Sulfur Removal and Recovery from Industrial ... - ACS Publications

15 Removal and Reduction of Sulfur Dioxides

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from Polluted Gas Streams P. STEINER, H . JÜNTGEN,

and K. K N O B L A U C H

Foster Wheeler Corp., Livingston, N . J. 07039

This new, second generation process was primarily designed to remove sulfur dioxide from polluted gas streams. front

end

Forschung

of

the

process was

developed

and operates as a sulfur dioxide

placing the sulfur dioxide-containing a special carbon.

Following

by

The

Bergbau

concentrator,

gases in contact with

the preferential

adsorption

of

sulfur dioxide, the special carbon adsorbent is regenerated by thermal treatment to yield a concentrated sulfur dioxide off-gas which is converted to sulfur in a coal bed by Foster Wheeler Corporation's

Resox process. This process repre-

sents a new way to achieve the desired reaction rate between sulfur

dioxide and crushed coal at approximately

650-

760°F.

>"phe idea to use the various forms of coal to remove sulfur dioxide is not new and was described in an English patent as early as 1879

(I).

However, massive research and development programs to develop commercially viable sulfur dioxide removal processes were not initiated until 80 years later, when ecological considerations forced public concern. The Bergbau Forschung-Foster Wheeler

sulfur dioxide

removal

process was originally developed for the utility industry. However, the basic system can, and will, be used to meet the specific requirements of other industries as well. This second generation sulfur dioxide removal process consists of three basic steps.

The first step removes the sulfur

dioxide from polluted gas streams by adsorption on carbon (activated coke).

The second step regenerates the adsorbent (coke), producing a

gas stream with high sulfur dioxide concentration. The third step treats the sulfur dioxide-rich stream by reducing it to elemental sulfur. 180

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

15.

STEiNER E T AL.

Sulfur Dioxide

Removal and Reduction

Sulfur Dioxide Removal and Adsorbent

181

Regeneration

Physical Chemistry and Process Technology of the Sulfur Dioxide Removal System.

T h e s u l f u r d i o x i d e r e m o v a l system w a s d e v e l o p e d

by

B e r g b a u F o r s c h u n g i n E s s e n , W e s t G e r m a n y a n d is b a s e d o n a n d d e s i g n e d for a s p e c i a l a c t i v a t e d coke adsorbent.

T h e a c t i v a t e d coke, t h e

most c r i t i c a l i n g r e d i e n t i n the system, is the result of a research a n d


d e v e l o p m e n t p r o g r a m i n i t i a t e d i n the late 1950s.

It has excellent s u l f u r

d i o x i d e a d s o r p t i o n , h i g h i g n i t i o n t e m p e r a t u r e , a n d g o o d p h y s i c a l strength. T h e b a s i c system consists of a g a s / s o l i d c o n t a c t i n g d e v i c e ( t h e a d s o r b e r ) a n d a regenerator ( t h e d e s o r b e r ) .

W i t h i n t h e a d s o r b e r the a c t i -

v a t e d coke moves d o w n w a r d i n the p l u g flow w h i c h is c o n t a i n e d

by

p e r m a n e n t l y fixed steel louvers o n the gas e n t r a n c e a n d exit sides of t h e unit. T h e p o l l u t e d gas stream is passed i n t h r o u g h the louvers, t h r o u g h the adsorbent, a n d out t h r o u g h louvers o n t h e opposite side of t h e a d sorber.

T h e s u l f u r d i o x i d e c o n t a i n e d i n the gas stream is a d s o r b e d

on

the i n n e r surface of the a c t i v a t e d coke a n d is t h e n o x i d i z e d to s u l f u r i c a c i d i n the presence of the o x y g e n a n d w a t e r v a p o r w h i c h are also i n the p o l l u t e d gas ( 2 ) .

C o i n c i d e n t a l l y , the a d s o r b e r f u n c t i o n s as a p a n e l b e d

filter to r e m o v e p a r t i c u l a t e s e n t r a i n e d i n the gas stream. T h e s u l f u r i c a c i d content of the a c t i v a t e d c o k e increases as a f u n c t i o n of coke d w e l l t i m e i n the adsorber.

