FACTORS GOVERNING SURFACE MORPHOLOGY OF SPRAY-DRIED AMORPHOUS SUBSTANCES

Changes in particle morphology (size, shape, and appearance) have been monitored during drying of drops of foods and food-related materials. The apparatus produces a single stream of drops of uniform size, using a vibrating-orifice device for drop production. The drop size and the time-temperature history of the drops as they fall can be varied and controlled.

Qualitative observations are reported for drying of aqueous solutions of lactose, maltodextrin, skim milk, and coffee extract, with different feed concentrations. Particular emphasis is placed upon the tendency for development of folds upon the particle surface. A mechanistic model is developed, relating the tendency for folding to the extent of viscous flow of surface material in response to a surface-energy driving force. This model gives semi-quantitative agreement with observations for solutes of different molecular weight (and hence different viscosity) and for different feed concentrations.     

Surface Stickiness of Drops of Carbohydrate and Organic Acid Solutions During Convective Drying: Experiments and Modeling

Abstract

Drying kinetics of low molecular weight sugars such as fructose, glucose, sucrose and organic acid such as citric acid and high molecular weight carbohydrate such as maltodextrin (DE 6) were determined experimentally using single drop drying experiments as well as predicted numerically by solving the mass and heat transfer equations. The predicted moisture and temperature histories agreed with the experimental ones within 6% average relative (absolute) error and average difference of ± 1°C, respectively. The stickiness histories of these drops were determined experimentally and predicted numerically based on the glass transition temperature (T _g ) of surface layer. The model predicted the experimental observations with good accuracy. A nonsticky regime for these materials during spray drying is proposed by simulating a drop, initially 120 µm in diameter, in a spray drying environment.     

Simulation of Drying on the Basis of Nonequilibrium Thermodynamics of Beterogeneous Multiphase Polydispersed Systems.Formation of the Morphological Structure of Emulsive Elastomers Using Method of Spray - Drying for Latexes

ABSTRACT

The process and the technology of fine - dispersed rubber powder production on the basts of spray - drying for latexes were considered. The practical recommendations on usage of physical modification method for elastomers on the basis of interaction mechanism between solid -phase dispersed filler and polymeric panicles were given.

The mathematical model for latex drops during drying in the presence of structured adsorptive layer of surface active substances on the surface of drops was worked out, that allowed us to give the recommendations for production of monolithic particles.     

MANUFACTURING PARAMETERS AND QUALITY CHARACTERISTICS OF SPRAY DRIED JAMEED

ABSTRACT

Spray drying of jameed - a dried fermented dairy product, is investigated. The study covers the effects of the operating variables upon the physical and chemical characteristics of the dried product. The investigated variables were: feed total solids, feed flow rate, inlet air temperature, air flow rate and atomizer pressure. The product characteristics measured were: total solids, bulk density, average particle size, wettability, dipersibility, color, ash content, salt content, fat content and pH. Best overall results were obtained for a feed total solids of 17%, feed flow rate of 36.5 ml/min, inlet air temperature of 100 /C, air flow rate of 632 cm₃/s, and atomizer pressure of 1.5 bar.     

SOME CRITERIA OF SPRAY DRYER DESIGN FOR FOOD LIQUID

Abstract

Spray drying has many applications for a wide variety of dried food powders. The quality of spray dried food is quite dependent on the atomization characteristics and the heat and mass transfer on drops inside the spray dryer. This paper deals with some design criteria of the spray dryer such as the atomizer, the drop trajectory and the heat/mass transfer between the drop and the drying air.     

Vacuum Contact Drying Kinetics: An Experimental Parametric Study

Abstract

Vacuum contact drying kinetics of a model system consisting of nonporous glass beads and water has been experimentally measured on a laboratory scale. A methodology for determination of drying curves from experimental data in a statistically robust way has been developed. The effects of jacket temperature, head-space pressure, particle bed depth, vessel diameter, and particle size on drying rate during constant and falling rate periods have been studied. It was found that in the range of parameters investigated, drying rate does not depend on the means of realization of the driving force (by temperature or pressure); drying rate in the constant-rate period decreases with increasing bed depth while the overall heat-transfer rate increases due to increased surface area. A very strong dependence of drying rate and regime on particle size was observed; the constant-rate period disappeared for small particles.     

