127
Roehr, J. D.                                                       11-208
Rolschau, D.  W.                                                   IH-251
Ruth, D.                                                  HH27, 11-441
Samuel,  E. A.                                                        II-l
Schliesser, S, P.                                                    1-56
                                  619

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AUTHOR NAME                                                         PAGE
Self, S.  A.                                                        III-309
Severance, R.  L.                                                    IV-321
Shale, C. C.                                                         1-390
Smit, W.                                                             1-297
Smith, S. B.                                                        11-502
Spafford, R.  B.                                                      1-202
Sparks, L, E.                                               11-417,  IV-411
Stenby, E. W.                                                        1-243
Stock, W. E.                                                        IV-333
Surati, H.                                                         11-469
Szabo, M. F.                                                      III-508
Tendulkar, S.  P.                                                    IV-338
Tennyson, R.  P.                                                   Ill-Ill
Tsao, K.  C.                                                          IV-14
Umberger, J.  H,                                                     11-296
VanOsdell, D.  W.                                                     11-74
VanValkenburg, E. S.                                               IV-351
Wang, J.  C.F.                                                       IV-396
Weber, E,                                                           IV-98
Wybenga, F.  A.                                                      11-242
Yung, S.                                                            IV-217
                                  620

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                                    TECHNICAL REPORT DATA
                             (Please read Imiructions on the reverse before completing)
  REPORT NO.
    EPA-600/9-80-Q39a
2.
     IERL-RTP-1061
                              3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
    Second Symposium on the Transfer and  Utilization of
    Particulate  Control Technology  (Denver,  July 1979)
    Volume I.  Control of Emissions  from Coal Fired Boilers
                              5. REPORT DATE
                                   Sept.  1980 issuing date.
                              6. PERFORMING ORGANIZATION CODE
 . AUTHOR(S)                                  '  "    '

    P.P.  Venditti,  J.A. Armstrong and Michael  Durham
                              S. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS

    Denver Research Institute
    P.O.  Box  10127
    Denver, Colorado  80210
                               10. PROGRAM ELEMENT NO.

                                  EHE624
                               11. CONTRACT/GRANT NO.

                                      R805725
 12. SPONSORING AGENCY NAME AND ADDRESS

     Industrial Environmental Research  Laboratory
     Office  of Research and Development
     U.S.  Environmental Protection Agency
              Trianplfi Park J NP   77711	
                               13. TYPE OF RE PORT AND PERIOD COVERED
                                   Proceedings:  6/79-6/80
                               14. SPONSORING AGENCY CODE
                                   EPA/600/13
 15. SUPPLEMENTARY NOTES
     IERL-RTP project officer is Dennis  C.  Drehmel,  MD-61, 919/541-2925.
     thru-044d are proceedings of the  1978  symposium.
                                             EPA-600/7-79-044a
 16. ABSTRACT
          The proceedings document  the  approximately 120 presentations at the EPA/IERL-RTP-
     sponsored symposium, attended  by nearly 800 representatives of a wide variety  of
     companies (including 17 utilities).   The keynote speech for the 4-day meeting  was  by
     EPA's Frank Princiotta.  The meeting included a plenary session on enforcement.
     Attendees were polled to determine interest areas:   most (488) were interested in
     operation and maintenance, but electrostatic precipitators (ESPs) and fabric filters
     were  a close second (422 and 418,  respectively).  Particulate scrubber interest appears
     to  be waning (288).  Major activities of attendees  were:  users, 158; manufacturers*
     184;  and R and D, 182.  Technical  presentations drawing great interest were the
     application of ESPs and baghouses  to power plants and the development of novel ESPs.
     As  important alternatives to ESPs,  baghouses were shown to have had general success
     in  controlling coal-fired power plant emissions.  When operating properly, baghouses
     can limit emissions to^5 mg/cu nm at pressure drops of^2 kPa.  Not all baghouse
     installations have been completely successful.  Both high pressure drop and bag  loss
     have  occurred (at the Harrington Station), but these problems appear to be solved.
17.
                                 KEY WORDS AND DOCUMENT ANALYSIS
                   DESCRIPTORS
                 b.lDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
     Pollution           Scrubbers
     Dust                 Flue Gases
     Aerosols
     Electrostatic Precipitators
     Filters
     Fabrics
                   Pollution Control
                   Stationary  Sources
                   Particulate
                   Baghouses
  13B
  11G
  07D
  131
  14G
  HE
07A
21B
18. DISTRIBUTION STATEMENT


    Release to Public
                 19. SECURITY CLASS (This Report)
                   Unclassified
21. NO. ijr FA
     637
                 20. SECURITY CLASS (This page)
                   Unclassified
22. PRICE
EPA Foim 2220-1 (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE
                                                               U.S. GOVERNMENT PRINTING OFFICE: 1980--657-165/Ol57
                                              621

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