Aof/auf arch build

[mountain man maple]

I'm starting to research on building auf/aof arch. I'm trying to figure out how to size the high pressure blowers that come with no motor and therefore no cfm ratings. How do I know how to size these blowers and can I get away with one blower for auf/aof? How do I decide how tall to make firebox? I see that I want firebox to be 40-60% of the length of evap. And last what have people used for grates in these homebuild arches already?

[nymapleguy607]

To figure out the cfms for a hiugh pressure blower you should be able to look at the wheel size for a blower that comes with the motor, that will tell you how many cfms. You can use one blower for AOF and AUF but you need a good set of dampers to control the amount of AUF because you will have less resistance and more air will want to flow through the AUF than the AOF. I figured the height of my firebox by figuring how tall I wanted the whole arch to be. I chose 30", then I left a 6" air space under the grates to run pipes for the air that is feed through the front of the arch, so I have 24" between the grates and the pans. For grates I used split fire bricks and drilled 3/4" holes for the air to come through, although I might replace them with bricks with a 3/8"-1/2" hole.

[maple flats]

My AUF AOF runs on one HP blower. My blower is likely a hundred years old, having come from an old factory and the motor did not come with it, thus I don't know what the CFM is. However I do know it works great. I'll try to get some measurements and that may help you. I have a 4" PVC pipe from the blower to under the arch, where it splits into 2- 3" followed by a 3" ball valve on each. The AUF valve is open about 20-25% and the AOF valve is open about 65-70%. Those never change, once I got to the best performance.

[mountain man maple]

For the aof manifold I am planning on using 2x4 tubing should it run all the way around firebox. Front sides and back? Should I build a preheater for that air and run under flue section arch with only bricks covering it or will it not help with combustion. Are bricks just sitting on angle in firebox? For top rails I am planning on using 3/16" thick angle. Is that heavy enough or should it be 1/4" to keep from warping?

[nymapleguy607]

I used 1/4" for arch rails, you need to make sure they are insulated from direct flame or it will warp the rails, I don't preheat the combustion air, some commercial arches do this but I can't tell you if it makes a difference. I built my arch with vertical sides so all the brick are cut and mortared in place, make sure you use high temp cement and bricks because the bricks will glow red after a couple hours boiling

[asknupp]

Someone please tell me the difference is between the blowers everyone is talking about. High pressure and squirrel cage? Is it how the shrouds are that make it high pressure?

[nymapleguy607]

High pressure blowers have about 4 paddles on the impeller wheel, A high pressure blower has less cfm than a squirrel cage blower but can produce pressure from 1-5" of water column. Squirrel cage blowers push lots of CFMS but they will not produce any pressure. AOF needs high pressure to make sure that the air still has enough velocity after coming through the duct work and nozzles to mix and reburn the unburnt gases.

[asknupp]

Thanks Jeff. Would that fan be a radial fan versus the backward fin ?

[Bernie/MA]

You asked about grates. Some use angle iron, vee point down. I built one and used 3/16x2x2 square tubing, placed diagonally spaced a half inch apart, that shows no problems after 4 seasons. I recently acquired some household steam radiators that will come apart in 2" thick sections. Shipping will probably prohibit that from MA.

[lpakiz]

I used 3 X 3 X 3/16 square tube. They are placed so they look like a diamond, and are just touching each other at their points. They have air under fire going thru them, so some heat is being removed. Ash builds up in the valleys, insulating them from the heat. They look new after two seasons.

[Flat Lander Sugaring]

It has been said you need around 1200 deg F for gasification to happen, so I built a aof preheater box. Think it works awesome can hold my hand 1/4" away from stack and doesn't really get to hot. I have pics on here showing the box I believe

[mountain man maple]

98199819For aof manifold should I run it along back wall up both sides and across front of arch? Or are sides and back wall of firebox only where it's needed? My thoughts were to feed from blower to a manifold that would separate the sides from the back wall portion. Thinking this would help to equalize flow. Is that necessary or would it help to distribute air better?

