Multicomponent Distillation Column Research Articles

Geometric nonlinear analysis of multicomponent nonideal distillation: a simple computer-aided design procedure

A simple noniterative design procedure for multicomponent distillation columns is developed. The procedure is based on the geometric theory of distillation presented in our previous work, and applies to constant relative volatility, ideal, nonideal, and azeotropic mixtures. The design technique provides an accurate and efficient method for determining the number of theoretical trays in the column, the optimum feed-plate location, and the exact product distribution, without the use of lengthy iterative schemes involving column simulations, as is the current practice. The procedure is easily extended to incorporate reactive distillation columns, as well as the retrofit design of distillation columns. The design procedure is illustrated using a number of multicomponent systems, including the mixture acetic acid—water—ethyl acetate—ethanol, which exhibits three binary azeotropes, one ternary azeotrope, and a nonideal vapor phase.

Application of energy-utilization diagram for graphic exergy analysis of multicomponent distillation columns.

A new method for graphic exergy analysis of multicomponent distillation and for visualization of rate characteristics of a distillation column is proposed by applying an energy-utilization diagram, EUD. By introducing the concept of a premixing model, the exergy losses in a distillation column can be decomposed into losses caused by premixing in liquid phase and those caused by premixing in vapor phase. Also, the energy exchange in a phase change such as condensation or evaporation of each component is displayed individually. By introducing the concept of partial molar quantities, those exergy losses in liquid phase and vapor phase can be categorized into losses caused by heating and mixing in liquid phase and losses caused by cooling and mixing in vapor phase. To use this method, the energy exchanged (ΔH ea ) and the energy levels (A ed and A ea ) are displayed systematically on EUD. As a case study, simulation of the separation of n-hexane, n-heptane and n-octane is conducted for a column with 11 plates. The effect of reflux ratio and side-cooling or side-heating is discussed by using EUDs

Multicomponent batch distillation column design

We are presenting a short-cut method for design of multicomponent batch distillation columns, operating under variable reflux and constant reflux conditions. The method is essentially a modification of the short-cut method widely used in the design of continuous multicomponent columns. The technique has been tested for both binary and multicomponent systems

Rigorous [formula omitted]namics and [formula omitted]ntrol of continuous [formula omitted]stillation [formula omitted]ystems—simulation and experimental results

The scope of this article is to focus the role of rigorous dynamic modeling and to present a simulation tool for multicomponent distillation columns. Comparisons between predicted dynamic profiles and available experimental results confirm that such kind of packages, based on rigorous dynamics, can nowadays be of real and practical value for engineering purposes. A short review of different applications of the DYCODIS program in a wide range of design and operating problems is also presented, namely: 1. — a general time domain approach to verify dynamic interactions among different control loops; 2. — the dynamic behavior of a superfractionator with a very large time delay; 3. — the dynamic stability analysis of multiple steady-states both for heterogeneous columns and interlinked distillation systems. In all these proposed examples, the program showed itself to be useful, reliable, robust and manageable with regard to both control synthesis or process analysis purposes.

Dynamic and control behavior of multicomponent distillation columns

A general purpose digital simulator that can be used for studying either the transient response or control behavior of multicomponent tray distillation columns has been developed. The DYCONDIST simulator, written in FORTRAN 77, utilizes a column model that solves the coupled nonlinear material and energy balance equations for each stage. Control performance of any column is analyzed by the user deciding upon a control strategy and then invoking one or more or the existing control algorithms or employing a user-written control algorithm. Features of the simulator are described and its use is illustrated for studying the open loop (dynamic) behavior and control behavior of a 29 tray depropanizer.

