I had started back in November with problems with the motor running the fan and auger, then I had problems with the ashgrate getting clogged with fine powdery-ash coal ash.
All along I was having a very significant amount of unburnt coal and partially burnt coal in my ashpan. I was going through large amounts of coal, and having to sift out the unburnt coal from the ash [I just couldn't throw it out
]. The recovered coal I burnt very easily and well in my underfeed stoker in 'Big Bertha'. With several phone calls to Axeman Anderson, AHS, and coal boiler servicemen who service AA boilers, I slowly worked through several potential issues causing my huge amounts of unburnt coal in my ashpan.
Many, many AA and AHS 130 owners reported that they had zero issues with unburnt coal in their ash..
I spent many hours talking with forum member U235a4 who is the only other AA 260 owner on the forum. He too had had in the past lots of unburnt coal in his ash, as well as clinkers, temp overshoots, and many other problems. Zach tried his best to help me get the problem solved, and his help was right on target, now that I see what the actual problem was,
So... what was it?? Why did I have an ashpan full of 10-20% ash and the rest unburnt coal?? How is this possible when if I looked through the inspection port at the top of the fire, it appeared to be burning all the way across the full firepot/firetube??
Here's how I discovered what was happening. First, remember that the AA firechamber is a steel cylinder surrounded by water sitting 4" above a sliding 'grate', actually a drawer with steps or notches in the drawer bottom. The column of coal and the fire all rest on the ash grate or drawer bottom, There is a 4" gap between the grate bottom and the bottom lip of the firechamber.
I had what appeared to be a full fire, and had had this for several days, I was having the ashgrate 'ash' or move at a high rate to purge the firechamber of the unburnt coal, this was per the directions of Pete Axeman and U235a4. But after days of sifting through wheelbarrows of 80-90% coal in the ash pan, I had had enough...
I laid down on the floor, on my back and reached up and cleaned off 'exit end' of the ashgrate, I was pulling handfulls of unburnt and partially burnt coal off the grate and into the ashpan. I kept at this, expecting to start seeing red hot coals in the ash pan. But I had pulled a lot of coal out and was reaching in really far when I realized I had my had inside the fire chamber, and was still removeing unburnt coal. So I stuck my head inside the base and looke above the grate...
What I saw was that I had cleaned out a ring or cylinder of unburnt coal from the firechamber, and that in the center of the fire chamber was a column of red hot coal, like a tree trunk or the stem of a mushroom with an upper cap or top of burning coal. When the coal is hot it slightly adheres to itself, but the loose unburnt coal just fell out of the firechamber.
What I had was an insulating ring or cylinder of unburnt coal surrounding a central core or column of burning coal that was topped by a spread out cap of burning coal. Since all I could see was the top of the cap of burning coal that appeared to be the full diameter of the firechamber, I ahd no idea what the real situation was under the cap of burning coal.
What was happening to keep feeding this outer cylinder of unburnt/partially burnt coal was that each time the ashgrate 'ashed', it shaved some ash and unburnt coal off the bottom of the column of coal and fire. The whole column dropped an inch or so, and fresh coal fell down on top of the fire from the feedtube above the fire. The fire is cone shaped on the top, so the fresh coal rolled down the slope and stopped at the outer perimeter of the firechamber, up against the waterjacket. Here the fire was barely burning, the main heat was in the central core or column in the firechamber. But it appeared that the outer perimeter WAS burning, but it WAS NOT. The outer perimeter of fresh coal sometimes burnt a little, producing my large quantities of partially burnt coal, but a lot just slid down the wall of the firechamber to the lower, cooler area under the cap of burning coal.
Visualize a big mushroom, with a stem 11" in diameter, with a cap 14-15" diameter on top, with fresh coal being pourd over the top, and the fresh coal collecting around the stem of the mushroom insulating it from the surrounding waterjacket.
This is what I had in my firechamber. Pete Axemand and U235a4 both had told me to increase the amount of ashing to purge the excess unburnt but it wasn't working because of the constant feed of fresh coal from above.
I cleaned out as much unburnt as I could, burnt up my glove pretty bad, then got up off the floor, and from above using a poker pushed the fire down from the top, spreading the hot coals over the whole ashgrate bottom, some spilling out into the ash pan. I then dumped fresh coal on top, and started the fan in the boiler.
I turned up the thermostats in the house, and turned on the hot water, and increased the hot water feed to the shop floor, putting as large a BTU load as I could on the boiler. I manually ashed the boiler as needed to keep red coals on the ashgrate, not letting the anthrastat control the ashing at all. I needed to create the hottest, largest fire I had ever had. I had NEVER since the beginning of November really had a full fire in the fire chamber, It LOOKED like a full fire, but because I can only see the top of the fire throgh the inspection port, I was fooled into believing that the whole firechamber was the same as what I saw.
Why on the AA firechamber will the fire not travel sideways and down?? I don't know, the fire will travel sidewasy and down against the airflow in my underfeed stoker, but it didn't for over two months in the AA boiler. I had to force a full diameter fire.
Now that a full diameter fire is established, it is maintaining itself, and even seems to be still purging the last of the unburnt coal off the grate.
I am generating only about 1/4 the quantity of ash, and it is all well burnt coal, many small 'mini-clinkers' and the ocassional fist-sized clinker and some powder-ash as well. My coal consumption is a fraction of before, since now it is only burning the coal, not running it through the firechamber into the ashpan, mostly unburnt.
The reason that I couldn't get the unburnt ash purged by over-ashing as Pete Axeman and U235a4 had directed, is [I think] because I needed to remove the outer cylinder of unburnt /partially burnt coal from the around the central column of burning coal to allow it to collapse and cover the entire diameter of the firechamber.
When/if I have to start another fire in the boiler, I will take great pains to create a perimeter of fire right up against the outer diameter of the firechamber, and make sure the fire is well established full diameter before filling the firepot with coal. The fire in the AA firechamber cannot be trusted to migrate out and burn through the entire firechamber.
Fingers are tired, going to add a few more thoughts in the next post.
Greg L
somewhere between heat up the chimney waste or unburnt coal in the ash pan waste .
