Design of an SOFC System Combined to the Gasification of Biomass

摘要

Alternative fuels, such as biomass crops and industrial wood residues, grow in interest as they have the potential to substitute fossil fuels in heat and power production. Use of biomass decreases the depletion of primary energy carriers and allows reduction of the environmental impact. The gasification or pyrolysis enables the conversion of this 'difficult' energy source into a gaseous fuel for use in a subsequent power cycle. Simultaneously, the promising hybrid concept of a high temperature fuel cell combined with a bottoming cycle, receives attention due to high efficiencies. With the great fuel flexibility of the solid oxide fuel cell and the simplicity of a gas turbine cycle, the integration of biomass gasification into an SOFC/GT system opens a viable path which meets the demands of resource preservation and high efficiency power production. In this paper, a plant concept of around 4-5 MWe power output is suggested comprising exhaust gas drying of the biomass, a pressurized gasifier, a SOFC of planar design and a gas turbine. The study evaluates this system thermodynamically and clarifies optimum parameter constellations. Two base cases have been calculated, one with a larger (100 %) and one with a smaller stack size (45 %). In the first case, system efficiency reaches 58% (LHV) at a pressure between 2 and 3 bar, whereas in the second case efficiency reaches 55 % at a pressure of around 5 bar. By reducing the stack area and increasing the gas turbine output a relatively high efficiency still can be obtained at the advantage of a reduced capital cost.