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.     

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.     

MULTIPHASE HYDRODYNAMICS AND SOLID-LIQUID MASS TRANSPORT IN AN EXTERNAL-LOOP AIRLIFT REACTOR—A COMPARATIVE STUDY

The solid-solid mass transfer performance of an external-loop airlift reactor was measured by dissolution of benzoic acid coated on nylon-6 particles, and the hydrodynamics of the gas-liquid-solid multiphase system in the airlift reactor were investigated. The solid-liquid system was designed to simulate the micro-carrier culture of animal cells, and some typical suspensions of immobilized enzyme particles.

The solid-liquid mass transfer coefficient remained constant below a superficial air velocity of 0.04 ms^-1 for the particles examined, but increased rapidly with further increase in gas velocity. Solids loading (0.3-3.5% w/w) did not affect the mass transfer coefficient in turbulent flow.

The mass transfer coefficient was correlated with energy dissipation rate in the airlift reactor. The mass transfer coefficient in stirred vessels, bubble columns, fluidized beds, and airlift reactors was compared.

Over an energy dissipation Reynolds number of 4-400, the solid-liquid mass transfer coefficient in the airlift device was comparable to that obtainable in fluidized beds. The performance of the airlift was distinctly superior to that of bubble columns and stirred tanks.     

气升式内环流反应器中的液相轴向返混

在５５Ｌ工作体积的气升式内环流反应器中，用羧甲基纤维素溶液模拟生物发酵液的粘性非牛顿流体行为，研究了表观气速及流体物性等参数对气升式内环流反应器中液相在上升段及下降段区域中轴向返混系数的影响，并与其他作用的实验结果进行了比较和分析。     

低分子量有机添加剂对内环流反应器中气含率和气液传质系数的影响

研究了气升式内循环气液两相流反应器中某些添加剂(脂肪醇类、酯类、氨基酸类等)对传质特性的影响.实验发现氨基酸对传质几乎没有影响;正丁醇和乙酸乙酯对气液间传质有强化作用;而正己醇和乙酸丁酯仅在一定范围内增强传质,从而使体积传质系数出现了峰值.分析了体积传质系数k     

LOCAL LIQUID SIDE MASS TRANSFER MODEL IN AIRLIFT LOOP REACTOR AND SELF-ASPIRATED REVERSED FLOW JET LOOP REACTOR

Combining Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence, a small-scale isotropic mass transfer model for the local liquid side mass transfer coefficients in a gas-liquid two-phase airlift loop reactor and a self-aspirated reversed flow jet loop reactor has been developed. Good agreement with the experimental data suggests a general applicability of the proposed model in these reactors.     

EFFECTS OF GEOMETRY ON HYDRODYNAMICS IN EXTERNAL-LOOP AIRLIFT REACTORS

Experimental investigations were carried out in model external-loop airlift reactors. Two reactors of laboratory scale (riser liquid height ranged between 1.16-1.56 m, riser diameter 0.03 m, A_D/A_R ratio between 0.111-1,000, total liquid volume V_T = (1.189-2.446).10^-3m³) and pilot-plant scale (riser liquid height of 4.4 and 4.7 m, respectively, riser diameter 0.200 m, A_D/A_R ratio of 0.1225 and 0.040 m, total liquid volume, V_T = (0.144-0.170) m³) were used.

The influences of reactor geometry characterized by some parameter as: A_D/A_R ratio, liquid height in riser and downcomer and liquid height in gas separator, together with the amount of introduced air, on the basic hydrodynamic design parameters: gas holdup and liquid circulation velocity were analysed.

The influence of gas sparger design on gas holdup and liquid velocity was found to be negligible.

The experimental liquid circulation velocity was correlated using a simplified form of the energy balance in airlift reactors, valid for external-loop airlift reactors with almost complete phase separation at the top.

An original dimensionless correlation for gas holdup prediction involving superficial velocities of gas and liquid, cross sectional areas, dispersion height, riser diameter, as well as Froude number, was obtained.     

