精馏塔负荷性能图分析技术新发展

系统介绍了按照流体力学极限和传质操作限制来构造精馏塔负荷性能图的方法.提出了适用于进料条件全面变化的可行稳定域分析方法,将塔板负荷性能图分析由一条线拓展到一个面;首次以平衡级离散填料床的方法构造了填料塔的负荷性能图;推荐以降液管入口液速作为负荷性能图的横坐标,不仅统一了塔板负荷性能图的纵、横坐标单位,也为塔板/填料混合型精馏塔实现全塔分析奠定基础.在此基础上提出了全塔负荷性能图的新分析方法,将精馏塔的分析由单层塔板、单段填料上升到全塔的范畴,进行精馏塔瓶颈分析、塔板/填料匹配设计十分容易、便利,是最简单的精馏塔瓶颈分析方法.     

悬挂式降液管塔板的抗堵功能研究及应用

为了延长精馏塔和吸收塔的运行周期,研究开发了悬挂式降液管塔板(DJ塔板)。DJ塔板采用悬挂式矩形降液管作为降液通道,筛孔或固定阀作为鼓泡元件,具有处理能力大、传质效率高、抗堵性能好等特点。论文根据DJ塔板的机械结构,分析了塔板上的气液二相流流动规律,在此基础上阐述了其抗堵机理。DJ塔板已成功应用于丁二烯装置丁二烯精馏塔、化肥装置变换气脱硫塔、气体净化和除尘塔等40余座塔,实现了扩产、节能和减排目的。DJ塔板具有很好抗堵性能,其应用前景良好。     

有助于掌握化工原理内容与实质的讨论题——(三)汽液传质设备

内容:1.明确塔板结构与塔板上的流体力学性能及操作状态的关系; 2.掌握塔板的负荷性能图,学会根据塔板结构及操作条件变化来调整负荷性能图上的各条界限曲线。 讨论题:某溶剂精馏塔,进料量为100T/h,进料浓度x为2%,要求塔顶产品浓度为70%,釜液浓度为0.5%,(以上浓度均为质量分率),泡点液相进料,回流比为4。该塔塔径D=2m,全塔各板的结构相同,板间距H_T=350mm,堰高h_w=50mm,塔板开孔率     

高效复合型塔板及其在甲醇精馏中的应用

高效复合型塔板采用筛板和薄层规整填料的复合结构,有穿流筛板复合填料和DJ型塔板复合填料两种型式.复合结构充分利用了塔板间的空间,改善了塔内的气液分布,抑制了板阍雾沫夹带,提高了操作弹性,具有优良的流体力学性能和传质性能.穿流型复合塔板在低温甲醇洗的甲醇精馏塔中成功地代换了林德泡罩和一般筛板或浮阀塔板,提高了分离效率20%以上,增加了处理能力,降低了回流比,改善了腐蚀问题,节省了系统的能耗.穿流型复合塔板还成功地应甩于甲醇生产装置的精馏塔系中.在甲醇三塔精馏塔系中,粗馏塔和加压精馏塔的精馏段采用穿流型的复合塔板,而提馏段则采用通量大弹性好的DJ型复合塔板.实现最佳的组合,满足塔内操作工况的要求.     

高效复合型塔板及其在甲醇精馏中的应用

高效复合型塔板采用筛板和薄层规整填料的复合结构，有穿流筛板复合填料和DJ型塔板复合填料两种型式。复合结构充分利用了塔板间的空间，改善了塔内的气液分布，抑制了板间雾沫夹带，提高了操作弹性，具有优良的流体力学性能和传质性能。穿流型复合塔板在低温甲醇洗的甲醇精馏塔中成功地代换了林德泡罩和一般筛板或浮阀塔板，提高了分离效率20％以上，增加了处理能力，降低了回流比，改善了腐蚀问题，节省了系统的能耗。穿流型复合塔板还成功地应用于甲醇生产装置的精馏塔系中。在甲醇三塔精馏塔系中，粗馏塔和加压精馏塔的精馏段采用穿流型的复合塔板，而提馏段则采用通量大弹性好的DJ型复合塔板，实现了最佳的组合，满足了塔内操作工况的要求。     

