直切式旋风分离器内非主流流动的研究

讨论了直切式分离器环形空间及排尘口附近二次涡流的非对称性及其形成原因,并研究了分离器处理量对二次流的影响关系。研究发现,随着分离器处理量的增加,芯管下口短路流量增加,无量纲短路流量保持不变,即短路流亦存在"自模化";排尘口附近的湍流强度随分离器处理量的增加而增强。     

Effects of Surface Roughness on the Performance of Tangential Inlet Cyclone Separators

This study is carried out to investigate the effects of surface roughness on the flow field and cyclone performance. The flow inside the cyclone separator is modeled as a three-dimensional turbulent continuous gas flow with solid particles as a discrete phase. The continuous gas flow is predicted by solving the governing equations by using the Reynolds Stress turbulence model, and the modeling of the particle motions is based on a Lagrangian approach. The results of the numerical simulations are compared with experimental data as well as with the results of mathematical models. Analysis of computed results shows that increase of relative roughness due to corrosion, wear, or accumulation of particles on the inner walls considerably influences the tangential velocity, cyclone separation efficiency, and cyclone pressure drop especially for high inlet velocities. Decreases in cyclone collection efficiency and pressure drop with the increase in surface roughness are found to be more pronounced for high values of relative roughness.     

A Theoretical Approach to Pressure Drop across Cyclone Separators

Based on investigation of the flow pattern in cyclone separators, a new theoretical model was developed for the prediction of pressure drop across cyclone separators. This model includes the effect of the geometrical dimensions and flow parameters, and assumes that the total pressure drop consists of four main partial pressure drops due to gas expansion at the separator entrance, wall friction within the separator, swirling motion of the gas, and gas flow through the outlet pipe. The availability of the method is verified by the comparison of calculated values with experimental data and with other models for different dimensions of cyclones.     

An Improved Cyclone Pressure Drop Model at High Inlet Solid Concentrations

Calculating the cyclone pressure drop, Δp_c, at a high inlet solid concentration, C_s,in, is important for the design and operation of circulating fluidized bed boilers. Three typical Δp_c models that consider the effect of C_s,in were selected and assessed. Compared with experimental results, it was found that only the model developed by Chen and Shi can correctly predict the variation trend of Δp_c with C_s,in at high values of C_s,in, but the predicted values are much greater than the measured values. It is suggested that the dissipative loss of swirling dynamic pressure should be excluded from the total dissipative loss of gas dynamic energy when the pressure tap is closely installed to the outlet and the swirl exponent could be assumed to be null for high C_s,in conditions. A set of equations modified from the original C‐S model is given. Compared with the experimental data obtained from the present study and some data from literature, the improved C‐S model can predict Δp_c at high C_s,in well. In addition, it was found that the correction of pressure tap position is more obvious than the correction of swirl exponent.     

蜗壳式旋风分离器减阻实验研究

根据蜗壳式旋风分离器环形空间流场研究结果,在分离器排气管特定位置上加装减阻片。加装直片减阻片后,最大减阻幅度达59%,但由于减阻片对环形空间内的切向速度影响较大,分离效率下降约5%,综合效率因子降低了2.2%;在排气管外壁周向270o处加装改进型减阻片对切向速度的影响较小,同时可以大幅度提高分离器中心部分的静压,从而可使分离器压降降低22%,效率仅下降0.3%,综合效率因子提高25%。     

不同形式导流板对旋风器性能影响的试验研究

通过对加设不同形式导流板的旋风器进行试验研究,结果表明:不同形式导流板均不同程度地降低了旋风器阻力,同时也对分离效率产生了不同的影响.其中3#、4#导流板降阻幅度较大,但分离效率相对较低;2#的降阻效果强于1#,但弱于3#、4#,同时并没有降低分离效率;1#导流板只在一定限制条件内有减阻效果,其总体分离效率却比较高.     

