流化床中旋风下料管的物理模型

In most industrial fluidization units, two- or three-stage cyclone systems are used to clean the product gases. To return the solids to the bed, these cyclones are fitted with diplegs. By pass of gas from the bed through the dipleg is partially overcome by the back pressure build-up in the dipleg and by adding a trickle valve at the bottom of the dipleg. Diplegs of primary cyclones, operating at a high solid loading behave differently from diplegs of secondary and tertiary cyclones which operate at low solid loading. Both types have been investigated by pressure drop measurements, visual observation and by measurements of the air flow rate flowing up the riser. The primary dipleg was also studied using electrical capacitance tomography. The results are reported hereafter and will give a first indication towards the right design of the dipleg and the selection of the trickle valve. The influence of gas flow in the dipleg on the conversion in a catalytic fluidized bed reactor is found to be negligible.     

ECT图像分析法用于贮料仓卸料过程中剪切区域测量(英文)

The paper covers the electrical capacitance tomography(ECT) data analysis on shear zones formed during silo discharging process.This is due to the ECT aptitude for detection of slight changes of material concentration.On the basis of ECT visualisations,wall-adjacent shear zone profiles are analysed for different wall roughness parameters.The analysis on changes of material concentration,based on ECT images,enables the calculation for the characteristic parameters of shear zones-size and material concentration inside the shear zone in a dynamic process of silo discharging.In order to verify the methodology a series of experiments on gravitational flow of bulk solids under various conditions were conducted with different initial granular material packing densities and silo wall roughness.The investigation shows that the increase in container wall roughness is an effective method for reducing the dynamic effects during the material discharging,since these effects are resulted from the resonance between hopper construction and trembling material.Such effects will damage industrial equipment in practical applications and need further investigation.     

硅藻土-木桨纤维为助滤剂强化过滤过程的研究(英文)

In this paper, a study to enhance the filtration for solid/liquid materials difficult to be filtered, such as highly viscous, highly compactible or gel like materials, is presented. Filter aids diatomaceous earth and wood pulp cellulose are used to enhance the filtration by improving filter cake structure and properties in the filtration of a biological health product and a highly viscous chemical fiber polymer melt product. The property of solid/liquid systems, filtration at different flow rates, specific cake resistance, cake wetness, filtration rate, filtrate turbidity for filter aid selection and evaluation, and operation optimization are investigated. The results are successfully applied to industrial process, and can be used as a reference for similar filtration applications.     

SOLID-LIQUID SUSPENSION SYSTEM IN AGITATED TANK WITH DRAFT TUBE

Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the distance from the inlet to the tank bottom are two importantparameters for draft tube design The NAX-4 impeller,developed in this study,is characterized byits high flow efficiency and low power consumption.Some modifications are made to the Bald′smodel by considering the effects of solid concentration and fluid viscosity on the critical speed forcomplete off-bottom suspension.The modified equation fits the experimental data satisfactority andcan be used in scale-up design     

利用计算流体力学方法研究精馏塔板上的液相流动

A computational fluid-dynamics model is presented for predicting the two-phase two-dimensional liquid phase flow on a distillation column tray based on the modification of Navier-Stokes Equation by considering both the resistance and the enhanced turbulence created by the uprising vapor. Experimental measurement of the local liquid phase velocity on an air-water simulator of 1.2 m in divaneter by using the hot film anemometer is briefly described. Two of the conventional fluid-dynamic constants are readjusted for the case of liquid flow on a tray byfitting the experimental data. The predicted local liquid phase velocity and direction of flow by the present model are confirmed satisfactorily by the authors‘ experimental measurements and by the data from literature. By the aid of the present model, the concentration field on the tray can be computed for the evaluation of the enhancement of liquid phase concentration across a tray. The advantages of applying computational fluid-dynamics to tray column design are discussed.     

