Study on Absorption Rate by Eccentric Mechanical Stirring in Gas Injection Refining for Iron and Steel Making

In gas injection refining processes, a great amount of gas is injected into molten metal in short time, so that very large bubbles are inevitably formed. Wide dispersion of small bubbles in the bath is indispensable for high refining efficiency. Eccentric mechanical stirring with unidirectional impeller rotation was tested using a water model for pursuing better bubble disintegration and dispersion. Absorption rate are used to research on the influence law of the bubble dispersion and disintegration and gas-liquid absorption by the influence of, rotation mode, rotation speed and gas flow rate. Compared to the experimental results of absorption rate under eccentric stirring and centric stirring ,provide the scientific experimental and theoretical guidance for high-temperature experiment of hot metal desulfurization .According to experimental and theoretical analysis, this paper has studied various factors effecting on gas absorption process and volumetric mass transfer coefficient using the system of CO2-NaOH-H2O.The results show that:the volumetric mass transfer coefficient and absorption efficiency of CO2 can be increased under eccentric stirring mode, Because bubble disperse quickly with eccentric mechanical stirring, which results in promoting complete reaction between CO2 and NaOH, and improving the mass transfer coefficient and absorption. Volumetric mass transfer coefficient and efficiency of CO2 increase with the increasing rotation speed under the condition of eccentric stirring .But volumetric mass transfer coefficient and efficiency of CO2 decrease with the increasing rotation speed under the condition of centric stirring.     

Computer simulation on the hydrodynamics of gas injection process in liquid steel

It is shown that with the aid of digital simulation methods complex multiphase interrelated systems, such as gas-injection process can be analysed. Interdependencies can be revealed and quantitative evaluation of characteristic system quantities are provided. The method of digital system simulation is a very convenient tool for process analysis or system engineering. Results of the computer-aided process simulations (Caps) yield a better understanding of complex phenomena and better aimed engineering of gas dispersion techniques in metallurgical processes. A particular interest of this investigation is to reveal the effect of mass-transfer rate on the hydrodynamic behaviour of a gas-injection process. The combined effects of total flow rate of injected gas and mass-transfer rate on the system quantities such as mixing power, induced liquid flow rate, holdup, interfacial area and volumetric mass transfer coefficient are evaluated under steady state conditions of the investigated systems and illustrated in simulation plots. The liquid velocity has a minor effect on bubble size at some distance from the orifice but controls the location of bubble breakup. The frequency of bubble breakup and final bubble size depends on the intensity of mass transfer. Mixing power due to gas bubbles and circulation velocity of the steel bath increase appreaciably if there is a chance of bath reactions producing more gas. The integral mean values of mixing power, induced velocity of liquid and holdup in plume, specific interfacial area and volumetric mass-transfer coefficient increase with increasing total flow rate of injected gas and intensity of mass transfer.     

Nonuniformity of NaOH concentration and effective bubble diameter in CO2 injection into aqueous NaOH solution

Mixed CO₂-N₂ gas was blown into an aqueous NaOH solution through a submerged nozzle of 3 mm ID, and the net absorption rate of CO₂ from the gas bubbles during their ascent was determined. The size distribution and the rising velocity of bubbles were also measured. The enhancement factor was estimated from the reported reaction rate constant as 1.16 to 8.20 at the NaOH concentration from 0.01 to 0.3 mol · dm^-3. It was deduced that NaOH concentration in the plume zone in which gas bubbles ascended was markedly lower than that of the bulk solution when NaOH concentration of the bulk solution was lower than 0.1 mol · dm^-3. The measured size distribution of bubbles had two peaks at approximately 0.15 and 2.3 cm. However, the effective bubble diameter defined as mean diameter based on the amount of absorbed CO₂ was 2.3 cm and it was close to the mean of larger bubbles.     

Turbulence characteristics of a gas-stirred steel bath outside the bubble plume

In order to understand the turbulence characteristic in melts stirred with injected gas, the relations for effective diffusion coefficient, turbulent kinetic energy and mean size of energy containing eddies were derived from the energy equation with an extended flow field for the steel bath, where strong bubble plume and surface currents are present. 67 or 23% of the energy is dissipated in the bubble plume or surface flow zone. An increasing entrainment coefficient leads to higher values of energy dissipation factor, effective diffusion coefficient and mean size of energy containing eddies, but to low degrees of turbulence. With increasing bath aspect ratio the energy dissipation factor increases, but the degree of turbulence decreases. With increasing gas flow rate and bath height the effective diffusion coefficient enlarges. Increasing bath size leads to large mean size of energy containing eddies, which reaches 17% of the bath diameter at high gas flow rates.     

