Accretion growth on single-pipe tuyeres: Part II. Model results and discussion

A mathematical model of accretion growth on single-pipe injectors has been used to analyze the process of accretion growth during copper converting and inert gas stirring of steel. A sen-sitivity analysis of the model developed in Part I of this article revealed that the critical unknown factor controlling the growth process is the local bath velocity. It is likely that the asymmetric forms seen in accretions are due primarily to nonuniformity in bath flow around the accretion. The important factors controlling the size of accretions in copper converting are bath superheat, gas flow rate, and oxygen content. Blockage of the tuyeres in the converter is a function of wall and bath superheat and likely is a result of the freezing of matte in the pipe. The effect of gas-flow rate on accretion size is clearly shown in the case of inert gas injection into steel. The transition between the different accretion types found on single-pipe tuyeres, pipes, porous pipes, and hemispheres, depends on events at the tuyere-pipe tip. Conditions of high back-attack frequency, low superheat, and small tuyere diameters tend to lead to accretions forming over the tip. If this takes place at high injection pressures and with a relatively ductile material, a “porous plug” will form, on which a hemisphere will grow. Under other conditions, it may result in a blockage. The presence of accretions at a tuyere has a strong influence on the thermal profile in the surrounding refractory and tuyere pipe. Steep thermal gradients near the tip in both regions will likely lead to refractory deterioration and pipe distortion. Formerly Associate Professor, University of British Columbia, Vancouver.     

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     

Accretion growth on single-pipe tuyeres: Part I. Model development and preliminary analysis

A mathematical model of the growth of accretions on submerged single pipes has been developed based on the heat transfer in the vicinity of the injection point. The model is able to predict the formation of either pipe or hemispherical accretions based only on the input con-ditions. It is assumed that a hemispherical accretion is formed only when a porous plug is formed within the tuyere tip by the freezing of bath material during regular penetration episodes. Gas flow within the bath is calculated from physical modeling results, and allowances are made for the possibility of a gas/bath reaction. A preliminary analysis of the model predictions for copper converter and steel ladle stirring applications has been carried out. The model predicts that, under normal operating conditions, the accretions formed in copper converters are very small but can become appreciable under low superheat conditions. The time required to reach steady state depends upon the final accretion length but can be as much as 5 minutes. In ladle stirring applications, the model predicts that the accretion formed will be approximately 4.5-cm high with a slightly larger basal radius. This accretion requires approximately 10 minutes to reach steady state. The final shape and size of an accretion are dependent upon the balance of heat flows around it, with steady state occurring when heat inputs to the accretion exactly equal heat outputs. Formerly Associate Professor, University of British Columbia, Vancouver.     

Flow regimes in submerged gas injection

The behavior of gas discharging into a liquid has been investigated in the labora-tory and in plant. The laboratory work has involved the injection of different gases from a submerged, horizontal tuyere into water, zinc-chloride solution, and a mercury bath. High speed cinematography and pressure measurements in the tuyere have been carried out to characterize the flow regimes. In the case of the mercury bath, a novel “half-tuyere” has been developed to permit visual observation of the gas. In this way, two regimes of flow, bubbling and steady jetting, have been delineated as a function of the modified Froude number and the ratio of gas to liquid densities. Pressure measurements at the tuyere tip have been correlated to the different stages of bubble growth in the bubbling regime, and can be used to distinguish one flow regime from the other. The measured bubble frequency and volume correspond reasonably well to predictions of a simple model of bubble growth under conditions of constant flow. The forward penetration of the jet centerline from the tuyere tip has been measured and found to depend both onN _Fr′ andρg/ρl. In the industrial tests, pressure taps have been installed in the tuyeres of a nickel converter to monitor the pressure wave of the jets under normal, low pressure blowing operations. The measurements show that the converter jets operate in the bubbling mode with a bubble frequency of 10 to 12 s⁻¹, similar to a gas jet in mercury. Tests involving higher pressure injection indicate that the steady jetting, or underexpanded, regime obtains at pressures of about 340 kPa (50 psi). Based on equivalent experiments in the laboratory, it is clear that low pressure blowing has the disadvantage of poor penetration of air into the bath so that the jets rise close to the back wall and locally accelerate refractory wear. Moreover between the formation of successive bubbles, the bath washes against the tuyere mouth and contributes to accretion formation. This necessitates periodic punching of the tuyeres which also contributes to refractory wear at the tuyere line. The use of high pressure injection to achieve steady jetting conditions, as currently practiced in the new bottom blown steelmaking processes, should be considered to solve these prob-lems, and possibly usher in a new generation of nonferrous converters.     

