Proceedings of the


            FIRST INTERNATIONAL CONFERENCE

                          ON

               FLUIDIZED BED COMBUSTION
                   Sponsored by the
    National Air Pollution Control Administration
                          at
        Hueston Woods,State Park,  Oxford, Ohio
                 November 18-22,  1968
 U. S. Department of Health,  Education, and Welfare
                Public Health Service
Consumer Protection and Environmental Health Service
   National Air Pollution Control Administration

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                   INTRODUCTORY REMARKS

                            by

                      Paul  W. Spaite
                  Robert  P.  Hangebrauck
           Process Control  Engineering Program
      National  Air Pollution Control  Administration
                 Cincinnati,  Ohio   45227
                     Presented During
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park,  Ohio
                   November 18-22, 1968

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            SUMMARY  OF NAPCA CONCERN AND  PLANS
           FOR FLUID BED 'COMBUSTION EVALUATION

                           by

            R. P.  Hangebrauck and  D. B. Henschel
            Process  Control Engineering Program
        National Air Pollution  Control Administration
                  Cincinnati, Ohio 45227
                     Presented During
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968

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                      SUMMARY OF NAPCA CONCERN AND PLANS




                     FOR FLUID BED COMBUSTION EVALUATION







Potential for Air Pollution Control




In addition to promise of achieving more compact and efficient com-




bustion systems, several features of fluid bed combustion contribute to




our interest in the process as a potential means for controlling air pollu-




tion.  Such systems offer one of the very few potential pollution control




solutions for small and intermediate industrial boilers.  Sulfur oxides




control is receiving the most attention in our program at present, and the




positive features of fluid bed combustion evident for control of S0? are




as follows:  (1) good reaction temperature for limestone/dolomite additives,




(2) excellent gas-solid contactor, (3) possibility of sufficiently long




additive residence time in bed to give good additive utilization, (A) attri-




tion of additive particles in the fluid bed may wear off unreactive shells




(for example, CaSO/) that are believed to limit limestone/dolomite utiliza-




tion when injected into conventional boilers.  Developing means for con-




trolling nitrogen oxides emission is also important, and the promising fea-




tures of fluid bed combustion system of interest here are lower combustion




temperatures than found in conventional boilers and the possibility of lower




excess air requirements.  Some promise is seen in the area of improved parti-




culate control considering that fluid beds may be operated at temperatures




that cause ash to agglomerate.  Also, the possible reduction in excess air




usage would lower the volumetric gas rates handled by dust control equip-



ment.        .   ..  -    .                                    .        .    -







NAPCA-Process Control Engineering Goals




In line with the National Air Pollution Control Administration's goal to

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                                      -2-                .    ...;._-




reduce air pollution from combustion of coal and other fossil fuels, we




have established a preliminary five-year fluid bed combustion program with




the--following goals-:    -   .'••'-"•..  -  .    " ."   •'.'':     ;  '    ....•-...




     1.  Define the potential of fluid bed combustion as a new combustion




process haying inherently lower sulfur oxides, nitrogen oxides., and parti-




culates than conventional small and intermediate industrial boilers and




power station boilers.




     2.  Demonstrate the technical and economic feasibility of fluid bed




combustion as a means of controlling pollution by designing, constructing,




and testing prototypes of small and intermediate industrial boilers.







Program to Meet Goals




During the period 1968 to 1970, we have or are planning bench-scale, pilot




design, and -evaluation studies.  We first became aware of fluid bed com-




bustion potential in 1967 in connection with an Office of Coal Research    :.




study undertaken by Pope, Evans and Robbins.  The study involved pilot-




scale studies aimed at development of a 500,000-lb/hr coal-fired package




industrial steam boiler.  In 1967 NAPCA extended the scope of Pope, Evans




and Robbins' work via an interagency transfer of funds to OCR.  This project




is entitled Characterization and Control of Air Pollutants from a Fluidized




Bed Combustor and consists of pilot and prototype module studies to deter-




mine the level of air pollutant emissions from  the high velocity fluid bed




system developed by Pope, Evans and Robbins.  The study is aimed at deter-




mination of operating and design features that  economically reduce  sulfur.




oxides and nitrogen oxides to levels well below those found in conventional




combustion systems.                                        ..._.-.

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Particular attention is being given  to evaluation and optimization  of  lime-



stone  Injection  into the fluid bed as a means  of sulfur  oxides  control.   The



"following variables are under investigation:  •-"•"-'    :          " '.    '.:'    •"-'-• .-."



     1.  Operating variables - bed temperatures, bed depth, bed composition,



excess air,  flyash recirculation.



    .2.  Fuel variables - ash, sulfur content.



     3.  Additive variables - nature of additive  (limestone and dolomite,



calcined and uncalcined), additive stoichiometric ratio,  additive particle



size,  and steam  injection.                                              ...-•-•



This work will he completed this  coming spring with the  development of a



conceptual design and  an economic evaluation of a coal^-fired  package fluid<-



bed boiler plant designed to release an economic minimum of SO  , NO ,  parti-
                                                              X    X


curates.,, and products  o.f incomplete  combustion.. Further work_will  be con-
 ducted to evaluate more  fully  the effects of coal composition,  additive com-



 position, and bed gas  velocity before prototype development will be considered



 by the National Air Pollution  Control Administration.   This study will be



 discussed more fully at  this conference by Pope, Evans and Robbins.





 To complement the work at Pope, Evans and Robbins, the National Air Pollution



 Control Administration has entered into an interagency agreement with the AEC



 for a laboratory and bench-scale project to allow exploration of wide range



 of design, operating,  and additive variables.  The work is being conducted



 at Argonne National Laboratory under the project title Reduction of Atmos-



 pheric Pollution by the  Application of Fluidized Bed Combustion.  Objectives



 for the project include:



      1.  A search for  and laboratory-scale thermo and-kinetic evaluation of- --



 potential additives suitable in fluid bed applications for the capture of S02,

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H9S, and/or NO .                                               ....
 £-            X



     2.  The testing of these additives in a coal-fired bench-scale fluid




bed combustor and evaluation of: the effects'.of" adjusting operating variables.




     3.  The investigation of various design and operating techniques in-




cluding operation of the bed at reducing conditions and pulsation of the com-




bustion air.       .            .....     .......    ..     .             	




     4.  A study of the fluid bed combustion of oil.




     5.  More detailed studies on promising systems including development of




preliminary designs for optimum systems.                         -     .




     6.  The-development of a-research and development plan .for work required




beyond the bench-scale stage leading .to the design, construction, and testing




of prototypes.                     .                   .-..-.




     7.  .Support work where required for the Pope, Evans and Robbins project.






A meeting was designed to promote cooperation.and exchange of information,




to stimulate work in the area, to define potential of fluid bed combustion,




to define barriers to commercialization, and to shorten the time and level




of effort required to obtain and apply the potential benefits.  This meeting




is  the First International Conference on Fluid Bed Combustion.              ,






Another project was recently started and is being carried out by A. M.Kinney




Inc.  The project is entitled Techno-Economic Assessment of Fluid .Bed Combustion




Process.  The study consists of an independent, critical engineering evaluation




.of  the state-of-the-art of fluid bed combustion and of the. technical and .eco-




nomic  feasibility of fluid bed coal combustion for application  in  the design




of  industrial-sized steam boilers and of power plant-sized boilers.






Finally, we  hope we will be able to participate in prototype  studies in 1971

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                                      -5-      -   -      ......







 to 1973 including design, construction, and testing of an industrial-sized




 packaged boiler with a steam capacity of 500,000 pounds per hour and deter-




 mination of its economic feasibility as a low pollution system for steam




 generation.







 Viewpoint of NAPCA




 In closing, I would like to briefly review our viewpoint.  Fluid bed com-




 bustion offers many potential advantages from the standpoint of air pollu-




 tion control.  The potential of fluid bed combustion requires further study  -




 to overcome the technical and economic barriers to commercial realization




 still  remaining.  No matter how promising fluid bed combustion may be from -•




 the air pollution control standpoint, the technique must prove to be an




 economically competitive method for generating steam arid power before it..




-can ever be accepted in practice.  We hope to see eventual scale-up of




 .fluidized bed combustors to utility size if the industrial steam unit proves




 successful.

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                       Session I

                Small Scale Development


                .Tuesday, November 19
Discussion--of bench- and pilot-scale studies designed to
characterize fluid bed combustor operation, to optimize
heat release rates and combustion efficiency, and to in-
dicate and overcome mechanical problems associated with
such combustors-.  Theoretical considerations.-

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                          OUTLINE

                   FLUIDIZED BED BOILER
                  SMALL  SCALE DEVELOPMENT

                            by

                        J.  W.  Bishop
                  Pope,  Evans and Robbins
                   Alexandria/ Virginia
                Presented During Session I
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968	       •••- 	

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                        OUTLINE                      .
                 FLUIDIZED BED BOILER
                SMALL SCALE DEVELOPMENT

1.   The object is to develop high capacity coal fired boiler

    of minimum size and cost.          -    , .    :            ;


2.   Fluidized bed combustion, where the oxidizing fluid bed

    transfers heat directly into the heating surfaces, has

    been selected to meet the pbjective,_ in view of:


    a.  High rate of direct contact heat transfer (up.to   ._

        60 Btu/0F/ft2/hr) .   _      .'_

    b.  Smaller space required for completing combustion

        (up to 400,000 Btu/ft3).


3.   Operational data and process development have been

    accomplished in rectangular water cooled columns.


4.   Boiler design parameters have been developed-on atmospheric

    pilot boiler and a single.module prototype boiler, the  .

    latter a full scale version of a multicell packaged boiler.
5.  Balancing the requirements for high output, .sufficient

    fuel residence time and fan power, heat -input: rate-is

    based on 106 Btus- per hour per ft2 of bedr


6.  Optimum bed heights' at this condition range from  2% "to  3 .ft,
                         iS A.KTO F

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 7.   Combustion air velocity range from 3 fps, cold air  to



     6 fps preheated air (at 500-600°F).





 8.   Superficial velocities at 12-15 fps with bed temperatures



     of 1700 to 2100°F.





 9.   Under these conditions, an 8 x 0 mesh, 2.4 spg inert



     bed material ( 8 x 20 after elutriation), is acceptable.
10.   The logical source of bed material is the ash  in  the  coal



     being burned.   This precludes the need for adding inert




     to makeup for attrition losses.  Excess ash  is removed,




     preferably on a classified size/density basis.  Classified



     bea removal has not yet been satisfactorily  developed.






11.   The system operates smokelessly with 5%. excess air, but



     carbon carryover is excessive.






12.   Reinjection of flyash into a bed operating at  40% excess




     air reduces carbon heat loss to within acceptable limits.




   .._..(.!%. or less)       .          ... ;.   ...-.  .•;_..   ......... ,1 l^. .......






13.   Any rank of coal is an acceptable fuel. .Coal  inventory



     within the bed while burning a high volatile bituminous




     is on the order of 2%.  With anthracite, this  inventory




     rises to 6-7%.                 	

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14.   Initial lightoff is•accomplished by oversupplying the



     bed with coal (15-20% inventory) and injecting a gas




     flame into one spot.






15.   Lightoff of adjacent beds is by means of allowing live



  .   bed from the live cell to intermingle with  cold material



     in the adjacent cell/ followed by coal  injection into




     the cold cell.                          .            .






16.   Coal feed ..is by injection Into the base of  the bed.  : In



-  .-a 2^-3 ft. .high .bed, one inj.ection point can  serve, a bed



     6' long with a maximum 50°F AT throughout  the bed.






17.   A 'b:1 turndown can  be accomplished by reduction of  air



     and coal.  The lower portion of the bed becomes static,



     impervious to coal  injection and. cold.






18.   Further turndown can be had by cutting  out cells.   Sudden



     cessation of coal and air reduces load  to  10% within




     one minute.       .






19.' Imbedded  superheaters require about a quarter of  the



     surf a-ee needed when-superheaters are placed In  an open.



     furnace or gas pass..  Overall ;heat. transfe.r coefficient




     measures  45  Btu/°F/ft2/hr.     -

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20.   The 6' long, 17~.5" wide single  cell boiler has produced



     4500 - 5000 Ibs of steam per  hour without convection



     cooling and 1600 — i700°F  exit  gas.  A 12' long, 25"



     wide cell with gases cooled to- 350 - 400°F will produce



     18,000 Ibs/hr.
              -•'l.?^?.!. ETVA.KS ".AMD .

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          COAL BURNING IN A SELF-AGGLOMERATING FLUIDIZED BED

                          -        by

                           W.  M. Goldberger
                     Battelle  Memorial  Institute
                        Columbus Laboratories
                           505 King Avenue
                        Columbus,  Ohio   43201

                      presented during  Session I
      First International Conference on Fluidized Bed Combustion
                    Hueston Woods State Park,  Ohio
                         November 18-22, 1968
                               Summary


          Bench scale and pilot plant experimental study has demonstrated

that pulverized coal can be burned efficiently in a fluidized bed with

simultaneous agglomeration of the ash within the bed.  The self-agglomerating

combustion system can produce hot gases low in fly ash for possible use

with the open cycle gas turbine.

          Factors influencing the efficiency of combustion and the ash

collecting efficiency were studied in a laboratory 4-inch ID fluidized

bed furnace and in a pilot plant furnace tapered from a 6-inch ID base

to a 12-inch ID top.  Two types of coal were used in the study: a

Pittsburgh No. 8 seam coal and a sub-bituminous coal from the Lake de

Smet, region of Wyoming.

          It was observed that collection of ash and agglomeration and

growth of ash particles in the bed occurred at temperatures as low as

1400 F.  However, ash collection efficiency was not high below 1900 F.

The ash collection rate increased rapidly above.1900 F and approached

90 percent collection under certain conditions.  Above 2100 F, the

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sticking tendency of the bed was too great to maintain stable fluidization.




Fluidization stability was also noted to be a function of fluidization




velocity, bed depth, and the size consist of the fluidized bed.




Fluidization velocities in the range of 5-7 fps were used.  A means




was developed to correlate the measured ash collection efficiencies.




          In combination with a conventional cyclone collector for




removal of any entrained coarse bed particles, the burner-cyclone




system was found to reduce dust loadings in the hot gases to less than




5 grains per 100 scf.  In comparison with other coal firing methods




considered for use with the open cycle gas turbine, only the experimental




gas producer would discharge a comparably clean gas.  In addition, the




operating flexibility of the fluidized bed method and possible use of




the sensible heat content of the bed solids are isasKBer advantages that




deserve attention in evaluating the merit of industrial application of




this method of burning coal for power generation.






                           Acknowledgement






          This research was undertaken through support of the Union




Carbide Corporation.  Patent No.  3,171,369 ^"Combustion of Carbonaceous




Solids"  .disclosing the process concept has been issued to Union Carbide.

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        A FUNDAMENTAL STUDY OF FLUIDIZED BED COMBUSTION OF COAL

                                 by

                       A.A. Oming or C.R. McCann
                         U.S. Bureau of Mines
                     Pittsburgh Coal Research Center
                        Pittsburgh, Pennsylvania

                      presented during Session I
        First International Conference on Fluidized Bed Combustion
                    Hueston Woods State Park, Ohio
                         November 18-22, 1968

     Objective of the Pittsburgh Coal Research Center fluidized

combustion project was to elucidate the properties of the fluidized

combustion process tha: govern its operation and are essential to an

evaluation of its potential usefulness.  A study was made of the -  -

thermal balances controlling temperatures within the fluidized bed.  -

It was assumed that the bed was in a steady state with the heat

liberated either absorbed directly from the bed or left remaining in

.the hot combustion productMeaving the bed.  In order for the bed to

remain in a  steady state, the flow of combustion products must be in

balance with the input flows of coal and air and the heat released

in the bed must appear either in gas leaving the bed or be trans-

ferred to sink within the bed.

     The rate of burning, at otherwise constant conditions, depends

upon the amount of fuel  in  the bed.  Increased fuel in the bed tends

to increase  the rate of  burning; decreased fuel in the bed decreases

the rate of  burning, so  that the amount of fuel in the bed automatically

 tends  to move towards that  needed  for a steady state condition.

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     The bulk volume of fuel needed to keep the steady state burning




rate equal to the coal feed rate may be less than an adequate bed




volume.  This volume must be adequate for proper fluidization and to




give sufficient coverage of heat sink surfaces to provide the desired




heat transfer.  A refractory grog, a crushed and double screened inert




solid, may be used as needed to fill the bed to the desired volume.




If temperatures are too low, the volume needed for fuel alone to




maintain a steady state may exceed the available space.  The coal feed




rate then becomes a dependent variable which must be adjusted as needed




to maintain the bed volume within the available space.




     Operation of the fluidized bed with excess air requires either




a low temperature so that the rate of burning is too low for complete




use of all the air supplied or a limited amount of fuel in the bed so




as to give the same result at higher bed temperatures.  The latter




condition might involve either almost instantaneous burning of the




fuel as it enters the bed or rapid burning of volatile matter with




slower burning of coke so that some residual fuel can remain in the




bed with excess air at higher temperatures.




     As the fuel air ratio is increased into the deficient air range,




the behavior must change.  In order to burn more coal with the fixed




air supply, H2 and CO must appear.  The percentage of H2 plus CO




increases with increase in the fuel-air ratio in the deficient air

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range.  Rates of the reaction producing CO and H£ are slow as  compared




to the rates of burning to C0£ and H20.  The production of CO  and H£




will be controlled by temperature and the amount and kind of fuel in




the bed.  The required amount of fuel may give an adequate bed volume




without use of the refractory grog.




     Calculated thermal balances showed that, as the fuel-air  ratio is




increased at constant air flow, the amount of heat that must be trans-




ferred to sink in order to maintain constant temperature, passes




through a maximum.  Conversely, an increase in fuel-air ratio  under




constant heat sink conditions will increase the bed temperature in the




excess air range and decrease the temperature in the deficient air




range.- v"	   ...    	   .



     Experimental work was conducted in a water cooled reactor, 17" I.D.




with 6 to 12" beds of coal and crushed refractory brick.  Experimental




results were generally in accord with the results of the thermal balance




calculations.  The bed temperature increases and oxygen in the flue gas




decreases with increased fuel rate in the excess air range. Work in




the deficient air range was limited to an experiment for measurement




of heat transfer rates but an opposite mode of operation was indicated.

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     Heat transfer coefficients  of 35 and 96 Btu per  hr.,  sq.  ft.,  °F




were observed depending on particle size, the fine size giving the




high coefficient*  Heat release  rates over 8000,000 Btu per hr.,




cu. ft. of bed volume were observed at one "percent excess  air  and'




1750°F bed temperature.




     Full development of the advantages will require  additional and




better information in several areas.  Loss of combustibles in  solids




carryover from the bed should be minimized.   It is probable  that




operation at higher bed temperatures would reduce the loss but this




should be verified.  The fluidized bed can be used as an ash




agglomerator.  This requires good control of temperature and develop-




ment of means for continuous extraction of solids from the bed with




size classification and return of fine material.  Control of bed




temperature requires control of the portion of the heat release that




is absorbed directly from the bed.  This is roughly controlled by




equipment design.  Fine control might be obtained by changing  the bed




volume so as to vary the amount of heat transfer surface in  contact




with the fluidized bed.




     There is much yet to be done, but fluidized bed combustion of coal




has attractive features that may make this the next major development




in fuels technology.

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                 PROCESS DEVELOPMENT IN FLUID-BED COMBUSTION
                                     bv
                               Paul S.  Lewis
                            U.S.  Bureau of Mines
                          Morgantown, West Virginia

             Presented during Session I, Small Scale Development
         First International Conference on Fluidized Bed Combustion
                        Hueston Woods State Park, Ohio
                            November 18-22, 1968
                                INTRODUCTION  	

     Fluid-bed combustion has potentialities for reducing the cost

oC sLeain ^euerat-ion because low grade coals and coal chars can be burned

and boiler designs could be simplified.  Because combustion temperatures

are in the range 1,400° to 1,800°F, boiler tube corrosion and fireside ash

deposition should be less extensive than experienced with high temperature

combustion; boiler costs may be reduced as a radiant heat section would

not be required and less costly construction materials would be required.

Emission of air pollutants may be reduced because smaller quantities of

nitrogen oxides are produced at the lower combustion temperatures.

     This paper describes the results obtained thus far in a,continuing

pilot study to obtain data for the design and evaluation of a conceptual

process.

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                              EXPERIMENTAL WORK




                          Description of Apparatus




     The conbustor, figure 1, consists of a steel shell .lined with insulating




brick which is faced with castable refractory.  Inside diameter is two




feet and the length is six feet.  The fuel bed is supported on a conical




shaoed plate perforated by 1/2-inch diam holes through which the fluidizing




air is introduced.  Additional fluidizing air is admitted through tuyeres.  ..




Two heat exchangers made of 3/4-inch pipe are located 15 inches and




A3 inches above the air distributor.                .  .  .. .            	-




     The flow diagram of the system, figure 2, shows that the coal feed




is mixed with recycled bed material and injected into the base of the




fuel bed,  .The residue is removed at the apex of the conical bed support




by a screw conveyor.  Products of combustion pass through two stages of




centrifugal separation where most of the entrained solids are removed




and returned to the combustion zone.




     Startup is accomplished by burning natural gas in the combustor and




in-|ecting coal into the combustion chamber.  After a bed of about one




to two feet is established at temperatures of about 1,200°F, the natural




gas is shut off.   Establishing the bed requires about two hours.  Coal




feed is  continued  at  a high rate until the desired bed level is attained




and then regulated  to maintain bed conditions .compatible with the particular




superficial air velocity.