T h e r e f o r e , the coke d i s c h a r g e d at the b o t t o m of

the

a d s o r b e r contains the highest possible a m o u n t of s u l f u r i c a c i d for the g i v e n c o n d i t i o n s a n d a d s o r b e r geometry. T h e adsorbent is regenerated after i t is d i s c h a r g e d f r o m the a d s o r b e r a n d is separated f r o m p a r t i c u l a t e s b y a v i b r a t i n g sieve. T h e r e g e n e r a t i o n is effected t h e r m a l l y b y h e a t i n g the s u l f u r i c a c i d - l o a d e d adsorbent i n a n inert atmosphere. T h e r e g e n e r a t i o n c o n d i t i o n s cause a d i r e c t i o n a l c h a n g e i n the d r i v i n g forces o f the reactions i n this system.

T h e participants

u n d e r g o a m o d i f i e d r e v e r s a l of t h e a d s o r p t i o n r e a c t i o n i n w h i c h the fixed c a r b o n of the adsorbent reduces the s u l f u r i c a c i d to s u l f u r d i o x i d e . T e c h n i c a l l y , the r e g e n e r a t i o n is c a r r i e d out i n a m o v i n g b e d reactor u s i n g s a n d as a d i r e c t heat c a r r i e r to heat the a d s o r b e n t to 6 0 0 - 6 5 0 ° C . T h e effluent gas of the r e g e n e r a t i o n contains 2 0 - 3 0 % v o l u m e as w e l l as w a t e r a n d c a r b o n d i o x i d e .

sulfur dioxide b y

It c a n b e f e d d i r e c t l y to

F o s t e r W h e e l e r s Resox process w h i c h converts the s u l f u r d i o x i d e content to s u l f u r . Mechanism of Adsorption.

T h e m e c h a n i s m of the s u l f u r d i o x i d e

a d s o r p t i o n a n d o x i d a t i o n o n c a r b o n shows t h a t the s u l f u r d i o x i d e p i c k - u p c a n b e d i v i d e d i n t o three subsequent phases i n w h i c h phase c h a n g e is a f u n c t i o n of t i m e . I n phase one, t h e a d s o r p t i o n rate is c o n t r o l l e d b y t h e rate of s u l f u r d i o x i d e d i f f u s i o n i n t o the i n n e r surface of t h e adsorbent. A s the a d s o r p t i o n proceeds, the n u m b e r of locations a v a i l a b l e for a d s o r p -


182

SULFUR

t i o n declines, a n d finally most becomes

REMOVAL

of the easily accessible

AND

RECOVERY

inner

surface

occupied.

It is necessary

to create vacancies

o n t h e i n n e r surface to a l l o w

c o n t i n u e d a d s o r p t i o n . V a c a n c i e s , h o w e v e r , are c r e a t e d b y s u l f u r d i o x i d e o x i d a t i o n a n d t h e subsequent

transport of t h e generated

to r e a d i l y accessible i n n e r pores.

sulfuric acid

T h e r e f o r e , t h e a d s o r p t i o n rate is n o w

c o n t r o l l e d b y t h e rate of o x i d a t i o n a n d transport.

This

interdependent


r e l a t i o n s h i p is c h a r a c t e r i s t i c of this phase o f a d s o r p t i o n . I n t h e t h i r d phase, t h e accessible i n n e r pores start to fill u p t o c a p a c i t y a n d , therefore,

t h e transport rate approaches

zero causing a n

excess o f s u l f u r i c a c i d to b u i l d u p s l o w l y o n the i n n e r surface. t i n u o u s presence of s u l f u r i c a c i d poisons

T h e con-

t h e active centers, a n d t h e

a d s o r p t i o n a c t i v i t y declines. S i n c e t h e b u l k of the a d s o r p t i o n is a c c o m p l i s h e d i n the s e c o n d phase u n d e r stationary c o n d i t i o n s , t h e adsorbent w a s d e v e l o p e d to o b t a i n h i g h s u l f u r d i o x i d e - t o - s u l f u r i c a c i d c o n v e r s i o n rates f o r a l a r g e p o r t i o n of its i n n e r surface. T h e r e l a t i o n s h i p b e t w e e n p o r e structure a n d s u l f u r d i o x i d e a d s o r p t i o n is s h o w n i n F i g u r e 1. T h e o r d i n a t e is t h e t i m e , i n hours, after w h i c h 1 0 % of t h e i n l e t s u l f u r d i o x i d e w i l l pass t h r o u g h t h e c a r b o n w i t h out b e i n g a d s o r b e d .

