demir cevheri-FerrousMetallurgy

8/3/2019 demir cevheri-FerrousMetallurgy

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PREPARED BY

TAYYAB TARIQ (2008-MET-04)

TOUSEEF AMIN (2008-MET-12)

DEPARTMENT OF METALLURGICAL AND

MATERIALS ENGINEERING.

UET, LAHORE


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FERROUS METALLURGY

ORE

Naturally Occurring substance from which a metal can be extracted at a profit

From a single ore more than one metal can be extracted.

ORE MINERALThe mineral containing ore from which a metal can be extracted at a profit

The naturally occurring materials containing iron are known as minerals of iron and mineral

deposits from which iron can be extracted at a profit (economically) are known as Iron-Ores.

GANGUEImpurities associated with the ores

METHODS OF REMOVAL OF GANGUE

1) Hand Picking(Sorting)

2) Crushing, Grinding and Dressing

3) Weathering (Removal of soluble impurities)

4) Calcinations (Heating @ high temp to remove volatile materials)

5) Roasting (Burning of ore in excess air)

6) Smelting (Fusing the ore by heating it in a suitable furnace)

EXTRACTIVE METALLURGY

It is a branch of Metallurgy which is a study of extraction of me tal, purification

and recycling


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Pyro metallurgical process Hydro metallurgical process Electro metallurgicalprocess

The process which is used toobtain metal from ore bythermal treatment.

In this process some salt orleaching agent or solution isused to obtain metal from ore

The process of winning andrefining of metal by the use of

electricity

LEACHANTChemical that dissolves a particular metal

EXTRACTION OF METAL FROM ORE

Separating the ore from gangue.

Driving away certain ingredients by heat short of fusion

Fusing the ore one or more times in the presence of certain reagents called Fluxeswhich combine with the non-metallic impurities and allow the metal to settle down in an

impure form. A metal thus obtained is further refined to be used.

RAW MATERIAL REQUIRED FOR MAKING IRONa) Iron Ore

b) Coking coal or Coke

c) Fluxes ( CaCO3, Dolomite: CaCO3.MgCO3 )

d) Air

APPROXIMATE QUANTITIES FOR MAKING 1 TONS OF IRONMaterial Quantity

Iron Ore 1.7-1.8

Coke 0.7-0.8

Fluxes 0.4-0.5

IRONSymbol: Fe

Atomic Number: 56

Commercial Forms %age of Carbon

Pig Iron 2.5-4.5

Wrought Iron 0.12-0.25

Steel 0.25-2.5


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ADVANTAGES AND DISADVANTAGES OF IRONAdvantages Disadvantages

Enormous deposits are present Poor Corrosion resistance

Easy to reduce than Non-Ferrous metals High density

Cheap metal Poor conductor of heat and electricity ascompared to Cu and Al

Forms series of alloys -

Magnetic in nature -

CLASSIFICATION OF IRON ORESa) Geological Classification

b) Mineralogical Classification

c) Impurities associated with Fe ore

d) Appearance/Texture

GEOLOGICAL CLASSIFICATION

Sedimentary Igneous Lateritic Replacement

These mainly includeSiO2 and iron ore inalternative bands. Iron is present

in the form ofstone

In the form ofpowder (Blue

Dust)

These are derivedfrom igneous materialof volcanic origin &occur mainly asmagnetite.

These are formed inconditions ofalternating dry & wetseasons resulting inleaching away ofSiO2 and alkalis fromthe mother-rockleaving behind mainly

Fe-ore.

The circulating waterremoves limestone(CaCO3) depositingiron carbonate in itsplace. Subsequentlythe surface weatheringoxidizes part of theiron carbonate to Fe-

oxide.


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MINERALOGICAL CLASSIFICATION OF IRON ORE

MinerologicalClassification

Magnetite Limonite

Liminite

Turgite

Geothite

Xanthosiderite

Limonite

Heamatite Chloropal Pyrite Siderite


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Properties Magnetite Limonite Heamatite Chloropal Pyrite Siderite

Formula Fe3O4 mFe2O3.nH2O Fe2O3 FeSiO3 FeS2 FeCO3

Commonname

Ferrosoferricoxide

Hydrousferric oxide

AnhydrousFerricoxide

IronSilicate

IronSulphide

IronCarbonate

%age of Fe 72.5% 52.13-66.31%

70% Decreasesdue toDolomite*

- Decreasesdue toDolomite*

Contribution 5% 40-60% - - -

SpecificGravity

5 - 5-6 - 4.95-5 -

Appearance Grey - Black Brown Red -Fool`sGold

-

EasyDetection

Magnetic innature

Mostly inall rocks,

Nonmagnetic

due to**d/c < 1.2

Highstrength

Insolublein water,

Fool`Gold,

Nonmagnet

Highstrength

Reduction Difficult Moderate EasyDifficut tobreak the

oreModerate

Difficut tobreak the

ore*Dolomite is self fluxing agent, Diabasic MgCO3.CaCO3 .

**orbital/shell ratio

LIMONITE ORE TYPES

Limonite Sub-Ore Formula

Liminite Fe2O3.3H2O

Turgite 2Fe2O3.H2O

Limonite 2Fe2O3.3H2O

Geothite Fe2O3.H2O

Xanthosiderite Fe2O3.2H2O


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CONCENTRATION OF IRON ORE

MECHANICAL CONCENTRATION OF IRON ORE

It involves mechanical concentration i.e. erosion of rocks containing iron ore by moving water.

More the speed of the water more will be the erosion. It also depends on the gradient of water.

So the corroded rock particles containing Fe ore moves with water, more dense the rock, earlier

will it settle down and dense rock will travel with water. Hence due to this mechanical factor the

concentration of Fe ore is different in different areas.

CHEMICAL CONCENTRATION OF IRON ORE

CRYSTALLIZATION

Magma inside the earth crust contains different iron ores along with other mineralcomposites. The solidification rate of magma is very slow hence the material having

similar composition will solidify or crystallize together. Hence due to this difference the

concentration of Fe ore is different in different areas.

PRECIPITATION

This involves water falling on rocks or water in the form of steam blowing the rock.

Chemical reactions take place on its surface and iron ores are separated from the rock

and are deposited there.

The chemical reaction or precipitation of iron ore depends on

Speed of moving water

Rate of the reaction

Chemical nature of gangue

Concentration of Iron

Ore

Mechanical

Chemical

Crystallization

Precipitation


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IRON ORE DEPOSITS IN PAKISTAN

Dilband

Nizampur

Chiniot

PachinkohRajoa

Langrial

Kalah Bagh

Chilgazi

Dommel Nisar

Name ofDeposit

Distancefrom

Karachi

Reserves % of Fe Ore Mineral Methods ofMining

km Million Ton

Kalabagh(Punjab)

1200 300 30-35 Silicates,Carbonates

Underground

Dilband(Balochistan)

800 200 35-45 Oxide,Heamatite

Open Cast

Nizampur(NWFP)

1600 100 30-35 Heamatite Underground

Pachinkoh(Balochistan)

1750 45 35-38 Heamatite,Magnetite

Underground

Langrial(NWFP)


Underground

Chilgazi(Balochistan)

1150 23 10-55 Magnetite Underground

Chiniot(Punjab)


Underground

Dommel Nizar

(NWFP)

1900 3 Upto 60 Magnetite Underground

Which is

better?

