Design of heat recovery steam generator (HRSG) and selection of gas turbine based on energy, exergy, exergoeconomic, and exergo-environmental prospects

The full repowering of an existing fossil fuel steam power plant is investigated. This study aims to introduce and examine the most important parameters, i.e., the design of the heat recovery steam generator (HRSG) and se-lection of the gas turbine (GT). The repowered cycle is studied in perspectives of energy, exergy, economic, and environmental views. Considering the pressure levels of the HRSG and the number of HRSGs in the new cycle, six different cases are evaluated. The produced power of the original units is 200 MW. The results of this study show that using two 180 MW GT and two HRSGs results the maximum possible thermal efficiency. By using a high-capacity GT (380 MW), the maximum efficiency will be obtained in case of using one HRSG. Moreover, in all cases, the CO2 production rate is reduced. Introducing new nondimensional parameters named x, y, and alpha, the balance of the axial force of the steam turbine shaft and the capacity of cooling system are considered. The effect of various parameters on these three parameters are analyzed.