Chemical Multiphase Flow Image Analysis System and Its Application in Liquid-Solid Circulating Fluidized Bed

Zhang Shaofeng\ Ren Yexu\ Liu Junjie\ Wang Yapeng2(1. School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, China; 2. China Daheng Co., Ltd. Beijing Image Visual Technology Branch, Beijing 100018, China), has been successfully used in vertical pipe fluids Study on the Motion Characteristics of Solid Particles in Solid Circulating Fluidized Beds . The test results show that: 1) The system can visually display the movement state of the measured flow field and meet the measurement requirements of a certain flow field; 2) The concentration distribution of particles in the tube is unevenly hooked, with the particle volume fraction and flow type. The results of the change; 3) The test results obtained can explain the liquid-solid fluidized bed heat exchanger enhanced heat transfer and anti-scaling mechanism.

Multiphase flow is a widely-existing mixed flow form, such as oil and gas, oil-water two-phase flow in the petroleum industry, gas-solid two-phase flow in a fluidized bed reactor in the chemical industry, and gas-liquid-solid three-phase flow, etc. . With the improvement of industrial level, the requirements for measuring multi-phase flow parameters become more and more urgent. For many years, the testing method for multi-phase flow field velocity field has received much attention. Various test methods have been developed to study the flow of multiphase flow, such as imaging, conductivity probe, capacitance tomography, optical fiber, fiber probe, and particle velocity imaging. Since the gas-liquid-solid three-phase fluidized bed uses the liquid phase as the continuous phase, the gas phase and the solid phase as the dispersed phase, and the gas-solid and the liquid are inherently different in nature, they are different in application. For example, conductivity probe method, optical fiber method, and optical fiber probe method are all built-in methods. Since the probe is directly placed on the measurement point of the device under test, it will have some influence on fluid flow and bubble movement in the bed. And it can only measure the characteristics of air bubbles at various local points in the system. Camera method, electrical capacitance tomography, particle imaging and velocity measurement methods are all external methods. They are non-contact measurement methods and can intuitively show the size and distribution of bubbles and particles and their movement process. There is no interference with the movement of bubbles and particles, but its cost and requirements for the test environment are high.

This article developed a chemical multiphase flow image analysis system, which is a non-contact measurement method, and has been successfully applied to the study of solid particle motion in a liquid-solid circulating fluidized bed in a vertical tube, and achieved satisfactory results. the result of.

1 Introduction to Chemical Multiphase Flow Analysis System 1.1 System Overview Card, computer and software analysis system components. Its structure is shown in Fig. 3. Measurement System Structure Fund Project: Hebei Provincial Natural Science Foundation of China (202016) The Journal of Hebei University of Technology is a new type of solid imaging device. The outstanding feature is that the charge is the signal rather than the current and the voltage; its function is to convert the two-dimensional optical signal into a one-dimensional video signal through the charge storage and transfer, and display a clearly visible image directly on the display. Its high sensitivity, high resolution, ideal "scanning" linearity and digital scanning capabilities, small size and low cost. The CCD solid-state camera used in this system belongs to an interline transfer type area array CCD and adopts an interlace scanning method. That is, scanning odd-numbered lines to form an odd-numbered field, scanning even-numbered lines to form an even-numbered field, and two fields to form a complete frame of an image. The frame frequency is 25 Hz and the field frequency is 50 Hz during scanning. The camera is connected to a computer processing system and can be acquired.

The brand model frame rate (256 line scanner) image acquisition card is based on PCI bus high-speed color / black and white image capture card DH-VRT-CG210 card. The data transmission process is controlled by the image acquisition card, without CPU participation, so the image transmission speed can reach 40MB/S. The real-time data transmission is the outstanding characteristic of the DH-VRT-CG210 card.

1.1.3 Software System This software system is designed with Visual Basic language and has powerful data processing capabilities. It can directly derive the projection curve, instantaneous displacement, curve velocity, and axial and radial velocity components of any particle motion trajectory. , And can make the curve after fitting. In terms of counting, the system realizes statistics on the number of particles in a group of consecutive images according to the difference in the gray value between the particles and the liquid, and obtains the distribution of particles in different regions at different flow speeds.

The system also realizes the visualization of the image, develops a good human-computer interaction interface, fully considers the user's needs and convenience, and makes the system flexible in operation and rich in functions. The form interface is as shown.

The upper side of the figure is a toolbar. All the commands of the software are in it. No keyboard input is required. On the side is the viewing zone. This zone displays the photographs of each frame taken. The frame-by-frame playback can be achieved with a click of the mouse. The upper left corner is the photo serial number; the middle is the main viewing area, the area displays the current photo, the existing test tube in the figure is the test tube; the lower light area shows the current photo serial number, acquisition time, and the mouse moves in the main viewing area The coordinates of the mouse and the end of the command can be displayed.

The man-machine interface of the collection system U 1.2 Working principle In the test, the tube to be tested is evenly partitioned, and the chip light source and the center of the CCD camera are placed at 90* angles on the same horizontal line, as shown.

By moving the plate light source, the slice light source illuminates each subarea of ​​the measured flow field, and the high-resolution CCD camera directly performs digital sampling on the flow field space, and the particles display a clear image on the human-machine interface of the system. Photographs of the liquid-solid two-phase flow after the unpadded light source and the addition of the patch light source are listed.

