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. Formerly Graduate Student     

Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace

A thin-slice computational fluid dynamics (CFD) model of a conventional tuyere blown slag-fuming furnace has been developed in Eulerian multiphase flow approach by employing a three-dimensional (3-D) hybrid unstructured orthographic grid system. The model considers a thin slice of the conventional tuyere blown slag-fuming furnace to investigate details of fluid flow, submerged coal combustion dynamics, coal use behavior, jet penetration behavior, bath interaction conditions, and generation of turbulence in the bath. The model was developed by coupling the CFD with the kinetics equations developed by Richards et al. for a zinc-fuming furnace. The model integrates submerged coal combustion at the tuyere tip and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with several user-defined subroutines in FORTRAN programming language were used to develop the model. The model predicted the velocity, temperature field of the molten slag bath, generated turbulence and vortex, and coal use behavior from the slag bath. The tuyere jet penetration length (l _P) was compared with the equation provided by Hoefele and Brimacombe from isothermal experimental work $ \left( {\frac{{l_{\text{P}} }}{{d_{o} }} = 10.7\left( {N^{\prime }_{Fr} } \right)^{0.46} \left( {\rho_{\text{g}} /\rho_{l} } \right)^{0.35} } \right) $ and found 2.26?times higher, which can be attributed to coal combustion and gas expansion at a high temperature. The jet expansion angle measured for the slag system studied is 85?deg for the specific inlet conditions during the simulation time studied. The highest coal penetration distance was found to be l/L?=?0.2, where l is the distance from the tuyere tip along the center line and L is the total length (2.44?m) of the modeled furnace. The model also predicted that 10?pct of the injected coal bypasses the tuyere gas stream uncombusted and carried to the free surface by the tuyere gas stream, which contributes to zinc oxide reduction near the free surface.     

Kinetics of the zinc slag-Fuming Process: part II. mathematical model

A mathematical model of zinc slag fuming has been formulated based on the kinetic conception of the process developed in Part I of this paper. Each of the major reaction zones in the furnace — the slag bath where reduction of zinc oxide and ferric oxide takes place and the tuyere gas column where oxidation of coal and ferrous oxide occurs — have been characterized mathematically. The two zones and the water-jacketed furnace wall have been linked by overall heat and mass balances. Insufficient information is available, however, to characterize quantitatively two of the important kinetic processes occurring in the furnace: the division of coal between entrainment in the slag, combustion in the tuyere gas column and bypass; and oxygen utilization. To overcome this problem the model has been fitted to the data from eleven industrial fuming cycles. Consistent values have been obtained for these kinetic parameters over five different fuming operations indicating that the kinetic conception of the process is sound. The results indicate that about 33 pct of the injected coal is entrained in the slag, 55 pet combusts in the tuyere gas column, and 12 pct bypasses the bath completely. Oxygen utilization has been found to be high and can be correlated to bath depth. Formerly Graduate Student     

Simulation of Flow Fluid in the BOF Steelmaking Process

The basic oxygen furnace (BOF) smelting process consists of different chemical reactions among oxygen, slag, and molten steel, which engenders a vigorous stirring process to promote slagging, dephosphorization, decarbonization, heating of molten steel, and homogenization of steel composition and temperature. Therefore, the oxygen flow rate, lance height, and slag thickness vary during the smelting process. This simulation demonstrated a three-dimensional mathematical model for a 100 t converter applying four-hole supersonic oxygen lance and simulated the effect of oxygen flow rate, lance height, and slag thickness on the flow of molten bath. It is found that as the oxygen flow rate increases, the impact area and depth increases, which increases the flow speed in the molten bath and decreases the area of dead zone. Low oxygen lance height benefits the increase of impact depth and accelerates the flow speed of liquid steel on the surface of the bath, while high oxygen lance height benefits the increase of impact area, thereafter enhances the uniform distribution of radial velocity in the molten steel and increases the flow velocity of molten steel at the bottom of furnace hearth. As the slag thickness increases, the diameter of impinging cavity on the slag and steel surface decreases. The radial velocity of liquid steel in the molten bath is well distributed when the jet flow impact on the slag layer increases.     

