A method for measuring critical flow velocity in slurry pipeline transportation

Abstract

The present invention discloses a method for determining the critical flow velocity in slurry pipeline transportation, comprising the following steps: (1) testing the initial mass concentration of the slurry in the slurry storage tank; (2) circulating the slurry in the test system through a pump, drawing a curve of the relationship between pressure drop and flow velocity change, and preliminarily predicting the critical flow velocity v0 and the flow velocity upper limit v1 during the critical flow velocity test; (3) running the slurry at v1 in the test system, judging the fixed bed condition in the pipeline at the flow velocity v1, and verifying the final flow velocity upper limit v2; (4) using v2 as the starting flow velocity, gradually reducing the flow velocity with a large step length, judging the fixed bed generation condition in the pipeline (solid particle bed surface in the pipeline), and determining the fixed bed flow velocity v3; (5) using v 3 As the starting flow rate, gradually increase the flow rate in small steps to determine the generation of the fixed bed (solid particle bed surface in the tube) and determine the flow rate v4 when the fixed bed is eliminated. This flow rate is the critical flow rate v c The present invention has the characteristics of wide application range of slurry and can more accurately determine the critical flow velocity of slurry.

Description

Technical Field

[0001] The invention belongs to the field of slurry pipeline transportation, and particularly relates to a method for measuring critical flow velocity in slurry pipeline transportation. Background Art

[0002] Critical velocity is a crucial parameter in slurry pipeline transportation. It refers to the slurry flow velocity corresponding to the time when solid particles in the slurry settle from a suspended state to form a solid particle bed. The critical velocity is affected by a variety of factors, primarily the pipe diameter, particle size and composition, particle density, and slurry concentration. These factors interact to form a complex relationship with the critical velocity. The importance of the critical velocity to slurry pipelines is obvious, representing the lower limit for safe operation. Lower flow rates will lead to the formation of a solid particle bed within the pipe, increasing frictional losses. If the flow is sufficiently slowed, the pipe will become clogged. Therefore, determining the critical velocity is directly related to the design flow velocity of the slurry pipeline project, the selection of pipelines and equipment, and the safety of system operation.

[0003] Currently, there are two methods for determining the critical velocity in slurry pipelines. One is through experimental observation, where a section of organic transparent glass tube is installed in the pipeline and the motion of the solid particles in the slurry is directly observed visually to determine the corresponding critical velocity. This method is difficult to observe when the slurry concentration increases, especially for darker materials such as coal. Furthermore, the movement and suspension of particles are manually judged, and the judgment criteria vary from person to person, which is highly subjective and subject to significant human error. The other method is empirical calculation. Existing formulas for calculating the critical velocity in pipelines are mostly semi-theoretical and semi-empirical relationships derived from experimental results. While these formulas consider generally similar influencing factors, the critical velocity calculated by different methods for the same system can vary significantly. These discrepancies are partly due to the different critical conditions used, but more importantly, they reflect the limitations of these formulas. To date, no universally applicable formula exists. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for determining the critical flow velocity in slurry pipeline transportation, which solves the problems of the existing methods such as difficult testing, strong subjectivity, large deviations in observation and calculation results, and lack of universal applicability.

[0005] The technical solution provided by the present invention is a method for determining the critical flow velocity in slurry pipeline transportation, comprising the following steps:

[0006] (1) In the slurry testing system, measure the initial mass concentration of the slurry in the slurry storage tank;

[0007] (2) The slurry circulates in the test system through the slurry pump, and a curve is drawn showing the relationship between the pressure drop and the slurry flow rate between the slurry pump outlet and the slurry tank return inlet, to preliminarily predict the critical flow rate v0 and the upper limit of the flow rate v1 during the critical flow rate test;

[0008] (3) Run the slurry at v1 in the test system, determine the fixed bed condition in the pipeline (solid particle bed surface in the pipeline) at the flow rate v1, and determine the final flow rate upper limit v2;

[0009] (4) Using v2 as the starting flow rate, gradually reduce the flow rate using the first step length to determine the formation of a fixed bed in the pipeline (solid particle bed surface in the pipeline) and determine the flow rate v3 at which a fixed bed can be formed;

[0010] (5) With v3 as the starting flow rate, gradually increase the flow rate using a second step length that is smaller than the first step length to determine the fixed bed condition (solid particle bed surface in the tube) and determine the flow rate v4 when the fixed bed is eliminated. This flow rate is the critical flow rate v c .

[0011] Furthermore, the slurry testing system includes a slurry storage tank and a slurry pump, the outlet of the slurry storage tank is connected to the inlet of the slurry pump, the outlet of the slurry pump is connected to the reflux inlet of the slurry storage tank through a conveying pipe, a first pressure gauge is provided at the outlet of the slurry pump, a second pressure gauge is provided at the reflux inlet of the slurry storage tank, a flow sensor and three sampling ports at the upper, middle and lower levels are provided on the conveying pipe, and the flow rate of the slurry in the pipeline is calculated by the flow measured by the flow sensor.

