气固流化床中倾斜分布板上射流深度的研究

在二维流化床中,用摄像法研究了锥形分布板上射流。实验中发现,锥形分布板上射流可分为I类射流和II类射流,60°分布板上射流都是I类射流,45°分布板上观察到了II类射流,随着条件的变化射流类型也发生了改变。射流的类型与分布板角度、孔速、颗粒性质、孔的位置有关。相同气速下,0°(水平)分布板上的射流深度要大于45°和60°分布板。床层高度对射流深度的影响可以忽略。对实验数据进行拟合得到了锥形分布板上单孔射流深度关联式。     

双射流流化床空隙率的分布

在 ３００ ｍｉｎ×５０ ｍｉｎ×２６００ ｍｍ的二维射流床中,采用内径为 １１ ｍｍ的对称双射流管,研究了等速射流条件下射流管间距、喷口射流气速、静床高度对床层空隙率分布的影响,发现射流管间距、喷口射流气速是双射流产生射流区合并的主要原因;并得到了具体实验条件下空隙率分布的数据．同时研究了双射流管不等速射流条件下空隙率分布的规律．     

喷动流化床流动特性数值模拟

为了捕捉喷动流化床中微观层次上的颗粒运动信息,建立了基于CFD的二维非稳态喷动流化床欧拉-欧拉两相流模型。分析了不同流化气速对喷动流化床气固流动特性的影响,即不同工况下的炉内压力降、颗粒浓度、床内空隙率分布、气体速度分布和固体颗粒速度分布。数值模拟研究结果表明:随流化气速的增大,压降和炉内平均空隙率逐渐增大,密相床层高度逐渐增加,沿着轴向方向的气体流量增大,喷动气的射流深度逐渐增加,同时射流半径也逐渐增加。     

流化床气固流动二维数值模拟

为了获得流化床中床层在不同气速下的流动特性,根据某一生物质发电厂中的HX220/9.8-IV1型纯烧生物质的循环流化床锅炉进行二维建模,通过FLUENT软件对床层冷态流态化进行二维数值模拟,调整一二次风入口风速以获得不同的表观气速,得到了鼓泡床、湍动床以及快速床的气固流动状态,并在快速床的基础上模拟了床层在气流作用下的稀相输送状态。模拟结果清晰展示了各个状态下的床层颗粒的分布情况。     

再分布板对环隙气升式反应器内多相流动的影响

为了考察环流反应器放大过程中再分布板对其内部多相流动的影响,采用欧拉双流体模刑模拟了再分布板小同高度的布置对环流反应器内气含率,循环液速,固体颗粒分布等参数的影响,并与部分冷模实验结果进行了比较,两者结果一致结果表明,再分布板高度的增加会使气升反应}州为气含率旱现先增后减的趋势,并导致导流管内的固含率上升。此外,小同高度的再分布板对环流反器内整体气含率及循环液速的影响小大结合CFD模拟和实验结果,优化了环流反应器内再分布板的设计,从而为实现强化环隙气升式环流反应器内多相流动、传递、反应等过程提供了一定的指导意义     

径向移动床反应器流场特性及其数学模拟

本文票据主流道变质量流及颗粒床层气固体力学理论,建立了完整的径向移动床反应器流体力学数学模型,开发了模拟计算床层气相二维流场的一种新的数学方法及相应的计算程序。黛此可以模拟计算床层气相压力和轴径向速度的二维分布、内外主流道压力和流速分布以及布气孔道的过孔气速和压降。根据模拟计算结果,提出首先优化设计两主流道截面积分配,然后采用变开孔率设计消除开孔区端效应的两步设计方法。借此实现径向移动床反应器的优     

方形气固密相床中局部颗粒浓度分布的实验研究

在368mm×368mm方形气固流化床中采用FCC颗粒研究了局部颗粒浓度分布的基本行为,实验测试了不同高度床层截面上的局部颗粒浓度分布。结果表明:局部颗粒浓度在床层中心最小,向外逐渐增加,边壁处颗粒浓度急剧增加到最大;表观气速(Ug)较低时,床层截面内不同方向上颗粒浓度分布的差异较大;随表观气速增大,床层截面内不同方向上的颗粒浓度分布规律趋于一致。局部流动结构的转变首先发生于床层中心,然后再向边壁逐渐扩展。颗粒浓度概率密度分布曲线(PDD)表明在湍动流态化下稳定的两相流动结构已被打破。     

振动流化床中流动结构的混沌分析

在内径90mm、静床高800mm的高床层流化床中,用动态压力传感器检测了不同气速条件下普通流化床和振动流化床中沿轴向的压力脉动信号,通过小波变换对信号除噪后,用混沌理论对信号进行了分析.通过关联维数和Kolmogorov熵定量表征振动流化床中的流动结构特征.结果表明:压力脉动信号的关联维数和Kolmogorov熵能够描述振动流化床中的流化状态;振动流化床中床层的流动结构存在两个区,在近分布板区域为射流区,床层主体部分为均匀流化区.     

