Development of geothermal power generation system using geothermal fluids under harsh conditions

• Scrubbing allows stable use of high-enthalpy geothermal fluids under harsh conditions. • Partial recovery of desuperheating losses enhances energy utilization efficiency. • Hybrid system works efficiently under high non-condensable gases without gas removal. • Exergy-based analysis quantifies improvements in gross power output for each system. • Proposed system offers a practical and robust approach for harsh geothermal resources. High-enthalpy geothermal fluids contain significant amounts of impurities, corrosive gases, and non-condensable gases (NCGs). In addition, steam is superheated and contains no liquid water, which can cause problems such as corrosion and scaling if introduced directly into power generation facilities. This study builds upon the proven conventional method of introducing scrubbed steam into a turbine, while also proposing the recovery of heat from the scrubber drain as flash steam. Three types of power generation cycles are analyzed quantitatively: a direct expansion system, a stand-alone Organic Rankine Cycle (ORC), and a hybrid system combining the two. The analysis includes calculations of power output and heat recovery for each configuration to better evaluate the quality of the recovered energy, based on exergy analysis. Results show that, in addition to the conventional approach, recovering flash steam from the scrubber drain can regain approximately half of the desuperheating losses caused by steam scrubbing. Under geothermal fluid conditions of 13.8 MPa, 450 °C, and 100 t/h of superheated steam, this corresponds to a gross power output of 24.1 MW, compared with 21.2 MW when the drain heat is not recovered. Furthermore, while an ORC alone is not well suited to high-enthalpy geothermal sources due to the small latent heat of low-boiling-point working fluids and the high exhaust temperature of the ORC turbine, combining a direct expansion turbine with an ORC enables efficient cascading use of heat. This hybrid approach eliminates the need for dedicated gas extraction systems, making it particularly advantageous under high-NCG conditions and robust against variations in gas concentration, achieving a gross power output of 22.1 MW for the hybrid configuration under the considered geothermal fluid conditions.