Belt Dryer Research Articles

Effect of drying temperature in hop dryer on hop quality

One of the qualitative characteristics of both green and dried hops is the content of hop essential oils which are contained in a quantity of 0.5 to 3.5%, depending on the hop variety. These essential oils are heat labile substances because the temperature has an influence on their content. Hop cones, dried either in belt or chamber dryers, are exposed to a drying medium temperature of 55 °C to 60 °C for the entire duration of drying, i.e. for 6–8 hours. Under current drying conditions there is a loss of approx. 15 to 25% of the total content of essential oils present in hops before drying. In case of special aroma hop varieties, such losses lead to a decline in the product quality. Comparative measurements have been carried out with a laboratory equipment to find out whether more aromatic essential oils are retained in hop cones at a drying temperature of 40 °C compared to a drying temperature of 60 °C. The measurement carried out with the most common variety of Saaz hop concluded that the essential oil losses were lower by 33.4% at a drying temperature of 40 °C, and with other seven mostly hybrid varieties the losses were lower on average by 13.9% than at a drying temperature of 60 °C. The measurements proved that each of the varieties retained, to a significant extent, its content of essential oils in the dried hop cones at a drying temperature of 40 °C.

Evaluation of exergy performance and onion drying properties in a multi-stage semi-industrial continuous dryer: Artificial neural networks (ANNs) and ANFIS models

In this research work, two intelligent methods, namely artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS) are applied to predict the moisture ratio (MR), energy utilization (EU), energy utilization ratio (EUR), exergy loss and exergy efficiency of onion slices drying process by a Multi-Stage Semi-Industrial Continuous Belt (MSSICB) dryer. The experiments are carried out for various temperature levels (40, 55, 70°C), air velocities (0.5, 1, 1.5m/s) and belt linear speeds (2.5, 6.5 and 10.5mm/s). The results demonstrate that by using the high levels of air temperature and velocity along with a low belt linear speed, the values of effective moisture diffusivity (Deff), color change (ΔE), EU, EUR, and exergy loss increase whereas the drying time, specific energy consumption (SEC) and exergy efficiency decrease. The highest values of Deff, SEC and ΔE are found to be 3.74×10−11m2/s, 484.54MJ/kg and 23.65, respectively. EU and EUR vary between 0.0641 to 0.2451kJ/s and 0.0848 to 0.5028, respectively. Moreover, exergy loss and efficiency vary in the ranges [0.0182−0.0555] kJ/s and [62.33–89.25] %, respectively. Moreover, the results showed that the prediction accuracies of MR, EU, EUR, exergy loss and exergy efficiency by the use of ANNs model were 0.9995, 0.9957, 0.9984, 0.9960 and 0.9979, respectively so that the values of 0.9998, 0.9972, 0.9991, 0.9962 and 0.9985, obtained by application of ANFIS model, respectively. Therefore, the selected ANN and ANFIS models can be used confidently to estimate the exergy efficient drying conditions for a sustainable drying process by MSSICB.

Drying of mangoes (Mangifera indica L. cv. Palmer) at changeable temperature conditions—Effects on energy consumption and quality of the dehydrated fruit

AbstractThis study evaluated the influence of heat input change on the drying kinetics, energy consumption, the color, and carotenoid retention during the drying of mangoes. The drying conditions in the first stage were 95°C for 40 min and 80°C for 40 min, so that the surface temperatures of the fruit at the end of this stage were around 60°C. The temperatures of the second stage and corresponding continuous drying (control) were 70 and 60°C. As a result, the thermal intermittence influenced the drying kinetics, causing significant reductions in the overall process time and providing energy savings when compared to continuous drying. The color parameters did not show relevant changes as result of the intermittent drying while good carotenoid retention was obtained in intermittent conditions, when the second stage was 60°C. Therefore, the carotenes were more sensitive to a temperature of 70°C, which highlights the importance of limiting the temperature of the mango to 60°C during the two drying stages to better preserve the quality of the dehydrated fruit. Moreover, the high air temperatures used in the first stage were advantageous for reducing the overall process time and providing energy saving.Practical ApplicationsDrying is an operation well known for the food industry. However, in so many cases, dryers are not designed with energy consumption in mind. Moreover, simple procedures can bring savings in convective drying, as shown in the present study, where the application of two‐stages in the convective drying of mangoes was advantageous to reduce the overall drying time and provide energy savings in relation to continuous drying. Besides that, good carotenoid retention was obtained using low temperature (60°C) at the second stage. The results can be useful for design of dryers and drying process, considering different temperatures. Intermittent drying of high moisture foods by varying the drying air temperature can be applied both on an industrial scale, in continuous belt dryers or in tunnel dryers, and on a small scale, using two or more dryers with different temperatures.

