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IS a person really drying their fuel, or just seperating the water?
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Hey there,

I think that whenever someone is bubble drying or splach drying (especailly at room temp) they are just coalescing the water together, and gravity pulls it to the bottom.

Havent you noticed the small amounts of water in the bottom of your drying tank after drying?

here's a detailed explanation:

-BD can absorb water (obviously)
-this water is entrained in the biodiesel by attaction (electrostatic forces).
-inorder to break these charges holding the the water and BD together, physical interaction with the same molecule has to take place (or demulsifiers, or boiling the BD,etc.... but I'm not talking about these here)
-when bubble/spray drying, you're causing the wet BD to collide with each other, this causes the water molecules to attract each other.
-when enough water molecules have combined, they form a large enough droplet to fall to the bottom as the force of gravity is larger than the force of attraction between the water and BD.
- this leaves you with clear BD on top, and a very small amount of water (which may be white from any soaps still present) on the bottom

IF heat is added (not boiling the fuel or course) during this process, then yes, you may actually be driving off some of the water through evaporation.....but the main process is the one stated above.

Does this make sense?


Thor.
 
Location: Edmonton | Registered: August 20, 2008Reply With QuoteReport This Post
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I am no chemist but for what its worth what you stated makes good logical sense to me!
However everyone uses heat as far as I know to dry the oil, no heat = very little if any evaporation. Another common way to dewater posted all over this board is to heat and then settle over night...
I find the best way for me is to heat under slight vacuum (5~10Hg) to around 95C then kill the heat and apply full vacuum which quickly evaporates the water out of my oil...

EDIT: I just realized your talking about biodiesel where I am talking about the WVO before processing, My bad! I dry wash so therefore have no experience with drying the biodiesel.
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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I've done plenty of both water washing/drying and resin purification. Never had a water retention issue, but then I sprayed the biodiesel out in a fan after heating it to 45C. In a couple hours is was bone dry (subsequent fridge and freezer tests attesting).

I have both my set ups on my web site (in the sig line) should you want a pictorial of each.



** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.


 
Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post
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Crazy, how is your back?? I see you guys got pounded with a nice batch of the white stuff today! Big Grin
You guys are lucky if today was your first pounding for the season?
Jon
 
Location: Wellington County, Ontario Canada | Registered: February 07, 2008Reply With QuoteReport This Post
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quote:
Originally posted by crazy CheMisT:
Hey there,

I think that whenever someone is bubble drying or splach drying (especailly at room temp) they are just coalescing the water together, and gravity pulls it to the bottom.

Havent you noticed the small amounts of water in the bottom of your drying tank after drying?

here's a detailed explanation:

-BD can absorb water (obviously)
-this water is entrained in the biodiesel by attaction (electrostatic forces).
-inorder to break these charges holding the the water and BD together, physical interaction with the same molecule has to take place (or demulsifiers, or boiling the BD,etc.... but I'm not talking about these here)
-when bubble/spray drying, you're causing the wet BD to collide with each other, this causes the water molecules to attract each other.
-when enough water molecules have combined, they form a large enough droplet to fall to the bottom as the force of gravity is larger than the force of attraction between the water and BD.
- this leaves you with clear BD on top, and a very small amount of water (which may be white from any soaps still present) on the bottom

IF heat is added (not boiling the fuel or course) during this process, then yes, you may actually be driving off some of the water through evaporation.....but the main process is the one stated above.

Does this make sense?


Thor.


That's just crazy, Crazy!
I just had to say it. Smile
How about if you get out of the shower and dry off with a towel? Are you really dry or is the towel just wet?

I have dried fuel in the past in a cone bottom drum where the water was recirculated with the bio and evaporation was definately the drying mechanism. It make perfect sense though that coalescing is what your seeing if you have H2O accumulating at the bottom of your dry tank. Smile

I know the best way I have found to dry feedstock is to heat it to 150F or so and allow it to cool over night then drain the water. Heat back up to 150+ and recirculate to thoroughly mix, turn off the heat, allow to settle over night, and drain any coalesced water. Then heat to 150 or so, recirculate and spray dry with a fan blowing into the top of the drum, allowing the remaining water to evaporate. After a few hours of heated spray drying, the feedstock is generally at around .3% H20.
 
Location: central virginia | Registered: March 13, 2008Reply With QuoteReport This Post
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quote:
After a few hours of heated spray drying, the feedstock is generally at around .3% H20.