双组分射流床中射流穿透深度的研究

使用多相流模型计算了灰熔聚流态化粉煤气化器中双组分的射流穿透深度。较科学地讨论了模拟计算中射流边界的定义；提出在工业气化器的操作条件下，用基于颗粒个数的算术平均法求混合物的平均直径，从而将双组分问题简化为单组分的计算，求出的射流穿透深度与实验值或文献值比较吻合，并发现床层表观气速的影响较大。     

大型射流流化床的流型转变与射流深度

在高 8m、直径 0 .5m的大型射流流化床中 ,通过摄像分析法 ,研究了射流、喷流两种流型的转变 .结果表明在低静床高、大射流气速下易出现喷流 ;喷流出现时 ,功率谱主频射流气速曲线上出现一转折点 .转折点射流气速与摄像法得出的流型转变射流气速相同 .提出了射流、喷流流型转变关系式 .同时发现射流深度随射流气速变大而增大 ,结合二维射流床射流深度的研究结果 ,得出了射流深度的预测式     

催化裂化再生器树枝状气体分布器喷嘴的射流特性

在催化裂化装置中再生器底部通常设置有树枝状管式气体分布器,通过分布器上的喷嘴分布气体。但在实际运行过程中喷嘴常出现布气不均和磨损问题,影响其自身的布气性能和使用寿命。为此,在二维床实验装置上针对喷嘴的射流特性进行了实验研究。实验物料为FCC催化剂颗粒,喷嘴出口气速范围为30～70 m·s^-1,喷嘴喷射角度范围为0°～67.5°。实验用摄影观察法测量喷嘴射流的射流长度和附近的流场流态。实验结果表明射流长度随喷嘴气速和喷射角度的增大而变长。射流气体在向上翻转过程中,在树枝状管式气体分布器两分支管之间产生旋转涡流现象,旋转涡流的大小与喷嘴出口气速和安装角度有密切关系。最后基于实验数据,建立了喷嘴射流长度的计算模型。     

锥型分布器床层的起始喷流速度和相间传质

本文对气固流化床内锥型气体分布器进行了研究，在实验的基础上提出了一个能描述床层在起始喷流点附近的气体行为的的数学模型。并用此模型，利用实验数据，进一步提出了计算起始喷流速度Ｕ（ｍｓｆ）和相间质量交换系数的经验关联式。     

流化床灰熔聚煤气化器中高速射流区的颗粒分离

本文研究了垂直射流喷入流化床时固体颗粒从喷口排出的稳定分离过程及初始分离速度U_(IJ)的确定;考察了射流区的几何结构对床层流动特性与分离过程的影响;提出用结构流动参数C_s来作为选取射流区合理几何结构的重要判据;指出了细粒组份对颗粒分离的改善作用.     

Numerical study of the effect of the gas and solids distributors on the uniformity of the radial solids concentration distribution in CFB risers

The non-uniform radial solids distribution usually has a negative effect on the performance of the circulating fluidized bed (CFB) riser since it may greatly decrease the reactor efficiency and controllability. In order to improve the performance of industrial CFB risers, the numerical study of the effects of the gas distributor and solids distributor at the CFB riser inlet on the uniformity of the radial solids distribution was carried out in this study. Two potential approaches to improve the uniformity of radial solids concentration profile were proposed: (1) the use of the center-sparse side-dense air jets arrangement for the gas distributor and (2) the use of the side-covered arrangement for the solids distributor. The Eulerian-Eulerian computational fluid dynamics (CFD) model with kinetic theory of granular flow was adopted to simulate the gas-solids two-phase flow in a CFB riser with FCC particles. The numerical results show that the patterns of the inlet gas distributor and solids distributor have significant effect on the flow structure in both the entrance region and the fully-developed region in the riser. The gas distributor with center-sparse side-dense air jet arrangement improves the uniformity of the radial solids distribution, while the center-dense side-sparse air jet arrangement steepens the non-uniformity of the solids radial profile. The core-annulus structure can be greatly flattened by applying a side-covered solids distributor, while it can be heavily steepened by employing the center-covered solids distributor.     

