Membrane gas separation - physical solvent absorption combined plant simulations for pre-combustion capture

Removal of carbon dioxide (CO2) from syngas generated by coal gasification is often currently achieved by absorption into physical solvents such as in the Rectisol Process. The vented gas from this process often does not have the CO2 purity required for carbon capture and storage purposes, because the focus is on recovery and recycling valuable syngas components, such as H-2. It is shown here that this can be rectified through the use of a CO2-selective membrane. For an existing Rectisol process, a CO2-selective membrane unit on the vented waste gas can achieve the necessary CO2 purity with a low CO2/H-2 selectivity polymer. This provides a simple and effective method to retrofit such a process to provide a CO2 stream suitable for storage. Alternatively, the standard multiple flash stages can be replaced by a single flash stage with a gas-separation membrane on the gas recycle. This Rectisol - membrane hybrid design can achieve high purity CO2 product streams with reasonable membrane CO2/H-2 selectivities, dependent on the solvent flash pressure. However, maximizing CO2 flux across the membrane means a high flashing pressure and therefore only partial solvent regeneration before recycle to the absorber. This results in a significant increase in solvent flowrate and hence absorber size to ensure high CO2 recovery. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of GHGT