Particle Trajectories in Dilute Phase Pneumatic Conveying

A nonintrusive cross-correlation method to measure the particle velocities in dilute phase pneumatic conveying is described. The cross-correlation function generated gives information about the time it takes for a particle to travel between two optimally placed measurement planes. Experiments and CFD simulations are used to estimate an optimal inter-plane distance for various flow conditions.     

Effect of Dune Formation on Pressure Drop in Horizontal Pneumatic Conveying System

Pneumatic conveying is widely used in industries handling large amount of granular materials to transport the solid particles; however, the process is energy intensive as an instability of flow sets in the transportation line even in the dilute regime, causing large fluctuations in the line pressure drop, the reason of which is not clearly understood. Here, we investigate, both by experiments and by using numerical simulations, the instability transition regimes and identify the reasons of the fluctuations observed in the line pressure drop in a horizontal pneumatic transport system operating at near-saltation conditions. It is observed that the increase in the pressure drop (immediately after the saltation) is accompanied by the formation of distinct dunes. It is also observed that the line pressure drop depends on the axial location of the dune and shows large fluctuations in the regime where the dunes are unstable. Results obtained from the numerical simulations suggest that the increase in the line pressure drop in the presence of dunes is essentially due to the shear stresses at the dune surface which are larger than that for the flows in clean pipe.     

石灰长距离气力输送系统的试验研究

基于气力输送理论,通过石灰的长距离输送试验系统的建立,研究输送过程中耗气量、管道压力损失、物料输送前后的状态等重要输送特性。结果表明,将气力输送应用在长距离的石灰输送上是完全可行的,可解决钢铁行业的高粉尘污染问题,极大地改善工作环境。     

A Numerical Simulation of Swirling Flow Pneumatic Conveying in a Vertical Pipeline

A numerical prediction for the axial and swirling pneumatic conveying in a vertical pipe was performed based on an Eulerian approach for the gas and a stochastic Lagrangian approach for the particles, where κ – ? turbulence model, the model of particle-particle and particle-wall collisions, was adopted. The numerical results are presented for polyethylene pellets of 3.2mm diameter conveyed through a pipeline of 12m in height with an inner diameter of 80mm. The initial swirl number was 0.0 and 0.68, the mean gas velocity varied from 11 to 17m/s, and the solid mass flow rate was 0.03 and 0.084 kg/s. From the numerical analysis, the swirl decay of the swirling gas-solid flow was found to be rapid in the acceleration region and approached the clean swirling flow in a fully developed region. The turbulent kinetic energy and energy dissipation rates of the swirling gas-solid flow increased near the wall and reduced in other regions. The comparison of predicted values with measured data showed a good agreement.     

小麦气力输送流场颗粒流化特性数值模拟

目的 探索仓泵式气力输送小麦颗粒时不同输送压力下罐体及引出管内颗粒的流化特性,从而得出最佳操作压力。方法 利用Solidworks建立简易的等比例发送装置三维模型,采用模拟仿真软件Fluent对0.25、0.3、0.35 MPa等3种不同输送压力进行数值模拟,并利用CFD–Post进行数据后处理。结果 当进气口压力为0.35 MPa时物料最先输送完毕,用时为10 s。整体发料过程从引出管入口至出口处三者压力分别降低了97.1%、96.8%、98.1%,其中当进气口压力为0.3 MPa时,压力降低最小,能量利用率最高。结论 输送压力越大输送速度越快,其压降也最大。考虑经济性与高效性可得,最佳进气口压力为0.3 MPa。     

Bend Pressure Drop Predictions Using the Euler-Euler Model in Dense Phase Pneumatic Conveying

Pneumatic conveying of powdered and granular materials is a very common transport technology across a broad range of industries, for example, chemicals, cosmetics, pharmaceuticals, and power generation. As the demands of these industries for greater efficiency increases and to comply with environmental regulations there is a need for a more fundamental understanding of the behavior of materials in pneumatic conveying systems. The approach presented in this article is to develop a model of a section of pneumatic conveying line, a horizontal or vertical 90° bend, in the commercial CFD software package FLUENT and to describe the multiphase flow behavior by the mixture or Eulerian method. Models of this type have been used in the past to show qualitative and quantitative agreement between model and experiment. The model results presented were compared with experimental data gathered from an industrial-scale pneumatic conveying test system. Broad qualitative agreement in trends and flow patterns were found. Quantitative comparisons were less uniform, with predictions from around 10% to 90% different from experimental results, depending on conveying conditions and bend orientation.     

