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。     

催化裂化沉降器旋流快分系统内两种旋流头的性能对比

通过冷态对比实验,研究了旋流快分系统（VQS）内两种新型旋流头的分离性能,结果表明B型旋流头采用大弧切向出口后,对含尘气流具有加速旋转的作用,可使颗粒喷出后获得更高的切向速度,从而提高系统的分离效率。采用Fluent软件对VQS内气固两相流进行了数值模拟,重点考察了A、B型旋流头的流场分布和分离特性。模拟结果表明：含尘气流由B型旋流头喷出后,切向速度较大,离心力较强,增加了颗粒在稳定分离区内分离的概率;同时,含尘气流喷出后气量大部分集中在封闭罩内壁附近下行流动,下行轴向速度较大,有利于颗粒下行分离。此外,相比于A型旋流头,B型旋流头的分离优势在于可大大提高对中粗颗粒的捕集能力。因此工业应用中推荐采用B型旋流头,以更好地满足工业生产的需求。     

双进气道旋风分离器内不同粒径颗粒流动特性

采用改进的RNG k-ε湍流模型和欧拉多相流模型,对一种单入口双进气道旋风分离器内的气固多相紊流过程进行数值模拟。计算得到旋风分离器内不同粒径颗粒速度和浓度分布规律,结果表明:大粒径颗粒比小粒径颗粒轴向速度分布更平坦,切向速度峰值位置和外准自由涡区也越向壁面靠近;与普通单入口旋风分离器相比,相同处理量时,此种旋风分离器内速度和不同粒径颗粒浓度分布轴对称性更好,大粒径颗粒切向速度峰值位置外移更明显,筒体段颗粒有更向壁面浓集的趋势,锥体段不同轴向位置处中心旋流区双进气道的颗粒浓度低于单进气道的。小粒径颗粒捕集能力增强,有助于提高分离器分离效率,减少不稳定流动导致结焦的颗粒源供给,从流动角度保证了抗结焦和长周期稳定操作。     

动态旋风分离器数值模拟及实验研究

旋风分离器具有结构简单性能稳定等优点,但对于粒径10μm以下颗粒,分离效率较低。本文对普通旋风分离器进行改进,设计了带有旋转叶片的动态旋风分离装置,并进行了实验和数值模拟研究。数值模拟气相采用RNG k-ε模型与RSM模型相结合的算法,颗粒相与气相之间采用以欧拉-拉格朗日气固两相流耦合思想为基础的DPM模型进行模拟,主要研究了装置内部流场和颗粒分离效率与进口气速和转子转速之间的关系,并与实验中通过静电低压悬浮颗粒取样器（ELPI）获得的装置分离效率进行了对比。模拟和实验结果表明,装置切向速度场中转子部分的切向速度主要由叶片转速决定,转子外部区域的切向速度则主要由进口气速决定,且在一定的转速和进口气速下,动态旋风分离器对粒径在5μm以上的颗粒有良好的脱除效果。     

催化裂化用短接触旋流反应器内气固滑移特性

利用欧拉-欧拉双流体模型对短接触旋流反应器分离腔内气固滑移特性进行了数值模拟,主要研究了切向气固滑移速度的分布规律,并考察了操作参数和物性参数对分离腔内切向滑移速度的影响。计算结果表明,分离腔内切向气固滑移速度沿径向呈“驼峰”分布;当气相入口速度增大或者剂气比减小时,切向气固滑移速度变小,颗粒切向速度增大,离心力增大,有利于提高气固分离效率;颗粒密度对切向滑移速度分布影响不大;颗粒粒径较大时,在排尘口易出现堵塞,不利于长周期运行;建立了截面平均切向气固滑移速度计算模型,计算值与模拟结果误差在±7.0%以内。     

