Building an oil tank evaporator

[Austin351]

Hello all-

Summer is for getting ready for spring, right? 

Picked up a cheap oil tank a month ago and recently started cutting / welding the other day. Couple questions to those that have had success with the wood fired, oil tank designs.

1. Is a 6" stack sufficient or will I be kicking myself for not putting in a 8"? ( I will build it to accept a fire box blower but may not use it all the time)

2. The firebox will be 24" deep by 27" wide, not counting fire brick. I'll arch up in the back and wondering how much gap I should have between the top of the arch and the bottom of the pan?

3. Thinking of making a continuous flow pan. Pros or cons with that pan on a oil barrel set up?

4. Anything else that may be helpful?



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[OCHTO]

I put a vogelzang kit on mine for the stack and door. I wish I had gone with a bigger stack. I get smoke out the door when I feed it .
My fire box is 24 inches also and it's fine. I would say I have 2 inches between the pan and the firebrick going to the stack. I get a solid 8 gal. per hour.
Paid $200. for my flat pan, new, and got over $300 in the evaporator with fire brick and all.
Very happy with it.
Good Luck

[psparr]

8". The gap under the pan should equal the square inches of the stack. Which on a 2' wide arch is about 2". You might find restricting it a little more will be beneficial. For the door, just make a vertical cut and attach hinges bridging the cut, then cut the remainder of the door. Weld angle to the perimeter of the door and opening and fab up a latch and your good. The vogalzang door is pretty small. It's hard to load wood and distribute it in the firebox quickly. Here's a video of mine. Not the best quality but you can get an idea. https://youtu.be/whRR8BlfocY

[Austin351]

Thanks for the responses!

Another question, is steel grating going to hold up in the firebox or should I use case iron grates? With a blower running, I would think the steel would get red hot and bend under the weight of the wood?

[Super Sapper]

You can use angle iron with the point pointing down so you can fill it with ash. This will insulate the steel from the heat and should not warp. I used unistrut and it is as good as the day I put it in 4 years ago. For comparison, I was using 1/8th inch Stainless sheeting to protect the insulation and that got eaten up in 2 years so you know there was some heat in there. Keep about a 3/4 inch gap between the angle to allow enough air to come through and so it does not plug with coals.

[wiam]

Thanks for the responses!

Another question, is steel grating going to hold up in the firebox or should I use case iron grates? With a blower running, I would think the steel would get red hot and bend under the weight of the wood?

Your grates will be cooler with a blower running.

[Rokee]

This would be my first post here. I am also in the starting/planning stages of an oil tank build. I have the large oil tank and am using an old wood fired furnace door with a built in damper/draft slide - still have to figure out how to fab that on. Its probably an 18"x 18" opening if memory serves.
We are using 6" for the stack but that is just because we have it laying around.
This is only a hobby for us and this would be our first year if everything is ready. It seems to me that most people that don't have the really nice drop flue pans with shiny evaporator hoods have a continuous flow system- correct me if I'm wrong please! I am only going on what I have gleaned from google image search and forums.
I have seen that people put loose sand in the bottom of their arches to help protect under the grating. For the actual grating itself I would go Cast iron personally. you may not get to custom fab your grate but they are inexpensive from TSC and last. Again I'm only a newbie and if I am wrong in information or concept please correct me. Thanks

[wiam]

Most home builds I have seen used angle iron for grates. Should not be a problem with heat unless you let too much coals build up. If you have a blower pushing air up through the grates there will be no problem.

[Johnny Yooper]

I have a 6" stack, seems to work well for my set up; that's what I had available from a previous stove so I used it on my 275 gal oil tank evaporator. According to multiple replies given on this forum, the area under the pan going up the chimney should equal the area of the stack, I sort of followed that when I added a second pan to the back of the stove; started with a 2x4 pan for the first few years and this spring added a 16"x24" pan that was my primary pan from a previous stove and couldn't bear to see it sit idle while the oil tank stove was cranking....might as well take advantage of the heat going through the system to heat the second pan. So I set the gap under this second pan to coincide-more or less- with the area of the 6" chimney. The fire box is about 18" or so high from the grates to the bottom of the 2x4 pan and at the back of that pan it ramps up to approx. 2" or so height under the 16"x24" pan, but I did make provisions to adjust that by installing and removing a steel plate that runs the width of the pan.....varies the height from 2" to 1" and I don't see much difference in performance one way or the other to be quite honest.

I don't have experience with continuous flow pans so I'll let others chime in on that.

Some additional info: I added a blower to my setup this spring after several seasons of no blower - Boil rate increased somewhere around 30% to 50%; I used an adjustable speed control to vary the CFM into the firebox thinking there might be a sweet spot, and with my particular setup, I get the best boil rate from 1/2 to 3/4 speed. I'll never go back to running without the blower, instantly noticeable difference in the boil with it in operation, so highly recommended, and agrees with what I read on here. Also, key to performance is heat loss, or more specifically adopting means to reduce that insofar as possible; you want maximum Btu's going to the pan surface vs any other locations; I lined the firebox with old (thick) firebrick and behind that I used one inch thick archboard and then sheet steel behind that simply as a backer to position the archboard in place......I can hold my hand on the sides of the unit while running; I also insulated the door with leftover archboard and covered it with sheet steel on the inside surfaces.
I used 3/4 inch dia. re-bar to support cast iron grates from an indoor wood boiler and setup is still going strong after several seasons. lastly, while those Btu's are going up my stack, they are heating 25' of coiled copper tubing around the stack which serves as a sap preheater - I have a gate valve on the output to regulate the flow into the pan; I did not have that hooked up this season as I barely got the modifications done for the second pan and blower assembly, but when I used the copper coil preheater in previous seasons, I was getting 160F sap out of it going into the pan. I don't know how much hotter that would be with the blower and assuming the stack temperatures would increase somewhat......will check next season.....always need to have something a little different (and hopefully better) each year to keep it interesting and fun. Good luck with the project!

[Mitchell tapper.]

I built my fire box base out of castable refractory after reading this publication. http://www.uvm.edu/~pmrc/Combustion.pdf It cost about $100 for the refractory so not the cheapest route to go. My pan is flat 28"x49". Aof and most importantly Auf makes a huge difference. It's a hobby so not a lot of time for boils. It will boil 15 gph. I can boil 75 gal of sap in 5 1/2 hours start to finish and all cleaned up. Also I run a 6" stove pipe with no problems.

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[Austin351]

Thanks for the responses!