Characterization of high-density gas–solids downward fluidized flow

A comparison of flow development in high density gas‐solids circulating fluidized bed downer and riser reactors

“…Zhu and Zhu proposed a novel circulating‐turbulent fluidized bed (C‐TFB) operated with low gas velocity and high solids flux, resulting in a high‐density flow with solids holdup of up to 0.25 through the entire C‐TFB with a nearly uniform axial solids flow and negligible downflow giving rise to a good gas‐solids contact. Conversely, in a special effort to achieve high solids holdup, Liu et al designed a special high‐density downer, where a 0.66 m tall funnel with 250 mm top diameter was placed at the top of a 25 mm and 5 m tall downer to preaccelerate the particles, so that they can be fed into the downer at their terminal velocity so as to facilitate high solids flux condition. With this particular apparatus, an average solids holdup as high as 0.07–0.09 was achieved at solids circulation rate ( G s ) over 400 kg/m 2 s using FCC particles.…”

Performance evaluation of high density riser and downer: Experimental study using ozone decomposition

“…Previous studies on the downers [4,5] have shown that both gas and solids distributions become much more uniform axially and radially than those in the risers. In spite of such significant advantages, downers have a very low volumetric solids holdup (mostly less than 0.01) [6], which results in limited reaction intensities, especially when a high solids/gas ratio is required.…”

“…In a special effort to achieve high solids holdup, Liu et al [6] designed a special high-density downer, where a 0.66 m tall funnel with 250 mm top diameter was placed at the top of a 25 mm and 5 m tall downer to pre-accelerate the particles, so that they can be fed into the downer at their terminal velocity so as to facilitate high solids flux. With this particular apparatus, an average solids holdup as high as 0.07-0.09 was achieved with solids circulation rate (G s ) over 400 kg/m 2 s using FCC particles.…”

Hydrodynamic Modeling of Dense Gas-Particle Turbulence Flows Under Microgravity Space Environments

“…Compared with the up-flow fast fluidized bed riser, downer reactors of fluidized bed have many advantages such as good gas-solids contact, less gas and solids back-mixing, a short contact time and more uniform residence time distribution. (Srivastava et al 1998;Lehner and Wirth 1999;Cheng et al 1999;Liu et al 2001;Li et al 2004;Lu and Gidaspow 2003;Lu et al 2005;Luo et al 2007;Wu et al 2008;He et al 2009a, b). Computational fluid dynamics (CFD) with an Euler-Euler two-fluid modeling approaches has been widely used to predict hydrodynamics in circulated fluidized bed.…”