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US 12,275,909 B1Granted
System and method for producing renewable natural gas from biogas
AssigneeUnconventional Gas Solutions, LLC
InventorBenjamin Bikson
Life of this patent
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Abstract
An improved method and apparatus for removing acid gases and other impurities from raw biogas streams, such as biogas from landfills or biogas from controlled anaerobic digestion, is disclosed. The method provides efficient generation of high-purity renewable natural gas from raw biogas. The biogas is treated in a multi-stage membrane system integrated with compression equipment. The membrane separation units are arranged into interconnected high-pressure and low-pressure gas recycling loops powered by high-pressure and low-pressure compressors. The combined system provides for the generation of efficient contaminant removal from raw biogas to generate high-purity methane products with reduced compression energy consumption.
Claims76
A method of generating a high-purity hydrocarbon stream from a raw biogas feed gas stream at a substantially atmospheric pressure, said method comprising the steps of:
- (i) compressing said raw biogas feed gas stream mixed with a first recycled permeate gas stream and a recycled retentate gas stream in a first compressor, thereby forming a first effluent stream;
- (ii) passing the first effluent stream into a first membrane separation unit, wherein the first membrane separation unit removes a portion of oxygen and hydrogen sulfide from the first effluent stream, thereby forming a retentate second effluent stream having a reduced content of oxygen and hydrogen sulfide as compared to the first effluent stream and a permeate third effluent stream enriched in oxygen and hydrogen sulfide as compared to the first effluent stream;
- (iii) passing the retentate second effluent stream to a second membrane separation unit, wherein the second membrane separation unit removes a portion of oxygen and hydrogen sulfide from the retentate second effluent stream, thereby forming a retentate fourth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate second effluent stream and a permeate fifth effluent stream enriched in oxygen and hydrogen sulfide content as compared to the retentate second effluent stream;
- (iv) compressing said permeate third effluent stream mixed with a second recycled permeate gas stream in a second compressor, thus forming a sixth effluent stream;
- (v) passing the sixth effluent stream to a third membrane separation unit, wherein the third membrane separation unit removes a portion of oxygen and hydrogen sulfide from the sixth effluent stream, thereby forming a retentate eighth effluent stream, having a lower oxygen and hydrogen sulfide content as compared to the sixth effluent stream and a higher oxygen content as compared to the raw biogas feed stream, and a permeate seventh effluent stream;
- (vi) passing the retentate eighth effluent stream to a fourth membrane separation unit, wherein the fourth membrane separation unit removes a portion of oxygen and hydrogen sulfide from the retentate eighth effluent stream, thereby forming a retentate tenth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate eighth effluent stream and a permeate ninth effluent stream with increased oxygen and hydrogen sulfide content as compared to the retentate eighth effluent stream;
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- (vii) collecting the retentate fourth effluent stream generated by the second membrane separation unit as a high-purity hydrocarbon product, wherein the retentate fourth effluent stream has an increased methane content and reduced hydrogen sulfide and oxygen content as compared to the raw biogas feed gas stream;
- wherein the retentate fourth effluent stream has a methane content of at least 95% mole, an oxygen content of at most 0.1% mole and a hydrogen sulfide content of at most 0.075% mole.
6 more elements
An apparatus for the purification of a raw biogas stream available at a substantially atmospheric pressure, said apparatus comprising:
- (i) a first compressor that compresses a combined feed gas stream comprised of the raw biogas stream, a first recycled permeate gas stream, and a recycled retentate gas stream, thereby forming a first effluent stream;
- (ii) a first membrane separation unit that receives the first effluent stream, the first membrane separation unit comprising a first membrane that removes a portion of oxygen and hydrogen sulfide from the first effluent stream, thereby forming a retentate second effluent stream having a lower oxygen and hydrogen sulfide content as compared to the first effluent stream and a permeate third effluent stream enriched in oxygen and hydrogen sulfide as compared to the first effluent stream;
- (iii) a second membrane separation unit that receives the retentate second effluent stream, the second membrane separation unit comprising a second membrane that removes a portion of oxygen and hydrogen sulfide from the second effluent stream, thereby forming a retentate fourth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate second effluent stream and a permeate fifth effluent stream enriched in oxygen and hydrogen sulfide as compared to the retentate second effluent stream;
- (iv) a second compressor compressing a combined gas stream comprised of the permeate third effluent stream and a second recycled permeate stream, thus forming a sixth effluent stream;
- (v) a third membrane separation unit that receives the sixth effluent stream, the third membrane separation unit comprising a third membrane that removes a portion of oxygen and hydrogen sulfide from the sixth effluent stream, thereby forming a retentate eighth effluent stream, having a lower oxygen and hydrogen sulfide content as compared to the sixth effluent stream and a higher oxygen content as compared to the sixth effluent stream, and a permeate seventh effluent stream;
- (vi) a fourth membrane separation unit that receives the retentate eighth effluent stream, the fourth membrane separation unit comprising a fourth membrane that removes a portion of oxygen and hydrogen sulfide from the retentate eighth effluent stream, thereby forming a retentate tenth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate eighth effluent stream and a permeate ninth effluent stream;
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- (vii) wherein the retentate fourth effluent stream generated by the second membrane separation unit is collected as a methane product, wherein the retentate fourth effluent stream has a reduced oxygen and hydrogen sulfide content as compared to the raw biogas stream;
- wherein the retentate fourth effluent stream has a methane content of at least 95% mole, an oxygen content of at most 0.1% mole and a hydrogen sulfide content of at most 0.075% mole.
