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.
(PCR)u=(FR-254)/{0.0142(C)pc+0.0425(H)pc-0.0056(O)pc+0.15}……(1)
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.
L≤(52dp*2-53dp*+17.5)/(PCR-30)……(2)
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 2050°C.
