To attain a high rate injection of pulverized coal into a blast furnace, it is required to increase a combustion efficiency of pulverized coal in the raceway. Therefore, it is important to design the injection lance with high combustibility based on the essential understanding of combustion behavior of pulverized coal.
Previous to the start up of the high rate injection operation at Fukuyama No.4 BF, a 2-dimensional mathematical model of pulverized coal combustion taking the lance arrangements and the dispersion of coal particles into account had been newly developed. As a result of the analysis using this model, it was found that the eccentric double lance, two lances arranged asymmetrically to avoid the interactions of the pulverized coal flows, had superior characteristics to increase the combustibility in the blowpipe and the raceway due to the intensified particle dispersion. Since the experiment using hot model also showed the same effectiveness, the eccentric double lance was adopted to all tuyeres of Fukuyama No.4 BF.
During the high rate injection operation in October 1994, pulverized coal rate was raised to 230 kg/t and little unburnt char was detected in the top waste dusts and the combustion efficiency of pulverized coal estimated by the sampled char from deadman during scheduled shut down just after the operation reached over 70%. These results suggests that the high combustion efficiency had been successfully achieved by using the eccentric double lance.