Kinetics of the zinc slag-Fuming process: Part i. industrial measurements

A study involving industrial measurements and mathematical modeling has been conducted to eluci-date kinetic phenomena in the zinc slag fuming process. In the first part of this three-part paper, the results of industrial measurements and observations are presented. In Part II a mathematical model of the process is developed, and finally in Part III the implications of a kinetic conception of the process for process improvement are explored. The industrial work consisted primarily of slag sampling through the fuming cycles of five different fuming operations. In addition, tuyere back-pressure mea-surements, tuyere photography using a tuyerescope, and sampling of the fume product were under-taken at one operation. Analysis of the slag samples has shown that, in general, the zinc elimination curve is linear with time and that a portion of the injected coal entrains in the slag. Analysis of tuyere back-pressure fluctuations and movie photographs of the tuyere tip indicate that the coal-air mixture enters the slag in the form of discrete bubbles. From these results it can be deduced that the fuming furnace consists of two reaction zones which are created by the division of coal between the slag and the tuyere gas stream. The coal entrained in the slag reduces ZnO and Fe₃O₄ in a “reduction zone” which is responsible for fuming. The coal remaining in the tuyere gas stream combusts in an “oxidation zone” although a fraction passes through the bath unconsumed and reports to the solid products. The oxidation zone supplies heat to the endothermic reduction reactions and heat losses. Formerly Graduate Student     

Modeling of an Impinging Oxygen Jet on Molten Bath Surface in 150 t EAF

 A transient three-dimensional mathematical model has been developed to analyze the three-phase flow in a 150 t EAF (electric arc furnace) using oxygen. VOF (multiphase volume of fluid) method is used to simulate the behaviors of molten steel and slag. Numerical simulation was conducted to clarify the transient phenomena of oxygen impingement on molten bath. When oxygen jet impinges on the surface of molten bath, the slag layer is broken and the penetrated cavity in molten steel is created. Simultaneously, the wave is formed at the surface of uncovered steel on which the slag layer is pushed away by jet. The result of numerical simulations shows that the area and velocity of uncovered steel created by impingement, jet penetration depth change from 0.10 m2, 0.0125 m/s, 3.58 cm to 0.72 m2, 0.1445 m/s, 11.21 cm, when the flow rate of an oxygen lance varies from 500 to 2000 m3/h. The results have been validated against water model experiments. More specially, the relation between the penetration depth and oxygen flow rate predicted by numerical simulation has been found to agree well with that concluded by water model.     

粉煤固定碳含量对烟化炉冶炼指标的影响

模拟烟化炉实际生产过程,采用冶金计算法研究粉煤固定碳含量对烟化炉冶炼煤耗、氧化锌烟尘质量及水淬渣质量的影响。结果表明,当粉煤固定碳含量从45%提高到55%时,烟尘中锌、锗含量从40.58%、459g/t提高到48.00%、543g/t,水淬渣锌含量由2.25%降至1.38%,吨锌粉煤单耗从4.64t降到3.80t。计算数据与生产数据对比,确定固定碳含量不低于55%为较经济的冶炼控制点。     

Heat-transfer phenomena in water-cooled zinc-fuming furnace jackets

In the zinc slag-fuming process, zinc is removed from lead blast furnace slag by reduction with a coal-air mixture injected into the slag through submerged tuyeres. The furnace is constructed of water-cooled jackets which freeze a slag layer and contain the bath. This greatly reduces vessel wear caused by the violently agitated and corrosive bath. The jackets, however, fail due to the formation of cracks which grow from the slag face through the working face of the jacket to the water channel. In this study, in-plant measurements and mathematical modeling of heat transfer in the jackets have been combined to elucidate the mechanism of failure. The working face of a water jacket was instrumented with thermocouples and installed in a fuming furnace at the Trail smelter of Cominco Ltd., Trail, BC. Measurements revealed the presence of large thermal transients or temperature “spikes” in the panel in the region immediately above the tuyeres. These were generally observed during charging and tapping of the furnace and are likely associated with disturbances on the surface of the bath or gas injection effects when the liquid level is low. Temperatures at the midthickness were seen to rise by as much as 180 °C above the steady-state level. Under these conditions, low-cycle fatigue may lead to crack formation and propagation. A mathematical modeling analysis of the transient freezing phenomena indicates that the temperature spikes are associated with sudden slag falloff and direct contact of molten slag on the jacket. In order to reduce slag falloff, an increased number of anchoring fins should be used in critical areas.     

