Reduction of Sulfur Dioxide to Sulfur: The Elemental Sulfur Pilot Plant


Jul 22, 2009 - Reduction of Sulfur Dioxide to Sulfur: The Elemental Sulfur Pilot Plant of ASARCO and Phelps Dodge Corp. JAMES M. HENDERSON and ...
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3 Reduction of Sulfur Dioxide to Sulfur: The Elemental Sulfur Pilot Plant of A S A R C O

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and Phelps Dodge Corp. JAMES M . H E N D E R S O N and J O H N B. P F E I F F E R Central Research Laboratories, American Smelting and Refining Co., South Plainfield, N . J. 07080

The thermodynamic

equilibria involved in reducing

dioxide with fossil fuels were used to specify the reactor operating conditions of 350°C

sulfur primary

and 1 atm with a ratio

of reformed gas to sulfur-bearing gas of 4.14:1. A pilot scale plant was built at ASARCO's initial phase of operation, covered: physical overheating

El Paso smelter. During

the

two process problems were dis-

degradation

of the catalyst pellets and

of the reactor, resulting in a major failure.

new primary reactor was designed and built using

A

boiling

media cooling with a new, stronger catalyst. After 90 days of operation with the new primary reactor on 12% dioxide

feed, neither

of

these operating

sulfur

problems

has

occurred.

' T h e elemental sulfur pilot plant financed by American Smelting and i

Refining Co.

(ASARCO)

and Phelps Dodge

Corp. is located at

A S A R C O ' s E l Paso, Tex., copper-lead smelter. Technology pioneered by both companies is used in this plant. The sulfur dioxide reduction process was developed by A S A R C O while a process for reforming natural gas developed by Phelps Dodge provides the reducing gases. A n y large scale process for reducing sulfur dioxide to elemental sulfur will likely depend on a fossil fuel.

Whether the fuel is used

to reduce sulfur to such compounds as hydrogen sulfide or carbonyl sulfide which are then used as the reductant for sulfur dioxide or whether the fuel itself is the sulfur dioxide reductant, the overall thermochemistry is similar. 35

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

36

S U L F U R

Thermochemistry

of Sulfur

Dioxide

R E M O V A L

A N D

R E C O V E R Y

Reduction

T h e H - C - O - S System. F o l l o w i n g the u s u a l c o n v e n t i o n , the h y d r o g e n c a r b o n - o x y g e n - s u l f u r system is r e p r e s e n t e d as a t e t r a h e d r o n w i t h

the

f o u r p u r e elements at the apexes as d e p i c t e d b y F i g u r e 1. I n t h e r e d u c t i o n of s u l f u r d i o x i d e b y fossil fuels, i f w e assume the f u e l to b e the sole

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H

Hydrogen-carbon-oxygensulfur system source of c a r b o n a n d h y d r o g e n , selection of a p a r t i c u l a r fossil f u e l fixes t h e a t o m i c r a t i o of h y d r o g e n to c a r b o n , thus l i m i t i n g t h e r e g i o n of i n terest i n the H - C - O - S system to a p l a n e .

If m e t h a n e , w i t h a n a t o m i c

r a t i o of h y d r o g e n to c a r b o n of 4.0, is the fossil f u e l , t h e n p l a n e A S O defines

the r e g i o n of t h e H - C - O - S

system w i t h i n w h i c h a l l p o s s i b l e

c o m p o s i t i o n s m u s t l i e . W h e n a p p r o p r i a t e e q u i l i b r i a c o m b i n a t i o n s consistent w i t h significant constituents h a v e b e e n selected, e.g. S 0 , H S , C O S , 2

2

C S , S 0 , H , H 0 , C O , C 0 , S - S and, where applicable, C ( s ) and S ( l ) , 2

3

2

2

2

2

8

a n d t e m p e r a t u r e a n d pressure h a v e b e e n specified, t h e n c a r b o n a n d s u l f u r s a t u r a t i o n lines m a y b e l o c a t e d .

C a r b o n a n d s u l f u r s a t u r a t i o n lines are

s y m b o l i c a l l y i l l u s t r a t e d i n F i g u r e 1 o n p l a n e A S O as are t h e i r projections onto the carbon-oxygen-sulfur projection.

ternary.

T h i s is not a s i m p l e v e r t i c a l

R a t h e r , t h e p r o j e c t i o n of a n y p o i n t o n this p l a n e lies at the

i n t e r s e c t i o n w i t h the c a r b o n - o x y g e n - s u l f u r t e r n a r y of a straight l i n e c o n n e c t i n g the h y d r o g e n apex a n d the p o i n t b e i n g p r o j e c t e d , i.e., i n F i g u r e 1, p o i n t D ' lies o n the extension of a straight l i n e c o n n e c t i n g the h y d r o g e n apex a n d p o i n t D . U s i n g this t e c h n i q u e , a t o m i c s t o i c h i o m e t r i c r e l a t i o n ships i n v o l v i n g c a r b o n , o x y g e n , a n d s u l f u r a p p e a r i n g i n t h e p r o j e c t i o n are i d e n t i c a l to those i n the p l a n e p r o j e c t e d .

T o s i m p l i f y the g r a p h i c a l

i l l u s t r a t i o n s , the p l a n e of interest w i l l be p r o j e c t e d onto the C - O - S t e r n a r y t h r o u g h o u t this discussion. I n F i g u r e 2, regions of c a r b o n , l i q u i d s u l f u r , a n d h o m o g e n e o u s gas s t a b i l i t y are p l o t t e d f o r the specified a t o m i c r a t i o of h y d r o g e n to c a r b o n , 3 2 3 ° C ( 6 0 0 ° K ) , a n d 1 a t m absolute pressure. I n a n y p r a c t i c a l process

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

3.

H E N D E R S O N

A N D

j

Elemental

PFEiFFER

Sulfur Pilot

37

Plant

\

I C(solid)\Gas

β

I

0

\

\

1

Carbon Saturation

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l^^^fSulfur

Maturation

'S(liquid)+ Gas)

Figure 2. Regions of carbon, liquid sulfur, and homogeneous gas stability. H/C = 4.0, S/O = 0.5, Τ = 323°C (600°Κ), Ρ = 1.0 atm.

