Simple air injection

[Brent]

Here is a shot of the simple air injection system I've put on my 2 x 6 evap. The tubes are heavy wall stainless that run through the back ramp, under the insulation and out the very back after passing through the chamber at the base of the stack. Last year I had two mild steel tube running 90 degrees from the current set up. Those tubes corroded badly in the firebox but they did offer some improvement in the fire, even with the mickey mouse little blowers I had. This year I'll have a Nederman high pressure blower and the tubes will be much longer the the cross tubes of last year.

I'm starting off with pretty small holes for the air injection and will try drilling them out larger a bit at at time.
The game plan is to inject just enough volume that I don't get back draft when I'm firing and hopefully the pressurized injection will have enough velocity to get the oxygen where it's needed. ( where ever that is )
I can rotate the tubes for drilling and to try different angles for the air blast. Tomorrow we light the fire to see how it goes.

[danno]

Brent - looks good. Are you following Dave's thread on air above the fire?

That mild steel does not hold up does it - last season I had 4 lengths running the same direction as your two - drilled with 1/8" holes every inch. They warped after the first fire and were trashed by the 3rd. The manifold that the pipe was screwed into lasted and I continue to use that to add air above the fire.

Good luck and let us know how you do. Fun drilling SS?

[KenWP]

I fixed up a blower with a old fan I had here and set it so it sends air just under the fire and it works but man does it eat wood. I have to work on it a bit more for next year.

[Brent]

Yeh Danno Fun Fun (new bit ) Fun.

Danno the tubes I got last year were gas manifold tubes from a fireplace dealer. If I'd cleaned them up at the end of last year they would have lasted this year at least - no warping, just surface corrosion.

So last night I did the first boil with this new air injector. I kept a log of when I added wood and stack temps. Worked out to a firing every 14 minutes ... a couple times I could have done it a bit sooner. Stack temps were 800 on the low side when I was late adding wood, up to 1000 - 1025.
(who knows how accurate these cheap thermometers are. bet if you put two in the stack side by side they'd never agree.) Anyway it averaged about 900 - 950. I had a good boil nearly to the back of the flue pan. Going to drill out a few holes a bit bigger in diameter before tomorrow's boil. Pleased so far :D

[johnallin]

Brent,

Nice picture and seems to be a pretty straight forward approach. Am I correct that you are running the tubes all the way back through the ramp to the stack area before exiting the arch and is that to pre-heat your injection air?

What rate were you firing before and does it looks like it cut down on your wood consumption.

Lots of questions here, as this is my first year with the 2x6 raised flue leader and it seems to be eating wood like crazy. Been following Dave Kish's posts and would like to explore for next season.

[Brent]

John
Last year I had a half-assed version of this with a couple of short tubes running cross ways and a tiny squirrel cage blower on each tube - not even sealed well. I was not taking notes but it seemed like 8 - 10 minutes. The year before I was blowing under grate and that was eating wood.
So this is a big step in the right direction. I think with a few more / larger holes, it will get even better.

The rig is a raised flue. You can tell by the archboard insulation across the back. (measuring tape on top ) So the tubes are burried in the vermiculite under the arch board, but somewhat exposed to heat as they pass through the stack area. If I get organized enough, which I doubt will be this year, I'll cut the tubes where they exit the back and aim them straight up and extend the tubes to be very close to the stack for heating. The blower would then be in the rafters taking in the hottest air. Not much moisture in the shack because both pans have hoods.

I actually got two of these blowers at a farm auction and I'm thinking of putting the disharge from one to the intake of another and that shoud give me almost double the pressure. The real deal would be a Gast regenerative blower. Dream on.

[johnallin]

Brent,

Couldn't you run a small pancake air compressor for the high pressure air into a reserve tank and have it manifold up into the stack and then back down into the fire box. Lines would not have to be any larger than the orfice you are drilling out now, would be pretty easy to run and could be controlled with simple valves.

Not knowing how much air is needed for secondary combustion, this method could get air in there with lots of cfms and pressure, and you would have preheated air to boot.

The pumps being referred to are not much less expensive that a decent compressor and plumbed in right, the compressor could be placed just about anywhere for the sake of peace and quiet.

Any thoughts?

[Brent]

John
I read somewhere that the new Force 5 Hurricane arches us 3 PSI. The blower I've got doesn't make quite that much pressure but it's much stronger than a squirrel cage blower.