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                          Combustion of Anthracite
     Initial operations for developing a reliable system and operating

procedures occurred in 1967 using a feed of anthracite passed through

a 3/64-inch round hole screen (76.7% FC, 6.3% VM, 9.0% ash, 8.0% moisture)

Results are shown below.      .    . .      .  .       ......      .


            Table 1. - Combustion of Anthracite, 3-foot bed depth
Duration, hr
Bed temp. , °F
Sup. vel. , ft /sec
P.O.C. analysis, %:
  CO
  CO   ......
Burning rate
Air/coal ratio, scf/lb
Percent carbon in
72
1,505
1.41
5.2
16.4
0.0
38.3
110.0
60-68
(63)
45-57
(52)
35-42
(39)
21
1,509
1.94
6.1
15.3
0.0
53.4
109.0
54-77
(67)
49-58
(54)
40-54)
(50)
75
1,540 '
1.77
4.6
15.9 -
N.D.
42.7 -
122.0
61-80
(72)
53-68
(62)
53-84
(66)
59
1,517
2.27
5.6
..-. 15.8
0.1
51.8
132.0
51-78
(67)
51-64
(58)
56-70
(63)
   Bottom, rain. -max.
     (avg.)
   Cyclone 1, min.-max.
     (avg.)
   Cyclone 2, min.-max.
     (avg.)
^Carbon loss from stack not accounted  for.


     The only operating difficulty  experienced with anthracite  was  some

clinker formation that occurred when bed  temperatures  exceeded  2,200°F.

Feeds  of bituminous coal, even a weekly caking coal, could  not  be introduced

directly into the fuel bed because  it  always  agglomerated before becoming

mixed  with  the noncaking  inventory  in  the bed.  However,  even a strongly

caking coal, such as Pittsburgh seam,  could be burned  without agglomer-

ating  in the bed provided it  was mixed with the recycled  bed material,

as  described above..

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                            Heat Transfer Results




     Heat transfer .coefficients have been determined  for  two  modes




of  fluid-bed combustion.  In one,  the  coal  is  injected  into a bed of




noncombustible material called "grog";  consequently,  carbon content  of




the bed  is  low.  In  the second, an inventory of  noncaking coal char




is  maintained in the bed, and raw  coal is added  continuously; in this




case, a  high carbon  inventory exists.




     Before the tests using low-carbon bed  could be made, a suitable grog




for the  bed had to be found.  Several  materials  were  tried, including




sintered" fly ash, sintered ash from a  chain-grate  stoker, and sand,  but




none of  them worked  well.  Crushed mullite  (A120_  + Si02), -8 + 20 mesh




sieve size  was found to be satisfactory except that loss  by attrition




'was considerable.	       .-.  .      ...„_.      -	 ...




     Water  flow rate through  the  exchangers was  varied  for each test.




Overall  coefficients were  calculated directly  from heat transfer data




by  the relation Q =  UoA0At, where                                      ...




          0 = heat removed, Btu per hour




          Uo = overall heat-transfer coefficient  based on outside area




              of pipe,  Btu/hr~ft2-°F




          Ao = outside area of pipe, ft




          At = average temperature  difference  from  water to fluid bed,  °F.




     A series of tests  was made with a low  carbon  inventory in the




bed. A  mixture of 100  pounds of  anthractie (#5 Buckwheat) and 100




pounds of mullite was used to start the bed.   Then,  a mixture of 200 pounds




of  hvab  coal, Pittsburgh  seam,  (-1/4  inch)  and 100 pounds of  mullite




was added.  Thereafter,  only  bituminous coal  was added.

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     Overall coefficients for the first test series were only 25 to 30

litu/hr-ft--°F,  which was lower than expected, probably because the heat

exchanger was not completely immersed in the bed.  In subsequent tests

with a deeper bed, coefficients were higher, ranging from 42 to 58

Br.u/hr-ft2-°F.   In the latter tests, a 100% minus 14-mesh mullite was used

and superficial gas velocities were somewhat lower (4 instead of 6 ft/sec)

than in the earlier tests.  Coal rates ranged between 70 and 90 lb/hr.  These

results are shown below.


Overall heat-transfer coefficients with a 2-ft bed of mullite and hvab
coal bed velocity 4.0 ft/sec

Bed
temp,
°F
1782
1786
1796
1802
1803
1550

Water
rate,
lb/hr
1368
1959
1093
1246
1783
1908
Lower
Water
temp ,
T r>
72.0
70.7
70.7
70.9
69.9
66.6
tube

0 F
Out
106.0
97.5
111.4
107.0
97.0
91.4

Uo
Btu/hr
ft2-°F
50
56
47
48
51
58

Water
rate
lb/hr
1431
1881
1030
1238
1766
1908
Upper
Water
temp,
In
69.0
68.7
68.5
68.0
69.9
66.0
tube

°F
Out
94.0
88.0
103.0
98.3
89.0
85.0

Uo
Btu/hr-
ft2-°F
38
38
38
40
35
45
         Values for heat-transfer coefficients for beds containing a high  carbon

inventory were obtained using a 3-ft bed of anthracite.  These values are  shown

below.
Overall heat-transfer coefficients with a 3-ft bed of anthracite  (no grog)
Bed
temp,
1617
1485
1450
1405
 Bed
 vel,
ft/sec
 1.5
 1.5
  .75
  .75

Water
rate
lb/hr
1299
2016
583
1225
Lower
Water
temp,
In
75.6
75.8
75.9
74.0
tube

°F
Out
97.3
88.6
107.2
93.6

Uo
Btu/hr-
ft2-°F
33
33
24
33
1252
1966
 750
1241
                                                        Upper  tube
Water
rate,
lb/hr
Water
temp,
In

°F
Out
Uo
Btu/hr-
ft2-°F
73.9
74.1
74.0
72.5
87.2
82.2
95.0
84.8
20
20
21
21

-------
                                      6




                                 CONCLUSIONS




     Results thus far have demonstrated that a wide range of coal can be




burned in a fluidized bed.  Improvements in the experimental system are




needed to eliminate dust losses through entrainment in the stack gas.




Bag filters have not been satisfactory, and a scrubber of water screen




design has been installed.  Gas analyzers giving continuous recording of




CO, C02 and 02 have been installed.   The diameter of the fuel bed has been




reduced to 18 inches from 24 inches,  making it possible to reduce the amount




of air neec?e
-------
                                               P.O.C.
CO
10
 I
                   Castable insulating
                   refractory
                                                          Port for
                                                          thermocouples
u - inch
carbon steel
         Insulat i ng
         f i rebri ck
         Castable
         refractory
            Thermocoupl e
            Water
     Thermocouple
            Water
      Thermocouple
        Igniter port
                                            Heat exchangers,
                                               - s.s. pipe
                                                             Ai r  distributor,
                                                             316  s.s.
             Thermocouple
   Sight
   glass
                           Air
                              Natural gas
                                                                       Coal 4- Ai r
                                                  Ash

                                                Fliud-Bed  Combustor.

-------
CO
«5
 I
   Ai r  to  tuyeres-
    Air



Natural  gas


  Inert  gas
                            Combustor
                           \
                             \
                                                                          P.O.C.
                                                                          1
                                                                 Cyclone
                                            Coal and Char
                                                                    Sampl e
                                                                                Coal

                                                                               hopper
                                                                2-inch screw
                                                             f\/\/\/\/\/\/\/\/\/
                                                                         Coal
                                                                     Air
                     3-inch  screw
                                         M
                                   Flowsheet Ho.  2 for Fluid-Bed Combustor

-------
        GRID PLATE DESIGN FOR PARTIAL CHAR COMBUSTION

                                   by

                             Martin E. Sacks
                            FMC Corporation
                          Princeton, New Jersey

                        presented during Session I
        First International Conference on Fluidized Bed Combustion
                     Hueston Woods State Park,  Ohio
                          November 18-22, 1968


         FMC Corporation has studied the partial combustion of coal char

as part of the COED process, an acronym for Char Oil Energy Development,

sponsored by the Office of Coal Research.  The COED process produces a

synthetic crude oil,  hydrogen or high Btu gas, and char by the pyrolysis of

co?l'in four or more fluidized beds in series.  Char is  combusted with oxygen

in the  last stage to provide heat for the process.  This  paper reviews grid

designs used in the last stage of pyrolysis.

         To give  a saleable product gas,  it is desirable to fluidize  the last

stage with pure oxygen.  For process heat balance the operating temperature

is 1600 °F.  To date, it has not been possible to fluidize with pure oxygen in

FMC's 100 Ib. per hour Process Development Unit in Princeton, New Jersey,

because of the formation of ash clinkers  in the last stage.  These clinkers

probably occur because of poor fluidization in the area  of the grid.  This

results in local overheating of char particles to above their  ash fusion

temperature.

-------
         Five different grid plate designs were used in the 8-inch diameter





last stage vessel of the Process Development Unit.  The first design employed




seven, 1/4 inch tubes embedded in a refractory.  This design quickly proved




inoperable.   The second design consisted of an approximately 3.5 inch diameter




multi-orifice plate connected to the 8-inch diameter vessel by a conical




transition piece.  This design proved unsatisfactory because of the formation




of clinkers on the walls of the conical transition piece.  The third design was




a 7-3/8 inch diameter multi-orifice plate.  This plate has been used for the




bulk of the experimental work conducted at Princeton.   Clinker formation





has been minimized with most coals,  but it has not been possible to operate




with pure oxygen.  To attain the desired fluidizing velocity at the grid, streams





containing 80 to 90 percent nitrogen must be employed.   Design 4 was a 7-3/8




inch diameter porous plate made from sintered stainless  steel.  Design 5 was





a cap distributor plate. The caps were supplied by Pope,  Evans and Robbins.




         Designs 3, 4 and 5 were evaluated under comparable operating




conditions.   Fluidizing velocities and grid plate  designs were varied from




run to run.   After  24 hours of operation,  clinker formation in the last stage




was  observed for each combination of variables.




         At a fluidizing velocity of 1.1 ft.  per sec., approximately four times-




the minimum fluidizing velocity,  clinker formations were observed with all




three designs.  The multi-orifice plate, .design 3,  gave the smallest clinker




buildup.  However, the clinker was hard and  unevenly distributed across  the

-------
plate.  Clinker formations with the porous plate and capped plate were ap-




proximately the same thickness.   The clinker formed when the porous plate,




design 4,  was used,  was soft,  friable and evenly distributed over the cross-





sectional  area of the fluidized bed.  The clinker formed when employing the




cap-type plate,  design 5,  was soft and friable, but unevenly distributed across -





the cross-section of the bed.  At a fluidizing velocity of 1. 8 ft. per sec.,  about




six times the minimum fluidizing  velocity,  negligible clinker build ups were




noted with all three grids.  The pressure drop across the grid was greatest




for the multi-orifice plate,  about  three times greater than  for the porous




plate and  about  six times  greater  than for the capped distributor plate.




         In fluidized beds, regions of high bed density had been reported to




exist near tne grid,  indicating a poor quality of fluidization.  Some investigators ..





have reported that the height of this high density region is maximized by the




use  of cap distributors and minimized by the use of porous plates.  Clinker




formation at 1. 1 ft.  per sec.  indicates that  the quality of fluidization near





the grid of the last  stage of pyrolysis is best with the multi-orifice grid.




This confirms the literature reports that a  cap-type grid results in a large,





high density region in the vicinity of the grid.




         It was  concluded that in this system a high pressure drop distributor





is required to maintain a good quality of fluidization in the vicinity of the grid.




It appears that the turbulence caused by a high pressure drop-type grid  is




more beneficial to a good quality  of fluidization than even distribution of the

-------
gas.  It also appears  that velocities greater than six times the minimum





fluidizing velocity should be employed to minimize clinker formation.





         At the present time a 36 ton  per day COED pilot plant is being





designed.  The last stage vessel of the pilot plant will be a two diameter





vessel.  In this way it is hoped to maintain a fluidizing velocity at the-grid





greater than six times the minimum fluidizing velocity employing pure





oxygen.

-------
          COMBUSTION EFFICIENCY AND HEAT TRAHSFER STUDIES
      	     by	
                          D.  F. Williams
                        National  Coal  Board
                    Coal Research Establishment
                   Stoke Orchard, Glos., England
                     Presented during  Session  I
     First International Conference on Fluidised Bed Combustion
                  Hueston Woods,  State Park, Ohio
                        November  18-22, 1968
        The National Coal Board is interested in the  development  of
fluidised combustion primarily for large scale power  generation.
Accordingly our initial bench-scale work was concerned with combustion
efficiency, as a high level of efficiency is required.  In this work
an unwashed coal containing 25$ of ash was used as feed, as the ash
particles then form the fluidised bed.

        Combustion was carried out in a 6 inch diameter bed.  The
fluidising air was distributed by a low pressure drop perforated
plate base covered with refractory pebbles.  A low-rank coal crushed
to minus 1/16 inch was fed pneumatically just above the base, and
the heat produced was removed by a water-cooled coil  in the bed.
Temperature control to - 2°C was achieved by this means.  The bed
height was determined by pressure probes, and was automatically held
constant by running off surplus ash through the base.  The gas
leaving the coabustor was dedusted by two cyclones in series, with the
facility for recycling the primary cyclone fines to the bed if
desired.

-------
                             - 2
        Over the rnn^s or aonrjT+.nor»« Investigated the only
combustible gas present above the bed vas carbon monoxide.  Its
concentration at TOO C with a fluidising velocity of 2 ft/sec
and with 2% of excess air was 0.7$, and at 800°C the concentration
was less than 0.1$.  Loss of unburnt carbon from the bed occurred
almost entirely by elutriation.  The loss was reduced fron 6.5$
by weight to 0.15$ by recycling primary fines to the bed.  Thus
at 800°C» fluidising at 2 ft/sec with fines recycle, the total
combustibles loss was equivalent to only 0.5$ carbon.  Further
experiments were carried out under these conditions.  When the
proportion of excess air was lowered below  20$, the loss of
combustibles did not increase markedly until stoichiometric
conditions were reached, the CO concentration then increasing to
l.U$.  A change in bed height between 1 ft and 3 ft had no effect
on the loss of CO and carbon:  neither did a change from a low-
rank coal to a Pittsburgh coking coal, although anthracite was much
less reactive.
        The bed ash contained less than 0.1$ carbon, and its
fluidised density was 35 Ib/cu.ft.  Little degradation of the ash
took place, and there was no difficulty in maintaining bed height
with the coals of 15 to 25$ ash content that were tested.  No
sintering or caking occurred, even with the highly swelling
Pittsburgh coal, and coal could be fed through the base without
difficulty.  It was also shown that bed temperature could be main-
tained constant by automatic control of coal feed rate when the coal
feed varied widely in ash content.
        Eeat transfer coefficients were measured in a 1 ft square
section combustor, between the bed of minus l/l6 inch particles and
a horizontal tube immersed in it.  Coefficients between 80 and 100
B.t.u./ft'li F were measured, depending upon whether the tube was

-------
cooled with water or air.   This  result agrees well with predictions
made froa literature data.   It indicates  that a large saving in
the cost of" high pressure steam  tubing can be made by immersing
the tubes in the bed.
         Experiments have also been carried  out in cold beds of  ash.
The elutriation rate of particles was measured  as a  function of
fluidising velocity, particle terminal velocity and  the concentration
of the particles in the bed.  In other experiments the elutriated
particles were recycled to  the bed and the recycle rate was measured
when it had reached a steady value.  The  results  followed the  same
relationships as had been  found  for the elutriation  rate. The mean
residence tine of the fines per  cycle, in a  bed fluidised at 2 ft/sec,
was found to be between 1  and U  minutes.
         In a 3 ft square bed, heat transfer coefficients were
measured between a fluidised bed of ash and  lj  inch  o.d.  tubes
arranged horizontally in a triangular pattern.  Hot  water was  passed
through the tubes and the  bed was fluidised  with  cold air. The
results shoved that increasing the fluidising velocity fron 2  to
U ft/sec increased the coefficient by 10$, and  increasing the  tube
spacing fron 2.5 inch to 10 inch increased the  coefficient by  25$.
Higher coefficients were measured when the tube bundle was near  the
top of the bed.  Changing the maximum particle  size  from minus l/l6
inch to minus 1/8 inch and recycling fines to the bed did not  affect
the coefficient significantly.
         A 5 ft dianeter vessel has also been constructed to neasure
the rate at which particles move laterally through a fluidised bed.
This will give information about the distance between coal feed
points in a wide bed.  With this equipnent it will also be possible
to study the air distribution achieved with different designs  of base.

-------
         Construction of a 3 ft square combustor is nearing
cosipletion.  It will be possible in this coiabustor to measure
coabustion efficiency,.after-burning, and beat transfer coeffic-
ients, end to acquire distribution data over a vide range of
fluidising velocities and particle sizes.  Cooling tubes can be
accommodated at different orientations and at different tube
temperatures;  alternative fluidising bases can be fitted and
the freeboard height can be altered.  It will also be possible to
operate vith or without fines recycle.

-------
 Pilot  Scale Studies of High Intensity Combustion
               in Fluidised  Beds.
     .by

                  S.J.  Wright

           BCUKA Industrial Laboratories
             Leatherhead, Surrey, England


             Presented, during  Session I

First International Conference on Fiuidised. Bed Coabustion

          Eueston Woods, State Park,  Ohio,

            . November 18  - 22,  1968.

-------
        Gas-solid fluidised beds have two major attributes, both arising



from the rapid agitation and nixing of a relatively dense particle phase;



there are high heat and. mass transfer rates-between the gas and the solids



and there are relatively high heat transfer rates "between, the bed and surfaces


            . -.  1.2:
m aAQ arounu j.~if
        Interest in the use of fluidised beds for the combustion of solid



fuels has been prevalent, mainly on the continent of Europe, for about



fifteen years.  The research and development effort has been largely directed



towards efficient release of the heat from various forms of solid fuel, such



as anthracite fines  , lignites '"^ , oil shale   and coal v/ashery tailings °,



which were almost incombustible by conventional methods.  I-iich of this work



has been successful, resulting in at least one commercial fluidised-bed stean-



bciler system J,   The basic approach of almost all investigators to the problem



of heat recovery has, however, been conventional in that they sought to heat



the combustion, gases to the highest obtainable temperature and to recover this



heat by passing the gases through conventional water-tube boiler systems.  That is,



they utilised only the property of high heat and mass transfer rates between



gases and particles in fluidised beds to release heat from otherwise intractable



solid fuels.-  It was found that,  for fuels having a combustible content in excess

-------
of about 35/->, c O.T. oust ion was so rapid that the equilibrium bod temperature



was in excess of the melting point of the ash .  Generally this feature has



oscn exploited by allowing agglomerated ash to accumulate at the bottom of



the bed, whence it can be conveniently extracted.






        V.'ith one exception, no attempt was made to utilise the other major



property of fluidised beds, the relatively high heat transfer rates between



the bed and surfaces in and around it.  This was because the maintenance



of cooling surfaces in a fluidised bed containing molten ash is an almost



insurmountable problem and also because the basic approach to steam raising



was conventional.  The exception was a specialised application where the



oil in oil shale provided heat not only for stean raising but also to

                                                                ..

calcine the shale for cement manufacture  .  JTomally the combustible content



of the shale was too low for the equilibrium temperature of the insulated



bed to exceed the softening point of the shale but, in cases where this was .  .



not so, cooling tubes were inserted to keep the temperature down and relatively



high heat transfer rates were obtained,


                                              *



        In 1964 the-SCUBA inaugurated a literature survey of fluidised


               9
bed combustion  , in order to assess the potential of this method of burning



coal for increasing combustion intensities in industrial shell boilers in the



steam rate range 2,500 to 18,000 kg/h.  It was concluded that it should be



possible to use the fluidised bed not only for combustion,  but also as the



primary heat exchanger by utilising the good. hea> transfer properties of



fluidised beds, thus making possible both a high heat release rate and an increasec



ho&t transfer efficiency as compared with conventional shell-boiler firing



systems.  The result should be a smaller boiler,  with a lower maximum combustion



temperature for a given steam rate, and the sane overall efficiency as a



conventional shell boiler.  •  •           -

-------
       Parallel to the BCURA work, the CB3B has pursued ctudies of



conbustion in cooled fluidised beds,, in order to apply the principle to



water-tube boilers for power generation.  This has led to a major effort



towards this application now being carried out by the National Coal Board.



Work is also proceeding at BCURA. on the use of pressurised fluidised beds



for the power generation application.






2.   Small Scale Ex
       Apart from the fact that heat-transfer coefficients at surfaces



within fluidised beds were considerably higher than at surfaces  in a gas



stream alone, there was no information in the literaturerelevant to fluidised



conbustion beds heavily cooled by surfaces inserted within them.  Therefore,



a series of saall scale experiments was initiated in the BCURA   ,  in an open



topped combustor 305 cm in diameter with a fluidised bed 305 cm  deep, to obtain



sufficient data whereby a pilot-scale apparatus could be designed for a thorough



investigation of the characteristics of fluidised conbustion beds burning



British coals.  It was found that, if a fluidised bed of coal was heated to



combustion temperatures in the presence of near-stoichiometric quantities of  air,



the combustion rate was so rapid that the bed temperature could  not be controlled



below the ash softening point;  extensive agglomeration and sometimes complete



solidification was unavoidable.  It was known   that the bed temperature could be



controlled by limiting the oxygen supply to the bed but that this resulted



in high carbon monoxide concentrations in the flue gases,  since  the fluidised



bed then behaved as a gasifier and this did not seem a useful way to control



a combustion appliance.  Research on static combustion beds has  shown that



the final formation of CO is due mainly to the reduction of C0?  in the



presence of carbon, and, therefore, any reduction in the carbon  content of



the bed may be expected to suppress the formation of CO.   That this would be  so



in fluidised combustion beds was suggested by the fact that those fluidised



combustion systems using a fuel having a very high ash content could maintain



bed .temperatures below the ash softening point whilst using etiochiometric or. ....!.

