| At present, blast furnace(BF) is still the predominant process for ironmaking, however, its sustainable development is constrained by many problems(e.g. natural resource, energy supply, ect) as the hot metal production increases year by year. One of the primary problems of BF is that its operation relys on high grade coal resource. The coking coal and fat coal in China will be exhausted in 50 years accroding to the consumption rate in 2009. In addition, the energy consumption of domestic BF remains high, for example, the average fule rate and coke rate of domestic BF is 50kg/t and 10kg/t higher than that of Europe in 2010, respectively. High energy consumption leads to not only high coal resource depletion, but also high CO2 emission. Therefore, the most concerned issue for ironmaking industry is how to use coal efficiently and reduce its energy consumption and CO2 emission. The research of ferro-cokes, which produced by the mixture of blended coal and iron ore, have been conducted aiming to solve the above problems. The effect of type of iron ores and carbonization process conditons on the quality of ferro-coke has been researched; reactivity of ferro-cokes has been investigated, and their starting temperatures of gasification have been determined; the effect of ferro-coke on iron ore reducibility and burden melting-dropping properties has been studied by laboratory test; the reaction kinetics of ferro-coke and iron ores have been analyzed; and the effect of ferro-coke on BF operations has bee predicted by one-dimentional mathematical model. The main results are as follows:(1) Ferro-cokes were produced by the mixture of blended coal from WISCO and ores(e.g. Canadian fine ores, Australian FMG fine ores and E’Xi high phosphorus ores), it was found that most of iron ores in the mixture had been reduced to metallic iron during carbonization, and the more the ores in the mixture, the higher the metallization rate was. compared to the ordinary coke, ferro-coke’s apparent density was larger, cold strength was lower, CRI was much higher, howerer, its CSR was lower. The Canadian fine iron ores was the best raw materias for ferro-coke production because its adverse effect on cold strength and high temperature properties was the least in the above three iron ores. For Canadian fine iron ores, the mixture ratio should not above 15%, and the best production condition was: bulk desinty was 1.0 t/m3, banking time was 150 min, and the granularity of ores was less than 0.2 mm.(2) The reactivity of ferro-cokes had been studied and their starting temperatures of gasification were determined, the results showed that: the metallic iron in the ferro-coke could promote the gasification, and the more the metallic iron content in ferro-coke, the higher the reactivity was. the higher the temperature, the higher the gasification rate was. It was confirmed by Fact Sage thermodynamic software that the phenomenon, of which the weight of ferro-coke was not only reduced but also increased at the initial stage, was due to the oxidation of metallic iron by CO2. The metallic iron could promote the decrease of starting temperature of ferro-coke gasification, and the higher the metallic iron, the lowre the gasification starting temperature was.(3) The effect of ferro-coke, which mixed with iron ores, on iron ores reducibility and burden melting-dropping properties was studied, the results showed that: ferro-coke mixed charging had obviously promotion effect on reduction, because the charging manner increased the reduction potential of reducing gas, and increased the driving force of the redction consequently. The promotion effect became more obvious when adding the amount of mixed ferro-coke or reducing the granuliaty of ferro-coke. And the promotion effect was better when ferro-coke mixed with the ores having better reducibility. The reuction degree increased, the gas permeability resistance decreased, and melting-dropping properties improved after the burden mixed with ferro-coke. And as the amount of mixed ferro-coke increased, the softening range increaded, softening-melting range decreased, so the melting-dropping properties were improved.(4) Reaction kinetics of ferro-coke and iron ores were anlyzed by using unreacted core model, and the rate limiting step of iron ores are estimated by sectional stepwise mehod, the gasification of ferro-coke was analyzed by mixed controlling condition. The fractal method was introduced into the kinetic analysis of sinter due to its irregular and complicated structure, which was hard to describe by ordinary method. And the main results were as follows:1) The controlling step of reducion of iron ores was interfacial chemical reaction at the initial stage, and gradually shifted to internal diffusion as the reaction proceeded.2) The reaction rate constant and diffusion coefficient of reduction in the tempreature range from 900 oC to 1000 oC were estimated, then the activation energies of interfacial chemical reaction and internal diffusion were gained, and the results showed that the interfacial chemical reaction activation energy and internal diffusion activation energy of sinter were lower than that of pellets.3) the result of microstructure analysis of iron ores showed that iron ores reduction proceeded in the order from higher oxides to lower oxides of iron and the application of the unreacted core model to kinetic analysis is appropriate.4) when ferro-coke reacted with gas mixture, of which the component was similar to the BF gas, the oxidation of metallic iron occurred slightly, and the extent of oxidation was weaker as the temperature increased.5) the estimated activation energy of 2# ferro-coke was lower than that of 0# ferro-coke, which meant that the gasification of 2# ferro-coke could proceed fiercely at a lower temperature.6) the analysis of resistance ratios of gasification was conducted, it was found that the controlling step of gasification was interfacial chemical reaction, however, the resistance of interfacial chemical reaction reduced, and the resistance of internal diffusion increased as the gasification proceeded, so the controlling step shifted to internal diffusion consequently.(5) A one-dimentional mathematic model for BF was established, of which the boundary conditions were determined by multi-objective genetic algorithm. The operation condition of the simulation model was from a Nordic BF, and the simulation results were in accord with the measured results at the operation period B of Kobe Steel Co. No. 2 BF. The effect of ferro-coke on BF operations was predicted at the basis of simulation results, it was found that the productivity was improved, and the equivalent coke ratio and fule ratio were decreaced by 8.87% and 7.74 respectively after using ferro-coke. |
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