A method and system for preventing and controlling negative pressure in paste pipeline transportation and insufficient pipe flow

Abstract

The present invention discloses a method and system for preventing and controlling negative pressure dissatisfaction of paste pipeline transportation, the method comprising: obtaining the pressure distribution variation law of aeolian sand fly ash paste slurry under different ground pipeline lengths; based on the pressure distribution variation law, using the Bernoulli principle, obtaining the limit ground pipeline length calculation relationship that does not generate negative pressure; based on the limit ground pipeline length calculation relationship, obtaining the limit ground pipeline length; when the ground pipeline length meets the preset limit requirement, based on the exponential relationship between the pipe diameter and the resistance loss, reducing the vertical pipe diameter or the downhole horizontal pipe diameter, to prevent and control the negative pressure vertical dissatisfaction of paste pipeline transportation. The present invention uses simulation technology to analyze the mechanism of dissatisfaction, proposes a solution, and is helpful to promote the development and improvement of pipeline transportation technology and promote the application of paste filling technology.

Description

Technical Field

[0001] The invention belongs to the technical field of paste pipeline transportation, and particularly relates to a method and system for preventing and controlling negative pressure dissatisfaction of the pipeline flow in paste pipeline transportation. Background Art

[0002] As coal mining gradually develops into deeper areas, long-distance, large-elevation, and large-flow pipeline transportation systems have become the key configuration for deep filling mining. Along with this, the problem of insufficient pipe flow has emerged. When insufficient pipe flow is formed, the paste slurry lacks restraint and develops wantonly under the action of its own inertia and gravity, causing many problems such as pipeline noise, pipe wall erosion, pipeline vibration, and pipeline blockage.

[0003] (1) Noise. When the flow in the pipe is not full, the stable solid-liquid two-phase flow in the pipe changes into a complex solid-liquid-gas multiphase flow, which leads to the generation of vortexes and pressure fluctuations. The internal gas is continuously compressed and released, generating noise. At the same time, the high-speed falling paste slurry in the pipe impacts the liquid surface below, which also generates noise.

[0004] (2) Erosion. Due to the lack of surrounding paste and pipe wall constraints, the speed of the free paste continues to increase under the action of gravity. When it contacts the pipe wall below, the solid aggregate with huge kinetic energy directly hits the pipe wall, causing erosion damage. The hard wall material eroded continues to impact other intact walls with the paste, accelerating the speed of wall destruction.

[0005] (3) Vibration. The freely falling paste slurry mass carries huge kinetic energy, and the sizes and speeds of the paste slurry mass are different, causing the liquid surface and pipe wall below to be impacted by water hammers of different frequencies and sizes, causing vibration and resulting in fatigue damage to the pipeline.

[0006] (4) Pipe blockage: In the area where the pipe flow is not full, on the one hand, the negative pressure causes the water inside the paste slurry to evaporate, and the paste concentration increases and separates; on the other hand, the low-concentration paste slurry is captured by the wall to form a slurry film that flows slowly, while the large-diameter aggregate breaks free from the restraint and falls freely, quickly reaching the liquid surface at the lower end of the vertical pipe. In the lower bend and horizontal pipe, the high-concentration paste and the rapidly accumulated large-diameter aggregate mix, causing pipe blockage.

[0007] (5) Damage to the filling pump. The stability of the paste inside the pipe flow is destroyed. The pressure transmission medium changes from a continuous solid-liquid two-phase flow to a complex solid-liquid-gas multiphase flow. The gas itself is compressible, which will cause the pump pressure fluctuation to increase. After the pipe is blocked, the paste in the pipe cannot flow and is incompressible, which will generate huge pressure, which can easily cause the filling pump to overload and burn out the motor.

[0008] However, due to the complex state of the fluid in the tube, it is impossible to use formulas for calculation, which is a very difficult problem in research. Summary of the invention

[0009] In view of the shortcomings of the prior art, the present invention proposes a method and system for preventing and controlling the problem of insufficient pipe flow in paste pipeline transportation due to negative pressure. The simulation technology is used to analyze the mechanism of insufficient pipe flow and propose solutions, which will help promote the development and improvement of pipeline transportation technology and advance the application of paste filling technology.

