size of fire box for 3 by 10

[huntingken111]

Ok been doing a lot of reading for my 3 by 10 pans that needs an arch. You guys have given a ton of ideas. My idea was to put auf/aof in it. My arch will be total of 12 feet for chimney (Which will be 12 inch dia). I read on here that my firebox should be 2/3 the length of arch for good gasification. That would be 8ft long is this is true or did I miss read it. I was planning on 40 inches long and after insulation and brick about 27 inches wide. Please give me some insight to length of firebox so confused now.

[Scribner's Mountain Maple]

Hmm, 8' is not right.

I have worked on two arch's, a 4*12 a 6*16. The 4 footer had a 5 ' firebox, that included the ramp. Essentially you want the ramp to end where the flue pan begins. So you are a 3*10. How big are your grates?That is how big to build the fire box and ramp it from there to where flue pan begins? Drop or raised flue?

Ben

[nymapleguy607]

If you are building a true gasifier, use 2/3 the length of the pans not the total arch length. For 10 ft pans it puts you in the 6-1/2ft range. The width of your firebox seems too narrow as well. If you are building it with vertical side walls try to keep the width of the arch rails so you have only 1" of the pan sitting on each side, that would make it 34" wide. If you build the rails using 2-1/2" angle iron you can insulate with 1" balnket and 2-1/2" brick, the total width of the fire box would be 32", the top brick is then cut on a taper so the edge of the top brick and the arch rail are equal.

[lpakiz]

On my 2 X 10 the grates are about 40 inches long. Syrup pan is only 24 inches, so wood has to be cut at 20 inches and be a little careful with the last few sticks, to not hit the drop flues.

[mapleguy]

I have a3 x10 Lapierre. Fire box is 3' long. My question would be is the 12" stack sufficient because mine is 15". Maybe with forced air it doesn't require a larger pipe?

[huntingken111]

So if I want true gasification I need 6.5 ft that makes sense to me. Me finish pan is 5 ft and my drop flue is 5 ft long both 3 ft wide. If I only go about 40 inches long like planned and have ramp to flues with auf/aof what is that then? Sorry for dumb questions but if I am going to build an arch I don't want to modify it next year I would like to do it right the first time. To me and please no offence to anyone but it sounds like I can do it all kinds of diferent ways and just play with air till it sounds and looks right. But even in my trade there is still usually one best way to do it.

[Sugarmaker]

Many arch designs out there! lots of them designed for gasification today have very large long fireboxes, some don't even have grates, building the fire right on top of bottom air tubes (AUF) and then AOF up near the top. All the big guys seem to have there own variations on this theme. Now there are a lot of older conventional arch designs that have been altered to add AUF and AOF. I think you will find many variations in arches. Go look at a bunch of new arches get dimensions and ideas.
I would stay open about changes. I have changed several things on my old style arch in the last 15 years. Continuous improvements are good. Expensive and extensive improvements are not so good.
Couple of basic things are important in my opinion:
1. keep as much heat/ fire under the pans as possible. Well insulated air tight arch and door. 12 inch stack is a small as you would want. 14 would be ok. make sure the stack is at least 20 + feet tall above the arch.
2. Have more air than you need in your AUF and AOF. To little and you will not be happy.
3. Have separate AUF and AOF air systems if possible.
4. Have controls on air flow for both blower systems. So you can tune the burn.
5. Design/build you arch to the best design you can. Lots of info on home built AUF and AOF systems on line.
In reading some of your details I believe you have pans that are 5 foot long. As you know this is not the most efficient pan system in today's designs. It will work and make syrup. That's what I am still using. Keep this in mind when you build your arch, what if you upgrade to a 3 x 7 flue and 3 x3 syrup pan in a couple years would that arch be able to easily handle that pan size combo?

If you can post some designs that you have in mind I am sure you will get comments and suggestions.:)
Regards,
Chris

[lpakiz]

Lots of good info so far. I would question the need for a tall stack, tho. With AUF and AOF, the stack does not have to generate draw like older units. I feel that my stack functions more like the exhaust pipe on a semi. That is, it is only a vent to conduct smoke out of the arch. The blower on mine keeps positive pressure in the arch, so I know that "draw" is not the primary concern of the stack. Of course, you need sufficient diameter to be able to handle the volume you will be sending out. I intend to try mine this season with one less (3 foot) length each of steam and smoke stack than last year.

[huntingken111]

Ok You have given a ton of info Thankyou. I am going with 6.5 ft fire box. Question is this do my fire grates have to go the 6.5 ft length or can I stop them at the 40 inch lenth and and stop bricking at 40inches (whole inside of arch will have 2 inch ceramic blanket) since I don.t plan on throwing in 6.5 ft of log. Also for auf do I use the thin walled 2x2 tubing I am using above. AUF and aof will have separate controls for flow

[lpakiz]

The shorter 40 inch grates will be fine. Be sure to brick over any insulation that might get hit with wood, or that you might push coals into.

