p. 1


# OAR Box 1828 Prepped by Ollie Stewart



## Document

Number: 

# 292 ) IV-A- 2 Docket Number: 

# A-83-2 7

Printed 11/12/200811:12:58AM Sheet 292 of 325P. 2 

# A-83-2 7

^ IV-A- 2 

# EPA-600/7-7B-030 D Marc h 1978



# FLU E GAS DESUFURIZATIO N SYSTEMS : DESIG N AN D OPERATIN G CONSIDERATION S Volum e II . Technica l Repor t

b y C
. C
. Leiv o Bechte l Corporatio n 5 0 Beal e Stree t Sa n Francisco , Californi a 9411 9 Contrac t No . 68-02-261 6 Progra m Elemen t No . EHE62 4 RADIA N LIBRARY , 

# DURHAM , N.C . EP AProject Officers : Joh n E . William s an d Kennet h R . Durke e Industria l Environmenta l Researc h LaboratoryEmissio n Standard s an d Engineerin g Divisio n ' Offic e o f Energy , Minerals , an d IndustryOffic e o f Ai rQualit yPlannin g an d Standard s Researc h Triangl e Park , N.C
. 2771 1 Researc h Triangl e Park , N.C
. 2771 1 Prepare d fo r U.S
. ENVIRONMENTA L PROTECTIO N AGENCY Offic e o f Researc h an d Developmen t an d Offic e o f Ai ran d Waste Managemen t Washington , D.C
. 2046 0P. 3

Sectio n 4 

### IMPLICATION S O F REQUIRIN G 9 0 PERCENT O R GREATE R S0 2 

### REMOVAL FO R NE W FGD INSTALLATION S Thi s sectio n discusse s the change s i n a demonstrate d FGD systemdesign of , fo r example , 8 0 percen t SO 2 remova l efficienc yt o obtai n a capabilit y o f 9 0 percen t o r more . I n summary , thes e desig n change s coul d involve :

Increas e i n absorben t circulatio n rate s Increas e i n scrubbing (contacting ) stage s o r i n con tacting intensit y(scrubber-type ) Mor e stringen t requirement s fo r unifor mflow distributio n Eliminatio n o f ga s by-pas s i f use d fo r rehea t Increase s i n absorben t concentration s whic h ma yi n tur n requir e residenc e tim e o r othe r change s t o con tro l enhance d scaling tendencie s I f th e increase d SO - remova l requiremen t i s als o accompanie d b ya n increas e i n coa l sulfu r content , thi s chang e wil l intensif yal l o f th e abov e requirements . Othe r fue l relate d factor s suc h a s coa l heating value , as h conten t an d composition , mus t als o b e accommodate d an d wit h increasing difficult ya s remova l requiremen t rises . LIM E AN D LIMESTONE SCRUBBIN G Thi s sectio n present s dat a t o illustrat e th e effect s o f proces s operat in g parameter s o n SO - remova l efficienc yfo r the lime an d limeston e scrubbing process . Mos t o f the dat a ar e take n fro mtes t result s a t the EP AAlkal i Scrubbing Tes t Facilit ylocate d nea r Paducah , Kentuck y (Ref . 1) . Th e tes t facilit yi s integrate d int o the flu e ga s ductwor k o f a 160-M

W coal-fire d boile r a t th e TV AShawne e Powe r Station . Two 

### 4- 1P. 4

paralle l we t scrubbe r system s ar e i n operation : a venturi/spray towe r systeman

d a turbulen t contac t absorbe r (TCA ) system . Eac h systemca n trea t approximatel y1 0 M W (equivalen t t o 33,00 0 nm-Vhr , o r 30,00 0 acf ma t 300°F ) o f flu e ga s containing 1,50 0 t o 4,50 0 pp m o f S0 2 - Th e bul k o f th e dat a i n thi s sectio n i s fo r limeston e scrubbing o n th e TCAsystem . Additiona l dat a ar e presente d i n Appendi x Afo r th e TCA wit h the lim

e an d the ventur i an

d spra ytowe r wit h lime an d limeston e operation . Th e Shawne e dat a ar e the resul t o f short-ter mfactoria l test s 6 t o 8 hour s i n lengt h an d long-ter

mtest s abou t on e wee k i n length . Th e short-ter mtest s wer e aime d a t determining SO 2 absorptio n efficiencie s withou t regard necessaril yfo r possibl e long-ter mscaling condition s tha t migh t b e associate d wit h th e proces s condition s chosen . Therefore , thes e particula r dat a ar e no t t o b e interprete d a s evidenc e o f long-ter

mreliabl e operation . However , durin g othe r portion s o f th e Shawne e progra

madequat e demonstration s hav e bee n mad e tha t thes e FGD system s ca n b e operate d fo r extende d period s withou t scaling problems . Approximat e equation s an d nomograph s fo r predicting SO 2 absorptio n efficienc yfo r th e Shawne e scrubber s ar e presente d i n Appendi x B . Fo r the TCAShawne e dat a i n thi s section , th e SO 2 remova l curve s hav e bee n predicte d b yEquatio n B-4 . Effect s o f Proces s Variable s o n SO 2 Absorptio n Efficiency . Th e effect s o f th e following variable s o n SO 2 absorptio n efficienc y ar e summarize d i n thi s section :