Bend Pressure Drop Predictions Using the Euler-Euler Model in Dense Phase Pneumatic Conveying

Pneumatic conveying of powdered and granular materials is a very common transport technology across a broad range of industries, for example, chemicals, cosmetics, pharmaceuticals, and power generation. As the demands of these industries for greater efficiency increases and to comply with environmental regulations there is a need for a more fundamental understanding of the behavior of materials in pneumatic conveying systems. The approach presented in this article is to develop a model of a section of pneumatic conveying line, a horizontal or vertical 90° bend, in the commercial CFD software package FLUENT and to describe the multiphase flow behavior by the mixture or Eulerian method. Models of this type have been used in the past to show qualitative and quantitative agreement between model and experiment. The model results presented were compared with experimental data gathered from an industrial-scale pneumatic conveying test system. Broad qualitative agreement in trends and flow patterns were found. Quantitative comparisons were less uniform, with predictions from around 10% to 90% different from experimental results, depending on conveying conditions and bend orientation.     

射流管在气力输送中的应用

对物料气力输送的各种供料方式的性能、特点和使用场合进行了比较 ,重点讨论了传统文丘里供料器实际应用中存在的问题 ,介绍了几种国内外新型的文丘里供料器结构及其特点和用途。指出采用组合式供料器 ,即将文丘里供料器与机械旋转式连续供料器进行组合使用 ,可以同时改善它们两者单独使用时存在的问题。文中介绍了LAVAL管密相输送气量控制方面的应用 ,指出LAVAL管在气力输送中主要起稳定空气流量和压力的作用 ,使输送过程稳定、均匀 ,并简要介绍了气力输送系统的设计方法和步骤     

粉体性能对浓相气力输送特性的影响

气力输送过程中物料性能是确定输送特性的重要因素,因此,粉料气力输送技术的实现要以对粉料的性能研究为基础。文中对影响气力输送的粉体基本性能及其相关参数做了较全面分析,其中粒子尺寸、粒径分布、形状是影响粉料是否可适用于浓相气力输送的关键参数,其它特性都与这3种特性相关联。介绍了几种应用广泛的粉料气力输送特性分组方法,并进行了简要评述,同时指出了今后的研究方向。     

不规则宽粒径石灰石粉脱硫及气力输送技术

通过分析干法脱硫技术及其影响因素,如石灰石性能和石灰石颗粒直径等,提出脱硫剂的选择及气力输送的方式,同时分析了气力输送中的问题,如透气性差和保气性差引起的不易流化等,并相应提出解决办法和输送设计方案。针对不规则宽粒径石灰石粉粒具有的特殊颗粒学特性和复杂气固两相流场,提出了解决方案,为更好地设计石灰石粉气力输送系统提供参考。     

低速高能效的浓相气力输送技术

低速浓相输送装置的出现,解决了物料在输送过程中易破碎、堵塞和磨蚀管道等难题,降低了耗气量。本文中综述了低速浓相输送的几种定义和输送过程中的相图、物料流动形态及相应的判定、影响浓相气力输送特性的因素等技术参数,并介绍了输送过程中经常遇到的堵管和磨损现象以及气力输送过程中的检测和自动控制技术,指出了今后的研究方向。     

