Column Height Vs Diameter ratio

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Column Height Vs Diameter ratio

Postby Lubavitcher » Sun May 23, 2010 11:57 am

MOD EDIT____Ive split this from --compact column design --- NOW PLAY NICE ---hmmm thanks lwtcs i guess the issues is best left until there is more data

on to a more productive question. Why is it that as diameter increases a taller height is needed to achieve the same purity all other things being equal like vapor rate, RR, packing, thermal heat loss, ect
for example if some one is useing a 2 inch er and they switch to a 4 incher why should they have to double the length of pipe to get the same purity? the vapor rate stays the same so the amount of time for the vapor and reflux to travel the length of the column doubles. which seams to knock out the theory that effective column height is determined by the distance reflux must travel, because if reflux was the main decider then a 4 incher should be the same height as a 2 incher.

the only way i can think to test this is to insert a thin strip of copper down the middle of a 4 inch with structured packing then then try the same experiment with a thin strip of wood this way we he can isolate weather the reason is because of reflux and vapor mixing or thermal gradient through the column

and to add fuel to the fire if you use the calculator on HD it seams that an increase in diameter of column does NOT demand an increase in height to get the same purity.. whats going on here? is a height to diameter ratio that every one is going on about (1:12-1:30) true or not?
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Re: compact column design

Postby kiwistiller » Sun May 23, 2010 1:02 pm

that pic you posted is a continuous column (a very different kettle of fish). you see the wash line going through the top (working as a dephlagmator) and then all through the second column, before depositing at the TOP of the next column. where it refluxes down through the plates and is heated by the steam injection. you control a still like that on feed rate.
actually the split column in that case is more to get a continuous cutting capability. Heads out the top of the recifier, hearts mid rectifier, tails go out with the spent wash. I'm not trying to bag on your design mate, it's awesome to see some new thinking. you asked what we thought...

I'm not a huge subscriber to the old diameter to height ratio thing. No one has ever explained why it's a good idea to think about it in those terms to my satisfaction. However some things do complicate as you get wider columns. One issue you run into as you get bigger is reflux distribution. As the reflux travels down the column, and the ABV drops, the surface tension of the reflux rises, and it wants to clump together and channel. This drops efficency. Those calculators are rough numbers at best... I think they were a work in progress that was never finished. you'll notice that the primary packing we use (structured mesh) is missing from them.
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Re: compact column design

Postby Lubavitcher » Sun May 23, 2010 1:36 pm

yeah so the question still stands: as the diameter increases is it necessary that the height increase? i want proof does any one have 3 stills of three different sizes with the same packing tested?

the best proof i can find is on page 6 they give a performance table by different sizes fo stills http://www.cannoninstrument.com/Pro-PakBulletin.pdf
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Re: compact column design

Postby kiwistiller » Sun May 23, 2010 1:52 pm

I don't have negative proof for you. maybe someone who does believe it can point you to something positive about it? But yes it is proven that reflux centering is a problem in wider columns, especially for mesh. It starts being a real issue at above 4", which is why you'd switch to plates as diameter increases. I know it is mentioned in designing and building automatic stills, and think it's in the compleat distiller (could be wrong with that). But that can be solved with centering rings and redistribution plates.

Put it this way. I'm designing a four inch column right now. it's going to be the same height as my 2". But it is going to have triple the centering collars (or maybe perforated plates, rings aren't as good as they tend to center rather than distribute). Having said that I'll bow out and let others speak their piece.
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Re: compact column design

Postby rednose » Sun May 23, 2010 2:09 pm

In one of my books are fomulas (which I didn't understand all till now :oops: ) for column diameter and length relation in plate stills but I'm too lazy to search for.

OD sent me a related link in a PM some time ago but it's deleted now, sorry.

I personally don't believe (but can't prove) that it's needed to have a superlong plate still, mine have only 60 cm on 4 six inch plates, apart of the dephlagmator.

The very large commercial stills have up to 21 plates as I remember.

I wouldn't like to use more plates in a whisky/rum still but for neutrals it would be needed at least 9 of 'em to get the nasties off.

The need of lenght in packed columns is slightly different as I remember but can't say how as it wasn't touching my interest so much, maybe one of our vodka freaks can give some more inside.

