Vapor Management Question

[minime]

I'm finally starting to build a 3" VM column. In Riku's new book Designing and Building Automatic Stills he shows an elbow turned down into the vapor path inside the column rather than relying on EVDP. I would think this is more akin to stream splitting than the traditional "alcohol vapor is heavier and sinks" method.

Any of you fellows running VM columns tried this new innovation??

[HookLine]

What is 'EVDP'?

[minime]

What is 'EVDP'?

Sorry, 'ethonol vapor density principle'

[HookLine]

Aah, I see.

Does Riku give reasons for doing it that way?

On the face of it I can't see any fundamental difference, but I could be wrong, Riku is a smart and experienced still builder so he might be onto something.

[manu de hanoi]

let me guess : could it be ARC ?

[punkin]

I've got a VM question too, if ya don't mind me sharing your thread mini?

Reading through a bit of vm stuff on the yahoo group this morning while the site was down, i came across some stuff on 2 things that i'd like to learn more about before i start soldering.

1) that some on ther reccomend an upside down reducer or some other way to funnel the condensed distillate into the centre of the packing?

And

2) that there was some people theorising that the auto shut off sorta non collection of lower tails was a result of the angle of the takeoff to the vapour collection valve.
That a low angle will allow the still to stop collecting at the density of air.
There was also some stuff from a guy there that i didn't fully understand about takeoff tube angles affecting purity. He said that unless he had an upward slope before his takeoff valve, that his purity was markedly (lots) lower, and after he changed that angle there was no problem taking off very pure distillate.

Any thoughts or explanations of this stuff from the VM operators in the know?

[minime]

Aah, I see.

Does Riku give reasons for doing it that way?

His statement is "to have a positive flow of vapor to the product condenser"

He incorporates a temperature controlled valve at the bottom of liebig allowing the still to jump to an extremely high reflux ratio when it reaches tails temperature (the liebig is now pressurized). Apparently the alcohol continues to enter the liebig very slowly and pools at the bottom until the increased reflux lowers the temperature and opens the valve.

My understanding is a VM column stops producing shortly after tails are encountered? This must be a way around that.

I think I'm going to install a one inch elbow in the three inch column which should give a 9 to 1 reflux ratio even with the valve wide open. I won't solder it in until I've satisfied myself it works well. I'm not sure I'd ever automate the still but his method can be retrofitted to any VM column so it's still a possibility.

[minime]

I've got a VM question too, if ya don't mind me sharing your thread mini??

Hey punkin no problem. I don't see much on VM columns anywhere. I don't think there's very many running them. I should be up and running by mid August (I've got lots of visitors 'till then) and will have some experience to share.

I don't want to make a mistake with my 3" copper. It was a freebe I'll never see again. I'm being very cautious and want to get everything perfect.

Any and ALL advice is welcome

[manu de hanoi]

Aah, I see.

Does Riku give reasons for doing it that way?

His statement is "to have a positive flow of vapor to the product condenser"

He incorporates a temperature controlled valve at the bottom of liebig allowing the still to jump to an extremely high reflux ratio when it reaches tails temperature (the liebig is now pressurized). Apparently the alcohol continues to enter the liebig very slowly and pools at the bottom until the increased reflux lowers the temperature and opens the valve.

My understanding is a VM column stops producing shortly after tails are encountered? This must be a way around that.

I think I'm going to install a one inch elbow in the three inch column which should give a 9 to 1 reflux ratio even with the valve wide open. I won't solder it in until I've satisfied myself it works well. I'm not sure I'd ever automate the still but his method can be retrofitted to any VM column so it's still a possibility.

-When the liebig output is closed: how could the liebig be pressurised if all vapor that goes in is condensed (and falls liquid to the bottom) ? Maybe if air is trapped in the liebig pipe then it would block vapour entry, but if vapour is heavier than air, then air in the liebig pipe will ultimately go up and escape through the vent... ?
Why isnt this security valve at the elbow in order to block vapour for good?
-a minimum of 9x ratio ? Seems a lot to me, how did you come up to that number ? How tall is your column ?

[Rudi]

1) that some on ther reccomend an upside down reducer or some other way to funnel the condensed distillate into the centre of the packing?

