【作者】 刘继东；

【导师】 张凤宝；

【作者基本信息】 天津大学 ， 化学工程， 2008， 博士

【摘要】 立体传质塔板(CTST)以梯形立体结构的帽罩为单元,将气液两相流动和传质从塔板上延伸至大部分塔板空间。罩内的气液流动是造成这种延伸的关键所在,同时又是促进传质的主要区域。对罩内气液流动和传质的研究既是优化帽罩结构的基础,又为预测整个塔板的传质效率提供理论依据。本文在直径600mm的工业规模冷模实验塔中,研究了喷射板倾斜角度(α)和塔板伸入罩内长度(Wb)对罩内气液两相流体力学参数的影响,获得了较优的帽罩结构参数为α=8o、Wb=10mm。对帽罩进行了传质实验研究,得到了罩内沿高度方向的浓度分布,以及提升段和喷射段的传质速率和传质效率。提出了采用不同模型对帽罩内气液两相流场分段模拟的方法。在充分考虑表面张力和气液相互作用力对两相流动影响的情况下,用VOF方法建立了能够较好追踪两相界面的提升段两相流模型。采用颗粒轨道模型模拟了喷射段的气液两相流动,模型中考虑了高速气体对液滴施加的曳力、液滴所受重力和虚拟质量力的影响,用随机轨道模型计算了液滴的湍流扩散。根据模拟结果,对提升段重点讨论了不同操作条件及帽罩结构对液膜流动的影响,得到了液膜流动的变化规律。在喷射段重点讨论了液滴粒度的分布规律,其结果与R-R分布函数符合较好,获得了液滴粒度的分布参数和特征尺寸。分别建立了提升段和喷射段的传质模型,并对罩内传质进行了计算。在提升段把夹带液滴的核心气流看作等效流体,利用两相流模型对其进行了浓度分布和传质效率计算。在喷射段,以特征液滴的传质来处理复杂的传质过程,对喷射段浓度分布和传质效率进行了初步预测。模型计算结果与实验数据的整体趋势一致。更多还原

【Abstract】 The trapezoid tridimensional structure caps are the key parts of Combined Trapezoid Spary Tray (CTST), which enlarge the area of gas-liquid mass transfer. The two phase flow inside the cap effects on mass transffer remarkably. Study on the gas-liquid two phase flow and the mass transfer in the cap is the basis of the cap structure optimization and the mass transfer efficiency prediction.The effect of the cap with different inclination angle (α)of spray plate and the dip length of the tray (Wb)on flowing characteristic was investigated in a experiment column with 600 mm diameter. The results showed that the optimized cap strcture was thatα=8o and Wb=10 mm. The concentration distribution, the mass transfer distribution inside the cap, and the mass transfer efficiency in lifting region and spraying region were obtained by mass transfer experiment.The different model was put forward respectively to simulate gas-liquid two phase flow on different regions inside the cap. In lifting region, the forces by surface tension and the gas-liquid interaction were considered into VOF model, so that the model can well trace two phase interface. The gas-liquid two phase flow in spraying region was simulated with particle trajectory model, and the effect of drag force, gravity, virtual-mass force was considered in the model. At the same time, the droplet turbulence diffusion was calculated with random trajectory model. In lifting region, the liquid film flow characteristic and its variability with operating conditions and the cap structure were analysed mostly. In spraying region, the droplets size distribution was mainly concerned, and the results showed that the size distribution has a good agreement with R-R distribution function. The distribution parameter and the feature size in the distribution function about the droplet size were obtained by simulation.The mass transfer models were established respectively for lifting region and spraying region. In the model of lifting region, gas phase that entrained in droplets was regarded as effective fluid and liquid phase as film. In spraying region the complex mass transfer process was treated with feature droplet’s mass transfer. After that, the concentration distribution and mass transfer efficiency inside the cap were calculated with the model. It showed that the calculated results of the models have a good agreement with the experiment data in tendency.更多还原