100% 18 80% 60% 40% 20% 0% 1071 Coal in C#

Decoding Code 128B in C# 100% 18 80% 60% 40% 20% 0% 1071 Coal

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521 Coal Formation The precursors to coal were plant remains (containing carbon, hydrogen, and oxygen) that were deposited in the Carboniferous period, between 345 and 280 million years ago (Fig 56) As the plant remains became submerged under water, decomposition occurred in which oxygen and hydrogen were lost from the remains to leave a deposit with a high percentage of carbon With the passage of time, layers of inorganic material such as sand and mud settled from the water and covered the deposits The pressure of these overlying layers, as well as movements of the earth s crust acted to compress and harden the deposits, thus producing coal from the vegetal matter The plant material (vegetal matter) is composed mainly of carbon, hydrogen, oxygen, nitrogen, sulfur, and some inorganic mineral elements When this material decays under

FIGURE 56 Formation of coal (Reproduced with permission Copyright 2000 Kentucky Geological Survey, University of Kentucky)

water, in the absence of oxygen, the carbon content increases The initial product of this decomposition process is known as peat The transformation of peat to lignite is the result of pressure exerted by sedimentary materials that accumulate over the peat deposits Even greater pressures and heat from movements of the Earth s crust (as occurs during mountain building), and occasionally from igneous intrusion, cause the transformation of lignite to bituminous and anthracite coal 522 Coal Types Coal occurs in different forms or types (Fig 57) Variations in the nature of the source material and local or regional variations in the coalification processes cause the vegetal matter to evolve differently Thus, various classification systems exist to define the different types of coal

FIGURE 57 Coal types (Reproduced with permission Copyright 2000 Kentucky Geological Survey, University of Kentucky)

Thus, as geologic processes increase their effect over time, the coal precursors are transformed over time into: 1 Lignite also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for steam-electric power generation Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age 2 Subbituminous coal whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation 3 Bituminous coal a dense coal, usually black, sometimes dark brown, often with welldefined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing industry and to make coke 4 Anthracite the highest rank; a harder, glossy, black coal used primarily for residentialand commercial-space heating Coal classification systems are based on the degree to which coals have undergone coalification Such varying degrees of coalification are generally called coal ranks (or classes) The determination of coal rank has a number of practical applications such as the definition of the coal properties The properties include the amount of heat produced during combustion, the amount of gaseous products released upon heating, and the suitability of the coals for producing coke The rank of a coal indicates the progressive changes in carbon, volatile matter, and probably ash and sulfur that take place as coalification progresses from the lower rank lignite through the higher ranks of subbituminous, high-volatile bituminous, low-volatile bituminous, and anthracite The rank of a coal should not be confused with its grade A high rank (eg, anthracite) represents coal from a deposit that has undergone the greatest degree of metamorphosis and contains very little mineral matter, ash, and moisture On the other hand, any rank of coal, when cleaned of impurities through coal preparation will be of a higher grade The most commonly employed systems of classification are those based on analyses that can be performed relatively easily in the laboratory, as described by the American Society for Testing and Materials (ASTM) on the basis of fixed carbon content, volatile matter content, and calorific value In addition to the major ranks (lignite, subbituminous, bituminous, and anthracite), each rank may be subdivided into coal groups, such as highvolatile A bituminous coal Other designations, such as coking coal and steam coal, have been applied to coals, but they tend to differ from country to country The term coal type is also employed to distinguish between banded coals and nonbanded coals Banded coals contain varying amounts of vitrinite and opaque material They include bright coal, which contains more than 80 percent vitrinite, and splint coal, which contains more than 30 percent opaque matter The nonbanded varieties include boghead coal, which has a high percentage of algal remains, and cannel coal with a high percentage of spores The usage of all the above terms is quite subjective By analogy to the term mineral, which is applied to inorganic material, the term maceral is used to describe organic constituents present in coals Maceral nomenclature has been applied differently by some European coal petrologists who studied polished blocks of coal using reflected-light microscopy (their terminology is based on morphology, botanical affinity, and mode of occurrence) and by some North American petrologists who studied very thin slices (thin sections) of coal using transmitted-light microscopy Three major maceral groups are generally recognized: vitrinite, exinite, and inertinite The vitrinite group is the most abundant and is derived primarily from cell walls and woody tissues Several varieties are recognized, for example, telinite (the brighter parts of vitrinite that make up cell walls) and collinite (clear vitrinite that occupies the spaces between cell walls)