AOF on a small evaporator

[berkshires]

Has anyone added AOF to a small evaporator? If so, how did it go? How big was the investment, and was it worth the trouble?

My situation: I have a 2x3 Mason evaporator. I originally ran it with just natural draw, and it boiled a respectable 7.5 GPH. I then added AUF. That boosted my GPH by 50%, to over 11 GPH. But it probably doubled or tripled the amount of wood I use. I used to go through about a cord of wood a season, and this season I think it will be more like three cords. This is a big problem. Yeah, wood does grow on trees, LOL, but bucking and splitting all that wood will take a lot of time that I don't have. So this leads me to AOF.

I've heard that with AOF you get the benefits of a hotter more efficient evaporator, but without burning so much wood. But I don't know if this is something people do on little hobby evaporators like mine. Can anyone share your experience on this?

Thanks!

Gabe

[ecolbeck]

I find the idea of AOF very interesting, I would like to burn more efficiently and cleanly. However, I ultimately decided that an RO yields many of the same benefits, probably costs less, and is simpler to engineer.

[ecolbeck]

Three cords of wood for 6 gallons syrup is crazy. I burn less than a cord for 17 gallons. The problem with short evaporators is that there isn't enough length to really make use of the available heat.

[craigwade2005]

Something seems off there. I have the 2x3 XL and made over 34 gallons last season with probably just over 2 cord of wood. Agreed that was with a RO, but we aren't going that high with concentrate. I'd be curious what stack temp you are at and how close the bricks are to the rear of your pan.

To answer your question, I plan to add AOF when I upgrade this arch. I plan either stainless or black iron pipe in behind the brick, spaced with the ceramic blanket. Even if I don't use it, having it in place will give me the option.

[berkshires]

Three cords of wood for 6 gallons syrup is crazy. I burn less than a cord for 17 gallons. The problem with short evaporators is that there isn't enough length to really make use of the available heat.

Okay, so that much wood really shouldn't be necessary? Good to know. I am sure you're right about the length of the evaporator, but something doesn't add up, because my base stack is not even glowing. I don't have a stack thermometer, but I don't think I'm putting out a ton of waste waste heat. Something must be screwy about how I'm operating. I may try closing down the AUF even more (I have been running it about 1/4 to 1/3 open) to see if my evaporation rate stays almost as high without using wood as quickly.

GO

[berkshires]

Something seems off there. I have the 2x3 XL and made over 34 gallons last season with probably just over 2 cord of wood. Agreed that was with a RO, but we aren't going that high with concentrate. I'd be curious what stack temp you are at and how close the bricks are to the rear of your pan.

I don't have a stack thermometer, but the pipe coming out the back of the evaporator is not glowing (maybe a tiny bit if I turn out the lights when it's really roaring) so I don't think it's crazy hot. As for bricking, it looks like this: https://wfmasonwelding.com/bricking-the-evaporator/ except I added a second wall near the back, since I read that helps drive the heat up at the back of the pan.


To answer your question, I plan to add AOF when I upgrade this arch. I plan either stainless or black iron pipe in behind the brick, spaced with the ceramic blanket. Even if I don't use it, having it in place will give me the option.

How much do you think it will cost? I assume you'll also have to rip out all the bricks and re-brick the evaporator?

GO

[82cabby]

Just to check, everyone is talking face cords (4’x8’x16” give or take) as opposed to full cords (4’x4’x8’) right? I run a 2x4 divided pan with AUF and homemade RO. This year so far 29 gallons of syrup on +2000 gallons of sap using 3 face cords of mixed wood. I’m also debating adding AOF to them setup.

[berkshires]

Just to check, everyone is talking face cords (4’x8’x16” give or take) as opposed to full cords (4’x4’x8’) right? I run a 2x4 divided pan with AUF and homemade RO. This year so far 29 gallons of syrup on +2000 gallons of sap using 3 face cords of mixed wood. I’m also debating adding AOF to them setup.

So far this year I've made about 7 gallons of syrup on 340 gallons of sap, and I'd estimate I've gone through between one and a half and two *full* cords of wood.

Previous seasons before AUF I made 2 to 5 gallons of syrup using between a face cord and a full cord of wood.

GO

[ecolbeck]

Just to check, everyone is talking face cords (4’x8’x16” give or take) as opposed to full cords (4’x4’x8’) right? I run a 2x4 divided pan with AUF and homemade RO. This year so far 29 gallons of syrup on +2000 gallons of sap using 3 face cords of mixed wood. I’m also debating adding AOF to them setup.

That's a really good point. For my situation I was talking about full cords.

[berkshires]

People add in RO and other things that complicate things. Maybe a better way to talk about it is simply how much wood used per hour. I've run my evaporator about 31 hours so far this season, and used about a full cord and a half of wood, maybe more. You know those bundles of wood you can buy, like at Home Depot or the grocery store? I had to buy a bunch because I'd used up all my prepared wood. Well I found I went through about two bundles every half hour.

