A method for detecting flow rate in low-velocity gas extraction pipelines using mixed air

Abstract

A method for detecting the flow rate of a low-flow gas extraction pipeline using mixed air relates to the technical field of coal mine gas extraction. It comprises a main body, a nozzle, an air cap, a nozzle joint sealing cover, a connector, a flange, a second gas nozzle, a first gas nozzle, a nozzle joint, and a third gas nozzle. The air inlet and air outlet ends of the main body are both provided with flanges, and the main body is sequentially provided with a second gas nozzle, a first gas nozzle, a nozzle joint, and a third gas nozzle from the air inlet to the air outlet; the diameter of the main body is equal to the diameter of the extraction pipeline, and the air inlet and air outlet ends of the main body are both connected to the extraction pipeline through flanges. After adopting the above technical solution, the beneficial effects of the present invention are as follows: the detection device has high measurement precision and good accuracy, and realizes accurate measurement of the flow rate of a low-flow gas extraction pipeline. It can be used for flow detection at the end of extraction systems such as drilling holes and drilling sites, which is helpful for accurate measurement of gas extraction volume and improves the accuracy of gas extraction compliance assessment, which is of great significance for coal mine gas prevention and control.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine gas extraction, and in particular to a method for detecting the flow rate of a low-flow-rate gas extraction pipeline by using mixed air. Background Art

[0002] Gas extraction is one of the most important gas prevention and control measures in my country's coal mines. Accurately measuring gas extraction pipeline parameters such as negative pressure, concentration, flow rate, temperature, and humidity is crucial for precise measurement of gas extraction volume, accurate assessment of gas extraction compliance, and ensuring coal mine safety. After years of development, on-site instrumentation and equipment in coal mines have achieved relatively accurate measurement of parameters such as negative pressure, concentration, temperature, and humidity. However, the detection of flow parameters has not been effectively addressed, and significant challenges remain. Currently, flow measurement in underground coal mine gas extraction pipelines primarily utilizes methods such as orifice flowmeters, pitot tube flowmeters, V-cone flowmeters, and vortex flowmeters. These methods generally suffer from low measurement precision and accuracy under low flow rates, failing to meet the needs of gas extraction flow measurement in low-flow environments such as on-site drilling and drilling sites. Therefore, measuring flow parameters in low-flow gas extraction pipelines has long been a technical challenge in the detection and measurement of coal mine gas extraction parameters. Summary of the Invention

[0003] The purpose of the present invention is to address the defects and shortcomings of the existing technology and provide a method for detecting the flow rate of low-flow gas extraction pipelines by using mixed air. By mixing a certain amount of air into the extraction pipeline and detecting the change in gas concentration before and after the air is mixed, accurate measurement of the gas flow rate of low-flow gas extraction pipelines can be achieved, which is of great significance for coal mine gas prevention and control.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A device for measuring flow in a low-flow gas extraction pipeline by mixing air, comprising a main body 1, a nozzle 2, a gas cap 3, a nozzle joint sealing cover 4, a connector 5, a flange 11, a second gas nozzle 12, a first gas nozzle 13, a nozzle joint 14, and a third gas nozzle 15. The main body 1 is provided with flanges 11 at both the air inlet and air outlet ends. The main body 1 is provided with the second gas nozzle 12, the first gas nozzle 13, the nozzle joint 14, and the third gas nozzle 15 in sequence from the air inlet to the air outlet.

[0006] The diameter of the main body 1 is equal to the diameter of the extraction pipeline, and the air inlet and outlet ends of the main body 1 are connected to the extraction pipeline through flanges 11;

[0007] The second gas nozzle 12 and the third gas nozzle 15 are both provided with a gas cap 3;

[0008] The first gas nozzle 13 is connected to the barometer;

[0009] The nozzle joint 14 is provided with a connecting piece 5 , which includes one of the nozzle 2 and the nozzle joint sealing cover 4 .

