Membrane gas separation processes for CO2 capture from cement kiln flue gas

The cement industry is a significant source of CO2 emissions for the non-power sector. Carbon capture and storage has been proposed as a strategy to mitigate these CO2 emissions. The high CO2 partial pressure of the cement kiln flue gas enables more options than in other post-combustion capture scenarios. Here, three distinct process designs for membrane gas separation are simulated for the capture of CO2 from cement kiln flue gas. The first design is based on a standard natural gas processing flowsheet and includes two membrane stages with a permeate recycle from the first stage. The second design uses a single membrane stage with downstream compression and cooling to achieve the necessary purity. The final design incorporates three membrane stages with similar downstream compression and cooling. It was found that the CO2/N2 selectivity of the membrane strongly influenced the performance of all three processes. The third design achieved the lowest energy demand of 1.2 MJ/kg of CO2 captured for membranes with CO2/N2 selectivity above 50. Below a selectivity of 25 the second design with a single membrane stage had the lowest energy demand. However, a different trend was observed with cost of capture, where below a CO2/N2 selectivity of 25 the second design provided the lowest cost of capture while above this selectivity the first design was cheapest. This design could provide a cost of capture of US$ 74 per tonne of CO2 avoided, based on current state-of-the art membrane permselectivity, which is competitive with solvent absorption carbon capture technologies. However, calcium looping and oxyfuel combustion would appear to have lower costs in this scenario.