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Session: Turbo expanders I
Session starts: Tuesday 08 October, 11:20
Presentation starts: 11:20
Room: Van Weelde Zaal

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Claudio Spadacini (Exergy)
Dario Rizzi (Exergy)
Claudio Saccilotto (Exergy)
Stefano Salgarollo (Exergy)
Lorenzo Centemeri (Exergy)

Abstract:
In the history of the Organic Rankine Cycle machines, typical applications have always been medium-low enthalpy heat recovery and small size biomass plants: derivation from steam Rankine cycle and turbines segregated initially the ORC into tight niches, where steam turbines were not competitive because of low power output or low temperature. Defined a certain fluid and thermodynamic cycle, the limits of a ORC in terms of efficiency and power are usually determined by: - First stage minimum blades height, in order to avoid partial admission, meaning o minimum power o maximum turbine inlet pressure - Last stage maximum blade height, in order to maintain optimal h/D ratio, meaning o maximum power o minimum backpressure - Maximum enthalpy drop, when rotational speed is fixed (direct coupling) - Maximum number of expansion stages, in order to have an efficient and reliable machine The innovation brought by the radial outflow turbine, when compared to an axial turbine, broadens the range of applications defined above maintaining optimal efficiency of conversion and operation, as: - The change in cross section helps higher volumetric flow ratio, thus: o Broader range of application in terms of power output o Higher efficiency of the cycle, thanks to an higher possible pressure ratio - The implementation of multiple stages (more than the 3 stages usually set as maximum on axial machines) on a single wheel allows higher enthalpy head, thus higher specific work of the cycle, meaning higher efficiency - The single-disk configuration allows very low vibrations in the over-hung machine, as lower mass and lower distance from the bearings are possible - On the single disk, multiple pressure levels are feasible, as there is no increase in distance between rotor and bearings when an admission/extraction duct is interposed between intermediate stages An overview of the advantages brought by the application of the radial outflow turbine in the ORC is carried out, comparing the results of this study with the competitor technologies on the market.