Slip velocity characteristics in the riser of circulating fluidised bed

Abstract

Experiments were carried out in a conventional circulating fluidised bed to measure the axial pressure profile and total pressure drop, which covered a wide range of operating conditions. Materials belonging to the Geldart A (fine material) as well as the Geldart B (coarse material) categories have been used in the present work. Slip velocity is determined from the total pressure drop and noticed that the slip velocity is much higher than the free fall velocity of single particle for Geldart A type material, while it is approximately equal to the free fall velocity of single particle for the Geldart B type materials.A model is developed for slip velocity taking into account all the hindrance effects: particleparticle, particle-wall, and particle agglomeration. Predictions of the present model are validated with the data due to present study and the data reported in the literature.

Numerical Simulation of Gas−Solid Dynamics in a Circulating Fluidized-Bed Riser with Geldart Group B Particles

“…Inspection of Figure 3 reveals that the cross-sectional averaged slip velocity predicted by the current simulation work is within the range of the particle terminal velocity (U t ) 1.2 m/s) and is in agreement with earlier studies. 14 Figure 3 compares the interphase momentum exchange factors that are predicted by the drag closures reported by Wen and Yu 23 and Syamlal and O'Brien 22 at a solids volume fraction of 0.1%. The interesting particular feature to be noted is that, unlike Wen and Yu's 23 drag closure, Syamlal and O'Brien's 22 drag closure shows two distinct regions.…”

“…Therefore, most of the research in the case of fast flows with group A particles has been focused on the formation and dissolution of clusters, and their effect on the overall dynamics. 13 In the case of CFB with group B particles, 14 slip velocities are in the range of the single particle terminal velocity (only ∼2-3 times greater) and, consequently, exhibit more-uniform flow. In group A particles, the minimum bubbling velocity is much higher than the minimum fluidization velocity, and a stable bubble size exists.…”

Hydrodynamic Aspects of a Circulating Fluidized Bed with Internals

“…U slip /U o is the ratio of true fall velocity of the particle in a finite medium to particle velocity in an infinite medium. This is related to bed voidage which accounts for the buoyancy effect (Balasubramaniam and Srinivasa kannan, 1997). U slip , predicted using eq 2, is plotted against bed voidage .…”