A warning against insulating the column of your still.

[peanutaxis]

Background:

Shortly after building it I insulated my pot still. I knew that it would have some reflux ramifications, but I considered that these would be minor, and it was something quite unexpected and specific that bit me: the insulation of the column.

My pot still with 'column' insulation.

My pot still without 'column' insulation.

Firstly, I have a phase angle controller so my heat input is not the issue. I have a temperature probe right at the swan neck and, in fact, thank goodness I do because otherwise I wouldn't have been able to deduce the problem. The problem was that - at least when doing a spirit run - the temperature of the probe, and the liquid output of the still, would vary wildly. It could easily jump 30°C in two minutes, and then drop just as fast. Even heating the still more slowly didn't seem to help much, and led to it taking many hours to heat up (and it's only 10 litres!). This first graph illustrates the problem I'm talking about. While heating up, the temp (and spirit output) was just all over the place. The temps do gradually converge, but the fluctuations were unacceptably large (click to enlarge):

Crazy temperature (and spirit output) fluctuations during still heat-up WITH insulation round the column.
(Black dots are data points, red line is interpolation)

I measured these data points last night while I was sitting there doing a run, watching the still get up to temp, and trying to figure out what on earth was going on. Clearly the charge was heating up, racing up the column (reflected by a large temperature spike at the swan neck) and then cooling and retreating back into the boiler again (reflected by a large temperature dip). And this pattern continued on and on. The question was: why was the pot, column and lyne arm not just gradually and steadily heating up like they should?

At some point it hit me that the insulation, not of the pot but of the column, was almost certainly the culprit. Why? Because at the point where the insulation ends it presents a large discontinuity to the vapour right before the temperature probe/swan neck. My hypothesis is that the charge heats up enough for the vapour to reach the swan neck, but at the very point that it reaches the neck, the insulation disappears and the vapour suddenly finds a whole lot of cold[er] copper which is not heated up yet. This cold copper absorbs the heat in the vapour and condenses it again. The process then repeats. It wouldn't be so bad if this was happening a good distance before the swan neck, but unfortunately my ending the insulation right before the neck ensures that much of the vapour in those surges makes it over the neck and it gets condensed and smears my product.

So after a while of collecting data I thought I'd test this. I stopped distilling, let the still cool down for a while, removed the insulation from around the column, and started heating up again. And here were the results(click to enlarge):

Temperature profile WITHOUT insulation around the column.
(Black dots are data points, red line is interpolation)

The first thing to notice is that the temperature DOES still fluctuate a little when the still is warming up, but far, far, far less. Also, it only took about 40 minutes for the temp to stabilize at 79°C. So this proves that without that particular insulation around the column of my still, the still performs insanely better.


Conclusions:(and extrapolations)

1. Starting or ending insulation near the swan neck of a (pot) still is not a good idea.

2(a). More generally, any discontinuities in a still will lead to fluctuations internal to the still, while the still is not in equilibrium (while it is heating up or cooling down).
2(b). The fluctuations will be most marked near where the discontinuity exists.
2(c) From (a) and (b): If the discontinuity is near the swan neck, those fluctuations will now present themselves as external fluctuations in the form of fluctuating distillate output.


Discussion:

In my still, and in many others' there are often large discontinuities. For instance where the column meets the pot, the diameter of the still decreases markedly. Even without the insulation in this experiment my still still (lol) fluctuated a bit while heating up (see graph 2). However - and here is the important point behind 2(c) - because this discontinuity (the decrease in diameter) is a fair distance away from the neck of the still, these fluctuations did not present themselves as output fluctuations.
You can bet that if I now decided to cut the column of my still so that the swan neck was only a few inches above the boiler - in other words near the discontinuity; the diameter change - that the distillate output would fluctuate again. My suspicion is that if I modified my still so that the diameter decreases slowly - as it does in a scotch whisky still - that I would mitigate the temperature fluctuations even more (I DO intend to do this once I have Spin Forming of copper sussed).


In more general terms - and these will be well known to skilled pot stillers and designers - any discontinuity in a still is going to produce fluctuations.
However, in many instances these fluctuations might be completely manageable, and may not manifest as output fluctuations. Discontinuities might include: changes in heat input, abrupt changes in dimensions, thickness, insulation, changes in material (e.g. SS to copper).

The phenomenon that is the subject of this experiment may not present itself so obviously to other still designs. Compared to the size of the boiler, my still is designed to have a comparatively large diameter over the swan neck. This results in a large mass of metal that needs to be heated up by a comparatively small boiler. Stills with large boilers compared to their output columns may not have such disastrous problems.

