Liquid entrainment in tray columns with downcomers

In this paper a new dimensionless correlation for calculating the liquid entrainment of trays operated in the spray regime is presented. This correlation is generally valid for all types of trays, such as sieve, bubble cup, valve, tunnel, and cross-flow trays, with downcomers. It describes the data from the literature and new data obtained in columns with large diameter by Kozio more exactly than any correlations known so far. Its validity was confirmed on systems with widely differing physical properties.

According to the presented analysis of the influence of errors in the determination of liquid entrainment on the calculation errors of tray efficiency, the mean weighted absolute deviation between the calculated and the experimental data is the most important factor. A further aim of this work was the formulation of a new criterion to compare the accuracy of the correlations used in describing the liquid entrainment on a tray.

Finally, a numerical example determining the entrainment according to the new correlation is presented.

Zusammenfassung

Im Beitrag wird eine neue dimensionslose Korrelation zur Bestimmung des Mitreißens in Bodenkolonnen im Sprühbereich vorgestellt, welche für Siebböden, Glockenböden, Ventilboden, Tunnelboden und Kreuzstromböden mit Überlaufwehren gültig ist. Mit dem neuen Ansatz werden die Meßergebnisse aus der Literatur sowie die neuen Daten von Kozio genauer wiedergegeben als es bis jetzt mit den bekannten Korrelationen der Fall war. Die neue Korrelation ist in den weiten Bereichen der variierten Stoffwerte anwendbar.

Desweiteren wird ein neues Kriterium für den Vergleich verschiedener Ansätze zur Bestimmung des Mitreißens in Bodenkolonnen angegeben. Aufgrund der durchgeführten Analyse zum Einfluß des Fehlers bei der Bestimmung der von Gas mitgerissenen Flüssigkeitsmenge auf den Fehler bei der Ermittlung des Punktver-stärkungsverhältnisses wurde festgestellt, daß die gewichtete, mittlere, absolute Abweichung zwischen den berechneten Daten und den experimentellen Daten einen wichtigen Faktor für die Bewertung von den einzelnen Korrelationen zum Mitreißen darstellt.

Anschließend wird an einem Zahlenbeispiel der Rechengang bei der Bestimmung des Mitreißfaktors e_L mit dem neuen Ansatz vorgestellt.     

A new experimental method for determining particle capture efficiency in flotation

A single bubble experiment has been developed for the determination of the capture efficiency of particles by bubbles in flotation under well-controlled hydrodynamics and physico-chemical conditions. In a glass column, small single bubbles (d_b=0.22−1.16 mm) are produced in pure water and then rise at their terminal velocity through a suspension consisting of spherical glass particles where bubble–particle capture takes place. The capture efficiency E_capt is calculated as the ratio of the number of particles captured by one bubble to the number of particles present in the volume swept out by this bubble. Images recorded at high optical magnification show that particles slip on the interface, then adhere to air bubbles individually or as aggregates and cover the rear part of bubble surface. The bubble's effective density and interface contamination level are increased by captured particles. As a result, bubble's rising velocity U_b is reduced along the experimental device. By establishing the relationship between capture efficiency E_capt, bubble rise velocity U_b and bubble clean angle θ_clean, a new approach to measure particle–bubble capture efficiency is proposed. This new experimental technique is applied to provide a new set of data for capture efficiency in the case of bubbles with a clean interface. E_capt is found to grow as d_b decreases and d_p increases, within the range between 0.02 and 0.20, which is in the order of magnitude of experimental results of Ralston and Dukhin (1999) as well as of numerical results of Sarrot et al. (2005). These data are favorably compared to numerical modeling of collision efficiency.     

筛板精馏塔的板效率研究

在直径为0.75 m,塔高4m的不锈钢热模塔内,以正庚烷—环己烷为物系、在常压、全回流条件下,进行筛板塔传质效率的研究,选取孔径为13mm和6 mm,开孔率为3.9％和6.4％的塔板,测试了这些塔板的气液相默弗里板效率,通过排列组合,考察了孔径、不同塔板位置和出口堰高对传质效率的影响,并进行了传质效果对比.此外还运用A...     

A new accelerated method for determining the potential alkali-carbonate reactivity

Many kinds of carbonate aggregates with different chemical compositions, structure, and geological characteristics have systematically been investigated. This research deals with chemical components and mineral analysis, petrographic examination of the aggregates, the dynamics of alkali-carbonate reaction with different cements, alkali contents, and particle sizes. A new method for evaluating the potential alkali-carbonate reactivity has been proposed according to the results, in which the major test factors include 1.5% Na₂O_eq. of alkali content, 1 M NaOH solution, 0.3 water-to-cement ratio, 5-10 mm particle size, and 4 weeks of test period at 80 °C. The results using this new method has also been compared with that of the performance of concrete structures in China.     

