Corn,Rice, and Wheat Seed Drying by Two-Stage Concept

Corn, rice, and wheat seeds with an initial moisture content (IMC) of 20–25% wb were dried to moisture content below 18% wb at 40–80°C in a fluidized bed dryer (FBD) and spouted bed dryer (SBD) and the seeds with IMC 18% wb were dried to below 14% wb at air temperatures 18–30°C and relative humidity 60–70% by an in-store dryer (ISD). As a result, it appears that a two-stage drying concept is feasible in drying high-moisture-content seeds due to the high germination rate of dried seeds. Nonetheless, the drying temperature must be carefully selected. A drying temperature of 40°C was clearly safe for all samples, whereas more than 90% of wheat seeds still germinated after drying at 60°C in FBD. Furthermore, drying seeds with IMC 18% wb by ISD was safe under specified drying conditions.     

ANALYSIS OF MECHANICALLY AGITATED FLUID-PARTICLE CONTACT DRYERS

Incorporation of agitation to spouted and fluidized bed dryer result in significant increases in the drying capacity (Q_s), although product retention persist, which is reduced by increasing the air flow. The physical phenomena occurring in these dryers with several liquid substrates was analyzed and the residence time distributions (RTD) were obtained by the use of dye tracers. The residence time (τ) was found to be a function of the rate of agitation (n) and reaches a minimum at n = n_opt, which was characteristic for each type of substrate, and where maxima also appeared for the drying capacity (Q_s = Q_{s max}) and the heat transfer coefficient (Nu_p = Nu_{p max}). The RTD can be modeled by series of consecutive dryers and a modified Vanderschuren and Delvosalle model can be employed to calculated moisture of the dry product.     

Analysis of the Drying Kinetics of Brachiaria brizantha (Hochst. Stapf) Grass Seeds at Different Drying Modes

Forage grass seeds have a high economical importance in the Brazilian bovine cattle breeding and seed drying is a fundamental stage of processing to guarantee their stability and allow their storage for long periods. In this context, the objective of this work was to develop a pilot-scale belt dryer, which operates also as a fixed and fluidized bed. Brachiaria brizantha seeds dehydration was analyzed under different air velocities and temperatures. Experimental data of moisture content variation along the drying time was successfully fit to a one-term exponential model. The experimental drying rate points were calculated by approximating the derivatives to finite differences. Its behavior was accomplished fitting curves of the drying rate versus water content and time. Finally, fissure, germination, and vigor rates were analyzed as a function of the drying conditions so that the experimental conditions combine the best process efficiency with the best physiological quality maintenance.     

Analysis of the Drying Kinetics of Brachiaria brizantha (Hochst. Stapf) Grass Seeds at Different Drying Modes

Forage grass seeds have a high economical importance in the Brazilian bovine cattle breeding and seed drying is a fundamental stage of processing to guarantee their stability and allow their storage for long periods. In this context, the objective of this work was to develop a pilot-scale belt dryer, which operates also as a fixed and fluidized bed. Brachiaria brizantha seeds dehydration was analyzed under different air velocities and temperatures. Experimental data of moisture content variation along the drying time was successfully fit to a one-term exponential model. The experimental drying rate points were calculated by approximating the derivatives to finite differences. Its behavior was accomplished fitting curves of the drying rate versus water content and time. Finally, fissure, germination, and vigor rates were analyzed as a function of the drying conditions so that the experimental conditions combine the best process efficiency with the best physiological quality maintenance.     

ANALYSIS OF MECHANICALLY AGITATED FLUID-PARTICLE CONTACT DRYERS

Incorporation of agitation to spouted and fluidized bed dryer result in significant increases in the drying capacity (Q_s ), although product retention persist, which is reduced by increasing the air flow. The physical phenomena occurring in these dryers with several liquid substrates was analyzed and the residence time distributions (RTD) were obtained by the use of dye tracers. The residence time (τ) was found to be a function of the rate of agitation (n) and reaches a minimum at n = n _opt, which was characteristic for each type of substrate, and where maxima also appeared for the drying capacity (Q_s = Q _{s max}) and the heat transfer coefficient (Nu _p = Nu _{p max}). The RTD can be modeled by series of consecutive dryers and a modified Vanderschuren and Delvosalle model can be employed to calculated moisture of the dry product.     

