Grid leakage (weeping and dumping) in a pilot plant size gas fluidized bed

Substantial grid leakage in large industrial fluidized beds is highly undesirable because it can lead, among other things, to grid erosion or plugging. Experiments have been carried out to study grid leakage using a cracking catalyst (arithmetic mean diameter 65 μm) in a 0.6 m diameter column. The flow pattern under the grid was charted with a hot wire anemometer. Micro-isokinetic probes were developed to study the particle flux returning from the windbox towards the grid. Particles were sucked in isokinetically, recovered in a filter, weighed and analyzed for particle size in a Coulter counter. Upward particle fluxes at the grid were determined by extrapolation of the flux at various distances below the grid. Grid leakage was studied for grids of various geometries which had holes of 1.27 cm diameter. Various measurement methods, a model for re-entrainment and correlations are given.