Numerical Modeling of Biogas Liquefaction Process with Two-Stage Expander Technologies

Biogas is a kind of promising energy for its clean and environmental. It can be obtained from many organic materials and wastes in our daily life. However, the raw biogas cannot be used directly for its low concentration of methane, so an upgrading process and a liquefaction process is need. In this paper, a kind of new system used for biogas liquefied technology was designed. The system consists of screw compressor, water cooler, turbo expander, separator and heat exchanger. Before the biogas enters the system, water scrubbing was carried out to upgrading the biogas. Aspen HYSYS was used for the study to understand the effect of physical parameters such as temperature, pressure and the concentration of the biomethane in the biogas. The results from the simulations show that the energy consumption increased with the increase of the biogas inlet temperature, whereas the liquefaction ratio stay stable. When the inlet gas pressure increased, the energy consumption decreased quickly but the liquefaction is increased. And with the increase of the biogas flow rate, the energy consumption increased and the liquefaction is decreased.