Air over fire ?

[Sugarmaker]

Spoke with SPA blower mfg yesterday and the 2hp blower is on its way. Hope to get this hooked up this weekend and maybe do a AOF trial.
Chris

[whalems]

finally got the AOF finished.:) Now to find and hook-up the blower:( but the plan was to only plumb for AOF while I was rebuilding the arch. and wait untill next year to buy the blower. But now that its all plumbed I WANT A BLOWER!!! What to do, what to do:confused:

[Sugarmaker]

Mike,
Looks like your ready for the blower. If you can swing it this year you may be able to save some wood.
Nice fabrication work.
:( My AOF trial run has been delayed due to the blower not getting here till early next week. But it has shipped.
Getting a little anxious to boil some sap.
Chris

[WESTVIRGINIAMAPLER]

I had them put in after I received the arch.

When you poured the refractory grate did you use any stainless steel needles for reinforcement? Also, do you have any supports under the refractory grate?

I'm trying to figure out if I need to run a support underneath the floor or if it will be strong to span the 2' without it.

Not sure what stainless steel needles are?? My grate is 19" W x 25" L and it is only supported on each end. I have 5 pieces of 1/2" rebar running lengthwise in the grate. Per Rutland, the rebar wasn't necessary but it couldn't do anything but make it stronger. Mine is about 3" thick and I have 27 holes that are 3/8" in diameter at the top and aprox 1.25" to 1.5" on the underside as I used waffle ice cream cones to give the holes a cone design for better injection. Meant to take a picture of the underside before I dropped it in place, but forgot.

[WESTVIRGINIAMAPLER]

Mike,

Nice looking job on the arch restoration and the AOF design!!!

[Sugarmaker]

AOF blower came in today. I am going to switch the 1.5 hp blower to the AOF and put the 2 hp on the WRU. Hope to be working on this during the blizard:)
Chris

[Sugarmaker]

Moved the 1.5 hp blower to the AOF and I cant get it to operate:(, Electrician is coming over tomorrow. Told you we would be working on it during the blizzard! The 2 hp SPA blower is mounted for the WRU and is working fine.
This AOF seems to be fighting me.
Chris

[Brent]

Chris I think you said you do not use a rheostat, but if you moved the blowers and didn't move the rheostat with it,
that could be your problem. A capacitor start motor won't work with a rheostat.

[moeh1]

Brandon, what did Rutland say about rebar vs the cement expansion rate. When I read some of the earlier posts on the cement grate I had thought about rebar, then thought maybe not if it introduced strain. Myabe that is what the stainless needles are for? Never heard of them before.
Marty

[WESTVIRGINIAMAPLER]

Marty,

Was told by Rutland rep that it couldn't do anything but help. Don't know, but she seemed very knowledgeable on their products as I have used a few of them in the past and they seem to be top quality. Little more expensive, but worth the extra money. Hope it doesn't create any problems, wouldn't think it would.

[Sugarmaker]

Brent,
Interesting! The mfg (tech guy) said I could use a reostat, but I may try just putting in a regular on and off switch first. That may be the issue thanks!
Chris

[WESTVIRGINIAMAPLER]

Chris,

I think a steamaway in that size has a 1/3 hp motor, so that may be more air then you need.

[Sugarmaker]

After Gary R and I hung tubing today. Gary had a look at the AOF wiring.
Gary checked out a couple of things but had to leave before getting to the final fix. I was able to review the wiring and now have determined that a new power wire will solve the problem. I did get the dimmer switch working and checked the amount of air coming out of the AOF system. Seems like quite a bit of air to me but don't have anything to compare to. I think the dimmer may be of value to reduce the SPA blower speed, so as not to cool the pan? So I just need to run another line to the dimmer switch and should be good to go.

Chris

[wiam]

Maple flats, you said you used refractory to cover your manifold. I was wondering what product you used.


William

[Gary R]

Sorry for bailing on you Chris. I left with wires hanging out everywhere:o I'm still curious as to the cause of the problem. You have plenty of circuits left in the panel. That will fix it for good. I still would like to see it boil. Keep us updated.

[WESTVIRGINIAMAPLER]

Maple flats, you said you used refractory to cover your manifold. I was wondering what product you used.


William

William,

Here is what I used and I also used it to pour my castable refractory grate out of also. It is a little pricey, but extremely good stuff. Probably cheaper for you guys in NE vs having to get it shipped all the way down here to a local dealer. I think four 25 lb buckets were $ 180. Could have gotten it a little cheaper off of ebay, but Rutland products are such high quality, I wanted to only have to do this one time.

http://www.rutland.com/productinfo/castable-refractory-cement.html

[WESTVIRGINIAMAPLER]

Here is a few pics of my AOF manifold after casting it over with the Rutland castable refractory cement.

http://s203.photobucket.com/albums/aa160/wvmapler/Air%20Injection/?action=view&current=IMG_3131.jpg#!oZZ6QQcurrentZZhttp%3A%2F%2F s203.photobucket.com%2Falbums%2Faa160%2Fwvmapler%2 FAir%2520Injection%2F%3Faction%3Dview%26current%3D IMG_3132.jpg

[Sugarmaker]

Gary,
I think the wires were loose on that two speed switch I tightened them up and buttoned it all back up. The 2 speed blower seems to run as good as it ever did.
Chris

[Sugarmaker]

I did get the new breaker and line run for the AOF blower. Running it through a dimmer as planned and I think that may work good for adjusting the air flow. All systems are go for a trial by fire:)
SM

[maple flats]

What kind of motor are you running on a dimmer? Many types will not work on a dimmer. Did you test it? I'm not an expert but I have heard you might need a shaded pole motor to use a dimmer. Somebody who knows better might chime in.

[Sugarmaker]

Dave,
I am not a electrician. So I really don't know the motor type.
I called the factory on this SPA blower and talked to there tech guy.
Told him what I wanted to do. Off the record he said they will run fine on the dimmer down to 18 volts. He has tried it. BUT he said that if I did hook it to a dimmer it would void the warranty! So of course I am not going to do that!:)
Chris

[Brent]

Chris, does your motor have a capacitor on it ? The capacitor will be enclosed in a metal cap like thing about 3" long, 1 1/4 across the base and normally have a rounded top about 1-1/4" high. About big enough to put a 3" peice of a hot dog inside.

