气液并流筛板式填料压降的数值模拟

基于欧拉-欧拉模型,采用CFX软件对筛板式填料的气液两相并流流动进行了模拟。将模拟所得的压降与填料的出厂特性值进行了对比,发现在液气动能参数较小的情况下,两者吻合较好。分析了该流场内的速度分布和压力分布的特点,射流卷吸作用使流场内两相流体混合,但涡旋使筛板下方压强减小,射流撞击使筛板上方压强增加。对不同结构的矩形筛板式填料的压降进行研究,结果表明：筛板孔径和液相流量是影响筛板压降的重要因素,开孔直径越小,液相流量对单板压降的影响越大;上层筛孔投影与下层筛孔相交的结构更能有效降低单板压降。液相流量较大时,两个不同板间距的单板压降曲线将相交于一点,气相流量低于此交点时,板间距越小,单板压降越大;气相流量高于此交点时,则相反。     

A modified model of computational mass transfer for distillation column

The computational mass transfer (CMT) model is composed of the basic differential mass transfer equation, closing with auxiliary equations, and the appropriate accompanying CFD formulation. In the present modified CMT model, the closing auxiliary equations [Liu, B.T., 2003. Study of a new mass transfer model of CFD and its application on distillation tray. Ph.D. Dissertation, Tianjin University, Tianjin, China; Sun, Z.M., Liu, B.T., Yuan, X.G., Liu, C.J., Yu, K.T., 2005. New turbulent model for computational mass transfer and its application to a commercial-scale distillation column. Industrial and Engineering Chemistry Research 44, 4427-4434] are further simplified for reducing the complication of computation. At the same time, the CFD formulation is also improved for better velocity field prediction. By this complex model, the turbulent mass transfer diffusivity, the three-dimensional velocity/concentration profiles and the efficiency of mass transfer equipment can be predicted simultaneously. To demonstrate the feasibility of the proposed simplified CMT model, simulation was made for distillation column, and the simulated results are compared with the experimental data taken from literatures. The predicted distribution of liquid velocity on a tray and the average mass transfer diffusivity are in reasonable agreement with the reported experimental measurement [Solari, R.B., Bell, R.L., 1986. Fluid flow patterns and velocity distribution on commercial-scale sieve trays. AI.Ch.E. Journal 32, 640-649; Cai, T.J., Chen, G.X., 2004. Liquid back-mixing on distillation trays. Industrial and Engineering Chemistry Research 43, 2590-2597]. In applying the modified model to a commercial scale distillation tray column, the predictions of the concentration at the outlet of each tray and the tray efficiency are satisfactorily confirmed by the published experimental data [Sakata, M., Yanagi, T., 1979. Performance of a commercial scale sieve tray. Institution of Chemical Engineers Symposium Series, vol. 56, pp. 3.2/21-3.2/34]. Furthermore, the validity of the present model is also shown by checking the computed results with a reported pilot-scale tray column [Garcia, J.A., Fair, J.R., 2000. A fundamental model for the prediction of distillation sieve tray efficiency. 1. Database development. Industrial and Engineering Chemistry Research 39, 1809-1817] in the bottom concentration and the overall tray efficiency under different operating conditions. The modified CMT model is expected to be useful in the design and analysis of distillation column.     

立体传质塔板板上液相流场的三维数值模拟

针对立体传质塔板(CTST)操作时的特点,对1 000 mm的CTST板上液相流场进行了三维计算流体力学(CFD)数值模拟.计算得出了板上液相流场的三维分布特征;实验测量和模拟结果对比,结果吻合较好,说明文中模型有较好的准确度,可以用于CTST板上液相流场的预测.对相同条件下筛板和CTST板上的液相流场分别进行模拟,...     

混合箱塔板流体力学性能实验研究

研究开发了一种大通量高效率的混合箱塔板 ,它的非传质区仅占塔截面积的 5 %左右 ,在塔板上设计了用于提高气液传质效率的混合箱结构。在冷模试验塔内对混合箱塔板的压降、漏液、雾沫夹带以及降液管清液层高度等流体力学性能进行了试验 ,试验表明该塔板的漏液和雾沫夹带都比传统筛板有所减少 ,且通量大幅度提高     

Hydrodynamics of reactive distillation tray column with catalyst containing envelopes: experiments vs. CFD simulations

We have studied the hydrodynamics of a reactive distillation sieve tray column in which catalyst containing wire-gauze envelopes are disposed along the liquid flow direction. The gas and liquid phases are in cross-current contact on the tray. Experiments were carried out to determine the clear liquid height on the tray as a function of tray geometry and operating conditions. The transient gas–liquid hydrodynamics on the tray was simulated using CFD techniques. The agreement between the experiments and CFD simulations was found to be very good, suggesting that CFD simulations can be used for design and scale-up purposes.     