Have a

look


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Dilband resources are better than all deposits of Pakistan (Fe ore deposits) and thus have a fair

chance of development due to good accessibility, moderate grade (% of Fe), large reserves and

open cast minebility. These deposits consist of Hematite and are low in P2O5; hence are better

than many iron deposits of the world.

Dilband Ore Ores from USA & Europe

35-45% Fe 5-35% Fe

Low P2O5 High P2O5

Heamatite Heamatite & Limonite

VALUATION OF FE ORE1. Richness

2. Location

3. Composition of Gangue

4. Procedure required before smelting

Richness

% of Fe present in the ore, How much Fe is required, How much ore is required is dependent on% of Fee.g.India requires 2 ton ore (55-60% Fe) to produce 1 ton Fe whereas Australia requires 1.5 ton ofore (68% of Fe)

Location

Geological GeographicalHilly Area Deep Valleys Mode of Transportation

Composition of Gangue

Gangue material will affect the cost of the iron. If the amount of the gangue in the Fe ore is morethen we have to add fluxes to separate gangue which will as a result increase the cost ofproduction

Some compounds in gangueOxides, Carbonates, Sulphates, Na2O, K2O, P2O5,As2O3

They are reduced in Blast furnace

a. Totallyb. Partiallyc. Non-reducible

Totally Reduced in BFPhosphorous Arsenic

The entire amount of P in the ore isreduced and joins the pig iron. Thepresence of phosphorous affects theproperties of iron.

Usually not present in Fe ore but if it ispresent then following treatments are used

Prior Reduction

Calcination (Volatilization)

Dilband


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In general, the phosphorous content ofan ore reduces the value of the ore.Phosphorous in iron causes ColdShortness during rolling.

Roasting

Zn PbZinc in the iron ore does not pass into thepig iron but it volatilizes during reduction

These Zinc vapours penetrate into therefractory material (lining) and affect itsproperties.

Pb is reduced during Blast Furnaceoperation, it settles at the bottom ofthe furnace due to its high specificgravity (SG).

Partially Reduced in Blast FurnaceS, Mn, SiO2

Silica, compounds of manganese and sulphur are partially reduced in the blast furnace so Si,Mn and S join the pig iron. Amount of these depends on the nature of Fe ore and the operation

of burning fuel.Non-Reducible

It contains the oxides the oxides like Al2O3, MgO and Alkalis. These entirely stay with the slagduring smelting.

Al2O3 Alkali

Its presence in the slag producesMagnesium Aluminate and CalciumAluminates.

o It increase melting point of slag.o Decreases the viscosity of slag.

Al2O3 should be 5% in the slag.Because increasing it would increase thefluxes requirement.

MgO, CaO react with Al2O3.

Alkalis affect the refractory lining.

As a flux, they react with impuritiesand make slag.If present in the ore they prove to beprofitable (self fluxing).

Treatments & Procedure required before Smelting

Situation Treatment CommentsBig Lumps ComminutionSmall Lumps Agglomeration Because otherwise, the

oxygen/air blasts will blowaway the small lumps.

Carbonates Calcination Reducing toOxides

This will produce CO2


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SMELTING

Any metallurgical process in which metal in pure or crude form is separated by fusion from its

impurities with which it may be chemically combined or physically mixed is called smelting.

SLAG

The molten oxide product of melting is known as Slag. It is formed by both gangue and flux.

Raw Materials in Blast Furnace

Fe, Metallurgical Coal, FluxesMetallurgical coal Flux

The coal which can be converted intocoke is called Coking coal/Metallurgicalcoal.

In the absence of air (O2).Why not use coal? Because coke has:

o Strengtho Permeabilityo Higher calorific valueo Less volatile content (Higher

fixed-C content)o Less moistureo Less heating requirement

Coke should contain:o Volatile 2%o Ash 10%

o Fixed Carbon 85%o P = 0.018-0.04%o S = 0.6-1.5%o S by 0.1% Coke requirement

by 2%

They are added during smeltingFor bringing down the melting point,softening point of gangue.

To reduce viscosity of slagTo reduce the activity of some of itscomponents to make themstable/unstable.


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FORMULA FOR THE EVALUATION OF FLUX

It indicates that the quantity of SiO2 should be less than MgO + CaO. In general CaCO3 content

should not be less than 95%, SiO2 should be less than 5%. Nearly 0.5 ton of CaCO3 is needed

for producing 1 ton of Fe.

THE BLAST FURNACE FUEL-COKE

Why Coke?

Strong

Less Ash S, P

Quality control

Size

As the rank of coking coal decreases, its coking properties also diminish.

Ideally Coal =

7% ashLess than 1% S

About 5% P

COKE

It is a solid coherent residue achieved by heating coal in the absence of air.

FUNCTIONS OF COKE

Coke serves these major functions.

1. It is a fuel

2. Providing heat requirement for chemical reactants, melting of slag and metal.

3. It produces and regenerates reducing gases for the reduction of Fe oxide.

4. It provides an open permeable bed through which slag and metal passes down into the

hearth and hot reducing gases pass outward.


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QUALITY OF COKEIt is related to the quantity of coal, its processing and subsequent carbonization process.

In general the properties which determine the value of coke as a the blast furnace fuel are:

a) Chemical compositionb) Chemical reactivity

c) Thermal Stability

d) Size

e) Abrasion resistance and Strength

Quality of coke

Composition

Chemically the useful component of coke is fixed carbon which is the fuel as well as thereducing agent in the blast furnace. the balance is made up of ash contents, volatilematters, other impurities.

The inorganic residue left after burning it usually contains refractory oxides like silica,

alumina etc. It also contains Sulphur & Phosphorous.Reactivity

Defined as rate of reaction b/w coke and Oxygen and any other gases capable ofreacting with coke e.g.

C + O2 CO2The rate of burning of coke controls the rate of production of the blast furnace. In generalthe rate of burning of coke is directly proportional to:

i. Area of coke exposedii. Temperature and Pressureiii. Affinity of coke to oxygen (it depends on the blending material used and

the carbonization process adopted.)

Thermal StabilityDuring descent in the the blast furnace, the coke gets progressively heated; when thecoke gets heated beyond the temperature at which it was made in the coke oven, theprocess of carbonization restarts and the coke begins to contract.The temperature gradient results in the contraction and expansion of coke stresses andits consequent tendency to degradation. So in order to achieve thermal stability, highcarbonization temperature and uniform coke is used.

Size

Among all the qualities of good metallurgical coke the most important are its size andstrength.

The size range is known to affect the distribution of material inside the furnace andconsequently the gas flow which has a direct bearing on the production rate. It wasfound that:

a) If mean size of burden = 13mm then coke size 53mmb) This corresponds to an average coke to burden ratio:

Coke : Burden4 : 1

In general it has been suggested that the optimum coke size should be 3-5 times thanthat of burden.


