Particle segregation in spouted beds

Abstract

Particle segregation in spouted beds is shown to result from different trajectories of heavy and light particles in the fountain region, lighter particles tending to scatter more in the radial direction than heavier ones. Some desegregation occurred due to rolling along the inclined annulus surface and due to mixing processes in the spout. Segregation is less severe for overdeveloped fountains, where the particles bounce off the outer wall, and for low bed depths, where the fountain is dilute. Segregation can also be countered by a conical baffle which deflects particles outwards from the core of the fountain.

Particle residence times in the continuous spouting of mixtures

“…This particularly corroborates the findings for mixture A. Kutlouglou et al (1983) argue that mixing occurs during the rolling of particles along the inclined top free surface of the annulus, but with large beds with a side outlet, it is hard to see how free surface segregation can be avoided since beds would generally be operated with the particles being deposited around the spout and the solids avalanching outwards undergoing segregation in this process. However, further fundamental studies of free surface segregation in the presence of an upward air flow are required to permit more general predictions.…”

Discharge composition and concentration profiles in a continuously operating spouted bed

“…Cook and Bridgwater (1978) showed quantitatively the non-homogeneous distribution of particles with different density along the radius and the bed depth as a function of the gas flow. Recently, Kutluoglu et al (1983) andUemaki et al (1983) confirmed those results. From these studies it is clear that denser and larger particles congregate in the upper and central part of a spouted bed and travel along shorter patterns in the spout, fountain and annulus.…”

Fluid Dynamics of a Sand‐Biomass Mixture in a Spouted‐Bed Reactor for Fast Pyrolysis

“…The biomass is concentrated at the top of the bed (I M > 1). According to Kutluoglu et al [20], denser particles (sand) rise to a lower height in the fountain region and tend to follow radial positions near the annular-spout interface when falling back into the spout zone [21]. Therefore, these particles travel a shorter trajectory than the bagasse (lighter particles) which circulates preferentially along the outer periphery of the annular zone with poorer flowability, thus causing segregation.…”

“…According to Kutluoglu et al [20], large particles have a lower recirculation time due to a shorter path. Coarse particles do not rise as high as fine particles in the fountain region, settling close to the central axis of the bed [21].…”

“…Despite the important contributions of some authors [20,[22][23][24][25][26], the mechanisms underlying mixing and segregation in a spouted bed still have not been fully understood. Therefore, additional investigations are needed to gain further insights into the fluid dynamics of spouted beds operating with particle mixtures, mainly for mixtures involving biomass particles.…”