Hydrodynamics of a Multi‐Stage Internal Loop Airlift Reactor

The local hydrodynamic properties in a multi‐stage internal loop airlift reactor were investigated in this study. The gas‐liquid two‐phase flow hydrodynamic properties, including gas holdup, bubble velocity, bubble diameter, and liquid circulation velocity at various stages were measured by dual electrical resistivity probes and conductivity cells. Detailed studies on the gas holdup, bubble velocity, bubble diameter, and liquid circulation velocity were conducted with respect to various values of superficial gas. The Zuber and Findlay drift flux model was used to represent the variation of slip velocity with total gas‐liquid velocity at various stages and the model fits the data well.     

气升式内循环反应器的数值模拟和结构参数

采用Euler-Euler双流体模型对内循环反应器(高1240 mm,直径165 mm,导流筒高590 mm)进行数值模拟,考察了表观气速、导流筒结构(导流筒内径比Dt/D,底隙高度)对反应器内上升区、下降区流体力学参数(气含率、液体速度)的影响. 结果显示,表观气速、导流筒内径、底隙高度对反应器气含率、液体速度有很大影响,随表观气速增加,反应器上升区、下降区气含率都增加,导流筒内径比为0.58时更易实现气液循环,底隙高度为30 mm时反应器内下降区气含率、气液速度都最小;气液分离器角度越大,进入下降区的气体越多,当气液分离器角度为45o时,能更好地实现气液循环.     

表观气速对气升式环流反应器性能的影响

利用计算流体力学(CFD)数值模拟方法.采用Euler法双流体模型研究了表观气速对气液两相气升式环流反应器的液体循环速率和气含率的影响.实验结果与数值模拟结果吻合较好.结果表明.气含率和液体速率在反应器内分布不均匀,气含率在相同的径向位置变化很小,液体速率随着表观气速的增加而增加.     

气升式三相内环流反应器中相含率的研究

在一个6．36L的气升式内环流反应器中,以空气-NaCl水溶液-K树脂为实验体系,在导流筒内的表观气速为1．21～7．28cm·s^-1时,考察了平均气含率、平均固含率随表观气速的变化规律,研究了转向面积比、NaCl水溶液浓度与平均气含率之间的关系。在均匀鼓泡流区域用模型方程Eg=aUgb来关联平均气含率,其中模型参数6=0．766,a与转向面积比、NaCl水溶液浓度关系为a=3．45×10^-5＋0．0146（Sb／Sr）0．0185＋1．35W。     

螺旋气升式内环流反应器流动特性

以水和空气两相系统为研究对象,建立螺旋气升式内环流反应器冷模实验装置,采用压差法测定导流筒升流区气含率,用电导法分别实测了升流区液相速度和反应器混合时间,研究螺旋气升式内环流反应器的流动特性,并与传统气升式内环流反应器的流动特性进行对比研究。结果表明,加螺环后反应器气含率明显增加,平均增幅为20%,升流区液相表观速度减小,混合时间增加。     

三相多室气升式环流反应器中上升室气含率研究

在一个4流道的多室气升式环流反应器中,以空气-水-K树脂为体系,考察了上升室气体表观速率和固体装载量对上升室气含率的影响。结果表明:上升室的气含率随着该室气体表观速率增加而增加,而随着另一上升室气体表观速率增加而略有降低;上升室的气含率均随固体装载量增加而降低。在鼓泡流下,根据漂流通量模型,建立了上升室的气含率模型;上升室气含率的模型计算值和试验值的平均相对误差为6.429%。     

气升式环流反应器液相流场的研究

运用粒子图像测速仪(PIV)技术测量了一拟二维气升式环流反应器内液相流动状态。避开了气液两相成像带来的图像处理困难。成功测取了时均液相速度、瞬时雷诺应力、剪切应力等在反应器下降段内的分布;考察了反应器上升段进气量和反应器液位高度对液相循环速度的影响;同时,对反应器三个具有代表性的流动部分进行了观测,获得了该反应器内液相流场具有代表性意义的速度分布图。研究结果为认识该类反应器的性能及进行反应器设计、优化提供了有价值的参考信息。     

