Studies of interface deformations in single- and multi-layered liquid baths due to an impinging gas jet

An impinging gas jet on a molten bath having a slag layer on top is encountered in various metal processing operations. The impinging region was studied using a physical model consisting of an air jet and water bath. Kerosene and corn oil were used as the second layer to investigate the role of the slag layer properties on interface shape and bath circulation. The interface shapes were measured both photographically and by using a surface-tracking resistance probe. The limiting condition at which the jet breaks through the kerosene or corn oil layer and reaches the water layer was determined experimentally. A phenomenological model for the prediction of penetration depth is developed for both short and long jet heights for liquid baths with and without a second liquid layer on top.     

The physical behavior of a gas jet injected horizontally into liquid metal

The gas fraction and bubble frequency distributions in a submerged air jet, injected horizontally into mercury, have been measured under isothermal, nonreactive conditions for nozzle diameters of 0.325 and 0.476 cm and jet Froude numbers ranging from 20.5 to 288. The measurements reveal that the jets expand extremely rapidly upon discharge from the nozzle with an initial expansion angle of 150 to 155 deg. This value, which is over seven times greater than is found with air jets in water, indicates that the physical properties of the liquid exert considerable influence on the jet behavior. In conjunction with the rapid expansion, the air jets in mercury were also found to penetrate extensively behind the nozzle, and in many respects resembled a vertically injected jet. The extent of backward penetration of the jets was constant for all blowing conditions studied while the forward penetration increased with both increasing jet Froude number and nozzle diameter. The measured jet penetration in both the forward and backward directions were considerably larger than expected from model predictions. The core of the jets consists of a high concentration of gas bubbles. Both the gas volume fraction and bubble frequency in the core increase with increasing jet Froude number and nozzle diameter. The gas concentration and bubble frequency decrease with increasing distance along the jet trajectory due presumably to entrainment of liquid metal and bubble coalescence. On the basis of these findings, it is likely that process jets, such as are injected into copper converters, also expand rapidly and penetrate only a short distance into the bath. Thus rather than reacting in the middle of the bath, the jets may be impinging on the backwall refractory and contributing to the erosion observed there.     

Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace

A thin-slice computational fluid dynamics (CFD) model of a conventional tuyere blown slag-fuming furnace has been developed in Eulerian multiphase flow approach by employing a three-dimensional (3-D) hybrid unstructured orthographic grid system. The model considers a thin slice of the conventional tuyere blown slag-fuming furnace to investigate details of fluid flow, submerged coal combustion dynamics, coal use behavior, jet penetration behavior, bath interaction conditions, and generation of turbulence in the bath. The model was developed by coupling the CFD with the kinetics equations developed by Richards et al. for a zinc-fuming furnace. The model integrates submerged coal combustion at the tuyere tip and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with several user-defined subroutines in FORTRAN programming language were used to develop the model. The model predicted the velocity, temperature field of the molten slag bath, generated turbulence and vortex, and coal use behavior from the slag bath. The tuyere jet penetration length (l _P) was compared with the equation provided by Hoefele and Brimacombe from isothermal experimental work $ \left( {\frac{{l_{\text{P}} }}{{d_{o} }} = 10.7\left( {N^{\prime }_{Fr} } \right)^{0.46} \left( {\rho_{\text{g}} /\rho_{l} } \right)^{0.35} } \right) $ and found 2.26?times higher, which can be attributed to coal combustion and gas expansion at a high temperature. The jet expansion angle measured for the slag system studied is 85?deg for the specific inlet conditions during the simulation time studied. The highest coal penetration distance was found to be l/L?=?0.2, where l is the distance from the tuyere tip along the center line and L is the total length (2.44?m) of the modeled furnace. The model also predicted that 10?pct of the injected coal bypasses the tuyere gas stream uncombusted and carried to the free surface by the tuyere gas stream, which contributes to zinc oxide reduction near the free surface.     