T h e m e a n p o r e d i a m e t e r of a d s o r p t i o n pores w a s

selected f o r t h e abscissa as t h e p a r a m e t e r t o c h a r a c t e r i z e t h e adsorbent structure

( 3 ) . Adsorbents

produced

w i t h o u t catalyst i m p r e g n a t i o n w e r e

from

bituminous coal w i t h a n d

tested.

I n b o t h cases, t h e s u l f u r

Time of 10% Break Thraugh

with Catalyst

Average Diameter of Adsorption Figure 1.

6

fjj

Sulfur dioxide sorption of various active carbons


15.

STEiNER E T AL.

Sulfur Dioxide

Removal and

183

Reduction

Reaction Parameters: / E*ôkca(/mol

ε * 17 kcal/moi k * 10 min-'

Reaction Rate .s X s2

far the format/on


CO

s

0

2.Q\4

dV fNcm*\ dTL#.grdJ __ „ /5

measured calculated

-

3

m-SV/min i.o

0.0+/

ο

Figure 2.

y 200 300 400 femperature C°c) Nonisothermal

kinetics of thermal

regeneration

d i o x i d e a d s o r p t i o n increases i n i t i a l l y w i t h i n c r e a s i n g m e a n p o r e

size

d i a m e t e r a n d t h e n declines after r e a c h i n g a m a x i m u m at a b o u t

8A

a n d 7.2A, r e s p e c t i v e l y . T h e d a t a f u r t h e r i n d i c a t e that a n adsorbent w i t h catalyst adsorbs m o r e s u l f u r d i o x i d e a n d therefore that p o r e diameters are less c r i t i c a l .

U n f o r t u n a t e l y , this difference

sufficient to offset e c o n o m i c

i n performance

is not

a n d process considerations w h i c h f a v o r a n

a d s o r b e n t w i t h o u t catalyst. T h e net result of the research a n d d e v e l o p m e n t w o r k is a n adsorbent for c o m m e r c i a l use, w h i c h is p r o d u c e d f r o m p r e o x i d i z e d b i t u m i n o u s c o a l a n d w h i c h has a p a r t i c l e d i a m e t e r of 9 m m , a hardness of over 9 0 % , an i g n i t i o n t e m p e r a t u r e over 4 0 0 ° C , a n d a s u l f u r d i o x i d e a d s o r p t i o n of 8 - 1 5 % Adsorbent Regeneration.

(4). A t temperatures a b o v e 2 0 0 ° C a c t i v a t e d

c o k e c o n t a i n i n g s u l f u r i c a c i d undergoes t h e f o l l o w i n g r e a c t i o n : H S0 2

4

+

1/2C

•> 1 / 2 C 0

2

+

H 0 + 2

S0

2

T o o b t a i n the n o n i s o t h e r m a l r e a c t i o n k i n e t i c s , the s u l f u r i c a c i d - c o n t a i n i n g coke as h e a t e d at a constant rate of 5 ° C / m i n a n d the v o l u m e of e v o l v i n g i n d i v i d u a l r e a c t i o n p r o d u c t s w a s m o n i t o r e d vs. the c h a n g e i n temperature.

U n d e r the c o n d i t i o n s of this e x p e r i m e n t the r e g e n e r a t i o n

r e a c t i o n starts a r o u n d 200 ° C a n d is p r a c t i c a l l y c o m p l e t e d at 450 ° C as i n d i c a t e d b y the e v o l u t i o n of the r e a c t i o n p r o d u c t s as s h o w n i n F i g u r e 2.


184

SULFUR

REMOVAL

AND

RECOVERY

T h e s l o w h e a t i n g rate u s e d i n this e x p e r i m e n t w o u l d b e i m p r a c t i c a l for a c o m m e r c i a l o p e r a t i o n as the regenerator vessel w o u l d be q u i t e large. C o m m e r c i a l l y , the r e g e n e r a t i o n heat is o b t a i n e d b y m i x i n g the adsorbent w i t h a h o t s o l i d . S a n d has b e e n f o u n d to b e a satisfactory s o l i d . A c c o r d i n g to the l a w s of n o n i s o t h e r m a l r e a c t i o n k i n e t i c s , the t e m p e r a t u r e r a n g e at w h i c h a g i v e n r e a c t i o n proceeds b e c o m e s h i g h e r as the h e a t i n g rate is i n c r e a s e d .

