双级活塞推料离心机分离过程的数值模拟研究

双级活塞推料离心机是连续操作的离心机的一种,广泛应用于轻工、化工、冶金、煤炭等行业。双级活塞推料离心机的一级转鼓由于在旋转运动的同时又进行往复运动,流体在转鼓内的流动过程极为复杂,尚没有理论方法能够描述其过滤分离的过程。以P-100型双级活塞推料离心机为例,运用FLUENT软件进行数值模拟,得到了离心机转鼓内的流体流动状态。并针对影响离心机生产能力和分离效果的物料浓度与转鼓旋转角速度进行了模拟研究,结果表明,随着进料浓度的增大,滤饼固含量、固相回收率和澄清液含固率都呈现不断变大的趋势,而离心分离达到稳定的最初时间和滤饼达到最大固含量的最初始轴向坐标值逐渐变小;随着转速的增加,固相回收率、澄清液含固率和滤饼达到最大固含量的最初始轴向坐标值逐步变小,滤饼固含量不断增大,而离心分离达到稳定的最初时间没有特定的规律。同时,数值模拟结果还为离心机结构的优化设计提供了依据。     

汽-液-固三相平衡计算

溶剂萃取-闪蒸结晶的分离方法也是一种汽-液-固三相分离的过程,本文建立了汽-液-固三相平衡的计算方法和程序 并以双酚A的精制为例 对结晶、离心分离等过程进行了计算,考核证明这是一种有效的计算方法。     

气-液-固三相搅拌槽反应器模型及模拟研究进展

综述了气-液-固三相搅拌槽反应器模型和模拟的研究进展。讨论了可用于气-液-固三相流的模拟方法,三相流模型适合于气-液-固三相搅拌槽反应器的数值模拟。给出了气-液-固三相搅拌槽反应器数值模拟的研究进展,目前研究中还缺乏基于机理的相间作用力模型,常用的湍流模型不能描述搅拌槽内的各向异性,没有局部性质的实验数据导致气-液-固三相搅拌槽反应器的模型和模拟无法得到充分验证。建议在今后的研究中构建"两尺度"气-液-固三相湍流单元胞模型,扩展两流体显式代数应力模型为三流体模型,开发局部照相探针技术及相应的图像处理软件。     

固-液-液三相水力旋流器内部固相颗粒受力分析研究

在进料浓度较低时,固相颗粒之间距离较大,相互之间的作用以及影响极微,颗粒的分离可以通过对其施加一个外力,将其往器壁方向推,这样就完成了固-液-液三相的分离。这个外即惯性离心力的大小很容易得到,但颗粒所受流体介质阻力则很难得到。文章文通过研究对对旋流器内部固相颗粒进行了受力分析并从理论上对细颗粒易受参数影响的原因进行了阐述。     

FLUENT软件在液-液混合器领域中的应用

对通用CFD模拟软件——FLUENT进行了综述,介绍了该软件的应用领域、主要特点。由于FLUENT软件的突出优点,对实际应用有重大的指导作用。通过简述FLUENT软件在混合器设备中复杂流场的模拟,为现有的混合设备的优化与新产品的研发提供指导性参数,指出了FLUENT软件在液-液混合领域潜在的发应用前景。     

气-液-固三相流数值模拟研究进展

气-液-固三相反应器广泛的应用于工业生产的诸多领域,因此对该系统中气-液-固三相流动行为的研究具有重要的意义。随着计算机技术的高速发展而兴起的数值模拟计算日益成为研究此类问题的重要途径。本文系统的对近几十年来数值模拟在该领域的发展进行了综述。首先依据模拟尺度的不同,阐述了当前的主要模拟手段:欧拉法、拉格朗日法和直接数值模拟法。接着分别对这三类方法展开了详细的介绍,指出欧拉法与拉格朗日法都能开展工业级计算,但精度依赖于本构方程;直接数值模拟法能够捕捉局部界面变化细节,但需要十分精细的网格。最后本文对该领域的研究前景进行了展望。     

