筛板结构对多级鼓泡塔中流体力学参数的影响

在外径0.3 m的多级鼓泡塔中采用双探针电导探头考察了筛板结构对鼓泡塔中筛板上下两处流体力学参数的影响,并与无筛板鼓泡塔中流体力学参数进行了对比。研究结果表明:带筛板的鼓泡塔中气含率径向分布规律和无筛板的鼓泡塔相类似,筛板上下二侧的平均气含率随表观气速的增加而增加;在鼓泡塔轴向位置上,筛板下侧的气含率普遍比筛板上侧气含率要高;筛板的孔分布方式对于气含率径向分布有着一定影响,但孔径大小对此影响较小。     

鼓泡塔中气泡尺寸分布和局部气含率研究

在内径为0.38 m的鼓泡塔中采用双电导探针法对不同通气速率下的气泡尺寸分布和局部气含率进行了实验研究,分析了气泡尺寸的概率密度分布。结果表明:气泡尺寸随轴向高度的增加而增大,随径向距离增加而减小;鼓泡塔中气液流动可分为过渡流域和充分发展流域,在过渡流域气含率随轴向高度增加而增大,在充分发展流域气含率趋于均值,径向局部气含率分布呈抛物线型下降。高气速下气泡尺寸概率密度分布比低气速下宽,且随轴向高度的增加分布变宽。     

采用电阻层析成像技术测量气液加压鼓泡塔局部气泡参数

在内径0.3 m,高6.6 m的加压气液鼓泡塔反应器中,采用电阻层析成像技术(ERT)研究了空气-水体系中气泡群平均上升速度、局部气含率及其径向分布。在表观气速0.119~0.312 m s 1,压力0.5~2.0 MPa,考察了表观气速、压力对气泡群上升速度、局部气含率及其径向分布的影响。实验结果表明,鼓泡塔中局部气含率随着表观气速与压力的增大而增大,其径向分布呈现出中心高边壁低的分布特征,但整个截面的分布并非严格对称,在r/R=0~0.3,气含率变化较小,且极大值出现在该范围内;气泡群的局部上升速度随着表观气速的增大而增大,但是随着压力的增大而减小。     

气液固三相流化床局部相含率

在以焦末为固相、空气为气相、水为液相的三相流化床中研究了局部气含率和局部固含率径向分布。实验用流化床内径100 mm,高1.7 m,焦末粒度1.07 mm。分别采用电导探针法和光纤法测定局部气含率和局部固含率。结果表明:表观气速为0.35—0.71 cm/s,表观液速为2.12—3.54 cm/s时,局部气含率在流化床中沿径向r/R=0—0.8处分布较均匀,在靠壁面处下降至约0.5%,且随表观液速增加而减小,随表观气速增加而增大,且在距分布板轴向高度分别为370 mm和470 mm时趋势一致,大小沿轴向增加,在表观气速一定时,液速小于2.12 cm/s时,气含率沿径向减小的趋势较明显。局部固含率沿径向分布较均匀,基本不随表观气速变化而变化,随表观液速增大而增大,且在距分布板轴向高度分别为370 mm和470 mm时趋势一致,大小沿轴向减小。     

鼓泡塔气液两相流内部流场的流体力学特性

采用计算流体力学CFD软件对鼓泡塔内部4种表观气速下内部流场的流体力学行为进行模拟。分析了鼓泡塔内部整体气含率及轴截面处（X=0）液相速度随时间的变化情况;并且对比了在不同表观气速下局部气含率和液相速度在不同高度处的径向分布情况。模拟结果表明,随着时间的增大,整体气含率增大速度比较快,到达稳定时间,整体气含率不再增大。在同一高度处局部气含率随着表观气速的增大而增大。H/D<3时,液相循环流动表现为单相循环流;当H/D=3时,表现为双循环流,流型较单相复杂。     

高气速下鼓泡塔中气含率分布的测定

在内径476 mm的鼓泡塔内用压差法测定全塔平均气含率与表观气速的关系,进一步利用响应特性良好的双电导探针,考察了不同气速下局部气含率的分布规律。实验结果表明,利用探针法计算得到的全塔平均气含率值与压差法测定值平均误差仅为4.5%,表明探针法测量局部气含率的可靠性良好。实验还表明在高气速下,除分布板影响区外,局部气含率均类似抛物线型分布;随着气速增加,气含率分布趋于陡峭。以实验为依据,拟合了不同气速下(0.05~1.0 m/s)鼓泡塔中局部气含率的关联式,认为塔内局部气含率与径向位置、表观气速和塔径等因素有关。     

