New narrow tube spray dryer for precise drying history control

Of all the operating conditions in a spray dryer, temperature of the drying medium holds the key parameter in affecting the degree of crystallinity in spray-dried particles. Previous experiments only focus on controlling the drying temperature at the inlet or outlet of drying chamber to delineate the drying history of particles, precluding any detailed studies on particle development throughout the drying duration. Hence, the objective of this work is to address the current limitation by introducing a modified narrow tube spray dryer which enables in situ control of drying history. Essentially, the drying chamber consists of 10 narrow copper tubes with an internal diameter of 1.7?cm. Each individual copper tube can be heated independently to create a unique controlled drying history. Scanning electron microscopy images demonstrate the significant impact of drying history on lactose morphology with possible crystallization by even slight variations in the drying history, which further accentuates the sensitivity of degree of crystallization to temperature. With this newly developed equipment, the detailed drying history conditions can be designed and manipulated to engineer the desired particle properties.     

A Taguchi approach production of spray-dried whey powder enriched with nanoencapsulated vitamin D3

Abstract

The objective of the present study was to investigate the effect of inlet air temperature of spray drying and different combinations of carrier agents (maltodextrin (MD), gum Arabic (GA), modified starch (MS), and whey protein concentrate (WPC)) on the physicochemical characteristics of spray-dried whey powder, enriched with vitamin D₃ to improve its usage as a functional ingredient. Firstly, vitamin D₃ was nanoencapsulated by nanoliposome prepared with egg yolk lecithin, sesame oil, and glycerol through thin-film dispersion method. The mean particle size of prepared nanoliposomes was 140?nm. Then, the prepared nanocarriers loaded with vitamin D₃ were added into the feed solution and dried through spray dryer. The effect of carrier agent types and inlet air temperature on the physicochemical (moisture content, solubility, porosity, color, and powder yield) and microstructure properties of obtained spray-dried powders were investigated. The optimal carrier agents and condition of spray drying were selected by Taguchi design. Our results showed that the inlet air temperature and carrier agent had significant effects on the characterization of powders. Powders produced by 2% WPC, 3% MS, and 25% MD at 170?°C inlet air temperature showed the highest powder yield (96.4%). Also, the morphology of powders was affected by carrier agent types; increase in MD concentration in feed solution causes to create smoother and spherical spray-dried powder particles.     

Artificial Neural Network Modeling of the Deposition Rate of Lactose Powder in Spray Dryers

A spray dryer is the ideal equipment for the production of food powders because it can easily impart well-defined end product characteristics such as moisture content, particle size, porosity, and bulk density. Wall deposition of particles in spray dryers is a key processing problem and an understanding of wall deposition can guide the selection of operating conditions to minimize this problem. The stickiness of powders causes the deposition of particles on the wall. Operating parameters such as inlet air temperature and feed flow rate affect the air temperature and humidity inside the dryer, which together with the addition of drying aids can affect the stickiness and moisture content of the product and hence its deposition on the wall. In this article, an artificial neural network (ANN) method was used to model the effects of inlet air temperature, feed flow rate, and maltodextrin ratio on wall deposition flux and moisture content of lactose-rich products. An ANN trained by back-propagation algorithms was developed to predict two performance indices based on the three input variables. The results showed good agreement between predicted results using the ANN and the measured data taken under the same conditions. The optimum condition found by the ANN for minimum moisture content and minimum wall deposition rate for lactose-rich feed was inlet air temperature of 140°C, feed rate of 23 mL/min, and maltodextrin ratio of 45%. The ANN technology has been shown to be an excellent investigative and predictive tool for spray drying of lactose-rich products.     

Comparing the crystallization of sucrose and lactose in spray dryers

The relative extent of crystallization for lactose and sucrose within spray dryers allows the WLF equation to be tested for this type of in-process crystallization, since this equation suggests that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature of that particular material. In this study, the amount of sucrose crystallization during drying was studied using a bench-top spray dryer (Buchi B290) over a practical range of inlet gas temperatures (95–220 °C). It has been found that very large changes in the degree of crystallinity for the final spray-dried product can be achieved for sucrose by using different inlet gas temperatures, compared with much smaller changes in the crystallinity of lactose for a similar range of inlet temperatures. This result supports the suggestion that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature, since sucrose has a much lower glass-transition temperature than lactose. The results have the potential to be implemented to achieve specified degrees of crystallinity in many powder materials produced from spray-drying processes.     

