炼钢英语论文.doc

Fuel90(2011)1350–1360
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Numericalsimulationofoff-gasformationduringtop-blownoxygen
convertersteelmaking
⇑
SenLi,XiaolinWei ,LixinYu
InstituteofMechanics,ChineseAcademyofSciences,No.15Beisihuanxi Road,Beijing100190,China
a r t i c l e i n f o
a b s t r a c t
Articlehistory:
Intop-blownoxygenconvertersteelmakingprocess,alargeamountofhigh-temperatureoff-gasispro-
duced,andtheoff-gasisapreciousvaluablefuelcontaininghighconcentrationofcarbonmonoxide(CO).
Numericalmodelisdevelopedfortop-blownoxygenconverteroff-gasformation,theoff-gasformationis
simulatedusingthedevelopedmodel,andtheinfluencesoftheoperatingmodelofconverteronthechar-
acteristicsofoff-gas(concentrations,temperature,flowrateandsensibleheatflux)areinvestigated.The
simulated results indicate that CO concentration varies gently, CO concentration can reach about 80%
Received13October2009
Receivedinrevisedform11January2011
Accepted12January2011
Availableonline26January2011
Keywords:
during10–80%blowingoxygentime,thechangetrendofCO concentrationiscontrarytothatofCOcon-
2
Numerical simulation
Converter off-gas
Concentration
Flowrate
centrationduring0–90%blowingoxygentime,andthedramaticchangesofoxygenlanceheightresultin
significantfluctuationsofoff-gasflowrate.Theoperationmodelofoxygen-blowingpressuresignificantly
affectsoff-gassensibleheatflux,andthesensibleheatfluxishighduring40–80%blowingoxygentime.
Ó2011ElsevierLtdAllrightsreserved.
Sensibleheatflux
1.Introduction
gas recovery and consider the requirement of off-gas quality by
users,therelevant restricted conditions mustbeset[7].Thesensi-
Oxygen blown converter steelmaking has developed for over
50years, and the process is retaining its predominance as the
world’s No.1 steelmaking method by technological innovation
[1].Oxygenblownconverter isgenerally dividedintotop-blowing,
bottom-blowing andmixedblowing. Top-blown oxygensteelmak-
ingproduces 85.5%ofsteelmadebyconverter [2].Acharacteristic
ofconverter production isthe formation of alarge amount of off-
gas. Converter off-gas isaprecious valuable fuel containing about
80% carbon monoxide (CO) during the period of high gas produc-
tion.Off-gas hasalarge amount ofsensible heat, anditstempera-
tureattheconverter outletcanreach1450–1700 °C[3].Converter
off-gas isan important secondary energy resource for steel enter-
prises. Therefore, itisimportant forsteelenterprises toeffectively
recover converter off-gas and itssensible heat.
Withthesharpriseinenergycosts,strenuous effortshavebeen
made in development of new technique. Improving the recovery
systems of converter off-gas and its sensible heat can effectively
reduce theproduction costofsteelmaking, laying thebasisforen-
ergy-saving steelmaking, and can remarkably decrease the total
quantities of pollutant emissions to realize cleaner production.
However, most of off-gas sensible heat becomes waste in spite of
its large potential [4,5], mainly because of the intermittent dis-
charge, the frequent change of composition concentrations, and
the possibility of the explosion [6]. To ensure the safety of off-
ble heat of converter off-gas is often utilized by cooling stack or
waste heat boiler. Owing tothe frequent fluctuations oftempera-
ture and flowrate of converter off-gas during steelmaking, the
operational parameters of hot water or stream cooling circuit of
stack and waste heat boiler fluctuate correspondingly, and the fa-
tigue breakdown of heating surfaces easily occurs. Therefore, the
change characteristics of converter off-gas during steelmaking
are important for the improvement of converter off-gas recovery
and itssensible heat utilization.
In the past decades, most researchers have developed mathe-
maticalmodelsformodeling theimpuritycontentinmoltenmetal
bath of oxygen converter, two-phase turbulent flow in the cavity
without chemical reaction and post combustion ofoff-gas [8–15],
but little work has focused on the simulation of converter off-gas
formation. In order to improve the system of converter off-gas
recovery and sensible utilization, the process model development
for predicting the converter off-gas formation is very necessary.
