Conveyor-belt Dryer Research Articles

Mathematical modeling of thin-layer drying kinetics and moisture diffusivity study of apple slices using infrared conveyor-belt dryer.

The drying features of apples at different infrared drying settings were investigated. The drying time, moisture-effective diffusion, and activation energy of infrared dried apples were measured experimentally and statistically as a function of slice thicknesses, radiation intensity, and air velocity. The infrared intensity of 0.225, 0.130, and 0.341W/cm2 , slice thicknesses of 6, 4, and 2mm, and airflow of 0.5, 1.0, and 1.5m/s were used to dry apple slices. The data shows that the drying time reduced as IR increased, but airflow and slice thickness increased. Eight statistical factors were used to compare 11 alternative mathematical drying models. The experimentally acquired drying curves were matched to the thin-layer drying equations. According to the calculations, the Midilli etal. equation had the greatest (efficiency and R2 ) and lowest (χ2 , sum of squared errors, standard error of estimate, standard error, standard deviation of difference) values. As a result, this equation is the best for modeling the drying curves of apple slices across all drying circumstances. The optimum moisture diffusivity value varied from 2.59 to 9.07 × 10-10 m2 /s. The mean activation energy was determined to be 19.02-29.83kJ/mol under various experimental conditions.

Effect of drying kinetics model on energy efficiency of drying systems

The effect of drying kinetics models on the energy efficiency of a conveyor-belt convective drying system was investigated. Experiments were conducted on the material to be dried, and the system was modeled using two drying kinetics models. Mathematical models incorporating the drying kinetics model were used to create a module that designs the drying system under given operating conditions. A comparison of the design results of two drying kinetics models under various operating conditions demonstrated that the total drying time of the material can be incorrectly estimated by an average of 35 % when an inappropriate model is used. Furthermore, this inaccurate estimation of the drying time leads to the total energy usage of the system being up to 32 % higher than necessary. These results demonstrate that a good dryer design cannot be guaranteed merely by using experimental data of the material to be dried; the design process must include selection of the most suitable model among various models considering the drying characteristics. Consequently, an appropriate algorithm that incorporates the selection of suitable drying kinetics models can contribute to reduced energy consumption and carbon emissions in various energy-intensive drying processes, especially with the widespread use of conveyor-belt dryers.

Evaluation of Thermal and Drying Characteristics of Dried Hazelnut (Corylus avellana L.) Shell Waste

As a biomass fuel, the hazelnut shell must be milled into sawdust and dried to contain a certain amount of moisture. For this purpose, calorific value, drying rates, thermal values, moisture diffusion, activation energy, and energy consumption at the end of the drying of the hazelnut shell, which is dried in the conveyor belt and microwave dryer, were calculated. The total minimum energy consumed by the hazelnut shell at the end of the experiment in microwave drying was measured as 0.2 kWh for 460 W and 4.65 kWh at 80°C drying temperature in conveyor belt drying until the final moisture value reached 1.1±0.8% wet basis at the end of the experiment. The effective diffusivity of moisture of hazelnut shell changed from 4.13×10-7 to 1.89×10-6 m2 s-1, and the activation energy was found as 2.275 W g-1 in microwave drying. The effective diffusivity of moisture of hazelnut shell changed from 6.39×10-7 to 9.21×10-7 m2 s-1, and the activation energy was found as 19 kJ / mol in the conveyor belt drying. In general, the diffusion coefficient increased with increasing air temperature and decreased with increasing microwave power. At the end of the experiments, the temperature in the product was measured as 72°C in microwave drying and 73.5°C in conveyor belt drying. According to these values, it has been determined that the most suitable drying system for waste disposal was the microwave drying system. The calorific value was measured as 20028.52 kJ/kg in conveyor belt drying and 20036.76 kJ/kg in microwave drying. Microwave drying yielded better results with an increase of 2.72%.

Drying of granular cellulosic fibers by-products: Material characterization, kinetics modeling, and costs analysis towards process optimization

The objective of this work was to study the drying kinetics of granular cellulosic fibers to provide qualitative and quantitative results for preliminary analysis of dryer design and capital costs estimation towards process optimization and feasibility. The drying curves were predicted by a mathematical model that considers the combination of both internal and external resistances to moisture movement to estimate the drying time for design calculations. Discussions regarding the drying kinetics and dryer selection and design were strengthened by the materials characterization, which consisted of determining physical properties, geometric and shape factors, morphology and microstructure, and thermal properties of the GCF particles. A reduction of at least 39% in the conveyor-belt dryer area for higher throughput conditions showed an effective reduction of capital costs. It was verified that the combination with thicker material layers with high inlet air temperatures yields higher dryer throughput, indicating significant possibilities for capital cost savings.