[0010] The distance between the nozzle joint 14 and the first gas nozzle 13 is not less than 2 times the inner diameter of the main body 1 , and the distance between the nozzle joint 14 and the third gas nozzle 15 is not less than 4 times the inner diameter of the main body 1 .

[0011] The nozzle 2 is a series of standard parts.

[0012] The inner wall of the nozzle joint 14 is provided with an internal thread.

[0013] The outer structure of the nozzle 2 is a combination of a hexagonal prism and a cylinder. The upper part of the nozzle 2 is a short hexagonal prism, and the lower part of the nozzle 2 is a cylinder. The short hexagonal prism and the cylinder are coaxial, with a spray hole in the middle, and a thread is provided on the outside of the cylinder.

[0014] The air cap 3 is a rubber cap.

[0015] The nozzle joint sealing cover 4 has the same shape as the nozzle 2. There is no spray hole in the middle of the nozzle joint sealing cover 4. The nozzle joint sealing cover 4 is a solid structure with threads arranged on the outside of the cylinder.

[0016] A method for measuring the flow rate of a low-velocity gas extraction pipeline by mixing air includes the following steps:

[0017] Step S1: installing a flow measuring device for detecting low-flow-rate gas extraction pipeline flow by mixing air in the gas extraction pipeline to be tested;

[0018] Step S2: Determine the gas concentration in the ambient air where the gas extraction pipeline is located ;

[0019] Step S3: Connect the barometer to the first gas nozzle 13 of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air to measure the negative pressure of the gas extraction pipeline. ;

[0020] Step S4: Select a nozzle 2 of appropriate type and install it on the nozzle joint 14 of the measuring device for detecting the flow rate of low-flow gas extraction pipeline by mixing air, inject air into the pipeline, and calculate the negative pressure. Injection flow rate of lower nozzle 2 , the calculation formula is as follows:

[0021]

[0022] in: is the flow coefficient of nozzle 2. After determining the nozzle 2 model is a fixed value;

[0023] Step S5: The second gas nozzle 12 of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air collects the gas sample in the gas extraction pipeline and measures the gas concentration of the pipeline gas not mixed with air in the upstream pipeline. ;

[0024] Step S6: Collect gas samples through the third gas nozzle 15 of the measuring device for detecting the flow rate of low-flow gas extraction pipeline by mixing air, and measure the gas concentration of the pipeline gas after mixing air in the downstream pipeline. ;

[0025] Step S7: Calculate the mixed flow of gas in the gas extraction pipeline under the working conditions :

[0026] .

[0027] Whether the nozzle 2 model is suitable or not is determined by: the nozzle 2 has a negative pressure on the upstream side of the pipeline. If the influence of is within ±10%, the nozzle model 2 is considered appropriate; otherwise, it is considered inappropriate.

[0028] The working principle of the present invention is as follows: the air inlet and outlet ends of the main body 1 are both provided with flanges 11, and the main body 1 is provided with a second air nozzle 12, a first air nozzle 13, a nozzle joint 14, and a third air nozzle 15 in sequence from the air inlet end to the air outlet end; the diameter of the main body 1 is equal to the diameter of the extraction pipeline, and the air inlet and outlet ends of the main body 1 are connected to the extraction pipeline through flanges 11; the second air nozzle 12 and the third air nozzle 15 are both provided with air caps 3; the second air nozzle 12 is used to collect the extraction pipeline gas sample of the upstream unmixed air and measure the unmixed air The pipeline gas concentration, the third gas nozzle 15 is used to collect the extraction pipeline gas sample after the downstream is mixed with air, and measure the pipeline gas concentration after mixing with air. The second gas nozzle 12 and the third gas nozzle 15 are both provided with a gas cap 3, which blocks the second gas nozzle 12 and the third gas nozzle 15 during the non-gas extraction pipeline flow measurement; the first gas nozzle 13 is connected to the barometer; the first gas nozzle 13 is connected to the barometer to measure the pipeline extraction negative pressure; the nozzle joint 14 is provided with a connector 5, and the connector 5 includes one of the nozzle 2 or the nozzle joint sealing cover 4. During the gas extraction pipeline flow measurement process, a nozzle 2 is provided on the nozzle joint 14 to spray air into the interior of the main body 1, thereby realizing mixing of air and extraction pipeline gas in the space of the main body 1; during the non-gas extraction pipeline flow measurement period, a nozzle joint sealing cover 4 is provided on the nozzle joint 14 to seal the nozzle joint 14, and a nozzle 2 is installed at the air inlet, which improves the air mixing efficiency, shortens the mixing distance, ensures sufficient mixing of air and pipeline gas, and ensures the accuracy of the test results; the nozzle 2 adopts a series of standard parts, and the mixed air flow is quickly calculated according to the negative pressure-flow relationship of the nozzle 2, fully considering the complexity and variability of coal mine underground gas extraction, ensuring the convenience and wide adaptability of the method, and can be used for accurate measurement of low-flow gas extraction pipeline flow under different conditions.

