Basic Research On Sticking Prevent Technologies During Fluidized Bed Iron Ore Reduction Process

Iron ore fines can be directly used as raw material of fluidization iron making to avoid the process of agglomeration in traditional blast furnace, which is helpful to energy saving and environmental protection, and is suitable for the characteristics of iron ore resources in China. But the sticking problem is the biggest obstacle to the development of this technique, the research target of this paper is to explore method to solve the sticking problem and achieve the nomal fluidization of iron ore fines.To explore the method of solving the sticking problem in fluidized bed iron making process, in this paper, the very nature of the particle is chosen as the research object. The particle morphology evolution control, particle-contact control and the particle surface coating method were tried to explore their sticking prevention effect. The main research contents and results are as follows:(1) The influence of hydrogen concentration and temperature on the morphology evolution and the sticking behaviour of Fe2O3 particles in the process of fluidized reduction were studied via a self-made visual silica fluidized bed. In order to exclude the influence of air flow under different hydrogen concentrations and temperature conditions on particle stirring ability. In this paper the particle drag force model was introduced, to consider the drag force of 1073 K,50% hydrogen concentration as the standard drag, the air drag force under different conditions was uniformed. Experiments showed that through increasing the concentration of hydrogen the reduction reaction speed can be increased and promoting Fe2O3 particles to form porous morphology, providing space for new generated metallic iron to diffuse from particles’surface to internal part, then the activity and viscosity of metallic iron on particles’surface can be decreased as well as the sticking tendency. Moreover, higher hydrogen concentrations can prevent the metalic iron to form into layered iron hindering the gas internal diffusion, so the reduction reaction speed can be further accelerated. Within 99 seconds of reduction, above 80% of metallization ratio can be obtained in this experiment.(2) The feasibility of rapid reduction of ultrafine Fe2O3 particles by the use of a down flow fluidized bed was studied. According to the theory of gas particle flow, the model of calculating the falling time of particles was established. The sticking problem can be avioded fundamentally when using the falling bed as the reactor to reduce the ultrafine Fe2O3 powder, and with high hydrogen concentrations the ultrafine Fe2O3 powder can be reduced very quickly. At the temperature of 1273 K and within the 1.5 m of effective falling distance more than 90% of metallization ratio was achieved.(3) The effects of coating MgO and Ca3(PO4)2 on the inhibition of the sticking were studied. It was found in the research that, the MgO coating method can achieve significant sticking inhibition effect. The high-temperature coating method and sintering coating method can help to improve the coating effect. Coating Ca3(PO4)2 on on the surface of iron ore particles can effectively inhibit the formation of iron whiskers, but this method had little effect on the inhibition of sticking. Most of the coated coating substance will fall off from the iron ore particle surface via the dry method. There are mainly two kinds of adsorption patterns on the surface of iron ore particles for the coating substance, one is through physical adsorption of Van Der Waals force, another is through chemical adsorption achieved by chemical reaction or solid state diffusion with materials on particles surface. The intensity of chemical coating is much higher than that of dry method, and increasing of chemical coating can effectively improve the coating efficiency.(4) In order to improve the coating effect and improve the coating amount, the heterogeneous precipitation method was firstly introduced in the experiment and the relative study was carried out. It was found that:a uniform MgO coating layer can be formed on the particles’surface by the heterogeneous precipitation coating method. The coating layer formed by this method has a high intensity, even after fluidized reduction treatment, the breakage of the coating layer is not obvious. According to the understanding of the the mechanism of heterogeneous precipitation, controling the ion concentrations in precipitation solution and extending the heterogeneous precipitation duration is the key to improve the coating effect of the heterogeneous precipitation method.(5) With certain master of inhibiting the sticking problem, of the fluidization iron making processes of Panzhihua vanadium titanium magnetite and Hubei West high phosphorous iron ore were studied. It was found that, coating MgO can inhibit the sticking problem of Panzhihua vanadium-titanium magnetite. The acid leaching dephosphorization operation will worsen the sticking trend of high phosphorous iron ore, but a small amount of MgO coating can solve this problem. In the experiment, the P element was not found in the form of Ca3(PO4)2 inclusion in the melting seperated iron phase. It was found that there was only a very small amount of Ca element in the iron phase, and there was no Ca element in the P inclusion. The acid leaching dephosphorization - fluidized reduction - melt seperation process is expected to become a viable efficient method of processing domestic high phosphorous iron ore.