I'm not sure what you mean by pancake compressor but most anything that I would call a compressor wouldn't delivery enough volume unless you got a real big one, like 5 Hp. I've got a 2 Hp single stage piston compressor and while it will make 120 PSI, at wide open it doesn't have enough volume. If you let the pressure build, of course you get a big blast when you open the valve, but in 45 seconds or slow the tank loses pressure and the blast becomes a fart.

I'm just going to drill the holes out a bit bigger.
If it doesn't get any better than this I'm still happy firing every 14 minutes or so. It will be nearly half the wood I used 2 seasons ago and still a lot less than last year.

[johnallin]

Brent,
Do you know how many CFM you are putting in the arch? That's the important number here.

I still think you could size a compressor to work even if it sent little jets of air at high velocity - turbulance?- on a rotating or timed basis so as not to empty out the tank but steady enough to bathe the flame with an additional constant source of air. If the total of all orfices is kept to less than the ID of the air line from the compressor, it should be able to keep up. I don't think a small "pancake" unit would do it but something larger that can run orbital sanders and similar high demand air tools should work.
It all comes down to how much you're putting in there though, for now that is the magic number.

[sapsick]

her is a little air compressor info for you guys. every 1hp is 4cfm. a 1/4" orifice at 100psi can flow 100 cfm (25hp)

[Brent]

The cfm doesn't mean anything with this kind of air flow. That was all the rage with under grate blowers that boosted temps and wasted huge amount of wood. The blower can put out a huge amount with a 3/4 hp motor. I'm sure you could do it with a compressor. More complicated and if the guys making the 4' x 14' Hurricane Force 5 use a blower rather than a compressor, I'm going more or less the same route.

To wit, here's what happened today.

I opened up every other hole to about 1/8" and did not take off the flue pan so I did not do the ones over the ramp.
I would have to go count to be accurate but there were maybe 8 new holes on each side and 8 old ones about 1/16".

So I started preheating with the propane flame thrower to warm the pans to reduce soot build up at 3:15 and at 3:30 had the fire going. Did that yesterday and the build up was less than normal for sure.

So I boiled until 9:00 and fired 14 times. That's and average of about 23 minutes between firings. I was pulling wood off a skid. Pretty well seasoned, mostly maple. The peices were 2' long and would average 2 1/2 to 3" in cross section. The pile was about 4' high and about 4' across. When I was done there were still 8 or 10 peices on the skid. Last year I would have easily used double that. Two years ago with the blower under the grate I would have used 4 or 5 times that much.

I should add that only once did the stack temp get down to about 825. Most of the time I fired when it got near 900. Most of the time it was between 975 and 1050 with peaks at about 1125. (I wish I had a digital stack thermometer )

All the time the bottom draft door for ash cleanout was open about 1 1/2". Nothing on the front doors were sealed. I never had to turn the blower off to fire it, and this is the proof that the CFM is nearly meaningless. No blowback.

I chuckled to myself when I was out there, thinking of the joke about the dummy on the plane flying trans-atlantic. The plane loses an engine and the captain announces that there was no problem, but the flight would take an extra hour. Later the 2nd and 3rd engines fail and the flight time gets extended more and more. The dummy says to his buddy, if that last engine goes we'll be up here forever.

So I'm thinking, Ha, if I drill enough bigger holes I won't use any wood at all.

At the end of the day I did notice one thing. There were more coals on the ramp and virtually nothing on grates. I did not clean out the ash after my first 5 hour boil and I don't think it will need a clean out tomorrow. Ennismaple said the Force 5 does not have an ash door, or a grate for that matter, at the front. There is an ash cleanout under the stack at the back. Now I'm begining to see why.

Man I think I've got enough wood for next year :D

[RileySugarbush]

Brent,

Do you have an estimate of your flow rate above and below the fire? I have a 200CFM squirrel cage below which was wonderful for evap rates but does use up a lot of wood. I have some over fire air but with higher pressure and lower volume blowers. It looks like I should switch them?

[Brent]

John at Rileys

I have no idea what the cfm is that is getting to the fire. Someone mathematical could figure it out.
About 16 holes at 1/8" and about 16 holes at 1/16" at about 0.8 PSI. Yes the blower doesn't quite make 1 PSI. The actual volume of air is miniscule. last year I tried a couple of tiny squirrel cage blowers, one on each of 2 pipes with 1/4" holes. Those little blowers did increase the efficiency but not like this rig with higher pressure blower. The fire really rumbles deep like a distant thunderstorm.
The squirrel cage you have will certainly help if you get the air above the fire blowing down into it.