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.

Convective Drying of Sewage Sludge Layer in Through-flow

Drying of the sewage sludge layer was investigated in a convective laboratory dryer at air temperatures of 65 °C and 80 °C and air speeds of 0.53 m/s and 0.83 m/s. The sludge layer was formed by loading cylindrical extrudates on a grate of 0.5 m × 0.5 m size. The drying air was directed through the layer, as typically encountered in industrial belt dryers. Under such setup, the sludge layer structure and porosity significantly affect the air flow conditions and thus the drying rates. Shrinkage and cracking of the material during drying caused changes in the layer’s porous structure, that affected the pressure drop and the drag force due to passing of air through the layer. The decreasing of drag force over time was modeled by a simple function that showed excellent agreement to the selected measured data. The sludge layer drying kinetics was determined by fitting the measured data to the most common drying models. Two models, the modified Nadhari and the Wang Singh model, were determined as most suitable for modeling of drying curves. The total drying time per kilogram of sludge was modeled as a function of drying air temperature, drying air velocity and initial sludge dry matter content. The coefficient of determination (R2) of the model is 0.944. Total drying times between 43 minutes per kilogram and 76 minutes per kilogram of sludge were obtained for the investigated range of drying air conditions.

Investigation on airflow distribution under different feed thickness combined CFD modeling and experimental verification

Belt dryer is commonly used in the production of the dried aquatic feed. Poor airflow distribution during the aquatic feed drying process leads to moisture content variation that could be lead to high energy consumption and poor feed quality. A newly designed belt dryer with improved drying efficiency was used to study airflow distribution. In order to analyze airflow distribution inside the dryer, a model for a new belt dryer was established. Airflow distribution under five different feed thicknesses (20 mm, 30 mm, 40 mm, 50 mm, 60 mm) were simulated using computational fluid dynamics (CFD) techniques and verified by experimental data. A finite volume method with porous media formulation was used to simulate airflow distribution inside the dryer. The experimental results showed that there was good consistency between the experimental and simulated values of airflow velocity. The airflow velocity on the feed layer range from 0.28 m/s to 0.98 m/s with a standard deviation of up to 0.17 m/s. Airflow distribution inside the dryer was affected by the feed thickness and air space size. When the feed thickness was 40 mm, the uniformity of the airflow velocity at the surfaces of the feed can reach the best results.

Conveyor belt structure of belt dryer: Analysis and optimization

The chain drive conveyor belt (CDCB) of the belt dryer is prone to generate impact load during operation, and the conveyor belt bedplate (CBB) will cause fatigue damage and fracture. This study presents an approach for calculating fatigue life, which combines the automatic dynamic analysis of mechanical systems (ADAMS), finite element analysis software (ANSYS), fatigue analysis software (FE-SAFE), and experimental stress analysis. The virtual prototype model for simulation of the CDCB is established, and its motion stability, contact impact force and motion trajectory are analyzed. The study shows that the chain drive polygon effect will cause periodic changes in velocity, and the motion trajectory has very good similarity. The stress experiment results show that the stress was considerable during the chain drive meshing process. The finite element analysis results show that the maximum stress of the old CBB is higher than the yield strength of the material, and the equivalent stress of the new CBB is lower than that of the old CBB. The area of the maximum stress of old CBB presents a fracture, which indicates the fatigue failure of the old CBB. The finite element calculation results were imported into FE-SAFE for fatigue life analysis, which compared the fatigue cycle number and safety factor of the old CBB and the new CBB. The results show that the new CBB can extend the service life of the belt dryer. The proposed analytical method for fatigue life is simple and effective and can serve as a reference for the fatigue life analysis of the key components of the belt dryer.

