Residence time distribution and modeling of the liquid phase in an impinging stream reactor

Based on some experimental investigations of liquid phase residence time distribution (RTD) in an impinging stream reactor, a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed. The calculation results of the model can be in good agreement with the experimental RTD under different operating conditions. The axial liquid dispersion coefficient increases monotonously with the increasing liquid flux, but is almost independent of gas flux. As the liquid flux and the gas flux increase, the liquid dispersion coefficient of center-to-wall decreases. The axial liquid dispersion coefficient is much larger than that of center-to-wall, which indicates that the liquid RTD is dominated mainly by axial liquid dispersion in the impinging stream reactor.     

生物柴油生产过程撞击反应器的停留时间分布研究

以水为工作介质,0.1 mm催化剂为示踪剂,采用脉冲示踪法,研究了撞击流反应器内物料的停留时间分布;考察了反应器进料循环比、导流筒结构、出料位置对反应器停留时间分布的影响。结果表明:反应器进料循环比≥98%、进料流速≥7.07 m/s,采用特殊管式导流筒结构,以及将反应器出料口位置设置在循环罐上,可明显改善反应器内微观混合效果,反应器内物料流型及停留时间分布十分接近全混流反应器;利用前短路Γ混合模型和组合模型分别对实验数据进行了验证,显示组合模型的计算结果与实验值更接近些,即考虑了死区影响的组合模型更接近于反应器内的实际流动状况。     

Experimental study and modeling of residence time distribution in impinging stream reactor with GDB model

Residence time distribution (RTD) in an impinging streams reactor with two or four nozzles was investigated with KCl solution as a tracer. The results showed that the flow pattern in the reactor was close to that in a continuous stirred tank reactor (CSTR). Macromixing process in the reactor was improved obviously when the opposite nozzles were added. Based on the analysis of flow region in the reactor, gamma distribution model with bypass (GDB) was applied for study on the RTD of the reactor. It was found that RTD in the impinging streams reactor could be finely described by the model. Also the effects of experimental conditions on parameters of model were analyzed according to the correlated values of the model parameters.     

撞击流反应器用于甲醇合成反应

撞击流反应器用于气液固三相甲醇合成反应可以充分发挥其优良的传热、传质性能。在撞击流反应器内,催化剂浆料经喷嘴雾化后成微米尺度的液滴,气液相间接触面积远大于其他三相合成反应器。考察了温度、压力、气体流量、浆料循环量以及喷嘴个数对甲醇合成反应的影响,结果表明,当压力从3.8 MPa上升到5 MPa时,反应器的时空产率增长了近1倍,气体流量达22.4 L·min^-1后时空产率几乎不再变化,增加浆料循环量以及在同一循环量下采用多喷嘴对置都可以增加催化剂时空产率。同时,与固定床、搅拌釜和浆态鼓泡床甲醇合成进行了对比,结果表明,在低空速下撞击流反应器与其他反应器时空产率相当,而在高空速下要优于其他反应器。     

自热转化炉停留时间分布

以氢气作为示踪剂,运用脉冲法测定自热转化炉内停留时间的分布。实验结果表明:随着催化剂床层的增高,停留时间分布密度函数变窄,平均停留时间和量纲一方差均减小;当进口气量增大时,平均停留时间减小,量纲一方差增大。应用N个全混流反应器(CSTR)、轴向混合模型和平推流模型串联建立自热转化炉停留时间分布模型,由Laplace变换法和阻尼最小二乘法对模型参数进行估算,模型估计停留时间曲线与实验测量曲线吻合良好。     

