Technical-economic assessment of different biogas upgrading routes from vinasse anaerobic digestion in the Brazilian bioethanol industry

This paper presents a technical-economic assessment of biomethane production from vinasse in the Brazilian bioethanol industry, considering five technological routes of biogas upgrading. The technologies assessed were pressure water scrubbing, organic-physical scrubbing, amine scrubbing, membrane separation and pressure swing adsorption. The biomethane costs of the five technological routes overlapped in the range between R$30/GJHHV (US$13/GJHHV) and R$34/GJHHV (US$14/GJHHV), which indicates a certain equivalence of the options. Those costs were comparable to the prices of potential alternative fuels at 2014 prices, such as the Bolivian natural gas, priced at R$20/GJ (US$8/GJ); imported LNG, at R$31/GJ (US$13/GJ); and diesel, at R$42/GJ (US$18/GJ). The effects of scale on biomethane cost were also assessed and pointed out that the likely minimum scale for vinasse-to-biomethane projects aiming at diesel substitution would be at sugarcane mills with a minimum capacity of producing 87 million liters of ethanol per season, whereas if the aim were to target natural gas markets, 174 million liters of ethanol per season would likely be the minimum capacity for competitive prices.