Sticky Region in Drying—Definition and Identification

Kudra, Tadeusz

doi:10.1081/drt-120024678

Cited by 109 publications

(78 citation statements)

References 18 publications

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“…As reported by Kudra [46], during stickiness period, the material deposits on the dryer wall causing the alteration of the hydrodynamics of the dryer and in extreme cases it leads to chocking the dryer leading to a notable decrease of the dryer performances. The author reports that non sticky materi als can present better heat transfer coefficient of about 60% than a sticky material during rotary drying.…”

Section: Conductive Drying Of Wastewater Sludgementioning

confidence: 99%

“…18. Ferasse et al [45], Kudra [46] and Deng et al [47] report that during conductive drying of wastewater sludge the product passes by respectively the pasty phase, lumpy and then the granular phase. These forms are detected by following the variations of the torque with the moisture content decrease (or time increase).…”

Section: Conductive Drying Of Wastewater Sludgementioning

confidence: 99%

See 1 more Smart Citation

Review on fundamental aspect of application of drying process to wastewater sludge

Bennamoun

Arlabosse

Léonard

2013

Renewable and Sustainable Energy Reviews

197

103

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a b s t r a c tThe objective of this work is to give the fundamental information that should be known about wastewater sludge drying. Three methods are mainly applied: convective drying, conductive drying and solar drying, each one presenting different characteristics. When applying convective drying three phases are distin guished: adaptation phase, constant drying rate phase and falling drying rate phase. Experimental works show that several parameters influence the drying kinetic during this process, such as the origin of the sludge and operating conditions. Imaging techniques allow observing three phenomena that happen during convective drying: shrinkage, cracks and skin formation. When applying conductive drying and considering the torque variations, the product passes through: pasty phase, lumpy phase and granular phase. The results show no regular shape of the drying kinetic with high values of the drying rate and the heat transfer coefficient during the first phase. A special focus is given into the sticky phase which reduces performances of the dryer. The third applied drying method is solar drying, which depends wholly on climatic conditions, such solar radiations and air temperature. Besides, for this method no regular shape of the drying kinetic can be observed, with high drying rate values during favorable conditions and low drying rate values during unfavorable conditions. The presented studies dealing with solar drying of wastewater sludge are limited to the variations of the different air temperatures registered inside and outside the drying chamber with the product temperature and their humidity with study of the pathogen reduction. Finally, some innovative developed methods are exposed in this review, such as the use of frying and super heated steam.

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Section: Conductive Drying Of Wastewater Sludgementioning

confidence: 99%

Section: Conductive Drying Of Wastewater Sludgementioning

confidence: 99%

Review on fundamental aspect of application of drying process to wastewater sludge

Bennamoun

Arlabosse

Léonard

2013

Renewable and Sustainable Energy Reviews

197

103

View full text Add to dashboard Cite

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“…Fitzpatrick et al [2] showed that increased temperature in the range of 10 to 30 °C, where most fat melting occurs, can increase powder cohesiveness in powders with significant fat content due to the formation of liquid fat bridges between particles. Furthermore, there is a sharp increase in the cohesiveness and adhesion of powders to surfaces when the temperature is elevated above the "sticky" temperature [11]. Cooling of milk powder may produce lumping and caking.…”

Section: Effect Of Storage Conditionsmentioning

confidence: 99%

Assessment of the flowability of spray-dried milk powders for chocolate manufacture

Fitzpatrick

Barry

Delaney

et al. 2005

Lait

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-This work reports on the flowability of novel milk powders that have potential for application in the manufacture of chocolate. Many milk powders are cohesive which can give rise to powder flow problems. Shear cell techniques were used to measure the following powder flow properties: powder flowfunction, effective angle of internal friction and angle of wall friction. These measurements were used in assessing cohesion developed within the powders under compaction and adhesion to a stainless steel surface. The work investigated how fat content, free-fat content, particle size, moisture content, lactose content, amorphous lactose content and storage conditions influenced the flowability of the milk powders. Increased fat content reduced powder flowability especially when comparing 1% and 26% fat powders. Varying free-fat content showed no effect on flowability. Particle size had a major influence on flowability, as increasing the particle size significantly improved the flowability of powders with 1% and 26% fat content. The concentration of amorphous lactose present increased the susceptibility of powders for sorbing moisture, resulting in reduced flowability and caking. Finally, powder flow property measurements can be applied in the design of hoppers and silos that give consistent reliable flow, which is essential in powder handling and processing operations. milk powder / flowability / shear testing / chocolate manufacture Résumé -Évaluation de l'aptitude à l'écoulement de poudres de lait séché par atomisation utilisables en chocolaterie. Cet article présente les propriétés d'écoulement de nouvelles poudres de lait utilisables dans la fabrication de chocolat. De nombreuses poudres de lait sont collantes, ce qui peut conduire à des problèmes d'écoulement. Des techniques de cisaillement ont été utilisées pour mesurer sur ces poudres les propriétés d'écoulement suivantes : fonction d'écoulement, angle effectif de friction interne et angle de friction à la paroi. Ces mesures ont été utilisées pour évaluer la cohésion à l'intérieur de poudres agglomérées et leur adhésion à une surface en acier inoxydable. Ce travail a montré comment les teneurs en matière grasse et en matière grasse libre, la taille des particules, l'humidité, les teneurs en lactose et en lactose amorphe et les conditions de stockage influencent la coulabilité des poudres de lait. L'augmentation de la teneur en matière grasse conduisait à une diminution de la coulabilité, en particulier en comparant des poudres à 1 % et à 26 % de matière grasse. La variation de la teneur en matière grasse libre n'avait pas d'effet sur la coulabilité. Par contre, la taille des particules avait un effet majeur puisque l'accroissement de la taille des particules améliorait de façon significative la coulabilité des poudres contenant 1 % ou 26 % de matière grasse. La concentration en lactose amorphe présent augmentait la susceptibilité des poudres à la sorption d'eau, entraînant une coulabilité réduite et un mottage. Finalement, les mesures des propriétés d'éc...

