desgasificado al vacío
TRANSCRIPT
4 June 2010
PROCESOS SIDERPROCESOS SIDERÚÚRGICOS IIIRGICOS III
Tema 4. Desgasificado al vacío
Fernando Contreras B.
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 2
Procesos Siderúrgicos III – Desgasificado al vacío
TEMARIO
1.1 Introducci1.1 Introduccióónn
1.2 1.2 VacuumVacuum technologiestechnologies
1.3 1.3 ReactionsReactions underunder vacuumvacuum
1.4 1.4 GenerationGeneration ofof vacuumvacuum
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 3
Procesos Siderúrgicos III – Desgasificado al vacío
INTRODUCTION
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 4
Procesos Siderúrgicos III – Desgasificado al vacíoINTRODUCCIÓN
-- VD VD consistsconsists in in thethe generationgeneration ofof veryvery lowlow pressurepressure atat thethe interfaceinterface betweenbetween liquidliquid steelsteel & & thethe atmosphereatmosphere..
-- As a As a consequenceconsequence, , thethe equilibriumequilibrium forfor gas gas solubilitysolubility changeschanges allowingallowing thethe removalremoval ofof thethe volatilevolatile elementselements dissolveddissolved in in thethe steelsteel. .
--InitiallyInitially, VD , VD waswas usedused toto decreasedecrease H H dissolveddissolved in in
thethe steelsteel. . ThenThen VD VD becamebecame
mandatorymandatory toto produce produce
ULC ULC steelssteels & & IF IF steelssteels. .
LowLow contentcontent ofof C & N. C & N.
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 5
Procesos Siderúrgicos III – Desgasificado al vacío
VACUUM TECHNOLOGIES
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Procesos Siderúrgicos III – Desgasificado al vacíoINTRODUCCIÓN – General classification
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Procesos Siderúrgicos III – Desgasificado al vacíoINTRODUCCIÓN – Stream degassers
LLD:Ladle to ladle
-- DegasificationDegasification ofof thethe steelsteel occursoccurs onon thethe streamstream duringduring thethe transferencetransference fromfrom oneone unitunit toto anotheranother..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 8
Procesos Siderúrgicos III – Desgasificado al vacíoINTRODUCCIÓN – Stream degassers
LMD:Ladle to mould
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Procesos Siderúrgicos III – Desgasificado al vacíoINTRODUCCIÓN – Stream degassers
TD: Furnace to ladle
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES – Ladle degassers
-- OccursOccurs withwith thethe liquidliquid steelsteel insideinside thethe ladleladle. . ItIt has has twotwo mainmain designsdesigns,,
-- WithWith externalexternal recirculationrecirculation: :
PartPart ofof thethe liquidliquid steelsteel isis suckedsucked out out ofof thethe ladleladle andand forcedforced intointo a a secondsecond vesselvessel wherewhere thethe vacuumvacuum isis appliedapplied andand thenthen returnedreturned toto thethe original original ladleladle. . ThreeThree typestypes ofof recirculatingrecirculating degassersdegassers havehave beenbeen developeddeveloped::
--DH: Dortmund DH: Dortmund HoerderHoerder
--RH: RH: RuhrstahlRuhrstahl HeraeusHeraeus
--RHRH--OB (KTB) Kawasaki OB (KTB) Kawasaki TopTop BlownBlown
-- WithoutWithout externalexternal recirculationrecirculation
--TheThe full full ladleladle ((steelsteel & & slagslag) ) isis permanentlypermanently underunder vacuumvacuum. . ThreeThree technologiestechnologies havehave beenbeen developeddeveloped,,
--VTD: VTD: VacuumVacuum TankTank DegasserDegasser, , oror TDTD
--VOD: VOD: VacuumVacuum OxygenOxygen DecarburizationDecarburization
--VAD: VAD: VacuumVacuum Arc Arc DegasserDegasser
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 11
Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES – DH Dortmund Hoerder
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES – Ruhrstahl Heraeus
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES – Ruhrstahl Heraeus -Kawasaki Top Blown (RH-KTB)
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 14
Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES –Vacuum degasser (VTD)
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES –Vacuum Oxygen Decarburization (VOD)
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES –Vacuum Arc Degassing (VAD)
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Procesos Siderúrgicos III – Desgasificado al vacíoVACUUM TECHNOLOGIES –Summary
-- TheThe vacuumvacuum technologiestechnologies mostmost usedused are RH & TD are RH & TD withwith thethe correspondingcorresponding versionversion forfor oxygenoxygen blowingblowing. . ComparisonsComparisons are are shownshown nextnext::
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 18
Procesos Siderúrgicos III – Desgasificado al vacío
REACTIONS UNDER VACUUM
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Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM –Decarburization & deoxidation
-- DeoxidationDeoxidation isis performedperformed throughthrough CC--O O reactionsreactions..
