REGENERATIVE RECOVERY OF SULFUR DIOXIDE FROM EFFLUENT GASES

• US 20120107209A1
• Filed: 10/28/2011
• Published: 05/03/2012
• Est. Priority Date: 10/29/2010
• Status: Active Grant

• Current Assignee: MECS, Inc. (DuPont de Nemours, Inc.)
• Original Assignee: MECS, Inc. (DuPont de Nemours, Inc.)
• Inventors: VERA-CASTANEDA, ERNESTO
• Granted Patent: US 10,272,380 B2
• Time in Patent Office: Days
• US Class Current: 423/242.2
• 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, 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; and

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

3. The process of claim 1 further comprising recovering sulfur dioxide from the aqueous sulfur dioxide-enriched absorption solution wherein

immediately following the step of heating the sulfur dioxide-enriched absorption solution in the sulfur dioxide stripper producing a regenerated sulfur dioxide absorption solution and a 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

cooling the sulfur dioxide-enriched stripper gas in a high temperature overhead condenser of the sulfur dioxide stripper to condense water vapor and produce a high temperature overhead condenser gas effluent comprising sulfur dioxide and water vapor and an aqueous condensate comprising sulfur dioxide;

heating the regenerated sulfur dioxide absorption solution in a reboiler of the sulfur dioxide stripper, wherein the high temperature overhead condenser comprises a heat pump system evaporator in which a refrigerant is evaporated upon heat transfer from the sulfur dioxide-enriched stripper gas and the reboiler of the sulfur dioxide stripper comprises a heat pump system condenser in which the refrigerant is condensed upon heat transfer to the regenerated sulfur dioxide absorption solution and wherein the regenerated sulfur dioxide absorption solution is heated to a temperature not greater than about 20°

C. in excess of the temperature of the aqueous condensate;

heating the aqueous condensate from the high temperature overhead condenser 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 high temperature overhead condenser 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 high temperature overhead condenser gas effluent and a stripped condensate effluent depleted in sulfur dioxide.

4. The process of claim 1 further comprising recovering sulfur dioxide from the aqueous sulfur dioxide-enriched absorption solution wherein

immediately following the step of heating the sulfur dioxide-enriched absorption solution in the sulfur dioxide stripper producing a regenerated sulfur dioxide absorption solution and a 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.

11. The process as set forth in any one of claims 1, 2 or 7 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.

12. The process as set forth in claim 11 wherein the temperature of the effluent gas is not reduced to below about 50°

C.

13. The process as set forth in any one of claims 1, 2 or 7 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.

14. The process of claim 1 or 2 further comprising prior to reintroducing the regenerated sulfur dioxide absorption solution to the sulfur dioxide absorber, treating a slip stream of the regenerated sulfur dioxide absorption solution wherein the treating process comprises:

diverting at least a portion of the regenerated 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; and

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

15. The process as set forth in claim 14 wherein water is evaporated from the slip stream of the regenerated sulfur dioxide absorption solution at a temperature of at least about 60°

C.

16. The process as set forth in claim 14 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).

17. The process as set forth in claim 15 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).

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

5. The process of claim 2 further comprising recovering sulfur dioxide from the aqueous sulfur dioxide-enriched absorption solution wherein

immediately following the step of heating the sulfur dioxide-enriched absorption solution in the sulfur dioxide stripper producing a regenerated sulfur dioxide absorption solution and a 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

cooling the sulfur dioxide-enriched stripper gas in a high temperature overhead condenser of the sulfur dioxide stripper to condense water vapor and produce a high temperature overhead condenser gas effluent comprising sulfur dioxide and water vapor and an aqueous condensate comprising sulfur dioxide;

heating the regenerated sulfur dioxide absorption solution in a reboiler of the sulfur dioxide stripper, wherein the high temperature overhead condenser comprises a heat pump system evaporator in which a refrigerant is evaporated upon heat transfer from the sulfur dioxide-enriched stripper gas and the reboiler of the sulfur dioxide stripper comprises a heat pump system condenser in which the refrigerant is condensed upon heat transfer to the regenerated sulfur dioxide absorption solution and wherein the regenerated sulfur dioxide absorption solution is heated to a temperature not greater than about 20°

C. in excess of the temperature of the aqueous condensate;

heating the aqueous condensate from the high temperature overhead condenser 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 high temperature overhead condenser 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 high temperature overhead condenser gas effluent and a stripped condensate effluent depleted in sulfur dioxide.

6. The process of claim 2 further comprising recovering sulfur dioxide from the aqueous sulfur dioxide-enriched absorption solution wherein

immediately following the step of heating the sulfur dioxide-enriched absorption solution in the sulfur dioxide stripper producing a regenerated sulfur dioxide absorption solution and a 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.

8. The process set forth in any one of claims 2, 5, 6, or 7 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.

9. The process of claim 8 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.

10. The process as set forth in claim 8 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.

7. A process for simultaneous removal of sulfur dioxide and NO_x from a effluent gas and recovering sulfur dioxide, the process comprising:

contacting a sulfur dioxide-containing effluent gas, which comprises NO_x, with a buffered aqueous absorption solution comprising a salt of a polyprotic carboxylic acid, ascorbic acid and a metal chelate (metal complex) comprising a chelating agent and a metal cation in an absorber, thereby absorbing sulfur dioxide and NO_x from the effluent gas into the absorption solution and producing an exhaust gas from which sulfur dioxide and NO_x has been removed and an absorption solution enriched in sulfur dioxide and NO_x and comprising bisulfite anion;

reducing NO_x absorbed in the absorption solution to form nitrogen and bisulfate anion;

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

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