Design considerations of an integrated thermochemical/biochemical route for aviation and maritime biofuel production

Abstract

Abstract An integrated thermochemical-biochemical Biomass-to-Liquid (BtL) pathway for the production of aviation and maritime liquid fuels from biogenic residues is introduced. The presence of a semi-commercially proven technology like Dual Fluidized Bed Gasification (DFBG) ensures extended fuel flexibility, syngas of high quality, complete fuel conversion, and optimal heat integration while avoiding CAPEX (Capital Expenditure) intensive equipment like air separation unit. Then, a two-stage biochemical route is proposed: initially syngas fermentation (anaerobic) into acetate and subsequently acetate fermentation (aerobic) into targeted triglycerides (TAGs) that will be finally purified and hydrotreated to form the desired drop-in biofuels. The tolerance of the bacteria to syngas contaminants minimizes the gas cleaning requirements. Moreover, the low-pressure requirements (1–10 bar) along with the mild operating temperatures (30–60 °C) reduce drastically the capital and operational cost of the process. The biological process of syngas fermentation inherently has limited side products, a fact that reduces the risk of deactivation of hydrotreatment catalysts. Heat and mass balances are calculated for the proposed concept via full-scale process simulations in Aspen Plus™ assuming a thermal input of 200 MWth with crushed bark as feedstock. Three different operational scenarios are examined mainly through overall performance indicators such as carbon utilization (CU) and energetic fuel efficiency (EFE). Competitive performance compared to technologies that exploit similar feedstock (i.e., biogenic residues) was noticed, since values in the range of 22–27% and 31–37% were obtained for the CU and EFE, respectively. The aim of this study is to determine the appropriate key process specifications and assess the potential of the proposed concept compared to other competitive technologies.