The Big Impact Small Particles Have on Fluidized Beds

Fluidized bed design and scale-up is relying more on computational fluid dynamic modeling. Such models can now capture the strong dependence on particle characteristics such as size and shape. However, recent research has shown that particle clustering has a significant effect on fluidized bed hydrodynamics, which impacts how these units should be designed and scaled-up. Indeed, successful scale up depends on the accurate estimates of the entrainment rate to determine the location and size of the cyclones. Yet, the amount of fines, particle shape and surface morphology play a role on the level of particle clustering in a fluidized bed which directly affects the entrainment rates. The fine particles are an excellent conduit for moving charge as electrons or ions which appear to be the dominant mechanism of electrostatics for Geldart Group A material in a bubbling fluidized bed. This electrostatic force trades off with particle momentum relaxation and rotational to translation momentum transfer with regard to forming a particle cluster. Preliminary work on particle shear in a packed and fluidized beds, suggest that particle clustering can be measured and may provide a quantifiable metric for the level of particle clustering.