A Novel Way to Measure the Concentration of a Spray in a Spray Dryer

A new experimental technique to capture milk concentrate droplets from inside a 150-kg powder/h pilot spray dryer is presented. The technique uses liquid nitrogen to capture the droplets in the dryer and to preserve their moisture content. The droplets are kept frozen until the moisture content can be measured. This technique can be applied to sample the sprays from any semi-commercial-scale spray dryer or similar apparatus.     

An Experimental Investigation of Lime Juice Drying in a Pilot Plant Spray Dryer

One of the major problems in spray drying of fruit juices such as lime juice is stickiness and thermoplasticity of their compositions. Lime juice consists of invert sugars and citric acid, which have low glass transition temperatures. Due to this characteristic, the particles stick on the dryer wall upon their collision with it. As a result, drying of these materials is very difficult. In order to solve this problem, various percent of silicon dioxide and maltodextrin (DE5), based on total soluble solid content of lime juice, have been used to reach a suitable drying condition. A cool chamber wall spray dryer was used in this investigation in order to decrease the probability of particles stickiness on the wall. Our investigation revealed that an addition of 10% silicon dioxide and 20% maltodextrin (DE5) to lime juice is the optimum amount for a complete and successful drying of lime juice. Sampling of particles from different longitudinal distances in the dryer tower is carried out to find the particle moisture contents as they fly downward in the dryer. The results show a very fast decrease in entrance moisture contents. Based on our experimental data, the variation of moisture contents are presented as a function of radial distance from central line and longitudinal distance from the entrance region.     

An Experimental Investigation of Lime Juice Drying in a Pilot Plant Spray Dryer

One of the major problems in spray drying of fruit juices such as lime juice is stickiness and thermoplasticity of their compositions. Lime juice consists of invert sugars and citric acid, which have low glass transition temperatures. Due to this characteristic, the particles stick on the dryer wall upon their collision with it. As a result, drying of these materials is very difficult. In order to solve this problem, various percent of silicon dioxide and maltodextrin (DE5), based on total soluble solid content of lime juice, have been used to reach a suitable drying condition. A cool chamber wall spray dryer was used in this investigation in order to decrease the probability of particles stickiness on the wall. Our investigation revealed that an addition of 10% silicon dioxide and 20% maltodextrin (DE5) to lime juice is the optimum amount for a complete and successful drying of lime juice. Sampling of particles from different longitudinal distances in the dryer tower is carried out to find the particle moisture contents as they fly downward in the dryer. The results show a very fast decrease in entrance moisture contents. Based on our experimental data, the variation of moisture contents are presented as a function of radial distance from central line and longitudinal distance from the entrance region.     

先进的闭路循环喷雾干燥机

介绍了弘腾公司开发的闭路循环啧雾干燥机系统的组成、技术创新要点、工艺流程、适用场合、企业标准及应用实例。     

CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.     

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.     

Fluxes and Patterns of Wall Deposits for Skim Milk in a Pilot-Scale Spray Dryer

The pattern of wall deposits in a pilot-scale spray dryer has been studied, using skim milk, by changing the flow rate to the nozzle and measuring the resultant deposition fluxes at different positions inside the dryer. The solids concentration was maintained at 30%. The deposition was measured at three locations of the conical section and in the cylindrical section of the spray dryer. Particle deposition can be either due to the inertia of the particles or turbulent diffusion, and it is not immediately obvious which of these mechanisms is dominant. Inertial deposition appeared to be present mainly at the bottom location of the conical section and was the largest amount in quantitative terms, being at least an order of magnitude larger compared with diffusion deposition, which seemed to be dominant on the side (cylindrical) walls of the spray dryer. In addition to the above observations, the deposition patterns in the conical section have been quantified. The relative deposition flux, in m^?2, which is the ratio of the deposition flux, in g m^?2 h^?1, to the solids flow rate into the dryer, in g h^?1, was between 0.04 and 0.09 m^?2 at a solids concentration of 8.8% and between 0.15 and 0.4 m^?2 at a solids concentration of 30%. The fused appearance of the microstructure in the wall deposits of skim milk powder, as seen in the Micro-CT study, suggests that re-entrainment of the wall deposits is unlikely.     

