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See detailModelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Shaft of A Blast Furnace
Hoffmann, Florian UL

Doctoral thesis (2014)

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 ... [more ▼]

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. [less ▲]

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See detailDetailed numerical modeling of pyrolysis in a heterogeneous packed bed using XDEM
Mahmoudi, Amir Houshang UL; Hoffmann, Florian UL; Peters, Bernhard UL

in Journal of Analytical and Applied Pyrolysis (2014), 106

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See detailApplication of XDEM as a novel approach to predict drying of a packed bed
Mahmoudi, Amir Houshang UL; Hoffmann, Florian UL; Peters, Bernhard UL

in International Journal of Thermal Sciences (2014), 75

A majority of solid fuels especially biomass contains moisture, which may amount up to the mass of the dry particles. Thus it is important to determine the details of drying when considering biomass as a ... [more ▼]

A majority of solid fuels especially biomass contains moisture, which may amount up to the mass of the dry particles. Thus it is important to determine the details of drying when considering biomass as a fuel. Therefore, the objective of this work is to apply the Extended Discrete Element Method (XDEM) as a numerical simulation framework to prediction of drying within a packed bed reactor. The novel numerical concept resolves the particulate phase by the classical Discrete Element Method (DEM), however, extends it by the thermodynamic state e.g. temperature distribution and evaporation of water content of each particle in conjunction with heat and mass transfer to the surrounding gas phase. The latter is described by a continuous approach namely a set of differential conservation equations as employed in Computational Fluid Dynamics (CFD) for porous media. Comparison with measurement was carried out and good agreement was achieved. [less ▲]

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See detail3D Modellierung von Festbettreaktoren mit Hilfe der XDEM
Hoffmann, Florian UL

Presentation (2013, July 05)

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See detailExtended Discrete Element Method (XDEM) to Model Heterogeneous Reactions in Packed Beds
Hoffmann, Florian UL; Peters, Bernhard UL

in PARTEC - International Congress on Particle Technology (2013, April)

Packed beds, due to their high surface-area-to-volume-ratio, are widely used for chemical reactors, such as catalytic or pebble bed reactors, blast furnaces or as heat exchanging units. Depending on the ... [more ▼]

Packed beds, due to their high surface-area-to-volume-ratio, are widely used for chemical reactors, such as catalytic or pebble bed reactors, blast furnaces or as heat exchanging units. Depending on the mode of packing, structured or random, a different degree of heterogeneity is introduced. For stable and efficient process handling local quantities such as temperature or concentration of chemical species are of major interest. Direct measurement of such quantities has proven very difficult or unfeasable due to the morphology of the bed. Hence, numerical modeling can help to gain insights into inaccessible parts of such reactors. The objective of this contribution is to introduce a discrete numerical approach that describes heterogeneous reaction processes within packed and moving beds. The so-called Extended Discrete Element Method (XDEM) is used to account for convective heat and mass transfer within porous media. Both motion and chemical conversion of particulate material can be dealt with. A granular medium consists of an ensemble of particles of which each exhibits individual chemical and mechanical properties. Dynamics of solid particles is accounted for by the known discrete element approach. In addition physicochemical conversion of an individual particle like drying, gasification or redox reactions are accounted for by transient differential equations (species, energy, momentum) on a particle scale. Predictions include properties such as temperature and species distribution inside a particle. The general and modular formulation of the model allows for application to any chemical process involving heterogeneous reactions. Chemical interaction between multiple particles takes place through gaseous intermediates by heat and mass transfer. Computational Fluid Dynamics is applied for the gaseous continuum in the voidage between particles. The presented model can act as tool to gain valuable insights into chemical processes inside packed beds such as blast furnace iron making or gasification of biomass. It can serve as a toolbox for prediction, analysis and optimization of a variety of process parameters such as residence time, conversion progress, burden charging and gas flow patterns. As an example a section of the burden in a blast furnace is focused on. [less ▲]

