The more alumina exists in the iron ore,more energy is used in producing molten iron in blast furnace.These contaminants produce thick scaling in the DRI kilns and impede heat transfer process and have to be removed periodically,requiring plant shut down.
Most iron ores contain Al2O3 & SiO2 as the gangue material. High Aluminous ores create a viscous slag in the blast furnace and partly Quartz is added to bring the slag to a more flowable state. Moreover high alumina requires additional basic fluxes to maintain a suitable slag basicity for removal other tramp elements. In essence blast furnace productivity is adversley affected
In the blast furnace burden 1% increase alumina content increases coke rate by 2.2%,decrease in the productivity by4% and an increase in flux consumption by 30Kg /t of hot metal production.The alumina to silica ratio in iron ore should be less than 1.5 and preferably below 1%.
Increase in alumina content increases the viscosity of the slag which is difficult to separate from molten slag. Usually the Alumina in iron ore should be less than 2%.
it depends. can u specify the area where u want to directly use the specified iron ore .
Effect of Alumina in Iron ore Sintering .
The most harmful effect of alumina is to worsen the sinter RDI, which increases as the alumina content rises. Industrial experience with the blast furnace shows that
within a 10-10.5% CaO content range an increase of 0.1% in the alumina content raises the RDI by 2 points . The strength and quality of sinter deteriorate as the alumina content rises. Alumina promotes the formation of SFCA, which is beneficial for sinter strength, but the strength of the ore components is lower, since a high alumina content in their lattice has been reported to be the main cause of
the observed lower strength . Alumina increases the viscosity of the primary melt that forms during the sintering process, leading to a weaker sinter structure with more interconnected irregular pores. Sinter reducibility is determined by the chemical and mineralogical composition and by the pore structure. Due to the complexity of the effects of alumina on each of these factors, consideration of how alumina affects reducibility has produced contradictory results.
One good reference to read about the topic is in link given below please go-through the related topics also at same place.
http://ispatguru.com/high-alumina-slag-and-blast-furnace-operation-2/
High alumina, usually found in Indian iron-ore conditions, are unsuitable for blast furnace process. Alumina being acidic, it decreases the basicity of slag, thereby leading to a thicker slag formation. The thick slag, which reduces the fluidity and flowability of slag, hinders the seperation of slag from hot metal during tapping operation. Moreover, since the contact area between slag and hot metal interface increases with the increase in viscosity caused due to high alumina in raw materials, the probability of Si going back to hot metal increases. Therefore, it is advised to operate the furnace with high basicity and high slag volume to reduce the effect of high alumina present in raw materials charged into the blast furnace.
If Al2O3% is increases in iron ore then basicity (%CaO/%SiO2) will decreases. So to maintain the basicity CaO supply will more. Results slag volume increases, productivity reduced and more iron will loss.
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