Char As Reducing Agent For Direct Reduction Of Iron Ore Pellets

As the main method of non-blast furnace ironmaking,the direct reduction process has attracted worldwide attention due to its free from reliance on coking coal resources and its compliance with the current requirements for energy conservation and emission reduction.Char,as a product of coal pyrolysis,possesses the potential of being the reducing agent for iron ore.In this paper,char is used as reducing agent for direct reduction,and the influence of different factors on the formation of iron ore pellets is investigated.The effects of reduction temperature,time,ratio of char and ore,atmosphere and gas concentration on the direct reduction results are investigated.The characterization of Chaoyang Iron Ore shows that the iron grade of the iron ore is66.10%,which belongs to high-grade magnetite.The content of harmful impurity element S is low,which makes it a kind of high-quality iron ore that can be directly applied to the direct reduction process.The reductant char was obtained by low-temperature pyrolysis of Hongliulin sub-bituminous coal,and the pyrolysis temperature of the reductant was determined to be 550°C by the fixed-bed pyrolysis test.Non-isothermal thermogravimetric analysis of iron ore and char mixtures was conducted using a thermogravimetric analyzer to investigate the reduction behavior of samples under different atmospheres and different gas concentrations.The results show that the reaction process under N₂ atmosphere can be divided into three stages.The reaction mechanisms are three-dimensional diffusion,random nucleation and subsequent growth and interfacial chemical reactions.The reaction process in CO₂ atmosphere is divided into two stages.The reaction mechanism is three-dimensional diffusion and interface chemical reaction.The reaction under H₂ and CO atmosphere is divided into three stages.The reaction mechanisms are chemical reaction,random nucleation and subsequent growth and three-dimensional diffusion.For the formation process of iron ore pellets,the effects of molding pressure,ratio of char and ore,amount of binder addition and particle size of iron ore on the strength of iron ore pellets were investigated.The test results show that within the scope of this test,the particle size of iron ore is 0.075⁰.09mm,the particle size of char is less than 0.05mm,amount of the binder addition is 10%,the molding pressure is 60kN,and the ratio of char and coal is 0.4:1?mass ratio?,can prepare iron ore pellets that meet the strength requirements of this test.For the direct reduction process of iron ore pellets,the effects of reduction temperature,reduction time,ratio of char and ore,reducing atmosphere and gas concentration on the direct reduction results were investigated.The total ironification rate and metallization rate were determined by chemical analysis method.X-ray diffraction and scanning electron microscopy characterized the phase composition and microstructure of the reduced products.The results of the direct reduction test show that at the temperature of 950°C,reaction time of 1.0h and char-to-coal ratio of 0.4:1,the metallization rate was 81.39%under N₂ atmosphere,which proved the feasibility of char being reduing agent for iron ore.DRI with a metallization rate of 84.30%was obtained under CO₂ atmosphere at the same condion,slightly higher than that under N₂ atmosphere,indicating that the Boudouard reaction?C+CO₂=2CO?occurred but the effect was not obvious.Both the metallization rates were lower than 90%which can not be directly used for electric furnace steelmaking.The reduction gas was introduced into gas-solid synergistic reduction.The results showed that the metallization rates were 91.43%and 91.17%when the reduction temperature was 1000°C,the reduction time was 1.0h,and the volume concentration was 50%under H₂ and CO atmospheres.Increasing the reduction temperature and prolonging the reduction time can increase the metallization rate,and the reduction results are superior to N₂ and CO₂ in the lower temperature range.Increasing gas concentration can promote the metallization rate of reduction product,but when the gas concentration exceeds50%,the increase of metallization rate is not obvious.