Experimental Study of Transient Hydrodynamics in a Spouted Bed of Polydisperse Particles

In industrial processes such as chemical looping combustion, single-component spouted beds of monodisperse particles are very rarely used but the spouted beds of polydisperse particles have been widely used. The flow characteristics of polydisperse particles are much more complex than the single particle fraction in a fluidized bed. To investigate the gas-solid two-phase flow characteristics of the particles with different diameters in a spouted bed, the segregation and mixing characteristics, bubble morphology, minimum spouting velocity, and pressure fluctuations of the particles with different sizes under different superficial gas velocities are studied experimentally. The results show that higher the initial bed height and larger the volume fraction of the bigger particles, higher is the minimum spouting velocity. Moreover, the magnitude of the minimum spouting velocity increases exponentially with increase in the volume fraction of the bigger particles. At low superficial gas velocity, there is a clear trend of segregation between the particles of different diameters. At moderate superficial gas velocity, the mixing trend among particles of different diameters is enhanced, and the pressure fluctuations in the bed present some degree of regularity. At high superficial gas velocity, the particles of different diameters tend to separate again, the pressure fluctuations become intense, and the particle flow turns into a turbulent state. Furthermore, when the bed becomes stable, the particles of different diameters distribute within the bed with regular stratification.