And

2) that there was some people theorising that the auto shut off sorta non collection of lower tails was a result of the angle of the takeoff to the vapour collection valve.
That a low angle will allow the still to stop collecting at the density of air.
There was also some stuff from a guy there that i didn't fully understand about takeoff tube angles affecting purity. He said that unless he had an upward slope before his takeoff valve, that his purity was markedly (lots) lower, and after he changed that angle there was no problem taking off very pure distillate.

Any thoughts or explanations of this stuff from the VM operators in the know?

I read an explination about your first question Punkin.It was from Harry ,not sure where but it was in relation to his crossflow condensor he said imagine a pile of twigs resting against a wall and water was running down the wall the twigs would wick the water away from the wall and onto the rest of the twigs.His short answer was if the column is packed correctly a reflux to centre device is not needed. Bear in mind this isnt a direct quote and only what I remembered.Also the shape of your condensor end can be a reflux centering device.

There was a post by Leftlanecrusier a while back that went into VM take off angles and the EVDP.I'm pretty sure Hook's takeoff tube is horizontal and he doesnt have any problems taking off pure distillate (Think its more reflux ratio etc.......not gona tell ya how to suck eggs)

keep us posted if you come up with any Ideas for your new build. Im planning a vm column when I get time, the way things are at the moment that may be never.

All the best Rudi

[minime]

When the liebig output is closed: how could the liebig be pressurised if all vapor that goes in is condensed (and falls liquid to the bottom) ? Maybe if air is trapped in the liebig pipe then it would block vapour entry, but if vapour is heavier than air, then air in the liebig pipe will ultimately go up and escape through the vent... ?
Why isnt this security valve at the elbow in order to block vapour for good?

Manu, the above questions I have no answers for, maybe Riku would

a minimum of 9x ratio ? Seems a lot to me, how did you come up to that number ? How tall is your column ?

I concluded that since this is really a stream splitting operation I think the area of a 3 inch column is about 9 times more area than the one inch elbow that will be facing the vapor path so the vapor that doesn't go in the one inch elbow will continue up to the reflux condenser and be condensed.

My column will have 60 inches packing before the product arm and will likely finish about 75 inches. It will sit on an 18 gallon stock pot so it's quite tall and heavy. That's why it's taken me so long to organize this build. Everything has to be heavy duty.and everything has to come apart and be stored. I don't have the luxury of leaving it assembled.

[manu de hanoi]

a minimum of 9x ratio ? Seems a lot to me, how did you come up to that number ? How tall is your column ?

I concluded that since this is really a stream splitting operation I think the area of a 3 inch column is about 9 times more area than the one inch elbow that will be facing the vapor path so the vapor that doesn't go in the one inch elbow will continue up to the reflux condenser and be condensed.

My column will have 60 inches packing before the product arm and will likely finish about 75 inches. It will sit on an 18 gallon stock pot so it's quite tall and heavy. That's why it's taken me so long to organize this build. Everything has to be heavy duty.and everything has to come apart and be stored. I don't have the luxury of leaving it assembled.

I m glad you got a big & tall one like me, with 60 inches height I believe you can cut down the reflux, too much reflux can force you to distill awfully slowly OR increase heating power to a level where your column is not efficient anymore (too much liquid refluxed + vapor ascending too fast).

I'd say setting the output pipe 1/2 (2:1) the section of the column is enough, and you can always set very high reflux by almost closing the output valve, but you cant do the opposite, if you have 9:1 section ratio then you cant go back to 2:1.

[minime]

Pictures of progress to date.

Only the takeoff tube has been soldered to date. The column and flange are not yet fixed to each other. I think I'll be using a 3 inch triclover setup to tie the column to the boiler when it's time.

http://i280.photobucket.com/albums/kk16 ... akeoff.jpg" onclick="window.open(this.href);return false;" rel="nofollow
http://i280.photobucket.com/albums/kk16 ... packed.jpg" onclick="window.open(this.href);return false;" rel="nofollow
http://i280.photobucket.com/albums/kk16 ... llhead.jpg" onclick="window.open(this.href);return false;" rel="nofollow

[punkin]

Hey punkin no problem. I don't see much on VM columns anywhere. I don't think there's very many running them. I should be up and running by mid August (I've got lots of visitors 'till then) and will have some experience to share.

