Vent for secondary combustion in maple evaporator

[MaplePittsburgh]

Hey guys. I made an evaporator from an old heating oil tank and put a baffle so that the exhaust heat has to run acrossed the bottom of the pans before exiting the chimney. Right now my middle pan is by far the hottest. I am considering running a tube as a vent that would pop up right at the front of the baffle. To do so, I would just cut a piece of junk exhaust header and run it through the baffle and exit out of the bottom or back side of the firebox. Thinking this might help to keep the exhaust gasses ignited right until the chimney and maybe heat up the back pan a bit more. I have seen things like this on woodstoves but wondering if anyone has any insight as to whether this would be a good or bad idea for my setup. One concern is that maybe it would draw in cold air and not ignite it which could cool things down. I guess if that happens I could always plug the tube though. Right now I have vents below my door, going across the hot coals but no vents near the baffle. Below are a couple pics of the evaporator for reference. Interested in some feedback if anyone has more experience with evaporator design... 17609176101761117612.

[RileySugarbush]

You are on the right track, but a simple vent will probably cool your pans since the added air will not mix evenly. What you are talking about is an AOF (air over fire) system. There is a lot of information on here about setting up such a system. The basics are small nozzles and a high pressure blower to get a small amount of high speed air to mix oxygen in just like you are hoping for.

It is unusual to try that on a barrel and steam pan setup, but it might work.

A better first step would be to put a fire grate under your wood if you don't have one yet and then add a low pressure blower to force air up and through the grate. You will see spectacular results with that. You might want to consider some insulation inside your arch so you don't melt your kneecaps! Have fun!

[MaplePittsburgh]

Thanks! The AOF system is probably a little much for my budget setup. I would love a blower if I can find one laying around. Right now it really boils hard enough for my volumes but anything that would be free to do, I am all about trying. It is just fun to try to make it more efficeint just for the heck of it. I might try to rig up a grate before this weekend and see what that does. I am thinking that even without a blower, it might be nice for the vents to be pulling air from under the logs. The chimney makes a pretty serious draft when I get it stoked up, so I get pretty good flow through the vents but nothing like a blower would create.

[maple flats]

Looking in your fresh air inlet, it appears very restricted, try keeping it clear there. Then, do you have a grate in it? That helps distribute the air under the fire better.
I also agree, trying AOF without a high pressure blower likely would do little or nothing to help and as Riley said, it may well cool the pans.
Even when you do put AOF the air points down into the fire not up at the pan.

[berkshires]

Putting a grate in will help a huge amount. Right now the fresh air is coming in and some of it is going through your fire, some is not. That's probably a big part of why your front pan is cool. I made a grate in an hour by just chopping up some fencepost and screwing the pieces together. Works perfectly, and it's cheap! Here are a couple of photos:

http://mapletrader.com/maplegallery/data/649/wings_cindrblock_grate.jpg

http://mapletrader.com/maplegallery/data/649/mod4_with_trough.jpg

One note - leave bigger gaps between the bars than I did. I think I'm probably not letting quite enough air through. I plan to open those up when I have time.

Gabe

[MaplePittsburgh]

Awesome Idea with the fencepost. I will totally do that before I fire it up this weekend. Looks like a pretty legit design you have there. What is the box hanging off the side for? Warming?

[berkshires]

Awesome Idea with the fencepost. I will totally do that before I fire it up this weekend.

Thanks! It really helped my boil a lot.



Looks like a pretty legit design you have there. What is the box hanging off the side for? Warming?

LOL, "legit" is one word for it. It's kind of a scraped-together-out-of-spare-stuff-lying-around evaporator, but for its size, it works great!

The troughs hanging off the sides are for pre-warming sap. Because my firebox is so small, there really isn't room for insulation and brick, so the sides get really hot. Figured I'd take advantage of it. The sap in the pre-warming troughs winds up around 150 - 180 as it cycles into the pans.

[MaplePittsburgh]

Awesome, berkshires. I will have to look around for some stainless steel containers that I can use to preheat/insulate. I don't really want to buy a bunch of fire brick, and I don't really mind some heat escaping to keep me warm but right now it is a knee-melter.

[maple flats]

Heat out the side is heat that adds nothing to the boil.

[berkshires]

Just be careful. If you really get it cooking, you can warp the sides of the evaporator. Mine is all warped like crazy after only two seasons. Didn't cost me anything to make, so I just chalk it up to a learning experience. I will probably have to replace it before too many more seasons.

[MaplePittsburgh]

This should help! I made a grate from steel fence posts that sits right above my vents, inspired by berkshires grate. I also threw a few pavers along the sides. They aren't fire brick, so there is a chance they will crack but for the price difference, I don't mind replacing a couple each season. 1762817629

[RileySugarbush]

That's much better! If you can, you should double the number of bars in the grates. You don't want the coals dropping down into the ash pit. Better if they sit on the grate and the air coming up through will burn them up. Less ash, more heat. Plus the air is better distributed across the width and length of the fuel. make sure there are no short cuts for the air in fort of or back of the grate. Block off any with more of the at brick. Air that goes around the fire will decrease your effective draft and cool the pans.

You are going to have fun with tis! I made lot's of great syrup with my old steam table pans!

[MaplePittsburgh]

I can do that! I just need to go grab another fence post from Lowes. Makes sense that you would want all the hot coals to stay above the air source so that it has to blow through them.

[MaplePittsburgh]

Ooh, I also have some chicken wire I could tack under the grate to hold the coals up. I might give that a try first and go from there.

[maple flats]

I don't think you want the chicken wire but you only want a space of about 3/8" opening between the posts. If you look at the picture where posts were suggested, those posts when installed give a U shape to hold ashes and then the spacing to the next post is on top of the open U shape. That way ashes fill the U to protect the post and air flows thru the space. I'm not sure the T post you used is ideal for that.

[berkshires]

Chicken wire will just burn up. Definitely more fence post, and yeah, I'd recommend the "U" style rather than "T" style.

[berkshires]

BTW, if you're curious to know any more of the details about my franken-stove-evaporator, here's a link to a post where I showed how I made it: http://mapletrader.com/community/showthread.php?29303-Evaporator-from-small-wood-burning-stove-cheap!

[MaplePittsburgh]

Thanks for sharing! I am going to boil tomorrow with this wire fence stuff I stuck in there. I don't think it will last long but I can at least test the idea. Probably my best bet is to go grab a u shaped fence post and fill in the areas in between with it so that the coals don't drop through. Thanks for all the info! This has helped a lot!17647