Sound Assisted Fluidized Bed Research Articles

The influence of acoustic field and frequency on hydrodynamics of group B particles

Sound Assisted Fluidized Bed (SAFB) of group B particles (180?m glass bead) has been studied in a 46mm I.D. column with aspect ratios of 1.4 and 2.9. A loudspeaker mounted on the top of the bed was supplied by a function generator with square wave to generate the sound as the source of vibration of the fluidized bed. The sound pressure level (referred to 20?pa) was varied from 102 to 140dB and frequencies from 70Hz to 170Hz were applied. The effects of sound pressure level, sound frequency and particle loading on the properties of SAFB were investigated. The experimental result showed that the minimum fluidization velocity decreased with the increase in sound pressure level, also minimum fluidization velocity was varied with variation of frequencies. At resonance frequency minimum fluidization velocity was found to be minimum. The bed height did not show an appreciable increase in presence of high acoustic field and at resonant frequency. Minimum fluidization velocity verses frequency curve in presence of sound intensity varied with variation of bed weight.

Simulation of cohesive particle motion in a sound-assisted fluidized bed

The effect of sound field on the cohesive particle motion in a 2-D sound-assisted fluidized bed is performed by means of discrete element method (DEM) in which the particle contact force, cohesive force, sound force and fluid force are considered. The distributions of concentration and velocity of cohesive particles is predicted in a sound-assisted fluidized bed. The effects of sound pressure level and sound frequency are studied. Computed granular temperature is increased with the increase of sound pressure level. The acoustic force increases, reaches maximum, and then decreases with the increase of sound frequency. A useful range of frequencies ranging between 100 and 120Hz is found with a sound pressure level of 120dB at which the effectiveness of the sound wave in improving fluidization of cohesive particles is most remarkable.

Development of a sound-assisted fluidized bed filter/afterburner for particle-laden gas clean-up

The paper reports a preliminary study on the application of sound assisted fluidization for hot gas clean-up, with a focus on the parallel agglomeration/removal of the particulates and afterburning of residual carbon. A 41-mm ID sound-assisted fluidized bed filter/afterburner has been developed and tested in experiments carried out at ambient temperature and at 850 °C. The application of an acoustic field of 140 dB and 120 Hz is able to increase filtration efficiency in terms of bed saturation time and removal of particulate by factors of 2 and 4, respectively. Experiments have been interpreted based on a simplified model which takes into account the role of sound in promoting the interaction between fine particles and coarse bed material.

Sound-Assisted Fluidized Bed Combustion of Fine Particles

The sound-assisted fluidized bed combustion of powders of tyre derived fuel (TDF) and of a biomass (Robinia Pseudoacacia) has been studied to assess the benefits deriving from the application of an acoustic field on the performance of the combustor. Experiments consisted of steady combustion, either ordinary or sound-assisted, of TDF and Robinia fine particles. High intensity acoustic fields of 120Hz reduce carbon elutriation rates by a factor of about 1.5, increasing the fixed carbon conversion efficiency by 5-8% and 2-3% for TDF and Robinia respectively. Sound frequencies either lower or higher than 120Hz reduce the effectiveness of sound, approaching the performances of ordinary fluidized bed combustors. Results have been analyzed assuming that fine particles are present in the bed either freely moving in the interstices of the bed (free fines) or attached onto coarse inert bed particles (attached fines). Accordingly the inventory of carbon under steady state conditions in the bed depends on the competition between the following processes: elutriation of free fines, adhesion of fines onto bed material, attrition of fine-coarse aggregates and combustion of fine particles. In this framework, acoustic fields have the property of enhancing the formation of fine-coarse aggregates.

Batch combustion of cohesive carbon fines in a sound assisted fluidized bed combustor

Batches of 1–45 μm carbon fines collected from a secondary cyclone of a gasifier are burnt in sound assisted fluidized beds of cohesive particles. The combustor is 40 mm ID. Unexpanded bed height is between 5 and 17 mm. Bed temperature is 1,120 K (850° C). Air is used as fluidizing gas. Its superficial velocity is about 60 mm/s. Sound wave frequency is maintained at 120 Hz whereas sound pressure level is varied up to a maximum value of 140 dB. The kinetics of carbon combustion is determined by means of a separate set of runs using a fixed bed microreactor. A comprehensive model accounting for both bed mechanics and particle combustion is presented. It embodies the kinetics of carbon burn off in the standard equations of fluidized bed reactors. There is a rather good agreement between theory and experiments at higher sound intensity. Under these conditions spouts, usually observed in aerated beds of cohesive powder, disappear because large agglomerates are broken down into clusters and subclusters made of primary particles. Generally, the size of subclusters is about 30 μm.