内过滤式喷射环流反应器混合特性研究

传统的喷射环流反应器应用于工业上的多相反应时一般采用外部分离,导致流程繁琐、能耗加大、甚至存在安全问题,本文在喷射环流反应器内设计了过滤式导流筒,以实现在反应器内进行多相反应和液固分离操作的连续化。用阶跃示踪法测定液相停留时间分布,考察了表观气速、过滤压力对该反应器混合特性的影响。结果显示:返混程度随表观气速的增大而增大;过滤压力增大,平均停留时间减小,返混程度增大,但过滤压力对返混的影响较弱。     

泰勒反应器中流体的停留时间分布研究

采用脉冲示踪法,实验考察了泰勒反应器结构参数、操作参数和物料粘度对其停留时间分布的影响规律,发现泰勒反应器中物料的混合程度随泰勒数(Ta)的增大而增大、轴向雷诺数(Reax)的增大而减弱.进一步采用多级混合模型,将泰勒反应器的当量全混釜数(N)与反应器结构参数、泰勒数和轴向雷诺数相关联,提出了一个N的测算公式.在实验考察的范围(Ta=280～3 230; Reax=0.89～6.78)内,由该式计算的N值与实验值很好地相符,具有广泛的适用性.     

新型流化床内流体重构的流体力学特性变化及其数值模拟

针对前期研究开发的新型三重环流与多重环流流化床,构建气液两相流的二维数值模型,分析微观流场、液体运动速度和气相含率,剖析环流数对流化床流体力学特性的影响和对内循环过程的改善,寻找反应器运行过程节能的结构与优化的操作条件。通过数值模拟发现:基于单重环流,多重环流作用主要改变流体在上升区和下降区之间的相互混合和交汇,增大环流数可缩短流体运动的循环路程和时间,有利于加强相际之间的混合,但床内整体流态仍接近推流,微循环的存在所占比例较小;多重环流流化床的流体力学性能优于三重环流,随着环流次数的增多,液速在径向和轴向上分布更均匀,气泡逆流进入下降区,有利于反应器整体氧传质效率的提高。通过流化床结构改变实现的流体重构支持流体力学性能的改善,是高负荷有机废水好氧生物处理期待选择的开发方向。     

管式搅拌反应器中流动特性实验及模型研究

为进一步研究带机械搅拌装置的新型管式反应器内流动特性,采用刺激-响应技术,测定流体在不同操作条件下的停留时间分布(RTD)曲线并与无搅拌停留时间分布曲线作对比,计算了平均停留时间分布的统计特征值。用混合时间表征混合特性,用Peclet操作准数表征轴向扩散特性。结果表明,适当增大转速、流量或降低水位,都有利于反应器内流体的均匀混合。大体上随流量的减少和液位的升高停留时间有延长的趋势,转速变化对停留时间的影响不显著。在搅拌转速不超过400 r/min时,混合时间随着搅拌转速的增大而缩短。在实验范围内,反应器相当于3个串联全混槽反应器。     

反向旋转卧式双轴捏合反应器混合特性的数值模拟

以差速反向旋转卧式双轴捏合反应器为研究对象,选用高黏牛顿流体糖浆为模拟物料,通过三维有限元数值模拟方法研究了高黏糖浆在捏合反应器中的流动过程,获取了流速和剪切速率的空间分布,进一步结合粒子示踪技术探究了分布混合过程与混合效率,并且考察了搅拌结构对流动与混合过程的影响规律。研究表明,捏合反应器中几乎不存在流动死区,桨叶末端和重叠区域的流速和剪切速率较高,且高流速和高剪切区域均随着捏合杆数目和捏合杆长度的增加而增大。捏合杆可以推动物料在圆周方向上的运动,在重叠区域存在周期性交互作用,进而可以强化分布混合过程。拉伸率随着混合时间以指数形式增加,且随着捏合杆数目和捏合杆长度的增加而增加。时均混合效率大于零,随着捏合杆数目的增大而增大,随着捏合杆长度的增加呈现先增大后减小的趋势。     

分段进气环流反应器传质性能及在葡萄糖氧化中的应用

在多级环流反应器的基础上,发展了一种新型分段进气、多级环流反应器(MS-MSALR)。在气流量为0.2～0.6m3/h的条件下,研究了MS-MSALR中体积传质系数、葡萄糖氧化反应速率随气流量的变化规律,并与多级环流反应器进行了比较。多级环流反应器的体积传质系数随气流量的增加而增大,葡萄糖氧化反应速率随气流量的增加而增加。MS-MSALR的体积传质系数呈抛物线状分布,最大值约为多级环流反应器的2.4倍;反应速率在Q2/Q1较小时取得最大值,并保持不变。     

