Repowering of an Existing Power Plant by Means of Gas Turbine and Solid Oxide Fuel Cell

Repowering is a process consisting in a transformation of an old power plant in order to have a greater nameplate capacity or more efficiency, which result in a net increase of power generated. As a consequence of the higher efficiency, the repow ered plant is characterized by higher power output and less specific CO2 emissions. Usually, a repowering is performed adding one or more gas turbines to an existing steam cycle which was built decades ago. Thus, traditional repowering results in combine d cycles (CC). High temperature fuel cells (such as SOFC) could also be used as a topping cycle, reaching global plant efficiency even higher and specific CO2 emissions even lower. Decreasing the operating temperature in a SOFC allows the use of less compl ex materials and construction methods, consequently reducing plant and the electricity cost. A lower working temperature makes it also suitable for topping an existing steam cycle, instead of gas turbine on the top. This is also the target of this study, r epowering of an existing power plant with SOFC as well as gas turbines. The plant used here for repowering is the Kyndby power station is an emergency and peak load facility for Zealand in Denmark. This means the facilities at the station can be started up within minutes if operational irregularities occur in the high voltage electricity grid or problems arise at other power stations. Nowadays this station is repowered with two gas turbines but the current study is about the original steam plant before re powering. Different repowering strategies are studied here, repowering by one gas turbine with and without supplementary firing, repowering by two gas turbines with and without supplementary firing and repowering using SOFC. Plant performances and CO2 emi ssions are also compared for the suggested repowering plants .