Process of removing pollutants from exhaust gases

• US 4,670,237 A
• Filed: 02/26/1986
• Issued: 06/02/1987
• Est. Priority Date: 06/21/1983
• Status: Expired due to Fees

• Current Assignee: Metallgesellschaft AG (GEA Group AG)
• Original Assignee: Metallgesellschaft AG (GEA Group AG)
• Inventors: Schroter, Michael, Graf, Rolf, Reh, Lothar
• Primary Examiner(s): HELLER, GREGORY
• Application Number:
  US06/834,498
• Time in Patent Office: 461 Days
• Field of Search: 423/242 A, 423/242 R, 423/244 A, 423/244 R, 423/210, 423/240 R, 423/242 S
• US Class Current: 423/244.07
• CPC Class Codes: B01D 53/501 by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• CPC Class Codes: B01D 53/508 by treating the gases with solids

Abstract

In a process of removing pollutants consisting substantially of sulfur oxides from exhaust gases at temperatures below 150° C. by means of a sorbent which contains calcium carbonate, calcium oxide and/or calcium hydroxide and which is included in a circulating fluidized bed system consisting of a fluidized bed reactor, a separator and a return line, a complete utilization of the sorbent is achieved in that a partial stream of laden sorbent is withdrawn from the circulating fluidized bed and is subjected at a temperature of 600° to 1200° C. to an oxidizing treatment, a major part of the sorbent that has been subjected to an oxidizing treatment is recycled to the circulating fluidized bed, and a partial stream which contains the sorbent mainly in the form of calcium sulfate is removed from the process. Fresh sorbent is supplied to the circulating fluidized bed and/or to the stage for the oxidizing treatment at the rate at which said partial stream is removed from the process.

Claims

1. A process of removing pollutants consisting substantially of sulfur oxides from an exhaust gas comprising:

introducing the exhaust gas at a temperature below 150°

C. into a circulating fluidized bed system consisting of a fluidized bed reactor, a separator and a return line;

introducing a calcium compound containing sorbent into the fluidized bed reactor for intimate contact with the flue gases to produce a laden sorbent;

withdrawing a partial stream of said laden sorbent from the circulating fluidized bed and subjecting the partial stream to an oxidizing treatment at a temperature of 600°

to 1200°

C. to generate said sorbent;

recycling a predominate part of the sorbent which has been subjected to the oxidizing treatment to the circulating fluidized bed;

removing a partial stream which contains the used sorbent mainly in the form of calcium sulfate from the process; and

introducing fresh sorbent into the process, at a rate corresponding to the rate at which used sorbent is removed from the process.

2. The process of claim 1, wherein the sorbent is calcium carbonate, calcium oxide, calcium hydroxide or mixtures thereof.

3. The process of claim 2, wherein the oxidizing treatment is carried out in a fluidized bed, preferably in a circulating fluidized bed.

4. The process of claim 2, wherein the oxidizing treatment of the withdrawn partial stream of sorbent is effected at a temperature in the range of 800°

to 1000°

C.

5. The process of claim 2, wherein the sorbent that has been subjected to the oxidizing treatment for recycle is activated by a direct injection of water.

6. The process of claim 2, wherein the sorbent is preheated with the exhaust gases from the oxidizing treatment.

7. The process of claim 2, wherein the exhaust gas contains fine dust which is removed, preferably by means of an electrostatic precipitator before said exhaust gas is introduced into said circulating fluidized bed.

8. The process of claim 2, wherein gases exhausted from the oxidizing treatment pass through a plurality of suspension heat exchanger stages and are treated with water or milk of lime in the last suspension heat exchanger stage for separation of heavy metals or a combination with halides.

9. The process of claim 2, wherein the sorbent, which has been withdrawn from the oxidizing treatment, is cooled.

10. The process of claim 9, wherein the sorbent is cooled in conjunction with preheating of sorbent to be introduced in the fluidized bed reactor.

11. The process of claim 9, wherein the sorbent is cooled in conjunction with preheating of air to be introduced into the fluidized bed reactor.

12. The process of claim 9, wherein the cooled sorbent is subjected to a classifying treatment.

13. The process of claim 2, wherein exhaust gases of the fluidized bed reactor contain entrained sorbent which is separated as a fine grain fraction in a classification treatment and which fine grain fraction is fed with preference to the stage for the oxidizing treatment.

14. The process of claim 2, wherein the laden sorbent containing CaCO₃ and the withdrawn partial stream is subjected to the oxidizing treatment to generate said sorbent with release of chemically bound carbon dioxide.

15. The process of claim 14, wherein the partial stream of laden sorbent contains sulfite which is oxidized to sulfate in said oxidizing treatment.

16. The process of claim 1, wherein the fresh sorbent is introduced into the stage in which the oxidizing treatment is carried out.

17. The process of claim 1, wherein the fresh sorbent is introduced into the circulating fluidized bed.

18. A process of removing pollutants consisting substantially of sulfur oxides from a CO₂ containing exhaust gas comprising:

introducing the exhaust gas at a temperature below 150°

C. into a circulating fluidized bed system consisting of a fluidized bed reactor, a separator and a return line;

introducing a calcium compound containing sorbent into the fluidized bed reactor for intimate contact with the flue gases to produce a laden sorbent;

withdrawing a partial stream of said laden sorbent from the circulating fluidized bed and subjecting the partial stream to an oxidizing treatment at a temperature of 600°

to 1200°

C. to generate said sorbent by decomposition of CaCO₃ formed in a side reaction with CO₂ of the exhaust gas;

recycling a predominate part of the sorbent which has been subjected to the oxidizing treatment to the circulating fluidized bed;

removing a partial stream which contains the used sorbent mainly in the form of calcium sulfate from the process; and

introducing fresh sorbent into the process, at a rate corresponding to the rate at which used sorbent is removed from the process.