Geometric behavior and minimum flows for nonideal multicomponent distillation

A simple algebraic method for calculating the minimum flows for nonideal multicomponent distillation columns has been developed. The method, which is based on an analysis of the geometry of the composition profiles in the state space, is quite general and applies to ideal, nonideal and azeotropic mixtures. Using the set of composition transforms developed by Barbosa and Doherty (1988, Chem. Engng Sci. 43, 1523–1537), the procedure can be extended to include multicomponent reactive distillation columns. For systems with constant relative volatilities, our method and Underwood's method are shown to be identical. The technique provides an accurate and efficient procedure for determining the minimum flows without the necessity of lengthy iterative schemes, as is the current practice. The method is demonstrated using several different multicomponent systems, including the mixture acetaldehyde—methanol—ethanol—water, which exhibits a pair of binary azeotropes, a ternary azeotrope, and a simple distillation boundary in the three-dimensional composition state space.

Calcul d'une colonne de rectification à multiples alimentations et soutirages latéraux

A new short-cut method for designing multi-component distillation columns involving multiple feeds and sidestreams is presented in this paper. The procedure is based on a principle of decomposition of the column into several sections, so that the minimum reflux ratio and the number of plates can be determined in each section using the classical correlations of Fenske, Underwood and Gilliland. The method gives, with a low CPU time, the operating reflux, the flows and compositions of the output streams, the location of the feeds and side-streams and the number of theoretical plates of the column. Various examples involving three or four component mixtures are presented. The results of the short-cut method are compared with those obtained by a rigorous simulation program. Good agreement of the results allows validation of this fast and attractive procedure for designing this type of complex separation process. Furthermore, this method opens up a new research area in the general problem of optimal synthesis of separation sequences: indeed the design of multiple feeds and sidestreams columns allows the number of columns to be decreased, and consequently the investment and operating costs can be significantly reduced. Finally, this short-cut method appears to be very attractive for an accurate initialization of rigorous simulation methods, whose convergence properties depend strongly on the initialization.

Two-part modular reduced-order model for multicomponent multistage distillation columns.

A new, efficient model reduction method for multistage distillation columns is proposed by combining the orthogonal collocation method and the two-part modular concept. To assess the performance of the proposed method, numerical simulation was performed for two distillation examples—the high-purity freon 11–12 binary system and the nonideal ethanol–1-propanol–water ternary system— and the results were compared with those obtained by the methods of existing collocation as well as rigorous equation solving.It was shown that the proposed method reduces the computing time by about 40% with accuracy comparable to that of the rigorous methods. Furthermore, while the existing collocation method could not properly reproduce the sharp changes of variables in the vicinity of the feed stage, the proposed method could successfully reproduce them as well.

Role of energy balances in dynamic simulation of multicomponent distillation columns

The role of energy balances in simulating the transient behaviour of multicomponent distillation columns is analyzed and discussed in this note. Despite the usual approaches referred to in the recent literature, a few examples show how big discrepancies can be observed as a result of neglecting the time derivative of the energy holdups. In the meantime, a few comparisons are presented in order to show the possible important benefits related to a simultaneous solution of the whole system of algebraic and differential equations.

Design and minimum-reflux calculations for single-feed multicomponent reactive distillation columns

A new set of transformed composition variables is introduced to simplify the design equations for single-feed, multicomponent reactive distillation columns. Based onthese equations, a general method of calculating minimum reflux ratios for reactive distillation columns is presented. The new composition variables are also used to derive simple relationships between the dependent design variables which are not evident when the design equations are written in terms of mole fractions.

Design and minimum-reflux calculations for double-feed multicomponent reactive distillation columns

A new set of transformed composition variables is introduced to simplify the design equations for double-feed, multicomponent reactive distillation columns. These new equations are used to develop a general method of calculating minimum reflux ratios for reactive distillation columns. The application of these equations to the design of reactive distillation columns for esterification processes is discussed.

Simulation und Optimierung der Mehrstoff‐Rektifikation

AbstractSimulation and optimization of multicomponent distillation. Different methods for simulating multicomponent distillation columns are presented and compared with respect to the effort required and the accuracy that may be obtained. Inclusion of mass transfer kinetics based on the laws of multicomponent diffusion in the models significantly increases computer time, but the additional accuracy in the prediction of concentration profiles may justify this effort also in design practice. In particular, the unusual behaviour of concentration profiles due to multidiffusion effects can only be explained by such improved models. The new methods of multicriteria optimization offer substantial advantages over a scalar‐optimization and, in addition to economic criteria, also allow inclusion of aspects of operational safety and of environmental requirements.

