VM Problems

[Almanac]

As most of you know I mainly run a 2" Pot Head on my boiler even though I am the proud owner of a self built VM column and head as seen here...



Because I am a Whisky man and my wife loves the vodka I make with my Pot Still I never run the VM - too much hassle

The column and head take up a lot of precious room in my workshop so I decided to "run it or get rid of it".

I built up a 40lt charge of low wines at 30% to run the VM. Filled up the boiler last night, put the column up and the head. I even connected up all the coolant hoses to make things handier for the morning. This morning I powered up at 0715 and by 0845 the boiler was getting up to temp and I reduced the power to 750W.

I turned on the coolant very low and watched the temp of the coolant water rise. Following Kiwistiller's advice I was going to allow the coolant to reach 45oC at the outlet while looking to keep the column temp, at the take off, at around 76-78oC

During equilibration, over the next hour, I watched as the column temp rose quite quickly to 80.9oC...and stayed there


...and nothing I did made any difference I reduced the power to 300W and the damn temp stayed stubbornly at 80.9oC. I had expected the the temp would fluctuate initially but it was rock steady at 80.9oC all the time. I even took the digi temp probe out of the take off and checked it against another and an old liquid thermometer - it was accurate.

Even at this higher temp in the take off there was no trace of vapour escaping through the top of the column. I use a mirror over the top opening to check from time to time...


Unable to figure out why my temps are off from what was expected I powered it all down and decided to let the column cool and start again later with greater control over the column temp and ignore the coolant altogether other than to maintain a steady trickle at the output.

Anyone got any observations, anything that I'm missing

AM

[Myles]

OK the vapour temperature at the top of the column is suggesting that your column is NOT achieving azeotrope. HOWEVER, this may be meaningless.

When you do take product off - WHAT IS IT? Have you already removed all the heads on a previous run? You did mention that you charged with low wines, did you do any cuts previously?

If your column is working as advertised and you are getting decent neutral out of it, this just reinforces what has been said elsewhere.

The actual temperature at the top of a VM column means nothing - what is important is the STABILITY of that temperature.

When you take product off at that indicated temperature of 80.9 deg C, what is the quality like?

[YHB]

Aidan,

Even with 100% reflux you are not guaranteed 95.6% ABV, If you do not achieve 95.6%ABV at the top of the column then you will not get the take off temperature you are looking for.

I have suggested to a few people on HD that they ditch the copper mesh and use scrubbers, from what I have seen of it and how people use it, the copper mesh is not dense enough to get the results you are looking for. All the others that have complained of low returns and have been using copper mesh have been pleased with the changes that the stainless steel scrubbers give.

If you want to invest £5.00 in some SS scrubbers, I honestly believe that the %ABV will go up, if it gets to 95.6% then the temperature in your column will be 76 degrees. Worry about the sulphides later.

[Capt-Cudellez]

Aidan, as you are seeing the VM design is really stable. You don't really need to worry about cooling temps like you do in the CM designs.

I like to have the cooling water come out "hot", but I don't give it any more thought than that. You can run the cooling so it comes off cold, you can run different power levels, it usually wont make a difference to the temp.

Where you need to think about the power going in, is when working out the reflux ratio. If you are putting in low power, and taking off product at a repetitively high rate, then you will destabilise the column, then you;ll see the temp change.

If putting in the correct power (for your gear) you can still take off slightly too fast, which wont destabilise the column, but the RR is lower, so the product isn't as clean as it would be with a slower take off speed. (ABV can be the same, but it has a hotter taste)

As other have pointed out, it sounds like the product wont be azeotrope due to the temps you are seeing, but when the valve is closed that is almost certainly down to the packing, rather than anything you are doing with the cooling or the boiler power.

With 2" column, something like 1100-1500w into the boiler, and taking hearts off at 1.0-1.2L an hour is a good place to start. Then you can start fine tuning to see what suits your gear.

[Almanac]

Well, I did as I said and let it cool and start up again. Same thing, got the temp to mid seventies then reduced the power input and the temp just sailed on to 80.9 again.

Everything was really stable just not as expected. Output was 92% but the flow rate was crap even with the valve fully open. I take the point about the copper mesh.

The column is packed with 700mm of copper mesh with centring rings immediately below the VM head and half way down the column.

The condenser seems to be operating fine and the bottom of it is packed with mesh so there should be plenty of vapour going out the valve when it's open, except there isn't.

After another couple of hours I threw in the towell, turned the power down and switched out the VM for the Pot Head and thumper. 15 minutes later I had product at 88% coming from my product condenser and I wondered, why am I giving myself this grief?

To me, the VM was an aspirational dream machine when all I had was an Airstill, so I built it and enjoyed the build, even though it drove me mad at times.

However, for Whisky I really needed a Pot Still so I built that at the same time and used it. Then I added the thumper and found I had increased the quality and purity of my product by a serious margin. Even herself is very happy with the carbon filtered Vodka I make for her now.

So, I've decided to stick to what I know because I obviously don't have the patience to run a VM. That means I have a three section stainless steel, insulated column and a VM head with twin concentric coil condenser up for grabs.

