Adding over fire combustion air

[maple flats]

I started getting set to add over the fire combustion air today. I am using the plan referenced here :
http://www.uvm.edu/~pmrc/Combustion.pdf
I have some 2" square tube, 1/16" wall that will be the duct behind the refractory. This year I will just try it using a 1/3 hp blower I have but if it seems to need more air I'll need to buy the blower suggested in the article, a $460 high pressure blower from Graingers for my 3' wide evaporator. I am making inline dampers with indexable (knotched repeatable settings) control rods for both above the fire and below the grates all on this blower. As progress proceeds I'll keep you advised, especially how effective it is when done. At the same time I am redesigning my firebox back wall. Originally I made it too high and forced too much heat up too fast making it jump real high in the front 2 feet of the flue and causing some to get splashed out the seam between the pan and the hood. I will lower the back wall 5" and make the taper 2x as long. When I did it I went straight up until only 4" below the pan and tapered back and up from there.
My above the fire air will be about 6" below the pans and angled down about 10-12 degrees with a nozzle hole thru the refractory every 6" roughly. The report calls for air set refractory and suggests "Max Bond", anyone know where I can get it? or equivalent? I googled it and get nothing helpful.

[Smitty]

Dave,
i built my over fire air last season, seems to help quite abit, ( burned
slightly green wood last year with improvement, can't wait to try dry
wood this year). i run a 3" thin walled pipe right threw the back of the
arch, i removed the brick from the slope of the fire box all the way to the
back of the arch.laid the pipe on the bottom of the steel arch , it exits right
below my stack, straight threw the back. when it reaches the down slope,
i teed it,( i hope that is spelled correctly) with 3" pipe, all the way across
my 2' arch, installed three 1/2" pipe nipples (3" long) at 10 degrees. i than
rebricked, adding refractory cement around the nipples. i left the top of the
3" pipe, that runs to the back exposed, hoping to preheat the air before
it gets to the fire. it has made a difference, but it sure is fun trying to put
all this stuff together, and making it work.:mrgreen:

good luck,
Al Smith

[C.Wilcox]

Dave,

When you say "1/3 hp blower" do you mean a squirrel cage fan?

[Gary R]

Dave,

I couldn't find the Max Bond stuff either. I used some plain refractory cement. The type that was already like clay in a bucket. If thinking right on how your building it, you'll have a layer of cement as high as your noozles all the way around.? Make sure about the directions on curing. Good luck and post some pictures:)

[Bucket Head]

A high pressure blower is not a squirrel cage blower. A sq. cage blower will not work. They are high volume, low pressure units.

Have you ever seen or used an engine driven, walk-behind style leaf blower? Thats a high pressure blower. A LOT of air with the speed to match comes out of those. Thats what is used on both the high efficiency arch's and the Steam-Away units.

Steve

[markct]

hmm weird the blower i have on a leaf blower engine is a squirel cage blower just with fewer fins, never seen any with a different design realy, even huge 3pt pto powered ones

[Haynes Forest Products]

The high pressure fans/blowers are more like a paddle blade. they are easer to balance and dont want to fly apart. Squirrel gage blowers are quiet and will move alot of CFMs but not crazy powerful.

[Haynes Forest Products]

http://cgi.ebay.com/Crelec-HB-129-AIR-BLOWER-Vacuum-Pump-800L-min-200w_W0QQitemZ390148770345QQcmdZViewItemQQptZAU_Bu siness_Industrial_Industrial_Supply_MRO?hash=item5 ad6adca29
This is the type of unit you want will suck the chrome off a trailer hitch. neds good power and they are noisy. If you mount this out side about a 1/4 mile from the bldg your all set.
you can find them under vacuum pumps. or try blowers.

[KenWP]

Long way to ship a fan. I had one ready to go when I moved here from Alberta and then ended up with a smaller trailer and had to leave a bunch of stuff back there. I sort of thought I might not need it until I got here. I had a bunch of ss sheets I had to leave behind also.

