下行床入口段流体力学及混合行为

针对工业快速反应对气固进料混合过程的特殊需求,在内径140mm,高4.7m的并流下行循环流化床中,采用双光路光纤密度测量技术及磷光颗粒示踪技术,对两种不同的气固并流下行床分布器结构的流动及颗粒混合行为进行了研究．分别考察了人口段颗粒浓度径向分布沿轴向的变化规律及颗粒轴径向混合行为．实验结果表明,下行床入口段颗粒浓度随轴向位置的变化可划分为分布器影响区及湍流控制区．分布器结构对入口段颗粒密度分布有较大影响,利用侧向喷嘴并降低入口处颗粒的射流可以获得较好的径向均布效果．侧向喷嘴的分布器结构更有利于颗粒的径向混合．还考察了入口结构对颗粒混合的影响因素,给出了对Pe_a及Pe_r的关联式．     

提升管反应器中颗粒浓度径向分布的力学特性

采用空气动力学中的Kutta-Joukowski升力定理分析了提升管内颗粒的受力,得到了Kutta-Joukowski力FK-J的计算公式FK-J=ρg(vg,Z-vp,Z)(?vp,Z/?r)r.根据在大型冷模实验装置上由PV-6D型颗粒密度两用仪测量的局部固含率和颗粒速度径向分布的实验数据,计算了Kutta-Joukowski力在提升管内的分布特征,分析了颗粒循环量、表观气速、轴向位置对其径向分布的影响.结果表明,当无因次半径r/R=0时,FK-J=0,在r/R=0.85时,FK-J最大;FK-J随颗粒循环量增大而增大,表观气速对FK-J的径向分布没有显著影响;在提升管内的充分发展段FK-J的数值明显大于提升管加速区和出口约束区.由实验数据回归出了提升管内FK-J径向分布的经验关联式,计算值与理论值吻合较好.     

气固逆流下行流化床中颗粒速度的径向与轴向分布

在内径90 mm、高7 m的逆流下行床冷态实验装置中,研究了气固逆流下行床中循环锅炉灰(dp=300 mm)颗粒速度的径向分布及其沿轴向发展. 结果表明,局部颗粒速度沿径向分布是不均匀的,在完全发展区,颗粒速度中心和边壁低、在r/R=0.85附近颗粒速度最大. 由大量实验数据回归出预测充分发展段局部颗粒速度的关联式,该公式计算值与实验值的平均相对偏差小于±11%. 不同径向位置的局部颗粒速度沿轴向的变化趋势不同,边壁区域(r/R>0.622)颗粒速度沿轴向单调递增,而中心区域(0相似文献   

入口结构对18 m气固循环流化床提升管内颗粒流动特性的影响

在高18 m、内径80 mm的循环流化床提升管内分别考察了三种入口结构对颗粒流动特性的影响。实验结果表明：入口结构主要影响提升管底部区域的颗粒流动特性,不同入口结构对颗粒流动影响不同。相同操作条件下,当采用多管式入口结构时,径向上提升管底部区域的颗粒浓度分布相对均匀,轴向上颗粒能够迅速达到充分发展状态,充分发展高度在9 m左右;当采用多孔板入口结构时,径向上提升管底部颗粒浓度差别较大,轴向上颗粒发展较慢,需要更高高度才能达到充分发展,充分发展高度约为11 m;当采用单管式入口结构时,径向上颗粒浓度分布和轴向上颗粒充分发展速度均处于前两者之间,底部颗粒浓度径向分布仍为中间稀、边壁浓的不均匀分布,颗粒浓度轴向充分发展高度约为10 m。     

上行气固两相流充分发展段颗粒浓度关联及预测

在高度分别为15.1m和10.5m的两套实验装置上,对快速流态化到稀相气力输送流型下提升管内的轴向压力梯度进行了系统测试,以研究提升管充分发展段内不同颗粒的浓度变化及其与操作参数的关系。实验在其中175组操作条件下展现出明显的充分发展段(>2.8m)。结果表明,表观气速在3~8m?s-1之间变化时,对充分发展段颗粒浓度随终端颗粒浓度的变化关系影响显著,但当表观气速>8m?s?1或<3m?s?1时,其对充分发展段颗粒浓度随终端颗粒浓度线性增加的关系影响极弱;在此基础上提出的预测关联式更明确地反映了操作条件等因素对充分发展段颗粒浓度的定量影响关系,其计算结果与本实验和相关文献的实验数据吻合良好。     

