Double wall base smoke stack?

[Sugarmaker]

Here's the scoop on what I call the Double wall base stack.

I have added a extra stainless cover on the outside of my base smoke stack. about 5 feet up the tapered portion of the stack base. It has some air gap all around between the original and the new skin. Heat can exit the top of the new skin. Kind of like double walled stove pipe.
Why.
Well several reasons (pick one!:)):
1. The heat off the base stack near the pans was scorching the sap on the back of the rear pan and inside the hood. I used a shield of stainless for several years just between the stack and the pan and it kept the heat off the pan.

2. The heat is excessive at the rear of the arch when passing between the rig and the back wall (about 4 feet). And was hoping to reduce this hot spot and direct the heat upward.

3. The 400 series stainless base stack was getting pretty rusty looking after 10 years:(. So I wanted to spruce it up a little for show. Its not fancy but it does look better.

4. I had extra stainless laying around and wanted another project!

Has anyone seen this done and your comments?
I don't anticipate problems but would like to hear ideas. Maybe the inside stack may get hotter?

Now I need to find a place to mount the stack thermometer. I think so that I can see it from the front of the rig.

Yes I can post pictures!

Regards,
Chris

[802maple]

There has been tests done in this area and the results were that because of the high heat in the base stack and and the lack of cool air to get to the stack the inner lining doesn't last long.

[maple flats]

You might do better adding high pressure over fire combustion air. I used to get stack temps after things really got going up in the 950-1050 range at times. This season I added the high pressure air, cut my wood consumption, went from every 5 minutes to every 15 (added about 1.5x as much as I used to) and had a faster boil. In the process my stack temps dropped to about 650-750 with rare readings of 800 max. Translation, better efficiency and lower stack temps. My boil rate was about 10% faster.

[Sugarmaker]

Fellow traders,
Here are some pictures of the double wall base stack and arch. Ready for the pans.
Since the picture I have reset the sap inlet line for the WRU.

I like the idea of the air over fire but that will have to wait till another year. :) I don't have a airtight front so not sure how well it would work? With the research I have done it looks like the high output blower is the key for the air over fire system.

Hope things are well in maple land!
Chris

[Dennis H.]

I agree with 802maple completely covering it will cause alot of heat inside and cause early failure of the stack.

I would maybe rig up a small blower into the back of the stack cover to blow cool air in between the cover and stack. Just a thought.

[Sugarmaker]

802 or Dennis,
Have you see early stack failures and can you describe them? Top of this is open and hot air can come out I don't have any bottom venting letting air in at this time.

Regards,
Chris

[802maple]

I think you would want to allow air into the bottom as it would need to cool.

[Dennis H.]

I have seen it on my evap with 6" steel pipe.

I had to add a heat sheild on my stack to help keep from melting the window. It wraps around it about 2/3 of the way. The seam of the stack is on te back side where the heat sheild is. 2 years and the seam started to curl inward and was causing flame and ash to fly out.

I would either give some room for air to circulate or wrap the old stack with ceramic blanket before putting the new outside skin is put on, just like double walled flue.

[Ausable]

Could too much forced air or combustion air be forcing some of the combustible gases out of the arch fire box, where ignition and burning should take place, and into the stack base and igniting there - burning up the stack prematurely and robbing the arch of some fuel and making the boil less efficient.......

[Sugarmaker]

Thanks for the thoughts on this.

I may try vent holes around the base of the outer skin to allow some cooling air to flow through. But the way it sounds this may not be a great idea if the inner stack is going to get way too hot!

Regards,
Chris

[Jim Schumacher]

I like the idea. Interior stove pipe is built this way, at least simpson dura-vent is (no insulation between the layers). I know that a wood stove isn't subject to as much heat as an evaporator, but I know that the stove in my cabin fills the first couple of feet of the chimney with flame when I am pushing it to warm up on a Friday night in the middle of winter. I also know that a lot of the old woodstoves and non-airtights allow a lot of flame into the chimney as well. I will be doing something similar for the purpose of safety. If anyone ever bumped their face against that base they would be marked for life, I think of that every time I look at it.

[Sugarmaker]

Jim,
Yes safety was one of my issues, the base stack is always HOT 500 to 800 F and we get a lot of folks in the sugar house.
Today I ventilated the back of the stack cover with 400 plus, 1/2 inch dia holes spaced 1 inch apart for the first 2 feet on the back side of the stack cover only. I then fabed a cover over that ventilated area that gives 2 inch air gap for draft to 'cool' the stack. I will closely monitor this set up and let you know. I did take some pictures but am to pooped to post!:)

Regards,
Chris

[Sugarmaker]

Folks some shots of the vented stack and vent cover.

Chris

[Pete S]

Set your "shield " up to allow air in at the base, and then able to release it at the top of the shield.