[0012] Furthermore, an agitator is provided in the slurry storage tank, and three sampling points, namely, upper, middle and lower, are provided on the side of the slurry storage tank.

[0013] Furthermore, before measuring the initial mass concentration of the slurry storage tank in step (1), the slurry in the slurry storage tank is fully stirred by an agitator, and the concentration test is sampled from the upper, middle and lower sampling points, and the slurry tank concentration is measured as the average value of the three sampling points.

[0014] Furthermore, in the step (2), the pressure drop Δp at the first and last points of the conveying pipeline at different flow rates v is tested, wherein the flow rate value range is: minimum flow rate 0.5-0.8m / s, maximum flow rate 2.5-3m / s, and the flow rate change step is 0.1-0.3m / s. A Δp~v relationship curve is drawn based on the test results, and the flow rate corresponding to the lowest point of the pressure drop Δp in the curve is taken as the predicted critical flow rate v0, and (1.5~2)v0 is used as the flow rate upper limit v1 during the critical flow rate test.

[0015] Furthermore, in step (3), the test system is operated at a flow rate of v1 and stabilized for 0.5 to 1 hour. By comparing the mass concentration in the slurry storage tank and the mass concentration in the delivery pipeline, it is determined whether a fixed bed is generated at this flow rate, thereby determining whether the flow rate upper limit v1 is greater than the true critical flow rate.

[0016] Comparison of mass concentration in the slurry tank and in the delivery pipeline is shown in C 浆罐 / C 管 Size is carried out, when C 浆罐 / C 管 When the concentration in the tank is 0.98~1, the concentration in the tube is consistent with that in the tank, no fixed bed is formed in the tube, and the flow rate upper limit v2=v1; when C 浆罐 / C 管 When it is less than 0.98, the concentration in the tank is lower than that in the tube, and a fixed bed is formed in the tube. Increase the v1 value by 0.2 to 0.3 m / s, stabilize for 0.5 to 1 hour, and re-measure C 浆罐 / C 管 , repeat the above steps until the ratio is in the range of 0.98-1, at which time the flow rate is v2.

[0017] Furthermore, in step (4), with v2 as the starting flow rate, the flow rate is reduced in the first step of 0.2-0.3 m / s and stabilized for 0.5-1 hour. The mass concentration of the slurry storage tank is tested and compared with the mass concentration in the delivery pipeline. When C 浆罐 / C 管 When the flow rate is between 0.98 and 1, continue to reduce the flow rate in steps of 0.2 to 0.3 m / s, stabilize for 0.5 to 1 hour, and then re-calibrate the C 浆罐 / C 管 Test and repeat the above steps; when C 浆罐 / C 管 When <0.98, the flow rate is the flow rate v3 that can form a fixed bed.

[0018] Furthermore, in step (5), with v3 as the starting flow rate, the flow rate is increased in a second step of ≤0.1 m / s and stabilized for 0.5-1 hour, and the mass concentration in the slurry storage tank and the mass concentration in the delivery pipeline are tested and compared.

[0019] When C 浆罐 / C 管 <0.98, continue to increase the flow rate in steps of ≤0.1m / s, stabilize for 0.5~1 hour, and re-calibrate C 浆罐 / C 管 Test and repeat the above steps; when C 浆罐 / C 管 When it is 0.98~1, the flow velocity is v4, which is the critical flow velocity v c .

[0020] Furthermore, the mass concentration in the delivery pipeline is measured by the average concentration of three sampling points: the center of the pipe, the upper end of the pipe, and the lower end of the pipe.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention provides a method for determining the critical velocity of slurry pipeline transportation. By using prediction, large step length, and small step length approximation methods, the range can be gradually narrowed down at a relatively fast speed, ultimately determining the critical velocity of the slurry more accurately. This method solves the problems of existing critical velocity technical methods, such as difficulty in testing, strong subjectivity, large deviations in observation and calculation results, and lack of universal applicability.