Plume characteristics and liquid circulation in gas injection through a porous plug

Various forms of plumes have been identified following the injection of air at different rates through a porous plug into water contained in a ladle-shaped vessel. Discrete bubbles form at the plug and rise uniformly through the column of liquid at gas flow rates up to 14 cm³/s cm² of plug surface; at higher flow rates, groups of bubbles increasingly coalesce into larger gas pockets, and beyond about 40 cm³/s cm², the gas globes are large enough to cover the entire plug surface before detachment and gradual disintegration as they rise through the body of liquid. The gas fraction, as well as bubble frequency, bubble velocity, and bubble size, have been measured in the various dispersion regimes by means of an electroresistivity probe. The radial distributions of gas fraction and bubble frequency are approximately bell-shaped about the axis of flow, and the reduced values are close to Gaussian functions of the reduced radial distance from the axis. The gas fraction along the axis has been correlated to the reduced height of the plume; it increases with decreasing distance above the plug and with increasing gas flow rate. The axial bubble frequency shows a decrease in the vicinity of the plug with the onset of bubble coalescence, but the values of the frequencies at all gas injection rates converge to about 12 s⁻¹ toward the surface of the bath. The mean bubble velocity increases with increasing flow rate but drops once coalescence is fully established. Conversely, there is a sudden increase in the mean bubble diameter with the onset of coalescence. The axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime. The axial flow which is upward in the vicinity of the plume decreases in magnitude with increasing radial distance, ultimately reversing to an in-creasing downward flow beyond a certain distance from the plug axis. Similarly, the radial flow which is outward from the plume near the liquid surface decreases steadily with depth and eventually reverses to an inward flow at a depth independent of the gas injection rate. The profiles of the axial velocities are almost sigmoidal, except in the coalescence regime, where the effect of turbulence is profound at the upper liquid layers. The radial liquid velocities are generally small relative to the axial components, only about one-fifth as large, considering the maximum average values.     

Fluid dynamics and mass transfer in submerged gas-particle jets

A room temperature model of a submerged gas-particle jet was used to investigate the hydrodynamics and gas-liquid mass transfer in such systems. Air or CO₂ was used to inject particles of silica sand into water. In some cases, the sand was coated with resin to produce a hydrophobic surface. The flow regimes of behavior were observed: In the bubbling flow regime large bubbles of gas are formed and penetrated by a stream of particles which did not entrain gas, and in the steady jet flow regime the gas and particles travel together in a narrow cone. The second flow regime is favored by a high gas velocity, a small particle size, and a high ratio of particles to gas in the jet. The surface characteristics of the injected particles do not appear to affect this transition. A CO₂-NaOH solution model was used to determine the effects of inert particle injection of the rate of mass transfer from gas to liquid. The rate of mass transfer was higher in steady cone jets, because under these conditions, the gas is dispersed into finer bubbles and carried deeper in the bath. Formerly Graduate Student in the Department of Civil Engineering, Mechanics, and Metallurgy, University of Illinois at Chicago     

CO2吸收模型中容积传质系数的确定

气泡微细化是“原位机械搅拌法铁水炉外脱硫技术”的关键.气液传质系数是研究气液吸收过程的基本参数.本文根据相似性原理建立水模型实验装置,并通过测定NaOH吸收CO2的速率来研究气泡微细化过程,同时根据吸收原理定量计算出容积传质系数Ak及CO2气体利用率η.当溶液pH值从12降低到9的过程中,容积传质系数为2.938×10 4m3/s,本实验所用CO2的利用率的公式可简化为:η=18.98/Qt.本论文的研究结果可为进一步研究吸收速率提供理论依据.     

