Method for determining conveying speed and pipe diameter of aeolian sand fly ash paste slurry based on fluent

Abstract

The present application relates to the field of numerical simulation calculation, in particular to a method for determining the conveying speed and pipe diameter of aeolian sand fly ash paste slurry based on Fluent, comprising determining the components and proportion of aeolian sand fly ash paste slurry; keeping the filling amount of the paste slurry unchanged, selecting a plurality of combinations of conveying speed and filling pipe diameter, selecting a horizontal straight pipe for the filling pipe, and simulating by using Fluent software; determining the conveying speed range [v a1 , v b1 ] based on a complete slip layer or an expected thickness slip layer; determining the conveying speed range of the paste filling [max(v a1 , v a2 ), v b1 ] by comprehensively considering the particle deposition rule; selecting a horizontal elbow pipe for the filling pipe, simulating by using Fluent software, and determining the conveying speed range of the paste filling [max(v a1 , v a2 ), min(v b1 , v b2 )] by comprehensively considering the wall erosion rule. The present application provides a method for reasonably determining the conveying speed and filling pipe diameter of aeolian sand fly ash paste slurry based on comprehensive consideration of the paste particle migration rule, the pipe wall erosion rule and the resistance loss rule, and provides certain reference.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation calculation in mines, and in particular to a method for determining the conveying speed and filling pipe diameter of aeolian sand-fly ash paste slurry based on Fluent. Background Technology

[0002] Paste backfilling is a common backfilling mining method in coal mines. The backfill material is in paste form, such as aeolian sand-fly ash paste slurry. Paste backfilling typically uses backfill pipelines to pump the paste slurry from the surface preparation station to the working face. Therefore, studying the flow characteristics of the paste backfill material in the backfill pipeline is crucial for guiding the determination of pipeline size and conveying speed. However, backfill pipelines are sealed and opaque, making it impossible to directly observe the flow state of the paste within the pipeline. Furthermore, the backfill paste is a mixture of various materials such as sand, fly ash, and cement, resulting in a multiphase flow with a certain viscosity, which cannot be calculated using ordinary fluid dynamics methods. This poses significant challenges to determining the appropriate conveying speed and backfill pipeline size. On-site testing is also costly and time-consuming.

[0003] In response to this, existing technologies commonly use Fluent software to study the characteristics of paste slurry in pipeline transportation. This mainly involves the relationship between paste flow velocity and friction loss, the evolution model of radial rheological parameter gradients in the pipeline during steady-state paste transportation, and the wear characteristics of self-flowing pipelines for high-concentration filling paste. This provides some guidance for the selection of materials for paste-filled pipelines. However, existing technologies do not provide a method for determining the transportation velocity and filling pipeline diameter of aeolian sand and fly ash paste slurry that comprehensively considers the particle transport characteristics, pipeline wall erosion characteristics, and friction loss characteristics. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for determining the conveying speed of aeolian sand-fly ash paste slurry and the diameter of the filling pipeline based on Fluent software. Using Fluent software, and comprehensively considering the particle transport law of the paste, the erosion law of the pipeline wall, and the resistance loss law, a reasonable method for determining the conveying speed of aeolian sand-fly ash paste slurry and the diameter of the filling pipeline is provided. This method is mainly applicable to the filling pipeline section on the ground or underground, and takes into account the situation of pipeline bending. Specifically, the method includes the following steps:

[0005] S1: Calculate the required strength of the paste slurry after solidification based on the coal seam burial depth and stratum control requirements, and adjust the proportion of each component of the aeolian sand and fly ash paste slurry accordingly. The paste slurry mainly includes aeolian sand, loess, fly ash, cement and water, and the content of fine particles smaller than 20 μm in the paste slurry is not less than 15%.

[0006] S2: Calculate the required amount of paste slurry filling per unit time based on the average daily output of the working face or the average daily volume of the goaf formed; while keeping the amount of paste slurry filling constant, select various combinations of conveying speed and filling pipe diameter. The filling pipe is a horizontal straight pipe and set to a horizontal state. Use Fluent software to simulate the thickness of the slip layer on the inner wall of the filling pipe and the particle deposition in the paste slurry during conveying under different combinations; the slip layer is a low-viscosity covering layer composed of fine particles and water formed on the inner wall of the filling pipe during the paste conveying process.

