Column Height Vs Diameter ratio

Vapor, Liquid or Cooling Management. Flutes, plates, etc.

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Re: compact column design

Post by Lubavitcher » Tue May 25, 2010 2:35 pm

listen im sory for saying that you were trolling. but thats just how i felt. rad made some statements. kiwi asked him some questions about some contradictions. rad didnt give a answer. i re-asked the questions he didnt give an answer he just spoke about grammar. i felt offended that i would ask a question and he would ignore it... thats all
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Re: compact column design

Post by rad14701 » Tue May 25, 2010 3:13 pm

Ok, we'll give this another go...

First, Lubavitcher, some of us lend support in these forums during our work hours which means we may not always have time to give a complete answer at a given moment... I could tell by the tone of your posts that you were getting worked up and chose not to "go there" at that exact moment but did notice your attempting to steer my words in a direction I have clearly steered away from more than a few times when this topic has come up...


@ kiwistiller

No, I have never said that a 4" column would need to be twice as tall as for a 2" column... That is why the range is so broad... I have always held the opinion that larger columns than 2" would require a lower ratio than 2" and columns smaller would require a higher ratio than 2"... Your comments on vapor speed help prove that out... You are also correct in that no calculator is going to relate to accurate real life results in practical application... As I eluded to in an earlier post, due to real world parameter differences, calculator results may be no more accurate than simple ratios... We've still got to use some common sense and be willing to experiment a bit...

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Re: compact column design

Post by kiwistiller » Tue May 25, 2010 3:24 pm

rad14701 wrote: @ kiwistiller
No, I have never said that a 4" column would need to be twice as tall as for a 2" column... That is why the range is so broad... I have always held the opinion that larger columns than 2" would require a lower ratio than 2" and columns smaller would require a higher ratio than 2"... Your comments on vapor speed help prove that out... You are also correct in that no calculator is going to relate to accurate real life results in practical application... As I eluded to in an earlier post, due to real world parameter differences, calculator results may be no more accurate than simple ratios... We've still got to use some common sense and be willing to experiment a bit...
Ok. So if the ratio changes, why is it better to use a ratio, which becomes inaccurate as diameters change and generally tends to confuse people, as opposed to just talking about column height? Why bring column diameter into at all?

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Re: compact column design

Post by rad14701 » Tue May 25, 2010 3:37 pm

kiwistiller wrote:Ok. So if the ratio changes, why is it better to use a ratio, which becomes inaccurate as diameters change and generally tends to confuse people, as opposed to just talking about column height? Why bring column diameter into at all?

Kiwi
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Re: compact column design

Post by kiwistiller » Tue May 25, 2010 3:49 pm

:?
Well I think it is worth discussing if it is going to be recommended to newbies. If it can't be justified more than you seeing it in your head, maybe we should change the way we explain the requirement of column height to newbies? Maybe in terms like, column height? I've asked snuffy about it as well, he hasn't gotten back to me yet.

I'd like it if you could think on it maybe for a bit, for a day or two or whatever, and see if you can explain it to me (I really want to know). Because surely advice that can't be explained is bad advice?
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Re: Column Height Vs Diameter ratio

Post by Lubavitcher » Tue May 25, 2010 7:36 pm

HomeDistillerBible wrote:HETP (Height Equivalent to a Theoretical Plate)
eg how much height of packing is needed to get the same performance as a theoretically perfect (equilibrium) plate. I've done the estimate using Onda's method (from Coulson, Richardson & Sinnott "Chemical Engineering").

Calculate the effective area (aw) using :

where:

aw = effective interfacial area of packing per unit volume (m2/m3)
a = actual area of packing per unit volume (m2/m3)
sc = critical surface tension for the particular packing material (see table below)
sL = liquid surface tension mN/m
L*w = mass flowrate per unit cross-sectional area, kg/m2s = L'

Critical surface tension
Material

sc [mN/m]
Ceramic 61
Metal (steel) 75
Plastic (polyethylene) 33
Carbon 56

Then calculate the liquid and gas mass transfer coefficients (kL and kG) using :

where:

K5 = 5.23 for packing sizes >15mm and 2.0 for sizes <15mm
V*w = gas mass flowrate per cross-sectional area [kg/m2s] = G'
dp = packing size [m]
kL = gas film mass transfer coefficient,[kmol/m2s atm or kmol/m2s bar]
kG = liquid film mass transfer coefficient [kmol/m2s or kmol/m3 = m/s depending on whether use R=0.08206 atm.m3/kmol K or R=0.08314 bar m3/mol K]

From these you can then calculate the film transfer heights:

where:

P = column operating presure, [atm or bar]
Ct = total concentration, kmol/m3 = r L / molecular weight solvent
Gm = molar gas flowrate per unit cross-sectional area, kmol/m2s
Lm = molar liquid flowrate per unit cross-sectional area, kmol/m2s

From these you can then estimate the height of the overall gas-phase transfer unit:

where:

m = slope of the equilibrium line (I reckon its about 0.49)
Gm/Lm = slope of the operating line

Now... for a section of the packed column in which the operating and equilibrium lines can be considered straight (hey- that's almost us !), theoretical stages can be converted to numbers of transfer units by :

and then

where:

Zp = packed bed height
Nt = number of theoretical stages
this is a quote from HD im sorry all the jpegs and charts dont appear if you look through you will see that there are NO variables for diameters...why? because diameter does not affect HETP!
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Re: Column Height Vs Diameter ratio

Post by HookLine » Tue May 25, 2010 11:23 pm

The main design parameter in a reflux column is vapour speed. Design your column around that. Keep it between 300-500 mm/s (12-20"/s)*, start with 400 mm/s (16"/s) and fine tune.

*This is for small, mesh/scrubber packed columns (maybe up to 100 mm diameter). Don't know if it is true for other types of packing (eg Raschig rings), or for larger or plate type columns.
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Re: Column Height Vs Diameter ratio

Post by rednose » Wed May 26, 2010 8:56 am

If I understand the physics right, the column lenght depends on the density of the packing material to simulate a ideal plate.

If the density of the packing material is too high the column will throw out liquid instead of vapor what already happened to some Bok users, me included.

As more vapor speed you produce as wider your column diameter have to be.

In plated columns the limitation of the high is the spraying effect of the bubbles, liquid should not reach the next plate once the column is stable.

I'm just thinking with a common sense but could be wrong somewhere.

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Re: Column Height Vs Diameter ratio

Post by rad14701 » Wed May 26, 2010 10:24 am

One issue that we need to remember, in our practical application, is that the vapor speed slows throughout the height of the column because there is less vapor left by the time it reaches the top of the packed column... We aren't getting as much vapor with the same density or speed at the top as enters the bottom of the column... We have reflux, resistance, and temperature drop, to thank for that... The idea of perfect vapor speed goes out the window as soon as the vapor hits the structured packing...

I have read and re-read the section on HETP's and column design on the parent site and even after all of the calculations and comments there are still a few holes in the theory that have never been fully examined unless Snuffy has done recent research in his mad lab... While Tony, Mike, and others have contributed a lot of useful information, I don't think that any additional follow-up information has been sought...

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Re: Column Height Vs Diameter ratio

Post by kiwistiller » Wed May 26, 2010 12:58 pm

I haven't heard of vapour speed slowing before rad. do you have a link or something to that info? I thought that due to mass transfer with reflux, it would stay more or less constant?
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Re: Column Height Vs Diameter ratio

Post by Lubavitcher » Wed May 26, 2010 6:55 pm

im posting a graph i made of the data of the the hetp off of the pro pack pdf.... dont get fooled and think that this is data for alcohol. but all i want to show is how distillation data from a lab proves that HETP in not related to diameter
HETP.png
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Re: Column Height Vs Diameter ratio

Post by Ayay » Thu May 27, 2010 12:21 am

Using a column packed with mesh/scrubbers we are limited to a 2"-3" column diameter because that's how far the reflux can spread sideways as it decends in a hobby environment. A column height between 20-30 diameters for 2" -3" columns is best for a neutral at 0.3-1.0 Litres/hour. Any more (pot and strip excluded), then you are somewhere other than homedistiller.org.

If you are using plates then the sideways spread is determined by the hole locations and can go much wider.

