Thermodynamics of Aqueous Systems with Industrial Applications

this paper focuses on sulfur control technologies due to the potentially .... to 1 ppm level. Yes, down to 4 ppm. Organic Sulfur. COS , CS 2 , some me...
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2 A Survey of Some Industrial Waste Treatment Processes W. T. ATKINS, W. H . SEWARD, and H . J. T A K A C H

Downloaded by UNIV QUEENSLAND on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch002

Mittelhauser Corporation, Downers Grove, IL 60515

This paper was prepared to give a brief overview of some of the technologies used for industrial pollution control. Among the many areas of possible discussion under this broad a topic, this paper focuses on sulfur control technologies due to the potentially major cost impact of these technologies on the indus­ trial processes with which they are associated. The process areas covered are acid gas removal, sulfur recovery, sulfur dioxide removal, and wastewater treating. In the first three process areas, alternative process types are described and guide­ lines for process selection are briefly reviewed. Because of the operating difficulties encountered with utility sulfur dioxide removal processes, information on industrial installation of these processes is given. For wastewater treating, a state-of­ -the-art industrial wastewater treatment system is discussed along with some major items to consider in process selection. Acid Gas Removal Acid gas removal is the removal of sulfur compounds and CO2 (acid gas) from process gas streams. The following sections describe available process alternatives, design options, and guidelines for selection among alternatives. Process A l t e r n a t i v e s . A c i d gas removal processes have been e x t e n s i v e l y surveyed i n the p u b l i s h e d l i t e r a t u r e (1,8.,3) . F i g u r e 1 shows how acid-gas-bearing process gases can be genera l l y t r e a t e d i n i n d u s t r i a l processes. The s u l f u r compounds and CO2 may be absorbed i n a l i q u i d medium, such as amines, a l k a l i s a l t s (NaOH, K C 0 ) , p h y s i c a l s o l v e n t s (methanol, propylene carbonate), or water (3). The absorbed a c i d gases are r e l e a s e d by r e d u c t i o n of pressure and/or by a p p l i c a t i o n o f heat. A l t e r n a t i v e l y , the H 2 S and CO2 may chemically combine w i t h the absorbent (as i n NaOH scrubbing) to form s a l t s which are removed i n a l i q u i d treatment u n i t . This r e q u i r e s c o n t i n u a l and expensive makeup of sodium t o the system. 2

3

0-8412-0569-8/80/47-133-015$08.25/0 © 1980 American Chemical Society

In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

IN

RICH

ON

LIQUID

LEAN

(IN

PLACE)

REGENERATION

HAS

ACID

SULFUR

SULFUR

TREATMENT

LIQUID

RECOVERY

GAS

PROCESS

Schematic of acid gas removal process alternatives

SOLID

SOLID

LIQUID

ACID-GAS

REGENERATION

ACID-GAS RICH SOLID

LEAN

Figure 1.

SOLID

LIQUID

ACID-GAS

ADSORPTION

LIQUID

ABSORPTION

TREATED

Downloaded by UNIV QUEENSLAND on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch002

ACID

RECYCLE

SOLID

WASTE

LIQUID

OR

EFFLUENT

SULFUR

SULFURIC

2.

ATKINS E T A L .

