Discrete Method Simulation Of Multi-Particle Gas-Solid Two-Phase Flow In A Fluidized Bed

Fluidized bed has the characteristics of high efficiency in the process of mixing and heat and mass transfer.It is widely applied in the combustion process,material separation and mixing,granulation and other industrial processes.The intense reaction in the fluidized bed between gas and solid phases affects the energy and momentum transfer,which directly determines the fluidized reaction speed and efficiency.The materials in fluidized beds are complex multi-component particles with different particle size and density during the actual industrial processes.However,most of the previous studies focus on characterizing the single-component or two-component particles.Few studies on the simulation of multi-particle fluidized beds have been reported.Thus,it is essential to explore the gas-solid characteristics in multi-particle fluidized beds which can provide reference for the design and optimization of industrial processes.Discrete Element Method is used in this paper to achieve the simulation of the gas-solid two-phase flow of class D multi-component particles with different particle sizes in a fluidized bed.Meanwhile,the simulation work of single-component particles is also conducted to make a comparison with the multi-component particles.Firstly,the theoretical analysis and experimental verification of the proposed model are carried out.Then,according to the particle motion information in the fluidized bed,the fluidized bed unlocking process,velocity distribution of particles and gas,velocity difference of multi-component particles,mass fraction distribution,void fraction distribution and mixing index in the bed were obtained.The results show that the fluidization characteristics of multi-component particles and single-component particles are obviously different,the flow of particles in the fluidized bed is also affected by the inlet air velocity.The expansion ratio of multi-particle fluidization is larger than that of single-particle fluidization whilst the initial bed filling height and inlet gas velocity are fixed.Increasing the velocity of inlet gas will increase the bed expansion ratio,the velocity of particles,and the bed unlocking time.The aggregation of particles with different sizes will occur in different areas of the bed with high gas velocity,but is not obvious at low gas velocity.The velocity of particles with different sizes in the same location is different.However,the average velocity distributions of multiple particles and single particles is similar in the same reaction area.Statistical analysis of the mixing degree of particles has shown that the mixing degree of multi-component particles is greater than that of single component particles.The simulation work displays that the EDM is capable of covering the shortages of theoretical analysis and experimental research,and is suitable for the study of multi-particle gas-solid two-phase fluidized bed.