Showing papers in "Drying Technology in 2009"

Low-Rank Coal Drying Technologies—Current Status and New Developments

Abstract: Despite their vast reserves, low-rank coals are considered undesirable because their high moisture content entails high transportation costs, potential safety hazards in transportation and storage, and the low thermal efficiency obtained in combustion of such coals. Their high moisture content, greater tendency to combust spontaneously, high degree of weathering, and the dusting characteristics restrict widespread use of such coals. The price of coal sold to utilities depends upon the heating value of the coal. Thus, removal of moisture from low-rank coals (LRC) is an important operation. Furthermore, LRC can be used cost effectively for pyrolysis, gasification, and liquefaction processes. This article provides an overview the diverse processes—both those that utilize conventional drying technologies and those that is not yet commercialized and hence in need of R&D. Relative merits and limitations of the various technologies and the current state of their development are presented. Drying characteristics ...

Influence of the Applied Acoustic Energy on the Drying of Carrots and Lemon Peel

Abstract: The application of power ultrasound could constitute a way of improving traditional convective drying systems. The different effects produced by the application of power ultrasound may influence the drying rate without provoking any significant increase in product temperature. Due to the fact that the effect of power ultrasound is product dependent, the aim of this work was to address the influence of the applied acoustic energy on the convective drying of carrot and lemon peel. Convective drying kinetics of carrot cubes (side 8.5 mm) and lemon peel slabs (thickness 7 mm) were carried out at 40°C and 1 m/s by applying different levels of acoustic power density: 0, 4, 8, 12, 16, 21, 25, 29, 33, and 37 (kW/m3). The application of power ultrasound during drying was carried out using an airborne ultrasonic transducer (21.7 kHz). Drying kinetics were described considering a diffusion model. In both products, the application of power ultrasound improved the effective moisture diffusivity (De ). The improvement ...

Comparison of Artificial Neural Network (ANN) and Response Surface Methodology (RSM) in the Prediction of Quality Parameters of Spray-Dried Pomegranate Juice

Abstract: Response surface methodology (RSM) is a frequently used method for empirical modeling and prediction in the processing of biological media. The artificial neural network (ANN) has recently grown to be one of the most efficient methods for empirical modeling and prediction, especially for nonlinear systems. This article presents comparative studies between an ANN and RSM in the modeling and prediction of quality parameters of spray-dried pomegranate juice. In this study, the effects of the carrier type, carrier concentration, and concentration of crystalline cellulose in a pomegranate juice spray-drying process were investigated on five quality parameters—drying yield, solubility, color change, total anthocyanin content, and antioxidant activity—using RSM and ANN methods. A central composite rotatable experimental design (CCRD) and a feed-forward multilayered perceptron (MLP) ANN trained using back-propagation algorithms for three independent variables were developed to predict the five outputs. The final ...

Effect of drying method on the microstructure and physical properties of dried apples.

Abstract: The purpose of this study was to determine the influence of the internal structure of dried apples on such physical properties as density, porosity, or shrinkage. Apple slices were dried using convection, microwave-convection, and infrared-convection methods. The apple slices dried by means of the microwave and infrared methods showed between 11 to 12% lower shrinkage, 30–34% lower volume, 18–23% lower density, and porosity of 25–28% higher than the slices dried exclusively by the convection method. Considerable differences in the density and porosity of the apple slices dried using the above methods were confirmed by analyzing the tissue images made with the help of scanning electron microscopy. Convective drying caused significant changes in the actual size and distribution of the apple cells. The cells dried using both the microwave and infrared methods had a larger cross-sectional area compared with the convective-dried material.

