Regenerative Aqueous Carbonate Process for Utility and Industrial

14 Regenerative Aqueous Carbonate Process for Utility and Industrial Sulfur Dioxide

Downloaded by NATL UNIV OF SINGAPORE on May 6, 2018 | https://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch014

Removal W . V. B O T T S and D. C. G E H R I Atomics International Division, Rockwell International Corp., P.O. Box 309, Canoga Park, Calif. 91304

The aqueous carbonate process (ACP) is a unique regenerative sulfur dioxide removal process which is applicable

to

utility and industrial installations. This process uses a dilute sodium carbonate solution

to remove sulfur dioxide from

flue gases. The scrubbant is atomized in a spray dryer. Sodium sulfites and sulfates are formed which are reduced and regenerated to carbonate in an aqueous regenerative subsystem which also produces sulfur.

The process elimi-

nates the great quantities of solid waste associated with open loop processes. Reheat is eliminated because the flue gas is not saturated during scrubbing.

Typical economics show a

capital cost of below $70/kw ($32 per 1000/SCF throughput).

Operating costs from 1 to 3 mills/kw-hr

of gas have

been estimated. The process, a summary of pilot test results, integration information, and system economics are discussed.

' T ' h e aqueous carbonate process ( A C P ) has been under development at Atomics International for the last 4V2 yr. The program aims to establish a technology which eliminates or minimizes the major problems encountered in operating most other sulfur dioxide removal processes. That technology includes the use of sodium carbonate as the scrubbant in the modified spray dryer and the complete regeneration of the sulfur dioxide removal products to recover elemental sulfur and produce sodium carbonate for reuse in the spray dryer-scrubber. The modified spray dryer provides intimate contact between the sulfur dioxide-containing waste gas and a finely atomized fog of sodium carbonate solution. Only small quantities of the reactive sodium car164

Pfeiffer; Sulfur Removal and Recovery Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

14.

BOTTS A N D G E H R I

Regenerative

Aqueous

Carbonate

165

Process

bonate s o l u t i o n are r e q u i r e d to a c h i e v e excellent s u l f u r d i o x i d e r e m o v a l . T h e r e a c t i o n p r o d u c t is a d r y p o w d e r easily c o l l e c t e d a n d stored, a n d the waste gas does not b e c o m e saturated w i t h w a t e r v a p o r . T h i s k i n d of s c r u b b e r is not subject to s c a l i n g or p l u g g i n g p r o b l e m s , does not r e q u i r e a gas reheater, a n d operates w i t h a l o w l i q u i d - t o - g a s r a t i o . B y p r o v i d i n g surge c a p a c i t y for the s o d i u m carbonate s o l u t i o n a n d storage

capacity

for the d r y r e a c t i o n p r o d u c t , the s c r u b b i n g system c a n b e easily a n d i n e x p e n s i v e l y d e c o u p l e d f r o m the r e g e n e r a t i o n system.

T h e net result

is a s u l f u r d i o x i d e s c r u b b i n g system w i t h a h i g h degree of o p e r a t i o n a l


reliability. C o m p l e t e r e g e n e r a t i o n i n the A C P system is a c c o m p l i s h e d b y three basic c h e m i c a l steps.

I n the first step the p r o d u c t s o d i u m sulfite a n d

sulfate are r e d u c e d to s o d i u m sulfide. A t o m i c s I n t e r n a t i o n a l has d e v e l o p e d a h i g h t e m p e r a t u r e r e d u c e r w h i c h accepts the p r o d u c t f r o m the s p r a y d r y e r - s c r u b b e r , melts i t , elevates its t e m p e r a t u r e , a n d reduces the s u l f u r - c o n t a i n i n g salts to the d e s i r e d sulfide f o r m w i t h coke or coal. second

The

r e g e n e r a t i o n step i n v o l v e s d i s s o l v i n g the sulfide i n w a t e r a n d

c a r b o n a t i n g it to r e f o r m s o d i u m c a r b o n a t e for r e c y c l e to the s c r u b b e r . A h y d r o g e n s u l f i d e - r i c h gas is e v o l v e d .

T e c h n o l o g y s i m i l a r to that u s e d

i n c h e m i c a l r e c o v e r y processes i n the p u l p a n d p a p e r i n d u s t r y is used. I n the final step the h y d r o g e n sulfide is c o n v e r t e d to e l e m e n t a l s u l f u r b y a C l a u s process.

S i n c e e l e m e n t a l s u l f u r is the o n l y system b y - p r o d u c t , the

p r o b l e m s of d i s p o s i n g of s l u d g e or sulfate b l e e d streams are e l i m i n a t e d . T h e A C P system c o m b i n e s a s u l f u r d i o x i d e s c r u b b i n g system b a s e d o n s p r a y d r y e r t e c h n o l o g y w i t h a r e g e n e r a t i o n system b a s e d o n a u n i q u e r e d u c t i o n step c o u p l e d to c h e m i c a l r e c o v e r y a n d C l a u s technologies.

This

c o m b i n a t i o n results i n a n efficient a n d r e l i a b l e process for a p p l i c a t i o n to sulfur dioxide pollution problems.

