Ironmaking SS

7/17/2019 Ironmaking SS

http://slidepdf.com/reader/full/ironmaking-ss 1/458

Smarajit Sarkar Department of Metallurgical and Materials Engineering

NIT Rourkela

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Ahindra Ghosh and Amit hatterjee! Ironmaking and Steelmaking Theor" and #ractice$ #rentice%

&all of India #ri'ate (imited$ )**+

Anil ,- .is/as! #rinciples of .last 0urnace Ironmaking$ S.A #ulication$1222

R-&-Tupkar" and 3-R-Tupkar"! An Introduction to Modern Iron Making$ ,hanna #ulishers-

R-&-Tupkar" and 3-R-Tupkar"! An Introduction to Modern Steel Making$ ,hanna #ulishers-

Da'id &- 4akelin 5ed-6! The Making$ Shaping and Treating of Steel 5Ironmaking 3olume6$ The

AISE Steel 0oundation$ )**7-

Richard 8-0ruehan 5ed-6! The Making$ Shaping and Treating of Steel 5Steeelmaking 3olume6$ The


A-Ghosh$ Secondar" Steel Making 9 #rinciple : Applications$ R #ress 9 )**1- R-G-4ard! #h"sical hemistr" of iron : steel making$ E(.S and Ed/ard Arnold$ 12;)-

0-#-Edneral! Electrometallurg" of Steel and 0erro%Allo"s$ 3ol-1 Mir #ulishers$12<2

.- =>turk and R- 8- 0ruehan$! ?,inetics of the Reaction of Si=5g6 /ith aron Saturated Iron?!

Metall- Trans- .$ 3ol- 1;.$ 12+@$ p- 1)1-

.- =>turk and R- 8- 0ruehan! ?The Reaction of Si=5g6 /ith (iuid Slags$B Metall- Trans-.$

3olume 1<.$ 12+;$ p- C2<- .- =>turk and R- 8- 0ruehan!B-Transfer of Silicon in .last 0urnace?! $ #roceedings of the fifth

International Iron and Steel ongress$ 4ashington D--$ 12+;$ p- 2@2-

#- 0- Nogueira and R- 8- 0ruehan!B .last 0urnace Softening and Melting #henomena % Melting

=nset in Acid and .asic #ellets?$ $ ISS%AIME lronmaking onference$ )**)$ pp- @+@-

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The Blast Furnace route is the dominant route for theproduction of iron for steel making.

India produces around 67 million tonnes of crude steel peranum out of which 57% is from the pig iron produced

through the blast furnace.

The respective gures are !"## million tonnes and 7$.5%world wide.

verage coke consumption in Indian blast furnace is around55#&6##kg'T()

*espective gure for advanced countries is around +5#&"##kg'T()

verage ,i content in pig iron is #.-&!.#% in India. *espective gure in advanced countries is #."&#.6%.

INTRODUCTION

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.-0- process is the first step in #roducing Steel

0rom Iron =ide-

This 4ould remain so proal" at least for the firstuarter of the centur" despite

◦ Speed" depletion of oking coal reser'es

◦ Enhanced adoption of alternate routes for iron making forultimate con'ersion to steel-

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The .-0- /orks on a counter current principle Ascending hot gases meet Descending solid

charge The charge includes Iron earing materials 5ore$

sinter$ pellets6$ coke : flu 5(ime stone$ Dolomite6 The ascending gases cause reduction of Iron

oide in the Iron earing materials /hileprogressi'el" heating it-

The result is #roduction of ◦ (iuid slag◦ (iuid Metal

◦ .-0- Gas of considerale calorific 'alue

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#.-&#.6t0.5-0.6t1.7-1.8t

2500 m3

0.6t1t

FuelReducing agent u!!l"ermeable bed/spacer0

3200m3

+80kg dust

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An iron last furnace produces pig iron of the follo/ing

composition!

0e%2)-+ F$ %C-+F$-Si%)-1F$ #%*-2F and Mn%*-7F

The ore smelted anal">es as follo/s!

0e)

=C

%<+F$ Si=)

%+-7F$ Al)

=C

%@F and rest is

Mn= $#)=@ etc-

Assume that 22-@F of the iron ore is reduced and *-@F

slagged- alculate the /eight of ore used to produce 1

ton of pig iron-

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All the reduced elements join the metal- A t"picalcomposition of the Metal 5Iron6 produced in .last0urnace is presented elo/.

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The Slag is a lo/ melting chemical compound formed "

the chemical reaction of the gangue and the flu in thecharge-

All unreduced ones join the slag

The major constituents of the slag include the follo/ing◦ Al)=C 9 )*-7@F

◦ a= 9 C)-)CF◦ Si=) 9 CC-*)F

◦ Mg= 9 2-2@F◦ S 9 *-+2F

◦ Mn= 9 *-@7F◦ Ti=) 9 1-*1F

◦ 0e= 9 *-71F◦ ,)=Na)* 9 1F

◦ T#ace O$ide % 0.5&

5urtse" TATA STEE(6

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NIT Rourkela

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.last furnace producti'it" depends upon an optimum gas

through flo/ as /ell as smooth and rapid urden descent-

The character of the gas and stock mo'ements is intimatel"

associated /ith the furnace lines-

The solid materials epand due to heating as the" descend

and their 'olume contracts /hen the" egin to soften and

ultimatel" melt at high temperatures in the lo/er furnace-

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A further 'olume contraction occurs /hen the solid coke urns

efore the tu"eres-

An enormous 'olume of the comustion gas has to ule

through the coke grid irrigated /ith a mass of liuid metal and

slag-

An optimum furnace profile should cater to the ph"sical and

chemical reuirements of counter flo/ of the descending solid$

'iscous past" or liuid stock and the ascending gases at all

places from the hearth t( t)e t(!

c(nt*

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=nl" then$ an optimum utili>ation of the

chemical and thermal energies of the

gases as /ell as a smooth$ uniform and

maimum iron production /ith minimumcoke rate /ill e reali>ed-

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o In an integrated steel /orks the capacit" of the

Blast Furnace depends upon The capacit" of the /orks- The process of steelmaking adopted-

The ratio of hot metal and steel scrap in thecharge-

onsumption of foundr" iron in the /orks- (osses of iron in the ladle and the casting

machine- The numer of furnaces to e installed

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Stock line! The distriution pattern at the top-

harge or stock le'el in the furnace throat

The materials or the stock or the urden should

e properl" distriuted for uniform distriution of

the ascending gas-

Zero stock line! &ori>ontal plane formed "

ottom of ig ell /hen closed- ;ft stock le'el forinstance located ;ft elo/ >ero stock line-

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It is the 'olume of .last 0urnace occupied " the charge

materials and the products $ i-e- the 'olume of furnace

from the stock line to the tap hole-

Hseful 'olume the furnace capacit" J -H-H-3-

-H-H-3 coefficient of utili>ation of useful 'olume-

The 'alue of -H-H-3- 'aries in a /ide range from *-7+%1-@* mCKton of pig iron

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3 k D)&

3Hseful 'olume

&Total heightDDiameter at the ottom of the shaft

,A coefficient usuall" lies /ith in the range of *-7<

to *-@C- &igh 'alue is for slim profile-

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Total height useful height distance et/een stock lineand the charging platform 5it is go'erned " the

construction of gas off%take and charging platform$ this

dimensions 'aries from C to 7m-6

Hseful height height from the tapping hole to the stockline-

The height of the last furnace is mainl" go'erned " the

strength of the ra/ materials$ particularl" that of coke-

cont* *

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The strength of the coke charged to the

furnace should e sufficient to /ithstand the

load of ra/ materials /ithout gettingcrushed- oke pro'ides permeailit"5in the

dr" as /ell as /et >ones 6and also

mechanical support to the large chargecolumn$ permitting the gases to ascend

through the 'oids-

Total height 5&6 @-@@3*-)7

Hseful height 5&*6 *-++J&

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Diameter !The ell" Kosh parallel is the c"linder that

connects the tapers of the shaft and the osh-

Its diameter$ dll$ and the ratio of this diameter to

the useful or inner height of the furnace as /ellas to the diameter of the hearth pla" an

important role in the operation of the furnace-

The correct descent of the stock$ ascent of the

gas and efficient utili>ation of the chemical andthermal energies of the gas depend greatl" upon

these ratios-

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The importance of an adeuate ell" diameter lies in the

fact that softening and melting of the gangue and

formation of the slag occurs in this region-

An increase in the diameter facilitates gas passage

through the stick" mass and also slo/s do/n stock

mo'ement$ thus increasing the residence time for indirect

reduction-

&o/e'er$ the ell" diameter cannot e increased

aritraril" as it is directl" related to osh angle$ osh

height$ hearth and throat diameters and useful height-

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The ell" height depends upon the softenailit" of the

ferrous urden and also on the shaft angle desired-

If the slag fusion occurs at higher temperatures and in a

narro/ temperature range as in the case of pre%flued

urden$ the h"draulic resistance decreases in the

'ertical cross%section and the ell" height can e

correspondingl" reduced-

dell" *-@2 J536*-C+

&elI" *-*<J&

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The hearth is designed such that its 'olumeet/een the iron notch and tu"eres is sufficient

to hold the molten metal and the slag-

The dia of hearth depends upon!

◦ The intensit" of coke consumption-

◦ The ualit" of urden-

◦ The t"pe of iron eing produced-

D hearth *-C)J 3*-7@

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A 'er" approimate relationship et/een the

coke urning rate and hearth diameter isgi'en " the follo/ing euation!D c L *-@

D hearth diameter$ m

L coke throughput$ tonnesK)7hc throughput coefficient /hich 'arieset/een *-)%*-C depending upon urdenpreparation-

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0or highl" prepared urden$ the 'alue of

c *-) has een achie'ed in modern largefurnaces -

Therefore$ for a furnace planned to produce

1*$*** T&M per da" /ith a coke rate of

@** kgKT&M$ i-e-$ a coke throughput of

@$*** tonnes per da"$ the hearth diameter

should e aout 17-1 m-

The 'alue /ill e )1-) m if the 'alue ofc*-C-

CC



4ith increasing diameter of the hearth$the gas penetration must e ensured

" pro'iding adeuate edpermeailit" /ith the use ofmechanicall" strong$ rich$ pre%flued

urden of uniform si>e and lo/ slagulk as /ell as strong lump" coke-

The &earth height should e 10% of thetotal height of the furnace

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The shaft height must e sufficient to allo/ theheating$ preparation and reduction of ore efore

the urden reaches the osh- In the upper

regions of the shaft $ 'olume changes due to

increase in temperature and caron deposition-

These demand an out/ard atter for smooth

flo/ of materials- In the lo/er region of the

shaft $ the material starts fusing and tends tostick to the furnace /all- So to counteract the

/all drag an out/ard utter is necessar"-

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Stack height &stack *-;C &% C-) m

Stack angle

The stack angle usuall" ranges from 85 0 to 87 0

5i6 85 0 for /eak and po/der" ores

5ii6 86 0 for miture of strong and /eak$ lump" or

fine ores5iii6 87 0 for strong$ lump" ore and coke-

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The 'ariations in the angles are necessar"



The 'ariations in the angles are necessar"

for otaining an adeuate peripheral flo/

/hich is an essential pre%reuisite for

forcing of the last furnace-Since the ore hump is located in the

intermediate >one and it mo'es almost

'erticall" do/n/ards pushing the lightercoke to/ards the /all and the ais-

A smaller shaft angle in the case of /eak

and po/der" ore helps to loosen theperipher"-

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Stack angle can e calculated from the formula

Stack angle 56 ot%15D%d1K)Stack &eight6

4here$ D .osh parallel Diameter

d1 Throat Diameter

.osh angle can e calculated from the formula

.osh angle 5O6 ot%15D%dK).osh &eight6

4here$ D .osh parallel Diameter

d &earth Diameter

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4hen the ra/ materials are charged into the

last furnace$ little 'olume change takes placefor a fe/ meters of their descent and hence the

/alls of the throat are generall" parallel Throat diameter can not e too small as it has to

allo/ the enormous 'olume of the gas to passthrough at a reasonal" lo/ 'elocit" to maintain

adeuate solid gas contact and to decrease the

dust emission$ throat hanging and channeling- ont--

C2



Throat diameter can not e too /ide as itma" compact the charge- A certain

'elocit" and lifting po/er of gas is

necessar" for losening the charge at top-

T)#(at Diamete# d t)#(at +0.5, 0.35

)e#e/ + ueul (lume

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A considerale amount of slag and iron descends tothe hearth through the inter%tu"ere >ones- If the" do

so /ithout ha'ing een adeuatel" heated$ the

thermal state of the hearth ma" e distured /ith

attendant high sulphur in iron$ sluggish slag

mo'ement$ erratic metal anal"sis$ freuent tu"ere

urning$ etc-

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The distance et/een the adjacent tu"eres

around the hearth circumference should e such

as to otain$ as far as possile$ a merging of the

indi'idual comustion >ones of each tu"ere into

a continuous ring-

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Capacity →

(THM/Day)

Parameter↓

2000 3000 5000

Useful Vlume (m3) !"00 2550 #250

Ttal Hei$%t (m) 33&0' 3&# #!&22

Useful Hei$%t (m) 2&!! 32&0' 3&2"

*s% Parallel Dia (m) & !!&2 !#&!!

*s% Parallel Hei$%t (m) 2&32 2&55 2&'

*s% Hei$%t (m) #&3" #&'! 5&##

Heart% Dia (m) &! !0&2 !3&"#

Heart% +rea (m2) 5&0# 3& !#'&2"

Heart% Hei$%t (m) 3&30' 3&# #&!22

,tac-/,%aft Hei$%t (m) !"&# !&"" 22&""

T%rat Dia (m) &'" "&'5 &2

*s% +.$le (0) '#&32 '5&'# ''&05

,tac- +.$le (0) '5 '#&55 '3&

s& f Tuyeres 20 25 3#

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This is a unique design in which

large bell is replaced by a distributor

chute with 2 hoppers A rotating chute is provided inside

the furnace top cone

Advantages:Advantages: Greater charge distribution

fleibility !ore operational safety and

easy control over varyingcharging particles "ess wearing parts: easy

!aintenance

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The ad'antages accruing from impro'ed distriution

control can e summarised as follo/s!

Increased producti'it"$ decreased coke rate$ impro'edfurnace life -

Reduced refractor" erosion

Impro'ed /ind acceptance and reduced hanging as /ell

as slips Impro'ed efficienc" of gas utilisation and its indirect

reduction

(o/er silicon content in hot metal and consistenc" in the

hot metal ualit"

Reduced tu"ere losses and minimisation of scaffold

formation

(o/er dust emission o/ing to uniform distriution of fines-

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As has een made clear that e'en the most efficient of the

modern last furnace /ould produce an effluent gas containing a

significant proportion of = /hich could not e used for iron

oide reduction- The actual = content ma" 'ar" around )*%C*F

" 'olume- This has a calorific 'alue of nearl" 2** kcalKmC- The

uantit" of gas produced depends upon the amount of fuel urnt-

0or one tonne of coke urnt nearl" 7*** mC of effluent gas ma"

e produced- &ence a last furnace reuiring 1*** t of coke per

da" /ould generate nearl" 7 1*; mC of gas /ith a total energ"

content of C;** 1*; kcal /hich is nearl" eui'alent to @** t of

coke-

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The effluent gas from the furnace cannot directl" e

used as a fuel since a sustantial uantit" of dust from

the urden is also discharged along /ith- It ma" lead

to accumulation of dust and /ear in the euipment

using the gas- The gas is$ therefore$ cleaned efore its

use and in so doing the sensile heat of the gas is

in'arial" lost- The chemical heat of the cleaned gas

is /hat is utilised-

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The a'erage dust content ma" 'ar" in the range of 7-30 g/m3- In general

cleaning is carried out in three stages viz. coarse, semi-fine and fine

cleaning- The coarse cleaning is done in dust catchers and cyclones in

dr" condition- The dust content of the coarse cleaned gas is nearl" 5-10 g/m3-

The semi-fine cleaning is carried out in scruers$ !entury "ashers$

cyclone se#arators, centrifugal disintegrators, feld "ashers or e'en in

electrostatic precipitators- The dust content is there" reduced to 0$5-1$5

g/m3- ine cleaning is carried out mainl" " electrostatic #reci#itators or at

times " high s#eed rotary disintegrators$ The dust content is there"

reduced do/n to 0&01 g/m3 The semi%fine and fine cleaning is carried out

either in /et or dr" condition- 4et methods are generall" preferred to dr"

methods for their etter efficienc" and smooth /orking-

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T/o adjacent uptakes are joined together to form one single duct

and the t/o such ducts$ thus formed$ are connected to form onl"

one duct /hich carries the gas do/n/ards into the dust catcher-

The do/ncoming pipe or duct is called do/ncomer -

A leeder 'al'e is a safet" de'ice$ /hich opens automaticall" or is

opened$ to release etra pressure de'eloped inside the furnace andthere" eliminate the danger of eplosion-

The uptakes and the do/ncomers are steel pipes and are lined

from inside /ith firericks- The si>es of the uptakes and

do/ncomers and the angle of their joints are such that gas flo/s out

of the furnace smoothl" /ithout an" hindrance-

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The uptakes should e located on the furnace%top

peripher" at those points /hich are not directl" 'erticall"

ao'e the iron%notch$ slag notch$ last main entrance to

the ustle pipe$ etc- These are acti'e points of the

furnace and if the uptakes are located right ao'e these

points it ma" cause une'en distriution of the gas

through the urden- The entire design should also

ensure that minimum of dust is carried form the furnace

/ith the gases-

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It essentiall" consists of a tall c"lindrical structure

comprising of a comustion chamer and heatregenerator unit of checker ricks- The clean last

furnace gas is urnt in the comustion chamer

and the hot products of comustion later heat upthe checker ricks- In this case the sto'e is said to

e on 'on-gas' and is maintained on gas until the

checker ricks are heated to a certain

temperature-

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0iring is stopped and cold last is passed through

checkers /hich impart the heat stored in them and

there " produce preheated last- The sto'e is

said to e 'on blast' . It can continue heating the

last till a certain minimum temperature of the

last is otainale- The sto'e is again put on gas

and the c"cle is repeated-

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The sto'e design and the numer of sto'es$ emplo"ed

should ensure a stead" suppl" of preheated last to thefurnace- This dut" demands that the amount of heat

generated " /a" of comustion of gas per unit time

should e adeuate to heat up the reuired amount of

last to the reuired temperature per unit time$ taking

into account the usual efficienc" of heat transfer 'ia

checker s"stem and the usual heat losses from the

s"stem.

;1



The thermal efficienc" of the sto'e 'aries et/een

<@%2*F- The checker /ork cools more rapidl"

/hereas it takes longer time to heat it up- In practice

a sto'e ma" e on gas for )%7 hours and on last for

1%) hours- 0or an uninterrupted stead" suppl" of

last at specified temperature therefore a atter" of

at least three sto'es is necessar"- A t/o sto'e

s"stem is uite unsatisfactor" and hence three or

four sto'e s"stem is preferred-

;)



The checker/ork has to asor maimum heat at faster rate /hile

heating and should desor heat euall" rapidl" to the incoming coldlast- The larger the /eight of ricks the more /ill e its heat storing

ca#acity& The larger is the surface area eposed as flues the faster is

the heat echange /ith gas- The ricks should ha'e maimum /eight

/ith maimum surface area of flues i.e. maimum openings to allo/ free

passage of gases- 't has een found that a ratio of "eight of ricks

in kilogram to heating surface in s(uare metres of aout 5-) in

minimum& .elo/ this structural difficulties ma" arise-

;C



The checker ricks are supported on steel grids /hich in turn

are supported " cast iron or steel columns- Since the

maimum temperature during comustion is generated near

the dome and since the top portion of checker ricks ha'e to

stand higher temperatures$ /ith progressi'el" decreasing

'alue do/n/ards$ the ualit" of checker ricks used also 'er"

accordingl"- &ea'" dut" firericks are essential for dome

construction- The top C%; m height of the checkers is made up

of higher alumina ricks or semi%silica ricks /hile the

remainder as of good ualit" firericks-

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;@



#.-&#.6t0.5-0.6t1.7-1.8t

2500 m3

0.6t1t

FuelReducing agent u!!l"ermeable bed/spacer0

3200m3

+

80kg dust

;;



;<



;+



;2



*ichness! Richness means the percentage ofmetallic iron in the ore- e-g- In order to produce atonne of pig iron aout1-@tonnes of ore is reuiredin Australia 5;+F 0e6$ aout ) tonnes are reuired

in India 5@@%;*F6 and nearl" C tonnes are reuiredin H-,- 5C*%C@F6

+om#osition of the gangue ! Thecomposition of gangue associated /ith an ore

ma" reduce the 'alue of an other/ise rich ore orin some case ma" e'en enhance that of a leanore-

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e-g- 3alue of an ore is drasticall" reduced " the

presence of alkali oides $ reduced to some etent

" the presence of alumina and is in fact

enhanced " the presence of lime andKor

magnesia-

ocation! The location of an ore$ oth

geographical and geological$ is 'er" important

reatment and #re#aration needed

efore smelting

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old strength #orosit" Decrepitation (o/%temperature reakdo/n under reducing

conditions 5(T.6 &ot compression strength Softening temperature and range S/elling and 'olume change &igh%temperature ed permeailit" under

compressi'e load and reducing conditions-

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old strength measurement comprises of tumler or

drum test for aradiilit"$ shatter test for impact and

compression test for load during storage-

umler or drum test. It measures the susceptiilit" of

ferrous materials 5coke as /ell6 to reakage due to

arasion during handling$ transportation$ charging on to

the last furnace ells as /ell as inside the furnace itself-

'n this test$ a certain /eight of the material /ithin a

selected si>e range is rotated in a drum of gi'en si>e for

a gi'en time /ith certain numer of re'olutions-

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The arasion strength is gi'en " the percentage

/eight of ;-C mm sur'i'ing the test and dust

inde " the percentage of % *-; mm- 0or good

pellets the respecti'e percentages are +@%2@ and

C%<$ for sinters ;*%+* and @%1* and for ores the"

