Comparison and optimization of CO2 purification units for CCS applications

Abstract

Several promising CO2 capture technologies, like oxy-combustion, adsorption and membranes, feature a purity of the captured CO2 stream which is insufficient for the storage site or the transport system. In these cases, a CO2 Purification Unit (CPU) is required to lower the concentrations of O2, N2 and Ar at the limits allowed by the storage site/transport system. In this work, the available CO2 Purification processes have been reviewed and the six main schemes have been simulated in Aspen Plus and optimized. Their performance have been ranked based on six selected key performance indicators: total annual cost, Specific cost per ton of captured CO2, specific energy consumption, recovery, purity, and O2 concentration in the purified CO2. The techno-economic optimization is repeated for different carbon tax values and for three different feed streams compositions. The results of the optimization show that flash-based CPUs cannot meet the requirements for CO2 storage due to a high concentration of O2 (>1000 ppm) but they feature a low specific cost (5.8–25.9 €/tonCO2 depending on the feedgas and plant size), low specific energy consumption (124.9–436.1 kJ/tonCO2) and acceptable recovery (94.60–99.46 %). The distillation-based CPU can meet the requirements for CO2 storage, but these CPUs have the highest cost (52–112 % higher than flash-based CPU) and the lowest recovery. The optimal CPUs are the ones which combine both distillation column and flash separation. These CPUs meet the oxygen requirements for CO2 storage (<10 ppm) while providing the highest purity (99.997–99.999 %), high recovery (90.61–99.32 %) at a limited cost (6.1–36.0 euro/tonCO2).