Experimental and numerical study on a bubbling fluidized bed with wet particles

Abstract

As liquid bridge between particles acts an important role in the particle system, it is of considerable significance to analyze the flow hydrodynamics of wet particles in fluidized beds, which will improve the reactor design and process optimization. Thus, experimental and numerical investigations on wet particles in a bubbling fluidized bed are conducted in current work. On experimental side, particle image velocimetry (PIV) technology is employed with a designed bubbling fluidized bed. The silicone oil is used in this work because it is nonvolatile and transparent. On numerical side, a modified discrete element method (DEM) numerical method is developed by compositing an additional liquid‐bridge module into the traditional soft‐sphere interaction model. Most of the physical parameters are chosen to correspond to the experimental settings. Good agreements of particle velocity are found between the DEM simulation and PIV measurement. The performance of different liquid contents and superficial gas velocities are examined. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1970–1985, 2016

Magnetic resonance imaging of gas–solid fluidization with liquid bridging

“…These results show qualitatively how cohesion due to liquid bridging makes it more difficult for bubbles to rise freely through beds, as it becomes more difficult to move particles relative to one another due to viscous and capillary forces. The decrease in speed of particles is consistent with previous studies in pseudo‐2D beds, a study using particle tracking to find average particle speed on a temporally unresolved level and a computational study of a 3D bed . The Supporting Information Video shows a set of videos of fluidization behavior for these dry and wet cases with values of U/U mf,dry and U/U mf,wet of 1.1, 1.3, and 1.5 to provide a fuller comparison.…”

“…We are unaware of prior experimental studies which have been able to investigate the effects of liquid bridging on bubble size or number of bubbles in 3D beds, pointing to the power of MRI. Previous studies have found discrepancies in the effect of adding liquid on the amplitude and frequency of pressure oscillations; this discrepancy can be attributed to different fluidization conditions, as well as the fact that pressure oscillations result from a variety of changes in hydrodynamics. We are unaware of any experimental studies which have investigated the validity of maintaining the same value of U/U mf between wet and dry conditions, but the prior computational study of Boyce et al produced insights consistent with those in this article.…”

“…On a larger scale, this leads to greater heterogeneity in gas and particle flow, affecting many aspects of fluidization hydrodynamics, which in turn alters heat and mass transport as well as chemical reactions. Previous studies have shown that the addition of small amounts of liquid alters the oscillations in pressure drop across the bed, slows the speed of particles, and increases the minimum fluidization velocity . Studies have also sought to map the behavior of wet fluidized beds into regimes based on the amount of liquid added as well as the surface tension and viscosity of the liquid; these regimes have included shifts in the Geldart grouping of the particles and the growth or breakup of agglomerates .…”

“…Difficulties in fully understanding the effects of liquid bridging on fluidization hydrodynamics stem in part from a lack of temporally and spatially resolved experimental data on gas and particle motion in wet fluidized beds. Previous studies have been limited to device‐scale measurements, such as pressure oscillations and fluidization curves, measurements on pseudo‐2D fluidized beds using optical imaging and tomographic measurements on 3D beds of tracer particles, which are unable to capture behavior across the entire device on a temporally resolved level. In recent years, magnetic resonance imaging (MRI) has been able to generate detailed maps of both particle and gas motion in fluidized beds.…”

Fluidization dynamics of cohesive Geldart B particles. Part II: Pressure fluctuation analysis

“…Nevertheless, due to the limitation of measurement methods, most of these researches focused on global and visual phenomenon, i.e. minimum fluidization [4,5], defluidization pattern [6], bubble behaviors [7,8], particle mixing [9] etc. Recently, lots of researchers made efforts for more insight into the fluidization dynamics of cohesive particles with the aid of advanced measurement approaches.…”