[0007] S3: Analyze the variation law of the slip layer thickness on the inner wall of the filling pipeline during transportation under different combinations, and determine the transportation speed range to obtain a complete slip layer or a slip layer of the expected thickness [v] a1 ,v b1 The corresponding pipe diameter is determined based on the conveying speed;

[0008] S4: Analyze the particle deposition pattern in the filling pipeline under different combinations, and determine the minimum conveying speed v required to achieve a stable suspension of the paste slurry particles based on the particle deposition pattern in the filling pipeline. a2 Compare v a1 With v a2 The larger of the two values ​​is taken as the minimum transport speed. Therefore, the range of transport speeds for paste filling is determined by considering both the slip layer thickness and particle deposition patterns: [max(v...]. a1 ,v a2 ),v b1 The corresponding pipe diameter is determined based on the conveying speed;

[0009] S5: While keeping the paste slurry filling volume constant, select various combinations of conveying speed and filling pipe diameter. The filling pipe is a horizontal bend set horizontally to simulate bends in the surface or underground filling pipe sections. Use Fluent software to simulate the erosion of the filling pipe wall during conveying under different combinations. Determine the maximum conveying speed v that prevents erosion at the bend of the filling pipe or keeps it within the expected erosion range based on the erosion law of the inner wall of the filling pipe. b2 Compare v b1 With v b2 The smaller of the two values ​​is taken as the maximum transport velocity. Therefore, the range of transport velocities for paste filling is determined by considering the slip layer thickness, particle deposition patterns, and wall erosion patterns, and is defined as [max(v...]. a1 ,v a2 ),min(v b1 ,v b2 The diameter of the conveying pipeline is determined based on the conveying speed.

[0010] Preferably, in step S5, the range of the conveying speed includes at least [max(v a1 ,v a2 ), v b1 ].

[0011] Preferably, the process further includes step S6: approximating the aeolian sand-fly ash paste slurry as a Bingham plastic fluid, the resistance loss of which can be calculated using the following formula:

[0012]

[0013] Where: f—friction loss along the way, pa / m; v—conveyor speed, m / s; τ0—shear stress, pa; μ—viscosity, pa.s; D—diameter of conveying pipe, m; Q—volume of paste slurry required per unit time, m 3 / s;

[0014] As shown in the above formula, the friction loss increases with increasing conveying speed. Therefore, within the conveying speed range determined in steps S1-S5 [max(v a1 ,v a2 ), min(v b1 ,v b2 In [ )], choose the smallest possible conveying speed.

[0015] This invention has the following innovative points: Using Fluent software, and considering the particle transport law of the paste, the erosion law of the pipe wall, and the resistance loss law, this invention provides a method for rationally determining the conveying speed of aeolian sand-fly ash paste slurry and the diameter of the filling pipe. This method is mainly applicable to the filling pipe section on the ground or underground, and takes into account the situation of pipe bending. This invention can provide a certain reference for determining a reasonable conveying speed and matching pipe diameter when filling aeolian sand-fly ash paste. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for determining the conveying speed of the paste slurry and the diameter of the filling pipe according to the present invention;

[0017] Figure 2 These are the velocity profile and cross-sectional cloud diagram inside the filling pipe at a conveying speed of 2.0 m / s in the embodiment;

[0018] Figure 3 This is a diagram showing the internal distribution of particles with a diameter of 0.15mm-0.6mm in the embodiment. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown, this invention proposes a method for determining the conveying speed and filling pipe diameter of aeolian sand-fly ash paste slurry based on Fluent, comprising the following steps:

[0021] S1: Calculate the required strength of the paste slurry after solidification based on the coal seam burial depth and stratum control requirements, and adjust the proportion of each component of the aeolian sand and fly ash paste slurry accordingly. The paste slurry mainly includes aeolian sand, loess, fly ash, cement and water, and the content of fine particles smaller than 20 μm in the paste slurry is not less than 15%.

