【作者】 史国敏；

【导师】 魏季和；

【作者基本信息】 上海大学 ， 钢铁冶金， 2008， 博士

【摘要】 概要介绍了不锈钢AOD炉的精炼原理及工艺发展过程,分析和综述了有关该精炼过程的数学模拟和物理模拟的研究进展。以宝山钢铁股份有限公司不锈钢分公司120 t侧顶复吹AOD转炉为原型,按与原型1:4的几何相似比设计和建造了一套水模型装置。以该炉内冶炼304不锈钢主脱碳期的吹炼过程为对象,合理确定了原型和模型用套管式等截面喷枪对气流的摩擦系数,并进行了侧吹用套管式等截面喷枪和顶吹用拉瓦尔顶枪内气流特性参数的理论计算,由此较合理地确定了模型用侧枪和顶枪的吹气量,从而保证了模型和原型间足够的相似性。利用水模拟研究了AOD转炉侧顶复吹过程中熔池内气体射流搅拌和流体流动状态、熔池液面的稳定性、液体的流动和混合特性、侧吹气体射流的反冲现象和及其对炉衬蚀损过程。考察了侧吹气量、侧枪支数、相邻两侧枪间的夹角、顶吹气量等因素的影响。结果表明,吹炼过程中熔池液体处于活泼的搅拌和循环运动状态,熔池内没有明显的死区,混合效果极好,混合时间短。侧吹主枪的吹气量对熔池内流体的流动和混合有决定性的影响,侧吹副枪气体射流对主枪气体射流有显著的物理屏蔽效应,适当提高侧吹副枪吹气量也可提高混合效率。顶吹气体射流会改变熔池内侧吹气体的搅拌和流体流动的状态,使紊流强度增大,混合效率降低,混合时间延长,且顶吹气量越大其效果越明显。在给定的侧枪支数和吹气量下,增大相邻两枪间夹角,有利于提高气体射流对熔池的搅拌效率,缩短混合时间。在给定的侧枪枪位和吹气量下,增加侧枪支数未必会有类似的效果,且单枪吹气量的减少,使得侧吹气体射流的水平穿透距离变短,熔池内的高温(反应)区会移向甚至贴近炉壁,影响炉衬寿命。仅就混合时间而言,综合考虑侧枪支数、枪位、侧吹及顶吹气量等因素的影响,对应于工艺规定的6600 Nm~3/h的顶吹气量,6枪27°的侧枪配置在各精炼期均可提供良好的熔池混合效果。对现行工艺中采用的18°枪间夹角,无论是采用7枪,还是6枪和5枪,均不能达到理想的混合效果。与纯侧吹和底吹过程中气体射流的反冲现象相比,侧顶复吹条件下水平侧吹气体射流的反冲现象具有自己的特征。在侧顶复吹条件下,侧枪主枪气流对水平侧吹气体射流的反冲现象具有决定性的作用;副枪气体射流对之有明显的抑制和缓解效应;顶吹气体射流则使之变得较均匀,同时使反冲强度(压力)增大。在侧顶复吹条件下,熔池内液体的循环运动也是引起水平侧吹气体射流反冲现象的另一个重要原因。浮力对侧吹气体射流的反冲有相当大的影响,它不仅使之强度增大,而且使炉衬蚀损区域扩大。与纯侧吹相比,在侧顶复吹条件下,浮力对侧吹反冲强度的增大作用相对要弱,但由于与顶吹射流冲力的相互作用,使反冲力的作用区域,即炉衬受损区域更大。对应于本工作给定的侧枪支数及侧吹和顶吹气量,在18°～27°范围内,合宜地增大相邻两侧枪间的夹角有利于缓解侧吹气体射流反冲的影响。相对而言,对于给定的侧吹和顶吹气量,采用7枪22.5°或6枪27°的侧枪配置时,无论是纯侧吹还是侧顶复吹过程,炉衬的受损程度都比采用其它配置要轻。基于气—液双流体模型和湍流的修正k-ε模型,提出了纯侧吹条件下AOD转炉熔池内流体流动的数学模型,确定了模型的有关参数。考虑到气体的加热摩擦流动,在侧吹用套管式等截面喷枪内气流特性参数计算和气流与钢液间传热估算的基础上,合理确定了侧吹气体的入口参数;应用该模型对该120t AOD转炉及线尺寸为其1/4的水模型装置内的流体流动作了模拟和计算,考察了侧枪支数和相邻两枪间夹角的影响。结果表明,该模型可以相当可靠地模拟AOD炉内液体的流动;在多股气流和液体的相互作用下,整个熔池流体处于活泼的搅拌和循环运动状态,不存在明显的“死区”;侧枪支数的变化没有改变熔池内气体搅拌和液体流动的基本特征,也不会改变熔池内液相的湍流动能和含气率分布规律,但在相同侧枪夹角和侧吹气量下,枪数的减少使气体的搅拌强度增大,从而使流场、湍流动能和含气率分布发生局部变化,采用6枪27°喷吹比7枪18°或22.5°喷吹更为均匀;在给定侧枪支数和侧吹气量下,枪间夹角的增大不会从根本上改变熔池内气体搅拌和液体流动的特征,但流场有较明显的变化,相邻两枪间夹角越大,侧枪所夹扇形区的总面积越大,气液两相区在熔池中所占面积也越大,各股气体射流间的相互作用因之减弱,相应的能量损耗因之减少,气体射流对熔池的搅拌则越均匀。与纯侧吹条件下AOD转炉熔池内流体的流动相比,侧顶复吹条件下AOD转炉熔池内液体的流场当是侧吹和顶吹气体射流共同作用的效果。基于这种考虑,本工作同时还提出和建立了纯顶吹条件下AOD转炉内钢液流动的三维数学模型,应用该模型对该120 t AOD炉及线尺寸为其1/4的水模型装置内的流体流动作了模拟和估计,再将所得结果与纯侧吹条件下得到的流场相叠加,从而得到侧顶复吹条件下熔池内液体的流场。所得结果表明,侧顶复吹条件下AOD转炉熔池内流体的流动是在顶吹气体射流的影响下由侧吹气体射流所引起的,整个熔池液体同样处于活跃的搅拌和运动之中,也不存在明显的“死区”;与纯侧吹过程相比,同时作用于熔池的顶吹气体射流并未改变熔池内气体搅拌和液体流动的基本特征和规律,但是,顶吹气体射流的存在使熔池内液体的局部流态发生明显的变化;侧顶复吹条件下,侧枪支数的变化同样没有改变熔池内气体搅拌和液体流动的基本特征,也不会改变熔池内液相的湍流动能和含气率分布的规律,在相同的侧枪夹角和侧吹气量下,枪数的减少使气体的搅拌强度增大,流场、紊流动能和含气率分布发生局部的变化,采用6枪27°比采用7枪18°或22.5°喷吹搅拌更为均匀;侧顶复吹条件下,给定侧枪支数和侧吹气量,相邻两枪间夹角增大,同样不会从根本上改变熔池内气体搅拌和液体流动的特征,但流场还是有较明显的变化,在给定的侧枪支数和侧吹气量下,相邻两枪间夹角越大,侧枪所夹的扇形区域的总面积越大,气液两相区所占面积越大,各股气体射流间的相互作用减弱,相应的能耗减少,气体射流对熔池的搅拌越均匀。根据上述结论,对宝山钢铁股份有限公司不锈钢分公司120 t侧顶复吹AOD转炉炉壳作了技术改造,并进行了工业性实验,证实上述结论是可靠的、可信的和正确的。本工业性实验条件下,采用7枪、22.5°代替7枪、18°的侧枪配置可使120 t侧顶复吹AOD转炉的炉龄大幅度提高,并可使精炼过程的各项技术经济指标有较大幅度的提高。更多还原

【Abstract】 The fundamentals and developments of argon-oxygen decarburization(AOD) refining process of stainless steel have briefly been introduced.The available studies in the literature on physical and mathematical modeling of the refining process have been analyzed and reviewed.Taken a 120 t side and top combined blowing AOD converter in the Stainless Steel Branch,Baoshan Iron & Steel Co.,Ltd.as a prototype,a water model with a geometric similarity ratio of 1:4 to its prototype has been designed and established. With the blowing process of the main decarburization period of the side and top blowing refining of 304 type stainless steel in the AOD converter as an object,the friction factors of the main tuyeres and sub-tuyeres used for the prototype and its model to gas stream have been determined;and the theoretical calculations of the parameters of the gas streams in the annular