Instantaneous mixing characteristics of binary mixtures differing in density in a gas‒solid fluidised bed--颗粒学报PARTICUOLOGY

Wan, Z., Lu, Y., & Wang, H. (2020). Instantaneous mixing characteristics of binary mixtures differing in density in a gas‒solid fluidised bed. Particuology, 53, 63-71. https://doi.org/10.1016/j.partic.2019.11.007

Instantaneous mixing characteristics of binary mixtures differing in density in a gas‒solid fluidised bed

Zhen Wan, Youjun Lu ^*, Hao Wang

State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, China

10.1016/j.partic.2019.11.007

Volume 53, December 2020, Pages 63-71

Received 25 September 2019, Revised 3 November 2019, Accepted 27 November 2019, Available online 20 February 2020, Version of Record 16 December 2020.

E-mail: yjlu@mail.xjtu.edu.cn

Highlights

• Instantaneous mixing characteristics of binary mixtures were studied.

• An equation was proposed to describe the mixing process.

• Effects of superficial gas velocity and density ratio on mixing were investigated.

• Axial concentration profiles were obtained for the stable fluidisation stage.

Abstract

Characterisations of instantaneous mixing behaviours in fluidised beds with binary mixtures has many challenges. We studied the instantaneous mixing characteristics of binary mixtures in a 2-D quasi gas‒solid fluidised bed using a capacitance probe method. This method enabled the quantitative assessment of instantaneous mixing behaviours, including mixing index, rate, and time. Three kinds of binary mixtures of similar size but different density were used for the transient and steady fluidisation experiments in a bubbling fluidised bed. The mixing curves of initially segregated binary mixtures were acquired, and the instantaneous characteristics for the entire process were analysed. An equation was proposed to describe the mixing process and predict the mixing degree over time. By comparing experiments with different working conditions, the effects of superficial gas velocity and density ratio on the mixing in the centre and at the wall of the fluidised bed were addressed. During the stable fluidisation stage, the axial concentration profiles of the mixtures were obtained, and the mechanisms of mixing were discussed. Results showed that the mixing level increased logarithmically with time and eventually reached a relatively stable value. Increasing the superficial gas velocity and reducing the density ratio promoted mixing and reduced mixing time. High superficial gas velocities tended to mix the mixtures well and quickly, regardless of the density ratio of the two components.

Graphical abstract

Keywords

Binary mixtures; Fluidised bed; Mixing; Instantaneous characteristics

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