Asymptotic Properties of a Probabilistic‐Statistical Model of Particle Classification in Hydrocyclones

The peculiarities of practical implementation of a probabilistic‐statistical model for a hydrodynamic stage of particle classification process of liquid‐solid polydisperse systems in cylinder‐conic hydrocyclones of small size have been investigated. Within reasonable assumptions, stationary solutions of the Fokker‐Planck‐Kolmogorov kinetic equation were obtained for the considered separation process. In order to describe changes in characteristics of suspension separation in hydrocyclones it was proposed to use stationary distributions, which parameters depend not only on hydraulic and dynamic features of flows inside an apparatus, but also are determined by relative magnitudes of the impact of particle classification and centrifugal forces in comparison with the intensity of random perturbations.     

水力旋流器分离过程的 Monte Carlo 模拟

根据颗粒在水力旋流器中的运动特点，提出了颗粒运动状态的交换构成三角马尔可夫链的观点，建立了水力旋流器分离过程的随机数学模型，并利用ＭｏｎｔｅＣａｒ┐ｌｏ方法进行了数值模拟，模拟程序中采用变参数设计，在输入一定的结构和工艺参数下，由计算机自动生成水力旋流器分离过程的级效率曲线，并给出总效率值；并计算了在不同容量下的模拟精度，结果表明样本容量越大，模拟精度越高     

An overview of solid–liquid separation of residues from coal liquefaction processes

Direct coal liquefaction process typically produces mixed oils (60%) and gases (15%). The remainder is a high‐boiling viscous residue that contains oils, asphaltenes, unreacted coal, mineral matter and potentially valuable liquefaction catalyst. Effective separation of the components of the residue stream is important to the economic and environmental performance of the process. Solid–liquid separation technologies, such as filtration, hydrocyclones, centrifugation, critical solvent deashing and distillation have been reviewed in relation to their use in coal liquefaction processes. Individual operations used have not been completely satisfactory, and a better overall result is obtained when they are used in combination. © 2012 Canadian Society for Chemical Engineering     

除油水力旋流器内油水分离过程数值模拟

采用计算流体力学的有限体积法(FVM),对液-液水力旋流器的轻相分离过程进行了非稳态的数值计算,得到了油相在旋流器内的逐渐分离、聚积和运移的过程。进一步分析发现,该旋流器的小锥段分离作用突出,而大锥段和旋流腔的分离作用较小,但大锥段具有重要的过渡作用。     

Identification of the multiscale fractional Brownian motion with biomechanical applications

Abstract. In certain applications, for instance, biomechanics, turbulence, finance or internet traffic, it seems suitable to model the data by a generalization of a fractional Brownian motion (FBM) for which the Hurst parameter H depends on the frequency as a piece‐wise constant function. These processes are called multiscale fractional Brownian motions. In this article, we provide a statistical study of the multiscale fractional Brownian motions. We developed a method based on wavelet analysis. By using this method, we calculated the frequency changes, estimated the different parameters, tested the goodness‐of‐fit and gave the numerical algorithm. Biomechanical data are then studied with these new tools.     

细颗粒杂质旋流脱水油田现场试验研究

针对大庆油田现场实际情况 ,在原有室内实验研究的基础上 ,采用水力旋流器对细颗粒杂质的分离处理做了试验研究。试验结果表明 ,随流量的加大脱水率有增加的趋势 ,最高可达 90 %左右 ,但并非流量越高越好 ;分流比为 8.75 %以下时效果较为理想 ,但分流比过小时 ,旋流器底流管路中出现明显堵塞现象 ;5°锥角旋流器的分离效果要优于 8°锥角旋流器 ,且压力损失相对较低。初步试验研究表明 ,采用水力旋流器对油田污水中的细颗粒杂质进行处理是可行的     

Influence of feed solids concentration on the performance of hydrocyclones

Even though the influence of solids concentration in the feed on the separation efficiency of hydrocyclones has long been recognized, a systematic research on the change in pressure drop across the hydrocyclone and the latter's separation characteristics has thus far been lacking. If all other operating parameters are kept constant, an increase in feed concentration generally leads to a coarser cut size, reduced sharpness of separation and a rise in pressure drop. Apart from the particles hindering one another's radial motion, the limited capacity of the apex valve and the changes in the flow field within the hydrocyclone cause additional particles to be entrained by the overflow. The flow ratio thus becomes an additional parameter in determining the cyclone efficiency. A theoretical model, which takes these effects into account, has been developed and successfully tested against experimental data.     

