hD proposal : Experimental study and numerical simulation of the pulsed and ultrasonically activated fluidisation of Geldart’s group A powders - application to the processing of bio-based products

Research project description : Fluidized bed contactors are widely used industrially in the pharmaceutical and chemical sectors, as well as for drying agri-food products, thanks to the excellent gas-particle they generate and the resulting intense heat and mass transfers. The development of innovative applications, particularly in the field of bio-based product valorization, and the energy efficiency requirements for industrial installations have led to an increasing use of Geldart’s group A powders, that is to say fine (median diameter less than 30 microns) and light (grain density less than 2000 kg/m3). Many of these powders often require an external energy supply to be fluidized due to the existence of high inter-particle forces. It is possible to activate fluidisation either by applying mechanical vibrations to the fluidisation column, or by imposing a pulsation on the gas flow, or by applying ultrasound (US) to it. The first route is efficient, but it consumes energy and induces risks of alteration of certain mechanically fragile powders and the installations themselves. The activation pathways by pulsation and US allow both to reduce the energy consumption of the fluidized bed, to improve the fluidization of powders in a gentler way and to increase the efficiency of certain operations such as drying, particularly of bio-sourced products. This can be particularly valuable for stabilizing fresh algae, in order to overcome their seasonality and accessibility. Such gentle drying would allow them to be preserved, without damaging their intracellular content. However, little experimental work and numerical simulation have been conducted to study the influence of pulsation or US in the activation of fluidization of group A powders. The objective of the thesis is to go beyond the state of the art by studying, through a complete set of experimental and numerical simulation tools, the hydrodynamic behavior of fluidized beds made up of group A powders either pulsed or activated by US. The work will start with model particles and will progressively be complexified in order to optimize the fluidization conditions of bio-sourced products and their gentle drying. Depending on the expertise of the PhD student, the simulation part could be more or less central in the thesis work.