环流预汽提组合旋流快分系统粒级效率的三区计算模型

在大型提升管冷模实验装置上,系统地考查了带有环流预汽提的旋流快分(CVQS)系统的气相流场和粒级效率。结果表明,随着旋流快分系统喷出口气速的增加,粒径小于7μm颗粒的粒级效率的变化较小,7~20μm颗粒的粒级效率逐渐变小,而超过20μm颗粒的粒级效率则逐渐增大。根据CVQS快分系统的气固分离原理和结构特点,建立了计算CVQS系统粒级效率的三区模型。计算结果表明,在颗粒粒径大于20μm时,模型预测的粒级效率与实验值吻合较好,其最大相对偏差不超过6.1%;在颗粒粒径小于20μm时,模型计算的粒级效率与实验值相差较大,其相对偏差在45.7%~80.3%之间变化,并且随着颗粒粒径的减小,其相对偏差逐渐增加。模型对于主要用于分离20μm以上颗粒的CVQS系统的工程设计,具有重要参考价值。     

基于离散相模型的用于高含硫天然气旋风分离系统内部流场数值研究

高含硫气田开发到后期会出现含水量增多的问题,需进行脱水预处理。设计了两级旋风分离系统,采用数值模拟方法,分析了不同粒径颗粒在不同入口速度下的轨迹、分离效率和分离器压力与速度场。结果表明:粒径越小受入口速度的影响越明显。10、30μm颗粒分离效率达100%,5μm颗粒分离效率达96%,内部压力与速度场具有较好的对称性。     

新型旋风分离器气相流场测试实验研究

针对高温高压的特殊情况提出了一种新型的旋风分离器,并用三维动态粒子分析仪PDA对不同结构参数和操作条件下的气相流场进行了测试,得出该旋风分离器内气相流场的整体特性———流场的切向速度分布在分离空间具有明显的对称性,任一截面上的分布分成内外2层旋流,外旋流是准自由涡,内旋流是准强制涡;同时分析了入口角度、排气管直径、高径比和入口气速等因素对其切向速度的影响规律,在此基础上依据实验数据关联出了计算内旋流直径和速度分布指数的公式。     

多喷嘴射流式分离器内气固流动特性的数值模拟

基于商用软件Fluent 6.3.26,采用雷诺应力模型及DPM离散相模型并结合理论分析,对基于喷嘴造旋的射流式分离器内两相流动特性进行了模拟计算,得到了较为全面的两相流动规律与细节.结果显示,分离器内部切向速度峰值可达160 m·s^-1,自由涡区的切向速度约为130 m·s^-1,旋流强度明显高于传统旋风单管;沿轴向下,下行流流量逐次减少,其中稳流体顶部下行流降低最为明显,下行流减少致使颗粒卷入内旋流概率增加,分离效果下降;分离器内部局部存在顶部贴壁射流、射流区二次流及灰斗口旋涡流等次级流动;分离器压降约为27.43 kPa,喷嘴区内外旋流能耗分别为4.57 kPa(21.8%)、5.76 kPa(27.6%),稳流体区内外旋流能耗分别为5.85 kPa(27.6%)、4.01 kPa(18.9%);分离器对应的切割粒径较小,约为1.6 μm,极限粒径约为10 μm,符合工业应用要求;基于所建颗粒受力模型及模拟条件下,分离空间可分离的临界粒径为1～2 μm,3 μm及以上颗粒的逃逸浓度小于 0.15 g·m^-3,满足下游烟机对气流的净化要求.     

天然气聚结过滤器气液分离性能的实验研究

为了系统地评价天然气聚结过滤器的气液分离性能,采用两种加入液滴方式,获得较大范围的液滴粒径分布,液滴中位粒径分别为8.7、40.0μm,在流量为94~220m3/h范围内进行实验研究,并通过Winner318B激光粒度仪对出口粒径进行在线测量。实验结果表明:压降会随加液时间发生变化,液滴粒径对分离效率的影响显著;当流量为94~182m3/h、入口液体浓度为30~75g/m3时,气液分离效率随着气体流量和入口液体浓度的增加而增大,当流量超过220m3/h时,分离效率迅速降低;分离器出口处粒径大于8μm的液滴基本除尽。     

