P. 1


# OAR Box 1865 Prepped by Charmelle Mathews



## Document

Number: 

# 63 ) IV-J- 6 Docket Number: 

# A-83-2 7

Printed 12/3/20089:15:30AM

Sheet 63 of 105P. 2 

# A-83-2 7 IV-J- 6 

## Fiel d Investigatio n o

f FG D Syste m Chemistr y

CS-379 6 Researc h Projec t 1031- 4 Fina l Report , TO L 6 , Decembe r198 4

Prepare d by RADIA N CORPORATIO N 850 1 Mo-Pa c Boulevar d Austin , Texas 7876 6 Principa l Investigator s S
. T
. Litherlan d J
. D
. Colle y R
. L
. Glove r G
. Maile r G
. P
. Behren s Projec t Director s P
. A
. Nasso s 0
. W
. Hargrov e Progra m Manage r T
. R
. Blai r

Prepare d fo r Electri c Powe rResearc h Institut e 341 2 Hillvie w Avenu e Pal o Alto , Californi a 9430 4 EPR I Projec t Manage r D
. Stewart Desulfurizatio n Processe s Progra m Coa l Combustio n System s Divisio nP. 3

Sectio n3 CRAI GGENERATIN GSTATIO N

Crai g Generatin g Station , locate dnea r Craig , Colorado , currentl y operate s tw o 400-M

W boilers , Unit s 1 and2 . A thir duni t i s schedule dfo r startu pi n 1983 . Th e boiler s ar e fuele db y a lo w sulfu r coa l whic hi s mine dnearby . Eac ho f th e operatin g unit s ar e equippe dwit helectrostati c precipitator s fo r particulat e remova l an dwe t limeston e scrubber s fo r contro l o f SO 2 emissions . Th e thir duni t wil l emplo y lime spra y

dryin g fo r reductio no f flu e ga s SO 2 emissions . Lik e Morrow , Crai g operate s i na zer o discharg e mode . A s discusse di nth e previou s section , zer o discharg e plant s typicall y hav e hig hconcentration s o f dissolve dsolid s i neac ho f th e wate r system s (excludin g th e boile r wate r system ) becaus e o f th e hig hleve l o f wate r reus e withi nth e plant . Thi s i s especiall y

tru e o f th e FG D syste m du e t o th e relativ e toleranc e o f th e system fo r a lowe r qualit y makeu pwate r source .
Th e potentia l fo r hig hTD S level s i nth e FG D syste m wa s on e o f th e reason s tha t th e Crai g FG D syste m wa s selecte dfo r investigation . Specifi c objective s o f th e progra m were :

• t o characteriz e th e FG D system , an d

• t o evaluat e th e syste m operatio nfro

m a performanc e stand poin t an

didentif y

area s fo r possibl e improvemen t i n operation .
T o achiev e thes e objectives , a preliminar y sit e visi t wa s mad e i nDecembe r 1981 , followe db

y a wee k lon g samplin g tri pi nMarc h1982 . Durin g th e initia l visit , samplin g point s wer e locate dandpreliminar y chemica l an

d proces s dat a wer e gathered . Durin g th e secon d trip , th e appropriat e



### 3- 1P. 4

liquid , soli dan

dga s phas e sampl e wer e collecte dfro m eac hproces s stream , alon g wit hth e necessar y proces s data , t o characteriz e th e Crai g FG D system . Inaddition , two operationa l problem s wer e examine db y Radian . Thes e were :

• th e poo r handlin g propertie s o f th e FG D sludge , an d

• pluggin g i

nth e mis t eliminato r section . Liqui dan

dsoli dphas e sample s wer e preserve donsit e andreturne dfo r analysi s t o Radian' s Austi nlaboratories . Th e analytica l result s and proces s dat a wer e use dt o evaluat e th e FG D syste m operatio nan

didentif y potentia l area s o f optimization . Thi s effor t include dth e us e o f bot hth e equilibrium

andth e FG D proces s compute r models . Also , recommendation s wer e mad e t o improv e th e handlin g propertie s o f th e FG D solid s andreduc e th e potentia l fo r mis t eliminato r plugging .
Inthi s section , a summar y o f th e Crai g program i s provided , followe db y a descriptio no f th e FG D syste m anda discussio no f th e progra m results . A complet e se t o f th e dat a generate ddurin g th e Crai g program i s include din Appendi xC .
SUMMAR YO F TH E CRAI GPROGRA

