Performance Comparison on Repowering of a Steam Power Plant with Gas Turbines and Solid Oxide Fuel Cells

Repowering is a process for transforming an old power plant for greater capacity and/or higher efficiency. As a consequence, the repowered plant is characterized by higher power output and less specific CO 2 emissions. Usually, repowering is performed by adding one or more gas turbines into an existing steam cycle which was built decades ago. Thus, traditional repowering results in combined cycles (CC). High temperature fuel cells (such as solid oxide fuel cell (SOFC)) could also be used as a topping cycle, achieving even higher global plant efficiency and even lower specific CO 2 emissions. Decreasing the operating temperature in a SOFC allows the use of less complex materials and construction methods, consequently reducing plant and the electricity costs. A lower working temperature makes it also suitable for topping an existing steam cycle, instead of gas turbines. This is also the target of this study, repowering of an existing power plant with SOFC as well as gas turbines. Different repowering strategies are studied here, repowering with one gas turbine with and without supplementary firing, repowering with two gas turbines with and without supplementary firing and finally repowering using SOFC. Plant performances and CO 2 emissions are compared for the suggested repowered plants.