I've had my Prill running for about 3 weeks. Using 50 lbs per day in this mild weather (30s at nite, 60 daytime). I added a barometric damper yesterday. It seems to be keeping the draft steady at 0.04" or 0.05". It would climb to 0.07" before the baro was installed, even in mild weather. Seems like the damper is mostly closed when the stoker is in operation, and opens slightly after the stoker stops. Once the flue cools some, it closes again.
I'm having trouble deciding how to set the amount of combustion air. The combustion fan is driven by the same motor as the coal auger. You control the air with a disk on the fan intake. As set, I'm getting about 1/4" of soot on the firebox tubes over the 3 weeks I've been burning it. When I bought it, the tubes were clean (I doubt the previous owner cleaned them, they looked untouched).
I know the bit. coal I've been burning has lots of volatiles. The previous owner burnt bit. coal that was about 8,000 btus per pound. Mine is 12,000 btus. More volatiles, maybe more moisture too. Wondering if I need to provide more combustion air. Any tips on how the set the air? And how does that work with my baro? Does one affect the other?
Also, 3 weeks of burning has produced a significant buildup of ash in the elbow at the back of the stove, and the thimble. As you can see from the pic below, I installed tee's when I put my baro in, to aid in cleanout (baro is in the top tee, bottom one is for dropping ash out). If I peak into the stovepipe from my baro, I can see ash and quite a few sparks flying when the combustion fan is running. That makes me think I have to much air. But the soot, coupled with the several minutes it takes to really get the fire burning once it starts stoking makes me think I don't have enough air. No sure what to do.
Another item to muddy the water - while setting the baro, I had the stove stoking for about 15 mintues (so far this season, it's mostly run on the "keep fire" timer, about 3.5 minutes per cycle). Stoking for 15 minutes produced lots of heat, seemed like I was overfiring it. The thin sheet metal the firebox is built of was warping a little. I had to turn it off it was getting so hot. I'd be afraid to run it that long again very often. The flames were over 12" long above the firepot. Granted, that was before I got the baro set. Maybe I should stay with 8,000 btu coal. Makes me think it would be nice to be able to set my feed rate - maybe I don't want an entire grate-ful of coal burning? I don't have that option though.
I'm full of questions. Any tips would be great. (how to set combustion air, mostly). Thanks.
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- Smokepipe on Prill bituminous stoker