The Effect of Particle Size on the Drying of Milled Peat

ABSTRACT

Milled peat production involves the atmospheric drying of a 20-30mm deep layer of milled peat (i.e. peat in a powder or crumb form) on the surface of the bog. Research from various sources indicates that the drying of rate of this layer is highly dependent upon its particle size distribution. Experiments were conducted to confirm this phenomenon for Irish peats.

A drying chamber was constructed that enabled both climatic and material variables to be controlled. Three peat types were evaluated (viz. low (150 g/l), medium (240 g/l), and high (330 g/l) bulk density peats)for three particle size distributions (i.e. small (2.0-5.6 mm), medium (5.6-9.5 mm) and large (9.5-16mm)) diameter particles.

Results showed that large diameter particles (viz 9.5-16 mm) dry some 10-25 % faster than smaller particles.     

An Investigation of Milk Powders Produced by a Laboratory-Scale Spray Dryer

ABSTRACT

A mini spray dryer has been used to investigate morphological changes that occur to milk particles during the spray drying process. We have found that the mini spray dryer is ideal for such investigations, because phenomena such as skin and vacuole formation in particles can be analyzed without the added complication of particle agglomeration, which only occurs in much larger spray dryers where particle number concentrations are higher. We have confirmed observations made by various researchers that the bulk density of spray-dried milk powder is greatly affected by the drying temperature, due to the strong influence of the latter on the porosity of the particles. In addition, we have attempted to explain observations made by various workers that fat accumulates preferentially at the surface of a particle during drying by postulating that fluid fat is transported towards the surface, via a network of cracks and pores, by the development of a vacuole overpressure which is also responsible for the inflation of the particle. Finally, we have shown that milk powders can be spray dried a second time, by reconstitution with water, with no change to the thermodynamic characteristics of the resultant powder. Thus, milk concentrates for spray drying research can be prepared from already-spray-dried milk powders rather than using the more arduous evaporation method to concentrate unprocessed milk.     

Spray Drying Tower Experiments

Abstract

The article presents a full set of spray drying experiments for selected products performed in a co-current spray drying tower developed at Lodz Technical University. The experiments enabled identification of process and atomization parameters (feed properties, feed rate and feed temperature, drying agent temperature, air flow rate, atomization ratio, etc.) on drying and degradation kinetics, spray structure, particle residence time, and final product properties. Drying agent temperature measurements showed, in all cases, the initial increase of gas temperature in the spray envelope caused by the spray expansion and then a decrease induced by liquid evaporation and heat losses to the environment. PDA analysis confirmed that the initial velocity of particles was a function of a diameter and also the function of the distance from the axis. Practically an identical particle size distribution was observed in each cross-sectional area of the dryer. Negative values of particle velocity in the vicinity of the axis and at the edge of the spray envelope were found which proved that recirculation of particles appeared in the column. Analysis of final product properties showed that for agglomerate-like materials a decrease of bulk density with an increase of air temperature was related to morphological changes that occurred during drying and affected the shape of particles, surface structure, etc. The experiments proved that air/liquid ratio for two-fluid atomization and gas temperature were the most decisive factors controlling drying and degradation process rate and final product properties.     

Continuous Drying of Slurry in a Jet Spouted Bed

ABSTRACT

he performance of a laboratory scale jet spouted bed (JSB) for drying rice flour slurry was studied. The bed consisted of ceramic balls (5028 mm diameter) and the rice flour slurry was sprayed onto the moving particle surface near the inlet part. All the experiments were carried out at the jet spouting regime. This regime has high bed void fraction and violent movement and collision of bed particles. As a result, the dried product layer is attrited from particle surface as a fine powder and entrained from the bed by the spouting air. The experimental result were presented to show the effects of static bed height, inlet air flow rate and temperature, and feed concentration and flow rate on the outlet air temperature, thernal efficiency, and mean particle size and moisture content of the product. Asimple mathematical model, which is based on the conservation of mass and energy equations, was developed. Predicted results agreed well with those obtained from the experiment.     