But the main moral of this story is to keep discontinuities away from the swan neck! I welcome comments/corrections/criticisms etc.


Thanks for listening!
[p

[Prairiepiss]

Why would you insulate a pot still riser in the first place?

[peanutaxis]

To save energy, of course!

[Prairiepiss]

To save energy, of course!

I can see a boiler. But from the looks of your pot still riser. It's small enough that you wouldn't need to worry about it? I guess I'm just missing something here. But the only time I've ever seen anyone use insulation on a pot still. Was the plumbing from a boiler to a thumper.

A reflux still would be a completely different beast.

[peanutaxis]

I should have used the word 'riser' and not 'column', as you point out.

Ultimately I'm glad I had this problem, though. I know so much more now.

[still crazy]

That was an awfully lot of post to explain what 5 minutes of reading would have told ya.
Step 1) learn from others mistakes (commenly reffered to as experiance)
Step 2) when you don't know, ASK, it's what the forums all about

[peanutaxis]

That was an awfully lot of post to explain what 5 minutes of reading would have told ya.
Step 1) learn from others mistakes (commenly reffered to as experiance)
Step 2) when you don't know, ASK, it's what the forums all about

About the 'reading' I'm afraid I simply don't believe you. I will gladly if you can reference that reading.

But the problem is, it's easy to know what to ask about (the insulation) in hindsight. But beforehand it could have been any number of things - you could ask a million questions. As it happens I asked about the issue itself, but got given the wrong answer! (Not the fault of the answerers, though.)

But in any case I'm interested in learning about exactly what's going on inside a still, and so as soon as I thought it might be the insulation it didn't take long to whip it off, test it, and add to the data pool. If someone had just said "take off your insulation" I probably would have learned nothing about what was going on.

[blind drunk]

Well then, there goes my belief out the window. My riser is insulated up to the lie big. I thought it was helping, but maybe it isn't. It's all so subjective, all alone in my little shed. But I must admit, it runs pretty rock solid stable. Out put fines tunes pretty good.

[peanutaxis]

Well then, there goes my belief out the window. My riser is insulated up to the lie big. I thought it was helping, but maybe it isn't. It's all so subjective, all alone in my little shed. But I must admit, it runs pretty rock solid stable. Out put fines tunes pretty good.

Hold on, hold on. It's insulated all the way to the liebig condenser?

[HookLine]

Try insulating to the blue line. See if that makes any difference. I suspect it will.

[BrooklynTech]

I run a pot still out on my side deck which can be exposed to wind. When the wind begins to blow abit the colume cools and the output stops or really slows down. So I wrap the whole upper part of the still in two flannel shirts. This seems to work pretty good at keeping the flow constant no matter wind conditions. I use a 2000 w electric hot plate so no open flame to worry about burning the shirts.

http://www.waianaecrider.com/Brewing/IMAG0760.jpg

[peanutaxis]

Try insulating to the blue line. See if that makes any difference. I suspect it will.

I run a pot still out on my side deck which can be exposed to wind. When the wind begins to blow abit the colume cools and the output stops or really slows down. So I wrap the whole upper part of the still in two flannel shirts. This seems to work pretty good at keeping the flow constant no matter wind conditions. I use a 2000 w electric hot plate so no open flame to worry about burning the shirts.

Yep, both of those'd fix it. Now that I've de-insulated it, though, I'll probably just leave it like that.

[Husker]

Honestly, I think some of what you are seeing, is the VERY sharp angle, and temp drop, due to lack of insulation.

The very sharp angle causes the vapor stream to slam into the tube. If that tube is 3 or 4° cooler than vapor condensation temp, then it can cause a quick vapor collapse, reflux some, and cool off the lower tubing, causing a 'cycle' to start.

Several things would have changed this (or even 'fixed' it).

1. Heat up a little, to make sure the vapor speed is faster and the pressure up, would make a difference.
2. A smoother elbow would make a difference.
3. lack of all insulation would have made a difference (as you found out).
4. insulation past the elbow would have made a difference (as you were informed).

A lot of people will still where there is a large air gradient (i.e. in the cold, or in the wind). Here, your advise of removing insulation is not a good thing. It will cause wildly fluxuating temps and flow rates.

Hook's suggestion about insualtion PAST the point of return for the vapor, is likely the best all around suggestion. All of my still heads have insulation that 'can' be put on them. I certainly use insulation on my columns, always. Also, on my pot stills, I insulate if it is cold, or I am outside and there is any breeze.

