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

1 Controlling the Industrial Process Sources of Sulfur Oxides KONRAD SEMRAU

Downloaded by UNIV OF MISSISSIPPI on June 19, 2015 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch001

Stanford Research Institute, Menlo Park, Calif. 94025

Industrial process or "noncombustion" sources of sulfur oxides emission are frequently more significant locally than fossil fuel

combustion

sources.

The

most important

process

sources are: primary copper, lead, and zinc smelters; Claus sulfur plants; sulfuric acid plants; coke plants; iron ore sintering and pelletizing plants; regenerators of fluid catalytic cracking units; and sulfite pulp mills. In the future, Claus sulfur plants will become still more important sources because of growing hydrodesulfurization

of increasingly sour

petroleum stocks and because of future coal desulfurization to produce clean solid, liquid, and gaseous fuels. Control of sulfur oxides emissions from the industrial process sources is closely related to the technologies of the sources themselves, and changes in the process technologies may greatly improve the effectiveness and economy of emission control.

T o u r i n g the past decade, the principal concern with control of sulfur -

L

/

oxides emissions has been focused on flue gases from fuel combus-

tion, primarily the flue gases from power plants. F u e l combustion accounts for about three quarters of the estimated total sulfur oxide emissions in the United States.

However, the emissions from industrial

processes are frequently more significant than is indicated by their contribution (about one fifth) to the total emission. Whereas many of the combustion sources are individually small and widely dispersed, industrial operations are often relatively large and concentrated sources and may cause severe local pollution problems. Copper, zinc, and lead smelters, in particular, have a long and notorious history as pollution sources. It is only in recent years that individual power plants have become large enough that their sulfur oxide emissions

compare with those

smelters. 1 In Sulfur Removal and Recovery; Pfeiffer, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

from

2

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 i n d u s t r i a l processes present b o t h s p e c i a l p r o b l e m s a n d s p e c i a l o p p o r t u n i t i e s t h a t are n o t e n c o u n t e r e d w i t h f u e l c o m b u s t i o n gases.

In

most cases, s u l f u r d i o x i d e concentrations i n t h e waste gases a r e h i g h e r t h a n i n c o m b u s t i o n gases, a n d there are greater o p p o r t u n i t i e s to r e c o v e r t h e s u l f u r d i o x i d e i n u s e f u l forms. T h e processes d e s i g n e d t o treat c o m b u s t i o n gases are n o t a l w a y s w e l l a d a p t e d to t r e a t i n g process F i n a l l y , changes i n t h e i n d u s t r i a l processes

f r e q u e n t l y present

gases. oppor

tunities f o r m o r e e c o n o m i c a l c o n t r o l a n d r e c o v e r y of t h e sulfur d i o x i d e . Emission Sources


T w o sets o f s u l f u r o x i d e e m i s s i o n estimates f o r t h e U n i t e d States, d r a w n f r o m E n v i r o n m e n t a l P r o t e c t i o n A g e n c y sources ( I , 2, 3) are p r e sented i n T a b l e s I a n d I I . T h e source categories i n t h e t w o tables are n o t consistent n o r a r e t h e estimates o f t h e total e m i s s i o n , e v e n a l l o w i n g f o r a 3-yr difference i n the base p e r i o d s . I t is also o b v i o u s t h a t c e r t a i n sources h a v e n o t b e e n a c c o u n t e d f o r i n t h e c o m p i l a t i o n s . N e v e r t h e l e s s , t h e esti mates d o i d e n t i f y most o f the i n d u s t r i a l sources a n d i n d i c a t e t h e i r r e l a t i v e m a g n i t u d e s . T h e d i s t r i b u t i o n s o f sources i n other nations a r e s i m i l a r t o those i n t h e U n i t e d States i n a n u m b e r o f r e p o r t e d instances Table I.

Estimated SO^ Emissions i n the United States (1970) SO χ Emission > tons/yr) a

Source

Category

Transportation F u e l c o m b u s t i o n i n s t a t i o n a r y sources I n d u s t r i a l process losses P u l p and paper C a l c i u m carbide Sulfuric acid plants C l a u s sulfur plants Coking P e t r o l e u m refining F l u i d catalytic cracking Thermal catalytic cracking Nonferrous metals Copper Z i n c a n d lead I r o n ore s i n t e r i n g a n d p e l l e t i z i n g S o l i d wastes d i s p o s a l Agricultural burning Miscellaneous C o a l refuse b u r n i n g Total a k

(4).

6

1.0 26.5 0.077 0.002 0.474 0.875 0.474 0.354 0.005 3.57 0.9 ?

Per cent of Total 2.88 76.42 0.22

—

6

1.37 2.52 1.37 1.02 0.01 10.30 2.72

—

0.1 0.1

0.29 0.29

0.2

0.58

34.68

100.00%

From Réf. 1. except as noted. Ref. 2.

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

1.

SE M R A U

Industrial

Table II.

Estimated SO* Emissions in the United States (1973)


Source

Process Sources

3

SOx Emission" (10* tons/yr)

Category

M o b i l e sources S t a t i o n a r y c o m b u s t i o n sources Steam—electric power I n d u s t r i a l boilers Metals P r i m a r y copper smelters P r i m a r y lead a n d zinc smelters Fuels industries P e t r o l e u m refineries N a t u r a l gas Chemicals Sulfuric acid Coking A c c i d e n t a l fires Total a

Per cent of Total

1.15

2.37

28.15 7.77

58.04 16.02

4.45 0.57

9.18 1.18

4.40 0.54

9.07 1.11

0.83 0.44 0.19

1.71 0.91 0.39

48.50

100.00%

From Ref. 8.

T h e s m e l t i n g of c o p p e r , l e a d , a n d z i n c f r o m sulfide ores is s e c o n d o n l y to f u e l c o m b u s t i o n U n i t e d States.

as a source of s u l f u r o x i d e emissions

H o w e v e r , i t seems c l e a r t h a t t h e greater p a r t of t h e refinery comes f r o m t h e c o m b u s t i o n heaters.

i n the

P e t r o l e u m refineries s t a n d i n t h i r d p l a c e i n T a b l e I I . emissions

o f h i g h - s u l f u r fuels i n boilers o r process

F r o m a process s t a n d p o i n t t h e y s h o u l d b e classified as o r i g i n a t -

i n g f r o m t h e category of stationary c o m b u s t i o n sources; this appears to h a v e b e e n d o n e i n T a b l e I . T h e s t r i c t l y process sources i n refineries consist p r i m a r i l y o f C l a u s s u l f u r p l a n t t a i l gases a n d t h e regenerators o f catalytic cracking units. T h e t a i l gases o f C l a u s s u l f u r plants a r e a p p a r e n t l y t h e s e c o n d largest process

source after

nonferrous

smelters.

T h e C l a u s plants

convert

h y d r o g e n sulfide, w h i c h is m o s t l y d e r i v e d f r o m p e t r o l e u m r e f i n i n g o r t h e treatment o f n a t u r a l gas. M o s t o f t h e largest C l a u s p l a n t s i n t h e U n i t e d States a n d C a n a d a are i n s t a l l e d at n a t u r a l gas-treating plants (2).

I t is

i r o n i c that a l t h o u g h n a t u r a l gas is o u r cleanest fossil f u e l , its p r e p a r a t i o n for u s e is sometimes a major source of s u l f u r o x i d e p o l l u t i o n . I n F r a n c e , the C l a u s plants at t h e L a c q n a t u r a l gas p l a n t w e r e e s t i m a t e d to y i e l d 10%

o f t h e t o t a l s u l f u r o x i d e e m i s s i o n i n t h e n a t i o n f o r 1970 (4) a n d

h a v e b e e n a serious source o f p o l l u t i o n a n d a g r i c u l t u r a l d a m a g e ( 5 ) . T h e emissions

from

C l a u s plants c a n b e e x p e c t e d to present a n

i n c r e a s i n g l y serious p o t e n t i a l p r o b l e m i n t h e f u t u r e as p e t r o l e u m r e f i n eries operate o n i n c r e a s i n g l y sour crudes elsewhere

from the M i d d l e East a n d

a n d as plants a r e b u i l t to d e s u l f u r i z e substitute n a t u r a l gas

( S N G ) a n d l i q u i d fuels f r o m c o a l .


4

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

S u l f u r i c a c i d plants c o n t i n u e to be s u b s t a n t i a l sources of s u l f u r o x i d e emissions.

T h e emissions

estimates p r e s e n t e d

u m a b l y refer o n l y to emissions emissions sludge

f r o m plants p r o d u c i n g

i n Tables I and II pre-

f r o m s u l f u r - b u r n i n g a c i d plants. by-product

acid from

a c i d , a n d other s u c h sources are p r o b a b l y

smelter

The gases,

classified w i t h

the

emissions f r o m the a p p r o p r i a t e industries. R e l a t i v e l y l i t t l e d i r e c t i n f o r m a t i o n has b e e n p u b l i s h e d o n the s u l f u r o x i d e emissions f r o m

fluid

catalytic cracking ( F C C ) unit

regenerators

(6, 7 ) , a l t h o u g h the estimate i n T a b l e I indicates that the t o t a l is s u b stantial.

T h e s u l f u r r e m a i n i n g i n the coke d e p o s i t e d

o n the catalyst is


r e l a t e d to the s u l f u r content of t h e p e t r o l e u m feedstock. T h e s u l f u r o x i d e content of t h e regenerator flue gases f r o m units t r e a t i n g r e l a t i v e l y l o w s u l f u r feedstocks is r e p o r t e d to b e several h u n d r e d p p m .

However,

the

a u t h o r has b e e n i n f o r m e d p r i v a t e l y that units t r e a t i n g h i g h - s u l f u r M i d d l e E a s t e r n feedstocks m a y y i e l d flue gases c o n t a i n i n g 1 %

or m o r e of sulfur

dioxide. I n t h e steel i n d u s t r y the m o s t c o m m o n source of s u l f u r o x i d e e m i s sions is the b u r n i n g of c o k e o v e n gas that has n o t b e e n

desulfurized.

H o w e v e r , emissions f r o m i r o n ore sinter plants are r e c e i v i n g

considerable

a t t e n t i o n i n G e r m a n y a n d J a p a n , i f not y e t i n the U n i t e d States. P e l l e t i z i n g plants are another p o t e n t i a l l y significant source. I n G e r m a n y , sinter plants are e s t i m a t e d to be responsible for a b o u t 6 % oxide emission

of the t o t a l s u l f u r

(8).

