ROLE OF LIQUID BRIDGE FORCES IN COHESIVE FLUIDIZATION

The roles of liquid bridging and particle surface washing with a surfa ctant have been demonstrated using Geldart D particles undergoing arti ficially induced cohesive gas-solid fluidization with thin-oil films. It has been shown that a number of factors, including the amount of li quid present and the liquid-solid contact angle, influence the interpa rticle bonding. The fluidization behaviour, including minimum fluidiza tion velocity, has been found to depend on liquid bonding, which is a function of both the liquid and particle surface properties. Treatment of particles with a surfactant raises the liquid-solid contact angle, thereby decreasing the capillary forces. The results of this work dem onstrate that this effect may be more significant than viscosity at co nditions between minimum bubbling and minimum fluidization. This confi rms that static bridge forces, dominated by capillary pressures and su rface tension, control fluidization under low velocity conditions. Sur face tension forces also play a significant role during bubbling and s lugging behaviour, but at these higher gas velocities, binder viscosit y increases in importance.The disadvantage of gas by-passing in fluidi zed beds has been shown to be a phenomenon which is subject to manipul ation. It has been demonstrated that controlled, and minimal liquid ad dition to a gas-solid fluidized bed reduces the bubble size and averag e bed voidage with little apparent agglomeration. These results confir m that more investigation is required in the design of fluidized beds where intimate gas-solid contacting is required.