Firing options for my half-pint

[phil-t]

So, this is new to me. I got this used half-pint last summer - the guy I bought it from had fabricated an AUF blower and tube to go in under the grates (in place of the draft door). Seemed to work great. He also fabricated a steel box, open top, and fitted it to the rear of the evaporator so the hot flue gases pass through it to the stack; this for the preheater pan.
Using the AUF setup, I seem to get a good fire, stack temps 450-500 (hard to keep it at 500) and black smoke out the stack. Very few coals at the end of a session. The preheater sap gets to about 150-160, I have a float box on the feed to that and regulate the sap to the pan with adjusting a ball valve by hand to keep about 1-1 1/4" in the pan. I fire with a timer every 5 minutes and check the pan level just as often. I get about 6gal/hr boil rate.

Today, the blower quit on me and I switched everything out to the original draft door. Stack temps went to 600 and stack smoke was nearly unnoticable. Sap temps in the preheter went to 200 or better and my thoughput was just about the same. Lots of coals and long lasting heat after the last firing. I'm using well seasoned (2 years old or better) mixed hardward split to 2-3" diameter.
I'm having a hard time understanding the stack temp difference (heat going up the stack). I've tried different air volumes on the blower, from almost none to open and causing smoke out the front door, with almost no difference in the stack or boil rate. I can understand why the natural draft is doing as well as the AUF, with the hotter preheated sap being fed the evaporator. What to do about the coals piling up? I usually run 6-8 hour boiling sessions.
Am I doing something wrong with the AUF? Is it design thing with the half-pint? It is a 3" tube with 1/4" holes drilled along the top length - down the center of the arch. Should that design be different?

[blaircountysugarin85]

Was the blower adjustable? I added a damper to my stack pipe and have an adjustable blower. Too much air will blow the heat right out the pipe. I use the damper and the adjustable blower to fine tune to get max heat. There are times the blower is on full and the damper is maybe 1/2 closed and is burning great. Enough draft to burn good but not too much to suck all the heat out the chimney. The blower keeps the fire burning nice and hot. I can't see doing this without at least one or the other to adjust. There are times I have to play around the get the best effect.

[mellondome]

Sounds like your blower setup is not allowing enough air into the firebox. Your stack temps are way too low for good boiling. The smoke is unburned fuel due to lack of oxygen.. if the blower fits tight to the arch ash door, try taking the pipe off it.

[phil-t]

I have both, flue damper and blower damper. I'll heed both responses and try some adjusting. I think the blower can supply plenty of air, compared to natural draft. Maybe placement of that air under the grates.
Thanks.

[mellondome]

It should just dump under the grates . You are restricting it with the pipe. You dont want a manual damper in the stack. It will only cause poor combustion. Those are for wood stoves heating an indoor space where you want a very slow burn.

[Super Sapper]

If you have black smoke you are starved on air with the blower. The blower is probably fine but how much space is there for the air to come out? Cut the pipe off and let it come under the grates without restriction. As far as the coals, use less wood when you fire but more often.

[buckeye gold]

I ran a half pint for 3 years and i had a blower on it. I never done as well with AUF, but when I went to AOF it made more difference. At peak my half pint would run at 7-8GPH. I agree with the others, get rid of the distribution pipe and open up your draft. Your blower air is goingg out the back as cold air and cooling your stack and thus damping your draft all together. Don't over load with wood, leave some air space under the pan, so flames lick at the pan bottom. You don't have a ramp to draw heat up so you want all your fire right under the pan.

I still have my half pint arch, but I extended it and put a Smokey lake Hybrid pan on it. I built a AOF system in the firebox and done away with AUF. I get about 12 GPH without disciplined firing, but if I am real attentive to my fire and sap depth I can get 14-15 GPH. Most days I don't have enough sap to worry about optimum firing and set up, but on those big days I work it hard. It also helps to watch how you fire. If I load one time putting wood straight in the next time I put it cross ways and load 4-5 small sticks every 7-10 minutes....she rumbles when I do this. I can also turn my air up. So there is a lot of art in running rigs, especially the small ones. when I was young my family and friends had big rigs and I remember we paid no attention to how we fired, we just threw in slab wood however it would fit. You can't do that with a small rig. I don't know how sensitive the new larger rigs are, someone else can explain that.

[phil-t]

I will try dumping the air under the grates by removing the distribution pipe. Not using the flue damper; I managed to maintain 500 deg.F on the flue yesterday and averaged 7+ gph on the flow, took 1 1/2 gal of syrup off in 7 hrs. ~50gal of ~3% sap. I had to dampen the blower intake to prevent smoke (a lot of it) from coming out the closed door. Smoke was still some black. I think maybe my wood is a bit large at 3-4", going to try splitting it again to see how that goes.
Thanks for all the comments - I'm having fun messing around with this rig. Goal is 10 gal of syrup and I'm more than 1/2 half way there. :cool:

I just don't see how I can be starving the fire for air and be forcing smoke out the door at the same time?

[phil-t]

I took the tube off the auf blower. Found the "right" damper setting on the blower. No black stack smoke. Higher stack temp. Higher preheat temp, and near 10 gph! Averaged 8.5 gph today,on 60 gal of sap. Nice! Also found splitting my wood to 2-2.5" made a huge difference. I have produced 12.5 gal. of syrup this season, surpassed my goal of 10 gal.
Hauling my sap to a buddy now - I'm done boiling, will be adding a RO Bucket next season. I can't take the 10-12 hr days.