Column insulation

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Column insulation

Postby tracker0945 » Wed Aug 29, 2007 7:14 pm

I understand the need for insulation to maintain consistant reflux results but how much of the column does one insulate.
I have a Bok mini still, so do I insulate as far up as the take-off point, as far as the bottom of the condenser or all the way to the top?
2"x38" Bok mini and
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Postby CoopsOz » Wed Aug 29, 2007 7:30 pm

Just up to the take off valve.
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Postby tracker0945 » Wed Aug 29, 2007 9:29 pm

So if one insulated up to the take-off valve and then had some left over, would it be detrimental to insulate further instead of wasting what I have or would it be of some small advantage to use it all up
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Postby CoopsOz » Wed Aug 29, 2007 9:54 pm

This is only my opinion, but once it gets to the condenser I don't think it would do anything, however it definitely won't be detrimental.
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Postby junkyard dawg » Wed Aug 29, 2007 10:17 pm

I wouldn't insulate the condensor section. You are encouraging the heat to flow out of the rising spirits with the condensor. Insulation reduces that heat flow...

You could put on some aluminum fins for cooling...
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Postby tracker0945 » Wed Aug 29, 2007 10:35 pm

You have me convinced. I will stop at the take-off valve
Thanks
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Postby fahdoul » Sat Sep 01, 2007 7:51 pm

I use corrugated cardboard to insulate my Bokabob, held on by twisted bits of wire. It's quick, cheap and easy, and works fine.
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Postby tracker0945 » Sat Sep 01, 2007 8:45 pm

Thanks for the hint.
I already have enough hot water pipe insulation to use up as far as the take-off point but have been thinking that to keep the angle plate a bit warmer to reduce condensation on the underside I may have to insulate slightly higher, so will use your suggestion while I try different heights.
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Postby pintoshine » Sun Sep 02, 2007 7:56 pm

Insulating a column? How do you get rid of the excess heat and achieve a heat gradient required for the fractions? Seams you would end up with the same fractions up and down, What good is that? you would end up putting the reflux into a over heated column and the packing would be worthless because the temperature all along the column would be the same.
You have to dissipate the heat somewhere to achieve the fractions. I hope you are not solely relying on the refluxing from the condenser. If this is the case why have packing at all? You could achieve the same results with a short column and lots of reflux.
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Postby Cruiser » Sun Sep 02, 2007 10:45 pm

Pintoshine, I think I have to disagree with you on this one (but this would be the first time).

From what I've read on the parent site it IS better to insulate the column. Theory is that the cooler distillate being refluxed is cooling the top of the column while the bottom is being heated from the boiler. You certainly want an even temperature gradient and I think that will happen regardless of insulation. Although copper is a very good conductor of heat, a thin walled tube doesn't conduct it that well from one end to the other even when insulated. I think the issue is that being un-insulated would cause vapour to condense on the inside wall of the column rather than in your packing. Also, sudden draughts may cause the column to surge or something. I'm just going on the advice of the parent site.

Anyway, mine is insulated, yours is not. We're both making good 'shine. So maybe it doesn't matter a hoot.

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Postby CoopsOz » Sun Sep 02, 2007 11:32 pm

That was my understanding too Cruiser....but I don't have the balls to question Pint. :D . I guess I've got some reading to do!
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Postby HookLine » Mon Sep 03, 2007 2:47 am

Might be pushing my luck here, but I am going to have to disagree with Pint twice on one day.

I thought the advantage of insulation was that it keeps the temp gradient very stable and even, and keeps heat loss (ie thermal inefficiency) to a minimum.

The temp gradient is not imposed by heat loss through the column walls, but by the differing boiling points of the various fractions as they reflux and separate up the column. Losing heat through the column wall just introduces another (and unnecessary) factor into the thermodynamics of the column, which is only going to make harder to achieve a stable gradient.

I suspect all Pint is doing is using more heat to do the same job, and maybe also not getting quite the same degree of temp stability in the column. I think he uses a stainless column, which would help stabilise it if left uninsulated. The problem would be more obvious in a copper column, which has a much higher rate of thermal conductivity (and hence heat loss).
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Postby pintoshine » Mon Sep 03, 2007 7:01 am

Maybe all the properties that you are discussing has to do with the size of the column, and which part you are working. The rate of temperature change will be inversely proportional to the mass. I have never seen an insulated column out in the industrial complexes I have worked in. When I asked why I was told what I related to the group, which was that the internal refluxing requires continual removal of the heat. I was told that if there was not cooling all along the column then all the plates would achieve the same temperature and liquid mixture and would be ineffective at doing their job because of the temperature differential required to condense the liquid from the previous level. I will try to find more information on this because the counter flow of the lighter liquids down should be able to do the same thing.