Determination of fat preferences of adult dogs

This study was carried out to determine the preferences of dogs for some commonly used fat sources in dog food. Three different types of food were produced using 5% additional sunflower oil, poultry fat, or beef tallow. The food was extruded using a twin-screw extruder at approximately 25% moisture and temperatures in the range of 90 °C to 135 °C. The extrudates were dried for 30-45 min at temperatures of up to 148 °C in a belt dryer. Next, the heated fats were sprayed onto the extrudates. The foods were cooled, sampled, and packaged. A total of 30 neutered adult (between 1 and 3 years old) male dogs were used. The preference of the dogs for the 3 different fat sources was determined via a 2-pan preference test. Preference tests were conducted for 12 days in pairs, and the dogs consumed each food for 8 days. The dogs had the greatest preference for food containing the additional sunflower oil, with a preference rate of 56%. Beef tallow was the least preferred fat, with a preference rate of 44%. Dogs preferred food containing sunflower oil more than food containing animal fats. It was concluded that dogs showed a preference in proportion to the linoleic acid level in each food.

Economic Evaluation of Drying of Soot Sludge and Sawdust Mixture at Low Temperatures Using the Characteristic Drying Curve Method

Soot sludge is a waste stream formed in the fuel oil gasification of formic acid and hydrogen peroxide production. The soot sludge has a high moisture content (95%) and is presently combusted with heavy fuel oil in order to dispose of the sludge. Experimental tests earlier conducted by the authors have shown that the sludge can be convectively dried with sawdust in a fixed bed. By upgrading the sludge from waste to fuel, the utilization of oil can be decreased. In this study, characteristic drying curves (CDC) are determined for the sludge and sawdust mixture. The CDCs are further used to evaluate the economy of the mixture drying in a belt dryer by using the payback period method. Results show that the linear CDCs of the mixture can be used to extrapolate drying data from specific drying conditions to another when the bed height is 200 or 300 mm, and the inlet air temperature 40–100 °C. The economic analysis shows that drying is economical for all inlet air temperatures if the oil price is ≥350 €/t-oil. Sensitivity analyses reveal that the heat, sawdust and emission prices have no remarkable influence on the economy of drying if the oil price does not fall below c. 300 €/t-oil.

The impact of biomass drying on the efficiency of a gasification plant co-producing Fischer-Tropsch fuels and heat – A conceptual investigation

This study examines the impact of biomass drying on the overall efficiency of a Biomass-to-Liquids (BTL) process co-producing Fischer-Tropsch (FT) syncrude and heat. The proposed BTL process is based on steam-blown dual fluidised-bed gasification of biomass, simplified gas clean-up and FT synthesis. Biomass drying was found to have a significant effect on both the FT product yield and the overall thermal efficiency of the BTL plant. In the considered concept, FT off-gases are used as supplementary feedstock in the oxidiser, alongside with char, to satisfy the heat demand in gasification. Drying of the biomass feedstock leads to reduced need of water evaporation during gasification. This in turn reduces the demand for off-gases in the oxidiser, and allows to produce more syncrude (and less off-gases) in the FT unit. The simulations indicated that more extensive drying could result in a significant increase in FT syncrude yield: the thermal efficiency of FT syncryde production increased from 47.7% to 54.6% as the moisture mass fraction of the biomass feed was reduced from 30% to 8%. The highest overall thermal efficiencies of 85–88% were obtained with a two-stage drying concept that combines a belt dryer and an indirectly-heated steam dryer.

Using Waste Heat to Dry RDF: a Technical and Environmental Assessment of the Low Temperature Belt Dryer Technology

In 2015, the Portuguese cement production company Cimpor modified the alternative fuel supply operation of refuse derived fuel (RDF) co-processing in the main burner of one of its cement kilns in Souselas. This modification resulted in the installation of an RDF drying unit with low temperature belt dryer (LTBD) technology that uses cascading energy available in Souselas cement plant. Implementation of the dryer project improves production and efficiency of the industrial process, while also resulting in environmental benefits as it decreases moisture and increases the lower calorific value of RDF, improving its quality. This paper intended to determine these environmental benefits and the added value that the project brings to the industry by presenting an energy balance and environmental assessment. This methodology allowed to compare the use of available heat as an energy source for the dryer instead of fossil fuels, such as natural gas or coal, which concluded that the waste heat available at the cement plant for the dryer would allow the saving of 75 to 84 kg of CO2-eq per tonne of wet RDF to be dried. Projects such as this one may greatly help address the main barriers of using RDF from municipal solid waste and other waste streams with high moisture content.

