加压气升式内环流反应器流动特性

在连续进料的操作条件下,选用水、氮气等作为实验介质,在Φ600mm?000mm的耐压不锈钢环流反应器内进行了实验。获得了下降环隙以及中心导流筒气含率的实验数据,并根据所获得的实验数据给出了中心导流筒以及下降环隙的关联式。从能量衡算的角度出发,对中心气升式加压环流反应器进行了理论分析,根据能量平衡推导出了连续操作模式下液相循环速度模型。同时根据实验所获得的数据确定了模型参数,通过计算可以发现,循环液速会随空塔气速以及体系压力的增加而增大,但是液相循环速度不会随着这两个操作工况无限制的变化,当体系压力与空塔气速大于某个值之后,液相循环速度的基本趋于平缓     

Bubble Behavior of a Large‐Scale Bubble Column with Elevated Pressure

Gas holdups and the rising velocity of large and small bubbles are measured using the dynamic gas disengagement approach in a pressured bubble column of 0.3 m in diameter and 6.6 m in height. The effects of superficial gas velocity, liquid surface tension, liquid viscosity, and system pressure on the gas holdups and the rising velocity of small and large bubbles are investigated. The holdup of large bubbles and the rising velocity of small bubbles increase with increasing liquid viscosity and liquid surface tension. Meanwhile, the holdup of small bubbles and the rising velocity of a swarm of large bubbles decrease. Moreover, the holdup of large bubbles and the rising velocity of a swarm of small bubbles decrease with increasing system pressure. A correlation for the holdup of small bubbles is obtained from experimental data.     

Hydrodynamic behaviour of a draft tube gas-liquid-solid spouted bed

Experiments were conducted using various types of solid particles to investigate the hydrodynamic properties of a gas-liquid-solid spouted bed with a draft tube. The hydrodynamic properties under study include flow modes, pressure profile and pressure drop, bubble penetration depth, overall gas holdup, apparent liquid circulation rate and bubble size distribution. Three flow modes were classified: a packed bed mode, a fluidized bed mode and a circulated bed mode. It was found that the friction factor accounting for the friction loss in the bed varies linearly on a logarithmic scale with the Reynolds number defined based on the apparent liquid circulation rate. The bubble penetration depth in the annular region, overall gas holdup and apparent liquid circulation rate increase with an increase in gas or liquid velocity. At high gas flow conditions an optimal solids loading exists which yields a maximum apparent liquid circulation rate. A model was proposed to describe the liquid circulation behaviour in the draft tube three-phas spouted bed. The average bubble size in the draft tube region is higher than that in the annular region for both the dispersed bubble regime and the coalesced bubble regime in the draft tube region.     

CFD analysis of two‐phase turbulent flow in internal airlift reactors

The hydrodynamic performance of three internal airlift reactor configurations was studied by the Eulerian–Eulerian k–ε model for a two‐phase turbulent flow. Comparative evaluation of different drag and lift force coefficient models in terms of liquid velocity in the riser and downcomer and gas holdup in the riser was highlighted. Drag correlations as a function of Eötvös number performed better results in comparison to the drag expressions related to Reynolds number. However, the drag correlation as a function of both Reynolds and Eötvös numbers fitted well with experimental results for the riser gas holdup and downcomer liquid velocity in configurations I and II. Positive lift coefficients increase the liquid velocity and decrease the riser gas holdup, while opposite results were obtained for negative values. By studying the effects of bubble size and their shape, the smaller bubbles provide a lower liquid velocity and a gas holdup. The effects of bubble‐induced turbulence and other non‐drag closure models such as turbulent dispersion and added mass forces were analysed. The gas velocity and gas holdup distributions, liquid velocity in the riser and downcomer, vectors of velocity magnitude and streamlines for liquid phase, the dynamics of gas holdup distribution and turbulent viscosity at different superficial gas velocities for different reactor configurations were computed. The effects of various geometrical parameters such as the draft tube clearance and the ratio of the riser to the downcomer cross‐sectional area on liquid velocities in the riser and the downcomer, the gas velocity and the gas holdup were explored. © 2011 Canadian Society for Chemical Engineering     

