Optimization of a 200 kW SOFC cogeneration power plant. Part II: variation of the flowsheet

An energetic and economic analysis of a decentralized natural gas-fuelled solid oxide fuel cell (SOFC) power plant in the range of 200 kW capacity is carried out. All calculations start from a basic plant concept with a simple flowsheet and a basic parameter set of SOFC operation and economic data. Changes in costs of electricity and plant efficiencies are determined for variations of the plant concept. Flowsheets with gas recycling by blowers or jet boosters are described. Cathode gas recycling by jet boosters turns out to be more advantageous with respect to the costs of electricity than gas recycling by hot gas fans. The influence of pressure drop in the cathode gas circuit is analyzed. In case of anode gas recycling an internal steam circuit exists. This has the advantage that the external steam generator is eliminated and that the steam concentration in the exhaust gas is reduced. Therefore, a higher amount of excess heat can be used. Removal of useful heat at higher temperature levels diminishes the driving temperature differences and enlarges the heat exchange area of the recuperative heat exchangers located downstream.