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2.3 MECHANICAL ENGINEERING, Thermodynamics, Chemical engineering (plants, products), Energy and fuels, Biofuels
Biomass is of major interest as a renewable energy source in the context of climate change and energy security. Traditional biomass conversion technologies achieve low electrical efficiencies. Biomass gasification (BG) coupled with fuel cells offer higher efficiencies. Gasification is a process in which a carbonaceous fuel is converted to a combustible gas. It occurs when a controlled amount of oxidant is reacted at high temperatures with available carbon in a fuel within a gasifier. Two technologies (circulating fluidised bed air gasification and dual fluidised bed steam gasification) were modelled. Solid oxide fuel cells (SOFCs) are well suited to integration with gasification due to their high operating temperature and fuel flexibility. They convert the chemical energy contained in a fuel directly to electrical energy via electrochemical reactions, making them highly efficient. The tubular SOFC configuration was selected. The main aim of the research work was to investigate the feasibility of BG-SOFC systems through thermodynamic modelling and economic analyses. Standalone models of the gasification technologies and the SOFC were developed and validated. These models were integrated considering gas cleaning, heat recovery and balance of plant. An engineering economic model was developed and applied to determine the commercial viability of the BG-SOFC systems. The results indicated that these systems are attractive with regard to their operating efficiency; however, they are not yet commercially viable. Capital costs and biomass fuel prices must fall dramatically if these systems are to become competitive. A cathode recycle or electric heater for syngas preheating is not attractive. Thermal integration between the gasifier and fuel cell is desirable. Lowering the syngas preheat temperature is highly recommended. High temperature syngas cleaning reduces plant complexity and improves performance. Gasification air preheating is more attractive than gasification steam superheating.
Doherty, W. (2014) Modelling of Biomass Gasification Integrated with a Solid Oxide Fuel Cell System, Doctoral Thesis, Dublin Institute of Technology. doi:10.21427/D76P5V