Catalytic fractionation tower bottom liquid level
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Regarding the liquid level at the bottom of the catalytic fractionation tower, there is a statement in some technical Q&A materials: when the liquid level drops too low, in order to prevent the slurry pump from running dry, it is necessary to reduce the amount of residue fed back for reprocessing. I don’t understand why the residue amount should be reduced; it seems to me that it should be increased instead
The residue you’re referring to is likely the oil slurry after the reaction or the reprocessed oil; when the liquid level at the bottom of the tower is low, it is this reprocessed oil, that is, the residue you mentioned.
What’s meant by the technical Q&A is to stop pumping the slurry back and forth from the bottom of the tower; this way, more slurry will remain at the bottom of the tower, and the liquid level will naturally rise a bit. And you’re right in your understanding – what you mean is to increase the density of the feedstock so that more slurry is produced as a result of the reaction, thereby raising the liquid level. But it’s clear that the low liquid level occurs when reusing oil slurry, which indicates that the effect of adding such slurry isn’t very significant. Increasing the amount of slurry reused might work, but after one cycle, it might be too late; the bottom of the tower could already be empty. Therefore, stopping the reuse of oil slurry is the most straightforward solution. There are actually other treatment methods as well, but they will not be discussed here.
The previous speakers have covered a lot; under normal circumstances, it refers to re-refining and oil slurry, so there’s no need to consider too much.
When the liquid level in the reactor drops too low, raw oil is used to replenish the bottom of the tower
Re-refining increases the single-pass conversion rate; a higher liquid level in the distillation column indicates a lower degree of reaction. By reducing the amount of oil used for re-refining, it is possible to increase the reactant-to-oil ratio under the existing operating conditions, thereby enhancing the degree of reaction, resulting in less slurry and dry gas and more light oil!