分流式降液管的流体力学性能研究

用分流式降液管以空气和水进行了塔盘冷模实验,研究了板压降、板上清液层高度和泡沫层高度、降液管泡沫层高度等流体力学性能,并在相同条件下与无分流式降液管进行了对比实验。结果表明:在相同的操作条件下,分流式降液管的塔板压降比无分流式降液管的塔板压降平均降低了39.3%,分流式降液管能有效降低塔板的溢流强度,提高了塔板的处理量。     

CFD在精馏分离中的应用

计算流体力学(CFD)是研究精馏塔内气液两相流动和传质的重要工具.本文介绍了板式塔和填料塔内气液流动状况,塔板上和填料层的流体力学模型,论述了国内外CFD技术在精馏塔流场模拟方面的应用,指出了CFD技术在精馏领域的发展方向,对于板式塔,应充分考虑气液两相间的相互作用,对于填料塔,应根据填料的具体形状建立每个孔道的流体力学方程,进行更接近实际的三维两相流模拟.     

新型多降液管塔板的流体力学性能及其流场CFD模拟

开发了一种流场均匀且液相处理能力大的新型多降液管塔板。本文以水和空气为介质，在内径1219mm的有机玻璃塔内，研究了新型多降液管塔板的流体力学性能。结果表明，在相同气液负荷下，相较于弓形降液管塔板，新型多降液管塔板具有湿板压降低、雾沫夹带量小和漏液少等优点。同时新型多降液管塔板继承了多降液管（MD）塔板液相负荷高的特点，在空塔动能因子2.4(m/s)·(kg/m³)^0.5的条件下，全塔喷淋密度仍可高达80m³/(m²·h)。对塔板上液相流场的流体流动特性进行了计算流体力学（CFD）分析，并将模拟结果与MD塔板进行对比。结果表明，新型多降液管塔板降液管的结构和排布方式使得塔板上液体流动更加均匀，预期可以获得更高的塔板效率。     

关于液汽比对筛板精馏塔塔板效率影响的研究

本文用乙醇-水系统,在一可将塔釜液打上循环回流的筛板精馏塔中,于恒定汽速下,研究了液汽比对塔板效率的影响;探讨了大液汽比时塔板效率下降的原因;探索了在大液汽比时提高塔板效率的途径和方法。     

精馏塔汽液负荷的计算

精馏是石油化学工业生产中广泛采用的、最重要的单元操作过程之一。精馏塔设计的成功与否,不仅关系到操作的稳定性,还直接影响到产品的质量。所以,精馏过程的研究受到普遍重视,国内外每年发表的论文数量相当可观。然而,这些论文主要集中于汽液相平衡、P-V-T关联式以及塔的工艺结构参数等方面,关于汽液负荷计算方面的论文却少见。众所周知,在精馏塔的工艺结构参数(诸如塔径、塔板间距、开孔率、溢流装置等)的设计和流体力学的计算中,汽液负荷则是基础数据。所以,准确地计算汽     

筛型精馏塔板喷射工况下三相流体力学性能的研究

在600×150mm矩形冷模塔内,进行了汽液液三相精馏塔板流体力学性能的研究.实验采用了两种物系和两种筛型板.提出了计算流体力学参数的关联式.针对三相精馏的特点,提出了作者的一些观点和建议.     

板式塔研究进展

对影响塔板传质效率的各种因素从理论上进行了分析 ;根据气液在塔内的相对流动将塔板分为三大类 ,然后依据塔板的结构简图对各种塔板的结构特点进行了详细介绍 ,对其流体力学和传质性能进行了分析 ,还比较了不同结构塔板之间的优缺点 ;对在不同情况下塔板的选择及塔板的发展提出了建议     

Overall efficiency evaluation of commercial distillation columns with valve and dualflow trays

