Flow-field analysis of a continuous gas–solid separation fluidized bed equipped with a moving scraper

Abstract

Continuous gas–solid separation fluidized beds are one of the most widely used practical operation units for the dry separation of coal in China, particularly in Northwest China, and they can effectively promote the efficient and clean utilization of raw coal. In a continuous gas–solid separation fluidized bed, the bed flow field is the concrete manifestation of the fluidization characteristics. However, the complexity of the flow field increases under the action of a moving scraper. In this study, a combination of computational fluid dynamics (CFD) simulations and experimental measurements was used to study the changes in the flow field of a fluidized bed. The results showed that when the scraper moved, the local flow field (mainly characterized by the movement of medium particles) near the scraper was affected not only by the common airflow or bubbles, but also by the lateral driving force of the scraper. When the scraper speed was vl<6.0cm/s, it reduced the frequency of the formation of large bubbles and alleviated the random fluctuation of the nearby particle collision stress signals, which improved the fluidization stability of the bed. Additionally, the movement of the scraper affected the global flow field. The flow field shifted to the right near the scraper, with the direction of the scraper movement, while the flow field exhibited a leftward trend on the surface of the bed, accompanied by some vortices, in the middle and lower parts of the bed. Additionally, the critical height of the area, directly affected by the scraper, increased from 52 to 54mm with an increase in its operating speed from vl=2.96cm/s to vl=4.44cm/s, respectively. This provides a theoretical basis for further understanding the hydrodynamic characteristics of fluidized beds.