May 23, 2016 at 5:33 pm #21639
Paul R OrlowskiKeymaster
Submitted by CARMEN BELLO
FCC PROCESS ENG. AT PDVSA
Hello everybody!, Recently we started our FCC unit turnaround. When we opened the regenerator, all the secondary cyclones diplegs were fallen. All of them broke up in the middle bracing. We never observed catalyst losses higher than 5 T/d. Have you ever seen something like this in your units? Is it possible to not have catalyst losses without secondary diplegs?
Joao Eduardo Karam Hi Carmen, at one Petrobras RFCCu, we have the same event in 2006, 4 regenerator secundary cyclones dipleg broken (there are 12 on total). Before that, on normal operation the catalyst losses don´t increase so much, because the ammount of catalyst on secundary cyclone is very low. The failure of the dipleg is because high stress on the bend by excessive vibration of the dipleg. We increase the mechanical supports to the regenerator wall.
In our case we have 10 secondary cyclones …all diplegs fallen …. do you have a vortex stabilizer in the secondary cyclones ?
Darryl James Carmen
Darryl James FCC Inspector
you won’t see the losses as mentioned by Joao the catalyst is low and will only vent into the cat bed. Erosion of the 2nd stage cone to dip leg is very common and some times missed in some plants due to access inside and out. Due you have vortex breakers?
Are your dip legs broken high at the cone or lower down? If the dip legs are damaged within the fluid bed there will be no loss in efficiency as the dip legs will be sealed.
Claus J. Mielicke
Sen. Proc. Eng. at MiRO GmbH & Co. KG
I fully agree with George Blairs comment. If the diplegs are broken within the bed, there should be no high losses. If they are broken above the upper bed Level below the cyclone there should be a short circuit with higher losses direct from the bed into the outlet tube.
Principle Process Engineer at BP
The catalyst loading to the secondary cyclones will depend on the unit configuration. If you have some sort of primary separation device (like a UOP High Efficiency Regen) then the loading to the second stage cyclones should be lower than it would be for a bubbling bed regenerator. The same type of situation might exist if you have a high cyclone inlet location relative to the transport disengaging height.
As George Blair implied, if your secondary diplegs run submerged in the catalyst bed, and the failure was below the bed level, then the bed may be providing the seal on the diplegs in operation. In that case the losses might not be evident during the run, you just might see higher losses on start-up.
Most often secondary diplegs fail just below the dust bowl due to erosion from the vortex in the cyclone. This location is usually above the catalyst bed and will usually result in an increased losses due to the cyclone pressure profile.Show less
Thank you everybody for your comments … the level of the bed didn’t reach the part of the dipleg which was broken …I mean the dipleg was not cover … the dipleg broke up after the middle bracing , to cover this height we must have 8 meters and our normal bed level is 6 meters … and yes we have vortex stabilizer in the secondary cyclones Show less
None the cone of the cyclone or any part of the body suffered damage just broke up the dipleg
Anuar Alexei Jimenez Garcia
Superintendente de construcción en USA Technologies de Mexico S.A. de C.V.
hello carmen if I play observe a case where the loss was considerable catalyst in catalytic plant in Mexico for which they had to make several arrangements cyclones to reduce losses and operate the plant normally.
Stephen Forry Carmen
General Manager at Emtrol-Buell Technologies
In our experience it is highly unusual for the diplegs to break in the location that you have described. It would be useful to understand if the diplegs eroded from the inside or if they broke due to fatigue or a manufacturing defect.
Rama Rao Marri
FCC Technology Manager at CB&I (Lummus)
I agree with Steve. It also could be a case of thermal/ stress related issue. Do you have 3rd/ 4th stage cyclones? It would be helpful to have some operating data, bracing details such as slots direction/ opening/ position, etc
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