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See detaileXtended Discrete Element Method used for convective heat transfer predictions
Estupinan Donoso, Alvaro Antonio UL; Hoffmann, Florian UL; Peters, Bernhard UL

in International Review of Mechanical Engineering (2013), 7(2), 329-336

Packed bed reactors dominate a broad range of engineering applications. In a packed bed reactor, heat is transferred from the solid particles to the gas flow stream through the void space between ... [more ▼]

Packed bed reactors dominate a broad range of engineering applications. In a packed bed reactor, heat is transferred from the solid particles to the gas flow stream through the void space between particles. Using a XDEM approach, continuous and discrete phases have been coupled in order to predict convective heat transfer between solid and fluid within packed beds. For the solid matrix a discrete intra-particle model, namely DPM, was used to solve for each particle of the bed, and a CFD tool was employed to resolve the fluid flow. [less ▲]

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See detailDie Extended Discrete Element Method (XDEM) für multiphysikalische Anwendungen
Peters, Bernhard UL; Besseron, Xavier UL; Estupinan Donoso, Alvaro Antonio UL et al

Scientific Conference (2013)

A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that ... [more ▼]

A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that involve both a continuous and a discrete phase are important in applications as diverse as pharmaceutical industry e.g. drug production, agriculture food and processing industry, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology. A novel technique referred to as Extended Discrete Element Method (XDEM) is developed, that offers a significant advancement for coupled discrete and continuous numerical simulation concepts. XDEM treats the solid phase representing the particles and the fluidised phase usually a fluid phase or a structure as two distinguished phases that are coupled through heat, mass and momentum transfer. An outstanding feature of the numerical concept is that each particle is treated as an individual entity that is described by its thermodynamic state e.g. temperature and reaction progress and its position and orientation in time and space. The thermodynamic state includes one-dimensional and transient distributions of temperature and species within the particle and therefore, allows a detailed and accurate characterisation of the reaction progress in a fluidised bed. Thus, the proposed methodology provides a high degree of resolution ranging from scales within a particle to the continuum phase as global dimensions. These superior features as compared to traditional and pure continuum mechanics approaches are applied to predict drying of wood particles in a packed bed and impact of particles on a membrane. Pre- heated air streamed through the packed bed, and thus, heated the particles with simultaneous evaporation of moisture. Water vapour is transferred into the gas phase at the surface of the particles and transported to the exit of the reactor. A rather inhomogeneous drying process in the upper part of the reactor with higher temperatures around the circumference of the inner reactor wall was observed. The latter is due to increased porosity in conjunction with higher mass flow rates than in the centre of the reactor, and thus, augmented heat transfer. A comparison of the weight loss over time agreed well with measurements. Under the impact of falling particles the surface of a membrane deforms that conversely affects the motion of particles on the surface. Due to an increasing vertical deformation particles roll or slide down toward the bottom of the recess, where they are collected in a heap. Furthermore, during initial impacts deformation waves are predicted that propagate through the structure, and may, already indicate resonant effects already before a prototype is built. Hence, the Extended Discrete Element Method offers a high degree of resolution avoiding further empirical correlations and extends the knowledge into the underlying physics. Although most of the work load concerning CFD and FEM is arranged in the ANSYS workbench, a complete integration is intended that allows for a smooth workflow of the entire simulation environment. [less ▲]

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See detailDie Extended Discrete Element Method (XDEM) für multiphysikalische Anwendungen
Peters, Bernhard UL; Besseron, Xavier UL; Dziugys, Algis et al

Scientific Conference (2013)

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See detailEnhanced Thermal Process Engineering by the Extended Discrete Element Method (XDEM)
Peters, Bernhard UL; Besseron, Xavier UL; Estupinan Donoso, Alvaro Antonio UL et al

in Universal Journal of Engineering Science (2013), 1

A vast number of engineering applications <br />include a continuous and discrete phase simultaneously, <br />and therefore, cannot be solved accurately by continu- <br />ous or discrete approaches only ... [more ▼]

