Drying Kinetics in the Riser of Circulating Fluidized Bed with Internals

Solid particles were dried in the riser of circulating fluidized bed with internals to study the drying kinetics. Experiments were conducted in a circulating fluidized bed, having perforated plates as internals covering wide range in the operating parameters. The effects of various operating parameters, i.e., initial moisture content, temperature, and flow rate, of the heating medium and solid circulation rate on the rate of drying have been critically examined. It has been observed from the present investigation that the presence of internals enhances the solids holdup in the riser of circulating fluidized bed. The drying efficiency of a circulating fluidized bed with internals has been compared with the drying performance of a circulating fluidized bed without internals under the same operating conditions.     

Analysis of Fluidized Bed Drying Kinetics on the Basis of Interphase Mass Transfer Coefficient

A particular way to define fluidized bed drying kinetics on the basis of interphase mass transfer coefficient and the conception of general kinetic curve has been described. The presented method, which allows for minimization of laboratory tests, has been checked experimentally. The method for calculating of mass transfer interphase coefficient in the constant rate period of fluidized bed drying based on Kunii and Levenspiel bubbling bed model is shown.     

Drying of Potato Slices in a Pulsed Fluidized Bed

This article presents experimental and modeled drying kinetics of potato slices of the Desiree variety (9 × 9 × 3 mm³) in a pulsed fluid bed as a function of the air velocity, air temperature, and rotating disk velocity of the pulse generator. A statistical multifactor experimental design (2³) was applied to analyze the drying process with two levels each of drying temperature, air velocity, and rotating disk velocity. The results showed that the significant factors were air temperature, air velocity, rotating disk velocity, and the binary interactions of air velocity with both the temperature and the rotating disk velocity. The simplified variable diffusivity model (SVDM) gave the least deviation for the experimental data. The effective diffusivity values determined in this work are similar to those reported in the literature.     

Drying Suspensions in a Pulsed Fluidized Bed of Inert Particles

The drying of carbohydrate suspensions on polypropylene particles in a pulsed fluidized bed was studied by means of a 2⁵ experimental design, to determine the effect of the air flow and temperature, suspension flow rate, and free section and rotating speed of the rotary plate on the Nusselt number, the moisture content of the product, and the percentage of solids retained inside the bed (which were minimized to 4.9 and 14.4%, respectively) with an air flow of 600 m³/h at 90°C and 720 mmHg, a suspension flow rate of 6 L/h, and a plate with 6% free section, rotating at 50 rpm.

Additionally, the effects of temperature, air flow, and suspension flow rate on the residence time distribution (RTD) were determined, using the stimulus-response methodology. The RTD was represented by 1.1 to 2 tanks in series, according to this model. The mean residence time of the dried carbohydrate particles was between 5.4 and 8.2 min.

Finally, an egg suspension could be dried at 4 L/h, with air at 90°C, with a mean residence time about 50% longer that that found for drying carbohydrate suspensions.     

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.     

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.     

含卤聚合物悬浮液在载体流化床中干燥研究

对含卤聚合物悬浮液进行了干燥试验。借助于DPS软件数据处理系统,对试验结果采用多因子及二次多项式逐步回归分析方法得出了回归方程。试验数据可供工业规模设备设计之用。     

Drying Sawdust in a Pulsed Fluidized Bed

The objective of this work was the experimental and theoretical study of sawdust drying, in batch and continuous experiences, using a pulsed fluidized bed dryer.

In the batch experiences, a 2³ factorial design was used to determine the kinetics of drying, the critical moisture content, and the effective coefficients of both diffusivity and heat transfer, all of them as a function of the velocity and temperature of the air, the speed of turning of the slotted plate that generates the air pulses in the dryer, using sawdust with 65% moisture in each run.

In the continuous operation, a 2³ factorial design was used to study the effect of the solid flow and the velocity and temperature of the air on both the product moisture and the distribution of residence times. In order to determine these last ones, digital image processing was used, utilizing sawdust colored by a solution of methylene blue as tracer.

