"3E" Analysis and Working Fluid Selection for a Cogeneration System for Geothermal Large Temperature Difference...

Area of Science:

• Renewable Energy Engineering
• Thermodynamics
• Environmental Science

Background:

• Geothermal energy offers a clean alternative to fossil fuels, but low-temperature sources present utilization challenges for combined heat and power (CHP) systems.
• Existing CHP systems often have limited efficiency when using low-temperature geothermal heat.

Purpose of the Study:

• To design and analyze a novel cogeneration system combining an organic Rankine cycle (ORC) and an absorption heat exchanger (AHE).
• To evaluate the thermal efficiency, exergy efficiency, and economic viability of the proposed system using low-temperature geothermal heat (85 °C).
• To identify the optimal working fluid for maximizing system performance.

Main Methods:

• System design integrating ORC and AHE for low-temperature geothermal applications.
• Thermodynamic and exergy analysis to assess system performance.
• Economic analysis to determine the levelized cost of energy (LCOE).
• Comparative study of different working fluids to find the optimal option.

Main Results:

• The optimal working fluid for the proposed system is identified as R245fa, achieving an exergy efficiency of 61.39%.
• The system demonstrates effective operation even with a low heat source outlet temperature of 23 °C when using R245fa.
• The lowest levelized cost of energy (LCOE) of $0.082/kW·h is achieved when using R22 as the working fluid.

Conclusions:

• The designed ORC-AHE cogeneration system effectively enhances the utilization of low-temperature geothermal resources.
• R245fa is the optimal fluid for maximizing exergy efficiency, while R22 provides the most economical operation.
• This system presents a viable solution for clean energy generation, reducing reliance on fossil fuels.