Agglomerations could be detected in a fluidized bed by utilizing wavelet analysis, on the basis of the mechanism that AE signals with different frequencies were emitted when the particles with different sizes impacted...Agglomerations could be detected in a fluidized bed by utilizing wavelet analysis, on the basis of the mechanism that AE signals with different frequencies were emitted when the particles with different sizes impacted the wall.The acoustic signals of particles were investigated in an externally heated fluidized bed 100 in diameter and in a pilot-scale industrial fluidized bed 420 in diameter respectively.In those experiments, the number of small particles decreased obviously while the number of large particles increased due to agglomeration.The signals were decomposed by multi-scale wavelet analysis.While the acoustic energy ratio increased from low scale to high scale layer by layer, the main frequency of acoustic signals transferred from high frequency to low frequency.Meanwhile, the d6th, d7th scales, which represented large size particles, increased suddenly,indicating the occurrence of agglomerations.Thus, the agglomerations in fluidized bed could be quickly and exactly detected online by the acoustic emission technique.展开更多
The flow pattern of a fluidized bed is a key factor for heat transfer and new reactor design.The flow pattern of the gas-solid fluidized bed was experimentally measured by a novel acoustic emission(AE)technique.The ac...The flow pattern of a fluidized bed is a key factor for heat transfer and new reactor design.The flow pattern of the gas-solid fluidized bed was experimentally measured by a novel acoustic emission(AE)technique.The acoustic energy generated by the collision of solids particles on the reactor wall or in the local space is a reflection of the speed and frequency of collision,and consequently the flow pattern of particles.The flow pattern of polyethylene particles with the average size 460 μm in a 150 mm fluidized bed in the range of superficial gas velocity from 0.3 m·s-1 to 0.7 m·s-1 was multi-circulation pattern with main-circulation zone,sub-circulation zone and stagnant zone.The multi-circulation flow pattern would transit to the single circulation flow pattern if superficial gas velocity exceeded 0.8 m·s-1 or average particle size decreased to below 365 μm.The height of stagnant zone remained unchanged with the increase of static bed height.It was also found that the type of the distributor had an evident effect on flow pattern.The single circulation flow pattern in the fluidized bed with a perforated stainless steel plate distributor would change to the multi-circulation flow pattern for the same particles and the same fluidized bed with a cone-shaped distributor.An empirical equation calculating the height of stagnant zone was presented and the experimental data could be correlated with the empirical equation with fairly good accuracy.展开更多
文摘Agglomerations could be detected in a fluidized bed by utilizing wavelet analysis, on the basis of the mechanism that AE signals with different frequencies were emitted when the particles with different sizes impacted the wall.The acoustic signals of particles were investigated in an externally heated fluidized bed 100 in diameter and in a pilot-scale industrial fluidized bed 420 in diameter respectively.In those experiments, the number of small particles decreased obviously while the number of large particles increased due to agglomeration.The signals were decomposed by multi-scale wavelet analysis.While the acoustic energy ratio increased from low scale to high scale layer by layer, the main frequency of acoustic signals transferred from high frequency to low frequency.Meanwhile, the d6th, d7th scales, which represented large size particles, increased suddenly,indicating the occurrence of agglomerations.Thus, the agglomerations in fluidized bed could be quickly and exactly detected online by the acoustic emission technique.
文摘The flow pattern of a fluidized bed is a key factor for heat transfer and new reactor design.The flow pattern of the gas-solid fluidized bed was experimentally measured by a novel acoustic emission(AE)technique.The acoustic energy generated by the collision of solids particles on the reactor wall or in the local space is a reflection of the speed and frequency of collision,and consequently the flow pattern of particles.The flow pattern of polyethylene particles with the average size 460 μm in a 150 mm fluidized bed in the range of superficial gas velocity from 0.3 m·s-1 to 0.7 m·s-1 was multi-circulation pattern with main-circulation zone,sub-circulation zone and stagnant zone.The multi-circulation flow pattern would transit to the single circulation flow pattern if superficial gas velocity exceeded 0.8 m·s-1 or average particle size decreased to below 365 μm.The height of stagnant zone remained unchanged with the increase of static bed height.It was also found that the type of the distributor had an evident effect on flow pattern.The single circulation flow pattern in the fluidized bed with a perforated stainless steel plate distributor would change to the multi-circulation flow pattern for the same particles and the same fluidized bed with a cone-shaped distributor.An empirical equation calculating the height of stagnant zone was presented and the experimental data could be correlated with the empirical equation with fairly good accuracy.