Electro-extraction of molybdenum from Mo2C-type carbide

A process for the preparation of molybdenum from molybdenum carbide was investigated. It involved fused salt electrolysis of the carbide in an inert atmosphere electrolytic cell using a KCl-K₃MoCl₆ electrolyte. The preferred conditions for electrolysis carried out in a 0.075 m (3 in.) diam cell were: voltage 0.2 to 0.5 V; cathode current density 8000 A/m2 (720 amp/f²);bath temperature 1203 K; and electrolyte composition 7.5 pct molybdenum. Under these conditions, electrolysis in a 0.15 m (6 in.) diam cell charged with 1.5 kg of the carbide yielded a total metal recovery of 71 pct at an average current efficiency of 60 pct. The metal purity was better than 99.9 pct. The electron beam melt hardness for the electro-extracted molybdenum was in the range of 150 to 160 DPH. The paper presents a part of the thesis to be submitted by A. K. SURI to the University of Bombay (India).     

Desulfurization of bath smelter metal

The purpose of the present work was to determine the mechanism and optimal conditions for desulfurizing bath smelter metal with a CaO-CaF₂ flux. The minimum silicon (0.1 pct), or aluminum (0.3 pct), contents in the metal for optimal rates were determined. It was found that 8 to 10 pct CaF₂ at 1450 °C is required and that the rate below the CaO-CaF₂ eutectic temperature (1360 °C) is very slow. It is proposed that a liquid phase at the surface of the CaO particles is required, which is provided by the addition of CaF₂. The Si or Al is required to reduce the number of phases for the reaction from three, when carbon is controlling the oxygen potential, to two when Si or Al is; two-phase reactions are inherently faster than those involving three phases. For the optimal conditions, the rate is controlled by mass transfer of sulfur in the metal to the CaO-CaF₂ surface. A simple model for continuous desulfurization indicates 95 pct desulfurization can be achieved at high production rates for metal containing 0.10 to 0.15 pct Si using a CaO-10 pct CaF₂ flux at 1450 °C. Formerly Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University     

Electrolytic recovery of molybdenum from molybdic oxide and molybenum sesquisulfide

An electrolytic process for molybdenum extraction in a KCl?K₃MoCl₄ electrolyte (containing approximately 7.5 wt pct molybdenum) was investigated using three types of anode feed —namely, molybdic oxide-graphite, molybdenum sesquisulfide-graphite, and molybdenum sesquisulfide without graphite. In the case of molybdic oxide-graphite anode, a maximum current efficiency of 99 pct was achieved at an operating voltage of 0.35V, a cathode current density of 5000 A/m² (450 A/f²) and a bath temperature of 1223 K. Electrolysis with molybdenum sesquisulfide-graphite, at an operating voltage of 1.2V, a cathode current density of 13,900 A/m² (1250 A/f²) and a bath temperature of 1173 K, yielded a maximum current efficiency of 84 pct. Electrolysis of molybdenum sesquisulfide without graphite incorporation, yielded under almost similar conditions, a maximum current efficiency of 87 pct. Extended electrolysis was carried out using molybdic oxide-graphite and molybdenum sesquisulfide cell charges and yielded metal with purity over 99.9 pct.     

Particle penetration during spray forming and Co-injection of Ni3Al + B/Al2O3 intermetallic matrix composite

Intermetallic matrix Ni₃Al + B/Al₂O₃ composite, with 11 vol pct of Al₂O₃ particles incorporated into the matrix, was synthesized using a spray atomization and coinjection method. The penetration behavior of ceramic particles into atomized droplets during spray atomization and coinjection of Ni₃Al + B/Al₂O₃ composite was investigated experimentally and numerically. It was found that the extent of incorporation of Al₂O₃ into Ni₃Al + B droplets depends on the solidification condition of the droplets at the time of droplet/particle interaction. Penetration was observed only in fully liquid droplets or partially solidified droplets. No penetration was observed for droplets smaller than ∼40 μm, because droplets in this size range were fully solidified at the point of coinjection, and penetration was not possible for fully solidified droplets. The distribution of penetrated Al₂O₃ in the Ni₃Al + B droplets was, in general, uniform, with no trends of segregation observed. However, it was noted that most Al₂O₃ particles were located at the grain boundaries inside the droplets, while some Al₂O₃ particles were trapped inside the droplets by primary dendrite arms resulting from a fast moving solidification front typically associated with rapid solidification processes such as spray atomization. Finally, it was believed that the Al₂O₃ particles facilitated nucleation upon penetration of the Ni₃Al + B droplets either by means of thermal gradients or compatibility of preferred growth planes.     

