High temperature solid oxide fuel cell integrated with novel allothermal biomass gasification. Part I: Modelling and feasibility study

摘要

Biomass gasification derived fuel gas is a renewable fuel that can be used by high temperature fuel cells. In this two-part work an attempt is made to investigate the integration of a near atmospheric pressure solid oxide fuel cell (SOFC) with a novel allothermal biomass steam gasification process into a combined heat and power (CHP) system of less than MW_e nominal output range. Heat for steam gasification is supplied from SOFC depleted fuel into a fluidised bed combustor via high temperature sodium heat pipes. The integrated system model was built in Aspen Plus~(TM) simulation software and is described in detail. Part I investigates the feasibility and critical aspects of the system based on modelling results. A low gasification steam to biomass ratio (STBR = 0.6) is used to avoid excess heat demands and to allow effective H_2S high temperature removal. Water vapour is added prior to the anode to avoid carbon deposition. The SOFC off gases adequately provide gasification heat when fuel utilisation factors are <0.75; otherwise extra biomass must be combusted with overall efficiency penalty. For SOFC operation with U_f = 0.7 and current density 2500 A m~(-2) the electrical efficiency is estimated at 36 percent while thermal efficiency at 14 percent. An exergy analysis is presented in Part II.