双组分颗粒声场流态化的实验研究

在内径为56 mm的玻璃声场流化床中,以5~10 nm未改性和有机改性的SiO2为实验物料主体颗粒,Fe3O4(粒径小于0.053 mm)为客体颗粒,在声压级为90~105 dB时系统考察了声场频率、声场强度和主客体颗粒不同配比关系对超细颗粒流化行为和聚团尺寸的影响。结果表明,当声场频率处于50 Hz,声压级大于100 dB时,声波可以有效地消除节涌、抑制沟流、降低临界流化速度,减小聚团尺寸,显著改善超细颗粒的流化质量。声场频率一定,声场强度越大,颗粒团聚体的直径越小。客体颗粒的添加比例存在一适宜范围。     

纳米TiO2颗粒在声场流化床中的流化特性

以原生纳米级TiO2颗粒为物料，在内径为130mm的声场流化床中，考察声压、频率对纳米颗粒的流化特性的影响。结果表明，适当的低频强声波的引入能很好的抑制沟流，消除节涌，大大降低了流化床中纳米颗粒聚团的尺寸，使之在低气速下实现稳定流化，从而显著改善纳米颗粒的流化质量。     

A类颗粒在声场流化床中的流化特性

在内径为120mm的半圆柱形声场流化床中,以平均粒径55μm的玻璃珠作为流化介质,考察了声压级和声波频率对玻璃珠在声场流化床中流化特性的影响。结果表明:声波的引入可以显著降低玻璃珠的临界流化速度。声波频率一定时,临界流化速度随声压的增大而减小;声压一定时,临界流化速度在声波频率为80Hz左后时达到最小值,低于或高于此值,声波作用效果均减弱。     

纳米TiO_2颗粒在声场导向管喷动流化床中的流化特性

在内径120 mm的半圆柱型声场导向管喷动流化床中,以平均粒径290 nm的TiO_2颗粒为原料,高速空气射流为喷动气,考察了操作条件、声参数(频率和声压)对纳米颗粒在声场导向管喷流床中的流态化特性的影响。结果表明:声波可以有效抑制沟流,改善环隙流化质量,防止射流旁路,从而促使粉体稳定循环,加快循环速率;同时声波可以显著地降低纳米TiO_2颗粒的最小喷动速度,声波频率一定时,最小喷动速度随声压的增加而减小;声压一定时,最小喷动速度在声波频率为80 Hz时达到最小值,低于或者高于80 Hz,最小喷动速度都会增大。     

声场流化床A类颗粒浓度分布研究

在内径140 mm,高1 600 mm的鼓泡流化床中,以流化催化裂化(FCC)颗粒为流化介质,采用光导纤维探针测定不同轴/径向位置的颗粒浓度分布.考察了操作气速和外加声场对密相区颗粒浓度的影响.结果表明,鼓泡床密相区颗粒浓度沿轴向逐渐减小,沿径向呈抛物线分布.声场的引入可以降低颗粒起始流化速度:声压级越大,起始流化速度越小:固定声压频率在150 Hz时颗粒起始流化速度最小.1随着声压强度的增大,床层中心区和上部密相区颗粒浓度增大.固定声压级,频率在100～400 Hz颗粒浓度较大,频率低于100 Hz或高于400 Hz时,声波的作用效果减弱.     

流化床中超细颗粒的聚团破碎与供料的实验研究

在内径为40 mm的流化床中,以平均粒径为10 μm的超细硅粉为物料,在引入振动力和搅拌力、添加粗颗粒的条件下,考察了振动强度、搅拌转速、粗颗粒粒径和添加比例、氮气流速等因素对超细颗粒聚团破碎和供料过程的影响.实验表明,对于10μm的超细硅粉,流化床供料的最佳操作条件为:搅拌转速90 r/min,振动频率13.9 Hz,粗颗粒粒径300 μm,添加比例20%.此时,可以有效破碎聚团,消除节涌,抑制沟流,降低临界流化速度和夹带速度,显著改善超细颗粒的供料效果.     

声场高温流化床流化特性

在内径50 mm、高1000 mm的声场高温鼓泡流化床中,研究Geldart A, B两类颗粒的流化特性,考察了床层温度、声波频率及声压级对流化床最小流化速度的影响. 结果表明,引入声场后,颗粒的最小流化速度随温度升高而下降;固定温度及频率,最小流化速度随声压级增大而减小;固定声压级与温度,颗粒最小流化速度随声波频率增大先减小后增大,存在一个最佳频率范围. 对床内压力波动信号进行分析,得出声场影响高温流化床流化质量的判据：当声压大于110 dB、频率在100~200 Hz范围内时压力波动偏差与最小流化速度值最小.     

