Renewable LNG production: Biogas upgrading through CO2 solidification integrated with single-loop mixed refrigerant biomethane liquefaction process

Abstract

Biogas upgrading followed by biomethane liquefaction is preferred for long-distance transportation and storage. Cryogenic upgrading technology is a promising option for producing high purity biomethane. Although the cryogenic approach is energy-intensive, its integration with the liquefaction process provides dual benefits (upgrading and precooling of biomethane), ultimately reducing the overall energy load. Herein, a biomethane liquefaction process followed by CO2 solidification is presented. The CO2 solidification phenomenon is studied using the Aspen Hysys® v11 and validated against available experimental data. The single-loop mixed refrigerant used for CO2 solidification consists of methane, propane, and CO2, whereas biomethane is liquefied using a conventional mixed refrigerant i.e., nitrogen, methane, ethane, and propane. The modified coordinate descent algorithm is employed to optimize the design variables of the proposed integrated process. The proposed optimal process offers an overall energy savings of 68.6% compared to the published base case. The exergy efficiency of the proposed process is 23.7%. Cryogenic exchangers are the major source of exergy destruction. An economic analysis is also performed to evaluate the preliminary feasibility of the proposed process. In terms of process configuration, energy consumption, exergy efficiency, and process economics, the proposed process is superior to the available base case. The findings of this study will help process engineers achieve sustainable renewable energy by significantly improving the biomethane value chain.