[0010] To achieve the above object, the present invention provides the following solutions:

[0011] A method for preventing and controlling the negative pressure in the paste pipeline when the pipeline is not full of flow, comprising the following steps:

[0012] Obtain the changing law of the pressure distribution in the pipe of aeolian sand fly ash paste slurry under different ground pipeline lengths;

[0013] Based on the changing law of the pressure distribution in the pipe and using the Bernoulli principle, a calculation formula for the limit ground pipeline length that does not generate negative pressure is obtained;

[0014] Based on the limit ground pipeline length calculation relationship, obtaining the limit ground pipeline length;

[0015] When the length of the surface pipeline meets the preset limit requirements, based on the exponential relationship between the pipe diameter and the resistance loss, the vertical pipe diameter or the horizontal pipe diameter downhole is reduced to prevent the paste pipeline from conveying negative pressure vertical dissatisfaction flow.

[0016] Preferably, the calculation formula for the limit ground pipeline length that does not generate negative pressure includes:

[0017]

[0018] Where f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, and L 1-max is the maximum ground pipeline length, f2 is the average resistance loss of the grouting body in the early stage, pa / m, and L is the total length of the pipeline, m.

[0019] Preferably, the calculation formula of the limit ground pipeline length without generating negative pressure also includes:

[0020]

[0021] Where P b-max The maximum pressure of the filling pump when pumping, pa, P max is the maximum pressure that the pipeline can withstand, pa, f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, L 1-min is the maximum ground pipe length.

[0022] Preferably, the exponential relationship between the pipe diameter and the resistance loss is:

[0023]

[0024] In the formula, f is the resistance loss of the fluid along the way, pa / m; v is the average flow velocity of the fluid, m / s, D is the pipeline diameter; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

[0025] The present invention also provides a system for preventing and controlling the paste pipeline conveying negative pressure not being full of pipe flow, comprising: a rule acquisition module, a relational calculation module, a length calculation module and a pipe diameter reduction module;

[0026] The law acquisition module is used to obtain the law of change in the pressure distribution of aeolian sand fly ash paste slurry under different ground pipeline lengths;

[0027] The relationship calculation module is used to obtain a calculation relationship of the limit ground pipeline length that does not generate negative pressure based on the change law of the pressure distribution in the pipe and using the Bernoulli principle;

[0028] The length calculation module is used to obtain the limit ground pipeline length based on the limit ground pipeline length calculation relationship;

[0029] The pipe diameter reduction module is used to reduce the vertical pipe diameter or the horizontal pipe diameter downhole when the surface pipeline length meets the preset limit requirements based on the exponential relationship between the pipe diameter and the resistance loss, so as to prevent the paste pipeline from conveying negative pressure vertical dissatisfaction pipe flow.

[0030] Preferably, the calculation formula for the limit ground pipeline length that does not generate negative pressure includes:

[0031]

[0032] Where f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, and L 1-max is the maximum ground pipeline length, f2 is the average resistance loss of the grouting body in the early stage, pa / m, and L is the total length of the pipeline, m.

[0033] Preferably, the calculation formula of the limit ground pipeline length without generating negative pressure also includes:

[0034]

[0035] Where P b-max The maximum pressure of the filling pump when pumping, pa, P max is the maximum pressure that the pipeline can withstand, pa, f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, L 1-min is the maximum ground pipe length.

[0036] Preferably, the exponential relationship between the pipe diameter and the resistance loss is:

[0037]

[0038] In the formula, f is the resistance loss of the fluid along the way, pa / m; v is the average flow velocity of the fluid, m / s, D is the pipeline diameter; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention proposes a method and system for preventing and controlling negative pressure and insufficient pipe flow in paste pipeline transportation, by obtaining the pressure distribution change law of aeolian sand fly ash paste slurry under different ground pipeline lengths; based on the pressure distribution change law in the pipe, using the Bernoulli principle, obtaining the calculation relationship of the limit ground pipeline length that does not generate negative pressure; based on the calculation relationship of the limit ground pipeline length, obtaining the limit ground pipeline length; when the ground pipeline length meets the preset limit requirement, based on the exponential relationship between the pipe diameter and the resistance loss, reducing the vertical pipe diameter or the horizontal pipe diameter downhole, to prevent and control the negative pressure vertical insufficient pipe flow in paste pipeline transportation. The present invention uses simulation technology to analyze the mechanism of insufficient pipe flow and proposes a solution, which is helpful to promote the development and improvement of pipeline transportation technology and promote the application of paste filling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0042] Figure 1 A schematic diagram of a filling pipeline according to an embodiment of the present invention;

