磁场流化床在生化工程中的应用

磁场流化床（Magnetically Fluidized Bed,以下简称MFB）是将磁场引入普通流化床,采用磁敏性颗粒为床层介质的流固相处理,MFB利用磁场调节颗粒和流体的运动,使流化床具有更宽的操作范围和适应性,其中,在一定磁场和流动条件下形成的磁稳定流化床（Magnetically Stabilized Fluidized Bed,以下简称MSFB）更是瘘有固定床的流固接触特性和流化床的压降低,传热传质效率高的优点,操作范围较普通流化床变宽,磁场流化床在生化工程领域已经地固穹生物反应器,发酵液固液分离,连续亲合色谱,细胸分离,以及植物细胞和酵母细胞培养等过程,本文介绍了磁场流化床的基本原理和特性及其在生化工程中的应用情况,并分析了该技术进一步应用所面临的困难和发展前景。     

离心流化床中气固传热特性的实验研究

本文使用玻璃细珠、黄砂和氧化铝球在不同操作条件下进行了离心流化床气固两相间传热特性的实验研究．测定了气体入口、出口和床层温度随时间的变化．分析了床层厚度、粒径、物料性质、床体转速和气体流速等因素对气固传热特性的影响．首次获得了离心流化床气固两相传热的准则方程．     

Solids Holdup of High Flux Circulating Fluidized Bed at Elevated Pressure

Experimental studies on the solids holdup of a high‐flux circulating fluidized bed (HFCFB) at an operating pressure up to 0.5 MPa were carried out. The effects of operating pressure, solids mass flux and superficial gas velocity on the solids holdup distribution were systematically tested. It was found that the solids holdup at elevated pressure increases with increasing solids mass flux but decreases with increasing superficial gas velocity, which is similar to the trends at atmospheric condition. As a result, the condition of a high‐density circulating fluidized bed (HDCFB), i.e., solids holdup in everywhere of the riser is larger than 10 %) is easier to be achieved at elevated pressure than in a HDCFB operated at atmospheric pressure. In the current work, the condition of a full HDCFB with Geldart group B particles has been achieved successfully at 0.5 MPa.     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

振动流化床浸没水平管传热特性研究

为了深入研究振动流化床浸没水平管的传热特性,分别以沙子和玉米细颗粒作为实验物料,用水平探头测定了振动流化床中这2种床层颗粒与浸没水平管间的传热系数,分析了操作气速、振动频率、空气进口温度等因素对传热过程的影响。结果表明:在低气速下,振动是影响振动流化床中传热的主要因素,振动的引入可以明显改善流化作用,可以在低气速下得到较好的传热效果,同时达到节能的效果。通过分析实验结果,建立了振动流化床的传热关联式,模型计算值与实测值能较好吻合。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

以非晶态合金催化剂SRNA-4为固相的气液固磁稳定床的界面传质研究

1 INTRODUCTION Magnetically stabilized beds (MSB) exhibit an unique combination of packed-bed and fluidized-bed properties. Gas-liquid-solid (G-L-S) three-phase MSB has recently attracted more attention in the field of biotechnology processes (such as bioseparation or immobilized enzyme systems) and chemical engi- neering(such as the hydrogenation reaction system). The interphase mass transfer behavior plays an im- portant role in the optimal operation of practical MSB. However, many…     

IONIC MASS TRANSFER IN THREE-PHASE FLUIDIZED BEDS IN THE PRESENCE OF DISC PROMOTERS

Three-phase fluidized beds have wide applications in process industries. The present investigation is carried out to identify the enhancement of ionic mass transfer coefficients due to the presence of a disc promoter in a three-phase fluidized bed. A diffusion-controlled electrode reaction—reduction of ferricyanide ion—was employed to obtain mass transfer coefficient data. The mass transfer coefficient data were obtained by varying the geometric variables of the disc promoter (disc diameter, disc spacing) and dynamic variables (superficial liquid velocity, superficial gas velocity). The effect of particle diameter was also investigated. The investigations revealed that the mass transfer coefficients were enhanced with decreased disc spacing, increased disc diameter, increased superficial gas velocity, increased superficial liquid velocity, and increased particle diameter.     

含内构件的循环流化床的动态压力特性

针对含内构件的循环流化床,以石英砂为物料,使用动态压力传感器测量了含内构件的流化床中气固两相流的动态压力,分析了床内的瞬时压力特性. 结果表明,在进出口总压降中,文丘里压降最大,占主床压降的60%以上. 表观气速和固体颗粒循环流率共同影响循环流化床内的压力特性. 压力瞬时波动功率谱分析表明,压力波动对应一个主频,表观气速越小、颗粒循环流率越大时,压力波动越大,且循环流化床底部压力波动比上部大. 加入内构件能有效引导气流,使流动更均匀.     