[0029] After adopting the above technical solution, the beneficial effects of the present invention are as follows: the detection device has high measurement precision and good accuracy. By mixing a certain amount of air into the gas extraction pipeline, the change in gas concentration in the gas extraction pipeline before and after the air is mixed is measured, thereby achieving accurate measurement of the flow rate of the low-flow gas extraction pipeline. It can be used for end flow detection of extraction systems such as drilling holes and drilling sites, which helps to accurately measure the gas extraction volume and improve the accuracy of gas extraction compliance assessment, which is of great significance for coal mine gas prevention and control.

[0030] The air mixing efficiency is improved, the mixing distance is shortened, the sufficient mixing of air and pipeline gas is ensured, and the accuracy of the detection results is guaranteed; the complexity and variability of underground coal mine gas extraction are fully considered, ensuring the convenience and wide adaptability of the method, and it can be used for accurate measurement of low-flow gas extraction pipeline flow under different conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0032] Figure 1 It is a structural schematic diagram of the present invention;

[0033] Figure 2 It is a schematic structural diagram of the nozzle 2 in the present invention;

[0034] Figure 3 It corresponds to Figure 2 A top view of

[0035] Figure 4 It is a schematic structural diagram of the gas cap 3 in the present invention;

[0036] Figure 5 It corresponds to Figure 4 A top view of

[0037] Figure 6 It is a structural schematic diagram of the nozzle joint sealing cover 4 of the present invention;

[0038] Figure 7 It corresponds to Figure 6 A top view of

[0039] Figure 8 It is a structural schematic diagram of the connecting member 5 in the present invention;

[0040] Figure 9 It is a schematic block diagram of the steps of the present invention.

[0041] Explanation of the reference numerals: main body 1 , nozzle 2 , gas cap 3 , nozzle joint sealing cover 4 , connecting piece 5 , flange 11 , second gas nozzle 12 , first gas nozzle 13 , nozzle joint 14 , third gas nozzle 15 . DETAILED DESCRIPTION

[0042] See Figures 1-9 As shown, the technical solution adopted in this specific embodiment is:

[0043] A device for measuring flow in a low-flow gas extraction pipeline by mixing air, comprising a main body 1, a nozzle 2, a gas cap 3, a nozzle joint sealing cover 4, a connector 5, a flange 11, a second gas nozzle 12, a first gas nozzle 13, a nozzle joint 14, and a third gas nozzle 15. The main body 1 is provided with flanges 11 at both the air inlet and air outlet ends. The main body 1 is provided with the second gas nozzle 12, the first gas nozzle 13, the nozzle joint 14, and the third gas nozzle 15 in sequence from the air inlet to the air outlet.