T h e p a p e r p u l p i n g i n d u s t r y is r e p o r t e d l y not, i n t o t a l , a v e r y l a r g e e m i t t e r of s u l f u r oxides, a l t h o u g h i n d i v i d u a l plants m a y present problems.

local

K r a f t mills emit more malodorous reduced sulfur compounds,

whereas sulfite m i l l s are m o r e i m p o r t a n t as emitters of s u l f u r

dioxide.

T h e p u l p i n g processes ( p a r t i c u l a r l y sulfite) are most i n t e r e s t i n g because the c h e m i c a l r e c o v e r y cycles use b a s i c c h e m i s t r y that c o u l d

well

be

a p p l i e d to r e c o v e r y of s u l f u r d i o x i d e a n d s u l f u r f r o m the flue a n d process waste gases of other types of sources. F r o m t h e s t a n d p o i n t of s u l f u r r e c o v e r y , emphasized

the

recent experience has r e -

d e s i r a b i l i t y , i n most cases, of

processes t h a t

permit

r e c o v e r y of e l e m e n t a l sulfur. S u l f u r i c a c i d is the u s e f u l b y - p r o d u c t

that

is u s u a l l y most r e a d i l y a n d e c o n o m i c a l l y p r o d u c e d f r o m s u l f u r d i o x i d e , b u t i t cannot b e e c o n o m i c a l l y s h i p p e d for l o n g distances or be e c o n o m i c a l l y a n d safely stored for l o n g periods. long

distances

or

stored

indefinitely

E l e m e n t a l s u l f u r c a n be s h i p p e d with

minimal

environmental

problems. Nonferrous

Smelters

A large p a r t of t h e p e r t i n e n t l i t e r a t u r e to 1970 o n c o n t r o l of s u l f u r oxides f r o m c o p p e r , l e a d , a n d z i n c smelters was r e v i e w e d b y the a u t h o r


1.

SE M R A U

Industrial

5

Process Sources

i n t w o p r e v i o u s papers (9, 10).

T h e o u t p u t of r e l a t e d p u b l i c a t i o n s has

g r e a t l y i n c r e a s e d since. T h e major n e w d e v e l o p m e n t s i n smelter e m i s s i o n c o n t r o l h a v e b e e n r e l a t e d to process changes outside t h e U n i t e d States.

and have

first

appeared

I n the U n i t e d States itself, c o n t r o l

devlop-

ments h a v e consisted m a i n l y of a d o p t i n g or a d a p t i n g systems or t e c h n i q u e s p i o n e e r e d a b r o a d . T h e c a p a b i l i t y for a h i g h degree of c o n t r o l b y l e a d a n d z i n c smelters is a c k n o w l e d g e d

{11,

12),

b u t w i t h respect

to

c o p p e r smelters, c o n t i n u i n g disputes center o n the a v a i l a b i l i t y of c o n t r o l methods for d i l u t e gases f r o m r e v e r b e r a t o r y furnaces a n d t h e a l l e g e d i m p r a c t i c a l i t y of

attaining 9 0 %

c o m p l e t e smelters ( I I , 13, 14).

or greater c o n t r o l of

emissions

from

I n a s m u c h as b o t h objectives h a v e b e e n


a t t a i n e d at c o p p e r smelters a b r o a d a n d are n o w b e i n g a p p r o a c h e d i n some installations i n the U n i t e d States, the disputes m u s t b e

regarded

as m o r e p o l i t i c a l t h a n t e c h n i c a l i n o r i g i n . Control Methods for Smelter Gases.

T h e favored control

method

for smelter gases continues to b e the m a n u f a c t u r e of s u l f u r i c a c i d b y t h e contact process, either d i r e c t l y or after p r e l i m i n a r y c o n c e n t r a t i o n of t h e s u l f u r d i o x i d e i n w e a k gases b y some c y c l i c a b s o r p t i o n process. as there is a use for the a c i d , this is u n q u e s t i o n a b l y the most

As long

economical

m e t h o d a v a i l a b l e . C o n s u m p t i o n of s u l f u r i c a c i d for l e a c h i n g of l o w - g r a d e a n d o x i d e - t y p e c o p p e r ores has i n c r e a s e d greatly. H o w e v e r , i t w i l l u l t i m a t e l y b e necessary to recover p a r t of the s u l f u r d i o x i d e i n s o m e other f o r m , p r e f e r a b l y as e l e m e n t a l sulfur. T h e A l l i e d C h e m i c a l C o r p . r e d u c t i o n process has b e e n a p p l i e d c o m m e r c i a l l y a n d o n a large scale to p y r r h o t i t e roaster gases c o n t a i n i n g a b o u t 1 2 % s u l f u r d i o x i d e (15, 16).

Application

to r i c h e r gases w i l l b e m o r e e c o n o m i c a l , a n d for leaner gases, use of a p r e l i m i n a r y c o n c e n t r a t i o n step is i n d i c a t e d (9,

10).

T h e A l l i e d C h e m i c a l process uses n a t u r a l gas as the r e d u c t a n t , w h i c h is u n d e s i r a b l e i n the face of the d i m i n i s h i n g supplies a n d i n c r e a s i n g costs of n a t u r a l gas.

H o w e v e r , there is no o b v i o u s reason w h y the process

cannot b e o p e r a t e d o n a p r o d u c e r gas g e n e r a t e d f r o m c o a l , as w a s d o n e earlier w i t h other processes ( 1 0 ) .

A n o t h e r process u s i n g o i l or p u l v e r i z e d

c o a l as the r e d u c t a n t has b e e n d e v e l o p e d b y O u t o k u m p u O y for use i n c o n j u n c t i o n w i t h the O u t o k u m p u flash s m e l t i n g process The

use

of

cyclic

absorption

processes for

(17).

concentrating

sulfur

d i o x i d e f r o m smelter gases is s t i l l v e r y l i m i t e d . If a n d w h e n s u l f u r d i o x i d e r e d u c t i o n is p r a c t i c e d , c o n c e n t r a t i o n processes m u s t b e u s e d m o r e extens i v e l y unless m e t a l l u r g i c a l processes are u s e d that d e l i v e r r i c h e r off-gases, p r o b a b l y w i t h s u l f u r d i o x i d e concentrations not l o w e r t h a n 20—25%.

The

A s a r c o D M A a b s o r p t i o n process (9,

use,

10)

is c o m i n g i n t o r e n e w e d

p a r t l y to p r o d u c e l i q u i d s u l f u r d i o x i d e a n d p a r t l y to p r o v i d e e n r i c h e d f e e d to s u l f u r i c a c i d p l a n t s .


6

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

A t the T a c o m a smelter, t h e D M A process is b e i n g u s e d o n c o p p e r c o n v e r t e r gas ( I S ) .

A t the A j o smelter, i t is also to be u s e d to treat

c o p p e r r e v e r b e r a t o r y f u r n a c e gases ( 1 9 ) .

T h e D M A process is n o t r e a l l y

w e l l s u i t e d to treat gases as d i l u t e as those f r o m r e v e r b e r a t o r y furnaces. It is m o r e e c o n o m i c for use o n c o n v e r t e r gases, o r p r e f e r a b l y , s t i l l r i c h e r gases ( 9 ) . A t the R o n n s k a r w o r k s of B o l i d e n A B i n S w e d e n , w h i c h i n c l u d e b o t h a c o p p e r a n d a l e a d smelter, a c y c l i c process u s i n g w a t e r as the absorbent concentrates s u l f u r d i o x i d e b o t h to p r o d u c e l i q u i d s u l f u r d i o x i d e a n d f o r f e e d to a c i d plants (20,21).

T h e process is r e p o r t e d to g i v e a n a b s o r p t i o n


efficiency of a b o u t 9 8 % o n gas c o n t a i n i n g 2 %

s u l f u r d i o x i d e . W a t e r is

n o t n o r m a l l y a f a v o r a b l e solvent for s u c h a n a p p l i c a t i o n b u t c a n b e u s e d i n this case b e c a u s e i t is a v a i l a b l e at a l o w t e m p e r a t u r e , less t h a n 5 ° C f o r most of t h e year.

Recovery

of s u l f u r d i o x i d e f r o m t h e

smelter is to b e i n c r e a s e d f r o m 90 to 9 5 %

by applying

complete

water-cooled

c o l l e c t i n g hoods a n d waste heat boilers to a l l the c o p p e r converters The Cominco

process,

(20).

w h i c h uses a s o l u t i o n of a m m o n i a as the

absorbent, has b e e n t r e a t i n g d i l u t e gases ( a b o u t 1 %

sulfur

dioxide)

f r o m l e a d ore s i n t e r i n g m a c h i n e s o n a l a r g e scale for m o r e t h a n 30 y r (10,

T h e gases m u s t be c l e a n e d a n d c o n d i t i o n e d b e f o r e e n t e r i n g

22).

the absorber.

T h e r e a f t e r , the o r i g i n a l source of t h e gases is i m m a t e r i a l ,

a n d the process c o u l d b e u s e d to treat gases f r o m c o p p e r r e v e r b e r a t o r y furnaces, a l t h o u g h i t has not a c t u a l l y b e e n so u s e d . A b s o r p t i o n processes for s u l f u r d i o x i d e t h a t use a m m o n i a as the absorbent h a v e b e e n w i d e l y s t u d i e d a n d a p p l i e d c o m m e r c i a l l y i n processes s u c h as p u l p a n d p a p e r m a n u f a c t u r e (23,

24).

T h e p r i n c i p a l variations appear i n the recovery

cycles f o l l o w i n g the a b s o r p t i o n step. I n the C o m i n c o process, the spent absorbent is a c i d i f i e d w i t h s u l f u r i c a c i d to release c o n c e n t r a t e d d i o x i d e a n d to f o r m a m m o n i u m sulfate as a b y - p r o d u c t . c o n j u n c t i o n w i t h a s u l f u r i c a c i d p l a n t is g e n e r a l l y necessary.

sulfur

Operation in W h e r e i t is

d e s i r a b l e to conserve a m m o n i a a n d r e d u c e a m m o n i u m sulfate p r o d u c t i o n , the s u l f u r d i o x i d e c a n be s t e a m - s t r i p p e d f r o m the r i c h solvent. process v a r i a t i o n w a s once u s e d for a p e r i o d b y C o m i n c o (10)

r e c e n t l y b e e n i n v e s t i g a t e d b y Electricité de F r a n c e for use o n p l a n t gases ( 2 5 ) .

This

a n d has power

I f i t is d e s i r e d to use a t h r o w a w a y process, t h e a m -

m o n i a a b s o r p t i o n process c a n be o p e r a t e d

as a d o u b l e - a l k a l i system.