T h e r e m a i n d e r of this p a p e r discusses

the details of t h e process a n d t y p i c a l i n s t a l l a t i o n characteristics a n d also presents process e c o n o m i c s w h i c h i n d i c a t e that the A C P system is econ o m i c a l l y feasible a§ w e l l as t e c h n i c a l l y s o u n d . Process

Description

T h e k e y c o m p o n e n t of t h e A C P s c r u b b i n g system is a m o d i f i e d s p r a y d r y e r w h i c h serves as a r e a c t i o n c h a m b e r for the s u l f u r d i o x i d e r e m o v a l . I n the spray d r y e r , the s o d i u m carbonate s o l u t i o n is a t o m i z e d b y a h i g h speed c e n t r i f u g a l a t o m i z e r a n d m i x e d w i t h the hot gas e n t e r i n g the d r y e r t h r o u g h a v a n e - r i n g . T h e fine m i s t of s o l u t i o n droplets absorbs s u l f u r d i o x i d e w h i l e the t h e r m a l energy of the waste gas v a p o r i z e s the w a t e r w i t h o u t s a t u r a t i n g or excessively c o o l i n g the gas.

T h u s , the s p r a y d r y e r

p r o d u c e s a gas l o w i n s u l f u r d i o x i d e b u t c o n t a i n i n g d r y p a r t i c l e s of t h e reaction products

f r o m the c o n t a c t o r — s o d i u m

carbonate,

sulfite, a n d


166

SULFUR

sulfate.

REMOVAL

AND

RECOVERY

T h i s p o w d e r is s u b s e q u e n t l y separated f r o m the gas a n d c o l -

l e c t e d for d i s p o s a l w i t h the o p e n l o o p system or for processing a n d reg e n e r a t i o n i n the regenerative

version.

After product

collection,

the

t r e a t e d waste gas r e m a i n s r e l a t i v e l y h o t a n d is v e n t e d t h r o u g h a stack. F i g u r e 1 is a b l o c k d i a g r a m of the k e y subsystems of a n A C P r e g e n erative system w h i c h are i n t e g r a t e d i n t o a n e x i s t i n g p o w e r p l a n t w h e r e the c l e a n gas is v e n t e d t h r o u g h a n existing stack after i t has b e e n t h r o u g h the s c r u b b e r a n d solids r e m o v a l systems. T y p i c a l l y , a n e w i n d u c e d draft


EXISTING STACK

Na2S0

Figure

1.

Regenerative

AC?

block

4

ELEMENTAL SULFUR

diagram

f a n is r e q u i r e d to p r o v i d e the pressure to m o v e the gas t h r o u g h the system. D r y p o w d e r f r o m the solids r e m o v a l system is t r a n s f e r r e d to the b l o c k s h o w n as the regenerative system. T h e c h e m i c a l s n e e d e d b y the r e g e n e r a t i o n system i n c l u d e m a k e u p s o d i u m carbonate (soda ash), a c a r b o n source for the r e d u c t i o n step, a n d w a t e r . T h e p r o d u c t s f r o m this system are ash, which

is d e r i v e d

mainly from

the

w h i c h is a h i g h p u r i t y b y - p r o d u c t .

flue

gas,

and

elemental

A d d i t i o n a l d e t a i l o n the

sulfur,

scrubber

system is s h o w n i n F i g u r e 2 s u c h as the s o l u t i o n f e e d tanks a n d p u m p s , the s p r a y d r y e r , cyclones, a n d , i n this case, for v e r y h i g h p a r t i c u l a t e rem o v a l , a s m a l l electrostatic p r e c i p i t a t o r .

I n a d d i t i o n , a solids transfer

system is s h o w n w h i c h conveys the d r y p o w d e r f r o m the cyclones

and

p r e c i p i t a t o r to a separate or adjacent r e g e n e r a t i o n system. T h e e q u i p m e n t s h o w n i n F i g u r e 2 is s u i t a b l e for retrofit i n t o a n e x i s t i n g p l a n t . A n A C P r e g e n e r a t i o n system flow d i a g r a m is s h o w n i n F i g u r e 3. T h i s d i a g r a m represents t y p i c a l processing steps w i t h o u t p r o p r i e t a r y m o d i f i c a tions or o p e r a t i o n a l details. A s s h o w n , the p r o d u c t salt is c o n v e y e d a l o n g w i t h coke or a n y other c a r b o n source to the m o l t e n salt r e d u c e r .

I n the

r e d u c e r the salt is h e a t e d , m e l t e d , a n d r e d u c e d i n a single z o n e b y a d d i n g a i r a n d coke. A i r p r o v i d e s some r e o x i d a t i o n of sulfide to generate sensible heat w h i l e the coke acts d i r e c t l y to r e d u c e the sulfite a n d sulfate to sulfide. T h e m o l t e n m i x t u r e is passed i n t o a q u e n c h tank w h e r e it is d i s s o l v e d a n d processed as a l o w t e m p e r a t u r e ( b e l o w the b o i l i n g p o i n t of w a t e r )


14.


Regenerative

Aqueous

Carbonate

167

Process

FROM EXISTING PLANT UTILITIES


COOLING WATER PIPING TYPICAL EACH MACHINE

r

Figure 2.

u

m

r

GAS STACK

Scrubber subsystem loop

aqueous s o l u t i o n . T h e r e d u c e r off-gas is u s e d as the c a r b o n d i o x i d e source for subsequent c a r b o n a t i o n steps a n d as a source of process heat. T h e aqueous s o l u t i o n is c o o l e d a n d filtered to r e m o v e a n y excess coke, c o k e ash, or fly ash. A f t e r

filtration,

t h e s o l u t i o n is p r e c a r b o n a t e d

w i t h p u r e c a r b o n d i o x i d e r e c o v e r e d f r o m the decomposer.

F i n a l carbona-

t i o n occurs i n the b i c a r b o n a t o r - c r y s t a l l i z e r w i t h c a r b o n d i o x i d e f r o m the r e d u c e r off-gas.

Gases e v o l v e d f r o m b o t h the p r e c a r b o n a t o r

a n d the

GAS TO SCRUBBER

W-1 W-2

Figure 3.