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“…An indirect approach correlates the sticky temperature, T s , to the glass transition temperature, T g , of the substance; T s is 10 to 30 degrees higher than T g [7,13]. In static methods, measurements of T s are based on dry powder property changes due to sticking, such as resistance to stirring (propeller-driven methods [4,6,8,10]), adhesion (ampule method [15]) or surface optical properties [9]. Other techniques generate powder flow in a humidified air stream within a fluidization cell [3] or in a cyclone [1].…”

Section: Introductionmentioning

confidence: 99%

Powder agglomeration during the spray-drying process: measurements of air properties

Gianfrancesco

Turchiuli

Dumoulin

2008

Dairy Sci. Technol.

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-Instant food powders are usually produced by spray drying of formulated liquid and powder agglomeration, either into the drying chamber or in an external fluid bed. During spray drying, according to the liquid composition, the viscosity of the initial liquid drops increases more or less rapidly, until the drop surface reaches a rubbery state considered as sticky, before further drying. This sticky property may be used to produce agglomerates inside the chamber by adding dry solid particles, as fines. The present study deals with a methodology to identify regions where the drying drops are sticky in relation to drying conditions (inlet air temperature 144-159-174 • C, liquid flow rate 15 to 75 mL·min −1 ), using a co-current pilot spray dryer with rotary atomizer. Assuming that drying air properties' (temperature and humidity) evolution is representative of drop drying (drying rate, amount of evaporated water), we realized a map of temperatures and relative humidity for drying air inside the drying chamber. Trials were performed with water (feasibility) and a maltodextrin aqueous solution (40% w/w, DE12) as a model product with sticky properties during drying. The results showed that drying behavior was different for water and aqueous maltodextrin solution. For both, in the tested conditions, the percentage of evaporated water was found to vary from 57 to 89% in the top part of the chamber, close to the atomizer. That represents a possible region where dry fines could be introduced for agglomeration. Résumé -Agglomération de poudres au cours du processus de séchage par pulvérisation : mesure des propriétés de l'air. Les poudres alimentaires instantanées sont habituellement produites par séchage par pulvérisation d'une solution formulée, suivi d'une étape d'agglomération, soit dans la chambre de séchage soit dans un lit fluidisé externe. Au cours du séchage, selon la composition du liquide, la viscosité des gouttes liquides augmente plus ou moins rapidement jusqu'à ce que la surface de la goutte devienne collante, avant séchage ultérieur. Cette propriété collante peut être exploitée pour produire des agglomérats dans la chambre par introduction de particules solides sèches, les fines. Cette étude cherche à établir une méthodologie pour identifier des zones où les gouttes qui sèchent deviennent collantes en fonction des paramètres de séchage (température d'entrée d'air 144-159-174 • C, débit liquide de 15 à 75 mL·min −1 ), en utilisant un séchoir pilote co-courant équipé avec une turbine de pulvérisation. En supposant que l'évolution des propriétés de l'air (température et humidité) au cours du séchage soit représentative du séchage des gouttes (vitesse de séchage, quantité d'eau évaporée), des cartographies des températures et des humidités relatives de l'air dans la chambre de séchage ont été réalisées. Des essais ont été effectués avec pulvérisation d'eau (faisabilité), puis d'une solution de maltodextrine (40 % w/w, DE12) comme produit modèle pouvant avoir un comportement collant au cours du séchage. ...

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Sticky Region in Drying—Definition and Identification

Cited by 109 publications

References 18 publications

Review on fundamental aspect of application of drying process to wastewater sludge

Review on fundamental aspect of application of drying process to wastewater sludge

Assessment of the flowability of spray-dried milk powders for chocolate manufacture

Powder agglomeration during the spray-drying process: measurements of air properties

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