T r e a t i n g the spent absorbent w i t h l i m e p r e c i p i t a t e s c a l c i u m sulfate a n d sulfite a n d releases a m m o n i a for r e t u r n to the a b s o r p t i o n system.

This

p r o c e d u r e w a s u s e d i n p a r t i n the G u g g e n h e i m process s t u d i e d i n t h e 1930's (26) 27).

a n d has b e e n r e c e n t l y r e v i v e d i n F r a n c e a n d J a p a n

(26,

T h e same a m m o n i a r e c o v e r y process is also u s e d i n the A r b i t e r

process for l e a c h i n g c o p p e r ores

(28).


1.

S E M R A U

Industrial

7

Process Sources

O t h e r a b s o r p t i o n processes u s i n g s o l u b l e bases, s u c h as s o d i u m , o r adaptations of the contact s u l f u r i c a c i d process (29, a v a i l a b l e for t r e a t i n g d i l u t e smelter gases.

30)

are p o t e n t i a l l y

H o w e v e r , there is no reason

to expect that a n y of t h e m s h o u l d be a p p r e c i a b l y , i f at a l l , less expensive t h a n the a m m o n i a - b a s e processes. T h e O n a h a m a smelter i n J a p a n illustrates the degree of

emission

c o n t r o l a t t a i n a b l e at a c o n v e n t i o n a l c o p p e r smelter, u s i n g c o n v e n t i o n a l control techniques fitted

(31,

32).

T h e converters are e q u i p p e d w i t h t i g h t l y

hoods a n d w a s t e heat b o i l e r s , w h i c h m i n i m i z e s a i r i n f i l t r a t i o n a n d

raises the average 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 1 1 % b e f o r e


it enters a n e w d o u b l e - c o n t a c t s u l f u r i c a c i d p l a n t . T h e average s i o n efficiency is 9 9 . 8 % .

conver-

T h e gases f r o m the r e v e r b e r a t o r y f u r n a c e are

t r e a t e d i n the r e b u i l t single-contact s u l f u r i c a c i d p l a n t o r i g i n a l l y u s e d to treat the converter gases.

T h e 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 r e v e r -

b e r a t o r y f u r n a c e gas has b e e n i n c r e a s e d b y m i n i m i z i n g air i n f i l t r a t i o n a n d b y u s i n g oxygen. T h e f u r n a c e is fitted w i t h o x y g e n - f u e l roof b u r n e r s s i m i l a r to those u s e d i n o p e n - h e a r t h steel furnaces.

T h e sulfur dioxide

c o n c e n t r a t i o n i n t h e gas e n t e r i n g the a c i d p l a n t is 2 . 5 % . to m a k e t h e a c i d p l a n t autogenous f u e l - f i r e d heater.

(10),

T h i s is too l o w

so the gas is p r e h e a t e d i n a

T h e c o n v e r s i o n efficiency is 9 6 . 9 % .

T h e gas c l e a n i n g

a n d c o n d i t i o n i n g system for t h e r e v e r b e r a t o r y f u r n a c e gas uses r e f r i g e r a t i o n for d e h u m i d i f i c a t i o n so that c o n c e n t r a t e d a c i d is p r o d u c e d even f r o m the d i l u t e gas. E v e n m i n o r r e s i d u a l emissions f r o m the O n a h a m a smelter are treated. T h e t a i l gases f r o m the a c i d plants are s c r u b b e d w i t h caustic soda to r e d u c e the final 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 to a b o u t 20 p p m . T h e c o n v e r t e r b u i l d i n g is enclosed to p r e v e n t escape to the atmosphere of u n t r e a t e d gases that leak f r o m the furnaces.

L e a k i n g gases are c o l l e c t e d as

close to the sources as possible a n d are s c r u b b e d i n a l i m e r o c k t o w e r b e f o r e release.

V i r t u a l l y a l l of the s u l f u r d i o x i d e f r o m t h e smelter is

reportedly contained

(32).

A f t e r the system d e s c r i b e d a b o v e was d e v i s e d , the O n a h a m a smelter was e x p a n d e d , a n d a c o m m e r c i a l magnesia-base a b s o r p t i o n system d e v e l o p e d b y the c o m p a n y w a s a p p l i e d to the r e v e r b e r a t o r y f u r n a c e gases (27).

As described

(27),

C h e m i c o - B a s i c process (33)

the process is essentially the same as

T h e m a g n e s i u m sulfite is d e c o m p o s e d i n a r o t a r y k i l n i n t h e presence added carbon.

the

a l t h o u g h e q u i p m e n t details are not r e p o r t e d . of

T h e m a g n e s i a is r e t u r n e d to the a b s o r p t i o n process, a n d

the r i c h k i l n gas stream ( 1 3 - 1 5 %

sulfur dioxide)

is sent to a s u l f u r i c

acid plant. H i g h degrees of s u l f u r oxides e m i s s i o n c o n t r o l are r e p o r t e d at the n e w e r Japanese c o p p e r smelters, w h e t h e r t h e y use c o n v e n t i o n a l or a d v a n c e d s m e l t i n g processes (31).

A l l the p l a n t s u s i n g r e v e r b e r a t o r y or


8 flash

S U L F U R

R E M O V A L

s m e l t i n g furnaces r e p o r t r e c o v e r y of at least 9 0 %

A N D

R E C O V E R Y

of the s u l f u r .

O f three plants u s i n g flash smelters, K o s a k a reports a s u l f u r r e c o v e r y of 9 5 % and T o y o and Saganoseki report 9 6 % . A s i l l u s t r a t e d b y the O n a h a m a smelter, it is essential to m i n i m i z e the v o l u m e of the off-gases f r o m a source. T h e c a p i t a l a n d o p e r a t i n g costs of a c o n t r o l system are d e t e r m i n e d p r i m a r i l y b y t h e v o l u m e of gas that m u s t b e t r e a t e d (9, 10).

T h e g r o w i n g a p p l i c a t i o n of e m i s s i o n controls has l e d

r e c e n t l y to m u c h m o r e active d e v e l o p m e n t of methods a n d e q u i p m e n t f o r c a p t u r e a n d c o o l i n g of waste gases as w e l l as heat r e c o v e r y f r o m t h e m (34,35).


Smelting Processes. (36)

T h e experience of the T r a i l l e a d - z i n c smelter

a n d the O n a h a m a c o p p e r smelter (32)

has d e m o n s t r a t e d t h a t h i g h

degrees of e m i s s i o n c o n t r o l c a n b e a t t a i n e d e v e n at c o n v e n t i o n a l smelters t h a t e m i t w e a k gas streams. N e v e r t h e l e s s , the r e l a t i v e costs of c o n t r o l l i n g s u c h e m i s s i o n sources are necessarily h i g h . Costs c a n b e r a d i c a l l y r e d u c e d o n l y t h r o u g h process changes t h a t r e d u c e off-gas v o l u m e s a n d increase s u l f u r d i o x i d e concentrations ( 9 , 37).

It is p a r t i c u l a r l y d e s i r a b l e to p r o -

d u c e off-gases r i c h e n o u g h to b e f e d d i r e c t l y to a s u l f u r d i o x i d e r e d u c t i o n p l a n t w i t h o u t u s i n g a p r e l i m i n a r y c o n c e n t r a t i o n process. T h e n e e d for process modifications or changes does not arise o n l y o r e v e n p r i m a r i l y f r o m a i r p o l l u t i o n c o n t r o l considerations, e v e n t h o u g h these m a y affect the t i m i n g . T h e p r i m a r y c o p p e r , l e a d , a n d z i n c s m e l t i n g i n d u s t r y i n the U n i t e d States is l a r g e l y obsolete. A n u m b e r of z i n c a n d l e a d smelters w e r e r e c e n t l y closed p r i m a r i l y because the installations were no longer economically competitive

(38)

w i t h the m o r e

modern

smelters o p e r a t i n g a b r o a d . N e w or r e n o v a t e d smelters are r e p l a c i n g the abandoned

ones.

A l t h o u g h means are a v a i l a b l e for c o n t r o l l i n g the b u l k of the e m i s sions f r o m the c o n v e n t i o n a l l e a d a n d z i n c smelters, n e w processes b e i n g d e v e l o p e d offer greater e c o n o m y as w e l l as better emission c o n t r o l ( 9 , 1 0 ) . C o m i n c o L t d . r e c e n t l y a n n o u n c e d the d e v e l o p m e n t of a n e w process to r e p l a c e the c o n v e n t i o n a l l e a d s m e l t i n g process w i t h its s i n t e r i n g p l a n t s a n d blast furnaces

(39).

A great d e a l of n e w c o p p e r s m e l t i n g t e c h n o l o g y r e c e n t years, b u t m o s t l y outside the U n i t e d States (40,

has a p p e a r e d i n 41).

This tech-

n o l o g y is b e i n g a d o p t e d i n the U n i t e d States o n l y v e r y s l o w l y a n d w i t h s e e m i n g r e l u c t a n c e , p o s s i b l y b e c a u s e the cost of s m e l t i n g has b e e n

a

r e l a t i v e l y s m a l l p a r t of t h e t o t a l cost of c o p p e r p r o d u c t i o n — a t least u n t i l r e c e n t l y (42).

T h e l i m i t s of cost r e d u c t i o n elsewhere are n o w b e i n g a p -

p r o a c h e d , h o w e v e r , a n d the expense of s m e l t i n g is b e i n g i n c r e a s e d b y s u l f u r oxides c o n t r o l a n d the s h a r p l y i n c r e a s e d cost of f u e l ( 42, 43 ).

The

r e v e r b e r a t o r y s m e l t i n g f u r n a c e , b e c a u s e of its p o o r heat a n d mass transfer characteristics, has a v e r y h i g h f u e l c o n s u m p t i o n .

T h e l a r g e v o l u m e of


1.

Industrial

S E M R A U

9

Process Sources

c o m b u s t i o n gases g e n e r a t e d n o t o n l y is a source of heat loss, b u t d i l u t e s the s u l f u r d i o x i d e p r o d u c e d a n d increases the gas c l e a n i n g p r o b l e m that exists e v e n w i t h o u t s u l f u r o x i d e c o n t r o l . C u r r e n t l y , t h e shortages of n a t u r a l gas a n d f u e l o i l are l e a d i n g the c o p p e r smelters to c o n s i d e r c o n v e r s i o n to c o a l firing (44).

