Effect Of Temperature And Alkali Carbonate On The Structure And Properties Of Coke

With the development of the blast furnace,the increase of pulverized coal ratio,the grade of iron ore and the quality of fuel declines and the alkali metal elements increase continuously resulting the cyclic enrichment of alkali metals in the blast furnace,and the destructive effect on the blast furnace is strengthened.So,the damage of alkali metals to the iron-making process has been paid more and more attention.Cyclic enrichment of alkali metals will not only cause serious erosion to the blast furnace lining,but also deteriorate the permeability of the blast furnace.Meanwhile,coke,as one of the most important raw materials for iron-making process,will also be harmed by alkali metals.Alkali metals will penetrate into the coke during the ascending process,which has a significant impact on the metallurgical properties of coke,so it is necessary to study the effect of alkali metals on carbon solution reaction.The macroscopic properties of coke are only an external manifestation of the internal optical texture of coke,so it is necessary to further study the effect of alkali metals and on the dissolution behavior of different optical texture of coke.Furthermore,the degree of carbon solution reaction is low in the lower part of blast furnace.Thermal stress is one of the main factors of coke degradation,which causes coke powdering that not only seriously affects the strength of coke but also is not conductive to the stability of the blast furnace.Thus,it is necessary to study the effect of heat treatment on the structure and properties of coke.Firstly,coke was heat treated at different temperatures in a silicon-molybdenum furnace.The particle size distribution,pore structure,microcrystalline structure,mineral transformation characteristics and compressive strength of coke at different heat treatment temperatures were analyzed by mechanical screening,optical microscope,X-ray diffraction,Raman spectrometer,N₂ adsorption and universal material testing machine.The results showed that with the increase of temperature,coke powdered seriously,the percentage of large coke particles decreased and the percentage of small coke particles increased.At the same time,small pores were interconnected to form large holes causing the increase of coke porosity and the average area of holes.In addition,with the increase of temperature,the Lc and La significantly increased,but the d₀₀₂ decreased causing the increase of graphitization degree.The structure of large aromatic ring increased firstly and then gradually reached saturation state and the content of C-C increased.Meanwhile the compressive strength decreased with the increase of temperature.Secondly,alkali carbonate was infiltrated into coke by impregnation adsorption method.The effect of alkali carbonates on the CRI and CSR of coke was investigated by NSC method,and the coke powdering was counted.The effect of alkali metal carbonates on the microcrystalline structure of coke was studied by XRD.The effect of alkali metal carbonates on the microstructure of coke was analyzed by SEM-EDS.Furthermore,the optical texture of coke was studied by polarizing microscope.It was found that alkali carbonates could increase the CRI and decrease the CSR,thus causing powdering phenomenon.With the increase of alkali carbonates concentration,the powdering rate of coke increases.Meanwhile,the Lc and d₀₀₂ increased with the increase of alkali carbonates.During the gasification process,nepheline and potassium nepheline strengthen the destruction of coke properties because of the presence of alkali carbonates.In addition,alkali carbonates had a certain catalytic effect on the gasification of anisotropy and also had a certain inhibitory effect on the gasification of isotropy.Finally,the kinetics of alkali carbonates catalysis for coke gasification was studied by thermodynamic calculation,TG experiment and modeling.The results showed that alkali carbonates had obviously catalytic effect on coke gasification,potassium carbonate has more obviously catalytic effect on coke gasification than sodium carbonate.Alkali carbonates could be effectively reduced the initial temperature,the final temperature and the intense reaction temperature of coke gasification reaction.The conversion of coke gasification reaction and the maximum reaction rate increased with the increase of alkali carbonates.The gasification process of coke mainly followed the reaction kinetics model.When the content of alkali carbonates was low,it was mainly controlled by the first-order reaction.While the content of alkali carbonates was high,it was controlled by the second-order reaction.Activation energy of coke gasification reaction could be reduced by the addition of alkali carbonates.At the same time,alkali carbonates could catalyze coke gasification reaction,however its catalytic gasification effect was exactly limited.The effect of potassium carbonate is higher than that of sodium carbonate.