The accuracy requirements of vortex flow meter for steam flow measurement
There are often some error factors in the calibration and use of flowmeter coefficient, which affect the accuracy of gas metering. The following are the factors that affect the accuracy of the steam flowmeter.
1. The coefficient of the instrument itself. The accuracy of the instrument is determined by its own coefficient, and once the instrument coefficient is selected for a suitable production environment, the accuracy of the instrument is determined.
2. The gas pressure in the field gas transmission pipeline is the pulsating pressure. When measuring the pulsating pressure, the normal gas should be 1/3 ~ 1/2 of the gas meter range. Therefore, in the process of natural gas measurement, it is necessary to adjust the switching degree of the gas valve to meet this condition.
3. The influence of the medium used in the gas meter verification process on the actual situation on site. The medium used in the verification process of the gas meter is air, which is provided by the pressure fan. Although the pressure fan can provide the instantaneous change of air, first of all, due to the difference in the density and expansion coefficient of air and natural gas, the pressure effect of the pressure probe of the cyclone gas meter is also different, so it will cause some errors; Secondly, the variable pressure and variable flow flow provided by the verified medium pressure fan are not as random as the field air flow, which will also reduce the accuracy of the verified gas meter in field application.
Measures to improve the accuracy of steam flowmeter
1. The influence of too narrow straight pipe section of gas meter pipeline inlet. In some transfer stations, it is found that the straight pipe section of some gas meter inlet is too thin, and the inner diameter of the straight pipe section is less than the inner diameter of the gas meter chamber. In addition, in this situation, when there is too much gas production in the transfer station, even if the gas valve is fully open, the natural gas can not be discharged from the thin pipe section in time, resulting in a gradual increase in the pressure in the gas meter inlet pipeline, and when the pressure in the tank reaches a safe value, in order to avoid pressure in the tank, the by-pass pipeline has to be opened again. There is no metering equipment in the by-pass, resulting in the gas production measurement value in the transfer station being lower than the actual value. It also makes the total amount of gas transported outside the transfer station inconsistent with the total export value.
2. Temperature influence and solution. The working environment of the gas meter is limited by temperature conditions, and the temperature conditions are in the range of -20 ~ 55 ° C, and only in this range can the normal operation be guaranteed. Once the ambient temperature is not suitable, especially in winter, in the absence of insulation measures, the gas meter works in the case of too low ambient temperature, affecting the accuracy of the measurement, and also causing damage to the four internal parts of the gas meter. Moreover, when the temperature of natural gas in the gas pipeline is lower than -20 ° C, it exceeds the lower limit of temperature, affecting the accurate measurement of the gas meter. Usually in winter to add a winter heating pipeline next to the gas meter pipeline measures, and its pipeline package in the same insulation layer, the project cost is not high, convenient construction.
3. Steam flowmeter backflow dry gas self-consumption gas measurement. In terms of self-consumption of dry gas, the main station is equipped with automatic regulating valve of return dry gas, and each transfer station is equipped with pneumatic regulating valve. Through observation, it is found that the effect of pneumatic regulating valve of each station is not ideal after putting into use, which affects the normal gas metering of return dry gas. The main reason is that when the dry gas pressure transmitted to the main station fluctuates, the electric regulating valve of the station is also adjusted accordingly, so that the air pressure of each station interferes with each other and affects the normal gas supply. Sometimes the air pressure is too low, it is necessary to close the regulating valve and pass the pipeline, so that the gas can be normally supplied, which makes the dry gas measurement of some stations inaccurate. It is recommended to temporarily stop the regulating valve, so that dry gas directly passes through the gas meter at each station.
4. The influence of oil and water vapor in the pipeline and the solution. In the field, a large amount of water and oil mixture can often be released from the vent valve, so it is known that natural gas contains a large amount of water and oil steam, and the pressure loss of wet gas in the pipeline transportation process is greater than that of dry gas, gas meter measurement standard condition, gas flow is based on the gas equation between pressure, volume and temperature by conversion to the standard condition volume. When each team performs unit measurement, the steam pressure loss is too large due to the large steam loss in the conveying process, which results in a large difference between the total output value of each transfer station and the total output value. In addition, the probe in the gas meter is surrounded by water and oil vapor, which seriously affects the normal working environment of the gas meter, resulting in a decrease in the accuracy of the gas meter, the accuracy of the gas meter can reach 1.0 after observation and verification, and the accuracy of the gas meter can be reduced to 4.0 for a year, which is caused by some defects in the external environment and process process. In view of these conditions, the position of the gas meter in the process is appropriately raised, so that the by-pass pipeline is below the gas meter and lower than the incoming gas pipeline, so as to prevent the steam from directly flowing into the gas meter when it forms a liquid. The by-pass is periodically emptied to drain the remaining liquid in the pipe.
