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7/27/2019 Iron Processing From Blast Furnace
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Marzia Hoque Tania
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Iron Ores:
Hematite (Fe2O3)
Magnetite(Fe3O4)
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Blast furnace existed in China about 5th century
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Medieval Europe
Fig: First blast furnace ofGermany
Early modern blastfurnaces
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Coke Blast FurnaceModern Blast Furnace
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To chemically reduce & physically convert iron
oxides into liquid iron called hot metal.
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Structure is analogous to Chemical Reactor.
It is a huge, steel stack lined with refractory
brick.
An impure substance goes in the top.
& comes out pure at the bottom.
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Charge consists-
Iron Ore
Coke &
Limestone
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Iron oxides
raw ore, pellets or sinter
Iron ore, pellets & sinter liquid iron
- produced in blast furnace
Remaining impurities liquid slag
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Removed from earth and sized into pieces
- either Hematite (Fe2O3) or Magnetite
(Fe3O4)
- iron content: ranges from 50% to70%.
-rich ore
-charged directly into blast furnace withoutany further processing
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Pellets -produced from lower iron content
ore.
- ore is crushed & ground into a powder
to remove gangue.
- remaining iron-rich powder is rolled
into balls &
- fired in a furnace
Strong, marble-sized pellets are produced -
contain 60% to 65% iron.
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Sinter- produced from fine raw ore, small
coke, sand-sized limestone & numerous
other steel plant waste materials that
contain some iron.
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Coke is produced from a mixture of coals
- high energy value
Furnace is kept at temperature continuously.Coke Source of heat
- provides permeability, heat and gases
Continues
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Continues
- Oxygen should be removed
Iron Ore (Iron Oxide) Metallic Iron
- Chemical detachment of Oxygen atoms from Iron
Oxide-
Coke Source of Reducing gas
- Reduces & melts the iron ore, pellets and
sinter.
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Acts as Flux or Purifying agent to assist inremoving other impurities in Iron Ore.
Flux: pure high calcium limestone,
dolomitic limestone containing magnesia,or blend of limestone.
-Limestone is melted
- slag removes sulphur and other impurities
- Blast furnace operator may blend differentstones to produce the desired slag to createoptimum properties e.g. low melting point, highfluidity
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Air
Supplies Oxygen Combusts Coke
- prompts Chemical Reduction of Iron Oxide
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All raw materials are stored in an ore field
transferred to the stockhouse before
charging
Charging into furnace top-
numerous chemical and physical reactions
descending to the bottom of the furnace.
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Iron ore, pellets & sinter are reduced
- oxygen in iron oxides is removed
Begins to Soften, Melt & finally trickle as Liquid
Iron
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Chemical reagents that change Iron Oxide tometallic iron are from Coke-
CO & CO2
coke descends to the bottom of furnace wherepreheated air or hot blast enters blast furnace
coke is ignited by this hot blast
Production of Reducing gas:
C (coke) + O2 (air)= CO2CO2+ C (excess coke) = 2CO
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Limestone descends in the blast furnace
Remains solid
CaCO3 = CaO + CO2
- requires energy & starts at 875C.
- CaO further is used to remove sulphur from ironwhich is necessary before hot metal becomes steel.
FeS + CaO + C = CaS + FeO + CO
- CaS becomes part of the slag.
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Slag is also formed from any remaining Silica(SiO2), Alumina (Al2O3), Magnesia (MgO) or
Calcia (CaO)
- entered with iron ore, pellets, sinter orcoke.
Liquid slag > dropped > through Coke bed >
bottom of furnace- less dense > floats on top of liquid iron
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In addition to molten iron & slag- hot dirty gases
- exit the top of the blast furnace
- proceed through gas cleaning equipment
- particulate matter is removed from gas
- gas is cooled
It has a considerable energy value
- burned as fuel in "hot blast stoves : used topreheat the air entering the blast furnace to become
"hot blast".
Gas not burned in the stoves is sent to boiler house
- used to generate steam which turns a turbo blower
- generates compressed air, "cold blast" that comes
to the stoves.
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Combustion of Coke
C(s) + O2(g) CO2(g) + heat CO2(g) + C(s) 2CO(g)
H2O + C => H2 + CO (DH =+31.4 Kcal)
2C + O2 => 2CO (DH = -58.3 Kcal)
Reduction of Fe2O3
2Fe2O3(s) + 3C(s) 4Fe(l) +3CO2(g)
Fe2O3(s) + 3CO(g) 4Fe(l) +3CO2(g)
3Fe2O3 + CO => 2Fe3O4 + CO2(DH = -27.8 Kcal)
2Fe2O3 + 8CO => 7CO2 + Fe +C (DH = -67.9 Kcal)
Fe3O4 + CO => 3FeO + CO2(DH = +5.9 Kcal)
FeO + CO => Fe + CO2 (DH = -3.9 Kcal)
Calcination
CaCO3(s) + heat CaO(s) +CO2(g)
Slag formation
CaO(s) + SiO2(s) CaSiO3(l)(slag)
CaO(s) + Al2O3(s) Ca(AlO2)2(l) SiO2 + 2C => Si + 2CO (DH =
+145 Kcal)
FeS + CaO + C => CaS + Fe +
CO (DH = +34.8 Kcal)
P2O5 + 5C => 2P + 5CO (DH =
+234 Kcal)
MnO + C => Mn + CO (DH =
+64.4 Kcal)
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Hot Blast
Melting Zone
Reduction zone of ferrous oxide
Reduction zone of
ferric oxide
Pre-heating zone
Feed of ore,limestone &coke
Exhaustgases
Column of
ore, coke &limestone
Removal ofslag
Tapping ofmolten pigiron
Collectionof wastegases
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2000 C
1700 C
750 C
1350 C
1350 C
600 C480 C
260 C
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Impure substance e.g. iron ore is
continuously dumped into the top.
Preheated air (sometimes with oxygen
enrichment) is blown into the bottom of
the chamber.
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So the chemical reactions take place
throughout the furnace as the material
moves downward.
The end products are usually molten
metal & slag phases tapped from the
bottom, &
Flue gases exiting from the top of the
furnace.
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Blast furnace-
solids descend & gases ascend.
Metallic Iron is tapped at the bottom ofFurnace: Pig Iron
- high carbon content
- not suitable for engineering material- brittle & weak
-must be refined.
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Final product: hot metal
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