新型膜流化床内镍/氧化铝催化剂颗粒流化特性的研究

在内径为53 mm,高800 mm的流化床冷模装置中安装两根垂直管束模拟透氢钯膜组件,研究膜流化床制氢装置的流动特性.以镍/氧化铝催化剂为实验颗粒,空气为流化介质,在0～0.14m.s-1气速范围内考察了膜管对压力脉动、床层轴向密度分布等因素的影响.结果表明,流化床中加入膜管内构件后床层的压力脉动降低,床层密度增加,说...     

基于混沌理论与Elman神经网络的气固流化床流型识别

采用混沌理论对气固流化床压力脉动信号进行混沌特性分析,包括求延迟时间τ、Hurst指数、关联维数、Kolmogorov熵、Lyapunov等混沌参数,并结合统计参数作为流型辨别的特征输入量,利用Elman神经网络对其训练.试验结果表明,气固流化床压力脉动信号具有混沌特性,Elman神经网络能够有效地快速地识别流化床的五种流型,识别率达95%,为在线识别气固流化床流型提供了一种新的有效方法.     

大颗粒鼓泡流化床压力脉动信号的小波分析

利用小波分析对试验所测得的大颗粒流化床的压力脉动信号进行小波包的完全分解,并对各个频段的信号的方差进行统计分析。结果表明,分解前后信号的能量是守恒的,脉动能随着流化数的增加逐渐集中在低频段;气泡经过测点的频率在0~12.5H z的范围内,且气泡的运动变化是影响测点压力数据波动的主要因素;通过分析流化床压力信号中的低频成分,可以判断床层物料的流化状态。     

工业废盐的流态化行为

目前工业废盐的处理方式较为单一,效果不理想。为了解决这一问题,提出了一种可用于处理工业废盐的流化床装置,采用自制的流化床对工业废盐进行流化,并对气固流化床的压力脉动信号进行实时监测,研究了流化数和床层压力波动的关系。介绍了温度对流化床临界流化速度的影响,并提出了临界流化速度与温度的关联式。对流化过程中产生的气泡进行了研究,讨论了气泡运动过程中的形貌和大小。介绍了一种可以考察床层物料流化效果的方法,并运用Improfile函数将三维空间内物料颗粒的混合情况转化为函数,通过强度和时间关系说明了返混程度的强弱。描述了工业废盐的床层塌落过程,最后通过扫描电镜对工业废盐表面上的有机物进行比较得出流化床处理工业废盐的可能性。     

挡板流化床中稳定湍流区的确定

本文通过实验,在φ60mm的挡板流化床中考察了Geldart分类中B组颗粒的流化特性.根据流化床压降、压降的脉动、床层膨胀和气体停留时间分布,了解到床层的流化性质随流化气速的变化有比较明显的差异,可以划分为鼓泡流化区和湍流流化区.而由鼓泡流化区向湍流流化区过渡时存在着一个临界状态点,该点对应的气速称为临界湍流流化速度u_n,根据实验结果可关联出以下表达式:Re_n=0.1358ρ~(0.6576)Ga_ρ~(0.5120)其中:Re_n=u_nρ_fd_ρ|μ;Ga_ρ=d_ρ~3ρ_f~2g|μ~2ρ=ρ_s|ρ_f该式可作为粗颗粒挡板流化床中稳定湍流流化区的判据,其误差在10%以内.     

快速流化床提升管中气固流动行为的非线性分析

对φ100mm×16m、FCC固体颗粒的快速流化床提升管内环-核流动区局部颗粒含量脉动行为进行了非线性分析,用Kolmogorov熵表征了其气固流动行为.结果表明,Kolmogorov熵沿提升管环-核流动区径向有3个显著变化区域,以此为依据将提升管环-核流动区的气固流动行为沿径向分成3个流域：单颗粒随机运动控制的核心流域;单颗粒混沌控制的过渡流域;边壁控制的环形流域.同时,从颗粒对垂直气固流动系统中气固湍动程度影响的角度,解释了Kolmogorov熵的径向分布特征及其与流动结构的关系.     

振动流化床临界流化速度理论预测与实验研究

根据振动流化床床层动力学特性,提出了第一、第二流化段,第一、第二临界流化速度的概念.从流化床临界流化速度的定义出发,得出了振动流化床第一临界流化速度数学模型.在二维振动流化床内,以不同粒径的玻璃珠为床料进行实验研究,分析了振动和其它操作条件对临界流化速度的影响,通过实验数据关联得到了振动能量传递系数的数学表达式,并将模型预测与实验结果进行了对比.结果表明振动强度增加,第一、第二临界速度均减小,振动对第一临界流化速度影响更显著,当振动强度超过1.57后,不通气体床层也能流化,第一临界流化速度降为零,模型预测与实验结果有较好的一致性.     

