Eulerian-Lagrangian simulation of pulverized biomass jet using spheroidal particle approximation

Abstract

Pulverized biomass has great potential to replace coal in many industrial systems such as suspension-firing furnaces and entrained-flow gasifiers. The shape of pulverized biomass deviates significantly from the quasi-spherical coal particle, however, it is common to simulate pulverized biomass particles as spheres as most biomass models are developed based on coal models. With the aim of obtaining a more realistic simulation of pulverized biomass, this work extends the treatment of pulverized biomass to spheroids. A spheroid model that accounts for spheroidal particle drag force and torque was implemented into an Eulerian-Lagrange computational fluid dynamic solver. Comprehensive verifications and validations were performed by comparing with experiments and direct numerical simulations. Furthermore, non-reactive simulations of a lab-scale entrained flow gasifier were carried out using a conventional spherical particle model, a simplified non-sphere model, and the implemented detailed spheroidal particle model. By studying the simulation results of particle and fluid velocities in axial, radial and tangential directions, differences were observed when comparing the sphere model, the simplified non-sphere model, and the spheroid model. The spheroid model shows that particle orientation, which is ignored in the sphere model and the simplified non-sphere model, plays a role in the behavior of the particle dynamics. It was also found that, under such conditions, the spheroid model, compared to the sphere model, yields a more dispersed distribution regarding the particle residence time and local concentration. These non-reactive simulation results imply that shortcomings may exist in the common practice of simulating conversion of pulverized biomass in which the sphere model or the simplified non-sphere model is applied.