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A wide variety of flow measurement products, according to the most widely classified can be divided into: positive displacement flowmeter, differential pressure flowmeter, float flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter and mass flowmeter. Various flow meters have their own characteristics. There is no measurement method or flow meter can adapt to a variety of fluids and all kinds of flow conditions. Different measurement methods and structures require different measurement operations, methods of use, and conditions of use. Each type of flowmeter has its own advantages and disadvantages. Therefore, based on a comprehensive understanding of various measurement methods and instrument characteristics, select the optimal flow measurement product that is suitable for specific production features, which is safe, reliable, economical and durable. .
1 Comparison of Differential Pressure Flow Rate Measuring Plates and Constant Velocity Tubes 1.1 Types of Differential Pressure Flow Measuring Devices Currently, the most widely used industrial measurement is differential pressure flow measurement. The mainstream of differential pressure type is throttling (holes). Boards, Venturis, etc.) and Dynamic Pressure Heads (Average Speed ​​Tubes).
The use of differential pressure principle for flow measurement is the most classic and reliable flow detection method in engineering today. Differential pressure flowmeter is based on differential pressure, known fluid conditions, and test pieces and pipes that are installed in the flow detection device installed in the pipeline. Geometry to calculate traffic. The differential pressure flowmeter consists of a primary device (test piece) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flowmeters are usually classified in the form of test pieces, such as orifice flowmeters, venturi flowmeters, and constant velocity tube flowmeters.
The greater the differential pressure generated by the flow detection devices in the pipeline, the more beneficial the differential pressure transmitter selection and cost, as well as the accuracy of the measurement. However, since the flow rate measurement device generally selects the shrinkage ratio (orifice, nozzle) according to the flow rate, the differential pressure increases and the pressure loss increases. The increase in the permanent pressure loss in the pipeline makes it necessary to increase the power of the pipeline, which requires high-powered fans, pumps, etc., which increases the energy consumption and increases the operating costs of the entire system. The representative product of differential pressure flowmeter is orifice plate, because people are very familiar with its installation, use, and overhaul, and the orifice plate is easy to copy, simple, firm, stable and reliable performance, long service life, low price, so long-term application universal. However, the long-term use of the orifice plate will result in a sharp drop in accuracy, requiring periodic inspection and cleaning.
1.2 Measurement principle of the equal flow tube flowmeter The average flow tube flowmeter replaces the cross-sectional flow velocity of the orifice plate by measuring the flow velocity at a certain diameter. With the constant development of the cross-section technology and the opening technology of the constant velocity tube, its measurement accuracy is continuously improved. Xi'an Sanlian Measurement and Control Technology Co., Ltd. introduced the Delta Bar equal flow tube flowmeter with a streamlined tubular design. The flow detection is performed by inserting two rows of unevenly distributed pressure taps on the constant velocity tube inserted in the media pipeline to detect the fluid. The resulting differential pressure results in an average differential pressure resulting from the average flow rate and transmits the differential pressure through the interface to the transmitter. Through a plurality of uneven pressure holes, the average flow velocity in the pipeline can be reflected as realistically as possible. This makes it not only maintains high accuracy, high strength, and large range ratio in flow measurement, but also greatly reduces pressure loss in the pipeline. Compared with the use of orifice plates, the use of plug-in flow probes has a significant economic benefit due to the reduction of pressure loss in the pipeline. At the same time, the unique probe design can meet the requirements of small pressure loss and high differential pressure at the same time, facilitating the selection of the transmitter.
Take a single-point signal plug-in flow sensor (such as plug-in turbine, vortex, electromagnetic, etc.) to detect the flow velocity at a certain point in the pipeline, and then analyze the detection point through the flow profile on the empirical chart to infer the average flow rate. Complex conditions such as pipelines and fluids are complex and changeable. Most of them are non-fixed velocity profiles. Using a single point of measurement to replace the average flow velocity is inaccurate, leading directly to poor measurement accuracy and low repeatability.
