DRYTNG OF PEPPER SEEDS USING A COMBINED MICROWAVE/FLUIDIZED BED DRYER

Abstract

The drying rates curves in terms of moisture content versus elapsed drying time for white pepper seeds were obtained experimentally using a fluidized bed and a combined microwave/fluidized bed. The combined microwave/fluidized bed employs a microwave field to assist convective drying. For both procedures, the drying rates were found to be dependent on the inlet air temperature and velocity. Significantly improved drying rates were achieved utilized a combined microwave/fluidized bed drying compared with a conventional fluidized bed.     

Combined Microwave/Fluidized Bed Drying of Fresh Peppercorns

Abstract

A fluidized bed dryer (FBD) and a combined microwave/fluidized bed dryer (CMFD) are used to dry the fresh ripe peppercorns. The average moisture content vs. elapsed drying time, and drying rate vs. average moisture content are experimentally investigated. It is found that the microwave field from the CMFD can increase the potential of the conventional fluidized bed drying. The drying rates of both dryers are dependent on the inlet air temperature and velocity. For the CMFD, the effects of the air velocity on the drying rate are found to be opposite to our previous results tested with white pepper seeds i.e., the drying rates of the fresh ripe peppercorns decreased with increasing air velocity. By using a CMFD, the drying time required to reach the desired moisture content can be reduced to 80–90% of the drying time required for a FBD at the same drying air temperature and velocity. The color of the product dried by a CMFD is also attractive: it becomes flaming yellow, instead of black as obtained from a FBD. The physical structure of the peppercorn, before and after the drying process is also investigated by a metallurgical macroscope and an image analyzer. Different from drying by a FBD, the external form and matter of the white pepper seed are still maintained, even after passing through the drying process.     

Combined Microwave/Fluidized Bed Drying of Fresh Peppercorns

A fluidized bed dryer (FBD) and a combined microwave/fluidized bed dryer (CMFD) are used to dry the fresh ripe peppercorns. The average moisture content vs. elapsed drying time, and drying rate vs. average moisture content are experimentally investigated. It is found that the microwave field from the CMFD can increase the potential of the conventional fluidized bed drying. The drying rates of both dryers are dependent on the inlet air temperature and velocity. For the CMFD, the effects of the air velocity on the drying rate are found to be opposite to our previous results tested with white pepper seeds i.e., the drying rates of the fresh ripe peppercorns decreased with increasing air velocity. By using a CMFD, the drying time required to reach the desired moisture content can be reduced to 80-90% of the drying time required for a FBD at the same drying air temperature and velocity. The color of the product dried by a CMFD is also attractive: it becomes flaming yellow, instead of black as obtained from a FBD. The physical structure of the peppercorn, before and after the drying process is also investigated by a metallurgical macroscope and an image analyzer. Different from drying by a FBD, the external form and matter of the white pepper seed are still maintained, even after passing through the drying process.     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

ABSTRACT

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

Evaluation of the air-borne ultrasound on fluidized bed drying of shelled corn: Effectiveness,grain quality,and energy consumption

The objective of the study was to investigate the influence of high power ultrasound on a laboratory-scale fluidized bed shelled corn dryer. The drying time, moisture content variation, specific energy consumption, and quality parameters including ultimate compressive strength, toughness, shrinkage and color of corn kernels were investigated. Furthermore, artificial neural network (ANN) simulation models were developed for predicting the drying variables. Machine vision techniques were used to determine color and shrinkage as qualitative indices. Results showed that the lower frequencies had better penetrations at lower temperatures and cause a significant reduction in drying time. In addition, the ultrasound application led to reduction of ultimate compressive strength and toughness of the dried samples although ultrasound has nonthermal character as the subsidiary factor, it plays an important role in shrinkage and color specification. Based on error analysis results, the prediction capability of ANN model is found to be reasonable for the developed models. Application of ultrasound significantly decreased the specific energy consumption of drying process at the optimal drying condition.     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

