Solid liquid mixing tank homogenisation

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Proceedings of Global 2015 September 20-24, 2015 - Paris (France) Paper 5204

WASTE HOMOGENISATION TANK: EXPERIMENTAL VALIDATION OF A NUMERICAL STUDY

C. Macqueron, J. William, R. Le Gall, R. Demarthon, G. Piot, A. Ragouilliaux AREVA E&P – Fuel Cycle 1 rue des hérons, 78182, Saint-Quentin-en-Yvelines Cedex – France corentin.macqueron@areva.com johann.william@areva.com ronan.le_gall@areva.com romain.demarthon@areva.com gregoire.piot@areva.com alexandre.ragouilliaux@areva.com Abstract – In the framework of final waste conditioning, legacy sludge produced by the original La Hague effluent treatment facility has to be processed by mixing, drying and compacting. The sludge mixing operation has to be performed in a tank in the most homogeneous way in order to guarantee the final quantity of radioactive material in each container. This homogenisation task is made difficult by high density particles and by the size of the tank, which is around 240 m3. As it is not economically feasible to perform experimentations on a tank of such size, a process qualification program based on a state-of-the-art methodology, including both complementary tools mock-ups at small scales and Computational Fluid Dynamics (CFD) numerical simulations has been set up (the homogenisation of the real size tank is only demonstrated by numerical simulations). Two mock-ups, respectively of 300 L and 2 m3 that are in perfect geometrical similitude, have thus been built in the HRB development facility close to the La Hague site in order to determine the suitable rotation speed of the real size tank impeller to ensure a good homogeneity, based on physical and scale-up/similitude reasoning. The mock-ups are used to validate the numerical simulations developed with the ANSYS FLUENT 15.0 software, by comparison with hydraulic power and solid volume fraction profiles measurements. I. INTRODUCTION In the nuclear field, validation of process equipment at real size can often be obtained only once the installation is built. In order to anticipate and to limit the industrial risks, it can be useful to rely on CFD (Computational Fluid Dynamics) numerical modeling that must be qualified on the equipment operating conditions. In this way, it contributes to obtain robustness in the demonstration of the safety report or for performance checking. The objective of the present paper is to detail the qualification methodology developed to deal with high capacity stirred tank homogenisation without performing full scale tests before building the final industrial tank. The methodology relies on a joint approach between numerical modeling and validation tests at different reduced scales. Once the qualification of numerical methodology is

demonstrated, extrapolation to the full scale in a numerical way can be considered. Only partial results will be presented here for confidentiality reasons. II. STATE-OF-THE-ART AND PROBLEMATIC Solid-liquid mixing processes have already been studied by several authors to investigate the influence of hydrodynamics and mixing on solids suspension. For example, Zwietering [3] described the rotation speed at which solid particles are just suspended from the bottom of the tank, and Mersmann [4] determined the minimum rotation speed for off-bottom lifting or for settling avoidance. These approaches are generally too specific to one mixing system to be extrapolated easily and are only


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Solid liquid mixing tank homogenisation by Corentin - Issuu