| Blast furnace is an important way to achieve high-efficiency iron ore smelting.The soft-melting properties of iron ore under high temperature and reducing conditions cause the formation of a cohesive zone in the blast furnace,which affects the gas flow distribution,transmission and chemical reaction in the furnace.Therefore,maintaining good feature and gas-liquid permeability condition of the cohesive zone is the basis for the smooth operation of the blast furnace.At present,scholars at home and abroad mostly evaluate the position,shape and thickness of the cohesive zone based on the simulation of blast furnace conditions by observing the soft-melting behavior of the iron ore,and then guide the operation of the blast furnace.Among many research methods of soft-melting behavior,the soft-melting under load test is adopted by the majority of research institutions.However,the current experimental methods often use constant load or stage-variable load,which is different from the actual burden load of the blast furnace.It will result in the inability to accurately evaluate the properties of the cohesive zone.Based on the Janssen formula,this paper establishes a load change equation that conforms to the actual load of the blast furnace burden for various domestic blast furnace parameters and charge systems.The influence of changes in blast furnace parameters and charge system on the effective load is discussed.The results show that there is a positive correlation between the effective load and the bulk density of the charge,and it has a significant impact on the charge of the large blast furnace.As the effective volume of the blast furnace increases,the maximum effective load on the charge first increases and then decreases.When the bulk density of the charge increases,the effective volume corresponding to the extreme point of the load will also increase.The influence of load change conditions on the soft-melting behavior of sinter ore is studied through the soft-melting under load test.The high-temperature reduction soft-melting index and primary slag characteristics of iron ore under different pressure changes are analyzed,and test suggestions for different levels of blast furnace conditions are given.The research results show that with the increase of the load on the iron ore,ΔT3moves forward,and the interval span is significantly widened.In terms of air permeability index,as the load increases,bothΔPmax and S tend to increase.The load affects the primary slag composition by affecting the reduction of the Fe O in sinter.The composition analysis results show that the load of ore increases,the Fe O content in it decreases,the Fe O in the primary slag increases,and the melting temperature of the slag decreases.Research on the properties of the primary slag shows that the surface tension of slag has a positive correlation with the maximum pressure drop,and the viscosity of the slag has a positive correlation with the effective width.The interruption experiment showed that the increase of the load on the charge,to a certain extent,increased the direct reduction of Fe O in the sinter ore at the bottom.The reduction kinetics conditions of Fe O in the top sinter are restricted,and the reduction degree is weakened.The effect of particle gradation on the soft-melting behavior of sinter is studied through the soft-melting under load test.The soft-melting index and primary slag distribution law of iron ore under different particle gradation are analyzed,and reasonable suggestions for optimization of charge particle size gradation are put forward.Drawing on the idea of phase diagram drawing,by constructing a multi-grain porosity phase diagram,it is found that the particle gradation directly affects the ore layer porosity.The results show that the particle gradation directly affects the porosity of burden layer.When the porosity increases,ΔT3 moves backward,the interval width decreases,andΔPmax and S both show a downward trend.The results of the interrupted experiment show that the kinetic conditions of the small-grained ore are better,the reduction of Fe O is faster,and the slag phase is evenly distributed in the particles.For the large-grained ore,only the Fe O at surface is reduced,and there is almost no change in the interior,and the slag phase is concentrated on the surface.The larger the size of ore,the larger the grain size of FeO. |
