Carbon capture and adjustment of water and hydrocarbon dew-points via absorption with ionic liquid [Bmim][NTf2] in offshore processing of CO2-rich natural gas

Abstract

Offshore oil production from huge reservoirs at deep waters with high gas-oil ratio and high carbon dioxide (CO2) content is a challenging puzzle because oil extraction imposes to process a huge flow rate of raw CO2-rich natural gas from which CO2 must be separated and sent to appropriate destination. Offshore gas processing comprises three steps: water dew-point adjustment (WDPA), hydrocarbon dew-point adjustment (HCDPA) and CO2 removal to avoid transport of inert and to boost oil production by injecting CO2 into the reservoir for enhanced oil recovery. In offshore rigs, gas is conventionally treated via TEG absorption for WDPA, Joule-Thomson expansion for HCDPA and membrane permeation for CO2 removal. This work discloses a new concept of CO2-rich natural gas processing using the ionic-liquid [Bmim][NTf2] for simultaneous WDPA, HCDPA and CO2 removal. All results were obtained via rigorous simulations, including the ionic-liquid implications in vapor-liquid equilibrium and heat-effects. The main novelty of the new process is its high-pressure selective stripping of CO2, lowering compression power for enhanced oil recovery utilization. Economic comparison of conventional gas processing with the ionic-liquid gas processing shows that the latter has 19.3% higher revenues, 23.6% less manufacturing costs and 18% less investment, entailing a 37% higher net present value.