A thermodynamics comparison of subcritical and transcritical organic Rankine cycle system for power generation

Abstract

A comparison on subcritical and transcritical organic Rankine cycle (ORC) system with a heat source of 110 °C geothermal water was presented. The net power output, thermal and exergy efficiencies and the products of the heat transfer coefficient (U) and the total heat exchange area (A) (UA values) were calculated for parametric optimization. Nine candidate working fluids were investigated and compared. Under the given conditions, transcritical systems have higher net power outputs than subcritical ones. The highest net power output of transcritical systems is 18.63 kW obtained by R218, and that of subcritical systems is 13.57 kW obtained by R600a. Moreover, with the increase of evaporating pressure, the thermal and exergy efficiencies of transcritical systems increase at first and then decrease, but the efficiencies of subcritical ones increase. As a result, the efficiencies of transcritical systems cannot always outperform those of the subcritical ones. However, the subcritical systems have lower minimum UA values and lower expansion ratios than the transcritical ones at the maximum net power output. In addition, the transcritical cycles have higher expansion ratios than the subcritical ones at their maximum net power output.

Keywords

organic Rankine cycle / low temperature heat source / parametric optimization

References

[1] ZivianiD, BeyeneA, VenturiniM. Advances and challenges in ORC systems modeling for low grade thermal energy recovery [J]. Applied Energy, 2014, 121: 79-95

[2] KarellasS, SchusterA. Supercritical fluid parameters in organic Rankine cycle applications [J]. Int Journal of Thermodynamics, 2008, 11(3): 101-108

[3] KarellasS, SchusterA LEONTARITIS. Influence of supercritical ORC parameters on plate heat exchanger design [J]. Applied Thermal Engineering, 2012, 33: 70-76

[4] ChenH, GoswamiD Y, RahmanM M, StefanakosE K. A review of thermodynamic cycles and working fluids for the conversion of low-grade heat [J]. Energy, 2010, 14: 3059-3067

[5] ChenH, GoswamiD Y, RahmanM M, StefanakosE K. A transcritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power [J]. Energy, 2011, 36: 549-555

[6] ChenH, GoswamiD Y, RahmanM M, StefanakosE K. Energetic and exergetic analysis of CO₂-and R32-based transcritical Rankine cycles for low-grade heat conversion [J]. Applied Energy, 2011, 88: 2802-2808

[7] BaikY J, KimM, ChangK C. A comparative study of power optimization in low-temperature geothermal heat source driven R125 transcritical cycle and HFC organic Rankine cycles [J]. Renewable Energy, 2013, 54: 78-84

[8] MikielewiczD, MikielewiczJ. A thermodynamic criterion for selection of working fluid for subcritical and transcritical domestic micro CHP [J]. Applied Thermal Engineering, 2010, 30: 2257-2362

[9] LiC, KosmadakisG, ManolakosD, PapadakisG, GoswamiD Y. Performance investigation of concentrating solar collectors coupled with a transcritical organic Rankine cycle for power and seawater desalination co-generation [J]. Desalination, 2013, 318: 107-117

[10] CayerE, GalanisN, NesreddineH. Parametric study and optimization of a transcritical power cycle using a low temperature source [J]. Applied Energy, 2010, 87: 1349-1357

[11] XiaoS, WuS-y, ZhengD-s. Slag-washing water of blast furnace power station with supercritical organic Rankine cycle [J]. Journal of Central South University, 2013, 20: 737-741

[12] GuoC, DuX-z, YangL-j, YangY-p. Performance analysis of organic Rankine cycle based on location of heat transfer pinch point in evaporator [J]. Applied Thermal Engineering, 2014, 62: 176-186

[13] CayerE, GalanisN M H, RoyP. Analysis of a carbon dioxide transcritical power cycle using a low temperature source [J]. Applied Energy, 2009, 86: 1055-1063

[14] AyachiF, KsayerE B, ZoughaibA, NeveuP. ORC optimization for medium grade heat recovery [J]. Energy, 2014, 68: 47-56

[15] XuJ-l, LiuC. Effect of the critical temperature of organic fluids on transcritical pressure organic Rankine cycles [J]. Energy, 2013, 63: 109-112

[16] VetterC, WiemerH J, KuhnD. Comparison of sub-and supercritical organic Rankine cycles for power generation from low-temperature/low-enthalpy geothermal wells, considering specific net power output and efficiency [J]. Applied Thermal Engineering, 2013, 51: 871-879

[17] SongJ, LiY, GuC-w, ZhangLi. Thermodynamic analysis and performance optimization of an ORC (organic Rankine cycle) system for multi-strand waste heat sources [J]. Energy, 2014, 71: 673-680

[18] LiuQ, DuanY-y, YangZ. Effect of condensation temperature glide on the performance of organic Rankine cycles with zeotropic mixture working fluids [J]. Applied Energy, 2014, 115: 394-404

[19] MaraverD, RoyoJ, LemortV, QuoilinS. Systematic optimization of subcritical and transcritical organic Rankine cycles (ORCs) constrained by technical parameters in multiple applications [J]. Applied Energy, 2014, 117: 11-29

[20] LeV L, FeidtM, KhiriA, SandrineP. Performance optimization of low-temperature power generation by supercritical ORCs (organic Rankine cycles) using low GWP (global warming potential) working fluids [J]. Energy, 2014, 67: 513-526

[21] PanL-sOptimization of organic Rankine cycle and investigation on performance of radial flow turbine for power generation with low grade heat source [D], 2012TianjinTianjin University