Research On Optimization Conditions And Reduction Characteristics Of Limonite Pellets Roasting

The steel industry is one of the world's largest energy-consuming manufacturing industries,accounting for 50%to 70%of the total energy consumption of China's steel industry production.Iron ore and coke are the main raw materials for steel production.Due to the gradual increase in demand and years of development and utilization,high-quality iron ore and coke have further decreased.On the other hand,traditional blast furnaces have high requirements for ore grade,a large amount of low-grade ore cannot be properly used,and the process is long,the investment scale is large,the energy consumption is high,and the pollution is serious,which affects the healthy and sustainable development of the steel industry.In recent years,experts at home and abroad have conducted a lot of research on the mechanism and kinetics of iron ore in the mixed atmosphere of CO,H₂ and CO-H₂ experimentally and theoretically.However,most of the previous studies have focused on the reduction process of magnetite and hematite,but few studies on the reduction process of limonite.Therefore,it becomes very important to study the direct reduction performance of limonite pellets.This article takes Guisha limonite as an example to study the roasting performance and direct reduction performance of limonite pellets.The research results provide the basis for the application of limonite.The main research work and results include the following aspects:?1?Using response surface method to optimize the experimental design of pure limonite pellets.The best roasting process to obtain the compressive strength of the pellets is:bentonite content 1.479%,roasting temperature 1557.684 K,roasting time18.870 min.The compressive strength of pure limonite pellets under optimal conditions is 1431.8 N/P,and this pellet can be applied to small blast furnaces below2000m³.?2?Study the isothermal reduction mechanism of limonite pellets in a mixed atmosphere of H₂,CO and two gases.The experimental results show that the reduction degree of the oxidized pellet particles increases with the reduction time and temperature.The reduction time decreases with increasing H₂/?H₂+CO?ratio and increasing temperature.Throughout the reduction process,the kinetic results show that the early stage of the gas reduction process is controlled by the interface chemical reaction and the later stage is controlled by diffusion.SEM results show that the particles reduced in H₂ atmosphere have a large number of micropores,which is more conducive to the reaction reduction.?3?Using coke and reducing gases?CO and H₂?as reducing agents,study the reducing characteristics and changing rules of limonite carbon-containing pellets.The research results show that the degree of reduction of pellets gradually increases with increasing temperature.The C/O molar ratio has a greater influence on the reduction degree of pellets in the N₂ atmosphere,but does not have a significant effect in the CO and H₂ atmospheres.And the maximum reduction rate increases with increasing temperature.The reduction reaction is most difficult to proceed in the N₂ atmosphere,and the reaction is most likely to occur in the CO atmosphere.The microscopic analysis of pellets using EPMA and XRD found that the pellets reduced in N₂atmosphere had the smallest porosity and the pellets reduced in H₂ atmosphere had the largest porosity,which was more conducive to gas diffusion.?4?The effects of temperature,atmosphere and C/O molar ratio on the volume change of limonite pellets during the reduction process were studied.The results show that the reduction configuration index of limonite oxide pellets under different reducing atmospheres is similar.The oxidation coefficient of limonite pellets increases first and then decreases as the degree of reduction increases,increases with temperature,and increases with CO/?CO+H₂?.With the increase of C/O molar ratio,the shrinkage coefficient of carbon-containing pellets gradually increases with the increase of C/O molar ratio,and the shrinkage coefficient of particles gradually increases with the increase of temperature.Carbon pellets will expand.