Simulation and economic evaluation of process alternatives for biogas production and purification from sugarcane vinasse

Vinasse, which is the main residue of ethanol production, is a promising alternative for the generation of biogas, due to its high generation rate and limited application. The objective of the present work is to simulate and economically compare alternative processes for the production and treatment of biogas from the anaerobic digestion of vinasse. Different water, H2S and CO2 removal technologies were evaluated: condensation, membrane separation, washing, Pressure Swing Adsorption (PSA), adsorptions with silica gel, activated carbon and metallic oxides, absorptions with triethylene glycol (TEG), ethylenediaminetetraacetic acid iron (III) (Fe/EDTA) and diethylamine (DEA). It was shown that an anaerobic lagoon is preferable over a set of Upflow Anaerobic Sludge Blanket (UASB) reactors due to the large processing scale, reducing the capital costs. Among the 12 evaluated routes, the best process alternative for biogas treatment was water removal through silica gel adsorption, followed by simultaneous H2S and CO2 absorption in a Fe/EDTA solution. In the best scenario, the entire biomethane production plant would require an investment of US$ 3.6 million, resulting in an annual net profit of US$ 1.99 million, with payback in the first year of operation.