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。     

分段进气多级环流反应器流动与传质特性研究

多级环流反应器通常在段间安装多孔分布板或其他内构件,增加了流体流动的阻力,导致环流液速降低。为此,文中在多级环流反应器研究的基础上,设计了一种新型分段进气、多级环流反应器,利用新通入气体的抽提力和喷射力,缓解了段间的流动压降,并加速气泡的破碎;重点考察了进气量在各段中的分配比例对分段进气多级环流反应器流体力学的影响。应用电导率仪和溶解氧分析仪分别测量环流液速、混合时间及体积传质系数。实验结果表明:分段进气时,第2段和第3段中的环流液速比较高,并明显高于多级环流反应器中的环流液速;不同的操作条件下,上下二端的混合时间差距明显,表现出串联反应器特性;体积传质系数远高于多级环流反应器,最大值约为多级环流反应器的2.4倍。     

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。     

环隙气升式气固环流反应器内颗粒速度特性

针对中心气升式气固环流反应器在工业化中暴露出来的问题,提出了一种新型的环隙气升式气固环流反应器,并建立了一套大型的冷态实验装置（装置总高4．56m,环流反应器筒体外径300mm）来考察环隙气升式气固环流反应器内颗粒速度特性。操作条件为环隙区表观气速0.10-0.54m／s,导流筒区表观气速0.059-0.200m／s。分别测量了环流反应器环流段内颗粒的密度和速度,基于实验数据对催化剂颗粒的运动速度和环流推动力进行系统分析。结果表明,环隙区颗粒分布形式为“中心稀两边浓”;环隙气升式气固环流反应器内,颗粒环流速度随着环隙区表观气速的增大而增大,而环流速度梯度逐步减小。随着导流筒高径比H／D的增大,环隙气升式气固环流反应器的环流推动力增大而颗粒环流速度减小。     

导流筒高度对气固环流反应器流动特性的影响

为了研究导流筒高度对环流反应器内流动特性的影响,基于欧拉-欧拉方法,采用基于多尺度结构的EMMS曳力模型,结合颗粒动力学理论,建立了环流反应器内气固两相流动模型,通过对比实验数据,确定了合适的模型参数。采用已建立的流动模型,对导流筒高度进行了优化研究,考察了导流筒高度变化对平均床层密度、质量流率和环流速率等参数的影响。结果表明,导流筒优化高度为1.4 m时,环流效果较好,其平均质量流率比原装置(HD为1.2 m)提高了36.17%。     

Modeling of modified airlift loop reactor with a concentric double-draft tube

In this work, mathematical modeling based on the tanks-in-series model was employed to characterize the performance of a novel modified airlift loop reactor. Liquid mixing characteristics, i.e., mixing time and circulation time, were employed to describe the performance of the proposed reactor. These values were determined by using the classical tracer response technique in a column 18.5 cm in diameter and 90 cm in height, and two concentric draft tubes 14 and 8.5 cm in diameter and 80 cm in height. Matlab 7.1 software was used to solve the model equations in the Laplace domain and determine the model parameter. A comparison between the numerical solution and experimental data showed that the applied model can accurately describe the behavior of a modified airlift reactor. Experimental results in the homogeneous bubble flow regime showed that the proposed airlift reactor configuration with a double-draft tube significantly improves the liquid mixing quality compared to a conventional concentric-tube airlift reactor with an identical operating volume. By using this high-performance reactor, the mixing and circulation times can be reduced by up to 48.3% and 35.5%, respectively.     

Applying rotary jet heads for mixing and mass transfer in a forced recirculation tank reactor system