If it is a capacitor start motor, you should be working on a
"Plan B" because there is a good chance the motor will crap out, especially if you run it slow. To be assured of a reasonable life exepctancy you need a "shaded pole" motor. They do not have capacitors. The most common place to see these is in ceiling fans. That is the kind of motor Leader and others use for air under the fire systems.
If the sap guys will take it back, ship it and order a proper high pressure radial blower with shaded pole motor from Grainger or McMaster Carr. After all that work you won't want to go without your air system 6 hours after the season starts.

[Maple1]

Brandon,
New to the site and sugar from CT. I'm trying to install air over this year with black pipe manafold. During your research is it nessary to enclose the manifold? Or was it to keep the fire box free and clear?
Look forward to hearing from you or anyone else that has an idea on this.

Doug

[Gary R]

Maple1, somewhere in this thread is a link to the research paper done on the air over fire. Black pipe is covered with ceramic insulation or refractory cement. Black pipe will not hold up to the heat in the fire box. That is why some of us used Stainless as it will.

[Maple1]

GaryR,
Thanks, I will be tapping tomorrow and will install the pipe for this season. Hopefully it holds up. Always work on new items days before the crazyness starts. Don't think I'm the only one.

[whalems]

you will need to cover black pipe w/ refractory cement or arch blanket or both.

[Sugarmaker]

Brent,
No this does not have a exposed motor like the Dayton units. So not sure it has a capacitor. I know what you mean but this is a self contained motor more like a shop vac type motor. I did not take it apart.
If any one wants to google it the just look for AquaPro spa blowers.
If it craps the bed I will be the first to say see "that didn't" work".
Regards,
SM

[WESTVIRGINIAMAPLER]

Brandon,
New to the site and sugar from CT. I'm trying to install air over this year with black pipe manafold. During your research is it nessary to enclose the manifold? Or was it to keep the fire box free and clear?
Look forward to hearing from you or anyone else that has an idea on this.

Doug

Doug,

I covered mine with refractory cement which is what I assume you are referrring to. I built it for long term and did this to protect it so it would last many years. If you didn't protect it, black pipe would probably burn out in 1 year or maybe last 2.

[WESTVIRGINIAMAPLER]

According to the research I did a few years ago, you can run a PSC(permanent split capacitor) motor with a fan speed control/rehostat but not a capacitor start motor. Not 100% certain on this but it is what I was told by some electrical experts I was referred to by Grainger.

[twofer]

Unless I messed up my research I believe you can use one of these on capacitor start motors.

http://www.solutionsforair.com/products/item.aspx?itemnumber=1DGV3

Here is the manual. In the manual it says it can be used with a PSC motor which is a permanent split capacitor motor, also known as a capacitor start motor.

http://www.solutionsforair.com/dayton_content/pdfs/5S5SpeedControls.pdf

Hopefully I'm correct or I just bought and installed a $64 paper weight.

[WESTVIRGINIAMAPLER]

No, a PSC and a capacitor start is two different things. PSC or permanent split capacitor and capacitor start are different. I don't know much about electrical but learned some before buying a PSC motor and running it with a fan speed control. I think a PSC only provides some start assistance but a regular capacitor start is what actually starts the motor. Either way, everyone I talked to told me not to use one on a motor with a regular capacitor start as it would burn it up. I ran one on a PSC motor for 2 or 3 years without any problem.

[twofer]

Awwww crap, you're right. It isn't going to work. Too bad too because it looked sweet mounted on the wall. :)

Time to file an RMA....

[whalems]

Where are you guys getting your castable refractory cement from? I can get find it on line but the shipping is outrageous. I talked to my local concrete service company and asked if they had it and they said yes. So I had my wife swing by and pick it up and when she gets home it is regular heat stop fire brick mortar. I call them to ask them about it again and the first 3 people I talked to didnt know what I was talking about. Finally got someone who did only to find out it will be at least a week before they can get it and w/ freight it will be over $100 a 55# bag. Does that price seem right? Any help would be greatly appreciated. Thanks, Mike

[jasonl6]

I'm making my grates out of kitty litter. I have read several areas where use can use it as long as it's with wood fire and underneath the fire. I plane to shread fiberglass mat into mine to give it extra strength.

Apparently you can either gring the little into small pcs and mix it with water or just let it soak in water for a couple days. You want a peanut butter consitancy. Should have it done this weekend and will let you know how it works.

Jason

[wiam]

I was quoted $25 for a 25 lb bag at a local building supply company. Hopefully they will have it in on Friday.

William

[WESTVIRGINIAMAPLER]

I got mine from Rutland and went on their website and found a local dealer and had it shipped to them in 25lb buckets.

[twofer]

I found a semi-local industrial refractory supply house that I could buy it from. They seemed very interested in what I was doing and helped me with what to use. I ended up using Sparcast 30 which you can see here: http://www.sparref.com/products/.

While I was there I also bought the plastic moldable refractory and firebrick.

[maple flats]

I got mine for free (did I mention I like free?) out of an airplane that used several bags for ballast. Long story! My brother works for a company who does major overhauls on the BIG planes. It seems one plane was brought in that among other things needed a new fuel tank in one wing. As I understand and remember it a big plane can't take off with fuel in one side only so they had to put ballast in the empty wing so they could take off. I guess flying as they use up fuel is manageble once in the air. After landing the castable refractory had to be thrown away. My brother and several other mechanics volunteered to "haul it to the dump" if you will. My brother got several bags, each weighing something like 90-100# (all the same I just do not remember exact size, just that they are too heavy.) He gave my 3 bags for free. (sorry he wants to keep the few he has left because that is what is used to cast the inside of the fill door on his outdoor wood boiler.)
I have not used mine yet because my grates are still good, but I hope to use it this summer. It puzzled me why they used such an expensive product instead of bags of sand but I am not complaining. I don't remember where it was shipped in from but it was from another country. Maybe the refractory is real cheap where ity is made.