-- TheThe equilibriumequilibrium ofof thethe systemsystem isis studiedstudied withwith thethe followingfollowing reactionsreactions,,
-- DecreasingDecreasing thethe pressurepressure ofof thethe systemsystem, , thethe equilibriumequilibrium ofof thethe reactionreaction movesmoves toto thethe rightright sideside toto generategenerate CO(gCO(g).).
-- DueDue toto thethe decreasedecrease ofof CO CO partialpartial pressurepressure, , reactionreaction betweenbetween C & O C & O dissolveddissolved in in thethe bathbath becomesbecomes more intense.more intense.
--OxygenOxygen can be can be availableavailable in in thethe bathbath as as lessless stablestable oxide (oxide (FeOFeO, , MnOMnO) ) oror as as dissolveddissolved O O whichwhich come come fromfrom thethe oxidationoxidation stagestage in EAF.in EAF.
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 20
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburation in Tank Degasser
-- WithoutWithout ArAr stirringstirring,,
--TheThe reactionreaction isis favoredfavored onlyonly nearnear bathbath surfacesurface ((thethe reducedreduced pressurepressure isis onlyonly effectiveeffective onon thethe surfacesurface).).
--TheThe reactionreaction raterate isis limitedlimited by C & O by C & O diffusiondiffusion in in thethe liquidliquid phasephase..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 21
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburation in Tank Degasser
-- WithWith ArAr stirringstirring,,
--TheThe reactionreaction raterate increasesincreases remarkablyremarkably..
--C & O are C & O are broughtbrought toto thethe reactionreaction surfacesurface more more rapidlyrapidly..
--TheThe argonargon bubblesbubbles increaseincrease thethe availableavailable reactionreaction surfacesurface..
--TheThe steelsteel isis permanentlypermanently recirculatingrecirculating fromfrom thethe bottombottom toto thethe surfacesurface..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 22
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburation in Tank Degasser
-- WithWith ArAr stirringstirring,,
--WhenWhen thethe reactionreaction occursoccurs underunder vacuumvacuum withwith strongstrong ArAr stirringstirring, , thethe diffusiondiffusion ofof [C] & [O] [C] & [O] toto thethe place place ofof reactionreaction toto formform {CO} {CO} isis enhancedenhanced..
--CO CO finallyfinally isis incorporatedincorporated intointo thethe ArAr bubblebubble & & draggeddragged out out ofof thethe systemsystem..
--ArAr & CO gas are & CO gas are draggeddragged out out throughthrough thethe vacuumvacuum systemsystem..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 23
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburation in Tank Degasser
--DecarburizationDecarburization can be can be studiedstudied usingusing thethe [C][C]--[O] [O] equilibriumequilibrium graphgraph forfor differentdifferent partialpartial pressurepressure ofof {CO}.{CO}.
-- EquationEquation relates relates thethe operativeoperative parametersparameters::
PcoPco= = partialpartial pressurepressure ofof COCO
[O]= [O]= ppmppm dissolveddissolved in in thethe steelsteel ((eqeq))
[C]= [C]= %C%C in in eqeq..
