MASS TRANSFER AND HYDRODYNAMICS IN AN AIRLIFT REACTOR WITH VISCOUS NON-NEWTONIAN FLUID

In an internal loop airlift reactor of 55L working volume,the gas-liquid volumetric oxygenmass transfer coefficient k_Lα,gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymethyl cellulose(CMC)to simulate the performance of a reactor with highly viscousbroth.Electric conductivity and oxygen probes were used to measure the local gas holdup,liquidcirculation time and oxygen mass transfer coefficient in the individual sections of the reactor(riser,downcomer and the gas-liquid separating section at the top of the reactor)and the total reactor,respectively.The values of k_Lα for the riser,downcomer and separation sections of the reactor were alsoestimated and compared with that for the total reactor.The results show that,both k_Lα and ε_G in-crease but t_c decreases with increasing gas velocity.Correlations and comparisons with works reportedin the literature are also presented.Data show that the methods developed for k_Lα measurements inthe individual section and     

Experimental determination of gas holdup and volumetric mass transfer coefficient in a jet bubbling reactor

The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, p H and superficial gas velocity. The reactor diameter and height were 11 and 30 cm,respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40℃, and two p H values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s~(-1) range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD) in different superficial gas velocities. The results indicated that at the same temperature but different p H, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the p H value of 6 was higher than that at the p H = 3. At a constant p H but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃ were higher than that of the same at 20℃. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.     

Influences of top clearance and liquid throughput on the performances of an external loop airlift slurry reactor integrated mixing and separation

A new developed external loop airlift slurry reactor, which was integrated with gas–liquid–solid three-phase mixing, mass transfer, and liquid–solid separation simultaneously, was deemed to be a promising slurry reactor due to its prominent advantages such as achieving continuous separation of clear liquid from slurry and cyclic utilization of solid particles without any extra energy, energy-saving, and intrinsic safety design. The principal operating parameters, including gas separator volume, handling capacity, and superficial gas velocity, are systematically investigated here to promote the capabilities of mixing, mass transfer, and yield in the pilot external loop airlift slurry reactor. The influences of top clearance and throughput of the clear liquid on flow regime and gas holdup in the riser, liquid circulating velocity, and volumetric mass transfer coefficient with a typical high solid holdup and free of particles are examined experimentally. It was found that increasing the gas separator volume could promote the liquid circulating velocity by about 14.0% at most. Increasing the handling capacity of the clear liquid from 0.9 m~3·h~(-1) to 3.0 m~3·h~(-1) not only could increase the output without any adverse consequences, but also could enhance the liquid circulating velocity as much as 97.3%. Typical operating conditions investigated here can provide some necessary data and guidelines for this new external loop airlift slurry reactor to upgrade its performances.     

加入分散有机相强化气体吸收的传质过程(英文)

Mass transfer enhancement of gas absorption by adding a dispersed organic phase has been studied in this work. Various dispersed organic phases (heptanol, octanol, isoamyl alcohol, heptane, octane, and isooctane) were tested respectively in the experiment. According to the theoretical model and experimental data, the overall volumetric mass transfer coefficient and enhancement factor were obtained under different dispersed organic phase volume fraction and stirring speed. The experimental results indicate that gas-liquid mass transfer is enhanced at different level by adding a dispersed organic phase. The best performance of enhancement were achieved with the dispersed organic phase volumetric fraction of 5% and under an intermediate stirring speed of 670 r·min-1. Among the organic phases tested in the experiment, alcohols show better performance, which gave 20% higher enhance-ment of overall volumetric mass transfer coefficient than adding alkanes.     

有无静态混合器时的机械搅拌气升式环流反应器传递特性研究

The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation or static mixers on gas hold-up, mixing time, liquid circulating velocity and volumetric mass transfer coefficient have been investigated with tap water and carboxymethyl cellulose (CMC) aqueous solution. The experimental results indicate that mechanical agitation is more efficacious than static mixer in highly viscous media for improving mass transfer in airlift reactors. The empirical correlation of volumetric mass transfer coefficient with apparent viscosity, and energy consumption for mechanical agitation and aeration is developed.     

筛板塔气-液-液系统内相含率和传质特性研究

The gas and dispersed phase holdups and mass transfer coefficients of liquid-iquid were determined for gas-liquid-liquid three phase system in a screen plate column. The flow pattern of gas-liquid-liquid three phase system was studied under different gas velocities. The shape factors showed the geometric properties of screen plates and the corrected drop chaxacteristic velocities were introduced. The phase holdup in two phases was correlated.The research results indicated that mass transfer coefficient for liquid-liquid system in a column with screen plates and gas agitation was found to increase apparently.     

