Replacing oil in a Bain Marie

[Thatch]

Any recommendation on whether or not oil should be replaced in a Bain Marie.  I found an old quote from Joe Dehner @Dehner Distillery"The Mobil product I use is $1750 a 55 gal drum and If I was going to sell it I would have to mark it up. O, and it has a flash point of 600 degrees. You never have to replace it."    Doesn't it ever break down?  Any insight from users or still manufacturers is appreciated.

[Skaalvenn]

Depends on the watt density per square inch of the heating elements used in the oil, and if there's active circulation.

Thermal oil can and will break down over time, especially if exposed to oxygen and brought past it's thermal boundaries.

[Thatch]

2 hours ago, Skaalvenn said:

Thermal oil can and will break down over time, especially if exposed to oxygen and brought past it's thermal boundaries.

Thanks, for the response.  Is there a way to tell if replacement is necessary?

[Skaalvenn]

43 minutes ago, Thatch said:

Thanks, for the response.  Is there a way to tell if replacement is necessary?

Basically from what I was told, if it looks like something you wouldn't run in your old lawnmower then it's done.  We had some heating elements that were not low watt density and the system was open to the air, so they had quite a bit of oil coked on them.  Heatup and cooldown of the system caused air exchange, which greatly increased oxidation.  The types of things learned years after building the still...

The still ran fine for years, but you could tell performance was suffering.  I did try replacing it with a non-oil based high performance heating fluid (glycol based if I remember right?), and that was a mistake--it smelled like permanent markers when the still was running, but again that was likely due to the high watt density.

Switched to steam about a year ago, and my god is it worth the up front cost.

[ViolentBlue]

If you have a local source for Bio-Diesel thats what you want. just make sure its 100% bio, not blended with petro. heavier lipids are eliminated in favor of light, so you wont get the same plasticizing that standard vegetable oil will do.