声场高温流化床流化特性的实验研究

本文系统分析了温度、声波频率、声压级对GeldartB类颗粒初始流化速度和反应器内压力波动的影响规律。实验结果显示:当反应器内加入声场,颗粒的初始流化速度随着温度的升高急剧下降,随声压级的增大而减小,随声波频率的增大先减小后增大,并存在一个最佳频率范围。当温度超过400℃后,声压级对颗粒最小流化速度的影响增大。压力波动标准方差随气速的增大而增大;当声压级大于110 dB和声波频率处于100～200 Hz时压力波动标准偏差和颗粒初始流化速度达到最小值。     

原生纳米颗粒SiO_2中添加大粒径组分的流化性能

以平均原生粒径为 10nm的SiO2 为原料 ,采用添加较大球形玻璃珠颗粒的方法 ,在内径为6 0mm的有机玻璃流化床中 ,考察了在不同添加量和不同添加颗粒粒径的情况下 ,纳米颗粒SiO2 的流化性能。实验表明 ,纳米颗粒SiO2 的流化经历了沟流、节涌、破碎和聚团 4个阶段 ,但当添加玻璃珠的量大于10∶1或添加玻璃珠粒径不大于 0 13mm时 ,SiO2 的流化质量较好 ,并可采用床层压降曲线来表示其流化性能     

声场强化微小流化床流动特性研究

在内径4.3mm微小流化床中,考察了声场对FCC及石英砂颗粒流化质量的影响。重点讨论了声压级与频率对微小流化床最小流化速度的影响。结果表明,声场能改善微小流化床流化质量。尤其对于51μm石英砂颗粒,声场可以使其消除沟流,实现稳定流化。声压越大,声场对微小流化床流化质量改善越明显。最小流化速度随声压增高呈单调下降趋势。相同声场条件下,声波对微小流化床最小流化速度数值降低幅度大于大尺度流化床。声场对微小流化床最小流化速度的影响存在最佳频率。但不同颗粒的最佳频率不同。内径4.3mm流化床,51,67,83μm石英砂颗粒与83μmFCC颗粒对应的最佳频率分别为90,90,140和140Hz。在一定的声压与频率下,声场可以降低最小流化速度约9%～21%。对于微小流化床,床径越小,则床层空隙率越大,越有利于实现外场强化,最小流化速度的降低幅度也逐渐增大。     

Wavelet Analysis of Particle Concentration Signals in an Acoustic Bubbling Fluidized Bed

The time series of fluid catalytic cracking (FCC) particle concentrations were measured by an optical fiber probe under conditions of different sound pressure levels and sound frequencies in an acoustic bubbling fluidized bed (? 140 mm × 1600 mm). The results show that the minimum fluidization velocity had a minimum value when the sound wave frequency was 150 Hz. Under the same sound frequency, the fluidization velocity decreased as the sound pressure level increased. The particle concentration signals in an acoustic fluidized bed were also analyzed by means of wavelet analysis. On the basis of discrete wavelet transform, an original signal was resolved into five detailed scale signals. By using wavelet energy analysis, it was found that the peak frequency of the scale 3 or 4 detail wavelet signals represents the bubbling frequency and the peak amplitude for the bubble size. The results indicate that the bubbling frequency and bubble size decreased with increasing sound pressure level at a given frequency. In addition they decreased with increasing sound frequency ranging from 50–150 Hz, but further increased with increasing sound frequency ranging from 150–500 Hz.     

Fluidization Characteristics of SiO2 Nanoparticles in an Acoustic Fluidized

Under the action of an acoustic field, the fluidization behavior of 5–10 nm SiO₂ nanoparticles, with and without surface modification, was investigated. In a packed bed, the sound wave energy has a significant influence on the compact ratio of the bed. Experimental results indicated that the bed of nanoparticle agglomerates can be fluidized smoothly with the assistance of an acoustic field, and the minimum fluidization velocity is initially reduced dramatically with increasing sound frequency and then rises with increasing sound frequency. Under the same experimental conditions, the minimum fluidization velocity of 5–10 nm SiO₂ nanoparticles is greater than that of 5–10 nm SiO₂ nanoparticles with surface modification. The collapse of the bed demonstrates that SiO₂ nanoparticles, surface modified using organic compound, have longer minimum collapse times than SiO₂ nanoparticles.     

