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09:00   Prototypes II
Chair: Prof. Vincenzo Dossena
20 mins
Teemu Turunen-Saaresti, Antti Uusitalo, Juha Honkatukia, Jaakko Larjola
Abstract: Organic Rankine Cycle (ORC) technology has proven successful from a technical and economic point of view in so-called high-temperature heat-recovery and biomass applications having an electric power output in the range of 100 kWe - 5 MWe. However, there are many small-scale energy systems where a micro-scale ORC energy converter with the electrical power output of about 10 kWe could be attractive. This kind of applications include heat recovery from small-scale gas turbines, gas engines, and diesel engines, as well as small-scale concentrated solar power applications, and distributed electricity production from biomass or biogas. The LUT micro-ORC project was started in 2011 aiming to provide knowledge on micro-scale ORC units based on the “high-speed technology” concept, combining the turbine, the pump and the electrical generator on one shaft, whereby the whole assembly is hermetically sealed, and the bearings are lubricated by the working fluid. The project includes a working fluid selection study, component design and performance measurements for a 10 kW micro ORC prototype, as well as a study of potential market and commercialization of waste heat recovery system of such size. A special attention is paid on a compact and simple design of the turbogenerator. The off-design and dynamic performance of the cycle is studied in order to evaluate a part load behaviour of the system. The turbogenerator design criteria are also evaluated based on this dynamic study. REFERENCES [1] A. Uusitalo, T. Turunen-Saaresti, J. Honkatukia, P. Colonna, J. Larjola, “Siloxanes as Working Fluids for Mini-ORC Systems Based on High-Speed Turbogenerator Technology”, J. Eng. Gas Turbines Power, Vol. 135, 042305, (2013) [2] J. Larjola, "Electricity from Industrial Waste Heat Using High-Speed Organic Rankine Cycle (ORC)", Int. J. Production Economics, Vol. 41 pp. 227-235, (1995).
20 mins
Sylvain Quoilin, Olivier Dumont, Vincent Lemort
Abstract: This paper presents an innovative system comprising a heat pump connected to a solar roof and a geothermal heat exchanger. This heat pump is also able to invert its cycle and operate as an ORC. By using the whole rooftop as a heat source, a large amount of heat is generated throughout the year. This heat is used in priority to cover the building annual heating needs and the surplus heat generated during the summer is utilized to generate electricity in the so-called HP/ORC module. The same module can be used during winter as an efficient heat pump which radically reduces the complexity of the total system. The main advantage of the proposed technology is due to the reversibility of scroll machines, which have proven to operate efficiently both as compressor and as an expander in lab testing.
20 mins
Antonio Rubino, Jürg Schiffmann
Abstract: In the last decade, distributed power generation has gained renewed interest. Two main driving forces are contributing towards this tendency: deregulation of electricity markets and environmental concerns. For selected applications, distributed generation has been proven to be more cost-e fictive than centralized generation, showing a high potential in terms of reliability and efficiency. Small-scale high-speed turbomachinery, combined with oil-free bearing technology, has been identified as a key enabler for enhancing the performance of distributed energy conversion systems. Typical applications range from gas turbine generators, compressors for domestic heat pumps, expanders for waste heat recovery using Organic Rankine Cycles (ORC). Prior work at EPFL has proven the feasibility of an electrically driven turbocompressor (1.8 kWel) supported on dynamic gas lubricated bearings. Pressure ratios in excess of 3.3 and isentropic eefficiencies up to 80% were achieved with a 20mm tip diameter impeller rotating at 210krpm while processing R134a. Key challenges in the design of small scale turbomachinery have been identified as being : 1) a thorough understanding of gas bearing supported rotor behaviour and 2) new integrated design and optimization approaches. An investigation has shown that a holistic design method allows to yield signi cant performance improvement as compared to more traditional design approaches. The optimum design was found by linking a previously validated reduced order system model to a multi-objective optimizer based on evolutionary algorithms. The integrated design approach will be adopted to further improve the performance of an oil-free heat pump, thermally driven by an ORC. A first proof-of-concept prototype has been tested successfully in our laboratory. An exergy analysis indicated that special focus is required on the mechanical and aerodynamic design of the oil-free compressor-turbine unit, made up of the heat pump single stage centrifugal compressor directly connected by a shaft to the ORC radial turbine. Both compressor and turbine are characterized by having tip diameters of about 20mm and rotational speeds in excess of 200 krpm.