【作者】 钱付平；

【导师】 章名耀；

【作者基本信息】 东南大学 ， 热能工程， 2006， 博士

【摘要】 旋风分离器作为一种重要的气固分离设备,因其具有结构简单、高效、能承受高温高压等优点,在能源、化工、冶金、环保等许多领域有着广泛的应用。旋风分离器比较成功的应用是PFBC(增压流化床燃烧)、IGCC(整体气化联合循环)、CFBC(循环流化床燃烧)以及FCC(催化裂化)装置等。在这些苛刻的运行条件下,旋风分离器是唯一一种可以商业应用的除尘和分离设备。然而,旋风分离器的主要缺点是对于粒径小于5μm的颗粒除尘效率较低。要提高旋风分离器的分离效率、改进结构和优化尺寸,必须深入地研究旋风分离器内湍流流场分布规律以及气固两相分离特性。本文利用试验和数值模拟两种途径分析了不同结构及操作条件旋风分离器内强旋流场以及气固两相分离特性。试验研究包括气相流场和分离性能的测试,即应用先进的粒子图像测速技术(PIV)测量不同排尘结构旋风分离器灰斗及直管内的气相流场;测试了不同排尘结构以及不同入口颗粒浓度下旋风分离器的压力损失和分离效率。数值模拟时,气相场采用能反映各向异性湍流的雷诺应力输运模型(RSTM),各方程对流项采用具有二阶精度的QUICK差分格式。对颗粒相的计算,针对不同的入口颗粒浓度,分别采用单、双向耦合的离散颗粒模型以及简化的欧拉模型-代数滑移混合模型(ASMM)。针对工作在高温高压以及高入口颗粒浓度条件下旋风分离器非常有限的试验数据,本文还利用数值模拟技术对不同温度和压力下旋风分离器分离性能进行了预测,并预测了PFBC、IGCC以及CFBC典型工作温度、压力以及入口颗粒浓度下旋风分离器的分离性能。同时,论文还比较了数值模拟结果和相关的试验数据,结果表明:1、数值模拟结果和有关的经验和半经验公式以及试验数据比较,能获得更为满意的结果,从而也表明,应用数值模拟技术来研究不同结构和操作条件下旋风分离器的分离特性是方便且可行的。2、旋风分离器底部加直管及直管底部少量抽气使得气流向下移动,增加颗粒有效分离空间,有效降低已分离颗粒的二次扬尘,改善分离效果。然而,当直管长度增至一定值后,分离效率却有下降的趋势。说明,直管有一个最优长度,对于一定筒体直径的旋风分离器,其最优直管长度约为2D(D为筒体直径)。虽然直管太长反而不利于粉尘的分离,但是,在直管底部抽取一定量的气体后,又能提高此时旋风分离器的分离效率。抽气量为2%时就能明显提高旋风分离器的分离效率。值得注意的是,和直管长度一样,抽气率也有一个最佳值,超过这个最佳值,分离效率增加不明显。本文中,旋风分离器的最佳抽气量约为2%。3、压力损失和分离效率都随着温度的升高而降低,而且温度主要对粒径较小颗粒产生影响;压力增加使得压力损失和分离效率提高。从这个意义上看,温度增加而导致减小的分离效率会由于操作压力的提高而得到一定程度的补偿;4、随入口颗粒浓度的增加,旋风分离器分离效率相应提高,尤其是小粒径颗粒,分离效率提高明显。但是,随着入口颗粒浓度的进一步增加,分离效率增加并不明显。在本文试验的入口颗粒浓度范围内,旋风分离器的压降会随入口颗粒浓度的增加而减小;5、利用简化的欧拉模型-代数滑移混合模型计算循环流化床旋风分离器不但可以节省大量的计算时间,还能获得较为满意的结果,在实际应用时,可以利用该模型来定性分析颗粒入口浓度对旋风分离器分离性能的影响。数值模拟以及试验所得结果对进一步认识不同排尘结构以及操作条件下旋风分离器的分离机理具有一定的指导意义。通过数值模拟和试验研究发现,对于常规旋风分离器,其锥体底部以及灰斗内仍具有较强的旋流,据此可以认为,常规旋风分离器内的涡旋反转点并非停留在锥体部分,如果给其提供分离空间的话,气流仍会向下运动。正是从这一点来看,可以认为,常规旋风分离器的自然旋风长会大于其本体长度。本文利用数值模拟技术,并基于响应曲面法对旋风分离器自然旋风长进行了较为全面的更多还原

【Abstract】 Cyclone separators have been one of the oldest and most popularly used industrial particulate control devices for the removal of dispersed particles from their carrying fluids because of their simplicity, easiness and low costs in terms of construction, operation, maintenance and energy consumption. With the use of suitable materials and methods of construction, cyclone separators can be operated under extreme operating conditions, especially at temperatures over 900℃, conditions that almost exclude the application of other separation technologies. Some of the best examples are cyclone separators employed in PFBC (Pressurized Fluidized Bed Combustion), IGCC (Integrated Gasification and Combined Cycle) and FCC (Fluidized Catalytic Cracking) processes. In these harsh environments, cyclone separators are nowadays the sole, fully commercial solution to the removal of particles from elevated-temperature gases. Their main disadvantage, however, is low efficiency for particles less than 5 microns in size.In order to increase the separation efficiencies, improve the geometries and optimize the sizes of cyclone separators, the rule of turbulent flow field and the gas-solid separation characteristic should be studied in detail. Experimental studies and numerical simulations are used to analyze the strongly turbulent flow field and the gas-solid separation characteristic in this thesis. Experimental studies of flow field are conducted by Particle Image Velocimetry (PIV), and the gas flow fields of the vertical tube and dustbin in cyclone separators with different dust outlet geometries and separation performances of different cyclone separators are measured. Under the RSTM in Fluent code, although the first-order upwind scheme discretization can yield better convergence, it generally will lead to less accurate results. Therefore, the QUICK discretization scheme is used in calculating momentum, turbulence kinetic energy, its dissipation rate equations and Reynolds stress equations. Numerical studies are conducted for different inlet particle concentrations of a cyclone separator. One-way coupling, two-way coupling of dispersed particle model (DPM) and simplified Eulerian model-Algebraic Slip Mixture Model (ASMM) are used. Aiming at very limited experimental data of the cyclone separator working at different temperature, pressure and inlet particle concentration, the separation performances of these operating conditions are predicted by means of computational fluid dynamics (CFD) technology, and the separation performances at the representative temperature, pressure and inlet particle concentration of PFBC, IGCC and CFBC are predicted. The predicted separation performances are compared with the presented empirical models and experimental data. The results show: (1) The predicted separation efficiencies are in more agreement with the experimental data comparing to the empirical and semi-empirical model. The results also show that it is feasible and cheap to investigate the separation performance of the cyclone separator by means of CFD technology.(2) The prolonged cyclone separator can make the vortex end locate in the vertical tube and even in the dustbin, and increase the efficient separation space, thus improve its separation performance. However, for an even longer tube, the separation efficiency is slightly reduced. Therefore, there is an optimal tube length for a given cyclone. On the other hand, the cyclone separator with bottom air extraction can increase the separation efficiency, but there is an optimal air extraction rate, which is the same as the length of the vertical tube. When the air extraction rate is in excess of this optimal value, the separation efficiency increases slightly. For the cyclone separator that is presented in this paper, the optimal vertical tube length更多还原