High-pressure coal injection in zinc slag fuming

Previous work has shown zinc slag fuming to be kinetically controlled by two basic processes: the rate of coal entrainment in the slag and the rate of oxidation of ferrous to ferric iron in the slag. In the present study, industrial trials and mathematical modeling analysis were undertaken to assess the efficacy of increased coal entrainment on zinc fuming rates. Various systems for increasing coal entrainment were assessed before a high-pressure, high-loading pneumatic system was selected for the tests. Three trials were conducted at the lead smelter of Cominco Ltd. in Trail, BC, under three different charge conditions. In each case, the regular low-pressure coal was cut back during high-pressure injection so that the total coal and air flow rates to the furnace were virtually unchanged. Analysis with the mathematical model showed that highpressure injection increased coal entrainment from about 25 pct, characteristic of low-pressure injection, to 65 to 90 pct. As a result, fuming rates were increased substantially, to between 70 and 90 pct, depending on the charge mix. Since the overall coal rate was unchanged, this also meant a corresponding increase in the amount of zinc fumed per unit of coal injected. These results are an important verification of the kinetics model and represent a potentially significant advance in the technology of slag reduction. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

基于VB的铅锌渣处理热力计算程序的开发与应用

利用VB平台,针对当前铅锌渣的处理状况,开发了一种适用于烟化炉烟化法处理铅锌冶炼渣的热力计算程序。文中重点介绍了该热力计算程序的功能要点、界面设计与核心计算模块,并以某企业烟化炉工业试验为基础,计算验证了该程序的可靠性与准确性,同时根据计算结果分析了生产能耗、生产炉时等,发现富氧吹炼生产可以大幅降低烟化炉生产能耗,提高烟化炉生产效率。     

锌渣烟化炉连续吹炼生产氧化锌研究

对该项目的主要研究情况进行了介绍,并对试验过程进行了一定的探讨。烟化炉连续吹炼生产氧化锌是一种锌渣处理的新的工艺方法,具有工艺流程短,降低能耗,改善作业环境,降低加工成本的优势,具备较高的应用推广价值。     

基于熔池混匀度的转炉烟气分析定碳模型

转炉冶炼终点碳曲线拟合模型避开了熔池初始碳含量难以精准确定的问题,假设吹炼后期脱碳速率与熔池碳含量具有一定的函数关系,通过这种函数关系预报钢水终点碳含量.终点碳的三次方模型和指数模型预报精度在±0.02%之间的命中率分别为85.9%和81.2%.运用熔渣分子理论,基于冶炼热轧板材(SPHC)的渣组元成分,计算得出渣中FeO的活度为0.241.出钢温度为1686℃时,C和Fe元素选择性氧化的临界碳质量分数为0.033%.本文在传统指数模型的基础上,充分考虑了枪位、顶吹流量、底吹流量等操作参数对熔池脱碳速率的影响,建立了基于熔池混匀度的指数模型.基于熔池混匀度的指数模型与其他烟气分析碳曲线拟合模型相比,命中率有所提高.以新钢生产热轧板材(目标碳质量分数为0.06%)时的烟气数据为研究对象建模,终点碳质量分数预报误差在±0.02%之间的有75炉次,占验证数据量的88.2%.      

提高烟化炉处理铅锌冶炼渣能力的实践

某铅锌冶炼厂通过烟化炉处理铅锌冶炼渣回收有价金属,由于烟化炉采用的钢制冷却水套使用寿命短,导致作业率偏低。同时,由于烟化炉冶炼渣的SiO₂含量高,烟化炉经常出现炉渣流动性恶化而影响作业率。随着该冶炼厂渣物料产量的增加,烟化炉能力不足的问题逐渐凸显,急需提升作业率和炉床能力。通过系统研究,对烟化炉的工艺和设备进行优化改造,烟化炉的实际作业率从改造前的85.01%提高到96.48%,床能力提高3.9 t/(m²·d),达到21～22 t/(m²·d)。     

