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Synopsis Regarding the reduction under load test for measuring high temperature properties of blast furnace burdens, the test conditions, i.e. the load, gas flow rate, particle size and bed height were examined through tests and calculations based on a reduction model for fixed bed. Examinations covered also evaluation criteria of test results for high temperature properties. The results obtained are summarized as follows: (1) Test results are influenced by each of the load, gas flow rate, particle size and bed height conditions. (2) It is desirable to minimize the longitudinal difference of degree of reduction and the dependence on load of test results. The optimal test conditions (Fig. 2) were decided from such a point of view. (3) The following evaluation criteria of test results for high temperature properties were proposed: (i) the temperatures at the beginning of softening and melt-down are high, with a small temperature difference; (ii) the integral and average values of index of permeability resistance between softening and melt-down are small; and (iii) the degree of reduction achieved at 1 000 to 1200 °C is high.

Synopsis In order to clarify the various phenomena in a blast furnace and its operational problems at the extremely low fuel rate, Nippon Kokan K.K. decided to execute a trial operation in No. 3 blast furnace (inner volume: 3 223 m3, blow in; January 1975) at Fukuyama Works. As a result, a monthly mean fuel rate of 396 kg/ T was recorded in November 1981. Comparing with the result of the previous test operation in the same furnace (428 kg/ I, January 1979), heat requirements at the lower part of the furnace could be much reduced. Both the high reducibility of sinter and adequate burden distribution control enabled to produce and keep the high shaft gas efficiency of 97.5%. As the heat flux ratio increased, temperature level at the shaft lowered and the three stages of thermal reserve zones were observed. The level o f cohesive zone also lowered and its shape changed from " inverse V " to " V " via " W " shape, furthermore some of the measured results indicated that the melting line would be very close to the raceway. In its transitional period, the burden descent became somewhat unstable, but got well again when the fuel rate reduced to around 400 kg/T.

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