The Allied Chemical Sulfur Dioxide Reduction Process for

2 The Allied Chemical Sulfur Dioxide Reduction Process for Metallurgical Downloaded via TUFTS UNIV on July 7, 2018 at 08:58:24 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Emissions W. D. HUNTER, JR., J. C. FEDORUK, A. W. MICHENER, and J. E. HARRIS Allied Chemical Corp., Industrial Chemicals Div., P.O. Box 1139-R, Morristown, N. J. 07960

Allied Chemical

technology for reducing sulfur dioxide to

elemental sulfur was commercialized

in 1970 as the emission

control system for a Canadian sulfide ore roasting which received up to 500 tons/day fur dioxide. than 90% reduction

facility

of sulfur as 12%

sul-

In the next 2 yrs, this plant recovered more of the entering sulfur.

Allied's

technology can now be applied

sulfur

dioxide

to gas streams

containing 4-100% sulfur dioxide, dry basis. Sulfur dioxide reduction

may be used directly to control emissions from

roasters and continuous dioxide

concentration

smelting processes. Where sulfur is below about 4%,

and/or

gas

composition fluctuates widely, the reduction process is combined with a preliminary concentrating

process.

Targe-scale commercialization of technology for sulfur dioxide reduction to sulfur was accomplished by Allied Chemical Corp. in 1970 with the start-up of a prototype facility for a large new metallurgical operation at Falconbridge, Ontario. The technology, used initially for the emission control system at this plant, was developed through a major R & D program in the 1960's. Specifically over 90%

of the sulfur dioxide was removed

from a gas stream resulting from fluidized bed roasting of nickel-containing pyrrhotite ore at rates

up

to

one-half

million tons/year.

The

process installed in the Canadian plant has been discussed in detail in earlier papers ( J , 2).

The single-train plant design, which is capable of

receiving sulfur dioxide equivalent to as much as 500 long tons/day of sulfur, and other operating experience in this unique emission control project have been described in previous publications (3,

4).

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

24

S U L F U R

R E M O V A L

A N D R E C O V E R Y

T h e reliability of A l l i e d Chemical's sulfur dioxide reduction tech n o l o g y w a s p r o v e d d u r i n g 2 yrs of successful o p e r a t i o n i n w h i c h the c a p a b i l i t y o f a c h i e v i n g a 9 0 % o n - s t r e a m factor w a s e s t a b l i s h e d . A l l of t h e o r i g i n a l process d e s i g n a n d p e r f o r m a n c e c r i t e r i a w e r e c o n f i r m e d .

Turn

d o w n characteristics of t h e s y s t e m w e r e d e m o n s t r a t e d d u r i n g e x t e n d e d o p e r a t i o n at as l o w as o n e - t h i r d of d e s i g n c a p a c i t y w i t h n e a r l y constant o p e r a t i n g efficiencies

( i n terms of o v e r a l l s u l f u r d i o x i d e r e m o v a l a n d

r e d u c i n g agent u t i l i z a t i o n ) b e i n g a c h i e v e d at a l l rates. E l e m e n t a l s u l f u r p r o d u c e d i n t h e process w a s u s e d i n t e r c h a n g e a b l y w i t h F r a s c h s u l f u r at v a r i o u s A l l i e d locations to p r o d u c e h i g h q u a l i t y s u l f u r i c a c i d f o r t h e U . S . merchant market. Commercial

Plant

Description

A flow d i a g r a m of the s u l f u r d i o x i d e r e d u c t i o n process as i t is a p p l i e d to a sulfide o r e r o a s t i n g o p e r a t i o n l i k e that at F a l c o n b r i d g e is s h o w n i n F i g u r e 1. T h e h o t s u l f u r d i o x i d e gas f r o m t h e roasters is passed t h r o u g h h o t gas heat exchangers ( 1 ) a n d ( 2 ) w h e r e p a r t of the heat content of the gases is u s e d to reheat other process gas streams.

These w i l l be

d e s c r i b e d i n m o r e d e t a i l later. A t this p o i n t the roaster gas s t i l l contains fine d u s t p a r t i c l e s as w e l l as gaseous c o n t a m i n a n t s w h i c h m u s t b e r e m o v e d before t h e gas reaches t h e r e d u c t i o n reactor. T h i s gas p u r i f i c a t i o n is a c c o m p l i s h e d i n a two-stage aqueous s c r u b b i n g system c o n s i s t i n g of a t w o - l e g gas c o o l i n g t o w e r ( 3 ) a n d a p a c k e d c o n d e n s i n g t o w e r ( 4 ) . T h e b u l k o f the dust a n d other c o n t a m i n a n t s a r e c o l l e c t e d i n t h e gas c o o l i n g SO, GAS

, •v 4

CONDENSING ί TOWER

COLD GAS BY-PASS STEAM

Τ^^ψ]

'

Ί

mm

1 &!

