喷嘴对液固外循环流化床内颗粒循环特性的影响

液固外循环流化床换热器可以用来蒸发浓缩单基药提取硝化棉的提取液.设计了实现液固外循环流化床内颗粒正常循环的关键部件喷嘴,构建了以喷嘴作颗粒循环装置的液固外循环流化床换热器,研究了喷嘴的结构参数及操作参数对起始循环流体流量、全床压降、负压和最大颗粒循环流量等的影响.结果表明,喷嘴的口径比及安装位置对提高颗粒循环效果均存在一个最佳值,为外循环流化床换热器的设计计算提供了依据.     

液固外循环流化床起始外循环液体流量的实验研究

为外循环流化床换热器的设计计算提供依据,以喷嘴为颗粒循环装置的液固外循环流化床换热器为研究对象,考察了颗粒直径、口径比、喷嘴安装位置、颗粒初始加入量及流体粘度对起始外循环液体流量的影响;得出了稳定操作情况下,液固外循环流化床换热器起始外循环液体流量与上述因素之间的经验关联式.结果表明:计算值与实验值吻合较好.     

喷嘴对液固外循环流化床内含固体积分数的影响

设计了实现液固外循环流化床中颗粒正常循环的关键部件——喷嘴,利用CCD图像采集分析系统,获得了其换热管束内固体颗粒的分布情况,考察了液体流量、口径比、喷嘴安装位置、颗粒直径、颗粒初始加入量以及液体黏度对液固外循环流化床换热器管束内含固体积分数的影响。结果表明:口径比及喷嘴安装位置对提高管束内的含固体积分数都存在一个最佳值,颗粒直径、颗粒初始加入量以及液体黏度对管束内含固体积分数也具有较大的影响,同时还通过对实验数据的综合分析,得到了喷嘴在最佳安装位置下液固外循环流化床内含固体积分数的经验关联式。     

用压差变化阈值确定外循环流化床的起始外循环流化速度

起始外循环流化速度是影响气液固外循环流化床正常操作的重要参数之一。提出了以流化床内压差随表观液速的变化阈值来确定流化床起始外循环流化速度的方法。通过实验研究,考察了颗粒直径、颗粒体积分率和表观气速等操作参数,对强制循环条件下流化床起始外循环流化速度的影响。结果表明,液固流化床起始外循环流化速度远大于单个颗粒终端速度,与颗粒体积分率、颗粒平均直径成正比;强制循环时,颗粒体积分率较小的情况下,加入气体后的起始外循环流化速度比液固两相起始外循环流化速度要大,颗粒体积分率较大时,几乎与液固两相相同。     

带有Kenics静态混合器的水平液固两相流化床换热管的压降研究

以饱和硫酸钙为介质,在安装Kenics静态混合器的水平液固两相流化床换热管上进行实验研究,考察介质流速、Kenics静态混合器扭率、颗粒体积分数及颗粒尺寸对压降的影响,并与冷态实验条件下的压降变化规律进行比较。结果表明：同等操作条件,安装Kenics静态混合器后压降比安装前提高20%～140%;压降随雷诺数的增大而增大,随Kenics静态混合器扭率的增大而减小;颗粒体积分数对压降也有影响。根据实验数据,得出了稳定操作条件下压降与上述影响因素之间的经验关联式,为带有Kenics静态混合器的水平液固两相流化床换热器的设计提供计算依据。     

循环流化床蒸发器中的压降与颗粒分布的研究

为研究汽-液-固三相多管循环流化床蒸发器中的压降和颗粒分布特性,设计并构建了汽-液-固多管循环流化床蒸发系统。利用压力传感器、CCD图像采集和数据处理系统,研究了液体循环流量、热通量、颗粒加入量等参数对于加热管束中压降和颗粒分布的影响。结果表明：随着液体循环流量和颗粒加入量的增加,颗粒分布的不均匀度明显降低,管束压降变大;随着热通量的增大,颗粒分布的不均匀度降低,管束压降呈现波动状态,但管束压降值始终小于加热功率为0时的值。     

外循环流化床换热器内最大颗粒循环流量的实验研究

利用CCD图像采集系统,对外循环管内颗粒流动状况进行考察,获得了外循环流化床最大颗粒循环流量,并考察了喷嘴直径、喷嘴安装位置以及液体粘度对外循环流化床内最大颗粒循环流量的影响。结果表明:喷嘴直径及其安装位置对外循环管内颗粒流量具有重要影响,并且对于提高最大颗粒循环流量都存在一个最适值,同时液体粘度对颗粒循环流量也具有较大的影响。     