Regeneration

STEAM CONDENSER STEAM CONDENSER

subsystem


168

SULFUR

REMOVAL

AND

RECOVERY

b i c a r b o n a t o r - c r y s t a l l i z e r are r i c h i n h y d r o g e n sulfide a n d are c o m b i n e d for subsequent r e c o v e r y of e l e m e n t a l s u l f u r i n the C l a u s p l a n t . T a i l gas f r o m the C l a u s p l a n t is r e t u r n e d to the s c r u b b e r for final c l e a n u p . T h e p r o d u c t f r o m t h e b i c a r b o n a t o r - c r y s t a l l i z e r is a s o d i u m c a r b o n a t e - s o d i u m b i c a r b o n a t e s l u r r y w h i c h is d e c o m p o s e d to p r o d u c e a s o d i u m carbonate s o l u t i o n for r e t u r n to the s c r u b b e r to p r o v i d e p u r e

carbon

d i o x i d e for the p r e c a r b o n a t o r . T h i s completes t h e r e g e n e r a t i o n c y c l e a n d closes the l o o p for t h e t o t a l A C P system. T h e t e c h n o l o g y i n v o l v e d is a c o m b i n a t i o n of a u n i q u e r e d u c e r a n d aqueous c h e m i c a l processing, most


of w h i c h is c o m m e r c i a l l y p r o v e d . So far, d e v e l o p m e n t efforts h a v e c o n c e n t r a t e d o n p i l o t d e m o n s t r a t i o n of the s c r u b b i n g system a n d t h e r e d u c e r . E x t e n s i v e test d a t a h a v e b e e n generated w i t h 5-ft a n d 7-ft d i a m e t e r spray d r y e r - s c r u b b e r s . P r o p r i e t a r y test results are a v a i l a b l e f r o m 4-ft a n d 9-ft d i a m e t e r reducers. K e y o p e r a t i n g a n d p e r f o r m a n c e characteristics of the aqueous r e g e n e r a t i o n steps h a v e also b e e n tested.

T h e s e p i l o t test results c o m b i n e d w i t h e x i s t i n g

d a t a a n d t e c h n o l o g y f r o m the s p r a y d r y i n g a n d p u l p a n d p a p e r i n d u s t r i e s p r o v i d e a firm t e c h n i c a l base for the d e s i g n a n d c o n s t r u c t i o n of large-scale ACP

systems. A k e y c o m p o n e n t of the r e g e n e r a t i o n subsystem is the r e d u c e r . T h i s

component

is a c e r a m i c - l i n e d vessel w h i c h contains the m o l t e n salt at

temperatures a p p r o a c h i n g 2000 ° F . T h e c o m p o n e n t is c o m m o n to several other s u l f u r d i o x i d e a n d c o a l gasification processes a n d has b e e n d e m o n strated at b o t h 4-ft a n d 9-ft d i a m e t e r size scales. I n the r e d u c e r , b o t h the o x i d a t i o n of sulfide to sulfate a n d the r e d u c t i o n of sulfate to sulfide b y the coke p r o c e e d s i m u l t a n e o u s l y . Test Results T h e first p i l o t s c r u b b e r tests w e r e c o n d u c t e d u s i n g s i m u l a t e d flue gas to e s t a b l i s h the f e a s i b i l i t y of s u l f u r dioxide's r e a c t i n g w i t h s o d i u m c a r bonate solutions a n d slurries i n a s p r a y d r y e r .

S u b s e q u e n t tests w e r e

c o n d u c t e d at t h e M o h a v e g e n e r a t i n g s t a t i o n , w h e r e a 5-ft d i a m e t e r m o d i fied s p r a y d r y e r was u s e d to test s u l f u r d i o x i d e r e m o v a l f r o m a side stream of flue gas f r o m this coal-fired p o w e r p l a n t ( F i g u r e 4 ). T h e s p r a y d r y e r h a d b e e n i n o p e r a t i o n for o v e r 20 y r i n v a r i o u s d r y i n g a p p l i c a t i o n s p r i o r to m o d i f i c a t i o n to a s u l f u r d i o x i d e scrubber.

It was u s e d i n over 100 tests

at M o h a v e w i t h o u t a single o p e r a t i o n a l p r o b l e m . M o s t of the M o h a v e test d a t a w e r e o b t a i n e d w i t h flue gas c o n t a i n i n g 400 p p m or less s u l f u r d i o x i d e since this is c h a r a c t e r i s t i c for a p o w e r p l a n t b u r n i n g l o w s u l f u r w e s t e r n c o a l . A f e w tests w e r e r u n at v a r i o u s c o n c e n trations u p to 1500 p p m , b u t most of the a v a i l a b l e d a t a at h i g h s u l f u r d i o x i d e concentrations w e r e o b t a i n e d u s i n g s i m u l a t e d flue gas i n a 7-ft


14.


Regenerative

Aqueous

Carbonate

169

Process

d i a m e t e r s p r a y d r y e r s c r u b b e r . A f t e r e s t a b l i s h i n g that the d a t a o b t a i n e d at M o h a v e w a s i d e n t i c a l to that o b t a i n e d w h e n u s i n g s i m u l a t e d flue gas, a n extensive r a n g e of tests w a s r u n w i t h the 7-ft u n i t at s u l f u r d i o x i d e concentrations r a n g i n g f r o m 200 to 8000 p p m . T h e s e d a t a c o v e r t h e r a n g e


of most u t i l i t y a n d i n d u s t r i a l s c r u b b i n g a p p l i c a t i o n s a n d c a n b e s u p p l e -

Figure 4.