The technology is actually like the modern, efficient airtight wood stoves. A small amount of air allowed in over the fire in a way that causes a bit of turbulence so that all the wood gasses are given oxygen and burn with less than about 8 - 10 % going up the stack unburned.

[Brent]

Here's a picture of the blower I'm using. Picture is from the factory web site at www.nederman.ca

[RileySugarbush]

So do you have any air coming up through the grate or all above?

[Brent]

The ash cleanout door was open at the first notch, which is about 1 1/2" gap at the bottom. I had placed a steel plate about 1 foot long over the center grate set to restrict the air going up the middle to try to get better heat distribution. Not so sure about how that worked.

I should mention that even without the larger holes in the ramp area, the boil in the flue pan was better than I've seen on this evap yet.

[Daryl]

We have a 18 x 63 D&G sportsman. I have 1 1/2 square tubing with 3/8 pipe on 2 inch centers under the rails on both sides. The pipes angle down about 10 deg. All is 304 SS. Both go down at 90 deg.out the bottom to a double ended blower like used on a pellet stove, I think, which I got thru E-Bay. I run with the draft door fully open and only close it when fireing. I don't know the stack temp but it has not changed the galvenize on the stack.
We get a great boil to the end of the drop flues. We fire about 8 - 10 min . with several small wrist pcs. of slabs . It's like a blow torch in less than 1 min. We tried a blower under the grates but the only thing that did was burn more wood. We do see a limited amount of sparks out the stack and no smoke.
We made over 11 gal so far with about 2 pallets 4 x4 x 3 1/2 foot each.
The rig has been over 20 gallon plus per hour all season. The temp of sap out of the preheater is 190 to 195 + .

[DanE.]

Daryl, how far from the bottom of the pan are the pipes? Do you have drop flue pans and are you also running it under it also? Dane.

[RileySugarbush]

This is pretty interesting. I've been doing the overkill 200CFM through the grates and getting 1200F internal stack temps and great 45gph evap rates. I have some limited flow over fire injection with higher pressure GAST blowers off an old fingerprint machine, but never ran them with the under fire air throttled back. Tomorrow I will.

Brent, what evap rate are you getting?

[Daryl]

The square tubing is screwed to the angle rail. It has 1" ceramic blanket between tube and side sheet metal. The tube turns down at a 90 deg just before the drop flues. The split brick are front and rear of the down part. It doesn't go under the flue pan.
Daryl

[Brent]

I've never got an accurate read on our GPH. I have an overhead feed tank that I operate with a pump on a plug. I can't go more than a couple hours without forgetting to unplug it, and then experience a cold sticky shower. About one every boil I'm getting coffee of something when it starts to overflow. My gut feeling is that its about 45 GPH.

The 5 1/2 hour run yesterday gave me 7 gallons, from a cold start with empty pans. First draw after sweeting was about 2 hours in.

I just found a table on the Gast web site under techincal information that gives air flow through and orifice .,. not valid for the day after pork and beans.

Anyway, if I'm reading it right the 1/16 holes at 1 psi pass 0.29 cfm. If I have 32 holes its a stunning 9.28 cfm. And I know this blower does not quite get to 1 PSI.

The cfm doesn't mean much. Turbulent fresh air into the fire where it's starved for oxygen is the key.

[Haynes Forest Products]

Surpluscenter.com I think page 184 has some nice blowers for cheap.

[roybar maple]

could we get pictures of the tubes or a drawing of how everything is? i so want to try this!!!

[johnallin]

The cfm doesn't mean much. Turbulent fresh air into the fire where it's starved for oxygen is the key.

Brent,

So if the CFM is not critical, maybe the compressor idea will work since your not bleeding the tank in one big blast. Seems that it could run all day with such a small demand in makeup air as 1/8" holes are not big.

Now someone needs to come up with a steam powered air compressor and all is good in the world.

You really started something here...it's cool to see someone take an idea from drawing board to nuts and bolts. Good on ya'.

