a brief outline of iron making notes

8/10/2019 A brief outline of Iron Making Notes

1/27

IRON MAKING COURSE NOTE

RAW MATERIALS AND THEIR PROPERTIES

The blast furnace raw materials are:

1. Iron ore (lump ore/Coarse ore)

2. Sinter/pellets3. Coke !n"thin# that promote $olume also promote pro%uction&. 'imestone (flu). *ot +last air ,. +- !%%iti$es (2 steam pul$erise% coal h"%rocarbon fuels)

Functions

Iron ore (lump ore/Coarse ore) 0 is the source of iron bearin# minerals.Sinter Source of iron (flu)'imestone 0 Source of flu+last air 0 source of 2 (2 21 20 45) use% for combustion of coke at the

tu"eres.

Coke

The function of coke in the blast furnace is fi$e fol% namel"i) !cts as fuel b" pro$i%in# for the thermal re6uirements in the furnace the reaction bein#

2C 2 7 2C

ii) 8ro$i%es permeabilit" (in the %r" as well as the the wet 9one) an% also mechanicalsupport to the lar#e char#e column

iii) 8ro$i%es #ases (C) for re%uction of iron oi%esi$) ;e%uction of oi%es of metalloi%s such as


2/27

Re(uci)i%ity0 is the eas" at which the o"#en combine% with ore can be remo$e%in%irectl".! hi#her re%ucibilit" means a #reater etent of in%irect re%uction that ma" be obtaine% inthe blast furnace resultin# in lower coke rate an% hi#her pro%ucti$it".

Si*e $n( Si*e Distri)ution

>iscosteel iron ore si9e ran#e 5 to 32mm

'ower si9e ran#e , 0 5mm?pper si9e ran#e shoul% be 2 0 3 times the lower si9e ran#e

A(+$nt$'es o! N$rro, Si*e Distri)ution

- Increase char#e permeabilit" an% uniform #as %istribution resultin# in better utilisation ofthe chemical an% thermal ener#ies of the #ases.

- isco re @ & -e


3/27

So!tenin' te#er$ture $n( so!tenin' te#er$ture r$n'e- This is temperature at which the ores start to soften or melt an% takes place

o$er a temperature ran#e.- -or ores the ran#e ma" be wi%e 4== 0 1 3=C an% that for sinters an%

pellets much narrower 1=== 0 1 3=C. The smaller the temperature ran#e of softenin# i.e the shorter the $ertical %istance in

which the hi#hl" $iscous semifuse% mass forms an% eists the better the #as flow an%hi#her the pro%ucti$it".

Li#estone

Si9e ran#e , 0 &=mm Chemical properties Ca abo$e &=


4/27


5/27

Those where sufficient flu has been a%%e% in sinter mi to pro$i%e a basicit" that is%esire% in the final sla# takin# into consi%eration onl" the bur%en aci%s.!n etra flu is a%%e% to the bur%en while char#in# to cater to coke ahs aci%s.

ii) Super -lue% Sinter!n a%%itional flu (at Sinter 8lant) is a%%e% to the mi to pro$i%e for the %esire% finalbasicit" takin# into account aci% content of both i.e ore as well as the coke ash.-lue% sinters ha$e better re%ucibilit" in comparison with aci% sinters.Eesulphurisation takes place %ue to the present of Ca.

Hner#" sa$er %urin# calcinations process e.# nona%%ition of Ca i.e limestone.'ess than A1= is preferre%.

A(+$nt$'es o! Sinterin'

1. !ci%s sinters

- !##lomeration of fines into har% stron# an% irre#ular porous lumps which#i$es #oo% be% permeabilit" (hi#h $oi% a#e)

2. Hlimination of ,=4= of all sulphur an% arsenic (in present)%urin# sinterin# (Ca -e(s) C

3. Hlimination of moisture h"%rate% water an% $olatiles on the sinter stran% with a cheap fuel. (2-e237 3*2 Si2!l237 *2)

&. Increase in softenin# temperature an% narrowin# %own thesoftenin# ran#e.

F%u2e( Sinter

(a) Calcinations of limestone insi%e the +/- is $er" epensi$e of carbon !ppro 0 ,=4=k# carbons per 1==k# C2 are ser$e% b" transferrin# thecalcinations to sinter stran%.

(b) Since in cooperation with lime lowers the $iscosit" an% li6ui%oustemp of the bon%in# sla# less coke (low temp) can be use% of the same stren#th an%hence a hi#h %e#ree of oi%ation an% re%ucibilit" can be achie$e%

(c) 'ime increases the acti$it" coefficient of -e in the silicate an%increase sinter re%ucibilit".

