Method for testing flow of high-vacuum negative-pressure pipeline

Abstract

The invention discloses a method for testing the flow of a high-vacuum negative-pressure pipeline. The method comprises the following steps of: determining a test point on a straight pipe section of the negative-pressure pipeline according to a test requirement; a test hole with the diameter of 8.5 mm is formed in the position of a test point on the surface of the negative pressure pipeline, and the pressure difference between a suction inlet of the vacuum pump and the local atmospheric pressure is measured through a pressure difference sensor so as to determine the vacuum degree and the absolute pressure value in the pipeline; when the flow of the high-vacuum negative-pressure pipeline is measured, a pressure difference measuring device and a thermometer are sequentially placed into the negative-pressure pipeline at a test point to measure dynamic parameters of gas in the pipeline, and the pressure difference and the temperature of gas flow at the test point are recorded respectively; and the gas density and flow of the corresponding position are calculated by combining the measured gas dynamic parameters. According to the high-vacuum negative-pressure pipeline on-site flow measuring device, on-site on-line flow measurement of the high-vacuum negative-pressure pipeline can be achieved, actual gas flow parameters of the high-vacuum negative-pressure pipeline can be accurately measured, and adaptive turbine vacuum pump equipment is selected according to the gas flow parameters.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline performance testing, and in particular relates to a high vacuum negative pressure pipeline flow testing method. Background Art

[0002] As the core equipment in the industrial field, single-stage high-speed turbine vacuum pumps are widely used in pulp molding, pulp and paper making, thermal power plants and other fields. In view of the high energy consumption and narrow adjustment range caused by the mismatch between the operating flow and vacuum degree of the turbine vacuum pump and the requirements of the process system, it is necessary to select an appropriate turbine vacuum pump according to the actual flow of the existing vacuum pipeline system to improve the energy utilization rate of the vacuum system and achieve the goals of energy saving, consumption reduction and green emission reduction. However, the existing high vacuum system still has the following problems during operation:

[0003] (1) The existing vacuum pipeline flow calculation is generally based on the nameplate flow parameters of the original vacuum pump equipment. Since the original vacuum pump equipment generally has no flow data detection, and many old vacuum pump equipment has been running for a long time, the difference between the actual operating flow and the nameplate flow is getting bigger and bigger, and the actual flow data error is large.

[0004] (2) If the flow design value of the selected turbine vacuum pump is smaller than the actual flow demand of the vacuum system, the equipment selection will be too small and the flow of the turbine vacuum pump will need to be redesigned. This process may need to be repeated many times. The design and production cycle is uncontrollable and long, and the equipment and labor costs increase.

[0005] (3) In order to meet the flow demand indicators of the vacuum system, a complicated design scheme is generally adopted, which increases the cost sharply and increases the energy consumption of the equipment. Summary of the invention

[0006] The purpose of the present invention is to provide a high vacuum negative pressure pipeline flow test method, which can realize on-site online flow measurement of high vacuum negative pressure pipelines, accurately measure the actual gas flow parameters of high vacuum negative pressure pipelines, and select suitable turbine vacuum pump equipment according to the gas flow parameters. In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] According to one aspect of the present invention, the present invention provides a high vacuum negative pressure pipeline flow rate testing method, the testing method comprising the following steps:

[0008] Step 1: Test point location selection: determine the test point on the straight section of the negative pressure pipeline according to the test requirements;

[0009] Step 2: Drill a hole at the test point, open a test hole with a diameter of 8.5 mm or more on the surface of the negative pressure pipeline test point, and determine the vacuum degree and absolute pressure value P1 in the pipeline by measuring the pressure difference between the vacuum pump suction port and the local atmospheric pressure;

[0010] Step 3, flow measurement. When measuring the flow, place a pressure difference measuring device and a thermometer into the negative pressure pipe in the test hole in turn, measure the dynamic parameters of the gas during the extraction, and then record the pressure difference ΔP and temperature T1 of the airflow at the test point respectively. After the measurement, plug the test hole with an M8×20 bolt.

[0011] Step 4: Calculate the gas density ρ1 and flow rate q at the corresponding position based on the measured gas dynamic parameters v .

