Centrifuge in the settler of a catalytic cracking unit

Is the settler also two-stage? Riser outlet: quick separation—coarse spinning—fine spinning. I don’t understand what the original poster means

It is likely intended to facilitate the rapid separation of oil and gas from the catalyst, thereby reducing side reactions

It turns out that sedimentators originally used a fast separation + two-stage centrifugation system. However, since only a small amount of catalyst needed to be recovered by the second-stage centrifuge, the catalyst stayed in that stage for too long, leading to coking that blocked the flow channels and thus affecting the separation efficiency. After discussions by experts, it was determined that a high-efficiency rough centrifugation for fast separation + a single-stage centrifuge would be sufficient to meet the separation requirements, which is how things are now. That’s roughly the reason, I guess.

What was said on the 4th floor is completely correct. It turned out that an inverted L-shaped quick separator was used at the outlet of the lift pipe, resulting in low efficiency in gas-solid separation. The centrifuge at the top of the settler still employed a two-stage series configuration; later, after switching to a coarse centrifuge and then continuing to use the original two-stage series centrifuge, the catalyst mass flow rate in the second-stage centrifuge was too low, leading to an excessive residence time and severe coking in that stage. As a result, a single-stage centrifuge was adopted, and years of operational experience have proven that this change was entirely correct.

It involves connecting the original fast separator with the stage 1 centrifuge; this combination is now called the coarse centrifuge, while the original stage 2 centrifuge is referred to as the fine centrifuge. In fact, it is still two-stage centrifugation, but not in series. This post was last edited by onewolf on 2009-2-26 14:14.]

I’m glad to see posts with such questions on the forum. I hope similar questions are asked often, more frequently. Clarify everyone's doubts.

It is necessary to maintain a certain line speed; too much centrifugation is not necessarily a good thing

Our factory uses two-stage cyclone separators. It seems that the information posted on floors 4 and 5 was very useful; it appears that our factory’s design isn’t perfect enough :'(

Our unit has coarse spin (a pair) + one spin (a pair). . . :lol Last edited by chengkang on 2009-3-29 20:23 ]

We also use coarse spinning combined with single spinning, but we have now found that the specifications for each single spin are inconsistent! ? I don’t know why it was designed this way; now that everything has been replaced with units of the same specification, I find that they still can’t be installed :(

These days, many systems use quick-speed classifiers combined with primary centrifuges, which work well and help reduce coking.

The oil-gas and catalyst particles are essentially separated by a rapid cyclone separator; the oil-gas contains a small amount of catalyst. By using a single-stage cyclone separator, the vast majority of the catalyst can be separated, so there is no need to invest in a two-stage cyclone separator.

The reason for not using a two-stage system is that the large pressure drop across two stages can lead to severe coking of the oil and gas, which in turn causes blockages in the legs of the cyclone separator and results in catalyst loss, affecting normal production

In the initial catalytic settlers, an inverted L-shaped rapid separator was installed at the outlet of the lift pipe; this separator utilized the principle of collision-based separation. In such settlers, the dilute and dense phases were separated – two sets of primary and secondary cyclones were used in the dilute phase. The linear velocity at the inlet of these cyclones after sedimentation was lower than that at the outlet of the lift pipe. Since the green catalyst contained oil and coke, coking tended to occur easily in the feed legs and at the connections between the primary and secondary cyclones. Later on, a coarse cyclone was directly installed at the outlet of the lift pipe, enabling rapid separation of oil and gas from the catalyst. With the use of this coarse cyclone, the concentration of catalyst in the dilute phase of the settler was reduced; since the catalyst did not burn and its particle size remained larger, one set of coarse cyclones together with one set of single cyclones was sufficient to meet the requirements. Moreover, it has now evolved to direct connection between coarse spinning and single spinning, with the installation of gas lift balance pipes to reduce the residence time of oil and gas in the settler, thereby minimizing coking.

Our unit uses coarse spinning combined with single spinning; it seems that the technology has become more advanced now

Although it’s a post from 8 years ago, I still learned a lot from it. My setup currently features four coarse spinners at the outlet of the lift pipe, followed by one fine spinner; the outlet of the fine spinner is connected to the internal gas collection chamber, while the outlets of the coarse spinners and the inlet of the fine spinner are not connected to each other. A new VQS settler has been released now. The inner cover is connected to the top rotor, and there is almost no coking inside the settler. I was wondering, won’t the inner cover coking?