Dear teachers, questions regarding electromagnetic flowmeters

1 It is possible to consider removing it in order to clean the electrodes. 2 Does it have a function for adjusting the excitation frequency? Try changing the frequency to see the effect.

I think it’s necessary to check your installation location; it might be in a place where bubbles tend to accumulate. Or the medium contains some light organic components that are insoluble in water; during operation, these components accumulate to a certain extent before being carried away by the medium. In principle, the conductivity of both desulfurization lean and rich streams is relatively high. However, bubbles or components of light, insoluble water can cause interference with the measurement signal or even its disappearance, as the electromagnetic flowmeter assumes that the measurement tube is empty; in reality, this is a false indication of emptiness caused by the low conductivity of the medium. Dual-frequency excitation or capacitive electromagnetic flowmeters have a wide tolerance for changes in conductivity; the electromagnetic flowmeter from Chengde is likely to be of the lower-cost type.

1. Is the installation location correct? Can it be guaranteed to stay at full capacity? 2. Is the dielectric conductivity within the range suitable for detection by an electromagnetic flowmeter? Does the medium contain a large amount of solvent? 3. Has the detection electrode been inspected and cleaned? Is there scaling? Have you checked the electrode selection? If that doesn’t work, it’s better to switch to a better flow meter – one of imported quality

I basically agree with what was said on floor 5; the expert covered everything very comprehensively. Although I don’t quite agree that there is any issue with the installation location of the electromagnetic flowmeter. Let me explain it in simple terms. There are two reasons related to the manufacturing process: First, the amine-rich liquid forms bubbles. MDEA tends to form bubbles easily; although manufacturers usually add antifoaming agents during production, a slight amount of bubbling does not affect the desulfurization efficiency. However, it might still give misleading readings on electromagnetic flowmeters. Try using less antifoaming agent and see what happens ； Secondly, there is oil present, usually light oil. As oil has a low density, it tends to slide along the walls of the pipes. The flow velocity is slower the closer to the pipe wall, which can lead to deposition on the walls at the location of the electromagnetic flowmeter. Light oil has an almost zero conductivity, which results in the flow rate being read as zero. I think that when problems arise in a processing process, one should first look for causes within the process itself. Based on my experience, most issues with equipment and instruments ultimately stem from problems within the process itself; therefore, replacing instruments should be considered as a last resort.

I fully agree with what was said above. I work in the field of process engineering, but I have more colleagues who work in mechanical, electrical, and instrumentation fields than those in process engineering. In my opinion, when problems arise, those working in process engineering should first look for issues within their own area of work. Based on my experience, most problems with equipment and instruments ultimately stem from issues related to the process itself; therefore, replacing instruments should be considered as a last resort. Many times, it’s not really due to electrical issues, instruments, or equipment. The process team should indeed rule out all possible causes they can think of; if no solution can be found, then the matter should be reported to the mechanical, electrical, and instrumentation team for handling. Although it’s a support workshop, it’s still hard work for the brothers and sisters. The mechanical pump at the bottom of the pure methanol tower, manufactured by Calit Ebara, showed that during testing the liquid level in the tower bottom was normal, yet the pump’s outlet flow rate experienced sudden large fluctuations, pressure fluctuations occurred, the current value fluctuated, and there was a whistling sound at the site. Close the outlet; it will fix itself in a bit. Then this situation occurs again, and the cycle repeats. The same is true when switching to the backup pump. The liquid level in the tower bottom is normal, and everything at the site is in order ； The inlet filter is functioning properly ； The outlet control valve of the pump is functioning properly ； The minimum return line is functioning normally ； The pipelines on site are normal. So they called in maintenance workers who spent day and night disassembling and repairing the two pumps, but the problem persisted. The DN350 field stop valve, outlet valve, and return valve need to be opened and closed, and the pump body is quite large. As a result, the three inspections and four adjustments were not properly carried out; local and remote level gauges were installed on the reboiler side. There is a baffle on the reboiler side of the tower bottom, so the liquid level remained normal, while there was always a possibility that no liquid would be available at the pump inlet for pumping. The maintenance brother was furious. . . . In fact, this is a typical situation; anyone familiar with such issues can immediately suspect that there is a problem with the pipeline at the inlet of the pump. But at that time, the process engineers conducting the tests trusted the instruments too much (even though they were indeed showing correct readings), and thus ruled out simple process-related reasons for this common operating condition of centrifugal pumps.

Are there bubbles in the medium? Impurities with low conductivity? Is the electrode contaminated or damaged? Is the installation location accurate?

Remove the electromagnetic flowmeter, clean the electrodes, check whether there is any bulging in the fluorocarbon coating, then examine the condition of the excitation coil (the resistance value should be normal, around several dozen ohms), and also check if the electrodes are in good contact with the ground. And whether there is electromagnetic interference in the surroundings.