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Injecting DMDS to coker heater

Home Forums Coking Injecting DMDS to coker heater

This topic contains 3 replies, has 3 voices, and was last updated by  Mike Kimbrell 5 years, 11 months ago.

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  • #24578


    The question is about injecting DMDS to coker heater to prevent metal catalyzed coke formation.
    Please refer to information below,

    As far as I am understanding, our coker heater is suffering from coking issues so that run-length is decreasing recently.
    Among many causes of coke formation, catalytic coke is result from metal catalyzed coke formation.
    In HDO’s CCR unit, we are injecting DMDS(0.25~1ppm/hr) to prevent metal catalyzed coke formation in reactors.
    I was wondering this would also work for coker heater.

  • #24579

    Evan Hyde

    So far as I know, DMDS will break down at the fluid conditions in the heater, especially at the wall film temperatures. Do you have a TGA analysis on this material?

    DMDS is used to breakdown in the H2S under reactor conditions to passivate the metal. In the DCU, we have lots of H2S around to achieve a similar goal. Metal catalyzed coking is relevent to heater fouling but it is just part of the process. Crarcking, mesophase seperation, ashphaltene instability, deposition on the tube ID, and eventual coke formation are also big contributors.

    If anyone knows of research testing this out, I would love to see it…..

  • #24666


    As far as i know, the decomposition temperature of DMDS is around 900’F(482),which means it will be broken down in the H2S. H2S can work as passivation to prevent catalytic coking.
    However, we already have lots of sulfur in the feed which can also work as passivation of metal surface.
    Are there any other concerns if you inject more DMDS?
    Would you give your e-mail address so that we can talk more in detail?

    Thank you

  • #24929

    Mike Kimbrell

    I believe that there is enough sulfur in the normal Coker heater feed to generate sufficient amounts of H2S to react with the metal surface of the heater tubes. Addition of DMDS would not increase the H2S content enough to have a significant impact on heater coking rates.

    The applications where this DMDS injection is utilized are those that do not have any sulfur in the feed. The CCR heater feed is typically desulfurized down to less than 0.5 ppm sulfur. Ethylene cracker heaters practice the same sort of sulfur passivation, but their feed is free of sulfur.

    I think the addition of DMDS will not change the Coker heater fouling rate. Heat flux is probably the most leveraging parameter on heater fouling as it controls the film temperature followed by the concentration of coke precursors in the Coker feed and the residence time at temperature.

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