Anthracite is mined from the oldest geological formations, and therefore has spent the longest time underground and been subjected to the most pressure and heat, making it the most compressed and hardest coal. Hard coals contain greater potential to produce heat energy than do the softer, geologically "newer" coals.
Anthracite is the hardest and most brittle of all coals, and when burned, produces a very hot blue flame. A shiny black rock, anthracite is primarily used for space heating by residences and businesses in and around the northeastern region of Pennsylvania, where much of it is mined.
In fact, anthracite has become such a part of the Scranton, Pennsylvania, area's history and culture that they established an entire museum devoted to it: the Pennsylvania Anthracite Heritage Museum.
Anthracite is considered the cleanest burning of all coal types. Anthracite produces more heat and less smoke than other coals, and is widely used in hand-fired furnaces. Some residential home heating stove systems still use anthracite, which burns longer than wood. Anthracite has been nicknamed "hard coal," especially by locomotive engineers who used it for fueling trains.
Heating value: Anthracite burns at the highest temperature of any coal (roughly 900 degrees or higher) and typically produces up to 13,000 to 15,000 Btu per pound. Waste coal discarded during anthracite mining, called culm, contains approximately 2,500 to 5,000 Btu per pound.
Characteristics: Anthracite contains a great deal of fixed carbon (80 to 95 percent) and very low sulfur and nitrogen (less than 1 percent each). Volatile matter is low at approximately 5 percent, with 10 to 20 percent ash possible. Moisture content is roughly 5 to 15 percent. It is slow-burning and difficult to ignite because of its high density, so few pulverized coal-fired plants burn it.
Anthracite is considered “non-clinkering” 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.
Particulate matter, or fine soot, from burning anthracite can be reduced with proper furnace configurations and appropriate boiler load, underfire air practices, and fly ash reinjection. Fabric filters, electrostatic precipitators (ESP), and scrubbers can be used to reduce particulate matter pollution from anthracite-fired boilers. Anthracite that is pulverized before burning creates more particulate matter.
Availability: Scarce. A tiny percent of all remaining coal resources are anthracite. Pennsylvania anthracite was mined heavily during the late 1800s and early 1900s, and remaining supplies became harder and harder to access because of their deep location. The largest quantity of anthracite ever produced in Pennsylvania was in the year 1917.
Location: Historically, anthracite was mined in a 480 square mile area in the northeastern region of Pennsylvania, primarily in Lackawanna, Luzerne, and Schuylkill counties. Smaller resources are found in Rhode Island and Virginia.
Additional notes: Inferior coal that was rejected from anthracite mines is called culm. Culm has less than half the heat value of mined anthracite and a higher ash and moisture content. It is used most often in fluidized bed combustion (FBC) boilers. The benefits of using rejected culm, or waste coal to produce energy is the subject of this documentary.
Ranking: Anthracite ranks first in heat and carbon content compared with other types of coal, according to ASTM D388 - 05 Standard Classification of Coals by Rank.
Learn about other types of coal