Numerical simulation of local and global mixing/segregation characteristics in a gas-solid fluidized bed

Researches on solids mixing and segregation are of great significance for the operation and design of fluidized bed reactors. In this paper, the local and global mixing and segregation characteristics of binary mixtures were investigated in a gas-solid fluidized bed by computational fluid dynamics-discrete element method (CFD-DEM) coupled approach. A methodology based on solids mixing entropy was developed to quantitatively calculate the mixing degree and time of the bed. The mixing curves of global mixing entropy were acquired, and the distribution maps of local mixing entropy and mixing time were also obtained. By comparing different operating conditions, the effects of superficial gas velocity, particle density ratio and size ratio on mixing/segregation behavior were discussed. Results showed that for the partial mixing state, the fluidized bed can be divided into three parts along the bed height: complete segregation area, transition area and stable mixing area. These areas showed different mixing/segregation processes. Increasing gas velocity promoted the local and global mixing of binary mixtures. The increase in particle density ratio and size ratio enlarged the complete segregation area, reduced the mixing degree and increased the mixing time in the stable mixing area. (c) 2022 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd.

Automated summary

This paper investigates the local and global mixing and segregation characteristics of binary mixtures in a gas-solid fluidized bed using a computational fluid dynamics-discrete element method (CFD-DEM) coupled approach. A methodology based on solids mixing entropy is developed to quantify the mixing degree and time of the bed. The effects of gas velocity, particle density ratio, and size ratio on mixing/segregation behavior are discussed. The results show that increasing gas velocity promotes the mixing of binary mixtures, while increasing particle density ratio and size ratio lead to greater segregation and reduced mixing degree.