T= T= temperaturetemperature
-- WhenWhen decarburationdecarburation startsstarts in in pointpoint a (a (atat 1 1 atmatm) ) andand thethe TD TD operatesoperates atat 0.2 0.2 atmatm, , thethe final final %[C]%[C]--ppmppm O O willwill correspondcorrespond toto pointpoint b.b.
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 24
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburation in Tank Degasser (kinetics)
--TheThe kineticskinetics ofof decarburizationdecarburization followsfollows thethe relationshiprelationship::
--WhereWhere kckc isis a a constantconstant & & dependdepend onon, a) , a) specificspecific flowflow raterate ofof stirringstirring
b) b) degassingdegassing time (t)time (t)
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 25
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Decarburization Chemistry
--WeWe can can rearrengerearrenge thethe massmass actionaction lawlaw equationequation toto,,
[O]=[O]=PcoPco/[/[C]KcoC]Kco
--IfIf thethe pressurepressure aboveabove thethe steelsteel isis reducedreduced toto 0.1 0.1 atmatm, , PcoPco willwill alsoalso dropdrop toto 0.1 0.1 atmatm andand thethe equilibriumequilibrium [C].[O] [C].[O] productproduct willwill decreasedecrease accordinglyaccordingly..
--C & O C & O willwill be removed in be removed in thethe ratio 12:16 as ratio 12:16 as determineddetermined by by theirtheir respectiverespective atomicatomic massesmasses..
--TheThe injectioninjection ofof additionaladditional oxygenoxygen intointo thethe steelsteel can be can be usedused toto produce produce veryvery lowlow C C steelssteels (e g., <0.001%). (e g., <0.001%).
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 26
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Hydrogen Equilibrium)
--TheThe reactionsreactions forfor dissolutiondissolution are:are:
--TheThe sourcessources ofof HH22 are:are:
--WaterWater whichwhich come come fromfrom humidityhumidity..
--AirAir oror anyany humidhumid material in material in contactcontact withwith thethe steelsteel
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 27
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Hydrogen equlibrium)
--TheThe basicbasic eqeq reactionreaction isis [H]=1/2 {H[H]=1/2 {H2}g. 2}g. TheThe eqeq constantconstant isis::
--TheThe H H concentrationconcentration atat EqEq isis proportionalproportional toto thethe pressurepressure squaresquare rootroot..
--TheThe dissolutiondissolution ofof H (H (alsoalso N) in N) in purepure ironiron obeysobeys SievertSievert’’ss LawLaw: :
gas gas atomicatomic concentrationconcentration = = EqEq constantconstant x x partialpartial pressurepressure ofof gasgas
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 28
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Hydrogen kinetics)
--ConsideringConsidering thatthat in in modernmodern VD VD thethe operatingoperating pressurepressure isis aroundaround 10 10 mbarmbar andand appliyingappliying thethe followingfollowing formula.formula.
[H] [H] ff =final H =final H contentcontent
[H] i=[H] i=initiallinitiall H H contentcontent
tt =VD =VD processprocess timetime
KKHH = H = H removalremoval constantconstant, , minmin--11
--ToTo accelerateaccelerate thethe reactionreaction kineticskinetics, , itit isis necessarynecessary toto stirrstirr thethe bathbath withwith ArAr. H . H removalremoval constantconstant dependsdepends onon thethe workingworking pressurepressure andand stirringstirring flowflow..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 29
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Hydrogen kinetics)
--IfIf no no ArAr stirringstirring isis promotedpromoted, , followingfollowing occursoccurs,,
--TheThe reactionreaction willwill onlyonly taketake place place atat bathbath surfacesurface..
--TheThe reactionreaction raterate isis limitedlimited by H by H diffusiondiffusion in in thethe liquidliquid phasephase..
2[H] = {H2}2[H] = {H2}
--IsIs ArAr stirringstirring isis promotedpromoted, , followingfollowing occursoccurs,,
--H H isis broughtbrought toto thethe reactionreaction surfacesurface more more rapidlyrapidly..
-- TheThe ArAr bubblesbubbles increaseincrease thethe availableavailable reactionreaction surfacesurface..
