Modeling of axial and radial flow in circulating fluidized bed risers

Circulating fluidized bed will provide fast fluidization zone where high velocity gas has intimate contact with a fine solids, which is to be entrained in conventional bed. The solid in the fast fluidized regime may typically occupy up yo 25% of the bed volume and is in a state of extreme turbulence marked by extense refluxing of dense clusters of packets of the particles. Although circulating fluidized beds have been in industrial use for nearly half a century, rigorous studies of circulating systems have only been published within the last decade, these studies reveal that the flow behavior of a CFB riser is very complex, more so, when solids concentration within the riser varies both axially and radially. Now withstanding the availability of a reasonable literature on axial and radial gas-solid flow patterns, the need for further investigation remains all the same since many of the complex problems like the analysis of the flow patterns, mathematical modeling and development of generalized correlations are yet to be solved. In the present work, an attempt has been made to develop a semi-empirical model for axial and radial voidage profile.