Techno-economic and environmental assessment of the main biogas upgrading technologies

Abstract

Five biogas-to-biomethane upgrading technologies were compared from the environmental and economic points of view: High-Pressure Water Scrubbing (HPWS), Amine Scrubbing (AS), Potassium Carbonate Scrubbing (PCS), Pressure Swing Adsorption (PSA) and Membrane Permeation (MP). Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods were used for the comparison. In order to provide a wider picture of the conversion system and its impacts, the biogas production processes, starting from source sorted organic fraction of municipal solid waste, were included. The intention was to maintain the same object for the LCA and the LCC, given that the cost of biogas production had to be included for the calculation of the economic indicators. The cost analysis included also the evaluation of the external costs, derived from the monetization of the air emissions of the systems. The selected functional unit was the upgrading of 1 Nm3 of raw biogas. Data were collected directly from companies providing upgrading plants and confirmed by literature review. A biogas-to-biomethane plant proved to have environmental and economic benefits and, as expected, for larger plant sizes the economic performances improved. AS showed the best environmental performances mainly due to its limited CH4 losses and lower electricity consumption. Considering the contribution from only the upgrading part, AS showed the lowest impacts for the global warming potential (GWP) indicator (respectively 13%, 1%, 23% and 3% less than HPWS, PCS, PSA and MP). However, the results changed for other impact categories: for human toxicity indicator PSA showed lower impacts compared to the other technologies, respectively 7%, 144%, 1% and 9% less compared to HPWS, AS, PCS and MP. For small size plants, HPWS proved to be slightly more cost-effective compared to other technologies. For large size plants, PCS showed the highest net present value. Moreover, the sensitivity analysis showed that the electricity consumption is a key parameter for the economic and environmental results. Its variation proved that for the 60% of cases AS was the best solution in terms of GWP, however 35% and 5% of cases respectively indicated that PCS and MP had the lowest GWP.