Inthispaper, numerical model isfocused ontheoff-gas formation
of the oxygen top-blown converter. Converter off-gas formation
during blowing oxygen steelmaking is modeled, and the change
characteristics of off-gas (concentrations, temperature, flowrate
and sensible heat flux) are investigated bynumerical simulation.
2.Process description ofconverter off-gas formation
⇑
The main role ofoxygen converter istoreduce the contents of
carbon and other impurities of pig iron liquid through oxidation
Corresponding author.Tel.:[phone]
E-mailaddresses:lisen@(S.Li),xlwei@(X.Wei).
0016-2361/$ -seefrontmatterÓ2011ElsevierLtdAllrightsreserved.
doi:10.1016/j.fuel.2011.01.022

S.Lietal./Fuel90(2011)1350–1360
1351
reactions by blowing oxygen [16]. The top-blown oxygen steel-
makingprocessisautogenous: therequired thermalenergyispro-
ducedduring theprocess. Theconverter istiltedandcharged, first
withscrapandthenwiththemolteniron,andthenreturnedtothe
uprightposition.Themoltenironaccountsforabout80%oftheto-
talcharge, therestconsisting ofsteelscrap. Atypical chemistry of
molten iron charged into the converter is: 4% C, 0.2–0.8% Si,
0.08–0.18% P,and0.02–0.08% Mn[16,17]. Theconverter issetup-
right and a water-cooled oxygen lance is lowered down into it.
High-purity oxygenisblownintoconvertervesselthroughthever-
tically oriented water-cooled lance. The oxygen lance blows 99%
purity oxygen onto the molten metal surface, igniting the carbon
dissolved in the metal and burning it to form carbon monoxide
Theimpurity removal reactions mainlyoccuronthecavitysur-
faceofmoltenmetalbathandslag–metal interface.Thecavitysur-
face is important to decarburize and remove silicon from the
molten metal, and the demanganization and dephosphorization
reactionsoccurnotonlyonthecavitysurfacebutalsoonslag–me-
tal interface, as shown in Fig. 1. During oxygen converter steel-
making, the oxygen is delivered into the converter by a top
lance,whichterminates inafittingthatcontainsseveralLavalnoz-
zles. Each nozzle produces ajet atapproximately twice the speed
ofsound, andthejetpenetrates deeply into themolten metal and
creates oscillation blowing cavity [21], as shown in Fig. 2. The
shape and area of the cavity surface are related with the oxygen-
blowing pressure (p ), oxygen lance height (L), the diameter of
0
(CO) and carbon dioxide (CO ),causing the temperature torise to
2
oxygen lance nozzle (d ) and nozzle number (n). Oxygen lance
1
z
about1700°C[17].Thismeltsthescrap,lowersthecarboncontent
ofthemoltenironandhelpsremoveunwantedchemicalelements.
Fluxes(burntlimeordolomite) arefedintothevesseltoformslag
which absorbs impurities of the steelmaking process. Typical
capacitiesare200–300tonsofliquidsteel,andthetap-to-tapcycle
isabout 30–40min with 13–18min blowing oxygen period.
The top-blown oxygen steelmaking process is a very complex
batch reaction course. Decarburization of molten metal is a basic
process ofoxygen converter steelmaking, andtheprocess isdeter-
mined bythedevelopment ofheat andmass transfer processes in
the bath [18–20]. For top-blown converter, the oxidization reac-
tions of impurities mainly occur on the cavity surface of molten
metalbathformed bytop-blown oxygen andslag–metal interface,
asshown inFig. 1.
heightisthedistancebetween oxygenlancenozzletipandmolten
metal liquid level, as shown in Fig. 2. The area calculation of the
cavity surface area can be referred to references [8,22,23], and
the area calculation of the slag–metal interface can be referred
to reference [23].
Whenoxygenisinjectedintoconverterthroughaverticallance,
theoxygen isadsorbed onthecavity surface and diffuses into the
moltenmetalliquid.ThesolventoxygencanreactwithC,Si,Fe,Mn
andPinmolten metalbath,andaseriesofoxidation reactions oc-
curs,asshowinFig.1.Thekinetic modelofthereactions ofcavity
surface can bereferred toreference [24].
