Top Blowing Research Articles

粉 CaO 上吹き溶銑脱りん法の開発

粉 CaO 上吹き溶銑脱りん法の開発

The Mixing Characteristics of Powder Injected through Top Lance in RH Degasser

With the increasing demand for high quality steel, various secondary refining techniques have been developed in the past decades. RH powder top blowing process (RH-PTB) is practiced in industry to decrease the impurity content of steel in a more economical way. In the present work, based on similarity theory, RH powder top blowing process was simulated by water model, and the effects of operating parameters on mixing time were investigated. The results show that the injected powder had a negligible effect on mixing time in RH-PTB, and the mixing time increases with top lance gas flowrate and decreases with lifting gas flowrate of up-leg. It was found that the mixing time was no longer decreasing as the lifting gas flowrate was over 15 L/min. Moreover, the height of top lance has some effect on mixing time in the reactor, and it should be adjusted to specific circumstances for purposes.

Numerical simulation of interaction during the top blow in a steel-making converter

The numerical modeling of interaction between oxygen high-pressure jets and a liquid–metal surface in a steel-making converter, where, under the force action of the jets, a cavern with a hydrodynamically unstable surface forms in the metal bulk, is studied. A simplified scheme of chemical reactions and mechanisms of metal-drop dispersing from the interface between the phases is proposed. This scheme permits an adequate description of the hydrodynamic flow pattern in the cavern. The modeling of a two-phase turbulent flow in the cavern is considered within the framework of the continuum model based on the averaged Navier–Stokes equations. To close the equations, a modified k– ε turbulence model is used, which takes into account the presence of the second phase. The flow structure in the cavern is studied. Practical recommendations for increasing the efficiency of the carbon-monoxide afterburning process in the cavern are given.

Penetration behaviour of an annular gas–solid jet impinging on a liquid bath: effect of the annular cross‐sectional area

Top blow injection of a gas–solid jet through a circular lance is used in the Mitsubishi continuous smelting process. One of the problems associated with such injection is the severe erosion of the hearth refractory below the lances. A new configuration of the lance to form an annular gas–solid jet rather than the circular jet was designed in this laboratory. With this new configuration, solid particles, fed through the centre tube, leave the lance at a much lower velocity than the gas, and the penetration behaviour of jet is significantly different than that of circular lance where the solid particles leave the lance at the same high velocity as the gas. In an earlier cold model investigation, the effects of gas velocity, solid feedrate and lance height of the annular lance were studied and compared to the circular lance. This paper reports on experimental work that includes the effects of the size of the annular lance, which greatly expands the applicable range of the developed correlation. It has been shown that the variation in penetration depth with the annular jet cross‐sectional area depends strongly on the mass loading of the solid particles. A correlation equation for the penetration depth that shows a good agreement with the measured values has been developed.

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

AbstractConsidering that the liquid flow field under the conditions of the combined side and top blowing would be a combined result from the common action of the side blowing gas streams and a gas top blowing jet, as the first attempt, the three‐dimensional mathematical models for the flows of molten steel in an AOD converter bath during the simple side and top blowing processes have been proposed and developed, respectively. And the mathematical model of the flow in the bath during the combined blowing AOD refining process of stainless steel has been given by the composition and superposition of the two models. In the composed model, the gas‐liquid two‐phase flow is described and treated in terms of the two‐fluid (Eulerian‐Eulerian) model. The especially modified two‐equation k−ε model for the turbulence in the liquid phase is employed. And, the surface of the sunken pit formed by impact of the gas jet blown from a top lance at the central location of the bath liquid surface is regarded as a revolution paraboloid. The related details of the composed model are shown.

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°.

Effect of Mixed Gas Top Blowing on Decarburization and Manganese Evaporation of Steel Melt in Low Carbon Content Range

Experimental and theoretical studies have been carried out to clarify the effects of mixed gas top blowing on decarburization and manganese evaporation of steel melt in low carbon content range.20 kg scale of induction furnace was used for decarburization experiment. Oxygen utilization efficiency for decarburization increased with an increase in inert gas flow rate and a decrease in oxygen flow rate of mixed gas top blowing. Decarburization rate below carbon content of 0.03 mass% depended on CO partial pressure caused by mixed gas of oxygen and inert gas. To explain these results, an index, IM for decarburization was introduced. The IM is found to be inversely proportional to the oxygen utilization efficiency for decarburization in the low carbon content range, and there is a good correlation between the IM and oxygen content in steel melt.Unexplained manganese content, which seems to depend on its evaporation, decreased with an increase in inert gas ratio of top blowing to oxygen. Manganese evaporation rate was introduced according to Hertz–Knudsen–Langmuir's equation which showed an increase with increasing temperature. Assuming that manganese evaporation occurs at the fire spot caused by top blowing during the final stage of refining, the temperature of the fire spot was estimated to reach 2890K for oxygen top blowing, and decrease to 2475K for mixed gas blowing of (Ar+N2)/O2=2/1.

