Abstract: A process for removing nitrogen from a feed gas containing at least nitrogen and methane comprises a) introducing the feed gas into a first membrane stage to produce a first permeate enriched in methane and a first residue enriched in nitrogen; b) forwarding the first residue into a second membrane stage to produce a second permeate enriched in methane and a second residue enriched in nitrogen; c) forwarding the second residue into pressure swing adsorption (PSA) beds to produce an high pressure overhead stream containing nitrogen and a low pressure offgas stream containing methane therein; d) combining the second permeate enriched in methane and the low pressure offgas stream containing methane to form a combined gas and forwarding the combined gas to the feed gas for recycle; e) collecting a first permeate enriched in methane as a product; and f) venting out the high pressure overhead stream containing nitrogen.

Abstract: A mixed membrane system for producing a conditioned fuel gas from a high-pressure raw fuel gas that contains methane, CO2, H2S, N2, ethane, propane, and heavy hydrocarbons, the system comprising a pre-heater, configured to temperature control the high-pressure raw fuel gas forming a feed fuel gas; a gas splitter, configured to split the feed fuel gas into a first and a second feed gases; a glassy membrane device, configured to reject CO2 and/or H2S from the first feed gas while retaining methane and heavy hydrocarbons therein as a first conditioned fuel gas; and a rubbery membrane device, arranged in parallel with the glass membrane, configured to reject CO2, H2S, and heavy hydrocarbons from the second feed gas while retaining methane therein as a second conditioned fuel gas, wherein the first and second conditioned fuel gases are combined to form the conditioned fuel gas.