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Abrasion resistance and strength

During the transportation of coke in the the blast furnace different abrasion actionsoccur.

In addition to this, coke has to withstand high temperature and nearly 20-25 meter tallburden lying over it, when it reaches the tuyere level.

A coke that breaks down under these additions will adversely affect furnace

permeability.It is an established practice to estimate the suitability of coke used in a the blast furnacein terms of its strength and abrasion resistance by measuring its shatter and abrasionindices.

SHATTER TEST (IMPACT RESISTANCE)It consists of carefully dropping of sample of certain fixed weight of coke from a standard height

on a standard quality floor. The shatter index is expressed as %age retained on various sieves

of certain fixed sizes.

TUMBLER TEST (ABRASION RESISTANCE)A standard weight of coke sample is part into a drum and rotating it for a fixed speed. The

abrasion index is expressed as the %age of the material retained on various sieves.


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ALTERNATIVE FUELS

Charcoal

It was used as alternative fuel to replace entirely the coke using small furnaces. Thecharcoal used should be strong and ferrous.

The Proportion of Fe made by charcoal is practically negligible.

Furnace height is to be lessened because it cannot bear the burden.

Wood is converted into charcoal on heating.Formed Coke

The solid fuel produced from non-coking lower rank coal is called formed coke.

Only that formed coke that has proper physical and chemical properties can be used inthe the blast furnace.

Formed Coke Conventional CokeCheaper CostlyLower manufacturing cost Higher manufacturing costContinuous operation of the plant unlikecoke ovens

Discontinuous manufacturing processes

Ferro Coke

Fe + C

A carbonized lump produced from a mixture of Fe bearing fines and non-metallurgicalcoal is known as ferro coke.

The %age of Fe bearing fines may vary from a few %ages to 15-20%. It has all thenecessary requirements for its use in the blast furnace.

Advantages:Non-metallurgical coal is used indirectly in the blast furnace.

The total fuel requirement reduces since certain proportion of pre-reduced Fe is already

inside the ferro coke.Coke consumption is reduced in the blast furnace and productivity is increased. Conclusion

The blast furnace cannot be run without a certain amount of coke in the charge.

The efficiency of the blast furnace mainly depends on quality of coke used as fuel. It istherefore necessary to understand certain properties of coke and devise means to obtainthese properties. Ferro coke and formed coke are being developed to substitute coke.


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MANUFACTURING OF FORMED COKE

The formed coal is charged to the carbonization furnace where the coal passes through

low temperature carbonizing zone and then it is heated @ 1000C.

The heating rate is controlled so as the coal not to be generated, collapse and break

caused by bulging and shrinking.

The carbonized coke is cooled to 1000C or lower temperature in the cooling zone before

it is discharged from the furnace.

Coking Coal

Dryer

Pulverization

Kneading

Forming

Carbonization

Formed Coke

Binder

Non-CokingCoal


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DISTRIBUTION OF BURDEN IN BLAST FURNACE

Burden contains Fe ore, coke and flux.

The blast furnace is essentially working on the counter current principle. The descending

solid charge meets the current of ascending gases and reduction of Fe ore along with its

progressive heating takes place during the passage.

Of all the reactions taking place inside the blast furnace, the reduction of the Fe ore is

the most important and the most difficult.

EFFICIENCY OF THE BLAST FURNACE (PRODUCTION RATE)

It is directly determined by 2 important factors

I. Rate of reduction of Fe-ore

II. Rate of heating of Burden

PERMEABILITY

The ability of the material to give way to the gases to pass is called permeability.

Higher the permeability, greater the gasses will pass through it. Otherwise choking takes place.

Permeability is necessary to reduce choking (resistance to flow of gases).

SHAPE AND SIZEIf the charge particles are of similar size then the burden would be automatically a uniformly

permeable burden irrespective of the way of charging in the furnace.

However, blast furnace charge consists of different sizes and shapes of coke and ore, therefore

it is very difficult to distribute them inside the furnace. In general finer the particles less will be

the permeability.

CHARGING MECHANISMIt consists of double bell charging mechanism. In this the materials are first charged in the small

bell which is then lowered to allow the material to drop into the lower big bell during which the

big bell remains closed. Then the small one is closed and the big bell is lowered to drop the

charge inside the furnace. Such an arrangement practically prevents the furnace exhaust gases

from escaping into the atmosphere while charging.

The above two factors depend on the time of contact and exposed volume

of charge to gas. The burden therefore inside the blast furnace should haveuniform and good bulk permeability.


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ELEMENTS OF DISTRIBUTION

A mass of material consisting of shapes, size and densities that falls inside the blast

furnace with various trajectories.

In general dense, small and irregular particles remain subsequently where they fall,

building ridges while light, large and smooth particles roll into troughs. As shown in the

figure.

This results in non-uniform permeability in the bed. The areas containing coarse particle

have less segregation while the areas containing fine particles have high segregation.

In general the coarse particles segregate in centre of the furnace shaft and the fine

particles segregate at or near the wall depending upon the clearance between the bell

and the furnace wall. As far as possible Fe ore should be present in area of maximum

gas flow for efficient reduction.

The size and system of charging are to be selected so as to have maximum utilization of

gas subject to ensure smooth performance of blast furnace.

FACTORS AFFECTING DISTRIBUTIONThe factors that affect the distribution of charge inside the blast furnace have been summarized

below

1. Design of the blast furnace and charging device

a) Angle and side of big bell

b) Speed of lowering of big bell

2. Inconsistency in physical properties of charging material

a) Size range of various charge materials

b) Angle of repose of raw material and other physical characteristics of charge

c) Density of charge

3. Level, system and sequence of charge program of revolving the distributora) Distribution of charge on big bell

b) Height of big bell from stock line i.e. the charge level in furnace throat

c) Order and proportions of charging of various raw materials

ANGLE AND SIZE OF THE BIG BELL

Angle = 50-530

Normal gap between the bell and the furnace wall is usually between 800-1000 mm.

Size of the bell depends upon the size of the throat of the blast furnace.

If the clearance between the bell and furnace wall is more, the crest is located furtheraway from wall.

If the gap is less between big bell and the furnace wall, the fines accumulate near the

wall and v-type contour is formed.

The V and M type contour formations at the stock-line, which are also called hoppers

depend upon the bell clearance from the wall

The more is the gap/clearance the crest is located further away from the wall and the

lesser is the gap the more fines accumulate nearer the wall.


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Too much or too narrow a gap between the bell corner and the throat wall tends to

segregate the sizes and prevents normal distribution from being achieved

Optimum ratio of throat to bell diameter results in optimum segregation of the burden

In the figure given below, a) is the V-type contour hopper and b) M- type contour hopper

1)STOCK LINE LEVELThe behavior of the particles immediately after their impact on the stock line controls the nature

of segregation i.e. uniformity and permeability in the burden. This behavior depends on

1. Height of fall of material from the bell on the stock line

2. Angle of Big Bell

The effect of height of the big bell above the stock line on the distribution of the charge is shown

in the figure. The lowering of the stock line to the point where the trajectory of fall of material

comes against the wall of the furnace results in the fine segregation near the wall.