Flow-guided sieve-valve tray (FGS-VT) – A novel tray with improved efficiency and hydrodynamics

Flow-guided sieve tray (FGST) has been widely used as column internal for mass and energy transfer between gas and liquid, or liquid and liquid, due to its low pressure drop, high efficiency, and high capacity. But as sieve tray, improving the operation flexibility is the urgent task which has to be resolved. Flow-guided sieve-valve tray (FGS-VT) was designed to overcome the shortcoming of FGST by putting some valves onto the FGST, which do not change the original structure before the valves are open. Comparison of the hydrodynamic and mass transfer performances of FGS-VT, FGST, and Glitsch V1 valve tray was done, using air–water–oxygen system in a 0.6 m diameter plexiglass column, and the mathematical model of dry-plate pressure drop for FGS-VT was established. The results showed that the FGS-VT has higher operation flexibility and tray efficiency than FGST and Glitsch V1 valve tray.     

筛孔型润德塔盘的流体力学性能

以空气和水为介质,对筛孔型润德塔盘的流体力学性能进行实验研究,通过冷模实验考察其固阀开孔率、F因子、喷淋密度对干板压降、总板压降、清液层高度、平均泡沫层高度、操作弹性的影响,并与传统筛孔穿流塔盘进行比较. 结果表明,在操作范围内,筛孔型润德塔盘的操作弹性比传统穿流筛孔塔盘平均提升34.15%,固阀开孔率为33.3%的筛孔型润德塔盘总板压降比传统筛孔穿流塔盘平均低72.38%,比固阀开孔率为50.0%和66.7%的塔盘的干板压降平均低88.8%和206.3%,最佳固阀开孔率为33.3%. 得到筛孔型润德塔盘干板压降关联式为pd=49.98F1.785.     

气体穿过筛板上固液两相流层时的阻力特性

对气体穿过筛板上固液两相流层的流动特性进行了研究,关联出了气体穿过筛板上固液两相流层时泡沫工况下的筛板压降公式,为工程应用提供实验基础。     

大型塔板液体停留时间分布与板效率研究

报导在直径 2m的筛板塔实验装置中 ,用电导率连续测量系统同时测定塔板上 12个点的停留时间分布曲线及给出典型数据 ,并提出由停留时间分布曲线换算成塔板上浓度分布曲线以及计算塔板效率的方法     

新结构95型塔板的流体力学性能

引　言传统的板式塔塔板开孔率有限 ,当处理量较大时 ,压降较高 ,板效率降低 .因此开发新型大通量高效率塔板具有重要的现实意义 .本研究通过改进降液管结构和板面设计 ,提高塔板的有效传质区面积 ,开发了一种新型大通量塔板——— 95型塔板 ,因该板的有效传质区面积约占全部塔板面积的95%而得名 .本文以水和空气体系对 95型塔板进行了流体力学和流动性能试验 ,同时与传统筛板进行了比较 ,对试验测定的数据进行了关联 .1　试验装置及筛板结构参数试验塔为一直径Φ1 0 0 0ｍｍ的不锈钢塔 .塔内设置两块塔板 ,上板为测试板 ,下板为气体分布板 …     

筛孔塔板上气相错流对液相流场影响的实验测量

利用热膜流速仪、测量了矩形塔内光板上液体单相流动以及筛孔板上气液两相流动时的液体流速分布，实验主要考察气液两相错流时，气体鼓泡作用对鼓泡区下游液体流速分布的影响，实验结果表明，单相流动时，受壁面效应的影响，靠近塔壁的液体的速度最低，气液两相错流时，受气体阻力作用的影响，靠近壁面液体的速度反而大于远离壁面处液体的速度，气相流量越大对液相流场的影响作用越强。     