Spray Drying of a Vaginal Probiotic Strain of Lactobacillus acidophilus

Abstract: This work presents a study of the spray-drying process of a vaginal strain of Lactobacillus acidophilus in order to enhance the cells viability and probiotics properties during storage. The results show that the powder obtained presents dried strain viability in the range of 10 8 –10 9 (CFU/g) with product moisture content below 10%. Additionally, the dehydrated strain maintains its viability during two months when stored at 4°C, although its viability drops 1 order of magnitude when stored at 25°C for 1 month. It was verified that the range of operating conditions studied during drying (e.g., pressure, feed concentration, and additive) did not affect bacteria viability, except for increased air-drying temperature. The strain did not suffer important changes in its identity, morphology, or probiotic properties due to the spray-drying process. Using the mass-energy balance in the dryer, the volumetric overall heat transfer coefficient was determined as 2 × 10−4 (kg water evaporated/m 3 K s) for the experi...

Optimization of Drying of Olive Leaves in a Pilot-Scale Heat Pump Dryer

Abstract: Recently, the interest in olive leaf has increased due to its high phenolic content. It has a high potential for industrial exploitation in food industry and the main process in olive leaf treatment is drying. Drying affects the product quality and is an energy-intensive process, so the use of heat pumps in drying processes that have low operating cost has attracted the attention of the investigators. In this study, response surface methodology was used to optimize operating conditions of drying of olive leaves in a pilot-scale heat pump conveyor dryer. The independent variables were air temperature, air velocity, and process time, and the responses were total phenolic content and antioxidant activity loss, final moisture content, and exergetic efficiency. Optimum operating conditions were found to be temperature of 53.43°C, air velocity of 0.64 m/s, process time of 288.32 min. At this optimum point, total phenolic content loss, total antioxidant activity loss, final moisture content, and exergetic effici...

Studies on Decreasing Energy Consumption for a Freeze-Drying Process of Apple Slices

Abstract: The shape, color, flavor, and rehydration capacity of freeze-dried (FD) products are all better than other dried products. However, the energy consumption during FD is very high, which limits the application of this drying method for common materials. In this article, microwave vacuum drying (MWVD) was applied before or after FD to decrease the energy consumption during FD. Moreover, energy consumption was divided into two parts: valid and invalid energy consumption. Apple slices were used as an example to calculate the saving percentage of invalid energy consumption by comparing combination drying with FD. Apple slices freeze dried for 8.28 h first and then dried by MWVD have the best appearance, with a savings of 39.20% in invalid energy consumption. But apple slices freeze dried for 6 h first followed by MWVD have the highest savings of invalid energy consumption, 54.02%, while still maintaining an acceptable appearance.

Drying-Induced Cracks in Thin Film Fabricated from Colloidal Dispersions

Abstract: As a colloidal dispersion is coated and dried on a nonporous rigid substrate, the enormous stresses developing during the drying process can fracture the thin film. The drying-induced cracks can produce serous technological consequences and even destroy the efficacy of coatings, which is not desirable in most industrial cases. Therefore, as the first step of controlling cracks in thin film, understanding of crack properties and cracking mechanisms leading to fracture is of vital significance. Although numerous experiments and models have been proposed for cracking during drying of colloidal dispersions, there is little consensus on even the most basic mechanisms, and the effect of heat transfer on cracks as well as optimization of drying process are rarely taken into account. Additional, the broad employments of nanosuspensions bring both opportunities and challenges for this area. This review will give a comprehensive physical picture of thin film fabrication by drying of colloidal dispersions and cracking phenomenon, present current investigations for drying-induced cracks, and point out some prospects for cracking researches especially for industrial R&D, as well as propose combination of thin film preparation with drying technique for exploring crack-free thin film.

Modeling Drying Kinetics of Pistachio Nuts with Multilayer Feed-Forward Neural Network

Abstract: Drying kinetics of pistachio nuts (Akbari v.) was simulated using a multilayer feed-forward neural network (MFNN). Experiments were performed at five drying air temperatures (ranging from 40 to 80°C) and four input air flow velocities (ranging from 0.5 to 2 m/s) with three replicates in a thin-layer dryer. Initial moisture content in all experiments was held at about 0.3 kg/kg d.b. To find the optimum model, various multilayer perceptron (MLP) topologies, having one and/or two hidden layers of neurons, were investigated and their prediction performances were evaluated. The (3-8-5-1)-MLP, namely, a network having eight neurons in the first hidden layer and five neurons in the second hidden layer resulted in the best-suited model estimating the moisture content of the pistachio nuts at all drying runs. For this topology, R2 and MSE values were 0.9989 and 4.20E-06, respectively. A comparative study among MFNN and empirical models was also carried out. Among the empirical models, the logarithmic model, with M...