固液分布器中主分布器的实验研究

在不同结构形式的主分布器条件下，研究了表观液速对换热管中固含率、下管箱内床层高度、静压降及平均固含率的影响。利用体积容积法测量了换热管束中的固含率、刻度尺测量了下管箱中的床层高度、U形管测量了下管箱的静压降，并运用差压法测量了下管箱中平均固含率。采用不均匀度函数衡量了不同结构条件下管束间固含率的不均匀程度。实验结果表明：在换热管下方增加优化后的主分布器可以均匀分布固液两相；主分布器直径变化时对下管箱内流动特性的影响大于主分布器轴向位置改变时的影响。     

Numerical and Experimental Study of Catalyst Loading and Body Effects on a Gas‐Liquid Trickle‐Flow Bed

The influence of tortuosity and fluid volume fractions on trickle‐flow bed performance was analyzed. Hydrodynamics of the gas‐liquid downward flow through trickle beds, filled with industrial trilobe catalysts, were investigated experimentally and numerically. The pressure drop and liquid holdup were measured at different gas and liquid velocities and in two different loading methods, namely, sock and dense catalyst loading. The effect of sharp corners on hydrodynamic parameters was considered in a bed with rectangular cross section. The reactor was simulated, considering a three‐phase model, appropriate porosity function, and interfacial forces based on the Eulerian‐Eulerian approach. Computational fluid dynamics (CFD) simulation results for pressure drop and liquid holdup agreed well with experimental data. Finally, the velocity distribution in two types of loading and the effect of bed geometry in CFD results demonstrated that pressure drop and liquid holdup were reduced compared to a cylindrical one due to high voidage at sharp corners.     

开孔转盘塔分散相滞存率及液滴直径分布的研究

本文在无传质条件下研究了开孔转盘塔(RPDc)内乳液—水体系(W/O/W)的流体力学性能。测定了塔内分散相滞存率x,考察了塔几何条件及操作条件对分散相滞存率x及特性速度U_o的影响。采用因次分析法,建立了x及U_o与塔几何条件及操作条件间的经验关联式。并采用摄影法,对分散相液滴直径及其分布进行了初步研究。实验结果表明,分散相液滴直径的分布可用上限对数正态分布来描述。     

Local hydrodynamic properties of gas phase in an internal-loop airlift reactor

The local hydrodynamic properties of the gas phase in an internal-loop airlift reactor were investigated in this study. The hydrodynamic properties including gas holdup, bubble velocity and bubble chord length were measured by dual electrical resistivity probes. The chord length distribution was then transformed to the bubble size distribution by modeling the bubbles as ellipsoids. It was found that the gas holdup increased with decreasing bubble velocity. In addition, most bubbles tended to rise along the riser central axis. Thus, the gas holdup in the axis was higher. The bubble size, bubble velocity and gas holdup were relatively constant in the axial direction of the riser except in the zones near the gas sparger and the gas–liquid separator. The bubble velocity became slower when the bubbles approached the gas–liquid separator. Moreover, the bubble size and bubble velocity for the three-phase system were relatively insensitive to the radial direction compared to those for the two-phase system. It was also found in this study that the bubble rise velocity and bubble size for the three-phase system were lower than that for the two-phase system. However, the gas holdup for the three-phase system were higher than that for the two-phase system due to bubble breakage caused by the solid particles.     