DRYING OF BIOMASS PARTICLES IN FIXED AND MOVING BEDS

ABSTRACT

The drying of biomass fuel particles in fixed and moving beds with hot gas or steam is considered both experimentally and theoretically. A single particle drying model is coupled with a model describing beat and moisture transfer in The gas phase of the bed. The size of the bed to reach a certain degree of drying depends mostly on the following parameters: particle size, panicle moisture content, gas inlet temperature, gas inlet moisture content and gas mass flow rate.     

DRYING OF PARTICULATE SOLIDS: DETERMINATION OF THE CHARACTERISTIC CURVE OF BROWN COAL.

ABSTRACT

Variation on the rate of drying of brown coal powder as a function of environmental and intrinsic properties has been studied in a gravimetric laboratory-scale drier.

Raw data have been treated to correlate the constant rate of drying and the equilibrium moisture content as a function of flow rate and temperature of the gas phase, particle size and surface additives. The characteristic drying curve occurs when the reduced rate of drying is plotted as a function of a dimensionless moisture potetial.     

Analysis of the drying behavior of suspension drops with spherical and ellipsoidal particles

ABSTRACT

Employing multispeckle diffusing wave spectroscopy (MSDWS) as a noncontact light scattering method, drying dynamics of suspension drops with spherical and ellipsoidal particles have been investigted in real time. Scattered light intensity data during drying are converted to calculate the autocorrelation fuction and moment of inetia (IM) through co-occurrence matrix (COM). Using IM data, it is found that drying patterns of drops could be clearly divided into compacting and air-invading stages. Compared with the case with spherical particles, ellipsoidal particles with lower mobility in a suspension drop augment the period of air-invading stage in drying process due to the loosely packed pore structures between particles.     

Drying of Inorganic Particulate Compounds

ABSTRACT

Inorganic particulates are usually dried in a fixed bed, fluidized bed, or spray dryers. These compounds are easy to dry, once their physical structure, with high porosity, allows moisture content removal with low resistances. For fluidized bed of alumina particle evaluations, a laboratory-scale drying unit was built. The drying experiments were carried out with alumina particles with different diameters to evaluate temperature and air flow rate effects on drying kinetics and bed height. In another case, the dehydration of a mixture of rare-earth chlorides in a fluidized bed was studied, aiming at the production of anhydrous rare-earth chlorides, used to obtain mischmetal by electrolytic and metallothermic processes. The spray drying experiments were carried out in a pilot plant. Spray drying is a technique largely applied in industrial processes to dry solutions or suspensions, converting their solid parts into a dried powder. A set of rare-earth drying experiments was carried out, aiming at the development of techniques to obtain a powder that could satisfy international morphological requirements. The results allowed evaluating the effects of air flow rate, feed concentration, atomizer model, rotation velocity, and atomization pressure on powder density and particle size distribution.     

In situ observation on particle formation process via single droplet drying apparatus: Effects of precursor composition on particle morphology

ABSTRACT

Eudragit® RS 30D/silica composite precursor containing either Rhodamine B or sucrose as model drug was dried in a single droplet drying apparatus. Microparticles with distinct core–shell structure were produced by one-step drying for all compositions, while Rhodamine B showed uneven distribution in core and shell regions. At 5% (w/w) loading, it influenced shell formation process by producing dispersible initial shell and altered particle surface morphology into wrinkling appearance, while similar effects were not observed for sucrose. Decreasing the loading to 0.017% reduced the influence. The observations might be attributed to the properties of Rhodamine B, which affect its migration behavior during drying.     

Microencapsulation in foam spray drying

Abstract

The article presents the results of the experiments of gas-admixing foam spray drying microencapsulation of oil in co-current spray drying tower. The introduction of a foaming gas resulted in a decrease of encapsulation efficiency: for high foaming gas/liquid ratio (GLR) 6.43·10^?3 kg/kg and T_air,0=215?°C by over 50% relative to the non-foaming process due to damage of the microcapsule structure and leakage of the oil phase to the particle surface. For moderate drying temperatures and GLR, 80% of microencapsulation efficiency might be achieved with simultaneous control of selected product properties like apparent and bulk density or angle of repose. Abbreviations GLR gas-to-liquid ratio

HR Hausner ratio

MDX maltodextrin

PSD particle size distribution

SEM scanning electron microscope.