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Re: compact column design

Postby rad14701 » Sun May 23, 2010 6:40 pm

Those ratios are based on calculations on the parent site with regard to the height between HETP's... Each column diameter has a different distance between HETP's and based on minimum to maximum plate counts for purity we can roughly estimate theoretical performance... Taking into consideration that the closer you get to 95% the more plates it takes to gain purity improvement we come up with the rough maximum of 4 - 5 HETP's worth of packed column... I use a figure of 2.5 column diameters equals 1 HETP as a rough approximation after running a range of column diameters, reflux ratios, and heat input...
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Re: compact column design

Postby olddog » Sun May 23, 2010 6:46 pm

Hey Luba, why don't you just build it and post the results, thats how we all learn about these things. I think you would be better with plates than scrubbers though, they would be a hell of a job to clean, whereas with plates you can give it a hose through, to clear out any crap.


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Re: compact column design

Postby kiwistiller » Sun May 23, 2010 6:51 pm

rad14701 wrote:Each column diameter has a different distance between HETP's

Could you elaborate on why that is rad? Or point me to experiment results or whatever it was that figured that out?
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Re: compact column design

Postby olddog » Sun May 23, 2010 6:59 pm

This link may be of use to you Kiwi. http://journeytoforever.org/biofuel_lib ... meCh7.html


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Re: compact column design

Postby rad14701 » Sun May 23, 2010 7:43 pm

I ran figures through the calculator on the parent site, kiwistiller... Then I tossed them in a spreadsheet and ran some averages... It should be noted that the 2.5 X diameter is skewed to the high side due to using all common diameters between 1.25" and 3" along with RR from 1 - 5 and watts from 1000 - 3000 with extremes removed... Not scientific but BevNap calculated close enough to know when you're within range...
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Re: compact column design

Postby Lubavitcher » Sun May 23, 2010 7:57 pm

yeah OD plates sound awesome! their hard to manufacture and they get really high abv your hearts were getting 80% on you plated The Evil Twins Still and it was really efficient like eight feet of column and they were equivalent to 3 plates! wow i want that!

yeah OD sarcasm aside i cant build any thing where i am in life now. im a student living in a 15x15 with two other guys. :?
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Re: compact column design

Postby olddog » Sun May 23, 2010 8:01 pm

Lubavitcher wrote: eight feet of column and they were equivalent to 3 plates! wow i want that!

Actually each column was about 3' and each column contained 6 plates.


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Re: compact column design

Postby kiwistiller » Sun May 23, 2010 8:06 pm

Rad -
Does that control for vapour speed? because I'm looking through Tony's working on the parent site, and not seeing where diameter should effect HETP except for in the mass flowrate per unit cross-sectional area. The way I see it, if the power is adjusted to be apropriate for column size to maintain the optimal flowrate, it should be the same HETP value for say 4" and 2", espeically because that calculator doesn't take reflux distribution into account...
Right?
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Re: compact column design

Postby kiwistiller » Sun May 23, 2010 8:11 pm

I've just plugged some numbers into the calc. leave most numbers default - change column diameter to .05m - calc HETP = 0.121m

Now we've got our theortical 2" still, increase it to 4" by changing the diameter to .1m and increase the power applied by the same proportion as the relative increase in diameter - x4. so up the distilling power to 4800, calc, and I get the HETP = 0.121m - unchanged.
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Re: compact column design

Postby Lubavitcher » Sun May 23, 2010 8:51 pm

yeah i know that you had 12 actual plates i read your post but your 12 plates are equivalent to 3 ideal plates. go back to HD and read about theoretical plates ect.
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Re: compact column design

Postby LWTCS » Mon May 24, 2010 1:51 am

viewtopic.php?f=27&t=15278&p=6834174#p6834174

I must say,, for not even having fired a basic potstill,,, your level of dialog is quite impressive. Not "novice " at all.

What is your background that enables you to stand and debate this subject matter. We have had chemistry major's with less awareness.

