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ProCaps vs. Regular Bubble Caps + Downcomer

This discussion was created from comments split from: Downcomers on Dash 4".

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  • So how about a heating element built into (a copper clad element, brazed onto the copper maybe?) the lowest plate, powered by a PID that senses liquid depth on the plate?

    Ow, I think I just threw my elbow out patting myself on the back.... unless it blows up, then it was NOT my idea!

  • @CothermanDistilling said: So how about a heating element built into (a copper clad element, brazed onto the copper maybe?) the lowest plate, powered by a PID that senses liquid depth on the plate?

    Ow, I think I just threw my elbow out patting myself on the back.... unless it blows up, then it was NOT my idea!

    Tough to adjust so that there is a naturally occurring gradient.

    StillDragon North America - Your StillDragon® Distributor for North America

  • steam tube 5-10 mm above the plate? only provides significant heat transfer when liquid touches it?

    have the drain from the bottom plate go to another chamber (possibly inside the still) that is heated somehow..

    a heat pipe (solid copper bar) that is immersed in the boiler liquid that heats the bottom plate via conduction?

  • ermmm... distilling 101. The longer the path of liquid on the plate, the more contact time afforded for vapor, heat and liquid to do its thing (separation & ester formation). Longest pathway is achieved by the entry and exit points (downcomers) for liquid being as far apart as possible (opposite sides of the plate). Procaps short-circuit the travel length of the liquid. Really they (procaps) behave similar to a sieve tray (which are way cheaper for a similar job). . Procaps are good for speed and volume, but they reduce heat & mass transfer capability. Sorry if this ruffles any feathers. Don't mean to.

  • @Harry said: ermmm... distilling 101. The longer the path of liquid on the plate, the more contact time afforded for vapor, heat and liquid to do its thing (separation & ester formation). Longest pathway is achieved by the entry and exit points (downcomers) for liquid being as far apart as possible (opposite sides of the plate). Procaps short-circuit the travel length of the liquid. Really they (procaps) behave similar to a sieve tray (which are way cheaper for a similar job). . Procaps are good for speed and volume, but they reduce heat & mass transfer capability. Sorry if this ruffles any feathers. Don't mean to.

    So there will be flavor loss with Procaps?

  • edited April 2015

    Kerfuffle, not ruffle.

    There is an optimal residence time for tray efficiency. You can achieve higher residence times in many ways - Reduced reflux ratio and increasing tray hold up immediately come to mind as even simpler ways to increase residence time (compared to complex tray designs). However, you can increase residence time to the point at which efficiency will begin to drop. Don't believe me? Turn off your dephlegmator mid-run and watch your take-off ABV drop. As residence time increases, efficiency falls, output ABV drops.

    Most tray designs that purport to have long liquid travel lengths completely disregard the short-cut path that exists below the bubble cap. More importantly however, is that the liquid mixing that takes place as part of a normal tray operating regime (which tends to be very active in beverage distillation), tends to short cut this as well.

    I would argue that at any point in time, the tray contents are always 100% mixed and any potential on-tray gradient that might exist is being largely overstated. Once you get past the 2nd or 3rd tray up the column, the potential theoretical gradient becomes tiny, even if you were to achieve that theoretical number.

    What further complicates this is that traditional beverage distillations are done with reflux ratios far greater than what are typical in industry. Just take a look at how few trays are used in the hobby community in comparison to the take off ABV. This can only be achieved with very high reflux rates, with the intent of short-circuiting any gradient that might exist in the column, and loading plates with the highest ABV liquid possible. Efficiency? Terrible. Take off ABV. High.

    Now, if you are arguing that there exists a required residence time necessary for a reactive distillation process to take place (esterification), I'd love to see some academic research on this. Would imagine that Fischer esterification would take place equally as well in either column given a specific reflux ratio. Less refluxing, less potential esterification. The best example I can think of here is that a rum can be made in a packed column, or in a pot still. Residence time can't be the only factor in play here.

    The comparison to sieve trays is only partially complete, it doesn't consider the fact that the pro caps retain the same turn-down ratio of a traditional cap design. The low turn-down ratios associated with sieve trays are their biggest issue in our types of operation. They are designed for one set of narrow operating parameters, and that's what you need to stay within. Unlike a traditional cap design which allows for a much wider set of operating parameters. I would not discount this as not being an important factor.

  • Either or anyway they work very well. ADI medals prove that and I know what comes from my parrot. And I'm not talking parrot. SHIT....