Flow Regime Transitions in an Internal‐Loop Airlift Reactor

The flow regime transitions of the riser and downcomer in an internal‐loop airlift reactor are investigated. Analysis of the effects of mean value, standard deviation and chaotic time series on pressure fluctuation signals is recorded to determine the transition of the hydrodynamics in the riser and downcomer of the internal‐loop airlift reactor. Two major chaotic invariants, the correlation dimension and the largest Lyapunov exponent, are employed to indicate the regime transitions. The regime transitions are determined by the sudden increase and decrease of the chaotic invariants, which are computed by the pressure fluctuation signals obtained by varying the gas flow velocity. The determination of chaotic invariants predicts that there is no heterogeneous phase existing in the downcomer of the internal‐loop airlift reactor. The experimental observations agree well with the predicted results.     

Experimental Study and CFD Simulation of Hydrodynamic Behaviours in an External Loop Airlift Slurry Reactor

The local hydrodynamic behaviours in an external loop airlift slurry reactor, including the gas holdup, bubble rise velocity, bubble size, were measured with a fibre optic probe. The liquid circulation velocity was measured with an ultrasound Doppler velocimetry. Two‐dimensional simulations were carried out in the framework of Two‐Fluid formulation coupled with a k‐? turbulence model. The lateral forces and interphase turbulence were taken into account and good agreement between the experimental and simulation results was obtained. The simulations show that the lateral forces and interphase turbulence have noticeable influence and should be included in the CFD model.     

气升式环流反应器的研究进展

环流反应器在工业上正得到越来越广泛的应用,对其进行深入研究对于此类反应器的设计与放大具有重要意义。对环流反应器的流动、混合及传质特性参数随表观气速、液相物性、系统压力和反应器尺寸等操作条件的变化关系进行了综述。介绍了各特性参数的测量方法,并指出了这些方法的优缺点及可能存在的误差。对环流反应器的流动、混合及传质特性的数学模型进行了评述,并在此基础上对环流反应器研究的发展前景进行了展望。     

Drift Flux Modelling for a Two‐Phase System in a Flotation Column

Using different two‐phase systems, a laboratory flotation column was operated over a wide range of bubble size from 250 to 1100 µm. The drift flux analysis for the tests was used to obtain a new correlation to relate the characteristic exponent m in the drift flux equation j_gf = U_tα_g(1 — α_g)^m, to bubble Reynolds number, where j_gf is the drift flux, U_t is the terminal velocity of an individual bubble, α_g is the gas volume fraction, and m is an exponent that depends on flow conditions. m = 20.26 + 1.89 Re_b/4.38 + Re_b.     

气升式环流反应器强制振荡周期对传质影响的研究

在同一反应器中比较了不同振荡周期下的气液传质特性,为最优强制振荡周期的确定提供了实验依据和分析基础。选择体积传质系数及气含率作为传质研究的主要评价指标,实验结果表明,动态操作下的传质效果明显优于稳态,而不同振荡周期传质效果也大不一样。在0.8~2.4m3h-1的气速范围内,由静压力、导流管顶部截面流体速度、全床气含率(及传质系数)周期性变化所确定的振荡周期TP、TV、TK比稳态操作下的全床平均传质系数分别提高了3.92%~27.3%,2.35%~24.5%,28.2%~43.3%。由反应器内全床平均气含率或传质系数确定的振荡周期TK是最佳振荡周期。     

超声内环流气升式反应器传质性能的研究

研究了超声内环流气升式反应器中空气-水-离子交换树脂体系的气液传质与液固传质性能.分别采用电极动态法和离子交换树脂法实验测定了气液传质和液固传质系数.重点考察了表观气速、超声电功率对于气液传质系数以及液固传质系数的影响.实验表明,内环流气升式反应器中表观气速对于气液传质性能影响较大,而超声作用对气液传质影响不大.该反应器中液固传质系数随表观气速的增加而增大;无超声作用情况下,当表观气速达到一定程度时,液固传质系数保持一恒定值.超声作用时,气速增加到4 cm·s-1左右,传质系数达到最大值,随后液固传质系数随着表观气速的增加而逐渐减小,传质系数仍然大于无超声作用时的值.超声对液固传质有较强的促进作用,电功率在150 W左右时,超声对液固传质的促进作用最佳,是不加超声作用时传质系数的两倍左右;但随着电功率的进一步增大,液固传质系数呈现下降趋势.     

