EVALUATION OF ALTERNATIVE CHEAP FUELS FOR INJECTION IN SAIL BLAST-FURNACES

The potential of several alternative cheap fuels as blast furnace inje ctants has been evaluated in terms of their effects on bosh slag basic ity, flame temperature, utilisation of hydrogen in indirect reduction of iron oxide, productivity, fuel requirement, and coke replacement ra tio with the help of a modified Ramm's complex model developed at RDCI S by examining the overall mass and energy balance under any desired o perating thermal (raceway adiabatic flame temperature, RAFT = 2004 deg rees 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 bos h 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 o ven/natural gas. A flame temperature compensation, equivalent to a bla st 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 co ke oven gas, and 44 g of natural gas. For any desired operating flame temperature, a higher injection rate of coal/lignite can be achieved a nd, 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) w hereas coal/lignite has the potential to replace a large quantity of c oke (303-407 kg/thm). The realisable production benefits are phenomena l. 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 th e solution loss reaction, the thermal requirement to make a tonne of i ron decrease markedly. When there is limited scope for raising the tem perature of the blast, a major coke saving can be obtained with coal/l ignite. The incentives for use of lignite rather than coal are lower p rice ratio, relatively high O-2 and H-2 contents, higher coke replacem ent ratio, and extensive reserves and availability in southern India. IS/1287 (C) 1998 The Institute of Materials.