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A gas separation process for treating exhaust gases from combustion processes. The invention involves routing a first portion of the exhaust stream to a carbon dioxide capture step, while simultaneously flowing a second portion of the exhaust gas stream across the feed side of a membrane, flowing a

A gas separation process for treating exhaust gases from combustion processes. The invention involves routing a first portion of the exhaust stream to a carbon dioxide capture step, while simultaneously flowing a second portion of the exhaust gas stream across the feed side of a membrane, flowing a sweep gas stream, usually air, across the permeate side, then passing the permeate/sweep gas back to the combustor.

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1. A process for controlling carbon dioxide exhaust from a combustion process, comprising: (a) combusting a mixture comprising a fuel and air, oxygen-enriched air, or oxygen in a combustion apparatus, thereby creating an exhaust stream comprising carbon dioxide and nitrogen;(b) routing the exhaust s

1. A process for controlling carbon dioxide exhaust from a combustion process, comprising: (a) combusting a mixture comprising a fuel and air, oxygen-enriched air, or oxygen in a combustion apparatus, thereby creating an exhaust stream comprising carbon dioxide and nitrogen;(b) routing the exhaust stream to a compression apparatus to compress the exhaust stream, thereby producing a compressed stream;(c) separating a first portion of the compressed stream in a carbon dioxide capture unit adapted to selectively remove carbon dioxide, thereby producing a carbon dioxide-enriched stream and a carbon dioxide-depleted off-gas stream;(d) providing a membrane having a feed side and a permeate side, and being selectively permeable to carbon dioxide over the nitrogen and to carbon dioxide over oxygen;(e) passing a second portion of the compressed stream across the feed side;(f) passing air, oxygen-enriched air, or oxygen as a sweep stream across the permeate side;(g) withdrawing from the feed side a carbon dioxide-depleted residue stream;(h) withdrawing from the permeate side a permeate stream comprising oxygen and carbon dioxide;(i) passing the permeate stream to step (a) as at least part of the air, oxygen-enriched air, or oxygen used in step (a); and(j) routing the carbon dioxide-depleted off-gas stream from step (c) and the carbon dioxide-depleted residue stream from step (g) as a part of a working gas stream to an expander unit, and operating the expander unit, thereby generating power and producing a vent stream. 2. The process of claim 1, wherein the combustion apparatus is selected from the group consisting of a boiler, a furnace, an oven, a gas turbine, and a gas-powered or a diesel-powered engine. 3. The process of claim 2, wherein the combustion apparatus is a gas-powered or a diesel-powered engine. 4. The process of claim 1, wherein the exhaust stream comprises at least 15 vol % CO2. 5. The process of claim 1, wherein the first portion of the compressed stream comprises between about 10 vol % and about 66 vol % of the compressed stream. 6. The process of claim 5, wherein the first portion of the compressed stream comprises between about 20 vol % and about 50 vol % of the compressed stream. 7. The process of claim 6, wherein the first portion of the compressed stream comprises between about 25 vol % and about 35 vol % of the compressed stream. 8. The process of claim 1, wherein the carbon dioxide capture unit comprises at least one process selected from the group consisting of absorption, adsorption, liquefaction and membrane separation. 9. The process of claim 8, wherein the carbon dioxide capture step comprises amine scrubbing. 10. The process of claim 8, wherein the carbon dioxide capture step comprises membrane separation. 11. The process of claim 10, wherein the carbon dioxide capture step comprises two or more membrane separation steps. 12. The process of claim 1, wherein the exhaust stream is compressed to a pressure of up to about 5 bar in step (b). 13. The process of claim 1, wherein the sweep stream follows a sweep flow direction across the permeate side, the second portion of the compressed stream follows a feed flow direction across the feed side, and the sweep flow direction is substantially countercurrent to the feed flow direction. 14. The process of claim 1, wherein the membrane exhibits a carbon dioxide permeance of at least 500 gpu under process operating conditions. 15. The process of claim 1, wherein the membrane exhibits a selectivity in favor of carbon dioxide over nitrogen of at least 10 under process operating conditions. 16. The process of claim 1, wherein the vent stream comprises 5 vol % carbon dioxide or less. 17. The process of claim 1, wherein the expander unit is a turbo expander mechanically linked to the compression apparatus. 18. The process of claim 1, further comprising the step of routing the exhaust stream from step (a) to a condensation unit, thereby producing a water stream, prior to step (b). 19. The process of claims 1 or 18, further comprising the step of routing the compressed stream from step (b) to a condensation unit or a second condensation unit, respectively, thereby producing a water or second water stream, prior to steps (c) and (e). 20. The process of claim 11, wherein a permeate stream from a second or additional membrane separation step in step (c) is passed as at least part of the air, oxygen-enriched air, or oxygen used in step (a). 21. The process of claim 1, wherein the carbon dioxide-enriched stream comprises at least 60 vol % CO2. 22. A process for controlling carbon dioxide exhaust from a combustion process, comprising: (a) combusting a mixture comprising a fuel and air, oxygen-enriched air, or oxygen in a combustion apparatus, thereby creating an exhaust stream comprising carbon dioxide and nitrogen;(b) routing the exhaust stream to a compression apparatus to compress the exhaust stream, thereby producing a compressed stream;(c) separating a first portion of the compressed stream in a carbon dioxide capture, unit adapted to selectively remove carbon dioxide, thereby producing a carbon dioxide-enriched stream and a carbon dioxide-depleted off-gas stream;(d) providing a membrane having a feed side and a permeate side, and being selectively permeable to carbon dioxide over nitrogen and to carbon dioxide over oxygen;(e) passing a second portion of the compressed stream across the feed side;(f) passing air, oxygen-enriched air, or oxygen as a sweep stream across the permeate side;(g) withdrawing from the feed side a carbon dioxide-depleted residue stream;(h) withdrawing from the permeate side a permeate stream comprising oxygen and carbon dioxide;(i) passing the permeate stream to step (a) as at least part of the air, oxygen-enriched air, or oxygen used in step (a); and(j) routing at least one of the carbon dioxide-depleted off-gas stream from step (c) or the carbon dioxide-depleted residue stream from step (g) as a part of a working gas stream to an expander unit, and operating the expander unit, thereby generating power and producing a vent stream, wherein the exhaust gas from the combustion apparatus is cooled prior to compression by heat exchange with at least a portion of the working gas stream being routed to the expander unit in step (j).