Clustering Phenomena during Iron Oxide Reduction in Shaft Furnace

Abstract

In the direct reduction shaft furnace it is favorable to raise reducing gas temperature blown from tuyeres to improve not only the productivity but also characteristics of the sponge iron for reoxidation. However, if the operating temperature is too high, the material become sticky and form so called clusters. Thus authors investigated clustering behavior of iron oxide during its reduction by a laboratory test.
Pellet with iron content of 64-68% and lime (CaO) content of 0.09-1.11% were produced by an indurating furnace of bench scale. Five hundred grams of fired pellets were charged into the reduction tube with inside diameter of 75 mm and were reduced with reducing gas (H₂: 55%, CO: 36%, CO₂: 5%, CH₄: 4%) under load at a temperature range of 700-960°C. The expansion or shrinkage ratio of the sample bed was continuously recorded using a strain gage. The strength of clusters formed during reduction was measured in a rotating steel drum with diameter of 120mm and length of 700mm. It was found that the shrinkage ratio of the pellet bed was clearly related to the cluster, and the higher the shrinkage ratio, the stronger the cluster.
The formation of the cluster during reduction depended on three factors., i. e. the temperature, load on the burden bed and properties of materials. The relationship of these factors as well as clustering mechanism of reduced materials were discussed based on the experiments.