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Séchage par atomisation : propriétés de collage des particules en relation avec l'agglomération

Abstract : Food instant powders like milk, soups, juices, coffee, are usually produced by spray drying followed by a further step of agglomeration to get larger particles (from 50-100 μm to 250-500 μm) with a narrow size distribution and modified structure (porosity) to obtain good handling and instant properties (wettability, dispersability, solubility). Agglomeration of spray dried powders is performed either outside or inside the drying chamber in a fluid bed, or by return of dry fines into the chamber. Agglomeration of particles requires collisions and adhesion to create links between particles. Stickiness of particle surface will depend on the presence of components able to develop such property. For carbohydrates, stickiness is related to the glass transition appearing when varying water content, water activity and temperature, three parameters representative of drying. A methodology was developed to associate the evolution of drying air properties to drops drying along the chamber. Measurements of air temperature and relative humidity allowed to calculate the drops water content at any position in the dryer, and to deduce the possible sticky conditions and positions. Spray drying of aqueous solution of a model product able to stick (maltodextrin DE12 and DE21) was performed in a co-current pilot spray dryer equipped with a rotary atomizer. Studied process parameters included liquid feed flow rate (1 to 3.2 kg.h-1 evaporated water), inlet air temperature (144 to 200°C), air flow rate (80-110 kg.h-1), rotary atomizer velocity (22500 to 30000 rpm). Maltodextrin DE12 drops were quickly dried below the glass transition temperature, and stickiness seemed possible only next to the atomizer. Maltodextrin DE21 might present a sticky behaviour in a wider part of the chamber due to conditions corresponding to lower glass transition temperatures, especially for high liquid flow rate and low inlet air temperature. Computational Fluid Dynamics was used to simulate the drying of solutions, and to predict possible sticky conditions and positions. These conditions were tested and validated by performing agglomeration trials introducing powder at different positions inside the chamber. Finally, this experimental approach using air properties measurements was applied to interpret the drying behaviour of a different product (protein hydrolyzate) in a pilot spray dryer at higher scale, equipped with fines return and internal fluid bed.
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Contributor : Ecole Agroparistech <>
Submitted on : Monday, January 11, 2010 - 8:00:00 AM
Last modification on : Saturday, June 6, 2020 - 9:28:34 PM
Long-term archiving on: : Friday, September 10, 2010 - 2:54:16 PM

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  • HAL Id : pastel-00005602, version 1
  • PRODINRA : 246732

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Alessandro Gianfrancesco. Séchage par atomisation : propriétés de collage des particules en relation avec l'agglomération. Sciences du Vivant [q-bio]. AgroParisTech, 2009. Français. ⟨NNT : 2009AGPT0029⟩. ⟨pastel-00005602⟩

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