The statistically significant factors were the velocity and the temperature of the heating air, for both the continuous and batch operations. Although the speed of turn of the slotted plate was not significant, it was observed that the air pulses increased the movement of particles, facilitating its fluidization, especially at the beginning of drying.

The heat transfer coefficients were adjusted according to the equation Nu = 0.0014 Re _p ^1.52, whose standard deviation of fit is 0.145.

The period of decreasing rate was adjusted to several diffusivity models, giving the best fit the simplified variable diffusivity model (SVDM). The curve of distribution of residence times was adjusted using the model of tanks in series, with values between 2.6 and 5 tanks.     

Drying Sawdust in a Pulsed Fluidized Bed

The objective of this work was the experimental and theoretical study of sawdust drying, in batch and continuous experiences, using a pulsed fluidized bed dryer.

In the batch experiences, a 2³ factorial design was used to determine the kinetics of drying, the critical moisture content, and the effective coefficients of both diffusivity and heat transfer, all of them as a function of the velocity and temperature of the air, the speed of turning of the slotted plate that generates the air pulses in the dryer, using sawdust with 65% moisture in each run.

In the continuous operation, a 2³ factorial design was used to study the effect of the solid flow and the velocity and temperature of the air on both the product moisture and the distribution of residence times. In order to determine these last ones, digital image processing was used, utilizing sawdust colored by a solution of methylene blue as tracer.

The statistically significant factors were the velocity and the temperature of the heating air, for both the continuous and batch operations. Although the speed of turn of the slotted plate was not significant, it was observed that the air pulses increased the movement of particles, facilitating its fluidization, especially at the beginning of drying.

The heat transfer coefficients were adjusted according to the equation Nu = 0.0014 Re_p^1.52, whose standard deviation of fit is 0.145.

The period of decreasing rate was adjusted to several diffusivity models, giving the best fit the simplified variable diffusivity model (SVDM). The curve of distribution of residence times was adjusted using the model of tanks in series, with values between 2.6 and 5 tanks.     

顶喷流化床中干燥过程研究

本文对用于造粒和包涂过程的顶喷流化床内的干燥过程进行了较为详细的实验和理论研究。从传质传热过程中分析可知，床层可分为三段。影响生产能力的最大允许喷淋速度受流化空气流量和入口温度影响最大。     

流化床干燥聚碳酸酯小试实验研究

使用流化床小试装置对聚碳酸酯粉料进行干燥,绘制聚碳酸酯干燥速率曲线,初步证明了卧式流化床干燥聚碳酸酯具有一定的可行性。     

Contact-Sorption Drying of Penicillium bilaii in a Fluidized Bed Dryer

A fluidized bed dryer and drying system have been designed, constructed and operated to produce a powdered formulation of the fungus Penicillium bilaii. The dryer includes an air-shear atomizer and rotatable air vibrator to produce particles which are evenly coated with P. bilaii. The drying system included a humidifier, oven, vacuum pump and instrumentation to ensure precise control of operating conditions. Instant skim milk powder was found to be the best particle source for fixing the spores due to its solubility in water, its highly porous nature and because its moisture isotherms were similar to those of the spores. The dryer was operated at 35°C to maximize the drying rate while still preventing thermal death of the spores. The fluidizing air was best provided at an RH of 30%, thereby producing skim milk/spore particles with just the right amount of moisture to ensure long term storage viability. Storage under refrigeration conditions showed little long term decline in spore viability after 3 months of tests. Room temperature storage demonstrated a small decline rate in spore viability with little significant change if held at room temperature for a few days. © 1997 SCI.     

