The coal classification standard of China stipulates that the coking coal is divided into two categories:
The ash content of the first type of coking coal is Vdaf=10% to 28%, the bonding index G>65, the maximum thickness of the colloidal layer, and Y less than 25mm. The coking property of this part of coal is very good, and the qualified blast furnace coke can be produced separately.
The ash content of the other coking coal is Vdaf=20% to 28%, the bonding index is G=50 to 65, and the coking property is worse than the former. Coking coal has moderate volatilization and good adhesion. It is a typical coking coal. When heated, it can form colloidal bodies with good thermal stability.