高压下多管旋风分离器压降模型

为了准确预测和计算天然气输气管线用旋风分离器的压降,在归纳常压下单管和多管旋风分离器的压降计算公式,以及现场测量高压下多管旋风分离器的压降基础上,建立了高压下多管旋风分离器的压降计算模型。利用实验验证压降模型的可靠性,实验结果表明,常压下单管、多管旋风分离器和高压下多管旋风分离器的压降计算模型都能准确地计算出对应旋风分离器的压降值,计算值与测量值之间的误差较小。因此,利用建立的高压下多管旋风分离器压降计算模型能够准确地计算出不同压力和温度下多管旋风分离器的压降值,从而为天然气用旋风分离器的选型提供技术支持。     

一种特殊进口导流管的新型高效旋风分离器

本文基于对现有旋风分离器流场的分析,提出了一种具有特殊进口导流管能抑制上涡流干拢的新型高效旋风分离器,该旋风分离器具有结构简单、分离效率高及操作弹性大的特点。并利用电子计算机进行回归计算,建立了压降及分离效率的关联式。     

旋风分离器料腿漏风对压降影响的实验分析

以直径300 mm的旋风分离器为实验对象,考察了在不同入口速度下料腿漏风量对旋风分离器压降的影响,并以此为基础,分析了某现场催化裂化装置旋风分离器压降出现的不稳定波动现象。实验结果表明,旋风分离器下部料腿是一个负压差立管,外部的压力大于料腿内的压力,易产生漏风,从而导致旋风分离器的压降降低。旋风分离器的压降随漏风量增大而降低,入口速度越低漏风量影响的作用就越明显。该旋风分离器的压降波动是由于不稳定的翼阀排料产生的漏风变化造成的。     

计算旋风分离器压降的一种较好方法

<正> 这里介绍一种简易的压降新公式,它比原来已发表的压降公式更准确。适用于进、出口无螺旋形导管的旋风分离器。旋风分离器广泛地用于净化气体。因为旋风分离器可有效地去除气体中直径大于5μ的微粒,能够处理较大的含尘量;且结构简单,没有运动部件,因此价格合理。设计旋风分离器的关键因素是压降的计算,这一点对于低压下操作的旋风分离器尤     

旋风分离器防磨减阻性能机理研究

为了提高旋风分离器的防磨减阻性能,运用计算流体动力学方法研究了常规和防磨减阻旋风分离器的防磨减阻机理。结果表明:常规旋风分离器容易发生严重的局部冲蚀,而防磨减阻旋风分离器冲蚀磨损区域较为均匀。在同一粒径下,防磨减阻旋风分离器的壁面冲蚀磨损远小于常规旋风分离器。两者的壁面冲蚀磨损速率随粒径增大而逐渐增大,当粒径大于15μm时,冲蚀磨损速率变化不大。两者的压降损失随着入口速度的增加而增大,当入口速度为15 m/s时,防磨减阻旋风分离器的压降为297 Pa远小于常规旋风分离器的821 Pa。防磨减阻板不会改变旋风分离器的流场特性,分离小粒径颗粒效率略小于常规旋风分离器,但粒径大于5μm时,防磨减阻旋风分离器具有很高的分离效率。     

旋风分离器的设计计算

本文给出旋风分离器的最佳设计方法,它既按临界粒径要求确定旋风分离器的尺寸,又满足不超过给定压降的要求,并且还计及粉尘浓度对压降及分离器尺寸的影响,从而给出高效旋风分离器的最佳结构。     

基于响应曲面法径向入口旋风分离器的结构优化

采用流体力学软件对不同结构径向入口旋风分离器的气固两相流场进行了数值模拟,并基于响应曲面法得到旋风分离器的压降模型及分离效率模型。结果表明升气管直径和入口角度对旋风分离器的分离性能影响较大,且两者对旋风分离器分离性能的影响有着很强的交互作用;直筒段高度、锥体高度及升气管插入深度对分离性能影响相对较弱;下降管直径对分离效率影响较大,但对压降影响较弱;随着下降管长度的增大,压降不断增大,分离效率先减小后增大;在考虑压降及分离效率权重的基础上,得到了最优性能的旋风分离器结构,通过比较该结构旋风分离器的分离性能,发现模拟值和模型预测值吻合良好。     

升气管插入深度对旋风分离器内部流场影响的数值模拟

针对旋风分离器内部复杂的三维强湍流,在仿真过程中,采用雷诺应力模型(RSM),利用贴体网格技术,模拟得到不同升气管插入深度时的旋风分离器内的切向速度分布、轴向速度分布和进出口压降。结果表明,当升气管插入深度减小时,会使总压力损失有所降低,但有一部分气流将从入口直接进入升气管形成短路,使旋风分离器的分离性能下降;对于特定的旋风分离器,升气管插入深度存在最优值,可保证较高的分离效率和较低的压降。     