~ u | COALESCER HEATl REGENERATOR:

.

g|

,„ 10

HEAT REGENERATOR

ι

t1 SULFUR

SULFUR \ SULFUR 1 SULFUR

J

TO STORAGE SULFUR HOLDING PIT

Figure

1.

Allied Chemical

sulfur dioxide reduction gas application

technology typical

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

roaster

2.

H U N T E R

E T

Allied

A L .

Chemical

Reduction

25

Process

t o w e r w h i l e the gas is c o o l e d a n d s a t u r a t e d b y a r e c i r c u l a t e d w e a k s u l f u r i c a c i d s o l u t i o n . T h e d e m i s t e r p a d at t h e t o w e r outlet is c o n t i n u o u s l y sprayed w i t h weak a c i d from the condensing tower. T h e underflow from the gas c o o l i n g t o w e r is t r e a t e d w i t h l i m e to p r e c i p i t a t e d i s s o l v e d m e t a l l i c impurities removed

f r o m the gas a n d to n e u t r a l i z e t h e a c i d i t y b e f o r e

b e i n g d e l i v e r e d to a waste p o n d w h e r e the solids are a l l o w e d to settle. T h e process gas is f u r t h e r c o o l e d i n the c o n d e n s i n g t o w e r ( 4 )

by

c i r c u l a t i n g w e a k a c i d w h i c h is c o o l e d e x t e r n a l l y i n i m p e r v i o u s g r a p h i t e heat exchangers ( 5 ) .

E n t r a i n e d droplets of a c i d m i s t are r e m o v e d f r o m

the gas i n electrostatic p r e c i p i t a t o r s ( 6 ) .

D r i p s f r o m the p r e c i p i t a t o r s

are r e t u r n e d to the gas c o o l i n g tower. T h e t e m p e r a t u r e of the c l e a n gas is t h e n r a i s e d a b o v e the d e w p o i n t of s u l f u r i c a c i d b y a d m i x i n g w i t h a r e h e a t e d s t r e a m of t h e same gas i n the mist tower

(7).

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

t h r o u g h the h o t gas heat exchanger

(2).

T h e process gas is d r a w n

t h r o u g h the w e t p u r i f i c a t i o n system a n d t h e n f o r c e d b y a c e n t r i f u g a l blower (8)

t h r o u g h the b a l a n c e of the p l a n t . N a t u r a l gas, w h i c h serves

as t h e r e d u c i n g agent, is i n t r o d u c e d i n t o t h e process gas s t r e a m at the b l o w e r d i s c h a r g e , a n d the m i x t u r e is passed t h r o u g h the h o t gas exchanger

(1)

heat

to raise its t e m p e r a t u r e a b o v e the d e w p o i n t of s u l f u r

before e n t e r i n g the r e d u c t i o n reactor system. T h e p r i n c i p a l f u n c t i o n of the c a t a l y t i c r e d u c t i o n system is to m a x i m i z e use of the r e d u c t a n t w h i l e p r o d u c i n g b o t h s u l f u r a n d

hydrogen

sulfide, so the h y d r o g e n s u l f i d e / s u l f u r d i o x i d e r a t i o i n t h e gas s t r e a m l e a v i n g the system is essentially that r e q u i r e d for the subsequent C l a u s reaction.

A l t h o u g h the c h e m i s t r y of

the p r i m a r y r e a c t i o n system

is

e x t r e m e l y c o m p l e x a n d i n c l u d e s reactions i n v o l v i n g 11 different elements a n d c o m p o u n d s , i t m a y be s u m m a r i z e d i n the f o l l o w i n g e q u a t i o n s :

CH

+

4

2

S0

4 C H + 6 S0 4

2

2

C0

2

+

2

H 0 + S 2

2

4 C0 + 4 H 0 + 4 H S + S 2

2

2

2

T h e p r e h e a t e d process a n d n a t u r a l gas m i x t u r e enters the c a t a l y t i c r e d u c t i o n system t h r o u g h a f o u r - w a y

flow

reversing valve (9)

a n d is

f u r t h e r p r e h e a t e d as it flows u p w a r d t h r o u g h a p a c k e d - b e d heat r e g e n erator ( 1 0 ) b e f o r e e n t e r i n g the r e d u c t i o n reactor T h e r m a l l y stable catalysts d e v e l o p e d

(11).

b y A l l i e d C h e m i c a l f o r this

f a c i l i t y cause r a p i d a n d efficient r e a c t i o n of the n a t u r a l gas w i t h the s u l f u r d i o x i d e to f o r m h y d r o g e n sulfide a n d e l e m e n t a l s u l f u r v a p o r w h i l e s u b s t a n t i a l l y e l i m i n a t i n g the f o r m a t i o n of u n d e s i r a b l e side r e a c t i o n p r o d ucts ( 5 , 6).

