Industrial Drying Research Articles

A review on development of solar drying applications

Abstract Drying is an essential process in the preservation of agricultural crops and in industries, such as textile production, dairy processing, cement production, clay brick production, tile production, wood and timber processing, wastewater treatment, and biomass treatment. The energy requirement for drying can be supplied from various sources, namely, electricity, fossil fuel, natural gas, wood, bark forest residual, and solar. Although the use of solar radiation for drying has existed since antiquity, it has not yet been widely commercialized, particularly in the industrial sector. Considering the rapid depletion of natural fuel resources and because of the rising fossil fuel cost, solar drying is expected to become indispensable in the future. Moreover, environmental considerations and damages caused by human beings due to increasing consumption of fossil fuel prompt governments and industries to use renewable energies as a clean and sustainable resource, thus, the use of solar energy for drying. The numerous solar drying applications are classified into two main categories, that is, agricultural and industrial. Many benefits could be exploited from solar energy for drying applications. Solar energy enables the industries and agricultural sectors to modify their energy requirement, improve their energy stability, and increase energy sustainability, which lead to improvement in the system efficiency. We review the role of the drying system in industry and agriculture, the energy consumption capacity, and the availability of the required energy for the products to be dried. In addition, the economical, environmental, and political aspects of using solar dryers are discussed. Special attention is given to industrial drying and in finding opportunities to use compatible dryers for a certain industry. In short, we conduct a comprehensive review of the new approach to use solar energy in industrial drying sector.

Mathematical Modeling the Drying of Poplar Wood Particles in a Closed-Loop Triple Pass Rotary Dryer

Closed-loop drying systems are an attractive alternative to conventional drying systems because they provide a wide range of potential advantages. Consequently, type of drying process is attracting increased interest. Rotary drying of wood particles can be assumed as an incorporated process involving fluid–solid interactions and simultaneous heat and mass transfer within and between the particles. Understanding these mechanisms during rotary drying processes may result in determination of the optimum drying parameters and improved dryer design. In this study, due to the complexity and nonlinearity of the momentum, heat, and mass transfer equations, a computerized mathematical model of a closed-loop triple-pass concurrent rotary dryer was developed to simulate the drying behavior of poplar wood particles within the dryer drums. Wood particle moisture content and temperature, drying air temperature, and drying air humidity ratio along the drums lengths can be simulated using this model. The model presented in this work has been shown to successfully predict the steady-state behavior of a concurrent rotary dryer and can be used to analyze the effects of various drying process parameters on the performance of the closed-loop triple-pass rotary dryer to determine the optimum drying parameters. The model was also used to simulate the performance of industrial closed-loop rotary dryers under various operating conditions.

Crystallization Behavior and Infrared Radiation Properties of Copper Ferrite-Doped MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Ceramics

MgO-Al2O3-SiO2 ceramics were recently explored as infrared radiance materials to provide an environmental friendly energy candidate for industrial heating and drying. Cu ferrite was selected to dope MgO-Al2O3-SiO2 ceramics, forming a series of composite ceramics via solid-state reaction method to enhance the infrared radiation properties. The phase identification and morphologies of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The infrared emissivity was examined by Fourier transform infrared (FTIR) spectrometer. The results showed that an improvement of infrared radiation properties can be achieved by doping Cu ferrite in MgO-Al2O3-SiO2 ceramics. With increasing the dopant content from 0 wt % to 10.0 wt %, the crystallization behavior changed accordingly. A positive correlation was found between the infrared emissivity and the lattice strain. The highest infrared emissivity (0.91±0.01) was obtained after sintering at 1150 °C for 2 h with Cu ferrite content was 7.5 wt %, in which the maximum lattice strain (0.282 %) occurred. MgO-Al2O3-SiO2 ceramics doped with Cu ferrite have potential for the application of infrared heating and drying fields.

Experimental and Modeling Study During Freeze Drying of Aqueous tert-Butanol–Based Formulations in Vials

In this study, using COMSOL Multiphysics software, we set up a two-dimensional model for the sublimation step a frozen aqueous organic cosolvent tert-butyl alcohol (TBA) formulation without a dissolved active principal ingredient contained in 4-mL glass vials. This model, based on the hypothesis of a sublimation process mainly governed by the conductive heat transfer between the shelf and the sublimation front, allowed precise prediction of the sublimation kinetics and the sublimation front movement for different operating conditions. Next, this modeling was validated by many experimental runs under operating conditions corresponding to very low total gas pressures (5 to 50 Pa) and low shelf temperatures (0 to −20°C) generally encountered during industrial freeze drying of thermosensible pharmaceuticals (vaccines, diagnostic proteins, serums, etc.).