[maple flats]

I didn't find it necessary to "balance" the flow on mine. My HP blower unit is 100+ yrs. old and I never found any specs. On my 3x8 arch, I have 1 2x2 sq. tube feeding thru the ramp. It is welded to the manifold at the center of the rear wall of the firebox. From there it goes both ways, all in 2x2 tube. Every 6" I have a 3/8" pipe nozzle welded over a 1/2" hole in the manifold, angled down about 15 degrees. Each nozzle faces the opposite wall. The manifold surrounds the fire, except on each side of the fill door it stops at the door, at a nozzle. While I have no test equipment to verify, I did a smoke test with the pans off and all nozzles looked to move the same amount and velocity. It functions very well. While making 2 sections would simplify installation, (I had to work on mine for about 30 minutes to get it into place, and had to remove the side bricks down to the grates and then re-brick. 2 sections may slide in much easier.) My firebox is only 32" deep, front to back.

[VTmaplehobby]

Is there a specific nozzle that needs to be used? I understand there is a specific size, but is it just a piece of pipe?

[nymapleguy607]

Is there a specific nozzle that needs to be used? I understand there is a specific size, but is it just a piece of pipe?

The nozzles are just pieces of pipe. Some people have used threaded pipe nipples so when the nozzles burn out they are easily replaced.

[mountain man maple]

What pipe is everyone using? Carbon or stainless steel?

[maple flats]

My nozzles are just black iron pipe. My plan was to shorten them after bricking but then I was afraid the vibration might loosen the refractory. Then I decided to just let the portions (ranging in lengths up to about 1.5") that stick out just self prune with the fire. After about 5 or 6 seasons they still look new. My guess is that the air flowing thru the nozzles cool the nozzles enough to protect them because the fire is very hot and turbulent in operation. My blower is started as soon as I light the fire and remains lit until the last coals are burned out. I turn the blower on (I have AOF/AUF on one blower), the valves for the balancing have not been moved in 4 or 5 years and the blower remains on during fueling. I get no smoke nor sparks out the fill door while ueling. The only smoke ever is about the first 4-5 minutes when lighting the new fire.

[mountain man maple]

I have 2 blowers to use on arch build. A. Squirrel cage blower for auf and a high pressure blower for aof. It looks like tubing is thing to use for grates can I place them tight enough together to keep ashes from falling through. Will this cause problems with warping? On a 12' arch is 66" firebox about right? Want to leave 4" under flues and place 2" of blanket then use 1.5" bricks to protect blanket. That should get me up to .5" below top rail which should be about right. With 66" firebox 18" of flue pan will be over firebox is that normal in newer design of arches. Thanks for all the ideas so far.

[mountain man maple]

Where is a good source for premade blast gates or other air flow controls? Would like to use a square or rectangle plenum since that is the shape of outlet on blower. Will a damper work as good as a blast gate to control volume of air?

[maple flats]

I don't think a damper will do, even if it has a lock in position feature. Just my opinion, but I thing a gate would be far better, or a ball valve. However I would not have ball valves if they weren't given to me free, just like the HP blower.

[asknupp]

I had my pipefitter brother price 3" PVC ball valves and he quoted 135. Found blast gates at Menard's for 6 bucks. Problem with them are I assembled everything in garage and went to move them and broke both. They are glued together on each side of gate. Got two new and will assemble directly to arch this time. I'll post pics later
http://www.menards.com/main/mobile/search.html?search=blast+gates

[mountain man maple]

I'm ready to insulate and brick arch. I would like to use 2" blanket in firebox and use split bricks on walls. Will splits hold up to this type of arch.

[nymapleguy607]

Looks really nice, good job. As far as insulating you might want to go wilth 1" blanket and then use full bricks. I used that combo in my arch, The larger brick are more stable when you make the vertical walls. You will have the bricks glowing after about an hour of boiling.

[Schiefe4]

You may want to try a high temperature refractory cement and pour a wall after you use insulation.

