PM2.5细颗粒物分离技术的数值模拟和性能改进

旋风切割器是分离细颗粒物的主流技术,为了提高其分离效率并减少能耗,本文分析了切割器参数对粒子分离的影响.基于计算流体动力学数值模拟的方法,分析了VSCC型旋风切割器的内部湍流流场,比较15~25L/min范围内不同流速下的涡流变化情况;基于"逃逸率"概念,模拟1~6μm内不同粒径的细小粒子逃逸率随流速的变化曲线,考察临界粒径dc并结合气溶胶实验进行验证,分析流速对分离性能的影响程度;之后考察了流速对压降的影响,提出一种几何参数改进方案,在避免压降升高的前提下提高分离性能.研究表明:流速影响旋风切割器内的湍流分布,随着流速增大,临界粒径变小,分离性能得到提升,模拟结果在16 L/min的流速下,临界粒径约为2.5μm,与实验结果基本一致,并且利用曲线给出计算总分离效率的思路;调节几何参数可以实现在低能耗的前提下,将临界粒径进一步降低为1.1μm,收集效率更高.研究结果可为PM2.5切割器的商业选择或工程设计提供理论参考.     

导叶式旋风管入口颗粒粒度分布对分离效率的影响

为深入研究导叶式旋风管的分离机理,用不同粒度分布的SiO2颗粒对分离总效率与粒级效率进行了对比研究。实验结果表明:入口颗粒的粒度分布不但对旋风管的分离总效率有影响,而且对粒级效率也有较大影响;不同粒径大小的颗粒在旋风管中的分离机理不同。     

安全壳内水池气泡破碎后夹带液滴的粒径分布

针对安全壳内气溶胶再夹带问题,设计液池表面气泡破碎特性研究可视化试验装置,进行典型试验条件下的气溶胶再夹带试验,验证高速摄影拍摄法对百微米级含气溶胶液滴进行测量的可行性;通过对液滴进行拍摄和分析,研究液池中气溶胶种类、质量浓度、水温对气泡破碎后液滴粒径分布的影响。结果表明:气溶胶种类、质量浓度、水温均对液滴粒径分布产生影响;升高温度和提高气溶胶悬浊液质量浓度,均使得液滴粒径分布变小; BaSO_4悬浊液较TiO_2悬浊液更不易生成夹带液滴;不同试验条件下的液滴粒径分布公式拟合结果较好。     

结构参数对小型旋风分离器分离性能的影响

采用雷诺应力模型(RSM)和离散相模型(DPM),计算不同结构尺寸下小型旋风分离器对微米级颗粒的分离性能。计算结果表明,小型旋风分离器排气管直径、排尘锥锥顶直径对除尘效率和压力降的影响显著,分离效率为50%时的临界粒径约为0.9μm。结果显示,此类小旋风分离器有望用于减少雾霾。     

循环流化床锅炉用旋风分离器性能的实验研究

结合水煤浆流化-悬浮燃烧的特点,通过全面测定循环流化床锅炉用旋风分离器在不同操作参数下的分离效率,研究了入口气速、入口颗粒浓度、入口颗粒物性等对旋风分离器的压降和分离性能的影响规律。实验结果表明,影响旋风分离器分离性能的主要物性参数是颗粒的中位粒径、密度,在入口颗粒的中位粒径相差较大时分离性能主要受粒径的影响,而当入口颗粒粒径相差较小时密度对分离器分离性能的影响则更为显著。     

凹版胶印油墨分离产生卫星液滴研究

目的研究凹版胶印过程中的第3阶段,即油墨从橡皮布滚筒向承印物转移时,油墨黏度和分离速度对卫星液滴的影响。方法利用Maxwell粘弹性模型,从理论的角度分析油墨黏度和分离速度与卫星液滴产生之间的关系,并模拟凹版胶印中油墨转移的第3个过程,即油墨在两平板间的分离,论证三者之间的关系。结果分离速度v=0.1 m/s、黏度μ=0.25 Pa·s时产生的卫星液滴为4个,且大小几乎相同并集中;分离速度和黏度较小时,所产生的卫星液滴数目越少,但其中一定有1个最大的卫星液滴;分离速度和黏度较大时,所产生的卫星液滴小而多,且分散。结论分离速度v和油墨黏度μ与卫星液滴产生的数目成正相关关系,在印刷速度(分离速度)一定时,减少甚至消除"卫星液滴"应当选择低黏度、高弹性模量的油墨,从而降低油墨的应力松弛时间。     

