Entwurf und Betrieb eines Rohrreaktors mit enger Verweilzeitverteilung

In process engineering the residence time is an important design parameter, and a narrow residence time distribution is advantageous to avoid possible by-products in complex chemical reactions. A good radial mixing with low axial dispersion provides a narrow residence time distribution in a tube reactor. The axial dispersion of laminar flow in a straight tube is very high and generates a wide residence time distribution. However, secondary flows improve the radial mixing, which are investigated in this paper for curved tube reactors. Design notes for good radial mixing and geometric designs of tube reactors with baffles are presented.     

Beschleunigter Sinkprozess fester Partikel bei laminarer und turbulenter Umströmung

Separation of particles is often designed based on the terminal settling velocity as separation parameter. Until now, the particle state of motion is described by solving the force balance equation numerically, which is highly complex. In this work, algebraic equations are presented, which describe the temporal changes of the setting velocity and the displacement at sinking in laminar and turbulent flows around the particle. These equations solely depend upon particle size, density and shape and are independent of the initial velocity. Using the characteristic values, the time period where a sufficient convergence to the terminal sinking velocity is reached, can be clearly identified.     

Particle residence time distributions in circulating fluidised beds

This paper gives experimental measurements of the particle residence time distribution (RTD) made in the riser of a square cross section, cold model, circulating fluidised bed, using the fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002a) 127). This technique depends upon all particles having phosphorescent properties. A small proportion of the particles become tracers when activated by a flash of light at the riser entry; the concentration of these phosphorescent particles can subsequently be detected by a photomultiplier. The influence of the solids circulation rate and superficial gas velocity on the RTD were investigated. The results presented are novel because (i) the experiments were performed in a system with closed boundaries and hence give the true residence time distribution in the riser and (ii) the measurement of the tracer concentration is exceedingly fast. The majority of previous studies have measured the RTD in risers with open boundaries, giving an erroneous measure of the RTD.Analysis of the results suggests that using pressure measurements in a riser to infer the solids inventory leads to erroneous estimates of the mean residence time. In particular, the results cast doubt on the assumption that friction and acceleration effects can be neglected when inferring the axial solids concentration profile from riser pressure measurements.An assessment of particle RTD models is also given. A stochastic particle RTD model was coupled to a riser hydrodynamic model incorporating the four main hydrodynamic regions observed in a fast-fluidised bed riser namely (i) the entrance region, (ii) a transition region, (iii) a core-annulus region and (iv) an exit region. This model successfully predicts the experimental residence time distributions.     

Numerische Simulation von Mehrkomponenten‐Diffusion und Gleitströmung in mikroporösen Medien

A method is presented, which enables the locally resolved calculation of multi‐component gas transport in microporous media. The theoretical basis is formed by a fluid‐dynamic model that comprises separate mass and momentum balances of each component in the gas mixture. By introducing component‐specific slip boundary conditions, the model is made applicable to regimes of increased Knudsen numbers. After implementation into a commercial CFD‐program the motion of a binary gas mixture in a virtual microporous structure is simulated. Analysis of the calculated velocity fields makes it possible to determine structural parameters that can be used in relevant 1D‐models.     

Mehrphasige Strömungen bei der Trennung und Zusammenführung in verzweigten Rohrleitungen

Multiphase transport networks consist of pipes in addition to apparatus and multiphase pumps. The phase distribution in connection with the occurring pressure drop as well as sorption effects in the so‐called nodes, i. e., in a separation or junction of a pipeline, have a significant impact on the transport performance. The influence of several operating parameters on the behavior of the multiphase fluid is investigated experimentally and theoretically with reference to the above‐mentioned flow characteristics.     

CFD‐Simulation der Feststoffeinbindung in einen Sprühstrahl

Sound‐absorbing mats consisting of cross‐linked Polyurethane (PUR) foam and metal reinforcements, door panels and centre consoles for the interior of vehicles became important products for automotive component suppliers. The leading technology for the production of foam on the base of PUR with noise absorbing properties is the application of powder insertion (e.g. metal) in the PUR spray. The numerical simulation (CFD) of the spray including the particle‐droplet interaction is presented. The theoretical background of the implemented models is explained and the experimental results achieved with a pilot plant are compared with the numerical results. The presented simulation offers the possibility to suitably predict the metal powder distribution in a PUR spray.     

