Comparing Efficiency per Volume of Uniflow Cyclones and Standard Cyclones

A competitive alternative to the standard reverse flow cyclone for gas-solids separation is the uniflow cyclone. Gas and particles passing through it in only one direction, allowing a cost-effective usage in space limited applications. Comprehensive studies of uniflow cyclones have strongly improved their understanding and led to approved design criteria and calculation methods. Here it is shown that uniflow cyclones can achieve higher efficiencies per volume with a low pressure drop than standard cyclones.     

Development of a new high‐efficiency simple structure cyclone

A novel uniflow cyclone design was evaluated using three prototype cyclones. For the first two, the efficiency and Euler number were determined using airborne solid particles with a number mean diameter of 12.5 µm. Then a larger scale prototype based on the optimized geometry was compared with an existing conventional high efficiency cyclone and a vane‐induced uniflow cyclone, using mineral oil droplets with a number mean diameter of 8.9 µm. Both sets of experiments showed that the newly designed cyclone had a higher efficiency at a higher pressure requirement, in addition to the feature of a small footprint.     

直流多管式旋流分离器的分离性能实验研究

设计了一种直流多管式旋流分离器,并对其进行了性能实验和结构改进。结果表明,直流多管式旋流器整体的阻力系数相对较小,约50左右;气液分离效率随流量和含液浓度的增大皆呈现明显的增大趋势,说明影响分离器效率的主要因素是离心力场的强弱和细小颗粒的逃逸,其在较高流量下分离效率可达90%左右。在原分离器的基础上在排气室内加了丝网聚结器,阻力特性变化很小,增加了对细小颗粒的聚结分离能力,分离效率提高了5%～10%。     

导叶式直流旋风分离器的研究与应用现状

与传统的逆流反转式旋风分离器相比,直流旋风分离器具有压降低的特点,在节能方面具有很大的优势,正逐渐引起研究者们的重视。通过对国内外资料的调研,对导叶式直流旋风分离器的研究和应用情况进行了综述,并对其结构和性能的改进提出了展望。     

Effects of separation space diameter on the performance of a novel reverse flow cyclone

ABSTRACT

A numerical study was carried out to investigate the effect of separation space diameter on the performance of a novel reverse flow tangential inlet cyclone design by using the Eulerian-Lagrangian approach. The design of this cyclone is based on the idea of increasing vortex length and decreasing pressure drop compared with traditional cyclones. This novel cyclone differs from the traditional cyclones with separation space and vortex limiter instead of the conical part. A qualitative numerical study was performed to analyze the effect of separation space diameter on the cyclone performance at different flow rates by evaluating velocity profile, pressure drop, fractional and overall efficiencies. The results show that the collection efficiency of smaller particles increases while pressure drop decreases significantly with the increase in separation space diameter for D₁/D < 0.5.     

An Extended Model for Determining the Separation Performance of a Cyclone

Most models on the working of cyclones are based on cylinders and cones whereby the vertical tube and dustbin should also be included in their geometries. These separation models of conventional cylinder‐on‐cone cyclones do not consider the effect of the dust collection system on the flow field. In actual fact, the inclusion of the dust collection system had a considerable effect on the flow pattern in the gas cyclone as well as on the separation efficiency. In this paper, an extended model is presented, which is based on the time‐of‐flight approach. In this model, the gas residence time is modified so that the entire cyclone geometry is used. The lift force of a particle in the boundary layer is considered because of the larger velocity gradient here. The availability of the extended model is verified by comparison of the calculated grade efficiency with experimental data and theoretical counterparts in the literature.     

一种新型旁路式直流旋风分离器的性能研究

针对传统的直流旋风分离器分离效率低的问题,提出了一种新型旁路式直流旋风分离器。通过模型试验,对比分析了传统的、旁路式和带稳流器的旁路式等三种直流旋风分离器的性能。结果表明,采用旁路和稳流器可显著提高直流旋风分离器的分离效率。进而又通过数值模拟的方法,研究了其内部流场,分析了旁路和稳流器提高直流旋风分离器效率的流体力学机理。     

Study of the gas circulation patterns in a uniflow cyclone

A uniflow cyclone is being studied to achieve the separation of hot solids from the gaseous products of ultra-rapid fluidized (URF) processes. An experimental method with hot wire probes was developed to study the gas flow around the gas outlet, where the solids exit. The vortex penetration in the solids exit could be determined. The presence of solids greatly reduced the vortex penetration in the uniflow cyclone. Restricting gas circulation around the gas outlet dramatically impaired the cyclone collection efficiency. Therefore, good cyclone performance requires a proper design below the gas outlet.     