Pilot scrubber

installation

m e n t e d as necessary i n the f u t u r e to c o v e r s p e c i a l or u n u s u a l s u l f u r dioxide removal problems. F i g u r e 5 is a p l o t of some of the d a t a t a k e n d u r i n g t h e M o h a v e test p r o g r a m a n d illustrates a n i m p o r t a n t a n d d e s i r a b l e o p e r a t i o n c h a r a c t e r istic of a s p r a y d r y e r - s c r u b b e r .

O n l y a b o u t 0.3 g a l of the 5.5 w t

%

s o d i u m carbonate s o l u t i o n was n e e d e d / 1 0 0 0 s t a n d a r d c u ft ( S C F )

of

flue gas to o b t a i n greater t h a n 9 0 % r e m o v a l of the 400 p p m i n l e t s u l f u r dioxide.

S u b s e q u e n t tests h a v e c o n f i r m e d that this same

liquid-to-gas

ratio ( L / G ) c a n b e u s e d to r e m o v e greater t h a n 9 0 % of the s u l f u r d i o x i d e f r o m gases c o n t a i n i n g 2 0 0 - 4 0 0 0 p p m s u l f u r d i o x i d e .

T h e concentration

of s o d i u m c a r b o n a t e i n s o l u t i o n is a d j u s t e d i n p r o p o r t i o n to the s u l f u r d i o x i d e c o n c e n t r a t i o n i n the gas to p r o v i d e sufficient a l k a l i n i t y to n e u t r a l i z e the a b s o r b e d s u l f u r d i o x i d e , b u t the L / G itself r e m a i n s at a b o u t 0.3 g a l / 1 0 0 0 S C F o v e r this r a n g e of concentrations.

A b o v e 4000

ppm

s u l f u r d i o x i d e , i t is necessary to increase the L / G to p r o v i d e e n o u g h d i s s o l v e d s o d i u m c a r b o n a t e to react w i t h the a b s o r b e d s u l f u r d i o x i d e .

How-

ever, e v e n at 8000 p p m s u l f u r d i o x i d e , t h e r e q u i r e d L / G is o n l y a b o u t



170

SULFUR

Figure

5.

REMOVAL

AND RECOVERY

Sulfur dioxide removal vs. absorbent flow rate

0.6 g a l / 1 0 0 0 S C F as c o m p a r e d w i t h most other scrubbers w h i c h w o u l d r e q u i r e 1 0 - 1 0 0 g a l / S C F for s u c h a n a p p l i c a t i o n . O n e of the p r i m a r y reasons that the s p r a y d r y e r - s c r u b b e r is able to a c h i e v e excellent sulfur d i o x i d e r e m o v a l w i t h s u c h l o w l i q u i d - t o - g a s ratios is the s m a l l size of the droplets p r o d u c e d b y the h i g h speed c e n t r i f u g a l a t o m i z e r . T h i s t y p e of a t o m i z e r also has a n easily c o n t r o l l e d t u r n d o w n c a p a b i l i t y w h i c h is a d e s i r a b l e feature that has b e e n d e m o n s t r a t e d i n the p i l o t tests. A s gas flow decreases, the a m o u n t of s o d i u m carbonate s o l u t i o n c a n be decreased i n d i r e c t p r o p o r t i o n w i t h o u t i n t e r f e r i n g w i t h s u l f u r d i o x i d e r e m o v a l efficiency. T h e a t o m i z e r a c t u a l l y p r o d u c e s finer droplets at the l o w e r l i q u i d flow rates. T h i s appears to compensate for a n y g a s l i q u i d m i x i n g p r o b l e m s that c o u l d i m p a i r p e r f o r m a n c e . T h e p r o p e r o p e r a t i o n of a s p r a y d r y e r - s c r u b b e r also r e q u i r e s that a d r y p r o d u c t b e f o r m e d a n d s u b s e q u e n t l y r e m o v e d f r o m t h e gas stream. P i l o t tests h a v e s h o w n t h a t the p r o d u c t salts w i l l be d r y a n d c o l l e c t a b l e if t h e gas t e m p e r a t u r e at the d r y e r outlet is m a i n t a i n e d a b o u t 2 0 ° F a b o v e its d e w p o i n t . T h i s also tends to m i n i m i z e p l u m e f o r m a t i o n . T h e c y c l o n e collectors u s e d i n the p i l o t tests r e m o v e d 8 9 - 9 9 %

of t h e p r o d u c t . A l -

t h o u g h this w a s excellent p e r f o r m a n c e b y m e c h a n i c a l collectors, p a r t i c u late e m i s s i o n standards w i l l r e q u i r e either r e p l a c e m e n t of the cyclones or a d d i t i o n a l c o l l e c t i o n devices i n series w i t h the cyclones.

T h e system

d e s i g n p r e s e n t l y f a v o r e d i n v o l v e s u s i n g cyclones to r e m o v e the b u l k of t h e p r o d u c t a n d a d d i n g a s m a l l electrostatic p r e c i p i t a t o r for final p a r t i c u l a t e r e m o v a l . T h e s o d i u m salts p r o d u c e d i n t h e s p r a y d r y e r - s c r u b b e r


14.