--TheThe ArAr bubblesbubbles dragdrag thethe H out H out ofof thethe steelsteel
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 30
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Hydrogen removal)
--[H] [H] dissolveddissolved in in thethe steelsteel reactsreacts toto formform HH22 gas gas moleculemolecule whichwhich isis absorbed by absorbed by thethe ArAr bubblebubble andand draggeddragged out out ofof thethe liquidliquid steelsteel..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 31
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Nitrogen equlibrium)
--TheThe basicbasic eqeq reactionreaction isis [N]=1/2 {N[N]=1/2 {N2}g. 2}g.
--N N concentrationconcentration atat EqEq isis proportionalproportional toto thethe squaresquare rootroot ofof itsits partialpartial pressurepressure ((SievertSievert’’ss LawLaw). ). TheThe EqEq constantconstant isis defineddefined as as followsfollows,,
--LikeLike H, H, NitrogenNitrogen removalremoval alsoalso occursoccurs duedue toto thethe decreasedecrease ofof itsits partialpartial pressurepressure in in thethe gaseousgaseous phasephase butbut differsdiffers in in somesome particular particular aspectsaspects::--
-- VelocityVelocity isis limitedlimited by by thethe pressurepressure ofof surfacesurface active active elementselements likelike [O] & [S][O] & [S]
-- SurfaceSurface active active elementselements blockblock thethe sitessites forfor N2 N2 passagepassage toto thethe interfaceinterface..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 32
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Nitrogen kinetics)
--A A simplifiedsimplified formula formula forfor N N removalremoval velocityvelocity isis::
--KKNN dependsdepends onon thethe operativeoperative pressurepressure andand onon thethe stirringstirring intensityintensity..
-- N N removalremoval isis more more difficultdifficult thanthan HH’’ss sincesince N N diffusivitydiffusivity in in liquidliquid steelsteel isis lowerlower. . HenceHence, , ArAr stirringstirring has has toto be more intense.be more intense.
--N N removalremoval isis retardedretarded alsoalso by by elementselements suchsuch as Al & Ti as Al & Ti whichwhich havehave a a highhigh affinityaffinity forfor NitridesNitrides..
[[N]fN]f= final N = final N contentcontent
[[N]iN]i= = initialinitial N N contentcontent
T= VD T= VD processprocess timetime
KKNN = N = N removalremoval constantconstant consideringconsidering O & S O & S equalequal toto zerozero ((minmin--11))
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 33
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Nitrogen kinetics)
--IfIf no no ArAr stirringstirring isis promotedpromoted, , followingfollowing occursoccurs,,
--ReactionReaction occursoccurs atat bathbath surfacesurface whichwhich isis reducedreduced by by presencepresence ofof S & O.S & O.
--ReactionReaction raterate isis limitedlimited by N by N diffusiondiffusion whichwhich isis slowerslower as N as N diffusivitydiffusivity isis lowerlower ((largerlarger atomatom).).
2[N] = {N2}2[N] = {N2}
--IsIs ArAr stirringstirring isis promotedpromoted, , followingfollowing occursoccurs,,
--TheThe gaseousgaseous phasephase isis generatedgenerated by by ArAr bubblebubble..
-- IncreasesIncreases thethe areaarea ofof thethe interphaseinterphase gas gas liquidliquid..
--AvailableAvailable surfacesurface forfor N N removalremoval..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 34
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Degassification (Nitrogen kinetics)
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 35
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Defulfurization under vacuum
-- ItIt isis controlledcontrolled by by thethe reactionreaction::
-- DuringDuring vacuumvacuum treatmenttreatment thethe reactionreaction isis stronglystrongly favoredfavored becausebecause operatedoperated atat::
--HighHigh temperaturetemperature
--StrongStrong ArAr bubblingbubbling
--HighHigh degreedegree ofof deoxidationdeoxidation
--IncreaseIncrease ofof specificspecific slagslag//steelsteel areaarea
--ForFor desulfurizationdesulfurization underunder vacuumvacuum nearnear equilibriumequilibrium conditionsconditions can be can be reachedreached..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 36
Procesos Siderúrgicos III – Desgasificado al vacíoREACTIONS UNDER VACUUM – Defulfurization under vacuum
-- A A equationequation has has beenbeen developeddeveloped in in termsterms ofof amountamount ofof slagslag requiredrequired toto achieveachieve a a specificspecific S S concentrationconcentration as as followsfollows::
-- EqEq considersconsiders equilibriumequilibrium conditionsconditions andand termsterms mean mean nextnext,,
WmWm = = weightweight ofof steelsteel
LsLs= = sulfursulfur distributiondistribution rationration givengiven by (by (%S%S)/[)/[%S%S]. ].
