Height of the spout of a gas plume discharging from a metal melt

In the present investigation, the height of the spout of a gas plume discharging from the surface of a metal melt has been measured in a laboratory model involving mercury and in real steel ladles. The spout geometry strongly fluctuates with time. This has to be taken into account in the measuring method and data evaluation. Long-term averages of the spout profile and momentary maximum height values have been determined, and it has been found that their nondimensional values are of similar size in the model and in the steel ladle. An engineering formula is presented for the estimation of maximum spout height in argon stirring.     

The spout of air jets upwardly injected into a water bath

The spout region of gas jets in liquids has received little attention, although it has both theoretical and practical significance. In this study, the spout of upwardly injected gas jets in water was characterized experimentally in terms of gas fraction, bubble frequency, and axial velocity distributions for ultimate incorporation into turbulent recirculating flow models. The measurements were made with a two-element electroresistivity probe coupled to a microcomputer. For the turbulent flow conditions prevailing in the jet plume and spout, special hardware and software were developed to analyze the signals generated by contact of the bubbles with the sensor in real time. Correlations of the gas fraction with axial and radial position for different gas flow rates have been established from the measurements. The dimensions of the spout were obtained from time-exposure photographs; when compared with the gas-fraction measurements, the spout boundary always corresponded to values ranging from 0.82 to 0.86. The radial profiles of bubble frequency at different levels in the spout exhibit a bell shape; the bubble frequency decreases with increasing height. The velocity of the bubbles in the spout drops linearly with increasing axial position. Formerly Graduate Student. Formerly Postdoctoral Fellow, The Centre for Metallurgical Process Engineering.     

渣罐底吹熔池表面突起特性的模拟研究

基于“选择性析出技术”,向渣罐内吹入空气氧化含钛高炉渣,以实现钛的选择性富集。渣罐内熔池的表面突起高度和宽度对于渣罐内自由空间的设计存在重要影响。通过摄像法测定了粘度、气体流量对底吹渣罐水模型表面突起高度和宽度的影响。结果表明：液面突起的形状服从高斯分布;液面突起高度随底吹气体流量的增大而变大,而基本不受熔池黏度变化的影响;液面突起宽度随气体流量和溶液黏度的增大而变大,但主要受气体流量的影响。通过对实验结果的分析讨论,得出了水模型溶液表面突起高度和突起宽度的经验关系方程式。     

Mass transfer between a horizontal,submerged gas jet and a liquid

The rate of reaction between a horizontal, submerged gas jet and a liquid has been measured in a model system under conditions where mass transfer in the gas phase is rate limiting. The gas was 1 pct SO₂ in air, and the liquid was a 0.3 pct solution of hydrogen peroxide in water. SO₂ absorption rates were measured as a function of jet Reynolds number (10,000 < N_Re < 40,000) and jet orifice diameter (0.238 < d₀ < 0.476 cm). The product of the gas phase mass transfer coefficient and the interfacial area per unit length of jet trajectory, k_SO2 α was found to increase linearly with increasing Reynolds number and to be a strong function of the orifice diameter. The ratio of k_so2 α to volumetric gas flow rate was shown to be independent of Reynolds number for a given orifice diameter. Extrapolated values of k_so2 α are lower than the coefficients measured for vertical CO jets blown upward through liquid copper. Extrapolation of the measured mass transfer data to the jet conditions in copper matte converting and in the gaseous deoxidation of copper has indicated that the gas utilization efficiencies in these processes should approach 100 pct if gas phase mass transport is rate controlling.     

The influence of gas phase resistance on mass transfer to a liquid metal

When a dilute gas is absorbed in a liquid metal in which Sievert’s law is obeyed, the gas phase resistance is likely to be significant. The influence of gas phase resistance will de-pend on the concentration of the transferred species in both the gas and the liquid as well as on the mass transfer coefficients in both the gas and liquid phases. An overall mass transfer coefficient is defined by: n″(X)₁=k_ov√pb -cb and equations are developed relating this to the variables mentioned. Experimental work has been carried out with dilute oxygen jets (p(O₂) = 0.1 and 0.2 atm) blowing onto molten silver, and the results have confirmed that the resistance in the gas phase contributes to the overall resistance. From these results it has been possible to estimate gas phase mass transfer coefficients which range from 1.4 cm/s for a jet momentum of 8000 dyne and lance height of 18.5 cm to 4.8 cm/s for a jet momentum of 56,000 dynes and lance height of 10.5 cm. A. CHATTERJEE, formerly in The John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology, University of London, England     

Effects of process conditions on mixing between molten iron and slag in smelting reduction vessel via water model study

