Numerical simulation method of gas-liquid-solid three-phase in pneumatic lifting system based on CFD-DEM

Abstract

The present invention relates to a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM. The method comprises: constructing a geometric model of a pneumatic lifting system, and meshing the geometric model; collecting gas-liquid flow rate through sensors in the experiment, collecting gas-liquid volume fraction and velocity inside the pipeline through ECT equipment, determining a gas-liquid two-phase calculation model for CFD calculation, and obtaining calculation results; selecting a particle phase mechanics analysis model according to the calculation results, and performing CFD-DEM coupled numerical calculation of gas-liquid-solid three-phase flow of a pneumatic lifting system based on a CFD-DEM bidirectional coupling method, obtaining a particle distribution cloud map, a particle velocity cloud map, and a simulated flow field velocity map, and mutually verifying and analyzing the flow field information and particle motion conditions obtained through the experiment with the numerical simulation results to obtain the particle motion characteristics of the pneumatic lifting system. The bidirectionally coupled CFD-DEM method is used to simulate the internal flow field of the pneumatic lifting system and the motion characteristics of the particles, providing guidance for the theory of the pneumatic lifting system.

Description

Technical Field

[0001] The invention relates to the technical field of deep-sea mining pneumatic lifting systems, and in particular to a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM. Background Art

[0002] Pneumatic lifting technology is one of the most promising deep-sea mining pipeline transportation methods. Its advantages are simple structure, low operating cost, no internal moving parts, small particle size limit, less environmental pollution, high work safety and reliability, etc. In mining engineering, the pneumatic lifting system uses an air compressor to inject compressed air into the lifting pipe through the air injection pipe, and uses the pressure difference caused by the different liquid densities inside and outside the pipe to lift the minerals from the seabed to the sea surface, completing the task of deep-sea mining mineral transportation. However, due to the particularity and complexity of the deep-sea operating environment, it is very difficult to directly operate the relevant mining equipment and conduct costly field tests. In addition, the application of gas lift technology to the research of gas-liquid-solid three-phase flow such as deep-sea mining is still in the exploratory stage, and the few successful cases are mostly based on experience.

[0003] Therefore, the traditional pneumatic lifting system does not have a complete and widely convincing three-phase flow theoretical model to support the application of gas-liquid-solid three-phase flow. Summary of the invention

[0004] Based on this, in order to solve the above technical problems, a gas-liquid-solid three-phase numerical simulation method of the pneumatic lifting system based on CFD-DEM is provided, which can provide guidance for the theory of the pneumatic lifting system.

[0005] A gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system based on CFD-DEM, the method comprising:

[0006] constructing a pneumatic lifting system geometric model and meshing the geometric model;

[0007] In the meshed geometric model, the gas-liquid flow rate is collected by the sensor in the experiment, and the gas-liquid volume fraction and velocity inside the pipeline are collected by the ECT equipment;

[0008] According to the gas-liquid flow rate, the gas-liquid volume fraction and the speed, a gas-liquid two-phase calculation model is determined to perform CFD calculation to obtain a calculation result;

[0009] According to the calculation results, a particle phase mechanical analysis model is selected, and a CFD-DEM coupled numerical calculation of the gas-liquid-solid three-phase flow of the pneumatic lifting system is performed based on the CFD-DEM bidirectional coupling method to obtain a particle distribution cloud map, a particle velocity cloud map and a simulated flow field velocity map;

[0010] According to the particle distribution cloud map, particle velocity cloud map and simulated flow field velocity map, the flow field information and particle movement conditions obtained through experiments are mutually verified and analyzed with the numerical simulation results to obtain the particle movement characteristics of the pneumatic lifting system.

[0011] In one embodiment, constructing a pneumatic lift system geometric model includes:

[0012] The bottom frustum silo, material particle inlet, water flow inlet, air injection port and lifting pipe are connected to form a geometric model of the pneumatic lifting system.

[0013] In one embodiment, meshing the geometric model includes:

[0014] Performing Bio local fine mesh division on the gas injection port;

[0015] Perform Curvature & Proximity surface mesh division on the bottom frustum silo, material particle inlet, water flow inlet, and riser;

[0016] Generate volume mesh based on Poly-Hexcore volume mesh generation method.

[0017] In one embodiment, in the meshed geometric model, the gas-liquid flow rate is collected by the sensor in the experiment, and the gas-liquid volume fraction and velocity inside the pipeline are collected by the ECT device, including:

[0018] Install sensors at the water flow inlet and the gas injection port respectively to collect gas-liquid flow at the water flow inlet and the gas injection port;

[0019] The flow field parameters inside the pipeline are collected through the ECT equipment to obtain the gas-liquid volume fraction and velocity inside the pipeline.

