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Session: Parallel Session: Systems Design, Optimization and Applications III
Session starts: Friday 23 September, 11:20
Presentation starts: 12:00
Room: Senaatszaal

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Tobias Erhart (University of Applied Sciences Stuttgart, zafh.net)
Ursula Eicker (University of Applied Sciences Stuttgart, zafh.net)
David Infield (University of Strathclyde Glasgow, IEEE)

Abstract:
Introduction: Within the EU-project POLYCITY over six years of supply and demand in a city quarter with app. 7000 people have been monitored. The cornerstone of the energy supply is a combined heat and power plant (CHP) with 5.3 MWth and 1 MWel nominal output based on an OR-Cycle. A district heating system is serves as sink for the power plant and a thermal cooling device (single effect absorption chiller) is connected to it. All applied systems such as biomass furnace, thermal oil system, district heating and heat rejection unit have been monitored long-term, to show the constraints of the heat guided operational mode for the grid feed-in. The measured states have been analysed to elaborate the influence of components in the process. Relevance: Many ORC systems fuelled by biomass are heat-guided. In order to increase the annual or seasonal overall performance, the interaction of heat losses, electric efficiencies and performance of thermal cooling systems have to be taken into account. Questions regarding solar thermal support of district heating in summer can only be clarified in this way. Method: Measured data from the control system have been collected and transferred via an OPC UA interface (OLE for process control – unified architecture). With custom software the values could be acquired and saved in a database. Combining and unifying the data from the internal control and the external metering systems a comprehensive view on the conditions of the system is given. Thermodynamic states of the silicone oil are computed by using the formulations in the Refprop library based on Colonna, Nannan and Guardone. The observed characteristic is compared to the expected results from a condenser model. Results: Various mass flows, temperature levels and temperature spreads result in varying pressure levels in the condenser. The pressure level ranges from 90 mbar to 140 mbar at feeding temperatures between 72 °C and 85 °C. High mass flows on the secondary side, respectively low temperature spreads, result in lower pressures. These lead to higher electric efficiencies due to higher pressure differences across the turbine. The findings give several conclusions for an economic operation of ORCs. Under normal operation conditions the overall influence of the condenser conditions sum up to one percentage point in electric efficiency. The question of higher efficiencies versus increasing pump power in the district heating network is discussed. REFERENCES [1] Colonna P., Nannan N.R., Guardone A., Lemmon E.W., Multiparameter equations of state for selected siloxanes, Fluid Phase Equilibria 244, 2006 [2] Colonna P., Guardone A., Nannan N.R., Siloxane: A new class of candidate Bethe-Zel’dovich-Thompson fluids, Physics of Fluids 19, 2007 [3] Colonna P., Nannan N.R., Guardone A., Multiparameter equations of state for siloxanes, Fluid Phase Equilibria 263, pages 115-130, 2008 [4] Flynn D., “Thermal Power Plant Simulation and Control”, IEE power Series, The Institution of Electrical Engineers, London, 2003 [5] Swamee P.K., Jain A.K., "Explicit equations for pipe-flow problems". Journal of the Hydraulics Division (ASCE) 102 (5): 657–664, 1976 [6] Churchill S. W., Friction factor spans all flow regimes, Chemical Engineering 84, p. 91, 1977 [7] Duvia A., Technical and economic aspects of Biomass fuelled CHP plants based on ORC turbogenerators feeding existing district heating networks, 2009 [8] REFPROP, NIST Standard Reference Database 23, Version 9.0, 2010