Three-Stage wiped-film molecular evaporator: Design and application

This paper describes the design principles of multistage molecular evaporators with a wiped film which are used for gentle distillation of low-volatility blends of thermolabile materials. The conditions of distillation in an evaporator with a convex evaporation surface are discussed, along with problems relating to the function of the segmented wiper in the formation of the retarded liquid film and the functional principles of closing elements in a multistage evaporator with a single evaporating cylinder and of the built-in entrainment separator in the distillation space, which is designed to retain splashing spray. A TMO 65 three-stage molecular evaporator is described, with an evaporating cylinder having a diameter of 65 mm and a total evaporating area of 0.19 m². This pilot-plant evaporator can be used in the small-capacity production of specialty chemicals or in technological research as a verification unit for establishing data necessary for the operation of large evaporators. These possible applications are documented by the results obtained on fractionation of various important materials. Fractional distillation of crude monoacylglycerols (M) containing 35 to 55% M afforded concentrates containing over 90% M, at yields of 78 – 95% M in the product fraction. Fractionation of oligomers of higher α-olefins gave distillate cuts with high contents of the respective n-mer, suitable for use as synthetic lubricating oils. Fractionation of polyalkylaromatic residue from the production of monoalkylbenzenes produced a distillate fraction with excellent electrical insulation properties. Finally, purification of technical diane-bis-glycidyl ether yielded over 75% of a product fraction which was found suitable for production of insulating material for electrical equipment operating at voltages of 6 to 15 kV.     

Heat and mass transfer in the evaporating film of a molecular evaporator

The hydrodynamic conditions in the wiped-film on the evaporating cylinder of a molecular evaporator have a considerable effect on the distillation output and composition of outlet streams from the evaporator. In this study, selected parameters are investigated in the laminar and turbulent regimes in the film, depending on the evaporator’s liquid load and temperature. Results show that in the case of a turbulent film without concentration and temperature gradients at the same temperature of the evaporating cylinder surface, a higher portion of the feed is evaporated at a lower content of the more volatile component in the distillate. The model studied shows that there are only small differences in the relative volatility as a measure of separation efficiency in the turbulent or laminar film on the evaporating cylinder. The qualitative agreement between experimental results and the results from the model proposed shows that the model describes well the phenomena that occur within the distillation space of the molecular evaporator.     

Numerical modeling of gas-jet wiping process

The proposed study focuses on the numerical modeling of the gas-jet wiping process, which is used to control the coating thickness applied on a solid substrate in various industrial processes. In the galvanization of steel strips, a turbulent slot jet is used to wipe the coating film dragged by a moving steel substrate after dipping in a liquid zinc bath. In the present study a numerical modeling approach of the process is presented using the VOF method for multiphase flows coupled with LES turbulence modeling. Simulations are carried out with three different codes, namely Fluent, OpenFOAM and the research code Thetis. A set of wiping conditions is selected to match a laboratory experiment on a dedicated setup, comparing the numerical results with the experimental data. In a case where the experimental value of the final to initial film thickness is 0.22, Fluent and OpenFOAM overestimate it predicting 0.36 and 0.31 respectively, while Thetis with 0.13 underestimates it. Thetis predicts the closest value to the experiments for the wave amplitude and OpenFOAM for the wavelength. A discussion of the observed differences in the results points out the best modeling practices for the jet wiping process.     

Technique for delaying splashing in jet wiping process

The current study presents an experimental investigation of a technique for delaying the occurrence of splashing in jet wiping process by means of a side jet. Gas jet wiping is a hydrodynamic method of controlling the film thickness applied on a substrate in coating processes. It consists of a turbulent slot jet impinging on a moving surface coated with a liquid film. The process is limited by splashing; a rather violent film instability which is characterized by the ejection of droplets from the runback flow and results in the detachment of the film from the substrate. In the present study an additional side jet is used close to the main wiping jet in order to stabilize the runback flow and avoid splashing. The mean film thickness after wiping is measured using a light absorption method and the results are compared for the single jet wiping and two jet configuration. It is shown that the use of the side jet allows for stronger wiping, resulting in lower values of the final film thickness which cannot be achieved with a single jet.     