side tuyeres as well as the top Laval top lance have been carried out;then,the gas flow rates of the side and top blowing used for the model have more reasonably been evaluated;thus,fuller kinematic similarity between the model and its prototype has been ensured.Water modeling has been employed to investigate the features of gas jet stirring, the fluid flow patterns,the stability of liquid surface,the characteristics of liquid flow and mixing,and the "back-attack" phenomenon of the gas jets through side tuyeres and its effects on the erosion and wear of the refractory lining in the bath of an AOD converter during the side and top combined blowing process.The influence of the gas flow rate for side blowing and the side tuyere number,the angle included between each tuyere and the gas flow rate of top blowing and others has been examined.It was shown that the liquid in the bath underwent vigorous stirring and circulatory motion during the blowing,and there was no obvious dead zone in the bath,leading to excellent mixing and a short mixing time.The gas flow rates of side tuyeres, particularly those of the main tuyeres,had a key role on the fluid flow and mixing characteristics.However,the gas jets of the sub-tuyere could give a physical shielding effect on the gas jets of the main tuyeres,and the mixing efficiency could be improved by a suitable increase in the gas blowing rate of the sub-tuyere.The gas jet from the top lance could change the agitation and fluid flow pattern caused by the gas jets from the side tuyeres in the bath,making the turbulent intensity increase and the mixing efficiency decrease,thus,the mixing time prolong.The larger the gas flow rate of the top lance,the more obvious these conditions.With a given number and flow rate of the side tuyeres,a larger angular separation between each tuyere would be benefit for improving the stirring efficiency of gas streams in the bath,so the mixing time would be shortened.Under a given angle included between each tuyere and flow rate of the side tuyeres,increasing the number of side tuyere would not necessarily enable to reach a similar effectiveness,but with a decreased gas flow rate of each side tuyere, thus reducing the horizontal penetration distance of gas jets from side tuyere and making the high temperature zone move towards and closer to the vessel wall,leading to decreasing the life of the refractory lining.As far as only the mixing in the bath is concerned,comprehensively considering the influence of the gas flow rate of side blowing,the side tuyere number,the angle between each tuyere and the gas flow rate of top blowing,using 6 side tuyeres with an angle of 27°included between each tuyere would all bring about a roughly equivalent mixing effectiveness,corresponding to an oxygen flow rate of 6600 Nm~3/h for the top blowing specified by the technology. For an angle of 18°separation between each tuyere utilized in the existing practice, using 7,6 or 5 side tuyeres would all be able to provide a good mixing result.Compared to the situation in a simple side blowing or bottom blowing,the back-attack phenomenon of the submerged horizontal gas jets under the conditions of the side and top combined blowing process had its own features.At the conditions,the gas streams of the main tuyere plaid a dominant role on the back-attack phenomenon of the gas jets horizontally submerged blowing,and the sub-tuyere streams showed an obvious alleviation and prevention effect to it.The top stream would make the back-attack action of the side blowing streams more