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Thermodynamic analysis and performance optimization of transcritical power cycles using CO2-based binary zeotropic mixtures as working fluids for geothermal power plants

Release Time:2025-04-30

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Title of Paper:: Thermodynamic analysis and performance optimization of transcritical power cycles using CO2-based binary zeotropic mixtures as working fluids for geothermal power plants

Summary:: Transcritical power cycles (TPCs) using CO2-based binary zeotropic mixtures for the conversion of lowgrade
geothermal water at 100–150 C into power are presented and analyzed when cooling water temperature
(Tcw) is 10–30 C in this paper. 6 refrigerants are selected as the additives into CO2 according to 2
criteria. Performances of TPCs with 6 selected CO2-based mixtures are optimized by pattern search algorithm
(PSA). Thermodynamic and economic analyses are conducted. The results reveal that R161/CO2 is
the best fluid for a TPC in terms of both thermal performance and economic performance while R290/CO2
might be an unsuitable working fluid in TPC due to its lower thermal performance. When Tcw = 10–20 C,
a TPC using R161/CO2 at XR161 = 0.7 can increase net power output by 14.43–50.46% and decrease cost per
net power by 27.96–48.72% compared with a TPC using CO2. The selected CO2-based mixtures can reduce
CPP of a TPC compared with CO2 although more heat transfer area is required. Meanwhile, the CO2-based
mixtures can decrease the high operating pressure, and enlarge the condensing temperature range compared
with CO2. In addition, the CO2-based mixtures except R161/CO2 and R152a/CO2 are not recommended
for a TPC when Tcw is low.