Need help – Sizing Slug Control Valves


Anyone know how to size slug control valves? What I can figure out is this:

  • Only applicable for multiphase flow and where you predict slugs will appear, ex. upstream of your slug catcher.
  • Steady state case, you want the valve fully open, if not you would be wasting energy throttling when it is not required. So, maybe you want to design a valve with 50 kPa pressure drop at 100% opening? I label this case N, for normal.
  • If your design has included sufficient room to handle a slug (ex. between NLL and LAHH), I suppose you wouldn’t need to include a slug control valve.
  • During the throttling phase, you assume the inlet stream is 100% liquid. What flowrate do you want to throttle to? Would it be the vessel design liquid flowrates? Or since the vessel design flowrates assume that liquid dump valve at 80% opening, do I use the maximum flow at 100%?
  • If you take the vessel design flowrate, what upstream pressure would you use? If you use the steady state pressure, doesn’t it make the required Cv for this case (call it S1, for slugging case 1) smaller than that required for N?
  • If you are using the results of a dynamic simulation, how would you interpret the results to use as your slug control valve design case? The reports I’ve seen give the slugging conditions, and I don’t know how they will change if the slug control valve throttles the slug. The upstream pressure on the valve must be higher than without it, but by how much?
  • Another sizing case is where you assume the inlet is 100% gas. However, I don’t think you do include this in the sizing case, as you would assume the flare control valve on the vessel would manage the vessel pressure.

4 Responses to Need help – Sizing Slug Control Valves

  1. jabbathehutt says:

    There is an methodological approach and this has been thought out by people at MSI (using Virtual Operator), Scandpower (using EDPM). For a mere few hundred thousand, you can buy the algorithm to do the slug suppression controls.

  2. Wata says:

    Jabba: Do MSI and Scand supply controls algorithms, or do they also do slug valve sizing as well. My clients may be cheap, so do you have a scheme in your left hand desk drawer for less than their cost?

  3. Alfie says:

    Currently I’m working closely with Gordon Duff who is an expert for Control valves..perhaps he can help you.
    more information please give me a buzz.
    He will be in Malaysia in this april 2009 for My International Workshop for Control valves (Practical Sizing and Selection)

  4. Jabbathehutt says:

    For this issue, the control valve sizing is the easiest bit, the more difficult issue is whether the slug is slowed to a level it actually backfloods the pipeline and then causes excessive backpressure (sometimes SD of WHP).

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