伞罩型湿式脱硫除尘器气液固三相流数值模拟

从数值模拟和试验研究的角度对新型脱硫除尘装置——伞罩型湿式脱硫除尘器气液固三相的除尘特性进行研究。利用FLUENT软件在Euler坐标系中考察气固二相,采用欧拉模型来表述气固二相的相互关系;同时在Lagrange坐标系中考察液滴的运动,并把液滴对气固二相的影响耦合于欧拉模型中,提出了气液固三相的Euler/Euler/Lagrange模型。分析了气相速度场、气相压力场、固相速度场以及液滴质量浓度等的分布情况,得到了除尘情况下装置内气液固三相的分布规律。数值模拟结果与试验结果吻合良好,对装置运行及其优化设计有一定的理论指导意义。     

三相流化床传热模型与计算式分析

为了增强对汽(气)-液-固三相流传热过程的基础理解,并为理论研究和工业应用提供有价值的信息,对三相流化床传热模型与计算式进行分析和比较。结果表明,在各种传热计算式和机理模型中,无因次准数关联式的预测精确度最高;建立反映传热机理的模型与计算式,开展多相流非线性研究和传热数值模拟是未来的研究方向。     

气固两相流穿越液池过程颗粒运动及分布特性

为了揭示气固两相流穿越液池过程中的气液固三相流动特性,建立了气液固三相实验平台和基于Euler-Lagrange框架下的数值模拟平台,对该过程中的气液固三相流动过程及颗粒运动分布规律进行研究。获得了5～15 μm、80～110 μm和380～530 μm 3种典型粒径颗粒在三相体系中的微观运动过程及其分布规律。实验与数值模拟结果均能反映出一致的客观规律。研究发现,颗粒浓度沿液池高度方向和径向均呈现多峰分布特征;5～15 μm粒径颗粒更易跟随气体一起穿越液池,其在液池内的浓度分布较为均匀;380～530 μm粒径颗粒与气体的跟随性较差,其浓度峰值主要集中在液池底部。随着下降管出口静态浸没深度的增加,液池内颗粒浓度分布趋于平缓。     

环隙式离心萃取器内部两相流动研究进展

环隙式离心萃取器是集成液-液混合与液-液分离于一体的高性能萃取设备,其广泛应用于核工业、化工环保、有色冶金、生物医药等领域。离心萃取器具有优异的水力学特性和传质特性,这主要得益于其环隙中的泰勒涡流以及转鼓内的离心分离流等特殊流动。本文主要依据离心萃取器结构和两相流动特点,综述了环隙内气-液界面变化规律、气泡流动特性、液-液两相流型、液滴流动特性,以及转鼓内的气-液界面等方面的研究进展,还总结了环隙螺旋隔板、转鼓径向叶片等结构的优化对于两相流动、混合或分离效果的影响。在后续研究中,可以从离心萃取过程中的液滴分散和聚并机理、三相流动测试及模拟、结构的模型化设计方法等方面开展更加深入的研究。     

我国环己烷氧化分解液碱水分离技术研究进展

废碱液的分离是环己烷氧化法制备环己酮的关键处理环节,若分离不彻底,将直接导致烷蒸馏塔再沸器结垢,造成物料消耗增加及装置运行周期大幅度缩短;因此如何高效降低环己烷氧化分解液中废碱含量一直是各个企业所面临的难题。本文对环己烷氧化分解液碱水分离技术进展进行了综述,分析了重力沉降+斜板分离工艺、重力沉降+聚结分离工艺、重力沉降+旋流分离+聚结分离工艺、斜板分离+旋流分离+聚结分离工艺技术的原理、特点及其应用效果。随着深度分离技术的升级,进入烷蒸馏塔物料中Na⁺含量从50~100mg/kg降至0.2mg/kg以下,环己酮装置开车周期从2~3个月延长到24个月以上。从工业应用效果来看,重力沉降+旋流分离+聚结分离工艺碱水分离效率最高、工业应用效果最好,值得大力推广应用。此外,斜板分离+旋流分离+聚结分离工艺作为新型组合分离技术,其分离效果有待进一步工业验证。     

