高长径比环流反应器中气、固含率的轴向分布研究

在高长径比(H/D=22.2)内环流反应器中,常温常压下,以空气-水-石英砂为物系,研究了表观气速和固体装载量对平均气含率、下降区气含率、上升区固含率、下降区固含率的影响,以及上升区气含率、固含率随轴向高度的分布规律.结果表明:平均气含率、下降区气含率随着表观气速的增加而增加,随ω(固体)增大而下降,ω(固体)≤2.6...     

三相多室气升式环流反应器气含率的研究

在1个4流道的三相多室气升式环流反应器中,以空气-水-K树脂为体系,采用压差法测量气含率,考察了上升室气体表观速率、固体装载量对上升室与下降室气含率的影响.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;下降室的气含率随着该室气体表观速率增加呈现3种变化趋势,而随着另...     

EFFECTS OF AERATED LIQUID LEVEL ABOVE DOWNCOMER ON HYDRODYNAMIC CHARACTERISTICS OF AN EXTERNAL-LOOP AIRLIFT REACTOR

Effects of the aerated liquid level above the downcomer on riser superficial liquid velocity, gas flow rates, and gas holdups in individual sections were investigated in an external-loop airlift reactor. The aerated liquid level is an important operating parameter, and the valve connected to the extension tube could adjust it. As the aerated liquid level was increased up to 0.158 m, which was slightly larger than the diameter of the riser, both the liquid circulation velocity and the gas flow rate in the extension tube increased, whereas the riser gas holdup, the downcomer gas holdup, and the gas flow rate in other individual sections except the extension tube decreased. A combination of the gas-liquid separation ability and hydraulic resistance of the head region and the surface aeration could explain the impact of the aerated liquid level on the hydrodynamic characteristics. However, the effect was negligible when the aerated liquid level was higher than 0.158 m.     

EFFECTS OF AERATED LIQUID LEVEL ABOVE DOWNCOMER ON HYDRODYNAMIC CHARACTERISTICS OF AN EXTERNAL-LOOP AIRLIFT REACTOR

Effects of the aerated liquid level above the downcomer on riser superficial liquid velocity, gas flow rates, and gas holdups in individual sections were investigated in an external-loop airlift reactor. The aerated liquid level is an important operating parameter, and the valve connected to the extension tube could adjust it. As the aerated liquid level was increased up to 0.158 m, which was slightly larger than the diameter of the riser, both the liquid circulation velocity and the gas flow rate in the extension tube increased, whereas the riser gas holdup, the downcomer gas holdup, and the gas flow rate in other individual sections except the extension tube decreased. A combination of the gas-liquid separation ability and hydraulic resistance of the head region and the surface aeration could explain the impact of the aerated liquid level on the hydrodynamic characteristics. However, the effect was negligible when the aerated liquid level was higher than 0.158 m.     

固体装载率对局部相含率与液体速率的影响

在高径比(H/D=22.2)的气升式内环流反应器中,以空气-水-石英砂为物系,研究了固体装载率和表观气速对导流筒内局部固含率、下降区固含率、下降区液体速率的影响,以及导流筒内局部气含率、固含率随轴向高度的分布规律。结果表明,固体体积分数小于或等于1.0%时,导流筒内局部固含率和下降区固含率与表观气速无关;下降区液体速率随表观气速和固体装载率的增加而下降;固定表观气速,在固体体积分数小于或等于2.0%时,导流筒内气含率在轴向是均匀分布的。     

Effect of a gas–liquid separator on the hydrodynamics and circulation flow regimes in internal‐loop airlift reactors

The role of the gas–liquid separator on hydrodynamic characteristics in an internal‐loop airlift reactor (ALR) was investigated. Both gas holdup and liquid velocity were measured in a 30 dm³ airlift reactor with two different head configurations: with and without an enlarged separator. A magnetic tracer method using a neutrally buoyant magnetic particle as flowfollower was used to measure the liquid velocity in all sections of the internal‐loop airlift reactor. Average liquid circulation velocities in the main parts of the ALR were compared for both reactor configurations. At low air flow rates the separator had no influence on gas holdup, circulation velocity and intensity of turbulence in the downcomer and separator. At higher superficial air velocities, however, the separator design had a decisive effect on the hydrodynamic parameters in the downcomer and the separator. On the other hand, the gas holdup in the riser was only slightly influenced by the separator configuration in the whole range of air flow. Circulation flow regimes, characterising the behaviour of bubbles in the downcomer, were identified and the effect of the separator on these regimes was assessed. © 2001 Society of Chemical Industry     