-------
 greater air rates without excessive CO formation •*'  .   Attempts to control the

 co-buc-oion of e fluidised bed  of coal only were abandoned,  therefore, in favour

 of an attempt to control the combustion of coal in a fluidised bed of inert

 _„ j. - „„• « -i
 Eci werj.&i.   .                                                   .



       This fluidised  bed consisted of crushed refractory sized 5.?. mm -

 0.8 re; and it v:as found  that,  once this bed was heated  to coabustion temperature,

 the combustion of coal in it was very rapid allowing heat release rates in excess
             p
 of 5.15" iv-'/m  (based on  distributor area) compared with the maximum for a
                                           o
 chain grate fired shell  boiler of 1.9 I'^/m  (based on grate area).  The heat
•v-

 capacity of the inert  bed and  the fact that the carbon  content of the bed

 at any  instant was only  froa 5fi ^° 10/o    allowed the bulk  bed temperature to

 be maintained between  800°C and 900°C, by extracting up to  50?o of the heat

 release  directly from  the fluidised bed.       -       .                   .



       The results from  the small-scale experiments  were utilised to

 cesi^Ti a more completely instrumented pilot-scale coabustor capable of heat

                             p
 release  rates up to 3.S"Iv2''/m ,  equivalent to the heat release rate of the  .

 smallest shell boiler  envisaged.  The plant is shown diagramaatically in Fig. 1.

 This  apparatus was commissioned in July, 1966 and considerable information has-

 since been amassed on  the coabustion and heat transfer  characteristics of      \

 fluidised  beds over a  wide range of conditions.



 5.   Ccrr.bustion



      .  Experiments have  been conducted burning four  different coals, one

 washed and three untreated,  whose main characteristics are  shown in Table 1.

-------
                      TABLE 1.   COAL ANALYSES

                          AS FIRED BASIS
•
C.R.C. No.
Moisture . %
Volatile Matter c/a
Fixed Carbon f*
Ash °fa
Chlorine Content %
Calorific Value kJ'kg
Ash Deformation OG
Temperature
B.S. crucible
swelling iTo.
w
Size analysis
i— i
6.4 - 3.2
3.2 - 1.6
1.6 - 0.8
0.3 - 0.5 ' -
0.5 - 0.2
- 0.2
i
WASHED
902
30.8
51.7
1Q. 9

'26,900
.,. 1290
1 .
.


17.4
25.3
24.1
.8.7
16.1
8.4
J
t
\ 701/801
! 3.9
28,4 ,
47.2
20.5
••
25,400 "
1250
3 -&'


18.0
24.6 •
23.8
9.0
12.8
11.8
UNTREATED
900
5.4
26.4. .;
45.7
22.5
0.8
23,600
1190
i-1 -


26.3
24.0
17.4
8.9
9.0
14.4
'
i
.
' 900
11.3 -
. 25..2
43.0
20.5
0.8 .
i
22,600
1250
.1


28.2
18.9
19.1
9.1 .
• 11.6
13.1
      All coals were sized 6.4 mm to zero,  as this appears to be about the

limiting size range which can be supplied without recourse to crushing on site.
                                 •
When the washed coal was being used the fluidised bed consisted of particles

of previously prepared crushed refractory sized 3«2 - 0.5 QQ.  The movement of

the fluidised bed caused continuous attrition and elutriation of the refractory,

requiring periodic additions of fresh refractory to maintain a constant bed depth,

since little of the coal ash remained in the bed.  When burning untreated coal,

however, the shale in the coal supply was more than adequate to replace any losses

-------
 due to  attrition and  the bed depth was controlled "by continuous drainage over one

 or other of the weirs.  The fluidised bed, under these circumstances, consisting

 of shale particles  sized 6.4 - 0.5 mm.


      The range of  combustion conditions investigated is shown in Table 2. •



•  •  •    .        '    TABLE 2.   RAJTGE OF COMBffSTION" CONDITIONS
Bed depth
Mean bed temperature
Heat input rate
i Excess air
,
Percentage of solids
cyclone recycled
mm
°C
. 305
GOO
M//m2 1 • 1.26
»
*
from
zero
•
zero
- 610
- 900
- 5.76
- 90£
-~80#-*
              The figures ^efer to the setting of a flap valve below
              the cyclone outlet.  The percentage division of the
              solics stream was affected to some extent by the flow
              pattern out of the cyclone which was in turn affected
              by gas and solids loading.  Therefore, the figures
              are indicative only.
      It was found that increasing the bed depth, from 305 to 610 mm,

not only decreased the heat lost from the combustor as carbon.monoxide and

elutriated carbon but also increased the proportion of the heat release

occurring within the bed.  Therefore, except for early experiments using the

washed coal, the bed depths were always between 450 - 610 on.  If the coal feed

was stopped the bed temperature began to fall steeply within 15 seconds,  .

indicating a combustible content of less than 5$ i& a "bed weighing approximately

135 '*g.  Samples taken from the operating bed, which, could not be rapidly quenched,

contained less than 2$ combustible matter and material drained over the weirs

had a negligible combustible content.               .          •           .

-------
      The mean bed temperature was usually controlled between 870 C and

900 C, above which the bed was liable to sinter.  This suggests that the

temperature of some particles in the bed is considerably in excess of the

mean temperature.  The bed temperature was kept as high'as possible to

obtain iraxicua conbustion rate and hence maximum combustion efficiency,

particularly for the smaller coal particles which are rapidly elutriated from

the bed.                                               .         . .            .


      With.the combustor operating at around its maximum  designed heat

input (5.15 KV/in ) a bed temperature of 870°C could be maintained with 10

to 20 percent excess air.  If, when burning untreated coals sized 6.4 ram - 0,

the heat (coal) input was reduced and the air rate reduced, in an attempt to

maintain constant excess air, the larger shale particles  began to settle

out progressively at the base of the bed as the fluidising velocity fell.  This

settling out reduced the heat-transfer efficiency of the  lower part of

the bed and the amount of heat being extracted from the bed fell faster than

the heat input, resulting in a tendency for the bed temperature to rise.  The

bed temperature was controlled between 870 C and 900 C by increasing the excess

air as the heat input was reduced.  Thus, at the lowest heat input investigated
          2
(1.26 Jv//m ),  the excess air percentage was between 80 and 90.


      The temperature of the fluidised bed responded very rapidly to any

change in the coal feed rate, owing to the low combustible content of the bed-

at any instant, and also to any change in fluidising air  rate, owing to the

high rates of heat exchange between fi^s and particles. Control was normally

obtained by adjusting the rate of air supplied,  to accommodate any changes in the

quality of the coal being fed at a fixed rate.


      It was found that the carbon monoxide content of the flue gases
                                                at
610 mm above above the bed surface was about l^/stoichiometric combustion

conditions,.falling below 0.5/tf, for 20 percent excess air  and falling below

0.2$6 for greater than 50 percent excess air.  The carbon  monoxide.level "•

-------
appeared unaffected by the combustion rate end vertical tranverses approaching



the bed surface detected only slight changes in flue gas composition,



suggesting that only a small proportion of the heat release was occurring above



the fluidised bed.






      The heat lost as carbon monoxide vas always less than 1$ of the



heat supplied and the major combustible loss was as solid carbon elutriated



from the fluidised bed.  If none of the solids trapped by the cyclone  were



recycled to the combustion bed then the heat lost as elutriated carbon could



be &s high as 25$ of the heat supplied.  However, when between 50$ and 80$



of the solids were recycled, via the coal feed, such losses were substantially



reduced.   '                  .                         .       .






      Fig. 2 shows, for the untreated coals, the heat lost as elutriated



carbon, expressed as a percentage of the heat supplied,  plotted against the



coal feed rate and the superficial fluidising velocity;  the data points are



differentiated according to excess air percentage, coal  swelling number and



the proportion of solids recycled.  Each data point represents an average over



at least one hour arid more usually two hours of operations,  the longest



continuous test to date being of 30 hours duration.  It  can be seen that  the



loss increases with both coal feed, rate and superficial  fluidising velocity



but that any decrease caused by increasing excess air is slight.  Increasing



the proportion of solids recycled from 50$ to 80$ had only marginal effects.



The nediun swelling coals give higher losses owing to an increased combustible



content of the elutriated solids.






      Although the data were widely scattered,  the heat  lost as elutriated



carbon increased from about 5$ to 12.5$ up the range of  heat inputs, which



compares with 1-^$ to 3$ over an equivalent proportion of the heat input range



in a chain grate fired shell boiler.  The minimum, excess air percentage of 25$



to 30$ required for & chain grate compares with 10$ to 20$ in a fluidised-bed.

-------
The. method  of recycling elutriated solids via the coal feed system in



the present experiments is not ideal as  the more reactive fresh coal is



likely preferentially to absorb the available oxygen.  If solids wore to be



recycled  separately a reduction in the combustible loss might be expected.



Chemical  analysis  of the elutriated solids according to size fraction showed



that  if all elutriated solids sized greater than J6 micron were recycled



to the coabustor,  smaller particles being caught by a secondary Collector,



then  the  heat lost as elutriated solids  could be reduced to between fy/» .and 5fo



over  the  coal feed rate range shown in Fig. 2.  Thus, bearing in mind the



reduced excess air requirement, the combustion efficiency of fluidised beds



should be ccspotitive with that of conventional firing appliances for shell



boilers,






4.    Heat Transfer from the Fj-ttidised Bed.






      Hea-u  transfer rates nave been measured to various arrangements of tubes



immersed  within a  fluidised bed burning washed coals sized 6,4 mm - 0, and



within a  bed  burning two sizes' of untreated coal,  3.2 mm - 0 and 6.4 mm - 0.



All particles smaller" than 0.5 ram were elutriated from the fluidised bed, so



that  the  range of particle sizes in the bed was 3.2 mm or 6.4 mm - 0.5 mm.
      Fig. 5 shows a representative selection of the data plotted as



heat transfer rates against superficial fluidising velocity.   This latter



quantity is related to the heat release rate by virtue of the operating



criterion of having minimum excess air.    All data points represent an average



over at least one hour, and more usually two hours, of steady conditions.  The



'tubes' were 60.3 mm O.D. inserted horizontally in rows of five on 15? mm



centres, each data point represents the average of the middle three tubes,  as the



effective area of the outer tubes was too small for accurate  measurements.



The 'coil1 consisted of a continuous length of 34 iwa O.D.  horizontal tubing



set on a 76.2 am triangular pitch filling  the cross section  of the combustor.

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       ?ig. -j shows that  up to  152 cm from the distributor the heat transfer


 rate is proportional to  the fluidising velocity, with a bed sized 6.4 .no  - 0,5"'cm«


 There is no significant  difference  between the  tubes and the coil and the velocity


 effect is probably due to  the  tendency of the larger particles  to settle  out at


 the bottom of the bed resulting in  only  sluggish fluidisation of this part of  the


 bed.  Between 152 mm and 505 ran from the distributor the heat transfer rates to


 the coil are higher than in the lower section,  apparently independent of  fluidising
                                                 *

 velocity,  and of the same  magnitude for. both particle size ranges in the  fluidised


 bed.  They are higher and  independent of fluidising velocity because the


 quality of fluidisation  is always reasonably good at- this levelr regardless of


 velocity.   Tho fact that heat  transfer rates are similar for both bed-size


 distributions is probably  due  to segregation when the bed was sized 6.4 mm - 0.5,


 the larger particles sinking to the bottom leaving a particle-size spectrum


 close to 5.2 mm  - 0.5 nun  in the upper part of  the bed.  The data are confined


 to the lower 505 ma of a fluidised  bed some 600 mm deep, but heat-transfer rates


 in the upper portion of  the bed will be  similar to those measured. 152 - 502 mm  .


 from the distributor, if even  fluidisation ia maintained.  This would give an

                                            9
 average heat-transfer ,rate of  about 180  kW/m  to surfaces immersed throughout


. the volume of a fluidised  bed  whose superficial fluidising velocity was around

                                                                   n
 4 m/s, equivalent to a heat-release rate of approximately 5.15  MW/m , based on


 distributor area, for a  bed 0.6 in deep.



       For all the data shown in Pig.  5 the mean bed temperature was between


 6pO C and  900 C and the  heat transfer surfaces  were vater cooled having an


 average water temperature  around 60 C.   Under these circumstances, calculations


 fron the reasonable assumption that thermal radiation to surfaces in a well


 agitated fluidised bed is  as from a black-body   , suggest that radiation


 contributes between 50j£  and 50$ of  the heat transfer.  For all  experiments the


 proportion of the heat input which  was extracted directly from  the fluidised bed


 and the walls of the carryover space directly above it fell from about 55$ at  low

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heat-release rates to 40y£ at the highest rate.  I-Iuch of this fall is due to

tho  increasing loss of carbon elutriated from the "bed, and any increase in combustic

efficiency will increase the proportion of the heat input extracted from the bed.



5.   Conclusions



      It is concluded that the combustion of coal in fluidised beds should

allow the heat release rate and heat transfer efficiency of coal-fired shell
    ->                      '                                          .          _
boilers to be increased, with a consequent reduction in size and capital cost

for a given steam rating.  The remaining problems are nainly of an engineering

nature, and are to be investigated by BCURA on an industrial scale.  To this end a

shell boiler, of novel design permitting utilisation of the fluidised

coabustion principle to raise 4000 kg/h of steam, has been designed and will 'be

installed at Leatherhead in the latter part of 1968.             .   •



6.   AcknowledCements



      The author wishes to thank the 3CURA for permission to publish this

paper, Mr. D.J. Keating for his invaluable work during the design and

cocnissioning of the pilot-scale combustor and Messrs. B.F. Pell, 1-I.C. Rogers,

P.D. Brown, P.J. Allen, D. Fitzgerald and B. V7aylen for their untiring

assistance through the various stages of the project.



7.   References                                                    '

  1.   Zenz F.A., and Othmer D.F.:  Fluidisation and Fluid Particle Systems j

       I960, Rheinhold, New York.

  2.   Leva M. i  Fluidisation;  1959, McGraw Hill,  New York.

  3.   Godel A.A.i C.S.A.  International Meeting;  1963,  London,  Doc.  No. 7595.

  4.   Panoiu N. and Cazacu C.:   Revue d'electrotechnique et Snergetique;  1962,

       Ser. B,  2j 7.

  5.   Kovotny P.»  Prace Ustavu Pro. Vyskum Paliv; 196J, j5,  116.

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6.   Novotny P.:  S.N.T.L. Technical Digest; 1965, No. 12, 885.
7.   Priese von G.:  Erdol und Kohle;  1961, 14. 702.
8.   Ifessotte A.D.H.L.:  Brit. Pat. Spec.; 1961, No. 858107.
9.   Tea£ue D.S. and Wright S.J.:  Private Communication, BCURA Keobers1
     Information Circular;  1966, No. 301.
10.  Wright S.J. and Keating 2). J.:  J6th Int. Cong. Chera. Ind.; 1966,
     Bruxelles, !_, 627.        ,

-------
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-------
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ORIGIN OF THE " IGNIFLUID COMBUSTION PROCESS"  AND




CONCEPTION DESIGN.  FOLLOWED BY THE DESCRIPTION




OF THE PROJECT OF A NEW  FLUID BED COMBUSTOR
                 by Albert A.  GODEL




        President of the "Societe Anonyme Activit"




                      Paris
            presented during Session I    (November 19.)




First International Conference on Fluidized Bed Combust'ion




         Hueston Woods State Park, Ohio




            November 18-22, 1968

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                                                                   -  1 -
              Since I was invited to take part to this first international




Conference on Fluidization organised by NAPCA, I feel that to begin with




I must make clear my position in regard to fluidization :








              The fluid bed technique was used for the first time in France




in 1947 at our factory of Vernon byoup Societ6 Anonyme Activit.




to manufacture activated carbon .




  	       Apart from this industrial production,  we have developed




on a semi-industrial scale from  1950 to 1953 a fluid bed process for the




reduction of iron-ore .




              Then from 1953 onwards,  iri cooperation with the Swiss Firm




CIPA (Compagnie Industrielle de Precedes & d'Applications SA) and with




our own funds, we have developed a fluid bed process applied to the




combustion of solid  fuel .




              The latter was thoroughly tested at Vernon with a great




number of fuels, from  anthracite to highly coking bituminous coal  ,




 and the results were sufficiently promising to justify the licensing of




the process under the trade-mark "IGNIFLUID" to Babcock-Atlantique,

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                                                                    - 2 -
former Societ6 Frangaise des Constructions Babcock & Wilcox, and to




various other boiler manufacturers in Europe,  South Africa and Asia .




              The first report on the above method of combustion was




presented to the "French Society  of Engineers" in 1955, an extract of which




was published in "Power" July 1956 .




              The Ignifluid process thus industrialized was since then




applied to boilers of increasing capacity for industrial  use and power




production .








              I will confine this first talk to the description of essential




and theoretical features concerning the  so-called Ignifluid process , after




w hich I shall disclose a new method of burning coal in  a fluid bed .




              This last prospective method is only at its very first stage




of development, I must say, as the cortesponding  U. S. Patent has only just




been granted .








              The very origin  of  the first above-mentioned Ignifluid  process




proceeds from the following observation :




              In a turbulent bed of solid fuel in combustion, as soon as more




or less molten ash particles come into contact , they stick one to the  other,




but on the contrary, molten ash particle will not stick  to  a coal particle .




This is how  particles of pure ash increase in size till they sink by gravity




through the bed on to the grate .

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                                                                 - 3 -





               By the ascending motion of this grate towards the rear,  the



 slag is automatically driven through the surface of the bed to the ash pot and



 this is one of the essential features of the process .



               Of course the grate is divided into sections in order to permit



 the adjustment of the pressure in dependence with the depth of the fluid bed .



 Fine coal of any type and grading below 3/4" is fed  continuously through



 an air blown injector located in the front of the combustion chamber, so as to



m aintain a constant level of the fuel in the bed . Primary air ,  in the



 proportion of about 50% of the total amount, is blown through the ~rate under



 the pressure of 12" water-gauge .                x   _   '



               As it has been proved possible to control the temperature by



 adjusting the bed to a given depth, no severe difficulty has been encountered



 in burning coals with either low or high fusibility ash .



               Secondary air , in the proportion of approximately 50%, is



 injected over the fluid bed in order to complete combustion and all the flue


                                                             the, ash of
 dust collected in the  gas is reinjected so that the entire amount of/the coal



 agglomerates into slag containing 3 to 5%  carbon  .



               The stoker is of such reduced dimensions that it can be adapted



 under boilers of any  size including power plant boilers,  even under pressurised



 boilers, so that we have often compared such a stoker to a "fluid bed burner",



 the difference is that it  handles minus 3/4 fines instead of pulverized coal .

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                                                                    _ 4 -






               As a conclusion,  I think that the very simple combustion method




 thus realized has allowed us to dispense with all innovations and further




 development work concerning the boiler proper ; funther the scheme has




 proved exceedingly profitable, napaely when applied to the level of utility




 power plants .




               I admit that we have not made full use in our present industrial




 program of all the advantages pertaining to fluid bed,  namely heat transmission




 possibility .  But undoubtedly the level of industrialisation now reached is




e nti rely due to our realistic approach to the complex problem of fluid bed




 combustion .                                              '     .




               HOY/ such fluid bed technique may help solving pollution




 problems is, I understand,  anohter essential point of this conference  but




 I must say that we have done little development work on this subject ,  the




 major reason is that nearly all French coals  are of a reduced sulphur content




 (round 1%) .




               Another reason,  of course,  is that in France, pollution problems




 Have only become specially acute in the last few years, with the exception




 of dust emission problems .




               As regards this last, but important point, we are in a position




 t-o ascertain  that Igniflv.id bed combustion  technique offers a considerable




 advantage over pulverizer!  firing since the amount of micronic particles




 contained in the flue  gas rs much smaller, making precipitation easier .

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This enables the use of multicy clones instead of electric precipitators in many


cases, namely for top sized industrial boilers or even small utility power


plant boilers .


              I may quote the following figures which were offically controlled


at the stack of a 50-55 t/h Babcock -Atlantique Ignifluid fired boiler burning


bitunsinous coal :


              O, 4 grams per Nm3 ,  that is 0, 174 grain :  per cubic foot cold


( which corresponds to O, 38 Ib per million BTU)  when reinjecting 84% of


the grit, and 0, 5 grams per Nm3 when the total amount of grit  is reinjected  ,


that is to say 0, 218 grains per cubic foot cold,( which corresponds to  0. 47 Ib
              The above figures result from an official test control made by


the CERCHAR which is, as you know, the Development and Research Departmetf


of the French Coal Board .


              Since I  am offered this opportunity to mention the CERCHAR,

    to say
I wan1/how much we are indebted for the help they gave us on many occasions,


namely when official controls were needed for the commissioning of plants,


also recently for bench scale experimentation made in their laboratory in


reference to our new method for reducing flue dust emission over  a fluid bed .