[Brent]

Today I did not have time to drill the extro holes. Lit the fire at 1:45 and did a real firing load at 2:00. Quit at 6:40.
Fired 11 times with an average of 6 or 7 chunky peices each time.

25 minutes between firings. I tried removing the 4" x 14" plate that I had laid on the grate yesterday and it seemed like the boil shifted back a bit. Needed more fire under the draw off partition above the doors.

Looks like I had about 175 gallons of 8.7% concentrate when I started. Had a bit of semi-syrup to put in the syrup pan but the flue pan was a cold start. Finished it all off so that looks like 38 - 39 gallons per hour, including sweetening the flue pan. The start up tomorrow will be with a full sweetened system, might get a better handle on it but I still think an established flow on this rig is about 45 GPH.

Had a great run here today. Because I was boiling I could not get to the bush until 7:00PM One tote overflowing. Total of about 725 gallons to finish hauling in tomorrow. The 100 bucket begrudginly gave up about 10 gallons.

[Brent]

Another day of boiling with this system. Still didn't enlarge the holes as planned. Had visitors show up so I had to fire it up to do the dog and pony thing.

The results continued pretty much as before. I went 30 minutes once without firing and the stack temp dropped to 750. That's definitely too long between firings.

Got 350 gallons of concentrate in the tanks so it will be a long long boil tomorrow. Going to cut the amount of wood I add in half and fire whenever the temp hits about 975 and see if that gives a more consistent rapid boil. That will be harder to asses but I think throwing in 6-7 peices of cold wood on a low fire is the wrong way to do it. Going to add a smaller amount to an already ripping fire and I think it will be better overall.

[RileySugarbush]

I tried copying your set up, cutting down my through grate air by blocking the blower inlet and injecting air above the fire. It really cut down the boil. Since we have more wood than time, I went back to my old ways.

Maybe I'll fool around with it again tonight

With the new probe type stack thermometer, we were getting Brandon like temps in the stack. I used to think he was nuts running 1300 to 1400° or higher stack temps, but it looks like I was too, but couldn't tell because the old magnetic stack thermometer reads so low. Brent, are your stack temps measured on the stack surface surface or internal?

[Brent]

My stact temps are internal, with the probe about 3 feet up the stack. I'm looking for a more accurate instrument, hopefully with a digital display.

I don't beleive the numbers on it are accurate within 100 degrees though. I do know that if I let it drop to 750 or so, no syrup comes off. I do like the boil I'm getting almost the full length of the flues. I need to get more heat under the last partition in syrup pan. I tend to put the wood in too far. Could just be operator error.

Going to have lots of time to practice today. 350 gallons of concentrate to work through.

[Brent]

I finally got into the arch to drill out the holes at the top of the slope. At the back there where the gasses are most starve of oxygen, it looks like there is a blow torch coming out of each hole. The noise is louder. The swirl more pronounced. And if what I heard about the force 5 burning with blue hot flames, I guess I'm getting close because you can see licks of them now.

Still planning to make a few more bigger holes.

[maple flats]

With mine I have both under and over air on the same blower with 3" ball valves to regulate each. I am still playing with the settings to decide what works best. I still have my wood split about wrist size on most with only an occassional bigger one. My bottom air is just a 4" 30 ga stove pipe run down the middle from the rear to within 8" of the front. I have 3 rows of 5/16 (or might have been 3/8") holes along the top. The valve has never been open more that about 3/4 and most of the time it is open about 40%. My over fire air in made of mild square tube, 2"ID, with a 1/4" black pipe nipple every 6" around the entire firebox, angled down 10 degrees. The valve for this is usually open 50-60%. I put refractory to protect the tube but the nozzles were not cut back to the refractory surface because it had not set hard enough to trust any vibration so T thought they would erode back. The fire gets extremely hotbut I see no erosion signs yet. I have never burned the fire without the high pressure blower running since adding this. I think maybe the air thru the nozzles is keeping them cool enough to protect them. I do not pre heat my air, the nozzles are blowing outside air with little if any warming before it exits the nozzles. Originally I tried 20 min fueling but went to 15 for a few hours. Now I am at 12 minutes and it seems to work best. I used to add every 5 by the timer, now 12. My wood savings is about 30-35% and my boil gained about 10%. I still think I can tweak it just by trial and error to find the best air settings. I have no air entering thru the draft door, it is blocked off completely, and I get no smoke nor sparks nor ashes out the front once it gets burning good but I do get a little smoke during the initial 2-3 minutes occasionally. After that warm up I get none out the door. I do not slow the fan nor stop the air, I just open the door, add wood and close it. Even if I throw in a piece or 2 that is wet nothing comes out the door. As far as CFM, I have no idea, but it is high pressure air, not hi volume. The original motor was 1750 rpm but I am driving it with a 6" pulley one the motor and a 3" on the blower shaft with a 1725 motor. A tac said i am getting 3400 but that was before the bearings and belt were loosened. I might be getting maybe 3425 now. I have not yet put a guage on to test the pressure but it is working good. After the season I will test the pressure. I'm thinking it is only like 2-4 lbs but that is purely a guess. I'll post the results when I test it.