I work my column, taking advantage of the cooling all along the column and am working the condenser very little. My column equalizes without the condenser at the top if I want it to. I push it a bit more and get the refluxing up there in the top. I am seeing very little input to output difference in my cooling water temperature so I am very sure that the column is doing most of the refluxing. The only reason I reconfigured the column to have the vapor splitter and reservoir inside the column was to remove more flavor. I was already getting 93+ with just careful temperature management and an external condenser. I was playing around trying to improve(reduce) the flavor. Since one of my cheapest feed stocks is molasses, I was trying to get decent vodka from the white rum. It worked.
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Postby markx » Mon Sep 03, 2007 9:21 am

I think I have to disagree too.......Temperature gradient will form in an insulated column because of the different boiling points of the fractions and not because of heat loss through the column. The heat loss is meant to happen in the condenser.....of course if you leave the column naked you can reflux most the vapours just by the heat loss through the column wall and achieve a similar temperature gradient without stressing your condenser. But that equlibrium is sensitive to outside disturbances....drafts and changes in the amient temperature. The insulation keeps these effects to a minimum. In a big plate column it may be benficial to create a cooling effect and internal reflux between the plates.....a big column is also thermally way more stable and small disturbances in the ambient conditions do not affect it that much.
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Postby pintoshine » Mon Sep 03, 2007 9:53 am

So far this is all opinion. I did an exhaustive search of all my chemical engineering books, the web with every combination of key words I could find, and every design criteria I could find and there is no mention of insulating a column, except when the column is out in the weather and it only says that the boiler should be sufficiently large to make up for the changing atmospheric conditions.
In all my classes and industrial experiences, I have never encountered an isolated, insulated column except where the fractions were in the distillation of air into its components. Of course the distillation of helium requires isolation for the atmosphere.
If someone could point me to some, any, discussion, except for anecdotal proof in the distilling forums, I would greatly appreciate it. I firmly believe you guys are selling snake oil in that this design criteria is often stated as negligible.

Such as in this site which plainly states heat effects (heats of solution, heat losses to and from column, etc.) are negligible

http://lorien.ncl.ac.uk/ming/distil/distildes.htm
Further in the site it states,
Weather Conditions
Most distillation columns are open to the atmosphere. Although many of the columns are insulated, changing weather conditions can still affect column operation. Thus the reboiler must be appropriately sized to ensure that enough vapour can be generated during cold and windy spells and that it can be turned down sufficiently during hot seasons. The same applies to condensors.


So the point is we have differing opinions. I can show evidence of the negligibility of column insulation as a design criteria. I want someone to prove me wrong so that I may justify adding the effort and expense for an appreciable quality or throughput enhancement.
Without cost justification I wouldn't dream of recommending the enhancements to others.
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Postby Fourway » Mon Sep 03, 2007 10:17 am

pintoshine wrote:I can show evidence of the negligibility of column insulation as a design criteria.



I've watched head temp crash on an uninsulated column from someone opening a door on a warm summer night.

you are wrong pinto.

all the books in the world could disagree... wouldn't matter. they'd be wrong too.
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Postby HookLine » Mon Sep 03, 2007 10:50 am

Pint

I agree that for an uninsulated column, the bigger the column (the thermal mass), the lower and more linear the proportional rate of thermal loss, and so the more inherently stable the thermal mass and temp gradient within the column.

But, the full context of that first quote is:

The McCabe-Thiele approach is a graphical one, and uses the VLE plot to determine the theoretical number of stages required to effect the separation of a binary mixture. It assumes constant molar overflow and this implies that:
-molal heats of vaporisation of the components are roughly the same
-heat effects (heats of solution, heat losses to and from column, etc.) are negligible
-for every mole of vapour condensed, 1 mole of liquid is vaporised


This is describing a theoretically ideal and stable system, in which they are assuming virtually no heat losses from the overall system (except via the reflux condenser), implying strongly that in practice the column (and boiler) is well insulated. They are not saying that heat losses don't matter, but that they don't (or shouldn't) occur.

And the second quote explicitly states that:

many of the columns are insulated


So why would many columns be insulated if it is either unimportant, or actually counterproductive?

What they are saying here is that insulation is not always enough to maintain stable temp gradients in columns open to the atmosphere (or directly exposed to weather like many huge petroleum columns are), and so boiler control also becomes important in helping to maintain a stable temp gradient. My guess is this only applies to large columns.

