Integration of Solid Oxide Electrolyzer and Fischer-Tropsch: A sustainable pathway for synthetic fuel

Because of their easy and widespread distribution and safe handling, liquid fuels are used in everyday life, to power vehicles, aircrafts, ships, etc. The use of fuels from conventional fossil sources is now called for a more sustainable alternative. Hence, chemical energy storage of electricity generated by renewable sources into synthetic fuels represents an interesting solution, solving also other typical problems with renewables, such as grid stabilization. Within this framework, the present study deals with the production of synthetic green fuels by means of the Fischer-Tropsch process, downstream a previous electricity-to-gas conversion achieved operating a Solid Oxide Electrolyzer (SOE) stack in co-electrolysis. With reference to the state of the art, this study developed the concept of integrating an SOE and a Fischer-Tropsch process in a small plant size, which is compatible with renewables power density. To this aim, fuel upgrading is supposed to be performed separately. Based on experimental results on a Solid Oxide Cells stack operated in co-electrolysis, three system-level models were developed, evaluating the most performing option. Thus, considering a plant capacity of 1 bbl/day of liquid fuel, in the best scheme, the electricity-to-liquid efficiency was estimated to be 57.2%. Materials introduced into the system are simply water (33,701 ton/MJ) and carbon dioxide (79,795 ton/MJ). While hydrogen is necessary to feed the SOE, net consumption is zero because it is recovered from Fischer-Tropsch product lighter fraction.