Number Of Tuyeres Research Articles

Assessment of Shaft Gas Injection Technology for Blast Furnace Ironmaking

Shaft injection of reducing gas into ironmaking blast furnaces (BF) helps mitigate BF carbon footprint. However, its effectiveness relies on the interaction between shaft-injected gas (SIG) and other phases. This paper numerically studies shaft gas injection operations based on a 380-m3 industrial BF. A recently developed three-dimensional process model has been adopted to do so. This model is extended to track SIG and hearth-generated gas (HGG), define SIG penetration, and quantify the respective contributions of the two gases to BF performance. After validation, the model is applied to study the effects of three variables related to SIG penetration into the particle bed: SIG flow rate, shaft tuyere number, and horizontal cavity depth. The detailed analysis of flow and thermochemical behaviors shows that increasing the SIG flow rate increases the gas penetration and indirect reduction rate by SIG and lifts the cohesive zone. However, it impedes the indirect reduction reaction by HGG and increases the bed pressure. These effects collectively identify an optimum SIG flow rate. In addition, as the shaft tuyere number or horizontal cavity changes, the SIG penetration zone size changes oppositely in radial and circumferential directions, leading to similar total penetration zone sizes. Consequently, these two variables can limitedly improve BF performance, especially compared with the effect of SIG flow rate. The results suggest that the model offers convenience for exploring the shaft gas injection technology.

On Modernization of Air Supply Systems for Improvement of Gas Distribution in Shaft Furnaces

The paper presents a developed method for assessment of gas distribution over the cross section of a shaft furnace working in the countercurrent conditions. This method is scientifically based on the fundamental principles of the countercurrent heat exchange theory in shaft furnaces, i.e. dependences of the temperature field throughout the burden bed height on the ratio between heat capacities of gas and burden flows. The ratio between the gas flow heat capacity and burden flow heat capacity at the stock line level is determined by the averaged gas temperature at the burden bed output. By comparing these data, we estimated directions for improving the gas distributing system. Efficiency of this method was assessed when analyzing the system of air supply to the shaft furnace at one of the Ural plants. The analysis showed the main drawbacks of the existing gas distributing system and enabled to determine the main directions for reconstruction of this system. On the basis of the analysis results related to operation of the tuyeres and distribution manifold, we proposed more efficient options of their parameters, i.e. manifold cross-section area, tuyere number and diameter, angle of tuyere inclination to the horizontal. These changes provided a uniform distribution of gases across the furnace and improved conditions for melt flow in the furnace. Thus, we established virtually equal conditions for development of heat and mass transfer processes in the work space of the shaft furnace. The modernized system of air supply to MMSK’s shaft furnace increased the furnace performance by 14.14% in terms of burden, by 23.27% in terms of matte, by 15.15% in terms of slag and by 6.65% in terms of thermal efficiency. At the same time, the following parameters were reduced: specific fuel consumption (anthracite) by 17.46% and dust discharge by 40.5%. When supplying air to the furnace through the inclined tuyeres, it became possible to reduce formation of accretions and provide new working conditions for operating personnel due to a more uniform gas distribution across the horizontal section of the furnace. Within six months of furnace operation the personnel had no problems related to its operation.

Use of physical modelling to study how to increase the production capacity by implementing a novel oblong AOD converter