[0022] S2: Calculate the required amount of paste slurry filling per unit time based on the average daily output of the working face or the average daily volume of the goaf formed; while keeping the amount of paste slurry filling constant, select various combinations of conveying speed and filling pipe diameter. The filling pipe is a horizontal straight pipe and set to a horizontal state. Use Fluent software to simulate the thickness of the slip layer on the inner wall of the filling pipe and the particle deposition in the paste slurry during conveying under different combinations; the slip layer is a low-viscosity covering layer composed of fine particles and water formed on the inner wall of the filling pipe during the paste conveying process.

[0023] Specifically, such as maintaining 350m 3 With a constant filling rate, four conveying speeds of 1.0, 1.5, 2.0, and 2.5 m / s were selected, corresponding to filling pipe diameters of 351, 287, 249, and 223 mm, respectively. All four filling pipes were placed horizontally, with a length of 5 m. Gravity was applied vertically downwards along the axis, and the paste slurry entered from the left inlet and exited from the right outlet. After importing the mesh into Fluent, transient simulation was initiated, with gravity set along the negative Z-axis, and Multiphase mode enabled. Model: Enable Eulerian model, select DDPM, set the first phase to liquid water and the second phase to solid particles, open DPM model, enable liquid-solid bidirectional coupling, iteration interval to 20 steps, particle time step to 0.00025, step factor to 5, maximum tracking steps to 5000, enable DEM particle collision model, add particle source, select surface-injected particles, enable injection along the surface normal direction, select inert material for particles, select double R distribution for particle diameter. This mode can be set to include particle phases with multiple different diameters by setting the maximum and minimum particle size and the inhomogeneity coefficient. Select Gidaspow for drag model, select K-omega SST for turbulence model, set the calculation residual to 1e-6, perform standard initialization, set the calculation time step to 0.005s, and calculate a total of 12000 steps.

[0024] S3: Analyzing the variation of the slip layer thickness on the inner wall of the filling pipe under different conveying combinations, it can be concluded that although a slip layer can be formed inside the filling pipe when the conveying speed is less than a certain speed, the slip layer is not complete. Therefore, to obtain a complete slip layer or a slip layer of the desired thickness, the conveying speed cannot be less than a certain critical speed v. a1 However, as the conveying speed increases and the pipe diameter decreases, the slip layer tends to thin. Therefore, to obtain a complete slip layer or a slip layer of the desired thickness, the conveying speed cannot exceed a certain critical speed v. b1 Therefore, to obtain a complete slip layer or a slip layer of the desired thickness, the conveying speed range should be [v]. a1 ,v b1 Correspondingly, the range of filling pipe diameters can be obtained (the conveying speed corresponds one-to-one with the filling pipe diameter);

[0025] like Figure 2 The figure shows the velocity profile and cross-sectional contour map inside the filling pipe at a steady state with a conveying speed of 2.0 m / s. Different colors represent pastes with different flow velocities within the pipe. Based on color, they can be roughly divided into: a red core region, characterized by high overall velocity, high viscosity, and large particles, which is the main force ensuring conveying capacity; a blue slip layer at the outermost edge, with extremely low velocity and closely adhering to the pipe wall, composed of low-viscosity fine particles; and a green shear layer sandwiched between the two. Although the paste varies significantly in color at different locations within the pipe, the velocity continuously decreases from the center to the pipe wall, exhibiting a normal distribution with the highest velocity at the center, decreasing towards the wall, and reaching zero at the outermost edge, indicating a laminar flow conveying state. The fine blue particles themselves have low kinetic energy. Inside the filling pipe, they are gradually captured by the rough pipe wall. At the same time, under the pressure of the filling pipe, the paste will exude water. The exude water combines with the fine particles to form an extremely thin film that adheres tightly to the filling pipe wall. The presence of the film can fill the roughness of the pipe wall and separate the internal paste slurry from the rough pipe wall. This changes the liquid-solid frictional motion of the paste slurry into a liquid-liquid sliding motion, which greatly reduces the resistance loss during transportation. This film composed of low-viscosity fine particles and playing a drag-reducing role is called the slip layer.

