Segregation In Fluidized Beds Research Articles

Modelling of particle segregation in fluidized beds

Mixing of different size and density particles plays a vital role in the hydrodynamics of fluidized beds. In this study, a multiphase model based on the kinetic theory of granular flow has been developed to study the mixing behaviour of biomass and sand particles in a bubbling fluidized bed. After validating the model using available experimental data from the literature, it was used to study the influence of various parameters such as superficial gas velocity, mixture composition and particle size. Emphasis was given on understanding the impact of these parameters on the particle segregation number, which is the parameter used to quantify the segregation behaviour of the fluidized bed. Results are plotted as the change in particle segregation number with respect to time for different mixture compositions, superficial gas velocities and particle diameters. The results show that mixing is promoted with the increase in gas velocities which give lower values of particle segregation number. Increase in ratio of biomass in the mixture leads towards segregation while increase in biomass particle diameter promotes mixing. The results of 2D simulations are also compared with the 3D configuration.

Segregation of fluidized binary mixtures of granular solids

AbstractFluidization behavior of binary mixtures of solids is addressed. Three binary systems were considered, obtained by mixing monodisperse granular solids of different size and/or density. A segmented fluidization column equipped with multiple pressure transducers was the experimental apparatus. Monitoring of pressure at different locations along the bed and direct characterization of solids contained in each segment were the experimental tools. The binary granular beds were in one of the following states, depending on gas superficial velocity and initial mixture fraction: fixed, bubbly‐free fluidization, transient fluidization, and bubbling steady fluidization. Fluidization regimes were mapped in a gas superficial velocity vs. initial mixture fraction phase plane. Axial solids concentration profiles along the bed and solids segregation rates were also assessed for the three systems as a function of the operating conditions of the bed. Differences and similarities between the systems were analyzed and interpreted in the light of the basic segregation patterns. In particular whether a defluidized bottom layer of jetsam‐rich solids is formed upon segregation appears to be an important key to the segregation phenomenology. The currently available models for the prediction of solids segregation in fluidized beds prove to be helpful to understand the qualitative features of the phenomenology, but fall short when quantitative prediction of segregation parameters is afforded. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3095‐3106, 2004

Hydrodynamics of particle segregation in fluidized beds

Hydrodynamics of particle segregation in fluidized beds

The influence of perforated baffles on the mixing and segregation of a binary group B mixture in a gas–solid fluidized bed

This paper presents a method of influencing the axial mixing of particles and promoting segregation in fluidized beds without otherwise changing the character of the bed substantially (at least at low to moderate gas velocities). The method is based on the introduction in the bed of horizontal screen-like baffles with a relatively large free area. It will be shown that such baffles promote the particle segregation significantly, producing a layer of almost pure heavy/large particles in a binary mixture which would be well mixed when fluidized in a conventional bed at the same velocity. The effect of three different types of baffles, of the number of baffles and of the fluidization velocity on the quality of separation is examined. A physical reason for the demixing effect is suggested.