A hard, compact coal characterized by high luster and low sulphur content. Anthracite is comprised of less volatile matter than bituminous coal, which provides for its nearly non-luminous flame. Extensive anthracite deposits, representing the majority of U.S. reserves, are located in Pennsylvania and used mainly for heating homes. Heat content range is over 14,000 BTU/lb.

The non-combustible and inorganic component of coal remaining after complete burning. Ash yields no heating value.

Ash Fusion Temperatures

  1. Initial Deformation Temperature
    Temperature at which the top of the ash cone begins to round.
  2. Softening Temperature
    Temperature at which the ash cone fuses into a spherical lump.
  3. Fluid Temperature
    Temperature at which the ash cone spreads out over the base as a flat layer.
    • 2,600 degrees F – A high ash fusion temperature.
    • 2,100 degrees F – The lowest approximate ash fusion temperature of coals in Pennsylvania and West Virginia.
    • 1,950 degrees F – The ash fusion temperature of several coals situated in Ohio.
    • 1,850 degrees F – The approximate ash fusion temperature of coals situated in Illinois and Indiana.

American Society for Testing and Materials. The ASTM provides a system for classifying coal as well as other testing parameters.

Auger Mining
A method of mining following a surface mining operation where the overburden becomes too costly to remove. The auger usually operates on a horizontal plane, comes in sections, and the diameter depends on the height of the coal.

Operation of refilling an area where overburden has been removed, including the grading of the refilled excavation.

Those levels of electricity output from generating stations necessary to satisfy steady demand. Plants for baseload production are usually conventional steam, nuclear and large hydroelectric. (b)

Bituminous Coal
A hard, black, combustible substance formed from decomposed vegetable matter subjected to pressure, temperature, and moisture for millions of years. Varying conditions of formation result in diverse coal chemistries and heat contents. Bituminous coal is one of several phases in an evolutionary development process which includes (from least developed to most developed): peat, lignite (sometimes called brown coal), subbituminous, bituminous, anthracite (sometimes called hard coal) and graphite. The latter phases have generally experienced greater extremes of pressure, temperature and time. It is used for generating electricity in certain parts of the country and for conversion into synthetic gas.

Bottom Dump Unloading
A method of unloading open top hopper cars. These cars have unloading gates placed at the bottom of each hopper section. They may have a series of dumping gates (saw tooth hoppers) or a system where the entire coal-supporting area is opened for quick unloading. (f)

British Thermal Unit. The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit under normal conditions.

BTU (as received)
Indicates the heating value of coal at the location of consumption.

BTU (dry basis)
The method of fuel analysis where the moisture is eliminated and the other constituents are recalculated to total 100 percent.


Clean Air Standards

Criteria for environmental safety established and regulated by the U.S. Environmental Protection Agency (EPA). One clean air standard is based on the sulphur content in coal and corresponding acceptable burning levels as follows:
EPA Compliance Levels Sulphur Content
sub-compliance under 0.8%
compliance 0.8% to 1.1%
non-compliance over 1.1%

Clean Coal Technology
Because of environmental pollution concerns from the burning of coal, increased efforts are being made to develop better emission control or reduction technologies. These technologies apply to cleaning impurities from the coal itself, improving the effectiveness of the burning process, and/or improving the pollutant recovery systems for the escaping products of combustion.

Includes all ranks of coal – anthracite, bituminous coal, sub-bituminous coal and lignite. (b)

Coal Seam
A "bed" or stratum of coal. The term "seam" usually is applied to a large deposit of coal.

Coal Washing
The process of separating coal of various sizes, densities and shapes by allowing them to settle in a fluid.

Generally, industrial, commercial, or other manufacturers that use steam, heat, or resultant energy for the dual use of processing materials and generating electricity. Cogenerators can sell excess electricity to the local utility. (b)

Coke (coal)
In general, coke is made from bituminous coal (or blends of bituminous coal) from which the volatile constituents are driven off by baking in an oven at temperatures as high as 2,000 degrees Fahrenheit, so that the fixed carbon and ash are fused together. Coke is hard and porous and has a gray, sub-metallic luster. It is used both as a fuel and for chemical reactions in smelting iron ore in a blast furnace in making pig iron and steel. Coke has a heating value of 13,000 to 14,000 BTU/pound.