[0044] The diameter of the main body 1 is equal to the diameter of the extraction pipeline, and the air inlet and outlet ends of the main body 1 are connected to the extraction pipeline through flanges 11;

[0045] The second gas nozzle 12 and the third gas nozzle 15 are both provided with gas caps 3; the second gas nozzle 12 is used to collect gas samples from the extraction pipeline that are not mixed with air upstream and measure the gas concentration of the pipeline that is not mixed with air; the third gas nozzle 15 is used to collect gas samples from the extraction pipeline that is mixed with air downstream and measure the gas concentration of the pipeline that is mixed with air. The second gas nozzle 12 and the third gas nozzle 15 are both provided with gas caps 3 to block the second gas nozzle 12 and the third gas nozzle 15 during the non-gas extraction pipeline flow measurement period;

[0046] The first gas nozzle 13 is connected to a barometer; the first gas nozzle 13 is connected to the barometer to measure the negative pressure of the pipeline extraction;

[0047] The nozzle joint 14 is provided with a connector 5, which includes either a nozzle 2 or a nozzle joint sealing cap 4. During the gas extraction pipeline flow measurement process, the nozzle 2 is provided on the nozzle joint 14 to inject air into the interior of the main body 1, thereby mixing the air and the extraction pipeline gas within the main body 1. During non-gas extraction pipeline flow measurement, the nozzle joint 14 is provided with a nozzle joint sealing cap 4 to seal the nozzle joint 14.

[0048] The distance between the nozzle joint 14 and the first gas nozzle 13 is not less than 2 times the inner diameter of the main body 1 , and the distance between the nozzle joint 14 and the third gas nozzle 15 is not less than 4 times the inner diameter of the main body 1 .

[0049] The nozzle 2 is a series of standard parts. The nozzle 2 is divided into multiple series according to different structures. Each series includes multiple models according to different nozzle 2 diameters and spray hole sizes. The flow coefficient μ of each model of nozzle 2 is obtained through laboratory testing.

[0050] The inner wall of the nozzle joint 14 is provided with an internal thread.

[0051] The outer structure of the nozzle 2 is a combination of a hexagonal prism and a cylinder. The upper part of the nozzle 2 is a short hexagonal prism, and the lower part of the nozzle 2 is a cylinder. The short hexagonal prism and the cylinder are coaxial, with a spray hole in the middle, and a thread is provided on the outside of the cylinder.

[0052] The air cap 3 is a rubber cap.

[0053] The nozzle joint sealing cover 4 has the same shape as the nozzle 2. There is no spray hole in the middle of the nozzle joint sealing cover 4. The nozzle joint sealing cover 4 is a solid structure with threads arranged on the outside of the cylinder.

[0054] A method for measuring the flow rate of a low-velocity gas extraction pipeline by mixing air includes the following steps:

[0055] Step S1: installing a flow measuring device for detecting low-flow-rate gas extraction pipeline flow by mixing air in the gas extraction pipeline to be tested;

[0056] Step S2: Determine the gas concentration in the ambient air where the gas extraction pipeline is located ;

[0057] Step S3: Connect the barometer to the first gas nozzle 13 of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air to measure the negative pressure of the gas extraction pipeline. ;

[0058] Step S4: Select a nozzle 2 of appropriate type and install it on the nozzle joint 14 of the measuring device for detecting the flow rate of low-flow gas extraction pipeline by mixing air, inject air into the pipeline, and calculate the negative pressure. Injection flow rate of lower nozzle 2 , the calculation formula is as follows:

[0059]

[0060] in: is the flow coefficient of nozzle 2. After determining the nozzle 2 model is a fixed value;

[0061] Step S5: The second gas nozzle 12 of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air collects the gas sample in the gas extraction pipeline and measures the gas concentration of the pipeline gas not mixed with air in the upstream pipeline. ;

[0062] Step S6: Collect gas samples through the third gas nozzle 15 of the measuring device for detecting the flow rate of low-flow gas extraction pipeline by mixing air, and measure the gas concentration of the pipeline gas after mixing air in the downstream pipeline. ;

[0063] Step S7: Calculate the mixed flow of gas in the gas extraction pipeline under the working conditions :

[0064] .

[0065] Whether the nozzle 2 model is suitable or not is determined by: the nozzle 2 has a negative pressure on the upstream side of the pipeline. If the influence of is within ±10%, the nozzle model 2 is considered appropriate; otherwise, it is considered inappropriate.

