单孔及微孔曝气低气速鼓泡床内气泡行为比较

引言鼓泡床反应器被广泛应用于吸收、液相氧化、好氧生化等气液反应过程,气体在液相中的分散情况对鼓泡床的反应和传质特性都有很大影响.为了提高气液传质效率,增加生产强度,工业反应器很多都是在高气速下操作(Ug>0·05m·s-1),很多研究都集中在高气速湍动鼓泡区[1~3].但对有机     

The influence of gas inlet design on gas hold-up values for water and various solutions in a loop-type air-lift fermenter

Gas hold-up was measured in an external loop air-lift fermenter for air in water, in sodium chloride and sodium sulphate solutions (concentrations between 0.025 and 1.0 kmol m⁻³), in glucose solutions (0.025 to 0.25 kmol m⁻³), sodium carboxymethyl cellulose (CMC) solutions (0.1, 0.2 and 0.5 mass %) and in suspensions of cellulose powder in water. Gas superficial velocities were up to 0.03ms⁻¹. Two types of gas spargers were used: one had six holes each of 1.6mm diameter, the other was of porous metal, which produced very small bubbles. Porous metal spargers with different diameters were also used, to alter the fraction of the cross-sectional area of the riser which was aerated (the ‘fractional aerated area’). The use of dimensionless gas velocities, obtained by dividing the superficial gas velocities by a characteristic velocity for each of the non-Newtonian liquids and solid suspensions, made possible a general correlation between gas hold-up, dimensionless gas velocity and the fractional aerated area, in bubbly flow conditions. The characteristic velocities for the electrolyte solutions could be related to the concentrations of the electrolytes. No general correlation could be obtained for gas slug-flow conditions, although theoretically-based relationships represent the results for each liquid. Gas slug-flow was observed for the non-Newtonian CMC solutions for most of the gas rates used at the lower concentrations; only at the highest concentration was bubbly flow found over a wide range of gas rates.     

Design and selection of sparger for bubble column reactor. Part II: Optimum sparger type and design

Bubble columns are widely used for conducting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Sparger is the most important accessory because it decides the bubble size/rise velocity distribution. These, in turn, govern the radial and axial hold-up profiles, the liquid phase flow pattern and hence the performance of bubble columns. In particular, the sparger design is critical if the aspect ratio is low and the sparger design dominates the performance of the bubble column. However, systematic procedure for the selection of sparger design and type are not available in the published literature. This is the specific objective of the present work. In Part I, the performance of different spargers, including the newly developed wheel type of sparger is discussed. Thus the important considerations required for the sparger design are highlighted. The bubble column used in the manufacture of hydrogen peroxide has been considered as a case for illustration.     

Determining equivalent pore diameter for rigid porous spargers

Prediction of the properties of gas dispersions (e.g., bubble size) generated by porous spargers requires a knowledge of the pore diameter. Three methodologies for determination of an equivalent pore diameter D_e of a rigid SS sparger of the type used in column flotation have been developed. In the first, D_e is determined by fitting the bubble diameter predicted by the Kumar/Kuloor model to that measured. In the second, an estimation of bubble diameter is substituted. Estimation was tested using drift flux analysis and Molerus' uniform bubbling model: the former gave acceptable agreement with the measured. Fitting to the estimated bubble diameter offers a simplification over using the measured bubble diameter. The third approach was a further simplification. By combining the Kumar/Kuloor model with drift flux analysis, D_e is estimated by fitting predicted to measured gas holdup. The methodologies are evaluated on a set of SS spargers using water with a flotation frother, Dowforth 250C. All three methodologies give similiar estimates of D_e.     

Gas hold-up behavior of mechanically agitated gas-liquid reactors using pitched blade downflow turbines

Fractional gas holdup was measured in 0.57, 1.0, and 1.5 m i.d. vessels. Pitched blade downflow turbines (PTD) were used as the impeller. Design details of the impeller, such as the impeller diameter (0.22 T to 0.5 T) and blade width (0.25 D to 0.4 D), were studied. The effect of sparger type, geometry and size on fractional gas hold-up has been investigated in detail. Four different types of spargers (pipe, conical, ring and concentric ring spargers) were used. Sparger location was varied for all the types studied. Further, design details of the ring sparger, which gave the highest hold-up were then studied in detail. These included ring diameter, number of holes and hole size. All the reported correlations for fractional gas hold-up in mechanically agitated gas-liquid reactors were tested and compared. A better correlation has been developed for pitched blade turbines.     