Film morphology and molecular orientation in oligothiophene-fluorene films

The effects of processing conditions on film morphology and molecular orientation were studied for a novel conjugated fluorene-bithiophene oligomer, oligo(9,9-dioctylfluorene-alt-bithiophene) (OF8T2). Depending on the method of film preparation, OF8T2 molecules adopt different orientations in the films. X-ray diffraction peak at 4.9° of the OF8T2 film deposited from petroleum ether/dichloromethane mixture is attributed to a layering distance between sheets of OF8T2 chains, which are separated by the octyl side chains. Preferred orientation is clearly inferred through the absence of peaks corresponding to π-π stacking. For the spin-coated film after annealing, X-ray diffraction patterns indicate the presence of lamellar structure with the plane of the conjugated backbone normal to the substrate. The molecules were aligned with long axes along the rubbing direction when the spin-coated film was rubbed and then annealed. These results suggest a convenient approach for preparing active layers for organic optoelectronic devices by simple solution methods.     

Numerical investigation of multiple-slot jets in air-knife wiping

Gas-jet wiping using an air knife is an effective hydrodynamic method to control the coating thickness of zinc on a moving steel substrate in the continuous hot-dip galvanizing process. The current generation of single-slot air knives is widely used in the galvanizing industry but has limitations in producing low coating weights at the higher line speeds desired for the current generation of automotive sheet steel products. In this work, a novel configuration of a multiple-slot jet (multijet) air knife is investigated through numerical simulations as an alternative to the traditional single-slot air knife. The aim of this study is to investigate the sensitivity of the coating weight to the pressure and shear stress profiles in order to determine whether there are operating regions that are more robust to air-knife geometry changes. A modified geometry for the multislot air knife is proposed based on computational fluid dynamics results obtained from a parametric study. The effects of different operating conditions such as the main jet Reynolds number (Re _m), auxiliary jet Reynolds number (Re _a ), and jet-to-wall distances (Z/D) on the final coating thickness were investigated. The results of the modeling showed that by setting the auxiliary jet Reynolds number at a fraction (25%) of the main jet Reynolds number, lighter coating weights can be achieved for higher strip velocities and higher wall-to-jet distances as compared to the single-slot jet design. It is believed that this geometry will provide a robust operating window to enable the prototype design to be employed in the industrial setting.     

硝钙装置蒸发器的清洗

通过对蒸发器积垢多种清洗方法的探索,研究制定出一种高效的化学清洗法,并对此方法进行了实施.实践证明,该方法清洗效果好,节省时间和人力.     

Two phase flow in a climbing-film evaporator

The climbing film flow is modelled on a hydrodynaniic and heat transfer basis taking into account the boiling point elevation due to increased liquid solute concentration along the evaporator tube. Some experimental data are compared with the prediction of the model.     

Heat transfer in a rotating disk evaporator

Experiments were carried out in a rotating disk evaporator with and without a wiper on the evaporation side. The tests were carried out with copper and with monel disks. Overall heat transfer coefficients were obtained directly from the measurements. In addition, evaporation heat transfer coefficients were calculated and the results were correlated. The effectiveness of the wiped film evaporator was clearly manifested in the larger heat transfer coefficients that were obtained.     