Microwave Freeze–Drying Characteristics and Sensory Quality of Instant Vegetable Soup

Abstract: Instant vegetable soup mix was dehydrated in a microwave freeze dryer to study the drying characteristics and sensory properties of the dried product. The mix was dried at different microwave power levels, material thicknesses, and material loads. As expected, microwave power significantly influenced the total drying time and sensory quality of the final product. The total drying time increased with the increase of material thickness and load. A material layer that is too thin causes the product quality to deteriorate.

An Investigation of the Effects of Drying Methods and Conditions on Drying Characteristics and Quality Attributes of Agricultural Products during Hot Air and Hot Air/Microwave-Assisted Dehydration

Abstract: Hot air and microwave-assisted hot air drying of apples (Golden delicious), strawberries (Fragaria vesca cv. Elsanta), tomatoes (Lycopersicon esculentom var. Roma), and mushrooms (A. bisporus) were performed in a commercial microwave oven that had been modified to incorporate a hot air dryer. The same microwave power intensity was used in all experiments. We investigated the effect of the above-stated methods on the structural, optical, mechanical, and rehydration characteristics of dried samples. Scanning electron microscopy (SEM) was used to evaluate the structural damage associated with two drying methods. The drying rate was significantly affected by microwave energy; therefore, drying time was reduced by 80, 70, 74, and 66%, respectively for apples, strawberries, tomatoes, and mushrooms, respectively. Specific volume, particle density, and porosity variation were estimated using models proposed in the literature. Some structural damage occurred, as observed in SEM micrographs. Optical, mechanical, an...

Influence of Spray Drying Conditions on Physicochemical Properties of Chicken Meat Powder

Abstract: The influence of spray-drying conditions on the physicochemical properties of chicken meat hydrolysate powder was studied in this work. Enzymatic reaction, using Alcalase® (Novozymes, Bagsvaerd, Denmark), was carried out at 52.5°C, 4.2 g enzyme/100 g protein, and pH of 8.0 to obtain protein hydrolysate. The spray drying was carried out on a laboratory spray dryer and maltodextrin 10DE was used as carrier agent. A central composite rotatable design was used to evaluate the effect of the independent variables inlet air temperature, feed flow, and maltodextrin concentration on the responses powder moisture content, bulk density, mean particle diameter, and hygroscopicity. All variables had a significant effect on the properties and morphology of protein hydrolysate powder.

An Experimental Study on Drying of Green Apples

Abstract: Drying behavior of green apples in a laboratory dryer was examined. Prior to drying, the apples were cut in 8 mm thick slices, which were then treated with citric acid solution and blanched hot wat...

Drying Characteristics and Kinetics of Vacuum Microwave–Dried Potato Slices

Abstract: Vacuum microwave dehydration characteristics and drying kinetics of potato slices were evaluated using a laboratory-scale dryer. The test materials were placed on a rotating tray to allow uniform exposure to the microwave field. The effect of drying conditions on the drying characteristics was investigated. As expected, higher drying rates were obtained with higher microwave power and lower vacuum levels. The effect of vacuum pressure on drying rate was not as significant as that of microwave power. The Henderson & Pabis model provided better simulation of the drying curves for potato slices. Empirical models are presented for the drying rate constant as a function of the microwave power and vacuum pressure for potato slices under the range of operating conditions tested.

