The Stability of Wet Spouted Beds

In granulation, coating or drying of slurries on inert particles a liquid phase is added to a gas-spouted bed. The effect of liquid injection on spouting velocity, fountain height, bed pressure drop and stability of the spouting regime is examined in a 0.15 m diameter bed with four types of inert particles 2 to 5 mm in size, 1140 to 2880 kg/m3 in true density, and 1.3 and 1400 mPa·s in liquid viscosity. Key factors are the liquid content and the presence of cohesive forces due to liquid bonds between particles. In a spoutability chart the maximum spoutable liquid content is related to the ratio of inertial force of a particle to the viscous or cohesive force exerted onto the particle by the liquid film. The spoutability chart serves to define regions of stable spouting.