级间隙高度和表观气速对多级环流反应器混合和传质的影响

针对应用广泛的简单多级环流反应器,研究了级间隙高度和表观气速对其混合和传质的影响规律。发现简单多级环流反应器的各级存在着非正常流动、过渡及正常流动三个典型流动状态,且流动状态的转变存在着受级间隙高度影响的两个临界表观气速,并提出了相应的预测模型。研究结果表明：级间隙高度越大,多级环流反应器内形成正常流型所需的表观气速越大;各级上升管和降液管的气含率会增高,且相同条件下第三级气含率最大,第二级次之,第一级气含率最小;各级的循环液速会增大,且第一级循环液速最大,第二级次之,第三级最小;混合时间会缩短,而传质系数会增大。本研究可为工业多级环流反应器的科学设计、放大和操作提供重要指导。     

Hydrodynamic Modelling of Internal Loop Airlift Reactor Applying Drift‐Flux Model in Bubbly Flow Regime

A new model for the liquid circulation rates in airlift reactor (ALR) is presented. The model is based on the energy balance for the flow loop (riser, turn riser‐downcomer, downcomer, and turn downcomer‐riser) coupled with a drift flux theory of two‐phase flow gas‐liquid system, considering a bubbly flow regime. The predicted values of the liquid circulation rates by the developed model are compared with experimental results performed in a 22 dm³ internal loop airlift reactor and with the results obtained in the literatures. The proposed model predicted the experimental results very well. Slip velocity relationship based on the drift flux model was proposed; including the gas holdup, bubble size and the liquid physical properties. The predicted slip velocity was similar to that obtained from the literature. The study revealed that appropriate arrangements of internal bioreactor parts can positively influence the liquid circulation velocity at the same energy consumption. The proposed models are useful in the design; scale up and characterization of the internal loop airlift reactors, and provides a direct method of predicting hydrodynamic behaviour in gas‐liquid airlift reactors.     

CIRCULATION OF GAS AND LIQUID PHASES IN EXTERNAL-LOOP AIRLIFT REACTORS

The effects of the horizontal connection length (0.3 ≤ L_c ≤ 0.6 mrpar;, the cross-sectional area ratio of downcomer-lo-riser (0.28≤A_d/A_r≤0.53rpar;, and the superficial gas velocity on the circulation gas flow rate were studied. The circulation liquid velocity, the downcomer gas holdup, and the bubble size in the downcomer were also investigated. In order to measure the circulation gas flow rate, a gas-liquid separator was installed at the bottom connection between riser and downcomer. Both of the circulation gas flow rale and the circulation liquid velocity strongly depended on the superficial gas velocity as well as the cross-sectional area ratio of downcomer-to-riser and the horizontal connection length. An useful correlation for the circulation gas flow rate was obtained in terms of the superficial gas velocity, the cross-sectional area ratio of downcomer-to-riser and the horizontal connection length.     

高长径比三相内环流反应器中相含率的分布研究

在长径比为22的三相内环流反应器中,常温常压下,以空气-水-石英砂为物系,根据无因次准数建立了气含率、固含率的预测模型,考察了在不同粒径下上升区气含率、下降区气含率和上升区固含率、下降区固含率随表观气速的变化规律和不同固体体积分数下轴向固含率的分布情况。结果表明：不同粒径下上升区和下降区气含率均随表观气速的增大而增大;当粒径（ds）≤0．3mm时,上升区固含率随表观气速的增加呈平缓趋势,下降区固含率随表观气速的增加而增加,当0．3mm〈d。≤1．2mm时,上升区固含率随表观气速的增加而呈先下降后增加的趋势,下降区固含率随表观气速的增加而下降;不同固体体积分数下的固体颗粒的固含率随着轴向高度的增大而变化平缓,能够均匀的分布在反应器中;气含率和固含率的计算值和实验值吻合较好,其平均相对误差分别为6．32％、4．56％。     