液固两相外循环流化床压力波动信号的统计及频谱分析

压力波动信号是表征流化床内流体运动特性的重要信息. 为了更好地了解液固外循环流化床内流体流动特征,在液固外循环流化床中,对床体壁面压力波动信号进行了时域、频域及自相关性分析. 结果表明,沿床体稳定流化段上的压力波动特征相似,流体流动和颗粒运动所引发的压力波动能量频带分别集中在0~10和30~40 Hz之间,压力波动的概率密度近似呈正态分布,液固两相外循环流化床中的压力波动信号介于周期信号和随机信号之间.     

液固循环流化床换热器中固体颗粒分布

利用CCD图像测量与数据处理系统对多管液固循环流化床换热器中的两相流动特性进行了研究。探讨了下管箱中的分布板结构对固体粒子的体积分数分布、固体粒子的速度分布,以及液固两相流压降的影响。实验结果表明:在循环流化床换热器进口段安装适当结构的多孔板分布器,即多孔板的面积小于床层截面积,且床中心处的遮挡面积大于边缘处的遮挡面积,可以有效地提高固相速度的均匀程度,在较高流速下,能较好地改善固体颗粒在管束中的不均匀分布。     

液固和气液固微型流态化研究进展

在百年流态化的研究过程中,涉及到直径不同的流化床。但是,多以流化床的大型化为研究目标,对微型流化床及其本身特性的研究很少。作为专门处理固体颗粒的流态化单元过程,其装置的微型化将兼具微通道反应器和宏观流化床各自的优点,是流态化研究的重要方向。鉴于气固微型流化床已有全面的国内外进展综述,本文仅对液固和气液固微型流化床的国内外研究进展进行分析。结论性内容包括：液固微型流化床床径减小,壁面效应增强,最小流化液速实验值大于Ergun公式计算值;需对描述液固均匀膨胀流化规律的Richardson-Zaki方程加以修正。气液固微型流化床内存在4种典型流型：半流化、弹状流、分散鼓泡流和液体输送流;由于床径减小,出现半流化状态,依据压降表观液速关系曲线等无法确定最小流化液速;气液固微型流化床的反应性能得以有效提升;最后给出了进一步研究的方向,以期为后续研究提供参考。     

Experimental study of filter clogging with monodisperse PSL particles

A fibrous filter is a common cleaning device often used to remove particle from industrial gas streams. The main question that often arises concerns the evolution of the pressure drop and the filtration efficiency during the filter clogging. The increase of pressure drop and filter efficiency was measured and was linked to both the clogging degree inside the filter bed and the deposit structure observed thanks to scanning electron micrograph. We have also studied the influence of various parameters such as air velocity, particle size, aerosol concentration and filter main characteristics. An empirical equation for predicting the pressure drop across the filter as a function of inverse particle diameter and Cunningham correction factor was suggested without considering the particle density in the cellulose paper filter. The values of porosity, obtained from the pressure drop responses of loading in the paper filter using Rudnick and First equation, were compared with other researchers.     

Venturi Scrubber Modelling and Optimization

An improved algorithm that optimizes Pease‐Anthony type venturi scrubber performance is presented in this work. This approach predicts the minimum pressure drop needed to achieve the desired collection efficiency by optimizing key operating and design parameters such as liquid‐to‐gas ratio, throat gas velocity, number of nozzles, nozzle diameter, and throat aspect ratio. A detailed assessment of four established pressure drop models and an extension of two of the models by providing an empirical algorithm to give better prediction of pressure drop in the venturi throat have been conducted by validating them with experimental data. This optimization algorithm provides a stepwise, effective, and accurate approach to optimizing both existing and new scrubbers.     

双喷嘴矩形导流管喷动床喷动压降

引言 传统的柱锥形喷动床(CSBs)的应用受到一些因素的限制,例如处理物料能力、起始压力大及难以放大等,为此,Romankov等[1]最早提出了长方形截面的矩形喷动床结构,来克服CSBs的缺点.此后,Rocha等[2]用矩形喷动床进行了片剂包衣的研究.     