T h e l i b e r a t i o n curves of s u l f u r d i o x i d e

for


different h e a t i n g rates b e t w e e n 5 a n d 1 0 , 0 0 0 ° C / m i n are s h o w n i n F i g u r e 3.

T h e c a l c u l a t i o n s are b a s e d o n parameters e s t a b l i s h e d i n l a b o r a t o r y

experiments a n d s h o w n i n F i g u r e 2. A t a n a p p r o x i m a t e d h e a t i n g rate of 5 0 0 ° C / m i n i n the s a n d regenerator, t h e m a x i m u m r e a c t i o n rate w o u l d b e expected at 5 2 0 ° C w i t h a n e n d p o i n t of 6 8 0 ° C .

dr

£ k

fiate of Heating = 5 10 50 /0*fx/O*/O

5x/0 I0 3

3

100

ZOO 300

400

500

*I7 kcal/moi - Sx to* //min

0

600

700

°C/min

4

800

900

Temperature t°C) Figure 3. Pilot Plant

Liberation

of sulfur dioxide for different heating rates

Testing

T h e process d e s c r i b e d here has b e e n tested for 2 yrs i n a c o n t i n u ously

operating

(ACFH)

(5).

p i l o t p l a n t processing

over

100,000

actual cu

D u r i n g 1969 the p i l o t u n i t processed 528 Χ

gas i n 6000 o p e r a t i n g h r . T h e d e s u l f u r i z a t i o n efficiency r a n g e d 60 a n d 9 5 % .

ft/hr

1 0 A C F of 6

between

T h e s e differences w e r e c a u s e d b y d e l i b e r a t e changes i n

o p e r a t i n g parameters s u c h as the gas a n d c o k e residence times i n the adsorber, t e m p e r a t u r e of a d s o r p t i o n a n d r e g e n e r a t i o n , etc.


15.

STEiNER E T AL.

Sulfur Dioxide


185

S i n c e the p i l o t u n i t a n d t h e d a t a o b t a i n e d f r o m i t are d e s c r i b e d i n n u m e r o u s p u b l i c a t i o n s o n l y some k e y c o n c l u s i o n s are m e n t i o n e d here. T h e p i l o t o p e r a t i o n e s t a b l i s h e d the t e c h n o l o g i c a l f e a s i b i l i t y of the process i n g e n e r a l a n d has s h o w n t h a t t h e assumptions, c a l c u l a t i o n s , a n d l a b o r a t o r y d a t a - b a s e d c o n c l u s i o n s c o n c e r n i n g p a r t i c u l a r features of the process s u c h as a d s o r p t i o n , r e g e n e r a t i o n at h i g h h e a t i n g rate, etc. are correct. D a t a o b t a i n e d d u r i n g the 2 yrs of o p e r a t i o n also has p r o v e d the ecoDownloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on November 10, 2016 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch015

n o m i c a l v i a b i l i t y of the process. Reduction

of Sulfur

Dioxide

by

Coal

T h e Resox process uses c o a l as a r e d u c i n g agent to p r o d u c e e l e m e n t a l sulfur.

It w a s d e v e l o p e d i n F o s t e r W h e e l e r C o r p o r a t i o n ' s J o h n B l i z a r d

R e s e a r c h C e n t e r a n d is the result of a research p r o g r a m i n i t i a t e d i n the late 1960s. T h i s process is d e s i g n e d to r e d u c e the s u l f u r d i o x i d e i n a n off-gas stream to s u l f u r a n d to condense the s u l f u r p r o d u c t f r o m the gas stream. It is c a p a b l e of h a n d l i n g a w i d e range of i n l e t gas c o m p o s i t i o n s a n d does not r e q u i r e gas c l e a n i n g , d r y i n g , or dust r e m o v a l systems. C r u s h e d c o a l is the o n l y m a t e r i a l a n d the o n l y catalyst c o n s u m e d .

