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Simulations of a multicomponent mixture in the reflux classifier todemonstrate the effect of dispersion coefficient on its internal state

Syed Naveedul Hasan, Khan Naseer Ahmed, Habib Muddasar

Physicochemical Problems of Mineral Processing

2020

Vol. 56, iss. 1

76--88

In this study, influence of the dispersion coefficient on the internal state of a multicomponent mixture comprising 35 types of particle species with five different sizes ranging -2.0+0.25 mm and seven different densities, 1400 to 2000 kg/m3, in a reflux classifier under continuous process conditions is presented. Simulations were performed to study the effect of dispersion coefficient on the separation density, D50, separation efficiency, Ep, and solid volume fraction of the multicomponent mixture. The simulation results provided a good agreement with the published experimental results of the reflux classifier, operated at full scale in 2005, for a relatively high value of the dispersion coefficient, 0.0030 m2/s, and a relatively small value of the dispersion, 0.00030 m2/s, in the fluidization and inclined sections of the device, respectively. Moreover, different fixed values of the dispersion coefficient and a published proposed model of the dispersion coefficient were incorporated in the model to examine variations in the system and were compared with the validated simulation results. It was found that the selected values of the dispersion coefficient had not much effect on the D50 values. However, the Ep values changed significantly with changes in the dispersion coefficient values. The smaller values of the dispersion coefficient provided lower values of the Ep that did not match well with the validated simulation results. Furthermore, the variations in the total solid volume fraction within the reflux classifier for different values of the dispersion coefficient has been demonstrated.

Simulations of mono-sized solid particles in the reflux classifier under continuous process conditions

Syed Naveedul Hasan, Khan Naseer Ahmed

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 3

631--642

In this study, a fluidized bed separator incorporating inclined channels, the Reflux Classifier (RC), was modeled to describe the transport behavior of mono-sized solid particles using a 2D computational segregation-dispersion model. The model is a volume flux-based model comprising the dispersion and segregation fluxes. Simulations were performed to examine variations in the solid volume fraction of particle species of size 0.163 mm and density 2450 kg/m3 by altering variables such as fluidization velocity, underflow rate and water flux in the feed. The system achieved a maximum solid volume fraction of 0.50 (v/v) near the base at a fluidization velocity 0.00020 m/s, that reduced to 0.20 at the fluidization velocity 0.0060 m/s. Overall, the results showed a decrease in the average solid volume fraction from 0.37 to 0.21 for the corresponding fluidization velocities. Simulation results also successfully demonstrated the capacity of the RC in retaining the solid particles at a superficial fluidization velocity 0.020 m/s, significantly higher than the terminal settling velocity, 0.015 m/s, of the solid particles, due to the presence of an inclined channel. Similarly, with increasing the underflow rate, the average solid volume fraction decreased from 0.29 to 0.055 due to the discharge of a larger quantity of solid particles from the base. Furthermore, a higher concentration of solid particles was observed in the inclined section at lower water flux in the feed stream. Additionally, flux balance calculations were carried out at different points within the RC to ensure the accuracy of the model predictions.