US 12,139,682 B1
System and method for producing renewable natural gas from biogas
Benjamin Bikson, Newton, MA (US)
Assigned to Unconventional Gas Solutions, LLC, Houston, TX (US)
Filed by Unconventional Gas Solutions, LLC, Houston, TX (US)
Filed on Jul. 8, 2024, as Appl. No. 18/766,045.
Int. Cl. B01D 53/22 (2006.01); B01D 53/00 (2006.01); B01D 53/02 (2006.01); B01D 53/62 (2006.01); C10L 3/10 (2006.01)
CPC C10L 3/104 (2013.01) [B01D 53/002 (2013.01); B01D 53/02 (2013.01); B01D 53/225 (2013.01); B01D 53/226 (2013.01); B01D 53/229 (2013.01); B01D 53/62 (2013.01); C10L 3/103 (2013.01); B01D 2256/245 (2013.01); B01D 2257/102 (2013.01); B01D 2257/104 (2013.01); B01D 2257/304 (2013.01); B01D 2257/504 (2013.01); B01D 2257/708 (2013.01); B01D 2257/80 (2013.01)] 43 Claims
OG exemplary drawing
 
1. A method of generating a high purity hydrocarbon stream from a raw biogas feed stream comprised of methane, carbon dioxide, nitrogen, oxygen, water vapor and hydrogen sulfide available at a substantially atmospheric pressure, said method comprising the steps of:
(i) compressing said raw biogas feed stream mixed with a recycled permeate gas stream and a recycled retentate gas stream in a first compressor to a pressure from 6 to 25 barg followed by aftercooling and condensate separation, 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, hydrogen sulfide, water vapor, and carbon dioxide from the first effluent stream, thereby forming a retentate second effluent stream having a reduced content of carbon dioxide, hydrogen sulfide, oxygen, and water vapor as compared to the first effluent stream and a permeate third effluent stream enriched in oxygen, water vapor, hydrogen sulfide, and carbon dioxide 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 carbon dioxide, hydrogen sulfide, water vapor, and oxygen from the retentate second effluent stream, thereby forming a retentate fourth effluent stream having a lower carbon dioxide, hydrogen sulfide, water vapor and oxygen content as compared to the retentate second effluent stream and a permeate fifth effluent stream enriched in carbon dioxide, hydrogen sulfide, water vapor and oxygen content as compared to the retentate second effluent stream;
(iv) compressing said permeate third effluent 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 carbon dioxide, hydrogen sulfide, water vapor, and oxygen from the sixth effluent stream, thereby forming a retentate eighth effluent stream having a lower carbon dioxide, and water vapor 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 with a carbon dioxide concentration above 95 volumetric percent, wherein the permeate seventh effluent stream is at substantially atmospheric pressure or a sub-atmospheric pressure;
(vi) passing said permeate fifth effluent stream to a front end of the first compressor, wherein the permeate fifth effluent stream defines the recycled permeate gas stream that is mixed with said raw biogas feed stream in step (i);
(vii) passing said retentate eighth effluent stream to a front end of the first compressor, wherein the retentate eighth effluent stream defines the recycled retentate gas stream that is mixed with said raw biogas feed stream in step (i);
(viii) wherein the retentate second effluent stream has a carbon dioxide concentration between 4 and 14% mole;
(ix) wherein a combined volume of the permeate fifth effluent stream and the retentate eighth effluent stream is from 20 to 40 percent of the volume of the said raw feed gas stream for a standard biomethane purity with carbon dioxide concentration between 2.0 and 0.2% mole and from 35 to 75 percent for a high biomethane purity with carbon dioxide purity below 0.2% mole;
(x) wherein the first and third membrane separation units are equipped with semipermeable polymeric hollow fiber membranes exhibiting a CO2/CH4 gas separation factor above 40, and the second membrane separation unit is equipped with semipermeable polymeric hollow fiber membranes exhibiting a CO2/CH4 gas separation factor above 20; and
(xi) 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 a carbon dioxide content below 2.0% mole.
 
24. An apparatus for the purification of a raw biogas stream comprised of methane, carbon dioxide, oxygen, water vapor, nitrogen, and hydrogen sulfide 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 recycled permeate gas stream, and a recycled retentate gas stream to a pressure from 6 to 25 barg followed by aftercooling and condensate separation, 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 carbon dioxide, oxygen, hydrogen sulfide, water vapor, and nitrogen from the first effluent stream, thereby forming a retentate second effluent stream having a lower carbon dioxide content as compared to the first effluent stream and a permeate third effluent stream enriched in carbon dioxide, hydrogen sulfide, water vapor and oxygen 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 carbon dioxide, hydrogen sulfide and oxygen from the retentate second effluent stream, thereby forming a retentate fourth effluent stream having a lower carbon dioxide, hydrogen sulfide and oxygen content as compared to the retentate second effluent stream and a permeate fifth effluent stream enriched in carbon dioxide, hydrogen sulfide and oxygen content as compared to the retentate second effluent stream;
(iv) a second compressor compressing the permeate third effluent stream to a pressure from 2 to 6 barg, 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 carbon dioxide, hydrogen sulfide, water vapor and oxygen from the sixth effluent stream, thereby forming a retentate eighth effluent stream having a lower carbon dioxide, and water vapor content as compared to the permeate third effluent stream and a higher oxygen content as compared to the sixth effluent stream and a permeate seventh effluent stream enriched in carbon dioxide content and depleted in oxygen and methane content as compared to the sixth effluent stream, wherein the permeate seventh effluent stream is at substantially atmospheric pressure or at a sub-atmospheric pressure;
(vi) wherein the permeate fifth effluent stream, containing recoverable methane, defines the recycled permeate gas stream combined with the raw biogas stream in step (i);
(vii) wherein the retentate eighth effluent stream defines the recycled retentate gas stream combined with the raw biogas stream in step (i);
(viii) wherein the retentate second effluent stream has a carbon dioxide concentration between 4 and 14% mole;
(ix) wherein a combined volume of the permeate fifth effluent stream and the retentate eighth effluent stream is from 40 to 100 percent of a volume of said raw biogas stream;
(x) wherein the first and third membrane separation units are equipped with semipermeable polymeric hollow fiber membranes exhibiting a CO2/CH4 gas separation factor above 40, and the second membrane separation unit is equipped with semipermeable polymeric hollow fiber membranes exhibiting a CO2/CH4 gas separation factor above 20; and
(xi) 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 hydrogen sulfide, oxygen, and carbon dioxide content as compared to the raw biogas stream.