Ash/Ember issues, temps drop throughout the day

[NTBugtraq]

I have an 18" x 5' CDL hobby arch with 42" of drop flues. The firing chamber is 25" long, so my wood was all cut to 24". No piece is more than 10sq.in. When I put it in the chamber, I make sure it doesn't touch any of the burning wood or embers. So for the first 4 hours of firing, I get great roiling boils with the chamber door closed and the flue on its first (smallest) opening setting. But after that, the temps seem to start dropping, and I am assuming its because the firing chamber is full of ash/embers. The result is that wood starts going in on an angle, higher towords the rear of the chamber, and as such, I get less heat under the finishing pan.

Anyone see this in their arch?

I'm actually considering letting the fire die at lunch time, removing ash, and starting anew for the afternoon.

What I don't get is why the ash doesn't fall through the grate to the chamber under the firing box. Every morning when I clean out the ash, 90% is in the firing chamber, and only a very small amount is under the grates. The grates are triangular, and I have them so the fire chamber has a flat bottom, meaning their widest dimension is facing up.

As it is, by the afternoon I have to open the flue wider and crack the door ajar to keep a full boil. This drops the temperature under the final channel of the finishing pan.

Thoughts?

[Super Sapper]

Sounds like you do not have enough space between the grates.

[buckeye gold]

I have two tools, a long poker and a flat hoe like poker that I push under the wood and work the ashes and coals through. You may need a little more space between the grates. This year when I extended the firbox i put new grates with big spaces in the back 8" and just push the coals and ash back. It worked well.

[NTBugtraq]

Tomorrow I am going to remove 1 grate and see what happens.

[Big_Eddy]

Russ
It is normal for the wood at the front to burn faster than at the back. It's getting more air at the front. Every few firings rake the coals forward to level out the bed before putting in new wood. You want to add wood at the rate it is burning away so if the coals are building up you should extend your firing cycle a minute or two.

A buildup of coals also suggests not enough air. Open that draft door all the way first thing in the morning and let it breathe. You mentioned somewhere else 9gpm - that arch should easily do 15gpm which suggest to me that you are not allowing enough air in.

10 sq in is pretty big. I'm currently burning 2x6 cedar decking and I split each piece into 3 before feeding so 4-6 sq in per piece.

Some wood is more prone to ash and coals than others. Just the way it is

[nymapleguy607]

When I start to get a big pile of embers I open the under fire air more and let it burn hard and it usually burns the coal pile down pretty well, granted I'm using a blower but you should be able to do the same thing by opening the arch door.

[loggerhead]

A better draw (longer flue, tighter seals) and raking the embers out twice a day helped us a lot with that problem. We rake them out with a metal dustpan. Tight grates, no blower, and burning white ash, so lots of ember buildup otherwise.

[NTBugtraq]

It's getting more air at the front. Every few firings rake the coals forward to level out the bed before putting in new wood. You want to add wood at the rate it is burning away so if the coals are building up you should extend your firing cycle a minute or two.

A buildup of coals also suggests not enough air. Open that draft door all the way first thing in the morning and let it breathe. You mentioned somewhere else 9gpm - that arch should easily do 15gpm which suggest to me that you are not allowing enough air in.

10 sq in is pretty big. I'm currently burning 2x6 cedar decking and I split each piece into 3 before feeding so 4-6 sq in per piece.

Hiya Big Eddy!

I assume you are suggesting I do a long fire periodically (like go more than 15 minutes without refueling) to get embers I can rake, as otherwise all I can rake are 24" long pieces of burning wood. Since I have been firing every 6 minutes with 2 pieces each time, I never have just embers in the firebox. Also, when I do open the draft door my boil at the front of the arch drops significantly. If I crack the arch door too, I can drop off boil altogether on the whole front pan. As for the wood, 10sq.in. is just a guess. All pieces have no side larger than 3", and all are wedges, so that would make them no more than 4-5 sq.in.

I went out this morning with the best of intentions, took out a single grate, lit it up and waited...only to then realize that the sap line is frozen...Yikes! Luckily I had an OMG bucket of sap that wasn't frozen...;-]

[Big_Eddy]

Good info Russ
For comparison I fire on 7 minute cycles. (My arch is a homemade knock-off of yours) Yesterday I would add the equivalent of 4 16" sections of 2x6 but spilt into a dozen or so smaller pieces. I open the door, use 1 pice to "flatten things out" and toss them in. After 7 minutes the last pieces added are still recognizable as burning sticks, but the ones from 14 minutes are not recognizable at all. I have been averaging 20 gallons an hour with the dry cedar - about 5gpm higher than normal.

As soon as I open the door, I hear the boiling change. I keep the open door time as short as I can. As soon as the door closes the boil will pick back up. I get the hardest boil about 45 seconds after firing. After 6 minutes the decrease is noticeable.

I had a time last year when I was having issues with coals. My solution at the time was to run my poker between the grates from below to clear out the gaps and allow air through. It worked well enough and did make a noticeable difference. That and emptying out the ash any time it started to build up. I have an old flat shovel that's been modified to suit.

[n8hutch]

I burn mostly oak & Hemlock. Some of it is probably split a little on the large side. Only time it really bothers is when I want to shut down & the big pieces take so long to burn. I have noticed that if I get into some Yellow Birch that I tend to get a lot of coals from that. I also try to push some of the coals back when I fire by the end of the day/night I usually end up with maybe 2 square shovel fulls of coals/embers that I will pull to the front. Definitely try to fire as quickly as possible, I try to only open one side at a time.