An experimental investigation of the electrophoretic sedimentation of fine particles in waste kerosene

This study concerns the separation, by electrophoretic sedimentation, of fine positively charged oxidized aluminum and iron particles from waste kerosene used in an aluminum foil rolling operation. Settling experiments were carried out in a laboratory-scale cell which allowed the influence of an electric field to be studied simultaneously with gravitational settling. The study spans the clarification and thickening concentration ranges and includes the effects of field strength, settling height and electrical heating on the observed settling rates of several different samples of the particle—kerosene suspension. A number of correlations were found for the experimental results generally based on correlations for gravitational settling modified to take into account the imposition of an electric field.     

絮凝剂对磷酸料浆沉降分离性能影响的实验研究

介绍了湿法磷酸料浆在加入不同剂量的聚丙烯酰胺时的重力沉降性能,通过比较A、B两种聚丙烯酰胺对实验料浆沉降性能的影响,得出的结论是:当加入B型聚丙烯酰胺,加入量为10ppm时,该料浆的沉降性能较好,且温度宜控制在60℃左右。实验结果对提高湿法磷酸料浆的分离效率以及分离机械的选型都具有重要的指导意义。     

Experimentelle und theoretische Untersuchungen zur Filtration mit überlagerter Sedimentation in Drucknutschen

Sedimentation superimposed on industrial cake filtration leads to longer filtration times and often has a detrimental effect on subsequent process steps such as washing and demoisturing. The influence of sedimentation is seldom recognised in laboratory filtration experiments. Methods are presented for evaluation of pressure filter experiments with superimposed sedimentation which avoid the error made in the usual evaluation methods. For the case of zone sedimentation the article presents a graphical evaluation and a numerical method of modelling permitting scale up to any desired cake height. In superimposed classifying sedimentation simultaneous measurement of filtrate volume and cake height provide information about local variation in filter cake resistance. It is shown for a model system that, owing to sedimentation, the cake resistance shows a minimum at mean cake height and increases rapidly towards greater heights. The local cake resistance corelates with particle size distributions measured for layers of a horizontally cut filter cake. The method of evaluation presented permints determination of the flow resistance of the uppermost layers of a cake and hence estimation of the gas pressure necessary for demoisturing. The profiles of local filter cake resistance show that the relative cake layering is largely independent of the level of suspension filling. A scale-up model is presented for use in those cases where classifying sedimentation cannot be suppressed.     

Local solidosity of microcrystalline cellulose during dead-end filtration and sedimentation

Solid–liquid separation by filtration and sedimentation are important operations used in a wide range of industries. One important characteristic of both the filtration and sedimentation processes is the solidosity of the filter cake/sediment that is formed, affecting the efficiency and design of the separation. In this study local solidosity was investigated using a γ-attenuation method during both filtration and sedimentation experiments for microcrystalline cellulose, a highly crystalline cellulose with particles of about 2–80 μm in diameter. Constitutive relationships for the solidosity were investigated using both filtration (i.e. cake build-up and expression) and sedimentation data for experiments at different pH and suspension concentrations. The sedimentation behaviour under these different conditions was also investigated. It was found that a three parameter empirical model could be used to describe the constitutive relationship between local solidosity and local solid compressible pressure for the sediment formed and the filter cake after both cake build-up and expression. This correlation worked well for the material investigated even at low solid compressible pressures.     