Computational Fluid-dynamics of Liquid Phase Flow on Distillation Column Trays

A computational fluid-dynamics model is presented for predicting the two-phase two-dimensional liquid phase flow on a distillation column tray based on the modification of Navier-Stokes Equation by considering both the resistance and the enhanced turbulence created by the uprising vapor. Experimental measurement of the local liquid phase velocity on an air-water simulator of 1.2m in diameter by using the hot film anemometer is briefly described. Two of the conventional fluid-dynamic constants are readjusted for the case of liquid flow on a tray by fitting the experimental data. The predicted local liquid phase velocity and direction of flow by the present model are confirmed satisfactorily by the authors' experimental measurements and by the data from literature. By the aid of the present model, the concentration field on the tray can be computed for the evaluation of the enhancement of liquid phase concentration across a tray. The advantages of applying computational fluid-dynamics to tray column design     

搅拌槽内液-固两相体系的数值研究(Ⅰ)流场的数值模拟

Three-dimensional solid-liquid flow is mathematically formulated by means of the “two-fluid” approach and the two-phase k-ε-Ap turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved “inner-outer” iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of the simulation with experimental data on the mean velocities and the turbulence quantities of the solid phase is made and quite reasonable agreement is obtained except for the impeller swept volume. The counterpart of liquid phase is presented as well. The predicted solid concentration distribution for three experimental cases with the average solid concentration up to 20% is also found to agree reasonably with the experimental results published in the literature.     

Reconstruction of electrical capacitance tomography images based on fast linearized alternating direction method of multipliers for two-phase flow system

Electrical capacitance tomography (ECT) has been applied to two-phase flow measurement in recent years. Image reconstruction algorithms play an important role in the successful applications of ECT. To solve the il-posed and nonlinear inverse problem of ECT image reconstruction, a new ECT image reconstruction method based on fast lin-earized alternating direction method of multipliers (FLADMM) is proposed in this paper. On the basis of theoretical analysis of compressed sensing (CS), the data acquisition of ECT is regarded as a linear measurement process of permittivity distribution signal of pipe section. A new measurement matrix is designed and L1 regularization method is used to convert ECT inverse problem to a convex relaxation problem which contains prior knowledge. A new fast alternating direction method of multipliers which contained linearized idea is employed to minimize the objective function. Simulation data and experimental results indicate that compared with other methods, the quality and speed of reconstructed images are markedly improved. Also, the dynamic experimental results in-dicate that the proposed algorithm can fulfil the real-time requirement of ECT systems in the application.     

Design of reactive distillation processes for the production of butyl acrylate:Impact of bio-based raw materials☆

The chemical industry is nowadays predominantly using fossil raw materials, but the alternative use of bio-based resources is investigated to account for the foreseeable scarcity of fossil feedstocks. A main challenge of using bio-based feedstocks is the complexity of the impurity profile. For an economic production of bio-based chemicals, the use of intensified processes is inevitable and approaches are needed for the various process intensification techniques to identify their applicability to be used for the production of bio-based components. In the presented study, an approach is shown for the reactive distil ation (RD) technology to identify the most critical bio-based impurities and their impact on the reactive distillation process. The investigated case-study is the production of n-butyl acrylate from acrylic acid and n-butanol. Among al initially identified impurities, the key impurities, having the biggest impact on the product purity in the reactive distil ation process, are found. These impurities are then studied in more detail and an operating window depending on the impurity concentration is identified for the reactive distil ation column. Furthermore, an integrated design of upstream and downstream processes is facilitated, as the presented results can be used in the development of the fermentation processes for the produc-tion of the bio-based reactants by decreasing the concentration of the critical impurities.     

循环硫化床上升管中动态行为的拟流体模拟

The kinetic theory of granular flow (KTGF) is modified to fit the Einstein′s equation for effective viscosity of dilute flow. A pseudo-fluid approach based on this modified KTGF is used to simulate the dynamic formation and dissipation of clusters in a circulating fluidized bed riser. The agglomeration of particles reduces slip velocity within particle clusters, and hence results in two reverse trends: discrete particles are lifted by air while particle clusters fall down along the wall. The dynamic equilibrium of these two types of motion leads to the characteristic sigmoid profile of solid concentration along the longitudinal direction. The predicted solid velocity, lateral and longitudinal profiles of solid volume fraction and annulus thickness are in reasonable agreement with experimental results.     

FCC沉降器粗旋工作性能的数值模拟

引言 催化裂化工艺(fluidized catalytic cracking, FCC)是目前我国重质油轻质化加工的主要方法之一.重质油裂化反应过程主要在提升管反应器内完成,提升管出口通常设置旋风分离器(简称粗旋)将反应后油气与催化剂快速分离,以避免发生过裂化反应.粗旋工作性能的优劣直接影响装置目的产物的收率、沉降器内部结焦以及油浆固含量.     

