Soot, Creosote and efficiency

[Brent]

This weekend I had the pleasant task (at least the weather was pleasant) of cleaning the bottom of my flue pan.

I was astonished first at how hard it was to get the crud off, and secondly how thick it was.

So about the middle of the 4th hour with the pressure washer I was thinking how much heat did NOT transfer into the sap because of this thick layer. Then I remembered last season noticing that when the fire had been going for a while and I had my little blowers injecting more air into the fire, there was virtually no smoke coming out the stack. But a few minutes later is was black and sooty .... right after I had put in a fresh armfull of wood. That cycle repeated. Black smoke for about 1 1/2 - 2 minutes after firing and then it burned clean until I reloaded.

So that has to be where some of the build up on the pans is coming from.
I'm thinking smaller more frequent refills will help. And warmer wood may help.
Ice cold wood is not going to burn clean and hot is it ?

The second thing that crossed my mind was starting the fire. Cold sap/syrup in the pans. Cold stainless steel. A cool poor fire for the first few minutes. That's got to be a recipe for getting creosote built up on the pans. I've got giant propane "flame thrower" ( Lee Valley sells them for killing weeds) I was thinking to put that in the fire box for maybe 5 minutes to pre-warm the cold pans, then start adding wood.
The flame thrower burns perfectly smokeless.

( by the way I got a couple of high pressure blowers at an auction this summer, and will be mounting them so I can put as much air as possible on top of the fire without blowing everything out around the non-sealed doors. )

This creosote/soot must have been 1/64" thick. It was hard, almost flaking off with the pressure washer. I tried smokehouse cleaner - a very strong basic formula, that did almost nothing. Castrol's SuperClean was helpful, but it seemed only the top thin bit would come off with each pass of the pressure washer.

Any thoughts on keeping the build up to a minimum ???

[KenWP]

If you coat the pan with bar soap really well the soot will remove a bit better when you do have to remove it. I would say your right the cold fire creates the soot. Neighbour has a fancy wood furnace and uses only maple or birch for firewood thats at least two years old and his chimney was thick from soot and he wondered why. Turns out he dosn't have a hot enough fire and it soots up. I burn softwoods and have less soot because I try to keep the temps on the chimney at the range it's supposed to be.

[brookledge]

Brent
It sounds like you are not getting complete combustion. I don't think that will have any impact on how much creosote you have on the flues. You are only losing efficiency on the heat transfer to the pans.
When you add the wood and it burns black for a minute or two it is from a lack of oxygen. This is where adding air over the fire will help with complete combustion.
Think of it this way with a gas engine if you pull the choke it will make black smoke because there is too much fuel and not enough oxygen.
Keith

[3rdgen.maple]

Brent I clean my flues before I start a fire everytime. A few strokes down each flue with a flue brush helps. Keep them flues as clean as you can throughout the season to keep the heat transfer in the pan. I was told by a guy once who had a ss flue pan that never ever cleaned the fireside of the flues that one year he decided to and when he was done the pan was so pitted and full of holes that it rendered it useless. Dealer told him the soot will destroy a pan if not taken care of. I do not know how true it is but Im not taking the chance. I also at the end of the season I give the fireside of the flues a bath in oven cleaner and pressure wash them. Works pretty good.

[Brent]

Good idea but impossible on a raised flu rig.

Never thought of that before I ordered raised flu.

[3rdgen.maple]

Brent I think they make a brush specifically for a raised flue. Mine is a drop so I don't know if they work or not. I just put a broom handle on the end of my brush and reach in through the firebox.

[WESTVIRGINIAMAPLER]

About every dealer sells brushes for raised flue pans and brush them before every boil is a good idea.

[Brent]

There's only a half inch between the arch insulation and the bottom of the flues. I think it would be real tough.

Of course I could also rig up a winch system and raise the whole thing, hood and all. Phooooeyy

[3rdgen.maple]

Brent is there no ramp going up to the flues? If not pulley system might be the way to go, lucky you more work.

[Thompson's Tree Farm]

I use a flue brush on my raised flue pan during the season. There is an opening under the chimney in the back and I can also go in through the firebox. I am sure that It gets cleaned much better at the end of season but cleaning daily will help your boiling efficiency because of better heat transfer. I don't know if your flame thrower idea would help keep flues clean or not.

[PerryW]

I can reach most of my back pan with a flue brush, but to reach the back third of the pan, I have to slide it forward (so it must be empty)

I use a flue brush on my pans only once each season after I'm all done boiling. I have never used water or any cleaner on them, just brush it dry. It takes about 5-10 minutes. I also have never noticed and difference between boiling rates at the beginning and end of the season.

