I too am seeing quite a bit of black coal in the ash pan of an Axeman Anderson.
It is the smaller boiler, an AA130, and the coal is supposedly from Stockton.
My fire is lower in the tube and the anthrastat
has been calibrated and set to 136*. I believe I am getting good heat from this coal in spite of what I am seeing in the ash bucket. Keep in mind, the draft fan (negative pressure) creates a very robust fire in these fire-pots.
I am not *Boo-Hooing" here, just trying to gain some insight and share my experiences here with others.
The black pieces in the ash are very noticeably burnt and reduced in size. Started out as pea size, but now looks like buckwheat size more or less.
These unburnt pieces are still black and have a finely layered
look about them.
Now the rest of the ash is a mix of fine power and crunchy clinkers that will break up easily, sometimes a bigger one but an AA chews most clinkers up before they drop to ash bucket.
As I understand, clinkers happen when a coal burns above it fusion temperature...so I have some of that going on, but with some of the coal that is not the case.
I have read of coal breakers blending different coals for achieving a better burning and more consistent product, and believe this is the case for this coal.
I have looked closely at the raw coal in the bin and after studying a bunch of different pieces can notice 3 different types of coals in the mix.
One coal is like what I saw when I burned Harmony coal...shiny black and fractured randomly with lots of sharp edges.
Second coal is dull black no shine and most pieces have 2 flat sides opposite. (shale like)
Third coal is glittery shiny with a flaky look, not sharp or flat.
I'll try to get some pictures up to allow a better understanding of what I'm trying to describe.