'ar" greatl"$ ;*%2@ and )%)@-

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The arasion strength is gi'en " the percentage

/eight of ;-C mm sur'i'ing the test and dust

inde " the percentage of % *-; mm- 0or good

pellets the respecti'e percentages are +@%2@ and

C%<$ for sinters ;*%+* and @%1* and for ores the"

'ar" greatl"$ ;*%2@ and )%)@-

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In order to minimi>e the amount of fines deli'ered to the

furnace$ a practice attracting an interest is to delieratel"

suject the materials$ especiall" coke and sinter$ to

mechanical reakdo/n and staili>e the charge$ e-g-$ "

means of 'irating screens- The" reak /here the onds are

/eak and the undersi>e screened out-

&o/e'er$ it cannot e helped if an" fines are generated

et/een charging into the skip car and then into the furnace-

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In order to minimi>e the amount of fines deli'ered to the

furnace$ a practice attracting an interest is to delieratel"

suject the materials$ especiall" coke and sinter$ to

mechanical reakdo/n and staili>e the charge$ e-g-$ "

means of 'irating screens- The" reak /here the onds are

/eak and the undersi>e screened out-

&o/e'er$ it cannot e helped if an" fines are generated

et/een charging into the skip car and then into the furnace-

<<



Shatter test! It measures the susceptiilit" to reakdo/n due to

impact during loading$ unloading and charging into the furnace-

In this test a certain /eight of material is allo/ed to fall on a steel

plate from a certain height for a pre%determined numer of times

and the amount of undersi>e measured- 0or strong sinters the

percentage 1*mm sur'i'ing is ao'e +*-

+om#ression test! It is used mainl" for pellets- #ellets$ unreduced

or reduced to 'arious degrees$ are sujected to compressi'e load at

amient or high temperatures and the percentage of @ mm "ieldmeasured and correlated /ith last furnace performance-

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orosity! 4hile ores and pellets possess mostl" open pores$ in

sinters there are macro% and micro%pores as /ell as open andclosed pores 5cut off from outside and cannot e reached "

gas6-

True porosit" and hence closed porosit" can e determined from

open porosit" /hich can e measured from the true and ulk

densities-

Although reduciilit" increases /ith increasing open porosit"$ the

latter changes continuousl" during reduction on load- Generall"$

a high initial porosit" results in earlier softening of the material-

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Decrepitation ! 4hen iron earing materials are suddenl"

eposed to the ehaust gas temperature at the stock le'el on

charging$ reakdo/n ma" occur due to thermal shock- This is

kno/n as decrepitation-

Eperimentall" it is measured " dropping a kno/n /eight of

material in a furnace pre'iousl" heated to a temperature le'el

of 7**;**P$ under normal atmosphere$ inert atmosphere or

under mildl" reducing conditions- After the charge attains the

temperature it is remo'ed$ cooled and sie'ed to measure the

reakdo/n-

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In a t"pical test @** g of )*%7* mm si>e undried ore is

dropped in a furnace pre'iousl" heated to a temperature

le'el of 7**P and retained there for C* min under a flo/

rate of @*** litres of nitrogen per hour- The sample is

then remo'ed$ cooled and the percentage of *Q@ mm and

%@Q; *Q@ mm material in the product is determined "

sie'ing-

It is elie'ed that ores /ith more than 1*F porosit" /ill

not decrepitate-

+1



In a t"pical test @** g of )*%7* mm si>e undried ore is

dropped in a furnace pre'iousl" heated to a temperature

le'el of 7**P and retained there for C* min under a flo/

rate of @*** litres of nitrogen per hour- The sample is

then remo'ed$ cooled and the percentage of *Q@ mm and

%@Q; *Q@ mm material in the product is determined "

sie'ing-

It is elie'ed that ores /ith more than 1*F porosit" /ill

not decrepitate-

+)

o"-em#erature reakdo"n est &&&&2



2

It has een oser'ed in the eperimental last furnace that the iron

earing materials do disintegrate at lo/ temperatures under mildl"

reducing conditions$ that is in the upper part of the stack$ affecting

the furnace permeailit" and conseuentl" the output ad'ersel"- It is

elie'ed that deposition of caron in this region of the stack is also a

contriutor" factor although /ith sinters the reakdo/n has een

associated /ith the presence of micro%cracks-

In essence the test consists of sujecting the charge to static ed

reduction at lo/ temperatures in a rotating furnace for a fied dura

tion- The percentage of fines generated is uoted as the

(- T-.- T- inde- +C



+7



(ump ores$ sinter and pellets disintegrate into smaller pieces during their

do/n/ard tra'el through the last furnace o/ing to the /eight of the

o'erl"ing urden$ as /ell as arasion and impact et/een the urden

materials-

It has een found that this tendenc" gets aggra'ated /hen the oides are in

a reduced state- Reduction of hematite into magnetite occurs in the upper

stack at @**%;**P$ and this is accompanied " 'olume epansion e'en to

the etent of )@F-

This results in compressi'e stresses eing de'eloped and contriutes

significantl" to reakdo/n of the iron oides-

.last furnace operators prefer a lo/ RDI 5elo/ )+ or so6 since the ad'erse

effect of high RDI has een clearl" demonstrated in practice-

+@



+;



*educiility is the ease /ith /hich the o"gen

comined /ith iron can e remo'ed indirectly .

A higher reduciilit" means a greater etent of

indirect reduction that ma" e otained in the

last furnace resulting in a lo/ered coke rate

and higher producti'it"-

+<



Reduciilit" of ferrous materials is characteri>ed " their

fractional o"gen remo'al rates in gaseous reducing

atmosphere- The percent degree of reduction or percent fractional o"gen remo'al is gi'en "

4here

n* numer of moles of o"gen originall" comined /ith iron onl"

n numer of moles of o"gen left comined /ith iron after eper i

mental time$ t-

++



A schematic representation of relationship et/een reduction at

7*F degree of reduction and ;*F degree of oidation le'els$

+2



2*



he reduction of the iron oides takes #lace in a series of

se(uential ste#s& he o!erall rate "ill e determined y the

slo"est of the #rocess or #rocesses in the series& he #ossile

consecuti!e ste#s are.

trans#ort of gaseous reductant from the ulk gas #hase to the

#article surface through a oundary gas film4

molecular diffusion of the gaseous reductant through the

#roduct layer to the reaction interface4

adsorption of the gaseous reductant at the interface1

reaction at the interface /reaction between adsorbed

reductant and o23gen of the lattice01

21



desor#tion of gaseous #roducts from the interface4

mass trans#ort of iron and oygen ions and transformations in the

solid #hase4 formation and gro"th of the reaction #roducts, !i&,

magnetite, "ustite and iron4 &

molecular diffusion of gaseous #roducts through the #roduct layer

to the #article surface4 ,

trans#ort of the gaseous #roducts from the #article surface

through the oundary gas film to the ulk gas #hase&

rom the ao!e #ossiilities, the rate limiting cases are.

chemical control 6 ste#s iii2 to !i2

diffusion control 6 ste#s i2 and !iii24 ii24 !i2 and !ii2

2)



particle si>e porosit"

cr"stal structure pore si>e 'olume change impurities

2C



Reduction of natural hematite ores " = or &) starts et/een )**%

@***$ depending upon the ph"sical characteristics and

mineralogical composition- &o/e'er$ the rate elo/ @*** is

sluggish-

&ematite is more reducile than magnetite although the amount of

o"gen to e remo'ed per unit /eight of iron is aout 1) percent

higher in the former-

The etter reduciilit" of hematite ma" e due to!

formation of porous /ustite from hematite$ easil" accessile to

reducer gas /hereas magnetite forms dense /ustite during

reduction

27



tendenc" of hematite to reak do/n and epose larger

surface due to epansion in 'olume during reduction to

magnetite

pores in hematite are more elongated and the microporosit"

larger magnetite has larger grain si>e and is more closel"

packed

a higher 'alue of o'erall rate constant for /ustite reduction

since the /ustite lattice formed during reduction of hematiteehiits a higher degree of disorder than that formed from

magnetite-

2@



2;



Since the last furnace is a counter%current process$ the tu"ere gas/ith high =%content comes into contact /ith the /ustite /hich

needs a 'er" high reduction potential for con'ersion to 0e- The

resulting lo/er potential gas$ as it ascends$ encounters magnetite

and hematite /hich reuire much smaller euilirium =K*) ratios

for reduction to lo/er oides- &ence$ the reduction of /ustite is of

prime importance in iron oide reduction$ especiall" ecause aout

<* percent of hematite o"gen is present as /ustite.

2<



2+

The efficienc" of operation of a last furnace ma" e




measured in terms of coke rate /hich should of course

e as lo/ as possile- The achie'ement of a satisfactor"

coke rate depends on optimising the etent to /hich the

caron deposition reaction proceeds- If the top gas is

high in *) sensile heat is carried from the furnace as a

result of the eothermic reaction-

)==)

If on the other hand the top gas is high in =$ chemical

heat lea'es the furnace-

22



1**



1*1

he comustion of caron to its monoide yields only aout 8



#ercent of the total heat #ossile to e otained and only oidation to

the dioide gi!es the largest amount of heat&

his has a great significance in the last furnace #rocess "here aout

30-90 #ercent of the coke caron is oidised to +: and the rest into

+:&

'n the last furnace aout half of the heating !alue of caron is

otained for a to# gas +:/+: ratio of & he rest is carried a"ay in the

outgoing gas&

;lthough a #art of this heat is redeemed y urning the gas out of the

furnace, it means con!ersion of e#ensi!e metallurgical coke to a gas

"hich could e otained from a less !aluale fuel&

1*)



he heat !alues in the gi!en e(uations are for #ure caron& or

a good (uality coke "ith 8)% +, the res#ecti!e !alues "ill eaout 000 and 7000 kcal/kg&coke&

+aron dioide, in the asence of caron, is stale at high

tem#eratures&

<# to aout 000=+, its thermal dissociation is small& ;t

atmos#heric #ressure, it amounts to aout #ercent&

;t high tem#eratures, caron dioide is unstale in the

#resence of caron and is reduced to caron monoide

according to the gi!en e(uation&

1*C



his is generally kno"n as oudouard or caron gasification

reaction and is highly endothermic4 the re!erse reaction is

eothermic and is called caron de#osition reaction& he

former reaction is of etreme im#ortance for the economy and

smooth running of the last furnace& 't occurs at high

tem#eratures, ao!e aout 10000+, and therefore consumes an

enormous amount of heat in the lo"er third of the last furnace&

he caron de#osition reaction is most #ronounced at

tem#eratures 500-550=+ and conse(uently takes #lace in the

u##er #ortion of the shaft&

1*7



1*@

Since moles of +: are #roduced from 1 mole of +:7

i lid2 th d d ti i



caron eing solid2, the oudouard reaction is

de#endent on #ressure&

he isoars in the #re!ious figure sho" that at any gi!en

tem#erature the e(uilirium %+07 increases "ith

increasing #ressure& he staility of +: decreases "ith decreasing

tem#erature and increasing #ressure& he maimum

instaility is et"een )00 to 800=+ as sho"n y the stee#

slo#e of the cur!es&

1*;



he reaction !elocity ecomes so slo" elo" aout

900=+ that a negligile amount of +: is decom#osedinto +: and +&

he reaction is accelerated in the #resence of catalysts

"hich #ro!ide nucleation sites for de#osition of caron& 'n the #resence of catalysts, the re!erse of reaction

accelerates ao!e 900=+ and reaches a maimum

et"een 500-5500

+&

1*<

hemical Influence



It is /ell kno/n that the reduction rate of /ustite is critical in the

o'erall kinetics of iron oide reduction-

The euilirium partial pressure or concentration of =) /ould

decrease if ae:

is lo"ered " solution andKor compound

formation- &ence$ the reduction rate /ould also decrease-

1*+



Natural ores can contain iron oides as compounds /ith gang materials$ such as$

)0e=-Si*)$ 0e=-AI

)*

C$ 0e=-r

)*

C$ 0e=-Ti=

) etc /here /ustite eists in a state of lo/

acti'it"- The acti'it" of /ustite can also decrease /hen it undergoes sintering /ith the

impurities present$ such as Si=)$ Al)=C etc-

1*2

The reduction rate of ore increases /ith increase in linear 'elocit" of



"

the reducing gas due to the reduction of the oundar" la"er

thickness at the ulk%gasKparticle interface- After a critical gas'elocit" is reached$ there is no further increase in the rate /ith

increasing gas 'elocit" since the o'erall rate ecomes controlled or

limited " other processes- The figure sho/s that the limit is only

0&9 m/s- The figure also sho/s that the critical !elocity is

inde#endent of the degree of oidation- In last furnace$ the

linear gas 'elocit" does not affect the reduction rate since it ranges

et/een 1%)* mKs and is often eceeded-

11*



111

0or the reduction of iron ores the reducing gas has to diffuse



0or the reduction of iron ores the reducing gas has to diffuse

into the interior of the od" /here transformations can occur-

In general$ the reduction rate increases /ith temperature ut

the degree depends upon the mechanism of the reaction -

The o'erall reduction rate depends upon the relati'e

contriutions of chemical control and gaseous mass

trans#ort and hence depends upon the particular reactions

occurring and the reaction temperature- Since chemical

reaction has higher acti'ation energ" than gaseous diffusion$

the former /ill increase at a muchQ greater rate /ith increase

in temperature than the latter-

11)

&ence a stage /ill arri'e /here diffusion /ill ecome rate%



&ence$ a stage /ill arri'e /here diffusion /ill ecome rate

controlling- Depending upon the degree of reduction$ at lo"er

tem#eratures of aout 500-)00=+, the chemical reaction

rate controls the reduction rate forming "hat is kno"n as

the kinetic region in the last furnace& ;t tem#eratures

ao!e )00=+, gaseous diffusion ecomes the dominant

rate controlling mechanism& The temperature regime in the

last furnace shaft is such that it can e assumed a >one of

mied%control eists-

11C



Reactions /ith high acti'ation energies are 'er"

temperature sensiti'e- on'ersel"$ lo/ acti'ation

energies impl" lo/er temperature sensiti'it" of rate-

Temperature sensiti'it" of rate is more pronounced at

lo/er temperatures-

The pre%eponential factor in Arrhenius la/ has little

effect on temperature sensiti'it" of reaction rate-

117



11@



In the last furnace $ the reducing gas is

predominantl" = /ith 'ar"ing amounts of

h"drogen depending upon the moisture content of

the last and other last additi'es like fuel oil or

natural gas- Stud" sho/s that a miture of = and

h"drogen appears to e a more efficient reductant

than either of them-

11;

RAW MATERIALS for BFRAW MATERIALS for BFCOKECOKE



Why COKE, not COAL? Why COKE, not COAL?

1.1. Natural COAL is too dense and fragile to be used in the modern BF.Natural COAL is too dense and fragile to be used in the modern BF.(a) The blast will not be able to penetrate it quickly for burning.(a) The blast will not be able to penetrate it quickly for burning.

(b) It is not strong enough to stand nearly 25 m high burden lying over(b) It is not strong enough to stand nearly 25 m high burden lying overit.it.

(c) The volatiles present will be released in the BF(c) The volatiles present will be released in the BF

However, we need C for giving heat and to reduce iron ore intoHowever, we need C for giving heat and to reduce iron ore intoiron metaliron metal

Can COAL properties be improved for this purpose?Can COALproperties be improved for this purpose?1.1. Yes, fortunately certain coals when heated out of contact with air Yes, fortunately certain coals when heated out of contact with airresult in a carbonaceous mass, which is strong, porous, volatile free,result in a carbonaceous mass, which is strong, porous, volatile free,

just suitable for use in BF. just suitable for use in BF.

This carbonaceous mass is called COKE and this coal is called This carbonaceous mass is called COKE and this coal is calledMETALLURGICAL COAL or COKING COAL.METALLURGICAL COAL or COKING COAL.

COKECOKE

11<

Reserves of metallurgical coals inReserves of metallur

gical coals inINDIAINDIA



Coal Fields

quality

Gross

Reserve (Mt)

Net Reserve

(Mt)

Prime Jharia

Coking (IX seam & above)5288 2312

Medium Jharia, Ram-

Coking garh, Raniganj20388 2752

Semi to Raniganj, Jha-

weakly ria, Jhilimili-Coking Sonhat

2067 47728

Total 27733 5569

11+

Types of typical metallurgical coals T

ypes of typical metallurgical coals



Type %F.C.

% H2 % V.M.

Cal.

Value

Kcal/kg

%Moist

ure

Prime coking 88-91 4.8-5.2 23-32 8800 1

Medium coking (HV)

Medium coking (LV)

86-88

90-91

5.1-5.44.7-4.9

22 max

22-32

8600

8800

1-2

1-2

Semi-coking

Weakly coking

83-85

83-84

5.4-5.8

5.1-5.6

37-44

38-46

8300

8300

2-3

3-5

112

FUNCTIONS OF COKEFUNCTIONS OF COKE



Coke fulfils the following major roles in a BF:Coke fulfils the following major roles in a BF:

1.1.It is a fuel – provides heat for endothermic chemical reactions andIt is a fuel – provides heat for endothermic chemical reactions andmelting of slag and metal.melting of slag and metal.

2.2. It produces and regenerates the reducing gases for the reduction ofIt produces and regenerates the reducing gases for the reduction ofiron oxides.iron oxides.

3.3. It provides an open permeable bed through which the slag and metalIt provides an open permeable bed through which the slag and metalmove down to hearth and hot reducing gases move upwards.move down to hearth and hot reducing gases move upwards.

4.4. It supports the overlying burden load specifically at the lowerIt supports the overlying burden load specifically at the lowerlevels/regions.levels/regions.

5.5. It carburizes iron thereby lowering its melting pointandIt carburizes iron thereby lowering its melting pointandconsequentlythe working temperature of the BF is reduced.consequentlythe working temperature of the BF is reduced.

1)*

QUALITY REQUIREMENTS

QUALITY REQUIREMENTSOF COKEOF COKE



Coke must possess the following properties:Coke mustpossess the following properties:

1.1.Proper chemical composition w.r.t. Fixed Carbon, ash, S, P etc.Proper chemical composition w.r.t. Fixed Carbon, ash, S, P etc.

2.2. Proper reactivity- (a) area exposed to blast, (b) temperature andProper reactivity- (a) area exposed to blast, (b) temperature andpressure of the blast, (c) affinity of the particular type of carbon forpressure of the blast, (c) affinity of the particular type of carbon foroxygen.oxygen.

3.3. Proper size range.Proper size range.4.4. Thermal stability at high temperature: (a) absence of large lumps, (b) Thermal stability at high temperature: (a) absence of large lumps, (b)uniform texture, (c) minimum inert inclusions, (d) high carbonisationuniform texture, (c) minimum inert inclusions, (d) high carbonisationtemperature and heat soak, (e) prior mechanical conditioning and (f)temperature and heat soak, (e) prior mechanical conditioning and (f)low chemical reactivity.low chemical reactivity.

5.5. Proper strength and abrasion resistance.Proper strength and abrasion resistance.

1)1

QUALITY REQUIREMENTS

QUALITY REQUIREMENTSOFCOKEOFCOKE



Value of coke is assessed in terms of its: Value of coke is assessed in terms of its:

1.1.Room temperature strength.Room temperature strength.

2.2.High temperature strength.High temperature strength.

3.3.Reactivity (RI).Reactivity (RI).

4.4.Chemistry andChemistry and

5.5.Strength after reduction (CSR)Strength after reduction (CSR)

OF COKEOF COKE

1))

INDIAN STANDARD SPECIFICATIONINDIAN STANDARD SPECIFICATIONFOR BF COKEFOR BF COKE



Characteristics

Grade I

Requirements

of Grade II Grade IIIProximate analysis (dry) %

Ash (max)

V.M. (max)

S

P

20

2

0.70

0.30

24

2

0.70

0.30

28

2

0.70

0.30

Shatter Index:Over 38 mm (% max)

Over 13 mm (%max)

Micum Index:

over 40 mm (% min)

Through 10 mm (% max0

85

97

75

14

8597

7514

--

-

-

Stability factor:

On 25 mm (% min)

Porosity, %

40

35-48

40

35-48

-

-

1)C

MODIFICATIONS IN COKEMODIFICATIONS IN COKEMAKINGPRACTICEMAKINGPRACTICE



The modifications include: The modifications include:

1.1.Pre-heating.Pre-heating.

2.2.Briquette blending.Briquette blending.

3.3.Stamp charging.Stamp charging.

4.4. Admixing oil in the charge. Admixing oil in the charge.

5.5. Admixing water in the charge. Admixing water in the charge.

6.6.Using a better coal blend.Using a better coal blend.