柱形流化床传热特性的数值模拟

对Shedid等搭建的圆柱体流化床采用欧拉?欧拉法进行三维数值模拟,考察了颗粒球形度、表观进气速度和床料初始堆积高度对流化床内垂直加热壁面与流动床料之间对流传热特性的影响,采用有效导热系数分别计算气相和固相的对流传热系数。结果表明,随表观进气速度增大,流化床内颗粒物料湍流运动加剧,加热壁面平均温度和流体平均温度下降,壁面流体间传热平均温度差减小,壁面流体间对流传热系数增大;随初始床料高度增加,流化床内颗粒与加热壁面的接触面积增大,导致固相平均对流传热系数增大。     

多段分级转化流化床提升管速度场的研究

针对流化床煤气化过程中需要长气固接触时间和高固体浓度,开发了耦合灰熔聚流化床和提升管的多段分级转化流化床。为了研究多段分级转化流化床提升管中局部颗粒速度的径向、轴向分布,在不同的操作条件下,采用PV-6型颗粒速度测量仪在冷态实验装置中系统测定提升管内局部颗粒速度。实验结果表明:提升管中任何径向、轴向位置的颗粒速度随着操作气速的增大而增大,随循环量的增加而减小。操作条件对中心区颗粒速度变化的影响明显高于边壁区。颗粒的加速首先发生在提升管中心区域,然后向边壁区域扩展。颗粒速度径向分布的不均匀性沿轴向逐渐增大,并且受操作气速影响比较大。     

三相循环流化床中的气液相界面积和传质系数

采用溶氧法测量了三相循环流化床中液相溶氧浓度的轴向分布,并按轴向扩散模型处理实验数据,优化得到气液体积传质系数kLa,同时用光纤探头测量了体系中的气含率和气泡大小分布,计算得到了气液相界面积a和气液传质系数kL,并研究了主要操作条件(表观气速、表观液速和固含率)对气液传质系数的影响规律.     

气液固三相循环流化床气液传质行为

<正>气液固三相流化床反应器在石油化工、湿法冶金、环境工程和煤的液化等工业领域得到了广泛应用,其基础研究也取得了很大进展.但是,传统三相床主要应用于低液速(U_L<     

循环流化床气固传质实验研究

This study is devoted to gas-solid mass transfer behavior in heterogeneous two-phase flow. Experiments were carried out in a cold circulating fluidized bed of 3.0m in height and 72mm in diameter with naphthalene particles. Axial and radial distributions of sublimated naphthalene concentration in air were measured with an online concentration monitoring system HP GC-MS. Mass transfer coefficients were obtained under various operating condition, showing that heterogeneous flow structure strongly influences the axial and radial profiles of mass transfer coefficients. In the bottom dense region, mass transfer rate is high due to intensive dynamic behavior and higher relative slip velocity between gas and clusters. In the middle transition region and the upper diluter region, as a result of low mass transfer driving force and the influence of flow structure, mass transfer rate distribution becomes non-uniform. In conclusion, among the operating parameters influencing mass transfer coefficients, the superficial gas velocity is the most important factor and the solid circulation rate should be also taken into account.     

Axial pressure profile in circulating fluidized beds

Design and operation of a circulating fluidized bed requires the knowledge of fluid mechanics. According to heat and mass transfer as well as chemical reactions, the effect of the set superficial gas velocity on the axial pressure profile is of particular interest. The axial pressure profile was measured for a variety of solids, as a function of the superficial gas velocity, in a cylindrical circulating fluidized bed with an inner diameter of 0.19 m and an overall height of 11.5 m. Depending on the solids content and superficial gas velocity, two or one sections can be observed in the plant where the pressure gradient is constant. A pressure profile with one pressure gradient exists only at high gas velocities, so long as the acceleration pressure drop immediately above the gas distributor is negligible. Comparison of measured pressure drops in circulating fluidized beds with those measured in vertical pneumatic conveying led to a state diagram for vertical gas-solid flows. The operation behaviour of different types of circulating fluidized bed plants can be explained with the aid of this diagram.     