[0023] (2) The method provided by the present invention has the characteristics of wide application range of slurries. When the type of slurry changes, the critical flow rate of the slurry can still be gradually obtained through this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of the slurry testing system of the present invention;

[0025] Figure 2 is a graph showing the relationship between pressure drop and flow rate change in Example 1 of the present invention;

[0026] In the figure: 1 - slurry storage tank, 2 - slurry pump, 3 - delivery pipeline, 4 - first pressure gauge, 5 - second pressure gauge, 6 - flow sensor. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments. The accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual drawings. They should not be understood as limiting the present invention. In order to better illustrate the specific embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted. Based on the specific embodiments of the present invention, all other specific embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood broadly. For example, "connected" can mean a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention on a case-by-case basis. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] The determination method of the present invention adopts Figure 1 The slurry testing system shown is complete, comprising a slurry storage tank 1 and a slurry pump 2. The outlet of the slurry storage tank 1 is connected to the inlet of the slurry pump 2, and the outlet of the slurry pump 2 is connected to the return inlet of the slurry storage tank 1 via a delivery pipe 3. A first pressure gauge 4 is provided at the outlet of the slurry pump 2, and a second pressure gauge 5 is provided at the return inlet of the slurry storage tank 1. A flow sensor 6 and three sampling ports, namely, upper, middle, and lower, are provided on the delivery pipe 3. An agitator is provided in the slurry storage tank 1, and three sampling points, namely, upper, middle, and lower, are provided on the side of the slurry storage tank 1. The flow rate of the slurry in the delivery pipe is calculated based on the flow rate measured by the flow sensor.

[0030] Before measuring the initial mass concentration of the slurry storage tank, the slurry in the slurry storage tank is fully stirred by an agitator. The concentration test is sampled from the upper, middle and lower sampling points, and the slurry tank concentration is measured as the average value of the three sampling points. The mass concentration in the conveying pipeline is measured by the average concentration of the three sampling points at the center, upper end and lower end of the pipe. Control valves are installed at positions such as the conveying pipeline, and a mobile lifting bracket for support is installed below the conveying pipeline. The slurry storage tank is equipped with a liquid level meter and a temperature sensor as needed. The critical flow rate is the flow rate (solid particle bed surface) when the solid particles in the slurry settle to form a fixed bed surface.

[0031] Example 1

[0032] The present invention provides a method for determining the critical flow velocity in slurry pipeline transportation, comprising the following steps:

[0033] (1) Test the initial mass concentration of the slurry in the slurry storage tank. The initial mass concentration of the slurry in the slurry tank is 50%.

[0034] (2) The slurry is circulated in the test system through a pump. The diameter of the system circulation pipeline is DN150. The pressure drop Δp at the beginning and end of the pipeline is tested at different flow rates v. The flow rate range is 0.5m / s to 2.5m / s. Based on the test results, a curve Δp to v is drawn to show the relationship between the pressure drop and the flow rate. Figure 2 shown.

[0035] According to the Δp~v relationship curve, the flow velocity of 0.53m / s corresponding to the lowest point of the pressure drop Δp is taken as the preliminary predicted critical flow velocity v0, and the upper limit of the flow velocity v1 during the critical flow velocity test is taken as 2v0, that is, 1.06m / s.

[0036] (3) The slurry is allowed to run in the test system at a flow rate of v1 = 1.06 m / s and stabilize for 0.5 to 1 hour. Samples are taken to measure the mass concentration in the slurry tank and the mass concentration in the tube and compare them. 浆罐 / C 管 =0.989>0.98, judging that there is no fixed bed in the pipeline at the flow rate v1, and the final flow rate upper limit v2=v1=1.06m / s.

[0037] (4) With v2 = 1.06 m / s as the starting flow rate, reduce the flow rate to 0.86 m / s in steps of 0.2 m / s, stabilize for 0.5-1 hour, take samples to measure the mass concentration in the slurry tank and the mass concentration in the tube and compare them, C 浆罐 / C 管 =0.967<0.98, it is judged that a fixed bed is generated in the pipeline at a flow rate of 0.86 m / s, and it is determined that the fixed bed flow rate v3=0.86 m / s can be formed.

[0038] (5) With v3 = 0.86 m / s as the starting flow rate, increase the flow rate to 0.96 m / s in steps of 0.1 m / s and stabilize for 0.5-1 hour. Take samples to measure the mass concentration in the slurry tank and the mass concentration in the tube and compare them. C 浆罐 / C 管 =0.983>0.98, it is determined that the fixed bed in the pipeline is eliminated at a flow rate of 0.96m / s, and the flow rate when the fixed bed is eliminated is determined to be v4=0.96m / s, which is the critical flow rate v c =0.96m / s.

