Analysis of the Zone Connecting Consecutive Sectors in Generalized Distillation Columns by Using the Ponchon-Savarit Method

Ponchon-Savarit is a classical graphical method for the design of binary distillation columns. This method is still widely used, mainly with didactical purposes, though it is also valid for preliminary calculations. Nevertheless, no complete description has been found in books and situations such as different thermal feed conditions, multiple feeds, possibilities to extract by-products or to add or remove heat, are not always considered. In this work we provide, a systematic analysis of the Ponchon-Savarit method by developing generalized equations for the operating lines or difference points, as well as a consistent analysis of what may happen in the zone between two consecutive trays of the corresponding sectors separated by a lateral stream of feed, product, or a heat removal or addition. The graphical interpretation of all situations shown allows a clarifying view of the different possibilities in the rectifying column and completes the existing literature about this method

Robust program for LLSE data correlation of ternary systems

The existing commercial software packages (like Dechema Data Preparation Package (DPP) and the regression utilities of Chemical Engineering simulators like Chemcad) have been widely used and their extensive capabilities are well-known. Nevertheless, and as long as LLE calculations is concerned, they have been designed for the simplest equilibrium behaviour. For example, for ternary systems it is only possible the correlation of type 1 and type 2 LLE data. None of these applications allows for the correlation of type 0 LLE, type 3 LLLE or type 4 LLSE systems. To enable a possible extension of such software, a robust calculation algorithm to compute phase equilibria among condensed phases for all these more complicated behaviours has been developed.Vicepresidency of Research (University of Alicante) and Generalitat Valenciana (GV/2007/125)

Analysis of the zone connecting consecutive sectors in distillation columns by the Ponchon-Savarit method

McCabe-Thiele and Ponchon-Savarit methods are two classical graphical methods for the design of binary distillation columns very useful for didactical purposes and for preliminary calculations. Nevertheless, their description in the literature is not complete and not all the cases are analysed. To complete the academic literature dealing with this subject we have generalized equations for the operating lines or DP that define the change between two consecutive sectors ΔkC for any feed condition, together with the different possibilities to extract products or to add or remove heat. A consistent analysis of what may happen when changing between sectors in the column is presented.Dpto. Ingeniería Química, Instituto de Ingeniería de los Procesos Químicos, Universidad de Alicante

Graphical Representation of the Changes of Sector for Particular Cases in the Ponchon Savarit Method

A graphical and systematic analysis of particular cases where the compositions of the streams developed in the rectification column coincide with one of the vapor (yGFk) or liquid (xGFk) portions generated from the GFk can be found in this material (i.e.: yGFk=yk+1,1 or xGFk=xk,NTk).University of Alicant

Supplementary Material: Analysis of the Connecting Zone Between Consecutive Sections in Distillation Columns Covering Multiple Feeds, Products and Heat Transfer Stages

Supplementary Material: J.A. REYES-LABARTA, M.D. SERRANO and A. MARCILLA. ANALYSIS OF THE CONNECTING ZONE BETWEEN CONSECUTIVE SECTIONS IN DISTILLATION COLUMNS COVERING MULTIPLE FEEDS, PRODUCTS AND HEAT TRANSFER STAGES. Latin American Applied Research an International Journal of Chemical Engineering. 2014, vol. 44(4), 307-312 (http://www.laar.uns.edu.ar/indexes/artic_v4404/44_04_307.pdf)A complementary analysis of the work Reyes-Labarta et al. (Latin American Applied Research an International Journal of Chemical Engineering. 2014, vol. 44(4), 307-312) applied to particular cases where the compositions of the streams developed in the rectification column coincide with one of the vapor (yGFk) or liquid (xGFk) portions generated from the GFk can be found in this supplementary material.University of Alicant

Geometrical study of the three-dimensional temperature–composition diagrams. An important aid to understand the behavior of the liquid–vapour equilibrium in ternary systems

In this work the usefulness of qualitatively studying and drawing three-dimensional temperature–composition diagrams for ternary systems is pointed out to understand and interpret the particular behavior of the liquid–vapour equilibrium of non-ideal ternary systems. Several examples have been used in order to highlight the interest and the possibilities of this tool, which should be an interesting support not only for lecturers, but also for researchers interested in experimental equilibrium data determination.The authors are grateful to the University of Alicante for the funding of the “Grupo de Innovación Tecnológica-Educativa (GITE) de Ingeniería Química”, where this work has been carried out