    Just sayin. Happy Stillin

    FS

  • so the longest residency might be the plate style where it goes from one side to the other?

    and the next shortest where it goes from the center to the outside, which is true for both a baby dragon or a huge Kothe...

    OK, anyone with a 8" bubblecap ever put all the downcomers on one side (and alternating sides every plate, of course) and compare to spreading them out?

  • edited April 2015

    Hold up on an 8" bubble cap tray is probably around 300ml per tray (7.5" ID, 1/2" liquid level, less volume for downcomers, hardware, etc).

    Given a take off rate for an 8" column is realistically 15 liters an hour (average) along with a 10:1 reflux ratio (conservative), would yield:

    150000ml reflux per hour : 15000ml take off per hour (10:1)

    150000ml reflux per hour is ~42ml per second of operation.

    Given a 300ml tray hold up, replacing 42ml per second will replace the tray contents in a touch over 7 seconds. In the case of an hour operating time, tray contents would be recycled more than 500 times.

    I would argue that reflux ratio is typically greater than 10:1, and during the start of a run the take off is significantly higher, you might see tray contents being replaced in 1/3 or 1/4 of that time, 2 seconds or so. Factor in the typical vigorous plate action, displacement of liquid by entrained vapor (which means less than 300ml hold up) and you can see why I believe plate contents are generally 100% mixed at any point in time.

    That's my cent (certainly not worth a whole 2 cents).

  • https://www.youtube.com/watch?v=00sQks-5Rn8

    Showing here a clear test column (large). To illustrate how long it takes for thorough mixing. This column has liquid flow rate of 60 litres / hr (60,000ml). When the dye is added, it takes 5 minutes to mix & distribute evenly across the tray.

    All this aside, I think we've convinced the OP that alternate side-to-side is the right way to position downcomers. Not all in line on one side as he saw somewhere else.

    As for Procaps, we'll need to see an accurate analysis comparison between products processed from the two tray cap types. Then we can judge any advantages or otherwise of procap type over bubblecap type.

  • Alright. All this theory is big fun. However, I live in Realville and have a question:
    I recently added five 4" procaps plates to my bubbler. I have two 4" additional bubble cap plates that I would like to add to the stack to have a seven plate stack for making neutral. Where in the stack would be the best place to put the two bubble plates - top, bottom, middle?

    I'm more like I am now than I was before.

  • If i push my stuff too hard i usually flood at the top...so i would say put the ProCaps on top and the standard ones on the bottom... just make sure you don't flood the top plate that has the standard caps n plate and the pro caps should be fine..

    That is where i would start if i didn't like the results i would move them to the top and try it in that configuration... It's a best guess for me as i have not mixed and matched em...

    FS

  • edited April 2015

    @Smaug agrees with that @FullySilenced. He said a procap under the deflegmater would be able to handle higher volumes of reflux than a standard bubble cap plate, especially when placed in 100% reflux.

    So, continuing down that path; a standard bubble cap on the bottom of the stack to reduce the amount of enriched reflux to the boiler/wash? Would a standard bubble cap plate located there be more prone to flooding? Would being on the verge of flooding the first plate be a bad thing?

    Gedankenexperiment - TBD in Realville in the near future...

    I'm more like I am now than I was before.

  • You can only run as fast as the slowest plate will run and reflux.. so... was my thinking anyways sir..

  • So... Hijacking this thread a bit further, in relation to entrainment with the different tray types.
    Which is the best tray type for neutral, which is best for flavoured??

  • I did some comparison runs between ProCaps and standard bubble caps. Nothing too scientific, just simple comparison.

    image

    My findings indicate the ProCaps have a wider range of operation and can exceed total output rate.
    While both columns were producing at equal rate of 4L/hr, the ProCaps produced a higher ABV than standard caps.
    And the range of operation seems to be good from well below perfplate speeds a to a bit above it.

    image

    This was standard caps versus pro, but I learned a lot from how they behaved. I now run ProCaps on all but one of my rigs, and I am very satisfied. Just my 2Cents.

    1.jpg
    800 x 600 - 103K
    2.jpg
    800 x 451 - 115K
  • I think the side flow across the plate is interesting in that it puts the lowest ABV on the plate down to the next plate... that is, after the liquid has run across the bubbles and expelled some of the alcohol vapor and absorbed some water vapor, it is 'spent' as far as that plate is concerned, so run it down to the next plate...

    short of making special plates and downcomers, a test could be to put all the downcomers on one side, and alternate sides... really think a 8" standard bubble cap plate would be the minimum to do this test....

