Estimation of collection efficiency depended on feed particle concentration for axial flow cyclone dust collector

INTRODUCTIONCyclonedustcollectorisappliedinmanyindustries.Especiallytheaxialflowcycloneisthemostsimpleconstructionanditkeepsthehighreliabilityforthecyclonemaintenance.Thereforetheaxialflowcycloneisveryeasytoarrangewithvariouspipelinesofthepneumatictr...     

Estimations of the Maximum Tangential Velocity V_(θm) in the Vortex Core Region and also the Mean Rotational Velocity V_(oi) near the Concave Wall Surface in the Returned Flow Type Cyclone Dust Collector

There are many types of cyclone dust collectors for separating the fine solid and dust particles from gases in the various industries and also in the home used purposes. For estimating the power loss and the collection efficiency, one of the most important factors is the maximum tangential velocity Vθm in the vortex core region in the cyclone body. In order to determine Vθm by the simple method, it is useful to apply the mechanical balance of the angular momentum fluxes under the assumption of Ogawa combined vortex model which is composed of the quasi-forced vortex in the vortex core region and also the quasi-free vortex surrounded the vortex core region and also under the assumption of the introduction of equivalent length Heq corresponding to the cone spaces of the cyclone body and the dust bunker. On the other hand, the mean rotational velocity Voi near the concave wall surface is also estimated by the mechanical balance of angular momentum fluxes with the moment of viscous friction force. For confirming the general applications of the obtained equations, the returned flow types cyclones changed the throat diameter D3 are designed. The material of the cyclone is the transparent acrylic resin. Therefore the inner surface of the cyclone body can be regarded as smooth surface. The comparisons of the measured velocities Vθm and Voi by a cylindrical Pitot tube are shown in good agreement with those of the proposed equations. The above stated results are described in detail.     

Modeling the gas and particle flow inside cyclone separators

This paper reviews the models developed for the flow field inside inverse-flow cyclone separators. In a first part, traditional algebraic models and their foundations are summarized in a unified manner, including the formulae for tangential velocity and pressure drop. The immediate application to the prediction of collection efficiency is also reviewed. The approach is the classical, treating first the dilute limit (clean-gas correlations), and afterwards correcting for “mass loading” effects. Although all these methods have had a remarkable success, more advanced ideas are needed to model cyclones. This is put forward by exploring the work done on the so-called “natural” length of the cyclone, that has led to the discovery of instability and secondary flows. The resort to computational fluid dynamics (CFD) in this case is difficult, however, due to the very nature of the flow structure. A closing section on the subject reviews past and recent CFD simulations of cyclones, both single- and two-phase, steady and unsteady, aiming at delineating the state-of-the-art, present limitations and perspectives of this field of research.     

Pressure drop and collection efficiency of cyclone and impact separators in a CFB

Experimental results of pressure drop and gas–solid separation of impact separators with three rows of impact blades with included angles (60°, 90° or 120°) in a cold CFB set‐up of 102 mm×102 mm cross section are presented for two different samples of sand and they are compared with the same of a conventional reverse flow cyclone. The pressure drop increases with higher superficial velocity for all the solid separators including cyclone at a constant solid circulation rate. ‘Overall collection efficiency’ (η_oc) remains practically unaltered for the cyclone within the range of superficial velocity of the experiment while it decreases with higher superficial velocity for the impact separators. ‘Fractional collection efficiency’ (η_fc) of cyclone increases monotonically with grain size while that of the impact separator becomes minimum for an intermediate grain size. The collection efficiency of impact separator is comparable to that of cyclone for either very small or very large particles. Copyright © 1999 John Wiley & Sons, Ltd.     

Prediction of heat transfer coefficient in the cyclone separator of a CFB

This paper deals with the study of heat transfer behaviour in the cyclone separator of a circulating fluidized bed (CFB) and how it is affected by relevant operating parameters. The experiments are conducted in a 140 mm diameter cyclone of a cold bed set‐up of 102 mm×102 mm bed cross‐section, 5.25 m height CFB. The cyclone separator is designed according to the high‐efficiency Lapple design and made to accommodate two identical heat transfer probes. From the experimental results, the heat transfer coefficient is found to increase with increase in solid circulation rate, as well as gas superficial velocity. The effect of bed inventory and heat flux on heat transfer coefficient has also been investigated. An empirical equation has been developed to predict the heat transfer coefficient in the cyclone separator based on dimensional analysis. The experimental results are compared with the predicted results and a good agreement has been observed. There is an optimal distance from the entry of the cyclone where the local heat transfer coefficient is maximum. The collection efficiency of the cyclone separator has been measured for all the operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.     