(%) Super flu ser$es much in more coke in the furnace

(e) *i#h blast furnace pro%ucti$it" better than e$en with pellets i%ea

blast furnace material because of b" far the best hi#h temps #as permeabilit"


6/27

Re$ction in t"e uer *one0

The bur%en is rapi%l" heate% from ambient temperature to abo$e 5==oC with a %istanceof &,m from the stock le$el.

The #ases comin# from the mi%%le 9one cool %own from a F== oC to 1==2== as itlea$es the furnace top.


7/27

;e%uction of -e23an% ma#netite (-e3&) to -e is not complete in this 9one. -e3&is re%uce% to -e mainl" at 4==F==C.

4e5 C$r)on Deosition

2C 7 C2C it happens at low temperature an% in the re$erse of the solution lossreaction (CC2 2C

The reaction occurs in narrow temperature ran#e &=,== presence of free iron (-e)

an% its oi%e catal"ses the reaction.

-e C -e C2 7 Sla# formation carbon %ecomposition 0in%irectreaction.

A(+$nt$'es o! C$r)on (eco#osition

i) Eecomposition of carbon on the ore surface minimise stickin# of the ores an% enhancespermeabilit"

ii) Hconomics fuel consumption since the reaction is eothermic.iii) The %eposite% carbon can %escen% alon# with the bur%en an% replace e6ui$alent

amount of coke there b" economise fuel consumption.

Dis$(+$nt$'es o! c$r)on (eco#osition

Eeposite% carbon reacts with ore to liberate% C which causes burstin# of the orelumps there b" %ecreasin# the mechanical stren#th of the ore. -e23C -e c.

This therefore affects #as %istribution an% permeabilit". Causes formation of bri%#es an% accretions. Carbon react %irectl" with ore C-e -e C

Deosition o! c$r)on$tes

Carbonates of -e


8/27

!n increase in in%irect re%uction can be achie$e% b":

(a) Increase% re%ucibilit" of ores(b) Htension an% enlar#ement of the mi%%le 9one b" use of less reacti$e coke (solution

loss).(c) 'on#er / #as ore contact time throu#h the use of hi#h top #as pressure (#as resi%ence

time to be increase%)(%) ?se of h"%ro#en bearers (tar steam)

8resence of limestone in the bur%en char#e shortens the mi%%le 9one (en%othermiccalcinations reaction) which starts to occur at F===c.

(ii) Carburetion of iron

(a) 2C7C2C3-eC 7-e3C

(b) 3-eC7-e3C&C2

(iii) ater Bas shift reaction

(a) C *2 7 C2 *2

(b) C*2 7 C*2at hi#h temps

Re$ctions in t"e %o,er *ones

Temp abo$e F==1===C Hten%s from 3m abo$e the tu"ere le$el to the hearth bottom. Temperature of molten materials reaches 1&==1&=C an% the #as cools %own to 5==

1===C. +urnin# of coke in front of the tu"ere create an empt" space aroun% the hearth peripher"

0 combustion 9one of %epth 12m.

Bau#e in a%miture with the flu starts to fuse in the bell" re#ion.

Important chemical reactions occurrin# in this 9one are:

(i) Hn%othermic calcinations of limestone 0 CaC37 Ca C2(ii) Hn%othermic %irect re%uction of -e: -e C 7 -e C(iii) Hn%othermic %irect re%uction of Si2:Si22C 7 Si 2C(i$) Hn%othermic %irect re%uction of


9/27

The burnin# of coke in front of a tu"ere is calle% race wa" 9one. ;ace wa" / hearth annulus or acti$e perimeter. The actual acti$e rin# area of 12m %epth aroun% the hearth peripher". The si9e an% shape i.e the %epth of the racewa" an% wi%th between nei#hbourin#

tu"eres which %etermines the race wa" area are of #reat importance for : -urnacepro%ucti$it" an% the thermal state of the hearth.

;eaction of the Combustion >one

(i) C 2 C2 heat F&&= calories (1.2m)(ii) C2 C C 0 *eat &1=== cal

Eurin# the 1streaction of 2 of the blast react with coke to initial form C2.This 9one is referre% as oi%isin# 9one because an" metal or sla# iron inclu%in# metaloi%es fallin# in this 9one are reoi%e to $ar"in# %e#rees.

1N( Re$ction

In this 9one C2 bein# unstable imme%iatel" reacts with carbon (coke) to pro%uce C.The reaction where C2 C is calle% re%ucin# 9one.It is here that a consi%erable re%uction of sla# an% metal oi%es.

