Optimized performances comparison of organic Rankine cycles for low grade waste heat recovery

Abstract

An organic Rankine cycle (ORC) can be applied to recover the low-grade waste heat. In this paper, the performances of five different types of ORC are evaluated. These configurations include a simple ORC, an ORC with an internal heat exchanger (IHE), an ORC with an open feed organic fluid heater (OFOH), an ORC with a closed feed organic fluid heater (CFOH), and an ORC with a reheater. First, the feasible working region is defined for an ORC operating together with an internal combustion engine. Subsequently, the thermal efficiency of each ORC is maximized using a genetic algorithm. Finally, the characteristics of each ORC are analyzed and compared using a combination of the first law and second law method. Our analysis indicates that the ORC with an IHE showed the best thermodynamic performance. The ORC with an OFOH and the ORC with a CFOH are sub-optimal while the simple ORC and the ORC with a reheater are the last choice. The effects of the expander inlet pressure, the condenser outlet temperature and the expander isentropic efficiency on system performance of each ORC were also analyzed.