Looking good minime.
I'm gunna steal hooklines idea for the boiler/column join and just get a stainless bsp reducer welded to the top of the keg. Just easier, more durable and fuss free for a clutz like me.
Dunno why there's not more running VM, from what i can see, it's the simplest build possible and aside from needing a liebig as well, much simpler than the slanted plate one that's so popular. Also seems the simplest to run.(hope i don't regret that statement)


Some of the stuff i've read over the last few days have me convinced that you still need the higher reflux ratio.
One of the simplest ways i saw it put over on yahoo was that there is a very real difference in 95% on the alchometer and 95% ethanol. Some said it was quite possible to get a 95% mixture that was certainly not what people are talking about when they say 'neutral'. There was talk that it was quite simple to get 95% out of a modern still, the trouble comes when you want that 95% to be comprised by as much ethanol as possible rather than all the other alchohols and stuff that are coming up in your vapour
From what i understand from my limited reading, that seperation is a function of reflux. So, yes, you could pull off 95% at a reflux ratio of 1:2, but what would that 95% consist of?

Spose that's why when someone here (pretty sure it was manu) had there 'neutral' analysed, they found a whole lotta nasties they didn't expect and didn't welcome.



Thanks for the simple explanation Rudi, you've definately alleviated that concern. I've been sitting here trying to figure out how to solder an upside down reducer into the bottom of my tee, but using that example you gave me, i can clearly see there would be no need.
Maybe if i was using marbles, but i have some nice mesh here from Amphora.

[BW Redneck]

Also seems the simplest to run.(hope i don't regret that statement)

Compleat distiller compares it to driving a large boat: any adjustments at the valve take a few seconds to be noticeable at the product collection, whereas a LM column is more immediate because you're managing the takeoff rate directly.

I imagine that once you have your still calibrated to the valve settings that you want, this point becomes moot. Just turn it to X number of turns at the valve and let 'er rip!

[manu de hanoi]

One of the simplest ways i saw it put over on yahoo was that there is a very real difference in 95% on the alchometer and 95% ethanol. Some said it was quite possible to get a 95% mixture that was certainly not what people are talking about when they say 'neutral'. There was talk that it was quite simple to get 95% out of a modern still, the trouble comes when you want that 95% to be comprised by as much ethanol as possible rather than all the other alchohols and stuff that are coming up in your vapour
From what i understand from my limited reading, that seperation is a function of reflux. So, yes, you could pull off 95% at a reflux ratio of 1:2, but what would that 95% consist of?

Spose that's why when someone here (pretty sure it was manu) had there 'neutral' analysed, they found a whole lotta nasties they didn't expect and didn't welcome.

I just passed the chemical analysis 2 days ago (in 2 different labs) and the numbers are all well fixed, the major improvement were : dilution + 2nd run + pH. The quality of alcohol doesnt improve by refluxing more than is necessary to reach 95%, it improves with cuts for the heads and dilution + re-run for the tails.

A lot of pple here reflux a lot because they have very short columns (below 1m for a 3 inch diameter is very short), reflux should be matching the height of the column, the higher the less reflux needed. Too much reflux is a waste of energy, water and time. If reflux ratio is 9 when it could be 3 it means that one can distill 3 times faster or use 3 times less electricity and water.

About the pics: Nice soldering job, I suggest you add a temp probe around the middle of the column for better control, unless of course you trust your thermometer for making the difference between 78.2 C => 95,5 % abv and 78.2 C=>92,5 %abv .

[minime]

unless of course you trust your thermometer for making the difference between 78.2 C => 95,5 % abv and 78.2 C=>92,5 %abv .

manu, I currently use an offset column with packed 42 inches. I typically collect at 92 to 93% and like my product. I also usually add a bit of late heads back to the product because I like the flavor. I usually run right on the edge of temperature runaway. (thats why I have to babysit the still, minimum reflux)
My distillate is very smooth and has a slight sweet taste that suits my palate. I can easily get 95+ but it just about doubles the time of my spirit run and adds no value for me.

I'm putting this 3 inch column together to try and shorten the run times. For me it's a matter of time not volume or quality as I'm quite happy with what I can produce now.

My typical routine is strip three 15 gallon washes at 14% and then do a spirit run on the low wines which usually takes 10 to 12 hours. If I could cut the time in half on the spirit run I'd be thrilled. The 3 inch column and longer length might just get me there.

It will definitely be an improvement.

