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Industry Information
Compared with other industries, the electromagnetic flowmeter is less used in the cement industry
2012-3-12 9:18:20

在化工、石化钢铁、电力、供热和水处理等行业各种流量计应用十分普遍,用于测量各种液体和气体的流量。 Electromagnetic flowmeters are widely used in chemical, petrochemical steel, power, heating and water treatment industries to measure the flow of various liquids and gases. As the requirements for flow measurement in the industrial field continue to increase, various new types of flowmeters have appeared on the market. They are given different modified terms according to the measurement mechanism, such as Coriolis, ultrasonic, electromagnetic, vortex flowmeters, etc. Compared with traditional volumetric, venturi, and mechanical orifice plate flowmeters, the new electromagnetic flowmeters have more novel features, and have accuracy, reliability, repeatability, and maintainability compared with old-style flowmeters. Significant differences. In these devices, there are few or no moving parts that are prone to wear; most of the flow meters are non-intrusive components, with smaller pressure drops and better safety; many meters are available The microprocessor can perform self-diagnosis and other functions, which can provide users with real-time feedback and historical data collection. Compared with other industries, electromagnetic flowmeters have fewer applications in the cement industry. This is because the main media in the production process are material flow and airflow. In the material flow, powder and particles are mainly used. In the main process, There is almost no middle liquid stream, and the air stream also carries certain dust and passes through large pipes, which brings great difficulty to flow measurement. Although at some process points, such as the air volume in the various rooms of the cooler, the high-pressure air flow is measured, and the diameter of the pipe is not large. Generally, the traditional venturi tube can be used to measure the differential pressure, but because the measurement accuracy is low, The flow value can only be used as a reference, and it can be used to adjust the opening of the damper. Constant air volume is also difficult. At present, some production lines with a daily output of 5,000 tons no longer measure the flow of high-pressure air. flow. Therefore, in the past, flow measurement was almost a blank in the cement industry. Automation technicians often only know about temperature, pressure, level and other measurement sensors. With the increase of the scale of cement production and the continuous updating of the process, flow measurement and new electromagnetic flowmeters have also begun to be applied in the cement industry.

在早期引进的一些干法水泥生产线,国外公司提出在窑尾出口处和废气处理的大管道中检测气体流量并相应调节有关阀门,曾选用过孔板式流量计、笛形均速管流量计等,但使用过程中难度太大,由于流量测量并不影响水泥的生产,后一直没有使用。 Some dry cement production lines introduced in the early days of electromagnetic flowmeters . Foreign companies have proposed to detect gas flow at the exit of the kiln and large pipes for exhaust gas treatment and adjust the relevant valves accordingly. Flowmeter, etc., but it is too difficult during use. Since the flow measurement does not affect the cement production, it has not been used since. With the continuous updating of cement technology and scale, large-scale vertical mills have been widely used. In the process of vertical mills, it is required to determine the air flow at the mill inlet and outlet and keep the circulating air volume constant. For example, China's 3300-ton daily cement production line exported to Oman, An extraordinary company's vertical mill is used, which is required in the list of measuring points. The outlet duct diameter of the raw material mill for a daily production 3000-ton cement production line is generally about 800 mm. In the flow measurement specification, the pipe diameter larger than 200 mm is a large-diameter flow measurement. For example, using a traditional orifice plate flow meter, during operation, due to the sharp edges of the orifice plate's orifice wear and contamination, the pipe accumulates and condenses. Ash, need to be replaced after wear; orifice plate flowmeter also has the shortcomings of small range ratio, low accuracy, large irrecoverable pressure loss and other shortcomings; for large diameter pipelines need large flanges, its price, installation cost and maintenance are also a Issues of concern. In addition, the measurement of gas flow is affected by changes in temperature and pressure. It will seriously affect the measurement of gas flow, mainly in terms of accuracy and repeatability. In the cement industry, most of the measured process gases contain dust. The measurement sensor There are generally small holes in the medium. Dust can easily cause the measurement sensor to be blocked. Therefore, it is difficult to measure the gas flow in large pipes in the cement industry. There are many problems to be solved. With the emergence of a new type of differential pressure averaging tube flowmeter in the market, it has solved the problem of measuring gas flow in large pipelines. It has the characteristics of large range ratio, high accuracy, and small irrecoverable pressure loss. It can also pass various measures. To prevent the measurement sensor from being blocked by dust in the gas. This article will focus on the working principle, basic structure, performance characteristics, and applications of the new differential pressure averaging tube flowmeter. 2. The new electromagnetic flowmeter is used in the auxiliary process. The auxiliary process in the cement industry is mainly used to improve the equipment operating rate and protect the equipment. For example, the humidification and spraying of water in the exhaust gas treatment process is to increase the specific resistance of the dust, thereby improving the efficiency of the electric dust collector. In the new dry process cement plants, there are automatic water spray adjustment loops. In the water volume control, electromagnetic flow meters are installed in each plant, and some are also equipped with bundled ultrasonic flow meters, which play a very good role in monitoring and make water spray. The automatic adjustment circuit can operate normally.

