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Investigation of Solids Mixing in Tapered Fluidized Beds

Sarafan, Kiana | 2024

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57607 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Molaei Dehkordi, Asghar
  7. Abstract:
  8. This work investigates the mixing process of binary solid mixtures in tapered gas-solid fluidized beds through a combination of experimentation and CFD-DEM simulation. Tapered beds exhibit unique dynamic characteristics due to the axial direction's velocity gradient, distinguishing them from cylindrical or columnar fluid beds. To explore this, experimental runs were conducted using a pseudo-2D tapered fluidized bed with an apex angle of 8.13º and a height of 0.9 m. White and red solid particles were used with the same density but different sizes and average diameters of 500 and 1000 μm, respectively. A digital image analysis technique was employed to evaluate the mixing index. In addition, the study examines various factors, including inlet gas velocity, percentage of heavier particles for the evaluation of minimum fluidization velocity and solids mixing degree, using the Lacey mixing index. Moreover, the tapered fluidized bed was simulated using the Eulerian-Lagrangian approach, where the solid motion was modelled by the discrete element method, and the Navier-Stokes equations described the gas flow. The transient simulations yielded a mixing time that agreed with our experimental data. The experimental data indicate that the Umf of the solid mixtures falls between the flotsam and jetsam particles. Furthermore, the previously established single-particle correlation was extended to binary solid mixtures in a tapered fluidized bed. The results also revealed that increasing the inlet gas velocity enhances the mixing process, leading to a quicker attainment of the equilibrium mixing index. For example, with a jetsam mass fraction (Xj) of 0.47, the complete mixing times at U0 of 0.52 and 0.67 m/s were 21.2 and 4.41 seconds, respectively. Additionally, the present work provides valuable data for the numerical modelling of tapered fluidized beds, especially when dealing with mixtures of different particle sizes
  9. Keywords:
  10. Tapered Fluidized Bed ; Digital Images Analysis ; Mixing Index ; Discrete Element Method ; Computational Fluid Dynamic-Discrete Element Method (CFD-DEM) ; Solids Mixing

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