Effect Of Graphitization Process On Microstructure And Metallurgical Properties Of Blast Furnace Coke

With the development of blast furnace in China toward large-scale,high efficiency,long life,energy-saving,environmental protection and oxygen-enriched coal injection intensified smelting,more and more strict requirements for coke quality have been put forward.Therefore,it is necessary to understand the deterioration process of coke in blast furnace hearth.This paper analyzes the deterioration process of coke in blast furnace hearth by combining laboratory experiment with theoretical calculation from the aspects of microstructure and macroscopic properties,clarifies the mechanism of coke deterioration,evaluates the quality of coke,saves resources,reduces costs and protects it.The modernization of environment and blast furnace is of great strategic significance.At present,the coke layer in low carbon blast furnace becomes thinner and the gas and liquid permeability of charging column is deteriorated.The coke powder produced during graphitization of coke in high temperature zone of hearth is one of the main reasons for this phenomenon.In order to study the effect of graphitization process of coke at the bottom of blast furnace on its metallurgical properties in hearth,the graphitization degree of coke at different temperatures from 1100 to 1500?,the relationship between graphitization degree of the same coke and reactivity of coke and strength after reaction,and the relationship between coke with different graphitization degree and corrosion of alkali metals were studied.The microscopic morphology of different coke samples after observation and analysis was observed and analyzed.The results show that the graphitization degree of coke increases with the increase of temperature,and the graphitization degree of coke increases by 1.8times,the d002 value of interlayer space decreases by 2%,the La value of microcrystalline lamellar diameter increases by 3%,and the Lc value of lamellar stacking height increases by 15%,especially the air pore.With the decrease of coke surface mosaic structure and isotropic structure,the ordering degree of coke structure is enhanced.With the deepening of graphitization degree of coke,the reactivity of coke decreases gradually,the strength of coke increases gradually after reaction,the deterioration of coke surface weakens,the formation of atmospheric pores decreases,and the tendency of pore wall destruction weakens.Alkali metal promotes the reactivity of coke,which increases the reactivity of coke and decreases the strength after reaction.The graphitization of coke can resist the alkali damage of coke and reduce the deterioration of coke surface.The results show that all coke in the hearth of blast furnace will be graphitized seriously regardless of its size,its microcrystalline structure will be changed obviously,the pore structure of Coke will be changed during graphitization,and the ash content of Coke will migrate under the action of high temperature thermal stress,thus affecting the micro-pore structure of coke.The influence of graphitization process and ash migration on the microstructure of micro-pores is not clear yet.Therefore,this paper simulates the hearth temperature of blast furnace,uses controlled temperature muffle furnace to reheat coke,uses X-ray diffractometer to investigate the microstructure of coke,uses nitrogen adsorption method and SEM to study the evolution of micro-pores and surface morphology,SEM combined with EDS studies the ash migration process of coke,and explores the internal relationship among the microcrystalline structure,pore structure and ash migration.The experimental results show that the graphitization of coke is promoted by reheating in N₂ atmosphere,and the effect is more obvious with the increase of reheating temperature.The pore evolution of coke changes regularly with the increase of reheating temperature,and the ash content of coke migrates around 1400?.As the gasification reaction of coke is one of the main reasons leading to its deterioration and damage,the experiment of coke gasification reaction was carried out by HCT-2 high temperature thermogravimetric analyzer under the action of CO₂atmosphere.From the calculated activation energy,it can be seen that according to the gasification performance of coke and CO₂,the order is:heating to 1300?>heating to 1100?>heating to 1500?>heating to 1400?>heating to 1200>heating to1600.On this basis,in order to further explore the factors affecting the gasification reaction of coke and CO₂,the microcrystalline structure,pore structure and light of graphitized coke were studied by combining the dissolution degree of gasification reaction with the microcrystalline structure,pore structure and light intensity of the graphitized coke,which were reheated to 1100?,1200?,1400?and1600?respectively.Considering the structure of coke,the results show that the active optical structure of coke can promote the gasification reaction of coke and carbon dioxide more obviously than the developed pore structure.When graphitization deepens to a certain extent,the inhibition effect of graphitization on the gasification dissolution reaction of coke is remarkable.In summary,regarding the deterioration of coke in hearth area,this paper deeply studies the graphitization process,pore structure evolution process,optical structure evolution process and coke gasification reaction process of coke,reveals the deterioration mechanism of coke in hearth area,and provides a theoretical basis for efficient utilization and rational evaluation of coke quality.