Enhanced infrared radiation properties of CoFe2O4 by single Ce3+-doping with energy-efficient preparation

Spinel ferrites were recently explored as an infrared radiance materials to provide an environmental friendly energy candidate for industrial heating and drying. Ce3+ was selected to dope cobalt ferrites, forming CoFe2−xCexO4 (x=0, 0.01, 0.05, 0.1 and 0.15) via the sol–gel auto-combustion method to enhance the infrared radiation properties. The samples were characterized by use of FTIR, TG/DSC, SEM and XRD measurements. The infrared radiation properties quantified by infrared emissivity was examined via a Fourier transform infrared spectrometer. The results showed that the Ce3+ content and the sintering temperature were the two crucial factors for regulating the infrared radiation properties of Ce3+-doped cobalt ferrites. An improvement of infrared radiation properties can be achieved from the accelerated lattice strain as well as the stable solid solution structure of single phase (CoFe2O4). The infrared emissivity of the ferrites decreased once the second phase (CeO2) appeared. Doping with small Ce3+ content (x≤0.05) and sintering at temperature no more than 600°C were found effective for the inhibition of second phase (CeO2) formation. There was a positive correlation between the lattice strain and the infrared emissivity. The highest infrared emissivity (0.92±0.01) was obtained from CoFe1.95Ce0.05O4 sintered at 600°C for 2h in which the maximum lattice strain (0.341%) occurred. Cobalt ferrites doping with single Ce3+ have potential for the application of infrared heating and drying field.

Equilibrium Moisture Content Isotherms of Codfish (Gadus morhua)

Industrial drying of salted fish is an extremely common practice in the Portuguese industry of codfish processing. The present study aims to obtain sorption isotherms of codfish, which will be useful in designing drying processes and prediction of storage conditions for this product. The equilibrium moisture contents (wet basis) were determined for salted codfish at 15, 18, 20, and 23ºC at relative humidities ranging from 40 to 70%. Experiments were also carried out for fresh codfish at the temperature of 20ºC for the same values of relative humidity. The sorption capacity of codfish decreased with an increase in temperature at constant relative humidity. Thirteen models were used to correlate the experimental data analysis of salted codfish: modified BET, Cauri, Chung-Pfost, modified Chung-Pfost, GAB, modified GAB, Halsey, modified Henderson, Kuhn, Oswin, modified Oswin, Smith, and modified Smith. Based on the mean relative percentage deviation, standard error of estimate, randomness of residual, and coefficient of determination, experimental data were well described by all the models. The equilibrium moisture content of salted codfish was best predicted using the modified GAB model, with a coefficient of determination of 0.99.

Energy and rice quality aspects during drying of freshly harvested paddy with industrial inclined bed dryer

The performance evaluation of any industrial dryer regarding energy consumption and product quality should be assessed to check its present status and to suggest for further efficient operation. An investigation was carried out to evaluate the impact of drying temperature and air flow on energy consumption and quality of rice during paddy drying with industrial inclined bed dryer (IBD) with average holding capacity of 15 ton in the selected complexes of Padiberas Nasional Berhad (BERNAS)-the national paddy custodian of Malaysia. In reducing paddy moisture content (mc) from 22% to 23% wet basis (wb) down to around 12.5% wb, the final mc, the specific electrical (in terms of primary energy) and the specific thermal energy consumption were found to be varied between 1.44 to 1.95MJ/kg water evaporated and 2.77 to 3.47MJ/kg water evaporated, respectively. Analysis revealed that the specific electrical energy consumption was around 20% lesser and the specific thermal energy consumption of IBDs was around 10% higher during drying with air temperature of 41–42°C than drying with 38–39°C in reducing paddy mc from 22% to 23% (wb) down to around 12.5% (wb). However, paddy being with almost same initial mc dried using drying temperature of 38–39°C, IBDs yielded 1–4% higher head rice yield while milling recovery and whiteness were comparable at acceptable milling degree and transparency. The bed air flows between 0.27 and 0.29m3m−2s−1 resulted in higher head rice yield slightly while its effect on drying time was not prominent so much. For paddy with initial moisture content below 23% wb, it is recommended that drying air temperature should not be higher than 39°C in order to maintain rice quality at reasonable energy consumption.

