Flow Characteristics of Fully Wetted Binary Solid Mixtures in Gas Fluidized Beds with Inclined Gas Distributors

A unique system in which gas-fluidization is enhanced by adding a little water has potential for soft abrasive washing of various products. Preliminary experiments were carried out for washing farm products. Gas fluidized beds of binary solids mixtures with inclined gas distributors provide hydrodynamic and mixing data, assisting the design of dry and wet gas-fluidized beds. INTRODUCTION Farm Product PLST Inclined Distributor Mud Discharge Air Fig.1 Fluidized bed with inclined gas-distributor When small quantities of water are added to gas-fluidized beds of large non-wettable particles, such as 6-mm polystyrene spheres, the water can cause a dramatic increase in the extent of fluidization. We have previously reported the characteristics of this unique fluidized bed. It has advantages for soft-abrasion, due to movement of light rounded particles, and also for reducing water usage for washing, due to the small quantities of water needed. These characteristics are desirable for industrial washing of farm products or fragile industrial devices requiring soft abrasive washing. For such applications, inclined gas-distributors, as shown in Figure 1, are effective for separating and removing solid wastes from the bed materials as a mud. This paper reports preliminary experimental results on the washing of agricultural products. 1 Nagahashi et al.: Flow Characteristics of Fully Wetted Binary Solid Mixtures Published by ECI Digital Archives, 2007 NAGAHASHI et al. 338 Possible gas-distributors, including inclined distributors, are discussed for dry singleparticle fluidized beds to optimize the system for discharge of the washing waste. The flow characteristics of gas-fluidized beds of binary solid mixtures with inclined gas-distributors are discussed for dry and wet fluidized beds. The two species in the binary solids mixture simulate the large washing solids medium and the small particles to be removed as waste solids (mud). APPARATUS AND METHODS 1) Bed Column and Distributors: The experimental apparatus is shown in Fig. 2. The two columns were transparent half-cylinders of 180 mm inside diameter x 1000 mm height, and 280 mm dia. x 1500 mm tall. The gas distributors were a horizontal plate, inclined flat plates with inclination angles to the horizontal of 10, 20, and 30°, convex and concave plates with 20° angle to the horizontal, and a cone drilled with 2.4 mm dia. holes (overall open area 1.3 %) and covered by a wire mesh #400 cloth plate, as shown in Figure 3. The plenum chamber wall was provided with three pressure taps. 2) Particles: We used 2 types of polystyrene particles (6-mm spheres and 3.2-mm rounded cylinders of mean diameter 3.2 and length 3.2 mm) and 2 sizes of spherical glass beads (mean diameters 1.0 and 0.6 mm). Table 1 Particle Properties Polystyrene Glass Beads Particles 6-PLST 3.2-PLST 1-GB 0.6-GB dP [mm] 6.0 3.2x3.2 1.0 0.6 Umf [m/s] 1.45 0.70 0.43 0.26 ρs [kg/m] 101