1.3 Delta Bar Flow Probe Advantages (1) Can measure a variety of media, a wide range of applications, minimal impact on physical properties and pipeline characteristics. Diameter range can be from 3mm to 15m; high temperature and high pressure probe can work in 650°C, 28MPa steam environment, if choose S3 type probe, its working temperature can be as high as 1040°C; S4 alloy steel type probe can also be selected, working in SO , SO2 gas or strong acid and alkali medium.
Delta Bar flow probe can be used for: 1 all kinds of gas measurement, including air, moist gas, various gases before and after purification, high temperature gas, compressed air, primary air, secondary air, etc.; 2 various types of steam measurement, Including steam, saturated steam, superheated steam; 3 various types of liquids, including H2O, fuel oil and benzene.
(2) High accuracy, good repeatability, and large range ratio (1:30). Delta Bar flow probes are non-uniform openings and open points are based on computational software complex calculations. Manufacturing parameters are determined based on pipe diameter, media, and major process parameters. The improved measurement accuracy of the probe makes the adjustment of the measured parameter more accurate.
(3) The probe is designed with pressure holes to prevent blocking. The maximum opening of the probe is 8mm. As long as the dust or particles in the medium is not more than 130mg/m3, maintenance and purging are not required. The addition of a nitrogen purge line allows accurate metering of high-dust gases such as blast furnace gas, coke oven gas, converter gas, and sintering gas in large pipelines.
(4) streamline probe cavity design, measurement signal stability, small fluctuations. The number and distribution of the pressure taps before and after are completely symmetric, and the two-way measurement can also be achieved without fear of mounting.
(5) The permanent pressure loss of the pipeline is small, and the requirement for the straight pipeline segment is low. The plug-in flow probe guarantees 1% accuracy in very short straight sections (first 4D, last 3D) and uses a non-shrink throttling design that is at least 90% lower than the permanent pressure loss of the orifice.
(6) The installation cost is low, basic maintenance free, and online installation and maintenance.
2 The use of deltabar flow probes in main steam measurement and thermal network reconstruction Deltaba flow probes are widely used, and have been widely used in 300MW/600MW large-scale thermal power units. The measurement of saturated steam at Tianwan Nuclear Power Station in Jiangsu proves more Its safety and measurement accuracy.
The delta flow probes in the main steam measurement and thermal network retrofit have their unique advantages of energy savings in micro pressure loss.
(1) The accurate measurement of the main steam flow is to meet the requirements of the unit detection and control, and the output of the steam turbine is adjusted through accurate steam measurement. The main steam flow of a general 300 MW/600 MW unit is measured by an indirect method, that is, the turbine is adjusted to adjust the pressure, and the steam is used to derive the power according to the mathematical model provided by the host manufacturer. The accuracy of the main steam flow measurement depends not only on the accuracy and accuracy of the mathematical model and the accuracy of the sensor, but also on the changes in the structure and operating conditions of the steam turbine equipment, the location of the installation of the parameter measurement points, and the representativeness of the measured parameters. The accuracy of the measurement, the calculation accuracy is difficult to meet the operating requirements.
(2) The measurement of the flow meter is the basis for the metering and charging of the heating system. Therefore, the flow meter is required to have a high measurement accuracy. In the past, orifice flowmeters and ultrasonic flowmeters were used more often in thermal network metering. Recently, deltabar flowmeters are increasingly used in heat network steam and circulating water applications. Not only because of its measurement accuracy can fully meet the measurement requirements of the heating network steam and circulating hot water, and when the pipe temperature is lower than 100 °C, the pressure is less than 1MPa, the existing pipeline can be implemented with pressure hole and installation, etc. Suitable for heating network and other technological transformation projects. The delta bar flowmeter can use the online plug-in flow probe, which meets the need for on-line demolition and maintenance of probes for long-term pipelines that cannot be stopped, and solves the problems of difficult installation and maintenance of orifices and other metering devices.
Application of Averaging Tube Flowmeter in Measurement of Industrial Power Plant
With the rapid development of the power industry, various high-efficiency new technologies and processes have been put into use. Advanced processes require high-precision control and measurement. Accurate and accurate measurement of steam, boiler H2O, gas, and air flow in boilers and turbines is one of the necessary conditions for ensuring the safe and economical operation of the unit.