Question: Pot Still Condenser Outlet Hissing

[BarleyBeard]

Hiya,

I've been running what I suppose you would call a "professionally made" rig from MileHiDistilling. Eight gallon Stainless Steel pot still with gorgeous welds or heavy duty clamps on every seam. I run it over a propane banjo burner intended for boiling Stainless Steel mash tuns. I'm a sucker for safety, so after I noticed hissing during my last two runs I figured I would come on here and ask some folks wiser than I.

On stripping runs and towards the end of spirit runs (Around 205 F vapor temperature) I notice that the 1/4" outlet will start to make a hissing noise. It has no effect on the distillate being produced, and there is no alcohol vapor escaping. It's been awfully cold during these runs, so the atmospheric temperature differential between the inside and outside of the still would be almost 190 F. The hissing continues until I shut the rig off, and will continue even if I bring the temperature down enough to stop the flow of distillate.

The top of the 2" column is plugged with a natural gum rubber bung/thermometer, so I feel like that would be the first seal to go if I were creating dangerous amounts of pressure.

Is this just heated air escaping from a heated container, or is it something I should be worried about?

With Respect and Gratitude,
-BB

[Coyote]

1/4" outlet is in most opinions to small.
Personally I would not use less than 1/2"

My guess is that you are actually pulling a vacuum
due to the temp differential, but with out seeing
it I can't give you any sort of real answer

Coyote

[BarleyBeard]

Thank you for your input, Coyote.

In retrospect, the entire lyne arm is 1/2", with a full inch sleeve for the condenser. I've been away from home for a while and was trying to recall the exact diameter

I hadn't thought at all about the possibility of creating a vacuum in the air cooled column -- This would explain why the distillate stream doesn't seem to be affected the way I imagine it would if hot gasses were creating back pressure behind it. I'll have to test this on my next cold run.

So is it still worth trying to regulate the outside air temperature? I'm not nearly as worried, but I've still seen rapid endothermic reactions turn 55 gallon steel drums into crushed soda-cans -- I can only imagine what a burning-hot mess that would be.

Much appreciated,
-BB

[bellybuster]

try turning down your cooling water supply. Usually will stop any huffing. That exit water needs to be quite warm.
I have just a trickle going through my leibig.

[BarleyBeard]

Thanks Buster, that's another likely scenario.

I generally shoot for a nice temperature gradient throughout the condenser, but it is entirely possible that my normal trickle is just too darn cold when it is 15 degrees F in my garage. I would, however, like to clarify that "huffing" seems like it may be a misnomer. This is a very steady movement of air, it sounds much like air coming from a compressed tank. I'll add this to the list of potential issues and report back with answers in the coming months.

With Respect and Gratitude,
-BB

[dakotasnake]

i often distill in temps in the -10 to -20 range with no problems as far as temp varients go. if you dont have vapor escaping then the cooling part should be good. it almost sounds like a bottle neck problem somewhere, think a steam whistle, vapor going thru an obstruction or bottleneck but not being closed creating a whistle sound. maybe give that a look. also propane tanks have a tendancy to whistle in cold wheather. try to dial in on the source of the sound.

[heartcut]

During the hissing, put a mirror above your condenser outlet and see if it's alcohol vapor escaping, it'll fog up if it is. A small piece of printer paper should be sucked against the condenser outlet if it's sucking air in, not to mention that you'll have an explosive mixture in your still if this is the case. Figure out a way to lose the rubber bung or wrap the vapor exposed part of it in teflon tape- it probably not too good for you. Good luck.

[BarleyBeard]

A quick update for anyone searching this same issue:

The hissing is indeed air coming out of the condenser outlet. The pressure/volume of air isn't nearly as much as it sounds, and running even lower and even slower seems to help. When I do 8 gallon runs and fill the boiler up, there isn't as much hissing.. Smaller spirit runs certainly push a lot more air out when things get hot.

I'll be trying out a new, much larger 3/4" copper condenser on my next run, to rule out any potential bottlenecking issues. More to come...

-BB

[jholmz]

try taking a piece of copper scrubbie inside the end of your condenser this will slow the vapor and give it a little more time to condense. should help with the huffing