Desulfurization in the gas-continuous impinging stream gas-liquid reactor

An investigation is made to evaluate the flue gas desulfurization (FGD) by absorption in a gas-continuous impinging stream gas-liquid reactor recently developed for systems involving fast reaction(s) in liquid. The mixture of air and SO₂ was used as the pseudo-flue gas and Ca(OH)₂-water suspension as the absorbent. By employing horizontal two-impinging streams, the reactor is simple in structure with few internal parts, while exhibits satisfied overall performance for FGD. Under moderate conditions, the content of SO₂ in the cleaned gas can achieve a level much lower than that permitted, while the pressure drop across the device is about 400 Pa only. The influences of some operating and structural parameters, such as V_L/V_G, Ca/S mole ratio, SO₂ concentration in flue gas, impinging distance S, and nozzle location, etc., are examined. The gas-film mass transfer coefficient, k_G, is determined based on Sauter mean diameter of spray droplets. The results show that k_G is essentially independent of concentration of SO₂ in flue gas, implying the process can be considered to be controlled by diffusion through gas film. The relationship between k_G and impinging velocity, u₀, is fitted to be with the standard deviation of , suggesting u₀ is a strong effecting variable on mass transfer, and, consequentially, important operating variable. In the range of u₀ from 5.53 to , the values determined for the volumetric mass transfer coefficient, k_Ga, are 0.577-, and those for k_G are ranged from 0.00641 to .     

液体连续相撞击流反应器中流体混合时间的数值模拟

在混合时间理论计算基础上利用CFD技术模拟连续操作的LISR混合过程, 数值计算与验证混合时间的变化规律。结果表明, 随着输入比有效功率增大, 混合时间先急剧减小后逐渐趋于平稳;LISR撞击区一次撞击局部混合时间在0.25 s以内, 与经验公式或理论公式计算所得结果在数量级上完全一致, 证明数值方法分析一次撞击局部混合时间是可行的, 而且可以弥补实验无法测定中间过程参量的不足;进一步数值分析宏观混合时间与微观混合时间发现, 二者大小相差1个数量级, 但二者变化规律处于一种联动平衡状态, 该结果与前期理论分析结果一致;本研究所得结论可为后续LISR混合强化机理与性能研究提供定量参考。     

撞击流反应器内快速生成甲烷水合物

为了快速制备甲烷水合物以利于天然气水合物法储运,在自行搭建的液相连续撞击流反应器内考察了纯水和纯水+十二烷基硫酸钠(SDS)2种体系中撞击强度、反应器内温度、初始压力对甲烷水合物快速生成的影响.实验结果表明:2种体系内撞击强度的增加可明显加快甲烷水合物的生成,在撞击强度为0.38、反应的前30 min,水合速率达到最大...     

撞击流反应器制取纳米钛酸钡

在浸没循环撞击流反应器中，以四氯化钛、氯化钡和草酸为原料，采用沉淀法制取纳米钛酸钡，并对产品进行了透射电子显微镜（TEM）表征。通过均匀实验设计，研究了反应温度、加料时间、反应后陈化时间及钡钛物质的量比等因素对产品粒径的影响；初步确定了制备纳米钛酸钡适宜的工艺条件为：反应温度75℃，陈化时间200min，加料时间20min，反应物中钡与钛的物质的量比1．01。制取的钛酸钡产品经TEM表征，其形状皆为球状，具有沉淀法制取的钛酸钡的典型粉体特征，在适宜工艺条件下制取的产品平均粒径为60nm。     

撞击流反应器撞击区流动特性研究

为研究撞击区的流动特性,在有效容积为160 L的撞击流反应器内,以水为介质,饱和KCl溶液为示踪剂,用电导法测定了不同导流筒出口间距和撞击流速下的示踪剂浓度曲线,并通过多釜串联模型拟合得到了撞击区的平均停留时间及模拟釜数。结果表明:导流筒出口间距减小,撞击流速增大,撞击区平均停留时间减小,釜数减小;撞击流速为2.0 m/s时,撞击区内流型接近于全混流。停留时间分布主要受撞击流速的影响,增大流速有利于促进撞击区中的宏观混合。     

