Fixed Bed Dryer Research Articles

Mathematical Modeling of Thin-Layer Drying Kinetics of Piper aduncum L. Leaves

As well as most agricultural products, some medicinal plants need to go through a drying process to ensure quality maintenance, however each product behaves differently. Therefore, the present study aimed to evaluate the drying kinetics of spiked pepper (Piper aduncum L.) leaves and determine their thermodynamic properties at different drying temperatures in laboratory scale. Leaves with initial moisture content of 78% w.b. (wet basis) were subjected to drying at temperatures of 40, 50, 60 and 70 ºC and air speed of 0.85 m s-1 in an experimental fixed bed dryer. The drying kinetics of the leaves was described by statistical fitting of mathematical models and determination of effective diffusion coefficient and activation energy. Enthalpy, entropy and Gibbs free energy were also evaluated for all drying conditions. It was concluded that, among the models evaluated, only Midilli and Valcam can be used to represent the drying of Piper aduncum leaves; the first for the two highest temperatures (60 and 70 ºC) and the second for 40 and 50 ºC. The activation energy was approximately 55.64 kJ mol-1, and the effective diffusion coefficient increase with the elevation of temperature. The same occurs with the values of Gibbs free energy, whereas the specific enthalpy and entropy decrease.

Classification of water forms in lignite and analysis of energy consumption on the drying processes by microwave and fixed bed

The water contained in lignite generally exists in various forms and the energy required to remove them from coal is also different. Thus, two different rank lignites with different water contents from Yunnan and Inner Mongolia provinces in China were selected for analyses of water forms and dewatering energy consumption. The forms of water contained in these two lignites were classified using differential scanning calorimetry (DSC). The results show that the water in the lignite mainly contains freezable water and non-freezable water, and further the freezable water can be divided into free water and freezable bound water. The water above 40% moisture content of dry coal weight in coal sample is free water; that between 27% and 40% of dry coal weight is freezable bound water; and that less than 27% of dry coal weight is non-freezable water, which is nearly independent of coal rank. Then, the microwave drying and the fixed bed drying devices were employed to dry these two lignites, and the dewatering energy consumption during drying processes were measured and calculated to compare the change of energy consumption for removing different types of water. The results show that 500–600 W microwave field is suitable for drying lignite because the water is difficult to be completely removed under 450 W and slight pyrolysis is prone to occur for lignite when the microwave power is higher than 700 W. The dewatering energy consumption of total moisture in microwave field under 500–600 W is 8.6–15.3 kJ/g H2O, and those of freezable water and non-freezable water are 8.7–12.5 kJ/g H2O and 8.5–21.8 kJ/g H2O respectively. In addition, the dewatering energy consumption of 50 g lignite in fixed bed drying at 120–160 °C is 1.3–3.6 kJ/g H2O. In order to take advantages of microwave and fixed bed, these two methods are coupled to dry lignite for reducing energy consumption and improving drying efficiency. For the best compromise between drying energy and drying time, it is recommended to use 600 W power microwave field to remove free water in lignite, and then to use the fixed bed to remove the remaining water at 160 °C. The water re-adsorption amount of the upgraded coal is about 1/3 lower than that of raw coal.

Primary energy demand and energy costs of fixed-bed drying using the example of chamomile flowers

Energy use efficiency in the drying of medicinal and aromatic plants is largely determined by weather conditions and process parameters. While the former are beyond control, the latter can be optimized. In order to achieve such optimization, different energy supply variants, based on typical operating conditions of batch-type grate drying in Thuringia, Germany, were analyzed. It was found that partial air recirculation and integration of heat pumps allow substantial savings in primary energy. However, under the constraint of German energy prices, significant savings in energy costs can only be achieved if combined heat and power generation systems are applied at the same time.

