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

Wei, Ji-He; Hong-li, Zhu; Yan, Sen-Long; Wang, Xinchao; Ma, Jinxing; Shi, Guopu; Jiang, Qingyan; Chi, He-Bing; Che, Li-Bing; Zhang, Kai

doi:10.1002/srin.200506023

Cited by 11 publications

(23 citation statements)

References 8 publications

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“…However, they ignored the influence of the gas jet from a top lance 3,5) ; and the kinematic similarity between the model and its prototype in their experiments was not full, thus their results obtained were not necessarily able to reflect truly the real situations in the prototype. At the prerequisite of keeping the kinematic similarity between the model and its prototype as high as possible, Wei et al 12,13) conducted preliminarily the physical modeling of the combined side and top blowing refining process of stainless steel in a 120 t AOD converter. Nevertheless, since the converter was not completed at that time, some key data, including the dimension of the side tuyere and blowing operation and others, were all set up in terms of the technological design and had considerable disparities from the actual practice.…”

Section: Physical Modeling Study On Combined Side and Top Blowing Aodmentioning

confidence: 99%

“…The completed 120 t combined side and top blowing AOD converter is equipped with seven tuyeres (annular tube type with constant cross-sectional area) and one top lance (Laval type with single hole); compared to the prototype taken in the preliminary investigation, 12,13) Here, u g is the gas velocity, m/s; d is the characteristic dimension of the system, m; r g and r l are, respectively, the density of the gas and the liquid, kg/m 3 ; g is the acceleration due to gravity, m/s 2 . Under the prerequisite of maintaining the geometric similarity between the both, taking d as the inner diameter of the tuyere or the throat diameter of the lance, the gas flow rates at the standard state for the tuyeres and lance of the model can be obtained from (FrЈ) m ϭ(FrЈ) p as follows, ..... (2) where Q is the volumetric flow rate of gas at the standard state, Nm 3 /h; r g0 is the density of the employed gas at the standard state, kg/Nm 3 ; r g is the density of the employed gas at the tuyere or lance outlet, kg/m 3 ; subscripts m and p denote, respectively, the model and its prototype.…”

Section: Similarity Conditions and Gas Flow Rates For The Modelmentioning

confidence: 99%

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

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Table 1. Values of friction factors of side tuyeres used for the 120 t AOD converter and its water model unit.And the gas side blowing rates of the main tuyere and subtuyere for the model corresponding to the gas blowing rates of the prototype during the practical refining process were determined in terms of the following two cases: 1) Considering only heating friction flow of the gas in the tuyere used for the real refining process.2) Taking both heating friction flow of the gas in the tuyere employed for the real process and heat expansion of the main tuyere gas after entering the bath into account. The results of theoretical calculations of the properties for the gas stream and evaluation of the heat transfer between the stream and liquid steel in the converter demonstrated that the outlet temperature of the subtuyere gas stream would have achieved or slightly exceeded the mean value of the gas in the bath, therefore, it would not be necessary to consider heat expansion of the subtuyere gas in the bath.The results obtained for the main decarburization period of the blowing process of 304 grade stainless steel in the 120 t AOD converter with the values of some related parameters are shown in Table 2, being markedly different from those given in the preliminary investigation, and having also much higher accuracies. Relevantly, the kinematic similarity between the model and its prototype is much better than that in the preliminary investigation.In addition, besides heating friction flow of the gas in the tuyere for the practical refining and heat expansion of the main tuyere gas after entry into the bath, an increase in the gas flow rate caused by formation of CO in side blowing process at a high initial carbon content of 3.5 mass% or so was also considered, and the corresponding gas blowing rate for the model was fixed.Since the hot metal employed for the practical refining in the 120 t AOD converter under consideration is all predesiliconized and the initial silicon concentration is very low, the influence of formation of solid and liquid oxides (especially SiO 2 ) during the side blowing process on the gas blowing rate of the main tuyere for the model was still ignored in the present work, like that done in the preliminary investigation.For the top blowing process with a gas-liquid two-phase system composed of a non-submerged gas jet and the bath liquid, the relevant r gp and r gm can be taken as (r g0 ) p and (r g0 ) m , and the gas flow rate for the top lance of the model at a given oxygen top blowing rate of the prototype can directly be attained from Eq. (2). Since the zone considered for a gas top blowing process is at the bath surface (which belongs to a gas-liquid system) and not at the lance outlet, the outlet March number of the gas jet from the lance for the model and the relevant gas supply pressure must be less than those for its prototype, in order to satisfy Eq. (2) thus ensure the kinematic similarity of the model with its prototype. Experimental MethodsExcept the tuyeres and top lance, the mo...