[buxtonboiler]

All this talk about ss versus black. Has anyone tried using automotive exhaust pipe? That is what i am using. It is fairly cheap, easy to work with, and should hold up to the heat pretty good.

[RileySugarbush]

This thread has been very helpful, and I have abandoned my old high volume blower under the fire for a high pressure manifold around the firebox and more control of the low pressure blower under the grates.

The manifold is mild steel, the nozzles 304 hydraulic tubing. Most will be wrapped in ceramic blanket, with the nozzles poked through it.

Rather than mess with rheostats, I decided to control both with inlet dampers by putting them in a box under the arch.

I reused my old under air blower that put out 210 cfm but only about 0.5 inch of H2o pressure. I anticipate this will be damped way down most of the time.

For over fire, I found a 7 3/4" radial high pressure blower on eBay. Took a while to find the high speed half hp motor but found one pretty cheap eventually. This combo puts out 250CFM at 1" H20 and I figure about 100CFM at 3.5 in H2O, which is where I plan on running it, with 16 nozzles of 0.4" ID. That is about 180 in/sec air velocity and should be OK for mixing over the fire. I hope.

Anyway, I just put up this youtube video so you can see what I am talking about. I'll post pictures of it in the arch when I get it in there.


http://www.youtube.com/user/cosmosGross#p/a/u/0/LhiEyMjVx5g

[SeanD]

John,

That box is ridiculously brilliant!

Sean

[Brent]

Looks pretty good. The draft door look to be simple and effective.

I am concerned about how hot the motors will get inside the box. Try a run of a few hours, monitoring the motor temp every 15-30 minutes. If they start getting so hot you can't leave you hand on for more than a second or two, you could have a problem. I don't how the motor cooling fans work, but if there is a heat problem, maybe you could design a box so only the blower end was inside where you want to regulate the flow, and the motor was outside. Might be a bit of a challenge.

If it does not get too hot, you're double lucky because the heat from the motors will be pre-warming the air and blowing in warm air is better than blowing cold.

[RileySugarbush]

Thanks!

It looks like motor heating won't be a problem. Keeping the blower inlet pointing away from the inlet was intended the keep the sound level down, but it should be helpful for cooling the motor as well. So in both chambers, the air come in through the damper and runs over the motor before entering the blower. So they should be adequately cooled when working hard. When damped down to low flow, the current drops down quite a bit. Plus it is not likely to be run like that much, mostly when stoking. I'll run it in both conditions and report back

[Brent]

Sounds pretty good. The air holes on the box are well up off the ground, I hope the motor mount is high enough that the air will go in through the cooling fan.

There is one big advantage to controlling air flow rather than motor speed with a rheostat. The motor cooling fan is mounted directly to the motor shaft. So when you slow down the motor with the rheostat, you slow down the cooling fan too. That is what can kill a lot of motors. On machine tools with variable frequency motors, the motor cooling fan is independant and runs full bore, regardless of the motor speed.

I think you've got a pretty neat rig. The box really should keep the noise level down. I may borrow that idea. Thanks :)

[Gary E]

Yes, I have also enjoyed this thread very much ….

This is what I did:

- Replaced grates with ¾ inch plate which I cut to fit, put holes in and bevelled the underside.
- Sealed up front doors and enlarged deflector plates
- Mounted large furnace type fan & ½ H.P motor outside Shack , ducting under Evaporator. (on off switch near evaporator)
- Fabed a manifold and remote controls for AOF ans AUF
- Mounted two S.S pipes along inside of firebox
- Blocked original air intake with s.s plate

Seemed to boil good, time will tell, SOOON !!!! thanks ! Merci !


http://pic100.picturetrail.com/VOL1094/4132218/22649715/395239973.jpg

Controls Top Left

http://pic100.picturetrail.com/VOL1094/4132218/22649715/395240208.jpg

http://pic100.picturetrail.com/VOL1094/4132218/22649715/395240125.jpg


http://pic100.picturetrail.com/VOL1094/4132218/22649715/395240004.jpg
Ducting Under

Gary

[RileySugarbush]

Motor heating test: (TENV motor)

1 hour with both dampers fully closed:
AOF motor cool to touch
AUF motor slightly warm

1 hour with both fully open
AOF motor cool to touch
AUF motor not checked but assumed fine since the motor is in the air intake of the blower

Here is the arrangement inside:

[len]

Lots of good info in this thread! It would be great if some boiling rates, rig stats for pan types, and surface areas could be included!

My rig (small wee gnomish thing :lol: ) before AOF (no AUF) was at 2.0 gal/ hr with a surface area of 1.6 ft^2. I was able to get it to 2.6gal/hr by adding AOF. 1/4 lamp pipe shaped with a pipe bender, and I believe 13 #60 drill bit holes. I use a compressor, and run it in the 1/2 psi +/- range, but higher would be better ( small 1/2 HP comp- set to cycle to help it cool off). It's helped to cut back on the smoke, which is actually a lot of uncombusted gases escaping. AOF helped raise the efficiency levels, and gets more of the cumbustion inside the stove.

[WESTVIRGINIAMAPLER]

OK, guess I was the first guinea pig this year with the AOF. I have boiled 3 times with it and have tried multiple settings and needless to say I feel it was a big waste of time and $$$. Yes, I can run it with basically no sparks out of the top of the stack at all, but I am giving up 10+ gph which is a lot on a 2x8. The syrup pan boils like crazy when running it on 80/20 air ratio with 80 being air over top of fire. For some, it may work good and it has advantages. Will be good on days when I have an open house and don't want sparks flying out of the top of the arch. Yes, it saves wood but if I am giving up 10+ gph, in the long run, I don't think the savings is much because when I am using more wood, I am getting a lot more gph. After seeing a lot of other designs on here, I wouldn't change anything on design. I think it is built correctly, so I don't feel it is a design issue. I have 27 holes that were 3/8" in the castable refractory grate I poured and the second boil I drilled them out to 5/8" and the last boil I drilled them out to 3/4". Each time I open them up I get better gph running the bottom air wide open.

