Liquid Radial Dispersion in Liquid-solid Circulating Fluidized Beds with Viscous Liquid Medium

Abstract

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15-0.45 m=s), solid circulation rate (2-8 kg=m 2 s), particle size (1-3 mm), and liquid viscosity (0.96-38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radial dispersion coefficient decreases with increasing liquid velocity or viscosity, but it increases as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient is related closely to the resultant behavior of fluidized particles. The radial dispersion coefficient has been well correlated with operating variables in terms of dimensionless groups.

Holdup and Flow Behavior of Fluidized Solid Particles in a Liquid-Solid Circulating Fluidized Bed

“…1. The details of experimental apparatus can be seen elsewhere [11,12]. The diameter and height of the main riser column were 0.102 m and 3.5 m, respectively.…”

“…The solid particles were circulated by adjusting the angle and length of the solid recycle guide and secondary liquid flow rate at the solid recycle device. The solid circulation rate (G S ) was determined by measuring the amounts of particles piled up above the butterfly valve in the downcomer [11,12]. The diameter of the glass beads was either 0.5, 1.0, 2.0 or 3.0×10 -3 m and density was 2500 kg/m 3 which were used as a solid particle phase.…”

“…(4). (4) It has been understood that the relative velocity between the continuous liquid phase and the discrete solid particles could create shear stress and force at the interface during flow, which is directly related to the mass and heat transfer between them and in the flow process [6][7][8][9][10][11][12]. Effects of particle size, solid circulation rate and liquid velocity on the slip velocity, U Slip , can be seen in Figs.…”

“…The liquid-solid circulating fluidized bed has been proposed to overcome the disadvantages of the conventional liquid-solid fluidized beds [6][7][8][9][10][11][12]. It can be operated with high liquid velocity to increase the production or operation efficiency per unit cross-sectional area of the column, by adopting the circulation mode of solid particles.…”

Solid Holdup and Circulation Rate in a Liquid-Solid Circulating Fluidized Bed With Viscous Liquid Medium

“…Zheng (2004), Cho et al (2005) and Shin et al (2005) studied the effects of liquid viscosity on hydrodynamics, transport properties, heat transfer coefficient and radial dispersion with the riser operated in the variable inventory mode. The effect of liquid viscosity on the fixed inventory mode was studied by Vidyasagar et al (2011) for different solid inventories and macroscopic flow properties such as pressure gradient, critical transitional liquid velocity to circulating fluidized bed regime, average solid holdup, axial solid hold up distribution and solid circulation rate.…”