Abstract

The present study has been conducted to investigate the effects of operating conditions, which include gas flowrate, tuyere size, tuyere number, and height of iron phase, on the extent of mixing between molten iron and molten slag in the direct iron ore smelting reduction process. A transparent acrylic water model, 30% of the size of the actual smelter, was constructed to study the mass transfer phenomena. In the water model, water and spindle oil were used to simulate molten iron and molten slag, respectively, while air was used to replace the bottom blown nitrogen gas. In addition, thymol (C₁₀H₁₄O₆) was used as a tracer material in the water model, added to the water at the beginning of the experiment. As mixing between water and spindle oil proceeded owing to stirring by the bottom blown gas, the concentration of thymol in the water decreased and that in the spindle oil increased. Water samples were taken from the bottom and 12 cm above the bottom of the water model at various operating times. Concentrations of thymol were then measured using a diode array ultraviolet visible spectrophotometer. By analysing the concentration data, the mass transfer rate k_wA, which is a direct index for evaluating the mixing efficiency, could be derived. The process conditions under investigation included 40-500 L min^-1 gas flowrate, 0·3^-1 cm tuyere size, four or five tuyeres, and 20-30 cm height of the water phase. The test results indicate that when the gas flowrate increases, the value of k_wA increases, which indicates better mixing between oil and water phases. However, as the gas flowrate approaches 40 L min^-1, the improvement becomes less obvious. The smaller tuyere gives better mixing, and the design of five tuyeres results in better mixing compared with four tuyeres when they are blown with the same total gas flowrate. However, mixing efficiency decreases with increased height of the water phase. Also, as the gas flowrate of bottom blowing approaches 40 L min^-1, gas blowing from the top has little effect on the mixing behaviour in the liquid bath. For a four tuyere system, the process conditions of height of oil phase 5 cm, height of water phase 25 cm, diameter of tuyere 0·75 cm, and gas flowrate for each tuyere 40 L min^-1, appear to be the optimal design.     

卡鲁金热风炉流场特性冷态实验研究

通过冷态模拟实验,研究了卡鲁金热风炉喉口至蓄热室间的流场特性、喷口流体的均匀性及蓄热室格子砖阻力特性对流场的影响。结果表明:卡鲁金热风炉流场均匀、稳定、对称性好,空、煤气喷口气流分布比较均匀。在空、煤气分别单吹的情况下,空气喷口的均匀度达到90%以上,煤气喷口的均匀度也接近90%。蓄热室格子砖阻力分布均匀与否对蓄热室流场无明显影响。     

A water model and numerical study of the spout height in a gas-stirred vessel

The height and width of spouts in a water model of a gas-stirred ladle were measured photographically. The shapes were found to be Gaussian, and correlations were developed for the height and width. To mathematically model the free surface effects, a novel combined staggered-grid and volume-of-fluid computational code was developed. It was tested successfully against an established code in the “broken dam” validation test. The new free surface code was added to an existing code for a gasstirred plume to model the entire vessel. It was found that the code under-predicted the actual spout height. The model handled the momentum of the plume accurately, but did not account for the phenomena associated with the bubbles breaking the surface. The importance of these inter-related phenomena had not been appreciated previously.     

Mathematical modeling of mixing phenomena in a gas stirred liquid bath

A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate, bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial vessels has been demonstrated. Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur     

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     

Neural-Net–Based Predictive Modeling of Spout Eye Size in Steelmaking

Gas stirring is commonly used in pyrometallurgical vessels to enhance mass and heat transfer and to promote impurity removal. In the case of secondary steelmaking, the spout eye area is caused by the escape of the gas from the top of the smelt where the liquid steel is directly exposed to the air, and oxygen can be picked up through the spout eye area that can reduce the quality of steel. Thus, controlling the size of the spout eye area is very important to improving the quality of the steel and to keeping the consistency of the product. The set of prevailing models to predict spout eye size are based on specific practically difficult variables, e.g., height of slag in hot upper layer of vessels and gas flow rate at nozzle exit. Recently, the cold model results showed that the stirring process can be conveniently monitored by the signals such as (1) the image signal from the top of the vessel, (2) the sound of the stirring process, and (3) the vibration on the wall of the vessel. This article outlines the key details of a novel research investigation using neural-network?Cbased predictive modeling such as general regression neural networks (GRNN) with genetic adaptive calibrations. Predictive capacities and generalization potentials of five model constructs (i.e., with different sets of input parameters) were explored, and the neural net modeling yielded encouraging outcomes, e.g., (1) excellent goodness-of-fit generalization measures including high values of correlation and R ² validation parameters (e.g., r?=?0.921 and R ²?=?0.845 in a model validation), and (2) low values of root mean square of errors (e.g., 3.034). Overall, the research outlined in this article demonstrates that the spout eye size can be effectively predicted by predictive neural net modeling with convenient and practically measurable variables such as sound and vibration observations on the steelmaking vessels. These results have only been demonstrated for a cold model of the process, and further work is required to show that this approach can be extended to industrial operations.     

