20 25 ch 4 2 7 h 2 o 15 25 with an oxidation level of between 0 4 and 0 5 the gas thus pre heated and mixed with natural gas exits the pre heater 36 at a temperature of between 650 u00b0 c and 950 u00b0 c it is subsequently divided into several currents of reducing gas into each of which oxygen and natural gas are injected before they enter the reduction furnace 10 so as to raise the temperature of the inlet gases to a value of between 800 u00b0 c and 1150 u00b0 c another part of the gas exiting the reduction furnace 10 is used as fuel to generate heat in the pre heater 36 by means of the pipe 30 the reactions which take place in the reduction furnace 10 are to pre heat and pre reduce the mineral in the upper zone 12 and to reduce the wustite feo with ch 4 h 2 and co in the reduction zone 14 in a variant ch 4 may be injected into the zone between the reduction zone 14 and the truncated cone shaped discharge end 15 in this way the ch 4 is pre heated cools the reduced material and.