垂直管中零净液流量气液两相流的持液率研究

Zero net-liquid flow (ZNLF) is a special case of upward gas-liquid two-phase flow. It is a phenomenon observed as a gas-liquid mixture flows in a conduit but the net liquid flow rate is zero. Investigation on the liquid holdup of ZNLF is conducted in a vertical ten-meter tube with diameter of 76 mm, both for Newtonian and nonNewtonian fluids. The gas phase is air. The Newtonian fluid is water and the non-Newtonian fluids are water-based guar gel solutions. The correlations developed for predicting liquid holdup on the basis of Lockhart-Martinelli parameter are not suitable to ZNLF. A constitutive correlation for the liquid holdup of vertical ZNLF was put forward by using the mass balance. It is found that the liquid holdup in ZNLF is dependent on both the gas flow rate and the flow distribution coefficient.     

气固循环流化床提升管环核区颗粒质量传递系数的估计

Based on analysis of energy dissipation in the core region of gas-solid fluidized bed risers,a simplified model for determination of core-annulus solids mass transfer coefficient was developed according to turbulent diffu- sion mechanism of particles.The simulation results are consistent with published experimental data.Core-annulus solids mass transfer coefficient decreases with increasing particle size,particle density and solids circulation rate, but generally increases with increasing superficial gas velocity and riser diameter.In the upper dilute region of gas-solid fiuidized bed risers,core-annulus solids mass transfer coefficient was found to change little with the axial coordinate in the bed.     

Experimental and Numerical Investigations of Single Drop Mass Transfer in Solvent Extraction Systems with Resistance in Both Phases

Numerical simulation of transient mass transfer to a single drop controlled by the internal resistance or by the resistance in both phases was mathematically formulated and simulated in a boundary-fitted orthogonal coordinate system. The simulated results on the transient mass transfer dominated by the internal resistance are in good agreement with the Newman and Kronig-Brink models for drops with low Reynolds number. When the drop Reynolds number is up to 200, the mass transfer coefficient from numerical simulation is very low as compared with the Handlos-Baron model. The cases with mass transfer resistance residing in both the continuous and drop phases were simulated successfully and compared with the experimental data in three extraction systems recommended by European Confederation of Chemical Engineering (EFCE). For single drops with Re < 200, the numerically predicted values of the extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. I     

第三分散相液滴增强气体吸收的一维非稳态非均相传质模型

A model for one-dimensional unsteady heterogeneous mass transfer was developed based on Danckwerts’ surface renewal theory in order to describe the mass transfer enhancement of absorption process for a slightly soluble gas in a gas-liquid-liquid system. The model accounts for the mass transfer resistance within the dispersed phase and the effect of emulsion viscosity on mass transfer. An analytical solution for enhancement factor was obtained by Laplace domain transformation. The absorption rates of carbon dioxide in the dodecane-in-water and castor oil-in-water systems were measured in a thermostatic reactor, and the enhancement factors were calculated at different volume fractions of dispersed phase and stirrer speeds. The model predictions agree well with the experi-mental data.     

Mass Transfer Studies in Stirred AirLift Reactor

In the present work, water and three phase compositions of Solka-Floc, a cellulose fiber for simulating the biomass in bacteria, yeast, and fungal fermentation were studied in a 1.4 m³ stirred airlift reactor. The fractional dispersed phase holdup and the overall volumetric mass transfer coefficients were measured. The dispersed phase riser gas holdup and overall volumetric mass transfer coefficients both increased with increasing riser superficial dispersed phase velocity (0.02-0.1 ms^-1) and agitator speed in the range of 0-5 rs^-1. An increase in the Solka-Floc concentration (1-3% w/v) was found to reduce ε_GR and K_La_L. Empirical correlations have been developed for fractional dispersed phase gas holdup and overall volumetric mass transfer coefficients.     

Gas-liquid mass transfer in bubble columns with a T-junction nozzle for gas dispersion

Bubble break-up, gas holdup, and the gas-liquid volumetric mass transfer coefficient are studied in a bubble column reactor with simultaneous injection of a gas and liquid through a T-junction nozzle. The theoretical dependence of bubble break-up and the volumetric mass transfer coefficient on liquid velocity in the nozzle is developed on the basis of isotropic turbulence theory. It is shown that correlations which are developed based on liquid jet kinetic power per nozzle volume explain average gas holdup and the volumetric mass transfer coefficient within an error of 15% for all gas and liquid flow rates and nozzle diameters used. Experiments with a larger scale column, height 4.64 m and diameter 0.98 m, show a transition from homogeneous to heterogeneous flow at a certain liquid flow rate through the nozzle. Liquid composition was found to have a significant effect on gas-liquid mass transfer. A phenol concentration of 10–30 mg/l in water increases the volumetric mass transfer coefficient of oxygen by 100%. This phenomenon may have significance in the chemical oxidation of wastewater.     