I think I will stick to an insulated column.
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Postby junkyard dawg » Mon Sep 03, 2007 11:38 am

How do you get rid of the excess heat and achieve a heat gradient required for the fractions?


I assumed the gradient was achieved as the concentration of ethanol decreased in the wash... that is the bulk of heat that is slowly rising in temp. at this scale we don't achieve that temp gradient in the column, but in the boiler. Our columns are designed to mimic the plates that takeoff in the 78 degree range... they do not operate like a big commercial plate column.

I like insulation around my column... :shock:

:lol: :lol: :lol:

hope im not the only one that thought that was funny...
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Postby pintoshine » Mon Sep 03, 2007 11:54 am

Ok, so is it my understanding, that based on a single observation of an instance of a head temp crash, that insulation is required for a good efficient column? And that in this regard I am completely wrong? Might it have been that this particular still was not adjusted correctly or that is was severely limited in its performance?

I have studied almost all the stills on Tony's site and thousands of others and I haven't seen many insulated columns. I'm afraid to tell you but you few are in the minority. And that can't make all of us wrong now can it? It just makes you different.
By the way, I still haven't seen any documentation and I wish I could. It would be nice to find a simple enhancement that could save me a load of time/money. But I am afraid that $2 worth of insulation isn't going to do much.

But let me ask you, for your insulation, what R value are you using. Is it like R16 or R20? Is it only R2 or R3? Would you say the conduction coefficient is that much different than stagnant air. It is not as high a value as vacuum is it? I would like to hear to see if there is significant difference to warrant a different temperature profile. If I treated the outside of the column as a condenser and the air as the coolant I could calculate the heat loss for the column. Also I need to know the material, the wall thickness and the diameter of the column. I bet there is not 5% difference in the cooling of the column with still air than there is with the 1.5 cm of fiberglass insulation.

Maybe we should also take a poll.
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Postby Fourway » Mon Sep 03, 2007 12:04 pm

pintoshine wrote:But let me ask you, for your insulation, what R value are you using.



*sigh*
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Postby pintoshine » Mon Sep 03, 2007 12:09 pm

You know I forgot to ask some questions. What metrics are we improving with insulation?
Are we saying we would need less reflux?
Or is it less heat?
Or is it we get more purity, better separation?

What are we talking about exactly?
I claim there is not enough difference with or with out insulation.
My column would be easy to insulate with a wrap on fiberglass or even some closed cell foam. I have enough stuff on hand to make a side by side comparison on a single unit. Lets design a test and see if there is significant difference.
So what is the criteria we are claiming would show the most difference?
I have a regular set of tasters and will always tell me their honest opinions(usually biased to the harsh side of course :lol: )
I can measure almost all the other parameters such as flow rates, temperature differentials of the coolant and many other factors.

You guys have to tell me what it is that the insulation is supposed to improve.
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Postby Fourway » Mon Sep 03, 2007 12:23 pm

pintoshine wrote:You know I forgot to ask some questions.



nobody disputes that you seem to know more science than anyone around.

if being right was just a matter of being able to barrage everyone in sight with a thousand questions challenging their mastery of arcane scientific knowledge you'd be right 100% of the time.

when I need to know what an "R value" is you're my go to guy.

Till then, you're wrong about column insulation.
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Postby junkyard dawg » Mon Sep 03, 2007 12:24 pm

You guys have to tell me what it is that the insulation is supposed to improve.


I like that I don't have to polish the parts under the insulation.

I have closed cell foam topped with aluminum tape. It prevents scratches and dents too...

Common sense says insulation is going to help stabilize the column, a good thing... I'm content with that, and especially with what I've observed... I don't need to quantify anything else... keep me posted tho... I'd sure like to know if I've been doing everything wrong again. :roll:
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Postby HookLine » Mon Sep 03, 2007 12:26 pm

Purity (%abv)

Taste (obviously :) )

Extraction efficiency (amount of ethanol recovered)

Energy efficiency

Time taken

Temp gradient in column, measured at say 50 mm (2 ") intervals up the column.

Coolant volume used (also need to list temps of coolant in and out). This will increase with the amount of insulation, as the heat is being exchanged by the reflux condenser, not the column wall. Reduced reflux coolant flow is one possible advantage of an uninsulated column.

Make sure you standardise all your measurements, and control for other variables, like the still charge, take-off rate, and ambient temp.

Take your time, and do it properly.

Very interested to see what the outcome is.

