New approach for biogas purification using cryogenic separation and distillation process for CO2 capture

Biogas - a renewable energy source encompassing primarily CO2/CH4 mixture, can fuel vehicles if it is properly purified. Recently, cryogenic biogas upgrading (CO2 Liquefaction) witnesses a significant progress as a promising purification technique; however, the obstacle hinders its implementation is CO2 freeze-out causing crucial issues as blockage pipes. Therefore, in-depth analysis for tackling this barrier is performed in this work through optimizing operating conditions of a typical low-temperature CO2/CH4 distillation process. Optimization is conducted towards avoiding frosting and lowering energy consumption via varying distillation pressure, temperature, reflux ratio and number of trays, biogas feed composition, and CH4 purity generated. We found that, without CO2 freeze-out, obtaining CH4 purity of 97.12% (mol) - besides a valuable by-product (liquid CO2, 99.92% purity) - is achievable using two columns through adjusting some key parameters. The results divulge that raising distillation pressure and reflux ratio significantly mitigates frosting danger. Moreover, for energy-efficient process, using one column is the most efficient way to produce methane purity below 96% whereas two columns for higher purities. Also, feeding cryogenic process with high-concentration CO2 biogas alleviates energy penalty, ameliorating its competitiveness against traditional technologies. With these new findings, cryogenic platforms can be applicable, competitive biogas upgrading approach. (C) 2018 Elsevier Ltd. All rights reserved.