Types of Coal

There are several different types of coal, each displaying different properties resulting from their age and the depth to which they have been buried under other rocks. In some parts of the world (e.g., New Zealand), coal development is accelerated by volcanic heat or crustal stresses. 

Peat is the layer of vegetable material directly underlying the growing zone of a coal-forming environment. The vegetable material shows very little alteration and contains the roots of living plants. Peat is widely used as a domestic fuel in rural parts of the world. 

Lignite. Lignite is geologically very young (upward of around 40,000 years). It is brown and can be soft and fibrous, containing discernible plant material. It also contains large amounts of moisture (typically around 70%) and hence, it has a low energy content (around 8 to 10 MJ/kg). As the coal develops it loses its fibrous character and darkens in color. 

Black coal. Black coal ranges from Cretaceous age (65 to 105 million years ago) to mid-Permian age (up to 260 million years ago). They are all black some are sooty and still quite high in moisture (sub-bituminous coal). A common name for this coal in many parts of the world is black lignite. Coals that get more deeply buried by other rocks lose more moisture and start to lose their oxygen and hydrogen they are harder and shinier (e.g., bituminous coal). Typical energy contents are around 24 to 28 MJ/kg. These coals generally have less than 3% moisture, but some power stations burn coal at up to 30% ash. 

Anthracite. Anthracite is a hard, black, shiny form of coal that contains virtually no moisture and very low volatile content. Because of this, it bums with little or no smoke and is sold as a smokeless fuel. In general, coals only approach anthracite composition where bituminous coal seams have been compressed further by local crustal movements. Anthracites can have energy contents up to about 32 MJ/kg, depending on the ash content. 

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Process Pa.ra.meters, The most notable effects ia gasifiers are those of pressure (Fig. 1) and coal character. Some initial processiag of the coal feedstock maybe requited. The type and degree of pretreatment is a function of the process and/or the type of coal (see Coal conversion processes, CLEANING AND DESULFURIZATION). 

Cmde gas leaves from the top of the gasifier at 288—593°C depending on the type of coal used. The composition of gas also depends on the type of coal and is notable for the relatively high methane content when contrasted to gases produced at lower pressures or higher temperatures. These gas products can be used as produced for electric power production or can be treated to remove carbon dioxide and hydrocarbons to provide synthesis gas for ammonia, methanol, and synthetic oil production. The gas is made suitable for methanation, to produce synthetic natural gas, by a partial shift and carbon dioxide and sulfur removal. 

Combustion Systems. Combustion systems vary in nature depending on the nature of the feedstock and the air needed for the combustion process (54). However, the two principal types of coal-buming systems are usually referred to as layer and chambered. The former refers to fixed beds the latter is more specifically for pulverized fuel. 

The conditions of pyrolysis either as low or high temperature carbonization, and the type of coal, determine the composition of Hquids produced, known as tars. Humic coals give greater yields of phenol (qv) [108-95-2] (up to 50%), whereas hydrogen-rich coals give more hydrocarbons (qv). The whole tar and distillation fractions are used as fuels and as sources of phenols, or as an additive ia carbonized briquettes. Pitch can be used as a biader for briquettes, for electrode carbon after coking, or for blending with road asphalt (qv). 

Trimesic acid is also referred to as 5-carboxyisophthahc acid [554-95-0] trimesinic acid, or trimesitinic acid. It is a smaH-volume, synthetic chemical and is sold commercially. Traces of trimesic acid as well as other aromatic carboxyUc acids with three or more carboxyUc acid groups are found in lignite (137), and when various types of coals or coal components such as brown coal, asphaltene, or coal-tar pitch are oxidized. 

Although a number of low temperature processes have been studied, only a few have been used commercially. These have been limited in the types of coal that are acceptable, and the by-products are less valuable than those obtained from high temperature processing. The Disco process is used in the United States to supply a limited amount of fuel to meet requirements of smoke ordinances. The British CoaUte and Rexco processes produced substantial amounts of domestic smokeless fuel. Development of fluid-bed methods of carbonizing finer coal at ca 400°C has been studied in the United Kingdom. A reactive char is briquetted without a binder to produce a premium open-fire smokeless fuel. 