Cohesi$e 9one is the 9one where iron an% sla# fusin#.

F$ctors $!!ectin' r$ce,$y *one:

-actors affectin# the si9e an% shape of the racewa":

(a) +last parameters: $olume $elocit" pressure an% temperatures.(b) Eiameter len#th an% shape of the tu"ere.(c) Inter tu"ere spacin# is the number of tu"eres aroun% the hearth peripher".(%) Coke si9e 0 narrow si9e ran#e.(e) +last mo%ification 0 blast a%%iti$es i.e tar natural #as steam 2 enrichment pul$erise%

coal fuel oil coke o$ens #as.(f) ature of stock mo$ement.

Furn$ce Irre'u%$rities-urnace pro%uction is beset with numerous %ifficulties an% irre#ularities a successfulcounter action of which onl" can #i$e rise to smooth operation an% hi#h pro%uction istherefore re6uire%.The interference of smooth operation i.e smooth counter flow of soli%s li6ui%s an% #asesoccurs %ue to abnormalities in the ph"sical character of the bur%en materials whichthemsel$es ma" arise on chemical #roun%s. The usual %ifficulties an% counter measure#enerall" a%opte% are %etaile% below.

H$n'in'

This is a con%ition that takes place in the furnace when %escen%in# material meets withresistance in its %ownwar% flow or the #as in its upwar% flow.This arises from the followin# causes:

1) bstruction to bur%en %ecent %ue to presence of scaffol%s scabs an% stick" bosh sla#.2) Increase% #as support %ue to fines.3) +lockin# of %rain holes in the bosh %ue to hi#hl" $iscous or resoli%ifie% sla# or fro9en

iron.

F


10/27

A0 Sc$)s $n( Sc$!!o%(s

-ormation of scabs scaffol%s bri%#es arches an% the like on the walls offer ph"sicalresistance an% obstruction to material %ownwar% mo$ement. +" $irtue of re%ucin# thepassa#e si9e material %escent is slowe% %own or e$en brou#ht to a *olt. !s a result#aps between suspen%e% material that is mo$in# %own form which when the" collapselea% to chillin# of the hearth an% %ama#e to the refractor" linin# flat coolers an% e$enthe tu"eres.hen the scaffol%s / scabs come awa" the su%%en %escent of material is calle% bosh

slip.

30 Peri"er$% O+er%o$(in'

Hcessi$e presence of ore fines in the peripher" of the furnace lowers its permeabilit".The furnace works har% stock %escent becomes erratic an% the blast $olumebackpressure rises rapi%l". In etreme cases the furnace han#s as a result. Solution tothis is usuall" alterin# the +/C ratio char#in# se6uences an% remo$al of fines (coke /ore) b" use of screens.

C0 Hot H$n'in'

This comes about as a result of an increase in flame temperature i.e in front of thetu"eres an% causes the bur%en in the furnace to %escent irre#ularl" %ue to cause thefurnace to han#.

So%ution to "$n'in' (ue to $)o+e is usu$%%y:

i) ;e%uction of flame temperature b" steam inDection.ii) +" lowerin# the hot blast temperature.iii) ?se of low carbon containin# coke.

D0 Co%( H$n'in'

Col% han#in# is %ue to lime" sla#s which %ue to their poor flow properties block thecoke pores in the bosh. 8oor sla# flow can be %ue to low bosh an% hearth temperatureswhich ma" arise from:

i) 'eakin# flat coolers or tu"eres.ii) Su%%en %ecrease in the coke carbon content.iii) Su%%en increase in team inDection.

So%ution9

i) ;eplacement of leakin# flat coolers.

ii) Char#e a li#ht bur%en i.e bur%en with a low bur%en to coke ratio.iii) Increase the blast temperatures an% temporaril" re%uce the blast $olume.

P%e$se Note:

! %ecrease in in%irect re%uction can also cause col% han#in#. The en%othermic heatre6uirement of the increase% %irect re%uction of wasta#e (-e )ma" result in free9in# ofiron in the $oi%s thus hin%erin# #as throu#h flow. -ree9in# of the iron if it occurs on thewalls woul% resemble scabs.

1=


11/27

So%ution

i) Increasin# blast temperatures an%ii) Coke /re/ ratio of char#e temporaril" an% impro$in# #as %istribution throu#h char#in#

control.