[0012] In summary, the invention adopts the above technical solution, and the invention has the following technical effects:

[0013] (1) The present invention detects and calculates the actual flow rate under different vacuum conditions, and selects an appropriate turbine vacuum pump according to the tested vacuum degree and flow parameter values, so that the vacuum degree and flow rate required by the vacuum pipeline system are within the optimal performance range of the centrifugal impeller, so as to improve the energy utilization rate of the vacuum system, thereby achieving the requirement of directional selection and adaptation of vacuum system parameters while meeting the actual vacuum system process requirements.

[0014] (2) The present invention also measures the flow data of the high vacuum negative pressure pipeline, and verifies the high vacuum pipeline test flow data and the flow data calculated by the standard collector, requiring the data deviation to be within 5%, so as to realize the accurate measurement and calculation of the flow of the vacuum negative pressure pipeline. According to the measured actual vacuum degree and flow parameter values, the suitable turbine vacuum pump equipment is selected, and the actual vacuum degree and flow parameter values ​​of the vacuum pipeline system can be accurately calculated. The present invention can greatly reduce the redundant design of the turbine vacuum pump, reduce the manufacturing cost and energy waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of a high vacuum negative pressure pipeline flow testing method of the present invention;

[0016] Figure 2 It is a test principle diagram of a high vacuum negative pressure pipeline flow rate test method of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the invention more clearly understood, the invention is further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are only for the purpose of enabling the reader to have a thorough understanding of one or more aspects of the invention, and these aspects of the invention can be realized even without these specific details.

[0018] Combination Figure 1 and Figure 2 As shown, the present invention provides a high vacuum negative pressure pipeline flow testing method, the flow testing method comprising the following steps:

[0019] Step 1, test point location selection, determine the test point on the straight pipe section of the negative pressure pipeline according to the test requirements; in the present invention, when selecting the test point location, try to select the straight pipe section of the negative pressure pipeline 1 and the position with the front-to-back length ratio of 5D:3D in the airflow direction as the test point. The test point location for measuring the negative pressure pipeline should be as far away from devices such as elbows and valves as possible. If the conditions do not meet the above conditions, the point opening test can be carried out according to the actual situation with the straight pipe section length ratio of 3D:2D, so as to reduce the measurement data error;

[0020] Step 2: Drill a hole at the test point, and open a test hole with a diameter of 8.5 mm or more on the surface of the negative pressure pipeline test point. According to the test criteria, the vacuum degree and absolute pressure P1 in the pipeline are determined by measuring the pressure difference between the vacuum pump suction port and the local atmospheric pressure;

[0021] Step 3, flow measurement. When measuring the flow, place a pressure difference measuring device and a thermometer into the negative pressure pipe in the test hole in turn, measure the dynamic parameters of the gas during the extraction, and then record the pressure difference ΔP and temperature T1 of the airflow at the test point respectively. After the measurement, plug the test hole with an M8×20 bolt.

[0022] Step 4: Calculate the gas density ρ1 and flow rate q at the corresponding position based on the measured gas dynamic parameters v .

[0023] In the present invention, the flow test of the high vacuum negative pressure pipeline is performed by using a pitot tube to perform a pressure difference test. By measuring the pressure difference in the pipeline at the suction port of the vacuum pump, the gas density of the airflow at the corresponding position is calculated in combination with the measured position vacuum degree, temperature, inner diameter of the pipeline and other parameters, and the corresponding mass flow rate and the corresponding volume flow rate are calculated. During the test, the pitot tube 2 is first extended into the negative pressure pipeline 1 from the test hole M in the direction of the high-pressure vacuum airflow facing the suction port of the vacuum pump. The airflow is transported to the differential pressure gauge 3 through the pitot tube 2, thereby testing the pressure difference value ΔP in the vacuum negative pressure pipeline 1, and the test data is measured and recorded for multiple times; the pitot tube 2 is taken out of the test hole M, and the thermometer is placed in the vacuum negative pressure pipeline 1 from the test hole M, the temperature T1 of the gas in the pipeline 1 is tested, and the test data is measured and recorded for multiple times to complete the test. The vacuum pump of the present invention adopts a supersonic turbine vacuum pump; in the present invention, the airflow density ρ1 at the test point satisfies:

