Hoping for help diagnosing uneven boiling on homemade rig

[BlueberryHill]

I had a mason 2x3 that I used last year. Had it bricked and had a small blower. Had some late nights, as you would imagine.

So after much procrastination, I decided not too long ago to upgrade. I had enough stainless on hand already for a 2x4 flat pan so that is what I went with. We welded up an extension to the back of the Mason 2x3 arch. So now I have a frankenstein 2x7. I had a blower that came off a powervent hot water heater and in a side-by-side test it blew considerably stronger than the little Mason blower so I slapped it on there. It blows up though the ash box and through the grate. I insulated everything with 1" ceramic blanket.

Problem: The back pan does not boil very hard.

The front pan screams! A massive plum of steam comes off the front pan now. Way better than last year. I attribute that to the larger blower and the insulation. The back pan is not even a full boil. Forget about a rolling boil or anything. There is steam coming off, but really, its more just like a big preheater than anything.

There is not much of an "arch" to the arch. The stack outlet is on the back still just like it was on the mason 2x3. I know it would be ideal to have it go straight up behind the pan and have a shroud, but there was no time for that and the current location would have been tricky to set it up. (I don't want to cut up the roof in this temporary location) New, real shack coming this summer. Then I figure I will mod the stack outlet.

I took a row of bricks off of the brick wall behind the fire box so that I could ramp up the vermiculite a bit to the stack outlet, but it does not go up very much. Maybe 3" rise over the 5 feet. Kinda stuck on this for the moment, I think though because of the location of the stack collar.

So is it the arch config that is my problem? Is my blower too strong? Stack too tall? Should I install a damper? Any advice would be greatly appreciated.

Don't be shy with comments. I want to get this right. If I am a dumbass and this whole thing belongs in the scrap heap please tell me! I am here to learn.

I am doing at least 15gal an hour now, so still very happy. My wife was shocked when I came inside on Wed. at 4:00pm and said I was out of sap. I think she expected me at closer to 4 a.m. But still, I know that this thing should be able to do a bit better, but I am just not sure what to try to adjust first.

Oh, one other thing... don't know if this is helpful or not... but there are a couple of spots on the arch extension that need to be tightened up a bit from shoddy fabrication and at times smoke will seep out of these corners. That made me think that maybe I have too little draft or maybe the blower is too strong? But maybe it's nothing? Cause on the other hand I thought maybe the stack is too big and the draft is pulling the flames right past the back pan too fast? Can you tell I am confused, haha?

[BlueberryHill]

rudimentary sketch9182

[DoubleBrookMaple]

Looks to me from the drawing, if it is anywhere near scale, and without dimensions, you have 8 inches between the ceramic blanket and the pan bottom at the rear. That is a tremendous gap. A 6 inch pipe, which is smaller than you should have in my opinion, has an area of just 28 square inches. Your area below the rear of the pan would be 176 square inches if 22 inches across. Your gap could be less than two inches easily.
I have built two arches, so minimal experience, but have studied a lot. My understanding is that the rear of the pan should be close to the area of your pipe. My pan with drop flues this year I designed with less than an inch gap, as recommended to keep heat close to pan. Your pipe is small, but I am not sure if that matters with a blower. Maybe someone can clarify that for us both. I would like to see an 8 inch pipe, as I have, in case of blower failure, and to keep a draft while stoking.
It appears from the drawing that you may be stuck, as the exhaust pipe is so far below the pan bottom, (if the drawing is correct).

[BlueberryHill]

Eric, Thanks for the reply and the info. The top of the stack collar is in fact about 2-3" below the bottom of the pan. That's how it was on the original 2x3 arch and we just cut the back off of that 2x3 and welded it onto the end of the new 2x7. We were rushing because 1. we thought the weather was about to turn 2. Doing it the right way also would have caused a problem with getting through the ceiling and or wall where it is currently housed.

For next year, I plan to make a real stack collar that feeds up behind the back pan and put this in a real sugar shack. If a larger diameter stack is ideal, then I would upgrade at that point.