用落球法研究气固浓相流化床表观粘度

用落球法对不同参数条件下的气固浓相流化床床层表观粘度进行测量和线性拟合,得到了流化床的床层屈服应力和塑性粘度与各因素的关系;研究了粘度对分选时间的影响,建立了振动流化床分选时间与表观粘度和物料密度之间的数学模型. 结果表明,在同一气速下,随石英砂颗粒粒级及床层高度增大,床层表观粘度整体增大. 在一定的流化气速范围内,石英砂介质粒级为0.25~0.125 mm、床高190 mm时,床层粘度稳定在0.39~0.51 Pa×s. 加入振动后,床层粘度明显下降,频率15 Hz、振幅1 mm时流化效果较好,床层粘度稳定在0.69~0.95 Pa×s.     

浅层流化床的研究——(Ⅰ)床层中的气相分布和流型

通常认为在浅层流化床的床层中,气泡相的流动可以作为平推流模式来处理,但是缺乏实验事实的证明。本研充工作在一台单层、浅层的矩形流化床(床截面积为300×500mm)中以氢气为示踪气体进行了示踪试验,据此来考察气泡相在床层中的分布及其流动模式。实验条件较宽:静床高 H_o=50～120mm,流化数 U_o/U_(mf)=1.25～4.0,空气为流化气体,活性炭和黄砂颗粒为流化粒子,平均粒径_p=0.2～0.4mm。对17组实验数据进行了统计分析,结果表明:在实验条件下,气泡相在床层中的流动确可以作为平推流模式来处理。     

浅层流化床的研究（1）床层中的气相分布和流型

通常认为在浅层流化床的床层中，气泡相的流动可以作为平推流模式来处理，但是缺乏实验事实的证明。本研充工作在一台单层、浅层的矩形流化床（床截面积为300×500mm)中以氢气为示踪气体进行了示踪试验，据此来考虑气泡相在床层中的分布及其流动模式。实验条件较宽；静床高H0＝50－120mm,流化数U0/Umf=1.25-4.0，空气为流化气体，活性炭和黄砂颗粒为流化粒子，平均粒径dp=0.2-0.4mm，对17组实验数据进行了统计分析，结果表明：在实验条件下，气泡相在床层中的流动确可以作为平推流模式来处理。     

High-velocity fluidization of solid particles in a liquid-solid circulating fluidized bed system

Particulate and aggregative fluidizations in a liquid-solid circulating fluidized bed system are characterized by chaotic time series analysis of local voidage and heat transfer fluctuations in terms of the correlation dimension and Kolmogorov entropy. Both correlation dimension and Komogorov entropy of the voidate fluctuation are found to decrease with decreasing bed voidage in both fluidization regimes, suggesting the suppression of chaotic motion of individual particles due to high solid concentration. The correlation dimension of the heat transfer fluctation in the aggregative fluidization regime is higher than that in the particulate fluidization regime. This reflects the complex convective motion of liquid and solid phases induced by the formation of the liquid streaks and aggregates of particles.     

Chaotic characteristics of local voidage fluctuation in a circulating fluidized bed

Local voidage fluctuations have been measured by using an optical transmittance probe at various axial and radial positions in a circulating fluidized bed riser with a 0.1 m i. d. and 10 m height. The chaotic time series analysis of the local voidage fluctuations has been adopted to characterize the nonlinear dynamics of the circulating fluidized bed riser. The variations of the correlation dimension and the Kolmogorov entropy of the voidage fluctuation were found to depend on the local time-average voidage. The axial and radial distributions of the correlation dimension and the Kolmogorov entropy were strongly affected by the solids flow structures (e.g. core-annulus flow) in various operating conditions. The correlation dimension of local voidage fluctuations increases along the riser, except the position near the distributor. Both, the correlation dimension and the Kolmogorov entropy of local voidage fluctuations near the wall, were found to be smaller than those at the center of the riser, independent of the solids circulation rate and the axial position.     

Influence of multiple gas inlet jets on fluidized bed hydrodynamics using Particle Image Velocimetry and Digital Image Analysis

A rectangular fluidized bed setup was developed to study the evolution of inlet gas jets located at the distributor. Experiments were conducted with varying distributor types and bed media to understand the motion of particles and jets in the grid-zone region of a fluidized bed. Particle Image Velocimetry and Digital Image Analysis were used to quantify the parameters that characterize these jets. A grid-zone phenomenological model was developed to compare these parameters with those available in the literature. It was determined from this study that jet penetration length behavior is consistently different for fluidization velocities below and above the minimum fluidization. For velocities above minimum fluidization, jet lengths were found to increase more rapidly with increase in orifice velocity than for operating conditions below minimum fluidization.     

