Process-integrated design of a sub-ambient membrane process for CO2 removal from natural gas power plants

This paper proposes an advanced sub-ambient membrane process that applies an improved CO2/N2 selectivity under cold temperatures for CO2 removal from a natural gas combined-cycle power plant. The use of a large excess of combustion air in a natural gas power plant results in a relatively diluted CO2 exhaust gas, typically by 3–4%, which makes it difficult to achieve an energy-efficient CO2 capture. The sub-ambient membrane process using exhaust gas recirculation and/or selective exhaust gas recirculation is designed to concentrate the CO2 from 4 to 6–10%. In addition, the heat integration of liquefied natural gas (LNG) regasification not only provides a nearly free cold energy source for producing a cold processing environment, it also maximizes the full potential of the heat recovery. Among the different membrane designs proposed, an integrated process using all design options demonstrates the lowest CO2 capture cost at $ 57/tCO2, which is a 55.1% reduction in capture costs, and a 70.1% decrease in parasitic load compared to an early configuration. A sensitivity analysis was conducted to understand the impact of the membrane performance, namely, the CO2 permeance and CO2/N2 selectivity, on the process design and economics of the CO2 capture process considered herein, through which guidelines for the development of membrane materials and a conceptual insight into the design and optimization of a membrane-based capture process can be obtained.