is a carbon-containing rock formed by the debris from the decay of ferns, vines, trees and other plants which flourished in swamps millions of years ago.
over time, the debris became buried and the actions of bacteria, heat and pressure transformed the debris first into peat (a precursor of coal) and then into the various types of coal as we know them today. in more technical terminology, that process of transformation is referred to as metamorphosis, coalification or lithification.
coal is extracted by mining from deposits that exist deep underground as well as deposits that are essentially at or near the surface of the ground.
because of the various degrees of transformation that occurred during the forming of coal deposits in different locations, the composition of coal varies from one deposit to another.
no two coals are the same in every respect. in general, coal consists of carbon, hydrogen, oxygen, nitrogen, sulfur and mineral matter (including compounds of silicon, aluminum, iron, calcium, magnesium and others).can supply you all kinds of silicon , aluminum ore cursher, iron ore crusher or iron crusher, calcium crusher, magnesium crusher etc.
there are many compositional differences between the coals mined from the different coal deposits worldwide. the different types of coal are most usually classified by rank which depends upon the degree of transformation from the original source (i.e., decayed plants) and is therefore a measure of a coal’s age.
as the process of progressive transformation took place, the heating value and the fixed carbon content of the coal increased and the amount of volatile matter in the coal decreased. the method of ranking coals used in the united states and canada was developed by the american society for testing and materials (astm) and is based on a number of parameters obtained by various prescribed tests:
- heating value: the energy released as heat when coal (or any other substance) undergoes complete combustion with oxygen.
- volatile matter: the portion of a coal sample which, when heated in the absence of air at prescribed conditions, is released as gases. it includes carbon dioxide, volatile organic and inorganic gases containing sulfur and nitrogen.
- moisture: the water inherently contained within the coal and existing in the coal in its natural state of deposition. it as measured as the amount of water released when a coal sample is heated at prescribed conditions. it does not include any free water on the surface of the coal. such free water is removed by air-drying the coal sample being tested.
- ash: the inorganic residue remaining after a coal sample is completely burned and is largely composed of compounds of silica, aluminum, iron, calcium, magnesium and others. the ash may vary considerably from the mineral matter present in the coal (such as clay, quartz, pyrites and gypsum) before being burned. zenith can supply you coal crushing equipments such as coal , coal , coal etc. according to the crushing application, mainly includes clay crusher, quartz crusher, pyrites ore crusher, gypsum crusher etc.
- fixed carbon: the remaining organic matter after the volatile matter and moisture have been released. it is typically calculated by subtracting from 100 the percentages of volatile matter, moisture and ash. it is composed primarily of carbon with lesser amounts of hydrogen, nitrogen and sulfur.
the anthracitic coals, with the highest contents of fixed carbon and lowest contents of volatile material, have the highest rank. the lignite coals, with the lowest contents of fixed carbon and highest contents of volatile matter, have the lowest rank. the bituminous and subbituminous coals (in that order) are ranked between the anthracitic and lignite coal.
the diagram below provides the estimated percentage of the world’s coal reserves for each coal rank. it also provides the typical uses of each coal rank.
as a broad generality, the anthracitic coals have the highest heating value and the lignite coals have the lowest heating values.