M Durin g th e week-lon g sit e visit , solid , liquid , andga s phas e sample s wer e collecte dt o characteriz e tw o o f th e fou r absorbe r module s o nUni t 1 (Module s A

andD) . Th e analytica l result s sho w a hig hleve l o f SO 2 remova l (-98% ) i s achieve da t a ninle t concentratio no f 29 0 ppm . Th e high remova l i s accompanie db y ove r 99 % natura l oxidation .
Th e TD S leve l i nth e Modul e A absorbe r fee dsampl e increase dfrom 21,00 0 mg/ L t o 44,00 0 mg/ L betwee nth e preliminar y sit e visi t i nDecembe r 198 1 and th e samplin g tri pi nMarc h1982 . Th e steady stat e operatin g leve l coul d reac h120,00 0 mg/ L o r mor e base do na wate r balanc e aroun dth e FG D system . Hig hTD S level s ma y decreas e SO 2 remova l andaffec t th e crysta l growt h rat e an dparticl e siz e distributio no f th e gypsum solids . Th e hig hTD S



### 3-2P. 5

leve l may

als o increas e th e potentia l fo r pluggin g i nth e mis t eliminato r section . It i s recommende dtha t th e TD S leve l i nth e absorbe r module s b e monitore dclosely .
Base do nth e result s o f compute r modeling , approximatel y 80 % remova l could be achieve da t one-hal f th e operatin g L/G . Thi s remova l woul db e adequat e t o mee t th e curren t emissio nrequirement s o f 0. 4 l bSO2/I0 6 Btu . Tw o change s inoperatin g procedure s ar e availabl e t o reduc e th e L/G : 1 ) shu t of f on e recirculatin g pum ppe r modul e o r 2 ) operat e two instea do f thre e absorber s pe r unit . Bot ho f thes e option s wil l reduc e pumpin g cost . Th e secon doptio nmay

als o reduc e fa npowe r requirements .
Th e calculate d limeston e reagen t ratio s fo r th e absorbe r fee dsample s ar e 5 t o 10 % lowe r tha nth e value s fo r th e thickene r fee dsamples . Thi s wa s though t t o b e cause db y th e hydroclon e overflo w bein g discharge d(throug h th e mis t eliminato r was htank ) nea r th e thickene r fee d(reactio ntan k overflow ) i na baffle dportio no f th e reactio ntank . Th e ultimat e resul t o f thi s pipin g arrangemen t wa s th e concentratin g o f calcium carbonat e and smalle r gypsu

m solid s i nth e thickene r feed . Th e concentratin g o f calcium carbonat e alon e i s no t o f majo r economi c concer nbecaus e o f th e relativel y lo w limeston e requirements . However , th e compositio nan drelativel y

smal l siz e o f th e particle s i nth e strea m

ma y contribut e t o th e poo r handlin g " characteristic s o f th e wast e sludge . Gypsum crystal s i nth e absorbe r andthickene r feed s ar e unusuall y shaped . Th e solid s ar e compose do f rounde dtablet s a s oppose dt o th e mor e typica l shar pedge dtabula r o r columna r crystals . Th e unusua l shap e couldb e cause d b y severa l factors , two o f whic hare :

• attritio no f th e solid s i nth e absorber/recycl e tan k loo pdu e t o th e wearin g actio no f th e hydroclone s andth e lon g soli d phas e residenc e tim e (> 5 days) , and

• - modificatio no f th e crysta l habi t b y inhibitor s introduce dt o tn e FG D syste m

inth e coolin g towe r blowdown .
Bot hth e relativel y

smal l siz e an

dth e unusua l crysta l shap e o f th e solid s reachin g th e thickene r wer e though t t o contribut e t o th e poo r handlin g