Discrete-event simulation of a sequence of multi-component batch distillation columns

The application of a discrete-event simulation system (GPSS) to modelling of a sequence of multi-component batch distillation columns, such as might be employed in a solvent recovery operation, is described. The primary objective of this simulation is to demonstrate the application of the GPSS system to determination of equipment and manpower utilization. The complete GPSS coding is included. Operating parameters corresponding to a particular installation are readily varied by an analyst.

Optimal reflux rate policy determination for multicomponent batch distillation columns

This paper describes a procedure to obtain optimal reflux or optimal distillate rate policy for multicomponent batch distillation columns using the Pontryagin's continuous maximum principle. For application to multicomponent systems, a reduced order model is used using short-cut procedure developed specifically for analysis and design of batch columns.

Numerical studies in solving dynamic distillation problems

The eigenvalues of the Jacobian corresponding to the equations describing the dynamic behaviour of a multicomponent distillation column are studied. An alternative estimation of the spectral radius is proposed and used to implement a policy to switch between non stiff and stiff integration method. Furthermore the sparse structure of the Jacobian is exploited to reduce computation costs. Comparative results are given using several multicomponent mixtures.

Experimental Application of a Multivariable Self-Tuning Controller to a Multicomponent Distillation Column

The multivariable self-tuning controllers of Chien et al. incorporate a Smith predictor-type of time delay compensation (STC-TDC). These are applied to dual composition control of a pilot-scale multicomponent distillation process. Both versions of the STC-TDC, i.e., with and without decoupling, are compared with a standard dual-loop PI controller and are seen to provide excellent control in the face of significant process interactions and nonlinearities.

Dynamic simulation of a multicomponent distillation column with asymmetric dynamics

AbstractThe dynamic behavior of an existing industrial distillation column with eight components and twenty trays has been investigated. The column exhibits “asymmetric dynamics”, since the time required to move from one steady state to another can vary significantly depending on the direction of the change. The column also exhibits highly nonlinear behavior and very long response times for intermediate ranges of step disturbances. These long response times are associated with the migration of key components through the column.

Reduced-order models for separation columns—V. Selection of collocation points

In the earlier parts of this paper, a method for developing reduced-order models for separation columns was presented. This article presents some guidelines for determining the degree of order reduction achievable for a given column. An index called ORP (Order Reduction Parameter) is developed to predict a priori, the extent of order reduction achievable and to provide guidelines for choosing a reduced-order model of the appropriate size. This, combined with a comparison with a steady state solution, can provide the engineer with a good estimate of the number and location of collocation points to be used in the reduced-order model. The method is developed using a simple binary absorber and illustrated by application to a more complex, multicomponent distillation column.

A new simulation procedure for multicomponent distillation column processing nonideal solutions or reactive solutions.

A powerful new simulation procedure is developed for multicomponent distillation columns processing nonideal solutions or reactive solutions. Although the tridiagonal matrix algorithm is incorporated, the main calculational loop is the Newton-Raphson method in which liquid mole fractions are chosen for the independent variables and the functions to be zeroed are originally defined. The procedure does not vitiate at all such great advantages of the conventional tridiagonal matrix method as the ready incorporation of heat balances, nonideality of the solutions and chemical reactions, and still the algorithm and computer programming are rather simple. Nevertheless, the procedure presents much greater stability in finding converged solutions. A total of eight numerical experiments are made under a variety of conditions, and in all cases rigorous solutions are obtained achieving convergence in three to nine iterations.

A simulation procedure for multicomponent distillation column within which three phases of vapor and two partially immiscible liquids are present.

Application aux colonnes a trois phases de l'idee de base d'une nouvelle methode de simulation des colonnes a deux phases constituees de solutions non ideales ou de solutions reactives. Exemple numerique