An analytical model for the fractional efficiency of a uniflow cyclone with a tangential inlet

An analytical model was developed to predict the fractional efficiency of a uniflow cyclone with a tangential inlet. The analysis showed that the separation efficiency is a function of particle Stokes number and the geometry of the cyclone body. Six sets of experiments were conducted under different conditions to validate the model. The experimental fractional efficiencies were determined by the total mass efficiency and the corresponding size distributions measured by using an offline particle sizer. Overall the experiments agreed with the modeling results well. Both model and experiments showed that the efficiency of this cyclone reached 99.5% and above when Stk > 1.0.     

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.     

Mathematical modelling of a hydrocyclone for the down-hole oil–water separation (DOWS)

In this study, a mathematical model is developed to predict the efficiency of a down-hole oil–water separation hydrocyclone. In the proposed model, the separation efficiency is determined based on droplet trajectory of a single oil droplet through the continuous-phase. The droplet trajectory model is developed using a Lagrangian approach in which single droplets are traced in the continuous-phase. The droplet trajectory model uses the swirling flow of the continuous-phase to trace the oil droplets. By applying the droplet trajectory, a trial and error approach is used to determine the size of the oil droplet that reaches the reverse flow region, where they can be separated. The required input for the proposed model is hydrocyclone geometry, fluid properties, inlet droplet size distribution and operational conditions at the down hole. The model is capable of predicting the hydrocyclone hydrodynamic flow field, namely, the axial, tangential and radial velocity distributions of the continuous-phase. The model was then applied for some case studies from the field tested DOWS systems which exist in the literature. The results show that the proposed model can predict well the split ratio and separation efficiency of the hydrocyclone. Moreover, the results of the proposed model can be used as a preliminary evaluation for installing a down-hole oil–water separation hydrocyclone system in a producing well.     

Effect of the Solid Loading on a PFBC Cyclone with Pneumatic Extraction of Solids

This paper presents the effects of solid loading on the performance of a cyclone with pneumatic extraction of solids. The cyclone is a non‐conventional design, especially used for hot‐gas cleaning applications such as pressurized fluidized bed combustors (PFBC). A scaled‐down cold‐flow model was employed for the research. Experiments were conducted at 9–14 m/s inlet gas velocities, inlet solid loadings ranging from 30 to 230 g/kg gas, and bottom gas extraction percentages from 0.3 to 1.5%. Experimental results of pressure drop resistance coefficients and collection efficiency were compared with literature predictions. At PFBC operating conditions, cyclone geometry and solid concentration are the main parameters influencing cyclone pressure drop and collection efficiency. The vortex penetration in dipleg causes lower pressure drop values and higher collection efficiencies than predicted. These parameters can be suitably predicted for PFBC cyclones by introducing a modified penetration length in Muschelknautz's model [1]. For the present cyclone design, a new correlation of pressure drop, including the influence of solid loading, is proposed. A new method for detecting cyclone fouling, not previously addressed, is also presented, based on the evolution of the pressure drop resistance coefficient. An enhanced separation efficiency has been found, related to collection efficiency, which is especially important for particle sizes below 10 μm revealing agglomeration effects.     