Measurement of physical characteristics of bubbles in gas-liquid plumes: Part II. Local properties of turbulent air-water plumes in vertically injected jets

The structural development of air-water bubble plumes during upward injection into a ladle-shaped vessel has been measured under different conditions of air flow rate, orifice diameter, and bath depth. The measured radial profiles of gas fraction at different axial positions in the plume were found to exhibit good similarity, and the distribution of the phases in the plume was correlated to the modified Froude number. Different regions of flow behavior in the plume were identified by changes in bubble frequency, bubble velocity, and bubble pierced length which occur as bubbles rise in the plume. Measurement of bubble velocity indicates that close to the nozzle the motion of the gas phase is strongly affected by the injection velocity; at injection velocities below 41 m/s, the velocity of the bubbles along the centerline exhibits an increase with height, while above, the tendency reverses. High-speed film observations suggest that this effect is related to the nature of gas discharge,i.e., whether the gas discharge produces single bubbles or short jets. In this region of developing flow, measurement of bubble frequency and pierced length indicates that break-up of the discharging bubbles occurs until a nearly constant bubble-size distribution is established in a region of fully developed flow. In this largest zone of the plume the bubbles influence the flow only through buoyancy, and the spectra of bubble pierced length and diameter can be fitted to a log-normal distribution. Close to the bath surface, a third zone of bubble motion behavior is characterized by a faster decrease in bubble velocity as liquid flows radially outward from the plume.     

Experimental studies on the flow velocity of molten metals in a ladle model at centric gas blowing

Experimental measurements of the flow velocity were carried out with liquid Wood's metal in a ladle-shaped vessel with an inner diameter of 40 cm at centric gas blowing. By means of permanent magnet probes the liquid flow field was measured under various blowing conditions. The results show that a circulating flow field is established in the vessel. In the bubble plume zone an upwardly directed liquid flow is formed. The radial distribution of the flow velocity in this zone follows a Gaussian function. The axial flow velocity increases with growing gas flow rate and is nearly constant in vertical direction. The width of the upward flow becomes larger with increasing distance from the nozzle and its dependence from the gas flow rate is not considerable. At centric gas blowing the liquid in the upper part of the bath streams quickly, whereas in the lower part so-called “dead zones” with very low flow velocity are present. Besides the time-averaged value of the flow velocity, the turbulent behaviours of the liquid flow such as fluctuation velocity, the turbulent kinetic energy and its dissipation rate were investigated on the basis of measured data. It was found that the liquid flow is turbulent particularly in the region of bubble plume and of bath surface. The radial profiles of these parameters can also be described by a Gaussian function. Only a small part of the gas stirring energy is changed into the kinetic energy of the directed liquid flow. Most of the stirring energy is already dissipated in the bubble plume zone.     

Study on Mass Transfer Characteristics in an AOD Converter Bath under Conditions of Combined Side and Top Blowing

The mass transfer characteristics in a steel bath during the AOD refining process with the conditions of combined side and top blowing were investigated. The experiments were conducted on a water model unit of 1/4 linear scale for a 120‐t combined side and top blowing AOD converter. Sodium chloride powder of analytical purity was employed as the flux for blowing, and the mass transfer coefficient of solute (NaCI) in the bath was determined under the conditions of the AOD process. The effects of the gas flow rates of side and top blowing processes, the position arrangement and number of side tuyeres, the powdered flux particle (bubble) size and others on the characteristics were examined. The results indicated that, under the conditions of the present work, the mass transfer coefficient of solute in the bath liquid is in the range of (7.31×10^?5‐3.84×10^?4) m/s. The coefficient increases non‐linearly with increasing angle between each tuyere, for the simple side blowing process at a given side tuyere number and gas side blowing rate. The gas flow rate of the main tuyere has a governing influence on the characteristics, and the gas jet from the top lance decreases the mass transfer rate, the relevant coefficient being smaller than that for a simple side blowing. Also, in the range of particle (bubble) size used in the present work and with all other factors being constant, raising particle (bubble) size increases the coefficient. Excessively fine powder particle (bubble) sizes are not advantageous to strengthening the mass transfer. With the oxygen top blowing rate practiced in the industrial technology, the side tuyere arrangements of 7 and 6 tuyeres with an angular separation of 22.5° and 27° between each tuyere, as well as 5 tuyeres with an angle of 22.5° between each tuyere can provide a larger mass transfer rate in the bath. Considering the relative velocity of the particles to the liquid, the energy dissipation caused by the fluctuation in the velocity of the liquid in turbulent flow and regarding the mass transfer as that between a rigid bubble and molten steel, the related dimensionless relationships for the coefficient were obtained.     

