DEVELOPMENT OF A TURBO-GENERATOR FOR ORC SYSTEM WITH TWIN RADIAL TURBINES AND GAS FOIL BEARINGS

The interest in ORC plant is increasing over recent years in terms of the energy and the environment costs. But the capital cost and maintenance cost of an ORC plant are the main obstacles of the wide spread in the global market. To overcome them, it is necessary to decrease the manufacturing and maintenance cost, and to increase the turbine efficiency and the system availability. Korea Institute of Energy Research (KIER) and Jinsol Turbomachinery have jointly developed a novel turbo-generator applicable to the low temperature heat sources to meet those needs. The turbo-generator developed is almost maintenance-free, highly efficient and completely hermetic. A high speed permanent magnet synchronous generator (PMSG) was applied to get the high efficiency. Radial turbines were directly coupled with the PMSG without a gear box to reduce the power transfer loss and cost. The rotor shaft was supported by gas foil bearings to increase the system availability through the non-contacting bearings. Twin radial turbines were assembled with the rotor shaft in the way of face-to-face to cancel out the axial load caused by the pressure difference. This configuration made it possible to apply a gas foil bearing as a thrust bearing despite of its low load capacity. A gas foil bearings is the simple and cheap solution for the rotor support system and the completely hermetic turbo-generator. The high efficiency of the radial turbine was acquired by the real gas modelled turbine design with optimum specific speed. The developed turbo-generator was integrated with the 100kWe ORC plant installed at KIER and it showed that the turbo-generator efficiency was about 80% as the result of the performance test with the temperature difference of 70℃ between the heat source inlet and the heat sink inlet.