气体分布器结构对气升式环流反应器内气液两相流动的影响

使用欧拉两流体模型研究气体分布器结构对气升式环流反应器内气液两相流动的影响,预测了环己烷氧化反应器内单环结构、三环结构、五环结构的气体分布器时反应器内液相速度分布、气含率分布、液相循环速度以及液相微观混合特性.模拟结果表明,在等量的进气流量下,气体分布器环数增加,液相速度分布和气含率分布更趋均匀;气体分布器环数增加,液相推动力增加,从而使得液相循环速度增加,液相的宏观混合效果增强;气体分布器环数增加,导流筒内外的平均气含率增加.随机游走模型模拟结果表明,气升式环流反应器与普通鼓泡床反应器对气体分布器结构要求不同.     

螺旋气升式内环流反应器流动特性

以水和空气两相系统为研究对象,建立螺旋气升式内环流反应器冷模实验装置,采用压差法测定导流筒升流区气含率,用电导法分别实测了升流区液相速度和反应器混合时间,研究螺旋气升式内环流反应器的流动特性,并与传统气升式内环流反应器的流动特性进行对比研究。结果表明,加螺环后反应器气含率明显增加,平均增幅为20%,升流区液相表观速度减小,混合时间增加。     

气升式环流反应器流动特性的数值模拟

应用Fluent计算流体力学软件,通过数值模拟的方法考察了气升式环流反应器内导流简直径、导流筒高度、导流筒安装高度以及液相进口速度对反应器内两相流动的影响。计算结果表明：导流简直径增大。液相循环量和上升段气含率均增大;导流筒高度增大,液相循环速度和循环量均增大,但是当导流筒的高径比增加到6．3后,液相循环速度和循环量反而减小;导流筒安装高度增加．液相循环速度及循环量均增大,升液管气含率降低;增加液相的进口速度,虽然上升段的液速有所增加,但是降液管循环液速及循环量基本不受影响。最后计算了反应器内液相速度随进口气速的变化情况,并与实际测量值进行了比较,模拟值和测氨值都表明随着进口气速的增加,液相循环速度随着进口气速的增加而增加．两者呈现良好的一致性。     

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.     

环隙气提式环流反应器中的气含率和液相循环流动

在筒体直径310mm、高2000mm的环隙气提式环流反应器实验装置中,对上流区的气含率、液相循环流动等流体力学特性作了研究.用漂流通量模型描述了上流区的气含率;通过对体系的能量耗散机理进行分析,基于体系总能耗最小的原理推导出液相循环流动方程,结果表明:用此方程能较好地模拟这种反应器内的液相循环状况.     

CFD在自吸式加氢反应器流场研究中的应用

目前自吸式反应器广泛应用于二硝基甲苯加氢等多相流反应过程,但由于其内部流动十分复杂,单纯依靠实验很难得到全面准确的研究结果。为了解决这一问题,以自吸式加氢反应器为研究对象,运用计算流体力学(CFD)Fluent建立三维反应器模型,采用欧拉两相流方法,对空心叶轮自吸式反应器与双圆盘叶轮自吸式反应器内的气液两相流动特性进行了研究,将反应器内的流动可视化。在此基础上将空心叶轮反应器内的吸气特性与实验数据进行对比,验证建立的CFD模型,并对比两种反应器内的局部气含率分布与液相速度矢量图分布。结果表明:空心叶轮自吸式反应器吸气特性的模拟结果与实验结果吻合较好;对于单层桨叶自吸式加氢反应器,相同桨径的空心叶轮比双圆盘叶轮的吸气性能与气液分散性能更好。     

环流反应器研究现状

环流反应器靠气相浮力和液相动能来实现反应器内规则的循环流动,具有不需要附设循环泵和机械搅拌装置等优点,文章对近几年环流反应器气含率、混合和传质的影响因素、测量方法和模型作了总结,并对进一步研究方向进行了展望。     

气升式内环流反应器流场及传质特性数值模拟

采用双流体模型和气液二相流体动力学理论建立了气升式环流反应器流体流动的数学模型,在此模型的基础上利用溶质渗透理论和各向同性湍流理论建立了局部液相体积传质系数数学模型。采用计算流体软件F luent对气升式环流反应器内气液二相流动状况进行模拟,模拟结果较好地解释了气升式环流反应器内的流动行为及传质特性。模拟计算值与文献实验值的吻合说明了模型的可行性。     

环隙气升式气固环流反应器内流体力学特性的理论分析

环流反应器的研究与应用一直局限于气液与气液固体系,将环流反应器移植到气固体系是一个具有独创性的探索。针对工业化中气固环流反应器的缺陷,提出了一种新型的环隙气升式气固环流反应器。并对床层空隙率、颗粒流动速度进行了实验研究与理论分析。建立了环隙区床层空隙率模型,发现环隙区床层空隙率随着环隙区表观气速的增加而增加;环隙区靠近导流筒外壁一侧颗粒流动速度明显大于靠近反应器内壁一侧,导流筒区颗粒流动速度沿径向的分布受气体分布器结构影响较大;环隙区颗粒流动速度基本不随轴向位置的变化而变化,导流筒区颗粒的流动属于密相输送,颗粒环流所受到的阻力主要集中在底部区域,其次为气固分离区,底部区域阻力大小由床层流化质量和导流筒下端距反应器底部的间隙所决定;建立了颗粒环流速度模型,发现环流速度随环隙区表观气速的增加而增加。     

