Electrical Capacitance Volume Tomography Imaging of Three-Dimensional Flow Structures and Solids Concentration Distributions in a Riser and a Bend of a Gas-Solid Circulating Fluidized Bed

Electrical capacitance volume tomography (ECVT) is a newly developed imaging technique that can quantify three-dimensional (3D) multiphase flows in a complex, geometric flow field. In this study, the 3D phase distribution images inside a gas solid circulating fluidized bed (CFB) are obtained using ECVT. Specifically, measurements are made at a riser section and a 90 degrees bend-shape riser exit section of the CFB. Inside the vertical riser, a symmetric core annulus structure with a low solids holdup in the riser center along with a high solids holdup near the riser wall is observed. The average volume solids holdup and the thickness of the annulus decrease with the superficial gas velocity. A core annulus flow structure is formed both in the vertical and horizontal parts of the bend. The annulus structure is noncentro-symmetric in the horizontal part of the bend. The solids holdup in the annulus near the top wall area in the bend is higher than that in other locations of the annulus. At a higher superficial gas velocity in the riser, the centrifugal acceleration increases due to high solids velocity in the bend, and more solids are separated to the outside of the bend from the main stream. A reversed-S shape solids holdup distribution along the diagonal line is also observed. The solids holdup increases and then decreases from the outer corner to the center of the bend, which indicates that a relatively dilute region is formed near the outer corner of the bend.