Techno-economic analysis of a biogas-to-methanol process: Study of different process configurations and conditions

Bio-methanol produced from renewable resources, such as biogas, represents an interesting low carbon energy carrier due to its versatility. Few publications are available on the topic and techno-economic assessments focusing on the production of renewable methanol are needed to properly design such plants and understand their potential. To this purpose, a detailed techno-economic analysis of a 20 MWLHV biogas to methanol process via steam reforming is presented in this work. The process was designed to treat biogas produced via anaerobic digestion of municipal solid waste and be autonomous from a thermal viewpoint. The analysis included the comparison of three different process configurations, differing in the presence and position of the carbon dioxide separation unit. Sensitivity analyses were carried out on key process parameters, namely MeOH synthesis loop Recycle Ratio (RR, in the interval 3 -7), methanol reactor pressure (pMeOH; 50 - 95 bar) and Gas Hourly Space Velocity (GHSV, 4000 -8000; Nm3/h.m3 ). The best plant configuration was achieved when carbon dioxide CAT separation was performed upstream of the reformer, which allowed to achieve higher carbon and fuel effi-ciencies. In the base case (RR = 5, pMeOH = 95 bar, and GHSV = 4000 Nm3/h.m3 ), such configuration pro-CAT duced 2480 kg/h of methanol, with a carbon and fuel efficiency equal to 51.4% and 72.2% respectively and a levelized cost of methanol of 378.0 euro /t. Reactor pressure considerably affected process profitability, whereas GHSV and RR had little impact on process economics. When methanol reactor pressure was decreased to 50 bar, methanol production kept almost constant, but overall costs were remarkably lower. This led to a higher prof-itability, with a levelized cost of methanol of about 357.7 euro /t.