T h e t e m p e r a t u r e of the gases e n t e r i n g the reactor is h e l d

constant b y c o n t i n u o u s l y b y p a s s i n g a v a r y i n g q u a n t i t y of c o l d process gas a r o u n d the u p f l o w heat regenerator.

T h e heat that is g e n e r a t e d i n


26

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

reactor ( 11 ) b y the e x o t h e r m i c reactions sustains t h e o v e r a l l heat i n t h e system. A f t e r l e a v i n g the reactor, the m a i n gas flow passes d o w n t h r o u g h a s e c o n d heat regenerator ( 1 2 ) , g i v i n g u p its heat to t h e p a c k i n g i n t h a t vessel before l e a v i n g the c a t a l y t i c r e d u c t i o n system t h r o u g h flow reversi n g v a l v e ( 9 ). A t h e r m a l b a l a n c e is m a i n t a i n e d i n the system b y p a s s i n g a m i n o r flow of the hot gases f r o m the reactor ( 1 1 ) , a r o u n d the d o w n f l o w regenerator a n d the flow r e v e r s i n g v a l v e ( 9 ) , a n d r e m i x i n g i t w i t h t h e m a i n stream b e f o r e e n t e r i n g s u l f u r condenser ( 17 ). T h e p r i m a r y f u n c t i o n of the heat regenerators ( 1 0 )

and (12), then,

is to r e m o v e heat f r o m the gases l e a v i n g the c a t a l y t i c reactor ( 1 1 )

and

to use this heat to raise the t e m p e r a t u r e of the i n c o m i n g gases to the p o i n t w h e r e the s u l f u r d i o x i d e - n a t u r a l gas r e a c t i o n w i l l b e g i n .

The

d i r e c t i o n of flow t h r o u g h the t w o regenerators is p e r i o d i c a l l y r e v e r s e d to i n t e r c h a n g e t h e i r functions of h e a t i n g a n d c o o l i n g the gases b y u s i n g the flow r e v e r s i n g v a l v e ( 9 ) a n d f o u r w a t e r - c o o l e d b u t t e r f l y valves (14),

(15), and (16).

T h e v a l v e a r r a n g e m e n t s h o w n i n the

(13),

flow

dia-

g r a m is s p e c i a l l y d e s i g n e d to m a i n t a i n the gas flow t h r o u g h t h e c a t a l y t i c reactor (11)

i n one d i r e c t i o n o n l y . A l l five valves are o p e r a t e d f r o m a

c e n t r a l c o n t r o l system w h i c h s y n c h r o n i z e s t h e i r m o v e m e n t so t h a t e a c h flow r e v e r s a l is c o m p l e t e d i n less t h a n 1 sec. T h e e l e m e n t a l s u l f u r t h a t is f o r m e d i n the p r i m a r y reactor system is c o n d e n s e d

i n a horizontal shell-and-tube steaming condenser

(17).

T h i s represents over 4 0 % of t h e t o t a l r e c o v e r e d s u l f u r . T h e process gas s t r e a m t h e n enters the first stage ( 18 ) of a two-stage C l a u s reactor system w h e r e the f o l l o w i n g e x o t h e r m i c r e a c t i o n o c c u r s : 2 H S + 2

S0

> 3/2 S

2

2

+

2 H 0 2

A f t e r the first stage of C l a u s c o n v e r s i o n , the gas is c o o l e d i n a v e r t i c a l s t e a m i n g condenser

(19)

v e r s i o n of h y d r o g e n i n the second

to condense a d d i t i o n a l sulfur.

Further con-

sulfide a n d s u l f u r d i o x i d e to s u l f u r takes

stage C l a u s reactor

a third steaming unit (21).

(20).

A coalescer

place

T h i s s u l f u r is c o n d e n s e d (22)

containing a mesh

in pad

t h e n removes e n t r a i n e d l i q u i d f r o m the gas stream. M o l t e n s u l f u r f r o m t h e three condensers a n d the coalescer is c o l l e c t e d i n a s u l f u r h o l d i n g p i t (23)

f r o m w h i c h i t is p u m p e d to storage.

R e s i d u a l h y d r o g e n sulfide i n

the gas f r o m the process is o x i d i z e d to s u l f u r d i o x i d e i n the presence

of

excess a i r i n a n i n c i n e r a t o r ( 24 ) b e f o r e b e i n g e x h a u s t e d to t h e a t m o s p h e r e t h r o u g h a stack

(25).

T h i s r e a c t o r - h e a t r e g e n e r a t o r system offers s e v e r a l i m p o r t a n t b e n e fits.

