Fixed Bed Reactors and Computational Fluid Dynamics

ixed beds are tubes packed with particles, through which gases and/or liquids flow. The fixed bed is the workhorse of the chemical industry, being used for many types of operation and chemical reaction. Our main interest is in fixed beds as reactors, where the packing is catalyst particles. These may be spheres, pellets, rings or other more complex shapes. Several uses of fixed bed reactors need energy to be transferred either out of the bed (e.g. exothermic partial oxidation reactions) or into it (e.g. endothermic steam reforming) through the tube walls. To do this, the tubes must be narrow, with only a few particles across a radius, so that the tube-to-particle aspect ratio N is typically in the range 3-10. Heat transfer problems in these beds are usually severe, especially near the tube wall, and the choice of catalyst particle shape can be critical.

In CFD simulation the Navier-Stokes mass and momentum conservation balances are solved for a large number of mesh volumes; additional balances for heat transfer and turbulence modeling are usually added. The basic equations and background of these balances are stated in standard references. Our research to date at WPI has concentrated on the use of CFD calculations to solve for the steady-state 3D flow fields in model fixed beds, with associated heat transfer. Our current and future work aims to extend this to include chemical reaction in catalytic particles of various shapes.

For our research group, by CFD for fixed beds we mean simulations in which the details of the packing structure are preserved. This is essential so that we can understand the details of what is going on near the tube wall, and how the catalyst particle shapes and internals can influence the phenomena. Particles pack near the wall in a relatively ordered arrangement so we can model representative bed segments to save computational time and also reduce the size of the flow and temperature fields that we need to analyze to understand what is going on. Some examples of our model geometries are shown on this page, click on them for more details.

If you would like more information on our projects using CFD to study transport and reaction in fixed beds, then please click on one of the links below:

• Catalyst Design and Analysis by Computational Fluid Dynamics (CFD)
  
  
• Fixed Bed Fluid Flow and Heat Transfer by Computational Fluid Dynamics (CFD)