Integrated vacuum pressure swing adsorption and Rectisol process for CO2 capture from underground coal gasification syngas

Abstract

An integrated vacuum pressure swing adsorption (VPSA) and Rectisol process is proposed for CO2 capture from underground coal gasification (UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO2 with a CO2 purity of 98.35% from UCG syngas (CH4/CO/CO2/H2/N2 = 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field, Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO2 remained in light product gas from the VPSA process using cryogenic methanol (233.15 K, 100% (mass)) as absorbent. A final purified gas with CO2 concentration lower than 3% and a regenerated CO2 product with CO2 purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg–1 of the single Rectisol process to 1.008 MJ·kg–1 of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO2 capture from UCG syngas. Additionally, the high-value gas (e.g., CH4) loss can be decreased and the effects of key operating parameters on the process performances were detailed.