Conceptual design of membrane-based pre-combustion CO2 capture process: Role of permeance and selectivity on performance and costs

Abstract

Pre-combustion CO2 capture is regarded as a promising option to mitigate the environmental pollution from coal combustion, due to its relatively low energy duty and prospects for the use of hydrogen in power generation and industrial sectors. Nowadays, research and development efforts are mainly focusing on advanced technologies to separate H2 and CO2 from a synthesis gas of a gasification-based power generation system. In this regard, membrane separation processes are attracting an increasing attention, due to their potential for a more cost-effective and environmental friendly CO2 capture compared to well-established solvent-based processes.A conceptual design and techno-economic analysis is presented of a pre-combustion CO2 capture process based on H2-selective polymeric membranes in an integrated gasification combined cycle (IGCC) power plant, including the water-gas-shift (WGS) system. The design approach is based on the selection of the most effective membrane separation process and economic optimization of operating conditions. The capture process is based on a three-stage membrane separation system, producing a hydrogen stream feeding the power generation unit and a liquid CO2 stream, ready for transport and geological storage. Considering a state-of-the-art polymeric membrane with a H2 to CO2 selectivity of 15 and H2 permeance of 300 GPU, the IGCC efficiency penalty states at around 5% pts when the separation process is operated with a pressure on membrane feed side of 70 bar, corresponding to an estimated cost of CO2 capture of 16.6 €/t CO2. A sensitivity analysis of operating pressure and membrane properties revealed that the cost of CO2 capture can be reduced to less than 15 €/t CO2 by moderately increasing the H2 to CO2 selectivity and adjusting the designed process accordingly. Additionally, a decrease in the feed-side pressure slightly disfavours the economic performance of CO2 capture for H2 permeances greater than 300 GPU. The membrane-based capture process compared most favourably in cost-effectiveness with the well-established solvent based Selexol process.