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Refractory Lining Damage

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This topic contains 7 replies, has 3 voices, and was last updated by  Bill Zill 12 years, 11 months ago.

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  • #4257

    Anonymous

    During our last Cat Cracker turnaround we discovered some severe problems in refractory linings in the catalyst transfer lines.  There was a lot of downtime in fixing them and it wasn’t easy.
     
    We’d like some help with root cause and how to mitigate or at least minimize in the future.
     
    Thanks in advance.
     
    Mr. Cat Cracker,
    Setzel Yanislov
     
     
     
     

  • #7673

    Bill Zill
    Participant

    There’s a lot of contributing factors to problems in the transfer linings.  How old is your unit?  They just wear out over time. 
     
    One thing your operators can do is control the temperature swings.
     
    Some of it’s rocket science, and other methods are easy.  For example during the cooldown, GO SLOW.  When starting back up, GO SLOW.  Raise the temperature gradually. Have your engineer make recommendations, but you’ll probably want to keep the catalyst under 500 degrees celsius.
     
    Hope that helps next time,
    Big Bad FCC 
      
     

  • #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

  • #7671

    Anonymous

    You can receive the whole article on Protecting Refractory Linings in the FCC unit, by sending an email to
     
    Articles@CatCracking.com
     
    You’ll receive an automated response in minutes.  If you can’t find the article, maybe your company filters us out, or moves it to the SPAM folder.  Try adding articles@CatCracking.com to your address book to get around that, or send me an email and I’ll forward it on. 
     
    Paul@CatCracking.com

  • #7418

    Anonymous

    It was found that there was a crack open in the welded portions of the regenerator secondary cyclone. From the historical data it was found that there is no temperature or pressure surge. Can someone  tell the possible reason for this.
     
    Satheesh

  • #7412

    Lucas Revellon
    Participant

    I agree with the remarks from Bruce.  One more thing to pay attention to is the dry out procedure and making sure the relevant hold temperatures take place.  I have seen many times were operations get to excited on putting feed in the unit and from the start of the run the refractory can be compromise.  Also, slow the amount of catalyst circulation if you can.  If you have too much blast steam at the bottom of the Y that can be a problem too.  Try to use lift gas and back out steam, as the velocities with steam can damage the refractory.

  • #7384

    Anonymous

    I would ensure that any new refractory was “Vibra-cast” into place as opposed to hand packed. This is a harder process & might require more engineering, but is a much more reliable approach to refractory installation, especially in the Wye section. As far as hold periods in dry-out procedures, there are two overall concepts that would help with any type of dry-out procedure. First, no matter what the refractory company recommends for timing of temperature raises, Do not continue to raise temp. if any vapor is visible. Hold until all visible vapor/steaming has ceased, only then proceed with your heat-up for dry-out. The second is that the goal should be to reach 230 deg. F on the outside skin(metal) and hold for 8 hrs. This will ensure all moisture has been removed & will prevent any spalling, exploding, or loosening of refractory after start-up. Using gas instead of steam should not be considered in the riser for refractory conservation, if you feel your steam is doing damage, make sure your steam is dry & is superheated(let down from a higher pressure source).
     
    The FCC Kid
     
     

  • #7203

    Anonymous

    It was found that there was a crack open in the welded portions of the regenerator secondary cyclone. From the historical data it was found that there is no temperature or pressure surge. Can someone  tell the possible reason for this.

    Satheesh
     
    One possible answer for the above question is Sigma phase, methalographic replicas on the weld zone will be required to confirm or not sigma phase attack
     
    Luis Marques

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