EDIT: And use a relatively high R value insulation. The stuff on my column is standard 3/4" thick, (2 & 1/8 ID) closed-cell foam pipe insulation used on hot water and air-con systems.
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Postby pintoshine » Mon Sep 03, 2007 12:44 pm

I currently have 400L of grape skins and juice that started out with 24.5 brix fermenting in my shop.
I'll strip it to about 45% and split the charge into two parts and test the first run with the a controlled ambient temperature and little circulating air to get the control. I'll then wrap the column and use the same adjustments to the takeoff valve and the input heat.
For both runs I will measure four criteria.

1. Reflux ratio. Full open output rate to collection rate with a fixed needle setting.
2. Temperature differential in and out of the condenser.
3. A chart of the take off purity for each run.
4. Taste test with no carbon filtering.

So. This is the game plan. I will do everything I can to document it all precisely and measure to best of my ability. I am curious to see if the myth is busted.

But, I predict, if the results do not show a significant difference, there will still be arguing.

I will be stripping during the week but I have to wait for a weekend to perform the test since large batches take a while to run.

Someone else do this test also.
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Postby HookLine » Mon Sep 03, 2007 12:58 pm

pintoshine wrote:But, I predict, if the results do not show a significant difference, there will still be arguing.


:lol: :lol: :lol: That is probably true.
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Postby junkyard dawg » Mon Sep 03, 2007 1:22 pm

I am curious to see if the myth is busted.



Pint, what myth are you trying to bust? You seem to be talking about the ideal column, or a full scale commercial column. Thats not how the small columns we are using work... We are doing small batches. The temperature gradient is determined by the mash. The column and packing and insulation function to reflux and redistill at what ever temperature the boiler is providing. Most of us are not developing a wide temp gradient were we could draw different products at different levels. We are only making a big column that will effectively redistill whatever is refluxed back to it...There is no need to develop the kind of temp gradients in the column like a continous plate still would have... thats what leads to 42 hour runs...

don't waste your time and skills trying to disprove me... thats wasteful and too easy...

I'd rather hear if you've tried using an insulated column... It seemed like an improvement when I insulated... have you had a negative experience with insulation?
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Postby CoopsOz » Mon Sep 03, 2007 1:50 pm

Once again you guys have made me feel like a preschooler. I don't have the time, equipment or inclination to test with or without insulation. In fact, I don't even use my reflux anymore. You guys are my ultimate resource, if the general consensus is insulate....then I insulate. I've never tried to re-invent the wheel, people much smarter than I have already invented it.
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Postby pintoshine » Mon Sep 03, 2007 2:00 pm

JD you have lots of good points.

As it seems to me, this falls into the "Oxygen Free Speaker Wire" sales pitch. Most electrical cable is 99.9% pure anyway.

No I have never ran one or saw the need to.
I love it when I'm wrong. I don't learn anything if I never make mistakes.

junkyard dawg wrote:The temperature gradient is determined by the mash. The column and packing and insulation function to reflux and redistill at what ever temperature the boiler is providing. Most of us are not developing a wide temp gradient were we could draw different products at different levels. We are only making a big column that will effectively redistill whatever is refluxed back to it...

If this is true, then you would not have a different product at the top than was going in from the bottom. If this is a true statement the why use a column at all?
junkyard dawg wrote:I'd rather hear if you've tried using an insulated column... It seemed like an improvement when I insulated... have you had a negative experience with insulation?

The only one I am trying to disprove is myself. It would not hurt for everyone to insulate the column. My fear is that it would mess up the columns efficiency at separating the alcohol from the water. I am aware that refluxing makes the column act as if there are more plates. But I also know that additional refluxing makes the run a lot slower and causes one to run at near flood conditions. Currently my column is seriously under powered. Maybe the insulation would increase my throughput without my having to add a power controller.
And besides whether the tests confirm or disprove the theory, the rest of the members may learn a bit about the testing methods and to question when someone says "Because I say so".
So like I said until there is some documentation, or some sort of quantifiable results to show that there is definitely a difference, then it is hearsay and propaganda and IMHO a needless waste of time and money to build a good efficient column.

But I admit at this point and time I really don't know for sure and I am going to find out. This at least gives me a good project for YouTube.
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Postby FlyboyTR » Mon Sep 03, 2007 2:50 pm

Since I am a newbie to this I honestly don’t have an opinion…other than several folks said I needed to insulate my column. I use the PS II High Capacity (3” column). All of my processing is under my open sided patio. Every time there was a slight breeze my column would destabilize and my output would stop for a few seconds up to a minute or two. During cold weather it was almost impossible for me to maintain a steady reflux. I used the aluminum faced bubble wrap insulation. Purchased at Lowe’s. It is about ¼” thick. The only thing that changed for me was the destabilization when the wind blew!

Again…I have no opinion but am most interested in seeing the differences between the two in a semi-controlled test. :D
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