Theory and practise mingle together and the result is what you git. Chicken an egg?
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Re: Column Height Vs Diameter ratio

Post by kiwistiller » Thu May 27, 2010 2:45 am

I've been talking with Riku and the Mike's from amphora, they say the 4" works fine with mesh. I'll be able to verify myself soon I guess :D
Ayay wrote:Any more (pot and strip excluded), then you are somewhere other than homedistiller.org.
I don't quite agree with that. I don't want to make any more, I just want to make it faster. Pot runs are interesting, reflux is a chore to me. want it over and done as fast as possible, so I can get to infusing gin with my pot still :D
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Re: Column Height Vs Diameter ratio

Post by olddog » Thu May 27, 2010 3:10 am

kiwistiller wrote:I don't quite agree with that. I don't want to make any more, I just want to make it faster. Pot runs are interesting, reflux is a chore to me. want it over and done as fast as possible,
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Re: Column Height Vs Diameter ratio

Post by Lubavitcher » Thu May 27, 2010 4:28 am

Ayay wrote: A column height between 20-30 diameters for 2" -3" columns is best
diameter has nothing to do with column height. what you meant to say is a 3 foot to 5 foot column will work just fine
Last edited by Lubavitcher on Thu May 27, 2010 8:18 am, edited 1 time in total.
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Re: Column Height Vs Diameter ratio

Post by Lubavitcher » Thu May 27, 2010 5:46 am

kiwistiller wrote:I've been talking with Riku and the Mike's from amphora, they say the 4" works fine with mesh. I'll be able to verify myself soon I guess :D
Mazel Tov! on the new still! you should use it in good health always.
"malt does more than Milton can, to justify G-d's ways to Man."

There is a famous story in which the Kaiser asks Bismarck, “Can you prove the existence of God?” Bismarck replies, “The Jews, your majesty. The Jews.”

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Re: Column Height Vs Diameter ratio

Post by theholymackerel » Thu May 27, 2010 7:26 am

Lubavitcher: yall feel free to "discuss" this subject all ya want... but do it politely.

Yer gettin' rude and ornery... so this is an official "Down Boy!"

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Re: Column Height Vs Diameter ratio

Post by Lubavitcher » Thu May 27, 2010 8:14 am

yeah a 4 icher shouldnt be a problem with mesh... i posted data up from a site i got that showed a 12 incher :shock: still had normal HETP values and yess the site said that any section of column that big can not go 3 feet with out proper reflux distributors but a three foot section of twelve inch pipe (without a collar) would still get the the same HEPT values as a 3 incher with the same packing
"malt does more than Milton can, to justify G-d's ways to Man."

There is a famous story in which the Kaiser asks Bismarck, “Can you prove the existence of God?” Bismarck replies, “The Jews, your majesty. The Jews.”

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Re: Column Height Vs Diameter ratio

Post by airhill » Thu May 27, 2010 4:21 pm

kiwistiller wrote:I haven't heard of vapour speed slowing before rad. do you have a link or something to that info? I thought that due to mass transfer with reflux, it would stay more or less constant?
I think it has more to do with energy transfer than vapour speed. You can measure speed at the bottom and the top, in between? If people were more concerned with temperature gradients it would to my mind simplify things.I very much doubt that a theoretical plate is a constant throughout a column in any practical situation.(there again this is only my opinion) :)

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Re: Column Height Vs Diameter ratio

Post by diesel4ever » Sat Jun 19, 2010 10:33 pm

WOW Just finished reading 4 pages of this post! Talk about getting off on a tangent! The only difference between a 36" long 2"dia. column and a 36" long 4"dia. column packed identical and using the appropriate heat to produce the exact same vapor speed going up the column is output. With the exact same vapor speed they will both produce the exact same ABV at a 1:1 reflux ratio only the 4" column will produce 4 times the output due to it having 4 times the surface area. Pi(3.14) X R (radius) squared. There put that in your pipe and smoke it... :wink:

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Re: Column Height Vs Diameter ratio

Post by Chasin' Tales » Sun Jun 20, 2010 9:15 am

First of all...Luba, in your two posts, the one where you qoute from the HD site and the one where you post the graph, you are saying that diameter doesn't affect HETP because you don't see diameter or radius in any of the equations. What you fail to see is that vapor speed/flowrate is very much a major factor in those equations and that gragh. Vapor speed/flowrate is directly proportional to column diameter. With all else equal, if you change just the column diameter your vapor speed will change. This will indeed change the HETP. Now it is possible to have the same HETP in columns w/ different diameters, but they will certainly not have the same heat input.

