Iron ore sintering consists of heating a layer of fines until partial melting occurs of the surface particles, so they will fuse together. For this purpose, a traveling-grate machine is used, and the burning of fine coke (known as coke breeze) within the ore generates the necessary heat.
The sintering machine can take ore as coarse as 10mm and as fine as all passing through 100 mesh, provided that efficient air flow through the bed is maintained.
Initially, the raw material mix is placed on a sintering strand, and the coke on the upper surface of the bed is ignited when the mixture passes under burners in an ignition hood, but thereafter its combustion is maintained by air drawn through the bed of materials by a suction fan.
As the bed moves forward, a very high heat (1,325°C 1,500°C) is generated that converts the tiny particles into lumps about 2.5cm (1 inch) in diameter suitable for burning in the blast furnace. Therefore by the time the sinter reaches the end of the machine it has completely fused.
The grate on which the sinter mix rests consists of a series of cast-iron bars with narrow spaces between them to allow the air through.
After cooling, the sinter is broken up and screened to yield blast furnace feed and an undersize fraction that is recycled.
THE FOLLOWING SHOWS:
Sintering also provides opportunities to incorporate fluxing agents (CaCO3) into the mix to make their use more efficient and to reintroduce mill scale (the iron oxide waste produced during rolling).
The natural raw materials for the blast furnace are of variable quality depending on their sources. Sintering is a process that combines iron-bearing particles once recovered from environmental control filters, into small pellets. Previously, these materials were too fine to withstand the air currents of the smelting process and were thrown away. The iron is now conserved because the chunks can be charged into the blast furnace.
The driving force in sintering is increasing the surface energy; as the sintering proceeds, adjacent particles partially coalesce owing to viscous flow (as in glass) or to diffusion processes (as in crystalline materials), and consequently the total surface area increases. If we reacted the iron ore and the coke together without any preparation the reaction rate would be considerably slow due to the fact the the surface area of the coke and iron ore where very small. As the reaction can only take place at the surface of the two materials there are considerable economic benefits to be gained from increasing the surface area of the two reactants. As a result ot the sintering process a porous lump is produced with a drastically increased surface area (179%) and thus the rate of the reaction is drastically increased as well.
The product is a grey coloured porous lump through which gases can circulate in the blast furnace.
This images shows the grey coloured porous lumps of sinter leaving the Sinter Plant.
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