Dense, vertical gas‐solid flow in a pipe

Abstract

The hydrodynamics of gas-solid flow, usually referred to as circulating fluidizedbed flow, wasstudied in a 7.5-em clear acrylic riser with 75-pm FCC catalystparticles.Data were obtained for three central sections as a function of gas and solids flow rates. Fluxes were measured by means of an extraction probe. Particle concentrations were measured with an X-ray densitometer. In agreement with previous investigators, these data showed the flow to be in the core-annular regime, with a dilute rising core and a dense descending annular region. However, unlike the previous studies conducted worldwide, the data obtained in this investigation allowed us to determine the viscosity of the suspension. The viscosity was a linear function of the volume fraction of solids. It extrapolates to the high bubbling-bed viscosities.

Hydrodynamic modelling of circulating fluidised beds

“…(5), a zero solids concentration in the tube centre is predicted which is contradictory to experimental observations (Dry, 1986;Miller and Gidaspow, 1992). In this work, therefore, eq.…”

“…Experimental investigations clearly demonstrated an inhomogeneous solids distribution in both the axial and radial directions (Kwauk et al, 1986;Bader et al, 1988;Miller and Gidaspow, 1992). The inhomogeneous solids distribution in the axial direction can be attributed to the acceleration of particles which enter the column at the bottom of the bed with low velocity.…”

Circulating fluidized bed hydrodynamics experiments for the multiphase fluid dynamics research consortium (MFDRC).

“…For gas velocities and particle sizes and loadings typical of riser flows, a low suction velocity results in an underestimation of the directional mass flux, while a high suction-velocity similarly results in an overestimation of the directional mass flux. Miller and Gidaspow (1992) present results demonstrating this phenomenon in a riser flow of FCC catalyst Additionally, failure to achieve isokinetic conditions can result in a particle-size distribution within the sample that is not reflective of conditions at the sampling location. Isokinetic sampling results have been reported by several experimental groups, including van Breugel et al (1970), Nguyen et al (1989), Harris and Davidson (1992), Coronella and Deng (1998), and Reinhardt et al (1999, in cyclone flows).…”

“…The resulting configuration is shown schematically in Figure 4.19. It is similar to configurations used by Miller and Gidaspow (1992), Wei et al (1997), andIssangya et al (1998); and similar in principle to that used by Wang et al (1995), whose sampling system was modified for use in a high-temperature system.…”

“…Several groups of workers (e.g., Miller and Gidaspow, 1992;Rhodes and Laussmann, 1992;Zhang et al, 1995;Malcus et al, 2002) have overcome this using non-isokinetic sampling, at suction rates far in excess of the local gas speed. While increased sampling-suction velocities correspondingly increased measured values of directional mass fluxes, they found that the net flux represented by the difference in directional fluxes remained relatively invariant.…”