There is no known example of an AOD converter with oblong cross sections in the literature. Changing the geometry of the converter vessel, from the traditional circular cross sections, to increase converter volume could potentially influence the performance of the converter and in particular the decarburisation rate. To study the feasibility of implementing an oblong converter, physical modelling was used to study the fluid flow of the proposed converter configuration, geometry and number of tuyeres, and the potential influence on the decarburisation rate. Two water models were employed using water containing NaOH and gas injected through six or eight tuyeres as fluids. In the model, CO2 gas was injected and the reaction of CO2 and NaOH was indirectly measured by detecting the pH value of the water. The mixing time is considered to be a good indicator of the decarburisation as kinetics will be diffusion controlled in the latter period of the process. The following three configurations were studied: (i) a circular converter with six tuyeres, (ii) an oblong converter with six tuyeres, and (iii) an oblong converter with eight tuyeres. The mixing time can be used to evaluate the different converter configurations. The average CO2 concentrations based on several experiments, differed by less than 5% between the circular and oblong models after 165 s of injection of air and CO2. The results also showed that no difference in mixing time could be found when using 6 and 8 tuyeres, respectively in the oblong model, where the CO2 concentrations differed by less than 2% after 165 s of injection time of air and CO2. Based on the findings, it has been observed that the influence of converter geometry on mixing time is small, it was concluded that decarburisation rate is likely to be the same irrespectively of converter geometry.

A novel method to detect the water leakage from tuyere nose cooling circuit in blast furnace

The water cooled tuyere noses, through which hot blast is blown into the furnace, are exposed to very high temperature region of raceway inside the furnace. As a result the chances of rupture of cooling pipes within the tuyere nose are significantly high. The rupture causes water dripping into the furnace and if it continues and unnoticed for a prolonged period it lowers down the local raceway temperature and thus adversely affects the product hot metal and slag quality. Moreover, with heavy water leakage, there is a danger of explosion; monitoring of the cooling water is therefore essential. Despite the availability of water flow metre at each tuyere it is difficult to identify the leaking tuyere at the early stage unless the rupture size grows bigger and so the leakage. In several cases the furnace is forced to shut down to manually inspect the leakage occurring without prior knowledge of the exact tuyere number. Identification of water leakage at an early stage is therefore necessary to prevent process disturbances due to chilling of the furnace and avoid the unscheduled downtime for tuyere replacement. This paper presents a method to identify the water leakage from tuyere nose cooling circuit in blast furnace and the adverse effect of water leakage on the performance of the blast furnace. A system called water leak detection system is developed for different blast furnaces in Tata Steel Jamshedpur to monitor the water leakage through tuyere nose and identify the exact leaking tuyere based on a dimensionless number called leak detection factor.

Use of the Blast Furnaces at Krivorozhstal to Illustrate the Prospects of Blast-Furnace Smelting and Certain Aspects of its Current State*

Many years of use of high pressure and oxygen enrichment of the blast to intensify blast-furnace smelting have shown that the main reason these measures are not very effective and are sometimes even harmful is that the wind rate is reduced when they are used together. In essence, the oxygen that is already present in the blast air is replaced by expensive technical oxygen. The article explores the reasons that this situation exists. It is shown that the problem of increasing the oxygen content of the blast – which is the only direct goal of using intensifiers – is more simply and more cheaply solved by reducing the resistance of the air-blower–blast furnace–gas-cleaning equipment system to the blast that is supplied to the furnace. In particular, more oxygen can be delivered to the furnace via the blast by increasing the number of tuyeres and/or increasing the tuyeres’ diameter.

Mathematical Modeling of Fluid Flow in Bath during Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Application of the Model and Results

AbstractThe mathematical model developed for the molten steel flow in the combined side and top blowing AOD refining process of stainless steel has been used to compute and analyze the flow fields of the liquid phases in the baths of the 120 t AOD converter and its water model unit with a 1/4 linear scale. The influence of the side tuyere number and the angle between each tuyere on the flows has been examined. The results demonstrate that the mathematical model can quite reliably and well model and predict the fluid flow in an AOD bath with the combined blowing. The liquid flow in an AOD converter bath with the combined blowing is resulted from the gas side blowing streams under the influence of a gas top blowing jet. The streams play a governing role on it; and the liquid in the whole bath is in active agitation and circulatory motion during the gas blowing process. The gas jet from the top lance does not change the essential features of the gas stirring and liquid flow in the bath, but can make the local flow pattern of the bath liquid obviously vary and its turbulent kinetic energy enhance. The changes in the tuyere position and number have similarly not altered the basic characteristics and patterns of the gas agitation and liquid flow and turbulent kinetic energy distribution in the bath. At a given tuyere number and gas side blowing rate or a given angular separation between each tuyere and gas side blowing rate, however, the variation of the angle between each tuyere or the tuyere number can locally change them. Using 6 tuyeres with 27° can reach the more uniform flow field and turbulent energy distribution of the liquid in the bath than taking 7 tuyeres with 18° or 22.5° and 6 tuyeres with 22.5°.

