KETEP 세계에너지시장정보

1. A process for removing acid gases from a raw biogas feed stream comprised of methane, carbon dioxide, nitrogen, oxygen and hydrogen sulfide, said process comprising the steps of: (i) passing a combined feed gas stream comprised of the raw biogas feed stream and a recycled permeate gas stream generated by a membrane separation unit through a biological hydrogen sulfide removal system at substantially atmospheric pressure, thus generating a first effluent stream with reduced hydrogen sulfide and oxygen content as compared to the combined feed gas stream; (ii) compressing the first effluent stream in a compressor to a pressure from 6 to 25 barg, thereby forming a second effluent stream; (iii) passing the second effluent stream into a first membrane separation unit, wherein a first membrane removes a portion of oxygen and carbon dioxide from the second effluent stream, thereby forming a retentate third effluent stream having a reduced content of carbon dioxide as compared to the second effluent stream and a permeate fourth effluent stream enriched in oxygen and carbon dioxide as compared to the second effluent stream; (iv) passing the third effluent stream to a second membrane separation unit, wherein a second membrane removes a portion of carbon dioxide and oxygen from the third effluent stream, thereby forming a retentate fifth effluent stream having a lower carbon dioxide and oxygen content as compared to the third effluent stream and a permeate sixth effluent stream enriched in carbon dioxide and oxygen content as compared to the third effluent stream; (v) wherein the sixth effluent stream comprises the recycled permeate gas stream combined with the raw biogas feed stream in step (i); and (vi) collecting the fifth effluent stream generated by the second membrane separation unit as a product.