Critical fluid-flow phenomenon in a gas-stirred ladle

Measurement of the velocities of bubbles and liquid with a two-element electroresistivity probe and laser-Doppler velocimeter, respectively, during bottom injection of air into a water bath, has confirmed the existence of a critical gas-injection rate. Above the critical flow rate, the change of axial bubble velocity in the air jet, and of liquid velocity with increasing volume flow rate, diminishes markedly. The existence of the critical flow rate is explicable from high-speed motion pictures of the vertical gas jets, which reveal four zones of gas dispersion axially distributed above the orifice: primary bubble at the orifice, free bubble, plume consisting of disintegrated bubbles, and spout at the bath surface. With increasing gas-injection rate, the free-bubble zone expands such that the point of bubble disintegration rises closer to the bath surface. Above the critical flow rate, the free bubbles rise with minimal breakup and erupt from the bath surface with maximum energy discharge. The combined Kelvin-Helmholtz, Rayleigh-Taylor instability theory has been applied to analyze the bubble breakup in the bath and the critical gas-injection rate in a gas-stirred ladle. The criterion for the critical diameter of bubble breakup has been found to depend primarily on the surface tension and density of the liquid. In the analysis, the propagation time of a disturbance on a bubble surface at the “most unstable” wave number has been compared with the bubble rising time in the bath in order to determine the critical gas-flow rate. The predicted critical values are in close agreement with the measured results. M. ZHOU formerly was Post Doctoral Fellow with the Centre for Metallurgical Process Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 J.K. BRIMACOMBE holds the Alcan Chair in Materials Process Engineering     

Mass transfer in a bottom blowing cold model converter

In a model converter containing oil and water the volumetric mass transfer of caprylic acid was determined in dependence of the gas flow rate. Several other parameters were varied such as the number and configuration of nozzles, gas velocity, oil viscosity and volume and model size. Partially the results could be described by dimensionless equations. Visual observations of the bath surface with special regard to the wave formation complete the results of the measurements. By knowledge of the drop size spectrum independently determined, the mass transfer coefficient under dispersion conditions could be evaluated. These values were compared with mass transfer coefficients which had been directly measured by the single rising drop technique as well as the bubble stirred interface without dispersion. It seems that turbulence in dispersed systems does not enlarge the mass transfer coefficient.     

Experimental investigation of mixing phenomena in a gas stirred liquid bath

Mixing phenomena in a room temperature water bath, agitated by injecting air through a straight circular nozzle fitted axially at the bottom of the vessel, were characterized by experimentally measuring mixing time(t _mix) by electrical conductivity technique. It was found thatt _mix defined at 99.5 pct homogenization did not depend on location and size of conductivity probe, location of tracer injection, and the amount of tracer injected. tpet decreased with increasing gas flow rate and bath height, but decreasing nozzle diameter. Visual observations of the two-phase plume and flow conditions in the bath revealed that the plume swirled above a certain gas flow rate which enhanced the mixing rates in the bath. The transitions in Int _mix vs In ε_b curves were found to correspond to onset of swirling; ε_b is the rate of buoyancy energy input per unit bath volume. Systematic analysis of experimental data revealed that a fraction of gas kinetic energy contributed to mixing in the bath. It was a function of bath height, being negligible at lower bath heights and almost 1 at larger bath heights. Further, it was experimentally found thatt _mix decreased with increasing bath height only up to a certain value, beyond which it started increasing. Visual observations of the bath revealed that the height at whicht _mix started increasing corresponded to a transition in which the bath was converted into a bubble column. The experimental data, for a particular bath height, were fitted into two separate straight lines of the formt _mix =cε ⁻ⁿ wherec andn are empirical constants and ε is the rate of energy input per unit bath volume. Formerly Graduate Student in the Department of Metallurgical Engineering at the Indian Institute of Technology, Kanpur, India     

Cold Model Study on Mg Desulfurization of Hot Metal Under Mechanical Stirring

The new method of in-situ desulfurization with mechanical stirring of new type impellers was introduced,in which the bubble′s dispersion and disintegration of magnesium vapor were the key to boosting the desulfurization efficiency and increasing the utilization rate of magnesium.Effects of different new type of impellers on bubble dispersion and disintegration were studied through bubble image analysis,gas-liquid mass transfer,and power consumption levels of different impeller structures.The results showed that the sloped swept-back blade impeller-2produces optimal bubble′s dispersion and disintegration,as well as higher volumetric mass transfer coefficient and CO2gas utilization while consuming the least power.Numerical simulation result with Fluent software also showed that the sloped swept-back blade impeller-2has higher turbulent kinetic energy and better velocity distribution than the other two impellers.     

