Method for operating blast furnace

In a method for operating a blast furnace having a plurality of tuyeres around the periphery of the lower portion thereof and coupled to at least one hot stove for heating air to be blown into said blast furnace, which comprises:

• adding a blast furnace gas containing CO and H.sub.2 to air to form a gas mixture;
• feeding said gas mixture into said hot stove to heat said gas mixture in said hot stove to thereby oxidize CO into CO.sub.2 and H.sub.2 into H.sub.2 O, to form a blast enriched with CO.sub.2 and H.sub.2 O and further heated through said oxidation reaction;
• and blowing said blast through said plurality of tuyeres into the lower portion of said blast furnace to bring said blast into contact with red-hot coke in the lower portion of the interior of said blast furnace to cause an endothermic reaction with said red-hot coke to thereby control the calorific value at the portion of the interior of said blast furnace around said tuyeres;
• the improvement comprising:
• the amount of said blast obtained from said hot stove blown into said blast furnace being an amount substantially equal to that of a blast which would be blown into said blast furnace without addition of a blast furnace gas, thereby decreasing the pig iron production from said blast furnace as compared to the pig iron production which would have been obtained if a substantially equal amount of a blast without addition of a blast furnace gas had been used, without deteriorating the furnace conditions.