Investigation of entrainment in tray columns

This paper describes a pilot plant for entrainment measurements on various types of column trays. The data obtained from different trays differ by up to a factor of 10. The measurements were compared with the theoretical model of Stichlmair. The Stichlmair entrainment diagram permits a fairly accurate prediction for most types of trays if the height of the two-phase layer is known. Prediction of the height and relative liquid hold-up in this two-phase system should be modified by a term reflecting the vapour flow profile, which requires further testing. These tests should examine the effect of tray spacing, fractional free area and, in particular, the influence of different media.     

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.     

陶瓷泥料可塑性的一种新型测试方法

1　测试原理陶瓷泥料是由多种原料按一定的配比混和制成 ,不同的产品对其泥料的塑性要求不同 ,我们在实际生产过程中根据不同工艺的环境要求 ,通过研究试样在受力过程中应力与应变之间的关系来确定泥料的可塑性 ,该方法更科学、更先进。根据这一原理制取直径2 8 × 38 的圆柱体试样 ,放在专用的测试架上 ,检测试样的受压和变形。在试样变形为10 %时 ,记录其所受的压力Ｆ10 ,此时其压缩的截面积变形为Ｓ10 ;试样变形为 50 %时记录其所受压力Ｆ50 ,此时其压缩的截面积变形为Ｓ50 。定义其“可塑度”Ｒ ,根据公式Ｒ =(Ｓ50 /Ｓ10 )× (Ｆ10 /Ｆ…     

十字旋阀塔板的板效率研究

在直径750mm的热模塔内,以环己烷-正庚烷为物系,在常压全回流条件下研究了出口堰高对十字旋阀塔板各板效率及全塔效率的影响,并将十字旋阀和F1型浮阀塔板的全塔效率进行了比较.实验结果表明:在正常操作状态下,堰高由30mm增加到50mm,板效率可提高5%-12%.堰高为30mm时,十字旋阀塔板的全塔效率比F1型浮阀塔板要...     

新型高效导向筛板的研究与应用

对高效导向筛板的结构进行改进和优化,开发出新型高效导向筛板.介绍了高效导向筛板实验研究内容和方法,以及工业应用实例.应用表明,高效导向筛板具有生产能力大、分离效率高、板压降低、抗堵性能好、塔板造价低等优点.     

一种具有机械消泡功能的新型塔板

研究开发了一种具有机械消泡功能的新型塔板。该塔板是在普通塔板上放置一种特制的新型机械消泡构件。该构件由相互平行的波纹消泡板组成,构件下半部分沉浸在塔板泡沫层中,起削弱泡沫层波峰高度和降低泡沫层高度的作用,上半部分处于泡沫层上部的气相空间,起惯性除沫的作用。实验结果表明:对于易起泡物系,机械消泡构件能降低雾沫夹带量61%~76%,并大幅削弱泡沫层表面过高的泡沫波峰;对不易起泡物系,机械消泡构件还能降低泡沫层高度15.2%~17.1%。因此,该塔板可以起到延缓塔板泡沫层过高液泛和过量雾沫夹带液泛的作用,具有良好的消泡效果。     

A new method for determining molecular weight distributions of copolymers

Measurement of the molecular weight distributions of copolymers by size exclusion chromatography (SEC) presents problems because the elution volume of any species may depend on its composition as well as its molecular weight. Also, the response of the usual concentration detectors may also be influenced by the copolymer composition as well as its concentration. These problems arise when the copolymer composition may vary with molecular size. Conventional SEC techniques are suitable for copolymers with invariant compositions. This article describes and illustrates a method for measuring molecular weight distributions of copolymers. In many cases, the variation of copolymer composition with molecular weight can also be determined. The technique uses three detectors: (a) an evaporative detector (ED) to measure the concentration, Δc, of the eluting species; (b) a differential refractive index detector (DRI) to measure the refractive index difference, Δn, between the solution and solvent at any given elution volume; and (c) a low-angle laser light scattering (LALLS) detector that measures the corresponding molecular weight of the eluting solutes. This latter measurement is possible because the appropriate values of Δn/Δc are available from the outputs of the other two detectors. For LALLS measurements of molecular weight all the species in the detector cell at any instant must have the same composition or, at least not have Δn/Δc that varies with composition. The method is illustrated with data from ethylene-propylene and ethylene-propylene-diene copolymers.     