[punkin]

I just passed the chemical analysis 2 days ago (in 2 different labs) and the numbers are all well fixed, the major improvement were : dilution + 2nd run + pH. The quality of alcohol doesnt improve by refluxing more than is necessary to reach 95%, it improves with cuts for the heads and dilution + re-run for the tails.

A lot of pple here reflux a lot because they have very short columns (below 1m for a 3 inch diameter is very short), reflux should be matching the height of the column, the higher the less reflux needed. Too much reflux is a waste of energy, water and time. If reflux ratio is 9 when it could be 3 it means that one can distill 3 times faster or use 3 times less electricity and water.

I just went and searched up what i was reading, i hope Harry and riku don't mind me cross quoting then, but here goes;....

........................................................
95.6% alcohol and neutral ethanol are two different things. Neutral
(of course neutral for one person is horribly tainted to other) is
difficult to achieve and takes time with todays standard gear. 95.6%
stuff comes naturally if you has have a proper column and run it at
proper reflux ratio.

Cheers, Riku
...........................................................................................
I'm not talking about that 4.4% that's water. What I mean is that the
95.6% alcohol can very well be a mixture of different boiling point
compounds. I.e. it's at ethanol's azeotrope but not pure
ethanol/water mix. To get ethanol/water mix that is pure enough to
taste neutral without carbon treatment takes a long time. This time
I've been trying to cut down and have had OK results. As an example
one simple column modification took off 15% of total time.

Joe, as soon as you get past 78.2C you start getting n-propanol out.
While you are only a little over (say 79C) it may not be detectable by
smell or taste as the amount in the mix is relatively small. Once you
get past 80C it is clearly noticeable. At 86C you get also other higher
boiling point components as they all mix together and with ethanol and
have lower boiling point as they would have individually. The same goes
for lower boiling point stuff, at 78C you are not getting pure ethanol
but rather a mix with some ethyl acetate + other compounds.

The proportions in percents may indeed be minimal but the problem is
that some of those compounds smell and taste through even in there's
only a minimal amount in mix. Ethyl acetate is prime example of these
and usually makes for the "bite" or "burn" in the spirits.

Sorry for soundig snobbish, but english is my third language - so I'm
not that well aware of high and low class language and their
differences.

Cheers, Riku
..................................
Riku,

Now you've opened a can of worms!
Many people confuse the terms AZEOTROPE ethanol (95.6%alc + 4.4%
water) with NEUTRAL alcohol, which of course it's not.

Neutral alcohol can be as low as perhaps 40% alc. The term "neutral"
means there is nothing else analytically detectable other than
ethanol and distilled water i.e. NO contaminants. That's why I
believe that vodka (true vodka) is very difficult to achieve without
carbon filtration and polishing. Whisky/rum etc. is much easier
because a small amount of contaminants (in parts per million) is
acceptable and even desirable.

Azeotrope alcohol can still carry the aforementioned contaminants.
That's why in commercial Coffey-type distilleries there are several
stages of columns (rectifiers) to reprocess and separate after the
first column (the analyser) has achieved the initial azeotrope feed.

Slainte!
regards Harry
................................................


One thing to note in general. If you use a good reflux still and run
it properly (ie. slow enough) you get relatively neutral (as
discussed before) ethanol straight out of your still. This means that
there's no need to carbon filter your product. The downside is that
it takes a long time to process a mash, 18 hours for a 25 liters mash
is quite typical with regular LM still.

Cheers, Riku
.......................................................


Complete thread is here.

Just seems to me that these guy's make sense. Of course i'm coming from a completely uneducated view and just guessing at who knows their shit, but i'm not always wrong

[manu de hanoi]

If you dont get the point about over refluxing from me, you may want to read it straight from Riku :
http://www.brygg.info/index.php?name=Fo ... pic&t=1577" onclick="window.open(this.href);return false;" rel="nofollow

[punkin]

If you dont get the point about over refluxing from me, you may want to read it straight from Riku :
http://www.brygg.info/index.php?name=Fo ... pic&t=1577" onclick="window.open(this.href);return false;" rel="nofollow

You musta posted the wrong link or something manu.
The one you posted goes to a thread with just a couplea posts, that links back to a thread here and he has a go at people here about their slowness in picking up problems associated with vapour speed ?

