Effect of feed body geometry on separation performance of hydrocyclone

ABSTRACT

The misplacement of coarse particles in overflow and fine particles in underflow are problems in hydrocyclone separation. This paper proposes improved feed body design of a hydrocyclone and the effect of feed body geometry on the flow field and separation performance is investigated experimentally and theoretically using PIV and CFD, respectively. The air core formation and the velocity field are in good agreement using both approaches. Further simulated results indicate that the tapered feed body causes a reduction in fines entrainment by underflow, suitable for fine particles classification. In contrast, the conical feed body is advantageous for eliminating short circuiting.     

CFD Study on the Effect of Hydrocyclone Structure on the Separation Efficiency of Fine Particles

Abstract

Effects of geometric structure parameters of 10 mm-diameter hydrocyclones on the particle separation efficiency are studied using computational fluid dynamics (CFD). The fluid velocity profiles and particle trajectories are simulated using RFLOW software with a standard isotropic k-ε turbulent model. The JIS standard CaCO₃-17 particles are adopted as a particulate sample in simulations and experiments. Comparing the simulated results with experimental data, a maximum deviation about 20% in partition curves occurs for 5–10 µm particles. However, fairly good agreements for the cut-size predictions and the fish-hook phenomenon are obtained. The simulated cut-size d ₅₀ is only 2 µm larger than that measured in experiments, while the value of d ₁₀₀ can be accurately predicted. An increase in overflow diameter or a decrease in underflow diameter leads to a lower separation efficiency but a clearer separation sharpness due to lower fluid underflow rate. A short-and-wide rectangular inlet is more efficient for particle separation than a tall-and-narrow one. An inclined inlet conduit plays an inessential role on the efficiency improvement but gains a 2 µm reduction in d ₁₀₀. Comparing the simulated results, the hydrocyclone used in the experiments of this study exhibits a higher separation sharpness than the Rietema type and a higher efficiency than the Bradley type based on the same operation capacity and hydrocyclone size.     

新型入口对石膏旋流器工作性能的影响

针对火电厂石膏旋流器分级效果不理想的问题,设计具有分离块和隔板的新型入口,以改善石膏旋流器的工作性能。采用Fluent软件,应用Reynolds应力模型(RSM)与离散相模型(DPM)模拟新型入口中不同粒度颗粒的运动情况,模拟结果表明:随颗粒粒径增大,颗粒的运动半径与运动距离均增大,不同粒径颗粒在新型入口内能实现初步分级。对普通入口与新型入口石膏旋流器分别进行性能实验,获得不同工况下生产能力、出流浆液密度以及旋流器分级效率等指标参数,经比较可知,采用新型入口后,石膏旋流器底流质量浓度明显增大,10～30 μm石膏颗粒的分级效率有显著提高,最大增幅可达15%,同时,6 μm以下石膏颗粒的底流夹细现象也有一定程度的改善,但由于入口段流动阻力增大,生产能力略有下降。     

旋流器分流比对剩余污泥的释碳性能影响

基于四川省某城市污水厂处理200 t/h剩余污泥的旋流器运行情况,比较了旋流器分流比（F）对底流和溢流污泥的形貌、污泥沉降性、污泥浓度、成分变化和碳源释放的影响,探究了污泥旋流释放物质作为反硝化碳源的可行性。结果表明：污泥经过旋流器处理后,底流污泥结构变得密实;溢流污泥松散。在不同分流比条件下,底流和溢流污泥蛋白质和多糖比值（PN/PS）均增大,底流污泥体积指数（SVI）较进口均降低。但是,溢流污泥在F<30%时SVI增大,在F≥30%时SVI降低。污泥的释碳情况随分流比不同而有变化,当F=30%时,底流污泥碳源释放量达到最大。在此分流比条件下,底流污泥反硝化速率较进口污泥和溢流污泥高,底流污泥旋流释放的碳源反硝化速率达到0.81 mg/(g·h),与分析级乙酸钠碳源相当（0.82 mg/(g·h)）,高于污水厂常用的工业级乙酸钠（0.64 mg/(g·h)）和微生物复合碳源（0.66 mg/(g·h)）。污泥旋流释放的SCOD和蛋白质可补充反硝化碳源,减少外碳源投加,为污水处理厂升级改造提供技术借鉴。     

Experimental study of the relationship between separation performance and lengths of vortex finder of a novel de-foulant hydrocyclone with continuous underflow and reflux function

To solve the blockage and defer the fouling of sewage heat exchanger, a novel de-foulant hydrocyclone with continuous underflow and reflux function was proposed. Experimental results demonstrated that the novel hydrocyclone had a remarkable behavior on separating the sand (75–250 μm) and foulant (<4 mm). The continuous underflow and reflux function could significantly improve the separation efficiency by relieving the particle re-entrainment and eliminating the air core without increasing energy consumption (<17 kPa) and split ratio (<10%) considerably. Besides, the range of optimum vortex finder length was proportional to the particle density.     