切流式三旋单管内固相颗粒运动规律的数值研究

采用商用软件Fluent 6.3,利用随机轨道模型对切流式三旋单管内固相颗粒运动轨迹进行了数值模拟,结果表明颗粒运动轨迹随机性较大,对气流的跟随性较好,受湍流脉动的影响较大。颗粒在单管内的逃逸与捕集运动规律的统计结果表明:不大于5μm的颗粒主要在排气管底部和分离筒体发生逃逸,随着粒径的增加,颗粒的分离效率增加,在排气管底部和分离筒体上部逃逸比重增加,而在分离筒体中底部颗粒的逃逸比重减少。总结来说,排气管短路流、分离筒体内旋流夹带逃逸是影响切流式三旋分离性能的主要原因,可以从这些方面进行三旋分离性能的优化与改进。     

直切式旋风分离器内气相流场的实验研究和数值分析

采用实验测量与数值模拟相结合的方法对直切式旋风分离器内气相流动的三维流场进行了研究。雷诺应力湍流模型对流场的计算与五孔球探针的测量结果基本相符。实验测量与数值模拟的研究结果表明,环形空间的流场呈现明显的非轴对称性,切向速度在0°方位最大,在300°方位最小;分离空间基本呈轴对称性,流场稳定,有利于颗粒分离;排气管内仍存在较强的旋转,产生较大的能耗。     

双入口直切式旋风分离器流场内旋进涡核现象的研究

主要研究了双入口直切式旋风分离器流场中的一种涡核非稳态现象———旋进涡核。实验表明 ,旋进涡核存在于分离器排尘口下部及锥体中下部 ,在排尘口处涡核摆动最强烈 ,同时涡核的摆动在一定操作参数下具有一定的频率和幅值 ,因此势必会造成粉尘的夹带返混 ,致使分离器效率降低。与单入口旋风分离器相比 ,双入口直切式旋风分离器内旋进涡核频率降低 ,幅值减小 ,但范围不变。说明入口形式是否轴对称对旋进涡核的存在与否不起主要作用     

旋风分离器入口结构改进及其对“短路流量”的影响

常规切向进口旋风分离器的气流进入旋风分离器后必定要经过排气芯管外壁和筒体内壁之间,因此不可避免会使得相当一部分气流没有经过分离空间而直接从排气芯管底部排出(短路流量),这也是影响旋风分离器分离效率的重要因素之一。在前人工作的基础上,对旋风分离器的进口结构进行了改进:使得旋风分离器的入口具有一定截面角,并借助数值计算技术,分别对传统的和具有一定入口截面角旋风分离器内的三维流场进行了数值模拟,计算了芯管底部的"短路流量",结果表明:进口具有一定截面角可以明显减小芯管底部的"短路流量",这对改善旋风分离器的分离效率具有重要的实际意义。     

旋风分离器结构优化试验

旋风分离器在石油化工和天然气集输领域应用十分广泛,利用化工方面的经验,通过大量的性能对比实验来对旋风分离分离效率进行优化,首先对分离单管按原设计尺寸进行对次重复对比标定实验,然后以此为基础进行改进单管的研制实验,针对加灰斗和4种不同的灰斗开缝结构展开试验,优选出一种在分离效率、压降两方面都具有优势的最佳结构,试验表明KD结构最优。     

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.     

排尘锥结构对旋风分离器内气固两相分离性能影响的研究

通过数值模拟的方法,采用RSM湍流模型对直切式旋风分离器三种不同排尘锥结构(排尘锥无缝、开对称缝、开阶梯缝)下的气固两相流场进行了研究。研究表明,三种排尘锥结构都可以将粒径大于8μm的返混颗粒再次分离下来;排尘锥开缝起到分流作用,有效改善排尘锥内气相流场分布,降低压降,便于返混颗粒从侧缝排出,提高抗返混能力,减少颗粒在排尘锥内部长时间停滞的机率,减小堵塞下口的可能性;排尘锥开阶梯缝可以减小涡核中心不对称性,明显提高侧缝的排尘能力,有效消弱返混夹带对3μm小颗粒的影响,提高分离器的操作弹性,减少颗粒间的磨损,为排尘锥结构的进一步优化、提高旋风管分离性能提供依据。     