化肥厂并联布置的旋风分离器组的优化研究

通过研究旋风分离器的特性,了解筒体直径和压降是影响旋风分离器成本的主要因素,建立了并联布置的旋风分离器组的成本模型。取某一化肥厂的实际参数进行实例计算,得出通过减少旋风分离器的个数、合理增大旋风分离器的筒体直径、改变旋风分离器的局部结构,可在一定程度上降低成本。分析成本模型的特殊性,通过数值计算,可以得到基于总成本最小情况下的最优旋风分离器筒体直径,为旋风分离器组的优化设计提供参考。     

螺旋型减阻器对旋风分离器减阻作用的研究

本文根据对旋风分离器内流场中切向速度及全压压降分布特性的分析，认为旋风分离器压降主要集中在对分离无效的内旋涡区和出口带走的气流旋转功能损失。据此提出一种抑制内旋涡流动并回收出口气流旋转动能的螺旋减阻装置。本文研究了这种装置的减阻特性，获得了降低压降４０％、而对分离效率影响＜１％的显著效果。     

CFD analysis of flow field in square cyclones

In this study, computational fluid dynamic method is used to predict and evaluate the flow field inside a square cyclone. The flow field is calculated using 3D Reynolds-averaged Naveir-Stokes equations. The Reynolds stress transport model (RSTM) is used to simulate the Reynolds stresses. The Eulerian-Lagrangian computational procedure is implemented to predict particle trajectory in the cyclone. The Newton's second law is used to study the particle trajectory with modeling the drag and gravity forces acting on the particles. The velocity fluctuations are simulated using the discrete random walk (DRW). Two square cyclones which have different geometries are studied. The cyclones are simulated at different flow rates. The details of the flow field are studied in the cyclones and the effect of varying the flow rates is observed. Tangential velocity is investigated in different sections inside the square cyclone. Contour of pressure and turbulence intensity is shown for different inlet velocities inside the cyclones. It is observed that different geometries, also different inlet velocities, could affect on the pressure drop. The collection efficiency and the flow patterns obtained numerically are compared with the experimental data and good agreement is observed.     

Modeling and multi-objective optimization of square cyclones using CFD and neural networks

Increasing of collection efficiency (η) and decreasing of the pressure drop (Δp), simultaneously, are important purpose in the design of cyclone separators. In the present study, multi-objective optimization of square cyclones is performed at three steps. At the first step, collection efficiency (η) and the pressure drop (Δp) in a set of square cyclones are numerically investigated using CFD techniques. Two meta-models based on the evolved group method of data handling (GMDH) type neural networks are obtained, at the second step, for modeling of η and Δp with respect to geometrical design variables. Finally, using obtained polynomial neural networks, multi-objective genetic algorithms are used for Pareto based optimization of square cyclones considering two conflicting objectives, η and Δp. It is shown that some interesting and important relationships as useful optimal design principles involved in the performance of square cyclones can be discovered by Pareto based multi-objective optimization of the obtained polynomial meta-models. Such important optimal principles would not have been obtained without the use of both GMDH-type neural network modeling and the Pareto optimization approach.     

A collection of experimental data for aerosol monitoring cyclones

Cyclone behavior is complex and difficult to model. Recent years have seen the development of new and better predictive models for cyclone performance, which are providing new insights into how cyclone performance is affected by cyclone geometry. Experimental data are essential for verification of such models. In this article we present a dataset of more than 250 experimental determinations of cyclone penetration. The dataset includes cyclones with a wide range of sizes and geometries, tested at a wide range of flow rates. We illustrate some empirical, semi-empirical and mathematical approaches to modeling these cyclone data. For our data, we show that mathematical modeling approaches developed for large gas-cleaning cyclones can also be applied to small aerosol monitoring cyclones, to diverse cyclone geometries, and laminar flow operating conditions.

Copyright © Crown copyright     

Effect of geometric configuration on the collection efficiency of axial flow cyclones

The particle collection efficiencies of axial flow cyclones with eight different geometric configurations, operated at 50 lpm aerosol flowrate, have been evaluated in this study. The geometric variation of test cyclones includes the optional addition of an upside-down cup, two vortex finder lengths, and two cyclone base shapes. Under various configurations, the cutoff aerodynamic particle size of axial flow cyclones changed from 272 to 448 nm. Our study shows that configuration effects on the collection efficiency of axial flow cyclones are different from those of tangential flow cyclones. The observation of different geometric effects on particle collection by axial and tangential flow cyclones is attributed to the flow pattern difference between cyclones of two types. It is further concluded that the optimal configuration for axial flow cyclones is with an abrupt contraction base, without an upside-down cup and with an increased vortex finder length. A simple model combining the model of Leith and Licht (1972) and the tubing loss in 90° bends at high Reynolds numbers has also been proposed to predict the particle collection efficiency curve of the optimal axial flow cyclone among those tested.     