入口结构对18 m气固循环流化床提升管内颗粒流动特性的影响

在高18 m、内径80 mm的循环流化床提升管内分别考察了三种入口结构对颗粒流动特性的影响。实验结果表明:入口结构主要影响提升管底部区域的颗粒流动特性,不同入口结构对颗粒流动影响不同。相同操作条件下,当采用多管式入口结构时,径向上提升管底部区域的颗粒浓度分布相对均匀,轴向上颗粒能够迅速达到充分发展状态,充分发展高度在9 m左右;当采用多孔板入口结构时,径向上提升管底部颗粒浓度差别较大,轴向上颗粒发展较慢,需要更高高度才能达到充分发展,充分发展高度约为11 m;当采用单管式入口结构时,径向上颗粒浓度分布和轴向上颗粒充分发展速度均处于前两者之间,底部颗粒浓度径向分布仍为中间稀、边壁浓的不均匀分布,颗粒浓度轴向充分发展高度约为10 m。     

气固循环床提升管内的局部颗粒浓度及流动发展

采用反射式光纤浓度探头对f100mm×15.1m循环床提升管8个轴向截面上11个径向位置的局部颗粒浓度进行了测量, 分析研究了颗粒浓度径向分布的不均匀性及其沿轴向的发展变化。结果表明:提升管内气固两相流的发展并不同步,而是一个由核心区向边壁区逐渐扩展,并最终达到总体充分发展的过程,该过程主要受边壁区发展过程所控制;相对于核心区,边壁区的发展不仅显著缓慢,而且受操作条件的影响也较显著。实验还发现:在颗粒加速段,无因次颗粒浓度的径向分布不具有相似性,不仅与径向位置有关,而且还与床层截面高度有关。     

双颗粒提升管中细颗粒的混合行为研究(Ⅱ)──弥散颗粒的轴径向混合行为

利用磷光颗粒示踪技术,使用点源示踪的方法在不同的径向位置测得反映颗粒径向扩散行为的停留时间分布曲线,并对弥散细颗粒的径向混合行为进行了分析．提出二维扩散模型描述所测量的停留时间分布曲线特征．实验发现弥散细颗粒的径向扩散Peclet数随粗颗粒加入量的增加而增加,随细颗粒浓度的增大而增大,而几乎不随气速变化．给出了一个与实验数据吻合较好并可适用于单颗粒提升管的关联式．     

双颗粒提升管中细颗粒的混合行为研究(Ⅱ)──弥散颗粒的轴径向混合行为

利用磷光颗粒示踪技术，使用点源示踪的方法在不同的径向位置测得反映颗粒径向扩散行为的停留时间分布曲线，并对弥散细颗粒的径向混合行为进行了分析．提出二维扩散模型描述所测量的停留时间分布曲线特征．实验发现弥散细颗粒的径向扩散Peclet数随粗颗粒加入量的增加而增加，随细颗粒浓度的增大而增大，而几乎不随气速变化．给出了一个与实验数据吻合较好并可适用于单颗粒提升管的关联式．     

上行气固两相流充分发展段的颗粒浓度

在Ф100mm× 16m循环床提升管实验装置上测试了134组操作条件下提升管 12个截面位置的平均颗粒浓度 ,其中 113组操作条件下提升管中的气固两相流展现出明确的充分发展段 .结果表明 ,充分发展段的颗粒浓度εs 随颗粒循环量G_s 的增加而增大且具有显著的线性关系 ,ε_s 随表观气速U_g 的增加以幂函数关系减小 .所提出的实验关联式不仅较好地拟合了本文所获得的充分发展段的平均颗粒浓度数据 ,而且诠释了以往有关提升管稀相段出口颗粒浓度预测结果之间的差异 ,更明确地反映了充分发展段颗粒浓度与操作参数之间的定量关系     

SCX超细分级机进料管内气固两相流数值模拟

以两相流理论为基础,对SCX超细分级机进料管改进后内部的气固两相流动特性进行了数值模拟。分析了气相压力、速度、湍动能和固相颗粒浓度的分布情况,得到了进料管内气固两相的分布规律。结果表明,加入导流片之后,进料管内气相压力、速度、湍动能径向梯度减小,偏流现象减弱;导流片阻碍了固相颗粒的横向运动,改变了颗粒的运动轨迹,使得颗粒浓度分布更加均匀,为后续的分级提供了良好的基础。     

Solid concentration and velocity distributions in an annulus turbulent fluidized bed

