Coal Properties / Improvements
 

There are two different types of analyses used to determine the nature of bituminous coal: Proximate and Ultimate analysis:
Proximate Analysis
Determines (on an as-received basis)
  • Moisture content
  • Volatile matter (gases released when coal is heated).
  • Fixed carbon (solid fuel left after the volatile matter is driven off).
  • Ash (impurities consisting of silica, iron, alumina, and other incombustible matter).

    



Source:  U.S. DOE - EIA, Coal Data: A Reference, 1989.
 

 Ultimate Analysis
Determines the amount of carbon, hydrogen, oxygen, nitrogen, and sulfur.
  • Btu - Heating value is determined in terms of Btu both on an as-received basis (including moisture) and on a dry basis.
 

Improving the Properties of Mined Coal

Kentucky coal is improved by the partial removal of the impurities—sulfur and ash.  The cleaning process to remove impurities from the coal is often called beneficiation, coal preparation, or coal washing.Teco Coal - Preparation Plant

In general, coal cleaning is accomplished by separating and removing inorganic impurities from organic coal particles.  The inorganic ash impurities are predominantly more dense than the coal particles.  This property is generally the basis for separating the coal particles from the ash impurities.

Western Kentucky had 13,090 tons per hour of coal preparation design capacity at approximately 20 coal preparation plants during 2005.  Eastern Kentucky had 46,495 tons per hour of coal preparation design capacity at approximately 67 coal preparation plants during 2005.

Each coal seam has a different washability characteristic.  The range of improvement to a particular seam by mechanical washing varies from plant to plant and location to location.Teco Coal - Preparation Plant

In Western Kentucky, sulfur (inorganic sulfur) and ash are the two main impurities removed.  Considering the seven principal mined seams in this area, 0.5% to 2.5% can be subtracted from the average sulfur content and 9% to 13% can be subtracted from the ash content after the coal washing process.

In Eastern Kentucky, coals with very high ash contents are washed.  High ash content results from seam impurities, splits, or partings in the seam.  In these seams the ash is the main impurity removed—10% to 15% can be subtracted from the ash content after the coal washing process and with only a slight reduction in the sulfur content.

 Source:  Kentucky Office of Energy Policy's Kentucky pre/rail directory.