三相流化床间歇操作中颗粒的混合与离析行为

在直径41 mm、高1500 mm的间歇操作三相流化床中对双组分固体颗粒的轴向浓度分布、混合和离析行为进行了实验研究. 实验所用固体混合物为密度相近、直径不同的大孔吸附树脂(H-103)与橡胶球. 采用多个百叶窗式金属网及床层膨胀法测量颗粒固含率及流化床气含率沿床层轴向的变化情况,借用描述液-固两相流化床的沉降-分散模型描述气-液-固三相流化床,并采用了Fan等的离析速度与床层高呈线性关系的假定. 实验结果证明,沉降-分散模型可以用来描述气-液-固三相流化床中的固体浓度分布,Fan等的假设是成立的.     

加压二维鼓泡床气固流动特性的数值模拟

采用欧拉双流体模型模拟了加压下二维鼓泡床内的气固流动特性,结果表明:在相同的表观气速下,加压使气泡体积分数增大,气泡相与乳化相间的分解越发明显,气固两相流动、混合剧烈;同时,床层中上部颗粒轴向速度的径向分布不均匀性增强:中心区颗粒速度增加,近壁区下降;随着操作压力变大,流化床膨胀高度增大,相应地,整体气含率增大,床层下部的颗粒浓度减小,而上部颗粒浓度增加,固含率在轴向上的分布更均匀;床层压力波动主要由两种成分构成:低频率高幅值和低幅值高频率成分.压力脉动强度随床高的增加呈现先增大后迅速减小的趋势;此外,加压下床层压力脉动强度变大,即床压波动更加剧烈;而且加压下颗粒拟温度增大,即颗粒速度脉动增强.     

三相循环流化床中气泡大小及其分布的实验研究

用光纤探头技术对三相循环流化床中的气泡大小及其分布进行了系统研究 ,实验测定了操作条件对气泡大小及其分布的影响规律 .实验结果表明 ,三相循环流化床中气泡的大小分布可用对数正态分布表征 ,在实验条件下气泡平均直径在床中心区域较小且沿半径方向由中心向边壁逐渐增大 ,并随表观气速的增大而减小 ,随固含率的增大而增大 ,表观液速对气泡平均直径的影响较小     

液固流化床内固含率时空分布特性的CFD模拟

采用Brandani等考虑拟平衡状态下颗粒与流体相互作用的双流体模型,通过在商业软件CFX4.4平台上增加用户自定义子程序模拟了高0.5 m、宽0.1 m的二维液固流化床内固含率的时空分布特性。为了保证数值模拟精度、节省计算机运行时间,首先确定了适宜的网格尺度、时间步长和收敛判据。随后,考察了液固两相物性和操作条件对流化床内固含率时空分布特性的影响,模拟结果表明：增大颗粒粒径或密度会使颗粒向下加速运动,导致床层高度下降而垂直方向上任一水平面的平均固含率呈现增大的趋势;减小液体黏度或密度则会使颗粒向下加速运动,导致床层固含率增大;突然增大液速会使颗粒向上加速运动,导致床层固含率减小;升高温度的实质是使液体的黏度和密度均呈现下降的趋势,结果使颗粒向下加速运动,床层固含率增大。上述模拟结果与颗粒受力的理论分析相一致。     

气—液—固三相磁场流态化床气泡特性及液相返混

在含磁性固定化细胞载体-海藻酸钙凝胶粒子的气-液-固三相磁场流化床生物反应器内,实验观察、测定了低气液速下反应器的气泡特性、相含率及液相返混。得到了磁场强度、气速、液速对局部气含率、气泡速度、直径分布概率影响的关联式。提出了合理的磁场分布板形式及经修正的液相混合模型。     

大颗粒循环流化床压力波动信号分析

应用功率谱分析法、R/S分析法及混沌分析法对大颗粒循环流化床压力波动信号的性质和组成进行了研究.功率谱分析法和R/S分析法从两个不同的角度均得出了压力波动信号中存在一定的周期成分,而混沌分析得出的关联维和K熵进一步证实了压力波动信号表面上是随机的,但实质上具有确定性,即表明大颗粒的气液固三相循环流化床的压力波动信号具有混沌信号的特征.     

