Thermodynamic optimization of a gas turbine power plant combined with/without a solid oxide fuel cell

Gas turbine (GT) power plants operating with Brayton cycle have many benefits and are convenient for combined operation. As a high-efficiency energy conversion device, the solid oxide fuel cell (SOFC) converts the chemical energy of fuel gas directly into electricity. To achieve a higher efficiency, a single Brayton cycle can be integrated to form a combined one with an SOFC. However, the criterion of the design pressure ratio of compressor is not clear enough up to now. Based on the thermodynamic analyses of an open Brayton cycle operating in the fixed temperature limits, this work suggests a criterion of maximizing the specific cycle net work (SCNW) for the pressure ratio of a compressor. The performance is examined and compared with the literature results for an SOFC combined with a conventional recuperative gas turbine (SOFC-GT) plant. The entropy generation for an endoreversible simple open Brayton cycle system operating between two heat reservoirs is larger than zero which is a basic requirement to drive an open Brayton cycle. An irreversible recuperative GT plant or an SOFC-GT plant should operate at the optimum pressure ratio determined by the criterion for a higher turbine inlet temperature (TIT). When a steam turbine (ST) is integrated with an SOFC-GT, an SOFC-GT-ST power plant achieves an increased performance.