Particles agglomeration in a conical fluidized bed in relation with air temperature profiles
Résumé
Particles agglomeration is obtained by spraying liquid over solid particles fluidized by hot air. The growth mechanism depends on the operating parameters (geometry and process conditions) and initial materials, influencing drying conditions and agitation, leading either to agglomeration or coating or wet quenching. It is linked to air temperature and/or humidity distributions appearing in the well-mixing system of the fluidized bed due to the penetration of the sprayed liquid jet.
In this study, air temperatures distributions in a conical fluidized bed of model particles (glass beads) top sprayed with water were measured varying the initial particles load (250, 500, 750g), the fluidizing air inlet temperature (60-70-80 degrees C), the liquid feed rate (2.65, 5.33, 7.55 ml min(-1)) and the relative air spraying pressure (1,2,3 bars). Three thermal zones were identified (heat transfer, isothermal, wetting-active), with sizes and shapes related to particles circulation patterns and drying and spraying conditions influenced by the operating parameters. Subsequent agglomeration trials, were carried out with glass beads and soluble maltodextrin particles agglomerated, respectively, with an acacia gum solution and water. They showed a relationship between the air temperatures distribution and the resulting growth mechanism. Particularly, controlled agglomeration was obtained for a wetting-active zone occupying 18-30% of the fluidized bed.