加压喷动床中细颗粒喷动特性

在内径分别为 186mm和 80mm的加压喷动床中 ,以空气为喷动介质 ,在 10 1～ 70 0kPa的压力范围内考察了几种不同粒度的细颗粒在加压下的喷动特性 .研究结果表明在不同的Re_t 内压力对最小喷动速度的影响不同 .实验还发现 ,随着压力的升高 ,喷动区直径增大 ,稳定操作区域增大 ,加压可明显改善喷动床的操作稳定性     

喷动流化床最小喷动流化速度的多因素影响与关联

在一Ф125 mm、锥角60°的喷动流化床内测定了混合和分离体系的混合二组分及其单一组分的最小喷动流化速度u_msf.实验表明,最小喷动速度随静床高增加而增大,随流化气速和浮升组分分率增大而减小;混合体系中最小喷动速度随浮升组分分率接近线性递减,而分离体系却呈曲线降低.对比分析了文献umsf数据,除喷口直径外,多孔分布板形式和床径明显影响u_msf的大小,采用cos(aθ)、sin(bθ)、tan(cβ)和f(D_c/D_cref)来分别修正分布板夹角θ、均匀布气结构、开孔方向角β和床径D_c的影响.根据本文和文献不同结构与体系的590组数据,又用6个量纲1参数和上述4个修正函数进行了多重影响因素的综合回归,得出新的预测u_msf的普适关联式,该式偏差±29.5%,平均偏差11.5%,相关系数0.97.     

导向管直径对喷动床流动特性影响的计算颗粒流体力学数值模拟

导向管喷动床是较为常见的一种喷动床改进床型,通过阻断喷动区与环隙区气固接触来提高颗粒循环的规律性与稳定性。本文采用计算颗粒流体力学（CPFD）方法对于直径150mm的柱锥式导向管喷动床进行了数值模拟研究,考察了导向管直径对于喷动床内颗粒流动特性的影响,从环隙区死区分布、颗粒速度分布、固体循环量等方面分析了具有不同直径导向管喷动床的运行状态。结果表明,加入导向管在减少床内死区的同时也降低了运行时的固体循环量,对于本次采用的喷动床结构尺寸与运行参数,只有在导向管直径为40～60mm时才能保证床内具有良好喷动状态,综合考虑各因素,选用直径50～55mm的导向管最为合适。对于具有类似结构与运行条件的柱锥喷动床,导向管直径可考虑选为无导向管运行时喷动区直径的1.2～1.375倍。     

串行流化床内气固流动控制

针对化学链燃烧分离CO₂技术特点,在一串行流化床（循环床+喷动床）冷态实验装置上,以CaSO₄载氧体为实验原料（d_p= 0.6 mm）,研究串行流化床气固流动特性。基于床内压力分布特征,提出将循环床（空气反应器）沿床高方向划分为鼓泡段和快速流化段2个流型区域,将喷动床（燃料反应器）沿床高方向划分为喷动段、鼓泡段和悬浮段3个流型区域,得出串行流化床内气固流动控制机理。研究并考察了循环床流化风速度、喷动床喷动风速度对串行流化床内反应器间（空气反应器和燃料反应器）气体串混、颗粒循环速率以及床层压降的影响。研究结果表明,流化风是床内颗粒循环的驱动力,流化风速度应控制在 3.77～4.05 m·s^-1;喷动风速度对床内颗粒循环以及系统稳定运行起着关键作用,建议将喷动风速度控制在0.42～0.56 m·s^-1。     

液-固混合悬浊液的压力雾化（Ⅱ）实验与结果

研究了混合液压力、固体质量分数、固体微粒直径、微粒密度对雾滴的体积-表面积直径（d₃₂）的影响.在实验中采用三维激光相位多普勒LDV/APV测试系统测定了最大概率分布的雾滴直径（d₃₂）,使用高速摄像仪记录了雾化的过程.研究发现混合液的压力和固体微粒密度对雾滴直径（d₃₂）的影响呈非单调性,雾滴直径（d₃₂）随其增大先减小、再增加;而雾滴直径随固体微粒的直径、混合液固体质量分数的增加而增大.实验结果与数学模型能较好地吻合,可为工业性设计提供理论依据.     

双喷嘴矩形喷动床流动性能实验研究

在120 mm×240 mm的双喷嘴矩形不锈钢床内,对新型双喷嘴矩形导流管喷动床的最小喷动速度和喷动高度进行了研究,考察了喷动气速、粒径、静床层高度、导流管直径、导流管安装位置对最小喷动速度和喷动高度的影响。结果表明:最小喷动速度随颗粒直径、导流管直径、导喷距的增大而增大,随静床层高度的增大而减小;喷动高度随喷动气速的增大而增大,随导流管直径的增大而减小,受静床层高度和导喷距的影响不大,并得出了最小喷动速度的关联式。     

气-液-固三相循环流化床局部相含率分布

应用自行开发的微电导探针测试技术,以玻璃珠(d_p=0.48 mm, ρ_s=2460 kg•m^-3)和苯乙烯颗粒(d_p=1.45mm,ρ_s=1264 kg•m^-3)为固相,空气为气相,水及0.05%、0.20% (质量)SCMC(羧甲基纤维素钠)水溶液为液相,对三相循环流化床(TCFB)的各相局部含率进行了同时测定.考察了不同表观液体速度、辅助液体速度、液体黏度及颗粒密度对局部相含率轴径向分布的影响. 在不同操作条件下,获得了1286套局部相含率实验数据. 给出了局部固含率和局部气含率与操作条件、流体物性及床层轴径向位置的关联式,关联式的计算值与实验值吻合较好.     

