Mixed membrane-type process for fuel gas upgrading

A process 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 process comprising the steps of:

• a) re-directing a portion of the high-pressure raw natural gas;
• b) optimizing a heat-exchanger;
• c) feeding the high-pressure raw natural gas to the heat-exchanger and forming a high-pressure and temperature controlled feed flow;
• d) splitting the high-pressure and temperature controlled feed flow into a first high-pressure and temperature controlled feed flow stream and a second high-pressure and temperature controlled feed flow stream and feeding the first and second high-pressure and temperature controlled feed flows to a glassy membrane and a rubbery membrane, respectively;
• e) removing a portion of CO2 and H2S contents to a permeate side in the glassy membrane and while retaining methane and heavy hydrocarbons therein as a first conditioned fuel gas;
• f) removing a portion of CO2, H2S and heavy hydrocarbons to a permeate side in the rubbery membrane and while retaining methane therein as a second conditioned fuel gas;
• g) controlling a balance of the first and second high-pressure and temperature controlled feed flows from the glassy and rubbery membranes, respectively, through using flow restricting valves installed along the first and second high-pressure and temperature controlled feed flows;
• and
• h re-directing and combining the treated first and second high-pressure and temperature controlled feed flow streams at steps d) and e) to meet a desired fuel gas specification of the conditioned fuel gas.