Exergetic Performance Analysis of a Gas Turbine Cycle Integrated With Solid Oxide Fuel Cells

Abstract

Energy and exergy assessments are reported of integrated power generation using solid oxide fuel cells (SOFCs) with internal reforming and a gas turbine cycle. The gas turbine inlet temperature is fixed at 1573 K and the high-temperature turbine exhaust heats the natural gas and air inputs, and generates pressurized steam. The steam mixes at the SOFC stack inlet with natural gas to facilitate the reformation process. The integration of solid oxide fuel cells with gas turbines increases significantly the power generation efficiency relative to separate processes and reduces greatly the exergy loss due to combustion, which is the most irreversible process in the system. The other main exergy destruction is attributable to electrochemical fuel oxidation in the SOFC. The energy and exergy efficiencies of the integrated system reach 70–80%, which compares well to the efficiencies of approximately 55% typical of conventional combined-cycle power generation systems. Variations in the energy and exergy efficiencies of the integrated system with operating conditions are provided, showing, for example, that SOFC efficiency is enhanced if the fuel cell active area is augmented. The SOFC stack efficiency can be maximized by reducing the steam generation while increasing the stack size, although such measures imply a significant and nonproportional cost rise. Such measures must be implemented cautiously, as a reduction in steam generation decreases the steam/methane ratio at the anode inlet, which may increase the risk of catalyst coking. A detailed assessment of an illustrative example highlights the main results.