Physical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Fluid Mixing Characteristics in Bath

Based on water modeling of the gas stirring and fluid flow in the bath, the fluid mixing characteristics in the bath during the combined side and top blowing AOD refining process of stainless steel were studied on a water model unit of a 120 t AOD converter. The influences of the angle included between each tuyere, the side tuyere number and the gas flow rates for both side and top blowing on the characteristics were examined. The results illustrated that the combined side and top blowing process possessed a good mixing effectiveness. The gas flow rate of the main tuyeres had a key role on the liquid mixing in the bath. With a physical shielding effect of the gas streams from the subtuyeres on the gas streams of the main tuyeres, increasing suitably the gas flow rate of the subtuyeres could enhance mixing efficiency; and the gas jet of the top lance could prolong the mixing time. For a simple side blowing, at a given tuyere number and gas side blowing rate, an increase in the angular separation between each tuyere could be advantageous for shortening the mixing time. At a given angle between each tuyere and gas side blowing rate, increasing the tuyere number could not necessarily reach definitely a similar result. Moreover, it could make the high temperature zone move towards the sidewall around the tuyere outlets and lower the life of the refractory lining due to reducing the gas flow rate of single tuyere and the horizontal penetration of the gas stream. Relevant to the oxygen top bowing rate of 6600 Nm3/h used in the practice, taking 5 tuyeres with 22.5° or 6 tuyeres with 27° could offer a roughly equivalent and good mixing result. As far as only the mixing in the bath is concerned, for the 120 t AOD converter, the existing 7 tuyeres with 18° would not be a proper equipment and arrangement of tuyere under the blowing operations employed for the practical refining. Using 6 tuyeres with 27° could give a perfect mixing in all the various refining periods. The relationships of the mixing time with the gas blowing rates of main tuyeres and subtuyeres and top lance, the angle between each tuyere, the tuyere number, the agitation power densities, and the modified Froude numbers were determined.

Physical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Back-attack Phenomenon of Gas Streams with Horizontal Side Blowing and Its Influence on Erosion and Wear of Refractory Lining

The back-attack phenomenon of the gas side blowing streams and its influence on the erosion and wear of the refractory lining during the combined side and top blowing AOD refining process of stainless steel were investigated on a water model unit of a 120 t AOD converter. Sufficiently full kinetic similarity between the model and its prototype was maintained. The influences of the gas flow rates for side and top blowing, the side tuyere position and number were examined. The preliminary industrial experiments were conducted. The results indicated that the presence of a gas top blowing jet and using of multiple tuyeres did not change the basic features of the back-attack, but could give it some distinctive behaviors. The back-attack could indeed bring about the evident and uneven erosion and wear of the lining. On the back-attack, the gas streams of the main tuyeres had a decisive role, and the subtuyere streams showed a certain suppression and alleviation effect. At a given tuyere number and position, its frequency and pressure and the total average pulse number in per unit time in the processes of this work increased with an increase in the gas side blowing rate. At a given tuyere position and gas side blowing rate, the back-attack and its influence on the erosion and wear of the lining enhanced with decreasing the tuyere number (increasing the gas flow rate for single tuyere). The gas top blowing jet could make the back-attack become more uniform and its frequency decrease, and its intensity and the total average pulse number increase; and it could reduce the eroded and worn rate of the lining at a given tuyere number and position and gas side blowing rate. The increased amplitude of the back-attack intensity and the extension of the damaged area of the lining caused by the buoyancy in a combined blowing were smaller and lower than those in a simple side blowing. As another important reason resulted in the back-attack and the erosion and wear of the lining, the effectiveness of the circulatory motion of the liquid in a combined blowing is different from that in a simple side blowing. At a given tuyere number, properly increasing the angle between each tuyere could be beneficial to alleviating the back-attack and to slowing down the erosion and wear of the lining. Under the conditions of this work, the back-attack actions and the lining eroded and worn extents and rates with 7 tuyeres and 22.5° or 6 tuyeres and 27° were all gentler and lower than those with the other tuyere equipments and arrangements. The results obtained from the physical modeling studies on the refining process were reliable, believable and valid. Suitably increasing the angle between each tuyere of the 120 t AOD converter could raise the life of its lining by a big margin, and remarkably improve the technical and economic indications of the process.