MAKING PRACTICEMAKING PRACTICE

1)7

COMPARISON OF EFFECT OFCOMPARISON OF EFFECT OFSOME PARAMETERSSOME PARAMETERS



Parameters

Conventional

Charging

Briquette.

blending

Binder-

less briq-uetting

Pre-

heating

Stamp

charging

Bulk Density of

coal charge(kg/m2)700-750 750-800 750-800

800-

850

1100-

1200

M 10 of coke

CSR of coke

Oven throughput I

10-11

30-40

100

8.5-9.5

35-45

105-110

9-9.5

35-45

105-110

8-9

45-50110-

115

5.5-6.5

60-65112-

115

Maintenance

requirement index100 105 100-105

150-

175

110-

115

1)@

The function of coke in the last furnace is fi'e%fold$ namel"$



5i6 it acts as a fuel " pro'iding for the thermal reuirements in the furnace$ the

reaction eing$

) =) )=! &* % )C** kcalKkg-

=n complete comustion to L) the heat e'ol'ed is +1@* kcalKkg-- Thus onl"

aout )+ percent of the otainale heat is supplied " coke

5ii6 it pro'ides = for the reduction of iron oides

5iii6 it reduces the oides of metalloids$ such as$ Mn$ Si$ # and others if present

5i'6 it caruri>es the iron and lo/ers its melting point

5'6 it pro'ides permeailit" 5in the dr" as /ell as the /et >ones6 and alsomechanical support to the large charge column$ permitting the gases to ascend

through the 'oids-

1);

oke is the uni'ersal fuel used in the last furnace It acts



oke is the uni'ersal fuel used in the last furnace- It acts

oth as a reductant as /ell as a supplier of heat- It alsocomprises the major portion of iron production cost- No/%a%

da"s other fuels are also eing used as part replacement of

coke- These fuels cannot e charged from the top and as

such the" are injected into the furnace through the tu"eres

along /ith the last- In some countries$ especiall" in .ra>il$

charcoal is used as a last furnace fuel-

1)<

+oke sie. oke comprises aout @*%;* percent of the 'olume of the



charge material- The coke si>e is important as it pro'ides

permeailit" in the dr" as /ell as in the /et osh >one he coke sie

is al"ays 3-9 times larger than the ore sie, since coke is partiall"

urnt as it descends- It also has a lo/er densit"$ and hence a greater

tendenc" for fluidisation- =f course$ in the lo/er osh region of a

last furnace$ coke is the onl" solid that remains$ and /hich helps to

support the urden- he o#timum sie range for lum# ore is 10-30

mm and for coke is 90-80 mm- Since the coke si>e ecomes

smaller as it descends through the last furnace due to mechanical

reakdo/n$ gasification$ attrition$ etc-$ the factor of prime importance

is the strength of coke-

1)+

oke strength! Mechanicall" considered$ it is the ualit" cohesion that



pre'ents the coke from collapsing and tends to a'oid the formation of

small particles- >igh cohesion or strength is related to se!eral coke

making #ro#erties- =n the asis of reakage " impact$ compression

or arasion$ the coke strength should e assessed oth at amient as

/ell as high temperatures- Studies of the structure of different coke

samples sho/ that the est 'arieties ha'e a regular distriution of pores!

/ith adeuate thickness and hardness of the /alls et/een the pores

and are free from cracks generated internall"- Such a structure ensures

/ithstanding of high compressi'e forces and high temperatures in the

all%important lo/er furnace-

1)2



he strength of coke #roduced in the coke-o!ens is

influenced y. lending ratio of coals of 'ar"ing caking components and

proportion of the firous portion

particle si>e and distriution of charging coal

coke%o'en temperature and comustion conditions

moisture and addition of oil

soaking time

/idth$ height and method of heating-

1C*

;sh and moisture content in coke& (o/ moisture : ash content

are desirale in metallurgical coke



are desirale in metallurgical coke-

(o/ moisture in coke can e achie'ed " suitale control of the

/ater suppl" during uenching- That is /h" dr" uenching using

inert gas has een suggested ut dr" coke is dust" and can create

handling nuisance- ?etallurgical coke should contain @ 1&5%

moisture& Aach additional 1% >0 in last furnace coke

increases fuel consum#tion y 1&%&

?aimum desirale ash in metallurgical coke is 8-10%& Each

additional 1F ash in last furnace coke increases fuel consumption

" )F- In addition$ high ash content ecomes 'er" undesirale$ if it

causes troule in fusion- Also$ 'olume of slag produced in last

furnace ecomes more /ith the use of high ash coke resulting in

reduction of the useful 'olume of the last furnace and hence

production of pig iron from last furnace is reduced- &igh ash cokehas high resistance to arasion and has high strength-

1C1

Density B orosity& The more completel" the coal is de'olatalised$ the

more closel" the densit" of coke approach that of the graphite (i.e. )-C6-

oking follo/s formation of a porous structure /hich increases in



oking follo/s formation of a porous structure /hich increases in

densit" " shrinkage during further heating at a high temperature- Since

all cokes contain traces of h"drogen and mineral matter of the coal$ itsasolute densit" ne'er reaches that of graphite- The higher the rank of

the coal$ the higher is the densit" of coke made 53aries from 1- < to 1-2@

for F in coal from +1 to +2F6-

4ith increase in time and temperature of caroni>ation 5/ith faster

heating rate6 the densit" of the coke increases /hile the porosit"decreases- Denser coke are stronger and harder- An important propert"

of coke for its storage and transport is its ulk density-

&igh porosit" is desirale in furnace cokes to otain high rates of

comustion-

'n last furnace, high strength is considered more im#ortantecause coke has to e dropped in the last furnace from a great height

and it should not reak efore reaching the hearth for etter

performance and reduciilit" in the furnace-

1C)

It th i t f k t k i t i f it



It measures the resistance of coke to reakage " impact i.e. of its

strength- @* l- of ) inches si>e coke is placed in a rectangular o

of dimension )+? 1+? 1@? placed ; ft ao'e a steel ase plate

inch thick- The hinged ase of the o is released suddenl"$ /hen

the content drop onto the ase plate-

.o is dropped se'eral times and coke is then screened through a

series of sie'es made of suare stamped sheet- The percentage of

coke retained on )?$ 1-@? and *-@? sie'es are recorded and called

shatter inde- Desirale 'alues of shatter inde for last furnace

coke are +*F on )? screen$ 2*F on 1-@? screen and 2<F on *-@?

screen-

1CC

This is a measure of oth hardness and strength of the coke @* kg of



This is a measure of oth hardness and strength of the coke- @* kg of

coke of @* mm si>e is rotated in the micum drum for 7 minutes at the

rate of )@ rotation per minute 5rpm6- Micum drum is a c"linderical steel

drum 5/hose length and diameter oth are 1 metre each6 fitted

length/ise /ith four angle irons 51** @* 1* mm6 2*P apart inside the

drum- After rotating the coke$ it is taken out and screened through ;*

mm$ 7* mm$ )* mm and 1* mm round hole screen-

The percentage of coke retained on a 7* mm screen is called M7* inde

5Micum fort" inde6 /hereas$ the percentage of coke that passes

through a 1* mm screen is called M1* inde 5Micum ten inde6

1C7



M7* gi'es the resistance of the coke to reakage " impact i.e. it is a

measure of the strength of the coke- M1* gi'es the resistance of the coke toreakage " arasion (i.e. ruing6 and it is a measure of hardness of the

coke-

>igh ?90 and lo" ?10 !alues are desirale for metallurgical coke- As

per ISI minimum M7* inde should e <@F and maimum M1* inde should

e 17F for metallurgical coke-

or use in 000 m3 !olume last furnace, coke ?90 should e more

than 78 and ?10 should e less &than 10&

1C@

't is defined as the aility of coke to react "ith :, +: or steam



>:6-

More reacti'e cokes ha'e higher thermal 'alues of their 'olatile matter-

oke of high reacti'it" ignites easil" and gi'es rapid pick up of fuel ed

temperature- &o/e'er$ lo/ reacti'it" coke gi'es a higher fuel ed

temperature than a highl" reacti'e coke

Reacti'it" is in'ersel" proportional to the asolute densit"- It is affected

" the presence of easil" reducile iron compounds in ash-

oke of high reacti'it" is otained from /eakl" caking coals or lends-

Strongl" coking$ high rank coals produce coke /ith lo/ reacti'it"-

1C;



rom a chemical stand#oint, the coke should e of

lo" reacti!ity& The 'ertical distance of the indirect

reduction >one of +**%1***P$ i-e-$ the residence time of

ore in this >one can e increased if the coke gasificationtemperature e raised /hich is possile " the use of

less reacti'e coke- As for eample$ it is reported that an

increase of reacti'it" " 1**F results in an increase inthe coke rate et/een C*%<*kgKT&M

1C<

or last furnace coke sie and hardness are more



or last furnace coke, sie and hardness are more

im#ortant than reacti!ity& Satisfactory hearth tem#erature is

otained "ith unreacti!e coke containing little reee&

Reacti'it" of coke is measured " ritical Air .last method and is

reported as ritical air last ( CAB ) 'alue of coke- The +;

'alue of coke is the minimum rate of flo/ of air in ftCKminute

necessar" to maintain comustion in a column of closel" graded

material 517 to )@ .-S-6 /hich is )@ mm deep and 7* mm in

diameter- The t"pical A. 'alue for o'en coke is *-*;@

ftCKminute- More reacti'e coke has got lo/er A. 'alue-

1C+

Another modern and current method of epressing the reacti'it" and

strength of coke is Coke Reactivity Index (CRI) and Coke Strength



g y ( ) g

Ater Reaction (CSR) /hich is eing follo/ed in Indian steel plants-

+oke *eacti!ity 'nde +*'2&

To determine RI$ )** gm of coke sample 5si>e )* % )@ mm6 is taken in

a stainless steel tue and heated in electric furnace to 11**P- =) gas at

@ kgKcm) pressure is passed through the coke ed for t/o hours- =formed 5" reaction =) )=6 is urnt in a urner and is ehausted

out- aron of coke reacts /ith =) 5depending upon the reacti'it" le'el

of the coke6 and there is a loss of /eight of coke depending upon its

reacti'it"- More is the loss in /eight of the coke$ reacti'it" is more- F loss

in /eight of coke is reported as coke reacti'it" inde 5Rl6- 'deal +*'!alue of a good last furnace coke should e aout 0%& y#ically

+*' of 'ndian last furnace coke is aout 5%&

1C2



oke Strength after Reaction 5SR6- The left out coke

from the RI determination test is rotated for ;* rotation

in a micum drum- And the F of coke retained on a 1*

mm si>e screen is reported as coke strength after

reaction 5SR6- Stronger the coke$ more is its SR

'alue- Ideal 'alue of SR for last furnace coke is a

minimum of aout @@F- T"picall" SR of Indian last

furnace coke is aout ;*%;@-

17*

;gglomeration of 'ron :re ines



;gglomeration of 'ron :re ines

Aout ;@ 9 <@ F of iron ore gets con'erted into fines5 % @ mm 6 during 'arious operations from mining to con'ersion

into (=- Majorit" of these fines are eported to other countries

at thro/a/a" price resulting in greater financial loss to the

nation- Most /idel" used methods for the agglomeration of these

fines to render them useful for .0 are Sintering and #elleti>ation-

Sintering 9 inte#ing i eentiall" a !#(ce ( )eating

( ma ( ne !a#ticle t( t)e tage ( inci!ient ui(n

(# t)e !u#!(e ( aggl(me#ating t)em int( lum!.

171



To increase the si>e of ore fines to a le'el acceptale

to the .0

To form a strong and porous agglomerate

To remo'e 'olatiles like =) from caronates$ S from

sulphide ores etc

To incorporate flu in the sinter

To increase the .0 output and decrease the coke rate

17)

Iron ore sintering is carried out " putting a miture Iron



Iron ore sintering is carried out " putting a miture Iron

earing fines mied /ith solid fuels on a permeale ed- The

top la"er of sinter ed is heated up to the temperature of 1)**

% 1C*** " a gas or oil urner- The comustion >one initiall"

de'elops at the top la"er and tra'els through the ed raising

its temperature la"er " la"er to the sintering lael- The cold

last dra/n through the ed cools the alread" sintered la"er

and gets itself heated-

17C



In the comustion >one$ onding takes placeet/een the grains and a strong and porous

aggregate is formed- The process is o'er /hen

the comustion >one reaches the lo/est la"er of

the ed- The screened under si>e sinter isrec"cled and o'er si>e is sent to .-0-

177



17@

T/o t"pes of onds ma" e formed during sintering-

Diffusion or *ecrystalliation or Solid State ond . It is formed as a result of



recr"stalli>ation of the parent phase at the point of contact of t/o particles in solid

state and hence the name-

Slag or Class ond. It is formed as a result of formation of lo/ melting slag or glass

at the point of contact of t/o Qparticles$ depending upon the mineral constitution$ flu

addition$ etc-

As a result the sinter can ha'e three different t"pes of constituents!

=riginal mineral /hich has not undergone an" chemical or ph"sical change during

sintering-

=riginal mineral constituents /hich ha'e undergone changes in their ph"sical

structure /ithout an" change in their chemistr"- Recr"stalli>ation is the onl" change

at some of the particle surfaces-

Secondar" constituents formed due to dissolution or reactions et/een t/o or more

of the original constituents

17;

The proportion of each of the ph"sical and chemical change during



sintering depends upon the time-tem#erature cycle of the process-

The higher is the temperature more /ill e the proportion of ne/

constituents " /a" of solutions and interactions /hereas lo/er is

the temperature and longer is the duration more is the process of

recr"stalli>ation in solid state-

The more is the slag onding$ stronger is the sinter ut "ith less

reduciility and$ more is the diffusion onding$ more is the

reduciility ut less is the strength- Since ores are fairly im#ure

slag ond #redominates& :n the other hand in rich sinters slagond is of minor im#ortance&

17<



17+

The area under the time tem#erature cur!es



The area under the time-tem#erature cur!es

essentially determines the nature and

strength of the onds de!elo#ed during

sintering of a gi!en mi& or a gi!en mi it is

most unlikely the onds of sufficient

strength "ill e formed elo" a certaintem#erature le!el "ithin a reasonaly short

time& >ence the area under the cur!e ao!e a

certain tem#erature, "hich may e around

1000=+ for iron ores, is the effecti!e factor indeciding the etent of sintering

172

rather than the "hole area under the cur!e from

room tem#erature to the comustion tem#erature



room tem#erature to the comustion tem#erature

le!el& he nature of the time-tem#erature gra#h "ill

de#end u#on the rate of heating and cooling of a

gi!en mi& he nature of this gra#h is of #aramount

im#ortance in assessing the sintering res#onse& hefactors that affect this cur!e are then the !ariales of

the #rocess and "hich should e adusted #ro#erly

for otaining effecti!e sintering&

1@*

. d ilit



.ed permeailit"

Total 'olume of air last dra/n through the ed

#article si>e of iron ore

Thickness of the ed

Rate of last dra/n through the ed Amount and ualit" of solid fuel incorporated in the sinter

miture

hemical composition of ore fines Moisture content in the charge

1@1

During sintering$ heat echange takes place et/een the solid charge



and air dra/n- At an" time$ the air takes the heat from comustion >one

and then transfers to the lo/er la"er of the ed- or faster rate of heat

echange, the !olume of air dra"n should e more- If suction rate of

air is too high$ transfer of heat ma" ecome less efficient- =n the other

hand$ the flame front /ill not mo'e do/n the ed properl" if suction is

less- >igher the ed #ermeaility, more "ill e the air dra"n- .ut$

higher permeailit" leads to loss of strength in the resulting sinter due

to reduction in ond strength- &ence a compromise is made et/een

these t/o factors- It is usual practice to dra/ aout <** 9 11** mC of

airKton of charge-

1@)

An increase in particle si>e increases ed permeailit" and the



'olume of air dra/n-

Strength of sinter gets reduced /ith an increase in particle si>e of

the ore due to reduction in contact area-

0or effecti'e sintering$ the use of larger ore lumps is undesirale-

Iron ore si>e 1*mm is rarel" preferred-

&igher proportion of 91** mesh si>e fines ad'ersel" affects the ed

permeailit"- .etter is that 9 1** mesh si>e fraction should e

screened off and used for pelleti>ation- 'deal sie of iron ore for

sintering is 0&07 E 10 mm&

1@

C



#elletisation essentiall" consists of formation of green



#elletisation essentiall" consists of formation of green

alls " rolling a fine iron earing material /ith a criticalamount of "ater and to /hich an eternal inder or an"

other additi'e ma" e added if reuired- hese green

alls of nearly 8-0 mm sie are then dried$ preheatedand fired$ all under oidising conditions$ to a temperature

of around 1)@*%1C@*P- .onds of good strength are

de'eloped et/een the particles at such high

temperatures-

1@

@

The #elletisation #rocess consists of the follo/ing

steps!



steps!

0eed preparation-

Green all production and si>ing-

Green all induration!

(a) Dr"ing

(b) #re%heating

(c) 0iring ooling of hardened pellets-

1@

;

The oser'ations on all formation that e'entuall" led to the



de'elopment of the theor" of alling are as follo/s!

Dr" material does not pelletise and presence of moisture is essential

to roll the po/der into alls- Ecessi'e /ater is also detrimental-

Surface tension of /ater in contact /ith the particles pla"s a

dominant role in inding the particles together-

Rolling of moist material leads to the formation of alls of 'er" high

densities /hich other/ise is attainale " compacting po/der onl"

under the application of a 'er" high pressure!

The ease /ith /hich material can e rolled into alls is almostdirectl" proportional to the surface area of particles$ i.e. its fineness-

1@

<

The capillar" action of /ater in the interstices of the grains causes a



contracting effect on them- The pressure of /ater in the pores of the

all is sufficientl" high so as to compact the constituent grains into a

dense mass- The compressi'e force is directl" proportional to

fineness of the grains since the capillar" action rises /ith the

decrease in pore radius and the latter decreases /ith increasing

fineness- ;n o#timum moisture is im#ortant since too little of

/ater introduces air inclusions in the pores and too much of /ater

/ould cause flooding and destruction of capillar" action- The

o#timum moisture content usually lies et"een 5-10 #ercent or

more, the finer the grains the larger the re(uirement&

1@

+



.esides the onds formed due to surface tension mechanical

interlocking of particles also pa"s a significant role in de'eloping the

all strength-

Maimum strength of a green all produced from a gi'en material

/ill e otained " compacting the material to the minimum porosit"

and /ith just sufficient /ater to saturate the 'oids- The rolling action

during pelletisation is eneficial in reducing the internal pore space

" effecting compaction and mechanical interlocking of the particles-

1@

2



0rom fundamental studies it has een concluded that there are three

different water-particle s"stems!

The !endular state$ /hen /ater is present just at the point of contact of

the particles and surface tension holds the particles together-

The f unnicular state$ /hen some pores are full" occupied " /ater in

an aggregate s"stem-

The ca!illary state$ /hen all the pores are filled /ith /ater ut there is

no coherent film co'ering the entire surface of the particles-

1;

*



1;

1

The all formation is a t/o stage process$ i.e. nucleation or seed

formation and their gro"th- The formation of alls on a pelletiser depends



g p p

primaril" on the moisture content- Seeds are formed onl" if critical

moisture le!el is maintained and /ithout /hich the process cannot

proceed properl"- Gro/th takes place " either layering or assi"ilation. It

has een oser'ed that the si>e of the alls produced in a pelletiser from a

charge containing right amount of moisture depends on the time and speed

of the pelletiser$ i.e. numer of re'olution-- Three regions can e clearl"

oser'ed$ during all formation- !

o Fucleii formation region

o ransition region

o all gro"th region&

1;

)



1;

C

4hen a /et particle comes in contact /ith another /et



4hen a /et particle comes in contact /ith another /et

or dr" particle a ond is immediatel" formed et/een thet/o- Similarl" se'eral such particles initiall" join during

rolling to form a highl" porous loosel" held aggregate

and crums /hich undergo re%arrangement and partialpacking in short duration to form small spherical$ stale

nucleii- This is the nucleation period$ a pre%reuisite for

all formation since these 'er" nucleii later gro/ into

alls-

1;

7



After nucleii are formed the" pass through a transition period

in /hich the plastic nucleii further re-arrange and get

com#acted to eliminate the air 'oids present in them- The

s"stem mo'es from a #endular state through funicular state

to the ca#illary state of onding- Rolling action causes the

granules to densif" further- The granules are still plastic /ith a

/ater film on the surface and capale of coalescing /ith other

granules- The si>e range of granules in this region is fairl"/ide-

1;

@



The plastic and relati'el" /et granules gro/ if the" are

fa'oral" oriented- In this process some granules ma" e'en

reak ecause of impacts$ arasion$ etc- Gro/th takes place

" t/o alternati'e modes-

gro"th y assimilation is possile /hen alling proceeds

/ithout the addition of fresh feed material-

gro"th y layering is possile /hen alling proceeds /ith

the addition of fresh feed material.

1;

;

Cro"th y ;ssimilation

If no fresh feed material is added for alling the rolling action ma" reak

some of the granules$ particularl" the small ones$ and the material



coalesces /ith those /hich gro/- The igger the all the larger it /ill gro/

under these conditions- Since smaller granules are /eaker the" are the first

'ictim and gro/th of the igger alls takes place at their epense-Cro"th y ayering

Gro/th of the seeds is said to e taking place " la"ering /hen the alls

pick up material /hile rolling on a la"er of fresh feed$ The amount of

material picked up " the alls is directl" proportional to its eposed

surface$ i.e. the increase in the si>e of the alls is independent of their

actual si>e-Cro"th y layering is more #redominant in the disc #elletisers and

gro"th y assimilation is more #redominant in drum #elletisers$ at

least e"ond the feed >one-1;

<

In general natural lump" ore or sinter or pellets or a suitale comination of

t f th f th d Th d l it f



t/o or more of these form the urden-- The modern large capacit" furnaces

necessaril" need full" prepared urden to maintain their producti'it" since the

reuired last furnace properties cannot just e met " natural lump" ore- The

selection of the process of agglomeration$ /hether sintering or pelletising$ /ill

depend upon the t"pe of ore fines a'ailale$ the location of the plant and other

related economic factors in'ol'ed-

Sintering is #referred if the ore sie is -10 mm to G 100 mesh and if it is

-100 mesh #elletising is generally ado#ted- #elletising in fact reuires

ultrafines of o'er <@F of %C)@ mesh- These processes are therefore notcompetiti'e-

1;

+

Minimum closure of pores " fusion or slagging open pore



s"stem 'er" good reduciilit" due to high microporosit" -

#orosit" of sinter is 1*%1+F and that of pellets is )*%C*F-

The shape of pellets is near spherical and hence ulk

permeailit" of the urden is much etter than that otainedfrom sinter /hich is non%uniform in shape-

The shape$ si>e and lo/ angle of repose gi'e minimal

segregation and an e'en charge distriution in the furnace-

1;

2

More accessile surface per unit /eight and more iron per unit of furnace 'olume



ecause of high ulk densit"$ C%C-@ tonnesKmC -(arger surface and increased time

of residence per unit /eight of iron gi'e etter and longer gasKsolid contact and

impro'ed heat echange

Degradation of sinter during its transit is much more than that of pellets- The

sinter therefore has to e produced near" the last furnace plant /hile pelletscan e carried o'er a long distance /ithout appreciale degradation- Ease in

handling

It should also e noted that If high rates of producti'it" demand elimination of

fines and since sinter happens to contriute more to the generation of fines than

that of pelllets$ the later /ill ha'e to e chosen as the urden in preference to

sinter-

1<

*

o The installation cost of a pelletising plant /ill e C*%7*F more than



p g p

that of sintering plant of an eual si>e-o The operating cost of sintering is slightl" less than that of pelletising-

o Difficult" of producing flued pellets-

o S/elling and loss of strength inside the furnace

o 0lued pellets reak do/n under reducing conditions much more

than acid and asic sinters and acid pellets-

o Strong highl" flued sinters$ especiall" containing Mg=$ are eing

increasingl" preferred to pellets-

1<

1

The life of lining$ under the conditions pre'ailing inside the furnace$ decides the

furnace campaign /hich should not e less than a fe/ "ears The chief causes of



furnace campaign /hich should not e less than a fe/ "ears- The chief causes of

failure of the lining are!

aron monoide attack-

Action of alkali 'apours-

Action of lim" and alkaline slags-

Action of other 'olatile matters-

Arasion "$ solids$ liuids and gases-

Temperature-

Action of molten metal-

onditions of operation and design-

.lo/ing%in procedure-

1<

)

All these factors ma" not e operati'e at all the areas in



a furnace- =ne or a fe/ factors$ at est$ ma" "

dominant at an"one area in the furnace- 0or eample$ in

the stack the lining has to /ithstand predominantl"

arasion " solid urden and attack of caron monoide$

/hilst in the osh region the lining has to stand high

temperature$ erosion " ascending gas and attack of

molten lime and alkali slags- Similarl" the hearth has- to

stand action of molten slag and metal /ithout reakouts-

1<

C

The chief causes of failure in the furnace lining are!



