Effects of feed gas concentration, temperature and process parameters on vacuum swing adsorption performance for CO2 capture

Abstract

Vacuum swing adsorption (VSA) is a commercial technology for gas separation, and is promising for CO2 removal from a range of process gases. In this study, a parametric analysis and process characterisation was conducted of VSA for CO2 capture from a variety of gas steams, using the commercial zeolite 13X-APIII as a benchmark adsorbent. Because deep vacuum levels (<5kPa) is not practical at large scale, vacuum pressures of up to 25kPa were tested in our experiments; inlet CO2 concentrations of 15%, 30% and 50% with varying operation temperatures from 20 to 120°C were studied to cover the range of concentration and temperatures expected in industry. The studies were conducted using both single and double bed CO2VSA systems. CO2 product purity and recovery are significantly affected by the vacuum pressure, operating temperature and inlet CO2 concentration. In addition to the detrimental effect of higher vacuum levels, the rate of evacuation can also impact the performance. Rapid evacuation results in high pressure drop which leads to inadequate desorption of the adsorbed CO2. High desorption flow rates also limit CO2 release from the solid phase to the gas phase due to mass transfer limitations. Pressure equalisation between two adsorption beds can remarkably improve the purity of CO2 product, compared with single-bed cycle. Based on our experimental work, a set of intrinsic “recovery-purity” curves for APGIII were generated to guide the user in selecting appropriate conditions for achieving desired performance. We found that achieving high purity (>90% CO2) at high recovery (>90%) for APGIII was not possible unless very deep vacuum levels are used (1kPa) if the feed contains 15% CO2 or less.