Bubble and liquid flow characteristics in a wood’s metal bath stirred by bottom helium gas injection

A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood’s metal with a melting temperature of 70 °C was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a two-needle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.     

The injection of solids using a reactive carrier gas

The injection of nonwettable powders into melts in the bubbling regime was studied experimentally using a cold-model system. Polyethylene powder was injected into a cylindrical vessel containing water, through a vertical top-submerged lance, with insoluble (air) and soluble (ammonia) carrier gases. The concentration of particles in the liquid and the penetration length of the particle-liquid jet into the bath were measured, as the carrier gas composition, the gas and solids flow rates, and the particle size were varied. It was found that the concentration of particles retained in the liquid was up to 10 times higher, and the penetration length of the jet was up to three times higher when the soluble carrier gas was used instead of the insoluble carrier gas. For both carrier gases, the dispersed particle concentration increased with increasing gas flow rate and increasing particle size, whereas the penetration length of the jet increased with increasing gas and solids flow rates.     

The breakup of bubbles into jets during submerged gas injection

There has never been any fundamental explanation presented for the transition from the bubbling regime to the jetting regime when gas is injected into liquid at high velocity through submerged tuyeres. This is an important issue in metallurgical processes, since the flow regime is known to influence refining rates, refractory erosion, and the penetration of the liquid into the tuyere. Based on the observation that many small droplets of liquid and gas bubbles are formed to create the jets, a combined Kelvin-Helmholtz and Rayleigh-Taylor instability analysis has been applied to bubbles forming at submerged tuyeres. For particular wavelengths of disturbances, the interface will be unstable and create bubbles and droplets. The critical injection velocity for instability depends on surface tension, tuyere diameter, and the gas-to-liquid density ratio, which can be summarized by We = 10.5(ρ*)^−1/2, where We is the Weber number based on the gas velocity and density and tuyere diameter, and ρ* is the gas-to-liquid density ratio. The importance of surface tension had not been appreciated previously for this regime of gas injection. There is considerable controversy in the literature concerning the measurement of the transition from bubbling to jetting. The 70 pct “linking” point, proposed by Ozawa and Mori, describes the situation where 70 pct of the bubbles link with the preceding bubbles and produce a reasonably steady jet. The theoretical correlation developed above predicts the velocity to reach this point ±20 pct (95 pct confidence level) in a variety of systems from six different groups of workers. The theoretical analysis demonstrates that the instabilities are primarily capillary in nature, not gravity waves, which explains the observation that orientation has little effect on the jetting transition.     

Metal vapor treatment for enhancing the dissolution of platinum group metals from automotive catalyst scrap

A new process for dissolving platinum group metals (PGMs) from automotive catalyst scrap using metal vapor was proposed. To improve the PGMs dissolution ratio from scraps, vapor of reactive metals (R), such as magnesium (Mg) or calcium (Ca), was reacted with the automotive catalyst scrap in a closed stainless steel vessel at 1173 K for 3 hours. Under these experimental conditions, Mg and Ca vapor was supplied to the entire body of catalyst scrap. After the reactive metal treatment, the specimens were crushed and dissolved in aqua regia at 323 to 333 K for 1 hour. The PGMs dissolution ratios were improved after the reactive metal treatment, and the dissolution ratios reached 88 pct in Pt, 81 pct in Pd, and 72 pct in Rh, while they were 77 pct in Pt, 69 pct in Pd, and 38 pct in Rh without the treatment. Even when the specimens were dissolved in aqua regia without heating, the PGMs dissolution ratios from the catalyst scrap after reactive metal treatment showed high values, 78 pct in Pt, 74 pct in Pd, and 57 pct in Rh at a maximum. These results show that the reactive metal treatment is effective for the recovery of PGMs from automotive catalyst scrap.     