外环流反应器的气含率及循环液速

研究了气体分布器的形式、体系的聚并特性及静液面高度对外环流反应器的气含率和环流液速的影响。实验结果显示,对于空气－１％乙醇体系（非聚并体系）,气体分布器的形式对外环流反应器的气含率及环流液速有显著的影响;在相同的操作条件下,空气－１％乙醇体系（非聚并体系）的气含率及环流液速明显高于空气－水体系（聚并体系）。静液面高度对下降区的气含率有较大影响。     

Effects of Orifice Orientation and Gas-Liquid Flow Pattern on Initial Bubble Size

In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat terns have been developed based on force balance. The effects of the orientation of gasliquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient airwater system, thesultable gasllquid flow pattern is important to obtain smaller bubbles under the low velocity liquid crossflow con ditions with stainless steel spargers. Among the four types of gasliquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found tobe insgnifican whenliq.uid velocity is.higher than. 3.2 m;sa or theorifice diameter is small enough.     

Effect of liquid properties on the performance of bubble column reactors with fine pore spargers

This work is a study of the effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Various liquids covering a range of surface tension and viscosity values are employed, while the gas phase is atmospheric air. A fast video technique is used for visual observations and, combined with image processing, is used for gas holdup and bubble size measurements. New data on average gas holdup values, bubble size distributions and Sauter diameters are presented and are consistent with existing physical models on coalescence/breakage. A correlation based on dimensionless groups for the prediction of gas holdup in the homogeneous regime is proposed and found to be in good agreement with available data.     

Bubble columns with fine pore sparger operating in the pseudo-homogeneous regime: Gas hold up prediction and a criterion for the transition to the heterogeneous regime

New experimental data concerning the gas holdup in bubble columns equipped with porous sparger were acquired. The effect of liquid properties and sparger characteristic (i.e., pore size, dimensions) on gas holdup at the pseudo-homogeneous regime has been studied and a correlation regarding the prediction of the transition point from the pseudo-homogeneous to the heterogeneous regime has been proposed and found to be in good agreement with available data. Moreover, a previously proposed correlation [Mouza, A.A., Dalakoglou, G.K., Paras, S.V., 2005. Effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Chemical Engineering Science 60(5), 1465-1475], for the prediction of gas holdup at the homogeneous regime for this type of equipment, has been modified to take into account the effect of the mean pore diameter and it is also found to be in good agreement with published data.     

The effect of sparger geometry on gas holdup and regime transition points in a bubble column equipped with perforated plate spargers

This paper investigates the effect of sparger geometry on flow regime of a bubble column. The experiments presented in this study were performed under atmospheric pressure with water/air in a cylindrical Plexiglas^® column of 33.0 cm i.d. and 3.0 m height. Three different perforated plate spargers were employed. Hole diameter was varied in the range of 1–3 mm, while the free area was 1.0%.The theory of linear stability is used for the prediction of regime transitions in the bubble column and a comparison has been presented between the predictions and the experimental observations. A good agreement between the predictions and the experimental values of transition gas holdup has been obtained.In addition, the data from the literature has been analyzed. Experimental values of transition gas holdups and predictions by the theory of linear stability have been compared with those of literature.A correlation based on dimensionless numbers (Archimedes, Froude, Eötvös and Weber) and the group (d_o/D_C) for the prediction of gas holdup in homogeneous regime is proposed. The average error between the correlation predictions and experimental values remains under ±10%.The proposed correlation is compared with the published data and found to be in fairly good agreement.     

Critical Rotational Speed for a Floating Particle Suspension in an Aerated Vessel

The critical suspension speeds of floating particles in a gas‐liquid‐floating particle three‐phase system were measured in a multiple‐impeller agitated vessel. Three types of impellers, i.e., simple axial‐flow impeller upflow (SPU) and downflow (SPD), disk turbine (DT) and wing turbine (WT), twelve types of baffles and three kinds of gas spargers were used. The influences of impeller types, baffle configurations, gas spargers, gas superfacial velocity and particle loading on the critical suspension speeds of floating particles were systematically investigated. The optimum regressions of critical suspension speeds were respectively obtained for some better combinations of impellers, bafffles and spargers, such as (a) the 45SPU+45SPD+DT triple impellers, two high‐level baffles and two low‐level baffles (symmetric allocation), gas spargers, (b) the 45SPU+45SPD+DT three‐impeller, standard baffle and small gas sparger. Their errors were smaller than 11 %.     

大型合成氨装置二段炉空气分布器综述

介绍大型合成氨装置二段转化炉空气分布器混合燃烧机理，以及国内大合成氨装置二段转化炉空气分布器的结构及缺点，提出了国内的研究开发方向。     

Mixing Time in a Short Bubble Column

Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D ? 5) with different spargers and for different clear liquid height to diameter (H_C/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter‐cell exchange velocity, V_e, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers.     