Choice of model for predicting the dispersion height in liquid/liquid gravity settlers from batch settling data

The design of liquid/liquid gravity settlers has attracted increasing interest in recent years due to the industrial importance of solvent extraction. Batch settling tests are easier to perform than continuous pilot plant runs, but require sophisticated interpretation if the behaviour of a steady-state dispersion is to be predicted. Both batch and continuous dispersions contain sedimentation and dense-packed zones in which the drops grow in size through binary coalescence and finally disappear when they coalesce with their bulk homophase. The rate of droplet sedimentation is a function of the drop size and dispersed phase hold-up, whereas the interfacial coalescence rate is dependent on the height of the dense-packed zone and the drop size at the coalescing interface. At the steady state the dense-packed height may shrink to zero if the interfacial coalescence is virtually instantaneous. On the other hand, the whole of the dispersion may be dense-packed if the conditions in the feed stream lead to a volume rate of sedimentation which is higher than the dispersed phase throughput. Similar extreme behaviour also occurs in batch dispersions under corresponding conditions. The variations in height of the sedimentation and dense-packed zones, and hence the total dispersion height with the throughput in a continuous settler, can thus be predicted using parameters determined from experimental batch sedimentation and coalescence data. A procedure based on the shape of the batch decay curves, hold-up and volume rates of sedimentation and interfacial coalescence is proposed for selecting the appropriate model which is verified with available experimental data.     

The Kinetics of Droplet Sedimentation in Liquid-Liquid Extraction

Liquid-liquid extraction is a major separation process in chemical industry. Beside appropriate design of mass transfer equipment, successful design of phase separation equipment is an important issue. Therefore, the separation of liquid-liquid dispersions was investigated and modeled with kinetic approaches to gain information for settler design. A modified first-order sedimentation rate model, a first-order consecutive step rate model, and a mixed-order rate model were applied and compared to the experimental data. The advantage of kinetic modeling of the rate of sedimentation, specifically addressing the impact of viscosity and electrolyte concentration, was successfully demonstrated.     

催化裂化油浆液固分离技术评述

介绍了分离催化油浆液固体系的方法及发展状况,这些方法包括自然沉降法、过滤分离法、静电分离法和离心分离法。     

Note on the movement of insecticide droplets through and out of a crop canopy after emission below canopy level

Coarse aerosol sprays with number median diameters in the range 30–40 μm were emitted at 0.25 m above the ground within the canopy of a cotton crop planted at 0.93 m row separation and standing 1.0 m tall. Movement of spray was monitored by vertical stepped paper tower samplers with narrowest section of width 0.13 cm, giving collection by inertial impaction down to 10 μm in a 1 m/sec wind. Horizontal paper targets were used to sample droplets depositing by sedimentation. Droplet number counts indicated that under conditions of moderate instability and associated convective turbulence, droplets were drawn rapidly out of the crop to a height of 2 m (the upper level sampled). The peak concentration of the spray cloud was centred at a height of between 1.0 and 2.0 m beyond 1.0 m downwind of the emission point in the first test, using droplet spectrum with volume median diameter of 41 μm, and beyond 2.5 m downwind of the emission point in the second test with spectrum of 57 μm volume median diameter. Inertial impaction at the 0.25 and 0.5 m levels was slight, except on the samplers within 0.5 m of the sprayer, and sedimentation was only significant at and below 0.5 m in the first two rows sampled. The moderate wind speed of 2.5 m/sec at canopy level produced marked inertial impaction over the first 4.5 m downwind of the sprayer at the 1.0 m level.     

Study on the mechanism of hindered sedimentation by ‘unified theory on solid-liquid separation’

The entire procedure of hindered sedimentation has been calculated by the introduction of new boundary conditions to the ‘unified theory on solid-liquid separation.’ During this study, the hindered sedimentation was defined as ‘a process of sedimentation with transmission of the gravitational force between the particles due to contact.’ The lower concentration limit, on which the ‘unified theory on solid-liquid separation’ is based, could not be applied. To understand the mechanism of hindered sedimentation, variations in the porosity during sedimentation were calculated by using our theory.