Mass transfer from an oxygen jet to liquid silver

A subsonic jet of pure oxygen discharging from a converging nozzle with a throat diameter of 2.5 mm was directed vertically on the surface of molten silver maintained at 1000°C. The effects of variation in lance height (5 to 25 cm), jet momentum (3000 to 56000 dyne), jet temperature (600° to 1000°C) and interfacial area (45 sq cm to 182 sq cm) were studied. In all cases the oxygen concentration in the silver was measured by lime stabilized zirconia probes. The mean liquid phase mass transfer coefficients calculated for transfer across the total surface area of the bath of 182 sq cm, ranged from 0.001 to 0.015 cmJs. The higher values were obtained with high jet momentums or with low values of the lance height. A decrease in the surface area of the bath to 45 sq cm only slightly reduced the rate of transfer and resulted in a threefold increase in the mass transfer coefficient based on the reduced area. The mass transfer coefficients were independent of the jet temperature providing the jet momentum was maintained constant and there were no thermal gradients in the liquid silver. A. CHATTERJEE, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology, London, England. D. H. WAKELIN, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology.     

Study of Penetration Depth and Droplet Behavior in the Case of a Gas Jet Impinging on the Surface of Molten Metal using Liquid Ga–In–Sn

To study the penetration depth in the case of a gas jet impinging on the surface of liquid steel, cold model experiments were carried out using a liquid alloy Ga–In–Sn, which had similar physical properties as liquid steel. A HCl solution was used to simulate the top slag. The top phase was found to have appreciable effect on the penetration depth. Comparison of the experimental data with the predictions of the existing models indicated that most the model predictions deviated from the experimental results at higher lance heights and gas flow rates. New model parameter was suggested based on the present experimental data. The observation of the formation and movement of metal droplets generated by the gas jet was also made. The velocity of the droplet was found to be at a level only about 1% of the terminal velocity. This low velocity suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.     

Physical and mathematical models of gas‐liquid fluid dynamics in LD converters

Fluid dynamics of gas‐liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing‐bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring.     

A model of post-combustion in iron-bath reactors,part 4: results for post-combustion with preheated air

This paper describes calculated results of post-combustion with pre-heated air, heat transfer from gas to the melt via a mixture of metal and slag droplets, reoxidation at the metal droplets, CO evolution rate from the melt, production rate of the reactor, and carbon consumption of various process modes of a 15-t reactor with or without oxygen blowing through the vessel bottom. Using pre-heated air, the achievable post-combustion degree is higher than using pure oxygen. Nevertheless, slag droplets as heat carrier are necessary. With 50 % slag droplets the real post-combustion degree can be higher than 45 %. With 90 % slag droplets it can be even higher than 80 %. The operating point of the reactor is discussed.     

The reaction behavior of Fe-C-S droplets in CaO-SiO2-MgO-FeO slags

The rate of reduction of FeO in the slag by carbon in iron droplets (2.9 wt pct C, 0.01 wt pct S) was studied for CaO-SiO₂-MgO slags containing between 3 and 35 wt pct FeO and temperatures ranging from 1643 to 1763 K. The effects of Fe₂O₃ additions to the slag and sulfur variations in the metal on the reaction rate were also studied. It was found that the behavior of the metal droplets in the slag, as observed by X-ray fluoroscopy, changed significantly with FeO content in the slag. Below 10 wt pct FeO, the droplet remained intact while reacting with the slag; however, above this FeO concentration, the droplet became emulsified within the slag. The large increase in surface area of the metal droplet due to emulsification caused the rate of reaction to be one to two orders of magnitude faster than for droplets that did not become emulsified. It was suggested that when the droplet is emulsified, the surface area and reaction kinetics are greatly increased, and the rate becomes controlled by mass transfer of FeO as Fe²⁺ and O²⁻ ions in the slag to the emulsified droplet. At low FeO contents for which the droplet does not emulsify, the rate is controlled by dissociation of CO₂ on the metal. It was also found that a critical temperature exists for a given FeO content at which point the rate of CO evolution increases dramatically. Additions of Fe₂O₃ to the slag and sulfur to the metal caused significant changes to the rate of reaction possibly by affecting the emulsification behavior of the droplet.     