Application of Mechanical Similarity Laws to the Collection Efficiencies of Geometrically Types of Uni—Flow Cyclone Dust Collectors

From the mechanical similarity point of view, the centrifugal effect, Ar, and the Stokes number, St, as well as the Reynolds number, Re_c for the motion of solid particles in the cyclone are the relevant parameters. In order to apply these similarity laws for the prediction of the characteristics of the collection efficiency, ηc, geometrically similar types of uni-flow cyclones were used. The body diameters of the cyclones were D_1=30, 50, 69 and 99 mm, respectively. The feed particle concentration of the fly-ash particles was up to C_o = 60g/m~3. From the experimental results: (1) the pressure drop, △pc, in the cyclones was a function of not only the Reynods number, Re_c, but also the body diameter, D_1; (2) the collection efficiency, η_c, did not always increase with decreasing body diameter but there existed an optimal body size; (3) application of the mechanical similarity laws to the collection efficiency was not always sufficient for estimating the collection efficiency, since the feed particle concentration was an additional important factor; (4) a new parameter which was the ratio, E_(pf), of the apparent separation energy, W_p, of the solid particles to the energy loss, E_c, of the gas flow in the cyclone was introduced for discussing the collection efficiency; (5) Fuchs theory, used to estimate the collection efficiency, was examined. Fuchs theory may be applied for high feed particle concentration.     

电晕极形式对静电旋风除尘器性能影响的实验研究

随着工业生产的迅速发展和生活水平的提高,工业设备的污染物排放（特别是大气污染物排放）日益成为国内外关注的焦点。为了提高旋风除尘器的性能,可利用高压静电技术将旋风除尘器改造成静电旋风除尘器。通过建立实验系统,对静电旋风除尘器中三种不同的电晕极布置方式进行了实验研究,并分析比较了其伏安特性以及电晕极布置方式对除尘器的除尘效率、分级除尘效率和压力损失的影响。实验结果表明,所研究电晕极中的一种不但可显著提高除尘效率,还使除尘器压力损失约降低30％,是一种新型的高效减阻电晕极,具有很大的应用和发展前景。     

A New Calculation Method of the Axial and Radial Velocity and Grade—Efficiency for High—Efficiency Cyclones

At present in China, the cyclones are widely used in the dust removal ventilation system of boilers, industry furnaces or pits etc., because of their simple structure, long life and cost efficiency. In order to improve efficiency of the cyclones, new theoretical calculation method is very important. In this paper, the concept of down-flow quantity is introduced and new formula is deducted based on Kilven law and the work has done by Zhao Weizhong^[1]. The formula is not only of advantage theoretically but also fit with experimental results quite well. On the basis, the effect of three-dimensional velocity distribution in the flow field within cyclones and other parameters on the grade-efficiency calculation are analyzed and a new equation for grade-efficiency estimation is introduced. The calculating accuracy of the equation is better than the others theoretically and experimentally.     

Experimental study on structural optimization of a supercritical circulating fluidized bed boiler with an annular furnace and six cyclones

Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was carried out in the cold-test rig of an annular furnace CFB with six cyclones. The influence of furnace structure and cyclone arrangement on the non-uniformity of gas-solid flow was obtained. On the basis of these findings, the structure of the annular furnace CFB with six cyclones was optimized, and an optimal structure was obtained. The results show that for newly designed annular furnace CFBs, the non-uniformity of gas-solid flow among loops is no greater than that of traditional CFBs. In terms of uniformity, side cyclones rotating inward are superior to those rotating outward. The position of the side cyclones determines the basic solid circulating rate distribution trend and can dramatically improve flow non-uniformity. The middle cyclone positions and the symmetric modes of the cyclones do not determine the solid circulating rate distribution trend and have less effect on DEVGs. Forty-five degree chamfers of outer ring walls can reduce wall erosion and the non-uniformity of gas-solid flow in the circulating fluidized bed. Regarding the operating and structural conditions in this work, the optimal structure of annular furnace CFBs is Type 6: side cyclones rotating inward and b = a/2, d = 0.1c; the center of the middle cyclone inlet located at the centerline of the furnace cross-section; cyclones on the two sides of the furnace in an axisymmetric arrangement; and a furnace corner shape of 45° chamfers. Under the given operating conditions, the DEV_(Gs) for the optimal structure are approximately 4.0%~10.3%.     

