Experimental Study of Solids Motion in an 18 m Gas–Solids Circulating Fluidized Bed with High Solids Flux

Abstract

A comprehensive experimental study of solids motion is conducted in an 18 m-high circulating fluidized bed with an extremely high solids circulation rate (G s) up to 1000 kg/(m2 s), which has never been achieved in such a tall riser in previous research studies. The axial distributions of the particle velocity show exponential curves and slight changes in the fully developed zone with G s higher than 400 kg/(m2 s). The radial profiles of the particle velocity have parabolic shapes and become steeper with increasing G s. The development of the gas–solids flow structure becomes slower with increasing G s or decreasing superficial gas velocity (U g). When G s reaches 800 kg/(m2 s), the full development is achieved until reaching an axial height higher than 12 m. Better correlations between the local particle velocity and solids holdup and less downflowing particles indicate better reactor performance with the reduction of solids back-mixing and uniform residence times at an extremely high G s.

Numerical Simulation of the Pilot-Scale High-Density Circulating Fluidized Bed Riser

“…As the value of A is equal to or higher than 0.05, the solid holdup at the bottom of the riser is higher than at the top. However, when a is less than 0.05, the middle part has a larger solid holdup, which is not consistent with the experimental observation . Overall, the simulation with A = 0.05 best predicts the experimental axial solid holdup.…”

“…However, when a is less than 0.05, the middle part has a larger solid holdup, which is not consistent with the experimental observation. 15 Overall, the simulation with A = 0.05 best predicts the experimental axial solid holdup. Meanwhile, with decreasing A, the solid holdup near the wall increases remarkably.…”

“…For example, for the industrial fluidized catalytic cracking (FCC) process, as focused currently, G s is about 400−1200 kg/m 2 •s, and the riser height can be higher than 20 m. Table 1 summarizes dimensions and solid circulation rates. To fill this gap, the research group of the present authors in the China University of Petroleum 15,16 has built up an HDCFB with a riser of 18 m in height (see Figure 1) to investigate the gas-solid hydrodynamics. This system can be operated over a broad range of conditions, with G s being up to 1400 kg/m 2 •s.…”

Prediction of Solid Holdup in a Gas–Solid Circulating Fluidized Bed Riser by Artificial Neural Networks

“…It is well known that the solid holdup is one of the most important hydrodynamic parameters in the CFB riser and great efforts have been made to measure and analyze the solid holdup by conducting experiments. − However, since the industrial riser reactor is rather tall, for example, the industrial FCC riser is usually at least 20 m high, the riser apparatus in a laboratory in a smaller scale can hardly fully mimic the characteristics in an actual riser reactor. Although some experimental CFB risers were reported to exceed 10 m recently, , which is more likely to reflect the hydrodynamics in the industrial riser reactor, extensive efforts are still required for the associated experiments, for example, to measure the solid holdup in large-scale experimental CFB risers. Meanwhile, prediction or simulation work on the hydrodynamics gradually plays a significant role in studying the flow structures in CFB risers.…”

Attenuated Periodical Oscillation Characteristics in a Nanoscale Particle-Laden Laminar Flow

“…12 It is simple and reliable and also has the disadvantage of great dependence on sampling probe shape and location, and it could also bring some disturbances to the whole flowing suspension. Probe techniques have been widely used to study the concentration and movement of particles in the solid−liquid suspension, including impedance, 13 optical, 14 and acoustic techniques. 15 All of these techniques are based on the different responses of electric, optical, or acoustic signals between continuous and discrete phases, which inevitably disturb the flow field because of the existence of probes.…”