An experimental study of spray flash evaporation

An experimental study has been conducted on spray flash evaporation occurring in a superheated water jet injected through a circular tube nozzle into a low-pressure vapor zone. The effects of superheat, flow rate and nozzle diameter on spray flashing were pursued at 60°C jet inlet temperature. From the experimental results, an empirical equation suitable for predicting the variation of liquid temperature with residence time was deduced.     

增压导向式喷动流化床固体颗粒循环速率的关联

实验考察了喷动气速度、流化气速度、压力以及颗粒尺寸对增压导向式喷动流化床固体颗粒循环速率的影响规律,并归纳出关联式,为正在开发的第二代增压流化床联合循环发电系统(2GPFBC–CC)中关键部件—炭化炉的放大设计提供了帮助.     

Depicting the role of gas-solid interactions on the hydrodynamics of converging pneumatic riser

The understanding of the flow characteristics and effect of gas-solid interactions in pneumatic risers is fundamental to investigate to ensure effective design cost-effective operation. Thus, to understand the effect of gas-solid interactions on the hydrodynamics of newly proposed conversing risers, this study mainly focused on predicting pressure drop in the dilute phase pneumatic conveying system. The experiments were conducted in a converging riser having a convergence angle of 0.2693°. Various solid particles such as sago, black mustard, and alumina have been considered to study the effect of particle sizes and density on the pressure drop. The experimental outcomes indicate that the total pressure drop increases with an increase in the solid density and gas mass flow rate. Moreover, smaller particle sizes are also increased the pressure drop. An empirical correlation is developed for the prediction of total pressure drop ΔP_T in converging pneumatic riser via dimensional analysis. All dependent variables such as particle and air density, drag force, acceleration due to gravity, the mass flow rate of air and particle, the diameter of particle and converging riser, the height of converging riser were considered to develop the empirical correlation. The established relationship is tested, and experimental data have been fitted for its validation. The estimated relative error of less than 0.05 proved the significance of the developed correlation. Hence, it can be stated that the established relationship is useful in studying the effects of various parameters on the pressure drop across the length of the conversing riser.     

Determining Cyclone Particle Holdup by Pressure Drop for a CFB Boiler

An experimental study was conducted to assess the possibility of determining particle holdup by measuring the pressure drop of a conventional cyclone used in a circulating fluidized bed (CFB) boiler. It was found that within a wide range of inlet solid concentrations, i.e., 0.54–4.42 kg/kg‐gas, the cyclone pressure drop increased linearly with inlet solid concentration at a given gas velocity, while the pressure drop between the dust exit and the vortex finder of the cyclone remained almost constant. Since particle holdup increases virtually linearly with solid flow rate, the particle holdup in the cyclone can be derived from the cyclone pressure drop, and therefore, an equation set was proposed to calculate the particle holdup from the cyclone pressure drop.     

Study of the pressure drop of dense phase gas-solid flow through nozzle

Pressure drops are measured on different nozzles of various pipe sizes in dense phase pulverized coal pneumatic conveying. From the experimental results, we conclude that the effect of the gas phase nozzle pressure drop is negligible when comparing with the solid phase pressure drop in the experimental range. The main influence factors contributing to the nozzle pressure drop are gas and solid mass flow rate, solids loading ratio, and the diameters of the nozzle inlet and outlet. A new model was developed to predict the nozzle pressure drop in dense phase pneumatic conveying of pulverized coal based on the Barth's pneumatic conveying theory. The pressure drop predictions from the model are in good agreement with the experimental values. The model quantified the important influence factors of the nozzle pressure drop.     

Pressure drop hysteresis in trickle bed reactors

An understanding of the hydrodynamics of trickle bed reactors (TBR) is essential for their design and prediction of their performance. Flow variables, packing characteristics, physical properties of fluids and operation modes influence the behavior of the TBR. The existence of multiple hydrodynamic states or hysteresis (pressure drop, liquid holdup, catalyst wetting, gas-liquid mass transfer) is due to the different flow structures in the packed bed and can be attained by a set of different operating procedures. Experiments were performed to study the effect of liquid and gas velocity, liquid surface tension, liquid viscosity and the particle diameter of the packing on two-phase pressure drop hysteresis. The parallel zone model for pressure drop hysteresis in the trickling flow was used for analysis of experimental data and flow structure. Theoretically predicted pressure drop hysteresis loop is in satisfactory agreement with experimental data.