Chemical multi-phase flow image analysis system and its application in the research of liquid-solid circulating fluidized bed The fourth area and the third area (photograph of unstamped light source) (photograph of liquid-solid two-phase flow after adding the light source) Photo comparison The true trajectory of the particles passes the image data to the computer for processing. In statistical analysis, the actual pixels are dimensioned in pixels.

Calculate the average displacement and average direction of the particles in the analysis window by using the small area elements (analysis window) at the same position of the odd-even (or multiple) images to perform mutual operations; when the analysis window is small enough (as opposed to the bed) Speed ​​can be considered as the instantaneous speed at this point. Because the particles can be clearly displayed on the human-machine interface, the position and size of the particles can also be analyzed. As shown, a is the true trajectory of the particle and b is a schematic diagram of velocity calculation. The particles are displaced in the r direction, the actual displacement is calculated by transformation, the particle diameter is subtracted, and then divided by the exposure time, the velocity of the solid particles is solved =f = the flow field is obtained in the liquid-solid two-phase flow field. The distribution of the tracer particles can be added to the tracer particles. Since the tracer particles and the added inert solid particles are significantly different in size, they can easily be distinguished and discriminated by software. Through the difference in color, the inert solid particles can be directly analyzed to obtain the distribution and velocity of the particles in the flow field. Solving the particle identification problem, it is easy to find the distributed particle pairs without having to construct a new set of devices to determine the particle pairs (ie, the display of the same particle in different positions in different frames). Coordinates of the same particle at different positions are recorded in the image. According to the continuous image of the same particle captured, the curve of these points is fitted by the least square method, and the axial velocity of the obtained particle is obtained by deriving these points. And radial velocity, and then determine the direction of particle velocity.

b Calculation of particle velocity diagrams Particle trajectory and velocity calculations Schematic system functions 1) For continuous acquisition and processing of high-speed moving images, images can be displayed dynamically or statically on a computer screen (where dynamic displays include real-time display, continuous playback,桢 Display) The image can also be printed and stored; 2) The target particle or bubble in the continuous image is marked and positioned so as to obtain the target motion trajectory. The motion trajectory can be displayed in the form of a picture or printed out, or it can be data The file is stored in the form of a hard disk; 3) Calculate the axial and radial displacement components of the target trajectory separately, and use the least square method to obtain the displacement curve of the target in the axial and radial directions, respectively; 4) Calculate the target motion in Axial and radial velocity components, and can be displayed or printed in the form of a velocity curve, or can be displayed or printed in the form of a velocity component; a flow rate of 0.5m3/h, volume fraction of 2% e flow rate l.OmVh, volume fraction Rate 8./.f flow 1.5mVh, volume fraction 8% Concentration distribution of particles in tube b Flow 0.5m3/h, volume fraction 5% 5) Set the area in the image The number of objects (particles or bubbles) appearing on the (up to 1 area) is automatically identified and counted, and the statistical results are displayed on the screen or printed out, or they can be stored on the hard disk in the form of data files - 3 Applications Using chemical multiphase flow The image analysis system studied the flow characteristics of the liquid-solid circulating fluidized bed in the tube, and used Ma's lab program to give the distribution of particle concentration in the tube, as shown. The test results show that the distribution of particles in the tube is not uniform. When the flow rate is constant (a, 6b, 6c), the non-uniformity of the particles decreases as the particle volume fraction increases, and when the volume fraction is constant (c , 6d, 6e, 60, the non-uniformity of the particles gradually decreases as the flow rate increases, in the laminar flow region, the particles are mainly distributed in the wall region, and there is a small amount of particles in the central region of the tube, or almost no particles. The ring nuclear model is basically the same; in the turbulent area, the particles are mainly distributed in the central area of ​​the tube, and as the flow increases, the particles are increasingly concentrated in the central area of ​​the tube. *Drawing chemical multiphase flow image analysis system and its liquid Application of a Solid Circulating Fluidized Bed Research Institute of Chemical Industry Multiphase Flow Laboratory of Hebei University of Technology The liquid-solid circulating fluidized bed technology has been applied to Jindan Lactic Acid Co., Ltd., Yucheng City, Henan Province. The application results show that the heat transfer can be enhanced while preventing scale removal. The above-mentioned test results strongly explain that the liquid-solid fluidized bed heat exchanger increases the heat transfer coefficient of the heat exchanger due to the frequent disturbance of the fluid boundary layer at low flow speeds. At the same time, the anti-scaling ability is greatly improved.

4 Conclusion 1) The chemical multiphase flow image analysis system has powerful functions, simple application, high measurement accuracy, can intuitively display the movement of the measured flow field, and completely meet the test requirements of a certain flow field; 2) the system has been successfully applied to the vertical The flow characteristics of solid particles in a liquid-solid circulating fluidized bed with straight tubes have been studied and good results have been obtained. 3) The distribution of particle concentration in the tubes is not uniform, and varies with the volume fraction of the particles and the flow patterns; 4 The experimental results obtained can well explain the enhanced heat transfer and anti-scaling mechanism of the liquid-solid circulating fluidized bed heat exchanger.