| Pulverized coal injection is a significant measure to reduce costs and improve competitive ability used by iron and steel making industry. And the aim of finding better coal types that have excellent performance and lower price to deal with the rise of coal injection rate and coal price becomes increasingly important. Semi-coke has been adopted gradually for its excellent performance and lower price by many iron and steel companies.As being mentioned in this thesis, five samples used for the theoretical and experimental research such as proximate analysis, elemental analysis, ash component are bitumite, anthracite, Tianyuan semi-coke, Fuyou semi-coke, Kelinsida semi-coke. The performance such as ash fusion temperature, grindability index, explosibility, ignition point, combustibility and reactivity of the related samples have been tested. In addition, based on the theory of combustion dynamics, the study determines the appropriate amount of semi-coke addition in order to achieve the best effect of injection and comprehensive utilization of semi-coke.The conclusions can be drawn from physicochemical properties of blast furnace coal and semi-coke injection: the coking property and sulfur content of the three kinds of semicokes are relatively low, which is suitable for injection into blast furnace and helps to reduce sulfur load in the blast furnace; while the ash content of the related semi-coke is relatively high, hydrogen content and calorific value are relatively low, which will cause some side effects on improving the theoretical combustion temperature of blast furnace tuyere zone. At the same time, the coal grindability of semi-coke is lower, and it will cause disadvantageous impacts on improving the output of the coal mill and increasing the power consumption of the coal mill.Pulverized coal and semi-coke combustion performance, reaction performance and conveying performance are important index for the choice of blast furnace injection coal. For the samples with lower combustion performance, reaction performance and conveying performance, reasonable blending before pulverized coal injection in order to improve the performance could be an efficient measure. In this paper, the measure of thermal gravimetric analysis was used to analyze the combustion performance and reaction performance of the samples. And combined with the theory of combustion dynamics, the mechanism of semi-coke combustion are further studied. It can be concluded that the combustion performance and reaction performance of pulverized coal injection with addition of semi-coke are improved with the increased amount of semicoke, but when the ratio of semi-coke exceeds 50%, the combustion performance and reaction performance of pulverized coal injection with addition of semi-coke change gently. This result can be explained by theory of combustion dynamics. The apparent activation energy of mixed sample increased rapidly. The mixed coal in blast furnace injection can not only improve the performance of a single sample, but also broaden the types of injection coals according to the respective chemical composition characteristics of coal and semi-coke. It was showed that pulverized coal injection with addition of Tianyuan semi-coke, Fuyou semi-coke or Kelinsida semi-coke can be used for blast furnace injection and the better metallurgical properties of mixed coal can be obtained.It is unfavorable for the improvement of pulverized coal in blast furnace tuyere combustion process and conveying process when the amount of semi-coke increased. Appropriate semi-coke ratio for PCI can be obtained by the comprehensive consideration of the combustion process and conveying process of mixed coal in blast furnace, as well as the consumption capacity of non-pulverized-coal, coal replacement ratio, blast furnace fuel ratio and production costs of pig iron in the blast furnace process. The appropriate amount of coal with addition of semi-coke can be 40% from the related research. |
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