GZQ型振动流化床干燥机在双氰胺干燥上的应用

介绍了ＧＺＱ振动流化床干燥机的性能、优点及该机在大氰胺干燥应用中取得的成效。     

Drying and Heat Transfer Characteristics for a Novel Fluidized Bed Dryer

Abstract

The use of a fluidized bed dryer with a lateral air flow and mechanical agitation to the drying of sludge from a wastewater treatment plant was investigated. Experimental curves of moisture content vs. drying time, as well as heat transfer coefficients and the size characteristics of the products, were determined at temperatures between 80°C and 110°C, a stirring rate of 55 rpm and air velocity of 0.9 m/s for 3 kg sludge batches with initial moisture contents of 0.55 and 0.65 (d.b.). Experimental drying kinetics were compared with values derived from three models based on Fick's second law, namely: the constant diffusivity model, the simplified variable diffusivity model, and the modified quasi-stationary model.     

鼓泡流化床内高灰煤气化过程的颗粒尺度特性研究

基于多相流体质点网格方法(MP-PIC)对高灰煤在三维鼓泡流化床气化过程进行了数值模拟研究。在欧拉-拉格朗日框架下将气相和固相分别视作连续介质和离散相处理。首先,将模拟得到的出口处气体组分结果与实验数据进行对比,实验数据与模拟结果具有良好的一致性。其次,研究了煤颗粒在气化炉内的温度、传热系数、速度和停留时间,从颗粒尺度揭示了鼓泡流化床气化炉内的颗粒分布特性和气固流动特征。结果表明:在气化炉入口附近煤颗粒与床层温差最大,传热系数最大;由于流化床内强非线性的气固流动,床中煤温度和传热系数的空间分布不均匀;煤颗粒和床料的瞬时速度具有稳定的波动幅度,其中垂直方向速度波动最明显,且煤颗粒的瞬时速度比床料的瞬时速度略大;由于颗粒间的剧烈碰撞,延长了煤颗粒停留时间。此外,对鼓泡流化床中煤气化过程颗粒尺度的研究,有助于深入了解固体颗粒的流动行为以及气固相相互作用特性,对鼓泡流化床反应器的设计优化具有重要意义。     

振动流化床在尤里卡沥青干燥中的应用

以工业原料尤里卡沥青为研究对象,分析和讨论了振动流化床干燥器的动力学特征,传热特性及干燥特性,对振动流化床干燥器设计选型的主要参数进行了整理和计算。     

液固流化床内床层塌落动态过程的数值模拟

在理论分析液固流化床内床层塌落过程的基础上,对水和玻璃球体系的床层动态塌落行为进行了多相流数值模拟,详细考察了液体速度突然减小后床层表面和分隔界面随时间的变化规律,模拟结果与经典模型预测值相吻合,表明多相流计算流体动力学模拟可以很好地预测液固流化床的床层动态塌落行为。     

离子交换树脂流化床干燥工艺的研究与改进

对离子交换树脂的两种流化床干燥工艺作了简单介绍,重点介绍了一种利用流化床连续干燥系统对离子交换树脂进行干燥冷却的工艺。此工艺针对离子交换树脂的特点进行设计。试验证明该工艺具有投资少和节能高效的特点,有很好的推广前景。     

3万t/a苯胺流化床反应器的设计

介绍了3万t/a苯胺流化床反应器整体结构,重点介绍了设备直径、高度的确定,内构件设计和分离段旋风分离器的设计,此设备已成功应用到生产中并稳定运行多年。     

双组分颗粒鼓泡流化床内气泡形状参数

在二维双组分鼓泡床实验装置上,采用高速摄像技术,对床内气泡的形状特性进行了研究,考察了不同形状气泡在床内的轴径向分布,探索了颗粒组成和操作气速对气泡形状的影响。结果表明:不同形状的气泡在鼓泡床内呈正态分布,球形度较好的气泡主要分布于床层底部和壁面附近,而细长的气泡则主要集中于床层中心区域。随着气体速率的增加,气泡的球形度和宽纵比降低,气泡形状趋于细长和不规则;随着重组分增加,气泡的球形度增大而宽纵比减小。双组分颗粒鼓泡流化床内气泡球形度的概率密度较单组分的分布更宽,而宽纵比的概率密度分布与添加的颗粒密度有关。