[0043] Figure 2 Schematic diagrams of modeling five pipeline transportation systems according to embodiments of the present invention;

[0044] Figure 3 A schematic diagram of mesh division of an inlet section according to an embodiment of the present invention;

[0045] Figure 4 The pressure distribution cloud diagram of the vertical pipeline in the five pipelines of the embodiment of the present invention;

[0046] Figure 5 Schematic diagram of pressure curves from inlet to outlet of five pipelines in an embodiment of the present invention;

[0047] Figure 6 It is a diagram of the actual filling and conveying process of an embodiment of the present invention;

[0048] Figure 7 Two diameter variation dimension diagrams of the embodiments of the present invention;

[0049] Figure 8 The graphs of the paste content of three pipelines of the embodiments of the present invention over time are shown, wherein (a) is a graph of the paste content of the original pipeline over time, (b) is a graph of the paste content of scheme 1 over time, and (c) is a graph of the paste content of scheme 2 over time;

[0050] Fig. 9 The pressure distribution cloud diagrams in the vertical pipelines of three pipelines of the embodiment of the present invention;

[0051] Fig.10 Schematic diagram of the pressure distribution curves in the three pipelines according to the embodiment of the present invention;

[0052] Fig.11 It is a velocity distribution cloud diagram in each pipeline of an embodiment of the present invention;

[0053] Fig.12 The present invention is a flowchart of a method for preventing and controlling negative pressure in a paste pipeline when the pipeline is not full of flow. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Embodiment 1

[0057] like Fig.12 As shown, the present invention proposes a method for preventing and controlling the negative pressure in the paste pipeline when the pipeline is not full of the pipe flow, comprising the following steps:

[0058] Obtain the changing law of the pressure distribution in the pipe of aeolian sand fly ash paste slurry under different ground pipeline lengths;

[0059] Based on the changing law of the pressure distribution in the pipe and using the Bernoulli principle, a calculation formula for the limit ground pipeline length that does not generate negative pressure is obtained;

[0060] Based on the limit ground pipeline length calculation relationship, obtaining the limit ground pipeline length;

[0061] When the length of the surface pipeline meets the preset limit requirements, based on the exponential relationship between the pipe diameter and the resistance loss, the vertical pipe diameter or the horizontal pipe diameter downhole is reduced to prevent the paste pipeline from conveying negative pressure vertical dissatisfaction flow.

[0062] In this embodiment, the filling pipeline layout principle is: the ground pipeline is a section of pipeline from the filling pump outlet to the vertical borehole. From an economic point of view, the ground pipeline has the advantages of low construction cost, convenient maintenance and disassembly, and no underground space compared to the underground pipeline. Longer ground pipelines should be given priority. However, in many filling and mining cases, longer ground pipelines often lead to negative pressure in the vertical pipelines, causing blockage, low transportation efficiency and many other unsatisfactory pipe flow problems.

[0063] Figure 1 This is a typical filling pipeline system. When the pipeline transportation system reaches stability, if you want to avoid negative pressure at the upper end of the vertical pipeline, the pressure P needs to meet the following requirements:

[0064] P=fL-ρgh-fl1>0 (1)

[0065] Where: f is the resistance loss along the pipeline, pa / m; L is the total length of the pipeline, m.

[0066] After transforming the formula, we can get the following formula:

[0067]

[0068] Since L=l1+h+l2, the formula can be transformed into:

[0069]

[0070] Therefore, when the vertical height h and the total pipeline length L remain unchanged, the greater the resistance loss f and the downhole pipeline l2, the smaller the density ρ of the paste material, and the more the equation is valid. Therefore, for pipeline transportation systems with high drop, it is recommended to select paste slurry with smaller density and greater viscosity, and at the same time appropriately increase the length of the downhole pipeline while keeping the total pipeline length L unchanged.

