气固并流系统中弥散颗粒混合行为的研究

采用磷光瞩拉瞬态点源注入示踪技术，研究了气固并流系统中弥散颗粒的轴、径向混合行为，并引入二维扩散模型加以描述，收到了良好的效果。对在气固并流上行和下行系统中的研究进行对比表明：在两种系统中弥散颗粒的轴、径向混合行为类似．研究还给出了在实验条件下气固并流上行系统弥散颗粒的轴、径向Peclet数的关联式．     

采用凝聚函数法进行气-固流化床轴向区域划分

本文采用床层压力脉动测试技术,通过凝聚函数法进行分析,对流化床气泡上升过程的变化规律进行了研究。表明气-固流化床浓相段沿床高可划分为三个区域,即初始气泡生成聚并区,气泡相对稳定区和气泡崩破区。并对操作条件,颗粒物性及床层结构因素,对于划分区域的影响进行了探索     

AN EXPERIMENTAL STUDY OF GAS HOLDUP IN TWO-PHASE BUBBLE COLUMNS WITH FOAMING LIQUIDS

Gas-liquid upward flow experiments have been performed in two bubble columns of different diameters (0.10 and 0.29 m,) using air as gas phase and several liquids: water, aqueous solutions of ethanol and glycerine, kerosene, and a solution of a surfactant in kerosene. The main goal of the study is the analysis of foaming systems, including the comparison of their behavior with respect to non-foaming systems. The gas holdup was determined experimentally as a function of the gas and liquid superficial velocities in bubbling, churn-turbulent and foaming regimes. It was found that, for foaming systems, semi-batch operation enhances foam formation, yielding higher holdups than those obtained in continuous operation at very low liquid velocities. Opposite to what is observed in non-foaming systems, the liquid superficial velocity affects the gas holdup appreciably in foaming systems. An increase in column diameter results in a decrease in gas holdup for all the systems studied. In aqueous foaming systems, this trend is more drastic since foam is inhibited as the column diameter increases.     

FLUIDIZED BED PRESSURE DROP IN PROMOTED GAS-SOLID BEDS WITH COAXIAL ROD,DISK, AND BLADE TYPE PROMOTERS

Bed pressure drop equations have been formulated for gas-solid fluidized beds with different types of promoters using Ergun's equation (Ergun, 1952 Ergun, S. 1952. Fluid flow through packed columns. Chem. Eng. Prog., 48(2): 89[Web of Science ®] , [Google Scholar]) and experimental data. Four rod promoters, seven disk promoters, along with one blade promoter were used in beds supported on five different distributors with open areas of 12.9%, 8.96%, 5.74%, 3.23%, and 1.43% of the column section. The predicted values of bed pressure drop using a modified (i.e., modified numerical constant) Burke-Plummer (Burke and Plummer, 1928 Burke, F. E. and Plummer, W. B. 1928. Gas flow through packed columns. Ind. Eng. Chem., 20: 1196[Crossref] , [Google Scholar]) equation were compared with the corresponding experimental as well as the respective values obtained with the help of Kumar et al. (submitted) and traditional gas-solid fluidized bed equations.     

滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量     

FLUIDIZED BED PRESSURE DROP IN PROMOTED GAS-SOLID BEDS WITH COAXIAL ROD, DISK, AND BLADE TYPE PROMOTERS

Bed pressure drop equations have been formulated for gas-solid fluidized beds with different types of promoters using Ergun's equation (Ergun, 1952) and experimental data. Four rod promoters, seven disk promoters, along with one blade promoter were used in beds supported on five different distributors with open areas of 12.9%, 8.96%, 5.74%, 3.23%, and 1.43% of the column section. The predicted values of bed pressure drop using a modified (i.e., modified numerical constant) Burke-Plummer (Burke and Plummer, 1928) equation were compared with the corresponding experimental as well as the respective values obtained with the help of Kumar et al. (submitted) and traditional gas-solid fluidized bed equations.     

EFFECT OF SURFACTANT CONCENTRATION ON GAS HOLDUP IN A BUBBLE COLUMN WITH AN ORGANIC LIQUID

This work presents an experimental analysis of the effect of the addition of a surfactant on gas holdup in a bubble column with an organic liquid phase. For the system considered, the addition of surfactant increases the gas holdup by increasing the volume of foam within the column. The surfactant concentration has negligible effect on the intrinsic gas holdup of both the bubbling and foaming regions.     

一种气,固流化床料位检测的新方法

料位高度是气、固流化床内重要的基本参数之一。虽然有压降法、测温法、电容法和回波法等可用于料位的测量,但是这些方法作为工业应用都不能令人满意。本文根据流化床内部特性提出了利用流化床内压力波动信号和料面附近的平均压力降测量流化床料位高度的新方法。实验表明,这种方法原理简单,测量精度高。不仅能测量流化床内料位的平均高度。而且还能得到料位的瞬时高度和波动范围;且测量结果不受流化床的几何尺寸、床内物料的特性及流化状态等因素的影响,从而为工业流化床提供了一种料位在线测量的新方法。     

AN EXPERIMENTAL STUDY OF LIQUID-PARTICLE FLOW IN CIRCULATING FLUIDIZED BED

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. LSCFB has potential applications in the fields of food processing, biochemical processing, and petrochemical and metallurgical processing. It is well known that the flow characteristics in a liquid-solid circulating fluidized bed are different from those of a conventional liquid-solid fluidized bed. The limited studies available in literature do not provide complete understanding of the flow structure in this typical regime.