You seem quite good. How so?
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Re: compact column design

Postby Lubavitcher » Mon May 24, 2010 8:22 am

ummm im not sure if my proficiency issues forth form any specific background, i was always good at science, my mother was a research librarian and my father is a is a big researcher hes in istanbul atm and later this week he will be in shanghai he gives a lot of graduate seminars in managerial science. simply put im good at research because my parents are

to end the topic kiwi and i seem to agree and so does the evidence there is no direct ratio of width to height for purity
a 2incher of the same height as a 4 incher might only preform 10-20% better but not the 100%-200% better claimed by the people that say that a ratio of 1to 20 is necessary.


if you want to look at laboratory data look at the table on page six http://www.cannoninstrument.com/Pro-PakBulletin.pdf the still that is 12" by 3' is half as good as the 6" by 6' indicating that it is the height that determines purity not diameter. just like it says in the distillers bible HD. we should all make a resolution to bury and censor all talk of 1:24 or 1:30 to make ultra pure stuff because its plain wrong and misleading.
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Re: compact column design

Postby kiwistiller » Mon May 24, 2010 2:34 pm

Well I'd still like to be proven wrong. A lot of very respected column designers use those numbers, they must be based on something, right? Just because you and I don't understand it doesn't mean it's wrong. We can take it to a different topic if you'd like?
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Re: compact column design

Postby rad14701 » Mon May 24, 2010 8:26 pm

The ratios, while generic, are based on what has been proven to work... Sure, I can get close to 95% out of my small scale 1.25" column with only ~9" of packed column, but I can run faster and stay more stable with ~24" of packed column... But let's look at some figures...

For a column of a given diameter:

Increased reflux ratio decreases HETP plate height and increases plate count
Invreased heat input (watts) increases HETP plate height and decreases plate count
Increasing column height increases HETP plate count


Taking these facts into consideration:

There is no direct correlation between column diameterand HETP plate height
Once datum has been compiled a generic ratio can prove helpful in determining packed column height
Using generic ratios is not exacting science, but gets you in the ballpark with margin for error when any of the cparameters mentioned above is changed, within reason

Example:
2"/50mm column
2:1 reflux ratio
1500 watts power input
Stainless Steel scrubbers for packing

12"/30cm height (6:1) = 3.8 HETP's 4.24"/10.8cm tall and 90.4% ABV
24"/60cm height (12:1) = 6.6 HETP's 4.24"/10.8cm tall and 93.4% ABV
30"/76cm height (15:1) = 8 HETP's 4.24"/10.8cm tall and 93.9% ABV
36"/92cm height (18:1) = 9.5 HETP's 4.24"/10.8cm tall and 94.5% ABV
48"/120cm height (24:1) = 12.1 HETP's 4.24"/10.8cm tall and 94.9% ABV
60"/150cm height (30:1) = 14.9 HETP's 4.24"/10.8cm tall and 95.2% ABV

With these figures in mind, and considering how we can adjust our reflux ratio and heat input, we can change the number of plates, plate height, and purity. Therefore the column height:diameter ratio can be used to get a somewhat accurate estimation of whether the column is capable of performing within expectations or not.

With a 24" X 2" column, or 12:1 ratio, we can still get darn near 95% ABV by adjusting reflux ratio and heat input. The same goes for a 48" X 2" column. Now, where the top end comes in is with a 60" X 2" column where we can adjust past our maximum attainable ~95.6% ABV, meaning that we have more fudge factor built into the column. And at the lower end, a 12" column only has 3.8 HETP's (less than 5 HETP's) and therefore it is all but impossible to produce spirits in the ~95% ABV range with all the reflux ratio and heat input adjustments in the world unless you collect at less than one drip per second.

So, what does this all mean? It means that those speculative ratios get us close enough to be considered a reliable guideline. We must also consider that depending on which end of the column diameter extremes we go, the more skewed the accuracy will be. A 1.25"/32mm column will be thrown off more than a 3"/76mm column. So stating that anything below 12:1 won't allow for ~95% ABV and a ratio above 30:1 will have diminishing improvements in ABV is a relatively accurate statement.

Edited: To specify SS scrubbers as packing.
Last edited by rad14701 on Tue May 25, 2010 6:19 am, edited 1 time in total.
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Re: compact column design

Postby kiwistiller » Mon May 24, 2010 9:54 pm

Ok, I've read that, but can't help thinking that as diameter has nothing to do with purity, why are we advising people to build stills based on a ratio with it? Even for a 3" still it's pretty far out of whack.