[0071] In this embodiment, in order to study the influence of different ground pipeline lengths on the pressure distribution in the pipeline system and seek the limit length value of negative pressure, a simulation is designed. Assuming that the pump port and the outlet are in the same plane, the total length of the pipeline is 110m, the vertical distance is 10m, and the ground pipeline length is designed to be 10m, 30m, 50m, 70m, and 90m respectively. The pipeline diameter is 200mm, all pipeline center lines are in the same plane, the delivery speed is 2m / s, and the pressure distribution at any point in the pipe is observed under full pipe flow. As shown in Table 1.

[0072] Table 1 Parameters of different pipeline systems

[0073]

[0074] like Figure 2 , Figure 3 As shown in the figure, the meshed model is imported into Fluent, Steady simulation is selected, gravity is turned on, and the turbulence model is selected as Realizable K-epsilon SWF mode; the inlet is Mass-flow; the wall roughness height is 0.05mm, without deformation and slip; the paste material density is set to 1860kg / m 3 , viscosity 0.45pa.s, yield stress 65pa, critical shear rate 70s -1 The key parameters such as the fluid material viscosity model are set to Herschel-Bulkley, the residual is set to 1e-6, the mixed initialization is performed, and the calculation is performed for 1000 steps.

[0075] Cut out the vertical section of each group of pipelines separately, and obtain the pressure distribution cloud diagram in the vertical pipeline under different ground pipeline lengths within the same pressure range. Figure 4 shown.

[0076] Depend on Figure 4 It can be seen that as the length of the ground pipeline increases, the overall pressure in the vertical pipeline gradually decreases, which is manifested as the color of the pressure cloud gradually changes from yellow-red to blue-green. The blue color first appears at the upper end of the vertical pipeline and gradually spreads to the left and downward. At the same time, the negative pressure limit value is also gradually increasing.

[0077] like Figure 5 As shown, the shape of the pressure curve is similar to the inverted and tilted pipeline layout diagram, and they overlap with each other. In the horizontal pipeline, the pressure decreases linearly with increasing distance. In the vertical pipeline, the pressure not only does not decrease under the influence of gravity, but also increases rapidly. The pressure at the inlet of all pipelines is equal, about 0.14MPa. Among them, the pressure at the lower end of the vertical pipeline in the 10m*10m*90m pipeline layout is the largest, reaching 0.24Mp, which is much higher than the pump inlet pressure. Among all pipelines, the pipelines with a ground pipeline length of 10, 30, and 50m did not produce negative pressure, while the 70m and 90m pipelines produced a maximum negative pressure of about 0.05MPa and 0.11MPa respectively. It can be seen that, first, unilaterally changing the length of the ground pipeline will not affect the resistance loss of the entire pipeline. As long as the total length of the pipeline and the length of the vertical pipeline remain unchanged, the pump pressure required at the inlet is a constant value; second, when the ground pipeline is shorter, the maximum pressure in the pipe will appear at the lower end of the vertical pipeline, and the pressure is even far higher than the inlet pump pressure; third, the negative pressure first appears at the upper end of the vertical pipeline and gradually spreads forward and backward. The longer the ground pipeline is, the larger the negative pressure area and limit value are.

[0078] Figure 5The intersection of the middle and 0MPa lines is about 51m, which means that under the above conditions, when the surface pipeline is 51m, the pump pressure can only transport the paste to the borehole at a speed of 2m / s, and the paste transportation in the vertical pipeline and downhole pipeline after 51m no longer depends on the pump pressure, but on the paste's own weight, that is, self-slip; when the surface pipeline is longer than 51m, the pump pressure cannot press the paste to the borehole at a speed of 2m / s, which will cause the paste in the pipeline from 51m to the upper end of the vertical pipeline to have a deceleration trend, and the paste in the vertical pipeline The pressure generated by its own weight is significantly greater than the total resistance loss generated in the vertical and downhole pipelines. The remaining pressure head will cause the paste to accelerate, and the paste in the vertical pipeline will be transported by positive pressure and then sucked by negative pressure. In the negative pressure environment, gas will precipitate inside the paste and liquid will evaporate to produce bubbles, resulting in a decrease in the stability of the paste. As the surface pipeline grows further, when the negative pressure increases to the critical threshold, the paste will be stretched to meet the acceleration due to the unchanged inlet flow and pipe diameter. The situation will then continue to deteriorate, and the paste will gradually be stretched to break, and the liquid level in the vertical pipe will drop rapidly, forming an incomplete pipe.

