Eco-Efficiency Analysis of Biomethane Production

This work was concentrated on upgrading an existing biogas plant, located in Wittmund (Germany; biogas volume flow, 3167.361 L min(-1); CH4, 67,51 mol %; CO2, 29,87 mol %; N-2, 1.98 mol %; O-2, 0.65 mol %; H2S, 5.99 mgS m(-3)), operated by EWE GmbH, to a biomethane plant. Scrubbing with alkanoalmine solutions was chosen as the carbon dioxide capturing method, since it has proven to be an efficient method of removing carbon dioxide and to obtain high methane slippage. Hence, this research was concentrated on a model based upon economical, social, and ecological assessment of the alkanolamines, used only for capturing the carbon dioxide, which include monoethanolamine (MEA), diethanolamine (DEA), 2-(ethylamino)ethanol (EAE), and diglycolamine (DGA). In the economical evaluation the energy consumption for the desorption step was evaluated, whereas the environmental assessment included marine toxicity and biodegradability. In order to complete the sustainability evaluation, the social aspects were evaluated with use of the reduced inherent safety index method. The environmental evaluation indicated that three amines, MEA, DEA, and EAE, fulfilled the criteria of the low toxicity to marine organisms and high biodegradability. DGA was recognized to be dangerous for the environment. Furthermore, the social assessment revealed that the evaluated amines have similar social acceptance, reflected by the similar chemical safety. Finally, the economical evaluation slightly favors 3.2 mass % EAE aqueous solution (energy efficiency of 0.262 MW per each mol of carbon dioxide recovered; 100% CO2 removal) and 30 mass % EAE aqueous solution (energy efficiency of 0.214 MW mol(-1); 100% CO2 removal) over 30 mass % MEA aqueous solution (efficiency of 0.307 MW mol(-1); 94.209% CO2 removal). As a consequence, 2-(ethylamino)ethanol and monoethanolamine were proved to be sustainable alkanolamines for biogas upgrading.