[Brent]

Dave: the effort you put into your rig makes me think I should have titled this thread "lazy man's air injection"

You're pretty much on the same track as me. I only have a little natural draft up through the grate. From what I see in the firebox I can see the hot spots and turbulence from each drill hole. My holes are on 2" centers and I think if I was doing it over I might go 1 1/2". I think 6" is too far apart. If you're between 2 and 4 psi you should be in great shape with the blower.


Yestday and today I went through a stack of wood 9' x 5' in 2' lengths. 90 cu ft; or 70% of a cord. 16 hours of boiling. I wish I had kept notes in detail like this last year but I FEEL that it's half of what I would have used last years. This made 31 gallons of syrup from about 6 - 7% concentrate.

I'm going to keep playing. To bad the season is ending in two days ... with a hot thud.

[Brent]

Drilled a couple of bigger holes ( all the small drills are dull from drilling stainless ) 5/32" big just 2" in from the doors, one each side.
The original holes was maybe 1/16 and was plugged on one side and barely open on the other. It "seems like this made yet another improvement. A load of hard maple will now go 20 minutes with the stack temp staying above 1000 deg.

It continues to amaze me how little air is needed. I can shut the ash clearout / draft door and there is almost no change in the burn.

[Brent]

PS to the 2 new holes near the door. My draws are smaller and more frequent now. I guess there is more burning under the front partition. I was somewhat afraid injecting air might have the opposite effect.

[Brent]

Wow, been boiling now for 6 hours or so with those two little new holes. The draw offs are 1/2 the size of yesterday and coming more frequently. I like this.

[johnallin]

Wow, been boiling now for 6 hours or so with those two little new holes. The draw offs are 1/2 the size of yesterday and coming more frequently. I like this.
Hey Brent..you got wi-fi in the shack or are you posting us from your maple berry?

[Brent]

The Maple Berry is sitting here beside me but the laptop is on a local wireless back to the house, which is only 125 feet away.

I'm a bit surprised that its working because the laptop on the bottle tray of the canner so the stainless double wall canner is directly between me and the house

Gotta love it

[Brent]

A couple of surprises along the way here.

With the air injection the fire seems to burn hot enough right down to coals .. and still give stack temps of about 950. Then it really collapses in a hurry.

Also the draw offs were more regular and smaller. Now making syrup only in the last partition. Before these changes when the temp alarm went off, the temp kept going up while I drew the first quart or two, then as I drew the next 2 quarts, it started down. I think the second of the 4 chambers was hotter than the first. Now I get a quart, maybe a bit more, and the temps start down.

Edit

I can now almost time the firing by the sound. When the wood is burnt down enough that the stack temp drops to 1000, the rumbling blow torch sound drops off. No more wood gas re-igniting. You can see it with the doors open to. While the fuel is fresh there's a whole series of red/blue flames jetting down from the tubes.

I boiled 12 hours yesterday, into the wee small hours, and used 1/3 of the wood that I would have needed 2 years ago.

[gar]

I've been in HVAC for years and I question the need for High presure (spelling) air? I am under the impression that it is the amount of oxegen not the turbulance that makes the difference. Has anyone tried larger air nozzles compared to high pressure? Only resion I'm asking is i'm building a new arch and was planning on using an old oil burner with large nozzles (1/2") for over the fire air!