EFFECTS OF DRYING, TEMPERING AND AMBIENT AIR VENTILATION ON QUALITY AND MOISTURE REDUCTION OF CORN

The objective of this work is to study systematically how to decrease corn moisture content using processes consisting of fluidized bed drying, tempering and ambient air ventilation. Effects of drying, tempering and ventilation on moisture reduction and quality of dried corn in terms of stress crack, breakage and color are experimentally investigated. Experimental results show that stress crack depends on final moisture content of com. Tempering is found useful for increasing the quality of dried com after fluidized bed drying. The optimum tempering time is 40 minutes. Among the ambient air velocity ranging from 0.075 to 0.375 m/s, the appropriate velocity is 0.15 m/s. Final moisture content of com after ambient air ventilation is about 13.0 - 14.5 %(w.b.) with breakage and stress crack lower than 2% and 5% by wt., respectively. Slight change of color of dried corn is observed.     

Simulation and Validation of Microwave-Assisted Fluidized Bed Drying of Soybeans

A general mathematical model of heat and mass transfer was developed to simulate the microwave-assisted fluidized bed drying of bulk grain. The model was solved using the well-known Runge-Kutta-Gill method. The model is capable of predicting the moisture content of soybean as well as the drying air parameters (i.e., drying air temperature and moisture content) during drying. The values of mean relative deviation (MRD) were less than 8 and 10% for prediction of grain moisture content and outlet air parameters, respectively, which reflects an acceptable accuracy. In comparison with conventional fluidized bed drying of soybean, microwave-assisted fluidized bed drying led to 83.39–98.07% savings in drying time and 82.07–95.22% savings in specific energy consumption when reducing soybean moisture content from 18.32 to 12% (db).     

DRYING CHARACTERISTICS OF CORN IN FLUIDIZED BED DRYER

A batch fluidized bed dryer was carried out for corn drying. Drying characteristics of corn were investigated The experimental results indicated that moisture transfer inside a corn kernel was controlled by internal diffusion by the following conditions : inlet hot air temperatures of 120 - 200 °C, superficial air velocities of 2.2- 4 m/s, bed depths of 4 - 12 cm, fraction of air recycled of 0.5 -0.9 and initial moisture content of corn of 43 % dry-basis. The Wang and Sing equation could describe in accordance with the results. Inlet hot air temperature and specific air flow rate were independent variables for drying constant model in the Wang and Singh equation.     

DRYING CHARACTERISTICS OF CORN IN FLUIDIZED BED DRYER

ABSTRACT

A batch fluidized bed dryer was carried out for corn drying. Drying characteristics of corn were investigated The experimental results indicated that moisture transfer inside a corn kernel was controlled by internal diffusion by the following conditions : inlet hot air temperatures of 120 - 200 °C, superficial air velocities of 2.2- 4 m/s, bed depths of 4 - 12 cm, fraction of air recycled of 0.5 -0.9 and initial moisture content of corn of 43 % dry-basis. The Wang and Sing equation could describe in accordance with the results. Inlet hot air temperature and specific air flow rate were independent variables for drying constant model in the Wang and Singh equation.     

循环流化床中C类颗粒连续干燥的研究

循环流化床(CFB)作为一种新兴反应器,其结构简单、气固接触效率高、处理量大,成为气固二相干燥应用研究的新方向.文中在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为C类颗粒,进行了连续干燥.实验初步研究了进料速率、进风温度及气速等操作参数对淀粉平均停留...     