Rehydration Behavior of Vacuum-Microwave-Dried Potato Cubes

Abstract: Rehydration properties and microstructure of vacuum-microwave and hot air–dried potato cubes were examined Two kinds of models were considered to describe the hydration kinetics: a diffusion model for a cube and two empirical equations, Peleg and Weibull The values of the effective moisture diffusivity of soaked potatoes were in the range 117 × 10−9 to 473 × 10−9 m2/s The vacuum-microwave drying technique resulted in puffed potato particles characterized by porous microstructure with a network of open cavities and the hot air drying gave the potato particles containing compacted cells with the low amount of open micro-caves Higher rehydration ability was observed for the samples dried with microwaves under low pressure Vacuum-microwave drying at 6 kPa seems to be the optimal drying condition for potato cubes, ensuring porous microstructure of dried material and low shrinkage of dried potato particles as well as their high recovery properties and rehydration

Microwave, Vacuum, and Air Drying Characteristics of Collard Leaves

Abstract: Collard leaves (Brassica oleracea L. var. acephala) with an initial moisture content of 6.65 on percentage dry basis (%db) were dried by three different drying methods: microwave, air, and vacuum. Samples of fresh leaves, 25 g each, were dried until their moisture was down to 0.1 on a dry basis. The following drying levels were used in each of the drying processes: 350, 500, 650, 750, 850, and 1000 W for microwave drying; 50, 75, 100, 125, 150, and 175°C for air drying; and 0.4, 50, and 100 mmHg at 50 and 75°C for vacuum drying, respectively. Drying times ranged between 2.5 to 7.5 min, 8 to 210 min, and 35 to 195 min for microwave, air, and vacuum drying, respectively. The data obtained compared well with a thin-layer drying model. Microwave drying at 750 W provided optimal results with respect to drying time, color, and ascorbic acid content (vitamin C).

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

Abstract: 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 part...

Thin-Layer Drying of Green Peas and Selection of a Suitable Thin-Layer Drying Model

Abstract: The thin-layer drying of three varieties of green peas was carried out in hot air-drying chamber using an automatic weighing system at five temperatures (55–75°C) and air velocity of 100 m/min. The green peas were blanched and sulphited before drying. The variety Pb-87 dried at 60°C was judged to be best for quality on the basis of sensory evaluation and rehydration ratio. The Thomson model was found to represent thin-layer drying kinetics within 99.9% accuracy. The effective diffusivity was determined to be 3.95 × 10−10 to 6.23 × 10−10 m2/s in the temperature range of 55 to 75°C. The activation energy for diffusion was calculated to be 22.48 kJ/mol. The variation in shrinkage exhibited a linear relationship with moisture content of the product during drying. The Dincer number at drying air temperature 60°C and drying air velocity 100 m/min was determined to be 2,838,087. The difference between temperatures of drying air and that of green pea kernels was found to decrease with drying time for all the dryi...

Drying of Lemon Myrtle (Backhousia citriodora) Leaves: Retention of Volatiles and Color

Abstract: Lemon myrtle plant (Backhousia citriodora) leaves were dried at three different drying temperature conditions (30, 40, and 50°C) in a fluidized bed dryer. The retention of the principal volatile compound, citral, was analyzed in dried products obtained at these three drying conditions. The changes in the color parameters L∗, a∗, b∗ of leaves were also analyzed. More than 90% of citral was retained at 50°C drying temperature, whereas the retention at 30 and 40°C was 81 and 85%, respectively, suggesting that higher temperature is beneficial to achieve higher retention of volatiles. However, in terms of the color, all the color parameters were changed maximum at 50°C drying temperature unfavorably, suggesting that the higher temperature drying causes more degradation of the pigment. Blanching of the leaves in hot water at 80°C for 1 min prior to drying did not result in any improvement in volatile retention or color.

Modeling of fertilizer drying in roto-aerated and conventional rotary dryers.

