HYDRODYNAMICS OF VIBRO-FLUIDIZED BEDS

Vibro-fluidized bed dryers are being extensively used in the industry to dry granular particles of wide particle size distribution. For drying applications of limited air inlet temperature and hard to dry granules--high diffusion resistance of moisture inside the qranules--baffles are normally provided in these dryers to increase the residence time of particles. The residence time distribution of granules in vibro-fluidized bed dryers is of high importance to successfully model such dryers. There has been some studies reported in the literature for average residence time of granules in vibro-fluidized beds without baffles, but there has been no work reported for average residence time in vibro-fluidized beds with baffles and residence time distribution for beds with or without baffles. Experimental runs were carried out in this study in the 0.93 m2 (10 ft2 ) pilot plant vibro-fluidized bed dryer with baffles to determine the residence time distribution of dry granules and granule height profile through the length of the dryer.

Among all the dryer operating variables considered in this study, vibration amplitude and baffle spacing were identified as most significant. Values of the average residence time and particle diffusivity were obtained for the entire range of the expected operation of the pilot-scale or commercial scale dryers. These values of average residence time and particle diffusivity, along with the appropriate drying rate (kinetic) data, enable full modeling of vibro-fluidized bed dryers.