Conference Dates

May 22-27, 2016


Spouted beds are extensively used in coating and granulation processes with the presence of liquid in the bed (1). The liquid may increase particle cohesiveness and result in de-spouting, leading to the bed malfunctioning. Hydrodynamic of the bed may alter over time due to instabilities imposed by particle size changes and cohesiveness. Therefore, conditional monitoring of spouted beds is crucial since the performance of these beds strongly depends on its hydrodynamics. A method capable of detecting bed instabilities may not be only useful for preventing undesirable situations (e.g., agglomeration and de-spouting), but also may be utilized to control the product quality, both in batch and continuous operations.

In this study, the feasibility of detecting instabilities of spouted beds via measuring pressure fluctuations (PF) and acoustic emissions (AE) was investigated. The experiments were carried out in a polyoxymethylene conical spouted bed with a conic angle of 45°. The bed consists of a 150 mm ID cylinder with a conical section at the base connected to a 6 mm ID gas inlet tube. Sugar particles of 720 μm mean diameter were used as solid and water was sprayed from the bottom to produce agglomerates during the operation. The PFs were measured by three differential pressure transducers connected to the inlet line, bed internal wall at the base and 9 cm above the gas inlet. The AE signals were recorded by an omnidirectional back electret condenser microphone attached externally to the outer surface of the bed at 12 cm above the base of the conical section. The signals were continuously measured during incremental injection of water at different inlet gas velocities. Also, a high speed camera (200 fps) was used for the half bed to visualize the flow structures during water injection and drying periods.

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