Optimal Experimental Study On Production Of Oxide Pellets From Hematite Burdened With Semicoke

With the rapid development of pellet industry and the increasing depletion of magnetite resources in China,expanding the scope of pellet raw materials and improving the quality of pellets are becoming important subjects of pellet technology.Imported hematite has gained world-wide recognition as an indispensable charge to replace magnetite for pelletizing plant due to its low price,low content of SiO2 and relatively high iron grade,but hematite pellet is limited by difficulty in forming spherical particles and roasting,as well as poor metallurgical properties of fired pellet.Semi-Coke as a new type solid fuel is an effective way to solve this problem.Therefore the successful application of semicoke-burdened hematite pellets has important practical significance on the development of pelletizing industry in China.Hematite concentrates burdened with certain proportion of solid fuel to produce oxidized pellet is studied in this paper.Through contrasting the difference of technical parameters of pelletizing and green ball quality between semicoke-burdened and nonsemicoke-burdened hematite pellet,this paper optimizes technical parameters of pelletizing.The optimal values of the technical parameters of pelletizing found at Na-bentonite additive amount is 1.5-2%,balling time 10 min,included compaction time3 min,moisture of green ball 8.9%-9.8%,semicoke amount 1%-2%.Drop strength of green ball is more than 4 times from 0.5m,compressive strength is greater than 10 N per pellet,and shock temperature is higher than 400 ?.Compared with non-semicoke-burdened hematite pellet,the quality of green ball is improved greatly,and Na-bentonite additive amount is reduced by 0.5%.Only in terms of properties ofgreen ball,the influence of semicoke and anthracite are basically identical.Therefore semicoke can be used as a solid fuel to produce carbon-burdened pellet.Through simulating grate-rotary kiln process,the parameters influencing the compressive strength of semicoke-burdened hematite pellets such as roasting temperature,roasting time,airflow volume,semicoke additive amount are researched,and response surface methodology(RSM)is used to discover the optimal roasting process.In terms of roasting properties,compared with non-semicoke-burdened,roasting temperature of semicoke-burdened hematite pellet is reduced,roasting time is shortened,and the compressive strength is improved obviously under the same roasting technology.The influence of semicoke and anthracite are basically identical,and anthracite is better in its entirety.The optimization results of response surface methodology show that the influence of roasting temperature,roasting time,semicoke additive amount on the compressive strength of semicoke-burdened hematite pellets is great,among which roasting time is most significant,then is roasting temperature,semicoke additive amount plays minimum effecting role,and airflow volume is not significant.The mutual influence between roasting time and semicoke additive amount is significant,the other is not significant.When the response target value is 2500 N,the optimal values of the roasting process parameters were found at roasting temperature1292?,roasting time 18.5min,airflow volume 3.2L/min and semicoke additive amount1.5%.dUnder the condition of optimized process conditions,the compressive strength of semicoke-burdened hematite pellets is 2578.3N,the error between experimental and predicted values is simply 3.13%.Furthermore,this paper verify the metallurgical properties of pellets products,the results show that the pellets can be used in large blast furnace.Through evaluating the FeO content and analysising microstructure,this paper reveals induration mechanism of semicoke-burdened hematite pellets in roasting process.The role of semicoke during roasting is releasing heat by combustion and reducing Fe2O3 to Fe3O4.Lower semicoke content does harm to reduce hematite to magnetite,semicoke burning reaction will lead to increase the porosity,and the compressive strength of pellets will be reduced.When semicoke content is higher,the reduction of semicoke will turn Fe2O3 to Fe3O4 in abundance,even to FeO,and thefayalite will be created.Meanwhile the excessive combustion of semicoke will lead up to double-layer structure pellet and lower the compressive strength of the fired balls.Test shows that the suitable amount of semicoke is 1.5%.