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TU Berlin

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Dipl.-Ing. Nico Jurtz

Lupe

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Teaching
CFD in der Verfahrenstechnik

Research

CFD simulation of transport processes and chemical reactions in fixed-bed reactors

Bachelor's / Master's Theses

Current offers for theses can be found here.

Motivation

Catalytic fixed-bed reactors are widely used in the chemical and process industry for processes like steam reforming (SRM), dry reforming (DRM) and the catalytic partial oxidation of methane (CPOX). These processes play an important role to produce hydrogen and syngas by using methane as feedstock. Since methane can be taken from renewable resources all the processes mentioned above can attribute to climate protection.

Heterogenous catalytic reactions are characterized by a high reaction enthalpy. For an efficient and secure process, it is therefore important to ensure an efficient heat transfer within the system. This constraint leads to reactors with a low tube diameter that are interconnected to so called tube bundle reactors. Furthermore, the pressure drop should be kept as low as possible. This leads to the use of rather large particles and therefore to reactors with a low tube-to-particle diameter ratio.

Surface temperature distribution and vizualisation of local channeling effects in a fixed-bed
Lupe

The widely used plug flow assumption caused by a homogenous radial void fraction profile is not valid in this reactor type since local flow effects are dominant. This affects the energy and mass transfer and possible chemical reactions significantly. The use of simplified numerical models, like pseudo-homogenous one- or two-dimensional models for the design of this reactor type is problematic, since important local phenomena like hot spots can’t be predicted. Furthermore, simplified models rely on the knowledge of effective transport parameters like the dispersion coefficient, the effective thermal conductivity or the effective viscosity. The use of correlations to determine those parameters is limited since they show quite large deviations.

Computational Fluid Dynamics (CFD) is a numerical tool that allows the simulation of fluid dynamics and the superimposed heat and mass transfer in a spatially resolved manner. The entire complex morphology between the particles gets geometrically resolved and the transport processes can be calculated by solving the Navier-Stokes-Equations. Also, the simulation of the conjugated heat transfer within the particles is possible. Hence, with particle-resolved CFD we have a numerical tool to perform detailed studies which we are not able to do experimentally.

Workflow

A DEM-CFD-coupled workflow is used for the numerical simulation of fixed-bed reactors. As a first step the Discrete Element Methode (DEM) is used for the generation of a representative random packing. After the simulation is finished the position and orientation of all particles is extracted and based on that data a CAD-representation of the bed morphology is generated. A special meshing strategy is used to mesh the geometry for the subsequent CFD simulation. In the following animation the workflow is shown schematically.

Scope

Beside extending and validating the capabilities of the proposed workflow the simulation results are used to enhance the phenomenological understanding of the fluid dynamics and transport processes in fixed-bed reactors. For process intensification new reactor concepts and particle shapes are tested to understand their impact on the reactor performance. To improve the quality of simplified numerical model, the numerical determination of effective transport parameters is also in the scope of my work.

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sec. FH 6-1
Room FH 629
Fraunhoferstr. 33-36
10587 Berlin
Tel.: +49 (0)30 314 23777
Fax: +49 (0)30 314 21134