A Draft-Tube Conical Spouted Bed for Drying Fine Particles

A study has been conducted on the performance of a draft tube conical spouted bed for drying fine particles. Batch operation has been performed with nonporous, porous, and open-sided draft tubes in order to ascertain the optimum configuration of this internal device. The nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the drying efficiency of the open-sided draft tube are superior to any other spouted bed configuration. Moreover, it allows for reducing the height of the fountain and, consequently, the height of the drying equipment.     

Microwave-Assisted Spouted Bed Drying of Lettuce Cubes

Microwave-assisted spouted bed (MSBD) drying of lettuce cubes was investigated experimentally. Response surface methodology was used to optimize the process with spouting air temperature, microwave power level, and superficial air velocity. The dried product obtained was compared with that obtained using other drying technologies such as hot air drying, air spouted bed drying, vacuum microwave drying, and vacuum freeze drying. The comparison is based on the rehydration ratio, chlorophyll content of the product, color, and the drying time required.     

Slot-Rectangular Spouted Bed: Hydrodynamic Stability and Effects of Operating Conditions on Drying Performance

A new spouted-bed configuration (rectangular cross-section with air entry through two bottom slots) was investigated as a dryer of milk and a paste mixture of milk and blackberry pulp. The aim was to analyze hydrodynamic stability and the effects of operating conditions on powder production efficiency. For the best conditions of paste-feeding flow rate, air temperature and inert type, hydrodynamic was stable and powder production efficiency was greater than 75%. The slot-rectangular spouted bed allowed for tripling of the paste-feeding flow rate at a lower air velocity compared to the conventional geometry, showing its potential for process scale-up.     

Distributor Induced Hydrodynamics in a Conical Fluidized Bed Dryer

The hydrodynamics induced by perforated, punched, and mesh (Dutch weave) distributor plates have been studied using dry placebo pharmaceutical granule in a conical fluidized bed dryer at inlet superficial gas velocities of 0.5 to 3.5 m/s. For superficial gas velocities up to 2.0 m/s, the punched plate design leads to improved hydrodynamics based on reduced bubble frequencies and limited segregation. Beyond 2.0 m/s, the influence of gas velocity supersedes that of distributor design, as coalescence dominates the hydrodynamic behavior resulting in low-frequency, high-intensity spectral density distributions for all distributor designs.     

超细粉在导向管喷动床中的流化行为

以料径5μm的CaCO3超细粉为物料,对其在半圆形导向管喷动床中的流化行为进行研究,考察床层压降特性及喷嘴直径、导喷距及导向管直径对起始流化行为的影响。     

Spouted Beds of Inert Particles for Drying Suspension

ABSTRACT

A brief review of Brazilian research on drying process in spouted beds shows its relevance and evolution trends. Needs for applying this technique to dry pasty materials are discussed, focusing on a new model approach in order to overcome operational problems with particle agglomeration and with thermal efficiency. Based on this approach, two cases, drying of black liquor in a conical spouted bed of inert polypropylene particles under intermittent operation and drying of egg emulsion in a conical spouted bed of inert glass beads under continuous operation, are presented and analyzed.     

Spouted Beds of Inert Particles for Drying Suspension

A brief review of Brazilian research on drying process in spouted beds shows its relevance and evolution trends. Needs for applying this technique to dry pasty materials are discussed, focusing on a new model approach in order to overcome operational problems with particle agglomeration and with thermal efficiency. Based on this approach, two cases, drying of black liquor in a conical spouted bed of inert polypropylene particles under intermittent operation and drying of egg emulsion in a conical spouted bed of inert glass beads under continuous operation, are presented and analyzed.     

Continuous Drying of Slurry in a Jet Spouted Bed

ABSTRACT

he performance of a laboratory scale jet spouted bed (JSB) for drying rice flour slurry was studied. The bed consisted of ceramic balls (5028 mm diameter) and the rice flour slurry was sprayed onto the moving particle surface near the inlet part. All the experiments were carried out at the jet spouting regime. This regime has high bed void fraction and violent movement and collision of bed particles. As a result, the dried product layer is attrited from particle surface as a fine powder and entrained from the bed by the spouting air. The experimental result were presented to show the effects of static bed height, inlet air flow rate and temperature, and feed concentration and flow rate on the outlet air temperature, thernal efficiency, and mean particle size and moisture content of the product. Asimple mathematical model, which is based on the conservation of mass and energy equations, was developed. Predicted results agreed well with those obtained from the experiment.     