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Evaluation of combined screening and drying steps for the improvement of the fuel quality of forest residue wood chips—results from six case studies

Wood chip quality is essential for failure-free and low-emission combustion in automatically stoked small-scale biomass boilers (< 100 kW). Screening and drying of wood chips might be suitable to reduce fuel heterogeneity and to guarantee defined qualities according to ISO 17225-4. Six case studies on screening and drying of forest residue wood chips were performed at German biomass terminals. Screening was done using drum, star, or jigger screens. Drying was done in storage piles and in rolling bed, walking floor, belt, and batch container dryer. Throughput rate was assessed on-site. Fuel properties were analyzed according to international standards. Moisture content of fresh wood chips was too high for small-scale biomass boilers (up to 51 w-%). Raw materials did not comply with specifications of ISO 17225-4 (i.e., ash content, particle size) while fuel indices (Fe/Mn, Al/200) implied contamination with soil material. Technical drying provided moisture contents ≤ 15 w-% while natural drying in piles resulted in values often exceeding 35 w-%. Screening reduced ash content, fines, oversized particles, and the share of N, S, Cl, K, and Si. Screening of pre-dried fuels seems to be beneficial compared to screening of fresh wood chips. After processing, chips could usually be classified as specification A2 to B1 according to ISO 17225-4.

Equipment Qualification of a New Laboratory Tray Dryer

This qualification study deals with the Installation and Qualification of a New Tray Dryer. Granules in the pharmaceutical industry are dried using the different equipment like Fluid Bed Dryer, Belt Dryer, Tray Dryer, Vacuum Tray Dryer, Spray Dryer and Rotary Dryer. In this case, the study was conducted on the newly installed laboratory Tray Dryer. Various documentation requirements like User Requirement Specification, Factory Acceptance Test, Site Acceptance Test, Installation Qualification, Operational Qualification and Performance Qualification were carried out for the equipment. Calibration of measuring devices, the prepared granules were dried using the tray drier and noted the time required to dry the granules. Equipment qualification of newly installed laboratory Tray Dryer was performed meeting all the qualification parameters.

Effect of rotors on the parameters of hop drying in belt dryers

Effect of rotors on the parameters of hop drying in belt dryers

Modeling of thermodynamic properties of carrot product using ALO, GWO, and WOA algorithms under multi-stage semi-industrial continuous belt dryer

In this paper, multi-stage continuous belt (MSCB) dryer was used for carrot slices drying. Experiments were performed at three air speeds (1, 1.5, and 2 m/s) three belt linear velocities (2.5, 6.5, and 10.5 mm/s), and three air temperatures (40, 55, and 70 °C) in triplicate. Three intelligent systems including Ant-Lion-Optimizer (ALO), Grey-Wolf-Optimizer (GWO) and Whale-Optimization-Algorithm (WOA) models were developed to predict the thermodynamic properties of carrot slices including of effective moisture diffusivity (Deff) and specific energy consumption (SEC). The results revealed that Deff and SEC values were in the range of 1.77–2.90 × 10−9 m2/s and 169.77–551.19 MJ/kg, respectively. The models of ALO, GWO, and WOA were able to predict the value of Deff and SEC. The amounts of correlation coefficient ( $$R$$ ), root-mean-square error ( $${\text{RMSE}}$$ ), and mean absolute error ( $${\text{MAE}}$$ ) for ALO, GWO, and WOA models for predication Deff were obtained (0.9989, 7.81 × 10−12, and 1.50 × 10−12), (0.9993, 5.39 × 10−12, and 1.03 × 10−12) and (0.9994, 4.95 × 10−12, and 9.54 × 10−13), respectively. In addition, The amounts of $$R$$ , $${\text{RMSE}}$$ , and $${\text{MAE}}$$ for ALO, GWO, and WOA model for predication SEC were obtained (0.9983, 0.6700, and 0.1289), (0.9988, 0.5274, and 0.0715) and (0.9996, 0.2566, and 0.0060), respectively. Therefore, model of WOA can be used to easily and accurately predict Deff and SEC values.