Coke Breeze
Following a screening process, the smallest coke particles remaining in the form of a residue.

Coke Button
A button-sized piece of coke produced during laboratory testing of the coking or free swelling characteristics of coal. Numerical references of one through nine are assigned to coke buttons based on the degree of swelling during the coking process.

Continuous Miner
A mechanical mining machine consisting of a cutting head, a coal- gathering device, a chain conveyor with flexible loading boom, and a crawler-equipped chassis. Its function is to excavate the mineral and to load it onto shuttle cars or continuous-haulage systems. It is electrically powered, with a hydraulic subsystem for auxiliary functions. Power is supplied through a trailing cable. (c)

Contour Stripping or Surface Mining
The removal of overburden and mining from a coal seam that outcrops or approaches the surface at approximately the same elevation, in steep or mountainous areas. (c)


Deep Mine
An underground coal mine.

Demonstrated Reserve Base
A collective term for the sum of coal in both measured and indicated resource categories of reliability that represents 100 percent of coal in place as of a certain date. Includes beds of bituminous coal and anthracite 28 inches or more thick and beds of sub-bituminous coal 60 inches or more thick that occur at depths of up to 1,000 feet. Includes beds of lignite 60 inches or more thick that can be surface-mined. Includes also thinner and/or deeper beds that presently are being mined or for which there is evidence that they could be mined commercially at this time. Represents that portion of the identified coal resource from which reserves are calculated. (h)

Distributed Power (DP)
A train in which one to four locomotives are placed at various points along the train. The locomotive engineer in the lead locomotive controls the distributed locomotives. DP trains are longer but have improved brake control and reduced slack action.

Double Screened Coal
A process of coal sizing. Minimum and maximum dimensions are attained in the process by passing coal through one screen and over a second screen.

An overburden removal machine used in stripping coal seams because of its great reach and its ability to cast spoil farther from the pit – used for the recovery of moderate depth coal seams. (h)

Dried Coal
Moisture, an inherent component of coal, requires heat for its evaporation and release in the products of combustion. Surface moisture in cold climates increases handling problems. Normal atmospheric drying of coal is accelerated by passing hot combustion gases over or through beds of coal to be dried (usually metallurgical coal).


Fixed Carbon
The combustible residue remaining after volatile matter has been driven off by heating of coal.

Fluidized Bed Combustion
A coal burning system which received attention in the U.S. because of its expected ability to produce low sulfur dioxide and nitrogen oxide emissions along with a high overall efficiency. Coal is burned as it is mixed with other materials and suspended in space by an upward moving stream of air and combustion gases. This bed of suspended particles moves much as a boiling liquid. (f)

Fly Ash
The finely divided particles of ash entrained in gases resulting from the combustion of fuel.

Fossil Fuel
Any naturally occurring fuel of an organic nature, such as coal, crude oil or natural gas.

Fossil Fuel Steam-Electric Power Plant
An electricity generation plant in which the prime mover is a turbine rotated by high-pressure steam produced in a boiler by heat from burning fossil fuels. (b)

The tendency of a coal to crumble or break into small pieces.

The production of gaseous fuels from coal for residential, commercial and industrial users. The type of conversion process determines the heating values of the produced gas.

Grindability Index
Indicates the ease of pulverizing a coal in comparison to a reference coal. This index is helpful in estimating mill capacity. The two most common methods for determining this index are the Hardgrove Grindability Method and Ball Mill Grindability Method. Coals with a low index are more difficult to pulverize. (c)


Hardgrove Grindability Index
A measure of the relative ease with which coal may be pulverized. On a one to 100 scale, the lower the value the harder the coal.