Residence time distribution in a single‐phase rotor–stator spinning disk reactor

A reactor model for the single‐phase rotor–stator spinning disk reactor based on residence time distribution measurements is described. For the experimental validation of the model, the axial clearance between the rotor and both stators is varied from 1.0 × 10^?3 to 3.0 × 10^?3 m, the rotational disk speed is varied from 50 to 2000 RPM, and the volumetric flow rate is varied from 7.5 × 10^?6 to 22.5 × 10^?6 m³ s^?1. Tracer injection experiments show that the residence time distribution can be described by a plug flow model in combination with 2–3 ideally stirred tanks‐in‐series. The resulting reactor model is explained with the effect of turbulence, the formation of Von Kármán and Bödewadt boundary layers, and the effect of the volumetric flow rate. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2686–2693, 2013     

外循环撞击流反应器微观混合性能研究

在有效容积为160 L的外循环撞击流反应器(ECISR)内,以酸碱中和与氯乙酸乙酯水解的平行竞争反应为工作体系,对反应器内微观混合性能进行了研究,考察了不同的进料时间、进料位置、循环流量对该平行竞争反应副产物分布的影响,通过副产物收率即离集指数X Q的变化来表征微观混合的效果。研究结果表明:撞击区上部(400mm)进料微观混合效果最好,反应器顶部最差;当进料位置和循环流量不变时,进料时间达40 min以上,X Q不再随进料时间的延长而降低;循环流量达到6 000 L/h时,微观混合效果最佳,再升高循环流量微观混合提升已不明显。     

Residence time distribution measurements in an external-loop airlift reactor: Study of the hydrodynamics of the liquid circulation induced by the hydrogen bubbles

A detailed study of the residence time distribution (RTD) analysis of liquid phase has been performed in an external-loop airlift reactor of 20 L nominal volume, regarded as a global unit and discriminating its different sections (riser, gas–liquid separator and downcomer) using the tracer response technique. The reactor was used as an electrochemical reactor in order to carry out the electrocoagulation/electroflotation (EC/EF). The gas phase created in the riser is the hydrogen produced by water electrolysis.In order to use this reactor for a continuous EC/EF, hydrodynamic studies were carried out to control the operating conditions and to help modelling the electrocoagulation. Current density, position of the electrodes in the riser and the volumetric liquid flow (inlet flow) are the key parameters for the hydrodynamics.The experimental results revealed that both in the downcomer and the riser–separator zones, the flow model is axial dispersion. Interesting results were obtained:

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  The superficial liquid velocity (ULd) at the downcomer, decreased when the volume inlet flow increased (0<QL<2 L/min).

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  The Peclet number obtained in the downcomer was correlated to the current density and the electrodes position.

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  In the riser–separator zone the Peclet number decreased with the superficial liquid velocity in the riser indicating that the dispersion increased with an increase of turbulence created in the separator by an increase of liquid velocity.

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  The percentage of flow that quits the reactor without reacting increased when the main flow increased and the current intensity decreased. The global RTD can be reconstituted by the signal resulting from the junction and that from riser–separator and downcomer zone by using the convolution technique. The experimental results confirm this reconstitution. The experiments confirm also that the liquid crosses the reactor without achieving loops in the case of the continuous flow.

     

小型气-液-固流化床液相的停留时间分布

采用脉冲示踪技术,研究了3 mm床径的小型气-液-固流化床内液相停留时间分布。以KCl为示踪剂,液相为去离子水,气相为空气,固相为平均粒径0.123~0.222 mm的玻璃微珠和氧化铝颗粒,测量流化床出口液相的电导率,得到其停留时间分布曲线。结果表明,增大表观液速和表观气速,分布曲线变窄,平均停留时间缩短,Peclet数增大;固相的存在使液相的平均停留时间增长。表观液速1.96~15.70 mm×s^-1,表观气速1.18~1.96 mm×s^-1的条件下,流动接近层流;平均停留时间的范围为（19.6±0.34）s~（48.0±0.92）s,建立的Pe经验关联式对实验结果有较好的预测,偏差在±25%以内。研究结果对于小型三相流化床的设计放大具有指导意义。     

