Thermal Separation Processes Research Articles

Definition von Destillationslinien bei der Trennung von Mehrstoffgemischen

AbstractDefinition of Distillation Lines in the Separation of Multicomponent Mixtures. In recent years “distillation lines” have been used for the assessment of the separation behaviour of multicomponent mixtures, with these distillation lines being defined differently by different authors. The theory of distillation of multicomponent mixtures shows that it is appropriate to distinguish between residue lines and rectification lines. While the profile of residue lines is determined solely by the thermodynamic phase equilibrium, that of rectification lines also depends upon the mass transfer model used. By analogy with VDI Guideline 2761: “Thermal Separation Processes in Process Engineering”, it is proposed that residue lines and rectification lines are designated by the collective term distillation lines.

Requirements of thermodynamic data in the chemical industry

Abstract Phase equilibrium thermodynamics is one of the most important fundamental sciences for process development in the chemical industry. The outstanding results achieved by thermodynamics in the last decades have led to a profound change in working methods for the development of thermal separation processes. The demands on availability, accuracy, completeness and range of application for thermodynamic data are discussed from the viewpoint of the chemical industry from product development to plant design. Practical examples from the different stages of process development are used to illustrate these points and indicate areas of future research.

Thermodynamics in process development in the chemical industry - importance, benefits, current state and future development

Phase equilibrium thermodynamics is one of the most important fundamental sciences for process development in the chemical industry. The outstanding results achieved by thermodynamics in the last decades have let to a profound change in working methods for the development of thermal separation processes. However, there remains a large number of unsolved problems in the field of phase equilibrium thermodynamics which often represent a significant restriction to process development for the chemical engineer. Current deficiencies are illustrated with some significant examples and desired developments for the future are suggested.

Modelling of pressure drop in packed columns

AbstractThe correct choice of packing is of decisive importance for optimum process efficiency in the operation of two‐phase countercurrent columns. An important criterion for this choice is the pressure drop in the gas flow. Theoretical relationships are derived for calculating the pressure drop in beds with dry and trickle packings. It has been demonstrated by comprehensive experiments that these relationships allow the pressure drop to be determined more accurately than by previous methods. The experiments were performed at the Department of Thermal Separation Processes of Bochum University on 54 different packed beds, using 24 different systems.

Contribution to Design and Scale‐Up of Packed Columns

AbstractThe demand for high accuracy in packed column design for countercurrent thermal separation processes, such as rectification, absorption and desorption, has been stepped up research in scaling of packed column efficiency in response to the growing application of packings for various systems in the chemical and allied industries. The investigations confirmed the suitability of relationships for describing the performance, the validity of which was proved with differing systems and packings. This equations takes due account of geometric, hydrodynamic and system‐related parameters that govern mass transfer and the fluiddynamics in packed columns.

Membranes and modules for transmembrane distillation

Aqueous solutions can be concentrated and pure water prepared via a thermal membrane separation process. Membranes used for this purpose must be microporous and hydrophobic. A temperature difference causes a vapour transfer from the warmer to the colder side. Modules for this process are, for practical reasons, counterflow devices with capillary membranes that have good flow conditions outside a capillary bundle, too. This requires special capillary arrangements and module constructions.

Relationship between residence time, fluid dynamics and efficiency in countercurrent flow equipment

AbstractThe suitability of any item of equipment for a given thermal separation process cannot always be judged solely in the light of efficient and loading range data. In vacuum rectification, involving a large number of theoretical stages, the vapour pressure drop per transfer unit exerts a considerable effect on the energy consumption and thus largely governs the choice of column fittings. Furthermore, the pressure drop per transfer unit determines the temperature at the bottom of a rectification column and, hence, the suitability of the equipment for the separation of heat‐sensitive products. It is also an important criterion for compressor requirements in absorption processes. Another factor of considerable importance in separating heat‐sensitive mixtures by distillation is the time during which the product, particularly the liquid phase, is exposed to a given temperature in the column. Therefore, a standardized liquid residence time has been adopted to evaluate the systems in their entirely. This residence time depends on the hydrodynamic conditions in the column and is thus closely related to pressure drop and efficiency. Further important factors, which may decide the selection of column internals, are the specific volume and mass of the column. Based on theoretical considerations, a flow model is derived for describing the main loading range of countercurrent packed columns; the relationships between the above mentioned parameters are presented.