碳酸盐反应活性的新快速鉴定方法

系统研究了大量具有不同化学组成、结构和地质特征的碳酸盐集料 ,并选择加拿大Kingston的碱活性碳酸盐集料作为标准进行对比试验。研究内容涉及集料的化学组成、矿物分析和岩相检验 ,集料不同颗粒大小的碱碳酸盐反应动力学 ,探讨并否定了 80℃下晶体热致膨胀因素的影响。根据试验结果提出了一种新的评价碳酸盐集料碱活性的方法。方法的主要试验参数为 :集料尺寸 5～ 10mm、水泥中碱质量分数 1.5 0 % (等当量Na2 O)、水灰比0 .3的小混凝土试件在 80℃、1mol/L的NaOH养护溶液中养护 14d的试件膨胀率大于 0 .10 %。     

A new test method for determining the fracture toughness of concrete materials

The Spiral Notch Torsion Test (SNTT) determines the intrinsic fracture toughness (K_IC) of structural materials by applying pure torsion to cylindrical specimens having a notch line that spirals around the specimen at a 45° pitch. K_IC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, as well as ceramic and graphite materials. One important characteristic of SNTT is that neither a fatigue precrack nor a deep notch is required for evaluation of brittle materials, significantly reducing the sample size requirement. Results are reported for a Portland cement-based mortar demonstrating applicability of the SNTT method to cementitious materials. The estimated K_IC of the tested mortar samples with compressive strength of 34.45 MPa was found to be 0.360 ± 0.017 MPa √m.     

一种计算搅拌槽混合时间的新方法

基于对混合时间定义的思考,提出了一种新的定义方法,在湍流流场数值计算的基础上通过求解示踪剂的浓度输运方程,研究了单层涡轮桨搅拌槽内的混合过程。结果表明：搅拌转速和搅拌桨安装位置都影响混合时间的大小,而进料位置对混合时间的影响不大。对于不同的搅拌转速而言,随搅拌转速的增大,相同体积分数对应的混合时间逐渐减小。当搅拌桨安装在槽中间位置时所对应的混合时间最小。利用适宜的尺寸和安装位置的导流筒可有效降低混合时间。     

全指标精馏塔全塔负荷性能图分析新方法

针对传统塔板负荷性能图在现代精馏塔分析中存在的问题,提出一种精馏塔全指标全塔负荷性能图新分析方法。与单指标的全塔负荷性能图相比,全指标全塔负荷性能图用于精馏塔瓶颈分析,不同塔内件合理匹配分析和最终施工图设计塔内件评价方面更加直观、容易、便于编程。     

不锈钢酸洗过程酸度测定的新方法

为解决不锈钢酸洗过程中存在的一些有色金属离子会对废液酸度的测定造成干扰的问题,通过理论计算,建立了一种新型的酸度测定方法:根据强酸滴定强碱的突跃范围为4.31～9.70,已知K_(sp)[Fe(OH_2)]=4.87×10^(-17),所得突跃范围内Fe(-17),所得突跃范围内Fe⁽²⁺⁾的浓度范围为1.938 8×10(2+)的浓度范围为1.938 8×10^(-8)～1.168 2×10(-8)～1.168 2×10³。将废酸稀释一定倍数,使其溶液中Fe3。将废酸稀释一定倍数,使其溶液中Fe⁽²⁺⁾的浓度在该范围内时,直接以Fe(2+)的浓度在该范围内时,直接以Fe⁽²⁺⁾作为指示剂进行酸碱滴定,将Fe(2+)作为指示剂进行酸碱滴定,将Fe⁽³⁺⁾沉淀时刻作为基准时刻,计算原酸浓度。新方法使用范围较宽,适用于多种钢铁酸洗过程酸度的测定。实验均取1 mL废酸分别稀释10,20,30倍时,利用加标回收法计算得到相对误差为0.23%。     

对水泥助磨剂使用效果检验方法的探讨

针对目前流行的用试验小磨和生产大磨检验水泥助磨剂的提产和增强效果的做法,首先用统计数据说明,球磨机试验结果波动较大,具有不确定性。从水泥原料、球磨机系统、水泥物理检验方法和环境温、湿度等几个方面分析了球磨机试验误差大的原因。根据多年的工作经验,对做好助磨剂球磨机试验提出了建议。     

A new method for judging efficiency of PVC impact modifiers

To determine the efficiency difference between impact modifiers, S-shaped polyvinyl chloride impact curves are compared. But in highly variable scatter regions, the position of the curves is uncertain. A new method focuses on the scatter region by statistically comparing percent ductility for different impact modifiers. If a sufficient number of samples are tested, percent ductility is a sensitive and reproducible function of impact modifier concentration and testing temperatures.