passages 12 through which the gas enters the furnace to flow upwardly in counter flow relation with the downwardly descending burden the reacted reducing gas is removed from the furnace at gas outlet 13 in the form of top gas then conducted to a gas washer 14 wherein it is cleaned blower 15 conducts the cleaned top gas through conduit 16 to a reformer for production of reducing gas in the preferred embodiment shown in fig1 top gas in part is conducted through conduit 17 and cooling gas inlet 18 to gas distributor member 19 at the lower end of the cooling zone 7 within the furnace at the upper end of the cooling zone a portion of the cooling gas is collected by cooling gas collecting member 20 and removed from the furnace by way of cooling gas outlet 21 from whence it is recycled to gas washer 14 a source of natural gas n is connected to conduit 17 by conduit 22 whereby natural gas can be added to the recycled cooling gas and top gas mixture below the plane of bustle 11 in which the hot reduction gas is injected into the furnace natural gas mixed with top gas is introduced into the reduction furnace this can be effected by horizontal gas distributor pipes 23 incorporated.