上置加热管筛板蒸发器流体力学及蒸发性能

对筛板上方液层内置有水平加热管束的载气蒸发器的流体力学和蒸发性能进行了实验研究,并对实验结果进行了分析。结果表明,在气速一定时,筛板单板阻力随着液体流量的增大而提高;在液体流量一定,气速较大时筛板单板阻力不随气速而变化;随着液体温度的提高,筛板单板阻力明显减小;在相同条件下,上置管束的筛板单板阻力比普通筛板单板阻力明显增大。对于常温下的空气水体系,在相同条件下,加热管束通入加热蒸汽可使出口空气的湿含量提高8. 7%—12. 6%。随着加热管束通入蒸汽流量的增加,出口空气的湿含量进一步提高。     

单、双溢流塔板液体停留时间分布和板效率的研究

在2米半园筛板试验装置上,用多点电导连续测量和微机数据采集系统研究了单、双溢流塔板的液体停留时间分布和流动型式.得到的等平均停留时间分布图表明,单溢流塔板上液体流动型式相当复杂.在双溢流板中,中央降液管塔板的流动情况与单溢流板的前半部相似;边降液管板的液体流动则要均匀得多.本文建立了由液体等平均停留时间分布曲线计算单、双溢流塔板板效率的数学模型,并给出了关系图.最后,本文提出两种改善液体流动均匀性的新结构,实验证明它们能够明显地提高板效率.     

大型塔板的模拟与板效率的研究(Ⅰ)——不均匀速度场的涡流扩散模型

本文介绍了直径为2m的半圆筛板塔试验装置,并得出塔板上液体流动型式和速度分布的一些实验数据。结果表明塔板上存在着相当复杂的流动和分区。 根据实验结果,在本文描述流动的微分方程中,引入了速度分布函数,并成功地用有限元素法来求解传质问题,从而得出了在不均匀的速度场下大型塔板上的液相浓度分布以及塔板效率。     

泡罩垂直筛板性能研究

选用BVS-1型和BVS-2型泡罩垂直筛板,用水和空气模拟塔内气液二相流动工况,在一定时间内采集雾沫夹带量和漏液量,研究其流体力学性能和操作弹性。结果表明:前者操作弹性比大于2,最大可达到3.5;用微差压计测得在操作弹性范围内的总板压降为850—1 400 Pa;采用氧解吸方法测试单板效率,对流体力学性能较好的BVS-1型泡罩垂直筛板和现有的垂直筛板在传质性能上进行了比较,前者比后者的单板效率提高了约20%。     

鼓泡破泡一体化高效精馏塔盘流动特性与CFD模拟

就痕量精馏中塔板传质效率低、需强化气液传质的问题,研究者提出了新型鼓泡破泡一体化高效精馏塔盘,通过在筛板上泡沫层高度范围内设置一层破泡装置,打破大气泡,减小气泡体积,强制界面进行更新,从而提高传质效率。采用双欧拉模型分别对鼓泡破泡一体化塔盘和筛板进行了气液流场的数值模拟,并对模型进行了验证。对比两种塔板的计算结果可以看出：在相同操作条件下,破泡装置将大气泡破裂成无数小气泡,使高气含率区域面积较普通筛板进一步增大,且气含率梯度变化更均匀;增加破泡装置后,在相同气速条件下气泡上升速度下降,气体在液层中的滞留时间延长,使鼓泡层高度增加,可显著提高传质效率,且降低了气体雾沫夹带量;破泡装置还明显改善了气相的纵向分布,气含率由塔板底部向上逐渐增大且存在明显分界;破泡装置附近湍动较剧烈,气泡破碎喷出的气体会进一步撕裂液膜,气体破碎作用会抑制气泡聚并,促进界面的快速更新更有利于传质过程的进行。研究结果可对工业塔板设计和优化提供指导。     

应用热膜风速仪检测塔板上气液两相流的局部气含率

<正>蒸馏塔板上气、液两相流局部气含率的测定对于研究塔板上流体的流动状态、塔板清液层高度、两相传质性能和设备优化设计等具有重要意义。过去,测量塔板上气液两相流的气含率主要采用γ射线吸收法。该法能检测总体的气含率,但无法测局部气含率,且使用复杂。热膜风速仪是检测气、液两相流速度和气含率的先进仪器,本文采用先进的智能热膜风速仪(IFA-100),并配以微机采样系统,用于测量大型塔板上两相流的局部气含率。