Mass flow meter application

The characteristics of a mass flow meter The mass flow meter measurement system adopts the Coriolis principle, which can not only directly measure and display the temperature and density of the measured medium, but also display the mass flow rate of the measured medium. Parameters such as density, temperature, pressure, viscosity and flow state are irrelevant. Due to the integrated design and continuous measurement, its structure is simple and reliable. The mass flow meter measurement system adopts the Coriolis principle, which can not only directly measure and display the temperature and density of the measured medium, but also display the The mass flow rate of the measured medium, the latter has nothing to do with other parameters of the measured medium such as density, temperature, pressure, viscosity and flow state. Due to the integrated design and continuous measurement, its structure is simple and reliable, and a completely linear signal proportional to the mass flow can be obtained without special calculations. In the case of liquid mixed with insoluble gas, solid-particle mixed fluid, and high-viscosity fluid, the continuous measurement of the mass flow of a variety of fluids can be carried out. There are no inserts in the tube, no interference to the flow state of the fluid to be measured, and easy maintenance. Its main characteristics are: accuracy is greater than 0.2, generally ±0.15%; there are no moving parts inside, the instrument has good stability from the factory to the use process; the range ratio is wide, which is much better than other traditional instruments; no machinery The transmission mechanism is small in size, light in weight, and easy to maintain; with the digital display instrument, it is convenient and intuitive to obtain the fluid online measurement value and fluid temperature, density and other parameters.　　 For this reason, the most advanced mass flowmeter is used as the measurement method for the main and by-products of the olefin plant. According to the actual situation of the site, the application is divided into two stages: measuring the main inter-plant liquid products of naphtha, ethylene, ethylene glycol, and raffinate; and measuring the mutual supply of liquid materials C3, C4, and C4 between the plants in the plant. C5, C6, C7, C8, propylene, etc. are all measured by mass flow meters. After years of hard work and actual operation, the 22 Huahai mass flowmeters used by the plant are in normal use and the accuracy is within ±0.2%, which meets the production requirements. At the same time, it has accumulated some experience in the use of mass flowmeters. . Matters needing attention in use Mass flow meters are generally simple in application, as long as they are installed correctly, they can be put into use after simple debugging. In daily use, you only need to adjust the zero point of the meter regularly, and there is almost no need for maintenance. Note when using: 　　 (1) When designing, choose a suitable flowmeter for the specific situation, especially to have a clear understanding of the fluid properties, such as flow, temperature, pressure, density, viscosity, etc., and select appropriate meters based on these conditions. In addition, it is necessary to use products from companies with good quality and reputation to ensure good applications. Must be familiar with the design standards; at the beginning, because we were not familiar with the design standards, in the design process, the mass flow meter (measuring medium liquefied gas) was designed after the regulating valve, which caused the regulating valve to be basically closed under the condition of low flow, so that the quality The pressure difference before and after the flowmeter is too small, and the medium flowing through the flowmeter is too small or interrupted, so that the flowmeter can not measure normally, causing measurement errors; the final solution is: know in advance that the pressure drop of the device is to a certain extent, adjust appropriately The opening of the downstream valve of the flowmeter ensures that there is a sufficient pressure difference between the two ends of the flowmeter to ensure continuous measurement by the mass flowmeter to avoid measurement errors.　　(2) The success of mass flow meter application is directly related to installation. In addition to the normal installation requirements, special attention should be paid to reducing the impact of vibration, because the mass flow meter is based on the principle of vibration, and additional vibration will introduce interference. Although the instrument has been designed with an integrated structure as much as possible to reduce the impact of vibration interference, the smallest possible external interference is undoubtedly beneficial to accurate measurement. Therefore, try to avoid vibration from pipelines and on-site environment. Add fixed piers and other methods to overcome vibration interference.　　(3) When the meter is put into use, the meter must be initialized strictly in accordance with the data in the factory calibration sheet, which is also a prerequisite for ensuring the accuracy of the measurement.　　(4) It is necessary to perform accurate zero calibration under the conditions of use during the use of the instrument. The mass flowmeter is a high-precision measuring instrument used online. The drift of the zero point has an impact on the measurement result. It must be calibrated regularly during long-term use. The key point is to calibrate the zero point on-line. After the meter is put into operation, it has been calibrated twice. From the results, there is a zero drift problem. Although the drift does not affect its actual accuracy, it also causes a certain measurement error. In this regard, the regular online calibration of the zero point should be included in the management scope of the mass flowmeter, and should also attract the attention of all users. The zero point stability of different products is shown in Table 1. (5) It is necessary to avoid situations that exceed the range of the instrument used, which will cause the measurement accuracy of the instrument to decrease, and in severe cases, it will cause the instrument to be damaged. For example, due to operations such as steam sweeping that exceeds the operating temperature range of the instrument, the detection coil will be damaged and the instrument can no longer be used. (6) The mass flowmeter has high accuracy and high price, which requires careful maintenance, such as equipping it with a high-quality regulated power supply, and conducting frequent inspections on site vibration and usage conditions to ensure accuracy. Degree and safety of the instrument. (7) Prevent artificial power off and disconnection. The method of cutting off the power and disconnecting the signal line makes the flowmeter not measure for a short time, which will cause measurement disputes. Such problems should be paid attention to. The solution is to lock the instrument box and a dedicated person is responsible for the management; in addition, the designer should consider the above problems and include such problems in the design category. Troubleshooting of mass flowmeters When measuring C3, C4, and liquefied gas, there are often two phases of gas and liquid, which are mostly caused by process reasons. Therefore, before checking the failure of the instrument, you should investigate the process first, and the common failures of the instrument itself And the processing method summary.