19-08-2014, 10:17 AM
Fluidization is an operation by which solid particles are transformed into a fluid-like state through suspension in a gas or liquid. When gas is passed upward through a bed of particles, different contacting patterns and flow regimes are observed. Gas-solid fluidized beds find numerous applications in chemical, petroleum, pharmaceutical, metallurgical, biochemical, power generation and food industries.
Fluidization is an operation by which solid particles are transformed into a fluid-like state through suspension in a gas or liquid. When gas is passed upward through a bed of particles, different contacting patterns and flow regimes are observed. Gas-solid fluidized beds find numerous applications in chemical, petroleum, pharmaceutical, metallurgical, biochemical, power generation and food industries.
In the present work, the effect of superficial gas velocity, presence of draft tube and type of sparging was studied on the solids hold-up and solids circulation patterns in a gas solid fluidized bed with the help of experiments and CFD simulations. Solid hold-ups were measured with the help of gamma ray attenuation technique. A 2D multifluid Eulerian model integrating the kinetic theory of solid particles is developed. The predicted solids hold-up profiles agrees reasonably with the experimental data. The model is able to predict the gas-solid behavior of the bubbling fluidized bed. It was found that at all the axial locations within the bed, an increase in the superficial gas velocity results in a decrease in the solids hold-up along the centre of the bed. This implies that along the centre of the bed, the gas holdup increases with an increase in the superficial gas velocity. The draft tube and type of sparging were found to have a variable effect on the solids hold-up profile depending upon the geometrical combination.
The solids circulation pattern of ascending near the wall and descending through the center of the bed for lower values of the U0/Umf and the existing core annulus structure during the various conditions has been predicted reasonably well by the simulations. In the absence of draft tube, partial sparging gives rise to lower solid hold-up at the centre and higher solid hold-up near the wall than complete sparging.
Partial sparging with out draft leads to a well developed core annulus structure than partial sparging with draft tube. The presented experimental data and CFD predictions provides useful information for understanding the solids hold-up and circulation patterns of the gas-solid fluidized bed.