Regenerative recovery of sulfur dioxide from effluent gases

• US 10,272,380 B2
• Filed: 10/28/2011
• Issued: 04/30/2019
• Est. Priority Date: 10/29/2010
• Status: Active Grant

• Current Assignee: MECS, Inc. (DuPont de Nemours, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Vera-Castaneda, Ernesto
• Primary Examiner(s): Davis, Sheng H
• Application Number:
  US13/283,671
• Publication Number:
  US 20120107209A1
• Time in Patent Office: 2,741 Days
• Field of Search: None
• CPC Class Codes: B01D 2251/304 of sodium
• CPC Class Codes: B01D 2251/306 of potassium
• CPC Class Codes: B01D 2257/80 Water
• CPC Class Codes: B01D 53/1425 Regeneration of liquid absorbents
• CPC Class Codes: B01D 53/1481 Removing sulfur dioxide or sulfur trioxide
• CPC Class Codes: B01D 53/507 by treating the gases with other liquids
• CPC Class Codes: B01D 53/60 Simultaneously removing sulfur oxides and nitrogen oxides
• CPC Class Codes: B01D 53/96 Regeneration, reactivation or recycling of reactants
• CPC Class Codes: C01B 17/0408 Pretreatment of the hydrogen sulfide containing gases
• CPC Class Codes: C01B 17/60 Isolation of sulfur dioxide from gases
• CPC Class Codes: C01B 17/96 Methods for the preparation of sulfates in general particular individual sulfates, see the relevant groups of subclasses C01B - C01G, according to the cation
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02P 20/10 Process efficiency
• CPC Class Codes: Y02P 20/129 Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
• CPC Class Codes: Y02P 20/50 Improvements relating to the production of bulk chemicals

Abstract

This invention relates to processes for selective removal of contaminants from effluent gases. A sulfur dioxide absorption/desorption process for selective removal and recovery of sulfur dioxide from effluent gases utilizes a buffered aqueous absorption solution comprising weak inorganic or organic acids or salts thereof, to selectively absorb sulfur dioxide from the effluent gas. Absorbed sulfur dioxide is subsequently stripped to regenerate the absorption solution and produce a sulfur dioxide-enriched gas. A process for simultaneous removal of sulfur dioxide and nitrogen oxides (NO_x) from effluent gases and recovery of sulfur dioxide utilizes a buffered aqueous absorption solution including a metal chelate to absorb sulfur dioxide and NO_x from the gas and subsequently reducing absorbed NO_x to form nitrogen. A process to control sulfate salt contaminant concentration in the absorption solution involves partial crystallization and removal of sulfate salt crystals.

Claims

1. A process for selectively removing and recovering sulfur dioxide from a sulfur dioxide-containing effluent gas, comprising:

contacting the effluent gas comprising the effluent gas and oxygen with a buffered aqueous absorption solution comprising a salt of a polyprotic carboxylic acid and an oxidation inhibitor selected from the group consisting of ascorbic acid, ethylenediaminetetraacetic acid, p-phenylenediamine, hydroquinone and mixtures thereof in a sulfur dioxide absorber, thereby absorbing sulfur dioxide from the effluent gas into the absorption solution and producing an exhaust gas from which sulfur dioxide has been removed and a sulfur dioxide-enriched absorption solution;

heating the sulfur dioxide-enriched absorption solution in a sulfur dioxide stripper to desorb sulfur dioxide and thereby produce a regenerated sulfur dioxide absorption solution and a sulfur dioxide-enriched stripper gas; and

reintroducing the regenerated sulfur dioxide absorption solution to the sulfur dioxide absorber;

immediately following the step of heating the sulfur dioxide-enriched absorption solution in the sulfur dioxide stripper producing the regenerated sulfur dioxide absorption solution and the sulfur dioxide-enriched stripper gas comprising water vapor and before reintroducing the regenerated sulfur dioxide absorption solution to the sulfur dioxide absorber, the process further comprises;

increasing the pressure of the sulfur dioxide-enriched stripper gas;

cooling the pressurized sulfur dioxide-enriched stripper gas by transfer of heat to the regenerated sulfur dioxide absorption solution in a reboiler of the sulfur dioxide stripper to condense water vapor and produce a reboiler gas effluent comprising sulfur dioxide and water vapor and an aqueous condensate comprising sulfur dioxide;

heating the aqueous condensate from the reboiler in a condensate stripper to desorb sulfur dioxide and produce a condensate stripper gas comprising water vapor and sulfur dioxide desorbed from the aqueous condensate; and

cooling the condensate stripper gas and reboiler gas effluent in a low temperature condenser to condense water vapor and produce a recovered sulfur dioxide stream comprising sulfur dioxide obtained in the aqueous condensate and in the reboiler gas effluent and a stripped condensate effluent depleted in sulfur dioxide.

