Gas and solid behaviours during defluidisation of Geldart-A particles

Bed collapsing experiments were carried out in a cold-air transparent column 192 mm in diameter and 2 m high. Typical Fluid Catalytic Cracking (FCC) catalyst with a mean particle size of 76 μm and a density of 1400 kg/m3 was used. Both single and double-drainage protocols were tested. The local pressure drop and bed surface collapse height were acquired throughout the bed settling.Typical results were found regarding dense phase voidage of a fluidised bed and the bed surface collapse velocity. In addition, bubble fraction was calculated based on the collapse curve.Experimental results showed that windbox effect is significantly reduced compared to previous works since the volume of air within the windbox was reduced. The comparison of single/double-drainage protocols revealed a new period in the defluidisation of Geldart-A particles concerning gas compressibility. Through the temporal analysis of local pressure drop, the progress of the solid sedimentation front from bottom to top was determined, analysed and modelled.

Graphical abstractGeldart-A particles defluidisation was investigated. A 2-front defluidisation was found: bed surface collapse and ascending solid sedimentation. Gas compressibility is non-negligible when using single-drainage defluidisation method. Solid sedimentation front was characterised through the analyses of local pressure drop data. Solid sedimentation front is 10 times faster than bed surface collapse.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► 2-front defluidisation: bed surface collapse and ascending solid sedimentation. ► Gas compressibility is non-negligible in Geldart-A particles defluidisation. ► Local pressure drop data provide information on the solid sedimentation front. ► Ascending solid sedimentation front is 10 times faster than bed surface collapse.