Relationship between Mixing Time and the Number of Holes of a Top Blowing Immersion Nozzle in a Cylindrical Bath

Relationship between Mixing Time and the Number of Holes of a Top Blowing Immersion Nozzle in a Cylindrical Bath

Mathematical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel

Mathematical modeling of the combined side and top blowing AOD refining process of stainless steel has further been studied. A new model proposed is generally based on the analysis and assumptions made for the process in our previous investigation. Particularly, the heat transfer characteristics of the vessel are analyzed in terms of the two-dimensional transient heat-conduction problems of composite walls. The heat and mass balances of the system are more comprehensively and precisely performed. The model has been applied to 28 heats of 304-grade austenitic stainless steel refining in a 120 t AOD converter. The results present that the changes in the composition and temperature of the liquid steel with the time during the whole process can be accurately predicted using the model. The competitive oxidation among the elements in the steel during the oxidative refining with the relevant oxygen distribution ratios, and the competitive reduction of the oxides in the slag during the Ar agitating and reductive refining with the appropriate oxygen supply ratios can be well characterized and reasonably determined using the Gibbs free energies of the reactions. The critical carbon concentrations (after which the decarburization alters to be limited by the mass transfer of carbon in liquid steel) for the top, side and combined blowing of 304-grade steel in this work are in the ranges of 0.895 to 0.942, 0.078 to 0.224, 0.144 to 0.255 mass%, respectively. The effects of some factors on the refining result and the optimization of blowing technology have been considered from the model predictions. The model can provide a reliable basis and useful information for determining and optimizing the technology of this AOD process of stainless steel, and controlling the process in real time and on-line.

Hydraulic Model Experimental Study on Coherent Jet Flow Field

Based on Anshan Iron and Steel Company 180t top-bottom converter prototype, the operating parameters and the structural parameters for best stirring effect of bottom-blowing converter and top-bottom converter was given by the hydraulic model test in this article. Coherent jet oxygen lance converter smelting effect was simulated under the condition of keeping the best top blowing gas flow rate. The experiment result shows that coherent jet oxygen lance may achieve the result of top-bottom converter stirring effect. If coherent jet oxygen lance could be applied in the converter, bottom blowing system of converter could be canceled. In that case, not only the converter equipment can be simplified, but also the converter lining life can be improved, bring steel-making technology transformation.

Cold Simulation of Oxygen Transfer Rate in BOF

By measuring the mass transfer coefficient of benzoic acid between water and oil, the oxygen transfer rate in BOF bath was researched, and the influence of top and bottom blowing gas flow rate on the mass transfer between metal and slag was discussed. The results show that with increasing the bottom blowing gas flow rate under the conditions of fixed top blowing, the mass transfer rate evidently increases, and the influence of fixed top blowing on the mass transfer is 10% of bottom blowing. The stirring intensity was determined as a function of top blowing gas flow rate, bottom blowing gas flow rate, and lance height. The equation of the mass transfer coefficient between metal and slag was established. The relationship between the emulsification ratio of oil to water and the bottom blowing gas flow rate under the conditions of top and bottom blowing was obtained. The result shows that with the increase in the bottom blowing gas flow rate, the emulsification ratio increases linearly, which increases the mass transfer rate of benzoic acid between water and oil.

Low intensity continuous copper smelting

As current advanced copper smelting processes are judged to be inherently inefficient, a case is made for a radical rethink of more appropriate technology to capture the energy content of high energy sulphides, such as chalcopyrite. Generic melt circulation employing non-oxygen enriched air top blowing in the non-splash mode with permanent linings of solidified copper matte is proposed. Two melt circulation loops are interconnected by a siphon to maintain automatically a continuous flow of high grade matte from the first melt circulation loop with a low copper metal activity into a copper saturated matte loop, which takes the place of traditional Peirce–Smith converters. Copper is removed continuously from the converting loop into two countercurrent packed bed gas–liquid contactors. The first packed bed employs controlled air oxidation of residual sulphur, followed then by the second packed bed using an excess of reformed natural gas for copper deoxidation in advance of continuous anode casting.