Is that what you meant to link to in your comdenation of 'over refluxing' ?

Like i said, i'm new to this and don't understand the science of design or operation real well, but you rarely make sense to me.

[manu de hanoi]

distilling is hard to understand, especially in swedish.
Over refluxing and over heating a still go hand in hand, in order to increase the output flow for a high reflux ratio (like 9) people tend to increase the heating. That guy had a too strong heater, and both the vapor ascending speed and the high amount of reflux liquid running down (what i call over refluxing) made the still inefficient to the point that :

highest purity was 93 at a slow drip with high reflux @5800watts

Back to the original point, you dont need more reflux than what is needed to get 95% abv, adding more reflux after that point doesnt increase the quality of your booze and besides the energy, time and water waste, can even be detrimental as in the exemple provided.

[punkin]

distilling is hard to understand, especially in swedish.
Over refluxing and over heating a still go hand in hand, in order to increase the output flow for a high reflux ratio (like 9) people tend to increase the heating. That guy had a too strong heater, and both the vapor ascending speed and the high amount of reflux liquid running down (what i call over refluxing) made the still inefficient to the point that :

highest purity was 93 at a slow drip with high reflux @5800watts

Back to the original point, you dont need more reflux than what is needed to get 95% abv, adding more reflux after that point doesnt increase the quality of your booze and besides the energy, time and water waste, can even be detrimental as in the exemple provided.

Ok mate, i'm fairly sure i understand what you are trying to say.




It'sJustThatIDon'tBelieveYouPunkin

[minime]

Ok mate, i'm fairly sure i understand what you are trying to say.
It'sJustThatIDon'tBelieveYouPunkin

I'm with Punkin on this one. I think you're wrong. Hookline says his valve is barely open on a spirit/reflux run. We can go on and on about theory but I'm going to get some hands on experience soon enough and compare that with theory and share my observations so others can comment.

That's what I have to work with so I'm going to give it a go. I will however be leaving the still head un-soldered for the trial run to see how it works. Silicone will hold it ok and I'll know within 30 minutes how this thing is going to perform. I'll take it all the way from full reflux to wide open and see what's coming out and how the temperatures react to those changes. I'll also know very quickly what kind of output to expect. i can strip 15 gallons in 3.5 hours with my burner so I have lots of heat input.

Nuff said, I'll be marching down this road soon enough and will share my experiences

[HookLine]

Interesting discussion, if a little heated. Here's my two cents worth:

1) that some on ther reccomend an upside down reducer or some other way to funnel the condensed distillate into the centre of the packing?

Depends a lot on your condenser design. If it already directs condensate to the centre you don't need anything else. Another way to do it is to wrap a few layers of mesh around the bottom of the condenser and tie it off underneath like a fruit bag, which will direct all the condensate back to the centre of the column.

2) that there was some people theorising that the auto shut off sorta non collection of lower tails was a result of the angle of the takeoff to the vapour collection valve.
That a low angle will allow the still to stop collecting at the density of air.
There was also some stuff from a guy there that i didn't fully understand about takeoff tube angles affecting purity. He said that unless he had an upward slope before his takeoff valve, that his purity was markedly (lots) lower, and after he changed that angle there was no problem taking off very pure distillate.

I can see that having an upward slope on the take off tube could be a problem in getting the ethanol vapour to fall down the product arm. There might be some value in putting slight downward slope on the horizontal part of the take off arm. Dunno for sure.

••••••••••••••••••••••

His statement is "to have a positive flow of vapor to the product condenser"

I do not have any trouble with vapour flow in my conventional basic VM column with a simple hole in the side of the column. (Though I have not tried Riku's elbow suggestion, so do not know for sure if it is better or not.)

He incorporates a temperature controlled valve at the bottom of liebig allowing the still to jump to an extremely high reflux ratio when it reaches tails temperature (the liebig is now pressurized). Apparently the alcohol continues to enter the liebig very slowly and pools at the bottom until the increased reflux lowers the temperature and opens the valve.

My understanding is a VM column stops producing shortly after tails are encountered? This must be a way around that.

I have never tried to go much past the point where the temp start seriously rising (a persistent 0.2C or so) in reflux mode, so do not know for sure if the tails will stop coming over completely on their own. I do know that by that point in the run the tails are already so compressed that their total volume is tiny, and the amount of ethanol left in them is virtually nil, so I don't think they are even worth collecting.