Hydroelectric Power
Electricity generated by an electric power plant whose turbines are driven by falling water.

Inherent Moisture
That moisture remaining in the coal after natural drying in the air. In general, the moisture that is present in the coal in the bed. (a)

Kilowatt (KW)
A thousand watts (also see Megawatt).


A brownish-black woody-structured coal, lower in fixed carbon and higher in volatile matter and oxygen than either anthracite or bituminous coal. Heat content ranges up to 8,300 BTU/pound. (c)

Load-Out Facility
The basic purpose of a load-out facility is to get coal into rail cars, barges or trucks for movement to the destination. Important elements of such a facility include some or all of the following: moving the coal from the mine to stockpiles or storage silos; preparing the coal for shipment; weighing and loading with equipment that ranges from single front-end loaders working from a coal pile to sophisticated, computer-controlled conveyors, surge bins, chutes and gates. Coal trains usually are flood-loaded at rates of 3,000 tons per hour and more while the cars are in motion. The loading process can be controlled by an operator or automated by various sensing devices.

Longwall Mining
A mining method in which a large rectangular section of coal is removed in one continuous operation. Equipment is installed along one side of the section (the longwall face) and the coal is removed in slices 2- to 4- feet thick and lengths of up to 200 meters. The roof is supported by hydraulic props; a revolving cutting wheel or plow cuts and breaks the coal, and the coal is moved from the mining face with a rugged chain conveyor. (c) (h)

Megawatt (MW)
A watt is a unit of electric power; the output capability of electric generating plants, companies and systems is usually expressed in terms of megawatts (millions of watts). One watt = 3.4 BTU/hr. One kilowatt = 1.3 horsepower.

Metallurgical Coal
The various grades of coal suitable for carbonization to make coke for steel manufacture. Also known as "met" coal, it contains four important qualities: volatility, which affects coke yield; the level of impurities, which affects coke quality; composition, which affects coke strength; and basic characteristics, which affect coke oven safety. Metallurgical coal has a particularly high BTU, but low ash content.

Metric Ton (TONNE)
A unit of weight equal to 2,205 pounds.

Coal mining is performed through two major methods; strip mining or underground mining.

Mining, Strip
Strip mining involves the use of large equipment which removes overburden (rock, dirt, etc.), exposing the seam of coal. This method is usually used when the coal seam lies close to the ground surface and the overburden can be removed economically.

Mining, Underground

  1. Drift Mine
    Driven into the side of the hill where the coal seam outcrops. The seam is above the valley floor or water level.
  2. Slope Mine
    Driven into the ground above the coal seam level. The seam usually has no outcrop and is situated below the valley floor level.
  3. Shaft Mine
    Driven into the ground vertically to the seam of coal. Most often used for deep seams.


  1. Surface Moisture
    wetness of coal from external sources such as weather or coal washing processes.
  2. Inherent Moisture
    water which comprises an integral portion of the composition of coal. Moisture percentage measured in proximate analysis of coal reflects inherent moisture only.


Open-Pit Mining
Surface mining, a type of mining in which the overburden is removed from the product being mined and is dumped back after mining; or may refer specifically to an area from which overburden has been removed, which has not been filled. (c)

Open Top Hopper Cars
Open freight cars with a floor sloping to one or more hinged doors for discharging bulk materials, particularly coal.

The earth, rock and other materials that lie above the coal seam. (c)

Those levels of electricity output from generating stations necessary to satisfy peak demand during relatively short periods. Peaking plants are usually gas turbine, internal combustion and some hydroelectric. (b)

Petroleum Coke
A residual by-product from the oil refining industry. Following heat processing or thermal cracking that extracts all the more valuable gases and oil liquids from the crude input, a basic hydrocarbon is left which, despite being known as the garbage can of the refining process, does have a number of important properties and applications to industry around the world. There are essentially three types of petroleum coke: specialty or needle coke; calcined or anode coke; and green, raw or fuel coke. (d)

Proximate Analysis
A percentage measurement of the physical properties of coal including moisture, volatile matter, fixed carbon and ash. Proximate analysis is usually accompanied by a statement of sulphur content, BTUs per pound, ash fusion temperature and grindability.