[0039] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining the critical flow velocity in slurry pipeline transportation, characterized in that: The steps include: (1) In the slurry testing system, measure the initial mass concentration of the slurry in the slurry storage tank; (2) The slurry circulates in the test system through the slurry pump, and a curve is drawn showing the relationship between the pressure drop and the slurry flow rate between the slurry pump outlet and the slurry tank return inlet, to preliminarily predict the critical flow rate v0 and the upper limit of the flow rate v1 during the critical flow rate test; (3) Run the slurry in the test system at v1, determine the fixed bed condition in the pipeline at v1 flow rate, and determine the final flow rate upper limit v2; (4) Using v2 as the starting flow rate, gradually reduce the flow rate using the first step length to determine the formation of a fixed bed in the pipeline and determine the flow rate v3 at which a fixed bed can be formed; (5) With v3 as the starting flow rate, gradually increase the flow rate using a second step length that is smaller than the first step length to judge the fixed bed condition and determine the flow rate v4 when the fixed bed is eliminated. This flow rate is the critical flow rate v c ; In step (2), the pressure drop Δp between the first and last points of the delivery pipeline at different flow rates v is tested, wherein the flow rate range is: minimum flow rate 0.5-0.8 m / s, maximum flow rate 2.5-3 m / s, and the flow rate change step is 0.1-0.3 m / s. A Δp-v relationship curve is drawn based on the test results, and the flow rate corresponding to the lowest point of the pressure drop Δp in the curve is taken as the predicted critical flow rate v0, and (1.5-2)v0 is used as the flow rate upper limit v1 during the critical flow rate test; In step (3), the test system is operated at a flow rate of v1 and stabilized for 0.5 to 1 hour. By comparing the mass concentration in the slurry storage tank and the mass concentration in the delivery pipeline, it is determined whether a fixed bed is generated at this flow rate, thereby determining whether the flow rate upper limit v1 is greater than the true critical flow rate. Comparison of mass concentration in the slurry tank and in the delivery pipeline is shown in C 浆罐 / C 管 Size is carried out, when C 浆罐 / C 管 When the concentration in the tank is 0.98~1, the concentration in the tube is consistent with that in the tank, no fixed bed is formed in the tube, and the upper limit of the flow rate v2=v1; when C 浆罐 / C 管 When it is less than 0.98, the concentration in the tank is lower than that in the tube, and a fixed bed is formed in the tube. Increase the v1 value by 0.2 to 0.3 m / s, stabilize for 0.5 to 1 hour, and re-measure C 浆罐 / C 管 , repeat the above steps until the ratio is in the range of 0.98-1, at which time the flow rate is v2; In the step (4), v2 is used as the starting flow rate, and the flow rate is reduced by the first step of 0.2-0.3 m / s, and stabilized for 0.5-1 hour. The mass concentration of the slurry storage tank is tested and compared with the mass concentration in the delivery pipeline. When C 浆罐 / C 管 When the flow rate is between 0.98 and 1, continue to reduce the flow rate in steps of 0.2 to 0.3 m / s, stabilize for 0.5 to 1 hour, and then re-calibrate the C 浆罐 / C 管 Test and repeat the above steps; when C 浆罐 / C 管 <0.98, the flow rate is the flow rate v3 that can form a fixed bed; In step (5), with v3 as the starting flow rate, the flow rate is increased in a second step of ≤0.1 m / s and stabilized for 0.5-1 hour. The mass concentration in the slurry storage tank is tested and compared with the mass concentration in the delivery pipeline. When C 浆罐 / C 管 <0.98, continue to increase the flow rate in steps of ≤0.1m / s, stabilize for 0.5~1 hour, and re-calibrate C 浆罐 / C 管 Test and repeat the above steps; when C 浆罐 / C 管 When it is 0.98~1, the flow velocity is v4, which is the critical flow velocity v c .

2. The method for determining the critical flow velocity in slurry pipeline transportation according to claim 1, characterized in that: The slurry testing system comprises a slurry storage tank (1) and a slurry pump (2), wherein the outlet of the slurry storage tank (1) is connected to the inlet of the slurry pump (2), and the outlet of the slurry pump (2) is connected to the reflux inlet of the slurry storage tank (1) through a delivery pipe (3), a first pressure gauge (4) is provided at the outlet of the slurry pump (2), a second pressure gauge (5) is provided at the reflux inlet of the slurry storage tank (1), and a flow sensor (6) and three upper, middle and lower sampling ports are provided on the delivery pipe (3).

3. The method for determining the critical flow velocity in slurry pipeline transportation according to claim 2, characterized in that: A stirrer is provided in the slurry storage tank (1), and three sampling points, namely, upper, middle and lower, are provided on the side of the slurry storage tank (1).

4. The method for determining the critical flow velocity in slurry pipeline transportation according to claim 3, characterized in that: Before measuring the initial mass concentration of the slurry storage tank in step (1), the slurry in the slurry storage tank (1) is fully stirred by a stirrer, and the concentration test is sampled from the upper, middle and lower sampling points, and the initial mass concentration of the slurry is measured as the average value of the three sampling points.

5. The method for determining the critical flow velocity in slurry pipeline transportation according to claim 1, characterized in that: The mass concentration in the delivery pipeline is measured by the average concentration of three sampling points: the center of the pipe, the upper end of the pipe, and the lower end of the pipe.

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