[0026] S4: Analyzing the particle deposition patterns within the filling pipe under different transport combinations reveals that when the transport speed is less than a certain speed, the particles of the paste slurry inside the filling pipe cannot form a stable suspension state. Therefore, based on the particle deposition patterns within the filling pipe, the minimum transport speed v required to achieve a stable suspension state for the paste slurry particles is determined. a2 and its corresponding filling pipe diameter, compare v a1 With v a2The larger of the two values ​​is taken as the minimum transport speed. Therefore, the range of transport speeds for paste filling is determined by considering both the slip layer thickness and particle deposition patterns: [max(v...]. a1 ,v a2 ),v b1 ];

[0027] like Figure 3 As shown, a two-dimensional cross-sectional view along the flow direction of the filling pipe is obtained at the axis, revealing the distribution cloud map of larger diameter particles (0.15mm-0.6mm). When the conveying speed is 1.0m / s, the large particles are not completely suspended. As the conveying distance increases, these large particles exhibit a stepped settling trend. At this conveying speed, the suspension stability of the particles is poor, easily leading to particle deposition at the bottom of the pipe. When the conveying speed is increased to 1.5m / s, although a small number of large diameter particles still deposit at the bottom, the overall proportion of particles in the pipe exceeds 80%, showing an improvement in particle suspension. This indicates that slightly increasing the speed helps reduce particle settling, but does not completely eliminate the deposition phenomenon. When the conveying speed is further increased to 2.0m / s, it can be observed that the particle distribution inside the pipe becomes more uniform, and the large particles have reached a stable suspension state at this speed. At this point, the conveying enters a more ideal laminar flow state, and the particle settling problem is effectively solved.

[0028] S5: As in step S2, while keeping the paste slurry filling volume constant, select various combinations of conveying speed and filling pipe diameter. In this case, the range of the conveying speed includes at least [max(v...]. a1 ,v a2 ),v b1 The filling pipeline uses a horizontal bend and is set horizontally to simulate bends in the surface or underground filling pipeline sections. Fluent software is used to simulate the erosion of the filling pipeline wall under different combinations of transport conditions. When the straight section of the filling pipeline has a complete slip layer or a slip layer of expected thickness, the filling pipeline wall will not be eroded; it will mainly experience wall abrasion. The wall erosion location is mainly at the bend of the filling pipeline, and the erosion area and degree increase with the increase of transport speed. Therefore, based on the erosion law of the inner wall of the filling pipeline, the maximum transport speed v that prevents erosion at the bend of the filling pipeline or keeps it within the expected erosion range is determined. b2 and its corresponding filling pipe diameter, compare v b1 With v b2 The smaller of the two values ​​is taken as the maximum transport velocity. Therefore, the range of transport velocities for paste filling is determined by considering the slip layer thickness, particle deposition patterns, and wall erosion patterns, and is defined as [max(v...]. a1 ,v a2 ),min(v b1 ,vb2 Since the amount of paste slurry required per unit time is fixed, the diameter range of the conveying pipeline can be determined based on this conveying speed range.

[0029] Pipeline erosion refers to a type of wear phenomenon that occurs when the inner wall of a pipe is impacted by solid particles in the grease, resulting in damage to pipe fittings. Generally speaking, the higher the fluid velocity, the more and harder the suspended solid particles in the fluid, and the more severe the erosion.

[0030] Specifically, in this embodiment, to study the erosion location and degree of the pipe wall under different conveying speeds, and to further determine the optimal conveying speed and corresponding pipe diameter, Fluent software is used for erosion simulation. The range of conveying speeds in the model includes at least [max(v a1 ,v a2 ), v b1 The filling pipe is a horizontal bend set horizontally to simulate the turning of the filling pipe section on the ground or underground. The horizontal bend is 5m long and bends 90° 3m from the inlet, with a radius of curvature of 0.5m. After importing the mesh into Fluent, steady-state simulation is started, gravity is set to downward along the X-axis, DPM model is started, Interaction with Continuous Phase coupling function is enabled, iteration interval is 5, Erosion / Accretion is enabled, the inlet is Velocity-inlet, Hydraulic Diameter is the pipe diameter, the outlet is outflow, the wall material is set to high carbon steel with no movement or deformation, the boundary type is set to Reflect, the discrete reflection function Polynomial is set according to the parameters of sand and steel, mixed initialization is performed, the residual is set to 1e-6, and 1000 steps are calculated.

