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Coke Drum Antifoam

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    4 drums coker

    Breakout Session 2  Wednesday 10/24/2012
    Facilitators: Evan Hyde, &  Ryan Koshykowski, CCRL
    Coke Drum Antifoam (AF)

    • Injection Point
      • Typically 180 degrees opposed from drum vapor nozzle to minimize reentrainment.
      • Typically a separate nozzle on the drum but can be incorporated into the PSV header nozzle.
      • Limited cases of AF injection nozzle horizontally oriented on the vertical side of the drum.  Effectiveness unknown.
      • Typically does not include any nozzle but is just an open pipe. 
      • Some indicated they had a nozzle but the type and opening was unknown.  Concerns about plugging limit the nozzle design
      • Steam purge is needed to keep this nozzle free of coke.  Some had restriction orifice and left the steam on all the time.  Some had just a block valve and stopped steam when the drum was offline.  In this case, one must ensure this block valve is opened every time, procedurally. 
      • Some expressed concerns about steam atomizing the AF and carrier causing increased carryover. 
      • Injection Rate and Time
        • One data point of 350 ml/hr AF injection was recently reduced to 50 ml/hr with no change in perceived effectiveness. 
        • Effectiveness was evaluated but measuring the time between the first k-ray signal, dosing with AF, and return of the signal.
        • Effectiveness can also be measured using distillation tower gamma scan vendors with stronger sources than continuous level drum instruments.  These sources can discern coke from foam and measure the antifoam effectiveness directly.  But this can be expensive.
        • Typically injected with carrier only 3-4 (some 6+) hours before the switch.  AF is started when the level signal is stong and consistent at the k-ray but varies for continuously level designs.
        • 60k cSt is used widely with the operators present but some were considering going to 600 cSt. 
        • General
          • No one knew why we used Silicon (siloxanes) in this service.
          • ExxonMobil patent for using ultrasonic destruction of foam.  Unknown if the technology has been tried in the field.


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