Study On The Interaction Of Iron-containing Burdens And Its Influence On Permeability Of Cohesive Zone In Blast Furnace

The greenhouse effect caused by massive emissions of CO2 has led to the continuous deterioration of the environment and climate.According to statistics,the CO2 emissions in iron and steel industry account for 5%of the global emissions,which is one of the main battlefields for energy conservation and emission reduction.For the emission reduction in iron and steel industry,it is a primary task to reduce the CO2 emissions of blast-furnace ironmaking process,where the key is to reduce the consumption of carbon-based materials in blast furnace.Even though the processes of top gas circulation and hydrogen rich gas injection can effectively cut down the usage of carbon-based materials,the permeability of the burden column will be weak due to the shortage of the coke.As the decisive factor of permeability in blast furnace,the cohesive zone is formed on the basis of the interaction between different burdens,and unfortunately,the influence mechanism of the interaction has not been fully clear on the permeability of the cohesive zone.Aim at the permeability improvement of the cohesive zone,the formation process and property evolution of the cohesive are systemically studied in this paper based on the interaction between different burdens.In addition,this study also can provide the theoretical basis and process guidance for low-carbon ironmaking process in blast furnace.The interaction of gangue phases between different burden was studied.An experimental method was designed to study the interaction of burden by using tablet which was made based on the gangue phase components in burden.By using the gangue phase tablet,the interaction between gangue phases with different properties was studied;the thermodynamic calculations by FactSage were carried outto explore the possible interaction reactions.The results show that there are multiple eutectic phases in the gangue phase of low-basicity pellets,and the solid phase is easy to dissolve.Moreover,liquid ratio in the low-basicity pellets is higher than gangue phases of high-basicity sinter and its melting temperature is lower.The molten pellet gangue phase diffuses into the sinter,which changes the phase composition of the sinter gangue phase,and produces more liquid phases due primarily to the eutectic phase melting reaction,so that the sinter gangue phase melts below its melting temperature.The liquid phase formation temperature is low and reaction is simple in CaO-SiO2-FeO system which is the bascic reaction of interaction to promote mass transfer and dissolve the solid phase.The interaction can be inhibited by increasing the indirect reduction degree and avoiding the mixing of different burdens,which will improve the permeability of the cohesive zone.The moderate mass transfer of MgO from sinter to pellet can improve the metallurgical properties of sinter and pelletThis paper further studies the influence of MgO on the interaction and the concept of MgO distribution index was proposed.The results demonstrate that the composition of the original gangue phase in the pellet changed with the mass transfer of MgO from the sinter to pellet,.This process reduced the liquid phase produced by eutectic phase melting reaction and thus decreased the liquid phase ratio of gangue phase in pellet.The decrease of the liquid phase ratio limited the mass transfer between the pellet and the sinter and inhabited the interaction between them.Moreover,the liquid phase ratio of gangue phase in sinter increased with the increase of MgO,which eventually promoted the interaction.In order to inhibit the interaction between burdens and improve the permeability of the cohesive zone,we can reduce the liquid phase production and limit the mass transfer.Therefore,this paper defines the distribution index I(%·?)of MgO to evaluate the distribution of MgO in pellet and sinter.The following equation expressed:The results show that the smaller the I value,the more reasonable the MgO distribution and the better the permeability of the soft melting process.The softening and melting behavior of burdens with different per-reduction degrees were investigated by softening,melting and dropping experiments.The results show that:as per-reduction degree increases,the softening temperature zone of burden expands,the melting temperature zone of burden shrinks and shifts to high temperature area simultaneously.As per-reduction degree of burden increases,the content of FeO in gangue phase was lower,resulting in the liquid ratio of gangue phase decreased during softening and melting process,which inhibited the carburization to the metallic iron phase through smelting reduction of iron oxide.Therefore,the softening and melting of gangue phase and metallic iron phase required higher temperatures,and temperature range from softening to dripping of burden obviously narrowed.Based on the above reasons,the high reduction degree burdens have the property of "drop immediately after melting",which can significantly improve the permeability in softening and melting processThe effects of different burden layer structure on the softening-melting behavior are investigated by softening,melting and dropping experiments.The results showed that:with the increasing mixing degree of burden layer,the melting temperature zone was basically unchanged,the softening temperature zone of burden was increasing,and the permeability of the burden layer trended poor.To increase the transmission distance of liquid phase and suppress the interaction,the mixed layer structure of different burden should be avoided.This provided a theoretical basis or the preservation of the cohesive zone permeability under the condition of high ball ratio production process.A cohesive zone model with three cohesive layers was established,and FLUENT commercial software was used to simulate the gas flow in the cohesive zone model.The results show that when the coke ratio is constant,as the reduction degree increases,the pressure drop of the cohesive zone model decreases;When the reduction rate of coke ratio does not match the increase rate of reduction degree,it will cause deterioration of gas permeability;no matter the traditional blast furnace or oxygen blast furnace,the coke layer is the main channel of gas.When the mixing degree of the burdens increased from 0%to 100%,the pressure drop of the model increased from 184.94KPa to 188.47KPa,and the gas distribution ratio of coke layer gradually increased from 90.71%to 91.78%.