T h e process r e p r e -

sents a n e w w a y to a c h i e v e the d e s i r e d degree of r e a c t i o n b e t w e e n s u l f u r d i o x i d e a n d c r u s h e d c o a l at temperatures as l o w as 600 ° C . T h e major process e q u i p m e n t consists of a reactor vessel a n d a s u l f u r condenser.

I n the reactor vessel, s u l f u r d i o x i d e - r i c h gases react

with

c r u s h e d c o a l to y i e l d gaseous e l e m e n t a l sulfur. T h i s s u l f u r is c o n d e n s e d f r o m the gas stream i n the s u l f u r condenser.

T h e high-purity l i q u i d sulfur

effluent of the process is a n o n p o l l u t i n g b y - p r o d u c t . F o s t e r W h e e l e r C o r p o r a t i o n s efforts t o w a r d f u l l c o m m e r c i a l i z a t i o n of this process are e x t e n d e d i n the f r a m e w o r k of a three phase p r o g r a m of process research a n d b e n c h - s c a l e f e a s i b i l i t y studies, p i l o t p l a n t o p e r a t i o n , a n d large scale d e m o n s t r a t i o n . O n l y the conclusions d i r e c t l y p e r t a i n i n g to the process are discussed here. A d e t a i l e d d i s c u s s i o n of the m e c h a n i s m a n d k i n e t i c s of this r a t h e r i n v o l v e d system is b e y o n d the scope of this p a p e r a n d w i l l b e r e p o r t e d at a later date. Research and Bench-Scale Feasibility Studies. T h e r e a c t i o n b e t w e e n c a r b o n a n d s u l f u r d i o x i d e at e l e v a t e d t e m p e r a t u r e s is w e l l k n o w n a n d has b e e n u s e d for n u m e r o u s processes.

F o r example, sulfur was produced

at T r a i l , B r i t i s h C o l u m b i a f r o m 1935 to 1943 b y b l o w i n g s u l f u r d i o x i d e a n d o x y g e n into the b o t t o m of a coke-fired r e d u c t i o n f u r n a c e . C o k e w a s c h a r g e d at the t o p a n d ash w a s r e m o v e d o n a r o t a r y grate at the b o t t o m of the f u r n a c e . T h e hot z o n e of the f u r n a c e w a s k e p t at 1 3 0 0 ° C to m a i n t a i n r a p i d r e a c t i o n rates a n d s m o o t h o p e r a t i o n . Sufficient s u l f u r d i o x i d e was a d d e d to the gas to react w i t h the c a r b o n m o n o x i d e a n d c a r b o n oxysulfide c o n t a i n e d i n the r e d u c t i o n f u r n a c e off-gas.

C o a l was


con-

186

SULFUR

REMOVAL

s i d e r e d unsatisfactory as a r e d u c i n g agent because of

AND

RECOVERY

the

hydrogen

sulfide f o r m a t i o n . C a r b o n w i l l also react w i t h s u p e r h e a t e d steam at elev a t e d temperatures to y i e l d c a r b o n m o n o x i d e a n d h y d r o g e n . F o s t e r W h e e l e r C o r p o r a t i o n ' s research p r o g r a m w a s b a s e d o n the a s s u m p t i o n that w h i l e h i g h temperatures are necessary to o b t a i n a c o m m e r c i a l l y p r a c t i c a l r e a c t i o n rate w h e n s u l f u r d i o x i d e or steam reacts i n d i v i d u a l l y w i t h c o a l , the t w o reactions w o u l d i n t e r a c t s y n e r g i s t i c a l l y w h e n Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on November 10, 2016 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch015

c o m b i n e d i n a single i n t e g r a t e d system. A s a result of this i n t e r a c t i o n , b o t h reactions w o u l d b e p r o m o t e d , a n d c o m m e r c i a l l y p r a c t i c a l rates for s u l f u r d i o x i d e r e d u c t i o n c o u l d be o b t a i n e d at s i g n i f i c a n t l y l o w e r t e m p e r a tures t h a n those r e p o r t e d i n the l i t e r a t u r e or u s e d c o m m e r c i a l l y .