[0024]

[0025] Among them, τ is the pressure ratio, and t is the temperature ratio, and they satisfy:

[0026]

[0027] In the formula, P1 is the absolute pressure at the test point, in kPa; T1 is the gas temperature at the test point, in K;

[0028] ρ2 is the air flow density when the pressure in the negative pressure pipe is P2 and the temperature is T2;

[0029] The air extraction volume at the test point q v satisfy:

[0030]

[0031] where q m is the flow rate at the test point, and the flow rate q m satisfy:

[0032]

[0033] In the formula, D is the inner diameter of the negative pressure pipe at the test point, in mm;

[0034] ΔP is the air flow pressure difference measured at the measuring point where the pressure difference measuring device is located, in kPa

[0035] If the local atmospheric pressure is the standard atmospheric pressure of 101kPa, according to the test criteria, select the measuring point on the inlet pipe of the water ring vacuum pump, and install the thermometer and vacuum gauge for measurement after drilling according to the test steps. The vacuum degree of the Pitot tube 2 suction volume test data is -42kPa, the pressure difference is 992Pa, the intake temperature is 27℃, and the inner diameter of the inlet pipe of the vacuum negative pressure pipe 1 is 317mm, as shown in Table 1.

[0036] Table 1 Pitot tube test parameters

[0037]

[0038] According to the above test data, the test point airflow calculation formula according to the test principle can be obtained:

[0039] The airflow density ρ1 at the test point is calculated as follows:

[0040]

[0041]

[0042] ρ2 is the air density at 20°C (corresponding to a Kelvin temperature of 293.15K) when the corresponding pressure is 101 kPa;

[0043] Air extraction from the test point:

[0044] The following is obtained:

[0045]

[0046] Quality air extraction at the test point:

[0047] From the parameters in Table 1, we can get:

[0048]

[0049] According to the above test data, if the actual demand is a vacuum degree of -42kPa, the air extraction volume is 257.08m 3 / min, combined with the performance characteristics of the supersonic turbine vacuum pump, comprehensive consideration of process demand fluctuations and a certain production margin, HGV300 was selected as the replacement model for the water ring vacuum pump. The specific performance parameters are shown in Table 2.

[0050] Table 2 HGV300 parameter table

[0051]

[0052] In the present invention, the standard pipeline test requires testing according to JB / T 3165 standard, a standard air intake pipeline is installed at the suction end of the turbine vacuum pump, and a standard flow collector, that is, a standard flow test device, is set on the standard air intake pipeline. A hole is opened on the standard air intake pipeline and a pressure difference measuring device is used to test the standard air intake pipeline. According to the standard pipeline test results, the flow measurement results of the standard flow collector and the pressure difference measuring device are compared and analyzed to determine whether the flow deviation between the two is within a preset range. If so, the test accuracy requirement is met.

[0053] If the deviation between the two is not within the preset range, it is necessary to optimize the test method or process of the pressure difference measuring device (Pitot tube) for the high vacuum negative pressure pipeline flow until the deviation between the two is within the preset range. Therefore, in order to improve the accuracy of the high vacuum negative pressure pipeline flow test method, the standard intake pipeline test and the Pitot tube test flow are compared to improve the accuracy of the Pitot tube test of the high vacuum negative pressure pipeline flow. Under the premise that the speed of the vacuum pump remains unchanged, the vacuum degree of the negative pressure pipeline is gradually increased, and the air extraction volume is gradually reduced. Then, the air extraction volume on the standard intake pipeline and the air extraction volume on the negative pressure pipeline are tested by the pressure difference measuring device respectively.

[0054] Therefore, in order to verify the accuracy of the high vacuum negative pressure pipeline suction volume test method, the standard pipeline test and the Pitot tube test suction volume were compared to verify the test accuracy of this method. The standard pipeline test was carried out according to the test standard of JB / T 3165, that is, by designing a standard air intake pipeline, opening a hole in the standard air intake pipeline to achieve a standard test, and comparing and analyzing the suction volume on the negative pressure pipeline with the suction volume of the standard test. The specific data are shown in Table 3.