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Section: Physical Modeling Study On Combined Side and Top Blowing Aodmentioning

confidence: 99%

Section: Similarity Conditions and Gas Flow Rates For The Modelmentioning

confidence: 99%

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

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“…They also studied the mixing time for the different reactors in metallurgical vessels. In addition, Wei et al [3][4][5][6][7] have done some work to show the influence of tuyere position, numbers of tuyeres and gas flow rate in the AOD converter. Overall, this research group has not studied the combined influence of the bath height, the vessel diameter and the gas flow rate on the mixing time.…”

Section: Introductionmentioning

confidence: 99%

Mixing Time in a Side-Blown Converter

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3/s and 800 cm 3 /s as well as bath heights ranging from 106 to 314 mm. The mixing times were also calculated based on an expression involving the Strouhal and Reynolds numbers. The experimentally determined mixing times were found to be within Ϯ20 % of the theoretical values, which is considered to be good in physical modelling. Overall, the mixing time was found to be influenced by the gas flow rate and the vessel diameter, but not by the bath height.KEY WORDS: physical modeling; mixing time; converter; side-blown; conductivity measurements. 663© 2010 ISIJ used to simulate steel and air to simulate argon/oxygen. The gas flow rates were determined by using the Froude number to scale the rate from a full scale converter to a physical model.The different flow rates were calculated by using the Froude number similarity criteria: (2) where r g is the density of air, Q g is the gas flow rate, r l is the density of water, g is the gravitational constant and d i is the nozzle inner diameter. In addition the following Froude number was used to scale the gas flow rate: Equation (3) was used to scale the gas flow rate, compared to a real converter. When this is determined, Eq. (2) was used to scale the size of the nozzle. The size of the nozzle was determined to be 3.2 mm for the smaller physical model. From experience it was determined that the nozzle size has a very small influence on the mixing time in the same manner as observed in a bottom blown bath. The mixing time is mainly governed by the gas flow rate, although the penetration depth of bubbles in the horizontal direction is affected by the nozzle size as well as the gas flow rate. Thus, the same nozzle was used in the larger physical model.A mass flow controller was used to regulate the gas flow rate during the experiments. Also, a conductivity probe was used to measure the change in conductivity. The probe was placed 30 mm from the bottom of the bath and near the side wall, as illustrated in Fig. 1. The output of the probe was fed to a conductivity meter and provided a 0 to 1 V DC output to a computer interface. In addition, the fluid flow was fully developed before the tracer injection of the KCl-solution was made. The solution had a concentration of 1 M KCl, and the amount added was 1 mL solution per 1 000 mL of liquid in the bath. Furthermore, the injection was made by a syringe close to the wall of the vessel. The conductivity of the bath was measured with an interval of 100 ms.The experimental mixing time was defined as the period required for instantaneous tracer concentration to settle within Ϯ5 % deviation around the final tracer concentration in the bath. Results and DiscussionExperiments were done using two vessel diameters of 200 mm and 300 mm, respectively. In addition, experiments were done for bath heights varying from 106 to 314 mm.Air was injected at the bottom of a side wall, as illustrated in Fig. 1. Flow rates between 30 cm 3 /s and 800 cm 3 /s were tested during the trials. Based on Eq. (2) the inner diameter of the side nozzle was determi...

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“…Its reasonability, to a great extent, is concerned to the efficiency and effectiveness of the refining process. The results of a whole series of the investigations by Wei et al [15][16][17][18][19][20][21][22][23] with the present work amply showed that the tuyere number and position considerably affect the fluid flow and mixing in an AOD bath, and the stability of the refining process, the lining life and others, thus directly influencing the technical and economic indications of the process. At a given gas side blowing rate, using too many or few tuyeres and an excessively large or small angle between each tuyere will all increase the energy consumption and reduce the effective agitation power input by the gas streams due to the stronger interactions among them.…”

Section: Preliminary Application Of Physical Modeling Results To Indumentioning

confidence: 58%

“…As a matter of fact, it was only an attempt to take this scheme at that time. The results of the physical modeling of the process in this converter [16][17][18][19][20]23) including this work illustrated that this scheme would not be so suitable, being difficult to offer the good stirring and mixing in the bath, and the erosion and wear of the lining being more serious.…”

Section: Preliminary Application Of Physical Modeling Results To Indumentioning

confidence: 99%

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

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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.KEY WORDS: stainless steel; AOD refining; combined side and top blowing; horizontal gas stream; back-attack phenomenon; erosion and wear of refractory lining; physical modeling. 1347© 2010 ISIJ fer...

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

Cited by 11 publications

References 8 publications

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

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

Mixing Time in a Side-Blown Converter

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

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