air over

[twitch]

Were is the best place to put the air nozzles when doing air over back front side? open to all opinions.

[Brent]

I don't know of anyone that has tried different positions. Almost everyone welds up some channel with the nozzels pointing somewhat down, bricks them in an says it works great. A (not) scientific study of ONE. If the guys building the Hurricane and Intenso-fire tried multiple positions, they aren't telling.

My solution to not knowing was to put in round stainless tubes that could be turned up or down and the holes could be drilled out larger or filled with a sheet metal screw. Not having instrumentation in the fire box I can only say that I "thought" the burn seemed best when they blew down at about a 30 deg angle from a point on each side about 2" below the pans. As the season went on I kept drilling the holes bigger and I liked what I saw and heard ( the roar got louder ) every time I drilled them bigger. I never did hit a point where I thought I had gone too far. I was using blower that delivered
just under 10". This year I'm going the same way on our new evaporator with a blower that will hit about 50" (inches not psi) It's a GAST regenerative blower. I have also got 2 digital high accuracy pyrometers, one for the arch and one for the stack, so I can get accurate numbers. If I could find a way to measure O2 in the stack I think I'd really learn how to tune
the burn.

I think the idea is to inject fresh O2 into the flame where it begins to get starved of O2. I also think watching the smoke coming out of the stack is
a good indicator. Seeing none is best. I think throwing in big loads of wood ( ice cold wood ) is counter productive. It really kills the fire for about 1-1/2 to 2 minutes. At the end of last season I was firing more frequently and only adding a layer at a time. The boil and stack temp and smoke emission seemed to be saying this was a better way to go.

Lot's of " I thought" and "seemed" impressions. But it makes sense to me.

Oh... and 2 years ago on the previous rig, I had now blower under the fire. And the air over the fire was low volume, relatively high pressure ( 2 or 3 times compared to a furnace type blower) and I never got blow back when I opened the door to fire. The natural draft was enough under the fire.
I used a lot less wood than the previous year.

[Flat Lander Sugaring]

here read all this
http://mapletrader.com/community/showthread.php?9364-Air-over-fire

[twitch]

Thanks for all the info but what size hole did you end up with?



I don't know of anyone that has tried different positions. Almost everyone welds up some channel with the nozzels pointing somewhat down, bricks them in an says it works great. A (not) scientific study of ONE. If the guys building the Hurricane and Intenso-fire tried multiple positions, they aren't telling.

My solution to not knowing was to put in round stainless tubes that could be turned up or down and the holes could be drilled out larger or filled with a sheet metal screw. Not having instrumentation in the fire box I can only say that I "thought" the burn seemed best when they blew down at about a 30 deg angle from a point on each side about 2" below the pans. As the season went on I kept drilling the holes bigger and I liked what I saw and heard ( the roar got louder ) every time I drilled them bigger. I never did hit a point where I thought I had gone too far. I was using blower that delivered
just under 10". This year I'm going the same way on our new evaporator with a blower that will hit about 50" (inches not psi) It's a GAST regenerative blower. I have also got 2 digital high accuracy pyrometers, one for the arch and one for the stack, so I can get accurate numbers. If I could find a way to measure O2 in the stack I think I'd really learn how to tune
the burn.

I think the idea is to inject fresh O2 into the flame where it begins to get starved of O2. I also think watching the smoke coming out of the stack is
a good indicator. Seeing none is best. I think throwing in big loads of wood ( ice cold wood ) is counter productive. It really kills the fire for about 1-1/2 to 2 minutes. At the end of last season I was firing more frequently and only adding a layer at a time. The boil and stack temp and smoke emission seemed to be saying this was a better way to go.

Lot's of " I thought" and "seemed" impressions. But it makes sense to me.

Oh... and 2 years ago on the previous rig, I had now blower under the fire. And the air over the fire was low volume, relatively high pressure ( 2 or 3 times compared to a furnace type blower) and I never got blow back when I opened the door to fire. The natural draft was enough under the fire.
I used a lot less wood than the previous year.

[Brent]

Actually I ended up with a lot of different sizes:D. Not because I wanted them but because it was stainless.
Even going dead slow with the drill and using coolant I could only get about 5 to 8 holes per drill bit. Opening up an existing hole made the death rate even worse. So I had a hold about every 4" and about 1/16" in diameter. I ended up using my letter and number drills all around that size. The holes were from right beside the front door to under the first 8" of the flue pan, ie about 30 to 32" of the pipe. I think I had about 10 holes on each side. Sorry I can't be more exact. I sold that 2 x 6 rig in the summer of 2010. I'm just fixing to drill the pipe for the 2-1/2 x 8. I had intended to do it last year but did the hernia thing putting the overhead tank in the rafters. Bummer.

