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摘要
Spout fluidized beds are important for industrial processing, and multiple-spout fluidized beds play an important role in chemical reactions. However, particle flow behaviors in multiple-spout fluidized beds are not well known in wet particle systems. In this study, the flow behaviors of particles were investigated in dry and humid multiple-spout fluidized beds using a discrete element method (DEM). The simulated spout fluidized beds are similar to the ones used in the Buijtenen et al.'s experiment (published in Chemical Engineering Science, 2011, 66(11): 2368-2376). In the reference, particle flow behaviors were measured and investigated by PIV and PEPT in multiple spout fluidized beds. In this work, the simulated results are compared with the experimental data in single and double spout fluidized beds from Buijtenen et al., and the time-averaged particle velocities are compared to validate the simulation method. In contrast, simulated results with a liquid content of 1% in the bed showed good agreement with the data in the experimental results with an air relative humidity of 50%. Different liquid contents of the particles were applied to investigate the particle flow behaviors in wet granular systems. The liquid bridge force had a strong influence on the flow behaviors of the particles in the dense region, which resulted in different hydrodynamic characteristics between the dry and wet particles. In addition, the drag force dominated the particle flow behavior in the dry and wet particle systems. Moreover, in a wet granular system, the mass particle fluxes decreased, and the fluctuation of the pressure drops increased with an increasing influence of the liquid bridge force on the particles. Furthermore, with an increasing liquid content, the energy fluctuation of the particles weakened gradually with less active motions. A comparison of the hydrodynamic flow behaviors in single-spout and double-spout fluidized beds was carried out as well. Comparisons of the solid circulation rate and the colliding characteristics between single-spout and double-spout fluidized beds were conducted. Particularly, a comparison of the mixing characteristics demonstrated that the particles were mixed more completely in a double-spout fluidized bed. Therefore, the double-spout fluidized bed could provide more adequate space for mass and heat transfer under the same condition. This was important in providing a theory for designing the industrial reactor.
