Particularidades del manejo ganadero tradicional

If refining is still predominantly occurring in the foam, then as before the foam structure group, Sg^, will be approximately unity. Hence equation 5.45 may be simplified,

2 m '

L co-7ijCri1; = ---— — 2— --- 5*46

^s,f ^ Aa 1 £■ °^<Ja

This is clearly a somewhat simplified approach to the problem since neither equation 5-43 for the model system or equation 5*44 for steelmaking conditions take into consideration the variation in solute concentration between droplets during their passage through the foam. The composition of droplets in the foam will also have fallen well below the critical value

some time before it is achieved in the bulk bath.

In steelmaking the transition to carbon transport control is associated with the collapse of the foam, since the rate of gas evolution is inadequate to sustain it. An advance model of the process would therefore have to take into consideration both decarburisation occurring in the jet impinge­ ment zone and as a result of the carbon boil in the bulk bath.

The nature of the variables in the denominator of equation 5»4& suggest that the metal composition at whiqh the mechanism change occurs may be

influenced by the structure of the foam. Similarities may possibly be drawn between this-term and the geometric factor proposed by Szekeley to explain the variability of the bath composition at which the mechanism change takes place 4\ The ability to predict the critical composition for the mechanism change would certainly be a useful control parameter. Clearly

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A room temperature model has been developed which simulates certain aspects of the slag-metal-gas reactions that occur in reaction generated foams of the type encountered in L.D. steelmaking. In the model the molten iron was represented by a pool of sodium amalgam, the slag by a mixture of water and glycerol and the oxygen by a hydrogen chloride-nitrogen jet. Droplets of amalgam ejected from the bath by the impinging gas jet, reacted with the hydrogen chloride dissolved in the model slag to produce hydrogen bubbles, thus forming a dynamic foam.

The behaviour of single droplets of amalgam in acid media has also been studied in order to gain more information about the fundamental re­ fining processes occurring in the model converter. With high sodium con­ centrations in the amalgam droplets, the refining rate was shown to be dependent upon the acid concentration in the aaueous phase, the process

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probably being controlled by the rate of discharge of hydrogen ions. The presence of hydrogen bubbles adhering to the droplet surface had an adverse effect on the refining rate achieved. Sodium chloride additions to the aqueous phase also tended to reduce the refining rate but the mechanism in­ volved is not fully understood. With low sodium concentrations in the amal­ gam droplets, the refining rate became dependent upon the sodium concent­ ration, implying that transport of this species to the reaction interface was controlling the rate of the overall process.

It has not been possible to develop a mathematical model for the re­ fining processes occurring within the model converter. For steelmaking conditions it has been shown that the rate of decarburisation during the stage I and II periods is influenced by two factors, the structure of the foam and the rate of transfer of oxygen from, the gas jet to the slag phase. When the surface area available for slag-metal reaction in the foam is very large, the decarburisation rate becomes self stabilising at some value strongly influenced by the rate of transfer of the reactant species from the jet gases to the slag phase.

The model converter has been used to qualitatively investigate the effect of lance height, jet momentum and mass flow rate of gaseous reactant into the reaction vessel on the mean stage II refining rate. The results obtained compare favourably with analogous variables in steelmaking practice. In addition the effect on the refining rate of pressurising the reaction vessel has also been investigated. An improvement in the refining rate was achieved, partly due to improved slag-metal drop contact and partly to increased hydrogen chloride flow rate. It is not believed that such a

significant improvement would be achieved for steel making conditions although there might be some advantage derived from improved control over slopping at high oxygen flow rates.

When the sodium concentration in the amalgam fell below some critical level the refining rate in the mode], converter decreased producing a third refining stage comparable with refining under carbon transport control in the L.D. converter.

1 M. D. Ward 2 K. W. Lange 3 R. D. Walker and D. Anderson 4 K. Kawakami 5 G. C. Smith 6 R. A. Flinn et al 7 A. Chatterjee 8 V. B. Okhotskii 9 D. J. Price 11 H. W. Meyer 12 F. B. Richardson and J. H. E. Jeffes 13 Y. V. Yakovlev, et al 14 Y. F. Mikhnevich et al 15 K. W. Meyer et al 16 B. Trentini, 17 B. V. Nikiforov et al 18 F. Bardenheuer et al 19 V. I. Yavoiskii et al 20 H. von Ende et al 197.0, 208, p 445

Archiv fur das Eisenhuttenwesen, 1971, 42,(4), p 233, B.I.S.I.T. 9410

Iron and Steel

Part I 1972, June, p 271