### 3- 3P. 6

characteristic s o f th e centrifug e product . Th e absorbe r solid s ar e dewatere d t o 8 0 weigh t percen t i na centrifuge . However , the dewatere d solid s ar e free-flowin g (thixotropic ) and difficul t t o transport . A recommendatio nwa s mad e t o mov e th e mis t eliminato r was htan k overflo w (was htank fe d b

y hydroclon e overflow ) ou t o f th e baffle d sectio no f th e reactio ntank . Thi s modificatio nshoul d provid e large r particle s t o th e thickene r an d may reduc e attritio no f th e solid s (rounding ) du e t o a decreas e i nth e soli d phas e residenc e time fo r th e large r particles . Pluggin g inth e mis t eliminato r sectio nappeare d t o b e cause d b y soli d depositio na s oppose d t o actua l scaling . Colorado-Ut e wa s plannin g t o instal l additiona l was hnozzle s fo r th e mis t eliminato r sectio nan d t o provid e a highe r qualit y was hwate r (coolin g towe r blowdown ) fo r th e mis t eliminato r washing . Thes e change s shoul d reduc e th e potentia l fo r mis t eliminato r pluggin g i nth e future .
FG D SYSTEM

DESCRIPTIO N Eac ho f th e two Crai g unit s ar e equippe d wit ha se t o f fou r wet limeston e spra y towers . Onl y

two o r thre e o f th e module s ar e operate d a t th e sam e time . Th e fou r tower s shar e commo nlimeston e preparatio nan d dewaterin g facilities . A

simplifie d flo

w diagram

o f th e FG D system

i s presente d i n Figur e 3-1 . Th e primar y

sourc e o f makeu p wate r t o th e FG D syste m i s coolin g towe r blowdown . Thi s wate r i s adde d t o eac hmodul e throug hth e mis t eliminato r was htank . Th e solid s produce d ar e dewatere d b y centrifug e and trucke d t o th e as hdisposa l site . Flu e ga s enter s th e lowe r portio no f th e absorbe r modul e a t 268°F . Th e ga s flow s a t a rat e o f approximatel y 250,00 0 SCF M

throug hfou r level s o f sprays . A knockou t tra y

an d tw o set s o f mis t eliminator s remov e entraine d slurr y fro m th e flu e gas . Treate d flu e ga s i s reheate d wit hbypas s ga s prio r t o enterin g th e stack .



### 3- 4P. 7

Flu e Ga s I n Flu e Ga s Ou t Absorbe r Makeu p

Absorbe r Modul e Was

h Tan k Overflo w

Absorbe r Effluen t 

# 3
_ Mis t

. , E l im
. Mis t Elim
. Was

h Water ] Was h Tan k

Reactio nTank Absorbe r Feed Hydroclon e

Overflow Hydroclon e 

# V Hydroclon e J Underflo w
Thickene r Feed (Reactio nTank Overflow )
Limeston e Fee d Thickene r Overflow

Ra w Limeston e Bal l Mil l

an d Classifier s Centrat e

Centrifug e Produc t 

### Figur e 3-1 . Simplifie d Flo wDiagra m o f th e Crai g FG D Syste m



## 3- 5P. 8

Slurr y i s recirculate da t a rate o f approximatel y 28,00 0 gp

m throug hth e fou r spra y

headers . A

slip-strea m

i s drawnfro

m th e recirculatin g slurr y an dpasse dthroug ha se t o f hydroclones . Solid s ar e concentrate dinth e hydroclon e underflo w an dreturne dt o th e reactio ntank . Th e hydroclon e overflow , containin g approximatel y 1. 0 weigh t percen t o f relativel y smal l solids , i s route dt o th e mis t eliminato r was htan k wher e i t i s combine dwit h bot hthickene r overflo w an dabsorbe r makeup . Wate r fro m th e mis t eliminato r was htan k i s spraye dcontinuousl y o nth e mis t eliminato r andth e tra y directl y oelo w th e mis t eliminators . Overflo w

fro m th e mis t eliminato r was htan k i s returne dt o th e baffle d sectio no f th e reactio ntank . From th e baffle dsection , th e thickene r fee d i s gravity-fe dt o th e sum pwher e i t i s pumpe dt o th e thickener . Thickene r underflo w

i s dewatere dina centrifuge . Th e wate r remove dfro m th e solid s (centrate ) i s returne dt o th e thickener .
DISCUSSIO N

