Spouted bed and spout-fluid bed behaviour in a column of diameter 0.91 m

Hydrodynamic measurements were obtained in a half-column of diameter 0.91 m equipped with a conical base using particles of diameter 3.3 to 6.7mm with operation both as pure spouted beds and in the spout-fluid bed mode. Comparison of the experimental results for minimum spouting velocity with equations in the literature generally gave unsatisfactory agreement. On the other hand, the correlations of McNab (1972) and Had?isdmajlovi? et al. (1983) gave reasonable predictions of spout diameters in spouted and spout-fluid beds respectively. Hydrodynamic regimes with auxiliary air present were broadly similar to those determined in smaller columns. However, there were substantial dead regimes at the bottom of the column. A finite difference model based on the vector form of the Ergun equation gave good predictions of air flow distribution and longitudinal pressure profiles.     

Study of the hydrodynamics within a draft tube spouted bed system

Two dimensional Darcy and Ergun models are used to describe the hydrodynamics within the annulus of a spouted bed equipped with a draft tube. Experimental pressure and stream function data for water spouting are shown to be in good agreement with theoretical predictions. Verification of a general spout-annulus interfacial boundary condition is also established and it is shown that the entry region below the draft tube functions as a classical spouted bed. In addition, an experimental procedure for determining the location of the spout-annulus interface is presented. Fluid residence time distributions are calculated for a few cases of practical interest.     

Pressure Fluctuations in Jet Spouted Beds

Jet spouted beds that consisted of a transparent Plexiglas cylindrical column of 1 m high and a conical base with cone angles of 30°, 36°, and 40° were used in this study. The particles used were spherical glass beads with an average diameter of 1.7, 2.1 and 3 mm, respectively, and particle size of 2.2 – 3.1 mm, non‐spherical rice particles. The effect of size and shape of particles, and static bed height on the minimum jet spouting velocity, and standard deviation of pressure fluctuations, was investigated. The results show that the minimum jet spouting velocity and pressure drop increased as the bed height and particle size increased. The minimum jet spouting velocity could be determined from the plot of standard deviation of pressure fluctuations vs. superficial gas velocity. The results obtained were in close agreement with the results of other methods in the literature.     

Determination of Minimum Spouting Velocities in Conical Spouted Beds

Minimum spouting velocities in conical spouted beds have been obtained from pressure drops versus the superficial gas velocity curves, based on both increasing and decreasing the superficial gas velocity. It has been shown that the minimum spouting velocity from decreasing the superficial gas velocity is lower than from increasing the superficial gas velocity in most cases. This phenomenon is similar to that in conventional spouted beds and different from the early works. The experimental results also showed that there isn't significant difference in the pressure drop and U_ms under identical operating conditions between semi‐circular and circular conical spouted beds, and the same U_ms can be obtained from absolute pressure drops at any position above the gas inlet. The U_ms is found to increase with increasing the cone angle and static bed height, as well as the gas inlet diameter to a less extent.     

狭缝式矩型喷动床中多粒度颗粒体系的最小喷动速度

在150 mm×50 mm×1100 mm的矩形喷动床中,采用宽度为2, 4, 6 mm 的3种狭缝式气体分布板,研究了单一粒度组成和多粒度组成玻璃珠的最小喷动速度. 实验证明,矩形喷动床的最小喷动速度与物料的粒度和组成有关. 给出了最小喷动速度与颗粒粒径和粒度组成的关联式,作出了多粒度组成颗粒体系最小喷动速度的相图.     

双喷嘴矩形喷动床流动性能实验研究

在120 mm×240 mm的双喷嘴矩形不锈钢床内,对新型双喷嘴矩形导流管喷动床的最小喷动速度和喷动高度进行了研究,考察了喷动气速、粒径、静床层高度、导流管直径、导流管安装位置对最小喷动速度和喷动高度的影响。结果表明:最小喷动速度随颗粒直径、导流管直径、导喷距的增大而增大,随静床层高度的增大而减小;喷动高度随喷动气速的增大而增大,随导流管直径的增大而减小,受静床层高度和导喷距的影响不大,并得出了最小喷动速度的关联式。     

Minimum spouting velocity in multiple spouted beds

Studies have been carried out in multiple spouted beds having 2, 3 and 4 spout cells; different fluid inlet orifices and different solids have been used with air and water as spouting fluids. The minimum spouting velocities are measured for different bed depths. The experimental data for particle Reynolds number at minimum spouting have been correlated and the square root mean deviation between the calculated and experimental values is found to be 8.75 %.     

Gas spouting hydrodynamics of fine particles

Hydrodynamic measurements for the spouting of fine particles were obtained in a conical‐based cylindrical bed of diameter 0.186 m, inlet orifice diameters of 6 to 14 mm, and included cone angles of 45 to 80 degrees. Four different types of fine particles with diameters ranging from 0.286 to 0.861 mm were investigated. Four different flow regimes—fixed bed, stable spouting, unstable spouting and slugging—were identified and mapped. The termination of the spouting of fine particles was caused by choking rather than by fluidization of particles in the upper bed. Stable spouting could be achieved when the ratio of the orifice diameter to mean particle diameter was less than 20. The measured minimum spouting velocities were within ±15% of those predicted by the Mathur—Gishler equation. Solids density measurements obtained by a gamma ray densitometer showed that the solid density in the spout increases with bed height and in the annulus is 3% to 10% higher than in a loosely packed bed.     