S u c h c o n v e r s i o n is itself e x p e c t e d to b e a costly a n d

time-consuming operation. T h e O u t o k u m p u flash s m e l t i n g process (35, 45) flash

s m e l t i n g process (46)

a n d the I n c o o x y g e n

were originally developed

to r e d u c e

fuel

r e q u i r e m e n t s , b u t t h e y h a v e i n c i d e n t a l l y l e d to other process efficiencies a n d to m o r e effective a n d e c o n o m i c a l p o l l u t i o n c o n t r o l . T h e I n c o process


is autogenous

a n d p r o d u c e s a gas s t r e a m c o n t a i n i n g a b o u t 8 0 %

sulfur

d i o x i d e . T h e o r i g i n a l f o r m of t h e O u t o k u m p u process is n o t c o m p l e t e l y autogenous,

but

produces

off-gases

containing about

10-14%

sulfur

d i o x i d e , d e p e n d i n g o n the s u l f u r content of the ore concentrate t r e a t e d . M o r e r e c e n t l y , the a i r has b e e n e n r i c h e d w i t h o x y g e n to m a k e the process c o m p l e t e l y autogenous, r e d u c i n g the gas v o l u m e a n d i n c r e a s i n g t h e 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 to 17 or 1 8 % (45).

O u t o k u m p u has also d e v e l o p e d

an associated process for r e d u c i n g t h e 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 w i t h c o a l o r o i l . T h i s process is n o w g o i n g into c o m m e r c i a l a p p l i c a t i o n T h e O u t o k u m p u flash s m e l t i n g process is w i d e l y u s e d t h r o u g h o u t

(17).

the w o r l d , b u t the first u n i t i n the U n i t e d States w i l l b e i n the n e w T y r o n e smelter

(18).

T h e e l e c t r i c s m e l t i n g f u r n a c e has a l r e a d y h a d a l o n g h i s t o r y of use a b r o a d (40, 47)

a n d has n o w r e p l a c e d the r e v e r b e r a t o r y f u r n a c e i n t w o

U . S . c o p p e r smelters, C o p p e r h i l l a n d I n s p i r a t i o n (18).

T h e volume

of

off-gas f r o m a n e l e c t r i c f u r n a c e is d e t e r m i n e d b y the tightness of the f u r n a c e enclosure, a n d i t is p r a c t i c a l to restrict a i r i n l e a k a g e sufficiently to p r o d u c e a gas r i c h e n o u g h for f e e d to a s u l f u r i c a c i d p l a n t (47). the I n s p i r a t i o n smelter, a n average 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 of is a n t i c i p a t e d (48).

At 4-8%

H e a t transfer a n d c o n t r o l are g o o d i n the e l e c t r i c

f u r n a c e , a n d the t h e r m a l efficiency is h i g h (47,

49).

H o w e v e r , electric

s m e l t i n g i n d i r e c t l y partakes of the t h e r m a l inefficiency of t h e t h e r m a l p o w e r p l a n t , i f t h a t is the source of p o w e r .

H e n c e , it m a y n o t be as g e n -

e r a l l y f a v o r a b l e as autogenous flash s m e l t i n g . T h e c o n v e n t i o n a l c o n v e r t i n g process, w i t h its b a t c h o p e r a t i o n , i n h e r ently involves

fluctuations

i n the v o l u m e a n d 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

of the off-gases a n d thus c o m p l i c a t e s s u l f u r r e c o v e r y (42, 50). lem

The prob-

has b e e n p a r t i a l l y a l l e v i a t e d b y u s i n g i m p r o v e d hoods a n d w a s t e

heat boilers a n d b y u s i n g o x y g e n i n c o n v e r t i n g ( 9 ) .

T h e flash smelter

p r o d u c e s a r i c h e r matte, w h i c h reduces the w o r k that m u s t b e d o n e b y the converter

(45).

N e w types of converters are a p p e a r i n g that offer

better facilities for gas c o n t a i n m e n t t h a n does the c o n v e n t i o n a l P i e r c e Smith

converter

(49).

The

I n s p i r a t i o n smelter is b e i n g

fitted


with

10

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

H o b o k e n s i p h o n converters, the first u s e d i n the U n i t e d States

(48).

T h e t o p - b l o w n r o t a r y converter, u s i n g o x y g e n , has b e e n a p p l i e d to n i c k e l s m e l t i n g a n d c o n v e r t i n g (51). f o r autogenous

concentrate

It is a p p l i c a b l e to c o p p e r s m e l t i n g , b o t h s m e l t i n g a n d for m a t t e c o n v e r s i o n

(49).

Tests h a v e i n d i c a t e d t h a t the average s u l f u r d i o x i d e concentrations i n the off-gases c a n b e as h i g h as 2 5 - 5 0 %

(49,

52).

I d e a l l y , a c o n t i n o u s process i n c o r p o r a t i n g b o t h s m e l t i n g a n d c o n v e r t i n g steps c a n y i e l d a single, steady processed for s u l f u r r e c o v e r y .

flow

of off-gas that is r e a d i l y

T h r e e s u c h processes, the W O R C R A , the

M i t s u b i s h i , a n d the N o r a n d a , h a v e b e e n tested o n a s e m i c o m m e r c i a l


scale (44,

53, 54),

a n d a f u l l - s c a l e c o m m e r c i a l p l a n t of the N o r a n d a

process is u n d e r c o n s t r u c t i o n ( 55 ). A l l the processes p r o d u c e gas streams r i c h e n o u g h for f e e d to a s u l f u r i c a c i d p l a n t , a n d the use of o x y g e n c a n p r o d u c e s t i l l r i c h e r gases.

W i d e a p p l i c a t i o n of a n y of these processes

a w a i t s c o m p l e t i o n of c o m m e r c i a l d e v e l o p m e n t . A n o t h e r a p p r o a c h to c o p p e r s m e l t i n g ( o x i d e s m e l t i n g ) , a l r e a d y i n use a b r o a d , is b e i n g i n c o r p o r a t e d i n t o a n e w smelter i n A r i z o n a b y H e c l a M i n i n g C o . (18).

T h e sulfide ore is to b e roasted to sulfate i n a fluid b e d

roaster ( 56 ) a n d the r i c h off-gas f e d to a s u l f u r i c a c i d p l a n t . T h e s u l f u r i c a c i d w i l l b e u s e d to l e a c h t h e c a l c i n e d ore, a n d t h e c o p p e r

will

be

r e c o v e r e d b y e l e c t r o w i n n i n g . A r e l a t e d c o m m e r c i a l process, the B r i x l e g g E l e c t r o - S m e l t i n g Process, e m p l o y s d e a d r o a s t i n g of the c o p p e r ore, f o l l o w e d b y p y r o m e t a l l u r g i c a l r e d u c t i o n of the oxide c a l c i n e w i t h c a r b o n i n an electric furnace

(57).

A m o n g the v a r i o u s h y d r o m e t a l l u r g i c a l processes f o r c o p p e r r e c o v e r y , those i n c o r p o r a t i n g a c o n t r o l l e d o x i d a t i o n of the sulfide ore to e l e m e n t a l s u l f u r are of p a r t i c u l a r interest (9, 58).

T h e y a v o i d the p r o d u c t i o n of

p o s s i b l y u n n e e d e d s u l f u r i c a c i d or t h e costly c o l l e c t i o n a n d subsequent r e d u c t i o n of s u l f u r d i o x i d e . Sulfuric

Acid

Plants

T h e means for r e d u c i n g the s u l f u r d i o x i d e emissions f r o m s u l f u r i c a c i d plants are a l r e a d y r e l a t i v e l y w e l l d e v e l o p e d .

contact

A n y sulfur

d i o x i d e r e c o v e r e d as s u c h c a n b e r e c y c l e d to the a c i d p l a n t for c o n v e r s i o n to a c i d . T h e most p o p u l a r a p p r o a c h , at least i n n e w p l a n t s , appears to b e the d o u b l e - c o n t a c t process (59, 60) b a s i c contact process itself.

w h i c h is s i m p l y a n extension of the

I n s u l f u r - b u r n i n g p l a n t s , this presents

no

serious p r o b l e m s , b u t w h e r e the a c i d p l a n t is o p e r a t i n g o n a r e l a t i v e l y d i l u t e process gas, i t m a y n o t b e p o s s i b l e to operate a u t o g e n o u s l y

(10).

I n t h e latter instance, the d o u b l e - c o n t a c t process c a n s t i l l b e u s e d , b u t a u x i l i a r y h e a t m u s t b e s u p p l i e d (61).

S o m e forms of the d o u b l e - c o n t a c t

process are r e p o r t e d c a p a b l e of o p e r a t i n g a u t o g e n o u s l y w i t h s u l f u r d i -


1.

Industrial

S E M R A U

11

Process Sources

o x i d e concentrations as l o w as 5 %

(62).

Applications now being made

to smelter gases are assisted b y measures to l i m i t infiltration of a i r i n t o gas c o l l e c t i o n systems. The

conversion

efficiencies

of

double-contact

systems

reportedly

r a n g e f r o m 9 9 . 5 % to as h i g h as 9 9 . 9 % , w i t h exit sulfur d i o x i d e c o n c e n trations r a n g i n g f r o m a b o u t 500 p p m to as l o w as 100 p p m (60, These conditions obviously depend

62).

o n the i n i t i a l gas c o n d i t i o n s a n d

system d e s i g n factors. E x i s t i n g single-contact a c i d p l a n t s c a n also b e c o n v e r t e d to d o u b l e contact plants (63).

I n s u c h cases, h o w e v e r , u s i n g a d d - o n

scrubber


systems is a n a l t e r n a t i v e , a n d s e v e r a l s u c h systems h a v e b e e n u s e d c o m m e r c i a l l y . T h e C o m i n c o a m m o n i a a b s o r p t i o n process has b e e n u s e d for m a n y years (22,

64).

L o r d process ( 6 6 )

T h e L u r g i S u l f a c i d process

(65)

and Wellman-

h a v e h a d m o r e recent a n d l i m i t e d use.

The Mitsu-

b i s h i - J E C C O process has also b e e n a p p l i e d to a c i d p l a n t t a i l gases

(27,

b u t t h e g y p s u m b y - p r o d u c t w o u l d b e essentially a waste i n the

67, 68),

U n i t e d States. I n J a p a n , o p e n - c y c l e s c r u b b i n g of w a s t e gases w i t h s o d i u m h y d r o x i d e or c a r b o n a t e solutions has b e e n p o p u l a r f o r t r e a t i n g gas streams ( i n c l u d i n g s u l f u r i c a c i d p l a n t t a i l gases ) that c o n t a i n r e l a t i v e l y s m a l l t o t a l q u a n t i ties of s u l f u r d i o x i d e (27).

