Operational Aspects of Sponge Iron Production in a Rotary Kiln

Abstract

On the background of the imbalance in the occurrences of vast deposits of high grade iron ore with that of coking coal, and simultaneous availability of enormous quantity of evenly distributed non-coking coals, extensive trials to ascertain the possibilities of their exploit-ation were conducted in an experimental rotary kiln of 10.67 m. length with 0.75 internal diameter. Several iron ores, or green and heat-hardened pellets and varieties of non-coking coals were employed. The prop-ortion of iron-coking coal in the charge was in excess of the stoichiometric requirement. A temperature profile of 950-1025°C in the reaction zone was maintained by the combustion of fuel oil from an axially located burner and partial combustion of coal volatiles, or exclusively by the combustion of coal volatiles, by throwing coal inside the kiln. In the two ways of meeting the thermal requi-rements, the alteration in the temperature profile was marginal. The retention time was 90 to 110 minutes. The degree of metallization varied between 87 to 92%, and no operational difficulties were experienced even with green pellets. Agglomeration' or ring formation was avoided by proper adjustment of operational parameters. The micro-scope examination revealed total absence of wustite and completion of conversion to metallic iron. The heat requirements of 4.6-5.25 million kilo-calories/ton of sponge iron could be lowered to 3.5-3.7 kilo-calories/ton of sponge iron with partial recirculation of char. The trials yielded adequate data for designing a commercial prototype, or for industrial production of sponge iron.