UPPER LIMITS TO COMBUSTIBILITY OF PULVERIZED COAL IN BLAST-FURNACE RACEWAY AND DESIRABLE INJECTION POSITION

1. An equation (1) for estimating the upper limit value (PCR)u (kg/t) of the pulverized coal injection rate in blast-furnaces was derived from an experiment on the combustion of pulverized coal in the coexistence of coke and a mathematical model of the tuyere combustion zone. [GRAPHICS] Where FR:fuel rate (kg/t), (C)pc, (H)pc, (O)pc: ultimate analysis of C, H, O, in pulverized coal (% (dry)). The upper limit to the coal injection rate at which the pulverized coal can burn 100% in the tuyere combustion zone is 180 kg/t when the fuel rate is 500 kg/t. 2. The upper limit to the particle size of granular coal injected into blast furnaces is 0.70 mm in terms of characteristic particle diameter (upper limit of particle diameter covering 80%(wt) of coal). 3. An equation (2) for estimating the upper limit to the distance L(m) between the coal injection position and the tuyere nose at which scab does not form on the tuyere nose was derived. [GRAPHICS] Where dp*:characteristic particle diameter (mm), PCR:coal injection rate (kg/t). It is necessary to bring the injection position near the tuyere nose when the injection rate is increased. 4. Since April 1990, Kimitsu No. 4 blast furnace has continued stable operation at a high-rate coal injection of 132 kg/t, proving that the coke replacement ratio does not decrease at a low theoretical flame temperature of 2 050-degrees-C.