Exergoeconomic optimization of a combined cycle power plant’s bottoming cycle using organic working fluids

Abstract

One of the measures to reduce carbon dioxide emissions and increase energy efficiency in a combined cycle power plant is the improving of its thermodynamic efficiency by optimizing the heat utilization s study, a mathematical model of the bottoming cycle of a combined cycle power plant was developed in Matlab. The heat recovery steam generator, which is a crucial element of the bottoming cycle, is modeled as a heat exchanger network. It consists of multiple pressure levels and a reheater that uses organic working fluids in the lower pressure levels. The mathematical model provides the possibility that the heat exchangers in each pressure level could be in parallel and serial arrangements. An exergoeconomic optimization was conducted, where the optimization variables comprised the heat exchanger layout and the operating parameters of the working fluid in each pressure level. The objective of the optimization was to minimize the sum of the cost of exergy destruction in the bottoming cycle and investment costs. The genetic algorithm and gradient optimization methods were used as optimization tools. The results show that lower cost of exergy destruction can be achieved by optimizing the heat exchanger layout and using organic fluids in the lower pressure levels of a heat recovery steam generator. This research work addresses a gap in the literature by taking into account the heat exchanger layout, optimization parameters, and organic fluids while optimizing a bottoming cycle, which is of essential importance.