[RileySugarbush]

Well that's not very encouraging. Like you, I ran with stack base temps or 1700°F or more with aggressive AUF. What did this rig bring it back down to, Brandon?

Time will tell up here. Still waiting for the first drop of sap.

[WESTVIRGINIAMAPLER]

Running AOF system, I was running stack temps of 800 to 1000 degrees which is what it is supposed to be and sometimes it might creep a little above 1000. It would be a step up for probably for someone going from a standard arch that is not an airtight arch. I boiled off 155 gallons of sap yesterday in less than 3 hours and by the time I was shutting down I was getting stack temps a little above 1500. I hope I can get them up to around 1700+ on days when I have longer boils. At that temp is when the rig will really boil.

[RileySugarbush]

Thanks.

I am about to go install mine in the arch. I'll report what happens when we get going up here in MN.

We get tons of sparks when we burn our baltic birch plywood scraps from longboard manufacturing. Since our sugarhouse is surrounded by trees and has asphalt shingles, cutting down on that was part of the reasoning for this. I don't want to give up too much production though.

[Sugarmaker]

Random info on AOF TRS (Air Over Fire Top Rail System) start up.
- Seemed to have less sparks out the top stack. Need to check this more
- Bottom of pans inside the arch were more gray than black.
- Stack temps ran about 550-650 F about 100-200 deg cooler than normal.
- Dimmer switch could not carry the amperage and got hot. removed dimmer.
- Exterior of the AOF pipe near the draw off boxes was about 240 F.
- Stack temps increased with more frequent firings.
- Tried firing at 10 minute intervals.
- Seemed to have less boiling in front pan than last year.
- I think this is going to save some wood. To early to tell.
- Had a thermal problem with the front of the stainless tubing as it tried to lift off the rails about 1/4 inch, during first boil. I added a 1x1 stainless angle to the sides and welded and screwed it to the arch rail. This should hold it in place:).
- Sounds like the roar of a jet plane in the fire box.
- Like Brandon, I think I may try to fire a little harder and see if the boil is improved.
- I may install a 2 inch plastic ball valve in the air line to control/ set/ adjust the air flow? Running wide open like all the other stuff right now.
- My approx cost for this system
$150 -- blower
$25 -- 2 inch PVC and fittings air inlet
$200 -- Stainless tubing and fittings
$75 -- Wiring

Hope this helps some one,
Chris

[Brent]

Random comments on random info

- you didn't say how ofter you were firing. Last year I could stetch it out to 15-18 minutes or so, but when I put in a big load of cold wood on a small fire, ( you pretty much have to let it burn down a lot to get the times longer) it took quite a while to get real hot again. Lots of black smoke outside. The more I played around, the more I liked shorter times. The fire was hotter when I added wood and I added less cold wood so the firebox stayed hotter. Got much less black smoke and for a much shorter time and the stack temps could be kept pretty steady near 1100.

- fewer sparks is generally good. Hopefully because the combustion is more complete

-the thermal warping is not surprizing. Pan temp about 200 ... top rail temp, likely closer to 300.

- check the amperage rating on the dimmer. Most are not rated for the kind of current your blower will draw. Toasty hot is to be expected. To hot to touch is not good.

- grey pans is better than black ... progress.

- less boiling at the front may mean you're blowing to much of the fire too far back, but that's hard to tell. Maybe try jamming something temporary in the holes blowing above the door. See if that helps. Maybe plug half the holes.

- the sound is awesome isn't it ... and I'm lost half my hearing.

When your finished all that, I need some help from a welder. Looks like we bent the frame on the new-to-me evaporator when we laoded with the front end loader in Vermont ... with 1500 lbs of bricks in it.

[maple flats]

I fired last year about every 15 minutes and then dropped to every 12 minutes. I saw no difference so I went back to 15 minutes. When I fill, I bring the level up to about 2/3-3/4 up in firebox and it is at about 1/3 or slightly more when I add. I do not shut off my blower to fill nor do I get black smoke. I can see no smoke outside except in thef minutes of the first firing from a cold start. My arch is not air tight. What are you burning? My wood is all seasoned at least 10 months and what I start with will be 3 years old because last year was so poor. I have all my wood split to about wrist size too, it light fast and burns HOT.

[maple flats]

OH, before I added the AOF I had smoke and sparks at filling but since I have no sparks or smoke. When I open the fill doors the draft still goes in even with the blower on over and under.

[WESTVIRGINIAMAPLER]

Dave,

I would say mine was doing about the same as yours and it was working well. Syrup pan was boiling so well it was going crazy, so I was holding a ton of heat in the front of the evaporator. The system worked great and performed like it was supposed to and I had confidence it would all along, but as I stated before I was hoping not to give up much gph which it does. I guess pick your poison. Boil with no sparks and a syrup pan that wants to get up and walk out the door or boil faster, get sparks and use more wood. Maybe if I get a steamaway on top of it, I would be more content with running it on the gasification mode. I am still not sold that I was saving a lot of wood because if I am boiling 15 to 20 percent harder I am using more wood but also evaporating significantly more. Running 625 taps on a 2x8 and working full time, I don't have a lot of extra time to play around with things even though I have others that help with the boiling.

[RileySugarbush]

OK, I am ready to try the AOF, and would like some advice from Dave and Brandon...

2x6 air tight arch

Last year, Firing every 6 minutes or so with full out low pressure 200+ CFM through the grates. that gave very high rates or up to 45gph for such a small rig, but burned through the wood and had stack base temps of 1600 so lots of the heat was heading up the stack. Tons of sparks too.


So now I have the same under fire air, with good control and I think good over fire air, with good control also.

Did you guys cut bak a lot on the under fire air to slow the overall flow rate and keep the combustion closer to the front? How much did you cut back?

