Adjusting air during each load for max efficiency

[CampHamp]

Here are the question running around the boiler's head...

(1) Is there a study that recommends airflow changes within a burn cycle?

(2) I have assumed that a smoking chimney is bad (you can see the lost fuel!), but am I causing the whole burn cycle to be too hot by cranking the air initially?

(3) Once the smoke has cleared with enough airflow, should I keep it on that "no-smoke line" by throttling down as the fire settles?

(4) Wood loading frequency seems important -- is there any study on load times and fuel-efficiency?


What I do now:
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My goal is to minimize wood usage rather than get the fastest evaporation.

I have a blower pushing air over and under the fire of a 2x6 (RF). I like to start off with high airflow speed (otherwise I see smoke) and then reduce the speed through the burn. It just "feels" efficient, but I'm not sure.

The stack goes from 950F down to 800F with about a 7 minute reload-- if I load slower, then I'll spike to 1050 at startup. I like to mix hardwood in with the soft, otherwise I'm fuming smoke or my stack is at 1200+ with enough air.


Why I care:
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Maybe getting this right only saves 5%, but it could be 50% for all I know. Either way, when you do your own wood and feeling the muscles getting older, you start to care!

Even though I have a rheostat (a voltage chopper) to throttle the air back during the burn cycle, I am often distracted and don't do it. So, I want to automate it with a small motor that slowly covers the air intake over 7 minutes and starts again with a new load. I could probably do it just with a motor and a flap, but I'll probably use a micro-controller so I could use stack temp as input.

I did this on my wood stove (https://www.hearth.com/talk/threads/automated-airflow.161316/), so the mechanics are possible and I just need the "firing science" to get started. Any help will be greatly appreciated!

[Sugarmaker]

Boil as hard as you can as fast as you can, and try to keep from burning down the rig, stack or building.
Remember at any one time your only 15 seconds from disaster!
Keep boiling. That wood cutting is our exercise too!
If you want great control, think fuel oil.
Regards,
Chris

[CampHamp]

I expect "full speed" is the prevailing technique. It's a different priority when you have as many taps as you do. I could keep the stack over 1000, but I think I'd need twice the wood each year.

btw - Can't get oil here (or to the house), so plenty of exercise here!

[Sugarmaker]

Jamie,
If your making 60 gallons of syrup on 118 taps we could all learn some things from you! Nice job!
I have not read much about controlled air during the burn cycle. Dr. Tim might have something?
AOF (air over fire) may be something for you to look at if you dont have it? I reduced the black smoke when I went to controlled AOF. I believe I reduced the amount of wood consumed too.
Have you considered a small RO? They are the real work horse. Probably would cut your wood consumption 75%.
Regards,
Chris

[maple flats]

I doubt keeping it over 1000 degrees is good at all. I had that often before I installed high pressure Air Over Fire/Air under fire (AOF/AUF). Since then my typical stack temp is 650, sometimes 700-750. I run my rig as hot as I can but with AOF/AUF the wood and gasses burn under the pans and hot unburned gasses are not sent up the stack.
When I added my AOF/AUF I went from fueling every 7 minutes to fueling every 9 or 10 minutes, 9 if I have some soft wood in the mix, 10 if all hardwood. In the process my boil increased about 30-35% and my wood consumption dropped by about 25-30%. That's a win/win in my book.
If you see a fireball at the top of your stack it is not because the flames went the whole distance, it is because hot wood gasses used up the oxygen and re ignited when they got new air. Hot gasses burning at the top of the stack are BTU's wasted. Give the wood all the air you can and use the heat to make syrup, do not slow it down, that will be a false sense of efficiency.

[CampHamp]

I've got air over, under and even some under the sap pan! And a fan that will make the stack look like a bellows, out of control.

My rig will do 50, but I run around 40GPH. I think keeping the stack within 800-900 seems right (not pushing too much heat outside).

I'd love to know if there is any wood "loss" in driving it fast (there must be some point of diminishing returns) and if anyone knows if altering the air during a burn is helpful (it certainly is with a wood stove).

And yes, I get great vacuum on good trees. I run solo, so March is busy!

[Sugarmaker]

Jamie,
Don't change a thing! Just tap'em and hang on for dear life!!! Nice work.
What type of controls do you have on the air systems?
I have a four position dampe (gate) on the AUF, plus two speed on the 550CFM blower.
I have a incoming valve for the AOF and then a control valve for each side of the arch too.
I watch stack temp and smoke and adjust accordingly. Also I don't shut any blowers down when firing.
Regards,
Chris

[CampHamp]

What type of controls do you have on the air systems?
I have a four position dampe (gate) on the AUF, plus two speed on the 550CFM blower.
I have a incoming valve for the AOF and then a control valve for each side of the arch too.
I watch stack temp and smoke and adjust accordingly. Also I don't shut any blowers down when firing.
Regards,
Chris

You've got tons of valves to play with! I have just on/off/speed.

I need to turn mine off or ashes in the face. I use a wireless remote by the door.

