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Numerical Investigation of Solid Particles Mixing and Segregation in Pulsation-Assisted Fluidized Beds

Heidarian, Setareh | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56661 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Fotovat, Farzam
  7. Abstract:
  8. Gas-solid fluidized beds are widely used in various industrial processes due to their multiple advantages and applications, such as enhanced heat transfer, improved mixing and separation of solid particles, drying, combustion, particle coating, etc. In many processes, the mixtures of solid particles in the fluidized bed reactors have a distribution of particle sizes or are different in terms of density or shape of particles. Despite the ability of fluidized beds to improve the mixing of particles, the existence of the aforementioned differences can cause separation of particles under certain conditions. Pulsed fluidized beds are beds where the gas flow enters the bed in a pulsating manner. These beds are usually used for particles that are difficult to fluidize, such as small or sticky particles. The behavior of these beds, under different conditions, has significant differences with the conventional beds. In this research, the main objective is to numerically investigate the solids mixing and separation phenomenon in pulsed gas-solid fluidized beds. For this purpose, using the experimental data from previous researches, a simulation of a fluidized bed reactor, containing a mixture of binary solid particles, with a density of 2650 kg/m3 and particle sizes of 330 and 920 µm, was performed. The gas-solid two-phase flow modelling was done using computational fluid mechanics and two-fluid method based on the kinetic theory of granular flow. The results of the simulations were primarily validated using the experimental data reported in the literature. Then, the non-pulsating flow velocities of 0.16, 0.30, 0.40, 0.50 and 0.60 m/s, and pulsating flow velocities of 0.16 and 0.30 m/s were applied to the bed as apparent velocities of the inlet gas. The apparent speed of 0.16 m/s increased the mixing index value of the mixture of particles, from 1 to about 0.92 in the non-pulsating state, and from 1 to about 0.86 in the non-pulsating state, which indicates a higher separation value in the pulsating state. At a velocity of 30 m/s, the value of the mixing index of the mixture, reaches from 1 to 0.6 in non-pulsating mode, and from 1 to 0.97 in pulsating state. The results show that using a pulsating flow leads to a higher separation rate at a lower apparent gas velocity. In other words, in a pulsed bed, the transition from separation to mixing of particles can be achieved at lower range of gas velocities compared to the conventional beds. Moreover, it was found that by adjusting the pulse frequency of the gas velocity, different levels of mixing or separation of particles can be achieved. The initial mixing state of particles could differently affect the ultimate degree of mixing when non-pulsating and pulsating flows at U= 0.3 m/s were applied to the fluidized bed
  9. Keywords:
  10. Fluidization Flow ; Computational Fluid Dynamics (CFD) ; Solids Mixing and Segregation ; Hydrodynamics ; Gas-Solid Pulsed Fluidized Bed ; Solid-Gas Fluidized Bed

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