1999 Volume 85 Issue 6 Pages 439-446
A single composite pellet composed of iron ore and coal char was reacted in an oxygen bearing nitrogen flow to very efficiently compensate the heat consumed by the strongly endothermic reaction, C+CO2=2CO. But the reactions are very complicated because oxygen not only generates heat by the combustion of carbon but also re-oxidizes reduced iron ore. In this study, the experiments were conducted principally using a single pellet containing 18 mass% coal char over the temperature range from 1273K to 1473K and O2 concentration range from pure nitrogen to 40 pet oxygen. The reduction started as the pellet was heated over about 1200K and reached the maximum net fraction, and followed by a rather predominant re-oxidation. The maximum reduction increased with increasing the pellet diameter and the temperature, and decreasing oxygen partial pressure, showing about 0.30. In this study, also, the swelling rate and crushing strength as the most important process parameter were also watched along the reactions. As the reactions proceeded, first, the crushing strength decreased to the minimum value, about 0.6 N common for all the experiments, at about 120 s. Thereafter, it turned to the increase and ultimately reached the individual maximum value at about 500 s, which is dependent on temperature. The drop in the swelling rate coupled with the rise in the crushing strength. That is, the densification of pellet, i.e. decrease in swelling rate resulted in the strengthening of the pellet.