Local porosity in conical spouted beds consisting of solids of varying density

Local bed voidage has been measured in conical spouted beds by means of an optical fibre, for different geometric factors of the contactor (angle and inlet diameter) and under different experimental conditions (height of the stagnant bed, particle diameter and air velocity). The study has been carried out with glass beads and materials of lower density (high- and low-density polyethylene, polypropylene and extruded and expanded polystyrene). From the results, a correlation has been proposed for calculation of the local bed voidage in the spout and annular zones. The effect of the experimental conditions on the bed voidage in the solid ascent (core) and descent (periphery) regions of the fountain has been studied and the fountain has been proven to be of greater importance in the design of conical spouted beds, as solid density and shape factor are lower.     

新颖环形喷动床颗粒喷动特性实验研究

一种新颖的环形喷动床由内外两个不同内径、同心的垂立圆筒组成,在环形空间底部设置多个喷口,在喷口两侧布置倾斜的导流板.研究颗粒在这种喷动床内的流动特性,探讨喷口结构、颗粒种类以及床内载料量对环形喷动床颗粒喷动特性的影响.实验结果表明:颗粒在环形喷动床内分为三个明显不同的区域,即颗粒填充移动区、密相喷动流化区以及稀相夹带区.当颗粒出现分区喷动后,随床内载料量的增多,填充移动区的高度维持不变,始终等于导流板的高度,而密相喷动区的高度不断增加.风量和颗粒种类对床层最大喷动量、密相喷动高度以及床层压力分布规律有着十分重要的影响.采用不同的喷口结构时,在相同的载料量下,直向喷口的密相喷动区高度更大,而且床内各测点的平均压力大于采用斜向喷口时的相应测点压力.     

Simulation Of Drying Suspension In A Conical Spouted Bed

A software for simulating the drying operation of diluted suspensions in conical spouted beds of inert particles has been developed. This computer program combines the fluid flow and the solids circulation models with the drying kinetic equations. The simulated results for drying animal blood in a spouted bed of inert particles compare with data reported in the literature.     

Optimization of Potato Cube Drying in a Microwave-Assisted Pulsed Spouted Bed

The drying homogeneity of the microwave–pulsed spouted bed drying (MPSBD) method was studied via preparing tubers granules by MPSBD under different predefined conditions. The effects of three parameters (microwave power, moisture content transition point, and loading) on the homogeneity of prepared tubers granules were studied. Based on response surface analysis results, it was concluded that the optimum conditions for tuber granules prepared by MPSBD method is 1.10 W/g microwave power, 80% moisture content transition point, and 90 g material loading. It was proven that the experimental result from the predicted optimal condition agreed with the model-predicted results, which evidenced the accuracy of the response surface analysis. Furthermore, the brighter color and higher rehydration capacity of samples prepared by MPSBD indicates that MPSBD is a promising method that can be applied in the food dehydration industry.     

Effect of Inert Particles Properties on Performance of Spouted Bed Dryers

Design rules for spouted bed dryers with inert particles are given to control size and size distribution of a dry material when changing the size and shape of inert particles as well as the material from which they are made. Implications on product quality, solids separation from the exhaust air, and energy requirements are discussed based on inert particles made of Teflon and stainless steel.     

喷动干燥床技术研究及应用

阐述了喷动干燥床技术研究的进展,介绍了喷动干燥床的工作原理和系统设计要求.并对喷动床干燥聚碳酸酯粉料效果进行研究。     

Drying of Burdock Root Cubes Using a Microwave-Assisted Pulsed Spouted Bed Dryer and Quality Evaluation of the Dried Cubes

Burdock cube samples were dried using hot air and microwave pulsed spouted bed drying (MPSBD). Hot air drying was carried out at three temperatures (70, 80, and 90°C). MPSBD was carried out at three microwave power levels (1.0, 2.0, and 3.0 W/g). The results showed that MPSBD samples dried at 2.0 W/g for 30 min and at 1.0 W/g for 40 min had desirable color, flavor, and textural attributes. Gas chromatography–mass spectrometry results showed that the samples dried using MPSBD were richer in flavor compounds, especially in esters, compared to the hot air–dried samples.     

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.     

惰性载体振动流化干燥机理与特性研究

介绍了惰性载体振动流化干燥机的结构,分析了干燥机理,研究了粉状、液状、糊状等不同形态物料的干燥特性。     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.