Hydrodynamics of a cold circulating fluidized bed

A cold circulating fluidized bed, an air-solids separation system, a solids circulating rate controlling system and an air-humidification system were designed and built. The riser of the cold CFB model made of Plexiglas stands 2.7 m high with an inside diameter of 11.43 cm. In most of the experiments presented in this dissertation, sand with an average particle diameter of 209 {dollar}mu{dollar}m was fluidized by air with a superficial gas velocity in the range of 3{dollar}sim{dollar}5 m/s at an overall solids flux of 10{dollar}sim{dollar}30 kg/m{dollar}sb2{dollar}. Two novel, isokinetic probes were designed and built. One measures the mass flux of particles moving up through the CFB, and the other does the same for particles moving down in the CFB.; The previous conclusion of the CFB riser consisting of a dilute, upward flowing core surrounded by a dense, downward flowing annulus was confirmed. Experimental results showed that the maximum net solids flux was at or near the radial center of the riser. The radius of the dilute core increased with increasing air superficial velocity and with the elevation. It decreased as the solids circulating rate increased. It was found that the solids mean size in the downward flow was much bigger than the average size in the total CFB loop. The upward solids mean size in the bottom section was bigger than that in the upper section.; The important effect of static electricity in circulating fluidized beds was studied. It was found that the electrostatic force generated by particle/particle and particle/wall contacts is a significant factor in the hydrodynamics of CFBs when the particle and the wall are not electric conductors. It caused the solids holdup and pressure gradient to increase. Near the riser wall, the electrostatic force may dominate the motion of smaller particles, causing the upward velocity to decrease and a higher concentration of small particles.; Effects of solids physical property on mass flux were also studied in this work. Upward solids flux profiles in the radial direction tend increasingly to be parabolic with increasing particle size, and downward solids fluxes increase quickly with an increase of the particle size.