An approximation to an ideally mixed tank reactor can be obtained by vigorous stirring with mechanical mixers. For an aerated reactor the gas dispersion contributes to the mixing process. Mixing can also be achieved by recirculation of a portion of the liquid through either an internal or an external loop.In this study, we determine mixing times in water and CMC solutions and oxygen mass transfer coefficients in water for a tank reactor system where a small fraction of the total liquid volume is rapidly circulated through an external loop and injected through the nozzles of rotary jet heads at 1-9 bar gauge pressure into the bulk liquid. Liquid feed can be added to the bulk volume or it may be injected into the pressurized recirculation loop. Gas is always fed to the recirculation loop, and the heat of reaction is removed in a plate-type heat exchanger inserted in the recirculation loop. The system has a very simple design with no internal baffles or heat exchange area, and between batches the rotary jet heads are used for cleaning in place.Mixing time decreases and mass transfer increases with increasing circulation flow rate. For nozzle diameters between 5.5 and and with one or two rotary jet heads, it is shown that a remarkable saving in power input for a fixed mixing time or mass transfer coefficient can be obtained by using a large nozzle diameter and two rather than one rotary jet heads.At the experimental conditions of the study the system is scaleable by simple formulas, and the power input to achieve a certain mixing time is proportional to the bulk liquid volume.     

无序环流混合器的流体力学特性和颗粒混合特性

在内径为Φ286 mm的无序环流混合器装置中,研究了无序环流混合器的流体力学特性和颗粒混合特性。以催化裂化(FCC)平衡剂为颗粒相,在中心区表观气速为0.3~0.5 m/s,边壁区表观气速为0.1 m/s,系统循环强度为0.25~1.00 kg/s的操作条件下,采用PV-6D型颗粒速度密度测量仪测量了混合器内床层各截面密度,并给出不同操作条件下的截面不均匀指数(RNI);采用热颗粒示踪技术给出了混合器内各测量截面的无因次温度分布,并引入混合指数用来定量描述不同操作条件下的颗粒混合程度,同时对比了传统环流混合器与无序环流混合器的混合能力。结果表明,无序环流混合器内部床层密度呈现中心低,边壁高的分布模式。随着循环强度的增加,RNI先减小后增大,随着表观气速的增加,RNI增大。预混合区混合指数为0.7~0.9,在高循环量,低中心区表观气速条件下(G_s为1.00 kg/s,u_(gd)为0.3 m/s),下料管进料影响区的截面混合指数低于其他操作条件。另外,无序环流混合器混合能力优于传统环流混合器。     

缩放型导流筒气升内环流反应器液体循环速度的研究

研究气升式内环流生物反应器液体循环速度,分别采用一种传统圆柱型导流筒和三种不同结构参数缩放型导流筒,试验条件分别为空气－水和空气－ＣＭＣ两相系统以及空气－水－树脂三相系统,试验结果表明,对于空气－水和空气－ＣＭＣ溶液两相系统以及空气－水－树脂三相系统,液体循环速度随能气速度提高而增大;     

The effect of the draft tube geometry on mixing in a reactor with an internal circulation loop – A CFD simulation

The main topic of this paper is to describe the effect of geometrical parameters on mixing time in a reactor with an internal circulation loop. The design of the draft tube inside the reactor is an important geometric parameter and has a big influence on two phase hydrodynamics as well as on mass transfer in the reactor. In the first section, the validation of the selected mathematical model is carried out. The results of experimental measurements (liquid velocity and gas hold-up) obtained on the laboratory scale reactor are compared with the CFD simulations. The CFD simulation (bubbly flow and mass transfer models) was made using COMSOL Multiphysics 3.5a. The results of the numerical simulation are in good agreement with the experimental data. In the second section, the study of mixing in the reactor is described with the new geometry of the draft tube. The standard experimental techniques for testing mixing processes are quite problematic because common tracers (soluble salts) have significant influence on two phase hydrodynamics inside the reactor. Though, an alternative nontrivial method had to be used. The split of the draft tube into two or three section has a significant effect on mixing (mass transfer) in the reactor.     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

搅拌管式反应器内流动特性的大涡模拟

采用实验和数值模拟的方法研究搅拌管式反应器内的混合过程,其中数值模拟采用大涡模拟的方法研究了反应器内流体的流动场,并就不同转速条件下流体的混合时间,将大涡模拟数值结果分别与标准k-ε模型的计算结果和实验测量值相比较,结果表明:管式搅拌反应器内的流动是非稳态的,具有不对称性。同时,大涡模拟方法可以预报漩涡,特别是桨叶背面的漩涡。与实验测量值相比,大涡模拟对混合时间的计算精度比标准k-ε模型计算精度高约22.8%,证明大涡模拟方法能够有效地模拟搅拌管式反应器内的流动特性。     

Gas holdup in a two‐phase reversed flow jet loop reactor

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two‐fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas–liquid mixture in draft tube only (E_gd) and gas holdup with circulation loop (E_g). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two‐fluid nozzle.