Does anyone know of a way to rig up something temporary in order to get the flames up under the pan. Maybe a baffle of sorts somewhere?

[DoubleBrookMaple]

I was just reviewing Mason pictures, and I wonder if it is a poor design to have the 6 inch round exhaust out the rear wall. Maybe you get away with it on a 2x3 or 2x4...
Maybe you will need to modify that..
http://billcarpenter4.files.wordpress.com/2013/01/wf-mason-evaporator-2013-01-02-003_thumb.jpg?w=646&h=486

[DoubleBrookMaple]

Does anyone know of a way to rig up something temporary in order to get the flames up under the pan. Maybe a baffle of sorts somewhere?
Reading again, you already knew all those things I guess.
I think you are on to something. Not flames, but hot gases. It is all about proper airflow. A series of baffles is probably a good idea. With the blower, you should not have to worry about flow restriction. A baffling system would keep the hot gases turbulent and not allow the colder gas to stagnate near the pan surface, and should help. I am of an aviation background, and high performance aircraft have vortex generators on the surface of the wings to keep a proper airflow over the surface. They call this a "boundary layer" (REF: http://en.wikipedia.org/wiki/Boundary_layer) (make sure you read the whole thing before continuing any further and the season will be over).
This is about vortex generators http://en.wikipedia.org/wiki/Vortex_generator
Really, just glance at these...
Here is a quote from one "A vortex generator creates a tip vortex which draws energetic, rapidly-moving air from outside the slow-moving boundary layer into contact with the surface."

Sorry for being so technical...
Hope it is some help.

[BlueberryHill]

Here is a modified drawing. I added a red box to represent where I am thinking about throwing some bricks in as a baffle to force everything up near the pan before dropping back down and out the stack.

I could even add some vermiculite (with blanket over it) to increase the ramp angle up to the top of my new brick wall baffle. All that stuff is easy. The tough part is getting the pan off. Would likely have to drain it first.

This was my first thought of a temporary fix to get me through this season. Wondering if someone thinks it is a bad idea for some reason. Also interested to hear if someone else has a better idea. Thanks again!

9183

[cpmaple]

Hello I've been reading your post since you started it but have not said anything till now. This is only my 6th season sugaring so I'm no pro but know enough to be dangerous. My first year was on a 2x3 and to help keep the heat under the pan I did what you just posted put a few firebrick to act as a wall that it had to go over before it exited the pipe which on my 2x3 was in the same location as your pipe. Trying to recall but I think I put the bricks about 8-10" infront of the stack exit and raise your ramp up to about 2" from your pan. Just my 2 cents hope it helps cpmaple

[Quagmire33]

I like the idea of the fire wall (red box). Although I haven't boiled on it yet, my half pint has a fire wall about 1 1/2" below the pan to make the fire stay up next to the pan then have to go down and out the chimney. Just my 2 cents.

[cpmaple]

if you also look in my photobucket you will see pics of a 2x6 that I made with flat pans and there is a pic of the ramp in there the photos are in (sugaring 2011 and changes to 2x6) hope this info helps cpmaple

[BlueberryHill]

Thanks everyone! Guess I am on the right track. Should be able to make some adjustments tomorrow and hopefully I'll have enough sap by the afternoon to give it a try

[BlueberryHill]

Alright, I just used bricks and the rest of my vermiculite to raise the ramp up pretty good to within about an inch of the rear of the pan. Then it drops off for the last 6" so the gasses get get down to the outlet. Hoping this will tune it up good enough to get a nice boil off the back pan. Gonna add some more taps in the morning and hopefully after that I'll have enough sap to get a couple hours of boiling in the afternoon.

[RollinsOrchards]

You might also try a variable speed control for your blower to see if you can fine tune it a bit. In electrician speak that is called a Rheostat control. You can check the amperage draw of your blower and perhaps get a ceiling fan switch that will do the job. For larger blowers Leader sells a rheostat box for $75, or my local electrician picked one up for me at a supply house for all of $5.