含内构件的循环流化床的动态压力特性

针对含内构件的循环流化床,以石英砂为物料,使用动态压力传感器测量了含内构件的流化床中气固两相流的动态压力,分析了床内的瞬时压力特性. 结果表明,在进出口总压降中,文丘里压降最大,占主床压降的60%以上. 表观气速和固体颗粒循环流率共同影响循环流化床内的压力特性. 压力瞬时波动功率谱分析表明,压力波动对应一个主频,表观气速越小、颗粒循环流率越大时,压力波动越大,且循环流化床底部压力波动比上部大. 加入内构件能有效引导气流,使流动更均匀.     

MODELING VENTURI SCRUBBER PERFORMANCE FOR PARTICULATE COLLECTION AND PRESSURE DROP

A computational model of gas-particle flows has been extended to predict venturi scrubber performance as measured by particle collection efficiency and pressure drop. The concept of regarding particle and liquid phases as sources of momentum and energy to the gaseous phase was incorporated into the model's computational scheme. Predicted pressure drop results showed good agreement with available experimental data, particularly when uniform liquid distribution across the venturi cross-section was achieved. Our model was also more successful in predicting particle collection efficiency than several other models previously reported in the literature. Differences between model predictions and experimental results were chiefly caused by maldistribution of injected liquid into the test scrubbers.     

Reduction of a model for single droplet drying and application to CFD of skim milk spray drying

In this work, a novel methodology for the development of a high-accuracy computational fluid dynamics (CFD) model for the spray-drying process is described. Starting point is an own spatially resolving model of droplet/particle drying, which was developed and validated on the basis of a series of single droplet drying (SDD) experiments. This sophisticated model is transformed to a much simpler version: the characteristic drying curve approach, after running the full SDD model in a wide range of operating conditions. Then, the obtained reduced model is implemented into the CFD solver. The CFD spray-drying model takes into account the hydrodynamics of the continuous phase, particle drying kinetics, changes in the particle diameter, and the heat loss from the drying chamber to the environment. Validation of the entire procedure is provided by data obtained from drying experiments performed in a co-current laboratory spray tower. High accuracy of the developed CFD model of skim milk spray drying has been found for both phases, for the mean outlet temperature of the continuous phase (air) and for the change in average particle moisture content along the spray tower (discrete phase).     

Growth of aerosol particles by adiabatic expansion at the throat of a venturi scrubber

The condensational growth of aerosol particles in the throat section of a venturi scrubber and the contribution of it to the dust collection efficiency were discussed.The condensable water vapor produced in the throat of venturi was quantitatively obtained for various conditions assuming the change in pressure and temperature to be adiabatic process. In terms of this condensable water vapor and the particle number concentration, the diameter of grown particles was determined, and the degree of contribution due to particle growth to the particle collection by venturi scrubber was evaluated as the change in particle collection efficiency involved in the particle growth.Experimental verification of the above results was qualitatively made by changing the humidity of the inlet gas, which is the most important property dominating the particle growth, in the particle collection by venturi scrubber.     

Mass transfer coefficient in the eductor liquid-liquid extraction column

In this research gasoil desalting was investigated from mass transfer point of view in an eductor liquid–liquid extraction column (eductor-LLE device). Mass transfer characteristics of the eductor-LLE device were evaluated and an empirical correlation was obtained by dimensional analysis of the dispersed phase Sherwood number. The Results showed that the overall mass transfer coefficient of the dispersed phase and extraction efficiency have been increased by increasing Sauter mean diameter (SMD) and decreasing the nozzle diameter from 2 to 1 mm, respectively. The effects of Reynolds number (Re), projection ratio (ratio of the distance between venturi throat and nozzle tip to venturi throat diameter, R_pr), venturi throat area to nozzle area ratio (R_th-n) and two phases flow rates ratio (R_Q) on the mass transfer coefficient (K) were determined. According to the results, K increase with increasing Re and R_Q and also with decreasing R_pr and R_th-n. Semi-empirical models of drop formation, rising and coalescence were compared with our proposed empirical model. It was revealed that the present model provided a relatively good fitting for the mass transfer model of drop coalescence. Moreover, experimental data were in better agreement with calculated data with AARE value of 0.085.     

