Analysis on Calibration Accuracy of Appropriate Gas Turbine Flow Meter

Abstract: The analysis information suitable for the calibration accuracy of gas turbine flowmeters is provided by excellent flowmeter and flowmeter manufacturers. Abstract: Various factors affecting the calibration accuracy of gas turbine flowmeters are analyzed, and the solutions are proposed. 1 Preface Due to the development of production, the use of coal and fuel oil has increased too fast, resulting in more and more serious environmental pollution. For this reason, natural gas and natural gas have been vigorously developed. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the details of the analysis article suitable for the calibration accuracy of gas turbine flowmeters. Abstract: Various factors affecting the calibration accuracy of gas turbine flowmeters are analyzed, and the solutions are proposed. 1 Foreword Due to the development of production, the use of coal and fuel oil has increased rapidly, resulting in more and more serious environmental pollution. Therefore, vigorously developing the use of natural gas, coal gas, biogas and other clean fuels has become an important means to solve environmental problems, and has been Great results have been achieved. The development of gas business makes the accuracy of gas trade measurement more important. Therefore, the pursuit of high-precision measuring instruments has become an important issue in the gas trade, and the selection of calibration methods and calibration systems is the key to the actual measurement accuracy of the flowmeter. Gas turbine flowmeter (hereinafter referred to as“Turbine table”) is a speed-type flow measuring instrument, which has the advantages of wide range (range ratio Qmax: Qmin can reach 10:1 to 20:1), good repeatability and so on. It has been widely used in gas, petrochemical and other industries at home and abroad. Although the turbine meter itself has accurate measurement and high precision, if its calibration is not accurate enough at the factory, it will directly affect its measurement accuracy. Before each turbine meter is put into use in foreign countries, it must be strictly calibrated. The standard devices used are mainly:“Standard Gas Turbine Flow Meter”,“Sonic Nozzle”,“Bell standard gauge”,“Standard Drum Gas Flow Meter”,“Standard Rotary Vane Gas Flow Meter”etc., of which the first three are commonly used standard devices. In order to ensure its notarization and accuracy as a basis for trade settlement, it is an urgent task to improve the calibration accuracy of gas turbine flowmeters. 2 Factors Affecting Calibration Accuracy 2.1 Influence of Standard Devices Briefly introduce 3 standard devices: Standard gas turbine flowmeter has the advantages of high calibration accuracy, fast calibration speed and low cost, but over time, due to its internal bearings and other Wear of moving parts can cause changes in the performance of the standard turbine itself, thereby reducing calibration accuracy. Therefore the standard turbine meter itself needs to be calibrated regularly. And the smaller the diameter of the standard turbine meter, the smaller the flow rate of the gas passing through, and the greater the tendency of its accuracy to be affected by the wear of the internal moving parts. Therefore, when the diameter of the turbine meter to be calibrated is small (less than 100mm), it is not suitable to use the turbine meter as the standard device. The hydrodynamic principle of the sonic nozzle is: when the gas on the upstream side of the nozzle flows out through the nozzle, if the ratio P1/P0 of the pressure P1 behind the nozzle to the pressure P0 before the nozzle is less than a certain critical value (0.528 when air is used as the medium) ), the airflow at the nozzle outlet section reaches the speed of sound, and when the pressure ratio P1/P0 continues to decrease, the airflow speed remains the same, so a constant critical flow is generated in the system connected to the calibrated flowmeter, Multiply by the time used to know the number of volumes passed through the standard device. Therefore, it can be used as a flow standard device to verify the flowmeter. Under ideal conditions, the calibration accuracy of the sonic nozzle is high, but the gas is viscous, so when the gas passes through the nozzle, energy loss will occur, resulting in calibration error. The size of the error is related to the nozzle shape, geometric dimensions, surface processing quality and the Reynolds number of the gas flowing through the throat. The flow range of the bell-type standard meter to calibrate the flowmeter is restricted by the volume of the bell. When the bell jar is smaller, the number of volumes compared to the meter to be measured during the measurement is smaller. Then the random error will increase, which will affect the calibration accuracy of the large flow test point of the turbine meter. Let the volume of the bell jar be V capacity and the falling time is about 1 minute, then the maximum flow rate that can be tested: Qmax=60×V capacity (m3/h) In addition, the factors that affect the calibration accuracy of the sonic nozzle and the bell jar standard package are the uneven temperature of the gas in the container in a short time, and the water content of the gas is too large. Environmental temperature, humidity and pressure changes, etc. Knowing the characteristics of different standard devices, you can choose the appropriate standard device in the actual calibration. Select a high-precision standard device as far as possible, because the accuracy of the standard device itself and operating procedures directly affect the calibration accuracy of the turbine meter to be tested. 2.2 Influence of calibration pressure and calibration temperature 2.2.1 Flow characteristics of turbine meter When the flow rate is greater than the starting flow value, with the increase of flow rate, the rotational angular velocity of the turbine will also increase. In the measurement range, the resistance torque T generated by the fluid will become the main factor affecting the characteristics of the flowmeter. Relatively speaking, the mechanical resistance torque generated by the friction of bearings and other mechanical transmission components is relatively small.

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