I usually will open the stack cover and wad up some newspaper and light it to get the draft to take most of the soot up the chimney while I'm brushing the bottom. I'll keep throwing small wads to newspaper to keep a real small fire going and most of the soot goes up the chimney. I still use a mask since breathing the stuff in is not good.

[petersp22]

Last season I learned what a good insulator soot is. I have a 20x36 flat pan and normally got 5.5 to 6 gph. It gradually got worse though, until one day last season I was down around 4 gph - very discouraging. I blamed it on my wood. But as I was cleaning up I noticed all the soot and creosote on the bottom of my pan. It was thick enough it was flaky. I used a wire brush on an angle grinder and it cleaned off real easy. Next boil was back up to 5.5 to 6.

After that I tried tweaking the flame path with vermiculite and cement board and got near 7 gph a couple times. A high performance machine!? Some of you big guys probably spill more than 7 gph.

[C.Wilcox]

The second thing that crossed my mind was starting the fire. Cold sap/syrup in the pans. Cold stainless steel. A cool poor fire for the first few minutes. That's got to be a recipe for getting creosote built up on the pans. I've got giant propane "flame thrower" ( Lee Valley sells them for killing weeds) I was thinking to put that in the fire box for maybe 5 minutes to pre-warm the cold pans, then start adding wood.
The flame thrower burns perfectly smokeless.


I think Brookledge is right that you are getting incomplete combustion in your fire and that is the main culprit in your soot formation, but I also agree with you that cold pans are part of the problem. Think of a glass of ice water on a hot day. Water condenses on the outside. Same thing with the bottom of your pan when you have cold sap over hot air. The pan sweats and gives your soot a place to stick to and starts the build up you're seeing. It would be further compounded if you were burning wood that wasn't fully dry. I have seen this first hand with chimney blockages in my dad's house. His chimney was tall (3 stories) and had a cold spot about 2/3 of the way up where someone used to have a pipe cut in, but it had been plugged with a pie plate. Every winter my dad burned wet wood and every winter the chimney would clog up at that point. I can remember him standing on the roof in January in the middle of the night with a brick on a rope knocking out the soot (with many choice words and phrases) so the smoke would leave the house. If you could bring the pans up to fire temperature before starting the fire you probably wouldn't have nearly the build up, but starting the fire and getting it hot takes time. Another thought would be to fill the pan with sap that was already 212F. Assuming you could keep the sap at 212 while the fire built up the pan shouldn't sweat. I'm curious as to how the weed burner experiment turns out. Keep us updated.

[Jeff E]

Agreed with the ideas, but I want to clarify that the pan bottoms will never get as hot as needed to keep soot from forming. The sap will always be below 220 Deg. So preheating the pans would seem to have a minor improvement.

Take a look at the fire brick in the arch. Mine look pretty much the same as when I put them in. Practically no soot or blackening. This tells me I have good combustion.

I do pay quite a bit of attention to my stack, if I am blowing visible smoke. For my arch, laying wood in in a cross hatch pattern, never letting more than 1/2 the wood burn down before reloading, and keeping the grates mostly clear helps me burn efficiently.

[Haynes Forest Products]

I would also choose wood that is low in creosote making pitch to start the fire and then use them during full heat firings. I also get build up on the pans burning oil but it cleans up with oven cleaner or a fine mist of deisel oil will help soften it up. Oven cleaner helps with both sides of the pans when you clean them.

[red maples]

try to get off what you can dry first then pressure wash then oven cleaner!!! Easy Off most common if you have a restaurant supply store near you they get industrial strength stuff. that they use to recondition old restaurant equipment. Spray it on let it sit for 5 minutes and spray it off with pressure washer.

air is one thing
is your stack legth ok
is your stack clean,
Green wood will create creasote
wet wood will create it
if your waiting too long between firing times especially burning pine so your fire might be cooling off too much before adding more wood
does your air feed in through the main doors or a third door underneath
get a stack temp gauge to make sure your getting it to proper temp.

even my wood stove in the house I try to keep it up around 400 during the day and at night I close it down, but I don't get much build up I usually clean it out in the begining of the season and in the mid february, just to make sure its not caked up and I rarely have a problem.

[220 maple]

Haynes Forest Products.
We abandoned Pine and Cedars several years ago, Sure it burns hot but it will creosote the bottoms of your pans, Locust and White Oak will burn just as good with no creosote. We always keep a couple peices of Pine handy if we're boiling in the day light hours and someone wants a picture of black smoke coming out of the smoke stack like a steam locomotive. Pine is for show not syrupmaking at are camp. just my 2 cents

Mark 220 Maple

[Bucket Head]

Has anyone else found pine wood to be a problem? What other woods are not reccomended for an evaporator?

