2004 Volume 44 Issue 4 Pages 673-681
The nine kinds of the composite pellets of 3.5 to 5.5 mm in diameter composed of the mixtures of wustite, magnetite or hematite and coal char, coke or graphite, in which the mol of the reducible oxygen was made equal to the mol of the fixed carbon, was heated in vacuum. The weight loss during heated at 1 000 to 1 200°C was gravimetrically measured. The influence of the diameter was negligible within 5.0 mm. The temperature dependence of the rate of the direct reactions of all the composite pellets was very strong. At 1 000°C, the rate was such slow that it requires more than 2 ks to reach Ft=0.2 and, at 1 200°C, the rate was so fast that it is completed in a few hundreds seconds. The direct reactions of the char or coke bearing composite pellets proceed in two steps; the first step is very fast and temperature-independent, and the second step is the temperature-dependent process. On the contrary, the direct reactions of the graphite bearing composite pellets proceeds in three steps at 1 100 and 1 150°C; the first step is also very fast and temperature independent, and the much slower second step follows until metallic iron is formed. Just after the metallic iron starts to form, the reactions are accelerated as the third step. This third step of the graphite composite pellets is much faster than the second step of the char or coke bearing composite pellets. The maximum pressure inside the pellets simulated by the uniform reaction model indicates the negligible effect of the indirect reactions.
