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。     

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。     

Prediction of jet penetration depth based on least square support vector machine

Experiments to investigate the jet penetration depth were carried out. The jet penetration depth increases with the increase of spouting gas velocity, spouting nozzle diameter and carrier gas density, but decreases with the rise of the static bed height, particle density, particle diameter and fluidized gas rate. The intelligent model to predict the jet penetration depth has been established based on least square support vector machine and adaptive mutative scale chaos optimization algorithm. The prediction performance of the intelligent model is better than empirical correlations and neural network.     

基于信息熵分析的喷动流化床流动特性

建立了300 mm×30 mm×2000 mm的喷动流化床煤气化炉冷态实验装置和多通道压力信号采集系统,引入压力波动时间序列的Shannon信息熵分析,讨论了不同喷动气速度和流化气流率下各床层区域的Shannon 信息熵,并结合高分辨率数码CCD相机所记录的流动状态,建立了Shannon信息熵与流型之间的联系.床层不同区域的Shannon 信息熵具有较大的差异,不同流型的Shannon 信息熵区分度较好.在较高的喷动气速度或流化气流率下,喷动流化床气固运动周期特性消失,呈现出明显的混沌特性,表现为床层各区域Shannon信息熵的急剧增长和床内不稳定的流动状态的发生.结果表明,Shannon信息熵分析有助于认识喷动流化床复杂的流型及其转变和床内气固两相流动的混沌动力学特性.     

基于颗粒流运动论的喷动流化床气固流动行为三维模拟

1 INTRODUCTION Spout-fluid beds have been of increasing interest in the petrochemical, chemical and metallurgic indus-tries since spout-fluid beds can reduce some of the limitations of both spouting and fluidization by su-perimposing the two type of systems[1―4]. In recent years, spout-fluid beds have become an alternative for gas/solid contactors in coal gasification. Spout-fluid bed coal gasifiers have been adopted for APFBC-CC (advanced pressurized fluidized bed combus-tion-combined…     

Annulus leakage and distribution of the fluid flow in a liquid spout-fluid bed with a draft tube

The distribution of flow between the annulus and the draft tube sections in a liquid phase spout-fluid bed with a draft tube was studied in a flat-based semi-circular column of diameter equipped with a semi-circular draft tube of diameter at superficial fluid velocities well above the minimum fluidization velocity. The particles used were glass spheres of diameter, and the spouting medium was tap water. A sodium chloride solution was injected into the reactor and the response recorded to determine the flow distribution between the draft tube and the annulus sections. The responses of the tracer injections prove that part of the flow originating from the annulus inlet leaks into the draft tube when any amount of annulus inlet flow is present. This finding makes a significant contribution to the understanding of the entrance region below a draft tube which has been modeled as a spout-fluid bed where fluid enters the annulus region based on the pressure distribution at the spout-annulus interface while the flow is in the radial direction from the spout into the annulus. This work shows that there is cross flow in the entrance region resulting in fluid exchange between the streams originating from the spouting inlet nozzle and the annulus inlet flow.The amount of leakage is found to increase with increasing inlet flow rates. An empirical correlation is developed to predict the fraction of the leakage of the annulus inlet flow. The superficial fluid velocity through the draft tube is found to vary linearly with the total flow rate through the bed under the experimental conditions studied. The pressure distributions in the entrance region favor the leakage of fluid from the annulus inlet flow into the draft tube.     

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     

Pressure drop and flowrate characteristics of a liquid phase spout-fluid bed at the minimum spout-fluid flowrate

Data on the minimum spout-fluid flowrates and the pressure drop in the annulus at that flowrate are presented as a function of bed height and nozzle diameter for a bed spout-fluidized with water. The column was 62.6 mm. in diameter and contained 3.09 mm. glass particles. The particle Reynolds number at the minimum fluidizing velocity was 91.6. A plot of the annular vs. the nozzle flowrate shows that the minimum spout-fluid flowrates fall on a straight line between the minimum fluidizing and minimum spouting flowrates. The annular pressure drop is explained using an extension of the theory of Mamuro and Hattori.     

Separation and residence times of larger particles in a spout-fluid bed

Optimum conditions for the separation of added large particles from a spout-fluid bed of Geldart Type B powder have been determined. A shallow bed, 100 mm in diameter, with porous conical distributor was used. Mean and distributions of residence time of the large particles depend on the two gas flow rates, especially that to the distributor, and on spout inlet diameter and large particle size. Bed regimes studied were mainly spouting with aeration and spout-fluidization. In the latter regime an optimum range of fluidizing gas flow rates that minimised mean and spread of residence times was identified. RTD data were correlated by a model incorporating a minimum time supplemented by a distribution for an ideally mixed system.     

Characterization of dynamic behavior of a spout-fluid bed with Shannon entropy analysis

Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds.     