We have burned just about everthing in ours over the years. Elm burns hot and smokes quite a bit too. But I really can't say for certain that it hinders the boil after prolonged use. We seem to have about the same amount of soot buildup each year at the end of the season.

Many times I have heard the reccomendation to burn both hard and soft woods in the evaporator. What soft woods are supposed to be used?

Steve

[3rdgen.maple]

Burning pine is not a problem. I burn alot of pine and there is never any black smoke coming out of the stack. Like another said as well the bricks in my arch are not sooted up at all. End of season I clean out what little grey ash is on there. I think how well wood burns from one guy to the next has alot to do with,,,,, The efficiency of your arch, how dry and not green it is, barametric pressure and elevation. If it is wood and not chemically altered burn it.

[red maples]

if your set up is right and your wood is well, all of what we have said already there shouldn't be black smoke. the pine tar(sap) From my unnderstanding is what makes the black smoke. Pine is cheap if you got hardwood to burn then go for it. but for me its pretty much what ever clean cheap wood I can get my hands on is what I'll use. And when starting your fire if yu can get it as hot as possible as fast as possible using newspaper, cardboard, fat wood what ever. and maintain that heat as even as possible and find a brush that you can get in those raised flues then you should have no problem.

[Brent]

Lots of good thoughts on this thread. Thanks guys

The stack and draw in the evap is good, the inside of the stack is pretty clear top to bottom.

We heat the house with wood and part way through the 3rd year we started to get poor performance so I shut it down and lifted the telescoping bottom pipe and got a flashlight to check for creosote. Nothing. Then I noticed I could hardly see any light at the top of the stack ... no daylight. Got out the ladder and found the cap on the stack was almost plugged with creosote. The stack goes up inside the house about 10' before switching to insulated pipe through the roof and on up to the cap another 8 - 10'. So the ice cold cap is getting creosote condensing on it and none anywhere else. I think the 40 degree sap is certainly not helping. I'll bet the bottom of the pan even gets wet with condensation the first few minutes. Gonna look in February when we start.

I think the cold wood issue is a big factor as well. There's a difference in burning wood gas, that you get when the wood gets cooked well, and sort of scorching the surface when you throw cold wood on the hot stuff. The evidence is the black smoke that I see for one minute after firing. The stack temp does not seem to react much. The bricks in the firebox are clean as a whistle, so the general combustion is pretty good, once it gets going.

As I mentioned in the first post, I picked up two 3/4 Hp blowers than I'm going to connect. Planning on putting a swinging gate on the end of the 4" pipe with 4 or 6 1" pipes going into the firebox. Then close the gate until I get blow back out the bottom, then back off a bit. Also planning to wrap some sheet metal around the stack so I can draw the air into the blower after it gets preheated coming down around the stack. The excess that does not get blown into the firebox will blow on the stack of firewood, to pre-heat that a bit.

All this sounds great. But I wonder how many times I'm going to scorch my balding head when I forget to open the pressure gate before I open the arch doors. I can only go so far before we get blow back and no air coming up through the grate.

By the way if you did not see it in another post, last year I had two little blowers, I think about 700 watts, blowing air into a couple pipes in the fire box. You could see the flames go to a white/yellow color and hear a rumble in the fire when the blowers were blowing. I can't get a 2 x 6 Hurricane but we're gonna have a rockin' little 2 x 6 this season.

[Brent]

Well after more grunting and pressure washing on Saturday, trying to get the creosote off, I took a bold step. Emptied the pan and let it dry. Maybe I should have left the soot wet. Anyway I took the giant blow torch to it.

In some areas I let it heat up to the point that the creosote started to flame with a red flame. I let it cool and then hit it with the pressure washer again.

The areas where I did little or no heating were just as stubborn as before. The areas that got the hotest flaked off !!!!:)

These appears to have been no effect on the pans. If the rains let up tonight I'll try it again. I left the pan upside down and full of water, hoping that when I heat it again the water may vaporized and help loosen the creosote. The heating made a huge difference in the time to clean the areas that got hottest. Like 50:1 Wish I'd tried this earlier.

As far as cleaning the syrup pan with nitre and calcium at the end of each day ... I think this heating may help. But the build up on the inside of the pans will have sugars and it may be tricky to heat to a point near, but not to scorching. We'll cross that bridge in March.