Regenerative

Aqueous

Carbonate

h a v e excellent r e s i s t i v i t y p r o p e r t i e s to p r o m o t e

171

Process

effective

electrostatic

precipitation. It w a s o b s e r v e d d u r i n g the M o h a v e tests that the fine fly ash p a r t i c l e s e n t e r i n g the s p r a y d r y e r w e r e often t r a p p e d i n the c y c l o n e a l o n g w i t h the b u l k of the p r o d u c t salt, a p p a r e n t l y because of a g g l o m e r a t i o n w i t h the a t o m i z e d droplets i n the s p r a y d r y e r . T h u s , the d r y e r itself helps to m i n i m i z e e m i s s i o n of fine ash p a r t i c l e s w h i c h are n o r m a l l y difficult to r e m o v e e v e n w i t h a n electrostatic p r e c i p i t a t o r . N u m e r o u s samples h a v e


b e e n t a k e n a n d extensive d a t a h a v e b e e n a c c u m u l a t e d o n the p h y s i c a l Table I. Inlet Flue Gas

T y p i c a l Scrubber System Performance

Properties

Low Sulfur

Temperature (°F) S 0 concentrations (ppm) A s h content (grain/SCF) 2

H 0 content (vol

%)

2

3%

Coal

Sulfur

Coal

300 400

300 2200

0.03 ( d o w n s t r e a m of m a i n power p l a n t electrostatic precipitator) 14

2.0 (no p r i o r ash removal)

10

Spray Dryer Operating Conditions Feed composition 4.4 20 (wt % N a C 0 ) 0.34 (0.70 l b F e e d rate 0.32 (0.12 l b Na CO /1000 SCF) (gal/1000 S C F ) Na CO /1000 SCF) 10 G a s pressure d r o p ( i n . 9 H 0 , including cyclone) 2

3

2

2

3

3

2

Exit Gas Properties T e m p e r a t u r e (°F) D e w p o i n t (°F) SO 2 concentration (ppm) Particulate loading (grain/SCF with cyclone)

Product Composition Na C0 NaHC0 Na S0 Na S0 H 0 Ash 2

3

3

2

2

4

2

3

(wt

155 134.5 40 ( 9 0 % r e m o v a l ) ~0.05 ( < 0.01 g r a i n / S C F w i t h electrostatic precipitator acc o r d i n g to m a n u facturer's g u a r a n teed specification)

155 132.5 130 ( 9 4 % r e m o v a l ) —0.2 (estimated 0.01 w i t h a d d i t i o n of p r e cipitator)

%) 6 12 17 62 1 2

5 10 12 50 1 22


172

SULFUR

REMOVAL

AND RECOVERY

a n d c h e m i c a l p r o p e r t i e s of t h e p r o d u c t salts, b o t h u p s t r e a m a n d d o w n s t r e a m of t h e c y c l o n e .

T h e s e d a t a are c o n s i d e r e d a d e q u a t e to specify,

d e s i g n , a n d w a r r a n t p r o d u c t i o n c o l l e c t i o n systems c a p a b l e of l i m i t i n g emissions to less t h a n 0.01 g r a i n / S C F . T y p i c a l s c r u b b e r system p e r f o r m a n c e is g i v e n i n T a b l e I. I t w a s d e


r i v e d f r o m test results, a n d it shows t w o cases—one r e p r e s e n t i n g a p o w e r

Figure 6.

Typical ACP system plot arrangement

p l a n t s u c h as M o h a v e w h i c h b u r n s l o w s u l f u r w e s t e r n c o a l a n d t h e other r e p r e s e n t i n g a p o w e r p l a n t w h i c h b u r n s 3 % s u l f u r eastern c o a l .

The

m a j o r difference i n the t w o cases occurs because of t h e w a t e r v a p o r a n d t h e a s h content i n t h e i n l e t flue gas. T h e i n l e t w a t e r v a p o r content i n the M o h a v e case l i m i t s the a m o u n t of s o l u t i o n that c a n b e s p r a y e d i n t o t h e gas a n d t h e r e b y l i m i t s s u l f u r d i o x i d e r e m o v a l . T h e i n l e t ash content i n t h e s e c o n d case causes a s l i g h t l y h i g h e r Δ Ρ a n d adds a significant b u r d e n to the p a r t i c u l a t e c o l l e c t i o n e q u i p m e n t . T h e h i g h p e r c e n t a g e of a s h i n t h e p r o d u c t w i l l also c o m p l i c a t e r e g e n e r a t i o n . B e n c h a n d p i l o t scale tests of the v a r i o u s steps i n A C P r e g e n e r a t i o n h a v e b e e n c o n d u c t e d s u c h as r e d u c t i o n , q u e n c h i n g ,

filtration,

precarbona-

t i o n , c a r b o n a t i o n , d e c o m p o s i t i o n , a n d h y d r o g e n sulfide s c r u b b i n g .

These

tests are c o n t i n u i n g i n t h e laboratories a n d the n e a r b y field test f a c i l i t y to o p t i m i z e t h e A C P r e g e n e r a t i o n system p e r f o r m a n c e a n d / o r to d e v e l o p n e w a n d better processing

technology.


14.


System

Regenerative

Aqueous

Carbonate

173

Process

Engineering

A n u m b e r of e n g i n e e r i n g studies h a v e b e e n c o n d u c t e d to e v a l u a t e the size, i n t e g r a t i o n a b i l i t y , cost, a n d interfaces of f u l l - s c a l e A C P systems. M o s t of this w o r k has b e e n d o n e i n c o n n e c t i o n w i t h p o w e r p l a n t i n t e g r a t i o n , b u t t h e results c a n be a p p l i e d to b o t h i n d u s t r i a l a n d p o w e r p l a n t s . F i g u r e 6 shows a p l o t p l a n for a n A C P system t h a t treats i n excess of 825,000 s t a n d a r d c u f t / m i n ( S C F M ) .

T h e inlet sulfur dioxide

t r a t i o n of this gas is a p p r o x i m a t e l y 2200 p p m .

concen

T h e system is d e s i g n e d

for a 9 5 . 5 % r e m o v a l a n d a n outlet p a r t i c u l a t e l o a d i n g of 0.01 g r a i n / S C F or 0.027 l b / 1 0 B t u . Downloaded by NATL UNIV OF SINGAPORE on May 6, 2018 | https://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch014

6

F i g u r e 7 is a p l a n v i e w of the s c r u b b e r i n s t a l l a t i o n w i t h t w i n s c r u b bers u s e d to treat the 825,000 S C F M .

