Never ran my boks in Potstill mode - does this sound right??

[joeymac]

I had about 24 gallons of finished wash so I split it up into two stripping runs. I've never run my rig with the LM boka head attached directly to the boiler for stripping, but I figured "why not" and decided to go for it. No column riser or packing at all, just the 2" Boka head tri-clamped directly to the keg boiler. The bottom plates couldn't be more than a few inches over the keg mouth. I did some research and reading beforehand and used the Pot Calc V2 simulation on the home site. I'm all done now and my product is not at all what the calculator predicted. I finished up each of the 12 gallon runs in only 1.5hrs (after 30mins of warmup) and stripped all the way until my vapor temps were over 98.5C because I wasn't sure how far to go without a true potstill. I ended up with about 3 gallons at 40% ABV (temp corrected) for each run... 6gal @ 40% total.

Does this sound right?? It's way off the calculator predictions. The product volumes are similar but the calc says I should be at 32% and I'm at 40%...

Setup:
15.5gal Keg Boiler
12 gallons 10% Birdwatchers TPW
5500w internal element on full power
2" Boka LM attached directly to boiler and valve removed (no riser/column, no reflux)

Pot Calc V2 predicts this for each 90 minute run:
Starting: 45.42L @ 10.0% (4.54 L pure Ethanol)
Main Run: 11.87L @ 32.5% (3.85 L pure Ethanol)
In boiler: 33.56L @ 2.05% (688mL pure Ethanol)

[der wo]

I think all in all sounds your result plausible. Or at least not much off.
Is it possible, that your tpw had more than 10%? How much sugar was in the 24gal?

[joeymac]

Unfortunately, I used 50LB of sugar for the 25gal wash so it should have given 14%... but the wash kept stalling out despite my best efforts. I fought it with Epsom salts and calcium carbonate for about 25 days and then decided to call it quits. It's possible it had more than 10%, but I'd say that's a pretty accurate starting estimation for 3 reasons.
a) 25 gallons @ 10% distilled down 6 gallons makes 41% final product with full extraction... and I got 6gal at 40% ABV.
b) My mash hydrometer OG/FG readings indicated about 10% (1.092 down to 1.012)
c) The finished wash still tasted sweet and the backset left sticky residue/mess when I was cleaning up after the run.

Honestly though, if my potstill setup is going to let me strip a 10% wash to 40% with almost no alcohol left in the boiler... then I'm going to stick with 10% washes. Low wines at 40% is near perfect for a second run and I'll probably end up with better flavor from lower ABV washes, too.

I'm mostly just curious why the potstill v2 calc was off by almost 10% final ABV... it was saying I should have had about 6 gal of 32%

[der wo]

Potstill v1 calc gives you 34%. A bit better...
The reason is passive reflux probably. Is the lid of your still insulated? Although you can set a higher "internal reflux" than 10% in the calcs, this setting affects only the time loss with reflux, not the increased purity. For example the first number of the calc results is way off always, because the still cold lid promotes a lot of reflux. That's why cutting the fores with a potstill works better slow. Slow means only little heat input. Little heat input means a higher reflux ratio, because the cooling ability of the lid remains the same, regardless of the heat you throw into the mash..

[der wo]

b) My mash hydrometer OG/FG readings indicated about 10% (1.092 down to 1.012)

The OG 1.092 is calculated or measured? I ask, because it's exact the number the hd-calculator calculates. If your hydrometer is a bit off, the OG is calculated, the FG measured, perhaps you had 11-12%?

[joeymac]

b) My mash hydrometer OG/FG readings indicated about 10% (1.092 down to 1.012)

The OG 1.092 is calculated or measured? I ask, because it's exact the number the hd-calculator calculates. If your hydrometer is a bit off, the OG is calculated, the FG measured, perhaps you had 11-12%?

Measured. I actually split the wash into 4 buckets because 25 gallons is quite a lot. Some buckets were higher, some were lower, but it all averaged out to right at 1.092 - so it worked out nicely. Likewise, the final ferments on the buckets were all different too. I think I had one stall out at 8% but another was nearly dry at 13% ... but all-in-all, the buckets averaged out to just about 10% combined.

[der wo]

joey,

I found in older posts an insulated stripping run, which I measured from the beginning to the end:
http://homedistiller.org/forum/viewtopi ... &start=330

12l 12% birdwatchers. After collecting 3l, the vapor temp was 98.2°C, the current distillate had 18%, the 3l low wines had 43.9%.
But:
- Calc V1 says the 3l should have 40% instead of 43.9%
- Calc V2 says 39% instead of 43.9%

Perhaps you should trust your measurements more than trust the calcs.

[joeymac]

I think your explanation of the uninsulated lid and walls is probably the answer. If there is a layer of condensation always whetting the surface, then hotter/heavier vapors rushing past would certainly cause a second distillation of condensation from the lid and walls. Sort of like a virtual partial plate.

[der wo]

But the experiment with the insulated lid proves it wrong. Of course a better more complete insulation than I used is possible, but it would not bring the abv 4-5% down.

[joeymac]

That thread was an interesting read and I don' t necesarily disagree... but I would not consider the set up "well insulated". The riser column was decently insulated but the boiler looked to be in a partially open wood box unless there was something I'm missing.

In the past I've played with insulating my boiler using foil backed fiberglass matting wrapped around the boiler and fiberglass pipe wrap on the column on a reflux still (like you would see industrially in a boiler room) and the difference in power delivered to the condenser coils was significant.

[der wo]

That thread was an interesting read and I don' t necesarily disagree... but I would not consider the set up "well insulated". The riser column was decently insulated but the boiler looked to be in a partially open wood box unless there was something I'm missing.

It sounds that you talk about Badmotivators still and experiment not mine. For my ugly still and experiment you have to scroll down.

[joeymac]

It sounds that you talk about Badmotivators still and experiment not mine. For my ugly still and experiment you have to scroll down.

Ahh yes, your setup was much better insulated. And your results are not significantly different than mine.
http://homedistiller.org/forum/viewtopi ... 0#p7387276

I suspect when considering only purity on a simple potstill with a small riser, there should be no difference between insulating or no insulation. I would expect the only difference to be on the time of the run - losing heat through the boiler means less vapor is made, but the concentrations should be unaffected.