I've read that near the end of a firing the AOF should be cut back and under fire AUF turned up, to burn down the coals. Did you guys do this?

thanks

[Brent]

Last year on the 2 x 6 I only had air over. Never shut down the blower during firing. I felt the natural draft was good enough or close to good enough. Had lots of stack to help the draft. Burned year old, well split maple.

[WESTVIRGINIAMAPLER]

John,

I was trying to get 80 percent above the fire and 20 percent below the fire, so I was running above air fire wide open and below air fire nearly closed off. Not sure I was getting exactly those ratios, but was coming fairly close. Not trying to discourage anyone, but after doing some better figuring, it appears running the system this way I was giving up about 25% of my gph rate before converting it.

[RileySugarbush]

Thanks.

I hope this works ok. I didn't invest too much in this but time since I scrounged on eBay. I still have the same blower under the grates I can switch back and forth between days if I feel it is holding me back.

Big snow storm due in a couple of hours. And a few weeks before I get going here.

[Sugarmaker]

Brent,
I was firing about every 10 min, May try 8 min. The pallet pieces I am burning burn hot and fast.
I have changed the flow path of the fire thru the flues by raising the pans 2 inches. More like a mini MAX pan. 2 inches raised and 5 inches dropped.
The Steam Away helped me get the gph rate equal to or greater than previous. Some where about 110 - 120 GPH? Still need more boils to evaluate all systems!
Thanks for the help!
Chris

[nymapleguy607]

Well I was able to try the AOF system over the weekend. Overall impression is that it still needs work. The center of my syrup pan was boiling like crazy but the outer compartments would not. I was getting a more grayish color on the bottom of my pans instead of brown. Stack temps ranged in between 900 and 1050 internal temp. My firing rate was around every 6 minutes. To be fair though my wood could have been drier.

Some things I took away from the first boil:
1. I need smaller air jets on the air manifold I started with 1/4" for about the fist half of the fire box and the used smaller drilled out pipe plugs.
2. My air dampers need to seal better, with the dampers fully shut I still needed to limit the amount of air going into the dampers.
3. I might possibly need to raise both pans slightly higher. With only 4" between the AOF manifold and the top arch rail I might be adding to much cold air under the sides of the pan causing the lack of boil.

I will try smaller Jets and sealing the dampers better first as well as some drier wood and then we will see.

[Sugarmaker]

Murfred,
How did your system work? Its very similar to what I built? Have you boiled yet?
Chris


We got a "new to us" evaporator this season & I've been converting it from oil to wood & installing air over fire. A few pictures of my version of manifold. Do you think I need to cover the pipe?

[Sugarmaker]

Ny..607,
Sounds similar to what I saw too. I was thinking that maybe there should be two systems, one damper in the left side and one in the right side so that when drawing off you could close the AOF for that side?
My head is starting to hurt.:)
Happy boiling
Chris

[nymapleguy607]

Chris

I tried a similar setup last year with independent valves and it made very little difference.
With the smaller lets I had last year I had no trouble keeping the outer partitions boiling.

Good luck with yours
Jeff

[len]

My Impression is that a combination of high and low pressure blowers won't work well, as the high pressure blower overpowers the low pressure one.

[Sugarmaker]

Interesting thought Len. All the more reason that I may need to throttle the AOF TRS system and balance the two systems.
SM

[RileySugarbush]

My Impression is that a combination of high and low pressure blowers won't work well, as the high pressure blower overpowers the low pressure one.

It's probably not the problem you think it is. Clearly if I hooked the outputs of my two blowers, the high pressure blower would probably blow the other one backwards. But that is not how that are connected in the firebox. High pressure blowers are used to get high velocity air through the AOF nozzles. By the time it comes out, the pressure is down.

[len]

It's probably not the problem you think it is. Clearly if I hooked the outputs of my two blowers, the high pressure blower would probably blow the other one backwards. But that is not how that are connected in the firebox. High pressure blowers are used to get high velocity air through the AOF nozzles. By the time it comes out, the pressure is down.

Think of the arch as a pressure vessel, with air added under grates for primary combustion/ pyrolysis, air over for secondary combustion, all having to exit the flue, which at a certain point gives some back pressure. At this point, the low pressure blower will stall, and not continue to provide the desired 80/ 20 mix. The fire will reach a limit of pyrolysis, and potentially limit the gal/ hr output.

[Brent]

It's probably not the problem you think it is. Clearly if I hooked the outputs of my two blowers, the high pressure blower would probably blow the other one backwards. But that is not how that are connected in the firebox. High pressure blowers are used to get high velocity air through the AOF nozzles. By the time it comes out, the pressure is down.

All that depends on how big the blower is and the size and number of orifices you have on the high pressure blower. Last year I used a meduim high pressure blower with NO blower under the grates. I could open the door with no backwash. The natural draft kept everything going up the stack. This year I have a new rig ... a modified Leader Inferno so I have an airtight arch and have no choice but to run the low pressure blower under the grates. But my high pressure blower will be very high compared to last year or what anyone else has mentioned they are using. I'll have lots of very small holes, about 1/8" and hope to get fresh air in small jets all over the place above the wood. I think most people have gone CFM crazy.

We're not trying to light up the sky. We don't want to blow the comustibles up the stack, we want to burn all of it
under the syrup pan or the very front edge of the flue pan.

[RileySugarbush]

I understand what you are saying, but the gage pressure in my firebox was obviously far lower than 0.5 in H20 last year, since my under fire blower tops out at that pressure and it clearly was adding air to that chamber.

A crude estimate based on spark velocity in a video shows a total flow out my stack last year was roughly 800 CFM. All that without significant pressure in the firebox, since it did not come blasting out when the door was inadvertently cracked open with the blower on. I think Brent was running with AOF and natural draft last year too. The negative pressure from the stack more than made up for his AOF and combustion products, or else he would have had flames coming out the draft door

My high pressure blower being added this year is sized to add about 100 CFM at high velocity through the nozzles, assuming a 3.5 in diff pressure on the nozzle. Time will tell if that flow will be too much for my under fire blower. I think it will be fine.


I just saw Brent's reply. Sounds like I recalled it correctly.