The two times I have collect all the tails at the end of a run I did it by removing the reflux coil, sealing the top of the column with aluminium foil and string, opening the gate valve wide and turning the boiler on flat out. All I got was about 300-350 ml of VERY stinky cloudy oily tails, from a run that used a 40 litre still charge of low wines, and which gave me many litres of clean ethanol. The tails just weren't worth the trouble.

I have a lot of respect for Riku's work, and don't want in any way to discourage experimentation and development, but I think it is also possible to over engineer something. New and more complicated is not always better. The principle and design of the basic VM column has a simple elegance to it, and it already does an excellent job and is very efficient at extracting the ethanol. It does not need any adjustment to the reflux ratio right through the hearts run, except maybe a small one right at the end to squeeze out the last 200-250 ml or so of hearts.

Put it this way, I have not seen any complaints about the results from the basic VM design.

I do not see any big advantage in going to the trouble to add auto reflux ratio to a small hobby VM column, the possible gains seem too small, though I can see how it could be well worth it for a big commercial column.

••••••••••••••••••••••

-When the liebig output is closed: how could the liebig be pressurised if all vapor that goes in is condensed (and falls liquid to the bottom) ? Maybe if air is trapped in the liebig pipe then it would block vapour entry, but if vapour is heavier than air, then air in the liebig pipe will ultimately go up and escape through the vent... ?
Why isnt this security valve at the elbow in order to block vapour for good?

Good questions, manu.

••••••••••••••••••••••

I think I'm going to install a one inch elbow in the three inch column which should give a 9 to 1 reflux ratio even with the valve wide open. I won't solder it in until I've satisfied myself it works well. I'm not sure I'd ever automate the still but his method can be retrofitted to any VM column so it's still a possibility.

I concluded that since this is really a stream splitting operation I think the area of a 3 inch column is about 9 times more area than the one inch elbow that will be facing the vapor path so the vapor that doesn't go in the one inch elbow will continue up to the reflux condenser and be condensed.

That is true, but only if the valve is wide open. Except, like in an LM column, the valve is never wide open during a reflux run, it is only opened a small amount, much less than the size of the take off arm it sits in, so the size of the take off arm in a VM is not important in determining the reflux ratio, (as long as it is significantly bigger than the amount the valve is open). I have a 3/4" take off arm and valve on a 2" column, and the valve takes 11 turns to fully open, but the maximum it is opened is only 3-3.5 turns (for the hearts cut). So the limiting factor to vapour flow into the product condenser (and hence the reflux ratio) is not the size of the take off arm, but the much smaller opening of the valve.

Having the elbow sticking into the column could in fact somewhat complicate and disrupt vapour flow and the separation process if not all of the vapour trapped inside the elbow is being taken off quickly. The advantage of the simple opening in the side of the column is that all the vapour that is not let through the valve is easily remixed with vapour in the column and redistilled.

Also, the stream splitting ratio you calculated does not take into account the area blocked by the horizontal part of the elbow that is still inside the column.

Manu made a good point about the amount of control you lose over the reflux ratio if you limit the vapour flow with the fixed minimum ratio (and 9:1 is a pretty high minimum, I run at around 4 or 5 to 1 during the hearts cut).

Lastly, even with valve wide open, I don't think it is just a straight stream splitting effect, because it is complicated by the vapour density question and the vacuum/chimney effect you get from the product condenser.

••••••••••••••••••••••

Compleat distiller compares it to driving a large boat: any adjustments at the valve take a few seconds to be noticeable at the product collection, whereas a LM column is more immediate because you're managing the takeoff rate directly.

I imagine that once you have your still calibrated to the valve settings that you want, this point becomes moot. Just turn it to X number of turns at the valve and let 'er rip!

Bingo.

It takes maybe 4 minutes after I first crack open the gate valve for the foreshots (just 1.5 turns) before the vapour reaches the actual product condenser (Liebig) and starts dripping out the bottom, though I think that once the vapour starts being condensed the vacuum/chimney effect helps reduces that reaction time quite a bit for subsequent changes to the take-off rate (reflux ratio). The turned down elbow may help shorten that initial lag, but I can't see how it improves the overall operation. Although, obviously I have not actually tried it to see what difference it makes, and I could be wrong.

