Research On Macerals Transformation During Coking Process And Coke Properties

The contradiction between the large demand of coke and the scarcity,regional limitations of coking coal resources is becoming increasingly prominent in China.It is urgent to promote the application of coal blending coking technology to increase the consumption of cheap weakly viscous coal,produce coke suitable for blast furnace(BF)smelting,and alleviate the problems of fuel supply shortage,large fluctuation and high cost in iron and steel industry.Coal petrographic method has become a scientific and effective method to solve these problems because of its microscopic and intrinsic properties.However,when it is applied to coal blending coking technology and coke properties research,there are some problems,such as unclear understanding of the influence of coal petrographic characteristics on coking process,unclear relationship between coke optical texture change and coke performance evolution in BF.Therefore,this paper finds out the genetic law of macerals and optical textures of different coal types,and explores the influence of different ash components on the law,so as to provide a theoretical reference for coal petrographic blending coking technology.At the same time,it is found that there is a good correlation between the behavior of coke in BF and its optical texture content.The relationship between the change of optical texture in BF and coke performance,microstructure is analyzed,which is helpful to further clarify the behavior of coke in BF.Firstly,the relationship between coal petrographic parameters,coking index and coke quality is studied,and the genetic relationship between macerals and optical textures is found out.The vitrinite of 1/3 coking coal mainly generates fine-grained mosaic texture,the vitrinite of fat coal mainly generates coarse-grained mosaic and medium grained mosaic texture,the vitrinite of lean coal and main coking coal mainly generates incomplete fibrous texture,complete fibrous texture and lamellar texture,and the inertinite of all kinds of coal all generates fragment and silk like carbon texture,basic anisotropic texture and isotropic texture.At the same time,through the coking experiment with blended coal,it is found that blended coal coking is helpful to enhance the optical anisotropy of coke and optimize its hot performance and cold wear resistance.Secondly,the addition of SiO₂ and Al₂O₃ can make the quality of coke deteriorate,and with the increase of the addition amount,the degree of quality deterioration and porosity increases,and the damage of pore wall structure aggravates.The effect of Al₂O₃ is stronger than that of SiO₂.The decrease of M₂₅ should be caused by the decrease of adhesive component content,the increase of M₁₀,CRI and the decrease of CSR should be caused by the decrease of high optical anisotropy texture content.Finally,the relationship between optical texture,properties and structure of coke is studied under simulated blast furnace conditions.It is found that the isotropic texture,fragment and silky texture and basic anisotropic texture are eroded first;At 1200 ^oC,the fine mosaic texture is eroded and the erosion rate is fast;At 1300 ^oC,the content of easily eroded optical texture is close to 0,while the high optical anisotropy texture has strong resistance to CO₂ gasification corrosion reaction,the corrosion rate decreases.There is a good correlation between the change of coke properties and its optical texture.The erosion of coke optical texture by CO₂ gasification reaction results in the increase of coke weight loss rate,resulting in the increase of coke structure compactness and porosity.The decrease of optical texture(mainly fine-grained mosaic texture)and structural change together cause the increase of coke pulverization rate(decrease of average particle size).The anisotropic texture of coke is helpful to increase its graphitization degree at high temperature.At the same time,it is found that the pressure promotes the pulverization of coke from the outside,mainly because it optimizes the kinetic conditions of carbon dissolution reaction,increases the weight loss rate and porosity,and intensifies the erosion of low optical anisotropy texture.