[0066] The working principle of the present invention is as follows: the air inlet and outlet ends of the main body 1 are both provided with flanges 11, and the main body 1 is provided with a second air nozzle 12, a first air nozzle 13, a nozzle joint 14, and a third air nozzle 15 in sequence from the air inlet end to the air outlet end; the diameter of the main body 1 is equal to the diameter of the extraction pipeline, and the air inlet and outlet ends of the main body 1 are connected to the extraction pipeline through flanges 11; the second air nozzle 12 and the third air nozzle 15 are both provided with air caps 3; the second air nozzle 12 is used to collect the extraction pipeline gas sample of the upstream unmixed air and measure the unmixed air The pipeline gas concentration, the third gas nozzle 15 is used to collect the extraction pipeline gas sample after the downstream is mixed with air, and measure the pipeline gas concentration after mixing with air. The second gas nozzle 12 and the third gas nozzle 15 are both provided with a gas cap 3, which blocks the second gas nozzle 12 and the third gas nozzle 15 during the non-gas extraction pipeline flow measurement; the first gas nozzle 13 is connected to the barometer; the first gas nozzle 13 is connected to the barometer to measure the pipeline extraction negative pressure; the nozzle joint 14 is provided with a connector 5, and the connector 5 includes one of the nozzle 2 or the nozzle joint sealing cover 4. During the gas extraction pipeline flow measurement process, a nozzle 2 is provided on the nozzle joint 14 to spray air into the interior of the main body 1, thereby realizing mixing of air and extraction pipeline gas in the space of the main body 1; during the non-gas extraction pipeline flow measurement period, a nozzle joint sealing cover 4 is provided on the nozzle joint 14 to seal the nozzle joint 14, and a nozzle 2 is installed at the air inlet, which improves the air mixing efficiency, shortens the mixing distance, ensures sufficient mixing of air and pipeline gas, and ensures the accuracy of the test results; the nozzle 2 adopts a series of standard parts, and the mixed air flow is quickly calculated according to the negative pressure-flow relationship of the nozzle 2, fully considering the complexity and variability of coal mine underground gas extraction, ensuring the convenience and wide adaptability of the method, and can be used for accurate measurement of low-flow gas extraction pipeline flow under different conditions.

[0067] To illustrate, here are some examples: For example, nozzles are divided into several series, such as cylindrical nozzles, conical nozzles, and Venturi nozzles, based on their different structures. Each series includes multiple models, and the nozzle diameters and orifice sizes of different nozzle models vary. Nozzle diameters include 4-inch, 6-inch, 1-inch, 1.5-inch, 2-inch, 2.5-inch, 3-inch, and 4-inch specifications, and orifice diameters include 4mm, 6mm, 8mm, 10mm, 15mm, 20mm, 30mm, 40mm, and 50mm specifications. Nozzles of different diameters can meet the requirements of different extraction pipeline sizes, and different orifice sizes can meet the requirements of different air mixing ratios. This makes this method highly adaptable to field applications and enables the measurement of flow rates in low-velocity gas extraction pipelines under different conditions.

[0068] After adopting the above technical solution, the beneficial effects of the present invention are as follows: the detection device has high measurement precision and good accuracy. By mixing a certain amount of air into the gas extraction pipeline, the change in gas concentration in the gas extraction pipeline before and after the air is mixed is measured, thereby achieving accurate measurement of the flow rate of the low-flow gas extraction pipeline. It can be used for end flow detection of extraction systems such as drilling holes and drilling sites, which helps to accurately measure the gas extraction volume and improve the accuracy of gas extraction compliance assessment, which is of great significance for coal mine gas prevention and control.

[0069] The air mixing efficiency is improved, the mixing distance is shortened, the sufficient mixing of air and pipeline gas is ensured, and the accuracy of the detection results is guaranteed; the complexity and variability of underground coal mine gas extraction are fully considered, ensuring the convenience and wide adaptability of the method, and it can be used for accurate measurement of low-flow gas extraction pipeline flow under different conditions.

