| Title | Analysis of Recuperative Transcritical Organic Rankine Cycle Using Mixture Working Fluids in Low Enthalpy Geothermal |
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| Authors | Jui-Ching HSIEH, Shao-Min Zheng, Bo-Heng LEE, David T.W. LIN, Chun-Ping JEN |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Transcritical organic rankine cycle, zeotropic mixtures, recuperator |
| Abstract | The low-enthalpy heat in geothermal fluids is extracted by using a binary cycle and is converted into electricity. Conventional Organic Rankine Cycles (ORCs) are used widely in low-enthalpy geothermal power plants as an effective solution to convert low-grade heat into power. However, conventional ORCs are characterized by high exergy destruction during heat transfer in the evaporator and condenser. The irreversibility of evaporator and condenser, and exergy loss of the heat source can be reduced by employing zeotropic mixtures and transcritical organic Rankine cycles (TRCs). A thermodynamic analysis model of TRC adopting recuperator associated with mixtures has been developed. This model was employed to investigate feasibility of the mixture R600a/R134a instead of R245fa/R134a in the low-enthalpy heat. Therefore, the mixtures are investigated by the first and second law efficiencies of thermodynamic, exergy destruction and specific power at various inlet expander temperatures and pressures. The results indicate that the optimal mole fraction corresponding to the maximal specific power is dramatically and unsignificantly affected by the inlet temperature and inlet pressure of the expander, respectively. Meanwhile, the maximal specific power occurred at temperature difference between Texp,in and Tcri approaching 40 ℃ under effects of condensing temperature glide. The peak value of the first law effficiecny is occurred at pure R245fa and R600a. The second law efficiency and the specific power are increased considerably by increasing inlet temperature and inlet pressure of the expander. The comparsions show the similar trend in terms of condensing pressure and heat transfer rate of recuperator, nevertheless the significant difference is in the condensing temperature glide. By the recuperator, the total exergy destruction can be reduced, especially for Texp,in ≥ 170 ℃. |