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。     

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。     

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。     

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。     

排尘结构对导叶式旋风管内流动分布影响的数值研究

通过数值模拟的方法研究了排尘结构对装有分流型芯管导向叶片式旋风管内流场的影响规律。研究发现,随排尘口直径增加,环形空间切向速度增加,分离空间内旋流区切向速度增加,外旋流区切向速度减小,经分流型芯管侧缝流量减小;旋风管压降随排尘口直径增加而减小,排尘口直径为200mm和250mm时,旋风管能耗最低;锥体尺寸增加可有效减小灰斗区及外旋流区的能耗。     

两种旋流板分离器压降和分离性能的对比

对φ300 mm的单程和双程旋流板分离器的压降和分离效率进行了测量分析.相对于单程旋流板分离器,双程旋流板分离器的减阻幅度为12.8%.双程旋流板分离器适应的气速范围大幅度提高,穿孔气速、喷淋密度对其分离效率和带出量影响均不大,在实验气速范围内,分离效率在99.9%以上.与单程旋流板分离器相比,当穿孔气速约从10 m/s增大到17 m/s时,双程分离器的带出量下降了72.7%到96.3%.分析认为,双程旋流板分离器压降的减小和分离性能的提高是其切向速度的增大、立面上大部分区域涡环的消除及分离距离缩短综合作用的结果.     

旋风分离器结构优化实验研究

为了在降低旋风分离器压降的同时维持较高的分离效率,设计了一种新型旋风分离器。采用弧形导流板分隔进气的入口结构、渐扩型排气的出口结构、加长型的筒体和锥体的结构,有锥顶过渡段的灰斗结构,并匹配了合理的尺寸。为了验证新型分离器的性能,将新型结构的旋风分离器与基准PV型分离器进行了并联对比实验。以空气为实验介质,实验粉料为滑石粉,在入口气速为14. 2～21. 2 m/s、入口含尘浓度为0. 01 kg/m~3时,同时测量了新型分离器与PV型分离器的效率和压降。对比实验结果表明,相对于基准PV型分离器,新型旋风分离器的平均压降降低了21. 91%,且分离效率基本保持不变。     

防返混锥对旋风分离器流场影响的大涡模拟

防返混锥可用于常规旋风分离器的改造以提升分离性能。基于大涡模拟(LES),从平均流场、湍流脉动和流场稳定性等方面,系统地研究了配置防返混锥后旋风分离器全局流场的变化情况。具体结论如下:圆筒段和圆锥段的平均切向速度略有提升、中心平均轴向速度轻微上移,灰斗壁面附近的切向速度几乎不变、轴向速度有所提升,灰斗底部中心区域的切向速度和轴向速度均明显降低;防返混锥附近切向与轴向的湍流脉动轴对称性有所恶化,且局部位置脉动数值增幅较大,但灰斗底部区域的脉动得以削弱;尽管在临近防返混锥的区域内旋进涡核(PVC)摆动有所增强,但全局流域的涡核平均偏心距仍降低了近21.3%。     

组合式旋流器处理污水的数值分析

利用RNG k-ε模型计算流量分配器,确定了组合式旋流分离器的结构形式,利用雷诺应力模型(RSM)对入口切向角度不同的旋流分离器内部流场进行了分析,利用离散相模型(DPM)计算了其分离效率,利用所设计的组合式旋流分离器进行污泥浓缩实验,确定了流量分配器的结构形式,得到斜切单入口式旋流分离器入口与分配器环形管外圆周面的最佳夹角为5°,该分离器可将污水的含固率从2.7%提升至7.1%.     

Analysis of the nutation and precession of the vortex core and the influence of operating parameters in a cyclone separator

Vortices motion in the anisotropic turbulent flow of cyclones makes a vital impact on flow stability and collection performance. Nevertheless, there remains a lack of clarity in the overall feature of vortices motion. In this work, a numerical analysis was conducted to clarify the complex motion of the vortex core in a cyclone separator. The validity of the numerical model was demonstrated by comparing the computational results with experimental data in the literature. As revealed by the results, the vortex core not only has a precession motion about the geometrical center axis but also does a nutation motion in the axial direction. The frequencies of the precession motions show two main peaks. And the magnitudes of the precession and nutation motions have non-uniform distributions in the cyclone. Moreover, the precession-nutation motions of the vortex cores exhibit a similar fluctuant pattern to the dust ring on the separator wall. The inlet gas velocity and the inlet solid loading show vital effects on the magnitudes and frequencies of precession and nutation motion.     

