旋风分离器内颗粒质量浓度分布数值模拟

采用颗粒随机轨道模型和单元内颗粒源法,对旋风分离器内不同粒径颗粒质量浓度分布进行了数值模拟。结果表明,粒径较小的颗粒(dp≤4μm)大部分在旋风分离器分离空间锥段进行分离,而较大颗粒(dp>4μm)大部分在环形空间与分离空间筒段即被分离。随着颗粒粒径增加,分离器外壁的颗粒质量浓度逐渐呈螺旋灰带分布,内旋流夹带减小,环形空间顶板下方出现顶灰环。升气管入口0.25D(筒体直径)附近的短路流对小颗粒的影响较大。在分离空间下部排尘口附近0.5D有明显的颗粒返混,返混量随着颗粒粒径增大而减少。     

高入口浓度下PV型旋风分离器的分离效率计算

基于Muschelknautz 分离模型,以PV型旋风分离器为对象,针对高入口浓度的分离效率的计算,将旋风分离器分离空间的气固分离过程划分为2个区域,提出了串级分离模型。当入口浓度大于临界入口浓度时,旋风分离器内有器壁附近的颗粒支配区和中心区域的气体支配区。颗粒支配区内颗粒速度大于气体速度,颗粒夹带气体沿器壁螺旋下行进入灰斗被全部捕集,形成了颗粒的一级分离;气体支配区内气体速度大于颗粒速度,气体携带颗粒做旋转运动进行离心分离过程,形成了颗粒的二级分离。旋风分离器总的气固分离过程是一级分离和二级分离的叠加。通过高入口浓度的实验对串级分离模型进行了验证,基于串级分离模型给出的PV型旋风分离器的分离效率与实测值较吻合。研究表明旋风分离器临界入口浓度对总效率的计算影响较大。串级分离计算模型包含了结构参数和气、固相物性等参数,具有很好的通用性,可以满足PV型旋风分离器的工程计算和设计要求。     

提高旋风分离器效率的研究和探讨

1前言旋风分离器在炼油、石油化工及能源工业等方面起着越来越大的作用，应用十分广泛。旋风分离器无论是哪一种结构类型，都是从旋分器内薄弱环节入手而加以改进的新型高效旋风分离器。但是，旋分器内气固两相流动十分复杂．迄今尚无成熟的分离理论与数学模型．因而从旋分器设计技术上来提高旋风分离器的效率．目前存在着两个缺陷：①只考虑单个颗粒的运动，忽视颗粒群间的相互影响。②只考虑典型断面上的气流分布情况，而没有考虑许多薄弱环节的综合影响。为此，本文着重从旋风分离器结构上入手，通过优化各部分尺寸的匹配，采用特殊内部…     

旋风分离器顶灰环灰量的实验测量

旋风分离器进行气固分离过程中,在顶板的外侧存在一个浓度比较高的旋转顶灰环。顶灰环的存在一方面增加了颗粒向内测逃逸几率,另一方面造成了旋风分离器器壁的磨损。对于分离FCC催化剂颗粒的旋风分离器,顶灰环的旋转是不稳定的,会发生周期性的脱落,因此存在一个最大顶灰环灰量。根据旋风分离器颗粒藏量的测量方法,测量了最大顶灰环灰量与入口速度和入口浓度的关系。实验结果表明最大顶灰环灰量随入口速度和入口浓度的增加而增大。     

蜗壳式旋风分离器全空间三维时均流场的结构

采用激光多普勒测速系统（LDV）对蜗壳式旋风分离器全空间内三维湍流的时均流场进行了实验测定与分析,重点讨论了灰斗、环形空间和排气管的流场特点.分离空间内时均流场是外侧准自由涡与内侧准强制涡的典型结构.环形空间的入口部位有多个纵向二次涡,其他大部分空间顶部出现纵向二次环流,切向速度和径向速度的分布呈现非轴对称性,入口气量沿高度分布不均匀.灰斗的顶部也存在纵向二次环流.排气管内轴向速度分布与分离空间内的分布形态迥异.     

