iron processing from blast furnace

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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iron processing from blast furnace

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