Pitfalls on computing liquid-liquid phase equilibria using the k-value method

Poster presented in the 11th Mediterranean Congress of Chemical Engineering, Barcelona, October 21-24, 2008.The present study illustrates some of the pitfalls of the LLE data correlation and proposes some ideas to overcome them. Convergence efficiency is compared for different strategies to calculate the LLE. First, the activity objective function (O.F.(a)) evaluated close to the LLE solution, uses to provide a poor definition of the objective function minimum (O.F.(a)<10-12), as shown in the example of Figure 1a. Next, a combination of the activity and the minor common tangent condition O.F.(t) based on Iglesias-Silva et al. [1] is used, and a sharper minimum for the objective function value is obtained. Finally, we present a modification of the vector method developed by Eubank et al. [2]. The original work used the vector method combined with the maximum area criterion as equilibrium condition, although it was later proved to be only applicable in the case of binary systems. Our algorithm, that is applicable for ternary systems, uses the minor common tangent equilibrium condition [3]. First, an α-angle range for each ternary global mixture M (Figure 1b) is defined. For a sheaf of straight lines passing through the composition of a mixture M, the two common tangent points (I, II) to the gM function in the corresponding sectional plane are obtained (necessary condition). Among all pairs of calculated compositions, the “true” tie-line corresponds to the minimum value for the Gibbs energy of mixing (gTL) (sufficient condition) and the objective function of activity must be minimum and equal to zero. The O.F.(a) is evaluated for each α-angle at the two common tangent points to look for the minimum (O.F.(a)=0). Those values (suggested method O.F.(a)) are compared to the other previous approaches (Figure 1a) showing that a sharper minimum, corresponding with the “true” tie-line, is obtained when the suggested method with the minor common tangent condition is used to obtain the activity objective function.Vicepresidency of Research (University of Alicante) and Generalitat Valenciana (GV/2007/125)

Review and extension of the McCabe-Thiele method covering multiple feeds, products and heat transfer stages

The McCabe-Thiele method is a classical approximate graphical method for the conceptual design of binary distillation columns which is still widely used, mainly for didactical purposes, though it is also valuable for quick preliminary calculations. Nevertheless, no complete description of the method has been found and situations such as different thermal feed conditions, multiple feeds, possibilities to extract by-products or to add or remove heat, are not always considered. In the present work we provide a systematic analysis of such situations by developing the generalized equations for: a) the operating lines (OL) of each sector, and b) the changeover line that provides the connection between two consecutive trays of the corresponding sectors separated by a lateral stream of feed, product, or a heat removal or addition.Chemical Engineering Department. University of Alicant

GE models and algorithms for condensed phase equilibrium data regression in ternary systems: limitations and proposals

Phase equilibrium data regression is an unavoidable task necessary to obtain the appropriate values for any model to be used in separation equipment design for chemical process simulation and optimization. The accuracy of this process depends on different factors such as the experimental data quality, the selected model and the calculation algorithm. The present paper summarizes the results and conclusions achieved in our research on the capabilities and limitations of the existing GE models and about strategies that can be included in the correlation algorithms to improve the convergence and avoid inconsistencies. The NRTL model has been selected as a representative local composition model. New capabilities of this model, but also several relevant limitations, have been identified and some examples of the application of a modified NRTL equation have been discussed. Furthermore, a regression algorithm has been developed that allows for the advisable simultaneous regression of all the condensed phase equilibrium regions that are present in ternary systems at constant T and P. It includes specific strategies designed to avoid some of the pitfalls frequently found in commercial regression tools for phase equilibrium calculations. Most of the proposed strategies are based on the geometrical interpretation of the lowest common tangent plane equilibrium criterion, which allows an unambiguous comprehension of the behavior of the mixtures. The paper aims to show all the work as a whole in order to reveal the necessary efforts that must be devoted to overcome the difficulties that still exist in the phase equilibrium data regression problem.Financial support from the Vice-Presidency of Research (University of Alicante) and Generalitat Valenciana (GV/2007/125)

Vapor-liquid equilibria using the Gibbs energy and the common tangent plane criterion

Phase thermodynamics is often perceived as a difficult subject that many students never become fully comfortable with. The Gibbsian geometrical framework can help students to gain a better understanding of phase equilibria. An exercise to interpret the vapor-liquid equilibrium of a binary azeotropic mixture, using the equilibrium condition based on the common tangent plane criterion (the Gibbs stability test), is presented in this paper. From a T-composition phase diagram for the mixture, the temperature is set at different values: above, intermediate to, and below the boiling temperatures of the pure components, to intersect different regions of the system. Students prepare an Excel spreadsheet where the Gibbs energy of mixing of the vapor and liquid mixtures are calculated and represented over the whole range of compositions and then, apply the Gibbs stability test to ascertain the aggregation state of the system and to calculate the VL phase equilibrium compositions. Finally, Matlab is used to generate the 3D Gibbs energy of mixing surfaces for both phases over the whole range of temperatures which facilitates the geometrical interpretation of the vapor-liquid equilibrium.The Vicepresidency of Research (University of Alicante) and Generalitat Valenciana (GV/2007/125)