Characterizing the dynamic property of the vortex tail in a gas cyclone by wall pressure measurements

To explore a determination method for cyclone vortex tail, the wall pressures at different axial and radial positions of a cylinder-on-cone cyclone were measured and analyzed by the Fast Fourier Transform (FFT) and probability density analyses in this paper. The cyclone vortex tail was also visualized by a red ink tracer. The results show that the cyclone wall pressure does not change in the cylindrical section and gradually decreases in the conical section. The magnitudes of wall pressure at different azimuths are almost identical, indicating an axisymmetrical wall pressure radial profile in these parts of the cyclone. Whereas in the lower part of the cone and/or the upper part of dipleg, there is a sudden fall of wall pressure and non-axisymmetrical pressure radial profile. The minimum wall pressure occurs at about 270° azimuth in this region. Underneath in the next part of the dipleg, the wall pressure rapidly rises and returns to axisymmetry. These characteristics indicate that the vortex tail is bended to wall, turns around in this region, and can be used as evidences of the vortex tail. The position determined by the pressure measurement is close to the position of the rotating ring observed in the tracing experiment. It is also found that the frequency of the inner vortex is different from that of the outer vortex. The inner vortex flow fluctuates stronger and faster than its outer partner. At the vortex tail zone, the vortex breaks and the inner vortex fluctuation is involved in the wall pressure signal. Therefore, the position and dynamic property of the vortex tail can be well identified from the wall pressure measurement. The pressure measurement could provide some solid experimental basis for assessing relations of natural vortex length.     

Effect of the Solid Loading on a PFBC Cyclone with Pneumatic Extraction of Solids

This paper presents the effects of solid loading on the performance of a cyclone with pneumatic extraction of solids. The cyclone is a non‐conventional design, especially used for hot‐gas cleaning applications such as pressurized fluidized bed combustors (PFBC). A scaled‐down cold‐flow model was employed for the research. Experiments were conducted at 9–14 m/s inlet gas velocities, inlet solid loadings ranging from 30 to 230 g/kg gas, and bottom gas extraction percentages from 0.3 to 1.5%. Experimental results of pressure drop resistance coefficients and collection efficiency were compared with literature predictions. At PFBC operating conditions, cyclone geometry and solid concentration are the main parameters influencing cyclone pressure drop and collection efficiency. The vortex penetration in dipleg causes lower pressure drop values and higher collection efficiencies than predicted. These parameters can be suitably predicted for PFBC cyclones by introducing a modified penetration length in Muschelknautz's model [1]. For the present cyclone design, a new correlation of pressure drop, including the influence of solid loading, is proposed. A new method for detecting cyclone fouling, not previously addressed, is also presented, based on the evolution of the pressure drop resistance coefficient. An enhanced separation efficiency has been found, related to collection efficiency, which is especially important for particle sizes below 10 μm revealing agglomeration effects.     

催化裂化沉降器内两端敞开型旋风分离器内气相流动规律

研究考察了催化裂化沉降器内两端敞开型旋风分离器内油气流动规律.用CFX软件采用DSM模型进行了数值模拟,并与用五孔探针测试的流场进行了比较,表明DSM模型有良好的预测精度.在此基础上,采用标量输运方程研究了气体在旋风分离器内的停留时间分布规律.实验和模拟结果均表明,该类旋风分离器内流场与常规旋风分离器的有很大的不同,升气管和料腿均存在回流区,升气管回流区最大可波及分离空间,对分离空间流场有很大干扰.气体示踪模拟结果表明,由入口进入旋风分离器,由升气管、料腿排出的气体的停留时间近似呈对数正态分布;升气管、料腿回流区内气体停留时间呈双峰分布;升气管回流区的存在可使总气体平均停留时间增大约5%～10%;料腿直径的减小以及灰斗的存在均可增大由升气管排出的气量并使升气管、料腿回流区大幅减小,进而减小粗旋风分离器内气体总平均停留时间.     

