How is cycling achieved in catalytic cracking – reaction and regeneration

After being regenerated in the regenerator, the catalyst enters the regeneration inclined tube. Once it reaches the bottom of the lift column, it mixes with the feed oil under the push of pre-lift steam (or dry gas), where a reaction takes place. The resulting oil and gas are separated in the cyclone separator at the end of the lift column; these oil and gas then proceed to the distillation system via the main oil and gas lines. The catalyst containing oil falls under the force of gravity into the stripping section of the settler, where it comes into countercurrent contact with stripping steam, allowing the oil and gas trapped within the catalyst to be stripped out. The catalyst that still contains oil then enters the regenerator through a plug valve (or slide valve) to be coked, thus completing one cycle. As for the circulation rate of the catalyst, it is determined through a series of calculations based on the properties of the oil supplied and other auxiliary facilities.

Thank you, it was explained very clearly

Catalyst circulation is achieved through the balance of the two vessels and the driving force of the two inclined tubes. The regenerating inclined tube delivers the regenerated catalyst to the bottom of the riser in a dense-phase bed; at the bottom of the riser, it is lifted by pre-lifting steam and then mixed with the feed oil for vaporization reaction, entering the settler in a dilute-phase bed. It is then returned to the regenerator via a slurry bed and through the raw slant tubes for regeneration. In this way, a cycle between the two devices is established. The catalyst from the two reactors is recovered through a cyclone separator. So the catalyst won’t escape. Of course, there is still some minor loss. First, it is carried away by the smoke; second, it is taken to the distillation system by the reaction gases and oils.

If solid catalysts are to be circulated between the two reactors in order to carry out processes such as reaction regeneration, it is necessary to introduce a fluidizing medium into them so that they acquire fluid properties, which makes such circulation possible. As for the prevention of mixing between flue gas and oil-gas, this can be achieved through pressure differences and material seals. As for how to determine the catalyst circulation rate during design, I don’t have an exact answer either. However, as a reference, based on the scale of the facility, the properties of the feedstock, the process scheme, and the coking rate, it is possible to determine the size of the regenerator, the amount of catalyst stored there, as well as the coking time – that is, the residence time of the catalyst in the regenerator. With these factors, it’s possible to estimate the circulation rate. Moreover, the current design oil-to-agent ratio is generally between 5 and 9; more precisely, it’s between 6 and 8. This is based on my own opinions – please don’t laugh if they’re incorrect – so let’s hear from those who are more experienced.

The circulation of the catalyst between the two vessels is achieved through the driving force before and after the slide valve; this driving force is composed of the pressures in the two vessels, the pressure drop in the dilute phase, the pressure drop in the bed layer, the pressure drop in the inclined tubes, etc., minus the resistances； Both units maintain a certain amount of inventory during circulation, and there is catalyst in each inclined tube, thereby creating a seal between the two units; as a result, flue gas and oil-gas do not mix with each other ； The catalyst circulation rate in the unit is determined by the catalyst-to-oil ratio and the feed rate, while the scale of the unit determines the processing capacity. The process employed determines the catalyst-to-oil ratio; typically, this ratio ranges from 6 to 9 in conventional catalytic cracking, and from 11 to 16.5 in DCC.

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The catalyst circulation rate is adjusted by the catalyst-to-oil ratio; that is, under a constant feed rate, the reaction temperature is controlled by the catalyst circulation rate

I’m not in the design field, and my personal views are for reference only: 1) Regarding the issue of the catalyst circulation rate. It is mainly related to the oil-to-agent ratio; in addition, the \"thermal balance\" of the reactor and regenerator, as well as the \"product control strategy\", must also be taken into account. The various parameters of the catalytic reactor-regenerator system are interrelated and mutually restrictive, so a comprehensive consideration is necessary. 2) Regarding oil and gas intermixing. The high-low parallel configuration is what was mentioned above: it involves maintaining proper pressure balance and material level. In a coaxial design, if the wall of the container is worn through, oil and gas will also mix with each other.