A

s i m i l a r b e h a v i o r f o r the c o a l gasification r e a c t i o n is n o w b e i n g s t u d i e d i n a separate research p r o g r a m . T h e bench-scale study was conducted i n a small pilot plant designed for the r e a c t i o n of c r u s h e d c o a l w i t h s u l f u r d i o x i d e at c a r e f u l l y trolled conditions.

con-

T h e i n l e t gas c o m p o s i t i o n , r e a c t i o n t e m p e r a t u r e , a n d

gas residence t i m e w e r e selected as the i n d e p e n d e n t v a r i a b l e s f o r the study. T h e outlet gas c o m p o s i t i o n a n d r e a c t i o n rate w e r e m o n i t o r e d as dependent

variables.

T h e r e l a t i o n s h i p b e t w e e n s u l f u r d i o x i d e c o n v e r s i o n a n d the w a t e r - t o s u l f u r d i o x i d e r a t i o is s h o w n i n F i g u r e 4.

S i n c e the gas residence t i m e ,

t h e r e a c t i o n t e m p e r a t u r e , a n d the d r y i n l e t gas c o m p o s i t i o n w e r e h e l d constant, i t is e v i d e n t that t h e r e a c t i o n rate increases w i t h the p a r t i a l

SO in -SO2out z

X/ÛO All other parameters constant

Mol. H Ο ~4 Mol.S0 2

ο

/

2

Ratio H 0 2

Figure 4.

to SO.

3

2

Relationship between sulfur dioxide conversion and the water-to-sulfur dioxide ratio


15.

STEINER

Sulfur Dioxide

ET AL.

Mot, product Mol* SO consumed


z

Removal and

Reduction

187

All otherparameters constant

I -

4 6À .5·

/Ιοί. H 0 Moi. SO 2

"J

Ζ

z

Ratio H 0 to S0 2

Figure 5.

Z

Relationship between hydrogen sulfide selectivity and the water-to-sulfur dioxide ratio

pressure of w a t e r i n the system. T h e c h a n g i n g slope of t h e c u r v e shows the different degree of increase of the r e a c t i o n rate effected w h e n t h e w a t e r c o n c e n t r a t i o n of t h e system is i n c r e a s e d over different p r e v i o u s levels o f c o n c e n t r a t i o n . T h e w a t e r , c a r b o n d i o x i d e , s u l f u r d i o x i d e , n i t r o g e n gas, c a r b o n , a n d the n u m e r o u s other c o m p o u n d s r e s u l t i n g f r o m different c o m b i n a t i o n of the elements c o n t a i n e d b y the c o m p o u n d s a b o v e represent a c o m p l e x system. D e p e n d i n g o n t h e r e a c t i o n parameters, different r e a c t i o n routes

will

d o m i n a t e t h e system a n d w i l l y i e l d different c o m p o u n d s as t h e m a j o r reaction products.

T h e recent research effort c o n c e n t r a t e d o n o b t a i n i n g

e l e m e n t a l sulfur or h y d r o g e n sulfide as the p r i n c i p a l r e a c t i o n p r o d u c t s . I n g e n e r a l , i t w a s f o u n d that the s e l e c t i v i t y of the r e a c t i o n t o w a r d s hydrogen

sulfide increases w i t h i n c r e a s i n g r e a c t i o n t e m p e r a t u r e s a n d

w a t e r concentrations.

T h e r e l a t i o n s h i p b e t w e e n h y d r o g e n sulfide selec

t i v i t y a n d the a m o u n t of w a t e r i n the system is s h o w n i n F i g u r e 5. N e a r l y a l l t h e sulfur d i o x i d e e n t e r i n g t h e process w a s c o n v e r t e d s e l e c t i v e l y to h y d r o g e n sulfide b e t w e e n 660 a n d 7 6 0 ° C . T h e process w a s also a p p l i e d to convert s u l f u r d i o x i d e to s u l f u r at l o w e r r e a c t i o n t e m peratures. A s s h o w n i n F i g u r e 6, w h e n 1 0 0 % of the s u l f u r d i o x i d e is c o n v e r t e d , 9 0 % reacts to f o r m e l e m e n t a l s u l f u r w h i l e 1 0 % y i e l d s different by-products

s u c h as h y d r o g e n

sulfide, c a r b o n

oxysulfide, c a r b o n d i

sulfide, etc. N e a r l y 1 0 0 % s e l e c t i v i t y to s u l f u r c a n b e o b t a i n e d at l o w e r conversions c o r r e s p o n d i n g to l o w e r r e a c t i o n temperatures. peratures c a u s e d l o w e r conversions

Lower tem

since t h e m a x i m u m contact


time,

188

SULFUR

Vsq*Converted to6

REMOVAL

AND

RECOVERY

.„„

χ

/00-i


All other parameters constant

H:

I 50

τ -

60

Figure 6.