喷动流化床最大喷动压降的多因素影响与关联

基于截面200 mm×20 mm,高1600 mm,锥角60°的矩形喷动流化床,以二组分混合颗粒、单一组分球形颗粒及非球形颗粒为物料进行最大喷动压降的实验研究.结果表明,最大喷动压降随静止床高、颗粒密度、颗粒球形度及二组分混合颗粒体系中沉积组分分率增加而增大,随流化气速增大而减小;增大颗粒粒径或喷口宽度,呈现先减小后增...     

Modeling of Gas‐Particle Turbulent Flow in Spout‐Fluid Bed by Computational Fluid Dynamics with Discrete Element Method

Gas and solid turbulent flow in a cylindrical spout‐fluid bed with conical base were investigated by incorporating various gas‐particle interaction models for two‐way coupling simulation of discrete particle dynamics. The gas flow field was computed by a k‐ϵ two‐equation turbulent model, the motion of solid particles was modeled by the discrete element method. Drag force, contact force, Saffman lift force, Magnus lift force and gravitational force acting on individual particles were considered in the mathematical models. Calculations on the cylindrical spout‐fluid bed with an inside diameter of 152 mm, a height of 700 mm, a conical base of 60° and the ratio of void area of 3.2 % were carried out. Based on the simulation, the gas‐solid flow patterns at various spouting gas velocities are presented. Besides, the changes in particle velocity, particle concentration, collision energy, particle and gas turbulent intensities at different proportions of fluidizing gas to total gas flow are discussed.     

Hydrodynamics of a Novel Biomass Autothermal Fast Pyrolysis Reactor: Flow Pattern and Pressure Drop

A novel biomass, autothermal, fast pyrolysis reactor with a draft tube and an internal dipleg dividing the reactor into two interconnected beds is proposed. This internally interconnected fluidized beds (IIFB) reactor is designed to produce high‐quality bio‐oil using catalysts. Meanwhile, the pyrolysis by‐products, i.e., char, coke and non‐condensable gases, are expected to burn in the combustion bed to provide the heat for the pyrolysis. On the other hand, the catalysts can be regenerated simultaneously. In this study, experiments on the hydrodynamics of a cold model IIFB reactor are reported. Geldart group B and D sand particles were used as the bed materials. The effects of spouting and fluidizing gas velocities, particle size, static bed height and the total pressure loss coefficient of the pyrolysis bed exit, on the flow patterns and pressure drops of the two interconnected beds are studied. Six distinct flow patterns, i.e., fixed bed (F), periodic spouted/bubbling bed (PS/B), spouted bed with aeration (SA), spout‐fluidized bed (SF), spout‐fluidized bed with slugging (SFS) and spouted bed with backward jet (SBJ) are identified. The investigations on the pressure drops of the two beds show that both of them are seen to increase at first (mainly in the F flow pattern), then to decrease (mainly in the PS/B and SA flow patterns) and finally to increase again (mainly in the SA and SF flow patterns), with the increase of the spouting gas velocity. It is observed that a larger particle size and lower static bed height lead to lower pressure drops of the two beds.     

大型双射流流化床的流体动力学特性

在Ф0 .5m× 8m大型双射流流化床中 ,通过摄像、放像逐帧分析法和sthVCD软件分析录像转换的VCD ,得到了不同管间距下双射流典型的运动图像 .同时研究了两射流独立存在区、过渡区和射流合并区 3种流型的相互转变 ,得出了流型转变的关系式 .不同射流管间距下相同射流气速的射流深度相比 ,管间距减小则射流深度减小 ;在较小的管间距和相对高的射流气速下 ,两射流在射流深度之内始终合并 ,表现为射流合并高度 .得出了射流深度、射流合并高度的定量关系式 .分数维关联维数表明大型双射流流化床是一个确定性混沌系统 ,考查了管间距、静床高度对关联维数的影响     

Numerical Simulation of a Spouted Bed Using Computational Fluid Dynamics (CFD)

In this article, computational fluid dynamics (CFD) technology is used to model a spouted bed(SB). The multifluid Eulerian-Eulerian approach based on kinetic theory of granular flows and Gidaspow's drag model for the interaction between gas and particles are applied in the modeling. The effects of the SB properties—that is, cone angle, particle size, cylinder diameter, and static bed height of particles—on its dynamics performance are investigated. The simulated results—that is, flow pattern of particles, fountain height, voidage, and particle velocity of the spout zone—are presented. It is shown that periodic fluctuation of spouting appears in an SB with conical angle of 30° and inlet velocity at 16.6 m/s. When the SB cylinder diameter becomes 0.52 m, periodic fluctuation appears, too. The stable spouting of the SB with a 90° cone angle could be obtained at an inlet air velocity of 24.3 m/s. The fountain height of particles decreased with an increase in particle size and the static bed height of particles. It is kept at about 0.19 m when different SB cylinder diameters in the range of 0.36 to 0.48 m are used. In the spouting region, the voidage decreased with static particle height in bed, but the particle velocity increased. For a certain particle size, the voidage decreased with an increase in particle height, but the velocity of the particles increased. It was also found that the cylinder diameter did not affect the volume fraction of particles except for the cylinder diameter 0.52 m and the change in particle velocity was minimal in the spout zone. With the different static bed height of particles used, the voidage and particle velocity did not change much at the same level of spout zone.     

