The Influence Of Blast Furnace Tuyere Area And Gasification Reaction On The Evolution Law Of Coke Microstructure

In recent years,with the development of large-scale blast furnace and oxygen enriched coal injection technology,combined with the national green,low carbon policy requirements,ironmaking process of blast furnace raw materials increasingly stringent requirements.As an indispensable raw material in blast furnace ironmaking,coke plays an important role in smelting process,and is also the key to low-carbon smelting and reducing carbon emissions in ironmaking process.Therefore,its quality,degradation behavior and evolution law in blast furnace have attracted much attention,and clarifying its microstructure evolution law has become a key common technical problem in the steel industry.In view of this,this paper adopts the research methods of wind caliber sampling,comparative analysis and gasification simulation.Based on the basic characteristics of coke in the furnace,the degradation behavior of coke from entering the furnace to the tuyere and the degradation difference at different positions of the tuyere plane are revealed from the microscopic level.At the same time,the gasification reaction of coke in the furnace was simulated in the laboratory,and the influence of CO₂ and CO₂+H₂O mixed atmosphere on the microstructure evolution of blast furnace coke and its characterization of macro performance were studied,which laid an important theoretical foundation for improving coke quality and reducing carbon emissions.Based on the analysis of basic characteristics and slag iron content of coke into the furnace and tuyere coke,it is found that the ash content in tuyere coke and alkali metal content in ash first decrease and then increase from the tuyere direction to the hearth,and all of them are higher than that of coke into the furnace.The coke particle size also decreased significantly,and the coke content with particle size≤5 mm in the furnace core area accounted for about 85%.And the content of slag iron in the tuyere plane shows an upward trend in the direction of tuyere pointing to the hearth,and the proportion of slag iron in the dead charge column area is as high as 53.8%,indicating that the activity of the hearth is low.The gasification reactivity of the tuyere coke is higher than that of the coke into the furnace due to the microporous expansion inside the tuyere coke and the catalytic effect of alkali metals.Through the analysis of the pore structure and microstructure of the furnace coke and the tuyere coke,it is found that the tuyere coke has a more ordered microstructure than the furnace coke.In the radial direction,the order degree of coke microcrystalline structure increases first and then decreases,and the order degree is the highest in the range of 1-2 m from the air inlet.It is found that the porosity of radial tuyere coke increases significantly,the pore wall becomes thinner,and the pore size of the original micropore inside the tuyere coke expands.And a large number of micropores and cracks are also generated,resulting in the specific surface area and pore volume of the tuyere coke are higher than those of the coke into the furnace.The graphite structure inside the tuyere coke increases and the crystal structure becomes larger.In the radial direction,with the increase of temperature,the number of amorphous structures in coke decreases,the ordering increases,and the graphite structure continues to grow.However,along the direction of the furnace core,the temperature decreases,resulting in the stagnation of amorphous structure content and the decrease of graphitization degree.The carbon dissolution reaction in blast furnace was simulated under laboratory conditions,and the evolution of microstructure after coke dissolution under CO₂ and CO₂+H₂O conditions was studied respectively.It was found that in CO₂ atmosphere,with the increase of reaction time,the specific surface area and pore volume of coke and the number of micropores in coke increased first and then decreased,and the average pore diameter decreased first and then increased.And in the gasification reaction of CO₂ and coke,I_G/I_All,which represents the relative content of graphitization,first increases,then decreases and then increases,while I_D3/I_G,which represents the disordered structure,and I_D4/I_G,which represents the unstable structure,are opposite,indicating that coke tends to be more orderly with time.In the mixed atmosphere of CO₂ and H₂O,the specific surface area of coke and I_G/I_All gradually increased with the increase of H₂O content.However,when the proportion of H₂O exceeds 50%,the specific surface area decreases slightly,and the pore size corresponding to the peak in the pore size distribution curve shifts to the right,and the average pore size increases.I_G/I_All increased significantly when the proportion of H₂O reached 50%,and I₃/I_Gand I_D4/I_G representing the relative content of disordered structure and unstable structure decreased accordingly,indicating that when the H₂O content was high,the reaction between disordered microcrystalline structure and H₂O was more obvious,accelerating the transformation of disordered structure to ordered structure.