Rapid Discharge Car
Open top hopper cars which are equipped with rapid opening doors in the bottom of each hopper. Unloading may be accomplished by methods as simple as a person attaching an air or electrical powered device to the door opening mechanism to automated systems that receive electrical signals from wayside devices to open or close the doors. The automated systems are usually powered by an in-train compressed air system separate from the air brakes. Rapid discharge cars allow the train to be efficiently unloaded in motion at speeds of up to 6 mph.

Raw Coal (Run-of-Mine Coal)
Coal extracted from the seam and not processed, washed, crushed or sized. (8)

Renewable Energy
Energy obtained from sources that are essentially inexhaustible (unlike, for example, the fossil fuels, of which there is a finite supply). Renewable sources of energy include wood, waste, geothermal, wind, photovoltaic and solar thermal energy. (b)

That portion of the demonstrated reserve base that is estimated to be recoverable with the technology and prices prevailing at the time of determination. The reserve is derived by applying a recovery factor to that component of the identified coal reserve designated as the demonstrated reserve base. (h)

Rotary Dump Unloading
A method for unloading bulk (coal) cars that are open top hoppers or gondolas. A car is locked into a dumping frame and completely inverted to discharge its contents. Cars equipped with rotary couplers can be dumped in this manner without being unhooked from the rest of the train. (f)

Various systems used for removal of impurities (primarily sulfur dioxide, but also fly ash) from flue gas emissions. An absorbent liquid or slurry is brought into contact with the flue gas. In the case of sulfur, SO2 in the flue gas is physically and/or chemically absorbed in the passing liquid. Two major types of equipment can be used in the flue gas desulfurization scrubber applications. One type can be used to remove particulates and sulfur dioxide simultaneously, while the other requires high efficiency particulate removal before the flue gas can be treated in the scrubber. Fly ash scrubbers have received limited interest. (g) (g)

A deposit or bed of coal which can vary in thickness from less than one inch to over fifty feet; from several acres to thousands of square miles in size; and from several feet in depth to thousands of feet below ground level.

Short Ton
A unit of weight equal to 2,000 pounds.

A mining method with a panel layout similar to longwall but at a panel width reduced by approximately 50%. It uses continuous-mining equipment for coal cutting and haulage and a specially designed hydraulic roof support. (c)

Coal ash that is or has been in a molten state.

Spot Price
A transaction price concluded "on the spot," that is, on a one-time, prompt basis; usually the transaction involves only one specific quantity of product. This contrasts with a term contract sale price, which obligates the seller to deliver a product at an agreed frequency and price over an extended period. (b)

Steam Generators – Furnace Design
The furnace design of steam generators may be classified into two categories by type: dry bottom and wet bottom.

The dry-bottom units are fired with pulverized fuel. About 10 to 20% of the fired ash goes to the bottom of the furnace in a dry form and is removed continually, while the remainder of the ash (80 to 90%) passes up through the furnace, through the boiler convection banks, and air heater into the dust collector.

Wet-bottom units may be fired by crushed coal, such as is fed to cyclone furnaces, or by pulverized coal. The pulverized coal-fired wet-bottom unit traps 50% or less of the ash as molten slag on the furnace walls; this slag runs down to the furnace floor and taps down into the slag tanks for removal. Cyclone furnace boilers are the wet-bottom type because they make slag that flows out on the furnace walls, then to the floor, and into slag tanks. Although hundreds of wet-bottom type boilers have been sold over the last 35 years, this type of firing is no longer being offered as a new product because of NOx emission considerations. (e)

Stoker Coal
Double screened bituminous coal variable in size but most often between 1" x." and 2" x.".

