Influence of Moisture on the Preparation and Coking of Coal Batch

The maximum moisture content is found to depend on the nature of the coal and its metamorphic stage, characterized by the volatile matter, the vitrinite reflection coefficient, the carbon and hydrogen content, and the calorific value. On moving to smaller size classes, the maximum moisture content increases on account of the increase in specific surface. The maximum moisture content is practically independent of the coal's degree of oxidation and the chemical composition of the ash. The packing density is a maximum for dry coal and falls to a minimum at a moisture content of 6-10% (depending on the size class). The oxidation of coal is accompanied by increase in the total and analytical moisture content as a result of physical and chemical sorption at the surface of the coal particles. Increase in moisture content increases the coal's resistance to crushing, which results in nonuniform particle size and impaired coal mobility. The consequences of increased moisture content are increase in the heat required in coking; coke of poorer quality (less uniform piece size, lower mechanical strength, and increased porosity); and shorter working life of the coke ovens.