Basic Research For Direct Reduction Of Carbon Bearing Pellets Of High Phosphorus Oolitic Hematite By Gas Based Shaft Furnace Process

The reserves of high phosphorus oolitic hematite are so abundant, and accounted for about 1/9 in china. It is extremely difficult to separation this kind of ore that lead to Long-term unused of high phosphorus oolitic hematite. Because it has high P content(0.4～1.0%), low grade(35～50%), the Fe can’t be enriched and the P can’t be removed.The inlay granularity of iron oxide grain is fine. It mixed together with apatite chamosite, and take shape of oolitic structure which is concentric lamellar interphase. The Fe can’t be enriched and the P can’t be removed if the occurrence form can’t be changed. In order to reach the aim of "enrich Fe and remove P", this paper raised to use gas based shaft furnace direct reduction process for dealing with this kind of ore. This paper is the basic research of the process, and it was studied from three aspects: thermodynamics calculation, experimental study and numerical simulation.Under gas based direct reduction, the Fe grain which take a shape of needle and dispersion in gangue minerals didn’t grow up together, its size is about 10μm. The result of magnetic separation is bad; the growth of Fe grain is obvious under the coal based direct reduction, the grain size is about 50μm, and the result of magnetic separation is excellent, but at the high temperature, the pellets melt adhesion, and make against to production of shaft furnace.In order to promotecohesion and pellets sticking at the same time, the coal-based shaft furnace process (gas heating carbon bearing pellets) is conducted for the experiments. And get the optimal blending amount (C/O) of the pellets and the best alkalinity (R). It was found that to ensure that iron grade of magnetic concentrate are over 75%, the iron recovery rate above 90%, the rate of dephosphorization reached 80% pellets of C/O should be between 0.8-1.0, R≥1.1.The simulation experiment for the optimal proportioning pellets was carried out, and the influence factors which contain temperature, time, atmosphere and rate of flow were discussed and analyzed during the reduction. And ensure restrictive part is mixed controlled by interface chemical reaction and diffusion after studying kinetics. The rate expression of direct reduction reaction is k+ = 0.324exp(-76.527 x 103/RT), and activation energy of reaction is 76.527kJ·mol-1 by means of Kinetic regression.Numerical simulation of shaft furnace shows that for a height of 9m shaft furnace, high phosphorus oolitic hematite pellet can be completely transformed into magnetite after running about 2m. After running about 5m, the pellets completely become FewO, within the scope of 5m to 9m depth, FewO reduction. With the increases of the gas temperature, and gas flow rate pellets metallization rate and reduction rate increase, with the reduction in feeding speed, increasing the pellet radius increases.