What issues should be considered when changing hydrocracking from a single pass to a full cycle (with recycled oil fed into the refining reactor)?
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Due to the current shortage of fuel in the country, the factory requires more diesel, so it is necessary to change the one-pass process in cracking to a full circulation system. However, for various reasons, the circulated oil can only be fed into the refining reactor. What are the disadvantages of this approach compared to the usual practice of feeding the circulated oil into the cracking reactor? (Our original process was a single-stage, sequential one-pass system.) In my opinion, 1) the space velocity in refining increases, which affects the quality of refinement; 2) it leads to an increase in pressure drop across the first refining bed; 3) the hydrogen-to-oil ratio in the cracking stage decreases. Please help add more points!
You’ve analyzed it quite comprehensively. If there’s no other way, then the only option is to reduce the processing capacity. As for the device, as long as it’s economically feasible and there are no technical issues, that’s fine.
The subsequent fractionation is designed for a single pass; if it is changed to a full circulation mode, the fractionation will become difficult to operate. If a change is necessary, the amount of fresh feed must be reduced.