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。     

酸洗和热氧化对氮化硅粉料表面特性与浆料流变性能的影响

选用四种商业氮化硅粉料(其中FD1、FD2和M11均由硅粉直接氮化法合成但后处理工艺不同, 而UBE粉的合成采用亚胺基硅热分解法), 系统研究了酸洗和热氧化处理对其表面特性和水基浆料流变特性的影响. 研究表明, 表面基团的种类和数量、可溶性高价反离子浓度以及离子电导率是影响氮化硅粉料在水中分散性能的关键因素. FD1粉料分散性能差的原因是可溶性高价反离子浓度太高, FD2粉料分散性能差的关键是颗粒表面存在Si-O-C-R憎水基团, M11粉料分散性能不好源于离子电导率过大, 而UBE粉料表面的大量Si-O-Si基团是其分散性能差的限制性因素. 经表面改性处理的四种氮化硅水基浆料具有良好的流变特性.     

水平圆管内海泡石矿粉的气力输送特性

针对海泡石矿粉颗粒在水平圆管内流动特性分析困难的问题,提出一种基于颗粒粒径和受力状况的海泡石矿粉颗粒的气力输送性能仿真分析方法;以颗粒平稳气力输送为目标,构建水平圆管内海泡石颗粒的切应力模型;分析不同粒径海泡石矿粉颗粒在稀相气、固两相中的受力状况,计算在特定工艺参数下颗粒各种受力变化,并分析其影响效果;基于COMSOL多相流分析软件,结合受力分析结论,采用双向耦合粒子追踪方法,对不同粒径的海泡石矿粉颗粒气力输送特性进行分析验证。结果表明:在特定工艺参数条件下,海泡石矿粉颗粒在水平圆管内的受力状况与颗粒粒径密切相关。     

液相烧结碳化硅喷雾造粒工艺控制

阐述了液相烧结SiC陶瓷喷雾造粒过程中的相关制备工艺,研究了浆料的特性、干燥温度、喷雾压力等因素对粉体性能的影响.并通过实验总结出一套合理的工艺参数,制备出球形实心颗粒粉料.粉料的松装密度0.88 g/cm3、休止角33.5°、平均粒径50μm,具有良好的流动性及快速填充性,可直接用于干压成型.     

密相气力输送系统中几种气量控制方式的比较

从调压范围、压力特性和流量特性方面介绍了减压阀的主要性能,讨论了气力输送交流中减压阀的选择和调节,分析了密相气力输送系统中各种气量控制方法,对其各自的优缺点进行了详细讨论,重点分析减压阀及减压阀与拉法尔联合气量控制系统的优、缺点,表明可调式拉法尔管是今后气力输送气量控制发展的方向。     

粒子群算法在气力输送管道压降预测中的应用

管道压降是气力输送系统设计的一个重要参数,传统的求解方法比较复杂.本文提出了以气体流速、颗粒浓度、混合比等作为神经网络输入,建立管道压降网络模型的方法.为进一步提高管道压降预测准确度,以预测误差作为适应度值,采用粒子群算法对网络权值和阈值寻优,优化神经网络,并利用样本数据训练出了有效的压降预测网络.通过将预测数据和粉料气力输送实验装置的实测数据相比较,结果表明,该方法预测误差小,准确度高,有较高的实用价值.     

不同粒径粉体颗粒气力输送特性的比较研究

气力输送在工程技术领域已经得到了广泛的应用。粉体的粒径对气力输送特性有很大的影响。本文以粉煤灰和石灰石粉为研究对象,结合实验和工程应用,根据它们的颗粒特性分别研究了其输送特性随操作条件的变化规律,并对输送设备的选型进行了研究。     

射流喷射器用于干渣气力输送的实验研究

针对燃煤电厂的锅炉干渣气力输送系统,采用气-固射流喷射器进行干渣气力输送实验,通过改变射流喷射器的结构参数和运行操作参数,分析各结构尺寸和运行参数对下料特性的影响,并通过数值模拟计算,对实验结果进行验证。结果表明,通过优化射流喷射器的结构尺寸和运行参数,在下料口可形成负压,提高落料均匀性及给料机运行可靠性。     

高原环境对粉体输送性能的影响

为研究高原环境对航空发动机气力输送粉体性能的影响,利用发动机相似分析和气固两相流理论计算,对比高原和平原环境下粉体气力输送的临界参数;通过高原试验验证并获得发动机转速和粉体输送量之间的匹配情况。结果表明:海拔4 500 m时的输送能力为平原环境下的1/2左右;通过提高发动机转速、降低粉体供料速率可以避免粉体输送堵塞。     