[0020] In one embodiment, a gas-liquid two-phase calculation model is determined according to the gas-liquid flow rate, the gas-liquid volume fraction and the velocity to perform CFD calculation, and the calculation results are obtained, including:

[0021] The gas-liquid flow rate is used as the boundary condition of CFD, and the gas-liquid volume fraction and velocity inside the pipeline are used as the model setting conditions of CFD;

[0022] CFD calculation is performed according to the boundary conditions and the model setting conditions to obtain calculation results.

[0023] In one embodiment, the method further comprises:

[0024] Compare the gas-liquid flow rate, the gas-liquid volume fraction and the speed with the standard gas-liquid flow rate, the standard gas-liquid volume fraction and the speed to obtain a comparison result;

[0025] When the comparison result shows that the error is less than the error threshold, a CFD calculation model is selected according to the calculation result.

[0026] In one embodiment, the method further comprises:

[0027] By tracing the trajectory of particles using high-speed photography in the experiment, the CFD-DEM bidirectional coupling numerical simulation calculation model was determined.

[0028] In one embodiment, the method comprises:

[0029] Establish a CFD-DEM coupled numerical model of gas-liquid-solid three-phase flow;

[0030] Calculation is performed using the gas-liquid-solid three-phase flow CFD-DEM coupled numerical model to obtain calculation results;

[0031] The calculation results are compared with the trajectory tracking of the particles captured by high-speed photography in the experiment, and a particle distribution cloud map, a particle velocity cloud map and a simulated flow field velocity map are calculated. The flow field information and particle motion conditions obtained through the experiment are verified and analyzed with the numerical simulation results to obtain the particle motion characteristics of the pneumatic lifting system.

[0032] The above-mentioned gas-liquid-solid three-phase numerical simulation method of the pneumatic lifting system based on CFD-DEM collects data through sensors, ECT equipment, etc., selects a suitable model for calculation and analysis based on the data, and uses a two-way coupled CFD-DEM method to simulate the internal flow field and particle movement characteristics of the pneumatic lifting system, thereby obtaining a particle distribution cloud map, a particle velocity cloud map and a simulated flow field velocity map. The flow field information and particle movement conditions obtained through the experiment are mutually verified and analyzed with the numerical simulation results to obtain the particle movement characteristics of the pneumatic lifting system. Since the simulation results are close to the actual experimental data, it has significant advantages such as high reliability, intuitive simulation results, and high calculation accuracy, providing guidance for the theory of pneumatic lifting systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a flow chart of a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM in one embodiment;

[0034] Figure 2 A schematic diagram showing the comparison of particle trajectories in the lifting section in an embodiment;

[0035] Figure 3 A schematic diagram of the distribution of high-concentration particles in one embodiment;

[0036] Figure 4 It is a flow chart of a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM in another embodiment;

[0037] Figure 5 This is a comparison chart of experimental and simulated gas velocity data;

[0038] Figure 6 It is a schematic diagram of the planar particle volume fraction curve;

[0039] Figure 7 Particle velocity distribution at different gas injection rates. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0041] In one embodiment, Figure 1 As shown, a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM is provided, comprising the following steps:

[0042] Step 102, constructing a pneumatic lifting system geometric model and meshing the geometric model.

[0043] Before building the geometric model of the pneumatic lifting system, the physical model needs to be simplified. Specifically, a large water tank can be used to simulate underwater conditions in the experiment to provide a certain water pressure for the bottom silo. In the components of the CFD geometric model, the large water tank can be simplified and replaced by a bottom velocity inlet. The part of the lifting pipe elbow that flows back to the large water tank can be simplified and replaced by an open pressure outlet.

[0044] In one embodiment, a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM may also include a process of constructing a geometric model, and the specific process includes: connecting a bottom truncated cone silo, a material particle inlet, a water flow inlet, an air injection port, and a lifting pipe to form a pneumatic lifting system geometric model. That is, the successfully constructed geometric model may be composed of a bottom truncated cone silo, a material particle inlet, a water flow inlet, an air injection port, and a lifting pipe.

[0045] In one embodiment, a CFD-DEM-based gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system is provided, which may also include a meshing process, and the specific process includes: performing Bio local fine meshing on the gas injection port; performing Curvature & Proximity surface meshing on the bottom frustum silo, material particle inlet, water flow inlet, and lifting pipe; and generating a volume mesh based on the Poly-Hexcore volume mesh generation method.

