Anthracite Coal

Anthracite coal is a hard, compact variety of mineral coal that has a high luster. It has the highest carbon count and contains the fewest impurities of all coals. Anthracite is the most metamorphosed type of coal in which the carbon content is between 92% and 98%.  Anthracite ignites with difficulty and burns with a short, blue, and smokeless flame.

Anthracite may be considered to be a transition stage between ordinary bituminous and graphite, produced by the more or less complete elimination of the volatile constituents of the former, and it is found most abundantly in areas that have been subjected to considerable earth-movements, such as the flanks of great mountain ranges. Anthracite is a product of metamorphism and is associated with metamorphic rocks, just as bituminous is associated with sedimentary rocks. For example, the compressed layers of anthracite that are deep mined in the folded (metamorphic) Appalachian Mountains of the Coal Region  of northeastern Pennsylvania are extensions of the layers of bituminous coal that are strip mined on the (sedimentary) Allegheny Plateau of Kentucky an West Virginia, and Western Pennsylvania.

In the United States, anthracite coal history began in 1790 in Pottsville, Pennsylvania, with the discovery of coal made by the hunter Necho Allen in what is now known as the Coal Region. Legend has it that Allen fell asleep at the base of Broad Mountain and woke to the sight of a large fire because his campfire had ignited an outcropping of anthracite coal.

From the late 1800s until the 1950s, anthracite was the most popular fuel for heating homes and other buildings in the northern United States, until it was supplanted first by oil burning systems and more recently by natural gas systems as well. Many large public buildings, like schools, were heated with anthracite-burning furnaces through the 1980s.

Current anthracite production averages around 5 million tons per year.

The principal use of anthracite today is for a domestic fuel in either hand-fired stoves or automatic stoker furnaces. It delivers high energy per its weight and burns cleanly with little soot, making it ideal for this purpose. Its high value makes it prohibitively expensive for power plant use. Other uses include the fine particles used as filter media, and as an ingredient in charcoal briquettes.

Anthracite is processed into different sizes by what is commonly referred to as a breaker. The large coal is raised from the mine and passed through breakers with toothed rolls to reduce the lumps to smaller pieces. The smaller pieces are separated into different sizes by a system of graduated sieves, placed in descending order. Sizing is necessary for different types of stoves and furnaces.

An important application has been developed in the extended use of internal combustion motors driven by the so-called "mixed", "poor", "semi-water" or "Dowson gas" produced by the gasification of anthracite with air and a small proportion of steam. This is probably the most economical method of obtaining power known; with an engine as small as 15 horse-power the expenditure of fuel is at the rate of only 1 lb. per horse-power hour, and with larger engines it is proportionately less.

In June 2008, anthracite was US$150/short ton wholesale.

Mining of Anthracite coal continues to this day in eastern Pennsylvania, and contributes up to 1% to the gross state product of the state. Over 2,000 people were employed in the mining of anthracite coal in 1995. Most of the mining currently involves reclaiming coal from slag heaps (waste piles from past coal mining) nearby closed mines. Some underground anthracite coal is also being mined. As petroleum and natural gas get more expensive, anthracite coal is growing in its importance as an energy source.

The largest fields of anthracite coal in the United States are found in northeastern Pennsylvania, where there are 7 billion short tons of minable reserves.

Surface mining and deep underground mining are the two basic methods of mining. The choice of mining method depends primarily on depth of burial, density of the overburden and thickness of the coal seam. Seams relatively close to the surface, at depths less than approximately 180 feet (55 m), are usually surface mined. Coals that occur at depths of 180 to 300 feet (91 m) are usually deep mined but, in some cases, surface mining techniques can be used. For example, some western U.S. coals that occur at depths in excess of 200 feet (61 m) are mined by open pit methods, due to thickness of the seam (60-90 feet). Coals occurring below 300 feet (91 m) are usually deep mined.