Investigation of a Novel CO2 Transcritical Organic Rankine Cycle Driven by Parabolic Trough Solar Collectors

Abstract

The objective of the present study is the detailed investigation and optimization of a transcritical organic Rankine cycle operating with CO2. The novelty of the present system is that the CO2 is warmed up inside a solar parabolic trough collector and there is not a secondary circuit between the solar collector and the CO2. Therefore, the examined configuration presents increased performance due to the higher operating temperatures of the working fluid in the turbine inlet. The system is studied parametrically and it is optimized by investigating different pressure and temperature level in the turbine inlet. The simulation is performed with a validated mathematical model that has been developed in Engineering Equation Solver software. According to the results, the optimum turbine inlet temperature is ranged from 713 up to 847 K, while the higher pressure in the turbine inlet enhances electricity production. In the default scenario (turbine inlet at 800 K and turbine pressure at 200 bar), the system efficiency is found 24.27% with solar irradiation at 800 W/m2. A dynamic investigation of the system for Athens (Greece) climate proved that the yearly efficiency of the unit is 19.80%, the simple payback period of the investment is 7.88 years, and the yearly CO2 emissions avoidance is 48.7 tones.

Sensitivity Analysis of Transcritical CO2 Cycle Performance Regarding Isentropic Efficiencies of Turbomachinery for Low Temperature Heat Sources

“…The subcritical working fluid is pressurized over critical pressure through the Pump (1-2) and isobarically heated by heat source in the Heater (2-3) to reach supercritical state. The supercritical working fluid is then expanded through the Expander (3)(4) and the high pressure and high temperature energy could be converted into electricity via a coupled generator (the generator will not be discussed in this study). Finally, the exhaust from the expander is isobarically cooled down by heat sink in the Condenser (4-1).…”

“…As such, much attention has been given to renewable energies. However, renewable energies are usually limited by their availability and cannot be used for providing base load power [3,4]. Using a heat-to-power system to recover the industrial waste heats, especially at low temperature levels, is another feasible way to reduce the fossil fuel consumption.…”

“…Therefore, the T-CO 2 cycles can make better use of the thermal energy from the heat sources [1,2]. Compared to the fully supercritical CO 2 cycles, less power consumption for pressurizing is needed in T-CO 2 cycles attributed to the high density of the condensed CO 2 [4,15,24,25]. Studies show that the T-CO 2 cycles have the potential to outperform ORCs and supercritical CO 2 cycles in recovering low temperature heat sources [23,25].…”

“…As for the working fluid, CO 2 possesses low environmental impact and potentially high energy performance [4,22,26]. CO 2 has zero ozone depletion potential (ODP) and the GWP of CO 2 is 1 over 100 years [18].…”