微藻柱状式光生物反应器流动特性及结构的数值模拟优化

微藻作为最具潜力的可再生生物质能源,在生物固碳和生物燃料生产领域优势显著,有助于碳达峰、碳中和目标的实现。通过改善反应器曝气装置的性能可以大幅度提高微藻的培养效率,本工作采用数值模拟方法对柱式光生物反应器的球型曝气结构进行了优化。模拟采用欧拉模型,湍流模型选取k-ε模型,研究分析了不同曝气装置条件下气含率、平均液相速度、湍流动能几种参数的变化和光生物反应器内的流场情况。结果表明,曝气装置结构的变化对光生物反应器内的流动特性具有很大的影响,通过曝气装置向反应器内通气,气含率、平均液相速度、湍流动能随着曝气量的增大而增大,随着曝气装置孔径的增大而减小。综合各相关参数得到当总曝气量为1400 mL/min、曝气孔数为50、曝气孔径为30μm时,曝气装置性能最好,此时测得气含率为68.6%,平均液相速度为0.905 m/s,湍流动能为0.149 m²/s²。     

Hydrodynamics of the flow transition from a bubble column to an airlift-loop reactor

The hydrodynamics of an airlift-loop reactor (ALR) and a bubble column (BC) were studied in the same reactor unit. When the liquid circulation in the ALR was impeded gradually in order to obtain a BC mode of operation, there was a transition flow regime inbetween that of the ALR-type flow and the BC-type flow. In the BC the heterogeneous flow was represented by an instationary circulatory flow pattern and characterized by a liquid circulation velocity. The liquid flow in the ALR was represented by a drift-flux model. In the transition flow regime, hydrodynamic calculations based on the plug-flow behavior of an ALR appeared to be valid up to a certain defined value of the total gas-liquid flow rate. To distinguish between BC and ALR flow characteristics, a simple criterion is proposed, qualifying that the distinction between both flow patterns is determined by the superficial liquid velocity and the liquid circulation velocity. If the latter velocity exceeds the superficial liquid velocity a hydrodynamic transition will occur from a uniform ALR type of flow to a heterogeneous BC type of flow. The criterion coincides with an empirical power law function in which the liquid velocity is given as a function of the gas velocity. The values of the power-law coefficients depended on the characteristics of the two-phase flow. The change in value cohered with the onset of a change in the flow pattern.     

反应器类型对流动影响的数值模拟

在油-氢气体系中使用欧拉-欧拉双流体模型考察了温度703.15 K和压力11 MPa下气升式环流反应器和鼓泡床反应器对气液两相流动的影响. 结果表明,环流反应器中气含率和轴向液速沿导流筒径向存在突增现象,环流反应器中气含率在径向0~0.5和0.75~1时明显大于鼓泡床反应器,在径向0.5~0.75处前者的平均气含率比后者高约6%;环流反应器中上升管内环流液速明显大于鼓泡床反应器,且在下降区有所增强,环流反应器平均轴向液速比鼓泡床反应器高约21%;反应器尺寸较小时环流反应器和鼓泡床反应器的流动特性相差不大,反应器体积放大过程中前者的流动特性优于后者的趋势逐渐明显.     

气升式环流反应器中的流体动力学研究(Ⅱ)——实验及模型结果分析

建立了一直径为0.186m、高3m的内环流气升式反应器。通过电化学方法测得了反应器中的气含率和速度。本文以文(Ⅰ)所得气升式环流反应器的一维两流体模型为基础,推导出了反应器的能量方程。分析了反应中的功耗分配规律,并以此对反应器中的流动规律作了较合理的解释。本文还从理论和实验上较全面地讨论了反应器操作参数和结构参数对气含率和循环液速等的影响。     

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     

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.     

气升式环流反应器中的流体动力学研究(Ⅰ)——一维两流体模型

从基本的一维两液体模型出发,全面地考虑了气升式反应器中气体膨胀、气液两相间相互作用和滑移等,建立了反应器的一维模型。通过数值方法求解整个反应器的流体力学方程组。解的结果包括气含率、气体和液体速度等,作者将模型计算结果与大量的实验数据进行了比较,两者相符较好。     

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.     

Motion of a magnetic flow follower in two‐phase flow — application to the study of airlift reactor hydrodynamics

A low‐cost and simple magnetic particle tracer method was adapted to characterize the hydrodynamic behavior of an internal‐ and an external‐loop airlift reactor (ALR). The residence time distribution of three magnetic particles differing in diameter (5.5, 11.0 and 21.2 mm) and with a density very close to that of water was measured in individual reactor sections. The measured data were analyzed and used to determine the velocity of the liquid phase. Validation of the experimental results for liquid velocity was done by means of the data obtained by an independent reference method. Furthermore, analysis of the differences found in the settling velocity of the particle in single‐liquid and gas‐liquid phases was carried out, using a simplified 3D momentum transfer model. The model considering particle‐bubble interaction forces resulting from changes in the liquid velocity field due to bubble motion was able to predict satisfactorily the increase in the particle settling velocity in the homogeneous bubbly regime. The effective drag coefficient in two‐phase flow was found to be directly dependent on particle Reynolds number to the power of ? 2 but independent of gas flow‐rate for all particle diameters studied. Based on the experimental and theoretical investigations, the valid exact formulation of the effective buoyancy force necessary for the calculation of the correct particle settling velocity in two‐phase flow was done. In addition, recommendations concerning the use of flow‐following particles in internal‐loop ALRs for liquid velocity measurements are presented. Copyright © 2006 Society of Chemical Industry