The Clusius-Dickel Thermal Diffusion Column – 50 Years after its Invention

On the occasion of the 50th anniversary of the appearance of the first paper on the thermal diffusion column published by Klaus Clusius and Gerhard Dickel a review on the development of this simple tool for the separation of gaseous or liquid mixtures is given. The pioneer work of the inventors is valued and an attempt is made not only to evaluate the development of the thermal diffusion separation process and its impacts to the theory of isotope separation but also to point out the restrictions due to low thermodynamic efficiency.

Application of modern packings in thermal separation processes

AbstractA report is presented on the performance of modern dumped and structured packings for application in the field of thermal separation processes. The evaluation of the results is based on extensive experimental investigations of rectification, absorption, and desorption systems. The following are indicated: the efficiency in terms of the number of theoretical stages per unit height or in terms of the height of transfer unit or volumetric mass transfer coefficient, the pressure drop per unit height as well as per theoretical stage or per gas phase transfer unit, and the liquid hold‐up, whereby either the gas capacity factor or the liquid load was adopted as influencing parameter, and finally the maximum gas capacity factor as a function of the flow parameter. The results are presented in diagrams and tables.

Wirtschaftlichkeit als Kriterium für die Entwicklung, Auslegung und Auswahl von Apparaten und Maschinen für Prozeßstufen

AbstractEconomy as a criterion for development, design, and choice of equipment and machines for process steps. The object of this paper is to show how a supplier of individual machines can influence the total costs of a chemical processing plant. This influence is quantified using actual examples based on the development of a product range, the optimizing and matching together of mechanical and thermal separation processes, and the selection of the most suitable types of equipment. Studies show that the products and services of an equipment manufacturer can influence substantially more than just capital investment costs and interest charges with their consequent effects on the annual running costs of a plant. It is possible to reach more economical solutions for important stages in a manufacturing process if the plant designers and the equipment manufacturers work closely together. A too tightly specified enquiry can prevent a manufacturer from offering the technically and economically optimized solution. By involving equipment manufacturers and correctly using their know‐how one can tap a substantial potential for the reduction of plant running costs.

Anwendung der Mischphasen‐Thermodynamik auf die Berechnung von thermischen Stofftrennverfahren

AbstractUse of multiphase thermodynamics in the calculation of thermal separation processes. The methods currently in use for calculation of the equilibrium between phases are reviewed. It is shown that such methods can be subdivided into those based on: (i) equations of state, (ii) the correspondence principle, and (iii) molecular behaviour. The latter methods have proved to be especially successful. They are based on simple and plausible representations of the interactions between atoms and molecules and can be further subdivided into methods according to the principle of local composition, in which further measurements are required, and into methods according to the principle of group increments, in which data can also be precalculated if no measurements are available. For practical purposes, however, rough methods of calculation also afford a good guide. They are often sufficiently accurate for an initial calculation and can be carried out, without the use of a computer, either with the aid of graphical methods or with a pocket calculator, so that parameter changes can be readily observed.

Energie‐Einsparung — eine Herausforderung

AbstractEnergy saving – a challenge. Between 1955 and 1976, the specific energy consumption – i.e. the energy consumption referred to the net production volume at constant prices – in the Federal German chemical industry fell by ca. 70%. Thus in 1977 this branch of industry accounted for only 8.4% of the primary energy consumption of the national economy. The possible reasons for this trend lie in a highly dynamic approach to product development, fast growth, and energy‐conscious training of process engineers. The future should see further savings resulting from advances in thermal separation processes by introduction of process computers and – in the long term – by developments in catalysis.

Calculation of thermal diffusion separation processes in a system with a traveling magnetic field

The equation of mass transfer in a column is used to calculate the separation factor and the separative power of a device with a traveling magnetic wave.

Thermal diffusion separation of isotopes in solutions

The thermal diffusion constant is determined for potassium isotopes in an aqueous solution of potassium iodide. Variants of the organization of the thermal diffusion separation process in solutions are discussed.

A combined relaxation-newton method as a new global approach to the computation of thermal separation processes

Two basically different methods, formerly used sequentially to solve multicomponent thermal separation problems, are now allowed to function simultaneously within a single algorithm to ensure a rapid yet stable convergence to the solution. By combining the stability of the Rose-Sweeney-Ball method with the rapidity of the Newton-Raphson method, the solution is easily reached without encountering the difficulties of employing these methods separately.