One‐Dimensional Modeling and Simulation of Bubble Column Reactors

Reactor models that feature a practical way to design bubble columns on the semi‐industrial or even industrial scale have been published only rarely in the usual scientific literature. Creating a one‐dimensional model in the equation‐oriented simulation software ASPEN Custom Modeler? (ACM), one can reach a compromise between model precision and modeling – i.e. computational power – based on correlations selected specifically for the application in question. The model quantitatively describes, with sufficient accuracy, the processes in a bubble column reactor. The paper discusses investigations for designing a pilot plant reactor for hydrogenating 2‐ethylhexanal as an example of its application. Geometry and operating conditions were optimized, and the results are shown in the form of spatially resolved reaction and temperature profiles.     

锥形鼓泡床内气含率特性的研究

本文分析了锥形鼓泡床内流型过渡、平均气含率及气含率轴向分布特性，考察了入口气体速度、静止液体（或淤浆）高度及淤浆浓度的影响，比较了与圆柱床的差异，结果表明对于鼓泡床内气体体积收缩的反应，用锥形床的冷态试验可以较精确地模拟其实际结果。     

Regional Mean Bubble Diameters and Gas Holdup in Agitated Gas‐Liquid Contactors

Gas‐liquid contacting in mechanically agitated vessels is widely used in the process industry. Bubble size measurements at different flow regions in the vessel provide useful information for the mechanisms of gas dispersion and gas‐liquid flow. In this work, bubble size distributions and distributions of Sauter mean bubble diameters at four different regions in air‐water and air‐NaCl solution systems agitated by a six‐blade disk turbine are measured by using the photographic method. The effects of gassing rate, impeller speed and electrolyte presence in the system have been examined.     

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。     

Measurement of Local Phase Holdups in a Two‐ and Three‐Phase Bubble Column

A new invasive sensing probe for the measurement of local phase holdups in two‐ and three‐phase reactors is described. The local gas and solids holdups in a bubble column with a volume of V = 2 m³ at varying operating conditions (gas velocity, sparger design, solids content and density) are measured by means of differential pressure measurement in combination with either time domain reflectometry or electrical conductivity measurement. The phase distribution profiles at two‐ and three‐phase operating conditions are described. The influence of the sparger design on the shape of these profiles, the influence of the solid phase on the gas distribution, the solids distribution and the gas‐stow effect above the sparger because of a dense particle layer are capable of experimental proof for the first time.     

逆流鼓泡塔气含率分布的试验测量与CFD模拟

利用热膜测速仪测得了气液逆流鼓泡塔内不同表观气速、表观液速和径向位置下的气液信号,采用改进的阈值法进行分析,得到塔内气含率的径向分布。结果表明气含率在各个截面上都是从塔中心到塔壁逐渐减小;同时利用计算流体力学方法对气液逆流的鼓泡塔内的气液两相流动进行了模拟,计算了不同气速和不同液速下的气含率,计算结果与试验数据吻合较好。     

Artificial Neural Networks Modeling of Ozone Bubble Columns: Mass Transfer Coefficient,Gas Hold-Up,and Bubble Size

This study aims at applying artificial neural network (ANN) modeling approach in designing ozone bubble columns. Three multi-layer perceptron (MLP) ANN models were developed to predict the overall mass transfer coefficient (k_La, s^?1), the gas hold-up (? _G , dimensionless), and the Sauter mean bubble diameter (d_S , m) in different ozone bubble columns using simple inputs such as bubble column's geometry and operating conditions. The obtained results showed excellent prediction of k_La, ? _G , and d_S values as the coefficient of multiple determination (R² ) values for all ANN models exceeded 0.98. The ANN models were then used to determine the local mass transfer coefficient (k_L , m.s^?1). A very good agreement between the modeled and the measured k_L values was observed (R² ?=?0.85).     

Bubble characteristics in shallow bubble column reactors

The bubble characteristics have been investigated in an air–water bubble column with shallow bed heights. The effect of bed height, location and the presence of solids on the bubble size, bubble rise velocity and overall and sectional gas holdup are studied over a range of superficial gas velocities. Optimal shallow bed operation relies on the combined entrance and exit effects at the distributor and the liquid bed surface. The gas holdup is found to decrease with an increase in H/D ratio but the effect is diminishing at high H/D ratios. A H/D ratio of 2–4 is found to be suitable for shallow bed operation. The presence of solids causes the formation of larger bubbles at the distributor and the effect is diminishing as the gas velocity is increased.     