[mountain man maple]

I ended up using the 1" blanket in firebox then fullbricks. Stopped bricks at aof nozzle and only used blanket to top rail in firebox. At back wall of firebox blanket went straight to top rail. Had 5" of fireblanket under flue pan no gap between pans and blanket. Flue pan has 9" raised flue. About 12" from back of flue pan blanket drops back down with 2" gap to go out stack. Does that seem about right for a high effeciency arch design? Didn't have a stack thermometer this year but my stack didn't discolor and never ran extremely hot. My problem is I couldn't get back 2' of flue pan to boil very hard. First 2' almost jumping out of pan next 4' was a hard boil but last 2' was a slow boil. I have a preheater in hood so concentrate was always warmed coming into flue pan. This setup always boiled about 90-120 gph. Firing times were 30 mins with slab wood and 45-60 mins with firewood. I am very happy with the way arch worked overall just thinking if I could tweak blanket a bit to get back of flue pan to boil a little better.

[Flat Lander Sugaring]

I'm ready to insulate and brick arch. I would like to use 2" blanket in firebox and use split bricks on walls. Will splits hold up to this type of arch.


when i was building my aof Beanie had me use 3" x 6" rectangle stock, couldnt tell you why but since he was the original designer of the CDL intensofire I listened to him.
only need brick where the wood gets thrown blanket and board every were else. Next arch build im using board on outside walls and covering with blanket.














.

[mountain man maple]

I have been reading through archives on here about stack lengths. What length stack does everyone run on forced draft arches? Local dealer suggested adding stack to make my flue pan boil better in the last 2'. According to a lot of older posts on here even for forced draft arches people were still using the 2x evaporator length rule. Does anyone think this will help pan boil better?

[Flat Lander Sugaring]

I have been reading through archives on here about stack lengths. What length stack does everyone run on forced draft arches? Local dealer suggested adding stack to make my flue pan boil better in the last 2'. According to a lot of older posts on here even for forced draft arches people were still using the 2x evaporator length rule. Does anyone think this will help pan boil better?
With forced air no need to do the 2x the length of arch just use wood stove specs you should be good

[maple flats]

Still use 2x just in case you have a power failure or other issue with the HP blower. No need for any extra.

[mellondome]

If your stack didnt discolor than you didnt have enough heat to boil the last foot. Also, that seems like a long time between firings. When I used wood, I fired every 7 min with hardwood (aof/auf) .
You might not be getting enough air in the firebox or wood is not split small enough.

[maple flats]

My AUF/AOF works great, but I fire every 9 minutes, before AUF/AOF I fired every 7 minutes. My first season I had the AUF/AOF I experimented with times up to 20 minutes, but I found that 9 worked best for me.

[mountain man maple]

Firewood is 2-6" diameter 30-55" in length. I don't split any of it. When I load it takes about 5-10 minutes to get back to full boil. So I could maybe shorten firing times a little. My stack you can almost lay your hand on. Even after boiling for a few hours. I get some smoke out of around pan gaskets when I first light a fire for 5 minutes. I do shut down aof blower or the flames come out of door when firing. I have aof nozzles on all sides of firebox. Maybe that's why the fire comes out door. I think right now I only have 12' of stack after a 4' base stack. I think I will add a few feet it can't hurt anything right?

[mellondome]

You are either burning down too far in the firebox... and not getting enough air to the fire. You should be able to make the stack glow if you add enough air.
What do you have for air coming in under the fire?
Also... split all wood over 2". It will burn much better with an open face.

[Flat Lander Sugaring]

Firewood is 2-6" diameter 30-55" in length. I don't split any of it. When I load it takes about 5-10 minutes to get back to full boil. So I could maybe shorten firing times a little. My stack you can almost lay your hand on. Even after boiling for a few hours. I get some smoke out of around pan gaskets when I first light a fire for 5 minutes. I do shut down aof blower or the flames come out of door when firing. I have aof nozzles on all sides of firebox. Maybe that's why the fire comes out door. I think right now I only have 12' of stack after a 4' base stack. I think I will add a few feet it can't hurt anything right?