Physical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Gas Stirring and Fluid Flow Characteristics in Bath

The gas stirring and fluid flow characteristics in the bath during the combined side and top blowing AOD refining process of stainless steel were investigated on a water model of a 120 t AOD converter. The geometric similarity ratio of the model to its prototype (including the side tuyeres and the top lances) was 1 : 4. Using the reliably evaluated friction factors of the side tuyeres for the model and its prototype to gas streams, based on the theoretical calculations of the gas flow properties in the tuyeres and the top lances and the modified Froude number, the gas blowing rates utilized for the model were still more reasonably and accurately determined. Thus, sufficiently full kinematic similarity between the model and its prototype was maintained. The influences of the gas flow rates for side and top blowing, the tuyere number and the angle between each tuyere on the characteristics were examined. The results showed that under driving of multiple gas side blowing streams, the liquid in the whole bath was in vigorous agitation and circulatory motion during the blowing process, and there was no evident dead zone in the bath. The gas blowing rate of the main tuyeres possessed a determined role on the gas stirring and liquid flow pattern in the bath. With regard only to the stirring, the larger the gas side blowing rate, the higher the stirring work input, the more vigorous the bath and its liquid surface were. At a given tuyere number and gas side blowing rate, the larger the angle between each tuyere, the more uniform the gas stirring to the bath became. The gas jet from the top lance could change the agitation and liquid flow pattern in the bath caused by the gas side blowing streams, making the liquid turbulence enhance, and the larger the gas top blowing rate, the more obvious the relevant change was. The existing tuyere equipment and arrangement of 7 tuyeres with an angular separation of 18° for the 120 t AOD converter could not provide a perfect stirring and uniform liquid flow pattern in the bath. The agitation power densities of the gas side and top blowing jets to the bath were estimated, respectively.

Effect of Gas Bottom Blowing Conditions on Mixing of Molten Iron inside an Ironmaking Smelter

To aid efficient use of the gas flow rate for a smelting reduction furnace, this study investigates the effect of gas bottom blowing and stirring on the mixing time of the molten iron phase. In this study, transparent acrylic is used to construct a water model, which is 60% as big as the original experimental melting reduction furnace of the China Steel Corporation. The mixing time of the molten iron phase in the water model is measured by using gas bottom blowing and changing the number of tuyeres (from three to five), the tuyere placement, the tuyere size (6.0–15.0 mm), and the gas flow rate per tuyere (80–120 NL/min).The mixing trials adopt KCl as an indicator and use water filtrated using reverse osmosis (RO) in place of liquid iron to investigate the effect of gas bottom blowing conditions on mixing of the molten iron phase. The experimental results indicate that in the cases of four tuyeres in the square-corner and triangle-corner-center placements, 10.0 mm tuyeres yield the shortest mixing time (and thus the best mixing effect) under different total gas flow rates. In the case of five tuyeres in the square-corner-center placement, 10.0 mm tuyeres also have the shortest mixing time under total gas flow rates of 400 NL/min and 500 NL/min. However, 12.5 mm tuyeres have the shortest mixing time under a total gas flow rate of 600 NL/min. In addition, in the case of three tuyeres in the triangle-corner placement, 12.5 mm tuyeres have the shortest mixing time under different total gas flow rates. When the gas flow rate per tuyere is 80 NL/min, the fewer the tuyeres, the shorter the mixing time. Depending on tuyere placement, some of the energy injected by the gas may be counteracted. For example, when a bottom-blowing tuyere exists in the center, the gas injection from that tuyere may be counteracted by that of adjacent tuyeres such that energy dissipates. In contrast, a tuyere placement without a center tuyere may yield better mixing effects. In this study, the best combination for mixing in the liquid phase is four 10.0 mm tuyeres in the square-corner placement and a total gas flow rate of 480 NL/min.