Fluxes and Patterns of Wall Deposits for Skim Milk in a Pilot-Scale Spray Dryer

The pattern of wall deposits in a pilot-scale spray dryer has been studied, using skim milk, by changing the flow rate to the nozzle and measuring the resultant deposition fluxes at different positions inside the dryer. The solids concentration was maintained at 30%. The deposition was measured at three locations of the conical section and in the cylindrical section of the spray dryer. Particle deposition can be either due to the inertia of the particles or turbulent diffusion, and it is not immediately obvious which of these mechanisms is dominant. Inertial deposition appeared to be present mainly at the bottom location of the conical section and was the largest amount in quantitative terms, being at least an order of magnitude larger compared with diffusion deposition, which seemed to be dominant on the side (cylindrical) walls of the spray dryer. In addition to the above observations, the deposition patterns in the conical section have been quantified. The relative deposition flux, in m^-2, which is the ratio of the deposition flux, in g m^-2 h^-1, to the solids flow rate into the dryer, in g h^-1, was between 0.04 and 0.09 m^-2 at a solids concentration of 8.8% and between 0.15 and 0.4 m^-2 at a solids concentration of 30%. The fused appearance of the microstructure in the wall deposits of skim milk powder, as seen in the Micro-CT study, suggests that re-entrainment of the wall deposits is unlikely.     

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.     

Design and Performance of a Laboratory Spray Dryer to Realize Evaporation-Induced Self-Assembly of Nanoparticles

This work discusses the design, development, and performance of an indigenous laboratory spray dryer with a relatively slow drying rate. The drying time of droplets of colloidal silica (5 wt%) and sodium chloride solution (20 wt%) in this spray dryer was nearly 10 s. The present system was composed of a four-jet compressed air nebulizer that generates a droplet size of 2–5 µm with a nebulization rate of nearly 60 mL/h. The generated powder can be collected using a cyclone or a wire mesh collector. Design and characterization of this system as well as characterization of the micrometric self-assembled powder grains obtained by this spray dryer are discussed.     

Physicochemical Characteristics of Date Powder Produced in a Pilot-Scale Spray Dryer

Date fruit is a good source of bioactive compounds and natural sugar. It has the potential to be utilized as a substitute for added sugar. Although several forms of dates—such as fresh dates, date paste, and date syrup—are available in the market and used for different applications, free-flow date powder would be highly beneficial in improving shelf-life, ease of handling, and blendability with various foods prepared domestically and in industry. The objective of this study was to produce date powder in a pilot-scale spray dryer and determine its physicochemical qualities. Date powder was produced at eight processing conditions (2 carrier agents (maltodextrin (MD) and gum arabic (GA) × 2 inlet air temperature (150°C and 170°C) × 2 feedstock flow rates (25 ml/min and 40 ml/min)). To the carrier agent was added at 0.4 kg per 1.0 kg of date fruits (dry weight basis), and the feedstock to the spray dryer was prepared at 20% concentration. Date powder was obtained in all eight treatments. Color (L*a*b* values), moisture content, bulk density, wettability, solubility index, hygroscopicity, microstructure analysis (using scanning electron microscope (SEM)), and total phenolic compounds were determined for the spray-dried date powder. The physicochemical characteristics of date powder varied significantly with respect to the processing conditions. Although physical properties of date powder were significantly affected by the carrier agent, there was no difference in total phenolic compounds between date powders produced with MD and GA. An SEM study revealed that date powder produced with MD had smooth, regular-shaped spherical particles but with severe agglomeration. Date powder with GA had relatively smaller particles of irregular sphere with dented surfaces.     

A Study of the Limitations to Spray Dryer Outlet Performance

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h^-1, 1.6 kg h^-1, 1.8 kg h^-1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s^-1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.     

A Study of the Limitations to Spray Dryer Outlet Performance

Abstract

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h^?1, 1.6 kg h^?1, 1.8 kg h^?1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s^?1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.     

喷雾干燥机节能探讨

本文简要介绍了陶瓷面砖原料制备设备喷雾干燥机的工作原理和使用特点,重点探讨了喷雾干燥机的节能方法。它将对陶瓷厂的节能具有一定的参考价值。     

The Effect of Rotary Disk Atomizer RPM on Particle Size Distribution in a Semi-Industrial Spray Dryer

Spray drying is the most commonly used method in industry to produce powders on a large scale. One of the major problems in spray drying is control of the product particle size distribution since it is very important for most industries; e.g., catalyst, chemicals, foods, pharmaceuticals, ceramics, etc. The objective of this work is to study the effect of the atomizer rotational speed on the product size distribution. In order to obtain the typical particle size distribution of the required product, a specially designed atomizer disk is used in the study. The particle size distributions under atomizer rotating speeds in the 9,000–10,000 rpm range were measured and discussed.     

