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

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.