Process for treating acid gas in staged furnaces with inter-stage heat recovery
View Patent ↗A process for treating acid gas comprising hydrogen sulfide comprises introducing a first acid gas into a reducing furnace to produce a first oxidized gas stream, cooling the first oxidized gas stream in a first heat recovery system, introducing the cooled gas stream into an oxidizing furnace to produce a second oxidized gas stream and cooling the second oxidized gas stream in a second heat recovery system. The acid gas is preferably produced in a refinery after treatment of sour gas or sour water. Spent acid may be fed into oxidizing furnace as part of a sulfuric acid recovery process. The spent acid can be spent sulfuric acid from a sulfuric acid alkylation process.
1. A process for treating an acid gas comprising hydrogen sulfide which comprises:
(a) introducing a first acid gas, which comprises hydrogen sulfide and a first oxygen-containing gas into a reducing furnace producing a first oxidized gas stream, wherein the temperature of the reducing furnace is in the range of 1100° C. to 1350° C., and wherein the amount of oxygen-containing gas in the reducing furnace is about 30-50% of the stoichiometric amount for oxidation of all of the sulfur-containing compounds to SO 2 and all of the carbon-containing compounds to CO 2 ;
(b) introducing the first oxidized gas stream into a first heat recovery system wherein the stream is cooled and heat is recovered therefrom;
(c) introducing the cooled first oxidized gas stream and a second oxygen-containing gas, into an oxidizing furnace, which comprises a burner and a chamber, producing a second oxidized gas stream, wherein the temperature of the oxidizing furnace is in the range of 950° C. to 1100° C. and wherein the amount of oxygen in the second oxygen-containing gas is greater than the stoichiometric amount required for complete combustion; and
(d) introducing the second oxidized gas stream into a second heat recovery system; wherein the second oxidized gas stream is cooled and heat is recovered therefrom.
2. The process of claim 1 wherein one or more of (i) a second supplemental fuel; (ii) spent acid, which comprises sulfuric acid, and (iii) water are introduced into the oxidizing furnace in step (c).
3. The process of claim 2 wherein the spent acid is a dilute acid stream produced in a sulfuric acid alkylation process, nitration spent acid, methyl methacrylate waste acid, or caprolactam spent acid.
4. The process of claim 3 wherein the spent acid is a dilute acid stream produced in a sulfuric acid alkylation process.
5. The process of claim 2 further comprising in step (c) introducing quench water into the oxidizing furnace.
6. The process of claim 1 wherein step (c) further comprises introducing spent acid into the oxidizing furnace.
7. The process of claim 3 further comprising treating the cooled second oxidized gas stream in a spent acid recovery plant to produce sulfuric acid.
8. The process of claim 1 wherein the acid gas is solvent-treated acid gas, sour water stripper gas, or a combination thereof.
9. The process of claim 1 wherein a first supplemental fuel is introduced into the reducing furnace in step (a).
10. The process of claim 1 wherein a second supplemental fuel is introduced into the oxidizing furnace in step (c).
11. The process of claim 10 wherein the second supplemental fuel is an ammonia-free acid gas.
12. The process of claim 1 wherein each of the first heat recovery system and the second heat recovery system is a waste heat boiler or a process-to-process heat exchanger.
13. The process of claim 12 wherein each of the first heat recovery system and the second heat recovery system is a waste heat boiler.
14. The process of claim 1 wherein a portion of the cooled first oxidized gas stream is introduced into the burner of the oxidizing furnace.
15. A combustion process in a spent acid recovery plant comprising:
(a) introducing a first acid gas and a first oxygen-containing gas, into a reducing furnace producing a first oxidized gas stream, wherein the temperature of the reducing furnace is in the range of 1100° C. to 1350° C., and wherein the amount of first oxygen-containing gas in the reducing furnace is about 30-50% of the stoichiometric amount for oxidation of all of the sulfur-containing compounds to SO 2 and all of the carbon-containing compounds to CO 2 ;
(b) introducing the first oxidized gas stream into a first heat recovery system wherein the first oxidized gas stream is cooled and heat is recovered therefrom;
(c) introducing the cooled first oxidized gas stream, a second oxygen-containing gas, and spent acid comprising sulfuric acid, into an oxidizing furnace, which comprises a burner and a chamber, producing a second oxidized gas stream, wherein the temperature of the oxidizing furnace is in the range of 950° C. to 1100° C. and wherein the amount of oxygen in the second oxygen-containing gas is greater than the stoichiometric amount required for complete combustion;
(d) introducing the second oxidized gas stream into a second heat recovery system; wherein the second oxidized gas stream is cooled and heat is recovered therefrom; and
(e) treating the cooled second oxidized gas stream in a spent acid recovery plant to produce sulfuric acid.
16. The process of claim 15 wherein one or both of (i) a second supplemental fuel and (ii) water, are introduced into the oxidizing furnace in step (c).
17. The process of claim 16 wherein the first acid gas comprises solvent-treated gas and sour water stripper gas.
18. The process of claim 16 wherein a supplemental fuel is introduced into the oxidizing furnace in step (c).
19. The process of claim 18 wherein the supplemental fuel is an ammonia-free acid gas.
20. The process of claim 16 wherein the spent acid is a dilute acid stream produced in a sulfuric acid alkylation process.
21. The process of claim 20 further comprising treating the cooled second oxidized gas stream in a spent acid recovery plant to produce sulfuric acid.