气固流化床外取热器内流动和换热特性分析

外取热器是维持催化裂化反应-再生系统热平衡和保持装置平稳运行的关键设备之一。外取热器的优化设计和合理调控，要求深入理解外取热器内的流动特性、换热特性及两者之间关系。在一套大型冷模热态实验装置上，分别考察了表观气速、颗粒质量流率对换热管附近的局部固含率和气泡频率、床层与换热管间传热系数的影响。结果表明：增加表观气速可以降低局部固含率、增加局部气泡频率、强化床层与换热管间换热；随着颗粒质量流率增加，局部固含率和局部气泡频率均增加；在较低表观气速下，增加颗粒质量流率不利于换热，而在较高表观气速下，传热系数随颗粒质量流率逐渐增加。不同流型下，气固流动特性对换热特性的影响不同。在鼓泡床流型下，过高的局部固含率不利于颗粒在换热表面的更新，增加换热管附近的局部气泡频率可以明显强化换热；而在湍流床流型下，换热管附近的局部固含率和气泡频率的增加，均使传热系数逐渐增大。建立了针对不同流型的换热经验关联式，预测值与实验值的平均相对偏差分别为6.9%和1.3%。     

Wärme- und Stoffübertragung in der Wirbelschicht

Heat and mass transfer in fluidized beds . Methods of calculation are presented which enable reasonably accurate prediction of heat and mass transfer coefficients in fluidized beds. Some well established equations already given in the literature could be used for estimating the range of existence of the fluidized bed and for calculating maximum fluidization velocities, bed expansion, and particle-to-fluid heat and mass transfer. However, a new model had to be developed for the wall-to-bed heat transfer from solid surfaces immersed in fluidized beds. This model makes use of some basic ideas adopted from the kinetic theory of gases in order to describe the mechanism of energy transfer through the moving particles. Predictions with this new model are in good agreement with most of the experimental observations, particularly regarding the effects of particle diameter, temperature, pressure, physical properties of gas and particles, and gas velocity.     

快速流化床床层与浸润表面间的截面平均传热系数变化规律

<正>快速流态化是介于密相流态化与稀相输送之间的操作区域.对于密相流化床内的传热研究,前人已提出许多模型和经验关联式.对于稀相输送过程的传热研究则集中于床展与     

Particle‐scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tube

A kind of new modified computational fluid dynamics‐discrete element method (CFD‐DEM) method was founded by combining CFD based on unstructured mesh and DEM. The turbulent dense gas–solid two phase flow and the heat transfer in the equipment with complex geometry can be simulated by the programs based on the new method when the k‐ε turbulence model and the multiway coupling heat transfer model among particles, walls and gas were employed. The new CFD‐DEM coupling method that combining k‐ε turbulence model and heat transfer model, was employed to simulate the flow and the heat transfer behaviors in the fluidized bed with an immersed tube. The microscale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient between gas‐tube and particle‐tube around the tube were obtained and the influences of fluidization parameters such as gas velocity and particle diameter on the transfer coefficient were explored by simulations. The computational results agree well with the experiment, which shows that the new CFD‐DEM method is feasible and accurate for the simulation of complex gas–solid flow with heat transfer. And this will improve the farther simulation study of the gas–solid two phase flow with chemical reactions in the fluidized bed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Particle scale study of heat transfer in packed and bubbling fluidized beds

The approach of combined discrete particle simulation (DPS) and computational fluid dynamics (CFD), which has been increasingly applied to the modeling of particle‐fluid flow, is extended to study particle‐particle and particle‐fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale. The development of this model is described first, involving three heat transfer mechanisms: fluid‐particle convection, particle‐particle conduction and particle radiation. The model is then validated by comparing the predicted results with those measured in the literature in terms of bed effective thermal conductivity and individual particle heat transfer characteristics. The contribution of each of the three heat transfer mechanisms is quantified and analyzed. The results confirm that under certain conditions, individual particle heat transfer coefficient (HTC) can be constant in a fluidized bed, independent of gas superficial velocities. However, the relationship between HTC and gas superficial velocity varies with flow conditions and material properties such as thermal conductivities. The effectiveness and possible limitation of the hot sphere approach recently used in the experimental studies of heat transfer in fluidized beds are discussed. The results show that the proposed model offers an effective method to elucidate the mechanisms governing the heat transfer in packed and bubbling fluidized beds at a particle scale. The need for further development in this area is also discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Experimental research on steady-state operation characteristics of gas–solid flow in a 15.5 m dual circulating fluidized bed system

Gas-solid hydrodynamic steady-state operation is the operating basis in a chemical looping dual-reactor system. This study reported the experimental results on the steady-state operation characteristics of gas–solid flow in a 15.5 m high dual circulating fluidized bed(CFB) cold test system. The effects of superficial gas velocity, static bed material height and solid returning modes on the steady-state operation characteristics between the two CFBs were investigated. Results suggest that the solid distributions in the dual CFB test system was mainly determined by the superficial gas velocity and larger solid inventory may help to improve the solid distributions. Besides, cross-returning mode coupled with self-returning is good for steady-state running in the dual-reactor test system.