[Brent]

John

800 CFM wow

Something to think about
your rig is a 2 x 6
the firebox/firewood is roughly 2 x 2 x 18" or 6 cu ft.
At 800 CFM you blowing a complete change of air throgh there in less than 1/2 a second. Think about how much energy it takes just to get the air up to combustion temperatures. A temp rise of over 1000 degrees in less that 1/2 a second.

There's gotta be a better way.
I'm still dreaming of getting an oxygen sensor. Increase the air until there is unburned oxygen in the stack and you've got total combustion.

[twofer]

Your 800 CFM seems really high to me. If you assume each pound of wood takes 70 cubic feet of air you would have to be burning ~11 pounds of wood a minute or ~685 pounds an hour.

ETA: That also assumes the evaporator is operating at 50% efficiency.

[Brent]

Twofer

my point exactly. This big blower thing has gone way beyond what it really needs. I'm sure some guys are still burning combustible in the stack and beyond.

When I first started with a blower on my Half Pint I have a red flare coming out the top of the stack 10' above the pan.
It boiled a lot harder buy my God the wood it ate !!!!

[ADKMAPLE]

Well I think they all eat wood unless you have a high output insulated arch. The 2x6 Leader drop flue that I work (not mine) is fired every 7 minutes

[RileySugarbush]

My estimate of 800 CFM is based on how fast sparks are leaving my stack in a video taken at night. Hardly accurate, but good estimate. 800 CFM is not unreasonable:

Don't forget that the volume of air expands in proportion to it's temperature according to Charles' law. 200 CFM going in at 50°F (283°K) expands to 800CFM at 1600°F ( 1144°K).

And that is just the air. There is also the gas generated by the combustion of the wood.

I agree that the it is bad to have combustion at the top of the stack. The goal of all this AOF is to get the combustion and release of heat in the fire box and at a slow enough velocity so that there is time to transfer it to the sap.

My point was just that the back pressure in the firebox is not high enough to stall the low pressure blower. We are getting off track, though the new track is interesting too!
[http://www.mapletrader.com/community/attachment.php?attachmentid=2786&stc=1&d=1298390608

[Sugarmaker]

Man you guys are so far out there! I want to come back to Kansas with toto! Keep clicking my heels and just get sore heels:)
Some pictures of the air control and the structure I added to the AOF. Seemed to work OK.
If this [AOF] doesn't get to boiling well I am going to shut it down and see if the AUF works as good as last year. I didn't build the WRU to boil at just above the same rate as last year. WE want more syrup faster. More data needed on my cobbled up, not to spec., jerry rigged, low rent AOF unit.
Sorry the pictures are a little blurry on the rails. I added them to limit the thermal raising of the front portion of the AOF. And yes I need to tuck my pan gasket back in.

Chris

[murferd]

Still finishing ours. Hope to get a few pictures in a couple of days. We plan to move the rig out to the shack on Saturday. I did lower the manifold down some, we got bashed so much I thought it must have to be better. Ha! Not really, I was planning on getting it as close to 6 in as possible, it ended up at 5 to 5 1/2. Still trying to figure out how to hook up my AUF & AOF pipes & regulate them. Still got a couple weeks, should be ok by then.

[Sugarmaker]

Murry,
Man Glad you came to my resuce! We have to stick together. Wow! and now you lowered your pipes to:(
Hope your system preforms for you. We are still tuning in NWPA.
I though yours looked like duals out the back of the rig.
Are you going with dampers in the pipes?
Regards,
SM

[RileySugarbush]

Sugarmaker,

Do you have any insulation on your air rails? If not, the difference in temperature inside and out is probably what is causing the distortion. It could have enough force to crank on the angles pretty hard.

My distribution pipes are not part of the arch, but I warped them in ceramic blanket just the same.

http://www.mapletrader.com/community/attachment.php?attachmentid=2812&stc=1&d=1298428369

[Sugarmaker]

John,
My side and end pipes are not insulated. I do have insulation on the cross pipe right in front of the flues. I was taking comments from other traders on the need for insulation, considered it and chose to try it without. I have boiled for 3 hours with the angles and they seem to hold the AOF pipes in correct position.
I like your set up too!
So how does it boil? Are you pleased with the addition of AOF to your rig?
Chris

[RileySugarbush]

Well Chris, I wish I could tell you. We just had 19 inches of snow and not a drop of sap yet. I'm anxious to find out if it was worth the trouble, and I'll report results as soon as I have them.

On the issue of insulation on your pipes, it is probably fine as long as the air is going through them. If you shut it off, the inside and bottom walls will get very hot and expand. The top will be at sap temp and the outside maybe a little cooler. That means it is really going to want to curl on you.

I like you idea of the spa blower, BTW.

[Sugarmaker]

John,
Man I hope you get some sap soon too. We are in a lull also. Gives us time to work the first bugs out of the add ons this year.
I think these spa blowers do a real nice job in both the WRU and the AOF. If I had it to do again I think I would have got 220V units and used less power and ran easier. They make some noise about 54 decibels. But a lot of the noise is in the actual evaporator from the bubbling in the WRU and thru the air nozzels too. Air out put is about 120 CFM. They run about $150, install easily, are weather proof, and could be mounted under the evaporator. Just run 2 inch PVC.
I think this was Dave 3% solutions idea. I will give him credit.
SM

[nymapleguy607]

Well I made some progress on ther AOF system. After the first boil I was having trouble with getting the outer syrup pan partitions to boil. I changed the 1/4" pipe AOF nozzles out to 3/16 drilled pipe plugs. This should keep cool air to a minimum and hopfully cause more turbulence. I also reworked how the air enters the dampers. Hope to test boil this weekend so I am 100% when we get the next run.

