Vacuum Dehydrator Design for Drying Waste Vegetable Oil


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Jul 8, 2024
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What can possibly go wrong?

Thought I'd share this design fresh off the drawing board to the group and if anyone wanted to build it feel free to and go for you life. Not easy to find much info around on maybe its that ppl are scared or that is look's like a scientific experiment. But in principle I'm not sure why its not a standard to dry oil as it one the most effective ways, they use it a lot in the hydraulic oil industry i noticed, although the more you read its near impossible to get every last once of water out but this way seems to suggest on most counts it gets very close and its good enough and better then other ways. Any feedback and design tweaks will help anyone else building one.

I have not built this myself and I am by far not very knowledgeable on vacuum chambers, safety etc and how things and fittings should be set up to work properly under pressures and heat etc. But my research online suggest an old A/C vacuum pump could be used and they get pretty good vacuums going and might be able to scrounged around for free. Although if things get going good i might buy a proper vacuum pump as they not that expensive.

I happen to have an old 45KG LPG tank in my back yard in Australia and looking to dry waste veg oil while on the road travelling and or at home and been thinking of this design over the last week and doing all sorts of research into vacuum etc using common fittings at a hardware store so the apparatus can simply screw into any old LPG 3/4" female thread in the top of the existing tank fitting and anyone could make one anywhere. My aim is for it to be as simple as possible and functional, "i just want it to work".

Design is as such so don't have to do any welding or cutting into the LPG tank. A 1/2" copper pipe fits down through a compression fitting nicely inside the 3/4" steel pipe as the inlet outlet to pump the WVO in or out to 80% full. Since 80% full is what is recommended with gas i assumed that similar for oil or WVO. A clear site tube would be good on the outside but would require welding in fittings and it could also get pretty hot and melt but might work as an extra i'm not that good at welding so haven't trusted myself to do this.

I've drawn up this this design and after critic and suggestions of it i have the valve placed correctly, and the types and what chances.

The run down on how i am thinking it would be used:
1). In a separate 44 gallon holding drum heat the WVO to 80C and dry it by cycling it around an open 44 gallon drum fanning the oil surface area and blowing air over it for a hr or a few and cycling through a 1 or 5 micron filter.
2). Open manual ball valve on the 1/2" copper inlet and the manual tap near the relief valve.
2). Have 80% of the 45KG capacity measured in another 44 gallon drum of WVO. Pump that into the LPG Tanks.
3). Leave the ball valves open to heat oil with a 2000 Watt heat band around the tank till the temp you want. Say 80C or 175F.
4). Turn the vacuum on and start the vacuum process at same time close the valves.
5). Run the vacuum x amount of time, I'm not sure how long that would be to dry the oil.
6). Turn vacuum off, open 1/2" copper pipe outlet ball valve and pump all the wvo out. At this stage the WVO is ready to pump straight into the vehicle fuel tank. The micron rating of the string wound filters (or what ever way you filter the oil) should be 1-5 micron. 1 preferable.


I'm not a plumber and or an engineer but i wish i was at this point, if anyone can see flaws and or design improvements please let me know. Few questions i have is:
1). Is the check valve in the vacuum line needed and how and what does it do to help the pump?
2). How can I stop water wrecking the vacuum pump? I put a water trap and float check valve in the design but I don't even know what one of them is and i cant seem to find anything where an purchase one online. So any idea on that.
3). Is the apparatus and the fittings and the valves set up in a way that you think it will work?

Common sense suggests heat and liquid esp waste veg oil will expand so it is VERY important to have a least one pressure relief valve in place and and even better two and or a steam pressure relief also install manual opening ball valves when heating oil or WVO and if heating hot enough to create steam 212F or 100C in the chamber that could be dangerous so you def want to be aware and have installed safety pressure relief valves etc. But aim to operate with temperature heating settings so that the oil stays within a moderate temperature to work with.

Design to Convert Old LPG Tank to Vacuum Dehydration Chamber for Drying Waste Vegetable Oil
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LPG Tank Vacuum Chamber Design


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Feb 5, 2024
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Cass County Missouri
I have run this type operation where I work. Vacuum allows water to boil/evaporate at a lower temperature. Basically you can boil water at room temperature with enough vacuum. The check/float valve is to keep liquid out of the vacuum pump to protect the pump. My industry would incorporate a seal pot to serve in that spot over check valve and to collect water vapor. You would want a PRD on the oil tank tank to prevent catastrophic rupture. Basically you would determine dryness when you reach a desired temperature at a determined mmhg. My two cents on doing it, I would not do it with manual valves and analog instruments. Plus, around here anyway no one wants you to take their used cooking oil.