Opportunities to improve the utilisation of granulated coals for blast furnace injection

• Blending coals improved the burnout of low volatile content semi anthracitic coals.
• Granulated samples showed a fragmentation effect in a drop tube furnace.
• Granulated particle fragmentation improved blend burnouts at lower residence time.
• Higher volatile content mass loss improved burnout at lower residence times.
• Included minerals with higher K/Al ratios gave non-additive burnout improvements.

Coal injection plays an important role to the economic success of ironmaking by substituting a portion of the coke input and improving the blast furnace productivity. Manufacturers are looking at opportunities to increase their coal selection options by using higher proportions of technically challenging lower volatile matter content coals; this paper investigates the kinetics, devolatilisation and burnout of these in granulated coal blends using thermogravimetric analysis (TGA) and a drop tube furnace (DTF).The char residue from the semi-anthracitic low volatile coal selected for this blending investigation had a much reduced reactivity at higher conversions which affected the blends in different ways. Burnout of the blends with the low volatile bituminous coals was improved by fragmentation of the granulated particles, but at longer residence times the lower reactivity of the more structurally ordered carbon in the semi anthracitic coal dominated. In contrast, the higher volatile coals showed improvements at low residence times corresponding to rapid volatile loss, but also showed non-additive blend improvement at longer residence times which may be explained by the more obvious presence of included minerals and the higher K/Al ratios associated with illite mineral phases known to improve burnout.