| 摘要 |
PROBLEM TO BE SOLVED: To attain the continuous operation of a heating furnace with a low air ratio, even in the case that a heating furnace with a high air ratio is not operated. SOLUTION: In an operating method of direct-firing heating furnaces provided with combustion burners, with which the combustion treatment is performed by supplying unburnt exhaust gas from the heating furnace with the low air ratio into the heating furnace with the high air ratio and thus, the unburnt exhaust gas is utilized as the heat source in the heating furnace with the high air ratio, plural sets 6A, 6B, 6C of the heating furnaces with the high air ratio, are set. In the case the heating furnace 6A with the high air ratio is not operated because of the carrying-out of steel material 13, etc., the supply of the unburnt exhaust gas from the heating furnace 5 with the low air ratio, is changed over into the heating furnace 6B with the high air ratio, and then, in the case the combustion treatment of the unburnt exhaust gas is insufficiently performed only to the furnace 6B, the unburnt exhaust gas is further supplied into the heating furnace 6C with the high air ratio.
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