Partial Crystallization Behavior during Spray Drying: Simulations and Experiments

Simulations of crystallization behavior in a spray dryer have been performed using modifications to a model developed by previous workers and applied to a Buchi-290 laboratory-scale dryer. The potential crystallization behavior has been modeled using Williams-Landel-Ferry kinetics. Explorations using the model have suggested that the air inlet temperature is an important variable affecting crystallization in the dryer. The explorations suggested drying conditions that permitted reasonable drying while controlling the degree of crystallization. These conditions were examined and tested experimentally, also showing that the apparent degree of crystallinity was affected by the inlet air temperature over the range of inlet temperatures from 134°C (∼55% crystalline) to 210°C (∼76% crystalline). The simulation also predicted the trends in the experimental results from previous workers where their experimental results are considered in terms of the measurement techniques used in each case, suggesting that the simulation is a reasonable tool for developing operating conditions for drying equipment to give low or high degrees of crystallinity in the products.     

Crystallization and Drying of Milk Powder in a Multiple-Stage Fluidized Bed Dryer

The rationale of this study has been to use fluidized beds to crystallize amorphous spray-dried skim milk powders with multiple stages of processing at different temperatures and humidities with the aim of rapidly making mostly crystalline powders. This paper discusses the performance of a multiple-stage fluidized bed dryer, and a combination of crystallization of lactose in spray drying at high humidity (lactose nuclei formation) and subsequent fluidized bed drying. Two different combinations of spray dryer and multi-stage fluidized-bed dryer have been suggested to crystallize lactose in skim milk powder. The results show significant improvements in the crystallinity of the powders. Moisture sorption test and X-ray diffraction analysis were used to assess the crystallinity of the powders. The processed powders that were crystallized in a humid-loop spray drying combined with a two-stage fluidized-bed dryer/crystallizer showed 92% improvement in lower amorphicity by processing at different stages of 70°C, 50% RH and 80°C, 50% RH for 15 minutes. The conventionally spray-dried powders that were crystallized in a three-stage fluidized-bed dryer/crystallizer showed 87% improvement in lower amorphicity (less moisture sorption) by processing at different stages of 60°C, 50% RH; 70°C, 40% RH; and 80°C, 40% RH for 20 minutes. The multiple-stage fluidized bed system showed distinctive potential to crystallize lactose significantly in skim milk powder using an industrial-feasible process.     

A New Technique for Spray-Dried Encapsulation of Lycopene

A new technique for lycopene microencapsulation by spray drying using dehumidified air as the drying medium was developed and the optimum operating conditions for encapsulation efficiency were determined. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted of connecting the dryer inlet air intake to an absorption air dryer. The dextrose equivalent (DE) of maltodextrin, ratio of core to wall material, feed temperature, inlet air temperature, drying air flow rate, and compressed air flow rate were the factors investigated with respect to encapsulation efficiency. The resulting microcapsules were evaluated in terms of moisture content, bulk density, rehydration ability, lycopene isomerization, and storage stability. The optimum operating conditions were found to be as follows: ratio of core to wall material, 1:3.3; feed temperature, 52°C; inlet air temperature, 147°C. Under these conditions, the maximum encapsulation efficiency was about 93%. The use of dehumidified air was proven to be an effective way of increasing lycopene encapsulation efficiency.     

Crystallization of Amorphous Components in Spray-Dried Powders

Spray-dried powders are typically produced as amorphous particles. Long storage of the particles tends to crystallize the powders, a reaction affected by moisture, time, and temperature. This work has examined partial crystallization from amorphous spray-dried powders by moisture sorption. Powders of citrus fiber with hibiscus extract, maltodextrin, coffee, tea, skim milk, and sucrose were produced with a laboratory-scale spray dryer. The powders were exposed to ambient temperature and various relative humidities, with weight measurements recorded over time. It has been found that, in different materials, the amorphous to crystalline state change is observed at varying rates depending on the relative humidities and molecular weights. This observation may be associated with all amorphous spray-dried materials.     

Crystallization of Amorphous Components in Spray-Dried Powders

Spray-dried powders are typically produced as amorphous particles. Long storage of the particles tends to crystallize the powders, a reaction affected by moisture, time, and temperature. This work has examined partial crystallization from amorphous spray-dried powders by moisture sorption. Powders of citrus fiber with hibiscus extract, maltodextrin, coffee, tea, skim milk, and sucrose were produced with a laboratory-scale spray dryer. The powders were exposed to ambient temperature and various relative humidities, with weight measurements recorded over time. It has been found that, in different materials, the amorphous to crystalline state change is observed at varying rates depending on the relative humidities and molecular weights. This observation may be associated with all amorphous spray-dried materials.     

