| Iron ore sintering is a critical process influencing the productivity, quality and energy consumption of the integrated iron and steel industry. With the rapid development of the iron and steel industry and the increasing consumption of iron ore sinter in China, larger-scale iron ore sintering equipments have appeared in China in recent years. At the same time, the bed height is getting higher and higher and the received iron ore types are varying greatly in sinter plants. The issues of high energy consumption and high pollutant emission and lack of iron ore resources have also getting more and more serious. Therefore, increasing attention has been paid to the investigation of the iron ore sintering mechanisms to explore environmentally-friendly and more efficient sintering technologies. The present work is proposed under this background. Numerical modelling of the iron ore sintering process is carried out in the present study.Iron ore sintering is a complex process involving the phenomena of phase change, heat and mass transfer, gas flow, combustion, mineral formation and conversion, etc. Considering its complexity, modelling the sintering process is very difficult. The present work has conducted systematic modelling of the iron ore sintering process. The major contents of the present work include the analyses of the physico-chemical changes during sintering, proposal of the basic model assumptions, construction of the governing equations, building of the key sub-models, numerical solution of the model, model validation as well as the analyses of the model results. The specific contents are introduced as follows.At the beginning of chapter one, the research background was introduced and relevant literature review was carried out. In this section, the current development status and the existing problems of the iron and steel industry in China were analyzed. The analyses results indicated that the iron and steel industry in China is developing rapidly, but still has some unsolved problems such as high energy consumption and high pollutant emission. Then the development of iron ore sintering technologies in China was also introduced. The results suggest that the iron ore sintering technologies have developed greatly but still have some significant problems. After that, the flow chart of the iron ore sintering process and its characteristics were introduced. The structure of the iron ore sintering bed was also discussed. Then the review of the iron ore sintering models reported in literature was carried out, in which the strengths and weaknesses of the models were discussed. The objective of the present work was given at the end of chapter one.In chapter two, the detailed mathematical description of the iron ore sintering process was given. Based on the common characteristics of the sintering process in the commercial sinter machine and the sinter pot, this section firstly showed the great changes of granule shape (or raw materials) in different zones and the possible physico-chemical changes during the sintering process. Fourteen different physico-chemical changes were indentified. The analyses results indicated the four distinctive features of the sintering process, i.e.1. involvement of a number of physico-chemical changes (including phase change, heat and mass transfer, fluid flow, combustion, melting and solidification),2. great structure changes of the sintering bed and granules during sintering.3. the strong coupling of the physico-chemical changes,4. one-dimensional characteristic. Then, the nine basic model assumptions were shown and analyzed in detail. The present iron ore sintering model takes into account thirteen species including eight solid species and five gas species, as well as eight chemical reactions. Eight governing equations of the sintering process and relevant boundary and initial conditions were given and discussed.In chapter three, the key sub-models and the numerical solution method of the iron ore sintering model were introduced in detail. The key sub-models are the models of coke combustion, limestone decomposition, dolomite decomposition, drying and condensation, magnetite oxidation, melting and solidification, heat and mass transfer.In the first part of chapter four, the pilot-scale sinter pot test in the Newcastle technology center of BHP Billiton in Australia was carefully introduced. The introduction of the sinter pot testing process indicates that the testing results can be used to validate the iron ore sintering model developed in the present work. Some testing results were introduced. All the experimental data used in the present work were from the Newcastle technology center.Latter in chapter four, the iron ore sintering model in the present work was fully validated against the sinter pot test results from the Newcastle technology center. Twenty five cases covering a wide range of experimental conditions were used for model validation. The validation results demonstrated that the present iron ore sintering model is reasonable.The iron ore sintering process was further analyzed using the model results in the chapter five. The gas and solid temperature profiles, the distribution of liquid fraction inside the bed, the two-dimensional distributions of temperature and liquid fraction, the gas pressure distribution, the bed structure and the sensitivity of some important parameters were discussed in this section. The results suggested that the model can predict the sintering process reasonably.The present work was finally summarized in the chapter six, in which the conclusions and the innovations and the future work were shown. The summarization results suggested that the present work mainly focus on the mechanisms of the physico-chemical changes in the iron ore sintering bed, the development of a new iron ore sintering numerical model, model validation and sensitivity analyses and the understanding of the sintering process using the model results. The innovations of the present work and the perspectives of the future work were also discussed at the end of this chapter. |
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