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8" ProCap Plate - Is 12 Caps really better than 8 or 9?

I sit and watch my ProCap plates, I can't help but think there is not enough free area between them... but I am not experienced enough to really know...

@Lloyd - did you ever try 8 or 9? (1 in the center and 7 or 8 around)


  • The center on the 8" plate is for the reflux via the flow directors.

  • Huh? only the center three ProCaps flow directors can reach the center, not the 9 outside ones, correct?

    FYI - I stopped using them, just use plate rotation.. in a dash where you could reach in and move them, maybe more useful.

    OK, correction - one slightly off center(10-15mm) ProCap, and 7 or 8 ProCaps in a circle surrounding it, so you can alternate the plates and not have to use flow directors..

  • edited February 2015

    Would probably work, but you'll hit a limit where they aren't any better than the old style caps. More caps means lower vapor speed through the tray, which is desirable. Greater the active tray area, the greater the tray efficiency.

  • The issue shouldn't be regarding the flow directors.

    The issue is the total area of all the slots relative to the area of the plate. The only reason to reduce the cap number would be if there was a increase in performance from doing so.

  • if making a 12 plate still, there is another reason.... $$$$... but the $$$$ isn't all that much in the grand scheme of things, just throwing out there that I think they kinda look crowded when they operate... heck, maybe that is a good thing... I dunno....

  • @grim said: Greater the active tray area, the greater the tray efficiency.

    I was thinking the longer you have the vapor in contact with the liquid the greater the efficiency... providing sufficient vapor was moving up the column and into the fluid bed..... Is my thinking skewed?

  • I suppose it depends what you want to achieve. My understanding is greater contact time between vapour and liquid results in more flavour removed.

    Shallow trays for flavoured product, deeper trays for neutral.

  • @Myles - That's my understanding as well, but then where's the breakpoint between # of plates to run, # of caps per plate and fluid level? In theory then, if you want more flavor, reduce the # of plates is equal to a lower level of fluid on plates, correct?

  • edited February 2015

    Optimal liquid level is going to be a function of the reflux ratio as well. Low reflux ratios may require higher liquid levels to remain efficient. The high reflux ratios we tend to run might not necessarily benefit from the additional depth. Problem is, it depends.

    The bigger problem that I've seen with deeper liquid levels, is bubble formation suffers. You go from a highly active tray regime to one where you are blowing a significantly lower amount of larger bubbles. If this happens, it's entirely counterproductive. Not sure if it's due to the backpressure of the liquid height, but I've seen situations where bubbles were only coming out of one tooth of one side of a bubble cap. Bloop, bloop, bloop.

  • It is a massive multi factor balancing act. Sort of like one of those wobble boards you stand on that pivot in the centre.

    There are so many combinations that there are no real answers. The truth is that you can manipulate your column configuration to do virtually anything - it all depends how you run it.

    Each plate design will work over a range of vapour speeds. Even using just that 1 factor you can get different products from the same plate. Then if you throw in liquid depth, slot height, even slot profile, the possible combinations are huge.

    At best the "conventional rules" are nothing more than starting points. A lot of it is just convention.

    Take even a simple thing like a slightly flavoured vodka. Not a mixer vodka but a sipping vodka. You can make it on a plated column but you can also make it in a pot still. The difference in equipment is staggering compared to a choice between shallow or deep plates.

    Pick the equipment you like, listen to the "wisdom" and then do what you have to, in order to make it do what you want it to do.

    At the end of the day only one opinion about your product actually matters. Your own. :)>-

  • edited February 2015

    @FullySilenced said: I was thinking the longer you have the vapor in contact with the liquid the greater the efficiency... providing sufficient vapor was moving up the column and into the fluid bed..... Is my thinking skewed?

    No, all a factor, but my comment on active area is more simple than you are thinking. A dual-flow sieve tray has a higher efficiency than a bubble cap tray for exactly this reason, it's nearly 100% active area. Great, but the trade off is the significantly narrower operating range.

    Efficiency is overrated anyway!

  • does it really matter what is below if I have 1" thick layer of coarse bubbles that make up the liquid/vapor interface?

  • back to the original topic... I can see how a single ProCap in an 8" plate would not be as good as 12 ProCaps... there would be a large ring of solid liquid doing nothing around the single ProCap... Now with 3 ProCaps in an 8" plate, there would be less standing liquid...

    Another way to look at it... think of arranging baby dragons without the glass... the one in the middle has a 2.5" ring around it... if we create another ring of ProCaps around that, it would be a 2.5" wide band.... with a total outside diameter of 7.5"... there is your 8" plate....

  • Another way to ask the question is "Are the ProCaps robbing emulsion area and replacing it with copper and deadspace in the downcomer" The cap itself is not 'active area', the area between the caps is active area, and if you runt it hard, 'some' of the area above the caps is active area... the area taken by the cap and above the downcomer is not active area...

  • edited February 2015

    While design and drawings would lead you to believe otherwise, I suspect that in the real world, liquid is flowing under the caps. I would find it implausible that given the tooth open area, that enough back pressure is being generated to keep the entire under-cap area free of liquid.

    If I could peer under a cap, I suspect what I'd see was a large bubble passing through the liquid, whose level would be equal with the top of the teeth, and that large bubble being broken up into smaller bubbles as they pass through the teeth of the cap and exit.

  • @grim what you just said is most likely correct. you can use caps with a high turndown ratio, a small fraction of the columns capacity. In this scenario you only use a small amount of the slot. As you increase power more of each slot is brought into use.

    Folks tend to use cap plates for flavoured product because they can run at low reflux ratios, and the other plate styles can't. The higher your reflux ratio, the more flavour you strip out. The reflux ratio is probably a bigger factor in the effectiveness of the plate, than the slot to active area ratio.

  • Just me or what when I see one giant bubble cap in an 8" to 16" column as wrong?
    I know @grim is right, there is vapor/liquid interaction inside the cap but I think the interaction is very limited compared to outside of the cap.

    @Myles said: ...The higher your reflux ratio, the more flavour you strip out....

    Totally agree with @Myles on this.
    I view a RC or, more precisely, a dephlegmator as a variable plate. Most folks count it as one distilling 'theoretical' plate but I've a mind to think it is not. I speculate that it is much more or much less than one plate because it can easily be tuned to under perform and thus be less than one plate.
    However, if it is tuned to "over perform" its one plate mandate then it has a literal trickle down effect for every plate under it, enriching each plate with a higher ABV.

  • Big Kothe bubble cap? There is absolutely a pool of liquid inside that cap.

  • Was actually thinking about some bubble caps I saw in Beijing at a fair a few months ago.
    It was a 12" column with one giant bubble cap per plate that covered about 60% or so of the plate. Looked like a huge SD regular cap except it had saw tooth slots.
    Nice looking rig but the cap kind of threw me. It left me feeling that the pretty flash on the outside had rotten guts inside.

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