T e m p e r a t u r e profiles i n h e r e n t l y f a v o r a p p r o a c h to c h e m i c a l e q u i -

l i b r i u m a n d m a x i m u m use of t h e gaseous r e d u c i n g agent over a w i d e r a n g e of o p e r a t i n g rates. Y e t , w i t h t h e c o n s i d e r a b l e heat c a p a c i t y of t h e


2.

H U N T E R

E T

A L .

Allied

Chemical

Reduction

27

Process

p a c k e d beds, the system is n o t seriously upset b y flow rate changes a n d m i n o r v a r i a t i o n s i n f e e d gas c o m p o s i t i o n . A t the same t i m e , the r e a c t o r heat regenerator d e s i g n solves the e n g i n e e r i n g m a t e r i a l s p r o b l e m s c a u s e d b y the h i g h l y corrosive n a t u r e of the s t r o n g l y r e d u c i n g sulfurous gases. I n fact, at the e l e v a t e d temperatures i n v o l v e d , the use of m e t a l l i c c o n s t r u c t i o n materials is i m p r a c t i c a l . C o m b i n i n g the regenerator f u n c t i o n of r e a c t i o n heat storage a n d use w i t h the fixed b e d single—stage reactor, t h e n , results i n a r u g g e d a n d efficient d e s i g n ( 7 ) .

T h i s system is p a r -

t i c u l a r l y advantageous for l a r g e process gas v o l u m e s s u c h as those e x p e r i e n c e d i n the F a l c o n b r i d g e f a c i l i t y . Continuing

Technology

Development

I n v i e w of the c o n s i d e r a b l e interest i n s u l f u r d i o x i d e r e d u c t i o n to s u l f u r b o t h i n this c o u n t r y a n d a b r o a d , A l l i e d C h e m i c a l e x t e n d e d t h e use of this t e c h n o l o g y to c o n t r o l s u l f u r d i o x i d e emissions f r o m other m e t a l l u r g i c a l operations as w e l l as f r o m fossil f u e l c o m b u s t i o n . T h e experience g a i n e d i n d e s i g n , c o n s t r u c t i o n , a n d o p e r a t i o n of facility p r o v i d e d the perspective

the large C a n a d i a n

for c o n t i n u i n g process research a n d

parallel engineering development. A t the outset, t w o major goals w e r e e s t a b l i s h e d to a c h i e v e a p p l i c a b i l i t y for s u l f u r d i o x i d e r e d u c t i o n i n emission c o n t r o l .

broad

The

first

g o a l was to d e v e l o p process c a p a b i l i t y e n c o m p a s s i n g the w i d e s t p r a c t i c a l r a n g e of i n l e t s u l f u r d i o x i d e concentrations w h i l e the s e c o n d w a s

to

d e v e l o p process modifications so that v a r i o u s gaseous a n d l i q u i d h y d r o carbons c o u l d be u s e d as r e d u c i n g agents. T h e first g o a l has b e e n a c h i e v e d , a n d the s p e c t r u m of f e e d sources

gas

to w h i c h t h e A l l i e d C h e m i c a l s u l f u r d i o x i d e r e d u c t i o n t e c h -

n o l o g y m a y n o w b e a p p l i e d is the p r i n c i p a l subject of d i s c u s s i o n i n this p a p e r . T h e effort to use r e d u c i n g agents other t h a n n a t u r a l gas i n these systems has also a d v a n c e d t h r o u g h f e a s i b i l i t y studies i n t o t h e m e n t stage, i n v o l v i n g alternatives r a n g i n g f r o m p r o p a n e

and

developbutane

t h r o u g h m i d d l e distillates s u c h as N o . 2 f u e l o i l . A l l i e d C h e m i c a l n o w expects to offer a f a m i l y of processes p e r m i t t i n g s u l f u r d i o x i d e r e d u c t i o n operations to b e t a i l o r e d to t h e specific r e q u i r e m e n t s of i n d i v i d u a l l o c a tions a n d projects. W h i l e the C a n a d i a n p l a n t o p e r a t i o n w a s d o c u m e n t i n g process p e r f o r m a n c e w i t h a 1 2 - 1 3 % s u l f u r d i o x i d e source, w o r k w a s b e i n g d o n e to establish the basis for designs of systems to process m o r e

concentrated

f e e d streams, c o n t a i n i n g u p to 1 0 0 % s u l f u r d i o x i d e ( d r y b a s i s ) .

