Agglomeration during spray drying: Air-borne clusters or breakage at the walls?

Particle agglomeration, wall deposition and resuspension are inherent to many industries and natural processes, and often inter-connected. This work looks into their relation in a confined particle laden swirling flow. It investigates how the size of detergent powder spray dried in a swirl counter-current tower responds to changes in the air flow. Four sets of sprays are investigated under varying combinations of air temperature and velocity that cause the same evaporation. The use of high air velocities accumulates more of the droplets and dry powder in the chamber swirling faster, but it leads to creation of a finer product. Particle-particle and particle-wall contacts are made more frequent and energetic but in turn the swirl troughs the solids to the wall where deposits constantly form and break. Past PIV and tracer studies revealed that the rates of deposition and resuspension are balanced; the data discussed here indicate that the dynamic nature of the deposits is a major contributor to particle formation. In contrast with the usual assumption, the product size seems driven not by inter-particle contacts in airborne state but the ability of the solids to gain kinetic energy and break up a collection of clusters layering on the wall. As a result, the dryer performance becomes driven by the dynamic of deposition and resuspension. This paper studies the efficiency of limiting operation strategies and shows that a low temperature design concept is better suited to control fouling phenomena and improve capacity and energy consumption

Caking behaviour of food powder binary mixes containing sticky and non-sticky powders

Caking of food powders is highly undesirable. Many food powders are powder ingredient mixes and there is little work reported on the caking of food powder mixes. This study focusses on the caking of food powder binary mixes consisting of a “sticky” powder (whey permeate WP or maltodextrin MD) and a “non-sticky” powder (salt, flour or paprika). The powders were exposed to 76% relative humidity to make the WP and MD sticky. Force-displacement testing coupled with visual assessment of 2 particles in contact using a microscope were used to investigate the caking behaviour of the binary mixes. A “sticky” powder mass fraction of at least 20% was required to initiate caking and formation of weak cakes. Increasing percentage “sticky” powder fraction above the initial caking percentage resulted in progressively stronger cakes, however the rate of this progression was much less for the stickiest MD powder. The “non-sticky” powders and how they interacted with the “sticky” powders influenced the caking behaviour of the mix. For example, salt formed the strongest cakes in the WP mixes but formed the weakest in the MD mixes. Ability of a “sticky” powder to deform and flow influenced caking behaviour

Identification of regions in a spray dryer susceptible to forced agglomeration by CFD simulations

Agglomeration during spray drying improves the rehydration and flow properties of produced powders. However, tools for predicting agglomeration are rare. In this work a rigorous mapping approach incorporating number density and stickiness state of particles was developed for CFD simulations, which identifies different zones prone to coalescence and agglomeration inside a spray dryer. This approach was found to be quick, informative, reasonably accurate and resource efficient, as it bypasses the modelling of collision phenomena. The predictions were validated with experimental data of particle size distribution and SEM analyses of the powder morphology performed on samples produced in a lab-scale counter current spray dryer with varying two-nozzle- configurations. For the investigated dryer, the optimum nozzle configuration to achieve effective agglomeration was successfully identified and configurations yielding size enlargement dominated by coalescence could be distinguished. The developed method is generic and hence can be applied to find suitable location and angle for multiple atomization as well as fine returns in industrial practice to achieve controlled agglomeration. This study forms the fundament of a rigorous CFD model for agglomeration, which along with the findings from this study will allow the agglomeration phenomenon to be better understood and thus attain more efficient design, scale-up and operation of spray dryers

Harnessing the capabilities of spray granulation in the food industry for the production of functional foods

The article is the literature review of a current state of production technologies of powdery foodstuff, concentrates and multicomponent mixes. The need of the food industry for qualitative methods of processing of raw materials of different physical and chemical structure is noted. The authors give the reasons about need and possibility of a choice of granulation as a method of data processing of products. Physical and chemical features of granulation methods of disperse environments of various aggregate states based on the studied regularities and works of other authors are considered. The authors made the assumption of the application prospects of the method of liquid dispersion on the surface of particles in a suspended state for a granulation of foodstuff and they offered the alternative option. The possibility to use whey as binding element is considered. At the end of article authors draw the conclusion about the prospects of use of a method of dispersion of liquid on the surface of particles in a suspended state for a granulation of foodstuff

Harnessing the capabilities of spray granulation in the food industry for the production of functional foods

The article is the literature review of a current state of production technologies of powdery foodstuff, concentrates and multicomponent mixes. The need of the food industry for qualitative methods of processing of raw materials of different physical and chemical structure is noted. The authors give the reasons about need and possibility of a choice of granulation as a method of data processing of products. Physical and chemical features of granulation methods of disperse environments of various aggregate states based on the studied regularities and works of other authors are considered. The authors made the assumption of the application prospects of the method of liquid dispersion on the surface of particles in a suspended state for a granulation of foodstuff and they offered the alternative option. The possibility to use whey as binding element is considered. At the end of article authors draw the conclusion about the prospects of use of a method of dispersion of liquid on the surface of particles in a suspended state for a granulation of foodstuff

Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties

The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids