barometric damper on wood fired evaporator

[mikeb]

I have a wood-fired oil-drum style evaporator. It's about 3' long. The stack is 6" in dia. and 6' tall. I'm adding forced air under the grates this year. Now, in the junk heap, I have an old barometric damper mounted on a 2' section of pipe.

I'm wondering if it makes sense to:
- add this damper and increase the stack length to 8'?
- add the damper but keep the stack at 6'?
- no change?

What does the barometric damper do for you on a wood-fired boiler? Is there such a thing as too much draft? If so, how do I adjust it? What would I be looking for?

Thanks. Mike

[mapleman3]

I don't think you should, the whole idea with the wood is to get great draft drawing the fire under the length of the pans as hot and fast as possible... Oil is constant temp so you can control the draft with a barometric damper so you don't suck the flame away from the burner and get incomplete combustion. oil burners need a constant -.02" overfire draft and -.05- -.07 breech(stack) draft to run clean and efficient....
so you adjust how much overfire draft with the Barometric....

Wood is just balls to the wall fire and draft

[mapleack]

I'd add the extra pipe without a damper. You'll get more draft and a little faster boil.

[parsissn]

Do you have enough draft when flames (not sparks) come out the top of your stack? Happens quite a bit on my 2x6 with a 10' stack and I don't have a blower on the rig either.

Mark

[nymapleguy607]

Mark
I would definitley say you have plenty of draft. But the only problem is that all of that fire out the top of the stack isn't doing you any good up there. You might want to try and close down the amount of space from your base stack towards the ramp. Then you could probly have the same boil with less fire. Just a thought Jeff

[Mac_Muz]

I wouldn't add that damper type either. I am confused some due to the oil drum you have is bigger than a 55 gallon barrel I have, and my pan is 33 inches long. Well it is really 33 and 3/4 inches long, but the last 3/4 inch is a mistake. I measured wrong. Thats ok I was able to make up for that.

I use 8 feet of 6 inch pipe and it draws air hard and fast. There is a cheap chinese cast iron wood stove damper I can flip in the 2nd section of stack.

My rig runs wood as long as the barrel can take and I stack wood to the bottom of the pan. I need to get rid of junk dead white pine, and this is one way, the other being brush pile fires where I gain nothing.

At times I get blue fire better than 6 long plumes out the stack, and can tip the damper slightly which increases the boil.

My pan will hold (5) 5 gallon and better jopint compond buckets of sap and boil all 3 sections in the pan at 5 inches deep and or somewhat more.

It would boil deeper, but the sides of the pan are not high enough at 6 inches high... I don't want to fill the pan past leaving 1 inch of free board, for safety reasons.

If you add that baro damper it will cut the draw you want. I would add another section of stack, and allow no air that doesn't pass the fire.

My rig wastes fire, and if anything I might next year attach another barrel with another pan and have this one as it is now be the fire box and feed heated gasses into a pan the same size as what I have now, as a sort of big pre heater.

The rig would begin to look like a train, and I would have to assure myself I had more sap, that might be 60 taps, but I am not to sure I want to work that hard.

It is probably important to add my little rig has a internal baffel just like 1/2 a coffee tin, with a bottom. This forces flames up under the pan before they must run down to escape.

Maybe one day I will make a stainless pan with a corregated bottom to speed things up, but at that pint I would want more sap still, so the time to fire would be about the same. I know there is a proper name for that, but I am not sure what it is..

[skinny78]

Mike,

I have a blower on my leader half pint and I use a sheet magnet on the blower intake to regulate the draft. I usually run it 3/4 open. If your flue pipe is turning red hot more than a couple of inches you are wasting heat. I have some pictures in my photo bucket link.

[802maple]

You are actually getting what I call the torch effect. The fire you are seeing is because you aren't getting enough air believe it or not. The gases that are escaping from your evaporator are igniting when they make contact with the outside air.


Do you have enough draft when flames (not sparks) come out the top of your stack? Happens quite a bit on my 2x6 with a 10' stack and I don't have a blower on the rig either.

Mark

[mikeb]

Thanks, everyone, for your advice. I think I agree that the barometric damper will not be useful. I will increase the stack length from 6' to 8', if I can support that extra length. I'm adding a blower at the lower back end of the drum. It's an old squirrel cage blower from a wood furnace. It has an adjustable baffle to control the amount of intake air. It will introduce the air behind the firebrick that ramps up the back end. I read in another thread that (much like a woodstove) you want to get 75% of the air over the fire and 25% under... and introduce the air to cause as much turbulence as possible. In my case, I'm going to put in some sheet metal baffles/diverters to force this air behind the firebrick along the sides of the barrel. Then I can control the air into the fire chamber using standoffs to create gaps in the firebrick. Kind of crude, but I think it will work.