Study on utilisation coal fines generated in sponge iron making through pelletisation

The present study has been made to utilise the coal chars generated in the rotary kiln/certain shaft based DR process through the pelletisation. The process aims to generate valued material from the generated wastes which could be used in the DR plant itself as additional feed.

Pelletisation experiments were conducted in a disc pelletizer with varying proportion of iron ore fines and coal fines ground to 85% passing through 63 micron size screen. Organic as well as inorganic binders were used for the pelletisation. Moisture in the green pellets was maintained in 9.5% to 10.5% range. The crushing strength and drop number of the green pellets immediately discharged from the pelletizer and after 24 hours were measured. Besides, the crushing strength and drop number of the oven dried (dried for 1 hour) pellets and that after 24 hours were determined.

A substantial increase in crushing strength was observed when the green pellets were oven dried for one hour over the pellets (green) immediately discharged from the pelletiser, however, drop number decreased. The crushing strength of the pellets increased considerably after the green pellets were cured under atmosphere for 24 hours.

Attempts to make concentrate pellets with seeds (core of the pellets) consisting of major portion of coal fines and outer layers consisting of only iron ore fines and inorganic binder did not help in improvement in the crushing strength.

Typical tests were conducted to study the strength parameter of the pellets on heat hardening. The green pellets were heat hardened in the 1000°C to 1200°C range under inert atmosphere with varying rate of heating and subsequently cooled to room temperature by passing N₂ gas. The said attempt has resulted in partial success.