Investigation of particle flow characteristics in a CFB recirculation system using electrical capacitance volume tomography

Abstract

Gas-solid fluidized beds have complex flow characteristics and opacity, and the particle motion characteristics in the recirculation system of circulating fluidized bed (CFB) have not been studied thoroughly. In order to study the motion of gas-solid two-phase flow in a CFB recirculation system, a 32-electrode electrical capacitance volume tomography (ECVT) system was developed with an imaging speed of 120 frames per second. Under various working conditions, the experimental platform of CFB was also built to measure the particle flow in the CFB recirculation system with the 32-electrode ECVT system, including the solid concentration and the flow velocity of particles in the branch pipe. When the velocity of fluidized gas U f is adjusted from 2.73 m/s to 1.76 m/s, the average solid concentration in the riser is roughly distribution of upper dilute and lower concentrated along the axial direction. With the decrease of U f , the average solid concentration generally showed an increasing trend, and the difference of solid concentration between different planes in the branch pipe gradually decreased. The slug length in the imaging area decreases, and the rising velocity of the slug in the riser above the branch pipe decreases. ECVT continuous images (U f = 2.73 m/s). • The 3-D solid concentration distribution in the CFB recirculation system was investigated. • ECVT continuous images under three different working conditions are given. • Solid concentration in the CFB recirculation system was acquired from the ECVT images. • Solid velocity was gained by analyzing the time lag of the neighbour planes.