Large Bubble Columns for the Oxidation of Cumene in Phenol Processes

A number of aspects of using large bubble columns for cumene oxidation were investigated in both laboratory and production reactors. Based on the dispersion model with an axial dispersion coefficient of 0.2 m²/s and a radial dispersion coefficient of 0.034     

用神经网络法预测鼓泡塔内的气含率

在 2 0 0 0多组公开发表的鼓泡塔实验数据组成的数据库基础上 ,提出了一个预测鼓泡塔内气含率的关联式 ,介绍了一种新的神经网络回归方法。将该方法与受力分析结合起来得到 4个对鼓泡塔内气含率影响较大的无因次准数 ,对所得到的模型作出评价     

Bubble Column Reactors and Fischer-Tropsch Synthesis

Three-phase slurry bubble column reactors have been used extensively in a number of chemical, petrochemical, and biochemical process engineering applications. For the success of these operations and their large scale industrial exploitation, it is essential that their transport and chemical characteristics be adequately understood on a mechanistic basis so that appropriate design criteria and optimum operating conditions can be established. It is the purpose of this review to present such available knowledge in relation to chemical catalytic operations. The mass transfer characteristics, catalytic activity, and mixing patterns of different phases necessitate a detailed understanding of the hydrodynamic behavior and catalyst dispersion in slurry bubble column reactors. The current status of these aspects is presented, discussed, and assessed in this review. Chemical and biochemical reactions are exothermic in nature and hence efficient heat removal devices must be installed in the reactor to preserve its isothermal behavior and chemical catalytic activity by avoiding temperature runaway. Extensive work recently conducted from this heat transfer viewpoint is reviewed and appraised. The bubble dynamics, and slurry mixing and movement characteristics of such baffled bubble columns are significantly different from those of unbaffled bubble columns. Very limited information is available on baffled bubble column operations and this is reviewed and critically examined. An important application of the slurry bubble column is in the synthesis of fuel gases on suspended catalyst particle surface to produce chemicals. One such example is the Fischer-Tropsch synthesis of hydrogen and carbon monoxide in what is referred to as indirect coal liquefaction technology. Pilot plant efforts of this nature and their successes are briefly mentioned. Mathematical details and models developed from time to time to characterize catalytic bubble column operations are briefly described and discussed. In the context of available information and its integration presented here, the specific needs for future experimental and theoretical research work are pointed out.     

A Novel Approach for the Determination of Mechanical Stresses in Gas‐Liquid Reactors

A new method for the determination of mechanical stresses in two‐phase reactors is described. The time‐dependent disintegration kinetics of a clay‐floc system are measured with a laser scanning microscope. By describing the flocs employing fractal geometry and by transforming the disintegration kinetics according to a multifractal‐approach for turbulent flow fields, effective stresses can be calculated for bubble columns in two‐phase operation mode by comparison to the mechanical stress in a turbulent single‐phase couette flow. Results are given for stresses measured in a bubble column at different operating conditions.     

Impinging-Jet Ozone Bubble Column Modeling: Hydrodynamics,Gas Hold-up,Bubble Characteristics,and Ozone Mass Transfer

A transient back flow cell model was used to model the hydrodynamic behaviour of an impinging-jet ozone bubble column. A steady-state back flow cell model was developed to analyze the dissolved ozone concentration profiles measured in the bubble column. The column-average overall mass transfer coefficient, k_La (s^?1), was found to be dependent on the superficial gas and liquid velocities, u_G (m.s^?1) and u_L (m.s^?1), respectively, as follows: k_La?=?55.58 · u_G ^1.26· u_L ^0.08 . The specific interfacial area, a (m^?1), was determined as a = 3.61 × 10³ · u_G ^0.902 · u_L ^?0.038 by measuring the gas hold-up (ε _G?=?4.67 · u_G ^1.11 · u_L ^?0.05 ) and Sauter mean diameter, d_S (mm), of the bubbles (d_S?=?7.78 · u_G ^0.207 · u_L ^{? 0.008} ). The local mass transfer coefficient, k_L (m.s^?1), was then determined to be: k_L?=?15.40 · u_G ^0.354 · u_L ^0.118 .     

鼓泡床反应器中气液分配器对气含率的影响

以水和空气分别模拟工业上的重质原油和氢气迚行冷模试验,考察鼓泡床反应器新型气液分配器对气含率的影响,迚而优化幵确定气液分配器的结构形式和结构参数。试验结果表明,气液分配器对总体平均气含率的影响,随表观气速的增大基本呈线性增长,与其他鼓泡床迚料内构件结构的影响基本一致,幵且稍高一些(3%~5%)。对局部气含率的影响:轴向上,在测试范围内,轴向位置越高,气含率越高,主要和泡罩式气液分配器结构有关;径向上,气体在床层中分布不均匀,中间多,近壁少,同一高度时,中心处气含率一般为近壁气含率的1.5~2倍。