This is shown at point h1 and as the level goes up the crest moves away from the wall (at higherlevel say h2 and h3). If the angle of inclination becomes steeper then the hopper will form in the

centre but if angle of inclination becomes deeper then the crust will move away from wall.


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2)SPEED OF LOWERING OF THE BIG BELL

1. The greater the speed of lowering of the big bell, the more the material will move toward

the wall and thereby alter the contour as well as distribution.

2. V type contour is formed if the speed is greater; on the other hand, the slower the speed,

more the material will move toward the centre and M type contour is formed. In short thespeed of lowering of the big bell should be maximum as far as possible because slower

speed tends to segregate the fines.

3)DENSITY OF CHARGED MATERIAL

Ore 5-6 g/cc

Flux 3-3.5 g/cc

Coke 1.5 g/cc

It means the rolling tendency of coke particles is more as compared to Fe ore. Since densities

cannot be altered the size may be so chosen that their differential rolling tendencies are offset tosome extent.

In general the size of the Fe ore is 3-5 times lower than that of coke.

4)ANGLE OF REPOSE

When a multi-particle material is allowed to gently fall on a horizontal plane, it tends to form a

conical heap. The base angle of this cone is called Angle of Repose.

Factors affecting Angle of Repose:

Particle size

Surface characteristics

Shape

PSD (Particle Size Distribution)

The smaller the Angle of Repose the more will be the homogeneity.

How to overcome Angle of Repose?

1. Eliminate the fines

2. Minimize the moisture

3. Remove the clay4. Dry the ore i.e. more dry ore (free from fines) more the angle of repose


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5)SIZE OF CHARGE PARTICLES

Increasing fines in the ore results in

1. Decrease in burden permeability

2. Increase in pressure drop

3. Decrease in reduction rate

The size ranges in order and practice;

More reducible 10-37 mm

Less reducible 10-25 mm

6)DISTRIBUTION OF CHARGE ON THE BIG BELL

Three systems are used for charging charge to furnace stock

1. Bucket Old one

2. Belt conveyer Modern

3. Double bell Present (>80%)

The distribution of charge on the big bell greatly affects the distribution in the furnace. For

distributing the charge on the the big bell different operations have been used. The Mckee

revolving distributor and its modifications are most widely used.


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MCKEE TOP OPERATION FOR CHARGING THE FURNACE

1) Both bells closed; skip discharging the charge in the small belt hopper.

2) The big bell closed. Small bell opened to allow the charge to fall in the big bell hopper.

3) Small bell closed, big bell opened to allow the charge to be dropped inside the furnace.

4) Both bells closed

MCKEE REVOLVING DISTRIBUTIONThe charging is carried out in the sequence of CCOO and the hopper is rotated through 60 after

every skip is dumped on the small bell which is lowered after every four (4) skips to dump the

charge on the big bell. After eight (8) such charges have been charged i.e. when 32 skips are

charged, the big bell is lowered to allow the whole charge to fall into the furnace.

Advantage;

Homogenous mixing of charge

4 skips

Small Bell (after

each skip 600)

THE BIG BELL

Furnace

After 8 times

Opened

Opened


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ORDER OF CHARGING

Mozumdar emphasizes the role of order of charging in the furnace distribution as change in the

system of the charging of raw material influences distribution and character of gas flow to an

extent considerably more than changes of level of charging and size of the charge, it is

therefore having all conditions similar on an average only 3.5% of the cases go to the credit of

control of distribution of gas flow by changing the size of the charge and 85% controls due to

change of system of charging.

The charging sequence in relation to the level of charging and the size of the charge has to be

adjusted so as to have maximum utilization of gas ensuring smooth performance of the furnace.

CHARGING SYSTEMS4 charging systems are commonly used.

1. Cn Om

2. Om Cn 3. Cn Om

4. OmCn

Cn Om Cn-1 (wide range of distribution of coke)

BURDEN PREPARATION-1

TREATMENT OF FE ORE

BURDEN QUALITY

In order to operate the blast furnace smoothly and for high production rate the burden shouldhave following properties.

Physical Chemical

1) A close size range with minimum of fines(PSD narrow)

2) Ability to withstand physical stresses3) Non-decrepitating nature4) Ability to withstand reducing conditions

without breaking5) Good bulk reducibility6) Low swelling index during reduction

7) A high softening temperature with anarrow temperature range of fusion

1) A high %age of Iron and low ganguecontents

2) A low %age of SiO2, Al2O3 etc3) Proper overall chemistry of the burden to

ensure clean slag and metal separationat minimum temperature.


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CRUSHING AND SIZEThe size of the Fe ore should not be too small or too large because;

If Fe ore contains too much fine particles

1) Permeability decreases2) Pressure drop inside the furnace increases (varying pressure of O2)

3) Reducibility decreases

If too large then

1) Material remains unreduced

2) Demand of heat increases

3) The maximum ore size is based on;

a) Ore chemistry

b) Bulk reducibility

c) Ore characteristics

In any crushing process we can reduce the size to 4-6 times

1st stage

150-250mm (reduced)

2nd stage

27-55mm (reduced)

BENEFICIATION TECHNIQUESConversion of low grade Fe ore to high grade Fe ore

1) Magnetic separation

2) Gravity separation

3) Froth floatation

4) Electrostatic separation5) Magnetic roasting

6) Low intensity magnetic separation

7) Washing

8) Calcination

Max. Size from run of mine = 100-

125mm


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MAGNETIC SEPARATION

Magnetite can be easily separated at low intensity magnetic field as it is strongly magnetic.

Weakly magnetic materials like hematite can be separated at high intensity magnetic field only.

Dry method is suitable in the particle size +6mm and wet method is suitable if the particle size is

-0.1mm. Magnetite can be separated at 1500 orested magnetic field intensity while hematite

can be separated at 12000 orested.

Usually ore is held on a rotating drum part of whose surface is magnetized. The non-magnetic

tailings fall from the drum. A series of magnetic separators are used in active beneficiation.

GRAVITY SEPARATION

HEAVY MEDIA

The method is used when the particle size is 6-40mm. An artificial heavy medium is prepared by

having ferro-silicon sand in a suspension in water such that the density lies in between that of

the Fe oxide and the gangue. The Fe oxide concentrate sinks and the gangue overflows as

tailing.

JIGGING

We use a perforated bottom on which ore particles are placed, the periodic impulses of water

flow are subjected through the perforation; as a result heavy particles move down and are

reduced as concentrate.

TABLING

It is suitable for sandy feeds. The feed moves over an inclined shaking table and is washed with

a cross stream of water. Its operation cost is high and output is very small i.e. 1-2 tons/hour.

