Modelling the combustion of thermally thick biomass particles

Abstract

A new combustion model is developed for thermally thick biomass particles by considering the intraparticle heat conduction, radiation, and reactions as well as the interaction of the internal and external flows of the particle. The particle temperature is solved in a continuous system with a finite element method, while the pyrolysis and char conversion are resolved in a discrete system. Furthermore, the flow fields both inside and outside the particle are modeled by a uniform multiphase CFD algorithm. The integrated model is first validated with the experimental data available in the literature. Numerical simulations not only provide the temperature and mass loss evolutions of the particle, but also reveal the flame structure, porosity evolvement, gas species distribution and streamlines inside and outside the particle which are quite difficult to be obtained in experiment. Moreover, the influences of inflow velocity, oxygen mass fraction, particle size and shape on biomass combustion behavior are also investigated. Results show that, the intraparticle heating and the char oxidation processes have a close relationship with the inflow velocity and particle size. The alteration in the oxygen mass fraction also has an important impact on the particle combustion behavior. In addition, different pyrolysis characteristics and flame structures are observed in the combustion of the square and rectangular particles.