Impact of inclined platforms on mixed marticle flow in down-tube based on CFD-DEM

Biomass particles can often be confined to the insufficient disturbance and mixing flow within the down-tube pyrolysis reactor. In this study, a systematic investigation was implemented to explore the influence of an inclined platform inside the down-tube on the flow behavior of ceramic balls and biomass particles. The particle mixing was also analyzed using experimental and simulation. The parameters of the inclined platform were treated as the experimental variables, including the position, tilt angle, and height. While the degree of particle dispersion was taken as the evaluation criterion. The particle flow was then simulated using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). particle image velocimetry (PIV) was employed to verify the simulation. The results indicate that the height of the inclined platform shared the most significant effect on the dispersion degree of the particles, followed by the platform’s position and tilt angle. The optimal working parameters were determined after optimization, where the bottom of the inclined platform was positioned 245 mm from the corner of the down-tube, with a height of 27 mm and a tilt angle of 149°. The degree of particle dispersion increased by 50.24% under these optimal conditions, indicating the better homogeneity of the particle mixture. The inclined platform was introduced to significantly enhance the flow characteristics of the particles. Furthermore, the axial average velocities of the biomass particles and ceramic balls decreased by 14.38% and 11.43%, respectively, compared with the conditions without the inclined platform. Concurrently, the average residence time of the particles increased by 20.00% and 5.75% for the biomass particles and ceramic balls, respectively. As such, the inclined platform effectively extended the residence time of the particles within the down tube. Thus, the pyrolysis reactions were enhanced for the high efficiency of the reactor. Moreover, the inclined platform also altered the flow characteristics of the particles. In the absence of the inclined platform, the particles exhibited a distinct centripetal flow, leading to the uneven particle distribution with the segregation, where some particles were denser at the bottom and sparser at the top. With the aid of the inclined platform in place, the parabolic flow of particles was obtained to effectively disrupt the segregation for the more uniform distribution of particles. The homogeneity of the particle mixture further facilitated the efficiency of the pyrolysis reaction. It was of significant importance to optimize the pyrolysis performance of reactors. The inclined platform also increased the mixing and flow behavior for the better homogeneity of the particle mixture. The findings can offer new insights into the design and optimization of down-tube reactors in the further development and application of biomass pyrolysis. Especially, the high efficiency of biomass energy utilization also contributed to the pyrolysis reactions. The findings can hold great potential for the practical implications of biomass energy conversion.