Comparative study for physical properties and corrosion mechanism of synthetic and in situ MgAl2O4 spinel formation zero cement refractory castables

Abstract

Magnesium aluminate spinel (MgAl₂O₄) is an excellent castable refractory product due to its high temperature thermal, chemical and mechanical properties. Alumina spinel castables are produced by addition of synthetic spinel or in situ spinel formation during the firing process. In the first part of the experimental studies, alumina rich MgAl₂O₄ spinel castable was produced using a solid state reaction technique. Tabular alumina and sea water magnesia (<100 μm) were used as starting raw materials. In the second part of the experimental studies, commercial synthetic spinel added castables were produced. In order to compare experimental results, both parts of the experimental study involved compositions with the same proportions of MgO. α-500 hydratable alumina was used as binder. Castables were sintered at 1500 and 1600°C. Water absorption, apparent porosity, bulk density and cold crushing strength values were considered and the optimum sintering temperature, proportions of synthetic spinel and sea water magnesia were determined. The XRD patterns confirm the phase formation of MgAl₂O₄. Moreover, the physical properties of the castables were supported by this XRD analysis. Scanning electron microscopy investigations of the fired samples were carried out to compare the effect of synthetic spinel addition and in situ phase formation on the physical properties of the castables. The mechanism of slag penetration to two types of zero cement castables for steel ladles was examined and the penetration layer chemically analysed by energy dispersive X-ray analysis studies.     

A way to reduce environmental impact of ladle furnace slag

Abstract

In the last decades the European steel industry has made continuous efforts to reduce residues and byproducts and to increase recycling in order to reduce its environmental impact. While some steelmaking slags have been widely characterised and, to a certain extent reused, ladle furnace (LF) slag is used in different applications because of its specific properties. The main purpose of the case study presented in this paper concerns the reduction of potential LF slag environmental impacts, because of its intrinsic physicochemical properties. During the handling and cooling of LF slag, it disintegrates into a powder due to instability of the dicalcium silicate, causing an increase in dust emissions to the environment. The approach presented in this paper aims to reduce this phenomenon in order to achieve a more sustainable solution in term of reduction of powder dispersion in the environment, of costs saving and of nuisance reduction in the surroundings areas.     

Impact of slag–refractory lining reactions on the formation of inclusions in steel

Abstract

The present study was carried out to investigate the impact of slag– refractory lining reactions on the formation of inclusions during ladle treatment of steel. The experiments were conducted on an industrial scale in the ladle at Uddeholm Tooling AB in Hagfors, Sweden. The inclusion chemistry and population during ladle treatment were studied along with the composition of the ladle glaze, taken from the ladle lining. The inclusions in the steel were classified into four groups according to the Swedish standard SS 111116. SEM/EDS analyses were carried out to identify the phases present in both the inclusions and the ladle glaze. The number of inclusions in the steel before deoxidation was found to increase with the ladle age, i.e. the number of times the ladle had been in use. A similar increase was also found after vacuum degassing and before casting. A great portion of inclusions before casting was found to be supplied by ladle glaze. This observation was further confirmed and explained by thermodynamic analysis. The present results show that ladle glaze is a major source of inclusions in the ladle at Uddeholm Tooling.     

The life of a plant builder in the modern metals industry

Abstract

The 2007 SMEA Celebrity Lecture (Sheffield Metallurgical and Engineering Association) was given by Roy Tazzyman, the outgoing Managing Director of Siemens VAI–UK, on 4 July 2007 at the University of Sheffield, in conjunction with the Association's annual conference. Ken Ridal summarises the proceedings.     

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 ore reduction/cementation: experimental results and kinetic modelling

Abstract

Iron ore reduction and iron cementation by H₂-CH₄-Ar gas mixtures were investigated in a laboratory isothermal fixed bed reactor in the temperature range 600-925°C. Iron ore was first reduced to metallic iron by hydrogen, then metallic iron was carburised to cementite by methane. Increasing temperature and hydrogen content accelerated the reduction process. However, for >55 vol.-%, the effect of H₂ content was not significant. Methane had almost no effect on the reduction process. Increasing temperature increased the rate of iron cementation and also the rate of free carbon deposition. Optimum conditions for cementite formation were: temperature 750°C and reducing/carburising gas contents of 40-55 vol.-%H₂ and 35 vol.-%CH₄. Under these conditions, reduction of iron ore to cementite was completed in ~15 min. A two interface grain model and a volume reaction model were used to simulate the process of iron ore reduction and iron cementation. The simulated results for both reduction and cementation were consistent with the experimental data.     

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.     

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.     

Optimum model for predicting temperature settings on hot dip galvanising line

Abstract

Controlling the annealing cycle in a hot dip galvanising line (HDGL) is vital if each coil treated is to be properly galvanised and the steel is to have the right properties. Current HDGL furnace control models usually take into account the dimensions of the coil to be dipped and, in some cases, the type of steel. This paper presents a new model for monitoring furnace temperature settings, which considers not just the coil dimensions but also the chemical composition of the steel. This enables the model to be adjusted more suitably to each type of steel to be dipped, so that the HDGL annealing cycle is optimised and rendered more efficient in dealing with new products. The ultimate aim is to find a model that is equally efficient for new types of steel coil that have not been processed before and whose dimensions and chemical compositions are different from coils processed previously. To find the best model, this paper compares various new and classical algorithms for developing a precise and efficient prediction model capable of determining the three temperature settings for heating on an HDGL located in Avilés (Spain) on the basis of the physical and chemical characteristics of the coils to be processed and the preset process conditions.