[lpakiz]

Or you can take a flap of tin and make a door to rotate over the intake of the fan.

[maple flats]

The flap of tin is your best choice, just design it so you can vary the inlet air as necessary. Between that and the raising of the ramp you should do much better. When you do rework the stack exhaust make sure it starts at least 18" wide, then taper to 8". Most commercial 2x6's have at least an 8" stack, some are even larger. Do not use a damper as you suggested early on, dampers are only for oil fired and they are barometric.

[BlueberryHill]

I ran it over the weekend and with the wall/ramp mod in the back I did notice some improvement in the boil rate on the back pan. A little improvement though, not a ton. Front pan is unchanged so still boiling awesome there.

I have about a 1" gap between the blanket and the pan right at the back before it drops down for the outlet. Maybe I'll squeeze it up a little more to see what happens?

I also threw a dimmer switch on the blower. It's just an old switch I had kicking around (major pack rat). It seems like the blower is a touch slower than it was without the dimmer switch, even with the dimmer cranked up. If I try to dim it at all, the blower speed drops drastically. So that was kind of a failure. I'm going to put a regular light switch in there in place of the dimmer. The one nice thing is I don't have to walk 8' away to where the blower is plugged in now when I fire. Having a switch right on the leg of the arch near the door is very convenient.

I will give it a go with the swiveling sheet metal at the blower intake. That sounds like a good idea. Hopefully it'll be something that shows results! If not, it's a free modification anyway.

[Big_Eddy]

If it were me - I would put in 2 dams. 1 at the top of the firebox back wall with a 3" gap above it, and a second about 6" from the back of the pans with a 2" gap above it.

That way the hot gasses must come up and over the first dam and right up against the pan bottom before they can travel to the stack. In my opinion, you're losing a lot of heat transfer opportunity by allowing the gasses to hug the bottom of the back section and a cooler stagnant air section to sit on the pan bottom. Once the gasses are up high, they will stay up there to travel back to the back dam and over it. You could fill in the whole back section, but I don't think it's necessary once the arch stabilizes.

[BlueberryHill]

I went out after work and took out the dimmer switch and put in a regular on/off switch. Then I pulled off the back pan (not much fun) and reconfigured a bit. I pulled up the ceramic blanket and added vermiculite and then put the ceramic blanket back on top. Now it is squeezed about 3/4" right before the drop off in the back and it slopes down evenly from there, getting closer to the firebox, but it's still pretty shallow all along the back pan. The underside of the "front" of the back pan has about a 3 inch gap to the face of the ceramic blanket. Looking at my sketch below, I don't know why I did not set it up like this in the first place. I have the steel nor to mod this up to a proper configuration with respectable stack collar and everything. Got all summer to do that though.

Can't wait to see how this is gonna boil now with these tweaks! Hopefully Wednesday!?!?

9257

[adk1]

Although I have a leader 2x6 when I installed my ceramic blanket at first I had about a 3" gap between the blanket any the bottom of my flues. I then added additional blanket so now I might have 1/4" of a gap. It did make a difference on the boil that is for sure

[BlueberryHill]

I got more sap than expected yesterday so I lit a fire after work for a few hours to burn off the sap I have on hand. Gotta make room for the big runs expected in the next few days.

Overall the boil was not much different than the last time. I think I might try to squeeze it up a bit more and see if that helps. I did get a chance to mess with the blower. I blocked half of the air intake hole and I noticed that it slowed the boil down everywhere. About 10 seconds after pulling off the sheet metal and running wide-open again, it was back up and boiling harder again. So I guess I can rule out having too much AUF.

My "preheater tank" does not do much of any preheating, so I know that is not helping. But a couple times I shut off the incoming sap for a few minutes to let the whole back pan heat up real good. Wanted to see if that was the problem. That helped it boiled harder by a bit, but it was still way less of a boil than the front pan. Am I just expecting too much from the back pan?

Next year I'll have a hood and a real preheater, but for this season I am just hoping to squeeze a little more out of this if possible.