Experimental study on flow characteristics of ash band in a cyclone separator using HPIV techniques

Abstract

In a reversed cyclone separator, the ash bands were frequently observed on the wall surface, which were formed by the separated particles and rotated down. Nevertheless, the flow characteristics of the ash bands are rarely measured and discussed in the previous literatures. In this study, the flow characteristics of the ash bands were experimentally investigated by use of the High-speed Particle Image Velocimetry (HPIV) method. The experiments were conducted on a ϕ160mm cyclone at inlet velocity of 12, 16, 20 m/s and inlet concentration of 30, 50, 70, 100 g/m3. The test powders were catalyst and iron powder. The ash band's geometric characteristics, including width, slope angle and pitch, were extracted through advanced image analysis algorithms. Results revealed that the slope angle and pitch of the ash band were different in the cylindrical section and cone section. The width decreased as the ash band moved downwardly. Additionally, the ash band's flow parameters were measured. As the particle movement changed from suspension pattern in the separation space to sliding pattern on the wall surface along the radial, the particle velocities decreased. And the particle velocities further decreased as ash band forming. Particle velocities exhibited non-uniform and fluctuating behavior within the ash band. Notably, the velocities were lower in the central region of the ash band than that at the outer layer. Meanwhile, the particle concentration gradually increased, leading to a particle concentration in the ash band being 450 times higher than the inlet concentration. Along the axial, the ash band averaged velocity initially increased in the cylindrical section and then decreased in the cone section, varied with the inlet velocity, inlet concentration and particle properties such as particle size and density. This study revealed mechanisms behind particle aggregation in cyclone separator and analyzed the dynamic flow characteristics of ash band in detail.