Simulation Of The Mixing Characteristics In Two-Component Pulsed Fluidized Bed

Pulsed fluidized bed has been widely used in energy, chemical engineering, and many other industrial fields as an advanced fluidized-bed technology. The pulsating gas can improve the flow, heat and mass transfer characteristics in the classic fluidized-bed, making it can be used to process the materials with high dispersion, conglobation and adhesion. The multiphase systems often involve the mixing of two or more components, which make the flow status in the fluidized-bed more complicated and too difficult to study by experiments. Numerical simulation can avoid many systemic and man-made errors, save time and cost with the drag model, turbulent model and so on, so it is a very important technique to the practical application of fluidized bed.The hydrodynamics of the systems with same density and same diameter in the fluidized-bed with rectangle-wave pulsating gas flow were simulated using a computational fluid dynamics software-Fluent6.3. Euler two-fluid model was used in numerical simulation with User-Defined functions (UDF) to describe the inlet pulsed air flow rate which includes the pulsating air flow modes, frequency, amplitude, etc. Time step, discretization and solution methods were suitably chosen according to the requirements of convergence relaxation factors.The mixing index was used to evaluate the mixing degree for the two-component fluidized-bed. The mixing characteristics of the fluidized-bed under the resonance frequency, high frequency and low frequency were analyzed. The pulsed period was changed to observe the mixing process with same pulse duration ratio, and the pressure drop wave as it was pulsed. At last, the effect of particle density and size to fluidization was compared.The simulation results indicated that the pulsed flow mixed the two components better under the resonance frequency rather than under high frequency and low frequency, then made the averaged-size distribution along bed height uniform, and the mixing process had a good stability. The mixing station of the system with same density was better than that with same diameter if other conditions were constant. It shows that different density is the main factor resulting to segregation. The mixing station with pulsed-gas is better than steady gas, which can save energy, so it has a broad foreground.