Erosion-resistant elbow

Abstract

The invention discloses an erosion-resistant elbow pipe, comprising a vertical section, a horizontal section and an elbow connecting the two, with a bend-diameter ratio R / D=2, and a plurality of staggered protrusions and depressions are arranged on the side wall of the elbow, and the inner cavity of the protrusion is connected with the inner cavity of the elbow; the invention changes the particle movement trajectory through the protrusion and depression structure, reduces the number of collisions between the particles and the wall surface, reduces the flow velocity near the wall surface, reduces the speed of the particles hitting the wall surface, and forms a stable double low-speed countercurrent zone with the top of the protrusion and the bottom of the depression, so that the particles are blown away from the pipe wall, thereby reducing erosion.

Description

Technical Field

[0001] The invention relates to the field of gas-solid two-phase flow conveying pipelines, and in particular to an erosion-resistant elbow. Background Art

[0002] Erosion is the most common failure form in gas-solid two-phase flow. ASTM International G40-13 standard considers erosion to be the phenomenon that raw materials gradually lose from the solid surface due to mechanical interaction between the solid surface and the fluid, multi-component fluid, impacting liquid or impacting solid particles. Erosion often occurs in industrial production fields such as mining, metallurgy, petroleum, and natural gas, especially in components such as pumps, cyclone separators, and pneumatic conveying pipelines. Among them, erosion damage in pneumatic gas-solid two-phase flow is more serious. This damage not only wastes materials, consumes energy, and reduces equipment efficiency, but also accelerates equipment failure and reduces the service life of the pipeline. As a component that changes the flow direction, the elbow is more likely to fail due to erosion. Studies have shown that the degree of erosion damage at the elbow of the conveying pipeline is about 50 times that of the straight pipe section.

[0003] At present, the traditional anti-erosion method mainly starts from the wall material, using composite materials, surface coatings, surface modification, etc. to improve the anti-erosion performance of the pipe wall. This method can reduce erosion to a certain extent, but it is difficult to manufacture, high cost, and not conducive to green energy. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an erosion-resistant elbow pipe, which has a simple structure and can improve the erosion resistance of the elbow pipe to a limited extent, thereby extending the service life of the elbow pipe and saving costs.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is: an erosion-resistant elbow, comprising a vertical section, a horizontal section and an elbow connecting the two, with a bend-diameter ratio R / D=2, and a plurality of staggered protrusions and depressions are arranged on the side wall of the elbow, and the inner cavity of the protrusion is connected to the inner cavity of the elbow. It should be noted that the bend-diameter ratio R / D refers to the ratio of the radius of curvature R of the arc of the inner diameter centerline of the elbow to the inner diameter D of the elbow; staggered arrangement means that a depression is arranged between any two adjacent protrusions, and a protrusion is arranged between any two adjacent depressions.

[0006] Further improvement, the elbow comprises a vertical rise section, a horizontal outlet section and an elbow connecting the two, the inner diameters of the vertical rise section and the horizontal outlet section are equal, and the lengths of the vertical rise section and the horizontal outlet section are more than 10 times of the inner diameters, thereby ensuring that the fluid flow is fully developed. The inner diameter of the elbow where the protrusion is located is larger than the inner diameters of the vertical rise section and the horizontal outlet section, and the inner diameter of the elbow where the depression is located is smaller than the inner diameters of the vertical rise section and the horizontal outlet section.

[0007] As a further improvement, the protrusions and recesses cover the outer side wall of the elbow along the outer diameter direction of the elbow, and the central angle corresponding to each protrusion is 180°, and the central angle corresponding to each recess is 180°.

[0008] Furthermore, the cross-section of the protrusion and the depression along the radial direction of the elbow is an equilateral triangle. The inventor has proved through many experiments that the equilateral triangle is the most ideal structure and can effectively improve the erosion resistance of the elbow.

[0009] As a further improvement, the vertical section, the horizontal section and the elbow are integrally formed.

[0010] By setting protrusions and depressions on the side wall of the elbow of the elbow, the movement trajectory of the particles in the elbow is changed. Experiments have shown that the flow velocity near the wall of the elbow with protrusions and depressions is significantly lower than that of the ordinary elbow, and there is a height difference between the top of the protrusion and the bottom of the depression, causing the airflow to rotate inside the protrusion and on the back of the depression, forming a stable "double low-speed countercurrent zone". This area acts as an "air cushion", enhancing the turbulence intensity of the fluid, causing changes in the surrounding flow field, and some particles will be blown directly away from the inner wall of the pipe under the influence of the gas, reducing the frequency of collision between the particles and the wall, thereby reducing erosion.