SLIPS

! slip is a su%%en rapi% %escent of the stock column in the furnace resemblin# a

collapse

Their occurrence is %ue to:

i) *an#in# in the upper furnace as a result of which material below continues to %escentan% smelte% while material abo$e remains suspen%e%.

i$) -ormation of arches insi%e the furnace.

hen the suspen%e% material collapses as a result of its own wei#ht a slip is sai% toha$e occurre%.

H$n'in' $n( su)se:uent s%iin' #$y )e tre$te( to9

a) Con%ensation of oi%ise% alkali metal an% 9inc $apours in the upper shaft an% formationof har% imper$ious mass protru%in# inwar%s.

b) *in%rance of counter flow of soli%s an% #ases %ue to carbon %eposition or lan%in# ofpow%er" coke or ore fines in the interstices of the lump" material.

c) ;esoli%ification of pre$iousl" fuse% sla#s %ue to operational $ariations.

%) Slips ma" result from %ifferential rates of stock %escent as a result of channellin#.


12/27

Scaffol%s are accretions of materials which buil% up on the furnace wall an% proDecttowar%s the furnace centre.! bri%#e forms ri#ht across the furnace hori9ontal cross section restrictin# stock %escentan% #as ascent.This buil% up occurs from the bosh to the upper part of the stack. Benerall" the termscaffol% refers to buil% up in the low temperature re#ions where li6ui% phases %o notnormall" occur i.e in the mi%%le an% upper shafts.The re%uction in cross sectional area at the place of scaffol% formation lea%s to%isruption of stock %ecent an% to an increase % #as mo$ement in unaffecte% re#ions. !s

a result

a) *i#h top #as temperatures ri#ht up to the uptakes are eperience%.b) Top #as C2 le$el %ropsc) Bas utilisation %rops%) In%irect re%uction of the ore is re%uce%e) Coke rate an% #as $elocit" increase.

C$uses o! Sc$!!o%(s

The" are forme% as a result of %eposition of compoun%s of $olatile alkali metals (a G)lea% 9inc tin low an% wi%e softenin# ran#e ores fine sinters carbon %eposition ba%

furnace operation an% non uniform coolin# with flat coolers.

Contro% o! Sc$!!o%( For#$tion

i) Control of input materials (6ualit" control choosin# ore containin# less alkalis lea% 9incan% tin).

ii) Impro$in# eit of the scaffol%in# formin# a#ents.

M$ni!est$tions o! Sc$!!o%(s

i) Su%%en increase in flue %ust emission (1== 2==) or e$en more.ii) *i#h top #as pressures

iii) 'ow #as temperatures abo$e scaffol% with low inwall temperatures in the re#ions of thescaffol%in#.

i$) *i#h C/C2ratio in the top #as$) on uniform bur%en %escent i.e han#in# an% slippin#.

Met"o( o! Contro%

i) Eecrease alkali le$els in the 5==1===C 9one b" increasin# their eit in the sla# (i.e b"lowerin# Ca / Si2ratio. N39 basicit" cannot be lowere% below a certain limit foroptimum %esulphurisation unless eternal %esulphurisation is practise%.ii) Control of flame temperature 0 low flame temperature re%uces alkali buil% up an%

facilitates their remo$al $ia sla#. (Coke rate #oes up).iii) 'owerin# 9inc input throu#h use of hi#her sinter le$els in the bur%en.i$) Steep boshes to pre$ent an" buil% up formation.$) ?se of compact bricks capable of resistin# alkali an% C seepa#e. (*i#h !l23 bricks

fire% at hi#h temperatures less prone.$i) Substantial wall workin# to %iscoura#e formation this can be achie$e% $ia stock line

control J or < t"pes increase% tu"ere %iameter to re%uce blast penetration an%encoura#e peripheral #as flow.

$ii) ?sin# raw materials with small softenin# ran#e.$iii) Screenin# of all char#e% materials.i) Suitable blen%in# to eliminate alkali le$els.

12


13/27

CHANNELLING

1.= C"$nne%%in'

$ens when #as mo$in# up the stack flows une$enl" %ue to $arie% properties. In amie% be% of si9es of materials the be% permeabilit" %ecreases as the proportions ofsmall particles or fines %ecreases. !s a result of %ifferential #as flow in the be% une$en#as %istribution of %ifferential #as $elocities occurs.In areas where the #as $elocit" is hi#h flui%isations ma" start smaller particles lifte% up

an% the #as will rush into those re#ions which become more an% more unstable untilthe maDorit" of the particles are suspension. The suspen%e% la"er ma" eten% toconsi%erable %epths.

Suspension of particles is the be#innin# of channellin# an% #as starts to show an acti$einfluence on the structure of the bur%en in the affecte% areas. In characteristic caseschannellin# is %irectl" relate% to aero 0%"namic transfer of particles.