[maple flats]

I came up with a 3" high pressure blower from a factory that closed. It is all cast iron and likely weighs close to 100# without the motor. I need to get a different motor because this is 3 phase and I have no access to 3 phase. It will put out up to 4" water column at 1750 rpm at some unknown specific constriction that was workable but I forgot what it was. The paddles are cast iron and are about 4" in diameter on a four paddle axle of about 10" overall diameter. I will try to get this one going if I can. My machinist building it has the parts all cut, the holes drilled for the nozzels, nozzles are made, the angles are mitered and it is ready to weld. I have the top 2 rows of brick out on each side and to the same height across the back. I should have it ready to install this weekend or early next week. The blower might take longer. The motor has a 5/8 shaft and is 5" long. Haven't found a motor with a shaft that long yet. I might need to use a pair of blocks and set up a jack shaft and pully arangement but will then need more power to run it because of power loss with the v belt.

[Gary R]

Dave,

I have an idea, it may work. If you go to Tractor Supply, they have couplings for motor shafts. They are about 3" long and about 3" dia. They have rubber coggs that engage each other. If you have the 3phase motor, could you cut the shaft off and leave it in the blower. Then use the coupler to couple that shaft to the new motor. You may need to grind a flat spot in the cut off shaft near the coupler. This would be for a set screw so the coupler didn't spin on the shaft. You would not need any pulleys then.

[Amber Gold]

You don't need a new motor. Buy a VFD to convert phases. My LR pump has 3 phase motor, but I'm using a VFD to convert from single to house phase. They're not cheap, but it's probably cheaper than a new motor and retrofitting.

[Gary R]

Josh,

Coluld you provide more information on the VFD (phase converter) please? Maybe a catalog (Grainger?) and part number where they could be found. Thanks.

[wattsup]

I am an electrician, I do n ot beleive you will find a VFD 240 1ph to 208 3ph used. Price depends on HP and the VFD needs to be matched to the motor. A 5 hp VFD will run in the $700 range. Another option is a device called a rotophase that creates 3 ph. A 3 ph motr will run on 1 ph if you can get it spinning a friend jerry rigged a pony motor to a 3 ph motor it worked but HP is about 1/2. I would look for a 1 ph motor if I where you.

[Loun]

im making a cinder block arch and want to try to add air to it. I am not in a position to go buy a large or expensive blower but would like to still rig "something" up. is this going to be about volume or velocity of air? I have a 2x4 pan. Looks like it will be a 2x2.5 or 2x3 firebox. how much air or how much air speed do I need to be looking for. Will a fan ducted in work?

[maple flats]

If you can swing it try firebricking inside the blocks. The fire will get too hot for the blocks otherwise.

[Smitty]

Loun,
you only need a pressure blower if you are adding over fire air,( to get
enough air threw the nozzles), any blower will work for a forced draft
blower, if you are only going to the fire box. i would calculate the volume
of your stack, and than find a blower to meet that.


hope this helps,:) :) :)
Al Smith

[Amber Gold]

Gary, my LR vac. pump has a 3 phase 1.5 or 2 hp motor. I bought a VFD (variable frequency drive) from driveswarehouse.com This is the 1hp version of the VFD I bought.

http://www.driveswarehouse.com/Drives/AC+Drives/Phase+Converter+VFD/X200-007NFU1.html

My VFD and pump should be hooked up tomorrow, although with the temperatures we're seeing I don't think I'll be filling the stock tank up to run the pump...will probably wait for a warmer day.

[maple flats]

I have the manifold set in place for over fire. Before I finish it with firebrick and refractory I need to make the under fire air set up. I am thinking coming off the high pressure blower with a Y and control each with a valve. What should the under air look like. This year I am keeping the cast grates and making a manifold under it. Next year I think I will remove the grates and pour a floor with inverted cone shaped air nozzles built in, as described by the report this whole project came from. For now I am thinking of making one inlet pipe, 2.5" go forward to 8" from front. Then weld 3/8" pipe nozzles crushed on the end to a 1/4" wide slit , put 5 faned out every 6". Does this sound good or should I do it differently? Is it not necessary to cover so much area?

