A novel method for the investigation of particle mixing in gas-solid systems

Presented at the 1st World Congress on Particle Technology held in Nuremberg (F.R.G.) April, 1986 A novel experimental technique for the investigation of solid particle mixing in gas-solid systems is suggested which is suited for on-line measurements under steady-state conditions. The method is based on subliming tracer particles. Its applicability is demonstrated by an investigation of the distribution of feed particles in gas-fluidized beds. Carbon dioxide snow particles have been used as the tracer material. The sublimation is an endothermal process where both the heat effect and the formation of a gaseous product may be used for the detection of the tracer particles. One method is to measure the local bed temperature, which will be lowered in the presence of tracer material, due to the low temperature of the carbon dioxide snow particles. Another method consists in measuring the concentration of the gaseous sublimation product carbon dioxide. While the former method is more suited for qualitative measurements of the spatial tracer distribution inside the bed, the latter method yields quantitative information about the local tracer concentration. Measurements have been performed in a pilot-scale fluidized bed with a cross-sectional area of 2.0 m × 0.3 m with bed heights up to 1.0 m. The solids mixing has been investigated by unsteady-state as well as steady-state measurements. The sublimation technique turned out to be a valuable tool in the investigation of the mixing process, which finally led to a new design correlation for the prediction of solids mixing in gas-fluidized beds.