Here is my thoughts:
rad14701 wrote:Invreased heat input (watts) increases HETP plate height and decreases plate count

:? sorta, it's increased vapour speed really, right?

rad14701 wrote:There is no direct correlation between column diameterand HETP plate height

ok...
rad14701 wrote:Once datum has been compiled a generic ratio can prove helpful in determining packed column height

Right now this step is the one that you've lost me at. Why? If the diameter isn't related to purity, why does a wider still require a taller column? Because that's what expressing it in a ratio implies.

rad14701 wrote:With a 24" X 2" column, or 12:1 ratio, we can still get darn near 95% ABV by adjusting reflux ratio and heat input. The same goes for a 48" X 2" column. Now, where the top end comes in is with a 60" X 2" column where we can adjust past our maximum attainable ~95.6% ABV, meaning that we have more fudge factor built into the column. And at the lower end, a 12" column only has 3.8 HETP's (less than 5 HETP's) and therefore it is all but impossible to produce spirits in the ~95% ABV range with all the reflux ratio and heat input adjustments in the world unless you collect at less than one drip per second.

ok, but the same goes for a 3" column of the same heights, right? or a 2.5"? or a 4"?

rad14701 wrote:So, what does this all mean? It means that those speculative ratios get us close enough to be considered a reliable guideline. We must also consider that depending on which end of the column diameter extremes we go, the more skewed the accuracy will be. A 1.25"/32mm column will be thrown off more than a 3"/76mm column. So stating that anything below 12:1 won't allow for ~95% ABV and a ratio above 30:1 will have diminishing improvements in ABV is a relatively accurate statement.

Wouldn't it be much easier to talk about this speculative guideline in terms that are actually directly related to purity and therefore useful across a wider range of diameters, namely column height? isn't it a more accurate statement to say 'anything below 24" won't allow for ~95% ABV and heights above above 60" will have diminishing improvements in ABV'?

Still not quite understanding this, but thanks for your time so far.
Kiwi
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Re: compact column design

Postby rednose » Mon May 24, 2010 10:13 pm

Looks like you folks love the topic, here a PDF I catched up some weeks ago.

That might help you a little, I still don't get it completely but if I have time I'll try to get deeper in.

I admit not to be the brightest light under the sun when it comes to theory and long math formulas. :lol:
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Re: compact column design

Postby kiwistiller » Mon May 24, 2010 10:24 pm

I couldn't find anything relating to ratios in there joe. what is it specifically that you thought might help?
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Re: compact column design

Postby rednose » Mon May 24, 2010 10:35 pm

I refere to the HETP calcs for packed columns under different packing materials.
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Re: compact column design

Postby rad14701 » Tue May 25, 2010 6:07 am

Yeah, rednose, I forgot to note that my calculations were all done with SS structured scrubber...

kiwistiller, I'm surprised that you don't see a correlation between the figures and the height:diameter ratio... Changing the diameter of the column, with all other settings left the same, will show that a larger diameter column will result in shorter HETP's and more plates within the length, just as a smaller diameter column will have taller HETP's and less plates... But the band of efficient operation will still be within the 12:1 to 30:1 ratio range... Trust me, I've tried to disprove the ratios but no matter how I slice and dice the numbers, the results are they same... A generic guideline, based on numbers compiled from formulas, remains almost every bit as effective as running off calculations... Based on the 2"/50mm figures, the ratios are pretty spot on... Remember, the reflux ratio and heat input are two adjustable parameters which can be used to skew the numbers for a column of a given diameter and height... And we can't forget the percentage of alcohol in the wash either as that will also change the results... The ratios only assure us that we have enough HETP's for decent operation, without direct relation to the plate count... If we want more exacting numbers we should refer to the calculator or use manual calculations... None of this has anything to do with take off rates, only whether we can get attain ~95% ABV by adjusting reflux and heat...

I guess the next step is to see numbers showing that with a given diameter and height that you can fall out of the ratio range, within the realm of practicality... By the realm of practicality I mean using realistic reflux ratios as well as heat input within the operational range with respect to the columns physical size...