[Gary R]

Dave, I am no expert but here is my opinion. If your goiong to use your grates this year, I'd use like 3" chimney pipe under the grate. use a tee and cap the ends. punch hole through the top for the air to go out. Make it removable so you can clean the ashes out that fall into the manifold. I was going to pour a floor in mine. I could not find the "high strength, castable" cement locally. I called a manufacture down south and they recommended a certain type (can't remember the name). The problem was with shipping it would be $80 a bag and I needed 3 bags. You would probably need 5-6 bags. If you can find it locally, I think it was about $20 a bag. I went with fire brick and drilling them. Chamber and ash door under the floor needs to be air tight. All the air will be forced up the holes. During my test fire a couple of holes did plug up with ash. A fire poker with a 90 degree bend on the end clears them up.

[maple flats]

The casting instructions call for an inverted cone shape hole. This might help. I wonder if you can ream the drilled holes in your brick by taking a carbide bit and go in a swival pattern. You might need a heavy steel plate with a hole in it to try to keep the top from getting too big. It might not work, just a thought. Too late now but a jig to do this with such a hole in the right spot and rotating to enlarge from the underside would have been easier and more effective. When i check on the castable I'll see about freight but I fail to understand how it could be that high. Just have them crate it and put on a skid and go by over road truck carrier. Would need a fork lift on your end but you can find a way. In the past before I had the ability to unload pallets I had a local business receive the freight and then load it on my truck. When I got to the sugarhouse I had to unpack and unload by hand. Now i can lift up to 900# with the tractor or 2500# with the excavator.

[Russ]

Here are some pics of what Rhino has done to our firebox. He still needs to trim the outlet pipes on the inside to make them flush with the firebrick. The other pic shows the section of 3" irrigation pipe he's using as the supply manifold on the outside. There will be another on the other side.

[Gary R]

The inverted cone hole does look to be the best. I doubt they would ever plug. I didn't think about truck ship. I have now where to send it.

Russ, is that Aluminum pipe? What is the nozzle material? Sure it will hold up behind the brick, I just thought it would be an expensive welding bill. Looks like the inside of a force 5. Good job!

[Rhino]

Gary, The outside manifolds are aluminum irrigation pipe. They are 4 feet long and i drilled 1/2 inch holes in them. The nozzle pipes are just mild steel pipes. When i rebricked our arch this year and added the over air system, I put 2 layers of fire brick along the walls. I have a ton of it from a auction so i thought why not? The manifold pipes will be hitched to 3" aluminum flex dryer hose which is tee'd off to inject the air on both sides of the arch walls. I just used the rest of the irrigation pipe (22 feet) to run out the side of the sugar house and get connected to the blower fan. For our air input control we are just going to slice into the irrigation pipe and use a thin piece of metal to slide in and out to regulate the air. I also made a behind the fire air manifold system so it should be interesting the first start up this season. As far as the nozzle pipes melting....they might a little, since i did use double bricks they are all about 6 inches long so i can spare some damage, also would think as long as the blower is on they shouldn't get to hot.

[maple flats]

After setting the manifold in place it was too cold to continue. I had a propane torpedo heater but it needs more pressure and volumn than the new 20# tanks allow. The gas kept shutting off on safety. So, I been waiting for the first warm day. Tomorrow is it, temp should be mid to upper 30's and about 32 overnight. I'll fire brick and refractory mortor it tomorrow, put the pans back on and run the genny all night with an infra red light to warm the inside. The next day it should be ready to fire very slowly and should now be able to tap this weekend. I have the high pressure blower in place as of yesterday. I need to find a way to warm the bearings to start it for the first few uses. After I can put some very light grease in it should be good to go without. Right now the bearings have some old hard grease that is making things difficult. A little use and then a half pump of light grease every 2nd or third day will help loosen things up I hope.
Right now I'm thinking I should have waited until summer but I haven't yet lost any good sap weather. Tomorrow might be the first one but like I said, I'll tap this weekend if all goes well. In years past even when I tapped earlier I never had my first boil until march 5th or later, before that I saved up sap to have enough to sweaten the pans.