外环流反应器液相流动模型的研究

应用脉冲示踪技术，在内径６０ｍｍ的两相外环流反应器中分别测定了空气－水、空气－尿素溶液、空气－乙醇溶液和空气－羧甲基纤维素钠溶液４个体系在不同气液速和不同浓度下的液相ＲＴＤ曲线，同时实测了相应条件下的物性参数。对实测数据分别用多釜串联模型和轴向扩散模型进行了关联比较，结果表明用如下关联式较为合适Ｎ＝１．６５３４－ｄＲρＬμＬ（１．６０５８×１０－４ｕＬ＋３．９２５８×１０－５ｕＧ）该关联式将模型参数与影响流动的重要物性参数和主要操作条件以及反应器的特性尺寸关联在一起，为进一步开发研究此类高效气液反应器提供了参考依据     

三相携带床的流体力学特性研究

研究了空气一水-黄沙三相系统在携带床反应器中的流体力学特性。反应器直径0．07m。实验考察了表观气速Ug、表观浆液流速UsL、固含率εs等因素对气含率εg和床层压降△P的影响以及三相携带床的操作特性。回归实验数据得到气含率及床层压降与各因素的关联式为εg=0.4084U△P=5783．672U研究结果为三相携带床工业反应器提供了流体力学依据。     

ESTIMATION OF EFFECTIVE SHEAR RATE FOR AERATED NON-NEWTONIAN LIQUIDS IN AIRLIFT BIOREACTOR”“

Effective shear rate is one of the indispensable parameters for the design of aerobic fermentors using a viscous non-Newtonian system. The estimation of effective shear rate in airlift loop bioreactors has been investigated with liquid circulation velocity. An empirical correlation of effective shear rate in airlift loop reactors is proposed.

γ_eπ= 3.26-3.51 ; 10²U_G + 1.48 10⁴U²_G

It is found that the effective shear rate is lower in airlift reactors than in bubble columns. This equation can be used for the cultivation of cells sensitive to shear stress.     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

气升式反应器中三相体系进行半连续操作的气含率和传质特性研究

就出现在细胞培养等气液固三相体系在气升式反应器(ALR)中气含率和传质系数同反应器结构参数、固含量及操作条件之间的关系作了理论推导,在不同结构形式的 ALR 中对空气/0.15NaCl 溶液(内含不同数量的固体颗粒)体系作了实验测定,估计了模型中的待定参数,求出气含率(■)和氧的传质系数(K_Lα):■由此可推算二氧化碳的传质系数,并讨论了反应器高度和气体分布器的影响。     

液位控制对聚丙烯装置长周期运行的影响

通过对聚丙烯装置近5年停车情况进行的分析，找出了聚丙烯装置停车的主要原因，通过对液相反应器液位测量方式的讨论，指出了现行液位测量与控制上的缺点及偏差；试图从液相反应釜搅拌电流来估算合适的液位区间，即最佳液位。并提出了改进液位测量与控制的技术措施和操作指导。     

下喷式环流反应器的气含率特性

本文以空气-水和空气-CMC 水溶液为实验体系,研究了气速、液速、体系物性以及反应器结构尺寸等参数对下喷式环流反应器全塔平均气含率的影响,得出最优的导流筒直径与反应器直径之比为0.57,提出了牛顿型与粘度较低的非牛顿型流体体系中气含率的计算关联式:■_G=0.3157[(D_E/D_R)~2-1.14D_E/D_R+0.55]~(-3.312)·n~(0.9142)·((ρ_G·μ_G)/(ρ_L·μ_L))~(0.01899)·Fr_■~(0.3884)·Fr_L~(0.2918)     

EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.     

三相外环流反应器的液相返混特性和气液传质特性

主要研究了气速与固相对三相外环流反应器液相返混特性和气液传质特性的影响规律,并用“组合模型”分析了反应器各局部区域的返混情况。实验结果表明:液相返混主要由循环返混所致,约占95%以上;固相的存在对液相返混特性和气液传质特性均有显著的影响。研究结果对开发这类反应器具有重要意义。     

滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量     

低温对螺旋升流式反应器系统营养物去除效果的影响及其流态释因

结合螺旋升流式反应器(spiral up-flow reactor,SUFR)的流态特点,分析低温(8～20℃)对SUHt系统处理效果的影响.结果表明,该系统COD和TN处理效果虽然随着温度的降低有所下降,但是COD及TN去除率仍分别达到86%、70%以上,TP的去除率一直在92%以上.流态模拟结果表明,SUFR 系统中单元反应器的推流流态容积利用率为59%.这说明SUFR系统反应器内螺旋流形成的以活塞流为主要特征的复合流态有助于减轻低温对污水处理的负影响.该系统具有更宽的温度适宜范围.