An in-depth study has been carried out on the reduction, softening and melting behavior of olivine based pellets in the experimental blast furnace. The aim of the project was to develop a fundamental understanding of the reduction mechanisms of olivine based pellets and to develop a correlation between the reduction rate and the softening behavior in the cohesive zone of blast furnace. The carburization characteristics of reduced iron were also investigated by examining olivine pellet and coke samples excavated and probed from an experimental blast furnace as well as the experimental investigations of pure hematite and heat treated coke. X-ray diffraction analysis was used to successfully determine the reduction degree of olivine pellets in different parts of the experimental blast furnace. These results were found to be consistent with assessments of reduction degree based on a detailed chemical analysis. The average reduction degree of iron oxide was seen to increase as the pellets descended towards lower zones of the EBF. Up to 75% reduction was completed before the pellet had reached the cohesive zone; remaining reduction was completed within the cohesive zone. Coke Lc showed a linear variation with experimental temperature above 11000C; a correlation was established to estimate furnace temperature as a function of EBF depth. The reduction degree of iron ore pellet showed a linear correlation with distance from the stock line of the EBF to the upper part of cohesive zone. But an abrupt increase in reduction rate was observed in the cohesive zone, a result observed in both EBF and experimental studies. The presence of olivine did not have much influence on the reduction degree of iron ore pellets for temperatures below 1100oC in the upper shaft zone of the EBF. However, olivine was found to increase the rate of reduction in the advanced stages of reduction in the cohesive zone for temperatures in excess of 1100oC. This effect was attributed to the formation of increased amount of molten iron oxide within the pellet. The initial melt formation and acceleration of the reduction rate in the cohesive zone of the EBF were also investigated. From the comparison between the reduction degree of excavated olivine pellets in this study and previous studies of EBF, it was found that the excavated pellets were located in the cohesive zone and increase of reduction rate in this zone could be verified by not only the change of gas composition, but also initial melt formation containing FeO phase. The chemical composition of slag phases of excavated pellet samples were located on the line between 2FeO??SiO2 and 2MgO??SiO2 in the FeO-MgO-SiO2 ternary phase diagram. This result is in good agreement with the assumption that the initial slag formation of the olivine pellets had proceeded from the fayalite and after reduction the FeO contents in the slag phase had decreased and eventually precipitated as slag with a higher melting point. From the analysis of carbon contents of the excavated pellets in cohesive zone, it was observed that the carburization of iron pellets began after the complete reduction. This study has established that the reduction rate of iron pellet is the rate controlling step for carburization irrespective of the carburization reaction by the solid carbon.
| Identifer | oai:union.ndltd.org:ADTP/258408 |
| Date | January 2009 |
| Creators | Lee, Si Hyung, Materials Science & Engineering, Faculty of Science, UNSW |
| Publisher | Awarded By:University of New South Wales. Materials Science & Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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