Three-Dimensional Simulation of the Pyrolysis of a Thermally Thick Biomass Particle

A three-dimensional thermally thick model is established, in which both the biomass particle and gas phase are treated as continua and their respective governing equations are solved. The intra-particle heat transfer, biomass composition evolution, and particle deformation as well as interphase couplings during pyrolysis are all considered. After validation, the integrated model is applied to simulate the pyrolysis process of a thermally thick biomass particle. The evolution histories of particle internal temperature, mass loss, morphology, and composition are captured. Meanwhile, the distributions and variations of gas properties (e.g., temperature, velocity, and mass flux) are also revealed. Furthermore, the influences of operation temperature, particle shape, and particle aspect ratio are explored. Increasing the operation temperature enhances the mass loss and shrinkage, induces an earlier gas release, generates a higher internal gas velocity, and promotes the compressive stress at the particle center. The cylindrical and cuboid particles present similar evolution characteristics, while the spherical particle undergoes the slowest heating up and conversion processes. Increasing the particle aspect ratio enhances its internal heat diffusion, accelerates the mass loss rate, and shortens the duration of the particle shrinkage process. All these observations can help us deeply understand the pyrolysis mechanism of thermally thick biomass particles.