And one last parameter that we may be overlooking is the actual packed density of an individual column... My packed density is going to be different than the next persons packed density and, in fact, that density could change by simply unpacking and repacking the column with the exact same structured material... That takes some of the exact out of the exact science of HETP's as they relate to our hobby... Only an un-compressible and uniform material will give repeatable results within a narrow range...
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Re: compact column design

Postby Lubavitcher » Tue May 25, 2010 11:19 am

kiwistiller wrote:
rad14701 wrote:There is no direct correlation between column diameterand HETP plate height

ok...
... Why? If the diameter isn't related to purity, why does a wider still require a taller column? Because that's what expressing it in a ratio implies.


answer kiwi. if you don't understand his question i will rephrase it:

if you have a 2 incher that is 60 inches high that is a 1:30 ratio and i want to build a 6 incher with the same level of purity does that mean i should build it 180 inches high? yes or no?

if yes your wrong look at the data again

if no then i ask "why do you express it in a ratio?" because expressing it as a ratio misleads people to think that a 6 incher should build it 180 inches high in order to have the same plate equivalent as a 2incher that is 60 inches high
Last edited by Lubavitcher on Tue May 25, 2010 1:16 pm, edited 5 times in total.
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Re: compact column design

Postby Lubavitcher » Tue May 25, 2010 11:56 am

Hey rednose thanks for the pdf... its a beautiful find!

from the way i read it, leaving out all the math i see that it mesh is the fool proof way to build a still and that to design a plate still you really need a lot of math. and dont fall into the pit of thinking that perforated plates are easier to clean cuz they arnt and they also can have flooding or weeping problems if not built right
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Re: compact column design

Postby rad14701 » Tue May 25, 2010 12:24 pm

Lubavitcher wrote:if no then i ask "why do you express it in a ratio?" because expressing it as a ratio misleads people to think that a 6 incher should be 180 inches high

The operative phrase should be "can|could be 180 inches high"... No "should" is implied...
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Re: compact column design

Postby Lubavitcher » Tue May 25, 2010 1:00 pm

i just edited my post (the part i added is underlined) so you can no longer, dodge the question and troll this topic.

and about my grammar are you REAALLY sugesting that my question should read "if you have a 2 incher that is 60 inches high that is a 1:30 ratio and i want to build a 6 incher with the same level of purity does that mean i could build it 180 inches high? "

dont use big words unless you know the meaning i had to study Kant in college and the construction i used was a hypothetical imperative. so i HAD to use the word should in order to satisfies the word earlier in the sentince "want"

this is the base form "i want XYZ so i should ABC"
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Re: compact column design

Postby rad14701 » Tue May 25, 2010 2:09 pm

Since you started this topic with the title "compact column design" and you think I'm trolling then I guess I won't continue allowing it to be pulled off-topic any further... I won't be lured into an argument within your topic, Lubavitcher... The troll comment was totally uncalled for, especially from someone as new to the HD community as you are...
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Re: compact column design

Postby kiwistiller » Tue May 25, 2010 2:29 pm

Steady on, Lubavitcher, no need to be rude. I've actually asked one of the mods to split this into a new topic from when we start talking about ratios, but I guess we can continue on here for now?

So rad, you often say that 24:1 is the ideal ratio. That's a 48" column. Is 96" the ideal height for a 4" column?

I still haven't seen why a wider column needs to be taller. can you explain this too me simply? I'm not particularly interested in your spreadsheet (no offense intended) because I'm fairly sure that your averaging method of calculating is a bit flawed.

Saying that the ratio is appropriate because it is robust over a range of variables is a little flimsy. wouldn't a simple height figure be just as robust? Also, talking of ranges of heat input is a little strange, when the main reason for a bigger column is so that you can apply more power and keep efficiency (or more correctly vapour speed) at the same level.

rad14701 wrote:Changing the diameter of the column, with all other settings left the same, will show that a larger diameter column will result in shorter HETP's and more plates within the length, just as a smaller diameter column will have taller HETP's and less plates...

That's because you haven't kept your vapour speed at the efficient spot in your calcs. adjust power so the vapour speed is always 20"/s (which is close enough to optimal for mass transfer while keeping a good production rate), like a tuned reflux column should have, and you'll see that your figures for HETP remain constant over column diameter. Aside from the obvious, this also shows how you can't rely on calculators to make inferences beyond their original purpose, because we all know that without reflux distribution the wider columns will suffer from channeling and a loss in efficiency (HETP increase towards the bottom of the column).

Yes, they hold up for as 2" still, because I'm picking that the numbers were made up based on a 2" still. They don't hold up for other diameters when the power is increased accordingly. when the power ISN"T increased accordingly, they are even more inaccurate, because the reduced vapour speed will decrease the HETP, meaning that you could have a shorter column if you increase diameter and keep power constant.

So, I'd like you to simply answer this. Should an ideal 4" column be twice the height of a 2" column?
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