| Althought the technology to strengthen the efficiency of ironmaking process in blast furnace(BF) are mature, it can’t meet the demand of energy consumption and environment in modern industry. Therefore, it is necessary to find other ways to meet the needs of energy saving. Coke is the main raw material in BF, its performances play a decisive role to determine the smooth process, especially the strength and reactivity. It has been proved that the use of highly reactive coke can improve the efficiency so that the coke ratio and carbon dioxide emissions can be reduced. Therefore, the deep study of carbonization mechanism of coal is a prerequisite for good quality of highly reactive coke. By combining our unique resources, the carbonization process of iron coke has been studied. Hence it not only provides a theoretical basis for the preparation of iron coke, but also gives a good significance in science and industrial applications.Firstly, the characteristic of weight loss of individual coals and blending coals bearing different iron minerals are investigated by thermogravimetric analysis(TG) during pyrolysis process. And then, the change of heat is observed by Differential Scanning Calorimetry(DSC). The results show that: three stages are divided by the characteristic temperatures and the second stage is main. With the increase of coal rank, the temperature of maximum weight loss rate of coal increases, the maximum rate reduces. Nantong coal(NT) and Yonghun coal(YH) have a similar rank and the activation energy while Shoumei coal(SM) has a minimum activation energy because of it’s highest rank. Three coals are mixed and then five iron minerals are added to obtained the blending coal. The range of activation energy of blending coal is 12~30 k J/mol in the first pyrolysis stage. The range of activation energy in second stage is 90~120 k J/mol and ordered by: BC-Fe S > BC-Fe3O4 > BC-RAW > BC-Fe > BC-Fe2O3 > BC-Fe C2O4. In the condensation stage, the activation energy is greater influenced by Fe S and Fe than iron oxides. The total apparent activation energy of blending coal bearing different iron minerals is also different. The DSC curve shows that the starting temperature of condensation moves towards the low temperature zone because of iron oxide, while there are little impact by Fe S and Fe. The most drastic condensation reaction is happened at the temperature of 800 ℃, Fe2O3 and Fe3O4 have an obvious promoting of condensation reaction while Fe C2O4, Fe S and Fe have an inhibition.Secondly, the different ratios of Fe2O3 and iron minerals are added to blending coal and then iron coke is obtained. The strength and reactivity of produced coke are measured by test of Nippon Steel Corporation(NSC). And then, the transformation of iron minerals and the microcrystal structure are investigated by X-ray diffraction analysis(XRD). The results show that: With the increase of Fe2O3, the mechanical strength and the strength of coke after gasification are reduced while the reactivity increases up to 5 % and reduces at 7 %. From the XRD patterns of coke we can know that the height of 002 peak has a downward tendency and the weight has a upward tendency along with the increase of Fe2O3. It means that the graphitization of coke is reducing and disorder of carbon layers is increasing. It also can be seen that a few of Fe2O3 reacts with sulfide to produce Fe S and the most of Fe2O3 can be reduced to metal Fe by coking gas and carbon during carbonization process. On the other hands, the mechanical strength of coke which added 5 kinds of iron minerals at the ratio of 3 % reduces obviously, the order of inhibition degree is: Fe C2O4 > Fe3O4 > Fe S > Fe > Fe2O3. The added Fe2O3, Fe3O4 and Fe C2O4 are reduced to metal Fe during carbonization and the reducing ratios are 62.44%, 62.63% and 37.64%, respectively. The reactivity can be ordered by: Fe S > Fe2O3 > Fe3O4 > Fe C2O4 > None > Fe. It has no explicit relationship between reactivity and the content of metal Fe or total Fe. Furthermore, the strength of coke after gasification has no correspondence with the order of reactivity, it’s ordered by: None > Fe > Fe3O4 > Fe C2O4 > Fe S > Fe2O3.Lastly, the performances of coke bearing different ratios of pitch are investigated and the surface characteristics of coke before and after gasification are observed by Scanning Electron Microscope(SEM). The results show that: With the increase of pitch, the mechanical strength of coke increases while has no obvious change upon 4 %. Along with the increace of pitch,the reactivity of coke reduce slightly while the strength of coke after gasification has a upward tendency and pulverization tatio has a downward tendency. According to the SEM pictures of coke, there are so many pores which have large diameter size in the coke so that the thickness of pore wall changes thin. Along with the increase of pitch, the smaller pores and denser stricture of coke can be obtained. |
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