[0079] In summary, if the horizontal pipeline on the ground is too long, the pipeline's ability to resist gravity pressure will decrease, resulting in negative pressure pull-off type unsatisfied pipe flow, reducing the pipeline transportation efficiency and stability. If it is too short, it will cause a large pressure at the lower end of the vertical pipeline. The water hammer effect generated when the pump is stopped may cause leakage or pipe collapse at the pipeline connection.

[0080] In order to avoid negative pressure and insufficient pipe flow, it is necessary to ensure that no negative pressure is generated in the pipe from the time the paste is pumped in to the time it flows out. As shown in the figure below, after the preliminary grouting work is completed, the paste material is pumped in from the inlet and gradually flows to the outlet. When the paste reaches the bottom of the vertical pipeline, the self-weight pressure ρgh it bears at this time reaches the maximum. If no negative pressure is generated in the pipe at this time, no negative pressure will be generated during the entire filling and transportation process.

[0081] like Figure 6 As shown, if P>0 at this time, according to Bernoulli's principle, the pressure in the tube must satisfy:

[0082] P=f1(L1+h)+f2L2-ρgh-f1L1>0 (4)

[0083] Where: f1—average resistance loss of paste material, pa / m f2—average resistance loss of grouting in the early stage, pa / m;

[0084] Since L=L1+h+L2, the above formula can be changed to:

[0085]

[0086] In the formula, except for L1, which is an unknown quantity, the rest are known quantities. Substituting them into the formula, we can get the maximum ground pipeline length L.1-max .

[0087] Correspondingly, the maximum pressure in the pipe occurs at the lower end of the vertical pipe, so the limit pressure in the pipe during filling must be less than the maximum pressure P that the pipe can withstand. max , then the minimum pipeline length formula is:

[0088]

[0089] Where: P b-max —The maximum pressure of the filling pump during pumping, pa; P max —The maximum pressure that the pipeline can withstand, pa. The formula is still based on the full pipe flow state, so there are disadvantages and it can only be used as a rough reference. In actual layout, the ground pipeline length should be as short as possible as possible. 1-max .

[0090] In this embodiment, the selection of the location of the filling station needs to consider many factors, such as the transportation of materials, the size of the protective coal pillar, etc. Sometimes, due to restrictions such as terrain and environment, it is difficult to select an ideal location, which may cause the ground pipeline to be too long and cause negative pressure problems in the vertical pipeline; in addition, for pipelines that have large height differences and small multiples, the gravitational potential energy that the system needs to resist is strong, and it is more likely to produce insufficient pipe flow problems, thereby affecting the normal progress of the filling work. In order to avoid this kind of situation, measures need to be taken to improve the pipeline.

[0091] To solve the problem of insufficient pipe flow, negative pressure must be eliminated. The key is to increase resistance. It is known that increasing paste viscosity, lowering temperature, increasing delivery speed, and reducing pipe diameter can increase resistance loss.

[0092] (1) Paste slurry is specially formulated for mine filling conditions in the early stage and is generally not suitable for modification. It is difficult to achieve physical conditions for lowering paste temperature, and the chemical conditions have not yet been studied. It is also greatly affected by the environment and environmental pollution issues must also be considered. It is generally not recommended for use.

[0093] (2) There is a linear relationship between speed and resistance loss. Increasing the conveying speed can increase the resistance loss without having to change the current pipeline and without hindering the filling work. It works better for short-distance conveying systems with mild negative pressure. However, for long-distance pipelines with severe negative pressure, a small increase in speed has little effect. A large increase in speed will bring huge energy loss, which is not worth the loss.