Sensitivity Study on Modeling an Internal Airlift Loop Reactor Using a Steady 2D Two‐Fluid Model

The sensitivity study of bubbly flow in an internal airlift loop reactor is presented using a steady Reynolds averaging two‐fluid model. Comparative evaluation of different drag formulations, drag coefficient correlations, turbulence effect on the drag coefficient, outlet slip velocity, and bubble size is performed and the respective influence to the simulation results is highlighted. It is found that a complicated drag formulation may not result in reliable predictions. All the drag coefficient correlations underpredict the gas holdup if the influence of turbulence on the drag coefficient is not well incorporated. Fortunately, the global hydrodynamics is not sensitive to the outflow slip velocity for a wide range, so a steady two‐fluid model can be used to simulate the bubbly flow when the flow field is fully developed. The correct estimation of bubble size with properly selected correlations play an important role in successful simulation of gas‐liquid bubbly flow in airlift loop reactors.     

多室气升式环流反应器传质特性

以Higbie的渗透理论为基础,建立了多室气升式环流反应器体积传质系数的模型方程．用亚硫酸钠空气氧化法测定反应器的比表面积和体积传质系数,讨论了表观气速和催化剂浓度对它们的影响,并验证了模型的适用性。     

三相环流反应器流体力学行为

气升式三相环流反应器综合了鼓泡塔和机械搅拌釜的优良性能,具有结构简单、无机械传动部件、易密封、造价低、容易实现工业放大等优点,在石油、化工、电化学和生物化工等领域得到了广泛应用．随着能源形势的日趋紧张,环流反应器在液相法合成甲醇、浆态床一步法合成二甲醚、煤液化等过程中的应用得到许多研究人员的重视,并取得了重要的研究进展．由于目前对其内部流动行为尚缺乏系统的认识,进行工业设计和操作过程中仍显理论指导不足     

Experimental Study on the Hydrodynamics and Mass Transfer Characteristics of Ultrasonic Loop Airlift Reactor

The promoting effect of ultrasonic wave on the hydrodynamics and mass transfer characteristics of the loop airlift reactor was studied. The gas holdup, liquid circulation velocity, mixing time and overall volumetric mass transfer coefficient were examined and compared, with and without ultrasonic wave in the reactor. The experimental results show that ultrasound has almost no notable effect on the gas holdup, but has a tendency to decrease gradually the liquid circulation velocity and increase the overall volumetric mass transfer coefficient; and the effect on the mixing time is relatively complex. At low superficial gas velocity, the low powered ultrasound promotes the radial mixing of fluid; with the ultrasonic power increasing, ultrasonic vibration obstructs the axial mixing of fluid. Moreover, the effect of ultrasonic wave on the mixing time gradually decreases with the increase in the superficial gas velocity. Therefore there exists an optimal ultrasonic power for hydrodynamics and mass transfer. Correlations were also proposed for the hydrodynamics and mass transfer characteristics of the reactor.     

气体分布器结构对气升式环流反应器内气液两相流动的影响

使用欧拉两流体模型研究气体分布器结构对气升式环流反应器内气液两相流动的影响,预测了环己烷氧化反应器内单环结构、三环结构、五环结构的气体分布器时反应器内液相速度分布、气含率分布、液相循环速度以及液相微观混合特性.模拟结果表明,在等量的进气流量下,气体分布器环数增加,液相速度分布和气含率分布更趋均匀;气体分布器环数增加,液相推动力增加,从而使得液相循环速度增加,液相的宏观混合效果增强;气体分布器环数增加,导流筒内外的平均气含率增加.随机游走模型模拟结果表明,气升式环流反应器与普通鼓泡床反应器对气体分布器结构要求不同.     

气升式环流反应器的理论研究进展

概述了气升式环流反应器的流体力学模型,对工程实用性较强的气液两流体模型和气泡导致的湍动模型进行了分类,并对常见相间作用力模型和多相流求解技术进行了总结和评价. 指出将Favre平均的两流体模型和采用Sato模型考虑气泡导致湍动的k-e模型相结合是现阶段气升式环流反应器设计和放大的有力工具. 在分析了气液两相流理论现状的基础上,指出了其存在的问题和进一步的研究方向.