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.

Preliminary Investigation of Fluid Mixing Characteristics during Side and Top Combined Blowing AOD Refining Process of Stainless Steel

The fluid mixing characteristics in the bath during the side and top combined blowing AOD (argon‐oxygen decarburization) refining process of stainless steel were preliminarily investigated on a water model unit of a 120 t AOD converter. The geometric similarity ratio between the model and its prototype (including the side tuyeres and the top lances) was 1:4. On the basis of the theoretical calculations for the parameters of the gas streams in the side tuyeres and the top lances, the gas blowing rates used for the model were more reasonably determined. The influence of the tuyere number and position arrangement, and the gas flow rates for side and top blowing on the characteristics was examined. The results demonstrated that the liquid in the bath underwent vigorous circulatory motion during gas blowing, without obvious dead zone in the bath, resulting in a high mixing effectiveness. The gas flow rate of the main tuyere had a governing role on the characteristics, a suitable increase in the gas flow rate of the subtuyere could improve mixing efficiency, and the gas jet from the top lance made the mixing time prolong. Corresponding to the oxygen top blowing rate specified by the technology, a roughly equivalent and good mixing effectiveness could be reached by using six side tuyeres with an angle of 27 degrees between each tuyere, and five side tuyeres with an angular separation of 22.5 or 27 degrees between each tuyere. The relationships of the mixing time with the gas blowing rates of main‐tuyeres and sub‐tuyeres and top lance, the angle between each tuyere, and the tuyere number were evaluated.

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

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 kwA, 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 kwA 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.

The Application of Two Phase Flow Simulation to the Development of Direct Iron Ore Smelting Reduction Process

The purpose of this research is to numerically simulate the fluid flow phenomena and the corresponding stirring efficiency in the iron bath induced by bottom blowing for the direct iron ore smelting reduction process. The processing conditions under consideration include gas flow rate, tuyere number, tuyere diameter. To verify the accuracy of the simulation model, the calculated results are also compared with the existing experimental observation from a water model.The numerical simulation tools employed in this study are a commercial package named PHOENICS and several generically developed modules to incorporate with PHOENICS for the specific needs of this study. For PHOENICS, the Scalar Equation Method (SEM) model is chosen to handle the two phase flow problems. For SEM model, it employs a function; h, to represent the extent of mixing between gas and liquid. A post-processing module to show the front-view of h distribution is developed to compare with the photograph taken from a 0.6 scale water model. Another post-processing module is also developed to calculate the mixing time, which is a direct index of stirring efficiency, based on the velocity profile simulated by PHOENICS. A shorter mixing time represents a better stirring efficiency. With the calculated mixing times under various processing conditions, the effects of individual processing condition on the stirring efficiency can be evaluated.