HornbçeneousGas

A %*0.5

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 , t h e r e g i o n of s a t u r a t i o n is a v o i d e d .

carbon

I n this r e g i o n not o n l y w o u l d t h e y i e l d of s u l f u r

v a p o r be v i r t u a l l y zero, b u t c a r b o n p r e c i p i t a t i o n w o u l d f o u l the catalyst bed. T h e r e are s i m i l a r reasons for a v o i d i n g the s u l f u r - s a t u r a t e d r e g i o n of the system, a l t h o u g h there are e q u a l l y v a l i d reasons f o r i n t e n t i o n a l s u l f u r c o n d e n s a t i o n o n a catalyst, f o l l o w e d b y a catalyst r e g e n e r a t i o n step,

e.g.,

to a t t a i n i n a single c a t a l y t i c stage s u l f u r y i e l d s otherwise o n l y a t t a i n a b l e i n t w o or t h r e e stages. A S A R C O chose to a v o i d s u l f u r c o n d e n s a t i o n o n the catalyst. T h e r e is, h o w e v e r , a n a d d i t i o n a l constraint o n the r e g i o n of p r a c t i c a l interest. S i n c e w e are c o n c e r n e d w i t h s u l f u r d i o x i d e r e d u c ­ t i o n , w e n e e d o n l y to e x a m i n e the system c h e m i s t r y o f the h o m o g e n e o u s gas r e g i o n l y i n g a l o n g or to the r i g h t of L i n e A C of F i g u r e 2, w h i c h denotes a n a t o m i c r a t i o of s u l f u r to o x y g e n of 0.5, i.e., at a n a t o m i c r a t i o of s u l f u r to o x y g e n e q u a l to or less t h a n that for s u l f u r d i o x i d e . Proportioning of Reformed Gas and Sulfur Dioxide.

W e w i s h to

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

L e t us

e x a m i n e the v a r i a t i o n i n e q u i l i b r i u m c o m p o s i t i o n a n d s u l f u r v a p o r y i e l d a l o n g L i n e A C of F i g u r e 2. T h e s e d a t a are g r a p h i c a l l y s h o w n i n F i g u r e 3,

I too ξ

sion

I

2°1

H

^^^^^ S0A V V Τ COS

1 1

i • 40 20

O.I

0.2

0.3 C/o

0.4

0.5

ο

I

a

Figure 3. Gas phase composition. H/C = 4.0, S/O = 0 . 5 , Τ = 323°C (600°Κ), Ρ = 1.0 atm.

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

38

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

w h e r e gas phase c o m p o s i t i o n is expressed i n terms of l o g p a r t i a l pressures. W i t h fixed a t o m i c ratios of h y d r o g e n to c a r b o n a n d s u l f u r to

oxygen,

F i g u r e 3 illustrates the c h a n g e i n e q u i l i b r i u m gas phase c o m p o s i t i o n w i t h v a r y i n g c a r b o n - t o - o x y g e n r a t i o , e.g., as t h e p r o p o r t i o n i n g of m e t h a n e a n d p u r e s u l f u r d i o x i d e is v a r i e d f r o m f u e l - l e a n to f u e l - r i c h . T h e c u r v e of F i g u r e 3 r e p r e s e n t i n g e q u i l i b r i u m p e r c e n t a g e 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 v a p o r illustrates the i m p o r t a n c e of p r o p o r t i o n i n g s u l f u r d i o x i d e a n d r e d u c i n g gas.

W i t h m e t h a n e as the r e -

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d u c t a n t , m a x i m u m s u l f u r v a p o r y i e l d occurs at a system a t o m i c r a t i o of c a r b o n to o x y g e n of 0.25, consistent w i t h the f o l l o w i n g s i m p l i f i e d o v e r a l l reaction: 2 S0

2

(g) +

CH

4

(g) -> S

2

(g) +

C0

2

(g) + 2 H 0 (g)

(1)

2

I n the A S A R C O s u l f u r d i o x i d e process, h o w e v e r , r e f o r m e d n a t u r a l gas is the r e d u c e r . If w e assume n a t u r a l gas to be c o m p r i s e d solely of m e t h a n e , reformed

n a t u r a l gas f o r m a t i o n i n the process d e v e l o p e d

by

Phelps

D o d g e C o r p . m a y be expressed i n terms of R e a c t i o n 2: CH

4

(g) + 0.5 0

2

(g) -> C O (g) + 2 H

2

(g)

(2)

S u l f u r d i o x i d e r e d u c t i o n to e l e m e n t a l s u l f u r v a p o r m a y be 1.5 S 0

2

(g) +

CO + 2 H

2

0.75 S

2

(g) + C 0

2

expressed:

(g) + 2 H 0 2

(3)

I n R e a c t i o n 3 as i n R e a c t i o n 1 the a t o m i c r a t i o of c a r b o n to o x y g e n is also 0.25. I n theory, the m a x i m u m y i e l d of s u l f u r v a p o r w o u l d d e p e n d o n a t e m p e r a t u r e - d e p e n d e n t a t o m i c r a t i o of c a r b o n to oxygen.

I n other

w o r d s , m a x i m u m y i e l d of s u l f u r v a p o r d e p e n d s o n a c a r b o n m o n o x i d e - t o c a r b o n d i o x i d e r a t i o ( o r a h y d r o g e n - t o - w a t e r r a t i o ) w h i c h is i n t u r n temperature dependent.

W h i l e the absolute v a l u e of the c a r b o n m o n -

o x i d e - t o - c a r b o n d i o x i d e r a t i o c o r r e s p o n d i n g to m a x i m u m 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 v a p o r changes w i t h t e m p e r a t u r e , e q u i l i b r i u m p a r t i a l pressures of c a r b o n m o n o x i d e or h y d r o g e n are essentially zero over a b r o a d t e m p e r a t u r e range. T h u s , i n a p r a c t i c a l sense, w h e n m e t h a n e or r e f o r m e d m e t h a n e is the r e d u c t a n t for s u l f u r d i o x i d e , m a x i m u m e q u i l i b r i u m 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 v a p o r w i l l o c c u r at a n a t o m i c r a t i o of c a r b o n to o x y g e n of 0.25 regardless of t e m p e r a t u r e i n a c c o r d a n c e w i t h the s i m p l e s t o i c h i o m e t r y of R e a c t i o n s 1 a n d 3. N a t u r a l gas of the s o u t h w e s t e r n U n i t e d States contains, i n a d d i t i o n to m e t h a n e , s e v e r a l p e r cent ethane a n d lesser percentages of h i g h e r m o l e c u l a r w e i g h t h y d r o c a r b o n s , u p to a n d i n c l u d i n g pentane. T h e a t o m i c r a t i o of h y d r o g e n to c a r b o n i n this f u e l is a b o u t 3.80.