In(ic$tions O! C"$nne%%in'

(a) Sharp rise on peripheral #as temperatures near the channel.(b) Sharp fall on C2 content of the top #as.

(c) ;ise an% closer approach of the top #as temperature(%) *i#h flue %ust losses.(e) Collapse of one or both of the stock line in%ications into the suspen%e% la"er(f) Se$ere erratic #as pressure pulsation %urin# lowerin# of the bi# bell.(#) Erop on blast pressure (when channels are lar#e).(h) 'ar#e blast $olumes enterin# the tu"eres close to the channels.

C"$nne%%in' Contro%

(i)


14/27

hen the scaffol%s/scabs come awa" the su%%en %escent of the material is calle% boshslip.

30 Peri"er$% O+er%o$(in'

Hcessi$e presence of ore fines in the peripher" of the furnace lowers its permeabilit". Thefurnace works har% stock %escent becomes erratic an% the blast $olume backpressurerises rapi%l". In etreme cases the furnace han#s as a result. Solution to this is usuall"alterin# the +/C ratio char#in# se6uences an% remo$al of fines (coke/ore) b" use of

screens.

C. Hot H$n'in'

This comes as a result of an increase in flame temperature i.e in front of the tu"eres an%cause the bur%en in the furnace to %escent irre#ularl" an% to cause the furnace to han#.

Solution to han#in# %ue to abo$e is usuall":

i) ;e%uction of flame temperature b" steam inDection.ii) +" lowerin# the hot blast temperature.iii) ?se of low carbon containin# coke.

D. Co%( H$n'in'

Col% han#in# is %ue to lime" sla#s which %ue to their poor flow properties block thecoke pores in the bosh. 8oor sla# flow can be %ue to low bosh an% hearth temperatureswhich ma" arise from:

i) 'eakin# flat coolers or tu"eres.ii) Su%%en %ecrease in the coke carbon content.ii) Su%%en increase in steam inDection.

So%ution

i) ;eplacement of leakin# flatcoolers or tu"ere.ii) Char#e a li#ht bur%en i.e a bur%en with a low bur%en to coke ratio.iii) Increase the blast temperature an% temporaril" re%uce the blast $olume.

P%e$se Note

! %ecrease in in%irect re%uction can also cause col% han#in#. The en%othermic heatre6uirement of the increase% %irect re%uction of $ustite (-e) ma" result in free9in# of

iron in the $oi%s thus hin%erin# #as throu#hflow. -ree9in# of the iron if it occurs on thewalls woul% resemble scabs.

So%ution

i) Increase blast temperature an%ii) Coke/ore ratio of char#e temporaril" an% impro$in# #as %istribution throu#h char#in#

control.

SCAFFOLDS

Scaffol%s are accretions of materials which buil% up on the furnace wall an% proDect

towar%s the furnace centre. ! bri%#e forms ri#ht across the furnace hori9ontal crosssection restrictin# stock %escent an% #as ascent. This buil% up occurs from the bosh to

1&


15/27

the upper part of the stack. Benerall" the term scaffol% refers to buil%up in the lowtemperature re#ions where li6ui% phases %o not normall" occur i.e in the mi%%le an%upper shafts.

The re%uction in crosssectional area at the place of scaffol% formation lea%s to%isruption of stock %escent an% to an increase% #as mo$ement in the unaffecte%re#ions. !s a result

a) *i#h top #as temperatures ri#ht up to the uptakes are eperience%.

b) Top #as C2le$el %rops.c) Bas utilisation %rops.%) In%irect re%uction of the ore is re%uce%.e) !n% coke rate an% #as $elocit" increase.

C$uses o! Sc$!!o%(s

The" are forme% as a result of %eposition of compoun%s of $olatile alkali metals (a G)lea% 9inc tin low an% wi%e softenin# ran#e ores finesinters carbon %eposition ba%furnace operation an% non uniform coolin# with flat coolers.

Contro% o! Sc$!!o%( For#$tion

i) Control of input materials (6ualit" control choosin# ore containin# less alkalis lea% 9incan% tin).

ii) Impro$in# eit of the scaffol%in# formin# a#ents.

M$ni!est$tions o! Sc$!!o%(s

i) Su%%en increase in flue %ust emission (1== 2==) or e$en more.ii) *i#h top #as temperatures.iii) 'ow temperatures abo$e scaffol% with low in wall temperatures in the re#ions of thescaffol%in#.i$) *i#h C/C2 ratio in the top #as.

$) on uniform bur%en %escent i.e han#in# an% slippin#.

