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
在φ250 mm 的流化床中,采用空气-聚乙烯颗粒体系和3种不同结构的气体分布板进行流化实验,通过声发射检测装置采集气体分布板下方不同位置的声信号,分别考察了3种小同结构的气体分布板上流化死区的存在情况与位置分布。实验结果表明,分...在φ250 mm 的流化床中,采用空气-聚乙烯颗粒体系和3种不同结构的气体分布板进行流化实验,通过声发射检测装置采集气体分布板下方不同位置的声信号,分别考察了3种小同结构的气体分布板上流化死区的存在情况与位置分布。实验结果表明,分布板局部的声信号平均能量可以反映对应位置的颗粒活跃程度,定义了颗粒活跃程度指数 R_i,并提出以 R_i=0.6作为流化死区存在的判据。声发射技术能有效地检测流化床分布板上的流化死区,对分布板的设计以及工业生产的故障监控都具有积极的意义。展开更多
Polymer particles having the same chemical makeup but different sizes would have their own special contributions to the generation of static charges,owing to the differences in catalyst residue and surface properties ...Polymer particles having the same chemical makeup but different sizes would have their own special contributions to the generation of static charges,owing to the differences in catalyst residue and surface properties among them.Experiments were performed in a gas-solid fluidized bed to determine the changes in the electrostatic charges with addition of various fine polyethylene particles,which were the same material as the coarse polyethylene particles,to better understand their role in influencing electrostatic charge generation/dissipation.By measuring the electrostatic potential at different bed axial heights,it was found that the electric field inside the bed was significantly influenced by the size of added fine polyethylene particles,mass fractions and catalyst residue.Consequently,an impact factor of fine particles(Fb) was proposed,which was the sum of particle diameter term and catalyst residue term.Within the experimental limits in this paper,after three kinds of fines with Fb all less than 1 were added in the fluidized bed,the electrostatic potential in the bed was just influenced slightly.However,the bed electrostatic potential changed significantly following the addition of the fines with the smallest particle diameter and highest residual catalyst content.While Fb of this kind of fines was less than 1,the static potential did not change much but even decreased slightly with the addition of fines.Once Fb of the fourth kind of fines was more than 1,the electrostatic potential in the bed increased greatly.With Fb of the fourth kind of fines increasing further,the electrostatic potential fell a little,and meanwhile it was found that a large amount of fine particles adhered to the column wall.展开更多
在内径0.14 m,高1.6 m 的气固流化床中,以空气和流化催化裂化颗粒为气相和固相,采用PV-6A 型光纤测速仪和 U 形管压差计分别测定三种不同开孔率分布板时的颗粒浓度分布和分布板压降,同时应用流体力学软件 Fluent 6.2分别对三种不同开孔...在内径0.14 m,高1.6 m 的气固流化床中,以空气和流化催化裂化颗粒为气相和固相,采用PV-6A 型光纤测速仪和 U 形管压差计分别测定三种不同开孔率分布板时的颗粒浓度分布和分布板压降,同时应用流体力学软件 Fluent 6.2分别对三种不同开孔率分布板压降,径向固含率分布进行了模拟计算,模拟结果与实验值吻合较好。研究结果显示,分布板压降随开孔率的增大而减小,分布板开孔率大于0.86%后对压降影响较小;径向固含率波动随开孔率的增大而增大,开孔率0.46%的分布板径向固含率分布曲线波动最小,气固分布最均匀。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.
文摘在φ250 mm 的流化床中,采用空气-聚乙烯颗粒体系和3种不同结构的气体分布板进行流化实验,通过声发射检测装置采集气体分布板下方不同位置的声信号,分别考察了3种小同结构的气体分布板上流化死区的存在情况与位置分布。实验结果表明,分布板局部的声信号平均能量可以反映对应位置的颗粒活跃程度,定义了颗粒活跃程度指数 R_i,并提出以 R_i=0.6作为流化死区存在的判据。声发射技术能有效地检测流化床分布板上的流化死区,对分布板的设计以及工业生产的故障监控都具有积极的意义。
文摘Polymer particles having the same chemical makeup but different sizes would have their own special contributions to the generation of static charges,owing to the differences in catalyst residue and surface properties among them.Experiments were performed in a gas-solid fluidized bed to determine the changes in the electrostatic charges with addition of various fine polyethylene particles,which were the same material as the coarse polyethylene particles,to better understand their role in influencing electrostatic charge generation/dissipation.By measuring the electrostatic potential at different bed axial heights,it was found that the electric field inside the bed was significantly influenced by the size of added fine polyethylene particles,mass fractions and catalyst residue.Consequently,an impact factor of fine particles(Fb) was proposed,which was the sum of particle diameter term and catalyst residue term.Within the experimental limits in this paper,after three kinds of fines with Fb all less than 1 were added in the fluidized bed,the electrostatic potential in the bed was just influenced slightly.However,the bed electrostatic potential changed significantly following the addition of the fines with the smallest particle diameter and highest residual catalyst content.While Fb of this kind of fines was less than 1,the static potential did not change much but even decreased slightly with the addition of fines.Once Fb of the fourth kind of fines was more than 1,the electrostatic potential in the bed increased greatly.With Fb of the fourth kind of fines increasing further,the electrostatic potential fell a little,and meanwhile it was found that a large amount of fine particles adhered to the column wall.
文摘在内径0.14 m,高1.6 m 的气固流化床中,以空气和流化催化裂化颗粒为气相和固相,采用PV-6A 型光纤测速仪和 U 形管压差计分别测定三种不同开孔率分布板时的颗粒浓度分布和分布板压降,同时应用流体力学软件 Fluent 6.2分别对三种不同开孔率分布板压降,径向固含率分布进行了模拟计算,模拟结果与实验值吻合较好。研究结果显示,分布板压降随开孔率的增大而减小,分布板开孔率大于0.86%后对压降影响较小;径向固含率波动随开孔率的增大而增大,开孔率0.46%的分布板径向固含率分布曲线波动最小,气固分布最均匀。