Diesel - before you tell somebody to "put that in their pipe and smoke it", you might want to make sure you've got things right first. A 4" column will have 4 times the cross sectional area, not surface area. There's a big difference.

Column diameter plays an important role in column design. It is one of several parameters that must be considered. The ratios (24:1-30:1) are probably very valid for the power input that most hobby distiller's apply. I know my columns fall within this range and have performed well.

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Re: Column Height Vs Diameter ratio

Post by diesel4ever » Sun Jun 20, 2010 11:09 am

Thanks for catching that for me CT. I stand corrected. I meant to say cross sectional area and volume. Most all of us get too wrapped up in formulas and ratio's but it all comes down to what end product are you looking for, how much do you need to produce to supply yourself (and maybe a few close friends) with drink, and how long are you willing to wait for a batch to run? If for example you are perfectly happy with 4 litres a month then a simple small scale still will suffice. If you do a lot of experimenting with using neutrals to make liquors and such and you like to run 10gal batches of mash at a time but don't want sit and wait 12 hours to produce 95% ABV... Then you need to decide if you want to go with a 2", 3" or 4" column and what height you use may be determined by whether you need to cut a hole in your ceiling or go with a shorter column and just simply increase your reflux ratio. Heat input is also going to determine your maximum column diameter and height. If all you have is a 1500 watt burner then your limited to your column design. If on the other hand you have a 150,000 btu propane burner and a 17 gal. keg boiler you will have more options. But after all that I guarantee a 4" dia. X 24" column has the capacity to produce more 95% ABV per hour then the equivalently packed and designed 2"dia. X 48" column. :wink:

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Re: Column Height Vs Diameter ratio

Post by rad14701 » Sun Jun 20, 2010 1:42 pm

Ahh... Nice to see that folks are finally figuring out the parameters I eluded to before... A 4" column will require more power to achieve the same vapor density/speed than a 2" column will require... Seems like I mentioned that when taking all other parameters into consideration and keeping them constant that HETP's will change for different diameter columns... You have to change another parameter along with the diameter for HETP to remain the same - either more heat or less reflux...

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Re: Column Height Vs Diameter ratio

Post by kiwistiller » Sun Jun 20, 2010 6:15 pm

Finally? Pretty sure constant vapour speed and heat input have been mentioned a few times before. Anyway, doesn't the lowering of vapour speed as column diameter increases (assuming here that someone would be silly enough to not put more heat into a bigger still) go completely against your ratio, which implies that as still diameter increases, HETP increases as well? :? A lower vapour speed (heat input relative to column diameter) will decrease HETP as far as I can tell from the relevent equations.

Still hoping for a rational answer on this one :roll:
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Re: Column Height Vs Diameter ratio

Post by diesel4ever » Sun Jun 20, 2010 7:08 pm

Still diameter doesn't increase HETP (assuming that same silly person didn't increase heat output) It simply slows vapor speed. Variations in HETP are packing dependant. Different packings will have different HETP depending on the totalsurface area per cubic inch. In fact the same type of packing (eg: copper scrubbers) can have differing HETP's simply by the density at which it's packed. The more dense it is the lower the HETP because more vapor is exposed to condensed liquid per cubic inch. That's why ceramic rings are quite effective because the surface area is porous and marbles are less effective because of a smooth surface and more vapor can "sneak past without contacting condensate. I think Rad was trying to say that but he didn't dumb it down enough for the rest of us. :mrgreen:

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Re: Column Height Vs Diameter ratio