Convective drying of sawdust-sludge mixtures: The effect of the sludge matrix

Thermal drying is an important treatment method for sewage sludge. Sludges from Oupeye, Grosses Battes, and Embourg wastewater treatment plants (WWTPs) were chosen for study. The effect of the mass fraction of sawdust (10%, 20%, 30%, and 40%) on sludge drying in a fixed bed dryer was investigated. A universal testing machine was used to determine the stiffness of the samples. X-ray tomography was employed to measure the structural properties of sample beds including the volume, total exchange surface, and void fraction. Both a lower moisture content of sludge and a higher mass fraction of sawdust lead to higher stiffness. The initial void fraction, bed volume, and total exchange surface of the sample bed are all related to sludge matrix and sawdust addition; however, the maximum drying rate is proportional to the initial total exchange surface, which is independent of the sludge matrix. This proves that sawdust addition is a positive means of sludge drying because of the increase in the initial total exchange surface.

Modeling of intermittent convective drying of walnuts in single layer and its influence on deep bed drying simulation

This research concerns the convective intermittent drying of in-shell walnuts, as well as the comparison between intermittent and continuous regimes. The collected data from the continuous drying experiment served as the basis for the modeling of intermittent drying, where the kinetic semi-theoretical model was implemented. Mathematical model for the intermittent drying precedes the computer simulation and experimental procedure for a single layer. As the validity of the proposed model is confirmed, deep fixed bed drying simulation was included as well. Intermittent drying regimes with shorter tempering periods gave better results compared to the longer ones. Deep bed simulations showed that a fixed bed of walnuts should not be bigger than 15-20 cm.

Moisture content estimation during fixed bed drying process with design of experiment and ANFIS methods

Moisture content estimation during fixed bed drying process with design of experiment and ANFIS methods

Moisture content estimation during fixed bed drying process with design of experiment and ANFIS methods

In this study, a two stage methodology was applied to predict the exit coal moisture content during the drying process. The first stage included a design of experiment (DoE) study which made easy to determine the significance levels of drying parameters. At the end of the DoE stage, it was determined that the most significant parameter was bed height, and the least significant parameter was exit air relative humidity. The second stage included an adaptive neuro-fuzzy inference system (ANFIS) method which was applied to estimate the exit coal moisture content at any time. The experimental studies were conducted with different levels of the parameters (air temperature, air velocity, bed height, particle size, and air relative humidity). At the end of the second stage, the applicability of the ANFIS in the estimation of the exit coal moisture content was showed with satisfying results. R2 value was increased from 0.465 to 0.842. [Received: March 28, 2017; Accepted: November 3, 2017]

Construction and Application of Fixed Bed, Fluidized Bed and Fluidized Drying Comprehensive Experiment

In order to establish a research-based experimental platform for students to fully mobilize initiative and learning creativity, it is necessary to establish design and exploratory experiments to highlight independent exploration and innovation. Through experimental device improvement and material screening, the three parts of fluidization curve measurement, fixed bed drying and fluidized bed drying of spherical molecular sieve are integrated into an organic entirety. Especially, the traditional basic experiment is promoted to a design and research experimental project. Results show that students experimental design ability and comprehensive quality have been improved, and it also stimulated their learning interest, cultivated the creative ability.

Barley: Effect of airflow reversal on fixed bed drying

This study evaluated drying barley in a fixed bed dryer either reversing the airflow every 10 min or with a conventional airflow input, with no reversal, and investigated the moisture distribution along the fixed bed and the effect of temperature and initial moisture content on the drying rates. Drying experiments were carried out under two air temperatures (40 °C and 50 °C), one air velocity (4.0 m/s), and three initial moisture contents (25%, 20% and 13.5% in a wet basis). The drying rates varied through the fixed bed height. As expected, for a high initial moisture content of grains, the process heterogeneity was higher than with grains at a low initial moisture content. At 50 °C, drying with an airflow reversal presented a better process homogeneity, and conventional drying led to improved energy performance. These results can be attributed to the shorter time required to achieve moisture content around 12% at 50 °C.