带加速段的卧式旋风分离器的数值模拟及工业应用

带加速段的卧式旋风分离器具有体积小、结构简单、造价低、分离效率高等优点,为了解其工作机理,应用Fluent软件,采用雷诺应力模型模拟气相流动、离散相模型模拟颗粒运动轨迹,同时计算并给出了加速段出口速度为25.46 m/s时,粒径为1μm、5μm、10μm和30μm的颗粒运动轨迹,结果表明该分离器对细小颗粒具有一定的分离效率,与实验吻合良好。最后应用Fluent软件对实际应用的卧式旋风分离器进行了数值模拟,在不考虑物料循环的条件下,该分离器分离效率为85.8%,分离效率较高。     

Control of Collection Efficiency for Axial Flow Cyclone Dust Collectors with Fixed Guide Vanes and with Funnel Shaped Exit Pipes

The experimental result of the collection efficiency of the axial flow cyclone with the fixed guide vanes is lowerthan that with the tangential inlet pipe to the cyclone body due to the weak angular momentum transfer given byflowing through the guide vanes.However,one of the interesting points is the control of the collection efficiencydepended on the funnel shaped exit pipes.The collection efficiencies for these funnel shaped exit pipes aredepended on the Froude number.Then,in this paper,the experimental results of the pressure drop and also thecollection efficiency using the fly-ash particles and also the comparison of the calculated results of the collectionefficiency with the experimental results are described in detail.     

高频脉冲电源除尘器的节能效果与除尘效率分析

叙述了高频电源的原理、特点以及上海能源大屯发电厂1号、2号机组高频脉冲电源除尘器的节能效果和除尘效率,指出,高频脉冲电源除尘器比工频供电的电除尘器节能效果显著,除尘效率也大幅提高.     

循环流化床锅炉旋风分离器选型的几个问题

文中论述了循环流化床锅炉旋风分离器的分离效率对锅炉性能的重要影响,探讨影响分离效率的一些因素,并就几种不同形式的旋风分离器作了比较。     

不同排尘结构旋风分离器的分离特性

在欧拉-拉格朗日坐标系中对常规旋风分离器和两个不同直管长度旋风分离器内气固流动特性进行了数值模拟．模拟时气相场采用雷诺应力输运模型,应用随机轨道模型模拟湍流流场中颗粒的运动轨迹,并考虑气固两相之间的双向耦合．给出了不同排尘结构旋风分离器的速度、湍动能分布．对不同排尘结构旋风分离器的分离性能进行了实验研究．结果表明,底部加延长的直管可以使灰斗中气流的速度和湍动能得到较大衰减,能有效防止已分离颗粒的二次扬尘．直管内仍具有一定的分离能力,分级效率实验表明,加直管后旋风分离器分级效率有一定的提高．对于给定的旋风分离器,直管长度应有一最优值．     

端盖与旋流子对轴流旋风分离器的性能影响

为了研究轴流旋风分离器性能的结构影响因素,采用Fluent软件对装有不同内径端盖和不同种类旋流子的旋风分离器的流场进行了数值模拟,同时用Fluent中的DPM模型分析了不同尺寸及种类的旋风分离器对水颗粒的分离效果。结果表明：较小的端盖内径可以提高旋风分离器的分离效率,但是带来更大的阻力;旋流子叶片的螺旋角度是影响分离效率的主要因素,螺旋角度越大则分离效率越高,但是阻力也会随之增加;叶片数量不是影响阻力的主要因素。     

Three‐dimensional computational comparison of mini‐pinned heat sinks using different nanofluids: Part two—energy and exergy characteristics

