The potential of several alternative cheap fuels as blast furnace injectants has been evaluated in terms of their effects on bosh slag basicity, flame temperature, utilisation of hydrogen in indirect reduction of iron oxide, productivity, fuel requirement, and coke replacement ratio with the help of a modified Ramm's complex model developed at RDCIS by examining the overall mass and energy balance under any desired operating thermal (raceway adiabatic flame temperature, RAFT = 2004 degrees C) and slag regime (CaO/SiO2 = 1.0, Al2O3 = 20.0%, MgO = 9.0%) of the blast furnace process. Lignite has the greatest impact on the bosh slag basicity (reduced from 1.64 to 1.32) of the injectants studied. The cooling effect in the raceway is less with coals than with coke oven/natural gas. A flame temperature compensation, equivalent to a blast temperature change of 100 K, is required for the injection of 157 g of coal/Nm(3) of dry blast compared with 114 g of lignite, 54 g of coke oven gas, and 44 g of natural gas. For any desired operating flame temperature, a higher injection rate of coal/lignite can be achieved and, as a result, more coke can be replaced. Coke oven/natural gas has the potential to replace the least quantity of coke (244-256 kg/thm) whereas coal/lignite has the potential to replace a large quantity of coke (303-407 kg/thm). The realisable production benefits are phenomenal. Coal/lignite has a higher effect on productivity (26-37%) than coke oven/ natural gas (18-20%). As fuel is injected, in effect, hydrogen replaces nitrogen in the tuyere gas. As hydrogen reduction replaces the solution loss reaction, the thermal requirement to make a tonne of iron decrease markedly. When there is limited scope for raising the temperature of the blast, a major coke saving can be obtained with coal/lignite. The incentives for use of lignite rather than coal are lower price ratio, relatively high O-2 and H-2 contents, higher coke replacement ratio, and extensive reserves and availability in southern India. IS/1287 (C) 1998 The Institute of Materials.