O F CRAI GRESULT S Liqui dan

dsoli dphas e composition s fo r th e key FG D syste m

stream s ar e summarize di nTabl e 3-1 . Eac hstrea m wa s sample da t leas t twic e durin g th e samplin g perio d(3/29/8 2 t o 4/2/82) . Th e value s reporte dar e average s o f th e sample s taken . Th e highe r liqui dphas e andsolid s concentration s measure di nth e Modul e A sample s an

dth e differenc e i nth e Modul e A and Modul e D soli dcompositions , reflec t a differenc e i nth e operatio no f th e tw o modules . Liqui dphas e absorbe r fee dconcentration s o f sodiu m an d magnesiu m

increase dapproximatel y 10 % ove r th e samplin g perio dfo r bot h modules . Chlorid e andsulfat e concentration s increase dapproximatel y 17% . Measure dcalcium

concentration s fo r al l sample s remaine dconstan t durin g th e week . Sulfit e concentration s i nth e absorbe r fee dsampl e range dfro m 1 0 t o 19 0 mg/ L fo r Modul e A andfrom

10 0 t o 14 0 mg/ L fo r Modul e D . Th e soli d phas e composition s fo r Modul e A sample s remaine dconstan t durin g th e samplin g period . Calcium andcarbonat e fraction s i nth e Modul e D solid s increase dan

dsulfat e decrease dove r th e perio dsuggestin g increasin g quantitie s o f limeston e i nModul e D .



### 3- 6

### Tabl e 3- 1 CRAIG--SUMMAR Y O F LIQUI D AM D SOLI D PHAS E ANALYSE S

(Samplin g perio d 3/29/8 2 t o 4/2/82 ) 

# 1

Liqui d Phas e Concentratio n (mg/L) a Soli d Phas e Compositio n (wt% ) Strea m Absorbe r Makeu

p Absorbe r Fee

d Mo d A Mo d D Mis t Eliminato r Was h Hate r Mod A Mo d D Reactio n Tan

k Overflo w Ho d A Mo d 0 Thickene r Overflow " E H .

n. i
5. 5 5. 8

6. 1 6. 1

6. 5 Tenp .

° F 5 0 U S U S

10 7 10 7

9 7 Solid s

(wt8 )

- - IS. 5 7. 2

1. 5 1. 1

3. 4 2. 3 0.0 ? C

a 30 0 51 0 56 0

52 0 S4 0

54 0 M

g 13 0 5,80 0 4,20 0
4,70 0 3,00 0

4,40 0 N

a 28 0 4,00 0 2.R0 0
3,20 0 2,50 0

2^80 0 _C J

16 0 3,08 0 2,13 0
2,31 0 1,85 0

2,15 0 SO 4

1,51 0 27,70 0 20,50 0
22,10 0 17,40 0

19,80 0 C

a

23. 0 24. 8

21. 3 25. 3

23. 6 26. 8 H

g

0. 4 0. 7

0. 6 1. 0

0. 5 0. 9 _c_o 3

0. 5 13. 3

2. 1 20. 5

3. 2 17. 6 S04

-

54 3 41 2

50 1 31 0

53 6 39 8

a S0- ; concentration s i n ahsorben t fee d range d fra n 1 0 t o 19 0 ng/ 1 durin g th e samplin g period , CO 3 concentration s range d fro m fin t o 12 0 mg/1
.P.1 0

•

Specie s

Liqui d Phas e Calciu m (mg/L ) Maynesiu m (mg/L ) Sodiu m (mg/L ) Chlorid e (my/L ) Sulfit e (mg/L ) Sulfat e (mg/L ) TD S (mg/L )
P H Temperatur e (°F ) Solid s (wt% )

Soli d Phas e (wt% ) Calciu m (wt% ) Magnesiu m (wt% ) Carbonat e (wt% ) Sulfit e (wt% ) Sulfat e (wt% ) Inert s (wt% ) Ta b