Met"o(s o! Contro%

i) Eecrease alkali le$els in the 5== 0 1==C 9one b" increasin# their eit in the sla# (i.e b"lowerin# Ca/Si2 ratio N039 basicit" cannot be lowere% below a certain limit foroptimum %esulphurisation unless eternal %esulphurisation is practice%.

ii) Control of flame temperature low flame temperature re%uces alkali buil% up an%facilitates their remo$al $ia sla#. (Coke rate #oes up).

iii) 'owerin# 9inc input throu#h use of hi#her sinter le$els in the bur%en.i$) Steep boshes to pre$ent an" buil% up formation).

$) ?se of compact bricks capable of resistin# alkali an% C seepa#e.(*i#h !123 bricks fire% at hi#h temperature less prone)$i) Substantial wall workin# to %iscoura#e formation this can be achie$e% $ia stockin#

control J or < t"pes increase% tu"ere %iameter to re%uce blast penetration an%encoura#e peripheral #as flow.

$ii) ?sin# raw materials with a small softenin# ran#e.$iii) Screenin# of all char#e% materials.i) Suitable blen%in# to minimise alkali le$els.

SLIPS

! slip is a su%%en rapi% %escen% of the stock column in the furnace resemblin# a

collapse.

1


16/27

Their occurrence is %ue to:

i) *an#in# in the upper furnace as a result of which material abo$e remains suspen%e%.ii) -ormation of arches insi%e the furnace.

hen the suspen%e% materials collapse as a result of its own wei#ht a slip is sai% toha$e occurre%.

*an#in# an% subse6uent slippin# ma" be trace% to:

a) Con%ensation of oi%ise% alkali metal an% 9inc $apours in the upper shaft an% formationof har% imper$ious mass protru%in# inwar%s.

b) *in%rance of counter flow of soli%s an% #ases %ue to carbon %eposition or lan%in# ofpow%er" coke or ore fines in the interstices of the lump" material.

c) ;esoli%ification of pre$iousl" fuse% sla#s %ue to operational $ariations.%) Slips ma" result from %ifferential rates of stock %escent as a result of channellin#


17/27

Stock %escent is slu##ish an% sla# appears in the tu"eres soon after tappin#. Iron carr"o$er in the sla# is pre%ominant an% loss of tu"eres an% sla# notches becomesea##erate%.Eue to %eposition of soli%s on the hearth walls the hearth $olume %win%les an% the le$elof li6ui%s rises 6uickl" after tappin#.

Contro% o! C"okin'

i) Impro$e mechanical stren#th of coke 0 break%own of coke is the most important cause

of chokin# an% burnin# of tu"eres.ii) If break%own of coke is %ue to alkali attack lower the alkali input if possible an%operates at low flame temperatures an% operates at low flame temperatures an% uselean sla#s

iii) 'ower hot blast temperature in or%er to increase coke/ore ratio.i$) Control bur%en %istribution to achie$e hi#h sinter le$els at the peripher" e .# SS CCC /

char#e.$)

14


18/27

thers are -e Ca an%


19/27

3. *earth or final sla# 0 Ca


20/27

(b) Too much sla# less coke burnt an% less pro%ucti$it"

Sulphur is the bi##est enem" in hot metal pro%uction causes fractures or breakin# ofour pro%uct an% cost.

The most important purpose of S%$' Contro%is the control of sulphur since it is the ke"to iron 6ualit".

It is unecono#ic$%to pro%uce a low 8 low Si an% hi#h sulphur iron. Si (silica) cause #raphite in iron or promote #raphitisation but eas" to shape. 'ean sla# are short 0 no chan#e to chemical composition.

'ime sla#s are lon# 0 %ue to chan#e in temperature an% chemical composition.

T"e Purose o! Criteri$ o! Goo( 38F S%$'

! proper/#oo% sla# shoul% perform a $ariet" of function for maimum efficienc" both infuel as well as furnace performance it shoul% %etermine control or posses the followin#:

1.


21/27

Tyic$% 3F Su%"ur 3$%$nce

Su%"ur Inut Su%"ur Outut

M$teri$% K' & K' &

Coke 4/&S5 @77k'8t"# ,= 5= C"$r'e #$teri$%

4Ore- !%u25

1. 2=

Iron 7076&S =.3 &F%ue (ust $n( '$s =.34 S%$' ,.52 F1

Sulphur remo$al much of it occurs when hot metal passes throu#h the sla# in the hearth.