T h e gas is r e m o v e d f r o m e x i s t i n g

d u c t w o r k , c o n v e y e d to the t o p of the s c r u b b e r , a n d passed t h r o u g h the s c r u b b e r , cyclones, p r e c i p i t a t o r , booster fans, a n d b a c k to the e x i s t i n g stack. T h e e x i s t i n g d u c t i n g or the s c r u b b e r system, c a n b e b y p a s s e d d e p e n d i n g o n o p e r a t i n g a n d m a i n t e n a n c e cycles i n the p o w e r p l a n t .

The

scrubbers are a p p r o x i m a t e l y the largest m o d u l e size p r o p o s e d for either

Iμ*-EXIST. COAL CONVEYOR EXIST. FLUE GAS DUCT AND STACK

SPRAY DRYER -EXIST. SOUTH ROAD

Figure 7.

Scrubber installation plan view

p o w e r or i n d u s t r i a l p l a n t s . T h e y are 52 ft i n d i a m e t e r a n d are m a d e of c a r b o n steel. F i g u r e 8 shows the s c r u b b e r i n s t a l l a t i o n stands 135 ft h i g h . W h i l e the e q u i p m e n t is o b v i o u s l y large, the costs associated w i t h these l o w energy s c r u b b e r systems are a c c e p t a b l y l o w . T h e t e c h n o l o g y is w e l l


174

SULFUR

REMOVAL

AND RECOVERY

OPERPT. EL. 131 ft 0 in.

7 ft 6 in. χ 21 ft DUCT 7 ft 6 in. χ 21 ft DUCT

16 ft χ 9 ft DUCT


NEW CONNECTION TO EXISTING (TYP 2 PLACES)!

ROTATE EXISTING ID FAN AS SHOWN EL. EXISTING ID FAN 17 ft 5-1/2 in. EL. 9 ft 6 in.

CONNECTION EXISTING (TYP 2 PLACES) SECTION A-A T

ELECTROSTATIC PRECIPITATORS

0

Figure 8.

Scrubber installation elevation view

e s t a b l i s h e d , a n d materials s u c h as c a r b o n steel c a n b e u s e d because of t h e u n i q u e i n t e r n a l e n v i r o n m e n t of a s p r a y d r y e r - s c r u b b e r . T h e r e g e n e r a t i o n system associated w i t h , b u t d e c o u p l e d f r o m , t h e s c r u b b e r i n s t a l l a t i o n o c c u p i e s a p l o t of a b o u t 7 / 1 0 acre ( F i g u r e 9 ) .

It

contains d u a l reducers a n d m u l t i p l e aqueous p r o c e s s i n g c o l u m n s t h r o u g h out. T h e system c a n p r o d u c e 17.7 t o n s / h r of s o d i u m c a r b o n a t e .

That

PRECARBONATION TOWERS PC-1 AND PC-2 SPENT ABSORBENT SYSTEM H-1b

CARBONATION TOWERS CT-1 AND CT-2

REDUCER R-1 \

CARBONATE UNLOADING SYSTEM CARBONATE HANDLING SYSTEM H-3a

CONTROL HOUSE AND MAINTENANCE

REDUCER R-2

BLDG. (25 ft χ 120 ft REDUCER AIR COMPRESSORS C-2a AND C-2b

AIR PREHTR B-4

PROCESS GAS COMPRESSORS C-3a, C-3b, C-3c

Figure 9.

Regeneration

MAXIMUM)

system plot


14.


Regenerative

Aqueous

Carbonate

175

Process


EL. 16 ft-0 in.

$8πί * Figure 10.

Regeneration

elevation

M 2 J

view

a m o u n t p r o v i d e s for p r o d u c t salt r e g e n e r a t i o n o n a c o n t i n u o u s basis w h e n t h e p o w e r p l a n t operates at f u l l c a p a c i t y o n 3 . 5 % s u l f u r c o a l . F i g u r e 10 shows a n e l e v a t i o n of this r e g e n e r a t i o n system. T h e largest e q u i p m e n t is associated w i t h the r e g e n e r a t e d carbonate h a n d l i n g a n d storage system. T h e r e d u c e r e q u i p m e n t , w h i c h is e l e v a t e d a b o v e the q u e n c h t a n k , is a b o u t 60 ft h i g h . T h i s p a r t i c u l a r regenerative A C P system i n c l u d i n g the C l a u s p l a n t r e q u i r e s a p p r o x i m a t e l y 2 % acres of l a n d , or a b o u t 300 s q f t / M w sq f t / 1 0 0 0

SCFM

treated).

T h e regeneration equipment can be

(140 de

c o u p l e d f r o m the s c r u b b e r system, y i e l d i n g h i g h o v e r a l l A C P system reliability.

T h e d e c o u p l i n g is a f u n c t i o n of the surge c a p a c i t y w h i c h is

p l a c e d b e t w e e n the s c r u b b e r a n d the r e g e n e r a t i o n e q u i p m e n t .

Table II

shows the e x p e c t e d p e r f o r m a n c e f r o m this p l a n t . T h e t w o c o l u m n s i n d i c a t e the d e s i g n p e r f o r m a n c e a n d the w a r r a n t e d p e r f o r m a n c e . T h e p l a n t w i l l b e d e s i g n e d for s o m e w h a t better o p e r a t i n g p e r f o r m a n c e t h a n w i l l be w a r r a n t e d . H o w e v e r , e v e n the w a r r a n t e d p e r f o r m a n c e is s u b s t a n t i a l l y better t h a n m a n y other a v a i l a b l e systems, a n d a l l f e d e r a l standards are m e t or e x c e e d e d b y the system. Table II.

