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World Geothermal Congress 2023

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Experimental Examination of The Supercritcal Organic Rankine Cycle Monika

Organic Rankine Cycles (ORC) are used to generate electricity from low temperature heat sources in the temperature range of 100 -260°C. In order to reduce the climate change environmentally friendly working fluids has to be use for these cycles and the maximization of the net electricity yield should be the major topic. For these reasons, we pursue the approach of a Supercritical Organic Rankine Cycle (SORC) with propane as the working fluid. In order to validate our simulation models, such an SORC power plant with a thermal heat source capacity of 1MW was built at the Karlsruhe Institute for Technology (KIT) Campus North. This study reports the first experimental results with a 4-stage axial turbine especially developed for propane. Additionally we compare these results with a steady state thermodynamic simulation. This self-developed in house Matlab code GESI allows simulating the SORC, based to the REFPROP database, at different boundary conditions and loading points. The experiments include three different load points with a propane mass flow in the range of 2.3 to 2.8 kg/s and a turbine inlet pressure of 4.5 to 5.6 MPa. In order to reduce the pressure loss due to the turbine control valve we fully open this valve after the synchronization, but it was recognized that above 18 % valve position the influence of the valve to the pressure level is neglectable. Due to the limitations in the operation of the heat exchanger, the turbine cannot be operated at the planned design point with turbine inlet temperature of 117°C. The maximal temperature reached in the test runs was 111°C. The max. power output for this off design point was 112,9 kW. The max. isentropic turbine efficiency was determined between 85% - 91%. In the measured range, there is an unexpected trend of the efficiency with the mass flow. The efficiency decreases with increasing mass flow. One reason for this could be the high liquid content at the turbine outlet. Additionally we devoloped an equation for the mass flow in relation to the live steam pressure, temperature and the outlet pressure based on the Stodola´s law formulation. With the experimental results, we are able to determine the coefficient of this equation in the examined range to 1.5542 and -1,3352 kg/s.

Hans-Joachim Wiemer
KIT-ITES
Germany

Joaquin Mardon Peréz
KIT-ITES
Germany

 


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