GB768018A - Improvements in or relating to the reduction of iron oxide - Google Patents

Abstract

768,018. Iron manufacture. FREEMAN. H. March 23, 1955 [April 9, 1954], No. 8396/55. Class 72 Sponge iron is produced by introducing into a furnace hardened porous iron oxide pellets and finely divided carbonaceous fuel which has a low hydrocarbon content and which when burned will form an infusible residue which will not sinter at the reduction temperature, the amount of fuel being in excess of that required to reduce the iron oxide completely to iron and to convert the carbon, dioxide evolved largely to carbon monoxide and the fuel and residue being such as to prevent the pellets striking together, providing an oxidizing atmosphere at the feed end of the furnace by supplying air sufficient only to produce carbon monoxide and the amount of heat necessary to reduce the iron oxide, maintaining a non-oxidizing atmosphere in the remainder of the furnace length, advancing the pellets and the fuel concurrently with the gas flow in the furnace and cooling the resultant mixture in a non-oxidizing atmosphere. In the arrangement shown, the iron oxide with a binder is pelletized in a rotary drum 11 and the pellets are dried in a tunnel dryer 112 and hardened in an air roasting column 112a. The hardened pellets are then mixed at 113 with 40 per cent by weight of anthracite coal fines and the mixture is fed together with a metered quantity of preheated air from a line 37 to a rotary furnace 15. The pellets are reduced at a temperature of 1900-2100‹F. in the furnace and the reduced pellets are cooled under a CO/CO 2 atmosphere in a water-cooled extension 17 of the furnace. The reduced mixture is discharged from the end 18 of the furnace and the sponge iron is separated from excess carbon by screening or magnetic separation and is crushed to powder. In alternative arangements, the reduction may be performed in a tunnel furnace with a continuously moving conveyer-type hearth or in a Herreshoff multiple hearth furnace. Lime, hydrated lime, limestone or dolomite may be added to the furnace charge to absorb any sulphur evolved from the fuel and small amounts of alkali metal or alkaline earth metal carbonates or sodium aluminate may be added to the charge to increase the carbon monoxide concentration in the furnace. Up to 7 per cent by weight of iron powder may be added to the iron ore to be pelletized to promote self-roasting of the pellets.