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Larsson I.A.S.,Lulea University of Technology | Johansson S.P.A.,Lulea University of Technology | Lundstrom T.S.,Lulea University of Technology | Marjavaara B.D.,Luossavaara Kiirunavaara AB publ
Experiments in Fluids | Year: 2015

The jet mixing in a downscaled, isothermal model of a rotary kiln is investigated experimentally through simultaneous particle image velocimetry and planar laser-induced fluorescence measurements. The kiln is modeled as a cylinder with three inlets in one end, two semicircular-shaped inlets for what is called the secondary fluid divided by a wall in between, called the back plate, where the burner nozzle is located. The scaling of the burner nozzle between real kiln and model and the corresponding jet flow through it is determined by the Craya–Curtet parameter. Three momentum flux ratios of the secondary fluid are investigated, and the interaction with the burner jet is scrutinized. It is found that the burner jet characteristics, its mixing with the secondary fluid and the resulting flow field surrounding the jet are dependent on the momentum flux ratio. A particular result is that stable shear layers give a more even mixing as compared to a case with shear layers subjected to a more prominent vortex shedding. © 2015, Springer-Verlag Berlin Heidelberg. Source


Sofia Larsson I.A.,Lulea University of Technology | Staffan Lundstrom T.,Lulea University of Technology | Daniel Marjavaara B.,Luossavaara Kiirunavaara AB publ
Flow, Turbulence and Combustion | Year: 2015

Rotary kilns are large, cylindrical, rotating ovens with a burner in one end that are used in various industrial processes to heat up materials to high temperatures. The kiln burners are characterized by long diffusion flames where the combustion process is largely controlled by the turbulent diffusion mixing between the burner fuel jet and the surrounding combustion air. The combustion air flow patterns have a significant effect on the mixing and hence the combustion efficiency, motivating a systematic study of the kiln aerodynamics. The objective of this work is to compare turbulence models when modeling the kiln aerodynamics of an iron ore pelletizing rotary kiln. Simulations of the non-reacting isothermal flow using three different ω-based turbulence models are performed on a simplified, down-scaled model of the kiln. Some of the results are validated against particle image velocimetry (PIV) experiments. The turbulence models used are the two-equation shear stress transport (SST) model, the Reynolds stress baseline (RSM-BSL) model and the delayed detached eddy simulation (DDES) turbulence model based on the SST formulation. It is found that the turbulence models produce quite different results yielding various predictions of the flow field. The SST model fails to capture the unsteady behavior of the flow field and the DDES model performs poorly on the grid applied. The Reynolds stress model agrees best when compared with the experimental data and provides a good trade-off between details captured and computational effort. © 2015 Springer Science+Business Media Dordrecht. Source


Larsson I.A.S.,Lulea University of Technology | Lundstrom T.S.,Lulea University of Technology | Marjavaara B.D.,Luossavaara Kiirunavaara AB publ
Journal of Fluids Engineering, Transactions of the ASME | Year: 2015

The rotary kiln is the middle part of a grate-kiln iron ore pelletizing process and consists of a large, cylindrical rotating oven with a burner in one end. The flame is the heart of the process, delivering the necessary heat. The combustion process is largely controlled by the turbulent diffusion mixing between the primary fuel jet and the combustion air, called the secondary air, which is mostly induced through the kiln hood. The relatively high momentum of the secondary air implies that the resulting flow field has a significant impact on the combustion process, justifying a systematic study of the factors influencing the dynamics of the secondary air flow field, by neglecting the primary fuel jet and the combustion. The objective of this work is thus to investigate how the geometry and the momentum flux ratio of the inlets affect the flow field in the kiln. Down-scaled models of the kiln are investigated numerically. It is found that the resulting flow field is highly affected by both the geometry and momentum flux ratio of the inlet flows, including effects from pressure driven secondary flow occurring in the semicircular inlet ducts. The dynamics of the flow is further investigated using proper orthogonal decomposition (POD) resulting in a deeper understanding of the forming, interaction and convection of the vortical structures. Copyright © 2015 by ASME. Source


Semberg P.,Luossavaara Kiirunavaara AB publ | Andersson C.,LKAB | Bjorkman B.,Luossavaara Kiirunavaara AB publ
Ironmaking and Steelmaking | Year: 2014

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO) 4(Fe2O3)7, whereas the one commonly reported in the literature is (CaO)(Fe2O3)2. During reduction at 500-700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wü stite at 800°C, the calcium began dissolving in the wü stite, and at 900°C porous calciowü stite had formed in the entire sample, except for some remaining magnetite left in the pellet cores. © 2014 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute. Source

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