Design study of the MONIKA ORC-Turbine and comparison with experimental results

This study presents the development, verification, and validation of a MATLAB code for conducting a mean-line analysis of a four-stage Organic Rankine Cycle (ORC) turbine with a power output of around 100 kW, operated with supercritical propane at the Karlsruhe Institute of Technology (KIT). Typically, a mean-line analysis is performed for an envisaged design point during the initial phase of turbomachinery design. In this study, it is used to analyse the performance and efficiency of a turbine at different operating conditions. Accuracy checks were carried out to validate the applied loss correlations. The ORC turbine was installed in the MONIKA test facility, a modular geothermal power plant, which was tested here using a simulated heat source instead. Propane at a design pressure of 5.5 MPa and a temperature of 390 K, undergoes expansion to an outlet pressure of 1.1 MPa. During the tests, however, the test conditions deviated significantly from the original design, and nitrogen leakage into the propane cycle could not be prevented from the turbine sealing system. The mean-line analysis confirms that the developed code can still predict the ORC turbine's performance and attributes with reasonable accuracy. Additionally, the software can analyse the impact of different design alterations on the thermodynamic properties of the fluid at the inlet and outlet, as well as on the performance of the turbine.