Flexibility in renewable fuel production from biomass – the role of electrolysis boosted Fischer-Tropsch synthesis

Abstract

When increasing the share of renewable, fluctuating energy sources, seasonal and short term mismatches have to be overcome. Especially seasonal mismatches pose a challenge as they require cost-intensive storage technologies. At the same time, reducing the dependency on fossil transport fuels increases the need for fuels made from renewable sources. The EU-project FLEXCHX proposes a polygeneration process producing renewable fuel from biomass alongside heat and electricity. Depending on the supply and demand on the energy market the FLEXCHX process can switch from a BtL to a PBtL process. In the “dark heating season” renewable fuel is produced via biomass gasification and Fischer-Tropsch synthesis whereby off-gas and steam are fed to a CHP plant to generate the desired heat and power. In the “solar energy season”, when enough renewable power is present, additional hydrogen is produced via electrolysis boosting the output of Fischer-Tropsch fuel. By applying this concept surplus electrical power can be converted into fuel. In times of high district heating demand or high energy prices the process can shift from fuel to heat production. In this contribution the efficiency of different process designs is examined based on an Aspen Plus model. Especially recycle strategies for the Fischer-Tropsch off-gas as well as different gasifier operation points are studied. The process deigns are assessed for their heat integration potential and a sensitivity analysis is performed for every key assumption. Finally, the most promising designs can be identified.