Research On Structural Evolution Characteristics And Kinetics Of Gas-Based Direct Reduction Process Of Iron Ore

The gas-based direct reduction ironmaking process can effectively solve the problem of relying on coke in the traditional ironmaking process and reduce the pollution caused by coking.It is one of the important directions of current ironmaking research.In the process of direct reduction ironmaking,the structural evolution of iron ore and the study of reaction kinetics have a significant impact on the process and production efficiency.In this paper,using a high-temperature tube furnace and a high-temperature hot stage microscope,using pellets and fine iron powder as raw materials,the structure evolution characteristics of different scale iron ore gas-based reduction processes are studied,and the H2/CO mixed atmosphere and H2 atmosphere are explored.The reaction kinetics and its influencing factors.The main contents are as follows.1.Revealed the change rule of phase structure in the reduction process of pellets at 750?? 950? under H2,H2/CO atmosphere.The results show that the Fe2O3 phase,Fe3O4 phase and FeO phase co-exist during the reduction process.The early stage of the single pellet reaction of pellets belongs to the three-interface reaction,and the middle and late stage of the FeO-Fe single interface reaction.The porosity of single pellets increased from 21.69%to 47.72%,and the porosity increased by 120%.The generated pores increase the specific surface area,which is conducive to the occurrence of the reduction reaction,and the pore growth rate shows a trend of increasing first and then decreasing.2.The kinetic characteristics of the single pellet reaction of pellets under H2 and H2/CO atmospheres at 750??950? were obtained.Combined with thermodynamic analysis,it is found that the exothermic heat of the CO reduction process can provide heat for the reduction of H2.The reduction rate of pellets with a diameter of 14 mm at 750??850? in a mixed atmosphere of H2/CO volume ratio of 8/2 is better than that of reduction under H2,the difference decreases as the temperature rises.The unreacted nucleus model is used to solve the related parameters.The apparent activation energy of H2 reduction is 37.18 kJ/mol,and the apparent activation energy of H2/CO volume ratio of 8/2 is 26.85 kJ/mol.3.The high-temperature microscopic visualization technology reveals the characteristic mechanism of the high-temperature structure evolution of the CO-reduced iron fine powder single particle.The time for the precipitation of iron on the surface of the particles has been shortened by 75%from 1100? to 1300?.In the unmelted state,due to the attachment of CO on the FeO surface,elemental iron is generated after deprivation of oxygen atoms.The elemental iron aggregates and forms nodules.The diameter of the nodules rises from 6 ?m at 1100? to 15 ?m at 1350?.Above 1400?,the produced intermediate FeO appears in amolten state and is dispersed in a liquid state,causing stratification.The inner layer is mainly reduced iron,and the middle layer is mainly tree-like metallic iron with reduced molten ferrous oxide.The layer also contains slag accumulated by elements such as Al,Ca and Si.