Reference : Modelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Sha...
Dissertations and theses : Doctoral thesis
Engineering, computing & technology : Chemical engineering
Modelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Shaft of A Blast Furnace
Hoffmann, Florian mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit >]
University of Luxembourg, ​​Luxembourg
Docteur de l'Université du Luxembourg en sciences de l'Ingénieur
Peters, Bernhard mailto
Greger, Manfred mailto
Senk, Dieter mailto
Dziugys, Algis mailto
Simoes, Jean-Paul mailto
[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
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.

There is no file associated with this reference.

Bookmark and Share SFX Query

All documents in ORBilu are protected by a user license.