Coalescence of an emulsion in a fibrous bed: Part II. Experimental

A model of a fibrous bed relating the ratio of the outlet and inlet particle number densities to the various system parameters is tested experimentally. The degree of bed saturation is also determined from single phase and two phase flow data. The inlet and outlet particle number densities are determined by light scattering. It was found that the model does predict the effect of particle size, fiber size, bed length, and degree of saturation consistent with experimental observations. However, the coalescence efficiency based upon aerosol filtration theory is not amenable to the fibrous bed over the widest range of flow velocities.     

内喷文氏管异常情况分析及改造

分析了某50kt／a硫铁矿制酸装置内喷文氏管出口气温超高、压力降上涨快的原因并采取相应改造措施，如改进喷头安装高度设计、优化工艺操作参数、加强设备和管道保温等。生产实践表明，必须加强内喷文氏管设计和操作，以保证设备稳定、高效地运行。     

回转窑二次风富氧燃烧的数值模拟

针对一实际尺寸的回转窑建立模型，分别进行了空气助燃(21% O2)和二次风富氧(23% O2)燃烧的数值模拟研究。结果表明，二次风富氧后，高温区覆盖形状没有明显变化，仍呈“棒槌状”；在回转窑前端，煤粉挥发分与焦炭燃烧速度加快，整体温度有所提升，最高温度由2386 K增至2427 K，壁面所接收的辐射量得到了提升；但NOx的生成量也大幅度提高，其中出口处NOx由247 mg/m3增至367 mg/m3。考虑到制氧成本问题及NOx排放问题，在二次风中进行富氧燃烧的总体效果不够理想。     

Modeling and comparison of different syngas cooling types for entrained-flow gasifier

A three-dimensional numerical model has been developed for studying the multiphase flow and heat transfer process in the syngas cooler. The realizable k−ε turbulent model and discrete random walk (DRW) model were adopted to simulate the gas phase and particle phase flow fields, respectively. The discrete ordinate model (DOM) was applied to solve the radiative heat transfer equation, and the gas radiative properties were calculated by weight-sum-of-gray-gases model (WSGGM). The ash particle radiative properties were also considered in the radiative heat transfer calculation. The convection heat-transfer between the gas phase and discrete phase is also considered. The flow field and temperature distribution results are in good agreement with the experimental data. Firstly, the results indicate that the RSC should be the better choice for integrated gasification combined cycle (IGCC) power plant. For cooling-syngas quenching cooler, the outlet region has higher risk of fouling and slagging because the outlet gas and particle temperature are about 940 °C, and exceed the criteria temperature 760 °C (suggested in the literature). Secondly, when the inlet velocity and flow rate of the quenching gas are fixed, the more the quenching gas inlets are, the better the flow field and temperature field are. A recirculation region with the diameter about 1.5–2.0 m is formed in the center of the cooler under the quenching gas profile, and the intensity of the reflux flow increases with the number of quenching gas inlets. The particles are rapidly quenched when the particle flow through the quenching gas profile. Furthermore, the temperature of the quenching gas, and the temperature of the water in the tubes of membrane wall also have important effect on the temperature field in the RSC.     

喷射式浮选机浸没式充气搅拌装置结构参数的试验

介绍了浸没式充气搅拌装置的结构,并与长喉管充气搅拌装置进行对比。通过浸没式充气搅拌装置结构参数的优化试验,确定了喉管内径、喉管长度及喉管出口至假底的距离3个参数。FJCA系列浮选机充气性能等指标达到了较高水平,具有使用寿命长、维护工作量小等特点,在多个选煤厂得到了推广应用。