Lower

s u l f u r d i o x i d e concentrations a n d the i n f l u e n c e of o x y g e n i n f e e d gases were

also b e i n g s t u d i e d so the l o w e r l i m i t b o u n d a r y c o n d i t i o n s

process a p p l i c a b i l i t y c o u l d b e

identified.

for

This was realized through


28

S U L F U R

R E M O V A L

AND

R E C O V E R Y

d e t a i l e d i n v e s t i g a t i o n of the k i n e t i c s of the c o m p l e x r e a c t i o n c h e m i s t r y i n this system. A c o m p r e h e n s i v e m a t h e m a t i c a l m o d e l of the system w a s subsequently

developed

w h i c h incorporated the unsteady

state

heat

transfer f u n c t i o n s i n a d d i t i o n to c h e m i c a l k i n e t i c s a n d t h e r m o d y n a m i c s . B e c a u s e of these efforts i t is n o w p o s s i b l e to evaluate p r e c i s e l y a b r o a d r a n g e of process alternatives a n d m o d i f i c a t i o n s , as w e l l as to c o n d u c t d y n a m i c s i m u l a t i o n s o n m o d e l s of p a r t i c u l a r interest. P r e s e n t e n g i n e e r i n g d e s i g n c a p a b i l i t y a l l o w s efficient process profiles to b e

estab-

l i s h e d over a w i d e s p e c t r u m of f e e d gas c o m p o s i t i o n s w h i l e o p t i m i z i n g m a j o r p a r a m e t e r s , i n c l u d i n g r e d u c i n g agent use, o v e r a l l s u l f u r r e c o v e r y , a n d m a j o r e q u i p m e n t duties. O p e r a t i n g considerations s u c h as t u r n d o w n a n d the influence of p o t e n t i a l system upsets m a y also b e e v a l u a t e d . Feed Gas

Considerations

M o s t s u l f u r d i o x i d e f e e d streams, a n d e s p e c i a l l y m e t a l l u r g i c a l sources, c o n t a i n dust p a r t i c l e s a n d other i m p u r i t i e s s u c h as arsenic a n d s e l e n i u m oxides. I n o r d e r to p r o d u c e h i g h q u a l i t y s u l f u r , t h e gases m u s t b e c l e a n e d as t h o r o u g h l y as i f s u l f u r i c a c i d w e r e to b e p r o d u c e d . T h i s c a n b e r e l i a b l y a c c o m p l i s h e d i n a w e t p u r i f i c a t i o n system s i m i l a r to t h a t u s e d i n t h e F a l c o n b r i d g e p l a n t . N o t o n l y c a n the gases be f r e e d of most c o n t a m i nants, b u t the s c r u b b i n g t r e a t m e n t recovers a n y v a l u a b l e m i n e r a l content w h i c h m a y h a v e b e e n c a r r i e d b y the e n t e r i n g gas. O n c e the f e e d stream has b e e n p u r i f i e d , the s u l f u r d i o x i d e a n d o x y g e n d i m e n s i o n s m u s t b e defined.

D e p e n d i n g u p o n its source, the s u l f u r d i -

o x i d e m a y v a r y f r o m a f e w tenths of 1 % to 1 0 0 %

(dry basis), in com-

b i n a t i o n s w i t h o x y g e n f r o m 0 % u p to the l i n e s h o w n o n F i g u r e 2.

The

d o t t e d l i n e represents the gas c o m p o s i t i o n that results w h e n 1 0 0 % s u l f u r d i o x i d e ( d r y b a s i s ) is d i l u t e d w i t h a i r . T h e o n l y gas c o m p o s i t i o n s

to

w h i c h A l l i e d C h e m i c a l s u l f u r d i o x i d e r e d u c t i o n t e c h n o l o g y is not d i r e c t l y a p p l i c a b l e are those i n t h e s h a d e d area at the l o w e r left of this d i a g r a m . T h i s l o w e r b o u n d a r y represents a p r a c t i c a l l i m i t w h i c h has b e e n establ i s h e d b y heat b a l a n c e a n d t h e r m o d y n a m i c considerations r a t h e r t h a n b y e c o n o m i c factors. I n the A l l i e d process, b o t h o x y g e n a n d s u l f u r d i o x i d e i n the f e e d gas react c h e m i c a l l y w i t h t h e r e d u c i n g agent i n i d e n t i c a l v o l u m e t r i c p r o p o r t i o n s . H o w e v e r , the heat released i n the r e d u c t i o n o f s u l f u r d i o x i d e is o n l y a f r a c t i o n of that l i b e r a t e d b y the r e a c t i o n of the r e d u c t a n t w i t h oxygen.

C o n s e q u e n t l y , the process d e s i g n m u s t not o n l y o b t a i n the o p t i -

m u m r e a c t i o n p r o d u c t c o m p o s i t i o n b u t also m u s t c o n t r o l t h e temperatures t h r o u g h o u t the system.

E v a l u a t i o n of t h e effects of v a r y i n g b o t h the

o x y g e n a n d s u l f u r d i o x i d e contents d u r i n g o p e r a t i o n is therefore i m p o r tant.