              On electric precipitation, we have yet no official figures .


However we can assume from very satisfactory  results obtained  at a 60 MW


plant burning anthracite fines and slurry,  which is the only Ignifluid fired plant


equipped with electric precipitators, that  there will be no problem to fulfill


the guarantees given : 0, 26 gr.  per cubic  meter normal (that is  to say 0, 113

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                                                                - 6 ~



grain per cubic foot cold ( which corresponds to 0, 25 Ib per million BTU .



              As I said before, we have little experience on the problem



of controlling sulphur oxydes in flue gas, but we are now considering the



following experimentation on a 3 t/h boiler of Babcock-Atlantique at La



Courneuve (France) :



              Finely granulated dolomite is fed into the fluid bed in admixture



with the  coal, so that it participates in the turbulent motion of the fuel ;  it is



expected that the action of the  dolomite will be somewhat double : operating



first during its rather long residence time in the fluid bed and afterwards



as a consequence of its erosion in the flue gas .



              In this same test plant,  we have also begun to study the problem



of neutralising hydroclorine acid in/lue gas emitted by the combustion of



town refuse containing plastic matter waste .



              Tests were made on demand of the French Coal Board,



by simply adding a certain proportion of coal ( 20 to 25%) itn admixture


       /town
with the  refuse burned in the furnace .



              Neutralisation was caused by the basic nature of ash in the



coal ,  so we obtained the following figures :



              When burning 25% of low volatile coal from Northern France,



.i*i±h 75% of town refuse, there is a reduction of 50% of the content  of



hydroclorine acid in the flue gas .  This falls from 10 per million to 5 per



million when compared with the combustion of pure refuse .

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                                                                   - 7 -




              Having now done with the essential of the Ignifluid Process,



I may enter the field of prospective development mentioned before, by



disclosing the principle of our new project .



              It  has been conceived, as you will see,  to benefit both from



inte: nsification of combustion and high heat transfer coefficient in the fluid bed.



              In this new conception, two or more fluid beds are superposed



in the same steam generator operating preferably in the following manner :



              The first fluid bed at the bottom of the boiler is of a conventional



Ignifluid type, thus operating in reducing atmosphere  ; it is made up of minus



3/4" or finetcoal, as received,  which is burned at a sufficiently high



temperature around 1100°C/ 130CTC ( i. e'. 2012/2372 ?F) to ensure slagging



of the ash .



              No heat transfer tubes are incorporated in the bed, but the



lateral walls of the furnace consist of radiating panels .



              Above the  first fluid bed is a second bed operating in a



slightly oxydising atmosphere,  made up with refractory granulated fragments



containing a certain proportion of ash-like carbon particles, coming with



the flue gas from the first bed and, if needed,  from an effective incorporation.



              The temperature of this second bed round 850° C is lower


                    /around 850°C.
than that of the first ; it is controlled in order to avoid slagging and yet



allow combustion .



              Heat transfer tubes constituting an essential part of the



evaporating system of the boiler are incorporate in it  .

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                                                                - 8 -


              Above this second bed has been devised a thirdand even a fourth


bed made up of the same refractory material mixed with incoming ash like


carbon particles and provided with heat exchange tubes for superheating the


steam and eventually heating feed water .


              These superposed beds are at decreasing temperature inferior


to the ignition point of the coal .  The effluent gas then passes through a multi-


yclone or an electric precipitator and all the flue dust collected is reinjected


into the first high temperature fluid bed , thus securing the maximum possible
 efficiency.
              Without entering into any detail. I may say that the above boiler

                                       and it is
is planned to use forced circulating water,/working in a pressurized atmosphere



    -  - _      Since extensive experimentation and industrial application have


been fulfilled by a number of our members on both slagging and non-slagging


fluid beds, I venture to hope that at the issue of this conference, it will be


deemed beneficial to initiate a cooperation .


              jn my mind,  this cooperation would be essentially aimed  on


experimental development work at semi-industrial scale to determine the


possibilities and merits of the at»ove-mentioned combination .


              For my part, I want to say that if such a cooperation was set up,


I would expert my utmost efforts to find the best way in which we could


participate for the benefit of all .

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                      Session II

                 Conceptual Design and
                 Economic Feasibility


            Wednesday morning, November 20
Discussion of prototype and full-scale studies, and of
conceptual design of a full-scale combustor.  Economic
comparison of envisioned fluid-bed boiler plants (pack-
age through large utility size) with existing conven-
tional plants.                                 '

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          POWER STATION BOILERS;   PRELIMINARY COSTING AND
                      DESIGN  CONSIDERATIONS
                          D.  F. Williams
                       Rational  Coal Board
                    Coal  Research Establishment
                   Stoke  Orchard, Glos»,  England
                    Presented during Session H
    First International Conference on Fluidised  Bed Combustion
                 Hueston  Woods, State Park, Ohio
                       November 18-22, 1968
         The interest of the N.C.B. in fluidised combustion  stemmed
from the difficulty in nicking significant reductions  in  the  cost  of
p.f. systeus in order to naintain the competitive position of coal-
fired pover stations in the U.K.  A preliminary assessment indicated
that the principal component of the saving offered by fluidised
combustion lay in the cost of the high pressure tubing for the boiler,
superheater and reheater.  Taking a bed temperature of 800 C and  a
heat transfer coefficient of 50 - 100 B.t.u./ft h°F,  at  least a four-
fold reduction in tube cost vas estimated.  In addition, fluidised
combustion offered savings in coal preparation, since the ccal would
be crushed rather than milled.  A further potential advantage arose
from the reduction in combustion temperature, vhich could be expected
to lead to a reduction in fouling and corrosion of the tubes and  hence
an increase in plant availability.  On the debit side vas an increase
in the fan cost, as a result of the back pressure exerted by the  bed
and the air distribution system.  On the basis of these  items alone,
the net saving in the capitalised cost of a 500 MW station,  including

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the present vorth of the operating costs, was estimated to be
just under 10$.  This vas a promising start because it brought us
vithin reach of our aim to provide a systen vhich would produce
power at not nore than 0.5d per unit in 19T5-
         At this stage, consultants have been engaged to provide
a conceptual design of full-scale power stations of output
660 11W and 120 MW, leading to a nore couplets and accurate cost
evaluation.  The preliminary calculation shows that if the
fluidising velocity is 3 ft/sec at full load, a bed area of about
         2
25tOOO ft  is required for a 660 M5-7 boiler.  This could be provided
by 15 beds, each 80 ft by 20 ft.  A bed height of about 2 ft is
envisaged, with tubes arranged in tvo or three horizontal layers
in the bed, and coal feed points spaced perhaps 10 ft apart along
the fluidising base.  The relative merits of arranging the beds
horizontally or vertically are being considered, particularly in
respect to prefabrication and standardisation of components and
to reductions in civils and erection costs that nay well be
possible with this systen.
         Other natters requiring attention include the even
distribution of air across each bed, including the design of the
off-gas outlets and the choice of freeboard height so as not to
interfere with this distribution;  the control and even distribution
of coal to each feedpoint;  the containment of each bed - whether
to cool the walls and roof or to use refractories;  the nethod of
start-up, and the method of accommodating large changes in load.
         In conjunction with this study  a prototype is being
designed, and a decision to build will be taken in 19&9.  The
estimates nade so far, and the preliminary views of our consultants,
indicate that there is good reason to press ahead with the programme
with all speed.

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         The Development of  (a) Industrial Fluid-bed Shell Boilers



              and  (b) Fluid-»bed Combustion under Pressure





                              by         .'



                         G.G.Thurlow



                BCUBA Industrial laboratories

                  Lea therhead, Sui.-ey, England




                   Presented during Session H     •



         First International Conference 'on Fluidised Bed Combustion



                Hueston Woods, State Park, Ohio,
                                                               e


                    November 18 - 22, 1968-
    BCUEA's work on fluid bed combustion is closely integrated with



 that carried out by the National Coal Board.   Consideration of



 conceptual designs is divided between the two establishments, the



 N.C.B. concentrating on the development of designs for large water-



 tube units operating at atmospheric pressure whilst BCUKA. is working on
                                    * '                                *

    (a)  small industrial boilers,                '



 an (b)  the extension of the combustion system to pressurised



         operation, primarily with large boiler plant in mind.

*                    .                                 »



                        Industrial boilers



 1.  Work so far has concentrated on the "shell" type of unit though



     consideration is now being given also to the  particular  problems



     of small water-tube boilers,  probably burning £"-0  coal  (rather .



     than 1/16"-0 preferred  for the large  water-tube  boilers).

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2.  The shell boiler is popular in the U.K. due to its relative




    low cost.  Whereas packaged oil-fired and gas-fired shell




    boilers are made up to at least 50,000 Ib/h steam, packaged




    coal-fired shell boilers are generally limited to about 30,000 Ib/h.




    Relative capital costs of coal, oil and gas firing are often in




    the ratio 1.35, 0.98, 1 respectively.  Market surveys suggest




    there is a market for a 30/^,000 Ib/h cheap coal-fired boiler.




3-  Research started (at a low level) at BCURA in 196^ to develop a




    fluidised combustion system capable of both cheapening coal-fired




    shell boilers and of extending their output - at least to the limit




    of current oil-fired boilers.  The effort increased significantly




   . in 1966.                                        .."'.,




k.  Fluidised combustion offers cost savings mainly because the high




    combustion and high heat transfer rates in the combustion bed lead




    to a substantially smaller (-J to 9") overall size of boiler.




    Other practical advantages are:




      (l)  the system is relatively tolerant of variable and poor




           quality fuels,.




      (2)  the low bed temperature (about 850 C) avoids the release




           of sticky solids and hence minimises the blockage of smoke




           tubes,




      (3)  the absence of local overheating prevents high thermal stresses and




           hence minimises the risk of furnace tube distortion (and




           incidentally permits the ready possibility of using the




           boiler for indirect chemical process heatingBusing an oil-




           based heating fluid).

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5.  Following encouraging results from an experimental combustor




    (burning rate up to 500 Ib/h coal) an experimental prototype




    four-pass vertical 8000 Ib/h steam shell boiler has been




    designed in collaboration with a manufacturing firm and an




    order placed for its manufacture and delivery in February 1969- • . .



6.  The fluid-bed will be contained in a k ft diameter by ^ ft 5 in long




    furnace tube.  The bed will be 2 ft deep and pierced by thirty 2^ in




    O.D. tubes at an angle of 10  to the horizontal, allowing about 5®%




    of the heat release to be extracted from the bed;  tube design has




    been tested at up to twice the heat transfer rates expected in the




    boiler by studies on a single inclined tube in a' test rig.  The




    boiler will incorporate a wholly enclosed pneumatic coal feeding




    system.




?.  The overall height of the boiler (including smoke box and supports)




    will be 11-g- ft and the diameter 8 ft.  This compares with an 8000 Ib/h




    steam chain-grate Economic boiler (heat transfer in furnace tube




    less than ^Q% of heat release) with dimensions 15? ft in length




    and 85- ft in diameter.  The actual volumes occupied by the pressure




    shells are respectively:




                fluid-bed fired boiler  - *K>8 ft5




                chain-grate  "     "    - ?66 ft5




8.  The boiler will burn a high-ash £"-0 coal to produce an estimated




    &i lb steam per Ib coal.  This represents a target of 80?£ thermal




    efficiency for a gas outlet temperature of 200 C and not more than




    5% heat loss due to carbon-in-ash.




9.  The actual capital cost considerations are somewhat complex.  For




    example, a saving of £850 sterling on the chain grate is offset




    by the added complications of drilling the furnace tube to receive

-------
     the inclined water tubes, and of welding the tubes.   Similarly,


     .there are other items that tend to balance one another.   Perhaps


     the firmest indication of capital cost is the cost of the prototype.


     If the price of this one-off prototype can be cut, as should be


     possible, by 20% when production methods are employed, it will be


     slightly cheaper than the equivalent oil-fired version.


10.  It is difficult at this stage to make precise estimates  of running .


     costs since these will be influenced by:


            price of coal (assumed throughout that the coal can be


               delivered on site -£"-0 size, preferably untreated and dry)


            thermal efficiency of boiler (.80% assumed but actual value


               has to be determined)


            cost of disposal of ash


            manpower costs (only one if pneumatic coal system.is used)


            electricity costs (fan power etc.)


            maintenance costs (including instrument maintenance)
                                                                     »

11.  Postive answers to the various unknowns in capital and running


     costs and to some technical questions such as to the greatest


     turn-down ratio that can be attained and the range of tolerance


     of coal quality,  are planned to be available by the  end  of 19&9-


     Instrumentation and automatic control should be completed by the


     third quarter of 1970.


12.  An estimate of possible reduction in construction time will be


     available after the manufacturers have the experience of building


     the prototype boiler.   Active design and development is  also in


     hand to find the  upper size at which this boiler can be  built


     to test simplified coal feeding systems,  etc.

-------
13.  Tests on a two-stage system in which the conventional smoke




     tubes used in the present design are replaced by a second




     fluidised bed may lead to an even more compact  design.




1^.  Consideration is now being given to extending the scope of the




     basic design of combustion chamber into the packaged water-tube




     boiler range up to 1000,000 Ib/h steam.






                  Fluid-bed Combustion under Pressure





 1.  Pressurised fluid-bed combustion systems are envisaged for




     combined gas/steam turbine driven power generating plant sized




     from about 15 MW upwards;  the benefits may well be greater in




     the sizes suitable for large industrial and central power




     stations (e.g. larger than about 80 MW).




 Advantages of operating under pressure




 2.  Fluid-bed combustion at atmospheric pressure offers potential




     technical advantages over conventional p.f. combustion for coal-




     fired power generating systems.   Even greater  benefits should




     result if. fluid-bed steam generators can be operated under




     pressure and if the energy of the combustion gases can be




     recovered in gas turbines (or similar heat engines).




 3.  Operation under pressure facilitates a major reduction in plant




     size.  It should be possible




       (a)  to reduce the volume of a fluid-bed boiler at least in proportion




            to the square root of the absolute pressure;    a conservative




            estimate suggests, for example,  that a fluid-bed boiler




            for a 500 MW power plant operated at 15  - 20 atmospheres could




            be contained in a vessel 20 ft diameter  and 80 ft long -




            which is 1/25th the volume of a conventional boiler of the




            same output.

-------
       (b)   to reduce the cross section area of the fuel bed in




            proportion to the increase in absolute pressure;  distribution




            of coal and air, and collection of steam, will as a




            consequence be simpler than at atmospheric pressure.




b.  Efficiency of power generation using combined gas/steam turbine




    cycles  should also be higher than that of conventional steam cycles,




    the precise extent of the improvement (1 - k%) depending on the




    temperature pressure and details of design of the steam plant;




    these can only be defined in the "light of the requirements of




    specific applications.                              . •




5.  Finally the pressure process should be able to accommodate load




    changes more easily




       (a)  cycle pressure will change in the same direction as the




  	    load;  some reduction in load will therefore be feasible




           without a reduction in fluidising velocity,               ...




       (b)  because higher pressure losses are acceptable in the air




          . distribution system the velocity can. be reduced to a greater ..




           extent before there is a risk of unsatisfactory distribution,




           and




       (c)  because CO formation is less likely to occur under pressure




           it may be feasible to operate at a lower fuel' bed temperature




           before the CO content of the combustion gases reaches an




           uneconomic level.




Investigations in Progress




6.  Before these additional benefits of operating under pressure can




    be quantified,  notional designs for fluid-bed power plant  have to




    be drawn up;                                 .            '

-------
7.  The main.objective of the programme of experimental work in


    progress at BCUEA is to demonstrate the feasibility of the process;


    the crucial factors are:


      (a)  whether the combustion gases from a fluid-bed can be


           sufficiently well cleaned to avoid uneconomic erosion of  .


I          6as turbine blades, without also incurring unacceptably
A.-J

           high power loss and capital cost, and


      (b)  whether volatilisation of constituents of the mineral matter


           occurs to a sufficiently small extent to avoid serious fouling


           or corrosion of turbine blades.


    Gas turbines have hitherto found products of combustion from coal


    unacceptable because of excessive deposition of,  and erosion by,


    the mineral matter0  It is confidently expected that the products from


    a fluid-bed combustor operating at under QOO C will not present


    comparable problems.


8.  The main experimental equipment being built to investigate these


    problems is a pilot scale combustor designed to burn 1000 Ib/h of


    1/16"-0 coal at a pressure of 5 atmospheres.  The rectangular fuel


    bed (operating at 650 - 800°C) V long,  2'  wide and about 2.5'  deep


    contains 1" outside diameter tubes spaced on 3" centres;   the tubes


    will absorb about 60$ of the heat on the fuel.  The gases leaving


    the bed pass through three high efficiency cyclone dust collectors


    in series and over a cascade (3" x 2") of turbine blades.   The


    erosion/corrosion/deposition characteristics of the gases will  be


    assessed by detailed examination of the  blades and cooled metal


    specimens that .follow them.

-------
 9.  The experimental work will also provide  information on:




       (a)  deposition/corrosion/erosion of tubes immersed in the




            fluidised fuel beds;  specially instrumented tubes are




            provided for this purpose;   conditions are more exacting




            under pressure because of the higher heat release/unit




            volume,




       (b)  fuel and air.distribution,




       (c)  engineering design of tube  arrangements in fuel beds,




       (d)  problems of part -load operation and control.




10.  Supporting investigations are in progress  on:




       (a)  erosion of tubes using a 2  ft square fluid-bed,  and




       (b)  release of alkali and sulphur using a small bench scale




            externally heated fluid-bed.




 -    - (c)  tube packing and air distributor  design using a full




            scale model.

-------
                          OUTLINE

              FLUID!ZED BED BOILER CONCEPTUAL
              DESIGN  AND ECONOMIC FEASIBILITY

                            by

                        J.  W.  Bishop
                  Pope, Evans  and Robbins
                   Alexandria, Virginia
                Presented During Session II
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968

-------
                        OUTLINE
                 FLUIDIZED BED BOILER
      CONCEPTUAL DESIGN AND ECONOMIC FEASIBILITY


1.   General design parameters are as follows:

    a.  Maximum width of 12', maximum height of 16' to permit

        factory assembled boiler shipment to around 80% of

        all potential customers.


    b.  Maximum capacity within these limits (estimate 300,000-

        350,000 Ib/hr with a 50-60' boiler length).


    c.  Lowest practicable capital cost.


    d.  Lowest practicable operating cost, all factors considered.


    e.  Capability to operate with a wide range of fuels.


2.   Specific parameters currently being used to govern our

    design are:


    a.  Use of common bed material, specifically the ash

        received with the coal.


    b.  Size consist, density and shape factor of bed material

        optium for operation at 0.8 to 1.2 MBtus per square

        foot fuel input.   (Average 3 fps ambient air velocity,

        12-15 fps superficial velocity)  (-8 mesh coal ash,

        2.4 spg currently employed).

-------
c.  Heat transfer rates on the order of 50 to 60 Btus/



    ft2/hr/°FAT MTD where the bed is in direct contact



    with the boiler ' tubes; 45 Btus/f t2/hr/°F MTD for



    imbedded superheaters.






d.  Beds of 18" static height and 36 - 42" effective



    expanded height.






e.  Limit of 20" w.g. draft pressure at the bottom of the



    bed, fan power not exceeding 1.2 hp per million Btu



    input.  Grid loss 30% of bed draft pressure.     I.






f.  All direct contact heat transferring surfaces vertical.






g. — Combustion chambers of rectangular cross section



    capable of easy access and maintenance with ratio of



    periphery  (ft.) to bed surface  (ft2) on the order of



     (1650) - (Tj., - Ts) , where Ts is the saturation



    temperature of the steam and Tfc is the bed temperature.
h.  Under conditions described above, bed temperatures



    between 1600 and 2000°F.   (1800-1900°F is actually




    being used) .






i.  Preheated air temperature at 500-600°F.






j.  Any single screened coal % x 0 to h x 0, 4 to  40%



    volatile, minimum 2100°F ash softening temperature,



    sufficiently "unwashed" to preclude bed level  shrinkage.

-------
k.  Coal fired sections to operate with 3 to 10% excess air.






1.  Flyash fired (reinjected) section to operate at 30 to



    40% excess air; all flyash reinjected into this zone,



    only.






m.  Minimum overbed combustion space, but sufficient to



    preclude elutriation of larger particles.






n.  Pneumatic feed of coal at bottom of bed, 6" intervals.






o.  Direct overbed ignition of one "lightoff" cell,



    4MBtu/hr required.






p.  Lightoff of subsequent cells by means of limited



    openings in intercell boiler tube walls.






q.  Classified removal of excess bed material  (+8 mesh)



    to permit use of larger size consist coal.






r.  Automatic control based on excess 02•






s.  Reduction of exit gas temperature to 350-400°F by



    air preheater and economizer.






t.  All particulate in excess of 44 microns will be collected




    in a low draft loss dust collector for reinjection; the




    balance which exhibits low carbon content will pass on to




    the pollution collector or scrubber.  Where stringent SC>

-------
        regulations are in effect,  the scrubber may incorporate



        SC>2 removal features.






3.   A design of a 250,000 Ib/hr factory assembled railroad




    transportable packaged boiler has been prepared.  This



    consists of 13 boiler cells, approximately 12' long x 25"



    wide plus a carbon burnup cell.  All reinjected ash is



    into the carbon burnup cell.