导向管喷动流化床的喷动气旁路分率

在内径为182 mm的喷动流化床中安装内径80 mm的导向管,以平均粒径为2.2 mm的尿素颗粒为物料,对喷动气旁路特性进行了实验研究,分别考察了夹带区高度、导向管长度、喷嘴内径、床层高度、喷动气速和流化气速对喷动气旁路分率的影响,结果表明随着喷动气速的增大,喷动气体旁路分率先增后减。导向管安装高度越高,气体旁路分率越大。床层高度增大喷动气体旁路分率略有降低。而喷嘴直径小于50 mm时气体旁路分率随喷嘴直径增大而提高,在大于50 mm时气体旁路分率随喷嘴直径增大维持不变。当气速较小时,导向管高度增大会引起气体旁路分率增大,引入少量流化气能有效地抑制喷动气旁路。     

小波分析方法在喷动床流型识别中的应用

在直径150 mm、静床层高280 mm的柱锥形喷动床中,采用平均粒径为1 mm、密度为2 770 kg/m~3的刚玉球为实验固相,采集不同气速下无导流管和带开孔导流管喷动床中的压力信号,通过小波分析与功率谱相结合的方法表征柱锥形喷动床的流型转变。首先利用平均压力法测得本实验条件下无导流管和带开孔导流管喷动床的最小喷动速度分别为0.57,0.50 m/s,然后采用Daubechies2小波对压力信号进行7层小波分解得出能反映喷动床流动特性的主频信号,再对主频信号进行功率谱分析。结果表明:无导流管和带开孔导流管喷动床的主频分别出现在D3(6.25—12.5 Hz)和D2(12.5—25 Hz)频段,且主频信号的功率谱图可以表征喷动床的3种流型:固定床、稳定喷动和不稳定喷动;开孔导流管喷动床的操作弹性(1相似文献   

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。     

Gas spouting hydrodynamics of fine particles

Hydrodynamic measurements for the spouting of fine particles were obtained in a conical‐based cylindrical bed of diameter 0.186 m, inlet orifice diameters of 6 to 14 mm, and included cone angles of 45 to 80 degrees. Four different types of fine particles with diameters ranging from 0.286 to 0.861 mm were investigated. Four different flow regimes—fixed bed, stable spouting, unstable spouting and slugging—were identified and mapped. The termination of the spouting of fine particles was caused by choking rather than by fluidization of particles in the upper bed. Stable spouting could be achieved when the ratio of the orifice diameter to mean particle diameter was less than 20. The measured minimum spouting velocities were within ±15% of those predicted by the Mathur—Gishler equation. Solids density measurements obtained by a gamma ray densitometer showed that the solid density in the spout increases with bed height and in the annulus is 3% to 10% higher than in a loosely packed bed.     

Attrition of porous glass particles in a fluidised bed

Fluidisation is frequently accompanied by unwanted attrition of the bed material. This paper focuses on the mechanical aspects of fines creation by attrition in fluidised beds supported by multi-orifice distributor plates. The attrition rates of low-density porous glass particles were measured; these particles show abrasive wear behaviour rather than breakage. Positron emission particle tracking (PEPT) was used to follow particle motion in three dimensions within the fluidised bed. For a single orifice distributor with background fluidisation, the attrition rate increased exponentially with increasing orifice gas velocity. For a multi-orifice distributor, however, attrition rates were roughly proportional to excess gas velocity, except near to a critical ratio of particle to orifice diameter; as this ratio approached 2, attrition was observed to increase by an order of magnitude. A method is proposed for estimating attrition rates from a combination of small-scale experimental results and theoretical calculations of distributor jet entrainment rates.     

Spouted bed hydrodynamics in a 0.91 m diameter vessel

Hydrodynamic measurements were obtained in a flat-based half-cylindrical column of diameter 0.91 m and inlet orifice diameters of 76 to 114 mm. Beds of 3.5 to 6.7 mm diameter particles with static depths of 0.53 to 1.83 m were spouted with air. In agreement with measurements by earlier workers in smaller columns, it was found necessary to operate with inlet orifice diameters less than about 30 times the mean particle diameter in order to be able to achieve stable spouting. Correlations for minimum spouting velocity developed on small vessels generally gave poor predictions for the large diameter vessel employed in this work and failed to predict the observed dependence of U_ms on the static bed height. Substantial dead regions where particles were stagnant were observed in the lower outer portion of the vessel. Other aspects of behaviour studied, including spout diameters and shapes, fountain heights, pressure profiles and gas velocities in the annulus, were qualitatively similar to those in smaller columns, although equations developed for the smaller vessels did not always provide accurate predictions.     