压密锌渣烟化炉连续吹炼的工业试验

文章主要描述了烟化炉在没有热源的情况下压密锌渣连续吹炼的工业试验情况，探讨了压密锌渣烟化炉全冷料连续吹炼的可行性和经济性，为烟化炉处理湿法锌渣开辟了新的途径。     

转炉超音速氧枪喷头磨损后的吹炼特性变化

 转炉氧枪喷头会随枪龄的增加发生不同程度的侵蚀,为了探究氧枪喷头侵蚀程度对超音速气体射流吹炼特性的影响,建立了120 t转炉及超音速氧枪的三维全尺寸几何模型,研究了氧枪喷头不同磨损角度对气体射流特性、熔池速度及壁面侵蚀的影响。发现随着磨损角度增加,射流速度衰减加快,射流核心区长度缩短,同一等速线长度缩短,射流中心最大速度和最大速度点距中心距离增大。射流动压衰减速度随磨损角度增加而加快,磨损角度由0增至20°,距喷头端面1.5 m处最大动压减小了14.84%,14 000 Pa等压线包围面积由0.038 m2减小至0.002 m2。钢液面处高速区面积随着磨损角度增加而减小,死区面积随着磨损角度增加而增大。熔池纵截面高速区域主要分布在冲击凹坑和底吹元件附近,低速区域主要分布在熔池底部,死区主要分布在熔池底部中心和炉壁下部区域。当熔池深度小于0.6 m时,顶吹气流对熔池的搅拌起主要作用,磨损角度增加,熔池搅拌能力变弱,熔池横截面高速区面积减小,低速区和死区面积增大;当熔池深度大于0.6 m时,底吹气流对熔池搅拌起主要作用,高速区面积基本不变。渣-金作用区域和底吹流股附近流体湍动能较大、壁面剪切应力较为集中,该部位耐火材料侵蚀严重。熔池壁面附近流体湍动能和壁面剪切力随磨损角度增加而降低,转炉炉衬侵蚀速度减小。     

菲尔普斯道奇迈阿密公司铜冶炼厂艾萨炉的操作

在菲尔普斯道奇迈阿密铜冶炼厂 ,艾萨炉是初炼装置 ,向电沉淀炉提供冰铜和炉渣的混合物。艾萨技术包括通过喷枪向熔池喷吹一定量的空气和氧气 ,同时向熔池内加入精矿、熔剂和返料。炉内物理和化学状况和综合熔炼效率在很大程度上取决于喷枪的性能。冶炼厂最近的研究表明提高喷枪的利用率给艾萨炉产量带来显著的影响。本文分析了喷枪故障并对影响艾萨炉性能的因素做一般介绍。     

烟化法处理铅锌冶炼渣的生产实践与探讨

铅锌冶炼渣含有锌、铅、银、锗等有价金属,且属重金属危废物。根据锌浸出渣和铅还原渣的特性,将固态锌浸出渣与液态铅还原渣按配比混合烟化处理。该技术应用实践表明：铅锌冶炼渣通过烟化炉搭配处理,具有生产效率高、资源利用率高、节能环保等优点。既能有效回收铅锌冶炼渣中的有价金属,又实现了铅锌冶炼渣的无害化处理。     

转炉炼钢氧枪枪位控制

在转炉炼钢中,氧枪枪位直接关系到造渣、脱碳、升温及冶炼过程的平稳进行。采用ＴＳ确定性模糊推理,基于声强与渣高成反比的原理,对氧枪枪位进行连续调节,并采用自学习技术确定每一炉各个阶段氧枪的基本枪位,从而克服了固定枪位吹炼无法及时适应炉况及炼钢原材料化学成分变化的缺点,使氧枪枪位在整个炉役期都能处于最优的位置。     

Preliminary Investigation of Mathematical Modeling of Stainless Steelmaking in an AOD Converter: Mathematical Model of the Process

Mathematical modeling of stainless steelmaking in an AOD (argon‐oxygen decarburisation) converter with side and top combined blowing has been preliminarily investigated. The actual situations of the side and top combined blowing AOD process were analysed. A mathematical model for the whole refining process of stainless steel has been proposed and developed. The model is based on the assumption that one part of the oxygen blown through a top lance reacts with CO escaping from the bath, another part of the oxygen oxidizes the elements in the molten steel droplets splashed by the oxygen jet, and the remaining oxygen penetrates and dissolves into the molten steel through the pit stroked by the jet. All the oxygen entering into the bath oxidizes C, Cr, Si, and Mn dissolved in the steel and also the Fe of the steel melt, but the FeO generated is also an oxidant of C, Cr, Si, and Mn in the steel. During the process, all possible oxidation‐reduction reactions occur simultaneously and reach their equilibria, respectively their combined equilibrium, in competition at the liquid/bubble and liquid/slag interfaces. In the simple side blowing after the top blowing operation is finished, the possible reactions take place simultaneously and reach a combined equilibrium in competition at the liquid/bubble interfaces. The overall decarburization rate in the refining process is the sum of the contributions of both the top and side blowing processes. It is also assumed that at high carbon concentrations, the oxidation rates of elements are mainly dependent upon the supplied oxygen rate, and at low carbon contents, the rate of decarburisation is primarily related to the mass transfer of carbon from the molten steel bulk to the interface. It is further assumed that the non‐reacting oxygen blown into the bath does not accumulate in the steel and will escape from the bath and react with CO in the atmosphere above the bath. The study presents calculations of the refining rate and the mass and heat balances of the system for the whole process. Additionally, the influences of the operating factors, including addition of slag materials, scrap, and alloy agents, the non‐isothermal conditions, the changes in the amounts of metal and slag during the whole refining process, and others have all been considered.