含油水处理用水力旋流器供液动力结构形式研究

为了适应各种小型、可移动水力旋流器的油水分离需要 ,从优选其结构方案的布置设计、改善其分离形式、增加其流场旋流强度、提高其分离效率入手 ,着重对其入口旋流供液动力结构及出液口处油水分离形式作以改进。通过大量研究发现所研制的水力旋流器有很好的分离性能。     

环流式旋风除尘器内颗粒运动的数值模拟

采用CFD软件Fluent提供的雷诺应力模型（RSM）和随机轨道模型,对环流式旋风除尘器内颗粒运动轨迹进行了数值模拟研究。预测了不同粒径颗粒的运动轨迹和分离效率。结果表明：颗粒在环流式旋风除尘器内的运动路径比常规除尘器长;特殊的流路设计,避免了常规旋风除尘器易产生的上灰环和颗粒短路问题,使除尘效率大幅度提高;除尘器内颗粒运动有较强的随机性,尤其对于小颗粒,受气流湍动影响显著。对不同粒径颗粒分离效率的预测表明：环流式旋风除尘器的分割粒径为1．25μm。     

The Effect Of the dust collection system on the flowpattern and separation efficiency of a gas cyclone

The influence of the presence of a hopper section, consisting of a dust hopper and swirl attenuator, under gas–solid cyclones has been investigated by numerical simulation. Inclusion of this configuration in the simulations was found to have a significant influence on both flowpattern and separation efficiency. Moreover, predicted axial gas velocity profiles agreed better with independent experimental measurements. The cyclone separation was predicted to be better with the hopper section included than without, a physical reason is proposed. Comparison of simulated grade-efficiency curves with experimental data indicates improved agreement, in some cases substantially so.     

Extended cyclone theory for gas flows with high solids concentrations

Large recirculation cyclones with high concentrations of particulate solids have gained considerable importance in the field of circulating fluidized bed technology. To calculate a combustion process, the influence of the cyclone on the circulating quantity of solids and their grain size distribution must be known. Measurements in a 105-MW-plant in 1989 showed that the existing cyclone theory was not sufficient for this purpose. In a laboratory cyclone (900 mm in diameter), the separation and classification of solids in a gas flow was investigated. The cyclone was fed from a fluidized bed and operated with cold air and quartz of various grain size distributions. Based on this experimental device and the theory of momentum transfer between solids and gas flow, a new, more accurate method of calculating the separation efficiency was developed.     

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.     

Collection efficiencies of various designs of post‐cyclone

Post‐cyclone (PoC) is a novel secondary dust separator, which collects a certain fraction of the particles escaping through the vortex finder of a reverse flow cyclone. Due to the residual swirl in the vortex finder, the particles in the effluent air are concentrated at the wall of the vortex finder in an outer annulus. The particles in the outer annulus are split from the main stream and collected in a bleed flow. This paper presents the experimentally determined collection efficiencies of various designs of PoC. Depending on the design, operating conditions and the size and density of the particles, PoC can reduce the emission of the parent cyclones by 5% to 50%. In some experiments, the bleed flow from PoC is recycled back to the inlet of the cyclone. Significant improvement in the removal of fines occurs when the bleed flow is recycled to the inlet.     

Investigation on Separation Efficiency in Supersonic Separator with Gas-Droplet Flow Based on DPM Approach

Supersonic separator is a new technology based on the adiabatic expansion of swirling gas flow, and at present it has demonstrated great application potential in separating and processing droplet liquid contained in natural gas. However, its coefficient of performance is still low and there seems to be a large gap in the method that evaluates the separation efficiency in a satisfactory manner. In order to promote the wide application of this technology in the dehydration field, it is necessary to find a new and feasible approach that can be used to predict the flow characteristic and separation performance inside a supersonic separator. In this paper, a comprehensive three-dimensional fluid numerical model to study the flow behavior and separation efficiency in a supersonic separator was established coupled with the discrete particle model (DPM). The mixture of air and water droplets was chosen as working fluid. The gas phase was modeled with compressible Navier–Stokes equations for two-phase flow and the RSM turbulence model was taken into account. The droplet phase was modeled with the discrete particle model (DPM), in which the droplets are assumed to have the same sphere shape and ignore the phase transition and nucleation process. A pilot test facility was carried out to validate the numerical model. The experimental results not only indicate that the new dehydration device can efficiently separate the liquid droplets from wet gas, but also prove that the numerical results were great agreements with the experimental results. Furthermore, based on the proposed numerical approach, the gas-droplet turbulent flow structures were predicted, the effects of different structure parameters and operation conditions on the separation efficiency were also investigated. The current works settle a foundation for further explorations on the supersonic gas–liquid separation flows inside a supersonic separator as well as the possible new applications.     

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。