[0094] (3) The relationship between pipe diameter and resistance loss is exponential. Reducing the pipe diameter slightly can increase resistance loss. In addition, the transmission pipeline is composed of multiple pipe sections, which can be partially reduced. For example, the diameter of the vertical pipeline or downhole pipeline can be appropriately reduced to achieve the effect of increasing resistance. This is currently the most widely used solution to the problem of vertical dissatisfaction in the pipe flow.

[0095] Judgment criteria: (1) Recovery ability from the transition from insufficient pipe flow to full pipe flow: For the insufficient pipe flow formed at the beginning of filling, when all conditions are reasonable, it can gradually recover from insufficient pipe flow to full pipe flow as the paste continues to flow. This requires that the pipeline has sufficient pressure to discharge the internal gas. Therefore, the recovery ability can be judged by examining the paste slurry content in the pipe per unit time under the state of insufficient pipe flow. The higher the content, the better the effect.

[0096] (2) Pressure and velocity distribution in the improved pipeline under full flow condition: By comparing the pressure distribution in the pipeline under full flow condition before and after improvement, the principles and advantages and disadvantages of different methods can be obtained. In addition, since the flow rate at the inlet is fixed, when the pipe diameter is reduced, the velocity will inevitably increase. Excessive velocity can easily lead to rapid wear of the pipe wall, increasing the cost of maintenance and replacement.

[0097] (3) Economic efficiency: For the pipeline transportation system that has been built, the standard is to make the smallest change, the shortest construction period and the highest efficiency.

[0098] In this embodiment, referring to the pipeline arrangement of 70m*10m*30m, the upper end of the vertical pipeline just generates a negative pressure of about 50KPa. According to the resistance loss formula:

[0099]

[0100] In the formula: f is the resistance loss along the fluid, pa / m; v is the average flow velocity of the fluid, m / s; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

[0101] To achieve zero negative pressure inside the pipe, the vertical pipeline needs to be reduced from 200mm to 150mm, and the downhole pipeline needs to be reduced from 200mm to 180mm, while other conditions remain unchanged.

[0102] Table 2 Solutions and parameters

[0103]

[0104]

[0105] For pipe diameter change, the increase in velocity will accelerate the erosion of the outer wall of the curved pipe, so the diameter change position is avoided from the curved pipe. The diameter change of the vertical pipe is between the upper and lower curved pipes, and the diameter change of the underground pipe is behind the lower curved pipe of the vertical pipe. The diameter change length is 1m. Figure 7 shown.

[0106] Open Multiphase Model, turn on the VOF multiphase flow model, select Implicit Body Force, set the Primary Phase to air, the Secondary Phase to paste, the turbulence model to K-epsilon Realizable model, the boundary model to Enhanced Wall Functions, the inlet to Mass-flow, the outlet to Pressure-out, the calculation residual to 1e-6, use Standard initialization, Adaptive Multiphase-Specific calculation mode, and the initial time step to 1e-5.

[0107] Cut off the vertical pipeline sections of the three pipelines, compare the paste slurry content per unit time under the condition of the same inlet flow rate, and judge its ability to remove air. Figure 8 As shown, there are cloud diagrams of paste slurry content in the three pipelines at 10, 30 and 60 seconds respectively.

[0108] After the vertical pipe diameter is reduced from 200mm to 150mm ( Figure 8 (b)), the full pipe rate reached 94.1% at only 10s, which was much higher than 21.5% of the original pipeline and 40.3% of the downhole variable diameter pipeline. At 60s, the full pipe rate in the pipeline was 94.5%, and the full pipe rate in the middle variable diameter pipeline reached 99.8%, but a small amount of gas pockets could not be discharged due to the existence of the low-pressure area in the lower bend. At 30s, the full pipe rate of the paste in the downhole variable diameter pipeline was 87.4%, which was higher than 33.8% of the original pipeline. At 60s, the full pipe rate reached 96.7%. The reduction in the diameter of the downhole pipeline increased the local resistance loss to a certain extent, increased the residence time of the paste in the pipe per unit time, and thus increased the full pipe rate.