SPIRAL

This method is suitable for materials having particle size 0.1-1.5mm. In it the ore is washed

down the spiral launder with a curved bottom. Fe mineral being heavier moves to the bottom of

the curved track while the lighter tailings sling toward the outer rim. The output of individual

spiral is very low. Therefore it is necessary to have no. of spirals.

FROTH FLOATATION

This method is based on the fact that surface property of some minerals can be temporarily

altered to make it either hydrophobic (abhorrence from water) or hydrophilic (water loving).

Hydrophobic minerals can be floated as froth if air is bubbled through a suspension of such

minerals in water. Various reagents are used according to the surface characteristics of metallic

minerals or gangue. Petroleum sulphonates, fatty acids and special oils etc are used to float iron

oxide. Starch tends to float silicon and depress iron oxide. Even though floatation reagents are

required in small amount but are costly so the overall cost of the process increases.


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ELECTROSTATIC SEPARATION

This involves the selective sorting of solid species by means of utilizing forces acting on the

charged bodies in an electric field. The difference in the electrical conductivities between iron

minerals and the gangue is made use of in separating the two with magnetic separation. The

use of electrostatic separation in the final stages improves the purity of the product and overall

concentration.

MAGNETIC ROASTING

Reduction

Hematite Magnetite

600-8000C, atm

It is better than high intensity magnetic separation

It is very easy to reduce hematite to magnetite under slightly reducing conditions at 600-800C

and the ore is then easily separated by using low intensity magnetic field.

WASHING

Washing means separation of particles based on their sizes by using such fluids in which finer

particles get suspended and hence washed away while the large particles completely fail to get

suspended and hence separated from the fines. Washing improves screening ability by

removing the fine particles.

DRYINGWet ores were initially being used by many operators from an economical point of view as the

hot gases of the blast furnace have the capacity to wet the charge. But the problem which was

faced was that the wet raw material cannot be screened efficiently so it is generally winded.

CALCININGFe is ultimately produced by reducing Fe oxide present in the ore. The use of OH, CO 3

2 or

sulphite type ores can be used for Fe making after calcining.

BLENDINGThis involves mixing two or more types of material from two or more sources to obtain a uniform

material of desired qualities over an extended period. The Fe ore blend may be made up of ore

from different sources or it may also include materials such as coke breeze and CaCO 3.


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AGGLOMERATION OF IRON OREThe fines in the iron ores need to be agglomerated into lumps of suitable physical

characteristics size/shape so it can be used in blast furnace. The techniques used are as:

1. Briqwetting

2. Nodulising

3. Extrusion

4. Sintering

5. Pelletising

BRIQWETTING

It essentially consists of pressing of ore fines with or without the binder into a block or briqwet of

some suitable size and shape and then subjected it to a hardening process. Cement briqwetting

is done with 1-5% cement as binder, press into blocks and harden in a tunnel kiln heated toabout 13500C. Production is 1000t/day from a single plant.

There are two types of briqwetting

Cold briqwetting

Hot briqwetting

COLD BRIQWETTING

It is produced by adding 10% cement and hardening them for several days like cement

concrete.

HOT BRIQWETTING

It is done by pressing ore fines at 800-10500C under normal or slightly reducing conditions.

NODULISING

Fine ore concentrate and some carbonesous material like tar are passed through a rotary kiln

which is slightly inclined to the horizontal. The temperature in the rotary kiln softens the ore, the

speed of rotary kiln is 1-2rpm, length is 30-60m, diameter is 2m and diameter of sinter zone is

4m. the charge takes 1-2 hour in the kiln. This technique is replaced by sintering and pelletising.

EXTRUSIONIt was used in 1950 on a small scale level. In this process moist ore with or without binder is fed

into a chamber and then extruded from that chamber. The product obtained is cylindrical and is

cut into a desired small size. The product is dried and fired before being used in blast furnace.


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SINTERING

It is a process of heating of mass of fine particles to the temperature little below the melting

point for the purpose of agglomeration of fines into lumps.

PELLLETISINGThe process consists of rolling of moist ore fines of less than 100 mesh size with or without a

binder into pellets usually 7-20mm in size. These green pellets are dried and fired before

charging to blast furnace.

SINTERING

It is a process of heating of mass of fine particles to the temperature little below the melting

point for the purpose of agglomeration of fines into lumps. In other words the sintering meansCasting without melting

PRINCIPLE OF SINTERINGIron ore sintering is carried out by putting a mixture of iron ore mixed

with solid fuel on a permeable grate. Coke breeze is normally used as

fuel. The top layer of this bed is heated to a sintering temperature by a

gas or an oil burner and air is drawn downward to the permeable grate

with the help of exhaust blowers. The narrow combustion zone

developed initially at the top layer that travels through the bed raising

the temperature of the bed. The cold blast drawn through the bed that

cools the already sintered layer and thereby gets itself heated. The

heat contained in blast is utilized in drawing and preheating the lower

layers in the bed. In the combustion zone the bonding takes place

between the grains and the strong and porous aggregate is formed.

The process is over when the combustion has reached the lowest layer

of the bed. The sintered coke is then removed from the grate in hot

condition or after partial cooling. It is broken, screen and cool to produce desired fraction. The undersized

is recycled and oversized is fully cooled and send to the Blast Furnace.

Permeable grate

Bed

Charge

hopper

Ignition

source


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QUALITY OF SINTERING

The main objective of sintering is to agglomerate of fines particles. The others are

1. Size of ore (specific size is required in order to do sintering)

2. Strong agglomeration with good bulk reduction that depends on nature of ore and

sintering process

3. To remove the volatile like CO2, H2O, SO2 etc

4. Flux incorporation in the burden

PROCESS VARIABLES OF SINTERING

There are certain variables that affect the process of sintering which are as

1. Bed permeability as decided by the particle size, shape of the mixture and thickness ofthe bed.

2. Thickness of the bed

3. Total volume of air blast drawn through the bed during sintering

4. Rate of blast drawn through the bed during sintering

5. Amount and quality of fuel added in the charge

6. Amount and quality of moisture added in the charge

7. Nature of ore fines

8. Any non-uniformity in the bed composition or in the process of sintering

During sintering heat exchange takes place between the solid charge and air blast that is drawn

through the bed. At any time during sintering the air blast initially gets heated that is it cools the

combustion zone and in turns heats the lower layer of the bed.

It is therefore essentially a phenomenon of gas solid heat exchange. In order to carry out both

the heating and cooling functions of gas phase affectively i.e to obtain a faster rate of heat

exchange the heat capacity of the blast drawn through the bed should be maximum, it means

that the volume of the air drawn through bed during sintering should be maximum. More

permeable the bed, the more will be air blast drawn through it. More permeable bed however

leads to loss of the strength in the resulting sinter. These two factors oppose each other and

hence should be adjusted at the optimum.

TYPES OF SINTER

There are three types of sinter

1. Acid sinter

2. Fluxed sinter

3. Super fluxed sinter


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ACID SINTER

In this process there is no addition of flux during agglomeration of fines of sintering. Fluxes are

added separately during reduction of iron ore in the blast furnace.

FLUXED SINTERIn this process the fluxes are added to make the basicity of the sinter equal to the basicity of

slag in the blast furnace.