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.     

三相环流反应器中的局部相含率

将压差法与气-液相间滑移速度相结合,提出了利用压差法测量三相区局部相含率的新方法,将测得的局部固含率进行轴向平均并与由颗粒装填量计算所得的固含率进行比较,证明了此方法的可靠性. 利用所提出的测量方法,考察了三相环流反应器中气含率和固含率随操作条件的变化规律. 结果表明,气含率随表观气速的升高而增大,且随轴向位置的升高而增大;大颗粒具有破碎气泡的作用,能够增大反应器内的气含率;固含率随表观气速的增加而降低,且沿轴向变化较大. 表观气速较高时,固含率沿轴向近似呈S形分布.     

气液固三相磁稳定流化床的操作状态对反应结果的影响

以氮气、水、铁粉为气液固三相研究了三相磁稳定流化床的床层操作状态；以重整生成油的烯烃饱和加氢过程为体系，研究了铁粉与大比表面非晶态合金催化剂混合颗粒为固相的磁稳定流化床中床层操作状态对反应结果的影响。找到了有利于气液固三相反应的磁稳定流化床床层操作状态     

强制内循环煤直接液化反应器流动性能的冷模与热模试验

采用玻璃珠-水-空气三相体系在煤直接液化强制内循环浆态床反应器中进行冷模试验,考察了强制内循环反应器内的固含率、气含率、压降、流速分布和湍动强度的分布情况。结果表明:反应器内固含率要高于进料中的固体含量;床层轴向压降保持不变,但受固相含量影响;气含率随床层增高而增加;同一截面上湍流脉动能量径向分布较均匀,而随气体表观速率和浆液表观速率增加,脉动能量增加;反应器内多相流在分布板区强烈混合引起的压力脉动沿轴向向上逐渐衰减;靠近反应器壁的有些区域存在回流现象。测定了工艺开发单元(PDU)中试装置反应器内的液体密度分布,并计算了其气含率。结果表明,冷模试验与PDU中试中的气含率在床层中的变化趋势相同,且反应器具有较好的操作稳定性。     

气液固三相流化床中局部相含率的随机分析

本文利用Markov过程原理获得了描述三相流化床中局部相含率的随机模型,并进行了实验验证,发现拟合很好.     

Measurement of longitudinal distribution of solids holdup in a three-phase fluidized bed by ultrasonic technique

A method of measurement of solids holdup in a three-phase reactor by analyzing the shape and the phase lag or lead of an ultrasonic wave has been proposed. The solids holdup in a solids-dilute three-phase fluidized bed could be measured without being affected by the presence of gas bubbles. The experimental values of solids axial dispersivity measured by the ultrasonic technique are in reasonable agreement with an empirical correlation of previous data obtained by other methods. The possibility of the application of the ultrasonic technique to the measurement of solids holdup in a three-phase fluidized bed has been suggested.     

ECT imaging of three-phase fluidized bed based on three-phase capacitance model

In this work, the electrical capacitance tomography (ECT) with neural network multi-criteria optimization image reconstruction technique (NN-MOIRT), early developed by the authors, is applied to imaging bubble column and three-phase fluidized bed systems in the real time manner. Air, norpar (paraffin) and glass-beads are used as the gas, liquid, and solid phases, respectively. A three-phase capacitance model coupled with a two-region model is proposed to attain the gas holdup and the solids fraction from the permittivity maps of the three-phase system. The two-region model assumes that the solids fraction in the emulsion phase in the no bubble region is the same as in the bubble region. The three-phase capacitance model combines series and parallel capacitance connections among gas, liquid and solid components to relate the three-phase permittivity to each phase holdup. A direct image calculation to obtain the gas holdup from the permittivity map of the three-phase system is also performed by determining the permittivity threshold for the gas bubbles. Comparisons of the gas holdup obtained by ECT with that obtained from liquid head measurement showed a good agreement, validating the applicability of the model and its associated image calculation.     