RECENT PROGRESS IN HYDRODYNAMICS OF INVERSE FLUIDIZED BED REACTORS: A REVIEW

Hydrodynamic characteristics of the inverse fluidized bed reactor such as phase holdup, pressure drop, minimum fluidization velocity, liquid circulation velocity, friction factor, bubble size and bubble rise velocity, and mass-transfer coefficient along with heat transfer studies, RTD studies, and the influence of these parameters on the extent of inverse fluidization are reviewed in this work. The importance of each of these is presented, and certain correlations developed on some hydrodynamic characteristics are provided. Our work has shown that the majority of investigations focused on phase holdup, pressure drop, and minimum fluidization velocity, and studies related to other characteristics such as friction factor, mass-transfer coefficient, and residence time distribution are generally scarce. This review also projects some of the areas on which future research work can concentrate.     

Prediction of Pressure Drop and Holdup for Homogeneous Ternary Mixtures of Spherical Glass Bead Particles in a Three-Phase Fluidized Bed

Hydrodynamic characteristics, viz. bed pressure drop and gas holdup, have been studied for ternary mixtures of homogeneous regular particles in a co-current three-phase fluidized bed. For this, a series of experiments have been carried out in a 5-cm diameter column with air as the gas phase, water as the liquid phase, and ternary mixtures of glass beads (1.54, 1.3, and 1.1 mm) as the solid phase. The dependence of bed pressure drop on the average particle diameter, superficial gas velocity, and initial static bed height has been discussed. Based on the dimensional and statistical analyses, correlations have been developed with the system parameters, for both bed pressure drop and gas holdup. Experimental values of bed pressure drop and gas holdup have been found to agree well with those calculated from developed correlations.     

DISPERSED PHASE HOLDUP AND DROP SIZE DISTRIBUTION IN A ROTATING PERFORATED DISK CONTACTOR

Hydrodynamic characteristics of rotating perforated disk contactor(RPDC)were studied with emulsionwater system.The emulsion was dispcrsed in water and its holdup was measured.The effects of columndimensions and operating conditions on holdup and characteristic velocity were studied.By using the methodof dimensional analysis,the authors obtained two experimental correlations for estimating holdup and characteristic velocity respectively.Drop size distribution was studied photographically.The experimental results showedthat drop size distribuiion could be described by upper-limit log-normal distribution.     

Flow through packed bed reactors: 2. Two-phase concurrent downflow

A model for the prediction of pressure drop and liquid holdup for trickling flow in packed bed reactors has been developed, based on the relative permeability concept. The relative permeabilities for gas and liquid as functions of corresponding phase saturations have been studied with 1300 newly measured data pairs of pressure drop and liquid holdup obtained for a wide range of commercially relevant operating conditions (including pressures up to 50 bar) as well as types of packing (both in terms of size and shape). The relative permeabilities are found to be solely the functions of corresponding phase saturations and it is shown that the functional form of the correlations developed, which are otherwise purely empirical by nature, has its roots in the physics of flow at the microscale level. The proposed model requires no prior experimental knowledge about the packed bed and is able to predict liquid holdup and pressure drop to within 5% and 20%, respectively, regardless of the type of packing or operating range investigated.     

Experimental investigation on multiscale hydrodynamics in a novel gas–Liquid–Solid three phase jet-Loop reactor

Multiphase flow hydrodynamics in a novel gas–liquid–solid jet-loop reactor (JLR) were experimentally investigated at the macroscales and mesoscales. The chord length distribution was measured by an optical fiber probe and transformed for bubble size distribution through the maximum entropy method. The impacts of key operating conditions (superficial gas and liquid velocity, solid loading) on hydrodynamics at different axial and radial locations were comprehensively investigated. JLR was found to have good solid suspension ability owing to the internal circulation of bubbles and liquid flow. The gas holdup, axial liquid velocity, and bubble velocity increase with gas velocity, while liquid velocity has little influence on them. Compared with the gas–liquid JLRs, solids decrease the gas holdup and liquid circulation, reduces the bubble velocity and delays the flow development due to the enhanced interaction between bubbles and particles (Stokes number >1). This work also provides a benchmark data for computational fluid dynamics (CFD) model validation. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16537, 2019     

Hydrodynamics of a flowing gas-solids suspension in a tube at high angles of inclination