Basicity of fluxed sinter= Basicity of slag in Blast Furnace

SUPER FLUXED SINTER

In this process the percentage of fluxes is added more than in fluxed sinter. The basicity of

super fluxed sinter should be greater than the basicity of slag in the blast furnace.

MECHANISM OF SINTERING

TYPES OF BOND IN PARTICLES OR FINES

The particles or fines during sintering form a bond between them. There are two types of

bonding exist between the particles which are

1. Solid state bonding

2. Slag or glass bonding

ORE BED

WET

DRY

CALCINING

COMBUSTION


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SOLID STATE BONDING

In solid state bonding the particles either diffuse or recrystallize. The physical change occurs in

the particles when they combined to form a bond. For example calcium carbonate heated at

high temperature and pressure is converted into marble.

SLAG OR GLASS BONDING

In this slag fuses and acts as binder between the fines and developed a bond. The chemical

composition changes during formation of bond. During chemical change iron ore fines convert

into ferrite, spinal, silicate. (Spinal) MgAl2O4 . Hercynite (FeAl2O4). Jacabsite (MnFe2O4)

Physical change occurs when time is large and temperature is low

Chemical change occurs when time is short and temperature is high

During bonding the probability may be

1. No chemical change no physical change

2. No chemical change but change physically

3. Both chemical and physical change

RAW MATERIALSThere raw materials specification should be proper in order to do better sintering process. There

are following raw materials specifications which are as

Charge size

Fuel content

Moisture

CHARGE SIZEIf the particle size of the charge is fine then the contact area will increase and on the other hand

permeability will decrease. So sintering process will be improper. In order to do better sintering

the particle size of the charge should be coarse, so that gasses can pass through the bed.

If we have less than 3mm fractions then above 6mm fractions along with are used.

FUEL CONTENT

Fuel content is used uniformly 6-8%. The percentage of fuel in the top layer of the bed should

be greater as compared to the lower layer because the heating is started from the bottom of the

bed and going upward.


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MOISTURE

Moisture controls the permeability of the bed. When moisture evaporates it produces porosity.

CONTROL OF SINTERING PROCESSSintering process is controlled by the following factors

Input heat

Ignition input source

Moisture content (permeability control)

Speed of grate/bed machine

Bed height

BLAST FURNACEIt is a steel tank lined with a refractory material (bricks).

PURPOSEThe purpose of blast furnace is to reduce iron oxide into molten iron called as hot metal.

RAW MATERIALSThe raw materials required for the production of iron are:

1. Iron ore

2. Limestone (fluxes)

3. Coke

4. Hot blast of air

DIAGRAM


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EQUIPMENTS/PARTS OF BLAST FURNACE

The blast furnace consists of the following parts

Foundation

Stack column

Hearth

Bosh

Charging facilities available

FOUNDATION

It is a massive steep reinforce concrete mass partially embedded below the ground level. It is

sufficiently strong to stand the loaded furnace weight.

SKIP CAR (CONVEYOR)

The skip cars and in some cases conveyors are used to deliver blast furnace charge to the top

of the furnace.

BOSH

The bosh is the inverted conical section. It has the maximum diameter.

RECEIVING HOPPER

The blast furnace charge is loaded into the receiving hoppers which in turn deliver the charge tothe rotating distributor. The rotating distributor helps in assuming the uniform distribution of

charge in furnace stack.

HEARTHIt is a crucible like vessel upon which the vertical shaft portion of the furnace sets. All the molten

metal and slag collect in the hearth before being drain.

BELLS (LARGE AND SMALL)

The large and small bells are conical shaped devices that form a gas tight lock hopper. Thehopper prevents the gas escaping from the furnace while it is being charge.

BUSTLE PIPESIt encircles the blast furnace and delivers the hot blast air from the blast line to furnace.


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TUYERES

The hot blast air is delivered to the furnace through water cooled opening called tuyeres. The

tuyeres are located at the top of hearth.

STACK COLUMNThe stack is the upper portion of furnace where the charge is preheated.

METAL AND SLAG NOTCHESThe molten metal is removed from the hearth through the metal notch. The metal is placed into

the transfer ladles, while the slag may be transferred through the slag pot.

PROCESSESThe production of iron in the blast furnace consists of the following steps which are as

INTRODUCTION OF THE CHARGEThe charge is introduced in the blast furnace through cup and cone arrangement.

INTRODUCTION OF HOT BLASTSimultaneously hot blast of air is introduced in the furnace through tuyeres.

COMBUSTION OF COKE

Coke present in the charge burns in the hot air producing CO2.

C + O2 CO2

PRODUCTION OF CO(REDUCING AGENT)The CO2 forms rise up reacts with C and produces CO.

CO2 + C 2CO

REDUCTION OF HEMATITE(Fe2O3)

CO formed is a powerful reducing agent. It reduces hematite to iron.

Fe2O3 + 3CO 2Fe + 3CO2

Fe2O3 + CO Fe3O4 + CO2


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Fe3O4 + CO FeO + CO2

FeO + CO Fe + CO2

DECOMPOSITION OF LIMESTONE

Due to high-temperature limestone decomposes into lime and carbon dioxide.

CaCO3 CaO + CO2

FORMATION OF SLAGCalcium oxide reacts with silica and formed calcium silicate which is called as slag.

The iron formed is collected at the bottom of the furnace and a slag formed a layer on it. The

iron obtained from this method is called pig iron. It contains carbon as major impurity.

REFRACTORY MATERIALSMaterials that retain their shape and chemical identity at a very high temperature are called

refractory materials. E.g. fire clay, Alumina, magnesia etc

These materials withstand at high temperature without fusing.

CLASSIFICATIONS OF REFRACTORY MATERIALSRefractory materials are classified on the basis of the following groups

Based on refractory material

Based on refractoriness

Based on method manufacturing

CLASSIFICATIONS ON THE BASIS OF REFRACTORY MATERIAL

REFRACTORY

MATERIALS

ACIDIC BASIC NEUTRAL


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Acidic refractries consist of acidic materials. They are not attacked by acidic materials but

easily attacked by basic materials E.g. Silica, quartz, fire clay

Basic refractries consist of basic materials. They are not attacked by basic materials but easily

attacked by acidic materials. E.g. Magnesite, dolomite refractroies.

Neutral refractories are made from weakly acidic and basic materials. They are not attacked

by both acidic and basic materials. E.g. Graphite, chromite, zirconia refractories.

CLASSIFICATIONS ON THE BASIS OF REFRACTORINESSAccording to the refractoriness, refractories are classified into four types.

CLASSIFICATIONS ON THE BASIS OF METHOD MANUFACTURING

DRY PROCESS: This process includes crushing the materials and presses it in a die and

produces the required shape. E.g. bricks refractory, tile refractory etc.

FUSED CAST: The refined raw materials are heated at 1900-2500C in a electric arc

furnace,until completely melted. The melted substance is poured into specific molds and left to

solidify gradually, resulting in a fused cast refractory. E.g. Alumina mullite, zirconia etc.

