Analysis of Common Problems in Application of Electromagnetic Flowmeter in Acetic Acid Industry

Many acetic acid devices use flow measurement instruments such as vortex and oval gears. These flowmeters have many shortcomings: easy to wear, leaking after being corroded by the medium, short life, and large maintenance workload, it is difficult to meet production requirements. With the technological transformation of the device, a new type of electromagnetic flowmeter is used instead of the designed flowmeter. This change not only satisfies the acetic acid production process requirements, but also greatly reduces investment and maintenance strength. Therefore, the electromagnetic flowmeter in the application of acetic acid failure analysis is as follows:
1. The measurement of the presence of air bubbles in the medium The medium is inhaled from the outside or the dissolved gas in the medium is converted into a free-form air bubble, which is the two ways to produce bubble-like gas in the liquid. If there is a large air bubble in the medium, the entire electrode is covered when the air bubble passes through the electrode, and the flow signal input circuit is opened instantaneously, so that the output signal will fluctuate. Judging the cause of such fluctuations can be done by cutting off the loop current of the magnetic field. If the flow meter still shows and is still fluctuating after cutting off, it can be proved that there are bubbles in the medium that can cause the electromagnetic flow meter to fluctuate. Using an analog multimeter to measure the resistance of the electromagnetic flowmeter electrode, you will find that the loop resistance of the electromagnetic flowmeter electrode is higher than the normal resistance value.
If the electromagnetic flowmeter installation position causes air to enter the measured medium, if the electromagnetic flowmeter is installed at the high point of the piping system and the gas is stored, or the flowmeter fluctuation due to the external air intake, the electromagnetic flowmeter needs to be replaced. The location modification is installed at the lowest point of the pipeline or U-tube installation. However, in some cases, since the size of the electromagnetic flowmeter is large or the installation position is not easily changed, a gas-collection bag and an exhaust valve may be installed upstream of the flowmeter to solve this problem.
2. The medium is not full There are occasional non-full tubes in daily production. This phenomenon can be seen as a typical case of bubbles in liquids. When the electrode level is lower than the liquid level of the medium, it is ideal to use a straight pipe section before and after the flowmeter, and the measurement data is relatively stable. However, the gas volume in the upper half of the tube is also counted as the medium flow, so the measurement error is large in this case; when the electrode level is higher than the medium level, the measurement loop of the electromagnetic flowmeter is in an open state, the measured data Seriously distorted. Dealing with the failure of this medium's non-full pipe can have the following methods: Install an electromagnetic flowmeter on a vertical pipe that flows from bottom to top; in the actual production, the electromagnetic flowmeter needs to be installed horizontally. In this case, it should be installed on the pipe. The lowest end of the electromagnetic flowmeter and the axis of the electrode parallel to the horizon, in order to avoid negative pressure in the measuring tube, the flowmeter sensor should be installed in the pump downstream, upstream of the control valve; flowmeter sensor installation port should have A certain amount of back pressure should be kept away from direct discharge.
3. The electromagnetic flowmeter electrode is corroded. During the production of acetic acid, some strongly corrosive media may be exposed. When the electrode material of the electromagnetic flowmeter is not selected properly, the medium will corrode the flowmeter electrode and eventually cause the sensor to fail. So there will be fluctuations in the flowmeter output. Only when the flowmeter malfunctions after the electrode has been corroded can we find that the electrode material is not resistant to corrosion, and the performance of the material itself cannot be discerned before it is used. Therefore, only replace the new electrode to solve this problem. Therefore, the electrode corrosion failure judgment processing belongs to the method of post-maintenance processing.
4. The nature of the liquid to be measured leads to a measurement failure If the conductivity of the measured medium is reduced, the output impedance of the electrode will increase. At this time, the input impedance of the converter will cause a load effect, and the flowmeter will produce a measurement error. If the electromagnetic flowmeter appears this fault, then only select the low-conductivity electromagnetic flowmeter that meets the requirements, or use an orifice flowmeter or other principle flowmeter.
5. Measurement variability due to deformation of the flow meter lining The lining of the electromagnetic flowmeter is generally made of fluoroplastic, so that the lining of the flowmeter is easily deformed and metering failure occurs. There are two main reasons for the deformation of the lining: thermal diffusion of the fluoroplastic lining into the steam, usually the lining material, thickness, temperature difference inside and outside, and the type of fluid and steam, pipeline pressure and many other factors determine the degree of penetration; Depending on the process structure of the fluoroplastic lining material, PTFE is generally used as the fluoroplastic lining material. The non-adhesive force of the PTFE material is only combined with the wall of the pressure, so the negative pressure pipeline does not use this. Kinds of materials.
6, external electromagnetic interference In the production site there are stray currents, static electricity, electromagnetic waves and magnetic fields and other interference sources. The flow signal of the electromagnetic flowmeter is very small, and it is very easy to be interfered by external electromagnetic interference, which affects the normal operation of the electromagnetic flowmeter. The so-called electric field disturbance refers to an abnormal fluctuation of the output signal after the potential balance in the flowmeter measuring tube is destroyed by noise.

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