酚醛树脂对氮化硅离心喷雾造粒特性的影响

以无水乙醇为介质,使用酚醛树脂作为粘结剂进行氮化硅粉末的离心喷雾造粒,研究不同含量的酚醛树脂对喷雾造粒粉料的性能、粉料形貌、粒径分布和烧结性能的影响。结果表明,当粉料中酚醛树脂的含量增加时,喷雾干燥的粉料松装密度增加,休止角减小,平均粒径增大,粉料的烧结收缩率增大,相对密度减小,气孔数量增多且孔径增大。     

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。     

Dilute phase pneumatic conveying of whey protein isolate powders: Particle breakage and its effects on bulk properties

Breakage of dairy powder during pneumatic conveying negatively affects the end-customer properties (scoop uniformity and reconstitution). A dilute phase pneumatic conveying system was built to conduct studies into this problem using whey protein isolate powder (WPI) as the test material. Effects of conveying air velocity (V), solid loading rate (S_L), pipe bend radius (D), and initial particle size (d) on the level of attrition were experimentally studied. Four quality characteristics were measured before and after conveying: particle size distribution, tapped bulk density, flowability, and wettability. The damaged WPI agglomerates after conveying give rise to many porous holes exposed to the interstitial air. V is the most important input variable and breakage levels rise rapidly at higher airspeeds. The mean volume diameter D[4,3] decreased by around 20% using the largest airspeed of 30 m/s. Powder breakage is also very sensitive to particle size. There appears to be a threshold size below which breakage is almost negligible. By contrast, S_L and D show lesser influence on powder breakage. Reflecting the changes in particle size due to breakage, tapped bulk density increases whereas wettability decreases as a result of an increase in conveying air velocity. However, breakage does not show a significant effect on powder flowability as powder damage not only decreases particle size but also changes the particle’s surface morphology.     

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。     

Changes of Dextrose Particles with Pneumatic Conveying: Analysis of Size and Shape

When conveying particulate materials, changes in size and shape of individual particles can be observed. These changes can have a great impact on the bulk powder and affect its flow properties in the pipeline. Changes can be wanted or unwanted depending on the whole process chain and final use of the powder. In this investigation, dextrose monohydrate particles were pneumatically conveyed repetitively in a pilot plant–scale rig, and the size and shape of the particles were characterized by a semiautomatic image analysis method. This characterization was done qualitatively by observing micrographs and quantitatively for each individual particle (a total of 16,120 dextrose crystals) by using two statistical diameters and two shape factors. The effect of the changes in shape and size of the particles on the mass flow rate in the system was studied. It was concluded that the mass flow rate of the pneumatic conveying tests was not affected considerably by the changes of the dextrose particles.     

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。     

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。     

Effect of particle size distribution on hydrodynamics of pneumatic conveying system based on CPFD simulation

The effect of particle size distribution on the hydrodynamics of dilute-phase pneumatic conveying system was analyzed using computational particle fluid dynamics (CPFD) simulation. The influence of a simulation parameter, i.e., correction factor of drag coefficient (k), on the hydrodynamics of pneumatic conveying system was determined via CPFD simulation. When results of simulation were compared with experimental data of previous studies, the average error of pressure drop per length predicted by the CPFD approach with the correction factor was below 4.4%. Saltation velocity and the pressure drop per unit length declined as the drag force coefficient increased. Simulation results also revealed that the pressure drop per length and the saltation velocity were decreased when the fine powder fraction in the particle size distribution was increased, although the width of particle size distribution was widened, and the standard deviation was increased. Finally, the Relative Standard Deviation (RSD) of pressure drop per length was measured and compared with median diameter (d₅₀), Sauter mean diameter, geometric mean diameter, and arithmetic mean diameter. The RSD of the Sauter mean diameter was 5.8%, approximately twice less than the RSD value of d₅₀ commonly used in pneumatic conveying.     

Particle dynamics analysis in bend in a horizontal-vertical pneumatic conveying system with oscillatory flow

The pneumatic system is frequently operated in the high air velocity region, which aggravates the power consumption and erosion of bend, and the intensive study of the particles motion characteristic on a horizontal-vertical pneumatic conveying in various curved 90° bends is necessary. This experimental study focuses on the particles motion characteristic of bend on the horizontal-vertical pneumatic conveying with oscillatory flow (generated by installing the oscillator) in terms of on pressure drop, powder consumption, the evolution of particle velocity and particle fluctuating intensity during flowing through bends. The results indicate that powder consumption can be reduced by using oscillatory flow, which is more obvious with a larger radius ratios bend. Meanwhile, the pressure drop proportion of bend is higher than average pressure drop of the system within the same distance. Otherwise, the total reduction particles velocity through bend is less while using oscillatory flow, which is more obvious using larger radius ratios bend. The particle velocity using oscillatory flow is higher than that of the conventional pneumatic conveying for the cases of larger radius ratios bend, and this effect is less evident while through a smaller radius bend.     

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.