[huntingken111]

Ok thanks that's what I was hoping

[Sugarmaker]

Most of the AUF systems just dump into the ash pit area below the grates. Have seen wide openings down to just the same opening as the blower your using. I think the forced auf air will get to the fire if you get it under there. Mine enters through a 6 in x 6 in hole about 2 inches under the grates. Using a 550 CFM blower with a damper in the tube to control air volume. With AOF you don't need as much air volume under fire. I think it is about 80% aof and 20% auf. These blowers do make some amount of noise, keep that in mind. I use a hot tub air blower/bubbler for the AOF and throttle that with a valve in the 2-1/2 inch air inlet pipe. Might find some pictures of my old stuff on here somewhere.
Regards,
Chris

[nymapleguy607]

The concept of some of the gasification arches are using short grates near the front of the arch, when you are ready to reload the arch you push the some of the coals to the back of the arch, what this does is great a heat source to keep the smoke and gases hot, so when you inject the over fire air there is enough heat and air it reburns the smoke. They also say that you want to pile the wood tight over the grates, pileing tight will cause the wood to produce more smoke.

[Flat Lander Sugaring]

shorter because you need that air space in front of the rear pan to achieve gasification alone with a fire box min.temp of approx 1100deg.
Is 40" the factory length of the grates? if so leave it that distance. Insulate insulate insulate keep all that heat in the arch I have 2" and need more.

[Robert K]

Just jumping in here because I am in the middle of my arch build also. The coals pushed behind the grate must create gases that react with the AOF to create more flames? Do I need a separate grate under this area to burn off excess coals or is this not a problem? I am currently building a 2x12 arch and gasification is my goal. Also building a preheater to use stack temps to heat up both AUF and AOF. Another question is could I cover AOF manifold in fire box with high temp mortar to prevent burnout of tubes, or must they be insulated with ceramic?
Great discussion!
Robert

[Flat Lander Sugaring]

Just jumping in here because I am in the middle of my arch build also. The coals pushed behind the grate must create gases that react with the AOF to create more flames? Do I need a separate grate under this area to burn off excess coals or is this not a problem? I am currently building a 2x12 arch and gasification is my goal. Also building a preheater to use stack temps to heat up both AUF and AOF. Another question is could I cover AOF manifold in fire box with high temp mortar to prevent burnout of tubes, or must they be insulated with ceramic?
Great discussion!
Robert
i insulated around my AOF tubes with ceramic blanket seem to be doing good. look for my pics of arch build. I preheated my AOF air with all the heat going out the chimney. buying temp probes this year so I know what the temps are.
http://mapletrader.com/maplegallery/g558-arch-build.html

[Robert K]

Flat lander
I am currently going to use a recycled 10" water pipe, it 10 feet long and should be full of 2-3 inch pipes when finished. The idea of using normally waste heat to increase efficiency is great. The water pipe is 1/4 inch thick so I hope to get away without insulation for this year, some have run a preheater sap line around stack, maybe down the road. still working on arch.
Thanks

[nymapleguy607]

Robert,

The idea of pushing the coals behind the grates comes from talking to the CDL reps about the intensofire arch. On that arch the air is injected at the rear wall of the firebox. I believe pushing the coals back just insures enough heat so the gases reignite. I think it also helps controll the rate of combustion and evens out the temperature swings inside the arch. I haven't done any scientific testing but to me it seems like the arch doesnt drop off near as much as when I used to just reload the fire wood and bury all the coals.

[Robert K]

Jeff, thats a good point because even with the coals burned down there still would be plenty of heat left. Especially with air being introduced AOF. Can anyone tell me if there is a height I should be aiming for in the firebox? distance from top of rail to floor. I am now re-measuring the firebox out to 6' in order to gain the extra area needed for gasification.
Thanks
Robert

[Flat Lander Sugaring]

Jeff, thats a good point because even with the coals burned down there still would be plenty of heat left. Especially with air being introduced AOF. Can anyone tell me if there is a height I should be aiming for in the firebox? distance from top of rail to floor. I am now re-measuring the firebox out to 6' in order to gain the extra area needed for gasification.
Thanks
Robert
i wont say whoes arch I measured but they had around 18" on a 2x6.

[murferd]

When you are saying that you put the coals behind grates, does that mean you are pushing them toward the slope or up on the slope?

[nymapleguy607]

My arch is about 24" from the top of the grates to the top rails. The overall arch height is about 30" The lower space is used to run the duct for the air through the door, and also serves as an ash pit.