••••••••••••••••••••••

The distinction Riku and Harry make between neutral and azeotrope is an important one, which is why it is not necessary to reach azeotrope to get a neutral product. What you are really after is ethanol and water, not azeotrope ethanol and water, though it is nice if you can get it. I have not hit azeotrope yet, I get 94.5-95%, but I am still getting a very clean product, probably better than most commercial vodkas. I am pretty sure that if I ran it through the column a third time it would be extremely clean indeed (must try that one day).

[minime]

Interesting discussion, if a little heated. Here's my two cents worth.

Lastly, even with valve wide open, I don't think it is just a straight stream splitting effect, because it is complicated by the vapour density question and the vacuum/chimney effect you get from the product condenser.
.

Brilliant, that's the piece of the puzzle I've not understood. It is also something I don't think you CAN calculate so I'll just go ahead and try it. This is exactly the kind of discussion I was hoping would develop. Your experience is far more valuable than all the theory I've read to date. I somehow missed the fact of the vacuum/chimney effect.

Thanks so much for your input Hook.........now I've got lots to think about.

Oh yea, I can remove the elbow any time. I ground out the stop in the tee and press fitted it in there so it is removable if things don't work.

[HookLine]

Thanks so much for your input Hook.........now I've got lots to think about.

Oh yea, I can remove the elbow any time. I ground out the stop in the tee and press fitted it in there so it is removable if things don't work.

No prob. I find this stuff pretty interesting, a nice combination of thermodynamics and fluid dynamics.

I am very interested in how it turns out. Try it both ways, with and without the elbow (and keep everything else the same), and let us know.

[rad14701]

I'm glad it's not just me that feels that the placement of an elbow in the column serves no purpose other than to add restriction and turbulence to the vapor path... The vapor pressure within the entire column will remain the same and the takeoff valve will still control actual reflux... I can virtually guarantee that doing runs with and without the elbow would yield identical results... The removable elbow is a great way to prove/disprove the theory...

I think it's safe to say that I'm not the only member here who would welcome comparison results, from subsequent runs of the same batch of wash if at all possible... Doing so would help in turning scientific theory into scientific fact...

[manu de hanoi]

I dont see how the turbulence created by the elbow would affect the column because it is above the packing. The only adverse effect i see is the splashing of centered reflux against the walls, the positive is that it prevents the reflux from the condenser chamber walls to slide straight into the column.


I believe Riku simply wanted to take advantage of the speed of ascendin vapor to give some extra pressure in the output pipe. I read some discussion somewhere too on the shape to the aperture (it should be more like a vertical slot than an horizontal one..... or the opposite).

[punkin]

Thanks Hook, as usual your experience and understanding of the theory shines through.

I wasn't a fan of the elbow idea, as i figured the reflux ratio was easily enough controlled by the valve opening.

Like Minime, i'm keen to try imy new toy in actual operation, and was already lying awake last night thinking i should be doing the construction outa 65mm pipe (i have some here) instead of 2"

I have a question about the restriction at the keg neck?

If we are running 2", 2.5" or even 3" columns but there is the short restriction where the opening of the keg is (maybe an 1" or 1-1/4" hole) is the restriction made up for just by a short quickening of the vapour speed before slowing again once in the column? Or is that restriction controlling the vapour quantity that's available at any one time for the column to operate?
I know i'm showing my ignorance of the science, but just one more answer i don't have. It may become important to me if i decide to upgrade my column in the near future....

Question #2, what would you guys say would be the theoretical point of diminishing returns ( or the max practical length) of a 2" packed column? Assuming structured copper mesh and a 2.4kw element ?

[rad14701]

As I pointed out, the pressure in the take-off tube will never be greater than the rest of the column, based on physics, it will remain constant throughout the column - even at the take-off valve... Vapor density, unlike pressure, could differ by an almost indistinguishable amount within the take-off, however, but this would not be consistent... To go one step further, under certain circumstances, it may even be possible to create a vacuum in the take-off due to vapor flow past it although this is a very remote possibility, again, due to almost instantaneous pressure equalization... Temperature differential of components would have to be considered in order to create a vacuum...

Long story short, I really don't see an elbow having much of an impact on reflux... Vapor density and pressure at a given temperature at a given column height will be what it is regardless of the elbow or lack thereof...