GO

[ecolbeck]

Based on those figures, you’ve used:

1.5 x 128 / 31 = 6.2 cubic feet of wood per hour

By contrast I’ve used:

15 cu ft/6 hours = 2.5 cubic feet of wood per hour

Having used AUF in the past, I’m surprised at how much it increased your wood consumption. That was not my experience.

[berkshires]

Based on those figures, you’ve used:

1.5 x 128 / 31 = 6.2 cubic feet of wood per hour

By contrast I’ve used:

15 cu ft/6 hours = 2.5 cubic feet of wood per hour

Having used AUF in the past, I’m surprised at how much it increased your wood consumption. That was not my experience.

Hmm... something is not right. I bought 18 bundles of wood, and they are .75 cu feet each, and they lasted about 6 hours. That's 2.25 cu ft per hour. Maybe the way I'm splitting my wood small it's not really 128 cubic feet in the wood crib, it's a lot less.

GO

[Pdiamond]

Most of the time that wood is typically a soft wood and it will burn really fast. You need to find some hard wood like beech, maple, or oak. Do you have access to any pallet wood. A lot of that is hard wood, even though it's cut small.

[maple flats]

Among other things, you need to prepare more wood for next year. Buying the high priced bundles is the most expensive way to buy wood. If you must buy wood, at least buy loose wood delivered, it will be cheaper, not cheap but at least cheaper.
I always tried and most times succeeded in having this year's wood and next year's wood as a season began.
When I first bought my RO I ended up having 4 season's worth ahead, even though I added about 700 more taps before the 4 years were finished..

[Chickenman]

To the OP, I too am interested in this idea. I'm running a Mason 2x3 and had considered AOF using black iron pipe on the outside of the evaporator and drilling through the sides for the nozzles to enter the firebox. Time and money constraints have prevented me from moving forward with the concept though.

[wvfdc4]

I'd be interested too, I have a 2x4xl. With the AUF I think I'm averaging about 15 gph firing every 7 minutes, but I am at 225ish taps this year and looking to hit 300 next year. I do run an RO but I will still take everything I can get.

[mol1jb]

Hey all,

Here is the thread for the home made AOF manifold I did for my 2x6 raised flue evap. It has held up incredibly well over the years and my welding skills are mediocre at best. It is all made from mild steel scraps I had around the shed.

http://mapletrader.com/community/showthread.php?33026-preheated-AOF-manifold-build

Let me know if you have any questions.

[bmbmkr]

Mine is a 2x6 raised flue. I bought used. The original owner had it bricked without mortar and claimed 25 gph on raw sap burning hardwood. I put 1" ceramic blanket in, mortered the brick, added AUF/AOF with a 650 cfm dust collector blower. I got it up to 54 gpm for about 20 min this season with 10% concentrate. I average 40-45 gph and this is a 20 ga Maple pro that was manufactured in 2008. She sat for many years un used, and thi year was the 5th season boiling. This year I added a 0.1-1 flow meter on my head tank so I could measure the evaporation rate. I'll also add that I'm boiling strictly with silver maple firewood, the next to least BTU wood you would ever thing to boil on, but my mature trees have been dying and dropping so cut em up & split em and boil with it. My firing time went from every 5 min on AUF on my old evaporator to 15-17 min with AOF on this one. This year I split the wood a little larger, 3-4" instead of 2-2.5" and it burns just as hot, a lot less labor during wood season. Stack temp running 800-900 when it drops to 800, I fire. I used all scrap 2" square tubing and only had to buy some 3" and 2" PVC for the manifold that I split the AUF/AOF air with. Definitely a time/money saver. I would recommend it, even on a smaller rig.

[tjanson]

The AOF ideas to increase fuel efficiency are very interesting as I also I have a Mason 2x4XL with blower. We run the blower at ~25% speed and get 13-15 GPH. The stack elbow glows a bit. The blower increases our boiling rate but it feels like it exponentially increases our wood consumption. I need to take some wood storage measurements but I think we used .6-.75 cord to make 4.5 gallons syrup off of 2% sap this weekend.

I had a suspicion I didn't do the bricking quite right and called up Bill Mason last week (after 3 seasons of my original bricking). He said to make the first wall after the firebox 2-3" to the pan and put in a 2nd wall 8" from the rear wall of the evap, also 2-3" from pan. I promptly got some more firebrick and just loose stacked them in to meet these specifications, as my first wall has 5" or so to the pan and I didn't have the 2nd one. I think it helped get a more even boil but it wasn't a night and day difference.

I think the 2x4XL could be improved with a traditional style pyramidal stack to put more heat into the preheater. I am going to at least change from a horizontal-ish exit to a wall thimble and external stack to a 90 degree elbow and internal stack to put more heat near the preheater. I don't expect it to make a huge difference to preheater performance but maybe worth a few degrees.

