Performance evaluation of an SOFC based trigeneration system using various gaseous fuels from biomass gasification

Abstract

Thermodynamic analyses of an internal reforming solid oxide fuel cell (IR-SOFC) system are carried out using three different practical gasifier products. Syngas products from bubbling fluidized bed (BFB), circulating fluidized bed (CFB), and dual fluidized bed (DFB) gasifiers are considered and comparatively studied. Fuels from the ThermoChem bubling fluidized bed gasifier (TRI), CUTEC circulating fluidized bed gasifier and SilvaGas&Taylor dual fluidized bed gasifiers are also considered. Some parametric studies are conducted to evaluate effects of fuel and air utilization factors, recirculation ratio, stack temperature, reference-state conditions, etc., on the system performance. An SOFC based integrated system is then proposed in order to utilize relatively high temperature waste heat from SOFC unit by producing power, water heating, and space cooling. The proposed system consists of (a) an internal reforming SOFC unit, (b) an organic Rankine cycle (ORC) working with Toluene, (c) an absorption chiller cycle, and (d) a water heating unit connected to an ORC condenser. Energy and exergy efficiencies of subunits and overall system are comparatively evaluated considering irreversibilities of the system components for the best fuel performance. The TRI fueled SOFC system shows the best energy and exergy efficiencies with lowest exergy destructions throughout the trigeneration system. Energy and exergy efficiencies of the SOFC system are determined as 42.2% and 36.5%, respectively. 24.6 kW of additional power production from ORC cycle, 69.9 kW of heating energy production from water heating, and 22.1 kW of cooling load from AC cycle are obtained by the system integration. Furthermore, the system integration for exhaust gas utilization enhances the energy and exergy efficiencies up to ∼78% and ∼50%, respectively.