Flow characteristics in an acoustic bubbling fluidized bed at high temperature

The pressure fluctuation of the quartz sand and SiO₂ particles was investigated using pressure transducer in high temperature fluidized bed with sound assistance. The effects of bed temperature, sound wave frequency, and sound pressure level (SPL) on the pressure fluctuation were examined. It indicates that the minimum fluidization velocity decreases with an increase in sound pressure level at the same sound frequency. At the same SPL and bed temperature, there always exists an optimal frequency range achieving good fluidization quality. As the sound frequency increases, the minimum fluidization velocity decreases firstly and then increases. Based on the statistical analysis of pressure signals, the effect of sound frequency on the fluidization quality at high-temperature fluidized bed was presented. On basis of discrete wavelet transform, an original signal was resolved into five-detailed scale signal. Furthermore, the peak frequency for Scale 3 detail signal represents the bubbling frequency.     

Effects of acoustic vibration on nano and sub-micron powders fluidization

Fluidization of nano and sub-micron powders with and without acoustic vibration was investigated. The effects of sound pressure level and frequency were studied. Loudspeakers located under the distributor plate were used as the sound source to disintegrate larger agglomerates concentrated at the bottom of the bed. Nanoparticles showed fluid-like behavior similar to Geldart's A group and application of sound vibration improved their fluidization quality. Submicron particles were hard to fluidize and their fluidization quality was partially improved by sound excitation. Bed compaction, caused by rearranging of the agglomerates, was observed for submicron particles at low gas velocities while the bed was fixed. Nanoparticles did not experience any bed compaction. Sound vibration led to a decrease in minimum fluidization velocity and an increase in bed pressure drop and bed expansion for both types of particles. The fluidization quality of both particles increased at low frequencies, while the reverse was observed at higher frequencies. Fluidization of these particles was improved by increasing sound pressure level. There was a critical sound pressure level of 110 dB, below which the effect of sound vibration was insignificant. A novel technique was employed to find the apparent minimum fluidization velocity from pressure drop signals.     

Aeration and mixing behaviours of nano-sized powders under sound vibration

The aeration and mixing behaviours of two nano-sized powders, Al₂O₃ (40 nm) and CuO (33 nm), have been investigated in a laboratory scale fluidized bed. The fluidization quality of both powders is very poor without application of acoustic fields. Sound intensities larger than 135 dB and frequencies in the range 100-125 Hz improve their fluidization quality resulting into a homogeneous fluidization regime with high bed expansion. Under the effect of sound, mixing between powders has been qualitatively characterized by the visual observation of the bed and the SEM analysis of captured samples. Under the operating conditions tested, mixing between aggregates of the two powders takes only few minutes. However, mixing also occurs inside aggregates but this process requires larger times, of the order of 80-150 min.     

可吸入颗粒物声场团聚实验研究

在中等强度驻波声场中,对燃煤可吸入颗粒物进行团聚清除实验研究。系统研究声场频率、声压级、可吸入颗粒质量浓度及颗粒在声场中的停留时间对团聚清除效率的影响。实验结果表明:颗粒在声场中团聚的最佳声波频率为1 416 Hz;声压级越高越有利于颗粒的团聚,声压为128 dB时颗粒质量清除效率高达27.8%;可吸入颗粒质量浓度增大,颗粒清除效率降低;颗粒在声场停留时间为9—11 s时,团聚清除效率达到最大值。颗粒粒径影响声波团聚过程,粒径1.1μm与4.7—10μm颗粒的清除效率高于1.1—4.7μm颗粒的清除效率。     

粒径及声场对SiO2超细颗粒流化行为的影响

采用内径为56 mm的玻璃管流化床,考察了平均粒径分别为5~10 nm(1#), 0.5 mm(2#)及10 mm(3#)的SiO2超细颗粒在无声场及声场存在下的流化行为. 无声场时,1#和2#颗粒可在较高的气速下形成稳定聚团,单位质量颗粒团间作用力与原生颗粒相比显著下降,因而可实现稳定的聚团流化,3#颗粒因颗粒间粘性力较大,无法实现稳定流化. 40~60 Hz的声场对3种超细颗粒的流化行为均可起到一定的改善作用,在此频率范围外,声场的作用不明显. 提高声压级,可以使1#和2#颗粒团发生一定程度的破碎,聚团尺寸减小,最小流化速度降低. 在实验范围内,添加声场无法使3#颗粒实现稳定流化.