For by-product coke ovens, it is general practice to blend two or more types of coals that have complimentary technical as well as economic characteristics. Because most by-product coke plants are located near the large industrial users of the coke and by-products, coals usually have to be transported from the coal mines to the coke plants. Thus coal blends are designed on integration of coke quaUty needs, by-product quaUty needs, coal costs, transportation costs, impacts of productivity, and impacts on the coke ovens themselves. The physical behavior of coal blends during coking can damage coke ovens. 

There are essentially three types of coal gasifiers moving-bed or countercurrent reactors fluidized-bed or back-mixed reactors and entrained-flow or plug-flow reactors. The three types are shown schematically in Eigure 2. 

Eig. 4. Product yields for EDS process on D on once-through and a bottoms recycle basis for various types of coal. DAF = dry ash free. 

Coal-based pitches are predommantly byproducts of metallurgical coke operations in recovery-type coke ovens. The volatile products from the coke oven are recovered and processed, in simplest terms, into gas, light oils, and tar. The quantity and character of the materials are influenced by the type of coal charge, the design of the cokmg equipment, and the temperature and time profile of carboni2ation. Table 1 shows a typical yield of products from the... 

World coal usage, inclusive ot the three major types of coal—anthracite, bituminous (by far the most prevalent form) and lignite—reached a plateau in the first decade of the twentieth centuiy and climbed only very slowly in the half century that followed. By 1880, coal use had equaled wood use on a worldwide basis. The usage around the turn of the centuiy was on the order of 2.2 gigatons per year (around 55 quads), of which about 600 million tons were in the United States. World oil production progressively supplemented the use of coal between 1900 and 1950, increasing by more than an order of magnitude in that period of time, from a little over a quad to some 20 quads. Coal s increase over those years was fractionally much less. 

NO, emissions are less dependent on the type of coal burned, and two oxidation mechanisms are associated with the release of NO, into the atmosphere during the combustion process. Thermal NO results from the reaction of nitrogen in the comhustion air with excess oxygen at elevated temperatures, and fuel NO., is a product of the oxidation of nitrogen chemically hound in the coal. 

Fluidized beds 1-50 All types of coal and waste sohd fuels 3.0 0.3-1.0m 2 1 and then by bed sectoring Removal and clean-up from bed Special vertical shell boilers and watertubes... 

A hard type of coal with a high calorific value. 

The grade of various types of coal based on size, calorific value, and ash content. 

Frankland discovered the fundamental principle of valency—the combining power of atoms to form compounds. He gave the chemical bond its name and popularized the notation we use today for writing chemical formulas. He codiscovered helium, helped found synthetic organic and structural chemistry, and was the father of organometallic chemistry. He was also the first person to thoroughly analyze the gases from different types of coal and—dieters take note—the first to measure the calories in food. 

Contents and Heating Values of Different Types of Coal... 

Synthoil A coal liquifaction process in which coal, suspended in oil from the process, is hydrogenated over a cobalt/molybdenum catalyst on alumina. The process was piloted by the Pittsburgh Energy Research Center at Bruceton, PA in the 1970s using several types of coal, but it was abandoned in 1978. See also CSF, H-Coal. 

The electrostatic precipitator in Example 2.2 is typical of industrial processes the operation of most process equipment is so complicated that application of fundamental physical laws may not produce a suitable model. For example, thermodynamic or chemical kinetics data may be required in such a model but may not be available. On the other hand, although the development of black box models may require less effort and the resulting models may be simpler in form, empirical models are usually only relevant for restricted ranges of operation and scale-up. Thus, a model such as ESP model 1 might need to be completely reformulated for a different size range of particulate matter or for a different type of coal. You might have to use a series of black box models to achieve suitable accuracy for different operating conditions. 

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