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.     

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。     

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.     

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.     

Model Development of the Transient Solid Hold‐up and Pressure Drop in Fabric Filters

There are different non‐idealities related to cloth filters, which are cleaned by jet pulses. The well‐known phenomenon of cake compaction causes progressive curves of the pressure drop versus time. Some experiments show degressive shapes of the pressure drop, though. It will be shown, that this behavior can be explained by dividing the filter in segments. Each model segment can have a different cake thickness, whereas the pressure drop of every single segment is the same at any time during filtration. The capacity of this model is pointed out to determine the cake load on existing filters and to simulate unknown operating points.     

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.     

Modelling of the Pressure Drop in Tangential Inlet Cyclone Separators

This article introduces a new mathematical model that predicts the pressure drop in a tangential inlet cyclone. The model calculates the pressure drop from the frictional losses in the cyclone body, using a wall friction coefficient based on the surface roughness and Reynolds number. The entrance and exit losses are also included in the model by defining new geometrical parameters. The pressure drop coefficient is obtained as a function of cyclone dimensions and operating conditions. The model is validated by studying 12 different cyclones presented in the literature. Comparison of the model results with predictions and measurements published in the literature show that the new model predicts the experimental results quite well for a wide range of operating conditions covering a flow rate of 0.3–220 l/s and a temperature range of 293–1200°K, in different cyclones. The pressure drop coefficient is also examined in view of the outlet pipe diameter, friction coefficient, surface roughness, and Reynolds number.     

Experimental Study and Analysis on Drag Reduction Mechanisms of Reducing Pressure Drop Stick in a Cyclone Separator

The mechanisms of mean mechanical energy losses in a cyclone separator with a Repds (Reducing Pressure Drop Stick) are studied. The results show that the energy losses are mainly caused by direct viscous dissipation, turbulent diffusion, and turbulent energy production, which is the same as in a conventional cyclone separator. In particular, the direct viscous dissipation and the turbulent energy production are of importance. Laser Doppler Velocimetry (LDV) is used to measure the flow field in the cyclone body and the exit pipe of a cyclone separator with and without a Repds, respectively. The drag reduction mechanism of the Repds is analyzed by examining the effects of the Repds on flow parameters which are related to energy loss factors. The measured results and analysis reveal that the drag reduction results from decreases of the direct viscous dissipation, turbulent diffusion, and turbulent production as a whole when a Repds is inserted into a cyclone separator. The resultant drag reduction is a tradeoff between the increase and the decrease of energy losses caused by the Repds.     

对干熄炉内压降的研究

测量了干熄炉内焦炭床层的阻力损失，研究了鼓风量、焦炭直径以及形状因子对阻力损失的影响。利用Ergun方程整理的实验常数，分析了与形状因子的关系。     

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.     

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.     

气体通过颗粒移动床除尘器压降的计算

本文在实验室装置上对气体通过颗粒移动床的压降进行了系统研究,包括固定床与移动床的压降对比、床层高度与床层厚度之比、砂层移动速度、颗粒直径以及床层侧面结构尺寸对气体通过床层压降的影响。     

Study of Single Phase Flow Heat Transfer and Friction Pressure Drop in a Spiral Internally Ribbed Tube

The experimental results of single‐phase flow heat transfer and pressure drop experiments in the turbulent flow regime in a spirally ribbed tube and a smooth tube are presented in this paper. The ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. Both tubes were uniformly heated by passing an electrical current along the tubes with a heated length of 2500 mm. The working fluids are water and kerosene, respectively. The experimental Reynolds number is in the range of 10⁴–5 · 10⁴ for water and is in the range of 10⁴–2.2 · 10⁴ for kerosene. The experimental results of the ribbed tube are compared with those of the smooth tube. The heat transfer coefficients of the ribbed tube are 1.2–1.6 fold greater than those in the smooth tube and the pressure drop in the ribbed tube is also increased by a factor of 1.4–1.7 as compared with those in the smooth tube for water. The corresponding values for kerosene are 2–2.7 and 1.5–2, respectively. The heat‐transfer enhancement characteristics of the ribbed tube are assessed. This tube is especially suitable for augmenting single‐phase flow heat transfer of kerosene. Correlations for the heat transfer and the pressure drop for the spirally ribbed tube are proposed, according to the experimental data.     

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.     

细颗粒滴流床的压降与传质

细颗粒滴流床在三种床径下实验,采用不同粒度的多孔玻璃球及实心玻璃球填料时的床层压降,可由两相摩阻因子f_(gl)的经验关系表示:lnf(gl)=7.38-1.32lnz+0.011(lnZ)~2-0.0077(lnZ)~3由氧解吸法测得床层内的容积传质系数K_la,它的关联方程为:k_la=0.00160E_L~(0.55)·u_g~(0.25)     

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。     

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%。     

纤维过滤介质过滤压力损失理论计算

为便于计算纤维过滤介质过滤压力损失,对目前各种纤维过滤介质过滤压力损失理论计算公式及半经验公式进行分析计算,将理论计算结果与实验测试结果进行对比分析发现各种理论计算结果普遍相偏大,需要对纤维的非均匀分布进行修正,修正后的大部分计算结果与实验结果基本吻合,同时对理论计算公式的鲁棒性进行了分析。计算结果准确性和鲁棒性兼顾的理论计算公式,较适宜于实际过滤材料压力损失的预测。     

Modeling of Differential Pressure Buildup during Flow through Beds of Fibrous Materials

Modeling of the pressure drop buildup across beds of fibrous materials at strainers is reported. Special attention is drawn to the compressibility of the fibrous filter cake. The influence of the penetration depth of sludge particles to the overall pressure drop in conjunction with the thin‐bed effect has been investigated. Numerical results are compared with pressure drop measurements.