In the present work, experiments were carried out in a 0.0762 m ID and 3 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as fluidizing medium. In the experimental setup, two distributors (specially designed) were used to monitor solid circulation rate in the riser. The effects of operating parameters, i.e., primary liquid flow rate in the riser (Up), solid circulation rate (G_s), and particle diameter (dp), were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 7.83%.     

A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

CFD SIMULATION OF THE GAS-SOLID FLOW IN THE RISER OF A CIRCULATING FLUIDIZED BED WITH SECONDARY AIR INJECTION

A comprehensive investigation was carried out to study hydrodynamics aspects of secondary air injection in circulating fluidized beds. This article presents modeling and results of computational fluid dynamics simulations of gas-solid flow in the riser section of a laboratory-scale (ID = 0.23 m, height = 7.6 m) circulating fluidized bed with a radial secondary air injector. The gas-solid flow model is based on the two-fluid (Eulerian-Eulerian) approach, where both gas and solids phases are treated as interpenetrating continua. A granular kinetic theory model is used to describe the solids phase stresses. The simulation results are compared with measured pressure drop and axial particle velocity profiles; reasonable agreement is obtained. Qualitatively, excellent agreement is obtained in predicting the increase in solids volume fraction below secondary air ports, the accumulation of solids around the center of the riser due to momentum of secondary air jets, and the absence of the solids down-flow near the wall above the secondary air injection ports, which are the prominent features of secondary air injection observed in the experiments.     

CFD SIMULATION OF THE GAS-SOLID FLOW IN THE RISER OF A CIRCULATING FLUIDIZED BED WITH SECONDARY AIR INJECTION

A comprehensive investigation was carried out to study hydrodynamics aspects of secondary air injection in circulating fluidized beds. This article presents modeling and results of computational fluid dynamics simulations of gas-solid flow in the riser section of a laboratory-scale (ID = 0.23 m, height = 7.6 m) circulating fluidized bed with a radial secondary air injector. The gas-solid flow model is based on the two-fluid (Eulerian-Eulerian) approach, where both gas and solids phases are treated as interpenetrating continua. A granular kinetic theory model is used to describe the solids phase stresses. The simulation results are compared with measured pressure drop and axial particle velocity profiles; reasonable agreement is obtained. Qualitatively, excellent agreement is obtained in predicting the increase in solids volume fraction below secondary air ports, the accumulation of solids around the center of the riser due to momentum of secondary air jets, and the absence of the solids down-flow near the wall above the secondary air injection ports, which are the prominent features of secondary air injection observed in the experiments.     

气—液鼓泡塔中流动域和气含率的分布

利用压力传感器测定了气、液两相鼓泡塔内不同轴、径向位置上压强的脉动信号,分析了压强的脉动特征,计算了各种操作条件下塔内不同轴向位置截面上的平均气含率,发现在不同操作条件下,塔内可能出现不同的流动域分布,即全塔均匀鼓泡域、全塔过渡域、全塔湍动鼓泡域以及均匀鼓泡域,过渡域和湍动鼓泡域中的相邻2种或3种流域同时出现在塔内不同高度上。提出了不同轴向位置流域转变的判据。并发现,同一截面的不同径向位置基本处于同一流域内。同时研究了鼓泡塔内气含率在轴向上的分布规律,给出了不同流动域内气含率的关系式。     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

并流下行循环流化床反应器中的气固传质特性

采用稳态吸附方法，测定了示踪剂在下行式流化床反应器中的轴向浓度分布，并与理论分布进行拟合，利用Ｍａｒｑｕａｒｄｔ法，求取了不同操作条件下的轴向扩散系数与气固传质系数，藉以揭示并流下行循环流化床反应器中的气固传质特性．基于实验结果，通过因次分析与线性回归，得到了轴向扩散系数Ｅａ及传质系数ＫＦａ与操作条件的经验关联式：Ｐｅ１≡（Ｌｕｆ）／Ｅａ＝０．２２６Ｒｅ０．４９９ＰΘ－０．３０２Ｐｅ２≡ｕｆ／（ＫＦａ．Ｌ）＝０．０００１８５Ｒｅ０．６１８ｐΘ－０．９８３Θ≡Ｇｓ／（ｕｆρｐ）＝ｕｓ（１－ε）／（ｕｇε）关联式与实验数据拟合较好．     

AXIAL DISTRIBUTION OF SOLID PARTICLES IN BUBBLE COLUMN SLURRY REACTORS IN THE BUBBLE FLOW REGIME

Physical mechanisms responsible for the suspension of solid particles in semi-batch bubble column slurry reactors in bubble flow are identified, thus allowing the classification of solids into four states: free, engaged, wake-entrained and captured particles. A theory is then presented to predict the axial distribution of solids when wake-entrained and captured particles are absent. Reasonable agreement is found between the theory and experimental data obtained in this work and those reported by otherinvestigators.     

AXIAL DISTRIBUTION OF SOLID PARTICLES IN BUBBLE COLUMN SLURRY REACTORS IN THE BUBBLE FLOW REGIME

Physical mechanisms responsible for the suspension of solid particles in semi-batch bubble column slurry reactors in bubble flow are identified, thus allowing the classification of solids into four states: free, engaged, wake-entrained and captured particles. A theory is then presented to predict the axial distribution of solids when wake-entrained and captured particles are absent. Reasonable agreement is found between the theory and experimental data obtained in this work and those reported by otherinvestigators.