Numerical analysis of isothermal flow in lower part of blast furnace considering effect of cohesive zone

Abstract

The increasing interest in minimising fuel consumption and reducing environmental problems of the ironmaking industry has led to efforts to optimise the blast furnace process. One of the undeveloped fields generated from the adoption of new operating conditions is the internal phenomenon in the lower part of the furnace following the change of cohesive zone shape. The effective liquid flow in the dripping zone of a blast furnace is important for stable operation with high iron productivity. Study of the liquid flow behaviour in a packed bed needs to investigate the effect of various operational changes in the dripping zone. As a stepping stone toward the comprehensive modelling which includes chemical reaction and its associated heat transfer, isothermal flow for three phases is simulated with the variation of the shape of cohesive zone to see the effect of charging condition.     

Behaviour of kaolinite coated olivine pellets in blast furnace

Abstract

Production olivine fluxed blast furnace pellets were coated with a water based slurry of kaolinite to give a coating of 5 kg t^-1 pellets. The LKAB experimental blast furnace in Lulea? was used to compare the behaviour of kaolinite coated olivine pellets (MPBO-KA) with that of regular olivine pellets coated with a water spray (MPBO-WA). Blast furnace operation with the kaolinite coated pellets was more stable, with higher productivity and slightly lower reductant consumption, than operation with the normal water coated pellets. In the lower shaft of the furnace, significant quantities of potassium oxide were found to have reacted with the olivine pellets and also with the kaolinite coating.     

Experimentally determined temperatures in blast furnace hearth

Abstract

In this study temperature measurements have been carried out at blast furnace no. 2 at SSAB Oxelösund. The temperature was measured in the hearth lining and at the outer surfaces of the hearth wall and bottom. The lining temperature was measured using permanently installed thermocouples and surface temperatures were measured using a hand held thermocouple. The aims of the study were to find a correlation between lining and surface temperatures as well as to find a method to determine the surface temperature based on readings from lining thermocouples. The overall conclusion is that the bottom and wall surface temperatures can be determined based on lining temperatures.     

Experimental and operational thermal studies on blast furnace cast steel staves

Abstract

The operating conditions of cast steel staves at Masteel blast furnace have been simulated to generate the temperature distribution under different operating conditions. The influence of the temperature and velocity of cooling water as well as the gas temperature of blast furnace on the temperature distribution of the cast steel stave was obtained. The main cause of stave damage is discussed. The result shows that cast steel staves possess better heat transfer ability and a lower temperature distribution field than nodular cast iron staves, but their performance is much less satisfactory than that of copper staves.     

Determination of thermal histories of coke in blast furnace through X-ray analysis

Abstract

A study has been undertaken to identify the source of coke fines sampled from the deadman area of the blast furnace. Using measurements of the coke crystallite dimension L _C, it was established that some of the fines found in the deadman area of a blast furnace were not simply the degradation products of the lump coke in this area. The L _C was measured using standard X-ray analysis techniques. The coke fines had a higher L _C than the coke lump and therefore have experienced a higher maximum temperature than the associated coke lump. This finding has been interpreted as at least some of the coke fines found in the deadman area (lower temperature region) have been blown there from the raceway by the high velocity hot blast.     

Variation in hot metal and slag composition during tapping of blast furnace

Abstract

To determine the quality of the hot metal and the thermal conditions inside the blast furnace, the composition of the hot metal and slag must be known. Obtaining representative metal and slag samples during tapping is thus highly important to blast furnace operation. The study covered in the present report focused on hot metal and slag composition variation during tapping from a commercial blast furnace. From the results, optimal sampling time points for obtaining elemental concentrations that can be taken as representative for the whole tapping sequence were identified. It was furthermore concluded that the reliability of hot metal composition data is significantly improved by averaging elemental concentrations determined from two samples, each taken at a particular time point. One sampling, however, was found to be adequate for slag. Results from the study also showed a fairly strong correlation between amounts of silicon and carbon, sulphur and carbon, and silicon and sulphur in the hot metal, while a weaker correlation between hot metal temperature and each of these elements was observed.     