[0070] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for measuring flow in a low-velocity gas extraction pipeline by mixing air, characterized by: It includes the following steps: Step S1: installing a flow measuring device for detecting low-flow-rate gas extraction pipeline flow by mixing air in the gas extraction pipeline to be tested; Step S2: measuring the gas concentration c0 in the ambient air where the gas extraction pipeline is located; Step S3: connecting the barometer to the first gas nozzle (13) of the device for measuring the flow rate of the low-flow gas extraction pipeline by mixing air, and measuring the working negative pressure p of the gas extraction pipeline; Step S4: Select a nozzle (2) of a suitable model and install it on the nozzle joint (14) of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air, inject air into the pipeline, and calculate the injection flow rate Q of the nozzle (2) under the negative pressure p. p , the calculation formula is as follows: Wherein: μ is the flow coefficient of the nozzle (2), and μ is a fixed value after the nozzle (2) model is determined; Step S5: collecting a gas sample from the gas extraction pipeline through the second gas nozzle (12) of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air, and measuring the gas concentration c1 of the pipeline gas not mixed with air in the upstream pipeline; Step S6: collecting gas samples through the third gas nozzle (15) of the measuring device for detecting the flow rate of the low-flow gas extraction pipeline by mixing air, and measuring the gas concentration c2 of the pipeline gas after mixing with air in the downstream pipeline; Step S7: Calculate the mixed flow rate Q of the gas in the gas extraction pipeline under the working condition: Q=(c2-c0) / (c1-c2)×Q p ; The measuring device for detecting the flow rate of a low-flow gas extraction pipeline by mixed air in step S1 comprises a main body (1), a nozzle (2), a gas cap (3), a nozzle joint sealing cover (4), a connecting piece (5), a flange (11), a second gas nozzle (12), a first gas nozzle (13), a nozzle joint (14), and a third gas nozzle (15). The main body (1) is provided with flanges (11) at both the gas inlet end and the gas outlet end. The main body (1) is provided with the second gas nozzle (12), the first gas nozzle (13), the nozzle joint (14), and the third gas nozzle (15) in sequence from the gas inlet end to the gas outlet end. The diameter of the main body (1) is equal to the diameter of the extraction pipeline, and the air inlet and outlet ends of the main body (1) are connected to the extraction pipeline via flanges (11); The second gas nozzle (12) and the third gas nozzle (15) are both provided with gas caps (3); The first air nozzle (13) is connected to a barometer; The nozzle joint (14) is provided with a connecting piece (5), and the connecting piece (5) comprises one of a nozzle (2) and a nozzle joint sealing cover (4); The distance between the nozzle joint (14) and the first gas nozzle (13) is not less than 2 times the inner diameter of the main body (1), and the distance between the nozzle joint (14) and the third gas nozzle (15) is not less than 4 times the inner diameter of the main body (1); The nozzle (2) is a series of standard parts; The inner wall of the nozzle joint (14) is provided with an internal thread; The outer structure of the nozzle (2) is a combination of a hexagonal prism and a cylinder. The upper portion of the nozzle (2) is a short hexagonal prism, and the lower portion of the nozzle (2) is a cylinder. The short hexagonal prism and the cylinder are coaxial, with a spray hole in the middle, and a thread is provided on the outside of the cylinder.

2. The method for measuring flow rate in a low-velocity gas extraction pipeline using mixed air according to claim 1, characterized in that: The air cap (3) is a rubber cap.

3. The method for measuring flow rate in a low-velocity gas extraction pipeline using mixed air according to claim 1, characterized in that: The nozzle joint sealing cover (4) has the same shape as the nozzle (2), has no spray hole in the middle of the nozzle joint sealing cover (4), and is a solid structure with threads arranged on the outside of the cylinder.

4. The method for measuring flow rate in a low-velocity gas extraction pipeline using mixed air according to claim 3, characterized in that: Whether the selection of the nozzle (2) model is appropriate is determined by the following method: if the influence of the nozzle (2) on the upstream extraction negative pressure p of the pipeline is within ±10%, the nozzle (2) model is considered appropriate; otherwise, it is considered inappropriate.

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