[0031] Furthermore, in order to reduce energy loss, the present invention also includes the following steps:

[0032] S6: If the aeolian sand-fly ash paste slurry is approximated as a Bingham plastic fluid, its resistance loss can be calculated using the following formula:

[0033]

[0034] Where: f—friction loss along the way, pa / m; v—conveyor speed, m / s; τ0—shear stress, pa; μ—viscosity, pa.s; D—diameter of the conveying pipe, m;

[0035] The required amount of paste filling material Q per unit time remains constant, according to Q = πD 2 v / 4, we can get

[0036]

[0037] Where: Q—the amount of paste slurry required per unit time, in meters. 3 / s;

[0038] As shown in the above formula, the friction loss increases with increasing conveying speed. Therefore, within the conveying speed range determined in steps S1-S5 [max(v a1 ,v a2 ), min(v b1 ,v b2 In [ )], choose the smallest possible conveying speed.

[0039] While the present invention has been described above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for determining the conveying speed and pipe diameter of aeolian sand-fly ash paste slurry based on Fluent, characterized in that, Includes the following steps: S1: Calculate the required strength of the paste slurry after solidification based on the coal seam burial depth and stratum control requirements, and adjust the proportion of each component of the aeolian sand and fly ash paste slurry accordingly. The paste slurry mainly includes aeolian sand, loess, fly ash, cement and water, and the content of fine particles smaller than 20μm in the paste slurry is not less than 15%. S2: Calculate the required amount of paste slurry filling per unit time based on the average daily output of the working face or the average daily volume of the goaf formed; while keeping the amount of paste slurry filling constant, select various combinations of conveying speed and filling pipe diameter. The filling pipe is a horizontal straight pipe and set to a horizontal state. Use Fluent software to simulate the thickness of the slip layer on the inner wall of the filling pipe and the particle deposition in the paste slurry during conveying under different combinations; the slip layer is a low-viscosity covering layer composed of fine particles and water formed on the inner wall of the filling pipe during the paste conveying process. S3: Analyze the variation law of the slip layer thickness on the inner wall of the filling pipeline during transportation under different combinations, and determine the transportation speed range required to obtain a complete slip layer or a slip layer of the expected thickness. The corresponding pipe diameter is determined based on the conveying speed; S4: Analyze the particle deposition pattern in the filling pipeline under different combinations, and determine the minimum conveying speed v required to achieve a stable suspension of the paste slurry particles based on the particle deposition pattern in the filling pipeline. a2 Compare v a1 With v a2 The larger of the two values ​​is taken as the minimum delivery speed. Therefore, the delivery speed range for paste filling is determined by considering both the slip layer thickness and particle deposition patterns. The corresponding pipe diameter is determined based on the conveying speed; S5: While keeping the paste slurry filling volume constant, select various combinations of conveying speed and filling pipe diameter. The filling pipe is a horizontal bend set horizontally to simulate bends in the surface or underground filling pipe sections. Use Fluent software to simulate the erosion of the filling pipe wall during conveying under different combinations. Determine the maximum conveying speed v that prevents erosion at the bend of the filling pipe or keeps it within the expected erosion range based on the erosion law of the inner wall of the filling pipe. b2 Compare v b1 With v b2 The smaller of the two values ​​is taken as the maximum transport speed. Therefore, the range of transport speeds for paste filling is determined by comprehensively considering the slip layer thickness, particle deposition patterns, and wall erosion patterns. The corresponding pipe diameter is determined based on the conveying speed; S6: If the aeolian sand-fly ash paste slurry is approximated as a Bingham plastic fluid, its resistance loss can be calculated using the following formula: ； In the formula: —Drag loss along the route, ; —Conveying speed, ; —Shear stress, pa; Viscosity, D—Diameter of the conveying pipe, m; Q—Quantity of paste slurry required per unit time, m 3 / s; As shown in the above formula, the friction loss increases with increasing conveying speed. Therefore, within the conveying speed range determined in steps S1-S5 [max(v a1 ,v a2 ), min(v b1 ,v b2 In [ )], choose the smallest possible conveying speed.

Images