[WESTVIRGINIAMAPLER]

I finally got enough sap yesterday to do a 4+ hour boil and with 280 gallons of sap, I was able to get about 65 gph including startup and shutdown. Forgot to brush the flue pan before starting and it was third boil since it was brushed or I could have possibly done a little better. Running the under fire air wide open and the top wide open too definitely uses more wood in an hour but I can also get 20 more gph vs running with 80% top air and 20% bottom air. Not sure how much wood if any I would be saving running 20 less gph if any by the end of the day because of the much slower boil rate. I am firing every ten minutes running it wide open. Was running stack temps staying between 1400 and 1600+ after a couple of hours of boiling and it was eating sap if it stayed in those temps probably during best hour was well over 70 gallons.

[len]

WVM, I checked out your rig construction pics, and the thought that comes to mind is the higher stack temps to get it really going well. Is this a symptom of the slope back of the fire box transitioning lower than optimal for the drop flues? An idea that comes to mind is placing a row of fire bricks flat across the area at the transition just aft of the AOF tubes. This might function like a "trip strip" on an airplanes wing. Perhaps think nascar and wind tunnel testing, but in this case it's inside of the firebox. Might help mix the burning gases better, and get them higher up into the flues. The flames might go up over, and back down though, so it might boil even harder in the front of the drop flue pan, and behave similar aft. 5 gal/ hr improvement?

[Gary R]

WVM, I think Len is on to something. Even though mine is a small flat pan rig, I made a change today. I was firing ever 7 minutes and I could get my stainless stack to glow red the first foot or so. Daryl suggested I put small pieces of brick in my flue area at the back of the pan. I'm boiling now. I've increased my firing to at least 9 minutes. No red stack. Haven't check GPH but full pan boil so it should be the same. What it comes do to is that I'm keeping more heat in the rig longer. I think every rig is just a little different. When adding the AOF we need to find that optimal set up.

[nymapleguy607]

Well I made some changes to the AOF system. I tried it out today and had alot better results. First thing I changed was the hole size, I changed from 1/4" pipe nipples to pipe plugs drilled out to 3/16". I also changed how my air dampers attach to the blower. The results were encouraging I boiled for about 45mins to heat up some water to clean the pans. The syrup pan was boiling the entire width of the pan and the flue pan was boiling very hard in the first 2ft the stack temp was about 650*. I am anxious to see how everything will work if I get a stack temp around 900*

[twofer]

Keep in mind, and I'll have to check my notes, but I believe the rule of thumb is every 100°F you raise your stack temp you are reducing the overall efficiency of to the tune of 5%.

I guess it depends on if you're after more GPH or more GPC (gallons per cord).

[MAPLE247]

We just picked up a furnace blower, and we want to hook it up to our 2x6 leader drop flue evap. Does anyone have any pics. to give us a feel on how to do it?
Also I'm not understanding what it means to have a % going over the fire and a % under the fire. Under the fire I get but I don't get what over the fire means?

[Brent]

Here's a couple pix of the progress on our re-build. The insulation is almost done using the Unifrax 2" thick ceramic boards. I'm pretty impressed with this stuff so far. Much much stronger than the vermiculite boards I tried last year. Just got the slope to cover, then start bricking.

The air over fire is almost the same as I used last year. This year it will be really high pressure, about 58" WC. In last years Phaneuf evaporator, the stainless tubes were burried in the loose vermiculite that filled under the flues, and emerged through the slope. This set up has the tubes in the bottom corners where they will be fully exposed to the heat so the injected air will be really hot and should give spontaneous combustion, which occurs at about 1200 degreees, to any unburned gas or particulate.

You can barely see the nozzles that the previous owner put around (and in ) the door. These are fed from a tube under the grates from the original Leader Inferno blower. The tube has a bunch of holes in it so some air will go up through the grate and some through the injection holes in the door and door frame. No time this year to put the controls on it that I wanted. Next year, along with some high temp thermometers and a viewing window.

Really looking forward to lighting the fire this year !

[Flat Lander Sugaring]

Thinking about throwing a AOF system together for this year with Black Iron any thoughts?

[WESTVIRGINIAMAPLER]

With the way I designed my AOF, the AOF air is very hot coming out of the nozzles. The 1/4" square tubing is getting heated very well behind the castable refractory cement and in between the fire brick and it is belching out hot air.

[Sugarmaker]

Our AOF system seemed to work very well at the end of the season with a small amount of natural draft under the fire [bottom draft door open about 1 inch] and about 1/2 throttle on the AOF blower using a ball valve. Stack temps were 500 to 600 deg F. and had a very good boil throughout the pans. I had to learn to not fill the fire box as much or the stack temps would go way up. firing 12 to 15 min. I feel we saved a lot of wood.
I did pinch closed the 5 nozzels across the pipe that pointed back towards the fire door.
193 gallons on 9 cord, of course the WRU was helping too:)
Chris

[Flat Lander Sugaring]

AOF deff. helps. Trying to figure out air ratio and wood is my issue right now. It probably helps to have all the right stuff and set up correctly so for this year is all experimental. I find when I run less air under and the max over when loading box I jiggle all the stuff around before loading, and the blue and purple flames that appear was awesome. When I had AUF 1/2 to 3/4 the steam was just rolling off the rig with stack temps 1000+ pre heater 178 not much blue n purple flames. I turned down AUF a lot of the steam stopped, stack temp 900 and preheater 140 but a lot of blue n purple flame. Out side temp, barometric, humidity, and dew point were all about the same on both loads. I had inside box so hot the black iron tubes were glowing red and I boiled off 30 gal n hr last night.
I think I have read you want a high pressure blower not volume and I can see where that would help make the air swirl more for a complete burn.

[jmp]

Although this is not a big rig like the rest of you guys the air over and under fire I rigged up has given me at least a 35% increase in boiling and has evened out the boil in all three sections of my pans. Had a lot of fun making it from a used oil burner blower. :) Also gives me a chance this season to tweak the system for this summer's arch build.

