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

asme-orc2015 Tracking Number 74

The interest in ORC plant is increasing steadily 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 in the wide spread in the global market. To overcome them, it is necessary to decrease the manufacturing and maintenance cost, and 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 for 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 gear box to reduce the power transfer loss and system cost. And the rotor shaft was supported by gas foil bearings to increase the system availability through the non-contacting bearings. Twin radial turbines were assembled to the rotor shaft at the both ends in the way of face-to-face to cancel out the axial load caused by the pressure difference. This configuration was helpful 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 turbine efficiency was more than 85% with the temperature difference, 70℃ between the heat source and the heat sink as the result of the performance test.