Effect of structural modifications on the drying kinetics of foods: changes in volume, surface area and product shape

Macro and micro-structural changes take place during food dehydration. Macro-structural changes encompass modifications in shape, area and volume. Studies of such changes are important because dehydration kinetics (essential for calculating industrial dryers) may be highly influenced by changes in food shape and dimensions. The overall changes in volume, surface area (“shrinkage”) and shape (Heywood factor, with provides a close description of food shape) were determined experimentally, and the results were correlated with simple expressions. Hence, although dehydration kinetics can be modeled with simplified overall shrinkage expressions, the possibility of selecting a suitable geometry and predicting the characteristics dimensions will provide higher accuracy. An additional unresolved problem is the lack of a general model that predicts macro-structural changes for various foods and diverse geometries. In this work, based on experimental data of sweet and sour cherries, and rose hip fruits, a simplified general model to predict changes in volume and surface area are proposed. To estimate how the changes in characteristic dimensions affect the kinetic studies, experimental drying curves for the three fruits by means of a diffusional model considered the following variants for the characteristic dimensions: (i) The radius of the fresh food, assumed constant; (ii) The radius of the partially dehydrated product; (iii) The radius predicted by the correlation for structural changes, especially volume, obtained in this work and generalized for the three fruits, and (iv) to demonstrate the need to study the macro-structural changes for all dehydrated foods, also be present the case of a restructured food.

Effect of structural modifications on the drying kinetics of foods: changes in volume, surface area and product shape

Macro and micro-structural changes take place during food dehydration. Macro-structural changes encompass modifications in shape, area and volume. Studies of such changes are important because dehydration kinetics (essential for calculating industrial dryers) may be highly influenced by changes in food shape and dimensions. The overall changes in volume, surface area (“shrinkage”) and shape (Heywood factor, with provides a close description of food shape) were determined experimentally, and the results were correlated with simple expressions. Hence, although dehydration kinetics can be modeled with simplified overall shrinkage expressions, the possibility of selecting a suitable geometry and predicting the characteristics dimensions will provide higher accuracy. An additional unresolved problem is the lack of a general model that predicts macro-structural changes for various foods and diverse geometries. In this work, based on experimental data of sweet and sour cherries, and rose hip fruits, a simplified general model to predict changes in volume and surface area are proposed. To estimate how the changes in characteristic dimensions affect the kinetic studies, experimental drying curves for the three fruits by means of a diffusional model considered the following variants for the characteristic dimensions: (i) The radius of the fresh food, assumed constant; (ii) The radius of the partially dehydrated product; (iii) The radius predicted by the correlation for structural changes, especially volume, obtained in this work and generalized for the three fruits, and (iv) to demonstrate the need to study the macro-structural changes for all dehydrated foods, also be present the case of a restructured food.

Novel high-humidity hot air impingement blanching (HHAIB) pretreatment enhances drying kinetics and color attributes of seedless grapes

Abstract Seedless grapes blanched by high-humidity hot air impingement blanching (HHAIB) at different temperatures (90, 100, 110, and 120 °C) and several durations (30, 60, 90, and 120 s) were air-dried at temperatures ranging from 55 to 70 °C. The PPO activity, drying kinetics, and the product color parameters were investigated to evaluate the effect of HHAIB on drying kinetics and color of seedless grapes. The results clearly show that HHAIB not only extensively decreases the drying time but also effectively inhibits enzymatic browning and results in desirable green–yellow or green raisins. In view of the PPO residual activity, drying kinetics and color attributes, HHAIB at 110 °C for 90 s followed by air drying at 60 °C are proposed as the most favorable conditions for drying grapes. These findings indicate a new pretreatment method to try to enhance both the drying kinetics and quality of seedless grapes. Industrial relevance Drying grapes into raisins is a major processing method in almost all grape-growing countries. Drying grapes is more difficult than some other biological materials, since a thin-layer of wax covers on its surface peel. Currently, chemical pre-treatment methods are used frequently to dissolve the wax layer and accelerate dry rate. However, the chemical additive residue in the raisins may cause food safety problems and how to deal with larger quantities of corrosive chemicals is a serious problem. HHAIB is a new and effective thermal treatment technology with advantages such as minimum solids loss, uniform, rapid and energy-efficient blanching process. The current work indicates that HHAIB may be a useful non-chemical pretreatment technology for seedless grape drying, which can not only accelerate drying kinetics but also improve color parameters of seedless grape.

Optimization Design of Dryer Machinery in Tunnel Washing System

The energy saving is the important principle of the future development of our country, reasonable and efficient use of resources in the industrial production has become increasingly concerned topic. This paper studies the industrial dryers in the washing system, through the analysis of flow field simulation, points out the existing dryers in the working process of the structure is unreasonable, inadequate energy utilization, etc. Based on flow field simulation, the internal structure optimization design of the dryer, the optimized flow field structure is more reasonable, dryer air in the dryer average velocity increased, thus improve the drying efficiency and energy saving.

