| Reference : Modelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Sha... |
| Dissertations and theses : Doctoral thesis | |||
| Engineering, computing & technology : Chemical engineering | |||
| http://hdl.handle.net/10993/16663 | |||
| Modelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Shaft of A Blast Furnace | |
| English | |
Hoffmann, Florian  [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit >] | |
| 11-Apr-2014 | |
| University of Luxembourg, Luxembourg | |
| Docteur de l'Université du Luxembourg en sciences de l'Ingénieur | |
| 204 | |
| Peters, Bernhard | |
| Greger, Manfred | |
| Senk, Dieter | |
| Dziugys, Algis | |
| Simoes, Jean-Paul | |
| [en] chemical engineering ; blast furnace ; Extended Discrete Element Method (XDEM) ; CFD ; multi-phase heat and mass transfer ; heterogeneous chemical reactions ; packed bed ; porous medium ; multi-phase modelling ; metal oxide reduction ; numerical modelling ; thermal conversion ; discrete particle model ; gas flow | |
| [en] Heterogeneous reactions in packed beds such as iron ore reduction or gasification of coke in
a blast furnace involve various aspects of thermodynamics, fluid dynamics, chemistry and physics. Unfortunately, inaccessible and hostile process environments make it very difficult to gain insights into such reactors and to operate the industrial processes. To address this problem extensive research has been undertaken in the past to develop numerical methods and models. However, little effort has been made to describe the complex thermochemical processes inside such reactors starting from the particle and especially intra-particle scale. The objectives of this thesis are to introduce a coupled approach which allows for the physical and chemical interaction of a granular material with a surrounding gas phase and to apply it to the reduction processes in the upper shaft of a blast furnace. Furthermore, a suitable model to investigate the gas-solid thermochemical interaction within a single particle and within a packed bed of particles was to be established. Thus, the classical discrete element method (DEM) was extended by thermodynamic state variables such as temperature, composition and chemical reactions. In addition, a coupling between the particulate phase and a continuous gas phase for convective heat and mass transfer was implemented. It should be noted that the application of the presented methodology is not only restricted to the blast furnace, but rather represents a rigorous approach that can be applied to other packed bed reactors as well. A validation study on the particle scale using experimental results shows that the dis- crete particle model accurately predicts the progress of indirect reduction of a pellet. The particle model is shown to be capable of resolving radial gradients on the particle scale avoiding rigorous assumptions or mathematical fits to a specific experimental setup. These qualities of the model permit its usage in the presented analysis of indirect reduc- tion within the shaft of a blast furnace where each particle is subjected to time-varying boundary conditions. On the packed bed scale heat and mass transfer from the discrete to the continuous phase was validated using experimental data. Moreover, the model showed accurate results when compared to experimental reduction data from a lab scale bed of iron ore particles. Finally, the reduction processes in the upper shaft of a blast furnace were analysed: Firstly, isothermal reduction of a packed bed of pellets according to ISO standards were analysed in terms of heterogeneity in temperature and reduction degree inside the cylindrical reactor. Results indicate that radial gradients inside the packed bed are caused by the higher mass flow rate close to the reactor wall. Axial gradients develop due reduction reactions and the direction of the fluid flow. The formation of these axial gradients is found to be inherent to the process of indirect reduction of iron oxides due to the sequence of exothermic and endothermic reaction steps. Secondly, a complex packed bed with a layered structure of coke and iron ore particles is analysed under time-varying reducing gas conditions simulating the journey of a packed bed column through the upper shaft of a blast furnace. Results highlight that the gas and the solid phase are highly coupled in space and time during the process of indirect reduction. Axial gradients in temperature and composition form due to the heat and mass transfer between the packed bed and the streaming gas. Energy released or consumed by the indirect reduction provides an opposing trend to the gradients formed from the hot gas stream, thus reducing axial gradients within the bed and the gas phase. The results indicate the mechanisms involved during the formation of the thermal reserve zones inside the blast furnace shaft due to the complex interaction of convective heat and mass transfer in conjunction with energy consumption and release by the reactions. Considering the findings presented, this thesis is understood to contribute to the better understanding of heterogeneous reactions in packed beds and as a particular example of such the upper part of the blast furnace. | |
| http://hdl.handle.net/10993/16663 |
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