Physicochemical Characterization of Whole Egg Powder Microencapsulated by Spray Drying

Physical characterization and oxidative stability of egg powder microencapsulated by spray drying were studied in this work. The wall material (gelatin, lactose, pullulan, and their mixtures) and liquid egg mixtures were prepared by homogenization at 22,000 rpm for 60 s. The spray drying was carried out at pilot-scale spray dryer (Niro Mobile Minor, Søborg, Denmark). The spray-dried egg powders were analyzed for moisture content, water activity, peroxide value, total cholesterol oxidation products (TCOPs), particle properties, and bulk properties. Using gelatin as wall material resulted in a significant increase in the moisture content and water activity of egg powder during storage and it improved flowability. Egg powders containing pullulan as wall material showed a fibrous structure and had the lowest bulk density. Adding lactose as wall material increased the oxidative stability, which was indicated with lowest peroxide value and TCOPs level of egg powder.     

Effect of Maltodextrin Addition during Spray Drying of Tomato Pulp in Dehumidified Air: II. Powder Properties

This work investigates the effect of maltodextrin addition on the main powder properties during spray drying of tomato pulp in dehumidified air. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted in connecting the spray dryer inlet air intake to an absorption air dryer. 21 DE, 12 DE, and 6 DE maltodextrins were used as drying agents. Tomato pulp was spray dried at inlet air temperatures of 130, 140, and 150°C and (tomato pulp solids)/(maltodextrin solids) ratios of 4.00, 1.00, and 0.25. The tomato powders were analyzed for rheological properties, moisture content, bulk density, solubility, hygroscopicity, and degree of caking. It was found that maltodextrin addition improved powder hygroscopicity, caking, and solubility, whereas it deteriorated slightly its moisture content and density. In addition, analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second-order polynomial, reduced second-order polynomials, and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second-order polynomials.     

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.     

Narrow tube spray drying

Spray drying conventionally necessitates relatively large or elongated drying chambers. The present study examined the possibility in shrinking the spray drying chamber into narrow tube-like geometry. The key was in utilizing fine droplets which had low transport response time. A narrow copper/steel tube spray dryer (internal diameters between 12.7 and 48.0 mm) was constructed and was fitted with a two-fluid atomizer producing droplets in the size range smaller than 10 µm. Maltodextrin, lactose, and sucrose were spray-dried. The narrow tube approach allowed direct manipulation of the drying conditions via heating or cooling along the wall of the tube. This form of manipulation in the drying conditions, surprisingly, resulted in very distinctly crystalline spray-dried sucrose particles. The tube spray dryer was further modified with a long coiled-up tube, extending the particle residence time with minimal space requirements. Endoscopic analysis revealed that particle deposition within the tube resembled loosely attached particle and granules. The tube spray drying concept can potentially be used to provide precise control of the particle drying history along the length of the drying chamber, not limited to the control of the drying conditions at the inlet or outlet of a spray dryer.     

Influence of Dryer Type on Surface Characteristics of Milk Powders

Reconstituted milk powders (skim milk, whole milk, and milk protein concentrate powders) were spray dried using research-scale (laboratory- and pilot-scale) spray dryers to investigate the influence of type on the dryer on the surface composition (protein, fat, lactose) and morphological characteristics (size and surface structure) of the powder particles. Milk powders produced by these research-scale dryers were compared to commercially produced and freeze-dried powders. The powders produced by the laboratory- and pilot-scale dryers were significantly different from the commercially dried powders in both surface composition and morphology. The milk powders produced by laboratory- and pilot-scale dryers provided reproducible results with similar surface morphologies between dryer types, despite varying surface compositions. The surface composition of the freeze-dried powder was also significantly different from than that of the spray-dried powders. The freeze-dried skim milk powder (SMP) was similar in surface protein to its bulk protein composition, indicating relative homogeneity of particle composition of the freeze-dried powder.     

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

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.     

New Engineered Particles from Spray Dryers: Research Needs in Spray Drying

This article reviews developments in the simulations of spray dryer behavior, including the challenges in modeling the complex flow patterns inside the equipment, which are often highly transient and three-dimensional in nature. There appears to be considerable scope for using CFD simulations for investigating methods to reduce the rates of wall deposition and of thermal degradation for particles by modifying the air flow patterns in the chamber through small changes in the air inlet geometry. Challenges include building particle drying kinetics and reaction processes, as well as agglomeration behavior, into these simulations. The numerical simulations should be valuable supplements to pilot-scale testing, enabling more extensive and accurate optimization to be carried out than hitherto possible. New understanding of reaction processes and materials science, in combination with recent knowledge of the application of CFD to these problems, may enable new engineered powder products to be developed from the one-step spray-drying process.     