基于微流控芯片技术的小尺寸微米级液滴制备

利用微流控芯片技术制备的皮升级微量液滴,作为独立的微反应器,由于其比表面大,高通量等优势,在生物、医学、化学、物理等领域得到了广泛应用。本工作利用软光刻技术制备流聚焦型微流控芯片,研究了微流控芯片中连续相和分散相的流速对微量液滴尺寸的影响。结果显示,增加连续相流速时,微量液滴的尺寸减小;而加快分散相流速时,微量液滴的尺寸增大。当微流控芯片的通道尺寸固定后,由于分散相和连续相的界面张力不变,通过改变连续相和分散相的流速,微量液滴的尺寸范围有限,本工作中微量液滴的尺寸为几百微米至25μm。本工作探究了微流控芯片中如何制备尺寸小于25μm的微量液滴的方法。通过添加活性剂,改变连续相和分散相的界面张力,可实现制备尺寸为10μm的微量液滴。本工作所利用的微量液滴制备方法,制备的10μm大小液滴具备更高的比表面积,反应活性将会更大、在药物释放,颜色显示等领域将有广阔应用前景。     

多效旋风分离器压降的实验研究

为了有效提高新型多效旋风分离器对粒径为0.1~3μm颗粒的分离效率,获取该设备的阻力性能,采用实验方法研究该新型多效旋风分离器压降与进口气速的关系,并与Lapple型旋风分离器进行比较。结果表明:进口风速为5~30m/s时,主体直径为0.25m的多效旋风分离器总阻力系数为7.29,其中,一级和二级预分离螺旋管的阻力系数分别为1.04和1.73;主体的阻力系数为4.52。直径为0.25m的Lapple型旋风分离器的阻力系数为7.21。     

煤的超细气流粉碎和分级对组成和结构的影响

利用超细气流粉碎及旋风分离对3种不同煤阶典型煤样进行超细粉碎研究,对粉碎前后各粒径煤样进行工业分析和元素分析,探讨超细气流粉碎及分级对各粒径煤样组成和结构的影响。结果表明,气流粉碎及两级旋风分离后煤样体积平均粒径分别达到约5.0μm和2.5μm,算术平均粒径可达亚微米级;煤岩组分及矿物质得到一定程度的解离,各粒径煤样的组成和结构发生明显变化,有利于煤岩显微组分的分离富集及无机矿物质的脱除。     

超细粉体在微型旋风分离器中的分级性能研究

研究了微型旋风分离器的分级特性,目的是通过微型旋风分离器将1μm左右的超细粉从细粉中分离出来。对4种微型旋风分离器在不同流速下的分级效率进行了实验研究,并采用无因次的Rosin-Rammler坐标对测试数据进行了整理。实验表明,分级效率与斯托克斯数Stk之间关系在Rosin-Rammler坐标上为一条直线,采用微旋风器可对微粉进行分级,分割粒径可以达到1．3μm。     

The effect of particle humidity on separation efficiency for an axial cyclone separator

The objective of this study is to investigate the effects of particle humidity on the inlet particle size distribution, overall efficiency, grade efficiency and cut size diameter for an axial cyclone separator with inner diameter of 150?mm. The collection and grade efficiencies of the cyclone separator were measured by on-line method for inlet velocities, particle concentration and particle humidity in the ranges of 12–18?m/s, 30–500?mg/m³ and 8–30‰, respectively. By employing a set of fixed parameters for inlet velocity and particle concentration, the effect of particle humidity on separation efficiency was investigated. The experimental results show that the volume ratio of larger particle increases with the increasing of particle humidity due to particle agglomeration. When the inlet velocity and particle humidity remain constant, the collection and grade efficiencies improve greatly as the increasing of the particle concentration because of the particle aggregation. However, it was noticed that the grade efficiencies did not always increased with the increasing of particle humidity under the same conditions of inlet velocity and particle concentration. The trends of grade efficiency curves for different particle humidity change at the particle diameter of approximately 10?μm. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10?μm, while a contrary tendency is observed when the particle diameter is smaller than 10?μm.     