Effect of Fluidized Bed Drying Temperature on Various Quality Attributes of Paddy

Abstract

As reported by many researchers, it was found that fluidized bed paddy drying using high drying air temperatures of over 100°C affected the head rice yield and whiteness of dried rice. However, only a few studies on fluidized bed paddy drying with drying air temperatures below 100°C were so far reported. The main objective of this work was therefore to study the effect of fluidized bed drying air temperature on various quality parameters of Suphanburi 1 and Pathumthani 1 Indica rice. Paddy was dried from the initial moisture contents of 25.0, 28.8, and 32.5% dry basis to 22.5 ± 1.2% dry basis using inlet drying air temperatures between 40 and 150°C at 10°C/step. After fluidized bed drying, paddy was tempered and followed by ambient air aeration until its final moisture content was reduced to 16.3 ± 0.5% dry basis. The results showed that the head rice yield of Suphanburi 1 was significantly related to the inlet drying temperature and initial moisture content whilst there was no significant relationship between the head rice yield, drying temperature and initial moisture content for Pathumthani 1. The whiteness of the two rice varieties was slightly decreased with increase in drying air temperature and initial moisture content. It was also found that the hardness of both cooked rice varieties exhibited insignificant difference (p < 0.05) comparing to rewetted rice, which was gently dried by ambient air aeration in thin layer. The thermal analysis by DSC also showed that partial gelatinization occurred during drying at higher temperatures. Using inlet drying air temperatures in the range of 40–150°C therefore did not affected the quality of cooked rice and paddy. The milling quality of paddy was also well maintained.     

ENERGY CONSUMED IN LOW TEMPERATURE CORN DRYING

Data collected on corn drying bins employing unheated air and bins utilizing electric heat for small air temperature rises indicate better energy efficiency when the energy is used to provide more air as compared to using a portion of the energy to increase the temperature of a smaller quantity of air. Unheated air drying of shelled corn was accomplished with an average of about 6.0 kWh per metric ton per percentage point of moisture removed as compared to an average of about 12.0 kWh/t- % when electric heaters were used to increase the air temperature. Final corn moisture content was approximately the same for both methods since the unheated air drying systems, with more air per unit of grain, completed drying earlier. Early fall weather, as contrasted to late fall, is generally more favorable to drying and the existence of lower average daily relative humidities permit the drying of corn to 15% or less, wet basis, without the addition of heat.     

Drying of Turnip Seeds with Microwaves in Fixed and Pulsed Fluidized Beds

This article presents experimental and modeled drying kinetics of turnip seeds as a function of the type of air-particle contact (fixed bed, pulsed fluidized bed), humidity of the air, and three levels of microwave irradiation. The effects of those factors on the drying time required to reach a moisture content of 0.1 kg/kg d.b. were determined with an experimental design of 12 experiments by using the software Statgraphics. It was found that in drying, a significant factor was the application of microwaves to a pulsed fluidized bed. The effect of the humidity of the air only became noticed when the moisture contents of the seeds was below 0.2 kg/kg d.b. The simplified variable diffusivity model (SVDM) gave the least deviations for the experimental data. The effective diffusivity values determined in this work are similar to those informed in the literature for experiments without microwave application. The application of microwaves in combination with pulsed fluidization of the turnip seeds resulted in a fourfold increase of the effective diffusivity.     

Drying of Turnip Seeds with Microwaves in Fixed and Pulsed Fluidized Beds

This article presents experimental and modeled drying kinetics of turnip seeds as a function of the type of air-particle contact (fixed bed, pulsed fluidized bed), humidity of the air, and three levels of microwave irradiation. The effects of those factors on the drying time required to reach a moisture content of 0.1 kg/kg d.b. were determined with an experimental design of 12 experiments by using the software Statgraphics. It was found that in drying, a significant factor was the application of microwaves to a pulsed fluidized bed. The effect of the humidity of the air only became noticed when the moisture contents of the seeds was below 0.2 kg/kg d.b. The simplified variable diffusivity model (SVDM) gave the least deviations for the experimental data. The effective diffusivity values determined in this work are similar to those informed in the literature for experiments without microwave application. The application of microwaves in combination with pulsed fluidization of the turnip seeds resulted in a fourfold increase of the effective diffusivity.     