浆态鼓泡床新型锐孔分布器气含率分布

在空气-水系统中,应用双头电导探针法,测量了采用新型锐孔分布器时浆态鼓泡床中气含率的轴向分布和径向分布规律,考察了表观气速、分隔板和液体循环等因索对床层气舍率分布的影响.结果表明,在实验范围内,气含率随轴向高度的增加而增加,表观气速较大时,主体区径向气含率分布比较均匀;气含率随表观气速的增加几乎成直线上升;加入分隔板,局部气含率增大且分布均匀.在主体区,对多组实验数据进行回归分析,得出了不同表观气速下气含率分布的关联式,关联式计算值与实验值吻合良好.     

气液鼓泡塔内的气含率和液相轴向返混系数

对直径为150和300毫米有一块气体分布板和六块筛板的有机玻璃鼓泡塔,在空塔气速为1～50厘米/秒范围内测定了不同体系的气含率和液相轴向返混系数,获得了实用的经验关联式。实验证实当D≥150毫米时,气含率与塔径无关。用差压法测得塔内气含率的分布,证实在高度不大的鼓泡塔中气含率是均一的。     

加压大型气液鼓泡床中气含率的实验和关联

对内径0.3 m、高6.6 m的加压鼓泡床中的气含率进行了系统研究，得出了表面张力、粘度、压力等对气含率的影响规律；结果表明，在实验范围内，鼓泡床中的气含率随表面张力和粘度的升高而降低，随压力的升高而升高；并用气泡聚并的能量理论作了定性的解释. 根据542组实验数据得出了气含率的关联式.     

煤直接液化鼓泡床反应器流场流动特性及强化机制

针对大型鼓泡床反应器存在返混增强、物料流场分布不匀匀性趋强以及传质效率低等影响反应器安全稳定高效运行的突出问题，开发了一种径向展开的新型阻尼分布器，在冷模试验平台上探索阻尼分布器对气泡聚并及破碎行为的影响规律，考察大型反应器中不同阻尼分布器组合方式的流场流动特性，探究了阻尼分布器组合在工业反应器放大过程中的流场强化效果。结果表明：设置阻尼分布器后，鼓泡床反应器冷模试验装置中湍流涡尺度减小，气泡破碎概率提高，不同气泡群经阻尼分布器后气泡群平均直径从13.48～24.38 mm降至9.40～20.38 mm,表面积增幅为8.5%～71.9%。设置阻尼分布器可提高反应器局部气含率和液速分布均匀性，适当增加阻尼分布器层数有利于扩大流场的轴向影响范围。增大阻尼分布器直径有利于减小各高度平面间局部液速的差值并提高局部气含率径向分布均匀性，不同高度平面中心液速的差值由0.6 mm/s降至0.3 mm/s,同一高度平面局部气含率方差可降至未设置阻尼分布器时的15%。在反应器放大过程中，流体绕流的径向范围扩大，设置阻尼分布器后局部气含率和液速分布均匀性进一步提高，同一高度平面局部气含率方差可降低至未设置...     

加压大型鼓泡床反应器内大小气泡气含率研究

在内径0.3m、高6.6m的加压鼓泡床反应器内采用床层塌落技术测量床层内的大小气泡气含率实验。由于大小气泡上升速度不同,床层塌落曲线存在一水平段,在此基础上,详细考察了表面张力、粘度、系统压力、表观气速对大小气泡气含率的影响,得出大气泡气含率随粘度和表面张力升高而升高,随压力升高而降低;小气泡气含率随粘度和表面张力升高而降低,随压力升高而升高;并根据质量守恒定理,进行了解释。     

Gas holdup in pulp fibre suspensions: Gas voidage profiles in a batch-operated sparged tower