R e f o r m i n g this

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

3.

H E N D E R S O N

Elemental

PFEiFFER

A N D

Sulfur Pilot

39

Plant

n a t u r a l gas b y t h e P h e l p s D o d g e process t y p i c a l l y p r o d u c e s a gas stream of the c o m p o s i t i o n g i v e n i n T a b l e I. T h e E l Paso e l e m e n t a l s u l f u r p i l o t p l a n t is d e s i g n e d to p e r m i t r e d u c ­ t i o n of 1 2 - 1 0 0 % s u l f u r d i o x i d e i n gas streams. I n the r e d u c t i o n of p u r e s u l f u r d i o x i d e , s t o i c h i o m e t r i c p r o p o r t i o n i n g of r e f o r m e d gas to s u l f u r d i o x i d e m a y be defined b y : S0

2

+

χ (0.170 C O +

-> 0.5 S

2

where χ = Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 13, 2015 | http://pubs.acs.org Publication Date: April 1, 1975 | doi: 10.1021/ba-1975-0139.ch003

0.313 H

+ χ (0.187 C 0

2

+

2

+

0.017 C 0

0.355 H 0 + 2

2

+

0.042 H 0 + 2

0.458 N ) 2

0.458 N )

(4)

2

moles of r e f o r m e d g a s / m o l e of s u l f u r d i o x i d e . S o l v i n g for x,

the s t o i c h i o m e t r i c p r o p o r t i o n i n g of r e d u c t a n t to s u l f u r d i o x i d e r e q u i r e d Table I. Constituent CO H C0 H 0 N 2

2

2

2

T y p i c a l Reformed Gas Composition Volume

%

17.0 31.3 1.7 4.2 45.8

4.141 moles of r e f o r m e d g a s / m o l e of s u l f u r d i o x i d e . P i l o t p l a n t process d e s i g n for r e d u c i n g p u r e s u l f u r d i o x i d e therefore p r o v i d e s for b l e n d i n g of r e f o r m e d gas a n d s u l f u r d i o x i d e i n the s t o i c h i o m e t r i c v o l u m e r a t i o of 4.141 to 1 a n d i n t r o d u c t i o n of this m i x e d gas stream i n t o t h e p r i m a r y or first-stage c a t a l y t i c reactor. T h i s leads to a system c o m p o s i t i o n defined b y the f o l l o w i n g a t o m i c r a t i o s : H / C = 3.797, S / O — 0.331, C / O =

0.257.

Temperature and Pressure Specification. S i n c e e q u i l i b r i u m 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 v a p o r increases w i t h d e c r e a s i n g t e m p e r a ­ ture, the r e d u c t i o n process was d e s i g n e d so t h a t the p r i m a r y r e d u c t i o n stage operates

at the m i n i m u m t e m p e r a t u r e consistent w i t h

reaction

kinetics w h i c h a v o i d s s u l f u r c o n d e n s a t i o n o n the catalyst. T a k i n g these factors i n t o account, the p r i m a r y c a t a l y t i c reactor is o p e r a t e d at 3 5 0 ° C (623°K). It was

e s t i m a t e d t h a t a c t u a l o p e r a t i n g pressure

at the p r i m a r y

reactor outlet w o u l d b e 2.7 l b / s q i n . gage, e q u i v a l e n t at the E l Paso e l e v a t i o n to 1.04 a t m absolute. S i n c e s u l f u r d i o x i d e r e d u c t i o n w i l l e n t a i l a v o l u m e s h r i n k a g e c a u s e d p r i m a r i l y b y f o r m a t i o n of p o l y a t o m i c s u l f u r v a p o r species, i t is e s t i m a t e d , w i t h the a i d of R e a c t i o n 4, t h a t t h e gas stream l e a v i n g the p r i m a r y reactor w i l l h a v e a n i t r o g e n content of 4 3 . 5 % , e q u i v a l e n t to a n i t r o g e n p a r t i a l pressure of 0.45 a t m . A t the temperatures a n d pressures of interest, n i t r o g e n m a y b e c o n s i d e r e d a n i n e r t gas.

In

terms of gaseous species i n v o l v e d i n e q u i l i b r i a w i t h i n the H - C - O - S sys­ t e m , the s u m of t h e i r p a r t i a l pressures m u s t b e e q u a l to t h e t o t a l pressure at the p o i n t i n the reactor w h e r e e q u i l i b r i u m is a p p r o a c h e d less the p a r -

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

40

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 i a l pressure of n i t r o g e n — a n e s t i m a t e d H - C - O - S system pressure i n this case of 1.04 m i n u s 0.45, or 0.59 a t m . Equilibrium Gas Phase Composition. H a v i n g d e f i n e d o p t i m u m p r o p o r t i o n i n g of

reformed

gas

and sulfur dioxide

and having

specified

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c

t e m p e r a t u r e a n d pressure at 3 5 0 ° C ( 6 2 3 ° K ) a n d 0.59 a t m , r e s p e c t i v e l y , the e q u i l i b r i u m gas p h a s e c o m p o s i t i o n m a y b e c a l c u l a t e d . T h e system c o m p o s i t i o n , d e n o t e d as p o i n t A , together w i t h c a r b o n a n d s u l f u r s a t u r a t i o n lines is d e p i c t e d i n F i g u r e 4. A t the specified p r i m a r y reactor o p e r a t i n g c o n d i t i o n s the system c o m p o s i t i o n is w e l l i n s i d e the h o m o g e n e o u s gas r e g i o n .