"—I

1—

70

SO

90

Sfy Conversion %

IOÛ

Sulfur dioxide consumed vs. sulfur

SO tn

v

z

produced

b a s e d o n e m p t y reactor v o l u m e , b e t w e e n s u l f u r d i o x i d e - c o n t a i n i n g gas a n d c a r b o n w a s fixed at 6 sec f o r a l l experiments. T h e v a r y i n g r e a c t i v i t y o f different coals u s e d i n this w o r k necessit a t e d different r e a c t i o n temperatures. T h e temperatures u s e d w e r e 5 5 0 7 0 0 ° C f o r b i t u m i n o u s coals a n d 6 5 0 - 8 0 0 ° C f o r a n t h r a c i t e coals. T h e results o b t a i n e d i n this phase of t h e p r o g r a m e s t a b l i s h e d process f e a s i b i l i t y a n d s h o w e d that t h e i n i t i a l assumptions c o n c e r n i n g process c h e m i s t r y a n d k i n e t i c s w e r e correct. Pilot Plant Operation.

T h e pilot plant operation was the second

phase o f t h e research p r o g r a m a n d w a s d e s i g n e d to d e l i v e r t h e d a t a necessary t o p l a n , b u i l d , a n d operate a c o m m e r c i a l size d e m o n s t r a t i o n p l a n t . I n o r d e r to a c c o m p l i s h these objectives, a p i l o t p l a n t of sufficient c a p a c i t y w a s c o n s t r u c t e d a n d o p e r a t e d f o r a n e x t e n d e d p e r i o d of t i m e . A d i a g r a m o f t h e p i l o t f a c i l i t y is s h o w n i n F i g u r e 7. T h e s u l f u r dioxide, carbon dioxide, nitrogen, a n d water were metered,

blended,

a n d b r o u g h t t o t e m p e r a t u r e b y a fired heater so that the m i x t u r e e n t e r e d the reactor at a t e m p e r a t u r e a n d c o m p o s i t i o n r e p r e s e n t a t i v e o f the off-gas f r o m t h e B e r g b a u F o r s c h u n g process.

T h e reactor of 2 c u f t v o l u m e

c o n t a i n e d a rice-size a n t h r a c i t e c o a l b e d w h i c h m o v e d d o w n w a r d s l o w l y


15.

STEINER E T A L .

Sulfur Dioxide

a n d c o u n t e r c u r r e n t to t h e gas stream.

189


T h e coal hopper located above

the reactor g r a v i t y f e d the system w i t h fresh c o a l as the b e d v o l u m e w a s d i m i n i s h e d b y the r e a c t i o n a n d b y t h e r e m o v a l o f spent m a t e r i a l . S a m p l e ports a r r a n g e d at q u a r t e r p o i n t locations a l o n g t h e v e r t i c a l reactor vessel p e r m i t t e d the gas c o m p o s i t i o n to b e m o n i t o r e d a t different reactor locations, r e p r e s e n t i n g different gas residence times.

T h e tem

peratures at e a c h o f these s a m p l e ports, as w e l l as at t h e i n l e t a n d t h e Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on November 10, 2016 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch015

outlet, w e r e

continuously monitored.

T h e effluent gas o f t h e reactor

vessel passed t h r o u g h t h e s u l f u r condenser.

T h e t a i l gases l e a v i n g t h e

s u l f u r condenser w e r e s a m p l e d a n d a n a l y z e d . A n u m b e r of i n d i v i d u a l p i l o t runs w e r e c o n d u c t e d at v a r i o u s process c o n d i t i o n s to d e t e r m i n e t h e cause a n d effect r e l a t i o n s h i p o f process p a rameters s u c h as pressure, t e m p e r a t u r e , a n d residence t i m e o n t h e process behavior.

