Energy and Exergy Analysis for Low-Temperature Refrigeration System for Biogas Upgrading

Abstract

Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps: removing most of the water content at-40°C, removing siloxanes and SVOCs at-85°C and frosting CO2 at temperatures varying from-90°C to-120°C. This process transforms biogas containing typically 60% methane, 35% CO2, 5% water vapor in methane containing 2.5% of CO2. This paper studies how a single low-temperature refrigeration system is able to cool biogas with an indirect system using low-temperature heat-transfer fluids. The exergy study defines the exergy losses and served as guidance for the energy/pinch analysis that is used for the design of the heat-exchanger series and the appropriate heat recovery. An optimal system could save up to 40% of the electric consumption of the refrigeration system.