7/31/2019 Engineering Materials Smelting of Iron Lect05

1/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Production of Iron

7/31/2019 Engineering Materials Smelting of Iron Lect05

2/27

E n g i n e e r i n g M a t e r i a l s L e c t u r e 0 4

OutlineBlast furnace chargeIron OresFluxMetallurgical Coke

Coke Manufacturing &its Quality

General view of Blast

Furnace plantSketch of Blast Furnace

Construction and

working of Blast Furnace

Charging Mechanism inBlast Furnace

Smelting operation

Chemical Reactions inBlast Furnace

Formation and tappingof slag

Pig Iron- Properties &uses

7/31/2019 Engineering Materials Smelting of Iron Lect05

3/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Blast Furnace Charge

BF charge consists of the following:

Iron ore ; iron oxide in lump or sinter form

Fuel ; coke

Flux ; limestone

In addition Hot air is admitted through the tuyeres

7/31/2019 Engineering Materials Smelting of Iron Lect05

4/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

The most important variety of iron ore are:

Nomenclature Composition Fe %age Location

Magnetite(Black oxide)

Fe 3O4 72.4 Makarwal, Swabi, Chitral (PAK),Land of midnight sun (Sweden),Pennsylvania (USA), Siberia (Russia)

Hematite (red,brown &black)

Fe 2O3 40-65Kala bagh, Chnari, Chaghi, Chalghazi(PAK),Lake superior, Utah (USA), Lorraine(France), Amazon basin (Brazil)

Limonite &otherhydroxide types of ores

2Fe 2O3 . H 2Oto

Fe 2O3 . 3H 2O

20-55 Not found in PAK,Britains East coast

Siderite FeCO 3 Low inFe

Hazara, Mardan (PAK),South Wales, Staffordshire & west York

Iron Pyrite (yellow) FeS 42Mardan, Chitral (PAK)

Iron Ores

7/31/2019 Engineering Materials Smelting of Iron Lect05

5/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Flux

Flux is a material, which is added to thecontents of a Blast furnace or a Cupola forthe purpose of purging the metal of impurities, and of rendering the slag moreliquid.

The flux most commonly used in iron andsteel furnaces is limestone , which is chargedin the proper proportions with the iron oreand fuel.

7/31/2019 Engineering Materials Smelting of Iron Lect05

6/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Metallurgical Coke

Coke is a solid carbonaceous materialderived from destructive distillation of low-ash, low-sulfur, high coking property

bituminous coal . The volatile constituents of the coal

including

water, coal-gas, and

coal-tar

are driven off by baking in an airless oven at temperatures ashigh 1000 C.

7/31/2019 Engineering Materials Smelting of Iron Lect05

7/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Metallurgical Coke Metallurgical coke is produced by

carbonization of coal at high temperaturesto produce a macroporous carbon material of high strength and relatively large lumpsize .

Notes:

Metallurgical cokes must have a high strength tosupport heavy loads in the blast furnace withoutdisintegration.

7/31/2019 Engineering Materials Smelting of Iron Lect05

8/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Coke Manufacturing Process Bituminous coal is pulverized by ball mill into fine

powder.Fine coal is heated in coke oven battery at 700 900C in absence of air. This process is called

Carbonization. After soaking at this temperature for about 7 8hrs ., it is allowed to cool in the furnace.

Due to coking property of bituminous coalpowdered coal converts into lump size andbecomes very hard and highly porous.

After cooling, the coke produced is crushed intodesired size.

7/31/2019 Engineering Materials Smelting of Iron Lect05

9/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Quality Testing of Coke

Following parameters are determined in thetesting laboratory for justifying the quality of thecoke.

Strength of the coke,

fixed Carbon (88-92%),

sulphur content and

ash content

By-products like tar may also be collected

during carbonization process.

