Gas-solid Trickle Flow Hydrodynamics in a Packed Column

The pressure gradient and the static and the dynamic hold-up have been measured for a system consisting ofa Fluid Cracking Catalyst (FCC) of 30-150 x 10m6 m diameter, trickling over a packed bed and with a gas streaming in countercurrent flow. The experiments were carried out at ambient conditions using a glass column of 25 x 10 ~’ m diameter. The packing material consisted of 8 x 8 x 3 mm ceramic Raschig rings, a mixture of 7 x 7 x 1 mm glass Raschig rings and 5 x 5 mm catalyst pellets and of stacked Kerapak ceramic mixing units of Sulzer, each unit 50 mm long and 25 mm in diameter. Four different gases have been tested. A correlation for the pressure gradient in the preloading region is derived based on the Ergun equation and taking into account the internal gas recirculation due to the solids trickles. The void fraction of the trickles is found to be independent of-the physical properties of the gas phase. The behaviour of the GSTF-system in the preloading regime and the phenomena of loading and flooding are discussed. A correlation is given which relates the boundary between preloading and loading with the particle and gas properties and the solids flow rate.