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Siemens Energy has developed two new turbines, one for geothermal, and another for biomass and waste heat applications. The SST-500 GEO steam turbine is aimed at geothermal plants operating at up to 120 MW. It follows the SST-400 GEO turbine, which was introduced in 2011. The SST-500 GEO is a single-casing, double-flow condensing turbine. It combines the casing and auxiliaries of the Siemens SST-500 and SST-600 steam turbines with additional geothermal and steam path technologies. It has been designed for single- and doubleflash applications.

Geothermal turbines frequently face highly corrosive steam which consumes conventional materials. Steam quality is low but with large volume flows. These challenging physical conditions require specially adapted steam turbines. Each SST-500 GEO turbine is designed for particular resource conditions by adapting the blade path. It has an impulse-type steam path. It can operate in steam temperatures up to 250°C, with steam pressures up to 15 bar absolute.

The SST-111 is another new model from Siemens serving primarily the biomass industry as well as waste heat recovery applications for industrial processes. According to Matthias Schleer, head of R&D for Siemens Turbomachinery Equipment GmbH, it can produce up to 12 MW but is typically used in the 3 MW to 7 MW range.

The new turbine type is intended to combine the benefits of a single- and a multi-stage machine. It can reach steam pressures of up to 131 bar and temperatures of up to 530°C.


The turbine has an integrated gearbox with a helical gear. Up to seven stages can be arranged in three turbine housings. “The low pressure (LP) condensation stage is a combination of an impulse-type third row and a two-stage reaction LP condensing stage,” said Schleer. He added that the multi-stage model can achieve up to 15% higher efficiency compared to a traditional single- stage turbine. The first machine was commissioned in June 2013.