Influence of Iron Ore Mineralogy on Cluster Formation inside the Shaft Furnace
ABSTRACT
Clustering, phenomenon of pellets was observed frequently in shaft processes operating at higher
temperatures. Decreasing the reducing temperature to avoid this problem can cause a significant drop in
throughput. Clustering is a result of the growth of fibrous iron precipitates (iron whiskers) that become
hooked to each other and finally become crystallized during the initial stages of metallization.
If clustering of the particles in a pellet bed is pronounced, the smooth descending movement of the
ferrous burden can be disturbed. In the worst case the burden descent can be held up, resulting in hanging,
followed by a slip when the burden suddenly again moves downwards. Also sometimes leads to blocking
inside the furnace and forced shutdown takes place. Since the iron morphology (whisker formation) is
expected to depend strongly on the nature of the ore (iron ore mineralogy), this work is focused to clarify
further the relation between metallic iron whisker growth and iron ore mineralogy. Various pellet sizes (6 –
12.0 & +12.0 mm) from three different ores (A, B & C) were (completely and partially) reduced at 985 o C
with H2/CO gas mixture using thermos-gravimetric technique.
It was found that Reducibility increases by decreasing the iron ore pellet’s size. Reducibility order
according to ore type; A is the highest then B and then C. Tendency for metallic iron whisker formation
decreases by decreasing the reduced iron ore pellet’s size (faster reducibility decreasing the whisker
formation). The order for metallic iron whisker formation according to ore type; A is the highest then B and
then C. The diffusion reaction mechanism is prominent compare to chemical reaction mechanism in iron ore
A than in B and C. The comparative porosity and basicity for such ores could be the reason for this behavior
(reducibility & whisker formation).
KEYWORDS
Shaft furnace, cluster, metallic iron whisker, Mineralogy