The most likely and logical future development for me is possibly a bigger column and maybe a more appropriately sized thumper with a self contained cooling system.

Thanks for the input and advice guys but Horses for Courses

AM

[Capt-Cudellez]

I can tell your down beat from it not working out for you. If you ever do decide to run it again and want to try and trouble shoot whats going on.

Try running without the collars

and I don't know if the top of your column is capped, if not put a cap on with a very small vent hole, it might help divert the vapour down the take off.

chin up

[Easydrinker]

Firstly,commiserations that things didn't go as expected.
Secondly,a clap on the back for posting it and sharing,for others to remark upon or learn.
Some bright spark may yet come back and tell you what went wrong,and how to correct it.
I'm a newbie here,with no real interset in VM,so cannot contribute to this problem.
However,I am this week-end,embarking upon the silliest still build this forum may have seen. And I mean silly (as in not admitted to failure)-I have given myself a let-out that I hope not to use.
Because of my limitations of producing wash,it may be 4-6 weeks before I post details,I hope that I have the "face" to do so if it is a dismal failure!
Hats off to you for the help your posts have given me,and if not already done,go and pour a drink for you and yours,and feel good with the world.
Have a good evening.
Robert.

[Runningman]

Hi Aidanmac
How close is your collars to the mesh.

If they are too close then your column will probably flood. This may be causing the temp problem
Regards
Runingman

[Myles]

700 mm of mesh style packing just won't do it - not unless you drastically reduce your product collection speed and increase your reflux ratio.

You could switch to a (more expensive) packing with a lower HETP or try increasing the vapour ABV that enters the column.

However you do need to ask if it is worth it for yourself. I do have a VM - but for me it just produces a neutral base for gin and other infused spirits. If I want vodka to drink I make it on the pot still - but that is just my personal choice.

Judging by what others have said you could use that 700mm column for white rum, but a lot of the column folks talk about taking rum at 94%.

There is some talk of using fine wire wool instead for the packing for vodka, but I have not tried it myself.

If you wish to try a low cost alternative packing you could try pumice gravel.

[RumJohn]

Myles: You mention column folks taking off rum at 94%. At that level it is not rum anymore. My spirit run on rum is ideal at 80%. My vodka I take to 96%. But I have to reconfigure the still and increase the column length by 3X to do that.

Aiden: I would have let the run continue. You had reached equilibrium and your temp was stable. You had lowered your heat source and temp remained stable. You just might have a great bit of kit there.

[Myles]

I am basically a pot stiller so I wouldn't know, just repeating what others have said. From what I have heard though the shorter column is a good bit of kit for making some products.

Refluxed rum at 80% - that is interesting - that is comparable to a pot and thumper combination. I was under the impression that you would aim to take it off at over 90 on the column. I don't make any flavoured products on mine so I can't comment, but perhaps the column is even more versatile than I had thought.

One thing that a lot of folks do say though is that your column tends to stabilise at a set point, whether that is 80% or 95% - trying to move it from that can be challenging without physically changing the configuration - for example by adding another packed section.

AM it looks like you run a 2" column that goes into a smaller dia T as the vapour splitter - do you have a short section of the smaller size below the T also?
I did try that inline configuration at first but fairly quickly changed to the offset condenser type. With the inline version you have to get the vapour speed in the T high enough to be turbulent or it bypasses the VM port, or use some sort of turbulence inducing device at the top of the column. With the offset version there is a physical obstruction so the vapour has to split - it has no alternative.

[Almanac]

Here's a more detailed look at the column, just click on it for full size. Drawings are not to scale.



Max power available in this boiler is 2Kw giving an actual power input of 1865W to the element.

The column is also heavily insulated right up to the take-off port as you can see from the pics in my first post here.

AM

[Capt-Cudellez]

Myles: You mention column folks taking off rum at 94%. At that level it is not rum anymore. My spirit run on rum is ideal at 80%.

I'm surprised this is possible - I struggle to get it under 93% with this very short column that I use for white rum.

The only way to get to get it lower is take off very quickly - but when it gets down below 90% its rotten with tails.

[RumJohn]

Myles: For rum I use a column but run it wide open with no packing on both the stripping and spirit runs. Don't want or need any reflux.It's all about maintaining the characteristics of the rum. As I said yesterday, a rum that is taken to a point above 90% ABV can no longer be classified as a rum. It might be a good clean product but its nearer a vodka/shine or what ever.

Capt.: cant remember your comment.

[RumJohn]

Capt: I don't know what controls you have on your gear, but if you have not tried the following - give it a shot.

A beer stripping run is essential. I get around 50-52% ABV for my low wine. I cant get fancy yeasts here. Everything is fairly standard. No packing in the column. Run it wide open. I use gas as a heat source so I may have better control. Once the boiler hits 75 C I back off the heat, but tend to push a stripping run harder than a spirit run.

When doing a spirit run I add about 25% water and throw a stainless steel pot scrubber into the boiler. Helps prevent surge boiling. The low wine heats up faster than the beer so keep an eye on it. Again, I use no packing, no reflux, no equilibration of column and a real low fire.

Let your rum sit around for a couple of months before bottling it.

Let me know how you do.