     

Drying of Solid Furl Particlbs in Hot Gases

ABSTRACT

Drying of solid fuel particles in hot gases ( 50–200c) is studied both theoretically and experimentally. The measurements are carried out by using a thermobalance reactor constructed for drying and pyrolysis studies of particles up to 30 mm by diameter. The model is based on the solution of the conservation equations for mass and energy. The drying is considered to consist of three successive periods: a short initial heating period, period of constant rate of drying and period of falling rate of drying. It is assumed that the particle moisture distribution is uniform during the constant rate of drying. Shrinking core model is assumed for the falling rate period. esides fuel particles, the model is applicable also for other solid particle drying processes. Model calculations are compared to measurements for wood chips. The model can predict the efFect of the main parameters reasonably well. These main parameters affecting the drying rate are: particle size, particle shape, initial particle moisture content, gas temperature and gas moisture content, emperature of the reactor walls and slip velocity. The irregular shape of practical fuel particles can approximately be simulated as one-dimensional case ( plate, cylinder, sphere) by using an equivalent volumc to surface area ratio.     

Physicochemical and nutraceutical properties of barley grass powder microencapsulated by spray drying

ABSTRACT

Barley grass (Triticum aestivum L.) is popular, commonly known as a nutritional supplement in China. To obtain the highest chlorophyll and flavonoid content as well as other physicochemical characteristics, spray drying from barley grass juice was carried out for two different maltodextrin concentrations (10 and 20%, dried basis) and four different inlet air temperatures (140, 150, 160, and 170°C). After drying, color, water activity, odor, taste, density, particle size, glass transition temperature, and chlorophyll and flavonoid contents of the dried product were measured. Highest contents of flavonoid (5.66?mg/kg) and chlorophyll (7.29?mg/kg) were obtained under 150°C inlet air temperature, 10% maltodextrin concentration, at a feed flow rate of 1.8?L/h for the drying. Corresponding particle size was 19.58–13.33?µm. The glass transition temperature (T_g) increased with the increasing of maltodextrin concentration; and two max T_g of powder obtained from 10 and 20% maltodextrin concentration were 74.4 and 77.4°C, respectively. Retention of taste and flavor were highest with 20% maltodextrin. High inlet air temperature was contributed to the large discrepancy of odor and taste substances. The best color (lightness L*?=?64.44 and greenness b*?=??11.53) was obtained at 150°C inlet air temperature and 10% maltodextrin concentration. Both maltodextrin concentrations resulted in poor flowability of the dried product (C_I?≤?32.51).     

A New Type of Modular Dryer Combining Solar Energy and Producer Gas

ABSTRACT

The main concept oithis research is to develop a flexible modular dryer that combines two different sources of non-conventional energy. In this study, solar energy and producer gas generated by an up-flow charcoal gasifier were considered.

The drying system was set out by using a 0.6 m3 modular cabinet supporting a solar collector of 2.5 m2 surface area. 16 kg of chatcoal was used in each bateb to feed the gasifier.

The experiment was performed for drying beef that required two different stages of drying temperture: the first. which used producer gas requires approximatly 60°C for four hours and the second used solar energy at 40° for six hours. The energy consumed for drying 16 kg of beef was 7.57 MJ7sol;kg H2o     

SIMULATION OF TRANSPORT DYNAMICS IN FLUIDIZED-BED DRYERS

ABSTRACT

A mathematical model for predicting three-dimensional, two-phase flow, heat and mass transfer inside fluidized-bed dryers has been developed. The model consists of the full set of partial-differential equations that describe the conservation of mass, momentum and energy for both phases inside the dryer, and is coupled with correlations concerning interphase momentum-, heat-, and mass-transfer.

It is shown that the model can predict the most important engineering aspects of a fluidized-bed dryer including pressure drop, particle holdup, temperature distribution in both phases as well as drying efficiency all over the fluidized-bed. Plug-flow conditions are predicted for the gas phase, while back-mixing is predicted for the particles.

The effect of particle mass-flow-rate on fluidized-bed dryer performance is evaluated. It is shown that the lower the particle mass flow-rate, the more intense the horizontal moisture gradients, while the higher the particle rate the more uniform the moisture distribution throughout the bed.