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Coal is an energy source used around the world as fuel for numerous tasks. People have been using it since antiquity, and while its use has waned somewhat in modern days, it still has a major role to play in many power systems. Its properties vary greatly, depending on its geological origin and the geological processes it has come through during its formation and burial.
One of the important factors that define coals properties is its adhesive index. Adhesive index is a measure of the ability of coal to form a cohesive mass and to bond with other substances. This can have a major impact on the way a coal is used. A high adhesive index indicates that the coal is able to bind well with other substances, ensuring a reliable combustion process. Conversely, a low adhesive index suggests that the coal is not able to form a cohesive mass or bond with other materials.
Adhesive index of coal is chiefly determined by its chemical composition. The three main elements in coal that affect its adhesive index are carbon, hydrogen and sulfur. Each of these elements can contribute to, or limit, the ability of coal to form a cohesive mass. Carbon and hydrogen form strong, stable bonds with each other, and with other molecules. This makes coal higher in carbon and hydrogen better for coal-to-coal binding. Sulfur, on the other hand, decreases coals adhesive properties, as sulfur molecules have difficulty bonding with other substances. The exact balance of these three elements in a coal determines its adhesive index.
In addition to their impact on coals adhesive index, these three elements have numerous other characteristics that are important in determining the suitability of a coal. These can range from the energy content and moisture content to the type of ash it produces when burned. The chemical composition of coal is therefore crucial in understanding the practical implications of different coals. For example, high-sulfur coal might have a lower adhesive index than low-sulfur coal, but it is also more liable to produce fouling, a problem in which ash deposits cling to the insides of combustion chambers.
Different geologies give rise to differently composed coals. For example, coals found in seams in sedimentary rocks are often bituminous, while coals found in igneous-metamorphic rocks tend to be anthracite. Bituminous coals tend to have a lower adhesive index than anthracites, due to their higher sulfur and moisture content. This is important, as it means that not all coal is suitable for all uses.
The adhesive index of coal is an important measure of its suitability for various uses. It helps to determine if it can form a cohesive mass or if it will be prone to forming loose particles. It also helps to inform decisions about which coals are more suitable for certain tasks. A high adhesive index means that a coal is better able to form a lasting bond, increasing its suitability for large-scale power generation. On the other hand, low adhesive index suggests that that coal is more suitable for low temperature applications, such as domestic heating.