水平辅助气对喷动床流动特性影响的研究

在上部内径为 195mm柱状、下部为 6 0°锥体的喷动床中水平引入辅助气 ,考察了水平辅助气对流动特性的影响。实验结果发现 ,辅助气的水平引入比竖直或法向引入可以更有效地抑制喷动气体向环流区扩散 ,降低最小喷动气速。在总气速一定的条件下 ,增大辅助气速的比例 ,可以降低喷动区空隙率而使颗粒浓度增大 ,提高颗粒的循环流动量。相比而言 ,喷动气速对喷动区颗粒的流动速度影响较大 ,而水平辅助气速对环流区颗粒的流动速度影响较大     

加压喷动床中细颗粒喷动特性

在内径分别为 186mm和 80mm的加压喷动床中 ,以空气为喷动介质 ,在 10 1～ 70 0kPa的压力范围内考察了几种不同粒度的细颗粒在加压下的喷动特性 .研究结果表明在不同的Re_t 内压力对最小喷动速度的影响不同 .实验还发现 ,随着压力的升高 ,喷动区直径增大 ,稳定操作区域增大 ,加压可明显改善喷动床的操作稳定性     

Flow in the annulus of a bed of fine particles spouted with water

The flow in the annulus of a water spouted bed of glass particles (275 to 774 μm) was studied experimentally in a cylindrical half-column 50.8 mm in diameter. An axisymmetric model, which assumes Darcy flow in the annulus and uses the experimental spout pressure distribution, predicts the flow and pressure fields in the annulus. The substantial differences between this flowfield and that for coarse particle beds that are observed are caused by differences in the normalized interfacial pressure profile. The model predicts that both the fluid velocity and the normalized fluid velocity at the top of the annulus decrease as the particle size and bed height are reduced. Particles are observed to enter the spout primarily near the spout inlet in agreement with predictions of the axial spout voidage distribution. The residence time distribution of the fluid in the annulus is relatively broad and the measured residence times are about 25% higher than those calculated.     

Minimum spouting velocity for binary mixture of particles in rectangular spouted beds

Minimum spouting velocity data are reported for seven mixtures of polystyrene, spouted with air in three rectangular spouted beds of square cross sectional areas, using nozzles of five sizes. Correlations for minimum spouting velocity in cylindrical columns were investigated for this geometry. A new dimensionless correlation for predicting the minimum spouting velocity is developed.     

The maximum spoutable bed heights of fine particles spouted with air

The maximum spoutable bed heights of systems of fine glass spheres spouted with air are studied in flat based semi circular columns of 80 and 152.4 mm diameters using particles with average diameters ranging from 0.3 to 1.3 mm. New correlations are proposed to predict the maximum spoutable bed heights of air spouted fine particle systems. It is concluded that the influence of the column diameter on the maximum spoutable bed height is significantly decreased compared to coarse particle systems and that it further varies with particle size within the fine particle spouting regime. Data reported in the literature agree with the proposed correlations.     

Minimum spouting velocity under vacuum and high temperature in conical spouted beds

A study has been carried out on spouting performance in conical spouted beds at high temperatures and under vacuum by using materials of different textures, densities and particle diameters. The applicability of existing correlations for determining the minimum spouting velocity has been checked and, based on a statistical analysis to assess the influence of the dimensionless modulus, a new one has been proposed for the prediction of the minimum spouting velocity under vacuum and at high temperatures. This correlation provides good predictions in the pyrolysis of tyres under vacuum.     

Minimum Spouting Velocity of Draft Tube Conical Spouted Beds Using the Neural Network Approach

A multilayer perceptron with back‐propagation learning algorithm is developed to predict the minimum spouting velocity (u_ms) in draft tube conical spouted beds. Six dimensionless variables involving ten essential geometric and operating parameters of the beds were taken as model inputs. To compare the model results with both experimental data and those predicted by the limited existing empirical equations, the root mean square error and the mean relative error are utilized. Although there is a complex relationship between the input variables and u_ms, and despite the huge number of data available, the steps of training and testing show good agreement with the corresponding experimental values. This demonstrates that an artificial neural network is a useful approach to predict u_ms, especially when the relationship between the geometric and operating parameters and u_ms is complex and difficult to define.     

喷动床研究与进展

叙述了近年来出现的几种改型喷动床，包括多喷头喷动床、喷动流化床、带导向管的喷动床、性粒子旋转射流式喷动床、射流喷动床的研究与进展。它们在传统柱锥形喷动床的基础上，通过增加喷口、导向管、流化气、惰性粒子或增加喷动气速等方法，来克服原有喷动床应用的局限性，拓展其应用领域。     

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.     

Minimum spouting velocity of conical spouted beds

Existing correlations for predicting minimum spouting velocity in conical spouted beds have been found to give poor agreement with available literature data. A new correlation has been developed based on literature data to give much better prediction of the minimum spouting velocity for both small and pilot-scale conical-spouted beds.     

Hydrodynamic Characteristics of a Powder‐Particle Spouted Bed with Powder Entrained in Spouting Gas

Spouting of 3.7 mm polyvinyl chloride particles in a cone‐based cylindrical column is subjected to entrainment of FCC powder in the spouting air. It is found that the powder entrainment reduces the minimum spouting velocity, increases the bed pressure drop and reduces the maximum spoutable bed height. At any given bed height and value of U/U_ms, there is a critical value of powder loading ratio above which spouting gives way to slugging.