Thermodynamic analysis of geothermal power plant with two-stage self-superheating system

Abstract

• Single-flash geothermal cogeneration with two-stage self-superheating. • Impact of separator, heat source, and superheating brine temperatures. • Comparison of single-stage and two-stage self-superheating systems. • Specific work output improves by 6.26 % over single-stage configuration. Renewable energy technologies such as wind, solar, and geothermal energy are being increasingly used to mitigate greenhouse gas emissions, owing to their low carbon intensity. In particular, geothermal energy whether harnessed through flash or binary systems can generate electricity or provide heat to meet base-load demand while maintaining relatively low carbon emissions. The flash power plants use saturated steam from the flashing process to produce power. Consequently, they produce relatively low power and low steam quality at the turbine outlet. This study proposes a cogeneration single-flash power plant incorporating a two-stage self-superheating process and heat exchanger to tap residual heat for combined power and heat generation. Thermodynamic principles were applied for system analysis. The effects of separator temperature (110–180 °C), geothermal brine temperature (140–260 °C), and dedicated superheating brine temperature (160–260 °C), were investigated. The separator temperature was optimized to maximize specific work output to 125.47 kJ/kg at 139.1 °C for a base case brine source temperature 260 °C. At this temperature, thermal efficiency reached 11.06 %, compared to 9.7 % and 10.4 % for single-flash and single-flash single-stage self-superheating systems, respectively. Exergy efficiency was 44.92 %, exceeding the reference values of 39.38 % and 42.26 %, respectively. The investigated cogeneration system further enhanced thermal and exergy efficiencies to 24.78 % and 48.03 %, respectively.