Eurin# the %ecent of the stock the sulphur in the char#e% materials is absorbe% in theshaft molten iron an% sla# an% the final transfer of sulphur from the metal to sla# occursin the hearth.

Coke starts #i$in# off its sulphur in the shaft (2=) ai%e% b" an increase in *2 contentof the stack #as an% %ecreasin# si9e of the coke.

+ulk of sulphur in the coke transfer b" chemical reactions %urin# combustion of coke infront of the tu"ere.

Note: lean sla# has a hi#h alkali retention capacit" because Ca is less in lean sla# than thealkalis (e.#. G a2) replaces Ca an% reacts in Sulphur silica an% e.t.c. 8art ofSulphur #oes to hot metal since %esulphurisation has been compromise%.

CHEMESTR< OF SULPHUR REACTIONS

NOTE9

Sulphur in iron %enote% as QSR

Sulphur in sla# %enote% as 0 (S)

1. Sulphur enters into the metal throu#h


22/27

The sulphur mo$ement in the shaft compromises of liberation of sulphur from the cokean% its absorption b" the bur%en components from the #ases.

!s sla# an% iron comes %own there is a pick in sulphur content but in sla# continue torise while %roppin# in hot metal.

=4= sulphur of the coke enters the #as phase before the tu"ere %ue to combustionof coke.

Sulphur is liberate% b" the coke an% is absorbe% b" the bur%en components. Sulphur is ascen%in# tu"ere #as is absorbe% b" the %escen%in# bur%en an% re%uce%

iron.

Sulphur in both sla# an% hot metal rises continuousl" up to the tu"ere le$el. In front of the tu"ere le$el there is a sli#ht %rop of iron sulphi%e (-eS an% is foun% in hotmetal) thereafter the -eS %rops #reatl" in the hearth up to the iron notch.

The sulphur in sla# rise onl" a little in the tu"ere 9one thereafter there is rapi% ofincrease/rise of sulphur in the sla#.

Di$'r$#s

-e shoul% not be more on sla# because nee%s more heat to keep sla# temp hi#h an%at hi#h flui%it" an% low $iscous. Thus we nee% less than 1= -e in sinter re6uires hi#htemp/ heat hence hi#h coke rate.

-e C 0 shoul% complete in mi% 9one

SULPHUR REACTION IN THE 3OSH

-or efficient %esulphurisation in the bosh sla# shoul% be flui% hi#h basic (hi#h basicit")an% low -e (i.e. re%ucin# sla#)

The hi#h the S in the bosh sla# the lower will be the loa% on the hearth sla# for the final

%esulphurisation of iron.

If the bosh sla# is (hi#h) $iscous it ma" be ma%e flui% b" increasin# the man#anese(


23/27

&. Sla# compositions 0 sla# basicit" shoul% be hi#h in Ca (lime) but lower in -e content.

. Sla# bulk sla# basicit" an% sulphur loa%low.

,. Sla# an% metal $iscosities 0 if too hi#h affects %esulphurisation because of surface areaan% temp to allow iron to pass throu#h sla# hence impro$e %esulphurisation.

4.


24/27

4. Coke mess5. Chille% hearthF. +urnin# of tu"eres1=. re shift

STOCK DISTRI3UTION AND CHARGING

+last furnace pro%ucti$it" %epen%s upon the 6uantit" of air that can be blown per unittime. The 6uantit" of #as that can be accepte% is #o$erne% b" the uniformit" of $oi%a#e

(pores) an% particle si9e both of which %epen%s upon proper material %istribution in thestock (bur%en) column.

Eurin# char#in# materials ten% to se#re#ate ra%iall" accor%in# to nature si9e an%%ensit". onuniform ra%ial %istribution of the bur%en materials results in a nonuniformra%ial %istribution of particle si9e $oi%a#e an% hence another of permeabilit" of thebur%ens.The stock line cross section can be %i$i%e% into 3 9ones i.e. (i) peripher" (ii)interme%iate (iii) Central.

The interme%iate 9one occupies = of the total cross sectional area an% 3= 0 3 ofthe #as passes throu#h this area.

Hach of the peripher" an% central occup" 2 of the area respecti$el" an% , 0 4= ofthe #as passes throu#h them.

Char#in# se6uence is %enote% b" e.#. CC/ where %enotes ore ' 0 limestone S 0sinter an% C 0 coke or roun% or batch.

The %istribution of materials when %umpe% on a heap on a stationar" be% #enerall"beha$es as follows:

(i) The finer particles ten% to accumulate in a peak or ri%#e rubble an% lumps sli%e %own to%istance accor%in# to their kinetic ener#ies the lar#est #oin# furthest.

