Edelbro C.,Lulea University of Technology |
Sjoberg J.,Itasca Consultants AB |
Malmgren L.,Luossavaara Kiirunavaara AB LKAB |
Dahner-Lindqvist C.,Luossavaara Kiirunavaara AB LKAB
Canadian Geotechnical Journal | Year: 2012
A likely result of changes in rock stresses due to progressing mining is an increased number of compressive stress-induced failures. This paper presents the results from numerical analysis and observations of stress-induced fallouts in footwall drifts in the Kiirunavaara underground mine. A brittle-plastic "cohesion-softening friction-hardening" (CSFH) material model was used for simulating brittle fallouts. To account for mining-induced stress changes, the local model stress boundary conditions were extracted from a global model. The rock mass properties were based on field observations in the footwall drifts as well as on results from laboratory testing. A multi-stage analysis was carried out to gradually change the stresses to simulate mining progress. A parametric study was conducted in which strength properties, location, and shape of the footwall drift were varied. Yielded elements and maximum shear strain were used as damage and fallout indicators. The modelling results were sensitive to the shape of the drift. The location of the predicted fallouts was in good agreement with the location of observed fallouts for the case in which the drift roof was simulated flatter than the theoretical cross section. The results indicate that the true shape of the drift is different from the planned one.
Okvist L.S.,Swerea MEFOS AB |
Hyllander G.,Luossavaara Kiirunavaara AB LKAB |
Olsson E.T.,SSAB |
Wikstrom J.-O.,Swerea MEFOS AB |
Lundgren M.,Swerea MEFOS AB
6th Int. Congress on the Science and Technology of Ironmaking 2012, ICSTI 2012 - Including Proceedings from the 42nd Ironmaking and Raw Materials Seminar, and the 13th Brazilian Symp. on Iron Ore | Year: 2012
A number of injection trials carried out over the years at the LKAB experimental blast furnace (LKAB EBF®) and in industrial BFs shows that tuyere injection is a feasible method for supply of various types of pulverized materials as different types of PC, BOF slag and BF dust to the BF. In this study, the effect on process, raceway conditions, hot metal quality, reductant agent consumption and slag formation due to the selection of injection materials are discussed based on trial data. A special attention is paid on the injection of alternative carbon containing residual material. Based on recent trials the efficiency in use of carbon in injected residual materials are discussed and pilot scale results compared with industrial trial results.
Sandeep Kumar T.K.,Lulea University of Technology |
Viswanathan N.N.,Lulea University of Technology |
Viswanathan N.N.,Indian Institute of Technology Bombay |
Ahmed H.M.,Lulea University of Technology |
And 3 more authors.
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2015
The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but also interdependent on each other. Therefore, a systematic study should involve understanding these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the present paper focusses on investigating the sintering kinetics of oxidized magnetite pellet. For the current investigation, sintering experiments were carried out on pellets containing more than 95 pct magnetite concentrate from LKAB’s mine, dried and oxidized to completion at sufficiently low temperature to avoid sintering. The sintering behavior of this oxidized pellet is quantified through shrinkage captured by Optical Dilatometer. The extent of sintering characterized by sintering ratio found to follow a power law with time i.e., Ktn. The rate constant K for sintering was determined for different temperatures from isothermal experiments. The rate constant, K, varies with temperature as lnTK(1/n)=lnK′-QRT, and the activation energy (Q) and reaction rate constant (K′) are estimated. Further, the sintering kinetic equation was also extended to a non-isothermal environment and validated using laboratory experiments. © 2014, The Minerals, Metals & Materials Society and ASM International.
Villegas T.,Lulea University of Technology |
Villegas T.,University of Sonora |
Nordlund E.,Lulea University of Technology |
Dahner-Lindqvist C.,Luossavaara Kiirunavaara AB LKAB
Engineering Geology | Year: 2011
Large scale surface subsidence has been experienced at the Kiirunavaara mine since sublevel caving was implemented as a mining method. Surface disturbances are affecting part of the city of Kiruna, the railway, and the power station. Continuous and discontinuous subsidences characterize the hangingwall deformation, which is periodically monitored using surveying techniques and mapping of surface cracks. A historic review of subsidence prognoses has been carried out and the results compared with the actual condition of the hangingwall. The review showed discrepancies between different prognoses. In addition, limit equilibrium analyses indicated that break angles flatten while the mining depth increases. However, this tendency is not clear in the field where break angles show a large dispersion of values. By using surveying data, two different analyses have been performed. The time-dependent movements of the hangingwall have been described using time-displacement curves and strain analysis has been performed for different sections of the hangingwall. Three different stages of the time-displacement behavior have been identified and described. It has been concluded that extension strain can reach values which may damage civil structures before surface crack can be observed. © 2011 Elsevier B.V.