Numerical Simulation of Gas-Solid Flow in CFB Riser Using Different Approaches of Kinetic Theory of Granular Flows

Abstract

In this paper is applied the two-fluid model to simulate the gas-solid flow in a riser of a circulating fluidized bed (CFB). The phases are modeled as a continuum medium computing the solid’s pressure and dynamic viscosity by the kinetic theory of granular flows (KTGF). The numerical simulations are performed with the MFIX (Multiphase Flow with Interface eXchanges) computational fluid dynamics (CFD) code developed in the National Energy Technology Laboratory (NETL). The main aim of this work is to perform a comparative analysis of the simulation results obtained from three different versions of the KTGF. In the work are presented time-averaged results comprehending the radial profiles of the axial velocities of gas and solid phases, the solid volumetric fraction and the solid mass flow. These results are compared with the available experimental data showing a different behavior for each version of the KTGF. For a more complete comparative analysis also are presented time-averaged and transient snapshots of the gas volumetric fraction in two risers sections disposed at two different heights of the column. In all the simulations is used a uniform two-dimensional computational mesh and the Superbee second order scheme for the discretization of the advective terms. The numerical results show that the procedure for the computation of the solid phase pressure and viscosity influences in a significant way the behavior of the gas-solid flow in a riser. These differences are obtained even when it is considered only the KTGF with slightly variations for the constitutive equations computations.