(500a) Process Simulation of Biogas to Renewable Liquid Fuels

Biogas is a product of anaerobic digestion of waste organic sources such as animal manure, food wastes and pretreated lignocellulosic biomass. Biogas is primarily composed of mixtures of 50–75% CH₄, 25–50% CO₂, 0–10% N₂, 0–5%O₂, 1000-2000 ppm H₂S. Biogas-to-Liquid (BTL) technology is relatively mature to produce wide range of fuels and chemicals via Fischer Tropsch synthesis. In this study, a process based simulation model was developed using an Aspen Plus^® simulation tool. The primary feedstock is a raw biogas from liquid state or solid state anaerobic digestion plant, which was upgraded to biomethane (>96% methane content) using a high pressure water scrubbing (HPWS^®) technology with a 96% upgrading efficiency. Biomethane, as similar to natural gas is converted to synthetic gas using both partial oxidation and Ni catalyst driven steam reforming in order to obtain the approximate H₂/CO ratio of 2 necessary for the FT process. A low temperature slurry-bed FT reactor was used for the conversion of syngas at a temperature of 220-240^oC in the presence of cobalt catalyst/support to generate a wide range of hydrocarbon chain products. Upgrading of the hydrocarbon products using distillation and hydrocracking processes yields diesel, LPG and gasoline fuels. The detailed mass and energy balance for each unit operation was conducted and presented along with products yield and distribution. Finally, the techno-economic model was developed to estimate the cost of drop-in fuels from biogas.