Combined Crystallization and Drying in a Pilot-Scale Spray Dryer

Combined crystallization and drying of lactose solutions was performed in a pilot-scale spray dryer over a wide range of operating conditions. The effect of different parameters, including temperature, moisture content, atomizing air flow rate, liquid feed rate, main drying air flow rate, and particle size, on the degree of crystallinity of the spray-dried powders was analyzed. Water-induced crystallization (WIC) and modulated differential scanning calorimetry (MDSC) were used to assess the effect of these parameters on the degree of crystallinity of the spray-dried powders. The particles were characterized in terms of the final moisture content using WIC and distinctive differences in the peak heights, which are indicative of the particle crystallinity, were found for spray-dried particles using different drying conditions, supporting the results from MDSC. MDSC showed that decreasing the inlet air temperature by 40°C increased the degree of crystallinity in the particles threefold from 22 to 72%. A decrease in the inlet air temperature may decrease the particle temperature, resulting in wetter particles, and a lower temperature meant a longer particle drying time and allowed the particles to rearrange themselves into a more crystalline form. Up to 72% crystallinity is achievable in a pilot-scale spray dryer by suitable adjustment of the operating conditions. The results suggest differences in the rate of crystallization and particle size between small and pilot-scale spray dryers.     

A Novel Laboratory-Scale Spray Dryer to Produce Nanoparticles

This paper reviews the advances in nanoparticle spray drying performed in a laboratory environment and with the Nano Spray Dryer B-90, which was introduced by BUCHI Labortechnik AG in 2009. Special regard will be paid to relevant published works. The technological novelty of the patented Nano Spray Dryer B-90 lies in the gentle laminar drying flow, the vibrating mesh spray technology, and the highly efficient electrostatic particle collector.

Recent studies prove the successful use of this spray dryer for a variety of drug delivery applications, such as poorly soluble drugs (e.g., griseofulvin, furosemide), enzymes (e.g., galactosidase), proteins (bovine serum albumin, whey protein), amino acids (e.g., leucine), polysaccharides (e.g., trehalose, lactose), salts, encapsulation of nano-emulsions in polymeric wall materials, as well as materials science applications (e.g., battery-grade lithium carbonate).

The Nano Spray Dryer B-90 makes it possible to produce spray-dried particles in the submicron scale and to create tiny particles of down to only 350–500 nm. In contrast to traditional laboratory-scale spray dryers, it can achieve uniquely high yields of up to 94% for powder amounts down to the milligram scale (e.g., 3.0–500 mg).     

Three-Dimensional Numerical Investigation of a Mono-Disperse Droplet Spray Dryer: Validation Aspects and Multi-Physics Exploration

Many studies have been carried out on using computational fluid dynamics (CFD) to explore spray-drying phenomena. However, due to the complexity of the drying process in a conventional spray dryer, including the wide droplet size distribution, complicated particle trajectory, and difficulty in taking online measurements, validation of the computational codes or the models remains a challenging task. In this study, experimental conditions employed in a more defined spray-drying condition, published recently on the spray drying of mono-disperse skim milk droplets in a vertical cylindrical chamber, are simulated using ANSYS FLUENT. We have examined the effects of droplet-dispersion patterns on the drying results and found ways to incorporate more practical shrinkage models into the code to make simulations more realistic. Through a comparison with the relevant experimental results on 10～50 wt% skim milk published recently by the same group, we have identified a few areas that urgently need more detailed research. Using the revised sets of codes established here, we simulated skim milk droplets (with a uniform size between 180 μm to 220 μm) spray dried by 90°C to 180°C hot-air streams. The quantitative drying history data predicted by our new model would help ensure better understanding of the system.     

Dairy Milk Particles Made with a Mono-Disperse Droplet Spray Dryer (MDDSD) Investigated for the Effect of Fat

Mono-disperse droplet generation and subsequent drying in a spray-drying chamber, i.e., mono-disperse droplet spray dryer (MDDSD), provides a better-defined “flight experience” for liquid droplets. The related particle formation can be investigated more easily than that in the usual poly-disperse droplet spray dryer (PDDSD). Previously, skim milk, which is of high protein and high lactose content and is one of the two main dairy fluids that are processed into powder form for consumer markets, was subjected to this kind of investigation in Australia. Here, whole milk, which is the other main dairy fluid, has been spray-dried in a MDDSD set-up at Xiamen University (China). Because the initial droplet size is uniform, measurable, and the particle morphology after drying is consistent, it was possible to investigate the initial solids content effect upon shrinkage and inlet air temperature effect upon shrinkage. In contrast to what had been found for skim milk particles, the formation of the fat-containing (whole milk) particles does not follow the perfect shrinkage model as the skim milk does. This work has improved our quantitative understanding of the whole milk drying process. A fundamental analysis invoked with a modified one-dimensional modeling of spray drying has been given that has shown some further insight about the process.