Improving the efficiency of corn drying in a conveyor belt dryer

The paper deals with the theoretical background of drying corn kernels in the moving bed. The authors present a system of the drying medium (drying air) uniform distribution in the dryer. They proposed a system that can improve the performance of the conveyor dryer. A rationale for the essential geometry features of the system is provided. The system implies air supply through two rows of multidirectional nozzles. The proposed layout increases the flow velocity at the nozzle outlet by 35–45%. The study determined the optimum values of the four-stage process for drying corn kernels in a conveyor dryer: for the drying medium, the average temperature was tdm =35 … 50 °C, the velocity at leaving the moving bed was Vdm = 1…1.5 m/s.

Bottlenecks in continuous hops drying with conveyor-belt dryer

Hops are an essential raw material in beer brewing, providing typical flavor and aroma characteristics to beer. Freshly harvested hop cones must be dried immediately. While conveyor-belt dryers are widely used, their operation is largely based on operator experience, which leads to energy-intensive operation whilst adversely affecting the quality. This work identifies the bottlenecks in hops drying by summarizing the results of previous studies, and experimentally analyzing an industrial dryer. Heterogeneous air-distribution, uneven drying and suboptimal control-strategies were identified as key issues which can be battled with accurate model-based process analysis and smart control systems, both of which need further research.

The influence of feedstock stacking shape on the drying performance of conveyor belt dryer

The influence of feedstock stacking shape on the drying performance of conveyor belt dryer

Mathematical Modelling of Conveyor-Belt Dryers with Tangential Flow for Food Drying up to Final Moisture Content below the Critical Value

This work presents the mathematical modeling of the conveyor-belt dryer with tangential flow operating in co-current, which has the advantage of improving the preservation of the organoleptic and nutritional qualities of the dried food. On the one hand, it is a more cumbersome dryer than the perforated cross flow belt dryer but, on the other hand, it has a low air temperature in the final section where the product has a low moisture content and, therefore, it is more heat sensitive. The results of the mathematical modeling allowed a series of guidelines to be developed for a rational design of the conveyor-belt dryer with tangential flow for the specific case of the moisture content of the final product XF lower than the critical one XC (XF < XC). In fact, this work follows a precedent in which a mathematical model was developed through the differentiation of the drying rate equation along the dryer belt with the hypothesis that the final moisture content XF of the product was higher than the critical one XC. The relationships between the extensive quantities (air flow rate and product flow rate), the intensive quantities (temperatures, moisture content and enthalpies) and the dimensional ones (length and width of the belt) were then obtained. Finally, based on these relationships, the rules for an optimized design for XF < XC were obtained.

Energy model-based benchmarking of the drying process in the stenter machine

Stenter machines are used widely in textile dyeing and printing houses for drying and heat setting of fabric. This is one of the most thermal energy-consuming equipment in the textile process. In this paper, the advanced energy model of the stenter machine is developed using primary mass and energy balance equations for ideal conditions as well as standard operating conditions, accounting for various energy losses to understand energy flow. To find out the scope for reduction in energy consumption, energy benchmarking is very important; compared with it, the appropriate energy consumption of a plant can be checked and changed. Furthermore, to eliminate problems such as life, process conditions, and quality of dyeing and printing houses considered during the study, unlike statistical energy benchmarking, in this paper, energy model-based benchmarking is proposed and applied for literature problems. Based on the data given in the literature for conveyor belt, stenter 1 and stenter 2, the specific energy consumption (SEC) for cotton is 4889, 3586, and 4304 kJ/kg of water evaporation, respectively, which is lower than the polywool fabric, having 5185 kJ/kg of water evaporation for another stenter machine. The energy efficiency index (EEI) of conveyor belt dryer, stenter 1, and stenter 2 are 1.56,1.18 and 1.34 for cotton, respectively, and for polywool with another stenter it is 1.92, indicating the polywool process is not energy efficient even polywool do not have bound moisture. Further, Energy flow analysis is carried out for the given stenter and fabric drying process, indicating the highest losses are in the exhaust process even after direct heat recovery by partial recirculation of exhaust gases. By analyzing the energy consumption of stenter machines through energy model based benchmarking and energy efficiency index presents the condition of process and machine from an energy perspective, and energy flow model gives the scope of the energy-saving potential. By using the developed model, the effect of change in atmospheric air temperature and humidity ratio due to season and geographic location on the performance of the stenter machine is investigated and found that there is a variation in performance up to 10% of the total energy required.

