旋风分离器流场与分离性能的数值模拟研究

【作者】 张海红；

【导师】 魏新利； 王定标；

【作者基本信息】 郑州大学 ， 化工过程机械， 2004， 硕士

【摘要】 旋风分离器是一种利用气固两相流体的旋转运动，使固体颗粒在离心力的作用下从气流中分离出来的设备。由于它结构简单、设备紧凑、无相对运动部件、价格低廉、操作维修方便，且可以满足不同生产特殊要求，所以被广泛应用于化工、能源、矿山、炼油、食品、建材、环保等众多行业，成为最常用的一种分离、除尘设备。近年来，随着人们环保意识的加强、炼油厂催化烟气能量回收、煤的清洁燃烧、旋涡流化床以及蒸汽燃气联合循环等高新技术的应用和发展，对旋风分离器的研究再次受到工程界的重视。 旋风分离器作为常用的气固分离装置，其应用历史虽然已有百余年了，但总的发展情况却是理论研究始终落后于实践。由于旋风分离器的工作过程是一种极其复杂的三维强旋转湍流、两相分离运动，且涉及气固相互作用以及凝聚、破碎、吸附和静电等许多物理现象，致使理论研究遇到了许多在现代流体力学中尚未解决的难题。而实验研究工作也十分困难，由于旋风分离器结构形式的不同、几何尺寸的不一，尤其是气固两相本身物理性质的差异、操作条件的变化等因素，都对旋风分离器的主要性能产生了显著影响。迄今为止，人们尚未充分认识旋风分离器复杂的内部流场规律和分离机理，仍无法全面掌握其气流运动的内在规律，更不能从理论上建立一套完整成熟的通用数学模型，致使各种旋风分离器的设计开发工作和操作运行都带有浓厚的经验主义。 由于实验条件的限制，单纯通过实验来研究旋风分离器的性能不仅周期长而且费用高。目前，人们对旋风分离器的研究重点已从整体特性的研究转向流动细节的研究，并借助于计算机模拟技术来解决这一问题。流场的数值模拟方法，是七十年代以来现代数字计算机、数值分析学、计算流体力学等学科最新发展的结果。这种模拟是基于计算流体力学的原理，建立各种复杂条件下的基本守恒方程组，确定适用的模型加以封闭，用数值方法直接求解这些非线性联立的偏微分方程组，从而可得到整个流场中各变量的时空分布。数值计算技术具有资金投入少、设计计算速度快、信息完全(数值模拟可以全面深入地揭示流体的内部结构，不存在因试验测试手段的限制而检测不到的“盲区”)、仿真模拟能力强等优点。因此，以流场湍流数值模拟为主研究旋风分离器内流体的流动规律，进而优化旋风分离器的结构，可以大大缩短研发周期，具有重要的工程应用价值。 本文利用计算流体动力学CFD商业软件FLUENT6.1.22对旋风分离器进行了数值模拟研究。在深入了解旋风分离器的基础上，模拟研究了多种情况下的气相流场、颗粒运动轨迹、压降及分离效率等。从预备阶段——确定最适合旋风分离器数值研究的模型和算法，到整个研究工作的结束，做了近二百个模型。通过本文的数值研究结果，主要得到了如下结论： (1) 通过研究最终确定了一套适合于旋风分离器的模拟的数值计算方法：对于旋风分离器内部复杂流场的模拟，必须以高质量的网格为前提，在采用基于各向异性的湍流模型(RsM)的同时，还要相应采用QUICK差分格式和PRESTO压力插补格式，才能获得较理想的预报结果。(2)旋风分离器内主流是双层旋流，以零轴速包络面为界，外部是向下旋转的外旋流，中心是向上旋转的内旋流，且它们的旋转方向是相同的。切向速度在分离器中起主导作用，其分布具有组合涡的特点，以最大速度点为界，内部是准强制涡，外部是准自由涡，其轴对称性较好，沿轴向的衰减也很小。静压分布在分离器气芯处最小，甚至出现负压，这可能引起灰斗内气流返混，影响分离效率。(3)即使旋风分离器的气流进出口的截面积相等，其动压降也不等于零，总压降应为静压降与动压降两部分之和。 (4)随排气管底口直径增大，分离效率越来越低、压降越来越小，但压降降低的变化率逐渐变小。随处理气量增大，分离效率有所提高，但却是以过大的能量消耗为代价的;另外，气流太强时，沉积到壁面的颗粒反而会被重新卷扬起来，而且所产生的颗粒被粉碎、壁面被磨损等负面效应，对分离也不利。 (5)旋风分离器中的颗粒运动非常复杂，且带有很大的随机性。尤其是小直径颗粒，即使颗粒直径相同、初始位置相同，它们的运动轨迹也可能不同。小颗粒受气流脉动影响和受大颗粒的携带作用较为显著，在二次流中出现的几率也较大，对分离性能的影响也较大。 (6)首次提出了一种新型的套管排气管型旋风分离器，并利用数值技术模拟研究了其基本特征及性能。这种结构的旋风分离器能同时分离出两种净化气体和一种被捕集的固体颗粒，综合考虑了压降和分离效率这对相互矛盾的因素。其内排气管比外排气管分离效率高，处理气流量越大，内、外分离效率的差距越小;而对于压降来说，内管比外管偏大，处理气流量越大，内管压降与外管压降的差距越大。更多还原

