Heating VO to 300F doesn't ensure there is no water

Collecting, filtering and dewatering of WVO SVO vegetable oil. For Biodiesel producers too.

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Heating VO to 300F doesn't ensure there is no water

Postby SunWizard » Wed Mar 05, 2008 3:36 pm

Heating your VO to 300F in a pot or getting it right from a fryer doesn't ensure there is no water. There are many reports of high water content right from the restaurant fryer which run at 350F. Best to do a hot pan test on it always.
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thin layer of oil vs deep oil when drying

Postby JohnO » Sun Mar 09, 2008 9:58 am

Wizard is correct, in my observation. I've seen positive hotplate tests on samples direct from the cubees that had the oil dumped back in after cooking. I'm also familiar with some similar tank heating systems where I work that also display a dramatic difference in the characteristics of liquid at the bottom of a deep tank vs the top. Part of the difference is due to pressure at the bottom of the tank being higher than pressure at the top surface, so any water down there needs a higher temperature to boil, but there's obviously more to it than that. I suspect the missing part of the puzzle is the presence of food particles, which trap water. If they're sitting in the bottom of a deep fryer, water turning to steam inside the particle may not escape, so the particles stay "wet". Since oil can also absorb water, and the particles are still in the oil, there's an opportunity for the water to migrate out into the oil at some later time. This is only a hypothesis of mine.

When I've "boiled oil dry" in a deep pot, heating it to 250F, then later conducted a hotplate test, the filtered oil passed, yet the unfiltered but boiled oil sometimes failed. The obvious difference is the remaining presence of food particles. When I've run wet dirty oil through the BirdWaterer, which is very shallow (about 1cm deep), and which the hot oil exits only from the surface layer, even the unfiltered oil later passes hotplate. The obvious difference, compared to heating in a deep pot, is the depth involved. My conclusion it that wet dirty oil does not "dry" unless it's exposed to the air. I would expect a spray dryer to work even better.

I've also observed dirty dry oil get wetter with time. I think the residual food particles are picking up moisture that finds it's way into the unsealed storage tank. For that matter, I've also seen dry, filtered oil stored in an unsealed tote get wet enough to fail hotplate. I think this says more about the need for attention to storage conditions than drying technique.

If in doubt, do a hotpan test. If you're absolutely sure your oil is dry, doing a hotpan test can be a shocking revelation.
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Re: Heating VO to 300F doesn't ensure there is no water

Postby canolafunola » Sun Mar 09, 2008 11:48 am

SunWizard wrote:Heating your VO to 300F in a pot or getting it right from a fryer doesn't ensure there is no water. There are many reports of high water content right from the restaurant fryer which run at 350F. Best to do a hot pan test on it always.


Yep. I did a test couple of years ago. Went to Hot Dog stand and asked the guy for a small cup of oil from their HOT french fryer fyrolator, took it home and did a hot pan test and it sizzled and popped.
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Postby David » Thu Mar 13, 2008 5:08 am

I too have looked at this a few times and come to the same conclusion that there is something unusual, defying the laws of physics even when it comes to drying oil in a bucket by heat.

I have boiled 20L drums of oil for hours getting it so hot I was expecting it to self ignite at any moment. After it had stopped boiling and sat on the fire for another hour, I let it cool overnight and was rather dissapointed to find water still present in the morning. I personally know 2 other people who have had the exact same results.
How water exists in probably 200o water and not boil out given sufficient time is a mystery to me. I can only agree with the above comment that the food particles must have something to do with it although I don't know how exactly.

I also think that the pressure of a bucket may have something to do with it although I would have thought in the scheme of things the pressure would have been insignificant.
If it takes 15 PSI to raise the temp of the boiling point of the water in my radiator, I'm dam sure there isn't sufficient pressure in a 2ft deep open top bucket of oil to raise it to over double its sea level boiling point !!!!

I have noticed however that in a hot pan test the water boils off relatively quickly even taking into account the much lesser amount of oil.
I have read of someones technique on infonot of what they call a flash dryer. I think this may be running a shallow stream of oil over a hot metal plate and cooking the water off that way. From my own experience, I think this would work well and be more effective and efficient than boiling in buckets. I also see a lot of potential for recuperating the heat from the process and further increasing it's efficiency.
If I wasn't so happy with my own drying setup, I'd build one of these!

I'm still amazed how many people will argue their oil is dry because they get it straight from the fryer. I think it's a case of some people convincing themselves because they don't want to work out how to dry it.

Having attempted boiling oil dry a few times, the thing that really freaks me about it is the potential for catastrophe. The last batch I was attempting to dry had come from a very vigorous boil to a gentle simmer making me think it was nearly there.

Feeling a bit warm from the fire and the coffee I was drinking, I was sitting back on a comfortable box further away than I had been sitting all evening previously Pondering the meaning of life staring into the flames trying to summon up the motivation to throw some more wood on the slowing fire. Completely without warning, there was this Thump I felt through the ground and the bucket erupted with a slug of what looked like about 5 litres of oil going Straight up in one lump. That wasn't much of a problem but when this oil slug landed, oil was splashed everywhere including onto the wood fire I was heating the bucket over which or course immediately flared up with a 12 ft flame. This of course quickly made the bucket boil over vigorously spilling still more oil onto the fire and perpetuating the process. Luckily I had another bucket of cold oil very close by, so resisting the heat that was waay too hot, I dumped the entire contents of the bucket on the fire and extinguished it only getting minimal splatters from the wet oil meeting the hot parts of the fire and metal supports and lightly singed on the side of my head I couldn't turn away.

I'm not an overly cautious person but the realization of what could have happened to me in personal injury let alone the damage the fire that was rapidly getting away could have caused to just my garage and what was in it scared me shit less.
I have had small but serious burns before and know what a sinister and mind numbing painful injury they can be. I have no doubt 20 L of boiling oil has the potential to kill many times over with little effort and cause life changing injury's with the tiniest mistake or bit of misfortune.

For me, Boiling oil is just waaay too far out there in the danger zone for me to ever attempt it again especially since it doesn't bloody work. There are just so many things that can happen and no matter how carefully you look at something, there is always the one in a million that will get you. With this, the potential for something really grim to happen through the most minor mistake or accident is just far too great for me to risk.
Personally, I would mix Bio in an open bucket and not give the meth fumes catching fire a second thought.

Boiling oil to dry it, Will take a braver man with far bigger ones than mine, or sillier man than me to try that one ever again! :shock:
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Postby John Galt » Thu Mar 13, 2008 12:19 pm

I use a much less hazardous method to remove the moisture from used VO.
http://www.burnveg.com/forum/viewtopic.php?t=9
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Postby Burbarian » Thu Mar 13, 2008 6:40 pm

That would be due to boundary layer capping. The water is trapped under the oil, and with gradual heating the water could reach supercritical, exceeding 100C boiling point while still remaining liquid. Then all it takes is an initiating nucleation site for the supercritical liquid to suddenly and explosively decompose into gas. Typically launching the oil cap that rests above it.
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Postby Welder » Thu Mar 20, 2008 5:25 am

Burbarian wrote:That would be due to boundary layer capping. The water is trapped under the oil, and with gradual heating the water could reach supercritical, exceeding 100C boiling point while still remaining liquid. Then all it takes is an initiating nucleation site for the supercritical liquid to suddenly and explosively decompose into gas. Typically launching the oil cap that rests above it.


Does that mean I should stop tossing handfuls of ice cubes into hot fryers? (bad joke, sorry)
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Postby djenkins6 » Mon Mar 31, 2008 6:09 pm

sounds like the same effect as can happen to liquid in a microwave, which I also hope never to see

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