• Inle t SO 2 concentratio n

• Liquid-to-ga s rati o

• Ga s velocit y



### 4- 2Scrubbe r inle t p H Scrubbe r internal s Magnesiu

madditio n Numbe r o f scrubbing stage s Lime versu s limeston e Inle t SO ? Concentration . Figur e 4- 1 show s the effec t o f inle t SO 2 con centratio n o n SO 2 remova l fo r fixed desig n an d operating conditions . Dat a hav e show

n (Refs . 2 , 3 , 4 ) tha t i n lime an d limeston e scrubbing ove r a wid e rang e o f inle t SO 2 concentrations , greate r remova l effi
ciencyi s realize d fo r lo winle t SO 2 concentration s tha n fo r high , fo r fixed design an

d operating conditions . Thi s happen s becaus e th e actua l quantit yo f SO 2 remove d pe r volum e o f ga s treate d goe s down , reducing th e loading o n th e absorbing liquor . Fo r high SO 2 concentrations , mor e SO 2 i s actuall yabsorbe d b yth e liquor . Fo r example , an absorbe r wit h 8 0 percen t reductio n fro ma ga s contain
in g 3,00 0 pp

mSO 2 migh t absor b 9 0 percen t fro ma 1,00 0 pp

mgas , al l thing s being equal . Bu t i n absolut e terms , 2,40 0 pp mwoul d actuall y hav e bee n remove d fro mth e highe r SO 2 case , an d onl y90 0 pp

mfro mthe lower . I t wa s a t on e time though t tha t a s inle t SO 2 concentratio n decreased , the driving forc e fo r absorptio n woul d decreas e an d high remova l effi
ciencie s woul d b e mor e difficult . Clearly , a s equilibriu mSO 2 bac k pressur e ove r the bul k liqui d approache s the SO 2 ga s concentration , thi s mus t pos e a problem . I n practice , however , the SO - bac k pressur e ove r fres h lime an

d limeston e scrubbing slurrie s i s verylow(les s than 1 ppm) , an

d scrubber s can b e designe d s o tha t the lowS0 „ concentratio n scrubbe d ga s exiting th e scrubbe r i s contacte d b ythe freshes t slurr y (counte r curren t o r cros s flows) . Fo r thes e reasons , remova l effi
ciencygreate r than 9 5 percen t ha s bee n achieve d during test s fro m
4- 3P. 6

10 0 - 1 T1 1 1 O EP APILO TTC A SPHER E HEIGH T-

- 7INCHES/8ED
. 3 BED S LIQUI D TO GA S RATI O = 8 5 gal/Mc f TC AGA S VELOCIT Y= 7. 5 ft/se c O 0 TV APILO TSPRA YTOWE R

LIQUI D T O GA S RATI O = 8 5 gal/Mc f 9 5 - -

> u z U J o I Z u » u i

_ i < > O 2 o e C M o Cf* » H 

## I 8 0 o c 9 0 - -

8 5 - -

7 5 - -

7 0 LIMESTON E SCRUBBIN G

1,00 0 2.00 0 3.00 0

INLE TS0 2 CONC , pp m 4,00 0 5,00 0 (Ref . 1 )
Figur e 4-1 . Effec t o f Inle t SO 2 Concentratio n o n S0 2 Remova l

Efficienc yfo r Fixe d Desig n an d Operatin g Condition s



### 4- 4P. 7

flu e ga s tha t average d onl y20 0 pp ma t the inlet , a s show n i n Figur e 4- 2 fo r a TC

