Numerical study of the effect of gas distributors and baffles on the bubble distribution, gas and solid mixing in a fluidized bed
Abstract
In this study, the multi-phase Eulerian-Eulerian two-fluid method (TFM) coupled with the kinetic theory of granular flow (KTFG) was used to investigate hydrodynamics of particle flows (Geldart Group B) in a lab-scale fluidized bed Geldart Group B particles, operating in bubbling and turbulent regimes. The effect of gas distributors and baffles on the distribution of the gas bubbles, and the mixing of gas and solids were investigated under various superficial gas velocities.
The numerical model is validated by experimental results from two different measurement methods with various gas distributor configurations and a superficial gas velocity ranging from 0.4 m/s to 1.0 m/s; the E-probe method measured the local gas flux while the radiation transmission method provided the local solid hold-up. Simulation with different gases and particles spanned the range from lab to industrial conditions. The gas distributor configuration and angle were found to have a significant impact on the gas bubble distribution.
Baffles are used to modify fluidized bed hydrodynamics in industrial processes. This work simulated the impact of various baffles on fluidized bed hydrodynamics. A ring baffle can redirect gas bubbles and induce strong liquid recirculation currents. Adding a vertical fluxtube to a baffle can significantly modify its impact on the gas flow patterns. With a fluxtube that does not extend past the baffle lip, the gas is more evenly distributed in the fluidized bed. The fluxtube length has a stronger impact than the fluxtube diameter on the fluidized bed hydrodynamics.
New methods were developed to characterize the gas and solids mixing patterns from the simulation results. Gas and solids mixing in both horizontal and vertical directions are affected by the gas distributor configuration and the presence of a ring baffle. The ring baffle separates the bed into two regions and reduces the back mixing of gas and solids between the upper and lower regions