Analysis of Seed Quality and Drying Performance of a Multistage Countercurrent Sliding‐Bed Dryer

The effect exerted by the number of stages (one, two, three, and four stages) of a countercurrent sliding‐bed dryer on the quality indices and drying performance of soybean seeds is evaluated by simulation. The two‐phase model is used to describe heat and mass transfer between air and soybean seeds. The constitutive model equations are taken from specific studies. The seed quality is determined based on germination and nonfissured seed indices obtained by empirical functions reported in the literature. The simulated results show that dividing the air mass flux and air velocity can produce a lower seed outlet temperature which may yield higher quality indices and better drying performance in multistage configurations.     

A Comparative Study on Exergetic Performance Assessment for Drying of Broccoli Florets in Three Different Drying Systems

This article deals with the exergy analysis and evaluation of broccoli in three different drying systems. The effects of drying air temperature on the exergy destruction, exergy efficiency, and exergetic improvement potential of the drying process were investigated. The exergy destruction rate for the drying chamber increased with the rise in the drying air temperature at 1.5 m/s, both in the tray and the heat pump dryer. The highest exergy efficiency value was obtained as 90.86% in the fluid bed dryer in comparison to the other two drying systems and the improvement potential rate was the highest in the heat pump dryer during drying of broccoli at the drying air temperature of 45°C and the drying air velocity of 1.0 m/s.     

Modelling Diffusion-Limited Drying Behaviour in a Batch Fluidized Bed Dryer

Fluidized bed dryers are often used to extract water from granular materials. When the drying process is mainly limited by the resistance against water transport inside the particle the drying behaviour is said to be diffusion-limited. In the literature there are several models that predict this drying process with very diverging results. In this study a model is set up to arrive at a better prediction for this drying process. The heat and mass transfer in the granular material and the drying air is described. The resulting equations are solved numerically. The model must be extended to incorporate the heat capacity of the dryer.     

Modelling Diffusion-Limited Drying Behaviour in a Batch Fluidized Bed Dryer

ABSTRACT

Fluidized bed dryers are often used to extract water from granular materials. When the drying process is mainly limited by the resistance against water transport inside the particle the drying behaviour is said to be diffusion-limited. In the literature there are several models that predict this drying process with very diverging results. In this study a model is set up to arrive at a better prediction for this drying process. The heat and mass transfer in the granular material and the drying air is described. The resulting equations are solved numerically. The model must be extended to incorporate the heat capacity of the dryer.     

Overall Energy Requisite and Quality Feature of Industrial Paddy Drying

Energy consumption and rice quality are the main concerns of millers and must be assessed to ascertain suitable industrial drying strategy. In this article, industrial paddy drying methods as usually practiced in the BERNAS paddy drying complexes of Malaysia have been evaluated. The analysis showed that the specific electrical and thermal energy consumption varied between 16.19 kWh to 22.07 kWh and 787.22 MJ to 1015.32 MJ, respectively, in single-stage paddy drying (SSPD) using an inclined bed dryer (IBD) to dry each tonne of freshly harvested paddy with average moisture content of 23.35 ± 0.86% wb. On the other hand, the energy consumptions for two-stage paddy drying (TSPD) with a fluidized bed dryer (FBD) followed by IBD were 21.37 kWh/t to 30.69 kWh/t and 666.81 MJ/t to 1083.42 MJ/t, respectively. SSPD at 35–39°C and TSPD using FBD at 120°C as the first stage, followed by IBD as the second stage at lower temperature of 35–39°C yielded 2–3.6% higher head rice yield than paddy-dried by a single stage with IBD using comparatively higher temperature of 40–44°C. Therefore, IBD is recommended to be operated using a temperature of 35–39°C both in single-stage drying and second-stage drying of paddy after fluidized bed drying to obtain quality rice.     

