Thermo-economic optimization of a Solid Oxide Fuel Cell - Gas Turbine system fuelled with gasified lignocellulosic biomass

Within the context of sustainable energy supply and CO2 emissions reduction a Solid Oxide Fuel Cell (SOFC) - Gas Turbine hybrid system, fuelled with gasified woody biomass for medium scale applications (8MWth,BM of dry biomass) is studied in detail. The system consists of an air dryer moisture removal unit, a gasifier, a hot cleaning section made of a particulate removal unit (cyclone and candle filter) and a two-stage TAR removal unit, a SOFC and a gas turbine with optional CO2 capture. This modern technology has the advantage of using a renewable and CO2-neutral source and to be economically competitive at medium scales. The competitiveness of different process options is systematically compared by applying a coherent approach combining flowsheeting, energy integration and economic evaluation in a multi-objective optimization framework. This analysis reveals the importance of process integration maximising the heat recovery and valorising the waste heat, by cogeneration for example. The studied process options include indirect circulating fluidized bed (using steam or oxygen as gasification agent) and Viking gasifier, atmospheric or pressurized systems and optional pre-reforming in the hot gas cleaning. To close the thermal energy balance, a fraction of the produced syngas can be burnt. The energy integration results reveal that the steam production for the gasification and reforming are key parameters (S/B and S/C ratio) defining the process performance. A multi-objective optimization maximizing the efficiency and minimizing the capital investment costs is performed with respect to the operating conditions and the process configuration in order to assess the trade-offs and identify optimal process designs. The analysis shows the potential of the system converting woody biomass into electricity with energy efficiency greater than 70%.