[Brent]

Gar

Most of ideas for this set up came from papers that I found last year. One was, if I recall correctly, by the Michigan Forestry Dept and the other by the University of Vermont Maple Research Extension (Proctor)

One this forum you will find hundreds of discussions about adding high volume lower pressure squirrel cage blowers, like traditional furnace blowers. The common way to do this was to add a duct that blasted air in under the grate, up through the fire and of coarse. (****, first mosquito bite of the year, right now while I'm typing) Anyway this raised stack temperatures big league and increased the boil rates and no doubt the risk of burning you pans. I was one of them. I put a blower in my Leader Half Pint. It boiled a bit faster and went through at least double the amount of wood. There's more to that story posted elsewhere. The announcement/ developement of the Force 5 Hurricane evaporator caught my attention too. It had piping embedded in the fire brick that was fed by a 3 Hp blower that generated about 3 PSI. They were big rigs that were at least double the width of mine. So I sort of scaled it down. Mine is only 2 feet wide. On my part not much original research, just a bit of improvised implimentation.

Instead of a high volume air under the grill rig that blows heat out of the stack at the cost of double the wood, I've got a small air volume system that seems to have cut my wood use in half and maintained the pan and stack temps that the rig was designed for.

[Brent]

Gar a further thought

Modern gas furnaces have tiny, by old standards, 4" shedule 40 pipe for exhausts. You don't want or need a big stack to make an efficient furnace.

[saphead]

From what I've read, shoot for 20% under fire air and 80% overfire air.The paper I read from Proctor didn't specify the evap. size but called for 3/8" nozzles
6" on center and 10 degree down angle.I'm sure air pressure and volume will be dependent on rig width and length.I've also noticed that the fire box is huge and the bricks in a Force Five don't direct the gasses up into a raised flue pan like the old style of arches. I know of one being installed somewhat nearby in a couple of weeks I'm looking forward to checking it out! Turbulence of the gasses is the key so that they all get burned before they enter the stack.

[KenWP]

I tried the under air thing and the wood kept disappearing in the fire. I need to design a way to get the air into the firebox instead and not so much as I just want hot not to see how much wood I can burn. One thing was the back flue pan boiled harder with the air but I had to throw logs in the fire to keep wood in it.

[lpakiz]

gar,
Last year I had over-fire air via a pipe with about 20 5/16 holes drilled into it to blow towards the fire. This did make it burn harder than no air. This year I made a new pipe with 6 3/8 diameter by 3 inch long nozzles on an identical pipe. HUGE DIFFERENCE!! You can see a plume of flame coming out of most of the nozzles when fresh wood is added. I also agree with the assessment of 20% under the grates and 80% over. I didn't have any air under the grate until a few days ago, when I replaced the small over fire fan with one off a power vent water heater exhaust. (Lotsa air and more pressure) The smaller fan went under the grates. Now I can control how much "coaling" I have in the forebox. More under grate= less coals.
The water heater fan is about 1inch wide by 6 inches diameter, versus the small one, which is about 2 inches wide and 3 inches diameter.
Just what I have found...

[gar]

I think you guys answered my question. It sounded like some of these guys were buying special blowers for HIGH pressure, and from my experience I didn't think it was needed, just more air. My operative word has been "balance". I plan on 4'' manifold, both sides of arch with 1/2'' nozzles that I can reduce in size easily with an oil burner for a blower. Also under the fire air run by anougther oil burner. The only reason I'm using oil burners is that I can get them for nothing, but had second thoughts after reading about this high "pressure". Guess I'll stick with my plan. Thanks.

[Brent]

Gar
From my experience you don't need a blower under the grate at all.

The pros, Force 5, use a high pressure blower at 3" WC
But they also inject some air under the fire, but not through a grate.

If you are striving for hot, blow lots of air of any kind

If you are striving for efficiency, you want the least amount of air the will burn everything.

The more you blow in the more goes up the stack. Whatever you do it will be fun and challenging to make it work the way you want. It added another dimension for me this year.

[Northern Ont. Maple]

I used air over fire this year and it made a big difference . I used about 20 face cords this year have not cleaned the ashbox yet. I used a large squirrel cage blower with 2hp motor the fan rpm at 1000 and a separate fan on the door with two 1'' nozzles directed into the fire.
The fire box temps were as high as 1600F and stack temps max of 600F.My home made arch has a large fire box 6.5X4 so I fill her up with all hard wood and get between 50 minutes to one hour on a fill up. I use protective clothing when filling because temps are still around 800F.
The air over manifolds are 2X4X3/16 square tube with around 100, 3/8'' nozzles. My grates are powered too, but are controlled by a gate valve, by shutting down the air in the grates I get more ash so I try to keep some air on them. I will try to post some pictures.