4.   A 250,000 Ib/hr packaged fluid bed boiler will cost less



    than a component assembled oil or gas fired boiler of



    equal capacity.






5.   Based upon a boiler installed in an existing plant with



    existing fuel handling and storage facilities, no



    differential in fuel price is needed to justify coal




    over gas.






6.   Based upon a completely new facility, a 2£ per million



    Btu differential in fuel price  (in favor of coal) is




    needed to justify  fluid bed firing, whereas a 7-8C




    differential is required for a spreader stoker when figured




    on the same basis.






7.  A 100,000 Ib/hr prototype unit is now being developed




    for correction of  deficiencies and for making fluidized



    bed boilers marketable.


-------
THE "IGNIFLUID" FLUID BED COMBUSTION PROCESS                      •
                                                                           (
                                                                           i
AT ITS PRESENT STAGE OF INDUSTRIAL DEVELOPMENT                  [
                   by Albert A. GODEL


            President of the "Sioci^te' Anonyme Activit"



                        Paris
                 presented during Session II  ( November 20)


   First International Conference on Fluidized Bed Combustion



              Hueston Woods State Park,  Ohio


                   November 18-22,  1968

-------
              Yesterday I explained the principle of the Ignifluid  process




of combustion., today I shall go into the industrialisation of the process.







              The 34 units completed up to date by three of our licen- .




cees of France,  Great Britain and Japan, cover the following range of




outputs :                                         .                "    .




              - from 3 t/h (6.600 Ib/h) to 115 t/h (250.000 Ib/h),




two of the latter built by Babcock-Atlanti.que are  . -_.i boilers  "twinned*1




to a  single 60 MW turbo-alternator ; now tenders for 250  MW power plants




comprising twin boilers each of 365  t/h (800.000 Ib/h) are being made.







                  All these furnaces include the  same essential items




which I will now  ."Enumerate as follows :




- a chain grate  stoker of approximately 1/1 Oth. of the surface of a corres-




ponding conventional stoker, rises at an inclination of approximately 8°




so that the upper moving strands  will discharge the  slag at the rear of the




furnace into the ash pot ; the chain  grate is made of self-cleaning  steel




links. As already  said, primary air is blown into the sections  of the chain-grate,

-------
  This stoker is placed between naturally formed fuel banks extending

  between lateral and front walls.

                The heat production developped by the chain is 10 million Kg/cal,

,  that is to say 4 million BTU per sq. feet.

                The banks play no part in the combustion except for avoiding

  slagging along the walls and for providing a wide extension of the fluid

  surface.



  - Above the level  of the fluid bed, a row of nozzles inject secondary air.

  Both primary and secondary air being blown by a single forced draught fan.

  The temperature of the primary and secondary air is atmospheric in certain

  plants or as  high as 190°Cfor primary air, and, for instance,  280°C for secundary
   air.                                                                 '
                A satisfactory proportion of excess air for the  final combustion

  in the furnace is 25 %, but promising tests are made to reduce this proportion

  to less  than  10 %.



  - Fly ash reinjection nozzles are usually placed at the  rear of the furnace

  at an intermediate level between the fluid bed and the secondary air rein-

  jection nozzles, that is in the hottest combustion zone of the furnace. They

  handle the total amount of fly ash collected from the flue gas. Grit arresters

  or electric precipitators have of course to be  used.

-------
                                                                     -  3  -
              We have seen that the level of the fluid bed is maintained as




a rule constant and this leads me to describe the control system which is




used for this purpose :




              Three essential!are used :




- the first loop controlling the level comprises a water cooled pressure probe




inserted at the bottom of the fluid bed which transmits the pressure to a con-




trolle/t, recorder ;  this recorder actuates a servo-raotor regulating the feed of




the coal to maintain constant the level of the bed.




- the second loop controls primary air in relation to the steam pressure.




- the third loop controls the adjustment of the proportion of secondary air




added in view of  completing combustion,  this is done by the usual method




of comparing through a "boiler-meter" the amount of flue gas with the steam




production.




              As usual  of course,  other loops are used to control the




draught created by the induced draught fan, and to control the steam su-




perheat and the water level.




               The control panels may be located near the boilers or in a




special control room in the case of power plant boilers.








               Experience has  proved that the  operation of Ignifluid fired




boilers involves  no particular problem and may be entrusted to any person




with normal qualification.

-------
                                                                     - 4  -
              The Ignifluid firing method insures a good flexibility as

the rating may vary between MCR and 15 to 20 % of MCR.

Now about the type of coal to be used any smalls from minus 1/8" to minus

3/4" may be burned ; this from anthracite to bituminous, coking or not, re-

gardless of the ash content .wjjftn below  50%.  Of course such versatility helps

standardising. This is  v.	,	:a due to  the fact that the fluid bed  actually

consists only of "red hot particles of coke" regardless  of the nature of the

coal.

              To show how near we approach standardizing I may give the

following example :  In August 1966 the CERCHAR carried out a fifteen day

sery of combustion tests in a 50/55 t/h Babcock-Atlantique boiler equipped

with Ignifluid furnace at La Rochette (France).

- Three types of coal were burned successively without any stop  for

adjustment and without switching off at any time the automatic control..:
total carbon content
hydrogen
nitrogen
sulphur
G.C.V.  on dry
fusibility
oxygen
ash content on dry
volatile  matter
anthracite
from
Dauphine
0/3 mm
73.5
1.4
0.6
1.1
6210
1210

21.6
5.8
0/6 treated low
volatile smalls
from Northern
French collieries
86
3.6
1.1
.8
8065
1450
2.2
6.6
7.8
0/1 8 bituminous
coking coal
from Freyming

78.5
5.2
1
0.9
7767
1240
9.4
4.3
36.7

-------
              I will simply extract from the official report of these tests




the following short sentences : "The performance of the boiler plant func-




tioning at a rate close to its  normal capacity are very satisfactory regard-




less of the fuel used..."   "... the thermal efficiency is around 88 %...".







              A year later, the firm operating the same 50/55 t/h boiler




at La Rochette gave the following data concerning availability which is




also a very important factor :




The percentage of  time of interruptions noted from September 1966 for




twelve months onwards is  :




    . 3 %   because of the stoker alone




    1.84  %  because of other difficulty
-2.14      altogether.




               Efficiency is another important point on which I think it is




of interest to give a few figures.




               For this I will rather refer to losses of efficiency on net




calorific value :




-  losses due to riddlings under the grate are                 0,25 to 0,5  %




- chimney losses due to unburnt gas when excess air for com-




bustion is over 20 % are                                     nil




-  chimney losses due to flue dust carry over when using carbon




with less than 20 % ash is less than                         0,2  %




-  heat losses due to unburnt combustible in the slag varies




with the ash content :

-------
                                                                     -  6 -
for  a   19 %  ..   	    ash coa^ the losses are          1.40  %



  ii  M   o c o/              ii   ii    n     it     ii           o  cr»  o/
         o o ^  —	             /                         o. D u  ^




               Of course apart from the above losses which are dependent




on the process, one must take into consideration other unavoidable losses




due to sensible heat of flue gas, such losses should be calculated on the




bas. of 25 % excess air.








               As efficiency results I may quote for the control  of a 50/55 t/h




boiler burning anthracite smalls containing 19 % ash the following specifications




was 83 % on LCV but official tests  have proved 88,7 on LCV.




For more important boiler plants I may simply say that the guaranteed




efficiency gitoen with Ignifluid firing compares favorably with that of pul-




verized firing.




As an example I will cite that the guarantees given for the 60 MW twin




boilers of Casablanca burning anthracite with 18 % ash is : 87.96  on GCV




dry coal. We  hope to exceed this figure when controlling the  efficiency .




As another example, the guarantees given for 250 MW twin boilers burning




anthracite of another type with 37 % ash, 8 % moisture and 5  % volatile




matter as received is : 88,83  on GCV.




I would like to mention that it is economically feasible to burn coals having




up to 50 % ash because there  is no expenses incurred w'hatever with pul-




verizing while this would probably not be the case with pulverized firing.

-------
              Now about burning high ash content anthracite coal




I want to seize this occasion to explain how unexpectedly we have become




involved into a scheme studied in Pennsylvania to solve a very important




pollution problem.




              Large aeras  of the Susquehanna and Lackawanna valleys




encumbered by silt or refuse banks with some on fire, suffer from air pol-




lution by sulphurous smoke or water pollution by acid drainage.  Last




month a Pennsylvanian newspaper published the following facts :




it is now being considered to use a 250 MW Ignifluid power plant to con-




sume during the next 30 years 65 million tons of anthracite refuses thus




restoring land for economic development.




              The Pennsylvanian authorities are also reported.to be con-




sidering that the same Ignifluid fired power plant could deliver low pressure




steam to a large demineralizing plant of the Westinghouse type ; to clean up




mine drainage in the aera and produce pure water.




              If this project becomes reality it will be a proof of the




virtues  of fluidisation in solving most unexpected pollution problems.

-------
                      Session III

                 Pollution Control.   1
         Control by Means of Corabustor Design
                 and Operating Factors


            Wednesday evening, November 20
Discussion of the control of particulates, hydrocarbons,
SO  and NO  by adjustment of fluid bed combustoi- design-
ana operating variables.                  .         ,

-------
             The Emission of Chlorine and Oxides of Sulphur
               and Nitrogen from Fluidised Combustion Beds

                               by

                            S.J. Wright


                   BCUEA  Industrial  Laboratories,
                   Leatherhead,  Surrey,  England.
                     Presented during Session III

        First International Conference on Fluidised Bed Combustion

                     Hueston Woods, State Park, Ohio,

                         November 18 - 22, 1968
      Experiments have been conducted burning %"-0 coal without additives

on the pilot-scale plant at the BCUEA, in which complete chemical analyses

were performed on the solids input to and output from the combustor,

whilst the flue gases were analysed for S0_, SO ,  NO and Cl.   Two coals

were used, .one containing 20$ ash. and having relatively high chlorine and

alkali contents and one containing ~55% ash and having a relatively high
calcium content.  The range of the combustion conditions covered was -
                                  2
heat inputs from 1.50 to jj»2^ MW/m  (based on distributor area); excess air

percentages from zero to 80^S;  mean bed temperatures from 825 C to 900 C '

and percentages of elutriated solids recycled to the fluidised bed from

zero to 809?.

      The results showed that chlorine passed into the flue gases in the

same proportion as did the carbon suggesting that, for 1OO# combustion

efficiency, all the chlorine would be found in the flue gases, probably

as EC1.

-------
      Analyses of the solid streams entering and leaving the  combustor


showed that between 5% and 10% of the sulphur was retained in the solids


along with between 80% ajid 90% of the alkalis.  The retention was •


apparently independent of combustion conditions with the exception of


the percentage.of elutriated solids recycled to the bed.  An  increase


in the percentage recycle tended to decrease the retention of sulphur.


The sulphur was present in the flue gases mainly as S0?  but with


traces of SO,.


      Oxides of nitrogen were not measured during all experiments but,

                            2
for a heat input of 2.7 MW/m  at 18% excess air and a mean bed


temperature of 880 C, from ^00 to k$Q ppm (v/v) of NO were measured


at the cyclone inlet.      .     .                "     .  .'.  '. .   -   •

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                     SULFUR-OXIDE CONTROL IN FLUIDIZED BEDS

                                       by

                                 William T. Reid
                           Battelle Memorial Institute
                              Columbus Laboratories
                                 Columbus, Ohio

                          presented during Session III
           First International Conference on Fluidized Bed Combustion
                         Hueston Woods State Park, Ohio
                              November 18-22, 1968


          Emission of sulfur oxides from fluidized combustion systems is controlled

by two major factors:  (1) temperature, which generally is lower than in other

methods of burning solid fuels, and  (2) excess air, which can be kept less than

v;hen coal is burned on grates, in suspension, or in pulverized form.  Other fac-

tors, such as reactive materials that can be added to a .fluidized bed to "capture

sulfur oxides, will be treat-ed by others and will not be considered here.

          It is important to recognize that all the sulfur initially in the fuel

will be converted to sulfur oxides in the flue gas except for the minor amount

caught by CaO and MgO present in the cOal ash.  Typically, the CaO + MgO content

of Eastern bituminous coals is less than 5 percent; in Midwestern coals they may

total 20 percent.  If, in each case, the coal is assumed to contain 10 percent

ash and 4 percent sulfur, then the CaO + MgO in the ash could capture at most

about one-tenth of the sulfur as CaS04 and MgS04 for the Eastern bituminous coals,

and somewhat more than a third for the Midwestern coals.  The rest of the sulfur

would appear in the flue gas.  Whether even these small fractions of the sulfur

would be caught by the ash depends almost entirely on the maximum temperature

reached by the system.

-------
                                       -2-
                                   Temperature






          The mineral matter in coal reacts in a series of steps as the coal is




heated.   Most important here is the fact that S02 and S03 are evolved when the




sulfur-containing minerals in coal are heated in the range 500 F to 1600 F.  In




the case of FeS, reactions begin at about 1600 F, and generally are completed by




the" time the ash reaches 2000 F.  Analyses of coal-ash slags, formed in the tem-




perature range of 1800 F to 3000 F, almost invariably show that these slags con-




tain no more than 0.1 percent sulfur oxides, confirming that all the sulfur in




the coal has been rejected by the silicate melt.  Organic sulfur in coal begins




to be evolved at about 500 F, and is completely converted into sulfur oxides




when the combustion process is finished.




          Many factors affect this evolution of sulfur oxides as a result of the




formation of silicate melts, such as the composition of the mineral matter, the




size of their particles, their distribution in the coal, the rate at which heat-




ing occurs, mixing of the inorganic matter while combustion is occurring, the




maximum temperature reached and how long this temperature is maintained, the gas




composition surrounding the surface of the burning particles of coal, and finally




the total time-temperature history of the ash in the combustion system.  Much  too




involved for analytical considerations - and  indeed, few data are available on




most of these factors - experience mainly has taught furnace designers how to




adapt large pulverized-coal-fired boiler furnaces to the problems of mineral




interactions.




          The same knowledge probably does not exist at present for  the conditions




existing in fluidized beds.  Ash reactions, and hence  the factors influencing  the




emission of sulfur oxides, needs much further study under the special conditions




existing in moderately  low-temperature combustors.

-------
                                       -3-






          It is worthwhile to review the influence of temperature on the reaction




between sulfur oxides and lime and magnesia.  Based on thermodynamic calculations,




and ignoring the problem of kinetics, the equilibrium concentration of S03 in flue




gas in contact with MgO will be about 2500 ppm at 1520 F.  For CaO, 2500 ppm S02




is in equilibrium with the solid at 2180 F.  Hence, at these temperatures, the




normal S0a content of flue gas will not be affected by the presence of MgO or




CaO; the temperature must be appreciably lower for these oxides to capture S0a.




To reduce the S02 by one half, the temperature at equilibrium cannot exceed 1480 F




with MgO, or 2150 F with CaO.  To reduce the S0a by ten times, to 250 ppm, the




corresponding temperatures are 1420 F for MgO and 2060 F for CaO.  Based on these




considerations, it is evident that a fluidized bed operating at 1800 F will not




remove any S02 by reaction with MgO that may be present, but it may remove all




but 2 ppc of the S02 with CaO present in the bed, assuming equilibrium conditions.




          It is evident, then, that the temperature of the fluidized bed is an




important variable if reaction between added limestone or dolomite and SOg is ex-




pected.  Under conditions usually specified for fluidized bed combustors, low




enough to minimize slagging reactions, lime theoretically offers complete removal



of S02 while magnesia would be ineffective.                                   •




                                                         • i              .



                                   Excess Air         .






          The most outstanding development over the past decade in the burning of




residual fuel oil in large central-station power plants has been the realization




that combustion with exceedingly  low excess air prevents the formation of flame-




produced S03.  Extensive research has shown that S03 is formed.in flames by the




reaction between S02 and oxygen atoms resulting from complex flame reactions.




Once the flame reactions are completed that produce oxygen atoms, no more S03 is




formed.  In  normal boiler furnaces, about one percent of the S03 is converted to

-------
                                       -4-






S03 in this manner.   That S03 is extraordinarily reactive.  Experiments at Battelle



                                                                 35
studying external corrosion of superheaters and reheaters using S   as a tracer




have shown that the  30 ppm of S03 normally present is hundreds of times more re-




active than 2500 ppm of S02 when Na2S04 and Fe303 are available and ample oxygen




is supplied.



          Low excess air as a means of eliminating S03 in flue gas was investi-



gated earliest in England, beginning about 1956.  The art was advanced markedly




in Germany in 1960.   It is now firmly established that limiting the oxygen in




flue gas to 0.2 percent (one percent excess air in place of the 15 to 20 percent




commonly used) essentially eliminates all problems with S03, both in corrosion




and in air pollution.  Although low excess air has no effect on the S02 content


                                                                  --••'

of flue gas, it can essentially eliminate acid smuts that can be a major source




of air.pollution.  Oxygen admitted after the flame reactions are completed, and




where the gas temperature does not exceed about 1750 F, does not oxidize S0a to




S03 homogeneously, although catalytic surfaces will increase the S03 level if




oxygen becomes available through leakage as the flue gas moves through a boiler.




          It is important to recognize that the excess air must approach zero




for its benefits to be obtained.  For example, based on laboratory measurements




made at Battelle in a noncatalytic combustor, it was shown that at 2 percent ex-




cess oxygen, the S03 level when burning a 5.5-percent-sulfur liquid fuel was



about 30 ppm.  At 1 percent excess oxygen it was 25 ppm or no significant decrease,



but at 0.1  percent excess oxygen the S03 was as low as 2 ppm.  With stoichiometric



combustion, or under mildly reducing conditions, the S03  level was zero.



          As a means of controlling air pollution from S03, but mainly as a method




of decreasing the dewpoint of flue gases  to increase efficiency without corroding




preheaters, low excess air is being given a great deal of attention today.  All




of the oil-burning boiler furnaces of  the CEGB in England are now operating with




low excess  air, although in some cases the oxygen is as high as  1 percent.  Low

-------
                                       -5-


excess air has not been taken over so completely in the United States largely be-

cause of the problems with controls to prevent smoke.  In the cases in this country

v/here it has been successfully applied, low excess air has been a boon indeed.

          So far, the usefulness of low excess air has been limited to oil-fired

equipment.  Pulverized coal in its present size consist, and using existing types

of burners, cannot be operated at anywhere near the necessary low levels of oxygen

without leading to excessive losses of unburned fuel.  One of the suggested advan-

tages of combustion in fluidized beds is that solid fuels can be burned effici-

ently with essentially no excess.oxygen.  If that expectation can be sustained,

the ability to eliminate combustion-produced S03 could well be one advantage of

fluidized-bed combustors perhaps not now generally recognized.

          A point worth noting is that the percentage of sulfur oxides occurring

as S03 at equilibrium increases as the temperature is lower.  Specifically, at

0.2 percent excess oxygen, about 0.4 percent of the total sulfur oxides will be

S03 at 2000 F, about 0.8 percent at 1800 F, about 2 percent at 1600 F, and about

6 percent at 1400 F.  At 1000 F, two-thirds of the sulfur oxides are S03 at this

oxygen level.  The significance here is that the S03 fraction increases as the

temperature is lowered, but at low excess air the total amount of S03 is moderate

at the temperature where fluidized beds would operate.
WTRrebk
11-8-68

-------
                         ABSTRACT

      POLLUTION CONTROL BY MEANS OF COMBUSTOR DESIGN
                   AND OPERATING FACTORS

                            by

                       E. B.  Robison
                  Pope, Evans and Robbins
                   Alexandria, Virginia
               Presented During Session III
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968

-------
                       ABSTRACT



      POLLUTION CONTROL BY MEANS OF COMBUSTOR DESIGN




                 AND OPERATING FACTORS






The research program in fluidized bed combustion, conducted




by Pope, Evans and Robbins for the National Air Pollution




Control Administration, has two primary objectives.  The



first is to characterize the pollutant emissions from the



fluidized combustion of coal and the second to investigate




the control of emissions, notably sulfur oxides, by addition




of dolomite and limestone.  The discussion to follow is



limited to the characteristic emissions observed in recent




tests and to the possibility of emission reduction by design




change.





Emission tests have been conducted in two units, one a pilot




scale fluidized bed column,  designated the FBC,  and the other



a full scale "boiler module referred to as the FBM.  Samples




of the flue gas from the units are analyzed continuously for



hydrocarbons, nitric oxide and sulfur dioxide concentrations.



Flame ionization and infrared recording instrumentation is



used with periodic sampling for wet tests.





Early in the development of the fluidized bed boiler it was




learned that a bituminous coal could be burned in a fluidized



bed at near"stoichiometric air flow without smoke in the flue




gas.  When emission testing was begun, this operating condition




was found to produce a high concentration of hydrocarbons in the

-------
'flue gas.  Increase in the oxygen concentration, however,


 sharply reduced the hydrocarbons emission.  Data are  pre-


 sented to show that hydrocarbons emission  from  the  FBC  is


 reduced to near zero with 3% oxygen in the flue gas.  A


 concentration of 4% appears to be necessary for the FBM.


 These Vcilues correspond  to 17% and 24% excess air for the


 coal being used.  Carbon monoxide emission is not a problem.




 Emission of hydrocarbons during the transient light off

                                               ;

 period is easily controlled .with excess air.  No appreciable


 effect v/as observed with change in bed temperature  and  bed
                                                "•'

 height.  An increase with water injection  above the bed


 indicates that the final concentrations are not established


 in  the bed.  Emissions with less volatile  coals have  yet


 to  be determined.