uniform and the action intensity (pressure) enhance.With a side and top combined blowing,the circulation motion of the liquid in the bath would also be another important reason for causing the back-attack;the buoyancy has a considerable influence,it is not only able to increase the back-attack intensity of a horizontal gas jet,but also to enlarge the locally eroded and worn zone of the refractory lining.Compared with the situation of a simple side blowing,the buoyancy in a side and top combined blowing could lower the increased amplitude of the back-attack intensity of a horizontally submerged blowing jet,but an interaction with the impinge force from the top blowing jet would make the acting area of the back-attack force,i.e.the eroded and worn zone of the refractory lining larger.With the given side tuyere number and flow rates of the top and side blowing in the present work,a proper increase of the angle included between each tuyere in the range of 18°-27°would be beneficial to alleviating the back-attack action of the side blowing stream.Relatively,at the given side and top gas flow rates,the combination of 7 side tuyeres with an angle separation of 22.5°,or 6 side tuyeres with an angle of 27°for both simple side blowing and side and top combined blowing would all be able to cause a less erosion extent of the refractory lining than other arrangement schemes.Based on the two-fluid(Eulerian-Eulerian) model for a gas-liquid two-phase flow and the modified k-εmodel for turbulent flow,a three-dimensional mathematical model for the flow of molten steel in the bath of an AOD converter under the conditions of a simple side blowing has been proposed and developed.The related parameters of the model have been determined.With considering a heating and friction flow of gas and on the basis of the theoretical calculations of the parameters of the gas streams in the annular side tuyeres and the estimations for heat transfer between the gas jets and the molten steel,the inlet boundary conditions used for the mathematical model were more reasonably predicted.The fluid flow fields in the 120 t side and top combined blowing AOD converter and its water model unit with a linear scale ratio of 1/4 linear scale ratio have been computed by using of this model, respectively.The influences of the side tuyere number,and the angle included between each tuyere were examined.The results indicated that the flow pattern of molten steel in the bath of AOD converter during a simple side blowing process could be well modeled by the model.The liquid in the bath underwent vigorous stirring and circulation motion during the blowing,and there was no obvious dead zone in the bath. Changing the number of side tuyere could not alter the essential characteristics of gas stirring and fluid flow,neither the distributions of turbulent kinetic energy and gas holdups.However,with a given angle separation between each tuyere and gas flow rate of side tuyere,decreasing the number of side tuyere could make the agitating intensity increase,thus bringing about the local variation of the flow field,and the distributions of turbulent kinetic energy and gas holdups were more uniform by using the arrangement scheme of 6 side tuyeres with an angle of 27°between each tuyere than by using 7 side tuyeres with 18°or 22.5°.At a given tyuere number and side gas flow rate,a larger angular separation between each tyuere could also not change the basic characteristics of gas agitation and fluid flow,but the flow field would have some evident differences from each other.In