No abstract

This work aimed to fulfill a technical evaluation of the applicability of gas-liquid membrane contactors (GLMC) to remove CO2 from CO2 rich natural gas in offshore rigs. For this purpose, a simulation case in HYSYS 8.8 (AspenTech) was performed to remove CO2 from a natural gas stream with concentration of 40% mol CO2 using an aqueous solution of monoethanolamine (MEA) 30% w/w. GLMC unit operation is not available in HYSYS, though. Hence, it was necessary to develop a mathematical model based on log-mean of differences of CO2 fugacities in both phases. Moreover, a GLMC Unit Operation Extension (UOE) was created for GLMC units to run in the process simulator HYSYS 8.8 using its thermodynamic infrastructure. The developed GLMC unit operation extension performed accordingly to the expected behavior. For a gas feed flow rate of 5 MMNm3/d (typical from FPSO's), the calculated total GLMC mass transfer area was 1,986 m2, which requires 14 GLMC modules. Consequently, this operation showed to be a feasible option for CO2 removal in natural gas conditioning on offshore rigs. The heat ratio in the reboilers of CO2 stripping columns was found to be 167 kJ/mol, compatible with data found in the literature of CO2-MEA-H2O systems.

Gas–liquid membrane contactor is a promising process intensification technology for offshore natural gas conditioning in which weight and footprint constraints impose severe limitations. Thanks to its potential for substituting conventional packed/trayed columns for acid-gas absorption and acid-gas solvent regeneration, gas-liquid membrane contactors have been investigated experimentally and theoretically in the past two decades, wherein aqueous-amine solvents and their blends are the most employed solvents for carbon dioxide removal from natural gas in gas-liquid membrane contactors. These efforts are extensively and critically reviewed in the present work. Experimentally, there are a remarkable lack of literature data in the context of gas–liquid membrane contactors regarding the following topics: water mass transfer; outlet stream temperatures; head-loss; and light hydrocarbons (e.g., ethane, propane, and heavier) mass transfer. Theoretically, there is a lack of complete models to predict gas-liquid membrane contactor operation, considering multicomponent mass balances, energy balances, and momentum balances, with an adequate thermodynamic framework for correct reactive vapor–liquid equilibrium calculation and thermodynamic and transport property prediction. Among the few works covering modeling of gas-liquid membrane contactors and implementation in professional process simulators, none of them implemented all the above aspects in a completely successful way.