A design study for a 150 kW class radial inflow steam turbine system for the bottoming cycle in 2.4 MW class gas engine systems has been completed. The total electrical efficiency of the gas engine can be increased from 41.6% to 44.2%. A two-stage condensing turbine system is applied to increase output power under the supplied steam conditions from the exhaust heat of the gas engines. The pressure ratio of a high-pressure turbine is 3.5, and that of a low-pressure turbine is 4.6. The blade profiles of both turbines are also designed to make sure the thrust does not exceed 300 N at the rated rotational speed of 51,000 rpm. To simplify the rotor system and to reduce mechanical losses, a permanent magnet generator rotor is applied that is composed of turbine rotors in a common shaft supported by two water-lubricated bearings. The oil supply system is completely eliminated in the turbine system. Design specifications of the turbines are shown, as are operating pressure ratio ranges of upper and lower limits from the start to the rated rotational speed for a stable starting operation.

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