[0046] Specifically, meshing can include two division processes, one for the gas injection port part and the other for the rest. Therefore, in this embodiment, the gas injection port part can be subjected to Bio local fine meshing, and the rest can be subjected to Curvature & Proximity surface meshing, with 3 boundary layers and a growth rate of 1.2, and finally a volume mesh is generated based on the Poly-Hexcore volume mesh generation method.

[0047] Step 104, in the meshed geometric model, the gas-liquid flow rate is collected by the sensor in the experiment, and the gas-liquid volume fraction and velocity inside the pipeline are collected by the ECT device.

[0048] The meshed geometric model can collect various data through various sensors set on the geometric model. The sensors may include gas-liquid flow sensors, pressure sensors, high-speed cameras, and weighing sensors, etc., which are used to collect different data.

[0049] Step 106, determining a gas-liquid two-phase calculation model according to the gas-liquid flow rate, the gas-liquid volume fraction and the velocity to perform CFD calculation and obtain calculation results.

[0050] Specifically, in one embodiment, a CFD-DEM-based gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system is provided, which may also include a process of performing CFD calculations, and the specific process includes: using the gas-liquid flow rate as the boundary condition of CFD, and using the gas-liquid volume fraction and velocity inside the pipeline as the model setting conditions of CFD; performing CFD calculations according to the boundary conditions and model setting conditions to obtain calculation results.

[0051] In this embodiment, gas-liquid flow sensors are respectively installed at the gas injection port and the bottom water velocity inlet of the pneumatic lifting system to provide accurate boundary conditions for CFD simulation. The flow field parameters inside the pipeline are detected by ECT equipment, and the gas-liquid volume fraction and velocity inside the pipeline are collected to make reasonable and reliable settings for the selection of CFD calculation model.

[0052] In one embodiment, a CFD-DEM-based gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system is provided, which may also include a process of selecting a CFD calculation model. The specific process includes: comparing the gas-liquid flow rate, gas-liquid volume fraction and speed with the standard gas-liquid flow rate, standard gas-liquid volume fraction and speed to obtain a comparison result; when the comparison result is that the error is less than the error threshold, selecting the CFD calculation model according to the calculation result.

[0053] Specifically, the error threshold may be 10%. When the comparison result shows that the error is less than 10%, the next step of selecting a CFD calculation model may be performed.

[0054] In one embodiment, a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM can also include a process of setting a particle phase, which mainly includes setting the particle phase of a discrete element software through the particle parameters prepared by the experiment, specifically including: the particles prepared by the experiment are round glass beads with particle sizes of 3 mm, 6 mm and 8 mm to simulate underwater minerals, with a density of 2616.27 kg / m3 and a Young's modulus of 8.5×10 7 N / m2, Poisson's ratio is 0.3, and the particle phase is set with these parameters. The Static Friction, Dynamic Friction, Tangential Stiffness Ratio and Restitution Coefficient of particle-particle interaction are 0.7, 0.7, 1 and 0.3 respectively. Continuous injection is selected for the particle inlet, and particles are injected at a speed of 0.4 kg / s. The simulation time is 16 s, and the particles occupy about 2 / 3 of the silo space.

[0055] Step 108, select a particle phase mechanical analysis model based on the calculation results, perform CFD-DEM coupled numerical calculation of the gas-liquid-solid three-phase flow of the pneumatic lifting system based on the CFD-DEM bidirectional coupling method, and obtain a particle distribution cloud map, a particle velocity cloud map and a simulated flow field velocity map.

[0056] In one embodiment, a gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system based on CFD-DEM is provided, which may also include a process of selecting a CFD-DEM bidirectional coupling numerical simulation calculation model. The specific process includes: determining the CFD-DEM bidirectional coupling numerical simulation calculation model by tracking the trajectory of particles with high-speed camera in the experiment.

[0057] By comparing the experimental and simulation results, Figure 2 As shown, Figure 2 This is a comparison chart of particle trajectories in the lifting section. The CFDCoupling Particle Statistics and Contacts Overlap Monitor models are selected, where the Drag Force and Pressure Gradient Force models are selected in the CFDCoupling Particle Statistics model, and the 2-way Fluent coupling method is selected in CFDCoupling, and the volume diffusion method is selected as the mapping method. Through multiple experimental comparisons, the selection of this model has excellent calculation convergence speed and simulation accuracy.