Carbon ono!ide Attac". #roal" the most common failure is due

to the disintegration of the ricks " caron deposition$ produced "

dissociation of the caron monoide in the last furnace gas- This

takes place in the upper portions of the stack according to the

reaction !)=U*) -

If the ricks are porous$ caron penetration takes place$ causing the

ricks to disintegrate-

Some authorities are inclined to select firericks for this portion of

the furnace on the asis of iron oide content

1<

7

*igy and Creen$ ho/e'er$ state that the total iron oide content of



the firerick is no criterion of the resistance of the material to caron

monoide attack$ as the ease /ith /hich the iron nodules can e

reduced to metallic iron appears to e the determining factor- This

'ie/ is supported " man" authorities-

The usual method of assessing the resistance of firericks to

caron monoide attack is to epose the material to a current of

pure caron monoide at a temperature of 7@** - and to note the

time necessar" to cause disintegration- If a rick /ill resist this

treatment for t/o hundred hours it is considered sufficientl" resistant

1<

@

more modern method is to pass a stream of caron monoide through a

column of crushed firerick for a period of four hours- The /eight of caron



dioide present in the eit gases$ determined " a =) asorption train$ is

taken as an indication of the materialVs resistance to caron monoide attack-

Scientists conducted a series of in'estigations to determine the sensiti'eness

of refractor" ricks to caron monoide attack at temperature ranges of 7)**

to @*** - The results of these eperiments seemed to indicate that the

manufacturers of last furnace linings should ascertain that!

The original cla" should e free from such ferruginous sustances as

p"rites and siderite

It /ill also e o'ious that caron monoide attack /ill e reduced " the use

of a dense rick of lo" #ermeaility-

1<

;

. The last furnace urden consists of small amounts of alkalis and some

i t d th i t ti f it d Th lk li



c"anogen is generated " the interaction of nitrogen and caron- These alkalis

and c"anides are 'olatili>ed in the hotter parts of the furnace$ and tend to collect

in the cooler places-

#raner sho/s that the alkalis react /ith the rick/ork forming nephelite 5Na)* -

Al)*C )Si*)6$ /hilst Rigby$ Booth and %reen uote microscopic eaminations of

rick/ork taken from furnace linings )* ft- do/n the stack$ /hich sho/s the

formation of kaliophilite 5,)*- A1)*C )Si*)6 and leucite 5,)*- AI)*a 7Si*)6-

%reen and &ugill state that eperience demonstrates that these 'apours$

particularl" c"anide 'apours$ can lead to general corrosion and modification

of the surface of the lining "ith conse(uent loss of strength and

refractoriness&

1<

<

. The action of last furnace slag on the refractor" lining is a function of the

asicit" of the slag- Since the ash of the coke is not released until the coke



is urnt in the tu"ere >one$ it follo/s that the a=KSi*) ratio must e high in

the osh- Therefore there /ill e a tendenc" for these high%lime slags to

attack the rick/ork-

ther olatile aterials . There are other 'olatile materials$ such as >inc and lead$ /hich ma" e

included in the last furnace urden- These metals 'olatili>e in the hotter

>ones and condense in the pores of the rick/ork in the cooler parts- Their

suseuent oidation causes a s/elling of the rick$ /hich results in

disintegration-

1<

+

#roal" the chief arasion occurs on the stockline as the urden



"

drops from the large ell- To some etent the se'erit" of thearasion in this >one /ill depend on the nature and si>e of the ra/

materials- 0urther arasion in the form of /all drag takes place

lo/er do/n the furnace-

Some authorities uer" the etent to /hich arasion is responsile

for disintegration of the ricks in these lo/er >ones* #raner appears

to suggest that the effect of arasion or /all drag is to accelerate

the disintegration due to carbon "onoxide and alkali attack*

1<

2



Hnless great care is taken and patience sho/n during the dr"ing of

the lining and the lo/ing in of the furnace$ considerale damage

ma" e done to the lining- The importance of dr"ing the lining

course " course as it is uilt is no/ appreciated-

4hen a last furnace is in normal production$ temperature gradients

are generall" gradual$ ut during the lo/ing%in period$ /ide

fluctuations are possile- are must therefore e eercised at this

period to see that the 'arious >ones are rought up to the /orking

temperatures as e'enl" and as graduall" as possile-

1+

*

The lining here should ha'e a very good abrasion resistance and



g y g

resistance to carbon "onoxide attack refractoriness is relati'el" ofless significance- A good dense refractor" is ideal for this purpose-

The ricks themsel'es should e true to shape and si>e so as to

reduce joints et/een ricks to a minimum thickness-

It is a common practice to use armour plates at the throat to

/ithstand arading action of falling urden- Immediatel" elo/ this$

o'er a length of nearl" )%C m$ high%fired$ super dut" firericks are

used- --

1+

1

Th ti t k l th t f t f h i ht i li d ith hi h



The entire stack elo/ the top fe/ metres of height is lined /ith high

dut" firericks- A +,-./ Al 0 . + firerick /ith a close teture is

usuall" preferred for the stack$

A )0% ;l03 rick ha'e een recommended for the lo/er parts of the

stack- These ricks are made " machine moulding under high pressures

and de%aired conditions since these lead to a high ulk density and

lo" #ermeaility&

In order to reduce the numer of joints to a minimum$ large speciall"

shaped locks ha'e een emplo"ed-

1+

)

In the osh the rick/ork has to /ithstand!



In the osh the rick/ork has to /ithstand!

&igh temperature conditions

Erosion " the last

(ime and alkali slag attacks-

onsidering the se'erit" of temperature and chemical attack in this region the

lining should possess good reractoriness$ reractoriness under load$ lo1

ater ex!ansion and resistance to action o "olten li"y and alkali slags -

The majorit" of osh linings are of high dut" or super dut" firericks /ith 95-

)5% ;l03$ laid in the con'entional anded osh construction /ith copper

cooling plates-

1+

C

The etremel" successful use of caron locks for lining the hearth and its

/alls led to its adoption e'en in the osh region since caron refractor"



possesses etter properties$ especiall" high thermal conducti'it"$ than those

of the con'entional high dut" firericks-

aron lined /alls can e cooled " either spra" coolers$ or /ater jackets-

The changeo'er from firerick lining to caron lining$ therefore$ eliminates

the corrugated pattern of construction produced " ro/s of coolers inserted

in the lining and permits simpler construction /hich also results in smoother

and uniform /ear-

The de'elopment and use of graphite%silicon caride rick in 8apan hasgi'en ecellent performance oth for osh and hearth and might find /ider

use in near future-

1+

7

The lining in hearth should primaril" #re!ent reakouts- The use of

ricks of high alumina to silica ratio lo/er permeailit" and porosit"



ricks of high alumina to silica ratio$ lo/er permeailit" and porosit"

/ith /ell laid joints can minimise reakouts- In spite of this the

earlier firerick hearth still suffered from freuent reakouts and the

attendant troules- The occurrence of reakout /as elie'ed to e

due to the oidation of iron " gases that penetrated firericks and

the conseuent effect of iron oide in lo/ering the melting point of

the refractor"$ resulting ultimatel" in its failure- Ramming of caron

plus tar miture at such 'ulnerale areas ehiited ecellent

resistance to such reakouts-

1+

@

This finall" lead to the de'elopment and use of caron lined



hearths- >igh refractoriness, high thermal conducti!ity, high

arasion resistance, high ulk density cou#led "ith lo"

#orosity, good crushing strength, almost com#lete inertness to

caron saturated iron and slag and such other #ro#erties make

caron as an almost ideal material for hearth construction

pro'ided ricks or locks of these are ke"ed into position /ith the

thinnest possile joints- It has een oser'ed that not onl" the

caron hearth contour is etter maintained during the campaign ut

the prolem of reakouts is 'irtuall" eliminated-

1+

;

f



In the earl" adaptation caron locks /ere used as onl" the facing

lining /ith high dut" firerick for acking- &o/e'er all caron hearth

i-e- the /hole /all thickness and a considerale ottom thickness$

has almost uni'ersall" een accepted as a standard method of

preparing the hearth! the remaining ottom thickness is made up "

high dut" firericks- The shape and si>e of the caron locks used

for making the ottom 'ar" consideral" ut all aim at achie'ing

ke"ed joint /ith thinnest possile joints$ preferal" /ithout the use

of eternal jointing material-

1+

<

I th d ll h th t ti f l l k f



In the modern all caron hearth construction use of large locks of

fe/ suare meter in si>e$ /ith length of approimatel" half the

hearth diameter are increasingl" eing adopted- These are laid

hori>ontall" and ke"ed together- Each lock is anchored firml" at the

hearth /all to pre'ent it from floating " molten iron-

areful control of the manufacture of hearth locks and its con

struction is of fundamental importance in achie'ing the desired

campaign life of the hearth-

1+

+



1+

2

The process of starting a ne/l" lined furnace is called lo"ing-in. In

general the operation in'ol'es four main steps$ viz. dr"ing$ filling$ lighting



g p p " g g g g

and operation until normal production is estalished- There is no standard

practice of blowing-in and the details of each of the ao'e mentioned

steps adopted depend on local conditions and customs-

Drying . The ne/ lining of a furnace contains a significant proportion of

moisture /hich must e slo/l" and completel" remo'ed efore the

temperature of the furnace is raised- This operation is kno/n as dr"ing in

/hich the furnace is slo/l" heated- An" amount of time and troule taken

in ensuring careful and gradual dr"ing of the furnace is more than repaid

in its suseuent operation-

12

*

At the end of dr"ing$ depending upon the method used for dr"ing$

the furnace is cleared off all the things used for filling- The coolers



are turned on and once the inside temperature is tolerale furnacepersonnel can get in and prepare for filling the furnace- The

inspection of coolers at this stage is a must since rectification of

fault" coolers is readil" possile at this stage- In fact a check list is

prepared and each item is checked off as reports are recei'ed of

their satisfactor" performance-- The tap holes are prepared and

coolers$ /hich /ere earlier remo'ed to ha'e access inside$ are

packed in position-

12

1

0illing of the furnace usuall" means filling the hearth /ith light kindling /ood

and sha'ings saturated /ith oil up to the tu"ere le'el and la"ing o'er this a



scaffold of old timer slippers- oke is charged ao'e the timer scaffoldfrom the top upto the osh le'el- A uantit" of limestone sufficient to flu the

ash in the charged coke$ is also charged along /ith the coke after the initial

coke lanks- A small amount of old last furnace slag is also incorporated

/ith coke after the coke le'el rises e"ond the mantle le'el- The earl" slag

'olume is delieratel" maintained at high le'el to heat up the hearth and

prepare it to recei'e iron- =n the coke lanks are laid light urden charges

of ore$ stone and coke i.e. the ratio of iron ore to coke is lo/$ aout *Q@%*Q;-

12

)

After filling the furnace as mentioned ao'e for lo/ing%in the ells are opened and the

dust catcher dump 'al'e is closed--



The furnace is lighted either " inserting red%hot ars through the tu"eres or slag hole andiron notch- Alternati'el" gas torch ma" also e used- Generall" highl" comustile material

is kept in front of the tu"eres during filling to light the furnace readil"- .urning is allo/ed

/ith natural draught alone for the first )7QC; hours a light last is put on onl" thereafter-

As soon as good amount of gas emerges from the furnace top the ells are closed and thedust catcher dump 'al'e is slo/l" opened to conduct eit gases through the gas cleaning

s"stem-

The last 'olume is fairl" rapidl" increased to normal 'olume of lo/ing- Hsuall" more than

three fourth of the standard 'olume of last is lo/n " the end of fourth da" and full lastis on " the end of a /eek after the furnace is ignited-

12

C

Tap holes are kept open for hot gases to escape out during the earl" period- =nce

coke urning and slag formation starts furnace cre/ are 'igilant in oser'ing the

tap holes- The first indication of a sudden decrease in the out coming gas through



the tap hole is taken as an indication of eginning of slag accumulation in the

hearth and the tap hole is immediatel" closed thereafter- Nearl" si to eight hours

ma" elapse after this efore sufficient slag has accumulated to /arrant flushing-

A#ter nearl" t/o da"s$ as the ratio of iron ore to increase in the urden$ that first

cast ma" e due- The amount of slag and metal flo/ing out of the furnace iscorrelated to the charge schedule and proportion in order to assess the progress

of lo/ing%in operation- After the first cast is o'er charging and tapping schedules

are estalished and are strictl" adhered to until routine production is estalished- It

generall" takes nearl" a /eek to estalish normal routine practice so that metal

and slag of desired composition /ill e tapped out of furnace at the desired

inter'als-

12

7




NIT Rourkela

12

@

urden distriution is one of the key o#erating



urden distriution is one of the key o#erating

#arameters influencing last furnace

#erformance, #articularly the #roducti!ity and

the coke rate& he #ro#er distriution of urden materials

im#ro!es ed #ermeaility, "ind acce#tance,

and efficiency of gas utilisation&

12

;

'n a ty#ical 'ndian last furnace e(ui##ed "ith a ell



'n a ty#ical 'ndian last furnace e(ui##ed "ith a ell-

less aul Hurth2 distriution system, the decrease

in coke rate that is due eclusi!ely to urden

distriution "as found to e 10E1 kg/thm&

12

<

Design of the last furnace Angle and si>e of the ig ell



Design of the last furnace

and its charging de'ice

5effect of these factors is

constant6-

Angle and si>e of the ig ell-

Additional mechanical

de'ice5s6 used for otaining

etter distriution-

Speed of lo/ering of large

ell-

12

+

Inconsistenc" in Si>e range of the 'arious



Inconsistenc" inph"sical properties ofcharge materials5deficiencies caused "this should eeliminated " impro'ing

ualit" of the urden-

Si>e range of the 'arious

charge materials

Angle of repose of ra/

materials and other

ph"sical characteristics of

the charge-

Densit" of chargematerials-

12

2

(e'el s"stem and Distriution of charge



(e'el$ s"stem and

seuence of

charging$ programme

of re'ol'ing the

distriutor 5conditionsdetermining major

means of last

furnace process

control from top6-

Distriution of charge

on the ig ell &eight of the ig ell

from the stock%line i.e.

charge le'el in thefurnace throat-

=rder and proportion

of charging of 'arious

ra/ materials-

)*

*



)*

1




q g

large bell is replaced by a distributorchute with 2 hoppers A rotating chute is provided inside


Advantages:Advantages: Greater charge distribution

fleibility !ore operational safety and

easy control over varying

charging particles "ess wearing parts: easy

!aintenance

)*

)



)*

C


control can e summarised as follo/s! Increased producti'it"$ decreased coke rate$ impro'ed



p "$ $ p

furnace life - Reduced refractor" erosion


as slips

Impro'ed efficienc" of gas utilisation and its indirectreduction


hot metal ualit"

Reduced tu"ere losses and minimisation of scaffold

formation

(o/er dust emission o/ing to uniform distriution of fines-

)*

7

The densit" of three important ra/ materials viz. the ore$ the

coke and the limestone are uite different-



coke and the limestone are uite different-

The hea'iest is iron ore /ith around @%; glcc$ the lightest is

coke /ith densit" of around %&5 glcc and the limestone is

intermediate /ith%a 'alue of densit" around '&0-'&5 glcc.

It means that the rolling tendenc" of coke particles is mai

mum and that of the ore is minimum- Since the densit" 'alues

cannot e altered$ the si>es ma" e so chosen that their

differential rolling tendencies are offset to some etent-

)*

@

T)e !#(4lem ( e#" dene (#e i e#i(u



T)e !#(4lem ( e#" dene (#e i e#i(u

#(m t)e !(int ( ie ( t)ei# luggi)

#educti(n #ate #at)e# t)an t)ei# tendenc"

t(a#d eg#egati(n. uc) (#e a#e

t)e#e(#e ina#ia4l" c#u)ed and inte#ed t(

(4tain m(#e !(#(u aggl(me#ate 4e(#e

c)a#ging t)ee in t)e u#nace.

)*

;

)en a multi-!a#ticle mate#ial i all(ed t(



gentl" all (n a )(#i(ntal !lane it tend t( (#m

a c(nical )ea!. T)e 4ae angle ( t)i c(ne i

n(n a angle of repose ( t)at mate#ial.

T)i angle de!end u!(n t)e !a#ticle ie/ it

u#ace c)a#acte#itic/ m(itu#e c(ntent/

)a!e/ ie dit#i4uti(n/ etc.

)*

<

0or an iron ore of 1*%C* mm si>e$ /ith an

a'erage mean si>e of 1+ mm$ the angle of



repose is around CC%C@P- 0or coke of )<%<@ mm

si>e$ /ith an a'erage si>e of 7@ mm$ the same

is around C@%C+P- Similarl" the angle of reposefor sinter is in the range of C1%C7P and for pellets

it is around );%)+P-

)*

+



)1

*



)1

1



)1

)

=n dumping as the materials fall on the stock



=n dumping$ as the materials fall on the stock

surface$ the" take a paraolic path and mainl"

t/o different profiles of the accumulated mass

emerge depending upon /hether the particles

hit the in%/all directl"53% shape6 or the stock

surface 5M%shape6

)1

C

The M%profile itself is generall" otained if the material



The M profile itself is generall" otained if the material

strikes the stock surface- This happens /hen the

ellKthroat diameter ratio is small 5larger ell%in/all

distance6 or the charging distance is small - 't is clear

that the peak of the M%contour approaches the in/all

5hence the peripheral permeailit" decreases6 as the

charging distance increases and ultimatel" the M

changes to 3 profile-

)1

7



)1

@




NIT Rourkela

)1

;



)1

<

Right at the top of the furnace is the granular zone that contains

the coke and the iron earing materials charged$ sometimes



g g $

along /ith small uantities of limestone and other flues- The

iron%earing oides charged get reduced to /ustite and metallic

iron to/ards the lo/er end of the granular >one-

As the urden descends further$ and its temperature rises on

account of contact /ith the ascending hot gases$ softening and

melting of the iron%earing solids takes place in the so%called

cohesive zone 5mush" >one6-

)1

+

=ut of fi'e >ones the cohesi'e >one pla"s the most



p "

important role in the .-0- operations- This is the >one /here the ferrous urden soften and

melt- Its shape$ position and etent in the .-0- affect the gas

flo/ pattern- The urden loses its permeailit"- Gas flo/ occurs onl"

through the coke la"ers- (oss of permeailit" is caused " liuid phase in the

ferrous urden- The liuid formation causes a pressure drop-

)1

2

# Also the solid phase gets defor!ed due to the weight of the burden$

# This defor!ed solid !ay occupy the gaps between the solid

ferrous pieces also causing loss of per!eability$



# The different pheno!ena si!ultaneously occuring in thecohesive %one are

a$ softening and !elting of the oide phase$ b$ carburisation of the !etalic phase

c$ softening and !elting of the !etallic iron phases# &oftening and !elting of the oide phase will be affected by :

a$ the quantity of non ferrous oide ' slag for!ers( present

b$ distribution) !orphology and che!istry of slag for!ers

c$ degree of pre reduction 'this will affect the availability of

*e as a slag for!er($

))

*

Softening and melting of the metal phase /ill depend on !

caron content of metal phase

cross sectional area of metal phase

These comple processes are simplified as under !



These comple processes are simplified as under !

5I6 ormation of the first oide melt&

a- It is formed at the interface of lo/est melting$ usuall" the

interface et/een an 0e= particle and another oide particle-

- The formation /ill depend on the microstructure 5phasespresent and their distriution6

c- The first liuid tends to /et the ore particles-

d- This /etting resists transport through it and slo/s do/n the

reduction kinetics-

e- This is often called reduction retardation-

))

1

II9 *eduction degree of the metallic urdena- Metallic urden in most .-0-s- reaches the softening >one/ith reduction degree higher than @* pct-

- The situation in the cohesi'e >one is a porous solid ironoide shell confining solid and liuid oide-



g

c- liuid slag co'ers the solid oide particles$ de'elops a semisolid material$ acts as a luricant for other particles-

d- the semi solid core has a reduced mechanical strength

e- resistance to deformation is determined " the porous Ironshell-

f- 'olume fraction of liuid slag increases /ith temperatures-

g- the Iron shell can no longer hold the liuid-

h- This results in the dripping of liuid slag from the urdenmaterial-

i- Iron shell gets carurised$ its melting point decreases$mechanical strength also decreases-

))

)

softening is defined as the moment /hen the metallic urden canno longer resist the action of mechanical forces-

this generall" considers /ith dripping of material from the urdencomponent-

the softening and the dripping depend on



the softening and the dripping depend on

a- increase of the molten slag 'olume-

- caron content in the Iron shell

.oth parameters increasing /ith increase in temperature-

The reduction degree /ill tend to remain constant during thisperiod due to reduction retardation-

(esser the reduction degree lesser is the softening temperatures5here the thickness of iron la"er is lo/$ lo/ering its mechanicalstrength$ assisting eas" dripping6-

&igher the reduction degree higher should e the softeningtemperatures 5lo/er is the 0e=$ the slag former6-

))

C

Different configurations of the cohesi'e >one are as follo/s !