旋风分离器有无灰斗对气相流场动态特性的影响

旋风分离器底端的排尘口依据气固分离工艺的要求分别采用有灰斗或无灰斗结构。但灰斗是否存在对旋风分离器内部流场影响的研究尚显不足。为此，采用热线风速仪对排尘口有灰斗和无灰斗的旋风分离器气相流场的切向速度进行了测量。结果表明旋风分离器内旋转流具有较强的不稳定性，表现为瞬时切向的速度低频高幅值波动变化。灰斗的存在进一步导致了排尘口附近瞬时切向速度的强烈波动。通过对瞬时切向速度的频谱分析表明，有灰斗结构的旋风分离器瞬时切向速度有2个主频，分别是存在于整个空间的全空间主频和出现在锥体下端排尘口附近区域的局部主频。无灰斗结构的旋风分离器仅有1个全空间主频。全空间主频是气体旋流中心围绕旋风分离器几何中心摆动造成的，而局部主频是灰斗气体回流造成的。灰斗气体回流主频与全空间旋转流摆动的主频叠加形成了锥体下端排尘口附近区域瞬时切向速度的2个主频。     

旋风分离器内流场的非轴对称性特点

采用Fluent6.1软件提供的代数应力模型(ASM)计算了旋风分离器内的气相流场,并在此基础上讨论了流场的非轴对称特点.在旋风分离器的三维速度中,切向速度在环行空间具有明显的非轴对称分布,向下进入分离空间后很快发展为轴对称分布;轴向速度和径向速度在环行空间存在一定的非轴对称性,而到分离空间后基本上是轴对称分布了.旋风分离器内流场的这种非轴对称特点是由于切向入口的非轴对称结构产生的.     

不同数量并联微旋风分离器分离性能影响研究

为了考察不同并联旋风分离器的分离性能,运用计算流体力学(CFD)软件对由不同数量、直径为30mm的微旋风元件构成的并联分离器性能特征进行了数值研究。结果表明,当微旋风元件入口气速一致时,增加微旋风元件数量,虽然各并联分离器对5μm以下、中位粒径3.5μm颗粒的总分离效率基本相同,但对3μm以下颗粒的分级效率有所下降;组合分离器灰斗中排尘管间间距减小,微旋风元件内切向速度分布几乎不变,中心轴向速度下降,排尘管尾端气流更加紊乱;随着微旋风元件数量增加,各组合分离器微旋风元件排尘管段旋流稳定性系数S_v沿轴向逐渐增大,微旋风元件内旋流稳定性变差。     

旋流分离-颗粒床耦合气固分离装备旋流场静压分布

针对一种集旋风分离器和内置颗粒床优势于一体的新型耦合气固分离装备在无灰负荷及固定床操作条件入口环形空间、分离空间和灰斗内静压场进行研究。结果表明，静压沿周向为非对称分布，轴向为非均匀分布，径向则呈中心低两侧高分布；且存在着静压分布的降压区(0?~180?，以入口处为0?)和增压区(180?~360?)；装备中心的负压及旋流作用在轴向高度H=6.41D(D为旋风壳体内径)以下对静压的影响不再显著；内置颗粒床外壁附近存在“滞留层”，有利于提高装备的分离性能。根据实验数据给出了静压周向分布和静压轴向分布的经验公式。     

1种侧壁开缝式防磨损旋风分离器性能模拟

针对旋风分离器壁面磨损严重的问题,设计了侧壁开缝式分离器。基于流体动力学软件进行了仿真模拟,对比分析了筒体侧壁开缝对分离器内切向速度、总压力、壁面附近颗粒含量以及分离效率的影响。模拟同工程案例描述相符,结果表明,开缝不改变分离器内的流场分布趋势,壁面颗粒含量分布明显降低,总分离效率不受影响。侧壁开缝式旋风分离器在防磨损方面较普通分离器有明显优势。     

A Mathematical Model to Compare the Efficiency of Cyclones

Tangential cyclones modified to form spiral cyclones are very efficient in separating solid particles from dust laden gases. They offer a lower gas pressure drop and higher particle separation efficiency when compared to basic tangential cyclones. Their high performance is believed to be related to their special structure. A mathematical model is introduced to explain why a spiral cyclone is more efficient than a tangential one. An experimental apparatus is designed to compare both the performances of spiral and tangential cyclones and to check the effectiveness of the model equations. The experimental data were found to be consistent with the model predictions.     