The main objective of this work is to establish appropriated ways for estimating the overall efficiencies of industrial distillation columns with valve trays with downcomer and dualflow trays. The knowledge of efficiencies has fundamental importance in the design and performance evaluation of distillation columns. Searching in the literature, a tree of alternatives was identified to compose the tray efficiency model, depending on the mass transfer models, the liquid distribution and vapor flow models on the tray, the liquid entrainment model, the multicomponent mixture equilibrium model, the physical properties models, the height of froth on the tray model and the efficiency definition. In this work, different methods to predict the overall efficiency of distillation columns with valve and dualflow trays were composed and compared with data from three commercial distillation columns under different operating conditions. The models were inserted in the Aspen Plus 12.1 simulator, in Fortran language, together with tray geometrical data, fluid properties and operating data of the distillation columns. For each column, the best thermodynamic package was chosen by checking the temperature profile and overhead and bottom compositions obtained via simulation against the corresponding actual data of industrial columns. A modification in the fraction of holes evaluation that is jetting parameter of the Garcia's hydraulic model of dispersion above the tray was proposed. This modification produced better results than the original model to predict the fraction of holes that are jetting and in the efficiency of dualflow trays and similar results to Garcia model in the efficiency evaluation of valve trays. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Hydrodynamic model for controlled cycling in tray columns

The paper describes a model for controlled cycling in tray columns. Gas phase dynamics and hydrodynamic relations are included in the proposed model. The model has been simulated on a digital computer.Gas phase dynamics is found to play an important role for cyclic operation of distillation columns, while as the effect of gas phase dynamics can be ignored for absorption columns.In a 5-tray distillation column reasonable separation between liquid and vapour flow periods can be achieved, but with increasing number of trays the switch-over from one period to another becomes less ideal. For a ten tray column the flow situation is unacceptable.The simulations also show that the plug flow condition in the liquid flow period is most difficult to satisfy in the top and bottom of the column. The risk of flooding on some trays and other trays running dry increases when the numbers of trays increases.Finally it is shown that the hydrodynamic behaviour may be improved by changing the geometry of some of the trays.     

Effect of two-pass trays on distillation efficiencies

Two important structural factors that affect distillation efficiencies, the outlet weir heigh and the liquid flowpath length, are investigated. Performance and efficiency data of an industrial scale i-butane/n-butane distillation column equipped with two-pass trays are used as a basis for the calculations. A mathematical development for a new method for predicting the numbers of vapor and liquid phase transfer units is given. This method together with some other NTU calculation methods is used to assess the effect of the outlet weir height on efficiencies. The effect of outlet weir height on the Murphree tray efficiencies is investigated using the observed point efficiencies and different point efficiency to the Murphree tray efficiency relation methods. The effect of varying liquid flowpath lengths on efficiencies is studied by calculating the Murphree tray efficiencies for one-pass and two-pass trays. The results obtained using the NTU calculation method presented in this study show that a certain outlet weir height point efficiency reaches its maximum. Most of the other methods give opposite results giving a minimum for point efficiency at a certain outlet weir length. The results also show that the Murphree tray efficiencies for one-pass trays are higher than for two-pass trays. Obviously, this is caused by the longer liquid flowpath length of one-pass trays. The Murphree tray efficiencies are also calculated for an industrial-scale MTBE purification column. The column is equipped with two-pass trays in the stripping section and with one-pass trays in the rectifying section. The Murphree tray efficiencies of one-pass trays are considerably higher than the two-pass tray Murphree tray efficiencies.     

Heterogenous azeotropic distillaion-homotopy-continuation methods

An algorithm for the simulation of three-phase distillation towers and associated phase separators is presented. The algorithm utilizes the homotopy-continuation method of Allgower and Georg[1] to accurately track the homotopy path, with extensions to avoid limit points when multiple solutions are encountered and when liquid phases are introduced on the trays. The Allgower and Georg algorithm is also extended to track solution paths in parametric studies. Emphasis is placed on the calculation of liquid—liquid equilibria, with a reliable, yet efficient, homotopy-continuation algorithm introduced. An effective method for incorporating the LLE algorithm in the homotopy-continuation algorithm for heterogenous distillation is also introduced.