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.

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: 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.

転炉型溶銑脱燐時の上吹き酸素による酸化鉄生成挙動の基礎検討

The effects of hot metal temperature, oxygen gas flow rate from a top lance and argon gas flow rate from an injection lance on iron oxide formation and dephosphorization rates in hot metal were investigated with 3 kg- and 200 kg-scale furnaces. The results were summarized as follows.1) Iron oxide formation rate increased with lower hot metal temperature, higher oxygen gas flow rate and lower argon gas flow rate.2) A kinetic model was developed to estimate the iron oxide formation on hot metal, and a mathematical model for hot metal dephosphorization has been made based on the aforementioned model of iron oxide formation and the coupled reaction model.3) Dephosphorization and the formation rate of iron oxide in 200 kg-scale tests agreed well with those were obtained by the mathematical model.4) Oxygen activity at slag/metal interface obtained by the mathematical model agreed with the equilibrium oxygen activity with FeO in slag.5) In the early stage of dephosphorization, the gas flow rate of the bottom blowing need to be lower in order to enhance the iron oxide formation. In the late stage of dephosphorization, that needs to be higher in order to enhance the mass transfer of phosphorus in hot metal.6) Industrial hot metal dephosphorization tests were carried out with a 350 t-scale top and bottom converter. The conditions of top blowing oxygen and bottom blowing nitrogen have been improved by adopting the mathematical model in order to increase the iron oxide content in slag. It has been possible to increase dephosphorization efficiency without fluor spar at lower hot metal temperature (below 1300°C) by improving the blowing conditions.

Prediction of Pressure Drop at the Entry Section from Top Discharge Blow Tank in a Pneumatic Conveying System

Although some literature can be found on the behavior of blow tanks, very few studies could be found on the pressure loss at the entry section to a pipeline (henceforth called entry pressure loss) from a top discharge blow tank in a pneumatic conveying system, even though its magnitude can be significant as compared to the total system pressure drop. This article presents the results of an experimental study carried out to assess this entry pressure loss. The results indicate that it is possible to scale up the entry pressure loss based on laboratory-scale tests with a reasonable degree of accuracy.

CFD Simulation Gas-Liquid Flow in a Copper Converter with Bottom Air Injection

Peirce-Smith converters (PSC) are chemical reactors where copper matte reacts with air. A conventional PSC is a long horizontal cylinder where air is injected laterally into the cooper bath through submerged tuyeres. In these PSC, air is injected at high velocities to obtain an adequate mixing of the copper bath and to avoid tuyere blockage. An alternative PSC configuration uses top blowing of air accompanied by gentle nitrogen bottom stirring. In this work, the direct bottom injection of air at low inlet velocity was studied by means of transient multiphase 3D CFD numerical simulations considering three blowing conditions. The ?-? turbulence model and the volume of fluid model (VOF) were used in order to model the turbulent nature of the flow and to deal with the multiphase flow. Special attention was paid to the air bubbles formation and its effect on the copper bath mixing. The dynamic behavior of turbulent kinetic energy and the average velocity of the copper matte were analyzed. The numerical simulations suggest that the relationship between air inlet velocity and bath mixing is non linear. However, using the air bottom injection at low velocities, the obtained copper bath nominal velocity is similar to that reported in a conventional PSC.

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.

Optimisation of the Bottom Tuyeres Configuration for the BOF Vessel Using Physical and Mathematical Modelling

An experimental perspex model of the BOF vessel was made to the scale of 1 : 6 on which mixing time measurements were done by injecting potassium chloride (KCl) at a certain point and measuring the conductivity of the solution with time. It was found that the mixing time in the vessel attained a minimum when the bottom nozzles (eight in number) were kept at a pitch circle diameter (PCD) ratio of 0.4 with combined blowing (top blowing as well as bottom blowing) but the mixing time became a minimum at a PCD of 0.5 when only bottom blowing was done. In order to get a finer position of the bottom nozzles so that the mixing time could still be minimized, a mathematical model was used (because experiment could not be done with so close placement of the nozzles in one setup) to simulate the flow in the vessel with the help of the two equation k–ε turbulence model along with a discrete phase model to simulate the air bubbles being injected in to the vessel. The mathematical model could predict the mixing time in the vessel to a very good degree of accuracy when compared with the experimental observations for the PCD of 0.5. From the mathematical model it was predicted that the mixing time in the vessel could still be lowered if the bottom nozzles were placed at a PCD of 0.56 instead of 0.5.