A study was made of pneumatic transport of particles of sand suspended in air in a 31.8 mm diameter Plexiglas tube inclined at either 72 or 90 degrees with respect to the horizontal plane. The solids holdup, pressure gradient and pressure drop fluctuations over a 4.55 m test section were measured as functions of the air velocity and the solids flux. Previously observed sudden changes in slope of plots of solids holdup versus solids flux at constant gas velocity in a vertical tube (Mok et al., 1989), which were identified as transition points between dilute and dense phases, were confirmed and extended to inclined tubes. Breaks were also found in plots of pressure drop fluctuations versus solids flux at constant gas velocity.     

Macroscopic properties of liquid-solid circulating fluidized bed with viscous liquid medium

Experiments were conducted in a liquid-solid circulating fluidized bed to study the effect of liquid viscosity and solids inventory on pressure gradient, critical transitional liquid velocity, onset average solids holdup, axial solids holdup distribution, average solids holdup and solids circulation rate in circulating fluidization regime with riser operated in fixed inventory mode. The results indicate that critical transitional liquid velocity decreases with increase in liquid viscosity. The onset average solids holdup, on the other hand, increases with increase in either auxiliary liquid velocity or solids inventory. The variation of axial solids holdup distribution, average solids holdup and solids circulation rate with liquid viscosity when solid inventory was 0.15 m was dissimilar with either 0.25 m or 0.35 m solid inventory. Correlations were proposed for estimating the average solids holdup and are satisfactorily compared with experimental values.     

组合式液固分布器中预分布器结构优化

介绍了一种用于液固循环流化床换热器中的组合式固液分布器。利用体积容积法、U形管压差计和刻度尺研究了固液预分布器的结构形式在不同表观液速和液体黏度下对各管束中的固含率、下管箱静压降及床层高度的影响。采用标准差函数进一步衡量了管束间固含率的均匀程度。实验结果表明,双层挡板式预分布器在较低的下管箱静压降和床层高度下能将固体颗粒均匀地分布到各换热管束中。     

Bubble and gas holdup characteristics in a bubble column of CMC solution

The local bubble behavior such as holdup, bubble frequency, bubble size and rising velocity in a bubble column of CMC solution was measured using the eleclroresislivity probe technique, and the effects of gas velocity and CMC concentration on the behavior were investigated. Also, the total gas holdup was measured from the liquid level in the column, and its relation with gas velocity and CMC concentration was studied. Two correlations of mean bubble size and total gas holdup with dimensionless groups, composed of gas velocity and physical properties of gas and liquid, were obtained from the experimental results.     

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.     

开孔转盘塔(RPDC)分散相滞存率及液滴直径分布的研究

本文在无传质条件下研究了RPDC内乳液-水体系的流体力学性能。测定了塔内分散相滞存率x,考察了塔几何条件及操作条件对x及特性速度u_6的影响。采用因次分析法,建立了x及u_o与塔几何条件及操作条件间的经验关联式。并采用摄影法,对分散相液滴直径d_滴及其分布进行了初步研究。实验结果表明,d_滴的分布可用上限对数正态分布来描述。     

Gas phase hydrodynamics in a surface-aerated tank with a long-short blades agitator

This work aims to study the gas phase hydrodynamics in a stirred tank with a surface-aerated long-short blades agitator by the Eulerian–Eulerian approach coupled with population balance model. Predicted local gas holdup and bubble size distribution agree well with those measured by a conductivity probe technique. The predictions demonstrate that the pressure depression in the center is the main driving force for gas suction and the downward flow carries the bubbles down to redistribute in the whole tank. The gas phase has higher gas holdup with large bubble size in the upper part and lower gas holdup but with small bubble size in the lower part of the tank. The predicted liquid-phase mass transfer coefficients agree well with our previous experimental results and just depend on the power consumption per unit volume when the aspect ratio of the liquid height to the tank diameter varies from 1.1 to 2.0.