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Session: Parallel Session: System Design, Optimization and Applications I
Session starts: Thursday 22 September, 10:00
Presentation starts: 10:40
Room: Senaatszaal

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Markus Preißinger ()
Theresa Weith ()
Dieter Brüggemann ()

Abstract:
Organic Rankine Cycle (ORC) is a state of the art technology in low temperature geothermal applications. Besides, ORC systems are used in biomass fired heat and power plants as well as for waste heat recovery at high temperatures. A promising way to further increase the efficiency of ORC systems is the supercritical mode of operation. In the present work subcritical and supercritical ORC for waste heat recovery at high temperatures are analyzed. Nine potential working fluids out of three chemical classes (alkanes, alkylbenzenes, siloxanes) are investigated with waste heat temperatures in the range of 633.15 K to 823.15 K and ORC working pressures up to 1.3∙pcrit. Simulations are carried out using Peng-Robinson Equation of State (EOS). In addition, the influence on thermodynamic and plant-specific properties using other EOS are discussed within this work. Simulations for supercritical octamethyltrisiloxane (OMTS) show an increase in electric net power of more than 5.5 % compared to subcritical process. The gain in electric power of the generator is even higher (8.5 %). However, it is pointed out that the enhancement of electric power is quite sensitive to waste heat temperature. This is also valid for the optimal working pressure in subcritical process in which net power is maximized at a working pressure of 0.58 MPa (0.80 MPa, 1.38 MPa) for heat source temperatures of 633.15 K (663.15 K, 693.15 K). In addition to thermodynamic analysis further aspects like overall size of the turbine and heat transfer characteristics of the heat exchange equipment have to be considered. Therefore, volume flow rates at turbine inlet and outlet as well as heat transfer coefficients are calculated to allow for a holistic evaluation of supercritical ORC.