As far as the air pressure goes, I think I'll be breaking new ground. Some of the guys here used the blowers that got about 8"WC and several got the same results I did, you could fire with the blower on, and no sparks flying out the stack. With about 50" WC ( about 1 PSI ) and the same size holes it should make a big difference.

With the set up last year, a modified Leader Inferno, I could blow a stream of embers 10' high above the stack.
The boiling was violent and so was the wood consumbtion. I didn't run it that way except when I was playing around. I had to turn the blower way down before I opened the door or it would burn my eyebrows off.

I looking forward to some fun this year. Small jets of high pressure penetrating deep into the flame, minimum volume to get complete combustion under the front pan.

[Teuchtar]

Brent, I picked up a Gast R3 Regen blower with the intention to follow your path. That blower is capable of 30"WC at 25cfm. Gast has a helpful guideline on their website for sizing blowers for this type applicaton. Steps you through pressure drop, flowrate, and hole size. For air manifold, I will get some 2" stainless exhaust tubing. Given your experience with drilling holes, maybe I'll try grinding a series of narrow slots with the dremel. That would give a sort of fan shaped jet instead of a spike. I have a set of K-type thermocouples that I can monitor temps in the firebox and stack. My intention is to go 100% AOF since I have tons of draft under the fire and usually run with the draught door closed.
My previous attempt with a blower was to shoot air 100 % under the fire. My peaceful evening boil was disrupted by a fire in the sugarhouse rafters. So that experiment was stopped pretty quickly. Aint doing that again.

[Brent]

Teuchtar
Ain't doing that again ... yup that's one of the problems with sugarmaking. We really only get a short time to try our stuff, and we're generally alone when we do it. Sometimes it challenges your pucker power.

That 1/2 Hp R3 will be a huge power increase from what most systems run. The 2-1/2' x 8' Leader Inferno that was originally all air under was factory fitted with a 1/2 Hp with a Dayton 2C820 that generated 5" WC. So on your smaller rig you'll have about 4 x the pressure but at lower volume, which to me is the way to go. I'd put a valve or blast gate on an open ended branch from your blower so you can bleed off some of the air. Start off with the blast gate wide open and then gradually close it down. My guess is you'll be dumping about 1/2 the air when you get optimum efficiency ... lots of emphasis on "guess". But if you hit days when you can't keep up you love being able to let 'er rip and increase the boil rate at the expense of efficiency. I'd put up with a half dozen broken 1/8 drill bits just so I had the option of easily plugging or expanding some holes.
A couple years from now we'll all learn from the trials of guys like you an me and be able to start out with the correct combination of holes, diameter, pressure and Hp. Until then I like to stay as flexible as possible.

Edit

Last year with about 50/50 air over / air under on the modified Infero arch I don't think I went over about 50% on the variable speed ( except when I wanted to really scare myself with syrup jumping out of the pan ) so 1/2 hp on your R3 will be gangbusters. The blower I picked up off eBay is an R4. I think it's bigger than I need too.

PS I don't think the motors Gast uses are shaded pole motors, so they should not be run through a dimmer/ speed controller. That means the only way you have to reduce air is with a blast gate to bleed some of it off. You could use something as simple as a flexible duct with a big set of clamps on it.

[jasonl6]

i don't think the fanning option would work that great as the air would spread out before getting into the center of the fire. I used 2"x4" box steel tubing for mine and welded 3/8" diameter x 2" long nozzels that inject the air into the fire. On the end of the nozzles I welded 1/4" steel washers. When i ran my ceramic blanket i just cut small slits in the blanket and let the nozzles poke through. I had no issues with them burning off or damage in any way.

Jason

[RileySugarbush]

I'd be cautious of using ground slots. Even holes through pipes may not be the best nozzles. I believe the goal is to get the air distributed well above the combustion zone to extend and promote that combustion. I suggest a better jet is formed with a longer nozzle, that allows the high velocity to penetrate and mix deeper into the firebox. Maybe make a few sample and feel how the air disperses with different types of nozzles. I used 1/2 inch stainless hydraulic tubing ( a little under .40 ID). Each was about 1.5" long.

With my high pressure blower ( nowhere near 30" H2O though) I get about 100 CFM total AOF out of 16 nozzles with exit velocity of 80 MPH.

[Sugarmaker]

I built a AOF getting ideas from this site, and then bulling forward and doing some of it my way.
I think I got good results. Probably pictures on here somewhere.
I did stainless 1/4 I.D nozzles coming off 1.75 dia stainless tubing setting right on the top of the arch. I had my learning moments as Brent said. and had to do some quick on the fly adjustments. Made more syrup with less wood. ( although I did add a WRU and we had a good season too) less black smoke out the stack.
Regards,
Chris