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Downcommer Rating?

edited September 2016 in Usage

I'm sure it's in the achieves somewhere but does anyone know offhand how much liquid a standard downcomer can shed? Is there some guidelines around their rated use somewhere?
Power or flow rates??

Comments

  • no idea, but I can tell you that in a 4 " column 3x procap plates will shed liquid up to 8580watts of input power and reflux set at 174f output. above that level it floods the top plate slowly.

    the same is true of my old mile-hi perf plates with 1/2" downcomer.

    maybe that will help you reverse figure the data you are asking for.

  • Thanks for the input but I was considering them for perf plates on a continuous stripper, not really interested in procaps.
    So about 8kW for a single cap?

    Q/L=m
    Q=8000 W
    L=838 J/g
    8000/838=9.55g

    ρ=0.789 g/cm3
    9.55*0.789=7.5ml/sec

    Is that constant with others?

  • edited September 2016

    @jacksonbrown said:
    ρ=0.789 g/cm3
    9.55*0.789=7.5ml/sec
    9.55/0.789=12.1ml/sec

    Is that constant with others?

    That's a bit better. About 40 l/h.

    But did I understand you right?

    @Fiji_Spirits said: the same is true of my old mile-hi perf plates with 1/2" downcomer.

    That's 8kW of reflux going through a single SD standard cap?

  • edited September 2016

    no each PLATE has 3 caps on it. I have 11 plates total with a super RC and lots of PC cooling.

    My perf plates have 3/32" holes and one 1/2 downcomer per 4" plate. the holes in my mile hi plate are larger than the SD stainless perf plates i have, and it handles MUCH more vapor. they seem to be equivalent in flow with the procap plates so I leave them in the column.

    If i put the SD perf plates back in, i'll drill minimum half the holes to the larger size first.

    I've had good luck with perf plates. when they work right, they work well.

    I dont think you'll be able to push anything near 40l/hr at useful ABV with a 2 or 4" column. I think (based on my setup) the 4" category will max out at around 10L/hr and you'd need at least 15 plates to even get close to that.

    I can put as much at 15Kw into the boiler but I'm already flooding above the 8500W range. Above that my vapor temp above the RC jumps dramatically if I try to stop flooding by reducing RC cooling, and my ABV drops as a result. I think I could increase my takeoff speed at azeotrope if I added another 3-4 plates.

    you need column rectification as well as vapor speed to get take-off speed at high ABV.

  • I'm not sure you're gettin' what I'm puttin' down.
    I just want to know how much liquid can pour through a standard downcomer before it floods. Not interested in take off rates etc.
    I'm pouring wash directly down a column in a continuous still.
    I thought you were giving me the max power at 100%RR before flooding started on a single downcomer, that's why I worked out the liquid volume.
    I'm trying to ball park some throughput, residence time figures.

  • edited September 2016

    Sounds like a job for (insert booming voice here) Empirical Man!

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

  • Nothing beats gathering the data yourself @jacksonbrown.

    It would be a pretty cheap exercise to construct a single plate test rig, using an SSR or similar you could dial up the power until you hit the flood. Repeat as many times as you needed over a range of feed strengths, temperatures and flow rates.

    I have all the parts you need to build it right here, by all means swing by and build to your hearts content.

    Cheers,

    Mech.

  • Weren't you working on a continuous stripper?
    Back burner I take it? :)

  • I think if you could use my wattage and column size to figure vapor flow then subtract my volume collected and make assumption based on my observation on the pro cap vs 1/2" down comer to figure the max down comer flow.

    Problem is that only the top plate floods and that's due to all the reflux. I have. I idea how to figure reflux rate of my column tho.

    Another way might be to figure how much back pressure a given vapor speed applies to 1/2" diameter tube. Then figure how much a 1/2" tube flows at the pull of gravity and subtract the first from the second.

    Sorry if this is not helping. I was just trying to provide some data points that might get you closer to what you want. I don't have a direct answer.

  • @jacksonbrown said: Weren't you working on a continuous stripper?
    Back burner I take it? :)

    Yeah, a little busy at the moment. That's why I have all the parts here for it. I really need a man Friday down here, someone I can rely on in the distillery that can also hold his/her own building the odd little project like this.

    I'll launch in November and I'll be looking for 2 full-time employees. I'll advertise next month.

  • I know it won't be entirely accurate, but why not just tip a bucket full of water down a column?

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

  • I can push 30 gallons a minute through my 12" pro cap column during cip.

  • @Grim, that's with a bit of added head pressure,yeah? plus still not a standard dowcomer :)

    @Punkin, I think that would work OK if there were a blank plate in it, effectively just pouring it down the downcomer. Without vapour pressure wouldn't it flow through the bubble caps (or perf plate) too. any liquid level above the cap would add to head pressure too and increases flow.

    @Fiji_Spirits said: Sorry if this is not helping. I was just trying to provide some data points that might get you closer to what you want. I don't have a direct answer.

    All good mate. If I can get the max power at equilibrium that won't flood a single downcomer then use the equation at the top it will be about right. Plate type and diameter should mater at this stage.

    @Mech, have you got your P&ID's organized? What's the feed-stock? Would you hire on a FIFO basis :D

  • 5 downcomers in a single plate, flow divided by 5?

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

  • That's why you earn the big bucks ;)

    Pouring in a constant flow rate is the next challenge. I have good flow meters here but no downcomers.
    My column has procaps in it.
    I'm a bit surprised this hasn't been dealt with elsewhere actually. There's so much content here, it's hard to get the most out of the search function.

  • No head pressure, this is pumping in above the lyne to an open condenser, gravity only.

    Real world, I think flooding due to subcooled reflux would trump pure fluid dynamics of downcomer flow rate.

  • So liquid level was at the top of the cap and not above it?

  • Ah no way, about 2 inches.

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