A New Criterion to Optimize ORC Design Performance using Efficiency Correlations for Axial and Radial Turbines

Abstract

Several studies on Organic Rankine Cycles (ORCs) in the literature search for the optimal cycle parameters and working fluids that maximize the net power output. Only few studies carry out a preliminary turbine design to calculate an accurate value of turbine efficiency, but this is done only after the cycle thermodynamic optimization is performed assuming a fixed and somewhat arbitrary value of turbine efficiency. Instead, a new design optimization procedure of ORCs is proposed here which embeds correlations for the design efficiency of both axial and radial turbines. The correlations are obtained from published data in the literature and use the volumetric expansion ratio (VR) and the size parameter (VH) as performance predictors. While been applied to a selected number of working fluids and single stage turbines, the procedure has a general validity being the correlations applicable to any fluid and turbine type. Results show how the turbine efficiency, and in turn the optimum cycle parameters, are influenced by the fluid properties through the turbine VH and VR values, highlighting that the procedure for working fluid selection cannot ignore the real turbine behaviour. So, the optimum design that is obtained is expected to give a behaviour much closer to reality.

Keywords

• Organic Rankine Cycle; synthesis/design optimization; turbine design; working fluid selection; power generation.

References

1. H. Chen, D.Y. Goswami, M.M. Rahman, E.K. Stefanakos, Energetic and exergetic analysis of CO 2 and R32-based transcritical Rankine cycles for lowgrade heat conversion, Appl Energ, 88, 2802-2808, 20
2. N. Yamada, M.N.A. Mohamad, T.T. Kien, Study on thermal efficiency of low- to medium-temperature organic Rankine cycles using HFO-1234yf, Renew Energ, 41, 368-375, 2012.
3. B.F. Tchanche, G. Papadakis, G. Lambrinos, A. Frangoudakis, Fluid selection for a low-temperature solar organic Rankine cycle, Appl Therm Eng, 29, 24682476, 2009.
4. Y. Dai, J. Wang, L. Gao, Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery, Energ Convers Manage, 50, 576-582, 2009.
5. A. Schuster, S. Karellas, R. Aumann, Efficiency optimization potential in supercritical Organic Rankine Cycles, Energy, 35, 1033-1039, 2010.
6. B. Saleh, G. Koglbauer, M. Wendland, J. Fischer, Working fluids for low-temperature organic Rankine cycles, Energy, 32, 1210-1221, 2007.
7. Y.-J. Baik, M. Kim, K.C. Chang, S.J. Kim, Power-based performance comparison between carbon dioxide and R125 transcritical cycles for a low-grade heat source, Appl Energ, 88, 892-898, 2011.
8. F. Marcuccilli, D. Thiolet, Optimizing Binary Cycles in Radial Inflow Turbines, GRC Transactions, 33, 737743, 2009.

9. Z. Shengjun, W. Huaixin, G. Tao, Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation, Appl Energ, 88, 2740-2754, 2011.
10. X.D. Wang, L. Zhao, Analysis of zeotropic mixtures used in low-temperature solar Rankine cycles for power generation, Sol Energy, 83, 605-613, 2009.
11. G.J. Zyhowski, A.P. Brown, A. Achaichia, “HFC245fa Working Fluid in Organic Rankine Cycle - A Safe and Economic Way to Generate Electricity from Waste Heat”, in ECOS 2010: Proc. of the 23rd Int. Conf. on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy, Lausanne, CH, 2010. E. Sauret, A.S. Rowlands, Candidate radial-inflow turbines and high-density working fluids for geothermal power systems, Energy, 36, 4460-4467, 2011.
12. H. Moustapha, M.F. Zelesky, N.C. Baines, D. Japikse, Axial and radial turbines. White River Junction: Concepts NREC, 2003.
13. D. Japikse, N.C. Baines, Introduction to turbomachinery. Norwich (VT): Concepts ETI, 1994.
14. E. Macchi, A. Perdichizzi, Efficiency prediction for axial-flow turbines operating with nonconventional fluids, J Eng Gas Turb Power, 103, 718- 724, 1981 A. Perdichizzi, G. Lozza, “Design criteria and efficiency prediction for radial inflow turbines”, in Proc. of the Gas Turbine Conf. and Exhibition, Anaheim, CA (USA), 1987.
15. E. Macchi, “The choice of working fluid: the most important step for a successful Organic Rankine Cycle (and an efficient turbine)” [Tech. Presentation], in: 2 nd Int. Seminar on ORC Power Systems, De Doelen, Rotterdam, NL, 2013.
16. J. Harinck, T. Turunen-Saaresti, P. Colonna, S. Rebay, J. van Buijtenen, Computational Study of a HighExpansion Ratio Radial Organic Rankine Cycle Turbine Stator. J Eng Gas Turb Power, 132(5), 2010.
17. O. Badr, S.D. Probert, P.W. O’Callaghan, Selecting a Working Fluid for a Rankine-Cycle Engine, Appl Energ, 21, 1-42, 1985.
18. S.L. Dixon, C.A. Hall, Fluid Mechanics and Thermodynamics of Turbomachinery, 6 th Ed. Burlington: Butterworth Heinemann, 2010.