Thermodynamic analysis of combined system with twostep reaction-comparison among them

In thermal power plants, a large amount of fuel exergy is destroyed during the combustion process. Thus, it seems convenient to consider studies of new systems to reduce irreversibilities in the conversion of chemical exergy into work. Some systems include a gas turbine with chemical-looping combustion where a metal oxide is used as an oxygen carrier. Instead of conventional combustion, the oxidation of the fuel is carried out in a two-step reaction. The first reaction step is an exothermic oxidation of a metal with air and the second reaction step is an endothermic oxidation of the fuel with the metal oxide from the first step. The low-grade thermal energy in the exhaust gas is used to drive the endothermic reaction. A novel combined cycle was recently proposed. This system consists of fuel-rich and fuel-lean combustors, two gas turbines, two compressors and a steam bottoming cycle. Important features of this system are the first turbine with C/C composite blades and the first combustion, which is fuel-rich. This technique entails no cooling of turbine blades and allows much higher turbine inlet temperature and, consequently, much higher exergy efficiency. Entropy productions and exergy losses are focussed in the analysis.