Preparation and characterization of spray-dried submicron particles for pharmaceutical application

The versatile use of submicron-sized particles (0.1–1?μm) requires new manufacturing methods. One possibility for the preparation of submicron-sized particles is spray drying. However, the generation of small droplets at a high production rate and the precipitation of submicron particles are quite challenging. In order to produce a sufficient amount of fine and uniform droplets, a two-fluid nozzle with internal mixing was combined with a cyclone droplet separator. The precipitation of particles was realized with an electrostatic precipitator. Considering the difficulty of electrostatic precipitation concerning explosion risks and to make it capable using organic solvents, the spray dryer was integrated in a pressure resistant vessel. Based on previous experiments, the now presented design is compact and the electrostatic precipitator is shortened. In addition, enhanced drying conditions ensured a controlled and reproducible preparation of submicron-sized particles. Thus, high separation efficiencies were shown. Spray-drying experiments were conducted with the model substance mannitol. With the cyclone droplet separator, a fine and uniform spray with a droplet size smaller 2?μm was produced. This robust atomizing technique is capable for high concentrations. For a 10?wt% mannitol solution, particles in the submicron range d_50,3?=?0.7?μm were produced.     

Investigation on separation performance and structural optimization of a two-stage series cyclone using CPFD and RSM

Cyclones are generally operated in series when the efficiency of a single cyclone is not sufficient for the process. This study firstly used computational particle fluid dynamics (CPFD) to simulate the gas-solid two-phase flow characteristics in a two-stage series cyclone separator. The separation efficiency and distribution of energy consumption was interpreted by analyzing particle distribution characteristics. Secondly, the structure of the two-stage cyclone separator was optimized via response surface methodology (RSM) to make up for the disadvantage that the distribution of the separation load was non-uniform. The results showed that the grade efficiency for 3 μm of the first-stage cyclone separator was increased from 45.408% to 59.932% compared to the original model. The pressure drop of the first-stage cyclone separator is about 2.147 kPa while the second-stage cyclone separator is about 2.774 kPa. It can be seen that the overall optimized two-stage cyclone separator has the advantages of high efficiency, low energy consumption and load-balanced separation performance.     

Effects of helical fins on the performance of a cyclone separator: A numerical study

This study aimed to investigate the separation performance of a cyclone separator after reshaping its cylindrical body by installing the helical triangular fins. A numerical simulation based on Fluent was adopted to perform an orthogonal test to optimise the structure of the cyclone separator with helical triangular fins. Three structural parameters of the helical triangular fins were selected as optimisation variables: base width, fin size, and fin pitch, and their influences on the evaluation indices of the cut-off diameter were investigated. The optimal combination scheme was determined by range analysis, and the cyclone separator performances before and after optimisation were compared and analysed. The significant influence of the structural parameters on the cut-off diameter was in descending order as the fin pitch, fin size, and base width. For particles with diameter of 0.1, 0.5, 1, 2, and 3 μm, the separation efficiency of the cyclone separator with optimized helical triangular fins increased by 7.4 %, 15.9 %, 20.1 %, 10.9 % and 14.8 % respectively. Moreover, the cut-off diameter of the finned cyclone separator is reduced by 30.7 %, while the pressure drop is only increased by 6.6 %. The short circuit flow and back-mixing were alleviated, thereby considerably enhancing the stability of the flow field. Therefore, the finned cyclone separator was found to play a critical role in increasing the separation of fine particulate matter.     

Effect of the operation temperature on the hydrodynamics and performances of a cyclone separator

The effect of the operation temperature on the cyclone hydrodynamics and performances is numerically investigated by Computational Fluid Dynamics (CFD). When increasing the temperature, the separation efficiency decreases and the separation quality improves due to the weakened double layer swirling flow structure. The radial drag and centrifugal forces exerted on 0.1 μm and 1 μm particles are recorded. A large radial drag force to centrifugal force ratio is required for escape: a ratio larger than 10⁴. When the radial drag force to centrifugal force ratio is in the range of 10¹ to 10³, it is the temperature-dependent flow field which determines the submicron particle separation. While the locus of gas zero vertical velocity is closely related to the particle’s separation, the gas turbulence intensity distribution also contributes the capture of the particles.     