A b s o r b e n t r e g e n e r a t i o n has b e e n u n n e c e s s a r y

because the s o d i u m sulfite or sulfate c o u l d b e s o l d to k r a f t p u l p m i l l s . T h e U n i o n C a r b i d e P u r a s i v S is a fixed-bed a d s o r p t i o n process u s i n g a m o l e c u l a r sieve adsorbent.

It removes s u l f u r d i o x i d e f r o m the c l e a n ,

d r y t a i l gases of contact s u l f u r i c a c i d p l a n t s . T w o or m o r e adsorbers are o p e r a t e d i n sequence;

the l o a d e d b e d is r e g e n e r a t e d b y a s t r e a m of

h e a t e d a i r that desorbs the s u l f u r d i o x i d e a n d t h e n is f e d to t h e i n l e t of the s u l f u r i c a c i d p l a n t . T h e first c o m m e r c i a l p l a n t of this t y p e is n o w o p e r a t i n g o n t h e t a i l gases of a single-contact a c i d p l a n t t h a t processes a m i x t u r e of spent a l k y l a t i o n a c i d a n d h y d r o g e n sulfide f r o m a r e f i n e r y (69,

70).

I t is r e p o r t e d to r e d u c e the exit sulfur d i o x i d e c o n c e n t r a t i o n

f r o m a b o u t 4000 p p m ( a v e r a g e ) to 1 5 - 2 5 p p m

Claus Sulfur

(69).

Plants

T h e h y d r o g e n sulfide present i n n a t u r a l gas, S N G , t o w n gas, a n d synthesis gas m u s t b e r e m o v e d for the sake of p r o d u c t gas

quality.

H e n c e , t e c h n o l o g y for r e m o v i n g h y d r o g e n sulfide f r o m gases has b e e n e x t e n s i v e l y d e v e l o p e d a n d is itself t h e subject of a v o l u m i n o u s literature (71, 72).

F r o m t h e s t a n d p o i n t of e c o n o m i c r e c o v e r y of sulfur, the c h e m -

istry of h y d r o g e n sulfide is s u b s t a n t i a l l y m o r e t r a c t a b l e t h a n that of sulfur dioxide.

F o r t h e most p a r t , these processes are n o t w i t h i n the

chosen scope of the present p a p e r .


12

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

O n c e r e c o v e r e d f r o m gas streams, h y d r o g e n sulfide m u s t g e n e r a l l y b e c o n v e r t e d e i t h e r to s u l f u r i c a c i d or, m o r e c o m m o n l y , to e l e m e n t a l sulfur.

T h e C l a u s process is the s t a n d a r d one for c o n v e r t i n g h y d r o g e n

sulfide to e l e m e n t a l s u l f u r .

A few

a b s o r p t i o n processes, s u c h as the

S t r e t f o r d (71, 72, 7 3 ) , t h a t also o x i d i z e t h e a b s o r b e d h y d r o g e n sulfide to e l e m e n t a l s u l f u r are u s e d p r i m a r i l y to treat gas streams c o n t a i n i n g o n l y r e l a t i v e l y l o w concentrations of h y d r o g e n sulfide. T h e c o n v e r s i o n of h y d r o g e n sulfide to e l e m e n t a l s u l f u r i n the C l a u s process is l i m i t e d b y a c o m b i n a t i o n of e q u i l i b r i u m a n d k i n e t i c factors. O v e r the past d e c a d e , t h e pressures of a i r p o l l u t i o n c o n t r o l r e q u i r e m e n t s


h a v e r e s u l t e d i n m a j o r i m p r o v e m e n t s i n the d e s i g n a n d o p e r a t i o n of C l a u s p l a n t s , w i t h consequent increases i n c o n v e r s i o n a n d r e d u c t i o n of s u l f u r oxides emissions ( 74-79 ). N e v e r t h e l e s s , emissions s t i l l c o m m o n l y e x c e e d the p e r m i s s i b l e l i m i t s c o m i n g into force b o t h i n the U n i t e d States a n d a b r o a d . S u l f u r d i o x i d e r e d u c t i o n plants present s i m i l a r p r o b l e m s . A p a r t f r o m the i n i t i a l f u r n a c e or reactor, t h e y are essentially C l a u s p l a n t s . T h e effluent streams f r o m C l a u s p l a n t s c o n t a i n u n r e a c t e d h y d r o g e n sulfide a n d s u l f u r d i o x i d e a n d e l e m e n t a l s u l f u r present as v a p o r a n d m i s t (77).

They commonly

also c o n t a i n c a r b o n y l sulfide a n d

carbon

d i s u l f i d e f o r m e d b y reactions w i t h h y d r o c a r b o n s present i n t h e f e e d gas (77).

I t is u s u a l l y r e q u i r e d that t h e t a i l gas b e i n c i n e r a t e d , e v e n t h o u g h

not otherwise t r e a t e d , to c o n v e r t t h e h y d r o g e n sulfide, c a r b o n y l sulfide, a n d c a r b o n d i s u l f i d e to the less toxic a n d m a l o d o r o u s s u l f u r d i o x i d e . S i n c e t h e c o n v e r s i o n l i m i t e v e n i n i m p r o v e d C l a u s p l a n t s is not r e a d i l y r a i s e d a b o v e a b o u t 9 7 % , the emphasis i n emission c o n t r o l has n o w passed to u s i n g t a i l gas-treating p l a n t s to attain o v e r a l l c o n v e r s i o n efficiencies of 9 9 % or m o r e .

T h e e c o n o m i c s of c o n t r o l at C l a u s p l a n t s

a r e p r o b a b l y m o r e f a v o r a b l e t h a n i n a n y other case r e q u i r i n g c o n t r o l of d i l u t e gas streams (i.e., those c o n t a i n i n g less t h a n about 2 - 3 %

sulfur

d i o x i d e ). T h e r e are three p r i n c i p a l approaches to t a i l gas t r e a t m e n t : 1. C o n t i n u a t i o n of the C l a u s r e a c t i o n at l o w e r e d temperatures, o n a s o l i d catalyst or i n a l i q u i d m e d i u m . 2. C a t a l y t i c hydrogénation of the s u l f u r d i o x i d e , c a r b o n y l sulfide, a n d c a r b o n d i s u l f i d e i n t h e t a i l gas to r e f o r m h y d r o g e n sulfide, w h i c h is subsequently recovered b y absorption. 3. I n c i n e r a t i o n of the t a i l gas a n d c o n v e r s i o n of a l l s u l f u r c o m p o u n d s to s u l f u r d i o x i d e , f o l l o w e d b y one of the s u l f u r d i o x i d e c o n t r o l systems. T h e first class of systems is i l l u s t r a t e d b y the S u l f r e e n (80, 81, a n d I F P (83, 84)

processes.

82)

I n the S u l f r e e n process the C l a u s r e a c t i o n

takes p l a c e o n t h e c a r b o n or a l u m i n a catalyst i n a

fixed-bed

reactor. A t

the r e d u c e d t e m p e r a t u r e , the c o n v e r s i o n e q u i l i b r i u m is i m p r o v e d , b u t the s u l f u r is r e t a i n e d o n t h e catalyst as a l i q u i d a n d m u s t b e r e m o v e d b y


1.

Industrial

S E M R A U

13

Process Sources

h o t inert gas i n a r e g e n e r a t i o n

cycle.

I n the I F P process the C l a u s

r e a c t i o n takes p l a c e i n a h i g h - b o i l i n g solvent glycol)

(typically a polyalkylene

c o n t a i n i n g a catalyst. C a r b o n y l sulfide a n d c a r b o n d i s u l f i d e are

not affected.

T h e p r o d u c t s u l f u r is d r a w n off as a l i q u i d . T h e

of the S u l f r e e n a n d I F P processes are about 7 5 - 9 0 % ,

efficiencies

so that n e i t h e r

process is e c o n o m i c a l l y s u i t a b l e for a t t a i n i n g the v e r y l o w exit c o n c e n trations r e a c h e d w i t h some of the other processes. T h e s e c o n d class of systems is i l l u s t r a t e d b y the B e a v o n ( 73, 85 ) a n d S h e l l S C O T (86)

processes. I n each process a c o b a l t m o l y b d a t e catalyst

p r o m o t e s hydrogénation of the s u l f u r d i o x i d e a n d e l e m e n t a l s u l f u r to


h y d r o g e n sulfide. It also catalyzes the h y d r o l y s i s of the c a r b o n y l sulfide a n d c a r b o n disulfide to h y d r o g e n sulfide. T h e gas stream is t h e n c o o l e d , the w a t e r v a p o r is c o n d e n s e d out, a n d t h e h y d r o g e n sulfide is r e c o v e r e d . I n the B e a v o n process, the h y d r o g e n sulfide is a b s o r b e d a n d o x i d i z e d to e l e m e n t a l s u l f u r b y the S t r e t f o r d process.

I n the S C O T process, the

h y d r o g e n sulfide is c o n c e n t r a t e d b y a b s o r p t i o n i n a n a l k a n o l a m i n e s o l u t i o n , a n d t h e c o n c e n t r a t e d h y d r o g e n sulfide s t r i p p e d f r o m the is r e c y c l e d to the C l a u s u n i t .

absorbent

B o t h the B e a v o n a n d S C O T processes

consist of c o m b i n a t i o n s of p r e v i o u s l y u s e d a n d essentially c o n v e n t i o n a l technologies.

The

concentrations

S t r e t f o r d system r e p o r t e d l y

of h y d r o g e n

gives m u c h l o w e r

sulfide t h a n does a l k a n o l a m i n e

exit

scrubbing,

b u t is c h e m i c a l l y a n d m e c h a n i c a l l y m u c h m o r e c o m p l e x . T h e t h i r d class of c o n t r o l systems m a y use a n y of t h e s u l f u r d i o x i d e c o n t r o l systems; a m o n g those u s e d c o m m e r c i a l l y are the H a l d o r T o p s o e (5, 8 0 ) , W e l l m a n - L o r d (27, 67),

a n d C h i y o d a (27, 67, 87)

systems.

The

circumstances are g e n e r a l l y h i g h l y f a v o r a b l e for r e c o v e r y processes that p r o d u c e a stream of c o n c e n t r a t e d sulfur d i o x i d e , since this c a n be r e c y c l e d to the C l a u s p l a n t . T h e a p p l i c a t i o n of processes that p r o d u c e s u l furic

acid

or

s o l i d wastes

will

be

dictated

only

by

peculiar

local

circumstances. O n e subclass

of

sulfur dioxide

recovery

processes incorporates

l i q u i d - p h a s e v a r i a t i o n of the C l a u s r e a c t i o n for r e g e n e r a t i n g

the

a ab-

sorbent a n d d i r e c t l y p r o d u c i n g e l e m e n t a l s u l f u r . Processes of this t y p e are the Stauffer A q u a c l a u s process (88),

w h i c h w a s d e v e l o p e d specifically

for C l a u s p l a n t t a i l gases, a n d the B u r e a u of M i n e s C i t r a t e process

(89).