The Determination of the Minimum and Operational Gas Flow Rates for Sidewall Blowing in the AOD-Converter

Gas flow rates from the sidewall tuyeres in the AOD-converter can vary within large range during processing. Back-attack phenomenon, blocked tuyeres, uneven wear of refractory lining and oscillation of the bath set inconsistent demands for the optimum tuyere diameter, number of tuyeres and the angle between each tuyere. Oscillation of the liquid bath, mixing and the penetration of the gas jets with different sidewall blowing procedures were studied by a physical model. The aim of the present study was to determine the criteria for minimum and operational gas flow rate in the actual AOD based on the studied physical phenomena. According to the tests, minimum and operational gas flow rates through the different sized sidewall tuyeres can be defined by modified Froude number based on the appearance of the tuyere blockage (or back-attack) and oscillation. In sidewall blowing, the main reason for the oscillation of the bath is the symmetry of the plume on the vertical axis of the vessel caused by deep penetration of the gas jets. The nominal frequency of the oscillation of steel bath in the actual AOD was determined by dimensional analysis. The gas flow rate, which should be avoid is limited by appearance of oscillation of the bath. Penetration of the molten steel into the tuyeres determines the minimum gas flow rate from sidewall tuyeres. Smaller number of sidewall tuyeres and also a smaller diameter of tuyeres provide larger operational area as far as gas flow rate is considered.

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. Physikalische und mathematische Modelle zur Strömung von Gas und Schmelze im LD-Konverter. Das Strömungsverhalten in einem LD-Konverter wurde besonders im Hinblick auf die Wechselwirkungen zwischen Gas und Schmelze physikalisch und mathematisch simuliert. Mit einem Wassermodell wurden drei Varianten des Gaseinleitens betrachtet: Aufblasen, Bodenblasen und kombiniertes Blasen. Beim Aufblasen nimmt die Zeit zur Durchmischung mit der Badhöhe als auch mit dem Abstand der Lanze vom Gasstrahl und der Badoberfläche zu. Es zeigte sich, daß die Eindringtiefe des Strahls von der modifizierten Froude-Nummer abhängt. Das instabile und unstetige Verhalten der Badtopographie, soweit vom Gasstrahl betroffen, ließ sich gut mit einem mehrphasigen Momententransfermodell simulieren. Beim Aufblasen läßt sich das Spritzen in drei Zonen unterteilen: geringes Spritzen beim Eindringen des Gasstrahls in die Schmelze, starkes Spritzen und Dimplebildung mit geringer Spritzintensität. Diese Bereiche hängen von den beiden Parametern Strömungsgeschwindigkeit des Gases und Abstand der Lanze von der Badoberfläche ab. Beim Bodenblasen verkürzt sich die Mischzeit mit der Anzahl der Düsen, steigender Badhöhe und Gasströmungsgeschwindigkeit. Beim kombinierten Blasen fällt die Mischzeit infolge der gegenläufigen Strömung, die sich aus den Gasstrahlen der oberen Düse und der Bodendüsen zusammensetzt, beträchtlich. Wenn die Position des aus dem Tauchrohr austretenden Strahls gleich unterhalb des oberen Strahls liegt, nimmt die Mischzeit im Vergleich zum reinen Auf- oder Bodenblasen nicht ab.

Fluid Flow and Mixing Phenomena in the Ladle Stirred by Argon through Multi-Tuyere.

Water model experiments and the numerical solution of a mathematical model with three dimensions have been conducted to investigate the flow pattern and mixing phenomena in argon-stirred ladles with six types of tuyere arrangement. It was found that the arrangement of tuyeres has a great effect on the flow patterns and mixing in the ladle, a placement of single tuyere at off-centric position gave the shortest mixing time whereas double tuyeres opposite placed at half radii was found to be the best arrangement considering the aspects of blowing, mixing, inclusion flotation and splashing. An empirical correlation for mixing time in the ladle considering the number of tuyeres was proposed. The predicted and measured results showed quantitatively good agreements.