I think your stack temp is good that means you keeping all the heat inside the arch and not helping with global warming:), when first starting you will have some smoke but you want it air tight might need to re-gasket pan. Nozzles all around shouldnt matter with fire coming out door, I do and no fire out door unless I put lathe in. being forced air I dont think you need stack to be as long as traditional fired arch.

[mountain man maple]

I'm running 463 cfm squirrel cage blower through 3/8"and 1/2" holes in grates. I may drill those larger also. Adjusting auf damper doesn't seem to change fire much. I have new gasket and gasket rope didn't like the soft ceramic gasket with changing crossflow pans. The smoke leaks out where I put pressure on front crossflow. I used a angle here and it leaks between angle and arch. Not sure how to seal that up and keep it adjustable. Besides that arch is airtight.

[nymapleguy607]

I ended up using the 1" blanket in firebox then fullbricks. Stopped bricks at aof nozzle and only used blanket to top rail in firebox. At back wall of firebox blanket went straight to top rail. Had 5" of fireblanket under flue pan no gap between pans and blanket. Flue pan has 9" raised flue. About 12" from back of flue pan blanket drops back down with 2" gap to go out stack. Does that seem about right for a high effeciency arch design? Didn't have a stack thermometer this year but my stack didn't discolor and never ran extremely hot. My problem is I couldn't get back 2' of flue pan to boil very hard. First 2' almost jumping out of pan next 4' was a hard boil but last 2' was a slow boil. I have a preheater in hood so concentrate was always warmed coming into flue pan. This setup always boiled about 90-120 gph. Firing times were 30 mins with slab wood and 45-60 mins with firewood. I am very happy with the way arch worked overall just thinking if I could tweak blanket a bit to get back of flue pan to boil a little better.

I think you are discovering the tipping point between a gasifying arch and a forced air arch. Right now you are gasifying with the long load intervals and low stack temp, your wood usage will be great but the pans won't boil quite as hard. If you want the last 2 feet to boil your going to need more heat which is going to mean feeding it every 10-15 minutes and running more under fire air and getting that stack temp up. Its all a trade offs, you just need to find a happy medium between economy and performance.

[mountain man maple]

Do I need more auf as in bigger holes? Or a bigger blower? I like the load times but also want pan to boil as hard as is possible.

[Flat Lander Sugaring]

Do I need more auf as in bigger holes? Or a bigger blower? I like the load times but also want pan to boil as hard as is possible.
UVM has a size chart for each arch on AOF/AUF blower

[mountain man maple]

I used a chart for aof blower. Went one size larger because was planning on one blower for both auf/aof. I decided against that then used two blowers . Can't remember where I found sizing for auf blower.

[Super Sapper]

I would increase your holes size or add more holes for auf. A squirrel cage blower will only put out so much pressure no matter the size. If you do not have enough open area for the air it is the same as throttling with a valve.

[nymapleguy607]

The air under fire is basically your gas pedal, the more AUF the hotter the fire and stack temp. That will bring evaporation up a bit, but it is a double edge sword. The more AUF you push, the faster the wood burns down and the more frequently you will need to load wood, these are the trade offs. Best thing to do is have a stack thermometer and find a temp that gives you an evaporation rate you want, the wood economy. Then just try to hold that temp. For my evaporator its 1300 degrees in the stack. Depending on the wood I'm burning I can reload every 8-15 minutes. With my steamaway it lets me boil an average of 75gph. These are both numbers I can live with so that's the temp I shoot for.

[Chicopee Sap Shack]

You need a different blower. Your squirrel cage can work for the AUF but for AOF you need a high pressure blower. You are trying to create turbulence and the squirrel cage can't do that.


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[Chicopee Sap Shack]

Never mind just saw that you are using a HP blower for AOF. 1/2" holes in grates should be fine. You might not have enough CFM from your AUF blower


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