1- 4%t"pe$ )- 0lat$ C- In'erted%H$ and 7- In'erted%3

5in'erted%3 configuration is elie'ed to result in the optimum

performance of the .-0-6

This in'erted%3 configuration is maintained " radial urden

distriution-

ohesi'e >one should e formed lo/er do/n the osh 5results in

increase in the granular >one$ increase in the gas utili>ation$

decrease in the 'olume of the dripping Wone$ decrease in the

contact time et/een Si= gas and hence Si pick up " the metal-6

))

(o/ering of cohesi'e >one can e achie'ed " a high

softening temperature of the urden material-



g p

The thickness of the cohesi'e >one should e lo/ 5a

thinner cohesi'e >one is epected to allo/ more air

passage for a gi'en pressure deferential6-

))

0urther do/n the furnace$ impure liuid iron and liuid slag are

formed- The asorption of caron lo/ers the melting point of iron



p g p

drasticall"- 0or eample$ an iron allo" containing 7 /t- F caron

melts at onl" 11+@P--

In the cohesi'e >one and elo/ it$ coke is the source of caron for

carurisation of liuid iron- &o/e'er$ caron directl" does not

dissol'e in liuid iron at this stage- The possile mechanism of

carurisation of iron entails the formation of = " gasification of

caron$ follo/ed " the asorption of caron " the reaction!

)=5g6 XYin 0e =)5g6

))

oke is the onl" material of the last furnace charge /hich descends to

the tu"ere le'el in the solid state- It urns /ith air in front of the tu"eres



in a 1%) m deep race/a" around the hearth peripher"-

.e"ond the race/a" there is a closel" packed ed of coke$ the central

coke column or dead manVs >one-

The continuous consumption of coke and the conseuent creation of an

empt" space permit the do/n/ard flo/ of the charge materials-

The comustion >one is in the form of a pear shape$ called racewa in

/hich the hot gases rotate at high speeds carr"ing a small amount ofurning coke in suspension-

))



The temperature of the gas rises as the coke consumption



proceeds and reaches a maimum just efore the race/a"

oundar"- Thereafter$ it falls sharpl" as the endothermal

reduction of =) " proceeds

=) )=%71*** cal

The concentration of =) fall rapidl" from the race/a"

oundar" and the gasification is completed /ithin )**%7**

mm from the starting point of the reaction-

))

2



)C

*

The primar" slag of relati'el" lo/ melting point /hich forms in the lo/er part

of the stack or in the ell" consists of 0e=%containing silicate and



aluminates /ith 'ar"ing amounts of lime /hich has ecome incorporated

depending upon the degree of calcination undergone -

As the slag descends$ ferrous oide is rapidl" reduced " caron as /ell as

" =- As the lime is continuall" asored$ the original 0e=%Si*)%AI)*C

s"stem rapidl" changes to the a=%Si*)%AI)*Cs"stem /ith some minor

impurities accompan"ing the urden- The dissolution of lime and the

approach to the a=%Si*)%Al)*C s"stem is more pronounced$

-

)C

1

As the liuid primar" slag runs do/n the osh and loses its fluing

constituent 0e=$ the liuidus temperature also increases- If$ therefore$

the slag has to remain liuid it must mo'e do/n to hotter parts of the



furnace as rapidl" as its melting point is raised- As the reduction of 0e=

is almost complete ao'e the tu"eres the resulting osh slag$ composed

mainl" of a=%Si*)%AI)*C

The hearth slag is formed on dissolution of the lime /hich /as not

incorporated in the osh and on asorption of the coke ash released

during comustion- The formation is more or less complete in the

comustion >one-

)C

)

This slag runs along /ith the molten iron into the hearth

and accumulates there and forms a pool /ith the molten



p

metal underneath- During the passage of iron droplets

through the slag la"er$ the slag reacts /ith the metal and

a transference of mainl" Si$ Mn and S occurs from or tothe metal$ tending to attain euilirium et/een

themsel'es as far as possile-

)C

C



)C

7



)C

;



)C

<



)C

+



)C

2

The different phases of iron oides in euilirium /ith &)K&)= mitures at 'arious

temperatures are sho/n in pre'ious fig- " the dotted lines- The reduction of



0e= " &) is endothermic and therefore the cur'e inclines do/n/ards /ith

increasing temperature /hereas the corresponding cur'e for reduction " =

5full line6 inclines up/ards ecause of the eothermic nature of the reaction-

These t/o cur'es intersect at aout +)1P$ i-e-$ at +)1P h"drogen and =

ha'e the same reducing po/er o'er 0e=- Thermod"namicall"$ elo/ this

temperature$ the reducing po/er of = is much greater-

)7

*

The cur'e for E- 5iii6 slopes up/ards ecause the reaction is

eothermic$ i-e-$ 0e= ecomes more stale /ith increasing



temperature in the presence of =-

The cur'e for E- 5ii6 slopes do/n/ards the reaction eing

endothermic-

At 2**P$ the euilirium concentration of = for 0eC*7%0e=

is )* percent /hereas that for 0e=%0e aout <* percent$ i-e-$

for the con'ersion of magnetite entirel" to /ustite the gaseous

phase must ha'e a C2 C 3 ratio greater than 0&@

/hereas- that for /ustite to iron the ratio should e higherthan &3&

)7

1



.elo/ ;**P !



#re%heating and pre%reduction

;** %2@*P!

Indirect reduction of iron oides " = and &)

2@** to softening temperature!

Direct reduction gasification of caron 5solution loss

reactions6 " =) and &) ecomes prominent-

)7

7

The formation of cohesi'e la"ers or partiall"

reduced and partiall" molten iron oide takes

l



place- The coke slits pro'ide passage for gaseous flo/-

Dripping or Dropping Wone Semi fluidi>ed region in /hich liuids drip and

fragments of cohesi'e la"ers drop- Wone through /hich liuids trickle do/n to the

hearth- It is the final stage of iron oide reduction

)7

@

.last$ injectants and coke are con'erted to hot reducing gas- This

gas reduces the ore as it mo'es counter currentl" to/ards the top of

th f



the furnace-

&earth

It is a container for liuids and coke /here slagKmetalZ cokeKgas

reactions take place- Metal droplets pass through the slagKcoke

la"er- (iuid metalKcoke la"er in /hich chemical reactions take

place onl" to a small etent-

)7

;



)7

<



)7

+

fluidi>ation of small particles /hen the local gas



'elocit" is ecessi'e

diminution of 'oid age due to s/elling and

softening%melting

flooding of slag in the osh >one /hen the slag

'olume and gas 'elocit" are ecessi'e-

)7

2

The charge in the last furnace descends under gra'it" against the

frictional forces of solids and uo"anc" of gas- 4ith increasing gas

l it th d i i t l d ti ll



'elocit"$ the pressure drop increases approimatel" uadraticall"

until the up/ard thrust of the gas and do/n/ard thrust of the solids

are held in alance-

4hen this critical 'elocit" is eceeded 5the point of incipientfluidi>ation6$ the packing in the ed ecomes loose$ the finer

particles egin to teeter and the pressure drop ceases to increase$

i-e-$ the resistance to gas flo/ drops 5due to increase in 'oid age at

places /here the fines ecome suspended6-

)@

*



)@

1

The mechanism of the softening%melting phenomena

is schematicall" illustrated in pre'ious 0igure- It is

id t th t ith th t f ft i th id i



e'ident that /ith the onset of softening$ the 'oidage inthe ed decreases and the ed ecomes more

compact 5origin of the terminolog" cohesive).

As a conseuence$ further indirect reduction of iron

oide " gases ecomes increasingl" difficult- Hponmelting$ dripping of molten 0e=%containing slag

through the coke la"ers increases the flo/ resistance

through the coke slits and the acti'e 5i-e- dripping6

coke >one ecause of loss of permeailit"-

)@

)

The cohesi'e >one has the lo/est permeailit"- &ence$

f fl



for proper gas flo/!

* s should e as high as possile

The thickness of the cohesi'e >one should e as small

as possile- This thickness depends on the difference

et/een * s and * m (* + % * s )$ and therefore$ the

difference should e as lo/ as possile-

)@

C



)@

7

Gas ow through Granular zone:For resistance to gas ow more importantthan the particle diameter is the relative sie ofthe materials in the bed.

In a mi2ed bed of widel3 var3ing particle sie



In a mi2ed bed of widel3 var3ing particle siethe small particles land in the interstices of thelarge ones and decrease the void age .,tarting with large uniform spheres the void

age decreases as the small ones are introducedand the bed becomes more and more compactas the proportion of the latter increases.The bed is most dense i.e. the voidage is

minimum when 6#&7# percent of the totalvolume of the particles consists of the largeones for about all the cases.

)@

@

The 8m increases on either side of the

minimum i.e. with increasing ordecreasing volume fraction of the smallparticles /approaching more uniformit3f th i di t ib ti 0



of the sie distribution0.The voidage decreases greatl3 as theratio d

s' d

! decreases.

This shows that for a good anduniform permeabilit3 and low resistanceto gas ow in a mi2ed bed the siefractions should be as narrow aspossible.9ne can easil3 visualie the adversee:ects of multi&granular bed of particlesof var3ing diameter on the voidage.

)@

;

; narro" sie distriution has the follo"ing ad!antages! charge permeailit" increases and the gas distriution is

more uniform /ith etter utili>ation of the chemical and

thermal energies of the gases



thermal energies of the gases

more e'en material distriution at the stock le'el and less

material segregation in the shaft during descent

gas flo/ is not impeded if the si>e ratio is /ithin limits ut

at the same time gi'es rise to a tortuous flo/ of gases /ith

continuous changing of flo/ directions$ pro'iding a larger

gasKsolid contact time-

)@

<

The fraction of iron earing material elo/ the limiting si>e

is therefore termed as #ines " the last furnace technologists

and is in'arial" eliminated " screening at e'er" possile

stage



stage-0rom the point of 'ie/ of reduction the maimum top si>e of

an iron earing material should e as lo/ as possile$ since the

rate of reduction decreases$ perhaps eponentiall"$ /ith

increasing si>e-

The si>e range of materials charged in the last furnace

represents a compromise to gi'e oth good stack permeailit"

and adeuate ulk reduciilit"-

)@

+

as ow n wet zone:

;et ones consist of the coke beds in thebosh and bell3 regions i.e. inactive coke oneactive coke one and the coke slits in the

cohesive one



cohesive one. (ere molten iron and molten slag owdownwards through the bed of coke. Thisreduces the free cross section available for gas

ow thus o:ering greater resistance thereb3increasing the pressure drop.n e2treme situation arises when at high gasvelocit3 the gas prevents the downward ow

of li<uid. This is known as loading. ;ith furtherincrease in gas velocit3 the li<uid gets carriedupwards mechanicall3 causing fooding.

)@

2

Scientists ha'e tried to estimate pressure

drop in last furnace &o/e'er the" are



drop in last furnace- &o/e'er$ the" are

approimate- Moreo'er$ the" are onl" for the

granular >one and coke >ones- The situation in the cohesi'e >one is 'er"

comple$ and reliale theoretical estimates

are etremel" difficult to come "-

);

*

Therefore$ for practical applications in last

furnaces$ an empirical parameter$ called ,low

esistance Coe##icient 50R6 has ecome



popular- The 0R for a ed is gi'en as

/here the gas flo/ rate is for unit cross section

of the ed$ i-e- either mass flo/ 'elocit" or

'olumetric flo/ 'elocit" -

);

1

0R1K ed permeailit"

The 0R for a furnace can e empiricall" determined

from measurements of pressure drop and gas flo/ rate



from measurements of pressure drop and gas flo/ rate-

Since it is possile to measure pressures at 'arious

heights /ithin a furnace$ the 'alues of 0R for indi'idual

>ones can also e determined-

);

)

These measurements ha'e indicated that

0Rs for the granular cohesi'e coke



0Rs for the granular$ cohesi'e$ coke tu"ere >ones are approimatel" )*F$ 50

and C*F of the o'erall furnace 0R-

This means that the cohesi'e >one is

responsile for the maimum flo/ resistance

and pressure drop$ to a 'er" large etent-

);

C




NIT Rourkela

);

7



);

@

Decreasing the etent of Si= formation "!o (o/ering ash in coke and the coke rate



(o/ering ash in coke$ and the coke rateo (o/ering RA0To (o/ering the acti'it" of Si*) in coke ash " lime

injection through the tu"eres-

Decreasing Si asorption " liuid iron in the osh" enhancing the asorption of Si*) " the oshslag- This can e achie'ed "!

o

Increasing the osh slag asicit"-o (o/ering the osh slag 'iscosit"--

);

;

Remo'al of Si from metal " slag%metal reaction



Remo'al of Si from metal " slag%metal reactionat the hearth "!

o (o/ering the hearth temperatureo #roducing a slag of optimum asicit" and fluidit"-

);

<

Desulphurisation of metal droplets through slag%



metal reaction in the furnace hearth !

5a=6 XSY X Y 5aS6 = 5g6

Desulphurisation through the coupled reaction!

5a=6 XSY X MnY 5aS6 5Mn=6

5a=6 XSY X SiY 5aS6 1K) 5Si=)6

);

+

Sulphur pick%up through the 'apour%phase

reaction!

aS5 in coke ash6 Si= 5g6 SiS5g6 a=



aS5 in coke ash6 Si= 5g6 SiS5g6 a= In the osh and ell" regions$ SiS decomposes

as

SiS5g6 XSiY XSYo Decreasing the 'aporisation of sulphur in the

race /a"o #referential asorption of SiS " the osh slag

);

2

Reducing slag i-e- 0e= content should e lo/

&igh asicit"



&igh asicit" &igh temperature$ since desulphurisation is an

endothermic reaction

,inetic factor

ontact surface of metal and slag 5[ " agitation6

0luidit" of slag5[ " adding Mg= $ Mn=6

Time of desulphurisation

)<

*



)<

1



)<

)



)<

C



)<

7


measured in terms of coke rate /hich should of course

e as lo/ as possile- The achie'ement of a satisfactor"





caron deposition reaction proceeds- If the top gas is

high in *) sensile heat is carried from the furnace as a

result of the eothermic reaction-

)==)

If on the other hand the top gas is high in =$ chemical

heat lea'es the furnace-

)<

@



)<

;



)<

<

he comustion of caron to its monoide yields only aout 8

#ercent of the total heat #ossile to e otained and only oidation to

the dioide gi!es the largest amount of heat&

his has a great significance in the last furnace #rocess "here aout



g g #

30-90 #ercent of the coke caron is oidised to +: and the rest into

+:&

'n the last furnace aout half of the heating !alue of caron is

otained for a to# gas +:/+: ratio of & he rest is carried a"ay in the

outgoing gas&

;lthough a #art of this heat is redeemed y urning the gas out of the

furnace, it means con!ersion of e#ensi!e metallurgical coke to a gas

"hich could e otained from a less !aluale fuel&

)<

+

he heat !alues in the gi!en e(uations are for #ure caron& or

a good (uality coke "ith 8)% +, the res#ecti!e !alues "ill e

aout 000 and 7000 kcal/kg&coke&



g

+aron dioide, in the asence of caron, is stale at high

tem#eratures&

<# to aout 000=+, its thermal dissociation is small& ;tatmos#heric #ressure, it amounts to aout #ercent&

;t high tem#eratures, caron dioide is unstale in the

#resence of caron and is reduced to caron monoide

according to the gi!en e(uation&

)<

2

his is generally kno"n as oudouard or caron gasification

reaction and is highly endothermic4 the re!erse reaction is

eothermic and is called caron de#osition reaction& he



former reaction is of etreme im#ortance for the economy and

smooth running of the last furnace& 't occurs at high

tem#eratures, ao!e aout 10000+, and therefore consumes an

enormous amount of heat in the lo"er third of the last furnace&

he caron de#osition reaction is most #ronounced at

tem#eratures 500-550=+ and conse(uently takes #lace in the

u##er #ortion of the shaft&

)+

*



)+

1

Since moles of +: are #roduced from 1 mole of +:7

caron eing solid2, the oudouard reaction is

de#endent on #ressure&

he isoars in the #re!ious figure sho" that at any gi!en



# g y g

tem#erature the e(uilirium %+07 increases "ith

increasing #ressure&

he staility of +: decreases "ith decreasing

tem#erature and increasing #ressure& he maimum

instaility is et"een )00 to 800=+ as sho"n y the stee#

slo#e of the cur!es&

)+

)

he reaction !elocity ecomes so slo" elo" aout

900=+ that a negligile amount of +: is decom#osed

into +: and +&



he reaction is accelerated in the #resence of catalysts

"hich #ro!ide nucleation sites for de#osition of caron&

'n the #resence of catalysts, the re!erse of reaction

accelerates ao!e 900=+ and reaches a maimum

et"een 500-5500+&

)+

C

CO2

emii(n

,ndustry -ontribution .

/ower 1

Transport 1

&teel 10

other 23



emii(n

)+

7



The purpose of > is to introduce more

o"gen to urn more caron " lo/ing more

air and at the same time maintaining thelinear gas 'elocit" 5and pressure drop6



a a d at t e sa e t e a ta g t elinear gas 'elocit" 5and pressure drop6

identical to that in the con'entional practice

/ithout an" formation of channels$

maldistriution of gas$ increase in coke rateor flue dust emission

Ad'antages!

◦

0or the same 'olume flo/ rate$ a greater mass of air5hence$ o"gen6 can e lo/n /ith &T# higher output

)+

;

A major enefit that is so o'ious is increased

production rate ecause of increased time of contact of

gas and solid as a result of reduced 'elocit" of gases

through the furnace Increased pressure also increases



through the furnace- Increased pressure also increases

the reduction rate of oide

Suppression of .oudouard reaction 5*) )=6 and

hence sa'ings in fuel

More uniform distriution of gas 'elocit" and reduction

across furnace cross%section smoother furnace

operation due to increased permeailit"

)+

<

less flue dust losses$ less 'ariation of coke input$ etter

maintenance of the thermal state of the hearth$ more

uniform iron anal"sis



More uniform operation /ith lo/er and more consistent

hot metal silicon content ha'e een claimed to e the

enefit of high top pressure

.hilai Steel #lant 5operati'e6$ RS# "et to implement

)+

+

Si=) \Si=] \=]

0rom ao'e euation it can e seen that partial



0rom ao'e euation it can e seen that partial

pressure of Si= can e rought do/n " increasing

the partial pressure of = in other /ords the Si=)

reduction reaction can e discouraged " application

of top pressure /hich enales a higher last pressure

and hence an increase in partial pressure of =-

)+

2



)2

*

The last 'olume and therefore the coke

throughput can e increased " C*



g p "percent /ith the maintenance of identical

pressure drop and gas 'elocit" conditions

in the last furnace " increasing the toppressure to )-1 from 1-1 ata and ottom

pressure to C-@ from )-@ ata under the

gi'en lo/ing conditions-

)2

1

racewa adiabatic #la+e te+perature/

This is the highest temperature a'ailale inside the

furnace- There is temperature gradient in 'ertical



g

direction on either side of this >one- This temperature is

criticall" related to the hearth temperature kno/n as

operating temperature of the furnace- It is euall"

related to the top gas temperature such that the hot

race/a" gasses ha'e to impart their heat to the

descending urden to the etent epected and lea'ethe furnace as off%gases at the desired temperature-

)2

)



)2

C



)2

7

The primar" purpose of using injectants /ith the

last is profitailit" /hich depends upon the



p " p p

relati'e price of coke and injectants and the

amount of coke that can e sa'ed per unit of the

latter$ i-e-$ upon the replacement ratio!

)2

@



)2

;

&)* = &) ^^^^^516

&= 51)**P6 )<** kcalKkg



#resence of moisture in the last generates doule the

'olume of reducing gas per mole of caron urnt- As per

E-1 for e'er" caron urnt one mole of = and an

additional mole of h"drogen /ill e a'ailale as product

of urning of coke for reduction in osh and stack-

)2

<

The more the moisture the more /ill e this additional

h"drogen a'ailale-

,ineticall" h"drogen reduction of iron oide is faster thanth t = f it ll i # f



that " = ecause of its small si>e- #resence of

moisture helps to urn coke at a faster rate /ith its

attendant fa'orale effects-

Some of the endothermic heat of moisture disintegration

is compensated " /a" of eothermic reduction of iron

oide " h"drogen-

)2

+

higher gasif"ing po/er /hich intensifies coke

consumption In the race/a"



smoothens the temperature gradient and facilitates stock

descent

enlarges the comustion >one and accelerates stock

descent heats up the aial >one maintains thermal

state of the hearth

)2

2

e'en /ith incomplete temperature compensation$ the coke

rate ma" not rise ecause of higher reducing po/er and



higher heat transfer coefficient of h"drogen

decreases pressure loss due to lo/er densit" and 'iscosit" of

h"drogen-

The last pressure ma" drop e'en b *-1%*-) atm- /hich

means the furnace can e lo/n at a higher last rate-

C*

*

It has een estimated that for an increase of )* g1+'

moisture in the last the endothermicit" can e

compensated " a rise of )**P in the last preheat-



p " p

." increasing moisture and compensating it "

additional rise of preheat means that cheaper heat

energ" can e used to feed the furnace and there"

decrease the coke consumption and economise the

operation-

C*

1

="gen enrichment of the last and moisture enrichment

ha'e uite opposite thermal effects- The t/o can e saddled

together to otain etter inputs



together to otain etter inputs-

&ot last temperature$ etent of o"gen enrichment and

humidification of last ha'e to e adjusted as interrelated

parameters simultaneousl" to otain optimum conditions of

operation for maimum enefits such as minimum coke rate$

higher producti'it" and so on-

C*

)

The reasons for the injection of coal ha'e een

economic as /ell as operational fleiilit" and include

the follo/ing!