CRAIG-ABSORBE R

Modul e Preliminar y Visi t 12/11/8 1
54 0 2,86 0 1,80 0 1,61 0 5 4 13,30 0 21,00 0
5. 4 11 8 6. 9

24. 0 0.5 8

- - <0.0 1 51. 5 1.0 1 e 3- 2 FEE D COMPOSITIONS

Absorbe rFee d ! A Samplin g Tri p 4/1/8 2
52 0 5,80 0 4.0U 0 3,19 0 87 28,50 0 45,00 0
5. 5 11 5 15. 4

23. 4 0.4 3 0.2 4 0.0 2 54. 0 0.7 2

3- 8 Compositio n Modul e Preliminar y Visi t 12/11/8 1
57 0 2,24 0 1.5U 0 1,37 0 12 0 10,50 0 17,00 0
5. 9 11 6 9. 3

25. 0 U.9 2

— <0.0 1 43. 3 1.4 6 D

Samplin g Tri p 4/1/8 2
56 0 4,40 0 2,90 0 2,29 0 140 22.UU U 33.7U O
5. 8 11 1 7. 3

25. 6 0.8 3 15. 8 0.0 9 39. 4 0.9 8P.1 1

Th e concentratio no f dissolve dsolid s i nbot hmodule s almos t double dbetwee n th e preliminar y

sit e visi t i nDecembe r andth e samplin g tri pi nMarc han d April . Thi s i s illustrate d b y th e absorbe r fee dliqui dphas e compositio n show ni nTabl e 3-2 . However , th e soli dphas e composition s di dno t chang e significantly . Th e result s o f ga s phas e samplin g ar e presente di nTabl e 3-3 . N o ga s samples wer e take ndurin g th e preliminar y visit . A

t leas t two sample s wer e collecte da t eac hlocatio nove r th e samplin g period . Th e rang e o f th e measure dvalue s i s reporte di nth e table .

Tabl e 3- 3 CRAIG—SUMMAR YO

F GA S PHAS E ANALYSE S (samplin g perio d3/29/8 2 t o 4/2/82 )

Rang e o f Compositio n
Temperatur e SO 2 CO ? O 2 H2 O Locatio n("F). . (pp m dry ) (% ) (% ) (% ) Inle t 28b-35 5 260-29 0 11.3-12. 4 7.4-8. 2 7.0-9. 7
Outle t Modul e A Modul e D 115 a

115 a 3.0-9. 9

1.2-1. 9 11.0-11. 1

10.8-12. 7 8.1-8. 5

6.7-9. 0 12.9-17. 8

13.4-14. 7

a 0utle t ga s temperatur e no t measured , assume dt o b e th e sam e a s absorbe r fee dtemperature .



### 3- 9P.1 2

Materia l Balanc e Calculation s As mentione dpreviously , th e TD S level s o f Module s A an dD o nUni t 1 double dbetwee n12/8 1 an d3/82 . I norde r t o estimat e th e TD S leve l a t stead y state , a serie s o f materia l balanc e calculation s wer e performed .
Th e TD S leve l i na nFG D syste m i s inversel y

proportiona l t o th e flo w rat e o f th e wate r containin g dissolve dsolid s leavin g th e system . A simplifie d wate r balanc e diagra m fo r Modul e A

i s presente di nFigur e 3-2 . Base do na flu e ga s flow

rat e o f 260,00 0 SCF M throug hth e module , 9 4 gp m o f wate r no t containin g dissolve dsolid s ar e los t t o evaporation , approximatel y on e gp m i s occlude dwit hth e wast e solid s from th e absorbe r an danundetermine d amoun t o f wate r i s remove das "miscellaneou s losses. " Thes e losse s coul d includ e any

wate r no t recovere ddurin g a shutdow nperio do r entraine dliqui d escapin g throug hth e mis t eliminators . Figur e 3- 3 illustrate s th e relationshi pbetwee nth e TD S leve l a t stead y stat e an dth e flo w rat e o f water , containin g dissolve dsolids , leavin g th e syste m pe r operatin g module .
A s showni nFigur e 3-3 , th e TD S leve l fo r th e Crai g FG D syste m a t stead y state , assumin g anaverag e los s o f 1. 0 gp m pe r operatin g module , woul db e approximatel y