[0109] Steady-state simulations were performed for the three pipeline arrangements, and the pressure diagrams and curves inside the pipelines before and after the improvements were obtained.

[0110] Depend on Fig. 9 It can be seen that the pressure in the vertical pipes of the three pipelines has increased to a certain extent after the improvement, which is reflected in the gradual disappearance of the blue negative pressure area and the increase of the red high-pressure area in the figure. Compared with reducing the vertical pipe diameter, the high-pressure area after reducing the downhole pipe diameter is larger, so reducing the vertical pipe diameter belongs to the low-pressure full pipe flow method, and reducing the downhole pipe diameter belongs to the high-pressure full pipe flow method.

[0111] Fig.10The pressure distribution curves of the three pipelines from the inlet to the outlet along the paste flow direction under full pipe flow conditions show that after the vertical pipeline is reduced in diameter, the inlet pressure increases from 0.14MPa to 0.19MPa, the pressure at the upper end of the vertical pipeline increases from -50KPa to 0.38KPa, and the pressure at the lower end is consistent with the original pipeline at 7.63KPa, as shown by the red curve in the figure. It can be seen that reducing the diameter of the vertical pipeline is to reduce the pressure difference between the top and bottom of the vertical pipeline, and has no effect on the pressure in the underground horizontal pipeline, which is suitable for long-distance high-pressure transmission systems; after the underground pipeline is reduced in diameter, the pressure at the inlet, the upper end and the lower end of the vertical pipeline are all increased by about 62KPa, so reducing the diameter of the underground horizontal pipeline is to increase the pressure in the entire pipeline, which is not recommended for pipelines with high overall pressure.

[0112] Fig.11 The cloud diagram of the change of paste velocity in the pipe under different schemes. Because the length of the vertical pipeline is shorter than the downhole pipeline, the internal velocity increases sharply after the diameter is changed, with the maximum velocity reaching 7m / s and the average velocity being 3.89m / s. The maximum velocity in the pipe of Scheme 2 is 4.88m / s, and the average flow velocity is 2.66m / s, which is slightly higher than the 2m / s of the original pipeline.

[0113] From the perspective of full pipe rate per unit time, the vertical pipe diameter change scheme has the greatest improvement on full pipe rate, but the problem of airbag retention in the lower end pipeline is prominent. The downhole pipe diameter change scheme has a more stable overall improvement, no obvious disadvantages, and more obvious advantages; from the perspective of full pipe flow transmission pressure distribution, reducing the vertical pipe diameter has a smaller impact on the overall pressure in the pipeline, and the advantage is more obvious; from the perspective of the change in speed in the pipe under full pipe flow conditions, reducing the vertical pipe diameter increases the internal speed significantly, which will increase the erosion damage rate of the pipe wall, and the vertical pipe is difficult to replace, which is not conducive to long-term use. In comparison, the speed change of the downhole pipe diameter change is more stable. Comprehensive consideration shows that the downhole pipe reduction scheme has no obvious disadvantages and is more applicable.

[0114] Embodiment 2

[0115] The present invention also provides a system for preventing and controlling the paste pipeline conveying negative pressure not being full of pipe flow, comprising: a rule acquisition module, a relational calculation module, a length calculation module and a pipe diameter reduction module;

[0116] The law acquisition module is used to obtain the law of pressure distribution change in the pipe of aeolian sand fly ash paste slurry under different ground pipeline lengths;

[0117] The relational calculation module is used to obtain a calculation relational expression for the limit ground pipeline length that does not generate negative pressure based on the change law of the pressure distribution in the pipe and using the Bernoulli principle;

[0118] The length calculation module is used to obtain the limit ground pipeline length based on the limit ground pipeline length calculation relationship;

[0119] The pipe diameter reduction module is used to reduce the vertical pipe diameter or the horizontal pipe diameter downhole when the surface pipeline length meets the preset limit requirements based on the exponential relationship between the pipe diameter and the resistance loss, so as to prevent the paste pipeline from conveying negative pressure vertical dissatisfaction pipe flow.