(ii) Two %ifferent materials %umpe% un%er the same con%itions ten% to ha$e their surfaces at%ifferent an#les with the hori9ontal i.e. the" ha$e %ifferent an#les of repose 0 ore: 3= 03o coke: 3& 0 &=o.Smaller particles ha$e #reater an#les than lar#er particles. !n#le of repose %epen%supon the moisture content coefficient of friction an% si9e as well as the %ensit" of thematerials.

(iii) An'%e o! reose o! )%$st !urn$ce c"$r'e #$teri$%s

M$teri$% Sinter Pe%%ets Coke R$, Ore

An'%e o! reose 313& 2,25 335 333Me$n si*e 4##5 $+er$'e si*e 2= 11 & 15R$n'e 4##5 3= 51& 24 1=3=

Two profiles forme% when materials are char#e% into the furnace are

(i) < 0 shape(ii) J 0 shape

< 0 shape% profile forme% when the material or bur%en particles hit the bur%en materialor stock column.

J 0 shape% profile forme% when the bur%en material/ particles hit the furnace walls.

2&


25/27

In a J 0 shape% profile the peripher" is packe% an% partiall" blocke% %ue to the presenceof fine materials near the furnace wall an% more $olume of #as will ten% to pass throu#hthe centre resultin# in low #as utilisation.

The m 0 profile obtaine% when the material strikes the surface of the material an% resultsin both peripher" an% central #as flow.

CHARGING C


26/27

(ii) 8ro%uction of heat on burnin# at the tu"eres for co$erin# the thermal re6uirements oncombustion it pro$i%es C for #aseous in%irect re%uction of iron oi%es C t(k#) (tu"ere(C) carbon).

(iii) Eirect re%uction of iron oi%es C%(k#) (%irect re%uction carbon).(i$) Eirect re%uction of metalloi%s Cm (k#).

Coke rate 7 Cc Ct C% Cm(k# carbon/thm

!ll reactions in the blast furnace (ecept #aseous re%uction of iron oi%es 0 in%irectre%uction carbon %eposition an% sla# formation) #i$e thermal %eficienc" (ore

en%othermic) i.e. %irect re%uction of iron oi%e an% metalloi%s (meltin# of sla# an% iron)sensible heat of the flue %ust an% top #as ra%iation an% coolin# looses calcinationse$aporation of moisture an% h"%rate% water.

Sensible heat lost in the top #as $aries between 0 1= of the total heat #enerate% atthe tu"ere an% F= 0F of heat is utilise% showin# the +- to be an efficient countercurrent apparatus.

N3: Eirect re%uction accounts for 3 0 = of the hi#h potential heat re6uire% in the lowerfurnace an% about 2= 0 3 of the total heat re6uire% in the blast furnace process e.#.%irect re%uction of iron oi%es.

Re(uction o! Coke R$te

The coke consumption rate per T*< can be %ecrease% b" an" metho% which:

(i) Increases %irect re%uction(ii) Eecreases the thermal loa% (those that re6uire heat e.#. moisture cal nation)(iii) Increases the sensible heat suppl" increase hot blast temp.(i$) Eecreases the sensible heat out flow or replace coke with other fuel.

These can be ba%l" realise% b":

(a) Increase the blast temp

(b) +ur%en preparation (si9in#)(c) Stack #as inDection at aroun% 1===C

(%) Super bur%en (Eirect re%uce% iron pre 0re%uce% ores)(e) +last a%%iti$es(f) *i#h top #as pressure (*T8) 0 utilisation of chemical ener#" 0 C #as

?tilisation of thermal ener#" temp

Note9


27/27

3ur(en Pre$r$tion

The primar" purpose is to use blast furnace char#e material which are optimum in si9eeasil" re%ucible passes a thermal loa% as low as possible in or%er to achie$e maimumpro%uction with a minimum of coke rate pro%uction cost an% capital outla".

3%$st Furn$ce Pro(ucti+ity

8ro%ucti$it" 7 Total hot metal pro%uce% per %a" 7 2=== t/%a"

orkin# $olume 1==m3

7 (Tonnes) t/m3per %a"

8ro%ucti$it" (8) 7 coke burne% (U)Coke rate (G)

8ro%ucti$it" %epen%s upon the amount of coke burnt in unit time at the tu"eres an%tu"ere carbon (coke) consume% for pro%ucin# a unit of iron.

Note9 The hi#her the blast $olume i.e. the hi#her the 2input the #reater will be the amount of

coke burnt an% therefore the lar#er will be the pro%uction.

a brief outline of iron making notes

Documents