Avaliação do efeito da temperatura na morfologia do ferro metálico e na formação da colagem em diferentes tipos de pelotas de redução direta

Abstract

The direct reduction process has been responsible for a considerable steel production volume, especially in countries where gas and electricity costs are more affordable. New projects have been very competitive in terms of technical and economic issues due to large capacities and expected productivities. One of the major advances which made it possible to achieve high rates of productivity was the temperature increase of the reduction gas. On the other hand, an undesired effect occurs with the use of higher temperatures, which is the sticking phenomenon of pellets. In this context, this work aimed to evaluate the effects that the temperature increase and morphology lead to the formation of clusters for different market pellets. It was foundthat the temperature has great influence on morphological evolution: at 850 °C the metallic iron is usually deformed and eroded; at 950 °C the fibrous iron happens to be more present, while in 1050 °C there is larger fibrous iron and fresh precipitated iron with high energy. Both, the fibrous iron and the newly precipitated iron were those who caused the highest clustering indexes. It was also observed that in 1050 °C, theclustering index was very high for all pellets and the presence of the coating agent was not enough to avoid the anchoring between the ferrous surfaces. Regarding the pellet, it was noted that at temperatures of 850 °C and 950 °C, the pellet with more MgO concentration, showed the lowest level of cluster formation. This fact can be explainedby the distortion that the Mg causes by the formation of magnesium ferrites, delaying the morphological evolution of the metallic iron.