How to ensure steam flowmeter accuracy measurement

　　The accuracy of steam flowmeters is one of the issues that customers are concerned about, and everyone is very concerned about its use effect. Supmea has also studied and accumulated a lot of experience in this regard, mainly focusing on the following three aspects.

　　1. Pay attention to the correct selection of steam flow meter

　　When choosing a steam flow meter, two factors should be considered. One is the range problem. The abnormal measurement of the steam flow meter is mainly caused by incorrect range when selecting the model. The steam consumption in the peak season is quite large, while the steam consumption in the off-season is very small. The difference in steam consumption is too great, and the flow range of the general steam flow meter is difficult to adapt. The flow measurement range must be clearly defined, and on this basis, a steam flow meter that meets the relevant operating parameters should be selected so that it can fully play its role. The second is the pipe diameter problem. When designing a throttling device, the nominal pipe diameter value provided by the process is basically used. In fact, there is still an error between the nominal pipe diameter value and the actual pipe diameter value, especially for coiled pipes. The nominal pipe diameter value and the actual value sometimes have a large difference, resulting in an increase in the measurement error, and the accuracy of the measurement is difficult to meet the design requirements.

　　2. Correctly install the steam flow meter

　　Any steam flow meter must be installed correctly, otherwise it will not work properly. For example, installing a steam meter near the steam outlet of the boiler, near the stop valve or pipe elbow, and at the bottom of the pipe are all incorrect installations. To correctly install a steam flow meter, five points must be achieved. ① A sufficiently long straight pipe section must be left before and after the installed instrument. ② The steam meter cannot be installed at the bottom of the entire pipeline. ③ The installation of the condenser must be highly valued. The two condensers must also be at the same level. The function of the two condensers is to condense the measured steam in the pressure pipe and make the condensate level in the positive and negative pressure pipes have equal heights and maintain long-term stability; in order to prevent the fluctuation of the condensate level from causing errors in the measurement, the effective volume of the condenser should be greater than 3 times the maximum volume change of the working space of the differential pressure transmitter used, and the cross-sectional area in the horizontal direction shall not be less than the working area of ​​the differential pressure transmitter. The system ensures good sealing and leakage is strictly prohibited; full consideration should be given to the convenience of maintenance, replacement, and purging. ④ The length of the pressure pipe is within 16m, and the inner diameter should be Φ10-16mm to prevent blockage. The pressure pipe is insulated throughout and the positive and negative pipes are kept at the same temperature to avoid errors caused by density changes. ⑤ The temperature measuring element is installed 10D away from the downstream side of the throttling device. When taking pressure on the pipeline or positive pressure pipe, if the pressure transmitter is installed below the throttling device, the pipeline liquid column value of the pressure transmitter must be corrected to improve the measurement accuracy.

　　3. Strictly regulate the operation of steam flow meters

　　(1) Instrument commissioning. When the steam flow meter is commissioned, first close the positive and negative valves of the differential pressure transmitter, open the primary valve slightly, and check whether there is any leakage in each valve, pressure pipe, etc. If there is no leakage, fully open the primary valve. Open the drain valve to drain the sewage and let the steam out, then close the drain valve. Wait for a while for the condenser and the pressure pipe to be filled with condensate before normal commissioning. The steps are as follows: ① Open the balancing valve; ② Slowly open the negative pressure valve; ③ Immediately open the positive pressure valve; ④ Pause for a while and then close the positive and negative valves at the same time; The static pressure error of the differential pressure transmitter is adjusted after step ④, and it must be carried out only when the liquid level in the condenser is consistent and balanced, otherwise it will cause a static pressure error of the liquid column; ⑤ Open the positive and negative valves again; ⑥ Close the balancing valve and start the instrument. Note that when filling the positive and negative chambers of the differential pressure transmitter with liquid, the exhaust screw on the container should be unscrewed first to discharge the gas before filling.

　　(2) Operation of the instrument. After long-term operation, both the pipeline and the throttling device will change, such as scaling, wear, corrosion, etc. The throttling device relies on the structural shape and size to maintain the accuracy of the signal. Any change in the geometric shape and size will cause errors in the measurement. The change in measurement error cannot be detected from the signal, so regular inspection of the throttling device is necessary. Due to the continuous production nature of the enterprise, it is generally carried out simultaneously with maintenance. If the geometric size does not change much, it can continue to be used, but the design data should be corrected according to the measured data to ensure the accuracy of the measurement.

　　(3) Maintenance of the instrument. Since the instrument is in a high-temperature, high-pressure water vapor environment for a long time, it is easy to cause damage, corrosion, impurity blockage, etc., so it needs regular maintenance and regular inspection. The steam flow meter should especially check whether the circular surface of the orifice plate opening is rusted and whether there is any dirt attached. It should be cleaned regularly and the orifice plate with severe rust should be replaced. When using the vortex flow sensor, it is necessary to check whether the triangular column gap is blocked by debris, whether the detection element is malfunctioning, etc.