Techno-economic evaluation of biomass drying in moving beds: The effect of drying kinetics on drying costs

Drying woody biomass holds the potential to improve the energy efficiency of certain processes, such as in CHP plants. Drying can also be a necessary unit process in several energy conversion processes (e.g. in biomass gasification). Belt dryers are typically used for drying when low temperature air (100–110 °C) is used. This article aims to produce new knowledge about the influence of the main design parameters on the drying costs of a low temperature belt dryer when three different materials (forest residue, bark, as well as sawdust and soot sludge mixture) are dried using it. The influence is analyzed by changing the following parameters: bed height, air temperature, air velocity and initial/final moisture contents of the material. The study aims to evaluate which of these parameters has an actual effect on drying costs. Results indicate that the lowest costs are achieved with the highest air temperature if the heat price is the same for every air temperature level. However, an optimal bed height depends on the material. Increasing the air velocity does not necessarily decrease the costs. In the sensitivity analysis, to factor in the influence of the temperature on the heat price, the price was changed for every drying air temperature (1, 5, 10 and 15 €/MWh). This analysis showed that the lowest drying costs are achieved by the lowest air temperature in all cases, thus indicating that the price of the heat has a remarkable influence on the economics of drying. Furthermore, the results support the use of low temperature heat sources in drying if they are clearly less expensive than higher temperature heat sources. However, if the prices for lower and higher air temperatures are of the same magnitude, the higher air temperatures are preferable. In general, this paper shows that it is important to pay attention to the main design parameters to optimize total drying costs. For example, if an overly low bed height is used in woodchips or bark drying, the total drying costs might be dozens of per cent higher than in the most economic case.

Utilization of Wet Forest Biomass as both the Feedstock and Electricity Source for an Integrated Biochar Production System

Abstract. A belt dryer and gasifier generator set were integrated into a biochar production plant to use process heat to dry biomass feedstock from forest residuals and to provide electric power to the plant using a side stream of dried biomass. Experiments were conducted to characterize the dryer throughput and drying capacity using process heat from a stack heat exchanger attached to the biochar machine flare. A matrix of tests was conducted at high and low flow rates for both the heat exchanger air flow rate (which varied the temperature and heat input to the dryer) and the residence time of feedstock in the belt dryer. Mean feedstock input moisture during dryer characterization was 45% and the mean moisture after exiting the dryer was 27%. The optimal test condition, providing the greatest water removal rate, was determined to have high air flow rate through the heat exchanger and short dryer residence time. This condition was used to demonstrate the integrated system for an 8-h production day. The integrated system dried incoming feedstock from 36% to 22% with a dryer throughput rate of 495 kg h-1 w.b. and an evaporation rate of 88.8 kg h-1, providing the necessary dry feedstock for the 20-kW gasifier generator set and the biochar machine, which produced 75 kg h-1 of biochar. This system required the operational effort of 0.92 labor hours per production hour. Results from this demonstration indicate that the integrated system provides key benefits in a biochar production operation including greater control of feedstock drying and the ability to operate without an external (non-biomass) source of fuel for electricity generation. Keywords: Biochar, Biomass, Biomass drying, Forest residuals, Gasification, Pyrolysis.

Parameters of the drying medium and dried hops in belt dryer

An important factor in hop growing is the process of drying. For this purpose belt dryers with follow-up conditioning are the most widespread but they are not ideal. In this respect, an analysis of the drying process was carried out in the belt dryer of Agrospol Velká Bystřice Co., Ltd. for the ‘Saaz’ hop variety. Drying parameters were monitored by means of fixed sensors, continuously sensing data loggers and samples taken for laboratory analysis (hop moisture, alpha and beta bitter acids, Hop Storage Index (HIS). The process of drying showed that hops are practically dry (10 ± 2.0% of moisture) already at the end of the second belt or possibly at the beginning of the third belt. It was also proved that hops are over-dried (moisture of 4 to 8%) and then they are adjusted by conditioning to the final moisture content of 8–10%. Excessive drying leads to cone disintegration, which makes any manipulation with hops for purposes of further processing difficult and results in greater losses of lupulin.

Computational fluid dynamic analysis of airflow in belt dryer: effects of conveyor position on airflow distribution

Belt dryers have been widely used in the drying process, a key process for quality control, of aquatic feed or pet food. An important criterion to measure the drying quality of a dryer is moisture uniformity, which directly affected by the distribution of airflow field. The airflow field is determined by several factors, including conveyor position and feed thickness. In this study, effects of conveyor positions on airflow distribution in three types of belt dryers are simulated and compared using computational fluid dynamic analysis. The simulation results show that the conveyor positions had significant effects on airflow rate in a two-layer belt dryer. Furthermore, the simulation provided three different airflow fields for three dryer models, and an optimal dryer model was selected for further analysis of air velocity on feed surface.