The worst offender was when I tried to use my all copper alembic on Dec 31th one year (to have to hours old good stuff to ring in the new year). It was about 20 °F with a little wind. I damn near could not get ANY output to flow at all. It even sucked my water seal back into the boiler, a couple of times. I will never still like that again, but for that one, I was not at home, and that was the still I happened to bring along with me (at my folks house).

H.

[blind drunk]

Hold on, hold on. It's insulated all the way to the liebig condenser?

I should have said the take off as I use a worm and bucket.

[Pop Skull]

Honestly, I think some of what you are seeing, is the VERY sharp angle, and temp drop, due to lack of insulation.

The very sharp angle causes the vapor stream to slam into the tube. If that tube is 3 or 4° cooler than vapor condensation temp, then it can cause a quick vapor collapse, reflux some, and cool off the lower tubing, causing a 'cycle' to start.

Several things would have changed this (or even 'fixed' it).

1. Heat up a little, to make sure the vapor speed is faster and the pressure up, would make a difference.
2. A smoother elbow would make a difference.
3. lack of all insulation would have made a difference (as you found out).
4. insulation past the elbow would have made a difference (as you were informed).

A lot of people will still where there is a large air gradient (i.e. in the cold, or in the wind). Here, your advise of removing insulation is not a good thing. It will cause wildly fluxuating temps and flow rates.

This is a great explanation of what could be going on. Very informative and goes into the mechanics of what could be going on. Salute Husker! This is a great (and constructive) contribution to the thread.

[peanutaxis]

Hold on, hold on. It's insulated all the way to the liebig condenser?

I should have said the take off as I use a worm and bucket.

Yeah If you've got it going all the way then that should be fine. The issue is with stopping/starting insulation near (before, really) a swan neck.

[peanutaxis]

Honestly, I think some of what you are seeing, is the VERY sharp angle, and temp drop, due to lack of insulation.

The very sharp angle causes the vapor stream to slam into the tube. If that tube is 3 or 4° cooler than vapor condensation temp, then it can cause a quick vapor collapse, reflux some, and cool off the lower tubing, causing a 'cycle' to start.

Several things would have changed this (or even 'fixed' it).

1. Heat up a little, to make sure the vapor speed is faster and the pressure up, would make a difference.
2. A smoother elbow would make a difference.
3. lack of all insulation would have made a difference (as you found out).
4. insulation past the elbow would have made a difference (as you were informed).

Hmmmn.

The sharp angle is not a problem. The fact that removing the insulation worked wonders shows that there is no 'slamming' going on. I certainly agree that a sharp angle might have a small effect (my pipes are fully two inches wide!), but I can all but guarantee that if I had smoothed the angle (and left the insulation) it would not have solved the problem. Hot gases would still have exited the insulation and suddenly encountered cold copper.
Also, because the pipes at the swan neck are soldered together, the heat is still conducted just as well beyond the neck. Maybe even better, in fact! because the two pipes are joined by an ellipsoid shape, which is a larger surface area than a circular one.

I completely agree that insulating beyond the neck would work too. In fact, I think I might do that in future. I didn't put it in the conclusions as I had rambled enough.

A lot of people will still where there is a large air gradient (i.e. in the cold, or in the wind). Here, your advise of removing insulation is not a good thing. It will cause wildly fluxuating temps and flow rates.

Huh? I don't get it. I'm not necessarily advising people to remove insulation. I would advise them to understand what was causing the problems with my still, and take that info onboard. This is the Research and Theory section, not the follow-this-recipe-blindly-and-it-will-solve-all-your-problems section. However, I gladly take your criticism on board. Next time I do a 'study' like this I will include an "Other Possible Remedies" section.


Thanks!
[p

[peanutaxis]

I run a pot still out on my side deck which can be exposed to wind. When the wind begins to blow abit the colume cools and the output stops or really slows down. So I wrap the whole upper part of the still in two flannel shirts. This seems to work pretty good at keeping the flow constant no matter wind conditions. I use a 2000 w electric hot plate so no open flame to worry about burning the shirts.

http://www.waianaecrider.com/Brewing/IMAG0760.jpg

So just to be clear, Brooklyn, if you decide to insulate your pipes more permanently, make sure you don't stop the insulation before the neck of your still. Go well over the neck and down the other side .Or even better, go right up to just before your condenser.

[Max_Vino]

Peanutaxis...I think your observation is brilliant.