2. New type of differential pressure averaging tube flowmeter: The differential pressure averaging tube flowmeter was introduced in the late 1960s. It is based on the principle of conservation of Bernoulli energy and the principle of pitot tube speed measurement. The custody speed measurement is actually a kind of plug-in flow meter that measures the flow rate of the diameter of the round pipe in the pipe or the length and width of the rectangular rhombus pipe by the principle of energy conservation. This round pipe or rhombus pipe is also commonly called a detection rod The Annubar flowmeter we often refer to is an Annubar actually a differential pressure averaging tube flowmeter, which is a name and a registered trademark. Because of its simple structure, convenient assembly and disassembly, low price and energy saving, it is often used as the preferred instrument for flow measurement in some industries for pipelines larger than 200 mm in diameter, such as the century of West-East Gas Transmission in China. In the project, Emerson's averaging tube flowmeter is used for more than 50% of the flowmeters on pipes with a main diameter of one meter. For the special gas conditions of the cement industry, if we want to choose a differential pressure averaging tube flow meter, we must consider the following aspects: 1. Provide correct flow and pipeline data. The mechanical size of the differential pressure averaging tube flowmeter is tailored according to the size of the pipeline to be installed, and its measurement range is calculated and calibrated according to the flow data provided by the process. When we choose, we must correctly provide the manufacturer with the flow data and the pipe size. The pipe size includes the outer diameter and wall thickness. 2. Select the detection lever correctly. The main structure of the differential pressure type averaging tube flow meter is an inserted detection rod. It has various forms, and its cross-sectional shape is different. There are round tubes or diamond tubes. Recently, wing, bullet, and T shapes have been introduced. Delta shape. Because various shapes of detection rods correspond to different fluid theories, if a cement plant determines to use an average velocity tube flow meter, the author recommends that only flow data and pipe size be provided. The manufacturer can determine the detection based on the measured airflow characteristics. The form of the rod and the number and location of the detection holes 3. High precision differential pressure transmitters should be selected. The differential pressure averaging tube flowmeter is based on the principle of pitot tube speed measurement, and calculates the flow rate by measuring the total static pressure. It is often used for large-caliber gas flow measurement. The differential pressure it generates is generally small, and the minimum may be only 20-30 Pa. This should try to avoid the use of impulse tubes, and choose high precision differential pressure transmitters, such as 3051. The best solution is to use a direct installation method that integrates a uniform speed tube, three valve groups, and a differential pressure transmitter. This can not only reduce the leakage caused by the use of the impulse tube, but also compensate the distortion of the differential pressure signal that is subject to changes in temperature and pressure. Such as the selection of multi-parameter transmitter integrated uniform speed tube flow meter series ProBar, etc. 3. The new flow measurement mechanism is used for material measurement in the cement process. In the cement process, the raw materials, intermediate products and final products are all solid, and mainly granular and powdery materials. The flow measurement of these materials in the cement factory is achieved by electronic belt scales and various solid flow meters. It is both process equipment and automation equipment, but it is not a flow meter. In recent years, some foreign companies have used the measurement mechanism of new flow meters, such as Coriolis and ultrasonic for weighing scales. The most typical example is the Cory developed by Schenck, a company that uses Coriolis force to measure the quality of fluids. According to Orly, compared with other pulverized coal weighing scales, it has the characteristics of simple structure, high control accuracy, and integrated measurement and transportation. It is now widely used in China's cement industry. The measurement developed by Orly claims that the indicators in all aspects are inferior to Schenck's products. 4. Ensure a certain length of straight pipe. The front piping of the differential pressure averaging tube flowmeter must ensure a straight pipe length of 7 to 9 times the pipe diameter. This data varies from 3 to 30 times in order to make the gas flow velocity in the large pipe as symmetrical as possible. It is distributed on the axis. Only in this way, only a few points of flow velocity can be used to estimate the flow through the entire cross-section. Otherwise, the flow velocity distribution of the gas in the large pipeline will be complicated, and the fluctuation of the flow coefficient K will be large. Accuracy. However, the process design of cement cannot guarantee very long straight pipes, which is indeed a contradiction. The author believes that if a certain type of averaging tube flowmeter is selected, it can be discussed with the supplier to keep the straight pipe as short as possible under the premise of ensuring the repeatability of the system. Some reports have stated that The ratio is less than 1/10, and the straight pipe length of the front pipe can be reduced to 3 ~ 4 times. 5. Repeatability and accuracy. In the automation system of the cement plant, the differential pressure averaging tube flow meter only provides the detection link of the information source at a certain process point. The gas flow information reflected by its output does not need to be an exact value, but should be It accurately reflects the change of the flow rate. For example, measuring the air volume at the mill inlet and outlet is not the exact value of the air volume. It mainly depends on the change in the process, and the air volume is kept constant by adjusting. Here, the averaging tube is required to work reliably, and the single value function relationship between the output and the flow does not change randomly, that is, the repeatability is good. Generally speaking, when the straight pipe section fails to meet the requirements, the repeatability can be 0.5%, and the error may exceed 6%. In the automation system, as a regulation and monitoring, the simple structure of the differential pressure type averaging tube flow meter has its advantages. 6. Install necessary dust filtering device. At present, although the average speed tube manufacturer claims that the problem of anti-clogging of the measurement sensor can be solved, due to the special circumstances of the cement process, the author still recommends the installation of necessary auxiliary equipment, such as dust filtering devices, to ensure the normal operation of the instrument.

也开始在水泥行业应用,而且发展的趋势看好。 With the increase of the scale of cement production and the continuous updating of the process, flow measurement and electromagnetic flowmeters have also begun to be applied in the cement industry, and the development trend is promising. In the automation system of cement factory, if it is used for regulation and monitoring, the differential pressure averaging tube flowmeter can be used for the measurement of gas flow in large pipelines. Because the large pipeline gas in the cement process contains dust, when selecting it, be sure to determine with the differential pressure equalizing pipe manufacturer that "the details are tailored and directly installed, and some necessary accessories must be determined in the order.