(273f) Insights in Secondary Gas Injection in a Bubbling Fluidized Bed Via Discrete Particle Simulations

Christensen, D. O., Delft University of Technology
Nijenhuis, J., Delft University of Technology
van Ommen, J. R., Delft University of Technology
Coppens, M. O., Rensselaer Polytechnic Institute
Van Wachem, B. G. M., Chalmers University of Technology

Previous work has shown that the injection of secondary gas via a fractal injector can significantly reduce the size of the bubbles in a bubbling fluidized bed(1). Further results indicated that the total bubble volume is also reduced, implying an increased gas flow through the dense phase(2). The objective of the present study is to elucidate the mechanisms behind these phenomena using numerical modeling.

Results from a discrete particle model used to simulate secondary gas injection in a quasi-2D bed containing 50 000 particles are presented. A discrete particle model was chosen because changes in local phenomena are being sought, e.g. local porosities.

Initial simulations were conducted on a system involving one secondary injection point in the middle of the simulated bed. The parameters studied were bubble size and local porosity. By comparing simulations with secondary injection to those without, the change in bubble size and local porosity could be obtained, allowing us to determine the magnitude of the effects as well as how far the effects extend into the bed. Further simulations include additional injection points in various orientations to determine whether any interactions exist between them, such as whether the effect is amplified or simply lengthened.

(1) Coppens, M.-O. and van Ommen, J.R., ?Structuring Fluidized Beds.? Chemical Engineering Journal, 96, 2003, pp. 117-124.

(2) Kleijn van Willigen, et al., ?Imposing Dynamic Structures on Fluidized Beds,? Catalysis Today, 105, 2005, pp. 560-568.