Phase hold-up and critical fluidization velocity in a three-phase inverse fluidized bed

We studied the hydrodynamic characteristics of a three-phase inverse fluidized bed made of a transparent acrylic column of 0.115 m inner diameter and 2 m heights. Air, water and polyethylene particles were used as the gas, liquid and solid phase, respectively. We used both hydrophobic low density polyethylene (LDPE) and hydrophilic LDPE as solid phase, and distilled water as liquid phase, and filtered air as gas phase. The LDPE was chemically treated by chlorosulfonic acid to change the surface property from hydrophobic to hydrophilic. We tried to solely investigate the effect of the surface hydrophilicity of polymeric particles on the phase holdup and the critical fluidization velocity of three-phase inverse fluidization. Thus, we measured the static pressure and eventually observed critical fluidization velocity. Critical fluidization velocity became smaller in case of using MDPE hydrophobic particles than LDPE hydrophilic particles. This was thought to be due to the retardation of rising bubbles near hydrophobic particles and, subsequently, the increase of gas hold-up.     

Photocatalytic degradation of trichloroethylene over TiO<Subscript>2</Subscript>/SiO2 in an annulus fluidized bed reactor

The effects of superficial gas velocity (Ug), wavelength and intensity of ultraviolet (UV) light, oxygen and H₂O concentration on the photocatalytic degradation of TCE (Trichloroethylene) over TiO₂/SiO₂ catalyst have been determined in an annulus fluidized bed photoreactor. The key factor in determining the performance of the annulus fluidized bed photoreactor is found to be an optimum superficial gas velocity (Ug) that provides the optimum UV lighttransmit through the proper size of bubbles in the photoreactor. The degradation efficiency of TCE increases with light intensity but decreases with wavelength of the UV light and H₂O concentration in the fluidized bed of TiO₂/silica-gel photocatalyst. The optimum concentration of O₂ for TCE degradation is found to be approximately 10%. The annulus fluidized bed photoreactor is an effective tool for high TCE degradation with efficient utilization of photon energy. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Gas yields from coal devolatilization in a bench-scale fluidized bed reactor

Devolatilization behavior of Australian bituminous coal-gasification was determined in a 0.1 m diameter fluidized bed at 650-900 °C. To predict gas yields from devolatilization, several correlations reported for gas yields were evaluated with the present experimental data. The correlation of Goyal and Rehmat [1993] was found to be good one. Also, a correlation for the product gas yields has been proposed from devolatilization of bituminous coals as a linear function of temperature with constants from the experiment. The experimental yields of product gas show good agreement with the values calculated by the proposed correlation. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Effect of secondary gas injection on the particle entrainment rate in a gas fluidized bed

The effect of secondary gas injection on the particle entrainment rate was measured in a cold model fluidized bed (i.d. 0.1 m, height 2.25 m) and discussed. Sand particles below 0.425 mm in screen size were used as bed materials. The particle size (0.128–0.363 mm), the overall superficial gas velocity (0.78–2.76 m/s), the secondary gas fraction (0–0.5), and the static bed height (0.1–0.3 m) were considered as experimental variables. The particle entrainment rate decreased with an increase of the secondary gas fraction. The injection level of the secondary gas was shown to have an important influence on its effect. The effect of the secondary gas was appreciable for over-bed injection; the effect was reduced, however, when the injection level was placed in the splash zone or in the dense phase by means of increasing the bed height.