Gas holdup in a semi-batch operated slurry (pulp fibre suspension) bubble column was investigated for two pulp types (softwood and hardwood kraft pulps) over a range of suspension mass concentrations (C_m=0–9% by mass) and superficial gas velocities (U_g=0.0027–0.027 m/s). Three techniques were used: height difference between gassed and ungassed operation; pressure difference as a function column height; and electrical resistance tomography (ERT). Depending on the technique used the average, axial and radial holdup profiles could be determined. In the pulp suspensions, the ERT determined gas holdups correlated well with those determined using the differential height method. In water, the ERT determined gas holdups were significantly lower, but the agreement was significantly improved by increasing the background conductivity by adding 1 g/L salt to the water. This, however, reduced the overall gas holdup due to the effect of the electrolyte on bubble coalescence. Other differences between the three measurement techniques were attributed to limitations in the detection methods and the averaging procedures used to compare results.The presence of pulp fibres reduced gas-holdup at all gas flow rates and suspension concentrations studied and is attributed to increased bubble coalescence which increases bubble size and consequently bubble rise velocity through the suspension. Gas holdup (as determined by ERT) increased with column height. The radial gas profiles were non-uniform and more peaked than the corresponding water profiles. At low suspension concentrations this was attributed to asymmetric suspension recirculation within the column. As suspension concentration increased, channels formed in the suspension with the average void fraction leveling off to a plateau.     

GAS-PHASE HOLDUP IN A SLURRY-BUBBLE COLUMN

Total and sectional gas-phase holdups are measured in a wide (0.305 m internal diameter) and long (3.7 m) glass bubble column al ambient conditions as a function of superficial gas velocity. Sectional gas holdup values vary along the length of the column and decrease as the height above the gas distributor plate increases in the transitional and turbulent flow regimes. In the discrete bubbling regime, the values are fairly constant in most of the column length except for a small lower portion where the values are significantly smaller than in the rest of the column. This is due to the formation of gas jets at the orifices of the distributor plate. The holdup values are dependent only on the mangitude of gas velocity and do not depend upon how it is approached, i.e., by increasing or decreasing the flow, in the turbulent-flow regime. This is not the case in the discrete and transitional gas-flow regimes. These characteristic variations in gas holdup are explained on the basis of the formation of bubbles in the lower region of the column and their growth by bubble coalescence prior to acquiring a stable bubble size.

Limited experimental data for the three-phase system (air-water-glass beads) indicate that gas holdup decreases as the concentration of glass beads is increased in the mixutre. This is attributed to the increased buoyancy effect in the presence of glass beads which increases the upthrust and hence the bubble velocity which results in the decrease of gas holdup. Total gas holdup data as a function of superficial gas velocity are compared with the predictions of four commonly used correlations and are also analysed in terms of the sectional measured gas-phase holdup data. The inferences that follow are significant.     

鼓泡床内气体分布器设计及其对水力学的影响

本文比较了目前常用的几种分布器，通过照像法观察了三种分布器（单孔板、多孔板和烧结金属板）上的气泡形成过程，然后测定了这三种分布器的于板压降和湿板压降，并就它们对水力学条件的影响进行了考察。其结果对鼓泡床内分布器的设计具有一定的参考价值。     

γ射线透射技术测量气液鼓泡塔内气含率的轴向分布

引　言鼓泡床反应器以其具有良好的传热、传质、相间充分接触和高效的可连续操作等特点在许多领域得到了广泛的应用 ,如氧化、加氢、烷基化、污水处理等工业过程 .在鼓泡反应器中气体以分散相的形式存在 ,轴向气含率分布是反映气泡在鼓泡塔反应器内运动行为的重要参数之一 .虽然采用了各种测量方法对流体力学行为进行了大量研究[1～ 3] ,取得了一定的研究成果 ,但工业过程往往是在高温高压的条件下操作 ,大部分的测量方法难以适应这种条件 ,所以探求新的测试技术尤为重要 .　　γ射线透射技术不仅用于塔设备的故障检测 ,而且用于其他的石油…     

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.     

EFFECT OF OPERATING CONDITIONS ON GAS HOLDUP IN SLURRY BUBBLE COLUMNS WITH A FOAMING LIQUID

This work presents experimental data on gas holdup in slurry bubble columns with a foaming liquid. The effects of solids concentration, solid particle size, superficial phase velocities and column dimensions on the gas holdup are analyzed. At low superficial gas velocities (less than 4cm/s), for which the liquid does not foam, the presence of solids with small particle size does not affect the gas holdup whereas solids with large particle size induce foam formation and thus their presence increases the gas holdup. In the foaming regime, an increase of solids concentration decreases the gas holdup. The operating mode has a strong effect on the gas holdup: the semi-batch operating mode (stagnant liquid-solid suspension) increases the ability of the liquid to foam with respect to the continuous mode. Regarding the effect of column dimensions, the results presented show that the height of the bubble column does not affect at an appreciable extent the gas holdup in the range 6 < LID < 12. At high gas velocities (greater than 6 cm/s) the gas holdups obtained in a 30 cm-internal diameter column are the same as those measured in a 10 cm-internal diameter column.