[0058] In one embodiment, a CFD-DEM-based gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system may also include a process of calculating through a gas-liquid-solid three-phase flow CFD-DEM coupled numerical model, and the specific process includes: establishing a gas-liquid-solid three-phase flow CFD-DEM coupled numerical model; calculating through a gas-liquid-solid three-phase flow CFD-DEM coupled numerical model to obtain a calculation result; comparing the calculation result with the trajectory tracking of particles captured by a high-speed camera in the experiment, and calculating to obtain a particle distribution cloud map, a particle velocity cloud map, and a simulated flow field velocity map. Among them, the high-concentration particle distribution status map is shown in FIG. Figure 3 shown.

[0059] Among them, in the process of establishing the gas-liquid-solid three-phase flow CFD-DEM coupled numerical model, the solution of the fluid continuous phase mainly relies on the continuity equation and momentum equation. Combined with other equations and models, the flow behavior of the fluid can be accurately simulated. The continuity equation of incompressible flow can be expressed as: in represents the partial derivative of density with respect to time, represents the divergence of the mass flow rate in the control volume, and v represents the velocity vector. The classic Navier-Stokes equation undergoes a volume averaging process, characterizing the phase of the fluid, and the resulting equation representing the conservation of average mass is: For compressible flows, the momentum equation includes additional terms to account for the compressibility effect and can be expressed as: Where α f is the fluid volume fraction, p is the static pressure, T f is the stress tensor of the fluid phase, F p→f represents the momentum source term that interacts with the particle phase. In the discrete element method (DEM), particles in the computational domain can be tracked using a Lagrangian approach, which requires the explicit application of Euler's first and second laws to accommodate the translational and rotational motion of the particles, respectively: In the formula, m p represents the mass of the particle, g represents the gravitational acceleration vector, F c represents the contact force considering the interaction between the particle and the wall, ω p represents the angular velocity vector, J p represents the moment of inertia tensor of the particle, M c represents the net torque produced by the tangential force causing the particle to rotate, F f→p represents the additional force generated by the interaction with the fluid phase, M f→pRepresents the additional torque generated by the fluid phase velocity gradient. The particle-particle interaction model is the Hertzian Spring-Dashpot Model, and the model formula can be expressed as: In the formula, s n is the contact normal overlap, indicating contact The time derivative of the touch normal overlap, is the stiffness coefficient, is the damping coefficient, E * is the Young's modulus reduction, ν represents the respective Poisson's ratio, R * is the effective or equivalent radius, m * is the effective mass, η H is the damping ratio of the Hertzian Spring-Dashpot Model. The expression of the tangential force in the model is: In the formula, F n is the normal force, F τ is the tangential force, s τ is the tangential relative displacement at the contact interface, s τ,max is the maximum relative tangential displacement of the particle when it starts to slide, μ is the friction coefficient, η τ is the tangential damping ratio.

[0060] Step 110, based on the particle distribution cloud map, particle velocity cloud map and simulated flow field velocity map, the flow field information and particle movement conditions obtained through the experiment are verified and analyzed with the numerical simulation results to obtain the particle movement characteristics of the pneumatic lifting system.

[0061] Specifically, based on the CFD-DEM coupled numerical model calculation of the gas-liquid-solid three-phase flow of the pneumatic lifting system, the particle distribution cloud map, particle velocity cloud map and simulated flow field velocity map obtained by the numerical model, the flow field information and particle movement conditions obtained through the experiment were mutually verified and analyzed with the numerical simulation results, so as to study the particle movement characteristics of the pneumatic lifting device. Since the simulation results are close to the actual experimental data, it has significant advantages such as high reliability, intuitive simulation results and high calculation accuracy, which provides guidance for the theory of pneumatic lifting systems.

[0062] In this embodiment, a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM is provided. The CFD method is used to calculate the gas-liquid two-phase flow field in the lifting pipeline, and a suitable model is selected based on the data of ECT equipment, gas-liquid flow sensor, pressure sensor, high-speed camera and weighing sensor collected in the experiment to be close to the actual experiment. The particle distribution cloud map, particle velocity cloud map and simulated flow field velocity map obtained by the numerical model, the flow field information and particle movement conditions obtained by the experiment are mutually verified and analyzed with the numerical simulation results, so as to study the particle movement characteristics of the pneumatic lifting system; the present invention adopts the Fluent-Rocky bidirectionally coupled CFD-DEM method to simulate the internal flow field and particle movement characteristics of the pneumatic lifting system. Since the simulation results are close to the actual experimental data, it has significant advantages such as high reliability, intuitive simulation results and high calculation accuracy, and provides guidance for the theory of pneumatic lifting systems.

