A new approach to determining the intermediate temperatures of endoreversible combined cycle power plant corresponding to maximum power

Abstract

Determining the optimal operating temperatures of power plants corresponding to maximum power is important for not only the analysis of cycle performance, but also the selection of appropriate working fluids and their pressures. This study develops a new and convenient approach to determining the intermediate operating temperatures of n-stage endoreversible combined cycle power plants comprising n (arbitrary number) Carnot heat engines corresponding to the twice maximized power output by using the entransy transfer efficiency as an auxiliary parameter. The new approach reveals that when the temperatures of the hot and cold reservoirs, the total thermal conductance as well as the stage number of the n-stage power plant are given, only two of these intermediate temperatures have fixed values, while the other ones are variable. It provides considerable flexibility for the designers to the selection of the optimal operating temperatures and appropriate working fluids. The procedures for determining all the possible values of these intermediate temperatures are demonstrated. Next, a practical optimization problem of a two-stage combined cycle power plant is taken as an example to illustrate the superiority of the newly proposed approach to the existing one. Finally, the physical meaning of entransy transfer efficiency, together with its limitation is discussed and a comparison between the entransy-based efficiency and exergy-based efficiency is presented.