Numerical and Experimental Biomass Separation from Fermentation Process by Minihydrocyclones

Biomass particle separation is challenging in the pharmaceutical industry because of the smallness and lightness of such particles. Centrifugation is applied conventionally for batch separation. However, imposing multiple wash steps in order to eliminate culture residues and the high risk of extrinsic contamination hamper batch techniques. In this research, minihydrocyclones were introduced to provide a better solution for the mentioned limitations in continuous processes. Numerical separation of methylotrophic yeast from fermentation broth was carried out in three hydrocyclones with different lengths, and the most efficient one was examined experimentally. Three various feed flow rates and seven feed concentrations were evaluated. The concentration of biomass suspension in the product was raised to 20 %.     

水力旋流器能耗机制与节能原理研究 Ⅷ.优化节能原则

研究了水力旋流器的节能与强化分离性能的匹配优化。结果表明,旋流器能耗的降减与分离性能的强化具有一致性,于是提出了兼顾节能与强化分离性能的优化节能原则;研究了能耗系数与运行费用准数之间的关系,表明最低运行费用准数并非对应最小能量耗损,并探讨了流场结构对运行费用准数的影响规律;系统地给出了旋流器在以不同工艺指标为目标函数时的优化结构组合基础数据库,为在不同工艺场合下运行的旋流器的优化节能提供出设计指导     

动态水力旋流技术发展综述

介绍了动态水力旋流器的结构、操作原理及国内外发展概况,对比分析了动态水力旋流器与静态水力旋流器在处理含油污水方面的不同利弊,总结了动态水力旋流器的主要结构特性、操作特性及分离性能,并归纳了动态水力旋流技术在应用中的一些研究结论。     

影响动态水力旋流器脱油性能的综合因素

介绍了动态水力旋流器结构组成及工作原理,总结了影响其脱油性能的若干因素,包括内在因素、配套工艺及外在条件,结构形式及参数,制造精度及加工工艺,主要运行参数等。由大量实验结果得到该装置构件的结构形式及操作参数的适用范围。     

基于离散相模型的双锥型水力旋流器磨蚀分析

基于计算流体动力学(CFD)方法,采用Gambit建模,利用Fluent软件中的离散相模型(DPM)进行分析,分析出了普通双锥型水力旋流器内壁的磨损部位包括切向入口处、旋流腔和大锥段的交界处,以及大锥与小锥的交界处等;改进后旋流器的磨损情况得到了明显的改善,分离效率也有所提高。同时,对双锥型水力旋流器的压力特性进行了分析。     

Performance of a New Geometry of Deoiling Hydrocyclones: Experiments and Numerical Simulations

A new geometry of liquid‐liquid hydrocyclones is proposed seeking to perform the separation of oil emulsified in water. The hydrocyclone performance was investigated by means of a factorial experimental design (2³) leading to a total of ten experiments. The results enabled the determination of empirical mathematical models that describe capacity, total separation efficiency, and flow ratio as a function of oil concentration in the feed inlet, operating pressure drop, and presence or absence of a vortex finder in the geometry. Numerical simulations were also carried out to further understand the flow field characteristics in the studied hydrocyclone.     

The Use of Simplified or Misspecified Models: Linear Case

Simplified models have many appealing properties and sometimes give better parameter estimates and model predictions, in sense of mean‐squared‐error, than extended models, especially when the data are not informative. In this paper, we summarize extensive quantitative and qualitative results in the literature concerned with using simplified or misspecified models. Based on confidence intervals and hypothesis tests, we develop a practical strategy to help modellers decide whether a simplified model should be used, and point out the difficulty in making such a decision. We also evaluate several methods for statistical inference for simplified or misspecified models.     

Optimization of Design and Performance of Solid‐Liquid Separators: A Thickener Hydrocyclone

Studies on hydrocyclones have evolved over recent years and various configurations of this device have been proposed in the literature for different purposes. Herein, an innovative geometrical configuration of hydrocyclones was developed by means of the response surface technique, combined with an optimization algorithm and supported by a computational fluid dynamics complementary study. The results obtained with these optimization techniques were validated by experimental data. The optimized hydrocyclone configuration is characterized by low energy consumption, i.e., low Euler number, with a small underflow‐to‐throughput ratio and can be used as a thickener hydrocyclone.     