充气条件下多层桨悬浮颗粒的临界转速

在直径为386 mm 的通气多层桨搅拌釜中,实验考察了下层搅拌桨型、挡板和气体分布器等对颗粒悬浮临界搅拌转速的影响,这对工业过程的设计和放大具有一定的指导意义.     

搅拌槽内气－液体系的分散、传质和传热

综述了搅拌槽内气－液体系分散、传质和传热特性，比较了搅拌器类型、通气方式和多级搅拌器对混合性能的影响。对文献中观点的分歧进行了探讨，由此得到两个传质系数关联式，并揭示出给热系数随操作条件变化的机理。     

CFD simulation for steam distribution in header and tube assemblies

The study of the flow characteristics in manifolds (dividing, combining, parallel or Z-manifold and reverse or U-manifold) is a classic subject of engineering fluid dynamics and hydrodynamics. These manifolds are widely used in chemical processes, electronic cooling equipment, solar collectors, spargers, microchannels, fuel cells, heat exchangers and refrigerant distribution in multi-split type of air conditioner, etc. In the literature extensive work has been done for finding out flow distribution in plate-fin heat exchanger, microchannels and spargers. Present work focuses on the flow and pressure distribution in piping networks, which has gained importance in many areas such as air distribution in diffuser system of aerobic biological treatment, steam distribution in passive decay heat removal systems, etc.     

Role of sparger design in mechanically agitated gas-liquid reactors. Part II: Liquid phase mixing

Liquid phase mixing time was measured in 0.57, 1.0 and 1.5 m i.d. mechanically agitated gas-liquid reactors. Transient conductivity technique was used for the mixing time measurement. Pitched blade downflow turbine was employed. The design details of PTD impellers such as diameter (0.22 T to 0.5 T) and blade width (0.25 D to 0.35 D) were studied. The influence of sparger types and their design on mixing time has been investigated. For this purpose, pipe, ring, conical, and concentric ring spargers were employed. The design details of the ring sparger, i.e. ring diameter, number of holes and hole size were also studied in depth. Sparger location with respect to the impeller was found to be the most important variable and, therefore, it was varied for practically all the spargers studied in this work. It was found that the liquid phase mixing time depends on the impeller design, sparger design, sparger location, impeller speed and superficial gas velocity. Correlations have been developed for the dimensionless mixing time.     

气液两相机械搅拌釜中翼型组合桨持气特性

研究了机械搅拌釜中翼型组合桨的组合方式、桨间距、通气位置及翼型桨的排出流方向对气含率的影响。在单位体积功率消耗相同的情况下,采用以翼型k5桨为下层桨、较低的通气位置及较大的桨间距为搅拌釜的几何结构,并采用翼型桨的排出流方向向上的搅拌方式,可以提高搅拌釜的气含率。给出了气含率与单位体积功耗和表面气速的关联式。     

Effect of geometrical parameters of draft tubes and clear liquid height on gas holdup in a bubble column for gas dispersion into tubes

The effects of the geometrical parameters of draft tubes and the clear liquid height on the average gas holdup E_G in a 0.16 m I.D. bubble column for gas dispersion into the tubes were experimentally studied in an airtap water system. The gas holdup depended on the superficial gas velocity U(ING), the kinds of gas spargers, the diameter and length of the draft tubes, clearance C_b between the lower end of the draft tube and the bottom of the bubble column, and the clear liquid height H_L. E_G increased with decreasing hole diameter of the gas sparger at a small gas velocity U_G, but did not depend on the kinds of gas spargers at a large U_G. E_G decreased with increasing clear liquid height H_L. The effect of H_L on E_G was well expressed by the modified three-region model. The experimental data of E_G were correlated.     

Dispersion and hold-up in bubble columns — comparison of rigid and flexible spargers

The performance of a new type of bubble generating device, the rubber sheet sparger, is contrasted and compared with rigid spargers. Impulse response tests were analyzed using the weighted-moments method to determine voidage and dispersion coefficients in counter-current bubble columns of nominal diameters two, four, six and twelve inches. The flexible rubber sheet sparger produced more uniform emulsions, smaller bubbles and larger voidages than perforated plates, while dispersion coefficients were reduced for a range of superficial gas velocities. The dispersion data seem to fit the isotropic turbulence model, with slight modifications. It is demonstrated that the rubber sheet sparger is self-regulating, with hole size increasing in direct proportion to pressure drop across the sparger.