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

An integrated vacuum pressure swing adsorption (VPSA) and Rectisol process is proposed for CO 2 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% CO 2 with a CO 2 purity of 98.35% from UCG syngas (CH 4 /CO/CO 2 /H 2 /N 2 = 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 CO 2 remained in light product gas from the VPSA process using cryogenic methanol (233.15 K, 100% (mass)) as absorbent. A final purified gas with CO 2 concentration lower than 3% and a regenerated CO 2 product with CO 2 purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·(kg CO 2 ) –1 of the single Rectisol process to 1.008 MJ·(kg CO 2 ) –1 of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO 2 capture from UCG syngas. Additionally, the high-value gas ( e.g., CH 4 ) loss can be decreased and the effects of key operating parameters on the process performances were detailed.