Experimental evidence for electrochemical nature of the reaction between iron oxide in calcia-silica-alumina slag and carbon in liquid iron

The electrochemical nature of the reaction between iron oxide in calcia-silica-alumina slag and carbon in liquid iron has been studied by measuring the kinetics of the slag-metal reaction. A base slag (48 pct CaO-40 pct SiO₂-12 pct Al₂O₃) containing iron oxide (≤8 wt pct FeO _t ) was reduced by an Fe-C metal bath (∼4 wt pct C) at 1400 °C. The reaction rate was calculated from measurements of the total inlet gas flow rate and the CO concentration in the outlet gas stream. The slag was “internally short circuited” by dipping an iron plate through the slag layer, and this resulted in an increase in the rate of CO evolution. An external circuit was produced by dipping a graphite rod (shielded from the slag) into the metal bath and a steel or molybdenum rod into the slag layer; the open-circuit voltage and short-circuit current were measured when iron oxide was added to the base slag layer. The reaction rate was enhanced by applying a voltage across the slag layer, and an electric arc cathode was employed in some of these “electrolysis” experiments.     

Computation of continuous cooling transformation diagrams for the heterogeneous nucleation in Sn-5 mass pct Pb droplets

A method was developed to compute continuous-cooling-transformation (CCT) diagrams for the heterogeneous nucleation of alloy droplets from a few experimental data. The developed model addresses both oxidation-catalyzed surface nucleation and internal nucleation caused by another catalyst. Droplet surface oxidation is regarded as a first-order reaction in order to account for the effects of the gradual increase in surface oxidation on the kinetics of surface nucleation. CCT curves were computed for Sn-5 mass pct Pb droplets cooling in atmospheres with various oxidation potentials using data determined with monosize droplets produced by capillary jet breakup. The developed model may be used to predict droplet nucleation kinetics in industrial thermal spraying processes.     

Modelling on the penetration depth of the coherent supersonic jet in EAF steelmaking

The coherent supersonic oxygen supplying technology is now widely adopted in EAF steelmaking process. However, there has been limited research on the impact characteristics of the coherent supersonic jet. In this work, integrating theoretical modelling and numerical simulations, a hybrid computing model was developed to predict the penetration depth of the coherent and conventional supersonic jet. The results show that the lance height has much significant influence on the jet penetration depth, and the penetration depth of the coherent supersonic jet is much larger than that of the conventional supersonic jet at the same lance height. The k value reflects the velocity attenuation of the main supersonic jet, which is a key parameter of the hybrid computing model. Finally, the hybrid computing model and its modified models can well predict the penetration depth of the coherent and conventional supersonic jet with the error being no more than 3.92?pct.     

Molybdenum extraction from molysulfide

Two different extraction processes were used to extract molybdenum metal from technical grade molysulfide. The first one involved two steps: open-aluminothermic reduction of molysulfide in presence of potassium chlorate as a thermal booster for obtaining massive molybdenum, and its conversion to high purity molybdenum metal by fused-salt electrore-fining in a KCl-K₃MoCl₆ electrolyte. The second approach aimed at direct recovery of molybdenum from molysulfide-carbon anodes by fused-salt electrolysis again in the KC1-K₃MoCl₆ electrolyte. In the electrorefining of the thermit metal, a metal recovery of 85 pct and an average current efficiency of 70 pct were achieved at 0.6 to 0.75 V using a cathode current density of 7499 A/m² (675 amp/f²) to 8332 A/m² (750 amp/f²), a bath temperature of 1173 K (900°C) and an electrolyte with 7.5 pct molybdenum content. With the same electrolyte and under almost similar conditions, electrolysis with molysulfide carbon anodes at a cathode current density of 14,998 A/m² (1350 amp/f²) to 15,554 A/m² (1400 amp/f²) gave a metal recovery of 82 pct, at an average current efficiency of 50 pct. Both the routes yielded molybdenum of comparable purity. The paper presents a part of the M.Sc. (Tech.) thesis submitted by T. K. Mukherjee to the University of Bombay (India).