Session: 06-11 Innovations in Steam and Bottoming Cycles

Submission Number: 177687

A Comparative Study of the Gemini Radial Outflow Turbine With a Multistage Axial Turbine in High-Capacity Geothermal Power 

In recent years, energy costs have shown a significant global volatility, driven by geopolitical crises, fossil fuel market instability, and the accelerating regulatory shift towards low-emission energy sources. Within this context, geothermal energy is experiencing increasing momentum, thanks to its constant availability and contribution to the decarbonization of the energy sector.

In the United States, over 1 GW of new-generation geothermal capacity has already been secured, and projections indicate a potential scale-up to 90–130 GW by 2050. In Europe, geothermal electricity capacity reached 3.5 GW by the end of 2023, alongside more than 400 geothermal district heating and cooling systems. In Italy, the deployment of at least 1 GW of new geothermal capacity has been targeted by 2030, reflecting growing national interest in this resource.

With the increasing installed capacity of geothermal power plants, there is a corresponding rise in the operational demands placed on system components, particularly the turbine. Large-scale geothermal power cycles are typically characterized by high volumetric flow rates and moderate-to-high enthalpy drops. These conditions necessitate the use of multistage turbine configurations—whether radial or axial—to effectively harness the available enthalpy and require substantial blade heights to accommodate the large volumetric flows.

This paper presents an innovative Radial Outflow Turbine (ROT), referred to as the Gemini Turbine, developed to improve energy conversion efficiency under such demanding conditions. The Gemini Turbine is specifically engineered to manage very high volumetric flow rates within a single machine thanks to symmetrical flow paths, enabling power outputs over 50 MW. A one-dimensional performance comparison is conducted between the Gemini Turbine and a conventional multistage axial turbine, showing the advantages of the proposed configuration for high volumetric flow applications. The analysis demonstrates the potential of the Gemini Turbine for application in large-scale geothermal power plants, offering a viable alternative to traditional axial turbines.

Presenting Author: Giorgia Ruffato Exergy International Srl

Presenting Author Biography: Mrs. Giorgia Ruffato – Turbine Engineer
Giorgia Ruffato has been the CFD Specialist of the Turbine Department at Exergy International since 2021. She holds a Master’s degree in Mechanical Engineering from Politecnico di Milano (2020). Her work focuses on preliminary turbine design and aerodynamic simulations for various turbomachinery applications, contributing to several R&D projects within the company.

Authors:

Giorgia Ruffato Exergy International Srl
Luca Vanini Exergy International Srl
Giacomo Rufo Menghetti Exergy International Srl
Marco Astolfi Energy Department of Politecnico di Milano