Desulfurization kinetics of molten copper by gas bubbling

Molten copper with 0.74 wt pct sulfur content was desulfurized at 1523 K by bubbling Ar-O₂ gas through a submerged nozzle. The reaction rate was significantly influenced not only by the oxygen partial pressure but also by the gas flow rate. Little evolution of SO₂ gas was observed in the initial 10 seconds of the oxidation; however, this was followed by a period of high evolution rate of SO₂ gas. The partial pressure of SO₂ gas decreased with further progress of the desulfurization. The effect of the immersion depth of the submerged nozzle was negligible. The overall reaction is decomposed to two elementary reactions: the desulfurization and the dissolution rate of oxygen. The assumptions were made that these reactions are at equilibrium and that the reaction rates are controlled by mass transfer rates within and around the gas bubble. The time variations of sulfur and oxygen contents in the melt and the SO₂ partial pressure in the off-gas under various bubbling conditions were well explained by the mathematical model combined with the reported thermodynamic data of these reactions. Based on the present model, it was anticipated that the oxidation rate around a single gas bubble was mainly determined by the rate of gas-phase mass transfer, but all oxygen gas blown into the melt was virtually consumed to the desulfurization and dissolution reactions before it escaped from the melt surface.     

A mathematical approach for the mass transfer between liquid steel and an ascending bubble

A mathematical model which is adaptable to practical conditions has been put forward to deseribe adequately the purging of liquid steel with an inert gas. The mass transfer between liquid steel with varying C, O, H, N, and S contents and an ascending argon bubble has been investigated. The simultaneous mass transfer of all possible gaseous compounds is considered as a function of the initial bubble mass, height of the steel bath, the bulk concentrations in the melt, and the external pressure. The model takes into account the change in size and form of the bubble resulting from its rise and the mass transfer between the bubble and the melt, and also the influence of surface active agents such as sulfur and oxygen. The following general conclusions can be drawn: 1) the gases flushed (out of the melt) by the bubble can be related to the amount of argon injected into the bath. 2) Increase in the initial bubble size and the content of the gas in the bath to be purged, and decrease in the external pressure result in more pronounced deviations from equilibrium saturation within the bubble. 3) Lower external pressure, increasing supersaturation of CO, and greater amounts of purging gas at higher dispersion are the chief factors responsible for increasing, purging efficiency for H, N₂, CO in steel melts. 4) Surface-active agents decrease the purging ratio for nitrogen in a carbon-free melt, but, in carbon-containing melts, increasing amounts of oxygen alone lead to a considerable increase in the purging ratios for nitrogen due to the high mass transfer of CO to the bubble. In the latter case, the effect of increasing sulfur content on the purging ratios is of no significance. KAZUO OKOHIRA, formerly Graduate Student at the Institut für Eisenhüttenkunde at Aachen HERMANN SCHENCK, Dr.-Ing., Dr.-Ing. E.h., Dr.h.e., formerly Director of the Institut für Eisenhüttenwesen, President of the German Iron and Steel Institute (VDEh) from 1950 to 1968 This paper is based in part on a thesis submitted by KAZUO OKOHIRA in partial fulfillment of the requirements for degree of Doktor-Ingenieur at the Technische Hochschale, Aachen.     

Effects of pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous nozzle

The effects of the pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous bottom nozzle placed in a water bath and on the behavior of rising bubbles were investigated with still and high-speed video cameras and a two-needle electroresistivity probe. Three types of bubble dispersion patterns were observed with respect to gas flow rate, and they were named the low, medium, and high gas flow rate regimes. The transition boundaries between these gas flow rate regimes were expressed in terms of the superficial velocity at the nozzle exit, i.e., the volumetric gas flow rate per unit nozzle surface area. These transition boundaries were dependent on the pore diameter but hardly dependent on the bath surface pressure and the porous nozzle diameter. The characteristics of rising bubbles in each gas flow rate regime were investigated as functions of the three parameters.     