My take on your problem is a little different. I think what you're seeing is a classic case of thermal oscillation. Some of the more advanced temperature controllers utilize strategies to overcome this oscillation. In your case the oscillations are occurring because of the headspace and its connection to your condenser. Inside that space at the top of your column is a cloud of vapor, condensing and falling back into the still. Your biggest problem, in my opinion is that you have no thermal isolation between your column and your condenser. That is to say, your column and your condenser are a single piece, energy is transferred from the column to your condenser cooling that vapor cloud at the top of your still.

You might try something like this....

Cheers,
Max

[rad14701]

peanutaxis, you discovered what we commonly call "huffing"... Cool air sucking up into the gooseneck and shock cooling the insulated riser and boiler charge...

[peanutaxis]

Peanutaxis...I think your observation is brilliant.

My take on your problem is a little different. I think what you're seeing is a classic case of thermal oscillation. Some of the more advanced temperature controllers utilize strategies to overcome this oscillation. In your case the oscillations are occurring because of the headspace and its connection to your condenser. Inside that space at the top of your column is a cloud of vapor, condensing and falling back into the still. Your biggest problem, in my opinion is that you have no thermal isolation between your column and your condenser. That is to say, your column and your condenser are a single piece, energy is transferred from the column to your condenser cooling that vapor cloud at the top of your still.

You might try something like this....

Cheers,
Max

Thanks. Hmmmn. I've never heard of thermally isolating the condenser before. That seems backwards to me because the very issue in my case case was a temperature(insulation) DIScontinuity, and you are suggesting to make another discontinuity!!??! Not sure if you're aware, but my condenser is actually quite far away from the neck:

I modelled my still on the dimension of a scotch still, except (thus far) the sudden diameter change from the boiler to the riser - they don't thermally isolate, so I guess I'm hesitant to as well. As I understand it a phase angle controller (like I'm using) clips the sine wave of the AC power, so we're talking about an oscillation of (in my country) 50 times per second, so the oscillation of the power is not an issue. I completely agree that the vapour is oscillating in and out of the column, but it's happening quite slowly if you look at the time axis of my graphs.

peanutaxis, you discovered what we commonly call "huffing"... Cool air sucking up into the gooseneck and shock cooling the insulated riser and boiler charge...

My wash still huffs. If I lick my palm and place it in front of the take-off I can feel the air pulsing in and out, perhaps 5 times per second - my understanding (correct me if I'm wrong) of Huffing is that it is a fast oscillation, whereas this phenomenon is slow. Again, look at the time axis of my graphs.

[peanutaxis]

I'm at quite a loss as to why people seem to keep offering fixes for my still. Perhaps people haven't read the OP properly, but my still is fixed. It was the INSULATION. End of story!

[Prairiepiss]

Maybe because some of us aren't convinced you have corrected the real problem. And or think that you could improve it even further.

I one am still not convinced. And after see the whole still. It leaves me wondering.

The fact that it takes you 4 hours to heat that thing up is just mind boggling. You add insulation to the boiler and still get 4 hours. I'm just thinking the heat source is way under powered? That boiler is what 2 or 3 gallons? That shouldn't take that long to heat up. If its that grossly under powered? It can surly cause problems.

What watt rating do you have on that hot plate? What kind of take off rates are you getting from it?

Maybe I'm wrong. But it shouldn't take that still 4 hours to heat up. Unless you stillin in a snow storm? And 4 hours is what you stated in the other thread?

[peanutaxis]

Maybe because some of us aren't convinced you have corrected the real problem. And or think that you could improve it even further.

I one am still not convinced. And after see the whole still. It leaves me wondering.

The fact that it takes you 4 hours to heat that thing up is just mind boggling. You add insulation to the boiler and still get 4 hours. I'm just thinking the heat source is way under powered? That boiler is what 2 or 3 gallons? That shouldn't take that long to heat up. If its that grossly under powered? It can surly cause problems.

What watt rating do you have on that hot plate? What kind of take off rates are you getting from it?

Maybe I'm wrong. But it shouldn't take that still 4 hours to heat up. Unless you stillin in a snow storm? And 4 hours is what you stated in the other thread?

(For others: The four hour thing is from here.) Hold on, hold on. What I said was that I was sick of it having to take four hours OR having to put up with the erratic-ness. It used to take me four hours to heat up if I wanted to avoid the erratic behaviour. Now it's fine! Not sure exactly how long it takes to heat up now (graph 2 says 30 minutes from 40°C) but easily less than an hour. There's enough power, I never even put it on full. I think it's 600W.

Given this, the insulation really was the problem. It was the only thing I changed in my 'experiment', and the still went from broke to fix'd.

You're right though, I shouldn't forget that people are trying to help. But it is fixed; I though that was quite clear from my Conclusion, but I could have made it clearer.