Formation of potassium slag in olivine fluxed blast furnace pellets

Abstract

Mineralogical evaluation of olivine pellets coated with kaolinite, taken from the LKAB experimental blast furnace, shows significant reactions with potassium. Sampling has revealed strong potassium deposition in pellets in the lower shaft close to the wall, but much less deposition towards the furnace centre. Iron reduction and the deformation of the pellets were enhanced in the zone of high alkali deposition. Thin sections of pellet samples were prepared to distinguish amorphous and crystalline slag phases for a better understanding of the formation of the potassium rich slag. Olivine breaks down to various extents to form a SiO₂–FeO–MgO–K₂O glass. The kaolinite coating shows strong reaction throughout the cross-section of the lower shaft to form kalsilite (KAlSiO₄) and K₂O rich glassy slag. Studies of thin sections of the slag products were shown to be very useful in separating amorphous phases such as the K₂O rich glass from the crystalline olivine rim.     

Mixed burden softening and melting phenomena in blast furnace operation Part 3 – Mechanism of burden interaction and melt exudation phenomenon

Abstract

This research was focused on expanding the current understanding of the mechanism of softening and melting of ferrous materials including liquid exudation and high temperature material interaction. The bulk softening and melting experiments were interrupted at temperatures of interest and samples were examined for morphological changes. The results of these experiments were complimented with viscosity, surface energy and deformation rate calculations which were helpful in understanding the melt exudation phenomenon. The microstructure of the materials showed a transition from heterogeneous to homogenous state with increasing temperatures. The melt dripping was predominantly observed in olivine fluxed pellets. The exuded slag was primarily composed of an alkali rich phase which was found least viscous of the slags present in this system. The viscosity of the liquid and the structure of metallic shell jointly control the flow of liquid from the ferrous materials. Addition of magnesia in lieu of lime was found to provide beneficial impact, in particular on the rate of liquid evolution at high temperature. Based on the metallographic examination of the samples a mechanism of burden interaction is proposed.     

Zinc accumulation during recycling of iron oxide wastes in the blast furnace

Abstract

Byproducts/wastes of iron- and steelmaking processes and steel scrap are the main sources of iron units recycled in the steel plants. Direct recycling of the iron oxide wastes (dusts and sludge) in the blast furnace (BF) is however hampered by its chemistry (>0·1%Zn in the charge). Vaporisation, condensation, oxidation and circulation of zinc may collectively lead to the accumulation in the furnace. Very fine particles are deposited on other particles that have high surface areas which diminish BF refractory life and impair the quality of high quality pig iron produced. For effective continuous recycling of iron units, it is necessary to identify their sources, determine their composition and evolve device and appropriate technology for the treatment of zinc bearing units. The present paper analyses the process of zinc accumulation in the BF and derives an algebraic model to determine the extent of the accumulation. On the basis of analysis of zinc base formation, its recirculation in the furnace and other related productive units, a homograph (alignment chart) of zinc accumulation is designed. The paper also outlines the feasible processes of zinc removal from the close-looped system (sinter plant–BF–sinter plant).     

Effect of coke reactivity and nut coke on blast furnace operation

Abstract

Two measures for coke saving and increase in blast furnace efficiency related to coke characteristics – reactivity and size – are discussed in this paper. Modern blast furnace operation with low coke rate and high injection rate causes a change in coke quality requirements. A discussion has arisen recently about highly reactive coke. Here, a theoretical analysis of influence of coke reactivity on the thermal reserve zone, direct reduction and carbon consumption in the blast furnace has been undertaken. Experiments have been performed using non-standard test scenarios that simulate coke behaviour under real blast furnace operating conditions. Coke reactivity and microstructure have also been investigated under the impact of alkali and pulverised coal ash and char. Operation of many blast furnaces has proved the possibility of coke saving and increase in productivity when using small-sized coke (so-called nut coke) mixed with the burden, but the reasons for this phenomenon, and consequently the limit for nut coke consumption, are still not very clear. An analytical method and cold model simulations have been used to quantify the change in shaft permeability and furnace productivity when using nut coke.     

