Method and apparatus for adjustably treating a sour gas

1. A method for treating a feed gas, comprising CO 2 , H 2 S and H 2 , to produce an H 2 -enriched product and an H 2 S-lean, CO 2 product, the method comprising:

separating the feed gas by pressure swing adsorption to form a stream of H 2 -enriched product gas and a stream of sour gas, the sour gas also comprising CO 2 , H 2 S and H 2 but being depleted in H 2 and enriched in H 2 S and CO 2 relative to the feed gas;

dividing the stream of sour gas into two parts;

processing one part of said stream of sour gas in an H 2 S removal system to form one or more streams of sweetened gas, depleted in H 2 S and enriched in CO 2 relative to the feed gas;

bypassing the H 2 S removal system with the other part of said stream of sour gas; and

combining said stream(s) of sweetened gas with said sour gas bypassing the H 2 S removal system to form a stream of H 2 S-lean, CO 2 product gas;

wherein the division of the sour gas between being sent to and processed in the H 2 S removal system and bypassing said system is adjusted responsive to changes in the H 2 S content of the sour gas, such that the proportion of the sour gas processed in the H 2 S removal system, as compared to bypassing said system, is increased if the H 2 S content rises and decreased if the H 2 S content drops.

2. The method of claim 1 , wherein the feed gas has an H 2 S concentration of from about 50 ppm to about 3 mole %.

3. The method of claim 1 , wherein the feed gas is a sour syngas mixture, comprising CO 2 , H 2 S, H 2 and CO, obtained from gasifying or reforming carbonaceous feedstock.

4. The method of claim 1 , wherein the H 2 -enriched product gas comprises at least about 90 mole % H 2 or a mixture of H 2 and CO, and is free or substantially free of H 2 S.

5. The method of claim 1 , wherein the sour gas comprises less than about 6 mole % H 2 S.

6. The method of claim 1 , wherein the or each stream of sweetened gas is free or substantially free of H 2 S.

7. The method of claim 1 , wherein the H 2 S-lean, CO 2 product gas contains at most about 200 ppm H 2 S.

8. The method of claim 1 , wherein the method further comprises separating the stream of H 2 S-lean, CO 2 product gas to form an H 2 S-lean, H 2 -lean, CO 2 product and a second H 2 -enriched gas.

9. The method of claim 8 , wherein the H 2 S-lean, CO 2 product gas is separated by partial condensation or membrane separation.

10. The method of claim 1 , wherein the H 2 S removal system comprises an adsorption system comprising one or more beds of adsorbent selective for H 2 S, and the processing of sour gas in the H 2 S removal system comprises passing sour gas through said beds of adsorbent to adsorb H 2 S therefrom and form said or one of said stream(s) of sweetened gas.

11. The method of claim 1 , wherein the H 2 S removal system comprises a system for converting H 2 S to elemental sulfur, the processing of sour gas in the H 2 S removal system comprising contacting sour gas with a reagent to convert H 2 S to elemental sulfur and form said or one of said stream(s) of sweetened gas.

12. The method of claim 11 , wherein the sour gas contains, in addition to H 2 S, one or more other sulfur containing species, and wherein the method further comprises treating a portion or all of said sour gas to be processed in the H 2 S to elemental sulfur conversion system to convert one or more of said sulfur containing species to H 2 S prior to said sour gas being processed in said conversion system.

13. The method of claim 1 , wherein the H 2 S removal system comprises a combustion system, and the processing of sour gas in the H 2 S removal system comprises combusting sour gas in the presence of O 2 to produce heat and a combustion effluent depleted in H 2 S and H 2 and comprising CO 2 , SO x and H 2 O, SO x being removed from said combustion effluent to form said or one of said stream(s) of sweetened gas.

14. The method of claim 13 , wherein the combustion system is an oxy-fuel combustion system.

15. The method of claim 13 , wherein the method further comprises passing the combustion effluent through a heat exchanger to recover heat therefrom via indirect heat exchange.

16. The method of claim 13 , wherein SO x is removed from said combustion effluent by cooling the combustion effluent to condense out water and convert SO 3 to sulfuric acid, and maintaining the cooled combustion effluent at elevated pressure(s), in the presence of O 2 , water and optionally NO x , for a sufficient time to convert SO 2 to sulfurous acid and/or SO 2 to sulfuric acid and NO x to nitric acid.

17. The method of claim 1 , wherein the H 2 S removal system comprises both a combustion system and a system for converting H 2 S to elemental sulfur via reaction with SO 2 , sulfuric acid and/or sulfurous acid, and wherein the sour gas to be processed in the H 2 S removal system is divided into two streams, said processing comprising:

contacting, in the H 2 S to elemental sulfur conversion system, a stream of sour gas with SO 2 , sulfuric acid and/or sulfurous acid to convert H 2 S to elemental sulfur and form said stream or one of said streams of sweetened gas; and

combusting, in the combustion system, another stream of sour gas in the presence of O 2 to produce heat and a combustion effluent depleted in H 2 S and H 2 and comprising CO 2 , SO x and H 2 O, and: (i) introducing at least a portion of the combustion effluent, or an SO 2 -enriched stream separated from the combustion effluent, into the H 2 S to elemental sulfur conversion system to provide at least a portion of said SO 2 for the reaction with H 2 S; and/or (ii) converting SO x in the combustion effluent to sulfuric and/or sulfurous acid, and introducing at least a portion of said acid into the H 2 S to elemental sulfur conversion system to provide at least a portion of said acid for the reaction with H 2 S.

18. The method of claim 17 , wherein the H 2 S to elemental sulfur conversion system converts H 2 S to elemental sulfur via reaction with SO 2 , and at least a portion of the combustion effluent, or an SO 2 -enriched stream separated from the combustion effluent, is introduced into said conversion system to provide at least a portion of said SO 2 for the reaction with H 2 S.

19. The method of claim 18 , wherein the combustion effluent is divided into two streams thereof, one of which is introduced into said conversion system to provide at least a portion of said SO 2 for the reaction with H 2 S, and the other of which forms a second of said streams of sweetened gas.

20. The method of claim 18 , wherein the combustion effluent is separated to form an SO 2 -enriched stream and an SO 2 -depleted stream, the SO 2 -enriched stream is introduced into said conversion system to provide at least a portion of said SO 2 for the reaction with H 2 S, and the SO 2 -depleted stream forms a second of said streams of sweetened gas.

21. The method of claim 17 , wherein the H 2 S to elemental sulfur conversion system converts H 2 S to elemental sulfur via reaction with sulfuric and/or sulfurous acid, SO x in the combustion effluent is converted to sulfuric and/or sulfurous acid, and at least a portion of said acid is introduced into said conversion system to provide at least a portion of said acid for the reaction with H 2 S.

22. The method of claim 21 , wherein SO x in the combustion effluent is converted to sulfuric or sulfuric and sulfurous acid by cooling the combustion effluent to condense out water and convert SO 3 to sulfuric acid, and maintaining the cooled combustion effluent, at elevated pressure(s) in the presence of O 2 , water and optionally NO x , for a sufficient time to convert SO 2 to sulfurous acid and/or SO 2 to sulfuric acid and NO x to nitric acid.

23. The method of claim 21 , wherein the SO x -depleted combustion effluent forms a second of said streams of sweetened gas.