Foroxygentop-blown converter, thereactions ofdemanganiza-
tion and dephosphorization mostly occur on slag–metal interface
[22].Theoxidationreactionsonslag–metal interfaceareverycom-
plex, and these reactions are coupled, as shown in Fig. 1. The ki-
netic model of the reactions of slag–metal interface can be
referred toRef. [22].
Itisassumed thattheoxidizations ofcarbonandsiliconinmol-
tenmetalliquidonlyoccuronthecavitysurface, andthattheoxi-
dizations of manganese and phosphorous occur not only on the
cavity surface but also on slag–metal interface. The model of the
change ofelement (C,Si,Feand P)concentration inmolten metal
liquidinmoltenmetalbathduringblowingoxygencanbereferred
toreferences [14,24].
Carbon oxidation in molten metal bath is influenced by the
temperature ofmolten metalbathandtheelement contents (such
as carbon, silicon, manganese and phosphorus), and it produces
carbonmonoxide, andcarbonmonoxideusuallyreactswithexcess
oxygen inconverter freeboard spacetoproduce carbon dioxide, as
showninFig.1.Inthemeantime, smallquantityofnitrogeniscar-
ried by oxygen jet stream. Therefore, the off-gas in the converter
freeboard ismainly composed ofCO, CO ,N and O2.
2
2
3.Mathematic model off-gas formation
Oxygen blown is mostly absorbed by molten metal bath to
decarbonize, and then a large amount of carbon monoxide is
produced andentersintoconverter off-gas.Secondary combustion
of CO with O2 occurs in converter freeboard space, and it is as-
sumed that the combustion reaches instantaneous equilibrium:
The area calculation ofcavity surface and slag–metal interface,
kinetic model of the reactions of cavity surface and the kinetic
modelofthereactionsofslag–metal interfacearegiveninthesup-
plementary materials.
Fig.1. Steelmaking usingtheoxygentop-blownconverter [18,19].

1352
S.Lietal./Fuel90(2011)1350–1360
dnCO2
dt
nCO2
¼ÀFout nv þRCO
ð6Þ
dnN2
dt
nN2 QO2½N ŠÂ10
2
22:4
¼ÀFout nv
þ
ð7Þ
ð8Þ
n ¼n þnCOþnO þnN
v
CO2
2
2
Theconverteroff-gasisconsidered asidealgas,andthustheto-
tal molar number of off-gas in converter freeboard space also can
beexpressed as:
According to the chemical equilibrium of CO and the material
conservation in converter freeboard space, CO consumption rate
(RCO)andthemolarflowrateofoff-gas(Fout)arerespectively calcu-
lated asfollows [22]:
EÀAÂD
RCO
¼
ð9Þ
CþDÂB
Fout¼AþBÂRCO
ð10Þ
where
2T þ273
FðT þ273Þ
T þ273
QO2½%N ŠÂ10
qnm
g
2
22:4
A¼
B¼
FO2þFCO
þ
þ
ð11Þ
ð12Þ
ð13Þ
ð14Þ
g
g
Fig.2. Thecavityformedbytop-blown oxygen.
2ðÀDHCOÞn ÀFðT À273Þ
v
g
2Fð2T þ273Þ
COþ1=2O2 CO2
ð1Þ
g
It is assumed that: converter off-gas completely mixes; excess
off-gasdischarges throughconverter mouthintheblowingoxygen
process; the oxidation reactions are controlled by mass transfer;
COconsumption rateofabovereactionisRco(mol/s);thedischarge
amountofoff-gasisFout(mol/s);thetotalamountofoff-gasincon-
verterfreeboard isn (mol);themolenumbers ofO ,COandN in
1
1
1
C¼n þn þ4n
CO2
CO
O2
1
2nv
D¼
v
2
andnN ,respectively. Theamount ofoxy-
2
off-gas arenO2,nCO,n
FCO
FO
2
CO
2
2
E¼
ð15Þ
genblownisQO (m3/s),theconcentration ofN inoxygenblownis
þ2nO2
nCO
2
2
[N ] (%), and then the residual oxygen flux after the oxidation of
2
impurities inmoltenmetalbath(FO2)(mol/s)according totheoxi-
F¼nO2
whereCPiisthegasspecificheat(i=O ,CO,CO ,N ),J(molK).