A vast number of engineering applications <br />include a continuous and discrete phase simultaneously, <br />and therefore, cannot be solved accurately by continu- <br />ous or discrete approaches only. Problems that involve <br />both a continuous and a discrete phase are important <br />in applications as diverse as pharmaceutical industry <br />e.g. drug production, agriculture food and process- <br />ing industry, mining, construction and agricultural <br />machinery, metals manufacturing, energy production <br />and systems biology. A novel technique referred to as <br />Extended Discrete Element Method (XDEM) is devel- <br />oped, that o ers a signi cant advancement for coupled <br />discrete and continuous numerical simulation concepts. <br />The Extended Discrete Element Method extends the <br />dynamics of granular materials or particles as described <br />through the classical discrete element method (DEM) to <br />additional properties such as the thermodynamic state <br />or stress/strain for each particle coupled to a continuum <br />phase such as <br />uid <br />ow or solid structures. Contrary <br />to a continuum mechanics concept, XDEM aims at <br />resolving the particulate phase through the various <br />processes attached to particles. While DEM predicts <br />the spacial-temporal position and orientation for each <br />particle, XDEM additionally estimates properties such <br />as the internal temperature and/or species distribution. <br />These predictive capabilities are further extended by an <br />interaction to <br />uid <br />ow by heat, mass and momentum <br />transfer and impact of particles on structures. [less ▲]

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See detailUnified Design for Parallel Execution of Coupled Simulations using the Discrete Particle Method
Besseron, Xavier UL; Hoffmann, Florian UL; Michael, Mark UL et al

in Proceedings of the Third International Conference on Parallel, Distributed, Grid and Cloud Computing for Engineering (2013)

This paper presents the enhanced design of the Discrete Particle Method (DPM), a simulation tool which provides high quality and fast simulations to solve a broad range industrial processes involving ... [more ▼]

This paper presents the enhanced design of the Discrete Particle Method (DPM), a simulation tool which provides high quality and fast simulations to solve a broad range industrial processes involving granular materials. It enables to resolve mechanical and thermodynamics problems through different simulation modules (motions, chemical conversion). This new design allows to transparently couple the simulation modules in parallel execution. It relies on a unified interface and timebase of the simulation modules and a flexible decomposition in cells of the simulation space. Experimental results study the behavior of the Orthogonal Recursive Bisection (ORB) partitioning algorithm. A good scalability is achieved as the parallel execution on a distributed platform provides a 17-times speedup using 64 processes. [less ▲]

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See detailModelling Thermochemical Processes in Granular Media
Hoffmann, Florian UL

Presentation (2012, October 26)

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See detailAn Integrated Approach to Model Blast Furnaces
Hoffmann, Florian UL; Peters, Bernhard UL

in Proceedins: METEC InSteelCON 2011, Düsseldorf, Germany, CCD Congress Center Düsseldorf, 27th June - 1st July, 2011 (2011)

The objective of this contribution is to introduce a discrete numerical approach that describes all relevant mechanisms above the cohesive zone within a blast furnace. It includes a thermal conversion ... [more ▼]

The objective of this contribution is to introduce a discrete numerical approach that describes all relevant mechanisms above the cohesive zone within a blast furnace. It includes a thermal conversion module describing physico-chemical processes for ore and coke and a motion module which allows for spacial movement of the particles within the blast furnace. Both aspects are dealt with by the Discrete Particle Method (DPM), so that the sum of particle processes represents the global process. Conversion of particles is described by one-dimensional and transient differential conservation equations (mass, momentum, energy). Interaction between multiple particles takes place through gaseous intermediates, namely CO, CO2 and H2. For the bulk gas phase within the voidage between particles Computational Fluid Dynamics (CFD) is applied. In order to calculate mechanical interaction of the particles in a packed bed a discrete element technique (DEM) based on classical Newtonian dynamics was employed. This permits the prediction of trajectories of coke and ore particles. The presented model can act as tool to gain valuable insights into blast furnace processes and can serve as a toolbox for prediction and optimization of burden charging, burden movement, gas flow, reduction rates and reduction of coke consumption. [less ▲]

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