Mathematical Modeling and Simulation of Drying Using Two Industrial Concurrent and Countercurrent Rotary Dryers for Ammonium Nitrate

Drying of ammonium nitrate (AN) is accomplished in the Shiraz Petrochemical Complex (SPC) using a concurrent rotary dryer following a countercurrent rotary dryer. A mathematical model for these rotary dryers including heat and mass transfer was developed. The model was checked against industrial-scale data, which showed a good agreement. The average absolute deviation of the simulation results compared to the industrial data for the concurrent dryer was 4.0% for solids moisture, 1.3% for solids temperature, and 1.8% for air temperature and for the countercurrent dryer it was 9.0% for the solids moisture, 2.0% for solids temperature, and 4.6% for air temperature. These simulation results reveal that for outlet solid moisture, inlet AN moisture, and air temperature as well as the outlet temperature of product, the inlet solid and air temperature have major effects for both concurrent and countercurrent flow.

Ultrasonic Convective Drying Kinetics of Clipfish During the Initial Drying Period

A hybrid drying system for high-intensity airborne ultrasound applied in convective drying was investigated for the drying of salted codfish (clipfish). Convective drying with ultrasonic assistance at 10, 20, and 30°C was compared to the same process without ultrasound. The Weibull model was used to model and investigate the drying behavior, and the effective diffusion in Fick's law was determined. The ultrasound decreased the drying time more at lower drying temperatures. The drying time was reduced by over 90% at a drying temperature of 10°C. For an industrial drying process at a temperature of 20°C, the drying time was reduced by 32.2%. The ultrasonic, convective drying of clipfish at a temperature of 20°C was faster than the same process without ultrasound at 30°C. The investigations showed a thermal effect for all products when ultrasound was applied. The specific moisture extraction ratio (SMER) in the investigated system was improved by 0.2 kgwater kWh−1. The heat transfer coefficient in the system used was increased by 32.6% for a heating process in a separate investigation, whereas for a cooling process no increased heat transfer coefficient was determined. The thermal effect might (at least partially) explain the faster drying of ultrasonic-assisted convective drying. The results obtained demonstrate the potential of airborne ultrasound in convective drying with regard to drying time, energy consumption, and product quality. Documentation of the thermal effect should be included in future R&D on this topic.

A Novel Developed Linear and Nonlinear System Identification for an Industrial Dryer

system is a controlled plant which is normally used in chemical industry. The proper modeling of this system facilitates its maintenance and keeping. Normally this is not an easy task, unless having a complete model of the process, due to sudden and nonlinear events. In this paper the linear identification of dryer plant in Arak petroleum, is introduced according to the Autoregressive with Exogenous Input (ARX) model and Box-Jenkins model and also the nonlinear identification based on Multi-Layer Perceptron (MLP) algorithm is investigated. The simulation results were satisfactory. It was concluded that these models can be used to design adaptive or robust controllers. KeywordsLinear system identification, Nonlinear system identification, ARX structure, Box-Jenkins model.

Drying of Apple Slices in Combined Heat and Power (CHP) Dryer: Comparison of Mathematical Models and Neural Networks

Abstract Consuming a high amount of energy in industrial dryer makes the drying as an important and highly energy-intensive industrial process. In this study, the required energy for drying of apple slice was supplied from the outlet heat of an engine generation set exhaust. The drying behavior of apple slice was studied in a combined heat and power (CHP) dryer system at four engine load levels (25, 50, 75, and 100%) in order to provide different temperatures (50, 65, 80, and 95°C), and at three levels of drying product thickness (3, 5, and 7 mm) with the constant air flow velocity of 1 m/s. The empirical data from experiments with variants of semi-theoretical and empirical models were evaluated and finally, a suitable model proposed by Midilli et al. was selected to be the best model, as for as the RMSE, R2, and χ2 criterion is concerned. Comparing the results from implementing artificial neural network (ANN) and mathematical models, it was found that the dynamic ANNs is more powerful for modeling the drying process of apple slice in a CHP dryer system than static ANNs and mathematical models.

