Why is burning oil injected during catalytic cracking shutdowns?
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Why is combustion oil injected during the shutdown of catalytic cracking?
Prevent the fluidized bed temperature in the regenerator from dropping suddenly.
If the bed temperature of the regenerator is below 400 degrees, it is necessary to remove the catalyst from the bed. The temperature of the main air is only around 150 degrees; without injecting oil, the bed temperature drops rapidly once the catalyst has been removed. At low temperatures, the flow properties of the catalyst are poor, which may result in it no longer being able to function properly
It’s not necessary to spray; our device doesn’t have a spraying function； The purpose of injecting combustion oil is to raise the temperature of the regenerator bed, thereby burning as much of the coke carried by the catalyst as possible, which makes it easier to remove the catalyst ； In fact, by not spraying combustion oil and shutting off the feed, the catalyst is allowed to undergo fluidized coking in a single container; based on experience, after more than an hour of this process, most of the coke on the catalyst has burned off. Even if there is some remaining coke, its impact is not that significant
The fluidity of the raw catalyst is much better than that of the regenerated catalyst; fluidization problems often occur in the regenerated inclined tubes, but rarely in the raw catalyst inclined tubes. I guess the reason for spraying burning oil to remove the sludge is to maintain the bed temperature and control the cooling rate of the two reactors (50°C per hour), with the aim of protecting the lining. This might be the set of procedures that the predecessors thought of and established, but which were later forgotten; people these days prefer to take shortcuts.
Let me summarize again: if the temperature drops and the catalyst needs to be removed as it may solidify, then burning the material is a good solution. Another point is that the furnace must be cooled in strict accordance with a specified cooling curve; this is because different materials contract at different rates, and sudden changes in temperature can accelerate equipment damage. I recall that in experiments using box furnaces, it was not possible to open the furnace door at 400°C – the temperature had to be lowered below that level first. For more detailed information, you should look into knowledge related to alumina refractory materials as well as the phase diagrams of alumina; this should help you find technical evidence to support this viewpoint.
After cutting, oil needs to be burned to maintain the bed temperature in the regenerator, to facilitate fluidized coking, and to maintain the temperature during agent removal.