Modeling Dense-Phase Pneumatic Conveying of Powders Using Suspension Density

This article presents results of an investigation into the modeling of pressure drop in horizontal straight pipe section for fluidized dense-phase pneumatic conveying of powders. Suspension density and superficial air velocity have been used to model pressure drop for two-phase solids-gas flow. Two applicable models formats (developed by other researchers using two different definitions of suspension density) were used to represent the pressure drop due to solids-gas flow through straight pipe sections. Models were generated based on the test data of conveying power-station fly ash and electrostatic precipitator (ESP) dust (median particle diameter: 30 and 7 µm; particle density: 2300 and 3637 kg m^?3; loose-poured bulk density: 700 and 610 kg m^?3, respectively) through a relatively short length of a smaller diameter pipeline. The developed models were evaluated for their scale-up accuracy and stability by using them to predict the total pipeline pressure drop (with appropriate bend model) for 69 mm I.D. × 168 m; 105 mm I.D. × 168 m and 69 mm I.D. × 554 m pipes and comparing the predicted versus with experimental data. Results show that both the models with suspension density and air velocity generally provide relatively better prediction compared to the conventional use of solids loading ratio and Froude number. For fly ash, the two formats result in considerable different predictions, whereas they provide relatively similar results for ESP dust.     

炭黑在气力输送系统中的破碎原因的分析

分析了炭黑在气力输送过程中的破碎机理。通过实验,介绍了气力输送系统中炭黑的种类和炭黑的物性对炭黑的破碎的影响,指出气力输送系统的输送管路长度和布置以及输送参数如输送压力和输送速度等的变化直接影响着炭黑的破碎率的大小。为更好地解决炭黑在气力输送中存在的问题,优化炭黑气力输送系统的设计提供了依据。     

密相气力输灰管道的设计与应用

对气力输灰工程中密相输灰管道的设计和计算确定管内压力和速度的公式进行整理 ,同时可以得到较合理的管径和不同管径的长度。运行参数当已知时 ,给出的计算公式可作为设计的依据     

气力输送在锅炉飞灰回燃技术中的应用

以山东省内几家热电厂75、130t/h循环流化床锅炉飞灰回燃、热效率提高为例,介绍气力输送系统在热电厂飞灰回燃过程中的应用,对热电厂飞灰含碳量高的原因进行分析,详细分析飞灰回燃系统的工艺流程,并对飞灰回燃前后的含碳量及成本进行对比。结果显示:飞灰回燃技术能够显著提高煤炭的燃烧率,提高锅炉的热效率。     

氧化铝粉体气力输送过程的流动状态检测

在气力循环输送提升管实验装置中检测氧化铝粉体的流动状态,在提升管的不同测点位置布置电磁感应线圈,添加铁磁颗粒作为输运物料氧化铝的示踪颗粒,利用电磁感应声卡信号采集装置测量电磁感应系数。结果表明,电磁感应系数与气力输送提升管内的氧化铝、铁磁颗粒流量存在线性关系,随着测点高度的增大,电磁感应系数逐渐减小;提升管发生堵塞时,堵塞测点截面以上的电磁感应系数开始减小,截面以下各测点的电磁感应系数开始增大;通过增大喷动风量,可有效改善提升管内颗粒的分布状态。     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

基于CFD-DEM方法的柱状颗粒在弯管中输送过程的数值模拟

针对物料在气力输送过程中特别是弯管部分易破碎的问题,采用计算流体力学(CFD)和离散单元法(DEM)耦合模拟弯管内的柱状颗粒气力输送过程,对弯径比k分别为1、2、3、4、6的90°弯管内柱状颗粒的运动状态、碰撞特性、破碎原因及相关的力学特性进行研究。结果表明:球形颗粒与柱状颗粒在输送过程中遵循基本一致的变化规律,同样外部条件下,柱状颗粒的悬浮速度小于球形颗粒。当k=3时气力输送过程颗粒的破碎率最低。同时,颗粒与管壁的碰撞是造成颗粒破碎的主要原因。     

岩石粉状乳化炸药气流输送管道积药问题探讨

岩石粉状乳化炸药管道内是否积药受风速、混合比、物料颗粒大小、加料是否均匀及物料温度等因素的影响,可以通过控制工艺参数来减少管道内积药,保证生产的安全和顺畅.