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Concept
Coal analysis
Summary
Coal analysis techniques are specific analytical methods designed to measure the particular physical and chemical properties of coals. These methods are used primarily to determine the suitability of coal for coking, power generation or for iron ore smelting in the manufacture of steel.
Coal comes in four main types or ranks: lignite or brown coal, bituminous coal or black coal, anthracite and graphite. Each type of coal has a certain set of physical parameters which are mostly controlled by moisture, volatile content (in terms of aliphatic or aromatic hydrocarbons) and carbon content.
Moisture is an important property of coal, as all coals are mined wet. Groundwater and other extraneous moisture is known as adventitious moisture and is readily evaporated. Moisture held within the coal itself is known as inherent moisture and is analysed quantitatively. Moisture may occur in four possible forms within coal:
Surface moisture: water held on the surface of coal particles or macerals
Hygroscopic moisture: water held by capillary action within the microfractures of the coal
Decomposition moisture: water held within the coal's decomposed organic compounds
Mineral moisture: water which comprises part of the crystal structure of hydrous silicates such as clays
Total moisture is analysed by loss of mass between an untreated sample and the sample once analysed. This is achieved by any of the following methods;
Heating the coal with toluene
Drying in a minimum free-space oven at within a nitrogen atmosphere
Drying in air at and relative loss of mass determined
Methods 1 and 2 are suitable with low-rank coals, but method 3 is only suitable for high-rank coals as free air drying low-rank coals may promote oxidation.
Inherent moisture is analysed similarly, though it may be done in a vacuum.
Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short- and long-chain hydrocarbons, aromatic hydrocarbons and some sulfur.
Official source
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