Abstract: In a shaft furnace for the direct reduction of iron ore in which hot reducing gas is introduced at the bottom of the furnace and removed from the top of the furnace, means for recirculating at least a portion of the furnace exhaust gas are provided along with means for introducing fresh gas into the recirculated gas stream and means to heat the gas stream introduced into the furnace. The improvement comprises providing means for desulfurizing the fresh gas stream prior to its joining the recycled exhaust gas and providing for dust removal, sulfur and CO removal in the recycled gas stream prior to its joining the fresh gas stream.

Abstract: Sponge iron is produced at a shaft furnace from iron ore, preferably in the form of pellets, whereby a hot reduction gas is passed upwardly through the shaft furnace and the iron ore descends therein. The hot reduction gas is formed in part by a desulfurized fresh gas produced by partial oxidation of a hydrocarbon (generally high sulfur residual oil) and desulfurization and, in part, by recirculated exhaust gas drawn from the head of the furnace and having its carbon-oxide content reduced by about ten volume percent. The fresh gas is mixed with the recirculated exhaust gas in a volume ratio of fresh gas/exhaust gas of 0.8:1.0 to produce a cold mixed gas. The cold mixed gas is heated to a temperature of about 1000.degree. C directly before being introduced into the shaft furnace as reduction gas.