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.     

Determination of EMC isotherms and appropriate mathematical models for canola

Canola seed needs to be dried to minimize damage during subsequent unit operations. In order to optimize the drying and storage processes of seeds it is necessary to know the equilibrium moisture content at different air equilibrium relative humidities and temperatures. In the present work adsorption equilibrium moisture content isotherms were determined for a specific local canola variety at 25, 40 and 55 °C and seven air relative humidifies within the range of 11-90%. Experimental data were used to model the adsorption isotherm process using non-linear regression analysis. Thirteen available mathematical and semi empirical models were employed to find the best fit isotherm curve model. The Halsey model showed the best results at 25 and 40 °C and the values of coefficient of determination (R²), chi-square (χ²) and root of mean square error (RMSE) were 0.993, 0.122 and 0.295 at 25 °C and 0.994, 0.042 and 0.174 at 40 °C. Another best fit mode was the GAB model at 55 °C which resulted in the values of 0.997, 0.023 and 0.120 for R², χ² and RMSE respectively. The adsorption monolayer moisture content (m₀) was also evaluated using BET equation. The m₀ values at 25 °C, 40 °C and 55 °C were 0.017, 0.016 and 0.015 g H₂O/g solid and the corresponding constant values of the BET equation were found to be −4.733, −5.129 and −10.299 respectively.     

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.     

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.     

Generalized desorption equilibrium equation of lignite in a wide temperature and moisture content range

Brown coal is the most abundant and economically viable source of energy. To increase the efficiency of power generation from brown coal predrying of lignite is probably the first step to be taken. Both air drying, or more energy efficient superheated steam drying, may be considered. For the design of both processes an equilibrium relationship between water activity, moisture content and temperature in a form of working desorption isotherm is needed. This work presents experimentally obtained results of sorption isotherms measurements at seven temperatures and one sorption isobar at atmospheric pressure obtained for Be?chatów brown coal. These results were compared to the results obtained by other authors for Australian and USA coals and due to relatively close fit of all data points one generalized equation of desorption equilibrium was fitted covering a wide range of temperatures from 5 to 260 °C and moisture contents up to 1.5 kg/kg. Adsorption isotherms are not described by the same equation since strong sorptional hysteresis was observed.     

An Experimental Investigation of the Wall Deposition of Milk Powder in a Pilot-Scale Spray Dryer

A pilot-scale, co-current spray dryer has been used to investigate the effect of varying the swirl vane angle for the inlet air, inlet air temperature and liquid feed flowrate on the wall deposition flux of skim milk powder. The spray dryer was a cylinder-on-cone unit with a diameter of 0.8 m and a height of 2 m. It was fitted with adjustable swirl vanes surrounding a Delavan GA1 two-fluid atomizer. Swirl vane angles of 0, 25, and 30°, inlet air temperatures of 170, 200, and 230°C and feed flowrates of 1.4, 1.6 and 1.8 kg h^-1 were used. Inlet air swirl was found to significantly influence the wall deposition flux, with the highest swirl vane angle of 30° giving rise to the largest wall deposition flux. The difference between the particle and sticky-point temperatures of the skim milk powder was also found to be important in influencing the wall deposition flux. The wall deposition flux was the highest, at 16 g m^-2 h^-1, when the outlet particle temperature was furthest above the sticky-point temperature, and this occurred at the lowest value of the inlet air temperature (170°C) and highest product moisture content. No significant effect on the wall deposition flux was evident when using a nonstick food grade material (nylon), adhesive tape or stainless steel as the surface materials for the wall deposition tests. Therefore, it is likely that cohesion occurs at a similar rate to adhesion in the wall deposition of milk powder. Grounding the spray dryer also did not have a significant effect on the wall deposition flux. Relating the wall deposition flux to the sticky-point curve in this way suggests that the same trends (increased wall deposition fluxes above the sticky-point curve) may apply for other materials as well.     

Sorption Isotherms and Drying Characteristics of Tomato Peel Isolated from Tomato Pomace

Tomato peel was separated from pomace by sedimentation and dried in cabinet and fluidized-bed dryer at 50–70°C using 4–12 kg/m²tray load. The drying of tomato peel took place under the falling rate period and the drying behavior was well described by Page's model with coefficient of determination greater than 0.99 and standard error of 0.003–0.016. A fluidized-bed dryer was much more efficient than a cabinet dryer to dry tomato peel. The moisture adsorption isotherms of tomato peel were obtained by equilibrating above saturated salt solutions of known a _w (0.113–0.92) at 20–60°C. The data were analyzed using fifteen sorption models based on coefficient of determination, standard error, and residual plots. Modified Henderson was the best model for tomato peel with coefficient of determination >0.99, standard error <0.210, and a scattered residual plot. The net isostearic heat of sorption, estimated using the Clausius-Clapeyron equation, was 0.74–23.23 kJ/mol at 2.0–2.5% moisture content (dry basis).     