Drying Behavior of Carrots Dried in a Spout–Fluidized Bed Dryer

The effect of water blanching treatment and the inlet air temperature on drying kinetics as well as the quality attributes of carrot cubes dried in a spout–fluidized bed dryer at 60, 70, 80, and 90°C were analyzed. The material shrinkage and the rehydration potential were calculated to assess the changes in quality of dried carrots. It was found that the value of the air velocity during the drying of carrot cubes in a spout–fluidized bed dryer should be related to the moisture content of the carrot particles. A high value of air velocity at the beginning of the drying cycle and a lower value for the later stages were also required. The linear equation was correlated to the data of shrinkage of raw and blanched carrots. Blanching significantly influenced the coefficients in the shrinkage model derived for drying of carrot cubes in a spout–fluidized bed dryer, while drying temperature did not influence the shrinkage of carrot particles. The intensity of heat and mass transfer during spout–fluidized drying of carrot cubes was dependent on the drying temperature. A correlation was developed to calculate the values of effective moisture diffusivity of dried carrot cubes as a function of the moisture content and temperature of the material. It was observed that for any given time of rehydration, both the moisture content and the rehydration ratio calculated for samples dried at 60°C were higher than for samples dried at temperatures of 60, 70, 80, and 90°C.     

AMARANTH GRAIN DRYING IN A FLUIDIZED BED

An empirical equation as a function of drying time and temperature was developed to calculate the moisture ratio required Tor balch fluidized bed dryers design for amaranth grain drying

The relative deviations of the moisture ratio values calculated with the proposed equation with regard to the experimental ones ranged between 0.014 and 0.095 for a drying air temperature between 60 and 100 ° C, and a grain initial moisture content between 23.5 and 16.6 % wb.     

AMARANTH GRAIN DRYING IN A FLUIDIZED BED

ABSTRACT

An empirical equation as a function of drying time and temperature was developed to calculate the moisture ratio required Tor balch fluidized bed dryers design for amaranth grain drying

The relative deviations of the moisture ratio values calculated with the proposed equation with regard to the experimental ones ranged between 0.014 and 0.095 for a drying air temperature between 60 and 100 ° C, and a grain initial moisture content between 23.5 and 16.6 % wb.     

Analysis of the drying process of a biopolymer (poly-hydroxybutyrate) in rotating-pulsed fluidized bed

A rotating-pulsed fluidized bed (RPFB) dryer was employed to conduct the drying of poly-hydroxybutyrate (PHB) cohesive granules. Along the experiments, it was possible to identify, visually, 3 different dynamic regimes that were related with the temperature profile, the drying kinetics and the fluid dynamic behavior. The drying kinetics of PHB showed a short constant drying rate period followed by a decreasing drying rate period. The constant drying rate (N_c) and final moisture content (dry basis) were related to the rotation frequency (responsible for the pulsation effect), temperature and velocity of the inlet air. Furthermore, measurements of molecular mass (gel permeation chromatography analysis) and Carr Index (flowability test) on PHB samples were done before and after the drying. The RPFB dryer showed to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamic behavior that provided uniform drying of the solid. The best conditions of drying were identified at 7 Hz of rotation frequency, 90 °C and 0.55 m/s of inlet air temperature and velocity. At these conditions the dried PHB reached final moisture content of 0.56% (wet basis) after 2 h of drying.     

Drying of water treatment process sludge in a fluidized bed dryer

The drying characteristics of water treatment process (WTP) sludge were investigated with a fluidized bed. The equilibrium moisture ratio of WTP sludge increased with relative humidity and decreased with temperature of drying air. However, equilibrium moisture ratio of WTP sludge was more sensitively dependent on relative humidity than temperature of drying air. When the sludge was dried in a batch fluidized bed, the drying rate of sludge decreased as the moisture ratio of sludge in the bed decreased. The periods of constant drying rates were apparently not observed on the drying rate curves. In addition, the maximum drying rates were increased with bed temperature and superficial air velocity. As the fluidized bed was operated continuously, the degree of drying of WTP sludge increased with bed temperature but was weakly dependent on superficial air velocity. However, the drying efficiency was decreased with bed temperature and relatively insensitive to superficial air velocity and increased with feed rate of sludge.