煤种对含煤球团还原速度的影响

Effect of Coal Types on Reduction Rate of Iron Ore Pellets Containing Coal

研究了在１２２３～１４７３Ｋ的氮气氛中３种不同挥发分煤粉的粒度、铁精矿粉粒度、温度及碳—氧摩尔比对含煤球团还原速度的影响。发现降低煤粉或铁精矿粉粒度，提高温度或碳—氧摩尔比可提高含煤球团的还原速度，且这４种因素对还原速度的影响程度随煤种挥发分的降低而增大。分别采用以碳气化反应、气相内扩散、界面反应为控制环节而得出的表达含煤球团反应过程的速度方程处理本研究数据，发现３种速度方程（４种表达形式）均能较好地与本研究数据吻合。比较由不同速度方程计算出的速度常数而得出的含煤球团的活化能，发现对含３种不同挥发分煤的球团，以气相内扩散为控制环节的活化能均较以碳气化反应或界面反应为控制环节的活化能大，由此可推断含煤球团还原过程应由气相内扩散控制。含高挥发分煤的球团的气相内扩散活化能较含低挥发分煤的球团的活化能低，可推断前者的还原速度较快。

The effect of coal size, iron ore concentrate size, temperature and carbon oxygen mole ratio on the reduction rate of iron ore pellets containing high, middle, low volatile coals as reductant has been investigated in nitrogen at temperature range of 1 223～1 473 K by using a thermal weight loss balance. The reduction rate of iron ore pellets has been increased with decreasing the coal and iron ore concentrate size, increasing temperature and carbon oxygen mole ratio, but the above mentioned four factors have greater effect on reduction rate for pellets containing low volatile coal. Most of the experimental data can be successfully represented by four well known kinetics equations based on carbon gasification, gas diffusion and phase boundary reaction as rate controlling step and the rate constant can be evaluated, then the activation energy for pellets containing different volatile coals can be calculated by Arrhenius equation. It has been concluded that gas diffusion should be the reduction controlling step of composite pellets as the calculated activation energy based on the assumption that gas diffusion is the rate controlling step, is the greatest. The higher the volatile content of coal is, the easier the pellets is to be reducted because the activation energy for gas diffusion is smaller for composite pellets containing higher volatile coal.