[CTguy923]

tjanson...i,m glad i saw your post, i run a Mason 2x4, but not the XL, i,m running a Smoky Lake divided flat pan on it...i noticed this year i couldnt get a boil thru out the whole pan, from the front to maybe midway back in all 3 chambers, i'll be revamping it over the summer to block it like you did yours, right now i have the front wall to about 2 inches under the pan and have the back filled with sand about 2 inches under the pan....also i run my exhaust vertical up thru the roof and my preheater pan gets to 125 or so degrees

[berkshires]

The blower increases our boiling rate but it feels like it exponentially increases our wood consumption. I need to take some wood storage measurements but I think we used .6-.75 cord to make 4.5 gallons syrup off of 2% sap this weekend.

Wow, so it's not just me. I think that's even more wood than I went through. I was able to do a clean calculation by buying those wood bundles. The ones I bought were hardwood. I split them to wrist size, and went through about 3.5 per hour. They say .75 square feet per cord. So to make about 14 gallons of syrup this season in 56 hours, I used 148 cubic feet, or 1.2 cords of wood.

I wonder if this is out of line with other folks who use AUF but not A OF with a small evaporator.

GO

[maple flats]

A full cord is 128 cubic feet. Use your off season, especially the spring shortly after maple season to cut and split firewood, split it to wrist size and give it time to dry. Even when I was boiling on a 3x8 raised flue, wood fired, the most I ever burned was just under 4 full cord, and that was with 1320 taps. However I did have AUF and AOF.
Right now I'm looking to get back into syrup production, but much smaller, and mostly sugar maples, but I will have some reds. I'm thinking about 200-300 taps, with about 225-250 on sugars, the rest on reds. Looking for a 2x6 and a 100-200 gph RO, plus a Guzzler 120V pump.

[berkshires]

A full cord is 128 cubic feet. Use your off season, especially the spring shortly after maple season to cut and split firewood, split it to wrist size and give it time to dry. Even when I was boiling on a 3x8 raised flue, wood fired, the most I ever burned was just under 4 full cord, and that was with 1320 taps. However I did have AUF and AOF.

Yeah, I definitely need to find time, and soon, to go bring down a few trees, buck, split, and stack them. I also need a day to make an additional wood crib, as the one I have just isn't big enough. Unfortunately, my family has been pretty patient with me running off most weekends for sugaring, and their patience may not extend to me continuing to run off every weekend now that sugaring is done, to play lumberjack. Well, I'll figure it out!

In an earlier post you pointed out that you tried to have two seasons of wood stacked and ready to go at the start of a season. Boy, I can see how that would come in handy. I was just going over my stats for this season, and depending on sap flow in a season, it seems to vary from 30 to 55 hours for me spent boiling. This year the weather lined up like it never has since I started sugaring. It was truly exceptional. If I'd had enough wood, I would have probably spent 60 hours or more boiling, and made three season's worth of syrup in one year. So I guess you want to be prepared in case you have a monster season like this one was for me.


Right now I'm looking to get back into syrup production, but much smaller, and mostly sugar maples, but I will have some reds. I'm thinking about 200-300 taps, with about 225-250 on sugars, the rest on reds. Looking for a 2x6 and a 100-200 gph RO, plus a Guzzler 120V pump.

I didn't realize you weren't sugaring. I thought you were still at it, just smaller. Anyway, good luck scaling it back up! Hope your health holds up and you can do it and have fun!

GO

[Chickenman]

Yeah, I definitely need to find time, and soon, to go bring down a few trees, buck, split, and stack them. I also need a day to make an additional wood crib, as the one I have just isn't big enough. Unfortunately, my family has been pretty patient with me running off most weekends for sugaring, and their patience may not extend to me continuing to run off every weekend now that sugaring is done, to play lumberjack. Well, I'll figure it out!

GO

How about making it a family event. Even little ones can carry wrist size pieces for a bit. I cut and buck, my wife runs the splitter. We both stack. Goes quick.

[Vtmbz]

2x4 drop flue pan here:
The old men in my Neighborhood say a cord of good dry softwood will make 20-25 gallons of syrup. Provably on a longer pan.
I cut and split fine a shed full of pine only, because it needs to be gone. The pile is 10x10x5 feet. Last year i made 85 gallons with some wood left over, usually boiling 4% sap.
I wonder if your blower is too large, making the heat go right out the stack. I bought a draft rgulator and thermocouple this year;
And found boiling at 900 deg seemed to waste wood. I dialed it back to about 750 d and got back on track.

[berkshires]

Maybe I'll get a stack thermometer next year. I doubt the stack is that hot, as it doesn't really glow. I only have my blower open around 1/3 of the way. When I dial it down more it seems like I get a fair amount of black smoke and the fire looks like it's starving when I open the door.

GO