A static approach towards coke collapse modelling in blast furnace

Abstract

Burden distribution control in a blast furnace has a close relationship with wind acceptance and gas utilisation. Quantification of radial distribution of ore and coke is important for proper control of blast furnace operation. Charging of metallic burden over a layer of coke causes a portion of the coke layer to get dislodged from its original position, similar to the situation observed when a heavy material is dropped on a bed of lighter particles. This phenomenon, designated 'coke collapse', significantly changes the ore/coke distribution in the radial direction and thus affects the permeability of the furnace shaft. In the present work a mathematical model for quantifying the amount of coke collapse has been proposed on the basis of 'stability of slope theory'. The calculation from this model has been compared with the results from experiments in simplified physical models. Predictions of the mathematical model are in good agreement with experimental results.     

Iron ores,fluxes and tuyere injected coals used in the blast furnace

Abstract

Iron ores, fluxes and tuyere injected coals used as burden materials in the blast furnace have been characterised by chemical and granulometric analysis, moisture, density and porosity, softening and melting temperatures, reductibility, X-ray diffraction, electronic microscopy and thermoanalysis. Theoretical calculations on the influence of both the chemical composition and ash content of coals on some aspects of the blast furnace operation have been carried out. The combustion behaviour of pulverised coals in a pilot plant equipped with a combustion chamber has been studied to indicate what the behaviour of each type of coal will be, when injected in blast furnace tuyeres.     

Testing of cement bonded briquettes under laboratory and blast furnace conditions Part 1 – Effect of processing parameters

Abstract

Cement bonded agglomerates made of iron rich byproducts from the iron and steel industry have been used as burden material for blast furnaces for over a decade. In spite of that, their use is restricted to less than 5% of the total burden material, because at higher percentages the blast furnace starts behaving erratically. It is suspected that this is due to the disintegration of the agglomerates under high temperature and reducing conditions. In order to improve the quality of the cement bonded briquettes, the effects of various parameters on their behaviour have been studied. The briquettes have been tested in the laboratory under isothermal test conditions and under simulated blast furnace conditions. The briquettes have also been tested in a pilot blast furnace. This paper describes the effect of different parameters on the performance of briquettes tested under the three conditions.     

Optimal configuration of blast furnace slag runner to reduce fluid flow stresses at wall using mathematical modelling

Abstract

A three-dimensional mathematical model was developed to predict the wall shear stresses due to flow of liquid slag in slag runner of 'G' blast furnace of Tata Steel under different conditions. The liquid slag flow in the slag runner was considered to be turbulent and incompressible. The model was developed for single phase, steady state and isothermal conditions. To this end, the Navier Stokes equations along with continuity and turbulence equations (standard k–? model) were simultaneously solved with appropriate boundary conditions at the associated physical boundaries of the calculation domain. Several configurations were numerically assessed with respect to reduced shear stresses on the wall of the slag runner to select the best one. Due to accelerating flow the operating heights of liquid slag (density 2800 kg m^–3 at 1500°C) within the slag runner for different configurations were estimated with the help of Bernoulli's and continuity equations and fixed before the computation. The different configurations comprised of three segments with different parameters of either elevation or radius of curvature. Relatively high shear stresses were numerically predicted at the joint area of second and third segments of the slag runner for all the configurations. The radius of curvature was found as the dominant factor to reduce the shear stress at the joint region.     

Cold model study of metal droplet descent through fluids including a treatment of the non-Newtonian behaviour as exhibited by molten slag system

Abstract

In the context of several high temperature metallurgical processes including blast furnaces, a cold model study simulating a metal droplet descent through the surrounding fluid system is presented. The study comprises an experimental programme employing wide range of fluids exhibiting both Newtonian and non-Newtonian behaviour. Such fluid systems are encountered in slag–metal droplet systems where viscosity of the slag system has a significant effect on the kinetics of refining reactions. Slag systems generally possess random network structures comprising internal regions of weak ordering and the presence of these regions may result in non-Newtonian behaviour of the slag. As the viscosity of the slag is very sensitive to structure, a treatment of non-Newtonian behaviour as exhibited by some molten slag systems is therefore required. Two parameters have been identified and estimated that help to determine the rheological characteristics of fluids in relation to their network structure. The underlying principle of the model development has been that the external pressure exerts a driving force that affects the motion of the fluid to a degree dependent on the rheological behaviour and the network structure of the fluid. The paper also describes some results of a cold model study of the momentum transfer to the fluid system by correlating the drag Reynolds number with the modified drag coefficient for non-Newtonian fluids