E q u i l i b r i u m gas phase c o m p o s i t i o n at p o i n t A is g i v e n i n

Table II. F r o m the gas p h a s e c o m p o s i t i o n i n T a b l e I I , it m a y be c a l c u l a t e d that 7 9 . 4 %

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

C o o l i n g this

gas i n the absence of a catalyst leads to no e q u i l i b r i u m shift other t h a n that associated w i t h s u l f u r v a p o r c o n d e n s a t i o n ; this has b e e n b o r n e out i n the C l a u s process. B y c o o l i n g a gas stream of the c o m p o s i t i o n c i t e d i n T a b l e I I to 1 4 0 ° C (413 K ) , e q u i l i b r i u m s u l f u r c o n d e n s a t i o n sponds to 7 8 . 4 %

first-stage

Table II. Constituent C0 H 0 H S S0 2

2

a

%

17.62 31.07 3.20 1.59 43.64

2

2

N

Equilibrium Composition of Gases Leaving First-Stage Reactor Vol.

a

2

Constituent

s

2

S

3

s s s

S S

4 s 6 7 8

Vol. 0.09 0.01 0.05 0.30 1.08 0.67 0.68

C O , H , COS, C S , and SO3 are present in negligibly small concentrations. 2

corre-

r e c o v e r y of l i q u i d sulfur.

2

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

%

3.

H E N D E R S O N

Elemental

PFEiFFER

A N D

Sulfur Pilot

41

Plant

A f t e r the c o n d e n s a t i o n of s u l f u r v a p o r , most of t h e s u l f u r r e m a i n i n g i n t h e gas phase is present as 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 i n t h e v o l u m e r a t i o of 2 to 1. W i t h s u l f u r c o n d e n s a t i o n , the a t o m i c r a t i o of s u l f u r to o x y g e n i n the gas phase is r e d u c e d w h i l e the other a t o m i c ratios r e ­ main unchanged.

G r a p h i c a l l y , this e q u i l i b r i u m c o n d e n s a t i o n of s u l f u r

v a p o r , d e c r e a s i n g the gas phase r a t i o of s u l f u r to o x y g e n to 0.071, is r e p r e s e n t e d i n F i g u r e 4 b y the shift f r o m p o i n t A to p o i n t Β a l o n g t h e l i n e h a v i n g a constant a t o m i c r a t i o of c a r b o n to o x y g e n of 0.257.

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W i t h the gaseous s u l f u r - b e a r i n g species b e i n g p r e d o m i n a n t l y 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 , f u r t h e r r e c o v e r y of e l e m e n t a l s u l f u r d e ­ pends o n the C l a u s r e a c t i o n : 2 H S (g) + S 0 2

2

(g) -

1.5 S

2

(g) +

2 H 0 (g)

(5)

2

T o a v o i d c o n d e n s i n g s u l f u r v a p o r o n the catalyst u s e d i n the secondary, or C l a u s - t y p e reactor, gases l e a v i n g the p r i m a r y s u l f u r condenser be reheated.

must

F o r the p l a n t o p e r a t i n g c o n d i t i o n s u n d e r d i s c u s s i o n , t h e

gas stream is r e h e a t e d to 2 0 5 ° C (478 K ) . A s the C l a u s r e a c t i o n is s l i g h t l y e x o t h e r m i c , i t is e s t i m a t e d that the t e m p e r a t u r e of the gas stream w i l l rise, a l l o w i n g for t h e r m a l losses, b y a b o u t 3 5 ° C to 2 4 0 ° C (513 K ) e q u i l i b r i u m is a p p r o a c h e d .

as

A l l o w i n g for the e x p e c t e d pressure d r o p as

the process gas s t r e a m passes t h r o u g h the process t r a i n a n d for the c h a n g e i n r e l a t i v e v o l u m e of inert n i t r o g e n as c o m p a r e d w i t h the t o t a l v o l u m e of " a c t i v e " gaseous species, w e c a n estimate that H - C - O - S system p r e s ­ sure w i l l b e 0.50 a t m . S u l f u r a n d c a r b o n s a t u r a t i o n lines c o n f o r m i n g to this pressure a n d the expected t e m p e r a t u r e of 2 4 0 ° C (513 K ) are also s h o w n i n F i g u r e 4.

P o i n t B , c o r r e s p o n d i n g to system c o m p o s i t i o n , lies

to the r i g h t of the s u l f u r s a t u r a t i o n line. conditions, avoided.

sulfur condensation

on

the

Therefore, under e q u i l i b r i u m secondary

reactor

catalyst is

T h e t h e o r e t i c a l e q u i l i b r i u m gas phase c o m p o s i t i o n is l i s t e d i n

Table III.

Table III.

Equilibrium Composition of Gases Leaving Second-Stage Reactor

Constituent"

Vol.

C0 H 0 H S

18.53 34.41 0.75 0.37 45.39

2

2

2

so N a

%

2

2

Constituent

s s

6 7

Se

Vol.

%

0.01 0.18 0.11 0.25

C O , H2, COS, C S , S , S3, and S 4 are present in negligibly small concentrations. 2

2

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

42

S U L F U R

R E M O V A L

A N D

R E C O V E R Y

F r o m t h e d a t a of T a b l e s I I a n d I I I , i t m a y be c a l c u l a t e d that e q u i l i b r i u m c o n v e r s i o n of 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 to s u l f u r v a p o r i n the s e c o n d a r y reactor is 7 8 . 0 % .

C o o l i n g this gas stream to

140°C

(413 K ) w i l l l e a d to a l i q u i d s u l f u r r e c o v e r y of 7 6 . 1 % of the s e c o n d a r y reactor o u t p u t .

O v e r a l l r e c o v e r y i n the t w o stages, t h e n , m a y b e c a l c u -

l a t e d to be 9 4 . 9 % . O v e r a l l recovery c o u l d be increased slightly b y a d d i n g a t h i r d catal y t i c stage.