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     

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     

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.     

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

The 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°.     

Bubble overlap in multipoint gas-injection systems

Factors affecting bubble overlap (interaction) in multipoint (multituyere/lance) gas-injection systems such as the Pierce-Smith converter and the zinc-fuming furnace have been investigated in laboratory room-temperature modeling experiments and at the industrial scale. Pressure changes have been recorded simultaneously from adjacent tuyeres both in the laboratory and in plant trials. It has been found that the factors which influence bubble overlap include the tuyere separation to tuyere diameter ratio, gas injection velocity, gas and liquid properties, and position and orientation of the tuyeres.     

Computational Fluid Dynamic Modeling of Zinc Slag Fuming Process in Top-Submerged Lance Smelting Furnace

Slag fuming is a reductive treatment process for molten zinciferous slags for extracting zinc in the form of metal vapor by injecting or adding a reductant source such as pulverized coal or lump coal and natural gas. A computational fluid dynamic (CFD) model was developed to study the zinc slag fuming process from imperial smelting furnace (ISF) slag in a top-submerged lance furnace and to investigate the details of fluid flow, reaction kinetics, and heat transfer in the furnace. The model integrates combustion phenomena 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 a number of user-defined subroutines in FORTRAN programming language were used to develop the model. The model is based on three-dimensional (3-D) Eulerian multiphase flow approach, and it predicts the velocity and temperature field of the molten slag bath, generated turbulence, and vortex and plume shape at the lance tip. The model also predicts the mass fractions of slag and gaseous components inside the furnace. The model predicted that the percent of ZnO in the slag bath decreases linearly with time and is consistent broadly with the experimental data. The zinc fuming rate from the slag bath predicted by the model was validated through macrostep validation process against the experimental study of Waladan et al. The model results predicted that the rate of ZnO reduction is controlled by the mass transfer of ZnO from the bulk slag to slag–gas interface and rate of gas-carbon reaction for the specified simulation time studied. Although the model is based on zinc slag fuming, the basic approach could be expanded or applied for the CFD analysis of analogous systems.     

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.     

High-pressure injection of air into a peirce-smith copper converter

Plant trials have been conducted at the Tacoma Smelter of ASARCO to assess the effect on tuyere blockage and refractory erosion at the tuyere line, of increasing the injection pressure of air into a Peirce-Smith converter. Four tuyeres each having an ID of 19.1 mm (0.75 inch) were installed toward one end of the tuyere line of the No. 4 converter. Air and oxygen-enriched air were injected at 414 kPag (60 psig) through these tuyeres and at the usual 83 kPag (12 psig) through the remainder of the tuyeres in an otherwise normal converter campaign. The test campaign consisted of 88 charges and lasted for 89 days. During this period, punching of the high-pressure tuyeres was found to be unnecessary; and when, as a precaution, the tuyeres were cleaned by hand at the end of a charge, they were always open. Also, it was observed that the flow of high-pressure air remained constant. Accretion formation around the tip of the high-pressure tuyeres varied from charge to charge and was influenced by the matte grade and the level of oxygen enrichment.     