Boiling now. Some fresh pics...

Air manifold releases underneath, then up the front and over fire by the door. Also, the air opening to under the sap pan shown.

1626216263

I'm using a plastic 5G paint lid to cover one side of the intake (slide it for more/less air), but am playing with this voltage regulator and there is a choke coil to reduce voltage (I have a permanent split-capacitor that really shouldn't be controlled with that type of rheostat, but had to try anyway).


1626516264

Stack reader i made that beeps at 800F, asking for wood.

16266

[CampHamp]

In the process my boil increased about 30-35% and my wood consumption dropped by about 25-30%. That's a win/win in my book.

Sweet! I need to keep track myself. I would need to weigh the wood feed to get this picture for a single-boil. Not too hard...

[Sugarmaker]

Well I think you have a good handle on making syrup. I would suggest adding throttling valves and or dampers to all your air systems. Gives you something else to play with too!
I do get some ash coming out the door but it keeps a pretty consistant boil.
Your much advanced on the stack temp monitor and alarm compared to me. I have a bolt on exterior thermometer and it hovered at 400 F all season when up to temp.
Its OK to have to much air available but with the controls you don't have to use all of it. And you then can adjust to optimum boil rate. I like to watch my pans and if I have full bubbles in every part of the old 3 x 10 then I think we are doing the best we can.
You posted that your rig will do 50 gph. (that's humping for a 2 x 6) But your running at 40 gph. So you have already dialed back a little. So did you get a feel at you used a lot more wood at 50 GPH? Pan and arch efficiency are also things that will change your wood consumption. And your stack temp!
FYI I think I am boiling about 130 GPH on my rig. Its a lot bigger. So I think your giving her all shes got and getting just about all you can out of it!
Like you, I have my systems set up to be able to do it all myself. Cut, move, stack wood, tap, gather, boil, filter, can, clean up and make value added products. Sometimes friends are around visiting or helping fire the rig for a while, and just to make sure I am still alive.
So you have grown, how big are you going to get?
Regards,
Chris

[CampHamp]

130GPH is flying! I'd have to remove my roof to let that much steam out.

I never really measured the wood intake at different boiling speeds. Without the blower, it seems so slow and less efficient. I'm obviously consuming wood much faster when cranking, but maybe the steam is proportional...

I don't sell any syrup, so I've kept it to this size for now. My family/friends can only consume so much syrup and any visitor gets a bottle already... even that guy I don't like.

I do have many more trees, so I have thought about going that next step into selling. I'd probably get an RO at that point. I'm afraid scaling up any more would take the fun out of it, though.

[Michael Greer]

This is interesting...My brain does callisthenics too. I'm not sure I would have time to pull off anything like what you describe. On my rig, I fire it, then fetch more wood for the next firing, glance at the level in the flue pan, check the thermometer, maybe there's a pot on the stove finishing and so another thermometer, get out some new bottles, rinse out the old filters, take a gulp of water and oh! it's time to fire again, I wonder what's left in the tank, add a drop of defoamer, check the pump that's filling the head tank, open the loft doors to let out some steam so that I can glance at the level in the flue pan, warm up the filter tank, oh and I changed gloves at least four times going from hot fluids to hot firebox. It goes on like that for six or eight hours sometimes, and maybe I remembered to put my sandwich on top of the steam hood to warm up. I haven't added thinking about the airflow yet, but it will probably pop up while I'm doing all the rest tomorrow. Yikes!

[nymapleguy607]

On my arch there are dampers for the AOF in the back, the air through the door and the air through the grate. When I boil I like to keep my stack temp at about 1000-1100 degrees. I am firing every 7 minutes usung hemlock slab wood. Typically I reload the firebox and then open the door air and back air and just crack the AUF. The temp might drop 100 degrees but starts climbing once the door is shut. I usually have to open the AUF about 1/2 way through the firing cycle, and usually open it fully at the last minute of the firing cycle. Otherwise I get a really big coal pile. I might be running a bit hot in the stack but running this way with the steamaway allows me to eat through about 90gph and make 5-6 gph of syrup depending on the concentrate level

[Sugarmaker]

Yikes 90 gph on a 2 x 6! That's movin some sap!
You guys are doing good.
I like Michael's comments, sounds about right. But I only use gloves to fire.
Regards,
Chris

[maple flats]

On mine, AOF/AUF all on one blower, the air comes into the sugar house and runs under the arch in a 4" PVC pipe with all ells being long sweep type. Under the arch it splits into 2 @ 3" each and each 3" has a 3" ball valve. The AOF ball valve is open about 70-75% and the AUF ball valve is open about 25-30%. Initially I shut the blower off at each fueling but then once my grandson fueled and forgot to shut the blower off. I noticed he got no smoke nor sparks out the front and the blower has run from about 3-5 minutes after lighting the fire until the last coals are burned up at shutdown. The first season I tried lots of different valve positions but found the best performance was what they have now been at and unchanged for 8-9 years.