BIODIESEL & SVO DISCUSSION FORUMS





Sponsors    Biodiesel and SVO Forums Home    Forums  Hop To Forum Categories  Biodiesel  Hop To Forums  Dry Washing Biodiesel    Demething BD- Tank Designs

Moderators: The Trouts
Go
New
Find
Notify
Tools
Reply
  
Demething BD- Tank Designs
 Login/Join
 
Member
posted
Hey guys I'm new here to the forums but I've been making fuel since I was 16, guess that puts me at 6 years of production. Unfortunately my washing methods are just as old, so I'm switching to dry wash. Right now my main concern is to safely demeth our bd. We make 120 gallon batches (might jump to 175 gallons). I've seen the inline heaters using an element and a couple elbows and bushings, but I'm not sure if that will be enough for 120 gallon batches. So what are some designs for building de-mething tanks? My other big question involves safety. Heating elements, biodiesel, and vaporized methanol seem like a bad combination. What can I do to make sure there is no way for explosions to happen?
Thanks,
Nick
 
Location: Central IL | Registered: January 31, 2012Reply With QuoteReport This Post
member
posted Hide Post
You can demeth of biodiesel in a way where you hope to get the methanol back. If you do that, then follow all the safety designs of any other methanol still: placing the electric element in a way where it can never go dry, wiring it so the element cannot be energized unless the pump is running, utilize all steel construction, incorporate overheating electrical cut-outs, etc.

You can also demeth biodiesel in a way where you don't care to get the methanol back. Cheaper & easier. Only 1/3, or thereabout, of the recoverable methanol is in the biodiesel, so just chalk it up as lost, get back the 2/3 you can get from the glycerine, and get the methanol out of the BD ASAP. The biggest safety aspect here is just ventilation. Move way more air outside and away than the amount of methanol coming off. Vent it in a direction that is neutral (not toward your neighbor's house, etc.). Airborne methanol, thoroughly diluted in a heavy air stream, is going to dilute itself further with water vapor (methanol loves water, hence its use as a gas line dryer) and end up back in the ground with dew, rain, etc.

I run with the second method. I keep my exhaust fan outside (no sparks near the tank), pulling the air from 12" above my demething tank and shoot it outside from 10ft up over my garden. The air intake to replace that air is on the roof, on the opposite side of the eave. Then I just recirculate the fuel until the soap all clumps up and I can filter it out.
 
Location: Southern WI, USA | Registered: May 18, 2006Reply With QuoteReport This Post
Member
posted Hide Post
Have a look for "whole batch demeth" where methanol is recovered from bio and glycerine together.
 
Location: New Zealand | Registered: August 15, 2006Reply With QuoteReport This Post
Member
posted Hide Post
So running 120V water heater elements is safe if 1) They are never exposed to air and 2) Biodiesel is circulated? What were to happen if circulation was cut off and bio sat stagnant around the heating element? I'm fairly certain I'll try and collect it. Basically just need to figure out what the best way to heat the bd back up is for me. Any suggestions as to how to heat it?
 
Location: Central IL | Registered: January 31, 2012Reply With QuoteReport This Post
member
posted Hide Post
The electric water heater element has way too much heat per square inch for the air to carry it away, so it has to be transferred away by a fluid to keep the element from overheating. By keeping fluid running over it you make sure the element can't overheat. By wiring it so that if the circulation is not running, the element is also de-energized you prevent the bio from sitting stagnant on the element.

Now, that doesn't necessarily stop the pump from being energized and energizing the element, but having the pump seize up and lead to stagnant bio on the element. So what happens is the the element will heat, bio will start to cook and smoke, there will be a hot spot, and the element with burn out. It can burn out internally, which just means it breaks and you have to go buy a new one. It could burn out externally, making a spark or an arc as it goes. If the element is submerged in fluid at the time, it might pop and make a bit of noise, but not really an issue, either. If the element is in the methanol-laden air, like say your pump leaked and the bio is all on the floor, and it overheated because the level dropped down enough that the element is in the air now...and you get that second spark-arc-failure...boom-whoosh.

Could just blow off a hose or two...if you have any. Could just fill your shop with fumes. Might just scare the crap out of you. There shouldn't be enough air for a rupturing-boom (like splitting a steel tank)...but if a flame shoots out of somewhere it could light off that methanol-laden biodiesel that is all over your floor now.
 
Location: Southern WI, USA | Registered: May 18, 2006Reply With QuoteReport This Post
Member
posted Hide Post
That clears up a few questions. Someone suggested using stove top elements on the bottom of a tank as a heat source. I'm beginning to lean towards that method so the element doesn't need to be submerged. Anyone else try something like that?
 
Location: Central IL | Registered: January 31, 2012Reply With QuoteReport This Post



member
posted Hide Post
I considered that at one point, but the wattage of those elements is so low: the one I had was 200-300W, compared to a common water heater element at 1500W. And you can find more rare WH elements that get up to 1650W. Though I am having a harder and harder time finding those at the local hardware stores as WH's get more energy efficient.
 
Location: Southern WI, USA | Registered: May 18, 2006Reply With QuoteReport This Post
Member
posted Hide Post
I don't run the pump when demething until the very end where I use it to power a venturi to introduce air into the system and wring out the last bit of methanol from my WBD process.
I use two 4000 watt elements wired in series to reduce the heat density on the element and have had no problems. (If I was redesigning my 500L plant I'd add 2 more 4000 watt elements in a separate series circuit) By the time I start opening valves to unload the processor / still there is not a lot of methanol retained should I forget to turn off the elements. Step one in unloading is to remove the glycerol which contains the bulk of the left over methanol which leaves the last stage with very little methanol retained.
I appreciate that there can still be an ignition event with plain oil or bio.
 
Registered: August 08, 2007Reply With QuoteReport This Post
Member
posted Hide Post
Does methanol need to be at its boiling point (I think around 158F) to evaporate out? Or will some sort of combination of heat (not necessarily up to 158) and aeration remove it?
 
Location: Central IL | Registered: January 31, 2012Reply With QuoteReport This Post
Member
posted Hide Post
Evaporation will work but it's a long process and produces unwanted fumes over that long period
 
Registered: August 08, 2007Reply With QuoteReport This Post
member
posted Hide Post
quote:
Does methanol need to be at its boiling point (I think around 158F) to evaporate out? Or will some sort of combination of heat (not necessarily up to 158) and aeration remove it?


It will start coming out before the BP, the BP is the point where the majority of it is changing phase, but the amount varies by a Bell-curve, with the peak of the Bell at 158F at 1 atm pressure.

You can lower the pressure and reduce the BP temp. Help it out with aeration, which is kinda like lowering the pressure too, as it lowers the liquid pressure by lowering the density of the block of fluid, sorta, so it lowers the vapor pressure.
 
Location: Southern WI, USA | Registered: May 18, 2006Reply With QuoteReport This Post
  Powered by Social Strata  
 

Sponsors    Biodiesel and SVO Forums Home    Forums  Hop To Forum Categories  Biodiesel  Hop To Forums  Dry Washing Biodiesel    Demething BD- Tank Designs

© Maui Green Energy 2000 - 2014