Segregation in spouted beds

Particle segregation in spouted beds

“…This explanation is also consistent with measured trajectories (Kutluoglu, 1980) for binary systems and with certain other observations: For example, operating with un-derdeveloped fountains so that particles had an opportunity to bounce back into the interior of the column from outer walls, led to a marked reduction or even elimination of segregation, a trend already reported by Piccinini et al (1977) and Cook and Bridgwater (1978). As noted above, segregation was more severe for deeper beds (which gave more congested fountains) than with shallow bed depths (where particles were widely dispersed, and therefore collided less frequently in the fountain region).…”

“…In order to eliminate any effects of the front face of the column, such as angular segregation, i.e. the tendency for larger particles to be excluded from the flat surface (Cook and Bridgwater, 1978;Cavanagh, 1980), some further experiments were conducted in a full-column. This column again had an inside diameter of 0.152 m. The cylindrical part was made of glass with a brass conical base and an inlet diameter of 19 mm.…”

“…Piccinini et al (1977) postulated that coarse particles do not rise as high as fine particles in the fountain and fall back to the annulus surface closer to the central axis of the column. Robinson and Waldie (1978) and Cook and Bridgwater ( 1978), while recognizing the probable importance of the fountain, also produced evidence of differences in particle trajectories due to percolation of finer particles through coarser ones. Robinson and Waldie (1978) even allow for possible segregation in the spout region, whereas McNab and Bridgwater (1979) state that there is good radial mixing in the spout.…”

“…For example, solids leaving a spouted bed through an outlet pipe at the outer bed free surface tend to be finer and less dense than the mean bed composition (Piccinini et al 1977, Piccinini 1980. There are indications, however, that such segregation may be greatly reduced (Piccinini et al 1977) or even reversed in direction (Cook and Bridgwater 1978) if the ratio U/U,,,, is increased significantly.…”

Particle residence times in the continuous spouting of mixtures

“…However, with very low concentrations of wheat in deep beds, the evidence points to the wheat either recycling around the inside top part of the annulus or following a track similar to the mustard seeds. This is corroborated by observations that the more massive component has been found to congregate at the upper inner part of the annulus (Piccinini et al, 1977;Cook and Bridgwater, 1978). Robinson and Waldie (1978) studied segregation in the annulus of a half-section spouted bed by the measurement of cycle time distributions.…”