Accordingtotheheatbalanceofconverteroff-gas,thechangeof
off-gas temperature iscalculated asfollows:
C
PO2þnCOCPCO
þnCO2
C
þnN2
C
ð16Þ
PCO2
PN2
dization reactions ofC,Si,Mn, Pand Fe(see Fig. 1)is
À"
#
2
2
2
b
½CŠ
QO2Â100À½N ŠÂ1000
dðW C Þ
2
100Â22:4
m
FO2
¼
dt
À2"
# "
À
#
À2
!
b
½SiŠ
dðW C
b
½MnŠ
dðW C
b
½PŠ
dT
dt
qÀF ðn
n
v
out
C
þ
n
COC
þ
n
C
þn
PCO2
C
ÞT þR ðÀDHCOÞ
g
dðW C
Þ
Þ
5
Þ
g
O2
PCO2
CO2
PCO2
N2
PN2
PCO
CO
m
m
m
ð17Þ
¼
nO2
C
þnCO
C
þnCO
C
þnN CPN2
dt
dt
dt
PO2
PCO
2
2
!
where,qistotalheatamountabsorbed byoff-gas.
dðW C
b
½Fe
ŠÞ
m
À
ð Þ
2
The model described above is used to simulate the converter
off-gas formation of a 203ton top-blown oxygen converter
charged with molten pig iron and scrap. The parameters used in
the model are shown in Table 1, the initial and boundary condi-
tionsareshowninTable2.Themainflowchartofcalculation pro-
gram isshown inFig. 3.
dt
where Wm is the mass of molten metal liquid, kg; C i
concentration inmoltenmetalliquid(i=C,Si,Fe,P),kmol/kg(Fe).
COflux produced bydecarburization reaction (FCO,mol/s) is:
b
½Š
is i element
FCO¼r J Ac
ð3Þ
C
O
4.Model validation
where JO is the average diffusion flux ofoxygen on the cavity sur-
face,mol/(sm2);A istheareaofcavitysurface,m2;r isthecon-
C
C
In the practical steelmaking process, since converter off-gas is
high-temperature and entrains large amounts of molten dust
(0.06–0.11kg (dust)/kg (off-gas)), the composition concentrations
of off-gas are hard to be monitored. The decarburization reaction
is the key link in the off-gas formation, and the validation of the
modelisverifiedbythemonitoreddecarburization rateandcarbon
content inmolten metal bath.
Inpractical steelmaking process, converter off-gas isoften dis-
charged into the cooling stack to be partial combusted, cooled
anddusted. Inordertoobtainthedecarburization rateandcarbon
content in molten metal bath, off-gas sampling probe is installed
onthehighest point ofthecooling stack, the location oftempera-
sumption oxygenratioofcarbonoxidation reactionsonthecavity.
The calculations of J , AC and rC are given in the supplementary
O
materials.
According to the mass equilibrium of converter off-gas, the
changes ofmole numbers ofO ,COandN inconverter freeboard
2
2
space are
dn
dt
n
nv
RCO
2
O2
O2
¼FO ÀFout
À
ð4Þ
ð5Þ
2
dnCO
dt
nCO
¼FCOÀFout nv ÀRCO

S.Lietal./Fuel90(2011)1350–1360
1353
Table1
Modelparametersinoxygentop-blownconverteroff-gassystem.
of CO and CO2 in flue gas is continuously measured by gas mass
spectrometer (EMG-20-1, therelative errorislessthan0.5%),tem-
perature of flue gas is measured by Platinum–Rhodium thermo-
couples (the measurement accuracy is ±1.5°C), and the flue gas
flowrate is measured by gas flow meter (Verabar 400). Based on
theconservation ofcarbon,thedecarburization rateofmoltenme-
talbath can becalculated as
Parameter
Value
Parameter
Value
kC
kSi/kC
1Â1012kg[Fe]/(kmol [C]Ás) DHSi
À817,682J/mol
À722,432J/mol
À11,76,563J/mol
30kg[C]/kmol [Si]
DHFe
DHP
1Â10À4kg[C]/kmol[Fe]
kFe
C
b
Fe
=kC
kSi/kC
kP/kC