I used 1.25" square tubing. Holes are 3/8 every six inches. I followed the UVM plan that I found on here. It really works great. -John

[allgreenmaple]

AOF deff. helps. Trying to figure out air ratio and wood is my issue right now. It probably helps to have all the right stuff and set up correctly so for this year is all experimental. I find when I run less air under and the max over when loading box I jiggle all the stuff around before loading, and the blue and purple flames that appear was awesome. When I had AUF 1/2 to 3/4 the steam was just rolling off the rig with stack temps 1000+ pre heater 178 not much blue n purple flames. I turned down AUF a lot of the steam stopped, stack temp 900 and preheater 140 but a lot of blue n purple flame. Out side temp, barometric, humidity, and dew point were all about the same on both loads. I had inside box so hot the black iron tubes were glowing red and I boiled off 30 gal n hr last night.
I think I have read you want a high pressure blower not volume and I can see where that would help make the air swirl more for a complete burn. Interesting setup you have there flatlander. Might have to swing over & see it sometime. I'm not far away, just over in North Granville, just a stones throw away. Randy has helped me set up a lot of my line this year, just over 700 taps. Not boiling this year, just got new pans in, & still have some setup work in the new sugarhouse. I was up there less than a week ago to scope out his new rig boiling, looks like he's getting it down in good shape. We'll be f iring my new 3' x 10' in the coming year.....

[Brent]

I think you've just invented the Lotus Elan of barrel rigs.
It ain't big but just watch it go !

[RyanB]

Here's a couple pix of the progress on our re-build. The insulation is almost done using the Unifrax 2" thick ceramic boards. I'm pretty impressed with this stuff so far. Much much stronger than the vermiculite boards I tried last year. Just got the slope to cover, then start bricking.

The air over fire is almost the same as I used last year. This year it will be really high pressure, about 58" WC. In last years Phaneuf evaporator, the stainless tubes were burried in the loose vermiculite that filled under the flues, and emerged through the slope. This set up has the tubes in the bottom corners where they will be fully exposed to the heat so the injected air will be really hot and should give spontaneous combustion, which occurs at about 1200 degreees, to any unburned gas or particulate.

You can barely see the nozzles that the previous owner put around (and in ) the door. These are fed from a tube under the grates from the original Leader Inferno blower. The tube has a bunch of holes in it so some air will go up through the grate and some through the injection holes in the door and door frame. No time this year to put the controls on it that I wanted. Next year, along with some high temp thermometers and a viewing window.

Really looking forward to lighting the fire this year !

Brent- Your AOF setup is intriguing. I am located 25 minutes west of Orangville...Would love to see your setup in person sometime! Thinking of doing AOF next year on my home built 2x4.
Ryan

[Brent]

You're certainly welcome to come by. The rig now has a modified Leader Inferno arch with a square tube fitted around the door and a series of nozzles so that a portion of the air from Leader's blower goes through the nozzles. I have not yet hooked up my own mods, ie the stainless tubes. These are essentially the same as I had on a smaller rig last year, except that my blower this year will output 10 x the pressure I had last year. I'm keen to get it going but I've still got 300 trees to tap so it will be cold outdoor work this weekend. Next week looks to be near perfect in our area.

[Flat Lander Sugaring]

Interesting setup you have there flatlander. Might have to swing over & see it sometime. I'm not far away, just over in North Granville, just a stones throw away. Randy has helped me set up a lot of my line this year, just over 700 taps. Not boiling this year, just got new pans in, & still have some setup work in the new sugarhouse. I was up there less than a week ago to scope out his new rig boiling, looks like he's getting it down in good shape. We'll be f iring my new 3' x 10' in the coming year.....

Your not far at all, Sugar Garage isn't much to look at (going to Curtis Lumber today to get prices on one of their kits) but the rig is interesting with modifications. I'm prob going to hit Randy's today after the gun show. Then back here to check sap and boil hopefully.

[RyanB]

You're certainly welcome to come by. I'm keen to get it going but I've still got 300 trees to tap so it will be cold outdoor work this weekend. Next week looks to be near perfect in our area.

Thanks for the invite. I will send you a PM for more info. Ya, after this deep freeze and looking at the up comming week...I am thinking we may have a gusher! I only have 50 taps and storage for 800L of sap which is more than enough for my 2x4 arch I just built.

Ryan

[TroutBrookSH]

Lots of great info in this thread from folks trying and succeeding with AOF! Just bought GravityTom's 2x8 Patrick Phaneuf and am planning some modifications to his original AOF work. Good thing I have some time...now.

So, Chris, I see you chimed in quite a few time on one of the threads, and that you made mention of WRU several times. The search feature does not allow for searches on short acronyms like AOF, AUF, WTF (Wild Turkey Federation), WRU, etc. Please tell me/us what is WRU. Thanks.

Greg


Our AOF system seemed to work very well at the end of the season with a small amount of natural draft under the fire [bottom draft door open about 1 inch] and about 1/2 throttle on the AOF blower using a ball valve. Stack temps were 500 to 600 deg F. and had a very good boil throughout the pans. I had to learn to not fill the fire box as much or the stack temps would go way up. firing 12 to 15 min. I feel we saved a lot of wood.
I did pinch closed the 5 nozzels across the pipe that pointed back towards the fire door.
193 gallons on 9 cord, of course the WRU was helping too:)
Chris

[Sugarmaker]

TroutBrookSH
The WRU is short for Water Reduction Unit, I built one last year and installed and used it the past season.
(This is similar to a steam away system.) There is a thread I believe it is " WRU in Progress" you might try sorting on that.

On the AOF: I will be using it again next season! As I believe it allowed good boiling, longer time between firings, reduced stack temps, and reduced wood consumption. If you follow the thread mine is a add on not a built in. But seemed to work OK with some minor mods.
Regards,
Chris

[treehugger]

Did aof improve things?

[Burnt sap]

Nice work are you a metal worker or welder by trade?

[deckers007]

Would this work as AUF, possibly start a secondary burn?14803

[mellondome]

Most likely you will only create a cold spot on your back pan. If you preheated the air to say 600°+ than it may work
With only 4 ft of flue pan.... and 18" of that open to the ramp/firebix and 4 -6 in open for flu gas drop out (your drawing looks to be raised flu).. that only leaves 24 inches to build 2 rises and with air nozzles between them...

I would suggest that your forced aof go close to the top of your ramp directed slightly downward toward the firebox and door.