H o w e v e r , it w a s not d e e m e d necessary to use a t h i r d stage

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i n the A S A R C O - P h e l p s D o d g e p i l o t p l a n t because i t represents

tech-

n o l o g y w e l l e s t a b l i s h e d i n the C l a u s process. Laboratory

Development

Program

T h e i n i t i a l l a b o r a t o r y i n v e s t i g a t i o n of t h e process n o w b e i n g p i l o t e d at the A S A R C O E l Paso p l a n t i n v o l v e d b e n c h scale evaluations of different p r i m a r y s u l f u r d i o x i d e r e d u c t i o n catalysts. A l s o , fluid-bed

catalysis w e r e c o m p a r e d ,

19

fixed-bed

and

a n d various construction materials

w e r e e v a l u a t e d i n the corrosive h y d r o g e n sulfide a n d s u l f u r v a p o r atmosp h e r e g e n e r a t e d i n gas phase r e d u c t i o n of s u l f u r d i o x i d e . F o l l o w i n g c o m p l e t i o n of the b e n c h scale test p r o g r a m , a n e n g i n e e r i n g c o n t r a c t o r c o n d u c t e d a s t u d y a n d p r e p a r e d the p r e l i m i n a r y d e s i g n for a p i l o t p l a n t h a v i n g a n o m i n a l p r o d u c t i o n c a p a c i t y of 20 short tons s u l f u r / d a y w h e n treating pure sulfur dioxide. fixed-bed

catalysis w a s

more practical.

d e s i g n , therefore, p r o v i d e d for a

fixed-bed

The

This study found preliminary pilot

of

that plant

p r i m a r y reactor of t h e s h e l l -

a n d - t u b e t y p e i n w h i c h the catalyst w o u l d b e i n the tubes. B a s e d o n this e n g i n e e r i n g s t u d y w e c o n c l u d e d t h a t f u r t h e r l a b o r a t o r y studies s h o u l d b e m a d e m o r e f u l l y to define the p r i m a r y reactor catalyst l o a d i n g s r e q u i r e d to a p p r o a c h e q u i l i b r i u m 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 v a p o r o v e r t h e r a n g e of p i l o t p l a n t o p e r a t i n g c o n d i t i o n s . T h e reactor u s e d i n this a d d i t i o n a l s t u d y d u p l i c a t e d as n e a r l y as possible the g e o m e t r y of t h e p r o p o s e d p i l o t p l a n t reactor. T h e l a b o r a t o r y reactor w a s f a b r i c a t e d of t y p e 304 stainless steel p i p e .

A n electrically heated

m o l t e n l e a d b a t h m a i n t a i n e d the d e s i r e d o p e r a t i n g t e m p e r a t u r e . G a s streams f o r the e x p e r i m e n t a l r e a c t o r c o n t a i n e d n i t r o g e n , h y d r o gen, c a r b o n m o n o x i d e , s u l f u r d i o x i d e , a n d i n some cases o x y g e n ,

from

c y l i n d e r s , w h i c h w e r e b l e n d e d to synthesize a m i x t u r e of r e f o r m e d n a t u r a l gas a n d a s u l f u r d i o x i d e - b e a r i n g gas stream of the d e s i r e d position.

T h e composition

of this h e a d gas stream w a s

m o n i t o r e d b y a n o n - l i n e process c h r o m a t o g r a p h .

com-

continuously

T h e m i x e d gas stream

w a s s a t u r a t e d w i t h w a t e r v a p o r at a c o n t r o l l e d t e m p e r a t u r e a n d pressure to p r o v i d e a w a t e r v a p o r content consistent w i t h t h a t i n a c t u a l p l a n t operation.

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

3.

H E N D E R S O N

A N D

Elemental

PFEiFFER

Sulfur Pilot

43

Plant

G a s samples f r o m the reactor w e r e a n a l y z e d b y mass

spectroscopy

a n d gas c h r o m a t o g r a p h y a n d conversions of s u l f u r d i o x i d e to s u l f u r v a p o r w e r e c o m p u t e d f r o m the c o m b i n e d a n a l y t i c a l d a t a . I n this large-scale test p r o g r a m , effects o n catalyst l o a d i n g of a n u m b e r of v a r i a b l e s w e r e e x a m i n e d i n d e t a i l . W h i l e the l a b o r a t o r y e x p e r i m e n t a t i o n h a d b e e n q u i t e extensive, o p e r a t i o n of a p i l o t p l a n t was c o n s i d e r e d necessary to p e r m i t scale-up of the process to the 2 0 0 - 3 0 0 t o n / d a y plants c o n c e i v a b l y r e q u i r e d i n the f u t u r e .

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The Elemental

Sulfur

Pilot

Plant

Operating Conditions of the Pilot Plant.

B e c a u s e of f u e l costs a

sulfur d i o x i d e - b e a r i n g gas s t r e a m of r e l a t i v e l y l o w o x y g e n content is n e c ­ essary to p e r m i t p r a c t i c a l a p p l i c a t i o n of the A S A R C O s u l f u r d i o x i d e r e d u c ­ t i o n process.

A d d i t i o n a l l y , for a n y g i v e n s u l f u r p r o d u c t i o n rate, e q u i p ­

m e n t size increases as 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 stream decreases.

T h e r e is, therefore, some l o w e r 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

w h e r e i t becomes m o r e e c o n o m i c a l

to concentrate

the s u l f u r d i o x i d e

before r e d u c t i o n . P r e l i m i n a r y c a p i t a l a n d o p e r a t i n g cost estimates i n d i ­ c a t e d that this b r e a k i n g p o i n t w a s i n the range of 1 2 - 1 5 % s u l f u r d i o x i d e . F o r these reasons, the p i l o t p l a n t w a s d e s i g n e d to treat gas streams c o n ­ taining 12-100%

sulfur dioxide.

W e a n t i c i p a t e d that t h e major

oper­

a t i o n a l effort w o u l d be d i r e c t e d first to t r e a t i n g a gas stream c o n t a i n i n g 1 2 % sulfur dioxide.

S u c h a gas stream is t y p i c a l of that generated i n

flash s m e l t i n g of c o p p e r concentrates or i n the n e w e r c o p p e r s m e l t i n g processes p r e s e n t l y u n d e r d e v e l o p m e n t .

T h e second p r i n c i p a l m o d e of

o p e r a t i o n w i l l r e d u c e p u r e s u l f u r d i o x i d e , i n response to the r e q u i r e m e n t for c o n c e n t r a t i n g the s u l f u r d i o x i d e i n m o r e d i l u t e gas streams b e f o r e r e d u c t i o n . S u l f u r p r o d u c t i o n c a p a b i l i t y i n the. latter case amounts to 20 short-tons/day.