Semi‐Empirical Equations for the Residence Time Distributions in Disperse Systems – Part 1: Continuous Phase

Residence time distributions (RTD) are often described on the basis of the dispersion or the tanks in series models, whereby the fitting is not always good. In addition, the underlying ideas of these models only roughly characterize the real existing processes. Two semi‐empirical equations are presented based on characteristic parameters (mean, minimum, maximum residence time) and on an empirical exponent to permit better fitting. The determination of the parameters and their influence on the RTD are discussed. The usefulness of the models is shown in this first part for single‐phase systems and for the continuous phase of multiphase systems using data from literature for laminar and turbulent flows in different apparatuses. A comparison with the results of other models is also done.     

Flow visualization and modelling of a filter-press type electrochemical reactor

A study of flow visualization and residence time distribution is provided in order to model the flow between two electrodes in a commercial filter-press reactor, the ElectroSynCell® from Electrocell AB. Flow visualization indicates that both axial and lateral dispersion phenomena occur and a global plug flow behaviour is observed. The flow distribution is asymmetric due to the design of the inlet system in the active zone. The flow throughout the cell is described by a dispersed plug flow model for which the mean residence time and the Pe´clet number are determined. The reaction area and the inlet system are separately analysed by locating conductimetric probes inside the electrochemical cell. The reaction area is also well described by a dispersed plug flow model, and characterized by high dispersion. The inlet system is, respectively, described by a dispersed plug flow model and by a cascade of continuous stirred tank reactors. The high number of reactors in the cascade denotes a quasi plug flow behaviour. The results are confirmed by two cascades of continuously stirred tank reactors in series. The dispersion coefficients obtained throughout the reaction area of the cell are not constant. This shows that the flow is not well established at the entrance of the reaction zone and depends on the entrance conditions.     

急冷废热锅炉进口分配器内分布管椭圆度对气体流动与分布的影响

针对10万吨/年大型乙烯裂解炉用四进口“浴缸式”急冷废热锅炉现存问题,采用稳态与瞬态CFD数值计算方法研究了急冷废热锅炉进口分配器内的流动状况。比较了圆形截面和椭圆形截面分布管对流动的影响,分析了不同分布管截面椭圆度时废热锅炉换热管内的气体分配不均匀性及分配器内的低速区、停留时间、涡量和湍流耗散率。采用综合考虑涡量、湍流耗散率和气体分配不均匀性的量纲1化综合性能指标比较各结构的综合性能,结果表明当分布管椭圆度e在1.12～1.2之间时气体流动状况较佳。     

Stochastic Modeling of the Particle Residence Time Distribution in an Opposed Multi‐Burner Gasifier

The gasification technology of impinging streams has been extensively applied to chemical production and power generation. Particle residence time distribution (RTD) is an important parameter required for modeling, designing and optimization of an impinging stream gasifier. A stochastic mathematical model based on the Markov chains model is developed for the opposed multi‐burner gasifier (OMBG), which closely describes the behavior of the flow pattern and particle RTD in the gasification system. The model simulates the motion of single particle moving in the gasifier using the Markov chains. The predicted results give a reasonable fit to the experimental data. This shows that the flow process of particles in the gasifier has recirculation eddies, which have a downward flow direction near the downflow core and an upward flow direction near the wall, but no short‐circuit. Finally, the effect of particle flux rate on the RTD is predicted, and the contrast between gas and particles RTDs at a laboratory scale and in an industrial gasifier are presented.     

Particle‐scale investigation of the solid dispersion and residence properties in a 3‐D spout‐fluid bed

Three‐dimensional modeling of the gas–solid flow in a spout‐fluid bed is conducted at the particle‐scale level. Both the local and systematic dispersion behaviors of solid phase are initially investigated. Then, the solid circulating and resident behaviors are discussed. The results demonstrate that vigorously lateral solid dispersion appears in the spout region and the periphery of the fountain, whereas intensely vertical dispersion exists in the central region of the bed. Moreover, the inlet configuration of bed strongly affects the distribution of lateral dispersion, while its influence on the vertical one disappears in the fountain. Strong anisotropy of solid dispersion along the three directions is obtained. Systematic dispersion intensity along the vertical direction is an order of magnitude larger than the lateral one. In addition, two circulating patterns of solid phase can be identified. Solid residence time is the smallest in the spout region and the largest in the bottom corner. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2788–2804, 2014     

撞击流气化炉内颗粒停留时间分布的随机模拟

根据多喷嘴对置式气化炉流场测试,将气化炉划分为若干区域,运用时间离散、状态离散的马尔可夫链随机模型,模拟了气化炉内颗粒相的停留时间分布(RTD)。当颗粒在撞击区和射流区间的回流比为0.5,向下撞击流股区和管流区为平推流模型,其他区域按全混流模型处理时,模拟值与实验值吻合较好。随着进料流量的增大,平均停留时间减小,量纲1方差减小;随着回流比的增加,平均停留时间增大;气固两相平均停留时间接近,但RTD存在一定差异。     