The barium sulfate seeding process

The maximum brine temperatures in the final heaters of multistage flash evaporators, being limited by calcium sulfate scaling, in the case of acid decarbonized sea water, might be enhanced by seeding processes. Use of barium sulfate (barite) as seed has recently been proposed in a feasibility study and reported to have the advantage of recycling of a given amount of barite, and the special advantage of inherent diminution of the calcium concentration in the circulating brine. Using the MEWAK I closed loop system, experiments have shown that barite particles remain active as seed when the suspension system is alternatively heated and cooled several times. The “loading” and “unloading” velocity is satisfactory. Further experiments are concerned with the separation of barite from its suspension in sea water brine by hydrocyclones.     

Numerical Simulation of the Separating Performance of Hydrocyclones

The flow behavior in hydrocyclones is quite complex. The Computational Fluid Dynamics (CFD) method was used to simulate the flow fields inside a hydrocyclone in order to improve its separation efficiency. The RSM turbulent model (Reynolds Stress Model), which abandons the isotropic eddy‐viscosity hypothesis, was used to analyze the highly swirling flow fields in hydrocyclones. The ASM Model (Algebraic Slip Mixture Model) was used to simulate the separation performance. The volume fraction distribution and grade efficiency curve are given. The separating efficiency for 60 μm water particles is more than 90 %. The majority of 60 μm water particles are carried to the underflow. An increase in particle size will improve the efficiency by increasing the centrifugal force on the particles. Based on the simulation, the effects of the overflow tube dimensions on the separation performance were studied. The overflow tube dimensions of the hydrocyclone were modified, and the results showed that the Reynolds Stress Model successfully predicted the characteristics of the flow, and the simulated performances were in good agreement with those obtained by tests.     

Computational investigation of the mechanisms of particle separation and “fish‐hook” phenomenon in hydrocyclones

The motion of solid particles and the “fish‐hook” phenomenon in an industrial classifying hydrocyclone of body diameter 355 mm is studied by a computational fluid dynamics model. In the model, the turbulent flow of gas and liquid is modeled using the Reynolds Stress Model, and the interface between the liquid and air core is modeled using the volume of fluid multiphase model. The outcomes are then applied in the simulation of particle flow described by the stochastic Lagrangian model. The results are analyzed in terms of velocity and force field in the cyclone. It is shown that the pressure gradient force plays an important role in particle separation, and it balances the centrifugal force on particles in the radial direction in hydrocyclones. As particle size decreases, the effect of drag force whose direction varies increases sharply. As a result, particles have an apparent fluctuating velocity. Some particles pass the locus of zero vertical velocity (LZVV) and join the upward flow and have a certain moving orbit. The moving orbit of particles in the upward flow becomes wider as their size decreases. When the size is below a critical value, the moving orbit is even beyond the LZVV. Some fine particles would recircuit between the downward and upward flows, resulting in a relatively high separation efficiency and the “fish‐hook” effect. Numerical experiments were also extended to study the effects of cyclone size and liquid viscosity. The results suggest that the mechanisms identified are valid, although they are quantitatively different. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Statistical Analysis of the Effect of the Temperature and Inlet Humidities on the Parameters of a PEMFC Model

An individual PEM fuel cell 6‐parameter mechanistic model was developed. In parallel, experimental polarization curves were obtained at different temperature and inlet gas humidities conditions. The 6 model parameters were determined by fitting the semi empirical model to the experimental curve using a non linear regression method. Finally, a statistical analysis was carried out in order to determine which operating conditions (temperature and inlet humidities) have a significant effect on which model parameters. A black box model was built in order to relate the model parameter values to the significant operating conditions for each one of them. The obtained model was able to satisfactory reproduce the experimental behaviour of the system at low current densities.     

充气水力旋流器用于油水分离的试验研究

研究了充气量、进料量、分流比以及底流出口压力等主要操作参数对充气水力旋流器分离效率影响的规律 ,得出了较好的工况点 ;与相同结构参数的未充气旋流器的分离性能进行了对比 ,结果表明 ,充气旋流器能明显改善油水分离条件 ,具有较宽的操作弹性和较高的分离效率 ;同时用库尔特粒径分析仪分别测定了它们进口和底流口油滴的粒径分布 ,发现在旋流器中充入空气 ,强化了气浮 ,能够进一步分离更细粒径的油滴。