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Agglomération de particules par voie humide en lit fluidisé

Abstract : Particles agglomeration allows to modify their initial physical properties (size, shape, density, porosity) and to improve powder end-use properties like flowability, mechanical resistance and dispersibility, very important for pharmaceutics and food products. Fluidized bed agglomeration is obtained by spraying a liquid (solvent, binder solution) on fluidized particles to allow liquid bridges formation when wet particles collide. These bridges consolidate due to drying by the hot fluidizing air. In this study, the sprayed liquid jet was characterized (shape, angle, liquid drop size and size distribution) for different spraying conditions and a wetting region, of low temperature, was identified in the bed performing air temperature measurements in a fluidized bed of glass beads top spraying water. The size and shape of this region, where the sprayed liquid wets the fluidized particles and where agglomeration predominantly occurs, were found to depend on operating conditions (inlet air temperature, particle load, liquid feed rate, spraying pressure). Agglomeration trials performed with spherical, non-soluble glass beads (~160 micrometers) spraying acacia gum solutions (20-30% w/w) and with irregular, soluble maltodextrin particles (~180 micrometers) spraying water or maltodextrin and acacia gum solutions (20% w/w) demonstrated that controlled agglomeration was achieved for a wetting zone occupying between 18 and 30 % of the fluidized bed. Non-soluble particles required a preliminary coating period before starting to agglomerate whilst soluble particles became sticky and agglomerated as soon as their surface was wetted by the sprayed liquid. For both types of particles, the growing period was stopped when a maximal size of agglomerates was reached. It was higher for soluble particles and increased when increasing the sprayed liquid flow rate. Analysis of powder properties demonstrate that small drops of the sprayed liquid lead to small and weak agglomerates. Bigger agglomerates had a more irregular shape but a better mechanical resistance. A model using population balance equations to describe the particle size increase and the evolution of the size distribution during agglomeration in the wetting zone, was proposed and validated.
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Submitted on : Wednesday, June 17, 2009 - 8:00:00 AM
Last modification on : Friday, August 5, 2022 - 2:54:00 PM
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  • HAL Id : pastel-00005196, version 1
  • PRODINRA : 246660


Maria-Teresa Jimenez-Munguia. Agglomération de particules par voie humide en lit fluidisé. Sciences de l'ingénieur [physics]. ENSIA (AgroParisTech), 2007. Français. ⟨NNT : 2007AGPT0091⟩. ⟨pastel-00005196⟩



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