Thermodynamic Modeling and Multi‐Objective Optimization of a New System Presented for Reutilization of the Lost Heat in Combined‐Cycle Power Plants

Abstract

In combined‐cycle power plants, a large amount of thermal energy is lost when the boiler and steam unit are out of order and the gas unit is operated in single mode. For the first time, this work suggests every combined‐cycle power plants should be equipped with this kind of energy system to recover the waste heat by producing hydrogen and generating electricity. This system combines a Rankine cycle with a thermoelectric generator, a finned‐tube heat exchanger, and a proton exchange membrane to produce hydrogen. Having been designed, the suggested energy system is assessed by energy, exergy, and exergo‐economy laws. Furthermore, the impacts of some effective factors on the efficiency and the costs are precisely analyzed. Eventually, the presented system is optimized considering two main purposes of exergy efficiency and costs. The achieved results show that the proposed system can effectively link to the gas unit to restore and even save the lost thermal energy in the single‐mode condition. The conducted optimization attenuates the objective parameter of exergy efficiency from 48.39% to 41.65% and diminishes the costs from 550.14 to 480.82 $ GJ−1. Eventually, the optimization causes to rise from 1.2 to 1.32 kg h−1.