Study On The Variation Law Of Macroscopic Properties Of Large Blast Furnace Coke

With the new concept of low carbon development put forward,as a high energy consumption,high CO₂ emissions of the steel industry bear the brunt.The carbon emission of blast furnace ironmaking process accounts for 90%of the whole iron and steel industry.The urgent task is to try to implement efficient smelting and reduce the coke ratio,so as to fundamentally reduce the carbon input of blast furnace,which will lead to an increase in coke load and more melting deterioration of coke in blast furnace,thereby affecting the smooth operation of blast furnace.At present,the research on coke in blast furnace mainly focuses on the microstructure and particle size distribution,and the research on the macroscopic strength of coke is less.The compressive and flexural strength of coke can directly reflect the ability of coke“pillar skeleton”,which is one of the restrictive links to determine the ultimate coal ratio of blast furnace.Therefore,in this paper,the deterioration behavior of coke in the blast furnace,the compressive strength,flexural strength and physical and chemical properties of coke at different positions were studied through the coke into blast furnace and tuyere plane coke obtained from the four blast furnaces,the hearth coke obtained from the intermediate repair of A#blast furnace.Through the high temperature gas-solid reaction device,SEM,and the compressive and flexural strength measurement device,firstly,the composition,strength and gasification characteristics with CO₂ of the coke into blast furnace and tuyere plane coke were compared and analyzed.Then the gasification reaction experiments of 2#blast furnace the coke into blast furnace and tuyere coke under different temperatures and reaction atmosphere were carried out to study the effects of temperature and reaction atmosphere on the gasification reaction and compressive and flexural strength of coke.Finally,the strength,micro-morphology and gasification characteristics with CO₂ of the tuyere plane and dead stock coke were analyzed,and the variation laws of coke compressive strength,flexural strength,dissolution loss rate and ash content in different parts of the hearth were studied.The main conclusions are as follows:（1）Compared with tuyere coke,the average particle size of coke into blast furnace decreased by 40.81%-52.9%,CSR decreased by 32.2%-47.3%,CRI increased by32.3%-42.9%,apparent porosity increased by 2.71%-11.82%,cold compressive strength and flexural strength decreased by 2.93 Mpa-5.48 Mpa and 0.28 Mpa-1.6 Mpa,respectively.The particle size of coke in the blast furnace is reduced,mainly because the surface structure of coke is damaged and continuously pulverizes and falls off,and the central structure is less damaged.The strength still meets the skeleton effect of the charge column of the blast furnace.At 1100℃,the melting rate of tuyere coke in the reaction with CO₂ was relatively fast.After 120 min,the melting rate was 1.23-1.93times that of coke into blast furnace.After the reaction,the compressive and flexural strength of coke into blast furnace and tuyere coke decreased with the increase of reaction time.（2）The gasification reaction results of 2#blast furnace the coke into blast furnace and tuyere coke under different temperatures and atmospheres show that the temperature has a significant influence on the gasification reaction of coke with CO₂.With the increase of reaction temperature,the dissolution rate of coke is accelerated,the gasification reaction time controlled by interfacial chemical reaction is shortened,and the decrease of compressive and flexural strength of coke after reaction is increased.The activation energy of the reaction between coke and CO₂ was 165.14 KJ/mol and the pre-exponential factor was 3098.27 min^-1.At 1100℃,the melting rate of the reaction between H₂O and coke was much higher than that under CO₂ condition.Under the mixed atmosphere of the two,the melting rate of coke increased with the increase of H₂O content.However,when the H₂O content was low,the compressive strength of coke after reaction was not much different from that under 100%CO₂.Under the mixed atmosphere of CO₂,CO and N₂,the melting loss rate of coke was less than that under CO₂ condition,and the compressive and flexural strength after reaction was higher than that under CO₂ condition.At 1100℃,with the increase of CO₂ content,the increase in the melting rate and the decrease in the compressive and flexural strength of the tuyere coke are smaller than those of coke into blast furnace.（3）For the coke on the tuyere plane,as the distance from the tuyere increases,the fixed carbon content,volatile content and apparent porosity decrease,and the ash content increases.In the reaction with CO₂ melting loss,the melting loss rate of coke of tuyere plane after 30 min is about 1.63-4.04 times that of the coke into blast furnace,and the melting loss rate increases with the increase of the distance from the tuyere.The cold compressive strength and flexural strength decrease with the distance from the tuyere area,while the strength fluctuates greatly due to the fact that the tuyere area falls into part of the furnace hearth coke during the downwind.The compressive and flexural strength of the coke after reaction decreased with the increase of distance from tuyere.（4）For the hearth coke.Horizontally,with the increase of the distance from the furnace core,the ash content of coke decreases and the fixed carbon content increases.With the increase of distance from the furnace core,the melting loss rate and cold compressive and flexural strength of coke in the furnace core and edge are higher than those in the middle,while the compressive and flexural strength of coke after reaction in the plane of 1.2 m and 2.5 m under the tuyere show the opposite law.Vertically,with the increase of the distance from the outlet plane,the apparent density and ash content of coke increase,the fixed carbon content and the melting rate with CO₂ reaction decrease,and the ash content is up to 51.21%.The apparent porosity first increased and then decreased,and the apparent porosity of coke decreased significantly below the3.5 m plane under the tuyere.It can be seen from the surface scanning that a large number of slag iron penetrated into the coke through the pore of coke.The order of cold compressive strength and flexural strength of coke in different plane coke with different heights from large to small is:ZX-4.5>ZX-1.2>ZX-2.5>ZX-3.5.The order of compressive and flexural strength after coke reaction from large to small is:ZX-4.5>ZX-3.5>ZX-2.5>ZX-1.2.