薄膜蒸发器在硫化碱蒸发过程中的应用

介绍了薄膜蒸发器在硫化碱蒸发工序中的应用情况。与以前的蒸发器比较，成品碱含量由60％提高到65％，年节约成本（蒸发工作）148万元，废气排放达标。     

升膜板式蒸发装置及其操作

介绍了阿法拉伐板式蒸发装置的生产原理、工艺流程、控制要点、开停车操作、异常现象的判断和处理以及操作中的注意事项。     

An improved MSF evaporator configuration

The paper describes an improved MSF evaporator configuration called “Paired Stage? Cross-Flow” which combines the best features of the well known long-flow and cross-flow designs. The paired stage configuration is well suited for lage unit capacities and, with the exception of a minor variation of the vapor flow path, is based completely on existing, well proven MSF technology. Air model tests were performed to determine the effect of the variation in vapor flow path.     

Application of improved high-performance evaporator

An improved horizontal-tube, thin-film evaporator that has a high heat transfer coefficient when working at low temperature is described. Applying this evaporator, it is possible to design a multi-effect distiller with a very large number of effects and a vapour compression distiller with an extemely small compression ratio, thus achieving a considerble reduction in energy consumption in those processes.Actual applications of this improved evaporator are described as used in a conventional multi-effect distiller, a solar heated multi-effect distiller, a double-effect reheat type distiller and a mechanical vapour compression distiller. A notable point of this paper is the introduction of a new vapour compression distiller that has a lower energy consumption than ever seawater reverse osmosis desalination plant.     

新型结构蒸发器的制造

蒸发器管程为蛇形加热管线。管束是蒸发器的核心部件 ,制造管束的关键是控制异径管以及异径管与封头管板的焊接质量。加热管线通过异径管的套管与封头管板相连接。异径管的套管与管板的连接是挠性结构 ,改善了连接点的应力状况 ;U形管的中心距和管板、支持板的中心距必须保持一致。加热管的对接焊缝必须进行 10 0 %射线探伤。由于管孔和U形弯头的中心距较小 ,异径管与封头之间的空间有限 ,为方便换热管与异径管、封头管板与异径管的焊接 ,采取从上到下 ,按排组焊、无损探伤的组装方法     

蒸发工序冷凝水的梯级利用

介绍了烧碱蒸发装置热源蒸汽冷凝水、二次蒸汽冷凝水的梯级利用措施,并分析了其经济效益。     

Melting model for modular self wiping co-rotating twin screw extruders

A model for the melting process in a self wiping co-rotating twin screw extruder is described. Self-wiping co-rotating twin screw extruders are modular and starve fed. This leads to melting mechanisms that are different from single screw extruders. The melting process in the modular screw configurations generally occurs in specialized sections such as kneading disk blocks. The model, based on our previous experimental observations, considers the formation of two stratified layers of melt in contact with the hot barrel and solid pellets in contact with the relatively colder screw. In the kneading disk blocks, a part of the solid bed is blocked because of the relative stagger between successive disks. The model predicts both the location of melting and melting lengths in a screw configuration. Calculations for individual screw elements and kneading disc elements are presented first. Melting in a modular configuration of these elements is then considered. The effect of operating variables such as mass flow rate and screw speed on melting is then studied. The model is put in a dimensionless form and the effect of various dimensionless groups is discussed. We make a comparison to the experiment and agreement is good.     

蒸发器末效二次汽管道增加挡水环有效提高蒸发器产能的应用

随着社会经济的快速发展,经济进入转型期,在这一过程中,如何降低资源、能源消耗,成为企业生产必须把握的一个关键点。蒸发器末效二次气管道增加挡水环,有利于使蒸发器产能得到提升,从而降低生产消耗,更好地实现生产效益。在对蒸发器末效二次气管道增加挡水环问题进行了分析,就蒸发器的产能情况进行了探究,以期更好地实现蒸发器产能效益。     

Modelling of flow in a wiped film evaporator

In a wiped film apparatus, the hydrodynamic conditions of the flow have a direct effect on the film thickness and on the residence time of the molecules and thus on the effectiveness of mass and heat transfer. Measurements of the residence time distribution (RTD), for different stirring velocities, allowed to propose a model for the flow as a series of perfectly mixed cells in parallel with a series of perfectly mixed cells exchanging mass with a dead zone.