(N*_Rem)^½?n′ = (N _Rem)^½?n′ (1/2C _Dm )^½     

Properties and microstructures of blast furnace carbon refractories with Al additions

Abstract

The effect of Al additions on the properties and microstructures of carbon refractories for blast furnaces was evaluated in terms of phase and microstructure evolutions as a function of the coking temperature. The formation and evolution of Al₄C₃, AlN and SiC crystalline phases in the matrix contribute to the excellent properties of such materials, namely high thermal conductivity and low mean pore diameter of open pores. The experimental results indicate that about 2–4 wt-%Al plus about 4–6 wt-%Si additions at ～1300°C were optimum for the manufacture of carbon refractories.     

太钢高炉上下部操作炉型相互作用及其影响

 通过太钢2座4 350 m3高炉生产、操作炉型监控和维护的实践,认识到高炉上下部操作炉型之间有密切的相互作用关系,其对炉缸寿命有一定的影响。高炉上部的操作炉型受到炉腹煤气量、炉身部位耐火材料的选择以及炉身冷却水流向的影响。适当的炉腹煤气量、减少冷却板与砖衬间可能形成的窜气通道、冷却水横向分段、分区冷却有助于形成合理的上部操作炉型。炉身操作炉型与渣皮厚度具有相互作用关系,风口以上操作炉型对炉缸炉底的侵蚀和结厚也存在相互作用关系。通过维持炉芯死焦堆透气透液性、高炉炉身硬质压入以及钒钛矿护炉等措施,维持合理的上、下部操作炉型,改善了炉况顺行和操作指标,同时减缓炉缸侧壁的侵蚀。     

氯元素对高炉冶炼的影响分析及展望

在分析高炉内氯元素的主要来源和相关化学反应的基础上,综述了氯对高炉炉料、耐火材料、风口以及设备的影响。指出氯元素对高炉原燃料的作用机理,提出降低氯元素对高炉耐火材料侵蚀的措施,寻找有效降低净煤气中氯含量的方法,以及研究氯元素在高炉渣铁形成过程中的分配规律,指出找到适宜的高炉渣排氯的操作条件是今后研究的重点,可为降低氯元素对高炉冶炼过程的影响提供理论依据。     

X射线荧光光谱法快速分析高炉渣中TiO_2

采用高炉渣标准样品为基体 ,加入不同量的纯TiO2 试剂 ,制备合成样品。以硼酸、碳酸锂为熔剂 ,大比例稀释样品 ,熔融制成一系列标准玻璃样片 ,用X射线荧光光谱法测定样片中TiO2 。研究了标样的合成、熔剂的选择、试样的制备和测量条件。用本法测定了渣样中质量分数为 0.3 %～ 5 %二氧化钛 ,与化学分析方法相比 ,省时 ,省力 ,分析成本低 ,无环境污染 ,满足了冶炼现场快速分析的需要     

高炉炉缸破损调研分析

高炉炉缸安全是高炉长寿的主要限制环节,首钢股份公司环保限产期间对2号高炉进行了在不切割炉壳情况下的炉缸保护性清理和浇注修复施工。在此期间对高炉炉缸的破损情况进行了调研,研究了首钢股份公司 2 号高炉风口以下炉缸渣皮、风口区域、出铁口前泥包的状态和炉底陶瓷垫的侵蚀状况,并分析了造成炉缸炭砖侵蚀的原因及炉缸中钛和锌元素的物相。研究发现炉底陶瓷垫未形成锅底状侵蚀,越是靠近炉墙位置,陶瓷垫侵蚀越严重,说明了炉缸活跃度不够。而象脚区炭砖侵蚀主要是受铁、钾和硫等元素的渗透侵蚀;炉底象脚区域发现大量古铜色碳氮化钛沉积物,沉积物呈带状分布;破损炉缸中发现的大量ZnO富集物是黄绿色而非传统的白色。此次破损调研为后期炉缸浇注、高炉操作以及今后的炉缸设计提供现实可靠的依据,其意义重大。