Research on how to improve the measurement accuracy of the orifice flow meter

Abstract: The research information on how to improve the measurement accuracy of the orifice flowmeter is provided by the excellent flowmeter and flowmeter manufacturers. With the rapid development of natural gas in my country, a very high-precision natural gas flow meter is required. At present, the natural gas flow measuring instrument used by most natural gas enterprises in my country is the orifice plate flowmeter, which has the advantages of simple structure, low cost and high cost. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the research article on how to improve the measurement accuracy of the orifice flowmeter. With the rapid development of natural gas in my country, a very high-precision natural gas flow meter is required. At present, the natural gas flow measuring instrument used by most natural gas enterprises in my country is the orifice flowmeter, which has the advantages of simple structure, low cost and high measurement accuracy. According to relevant data, more than 95% of oil and gas companies use orifice flowmeters in trade meters. Orifice flowmeter is a kind of detection instrument that detects the pressure difference on both sides of the concentric orifice plate installed in the pipeline to obtain flow data. It is mainly composed of throttling device, differential pressure gauge, pressure gauge and thermometer. It is designed and manufactured according to the principles of energy conservation and flow continuity equation. Its method of calculating the natural gas flow is to generate a pressure difference through a throttling device, and then enter some instruments to measure the pressure difference, pressure, and temperature, and finally obtain the data by using a flow totalizer or a computer control system. 1 The working principle and characteristics of the orifice flowmeter The orifice flowmeter is designed based on the law of energy conservation and the flow continuity equation. The calculation method is calculated according to the pressure difference on both sides of the concentric orifice installed in the pipeline. Its structure It is composed of a thermometer, a pressure gauge, and a throttling device. Because of its low cost, simple structure and high measurement accuracy, it is suitable for engineering measurement and trade that do not require high precision. my country has been using orifice flowmeters for a long time, and has very mature experience in the design, production and processing of orifice flowmeters. The orifice flowmeters produced by it can also measure the flow of natural gas in some unknown ranges. At present, the mainstream natural gas measuring instrument in my country is still the orifice flowmeter. 2. Calculation method of natural gas flow 2.1 Basic formula of natural gas volume flow calculation Qn in formula (1)———Natural gas volume flow in standard state, m3/s; C———outflow coefficient;β———diameter ratio; ε———expansion coefficient; d———Orifice opening diameter, mm; Δp———The pressure difference before and after the throttle, Pa;ρ1———Density of natural gas under upstream working conditions, kg/m3;ρn———Density of natural gas in standard state, kg/m3. 2.2 Practical formula for calculating the volume flow of natural gas In formula (2), As———Second measurement coefficient, depending on the measurement unit, this formula As=3.1794×10-6;E———Progressive speed factor; FG———Relative density coefficient; Fz———Hypercompression factor; Fr———Flow temperature coefficient; P1———The absolute static pressure of the pressure hole upstream of the orifice plate, MPa. 3. Measurement error analysis of orifice flowmeter 3.1 Influence of outflow coefficient C on measurement accuracy The calibration of orifice flowmeter is related to the outflow coefficient. It needs to reach a sufficient length in the upstream straight pipe section, and its throttling device needs to reach the necessary technical Require. The flow coefficient is related to and varies with the Reynolds number. When the value of c increases, the Reynolds number will decrease, and vice versa, when the value of c decreases, the Reynolds number will increase. The flow coefficient C also changes with the flow rate, and its change decreases with the increase of the flow rate. When the actual flow rate is smaller than the calibrated flow rate, the flow error caused by it will increase. At the same time, the C value is a variable, which changes according to the Reynolds number. When the Reynolds number reaches a certain value, the amount of change will become smaller. Regarding flange pressure, the Reynolds number should exceed 106, while the value of handover pressure should exceed 210.3.2 Uncertainty factors of actual physical properties of the measured medium (1) Influence of relative density of natural gas on flow measurement. The natural gas flow value will change with the change of 1/Gr, and the relationship between the two is a proportional relationship, which can be seen from the above formula (2). If Gr is regarded as a separate quantity, then when the uncertainty of Gr is plus or minus 0.5%, the uncertainty factor of the standard volume flow of natural gas is plus or minus 0.25%, so it is obvious Flow metering will be affected by the actual relative density of natural gas. The reason for the emergence of Gr uncertainty is that there is no measurement and analysis to determine the relevant physical parameters of the real natural gas. For example, the degree to which the composition of actual air deviates from the standard composition, and the uncertainty in the measurement of the molecular weight of each relevant component. At present, there are two ways to confirm Gr. The first is to use buoyant gas balances, momentum hydrometers and other instruments to detect its actual relative density; the second is to use gas analysis instruments to first know all the components of natural gas, and then calculate the Cr value based on it. . Now our country usually uses the latter method. But because there is a pressure temperature difference, Gr is a variable. At this time, it is necessary to use online chromatography to observe its changes, thereby further increasing the accuracy of measurement.

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