Stack question

[dano2840]

i know your stack is supposed to be 2x as long as the evap, mine is a 3x8 but is that including the 6ft base stack or not? i have 16 ft including the base stack but i get 6ft flames out the stack when im REALLY going, but im burning alot of wood i think ive used 7 cord to make 94 gal of syrup mixed slap and split hard wood, but alot of the heat goes up the stack, my rig boils hard and by no means is there no spots where air can get in, (arch gasket is on the list for next year) but i have probably another 16 ft of stack i can put on it, my question is will this create even more draft and suck even more heat out, when i get the rig going hard the stack shakes when i stoke it, or will putting the other stack up keep more of the heat in??

[PerryW]

Yes, you should have 16 feet of stack including your base stack (at least that's what they told me). I agree that you should NOT add extra stack.

My 3x10 (with 20 feet of stack) often has a flame shooting out the top (looks like a big christmas candle). For the last few years, I have been running the damper almost closed, which seems to eliminate the flaming stack. It might boil a little slower, but I think I'm using a lot less wood.

I'm guessing 9 cords of softwood slabs will make me 120 gallons

[mountainvan]

You should be getting 20-25 gals of syrup/ cord. I would do some major insulating of my rig, arch gasket, ceramic wool under the flue pan, maybe even some typo of damper in the stack. Blowing flames out of the stack is not good, you want the heat to go to the pans. For now I would slow my firing to use less wood and see if the evaporation rate dropped a lot. As for the stack I would say you have enough.

[PerryW]

Here's a comparison of the Heat Produced Per cord (Million BTU's) for different species of wood for comparison.


Softwood make slightly better than 50% of what hardwood will give you.



Hickory 27.7
White Oak 25.7
Beech, Sugar Maple, Red Oak 24.0
White Ash 23.6
Red Maple 18.7
Hemlock 15.9
Eastern White Pine, Balsam Fir 14.3

[H. Walker]

If you are using a blower, damper it down!!! You are melting the polar ice cap.

[brookledge]

The flame at the top is probably caused from unburnt gases that are still hot enough to ignite when they reach the top of the stack and can get oxygen.
With inferno and intensifire arches they inject air over the fire to burn those gases in the arch instead of when they reach the top of the stack.
Keith

[3% Solution]

Dano,
Brookledge is right, it is the gasses from the wood and when you crowd the gasses in the arch (making more gasses than can burn), some of them don't burn where you want them to and they go out the stack.
Those gasses are burning around 1800 to 2000 degrees, so just think if you could keep them in the arch burning.
I haven't had fire come out of the stack for a year or so, until this year when I got to firing pretty hard and often.
That night we got some real cool (or hot) pictures of it.
The problem is, your efficientcy is going out the stack.
Once you get things heated up in the arch it's not going to take much to really move things right along.
We never fill the firebox full when firing.
We pull the wood from the last firing to the center and put 2 -3 pieces of wood on each side, that's it.
We are getting 25 gallons per cord.
Now if any one doubts using less wood per firing try this, at the end of the boil when your done and your down to a few coals, throw in 2 or 3 pieces of wood and watch the boil in both pans come right back up.
More wood is not always the answer, technique is the answer.
Hope this helps.
It seems to work for us.

Dave

[gmcooper]

Brooklege and others are correct on the flue gasses burning when they hit the air and get oxygen. Mine will do that depending on how I fire. Try firing at a steady rate and adjust the volume of wood till you get a hard steady boil without the flue flames. Too much wood will put a lot of gas up the stack as the fire cannot get enough oxygen in the fire box.
Mark

[dano2840]

the flame goes right under the pans and p the stack its flame through out the whole rig and stack, i usually have the draft door open all the way, maybe i will try it with only 1/3 open or 1/2, if i get any more sap, reds are budded, sugars not yet,

[dano2840]

would putting a blower that was the right size that i point up at the fire inject enough air into the arch to burn those gasses and boil 2x as hard with out those flames? and get more btus in the arch?

[RileySugarbush]

Dano,

I don't think it works out as well. A bigger blower under the grates will make a hotter fire and boil faster, but will not help our efficiency since it increases the flow rate through the arch and pushes the heat out the stack faster.

It looks like the optimal solution is to have enough air under the grates to get the combustion you want, than add air over the fire to get complete combustion before the fuel gets past the flue pan. It's tricky to get it right. Someone posted a link to a big technical paper on it.

This year I added some air injection, but not nearly as much as is recommended. With my 200 cfm blower still shooting through the grate, I added two 60 cfm high pressure blowers feeding over the fire through 20 small nozzles. I think it worked better on efficiency, maybe better on evaporation rate, but I had a strange mix of fuel wood this year, burning lot's of scraps so I can't do a good comparison.

[PerryW]

Try burning shorter wood.

[dano2840]

air over fire? how do you do this?

[Uncle Tucker]

Dano,
I tried this 2 years ago, and I was getting 40-50 GPH on a 2x6. I redid my fans last summer and made it so I could shut them down individually. This year I was running low on wood so I shut off the one under the greats and left the one in the ramp on. I would fire with the ramp fan on, and WOW it looked like two oil burners blowing under the pans. The flames were bright yellow and 12-18” long.