Behavior of gas bubbles in a concentric cylindrical airlift column

Using a light transmission optical probe, the effect of superficial gas velocity on bubble properties(bubble size, bubble rising velocity, bubble frequency and local gas holdup) at axial and radial positions was determined in the riser and the downcomer of a concentric cylindrical airlift reactor. The vertical bubble length, the bubble rising velocity and the bubble frequency at axis in the riser increased with increasing superficial gas velocity and the bed height. The radial distribution of the local gas holdup, vertical bubble length and bubble frequency in the riser and the downcomer were found to be non-uniform. The profiles of the local gas holdup, vertical bubble length and bubble rising velocity in the riser were shown as parabolic shapes. The local gas holdup, the vertical bubble length and the bubble frequency in the downcomer changed with superficial gas velocity and the distance from the top of the draft tube.     

Effect of liquid volume in the gas‐separator on the hydrodynamics of airlift reactors

Gas hold‐up and liquid circulation velocity measurements were made using a 167 dm³ external loop airlift reactor. The gas‐separator was of the open channel configuration. The reactor height was 2.5 m with riser and downcomer diameters of 0.19 m and 0.14 m respectively. The systems investigated were Newtonian air–water and air–glycerol with the superficial air velocity varying between 0.02 and 0.12 m s⁻¹. The ratio of the liquid volume in the gas‐separator to the liquid volume in the reactor (volume‐ratio) was varied from 0.0% to 37%, to find its minimum critical value for optimum operation of the airlift reactor. For the air–water system, discernible effects of the volume‐ratio on riser and, downcomer gas hold‐ups and liquid circulation velocity were observed at volume ratios ≤7%. Beyond this value, the volume‐ratio had no effect. For a viscous and foaming air–glycerol system the critical volume‐ratio was increased to 19%. New and simple correlations for predicting gas hold‐up in the riser, gas hold‐up in the downcomer, and liquid circulation velocity were developed with reasonable accuracy. © 1999 Society of Chemical Industry     

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.     

Scale influence on the hydrodynamics of an internal loop airlift reactor

The overall circulation velocity, the overall riser and downcomer gas hold-ups and the effect of reactor scale on a two-phase circulation regimes were studied in this work in three airlift reactors of different scale. The measurements were carried out in airlift reactor with internal loops (IALRs) with a working volume of 10.5, 32 and 200 l at the range of temperatures 18–21 °C, under atmospheric pressure. Air and water were used as gas and liquid media. The three reactors were of similar geometry, the ratio between riser and downcomer cross-sectional areas, the aspect ratio of the column and the shape of the column bottom were taken as similarity criteria. In order to determine the linear circulation velocities, the magnetic tracer method was used. The riser and the downcomer were studied separately. Based on gas hold-up in both the riser and the downcomer, two regimes (homogeneous bubble (HMG) and heterogeneous churn-turbulent (HTG)) of the two-phase flow were observed. These were defined by Daniels [Chem. Eng. 70 (1995)] and described using the correlation proposed by Chisti [Airlift Bioreactors, Elsevier, London, 1989]. The average of the liquid circulation velocities increased with increasing reactor scale for the same superficial gas velocity. The overall circulation velocity was modelled on the basis of the momentum balance proposed in paper [Chem. Eng. Sci. 52 (1997) 25]. The parameters of both the correlation and the model tend to be constant for larger reactor scales. The value of the driving force (_R−_D) was found to be important only for lower values of gas flow rate, because at higher values, the circulation velocity seemed to be governed only by friction in the reactor vessel.     

Characterization of an airlift reactor with helical flow promoters

The helical flow promoter (HFP), inserted in the downcomer of an airlift reactor (ALR), generates a helical flow pattern in the circulating gas–liquid (solid) mixture. Data on the fluidization capacity, gas holdup, liquid velocity and mass transfer rate for two- and three-phase systems with two different carboxymethylcellulose solutions collected in a 58 L ALR-HFP are presented and compared with those of common pneumatic reactors. Generally, an increasing solid concentration led to a slight decrease in gas holdup and liquid velocity but to a considerable decrease in mass transfer rates. Insertion of HFPs produced a significantly enhanced fluidization capacity of solid particles compared to the common systems.     

