Request for Air Over Fire Pictures

[82cabby]

Hi all!

I am working up plans to add air over fire to my barrel evaporator. I have been using AUF for years and it works well, but I am not real efficient when it comes to cords of wood / gallons of syrup. I am hoping to up the GPH of my set up and hopefully use less wood to make the same amount of syrup.

I have read every post I can find on AOF and I think I get the idea, but could really use a few images to get me started. If you have pictures of your Air Over Fire set up, would you mind posting them here?

To start off, here's what my stack looks like during a boil with my current set up..... I think I might be blowing a lot of excess heat out the stack!

http://img.photobucket.com/albums/v282/dkutina/Maple%20Evaporator/2013-03-101914271_zps60f90e9e.jpg (http://smg.photobucket.com/user/dkutina/media/Maple%20Evaporator/2013-03-101914271_zps60f90e9e.jpg.html)

thanks in advance!

[RileySugarbush]

(https://www.youtube.com/watch?v=LhiEyMjVx5g)
Here is a walk through of my over/under system that has been installed in my 2x6 for several years. This is the manifold and blower system before it was installed.


(https://www.youtube.com/watch?v=LhiEyMjVx5g)

https://www.youtube.com/watch?v=LhiEyMjVx5g


As it is, the AOF is roughly 100CFM through 16 jets at about 80 mph exit velocity. I think that is too much air, and I will probably get a higher pressure blower and reduce the nozzle size for higher speed and less volume. I might try one of those bounce house blowers from Koala.

[adk1]

Wow that's a hot stack may wanna a damper in that rigs stack

[82cabby]

Wow that's a hot stack may wanna a damper in that rigs stack

Believe it or not...there is one.

[82cabby]

(https://www.youtube.com/watch?v=LhiEyMjVx5g)
Here is a walk through of my over/under system that has been installed in my 2x6 for several years. This is the manifold and blower system before it was installed.



COOL! Thank you for posting that. I really helps to see it. I like the method you designed for controlling the flow.

[CharlieVT]

I can't tell you how this is going to work as it is an experiment in progress; I have only done one brief test fire so far. Last year I converted a Grimm oil fired 4x10 to wood burning with AUF. I used the oil burner as a blower by disconnecting the burner section which left a squirrel cage blower. This worked really well, but I wanted to increase efficiency and burn less wood.

I can weld, but building a manifold inside the arch seemed time consuming, so I decided to try another approach. I installed two rows of 3/8" nozzles along both sides of the fire box by removing the top courses of fire brick and then re-mortaring the nozzles in between the bricks. I drilled holes through the outside of the arch so the nozzles communicate to the outside. This document http://www.uvm.edu/~pmrc/Combustion.pdf suggests nozzles every six inches, my spacing was determined by the length of the fire bricks broken in half. I have two rows of eight nozzles on each side of the firebox for a total of 32 nozzles. They are flush with the face of the brick and angled down as descriped in the UVM document.

I bought a couple of low profile clothes drier vents like this: http://www.lowes.com/pd_84556-131-L3006_4294857914__?productId=3240566&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FNs%3Dp_product_qty_sales_dollar%7C1&facetInfo=

With tin snips, pop rivets, and high temp sealant, I fabricated manifolds from the dryer vents that I fastened to the outside of the arch. In this pic you can also see the knotted nylon cord used to open the damper. By using a pull cord to open the damper and a bungee to close it, I avoided fabricating a "push-pull" control rod.

http://mapletrader.com/community/attachment.php?attachmentid=8265&d=1388230450

I bought a Grainger #7C447 high pressure blower. This blower is connected to the dryer vent manifolds using a "T" and flexible aluminum ducting.

http://mapletrader.com/community/attachment.php?attachmentid=8267&d=1388230453

I built two dampers, one for the AOF and one for AUF blower. These dampers are self closing by bungee cords, and held open by nylon cords with knots in the cords.
http://mapletrader.com/community/attachment.php?attachmentid=8271&d=1388233970

I mounted a flange with a notch in it on each side of the arch for adjusting the dampers.
http://mapletrader.com/community/attachment.php?attachmentid=8270&d=1388233440

Advantages as I see them at this point: The manifold setup is quick and cheap; no welding, no steel purchased. The firebox remains essentially unchanged, the only modification being the nozzles mortared in between the bricks.

Disadvantages as I see them at this point: I have not installed nozzles across the ramp at the back or the front of firebox. After I see how it works this year, I may make that a project for next summer. Another thought I have is that the injected air is going to be a little colder that it would be if the manifold was inside the firebox; not sure how much difference this might make. I might eventually figure out how to capture some stack heat for the blowers.

[CharlieVT]

Do you have a damper on your AUF blower? If not, I think that is your first project. It looks to me like you want to throttle back that blower.
From what I have read, using a damper on the stack is not advisable.