After the steep rise in oil prices follo/ing the oil crisis$iron makers /ere compelled to aandon hea'" oil



iron makers /ere compelled to aandon hea'" oil

injection and /ere looking for a less epensi'e auiliar"

fuel-

#I accommodate shortages of coking capacit"$ "replacing coke " coal in the last furnaces- After a

thorough in'estment anal"sis$ it has een found that a

reliale coal injection s"stem reuires much lo/er

capital cost and in'ol'es operating cost than theetension of coking capacit"--

C*

C

oal causes a lo/er reduction in flame

temperature per unit injection than oil or natural

gas- It$ therefore$ allo/s more scope for last

temperature adjustmentKo"gen enrichment for



increased rates of injection and conseuentl"$ less

coke consumption-

The #I s"stem design is capale of

injecting coal on a continuous and stale asis and

ensure accurate and uniform distriution

C*

7

The coke sa'ings from flued urden emanate from the follo/ing

causes !

etter reduciilit" and enhanced indirect reduction 5;%< kg- sa'ed from

e'er" 1 percent increase in indirect reduction6



use of higher last temperatures ecause the thermal load is smaller

and the slag is pre%made the primar" slag melts at higher temperatures

and does so /ithin a 'erticall" narro/ softening >one

a'oidance of caron dioide generated from limestone in the stack

/hich ad'ersel" affects indirect reduction

transference of heat of calcination from the furnace to the

agglomerating plant-

C*

@


large bell is replaced by a distributor

chute with 2 hoppers A i h i id d i id



A rotating chute is provided inside


Advantages:Advantages:

Greater charge distributionfleibility !ore operational safety and

easy control over varying

charging particles "ess wearing parts: easy

!aintenance

C*

;



C*

<


control can e summarised as follo/s

Increased producti'it"$ decreased coke rate$ impro'ed



furnace life

Reduced refractor" erosion


as slips

Impro'ed efficienc" of gas utilisation and its indirect

reduction

C*

+


hot metal ualit"

Reduced tu"ere losses and minimisation of scaffoldformation



formation

(o/er dust emission o/ing to uniform distriution of

fines- All these ad'antages ha'e impro'ed the o'erall

efficienc"$ there" making the process more competiti'e-

C*

2

oal%ased #rocesses oal%ased Rotar" ,iln #rocesses like S/*F

+odir, ;ccar, D*, D*+ oal%ased #rocesses Hsing Rotar" &earth 0urnaces



oal%ased #rocesses Hsing Rotar" &earth 0urnaces

like ;S?A, +:?A, 'F?A+: Gas%ased #rocesses

Gas%ased Reduction in Stationar" Retorts >I-rocess

Gas%ased Shaft 0urnace #rocesses! Midre Gas%ased Direct Reduction in 0luidised .eds! 0inmet

C1

*



C1

1

Non%metallurgical cheaper coals are readil" a'ailale and

processes ha'e een de'eloped /herein caron of such coals

is used to pro'ide heat as /ell as the reducing gas-



Iron oide in contact /ith caron /hen heated results in

reduction of oide to metallic iron- This reduction is more due to

the urning of caron first follo/ed " reduction " the caron

monoide gas generated from urning-

C1

)

This is the reason /h" these processes are termed as coal-based

processes- These are more popularl" carried out in hori>ontal rotar"

kilns- .ut 'ertical shaft furnaces ha'e also een used as reactors

for this process in some rare cases-



This is also a counter current process to the etent that solid oide

tra'els do/n/ards and the gases formed on urning of coal ascend

/ith respect to the inclination of the kiln or the shaft reactor- A long kiln$ easil" <*%+* m in length and fe/ meters in diameter$

slightl" inclined to the hori>ontal and rotating slo/l" around its o/n

ais is emplo"ed as a reactor in these processes-

C1

C

The indi'idual designs do differ in details- The charge is fed from

that end /hich is at a higher le'el- The charge tra'els under gra'it"

aided " the rotation motion$ through se'eral heating >ones and thereduced iron oide product comes out of the other end of the kiln-



p

The throughput rate of solid iron oide$ its reduciilit"$ its si>e$

gangue contents$ the rotation of kiln and other related factors are

adjusted such that the oide is reduced to the etent of 2C%2@F "

the time it tra'els the /hole length of the kiln- This reduction is slo/

and continuous and takes place o'er the length of the kiln- In this

process the iron oide gets heated to a maimum of 1*@*P-

C1

7

The gas%ased shaft furnace processes$ /hich ha'e ecome " far the

most popular for the production of sponge iron$ emplo" a 'ertical shaft

furnace in /hich$ as in the case of a last furnace$ lump ore and pellets

are charged at the top using a charging s"stem similar to a last furnace-



a e c a ged a e op us g a c a g g s"s e s a o a as u ace

Reformed natural gas after pre%heating is introduced in the lo/er portion

of the shaft- As the hot reducing gas flo/s up/ards$ reduction takes

place continuousl"- &ence$ these processes are often referred to as

continuous countercurrent +oving bed processes. In this categor"$ the

?idre #rocess is dominant$ follo/ed " >I ''' and >I 'J&

C1

@

This process /as de'eloped " Midland Ross orporation of

le'eland$ HSA in 12;<- The reducing gas is$ as usual$ generated "

reforming natural gas- In the Midre reforming s"stem$ a proprietar"nickel catal"st is used- A single reformer is utilised instead of a



" g

reformerKheater comination

The iron oide feed to a Midre shaft can e in the form of pellets or

lump ore &o/e'er$ generall" speaking$ the charge consists of around

;*F pellets and 7*F lump ore of a particular t"pe- #ellets are the

preferred feedstock o/ing to their superior ph"sicochemical

characteristics compared /ith lump ores-$

C1

;



C1

<

The spent reducing gas 5or top gas6 lea'ing the shaft furnace at a

temperature of 7**%7@*P is cooled and cleaned in a gas scruer

efore approimatel" ;*F of the gas is returned to the reformer and

the rest used as a fuel- The process gas is compressed and pre%

heated efore entering the reformer at around 2**P$ /here it is

mied /ith make%up natural gas- The reformed gas made up mostl" of



caron monoide and h"drogen eits from the reformer at aout

+@*P- The ratio of & 0 to +: is controlled at aout 1&5-1&8$ so that

the reducing 2ualit o# the gas is maintained for est operations- The

iron oide urden is first heated to the process temperature efore it is

metallised " the up/ard flo/ing$ countercurrent reducing gas

injected at +**%+<*P through tu"eres located at the ottom of the

c"lindrical section of the shaft-

C1

+

The reduced material then passes through a transition >one efore

reaching the lo/er conical section of the furnace- (o/ caron DR1 5less

than 1-@F 6 is directl" cooled using a circulating stream of cooled

ehaust gas introduced in the conical section$ efore cold DRl is

discharged- 4hen higher caron DRl 5up to 7-*F 6 has to e produced$



natural gas is introduced along /ith cooling gas into the conical section-

In this >one$ natural gas readil" decomposes 5cracks6 in the presence of

highl" reacti'e metallic DRI$ there" generating nascent caron$ /hich

gets asored in the product efore it is discharged- In oth cases$ the

final product is D*l "ith K3-K9% metallisation, "ith the desired

caron content& A large numer of Midre plants are operating

successfull" all o'er the /orld-

C1

2



C)

*

Hntil recentl"$ last furnaces /ere the onl" source of hot

metal on a ulk scale- &o/e'er$ /ith the /orld

i i d l hif f i d l l



/itnessing a gradual shift from integrated steel plants

using the .last 0umace%.=0 comination to a

multiplicit" of smaller mini%mills essentiall" ased on

electric arc furnaces$ alternati'e means of producing hot

metal using 3+elting eduction 5SR6 ha'e come into

eistence.

C)

1



C)

)

As the name implies$ smelting reduction in'ol'es oth reduction and

smelting$ i-e- melting accom#anied y chemical reactions2&

The unit operations that take place in an" smelting reduction process

are summarised in net figure- In an ideal SR reactor$ in the strictest sense$ all the reduction

reactions should take place together in the liuid state in a single%step



reactions should take place together in the liuid state in a single%step-

In actual practice$ for effecti'e process control$ most SR processes

utilise t/o reactors and at least t/o$ if not three$ process steps that

include! the remo'al of o"gen from the oide in the solid%state to

'ar"ing etents in stage one$ follo/ed " the remo'al of the remaining

o"gen 'ia liuid phase reduction reactions in stage t/o- Sometimes$

the latter is completed in t/o steps rather than one$ i-e- SR then

ecomes a three%stage operation-

The initial reduction of iron oide egins in the temperature range of

+@*P to 1*@*P- The asic reactions in'ol'ed are as follo/s!

C)

C



C)

7



C)

@

Hp to this stage$ SR is similar to solid%state DR- .e"ond solid%state

reduction of haematiteK magnetite to /ustite$ smelting reduction$

essentiall" in'ol'es reduction of molten e: y +:&

This gi'es rise to far higher transport rates o/ing to con'ection and



This gi'es rise to far higher transport rates o/ing to con'ection$ and

a remarkale increase in the con'ersion rate ecause of

enlargement in the specific phase contact area- The latter is a direct

conseuence of the- dispersed nature of the phases- These t/o

major ad'antages of SR accrue ecause of the formation of liuid

phases$ /hich does not happen in DR-

C)

;

0rom studies on the oidation and reduction eha'iour of pure molten

iron oide " =K =) mitures at l@**P$ it has een concluded that the

rate controlling step for oth oidation and reduction is the inter%diffusion

of iron and o"gen atoms /ithin the melt- It has also een found that

mass transport pla"s an important role in the reduction kinetics- The



o'erall reaction rate is proportional to the suare root of the gas flo/ rate-

herefore, all out efforts are made to increase the amount of gas

that is a!ailale for reduction&

To generate sufficient amount of reducing gas$ all SR processes

consume fairl" large uantities of reductant 5normall" coal6- &a'ing

generated the large 'olume of gas that is reuired$ its effecti'e utilisationecomes etremel" important-

C)

<

&o/e'er$ this gi'es rise to one of the inherent deficiencies of SR$i-e- /ith most SR reactor configurations gi'en the producti'it"

reuirements$ the entire gas cannot e full" utilised in the process$

and rich gas at a high temperature lea'es the SR reactor-

It is for this reason that the use of the eport gas in an" SR process

has a marked influence on the cost of the hot metal made- 'n fact$ inman" cases$ unless the net eport gas from the SR reactor is

gainf ll tilised ironmaking itself ecomes totall neconomical



gainfull" utilised$ ironmaking itself ecomes totall" uneconomical-

4ithout sufficient credit for the off%gas$ the cost of hot metal made

" smelting reduction can e as much as 90-50% higher than that

of last furnace hot metal, des#ite starting "ith less e#ensi!eand inferior grade ra" materials-

The re'erse is the case if adeuate credit can e otained from the

utilisation of the off%gases- The most con'enient /a" to utilise the

eit gas is to cogenerate electrical po/er- Alternati'el"$ the eit gas

can e fed to a shaft furnace direct reduction unit$ located adjacentto the smelting reduction reactor-

C)

+

This essentiall" eliminates the cokemaking step and uses directl"

coal as the fuel as /ell as the reducing agent- This process

produces molten iron in a t"o-ste# reduction melting o#eration-

=ne reactor is melter-gasifier and the other is #re-reducer - In the



= e eacto s e te gas e a d t e ot e s # e educe t e

pre%reducer$ iron oide is reduced in counter%flo/ principle- The hot

sponge is discharged " scre/ con'e"ors into the melting reactor-oal is introduced in the melting%gassif"ing >one along /ith

o"gen gas at the rate of @**%;** NmCKthm- The flo/ 'elocit" is

chosen such that temperature in the range of 1@**%1+**P is main

tained-

C)

2

The reducing gas containing nearl" 85% +: is hot dedusted and cooled

to +**%2**P efore leading it into the pre%reducer- The process is

designed to operate at up to @ ars-

0lues like limestone$ dolomite$ silica sand$ etc- are added along /ith the



ore to finall" make up the right ualit" of slag-

Around 500-700 Lg of fied caron is reuired to make a tonne of hot

metal- Along /ith 300 Fm3 /thm oygen gas-

The e#ort gas generated in the melting >one is rich and ma" ha'e

calorific 'alue of around 7500 kM/Fm3 and can e used in the plant

usefull"

CC

*



CC

1



CC

)

In the 0INE_ #rocess fine ore is preheated and reduced to DRI in a

train of four or three stage fluidi>ed ed reactors-

The fine DRI is compacted and then charged in the form of &otompacted Iron 5&I6 into the melter gasifier- So$ efore charging



to the melter% gasifier unit of the 0INE_ unit$ this material is

compacted in a hot riuetting press to gi'e hot compacted iron

5&I6

since the melter% gasifier can not use fine material 5to ensure

permeailit" in the ed6-

Non%coking coal is riuetted and is fed to the melter gasifier /here

it is gasified /ith o"gen

CC

C



B3

=r. ,mara>it ,arkar

ssociate rofessor=ept. of )etallurgical and )aterials?ngg.

@ational institute of Technolog3*ourkela

CC

7

Int#(ducti(n

C)anging ;atte#n ( teel <aing

<(de#n teel maing % =OF > ?D teel maing

ili R i



ilic(n Reacti(n

<anganee #eacti(n

;)(!)(#(u Reacti(n

Ca#4(n Reacti(n

acuum Degaing

CC

@

Steelmaking is con'ersion of pig iron containing aout

1* /t /eight of caron $ silicon$ manganese$

phosphorus$ sulphur etc to steel /ith a controlledamount of impurities to the etent of aout 1 /eight

percent



percent-

4ith the eception of sulphur remo'al of all other

impurities is fa'ored under oidi>ing conditions-

In the case of oidation of caron the product$ eing a

gas$ passes off into the atmosphere ut rest of the oide

products shall remain in contact /ith the iron melt in the

form of a slag phase-

CC

;

Si=)$ Mn= and #)=@ formed " oidation of Si$ Mn and #$

respecti'el" /ill join the slag phase-

The formation of these oides can e facilitated "

decreasing their acti'ities /hich is possile " pro'iding

oides of opposite chemical character ser'ing as flu-



pp g

As Si=) and #)=@ are acid oides a asic flu is reuired

for formation and eas" remo'al of the slag- A strong asic slag is formed " addition of a= and K or

Mg= to asor #)=@ and Si=)-

The remo'al of caron /ill take place in the form ofgaseous products 5=6-

CC

<



CC

+



CC

2



C7

*

During refining$ controlled oidation of the impurities in hot metal

5/ith the eception of sulphur6 takes place once o"gen is lo/n at

supersonic speeds onto the liuid ath- The interaction of the o"gen jet5s6 /ith the ath produces crater5s6



on the surface$ from the outer lip5s6 of /hich$ a large numer of tin"

metal droplets get splashed-

These droplets reside for a short time in the slag ao'e the ath-

Therefore$ the eistence of a metal%slag%gas emulsion /ithin the

'essel$ 'irtuall" during the entire lo/ingKrefining period is an integral

part of .=0 steelmaking-

C7

1

This is the reason /h" the slag%metal reactions like

dephosphorisation and gas%metal reactions like decarurisation

proceed so rapidl" in the .=0 process

The droplets ultimatel" return to the metal ath- The etent of

emulsification 'aries at different stages of the lo/ing period as



emulsification 'aries at different stages of the lo/ing period$ as

depicted schematicall" -

A minimum amount of slag$ /ith the desired characteristics$ isnecessar" for ensuring that the emulsion is stale$ i-e- the slag

should not e too 'iscous$ or too V/ater"V- =nl" in this /a" can the

kinetics of the remo'al of the impurities e enhanced-

C7

)

0or encouraging uick formation of the appropriate t"pe of slag$

limeKdolomiteKother fluing agents /ith adeuate reactivit are added right from

the eginning of the lo/- The reacti'it" of the fluing agents$ primaril" lime5consumption ;*%1** kgKtls6$ determines ho/ uickl" slag is formed 5t"picall"



/ithin 7%@ minutes after the commencement of the lo/6-

The rate at /hich o"gen is lo/n through the lance$ the numer of openings

5holes6 on the lance tip$ the distance et/een the lance tip and the ath surface

5lance height6$ the characteristics of the o"gen jets as the" impinge on the ath

surface$ the 'olume$ asicit" and fluidit" of the slag$ the temperature conditions

in the ath and man" other operational 'ariales influence the refining-

C7

C



C7

7



C7

@

There are t/o distinct >ones of refining in a (D 'essel viz. the

reactions in the emulsion and in the ulk phase- The

contriution of ulk refining$ i.e. refining in impact >one and at

the ulk slag%metal interface$ is dominant in the eginning

since emulsion is "et to form properl" It has also een



since emulsion is "et to form properl"- It has also een

elie'ed that sustantial decarurisation of droplets can occur

ecause of its free eposure to an oidising gas$ particularl"

in the eginning- As the emulsion uilds up the emulsion

refining attains a dominant role- The ulk phase refining

dominates again to/ards the end /hen the emulsioncollapses-

C7

;

onditions for dephosphorisation are that the slag should e asic$ thin and

oidising and$ that the temperature should e lo/-

Dephosphorisation$ therefore$ does not take place efficientl" until such a slag is

formed- Such a slag is formed in (D process onl" after the initial 7%; minutes of

lo/ing-



The rate of dephosphorisation picks up concurrentl" /ith the rate of

decarurisation-

0or efficient decarurisation as /ell as dephosphorisation the slag should$

therefore$ form as earl" as possile in the process- If a preformed slag is

present as in a doule slag practice /herein the second$ slag is retained in the

'essel in part or full$ the decarurisation rate cur'e rises more steepl" in the

eginning

C7

<

Dephosphorisation is 'er" rapid in the emulsion ecause of the

increased interfacial area and efficient mass transport-

#hosphorus should$ therefore$ e full" eliminated efore the

emulsion collapses- If this is not achie'ed the heat /ill ha'e to



e kept /aiting for dephosphorisation to take place and$ in the

ulk phase$ it is etremel" slo/ as compared to that in theemulsion- In general dephosphorisation should e o'er " the

time caron is do/n to *Q<%1Q*F$ i.e. /ell ahead of the collapse

of emulsion /hich egins at around *QCF-

C7

+

The relati'e rates of dephosphorisation and decarurisation can e

controlled " adjusting the lance height or " adjusting the flo/ rate of

o"gen-

Raising the height of the lance or decreasing the o"gen pressure

decreases the gas%metal reactions in the emulsion 5i e decarurisation6



decreases the gas%metal reactions in the emulsion 5i-e- decarurisation6

and vice versa.

The dephosphorisation reaction is thus relati'el" increased " the ao'e

change and vice versa. To/ards the end /hen temperature is high the

danger of phosphorus re'ersion does eist ut it can e pre'ented "

maintaining a high asicit" of the slag-

C7

2

The process of decaruri>ation includes at least three stages!

suppl" of reagents % caron and o"gen % to the reaction site

the reaction XcY X*Y proper and

e'olution of reaction products % = ules into the gaseous phase -

The apparent acti'ation energ" of the reaction XY X*Y = is



- The apparent acti'ation energ" of the reaction XY X*Y = is

relati'el" small 5according to 'arious researchers$ 4 +****%1)****

+ol)$ /hich suggests that the reaction occurs practicall"

instantaneousl"- The soluilit" of = in molten steel is also negligile-

Accordingl"$ the process can e limited " either the first or the third

stage-

C@

*

The nature of kinetic cur'es of caron urning%off at its 'arious

concentrations is different! on attaining a certain Vcritical` le'el of

concentration of caron 5*-1@%*-C@F6$ the rate of caron oidation is

oser'ed to drop noticeal"-

It has also een estalished in eperiments that the critical caron



It has also een estalished in eperiments that the critical caron

concentration is determined " the intensit" of suppl" of oidant to the ath

5it increases /ith increasing intensit" of o"gen suppl" and decreases

during ath oil or metal stirring6-

C@

1

Thus$ at caron concentrations ao'e the critical 'alue`$ the intensit" of

decarurisation reaction is determined " the suppl" of the oidant and at

those elo/ the critical 'alue$ " caron diffusion to the reaction place - This means practicall" that$ if the caron content of the metal is sufficientl"



high$ the rate of caron oidation /ill e higher at a higher intensit" of o"gen

suppl"- At lo/ concentrations of caron$ ho/e'er$ a higher le'el of intensit" of

o"gen suppl" /ill not produce the desired effect and the ath should e

agitated forcedl" 5in order to intensif" the suppl" of caron to the reaction

place6 so as to increase the rate of caron oidation-

C@

)

The rate of decaruri>ation can also e limited " the third stage$ the e'olution of =-

0or a ule of = to form in metal$ It must o'ercome the pressure of the column of

metal 5pm6$ slag 5psl6$ and of the atmosphere 5pat6 ao'e the ule and also the forces

of the cohesion /ith the liuid$ )bKr i-e-

p=e' pm psl pat )bKr



The 'alue of )bKr ecomes practicall" sensile at lo/ 'alues of ule radius! at r I

mm it can e neglected- 0ormation of ules in the ulk of liuid metal is practicall"

impossile-- The" can onl" form on interfaces et/een- phases$ such as slag % metal$

non%metallic inclusion % metal$ gas ule % metal or lining % metal- The most fa'orale

conditions for the nucleation of = ules eist on oundaries et/een the metal

and refractor" lining /hich has a rough surface and is poorl" /ettale " the metal

C@

C



C@

7



C@

@



C@

;

lag e(luti(n

Du#ing =l(



C@

<

@ig) ilic(n !ig i#(n i #e:ui#ed in t)e acidteelmaing !#(cee t( mae #elatiel" acid lag

t( enu#e l(nge# lie ( t)e #e#act(#" lining.