大颗粒三相环隙气升式环流反应器流体力学行为

研究了大颗粒体系气升式环流反应器的流体力学行为,考察了表观气速和颗粒质量分数对床层膨胀高度、循环液速和固含率分布的影响。实验结果表明,按颗粒的运动状态不同可以将反应器内的流动分为3个区域,即固定床区域、膨胀床区域和循环床区域,各流动区域内的流动行为存在显著差异。随着颗粒质量浓度的增大,起始流化气速和最小循环气速均显著增大。基于三相流化床的流化模型和环流反应器的特点建立了相应的数学模型,对大颗粒三相气升式环流反应器的起始流化气速和最小循环气速进行了预测,模型预测值与实验测量值吻合良好。     

A highly elevated mass transfer rate process for three-phase,liquid-continuous fluidized beds

Average gas holdup and gas-to-liquid mass transfer in three-phase fluidized beds with non-Newtonian fluids were studied. The effects of liquid property, gas distributor type and magnetic field intensity on mass transfer coefficient and overall gas holdup were examined. The volumetric gas-to-liquid mass transfer coefficient was determined by fitting the oxygen concentration profile data across the bed to the axial dispersion model. The average gas holdup and mass transfer coefficient were all correlated with operating parameters including gas velocity and effective viscosity.Experimental results showed that a three-fold increase in mass transfer coefficient and a two-fold increase in average gas holdup were observed with properly designed liquid property and gas distributor. A modified process was developed to highly elevate the volumetric gas-to-liquid mass transfer rate. The bubble coalescing property of three-phase fluidized beds with small particles is eliminated, and its application to biotechnology and enzyme-catalyzed processes with high gas-to-liquid mass transfer rate could be achieved.     

磁场生物流化床特性的研究

本文对含磁粉固定化细胞载体—聚丙烯酰胺凝胶粒子的液固、气液固流化床在均匀磁场中的流化特性进行了研究.测定了液固床的空隙率及气液固三相床的相含率,并获得了相应的关联式.本文同时研究了磁场流化床用于固定化细胞处理含酚废水,进行催化降解反应的应用效果.     

大直径三相流化床相含率与缝隙液速的研究

本文对大直径三相流化床的局部气含率(?)固含率及液体缝隙速度进行了测定,并结合小直径床的数据作了系统的分析.结果表明,局部气含率基本符合抛物线分布;局部固含率可以由方程式(7)来表示;利用本文修正的液体循环流模型能够合理地描述液速分布.     

三相流化阳离子交换-除CO_2联合水处理装置的气含率与数值模拟

研究了一定条件下气、液、固三相流化阳离子交换 -除 CO2 联合水处理装置的气含率分布 ,讨论了树脂层高及气、液表观速度对气含率分布的影响。用拟两相的双流体模型计算了三相流态化阳离子交换 -除 CO2 联合水处理装置的气含率。结果表明 ,模拟结果与实验结果一致     

Axial distribution of solids holdup for both hydrophilic and hydrophobic particles in three‐phase fluidized beds

The axial concentration distribution of the hydrophilic and hydrophobic particles, corresponding to poor and good attachment to rising bubbles in water, was investigated in a gas‐liquid‐solid fluidized bed. The sedimentation‐dispersion model depicted satisfactorily the axial distribution of solids holdup by modifying only the terminal settling velocity, which considered the effect of an additional drag force resulting from the attached rising bubbles. This model explained correctly the different phenomena, i.e. solids holdup decreased with increasing the axial height in the non‐attached system, but increased in the attached system.     

LOCAL HOLDUPS AND LIQUID INTERSTITIAL VELOCITY IN LARGE-DIAMETER THREEPHASE FLUIDIZED BED

Radial profiles of local gas and solid holdups and liquid interstitial velocity were measured in a largediameter three-phase fluidized bed, and a systematic study was carried out in comparing the present data with those obtained in small-diameter beds. Radial profiles of local gas holdup were found to be parabolic; the distribution of local solid particle holdup could be expressed by Eq. (9); liquid interstitial velocity was well described by the modified circulating flow model.