| During the past ten years, the self-sufficient rate of iron ore for steel industry in China is continuously less than 50%. Heavy shortage of domestic iron ore is limiting the development of iron and steel industry of China, and the exploiture of new iron ore reserves is an emergent task for China. More than 10 billion tons of iron ore reserves, such as siderite, limonite and oolitic hematite, cannot be utilized effectively. Magnetizing roasting followed by magnetic separation is an effective technique to convert iron ore, however, such a kind of new technology isn't well developed in China up till now for its very complexity. Traditional magnetizing roasting technology of shaft-type and rotary furnace also has the problems of high-cost and process-complication. To take the advantage of fast heat and mass transferring of fluidization of gas-solid, a kind of new technology named Multi-grade Circulating and Fluidizing Magnetizing Roasting (MCFMR) was developed to convert siderite to high magnetic oxidized iron ore. Therefore, current work is indulged to make a systematic and deep research on the kinetics of siderite decomposition and the new technology of MCFMR furnace through theoretical analysis, simulated experiments, CFD simulation and experiment in full-scale plant.Thermal decomposition of two kinds of siderites were investigated under pure N2 atmosphere, one is from Daxigou and the other is from Wangjiatan. The non-isothermal method with thermo-gravimeter (TG) by multi-scanning is used in the experiment research and the data processing method includes Kissinger, FWO and Friedman methods. Reactive mechanisms and kinetic parameters of thermal decomposition of siderites were obtained. The results indicates that the shrinking cylinder model is the best model fitting the experiment data of Daxigou siderite, while the first-order reaction model is the best model fitting that of Wanjiatan's. However thermal decomposition mechanisms of the two siderites are both controlled by the same reaction rate. The value of pre-exponential factors exhibited a strong dependence on the Wanjiatan siderite particles with a certain size, and a new equation of first-order reaction model with the effect of particle size was developed which matches great with the data of TG experiments.To verify the magnetizing effectiveness of roasting ore, the chemical phase of the siderites in inert atmosphere was researched by using X-ray diffraction method and the optical microscopy method. The X-ray diffraction patterns and the optical microscopy patterns of the solid residue show that magnetite of the siderite ore is mainly consists of brown gray Fe3O4 and small amount of white Fe2O3 sometimes can be found at the surface or at the crack edge of siderite particle, which was converted from middle product, FeO, by the trace oxygen in the atmosphere. The roasted siderite ore was well grindable for the rich cracks in the solid residue.To analysis the influence of temperature and atmosphere to the siderite ore, an isothermal decomposition experiment of siderite ore in the dilute phase suspension condition was executed in current work. The pyrolysis kinetic mode and parameters are obtained from the experiment, and the results are helpful to construct the simulation model which was solved next. It was found that the shrinking sphere model with surface reaction rate controlling mechanism is the best model fitting the experiment data. The experiment results showed that the peak concentration of CO in the off-gas came out 5～10 seconds later than that of CO2. The magnetization rate of FeO was speeding-up obviously between 600℃and 650℃and a maximum speed appeared at around 700℃. With the increase of concentration of CO2 in the atmosphere, the decomposition rate of siderite ore was reducing and the magnetization rate of FeO was rising first, and then both showing a tendency to a limit at the concentration of 16% CO2.A numerical simulation for the decomposition of Wangjiatan siderite in MCFMR furnace was done by using particle stochastic trajectory model coupled with partical surface reaction model. The results indicated that the gas flow in the tubular reactor is plug flow, and it was adverse for the diffusion of the species and the detention of the particles in the reactor. Furthermore, a long and narrow eddy flow in the feed inlet of flat nozzle would stagnate the siderite particles and it may induce a block in feed nozzle. However such a hidden trouble can be greatly improved by using a insert feed nozzle. It also shows that the flue gas temperature and the particle delay-time in the fourth grade has great influence on the decomposition rate of siderite, while the tubular reaction has a much smaller influence on the ratio of decomposition which is no more than 50%.To verify the numerical simulation results, a half-industry test was executed for Wangjiatan siderite. Experiment results shows that the decomposition ration of siderite is between 90.3% and 94.5% in a weak reduction atmosphere (the content of CO is less than 1.5%) with a temperature of 1028℃. This value is roughly consistent to the result of numerical simulation which is 86.49%. It can also be concluded that the neutral atmosphere is more benefit of the decomposition and magnetic convert of siderite and the content of CO should be kept no more than 1.5% or the content of O2 no more than 1.85%.
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