采用切圆射流及旋流布风板改进鼓泡床行为

用侧面切圆射流和旋流布风板造成了鼓泡流化床内气固流动的新流型。本文将改进鼓泡床与普通鼓泡床进行比较,在同样的空气量下,气泡尺寸减小,床面波动降低,加强了固体颗粒的横向混合,延长了颗粒床内停留时间。还研究了侧面切圆射流占总风量的份额、射流速度、喷入位置及角度对流化质量的影响。     

Effect of air distributor on the fluidization characteristics in conical gas fluidized beds

The effect of an air distributor on the fluidization characteristics of 1 mm glass beads has been determined in a conical gas fluidized bed (0.1 m-inlet diameter and 0.6 m in height) with an apex angle of 20‡. To determine the effect of distributor geometry, five different perforated distributors were employed (the opening fraction of 0.009–0.037, different hole size, and number). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. From the differential bed pressure drop profiles with the distributors having different opening fractions, demarcation velocities of the minimum and maximum velocities of the partial fluidization, full fluidization, partial defluidization and the full defluidization are determined. Also, bubble frequencies in the conical gas fluidized beds were measured by an optical probe. In the conical bed, the gas velocity at which the maximum bed pressure drop attained increases with increasing the opening fraction of distributors.     

CFD simulation of flow pattern and jet penetration depth in gas-fluidized beds with single and double jets

A simple two-fluid model is validated by comparing single-jet fluidization experiments and numerical predictions. Subsequently, flow pattern and jet penetration depth are explored numerically in the bed with double jets under equal and unequal gas velocities. Glass balltoni with a density of 2550 kg/m³ and a diameter of 275 μm is employed as solid phase. The model used in this study considers the effect of the dispersed solid phase on both gas and particle momentum equations of the inviscid model A (Gidaspow, 1994). Numerical simulations are carried out in the platform of CFX 4.4, a commercial CFD code, together with user-defined FORTRAN subroutines. Both jet penetration depth and jet frequency predicted are in good quantitative agreement with measurements in an incipiently fluidized bed with a single jet. By combining solid volume fraction distribution and particle-phase velocity vector profile, three flow patterns (isolated, merged and transitional jets) are identified in the gas-fluidized bed with double jets, which depend more on the nozzle distance than the jet gas velocity. For the equal jet gas velocity, the jet penetration depth decreases with increasing nozzle distance in the merged-jet and transitional-jet regions, then reaches a minimum value in the transitional-jet region, and finally keeps steady in the isolated-jet region. For the unequal jet gas velocity, the merged jet penetration depth increases with increase in the velocity of one jet as the other jet gas velocity is fixed, whilst the jet penetration depths change a little in the transitional-jet region and remain a constant in the isolated-jet region.     

Aerodynamics of a novel rotating jet spouted bed

A novel rotating jet spouted bed (RJSB) is developed and tested. It consists of a rotating air distributor with two radially located spouting air nozzles. The effects of bed height, distributor rotational speed, nozzle diameter and particle properties on the flow characteristics were examined. Various flow regimes were mapped as functions of distributor rotational speed and superficial air velocity for different materials and column dimensions. Empirical correlations were developed for the minimum spouting velocity, peak pressure drop and steady spouting pressure drop.     

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.     

气固流化床内射流穿透深度的CFD模拟及其实验验证

在经典的Gidaspow无黏性双流体模型中考虑离散颗粒对流体和固体动量守恒方程的影响后,建立了一个具有模拟大规模流化床内气固两相流体动力学特性潜在优势的简化数学模型。在CFX4.4商业化软件平台上通过增加用户自定义子程序考察了二维气固流化床(高2.00 m、宽0.30 m)内射流气速、喷嘴尺寸、环隙气速和静床高度对射流穿透深度的影响,并以树脂颗粒(粒径670 μm、密度1474 kg·m^-3)为研究对象在厚度为0.025 m的矩形床内进行了对比实验。结果表明,选取空隙率为0.8的等高线作为射流边界比较合适;射流穿透深度随射流气速或射流喷口尺寸的增加而增大;射流周围环隙气速由0变到最小流化速度时,射流穿透深度随环隙气速增加而增大,在最小流化速度时达到最大值,然后随环隙气速增加单调减小,当环隙气速大于2.5倍最小流化速度时,射流穿透深度减小程度变缓;在相同射流气速下射流穿透深度随着静床高度的增加而减小,静床高度对射流穿透深度的影响随着射流气速增加呈现扩大的趋势。