[0055] Table 3 Comparison of air extraction test data

[0056]

[0057] It can be seen from Table 3 that the air extraction values ​​obtained by the two test methods are basically consistent, and the flow value deviations obtained by the two test methods are both less than 5%, which meets the test accuracy requirements of engineering applications. The obtained air extraction volume is larger than the data obtained by the standard test method, which has important guiding significance for the selection of supersonic turbine vacuum pumps. Through the comparison and verification of the standard performance test of the supersonic turbine vacuum pump, the test method of the present invention has good test accuracy for the air extraction volume test of the high vacuum negative pressure pipeline, which meets the requirements of engineering applications; in addition, under the premise that the speed of the vacuum pump remains unchanged, with the increase of the vacuum degree, the air extraction volume gradually decreases, the gas flow rate in the inlet pipeline decreases, and the test deviation gradually decreases. Therefore, in the field test, the result can also be corrected by the pipeline flow rate obtained by the test, and more accurate inlet air extraction volume data has been obtained.

[0058] The above is only a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the invention. These improvements and modifications should also be regarded as the scope of protection of the invention.

Claims

1. A high vacuum negative pressure pipeline flow test method, characterized in that: The flow rate testing method comprises the following steps: Step 1: Test point location selection: determine the test point on the straight section of the negative pressure pipeline according to the test requirements; Step 2: Drill a hole at the test point, open a test hole with a diameter of 8.5 mm or more on the surface of the negative pressure pipeline test point, and determine the vacuum degree and absolute pressure value P1 in the pipeline by measuring the pressure difference between the vacuum pump suction port and the local atmospheric pressure; Step 3, when measuring the flow rate, put the pressure difference measuring device and the thermometer into the negative pressure pipe in the test hole in turn, and measure the dynamic parameters of the gas during the extraction, and then record the pressure difference ΔP and temperature T1 of the airflow at the test point respectively. After the measurement, plug the test hole with an M8×20 bolt; Step 4: Calculate the gas density ρ1 and flow rate q at the corresponding position based on the measured gas dynamic parameters v .

2. A high vacuum negative pressure pipeline flow rate testing method according to claim 1, characterized in that: The airflow density ρ1 at the test point satisfies: Among them, τ is the pressure ratio, and t is the temperature ratio, and they satisfy: In the formula, P1 is the absolute pressure at the test point, in kPa; T1 is the gas temperature at the test point, in K; ρ2 is the air flow density when the pressure in the negative pressure pipe is P2 and the temperature is T2; The air extraction volume at the test point q v satisfy: where q m is the flow rate at the test point, and the flow rate q m satisfy: In the formula, D is the inner diameter of the negative pressure pipe at the test point, in mm; ΔP is the air flow pressure difference measured at the measuring point where the pressure difference measuring device is located, and the unit is kPa.

3. A high vacuum negative pressure pipeline flow rate testing method according to claim 1 or 2, characterized in that: The standard pipeline test requires testing in accordance with JB / T 3165. A standard air intake pipeline is installed at the suction end of the vacuum pump, and a standard flow collector is set on the standard air intake pipeline. A pressure differential measuring device is used to test the standard air intake pipeline. According to the standard pipeline test results, the flow measurement results of the standard flow collector and the pressure differential measuring device are compared and analyzed to see if the flow deviation between the two is within the preset range. If so, the test accuracy requirements are met.

4. A high vacuum negative pressure pipeline flow rate testing method according to claim 3, characterized in that: If the deviation between the two is not within the preset range, it is necessary to optimize the test process of the pressure difference measuring device for the high vacuum negative pressure pipeline flow until the deviation between the two is within the preset range.

5. A high vacuum negative pressure pipeline flow rate testing method according to any one of claims 1 to 4, characterized in that: The pressure difference measuring device is a Pitot tube, and the punching position is a straight pipe section of the pipeline and the position with the front-to-back ratio of the airflow direction being 5:3 or 3:2 is used as the test point.

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