Kinetic behavior and heat transfer characteristics of binary spherical and spherocylindrical particles in a spouted bed

Biomass fuels are seen as an important energy alternative to fossil fuels due to their low cost, sustainability and eco-friendly advantages. However, due to the nature of biomass particles, fluidization is poor and often requires the addition of inert particles of high density and small size to assist. Furthermore, the size, shape and density of the particles significantly affect the gas–solid two-phase flow. This can be even more difficult to predict and control in binary particle systems involving non-spherical particles. Therefore, in this paper, the effects of mixing spherocylindrical biomass particles with spherical inert particles of different diameters (2.5 mm, 3.0 mm, and 3.5 mm) in a spouted bed on the flow and heat transfer behaviors of the particulate system are discussed by using the CFD-DEM method. The results show that when the difference between the diameter of spherical particles and the equivalent diameter of spherocylindrical particles is larger, the difference between the average heights of the two kinds of particles gradually increases, the average number of particle collisions of spherocylindrical particles- spherocylindrical particles decreases, and the average number of collisions of spherical particles-spherical particles increases. In binary particle systems where the diameter of the spherical particles is smaller, the aggregation of spherical particles at the bottom of the bed is more pronounced. Furthermore, the larger the diameter of the spherical particles in the binary particle system, the larger the drag force on the spherocylindrical particles, and the convective heat transfer and rotational kinetic energy of the two particles increase, but the law of variation of the translational kinetic energy of the different particles is different. It was also found that increasing the gas velocity helped the cooling of particles, but the particle collision frequency did not necessarily increase. Furthermore, the cooling rate of spherocylindrical particles can be accelerated when the difference between the diameter of added spherical particles and the equivalent diameter of spherocylindrical particles is smaller, but the cooling rate of the spherical particles is reduced.