Fluidization in food powder production

Fluidization allowing efficient energy transfer is widely used in food production for drying, cooling, agglomeration, coating and mixing of powdered or granulated materials. Big tonnages of powders with diameters between about 50 μm and some few millimetres are handled daily in fluidized beds, either batchwise or in continuous mode. In this chapter, the principles of gas–solid fluidization are first reviewed. Then the main types of fluidization equipment used are described. And, finally, some examples of the main applications of fluidization in the production of food powders are given

Aroma encapsulation in powder by spray drying, and fluid bed agglomeration and coating

11. International Congress on Engineering and Food (ICEF) - Athens (Grèce) - 22-26 mai 2011Aroma encapsulation in powder by spray drying, and fluid bed agglomeration and coatin

Influence of structural properties of alum and ferric flocs on sludge dewaterability

Sludges are made of floes produced during the coagulation stage. Their dewatering not only depends on the equipment used but also on the chemical, structural and physical characteristics of flocs. In this study, the relation between floc structure and sludge dewaterability is investigated beside the influence of the operating conditions during coagulation. Eight synthetic clay flocs families are produced using clay suspensions with four initial solids concentrations ranging from 0.5 to 5 g L-1 and two coagulants (Al-2(SO4)(3) and FeCl3). Flocs structure is characterised by their fractal dimension and by the size of the basic units (clusters, aggregates) they are made from. Fractal dimension values about 2.5 are indicative of rather compact structures with slightly looser flocs obtained when using FeCl3. Except for clusters, larger in ferric flocs, the basic units sizes are similar whatever the coagulant used and they decrease when the solids concentration during coagulation is increased. Sludge dewaterability is estimated from the bound water content and the capillary suction time (CST) giving respectively information on the extent and on the rate of water removal. Ferric flocs contain about 20% less bound water but exhibit higher CST values and therefore higher resistance to water removal than alum ones. Flocs structure and sludge dewaterability are found linked. The sludge bound water content is found to decrease with the floc fractal dimension: less compact flocs contain more water but less bound water. And the capillary suction time is lower when sludges are made of smaller flocs

Structural characterization of flocs in relation to their settling performances

fractal; floc structure; coagulation/flocculation; settling; size distributionsT his paper reports on the use of particle size analysis and settling tests for characterizing the structure of metal coagulation floes and further identifying optimum conditions for their settling and dewatering. A velocity-size variation law was established for model floes created from colloidal clay particles suspensions with different initial clay concentrations using two coagulants [aluminium sulphate, Al-2(SO4)(3) and ferric chloride, FeCl3]. It allowed deduction of the volume fractal characteristic D-3 of each clay floc family and their settling performances. Floes also appeared to be made from three basic units, the size of which was estimated from particle size analyses performed at different stages of the coagulation/flocculation. All the D-3 values obtained were high, about 2.5, nearly independent of the initial clay concentration. In contrast, the floc and the basic unit sizes decreased with the clay concentration increase. More concentrated suspensions led to lower settling rates. Ferric floes appeared to be made from larger basic units than aluminium ones and to be less dense and less compact with lower settling rates. They were therefore thought to contain more water

Role of emulsion size in oil compounds encapsulation in spray-dried powders

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Identification of thermal zones and population balance modelling of fluidized bed spray granulation

Air temperature measurements in a fluidized bed of glass beads top sprayed with water showed that conditions for particles growth were fulfilled only in the cold wetting zone under the nozzle which size and shape depended on operating conditions (liquid spray rate, nozzle air pressure, air temperature, and particles load). Evolution of the particle size distribution during agglomeration was modelled using population balance and representing the fluidized bed as two perfectly mixed reactors exchanging particles with particle growth only in the one corresponding to the wetting zone. The model was applied to the agglomeration of non-soluble glass beads and soluble maltodextrin particles spraying respectively an acacia gum solution (binder) and water. Among the three adjustable parameters, identified from experimental particle size distributions evolution during glass beads agglomeration, only one describing the kinetics of the size distribution evolution depended on process variables. The model allowed satisfying simulation of the evolution of the particle size distribution during maltodextrin agglomeration

Encapsulation of aroma

Encapsulation of arom

Particles agglomeration in a conical fluidized bed in relation with air temperature profiles

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