E x c e p t f o r cases i n v o l v i n g v e r y w e a k s u l f u r dioxide—oxygen

con-

centrations, the q u a n t i t y of gas b e i n g t r e a t e d is not a m a j o r factor because


2.

H U N T E R

Allied

E T A L .

Chemical

Reduction

29

Process

loo r v 100% S 0 Diluted With Air 2

60 h

%so

Operating Range

2

Direct S O 2 Reduction 40 h

Falconbridge

20 h

' 0 2

4

6

%o Figure 2.

8

10

2

Allied Chemical sulfur dioxide reduction, positions in volume % (dry basis)

gas com-

the d e s i g n a n d o p e r a t i o n c a n b e adjusted to a c h i e v e a w o r k a b l e heat b a l a n c e for duties as s m a l l as 5 - 1 0 t o n s / d a y o f s u l f u r i n the feed. T h e gas c o m p o s i t i o n f r o m the fluidized b e d roasters at F a l c o n b r i d g e w a s a s o m e w h a t s p e c i a l c i r c u m s t a n c e i n that the o x y g e n content

was

q u i t e l o w , a p p r o x i m a t e l y 1 % , a n d 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 a p proached

t h e t h e o r e t i c a l m a x i m u m f o r p y r r h o t i t e o r e roasting. T h e

A l l i e d r e a c t o r - r e g e n e r a t o r system was i d e a l l y s u i t e d t o this gas c o m position. Combination

with Sulfur

Dioxide

Concentration

S i n c e the p r o p o r t i o n o f r e d u c i n g agent i n t r o d u c e d s h o u l d b e r e g u l a t e d p r e c i s e l y to a c h i e v e t h e d e s i r e d p r o d u c t gas c o m p o s i t i o n , t h e s u l f u r d i o x i d e a n d o x y g e n concentrations i n the f e e d gas t o the r e d u c t i o n u n i t s h o u l d b e f a i r l y stable.

A c c o r d i n g l y , the direct application of sulfur

d i o x i d e r e d u c t i o n to gases f r o m the c y c l i c o p e r a t i o n o f the converters u s e d i n c o n v e n t i o n a l c o p p e r s m e l t i n g is not c o n s i d e r e d p r a c t i c a l . I n these cases, s u l f u r d i o x i d e s h o u l d b e r e m o v e d b y a regenerable r e c o v e r y system a n d s u b s e q u e n t l y released i n c o n c e n t r a t e d , l o w o x y g e n f o r m at a c o n t r o l l e d rate. Some s u l f u r d i o x i d e c o n c e n t r a t i n g systems c a n b e d e s i g n e d t o a c c e p t gases w i t h

fluctuating

volumes a n d sulfur loadings.

T h e sulfur dioxide

is either p h y s i c a l l y o r c h e m i c a l l y b o u n d i n a s o l i d o r l i q u i d m e d i u m i n


30

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

these systems a n d is r e t a i n e d i n i n v e n t o r y . T h e m a t e r i a l is t h e n t h e r m a l l y r e g e n e r a t e d or steam s t r i p p e d , a n d the s u l f u r d i o x i d e is d e l i v e r e d to the final p r o c e s s i n g step at a constant rate. O n l y m i n o r modifications of the F a l c o n b r i d g e process are t h e n necessary to r e d u c e s u c h r e g e n e r a t e d gas streams c o n t a i n i n g u p to 1 0 0 % s u l f u r d i o x i d e ( d r y b a s i s ) to elemental sulfur. T h e a d a p t a b i l i t y of this s u l f u r d i o x i d e r e d u c t i o n t e c h n o l o g y

to a

f e e d gas c o n t a i n i n g 1 0 0 % s u l f u r d i o x i d e ( d r y basis) w i l l be d e m o n s t r a t e d at t h e D . H . M i t c h e l l S t a t i o n of the N o r t h e r n I n d i a n a P u b l i c S e r v i c e C o . ( N I P S C O ) at G a r y , I n d i a n a ( 8 ) .

I n this a p p l i c a t i o n the process w i l l be

c o m b i n e d w i t h t h e W e l l m a n — L o r d s u l f u r d i o x i d e recovery provide

a complete

flue

gas

d e s u l f u r i z a t i o n system

for

process a

to

115-MW

coal-fired b o i l e r i n a project j o i n t l y f u n d e d b y N I P S C O a n d the E n v i r o n mental Protection Agency. As

is the case i n c y c l i c c o p p e r

converter operations, s u b s t a n t i a l

changes i n s u l f u r l o a d i n g are e n c o u n t e r e d i n emissions f r o m fossil f u e l fired boilers. V a r i a t i o n s i n gas v o l u m e , a n d hence i n the s u l f u r l o a d i n g , w i l l be accommodated

