Hydrodynamic modeling of gas-solids riser flows

Hydrodynamics plays a crucial role in optimum design and performance of circulating fluidized beds (CFB). The traditional approach of equating the static pressure drop to the bulk weight in a riser section overlook the effects of solids acceleration and kinetic energy dissipation due to solids collisions and inter facial frictions, which leads to an overestimation of local solids holdup. The overestimation of solids holdup is very significant in the acceleration and dense phase transport regions. This paper presents a mechanistic model based on gas-solid continuity and momentum equations, along with the modified drag force correlation and new formulation for moment dissipation of solids due to solids collisions. The proposed model yields the coupled hydrodynamic parameters of solid volume fraction, gas and solid velocity, and pressure distribution along the whole riser. The model predictions are reasonably validated against the published experimental data from four independent research groups for a wide range of operation conditions.