【Abstract】 Cyclone separator is a sort of equipment that solid particles operated by means of centrifugal force are separated from gas current when they revolved together. For structure being simple, fixture being compact, without relatively moving component, price being low, operating and maintaining conveniently, and satisfying different demand, it has been applied in numerous industries as a equipment separating particles and catching dust in common use, for example in chemical engineering, energy source, mine, oil refining, grocery, material and environment. These years later, the study on cyclone separator gets the regard of engineering field again, along with the technology’s applying and development, including the environment consciousness enhancing, energy of the catalyzed smog of refinery reclaiming, coal cleaning and burning, vortex fluidized bed, steam and burned gas combining cycling.As a sort of equipment in common use, the history of cyclone separator is about a hundred years, but its study in theory gets behind of its practice all along. Its study in theory falls across many unsettled problems in modern hydrodynamics, because its work-process is a most complex three-dimension movement of revolve turbulent and two-phase separated, also related to many physics phenomena including reciprocity between gas and solid, coherence, crash, adsorption and static. The laboratorial investigation is also very difficult. The cyclone separator’s difference of configurations or geometry dimensions, and especially the difference of physics properties between gas and solid or operation conditions, all affect its most performances distinctly. So far, we have still not known its complex law of flow field and separated mechanism, not held its internal law of the gas current, and still not theorized for a current full mature mathematics model, so that the design and operation of cyclone separator are much more experiential.The study on performance of cyclone separator only by experiment is not only long term, but also expensive. Now, we have already started to turn the study emphases of cyclone separator from the whole characteristic to flow detail, and settle the problem via the simulation by computer. The numerical simulation of flow field is the developmental outcome of modern numerical computer, numerical analysis and computed hydrodynamics up to the minute. The simulation is based on the theory of computed hydrodynamics. We set up a set of basic conserved equations in diversified complex conditions, make the suited model close it in, then solve direct these non-linearity simultaneous partial-differential equations, and accordingly get the spatio-temporal distributing of every variables in the whole flow field. The numericalcomputed technology has many merits, for example, the devoted finance is less, the speed of design and computation is quick, the information is full (it can reveal the interior mechanism thoroughly, and have no blind spot that can not be checked by experimentation), and the ability of emulation and simulation is better. Therefore, studying on the law of fluid in cyclone separator by numerical simulation of the turbulent flow field, and then optimizing its configuration, may shorten the period of study and design of it greatly, and so have a important application worth in engineering.This thesis does the research for the numerical simulation of cyclone separator, using FLUENT6.1.22, the business software of CFD. On the base of deeply understanding of cyclone separator, does the research for the flow of gas, moving tracks of particles, pressure drop and separated efficiency in many different conditions. Approximately two hundred models for the research had been made, from the preparation that defined the most appropriate model and method for the numerical research of cyclone separator, to the finish of all the work. We have got the following conclusions from the results of numerical research in this thesis:(1) Through studying, the method of numerical computation for simulating cyclone separator h更多还原