My good friend has a Hot Blast and he burns 95% coal ( bituminous) in his and has for years with zero problems. He recently put a very large addition on his house and needed a bigger coal furnace. He did not hesitate to go buy another Hot Blast, although I could not tell you the model numbers.
I have read alot of threads on here about coal not burning or furnaces/stoves not producing heat, producing heat to quickly, making klinkers etc... I believe it all boils down to the quality of coal burned and just as important the method in which it is burned. Coal quality is REALLY important when burning bituminous coal. I burn only Bit coal and I have had coal that burns down to just a fine ash and coal that will just produce nothing but klinkers. I have also learned how to burn Bit coal to where one boiler full will last me 10-14 hours. When I first started burning coal I could not make good heat or get it to burn for an extended period of time...
My point is this, If a furnace is having an issue burning Bit coal it is probably 50% coal quality, 25% burning technique and possibly 25% furnacr issues ( fire box design)
This is just my opinion and ONLY based on my experience burning bituminous coal. As far as Anthracite, i will leave that up to the guys that burn it and know how to burn it correctly.