三重环流生物流化床的流体力学与传质特性

从气相含率,液体循环速度和体积氧传质系数方面研究自行设计新型结构的三重环流生物流化床的流体力学与传质特性。流化床反应器的有效体积２３Ｌ,实验条件是以空气为气相,水为液相,树脂为固相,固含率分别为０％,３％,６％和９％。实验结果表明,气相含率是影响反应器流体力学和传质特性的主要因素,气相含率增大可降低液体循环速度,增大体积氧传质系数。     

鼓泡反应器中幂律型流体流动与传质特性

很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题,研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠（CMC）水溶液为实验对象,分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明,液相的流变特性对其传质特性参数均有较大影响。与清水相比,CMC水溶液中气泡平均直径和分布范围更大;清水和CMC水溶液的全局气含率均随表观气速的增加而增大;CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究,得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式,可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。     

OXYGEN TRANSFER IN THE WATER-JET VESSEL

This is an investigation of the gas holdup and the volumetric mass transfer coefficient of a plunging water jet in an air-water system. We sound k_La to be directly proportional to gas holdup in two regions. For the first time, this has been clarified in the plunging liquid jet system. The volumetric mass transfer coefficient and the gas holdup have been well correlated in terms of the Froude number, liquid jet length, nozzle diameter and vessel diameter.     

A highly elevated mass transfer rate process for three-phase,liquid-continuous fluidized beds

Average gas holdup and gas-to-liquid mass transfer in three-phase fluidized beds with non-Newtonian fluids were studied. The effects of liquid property, gas distributor type and magnetic field intensity on mass transfer coefficient and overall gas holdup were examined. The volumetric gas-to-liquid mass transfer coefficient was determined by fitting the oxygen concentration profile data across the bed to the axial dispersion model. The average gas holdup and mass transfer coefficient were all correlated with operating parameters including gas velocity and effective viscosity.Experimental results showed that a three-fold increase in mass transfer coefficient and a two-fold increase in average gas holdup were observed with properly designed liquid property and gas distributor. A modified process was developed to highly elevate the volumetric gas-to-liquid mass transfer rate. The bubble coalescing property of three-phase fluidized beds with small particles is eliminated, and its application to biotechnology and enzyme-catalyzed processes with high gas-to-liquid mass transfer rate could be achieved.     

微曝氧化沟气液两相传质模型构建及传质影响因素分析

基于ANSYS Fluent软件建立了微曝氧化沟气–液两相流动和溶解氧输运模型,对比不同工况下氧体积传质系数的实验测量值和模拟结果,误差在7%以内。采用验证可靠性的模型模拟研究了气泡直径、曝气量和横向流动速度对微曝氧化沟内氧传质的影响。结果表明,气泡直径由1.5 mm增至3 mm时,氧体积传质系数由15.80 h?1降低至5.83 h?1;曝气量由0.5 m3/h增大至2 m3/h时,氧体积传质系数由4.21 h?1增至14.15 h?1,减小气泡直径和增大曝气量能明显提高氧体积传质系数。微曝氧化沟内气–液相间传质及溶解氧的分布受横向流动影响,开启单台和两台推流泵时,氧体积传质系数分别比无横向推流工况增大27.7%和42.4%,横向流动能有效提高气泡羽流内的气含率,增强氧传质效果。     

基于介尺度PBM模型的生物反应器放大模拟及实验研究

对于通气搅拌式工业生物反应器的放大设计而言,精确预测气泡尺寸和体积传质系数非常重要,因此需要建立合适的气泡聚并和破碎模型,以保证反应器的高效操作。以5 L通气搅拌式生物反应器为对象,以气泡尺寸和体积传质系数的实验数据为基准,模拟并考察了两种聚并模型和四种破碎模型对生物反应器内流体流动行为以及传质能力的影响。结果表明,基于介尺度理论的修正聚并模型与考虑黏流剪切的破碎模型组合,所得模拟结果与实验数据吻合最好,这为大型生物反应器的桨型优化提供了模型基础。因为工业化生物发酵通常是在大型生物反应器中进行,搅拌桨型对生物反应器效能至关重要,故本研究在选定最优气泡聚并破碎模型的基础上,通过叶轮末端剪切力相等的放大原则将5 L通气搅拌式工业生物反应器放大到400 m³,同时考察了六斜叶圆盘搅拌桨、非对称式抛物线搅拌桨、布鲁马金式搅拌桨以及六直叶圆盘搅拌桨等桨型组合对气泡破碎能力和气体分散效果的影响,并通过综合对比气含率、体积传质系数等参数,得到400 m³通气搅拌式生物反应器的最优桨型组合。