Processes for gas separation by solvent or absorbent
Solvent absorption processes for separating components of an impure feed gas are disclosed. The processes involve two stages of gas purification. The acid gases including hydrogen sulfide, carbon dioxide and other sulfur compounds are simultaneously removed from the feed gas by contact with a physical solvent in two stages. The subject matter disclosed provides improved processes to reduce the operating costs of the system.
1. A gas purification process comprising:
contacting an impure feed gas stream comprising hydrogen sulfide, carbon dioxide and sulfur compounds and a solvent stream in a counter-current absorber to provide a first overhead gas stream and a first solvent effluent bottoms stream comprising absorbed hydrogen sulfide, absorbed carbon dioxide and absorbed other sulfur compounds;
passing the first solvent effluent bottoms stream to a concentrator/reabsorber and contacting the stream with a gas stream from a first downstream rich solvent flash drum or an inert gas stream in the concentrator/reabsorber to provide a second overhead gas stream and a second solvent effluent bottoms stream;
splitting the second solvent effluent bottoms stream into a first stream and a second stream, heat-exchanging the first stream with a solvent stream from a downstream regenerator, heat-exchanging the second stream with a portion of a solvent stream from a second downstream rich solvent flash drum;
after the heat-exchanges, combining said first stream and said second stream to produce a combined stream and passing the combined stream to the first downstream rich solvent flash drum, passing the solvent stream from the first downstream rich solvent flash drum to the second downstream rich solvent flash drum; passing partial of the solvent stream from the second rich solvent flash drum back to the counter-current absorber, passing a remaining portion of the solvent stream from the second downstream rich solvent flash drum to the downstream regenerator to provide an overhead gas stream and a bottom solvent effluent stream, and passing the bottom solvent effluent stream from the downstream regenerator back to a top of the counter-current absorber.
2. The process of claim 1 wherein said first overhead gas stream comprises a purified product gas stream.
3. The process of claim 1 wherein said first solvent effluent bottoms stream is passed to a high pressure rich solvent flash drum before it is passed to the concentrator/reabsorber.
4. The process of claim 3 wherein an overhead stream of the high pressure rich solvent flash drum is compressed, passed through a cooler and returned to said counter-current absorber.
5. The process of claim 3 wherein a bottoms stream is sent from said high pressure solvent flash drum to said concentrator/reabsorber.
6. The process of claim 1 wherein said impure feed gas stream is a gas stream selected from the group consisting of natural gas, synthesis gas, refinery flue gas and biogas.
7. The process of claim 6 wherein said impure feed gas stream comprises up to 70% by volume acid gas.
8. The process of claim 1 wherein said solvent stream comprises a physical solvent.
9. The process of claim 1 , wherein the second overhead gas stream comprises carbon dioxide.
10. The process of claim 1 wherein said counter-current absorber is operated at a pressure from in a range of about 2700 kPa to about 10,000 kPa.
11. The process of claim 1 , wherein the solvent is selected from group consisting of alcohols, glycol ethers, lactams, sulfolane, N-alkylated pyrrolidones, N-alkylated piperidines, cyclotetramethylenesulfone, N-alkyformamides, N-alkylacetamides, ether-ketones, propylene carbonate, N-methyl-2-pyrrolidone, N-formyl morpholine, and alkyl phosphates.
12. The process of claim 7 wherein the solvent comprises dimethyl ethers of polyethylene glycol.
13. The process of claim 1 , further comprising:
passing the first solvent effluent bottoms stream to a rich flash drum upstream of the counter-current stripper;
passing the first solvent effluent bottoms stream to a high pressure flash drum to provide a second overhead gas stream and a second solvent effluent bottoms stream;
sending at least a first portion of the second solvent effluent stream to a concentrator/reabsorber;
passing a third solvent effluent bottoms stream from said concentrator/reabsorber to a regenerator to provide a third overhead gas stream and a third solvent effluent bottoms stream;
recycling the third solvent effluent bottoms stream to a top of the counter-current absorber; and
recovering a purified product gas stream at an overhead of the counter-current absorber.