O$idati(n ( ilic(n al( gene#ate uAcient )eat



O$idati(n ( ilic(n al( gene#ate uAcient )eat#e:ui#ed in cae ( t)e =eeme# !#(ce.

@(ee# 4aic teelmaing !#(cee need l(ilic(n i#(n 4ecaue t)e enti#e am(unt ( acid ilicadue t( t)e ($idati(n ( ilic(n )a t( 4e neut#alied4" lime t( !#(duce lag it) 4aicit" CaO > iO2

#ati(9 4eteen 2 and B needed (# eectiedeul!)u#iati(n and de!)(!)(#iati(n.

C@

+

Due t( t)e t#(ng att#acti(n 4eteen i#(n and ilic(n/t)e Fe-i "tem e$)i4it la#ge negatie deiati(n#(m t)e Ra(ult l(. T)e actiit" c(eAcient ( ilic(nin i#(n in !#eence ( (t)e# element i gien 4"

l(g i + 0.18E&C 0.11E& i 0.058E& Gl



g i

-0.058 E & 0.025 E & 0.01B E & Cu

0.005 E & Ni

0.002 E & <n % 0.0023 E & C( % 0. 23 E &O

O$idati(n ( ilic(n i an e$(t)e#mic #eacti(n and!#(ide (me ( t)e )eat necea#" (# #ie (

tem!e#atu#e ( t)e 4at) du#ing 4l(ing.

C@

2

Si 9= reaction is go'erned " G* 's T euation!

XSi Y ) X=Y 5Si=) 6$ Go %17)** @@-* T cals-

The acti'it" coefficient of o"gen decreases and that of silicon increases/ith increasing silicon content in iron-

Silica is a 'er" stale oide$ hence once silicon is oidised to Si=) the



" )

danger of its re'ersion does not arise-

C;

*



C;

1



C;

)

T)e e$t#emel" l( actiit" ( ilica in 4aic teelmainglag !(e n( dange# ( !#ee#ential #educti(n ( ilicalie t)at ( !)(!)(#u #em(al.

In 4aic teelmaing !#(ce t)e ilic(n c(ntent ( !ig

i#(n )(uld 4e e!t a l( a !(i4le t( dec#eae t)elime c(num!ti(n it) t)e !#ime (4Hectie ( c(nt#(lling



lime c(num!ti(n it) t)e !#ime (4Hectie ( c(nt#(llingt)e #e:ui#ed 4aicit" (# !)(!)(#u #em(al at a

minimum lag (lume.

In cae ( )ig) ilic(n ente#ing t)e 4aic teelmaingu#nace d(u4le lag !#actice )a t( 4e ad(!ted.

Glte#natiel"/ e$te#nal deilic(niati(n ( t)e )(t metal)a t( 4e d(ne (utide t)e 4lat u#nace 4e(#e c)a#ging

it in a 4aic teelmaing u#nace.

C;

C

G4(ut 50 t( 75& ( t)e manganee in t)e4u#den get #educed al(ng it) t)e !ig i#(n#eulting it manganee c(ntent 4eteen 0.5t( 2.5&.



Du#ing teelmaing maH(# am(unt (manganee i l(t int( t)e lag and e#" littlei utilied t( meet t)e !ecicati(n.

(me manganee i #e:ui#ed t( c(nt#(l t)edelete#i(u eect ( ul!)u# and ($"gen andal( (# im!#(ement ( mec)anical !#(!e#tie( t)e teel.

C;

7

@ence c(nditi(n (# ma$imum #ec(e#" (manganee can 4e de#ied 4" c(nide#ing t)ee:uili4#ia

Fe29 <nJ + <n29 FeJ

FeO9 <nJ + <nO9 FeJ

[ ] [ ](23'

.('(' 22 Fe f aaK

FeMnFeMn++

χ



Gt e:uili4#ium t)e <n lag-metal dit#i4uti(n#elati(n i gien 4"

[ ] [ ]

[ ][ ](24'

.('.('or

(23'.('('

2

2

22

Mn Fe K

Mn f aa K

Fe

Mn

Mn Fe

Fe Mn

Mn Fe

Fe Mn

+

+

++

=′

==

χ

χ

χ

[ ] [ ] (20'.

('

.

(' 22

Fe K

Mn

Fe Mn ++

′=

χ χ

C;

@

F#(m t)e e:uati(n it i a!!a#ent t)at t)ec(nditi(n (# t)e )ig)et !(i4le #ec(e#" ( <n

i.e. minimum lag-metal dit#i4uti(n #ati( a#e i9 min KFe29/ #e:ui#ing a l( FeO c(ntent in t)e

l



lag. ii9 min LM #e:ui#e a l( iO2 c(ntent and a )ig)

tem!e#atu#e a eident #(m t)e #elati(n )(ingeect a#i(u ani(n in t)e lag. 0$14$20$21$3log 23

4

4

4

−−−− +++=′ F O POSiO

K χ χ χ χ

C;

;

From the gure it isevident that for slagscontaining about $#%

)n9 a ma2imum of #.!%)n is found in metal.



The slag containing 5#%,i9$ /the rest being Fe9

and )n90 with increasing)n content of the metalthe /)n90 content of theslag increases whereasthe o23gen content of the

metal decreases andsilicon content increases.

C;

<

De!ite it e#" l( 4(iling !(int ignicantam(unt ( ; get di(led in !ig i#(n due t(t#(ng att#acti(n (# i#(n.

<aing ue ( t)e inte#acti(n c(eAcient (#



gt)e eect ( a#i(u element (n t)e actiit"

c(eAcient ( !)(!)(#u in i#(n/ t)e actiit"( ; can 4e etimated 4" t)e e$!#ei(n l(g ; + 0.13E&C 0.13E&O 0.12E&i

0.062E&; 0.02BE&Cu 0.028E&

0.006E&<n % 0.0002E&Ni % 0.03E&C#

C;

+

G e#" cl(e ta4ilit" ( FeO/ Fe2O3 and ;2O5 i

eident #(m t)e i#(n and !)(!)(#u line int)e lling)am diag#am.

@ence !#acticall" all t)e !)(!)(#u !#eent in



t)e (#e get #educed al(ng it) i#(n in t)e 4latu#nace and H(in !ig i#(n.

Du#ing teelmaing t)e actiit" ( ;2O5 in t)e

lag ( 4aicit" 2.B i #educed d#aticall" t( 10-

15-10-20. Gctiit" ( ;2O5 in teelmaig lag i e#" l(

een i it c(ntain 25& ;2O5.

C;

2



C<

*

T)u (# eectie #em(al ( !)(!)(#u 4aicteelmaing !#(cee )ae t( em!l(" lag ()ig) 4aicit".

T)e dit#i4uti(n ( !)(!)(#u 4eteen lag andmetal can 4e de#i4ed a

#i-e- )

X#Y @X=Y C5=)%6 ) 5#=7C%6 51)6



2;J 5FeO9 3 CaO9 + 3 CaO.;2O59 5FeJ

i.e. 2;J 5OJ 3O2-9 + 2 ;OB3-9

[ ] [ ]

[ ] [ ]

[ ] [ ] (10'('.

.

('5

asgivenis!etal)inthattoslagin phosphorusof ratiotheiswhich5inde)isingdephosphor The

(14'..

'13(:ruleTe!kinApplying$$

263260

/

/

302

2

3

('

02

2

2

26134

2

34

2

34

−

−

−

−

−

−

′==∴

=

=

O

PO

OO P

PO

OO P

PO

O K P

O f P f

aaa

a K

χ

χ

χ

χ

C<

1

From the gure it is clear that =

increases with increase in the/Fe90 content upto !5% due to

the high o2idiing power.

Be3ond this = decreases due to

decrease in the lime proportion



decrease in the lime proportion.

=ephosphorisation is moree:ective at lower temperaturebecause = increases with

decrease of temperature.

C<

)



C<

C

T)e (da a) i 100 time m(#e eectie c(m!a#ed t(lime (n m(la# 4ai 4ut it i a(ided in !#actice due t( itee#e c(##(ie acti(n (n u#nace lining.

T)e magneia c(ntent ( a 4aic teelmaing lag#eac)e e:uili4#ium it) t)e lining )ence n(t unde#c(nt#(l and <nO de!end (n c)a#ge and )ence n(t muc)dH 4l



adHuta4le. T)e teel mae# )a t)e (!ti(n ( c(nt#(lling lime/ ilica

and FeO. F(# c)a#ge c(ntaining )ig) & ; m(#e t)an (ne lag a#e

made t( de!)(!)(#ie metal 4at) t( t)e dei#ed leel. In 4#ie )ig) 4aicit"/ l( tem!e#atu#e/ and FeO c(ntent

a#(und 15& a(u# de!)(!)(#iati(n ( metal 4" 4aiclag.

C<

7

T)e (!timum c(nditi(n (# de!)(!)(#iati(ncan 4e

de#ied #(m t)e e:uati(n dening t)e inde$

[ ] [ ] 263260

('..

('2

26134

−

−

′==O

PO

P O K P

D χ χ



1.=aic lag gie a )ig) alue ( KO2-

2.@ig) lime c(ntent % lime i t)e dialent ($idemaing t)e la#get c(nt#i4uti(n t( LM l(g L +21NCa 18 N<g 13N<n 12 NFe

3.Fe##(u ($ide cl(e t( 15& .

B.?( tem!e#atu#e gie a )ig) alue ( LP.

C<

@

In #ening ( teel ($idati(n ( i/ <n and ; tae!lace at t)e lag-metal inte#ace.

T)e ($idati(n ( ca#4(n !#acticall" d(e n(t tae !laceat t)e lag-metal inte#ace 4ecaue ( t)e diAcult" (nucleati(n ( CO 4u44le t)e#e.

C O ti t l t t) t l i t



C-O #eacti(n tae !lace at t)e ga %metal inte#aceince it eliminate t)e neceit" ( nucleating ga

4u44le. Du#ing #ening ( teel ($"gen )a t( di(le #t in

t)e 4at) 4e(#e it #eact it) t)e di(led im!u#itie.

In t)e a4ence ( (t)e# lag (#ming c(ntituent at

1600(C li:uid i#(n can di(le ($"gen u! t( at 0.23t.&

C<

;

In teel maing t)e #eacti(n 4eteen ca#4(nand di(led ($"gen i ( utm(t im!(#tance.

Qene#all" !ig i#(n c(ntain a4(ut B t&ca#4(n.

T) l 4ilit 4 i t l i t d 4



T)e (lu4ilit" ( ca#4(n in teel i eected 4"t)e !#eence ( im!u#itie and all("ingelement.

;#eence ( N4/ / C#/ <n and inc#eae(lu4ilit" ( ca#4(n in i#(n )e#e a !#eence

( C(/ Ni/ n and Cu dec#eae it.

C<

<

#Thus soluilit" of caron in steel can e calculated " comining the inar" data from the follo/ing euation!



C<

+

O$idati(n ( Ca#4(n can 4e dicuedacc(#ding t( t)e #eacti(n

C O + CO/ Q0+ -5350 % ,.B8T cal.

pp COCO



Gt an" c)(en !#eu#e ( CO/ & C & O

indicate ine#e )"!e#4(lic #elati(n)i!

7.87.8 O foC fc

p

aa

p K CO

Oc

CO==

78.78. K

p

fo fc K

pOC COCO

==∴

C<

2



=uring o2idation period o23gen is continuousl3 transferredfrom the slag to the bath where it continuousl3 reacts withcarbon to give A9.The main resistance to the o23gen ow is the slagmetal and

the metalgas interfaces whereas inside the steel bath thetransfer of dissolved o23gen is ver3 fast.

C+

*

T)e actiit" c(eAcient( ca#4(n in i#(ninc#eae it)

inc#eaing ca#4(nc(ntent and t)at (($"gen dec#eae it)inc#eaing ca#4(n



inc#eaing ca#4(nc(ntent.

T)e net #eult i t)at t)e!#(duct & CJ & OJ (#a gien !CO dec#eae

lig)tl" it) inc#eaingca#4(n c(ntent a

)(n in Figu#e

C+

1

ince teel maing i a d"namic !#(ce/ t)ec(ncent#ati(n ( ca#4(n and ($"gen in t)e 4ulmetal !)ae i n(t in e:uili4#ium it) t)e!#eailing CO-!#eu#e in t)e 4u44le.

Gt t)e ga 4u44le%metal inte#ace t)e #eacti(n i



Gt t)e ga 4u44le metal inte#ace t)e #eacti(n icl(e t( e:uili4#ium.

T)e e$!e#imentall" (4e#ed e$ce ($"gen andca#4(n in t)e 4ul metal !)ae i t)u )el!ul int#ane# ( t)e #eactant 4" diui(n t( t)e ga-metal inte#ace in t)e i(lentl" ti##ed metal 4at).

C+

)

G & OJ inc#eae it) aFeO9 in lag and & OJ

dec#eae it) & CJ in t)e 4at).

it (ll( t)at t)e i#(n ($ide c(ntent ( t)e laginc#eae it) dec#eaing ca#4(n in teel du#ing#ening.



@ence t)e#e i a gene#al t#end in t)e a#iati(n ( lag

c(m!(iti(n it) t)e ca#4(n c(ntent ( t)e metal.

F(# a gien t(tal i#(n ($ide in a lag/ a l(e# ca#4(n int)e teel c(##e!(nd t( a )ig)e# um ( & iO2 &

;2O59 in t)e lag.

C+

C



it)in t)e #ange ( 4aic lag/ (# a gien um ( &CaO & <gO & <nO t)e ca#4(n c(ntent ( teel

d(e n(t a#" muc) it) t)e FeO c(ntent ( t)e lag.

C+

7

Du#ing teelmaing i.e. #ening ( !ig i#(n )e#eim!u#itie lie ca#4(n/ ilic(n/ manganee and!)(!)(#u a#e eliminated t( t)e #e:ui#ed leel ($"gen/

nit#(gen and )"d#(gen get di(led a )a#mulim!u#itie.

G (lu4ilit" dec#eae it) dec#eae ( tem!e#atu#e



" !e$ce gae di(led in teel a#e li4e#ated du#ing

(lidicati(n. T)e e(luti(n ( t)e ga gie #ie t( t)e (#mati(n (

in (# !in )(le/ 4l( )(le/ !i!e etc.

T)e un(undne caued 4" t)ee caitie aect t)e

mec)anical !#(!e#tie ( teel

C+

@

Nit#(gen !ic u! du#ing teel maing◦ (!en atm(!)e#e

◦ #a mate#ial c)a#ged

◦ du#ing melting and>(# #ening

ect ( nit#(gen in teel◦ "ield-!(int !)en(mena



◦ GlN caue inte#g#anula# #actu#e

◦

nit#(gen ta4ilie t)e autenitic t#uctu#e Fact(# aecting t)e nit#(gen (lu4ilit" in teel.

◦ !a#tial !#eu#e ( nit#(gen in t)e 4lat

◦ time ( c(ntact

◦ lengt) ( ate# 4l( and

◦ t)e 4at) tem!e#atu#e

C+

;

ince nit#(gen di(le at(micall" in li:uid i#(n and teelin e#" mall !#(!(#ti(n it (lu4ilit" can 4e dicued inte#m ( iee#tM and @en#"M la

T)e#e i l( #ie in (lu4ilit" in (lid tate it) inc#eaing

-



tem!e#atu#e 4ut at t)e melting !(int it inc#eae e#"#a!idl". It al( #ie in li:uid teel 4ut at a l( #ate.

;#eence ( anadium/ ni(4ium/ tantalum/ c)#(mium/manganee/ m(l"4denum/ and tungten inc#eaenit#(gen (lu4ilit" in i#(n )e#ea it dec#eae in!#eence ( nicel/ c(4alt/ ilic(n and ca#4(n

C+

<



C+

+

@"d#(gen !ic u! teel maing◦ et (lid and #ut" c)a#ge mate#ial

◦ atm(!)e#ic )umidit"

◦ et #e#act(#" c)annel/ #unne# and c(ntaine#

ect ( )"d#(gen in teel



ect ( )"d#(gen in teel◦ Dec#eae ductilit"

◦ G!!ea#ance ( )ai#line c#ac e#i(ul" aect t)emec)anical !#(!e#tie

◦ F(#mati(n ( 4l( )(le and !in )(le.

C+

2

ate# a!(u# c(ming inc(ntact it) teel (# lag leadt( t)e (#mati(n ( )"d#(gen

)ic) get di(led in teelmelt a !e# #eacti(n

@2O g9 + 2@J1t.& 0J1 t.&



Gt t)e melting !(int ( i#(n

(lu4ilit" in delta i#(n ia!!#($imatel" 10 m?> 100g.

=e"(nd t)i )"d#(gen ill 4e#eHected du#ing (lidicati(n t(!#(duce un(und !(#(u ing(t

due t( ga e(luti(n.

C2

*

T)u !a#tial !#eu#e ( )"d#(gen/ andc(m!(iti(n ( teel and it tem!e#atu#e

c(nt#(l t)e )"d#(gen c(ntent ( teel.Gcc(#ding t( iee#tM la (lu4ilit" ()"d#(gen in !u#e i#(n i e$!#eed a



)"d#(gen in !u#e i#(n i e$!#eed a

;#eence ( ni(4ium/ tantalum/ titanium andnicel inc#eae t)e (lu4ilit" ( )"d#(gen ini#(n )e#ea it dec#eae in !#eu#e (ca#4(n/ ilic(n/ c)#(mium and c(4alt.

C2

1

T)e (4Hectie ( acuum degaing include #em(al( )"d#(gen #(m teel t( a(id l(ng annealing

t#eatment/ #em(al ( ($"gen a ca#4(n m(n($ideand !#(ducti(n ( teel it) e#" l( ca#4(n c(ntentS 0.03&9.



T)e !#inci!le i 4aed (n t)e ueulne ( t)e

iee#tM la #elati(n)i!.

T)e e:uati(n dem(nt#ate t)at u4Hecting t)em(lten teel t( acuum ill dec#eae t)e )"d#(gen/nit#(gen a ell a t)e ($"gen c(ntent ( t)e teel

acc(#ding t( t)e (ll(ing #ea(n

C2

)

2@J + @2 g9

2NJ + N2 g9CJ OJ + CO g9

T)e eectiene ( acuum t#eatment



inc#eae it) inc#eae in t)e u#ace a#ea

( li:uid teel e$!(ed t( acuum. F(# t)i !u#!(e metal i all(ed t( ( in

t)e (#m ( t)in t#eam (# een all ad#(!let t( accele#ate t)e degaing

!#(ce.

C2

C

G num4e# ( met)(d aaila4le (n c(mme#cial cale (#

acuum t#eatment ( teel ma" categ(#ied int( t)#eeg#(u!

1. ?adle Degaing T)e teeming ladle lled it) teel t( (ne (u#t) ( it

)eig)t i !laced inide a acuum c)am4e#.



t)e melt i ti##ed eit)e# 4" 4u44ling a#g(n (# 4"

elect#(magnetic inducti(n Int#(ducti(n ( ga (# ti##ing !#(ide inte#ace )ic)

acilitate degaing. In gene#al !um!ing i ca##ied (ut t( attain t)e

ultimate acuum ( 1-10 mm @g. )ic) i u!!(ed t(

4e ade:uate (# degaing.

C2

7

2. t#eam Degaing In t)i cae m(lten teel i all(ed t( (

d(n unde# acuum a a t#eam #(m t)eu#nace t( ladle t( an(t)e# ladle (# a m(uld.

G e#" )ig) #ate ( degaing i ac)ieed



G e#" )ig) #ate ( degaing i ac)ieed

due t( la#ge inc#eae in u#ace a#ea (m(lten teel in t)e (#m ( alling d#(!let. T)u c)(ice ( !#(!e# acuum !um! and

acuum c)am4e# i im!(#tant t( ac)iee

t)e ade:uate leel ( degaing.

C2

@

3. Ci#cuilati(n Degaing

R-@ degaing !#(ce

T)e ae#age #ate ( ci#culati(ni



i

12 t(n>min. Tent" minute a#e #e:ui#ed

t(

t#eat 100 t(n ( teel t( 4#ing

d(n ,0& #educti(n (

)"d#(gen c(ntent.

C2

;

D-> Jessel&The chamber is movedthrough 5#&6# cm with ac3cle time of $# sec. !#&!5%

steel is e2posed at a time.

7&!# c3cles are re<uired toe2pose the entire steel



e2pose the entire steelonce.

de<uate degassing isobtainedin $#&+# c3cles in !5&$#minutes.

C2

<




NIT Rourkela

C2

+



C2

2

!idation o# carbon .ottom lo/ing increases sharpl" the

intensit" of ath stirring and increases the area of gas%metal

oundaries 51*%)* times the 'alues t"pical of top lo/ing6 -

Since the h"drocarons supplied into the ath together /ith

o"gen dissociate into &)$ &)= and C8 gas ules in the



ath ha'e a lo/er partial pressure of caron monoide 59co )

All these factors facilitate sustantiall" the formation and

e'olution of caron monoide$ /hich leads to a higher rate of

decaruri>ation in ottom lo/ing

7*

*

The degree of oidation of metal and slag

Rem(al ( !)(!)(#(u ince t)e lag (



! ! gt)e 4(tt(m-4l(n c(ne#te# !#(ce )ae a

l( deg#ee ( ($idati(n alm(t du#ing t)e)(le (!e#ati(n/ t)e c(nditi(n e$itingdu#ing t)ee !e#i(d a#e una(#a4le (#

!)(!)(#u #em(al

7*

1

#rolems arise /hen the la"er of foaming slag created on the

surface of the molten metal eceeds the height of the 'essel and

o'erflo/s$ causing metal loss$ process disruption and

en'ironmental pollution- This phenomenon is commonl" referred to

as slopping-

http://www.sciencedirect.com/science?_ob=MiamiCaptionURL&_method=retrieve&_udi=B6V4N-4VKMW49-1&_image=fig3&_ba=3&_user=1657113&_coverDate=06/30/2009&_rdoc=1&_fmt=full&_orig=search&_cdi=5763&_issn=09591524&_pii=S0959152409000079&view=c&_acct=C000053917&_version=1&_urlVersion=0&_userid=1657113&md5=d44fd2f96211dfc97ca1f5b1058f5185



7*

)

.etter miing and homogeneit" in the ath offer the follo/ing

ad'antages!

