@Hot Water
Prb coal comes from seams 100 ft thick. Powder River Basin is the name of the geological area. The Power River was so named because of extremely fine sand along its bank that resembled powder.
As to its combustible and physical form, prb fuel is quite friable, ie it breaks up easily when handled. It still comes out of the ground in large lumps. When dried in lab conditions it has just as much btu/lb as eastern bituminous, but the high inherent moisture, 24 to 27% , results in an effective heating value of 6500 to 8900 btu/lb. The reason for the lower value is that during combustion you have to drive off the moisture. 7800 to 8500 btu/lb were pretty typical as delivered numbers.
Prb has a very high volatile matter percentage compared to other coal's, around 34%. The primary constituent of the ash is calcium. Due to the friable nature you do get a lot of dust. This results in a high surface area by volume.
Anyone who has poured concrete can tell you it is exothermic while it dries, i.e. it throws heat. The calcium in prb ash does the same thing. When you combine high surface area, extremely flammable gas, an exothermic reaction, and a slight breeze, you get fire.
Fire in a hopper or barge can be extinguished with water or foam, but foam definitely works better. Fire on the coal pile can be handled with these methods and also creative bulldozing work. Fire in a coal silo really sucks. It's hard to put out and a serious pain to get the silo empty later. Usual max safe dwell time in a silo is two weeks. Coal pile stack out for prb requires special techniques not needed for other fuels.
Due to the combustible nature of the dust, cleanliness in a prb fired plant is super important. Much of the savings in reduced fuel costs is eaten up by extra cleaning costs.
Yes the sulfur is very low. This allowed some coal fired plants to operate longer without a scrubber by switching to prb.
Plant output rating is often reduced on prb. This is because extra fuel is required to make up for the lower but rating, and extra fuel requires extra air flow, which is often not available.
On the plus side, the ash is super clean and is a sought after commodity for concrete production.
You can check my numbers since I am working from memory, but I think they are going to be pretty darn close if not spot on. I am primarily a rotating equipment guy now, but I was a coal mill engineer for many years.