[0011] The technical solution provided by the present invention has the following beneficial effects:

[0012] (1) The convex and concave structures arranged on the side wall of the elbow of the bent pipe change the movement trajectory of the particles entering the elbow, thereby reducing the direct collision between the particles and the wall surface and reducing erosion to a certain extent.

[0013] (2) Compared with the high-cost and difficult-to-manufacture anti-erosion methods such as composite materials, coatings, and surface modifications, the convex and concave structures can not only improve the anti-erosion properties of the inside of the bent pipe, but also have the advantages of low technical difficulty, simple manufacturing process, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of the erosion-resistant elbow pipe of the present invention;

[0015] Figure 2 It is a schematic diagram of the elbow structure of the erosion-resistant elbow pipe of the present invention;

[0016] Figure 3 is a cross-sectional view of an elbow of the erosion-resistant elbow pipe of the present invention;

[0017] Figure 4 It is the erosion simulation cloud diagram of two types of elbows;

[0018] Figure 5 It is the cloud diagram of the movement trajectory of particles in two types of curved pipes;

[0019] Figure 6It is the velocity vector distribution cloud diagram of particles in two kinds of curved pipes. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0021] In the description of the present invention, it should be noted that the terms "up", "down", "left", "right", "top", "bottom", "side", "center", "vertical", "horizontal", "inside" and "outside" etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0022] Figures 1 to 3 As shown, an erosion-resistant elbow comprises a vertical rising section 10, a horizontal outlet section 20 and an elbow 30 connecting the two, wherein the vertical rising section 10, the horizontal outlet section 20 and the elbow 30 are integrally formed. The inner diameters of the vertical rising section 10 and the horizontal outlet section 20 are equal, the bend-diameter ratio R / D of the elbow 30 is 2, the lengths of the vertical rising section 10 and the horizontal outlet section 20 are more than 10 times the diameter, and the side wall of the elbow 30 is provided with a plurality of staggered protrusions 31 and recesses 32, the inner diameter of the elbow at the location of the protrusions 31 is larger than the inner diameters of the vertical rising section 10 and the horizontal outlet section 20, and the inner diameter of the elbow at the location of the recesses 32 is smaller than the inner diameters of the vertical rising section 10 and the horizontal outlet section 20.

[0023] The protrusions 31 and the depressions 32 are evenly distributed on the outer wall of the elbow along the outer diameter direction of the elbow 30, and the radial cross-section of the protrusions 31 and the depressions 32 along the elbow 30 is an equilateral triangle with a side length of 4 mm; specifically, there are 11 protrusions and 10 depressions evenly distributed along the 90° direction of the elbow, presenting a staggered arrangement of one protrusion 31 and one depression 32, and the central angle corresponding to each protrusion 31 is 180°, and the central angle corresponding to each depression 32 is 180°, covering half of the elbow along the annular direction of the elbow.

[0024] The following uses the erosion rate of the elbow as the main indicator to determine the erosion resistance of the anti-erosion elbow of this scheme. In this embodiment, the pipe material is aluminum, the diameter is 50 mm, and the gas-solid two-phase flow in the pipe is air and sand. The density of air is 1.18 kg / m 3 , viscosity 1.8×10 -5 Pa·s, flow velocity is 30m / s, sand density is 2650kg / m 3 , the particle size is a single particle size of 100 μm, the particle mass flow rate is 0.02 kg / s, and the inlet velocity is the same as the continuous phase air flow rate.

[0025] Fluent software is used to conduct numerical simulation of erosion of anti-erosion elbows and ordinary elbows. The solid particles in gas-solid two-phase flow erode the elbow wall. The erosion model is as follows:

[0026]

[0027] Where, E is the erosion rate of the elbow, F is the empirical constant, and B h is the Brinell hardness of the wall material, n is the velocity index, V is the flow velocity, k is the erosion index, γ is the intrusion angle, and f(γ) is the intrusion angle function.

[0028] The calculation formula of the intrusion angle function f(γ) is:

[0029]

[0030] The model constants are: A = 1.44 × 10 -8 , γ lim =23°, n=2.2, b=-7, c=5.45, x=0.4, y=-0.9, ω =-3.4.

[0031] The improvement of the erosion resistance of the erosion-resistant elbow compared with the erosion resistance of the ordinary elbow is expressed by η, and the calculation formula is:

[0032]

[0033] Among them, E 1 is the maximum erosion rate of ordinary elbows, E 2 It is the maximum erosion rate of the erosion-resistant elbow.