REFRACTORYMATERIALS

LOW HEATDUTY

(1520-16300C)

MODERATEHEAT DUTY

(1630-16700C)

HIGH HEAT DUTY

(1670-17300C)

SUPER HEAT DUTY

(Greater than 17360C)

REFRACTROY

MATERIALS

DRY

PROCESSFUSED CAST

HAND

MOULDING


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These refractroies have

Poor spalling resistance

Sudden expansion and contraction

High erosion and abrasion strength

HAND MOULDING: These refractroies are made from slurry materials. E.g. Gun type refractory,

Spray type refractory.

PROPERTIES OF REFRACTORY MATERIALS

1-REFRACTORINESSIt is the ability of a material to withstand very high temperature without softening or deformation

under particular service condition.

HOW TO MEASURE REFRACTORINESS

Since most of the refractories are mixtures of several metallic oxides, they dont have sharp

melting points. So the refractoriness of a refractory is generally measured as the softening

temperature and is expressed in terms of pyrometric cone equivalent (PCE).

PYROMETRIC CONE EQUIVALENT (PCE)

Pyrometric cone equivalent is the number which represents the softening temperature of a

refractory specimen of standard dimension and composition.

OBJECTIVE OF PCE TEST1. To determine the softening temperature of a test refractory material

2. To classify the refractoies

3. To determine the purity of refractories

4. To check whether the refractory can be used at a particular serving temperature

2-POROSITY

Porosity is defined as the ratio of its pore volume to bulk volume. Porosity is an important

property of refractory materials because it affects many other characteristics like chemical

stability, strength, abrasion resistance and thermal conductivity.

It reduces the strength

It reduces the resistance to abrasion

It reduces the resistance to corrosion

Highly porous refractory possess the thermal conductivity. This is due to presence of

more air voids, which act as insulators, and hence it is used in furnace lining.

High porous refractory reduces the thermal spalling. Gases and slag attack more easily


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3-THERMAL SPALLING

Thermal spalling is the property of cracking, breaking, peeling off a refractory material under

high temperature.

It is due to the following factors

1. Rapid change in temperature

2. Slag penetration

RAPID CHANGE IN TEMPERATURE

This causes uneven expansion and contraction within the mass of a refractory material and

leads to development of uneven stresses and strains.

SLAG PENETRATION

This causes the variation in the co-efficient of thermal expansion and leads to spalling. Thermal

spalling can be decreased by using high porosity, low co-efficient of expansion and good

thermal conductivity refractory.

4-SLAG RESISTANCE

Slag attacks the refractory at high temperature and alters its composition by forming of certain

compounds with the refractory material. A basic slag attacks acidic refractory and vice versa.

Rate of slag attacks is accelerated because of following reason

Defective joints and cracks in refractory material

Rough and extra porous surface

The movement of slag

The rate of slag attack is reduced if refractory is dense and smooth surface.

5-ABRASION RESISTANCEA refractory is subjected to wear when it comes in contact with the moving charge as in case of

blast furnace. Descending charge material result in abrasion or wearing off refractory lining

material

6-ERROSION RESISTANCEIt damages due to mechanical action occurs when metal or gas carrying dust and slag particles

hit against the refractory lining resulting in chipping off of particles from the refractory


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SELECTION OF REFRACTORIESThe refractories are selected on the basis of the following factors

1. Area of application

2. Working temperature

3. Extent of abrasion and impact

4. Structural load of furnace

5. Stress due to temperature gradient

6. Chemical composition/furnace environment

7. Heat transfer

8. Cost concentration

SOME IMPORTANT CLASS OF REFRACTORY

FIRE CLAY

It is hydrated alumina silicate Al2O3.2SiO2.2H2O containing about 25-45% Al2O3 and 50-80%

SiO2. The term fire bricks are referred to fire clay bricks. There crushing strength decreases with

increasing temperature. Porosity varies from 8-24% depending on the temperature on which it is

fired. Higher the porosity less will be the slag penetration and less will be the effect of sudden

changes in temperature. It is used in the upper part of Blast Furnace.

SILICA REFRACTORY

Raw material SiO2 refractory are the various forms of natural deposits of SiO2. For examplequartz, ganister, sandstone, sand. One of the great difficulties of SiO 2 refractory is that SiO2

occurs at different allotropic forms which are stable at different temperature. Sudden changes in

temperature causes fire crack in silica bricks and this causes disintegration or spalling.

HIGH ALUMINA REFRACTORY

They are not used extensively because they are very costly. As the general rule the

refractoriness increases with increasing alumina content of alumina silicate refractory compare

to fire clay refractory. It contains 45-95% alumina. High alumina refractory gives better service

under severe condition due to

High abrasion and erosion resistance

High spalling resistance/slag

Good volume stability

High refractoriness


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CARBON/GRAPHITE REFRACTORY

Carbon occurs in nature both in amorphous and crystalline form. Graphite is crystalline form of

carbon. In graphite carbon atoms are arranged in hexagonal structure. Graphite is infusible and

stable at about 36000C. It is not attack by slag and is resistant to thermal shock. Graphite is

less prone to oxidation compare to other amorphous form of carbon.

USES

1. Carbon bricks find more extensive use in lining bosh/hearth of Blast Furnace.

2. They are also used in furnaces where temperature is high and atomosphere is non

oxidize

3. Due to the presence of reducing atomoshpere in Blast Furnace the life of carbon

refractory is prolong

4. High thermal conductivity of carbon lining helps in easy temperature control in the lower

part of Blast Furnace

5. Iron and slag runner are also lined with carbon

CERAMIC GRAPHITE REFRACTORY

They are used in steel making process due to their high resistance of spalling and inactive

nature.

MgO graphite refractory is used in ladle lining

Alumina graphite refractory is used in nozzle, sliding gates


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MAJOR CAUSES OF FAILURE OF BLAST

FURNACE REFRACTORY

There are following factors that cause the failure of blast furnace refractory

Attacking of carbon mono oxide (CO) gas on the refractory

Action of alkali vapours

Action of other volatile matters

Action of acidic and basic slag

Abrasion of refractory by solid, liquid and gases

Action of molten metals

Condition of operation

Blowing in procedure

All these factors do not affect all the areas of blast furnace. One or more factors can affect atone area. For example in the stack, the lining has to stand with abrasion with solid burden and

CO attack, while in bosh region lining has to stand high temperature, erosion, attack of molten

acidic and basic slag. Similarly the hearth has to withstand the attack of molten metal and slag

without breaking.

BLOWING INThe process of starting a newly lined blast furnace is called blowing in.

In general the operation involves the following main steps

1. Drying

2. Filling

3. Lightening

DRYING

The new lining of the furnace contains significant portion of moisture which must be completely

removed before the temperature of the blast furnace raised. The operation is called drying in

which the furnace is slowly heated. The slowly temperature is about 200 0C which is slowly

increased to about 425

0

C. But furnace drying can be accomplished by

Hot blast from stove

Use of coke oven to generate and supply hot gasses

Use of coke fire in the hearth

In this process care must be taken to heat up and dry the furnace slowly to avoid cracks in the

newly built or required parts.