Numerical Study of the Drying Process of Different Sized Particles in an Industrial-Scale Spray Dryer

Development of high-performance spray dryers that are more energy efficient and are able to produce high-quality milk powders is very important for the future of the dairy powder industry. Understanding and optimization of the exiting dryers are also of great value. Computational fluid dynamics is a powerful tool to simulate and help understanding the characteristics of spray drying and to introduce potentially improved designs. The present study has concentrated on the multiphase flow in an industrial-scale spray dryer using the CFD package FLUENT. A Eulerian-Lagrangian approach is used in the simulations. A new drying model, REA model, for milk particles has been implemented for the first time in a CFD application. The numerical results match well with the plant data. It is argued that the “reflecting wall” boundary condition produced more physically correct results for normal dryer operation than the “escaping wall” boundary condition. The second one is an oversimplification. The influences of the particle size and particle size distribution, residence time, kinetic energy, and maximum temperature have been analyzed. The initial droplet size range was set to be from 100 to 500 µm with Rosin-Rammler distribution function. One significant result of this study is that rather dense particle clouds of medium-size particles (224–285 µm) are found near the side walls. They are transported upwards along the side wall (conical wall surface) and then are dispersed. It is found the particles with initial diameters of between 225 and 270 µm have the largest residence times.     

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).     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

Abstract

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

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.     

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。     

真空油炸胡萝卜脆片等温吸湿规律的研究

重点研究了脆片在水分活度为0．06-0．95。温度分别为10℃、25℃、40℃条件下的吸湿平衡含水率变化规律。根据目前在农产品吸湿规律研究中常用的六种模型对三个温度条件下胡萝卜脆片的吸湿试验点进行了模拟比较。以模型的确定系数、标准误差以及平均相对预测误差作为评价指标，得出了Peleg、Halsey以及GAB模型，可以较好地预测胡萝卜脆片在不同温度条件下的吸湿规律，并确定了它们的模型系数。     

A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study

A computational fluid dynamic study was carried out to investigate airflow pattern, temperature, and humidity profile at different levels in the drying chamber. Good agreement was obtained with published experimental data. The effects of operating pressure, heat loss from the chamber wall and inlet air conditions on the gas flow pattern, droplet trajectories, and overall dryer performance also were investigated. Results are presented and discussed in terms of the gas velocity, temperature, and humidity profiles within the chambers. The volumetric evaporation values, heat transfer intensity, and thermal energy consumption per unit evaporation rate were computed and compared for drying of a 42.5% solids solution in a spray chamber 2.215 m in diameter with a cylindrical top section 2.005 m high and a bottom cone 1.725 m high. Wall regions subject to formation of undesirable deposits are also identified.     

A Parametric Study of the Gas Flow Patterns and Drying Performance of Co-current Spray Dryer: Results of a Computational Fluid Dynamics Study

Abstract

A computational fluid dynamic study was carried out to investigate airflow pattern, temperature, and humidity profile at different levels in the drying chamber. Good agreement was obtained with published experimental data. The effects of operating pressure, heat loss from the chamber wall and inlet air conditions on the gas flow pattern, droplet trajectories, and overall dryer performance also were investigated. Results are presented and discussed in terms of the gas velocity, temperature, and humidity profiles within the chambers. The volumetric evaporation values, heat transfer intensity, and thermal energy consumption per unit evaporation rate were computed and compared for drying of a 42.5% solids solution in a spray chamber 2.215 m in diameter with a cylindrical top section 2.005 m high and a bottom cone 1.725 m high. Wall regions subject to formation of undesirable deposits are also identified.     

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.     

The Drying Kinetics and Equilibrium Moisture Content of MDF Fibers

An experimental device was constructed to study the drying kinetics of wood fibers under controlled conditions. The device consisted of a drying chamber in which a net basket filled with the fiber material was connected to a load cell. The drying medium was then forced through the basket at controlled levels of humidity and temperature.

Experiments were performed with spruce fibers and the drying medium at varying temperature (50–170°C) and relative humidity (1–86%). In general, the drying rate increased with increasing temperature and decreasing relative humidity. A constant drying rate period was observed in all cases. The critical moisture content was approximately 1.25. The characteristic drying curve has a slight downward concave shape. The equilibrium moisture contents obtained at ambient temperature agree well with data in the literature.