Conveyor-Belt Dryers with Tangential Flow for Food Drying: Development of Drying ODEs Useful to Design and Process Adjustment

The mathematical investigation presented in this paper concerns the conveyor-belt dryer with tangential flow operating in co-current. This dryer is bigger than the continuous through-circulation conveyor dryer but has the advantage of better preserving the organoleptic and nutritional qualities of the dried product. In a previous work a mathematical modeling of the conveyor-belt dryer with tangential flow was carried out to offer guidelines for its optimized design. The last of those design guidelines indicated the need for an optimized adjustment of the dryer to ensure the constant maintenance of the final moisture content of the product. The fast and very precise measurement of the moisture content as the first step in the feedback chain was therefore necessary. Considering the difficulty of this type of measurement, two specific ordinary differential equations (ODEs) were obtained with the mathematical investigation of this work. Their solution became a relationship between the final moisture content of the product, the outlet air temperature, and other quantities that could be easily implemented in an automatic dryer control system. Therefore, the fast and accurate and much less expensive measurement of the temperature of the air leaving the dryer, owing to the relationship found, replaces the measurement of moisture content for the adjustment system. The experimental verification of the relationship highlighted the need to introduce a modification by which the relationship was finally validated.

Mathematical model of high-temperature tube-shaped pasta drying in a conveyer belt drier

Abstract The drying procedure is a key to producing pasta of intended quality and with a specific price tag. However, the existing models are mainly to describe the drying process in a steady state. A mathematical model of tube-shaped pasta drying in a conveyor belt dryer with a stepwise heating supply allows determining the curve of temperature and moisture gradients for a tube-shaped pasta unit. It also helps select the best settings to minimize the heat-power costs while maintaining the good quality of a dried product. The given model describes the drying process in a true-to-life form and ensures the convergence of calculations to observations (deviation: 12.5%). The model was utilized to design a transient drying protocol for conveyor belt dryers with a stepwise heating supply. The proposed dryer has high service reliability and produces uniformly dried high-quality product.

Conveyor-Belt Dryers with Tangential Flow for Food Drying: Mathematical Modeling and Design Guidelines for Final Moisture Content Higher Than the Critical Value

The mathematical modeling presented in this work concerns the conveyor-belt dryer with the tangential flow of air with respect to food. This dryer, if operating in co-current, has the advantage of well preserving the organoleptic and nutritional qualities of the dried product. In fact, it has a low air temperature in the final stretch where the product has low moisture content and is therefore more temperature sensitive. It is a bulkier dryer than the continuous through-circulation conveyor dryer with a perforated belt. The latter is therefore more frequently used and has received greater study attention from researchers and designers of the industry. With the aim to propose guidelines for a rational design of the conveyor-belt dryer with tangential flow, a mathematical model was developed here through the differentiation of the drying rate equation followed by its integration performed along the dryer belt. Consequently, and with the assumption that the final moisture content XF of the product is higher than the critical moisture content XC, the relationships between the intensive quantities (temperatures, humidity and enthalpies), the extensive quantities (air and product flow rates) and the dimensional ones (length and width of the belt), were obtained. Finally, on the basis of these relationships, the rules for an optimized design for XF > XC were obtained and experimentally evaluated.

Conveyor-belt drying of Eugenia uniflora L. leaves: Influence of drying conditions on the yield, composition, antioxidant activity and total phenolic content of supercritical CO2 extracts

Eugenia uniflora L. leaves were dried in a conveyor-belt dryer to assess the influence of drying conditions (air temperature and number of passes/residence time in the dryer) on the yield, composition, antioxidant activity and concentration of phenolic compounds found in the extracts obtained from supercritical extraction. An analysis of leaf drying in the conveyor belt was carried out by investigation of sorption isotherms and drying curves obtained under air temperatures of 50, 60 and 70°C. The sorption curves were fitted to the GAB thermodynamic model and the drying curves to a one-parameter empirical equation. The fitted equations were effective to predict the discharge moisture as function of the residence time under different temperatures. The samples for extraction were dried under 50°C/120min, 60°C/60min and 70°C/60min and their moisture levels were reduced respectively to 15wt.%, 10wt.% and 6wt.%. The extractions were carried out at 80°C and 250bar using as solvents either the pure supercritical CO2 or a mixture of ethanol and supercritical CO2 at a mass ratio of 0.5:1. The higher extraction yields (9.9±0.1wt.%), phenolic content (85±2mg GAE/g extract) were found in the extracts from samples dried under 60°C/60min using ethanol as a co-solvent in extraction.