 The fact that a combustion fluidized  bed could  be operated


 at  a temperature below that of conventional coal firing


 systems held promise of  significant reduction in nitrogen


 oxides emission.  Rapid  heat loss from the bed  permits


 operation in the range of 1500°F to 1900°F.  Emission tests


 show that nitric oxide concentrations vary in the range of


 300 to 400 ppm depending primarily on the  oxygen content  in


 the flue gas.  These values roughly correspond  to values  of


 1 to 3% oxygen concentration.

-------
                                                         3
Unexpectedly, the nitric oxide concentrations were found



to be independent of "measured" bed temperature.  The




term "measured" is used because the analysis indicates the




presence of local high temperatures, possibly at the bottom




of the bed where oxygen concentration is highest.  Data are



presented to show the theoretical equilibrium concentrations




of nitric oxide formed with 20% oxygen  (at the bottom of




the bed) and 3% oxygen  (at the top).  The measured NO concen-




trations suggest that even though the bed is operated at a



measured temperature of 1500°F, a minimum of 1800°F exists



somewhere in the bed.  Failure of the NO concentration to




readjust to a lower theoretical value at 1500°F can be ex-



plained by slow reaction rate at the low concentrations



relative to the system residence time.






Equilibrium constant data for the oxidation of nitric oxide




to nitrogen dioxide show that if time permitted, all the




NO would be oxidized in the flue passages.  The rate of this



termolecular reaction is very slow, however.  It is esti-



mated that in the 4 second transit  time of the gas thru the




entire FBC system the conversion is less than 0.1%.  This




situation is unfortunate since present removal techniques



require its oxidation.

-------
In the matter of sulfur oxides emission there appears to


be no advantage to fluidized bed firing over conventional


methods when sulfur capture additives are not employed.


Most of the sulfur in the coal appears.in the flue gas.



Nitric oxide emission might be reduced by cooling the


bottom of the bed with water cooled projections.  A scheme


is described.



Particulate emission from the fluidized bed boiler is a


function of the efficiency of.the ash collection system


since most of the ash in a coal is elutriated from" the'bed.



From the results of tests conducted thus far it would
                            \

appear the fluidized bed boiler will be operated with 4%


oxygen in the flue gas to limit hydrocarbons emission at a


slight penalty in nitric oxide emission.  This oxygen


content is less than the 7-8% normally found in conventional


boilers.  For this reason emission of nitric oxide should


be less for the fluid bed boiler even though concentrations


are comparable.



Heat release rates with the fluidized bed combustor opera-


ting at a 14 fps superficial, velocity are higher than have


ever been achieved by any system yet devised for the combus-


tion of coal.  At the same time a fair approach to stoichio-


metric combustion is achieved.  It is not unreasonable to
                 -: . Er,\>rAT'-3.—• A 'NTT"-', C? O-p-J pp, T fs.]

-------
expect that a more perfect combustion with less oxygen



and less hydrocarbon emission could be attained with some



sacrifice in the heat release rate.  Local high tempera-



tures , which are probably diffusion controlled, might be



reduced and the nitric oxide in proportion.

-------
                      Session IV

                 Pollution Control.   2

        Control by Means of Additive Injection


                 Thursday, November  21
Discussion of additive selection,  kinetics studies,  and
injection tests.   Economics of control.

-------
                Reduction of  Atmospheric Pollution by  the

                 Application  of  Fluidized-Bed  Combustion

                                   by

                A.  A.  Jonke,  R.  L.  Jarry and E.  L. Carls

                      Argonne National Laboratory
                        9700  South  Cass Avenue
                       Argonne,  Illinois   60439

                       Presented During Session  IV

        First International Conference on  Fluidized-Bed Combustion
                     Hues ton  Woods  State Park, Ohio
                          November  18-22,  1968


     A study of fluidized-bed combustion as a  means  of reducing the

quantity of atmospheric pollutants  (oxides of  sulfur and  nitrogen) released

during the combustion of fossil  fuels  is under way at Argonne National

Laboratory.  Initial emphasis will  be  on  fundamental studies with the

primary objective of optimizing  the pollution  control aspects of fluid-

bed combustion.  Fluid-bed materials and  additives  that react with

sulfur (and possibly nitrogen) compounds  released during  the combustion

process will be studied.  The program will involve  laboratory-scale ex-

perimental studies to evaluate additives,  bench-scale fluid-bed tests

to study the effects of operating variables,  and appropriate evaluations

and assessments of technology relevant to pollution  control and fluid-

bed combustion.

     Exploratory studies of a variety of  alternative schemes for

fluidized, pollution free combustion will be  made.   For example, the

fixation of sulfur in a form which will allow recovery of a sulfur

value directly or via a regeneration cycle appears  to be an economically

-------
                                  - 2  -






sound and desirable objective.   This might be more readily accomplished




if a sulfide rather than a sulfate is  formed.  The operation of the




fluidized-bed combustor under partial  reducing conditions might result




in the formation of a sulfide product.  Such a scheme of operation




could utilize a multistage fluid-bed combustor with counter-current




flow of gas and solids to increase the efficiency of SO- capture and




additive utilization.




     The initial laboratory-scale experiments for the evaluation of




potential additives for sulfur dioxide capture in a fluidized-bed com-




bustor have been performed. (Most of the previous work of this type done




by others has been at temperatures lower than those of interest in




fluidized-bed combustion.)  Preliminary screening for SO- absorption




capacity has been done for the following materials:  phosphate rock,




spent oil shale, "red mud", a calcareous shale, the oxides of manganese,




copper, cobalt, lead, zinc, and nickel,  and a dolomite (BCR-1337).




The experiments were performed at 1700°F using a gas phase containing




5000 ppm S0? in air at a superficial gas velocity of .0.05 ft/sec.  The




elapsed times were noted for the first breakthrough of SO^ from the




additive bed and for breakthrough at an S0_ content in the effluent gas




stream of 20% of the original concentration, as measured by a thermal




conductivity cell.  The sorption capacity, expressed as g S02/100 g




additive, ranged from 0.3 to 2 and from 0.5 to 3.2 at the 100% and 80%




capture levels, respectively, for most of the additives tested other




than the dolomite.  Zinc oxide and phosphate rock had no measurable

-------
                                  - 3 -


sorption.   In comparison,  the dolomite (BCR-1337) had sorption capacities

of 5.5 and 14.8 g SC>2/100  g dolomite at the 100% and 80% capture levels,

respectively.

     These results indicate that additives other than dolomite are

probably not desirable choices since they did not approach the capacity

of dolomite.  However, the possibility of easier regeneration of some

of the lower capacity sorbents will be evaluated, and some of the

potential additives might  be preferred on this basis.

     A model has been developed which relates the extent of S09 capture

in a fluidized-bed combustor to the stoichioinetric equivalents of CaO

added as limestone or dolomite, taking into account the reaction parameters;

bed depth, superficial gas-velocity, and particle size.  The reaction rate

data selected for use were derived from data generated in the NAPCA in-

house program.  Two hypothetical cases of gas mixing in a fluidized bed

were considered—no gas mixing and perfect gas mixing.  The fractions

of the S0? captured are given by the expressions 1 - e   and r/1 + r

for no gas mixing and perfect gas mixing, respectively.  For the

dolomite BCR-1337 at 1600°F, the parameter _r is given by the following

expression
                                        . R  f L
                           r = 1.04 x 10  —	
where,
      R  is the reaction rate, Ib SO^/lb calcined stone-min

      f is the fraction of the bed as initial calcined stone

      L is the bed height, ft

      v is the superficial gas velocity, ft/sec.

-------
                                  - 4 -






     Using the equation derived from the model and the rate data for




the dolomite BCR-1337 from the NAPCA study, a computer program was




written.  The inputs for the computer program were particle size (96,




282, 507, and 1095 pm); superficial gas velocity (1, 2, 4,  6,  10, and




14 ft/sec); and bed height (0.5, 1, and 2 ft).




     For all of the cases considered, the percentage of SO- removal is




greater for the assumption of no gas mixing than for the assumption of




perfect gas mixing.  The spread between the two values increases with




greater gas velocity, larger particle size of the additive, decreased




bed depth, and fewer stoichiometric equivalents of calcined stone




added.  The effects of the variables were analyzed, using average




values of the no gas mixing and perfect gas mixing cases.  These cal-




culations, in effect, quantified the expected relationships between the




extent of S0_ removal and the operating parameters of a fluid-bed




combustor.  Results indicate that S0_ absorption will be enhanced by




decreasing the additive particle size and superficial gas velocity and




by increasing the bed depth.




     The following examples indicate the effect of particle size on




the degree of S0~ removal from the gas stream.  To achieve 90% removal




of SO  at a superficial gas velocity of 1 ft/sec in a 1-ft deep bed




would require little more than one stoichiometric addition of CaO




(as BCR-1337 dolomite) for a particle size of 282 um, but would require




about 1.7 stoichiometric additions .for a 1095 ym particle size.  At a




gas residence time of two seconds or less and a S0? removal level of




90%,  the maximum fractional CaO utilizations  that can be expected in

-------
                                  -  5  -






the fluid-bed are:   0.99,  0.90,  0.75,  and  0.60  for  particle  sizes  of




96, 282, 507, and 1095 urn,  respectively.




     An extension of the above correlation will be  made,  using  NAPCA-




generated reaction data for BCR-1360,  a  calcitic limestone.   Comparison




of the results of pilot plant tests  of other workers with the model will




also be attempted.




     Argonne bench-scale experiments on  the control of  the emission of




S0_ during the fluidized-bed combustion  of coal will employ  a 6-inch




diameter stainless steel coal combustor.   The equipment has  been designed




for operation over a relatively wide range of conditions, whether within




or without the range of practicality for full-scale systems, so that the




effects of variables such as bed height,  superficial gas  velocity, and




particle size of the additive can be thoroughly evaluated.  A schematic




diagram of the reactor is shown in the accompanying figure.   Spaced




vertically over the bottom two feet of the unit are four  annular




chambers (each 2 1/2 inches high) through which a mixture of air and




water can be circulated to effect heat removal in each  zone. This




capability will allow for varying the heat removal  of  the unit  so that




it can be operated over a range of coal feed rates  (directly related




to fluidizing air velocity) and a range of bed depths.




     The fluidizing air, after passage through an electrically  heated,




stainless steel ball-packed preheater, will enter the  reactor through




a bubble cap type gas distributor.  Coal and additive  will be fed by




volumetric screw feeders and will be entrained in an air  stream for




introduction into the fluidized bed.  The off-gas from the unit will

-------
                        ANL Fluidlzcd-Bcd Cotnbustor
                Viev;ing Port
Air-Water Coolant Inlet
      Auxiliary Inlet
      View Port, or
      Overflow Solids
      Take-Off
           Air-Water
         Coolant Inlet
    Coal and Additive
       Feed Point
           Combustion
           Air  Inlet
                                                                   Vent Gas to
                                                                Cyclone Separators
                                                       Openings  for
                                                       Thermocouples,
                                                       Pressure  Taps,
                                                       and Solids  Sampler
                                                    Solids Bottom Take-Off
                                                                   NOT TO SCALE

-------
                                  — 7 —






be passed through cyclone separators to separate most  of  the solids




before final filtration.   Provisions have been made for recycle of




entrained solids to the fluid-bed reactor.  A constant bed depth can




be maintained either by withdrawal of solids from the  bottom or by




overflow from the top of the bed.  The unit will be capable of




operation at superficial gas velocities up to 14 ft/sec and bed depths




up to 2 ft.  Continuous analysis of the off-gas will be provided, as




well as intermittent analysis of solid samples withdrawn from the bed.

-------
          NAPCA's Dry Limestone Injection Program
                      E.  A.  Zawadzki
                     PCEP, NAPCA, DREW
        5710 Wooster Pike, Cincinnati,  Ohio    45227
                presented during Session IV
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park,  Ohio
                   November 18-22, 1968

-------
     The National Air Pollution Control Administration through the




Process Control Engineering Program  has initiated a comprehensive




research effort consisting of bench-, pilot-,  and full-scale testing




of the dry limestone injection process.  This  process consists of




injection of limestone or dolomite into the combustion zone of a boiler




at a point above the burners.  The limestone is calcined and subse-




quently reacts with S02 and oxygen present in  the flue gas to form




calcium sulfate.  Calcium sulfate and unreacted lime are removed with




the particulates in existing dust collection equipment.  Many factors




influence the efficiency of the process.  It is the purpose of this




study to resolve these problem areas.






     A   summary of the activities which NAPCA is sponsoring in the




area of dry limestone injection is as follows:




     a)  Process Control Engineering Program  - In-house research.




         This program deals primarily with the characterization of a




         wide range of U. S. limestone and dolomites.  Samples are




         screened into the size fractions and subjected to tests in




         a fixed bed reactor, in which the capacity of the stone,




         previously calcined at a standard conditions, is measured




         synthetic flue gases are passed through the fixed bed,




         breakthrough-time and capacity are measured.  The other test

-------
     is  an  attempt  to measure the kinetics of the reaction of




     S0« and  lime over lime and magnesia in a differential




     reactor.  Activation energies and reaction rates are ob-




     tained.  In support of this activity, measurements are made




     by  American Instrument Company for PCEE on the pore size




     distribution and surface area of the limestones and dolomites




     tested.






 b)   Battelle Memorial Institute under contract from NAPCA has




     initiated a program to study the kinetics of the reactions




     of  alkaline earth oxides, hydrates, carbonates in^a dispersed




     phase  contact  reactor in which temperature and residence time




_. _ .  can be accurately controlled.  In support of this activity




     Battelle has also examined a series of test stones in a




     differential thermal analyser to obtain data on the mechanism




     of  the reaction of SO  with limestone.






 c)   Babcock and Wilcox Research has undertaken a study of the




     measurement of the capacity of the limestones and dolomites




     to  absorb S0_  using a small coal combustion unit.  B and W




     is  examining not only the capacity of  the stones for reaction,




     but also obtaining data on the degree  of interaction of  the




     stone  with  fly ash.  An attempt is being made  to evaluate the




     effects of  temperature and degree of dead burning of the stone




     and as a supplementary program attempting  to obtain information

-------
                                                                   3






    on the resistivity of the limestone modified fly ash both




    at the test site and in the lab.   THis work is  being done




    by Research Cottrell on a subcontract to B and  W.






d)  Esso Research and Engineering Corporation at Linden, New




    Jersey, has been studying  the application of fluidized bed




    techniques through the development of a dry limestone injec-




    tion process for controlling sulfur dioxide.  In addition,




    they are looking at the possibility of regenerating calcium




    sulfate for reuse in the. fluidized bed with the additional




    objective of recovery sulfur value from the spent limestone.






e)  TVA Fundamental Research Laboratory at Muscle Shoals, Alabama,




    is examining basic chemical and physical properties effecting




    the reaction of SO^ with calcium and magnesium oxides, hydrates,




    and carbonates.  Emphasis is placed on attempting to establish




    the mechanism of the reaction and in establishing the role of




    various physical properties of limestones and dolomites which




    contribute to the reaction.






f)  The Coal Research Board, West Virginia University, Morgantown,




    West Virginia, is examining the potential utilization of




    limestones-modified fly ash and is also evaluating a process




    for recovering unused lime from the limestone modified




    fly ash.

-------
     g)   TVA through  the Applied Research  Branch Division  of  Chemical


         Development  has prepared  a  detailed  conceptual  design and  cost


         study of the dry  limestone  injection process  as it is applied


         to the removal of sulfur  dioxide  from power plant stack gas.



     h)   TVA Division of Power  Production  will conduct a full scale


         field trial  of the dry limestone  injection process at Shawnee


         power plant, Shawnee Unit //10.  The  study is  to be conducted


         in the fall  of 1969.   It  will  lead to the evaluation of the


         process in the field and  development of engineering  and


         operating data which might  be  used by others  in applying


         the process.



     i)   NAPCA is sponsoring a  program  at  the Peabody  Coal Company


         at Columbia, Tennessee, to  obtain test data on  dry limestone


         injection using a - pounds  per coal  fired per hour moving


         bed stoker.   The  object of  this program is to obtain informa-


         tion under controlled  test  conditions. The objective to


         determine extent  to which dry  limestone injection can be


         applied to small  industrial stoker units.
                                                              •"»


Field tests conducted by PCEP and  Florida  Power Company  have  provided


samples of lime which have been subjected  to  furnace temperatures and


actual flue gas coal fired unit.   These samples will be  used  to study


the "dead burning" characteristics of the  stones.

-------
               USE OF FLUIDIZED BEDS OF LIMESTONE BASED
                MATERIALS FOR DESULFURIZING FLUE GAS
                                  By
                              A.  Skopp
                  Esso  Research  and  Engineering Company
                  P.  0.  Box 8, Linden, New Jersey 07036

                     Presented  During Session IV
                   First International Conference on
                       Fluidized Bed Combustion
                    Hueston Woods  State  Park, Ohio
                         November  18-22, 1968
          Among the many processes  being investigated  for  the  removal of

sulfur dioxide from power plant flue gas,  the  injection  of finely sized

limestone or dolomite into the furnace  offers  the  advantage of simplicity

and low initial capital charges.   These advantages are partially offset,

however, by the apparent inability of injection processes  to provide high

sorbent utilization and complete  flue gas  desulfurization.  The reason

for this is that in the short time available to the adsorbent  for the

reaction in a boiler, only the oxide at or  near the surface can sulfate.

Figure 1 shows the range of results which  have been obtained with injection

processes.

          As part of its program to study  ways of  improving sorbent utiliza-

tion, the National Air Pollution Control Administration  contracted a pro-

gram with the Esso Research and Engineering Company to investigate the

use of a fluidized bed reactor for contacting flue gas with limestone

based materials.  Two sorbents were studied extensively  in this program,

a limestone BCR 1359* and a dolomite BCR 1337*. These materials were

evaluated in both a coarse and a fine solids fluid bed.
* Bituminous Coal Research, Inc. designations

-------
                                  - 2  -





          Using the coarsely ground limestone  and dolomite,  high sorbent




utilization could not be obtained, even  when the sorbents were calcined




under pressure-induced conditions chosen to produce porous materials.




With the large particles, only the oxides at or near the surface reacted




rapidly.  Further reaction took place  at reduced rate and for the limestone




was in fact practically non-existent (Figure 2) .




          Additional studies with large  particles were made using fluidizing




conditions selected to promote attrition of the outer sulfated surface as




it formed.  It was felt that this might  provide a continuous method of




removing this surface, thereby exposing  reactive oxide for further reaction.




Particle attrition was promoted by using increased fluidization velocities




and deeper beds.  As shown in Figure 3,  such techniques provided only




limited success because the sulfated surface was found to be harder to




break up than the oxide core.  Consequently, the fluidized particles




decrepitated in their entirety to produce fines of about the same composi-




tion as the coarse sorbent from which they had been formed.




          To demonstrate high oxide utilization, the use of finely ground




sorbent was then evaluated in our program.  As Figure 4 shows, the




dolomite when sized to about 100>y provided calcium oxide utilizations




of 7070  to 80% at conditions which provided nearly complete sulfur dioxide




removal.  Using the fine particle results, commercial process designs




were established and economic analyses made.  Figures 5A and 5B show that




a fine particle fluid-bed process is expensive  (~$2 ton/coal) and requires




single reactor sizes well outside the present state of the art.

-------
                                  -  3  -


          Currently,  the program is  proceeding in  two  directions.  First,

conditions are being  investigated in which coarse  particles  or  a  combina-

tion of coarse and fine particles are  used to achieve  high  sorbent utiliza-

tion.  Second, the possibility of regenerating the partially sulfated

sorbent is being explored actively.  Regeneration  could  be  coupled with

either a direct boiler-injection process  or with a fluid-bed reactor,

shown in Figures 6A and 6B.   In a regenerative process,  the sale  of  a  by-

product such as H9SO,  would  affect part  of the desulfurization  costs.

