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In our FCC, catalyst has been observed to get carried over to the fractionators during start up activity. This upsets the fractionators bottom pumps. What can be probable reasons for such carry over and how this can be mitigated?
 
Answers
15/02/2018 A: Victor Scalco, General Atomics Electromagnetic Systems (GA-EMS), Vic.Scalco@ga.com
During most start ups this is a common occurrence. The reactor and process will need time to equalize, in the meantime you can mitigate the carry over by separating your slurry rundown to reduce the cat loss. If you are using settling in the DCO rundown a consideration might be made to introduce a filtration system or Electrostatic separator to reduce the carry over in the bottom pumps. More info can be found by looking into a Gulftronic Separator or a MOTT slurry filter.
15/02/2018 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
If the startup follows a crash shutdown and your has followed procedures successfully used before, a possible explanation is that some coke or refractory has spalled off a reactor cyclone body and is blocking a cylcone dipleg - or perhaps a trickle valve has jammed closed. If the startup follows a turnaround, another possible explanation is that the catalyst stripper bed level is too high due to a faulty level indication (eg. failure to recommission instrument purge gas to the level taps).
14/02/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
We sometimes forget that cyclones operate well only within a narrow range of inlet velocity. Try to minimze the length of time of the reduced feedrate during startup.
14/02/2018 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Cat from Rx to main frac can happen only when Rx cyclones are not able to capture the fines. Get PSD done of spent catalyst recovered from bottom circuit. Also, control the fines < 20 microns in fresh catalyst at the time of buying. This also if high can lead to such. Last but not the least during startup check the cyclone velocity in Rx. Too low can lead to such. Additionally check the cyclone design as well which can be corrected, if found so, for any carry over occurring from conical portion of cyclone barrel. Good luck.