关于高炉风口面积调节方法的探讨

通过建立高炉送风系统模型,模拟了风口尺寸对风口速度、流量和鼓风动能的影响,纠正了高炉操作认识上的一些错误。研究表明,缩小少数几个风口面积会减小鼓风动能,但却增大了其它风口的鼓风动能;只有减小多个风口的面积,才会增大所有风口的鼓风动能。减小少数几个风口的操作之所以能抑止边缘气流是其风量明显减少所致。     

关于高炉风口面积调节方法的探讨

通过建立高炉送风系统模型,模拟了风口尺寸对风口速度、流量和鼓风动能的影响,纠正了高炉操作认识上的一些错误。研究表明,缩小少数几个风口面积会减小鼓风动能,但却增大了其它风口的鼓风动能;只有减小多个风口的面积,才会增大所有风口的鼓风动能。减小少数几个风口的操作之所以能抑止边缘气流是其风量明显减少所致。     

Improvement in prolonging AOD refractory lining life in Baosteel

A series of improvements in prolonging the AOD refractory lining life in Baosteel are introduced and analyzed in this paper,including modification of the AOD shell shape,adjustment of the top slag components and selection of the side-blowing tuyeres. Firstly,the layout of side-blow tuyeres was altered with the angle between each two tuyeres being 22.5° instead of the original 18°,and the connection of the outside steel shell in the side-blow area was modified from the former platform shape with great stress concentration into a new smooth circle shape. Secondly,the slag components were changed from the former CaO-FeO-SiO2 system to the CaO-MgO-SiO2 system. Besides,the basicity of the top slag was kept higher than 1.8,and the MgO content in the slag was kept within the range of 8%-12%. Finally,tuyeres with an inner diameter 13% smaller than that of the original tuyeres were used. Based on these research and optimization work,the thermodynamics and kinetics in the AOD refining bath has been improved markedly,and the campaign of the AOD has been prolonged from 45 heats at the beginning of its start-up to the current 185 heats. Meanwhile,the yield of chromium alloy and the decarburization efficiency have also been improved.     

铜富氧侧吹熔池熔炼的生产实践

根据奥斯麦特炉、艾萨炉、三菱炉的熔炼炉渣的化学成分,确定了富氧侧吹熔池熔炼炉渣的化学成分。富氧侧吹熔池熔炼炉投产过程中出现的问题主要有:烟气中单体硫含量高、炉体和余热锅炉振动较大、余热锅炉上升段和辐射区炉结较重、烟气产生冷凝酸、烟尘量较大降低了铜直收率和铜回收率。经过两年的改进,日处理铜精矿量、粗铜日产量、电单耗、煤单耗、综合能耗和生产成本均达到设计要求。     

Simulation of tuyere–raceway system in blast furnace

Abstract

A uniform distribution of the blast is an important prerequisite of a balanced blast furnace operation, because the blast is the main source of the hot gases that are needed to preheat, reduce and melt iron ores. The supply of hot gas from the raceways is not necessarily uniform along the furnace periphery, but depends on flow resistances encountered on the individual bustle main tuyere–raceway–raceway boundary routes. A model for this system has been developed in order to study and analyse the effects of changes in tuyere parameters and boundary conditions. Variables such as the total blast volume, blast pressure, tuyere diameter and the combustion degree of injected reductants in the tuyeres can be studied. An online version of the model has also been developed to track how the conditions on the tuyere level change with time in operating blast furnaces.     

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.     

Tuyere failure analysis in Corex process

Abstract

Corex is an alternative smelting reduction ironmaking process where non-coking coal and pure oxygen is used instead of coke and air. The temperature of the tuyere region is much higher than in a blast furnace, and sustainability of tuyeres is a major challenge. At JSW Steel Ltd, almost 15% of the total shutdown is due to burnt tuyere replacement. A detailed analysis of tuyere failure and process parameters effecting tuyere burning was conducted to understand the failure mechanism and the root causes. A common reason does not exist for all types of tuyere failure; however, the collective reasons for failure are excessive coal fines (–6·3 mm) and small mean particle size, low back pressure, blocking of tuyeres, scab formation and slip.     

Hydrodynamics and optimization of bottom-tuyere parameters for steel injection in the intermediate ladle

Physical simulation of steel injection in the intermediate ladle of a continuous slab-casting machine permits the determination of the supply channels for the bottom tuyere such that bubble injection of the metal extends over the whole bath depth in the intermediate ladle and the gas bubbles reliably pass through the slag coating layer. Practical results are presented for the proposed tuyere.