Siemens' new steam turbine

With a rating of up to 60 MW, Siemens Energy's SST-400 GEO steam turbine for geothermal applications combines the casing and turbine-generator package (gearbox, generator and base frame) of the Siemens SST-400 steam turbine with the steam path technologies developed, tested and applied by the steam turbine service provider TurboCare. The SST-400 GEO steam turbine 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 U.S. currently leads the world with an installed geothermal capacity of 3.1 GW, followed by the Philippines with an installed geothermal capacity of approximately 1.9 GW, and Indonesia with 1.2 GW. There also exists the potential for the utilization 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.

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 sulfide in the thermal fluid. The SST-400 GEO steam turbine can be deployed in geothermal power 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 is 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.