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headspace dryer
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As some of you know Im a bit of a fanatic about water content. I dry my biodiesel to below 200ppm of water because I live in a very damp climate. I read recently about how oil is kept dry in various industries and came across the idea of headspace drying. This means that rather than drying the oil itself you dry the air above the surface of the oil, the oil releases water into the dried air which you then dry again, and so on until the oil has no more water to give up. Based on this idea I have designed and built a headspace dryer for a 55gal oildrum.
A plastic bucket with an airtight lid is mounted onto the lid of the drum. A 4 inch hole is made in the floor of the bucket and the lid, joining the headspace of the drum with the bucket. The hole is covered with flyscreen mesh and a short length of pvc pipe placed on top of the mesh. The pipe is filled with 400gms of silica gel. An aquarium air pump is installed inside the bucket with about 3 feet of tube and an airstone as shown in the illustration.



The air pump pumps air down the tube and bubbles of air rise up through the fuel collecting moisture. The pump sucks the moist air through the silica gel, drying it as it passes and then pumps it through the fuel again.
As a test I installed the dryer above a drum containing 150 litres of waste motor oil which contained 1000ppm of suspended water, verified by the carbide manometer. After a week I removed the silica gel. I weighed it and then dried it in an oven for 2 hours. It gave up 90 gms of water. The carbide manometer now read 260ppm of water content.
Ive now filled the pipe with dried silica gel and will run it for another week. Im confident that I will have completely anhydrous oil by the end of the week.

Most methods of drying fuel cannot dry much beyond the ambient moisture level in the air. Those that do involve large expenditure of energy and heat. The headspace dryer can achieve virtually zero water levels without using heat.

I should point out that this will only work for suspended or dissolved water. Free water should be drained off before using a headspace dryer.
 
Location: Lismore Ireland | Registered: November 25, 2007Reply With QuoteReport This Post
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Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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I always wondered if I built a (somewhat) airtight storage shed, say large enough for a tote or a few 55 gal storage barrels and put an old dehumidifer in there with the storage container(s)(tons on Craigslist), would that by virtue of the enclosed space draw moisture out of the biodiesel? Your idea obviously is virtually free of course but I would think it should work. Then again I'm an accountant by trade and not a thermal dynamics engineer.


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Location: Detroit, Rock City | Registered: August 16, 2007Reply With QuoteReport This Post
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Yes it would work as long as the temperature was high enough. A lot of dehumidifiers hardly work at all below a threshold of about 18 degrees C,
 
Location: Lismore Ireland | Registered: November 25, 2007Reply With QuoteReport This Post
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