METHOD FOR OPERATING BLAST FURNACE

PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace with which even in the state of blasting a large amount of dust coals, ventilation in the furnace is kept good and pig iron can be produced at a low cost. SOLUTION: In the method for operating the blast furnace blasting >=180 kg/ton of molten iron of the dust coal as an auxiliary fuel into the furnace from a tuyere, the method for blasting a large amount of the dust coals, is found out, from which the blasting limit of the dust coal largely depends on a cold strength and a grain diameter at charging time of coke charged to the top of the furnace and the maximum blasting ratio of the dust coal can be obtained from the above conditions, the maximum ratio PCRMAX (kg/ton of molten iron) of the dust coal which can blast while keeping the stable operation, is obtained with the following equation (1) from values of the cold strength and the average grain diameter of the cokes at charging time of the coke charged from the furnace top part. Then, the blasting of the dust coal from the tuyere is performed by using this maximum blasting ratio PCRMAX of the dust coal as the upper limit. PCRMAX=14.29×DI-1.517×10 +200... (1) Wherein, DI: the cold strength of the coke regulated in JIS K2151 and dco: the average grain diameter (mm) of the coke at charging time.