135,00 0 mg/L . Base do nth e tota l syste m volum e andth e liqui d turnove r rate , ove r on e yea r o f continuou s operatio nwoul db e require dt o achiev e stead y

state . Any

additiona l losses , abov e th e 1. 0 gpm , coul d significantl y

reduc e th e TD S leve l a t stead y state . Hig hTD S level s i nlaborator y FG D system s (EPR I Researc hProjec t No . 1031-4 ) hav e bee nshownt o reduc e SO 2 removal . Inaddition , hig hconcentration s o f dissolve dsolid s ca naffec t th e crysta l growth.rat e an dparticl e siz e distributio no f th e resultin g sludge . Usin g a hig hTD S wate r fo r mis t

3-1 0eliminato r washin g may increas e th e potentia l fo r mis t eliminato r plugging . Sinc e eac ho f thes e factor s coul dadversel y affec t th e Crai g FG D syste m operation , th e TD S leve l shoul db e monitore dclosely . Evaluatio no f Absorbe r Operatio n Key operatin g condition s fo r th e Crai g FG D syste m ar e summarize di nTabl e 3-4 . Th e reporte dflu e ga s flow rate s wer e estimate dbase dona combustio n calculation , th e fanenerg y usag e an

da 30 % bypass . A

direc t measuremen t coul dno t b e made . Base donth e recycl e pum p rating , slurr y

wa s recycle d a t a rat e o f 28,00 0 gp m fo r eac hmodule .
SO ? Removal . Bot hmodule s exhibite da hig hleve l o f SO 2 remova l (>95% ) durin g th e samplin g period . Remova l i nModul e D appeare dt o be slightl y highe r possibl y

du e t o th e highe r L/ Gi ntha t modul e andth e highe r limeston e reagen t rati o (highe r operatin g pH) . However , a t th e lo w outle t ga s concentration s (1. 2 t o 9. 5 ppm ) thes e difference s ma y no t b e significant .
Becaus e o f th e hig hleve l o f SO 2 remova l achieve di nth e absorbers , reductio no f th e L/ Gwa s considere d t o reduc e FG D syste m operatin g costs . Operatio no f th e system at a lowe r L/ Gwa s predicte dusin g th e FG D proces s compute r model . A

drivin g forc e fo r SO 2 remova l i s calculate db y th e mode l t o determin e th e abilit y o f th e syste m

t o operat e a t th e condition s specified . Experienc e ha s show ntha t a 1 0 t o 1 drivin g forc e (p$0 o i n th e exi t ga s te ntime s greate r tha np* s o abov e th e scrubbe r effluen t liquor ) i s require d fo r SO 2 remova l i na spra y towe r fo r a hig hsulfu r coa l system . Th e actua l drivin g forc e coul dno t b e calculate dfo r th e Crai g syste m becaus e o f th e inabilit y t o obtai nanabsorbe r effluen t sampl e du e t o th e particula r syste m design .

3-1 3Tabl e 3- 4 CRAIG--SUMMARY O

F KE Y OPERATIN G CONITION S P.1 4

Flu e Ga s Treatmen t Rate , (SCFM a ) L/ G(gpm/100 0 acfm-out) b » c SO 2 Remova l (% ) Oxidatio n(% ) Absorbe r Fee dp

H Reagen t Rati o (mol e calcium/mol e sulfu r i n solids ) Absorbe r Fee d Thickene r Fee d Thickene rUnderflow , Module s A an d D combine d Modul e A 260,00 0



### 1.0 1 1.0 6 Modul e D

151,00 0 

### 69 

### 96. 4 99+ 5. 5 11 8



### 99. 2 99 + 5. 8



### 1.1 8 1.4 3

1.6 2

a Value s estimate dbase don combustio ncalculatio nan d rati o o f fa nenerg y

usage . b 28,00 0 gp

m recycl e assumed .
c 0utle t conditions : Saturate dgas , 116°F , an d 10. 8 psia .