Simulation Study for Pneumatic Conveying Drying of Sawdust for Pellet Production

Pneumatic conveying drying (PCD) is a combination of heat and mass transfer and pneumatic handling technology. This technology has been extensively used in chemical, pharmaceutical, and food industries, as well as many others. The PCD technique is beneficial for agricultural products, because it can achieve high-quality drying with reduced heat damage in a very short time. In this study, one-dimensional and three-dimensional mathematical models for the drying of sawdust particles in a pneumatic dryer were developed and verified with experiments. The three-dimensional modeling was done with a computational fluid dynamics (CFD) package (ANSYS FLUENT, Ver. 13.0, Ansys, Inc.), in which the gas phase is modeled as a continuum using the Euler approach, and the droplet/particle phase is modeled by a discrete phase model with a Lagrange approach. One-dimensional analysis was performed in MATLAB (Ver. 7.0). The experiments were carried out to validate the model in a pneumatic dryer with a horizontal length of 1 m, vertical height of 1.1 m, and diameter of 0.14 m. Sawdust, a raw material used for producing pellets, was prepared from well-seasoned pinewood timber. The initial moisture content of the sawdust was 22% (wb). The hot air inlet temperature in the dryer was fixed at 100°C. The variations in air pressure, air velocity, air temperature, and particle moisture content were investigated along the length of the dryer. The final moisture contents of sawdust and air temperature were reduced by 2% (wb) and 5°C, respectively. The simulated values were in good agreement with the experimental values. The developed model was then employed for the design of a pilot-scale pneumatic dryer (length 7 m and diameter 0.14 m). The final moisture content of the sawdust particles was reduced to 14% (wb) when the dryer length was increased from 1 to 7 m. In addition, the modeling was performed using buffers in the pilot-scale dryers. The use of a buffer noticeably increased the drying efficiency.     

Spray Drying of Tomato Pulp: Effect of Feed Concentration

The effect of feed concentration on spray drying of tomato pulp preconcentrated to 78, 82, and 86% wet basis is investigated in two spray drying systems: a pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer, and the same connected with an absorption air dryer (Ultrapac 2000). Data for the residue on the chamber and cyclone walls were gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Tomato powders were analyzed for moisture, particle size, and bulk density. In both spray drying systems, with increases in tomato pulp concentration overall thermal efficiency, evaporative efficiency, material loss in the cyclone, powder moisture content, and bulk density decreased, whereas powder particle size increased. On the contrary, the effect of feed solids content on residue formation and product recovery was dependent on the drying medium. In the standard dryer, the higher the feed concentration, the higher was the residue accumulation, and the lower the product recovery, whereas in the modified system increases in pulp concentration resulted in lower residue formations and higher product yields.     

Effect of spray drying conditions and feed composition on the physical properties of black mulberry juice powder

In this study, the effects of some processing parameters on moisture content, water activity, drying yield, bulk density, solubility, glass transition temperature (T_g), and microstructure of spray dried black mulberry (Morus nigra) juice powders were investigated. A pilot-scale spray dryer was employed for the spray drying process and maltodextrin with different dextrose equivalent (6, 9, and 20DE) and gum Arabic were used as carrier agent. Independent variables were inlet air temperature (110, 130, and 150 °C), compressed air flow rate (400, 600, and 800 L/h), concentration of drying aids (8, 12, and 16%) and percent replacement of maltodextrin (6 and 9DE) by gum Arabic and maltodextrin 20DE (25, 50, and 75%). Between the different drying aids, maltodextrin 6DE shows the best effect on the properties of black mulberry juice powders. The process drying yield ranges from 45 to 82%. The highest drying yield (82%) and solubility (87%) refer to the blend of maltodextrin 6DE and gum Arabic. The lowest moisture content powders (1.5%) produced at the compressed air flow rate of 800 L/h. Inlet air temperature negatively influenced the bulk density due to the increase of powder's porosity. The lower the bulk density, the higher the solubility of powder is. With regard to morphology, powders produced with maltodextrin and gum Arabic presented the smallest size.     

Manufacturing Better Quality Food Powders from Spray Drying and Subsequent Treatments

In this article three major aspects of spray-dried food powders are discussed. We first address several practical problems involved during spray drying that may greatly influence product quality. The second issue identifies how an accurate drying kinetics model can form a useful tool to predict changes in the physical and biological quality aspects and the microstructure of the particle during processing. Dryer-wide simulations using the accurate drying kinetics model can significantly reduce the number of experimental trials for optimizing the process. To date, such success has been restricted to production runs for pilot-scale or small-scale industrial operations. The final issue addresses some of the challenges encountered when evaluating the functionality of the spray-dried powders during their reconstitution. The superior functionality of the spray-dried food product needs to be established more scientifically, which can help commercial operations to achieve high-quality reconstitution.