Inhomogeneity in low pressure fluidization

Low pressure fluidization has been one of the most promising advances in the fluidization topic since its inception. Its low mass consumption is a key benefit, but equally, it is known for its low fluidization quality due to inhomogeneous fluidization. In this work, an experimental study was conducted to study the cause, mechanism and possible remedies to the inhomogeneous fluidization behaviour at low pressure. A 2D pseudo bed was used to capture the bubbling phenomenon and pressure drop characteristics for alumina powder at a wide range of operating pressures (0 to −98,185 Pa), bed heights (221, 534 and 727 mm) and inlet flow rates (0.1 to 18 l/min). The high pressure differential between the bottom and top of the bed at low pressure was the main cause of the inhomogeneous fluidization behaviour. The pressure differential causes a steep rise in the gas velocity profile within the bed, resulting in the two different fluidization states within the same bed. The bed height, voidage and particle density were found to improve the fluidization quality with some drawbacks. An alternative approach was to increase the bed area with height. This alteration can be used to improve the fluidization quality for any given powder and operating condition.