The combined algorithms have located two steady-state solutions for an industrial azeotropic distillation tower a very narrow range of the reflux ratios, one with a single liquid phase on the trays, the other with two liquid phases on 70% of the trays. In addition, for the dehydration of ethanol with benzene, it has detected a region in which five steady-state solutions exist for the same specifications. Three of these solutions were reported by Magnussen .[2] and observed in dynamic simulations by Prokopakis and Seider[3].     

Hydraulics and efficiency of screen trays for distillation

Screen trays are proprietary devices similar to sieve trays which are used in distillation and absorption applications. The pressure drop, liquid holdup and entrainment are measured for screen trays in an air/water column and compared to results obtained with sieve trays. The effciencies of both types of trays were compared in a distillation column using systems of various physical properties (methanol/water, acetic acid/water and cyclohexane/n-heptane mixtures). It was found that the screen tray has a lower dry pressure drop, higher liquid holdup, lower entrainment and weeping, and higher jet flooding capacity than the sieve tray. However, the effciencies of both trays are similar for the systems studied. A model was developed for predicting total pressure drop for screen trays using an air/water column. The model was tested using results for methanol/water, cyclohexane/n-heptane and acetic acid/water systems at total reflux. The deviations are within +/- 20% for 90% of the data points. The effect of a bed of mesh packing on the screen tray was also studied. It was found that the packing led to a higher tray effciency, but resulted in a higher tray pressure drop.     

离子液体催化反应精馏合成乙酸乙酯工艺模拟

为研究离子液体在反应精馏中的作用,采用离子液体1-丁基-3-甲基咪唑硫酸氢盐（[BMIM]HSO₄）作为催化剂,对乙酸和乙醇合成乙酸乙酯的反应精馏流程进行了计算模拟。在确定了参数的酯化反应动力学的基础上,用Aspen Plus软件建立了反应精馏流程,研究了催化剂用量、精馏段理论板数、反应段理论板数、乙醇进料位置、进料摩尔比、持液量及回流比等参数对反应精馏过程的影响。研究结果表明,塔顶乙酸乙酯的质量分数随催化剂用量、精馏段理论板数、反应段理论板数和持液量增大而增大,工艺流程存在最佳回流比以及最佳进料酸醇摩尔比。得到的优化条件如下：离子液体与乙酸摩尔比为1：2.5,进料酸醇摩尔比为4：1,理论塔板数为21块,乙酸和催化剂在第7块理论塔板进料,乙醇在第19块理论塔板进料,塔板持液量0.1L,回流比为4,塔顶乙酸乙酯的质量分数可以达到98.73%。     

B型导向浮阀塔板实验研究

为增大导向浮阀塔板对液体流动的推动力,在1600 mm×400 mm实验塔内,利用空气-水系统,对B型导向浮阀塔板进行实验研究。与导向浮阀塔板相比,它具有更好的流体力学性能和更大的液体负荷适用范围。实验研究和工业应用表明,B型导向浮阀塔板具有处理能力约提高20%、塔板效率约提高10%、操作弹性约提高30%等突出特点,用于蒸馏、吸收、汽提等传质过程,可获得良好效果。     

HYDRAULICS AND EFFICIENCY OF SCREEN TRAYS FOR DISTILLATION

Screen trays are proprietary devices similar to sieve trays which are used in distillation and absorption applications. The pressure drop, liquid holdup and entrainment are measured for screen trays in an air/water column and compared to results obtained with sieve trays. The effciencies of both types of trays were compared in a distillation column using systems of various physical properties (methanol/water, acetic acid/water and cyclohexane/n-heptane mixtures). It was found that the screen tray has a lower dry pressure drop, higher liquid holdup, lower entrainment and weeping, and higher jet flooding capacity than the sieve tray. However, the effciencies of both trays are similar for the systems studied. A model was developed for predicting total pressure drop for screen trays using an air/water column. The model was tested using results for methanol/water, cyclohexane/n-heptane and acetic acid/water systems at total reflux. The deviations are within +/- 20% for 90% of the data points. The effect of a bed of mesh packing on the screen tray was also studied. It was found that the packing led to a higher tray effciency, but resulted in a higher tray pressure drop.