A C P System Performance Warranty

S 0 r e m o v a l " (%) S 0 émissions» ( l b / 1 0 B t u ) P a r t i c u l a t e emissions ( g r a i n / S C F ) E l e c t r i c a l power d e m a n d ( k w , 24-hr average) P e t r o l e u m coke ( t o n / h r ) 2 2

a b

6

90 ( m i n i m i u m ) 0.55 0.02 6

9900 8

Design 95.5 0.25 0.01 7580 6.6

3.5 wt % sulfur coal. T o meet mass and opacity standards.


176

SULFUR

REMOVAL

AND

RECOVERY

Economics A t h o r o u g h analysis of the c a p i t a l a n d o p e r a t i n g e c o n o m i c s w a s m a d e for the system d e s c r i b e d above. T h e basis for this estimate is s h o w n i n T a b l e I I I , a n d r e l a t i v e l y conservative assumptions h a v e b e e n m a d e

for

the cost of the v a r i o u s u t i l i t i e s , m a i n t e n a n c e , o p e r a t i n g s u p p l i e s , overh e a d , a n d c a p i t a l c h a r g e rate. T h e analysis w a s b a s e d o n d e s i g n i n g t h e p l a n t f o r the e q u i v a l e n t of 7000 h r / y r of f u l l l o a d o p e r a t i o n . T h e c a p i t a l costs, b r o k e n d o w n i n t o the gas i n t e r f a c e l o o p a n d the r e g e n e r a t i o n sys-


t e m , are s h o w n i n T a b l e I V . T h e cost for the s c r u b b e r l o o p a n d its assoTable III.

Total A n n u a l Cost Assumptions

O p e r a t i o n at f u l l p o w e r — 7 0 0 0 hx/yr Natural gas—$0.40/Mcf Coke—$20/ton E l e c t r i c a l power c o s t — 1 0 m i l l s / k w - h r Operation labor—$10/hr M a i n t e n a n c e — 3 % of c a p i t a l cost O p e r a t i n g s u p p l i e s — 0 . 5 % of c a p i t a l cost Overhead P a y r o l l — 4 0 % of l a b o r P l a n t — 5 0 % of l a b o r , m a i n t e n a n c e , a n d supplies C a p i t a l charge r a t e — 1 5 % / y r Table IV. Capital Cost Estimate U t i l i t y Systems for a 330-Mw Plant Using 3.5% Sulfur Coal G a s interface l o o p — i n s t a l l e d Engineering and management

$ 7,343,000 1,586,000 Subtotal

Regeneration system installed Engineering and management

8,929,000 ( 2 7 / k w ) 9,201,000 2,917,000

Subtotal Total

12,118,000

(36.8/kw)

$21,047,000

(63.8/kw)

c i a t e d e q u i p m e n t is a p p r o x i m a t e l y $ 2 7 / k w . T h i s i n c l u d e s a l l e n g i n e e r i n g , m a n a g e m e n t , e q u i p m e n t , c o n s t r u c t i o n , startup, a n d d e b u g g i n g .

T h e re-

g e n e r a t i o n s u b s y s t e m is s o m e w h a t m o r e expensive a n d is estimated at $36.80/kw.

T h i s cost is for r e g e n e r a t i o n associated w i t h h i g h s u l f u r f u e l .

T h e t o t a l cost t h e n for the regenerative aqueous c a r b o n a t e process o n a n eastern u t i l i t i e s site is $ 6 3 . 8 0 / k w .

T h i s compares

quite favorably with

the cost for n o n - r e g e n e r a t i v e l i m e a n d limestone systems, a n d the system has the a d v a n t a g e of b e i n g f u l l y regenerative. T a b l e V shows the utilities costs for this specific p l a n t site a n d c o n ditions.

T h e largest o p e r a t i n g cost i n the u t i l i t y category is s u p p l y i n g

p e t r o l e u m c o k e at $ 2 0 / t o n .

T h e next largest expense is e l e c t r i c a l p o w e r ,


14.


Regenerative Table V .

Aqueous

Carbonate

Utility Costs

Parameter

380 Mw Plant

E l e c t r i c i t y a t 10 m i l l s / k w - h r N a t u r a l gas a t 4 0 ° F / 1 0 0 Coke at $20/ton Cooling water Process w a t e r B o i l e r feed w a t e r Steam M a k e u p carbonate

(mills/kw-hr)

0.230 0.039 0.400 0.0087 0.0136 0.0022 0.0114 0.0076

T o t a l u t i l i t y cost Downloaded by NATL UNIV OF SINGAPORE on May 6, 2018 | https://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch014

177

Process

0.7125

w h i c h is to b e e x p e c t e d w i t h a n y s u l f u r d i o x i d e r e m o v a l system.

With

r e g a r d to t h e coke r e q u i r e m e n t , one c o u l d d e s i g n this p l a n t to use c o a l as t h e r e d u c i n g agent i n t h e r e d u c e r at some p e n a l t y i n r e g e n e r a t i o n a n d filtration

equipment.

H o w e v e r , a n e t savings i n o p e r a t i n g costs c o u l d

w e l l o c c u r because of t h e m a g n i t u d e of t h e costs. T h e other o p e r a t i n g costs associated w i t h t h e p l a n t i n c l u d e l a b o r , m a i n t e n a n c e , s u p p l i e s , p a y r o l l , p l a n t o v e r h e a d , c a p i t a l c h a r g e , etc. T a b l e V I s u m m a r i z e s u t i l i t y a n d m a t e r i a l costs f o r e a c h s u b s y s t e m , i.e., t h e gas

a n d regenerative

subsystems,

a n d gives

total

operating

costs.