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.     

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.     

Zyklonabscheider zum Trennen von Gas/Feststoff-Strömungen

Cyclone separators for separation of gas/solids flow systems . Cyclones are used for separation of particles of solids from gas flow. Although cyclones have been in industrial use for nearly a century, it is still impossible to completely calculate the flow processes involved. This contribution deals with the theory of the separation process with separation behaviour, limiting particle size, generation of twist, and pressure drop. The article describes optimization of the cyclone by aerodynamic calculations with the separation performance, energy requirement, and investment costs as parameters. The separation performance and the energy requirements of cyclones are largely determined by the mode of construction and the operating conditions. Cyclones used industrially are discussed.     

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.     

Gas flow behavior and residence time distribution in a FCC disengager vessel with different coupling configurations between two-stage separators

To deeply understand the effect of coupled configuration between two-stage separators on the gas flow behavior in fluid catalytic cracking disengager space, the gas flow field and residence time distribution in a bench-scale disengager is numerically studied on the platform of the commercial computational fluid dynamics software package, Fluent 6.1. Two conventionally used coupling configurations in refineries and a newly-designed configuration are investigated. The Reynolds stress model is applied to simulate the gas flow field and the results agree well with the experimental values measured by a smart five-hole probe. Coupled with the Reynolds stress model, a scalar transport equation is used to obtain the gas residence time distribution. It is shown that the coupling configuration between the primary and secondary cyclones has an apparent effect on the gas flow behavior. The newly-designed configuration is better to quickly discharge the gas into the secondary cyclone inlet with a maximum residence time of 0.38 s, compared to 7.72 s and 2.79 s for the two conventional configurations. The simulation results indicated that the appropriate modification of the coupling configuration can help to improve the gas flow. The knowledge of the gas flow field also help to understand the coke formation process in the disengager space.     

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.     

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。     

Effect of inlet particle arrangement on separating property of a cyclone separator

Different arrangements of particles on the inlet section exert different effects on the separation property of a cyclone separator. Sorting classifier with different heights was connected in series with a conventional cyclone, positive rotation cyclone, and reverse rotation cyclone respectively, to investigate the effect of particle arrangement on the separation property and inner flow field. Results indicate that the implementation of a sorting classifier increases the pressure drop and energy consumption of a cyclone separator. The taller the sorting classifier, the larger the flow is. The energy consumption in positive rotation cyclone is closer to that in reverse rotation cyclone. Meanwhile, the tangential velocity in inner flow field is higher and the separating property is enhanced. The reverse rotation cyclone relieves the fishhook effect, whereas the positive rotation cyclone eliminates such effect. The reverse and positive rotation cyclones demonstrate an improved separating property for particles smaller and greater than 1 μm, respectively. Moreover, the reverse rotation cyclone demonstrates superior overall separation, but the positive rotation cyclone demonstrates a greater classification effect than the reverse rotation cyclone.     

Experimental Study of a New Hydrocyclone for Multi-Density Particles Separation

Abstract

A new structure of hydrocyclone is designed to meet the demand of separating particles heavier or lighter than water simultaneously. Based on the conventional hydrocyclone, the structural modifications with a section in the middle and a volute chamber on the top of the hydrocyclone to accumulate the separated low density particles. Some factors that influence the separation efficiency of hydrocyclone were investigated in this paper. For the heavy phase, those influencing factors included the inlet flow rate and underflow split ratio. For the light one, different outlets for discharging the light phase were taken into account. The results show that there exists an optimum inlet flow rate for a series of underflow split ratios. The top outlet for separating light phase particles is better than the side outlet's.