          Studies made thus  far indicate  a regenerative  process to be

technically feasible.   At temperatures near 2000°F, sulfated sorbent

can be reduced back to its oxide.  This  reduction  is fast and with good

gas-solids contacting sulfur dioxide concentrations close to those pre-

dicted by equilibrium a^e. obtained (Figure 7) .  The regenerated oxide  can

re-adsorb sulfur dioxide although at a reduced capacity  as  shown  in  Figure

8.  Current efforts are being directed at further  defining  the  capacity

loss rate for the cycled sorbents and  at determining the reasons  for

this loss.
A. SKOPP/jmt
10/25/68

-------
                       FIGURE 1
DRY INJECTION PROCESS GIVES LOW LIMESTONE
UTILIZATION & INCOMPLETE

5 . 80
o
^ 60
^
'o
2" 40
CvJ
O
oo 20
0

GAS DESULFURIZATION

1
a 3


CaO + S02 + 1/2 0

_

srf\
^WAWi
/^
i







-

2
MOLES CaC03 IN.


2




"




— >

it

1
l>-


CaO + C02
-r
o




***


aSO^



^
^f^1


^-



3
JECTED/MOLE
630 1260
TONS/DAY -CaC03 FOR 800 MW
so2
1890
*>


-'-



•*"


^-*





••




r
' —




—
'








4
IN
GAS
1
2520
PLANT - 3% S
IN FUEL
68-11101

-------
                                FIGURE 2
                 SORPTION CHARACTERISTICS  OF LARGE  PARTICLES
                  IN A FLUID BED OPERATING WITHOUT ATTRITION
     2700

     2400

  co  2100
  LU
  LU
     1800
     150°
  -  1200
   CM
  O
  CO
  S   900
  (X
  Qu
      600


      300


        0
         INLET S02 CONC.
        12-16 MESH
    CALCINED LIMiESTONE
         BCR 1359
    (MOLE % CaO REACTED)

(5.4%)
(5.1%)
[28%)
                  T = 1600°F
                              12-16 MESH CALCINED
                               DOLOMITE BCR 1337
                             '(42%)
                        20% SO
                                      BREAKTHROUGH
                                TIME ON ADSORPTION'
68-11103

-------
                                ..FIGURE 3
           INCREASING ATTRITION PROVIDES ONLY SMALL IMPROVEMENT
            IN CAPACITY BECAUSE THE ATTRITION IS NON-SELECTIVE
 c
I
 O)
 LLJ
 H-
O

V
                                ACTUAL PARTICLE
                                BREAKUP
                                                            (14.8)
                PREFERRED
                BREAKUP
                FORMATION RATE OF  XFRESH CaO SURFACE REQUIRED
FOR STOICHIO
METRIC REACTION WITH INLET SO.
                    (5.5)
                                           V = 7.0 FT/SEC
                                           T = 1600°F
                                           (%CaO REACTED)
       0
            12         18

              BED  HEIGHT - INCHES
                   24
30

-------
                           FIGURE 4
       HIGH  CaO UTILIZATION POSSIBLE WITH SMALL PARTICLES
      100
  <
  M
  O
  ro
  O
       50
       20
         50
                                          I
               CALCINED DOLOMITE

                   AT 1600°F
                                         _L
100       200          500      1000


AVERAGE PARTICLE DIAMETER, MICRONS
2000
68-11105

-------
                      FIGURE 5A
                   COSTS ARE HIGH FOR
            FINE-PARTICLE FLUID-BED PROCESS
    FLUIDIZING VEL.-FT/SEC
    FLUID BED D1AMETER-FT
    PARTICLE SIZE,M
    INVESTMENT, $MM
    OPER. COST, $/T COAL
       90% LOAD FACTOR
       60% LOAD FACTOR
                             800 MW PLANT - 3% S COAL
  6
 140
100


 12

 2.10
 2.60
  24 :
  73
50-100
   10

  1.90
  2.30
68-11106

-------
                                FIGURE 5B
            COSTS ARE HIGH FOR FINE-PARTICLE FLUID-BED PROCESS
               BECAUSE  OF REACTOR SIZE & SOLIDS ENTRAPMENT
  h-
  U.
   i
  0£
  LU
  H-
  LiJ
  Qi
  O
  h-
  O
  <
  LU
  o:
      500
200
100
       50
         1.0
            2.0       4.0   6.0     10.0      20.0

                 SUPERFICIAL FLUIDIZING VELOCITY
                                                             500
      200
40.0
                                                                  CO
                                                                  2
                                                                  O
                                                                  o;
                                                                  o
                                                                        LU
                                                                        NJ

                                                                        CO

                                                                        LU
      ioo  y
68-11107

-------
                                          FIGURE 6A
                     REGENERATIVE PROCESS WITH COARSE-PARTICLE FLUID BED
                                 DESULFURIZED GAS
                               RETURNED TO FURNACE
                  FURNACE
          TO
         STACK •*
                                          ADSORBER
REGENERATOR
  ~2000°F
                                                                         ACID
                                                                        PLANT
                                                                        H2S04
                     MAKE-UP
                     SORBENT

                     FUEL
                     AIR
68-11110

-------
                                  FIGURE 615
              REGENERATIVE PROCESS WITH FINE PARTICLE INJECTION
              FURNACE
                              DESULFURIZED GAS
                                  TO STACK
                FINELY SIZED
             MAKE-UP SORBENT
                                         GAS/SOLIDS
                                         SEPARATOR
                                     n
 ACID
PLANT
                                                        REGENERATOR
                                                       ~  ~2000°F
                                                            FUEL
                                                            AIR
68-11109

-------
                             TIGURE 7
        EQUILIBRIUM GOVERNS FLUID BED REDUCTION OF CaSO
   UJ
   Z3
   _J
   LL-
   u_
   UJ

   o;
   o
   h-
   <
   C£
   UJ
   2
   UJ
   O
   UJ
    CM
   O
   CO
   UJ
   _l
   o
       10
8
        0
                     0
                     Q
PREDICTED
  EQUIL.
                           REDUCING GAS


                               CO OR H0
                         20%  'C02 OR H20

                         70%   N0
                    SUPERFICIAL FLUIDIZING VEL.,
                         0.8 TO 1.6 FT/SEC
            1800     1900     2000      2100     2200

                    REGENERATION  TEMPERATURE, °F
68-11111

-------
                       . FIGURE 8
           RELATIVE CAPACITY OF CYCLED SORBENT
O
J-
  O
  <
  CL
  <
  O
D_
Ctl
O
CO
o
  I—
                                I
                                        I
                     ADSORPTION —1600°F
                    REGENERATION ~2000°F
                     © ANHYDRITE (CaS04)

                      DOLOMITE
                          _L
                             I
J_
                     34567
                       ADSORPTION CYCLE
                                             8
68-11112

-------
A ROLE FOR FLUIDIZED COMBUSTION IN CLEAN POWER SYSTEMS


Arthxir  M.  Squires
Department of Chemical Engineering
The City College of The City University of New York
New York, New York 10031

presented during Session IV
First International Conference on Fluidized  Bed Combustion
Hueston Woods State Park, Ohio
November 18-22,  1968


        This paper  examines a steam cycle believed to deserve consideration

in equipment cost studies for "clean power systems" which utilize low-sulfur

coke in fluidized combustion.  Also,  an improved processing scheme is

described to provide such a coke.  Heat rates are  given for a complete clean

power system incorporating the proposed features and using cycle parameters

felt to represent reasonable near-term objectives.


Introduction:  An Argument for Higher Steam Temperatures

        With development of the fluidized combustion technique,  re-examination

of steam cycle parameters would appear to be timely.  Most large recent

stations employ either  2,400 or 3, 500  psi steam at about  1000° F.  These

steam conditions evolved following experience gained about a decade ago from

units  designed for 4, 500 to 5, 000 psi and 1150 to 1200°F.  In 1958 Sporn and

Fiala (1) wrote:  "Studies  of the effect  of initial temperature indicated that

all operating temperatures above 1050 required extensive use of stainless

steel in steam generating  tubes [and] in piping and turbine  parts.  In the

range of temperatures  from 1050 to 1250 F  the gains of increased performance

are not adequate to bear the heavy capital burden of the austenitic materials.

-------
.  .  . Temperatures higher than 1050 F cannot be economically justified

at this time." One gathers that troubles with both hot-side and cold-side

corrosion in the 4, 500 to 5, 000 psi experimental boilers led to the conclusion

that temperatures as high as 1250°F would be a practical impossibility in a

conventional boiler.

       With fluidized combustion, steam temperatures appreciably above

1000°F come again into view.  Higher tube-wall temperatures and a higher

heat flux across steam-superheating surface can be achieved -- reducing the

quantity of high-cost stainless  steel tubing required -- yet the tubes are not
                                                        . /            '    '
necessarily subjected to conditions which are dangerous for  either hot-side

or cold-side corrosion.   The complex, molten alkali-iron sulfates which are

responsible for hot-side corrosion at about 1200° F in  a conventional boiler

cannot form at the higher temperatures suitable for fluidized combustion.

Cold-side corrosion should also be less of a problem,  since metal temperatures

cannot rise unduly if deposits form within a tube.  If the fluidized combustion is

conducted at an elevated pressure — at around 8 atmospheres,  say --

a higher heat-transfer coefficient could be exploited in part to permit a still

higher heat flux and in part to  reduce the bed temperature,  giving greater

insurance against cold-side corrosion.

       What is suggested is that equipment cost studies are now in order

to see whether or not the 1200°F and higher steam temperatures contemplated

around 1955 might today seem again an economic proposition.  If so,  the

improved heat rate which such temperatures can afford may provide an offset

against the cost of measures taken to eliminate sulfur oxides from boiler

stack gases.

-------
A Steam Cycle for a Clean Power System


       Both Consolidation Coal Company (a subsidiary of Continental Oil Co.)


and the FMC Corporation (2, 3) have proposed schemes yielding a low-sulfur


coke for power-station use.  Such a fuel is nearly ideal for fluidized combustion.


A case to consider in studies of equipment for clean power would be a fluid-bed


boiler fueled with such coke, operating at atmospheric pressure, and serving


a conventional steam cycle at 5,000 psi and 1200°F,  say.   Two factors, however,


argue the advisability of examining other cycle alternatives:  (1) The idea of


"supercharging"  the fluid-bed boiler is appealing and indeed may be necessary


to achieve attractive  costs for  high steam temperatures.   (2) Requirements of


water purity are so  stringent if 5, 000 psi steam is to be carried to 1200°F that


one may wish to examine cycles employing sub-critical steam pressures on


that account.


FIG.  1      A Steam  Cycle to Exploit the Fluid-Bed Boiler's
            Ability to Superheat Steam to High Temperatures



                         STEAM  TURBINES
   FLUE GAS
  LOW-SULFUR
   COKE
   AIR
                       LOW-LEVEL HEAT RECOVERIES

-------
     12.OO

     IIOO

     1000

   u.  qoo
  o
      8OO
   UJ
      700
   <  GOO
   CC
   HI  BOO
   a
   S  400
   UJ
   {-  3OO

      200

       !OO
  I.HI IBS. VAPORIZED
   /     I.Q IB.TO CONDENSER  V
            i  I  i
           '  I  I
             1.0.       1.5       2.0        2.5        3.0       3.5
                 ABSOLUTE  ENTROPY,  BTU PER °R
FIG. 2.
Temperature-Entropy Diagram for the Steam Cycle of FIG.  1.
[ NB.  Entropy is treated as an extensive variable, rather than
as an intensive one in the more usual manner. ]
       Figure 1 illustrates diagrammatically a steam power cycle (4) adapted

for sub-critical steam pressure and well suited to receive heat from a fluid-bed

boiler operating at high pressure.  The cycle is characterized by the addition

of an unusually large amount of superheat to the steam.  Three high-temperature


steam-expansion turbines are provided.   Steam from the third turbine is cooled

against water ahead of a fourth, low-temperature steam turbine, which exhausts

to a condenser.  Figure 2 is a temperature-entropy diagram of the cycle for


the following conditions:  2,400 psia and 1200°F to  the first turbine;  two reheats


to 1200°F;  15 psia exhaust from the third turbine (at 767°F);  260°F entering

-------
the final turbine; and 100°F exhaust (at 7.89% wetness).




       An advantage  of .the  cycle illustrated by Figures 1 and 2 is the fact that




the water receives  an appreciable amount of low-level heat in addition to the




heat picked up regeneratively from the 15 psia third-turbine exhaust. This




can be understood when it is remembered that water has a higher heat capacity




than steam.  This advantage of the cycle is important when combustion is




conducted at high pressure. Since air to such combustion is heated by




compression,  cold air is not available for cooling flue gas to a low stack




temperature.  The  cycle  of. Figures 1 and 2 provides cold boiler-feed-water




for heat exchange against flue  gas without a penalty in efficiency.




        The advantages of the cycle can be understood by  comparing Figure 2




with Figure 3,  which gives  a temperature-entropy diagram for a conventional




cycle using 2,400 psia steam at 1000°F,  one reheat to 1000°F, seven




regenerative boiler-feed-water heaters,  and 100°F exhaust.  The net cycle




efficiencies in Figures 2 and 3 are 47. 1 and 44. 7 per cent respectively




(net  work divided by  net heat intake to water).  All heat taken into the




conventional cycle  of Figure 3 is at a level above 477° F,  and cold boiler-




feed-water can be provided for heat exchange against flue gas  only with a




penalty in efficiency.  If heat is furnished to  the cycle below 477° F *•-




at expense of reduction in size of all except two coldest regenerative heaters




-- such low-level heat is converted to work at only 29. 2 per cent efficiency.




By contrast, the cycle of Figure 2 receives 10. 5% of its net heat intake at




levels below 477° F.  The throttle steam flow in Figure 2 is more than 30%




less than that in Figure 3 for the  same net work.

-------
     I2OO


     IIOO


     IOOO
LL qOOr-


jaooh

5~ TOO -


< ©OO

DC
yj 5OO
CL

S 4O°
UJ
»- 3OO


   200


    too
                       1.455 IBS. VAPORIZED
                  .,



                    1.0 LB. TO CONDENSER   \"
                !
                                                             ±
             1.O        I.5       2.O       2.5        3.O       3.5

                 ABSOLUTE ENTROPY, BTU PER  °R
FIG. 3.  Temperature-Entropy Diagram for a Conventional Steam Cycle.



       The equipment of Figure 1 could operate in cooperation with a gas-turbine



cycle providing air and expanding flue gas.  At 1600° F gas-turbine-inlet



temperature and 300° F stack temperature, a heat rate of about 7, 534 Btu



per kilowatt-hour sent out would  appear attainable for a typical low-sulfur coke.




A Process for Converting  Coal into Low-Sulfur Fuels



       The aforementioned schemes proposed by Consolidation Coal and



FMC (2, 3)  would provide a low-sulfur coke as a byproduct of operations



yielding products of higher value: in the case of Consolidation Coal, either



hydrogen or pipeline gas;  in the  case of FMC,  a liquid feedstock for refining



into gasoline and other liquid products.   Both schemes rely upon a lime-containing

-------
acceptor to promote the action of hydrogen in desulfurizing a char obtained


from a prior coal-carbonization step.


       Figure 4 shows an improved procedure whereby coal is carbonized


and the products  are desulfurized in a single unitary operation,  having production


of low-sulfur fuels as a sole objective. The fuel-processing vessel depicted in


Figure 4 consists of three zones:  (1) a coal "hydrocarbonizing" zone,  in which


coal is converted into gaseous products and coke pellets roughly 1/4 inch in


diameter,  say;  (2) a desulfurizing zone, in which sulfur is removed from both


gaseous products and coke by action of hydrogen and a lime-containing acceptor;


and (3) a calcination zone, in which CaCO^ is decomposed and gaseous


carbonization products are partially burned with air to provide a lean fuel gas


containing hydrogen.  The air flow is approximately 11 per cent of the


FIG. 4. -   Processing Scheme to Convert Coal into Low-Sulfur Fuels
CALCINATION
                                  LEAN FUEL GAS
                                 (LOW IN SULFUfc)
                                            cuus
                                            SYSTEM
 DESULFUR1ZJNG
        ZONE'
                                     ELEMENTAL
                                        SULFUR
                                      TO MARKET
              COAL
                AND COKS 6SLF-
              'AGGLOMERATING ZONE
 LOW-SULFUR
COKE PELLETS
                                   RECYCLE OF PORTION
                                    OF LEAN FUEL GAS
                                  (CONTAINING HYDROGEN)

-------
stoichiometric for  complete combustion of the coal.  A portion of the lean




fuel gas is recycled to provide fluidizing gas to the coal hydrocarbonizing




zone.  The lime-containing acceptor is much smaller in size than the coke




pellets -- the acceptor might be smaller than 40 mesh, say.  Fluidizing-gas




velocity is much higher in the coal hydrocarbonizing zone than in the other




two zones, to prevent the acceptor from sinking into the former  zone.  The





desulfurizing zone  contains an intermingling of coke pellets and acceptor.




Coke  pellets circulate at a high rate between the hydrocarbonization and





desulfurising zones,  the pellets tending to be ejected from the former zone





into the middle of the latter,  and thereafter tending to sink downward near




the walls of the latter because its fluidizing-gas velocity is below that needed





to maintain a high  concentration of coke pellets therein.




       Finely ground coal is fed to  the hydrocarbonizing zone, which operates




at 1400°F, say.  A coal particle is  heated almost instantaneously to bed




temperature, and almost at once, the  coal is split into a gaseous fraction,




comprising mainly methane and hydrogen, and a sticky, semi-fluid residue.




The latter  is  "captured" by a coke pellet, sticking thereto to form a "smear"




upon the surface of the pellet.  Further coking reactions, which occur in the





order of a  second or so, transform the sticky smear into dry coke and  cause





additional gases  and  vapors to evolve.  Soon thereafter, the given coke pellet





finds  itself in the desulfurizing zone, and the freshly-made coke is desulfurized





by action of hydrogen and acceptor.  Thus, desulfurization is substantially





simultaneous with  hydrocarbonization.  Practically speaking, no "aging" of





the coke product occurs between its formation and its exposure to desulfurizing





conditions.   Desulfurization should be rapid, because H2S formed by action

-------
of hydrogen upon the coke need not diffuse outward from within micropores




deep inside a char or coke structure, as in the Consolidation Coal and FMC




operations  (3).





       For operation at 21 atmospheres, a calcination zone  temperature of




1740°F is adequate.  Many lime-containing solids -- especially many natural





dolomites -- can be subjected to this temperature repeatedly without loss of




reactivity for desulfurization at 1400°F (5,  6).   At this pressure,  the





coal-treating capacity of the vessel in Figure 4 is such that one can visualize




a single vessel to serve 1, 000 megawatts of electricity-generating capacity.





At a fluidizing-gas velocity of 1. 5 feet per second,  the calcination zone  would





be 30 feet in diameter.  Since only a shallow bed is needed,  this zone might




be housed in a sphere  communicating to a 20-foot desulfurizing zone below.





       Calcium sulfide can be regenerated by action of steam and carbon





dioxide at about 1000°F to form a gas rich in hydrogen sulfide  (7),  which




is readily converted to sulfur.






A Clean Power System for Coal




       Figure 5 illustrates a combination of power-generating equipment




with the coal-desulfurization process of Figure 4.  In working  up an example




of this combination, the steam cycle of Figures 1 and 2 was  assumed.   Coal





containing 3. 72 per cent sulfur (moisture-and-ash-free basis)  was used.  Air




can be compressed to about  8 atmospheres and flue gas can be expanded in





conventional gas-turbine equipment.  A gas-turbine inlet temperature of





1600°F and a stack temperature  of 300°F were taken. About 10. 5 per cent





of the air was further compressed and supplied to the coal-desulfurization





process.  Lean fuel gas was  reheated to 1300°F by indirect heat exchange

-------
                                                       FLUE GAS
                                                        TO STACK
                                               CO* RECOVERY
                                                            C02TO
                                                            SULFUR
                                                         DESQRPTSON
                                                     REMOVAL
         PUBS. 6AS
                                              FLUID-BSD
        LEAH FUEL GAS
                           COKE PELLETS
        COAL DESULFURIZATION
FIG. 5.  Power-Generating Equipment to Cooperate with the Scheme of FIG. 4.



and was expanded from about 21 atmospheres to a combustion at about 8


atmospheres.


       For generation of electricity at a rate of 1, 000 megawatts,  some


features of the plant are as follows:


           Air flow = 6, 188, 000 pounds per hour, easily handled by 4 machines


           Throttle steam flow = 3, 902, 000 pounds per hour


           Coal  feed = 272.25 tons per hour (m. a. f.)


           Heat  rate = 7, 887 Btu per kilowatt-hour of electricity sent out


                (allowing 5% for losses and station auxiliaries)


           Sulfur production =199 long tons per day

-------
TABLE 1.

Energy Balance for Clean Power System Producing Electricity and Sulfur Only

Basis:  Higher heating value of coal (HHV) = 100.00

       Net shaft work                  45. 13

       Heating value of sulfur           0. 93

       Heat to cooling water            45. 34

       Sensible heat to stack            4. 64

       Latent heat to stack              3. 98
                                      100.02

Heat rate (taking credit for sulfur and allowing 5% losses):

  3,412. 75x (100. 00  - 0.93)/45. 13x0. 95 =  7, 887 Btu per kilowatt-hour


Table 1 presents an energy balance (before allowance for losses) and illustrates

the calculation of heat rate.

       The coal-desulfurization process of Figure 4 might  also be operated to

furnish baseload power from the combustion of the lean fuel gas  and  to supply

low-sulfur coke to other power stations at a distance.   If four vessels of the

size already  described are provided, the plant would have features as follows:

           Electricity rate =  1,082 megawatts

           Air flow = 7, 298, 000 pounds per hour

           Throttle steam flow = 3, 714,000 pounds per hour

           Coal feed = 1, 098 tons per hour (m. a. f.)

           Heating value of coke product = 68. 5  per cent of coal

           Heat rate = 9, Oil  Btu per kilowatt-hour of  electricity sent out

           Sulfur production = 797 long tons per day

Table  2 presents an energy balance.

-------
TABLE 2.

Balance for System Producing Electricity,  Sulfur, and Low-Sulfur Coke

Basis: Higher heating value of coal (HHV)  = 100. 00

       HHV of coke              •       68.46

       Net shaft work                  12.20

       Heating value of sulfur           0. 93

       Heat to cooling water            13. 79

       Sensible heat to stack            1. 76

       Latent heat to stack              2. 87
                                      100.02

Heat rate (taking credit for sulfur and coke and allowing 5% losses):

  3,412. 75 x (100. 00 - 68. 46  - 0. 93}/12.20x0. 95 =  9,011 Btu per kilowatt -hour


       If the coke product is  shipped to stations producing electricity at the

aforementioned heat rate of 7, 534, the average heat rate for all of the

electricity produced from the coal  is 7, 990.

