Direct Reduction of Iron Ore

processes for the production of iron and steel directly from ore without the smelting of pig iron in blast furnaces. The development of direct-reduction processes is related to the decreasing supply of the coking coals required for blast-furnace production and the limited supply of high-grade metal scrap for the production of high-quality steel in electric furnaces.

The numerous methods proposed, developed, and partially in use in pilot plants and on an industrial scale in various countries may be classified according to the type of final product and the temperature conditions of the process into three basic groups: (1) the production of sponge iron at temperatures below the temperature of the formation of the liquid phase, in which all the gangue remains in the final product, which retains the shape and size of the original ore; (2) the production of bloom at temperatures between 1250° and 1350°C below the melting point of metallic iron but sufficient to melt the gangue; and (3) the production of molten metal.

The most common processes for the production of sponge iron using a gaseous reducing agent are retort, shaft-furnace, and fluidized-bed processes. Installations operating in Mexico, Brazil, and other countries using retort processes have an output capacity of approximately 1 million tons per year; industrial installations using shaft-furnace processes in the USA, Canada, the Federal Republic of Germany, and other countries have an output capacity of approximately 1.6 million tons per year. An industrial installation using a fluidized-bed process with a planned output of 1 million tons per year has been built in Venezuela. Processes have been devised using solid reducing agents in rotary kilns with a total projected annual output capacity of approximately 1.5 million tons, but several of these furnaces have been idled as a result of low profitability.

The total annual output capacity of installations designed to produce sponge iron by various methods (chiefly in the form of metallized pellets for the smelting of electric steel) was estimated at 3–4.5 million tons in 1975. The production of bloom using the Krupp-Renn process was developed in several countries prior to the 1960’s, but it has since lost its industrial importance. The production of molten metal has been carried out in pilot plants capable of producing 200-500 tons per year. These installations use combined processes that include stages for the prereduction of iron in the solid state in rotary or car-bottom furnaces and the melting of the resultant sponge iron or metallized iron-ore pellets in electric furnaces. Single-stage processes have been developed for obtaining molten metal in rotary or stationary furnaces.

The prospects for the industrial development of the direct reduction of iron ore depend on two possibilities: the organization of metallurgical enterprises, including high-quality metallurgical factories, using local resources of raw materials and fuel (principally natural gas and noncoking coals) and the production of sponge iron for powder metallurgy. By the end of the 1970’s, a metallurgical factory will be constructed in the USSR with an entire operating cycle based on the direct reduction of iron ore. It will produce sponge iron in shaft furnaces using a gaseous reducing agent.