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 10000C to 12000C range under
inert atmosphere with varying rate of heating and subsequently cooled to room
temperature by passing N gas. The said attempt has resulted in partial success.