7/31/2019 Engineering Materials Smelting of Iron Lect05

10/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

General view of Blast Furnace plant

7/31/2019 Engineering Materials Smelting of Iron Lect05

11/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Sketch of Blast Furnace Plant

7/31/2019 Engineering Materials Smelting of Iron Lect05

12/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Sketch of Blast Furnace

7/31/2019 Engineering Materials Smelting of Iron Lect05

13/27

E n g i n e e r i n g M a t e r i a l s L e c t u r e 0 4

Construction and working of Blast Furnace Blast furnace consists of a vertical steel shell ~100 ft

high & ~ 21 ft dia and lined with refractory material . It has a charging arrangement (Bell & Cone) at the

top . Raw material is charged by a skip car throughthis charging mechanism into the blast furnace.

It has a means of running off Pig iron & Slag at thebottom.

Air is blown in near the bottom of the furnace. Thisforced draught increases the speed of combustion &maintains the necessary high temperature .

Cooling water is circulated around the Bosh area in

order to protect the furnace from high temp.

7/31/2019 Engineering Materials Smelting of Iron Lect05

14/27

Various zones inBlast Furnace

7/31/2019 Engineering Materials Smelting of Iron Lect05

15/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Charging Mechanism in Blast Furnace

7/31/2019 Engineering Materials Smelting of Iron Lect05

16/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Smelting operation

Smelting consists of two operations :a - Chemical reduction of iron from its oxides byCO, which is formed by the combustion of C in the

coke with the O 2 of the air blast admitted throughthe tuyeres near the base.

b - The liquefaction of the gangue by means of flux (limestone) to form a fusible slag which will runfrom the furnace.

7/31/2019 Engineering Materials Smelting of Iron Lect05

17/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Smelting operation

During the production of pig iron (smelting

operation) large amount of gases are evolved ,

which contain about 30% CO having considerable

calorific value. The exit gases are collected , led through down-

comer pipe to a cleaning chamber and electrostatic

dust precipitator & then used as fuel gas in Cowper Stoves in order to pre-heat the air blast to the

furnace.

7/31/2019 Engineering Materials Smelting of Iron Lect05

18/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Chemical Reactions in Blast Furnace The air , which is blown at the bottom of the

furnace causes partial combustion of the coke :2C + O 2 = 2CO + Heat 1

CO , which is powerful reducing agent , risesthrough the charge, & chemically reduces theiron oxide :-

Fe 2O 3 + 3CO = 2Fe +3CO 2 2

7/31/2019 Engineering Materials Smelting of Iron Lect05

19/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Reduction sequence of iron oxide is as

Fe 2O3 Fe 3O4 FeO Fe , when temp is > 570 C

Fe 2O3 Fe 3O4 Fe, when temp is < 570 C

The equation # 2 takes place in the upper part of the furnace, where the temp is too low to melt the

iron formed. The iron remains as a spongy mass until it moves

down into the lower part of the furnace, where it

melts & runs down over the hot coke, dissolving C,S, Mn, P & Si as it goes.

7/31/2019 Engineering Materials Smelting of Iron Lect05

20/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

SLAG : The slag is a liquid mixture of ash,

flux, and other impurities.Formation and tapping of Slag At the time of the reduction of iron oxide,

the gangue , which is composed of silica,combines with lime to produce slag as :-

SiO 2 + 2CaO = 2CaO.SiO 2(Calcium silicate slag)

7/31/2019 Engineering Materials Smelting of Iron Lect05

21/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

SLAG

Calcium silicate slag has much lower melting pointthan silica and can run from the furnace quite easily .

The furnace is tapped at regular intervals & the pigiron is run either into large ladles for transference,while still molten, to steel making plant, or alternatively, cast into pigs for subsequent use in the

cupola or open hearth furnace.

7/31/2019 Engineering Materials Smelting of Iron Lect05

22/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Slag (Continue)

Limestone has an other function

the removal of sulphur. This entails having an excess of lime in the slag

and is often impracticable with low grade ores,

since they contain so much silica, which must beneutralized first.