[0034] Figure 4 The following is a simulated erosion cloud diagram of two elbows, with the left one being a common elbow and the right one being an anti-erosion elbow. It can be seen from the figure that a large area of ​​erosion is formed on the outer wall of the common elbow, and the local erosion rate reaches 8.55×10 -5 kg·m -2 ·s -1 The erosion area formed by the outer wall of the erosion-resistant elbow is smaller than that of the ordinary elbow, and the erosion rate of the erosion area is concentrated at 5.7×10 -5 kg·m -2 ·s -1 Therefore, it can be seen that the erosion resistance of the anti-erosion elbow with convex and concave structures is improved compared with the erosion resistance of the ordinary elbow. The maximum erosion rate E of the ordinary elbow is calculated by the software. 1 1.14×10 -4 kg·m -2 ·s -1 , the maximum erosion rate E of the erosion-resistant elbow 2 7.48×10-5 kg·m -2 ·s -1 The anti-erosion performance η increased by 34.39%.

[0035] Figure 5 It is a cloud diagram of the movement trajectory of particles in two types of elbows, with the left side being a common elbow and the right side being an anti-erosion elbow. It can be seen from the figure that after the continuous phase gas carrying solid sand particles flows into the elbow area of ​​the common elbow, it directly collides with the outer wall of the elbow and rebounds. After rebounding, the particles follow the gas flow out of the elbow area, thus forming a collision-free area on the inside of the elbow. This also explains why the erosion area in the figure is mainly concentrated on the outer wall of the elbow, while the inner wall of the elbow is almost not eroded. When the continuous phase gas carrying solid sand particles flows into the anti-erosion elbow, due to the existence of the convex and concave structures, the particles enter the elbow to facilitate the collision of the convex and concave structures, thereby changing the particle trajectory, and the particles rebound back to the calculation domain (i.e., the inner area of ​​the elbow) after colliding with the structure, reducing the direct collision between the particles and the outer wall of the elbow, thereby reducing the erosion of the outer wall. It can be seen from the figure that the traces near the wall of the anti-erosion elbow are vortex-shaped.

[0036] Figure 6 The velocity vector distribution cloud diagram of particles in two types of elbows, of which the left side is a common elbow and the right side is an anti-erosion elbow. It can be seen from the figure that when the continuous phase gas carrying solid sand flows through the convex and concave structure, its surface velocity is significantly lower than that of the common elbow, and the low-speed area (<25m / s) in the elbow area is larger. This is because most of the kinetic energy of the particles is consumed when the particles collide with the convex and concave structures, thereby reducing the movement speed of the particles; at the same time, when the air flows through the convex and concave structures, there is a height difference between the top of the convex and the bottom of the concave, causing the airflow to rotate inside the convex and on the back of the concave, forming a stable "double low-speed countercurrent zone", which acts as an "air cushion", enhancing the turbulent intensity of the fluid, causing changes in the surrounding flow field, and some particles will be directly blown away from the inner wall of the pipe under the influence of the gas, reducing the collision frequency between the particles and the wall, thereby reducing erosion and extending the service life of the pipe.

[0037] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. An erosion-resistant elbow, characterized in that: The invention comprises a vertical section, a horizontal section and an elbow connecting the two, with a bend-diameter ratio of R / D=2, a plurality of staggered protrusions and depressions are arranged on the side wall of the elbow, the inner cavity of the protrusions is connected with the inner cavity of the elbow, the inner diameter of the elbow where the protrusions are located is larger than the inner diameters of the vertical section and the horizontal section, and the inner diameter of the elbow where the depressions are located is smaller than the inner diameters of the vertical section and the horizontal section; when a continuous phase gas carrying solid particles flows into the erosion-resistant elbow, the solid particles collide with the protrusions and the depressions, thereby changing the trajectory of the solid particles, and the solid particles rebound to the inner area of ​​the elbow after colliding with the protrusions or the depressions, thereby reducing the direct collision between the solid particles and the outer wall of the elbow, thereby reducing the erosion of the outer wall; the protrusions and depressions cover the outer wall of the elbow along the outer diameter direction of the elbow, the central angle corresponding to each protrusion is 180°, and the central angle corresponding to each depression is 180°.

2. The erosion-resistant elbow according to claim 1, characterized in that: The elbow comprises a vertical rising section, a horizontal outlet section and an elbow connecting the two. The inner diameters of the vertical rising section and the horizontal outlet section are equal, and the lengths of the vertical rising section and the horizontal outlet section are more than 10 times of the inner diameter.

3. The erosion-resistant elbow according to claim 1, characterized in that: The cross-section of the protrusion and the depression along the radial direction of the elbow is an equilateral triangle.

4. The erosion-resistant elbow according to claim 1, characterized in that: The vertical section, the horizontal section and the elbow are integrally formed.

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