I n e a c h , the absorbent is t h e s o d i u m salt of a stable, n o n v o l a t i l e w e a k a c i d , w h i c h forms a basic s o l u t i o n b y h y d r o l y s i s . T h e a n i o n of the a c i d buffers the s o l u t i o n as a c i d is f o r m e d b y the a b s o r p t i o n of s u l f u r d i o x i d e . T h e spent absorbent, w h i c h consists of a s o l u t i o n of s o d i u m sulfite a n d bisulfite a n d of the w e a k a c i d , is c o n t a c t e d d i r e c t l y w t i h h y d r o g e n sulfide. T h e h y d r o g e n sulfide reacts w i t h the sulfite a n d b i s u l f i t e to y i e l d elem e n t a l s u l f u r , a n d the regenerated basic salt s o l u t i o n is r e c i r c u l a t e d t o the a b s o r p t i o n step.


14

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

I n the B u r e a u of M i n e s process the absorbent is s o d i u m c i t r a t e ; that u s e d i n the A q u a c l a u s process has b e e n i d e n t i f i e d as s o d i u m (90).

phosphate

A s is c o m m o n i n s i m i l a r processes, some of the s u l f u r d i o x i d e is

o x i d i z e d to sulfate, w h i c h is n o t r e a d i l y regenerated, a n d t h i o s u l f a t e a n d p o l y t h i o n a t e s are also f o r m e d (88, 89).

C o n s e q u e n t l y , i t is necessary to

d r a w off p u r g e streams of the absorbents, recover t h e citrate a n d p h o s p h a t e for reuse, a n d d i s c a r d t h e sulfate a n d thionates. Losses of citrate a n d p h o s p h a t e i n this o p e r a t i o n c a n g r e a t l y affect the e c o n o m i c s of the processes. I F P has d e v e l o p e d

a n a m m o n i a a b s o r p t i o n process

t h a t is

(91)


p a r a l l e l to the C i t r a t e a n d A q u a c l a u s processes i n s o m e respects.

The

s u l f u r d i o x i d e is a b s o r b e d i n a m m o n i a s o l u t i o n i n a g e n e r a l l y c o n v e n t i o n a l m a n n e r . T h e spent absorbent c o n t a i n i n g a m m o n i u m sulfite a n d bisulfite is d e c o m p o s e d b y h e a t i n g i n a n evaporator, a n d the r e s u l t i n g a m m o n i a , s u l f u r d i o x i d e , a n d w a t e r v a p o r are sent to a n I F P l i q u i d - p h a s e C l a u s reactor (83)

i n t o w h i c h h y d r o g e n sulfide is also injected. T h e h y d r o g e n

sulfide a n d s u l f u r d i o x i d e react to f o r m e l e m e n t a l s u l f u r , a n d the a m m o n i a , w h i c h is not affected, passes t h r o u g h the reactor a n d is r e c y c l e d to the absorber.

T h e n o n v o l a t i l e sulfate a n d thionates f r o m t h e sulfite

e v a p o r a t o r pass to a sulfate r e d u c t i o n reactor w h e r e t h e y are r e d u c e d to s u l f u r d i o x i d e w i t h h y d r o g e n sulfide (27,

91).

T h e sulfur dioxide from

this o p e r a t i o n also is sent to the I F P reactor. I t has b e e n suggested (80, 88)

t h a t the A q u a c l a u s or C i t r a t e process

m i g h t be s u b s t i t u t e d for the c o n v e n t i o n a l C l a u s p l a n t to c o n v e r t a l l t h e h y d r o g e n sulfide to e l e m e n t a l sulfur. O n e m a j o r factor d e t e r m i n i n g the p r a c t i c a l i t y of this a p p r o a c h is t h e p r o b l e m of s e p a r a t i n g the sulfate a n d thionates f r o m t h e p h o s p h a t e o r citrate. A secondary process system to r e c o v e r s o d i u m a n d s u l f u r f r o m the p u r g e d absorbent w i l l b e a v i r t u a l necessity at a n y l a r g e i n s t a l l a t i o n . T h e c a p i t a l cost of a C l a u s s u l f u r p l a n t s t r o n g l y depends t o t a l gas flow (77),

d e t e r m i n e d p r i m a r i l y b y the gas flow

o n the

a n d the costs for a t a i l g a s - t r e a t i n g system w i l l b e flow.

C o n s e q u e n t l y , r e d u c i n g the gas

c a n s i g n i f i c a n t l y r e d u c e b o t h c a p i t a l a n d o p e r a t i n g costs.

A major,

i f not the largest, p a r t of the gas i n the C l a u s system is n i t r o g e n w h i c h is i n t r o d u c e d i n the a i r u s e d to c o m b u s t the h y d r o g e n sulfide, a n d i n t o the t a i l gas w h e n t h e latter is i n c i n e r a t e d (72,

77).

T h e gas v o l u m e c o u l d

b e g r e a t l y r e d u c e d b y u s i n g o x y g e n i n s t e a d of a i r to s u p p o r t the c o m b u s t i o n (72,

77).

T h e cost savings f r o m t h e use of o x y g e n w o u l d p r o b -

a b l y not b e sufficient to j u s t i f y c o n s t r u c t i n g a n o x y g e n p l a n t solely t o s u p p l y the C l a u s p l a n t , b u t i f a n o x y g e n p l a n t w e r e r e q u i r e d f o r other purposes

a n y w a y , p r o v i d i n g i n c r e m e n t a l c a p a c i t y to s u p p l y t h e C l a u s


1.

SE M R A U

Industrial

15

Process Sources

p l a n t as w e l l m i g h t h a v e m e r i t . I n p e t r o l e u m refineries p r o d u c i n g i n t e r m e d i a t e - B t u f u e l gas f r o m o i l or i n S N G p l a n t s , s u c h o x y g e n p l a n t s w i l l g e n e r a l l y be r e q u i r e d .

Petroleum

Refineries

P e t r o l e u m refineries, a l o n g w i t h n a t u r a l gas p r o c e s s i n g p l a n t s , are p r o b a b l y the best situated s u l f u r oxides sources w i t h respect to e m i s s i o n c o n t r o l . T h e a v a i l a b i l i t y of h y d r o g e n sulfide a l l o w s r e a d y processing

of

r e c o v e r e d 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 for d i s p o s a l . Downloaded by UNIV OF MISSISSIPPI on June 19, 2015 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch001

I n U . S . refineries at least, the largest source of s u l f u r o x i d e emissions is u n d o u b t e d l y the b u r n i n g of h i g h - s u l f u r fuels, i n c l u d i n g sour refinery gases, r e s i d u a l o i l , h e a v y refinery residues, a n d p e t r o l e u m coke. D u r i n g refinery upsets, the flaring of large amounts of u n t r e a t e d refinery gas m a y also result i n h i g h s h o r t - t e r m s u l f u r oxide e m i s s i o n rates. T h e pressure of air p o l l u t i o n c o n t r o l regulations is r e s u l t i n g i n g e n e r a l treatment of r e finery

gases.

H y d r o g e n sulfide is b e i n g r e m o v e d

b y w e l l established

t e c h n o l o g y a n d 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 C l a u s p l a n t s .

Desulfur-

i z e d r e s i d u a l o i l m i g h t be u s e d , w h e r e a v a i l a b l e , to r e p l a c e t h e l i q u i d fuels, b u t it has b e e n c o m m o n p r a c t i c e for refineries to c o n s u m e t h e i r lowest g r a d e residues i n t h e i r o w n operations. F l u e gas s c r u b b i n g systems m i g h t be u s e d to c o n t r o l the s u l f u r d i o x i d e e m i t t e d f r o m b u r n i n g of s u c h fuels. T h i s is b e i n g d o n e to a l i m i t e d extent i n J a p a n (27).

However, an

a l t e r n a t i v e a p p r o a c h is to gasify the residues to p r o d u c e a l o w - B t u f u e l gas, u s i n g a process s u c h as the S h e l l G a s i f i c a t i o n Process, ( S G P )

(92).

T h i s w o u l d p e r m i t r e c o v e r y of the s u l f u r as h y d r o g e n sulfide, u s i n g the same processes e m p l o y e d to treat the refinery gases. T h e S h e l l G a s i f i c a t i o n Process has b e e n a p p l i e d o n a f a i r l y large c o m m e r c i a l scale T h e s u l f u r oxide emissions f r o m the regenerators of

fluid

(93). catalytic

c r a c k i n g units m a y b e c o n t r o l l e d either b y h y d r o t r e a t i n g the f e e d to the c a t a l y t i c c r a c k e r or b y s c r u b b i n g the flue gas f r o m t h e regenerator

(7).

H y d r o t r e a t i n g the feedstock presents several process advantages i n a d d i t i o n to emission r e d u c t i o n a n d is a l r e a d y i n use (7, 94, 95). t h e regenerator flue gas has b e e n p r o p o s e d (7, 96), tions a p p e a r to be i n service.

I t is r e p o r t e d

(97)

Scrubbing

b u t no s u c h i n s u l a that t h e first k n o w n

w e t s c r u b b e r i n s t a l l a t i o n for regenerator flue gas w i l l go i n t o service at the E x x o n refinery at B a y t o w n , T e x .

T h e scrubber w i l l remove sulfur

d i o x i d e as w e l l as collect catalyst fines, r e p l a c i n g the c o n v e n t i o n a l electrostatic p r e c i p i t a t o r for the latter d u t y .

It appears that the m a i n d u t y

of t h e s c r u b b e r w i l l be p a r t i c u l a t e c o l l e c t i o n .


16

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

Steel Mills T h e c o k e o v e n gas p r o d u c e d a n d u s e d i n i n t e g r a t e d steel m i l l s has very

commonly

not b e e n d e s u l f u r i z e d

except w h e r e

the

combustion

gases c a m e i n contact w i t h m o l t e n m e t a l . C o n s e q u e n t l y , the c o m b u s t i o n of coke o v e n gas has b e e n one of the p r i n c i p a l sources of sulfur d i o x i d e emissions f r o m steel m i l l s , e v e n t h o u g h a d e q u a t e t e c h n o l o g y for c o n t r o l has l o n g b e e n a v a i l a b l e . O c c a s i o n a l l y , the h y d r o g e n sulfide i n the gas has b e e n c o n c e n t r a t e d b y a n a b s o r p t i o n process a n d c o n v e r t e d to s u l f u r i c a c i d i n a contact p l a n t or to e l e m e n t a l s u l f u r i n a C l a u s p l a n t .

