Frequent fluctuations in the 600,000-ton catalytic stripping section of the coaxial system
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In the case of a 600,000-ton catalytic system in a coaxial configuration, the phenomenon is a rapid decrease in density at the upper or lower part of the raw material riser, sometimes dropping to near zero; meanwhile, the inventory in the stripping section increases, after which the density suddenly rises and the inventory in that section drops rapidly. It is now switched to manual operation; sometimes, even if the plug valve doesn’t move, it will return to normal on its own. It seems that the fluidization is poor somewhere in the riser or at the cone section, but it’s not possible to determine the exact cause. Is there a possibility of coking?
What is the differential pressure between the two devices? Does the valve opening degree change frequently? How long has it been in operation?
Inspect the plug valve on-site to see if it operates on its own. It’s not coking, right? If it were coking, it wouldn’t be able to flow downward. Is the gas section grid blocked by some lining?
We have encountered a similar situation in the past, where the thermometer sleeve in the stripping section was worn out towards the end of operation. At that time, the valve opening was abnormal; it was suspected that coking might be the cause, but it was not until production was stopped that it was found to be the thermometer sleeve in the stripping section.
Excluding pressure fluctuations and valve-related issues, apart from adjusting the loosening air in the feed line and the fluidization air for the sleeves, I think it’s only possible to figure out the rest after shutting down the system and taking it apart (operations can be difficult to predict; one has to keep trying different approaches, as different systems have their own characteristics).
Don’t rush to draw conclusions; first switch the automatic control related to the device and the two instruments to manual mode, and then observe what is causing the issue.
If it appears to be suffering from some kind of blockage, that possibility should be ruled out first; if there are no issues with the check valves, loose risers, reverse pressure differences, or the stripping steam, then it’s fine. Next, analyze the catalyst; then determine the carbon content of the reagent and the material to be treated. If everything is fine, that’s good. The grilles can get clogged--sometimes, the vertical pipes or gas sections can get worn out--in such cases, it’s advisable to have an expert come and assess the situation on site, in order to minimize downtime--this is a great time to make money. Good luck!
Our unit has experienced fluctuations in reaction temperature before; during subsequent inspections, the valve acted on its own. I think it would be advisable to check whether the valve operates on its own.
What everyone has said makes sense; it is essential to pay close attention to the differential pressure in order to determine whether the instrument is functioning correctly. My opinion is to check whether the amount of stripping steam is too high, especially the amount of stripping steam in the second stage. If it is too large, it will cause abnormal fluidization of the green slurry, poor flow downward, and piping phenomena. It can be turned down for a short time to conduct testing. Also, be mentally prepared. The standpipe is likely to develop a perforation. The flue gas meets the raw material. Check the density of the standpipe and whether pressure tapping points such as those for loose air might get worn through or broken. If the amount is small, there won’t be any major problems, but if it’s large, the risk is high; an explosion is possible. To determine this, check whether the opening degree of the valve to be sealed is decreasing; if it gradually decreases, it is likely that the leakage rate has increased as well as the wear and perforations have become worse. If there is no change, it might not be the reason in this area. For reference only