两级气液内环流反应器内气含率和循环液速

基于多釜串联可以有效减小返混的原理,通过引入特殊设计的级间构件构建了一种新型的两级内环流反应器。实验研究了级间构件形式、表观气速、表观液速和气液分离器对每一级内气含率和循环液速的影响。实验结果表明,表观气速对反应器二级(上一级)中上升管与下降管气含率之差和循环液速影响较大,而对一级(下一级)的影响较小;各级内上升管和下降管的气含率均随表观液速的增大而减小,但影响程度较小。基于推动力和阻力平衡建立了预测反应器中每一级的气含率和循环液速的流体力学模型,模型预测值与实验结果吻合较好。     

底部间隙对多室环流反应器流动特性的影响

在空气-水-石英砂三相多室气升式环流反应器(MALR)中,调节底部转角连接处间隙高度分别为18,28,38mm,在表观气速1.2～4.2cm/s范围内,实验研究了底部阻力系数、相含率、循环液速随反应器底部间隙的变化规律。结果表明,随着底部间隙的增大,底部转角处的局部阻力系数减小,循环液速增大,流体夹带进入下降室的气泡和固体颗粒均增多,下降室的气含率和固含率均增大。     

气液外环流反应器中气泡行为的实验研究

详细考察了气液外环流反应器中上升管、下降管的气泡行为随轴向、径向的变化规律. 由于外环流反应器的结构特点,发现在上升管底部存在偏流,并对分布板区气泡行为随角向的变化规律进行了研究. 分析实验结果得出,气含率和气泡速度均随表观气速的升高而升高;在上升管内,气含率和气泡速度自中心向边壁逐渐降低,而沿轴向变化很小;在分布板区,由于受分布器及下降管的影响,使气含率和气泡速度在不同角向存在不同的径向分布. 在下降管中,气含率自中心向边壁逐渐降低,而气泡速度则基本不变;且下降管中的气体循环率随表观气速的升高而升高.     

用CFD研究气升式内环流生物反应器下降管中的流体力学性质

在对气升式内环流生物反应器内部流动分析基础上,全面考虑反应器下降管中气泡的并聚破碎、气液两相间相互作用和滑移等, 建立了能描述反应器下降管中复杂流动的CFD数学模型. 运用CFX-4.4对模型方程进行求解, 通过求解得到了包括气液两相速度场、局部气含率分布等详尽信息,并就液相流动速度与相应条件下的PIV测试结果进行了比较,主体流动速度的偏差在20%以下,且两者总的变化趋势一致.该模型能较好地预测反应器下降管内的复杂流场.     

CFD simulation and experimental measurement of gas holdup and liquid interstitial velocity in internal loop airlift reactor

This paper documents experiments and CFD simulations of the hydrodynamics of our two-phase (water, air) laboratory internal loop airlift reactor (40 l). The experiments and simulations were aimed at obtaining global flow characteristics (gas holdup and liquid interstitial velocity in the riser and in the downcomer) in our particular airlift configurations. The experiments and simulations were done for three different riser tubes with variable length and diameter. Gas (air) superficial velocities in riser were in range from 1 to 7.5 cm/s. Up to three circulation regimes were experimentally observed (no bubbles in downcomer, bubbles in downcomer but not circulating, and finally the circulating regime). The primary goal was to test our CFD simulation setup using only standard closures for interphase forces and turbulence, and assuming constant bubble size is able to capture global characteristics of the flow for our experimental airlift configurations for the three circulation regimes, and if the simulation setup could be later used for obtaining the global characteristic for modified geometries of our original airlift design or for different fluids. The CFD simulations were done in commercial code Fluent 6.3 using algebraic slip mixture multiphase model. The secondary goal was to test the sensitivity of the simulation results to different closures for the drag coefficient and the resulting bubble slip velocity and also for the turbulence. In addition to the simulations done in Fluent, simulation results using different code (CFX 12.1) and different model (full Euler–Euler) are also presented in this paper. The experimental measurements of liquid interstitial velocity in the riser and in the downcomer were done by evaluating the response to the injection of a sulphuric acid solution measured with pH probes. The gas holdup in the riser and downcomer was measured with the U-tube manometer. The results showed that the simulation setup works quite well when there are no bubbles present in the downcomer, and that the sensitivity to the drag closure is rather low in this case. The agreement was getting worse with the increase of gas holdup in the downcomer. The use of different multiphase model in the different code (CFX) gave almost the same results as the Fluent simulations.