Siemens Energy has launched a new version of its SST-400 steam turbine afapted for use in geothermal power plants.

With a rating of up to 60 MW, the SST-400 GEO combines the casing and turbine-generator package (gearbox, generator and base frame) of the established SST-400 unit with the steam path technologies developed, tested and applied by the steam turbine service provider TurboCare. The new ST can be deployed in geothermal power plants with different thermal fluids.

At the end of 2010, the global installed power generating capacity of geothermal power plants was more than 11 GW. The USA currently leads with an installed capacity of 3.1 GW, followed by the Philippines with approximately 1.9 GW, and Indonesia with 1.2 GW. There also exists the potential for the utilisation of geothermal energy for power generation in East Africa, Central America, Chile, Russia, Italy, Iceland and Turkey. Based on a study conducted by IHS Emerging Energy Research, the installed capacity of geothermal power is predicted to nearly triple worldwide to approximately 31 GW by 2020.

“We’ve done intensive groundwork on the specific requirements of geothermal plants and are now going to market with a proven turbine concept,“ said Markus Tacke, CEO of Siemens Industrial Power Business unit. “Worldwide a pronounced increase in the demand for geothermal steam turbines is evident.”

The sites for geothermal plants vary significantly in terms of thermal fluid mass flow, temperature, pressure, pH and the fraction of minerals and gases such as hydrogen sulphide in the thermal fluid. The SST-400 GEO can be deployed in plants that operate with superheated direct steam (dry steam) or with saturated steam produced on pressure reduction of the thermal fluid (flash principle). The turbine can also be deployed in the direct or flash steam cycle of combined direct or flash steam/binary systems (flash/binary combined cycle).The low steam parameters and the aggressive constituents of the thermal fluid sometimes result in extensive corrosion. As a result, these plants require specially adapted steam turbines. The features demanded include special high-grade materials to combat corrosion and to prevent fatigue-related crack formation and fractures. The SST-400 GEO has therefore been made suitable for live steam temperatures up to 250°C, with steam pressures up to 12 bar absolute, and includes resource- and turbine-stage-specific high-grade materials as well as special features for moisture removal at every stage.