Stereoscopic PIV studies on the swirling flow structure in a gas cyclone

Understanding the swirling flow in a gas cyclone is of great importance in improving the cyclone design. Once the three-dimensional strong swirling flow is fully understood, cyclone performance such as pressure drop and separation efficiency can be improved by optimizing the cyclone design. The swirling flow was investigated by the stereoscopic particle image velocimetry (Stereo-PIV) in this work. The instantaneous whole-field tangential, axial, and radial velocities were measured simultaneously in the cylindrical and conical separation zone, and in the dust hopper area of the cyclone with gas inlet velocity of .The time-averaged flow pattern in the cylindrical and conical sections of the cyclone showed: a typical Rankine vortex with inner quasi-forced vortex and outer quasi-free vortex which is generated by tangential gas velocity; inner upward flow and outer downward flow of axial gas velocity; and centripetal flow in the region close to the wall due to the presence of radial gas velocity. In the dust hopper, a secondary longitudinal circular flow is formed in the annulus area between the conical body and the cylindrical wall. Experimental results indicate that the separated particles may be re-entrained into the cyclone from the bin to degrade the separation efficiency of the cyclone.     

Characteristics of the collection efficiency for a double inlet cyclone with clean air

Two single inlet cyclones and a double inlet cyclone were designed and fabricated to evaluate, and compare, their collection efficiencies. Two single inlet cyclones had different inlet sizes and vortex finder diameters. The double inlet cyclone had two inlet parts that divided the cyclone inlet in two. Clean air was introduced to the inlet near the cyclone wall, and particle-laden air was introduced to the inlet away from the cyclone wall. This double inlet made the clean air swirl in the region near the vortex finder, and the particle-laden air swirl in the region close to cyclone wall. The performance of the double inlet cyclone was evaluated at various clean air flow rates, keeping the particle-laden air flow rate constant.The collection efficiency of the double inlet cyclone was found to be 5–15% greater than that of the single inlet cyclone with the same inlet size and vortex finder diameter. As the flow rate of clean air was increased, the collection efficiency increased. This result indicates the possibility of achieving higher collection efficiencies with a double inlet 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.     

Effects of the Inlet Section Angle on the Flow Field of a Cyclone

The gas flow fields of a cyclone with different inlet section angles have been studied numerically. The gas flow fields were simulated by means of the Reynolds Stress Transport Model (RSTM). The velocities and pressure drop profiles of these cyclones were investigated. The shortcut flow rates at the bottom of the vortex finder were calculated with different inlet section angles. To analyze the relationship between the inlet section angle and the vortex finder insertion deepness, this paper details the shortcut flow rates at the bottom of the vortex finder for three vortex finder insertion depths. The results indicate that the inlet section angle can decrease the shortcut flow from the bottom of the vortex finder, which has practical importance for the improvement of the separation efficiency. The inlet section angle can also decrease the pressure coefficient of a cyclone. When the inlet section angle is 45 °, the level of decrease is up to 30 %. However, the effect of the inlet section angle on the separation performance is related to the dimension of the vortex finder, i.e., the insertion depth and diameter of the vortex finder, and the effect is different when the cyclone has different vortex finder insertion depths.     

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.     

旋风分离器内颗粒运动规律的数值模拟

采用单颗粒动力学模型计算了旋风分离器内颗粒的运动轨迹。计算结果表明：进入旋风分离器的颗粒绝大多数在环形空间内就被甩向器壁；从入口上部进入的部分较小颗粒由于局部二次流作用而上升形成顶灰环；还有少量颗粒进入下部分离空间。在下部分离空间内，有灰斗返气夹带上来的颗粒，处于内旋流的颗粒则有可能随上升气流而逃逸，所以一定的分离空间高度有利用颗粒的二次再分离。     

A universal model to calculate cyclone pressure drop

The definition and composition of the pressure drop over a tangential inlet, reverse flow cyclone have been analyzed. It is assumed that two factors mainly contribute to the pressure drop, i.e., the local loss and the loss along the distance. The former includes the expansion loss at the cyclone inlet and the contraction loss at the entrance of the outlet tube (or vortex finder). The latter consists of the swirling loss resulting from friction at the cyclone walls and the dissipation of gas dynamic energy in the outlet tube. By use of the measured results of the flow field in cyclones, the calculation methods for each loss have been developed. And a universal model to predict the cyclone pressure drop is thus obtained simply by summing each loss. A detailed comparison between the calculated and experimental results shows that this accurate model is suitable either for pure or for dust laden gases at normal or high temperatures and can meet the requirement of most cyclone designs.     

不同排尘结构对导叶式旋风管内气固两相流动影响的数值研究

通过数值模拟的方法对3种不同排尘结构的导叶式旋风管内气固两相流场进行了研究。结果表明,直筒型排尘结构的排尘口处上、下行流交错容易产生返混夹带现象,对细颗粒的分离不利;锥形排尘结构可以增加旋风管内气流旋转强度,控制进入灰斗的下行气量,有利于分离效率的提高,但排尘锥内部存在环形旋涡,易磨损器壁;在排尘锥侧面开缝,可改善旋风管内流动分布状态,实现排尘区气固两相分流,进入灰斗内的气流更加稳定,从而有效减少颗粒返混夹带,提高旋风管分离性能。