H o w e v e r , since p l a n t d e s i g n p r o v i d e s for h a n d l i n g es­

s e n t i a l l y the same t o t a l process gas v o l u m e regardless of 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 h e a d gas, s u l f u r p r o d u c t i o n decreases m a t e l y 8.5 s h o r t - t o n s / d a y w h e n t r e a t i n g a 1 2 %

to a p p r o x i ­

sulfur dioxide-bearing

gas stream. A s u s u a l i n the c o n v e n t i o n a l c o p p e r

or l e a d smelter, n o n e of

the

E l Paso smelter gas streams has a 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 as h i g h as 1 2 % .

I n the p i l o t p l a n t , t h e n , the 1 2 % s u l f u r d i o x i d e gas stream is

generated b y b u r n i n g m o l t e n s u l f u r i n a s p r a y - t y p e s u l f u r b u r n e r to p r o d u c e a gas stream c o n t a i n i n g 1 8 % s u l f u r d i o x i d e . T h i s hot gas stream, at 1 3 5 0 ° C (1623 K ) , is c o o l e d to a b o u t 3 6 0 ° C (633 Κ ) i n a waste heat boiler.

W h e n t h e p i l o t p l a n t is o p e r a t i n g w i t h this 1 8 %

gas,

process

t a i l gases are r e c y c l e d to d i l u t e the 1 8 % h e a d gas s t r e a m to 1 2 % . I n a n alternate m o d e of o p e r a t i o n , l i q u i d s u l f u r d i o x i d e is v a p o r i z e d to generate t h e p u r e gas.

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

44

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 P h e l p s D o d g e r e f o r m i n g process ( 1 ) uses c a t a l y t i c p a r t i a l c o m b u s t i o n of n a t u r a l gas w i t h p r e h e a t e d a i r to p r o d u c e

a reformed

gas

s t r e a m h a v i n g a t o t a l h y d r o g e n p l u s c a r b o n m o n o x i d e content of 4 8 - 5 0 % by volume.

T h e r e f o r m e r is a r e f r a c t o r y l i n e d , v e r t i c a l , c y l i n d r i c a l steel

vessel p a c k e d w i t h n i c k e l i z e d a l u m i n a pellets.

A i r , p r e h e a t e d to

430-

4 8 0 ° C ( 7 0 3 - 7 5 3 K ) , together w i t h n a t u r a l gas at a v o l u m e r a t i o of 2.8-3.0 to 1, r e s p e c t i v e l y , is i n t r o d u c e d t h r o u g h a m i x e r i n t h e t o p of t h e r e f o r m e r . I n p a s s i n g t h r o u g h the catalyst b e d , the gas stream approaches the e q u i -

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l i b r i u m c o m p o s i t i o n c o r r e s p o n d i n g to the outlet t e m p e r a t u r e a n d pressure of 1 0 0 0 ° C (1273 K ) a n d 1.15 a t m absolute. T h e r e f o r m e d gas w h i c h is g e n e r a t e d is free of c a r b o n p a r t i c l e s a n d contains o n l y traces of u n reacted hydrocarbons.

A c o n t r o l l e d p o r t i o n of the h o t r e f o r m e d gas is

d i v e r t e d t h r o u g h a w a t e r - c o o l e d s h e l l - a n d - t u b e heat exchanger to m a i n t a i n a r e f o r m e d gas t e m p e r a t u r e of 4 2 0 - 4 6 0 ° C ( 6 9 3 - 7 3 3 K ) . R e f o r m e d n a t u r a l gas a n d gases f r o m either the s u l f u r b u r n e r or the s u l f u r d i o x i d e v a p o r i z e r are c o m b i n e d s t o i c h i o m e t r i c a l l y a n d i n t r o d u c e d i n t o the p r i m a r y c a t a l y t i c reactor at 3 5 0 ° C

(623

K).

The

reformed

a n d s u l f u r b u r n e r gases are c o o l e d to m a i n t a i n the m i x e d stream at this temperature.

T h e p r i m a r y reactor is a v e r t i c a l s h e l l - a n d - t u b e heat ex-

c h a n g e r w i t h the t u b e filled w i t h catalyst. S i n c e s u l f u r d i o x i d e r e d u c t i o n is h i g h l y e x o t h e r m i c , a n o r g a n i c heat transfer fluid is c i r c u l a t e d t h r o u g h t h e s h e l l side to c o n t r o l reactor t e m p e r a t u r e . C o o l a n t l e a v i n g the p r i m a r y r e a c t o r is s p l i t i n t o t w o streams.

O n e stream is c i r c u l a t e d t h r o u g h a

k e t t l e - t y p e heat exchanger w h e r e steam at 35 l b / s q i n . gage is generated. T h e o t h e r stream passes t h r o u g h a s h e l l - a n d - t u b e heat exchanger w h i c h reheats the process gas s t r e a m before i t is i n t r o d u c e d into the

second

c a t a l y t i c reactor. T h e gas stream leaves the p r i m a r y reactor at a p p r o x i m a t e l y t h e i n l e t t e m p e r a t u r e a n d is essentially at e q u i l i b r i u m , w h i c h amounts to c o n v e r sions of s u l f u r d i o x i d e to s u l f u r v a p o r of a p p r o x i m a t e l y 6 9 % w h e n t r e a t i n g a 12%

s u l f u r d i o x i d e gas a n d a b o u t 8 0 %

w h e n reducing pure sulfur

dioxide. F o l l o w i n g the p r i m a r y reactor, the A S A R C O - P h e l p s D o d g e

pilot

p l a n t d u p l i c a t e s t y p i c a l C l a u s process p r a c t i c e . T a i l gases f r o m the p r i m a r y r e a c t o r are c o o l e d i n a h o r i z o n t a l s h e l l - a n d - t u b e condenser to c o n dense s u l f u r a n d are t h e n r e h e a t e d to a p p r o x i m a t e l y 205 ° C (478 K ) a n d p a s s e d t h r o u g h a second c a t a l y t i c stage. T h i s is a

fixed-bed

reactor w i t h

n o i n t e r n a l c o o l i n g . T h e o n l y r e a c t i o n i n v o l v e d i n t h e second stage is a shift i n the e q u i l i b r i u m b e t w e e n 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 to y i e l d a d d i t i o n a l s u l f u r v a p o r . T h e process gas stream f r o m the s e c o n d a r y reactor passes t h r o u g h a s e c o n d a r y condenser to recover a d d i t i o n a l s u l f u r a n d , thence, to a n i n c i n e r a t o r w h e r e r e s i d u a l h y d r o g e n sulfide a n d traces of s u l f u r v a p o r are b u r n e d a n d exhausted to the atmosphere.

