Anthracite is considered “nonclinkering” and free-burning because when it is ignited it does not "coke" or expand and fuse together. It is most often burned in underfeed stoker boilers or single-retort side-dump stoker boilers with stationary grates. Dry-bottom furnaces are used because of anthracite's high ash fusion temperature. Lower boiler loads tend to keep heat lower, which in turn reduces nitrogen oxide emissions.
Inferior coal rejected from anthracite mines is called culm. This has less than half the heat value of mined anthracite and higher ash and moisture content. It is used most often in fluidized bed combustion boilers.