Gas–solid flow in a high-density circulating fluidized bed riser with Geldart group B particles

Abstract We carried out experiments to explore and characterize the gas–solid flow dynamics of Geldart group B particles in a dense circulating fluidized bed riser. By reducing the pressure drop across the solid control valve and increasing the solid inventory in the storage tank, a high solid circulation rate and a solid holdup above 0.075 throughout the riser were simultaneously achieved. At a solid-to-gas mass flux ratio of approximately 105, flow transitioned from fast fluidization to a dense suspension upflow. In the axial direction of the riser, solid holdup had an exponential profile, increasing with increasing solid circulation rate and/or decreasing superficial gas velocity. From the riser's center to its wall, the solid holdup increased markedly, exhibiting a steep parabolic profile. Increasing the solid circulation rate increased the radial non-uniformity of the solid concentration, while increasing the superficial gas velocity had the opposite effect. In our dense circulating fluidized bed riser, Geldart group B particles had similar slip characteristics to Geldart group A particles.