3‐D Simulations of an Internal Airlift Loop Reactor using a Steady Two‐Fluid Model

Three‐dimensional (3‐D) simulations of an internal airlift loop reactor in a cylindrical reference frame are presented, which are based on a two‐fluid model with a revised k‐? turbulence model for two‐phase bubbly flow. A steady state formulation is used with the purpose of time saving for cases with superficial gas velocity values as high as 0.12 m/s. Special 3‐D treatment of the boundary conditions at the axis is undertaken to allow asymmetric gas‐liquid flow. The simulation results are compared to the experimental data on average gas holdup, average liquid velocity in the riser and the downcomer, and good agreement is observed. The turbulent dispersion in the present two‐fluid model has a strong effect on the gas holdup distribution and wall‐peaking behavior is predicted. The CFD code developed has the potential to be applied as a tool for scaling up loop reactors.     

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     

振荡流反应器的物料停留时间分布模型研究

提出了一个基于马尔柯夫链（Markov chains）的考虑腔室间返混的振荡流反应器物料停留时间分布模型。通过对在内径50mm,长1．95m的振荡流反应器进行的理想脉冲示踪试验数据的统计分析,给出了模型的唯一参数回流比R的经验计算公式。发现在试验条件下,存在一个与最小回流比R相对应的振荡条件。这振荡条件可表示为振荡流雷诺数（Reo）与净流雷诺数（Ren）的比值ζ,其范围为1．6〈ζ〈2．5。     

Casson流体层流反应器中连串反应的产品分布

引　言目前化工流体力学涉及的范围已由传统的牛顿流体发展到非牛顿流体 .常见的非牛顿流体包括幂律流体、Bingham流体和Casson流体 .有许多高聚物反应物系和生化反应物系属于非牛顿流体 .特别是某些生化反应系统 ,所处理的物系常由各种天然物质组成 ,因而表现出典型的非牛顿流     

Residence Time Distribution Models Derived from Non‐Ideal Laminar Velocity Profiles in Tubes

The theoretical E‐curve for the laminar flow of non‐Newtonian fluids in circular tubes may not be accurate for real tubular systems with diffusion, mechanical vibration, wall roughness, pipe fittings, curves, coils, or corrugated walls. Deviations from the idealized laminar flow reactor (LFR) cannot be well represented using the axial dispersion or the tanks‐in‐series models of residence time distribution (RTD). In this work, four RTD models derived from non‐ideal velocity profiles in segregated tube flow are proposed. They were used to represent the RTD of three tubular systems working with Newtonian and pseudoplastic fluids. Other RTD models were considered for comparison. The proposed models provided good adjustments, and it was possible to determine the active volumes. It is expected that these models can be useful for the analysis of LFR or for the evaluation of continuous thermal processing of viscous foods.     

Estimation of liquid phase mixing due to solids in a turbulent bed contactor

The mixing in two-phase gas-liquid and three-phase gas-liquid-solid system (turbulent bed contactor) is evaluated through residence time distribution (RTD) studies in terms of Peclet number. RTD experiments are conducted for various gas and liquid velocities, and number of stages for two- and three-phase systems. Since the mean residence time is very short in both the systems, a mixed flow tank with exponential decay RTD is used in series. After deconvolution, the RTD of the system is obtained. The experimental RTD curves are satisfactorily compared with the axial dispersion model and Peclet numbers are evaluated for all the experiments. The axial dispersion coefficients are calculated from Peclet numbers. With this study, it is thought that liquid phase mixing may be controlled by changing the quantity of solid particles in the bed.     

Residence time distribution analysis from a continuous couette flow device around critical taylor number

This paper presents an experimental study of residence time distribution (RTD) analysis by pulse response technique in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. Two kinds of experimental tests using pulses of tracer dye solution and particles resulting from a fast precipitation were performed in the region near the critical Taylor number characterizing boundary between laminar and laminar vortex flow. For most experiments performed in laminar and laminar vortex flow regime around the critical Taylor number over the ranges 0 < T_a < 120 and 0 < R_e < 5.5 the normalized response can be described by a dispersion model. The results of the critical Taylor number as characterized by the minimum dispersion number appear consistent with both theoretical predictions and other empirical observations.