Heat and mass transfer of fruit residues in a fixed bed dryer: Modeling and product quality

This study analyzed the simultaneous heat and mass transfer between acerola residues and the air in a fixed-bed dryer with a thick layer. We used a two-phase model with a set of adequate constitutive equations, which was numerically solved using the method of lines. We compared simulation results with the experimental data obtained in a pilot unit at different positions throughout the bed. The simulated results show a good agreement with experimental data. The proposed model was also able to predict the heterogeneity of the process. The drying conditions in which the content of the main bioactive compounds (ascorbic acid, phenolics, and flavonoids) were in high levels were identified.

Effective diffusivity in yacon potato cylinders during drying

ABSTRACT The aim of this study was to obtain the effective diffusivity of yacon potato in fixed-bed dryer at different temperatures (50, 60 and 70 oC) and drying air velocities (1.0, 1.5 and 2.0 m s-1). Non-linear regression analysis was performed by the Quasi-Newton method using the program Statistica 7.0, where the parameters of the models were estimated as a function of the drying air temperature. Approximation of Diffusion, Two Terms, Henderson & Pabis, and Page models fitted well the experimental data. Drying air temperature and speed influenced the drying time of the samples. The effective diffusivity increased with increasing temperature, ranging from 1.18 x 10-9 to 2.15 x 10-9 m2 s-1.

Drying kinetics of blackberry leaves

ABSTRACT Blackberry leaves have some pharmacological properties and one of the most widespread and studied uses is to relieve symptoms of the climacteric and other symptoms during the premenstrual period. Thus, drying becomes important for the conservation and storage of the product until its use or processing. The present study aimed to evaluate the drying kinetics of blackberry leaves, as well as to determine the effective diffusion coefficient and the activation energy during the drying process. Blackberry leaves were dried in an experimental fixed-bed dryer under four controlled temperature conditions (40, 50, 60 and 70 °C) and two drying air speeds (0.4 and 0.8 m s-1). With the experimental data of moisture ratio, eight mathematical models were fitted to represent the process of thin-layer drying of agricultural products. Based on the obtained results, it was found that the Midilli model represented best the phenomenon of drying of blackberry leaves. The increase in temperature and air speed reduced the drying time of blackberry leaves and increased the values of the effective diffusion coefficient. This relation can be described by the Arrhenius equation, which has an activation energy for the liquid diffusion during drying of 65.94 and 66.08 kJ mol-1, for drying air speeds of 0.4 and 0.8 m s-1, respectively.

Fragmentation of a Turkish Low Rank Coal During Fixed-bed Evaporative Drying Process

ABSTRACT In the present study, a new approach was utilized to investigate the fragmentation of low rank coal during the thermal drying process. Drying experiments were conducted at different drying air temperatures (70, 100, 110 and 130°C), drying air velocities (0.4 and 0.7 m/s), bed heights (100, 150 and 250 mm) and particle fractions (20–50, 28–50 and 35–50 mm) for a Turkish lignite (Konya-Ilgın lignite) in a fixed-bed dryer. Konya-Ilgın lignite was used in the heating sector. Particle sizes used in these experiments were coarser than the studies in the literature due to legal constraints. The effects of drying parameters on coal fragmentation were evaluated. The fragmentation increased as the drying air temperature and the velocity increased, and it decreased as the bed height and the particle size increased. Results of this study may be used in the design of a suitable dryer for low rank coal.

Influence of Drying in Hyptis pectinata Essential Oil

The present study assessed the effects of drying at different temperatures (35, 45 and 55 °C) and air velocities (1 and 2 m s-1) on the content and chemical characteristics of Hyptis pectinata essential oil. Drying was conducted in a fixed-bed dryer, and the temperatures and air velocities were controlled and recorded by an automated system. A 350±0.12 g quantity of fresh leaves was used for each of the four repetitions in each dryer. From the material obtained after drying, 60 g of each repetition was used to extract essential oil by the hydrodistillation method. Dichloromethane was used as the solvent, and anhydrous sodium sulfate was used as the desiccating agent. Gas chromatography in the forms of GC-MS and GC-FID were used for the chemical characterization of the essential oil compounds. Decreasing drying times and decreasing concentrations of essential oils were observed with increasing temperatures. A GC-MS analysis of the essential oil from H. pectinata leaves led to the identification of 19 compounds. A sesquiterpene called caryophyllene oxide was the most abundant compound under all drying conditions, with the highest concentration at a temperature of 55 °C, ranging from approximately 42 to 53%.