%So%So & & %S%S aimaim = = InitialInitial & & aimaim S S concentrationconcentration..
-- TheThe LsLs valuevalue dependsdepends onon thethe S S capacitycapacity ofof thethe slagslag andand isis relatedrelated toto::
--UnderUnder goodgood conditionsconditions, , valuevalue ofof LsLs=500 are =500 are assembleassemble in in practicepractice..
Example
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 38
Procesos Siderúrgicos III – Desgasificado al vacío
GENERATION OF VACUUM
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 39
Procesos Siderúrgicos III – Desgasificado al vacíoGENERATION OF VACUUM – Vacuum treatment
In general In general thethe specificationspecification ofof a a VacuumVacuum SystemSystem considersconsiders,,
--VolumeVolume ofof thethe vesselvessel toto be be evacuatedevacuated..
--FlowFlow ofof ArAr toto be be injectedinjected in in thethe vesselvessel..
--LastLast operativeoperative pressurepressure toto be be attainedattained..
--PumpingPumping capacitycapacity atat thethe operativeoperative pressurepressure..
--Time Time toto reachreach thethe operativeoperative pressurepressure..
ThreeThree typestypes ofof equipmentequipment are are generallygenerally usedused,,
--LiquidLiquid ringring pumpspumps..
--MechanicalMechanical pumpspumps..
--SteamSteam ejectorsejectors..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 40
Procesos Siderúrgicos III – Desgasificado al vacíoGENERATION OF VACUUM – Liquid ring punps
PROS,PROS,
--HighHigh suctionsuction capacitycapacity..
--NotNot affectedaffected by by liquidliquid oror dustdust entrainedentrained in in thethe processprocess gas gas streamstream
--HighHigh reliabilityreliability duedue toto simple simple designdesign
--LowLow maintenancemaintenance requiredrequired
CONS,CONS,
--CannotCannot achieveachieve a a pressurepressure belowbelow 150 150 mbarmbar ((whenwhen waterwater isis usedused forfor thethe productionproduction ofof thethe liquidliquid ringring))
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 41
Procesos Siderúrgicos III – Desgasificado al vacíoGENERATION OF VACUUM – Mechanical Pump (Roost type)
PROS,PROS,
--SteamSteam isis notnot requiredrequired thereforetherefore somesome energyenergy can be can be savedsaved..
CONS,CONS,
--MustMust treattreat relarivelyrelarively cold cold andand absolutelyabsolutely dustdust--free free fluidsfluids onlyonly. . ThereforeTherefore a a heatheat exchangerexchanger andand bagbag filterfilter mustmust procede procede thethe pumpspumps. .
--CostCost exceedsexceeds thatthat ofof thethe steamsteam jet jet pumppump systemsystem..
4 June 2010Desgasificado al vacío Instructor: Fernando Contreras 42
Procesos Siderúrgicos III – Desgasificado al vacíoGENERATION OF VACUUM – Steam Ejectors (Jet pumps)
PROS,PROS,
--HighHigh suctionsuction capacitycapacity..
--NotNot affectedaffected by by liquidliquid oror dustdust entrainedentrained in in thethe processprocess gas gas steamsteam..
--HighHigh reliabilityreliability duedue toto thethe absenceabsence ofof movingmoving partsparts..
--PracticallyPractically no no maintenancemaintenance requiredrequired..
CONS,CONS,
--RequiresRequires a a steamsteam generatorgenerator..