Abstract: Conventional rotary dryers are equipped with flights placed parallel along the length of the shell to promote a rain of solids across the dryer section In the roto-aerated dryer the hot air flows through the particles that run on the bottom of the drum through a series of mini-pipes and there is no cascading This study analyzed heat and mass transfer modeling between the air and the fertilizer particles in conventional rotary and roto-aerated dryers, as well as the simulation results with the experimental data A good agreement between the simulated and experimental results was obtained for the two rotary dryer configurations analyzed

Color Change Kinetics of Microwave-Dried Basil

Abstract: The aim of this study was to investigate the effect of microwave output power and sample amount on color change kinetics of basil (Ocimum basilicum L.) during microwave drying. The color parameters for the color change of the materials were quantified by Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. These values were also used for calculation of the total color change (ΔE), chroma, hue angle, and browning index. The microwave-drying process changed color parameters of L, a, and b, causing a color shift toward the darker region. The mathematical modeling study of color change kinetics showed that a and b fitted to a first-order kinetic model, while L and total color change (ΔE) followed a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, whereas hue angle followed a zero-order kinetic model. For calculation of the activation energy for colour change kinetic parameters, the exponential expression based on Arrhe...

The Development of Ginger Drying Using Tray Drying, Heat Pump–Dehumidified Drying, and Mixed-Mode Solar Drying

Abstract: Mature ginger was pretreated by soaking in citric acid prior to drying in a single layer in a tray and heat pump dehumidified dryer at three temperatures of 40, 50, and 60°C and in a mixed-mode solar dryer at 62.82°C and a radiation intensity of 678 W/m2. The drying data were applied to the modified Page model. Diffusivities were also determined using the drying data. Quality evaluation by color values, reabsorption, and 6-gingerol content showed best quality for ginger with no predrying treatment and dried at 40°C in a heat pump–dehumidified dryer. At drying temperature of 60 to 62.82°C, no pretreated dried ginger from mixed-mode solar dryer provided the shortest drying time and retained 6-gingerol as high as heat pump–dehumidified dryer.

Exergy Analysis of Drying Process: An Experimental Study in Solar Greenhouse

Abstract: This article examines the exergy variation during drying in solar greenhouses. Exergy efficiencies were derived as functions of drying time and temperature of the drying air. An illustrative example is considered to verify Dincer and Sahin's model and to show the applicability of the model to actual drying processes at different drying air temperatures. This work is intended not only to demonstrate the usefulness of exergy analysis in thermodynamic assessments of drying processes but to provide insights into their performances and efficiencies. In this study, the drying performance of the passively heated solar greenhouse has been investigated. Experimental results under the meteorological conditions of Izmir, Turkey (latitude 38.24 N, longitude 27.50 E), are presented.

Drying of Betel Leaves (Piper betle L.): Quality and Drying Kinetics

Abstract: This work studied the effects of drying temperature on the quality and drying kinetics of betel leaves (Piper betle L.). As the drying process applies heat on the product, this might lead to the degradation and decomposition of valuable phytochemicals within the herbs. In this study, the effect of drying temperature on the quality of dried leaves was studied by analyzing the change of major phytochemicals found in the leaves, which are hydroxychavicol and eugenol. The results indicate that the content of major compounds increased with temperature from 40 to 70°C but underwent decomposition when the leaves dried at 80°C. Besides that, the drying kinetics for different drying temperatures also studied. The kinetics results show that the increase of drying temperature shortened the total drying time. Five thin-layer models were selected in describing the drying process of betel leaves. The logarithmic model was found to be the most suitable one.

Drying of Lignite in a Pressurized Steam Fluidized Bed—Theory and Experiments

Abstract: The present article describes the basic principles of drying of lignite in a pressurized steam fluidized bed and a test facility of the Chair of Power Plant Technology as well as results achieved during experiments. At first the water binding of lignite, the heat transfer, and the influence of pressure and particle size are explained. A description of the two facilities available at the Chair of Power Plant Technology—cold and hot models—and a presentation of the experiments done and results obtained follows. The construction of a 10 tons/h pilot plant is briefly reported.