Post by kiwistiller » Sun Jun 20, 2010 7:51 pm

diesel4ever wrote:Still diameter doesn't increase HETP (assuming that same silly person didn't increase heat output) It simply slows vapor speed
Really? I was under the impression from the equations used that slowing vapour speed in the column does in fact decrease HETP, as the effective area of the packing will decrease with a higher mass flowrate per unit cross-sectional area.
If you don't like looking at equations, you can use the calculator on the parent site to verify this without having to crunch any numbers yourself: http://homedistiller.org/reflux_calc.htm" onclick="window.open(this.href);return false;" rel="nofollow
Leave all the figures as default, calculate, note the HETP. then increase the diameter of the column, and watch what happens to HETP.
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Re: Column Height Vs Diameter ratio

Post by diesel4ever » Sun Jun 20, 2010 10:50 pm

Sorry but what you said makes no sense. How can slowing the vapor speed have anything to do with the efficiency of the packing? Your packing efficiency is a constant. Your HETP MAY decrease marginally at an extremely slow vapor speed simply due to the fact that it has more time to sit there and exchange with the condensate BUT if there is not enough vapor pressure to reach the top of the column to reflux properly you will loose output due to stalling. The whole point is to get your finished product out of the still as efficiently as possible.

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Re: Column Height Vs Diameter ratio

Post by diesel4ever » Sun Jun 20, 2010 11:26 pm

Well I decided to skim through the HD bookmarks that you are so sold on. I can tell you that not all the info in those sections are true and the author said himself he wrote it as a general guideline.

For example: This chart is wrong. It shows that as purity increases so does temperature at equilibrium (the point at which a particular vapor condenses). It's actually the opposite (it would be correct if both arrows pointed to the right). As purity increases temp. decreases. This is because water boils at 212deg F / 100C which is quit higher than pure alcohol so the more water contained in a particular vapor the higher the temp. at equilibrium.

Not trying to argue with you but sometimes you have to do some free thinking otherwise we'd all still believe the world was flat.
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Re: Column Height Vs Diameter ratio

Post by airhill » Mon Jun 21, 2010 12:29 am

diesel4ever wrote:Sorry but what you said makes no sense. How can slowing the vapor speed have anything to do with the efficiency of the packing? Your packing efficiency is a constant. Your HETP MAY decrease marginally at an extremely slow vapor speed simply due to the fact that it has more time to sit there and exchange with the condensate BUT if there is not enough vapor pressure to reach the top of the column to reflux properly you will loose output due to stalling. The whole point is to get your finished product out of the still as efficiently as possible.
Sorry Diesel but if you forget vapour speed and concentrate more on energy it does make sense. This vapour speed discussion is IMHO not very practical; if vapour moved from bottom to top of a column in an orderly fashion it would be a waste of time for distilling, it moves in a chaotic series of jumps as a result of the effects of phase change (which is effectively energy exchange). Increasing or decreasing the energy input has an effect on phase change (if it didn't Power Management would not work). :)

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Re: Column Height Vs Diameter ratio

Post by kiwistiller » Mon Jun 21, 2010 1:20 am

diesel4ever wrote:Not trying to argue with you but sometimes you have to do some free thinking otherwise we'd all still believe the world was flat.
Don't worry, I have no problem with debate, but I thought I was doing some free thinking, in challenging what appears (to me) to be a misleading piece of advice that's been thrown around so much it is right "just because".
diesel4ever wrote:Well I decided to skim through the HD bookmarks that you are so sold on
did you look at this one?
Image
where:
aw = effective interfacial area of packing per unit volume (m2/m3)
a = actual area of packing per unit volume (m2/m3)
sc = critical surface tension for the particular packing material (see table below)
sL = liquid surface tension mN/m
L*w = mass flowrate per unit cross-sectional area, kg/m2s = L'
The source of that is a chemical engineering text (Coulson, Richardson & Sinnott), so I'd say it's safe to be sold on it.
If you think about it, you'll probably see the sense in it, think of what happens when too much mass is thrown at the column.
airhill wrote:This vapour speed discussion is IMHO not very practical; if vapour moved from bottom to top of a column in an orderly fashion it would be a waste of time for distilling, it moves in a chaotic series of jumps as a result of the effects of phase change (which is effectively energy exchange). Increasing or decreasing the energy input has an effect on phase change (if it didn't Power Management would not work). :)
I agree, lets move on. Was just wanting to point out that it isn't a reason to talk design in a ratio.
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