Norm

Photos (http://s172.photobucket.com/albums/w26/thegrogster/Syrup%20Stuff/)

[Brent]

That's pretty impressive Norm. How big is the rig, Looks like about 4 x 12

[Northern Ont. Maple]

It's 6.5 X 12.

I'll try and get some more pictures of the whole rig when I take it apart to clean and fix it to show a new flue design for exhaust gases.

[Brent]

As a general comment I think we are just at the beginning of developing more efficient wood fires evaporators. There has been tremendous progress in wood stoves for heating houses. We've got lots of catch up.

[WESTVIRGINIAMAPLER]

Are you guys dampering the air over the fire when you have to fire the evaporator or just letting it run the same amount of air all the time?? Also, I assume you have some kind of gate valve to adjust the amount of air flow if you are not dampering it??

[Brent]

I turn on my blower about 15 minutes after the fire is established. If you're concerned about a damper valve to control flow when you open the doors for firing, you're still thinking about the massive blowers under the grates.

I got no hint of backwash of flames when I fired. There certainly will be a point with lot of air, over or under the fire, when a damper will be needed. At that time you'll also need a pretty airtight door. The small jets that I got seemed to be pretty effective with a very small of air.

But we've got a lot to learn. Every time I added more and larger holes I liked it more, so next year ..........

[wanting to get into it]

I am just curious. I am going to add this to my rig this summer and was thinking. Would copper tubing work for the air over fire manifold? It has good corrosion resistance and its melting point is high enough I believe. I thought it was in the neighborhood of 2100 degrees. I may be wrong though. Now, if it would work, surely you would want to drill and tap the holes for the nozzles. I don't know, just curious. After reading your posts Brent I definitely want to hear the rumble and cut down on wood consumption. How are the boiling rates though? I read where your draws were more consistent and I may have missed that info. Didn't know if you noticed better boiling rates or not.

[Northern Ont. Maple]

On my evaporator I have to shut the air completely off before reloading it's just too hot. I do use a gate damper for grates only because the air header feeds both the grates and the air over fire nozzles. You can get a cheap high pressure blowers with 2hp motor for under $200 from Harbor Freight in the US. It's used on their woodworking equipment as a dust collector. I also added more photos of my evap construction. Norm

[KenWP]

I am just curious. I am going to add this to my rig this summer and was thinking. Would copper tubing work for the air over fire manifold? It has good corrosion resistance and its melting point is high enough I believe. I thought it was in the neighborhood of 2100 degrees. I may be wrong though. Now, if it would work, surely you would want to drill and tap the holes for the nozzles. I don't know, just curious. After reading your posts Brent I definitely want to hear the rumble and cut down on wood consumption. How are the boiling rates though? I read where your draws were more consistent and I may have missed that info. Didn't know if you noticed better boiling rates or not.

If you used copper anything it would be gone in the first hour of operation. The fire gets hot enough to melt the copper down inside the arch. Even heavy steel gets red hot in a short time. Copper melts at 1981 degrees F

[wanting to get into it]

I wasn't quite sure about the copper. But, thanks for answering my question though. :)

[Brent]

I did not get any increase in evaporation rates. If you want that you want a hotter fire and you'll get that by blowing more air in up through the grates, and increase the wood consumption.

Every time I added or enlarged holes, it seemed that I was getting more efficiency ... less wood, and my stack temperatures did not change much. I'm uncertain what I'll do next year. I need to put more GPH through and I may add some air under the grate to increase the burn, or just get a bigger evaporator.

Copper will be an expensive disaster. The stainless heavy wall tubes stood up to the heat very well. No warping at all.

[Brent]

Northern Ont Maple

The one serious arch you've made. I can see why you want more heat on that one. You've got a huge surface area on you pans compared to the size of the firebox with that enormous flare. I think some air under the grate will help that.

I don't understand what you're doing with the big partition down the middle under the syrup pan, and what looks like a wall half way across between the firebox and the back of the arch.

