(399b) Heterogeneous Flow Structure in Gas-Solid Risers: Continuous MODELING

Gas-solid riser flow exhibits strong heterogeneous structure in both axial direction and radial directions. Our previous model suggests that a ?core-annulus-wall? 3-zone structure could exist when riser operates with conditions of small diameter and the dense flow transport at low gas flow velocities. Whereas, a typical so-called ?core-annulus? 2-zone flow structure exists with large diameter riser or with high gas transport velocity. This paper is focused on a comprehensive modeling of continuous gas-solids flow structure both in radial and axial directions which takes into account of the effect of wall boundary on the formation of heterogeneous flow structure. The characteristic values at the wall boundary and the centerline are employed to describe the heterogeneous flow structure, which is beneficial both to the modeling of formation mechanisms of heterogeneous flow structure and to the convenience of experimental validations. The transport mechanisms due to collisional diffusive mass transfer and turbulent mass transfer as well as the effect of wall boundary are modeled. Based on conservation laws of mass, momentum and intrinsic mechanisms of both gas and solids phases, this mechanistic model, consists of a set of coupled integral-differential equations along with a set of radial transport mechanistic sub-models. The proposed model predicts the phase transport profiles such as the solids concentration, phase velocities and pressure drops in different regions along the riser. The model also could yield the critical information of flow structure characteristics such as back flow, wall frictions and choking.