Indurating Furnaces are circular shaped furnaces like a Rotary Kiln and form a key part of one of
the process routes for preparing iron ore fines for use in blast furnaces, and
are specifically used to produce iron ore pellets.
Raw
or “green” pellets need to be baked to give them sufficient mechanical strength
to withstand further handling during transportation and charging to a blast
furnace or to a direct reduced iron furnace.
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| Indurating Furnace - Arrangement of Pellets |
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| Indurating Furnace |
In
an Indurating Furnace, the pellets are loaded on to a travelling grate to a
depth of approximately 30-60cm where they are preheated (typically to 800-9000C),
before entering a higher temperature stage (around 1,200-1,3500C)
which in some designs is a continuation of the travelling grate, and in others
take the form of a rotary kiln. Once hardened the pellets are cooled ready for
use. In a modern Indurating Furnace, there are 6 to 7 processing zones: Updraft
drying (UDD) => Down draft drying (DDD) => Preheating (Ramp) => Firing
=> After-firing => Cooling.
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| Iron Ore Pellets |
The
thermal treatment done in an indurating furnace is similar to that of a
straight line travelling grate. The gas and cooling air flow is down-draught. The
grate bars are protected by hearth layer and the green pellet bed height is
maintained about 20 cm in order to provide a better gas permeability. The side
walls are protected with refractory lining. The fire pellets are removed from
the grate by a scraping device which is installed at a sufficient distance
between grate bar and hearth layer (with a depth approximately 5 cm) to leave
the hearth layer in its position. The other route to preparing iron ore fines
is to agglomerate them by sintering with coke and limestone.
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