多进口旋流器流场特征及分离性能

为了改善单进口旋流器稳定性差、分级效率低等问题,本文提出了多进口旋流器结构。通过数值模拟方法,在恒定入料工况下,对比分析了单、二、三、四进口旋流器的流场特征和分离性能。研究结果表明：增加旋流器进口数量,会对旋流器流场和分离性能产生积极影响,有利于旋流流场径向压力的增大,且进口数量为偶数时,流场径向静压力增强效果更好;旋流器柱段区域流场切向速度增大,有利于强化旋流器分离能力。同时使用Mixture耦合RSM模型预测了离散相CaCO₃颗粒的分离效率,结果表明多进口旋流器可以在低速度入口条件下完成离散相的高精度分离。入料速度为3m/s的工况条件下,多进口旋流器分离50μm、57.5μm颗粒的底流分配率较单进口旋流器分别提升了10.60%、5.59%,对抑制旋流器溢流产品错配率和提高分级精度有积极的影响。因此,增加旋流器进口数量,可以有效提升旋流分级效率和分离精度。     

宽域水力旋流器压力能耗模拟与分析

提出一种可同时分离重质和轻质固体颗粒物的液-固旋流器。实验研究发现该新型水力旋流器在流量为25m^3／h,分流比为6％时对重质颗粒分离效率最高;流量25m^3／h,分流比为8％时轻质颗粒分离效率最佳。利用CFX流体软件,在流量为20～35m^3／h条件下对旋流器内的静压、动压和压力降的分布进行模拟分析。结果表明：在旋流器圆柱段从上到下,动压逐渐降低,在锥体段从上到下,动压逐渐升高;在一定范围内,为进一步提高分离效率和减少旋流器内压力损失,应避免增大入口流量而适当增加分流比。     

Enhancement of Hydrocyclone Classification Efficiency for Fine Particles by Introducing a Volute Chamber with a Pre‐Sedimentation Function

A new hydrocyclone was designed with a volute chamber positioned prior to the inlet. Since the volute chamber prior to the inlet has a pre‐sedimentation function due to the centrifugal sedimentation effect, coarse particles are concentrated on the outer side and fine particles are concentrated on the inner side as the particles reach the entrance of the hydrocyclone. Consequently, coarse particles in the hydrocyclone are easily separated into the underflow and fine particles are easily transferred into the overflow. As a result, the separation or classification performance of the hydrocyclone was improved effectively. Compared with the traditional type of hydrocyclone, this new type of hydrocyclone with a volute chamber before the inlet was shown to possess a much higher classification efficiency for fine particles.     

Effect of Inlet Diameter on the Performance of a Filtering Hydrocyclone Separator

An innovative hydrocyclone was designed, in which a conical filtering wall replaces the conical section, producing another liquid stream leaving the equipment, besides underflow and overflow streams. The influence of the inlet diameter of a filtering hydrocyclone was analyzed by an experimental and computational fluid dynamics study. Data from conventional hydrocyclones of the same configurations were also obtained. Under identical operating conditions and geometry, the filtering hydrocyclone presented a better performance than the conventional device. Under the experimental conditions evaluated, an about twofold increase in inlet diameter reduces the Euler number significantly.     

除油旋流器压降比的数学模型

实验研究了直径为 35mm的除油水力旋流器能量耗散与分流比的关系 .结果发现 ,当改变溢流孔径 (分别为 4、 6、 8mm)和入口流量 (分别为 30、 40、 5 0、 6 0、 70L·min^-1)时 ,只要分流比小于 2 5 % ,旋流器的能量耗散在不同入口流量下都能保持与入口流量对应的某一常数值 .当入口流量分别为 30、 40、 5 0、 6 0、 70L·min^-1时 ,旋流器的能量耗散大约分别为 10、 30、 80、 140、 2 0 5N·m·s^-1.根据旋流器的这一特征 ,并结合理论分析 ,建立了除油水力旋流器压降比数学模型 .该模型预测计算的压降比与分流比关系曲线与实验室测定的结果能很好地吻合     

Development of a new type high-efficient inner-cone hydrocyclone

Performance of a hydrocyclone can be influenced by many factors, such as structural type, geometric parameters and operation parameters, among which the structural type plays a very important role. The separation principle of a typical hydrocyclone was introduced. Focused on a gas–liquid separation, numerical simulation of the typical hydrocyclone was carried out. The gas phase fraction distribution was analysed. It is shown that the separation effect was not satisfactory. A revising idea was thus proposed and developed step by step, so a new inner-cone hydrocyclone (ICH) was designed. The inner-cone structure was thought to provide a more stable flow field for phase separation. It functions like a gas carrier that is beneficial for radially separated gas congregating on and growing into larger gas bubbles. It also produces an upward pushing force to gas bubbles, so as to enhance the gas–liquid separation performance, although the ICH has lower inner tangential velocities than the typical hydrocyclone. Numerical simulation and experimental study verified the analysis. Pressure drop of the ICH is much lower than that of the typical hydrocyclone; and the ICH has a wider scope for the change of liquid split ratio or inlet gas–liquid ratio. Development of the ICH would provide a new thought for the design of other separators.     