<b>Validation of an experimental prototype of thick-layer fixed bed dryer and determination of the quality of the dried soybean grains

The aim of this study was to validate an experimental prototype dryer with a thick-layer fixed bed and determine the quality of the dried soybean grains. The drying system was designed as a chamber with four independent drying cells, with a capacity of 164 kilograms, an air ventilation system and heating with electric heaters. This prototype was used for soybeans with an initial water content of 17% (w.b.). The samples were collected from the top, middle and bottom of the four cells to evaluate the quality of the grains. The experimental design was completely randomized factorial (3 x 4 x 3), with three temperatures settings for the drying air (30, 40, and 50°C), four drying cells and three evaluation positions (upper, middle and lower). The grains did not undergo quality changes as a function of the drying cells. In the upper part of the drying cells, there was a reduction in the specific grain mass (851 kg m-³), an increase in electrical conductivity (140.02 μS cm-1 g-1), reduction in germination (63%) and oil content (7%) compared with the middle and lower dryer positions. The experimental prototype of the fixed bed dryer allowed a uniform distribution of the heated air in the drying cells, which was effective in the drying operation and in maintaining the quality of the soybean grains.

Kinetics of drying inorganic spheres: Simultaneous modeling of moisture and temperature during the constant and falling rate periods

ABSTRACTThe kinetics of the dehydration of four sizes of spherical inorganic materials was studied experimentally with warm air using a fixed-bed dryer at laboratory scale. Following the evaluation of the effect of bed thickness, air mass rate, and air temperature on drying kinetics, a kinetic model consisting of two equations was proposed. The main novelty of this study resides in the possibility of utilizing a new model for simultaneous heat and mass transfer in an efficient manner for practical applications and appropriate system optimization, especially during the falling rate period.

Effect of the operating conditions in the drying of anhydrous lactose in a square fixed bed dryer

Effect of the operating conditions in the drying of anhydrous lactose in a square fixed bed dryer

Temperature profile during the drying of anhydrous lactose in a square fixed bed dryer

Temperature profile during the drying of anhydrous lactose in a square fixed bed dryer

Energy cost of seed drying

In this work, the energy costs of drying corn, rice and wheat seeds between 3 drying options were compared. They consisted of 1) two-stage drying by using fluidised bed dryer (FBD) in the 1st stage and in-store dryer (ISD) in the 2nd stage, 2) single-stage drying by fixed bed dryer (FXD) and 3) two-stage drying by using FXD in the 1st stage and ISD in the 2nd stage. The drying conditions selected for comparison were proved to be safe for seed viability by the previous studies. The results showed that the drying options 2 and 3 consumed less energy than option 1. However, the benefits from lower energy cost must be weighed against some advantages of using FBD. Furthermore, it appeared that running the burners of FXD and ISD for warming up the ambient air during humid weather condition could shorten drying time significantly with a little higher energy cost.

Energy cost of seed drying

In this work, the energy costs of drying corn, rice and wheat seeds between 3 drying options were compared. They consisted of 1) two-stage drying by using fluidised beddrye (FBD) in the 1ststage and in-store dryer (ISD) in the 2ndstage, 2) single-stage drying by fixed bed dryer (FXD) and 3) two-stage drying by using FXD in the 1ststage and ISD in the 2ndstage. The drying conditions selected for comparison were proved to be safe for seed viability by the previous studies. The results showed that the drying options 2 and 3 consumed less energy than option 1. However, the benefits from lower energy cost must be weighed against some advantages of using FBD. Furthermore,it appeared that running the burners of FXD and ISD for warming up the ambient air during humid weather condition could shorten drying time significantly with a little higher energy cost.