[maple flats]

I have the manifold refractoried in place. I kept an infrared light on it for 48 hrs to keep it from freezing. I then set the pans back on the evaporator. I am ready to fire a slow fire tomorrow to help it cure while I clean the pans in preparation for tapping. I had to plow for 2 hrs today because of the storm. The tractor wouldn't do it so I fired up the excavator, with a blade. It worked but the ground speed is only 1.1 mph, real slow.
When I go to the poured floor I am going to try some I have. My brother works at a repair facility where they do major service on commercial aircraft, like 727, 747, 767, airbus etc. One plane had to have some weight in the cargo area to stabilize it to be flown in for repairs. For some reason they used 50 KG bags of castable refractory. When it arrived the refractory was to be disposed of. My brother got 8 bags, others took the rest of the 20 some bags in the hold. I now have 3 of them to use, my brother is keeping the rest to re-pour the door on his outdoor Wood Boiler when needed. This may not be the right stuff but the price is right to try it. My plan is to make a 1/4" steel plate with holes on the prescribed pattern and then I'll make wooden tapered plugs to fit the holes and support them from underneath until the refractory sets. Then I'll remove the supports and drive the dowels down and remove them. I figure the 1/4" plate under floor will give all the strength needed. If not, I'll be casting another floor when this one fails.

[maple flats]

Spent too much time today moving snow, first at home for 2 hrs then at the sugarhouse for 2.5 hrs. After that I didn't want to boil water to clean up the evap because I wouldn't have had enough time to clean everything and then I would need to drain the pans, so I did some connection work on the air into the evaporator from the high pressure blower. A while back someone had a question about a high pressure blower. This one has 4 flat paddles in a cast iron cyclone housing. The paddles are flat, have rounded corners and really "throw" air out whereas a squirrel cage blower spins air out by centrifical force. There is no real pressure on a squirrel cage but this blower has a lot of pressure. When I have it all hooked up I have a gauge to tell me the pressure in both " of water column and PSI. I will then see if my pulley is the proper size, if needed I can change pulleys to go in either direction on rpm's to have the right pressure available. Then I can adjust my valves to regulate the flow. The guy who helped me says I will have too much pressure so I may need to reduce the drive pulley size if he is right, at present I have a 6" on the motor and a 3" on the driven, the motor is rated 1750 and I get 3490 on the driven at open discharge. The pressure at that was great enough that big bolts (5/8 x 6) setting on the bench about 20 feet away were blown onto the floor. He might be right.

[maple flats]

I thought I'd update this thread. Now that I have boiled on it all I can say is WOW.To bring you up to speed, I added high pressure air both under and over the fire as per the plans shown in the beginning of this thread.
I am getting 20 minute firings instead of 5 minutes. My boil is much faster and more even. My stack temps are up slightly at the top end and i am using much less wood. I can't yet report what boil rate I get because I have only boiled 265 gal down to about 30 which is all in the pans now (in the course of 3 short boils). I still have not been able to draw any but thought I might towards the end today (it got to 6 above). I add wood every 20 minutes, never shut the blower down and do not get sparks or ash out the door. The only time any comes forward is just a very slight bit on the initial lighting, which only lasts a few seconds. (I light using a 20# propane tank and a weed burner torch and make it roar into a 2/3 filled loading of well split cross stacked wood that has dried for at least 18 mos.) As soon as it lights I shut the doors, turn on the blower and it's off to the races. The first firing takes a few minutes to get going like an inferno but re fuelings only take 20-40 seconds. The boil is very uniform and all the way back and fully across the entire width once going good. Refuelings are going uniformly in seconds. I am using in the neighborhood of 35% less wood. I fuel every 20 minutes if all hardwood and every 15 if mixed with soft (I have a sawmill and the slab all gets burned)

[maple flats]

I posted some numbers in another thread called "things you see at night"

[Bucket Head]

Dave,

I'm glad to hear your rig is working well!

