Design of a rapid vacuum pressure swing adsorption (RVPSA) process for post-combustion CO₂ capture from a biomass-fuelled CHP plant

It was aimed to design a novel RVPSA (Rapid Vacuum Pressure Swing Adsorption) unit for CO₂ concentration and recovery in order to achieve the aggressive CO₂ capture target, i.e. 95+% CO₂ purity and 90+% CO₂ recovery at the same time, applied to an existing 10 MW_th biomass-fuelled CHP plant. Biomass-fuelled CHP plants are deemed carbon-neutral on the grounds of the net CO₂ addition to the atmosphere as a result of its operation being practically zero, ignoring the CO₂ emissions involved in the ancillary processes, such as soil enhancement, biomass transport and processing, etc. Furthermore, integrating the biomass-fuelled CHP plant with carbon capture, transport and storage enables carbon-negative energy generation, as its net effect is to recover some CO₂ in the air and then store it underground through this plant operation. By the way, a RVPSA process features more efficient utilisation of the adsorbents in the column, leading to much higher bed productivity than a conventional adsorption process. Such a high bed productivity makes it easier to scale up this adsorption process for its application to industrial post-combustion capture. A two-stage, two-bed RVPSA unit was designed and simulated to capture CO₂ from the biomass-fuelled CHP plant flue gas containing 13.3% CO₂ mole fraction. Effects of operating conditions such as the Purge-to-Feed ratio (P/F) and desorption pressure on the specific power consumption were investigated in detail. It was found that the integrated two-stage RVPSA unit was capable of achieving the following overall performances: CO₂ recovery of 90.9%, CO₂ purity of 95.0%, bed productivity of 21.2 mol_CO2/kg/h and power consumption of 822.9 kJ/kg_CO2. The productivity of the RVPSA unit designed in this study was 20-30 times higher than those of the conventional CO₂ capture VPSA processes.