Numerical and experimental study on the effect of solid particle sphericity on cyclone pressure drop

The continuous flow inside cyclone separator is usually simulated by solving the Reynolds averaged Navier–Stokes equations in Eulerian reference frame whereas the dispersed phase is modeled using Lagrangian approach. Although these methods have had a remarkable success, more advanced ideas are needed to model particulate phase in cyclones, especially the non-spherical shaped particles. Numerical simulation is verified with experimental results for the gas-solid flow in a cyclone separator. Reynolds Averaged Navier–Stokes equations (RANS) employing the RNG-based k–ε turbulence model are used to simulate the gas phase. 3-D particle tracking procedure is used for the solid phase. Three different equations for the drag coefficient are utilized in the numerical modeling to acquire more understanding of the behavior of non-spherical particles in cyclones. Computations resulted in the difference of pressure between the inlet and exit of the cyclone, and results are compared with experimental data. Experiments included measuring the separation efficiency of different shapes and sizes of particles. The results indicate that the CFD simulation can effectively reveal the pressure drop behavior as well as separation efficiency of gas-non-spherical particle flow in cyclone.     

差异旋风分离器并联性能测量及流场分析

通过改变旋向和芯管直径,设计了3种差异旋风分离器,并按中心对称方式组成了3种并联方案：相同分离器、旋向差异分离器和芯管差异分离器并联。在冷态实验装置上,测量了单分离器和并联分离器的性能,并利用FLUENT软件分析了并联分离器的流场。结果表明,并联分离器的效率均高于单分离器,且效率-气速曲线未出现“驼峰”;与相同分离器并联相比,旋向交替变化时并联总压降较小,分离效率也更低,但各分离器流量分配均匀,未发现“窜流”现象;当芯管有差异时,并联总压降增大,各分离器进口流量分配不均匀,且进、出口流量平均相差6.0%,公共灰斗中存在“窜流”,旋流稳定性变差,效率降低。为了保证并联分离器的性能,应采用相同分离器对称并联的方式。     

Continuous production of single-walled carbon nanotubes using a supported floating catalyst

Using catalytic decomposition, a technique for the production of singe-walled carbon nanotubes (SWCNTs) is reported with a production rate up to 6 g h⁻¹ after purification, and scaling capability up to 220 g h⁻¹. This is achieved by injection of pre-prepared alumina supported catalyst powder into a modified vertical floating reactor. The product is collected in several cyclones connected in series. Wide range Raman studies (laser excitations from λ = 1064 to 488 nm) and temperature programmed oxidation measurements of the samples collected from the different cyclones show that SWCNTs were separated in situ by tube diameter. This is attributed to the different residual times of the catalyst in the reaction zone depending on particle diameter. A series of computational fluid dynamics calculations of the flow and heat transfer in the reactor, as well as modeling of catalyst particle transport reveals the parametrical dependence of the process.     

A CFD study of the effect of cone dimensions on sampling aerocyclones performance and hydrodynamics

This work presents a Computational Fluid Dynamics calculation to evaluate the effects of cone dimensions on the performance, hydrodynamics and centrifugal forces of sampling aerocyclones (gas cyclones). The problem of modeling highly swirling flow is overcome by means of an algebraic turbulence model. The axial and tangential velocities in a cyclone are successfully simulated. The refined mesh on the cyclone cone was also applied to ensure a better prediction on the effect of cone tip diameter to its performance, centrifugal forces and hydrodynamics. The pressure drop, grade efficiency and cut-off size of a cyclone of different cone dimensions was predicted very well with average deviation of about 2.9%, 5% and 2.1% respectively from experimental data presented in the literature. The findings suggest that the higher peak of tangential and axial velocity in a cyclone of a small cone lead to a higher collection efficiency and pressure drop. This helps to assess the benefit of enlarging or reducing the cone of a given cyclone. Results obtained from the computer modeling have demonstrated that CFD is suitable for modeling an effect of cyclone dimension on its performance.     

并联旋风分离器的旋流稳定性分析

分别选用2台和4台直径300 mm的相同PV型旋风分离器作为分离元件,共用进气管、集气室和排尘室,以中心对称方式组成两种并联分离器,并通过数值模拟比较单分离器与两种并联方案中各分离元件气相流动的特点. 气体介质为常温常压空气,入口气速15~30 m/s. 结果表明,2台或4台并联时各分离元件流量偏差分别不超过0.35%和0.28%,压降最大偏差为0.79%和0.43%,流量分配均匀,灰斗内窜流返混不明显,且4台并联时效果更好. 4台并联时分离元件排尘段的稳定性指数比2台并联或单分离器降低过半,旋流稳定性显著增强. 对称排列的分离元件在公共灰斗中会形成具有自稳定性的对称涡系,对分离元件内旋进涡核的摆动有约束作用,旋流稳定性增强.     

Analytical Approach for Calculating the Separation Efficiency of Uniflow Cyclones

An approach for calculating the separation efficiency of uniflow cyclones for the separation of solid particles from gases is proposed. The analytical model is based on an equilibrium orbit concept, similar to that used in the Barth‐Muschelknautz model for conventional reverse‐flow cyclones, which has been proven to be successful for designing and calculating cyclones in a wide range of industrial applications. The proposed model takes into account the special flow pattern of uniflow cyclones, which differs substantially from that in reverse‐flow cyclones. The model provides correct dependencies of the separation efficiency on the main geometry and operation data of low‐loaded uniflow cyclones. Applying the calculation method to uniflow cyclones operated in test facilities indicates good agreement with experimental data.