New Turbines to Enable Efficient Geothermal Power Plants

Abstract

Efficient resource utilization is critical in the viability of geothermal projects. Novel thermodynamic energy conversion cycles exist that are superior to the traditional organic Rankine cycle. Two new turbines have been developed that enable the economic and efficient implementation of these cycles that maximize the geothermal resource utilization. The turbines, the Euler Turbine and the Variable Phase Turbine, can increase power production by as much as 30-50% from low temperature resources and enhanced geothermal resources when compared to commercially available organic Rankine cycles. The Euler Turbine is a radial outflow turbine originally developed for energy recovery in steam systems. Commercial units of 275 kWe capacity are operating on steam, some with isentropic efficiencies above 80%. The Euler Turbine is also currently being implemented in a 600 kW Kalina cycle in Bruchsal, Germany. The Variable Phase Turbine uses axial impulse turbine technology that is well adapted to the expansion of transcritical or flashing liquid flow. The high isentropic efficiency, typically greater than 80%, enables a liquid heat exchanger cycle1 to be used, avoiding the pinch point limitations of the evaporator in an organic Rankine cycle. Because this cycle can use a significantly lower exit temperature, significantly more energy can be extracted from a given resource. The resulting power advantage of 30-50%, leverages the total development cost of the geothermal project. A 40% increase in power production from a given geothermal resource lowers the total capital cost—including exploration, drilling, and surface plan— by 29%. Results of analytical models for cycles utilizing the Euler Turbine and Variable Phase Turbine will be presented along with geothermal power plant designs for both. Additionally, experimental results of operating the first two-phase closed cycle power system with a Variable Phase Turbine will be presented.