CHAPTER 1
HISTORY AND TERMINOLOGY

1.1 INTRODUCTION

Coal is an organic sedimentary rock that contains varying amounts of carbon, hydrogen, nitrogen, oxygen, and sulfur as well as trace amounts of other elements, including mineral matter, as well as methane which is found within the pore systems of the coal (ASTM D121; Speight, 2013a). It is a solid, brittle, combustible, carbonaceous rock formed by the decomposition and alteration of vegetation by compaction, temperature, and pressure and varies in color from brown to black and is usually stratified as a coal seam. The source of the vegetative precursors to coal is a variety of ancient plant forms as well as ancient woody precursors. The plant precursors that eventually formed coal were deposited as dead and decaying carbonaceous materials that were compacted, hardened, chemically altered, and metamorphosed by the pressure (in some cases accompanied by heat) of overlying sediments over geologic time (Table 1.1). When the plants died, the biomass was deposited in anaerobic, aquatic environments where the low oxygen level prevented the reduction of the biomass and release of carbon dioxide.1

Table 1.1 The Geologic Timescale

Evidence of the types of plants that contributed to carboniferous deposits can occasionally be found in the coal as fossil imprints as well as in the shale and sandstone sediments that overlie coal deposits.

Coal sediments (coal beds, coal seams) can range from fractions of an inch to hundreds of feet in thickness and are found in all geologic periods from Silurian through Quaternary, but the earliest commercially important coals are found in rocks of Mississippian age (Carboniferous in Europe). Coal is generally formed in either a fluvial environment or in a basin that is open to marine incursions and consists of more than 50% w/w (typically more than 70% v/v) carbonaceous material (organic material containing carbon, hydrogen, and other elements as well as inherent moisture, which is a moisture that occurs within the coal).

1.2 DEFINITIONS AND TERMINOLOGY

Simply and by definition, coal is an organic rock. In addition, coal is also defined as a black or dark-brown combustible mineral substance consisting of carbonized vegetable matter, used as a fuel.

It is customary (especially through this text) to use the word coal in the singular form but the word is, in reality, applicable to materials having a rather wide range of properties - this is similar to the use of the word petroleum (or crude oil), which encompassed a variety of materials from low-boiling (light) conventional crude oil to the thicker viscous high-boiling heavy oil (Speight, 2014). In terms of coal, one sample might be a wet, easily crumbling brown material looking like partially decayed wood (Lignite) while another would be a very hard, glossy black, lustrous material (anthracite). In addition, the heating value (Chapter 8) of these samples would range from about 5000 to about 15,000 BTU/lb. Thus, the use of the word coal in this text implies either a single family member of a uniquely defined material as well as a family of natural-occurring family of organic rocks having both similarities and differences within the members of that family.

The name coal is thought to be derived from the Old English col that was a type of charcoal at the time. Generally, coal was not mined to any large extent during the early Middle Ages (prior to 1000 AD) but there are written records of coal being mined after 1000 AD. Moreover, coal is, in some areas, referred to as sea-coal as it is occasionally found washed up on beaches, especially those in the north east area of England. However, the rapidly expanding use of coal throughout the nineteenth century and the early part of the twentieth century has seen a phenomenal increase in coal use. This increased popularity has made it necessary to devise acceptable methods for coal analysis with the goal of correlating fuel composition and properties with behavior (Vorres, 1993; Speight, 2013a).

In the modern system of terminology, coal is subdivided into various types that are the result of geological processes pressure to the dead precursors over time and under suitable conditions (which are difficult to define), it is transformed successively into: (1) lignite, (2) sub-bituminous coal, (3) bituminous coal, and (4) anthracite (Speight, 2013a,b).

Lignite (sometimes referred to as brown coal) is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Sub-bituminous coal, which has properties that range from similar properties of lignite to those of bituminous coal, is used primarily as fuel for steam-electric power generation (Speight, 2013b) and is an important source (through pyrolytic decomposition) of low-boiling aromatic hydrocarbons for the chemicals industry (Speight, 2013a). Bituminous coal is a dense black sedimentary rock that often has well-defined bands of bright and dull material; it is used primarily as fuel in steam-electric power generation, with substantial quantities used for heat and power applications in manufacturing and to make coke. Anthracite (black coal, hard coal, stone coal, blind coal, black diamond, and crow coal) is a hard, glossy black coal and is the most metamorphosed type of coal (the highest rank of the coal series) in which the carbon content is between 92.1% and 98%. Anthracite does not emit tar or other hydrocarbonaceous vapor when heated below the point of ignition - it ignites with difficulty and burns with a short, blue, and smokeless flame. Finally, although not an official definition in the sense of the four previous definitions, steam coal is the name given to a grade of coal that has properties between those of bituminous coal and anthracite and which was once widely used as a fuel for steam locomotives. With respect to this specialized use, it is sometimes known as sea coal in the United States.

Peat is considered by some observers/scientists/engineers to be a precursor of coal and to be a type of coal but the lack of any obvious resemblance to any other four coal types presented earlier tends to negate such inclusion into the coal sequence.

It was during the Industrial Revolution in the eighteenth and nineteenth century the demand for coal surged. The great improvement of the steam engine by James Watt, patented in 1769, was largely responsible for the growth in coal use. The history of coal mining and use is inextricably linked with that of the Industrial Revolution - iron and steel production, rail transportation, and steamships. Coal was also used to produce gas for gas lights in many cities, which was called town gas. This process of coal gasification witnessed the growth in gas lights across metropolitan areas at the beginning of the nineteenth century, particularly in London. The use of coal gas in street lighting was eventually replaced with the emergence of the modern electric era. With the development of electric power in the nineteenth century, the future of coal use became closely tied to electricity generation. The first practical coal-fired electric generating station, developed by Thomas Edison, went into operation in New York City in 1882, supplying electricity for household lights.

Steam coal, also known as thermal coal, is used in power stations to generate electricity (Speight, 2013a, 2013b). The earliest conventional coal-fired power stations used lump coal, which was burnt on a grate in boilers to raise steam. Currently, the coal is first milled to a fine powder, which increases the surface area and allows it to burn more quickly. In these pulverized coal (PC) combustion systems, the powdered coal is blown into...