Solid concentration and particle velocity distributions in the transition section of a?200 mm turbulent fluidized bed (TFB) and a?200 mm annulus turbulent fluidized bed (A-TFB) with a?50 mm central standpipe were mea-sured using a PV6D optical probe. It is concluded that in turbulent regime, the axial distribution of solid concen-tration in A-TFB was similar to that in TFB, but the former had a shorter transition section. The axial solid concentration distribution, probability density, and power spectral distributions revealed that the standpipe hin-dered the turbulence of gas–solid two-phase flow at a low superficial gas velocity. Consequently, the bottom flow of A-TFB approached the bubbling fluidization pattern. By contrast, the standpipe facilitated the turbulence at a high superficial gas velocity, thus making the bottom flow of A-TFB approach the fast fluidization pattern. Both the particle velocity and solid concentration distribution presented a unimodal distribution in A-TFB and TFB. However, the standpipe at a high gas velocity and in the transition or dilute phase section significantly affected the radial distribution of flow parameters, presenting a bimodal distribution with particle concentration higher near the internal and external wal s and in downward flow. Conversely, particle concentration in the middle an-nulus area was lower, and particles flowed upward. This result indicated that the standpipe destroyed the core-annular structure of TFB in the transition and dilute phase sections at a high gas velocity and also improved the particle distribution of TFB. In conclusion, the standpipe improved the fluidization quality and flow homogeneity at high gas velocity and in the transition or dilute phase section, but caused opposite phenomena at low gas ve-locity and in the dense-phase section.     

颗粒黏度模型对采用欧拉多相流模型模拟超密相颗粒流动行为的影响

颗粒黏度是欧拉多相流模型计算固体流动的重要参数之一，其数值大小依赖于摩擦压力和径向分布函数。通过与实验值对比，评估了常用的摩擦压力模型（Based、Johnson）和径向分布函数模型（Lun、Syamlal O’Brien）对密相颗粒流动体系的预测能力。模拟结果表明，Johnson模型的固体体积分数预测值低于Based模型；Syamlal O’Brien 模型固体流率的预测值远大于Lun模型。采用根据实验结果修正的欧根系数后，Based-Lun、Johnson-Lun和Johnson-SO模型组合预测的平均压降相对误差分别由68.6%、73.3%和78.2%降低至13.2%、29.7%和42.3%。综合考虑压降、固体出口质量流率、固体体积分数、壁面区域固体速度的模拟结果与实验值的偏差，发现Based-Lun模型组合的平均预测误差最小，适用于气固移动床的欧拉多相流模拟。研究还发现，欧根系数与内摩擦角对固体速度与压降有着显著的影响，而临界固含率对固体速度与压降的影响较小。     

快速流化床中颗粒浓度及颗粒速度的径向分布

本文在φ140mm的气固并流下行快速流化床中,研究了颗粒浓度及颗粒速度的径向分布随操作气速、颗粒循环速率以及床层轴向位置的变化规律。并探讨了颗粒质量通量的径向分布及颗粒流动的均匀性,表明在相同操作条件下,下行快速流化床中气固流动远比上行快速流化床均匀。     

补充风对水平管高压密相气力输送影响的模拟研究

针对水平管高压密相气力输送数理模型的缺陷与不足，引入Savage径向分布函数修正的颗粒动理学理论、基于Berzi摩擦压应力模型构建的摩擦应力模型以及修正的三段式曳力模型，在欧拉-欧拉方法的基础上建立了一个能同时兼顾水平管高压密相气力输送中稀相流、过渡流以及密相流输送特性的三维非稳态数理模型。并采用该数理模型考察了补充风对水平管高压密相气力输送的影响，模拟结果精准地预测了水平管压降及其随补充风的变化规律，而且其预测的水平管固相体积浓度分布与ECT图也是相吻合的，从而验证了数理模型的可靠性。模拟结果表明：随着补充风的增加，气固两相速度和湍动能以及颗粒拟温度增大，固相体积浓度减小。     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

基于图像法的稀相气／固两相流混合比及空隙率分析

通过使用高速摄影系统获得稀相气／固两相流流动图像,并利用图像处理技术对获得的图像进行均匀光照、二值化及粘连颗粒分割等预处理,统计出图像中颗粒尺寸参数。利用数学公式,计算出稀相气／固两相流流混合比与空隙率的纵向分布和横向分布,以及不同截面积的混合比与空隙率分布,并对混合比与空隙率的分布进行比较分析。最终得出在稀相气／固两相流中,混合比比空隙率能更好地描述气／固两相流流动特性的结论。