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

3.

H E N D E R S O N

A N D

PFEiFFER

Elemental

Sulfur Pilot

Phnt

45

Operational Problems of the Pilot Plant. P i l o t p l a n t o p e r a t i o n b e g a n i n late A u g u s t 1971 a n d i n i t i a l l y i n v e s t i g a t e d t r e a t m e n t of a 1 2 % s u l f u r d i o x i d e gas stream. A n u m b e r of m i n o r s t a r t - u p p r o b l e m s w e r e r e s o l v e d , and

a r e l a t i v e l y stable, a r o u n d - t h e - c l o c k

mid-September.

operation was

achieved

by

O p e r a t i o n i n this m o d e c o n t i n u e d , w i t h some i n t e r r u p -

tions, u n t i l late F e b r u a r y 1972. D u r i n g this p e r i o d 91 days of o p e r a t i o n w e r e logged.

T y p i c a l l y , s u l f u r recoveries a v e r a g e d 8 8 - 9 2 % as c o m p a r e d

w i t h a t h e o r e t i c a l r e c o v e r y of a p p r o x i m a t e l y 9 3 % . E l e v e n days of d o w n -

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t i m e w e r e a t t r i b u t e d to c u r t a i l e d i n d u s t r i a l use of n a t u r a l gas.

Other

t h a n this, most of the d o w n t i m e w a s caused b y t w o p r o b l e m s . T h e first p r o b l e m i n v o l v e d g e n e r a t i o n of the 1 2 % b e a r i n g gas stream.

sulfur dioxide-

C o n d e n s a t i o n of trace amounts of s u l f u r t r i o x i d e ,

g e n e r a t e d i n b u r n i n g s u l f u r , caused severe c o r r o s i o n of tubes a n d t u b e sheets i n t h e w a s t e heat b o i l e r . W h i l e not t y p i c a l of p o t e n t i a l p r o b l e m s w h i c h m i g h t be encountered

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

process, this c o r r o s i o n p r o b l e m d i d cause t h e p l a n t to be shut d o w n for almost a m o n t h w h i l e the b o i l e r w a s r e p a i r e d . O p e r a t i n g the b o i l e r at a h i g h e r pressure, l e a d i n g to a h i g h e r t u b e w a l l t e m p e r a t u r e , has l a r g e l y eliminated sulfur trioxide corrosion. T h e second major p r o b l e m i n v o l v e d the catalyst u s e d for the p r i m a r y reactor.

S p e c i f i c a l l y , d e c r e p i t a t i o n of catalyst pellets i n the

first

few

inches of the b e d i n c r e a s e d t h e pressure d r o p t h r o u g h the p r i m a r y reactor. N o loss of catalyst a c t i v i t y has b e e n detected.

A n extensive l a b o r a t o r y

i n v e s t i g a t i o n i s o l a t e d the cause of p h y s i c a l f a i l u r e a n d e v a l u a t e d possible a l t e r n a t i v e solutions. T h e p i l o t p l a n t b e g a n o p e r a t i n g w i t h a m i x t u r e of r e f o r m e d n a t u r a l gas a n d v a p o r i z e d s u l f u r d i o x i d e i n late M a r c h 1972. A f t e r o p e r a t i o n i n this m o d e for a p p r o x i m a t e l y 10 days, a second l i q u i d

flowing

out of the

p r i m a r y s u l f u r condenser was n o t e d , a n d the p l a n t was i m m e d i a t e l y shut d o w n . A t that t i m e the p l a n t w a s p r o d u c i n g s u l f u r at the m a x i m u m d e s i g n t h r o u g h p u t o f 20 t o n s / d a y w i t h 9 0 - 9 2 %

r e c o v e r y as c o m p a r e d w i t h a

t h e o r e t i c a l r e c o v e r y of s l i g h t l y over 9 4 % . T h e second l i q u i d p r o v e d to be the o r g a n i c heat transfer fluid. L e a k s w e r e f o u n d i n the p r i m a r y reactor a n d the s e c o n d a r y reactor preheater.

T h e leaks i n the preheater w e r e

r e l a t i v e l y m i n o r , b u t the p r o b l e m i n the p r i m a r y reactor i n v o l v e d a m a j o r failure. R e m o v a l o f the p r i m a r y reactor heads r e v e a l e d w a r p a g e over a p p r o x i m a t e l y o n e - h a l f of the u p p e r t u b e sheet a n d s h o w e d e v i d e n c e leakage at a n u m b e r of points o n the b o t t o m t u b e sheet.

of

M a n y tubes i n

the area of the u p p e r t u b e sheet w a r p a g e w e r e b u r n e d t h r o u g h w h i l e the space b e t w e e n these tubes w a s s o l i d l y b l o c k e d w i t h c a r b o n t h e r m a l d e c o m p o s i t i o n of t h e o r g a n i c coolant.

from

R e v i e w of t h e reactor

d e s i g n i n d i c a t e d that c o o l i n g of the reactor s h o u l d h a v e b e e n m o r e t h a n

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

46

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 d e q u a t e i f the coolant flowed u n i f o r m l y to a l l parts of the reactor.

The

f a i l u r e was a t t r i b u t e d to a c o m b i n a t i o n of the c o n d i t i o n s discussed b e l o w . B y p a s s i n g of t h e c o o l a n t t h r o u g h the a n n u l a r space b e t w e e n tubes a n d baffles w a s c a u s e d b y t i g h t t u b e p i t c h , close baffle s p a c i n g , a n d s m a l l w i n d o w area, a n d this r o b b e d the far side of the reactor of coolant.

By-

p a s s i n g i n this m a n n e r w a s the o n l y w a y i n w h i c h flow c o u l d h a v e b e e n m a i n t a i n e d f o l l o w i n g h e a v y c a r b o n d e p o s i t i o n . It is l i k e l y that b y p a s s i n g r e s u l t e d i n o v e r h e a t i n g m o r e t h a n h a l f of the reactor, c a u s i n g c a r b o n i z a -

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t i o n of the coolant a n d subsequent t u b e f a i l u r e . A

v a p o r l o c k i n the reactor c o u l d h a v e p r e v e n t e d l i q u i d

phase

c o o l i n g near the t o p of the reactor. O r g a n i c heat transfer fluids u n d e r g o some d e g r a d a t i o n w i t h use, l e a d i n g to the f o r m a t i o n of m o r e v o l a t i l e compounds

or to p o l y m e r i z a t i o n , f o r m i n g h i g h e r b o i l i n g

compounds.

