In catalytic operations, does increasing the bed temperature after reprocessing the reprocessed oil necessarily lead to an increase?
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During one of our operations in the catalysis workshop, after increasing the amount of reprocessed oil used, the reaction temperature and bed temperature dropped significantly. When the amount of reprocessed oil was reduced, these temperatures gradually returned to normal. Upon analyzing the reasons later, the shift leader insisted that it was due to the lighter quality of the crude oil; increasing the amount of oil fed back for reprocessing should raise the bed temperature, and if the temperature did not rise, then it couldn’t be the result of reprocessing the oil. I don’t understand, because I was monitoring the process at that time, and the change in the temperature of the reactor bed after increasing the reprocessing rate was quite obvious. I would like to ask whether the bed temperature must increase after reprocessing in a large-scale refinery?
This post was last edited by mmhgb on 2011-3-7 at 11:42. At the beginning of the reprocessing process, the reaction temperature decreases while the bed temperature drops; gradually, the regeneration temperature rises as well, and the reaction temperature increases accordingly. I’m not entirely sure about the exact reasons for this, so I hope experts can explain it!
Reply to 1#: “Only through learning do we realize our own shortcomings.” It’s not that the crude oil becomes lighter! On the contrary, it’s a bit heavier. This is mainly related to the composition of the reprocessed oil. Reprocessed oil contains more aromatics than the crude oil before cracking, and it has a higher boiling point. The first step in reprocessing reprocessed oil is to vaporize it, which often requires a large amount of reaction heat. As a result, when more reprocessed oil is used for reprocessing, the required heat increases, causing the reaction temperature and the temperature of the regeneration bed to drop significantly. When no reprocessed oil is used, the catalyst has higher activity and a stronger cracking capacity. At this time, a small amount of reprocessed oil is used; as a result of the condensation reactions of certain aromatics, especially heavy aromatics, coke formation increases slightly, which leads to an increase in the regeneration temperature. When the amount of oil reprocessed is very large, the high heat demand exceeds the coking capacity of the main air in the regenerator, preventing the regenerant from recovering its full activity. As a result, both the reaction temperature and the bed temperature tend to decline continuously. If this trend is not halted, it leads to a vicious cycle, ultimately resulting in a carbon buildup accident. Therefore, the amount of oil reprocessing is not the more the better; it needs to be controlled so that the reaction temperature, the temperature of the regeneration bed, and the oxygen content in the regeneration flue gas do not drop significantly.
The 3rd floor has explained it in great detail; I’ll add a few more points: After reprocessing, the heat required for vaporization in the lift pipe increases, which leads to a decrease in the reaction temperature. As a result, the temperature of the catalyst that enters the regenerator after the reaction is complete also drops； The reaction temperature decreases, which in turn increases the opening degree of the regenerating slide valve and raises the catalyst circulation rate. Both of these factors lead to a drop in the temperature of the regenerator after reprocessing the oil, that is, a decrease in the bed temperature.