Exergy analysis of a three stage expansion and regenerative Rankine cycle

The importance of combined heat and power generation systems has greatly increased in recent years because as these systems produce electricity, the waste heat is utilized in processes such as heating, cooling, and process vapor. In this study, the proposed combined heat and power generation system consisted of a three-stage turbine, condenser, boiler, open feed water heater and two pumps. The second law analysis of the elements of the combined heat power system was performed. Exergy destructions of condenser, pumps, boilers, turbines, throttling valves, and open feed water heater were investigated with respect to the turbine inlet temperature and pressure. In this context, a computer program was developed by using EES (Engineering Equation Solver) software. The turbine inlet pressure varied from 8,000 kPa to 18,000 kPa and the turbine inlet temperature ranged from 460°C to 560°C. As the turbine inlet temperature increased, the exergy destructions of the boiler, turbines and condenser increased, while the exergy destructions of the pumps and open feed water heater did not change. As the turbine inlet pressure increased, the exergy destructions of the boiler, turbines and condenser decreased, while the exergy destructions of the pumps and open feed water heater again did not change. The maximum exergy destruction occurred in the boiler, while the minimum exergy destruction occurred in pump1.