Also, a stack thermometer is a good idea, I think you can find recommended stack temps for wood firing. You could control the stack temp and boil rate by adjusting the damper on the AUF blower.

If you go ahead with AOF, these are things you are going to want to do anyway.



Hi all!

I am working up plans to add air over fire to my barrel evaporator. I have been using AUF for years and it works well, but I am not real efficient when it comes to cords of wood / gallons of syrup. I am hoping to up the GPH of my set up and hopefully use less wood to make the same amount of syrup.

I have read every post I can find on AOF and I think I get the idea, but could really use a few images to get me started. If you have pictures of your Air Over Fire set up, would you mind posting them here?

To start off, here's what my stack looks like during a boil with my current set up..... I think I might be blowing a lot of excess heat out the stack!

http://img.photobucket.com/albums/v282/dkutina/Maple%20Evaporator/2013-03-101914271_zps60f90e9e.jpg (http://smg.photobucket.com/user/dkutina/media/Maple%20Evaporator/2013-03-101914271_zps60f90e9e.jpg.html)

thanks in advance!

[82cabby]

Charlie-
Thanks for posting the pictures. Great setup!

I don't have a damper set up. You're right, I will make that top of the to do list. I use an electric leaf blower for AUF and have been controlling the flow with a speed controller from a ceiling fan. That was working so-so but I found I had to really slow the motor down a lot which it didn't seem to like. So I tried using duct tape to block off about 80% of the air intakes and running the blower at about 3/4 speed. That worked better and I had more control, but nothing like I would get with an adjustable damper such as what you have.

Thanks!

[BreezyHill]

With all that waste heat in the pipe I would think about a AOF preheater in the stack to reclaim some of those btus; and a little less air under, would help a little. I found that keeping the holes to the back of the fire box open and uncovered mixed air into the fire box and lowered my stack temp. You must be running around 1500 or better to glow that red.
Good Luck!

[Sugarmaker]

Wow I think you have plenty of heat in the rig, The stack is getting way to hot and you need to control that, maybe by turning down your AUF system with a damper. AOF systems at best try to burn the fuel more efficiently therefore as you suggested saving fuel. If you have flat pans then the system you have may not see much advantage with AOF. But if you want my concept I added my AOF system on top of the rails and it works pretty well. Both the AOF and the AUF do need to be controlled or you can get the arch and stack way too hot. Pictures of the AOF are on here somewhere. Good luck.
Regards,
Chris

[maple flats]

A couple of points. The damper is counter productive in an evaporator. Remove it for better results. Then the addition of AOF will burn more of the fuel gasses farther forward so it can be used to heat the pans. Heating the stack is too late, it does no good there. You also likely have a ball of fire at the top of the stack when viewed in the dark, also a waste of energy. The stack temp will drop and you will have no ball of flame at the top of the stack when you add AOF and get it adjusted properly.
You guys with those fancy adjustments for your AOF blowers, I question their use. I have both AOF and AUF running off the same HP blower (model unknown, but it is 16" in diameter and the paddles are 3.5" wide). My first season I experimented with settings and by my second season I found my best balance and effectiveness. I have not moved my 2 flow adjustment valves in years now. They stay the same from start to finish and the blower remains on while adding wood with no smoke nor sparks coming out the front. All I do is light a full lay up of wood (no kindling, just criss crossed wrist size wood filling about 2/3 high in the firebox. I then light a weed burner torch and hold the flame blowing into the space above the wood for maybe 5-7 seconds to warm the stack, then I aim the flames at the bottom of the stack of wood. In about 2-3 minutes the stack is fully involved, I turn off the torch, shut the door and turn on the blower. The blower then run until the coals are almost burned out at shut down. I make no adjustments. My HP blower feeds into the sugar house in a 4" PVC pipe, under the arch it y's into 2 three inch PVC pipes, and each has a 3" ball valve. One feeds the AUF and is only open about 25%, it connects to a 4" stove pipe that lays on the floor and has 3 rows of holes drilled 1/4" and it stops at a plug 8" from the front of the arch, the other feeds the AOF manifold and that valve is open about 65%. I did not test the WP of the AOF but it creates a super turbulence in the firebox. My boil is much harder in both the syrup and flues pan but my stack temperature runs lower than before. (I am using the heat to better boil the sap and less to heat the stack.) I had stack readings of 1200-1300 often, before AOF and a few times as high as 1500, and also had a ball of flame at the top of the stack. I now run between 800-900 stack temp mostly with a rare 950 and I have no flame at the top of the stack (because the gasses were burned under the pans). My boil is faster and my wood use fell. I used to fuel at 7 minute intervals befor AOF, since I have tried and used everything from 8,9,10, 12 and even 15 minute intervals. While all work, my best seems to be with 10 minute intervals. If I fuel at 8-9 or 10 the hard boil resumes as soon as I close the door and while the boil slows during fueling it does not quit. When I stretch out the fuelings longer than 10 minutes, I lose the boil while fueling and it takes several seconds to almost a minute to get back to full boil. Thus I have stuck with 10 minutes unless I have an open house or other visitors. Then I go 15 minutes and even 20 minutes depending on if I am running solo or have help. With a dedicated fueler I stay at 10 minutes, while I talk but more often I don't have a dedicated fueler when visitors come and I go to 15 or 20 minutes.