3-1 4Base do nth e 1 0 t o 1 drivin g force , th e result s o f compute r simulatio n

indicat e tha t 80 % SO 2 remova l ca nb e achieve da t one-hal f th e operatin g L/G . Reducin g th e L/ Gcoul db e accomplishe d b y turnin g of f on e o f th e two recirculatin g pump s o neac hmodul e o r operatin g wit hfewe r modules . I n eithe r case , adequat e SO 2 remova l woul db e achieve dt o mee t curren t emissio nrequirement s an dth e operatin g cos t coul db e reduce dsignificantly . Oxidation . Natura l oxidatio ni nth e Crai g FG D syste m account s fo r th e conversio no f ove r 99 % absorbe dSO 2 t o liqui d phas e sulfate . Thi s hig h leve l o f oxidatio nwoul dbe expecte dbecaus e o f th e hig hoxyge nt o SO 2 rati o i nth e flu e ga s an di s responsibl e fo r th e lo w concentration s o f sulfit e foundinth e system (<15 0 mg/L) . Reagen t Ratios . Th e limeston e reagen t rati o ca nb e use dt o evaluat e th e efficienc y

o f anFG D syste m

wit hrespec t t o limeston e usage . Th e highe r valu e fo r Modul e D indicate s mor e limeston e i s bein g adde dt o th e syste m pe r mol e o f SO 2 remove dtha ni nModul e A . Thi s i s als o reflecte db y th e highe r Modul e D operatin g pH . Th e highe r reagen t ratio s fo r Modul e D coul d b e cause db

y difficult y

incontrollin g th e modul e p H (e.g. , excursion s abov e pH se t point) .
Tw o reayen t ratio s ar e reporte di nTabl e 3- 4 fo r eac hmodule . Th e differenc e inthes e value s i s du e t o enrichmen t o f th e reactio ntan k overflo w

stream (thickene r feed ) wit hcalciu m carbonate . Two factor s ma y contribut e t o thi s enrichment . First , th e mis t eliminato r was hwate r tan k overflo w

i s discharge dint o th e baffle dare a o f th e reactio ntan k wher e th e reactio noverflo w

lin e i s located . Operatio no f th e hydroclone s appear s t o concentrat e calciu

m carbonat e particle s i nth e hydroclon e overflo w strea m whic hfeed s th e was htank . Second , th e presenc e o f th e baffl e i nth e reactio ntan k ma y

allow segregatio no f solid s du e t o settling . Since , i n general , th e smalle r particle s ar e calciu m carbonate , enrichmen t o f th e thickene r fee d(reactio ntan k overflow ) ma y occur .

3-1 5, 1 1 ur i •-

J > ff o . c n > x> ff a. c rt J » ff Om c C D * • f f a . c n > o i f c x e a > o ff a. c to o ff C L C r o o ff O . C r v o ff c x c re r » C D C O

ten C L rt > O D L O C X n » O D (• > C X to Zt* o o C X CD Zt> «/ » C X.let

U J O J O J O J O J r o r o O J -S--. -*.--- elm. U J O J I I I I I mm-*
_ » meet

O J U * 

## I 

## s

o —— f O A - U J C h C D r o r o J * C J r o * •— * r o .«*

> © U l O ( D - 6

U J r o u i .*• » u > m * u -» J * J

c n A u —» —c/ > C O ^ J I ri

l l " I S — • » u » r o

- J 0 0 O J t n © O

—o

—I m -» j r o r o - J * o

i r o i i o i i i • •* J C

D O J r o r o r o

i u i \o

C o c o t u i r o o n c n

i i —

* i r o « © I I * i r—"' M

a. i • i *«* t i t o

i • o 0 0 1 1 i i r o i t •*-* [»? © l^ * I

cn c o

C O 3 » zz. 3 =

- < c o e r
o i c n

%m) lm> mm •ml lml S-* S 4> em a to\ o e a» -s i C O I O « 0 O D 

## (

5

r o r o r o r o r o c n c n c n -- J *- J O O J O * 0 OD
.

eQ 1

• a 0 )