(ess slopping$ since non%homogeneit" causes formation of regions /ith

high supersaturation and conseuent 'iolent reactions and ejections-

http://www.sciencedirect.com/science?_ob=MiamiCaptionURL&_method=retrieve&_udi=B6V4N-4VKMW49-1&_image=fig3&_ba=3&_user=1657113&_coverDate=06/30/2009&_rdoc=1&_fmt=full&_orig=search&_cdi=5763&_issn=09591524&_pii=S0959152409000079&view=c&_acct=C000053917&_version=1&_urlVersion=0&_userid=1657113&md5=d44fd2f96211dfc97ca1f5b1058f5185



.etter miing and mass transfer in the metal ath /ith closer approach

to euilirium for XY%X=Y%= reaction$ and conseuentl"$ lo/er ath

o"gen content at the same caron content

7*

C

.etter slag%metal miing and mass transfer andconseuentl"$ closer approach to slag% metal euilirium$

leading to!

o lo/er 0e= in slag and hence higher 0e "ield

o

transfer of more phosphorus from the metal to the slag 5i-e-etter ath dephosphorisation6

o transfer of more Mn from the slag to the metal$ and thus

etter Mn reco'er"



etter Mn reco'er"

o lo/er nitrogen and h"drogen contents of the ath- More reliale temperature measurement and sampling of

metal and slag$ and thus etter process control 0aster dissolution of the scrap added into the metal ath

7*

7

A small amount of inert gas$ aout CF of the 'olume of o"gen

lo/n from top$ introduced from ottom$ agitates the ath so

effecti'el" that slopping is almost eliminated-

&o/e'er for otaining near euilirium state of the s"stem

inside the 'essel a sustantial amount of gas has to e

i t d d f th tt



introduced from the ottom-

If )*%C*F of the total o"gen$ if lo/n from ottom$ can cause

adeuate stirring for the s"stem to achie'e near euilirium

conditions- The increase e"ond C*F therefore contriutes

negligile addition of enefits-

7*

@

The more the o"gen fraction lo/n from ottom the

less is the post comustion of = gas and

conseuentl" less is the scrap consumption in the

charge under identical conditions of processing-

.lo/ing of inert gas from ottom has a chilling effect



on ath and hence should e minimum- =n the

contrar" the more is the gas lo/n the more is the

stirring effect and resultant etter metallurgical results-

A optimum choice therefore has to e made

judiciousl"-

7*

;



7*

<

As compared to top lo/ing$ the h"rid lo/ing

eliminates the temperature and concentrationgradients and effects impro'ed lo/ing control$ less

slopping and higher lo/ing rates- It also reduces o'er



oidation and impro'es the "ield- It leads the processto near euilirium /ith resultant effecti'e

dephosphorisation and desulphurisation and ailit" to

make 'er" lo/ caron steels-

7*

+

4hat is lo/n from the ottom$ inert gas or o"gen&o/ much inert gas is lo/n from the ottom At /hat stage of the lo/ the inert gas is lo/n$

although the lo/$ at the end of the lo/$ after the

lo/ ends and so on4hat inert gas is lo/n$ argon$ nitrogen or their

comination



&o/ the inert gas is lo/n$ permeale plug$ tu"ere$

etc-4hat oidising media is lo/n from ottom$ o"gen or

air If o"gen is lo/n from ottom as /ell then ho/ much

of the total o"gen is lo/n from ottom

7*

2



The processes ha'e een de'eloped to otain the comined ad'antages of

oth D and =.M to the etent possile- Therefore the metallurgical

performance of a h"rid process has to e e'aluated in relation to these t/o

etremes$ namel" the D and the =.M- The parameters on /hich this can

e done are !

Iron content of the slag as a function of caron content of ath

=idation le'els in slag and metal



Manganese content of the ath at the turndo/n

Desulphurisation efficienc" in terms of partition coefficient

Dephosphorisation efficienc" in terms of partition coefficient

&"drogen and nitrogen contents of the ath at turndo/n

ield of liuid steel

71

1



71

)

The oidi>ing conditions of a heat in a steelmaking plant$ the

presence of oidi>ing slag$ and the interaction of the metal /ith the

surrounding atmosphere at tapping and teeming % all these factors

are responsile for the fact that the dissol'ed o"gen in steel has a

definite$ often ele'ated$ acti'it" at the moment of steel tapping- The

f



procedure " /hich the acti'it" of o"gen can e lo/ered to the

reuired limit is called deoidation- Steel sujected to deoidation is

termed Vdeoidi>edV- If deoidi>ed steel is Vuiet during solidification

in moulds$ /ith almost no gases e'ol'ing from it$ it is called Nkilled

steelN&

71

C

If the metal is tapped and teemed /ithout eing deoidi>ed$ the reaction

X=Y XY Cg /ill take place et/een the dissol'ed o"gen and

caron as the metal is cooled slo/l" in the mould- .ules of caron

monoide e'ol'e from the solidif"ing metal$ agitate the metal in the

mould 'igorousl"$ and the metal surface is seen to VoilV- Such steel is

called V/ildV /hen solidified it /ill e termed Nrimming steelV



called /ild /hen solidified$ it /ill e termed rimming steel -

In some cases$ onl" partial deoidation is carried out$ i-e- o"gen is onl"

partiall" remo'ed from the metal- The remaining dissol'ed o"gen

causes the metal to oil for a short time- This t"pe of steel is termed

Nsemi-killedC.

71

7

Thus$ practicall" all steels are deoidi>ed to some or other etent so

as to lo/er the acti'it" of dissol'ed o"gen to the specified limit-

The acti'it" of o"gen in the metal can e lo/ered " t/o methods! 5I6

" lo/ering the o"gen concentration$ or

5)6 " comining o"gen into stale compounds-

Th th f ll i i ti l th d f d id ti f t l



There are the follo/ing main practical methods for deoidation of steel!

5a6 precipitation deoidation$ or deoidation in the ulk

56 diffusion deoidation

5c6 treatment /ith s"nthetic slags and

5d6 'acuum treatment-

71

@

The ad'antages of continuous casting 5o'er ingot

casting6 are! It is directl" possile to cast looms$ slas and

illets$ thus eliminating looming$ slaing mills

completel"$ and illet mills to a large etent-



p "$ g

.etter ualit" of the cast product- &igher crude%to%finished steel "ield 5aout 1* to

)*F more than ingot casting6- &igher etent of automation and process control-

71

;



Solidification must e completed efore the /ithdra/alrolls-

The liuid core should e bowl-shaped as sho/n in the0igure and not pointed at the ottom 5as indicated " thedotted lines6$ since the latter increases the tendenc" forundesirale centerline 5i e aial6 macro segregation and



undesirale centerline 5i-e- aial6 macro%segregation and

porosit" The solidified shell of metal should e strong enough at

the eit region of the mould so that it does not crack orbrea"out under pressure of the liuid-

71

+

The surface area%to%'olume ratio per unit length of

continuousl" cast ingot is larger than that for ingot

casting- As a conseuence$ the linear rate of

solidification (d!dt) is an order of magnitude

higher than that in ingot casting-



The dendrite arm spacing in continuousl" cast

products is smaller compared /ith that in ingot

casting-

71

2



7)

*

Macro%segregation is less$ and is restricted to the

centreline >one onl"-

Endogenous inclusions are smaller in si>e$ since the"

get less time to gro/- 0or the same reason$ the lo/

holes are$ on an a'erage$ smaller in si>e-



Inclusions get less time to float%up- Therefore$ an"

non%metallic particle coming into the melt at the later

stages tends to remain entrapped in the cast product-

7)

1

In addition to more rapid free>ing$ continuous casting differs

from ingot casting in se'eral /a"s- These are noted elo/-

Mathematicall" speaking$ continuousl" cast ingot is infinitel"

long- &ence$ the heat flo/ is essentiall" in the trans'erse

direction$ and there is no end%effect as is the case in ingotcasting 5e-g- ottom cone of negati'e segregation$ pipe at the

top$ etc-6-

Th d th f th li id t l l i l t l



The depth of the liuid metal pool is se'eral metres long-

&ence$ the ferrostatic pressure of the liuid is high during the

latter stages of solidification$ resulting in significant difficulties of

lo/%hole formation-

7)

)

Since the ingot is /ithdra/n continuousl" from the mould$ the fro>en

la"er of steel is sujected to stresses- This is aggra'ated " thestresses arising out of thermal epansionK contraction and phase

transformations-

Such stresses are the highest at the surface- Moreo'er$ /hen the

ingot comes out of the mould$ the thickness of the fro>en steel shell is

not 'er" appreciale- 0urthermore$ it is at around 11**%1)**P$ and is



therefore$ /eak- All these factors tend to cause cracks at the surface

of the ingot leading to rejections-

Hse of a tundish et/een the ladle and the mould results in etra

temperature loss- Therefore$ etter refractor" lining in the ladles$

tundish$ etc- are reuired in order to minimise corrosion and erosion

" molten metal-7)

C



Smarajit Sarkar

Department of Metallurgical and Materials EngineeringNIT Rourkela

7)

7

#rimar" steelmaking is aimed at fast meltingand rapid refining- 't is capale of refining ata macro le'el to arri'e at road steelspecifications$ ut is not designed to meetthe stringent demands on steel ualit"$ andconsistenc" of composition and temperature



that is reuired for 'er" sophisticated gradesof steel- 'n order to achie'e suchreuirements$ liuid steel from primar"steelmaking units has to e further refined in

the ladle after tapping- This is kno/n asSecondary Steel"aking .

7)

@

impro'ement in ualit"

impro'ement in production ratedecrease in energ" consumptionuse of relati'el" cheaper grade or



alternati'e ra/ materialsuse of alternate sources of energ"higher reco'er" of allo"ing elements-

7)

;

(o/er impurit" contents -

.etter cleanliness- 5i-e- lo/er inclusioncontents6Stringent ualit" control- 5i-e- less 'ariation

f h t t h t6



from heat%to%heat6Microallo"ing to impart superior properties-.etter surface ualit" and homogeneit" in

the cast product-

7)

<

The term clean steel should mean a steelfree of inclusions- &o/e'er$ no steel can

e free from all inclusions-M i l i th i h f l



Macro%inclusions are the primar" harmful

ones- &ence$ a clean steel means a

cleaner steel$ i-e-$ one containing a much

lo/er le'el of harmful macro%inclusions-6

7)

+

In practice$ it is customar" to di'ideinclusions " si>e into +acro inclusions and+icro inclusions. Macro inclusions ought toe eliminated ecause of their harmfuleffects- &o/e'er$ the presence of microinclusions can e tolerated$ since the" donot necessaril" ha'e a harmful effect on the



not necessaril" ha'e a harmful effect on the

properties of steel and can e'en eeneficial- The" can$ for eample$ restrictgrain gro/th$ increase "ield strength andhardness$ and act as nuclei for the

precipitation of carides$ nitrides$ etc-

7)

2

The critical inclusion si>e is not fied ut

depends on man" factors$ including ser'ice

reuirements-.roadl" speaking$ it is in the range of @ to @**

m 5@ _ 1*%C to *-@ mm6- It decreases /ith an



5 6

increase in "ield stress- In high%strength steels$its si>e /ill e 'er" small-Scientists ad'ocated the use of fracture

mechanics concepts for theoretical estimation of

the critical si>e for a specific situation-

7C

*

#recipitation due to reaction from molten steel or during

free>ing ecause of reaction et/een dissol'ed o"gen

and the deoidisers$ /ith conseuent formation of oides

5also reaction /ith dissol'ed sulphur as /ell6- These are

kno/n as endogenous inclusions. Mechanical and chemical erosion of the refractor" lining Entrapment of slag particles in steel



="gen pick up from the atmosphere$ especiall" during

teeming$ and conseuent oide formation- Inclusions originating from contact /ith eternal sources

as listed in items ) to 7 ao'e$ are called e!ogenous

inclusions.

7C

1

4ith a lo/er /ettailit" 5higher 'alue of bMe 9 inc 6$

an inclusion can e retained in contact /ith the

metal " lo/er forces$ and therefore$ can reak

off more easil" and float up in the metal =n the



off more easil" and float up in the metal- =n the

contrar"$ inclusion /hich are /etted readil" " the

metal$ cannot reak off from it as easil"-

7C

)



Stirring of the melt in the ladle " argon flo/ing throughottom tu"eres is a must for miing and homogenisation$faster gro/th$ and floatation of the deoidation products-&o/e'er$ 'er" high gas flo/ rates are not desirale fromthe cleanliness point of 'ie/$ since it has the follo/ing

ad'erse effects!o Too 'igorous stirring of the metal can cause

disintegration of earlier formed inclusion conglomerates-

o Re%entrainment of slag particles into molten steel



Re entrainment of slag particles into molten steel-

o Increased erosion of refractories and conseuentgeneration of eogenous inclusions-

o More ejection of metal droplets into the atmosphere /ith

conseuent oide formation-

7C

7



7C

@

T)e a#ietie ( ec(nda#" teelmaing!#(cee t)at )ae !#(ed t( 4e (

c(mme#cial alue can 4#(adl" 4e categ(#ieda unde#

ti##ing t#eatment "nt)etic lag #ening it) ti##ing



"nt)etic lag #ening it) ti##ing

acuum t#eatmentDeca#4u#iati(n tec)ni:ue InHecti(n metallu#g" ;lunging tec)ni:ue

;(t-(lidicati(n t#eatment.

7C

;



7C

<

(adle degassing processes 53D$ 3=D$ 3AD6

Stream degassing processes

irculation degassing processes 5D& and R&6-



7C

+



7C

2



77

*

Molten steel is contained in the ladle- The t/o legs of the 'acuum

chamer 5kno/n as 3nor"els) are immersed into the melt- Argon is

injected into the up leg-

Rising and epanding argon ules pro'ide pumping action and lift the

liuid into the 'acuum chamer$ /here it disintegrates into fine droplets$

gets degassed and comes do/n through the do/n leg snorkel$ causing

melt circulation



melt circulation-

The entire 'acuum chamer is refractor" lined- There is pro'ision for

argon injection from the ottom$ heating$ allo" additions$ sampling and

sighting as /ell as 'ideo displa" of the interior of the 'acuum chamer-

77

1



77

)

4h" R&%=. #rocess

To meet increasing demand for cold%r olled steel sheets /ith impro'ed

mechanical properties$ and to cope /ith the change from atch%t"pe to

continuous annealing$ the production of H( steel 5 )* ppm6 is

increasing-

A ma jor pr olem in the con'entional R& pr ocess is that the time

reuir ed to achie'e such lo/ caron is so long that car on content at



.=0 tapping should e lo/ered- &o/e'er $ this is accompanied "

ecessi'e oidation of molten steel and loss of ir on oide in the slag-

It ad'er sel" affects sur face the ualit" of sheet as /ell-

77

C

@ence/ deca#4u#iati(n in R@ degae# i t( 4e !eeded u!. T)i i ac)ieed 4" (me ($"gen 4l(ing O=9 du#ing

degaing.

T)e RH-OB !#(ce/ )ic) ue an ($"gen 4l(ing acilit"du#ing degaing/ a (#iginall" deel(!ed (#deca#4u#iati(n ( tainle teel 4" Ni!!(n teel C(#!./

a!an/ in 1,72.

u4e:uentl"/ it a em!l("ed (# t)e manuactu#e ( U?Cteel.



T)e !#eent t)#ut i t( dec#eae ca#4(n c(ntent #(m(met)ing lie 300 !!m t( 10 (# 20 !!m it)in 10 min.

C(nt*

77

7



77

@

on'entional A=D$ no top lo/ing is in'ol'ed- =nl" a

miture of argon and o"gen is lo/n through the

immersed side tu"eres- &o/e'er$ the present A=D

con'erters are mostl" fitted /ith concurrent facilities for

t l i f ith l l i t



top lo/ing of either onl" o"gen$ or o"gen plus inert

gas mitures using a supersonic lance as in .=0

steelmaking-

77

;

Initiall"$ /hen the caron content of the melt is high$ lo/ing

through the top lance is predominant though the gas miture

introduced through the side tu"eres also contains a high

percentage of o"gen-

&o/e'er$ as decarurisation proceeds$ o"gen lo/ing from

the top is reduced in stages and argon lo/ing increased- As



stated earlier$ some stainless steel grades contain nitrogen as

a part of the specifications$ in /hich case$ nitrogen is

emplo"ed in place of argon in the final stages-

77

<



Simplified " &ilte" and ,a'ene"

77

+



77

2



7@

*



7@

1

This process produces molten iron in a t/o%step reduction melting

operation- =ne reactor is melter%gasifier and the other is pre%

reducer- In the pre%reducer$ iron oide is reduced in counter%flo/

principle- The hot sponge is discharged " scre/ con'e"ors into the

melting reactor-

oal is introduced in the melting%gassif"ing >one along /ith

o"gen gas at the rate of @**%;** 1+' th+. The flo/ 'elocit" is



chosen such that temperature in the range of 1@**%1+**P is main

tained- The reducing gas containing nearl" +@F = is hot dedusted

and cooled to +**%2**P efore leading it into the pre%reducer

7@

)



7@

C

In the 0INE_ #rocess fine ore is preheated and reduced to DRI in a

train of four or three stage fluidi>ed ed reactors-

The fine DRI is compacted and then charged in the form of &ot

ompacted Iron 5&I6 into the melter gasifier- So$ efore charging

to the melter% gasifier unit of the 0INE_ unit$ this material is

compacted in a hot riuetting press to gi'e hot compacted iron



5&I6 since the melter% gasifier can not use fine material 5to ensure

permeailit" in the ed6-

Non%coking coal is riuetted and is fed to the melter gasifier /here

it is gasified /ith o"gen

7@

7

As a standard guide the temperature rise attainale "

oidation of *Q*1 F of each of the element dissol'ed in

liuid iron at 17**P " o"gen at )@P is calculated

assuming that no heat is lost to the surroundings andsuch data are sho/n elo/-



7@

@

Ahindra Ghosh and Amit hatterjee! Ironmaking and Steelmaking Theor" and #ractice$ #rentice%

&all of India #ri'ate (imited$ )**+

Anil ,- .is/as! #rinciples of .last 0urnace Ironmaking$ S.A #ulication$1222

R-&-Tupkar" and 3-R-Tupkar"! An Introduction to Modern Iron Making$ ,hanna #ulishers-

R-&-Tupkar" and 3-R-Tupkar"! An Introduction to Modern Steel Making$ ,hanna #ulishers-

Da'id &- 4akelin 5ed-6! The Making$ Shaping and Treating of Steel 5Ironmaking 3olume6$ The

AISE Steel 0oundation$ )**7- Richard 8-0ruehan 5ed-6! The Making$ Shaping and Treating of Steel 5Steeelmaking 3olume6$ The


A-Ghosh$ Secondar" Steel Making 9 #rinciple : Applications$ R #ress 9 )**1-

R-G-4ard! #h"sical hemistr" of iron : steel making$ E(.S and Ed/ard Arnold$ 12;)-

0-#-Edneral! Electrometallurg" of Steel and 0erro%Allo"s$ 3ol-1 Mir #ulishers$12<2



.- =>turk and R- 8- 0ruehan$! ?,inetics of the Reaction of Si=5g6 /ith aron Saturated Iron?!Metall- Trans- .$ 3ol- 1;.$ 12+@$ p- 1)1-

.- =>turk and R- 8- 0ruehan! ?The Reaction of Si=5g6 /ith (iuid Slags$B Metall- Trans-.$

3olume 1<.$ 12+;$ p- C2<-

.- =>turk and R- 8- 0ruehan!B-Transfer of Silicon in .last 0urnace?! $ #roceedings of the fifth

International Iron and Steel ongress$ 4ashington D--$ 12+;$ p- 2@2-

#- 0- Nogueira and R- 8- 0ruehan!B .last 0urnace Softening and Melting #henomena % Melting

=nset in Acid and .asic #ellets?$ $ ISS%AIME lronmaking onference$ )**)$ pp- @+@-

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#aulo Nogueira$ Richard 0ruehan! ?.last 0urnace .urden Softening and Melting

#henomena%#art I #ellet .ulk Interaction =ser'ation?$ $ Metallurgical and Materials

Transactions .$ 3olume C@.$ )**7$ pp- +)2-

#-0- Nogueira$ Richard 8- 0ruehan! V0undamental Studies on .last 0urnace .urden

Softening and Melting?$ #roceedings of )nd International Meeting on lronmaking$

Septemer )**7$ 3itoria$ .ra>il-

#aulo 0- Nogueira$ Richard 8- 0ruehan$ ?.last 0urnace Softening and Melting#henomena % #art III! Melt =nset and Initial Microstructal Transformation in #ellets?$

sumitted to Materials and Metallurgical Transactions .-

#aulo 0- Nogueira$ Richard 8- 0ruehan !.last 0urnace .urden Softening and Melting

#henomena%#art II E'olution of the Structure of the #ellets?$ Metallurgical and

Materials Transactions$ 3olume C;.$ )**@$ pp- @+C



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MA 8itang! Injecuion of flu into .last 0urnace 'ia Tu"eres for optimi>ing slagformationB ISI8 International$ 3olume C2$ No< 1222$pp;2<

-S-(ee$ 8-R-,im$ S-&-i and D-8-Min! 3iscous eha'ior of a=%Si=)%Al)=C%Mg=%

0e= SlagB$ #roceedings of 3IIInternational onferenceon %Molten slags$flues and

salts$ The South African Institute of Minig and Metallurg"$ )**7$pp))@

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Ironmaking SS

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