Particle velocity measurements in a circulating fluidized bed

Abstract

In recent years, circulating fluidized beds (CFBs) have been extensively employed in a variety of industrial applications related to coal combustion and gasification, solid waste incineration, catalytic cracking of oil, and so on. To accomplish successful and reliable operation of CFBs, a number of in- Detailed researches in this direction will considerably help in the optimum and economic designs of CFB boilers. To aid in this direction, we have measured the three-dimensional particle velocities in a square-section CFB cold model under certain operating conditions at ambient temperature and pressure. Particle turbulent intensities and bed cross-sectional averaged voidage along its height are also measured. A majority of the investigations have been conducted in circular cross-section CFBs, but industrial preference is for a square cross-section boiler, and hence we have adopted this configuration in our present work. Our measurements, while confirming the coreannulus flow structure for CFBs, also provide a more comprehensive microscopic detail of particle velocities in the two regions, in addition to providing a basis for particle aggregation. Experimental Apparatus and ResultsThe schematic of the CFB employed in the present work is shown in Figure 1. The riser section is 3 m long and has a square cross-section, 222 mm by 222 mm. Seventeen pressure taps (13) are installed along the metal bed wall starting from a height of 250 mm' above the air distributor plate (3) and up

Modeling of Carbon Combustion Efficiency in Circulating Fluidized Bed Combustors. 1. Selection of Submodels and Sensitivity Analysis

“…The dilute region was characterized by a coreannulus structure with the solids rising through the core with a voidage ec and descending through the annulus at a velocity of 1 m/s (Horio et al, 1988;Grace, 1990; Wang et al, 1993) in a denser suspension. It was assumed that the gas rises only through the core.…”

Experimental estimation of particle flow fluctuations in dense unsteady two-phase flow using phase Doppler anemometry

“…Furthermore, the local concentration and velocity of particles may be correlated (the particles may flow in clusters) causing additional bias, and this also requires attention. These two cases of bias have generally not been considered in work on unsteady two-phase flow, such as that related to fluidized bed (Levy and Lockwood, 1983;Hamdullahpur and Mackay, 1986;Berkelmann and Renz, 1991;Yang et al, 1992;Wang et al, 1993;Zhang and Arastoopour, 1995;Samuelsberg and Hjertager, 1996;Werther et al, 1996;van den Moortel et al, 1997;van den Moortel et al, 1998;Mathiesen et al, 2000;Ibsen et al, 2001Ibsen et al, , 2004. Furthermore, the measurement area and volume of the PDA probe may depend on diameter d and direction c of the sampled particle (c is the angle between the velocity vector of the particle, u, and the main flow direction, x, as shown in Fig.…”

Numerical modeling of bed-to-wall heat transfer in a circulating fluidized bed combustor based on cluster energy balance

“…The size of a cluster for a scale-model CFB was measured by Rhodes et al [3] and Lim et al [4] as 0.5-2.0 cm and verified by Noymer and Glicksman [5]. The typical descent velocity for the cluster is between 0.5 and 2.0 m/s as reported by Rhodes et al [3] and Wang et al [6] and verified by Noymer and Glicksman [5]. Proximity of the cluster to a wall was observed by Lints and Glicksman [2] and is as close as 100 lm from the wall.…”