[CharlieVT]

Dave,
Thanks for this post. I always read your posts with interest and have learned a lot. I've only done two short test boils with my new AOF setup but it does seem to settle in at one particular setting. I look forward to finding the "sweet spot" for AUF and AOF settings and not fussing with them thereafter. I too find that I can fuel without shutting down blowers and get no blow back of anything out the door. I use your propane torch method for start up, that is a real time saver and uses very little propane. I have also noted much lower stack temps than before and yet my pans come to boil faster than the did before. I also look forward to experiencing your firing times. Last year was my first year burning wood and I am running my 4x10 solo, firing every 5 minutes in addition to doing the draw offs makes for a tiring session on the big sap days. :o
Thanks for all your guidance.


A couple of points. The damper is counter productive in an evaporator. Remove it for better results. Then the addition of AOF will burn more of the fuel gasses farther forward so it can be used to heat the pans. Heating the stack is too late, it does no good there. You also likely have a ball of fire at the top of the stack when viewed in the dark, also a waste of energy. The stack temp will drop and you will have no ball of flame at the top of the stack when you add AOF and get it adjusted properly.
You guys with those fancy adjustments for your AOF blowers, I question their use. I have both AOF and AUF running off the same HP blower (model unknown, but it is 16" in diameter and the paddles are 3.5" wide). My first season I experimented with settings and by my second season I found my best balance and effectiveness. I have not moved my 2 flow adjustment valves in years now. They stay the same from start to finish and the blower remains on while adding wood with no smoke nor sparks coming out the front. All I do is light a full lay up of wood (no kindling, just criss crossed wrist size wood filling about 2/3 high in the firebox. I then light a weed burner torch and hold the flame blowing into the space above the wood for maybe 5-7 seconds to warm the stack, then I aim the flames at the bottom of the stack of wood. In about 2-3 minutes the stack is fully involved, I turn off the torch, shut the door and turn on the blower. The blower then run until the coals are almost burned out at shut down. I make no adjustments. My HP blower feeds into the sugar house in a 4" PVC pipe, under the arch it y's into 2 three inch PVC pipes, and each has a 3" ball valve. One feeds the AUF and is only open about 25%, it connects to a 4" stove pipe that lays on the floor and has 3 rows of holes drilled 1/4" and it stops at a plug 8" from the front of the arch, the other feeds the AOF manifold and that valve is open about 65%. I did not test the WP of the AOF but it creates a super turbulence in the firebox. My boil is much harder in both the syrup and flues pan but my stack temperature runs lower than before. (I am using the heat to better boil the sap and less to heat the stack.) I had stack readings of 1200-1300 often, before AOF and a few times as high as 1500, and also had a ball of flame at the top of the stack. I now run between 800-900 stack temp mostly with a rare 950 and I have no flame at the top of the stack (because the gasses were burned under the pans). My boil is faster and my wood use fell. I used to fuel at 7 minute intervals befor AOF, since I have tried and used everything from 8,9,10, 12 and even 15 minute intervals. While all work, my best seems to be with 10 minute intervals. If I fuel at 8-9 or 10 the hard boil resumes as soon as I close the door and while the boil slows during fueling it does not quit. When I stretch out the fuelings longer than 10 minutes, I lose the boil while fueling and it takes several seconds to almost a minute to get back to full boil. Thus I have stuck with 10 minutes unless I have an open house or other visitors. Then I go 15 minutes and even 20 minutes depending on if I am running solo or have help. With a dedicated fueler I stay at 10 minutes, while I talk but more often I don't have a dedicated fueler when visitors come and I go to 15 or 20 minutes.

[82cabby]

Thanks everyone for the help and especially for the images! I am going to start gathering materials for fabrication.

I should also mention that this a barrel evaporator with a flat pan which is approximately 2.5 x 2.5. This is the evaporator, but I have since removed some of the firebrick and replaced it with insulation.

http://img.photobucket.com/albums/v282/dkutina/Maple%20Evaporator/P1030501.jpg (http://smg.photobucket.com/user/dkutina/media/Maple%20Evaporator/P1030501.jpg.html)

[maple flats]

For best use of the potential with that barrel arch, after you get bigger, extend it back to about twice the length. It won't burn any more wood, but it will make lots more syrup per hour.