Thermodynamic study of different configurations of gas-steam combined cycles employing intercooling and different means of cooling in topping cycle

Abstract

Various options for improving the performance of gas/steam combined cycle, the performance enhancement can be achieved by increasing the turbine inlet temperature and/or increasing the cycle pressure ratio along with intercooling for reducing compression work and reheating for increasing the expansion work. The present paper analyses eight novel configurations of the intercooled gas turbine based combined cycles having the gas turbine blade cooled using closed loop cooling scheme. Combined cycle configurations differ in respect to cooling medium being steam or ammonia-water, intercooling, reheating, single/dual/triple pressure heat recovery steam generator, steam turbine, and ammonia water turbine. The comparative evaluation of combined cycle arrangements is based on thermodynamic modeling using first law and the second law of thermodynamics for the inlet temperature to turbine of 2000 K and ambient temperature of 303 K. Study aims at furnishing results for understanding the implications of modifications on the cycle performance. The results show that maximum 1142 kJ/kg of work is obtained for ammonia concentration of 0.6 while the maximum cycle efficiency of 53.87% and second law efficiency of 58.46% is obtained for ammonia concentration of 0.7 at cycle pressure ratio of 40 for combined cycle with triple pressure heat recovery vapor generator having ammonia-water cycle at high pressure& intermediate pressure and Rankine cycle at low pressure.