[beaglebriar]

With my 2x3 I split all my wood wrist thick or smaller and cut it about 18" long. 3-4 PCs every 6-8 minutes. I put them straight in first then the opposite way the next time. It keeps lots of air in the fire and burns up completely. With the real small wood I can shut down pretty quick. My grates have 1/2 " spacing. I prop my damper door about 1/3 of the way open and leave it. I'm kind of a rookie with this evaporator stuff but I've been playing with fire a long time. Burning standing dead unseasoned but dry maple,apple and ash and had no problem keeping a good boil.

[NTBugtraq]

So, bottom line up first.

My 18"x5' CDL Hobby arch came with 4 pieces of grating for the arch floor. 3 Doubles and a single grate. They left like ~.5" between the grates. Roughly speaking, that let 84sq.in" of air through a 432sq.in place (~25%). I took out the single grate, and re-spaced the others, and I went from boil to roil. I went from back pan 1/3 boiling, to whole pan roiling. I went from ashes/embers making firing difficult, to no problems. I went from flue door open wide and arch door ajar, to arch door closed and flue door at 1/3. I went from nothing @ +7F or above, to a continuous draw at +7F for 3 hours.

Down-side, the ash removal in the morning is harder cause a lot more is below the grates.

[maple flats]

I pull the coals forward when they start to build up, it might happen every 2-3 hrs. My firebox is 30" deep, but I cut mine at 21", leave about 5" open in front. I fuel every 9 minutes (but I have AUF and AOF, both high pressure). My wood is all split at about wrist size or slightly larger. It seems to work well. I burn mostly hardwood, but burn some softwood slab off my sawmill, mixed in.

[wnybassman]

Sounds like you were starving for air then, not making good draft to burn more thoroughly? In my 18x60 if I go 5 minutes too long between firings I have a thin layer of ash over bare grates. Hard to believe wood disappears that fast. lol

[NTBugtraq]

I finally had a day where I got no sap but did boil, and low and behold the boil rate is smack on 15 gal/hr, just what the arch is advertised as being capable of. I had been getting 9 gal/hr with the full grate in. Today I finished up another 2.6gal making my 2 day total (only 9 hours of boil) to 4.1gals. That suggests my sap is 33gals to the gal of syrup, or ~3%.

[Cedar Eater]

That suggests my sap is 33gals to the gal of syrup, or ~3%.

Is that how that works? I thought syrup was about 1/3 water and 2/3 sugar, so that would mean 2%, assuming no sugar loss during the boil.

[NTBugtraq]

Is that how that works? I thought syrup was about 1/3 water and 2/3 sugar, so that would mean 2%, assuming no sugar loss during the boil.

Well, syrup is what syrup is, what I was figuring was what sugar content my sap had. The variable in syrup is how much sap it takes to make 1 gallon.

[Cedar Eater]

Well, syrup is what syrup is, what I was figuring was what sugar content my sap had. The variable in syrup is how much sap it takes to make 1 gallon.

And if your sap was 2% sugar and 98% water and you boiled away 97% of 33 gallons, that would leave you with one gallon of concentrate that was 33% water and 67% sugar. Isn't that what 67 Brix means?

[NTBugtraq]

And if your sap was 2% sugar and 98% water and you boiled away 97% of 33 gallons, that would leave you with one gallon of concentrate that was 33% water and 67% sugar. Isn't that what 67 Brix means?

Fun with math.

Do you know how much sap you had?
Do you know how much syrup you got?
Do you know how much is left in your arch??

See, Turkey boilers always know things exactly, they know they had some known amount of sap, know some known amount of syrup, and there's no questions. I have some unknown quantity of nearup on my arch. I only know how much sap went down boiling, and how much I took off, not an exact science by any stretch of the imagination.

[Cedar Eater]

Fun with math.

Do you know how much sap you had?
Do you know how much syrup you got?
Do you know how much is left in your arch??

See, Turkey boilers always know things exactly, they know they had some known amount of sap, know some known amount of syrup, and there's no questions. I have some unknown quantity of nearup on my arch. I only know how much sap went down boiling, and how much I took off, not an exact science by any stretch of the imagination.

I'm just trying to make sure that I'm using the right formula for estimating the sugar content of sap from knowing the sap in vs. syrup out. It seemed like that's what you were doing. Sorry if I underestimated the sugar content of your sap.

[NTBugtraq]

I'm just trying to make sure that I'm using the right formula for estimating the sugar content of sap from knowing the sap in vs. syrup out. It seemed like that's what you were doing. Sorry if I underestimated the sugar content of your sap.

No need to be sorry, that is exactly what I am doing to guestimate the sugar content of my sap. I should add that I am not mentioning the varying brix level of my syrup draws. My first 1.65 gals were 69.2 brix, and yesterdays 2.6 gals were 68 brix. That would put the average over the 9 hours at 68.4 brix (or ~68.4% sugar), suggesting an even higher sugar content in the sap.

[maple6275]

Russ,

Great advice on removing one grate section. Just last night I was noticing the same coal buildup you describe. Looks like I'll be doing the same thing on my 18"x5'!

[NTBugtraq]

Russ,

Great advice on removing one grate section. Just last night I was noticing the same coal buildup you describe. Looks like I'll be doing the same thing on my 18"x5'!

Let us know if it works for you too!