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RE: Refractory Lining Damage

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#7672

Anonymous

Protecting Refractory Linings in FCC Units
 
Frequently, on a turnaround of an FCC unit, refractory linings in the major vessels and transfer lines are found to have sustained significant damage.  Repairs are time consuming, and can be difficult to effect, for example in catalyst transfer lines, reactor riser, or reactor overhead vapor line to the main fractionator. 
 
These refractory failures occur for various reasons, one of which is obviously age of the linings.  However, one of the major factors impacting refractory failures is exposure to the thermal cycle which occurs when a unit has a feed outage, and certainly the inevitable thermal cycle associated with a full unit shutdown, such as for turnaround.  Although these great changes in temperature in the unit cannot generally be avoided, there are some steps and precautions that can be taken to minimize damage to refractory linings.
 
I agree with BigBadFCC’s observations on the temperature. 
During a unit startup, when the initial heatup is usually with blower air through an air heater, it is fairly easy to achieve this heatup rate and thus protect the regenerator vessel and flue gas line refractories.  Controlling the temperature in the feed riser during initial transfer of catalyst from the regenerator is, however, more difficult, and requires close attention, and it must be stated, patience on the part of the operator. The required slow transfer is achieved by careful and slow opening of the regenerated catalyst slide valve.  The process is made easier if the catalyst temperature in the regenerator at this time is maintained relatively low, for example, 1000°F (538°C).  Also, minimizing pressure differential between regenerator and reactor to that which is just sufficient for catalyst transfer, reduces the driving force for that transfer.
 
I’m putting together a paper which will go into more detail on Rate of Temperature Change and Failure caused by explosive spalling due to wet refractory.   I’ll put a link to it here.
 
 
Bruce@CatCracking.com
 
 
 
 
 
I agree

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