Simulation Model for the Model-Based Control of a Biofuel Dryer at an Industrial Combined Heat and Power Plant

The primary aim of this article is to present a simulation model for a bark dryer integrated into a combined heat and power plant. The same model can be used for the model-based control of the dryer. The secondary aim is to evaluate how useful the control is from an economic point of view. Results show that the final fuel moisture content can be stabilised by controlling the drying temperature(s). On the other hand, the deviation in final bark moisture decreases even when the dryer has no control at all. Net incomes resulting from drying increase in most cases compared to dryers without control. The need for control cannot be justified on economic grounds.     

Simulation Model for the Model-Based Control of a Biofuel Dryer at an Industrial Combined Heat and Power Plant

The primary aim of this article is to present a simulation model for a bark dryer integrated into a combined heat and power plant. The same model can be used for the model-based control of the dryer. The secondary aim is to evaluate how useful the control is from an economic point of view. Results show that the final fuel moisture content can be stabilised by controlling the drying temperature(s). On the other hand, the deviation in final bark moisture decreases even when the dryer has no control at all. Net incomes resulting from drying increase in most cases compared to dryers without control. The need for control cannot be justified on economic grounds.     

Improvement in the Efficiency and Capacity of Chopped Spring Onion Drying

ABSTRACT

Appropriate strategy for drying chopped spring onion with a batchwise flat bed was investigated. Both experimental and simulated results such as product quality, drying capacity and energy consumption were taken into consideration. For simulation work, equations of drying parameters such as specific heat, equilibrium moisture content and thin layer drying were first developed from the lab-scale experimental results. Then a mathematical model including shrinkage for a batchwix flat bed drying was developed. The model was lested with the results obtained from a food processing plant with an acceptable accuracy. Appropriate drying strategy war then investigated. The approximate conclusion was that the drying should be devided into 3 stages. In the 1^st stage, drying air temperature was 80°C, specific air flow rate was 33.9 m³/min -kg dry matter and drying time was 0.5 h. In the 2nd stage, drying air temperature and drying time were kept unchanged but specific air flow rate was decreased to 13.5 m³/min - kg dry matter. In the final stage, drying air temperature was decreased to 67°C, specific air flow rate was also decreased to 6.8 m³/min - kg dry matter and drying time was approximately 1.7 h. Following the suggested strategy, specific primary energy cornsumption was 6.2 MJ/kg H₂O, drying time was 2.7 h and product quality was maintained. It was proven that energy consumption was approximalcly 70% of that of the present practice in the plant.     

Monitoring the Moisture Content of Solids in Fluidized Bed Dryers by Analysis of Pressure Fluctuations

Perusing the hydrodynamic changes of fluidized bed dryer is important for online monitoring of the drying process. The present study investigates the drying process of wetted rice particles. Air at ambient conditions with superficial velocity of 1 ms^?1 was used for drying. Absolute pressure fluctuations were measured to monitor the fluidization status of the dryer. Fast Fourier transform, discrete wavelet transform, and statistical analyses of detailed signals were employed to evaluate the fluidization quality in the bubbling regime. Pressure fluctuations were decomposed by the wavelet transform to 10 subsignals. It was shown that the energy of subsignals is more sensitive to moisture changes than other studied parameters. Specifically, the energy of the subsignals corresponding to the macrostructure (large bubbles) can be used for determining the moisture content of the solids during the drying process. This method can be used for online monitoring of drying processes in a wide range of processing conditions in fluidized beds.     

SLURRY DRYING IN GAS-PARTICLE CONTACTORS: FLUID-DYNAMICS AND CAPACITY ANALYSIS

The fluid-dynamic characteristics and evaporation capacities of several substrates (pure water, a mixture of water and carbohydrates, and apple pulps with maltodextrines) for conical spouted bed, fluidized bed and pneumatic dryers was compared.