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FILLING

The blast furnace is then filled with the start of charge with generally consist of coke and fluxes

in the lower part and coke, flux and an increasing amount of ore in the upper part. So the fuel

ratio is much larger than the furnace operation.

It is so because we have to raise the temperature up to smelting temperature before the ore

reaches to the bottom of the furnace. Once the smelting temperature is reached, the burden or

proportion of ore is gradually increased as the furnace is operated until about two weeks it starts

carrying the normal burden.

LIGHTENING

The most common method to light the blast furnace is by using the low volume hot blast of

approximately 5500-6500C to ignite the coke in front of tuyers. The blast volume is increased

every few hours and after about 24hour 40-50% of full blast is achieved. It is increased until the

full blast is achieved that is 100%

OPERATION UNTIL REGULAR PRODUCTION

Soon after the furnace is lighted the slag begins to accumulate in the hearth and a little later the

iron as well. As soon as the slag reaches about the level tuyers it is drawn off at the sinter notch

and the operation continuous until sufficient iron has accumulated to tape. The first iron tape off

is not of proper grade as it is at this time impossible to have such temperature and composition

of slag as to produce iron of given grade. Within a few tapes however the furnace is usually

brought up to the production of desired grade.

BLOWING OUTThe process of shutting down the blast furnace i.e. for relining is called blowing out.

When a furnace is to be shut down or blown out the ore charge is gradually reduced and

stopped. Flux and fuel are continued until all metal and slag are tapped out and flux is then

discontinued. The fuel is gradually reduced and finally shut off and fired slowly burns out. The

furnace must be allow to cool gradually before being emptied


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BLAST FURNACE PRODUCTSThe blast furnace products contain

Pig iron

Slag

gasses

COMPOSITION OF PIG IRON

Pig iron is major product of blast furnace that contains the impurities carbon, silicon,

manganese, sulphur and phosphorus.

These impurities in the pig iron have the maximum range and depend on the burden chemistry

of the charge.

If the sulphur contents are very high in the pig iron then it will create hot shortness during

rolling, forging. This is because at high temperature sulphur reacts with iron and forms

iron sulphide (FeS) that produces cracks.

S, Si, P are not completely reduced in the blast furnace they should have the minimum

percentage in the pig iron in order to make steel.

Whatever is the phosphorus content in the burden; the whole of it is reduced and finally joins with molten metal. The presence of carbon in the pig iron is beneficial during its

conversion to steel. Whereas the presence of phosphorus in pig iron is detrimental, and

it adds to the cost of steel making. The contents of Si and S depends on the volume of

slag its basicity and operating temperature furnace and burden chemistry of charge.

These can therefore be varied within certain limits by adjusting the burden chemistry,

fuel rate and those conditions will affect the temperature of the blast furnace.of the

Elements Percentage impurities

Carbon 3.5-4.2%Silicon 0.5-2.5%Manganese 0.5-1.5%Phosphorus 0.04-2%Sulphur 0.04-0.15%


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SULPHUR PROBLEMIt is difficult for steel maker to control the sulphur specification and S content of steel. S

content of steel should not be more than 0.025-0.04. The process of steel making is capable of

reducing the S contents up to 40% in the hot metal charge. Its me an in order to achieve therequired percentage of S the hot metal should not contain more than maximum 0.06%. This

can be achieved by using coke having maximum 0.6% S. if the S in the ore is around 1% then

it is difficult to meet hot metal specification with respect to S contents. The sulphur problem is

more severe when the continuous casting of steel is adopted. The finished molten steel should

have no more than 0.025% S for continuous casting to operate smoothly. The coke use as a

fuel in the blast furnace should low in sulphur. The cost of fuel is in inverse proportion to its S

content.

For economical reason therefore every efforts must be made to eliminate S and produce

required quality of hot metal before putting it in the steel making furnace.

HOW TO CONTROL SULPHURDesulphurization inside the blast furnace can be affected in three different ways

By having higher basicity

By increasing the volume of slag

By increasing the hearth temperature

FeS + CaO + C CaS + FeO + CO

When the pig iron is tapped off from the blast furnace and is going to the steel making unit then

during its rout the following process are run to remove either silicon or sulphur

Basic burdening and desiliconization

Acidic burdening and desulphurization


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BASIC BURDENING OF BLAST FURNACEIf the alumina (Al2O3) content in the burden is high the furnace hearth temperature has to be on

the high side to keep the slag thick and free flowing. The basicity has also to be raised to obtain

proper slag in this case. These conditions are more favorable for disiliconisation of metal insidethe furnace. This can be fully used in obtaining pig iron containing less than 0.06% or preferably

0.04% sulphur. This often leads to high silicon contents of pig iron. Since silicon reduction is

favored at high temperature. The pig iron is treated externally to remove silicon and produce hot

metal of the specification required for steel making. This external treatment for elimination of

silicon from molten iron is known as external disiliconisartion

REMOVAL OF SILICON

Silicon is removed externally by lancing the oxygen in the hot metal before carrying it in the

steel unit. When oxygen is lanced then temperature of the hot metal increases due to the

exothermic reaction. The temperature is maintained around 1400-14500

C by adding iron oxide(Fe2O3) and calcium oxide (CaO) because at this temperature silicon reacts with oxygen and

forms silica (SiO2) and go to the slag. If the temperature is very high means above 1450 0C then

carbon has high tendency with oxygen. So decarburization takes place which we dont want. So

we use mill scale (iron oxide) and lime as reagent to maintain temperature of molten iron in

order to remove silicon.

For dephosphorisation and desiliconisation of molten pig iron we have to provide sufficient

amount of oxygen in order to oxidize all the amount of Si, P, Mn.

ACIDIC BURDENING OF BLAST FURNACEThe acidic burdening of blast furnace can be readily practiced if the total gangue in the ore and

coke are salacious in nature. The slag basicity is also reduced since high basicity is no longer

necessary. The furnace is often operated with basicity less than 1 that is the slag produced is

acidic and for which the burden chemistry is adjusted with more acidic and less basic oxides.

The net result is that the silicon content of the metal is low which is advantageous for

subsequent basic process of steel making.

REMOVAL OF SULPHURA lance of oxygen is lowered into molten iron ladle and several kilogram powder of magnesium

is added. Sulphur is reduced to magnesium sulphide in violent exothermic reaction


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DISPOSAL OF METAL

Major portion of molten iron is sent to steel making plant for its conversion to steel

DISPOSAL OF SLAG

Slag is carried in ladle to the slag dumping yard where it is tipped as waste material.

Alternatively the slag granules are produced in a granulation plant where molten slag is poured

in turbulent water. These granules are increasingly being used as construction material.

CONCLUSION

The main product of blast furnace is molten iron along with slag. The chemistry of metal is

important and is adjusted as per the overall economy of steel production from ore. The

chemistry of slag is adjusted to obtain efficiency operation of blast furnace. The waste product

that is slag is also being put to some use.

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