Direct reduction processes are of significance and can form an alternative to a conventional Blast furnace. Solid sponge iron ( direct reduced iron or DRI) is produced by removing oxygen from the ore .The technique of Direct reduction varies according to the type of reducing agents employed and the metallurgical vessel in which they are reduced. The reducing agents used normally are :
Reducing gasses are carbon monoxide , hydrogen and their mixture which are generally found in natural gasses. The directly used solid reducing agents are coals of any size, so that there is no need for expensive coke. The continuous shaft furnace which uses reducing gasses is more common. Midrex, HYL III process are of this type. HYL I process is of discontinous retort type. SL/RN and Krupp-Codir are of rotary kiln type . These processes use solid reducing agents and operate in continuous flow. Ores for direct reduction have to meet stringent specifications with high percentage of Fe and low content of tramp elements. Pellets are used mainly for this purpose. The output of all DRI processes is Sponge Iron Sponge iron is also hot briquetted to HBI .DRI combined with an EAF is considered as an efficient steel making technique.