Modeling the Rehydration Process of Dried Tomato

Abstract: Rehydration of air-dried tomatoes was investigated at four temperatures (25, 40, 60, and 80°C). To describe the rehydration kinetics, two empirical models, Peleg and Weibull, were considered. The empirical models described the rehydration process properly. The equilibrium moisture content decreased as rehydration temperature increased, whereas the kinetic constants of the Peleg and Weibull models, k 1 and β, respectively, increased with increasing temperature. This influence was described in terms of an Arrhenius relationship. The Peleg constant k 2 was also found to be a function of temperature, increasing as temperature increased, whereas the Weibull shape parameter α decreased with increasing temperature. In addition, a mathematical model based on one-dimensional, steady-state, fully developed capillary flow of water with negligible inertia effects within the air-dried tomato was developed. This model was found to adequately describe the rehydration behavior of dried tomatoes.

Freeze Drying of Pharmaceutical Excipients Close to Collapse Temperature: Influence of the Process Conditions on Process Time and Product Quality

Abstract: The aim of this article is to investigate the characteristics of a vial freeze-dried product as a function of the temperature at which the primary drying is carried out. The effect of the drying temperature and composition on the product appearance and final characteristics (apparent density and rehydratability) of pure substances (mannitol, sucrose, and dextran) has been studied: rehydratability is faster for the product freeze dried at lower temperature, when the structure of the product is more porous and softer; higher rehydration rates were also observed for samples obtained from lower initial concentration. In case of binary mixtures (mannitol and dextran, sucrose and dextran) the rehydratability gets worse when higher drying temperatures are used, whereas the relative composition has a smaller effect. Nevertheless, high drying temperatures are required to shorten the process, both in case of pure substances and in case of binary mixtures; thus, it is important to consider the process time–product q...

Effect of Immersion Time in Osmosis and Ultrasound on Papaya Cell Structure during Dehydration

Abstract: The effect of ultrasound-assisted osmotic dehydration applied at atmospheric pressure for different lengths of time on papaya tissue structure was evaluated. Ultrasound induced the loss of cellular adhesion, formation of large cell interspaces, and light rupture of the cell walls. The changes in the tissue structure caused by ultrasound application increased sugar loss, water loss, and effective water diffusivity. Ultrasound-assisted osmotic dehydration induced a gradual distortion in the shape of the cells, loss of cellular adhesion, and the formation of large channels caused by rupture of the cell walls. The changes caused by the application of osmotic dehydration resulted in high water loss and sugar gain.

Optimizing Drying Conditions for Vacuum-Assisted Microwave Drying of Green Peas (Pisum sativum L.)

Abstract: Green peas were dried in a vacuum-assisted microwave drying system. The effects of microwave power levels (100–300 W) and system vacuum (50–400 mm Hg) on drying parameters (viz. drying efficiency and drying time) and some quality attributes (viz. linear shrinkage, apparent density, green color, rehydration, and sensory attributes) of dehydrated peas were analyzed by means of response surface methodology. A face-centered central composite design was used to develop models for the responses. Analysis of variance showed that a second-order polynomial model predicted well the experimental data. The system microwave power level strongly affected quality attributes of dehydrated peas and drying parameters. A higher vacuum during drying resulted in a better quality product. Microwave power of 237.31 W and a 360.22 mm Hg vaccum were found to be optimum drying conditions for vacuum-assisted microwave drying of green peas.

Effect of osmotic pretreatment on hot air drying kinetics and quality of Chilean papaya (Carica pubescens).

Abstract: The effect of osmotic pretreatment on the mass transfer kinetics and quality of dried rehydrated Chilean papaya was researched. Osmotic treatments were sucrose solutions of 40, 50, and 60% w/w and dried at 60°C; non-pretreated samples were dried at different temperatures (40, 60, and 80°C). Quality parameters were analyzed: proximal composition, rehydration ratio, water-holding capacity, color, vitamin C content, firmness, and microstructure. Non-pretreated samples showed a clear turgor loss, color loss. and low ascorbic acid retention when rehydrated. Osmotic pretreatment improved the quality of rehydrated papayas, showing higher ascorbic acid retention and best firmness and color. Microstructure is better preserved in the pretreated papayas than in the non-pretreated samples, although this difference is minimal.