[0063] like Figure 4 As shown, in one embodiment, a gas-liquid-solid three-phase numerical simulation method of a pneumatic lifting system based on CFD-DEM is provided, and the specific process includes:

[0064] Construct geometric model of pneumatic lifting system;

[0065] Meshing the geometric model;

[0066] Perform gas-liquid two-phase calculations, including selecting multiphase flow models, selecting turbulence models, and CFD calculations;

[0067] Determine whether the gas velocity comparison error collected by ECT in the experiment is less than 10%. If not, reset the CFD model and calculate it again; if so, proceed to the next step of judgment; among them, the comparison chart of experimental and simulated gas velocity data, that is, the gas velocity collected by ECT is as follows Figure 5 As shown;

[0068] The CFD-DEM coupling calculation includes selecting the particle phase mechanical analysis model, selecting the CFD-DEM coupling model, and performing the CFD-DEM coupling numerical calculation of the gas-liquid-solid three-phase flow of the pneumatic lifting device;

[0069] Based on the high-speed camera trace experiment, the comparison is based on whether it is consistent. If not, it returns to perform CFD-DEM coupling calculation and re-sets the particle phase model for calculation; if so, it generates particle distribution cloud map, particle velocity cloud map and simulated flow field velocity map, and studies its three-phase flow through the flow field information and particle movement obtained from the experiment; among them, the plane particle volume fraction curve is as follows Figure 6 As shown; the particle velocity distribution diagram under different gas injection speeds is shown in Figure 7 As shown;

[0070] Analyze and study the particle movement characteristics of the pneumatic lifting system.

[0071] It should be understood that, although the steps in the above-mentioned flowcharts are shown in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the above-mentioned flowcharts may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

[0072] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A gas-liquid-solid three-phase numerical simulation method for a pneumatic lifting system based on CFD-DEM, characterized in that: The method comprises: Constructing a pneumatic lifting system geometric model, including: connecting a bottom truncated cone silo, a material particle inlet, a water flow inlet, an air injection port and a lifting pipe to form a pneumatic lifting system geometric model; and meshing the geometric model; In the geometric model after meshing, the gas-liquid flow rate is collected by the sensor in the experiment, and the gas-liquid volume fraction and velocity inside the pipeline are collected by the ECT device, including: installing sensors at the water flow inlet and the gas injection port respectively to collect the gas-liquid flow rate at the water flow inlet and the gas injection port; collecting the flow field parameters inside the pipeline by the ECT device to obtain the gas-liquid volume fraction and velocity inside the pipeline; Determining a gas-liquid two-phase calculation model according to the gas-liquid flow rate, the gas-liquid volume fraction and the velocity to perform CFD calculation and obtain a calculation result, including: taking the gas-liquid flow rate as a boundary condition of CFD, taking the gas-liquid volume fraction and the velocity inside the pipeline as a model setting condition of CFD; performing CFD calculation according to the boundary condition and the model setting condition to obtain a calculation result; A particle phase mechanics analysis model is selected according to the calculation results, and a CFD-DEM coupled numerical calculation of a gas-liquid-solid three-phase flow of a pneumatic lifting system is performed based on a CFD-DEM bidirectional coupling method, including: establishing a CFD-DEM coupled numerical model of a gas-liquid-solid three-phase flow; performing calculations using the CFD-DEM coupled numerical model of a gas-liquid-solid three-phase flow to obtain calculation results; comparing the calculation results with the trajectory tracking of particles captured by high-speed photography in the experiment, and calculating a particle distribution cloud map, a particle velocity cloud map, and a simulated flow field velocity map; the flow field information and particle motion conditions obtained through the experiment are mutually verified and analyzed with the numerical simulation results to obtain the particle motion characteristics of the pneumatic lifting system.

2. The gas-liquid-solid three-phase numerical simulation method of the pneumatic lifting system based on CFD-DEM according to claim 1 is characterized in that: The method further comprises: Compare the gas-liquid flow rate, the gas-liquid volume fraction and the speed with the standard gas-liquid flow rate, the standard gas-liquid volume fraction and the speed to obtain a comparison result; When the comparison result shows that the error is less than the error threshold, a CFD calculation model is selected according to the calculation result.

3. The gas-liquid-solid three-phase numerical simulation method of the pneumatic lifting system based on CFD-DEM according to claim 1 is characterized in that: The method further comprises: By tracing the trajectory of particles using high-speed photography in the experiment, the CFD-DEM bidirectional coupling numerical simulation calculation model was determined.

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