17

Industrial Waste Treatment Processes

Released a c i d gases i n the same form as captured, i . e . , H S, COS, C 0 , e t c . a r e converted i n the s u l f u r recovery u n i t t o forms i n which they may be exported from the i n d u s t r i a l f a c i l i t y . S u l f u r recovery i s d i s c u s s e d l a t e r i n the paper. Some l i q u i d a b s o r p t i o n processes produce two separate a c i d gas streams ( s e l e c t i v e AGR). One stream, c o n t a i n i n g the m a j o r i t y of s u l f u r compounds, i s sent to the s u l f u r recovery u n i t , w h i l e the other i s vented t o atmosphere, environmental r e g u l a t i o n s p e r m i t t i n g . Alkanolamines, g e n e r a l l y r e f e r r e d to as amines, a r e organic compounds of the form H -N-(ROH) 3- (3) ' > h y d r o x y l group g e n e r a l l y provides f o r the compounds s o l u b i l i t y i n water, w h i l e the HN group provides the a l k a l i n i t y i n water s o l u t i o n s to cause the a b s o r p t i o n of a c i d gases. Amine processes used commercially are shown i n Table I . These compounds a r e chemical s o l v e n t s ; they combine c h e m i c a l l y w i t h H S, C 0 , and other s u l f u r compounds. They a r e c u s t o m a r i l y regenerated by the a p p l i c a t i o n of heat. A l k a l i s a l t s o l u t i o n s a r e aqueous s o l u t i o n s of sodium o r potassium s a l t s . They, too, a r e chemical s o l v e n t s , r e a c t i n g w i t h H S and C 0 as f o l l o w s (e.g., f o r K C 0 ) : 2

2

t

n

n

e

n

Downloaded by UNIV QUEENSLAND on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch002

1

2

2

2

2

2

3

K C0

3

+ C 0 + H 0 + 2KHC0

K C0

3

+ H S -> KHS + KHC0

2

2

2

2

2

3

3

This s o l u t i o n i s regenerated by pressure letdown and steam s t r i p ping of the s o l u t i o n (2_) . The p h y s i c a l s o l v e n t s shown i n Table I operate by d i s s o l v i n g the a c i d gases i n the absorbing medium a t e l e v a t e d pressures and low temperatures. Regeneration of the s o l v e n t i s p r i n c i p a l l y by r e d u c t i o n of p r e s s u r e , although h e a t i n g i s o f t e n necessary i n h i g h - e f f i c i e n c y a p p l i c a t i o n s , where H S i s t o be removed to a few ppmv ( 3 ) . Mixed s o l v e n t s a r e combinations of p h y s i c a l and chemical s o l v e n t s which i n c r e a s e the f l e x i b i l i t y of t r e a t i n g ( 1 ) . The chemical s o l v e n t a l l o w s f o r treatment of lower-pressure streams w h i l e the p h y s i c a l s o l v e n t a l l o w s f o r bulk removal of the a c i d gas. A b s o r p t i o n - o x i d a t i o n processes o x i d i z e absorbed H S d i r e c t l y to elemental s u l f u r i n s o l u t i o n ( 1 ) . The p r i n c i p a l example i n c u r r e n t i n d u s t r i a l use i s the S t r e t f o r d process (3)· The chemist r y of the process can be represented by the f o l l o w i n g i d e a l i z e d equations (ADA represents anthraquinone d i s u l f o n i c a c i d ) : 2

2

Na C0 2

3

+ H S + NaHS + NaHC0 2

3

4 NaV0 + 2 NaHS + H 0 + Na Vi,09 + 2S + 4 NaOH 3

Na Vi 0 2

t

9

2

2

+ 2 NaOH + H 0 + 2 ADA + 4 NaV0 + 2 ADA (reduced) 2

3

2 ADA (reduced) + 0 + 2 ADA + H 0 2

2

In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

18

THERMODYNAMICS O F AQUEOUS SYSTEMS W I T H INDUSTRIAL APPLICATIONS

Table I.

Acid Gas Removal Processes

Principal Absorbent^

Process Name

T y p i c a l Absorber Temperature, °F

Absorber Pressure, psi

Components Removed Organic Sulfur

AMINE PROCESSES

Downloaded by UNIV QUEENSLAND on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch002

Monoethanolamine

Atm-1000; not highly sensitive

Yes, down to 1 ppm level

COS , CS 2 , some mercaptan

Diethanolamine

Atm-1000; not highly sensitive

Yes, down to 4 ppm

COS, CS absorbed r e v e r s i b l y (some mercaptans)

Société National des P e t r o l s d'Aquitaine SNPA-DEA

500-1100; high a c i d gas pressure desirable (