Energy and economic analysis of a water scrubbing based biogas upgrading process for biomethane injection into the gas grid or use as transportation fuel

This works describes the biogas upgrading process to substituted natural gas (SNG), specifically calledbiomethane, for grid and vehicle application. The physical processes of carbon dioxide absorption anddesorption respectively in a pressurized water scrubber and a stripper are described by means of theHenry’s law. Both the water scrubber and CO2stripper columns are designed by means of the TransferUnits Method in order to handle the biogas stream that is available from an anaerobic digestion of manure.In particular, a case study of a small scale plant located in the centre of Italy is analysed with the aim toassess the energy conversion efficiency and economics of the upgrading process for grid injection andvehicle application. It is found that the whole process efficiency is respectively 89.8% in the case of gridinjection and 87.3% in the case of vehicle application.Concerning with the economic analysis of the plant, the capital and operating costs of the plant aredetermined and the Italian legislative framework is included to account for subsidies. Results show thatthe unit production cost of biomethane for grid injection is 0.54V/Sm3while it is 0.73V/Sm3in the caseof vehicle application