液-液旋流器分流比特性系数研究

通过实验证明 :分流比特性系数的大小决定了溢流口、底流口含油浓度高低 ,影响了旋流器油水分离性能。对预分离旋流器 ,分流比特性系数的合理选择 ,尤其显得重要。     

Mechanism of Particle Separation in Small Hydrocyclone

The mechanism of particle separation in a small hydrocyclone is analyzed in this study. The separation efficiency of particles is affected by two major effects, the centrifugal and underflow effects. The fundamentals of these effects on the selectivity curve are derived from the theories of hydrodynamics. Three JIS particulate samples are separated in a 10-mm hydrocyclone. The proposed mechanism can be demonstrated by the available data. An increase in split ratio leads to an increase in the separation efficiency only for fine particles; consequently, a decrease in the separation sharpness results in a remarkable fishhook phenomenon. When the feed rate is increased by increasing the pressure drop through the hydrocyclone, the entire partial separation efficiency will be improved, but the separation sharpness and fishhook depth have no substantial varieties. The proposed mechanism can be used for explaining these phenomena, for the selection of optimum operating conditions, and for the hydrocyclone design.     

单锥脱油旋流分离器流压特性分析及预测

通过实验，研究了液—液旋流器的流量、压力和分流比之间的关系，首次建立了预测旋流器流压特性的方法。应用该方法分别预测了定流量和定底流出口背压的不同工况，其预测值和实测值的一致性是相当好的，具有相当高的精度。对旋流器的设计和使用具有重要的指导作用。     

注气对油水分离水力旋流器流场影响模拟分析

采用雷诺应力湍流模型、混合模型和离散相模型对注气型油水分离水力旋流器进行数值模拟,得到其内部流场的速度分布和油滴粒子运动轨迹,分析对比了注气前后进口流量、分流比和充气量对分离效率的影响,数值计算结果与文献实验值进行了比较。结果表明,充气后流场速度增加,油滴粒子逃逸时间缩短,旋流器分离效率提高5%~10%,在一定条件下气浮对旋流分离起到强化作用。     

水力旋流器分离细颗粒的试验研究

介绍了用于细颗粒分离的水力旋流器的基本结构形式及主要结构参数。并针对旋流器雷诺数、分流比、旋数等无因次参数对压力特性的影响进行了细致的试验研究,找出了这些参数与欧拉数和压降比的相互关系。所有试验均在不含气的条件下进行。结果表明,随着雷诺数、分流比和旋数的分别加大,水力旋流器的压力降呈增加趋势,压降比则呈下降趋势。另外,针对当量直径45μm尿素复合颗粒进行了分离特性研究。结果表明,随着雷诺数的加大,分离效率逐步提高,但并非雷诺数越大越好;对于分流比,则只在低雷诺数时有利于分离效果的改善;旋数分别为9、16和29的实验结果表明,旋数16的总体效果为最优。     

水力旋流器溢流管结构对微细颗粒分离的影响

针对直径为50 mm的小直径水力旋流器,考察了溢流管插入深度和壁厚以及进口流量对微细物料分离效率的影响,并利用正交分析法得到了溢流管最优的插入深度、壁厚及最适的进口流量。此外,考察了两种套筒式溢流管对水力旋流器分离性能的影响。最后,在最优溢流管结构的基础上,探讨了分流比对分离效率的影响。结果表明：水力旋流器的直筒段具有一定的分离作用;对于微细物料的分离,溢流管采用薄壁且插入深度与水力旋流器直筒段长度相当的设计,有利于提高微细颗粒的分离效率。针对水力旋流器溢流管插入深度与其直径的最佳比例,小直径水力旋流器的比大直径水力旋流器的大,表明它们的分离行为存在着较大的差异。     

倾斜入口流道的水力旋流器数值模拟分析

研究入口流道带倾角的水力旋流器模型,用GAMBIT软件建模并划分网格,运用FLUENT软件对其油水分离情况进行数值模拟,分析了传统直入口流道与带倾角入口流道的区别。发现倾斜入口模型压力降明显降低,有助于降低旋流管能耗。倾斜入口模型模拟中,底流处油的浓度较低,分离效果较好。     

Designing W-shaped apex for improving the separation efficiency of a full-column hydrocyclone

ABSTRACT

To improve the separation performance of hydrocyclones, a full-column hydrocyclone with a W-shaped apex structure is proposed. According to the height and width of the W structure, the hydrocyclones are divided into nine structures, A-I to C-III. To obtain an optimized underflow structure, a computational fluid dynamics-based numerical simulation is conducted to compare the performance of different hydrocyclone structures. The variations of the pressure field, velocity field, air-core shape, density field, and separation performance were investigated, and the results were compared with classical experimental data to verify the accuracy of the numerical simulations.     

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.