Offshore decarbonation of CO2-rich natural gas intensified via gas-liquid membrane contactors with blended aqueous-amines

Abstract

A battery of high-pressure countercurrent gas-liquid membrane contactors (GLMC) using aqueous-methyl-diethanolamine(39% w/w)-piperazine(5% w/w) solvent is demonstrated for offshore decarbonation of 5MMNm3/d carbon-dioxide-rich natural gas. To accomplish this, a Gas-Liquid Membrane Contactor Unit Operation Extension (GLMC-UOE) was built for HYSYS simulator. Mass/energy balances, pressure-drop, vapor/liquid equilibrium properties are solved by GLMC-UOE with rigorous thermodynamics provided by the HYSYS Acid-Gas Chemical-Solvents Package appropriate for high-pressure carbon dioxide chemical-absorption. GLMC-UOE discretizes a countercurrent GLMC module as a cascade of countercurrent GLMC elements, which are solved via adapted simultaneous corrections of variables. Each GLMC element adopts a multicomponent interfacial heat/mass transfer model based on logarithmic-mean of transmembrane temperature-difference and component fugacity-differences for vapor-to-liquid or liquid-to-vapor transfers. The transferable species comprehend carbon dioxide, methane, ethane, propane, water, methyl-diethanolamine and piperazine. GLMC-UOE was validated against the literature. The process comprises the high-pressure GLMC battery, reboilered low-pressure stripping column, heat exchangers, multi-staged carbon dioxide compression and triethylene-glycol dehydration unit. A stripper heat-ratio of 167.7 kJ/molCO2 was required for solvent regeneration, a value compatible with the literature. The process dispatches dry dense carbon dioxide for enhanced oil recovery in the same offshore field. GLMC-UOE correctly predicts GLMC temperature effects, gas hydration, methane losses in the solvent and pressure-drop.