Verification of fluidized bed electrical capacitance tomography measurements with a fibre optic probe

Statistical diagnosis of a gas–solid fluidized bed using Electrical Capacitance Tomography

“…The shock waves form when porosity waves rise faster than a proposed equilibrium distance [11]. Another explanation was given by Chen et al [12] who stated that bubbles occur due to instabilities in the state of smooth or homogeneous fluidization. Bubbles provide a means for excess gas to avoid the dense phase and thus reducing instabilities (in the dense phase) to concentrated perturbations (bubbles) [12].…”

“…Another explanation was given by Chen et al [12] who stated that bubbles occur due to instabilities in the state of smooth or homogeneous fluidization. Bubbles provide a means for excess gas to avoid the dense phase and thus reducing instabilities (in the dense phase) to concentrated perturbations (bubbles) [12]. In the 1960s the finding of bubble fluid dynamics in fluidized beds increased the impact of fluidized beds in the chemical engineering sciences [3] and bubbling beds continue to be of great importance due to its mixing capabilities.…”

“…These slugs are typical for large particles. Generally slugging behaviour is viewed to be detrimental to fluidized bed performance but occur commonly in the industry and thus knowledge about this phenomena is needed [12]. Slugging behaviour is not always detrimental and do pose some advantages, such as reduced spread in residence time for both gas and solid phases [12].…”

“…Thus the minimum fluidization velocity (u m f ) and minimum bubbling velocity (u mb ) occur at two distinct superficial velocities, with u mb > u m f . Thus according to the explanation on the origin of bubbles described by Chen, instabilities in the smooth or homogeneous fluidized state will only occur at superficial velocities higher than minimum fluidization velocity [12]. These powders are also known to produce a maximum bubble size and is thus characterised by the coalesces and splitting of bubbles.…”

“…Thus as soon as the bed is fluidized, bubbles appear. Therefore Geldart B particles are known to form instabilities in the homogeneous fluidization state right from the onset of fluidization [12]. The bed expansion is not significant for these powders, given the tower is operating at ambient conditions [11].…”