气基竖炉直接还原数值模拟分析

Numerical simulation analysis of direct reduction of gas-based shaft furnace

针对气基竖炉直接还原过程无法直接观察还原反应运行程度的难点,基于三界面未反应核模型,在忽略模型球团内部温度及假设球团还原反应的热效应完全发生在固相的条件下,建立了气基竖炉直接还原模型,对铁氧化物价态转变进行了数值模拟和验证。结果表明,由于所建立的气固模型包含3个界面,随着铁氧化物的逐级还原,每个界面的反应半径最终趋于0,而还原反应速率随着竖炉深度的增加呈现出先升高后降低的趋势。球团在竖炉内下降到3 m深度时,出现半径为15 mm的FeO反应界面,此时球团还原率约为28%。随着球团继续在竖炉内下行约2 m到达5 m的深度时,Fe_(3)O_(4)的界面半径减小为0,此时铁氧化物完全转变成了浮氏体形态,球团还原率约为34%。通过改变不同的工艺参数进行模拟可以发现,还原球团金属化率和还原率随着气体温度的升高而增大。当气体温度以50℃、还原气体流量以5040 m^(3)/h梯度增大时,其对应的球团金属化率分别增大8%和4%左右。相比之下,球团金属化率受下料速度的影响远超过气体温度和还原气体流量,具体表现为,当下料速度增大0.02 t/h时,金属化率降低约0.07%。而当球团粒度减小时,金属化率会表现增大的趋势,球团粒度减小1 mm,球团金属化率增大2.23%。

Aiming at the difficulty that the operation degree of the reduction reaction cannot be directly observed during the direct reduction process of the gas-based shaft furnace,based on the three-interface unreacted nuclear model,a direct reduction model of the gas-based shaft furnace is established under the condition of ignoring the internal temperature of the model pellet and assuming that the thermal effect of the pellet reduction reaction completely occurs in the solid phase,and the valence state transformation of iron oxide is numerically simulated and verified.The results show that since the established gas-solid model contains three interfaces,the reaction radius of each interface eventually tends to zero with the stepwise reduction of iron oxides,and the reduction reaction rate increases first and then decreases with the increase of shaft furnace depth.When the pellets descend to a depth of 3 m in the shaft furnace,a FeO reaction interface with a radius of 15 mm appears,where the pellet reduction rate is about 28%.As the pellets continue to descend about 2 m in the shaft furnace to a depth of 5 m,the radius of the interface of Fe_(3)O_(4)decreases to 0,at which point the iron oxide completely transforms into the floatite form,and the pellet reduction rate is about 34%.By changing different process parameters for simulation,it can be found that the metallization rate and reduction rate of the reducing pellet increase with the increase of gas temperature.When the gas temperature increases at 50℃and the reducing gas flow rate increases at a gradient of 5040 m^(3)/h,the corresponding pellet metallization rate increases by about 8%and 4%,respectively.In contrast,the metallization rate of the pellets is much more affected by the cutting speed than the gas temperature and reducing gas flow,which is manifested as follows:when the cutting speed increases by 0.02 t/h,the metallization rate decreases by about 0.07%.When the pellet size decreases,the metallization rate will show an increasing trend,and the pellet size decreases by 1 mm,and the pellet metallization rate increases by 2.23%.