Features of blast furnace smelting technology with pulverized coal injection from different coal mixtures under conditions of variable coke quality

The article presents practical results of blast furnace (BF) smelting technology with pulverized coal injection (PCI) from various coal mixtures under conditions of variable coke quality. The effectiveness of using mixtures of lean and long-flame gas coal as part of PCI was investigated; lean coal of Australian, Czech, and North American origin and long-flame gas coal of Ukrainian origin were used. The periods of operation of three BFs in Ukraine were studied. The first two BFs (BF-A and BF-B) operated in similar technical and technological conditions with low coke quality with a hot strength index (CSR) of 45.4% and a specific PCI consumption of 86 kg/tHM. On average, the third BF (BF-C) operated in significantly better conditions during the experimental periods with a CSR of 61.1% and a specific PCI consumption of 145 kg/tHM. The actual coke replacement ratio with PCI was determined in comparison with the calculated replacement coefficients. For BF-A and BF-B, the actual coke replacement ratio of PCI, on average, was 0.75; for BF-C, it was 0.82. The results presented showed the advantages inherent in BF-C, compared to BF-A and BF-B, which are necessary to achieve the most efficient PCI: high-quality coke, a modern shaft cooling system, a dusting system using OXYCOAL technology, and distribution of charge materials using a bell-less top charging device. The paper shows the features of RAFT (Raceway adiabatic flame temperature) regulation when using different mixtures of PCI. Using the example of BF-A during four years of its operation, it is shown that obtaining minimum values of specific total fuel consumption, which characterize the reduction of the carbon footprint of BF technology, is possible both at PCI consumptions of 140–150 kg/tHM and at 80 kg/tHM, which is primarily due to the stable quality of coke and iron ore components of charge materials. The article presents recommended ranges of rational PCI consumption depending on the quality of coke. The dependence of the specific consumption of total fuel on the stability of the thermal state of BF smelting, which is estimated by the root-mean-square deviation of the silicon content in cast iron, is obtained, since ensuring a stable thermal state of BF smelting is an important component of effective PCI. The feasibility of improving the drainage capacity of the BF hearth under conditions of PCI when using coke of variable and low quality, which is ensured by introducing materials that are difficult to recover into the BF charge, is shown.