Thermodynamic and technical criteria for the optimal selection of the working fluid in a mini-ORC

Waste energy recovery (WER) is a suitable solution to improve the fuel utilization of Internal Combustion Engines (ICEs) by producing an eco-friendly electrical power from an energy source currently wasted. Organic Rankine Cycle (ORC) technology has been developed in the past few years to generate electric power from medium temperature (500 K – 800 K) ICE wasted thermal sources. Working fluid selection represents the first step in the design of an ORC. At the state of the art, authors where not able to select a single optimal organic fluid. This is mainly because of the different thermodynamic conditions of the heat sources which offer wasted thermal energy. This paper proposes a procedure for the ORC system preliminary working fluid selection, which takes into consideration thermodynamics and design parameters of the system components. The study is applied to WER systems specifically designed as bottoming cycles to ICE for transport applications. However, the method is quite general and makes the model easily adaptable to different heat sources. A steady state thermodynamic model of the system is developed via the software MATLAB. A wide variety of organic fluids (OF), such as R245fa, Solkatherm (SES36) and hexane have been investigated to identify the candidate which offers the best recovery opportunity. Regeneration is also included in this work. Results show that recover thermal energy in the regenerator is an essential method to improve power recovery when applying ORC to WER systems. The effect of superheating on the system power output has been investigated as well. It is capable to increase the cycle power output only when coupled with regeneration. The paper shows that the addition of a bottoming ORC to the ICE is convenient both in terms of recovered electric power (up to 14% of the engine nameplate power) and heat source utilization rate (up to 11 % heat source conversion into electricity). In addition, it is shown that water offers lower performance with respect to organic fluids when considering single stage radial expanders.

[1]  Andrea Lazzaretto,et al.  A New Criterion to Optimize ORC Design Performance using Efficiency Correlations for Axial and Radial Turbines , 2014 .

[2]  Ulli Drescher,et al.  Fluid selection for the Organic Rankine Cycle (ORC) in biomass power and heat plants , 2007 .

[3]  Ying Chen,et al.  Multi-criteria Design Optimization and Screening of Heat Exchangers for a Subcritical ORC , 2015 .

[4]  François Maréchal,et al.  Methodology for Identification of Suitable ORC-Cycle and Working-Fluid using Integration with Multiple Objectives , 2014 .

[5]  S. K. Wang,et al.  A Review of Organic Rankine Cycles (ORCs) for the Recovery of Low-grade Waste Heat , 1997 .

[6]  Vincent Lemort,et al.  Working fluid selection and operating maps for Organic Rankine Cycle expansion machines , 2012 .

[7]  Gequn Shu,et al.  Fluids and parameters optimization for the organic Rankine cycles (ORCs) used in exhaust heat recovery of Internal Combustion Engine (ICE) , 2012 .

[8]  Vincent Lemort,et al.  Techno-economic survey of Organic Rankine Cycle (ORC) systems , 2013 .

[9]  Daniele Fiaschi,et al.  Design and performance prediction of radial ORC turboexpanders , 2015 .

[10]  Christos Katsanos,et al.  Thermodynamic analysis of a Rankine cycle applied on a diesel truck engine using steam and organic medium , 2012 .

[11]  Chi-Chuan Wang,et al.  Effect of working fluids on organic Rankine cycle for waste heat recovery , 2004 .

[12]  Ricardo Martinez-Botas,et al.  Design methodology for radial turbo expanders in mobile organic Rankine cycle applications , 2015 .

[13]  Paolo Iora,et al.  Evaluation of ORC modules performance adopting commercial plastic heat exchangers , 2015 .

[14]  O. E. Baljé,et al.  Turbomachines—A Guide to Design Selection and Theory , 1981 .

[15]  Gequn Shu,et al.  Simulation and thermodynamic analysis of a bottoming Organic Rankine Cycle (ORC) of diesel engine (DE) , 2013 .

[16]  N. Lai,et al.  Working fluids for high-temperature organic Rankine cycles , 2007 .

[17]  Gequn Shu,et al.  Alkanes as working fluids for high-temperature exhaust heat recovery of diesel engine using organic Rankine cycle , 2014 .

[18]  T. Hung.  Waste heat recovery of organic Rankine cycle using dry fluids , 2001 .