the range of 18°-27°,the larger the angle included between each tuyere,the large the total sector area between the tuyeres,and the larger the area occupied by the plume at the surface of the bath,thus making the interaction among the gas jets weaken,and the related energy dissipation reduce,so the gas agitation would be more homogeneous.Compared with the situation in a simple side blowing AOD converter,the flow field under the conditions of the side and top blowing had the different features,which would be attributed to a combined effect of the both blowing processes.On this consideration,a three-dimensional mathematical model for the flow of molten steel in the AOD converter bath during the simple top blowing process had been proposed and developed.And the flow fields and turbulent kinetic energy of liquid phases in the 120 t AOD converter and its water model unit under the conditions of simple top blowing had been computed using this model.Then,the flow field of side and top combined blowing could be obtained from the superposition of flow fields of the simple side blowing and simple top one.The results demonstrated that the liquid flow in the bath of the AOD converter with the side and top blowing was in combining resulted from the side blowing streams under the influence of the top blowing jet.The liquid in the bath underwent vigorous stirring and circulatory motion during the combined blowing, and there was also no obvious dead zone in the bath.The top lance injection did not change the essential features of the liquid agitation and fluid flow,compared with the situations in a simple side blowing AOD converter,but evidently changed the local flow field in the bath.Similarly,under the conditions of the combined blowing,the change of the number of side tuyeres did not alter the basic features of the gas stirring, fluid flow and the distribution pattern of turbulent kinetic energy.And with a given angle between each tuyere and side tuyere blowing rate,the agitating intensity would be increased with decreasing of the side tuyere number,thus the flow field and the distribution of turbulent kinetic energy would be locally changed.Using 6 side tuyeres with an angle of 27°would give more effective stirring than using 7 side tuyeres with an angle of 18°or 22.5°;this is the same as that of the simple side blowing.And similarly,for a given number and gas flow rate of side tyueres,a larger angular separation between each tyuere would not change the characteristic patterns of the gas stirring and fluid flow,but change obviously the characteristics of gas agitation and flow field,but the flow field would have some more obvious discrepancies.In the range of 18°-27°,the larger the angle between each tuyere,the larger the total sector area between tuyeres,and the larger the area occupied by the plume at the surface of the bath,thus making the interaction between gas jets decrease,and the relevant energy dissipation reduce,the gas stirring would be moreAccording to the results mentioned above,the shell of the 120 t AOD converter has technically been reformed and the industrial experiments have been carried out. The conclusions given above have been confirmed to be entirely reliable,believable and correct.Under the conditions of the industrial experiments,using 7 side tuyeres with 22.5°to replace the arrangement scheme of 7 tuyeres with 18°could make the life of the refractory lining of the converter obviously increase,and the economic and technical indications of the refining process raise with larger amplitude.更多还原