Insights into the instantaneous freeboard flow above a bubbling fluidised bed

Abstract

The freeboard of a fluidised bed reactor, that is, the space above the bed material where the fluidising gas disengages from solids before leaving the fluidisation vessel, can be a place where unexpected additional reaction can take place. In this study particle image velocimetry (PIV), implemented by image shifting, has been used to provide instantaneous gas velocity vector maps of the central vertical plane of a bubbling fluidised bed freeboard in order to study the flow pattern in a cold model of a fluidised bed used for polymer recycling. The velocity vector maps obtained show that the freeboard gas flow is characterised by the presence of eddies and vortices generated by bubble eruption at the bed surface.