Asystemoperate d a t th e Souther n Californi a Ediso n Mohav e Sta tio n (Ref . 5) . Th e outle t SO - concentratio n i n thi s cas e i s les s than 1 0 ppm . I t i s importan t t o recogniz e tha t t o obtai n equivalen t effi
cienc yfo r 3,00 0 pp mSO 2 gas , a n FGD systemwoul d nee d t o absorb an d proces s abou t 1 5 time s a s muc h SO 2 (2,85 0 v s 19 0 ppm) . Achievemen t o f comparabl e efficiencie s a t th e high loading corresponding t o 3,00 0 pp m SO 2 ga s canno t b e considere d t o hav e bee n demonstrate d b ythe Mohav e example . Th e ga s S0 2 concentration , o r coa l sulfu r content , mus t alway s b e accounte d fo r whe n extrapolatin g th e performanc e o f differen t instal
lations . LiquidTto-Ga s Ratio . Figur e 4- 3 illustrate s the effec t o f L/ G o n S0 _ rempva l efficienc yi n a TCAfo r limeston e scrubbing . Simila r effect s ar e observe d fo r lime an d i n th e ventur i an d spra ytowe r scrubber s a s show n i n Appendi x A . Liquid-to-ga s rati o i s a majo r desig n variabl e i n scrubbing systems . A s th e liqui d pumping rat e i s increased , addi
tiona l alkal i i s adde d t o th e scrubbe r an d th e gas-liqui d interfacia l are a increases , resulting i n greate r absorptio n efficiency . I n mos t scrubbe r types , th e benefit s o f increasing L/ G fo r fixe d scrubbe r conditio n ca n b e designe d int o th e systemu p t o th e poin t wher e problem s suc h a s flooding o r nonuniformga s an d liquo r distri
bution s occur . I t ca n b e see n fro mth e wayth e curve s flatte n ou t a t high L/ G i n Figur e 4- 3 tha t th e incrementa l increas e i n pumpin g t o improv e the absorptio n from , say , 8 0 t o 9 0 percen t (a n increas e fro mabou t 5 0 t o 8 0 L/ G a t a p H o f 5.8 ) woul d b e significantl ygreate r than tha t require d t o improv e i t fro m7 0 t o 8 0 percen t (a n increas e fro mabou t 3 5 t o 5 0 L/G) . Highe r L/ G coul d als o b e obtaine d b yopera ting a t lowe r ga s velocity , a t the expens e o f increase d scrubbe r size . A n increas e i n the desig n L/ G fo r a n FGD syste mrequire s th e us e o f large r pumps , pipes , an d spra yheaders . Scrubbe r recirculatio n tank s



### 4- 5P. 8

100 - 

### 99- j
98- H > 

## u z *97
- 

## o [ Z u . U J 

### < 96 H O U J O C C M 95
- O C O H 

## z U J 

### g.94 - L U 

### a . 93- I
92—I 

### 9 H TC A4 STAGE S LIMESTON E

90
- INLETS0 2 ; GA S RAT E 20 0 PP M

450,00 0 SCF M (Redraw n fro m Reference 5 ) T " 1 -

2 0 

# T T 6 0 LIQUI D T O GA S RATIO , gal/Mc f 

### Figur e 4-2 . Effec t

o f Liquid-to-Ga s Rati o o n SO
- Remova l Efficienc y wit hLo w Sulfu r Coa l a t

th e Mohave Power

Statio n

4- 6P. 9

mus t b e large r t o maintai n design residenc e tim e fo r the increase d L/ G an d t o provid e residenc e time fo r th e increase d S0 2 absorption . Th e energ ypenalt yfo r increase d L/ G i s show n i n Figur e 2-3 . A t highe r L/G's , ga s pressur e drop mayals o increas e i n some type s o f scrubbers , causing additiona l penalt ya s show n i n Figur e 2-2 . Highe r L/G' s ma

yten d t o reduc e scaling potentia l i nth e scrubber b

y reducin g th e SO - absorbe

d per gallo

nof absorbent . Scrubbe r Ga s Velocity . Figur e 4- 4 show s th e effec t of ga s velocity o n SO - remova l efficienc y i na TCA . Th

e smal l velocity

effec t a

t a fixe d slurr y flo w rat e represent s a trade-of f betweenfactor s tendin g t o increas e efficienc y wit hvelocity

(e.g. , superior sphere agitatio n an d increase

d liquid-ga s contact ) an d th e correspondin

g decreas e in L/G . O nth e other hand , a scrubbe r suc ha s th e spra y tower (Figur

e A-14 ) wil l hav

e highe r efficiencie s a t lower ga s velocities , a t a fixe

d slurr y flo w rate . Inth

e spra y tower , there are n o internal s an

d littl e liqui d hold-up , s o that th e decreas e inL/ Gwit hincreasin g ga s veloc it y i s no t offse t b

y other factors . For cos t reasons , scrubber s ar e designe d t o operat e a

t maximu

m prac tica l ga s velocities , thereb y keepin g vesse l diameter s minimal . Thes e maximu m velocitie s are dictate d b y gas-liqui d distributio ncharacter istic s o f th

e scrubbe r an

d b y th e maximu

m allowabl e slurr

y entrainment that th e mis t eliminator ca nhandle . Designer s generall y achiev e th e require d L/ Gb y increasin

g th e slurr y pumpin g rat e rather tha

nb y de creasin g th e ga s velocity . Designin g for lo

w ga s velocitie s introduce s larger an

d costlie r scrubbe r system s (modules) . Inspecifyin

g hig hremova l efficiency , i t shoul d be kept inmin d that som e ver y efficien t scrubber s (includin g certai ntra

y towers ) hav

e poor modula r turndow ncharacteristics , s o tha t absorptio nefficienc

y

4- 8