The

i n c r e a s i n g l y stringent a i r p o l l u t i o n c o n t r o l regulations are f o r c i n g i n s t a l Downloaded by UNIV OF MISSISSIPPI on June 19, 2015 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch001

l a t i o n of m o r e s u c h systems b o t h i n the U n i t e d States a n d a b r o a d (27, B e c a u s e c o k e o v e n gas does n o t c o n t a i n e x t r e m e l y h i g h

hydrogen

sulfide concentrations of h y d r o g e n sulfide, i t c a n b e effectively b y processes s u c h as the S t r e t f o r d (73,

85)

or T a k a h a x (27,

98).

72),

treated which

b o t h a b s o r b the h y d r o g e n sulfide a n d o x i d i z e it to e l e m e n t a l sulfur. A b o u t h a l f the s u l f u r oxides emission f r o m steel p l a n t s originates i n s i n t e r i n g p l a n t s (99),

w i t h m u c h h i g h e r p r o p o r t i o n s at some m i l l s

(100).

T h e q u a n t i t y , of course, d e p e n d s o n t h e s u l f u r content of the ore b e i n g s i n t e r e d , a n d t h e s i t u a t i o n w i l l be s i m i l a r at p e l l e t p l a n t s , w h i c h are g e n e r a l l y l o c a t e d at the mines r a t h e r t h a n at the steel m i l l s . I n the U n i t e d States, c o n c e r n w i t h sinter p l a n t p o l l u t i o n has b e e n f o c u s e d l a r g e l y o n p a r t i c u l a t e matter, b u t i n G e r m a n y a n d J a p a n the s u l f u r oxides emission is of serious concern.

I t is l i k e l y t h a t at some sinter plants,

fluoride

emissions are a c t u a l l y a m o r e serious p o l l u t i o n p r o b l e m t h a n s u l f u r oxide emission. F l u o r i d e emissions f r o m sinter plants are r e c e i v i n g i n c r e a s i n g l y serious attention i n G e r m a n y a n d the N e t h e r l a n d s . I n J a p a n , s c r u b b i n g systems are b e i n g a p p l i e d to sinter p l a n t s to c o n t r o l s u l f u r d i o x i d e a n d s h o u l d also be v e r y effective hydrogen

fluoride.

K a w a s a k i Steel C o r p . has tested

l i m e s c r u b b i n g process o n a d e m o n s t r a t i o n i n s t a l l a full-scale system, h a n d l i n g 750,000 m

scale 3

in removing

Mitsubishi-JECCO (27)

and will

now

gas/hr, on a new sintering

p l a n t that m a y b e t h e largest i n the w o r l d ( 100). N i p p o n K o k a n has d e v e l o p e d

a n d tested a n a m m o n i a - b a s e

a l k a l i s c r u b b i n g process for sinter plants (27).

double-

B o t h i n this system a n d

the M i t s u b i s h i process, l i m e w i l l p r e c i p i t a t e the s u l f u r oxides as w e l l as t h e fluoride that is p r o b a b l y present. T h e concentrations of s u l f u r d i o x i d e i n sinter p l a n t gases are v a r i o u s l y r e p o r t e d to range f r o m a b o u t 0.02 to 1.5 v o l %

(8,68,101).

There

appears to be n o w a y to increase the s u l f u r d i o x i d e concentrations levels s u i t a b l e for e c o n o m i c recovery, a n d t h e presence of

fluorides

b e a h i n d r a n c e i n a n y case. H o w e v e r , it m a y b e feasible to r e d u c e


to

would the

1.

SE M R A U

Industrial

17

Process Sources

waste gas v o l u m e b y a p p l y i n g t h e t e c h n i q u e s of u p d r a f t s i n t e r i n g a n d gas r e c i r c u l a t i o n that h a v e b e e n u s e d i n the nonferrous s m e l t i n g i n d u s t r y .

Pulp

Mills I n t h e p u l p i n g i n d u s t r y , s u l f u r oxides emissions represent loss of

p u l p i n g c h e m i c a l , b u t t h e e c o n o m i c loss is a p p a r e n t l y n o t r e g a r d e d as v e r y serious, at least i n this p e r i o d of r e l a t i v e l y a b u n d a n t a n d c h e a p sulfur. I n c u r r e n t p r a c t i c e , m u c h s u l f u r is e v i d e n t l y lost to b e c o m e either a w a t e r o r a i r p o l l u t a n t (16, 53, 102),

but pollution control regulations


are f o r c i n g i n c r e a s e d r e c o v e r y a n d r e c y c l i n g of s u l f u r a n d other p u l p i n g c h e m i c a l s . T h e n e e d to increase heat r e c o v e r y a n d use s h o u l d also i n f l u ence e m i s s i o n controls. I n t h e k r a f t process, the most serious a i r p o l l u t a n t s are h y d r o g e n sulfide a n d other r e d u c e d s u l f u r c o m p o u n d s (103).

E v e n though their

mass emissions m a y n o t b e h i g h , t h e i r extreme malodorousness constitutes the major p r o b l e m . T h e emissions of s u l f u r d i o x i d e f r o m k r a f t r e c o v e r y furnaces m a y range f r o m s m a l l to s u b s t a n t i a l , d e p e n d i n g o n t h e c o m p o sition of t h e b l a c k l i q u o r a n d o n t h e o p e r a t i n g c o n d i t i o n s i n the f u r n a c e (104-109).

S e v e r a l recent studies h a v e t r e a t e d factors i n f l u e n c i n g t h e

s u l f u r d i o x i d e e m i s s i o n (104, 106, 107, 108). T h e s u l f u r d i o x i d e i n k r a f t r e c o v e r y f u r n a c e gases c a n b e r e a d i l y s c r u b b e d w i t h s o d i u m c a r b o n a t e to p r o d u c e s o d i u m sulfite or sulfate as m a k e u p f o r c o o k i n g l i q u o r p r e p a r a t i o n . T h e absorbent l i q u o r c a n b e u s e d i n the s c r u b b e r units that collect p a r t of t h e s o d i u m

carbonate

a n d sulfate p a r t i c u l a t e s t h a t escape c o l l e c t i o n b y t h e electrostatic p r e c i p i t a t o r . P a r t i c u l a r l y i n S w e d e n , s u c h afterscrubbers are sometimes u s e d also to r e c o v e r l o w l e v e l heat (110), cover s u l f u r d i o x i d e as w e l l (111). sulfur dioxide from kraft recovery common i n Japan

a n d t h e y c o u l d b e e x t e n d e d to r e T h e use of afterscrubbers to c o l l e c t f u r n a c e gases a p p e a r to be f a i r l y

(27).

S u l f u r d i o x i d e e m i s s i o n is a m u c h m o r e serious p r o b l e m i n sulfite m i l l s . T h e s u l f u r d i o x i d e m a y b e e m i t t e d i n t h e t a i l gases f r o m a b s o r p t i o n towers u s e d to p r e p a r e c o o k i n g l i q u o r , i n b l o w p i t gases, i n digester r e l i e f gases, a n d i n v e n t i n g n o n c o n d e n s i b l e s l i q u o r evaporators

(102, 103, 112).

f r o m m u l t i p l e - e f f e c t spent

T a i l gas s c r u b b e r s a r e sometimes

a p p l i e d to r e d u c e t h e emissions f r o m a b s o r p t i o n towers

(113).

Vent

gases m a y also b e sent to the absorbers to r e c o v e r the s u l f u r d i o x i d e c o n t a i n e d (102, 103, 112).

B l o w p i t gases c a n b e s c r u b b e d w i t h w a t e r

to r e c o v e r b o t h s u l f u r d i o x i d e a n d heat (6, 114).

A l t h o u g h this p r o -

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


18

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 r e q u i r e m e n t s for w a t e r p o l l u t i o n c o n t r o l h a v e b e e n f o r c i n g a shift to c o n c e n t r a t i n g spent sulfite p u l p i n g l i q u o r b y e v a p o r a t i o n , f o l l o w e d b y incineration w i t h heat recovery

(102).

When

calcium-base

l i q u o r is b u r n e d , t h e s u l f u r emerges as c a l c i u m sulfate a n d is n o t a v a i l a b l e f o r r e c y c l e to the p u l p i n g process.

T h e flue gas f r o m s u c h furnaces

i n S w e d e n is r e p o r t e d to c o n t a i n 0.2—0.3%

s u l f u r d i o x i d e , a n d i n one

S w e d i s h m i l l a B a h c o w e t limestone s c r u b b e r is u s e d to treat t h e gases (115). W h e n a m m o n i a - b a s e sulfite l i q u o r is b u r n e d , t h e s u l f u r is released as sulfur dioxide.

H o w e v e r , i t has n o t b e e n t h e p r a c t i c e to r e c o v e r t h e


s u l f u r d i o x i d e f o r re-use, a l t h o u g h a b s o r p t i o n systems w e r e for t h e p u r p o s e (23, 24, 102, 103, 112).

developed

Nevertheless, recovery

are n o w g o i n g i n t o service w i t h a m m o n i a - b a s e m i l l s

systems

(116).

M o s t of sulfite m i l l s u s i n g a s u l f u r d i o x i d e r e c o v e r y c y c l e h a v e u s e d the w e l l e s t a b l i s h e d magnesia-base process (117, 118, 119, 120,

121).

W h e n the magnesia-base spent l i q u o r is b u r n e d , or m a g n e s i u m sulfite a n d sulfate are s m e l t e d i n t h e presence of excess c a r b o n , t h e s u l f u r goes off as s u l f u r d i o x i d e , a n d t h e m a g n e s i u m r e m a i n s as t h e oxide.

I n the

c a l c i u m system, t h e e q u i v a l e n t reactions t a k e p l a c e o n l y at m u c h h i g h e r temperatures.

E x p e r i e n c e w i t h t h e magnesia-base p u l p i n g process w a s

u n d o u b t e d l y t h e i n s p i r a t i o n f o r d e v e l o p m e n t of the C h e m i c o - B a s i c and

other

s i m i l a r processes u s i n g m a g n e s i a i n c y c l i c

sulfur

(33)

dioxide

r e c o v e r y systems. T h e s o d i u m - b a s e sulfite systems present experience w i t h s u l f u r r e c o v e r y processes t h a t m a y h a v e w i d e a p p l i c a t i o n outside t h e p a p e r p u l p industry.

