I. Blast furnace is a counter current heat and mass exchanger in which reduction and smelting of metallic mineral takes place.

Chemistry• Elements lying at top of reactivity series are more reactive than elements lying below them in series.

Thermodynamics• From Ellingum diagram : A metal/element that forms stabler oxide (lower line) would replace metal from less stable oxide (upper line).

The Reactivity Series

potassiumsodiumcalciummagnesiumaluminium

zinciron

copper

gold

(carbon)

Incr

easi

ng re

activ

ity

Metals above carbon must be extracted using electrolysis.

Metals below carboncan be extracted from the ore by reduction using carbon, coke, or charcoal.

Gold and silver often do not need to be extracted. They occur native.

The reactivity of a metal determines the method of extraction.

lead

silver

1)Free energy vs temperature plot.

2)Gives stability of oxides.

3) Oxides lying at lower positions are more stable than oxides lying at top positions.

Iron ore: iron bearing materials ,provides iron to hot metal.

Coke: Reductant , fuel, provides permeability to bed.

Limestone: acts as flux.Others: Manganese ore, coal

dust, coal tar, pellets, sinter …….

Iron Ore

Sinter

Limestone

Coal Dust

Hearth Dia.=8-9 m. Bosh Dia.=9-10 m Hearth Height=3-3.5

m. Bosh Height=3-4 m. Throat Diameter=5.5

-6.5 m. Stack Height=18-20

m. Overall Useful

Height = 30-32 m. Working Height =

21-24 m .

BSP

• Decomposition of carbonates other than that of Ca.• Vaporization of moisture.• Carbon Deposition, 2CO = CO2 + C• Haematite to Magnetite; 3Fe2O3 + CO = 2Fe3O4 + CO2

• Magnetite to Wustite; Fe3O4 + CO = 3FeO + CO2

• Water-Gas Shift Reaction; CO + H2O = CO2 + H2

• Endothermic calcinations of limestone : CaCO3 = CaO + CO2 • Endothermic direct reduction of FeO : FeO + C = Fe + CO • Endothermic direct reduction of SiO2 : SiO2 + 2C = Si +2CO • Endothermic direct reduction of P2O3 : PO3 +5C = 2P + 5CO • Endothermic sulphur removal : FeS + CaO +C = CaS +Fe + CO • Exothermic combustion of carbon : C+ O2 (air) = CO2

• Exothermic reduction of CO2 : CO2 + C = 2CO • Endothermic reduction of moisture in blast : C + H2O = CO +H2 ( >1000⁰

C)

• Temperature of hearth zone is about 1500 – 1550 ⁰C.

• The reactions occuring in this zone are electrochemical in nature :1.[Mn ] = (Mn2+ ) + 2 e- [ anodic reaction ] 2.( Fe 2+ ) + 2e- = [ Fe] [cathodic reaction ]

Hence, [Mn ] +( FeO ) = ( MnO) + [Fe ] [Mn] +( Fe 2+ ) = ( Mn2+) + [ Fe ] .

Metal (pig iron).SlagGas

The quality of slag and metal produced depends mainly on the burden chemistry and temperature at which furnace is operated.

• Pig iron composition:o carbon = 3.5 – 4.2 %oSilicon = 0.5 - 2.5%oManganese = 0.5 – 1.5 %oPhosphorous = 0.04 – 2.0 %oSulphur = 0.04 – 0.15 % ..

Cast House - BSP