Effect of Different Milling Operations on the
Coking Potential of Coals

Abstract

Coke being an important raw material in the production of hot metal from blast furnace in the steel industry. It requires the coal/coal blends in proper proportions with certain characteristics of such blends for better yield of coke. The characteristics of coals vary from a coking coal to a non-coking one. For the effective utilization of non-coking coals, these are blended with coking coals to achieve those certain characteristics required for coke making. These characteristics of coals of any kind are altered by the means of comminution mechanism. The basic comminution mechanism imparts different kinds of forces on the coal particle leading them to fragment the larger ones to small and also helps in the liberation of macerals (minerals in coal) from such bigger particles. This comminution mechanism varies with different comminution equipment of which some are crushers and grinders. Presently in Tata steel, hammer mill is being utilized as an comminution equipment for the fragmentation, liberation and to achieve the specific size of which 90% of <3.2 mm and 40-50% of 0.5 mm coal particles are blended for coal cake preparation for coke making.
The present study shows the effect of impact based mechanism mills such as planetary ball mill, rod mill and cryomill on the characteristics of the coal sample grinded in such mills. The comminution characteristics (particle size distribution) of the three mills is studied and the effect of comminution parameters on the coal properties are studied. Also the efficiency of the mills are compared based on their energy consumption levels using an energy mater connected to each of the mills connected to common HMI (human machine interface).
The results shows that fragmentation of the coal particles is more in planetary ball mill and cryomill than the rod mill making them to generate more amount of fines. There is not much significant variation in the CSN (crucible swelling number) of the product coal grinded from all the three mills. The dilatation of the product coal from the planetary ball mill shows negative dilation which may be due to huge generation of fines than the rod mill. The petrographical analysis results also proves the same with increase in the amount of inertinite. The energy consumption calculated among the three mills id high in rod mill compared to the other two mills.