For fluidized and spouted beds, the presence of fluids increased the fluid-dynamics parameters over the values when only inert particles were present in the beds. In both cases it was proposed correlations to predict those effects. In the spouted bed drier, increasing the load of inert particles resulted in a slight increase of the water evaporation capacity, while in the fluidized bed drier the effect was more marked. For fluidized and spouted beds, under similar operation conditions, the maximums of the suspension drying capacities are lower than the values of water evaporation, but for pneumatic drying this effect was the opposite. In general terms, the maximal capacities of fluidized bed dryers are higher than those observed in the spouted bed dryers.     

污泥干燥工艺介绍

社会经济的发展导致了污水大量产生,污泥是伴随污水处理产生的又一种污染物,它的数量已经严重影响到城市居民的健康和生活环境,所以合理处理污泥显得非常重要。目前,污泥资源化利用是处理污泥的优选途径,其首要条件是将污泥进行干化或半干化。本文介绍了几种污泥干化工艺的原理及特点。     

OPTIMUM OPERATING CONDITIONS IN DRYING FOODSTUFFS WITH SUPERHEATED STEAM

It is inferred from experimental data that in drying foodstuffs with superheated steam, the initial drying rate has a direct effect on the rate at which the overall drying takes place. That is, the faster the initial drying rate, the shorter the overall drying time. This criterion is very convenient because at the beginning, water moistens the sample external surface so evaporation does not depend on internal sample characteristics, but only on external convective heat and mass transfer rates. Mass and energy balance equations are solved and the result converted into a general initial drying rate equation, in which all dryer characteristics are grouped into one dimensionless parameter. The initial drying rate equation is mathematically maximized and the optimum working conditions determined. The result shows that initial drying rate always increase with increases of either the superheated steam temperature or velocity, but once these two variables are fixed, there exists at least one “optimum” pressure at which the initial drying rate is a maximum. Finally, the initial drying rate and optimum condition equations are applied to three model dryers, a dryer for a flat sheet, a fixed bed dryer and a rotary dryer. In each case, numeric values are computed and plotted as drying rate versus pressure curves, in which the optimum drying rate is also included. Also presented is a chart to compare the optimum pressures as functions of temperature and steam velocity for the three dryers.     

An Experimental Study and Mathematical Simulation of Wheat Drying

A fixed-bed dryer was designed and constructed and drying experiments with fixed beds of wheat were carried out under various conditions of drying air with wheat of several initial moisture contents. The air temperature and moisture content of wheat at various levels within the beds were measured periodically. A computer program based on energy and mass balances was developed to simulate the deep bed drying process. Experimental data from the dryer were compared with the results from this program. The results showed that there was good agreement between the simulated drying rates between the layers and those experimentally observed. In addition, there was a good agreement with respect to the shapes of the drying air temperature profiles.     

Design and Modeling of Plug Flow Fluid Bed Dryers

Plug flow fluid bed dryers (PFFBD) have been used for drying of particulate solids such as salts, ion exchange resins, grains, and a variety of other products. The present article describes the use of a mathematical model for the scale-up of lab-scale batch fluidization data to design an industrial-scale PFFBD. Axial dispersion theory was used in conjunction with the tanks-in-series model to describe the non-ideal flow. The model was implemented in Matlab 6.5 and it can be used for easily fluidizing particulate materials. The proposed model is capable of analyzing both the exponential falling rate and constant rate drying periods. The model predicts the required dryer dimensions for a given throughput and desired final moisture content. The model can also be used to study the effect of different process parameters such as solids feed rate, inlet air velocity, and temperature on the required dryer dimensions and it can also be used to predict the moisture and temperature profiles along the length of the PFFBD.     

聚合物干燥技术进展

根据不同的聚合工艺和聚合反应,聚合物有多种多样的干燥方法。介绍了聚合物滤饼、聚合物分散体、溶液物料及脱除挥发性有机化合物的干燥工艺和干燥技术,对典型的干燥设备操作系统进行了综述。