Kinetics of the zinc slag-Fuming process: Part III. model predictions and analysis of process kinetics

In the final part of this paper the mathematical model of the slag fuming process, developed in Part II based on the analysis of industrial measurements from Part I, has been subjected to a sensitivity analysis, then employed to elucidate the rate limiting steps and to predict the influence of process variables on fuming. The kinetics analysis has been based on model predictions of fuming efficiency (Zn/coal) of the coal particles injected into the slag. The model predicts that fuming efficiency passes through a maximum with increasing residence time of coal particles in the slag. At shorter times, the zinc reduction kinetics are governed by the Boudouard Reaction, but at longer times, beyond the time at which the peak fuming efficiency is reached, the diffusion of ferric iron to the interface between the secondary bubbles containing the coal and the slag is rate determining. The level of ferric iron in the slag, which depends on ferrous iron oxidation rate, melting/freezing of slag at the water-cooled jacket, and ferric iron reduction by coal entrained in the slag, is therefore an important variable affecting the fuming kinetics. With respect to the influence of manipulable process variables, the model predicts that zinc fuming can be enhanced by increasing the fraction of coal entrained by the bath up to an optimum value at a fixed coal rate. An increase in entrainment could be achieved by injecting the desired portion of the coal at high pressure and solids loading through a small number of tuyeres. This strategy is preferable, from the standpoint of fuming efficiency, to simply increasing the rate of coal injection at normal pressures. Similarly, there is an optimum charge weight and bath height for a given furnace size. The best coal for zinc fuming, according to the model, has the following properties: low moisture and ash content, high fixed carbon (or volatiles), and high reactivity. Model predictions also suggest that there are advantages to fuming in a continuous operation rather than in a batch mode.

A water model study of bottom-blown oxygen steelmaking processes

Investigations were carried out in a water model of bottom-blown oxygen steelmaking processes like OBM/Q-BOP to understand certain aspects of the dynamics of these processes. Wall shear stress along the bottom of a cylindrical plexiglass model vessel was measured as a function of process parameters, using the electro-chemical technique. Experiments were conducted with one, three, six and twelve tuyeres in various geometrical configurations. Air was used to simulate the gases blown into the bottom-blown converters. In single-tuyere experiments, two concentric pipes were employed and air was distributed between the inner pipe and the annular region to simulate oxygen and the shrouding gas respectively. It was found that the wall shear stress (τ) decreased drastically with increasing distance from the tuyere. The rms value of the fluctuations (τ′) in shear stress were directly proportional to the time-averaged value (τ). Percentage air in the annulus and the length of tuyere protrusion into the bath had significant effect on t only at points close to the tuyere. Dimensionless correlations have been attempted for these variables at the point closest to the tuyere at which measurements have been made. Results of visual observations and photogaphy are also reported. Multiple-tuyere experiments were conducted with the tuyeres in symmetric and asymmetric arrangements. It was observed that for any tuyere configuration rms value of τ′ was proportional to t. There seem to be an optimum number of tuyeres for minimizing shear stress along the bottom. Asymmetric arrangement of tuyeres resulted in higher level of shear stress. An attempt has been made to relate the observations of the study to the wear of the bottom ref actory lining.

コールド・モデルによる底吹き転炉内スラグ,メタルの混合速度

Synopsis:Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in Q-BOP with a particular emphasis on the comparison with those of LD.Complete mixing time of molten steel determined by a tracer dispersion technique is, respectively, 23 to 26 sec for Q-BOP, and 100 to 200 sec for LD. This indicates that the stirring intensity in Q-BOP is remarkably larger than that of LD when compared with the same flow rate of gas. A simple relationship obtained between the mixing time, τ (sec), the flow rate of gas, Q(Nl/min) and the number of tuyeres, N is τ=41.80 (Q/N)-0.33, from which it is clear that the flow rate of gas per tuyere should be increased to realize the better mixing. Mass transfer capacity coefficient between slag and metal designated by the product of the mass transfer coefficient and the interfacial area, kBa, is given by kBa=3.49 × 10-5 Q3 for Q-BOP and by kBa=-1.53 × 10-5 Q3 for LD, respectively. Through these results, it can safely be concluded that the mass partition between slag and metal in Q-BOP is more closely linked to the thermodynamic equilibrium than that of LD.