Assessment of dynamic characteristics of fluidized beds via numerical simulations

Euler–Lagrange simulations coupled with the multiphase particle-in-cell (MP-PIC) approach for considering inter-particulate collisions have been performed to simulate a non-reacting fluidized bed at laboratory-scale. The objective of this work is to assess dynamic properties of the fluidized bed in terms of the specific kinetic energy of the bed material $k_S$ in J/kg and the bubble frequency $f_B$ in Hz, which represent suitable measures for the efficiency of the multiphase momentum exchange and the characteristic timescale of the fluidized bed system. The simulations have reproduced the bubbling fluidization regime observed in the experiments, and the calculated pressure drop $\Delta p$ in Pa has shown a reasonably good agreement with measured data. While varying the bed inventory $m_S$ in kg and the superficial gas velocity $u_G$ in m/s, $k_S$ increases with $u_G$ due to the increased momentum of the gas flow, which leads to a reinforced gas-to-solid momentum transfer. In contrast, $f_B$ decreases with $m_S$, which is attributed to the increased bed height $h_B$ in m at larger $m_S$. An increased gas temperature $T_G$ from 20 to 500 °C has led to an increase in $k_S$ by approximately 50%, whereas $\Delta p$, $h_B$, and $f_B$ are not sensitive to $T_G$. ... mehrThis is due to the increased gas viscosity with $T_G$, which results in an increased drag force exerted by the gas on the solid phase. While up-scaling the reactor to increase the bed inventory, bubble formation is enhanced significantly. This has led to an increased $f_B$, whereas $k_S$, $h_B$, and $\Delta p$ remain almost unchanged during the scale-up process. The results reveal that the general parameters such as $h_B$ and $\Delta p$ are not sufficient for assessing the hydrodynamic behavior of a fluidized bed while varying the operating temperatures and up-scaling the reactor dimension. In these cases, the dynamic properties $k_S$ and $f_B$ can be used as more suitable parameters for characterizing the hydrodynamics of fluidized beds.