In British practice, the sulphur is removed at a

later stage by adding soda-ash to molten pig ironas it runs from the blast furnace into the ladle:-

FeS + Na 2CO 3 = FeO + Na 2S + CO 2

(Iron sulphide Soda ash joins the slag

7/31/2019 Engineering Materials Smelting of Iron Lect05

23/27

E n g i n e e r i n g M a t e r i a

l s L e c t u r e 0 4

Tapping of Slag

7/31/2019 Engineering Materials Smelting of Iron Lect05

24/27

E n g i n e e r i n g M a t e r i a l s L e c t u r e 0 4

Pig Iron - Properties & uses

Definition :- Itis a high-carbon iron made by reduction of

iron ore in the blast furnace .

Metallic iron, which is a product of reduction of ironore, appears in the lower part of stack & in thebosh.

It contains ~ 1 % C and found to in spongy form. Asthis material sinks down in the B.F. and is heatedfurther, iron dissolves C in increasing quantities.

This reduces the melting temp & it melts and drawsoff to the hearth in the form of drops.

7/31/2019 Engineering Materials Smelting of Iron Lect05

25/27

E n g i n e e r i n g M a t e r i a l s L e c t u r e 0 4

Pig Iron (Continue)

Pig iron is really a complex alloy . In additionto Fe, it contains up to 10 % of other elements , mainly, C, Mn, Si, S & P.

Total amount of C in the pig iron is usuallybetween 3 4% & is present either

as compound, iron carbide (Fe 3C) or

as un-combined carbon in the form of graphite . Pig iron low in S & high in P may be used in

the manufacture of acid steel & high-duty

iron castings.

7/31/2019 Engineering Materials Smelting of Iron Lect05

26/27

Thanks

Bl t f di

7/31/2019 Engineering Materials Smelting of Iron Lect05

27/27

E n g i n e e r i n g M a t e r i a l s L e c t u r e 0 4

Blast furnace diagram

1. Hot blast from Cowperstoves

2. Melting zone ( bosh )3. Reduction zone of ferrous

oxide ( barrel )4. Reduction zone of ferric

oxide ( stack )5. Pre-heating zone ( throat )6. Feed of ore , limestone ,

and coke 7. Exhaust gases8. Column of ore, coke and

limestone9. Removal of slag 10. Tapping of molten

pig iron 11. Collection of waste gases

http://encyclopedia.thefreedictionary.com/Hot+blasthttp://encyclopedia.thefreedictionary.com/Cowper+stovehttp://encyclopedia.thefreedictionary.com/Cowper+stovehttp://encyclopedia.thefreedictionary.com/ferrous+oxidehttp://encyclopedia.thefreedictionary.com/ferrous+oxidehttp://encyclopedia.thefreedictionary.com/ferric+oxidehttp://encyclopedia.thefreedictionary.com/ferric+oxidehttp://encyclopedia.thefreedictionary.com/Iron+orehttp://encyclopedia.thefreedictionary.com/limestonehttp://encyclopedia.thefreedictionary.com/Coke+(fuel)http://encyclopedia.thefreedictionary.com/slaghttp://encyclopedia.thefreedictionary.com/pig+ironhttp://encyclopedia.thefreedictionary.com/pig+ironhttp://encyclopedia.thefreedictionary.com/slaghttp://encyclopedia.thefreedictionary.com/Coke+(fuel)http://encyclopedia.thefreedictionary.com/limestonehttp://encyclopedia.thefreedictionary.com/Iron+orehttp://encyclopedia.thefreedictionary.com/ferric+oxidehttp://encyclopedia.thefreedictionary.com/ferric+oxidehttp://encyclopedia.thefreedictionary.com/ferric+oxidehttp://encyclopedia.thefreedictionary.com/ferrous+oxidehttp://encyclopedia.thefreedictionary.com/ferrous+oxidehttp://encyclopedia.thefreedictionary.com/ferrous+oxidehttp://encyclopedia.thefreedictionary.com/Cowper+stovehttp://encyclopedia.thefreedictionary.com/Cowper+stovehttp://encyclopedia.thefreedictionary.com/Cowper+stovehttp://encyclopedia.thefreedictionary.com/Hot+blast