2. The process of claim 1, wherein the aqueous absorption solution comprises a polyprotic carboxylic acid or salt thereof, the polyprotic carboxylic acid or salt thereof being able to undergo a plurality of dissociations each having a pKa value, wherein at least one of the pKa values is between about 3 and about 10 at 25°

C. and the acid or salt thereof in the aqueous absorption solution is neutralized to within about 20% of the equivalence point of the at least one dissociation having a pKa value between about 3 and about 10 at 25°

C.

3. The process of claim 2 wherein the aqueous absorption solution comprises a polyprotic carboxylic acid or salt thereof, the polyprotic carboxylic acid or salt thereof being able to undergo a plurality of dissociations each having a pKa value, wherein at least one of the pKa values is between about 4 and about 7 at 25°

C. and the acid or salt thereof in the aqueous absorption solution is neutralized to within about 20% of the equivalence point of the at least one dissociation having a pKa value between about 4 and about 7 at 25°

C.

4. The process as set forth in claim 2 wherein the aqueous absorption solution comprises a metal salt of malic acid, the metal salt of malic acid in the aqueous absorption solution being neutralized to within about 20% of the equivalence point of the less acidic carboxylic group having a pKa value of about 5.11 at 25°

C.

5. The process as set forth in claim 1 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution without the addition of extraneous heat.

6. The process as set forth in claim 5 wherein the temperature of the effluent gas is not reduced to below about 50°

C.

7. The process as set forth in claim 1 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution and the difference in temperature between the sulfur dioxide absorption solution introduced to the stripper and the regenerated absorption solution is less than about 40°

C.

8. The process of claim 1 wherein the polyprotic carboxylic acid is malic acid.

9. A process for selectively removing and recovering sulfur dioxide from a sulfur dioxide-containing effluent gas, comprising:

contacting the effluent gas comprising the effluent gas and oxygen with a buffered aqueous absorption solution comprising a salt of a polyprotic carboxylic acid and an oxidation inhibitor selected from the group consisting of ascorbic acid, ethylenediaminetetraacetic acid, p-phenylenediamine, hydroquinone and mixtures thereof in a sulfur dioxide absorber, thereby absorbing sulfur dioxide from the effluent gas into the absorption solution and producing an exhaust gas from which sulfur dioxide has been removed and a sulfur dioxide-enriched absorption solution;

heating the sulfur dioxide-enriched absorption solution in a sulfur dioxide stripper to desorb sulfur dioxide and thereby produce a regenerated sulfur dioxide absorption solution and a sulfur dioxide-enriched stripper gas;

diverting at least a portion of the regenerated sulfur dioxide absorption solution exiting the stripper as a slip stream;

evaporating water from the slip stream of the regenerated sulfur dioxide absorption solution at a temperature of at least about 40°

C. to produce a concentrated absorption solution supersaturated in the sulfate salt;

precipitating sulfate salt crystals from the concentrated absorption solution to form a crystallization slurry comprising precipitated sulfate salt crystals and a mother liquor;

separating the sulfate salt crystals from the mother liquor to form a treated absorption solution comprising the polyprotic carboxylic acid salt; and

combining the treated absorption solution with the remainder of the regenerated sulfur dioxide absorption solution, which is reintroduced to the sulfur dioxide absorber.

10. The process as set forth in claim 9 wherein water is evaporated from the slip stream of the regenerated sulfur dioxide absorption solution at a temperature of at least about 60°

C.

11. The process as set forth in claim 10 wherein the sulfate salt crystals precipitated from the concentrated absorption solution comprise sodium sulfate crystals and water is evaporated from the absorption solution under conditions to substantially inhibit formation and precipitation of sodium sulfate decahydrate or Glauber'"'"'s salt (Na₂SO₄.10H₂O).

12. The process as set forth in claim 9 wherein the sulfate salt crystals precipitated from the concentrated absorption solution comprise sodium sulfate crystals and water is evaporated from the absorption solution under conditions to substantially inhibit formation and precipitation of sodium sulfate decahydrate or Glauber'"'"'s salt (Na₂SO₄.10H₂O).

