diy oil tank evaporator question

[pathfinder22]

I made an oil tank evaporator this year. seems to work... I think my build was ok, (pics posted on my previous posts).
I do have a question for anybody else that might be using a similar cooker.
Short and sweet, the front part of the pan boils like crazy,(directly over the firebox) the back part only streams, no boil.
I know I have a small drafting issue because of a short stack but the heat is there.

Seems to me that most of the pan should boil with a good fire......
Any thoughts or suggestions from my peers?

[sugarman3]

Try addind another piese of smoke stack,stack should be twice lengh of pans

[pathfinder22]

yeah this year I am running under a canopy tent, my stack is 36" vertical, an elbow, then another 24" horizontal to get me out from under the tent.
hopefully building a shack this summer....
so the answer is,,,, ultimately both pans should boil? I just don't have enough drafting to get enough heat?
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[therealtreehugger]

I have a similar setup. Originally, the stack was similar to yours, up, 90deg bend, out a window of my barn, another 90 deg bend, then up another 8 ish feet. The bend severely hurts the draft, but at that time, I was not willing to put a hole in the roof.

Modifications that I have made over the years include:
1. new roof, and therefore was able to put a roof boot in properly so the stack could go straight up
2. Went from a 6 inch stack to an 8 inch stack
3. Total stack height is now 16 feet
4. Built up the back half of the evaporator so there was only 2 inches underneath the pan, so the heat literally only had 2inches to go through. I figured his out by determining the area of the 8 inch stack, and making the area under the pan the same. You don’t want to make it less than the stack. This keeps the heat up against the bottom of the pan. Otherwise it will escape unused. I built it up with brick (didn’t care if it was fire brick or not, it didn’t matter if it cracked because it wasn’t supporting anything) and ceramic blanket.
5. We raised the grate under the fire to get better air flow from under the fire. Went from 4 inches to 6 inches measured from the center (deepest) of the bottom.

As a result of all that, we went from boiling 8-10 gph to about 20 gal per hour, and the only part that has a hard time boiling is the first channel where the colder sap dribbles in from the header tank. I also keep the sap level at about an inch, and watch it like a hawk. Had a close call last year but escaped without a burnt pan. I also fill the wood box full full. I end up putting 6 or so pieces of wood in every 8 minutes ish.

I hope all that helps! Good luck!

[pathfinder22]

The back is ramped up. I have about 3" under the back part of the pan..
Guess I could move the canopy a little so I can go straight up. was just
trying to keep it out of the weather.
I run the pans at about 1.5"...top of the nut for the drain, Its a good gauge to look at.
All that said, I have made 4.75 gallons from 25 taps in the last 2 weeks. I am happy about that.
Thanks for the info...
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[pathfinder22]

I just don't understand why the pics come out sideways...sorry ya'll.

[Pdiamond]

Your pictures are fine. You can do what you have mentioned, move the canopy. then run your stack straight up. Maybe add a 1" piece of ceramic blanket under the pan and decrease the area to 2" instead of 3".

[crzypete]

It looks like you have no grate? You need air under the fire to get the right draft. Mine has a blower which increases that air. But I can run it without the blower and still get the back of the pan boiling. I don't think its a stack issue


Pete

[pathfinder22]

Yep I have a grate in there. Pics were from while I was bricking it.
Cut up and re-welded an old iron railing I had laying around.
Grate sits about 4" up just above the vent.
Figured I need more stack because I could hear the boil change when I open the door about 3".
Just was not sure that was the reason for the back pan not boiling.
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[The Heldeberg Sapper]

How are you adding sap and do you have a continuous flow pan? I have a 2x5 (2x3 back pan and 2x2 front syrup pan) on a oil tank and i can get a full boil in all of my channels except for where my sap is dripping in it will only boil about a third of that channel. I am evaporating a steady 20gph with my setup so even with a warming pan its a decent amount of "cold" sap dripping into the pan. For reference i have 8' of 8" stack plus a 2' high base stack for a total of 10', this seems to draft very well even with an air under fire blower., i have 2" of clearance under the pan after the ramp. 22910 I learned very quick that i have cant overload the fire box or the stack might meltdown on me.

[pathfinder22]

Seems like almost the same set up pan wise, I have a preheater on the back shelf slow dripping into the pan to maintain level.
It is fitted only for 6" stack and no blower,,, YET!
This is a new cooker, I figured I would have to make some tweaks....
Something to work on for next year.
I will be boiling again saturday, and will be adding some stack to the height, it should make some difference.
My old barrel cookers I made would shoot flames out the stack..was great for roasting hotdogs on a stick...lol
Thanks for all the info guys.

[crzypete]

What is your air supply under the grate?

Pete

[pathfinder22]

Just the slide vent need the bottom and the door open a little, hence the drafting problem.
I will probably take the vent off and add a small blower next year, no time to
mess with that right now though.

[pathfinder22]

Just the slide vent near the bottom and the door open a little, hence the drafting problem.
I will probably take the vent off and add a small blower next year, no time to
mess with that right now though.

[pathfinder22]

just a little update, I added another 4' of stack saturday, total about 7 feet straight up now.
it helped the back pan boil a little better, only about half of it.
It was easier to maintain overall temperature thoughout the boil though.
Really was hoping to get a higher evap rate then I am getting. the other issue is I pack it full of wood then
4-5 hours in I have to scoop coals cause it starts to block the vent.
well its a learning process, more stack height next season.

[therealtreehugger]

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Here are some pics from my homemade oil tank evaporator. Under the door, we cut a vent for draft. The grate sits even with the bottom of the door, so all the air coming in the vent goes up through the grate. Burns really efficiently, very few ashes left after a boil.

That last pic is upside down, have no idea why . . . Sorry!