Evaporator from small wood-burning stove - cheap!

[berkshires]

Hi Folks,

I've gotten so much help from everyone here! Thought I'd pass along how I've built a small hobby size evaporator, in case it might be helpful to someone in the future.

By the way, as you read through this, be aware that I don't know how to weld. Oh, and I'm cheap. So all of this probably cost me well under $100. Okay, so here we go...

I started off with an ancient small, cheap, sheet metal woodburning stove. It had been retired for some time, so I didn't feel bad about chopping it up.

To give you a sense of scale, it's only around 13" wide. And the top is not long enough for even one steam tray pan to fit on it.
I first tried boiling sap in a pot on top.

stove_original.jpg

You can guess how well that went (not!)

So next I cut a chunk out of the top of the stove so I could fit a steam tray pan into it. I had to fit the pan sideways to have room in front of the smokestack.
mod1_boil.jpgmod1_boil_side.jpg

Now I could at least start boiling sap. But I wanted to fit a second steam tray pan on the "arch". But the stovepipe was in the way. I needed the stovepipe to come out the back of the stove instead of the top.

So next I cut out most of the rest of the top. This includes the part where the stovepipe came out. I also cut a chunk out of the back of the stove, and put a new flue in (using sheet metal screws and furnace cement).

Here's the new duct/flue connector: https://www.lowes.com/pd/IMPERIAL-6-...t-Boot/3134369
duct_flue.jpg

And here's how it looked after the work was complete:
evaporator_mod2.jpg

That worked fine for the rest of the season. After I got my systems dialed, I was able to boil off two gallons per hour. But there were still some big issues.

Problems:
1 - Sides of pans sticking off the sides of arch. Not only was that wasted square inches on the bottom of the pan, but the cold air under the part of the pan not over the stove wicked away heat from the sap and the pan. Not good.
2 - No grate means the fire burns inefficiently.
3 - To get enough air to the fire, I had to open the door a crack. This made the fire cooler. Especially since the air was coming in right under the front pan!
4 - The fire doesn't hit the bottom of the pans well. Unless I really worked to arrange the logs right, nearly all the heat was in the middle/back, and very little under the front pan.
5 - Needed a way to pre-warm sap.

In my next post, I'll talk about what I did to solve these problems.

[psparr]

You've got the bug!

[Haynes Forest Products]

Berkshires Nice use of available materials. I bet when its said and done you might be more efficient if you ran the deep pan only and set it down into the arch/stove and ran the sap deeper. Having a single pan that rips and roars is better than 2 pans just simmering. Now if you get a nice fit it will help. You might consider a few holes under to firebox so air can come from below so the fire goes straight up to the pans and keep the blanket of cold air out of ther arch. Now about that old hair blower and some simple duct work.......................never mind.

[barnbc76]

I always admire what people can improvise with what they have. A few years ago before I moved in my house i took an 275 gal fuel tank and a woodburning/electric stove to the junk yard, needless to say a coulple years later i wish i had not, o well never know what you are going to need and the possibilities are nearly endless with what you can build to make maple syrup.

[Zucker Lager]

Hey Birkshires:
What about adding just thin sheet metal sides to the stove that start at the bottom of the stove and run up to the sides of the pans on each side also closing off the front and back of each side so that the heat from the sides of the stove stays under the pans that are hanging over. Every little bit will help. Like Pspar said "youve got the bug" he he Don't we all. Jay

[Shaggy acres]

That looks almost exactly what I started with. I cut off the top and my father in law made me a new pan custom fit to sit 2" deep on the top. I also bent cheap flashing to run up the sides to keep in the heat. I found that pan is a big heat sync in the cold weather so the sides kept the heat on the pan.

I have since retired the stove and built a "rocket" stove base for the pan out of a metal file cabinet and fire brick. My first attempt at the rocket worked great with 6" square steel conduit 1/4" thick. The intense heat carbonized the steel and it disintegrated in the fire box. That is why it is now made of fire brick!

Most of all have fun!

[berkshires]

Where we left off, I was saying there were some serious issues.

Problems:
1 - Sides of pans sticking off the sides of arch.
2 - No grate means the fire burns inefficiently.
3 - To get enough air to the fire, I had to open the door a crack. This made the fire cooler. Especially since the air was coming in right under the front pan!
4 - The fire doesn't hit the bottom of the pans well. Unless I really worked to arrange the logs right, nearly all the heat was in the middle/back, and very little under the front pan.
5 - Needed a way to pre-warm sap.

So now on with the story. Here's what I did to address the above.

Solutions:
1 - Added "wings" on the sides of the arch to go under the sides of the pans. I cut out the side of the stove about three inches down below where the pans stick out, and added stainless steel "wings". These essentially extend the arch out to the sides of the pan. Here's a couple photos (with fire blanket as a seal).
mod4_no_heating_troughs.jpgwing_blanket.jpg

2 - Made a grate by chopping up fencepost, drilling holes in it, and screwing it together. Here's a pic where you can see the grate. You can also see the inside of the "wings".
wings_cindrblock_grate.jpg

3 - Opened up space under door so there is plenty of AUF coming in under the door and getting sucked through the grate into the fire.

4 - To force fire up under the pans, I chopped down a cinderblock to the right size to create an internal "flue" for the back nine inches inside the stove. Filled the sides around it with vermiculite to keep air from leaking around. You can see what this looks like in the photo above.

Then I added a thin capping cinderblock to close off the top of the regular one:
cindeblocks_blanket_wing-cutout_underpan.jpg

5 - Added warming pan "troughs" hanging from the sides.

Here's the finished arch, showing the trough on one side:
mod4_with_trough.jpg

So that's it! Any thoughts? Suggestions? Throw the whole thing out and buy a "real" arch? LOL!

I've only done a very quick test, but the fire really roars now. Can't wait to start tapping and put it through its paces!

Of course I already have ideas for what else I want to improve my "FrankenArch", but I think I'll save most for after this season is done. I expect to boil off close to 3 GPH. Not bad, starting with a stove that was about 13" by 16" on top!

[barnbc76]

How many taps do you plan, and how many potential taps? If all you are going to do is 6 then it will do well. Once you get to 10 or 15 you will likely be thinking of something bigger and better but it will still work. 10 taps x 2 gal/day = 20 gal at 3gal/hr will be just under 7hrs of boiling. I dont think i can make any other suggestions.

[berkshires]

How many taps do you plan

15 this season. I know it's going to be a stretch, and I'll have some long nights!

The next thing on my to-do list is to add drop-tubes to the back pan. That should add a good bit of capacity, but that won't happen until next season.

[barnbc76]

Yeah you will be busy, got anything else you can use? A galvanized trash can ($20 at Walmart) with a 4 gal pot ($12 walmart) will give you just under a gal/hr Ive used mine as a preheater mainly but it will boil well if you keep the fire stoked. Cut a hole in the bottom of the trash can for the pot, a hole for the smoke stack and a small hole for wood on the bottom. It works.IMG_20160227_092813.jpg