[0120] In this embodiment, the calculation relationship of the limit ground pipeline length that does not generate negative pressure includes:

[0121]

[0122] Where f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, and L 1-max is the maximum ground pipeline length, f2 is the average resistance loss of the grouting body in the early stage, pa / m, and L is the total length of the pipeline, m.

[0123] In this embodiment, the calculation relationship of the limit ground pipeline length without generating negative pressure also includes:

[0124]

[0125] Where P b-max The maximum pressure of the filling pump when pumping, pa, P max is the maximum pressure that the pipeline can withstand, pa, f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, L 1-min is the maximum ground pipe length.

[0126] In this embodiment, the exponential relationship between the pipe diameter and the resistance loss is:

[0127]

[0128] In the formula, f is the resistance loss of the fluid along the way, pa / m; v is the average flow velocity of the fluid, m / s, D is the pipeline diameter; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

[0129] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preventing and controlling the negative pressure in the paste pipeline when the pipeline is not full of flow, characterized in that: The following steps are involved: Obtain the changing law of the pressure distribution in the pipe of aeolian sand fly ash paste slurry under different ground pipeline lengths; Based on the changing law of the pressure distribution in the pipe and using the Bernoulli principle, a calculation formula for the limit ground pipeline length that does not generate negative pressure is obtained; Based on the limit ground pipeline length calculation relationship, obtaining the limit ground pipeline length; When the length of the surface pipeline meets the preset limit requirements, based on the exponential relationship between the pipe diameter and the resistance loss, the vertical pipe diameter or the downhole horizontal pipe diameter is reduced to prevent the paste pipeline from conveying negative pressure vertically and not being full of pipe flow; The calculation formula for the limit ground pipeline length without generating negative pressure includes: Where f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, and L 1-max is the maximum surface pipeline length, f2 is the average resistance loss of the grouting body in the early stage, pa / m, L is the total length of the pipeline, m; The calculation formula for the limit ground pipeline length without generating negative pressure also includes: Where P b-max The maximum pressure of the filling pump when pumping, pa, P max is the maximum pressure that the pipeline can withstand, pa, f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, L 1-min is the maximum ground pipeline length; The exponential relationship between the pipe diameter and the resistance loss is: In the formula, f is the resistance loss of the fluid along the way, pa / m; v is the average flow velocity of the fluid, m / s, D is the pipeline diameter; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

2. A system for preventing and controlling the negative pressure in the paste pipeline when the pipeline is not full of flow, characterized in that: include: A rule acquisition module, a relational calculation module, a length calculation module and a pipe diameter reduction module; The law acquisition module is used to obtain the law of change in the pressure distribution of aeolian sand fly ash paste slurry under different ground pipeline lengths; The relationship calculation module is used to obtain a calculation relationship of the limit ground pipeline length that does not generate negative pressure based on the change law of the pressure distribution in the pipe and using the Bernoulli principle; The length calculation module is used to obtain the limit ground pipeline length based on the limit ground pipeline length calculation relationship; The pipe diameter reduction module is used to reduce the vertical pipe diameter or the downhole horizontal pipe diameter based on the exponential relationship between the pipe diameter and the resistance loss when the surface pipe length meets the preset limit requirements, so as to prevent the paste pipeline from conveying negative pressure vertical dissatisfaction pipe flow; The calculation formula for the limit ground pipeline length without generating negative pressure includes: Where f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, and L 1-max is the maximum surface pipeline length, f2 is the average resistance loss of the grouting body in the early stage, pa / m, L is the total length of the pipeline, m; The calculation formula for the limit ground pipeline length without generating negative pressure also includes: Where P b-max The maximum pressure of the filling pump when pumping, pa, P max is the maximum pressure that the pipeline can withstand, pa, f1 is the average resistance loss of the paste material, h is the vertical height, ρ is the density of the paste material, L 1-min is the maximum ground pipeline length; The exponential relationship between the pipe diameter and the resistance loss is: In the formula, f is the resistance loss of the fluid along the way, pa / m; v is the average flow velocity of the fluid, m / s, D is the pipeline diameter; τ0 is the yield stress, pa; μ is the slurry viscosity, pa.s.

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