Concluding Remark

       Study is needed to evaluate  the proposals  of this paper.  The author

fully recognizes that other steam cycle  arrangements and parameters are

capable of providing the  heat  rates stated here.   He also recognizes that the

cost to achieve such heat rates in steam cycle equipment,  of whatever type,

may prove uneconomic,  even with the help of fluidized combustion.  It is too

early to  conclude  that "clean  power" may also be cheaper power,  but to the

author, this  seems at least a sporting proposition.

-------
           References

           1. Philip Sporn and S. N. Fiala, "Evaluation of Supercritical Pressure Steam
                  Plants Based upon the First-Time Operating Experience at Philo",
                  World Power Conference, Montreal, September 1958, Paper  111 Bs/5.
j
j           2.  F. W. Theodore, "Low Sulfur Boiler Fuel Using the Consol CO£ Acceptor
:                  Process:  A Feasibility Study",  Report from Consolidation Coal Co.
'                  to Office of Coal Research,  November 1967, OCR Contract 14-01-
•                  0001-415.
5
i           3.  John  F. Jones, Michael R.  Schmid, Martin E.  Sacks,  Yung-chuan Chen,
:                  Charles A. Gray,  and R.  Tracy Eddinger,  "Char Oil Energy
                  Development",  Report from FMC Corporation to Office of Coal
                  Research, January 1967,  OCR Contract 14-01-0001-235.

           4.  Arthur M.  Squires, "Clean Fuel Power Cycles",  ASME Paper 67 —
                  WA/PWR-3,  November 1967.

           5.  Arthur M.  Squires, "Cyclic Use of Calcined Dolomite  to Desulfurize
                  Fuels Undergoing Gasification", Advances in  Chemistry Series 69,
                  205-229, American Chemical Society, Washington, D. C.,  1967.

           6.  George P.  Curran,  Carl E.  Fink,  and  Everett  Gorin,  "CO2 Acceptor
                  Gasification Process:  Studies of Acceptor Properties",  ibid., 141-165.

           7.  Arthur M.  Squires, "Processes for Desulfurizing .Fuels", U. S. Patent
                  3,402,998 (September 24, 1968).

-------
                   RETENTICIT OF SULPHUR BY LIMESTOKE
                           D.  F.  Williams
                         Rational Coal Board
                     Coal Research Establishment
                    Stoke Orchard, Glos., England
                      Presented during Session IV
      First International Conference on Fluidised Bed Combustion
                   Hueston Woods, State Park, Ohio
                         November 18-22 „ 1968
         Measurements have been made of the emission of sulphur as .
sulphur dioxide and trioxide, and its retention as sulphate in the ash,
secondary cyclone fines and dust, during the combustion of coal in a
6 inch diameter fluidised ted.  The combustion conditions in these runs
were as follows:   temperature, 800 C;  fluidising velocity, 2 ft/sec;
bed height, 2 ft;  excess air, 10 - 20$;  primary cyclone fines
recycled to the bed.
         It was found that the amount of sulphur retained depended on
the relative proportions of sulphur and carbonates in the coal.  Thus,
Babbington coal contained 0.6% sulphur and its stoichiometric equivalent
of calcium and magnesium carbonates, and more than Uo$ of the sulphur
was retained, whereas Goldthorpe coal contained 2% sulphur and 0.5$
carbonate, and only 10 - 15$ of the sulphur was retained.  Farmington
Ho. 9  coal contained a similar amount of sulphur to Goldthorpe coal
(2.3$), but more calcium carbonate (l.25$, as CO), and about 25$
of the sulphur was retained.

-------
;                      In  further experiments limestone ground to the same size
I             as the  coal  (minus l/l6 inch) was added to the Goldthorpe or
3             Farmington coal  feed and was found to increase the retention of
i
I             sulphur.  Addition of about twice the stoichiometric quantity of
|             lir^estone (12$ by weight) to Goldthorpe coal led to the retention
j             of virtually all the sulphur, only about 10 p.p.m. remaining in
]             the  off-gas.  On addition of a similar proportion of limestone to
j             Farmington coal, 80$ of the sulphur was retained.
j                      It was noted that, following the addition of limestone,
\
I             the  sulphur content of the off-gas reached its new equilibrium
i             level much more rapidly than the  free lime content of the bed,
I             which continued to increase for several hours.  Comparison of the
]             data from different runs  also indicated that the proportion of  free
1
             line in the bed did not affect the sulphur content of the gas.
\             This suggested that most  of this  lime lay in the interior of each
             particle and  was  not readily accessible.  Accordingly, for a further
             run  the limestone was crushed to  minus 120 B.S.S. mesh (12U microns)
             before addition to the Goldthorpe coal, and it was found that less
             than lg times the stoichiometric  amount of limestone was required
             to retain all the sulphur.

-------
              The Control of Sulphur Emicsion by
            adding Limestone to the Combustion Bed
                             by
                          S.J,Wright


                BCUBA  Industrial  Laboratories
                 Leatherhead, Surrey, England
                 Presented during Session IV

    First International Conference on Fluidised Bed Combustion

               Hueston Woods,  State I&rk, Ohio,

                     November 18 - 22, 1968,
      Work on the addition of limestone to the combustion bed of the


BCUKA pilot-scale combustor is in its early stages and a. comprehensive


investigation will involve a variety of types and size ranges of


limestone and experinents of up to JO hours duration.


      Preliminary results, however, suggest that, whilst the


addition of limestone improves the percentage retention of sulphur

                                                   fno t-S-.
in the solids, the reactions CaCo_  -r> CaO ~* CaSO^ are very inefficient


especially in the £"-0 bed, and it will be necessary -to ensure the nost


favourable conditions - high surface area and reactivity together with


limestone additions well in excess of stoichiometric - before a

satisfactory level of sulphur retention is obtained.

-------
                          OUTLINE

          POLLUTION CONTROL BY MEANS OF ADDITIVE
                         INJECTION

                             by

                       E.  B.  Robison
                  Pope, Evans and Robbins
                   Alexandria, Virginia
                Presented During Session IV
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968

-------
     POLLUTION CONTROL BY MEANS OF ADDITIVE INJECTION







A number of potential advantages of the fluidized combustion



process have been pointed out in the past for control of air



pollution by additives.  Among these are the following:



(1) The random motion of the fluidized bed of inert granules



could provide an ideal environment for contacting additives



for sulfur capture from a coal flame.





(2) The fluidized bed can be operated in the 1500-1800°F tempera-



ture/ a range which some investigators have found to be optimum



for sulfur capture.





(3) Additional gas-solids contacting is provided by a dilute



phase of solids above the bed.





(4) The turbulence and rapid mass transfer in the fluidized bed



could provide for a uniform distribution of the solid for further



contacting in the flue passages.





(5) The random motion of the bed could possibly erode away a



sulfate product shell and continuously expose an unreacted surface



for further sulfur capture.






One major objective of the current research effort for the




National Air Pollution Control Administration is to determine



the effectiveness of adding limestone to the fluidized combus--



tion process for emission control.





Additive tests have been conducted in both the pilot scale



fluidixed bed column  (FBC) and the full scale boiler module  (FBM)

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with continuous monitoring of sulfur dioxide, hydrocarbons and



nitric oxide emissions.  The additive used in the tests were




selected on the basis of reactivity tests conducted by NAPCA.



One additive was a 50-50 dolomite designated BCR 1337 and the



other a high calcium limestone BCR 1359.  The additive particle



size was selected at -7 + 14 mesh for retention in a bed



material of -8 -f 16 mesh sintered coal ash.






The continuous monitoring of emissions permitted relatively



rapid change in the operating variables in the course of a



single test.  The operating variables included the bed tempera-



ture, bed height, excess air, the additive and coal rateo,




coal type, ash recirculation rate and water injection.  The



coal vised in tests conducted thus far has been a high sulfur



(4.5%) high volatile, unwashed coal.  The coal and additive



were screw fed into a pneumatic line and injected into the



bottom of the bed.





The test results showed that sulfur capture by the BCR 1337



dolomite is favored by low bed temperatures, high beds and



excess air.  The most favorable sulfur dioxide reduction with



this additive in this size consist was 54%  a va•   obtained



at 3% excess oxygen in the effluent and a 10 inch L>-^d operating



at 1500°F and an additive ratio of 1.4.  A 65% reduction was



achieved but at a less favorable stoichiometric ratio.

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 The  BCR  1359  high  calcium  limestone  was  less  effective.




 The  best sulfur  dioxide  reduction values were 28%  at  a



 stoichiornetric ratio  of  1.5.   The reduction was  less



 sensitive to  bed temperature  than the  BCR 1337 additive



 but  was  again favored by high beds .and excess air.  With




 both additives a small improvement was noted  with  ash



 recirculation.






 As a rule,  the additive  shows very little effect on either



 the  hydrocarbons or nitric oxide  emissions.  In  one excep-




 tion,  however, -a 44%  reduction in nitric oxide emission



 was  noted in  one test while feeding  BCR  1337  at  a  1.75 ratio.



 A check  on the possibility of leaks  or a gain change  in  the



 recording system indicated that the  result was real.  About




 the  same time a  clinker  formed in the  bed as  indicated by




•a sudden divergence in the temperature indications of adja-



 cent theriaoscouples.






 Mixtures of dolomites and  ashes are  known to  form  eutectics



 with melting  points Tower  than either  component.  Melting



 of the additive  may ."  ve interfered  with the  formation of




 NO by limiting a local high temperature  in the fusion process



 Another  possibility is that calcination  of the stone  could



 have reduced  local temperatures.

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At this point in the program NAPCA suggested thcit we might


improve the sulfur capture by reducing the additive parti-


cle size to -325 mesh.  This reduction in particle size


from the -7 + 14 mesh increases the lateral surface per unit


mass by a factor estimated at 40.  The only adverse effect


of using fine particles could be a shortening of the particle


residence time in the bed.


                             *
Tests were begun with the hydrated form of the D.imestone which


occurs naturally in a 97% -325 mesh -- commonly known as


"milk of lime."  The hydrate addition produced a sharp reduc-


tion in sulfur dioxide emission.  With the BCR 1337 dolomitic


hydrate a reduction of 89% was achieved at a 1.8 stoichio-


metric ratio based on the calcium fraction of the dolomite.


Similar reductions were achieved with the BCR 1359 high


calcium hydrate.

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                    PILOT STUDIES IN FLUIDIZED COMBUSTION

                            ^p»      by

                         -f      Paul S. Lewis
                            U.S. Bureau of Mines
                          Morgantown, West Virgini:iaj?t
                                                   *'•
               Presented during Session IV, Pollution  Control,
                   Control by Means of Additive Injection
         Firs-t International Conference on Fluidized Bed Combustion
                       Hueston Woods State Park, Ohio
                            November 18-22, 1968
     Fluid-bed combustion offers possibilities  for  retention of sulfur

in the solid .discharge.  The capacity of a given  coal  ash  to retain

sulfur will depqsid upon its composition, but  this can  be adjusted and
               ™'':' •.•"..
controlled by the ^addition of other material  to "trie fuel bed.   Our experience

                       s                        *"           '      '   •
in burr.ir.q hvab coc.1, rfttsburgh seam, having an  ash containing 6% CaO,

with mullite grog containing no CaO is that about 10%  of the coal sulfur

is in the solid discharge and 90% appears in  the  stack gas as sulfur
                                              f
dioxide.  The distribution of sulfur in the solids  for one experiment

burning Pittsburgh coal is as follows:

                                        Sulfur  content, percent

               Coal feed                          2.6

               mullite feed                       trace

               flue dust                          0.3

               raullite discharge                  0.02

     An investigation will be started in the  near future  to determine

the effect of limestone addition on retention of  sulfur.

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                       Session V

             Barriers to Commercialization


             Thursday evening, November 21
Discussion of the practical technical,  economic,  and social
problems associated with developing widespread utilization
of fluid bed combustors for steam and power generation.

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                         ABSTRACT

 BARRIERS  TO COMMERCIALIZATION OF THE FLUIDIZED BED BOILER

                            by

                       A.  H.  Bagnulo
                  Pope, Evans and Robbins
                   Alexandria, Virginia
                Presented During Session V
First International Conference on Fluidized Bed Combustion
              Hueston Woods State Park, Ohio
                   November 18-22, 1968

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                       ABSTRACT


BARRIERS  TO  COMMERCIALIZATION  OF THE FLUIDIZED  BED  BOILER
          » ..            •.




•A proper  analysis of  the  problem of  bringing  a  new  idea to



full  fruition  must  take as  its first consideration  the



competitive  superiority of  a new idea or  its  potential



superiority  as far  as these can be determined on  a  realis-



tic plane.   This superiority is the  driving force toward



final accepteince and  utilization.





Major problems in promoting the commercial  use  of the



fluidi'zed bed  boiler  stem from the following:



   a.  The fluidized  bed  boiler shares the  problem  common



to the development  of all new  ideas:  the development process

                            \

from  concept through  demonstration of commercial  feasibility



requires  expenditure  of a significant amount  of money.




   b.  The trend away from coal in'the direction  of oil, gas



and nuclear fuels has gained a momentum which is  difficult



to reverse.  This makes, it difficult to obtain  support  for



the development, effort from government or private sources.





   c.  The new air  pollution control regulations  being



'promulgated are acting as a deterrent against coal.  Even
                                               \


where favorable economics under present conditions  can  be



demonstrated,  uncertainty about the  future  increases the



 risk  factor in the  minds  of supporters and  users.

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   d.  Boiler manufacturers have backlogs of orders for




conventional boilers.  This destroys motivation for incur-



ring the costs for a ne.w product.






On the positive side, when competitive superiority can be



demonstrated, interest will develop.  The fluidized bed




boiler concept has been carried a long way in the develop-




ment phase.  A complete picture of its superiority in our



present environment and its potential in the future for




air pollution conti'ol and capital cost reduction is




emerging.






Both of the government agencies sponsoring the development,




NAPCA and OCR, are interested and have indicated the
                            •:


intention of continued support depending on the funding



situation.

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             Getting KLuid Bed Boilers into Service




                            by



                        G.G.Thurlow



                 BCURA. Industrial Laboratories

                 Leatherhead,   Surrey, England




                 Presented during Session V


     First. International Conference on Fluidised Bed Combustion


              Hueston Woods State Park,   Ohio,


                     November 18 - 22, 1968
1.  There are obviously still many technical problems to be solved before



    the full benefits of fluidised combustion systems can be realised.



    Whilst a better understanding of the processes taking place in the  bed



   (rate of coal distribution, residence times,  local heat transfer rates)



    will be most useful, most of the technical problems are of a nature


    that can, now,  only be solved by working on  plant representative



    of the actual,  commercial unit.



          These problems include -


              reduction of carbon loss by the optimum design of recycling systems,



              turn down ratio



              erosion and corrosion



              ignition


2.  Technical developments must be matched by market research and



    economic studies.  The conclusions of these  will be specific to the



    size of plant and to the country in which the studies are carried



    out.



3.  Design studies on a large number of alternative designs of plant should
                            j


    be a continuing activity.  While it is obviously necessary to select a

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    limited number of what appear to be the most promising designs  and  to




    develop these as fast as possible,  it is equally important not  to




    "freeze" the design of plant prematurely.




k.  The commercial exploitation of the  industrial boiler (up to say




    100,000 Ib/h) is simplified by the  fact that it is economically




    feasible to build, test and modify  prototype plant.




5.  The problem is more difficult when  one considers power station




    applications.  While useful design  data are and will be gained  by




    tests on pilot-scale plant (some of which is already of considerable




    size'and complexity) it is imperative (at least in the U.K.) to




    "prove" the value of this system in the shortest possible time  and




    this can only be done by building in the next year or two, plant at




    least representative of a section of a large boiler.  Such a pilot-




    scale plant (which will probably be of the order of J>0 MW) will be




    costly and it will probably be necessary to finance such projects




    by collaborative effort.

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" DEVIL'S  ADVOCATE"  COMMENTS ABOUT  BARRIERS




                 TO COMMERCIALIZATION
                By Albert A. GODEL




      President of the "Societe Anonyme Activit "




                      Paris
           presented during Session V (November 21)




   First International Conference on Fluidized Bed Combustion




                 Hueston Woods State Park , Ohio




                   November 18-22,  1968

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                                                                       1  -
             As far as barriers to commercialization are concerned,


I am afraid that I will have to take the uncomfortable position of the


'Devil's advocate" in putting forward for your reflection a number of


objections which I do not wholly accept myself.


             Though many problems have been solved by American


and British development Organisations, I believe that difficulties still

     '   /be
remain to overcome. Namely the flifficulty of reaching the highest pos-


sible thermal efficiency which means first of all solving the difficult


problem of heat Change  in fluid beds at low temperature. Secondly


burning to its last content of carbon  the entire amount of fly ash


carried over by flue gas. On this last point, I understand that serious


improvments  have been accomplished in this country and in Great Britain,


but I would be very interested to know whether the problem  has. really


been solved by any other method than the one I have proposed of total


reinjection in a high temperature slagging fluid bed. It is only when


this is achieved that industrialisation and regular sales can be thought


of and this will probably require  several years ; then who knows what


the trend  of the coal industry will be ? .


             I think that a distinction should be made  between processes


using fluid beds as heat exchange medium and other combustion fluid bed

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                                                                  -  2 -
  processes simply built under standard boilers.




               To this latter type belongs the Ignifluid process which has




  now become more or less conventional so that the only development pro-




  blems lies in increasing the size of a conventional unii .




  But since we are dealing with such conventional types of boilers,  there




  will be no serious problem to pass from the present 60 MW to a larger   plant.




,.. Yl should  mention also that to accomplish the corresponding expansion of




  the furnace,  the necessary widening of the stoker from 1.40 m to 2 m.




  presents little difficulty.




               It remains to be determined  of course, whether such




  simplified process which does  not make use of heat transmission in




  fluid beds is really competitive with the conventional method of burning coal




  namely P.P.




               I believe I may be positive on this point : though not pre-




  tending to drastic savings, the saving on investment cost would still be




  about 12 % to 15  % for a utility power plant boiler burning bituminous coal,




  or 18 % to 25 % when burning anthracite,  and these figures will be improved




  in the future.




               Moreover, savings on power consumption for crushing are




  to be considered to the extent of 0,5 to 0,75£of the power production when




  using treated coals, savings are much more important for high ash coal.

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             Now coming back to the process with heat exchange tubes
in the fluid bed, I am afraid that there is no evidence that this technique
can be reasonably and profitably applied all along the circuit of  the flue
gas. For in fact,  if we compare the amount of heat transmitted to radiating
panels at 250°C in a conventional P.P.  furnace (or an Ignifluid furnace), at
about 1300°C, to the amount of heat transmitted to vaporizing tubes at 250°C
in a fluid bed at about 850°C, we find the following  figures :
                                 Heat  coefficient           Transferred ambuhf
                          per Kcal/C°/sq.m./hr.     of heat  / Kcal/sq.m./hr.
first case (radiating  panels)          160                   170.000
second case  (tubes in fluid  bed)      300                   180.000
             These figures  show that the operation is not certainly _ec~
of flue gas passing in a much cooler zone, say from 850°C to 200°C for
instance, we are confronted with another difficulty which is the necessity
of using several beds and this, I admit, is what I have advocated Vo? our
prospective development. My excuse is that it would seem desirable in such
case .    to take advantage of high heat transmission coefficient in the bed,
when heat trasmission needs increasing surfaces, but it is  a fact that
recovery of heat in flue gas at reduced  temperature should also  be extended

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                                                                     - 4  -
to its extreme limits even at the cost of grave difficulty.


             As regard, this problem of limiting efficiency, it is well


known that when comparing ivestment cost for boilers having different


thermal efficiencies, one generally c.orivarts :-: intouweiVmtnfthe actual


amount of loss on  efficiency.


             In this respect, the following example will be of interest :


the French Electric Authorityd.etermine^ few years ago that "one point "


lost over efficiency in a 250 MW P.P.  power plant, which cost appro-


ximately 215 millions frs., if amortized over thirty  years, corresponds


to an actual   .  cost of : 3 million frs.


             This as you see, corresponds to  1,39 % of the cost of the


plant. But if the loss of 3 millions frs.  is affected, as it will surely be

                /single
to the cost of the  ._   . boiler which is approximately 50 millions frs., then


the actual,     loss would be 6 %.


             This gives a good idear of how necessary it is to pbtain


high efficiency whatever be the cost'. Although the problem is different for


small giants, it would be uneealistic to believe that customers will be


impressed by the low cost of a boiler if the thermal efficiency is not


sufficiently high Therefore, a drastic effort must be made in our deve-


lopment work to comply with this obligation.


              Now another observation  I want to submit to your reflection


is that I am afraid most of the important boiler manufacturers with order.


^backlogs         will hesitate  before  entering into the study of drastically


new types of coal fired boilers with uncertain future, and the same reluctance

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                                                                 -  5  -
might be felt for exploitation by customers .


             This shows how wise you were in the United States to coor-


dinate such development work under government authority.





             Last of all, I want to call your attention to the following


 .disadvantage   •       . through developing coal combustion and heat


exchange processes in fluid beds, we are perhaps running the risk of


"making the bed" of competitors interested in burning gas  or fuel oill!


             Yet, all this taken into account, I am still convinced that


most of the above difficulties will be overcome and also that the fluid


bed combustion technique has an attractive  future - because

               /reduce
of its ability to      pollution problems.

-------