T h e b a s i c c h e m i s t r y i n v o l v e d is h i s t o r i c a l l y v e r y o l d

(122).

E s s e n t i a l l y , f o u r steps u n d e r l i e t h e v a r i o u s processes: 1. T h e spent s o d i u m - b a s e sulfite l i q u o r is b u r n e d u n d e r r e d u c i n g c o n d i t i o n s , as i n the k r a f t process, y i e l d i n g a smelt of s o d i u m sulfide. 2. T h e s o d i u m sulfide is t r e a t e d w i t h steam a n d c a r b o n d i o x i d e . S o d i u m c a r b o n a t e is f o r m e d , a n d h y d r o g e n sulfide is d r i v e n off. 3. T h e s o d i u m c a r b o n a t e is u s e d to absorb s u l f u r d i o x i d e , p r o d u c i n g f r e s h s o d i u m sulfite or b i s u l f i t e f o r use as c o o k i n g l i q u o r . 4. T h e h y d r o g e n sulfide is b u r n e d to p r o v i d e t h e s u l f u r d i o x i d e f o r c o o k i n g l i q u o r p r o d u c t i o n , o r i n some processes, i t is sent to a C l a u s p l a n t f o r c o n v e r s i o n to e l e m e n t a l s u l f u r . A m o n g t h e v a r i o u s p u l p i n g c h e m i c a l r e c o v e r y systems a r e t h e S t o r a (123),

S i v o l a (124),

a n d T a m p e l l a (125)

processes, w h i c h h a v e

been

d e m o n s t r a t e d c o m m e r c i a l l y . T h e first of t h e process steps g i v e n a b o v e c a n b e a c c o m p l i s h e d w i t h s o d i u m sulfate o r sulfite b y s m e l t i n g u n d e r r e d u c i n g c o n d i t i o n s , w h i c h is t h e oldest m e t h o d f o r p r o d u c i n g s o d i u m sulfide

(126).


1.

SE M R A U

Industrial

19

Process Sources

T h e process c o m p o s e d of t h e a b o v e sequence of steps c a n b e u s e d t o recover e l e m e n t a l s u l f u r f r o m s u l f u r d i o x i d e - b e a r i n g gases, u s i n g s o d i u m c a r b o n a t e as t h e p r i m a r y absorbent.

A l t e r n a t i v e l y , i t c a n b e u s e d to

recover s u l f u r a n d s o d i u m c a r b o n a t e f r o m t h e s o d i u m sulfate f o r m e d i n the c y c l i c a b s o r p t i o n processes, s u c h as the W e l l m a n - L o r d , t h a t a r e u s e d for c o n c e n t r a t i n g s u l f u r d i o x i d e f r o m d i l u t e gas streams (10).

A purge

s t r e a m o f t h e absorbent m u s t b e w i t h d r a w n to p r e v e n t b u i l d u p of exces sive sulfate. D i s p o s a l of the s o d i u m sulfate as s u c h w i l l p r o b a b l y b e c o m e difficult i f the s o d i u m - b a s e

a b s o r p t i o n processes are u s e d o n a l a r g e

scale f o r s u l f u r d i o x i d e r e c o v e r y .

N i t t e t u C h e m i c a l E n g i n e e r i n g has

d e v e l o p e d a process u s i n g t h e same b a s i c c h e m i s t r y to d e a l s p e c i f i c a l l y Downloaded by UNIV OF MISSISSIPPI on June 19, 2015 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch001

w i t h t h e sulfate b u i l d u p i n s o d i u m - b a s e absorbents u s e d to d e s u l f u r i z e c o k e o v e n gas Literature

(127).

Cited

1. Cavender, J. H . , Kircher, D. S., Hoffman, A. J., "Nationwide Air Pollutant Emission Trends—1940-1970," E P A Publ. No. AP-115 (Jan. 1973). 2. Beers, W . D., "Characterization of Claus Plant Emissions," Processes Re search, Inc., E P A Report EPA-R2-73-188, Apr. 1973, NTIS: PB-220376. 3. Environmental Protection Agency, "Cost of Clean Air—1973," U.S. Senate Document No. 93-40, U.S. Government Printing Office, Washington, D.C. (1972). 4. Economic Commission for Europe, "Desulfurization of Fuels and Com bustion Gases," Report on the Proceedings of the Seminar, Geneva (Nov. 16-20, 1970), United Nations, Ν. Y., 1971. 5. Bailleul, M . R., Bapseres, Ε. Α., Guyot, G . L., in "Sulfur and S O Develop ments," pp. 119-122, A I C h E , 1971. 6. Lea, N . S., Christoferson, E . A., Chem. Eng. Progr. (1965) 61(11), 89. 7. Wollaston, E . G., Forsythe, W . L . , Vasalos, I. Α., Oil Gas J. (1971) 69(31), 64. 8. Brocke, W., VDI-Berichte (1970) 149, 98. 9. Semrau, Κ. T., J. Metals (1971) 23(3), 41. 10. Semrau, K. T., J. Air Pollut. Contr. Ass. (1971) 21, 185. 11. U.S. Bur. Mines, Inform. Cir. 8571 (1971). 12. Gibson, F. W., Chem. Eng. (1969) 76(26), 66. 13. Mining Eng. (1973) 25, 19. 14. Smelter Control Research Association, "The Removal of Sulphur Dioxide from Copper Reverberatory Furnace Gas by Wet-Limestone Scrubbing," New York (1973). 15. Hunter, W . D., Jr., Power (1973) 117(9), 63. 16. Hunter, W . D., Jr., Michener, A. W., Eng. Mining J. (1973) 174(6), 117. 17. Malmstrom, R., Tuominen, T . , Advan. Extract. Metallurgy Refining, Paper 20, Institution of Mining and Metallurgy, London, Oct. 1971. 18. Beal, J. V., Mining Eng. (1973) 25(4), 35. 19. Mining Eng. (1972) 24(4), 27. 20. Petersson, S. Α., in "Environmental Control," C. Rampacek, ed., pp. 3-18, The Metallurgical Society of A I M E , 1972. 21. Petersson, S., Kem. Tidskr. (1970) 1, 34. 22. King, R. Α., Ind. Eng. Chem. (1950) 42, 2241. 23. Clement, J. L . , Sage, W . L . , Tappi (1969) 52(8), 1449. 2



20

SULFUR REMOVAL AND RECOVERY

24. Palmrose, G. V., Hull, J. H . , Tappi (1952) 35, 193. 25. Mascarello, J., Auclair, J., Hamelin, R., Pelecier, C., Proc. Amer. Power Conf. (1969) 31, 439. 26. Dean, R. S., U.S. Bur. Mines, Rep. Invest. 3339 (May 1937). 27. Ando, J., "Recent Developments in Desulfurization of Fuel Oil and Waste Gas in Japan—1973," E P A Rept. No. EPA-R2-73-229, May 1973, NTIS: PB-221-439. 28. Eng. Mining J. (1973) 174(2), 74. 29. Guyot, G., Chim. Ind., Genie Chim. (1969) 101, 31. 30. Ibid., 101, 813. 31. Eng. Mining J. (1971) 172(11), 69. 32. Ibid., 173(8), 69. 33. Shah, I. S., Chem. Eng. Progr. (1971) 67, 51. 34. Kakaria, V. K., Turner, A . L . , Teter, Ε. K., in "Environmental Control," C. Rampacek, ed., pp. 89-102,The Metallurgical Society of A I M E , 1972. 35. Mealey, M . , Eng. Mining J. (1972) 173(6), 130. 36. Donovan, J. R., Stuber, P. J., Chem. Eng. (1970) 77(26), 47. 36. McMeekin, G . R., Can. Inst. Mining Met. Bull. (1973) 66(738), 51. 37. Semrau, K. T., Eng. Mining J. (1971) 172, 115. 38. Eng. Mining J. (1972) 173(2), 69. 39. Wall Street J. (Aug. 20, 1973) 7. 40. Treilhard, D . G., Chem. Eng. (1973) 80(9), P-Z. 41. White, L . , Chem. Eng. (1973) 80(9), A A - C C . 42. Milliken, C. L . , J. Metals (1970) 22(8), 51. 43. Kellogg, H . H . , Latin Amer. Conf. Mining Metallurgy, Santiago, Chile, Aug. 26-Sept. 1, 1973. 44. Pay Dirt (Bisbee, Ariz.) (1974) 415, 15. 45. Lutjen, G . P., Dayton, S. H . , Tinsley, C. R., Eng. Mining J. (1973) 174(11), 73. 46. Merla, S., Young, C. E . , Matousek, J. W., in "Environmental Control," C. Rampacek, ed., pp. 19-35, The Metallurgical Society of A I M E , 1972. 47. Persson, J. A., Treilhard, D . G., J. Metals (1973) 25, (1), 34. 48. Rodolff, D . W., Marble, E . R., Jr., J. Metals (1972) 24(7), 14. 49. Queneau, P. E., J. Metals (1973) 25, 15. 50. Holderreed, F . L . , Mining Eng. (1971) 23(9), 45. 51. Guccione, E . , Eng. Mining J. (1973) 174(12), 81. 52. Daniele, R. Α., Jaquay, L . H . , " T B R C — A New Smelting Technique," A I M E - T M S Paper A72-101 (1972). 53. Eng. Mining J. (1972) 173(8), 66. 54. Reynolds, J. O., Phillips, K. J., Fitzgerald, D. E . , Worner, Η. K., in " E n vironmental Control," C. Rampacek, ed., pp. 67-85, The Metallurgical Society of A I M E , 1972. 55. Themelis, N . J., McKerrow, G . C., Tarassoff, P., Hallett, G . D.,J.Metals (1972) 24(4), 25. 56. MacAskill, D., Eng. Mining J. (1973) 174(7), 82. 57. Kettner, P., Maelzer, C. Α., Schwartz, W . H . , in "Environmental Control," C. Rampacek, ed., pp. 37-63, The Metallurgical Society of A I M E , 1972. 58. Eng. Mining J. (1973) 174(12), 33. 59. Remirez, R., Chem. Eng. (1969) 76(2), 80. 60. Tucker, W . G., Burleigh, J. R., Chem. Eng. Progr. (1971) 67(5), 57. 61. Furkert, H . , Chem. Eng. (1969) 76, (1), 70. 62. Browder, T . J., Chem. Eng. Progr. (1971) 67(5), 45. 63. Connor, J. M., Chemico World (1969) 4(5), 4. 64. Kronseder, J. G., Chem. Eng. Progr. (1968) 64(11), 71.



1.

SEMRAU

Industrial Process Sources

21

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RECEIVED April 4, 1974


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