  • Good point Michael. I am limited to 4", you, on the other hand have 8". Lets give it a try :-bd

  • need someone with regular bubble caps, I have 4 pro-cap plates...

  • I have a bunch of standard caps. Will be out of town for a while, if you want to borrow them, I can post em to ya today.

  • Oops , they wont fit pro cap plates, but if you want to malke some plates...

  • i have 2 standard cap 8" plates, but really need 4 at a minimum...

  • this has me thinking about a custom downcomer for the 8" perf plates..

  • I agree with FS @Kapea , through my experiments, I would put the standard bubble cap plate at the bottom.

  • I use regular bubble caps on a 6" plate and I've always alternated my plates so the downcommers are 180o away from the downcommers above/below. Never tried it any other way to determine the impact, figured this made sense for the best results and so just never touched it.

  • Thanks guys i really appreciate having the input from real world users and knowledgeable pros here. It dispels a lot of theory and bullshit to see real world results.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • edited April 2015

    @Harry said: Showing here a clear test column (large). To illustrate how long it takes for thorough mixing. This column has liquid flow rate of 60 litres / hr (60,000ml). When the dye is added, it takes 5 minutes to mix & distribute evenly across the tray.

    Harry,

    It's a nice video, and I completely understand your position, but my argument is that in a typical beverage distillation of our scale, at the reflux rates that are typically used, and with the column diameters typically used, the overall impact of this is minimal (real world). The video you post proves my point, not yours.

    At a tray diameter of 86" inches, we are talking about anywhere from 7 times larger than a 12" tray, and 21 times larger than a 4" tray. You could fit 350 4" columns in that jacuzzi of a column.

    In addition, 60l per hour reflux for an 86" tray diameter? I would argue that most users running 4-8" columns are running 60 liters per hour of reflux. So in reality, the slow transition speed has more to do with the specific operating parameters of that demo column, it's not comparable.

    So of course it's going to take 5 minutes to traverse that massive tray. But let's scale down their numbers, assuming a linear flow rate across the full tray. We are talking about 15 seconds to move across a 4" tray, and I would still argue that's not realistic.

    Increase the reflux rates into something that would be a bit more typical of what we would see, and you are back to the calculations I posted above. Even with alternating downcomers and flow directors within the tray, at typical reflux rates, on a 4-5 tray 4-5" column, I would argue that if you dosed the top tray with dye, you probably wouldn't go more than a few seconds seconds before the entire column showed traces of dye, probably less than 10 seconds, for sure.

    This completely ignores the local mixing impact of the spray and froth in the tray, which is absolutely non-linear. In a 4-5" column, hell even a 12" column, the a single droplet of spray can probably traverse the entire column area in less than a second. Even if you managed to get the liquid to follow a lazy-river across the tray, the spray and froth completely short-circuit that. You've got spray from all areas being sent to all areas. You've got spray flowing down the column walls. Likewise, the agitation across the tray from the bubbles is further keeping the tray contents mixed. These factors decrease as the tray size increases. They clearly state droplet height measured at 350mm in the video (~13"). This tells me that a single droplet can easily travel anywhere within a 700mm/26" radius of the source. You see?

    I'm not saying this isn't an absolutely real phenomenon, or even a potential goal. What I'm saying is that the potential impact of this is absolutely overstated in small column diameters (below 12" or 16"). In our scale, it's more realistic to assume that the tray contents are always 100% mixed and homogeneous and do not display any appreciable gradient across the tray.

    From a "reaction time" perspective, the tray reaction time is a function of the tray design (as you state), but also production volume, the reflux ratio, the number of trays, and the tray hold up volume. You can adjust any of these parameters to increase or decrease the time the liquid stays in the column. This is not a single pass process. A single molecule of ethanol could theoretically go up and down between the boiler and dephlegmator, thousands of times before it passes to the product condenser, it could be condensed and vaporized even more times than that.

  • The level of knowledge you guys have blows my mind!

  • Not to mention that the sheer nature of how fractional distillation works, as you ascend the trays, the purity and homogeneity of the tray contents is forced to increase. Which means the maximum possible on-tray gradient that could exist would only be on the first tray. As you ascend upwards, the maximum possible gradient for each tray decreases, and would decrease further as you move up the column. So even if you were to optimize a tray design for cross-flow, you would find that it would result in diminishing returns as you move up the column.

  • Thank you for that wonderful explanation @grim +1 ^:)^

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