T h r o u g h o u t the p i l o t p l a n t o p e r a t i o n there was n o t i c e a b l e f o r m a t i o n of " l o w b o i l e r s / ' W h i l e these w e r e a u t o m a t i c a l l y v e n t e d f r o m t h e system, there is some e v i d e n c e that v e n t i n g w a s not adequate. A f t e r a t h o r o u g h r e v i e w of possible alternatives, w e d e c i d e d that b o i l i n g m e d i a heat r e m o v a l w a s c o n c e p t u a l l y a better c h o i c e for r e a c t i o n system.

T h e b o i l i n g heat transfer coefficient

our

is several times

greater t h a n the l i q u i d film coefficient, so i t is advantageous to use t h e b o i l i n g m e d i a over

as m u c h of

the reactor l e n g t h as possible.

An

extensive l a b o r a t o r y scale test p r o g r a m g e n e r a t e d heat transfer d a t a to c o n f i r m that e x p e c t e d heat fluxes are l o w e n o u g h t o p r e v e n t t r a n s i t i o n f r o m n u c l e a t e to film b o i l i n g . T h i s t r a n s i t i o n c o u l d cause v a p o r b l a n k e t i n g of the tubes a n d possible t u b e f a i l u r e . B a s e d o n the results of this p r o g r a m , a n e w p r i m a r y reactor has b e e n d e s i g n e d a n d i n s t a l l e d at E l Paso.

10 tons

of

s u l f u r / d a y w h e n u s i n g p u r e s u l f u r d i o x i d e feed a n d 7.8 t o n s / d a y

T h i s reactor p r o d u c e s

on

1 2 % s u l f u r d i o x i d e f e e d gas. O p e r a t i o n was r e s u m e d at E l Paso o n O c t o b e r 28, 1973, u s i n g a 1 2 % s u l f u r d i o x i d e f e e d gas.

O n l y m i n o r o p e r a t i o n a l difficulties h a v e

e n c o u n t e r e d to d a t e w i t h this feed.

been

H o w e v e r , c u r t a i l e d n a t u r a l gas use

f o r c e d s h u t d o w n of the p l a n t o n several occasions. T h e f u t u r e a v a i l a b i l i t y of n a t u r a l gas for i n d u s t r i a l use c o u l d l i m i t a p p l i c a t i o n of the A S A R C O s u l f u r d i o x i d e r e d u c t i o n process.

It is p r o b a b l e that a s u i t a b l e r e d u c i n g

gas c a n be generated u s i n g other fossil fuels, a l t h o u g h this a l t e r n a t i v e has yet to b e p r o v e d . B a s e d o n the l a b o r a t o r y w o r k discussed a b o v e , a s o m e w h a t different catalyst w a s specified for this p i l o t r u n . T h e r e is e v i d e n c e that the r a t e o f catalyst d e c r e p i t a t i o n has b e e n decreased.

T h e catalyst d e c r e p i t a t i o n

p r o b l e m w i l l b e c o n c l u s i v e l y r e s o l v e d t h r o u g h l o n g e r t e r m o p e r a t i o n of the plant.

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

3.

H E N D E R S O N

A N D

Costs of the Pilot

Elemental

PFEiFFER

Sulfur Pilot

47

Phnt

Plant

T h e c a p i t a l cost of t h e A S A R C O - P h e l p s D o d g e p i l o t p l a n t w a s $1,610,000.

A n o t h e r $1,300,000 has b e e n b u d g e t e d f o r o p e r a t i o n .

Many

questions w i l l b e a n s w e r e d b y t h e o p e r a t i o n o f this p l a n t , i n c l u d i n g s u c h cost-related questions as catalyst l i f e f o r t h e d i f f e r i n g m o d e s of o p e r a t i o n . I n terms of c a p i t a l cost, i t is e s t i m a t e d that a p l a n t c a p a b l e of r e d u c i n g p u r e s u l f u r d i o x i d e gas to p r o d u c e 200 tons of e l e m e n t a l s u l f u r / d a y c a n be c o n s t r u c t e d f o r a p p r o x i m a t e l y $10,000,000.

A l l o w i n g f o r t h e cost of

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c o n n e c t i n g flues, t h e r e q u i r e d h i g h l y efficient gas c l e a n i n g

equipment,

a n d a p l a n t f o r a b s o r b i n g a n d c o n c e n t r a t i n g t h e s u l f u r d i o x i d e , s u c h as a p l a n t u s i n g t h e A S A R C O d i m e t h y l a n i l i n e process, i t also has b e e n estim a t e d that the o v e r a l l c a p i t a l r e q u i r e m e n t f o r facilities c a p a b l e of recoveri n g 2 0 0 s h o r t - t o n s / d a y of e l e m e n t a l s u l f u r f r o m c o p p e r converter gases w o u l d b e about $30,000,000.

D i r e c t o p e r a t i n g cost o f s u c h a p l a n t is

e s t i m a t e d at $ 3 0 - 3 5 / s h o r t - t o n o f sulfur, d e p e n d i n g o n f u e l costs.

These

estimates a r e b a s e d o n 1972 c o n s t r u c t i o n a n d o p e r a t i n g l a b o r costs a n d m u s t b e v i e w e d as b u d g e t a r y estimates o n l y , b a s e d o n i n c o m p l e t e p i l o t p l a n t e v a l u a t i o n of t h e process. Literature

Cited

1. Kuzell, C. R., Fowler, M . G . , Klein, L . , Davis, J. H . , Jr., U.S. Patent #3,071,454 (Jan. 1, 1963). R E C E I V E D A p r i l 4, 1974. Certain process details and specific laboratory and pilot data have been omitted from this discussion of the A S A R C O sulfur dioxide reduction process because of their proprietary nature.

American Chemical Society Library 1155 16th St. N. W. Washington, D. C. 20036 In Sulfur Removal and Recovery; Pfeiffer, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.