Combined Convective and Microwave Drying of Agglomerated Sand: Internal Transfer Modeling with the Gas Pressure Effect

In order to improve the industrial drying (hot air and microwave) of inserts made of agglomerated sand, a comprehensive internal heat and water transfer model has been proposed. In this model, the internal gas phase pressure effect was made perfectly explicit, especially the phenomena of liquid and vapour transfer by filtration and of liquid expulsion at the surface. This model was validated on the basis of the experimental mean water content and core temperature curves for drying trials at different microwave powers. Then, it was used for comparing the drying time and the internal pressure level calculated for four particular processes: a standard process with high temperature air applied all over the time, a strong process with high power microwaves applied all over, and two processes which alternate the two heating modes. It was demonstrated that the combined and alternative processes provide a real possibility for faster drying with less internal pressure and thus with less cracking risk. The microwaves should be applied only in the first hour of the process and with decreasing power. The decrease of the drying time was around 30% with regard to the hot air standard process.

Online probabilistic operational safety assessment of multi-mode engineering systems using Bayesian methods

In the past decades, engineering systems become more and more complex, and generally work at different operational modes. Since incipient fault can lead to dangerous accidents, it is crucial to develop strategies for online operational safety assessment. However, the existing online assessment methods for multi-mode engineering systems commonly assume that samples are independent, which do not hold for practical cases. This paper proposes a probabilistic framework of online operational safety assessment of multi-mode engineering systems with sample dependency. To begin with, a Gaussian mixture model (GMM) is used to characterize multiple operating modes. Then, based on the definition of safety index (SI), the SI for one single mode is calculated. At last, the Bayesian method is presented to calculate the posterior probabilities belonging to each operating mode with sample dependency. The proposed assessment strategy is applied in two examples: one is the aircraft gas turbine, another is an industrial dryer. Both examples illustrate the efficiency of the proposed method.

Definition of efficiency criteria for a fuel cell humidifier: Application to a low power proton exchange membrane fuel cell system for negative surrounding temperatures

The humidifier plays a key role in fuel cells system by ensuring good hydration of membranes and transferring part of the exhaust heat to the cells. To characterise this device and evaluate its performance at negative ambient temperatures, several methods from different fields of engineering can be adopted. In our investigation, we first tested the performance criteria applicable to a heat exchanger since the humidifier can be considered a heat and mass exchanger. To estimate mass exchange, i.e., moisture transfer, the criteria used in industrial drying were tested. Eventually, to consider irreversibilities involved in the humidification process, exergetic criteria were defined. Following the design of experiments (DOE) method, we fit all performance criteria into a linear model. An analysis of variance showed that only the exergy yield ζ model is robust and reliable. A study of this model helps us present several recommendations for optimizing humidifier performance. The DOE results reveal that between −20 °C and 0 °C, the ambient temperature does not have a significant impact on the exergy yield. This indicates that humidifier sizing and optimisation made at a given ambient temperature would be applicable for other ambient temperatures.

Testing New In-Kiln Meter for Monitoring Lumber Moisture Content during Drying

The objective of this study was to test a new in-kiln sensor for monitoring lumber moisture content during industrial drying. The theoretical foundation of the technology was already known, because it is based on electrical conductivity, but the mechanism of implementation was new and required validation. For this reason, the technology was compared with two other widely used methods for assessing lumber moisture content, namely, the oven-drying and electrical capacitance methods. The tests were performed in a 120-m3 industrial kiln operated by a sawmill in the eighth region of Chile, and the results showed that the average moisture content at the end of drying was satisfactorily determined by the new in-line sensor. As predicted by theory, the sensor was not able to accurately measure moisture content above 25%, but it was still able to provide the equivalent of a drying curve for monitoring of the drying process.

Drying Kinetics, Energy Consumption, and Quality of Paddy (MAR-219) during Drying by the Industrial Inclined Bed Dryer with or without the Fluidized Bed Dryer

The performances of industrial dryers, namely the inclined bed dryer (IBD) and the fluidized bed dryer (FBD) combined with IBD, in terms of drying kinetics, energy consumption, and quality of paddy were investigated in this study. Drying parameters used in a single-stage paddy drying using IBD and a two-stage drying using FBD combined with IBD were analyzed to assess the existing performances of the drying techniques. The overall performances of the current drying practices exhibited inconsistent results with the operating parameters, such as drying air temperature, drying time, and air flow rate among the drying process lines. Distinct variations in moisture reduction and energy consumption of the drying systems were identified. Poor performance of the industrial fluidized bed dryer was observed in the case of drying in low capacity that caused higher specific energy consumption. However, the quality of milled rice obtained from both drying systems was found to be almost similar. Minimal process time (i.e., up to 24.5% less) was found in the paddy dried with FBD as the first-stage drying, followed by IBD as the second-stage drying.