How to ensure accurate operation of gas ultrasonic flow meter

　　1. Make efforts to create conditions to complete pipeline drying. The clause "After the pressure test and pigging of the gas pipeline, it is advisable to dry it" stipulated in GB5025I-2003 "Design Specifications for Gas Pipeline Engineering" is formulated with reference to the corporate standards of Royal Dutch Shell Group and domestic construction experience. Gas ultrasonic flowmeters were used earlier in developed countries such as Western Europe, which is also the experience they have summarized through practical exploration. At present, there are not many overall drying of long-distance natural gas pipelines in China, and the word "should" is also used in the specifications, and there is no hard and fast regulation on whether to dry it. In the past, flowmeters such as orifice plates were used, and the accumulated water in the pipeline had little effect on the measurement. However, after switching to gas ultrasonic flowmeters, ultrasonic flowmeters are quite sensitive to moisture, so it is very necessary to dry the pipeline.

　　2. The selection of the separation system should take into account the treatment of liquid water. In the past, cyclone separators were mostly used in the process design of the station. Gravity separators can also be used in places with low requirements. In recent years, filter separators have also been selected. The main function of setting up separators at the first and last stations of the gas pipeline is to remove various solid particles in the natural gas. The filter separators that are now being promoted (taking the filter element blade combination as an example) can not only remove solid particles of various sizes, but also 100% separate water vapor larger than 8 to 10 μm. However, the introduction of liquid water will seriously reduce the separation effect of the separator. When setting up a separator in the station, whether it is a cyclone type or a filter separation type, it should be considered to add a liquid water treatment device in front of the separator to separate the liquid water brought in from the pipeline. The separation accuracy does not need to be too high, and a general gravity separator can be selected. Among the stations in China that use gas ultrasonic flowmeters, some have chosen the two-stage separation process mode, with good results. Issues to pay attention to for gas ultrasonic flowmeters

　　3. The filter separator should be well protected during replacement. When using the filter separator, water or rust dust in the pipe will make the filter element of the filter separator ineffective. Therefore, before replacement, it is best to remove the filter element of the filter separator. After the replacement is completed, clean the inner cavity of the filter separator before installing the filter element, which protects both the filter element and the gas ultrasonic flowmeter.

　　4. Strengthen operation management and discharge the wastewater from the separator in time. The separator is equipped with a sewage pipe to manually discharge the separated sewage. However, due to various reasons, it is likely that the sewage will not be discharged in time, the sewage in the accumulator is full, causing the separator to fail, and the liquid water will enter the gas ultrasonic flowmeter with the natural gas, resulting in metering failure. If you want to fundamentally solve this problem and eliminate the influence of human factors, you should install an automatic sewage valve on the sewage pipe of the separator to ensure timely drainage. In addition, in the early stage of production and operation, the replacement frequency of the filter separator filter element should also be appropriately increased.

　　5. It is best to use online calibration for calibration. The accuracy of the gas ultrasonic flowmeter is greatly affected by the installation environment. After the calibrated gas ultrasonic flowmeter is installed on site, its measurement accuracy will change due to changes in its installation conditions. Therefore, in the station process design, it is necessary to consider setting up an online calibration system, adding calibration pipes and valves. When calibration is required, the calibration unit can drive the calibration vehicle to the site, connect the standard meter on the calibration vehicle with the flowmeter on site in series, and complete the calibration of the flowmeter. At present, domestic units with calibration qualifications already have such calibration vehicles.

　　6. Meet the installation requirements of the gas ultrasonic flowmeter. The installation requirements of the gas ultrasonic flowmeter have been stated in the product manual. The gas ultrasonic flowmeter measures the gas flow rate and has high requirements for the concentricity of the flowmeter body and the upstream and downstream straight pipe sections. Therefore, the construction unit is required to strictly implement the installation regulations during installation to achieve the required concentricity. The installation position of the gas ultrasonic flowmeter in the station is different from that of the orifice flowmeter. When using the orifice flowmeter, whether it is pressure regulation first and then metering, or metering first and then pressure regulation, the orifice flowmeter and the pressure regulator are mostly installed in the same space, that is, the orifice flowmeter and the pressure regulator are installed between the two manifolds at the same time. If a gas ultrasonic flowmeter is selected, this installation position will have a serious impact on the metering accuracy of the gas ultrasonic flowmeter, because the gas ultrasonic flowmeter is very sensitive to noise. If it is installed in the same space with the pressure regulator, the noise generated by the pressure regulator will make the gas ultrasonic flowmeter's metering ineffective. Therefore, if a gas ultrasonic flow meter is selected, it should be installed separately on the pipeline between the two manifolds when the process equipment is arranged. If the site is small and it needs to be installed on the pipeline between the two manifolds together with the pressure regulator, a noise reducer or noise reduction pipe should be added between the flow meter and the pressure regulator.

　　7. Choose the right type of flow meter. The structural types of gas ultrasonic flow meters currently used worldwide are generally divided into two types: through-beam type and reflection type. Both probe arrangements can meet the accuracy requirements of gas trade measurement, but the applicable gas environments are different and should be selected based on the quality of the natural gas being transported. In terms of the current quality of natural gas in China, through-beam ultrasonic flow meters are more suitable.

　　8. Clean the flow meter regularly. If the solid impurities and liquids carried in the natural gas adhere to the inner wall of the flow meter or the sensor surface to a certain extent, it will affect the metering accuracy of the flow meter, which requires timely cleaning.