Investigation of Energy Loss Mechanisms in Cyclone Separators

Based on the transient Navier‐Stokes equation of an incompressible Newtonian fluid, a vorticity form of the mean mechanical energy equation is derived which is suitable for strongly swirling flow or vortex flow, and reveals the mechanism of mean mechanical energy losses in cyclone separators. Results show that the mean mechanical energy losses in cyclone separators are mainly caused by mean viscous dissipation, turbulent diffusion, and turbulent energy production in a steady turbulent flow. Order‐of‐magnitude analysis indicates that the rate of local turbulent energy production and mean viscous dissipation is related to the local turbulent Reynolds number at each point in cyclone separators. A large local turbulent Reynolds number designates the turbulent energy production as the primary contributor to mean mechanical energy losses, whereas in the case of a small turbulent Reynolds number the order‐of‐magnitude quotient between the two quantities decreases, indicating the increased significance of the mean viscous dissipation contribution to mean mechanical energy losses. A combination of theoretical analysis and LDV experimental results indicates the mean viscous dissipation is larger in the quasi‐forced vortex region and the boundary layer than in other regions of cyclone separators. The energy losses are mainly caused by turbulent energy production in a majority of the regions (except in the laminar sublayer very close to the wall), especially the largest energy losses in the central quasi‐forced vortex region. Hence, decreasing turbulence is an effective approach for drag reduction in cyclone separators.     

Determining Cyclone Particle Holdup by Pressure Drop for a CFB Boiler

An experimental study was conducted to assess the possibility of determining particle holdup by measuring the pressure drop of a conventional cyclone used in a circulating fluidized bed (CFB) boiler. It was found that within a wide range of inlet solid concentrations, i.e., 0.54–4.42 kg/kg‐gas, the cyclone pressure drop increased linearly with inlet solid concentration at a given gas velocity, while the pressure drop between the dust exit and the vortex finder of the cyclone remained almost constant. Since particle holdup increases virtually linearly with solid flow rate, the particle holdup in the cyclone can be derived from the cyclone pressure drop, and therefore, an equation set was proposed to calculate the particle holdup from the cyclone pressure drop.     

循环旋风分离器内流场的数值模拟

采用CFD模拟软件Fluent6．2提供的雷诺应力模型（RSM）对循环旋风分离器内的流场进行了数值模拟研究,并与实验结果进行了比较,模拟结果与实验结果基本吻合。结果表明,循环旋风分离器特殊的流路设计,提高了内部流场的对称性,规整了气流,减少了紊流的产生,降低了设备的压降。时局部涡的分析,为进一步了解循环旋风分离器的分离机制和优化结构提供了参考依据。     

旋风分离器速度分布指数及压降计算通用模型

建立了计算旋风分离器压降及速度分布指数的通用计算式。只需根据不同结构旋风分离器的进出口结构,确定相应的阻力系数及进口速度校正值,即可进行压降及速度分布指数计算。对常用的一些旋风分离器的计算对比表明,本模型优于其它计算式。     

旋风分离器料腿漏风对压降影响的实验分析

以直径300 mm的旋风分离器为实验对象,考察了在不同入口速度下料腿漏风量对旋风分离器压降的影响,并以此为基础,分析了某现场催化裂化装置旋风分离器压降出现的不稳定波动现象。实验结果表明,旋风分离器下部料腿是一个负压差立管,外部的压力大于料腿内的压力,易产生漏风,从而导致旋风分离器的压降降低。旋风分离器的压降随漏风量增大而降低,入口速度越低漏风量影响的作用就越明显。该旋风分离器的压降波动是由于不稳定的翼阀排料产生的漏风变化造成的。     

丙烯腈反应器国产旋风分离器的性能及工业应用

介绍了丙烯腈反应器国产三级、新型两级旋风分离器的设计思想、性能水平以及推广应用情况。丙烯腈反应器国产旋风分离器操作弹性大 ,稳定性好 ,压降小于 7kPa ,吨丙烯腈催化剂损耗低于0 .4kg ,可以满足丙烯腈生产的要求。新型两级旋风分离器还可满足现有装置扩能改造的要求     

Effect of a Stick on the Flow Field in a Cyclone and the Pressure Drop Reduction Mechanism

Measurements of the flow field in a cyclone separator with and without a reducing pressure drop stick (Repds) showed that the Repds reduces the peak tangential velocity, the axial velocity gradient, and the radial gradients of static and total pressure and reverses the axial static pressure gradient. These changes reduce the energy consumed by the rotating kinetic energy, the internal friction, the turbulent kinetic energy, and the drag of the negative pressure difference. The results are used to discuss why the separation efficiency remains high while the pressure drop is reduced. The results also show that a 24% "short flow" occurs near the cyclone entrance. Analysis of the changes in the flow field and the pressure drop due to the thin stick shows that the Repds increases the pressure drop in the outer vortex zone and reduces the pressure drop in the inner vortex zone. Therefore the pressure drop reduction with the Repds is due to its wake vortex, which leads to the hypothesis that the pressure drop in turbulent flow can be reduced by adding vortexes.