Techno-economic feasibility of a biomass-to-X plant: Fischer-Tropsch wax synthesis from digestate gasification

A techno-economic analysis is performed, assessing the production costs of Fischer-Tropsch syncrudeand waxes of carbon number C20þ. The products are obtained from the gasification of digestate fromanaerobic digestion inside a dualfluidized bed gasifier (3.11 MWth). The results are compared against thesame system fed with lignocellulosic biomass. The syngas is cleaned from impurities and conditioned toreach the desired H2/CO molar ratio of 1.8 at the inlet of the Fischer-Tropsch reactor. The Fischer-Tropschproducts distribution is based on experimental data of a cobalt-based catalyst. Two process configura-tions are studied: (1) the Fischer-Tropsch off-gas are employed to produce electricity; (2) the off-gas arerecirculated to the gasifier for enhanced wax production. Co-production of steam is also investigated. Theresults show an advantageous production of Fischer-Tropsch compounds utilizing digestate over woodbiomass. The highest plant efficiency (i.e., biomass-to-liquid fuel) of 56.3% is reached with digestatefeedstock and off-gas recirculation, outputting 61.5 kgwax/tdig. The minimum wax production cost is of3.04V/kgwax, assuming 7.5% discount rate and 25-years plant operation