at N I P S C O b y p r o v i d i n g l a r g e storage c a p a c i t y

for the sodium sulfite-bisulfite scrubbing solution. T h e sulfur dioxide w i l l b e d e s o r b e d f r o m the s o l u t i o n b y h e a t i n g , a n d a steady flow of s u l f u r d i o x i d e gas w i l l be d e l i v e r e d to the r e d u c t i o n u n i t . E n g i n e e r i n g , p r o c u r e m e n t , a n d c o n s t r u c t i o n of the entire f a c i l i t y at N I P S C O is t h e r e s p o n s i b i l i t y of D a v y P o w e r g a s , I n c . A l l i e d C h e m i c a l is p r o v i d i n g the s u l f u r d i o x i d e r e d u c t i o n process

Figure 3.

technology

Typical compositions of gases from metallurgical

as w e l l as

operations


2.

Allied

HUNTER E T A L .

Chemical

Reduction

Process

31

Total Reductant Requirement M SCF CH4/LT. Sulfur 48 r

12

!

GAS

ι 1

L

COMPOSITION IN VOLUME % (DRY BASIS)

0% 02 S O 2 Requirement Only

8 4 0 5

Figure 4.

%

SO

10

15

Gases from roasters and continuous smelting processes

t e c h n i c a l a n d start-up services u n d e r contract w i t h D a v y P o w e r g a s . T h e n , u n d e r a separate agreement w i t h N I P S C O , A l l i e d w i l l operate t h e entire flue gas d e s u l f u r i z a t i o n system a n d w i l l m a r k e t salable b y - p r o d u c t s o n a c o n t i n u i n g basis. Metallurgical

Applications

T h e selection of processes f o r c o n t r o l l i n g s u l f u r d i o x i d e emissions f r o m m e t a l l u r g i c a l sources is l a r g e l y g o v e r n e d b y t h e c o m p o s i t i o n o f t h e gases b e i n g treated.

T y p i c a l gas compositions f r o m non-ferrous m e t a l

l u r g i c a l operations w h i c h h a v e r e l a t i v e l y constant s u l f u r d i o x i d e a n d o x y g e n contents a r e s h o w n i n F i g u r e 3. A l l i e d C h e m i c a l s u l f u r d i o x i d e r e d u c t i o n t e c h n o l o g y c a n b e a p p l i e d d i r e c t l y to m e t a l l u r g i c a l gases across the e n t i r e range of compositions

represented b y t h e w i d e b a n d . T h e

A l l i e d t e c h n o l o g y is n o t d i r e c t l y a p p l i c a b l e to gases f r o m r e v e r b e r a t o r y furnace operations i n w h i c h b o t h t h e s u l f u r d i o x i d e a n d oxygen contents are g e n e r a l l y less t h a n 3 % . B e c a u s e of the l o w 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 a n d large v o l u m e of gases f r o m these sources, a c o n c e n t r a t i n g system w o u l d b e used to recover the s u l f u r d i o x i d e f o r subsequent r e d u c t i o n . A i r d i l u t i o n of t h e gas at t h e source s h o u l d b e r e s t r i c t e d w h e r e v e r possible, as this m i n i m i z e s t h e v o l u m e o f gas to b e h a n d l e d i n the system


32

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

Figure 5.

Composition of gases from sulfur dioxide trating systems (dry basis)

Figure 6.

Gas compositions in emission control systems (dry basis)

concen-


2.

H U N T E R

E T

Allied

A L .

Chemical

Reduction

33

Process

a n d the q u a n t i t y of r e d u c t a n t r e q u i r e d as s h o w n i n F i g u r e 4 . T h e s h a d e d a r e a represents the r a n g e of c o m p o s i t i o n s n o r m a l l y f o u n d i n gases f r o m roasters a n d c o n t i n u o u s s m e l t i n g processes. T h e r e is o b v i o u s l y a cost p e n a l t y i n terms of a d d i t i o n a l r e d u c i n g agent c o n s u m p t i o n associated w i t h the d i r e c t r e d u c t i o n of gases h a v i n g h i g h e r o x y g e n contents.

A l t h o u g h there p r o b a b l y w i l l b e situations i n

w h i c h i t w i l l b e advantageous to a c c e p t a h i g h e r r e d u c i n g agent

con-

s u m p t i o n , the p e n a l t y m u s t be w e i g h e d against t h e t o t a l costs w h i c h w o u l d b e i n c u r r e d i f a s u l f u r d i o x i d e p r e c o n c e n t r a t i o n f a c i l i t y w e r e to be used. T h e c o m p o s i t i o n of gases o b t a i n e d f r o m s e v e r a l types of s u l f u r d i o x i d e r e c o v e r y a n d c o n c e n t r a t i n g systems is s h o w n i n F i g u r e 5. O n e of the features of the A l l i e d C h e m i c a l s u l f u r d i o x i d e r e d u c t i o n system is that i t is c a p a b l e of p r o c e s s i n g t h e gases f r o m these s u l f u r d i o x i d e c o n c e n t r a t i n g systems d i r e c t l y w i t h o n l y the r e d u c t a n t a d d e d .

