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Session: Parallel Session: Cycle efficiency
Session starts: Friday 23 September, 16:00
Presentation starts: 16:20
Room: Senaatszaal

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Hilel Legmann ()

Abstract:
Efficiency of Organic Rankine Cycle: Potential and Limitations Hilel Legmann Ormat Technologies, Inc. e-mail: hlegmann@ormat.com ABSTRACT Organic Rankine Cycle (ORC), sometimes referred to as “Binary power generation systems,” are typically used to exploit low- and medium-temperature geothermal and recovered energy resources. There are numerous technical variations of such plants using different organic fluids, as well as Kalina and Trilateral cycles. Optimizing the efficiency by matching the cycle to the heat source: This presentation will compare theoretical cycle efficiency, field measured and net power output and performance for the different heat sources and cycle configurations. The maximum available energy produced as work for electricity from any heat source is specified by the second law of thermodynamics. Because the rate of the sensible heat carrying fluid is not infinite, its temperature decreases as it transfers the heat to the motive fluid in the heat engine. Thus, the overall process must be envisioned as a summary of an infinite number of infinitesimally small engines. Any heat exchange increases the irreversibility i.e.: reduces the efficiency. A temperature heat transfer diagram illustrates the differences in the temperature drop between a Steam Rankine Cycle and an Organic Rankine Cycle. Because of the lower heat capacity of organic liquids and their much smaller latent heat of vaporization, these fluids let too much smaller losses of availability in the utilization of the low- or medium-temperature predominantly sensible heat streams. The process of designing a geothermal or waste heat recovery power plant can be considered one of matching and optimization. We have a source and a sink of heat of certain characteristics and the problem is to match them with the working cycle, match the working cycle with the working fluid, and match the working fluid with the expander. What matters most is the optimization of the whole system, involving the well-known process of trading-off a loss or gain. Examples will be given showing the impact of different factors on the net power delivered to the grid. REFERENCES [1] Bronicki, L.Y., 1984, “Twenty Five Years of Experience with Organic Working Fluids in Turbomachinery”, ORC-HP Technology Conference, Verein Deutscher Ingenieure, Zurich [2] Bronicki, L.Y., 1989, “Organic Vapor Turbogenerators using Locally Available Heat Sources – 25 Years of Industrial Experience”, Congress of the World Energy Conference, Montreal [3] Legman, H., 1999, Power Returns from Waste Heat, International Cement Review [4] Bronicki, L.Y., 2002, “Geothermal Power Stations”, Encyclopedia of Physical Science and Technology, Third Editions, 6, Academic Press, San Diego [5] Legmann, H., 2003, “The Bad-Blumau Geothermal Project”, Proceedings of European Geothermal Conference [6] DiPippo, R., 2004, “Second Law Assessment of Binary Plants Generating Power from Low-Temperature Geothermal Fluids”, Geothermics, University of Massachusetts, Dartmouth, USA [7] Bronicki, L.Y., 2008, “Ormat Rankine Cycle Configurations for Utilization of Low Temperature Heat Sources”, Proceedings of the 9th Biennial ASME Conference on Engineering Systems Design and Analysis ESDA08