撞击流反应器内涡特性研究进展

撞击流技术具有良好的混合效果,广泛应用于能源、环保、化工等工程领域。由于撞击流反应器流场内存在大量无序的湍流涡结构,使其具有良好的混合效果。本文基于撞击流的混合原理,详细叙述了撞击流反应器内不同混合尺度下的混合过程以及涡的演变对混合的影响。结合实验和数值模拟等研究结果,阐述了不同类型撞击流反应器和撞击流反应器多相流场涡特性,归纳了撞击流反应器流场涡的特点。论述了撞击流反应器涡的产生和脱落机理。着重对圆柱射流、平板射流和撞击流流场内涡特性的本征正交分解（POD）分析进行总结,利用流场能量的角度揭示涡演化和消散规律。最后,对开发新型撞击流反应器、优化分析方法等研究前景进行展望。     

浸没循环撞击流反应器的压力脉动特性

The characteristics of pressure fluctuation in a submerged circulative impinging stream reactor (SCISR) were experimentally studied. The instantaneous signals of pressure fluctuation resulting from the turbulence in the SCISR were measured by sensors and recorded by a computer. The pressure signals at some special positions were sampled at different rotary speeds of propeller. After analyzing the signals with the Power Spectrum method, it was found that there was an inherent frequency in the dynamic pressure signals. The inherent frequencies of the point on the impinging plane were greater than 1000 Hz, so the pressure fluctuation was called high-frequency fluctuation. The fluctuation velocities with high inherent frequency resulted in a strong shear force field, which enabled the fluid to mix quickly on the micro-scale and the agglomerates of solid particles to disperse effectively.     

Residence time distribution of plug flow in a finite packed-bed chemical reactor

The residence time distributions in a finite packed-bed chemical reactor under plug flow conditions have been studied. Analysis was performed upon the well-known axial dispersion model in one dimension. Of paramount importance it was to construct a high order approximate solution to the corresponding initial-boundary value problem which appeared to be extremely convenient for fast numerical calculations. To this purpose singular perturbation techniq were applied using the reciprocal of the Péclet number as a small parameter. An error analysis was subsequently established for the special case of a pulse-function tracer input. The so-called “tailing phenomenon” of the response curve was simulated by an appropriate parameter-depending boundary condition of diffusion type.     

Residence time distribution of the liquid in gas-liquid cocurrent upflow fixed-bed reactors

The authors present an experimental investigation of the residence time distribution (RTD) of the liquid in a gas-liquid upflow fixed-bed reactor with porous and nonporous particles and air/Newtonian or non-Newtonian systems. The piston-dispersion-exchange model with Danckwerts boundary conditions was used to describe the liquid flow. In the case of porous particles, the dynamic evolution of the tracer concentration in the particles was described in terms of diffusion phenomena. An imperfect pulse method was used to estimate the model parameters directly from the experimentally nonideal input and output response.     

浸没式撞击流反应器流场涡特性的数值研究

利用大涡模拟（LES）方法研究了撞击流反应器内流场涡特性,分析撞击区域流体流动特征。改变进口速度、喷嘴间距,讨论流场速度、涡量和平面涡能量分布规律,并分析了流场流型、涡演化过程和涡核形式。在反应器内靠近撞击驻点的涡尺寸小、脉动性高,随着撞击距离的增加,流体速度逐渐减小,涡影响范围变大。平均涡量和平均涡能量随进口速度的增加,先增加后减小。结合Q判据分析了反应器内涡的演化过程和流体流型。根据径向射流涡的演变过程,得到径向射流两侧涡演化的周期,在0.15~0.20 s之间。撞击区的涡结构主要为马蹄涡和肋状涡,在出口位置存在涡环。研究结果为深入分析撞击流反应器流体运动规律和优化反应器提供了理论参考。