| The essence of the blast furnace ironmaking is the reverse movement of high temperature reducing gases with iron ore. Coke which acts as the core supporter of this movement, must have a sufficiently high thermal strength. Xinjiang is located in the northwest part of China. Because of a late forming geological time of Xinjiang coal and its unique coal forming geological conditions, Xinjiang coking coal and coke have unusually high reactivity characteristics.The CRI of Xinjiang coke is about 50%, which lead to the CSR is about 40%. Therefore, Xinjiang coke can only be limited to be used in small blast furnace of 100~300m3, and it is very difficult to apply to medium and large blast furnace with more than 1000 m3. In view of the unique properties of Xinjiang coking coal and coke, this investigation,based on the requirements of practical feedback on coke quality(mainly about high thermal strength) of blast furnace in Xinjiang, aimed to use one hundred percent Xinjiang high activity coking coal to make relatively low reactivity and high strength coke(CRI<35%, CSR≥60%), which is based on the existing coal blending coking test and combined with modern coking basic theory, and to realize the medium and large blast furnace, which above 1000m3, can be high indexes and 100% quantitative application of Xinjiang coke.At first, this investigation discussed coke reactivity, analysed the properties of Xinjiang coking coal and studied the reactivity of Xinjiang single coal coke. Combining evolution causes of coking coal and geological time of Xinjiang coal, this investigation preliminarily identified the fundamental factors affecting the Xinjiang coke reactivity. According to the theory analysis of the coke, the researches adopted a variety of modifier on the Xinjiang coking coal and coke. In order to determine the expected effect of modifier on the coking, 2kg modification coking experiment in a laboratory oven and 10 kg modification coking test in an industrial coke oven were conducted. In addition, the research has conducted the thorough research and analysis on the modification mechanism of HSM using the thermal analysis and scanning electron microscope and X-ray diffraction(XRD). The theory analysis shows that the molecular structure of the Xinjiang coking coal didn’t condensate too much, which led to the high reactivity of Xinjiang coke. The tests results show that High Strength Modifier(HSM) has excellent modification effect on Xinjiang coking coal. Co carbonization of Xinjiang coking Coal together with HSM can significantly reduce the reactivity of Xinjiang coke(CRI<35%), and the strength of the coke after reaction increased significantly(CSR≥60%). The quality of Xinjiang coke can meet the demand of the medium and large blast furnace, which above 1000m3. And its can be high indexes and 100% quantitative application of Xinjiang coke. The influence of high strength modifier on coal pyrolysis is mainly concentrated on the bonding interaction between HSM and condensed aromatic ring free radicals in the high temperature above 700℃. The interaction of chemical bonding can reconstruct the carbon atoms bonding of coal polycondensation process and greatly reduce the inherent polycondensation desultorily building. The reconstruction microcrystalline carbon layer is larger in diameter than before. The structure is more ordered, regular and stable. Those unstable layer edge carbon atoms decreased and the number of carbon atoms structure defect is reduced. As a consequence, Coke active sites greatly reduced and coke reactivity is significantly decreased. What’s more, HSM ingredient will have certain melting adhesion effect under the oxidation condition of high temperature, which, to a certain extent, can also inhibit the oxidation of coke. Contrast to the traditional viewpoint, the most important factor that affects the reactivity of coke is not optical tissue types but the bonding and arrangement of carbon atoms in the semicoke contraction stage. |
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