Can you explain how your nozzles are oriented? How many are on each side and front and rear of your firebox? Or are they not on all sides? Are they all in a single row or do you have multiple rows?

You may have covered this and I missed it, I don't know. Or you might have covered this and I was a little slow on the uptake.

Thanks Dave.

Steve

[Gary R]

Dave,

That sounds terrific! Be prepared for lots of questions. I think alot of guys might be tearing apart there arches. Looking forward to hear if the boiling rate increased.

[DanE.]

Maple Flats, How is the air over combustion working for you so far. when you get a chance could you post a picture or two. Thanks, Dane.

[michiganfarmer]

This is the type of unit you want will suck the chrome off a trailer hitch. neds good power and they are noisy. If you mount this out side about a 1/4 mile from the bldg your all set.
.

LMAO too funny

[maple flats]

Here's a link to pictures:
http://s1041.photobucket.com/albums/...sure%20blower/
I tried several different firing times but settled on 15 minutes which seemed to be the best. As the pictures will show, this gets built right into the arch. It was time well spent. I use about 1/3 less wood, boil about 10% faster and have a more uniform boil in the pans. I am still adjusting the valves to find the best setting and I have to adjust them by hand for now. I will be adding 2 large wheels to turn the handles and will make some reference marks for repeatability. What I need most is enough sap to get this all worked out. Now I'm thinking I will add the turning mechanics both on the same side, with one axle turning inside another and making an arm linkage from the axle to the valve handles which I will make longer to turn them easier. Only an idea so far but I'll make it during the off season. Also this summer I plan to remove the grates and cast a floor with 12 holes/sq ft for air as suggested in the report I got this from. I already have the refractory needed.

[murferd]

Can't get the link to work. Am I doing something wrong?

[erhino10]

with everyone looking for a high pressure blower why dont you just get a air pump for a hot tub that will work just fine they are less than $125 and will supply plenty of combustion air i use one now for air injection in my steamaway

[maple flats]

Try this one:
http://s1041.photobucket.com/home/Daveandjoanssugarhouse/index
The other one somehow got corrupted. Sorry. Let me know if this one fails.

[maple flats]

With new discussion surfacing about AOF, I thought this thread might be reopened. Reading from the top you will see the references for AOF design.

[WoodButcher]

Glad you unburied this Dave .

so , with the price and lack of availability of high pressure blowers, anyone look into the validity of using an air pump from a hot tub ? would be nice to save some bucks...

[maple flats]

The term high pressure is somewhat deceiving. The term here simplified: For AOF you want a blower capable of producing 3" w.c. (water column), this is actually less pressure than you might think. 3" wc=.108 psi, notice the decimal point is in front of the 1. The pressure is small but necessary. To achieve proper turbulence in the firebox for combustion it is necessary. If you can measure the psi that small, try it. However a squirrel cage blower does not generate that pressure, just lots of volume.
Can you see the impeller on the hot tub blower? if it has paddles rather than a design that resembles a squirrel cage, maybe. The next point is that it may have too much pressure or volume, either one will be counter productive, blowing the heat up the stack before the pans can use it.
If you read the link in the initial post, you will see that an old oil burner blower(post 1980) will work as a high pressure blower (that might be when oil burners started utilizing high pressure air to increase efficiency).

[tuckermtn]

I got my high pressure blower off ebay- its a dayton 4C129- was a surplus from a factory in Texas. Grangier wanted something like $650 without a motor. Mine came with a motor and was $350 with shipping. This for a 2.5 x 8 Jerry 802maple special...