Steel dissolution in quiescent and gas stirred Fe/C melts

The dissolution rates of commercial black iron rods in iron/carbon melts under isothermal conditions were measured. The effect of melt carbon content, temperature, natural convection, and gas stirred forced convection conditions were investigated. The experimental data under natural convection conditions (no external stirring) were fitted with a dimensionless correlation for vertical cylinders: Sh = 0.13(Gr . Sc)^0.34, representing mass transport control dominated by turbulent natural convection. Under bottom injection gas stirring conditions, it was found that the kinetic power input had little effect on the rod dissolution rates which were controlled by the total gas flow rate. Derived mass transport coefficients under gas stirring conditions were found to have the following dependence on the gas injection rates:k _m ∝Q ^0.21, wherek _m = mass transport coefficient andQ = gas flow rate. A comparison of the experimental results with previously measured mass transfer coefficients under forced convection conditions gave a plume velocity flow rate dependence ofU ∝Q ^0.3. A general discussion of gas stirring fluid dynamics and resulting mass transport effects is presented.     

Numerical Simulations of Inclusion Behavior in Gas-Stirred Ladles

A computation fluid dynamics–population balance model (CFD–PBM) coupled model has been proposed to investigate the bubbly plume flow and inclusion behavior including growth, size distribution, and removal in gas-stirred ladles, and some new and important phenomena and mechanisms were presented. For the bubbly plume flow, a modified k-ε model with extra source terms to account for the bubble-induced turbulence was adopted to model the turbulence, and the bubble turbulent dispersion force was taken into account to predict gas volume fraction distribution in the turbulent gas-stirred system. For inclusion behavior, the phenomena of inclusions turbulent random motion, bubbles wake, and slag eye forming on the molten steel surface were considered. In addition, the multiple mechanisms both that promote inclusion growth due to inclusion–inclusion collision caused by turbulent random motion, shear rate in turbulent eddy, and difference inclusion Stokes velocities, and the mechanisms that promote inclusion removal due to bubble-inclusion turbulence random collision, bubble-inclusion turbulent shear collision, bubble-inclusion buoyancy collision, inclusion own floatation near slag–metal interface, bubble wake capture, and wall adhesion were investigated. The importance of different mechanisms and total inclusion removal ratio under different conditions, and the distribution of inclusion number densities in ladle, were discussed and clarified. The results show that at a low gas flow rate, the inclusion growth is mainly attributed to both turbulent shear collision and Stokes collision, which is notably affected by the Stokes collision efficiency, and the inclusion removal is mainly attributed to the bubble-inclusion buoyancy collision and inclusion own floatation near slag–metal interface. At a higher gas flow rate, the inclusions appear as turbulence random motion in bubbly plume zone, and both the inclusion–inclusion and inclusion-bubble turbulent random collisions become important for inclusion growth and removal. With the increase of the gas flow rate, the total removal ratio increases, but when the gas flow rate exceeds 200 NL/min in 150-ton ladle, the total removal ration almost does not change. For the larger size inclusions, the number density in bubbly plume zone is less than that in the sidewall recirculation zones, but for the small size inclusions, the distribution of number density shows the opposite trend.     

Investigation of the kinetics of breakup of gas bubbles in liquid metals with digital simulation method

The method of digital system simulation can be effectively used to quantify the complex multiphase interactions within a gas injection process. Process simulation results yield a better understanding and a better aimed engineering of gas dispersion techniques in metallurgical processes. In this paper the breakup phenomenon of gas bubbles in stagnant liquids is simulated and the dependencies between breakup of bubbles and various parameters of a gas dispersion process such as operative parameters, system parameters and mass transfer rates are investigated. The bubble diameter after breakup is almost independent of the nozzle diameter and gas flow rate. The frequency of bubble breakup and critical bubble size depend on the rate of mass transfer into the bubble. An almost constant rising velocity is achieved only in those cases investigated where mass transfer and bubble breakup are considered. In all other cases no stationary rising velocity is obtained. The interplay between bubble size, rising velocity and the inertia of the surrounding liquid and the influence of mass transfer and breakup are investigated. Simulation results reveal that the behaviour of an ascending bubble is strongly influenced by the mass transfer rate, i. e. by the composition of the melt. Verification of the simulation results with empirical equations from literature shows a very good agreement in all dispersion systems investigated.