Hydrodynamics of gas fluidized beds with mixture of group D and B particles

The dynamics of a gas‐solid fluidized bed containing Geldart Group D particles mixed with a small proportion of Geldart Group B particles are investigated using pressure fluctuations data. Time series analysis, using a variety of nonlinear dynamics tools, shows that the slugging present with Group D particles can be suppressed by the addition of a small proportion of Group B particles. The power spectra and the auto‐correlation function are used for a preliminary evaluation of dominant slug frequencies. It is shown that the bed fluidized with the mixture of Group D and B particles behaves in a less periodic manner and is dominated by more random bubble motion. On the other hand, the correlation integral is used to analyze the chaotic behaviour of the flow, through evaluation of the fractal structure of the reconstructed attractors. It is shown that the bed fluidized with Group D particles is characterized by a combination of steady slug motion and irregular particles motion. The behaviour of the fluidized bed of Group D/B particles mixture is characterized by a single correlation dimension for a wide range of fluidization velocities.     

Dimension measurements of hydrodynamic attractors in circulating fluidized beds

Experimental measurements of the correlation dimension, Kolmogorov entropy, and Lyapunov exponent of circulating fluidized bed (CFB) chaotic attractors were obtained by recording differential pressure and γ-ray porosity time series along the height of a cold experimental CFB operating with 75 μm diameter fluid catalytic cracking (FCC) catalyst. The attractor dimension did not vary with respect to the type of measurement taken. Both differential pressure and localized γ-ray densitometry measurements showed the existence of a low order hydrodynamic attractor, whose dimension varied between 1.5 and 2.0 over the range of gas velocities and solids fluxes studied. Differential pressure measurements indicated that the attractor dimension decreased slightly in the lower section of the CFB and at higher solids fluxes. Localized radial γ-ray bed porosity measurements indicate that the attractor dimension did not significantly vary across the bed cross-section but did show a tendency to be slightly lower near the riser wall.     

气固搅拌流化床压力脉动的小波分析

在内径188 mm、静床高400 mm的搅拌流化床中,采用Geldart D类颗粒为实验物料,通过小波分析研究了不同气速和搅拌桨转速下搅拌流化床的压力脉动行为.实验发现,搅拌桨的转动作用促使在普通流化床中不易散式流态化的D类颗粒形成了散式流态化.随着气速的增加,第1尺度的小波能量特征值在某一个气速范围内发生急剧变化,进而提出了将该气速范围的下限和上限分别定义为临界鼓泡速度和充分鼓泡速度的判据.随搅拌转速的增加,散式流态化的气速操作范围线性增加.在鼓泡流态化状态下,气速是流化床气泡行为的主导因素,搅拌桨转速的增加对气泡产生的频率无明显影响但可使气泡的直径变小.     

CHAOS PREDICTION OF PRESSURE FLUCTUATION IN FLUIDIZED BED

基于混沌理论 ,通过建立重构相空间轨迹演化的离散动力学映射方程 ,提出了流化床压力波动预测方法 ,以流化床压力波动时间序列反演系统动力学行为 .对比了模型产生的压力波动时间序列和实验测得的压力波动时间序列的混沌特征参数 :关联维、Kolmogorov熵和Lyapunov指数谱 ,两组非线性混沌特征参数趋于一致 ,说明该模型能捕获系统的非线性动力学特征 .并研究了压力波动预测指数分离过程的长期不可预测性 .     

流化床压力波动混沌预测

基于混沌理论 ,通过建立重构相空间轨迹演化的离散动力学映射方程 ,提出了流化床压力波动预测方法 ,以流化床压力波动时间序列反演系统动力学行为 .对比了模型产生的压力波动时间序列和实验测得的压力波动时间序列的混沌特征参数 :关联维、Kolmogorov熵和Lyapunov指数谱 ,两组非线性混沌特征参数趋于一致 ,说明该模型能捕获系统的非线性动力学特征 .并研究了压力波动预测指数分离过程的长期不可预测性 .     

Detection of the minimum gas velocity region using Gaussian spectral pressure distribution in a gas-solid fluidized bed

The undesired phenomenon of partial or complete defluidizing can occur in industrial applications involving fluidized beds. That could be prevented by increasing the gas velocity, provided an adequate observation of changes in the hydrodynamic of the fluidized bed is detected early enough. Since the value of gas velocity on defluidization of bed is near the gas velocity at minimum fluidization condition, it is very important to use a methodology that can promptly detect the minimum fluidization velocity region, so that shutting down the process can be avoided. The literature shows that the methods to detect the region of such a velocity are limited, and in practice, the traditional method for determination of minimum fluidization velocity (pressure drop across the bed versus superficial gas velocity) is still the most used. In the present work, a methodology is proposed to detect the region where the minimum velocity takes place in a gas-solid fluidized bed, based on the spectral analysis of pressure fluctuation measurements using a Gaussian distribution curve. Results indicate that the method is satisfactory, and it could be used as a more practical indicator of the region where the defluidization phenomenon occurs.     

纳米TiO2在环隙流化床中流动特性的实验研究

在环隙流化(AFB)床中,应用实验测量技术研究了床层压降和床层膨胀曲线以及最小流化速度的变化规律.研究结果显示,在升速流化时,随着气速增大,床层压降和床层膨胀比也随之增大,当气速超过一定值时,纳米TiO2颗粒完全流化,压降波动和床层膨胀比趋于平稳.最小流化速度随着纳米TiO2质量的增加而增大.