Strip Mine
Refers to a procedure of mining that entails the complete removal of all material from over the product to be mined in a series of rows or strips; also referred to as "open cut," "open pit," or "surface mine." (c)

Sub-bituminous Coal
A glossy-black-weathering and nonagglomerating coal which is lower in fixed carbon than bituminous coal, with more volatile matter and oxygen. Heat content ranges from 8,300 to 11,500 BTU/pound. (c)

A non-metallic chemical element comprising varying degrees of coal's composition. Sulphur burns off when coal is heated but promotes clinkering, slagging and corrosion. Coals with high sulphur contents are susceptible to spontaneous combustion in storage piles. Sulphur present in stack emissions is regulated by EPA clean air standards.

Sulphur Classifications

  • Pyritic
    The only inherent form of sulphur in coal which can be removed by washing.
  • Organic
    Inherent and generally cannot be removed from coal.
  • Sulphates
    Oxidation products, present on the surface of fresh coal in small amounts. Sulphates can be removed conveniently through standard cleaning processes.

Surface Mine
A coal-producing mine that is usually within a few hundred feet of the surface. Earth above or around the coal (overburden) is removed to expose the coalbed, which is then mined with surface excavation equipment such as draglines, power shovels, bulldozers, loaders, and augers. It may also be known as an area, contour, open-pit, strip or auger mine.


oal Tipple
Originally, the place where the mine cars were tipped and emptied of their coal; still used in that sense, although now more generally applied to the surface structures of a mine, including the preparation plant and loading tracks. The tracks, trestles, screens, and so on, at the entrance to a colliery where coal is screened and loaded. (c)

Track Configurations (for loading)
Sufficient trackage should be provided for the handling of a full train, without breaking the train or recoupling cars while being pulled through the loading facility.

Loading Track Configurations:

  1. Loop Track
    Loop is sufficiently large to handle shipments between 7,000 and 13,000 tons.
  2. Shoo-fly Track
    Siding with switches at each end, designed to allow the train to "hang out" on main running track during the loading operation. Actual loading is performed on the siding to prevent coal spillage on the running track.
  3. Dead-end Siding
    Track should be lengthy enough to accommodate the trains to be loaded.
  4. Ladder Track
    Two or more dead-end tracks with sufficient capacity (empty and loaded) to handle trains being shipped.
  5. On-branch Loading
    Permitted conditionally if the coal loading facility is situated at the end of the branch, with no patrons located beyond.

    Note: Variations in track configurations may be permitted under certain circumstances.

Ultimate Analysis
Chemical properties of coal represented in percentage of weight. Included are carbon, hydrogen, sulphur, oxygen, moisture and ash.

Underground Mine
A mine where coal is produced by tunneling into the earth to the coalbed, which is then mined with underground mining equipment such as cutting machines and continuous, longwall, and shortwall mining machines. Also called deep mines, underground mines are classified according to the type of opening used to reach the coal; i.e., drift (level tunnel), slope (inclined tunnel), or shaft (vertical tunnel).

Unit Train
Volume shipment of coal from one origin to one destination.

Volatile Matter
Portion of coal which is driven off in a gaseous form when the coal is heated. Volatility is classified as follows:

  Composition by Weight
high volatile over 31%
medium volatile 22% to 31%
low volatile under 22%


(a) A Dictionary of Mining, Mineral, and Related Terms, Bureau of Mines, compiled and edited by Paul W. Thrush, 1968

(b) Annual Energy Review 1987, Energy Information Administration

(c) Coal Handbook, edited by Robert A. Myers, 1981

(d) "Petroleum Cokes – Focal Point USA," International Bulk Journal, August 1988

(e) "How Coal Quality Affects Boiler Design," by Donald W. Pacer and Albert F. Duzy, Coal Mining and Processing, May 1982, p. 72

(f) Solid Fuels for U.S. Industry, Volume II, Cameron Engineers, February 1979

(g) Coal Preparation, Joseph W. Leonard, editor, 1979

(h) A Cost Comparison of Selected U.S. and Canadian Coal Mines, U.S. Bureau of Mines, April 1988