A Physical Model Study of Swirl Phenomena in a Top Blown Bath

The present study is focused on swirl motion in a top blown water model, where a deep water swirl motion is observed. During the experiments, the top lance, with cylindrical nozzles, was placed above the water surface and thereby produced an external force on the bath. The effect on how different parameters, such as nozzle diameter and the distance between the bath surface and nozzle exit, i.e. the lance height, affect the swirl motion were studied. More specifically, the amplitude and period of the swirl as well as the starting and damping time of the swirl were determined. The amplitude was found to increase with an increased nozzle diameter and gas flow, while the period had a constant value of about 0.5 s for all nozzle diameters, gas flows and lance heights. The starting time for the swirl motion was found to decrease with an increased gas flow, while the damping time was found to be independent of gas flow rate, nozzle diameter, lance height and ratio of depth to diameter.     

Mathematical modelling of divided blast cupola

A pseudo 2-D mathematical model has been developed to simulate a cupola with one row and two rows of tuyère. The simulation results predicted higher spout temperature and combustion ratio for cupola with two rows of tuyère compared to that with one row. Further, the model has been used to study the effect of the distance of separation between the two rows of tuyère on cupola performance. The computed results shows that the spout temperature increases with tuyère level separation and attains the maximum at an optimum distance of separation between two rows of tuyère. Above the optimum, the spout temperature starts decreasing. The exit gas temperature and combustion ratio increases monotonously with the increase in tuyère level separation. These results agree well with the reported experimental observations. The mechanism behind the improved cupola performance with two rows of tuyère has been deduced from the computed temperature and composition profiles inside the cupola.     

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.     

Design Characteristics of Single Hub Paddle Wheel Aerator

Aeration experiments, based on dimensional analysis, were conducted in brick masonry tanks of dimensions 2.9×2.9×1.6?m3 and 5.9×2.9×1.6?m3 to study the design characteristics of a single hub paddle wheel aerator. A generalized equation has been developed to estimate the optimum volume of water to be aerated at a given paddle wheel diameter (d) and speed (N). A simulation equation with E [nondimensional number characterizing standard aeration efficiency (SAE)] and P* (nondimensional number characterizing power input per unit volume) provided a correlation better than that with E and F (Froude number) and E and R (Reynolds number) only. A simplified generalized equation correlating E and P* was developed which can be used to predict aeration efficiency for P* ? 6.56. Similarly, a simulation equation with Ne [(power number)(nondimensional number charcterizing power consumption)] and P* provided a correlation better than that with Ne and F and Ne and R only. The optimum dynamic condition at which maximum SAE is produced has also been presented. All the above results are valid subject to 1.47 ? P* ? 15.54.     

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.     

Large-scale measurements of the physical characteristics of round vertical bubble plumes in liquids

The hydrodynamics of air/water plumes in a large-scale model of a metallurgical ladle were investigated. The dimensions of the cylindrical vessel were 1600-mm ID and 2250-mm total height. The air was injected through a centered nozzle. Axial and radial profiles of gas concentration, bubble frequency, and liquid and gas velocities were measured using electrical resistivity probes and a propeller flowmeter. It was found that the bubble plume is not at a fixed position but wanders away from the vertical vessel axis. This causes difficulties in the measurements, and special methods have to be designed to define and deduce reproducible values for the characteristic plume quantities. In the analysis of the data, the various physical characteristics were related toz ₀, the distance from the nozzle where the axial gas concentration is 50 Pct. The maximum values of the radial profiles are presented in nondimensional correlations. MARCO A.S.C. CASTELLO-BRANCO, formerly Scientist, Institut für Allgemeine Metallurgie, Technical University of Clausthal     

Measurements of bubble plume behaviour and flow velocity in gas stirred liquid Wood's metal with an eccentric nozzle position

The distribution of gas fraction and the flow field of gas-stirred liquid metal in steel ladles at eccentric injection of the stirring gas through the bottom of the vessel were measured in melts of 437 kg liquid Wood's metal. The melts had a temperature of 100°C. The bath height was 37 cm and the vessel diameter 40 cm. The blowing nozzle was positioned at half of the vessel radius. Gas flow rates were between 100 and 800 cm³(STP)/s. The gas fractions were measured by electrical resistance probes. The flow velocity of the liquid metal was determined by magnet-probes. The gas fraction and the velocity distribution in the plume were found to have a Gaussian shape. The cross-section of the plume is ellipsoid, as the plume width in the direction of the radius was a little smaller than the width in the direction perpendicular to it. Moreover the plume was inclined to the wall. The results which were found for the plume are mathematically described. The flow field at eccentric gas-stirring consists of one great loop, which fills almost the entire vessel. This is contrary to centric blowing, where for aspect ratios of the ladle in the order of 1, a toroid is formed in the upper and a dead zone exists in the lower part of the vessel. The consequences of this behaviour, especially for mixing in the melt, are discussed.     

Spout eyes formed by an emerging gas plume at the surface of a slag-covered metal melt

This article deals with the spout eyes developing, at the surface of a metal melt, in the ladle during argon stirring. Cold model experiments involving a mercury bath with an oil layer as slag and industrial experiments on a 350 t steel ladle have been carried out. The eye geometry as measured with a video technique is highly dynamic. The time average of the free surface area and the time fraction of complete coverage have been determined and are represented with dimensionless correlations.