Emulsification and mass transfer in ladle metallurgy

Abstract

Measurements of slag emulsification in gas-stirred ladles were carried out in cold-model systems of different geometric sizes. Detaching of slag droplets -necessary for efficient emulsification -only takes place if the flow velocity at the slag/metal interface exceeds a certain level. The use of a centric nozzle leads at high gas flow rates to considerably larger degrees of emulsification than eccentric stirring. The reason of this phenomenon is that the recirculation flow during centric gas injection transports larger amounts of emulsified droplets into deeper regions of the melt while during eccentric stirring there is more time for reseparation of slag droplets into the top slag. Comparing emulsification results with mass-transfer measurements, the dependence between rate constants as well as degrees of emulsification and Froude number shows similar behaviour. Emulgierung und Stoffiibergang in der Pfannenmetallurgie. An Kaltmodellsystemen unterschiedlicher geometrischer Abmessungen wurden Messungen zur Schlackenemulgierung in gasgeruhrten Pfannen durchgefUhrt. Das fUr eine wirksame Emulgierung notwendige AbreiBen von Tropfen aus der zusarnrnenhanqenden Schlackenphase ist erst nach Oberschreiten einer krltischen Stromungsgeschwindigkeit an der Grenzflache Schlacke/Metall rnoqlich. Die Verwendung einer zentrischen Elnblasduse liefert bei hoheren Gasvolurnenstrornen deutlich groBere Emulgierungsgrade als das exzentrische Gaseinblasen. Die Ursache hierfur liegt darin, daB beim zentrischen Huhren einmal emulgierte Tropfen eher von der Umlaufstromung in tiefere Bereiche transportiert werden, wah rend beim exzentrischen Einblasen mehr Zeit zum vorzeitigen Wiederabscheiden in die Topschlacke zur Verfugung steht, Vergleiche der Emulgierungsmessungen mit Ergebnissen von Stoffuberqanqsrnessunqen zeigen gute Obereinstimmungen hinsichtlich der Abhangigkeit des Emulgierungsgrades und der Geschwindigkeitskonstanten von der Froude-Zahl.

Modeling of Slag Entrainment and Interfacial Mass Transfer in Gas Stirred Ladles

“…Three regimes of mass transfer rate are delineated: Regime I is before any entrainment, Regime II is due to the entrainment of UP and Regime III occurs when the entire bulk UP is entrained into the LP as observed in past work. 7,8) These results demonstrate the capability of the model to calculate the mass transfer rate incorporating the degree of entrainment. …”

“…(2) has occurred several times in the literature, 7,[21][22][23] modeling the critical conditions for onset of entrainment, as mostly directly proportional to a velocity scale, a feature that is also present in Eq. (2).…”

“…5) The entrainment rate was estimated using the models of Oeters 31) (also found elsewhere 32,33) ) for a given average droplet size. For droplet residence time a value of 45 s was obtained as a fitting parameter to their overall model so as to yield an 'emulsification fraction' of 45 to 100%.…”

“…Given their measured droplet sizes to be smaller than 2.5 mm, their predicted residence time is quite low. The models of Oeters [31][32][33] have not been adequately validated and in the light of these contradictions its use is questionable. In contrast, the present work has dedicated models developed for each entrainment parameter leading to mass transfer rate predictions that are self consistent and agree with literature correlation; the overall model is not simple due to the complexity of the slag entrainment phenomena.…”

An investigation of slag floatation and entrapment in a continuous‐casting tundish using fluid‐flow simulations, sampling and physical metallurgy

“…Specifically, the model reflects the penetration of the steel and slag phases into each other and other conditions at the slag/metal interface. Many authors have studied the dispersion of the slag phase into the steel using physical modelling [8][9][10][11][12][13][14][15]. Among them Kim et al [13] determined a critical stirring rate for the break up of the interface in a ladle.…”