[Northern Ont. Maple]

Brent I put a 1/4'' steel plate at the back of the firebox to contain the heat longer under the syrup pan. The flue gas will travel up the right side heating the coldest sap above it in the flue pan. The photo does not show the completed arch. There is another wall parallel to the first one giving three flue runs 18''X8' each .That is why my stack temps don't get over 600F. There is a sliding stack damper but it's always run wide open. Hope this helps. Norm

[Brent]

wow that's certainly different, ( don't react like my wife when I not she's changed her hair ). The low stack temp certainly means you're sucking a lot of heat out before it goes up the stack. I think I would have done it the other way around, that is introduce the coldest sap over the last point before the gasses go up the stack, and have the best boil over the area where the hottest gasses leave the firebox and just before they transfer to the syrup pan.

The coldest sap will absorb more heat from lower temperature gasses.

My one minute analysis. I'm sure you poured hours and hours of thought into before you lit your torch.

[Northern Ont. Maple]

Brent I have 100' 3/4'' copper series preheater in the hood and when this rig is rolling [ takes about 1 hr ] the sap entering the flue pan is 205F average with a high of 209F. I have a damper in the steam hood stack to keep as much heat as possible without leaking steam into the room, for awhile I would put a felt blanket over the hood as well . I hate to see all that energy going up the stack. Norm

[Brent]

We should share a beer one day. I got some of the mylar silvered bubble wrap and covered my hood/preheater and even wrapped my float boxes in it. Don't know how much good it did, but it felt good.

[danno]

[ I have a damper in the steam hood stack to keep as much heat as possible without leaking steam into the room,

I was considering this, but was concerned that a damper in the steam stack would prevent steam from escaping up the stack, thus reducing evap. rate. What's your thoughts on this?

I also considered lengthening the steam stack with the idea of increasing the steam draw using the same theory as the smoke stack - but figured as the steam cooled higher in the stack, it would condensate back into the flue pan.

[Brent]

It would take one really good fitting damper to impede the flow of steam to the point that it effected the evaporation rate. Steam would come out through your inspection doors and many other places. It would take a lot of pressure before the atmosphere inside the evaporator raised enough to raise the boiling point. If you calculate the area of you hood and the weight you could see how little in PSI it would take to actually lift the whole hood off the rig.

I think what will help us is reducing heat loss from anywhere that is not steam. I have often wondered why the sides of pans are not double walled with fibreglass inside.

[Northern Ont. Maple]

Danno Every hood should have a condensate tray and internal gutters and drain to remove all condensated steam. Without these you will be continually boil the condensate falling back in your flue pan. The damper 8'' disc in a 9'' stack just restricts steam . I can raise the temp of the sap from 50F to 205F in around 30 seconds and I get all the wash water I can use. If you have a hood without these features then insulating the stack and hood would be needed to prevent condensation from happeninginside the hood. You will never make your hood and flue pan a pressure vessel because of your inlet float box is open to atmosphere. Just my thoughts. . Brent I'm always open for a beer or two and talking maple.

[maplemark]

this is very interesting. I was planning just a blower stuck in the back , but this makes much more sense . I have a few ?'s . I guess you cut 2 holes in the back of the arch? do you have some way to join the 2 pipes so you use 1 blower? Are the pipes capped at the front of the arch ? I wish I could see a drawing of the whole set- up , I'm a visual type

Mark

[Brent]

I think your questions are directed to me so here goes.

I used a single blower with 1 1/2" hose, ran that to a T and looped each side of the T to the pipes. I drilled a pair of 1 1/2" holes in the very back of the arch and run the pipes all the way to the front door. Under the flue pan they were burried in the vermiculite inuslation. They were capped on the end. Next year I will play with it a bit more, continuing to drill out the holes a bit larger at a time. As you can see from other folks that put in 3/8" holes, they have needed to put ball vavles or other gateways to restrict the air flow, so it seems pretty clear that 3/8" holes are too big.

At first I had the blower inside but the noise was enough to get me to move the blower outside. I had intended to put it in the rafters where it would get the hottest air.

[maplemark]

thanks Brent , that gives me good idea of how to proceed . got to find the pipe - blower - fittings - but what else is new in sugaring, always tinkering with something. If it's at all possible could you post some more photos of the set up.

[WESTVIRGINIAMAPLER]

Brent,

Do you have air injection all the way back under the flue pan too??

[Brent]

Nope. The pipes emerge through the firebricks near the top of the ramp which is about 1 foot back under the flue pan.

I have been toying with the idea that there might be some gas combustion further back than that but I havn't heard of anyone else doing that.