How to select a gas flow meter_How to use a gas flow meter

　　How to select gas flow meter

　　There are many types of gas flow meters, and different gas flow meters are suitable for different industries. Today, I will share with you the selection principles of gas flow meters!

　　1. The selection of flow meter is based on production requirements. It should start from the actual supply of instrument products and comprehensively consider the method of flow sampling device and the form specifications of gas flow meter!

　　2. Choose a reasonable measurement method according to the characteristics of the measured medium. According to the characteristics of the measured medium and the measurement accuracy requirements, use insertion flow meter, speed measuring element with differential pressure gauge, ultrasonic flow meter, or use marking method, simulation method and other non-loss methods to measure flow.

　　3. Pay attention to the shockproof requirements of the gas flow meter and correctly select the specifications of the gas flow meter. The pressure resistance of the gas flow meter should be slightly greater than the working pressure of the measured medium, generally 1.25 times. Ensure that the gas flow meter will not leak!

　　4. For gas flow meters installed on production pipelines and running for a long time, the energy loss caused by the flow measurement element should also be considered. Generally, multiple measurement elements with large pressure loss, such as throttling elements, should not be selected in the same production pipeline.

　　How to use gas flow meter

　　Application of vortex gas flowmeter in cement industry

　　Various flow meters are widely used in industries such as chemical, petrochemical, steel, electric power, heating and water treatment to measure the flow of various liquids and gases. As the application of flow measurement in the industrial field continues to advance, various new types of flow meters are no longer new things in the market. They are named with different modified terms according to the measurement mechanism, such as Coriolis, ultrasonic, electromagnetic, and vortex flowmeters. Compared with traditional volumetric, venturi, and mechanical orifice flowmeters, new flowmeters have more unique characteristics and are significantly different from old flowmeters in terms of accuracy, reliability, frequency, and maintainability. In these devices, there are few or no moving parts that are prone to wear; most of the flowmeters are non-invasive components, with smaller pressure drops and better safety; many instruments are equipped with microprocessors, which can perform self-diagnosis and other functions, thereby providing users with real-time feedback and historical data collection.

　　The measurement mechanism of swirl gas flow meter is used for material measurement

　　In the cement process, raw materials, intermediate wastes and final products are all solid, and mainly in granular and powdery form. The flow measurement of these materials in cement plants is achieved by electronic belt scales and various solid flow meters, which are both process equipment and passive equipment, but do not belong to flow meters. In recent years, some foreign companies have used the measurement mechanism of new flow meters such as Coriolis and ultrasonic for metering scales. The most typical example is the Coriolis scale developed by the German Schenck Company using the mechanism of Coriolis force to measure fluid quality. It is used to measure coal powder. Compared with other coal powder metering scales, it has the characteristics of simple structure, high control accuracy, and integrated metering and transportation. It is now widely used in my country's cement industry. Some foreign companies have metering scales that use Coriolis force, but most of them are not as good as Schenck's products in various aspects.

　　The open channel flowmeter is suitable for open channel, culvert and river measurement. It is suitable for circular, rectangular, trapezoidal and other shaped channel measurement. It is not affected by river water level changes, tides and high and low water level changes.

　　The open channel flow meter uses a simulation sensor (diversion model) to expand the flow measurement range.

　　Submersible electromagnetic flowmeter (open channel flowmeter) is used to continuously measure the volume flow of conductive liquid in open channels, culverts or pipelines. The MGG electromagnetic flowmeter has been widely used for flow measurement in urban water supply and drainage, industrial wastewater discharge, sewage treatment, farmland irrigation and other departments.

　　Gas flow meter use precautions

　　1. When the working conditions of the instrument change (such as changing the medium, the ambient temperature changes greatly, etc.), the zero position of the instrument should be readjusted. At the same time, the instrument's conduit must be installed horizontally and calibrated with a level. Otherwise, the impact of the change in working conditions on the zero drift will increase. The frame must not vibrate or sway, so it is not suitable for use on ships.

　　2. A large amount of test data in the range of 0-100kg/cm2 pressure and 0-7 standard liters/hour flow (air) is correlated and calculated using the least squares method to find the linear regression equation. The correlation coefficient λ is in the range of 0.999-0.9999, proving that the instrument has good linearity. However, the linearity and range size are related. The larger the flow rate, the more serious the nonlinearity. Therefore, the range is generally limited to 0-4 standard liters/hour (air) to ensure good linearity. In order to measure large flow rates while ensuring linearity, the flow splitting principle can be used to expand the range of the instrument. If bypass pipes, Venturi tubes, orifice plates, etc. are used in combination, the range can be expanded to tens, hundreds, thousands of standard liters per hour, and even tens of thousands of standard cubic meters.

　　3. Although the specific heat of real gas varies with pressure and the fluctuation range of some gases is even relatively large (see Table 1), the measurement accuracy of the instrument can still be maintained within a certain range (see Table 2).

　　4. In addition to considering corrosion resistance, it is better to choose materials with good thermal conductivity when choosing the material of the conduit. Taking nitrogen as an example, the measurement accuracy of nickel tubes is 2-2.5% and that of stainless steel is 3-4% (the thermal conductivity of nickel is about three times that of stainless steel).

　　5. Since the gas flow meter can only work normally when the gas specific heat is relatively stable, it is not suitable to use this instrument when the gas composition is unstable, the gas has mist in the center, and the working conditions are close to the critical zone of gas liquefaction, because the specific heat value is very unstable. For example, the critical point of ethylene liquefaction is 50 kg/cm2 and 9.9℃. When the pressure exceeds 30 kg/cm2 during the test, the instrument reading begins to become unstable.

　　6. If you change a gas medium, you must recalibrate. In the manual of the instrument, it is often introduced that it is not necessary to recalibrate, but only to convert the uncalibrated gas flow according to the specific heat of the two gases. Although it is simple and convenient, it will cause a large error, especially when working under high pressure. We found that the sensitivity of the instrument is not completely proportional to the specific heat. It is better to recalibrate the meter.

　　7. This instrument must be preheated before use. Before it is fully preheated, the instrument will be unstable. For better models, the preheating time is within two hours.

　　8. During use, when the gas flow rate suddenly changes, the temperature in the tube must be redistributed through heat transfer, so it takes a certain amount of time for the output signal to stabilize again. In order to reduce this lag phenomenon, manufacturers often add a differential network to the electrical circuit of the instrument to make the output signal respond quickly. This is especially necessary when cooperating with other instruments for flow rate automatic control.