vapor temp swings and bursts

[bigbatch]

I use a bain marie heated pot still for both both stripping and spirit runs. Lately on my spirit runs, I have been having an issue with extreme temperature fluctuation as measured by my vapor probe. I will get product to begin coming off at about 80 C, then it will stop as the temperature drops to 76C, then there will be a big burst of vapor and product come through the condenser that is extremely hot as the vapor probe jumps to 83-85C. It will repeat this process for more than hour until it seems to equalize. Not sure what is going on as the the temperature of the water I am pumping through the jacket to heat the low wines remains constant.
What I've tried:
1) Keep the agitator on low instead off to break the surface tension
2) Keep the jacket temp really low so that it heats up slower.
3) Keep the jacket temp really high so that it heats up faster.
4) Add water to the low wines so I have a full pot rather than a half pot
5) Wear my shirt backward and hop up and down three times before turning on the still
None of these seem to make a difference. Neither do the type of low wines, happens with fruit and grain spirit runs alike.
Thoughts?

[OtisT]

What is your heat source? Is it on a controller for consistent power, or perhaps a hot plate or stove that cycles on/off?

Otis

[seabass]

And this is in pot still mode? What's the heating liquid you're using? This sounds like PID issues. Water in the Bain Marie being controlled by a PID maybe?

[still_stirrin]

—> 5) Wear my shirt backward and hop up and down three times before turning on the still...Thoughts?

There’s your problem....you should “remove your shoes and socks and stand on your head”. Oh, and closing your left eye helps too!

[bigbatch]

I am using water as the heating liquid in the jacket. I switch the control panel to manual control so I can adjust how much power is going to the elements and keep it at a constant temperature. The probe that measures the water in the jacket never varies, and like I said, the vapor temperature swings eventually evens out and I can complete the run normally.

[still_stirrin]

What about the vapor path? Is there packing, or plates in the path? Does the flow diameter (cross sectional area) vary between the boiler and the vapor temperature probe?

I wonder if the variance in measured temperatures is the result of unstable vapor flow speeds, especially since you claim it stabilizes as the run progresses....as the vapor production stabilizes. It appears to be a “transitional condition” early in the production when the volatiles are stacking.

A photo of your system would help a lot.
ss

[Swedish Pride]

could there be an obstruction in your condenser?

[bigbatch]

No obstruction in condenser. Here's a rough drawing of the system

[OtisT]

He is running a pot still, so no packing.

The way this is described, I’m not sure if your product stream is consistent or not. Is your product stream consistent while your thermometer is seeing temp surges? It could just be early condensation drops on the thermo probe that stop dripping when things equalize.

Also, if you are using fresh ferment in your spirit run, this could be foam rising and dropping that is messing with the temp reading.

I say ditch the thermo and go by your product stream. That is what you should be paying attention to anyway, not the temp.

Otis

[still_stirrin]

A pot still? A temperature probe on the vapor path is “an illusion”.....get rid of it! You run a potstill by the product stream off the spout. Period!
ss

edit - Otis said it first. +1.

[bigbatch]

Product stream is not consistent. when the surges in vapor temp comes, get spitting of both vapor and hot product shooting out of parrot. Then temp drops and no product comes out until temp rises again.

[still_stirrin]

“Huffing”....do a Google search and learn how to manage it.

[seabass]

I am using water as the heating liquid in the jacket. I switch the control panel to manual control so I can adjust how much power is going to the elements and keep it at a constant temperature. The probe that measures the water in the jacket never varies, and like I said, the vapor temperature swings eventually evens out and I can complete the run normally.

This stated manual mode, but also that it keeps it at the same temperature. I'm hoping that's just an error. What % power are you running? Any idea how many watts? Is there a possibility that the power is not consistent due to the controller?

Maybe you're also not actually boiling the water. If you're not providing enough power, you won't achieve a consistent boil.

[NZChris]

You haven’t fully explained how you are controlling the heating and what controller/s you are using.

[Saltbush Bill]

Something very wrong going on here....just for starters water is far from ideal to use for this job......couple that with a thermostate or PID and your sure to have trouble.

[silverbean]

What about air or vapour locks in water jacket causing temperature swings?

[JesseMarques]

This happens to me all the time, but I'm using wood to heat my boiler. The way you described looks like some heat inconsistence just like mine.
I'm learning how to menage my still with wood, it's hard, take longer and it's full of emotions

[cranky]

—> 5) Wear my shirt backward and hop up and down three times before turning on the still...Thoughts?

There’s your problem....you should “remove your shoes and socks and stand on your head”. Oh, and closing your left eye helps too!

You also have to jump up and down exactly 4 1/2 times

Like someone else said we need a better description of the heat source. What exactly is controlling it? How are you running it?

Some of your other posts seem to indicate you are running a large-ish commercial type still? What type of still is it?

Has it always run like this?

One basic question I have is, is your parrot vented?

Can you run it without the parrot?

[Yummyrum]

One basic question I have is, is your parrot vented?

Good point cranky . Unvented parrots surge and spurt .

[LWTCS]

Not withstanding manual mode, PID to control heat input will only work if oil is the heating medium.

Talk about the fill level of your heating medium reservoir.
Does your heating medium occupy jacket space? If it does,,,it should not.
If you don't have a way to separate the jacket space from the reservoir then perhaps oil is a better heating medium for you.
Are you purging the air out of your jacket when you bring the kettle to temp?

[LWTCS]

I am using water as the heating liquid in the jacket. I switch the control panel to manual control so I can adjust how much power is going to the elements and keep it at a constant temperature. The probe that measures the water in the jacket never varies, and like I said, the vapor temperature swings eventually evens out and I can complete the run normally.

I don't think measuring your water temp is giving you enough information. Vapor temp under pressure is going to provide more info. Do you have a pressure gauge in service?

[HDNB]

if this happens early on...

i use a steam jacket. if it is not agitated fast enough i have seen the mash foam up.
the symptom sounds the same: early onset of a bit of high proof booze then all goes quiet when the foam covers the mash, the column cools and temp drops with no output. then enough heats builds and she pukes.

faster agitation is the answer.

[HDNB]

i'm no scientist but i *think* it's because stainless is a poor conductor of heat, so you really got to move the mash past it to keep the temperature equal in the mash, otherwise the stuff in contact with the jacket boils too fast, while the rest of the mash is cooler- only at the foaming heat stage.

[LWTCS]

i'm no scientist but i *think* it's because stainless is a poor conductor of heat, so you really got to move the mash past it to keep the temperature equal in the mash, otherwise the stuff in contact with the jacket boils too fast, while the rest of the mash is cooler- only at the foaming heat stage.

Yeah that's why its important to have a reservoir that does not utilize the head space within the jacket to store cooling medium. Only vapor should occupy the jacket space when using water.

[bigbatch]

Thanks everyone! I knew it wasn't huffing and had something to do with uneven heating. I changed out my water pump for the jacket as it was over a year old and not performing well. I also increased the agitator speed per HDNB's recommendation, and everything is working like a charm. Nice even flow of spirit and consistent vapor temp readings. Thanks again for all the suggestions, I really appreciate it.