Mineral matter high temperature behavior

The grade of a coal establishes its economic value for a specific end use. Grade of coal refers to the amount of mineral matter that is present in the coal and is a measure of coal quality. Sulfur content, ash fusion temperatures, that is, measurement of the behavior of ash at high tanperatures, and quantity of trace elements in coal are also used to grade coal. Although formal classification systems have not been developed around grade of coal, grade is important to the coal user. 

The ash fusion temperatures. They indicate the behavior of the ash residues from the coal at high temperatures and are mainly related to the chemical composition of the ash and the nature of the coal s mineral matter. They are nsed to indicate whether the ash will remain as a fine powder within the fnmace system after the coal is burned or whether some of it might melt to form a slag on the boiler s heat exchange surfaces. 

---