13. The process of claim 9 wherein the polyprotic carboxylic acid is malic acid.

14. The process of claim 9, wherein the aqueous absorption solution comprises a polyprotic carboxylic acid or salt thereof, the polyprotic carboxylic acid or salt thereof being able to undergo a plurality of dissociations each having a pKa value, wherein at least one of the pKa values is between about 3 and about 10 at 25°

C. and the acid or salt thereof in the aqueous absorption solution is neutralized to within about 20% of the equivalence point of the at least one dissociation having a pKa value between about 3 and about 10 at 25°

C.

15. The process of claim 14 wherein the aqueous absorption solution comprises a polyprotic carboxylic acid or salt thereof, the polyprotic carboxylic acid or salt thereof being able to undergo a plurality of dissociations each having a pKa value, wherein at least one of the pKa values is between about 4 and about 7 at 25°

C. and the acid or salt thereof in the aqueous absorption solution is neutralized to within about 20% of the equivalence point of the at least one dissociation having a pKa value between about 4 and about 7 at 25°

C.

16. The process of claim 14 wherein the aqueous absorption solution comprises a metal salt of malic acid, the metal salt of malic acid in the aqueous absorption solution being neutralized to within about 20% of the equivalence point of the less acidic carboxylic group having a pKa value of about 5.11 at 25°

C.

17. The process of claim 9 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution without the addition of extraneous heat.

18. The process of claim 17 wherein the temperature of the effluent gas is not reduced to below about 50°

C.

19. The process of claim 9 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution and the difference in temperature between the sulfur dioxide absorption solution introduced to the stripper and the regenerated absorption solution is less than about 40°

C.

20. A process for selectively removing and recovering sulfur dioxide from a sulfur dioxide-containing effluent gas, the process comprising:

contacting the effluent gas with a buffered aqueous absorption solution comprising sodium malate in a sulfur dioxide absorber, thereby absorbing sulfur dioxide from the effluent gas into the absorption solution and producing an exhaust gas from which sulfur dioxide has been removed and a sulfur dioxide-enriched absorption solution;

heating the sulfur dioxide-enriched absorption solution in a sulfur dioxide stripper to desorb sulfur dioxide and thereby produce a regenerated sulfur dioxide absorption solution and a sulfur dioxide-enriched stripper gas;

diverting at least a portion of the regenerated sulfur dioxide absorption solution exiting the stripper as a slip stream;

evaporating water from the slip stream of the regenerated sulfur dioxide absorption solution at a temperature of at least about 40°

C. to produce a concentrated absorption solution supersaturated in a sulfate salt;

precipitating sulfate salt crystals from the concentrated absorption solution to form a crystallization slurry comprising precipitated sulfate salt crystals and a mother liquor;

separating the sulfate salt crystals from the mother liquor to form a treated absorption solution comprising the sodium malate; and

combining the treated absorption solution with the remainder of the regenerated sulfur dioxide absorption solution, which is reintroduced to the sulfur dioxide absorber.

21. The process as set forth in claim 20 wherein water is evaporated from the slip stream of the regenerated sulfur dioxide absorption solution at a temperature of at least about 60°

C.

22. The process as set forth in claim 20 wherein the sulfate salt crystals precipitated from the concentrated absorption solution comprise sodium sulfate crystals and water is evaporated from the absorption solution under conditions to substantially inhibit formation and precipitation of sodium sulfate decahydrate or Glauber'"'"'s salt (Na₂SO₄·

10H₂O).

23. The process as set forth in claim 21 wherein the sulfate salt crystals precipitated from the concentrated absorption solution comprise sodium sulfate crystals and water is evaporated from the absorption solution under conditions to substantially inhibit formation and precipitation of sodium sulfate decahydrate or Glauber'"'"'s salt (Na₂SO₄·

10H₂O).

24. The process of claim 20 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution without the addition of extraneous heat.

25. The process of claim 24 wherein the temperature of the effluent gas is not reduced to below about 50°

C.

26. The process of claim 20 wherein the sulfur dioxide-enriched absorption solution is heated by transferring heat from the effluent gas and/or regenerated sulfur dioxide absorption solution and the difference in temperature between the sulfur dioxide absorption solution introduced to the stripper and the regenerated absorption solution is less than about 40°

C.