Coal is a universally known substance. Being formed after hundreds of millions of years of pressure on prehistoric vegetation that originally accumulated in swamps and peat bogs, this fossil fuel provides a great amount of energy through harvesting. Coal is a relatively inexpensive fuel, and even though its use has dwindled in the past decade, over 40% of worldwide energy is produced by coal.
A material less known than coal is that of the fuel coke. Coal generally is burned to be used as a source of energy, but when it is heated without air through the process of destructive distillation, it produces byproducts coke, coal tar, amino acid liquor, and coal gas. Each has unique qualities that make it ideal for a different purpose. Coke is a hard, gray, massive, porous fuel that is characterized by having incredibly large carbon content. Coke contains all of the mineral matter in the original coal from which it was derived, except that it has chemically altered and decomposed. Coke is generally used as a fuel for stoves and furnaces in in which the environment is unsuitable for the complete burning of coal itself. An example of this is the use of coke in a blast furnace to chemically reduce and physically convert iron oxides into liquid iron called “hot metal”.
The standard terminology of both coal and coke fuels is covered in ASTM D121-15: Standard Terminology of Coal and Coke. In addition to defining coke, which it refers to as “a carbonaceous solid produced from coal, petroleum, or other materials by thermal decomposition with passage through a plastic state”, the standard also provides descriptions of coke types: beehive coke, by-product coke, coke breeze, and dry coke.
In discussing the terminology of coal and coke, it would be somewhat irresponsible to overlook the origin of the word that is now attached to the substance produced from destructive distillation of coal. It is difficult to think of “coke” without in some way connecting it with the iconic use of the word as an abbreviation for the soft drink and even the street drug. However, this coal byproduct is in no way connected to the other uses of the word, instead deriving from the Middle English colke, meaning “core, charcoal”. This is an interesting connection because coke fuel is to coal essentially what charcoal is to wood, as it is a byproduct from burning the initial substance under particular conditions.
|Coke as it is burned in a blast furnace|
The variation in coal and coal-related substances is remarkably vast, encompassing many different materials that have different qualities for the generation of energy and other purposes. There are several different types of coal alone, depending on the timespan in which the carbon matter remained in the ground and the amount of pressure and depth that it was exposed to during that time. These main types of coal are anthracite, bituminous, lignite, and peat, and they each burn at different rates.
Some of the byproducts of coal are used for energy, while others are given completely different purposes in the modern world. For example, coal tar is a highly viscous byproduct of coal produced under the same conditions as coke. Coal tar is not used as a fuel source to generate energy, but is instead utilized as a healing applicator to skin rashes, treating the itching, scaling, and flaking due to skin conditions such as psoriasis or seborrheic dermatitis.
ASTM D121-15 provides a reference for comprehending the heavy amount of material relating to the coal industry, and should be used as a supplemental document to many other ASTM International standards that provide guidelines for the creation, use, and management of coal and coke. It provides the foundation for which comprehension of these standards is possible. Examples of these include:
ASTM D388-19a: Standard Classification of Coals by Rank
ASTM D2013/D2013M-21: Standard Practice for Preparing Coal Samples for Analysis
ASTM D3172-13(2021)e1: Standard Practice for Proximate Analysis of Coal and Coke
ASTM D3173/D3173M-17a: Standard Test Method for Moisture in the Analysis Sample of Coal and Coke
ASTM D6316-17: Standard Test Method for Determination of Total, Combustible and Carbonate Carbon in Solid Residues from Coal and Coke