A q u a n t i t y of 1200-1500 A C F H of s u l f u r d i o x i d e - c o n t a i n i n g

gas w a s processed c o n t i n u o u s l y i n the p i l o t f a c i l i t y . T h e i n t e g r a t e d results o f these i n d i v i d u a l runs h a v e p r o v e d that t h e system is p r a c t i c a l f o r large scale operations a n d c a n treat a v a r i e t y of sulfur d i o x i d e - r i c h effluent gases.

T h e c o m p l e t e d p i l o t test p r o g r a m has

d e m o n s t r a t e d t h a t 9 0 % o f the s u l f u r d i o x i d e i n a t y p i c a l f e e d gas c a n b e 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 i n a p r o t o t y p e

apparatus h a v i n g design

features c o m p a t i b l e w i t h c o m m e r c i a l r e q u i r e m e n t s .

GAS SYNTHESIS

OFF-GAS TREATMENT

Figure 7.

Commercial

Scale

GAS COOLING

Foster Wheeler Resox pilot unit

Demonstrations

T h e first c o m m e r c i a l - s i z e d e m o n s t r a t i o n p l a n t was c o m p l e t e d i n e a r l y 1974 b y B e r g b a u F o r s c h u n g i n L u n e n , W e s t G e r m a n y . T h e p l a n t , s h o w n i n F i g u r e 8, is s u b s i d i z e d b y the W e s t G e r m a n g o v e r n m e n t . to process 5.3 χ

1 0 s t a n d a r d c u f t / h r of gas. 6

I t is d e s i g n e d

T h i s gas is p a r t o f t h e



190

SULFUR

Figure 8.

Bergbau Forschung

REMOVAL

A N D RECOVERY

unit in West Germany

flue gas f r o m a 350 M W coal-fired b o i l e r of t h e Steag. T h e p l a n t consists of a n adsorber, regenerator, a n d a m o d i f i e d C l a u s u n i t to process t h e s u l f u r d i o x i d e - r i c h r e g e n e r a t i o n off-gas. C o n t i n u o u s o p e r a t i o n w a s s c h e d u l e d t o start i n A p r i l 1974. P a r a l l e l w i t h B e r g b a u F o r s c h u n g ' s efforts i n W e s t G e r m a n y , F o s t e r W h e e l e r C o r p . is c o n s t r u c t i n g t h e first d e m o n s t r a t i o n p l a n t i n t h e U n i t e d States. T h e p r o t o t y p e u n i t is b e i n g erected f o r G u l f P o w e r C o . i n C h a t t a hoochee, F l o r i d a a n d is s c h e d u l e d to b e c o m p l e t e d i n S e p t e m b e r 1974. Compared

with

the Bergbau

F o r s c h u n g unit i n L u n e n , the Foster

W h e e l e r p l a n t w i l l substitute t h e Resox process f o r t h e m o d i f i e d C l a u s u n i t a n d c o n s u m e c o a l i n s t e a d of n a t u r a l gas to r e d u c e t h e s u l f u r d i o x i d e r i c h regenerator off-gas. I n conclusion, w h e n sulfur dioxide must be removed from polluted gas streams a n d a c c u m u l a t e d i n some f o r m , r e d u c t i o n to e l e m e n t a l s u l f u r is t h e o p t i m u m f o r m f o r a c c u m u l a t i o n , a n d c r u s h e d c o a l is t h e least expensive r e d u c i n g agent. Literature

Cited

1. British Patent 189 (1879). 2. Dratwa, H . , Jüntgen, H . , Peters, W., Chem. Ing. Tech. Z. (1967) 39, 949965.


15.

STEiNER

ET

AL.

Sulfur Dioxide


191

3. Jüntgen, H . , Knoblauch, K., Peters, W., Chem. Ing. Tech. Z. (1969) 41, 798-805. 4. Jüntgen, H . , Knoblauch, K., Zündorf, D., Chem. Ing. Tech. Z. (1973) 45, 1148-1152. 5. Jüntgen, H . , Knoblauch, K., Peters, W., " S O Removal From Flue Gases By Special Carbon 2," Kongr. Reinhalt. Luft, Washington, D . C . , 1970. 2

1974


R E C E I V E D April 4,


Sulfur Removal and Recovery from Industrial ... - ACS Publications

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