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Posts
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Hi,
I’m working in UOP Side by side type FCC unit. As you know, cyclone velocity important for monitoring cyclone efficiency. but, we have a situation that inlet cyclone velocity is about 24 m/s because of high feed rate . As I know from literature, it should be 18-21 m/s. With respect to our lab results and calculations, there is no abnormal catalyst loses. So; we are wondering about consequences of high velocity. what are the consequences of this situation?
Thanks
finwe -
AnonymousHigh velocities can cause erosion of the cyclone refractory (long term reliability issue) and catalyst breakage (thus increased losses). High velocity will also increase pressure drop in the cyclone, which can lead to dipleg backup (more likely a problem in the regenerator) and high outlet velocity (which can increase erosion at the top of the dipleg). Doesn’t sound like your velocity is all that high though. Recent designs have included 1″ thick hardface refractory to increase allowable wear between turnarounds.
What’s your turnaround interval? If it’s 3 years or less, I wouldn’t worry much. -
Agree with the last response. In five yrs or so you should be replacing cyclones or at least doing repairs on them. They will eventually erode with time if you run above the 24 number.
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Anonymouswell i know of a fccu that got ate up in 13 months due to high velocity… its not pretty or cheap… is it better not to push the velocity high or to push it till erosion occurs?
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Anonymouslyst+erosion
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AnonymousI agree with all the other post but with out knowing the specifics can’t really give a proper recommendation. You may want to run a higher Regenerator pressure if all other parameters may allow. A slight pressure increase in the Regen on a UOP design does quite a bit. Its all about the T/A interval here and whether the increased erosion/fines are okay. Another thing to consider is if your TSS system is capable of handling the fines loading and if not, will it build up on your expander blades quicker? That is if you have one. Also you may want to weigh the price of Cyclone replacement versus the extra conversion your getting from running so much more cat circulation. A small increase in feed temperature to decrease cat circ may be more profitable than gutting your entire regen on next T/A.
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In your case, an economic driver to increase feed is working against the unit reliability, so you should work very hard to demonstrate the unit reliability is in jeopardy before being able to convince your managers to reduce the feed rate.
The main risk is to prematurely erode the cyclones, which will cause high catalyst losses on the reactor side, high catalyst content on the slurry and a possible plug off of the slurry circulation. Erosion could be an issue on the reactor overhead line elbows or main column feed nozzle so watch for erosion on them too and if the safety is in jeopardy recommends against the feed increase. However, tracking erosion on this hot line is not easy, there are some companies like SES or Capstone, that might know about how to do this.
Eventually a shut down might be required to repair the damage if the economics show that the catalyst losses are to high to maintain the operation.
Finally, my recommendation is to give it a try but closely monitor all variables, specially those related to safety issues. -
Anonymouswhat is the % of catalyst loss in an fccu reactor?
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High cyclone veolcities will causes excessive erosion; leading to a shorter operating campaign length.
Erosion increases to the 4th power of velocity.
The most typical aress fpr erosion occur in the inlet sweep areas, the cross-over duct (for 2-stage cyclones)
and the dust-bowl to dipleg transition area.
Once the excessive erosion breaches the refractory, the metal shell/skin is not far behind
and catalyst losses begin to increase. -
I am not entirely sure that I understand your question. Can you please elaborate?
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Typical Cat loss is 0.03-0.06 lbs/BBL for a well designed and well operated designs
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AnonymousOne may need a long shutdown duration to repair/replace cyclone. If it is a replacement, you can understand how difficult to procure cyclones and you may end up in temperary repairs and one more subsequent shutdown in short interval for replacement .
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