Why bigger cooling coil and reduced water flow?

[pomiataa]

I have a Bokabob mini reflux still and I was wandering – usually everybody tries to make bigger cooling coil, but when distilling, the water flow should be reduced and the cooling water should come out hot.
What is the difference between lets say 40 turns cooling coil with hot water output and 10 turns coil with cold water output?
Thank's!

[Nightforce]

In my experience, surface area! No matter what you've got, 15L/min coolant flow, etc., if you don't have the surface area to handle the vapor it doesn't matter. I had an 8" coil in my old valved reflux, no matter how fast I ran coolant through it, ethanol vapor would escape past it. With a 9" double coil, coolant flow can be a trickle and still knock down he vapor.

[pomiataa]

Thank you!
What exactly changed when you made the bigger coil?
The reason I am asking is - to know if it is worth to make another still.
Mine is 1 ½ inch and probably I’ll have to upgrade to 2” to be able to make a double layer coil.

[Hawke]

Just a matter of economics. If you can knock down vapor at .5 litres per hour, instead of 5 litres an hour water flow, you have saved several dollars for the run.
Really not important for me, I'm on a private well. I just run out and move my discharge hose around the yard

[HookLine]

In my experience, surface area! No matter what you've got, 15L/min coolant flow, etc., if you don't have the surface area to handle the vapor it doesn't matter. I had an 8" coil in my old valved reflux, no matter how fast I ran coolant through it, ethanol vapor would escape past it. With a 9" double coil, coolant flow can be a trickle and still knock down he vapor.

You saying that your 8" coil was a single coil? Was it in a 3" shell? Did it have any mesh or scrubbers down the middle?

[Nightforce]

Hookline,

My old valved reflux was 1½"OD × 8" single coil housed in a 2" diameter shell. I put a scrubber down the center and let it mushroom over the top and I had to run about 3L/min coolant water to keep vapor from escaping, along with reducing the heat some.

The double coil I'm running now takes a mere trickle of water to knock down everything.

[HookLine]

Hookline,

My old valved reflux was 1½"OD × 8" single coil housed in a 2" diameter shell. I put a scrubber down the center and let it mushroom over the top and I had to run about 3L/min coolant water to keep vapor from escaping, along with reducing the heat some.

The double coil I'm running now takes a mere trickle of water to knock down everything.

Gotta admit I am pretty surprised that single coil did not do the job. But double coils are much better, that is true.

[Nightforce]

It would "do the job" but my collection rate suffered. Best I could achieve getting some decent product was just about 600ml/hr of 92%±. A 6 hour run was more than I wanted to do, especially at 2:30am when I shut it down. If pushed to hard vapor would escape; the scrubber helped a lot, but I still wasn't satisfied with the old valved reflux. I'm totally happy with the bok and doubt I'll ever build another still unless I have some extra $$$ on hand and just want to try a VM design. The bok will do all I foresee of my needs.

[HookLine]

Won't do much better than 600 ml/h from a 1.5" column, though the abv is a bit low.

And 6 hours, is that all? A 40 litre charge of 40 % takes me a weekend to run through my 2" column. On day one I set it up and take of the fores and head, and start into the hearts. Then on day two I take off the rest of the hearts at about 1000 ml/h. Can't rush good spirits, especially clean neutral.

You can add VM onto most LM columns. Just add a take-off port right below the slanted plates.

[Nightforce]

Wow, I don't think I'll ever have that kind of patience. You must set a really high reflux rate and pull off product at a snails pace. My boiler would only allow me to run a 30L charge at max anyway, and at a reasonable amount of headroom, only realistically about 20L. Since I've got about 3/4 gallon of 190 saved up, maybe this next run I'll try a good long slow run and see if there is a difference.
I notice with the bok it's possible to fine tune it so that the column is running at under the boiling point of ethanol, about 77.6-7, which I'm assuming is all fores being concentrated at the top. In theory I'm assuming that you could run it at a slow enough pace that all the fores will be pulled off and when the temp gets to 77.9-78.0 range, start pulling off the hearts at a much higher rate. Then when the temp starts to go up, stop the hearts and just pull off the last little bit of tails.