Bubble free fluidization of a binary mixture of large particles

•Bubble free fluidization is demonstrated experimentally and using CFD.•The binary mixture of large particles fluidizes over a large range of velocities.•The mixture has a large bed expansion.•But gas slugs form in small diameter beds.•For a group B binary mixture bubbles form only in the upper half of the bed.

Many chemical processes, such as polysilicon production in fluidized beds, can be improved by elimination of bubbles. Theory suggests that this can be done using coarse particles in place of Geldart B particles used to-day. CFD simulations using a mixture of 3.5 mm and 5 mm glass beads show that in a large bed this coarse mixture fluidizes without bubble formation over a large range of gas velocities. Visual observations and measurements in a two-dimensional bed confirm this discovery. Both CFD computations and experiments in small diameter beds show that this mixture undergoes slugging, as expected for fluidization in small diameter beds. For B particles a bottom bubble-less layer is computed.