Hydrodynamics of a gas-driven gas-liquid-solid spouted bed with a draft tube

A cylindrical gas-liquid-solid spouted bed, driven exclusively by gas flow, has been developed with a high potential for use in biochemical processes, such as a biological wastewater treatment. A plexiglass column with a 152 mm inner diameter was used in combination with a 53 mm inner diameter plexiglass draft tube. Three particle types were studied with densities ranging from 1044 kg/m³-1485 kg/m³ and average particle sizes ranging from 0.7-2.5 mm. Four flow regimes were observed when increasing the gas velocity, including fixed bed, semispouted bed, full spouted bed, and internal circulating fluidized bed. The transition gas velocities between those regimes were experimentally measured and termed as minimum spouting velocity, full spouting velocity, and minimum circulating velocity, respectively. A measurement of the downward particle flux in the annulus was used to identify the minimum spouting velocity, while the particle velocity and dense phase retraction in the annulus were monitored for the full spouting and minimum circulating velocities. All regime transition velocities increased with more dense particles and longer draft tubes. The minimum spouting velocity and full spouting velocity were not affected when varying the nozzle-tube gap, while the minimum circulating velocity increased with longer nozzle-tube gaps. Experiments without a draft tube were carried, though the spouting stability was significantly reduced without the draft tube.     

流化床与固定床耦合反应器中的颗粒磨损

在直径50mm的冷模流化床与固定床耦合反应器中,考察了活性炭颗粒在130～150℃及不同气速下的磨损情况,得到了不同气速下固定床中圆柱状颗粒的磨损率随时间的变化关系,同时分析了滞留在流化床、固定床及袋滤器中的细颗粒在不同气速下的粒径分布与质量分布.结果表明,颗粒在该耦合反应器中磨损严重,在0.212～0.424m/s气速下,固定床中颗粒质量损失可达3%～4%,流化床中颗粒平均粒径由200μm降至100μm以下.     

Spouting characteristics of spf wood pellets

The spouting characteristics with ambient air of cylindrical wood pellets, 6.5 mm in diameter and 11.1 ± 4.1 mm long, were investigated using a transparent 152.4‐mm diameter semi‐circular cone‐based cylindrical column. Despite the previously unexplored shape of the pellets in the spouted bed mode, the measured minimum spouting velocities at different bed heights, the maximum spoutable bed height and the mean spout diameter above the conical base were all well represented by equations from the literature developed mainly for more rounded particles. Pellet attrition was found to be severe, so that the possible torrefaction of the pellets by the spouting technique without sacrifice of their integrity appears to be unlikely. © 2012 Canadian Society for Chemical Engineering     

THE STABILITY OF WET SPOUTED BEDS

In granulation, coating or drying of slurries on inert particles a liquid phase is added to a gas-spouted bed. The effect of liquid injection on spouting velocity, fountain height, bed pressure drop and stability of the spouting regime is examined in a 0.15 m diameter bed with four types of inert particles 2 to 5 mm in size, 1140 to 2880 kg/m³ in true density, and 1.3 and 1400 mPa·s in liquid viscosity. Key factors are the liquid content and the presence of cohesive forces due to liquid bonds between particles. In a spoutability chart the maximum spoutable liquid content is related to the ratio of inertial force of a particle to the viscous or cohesive force exerted onto the particle by the liquid film. The spoutability chart serves to define regions of stable spouting.     

The maximum spoutable bed heights of fine particles spouted with air

The maximum spoutable bed heights of systems of fine glass spheres spouted with air are studied in flat based semi circular columns of 80 and 152.4 mm diameters using particles with average diameters ranging from 0.3 to 1.3 mm. New correlations are proposed to predict the maximum spoutable bed heights of air spouted fine particle systems. It is concluded that the influence of the column diameter on the maximum spoutable bed height is significantly decreased compared to coarse particle systems and that it further varies with particle size within the fine particle spouting regime. Data reported in the literature agree with the proposed correlations.     

THE STABILITY OF WET SPOUTED BEDS

ABSTRACT

In granulation, coating or drying of slurries on inert particles a liquid phase is added to a gas-spouted bed. The effect of liquid injection on spouting velocity, fountain height, bed pressure drop and stability of the spouting regime is examined in a 0.15 m diameter bed with four types of inert particles 2 to 5 mm in size, 1140 to 2880 kg/m³ in true density, and 1.3 and 1400 mPa·s in liquid viscosity. Key factors are the liquid content and the presence of cohesive forces due to liquid bonds between particles. In a spoutability chart the maximum spoutable liquid content is related to the ratio of inertial force of a particle to the viscous or cohesive force exerted onto the particle by the liquid film. The spoutability chart serves to define regions of stable spouting.