Numerical study on the performance of swirl tube based on orthogonal design

Here, an axial flow cyclone separator is design is proposed. The effects of varying the structural parameters and operating conditions on pressure drops and separation efficiency were investigated via a numerical simulation approach. The results show that of the three structural parameters considered, the distance between the diffuser and blade is the most significant factor impacting separation performance compared to the blade pitch and blade shaft diameter. Increasing the distance between conical outlet and blade can decrease its pressure drops and increase separation efficiency; while increasing the shaft diameter can increase pressure drops, and the increasing blade pitch can decrease both the pressure drop and the separation efficiency. The pressure drop of the optimized swirl tube was 102.1 Pa, with a corresponding separation efficiency of 95.04% for 100 μm particles at an extraction ratio of 10%. Further, the cut-off particle size can reach 3 μm, demonstrating that the swirl tube offers good separation performance and has the potential to be widely applied in industrial gas–solid separation applications.     

入口带有加速段方型分离器结构优化的试验研究

分离器是循环流化床锅炉的关键部件,入口带有加速段的方型分离器结构紧凑,性能良好,适用于循环流化床。通过一系列的试验,对其结构进行了优化,结构参数存在最佳值,整体结构应做优化设计。优化设计条件下,该型分离器切割粒径ｄ５０ ＝ ～２５μｍ ,临界粒径ｄ９０ ＝ ～１１０μｍ ;流动阻力Δｐｆ＝１０００Ｐａ。当筒体采用八角形型式时,分离器性能将会有一定提高。     

页岩灰与催化裂化催化剂细粉旋风分离性能的对比试验研究

试验测定和对比页岩灰和流化催化裂化三旋灰(FCC三旋灰)的旋风分离器性能,考察入口气速、入口浓度对分离效率和分离器压降的影响.结果表明,在相同操作条件下,同一台旋风分离器上,粒度小于75 μm的页岩灰与FCC三旋灰的分离效率和分离器压降曲线差别显著;页岩灰的分离效率与分离器压降都明显低于FCC三旋灰,且入口浓度增大,页岩灰分离器压降的下降幅度高于FCC三旋灰;页岩灰分离效率最高的入口气流速度也低于FCC三旋灰.颗粒特性对旋风分离器的分离性能有明显影响,页岩灰和三旋灰的颗粒特性与形状差别是导致其旋风分离特性不同的一个基本原因;油页岩旋风分离器的设计应当考虑油页岩颗粒特性的影响.     

Experimental study on the separation performance of a novel gas–liquid separator

A novel two-stage dynamic separator called high-gravity cyclone separator (HGCS) has been designed for gas–liquid separation. It is mainly composed of a cyclone chamber and rotary drum. In this study, its performance, including the separation efficiency and pressure drop, is experimentally investigated, and the effects of the operating conditions and drum parameters are evaluated. For droplets with a mean diameter of 7 μm, the results indicate that the optimal gas inlet velocity and high-gravity factor are 12 m/s and 59.4, respectively, and the separation efficiency reaches 98 %. The effect of liquid concentration is sensitive to the high-gravity factor. At a liquid concentration of 57 g/m³, the maximum efficiency will be 98.75 % when increasing the high-gravity factor to 85.6. Furthermore, a smaller radial height is preferable when the gas inlet velocity is greater than 12 m/s, and a better separation efficiency can be obtained by increasing the drum length to 190 mm. However, when the length is 235 mm, the efficiency will be poor because of the Kelvin–Helmholtz and Rayleigh–Taylor instabilities. Compared with the predominant roles of gas inlet velocity, drum length and radial height in pressure drop, the effects of liquid concentration and high-gravity factor are small.     

CFD simulation of a novel design of square cyclone with dual-inverse cone

The objective of the present study is to propose a novel design to improve the separation efficiency of the conventional square cyclone. For this purpose, the conical section of the conventional square cyclone with single-cone is modified to dual inverse-cone. In addition, the effect of second-cone length on the performance of cyclone is considered. A three-dimensional numerical simulation is done by solving the Reynolds averaged Navier-Stokes equations with the Reynolds Stress Model (RSM) turbulence model and applying the Eulerian-Lagrangian two-phase method. The turbulent dispersion of particles is predicted by the application of the Discrete Random Walk (DRW) model. The numerical results demonstrate that dual inverse-cone square cyclone although produces higher pressure drop but its separation efficiency is higher than the square cyclone with single-cone. This is due to a smaller separation zone and shorter path of particle movements which force the particles exit from the outlet section of the cyclone. Finally, using dual-inverse cone square cyclone reduces the 50% cut size about 10% and 30% for inlet velocities of 12 m/s and 28 m/s, respectively.