Measurement of particle concentration in a Wurster fluidized bed by electrical capacitance tomography sensors

It is essential to measure and monitor the particle flow characteristics in a Wurster fluidized bed to understand and optimize the coating processes. In this article, two electrical capacitance tomography (ECT) sensors are used to measure the particle concentration in different regions in a Wurster fluidized bed for the “cold” particle flows. One ECT sensor has a 12‐4 internal‐external electrodes and another has eight electrodes. The 12‐4‐electrode ECT sensor is used to measure the particle concentration in the annular fluidization region (outside of the Wurster tube) and the eight‐electrode ECT sensor is used to measure the particle flow in the central region (inside the Wurster tube). The effect of particle type, particle moisture, fluidization velocity, and geometrical parameters on the Wurster fluidization process is studied based on the two ECT measurements. The radial particle concentration profiles in the annular fluidization and central flow regions with different operation parameters are given. Fast Fourier Transform analysis of the particle concentration in the Wurster tube is performed with different superficial air velocities. The optimum operating ranges of the Wurster fluidization process for different particles are given. In the end of the article, computational fluids dynamics simulation results are given and used to compare with the measurement results by ECT for a typical Wurster fluidized bed. © 2014 American Institute of Chemical Engineers AIChE J 60: 4051–4064, 2014     

带翼阀旋风分离器料腿内静压分布试验研究

在φ800mm×12000mm流化床试验装置上,用多点压力测量仪测量料腿内的静压分布。试验结果表明,二级料腿内气固两相流的流态一般由入口旋转段、稀相下落段和下部密相段3部分组成,料腿内的料封高度随料腿两端负压差的增大而升高,颗粒质量流率对轴向空隙率影响明显,翼阀浸没在密相床时颗粒流动稳定性和流动失流化的机会都增加。     

Deep learning-based tomographic imaging of ECT for characterizing particle distribution in circulating fluidized bed

The gas and solids in a circulating fluidized bed (CFB) are heterogeneously dispersed and a multiscale flow regime may form both in time and space. Accurate measurement of the fluidizing process is significant for investigating the multiscale gas–solid flow characteristics and the design, optimization, and control of CFBs in various applications. This article develops a deep learning-based tomographic imaging of electrical capacitance tomography (ECT) to characterize the particle concentration distribution in a CFB. The deep tomographic imaging approach is realized through training a well-designed convolutional neural network (CNN) with the numerically built dataset. Simulation results demonstrate that the average values of the relative image errors reconstructed by CNN in the test set are 0.1110 and 0.1114 for the 60 and 100 mm pipes, respectively, which are better than the average values of 0.1819 and 0.2519 by the Landweber algorithm. With the verification of the trained model based on the prepared data can image the unseen typical flow patterns better than Landweber, it is further used to investigate the particle flow characteristics of a lab-scale CFB. Experimental results reveal that the developed deep tomographic imaging of ECT can successfully measure the fluidized particle distribution in both the 60 and 100 mm pipes, showing good prediction and generality of the designed CNN model. A flow regime transformation from “annular” flow to “core-annular” flow and pneumatic conveying is observed under the tested conditions. Besides, the flow regime would be highly affected by the fluidized gas flow rate and the initial bed height.     

基于数据驱动的卷积神经网络电容层析成像图像重建

针对电容层析成像技术的图像重建问题，提出了基于数据驱动的卷积神经网络图像重建方法。根据气固两相流的流型特点，通过数值模拟的方法随机生成了60000组介质分布图像，并利用有限元法计算了与之对应的电容向量，从而建立了一个“电容向量-介质分布”数据集；然后根据电容层析成像图像重建特点建立了卷积神经网络模型，对数据集中的训练集进行学习和训练，并利用测试集对训练结果进行了验证与评价。在此基础上，对获得的ECT图像重建卷积神经网络模型进行了静态实验和流化床测试实验研究。模拟和实验结果表明：所建立的卷积神经网络能较好地实现ECT图像重建，可直接用于流化床内的颗粒浓度分布测量。     

甲醇制烯烃装置降低催化剂跑损及负荷提升的改造实践

针对某甲醇年处理量180万t的甲醇制烯烃装置自投产以来存在的细粉损失严重问题进行了原因分析,发现是由再生器中沉降高度低、旋分入口浓度高、入口气速高于设计值导致的压降高、料腿排料困难所致。通过将再生器外取热器流化风由氮气改为空气,之后引入氧气进一步提升再生烧焦能力,在维持再生器旋分系统入口气速和压降合适的基础上,改善了装置的跑剂问题,实现了装置处理量最高8.3%的提升,初步预估年效益可增加0.9亿元。