[rad14701]

The insulation was merely moving where the huffing was being caused, and perhaps amplifying it... I'm not doubting that removing the insulation has helped resolve the problem, at least to your satisfaction... I just don't think the insulation was the entire problem...

Think of it like an auto mechanic making a magic tweak to make an engine perform better yet not actually fixing the root of the problem... But as long as the customer is happy that's what the mechanic is concerned with whether emissions are within range, or the fix is consider proper...

Case in point... Some mechanics I used to work with would put a BB in the vacuum line to the engines EGR valve, effectively disabling it, to improve performance simply because they lacked the knowledge to fix the engine properly... I fixed the root of the problem and let the EGR valve do its intended job... And then I taught those other mechanics how to fix things right as well...

[mash rookie]

The problem I have with this post is that it is very misleading. Even if the poster has made correct observations about what works for him it should be posted in novice or the pot still category.

It certainly does not qualify to be in the Research and Theory. Rad. Please move it to a more appropriate category if possible.

It is a scientifically accepted fact that reflux columns will not perform to designed efficiency without insulation to reduce wall affect channeling. The post title will influence and confuse column builders.

MR

[peanutaxis]

The insulation was merely moving where the huffing was being caused, and perhaps amplifying it... I'm not doubting that removing the insulation has helped resolve the problem, at least to your satisfaction...

And, for the second time, if you actually read what I wrote, you'll see that I say exactly that; I've fixed and/or moved the fluctuations AWAY from the neck. But these fluctuations are going to happen on any still that has a drastic change in diameter (virtually all pot stills)

I just don't think the insulation was the entire problem...

Sounds to me like you don't want it to be the only problem, or perhaps you can't bear to back down. Here in the real world, it is fixed. In fact it is beyond fixed: usge says that jumps are normal. My still doesn't even do that now!

[peanutaxis]

The problem I have with this post is that it is very misleading. Even if the poster has made correct observations about what works for him it should be posted in novice or the pot still category.

It certainly does not qualify to be in the Research and Theory. Rad. Please move it to a more appropriate category if possible.

It is a scientifically accepted fact that reflux columns will not perform to designed efficiency without insulation to reduce wall affect channeling. The post title will influence and confuse column builders.

MR

I certainly should have used the term "riser". If I could change it I would, but you can't change a title after posting.

If this thread is not 'Research and Theory', nothing is.

[Prairiepiss]

Sounds to me like you don't want it to be the only problem, or perhaps you can't bear to back down. Here in the real world, it is fixed. In fact it is beyond fixed: usge says that jumps are normal. My still doesn't even do that now!

Then you can count me in on that statement to. Because I feel the same way Rad does.

Buy as MR pointed out. The way you labled this thread dictates the need for more or further investigation. And all the information needs to be on the table. So when someone new sees it they don't think that is the only thing that can cause this problem.

If your happy with the outcome and don't want to participate in the further discussion. That's up to you. But you could let the rest of us throw our thoughts on the table. So maybe we can discuss them. Without taking jabs at us?

[peanutaxis]

Then you can count me in on that statement to. Because I feel the same way Rad does.

Buy as MR pointed out. The way you labled this thread dictates the need for more or further investigation. And all the information needs to be on the table. So when someone new sees it they don't think that is the only thing that can cause this problem.

If your happy with the outcome and don't want to participate in the further discussion. That's up to you. But you could let the rest of us throw our thoughts on the table. So maybe we can discuss them. Without taking jabs at us?

Look I completely agree that I used the wrong term: 'column'. Perhaps a moderator can change the title.

My position is simply that it was the placement of the insulation that caused an erratic output, and once that was changed it now behaves like any normal, functioning still. I am completely open to any other explanations. However, ALL of those further explanations (thus far) have been at odds with the facts, and so have been easy to disprove.

Put simply, if someone wants to disagree with my findings, then they are going to have to disprove one or more of the following statements,

1. My still had an erratic output.
2. I removed the insulation.
3. My still behaves like an ordinary still.

or prove that the conclusion (4.That fluctuations adjacent to the swan neck were to blame) is not the correct inference from 1-3.

And I am quite open to this; I am not being precious about it. For instance, the temperature fluctuations of my 'fixed' still (graph 2) might prove that 3. is wrong. Perhaps a normal still does not fluctuate even by small amounts. (But I am led to believe that normal stills DO fluctuate - see my reference to usge three posts back.)

I am completely open to opinions which make sense. Maybe your feelings are completely correct, but they need rational Research, Theory, or both. Otherwise this is a thread about discussing feelings. And I will jab at those, I can't countenance that.