A s a result,

e q u i p m e n t size is m i n i m i z e d . B y contrast, i n m a n u f a c t u r i n g s u l f u r i c a c i d , the gases f r o m these c o n c e n t r a t i n g systems t y p i c a l l y w o u l d be d i l u t e d w i t h a i r to g i v e a n o x y g e n / s u l f u r d i o x i d e r a t i o of 1.3:1 to o b t a i n satisf a c t o r y c o n v e r s i o n of s u l f u r d i o x i d e to s u l f u r t r i o x i d e .

The resulting

gas v o l u m e s are c o m p a r e d i n T a b l e I. I n the soda s c r u b b i n g case ( t h e system to b e d e m o n s t r a t e d at N I P S C O )

the gas v o l u m e to the s u l f u r

d i o x i d e r e d u c t i o n u n i t is less t h a n one q u a r t e r the v o l u m e to the a c i d plant. Table I.

Relative Process Gas Volumes" Total Gas Volume—M

Sulfur

Dioxide

Recovery

From Recovery Unit

System

0

M a g n e s i u m oxide s c r u b b i n g 12% S 0 , 1% 0 C a r b o n sorption 40%SO ,0%O S o d a s c r u b b i n g or organic solvent 1 0 0 ^% SO S0 2

2

2

2

f 2t

a b c d e

To Reduction Unit d

SCFM

b

To Acid Plant

6

12.1

13.0

21.2

3.6

4.4

12.7

1.5

2.3

10.6

Basis 100 long tons/day sulfur equivalent in process gas. D r v basis at 60°F. and 14.7 psig. S 0 volume 1.46 M S C F M (standard cubic ft/min). Includes reductant as 100% C H . Includes dilution air to give 1.3:1 0 / S 0 ratio. 2

4

2

2

I n s u m m a r y , A l l i e d C h e m i c a l t e c h n o l o g y for r e d u c i n g s u l f u r d i o x i d e to e l e m e n t a l s u l f u r c a n be a p p l i e d d i r e c t l y to a b r o a d range of s u l f u r d i o x i d e concentrations. A s i l l u s t r a t e d i n F i g u r e 6, the p r a c t i c a l range f o r a p p l i c a t i o n of this t e c h n o l o g y extends f r o m a b o u t 4 % u p to 1 0 0 %


(dry

34

S U L F U R

R E M O V A L

A N D R E C O V E R Y

b a s i s ) w i t h o x y g e n contents u p to t h e a f o r e m e n t i o n e d e c o n o m i c b r e a k p o i n t . I n some instances, process considerations m a y j u s t i f y d i r e c t s u l f u r dioxide

reduction with

higher oxygen

attendant higher reductant consumption.

contents

i n the feed

gas a n d

H o w e v e r , w i t h sulfur dioxide

contents of less t h a n a b o u t 4 % , use of a s u l f u r d i o x i d e p r e c o n c e n t r a t i n g system w i t h t h e s u l f u r d i o x i d e r e d u c t i o n process a p p l i e d d i r e c t l y t o t h e p r o d u c t gas is r e c o m m e n d e d . Literature

Cited

1. Wright, J. P., "Reduction of Stack Gas S O to Elemental Sulphur," Sulphur (May/June, 1972) No. 100, 72. 2. Hunter, W . D., Jr., "Application of S O Reduction in Stack Gas Desulfurization Systems," E P A Flue Gas Desulfurization Symposium, New Orleans, May 1973. 3. Hunter, W . D . , Jr., Michener, A. W . , "New Elemental Sulphur Recovery System Establishes Ability to Handle Roaster Gases," E/MJ (June 1973) 174 (6), 117. 4. Hunter, W . D . , Jr., "Reducing S O in Stack Gas to Elemental Sulfur," Power (September, 1973) 117 (9), 63. 5. U.S. Patent 3,653,833 (April 4, 1972). 6. U.S. Patent 3,755,551 (August 28, 1973). 7. Bierbower, R. G . , VanSciver, J. H . , "Design of Allied Chemical S O Reduction System Circumvents Major Corrosion Problems," Chem. Eng. Prog. (Aug. 1974) 70 (8), 60. 8. Mann, E . L . , " S O Abatement System Builds on Success," Elec. World (November 1, 1972) 70. 2

2

2

2

2

R E C E I V E D A p r i l 4, 1974


The Allied Chemical Sulfur Dioxide Reduction Process for

Recommend Documents