bricking a drop flue rig

[ejmaple]

last year i bought my first "real evaporator" a 2 x 4 grimm drop flue. i did some research on maple trader on how to brick it and thought i found the correct way. the way i did it i built a vertical wall right at the end of the syrup pan right up to the bottom of the flues and ran that to the end. my question is other than did i do it right, is should i have followed the arch angel built up to say the midpoint of the flue pan. last year it seem to boil real hard at the front but not as much in the back. thanks ed

[Brent]

I don't think you should have a vertical wall in it. If there is a sloped wall from the back of the grates to the mid point of the flue pan, then you should cover that slope and the sides with brick or 1" arch board covered by bricks.

[dschultz]

By bricking up tight to your flues I think you just lost 3/4's of your draft

[3rdgen.maple]

You should follow the ramp. The ramp directs the heat up into the flues. From the top of the ramp the brick should be relativevly close without touching the flues. A ramp going to the midpoint of the flues is the norm.

[RileySugarbush]

But it's a drop flue, and there is no reason for a ramp. A vertical back wall works absolutely great and a ramp is less efficient. There is plenty of flue area between the drops, certainly more than the stack area. I'd leave it the way it is.

My 2x6 drop is configured this way and works great.

[3rdgen.maple]

It might work great now but if you had a it would work better. Atleast that is what the guy told me who built my evaporator for a living. I questioned this when I asked him about bricking. He said brick it like I built it if you don't you will choke it out and not get the most out of the heat. I gotta take his word for it. My flue pan boils hard front to back.

[Jeff E]

The only downside of having the brick right up to the bottom of the flues is that as soot drops off the flues, you will loose surface area of you pan getting touched by hot gases. I kept a 1" gap under my flues, and it was mostly filled in in a season worth of burning (7 logger cords of wood).
Regarding the wall or ramp question: was your boil good on you pan? You can make changes based on your boil. I would go with that rather than input from some dude in Wisconsin (me) :)

The goal is a full boil in you whole pan. For example, if it is only boiling in the back half, you need to move your wall forward.

[RileySugarbush]

Mine boils hard front to back. 45 to 50 gph in a 2x6 with a short flue pan There is no noticeable difference front to back, though if I didn't have forced draft I may see a reduction in draft with the vert wall, but I really doubt it. There is plenty of flue area. If your stack bases temp is high, the back of the pan will boil hard.

Also, to set the record straight, I have a less than 1" between the arch flue floor and the pan flue bottoms. They don't touch the blanket there.

[Brent]

Getting a hard boil front to back is one thing. As you say with the blower you've got it. What's next to impossible to determine is how efficient your wood consumption is.

If you have a hard boil at the back, you're likely losing more heat up the stack than you should. But if you've got more than enough wood and more than enough time to cut it, go for it.

[3rdgen.maple]

Riley you are on a home built arch though. There may well be a difference in your setup compared to ejmaples arches. Such as stack diameter, size of the firebox, how wide it is. Stack height etc etc etc. Yours might work great with a wall but his was designed for a ramp. By the way 50 gph on a 3 foot flue pan is one heck of a number. Are you running any add ons to get that?

[RileySugarbush]

Nothing too special about my geometry. I have a well insulated arch, small firebox, only about 20" deep. I think that the firebox should be a small as practical to maximize the length of the narrow flue path. We cut our wood to 16" long to fit in the small area. My flue area has about a 1/2 to 3/4" gap under the flues and there is a turbulence inducer (a intermittent row of extra fire brick pieces) at leading edge. These stick up a couple of inches above the bottom of my drop flues so it is hard to even see the flues from the firing door.

Combustion air is forced up through grates at 200CFM, with a little added air over (maybe 60 CFM) that I'm not sure is doing much yet. I may switch the fans around for more over and less under based on what I have learned here.

8" diameter stack 14 feet tall and wide oval base stack. Base temp with external magnetic thermometer is 600-700°F. Occasionally hot enough to make the magnet let loose. Hood over the flue pan with serpentine preheater for 180° sap.

Small split wood hardwood, mixed with scrap baltic birch plywood, fired regularly is needed to hit a steady 45gph plus as measured on a flow meter on the sap inlet. Never under 40, occasionally up to 50 gph. We get no smoke out the stack, though the birch sends sparks to a remarkable degree. Virtually no ash at the end of a season. We can hold that rate for hours if we keep on it, (firing about every 6 min) without the pan level changing so I believe it is real. It is born out over a day in how much sap we go through too.

I really like this rig and add or change a little bit every year. New airtight front this year to reduce the ash in the sugarhouse. I'm not changing the flow path from the firebox through the flues though. It works great!

[Woodland Acres]

I assume your talking about your flu pan.Cold sap is entering the back of the pan and due to the small surface area it would boil harder. Also you lose a certain amount of heat thru the fire brick, put in arch board before bricking and follow the way the arch was built.

[vtsnowedin]

Virtually no ash at the end of a season. We can hold that rate for hours if we keep on it, (firing about every 6 min) without the pan level changing so I believe it is real. It is born out over a day in how much sap we go through too.

I really like this rig and add or change a little bit every year. New airtight front this year to reduce the ash in the sugarhouse. I'm not changing the flow path from the firebox through the flues though. It works great!

This puzzles me. I think a cord of wood has a fixed amount of ashes in it as ashes are the chemical components of wood that are not converted to gas and burned away in the fire. If you have no ashes left in the ash pit at the end of the season then you must have blown them all out the stack and they have rained down on the trees and cars down wind of the sugarhouse. You could have more ashes if you had a very poor fire that left bits of charcoal and clinkers in the ash pit but any serious arch fire should have very little of them. Even so you should have a five gallon pail full or so for each cord of hardwood burned. Where am I wrong here?

[ejmaple]

thanks for all the input maple trader users. just a comment about a few responses about following the ramp or design of the arch. my arch is a constant angle starting from the fire box to the end of the arch with no added sheet metal ramp inside the arch. iam fairly new to evaporaters but from what ive seen this type seems typical, i have also seen added sheet metal ment for a ramp that seems to end around the center of the flue pan. since my doesn't have that, is it ment to be bricked with a constant ramp all the way to the back? or should one know to build the ramp steeper and end it the center? like i stated in the begining i built a vertical wall right at the end of the fire box and continued it to the back. it seemed to work well, it boiled harder in the front and one time at the end of the season after a real long boil soder started to drip off some flue welds and caused a leak.

[KenWP]

It is possible to totally burn wood up and have nothing left. Just depends on the amount of heat present. Ashes that drop thru the grate just haven't been exsposed to enough heat before they drop thru. All the little bits of charcoal are potential heat not used up.

[RileySugarbush]

Certainly some small amount of ash escapes up the stack, as evidenced by the sparks seen an night. The forced draft does blow the fine stuff around, but it also assures that anything that could fall through the grate will be consumed by the up flow of air instead of falling down and slowly burning out.

I'm not kidding, I cleaned it out after two seasons full seasons and it was less than a half a 5 gallon bucket. And no, the area around the shack isn't grey with ashes!

[RileySugarbush]

EJ,

If solder is dripping you are on the verge of a serious problem! All parts of pan that are exposed to the fire/flue gases should be filled with sap and never get even close to melting.

[Slatebelt*Pa*Tapper]

heres the inside of my maple pro un-bricked

you can see the ramp going up, looks like its going up to about mid way of the drop flues..

http://img.photobucket.com/albums/v185/hinkjc/Maple%20syrup%20Making/U3101009.jpg