Energy and exergy analysis of a combined system: cascade organic Rankine cycle and cascade refrigeration cycle

Touaibi Rabah,Hemis Mohamed,Boudjema Fadhila,Selmane Salma,Hasan Koten

doi:10.18186/thermal.977992

Abstract

In this paper, a new combined system is proposed for recovering thermal energy at medium temperature using a cascade organic Rankine cycle to feed a cascade refrigeration cycle. Energy and exergy analysis is applied to the combined system to determine its performance using different working fluids under the same operating conditions taking into account the effect of some operating parameters and the selection of organic fluids on cycle performance. The pair of organic fluid (Toluene/R245fa) used for the cascade organic Rankine cycle and the pairs (R717/R744, R717/R23, R134a/R23) used for the cascade refrigeration cycles. The results show that the combined system function with the couple (R717/R23) for cascade refrigeration cycle gives better exergy efficiency 50.03% compared to other couples, 49.57% for the couple (R717/R744), and 48.01% for the couple (R134a/R23). The thermodynamic evaluation shows that the operating temperatures, such as the cascade organic Rankine cycle evaporation temperature and the cascade refrigeration cycle evaporation temperature influence the performance of the combined system.

Highlights

Industrial processes are generally characterized by the loss of energy in a form of heat
A novel design of the organic Rankine Cycle (ORC)-cascade refrigeration system (CRS) combined system is based on a thermodynamic analysis
A couple of working fluids (Toluene/R245fa) is used for the cascade ORC cycle with R717/R23 as working fluid for the cascaded CRS cycle taking into account the fact that the thermodynamic properties are determined using Solkane and Coolpack software and that Wnet ORC = WCom_CRS

Summary

Introduction

Industrial processes are generally characterized by the loss of energy in a form of heat This dissipated energy reduces the effectiveness of these processes and contributes to the environmental impacts associated with the use of the fossil fuel. These low-temperature discharges cannot be used to generate electricity via a steam thermal plant (Conventional Rankine Cycle). Alternative technologies like the organic Rankine Cycle (ORC) can convert the waste heat to electricity at a relatively low temperature They contribute significantly to reduce fuel costs and pollution as well. Bellos and Tzivanidis optimized a system with Organic Rankine Cycle (ORC), an absorption chiller for cooling, heating, and electricity production. The heat source generally comes from geothermal energy [5,6,7,8], biomass energy [9, 10], or industrial waste streams [11, 12], otherwise solar energy [13, 14]

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Results

Conclusion