Performance Analysis and Working Fluid Selection of a Supercritical Organic Rankine Cycle for Low Grade Waste Heat Recovery

Hong Gao,Xiaoxiao Xu,Yourong Li,Chao Liu,Chao He,Shuangying Wu

doi:10.3390/en5093233

Abstract

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a.

Highlights

Over the past years, with the increasing consumption of fossil fuels, more and more low-grade industrial processes are producing a great amount of waste heat
The results showed that when fluids go in supercritical organic Rankine cycle (ORC) from subcritical ORC, cycle thermal efficiency varies continuously, while mass flow rate and net power generation vary discontinuously
This paper presents an analysis of the performance of supercritical ORC using 18 organic working fluids

Summary

Introduction

With the increasing consumption of fossil fuels, more and more low-grade industrial processes are producing a great amount of waste heat. Being discharged into the environment, this exhaust energy could cause serious heat pollution. If made good use of, this exhaust energy could reduce fossil fuel consumption. To recover and utilize this type of energy, the organic Rankine cycle (ORC) system was proposed. The ORC is similar to the steam Rankine cycle, except for using organic working fluids with low boiling points. Besides the ORC, researchers have proposed various thermodynamic cycles, such as Kalina cycle, Goswami cycle, and trilateral flash cycle, to convert this low-grade heat sources into electricity

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