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LCO Quench and Outlet Temperature

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This topic contains 2 replies, has 3 voices, and was last updated by  darsh97 6 years ago.

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  • #11566


    We are in the middle of a test run to determine yields at different ROTs. The unit’s procedures call for an LCO quench once the ROT reaches 1010F. Last week, the operators tried to put in the LCO but found the nozzles were plugged. There is steam going to the nozzles, so I’m not sure exactly how they got plugged. The current discussion between everyone is whether or not we should keep going with the test run.

    I wanted to make sure the LCO quench was more for process optimization rather than equipment constraints. I always heard that the quench is to keep the process material from cracking once it leaves the Ramshorn. The original plan is for an ROT of 1020F. Do you see any negatives from continuing to raise ROT?


  • #24140

    Paul R Orlowski

    It is OK/safe to proceed with the FCCU Rx Outlet Temp (ROT) test run.
    The LCO quench is for yield optimization.
    The LCO quench does not have any impact on the metallurgy or mechanical integrity.
    From a metallurgy/integrity point-of-view, the Rx is good up to 1050F; but, let’s use 1025F just to err on the side of safety.

    Also, the unit volume balance for your unit process conditions should be 110-112 vol%.
    The 97+% wt. balance and the 107+% vol. balance suggests that either one or both of the LPG flow-meters C3 and C4 are off.
    -comments by KP

  • #24211


    Note that LCO product will in general not crack significantly under every catalytic system/operating conditions.
    Concerning the purpose of the LCO quench, it is indeed for process optimization (even though there might be, here and there, an FCCU under severe mechanical constraint utilizing this feature to make sure a design temperature or limitation of some kind is not exceeded).
    The quick cooldown of the effluent will allow limiting the prevalence of the thermal cracking in an area where there is substantially less catalyst particles available for the hydrocarbons to undergo catalytic cracking.
    As such, there is no major risk in trying to operate without the quench.
    Note though that, beyond the expected shift in yield structure which could result in a saturation of the columns processing lighter ends or rotating machines, this will normally result in a significant increase in gasoline diolefins concentration.
    So, as usual, some precautions must be taken to ensure you will not mess with downstream hydroprocessing, if any, of with you mogas pool quality.

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