| Blast furnace (BF) pulverized coal injection (PCI) is one of the main ways to regulate the lower zone of modern blast furnace. The so-called PCI, is to inject finely ground coal particles into the BF from tuyeres. It is of great significance to study PCI to reduce iron-making cost and strengthen the smelting process.In the BF production, we use amount of PCI of unit pig iron which indicator is called coal ratio to measure the PCI case. However, though PCI brings economic benefits, when coal ratio rises to a certain extent, the gas utilization become worse, the coal replacement ratio fell, BF even will hang material, descend irregularly in burden and occur other accidents, seriously affect the BF process. So,the higher coal ratio of BF is not the best, for coal ratio there is a balance of each BF, we define the balance as optimal coal ratio, if smelted at the optimal ratio, the BF will gain the best benefit.At first, this study establishs the physical model of PCI, using the physical model combined with complex chemical reactions in BF, the mathematical model of PCI is established through deriving formula. Then, with the field data and operating record of NO.1BF of a steel factory in Yunnan province, it calculates and analysis the influence on each index and the limit restrictions of coal ratio after PCI. Process and the results are as follows:By combining with the increase of coal ratio, it gets the variation of theoretical combustion temperature with the increase of coal ratio through calculating the values of theoretical combustion temperature; it gets the result that the blast kinetic energy increases through calculating the values of blast kinetic energy after coal ratio increase; By using the mathematical model of tuyere raceway and dead stock column, the shape of tuyere raceway and the height of dead stock column are calculated; By using the formula of need to calibrate wind heat compensation after PCI, the determination of blast temperature and coal ratio are calculated; The relationship between coal ratio and the value of oxygen-enriched is calculated; By using burn smelting of NO.1BF as a benchmark, the replacement ratio after coal ratio increasing is calculated and the variation of coke rate and fuel ratio are analyzed; Through detecting the composition of top gas, the gas utilization rate of NO.l BF is calculated; The behavior of unburned coal powder in NO.1BF is analyzed.On the basis of the above research, the concept of comprehensive benefit index is proposed, its computational formula is established. By using the computational formula, it calculates the index values of comprehensive benefit and gets the changes of comprehensive benefit index with different coal ratio. By combining effects of various factors on PCI, the conclusion is that:Under the current technological conditions, the optimal coal ratio is150kg/t for NO.1BF. The systematic approach to computing optimal coal ratio is established by calculating the optimal coal ratio of NO.1BF. The specific improvements to reach optimal coal ratio are proposed by combining with raw material situation on the NO.1BF.Finally, through the established mathematical model of gas distribution, the gas flow patterns in BF which PCI operation is simulated and analysised by means of fluid dynamics software FLUENT. The result is in accordance with the conclusion. |
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