6 more elements
A method of generating a high-purity hydrocarbon stream from a raw biogas feed stream available at a substantially atmospheric pressure, said method comprising the steps of:
- (i) compressing said raw biogas feed gas stream mixed with a first recycled permeate gas stream and a second recycled permeate gas stream in a first compressor to a pressure from 6 to 25 barg, thereby forming a first effluent stream;
- (ii) passing the first effluent stream into a first membrane separation unit, wherein the first membrane separation unit removes a portion of oxygen and hydrogen sulfide from the first effluent stream, thereby forming a retentate second effluent stream having a reduced content of oxygen and hydrogen sulfide as compared to the first effluent stream and a permeate third effluent stream enriched in oxygen and hydrogen sulfide as compared to the first effluent stream, said permeate third effluent stream being removed at substantially atmospheric pressure or a sub-atmospheric pressure;
- (iii) passing the retentate second effluent stream to a second membrane separation unit, wherein the second membrane separation unit removes a portion of oxygen and hydrogen sulfide, thereby forming a retentate fourth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate second effluent stream and a permeate fifth effluent stream enriched in oxygen and hydrogen sulfide content as compared to the retentate second effluent stream;
- (iv) compressing said permeate third effluent stream mixed with a third recycled permeate gas stream in a second compressor to a pressure from 2 to 6 barg, thus forming a sixth effluent stream;
- (v) passing the sixth effluent stream to a third membrane separation unit wherein the third membrane separation unit removes a portion of oxygen and hydrogen sulfide from the sixth effluent stream, thereby forming a retentate eighth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the sixth effluent stream and a higher oxygen content as compared to the raw biogas feed stream, and a permeate seventh effluent stream, wherein the permeate seventh effluent stream is at substantially atmospheric pressure or a sub-atmospheric pressure;
- (vi) passing the retentate eighth effluent stream to a fourth membrane separation unit wherein the fourth membrane separation unit removes a portion of oxygen and hydrogen sulfide from the retentate eighth effluent stream, thereby forming a retentate tenth effluent stream having a lower oxygen and hydrogen sulfide content as compared to the retentate eighth effluent stream and a permeate ninth effluent stream, said permeate ninth effluent stream being removed at substantially atmospheric pressure or a sub-atmospheric pressure;
- (vii) passing said permeate ninth effluent stream to a front end of the second compressor, wherein the permeate ninth effluent stream defines the third recycled permeate gas stream that is mixed with said permeate third effluent gas stream in step (iv);
- (viii) passing the retentate fourth effluent stream to a fifth membrane separation unit wherein the fifth membrane separation unit removes a portion of oxygen and hydrogen sulfide from the fourth effluent stream, thereby forming a retentate twelfth effluent stream having a lower oxygen and hydrogen sulfide, content as compared to the retentate fourth effluent stream and a permeate eleventh effluent stream having a higher oxygen and hydrogen sulfide content as compared to the retentate fourth effluent stream, wherein the permeate eleventh effluent stream is at substantially atmospheric pressure or a sub-atmospheric pressure;
- (ix) passing said permeate eleventh effluent stream to a front end of the first compressor, wherein the permeate eleventh effluent stream defines the second recycled permeate gas stream that is mixed with said raw biogas feed gas stream in step (i);
- (x) passing said retentate tenth effluent stream to a permeation side of the second membrane separation unit to act as a sweep gas, wherein the retentate tenth effluent stream combined with the permeate fifth effluent stream generated by the second membrane separation unit defines the first recycled permeate gas stream that is mixed with said raw biogas feed gas stream in step (i);
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- (xi) collecting the retentate twelfth effluent stream generated by the fifth membrane separation unit as a high-purity hydrocarbon product, wherein the retentate twelfth effluent stream has an increased methane content and reduced oxygen and hydrogen sulfide content as compared to the raw biogas feed gas stream.
9 more elements
Dependencies are inferred from the claim text.