I burn Wyoming Bit. coal and have experienced soot problems with my handfed stove. From what I can tell, you have to burn the coal pretty hard to get enough heat to actually burn the volatiles, instead of letting them go up the chimney and form soot. The problem then is usually that you get too much heat when you burn the average sized firebox hot enough to burn the volatiles.
I tried using firebrick in place of my baffle plate to direct heat back down to the coals, to burn the volatiles, but I had limited success.
Berlin, one of the bit. experts, claims that if you can provide preheated seconday air over the fire, you can burn the volatiles also. I never was successful at doing this, mostly because I refused to cut a hole in the front of my stove to accomdate something similar to Berlin's secondary air design (see that thread at coal/wood stove plans
). If you were handy, I think that his secondary air design would be worth a try.
The conclusion I came to is that it's best to have a firebox that has a small area (footprint), and also a very deep firebox. That way you can burn it hard, and not get too much heat out of it.
But that creates problems also, as when the volatiles have burned off after a few hours, you may be left with not quite enough heat.
That all led me to find an underfeed stoker, which burns a small amount of coal very fast. It seems to work very well, though even then I have some soot. Still working on that.
Good luck. If you can reduce your firebox somehow, by laying firebrick on some of the grates, and still maintain a system to shake the ashes out, you might want to try that. Preheated secondary is also required, but tricky to fabricate.
Steinke in WY