Discrete element simulation of a flat-bottomed spouted bed in the 3-D cylindrical coordinate system

A spouted bed is simulated in three dimensions by a discrete element method (DEM) in a cylindrical coordinate system. The numerical scheme is based on a second order finite difference method in space and a second order Adams-Bashforth method for time advancement. Gas-particle interaction is assumed to obey the Ergun equation (for void fraction less than 0.8) and its corrected model by Wen and Yu (for void fraction greater than 0.8). The spouted bed vessel is a flat-bottomed cylinder in height and in diameter. The gas inlet diameter is . Three hundred thousand monosized spheres of diameter are used in the simulation. The typical characteristics of spouted beds, such as spout, annulus and fountain, are reproduced. Particle velocity profiles show good agreement with experimental results and self-similarity of the radial distribution of axial particle velocities is reported. Gas flow patterns are also studied and the effect a vortex ring fixed at the bottom of the vessel is investigated. The simulation is validated through comparisons with results reported in the literature.     

Three-dimensional vortex simulation of particle-laden air jet

The effect of particle diameter on the gas-particle two-phase compound round jet is numerically analyzed by the three-dimensional vortex method presented in a prior study. The air jet issues from a round nozzle into the co-flowing air stream, where the Reynolds number based on the air velocity at the nozzle exit is 2×10⁴ and the velocity ratio between the co-flowing stream and the jet at the nozzle exit is 0.27. The flow direction is vertical downward. Spherical glass particles having diameters 60, 80 and are loaded from the nozzle. The mass loading ratio is 0.27. The analysis made clear the air turbulent modulations due to the particles, such as the relaxation of velocity decay, the increment and decrement of momentum diffusion at the developing and developed regions, respectively. It also clarified that the air turbulent modulations become markedly as the particle diameter decreases.     

Hydrodynamics of spout-fluid beds

Experiments were carried out in a half-column incorporating auxiliary flow, introduced through up to five slots along a 60° conical base, in addition to a central flow of air. The column had a diameter of 0.15 m and inlet diameters of either 19 or 25 mm. Three different types of particle were investigated, all with mean particle sizes in the 2 – 4 mm range. Four different flow regimes — fixed bed, spouting with aeration, spout-fluidization and jet in a fluidized bed — were identified and mapped. The minimum total gas flow required for spouting with aeration and for spout-fluidization was always greater than that corresponding to minimum spouting. Gas percolation through the annulus increased by as much as 50% as the proportion of auxiliary flow was increased for a given total gas flow rate. Solids circulation was increased somewhat by addition of auxiliary flow for deep beds, but a decrease occurred for shallow beds. The overall bed pressure drop under minimum spouting with aeration conditions increased linearly with auxiliary flow. On the other hand, the fountain height decreased as the fraction of auxiliary flow was increased for a fixed total gas flow, and increased with auxiliary flow for a fixed central gas flow. The empirical correlation of McNab predicted the average spout diameter well if the sum of the central and auxiliary flows was used in the correlation.     

DEM-LES simulation of coal combustion in a bubbling fluidized bed Part II: coal combustion at the particle level

The discrete element method-large eddy simulation (DEM-LES) is used to model coal combustion at the particle level in a bubbling fluidized bed. The gas phase is modelled as a continuum and the solid phase is modeled by DEM. Chemical reactions consist in the heterogeneous reactions of char with O₂, CO, CO₂, NO, and N₂O, and in the homogeneous reactions involving CO, O₂, NO, and N₂O. The colliding particle-particle heat transfer is based on the analysis of the elastic deformation of the spheres during their contact. The model predicts the effects of the particle heterogeneous flow structure on the thermal characteristics of coal particles when heating and burning, and the gaseous emissions from a fluidized sand-coal binary mixture. The heating rates are 1627 and for, respectively, 0.8 and diameter coal particles fed into the fluidized bed. The instantaneous contribution of the collision heat transfer is weak, less than 5.0% of the total power exchanges (coal combustion, radiation, convection and collision) during the heating and 1.5% during the combustion. The temperature of the coal particles exceeds the bed temperature, which is in qualitative agreement with experimental data from literature. The effects of the diameter of coal particles, of the bed temperature, and of the inlet gas velocity on the thermal characteristics are also studied.