The energy and exergy characteristics of 3D‐pinned heat sink (HS) designs have been computationally compared as the second part of a three‐part investigation. Different pin profiles, such as circular, square, triangular, strip and elliptic pins, and without pin HS are conducted with three different types of nanofluids—Al₂O₃‐water, SiO₂‐water, and CuO‐water for laminar forced convection. The concentrations of nanofluids vary from 0 to 5 vol% with different Reynolds numbers ranging between 100 and 1000. The finite volume method employing the SIMPLE algorithm for a computational solution is applied to solve the Navier–Stokes and energy equations. Four criterions studies are explained—energy efficiency, exergy loss, and exergy efficiency of HSs with pressure drop. The results showed that the highest energy and exergy efficiencies are nearly 76% and 57%, respectively, for elliptic‐pinned HSs using pure water, while about 82% and 62% using 5 vol% of SiO₂‐water nanofluids. Besides, the elliptic‐pinned HSs have a favorable reduction in the exergy loss, nearly 17% using 5 vol% of SiO₂‐water nanofluids. Subsequently, the elliptic‐pinned HS is recommended to apply with pure water considering the development in pressure drop required. However, the elliptic‐pinned HSs could be employed with 5 vol% of SiO₂‐water nanofluids regardless of the development in pressure drop required for thermal energy dissipation applications with more exergy efficiency and reduction of exergy loss.     

Effect of turbulence on flame propagation in cornstarch dust-air mixtures

Following the quantitative determination of dust cloud parameters, this study investigated the flame propagation through cornstarch dust clouds in a vertical duct of 780 mm height and 160×160 mm square cross section, and gave particular attention to the effect of turbulence on flame characteristics. The turbulence induced by dust dispersion process was measured using a particle image velocimetry (PIV) system. Upward propagating dust flames were visualized with direct light and shadow photography. The results show that a critical value of the turbulence intensity can be specified below which laminar flame propagation would be established. This transition condition is about 10 cm/s. The measured propagation speed of laminar flames appears to be in the range of 0.45–0.56 m/s, consistent with the measurements reported in the literature. For the present experimental conditions, the flame speed is little sensitive to the variations in dust concentration. Some information on the flame structure was revealed from the shadow records, showing the typical heterogeneous feature of dust combustion process.      

细微尘粒的预团聚对旋风分离器高温除尘性能影响的实验研究

通过理论分析和实验研究了细微尘粒的预团聚对旋风分离高温除尘性能的影响规律,得到了一个新的启示,即利用细微尘粒在高温状态下的预团聚现象可提高旋风分离器的高温除尘效率。文中的实验证明了这一点。     

方形分离器结构优化试验研究

在冷态试验台上对特征尺寸D=300 mm的入口带加速段的方形分离器进行结构优化研究。结果表明:分离效率随着芯筒直径(d)、芯筒插入深度(s)的增大均呈先增大后减小的趋势;入口高宽比(a/b)与直段高度(h)对分离效率的影响存在交互作用;随着a/b的增大,分离效率先增大后减小;不同入口高宽比时,分离效率随直段高度的变化趋势不同,当a/b>5.92时,随着直段高度的增大,分离效率先减小后增大,在h/D=2.3时最低;当a/b<5.92时,分离效率随着直段高度的增大而减小;分离器阻力随着入口高宽比的增大而增大,随着直段高度的增大而减小。4个参数的最优值分别为:d=0.4D、s=0.6D、a/b=8和h=1.8D,此时对应的分离器阻力为1.22 kPa。     

Effects of vortex finder length on flow field and collection efficiency of cyclone in an industrial-scale circulating fluidized bed boiler: Numerical study

Cyclone separators are key components of circulating fluidized bed (CFB) boilers. The factors that can affect the cyclone performance include body diameter, total height of the cyclone, and diameter and length of the vortex finder (VF). In this study, the effect of the VF length on the cyclone performance in a 340-MWe CFB boiler operated by Korea South-East Power Corporation was analyzed using computational fluid dynamics. A dense discrete phase model with kinetic theory of granular flow approach was employed for modeling the interactions of sand with a gas phase. As the VF length decreased, the unexpected short-circuit flow around the VF reduced the pressure difference between the center and the cyclone wall. This reduced the swirl intensity, decreasing the natural vortex length. As the VF length increased, the short-circuit flow decreased, along with the pressure difference and swirl intensity, reducing the natural vortex length. Thus, increasing the VF length beyond a certain value is not recommended, and there is an optimum VF length for maximizing the cyclone collection efficiency.