Fuel oil tank evaporator - Tips on upping the boil rate?

[mantispid]

This year I made an evaporator from an old 275 gallon fuel oil tank. I welded in an insert that restricts the void space, narrowing the draft area toward the stack (I believe this is called an arch?). I've lined the top of the insert, the inner back, and the inner sides of the unit with half-thickness fire bricks. The top can accomodate a 2'x4' pan, but I created a modular insert that accommodates 3 steam table pans. I'll eventually upgrade to a 2'x4' pan at some point... Plus, with the modular insert design I can use the evaporator as a hibachi grill or similar off season.

When running it, I noticed that the middle pan was the hottest. I am used to the pan closest to the fire door being the coolest, and the pan closest to the stack being the hottest... but in this case, it isn't so. The back and front pans are about even, but not as hot as the middle. I have the stack draft door fully open, and I cut out a smile-shaped (:D) hole beneath the fire door under the grate to allow for ample draft. I've even put a fan there to boost burn rate to see if it helps even out the heat (it ups burn rate but doesn't cause the back pan to get hotter than the middle).

Any advice on how to get the back pan hotter? Should I restrict the draft space a bit more and retain more heat with full-thickness fire bricks? I can stack more bricks to restrict that space even further, too.

I'm guessing that full open draft doors should always result in the most heat? I'm not entirely up on how controlling draft may help with boil efficiency.

Here's an image and a short vid of the rig in operation to give you some idea of how the pans are set up:

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https://www.youtube.com/watch?v=oS3aoR1bDLc


Thanks!

[Sugarmaker]

Looks good! keep boiling. You may try some adjustments to the ramp under the rear pan.
Regards,
Chris

[Gary R]

Lighted pictures of the inside cold may help us. Your fire box probably should not be deeper than the first pan. Then there should be minimal space under the last two pans. The front pan should boil hardest with all remaining heat having to go by the other two. Fire brick does not insulate much. Ceramic blanket or arch board is best. However most beginner's don't spend for that. It's a nice looking rig. Keep working on the right restrictions and it should boil fine.

[maple flats]

How much space do you have under each pan, starting from the front? My guess is that the firebox portion should be about 16" to maybe 20" deep and should be about 14-16" below the first pan. At the back of that, a firebrick wall up to about 3-4" below the second pan, and ramp up in a distance of maybe 8" to only 1" under the pans from there to the back. Just behind the last pan a wall should go from the bottom to the 1" space and behind that you want all the space except 1 layer of the firebricks for the "smoke" to go to the stack transition. Something like that should force the heat up and get more uniform distribution of heat for a more even boil. If you can, a cleanout door on the back to access the area under the stack for cleaning would be nice, but since you can just lift the pans and the modular insert out to access. You might also do better, making the air inlet (half moon) larger and close the door except when firing. Anytime that door is open, you are cooling the front pan, just like when I open a door to add wood (the boil slows considerably when the door opens).
Good luck.

[mantispid]

Great tips, folks! The depth under the first pan is about 1.5' to the grate. The depth under the 2nd and 3rd pans is about 1' to the bricks. I'll stack up more bricks to narrow the space between the last two pans as suggested above and see how that affects the heating efficiency.

I will say that even without those above tweaks, this rig burn about a fifth the wood my old block arch used to.

Here are some additional pictures as requested:

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Inside


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Before placing fire bricks

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Initial firing. Excuse the imperfect door support frame. >_> I cut the smile-shaped opening just below here about an hour later.

[optionguru]

Couple of things. Too much space between the ramp and the pans, also the stack looks a little short to me. Mine was similar last year and this year I added 4' to it which dramatically increased the boil of the rear pan. Caused a much more aggressive draft.

I also noticed you're adding sap from your preheater pan to the front pan, thus further cooling it down. I would ladle forward so you have hot sap from the middle pan being ladled into the front pan.

[mantispid]

optionguru,

Yeah, I'll definitely be closing up that space with fire bricks. And I worried about the stack length... I have several extra sections to lengthen it with, but the temporary location under the deck doesn't make for a lot of space. I'll see what I can do though. Won't be a problem once my sugar house is built this summer for next season.

Yeah, I wasn't quite sure how this rig would 'pan out' (sorry) in terms of where to add the pre-heated sap. I later added the preheater to the front of the rig with a trickle stream into the front pan. I could do so to the rear pan, but it will take a bit of engineering.

[Ausable]

Hey! Nice Work. --- A question though? How do You clean out your wood ash? Another advantage to having an ash cleanout door under the grate - separate from the fuel feed door is air under fire. Helps control your burn rate by providing more combustion air - or am I missing something?

[mantispid]

Hey! Nice Work. --- A question though? How do You clean out your wood ash? Another advantage to having an ash cleanout door under the grate - separate from the fuel feed door is air under fire. Helps control your burn rate by providing more combustion air - or am I missing something?

Oh, that's what the 'smiley' cut under the fuel feed door is for. I cut that after taking these photos though. It does allow me to easily remove the ash, and provides air flow under the grate and up into the burning wood.

[5050racing]

94679466The top is the bottom part I used of the tank there is a 2" hole I use the first one from the front about 1' from door,no holes under door,plumbed in 2"-4" street 90 to my squirrel fan with a 2" space above the inlet covered by a piece of 1/4" plate 8" diameter so ash don't clog it and watch out ! You have to use the blower or your wasting your time I feel,blower has 3 speeds works great,doubled my rate I feel.!9465 I'm at about 10gal/hr the door don't turn red with out it,I know I need to insulate can't take the time yet but will

[mantispid]

I've been wondering about adding a blower to this rig... Hmmmm.

[sugarmangraham]

I have a very similar setup to yours. I have a 2x3.5 flat pan instead of the pans like yours. What helped my boil out the most I feel was ceramic blanket and a layer of split fire bricks. Also enclosing my pavilion style shack made a difference aswell. I do have a new blower for this year but haven't gotten to use it yet.

[5050racing]

Gota add the blower you will see!! I have 2. 2#2 pans

[mantispid]

If one uses a ceramic blanket, does one not have to use the fire bricks as well? If I swapped all the fire bricks for ceramic blanket, it would lighten the weight of the rig considerably...


Oh, and the advice to brick up to narrow the air space under the pans worked beautifully. I easily doubled my boil rate.

[Twindadx2]

Mantispid, what are you using for a door on your arch? And where did you get it? This is my second year running an oil tank arch with a 2x5x10" flat pan with a preheater on top. When I built it I just used a piece of metal from the oil tank. This year I took the blower out of our old furnace and ran it under the fire. She heats up real well, but I'll need a better door for next year.