That's 3000 ppm, and still quite wet. How long does it take to get below 500ppm H2O, the generally accepted standard for dry fuel?



 
Location: coldest N.America | Registered: May 03, 2005Reply With QuoteReport This Post



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I don't know John,
I haven't tried to consistently get that low.
I have had oil finish at .1% on several occasions using the same process but I think that oil cleanliness and possibly ambient temperature were the contributing variables.
 
Location: central virginia | Registered: March 13, 2008Reply With QuoteReport This Post
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quote:
Originally posted by Jon Heron:
Crazy, how is your back?? I see you guys got pounded with a nice batch of the white stuff today! Big Grin
You guys are lucky if today was your first pounding for the season?
Jon


Thanks for the prev. reply (even though it was WVO as you mentioned)

Yup, got hit hard with snow. Good times. First true day of winter.

Production is put on hold until better weather (will be -28 tomrrow afternoon!!!!)

Thor
 
Location: Edmonton | Registered: August 20, 2008Reply With QuoteReport This Post
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Thanks for all the replies guys......but you're avoiding the main fact that i'm trying to explain.

And that is BD/water interaction WITHOUT heat. All of you mentioned your experience using heat for dewatering BD.

I guess this leads to my next question.....has anyone built or heard of a two phase seperator for BD/water washing and/or drying process??

I know the big dogs use them, but is thier a home-built unit that exists?

Just a thought.


Thor
 
Location: Edmonton | Registered: August 20, 2008Reply With QuoteReport This Post
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I think the point here is that nobody dries their fuel without heat because it does not work. My set up is 55 gal steel drum with a heater and a bubble shaped fountain powered by a small pump. The drying air is supplied bu a 1600 watt heat gun mounted above the drum.
I heat the fuel to 50 degrees C and then turn on the fountain. 2 hours of hot air drying will dry fuel with 2500- 3000 ppm down to under 200 ppm.
If I use the same system but blow cold air over cold fuel it will have no effect at all.
The separation process you describe is not the main process of our drying systems, evaporation is. An efficient evaporation system requires hot fuel, hot air flow and a large exposed surface area of fuel.
 
Location: Lismore Ireland | Registered: November 25, 2007Reply With QuoteReport This Post
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Spray drying is a normal process used in many industries. Adding heat only speeds it up, as does any other method that increases the difference between the water content of the stuff being dried and the air. That's what drives evaporation. I've never heard of a spray that caused water to coalesce. The point of spraying the liquid is to increase the surface area, so water can evaporate into the air faster.

At the biodiesel plant in Ellensburg they dry the fuel with a vacuum while bubbling air through it. At another nearby plant they spray dry in a vacuum chamber in a single pass (only takes seconds, but is continuous). I've also seen a (Danish?) system that used a coalescing filter to separate the water, but have no data on how dry it was. I would not trust it by itself.

I don't add heat, only lots of air flow to my spray dryer. The spray nozzle is in the top of a 4-foot tall, 6-inch pipe, mounted above the fuel barrel. A fan in the top of the pipe blows down. In dry weather it only took about 4 hours to dry a 42 gallon batch. Since I don't water wash anymore, it is only used to evaporate the residual methanol, letting the soaps and glycerin drop out.

To dry oil I use heat (250F) and surface area.

Cheers,
JohnO
 
Location: Moses Lake, WA, USA | Registered: August 15, 2001Reply With QuoteReport This Post
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Yes, I stand corrected, its wrong to say that drying systems dont work without heat, they will just take a lot longer to work, days instead of hours.
Here in the emerald isle at this time of year the humidity is around 90%. Blowing cold air over cold fuel will actually make dry fuel wetter!
Going back to the point about heat causing the oil to coalesce and the water to drop out, I use this system to dry my heating fuel. I burn yellow grease in a vaporizing pot burner to run my central heating. The fuel which is semi solid, has to be heated to 50 degreesC, filtered to remove any particles larger than 3 mm, and then poured into a heated storage tank. Within hours the water drops to the bottom of the tank and can be drained off along with any sludge. However this systen only reduces the fuel to about 1000 ppm of water so while its good enough for my burner its not even close to good enough for motor fuel
 
Location: Lismore Ireland | Registered: November 25, 2007Reply With QuoteReport This Post



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