Which is more effective for reprocessing oil: reprocessing it separately or mixing it with the raw material before reprocessing?
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I have connected it to the feed tank in the re-refining section, so that it enters the lift pipe together with the feed material. Which approach yields better results – re-refining it separately or integrating it with the feed material – in terms of yield, energy consumption, etc.?
It’s better to separate them. Re-refining itself is not an effective method for cracking; the yield is low, the quality of the products is poor, and these substances have a strong tendency to adsorb onto the catalysts, occupying their active sites. When mixed together, this affects the overall yield. However, mixing them together might result in lower energy consumption, as cracking is an endothermic reaction – less coke is produced, and since less of the raw material reacts, the energy consumption should be lower
I think it’s better to recycle them separately, because the recycle oil nozzle is located above the feedstock nozzle; if they are mixed together, it becomes difficult to crack the recycle oil, which in turn affects the cracking of fresh feedstock and results in a lower overall conversion rate as well as increased formation of coke； If reprocessing is carried out separately, injecting reprocessed oil above the riser after the fresh feed has been largely cracked can act as a form of catalyst deactivation, reducing over-cracking reactions and increasing the yield of the desired product.
Agree with the person above; it’s better to keep them separate
On the other hand, when the preheating temperature of the feedstock is not high, returning the reprocessed oil to the feedstock tank can increase the preheating temperature of the feedstock, improve its atomization, and reduce coking; therefore, it is necessary to take into account the actual conditions of the plant as a whole
We have a 800,000-ton heavy catalytic cracker unit designed in Luoyang; we do not have re-refining nozzles – the re-refined oil, re-refining stones, and crude oil are mixed together in a mixer before entering the feed nozzles! Later, during maintenance, we connected the re-refining stream before the slurry re-refining nozzle. After putting it into use, the yield improved, but not significantly.
It is better to reprocess them separately, as the reprocessing oil nozzle is located above the raw material nozzle; if they are mixed together, it becomes difficult to crack the reprocessing oil, which in turn affects the cracking of the fresh raw materials and results in a lower overall conversion rate as well as an increase in coke formation； If reprocessing is carried out separately, injecting reprocessed oil above the riser after the fresh feed has been largely cracked can act as a form of catalyst deactivation, reducing over-cracking reactions and increasing the yield of the desired product.
The re-refining oil return to the feed tank line still cannot be shut down due to concerns about blockages; therefore, a slight excess flow is currently used. I’m not sure how it is in other units
Do not recycle it, as it has a significant impact on the equipment, especially on the catalysts, and can easily cause poisoning of the catalysts
It’s better to separate them; appropriately increase the pyrolysis temperature to enhance the reaction depth
There seems to be no definitive answer to this; it’s similar to the situation with separate devices, such as those between the re-refining nozzle and the fresh feed nozzle. In some cases, the fresh feed nozzle is located below, while in other cases it’s above. Each arrangement has its own rationale, and it’s necessary to consider the specific device in question.