Coal Properties for Coke Production

Coal Parameter Typical Values

Volatile matter content (dry, ash-free) (wt.%) 24-28

H/C ratio 0.725

O/C ratio 0.04

Heating value (moist, mineral-matter-free) (Btu/lb) ~ 15,500

Vitrinite reflectance (%) ~ 1.25

Vitrinite/inertinite/exinite (dry basis) (%) ~55/35/10

Free swelling index 6.5-8

Maximum fluidity (dial divisions per minute) ~1000

Roga index ~45

Gray-King assay >G4

It is common practice to blend high-volatile coals with low-volatile and/or medium-volatile coals to improve the strength of the coke.

The ability of a coal to melt upon heating and to form a coherent residue on cooling is termed caking; an essential prerequisite for a coking coal is that it should cake or fuse when heated. Coals that are low in rank, such as lignites, or high in rank, such as anthracites, do not cake and therefore are not capable of forming coke. Several properties of coals are measured to identify appropriate coking coals, including swelling, fluidity, composition, maceral analyses, and vitrinite reflectance. These coal characteristics are listed in Table 5-6 along with typical values [1,19,34]. The mineral matter, or ash, content of the coal is of interest in coke production because the ash dilutes the coal and affects its caking properties. The composition of the ash is also important, as the quality of iron and steel is affected by the sulfur and phosphorus content. It is necessary for the formation of coke that some of the coal's organic constituents or macerals melt when the coal is heated. A caking coal behaves as if it were a pseudo-liquid when this occurs, and the viscosity of this material at various temperatures plays an important role in coking operations. The relative proportions of reactive and inert materials in a coking coal affect the strength of the final carbonized product.

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