In order to seize the operational problems and clarify the various phenomena in a blast furnace operated at the extremely low fuel rate, Nippon Kokan K. K. had decided to execute a trial operation in No. 3 blast furnace (inner volume : 3 223 m3, blow in; Jan. 1975) at Fukuyama works.As a result, a monthly mean fuel rate of 396 kg/t was recorded in Nov. 1981. Comparing with the previous result of the same furnace (428 kg/t, Jan. 1979), necessary heat at the lower part of a furnace could be much reduced. Both the high reducibility of sinter and adequite burden distribution control enabled to maintain the high shaft gas efficiency of 97.5%. As the heat flux ratio increasing, temperature level at the shaft lowered and the three stages of thermal reserve zones were observed. The level of cohesive zone also lowered and its shape changed from "inverse V" to "V" bia "W" shape, furthermore some of measured results indicated that melting line would be very close to the raceway. In its transition period, burden desending became a little unstable, but got well again when fuel rate reduced to around 400 kg/t.The essential hindrances to get further low fuel rate in future are seemed to be the reducibility of are at the short effective zone for its reduction and the fusing capacity of ore around the raceway.

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