T h e costs a r e s o m e t h i n g less t h a n 1 m i l l / k w - h r f o r t h e gas interface syst e m a n d a b o u t 1.8 m i l l s / k w - h r f o r t h e r e g e n e r a t i o n system, o r a t o t a l o p e r a t i n g cost o f 2.8 m i l l s / k w - h r to p r o v i d e s u l f u r d i o x i d e r e m o v a l . N o c r e d i t w h a t s o e v e r has b e e n t a k e n f o r t h e s u l f u r p r o d u c e d , b u t t h e t o t a l o p e r a t i n g cost of t h e C l a u s p l a n t is i n c l u d e d . If o n e evaluates t h e cost effectiveness of s u c h a system b y l o o k i n g at f u e l costs as a f u n c t i o n of s u l f u r content a n d c o m p a r i n g t o t a l o p e r a t i n g Table V I . A n n u a l Operating Cost Estimate ($000) (17.7 tons Sodium Carbonate/hr, 7000 h r / y r ) Regeneration

Total

303 100 268 44

1340 200 364 61

1643 300 632 105

Gas Interface Utilities and materials L a b o r and supervision at $10/hr M a i n t e n a n c e a t 3 % d e p r e c i a t i o n base S u p p l i e s a t 0 . 5 % d e p r e c i a t i o n base P a y r o l l overhead a t 4 0 % l a b o r a n d supervision P l a n t overhead a t 5 0 % l a b o r a n d s u p e r v i s i o n , m a i n t e n a n c e , a n d supplies C a p i t a l charge a t 1 5 %

40

80

120

206 1340

312 1820

518 3160

T o t a l ($000/yr)

2301

4177

6478

Total (mills/kw-hr)

0.99

1.81


2.80

178

SULFUR

REMOVAL

AND RECOVERY

costs f o r the A C P system w i t h p o t e n t i a l savings i n f u e l costs, t h e result is q u i t e s u r p r i s i n g . F i g u r e 11 is a c u r v e f r o m Gas Turbine

World

of October

1972 t h a t shows f u e l costs as a f u n c t i o n of s u l f u r i n the f u e l . A l t h o u g h there is a great d e a l of scatter, i t c a n b e seen that F o s t e r - P e g g has p u t i n a c o r r e l a t i o n suggesting a b o u t a 350 p e r m i l l i o n B t u savings b y g o i n g f r o m 0 . 3 % s u l f u r f u e l to 2 %

sulfur fuel.

B e i n g a b l e to b u r n

3 . 5 % s u l f u r c o a l a n d s t i l l meet p o l l u t i o n standards p r o b a b l y w o u l d result i n a n even l a r g e r savings.

Based on a conservative 3 5 0 / m i l l i o n B t u ,

the analysis s h o w n i n T a b l e V I I shows a 6V2 m i l l i o n d o l l a r / y r a n n u a l


cost associated w i t h t h e p a r t i c u l a r p l a n t d e s i g n (as p r e s e n t e d i n T a b l e V I ) , a n 8.1 m i l l i o n d o l l a r f u e l savings, a n d a s u l f u r c r e d i t of $630,000.

about

T h e result is a n e t savings of 2.25 m i l l i o n d o l l a r s / y r or 1.0

m i l l / k w - h r , as o p p o s e d to t h e o p e r a t i n g loss u s u a l l y associated w i t h s u l f u r dioxide removal plants. Summary I n c o n c l u s i o n , this s e c o n d - g e n e r a t i o n s u l f u r d i o x i d e r e m o v a l process is n o w r e a d y f o r f u l l - s c a l e i n s t a l l a t i o n . I t promises to solve m a n y of t h e D A T A = FOSTER-PEGG

OCT. 1972 (FOR GAS TURBINE WORLD)

0CRUDE

83 80

60

48

AOél

20i\-

0 PERCENT S U L F U R

Gas Turbine World

Figure 11.

Fuel cost vs. sulfur content


14.


Regenerative

Table V I I .

Aqueous

Carbonate

Process

A C P C o s t Effectiveness 330 Mw

A n n u a l o p e r a t i n g cost ( $ / y r , 0 0 0 ) A n n u a l o p e r a t i n g cost ( m i l l s / k w - h r ) F u e l savings ( $ 0 0 0 / y r ) S u l f u r v a l u e at $ 2 0 / t o n ( $ 0 0 0 / y r ) T o t a l credit ( $ 0 0 0 / y r ) T o t a l savings ( $ 0 0 0 / y r ) (mills/kw-hr)


179

Plant

6480 2.8 8100 630 8730 2250 1.0

p r o b l e m s associated w i t h past s u l f u r d i o x i d e s c r u b b i n g systems.

Spe-

c i f i c a l l y the A C P r e g e n e r a t i v e s y s t e m : 1. P r o v i d e s a n e c o n o m i c a d v a n t a g e b y a l l o w i n g the use of s u l f u r f u e l w h i l e p r o v i d i n g l o w s u l f u r d i o x i d e emissions

high

2 . E l i m i n a t e s s l u d g e p r o d u c t i o n a n d the r e l a t e d d i s p o s a l p r o b l e m 3. Eliminates maintenance plugging

problems

associated

with

scaling and

4. M i n i m i z e s t h e i m p a c t o n p l a n t r e l i a b i l i t y b y u s i n g a s i m p l e s c r u b b i n g scheme s o m e w h a t d e c o u p l e d f r o m the r e g e n e r a t i o n e q u i p m e n t RECEIVED April 4, 1 9 7 4


Regenerative Aqueous Carbonate Process for Utility and Industrial

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