Interview

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개방형 마이크로파 컨베이어 벨트 건조기의 요철 직사각형 도파관 차폐효과

개방형 마이크로파 컨베이어 벨트 건조기의 요철 직사각형 도파관 차폐효과

Economic analysis of drying microalgae Chlorella in a conveyor belt dryer with recycled heat from a power plant

The objective of this research is to estimate the cost of drying microalgae chlorella in a conveyor belt dryer using waste heat from an industrial source. The recycling system consists of a run around thermal fluid between two tube heat exchangers. The dryer is mathematically modeled and the mass transport coefficient is obtained from empirical thin-layer kinetic data.The dryer and heat recovery system are designed for the production of 1000kg/h dried microalgae at a moisture content of 10% (wet basis, w.b.). The input moisture content can range from 35 to 75% (wet basis). Depending upon the applied Hand factor, the total cost to dry microalgae from 55% to 10% ranges from $46.13 to $109.64 per ton of dried product. Using natural gas assumed at $6.27/GJ, the drying cost increases to $83.47 per ton (using hand factor equal to 1). The drying cost using a commercial spray dryer is $109.05 per ton of dried product (using hand factor equal to 1). The paper discusses the sensitivity of drying costs to initial moisture content as well. The results show that integrating waste heat recovery with conveyor belt dryer decreases the drying costs of chlorella drying in comparison to two other drying methods.

Drying and energy aspects of tapioca sago processing-an experimental field study

The drying characteristics of tapioca sago were studied using four different drying methods—Open sun drying (OSD), Conveyor belt drying (CBD), Bin drying (BD) and Fluidized bed drying (FBD)—in an industry located in Tamilnadu, India (Latitude: 11.494347° N; Longitude: 78.272264° E). The BD and FBD dryers were designed and fabricated as pilot scale models in the laboratory with respective capacity of 5 kg/h and 10 kg/h; CBD (1000 kg/h) and OSD are the commercial drying operations currently employed in industrial processing. The drying time, energy and exergy aspects of all the drying methods were compared along with the achieved final moisture content, color and quality of the dried products. The highest Energy utilization ratio (EUR) was found in CBD and FBD in the range of 20-76 % and 10-67 %, respectively. The exergy efficiency was initially low in all the cases but increased to 80 % towards the end of the drying process.

Two-dimensional mathematical model for simulation of the drying process of thick layers of natural materials in a conveyor-belt dryer

This paper presents the mathematical model and numerical analysis of the convective drying process of thick slices of colloidal capillary-porous materials slowly moving through conveyor-belt dryer. A flow of hot moist air was used as drying agent. The drying process has been analyzed in the form of a 2-D mathematical model, in two directions: along the conveyor and perpendicular on it. The mathematical model consists of two non-linear differential equations and one equation with a transcendent character and it is based on the mathematical model developed for drying process in a form of a 1-D thin layer. The appropriate boundary conditions were introduced. The presented model is suitable for the automated control of conveyor-belt dryers. The obtained results with analysis could be useful in predicting the drying kinetics of potato slices and similar natural products.

Mechanisms of heat and mass transfer during drying of mate (Ilex paraguariensis) twigs

ABSTRACTExperimental results of surface temperature and moisture content of twigs of mate were obtained in a conveyor-belt dryer operated batchwise. The first response was determined with an infrared sensor, while the second was by conventional gravimetry. A set of 0.04-m-long cylindrical twigs classified manually into three different subgroups on the basis of their diameters (3.5 × 10−3, 6.5 × 10−3, and 10 × 10−3 m) were used in the experiments. Drying always took place in a chamber fed with a thin single layer of material 0.5 m in length and 0.05 m wide. The fresh twigs without leaves at ambient temperature (≈27.2 ± 2.6°C) and with an initial moisture content close to 0.8 ± 0.1 were dried at three different average air temperatures (65.5, 80.2, and 83.8°C) for 7200 s. A full set of nine (31 × 31) drying experiments were performed by varying the examined factors (particle diameter and drying temperature) at three levels. The low estimated Biot numbers (<0.55) indicate that convection plays a much more important role than conduction in heat transfer. Because of this and since heating was much faster than drying, the Newton’s law of cooling alone was successfully applied to describe the increase of particle temperature with time. From a similar analysis involving a convective mass transfer coefficient calculated with the Chilton-Colburn analogy emerged high-mass-transfer Biot numbers (≈5.37 × 103 − 3.65 × 105) that reveal drying of twigs is governed by diffusion. In fact, the equation that represents the Fick’s second law of diffusion in a long cylinder (one-dimensional transfer), solved analytically and coupled to the model of heat transfer, was able to describe the kinetics of drying of mate twigs.

A mathematical model and simulation of the drying process of thin layers of potatoes in a conveyor-belt dryer

This paper presents a mathematical model and numerical analysis of the convective drying process of small particles of potatoes slowly moving through the flow of a drying agent - hot moist air. The drying process was analyzed in the form of a one-dimensional thin layer. The mathematical model of the drying process is a system of two ordinary nonlinear differential equations with constant coefficients and an equation with a transcendent character. The appropriate boundary conditions of the mathematical model were given. The presented model is suitable in the automated control. The presented system of differential equations was solved numerically. The analysis presented here and the obtained results could be useful in predicting the drying kinetics of potatoes and similar natural products in a conveyor-belt dryer.