Wrapping the pipe could be fatal. Air is a wonderful and safe insulator.

[DrTimPerkins]

Yes safety was one of my issues, the base stack is always HOT 500 to 800 F and we get a lot of folks in the sugar house.

You could always add a "Caution - HOT" sign for about $15 to let people know about the hazard. It would have to be aluminum, not the stick-on vinyl type.

[TF Maple]

That would be a great place for some preheater tanks to use the heat and protect people from high heat. I don't have a plan on how one would do that.

[WF MASON]

Chris , I believe you had a CDL stack preheater almost made, to many holes to plug now though.....

[Slatebelt*Pa*Tapper]

http://www.mapletrader.com/community/attachment.php?attachmentid=1706&d=1273622193

Hi Sugarmaker, in your first pic (link above) i see you have an arch foundation under your evaporator with additional ash clean out. when you look around at most other folks set ups you don't see a whole lot of these under there arch's.
May i ask how tall is your foundation. few more questions for you or any others with imput if i may, is this a must for a set up and what benefits does it have other than just using the ash door on the arch. debating on making one of these instead of just setting my whole arch onto the flat concrete slabbed block floor.


Thanks in advance for any advice
Charlie

[Thompson's Tree Farm]

Slatebelt,
One advantage is less bending over when feeding the fire! It does help with the exhaustion factor in a long boil.

[Sugarmaker]

Charlie,
As Thompson mentioned this was designed mainly for the exhaustion factor.:) I am 6'-1" and I wanted the rig to be set up higher for ease of firing. I saw this raised version on another wood fired rig and really liked it. The foundation is basically 1 block high (8 inches). I used the narrow width 4 inch solid concrete blocks. I fabricated the ash pit door from steel angle iron and a steel plate with simple swing hinges and pins.

BTW since I have forced draft I have the original draft door bolted shut. The lower ash pit door can be opened for draft if needed.
Hope this helps!

Regards,
Chris

[Sugarmaker]

Dr. Tim
Great idea.
Chris

[Sugarmaker]

Chris , I believe you had a CDL stack preheater almost made, to many holes to plug now though.....
WF,
Give me some more hints on the CDL base stack preheater.
Regards,
Chris

[PerryW]

If you have a hot spot at the rear of your arch; Could it be that you are getting too much draft? Or your ramp needs to be moved forward to move the hot spot back toward the middle of the back pan?

Sounds like a lot of your heat is going up the stack.

[Sugarmaker]

Perry,
We burn mostly pallets, they burn very quick and hot. The Arch is patterned after a leader. I would be changing the arch shape in the near future so I will have to live with the heat loss.

Regards,
Chris

[Brent]

A few thoughts

First: put a couple of 2" diameter holes on one side and a 1/4" on the opposite. This will allow inserting a BBQ spit and you can cook hot dogs and sausage between the walls:lol:

Second. I agree with Perry that your forced draft may be blowing your fire way back under the flue pan causing the very high stack temps. What were your stack temps last year ??? Of coarse if you dial back the blower you may lower the boil rate. Re-directing some of the air to an over-the-fire will give you more complete combustion and may still give you higher temps under the pans with a faster temp drop near the back of the flue pan and at the bottom of the stack.

Maybe we will get to talk about this in a couple weeks. My trip down your way is not likely going to be until Oct 1-2 weekend. (hope the buyer is tolerant)

[Sugarmaker]

Brent I really like the BBQ idea and may be working on that this winter. :)

Stack temps run about 700-800 with the $16 bolt on external thermometer.

I did boil with out the blower a few times last year with same stack temps. We have very good natural draft too. The blower on low speed and about 1/2 throttle on the air damper seems to be about the same as natural draft.

Maybe I will see you as you arrive or depart our area when you deliver the evaporator.

Regards,
Chris

Regards

[Sugarmaker]

Folks,
Good news I boil a test run on Sunday and at this time the sugar house is still standing! Boiled for about 2-1/2 hours. The double walled based stack with vents and vent cover preformed well. It met all my expectations. A lot less heat at the back of the arch where we walk thru! Cobwebs at the top of the double wall indicated that we had a good strong draft around the inside pipe.
I was running stack temps from 500 to 7850 degrees.
Time will tell if we will have a problem. At this time it seems OK.

Regards,
Chris

[Sugarmaker]

Year one report on this triple wall vented base stack.
This preformed way above my expectations. With the AOF keeping the stack temps lower at 500 to 600 F you could almost keep your hand on the exterior third layer of the vented base stack system.
It was much more pleasant to work around the back of the arch. Also safer from a potential burn standpoint, and kept the rear wall of the sugar house much cooler.
All in all a success.
Chris

[Jim Schumacher]

Thanks for the update Chris!