Industrial Distillation Column Research Articles

Selection of the Best Control Configuration for an Industrial Distillation Column

Abstract The best regulatory control structure is determined for an industrial, multicomponent, high purity ethylbenzene distillation column with 50 trays- Steady-state plant data and the design in-formation is utilized with a steady-state model of the column. The column-model match is obtained by adjusting the column efficiency. Dynamic column behaviour is experimenta11y obtained by pulse and step testing. Steady—state rating programs are used to obtain the steady-state process and disturbance gain matrices of the (L,V), (D,V), (L,B) and (L/D,V/B) control configurations. Steady-state control configuration selection methods RI, RGA, NI, MRI, JEC, SVD and RDG and the Eigenstructure concept are made use of Single-end and dual composition control of the column is examined by IMC based PI controllers. The results revealed that for feed flow rate and composition disturbances, column can be controlled with a single-end structure.

Design, analysis and realization of a state control system for an industrial distillation column

A systematic method for the development and practical implementation of a control system on the basis of a state observer and controller for the bottom concentration of an industrial distillation column is described. The development and testing of the state observer and state controller together with the system identification were carried out exclusively on the basis of simulation calculations. Initially the control system was studied in short individual tests, before a final long-term test was carried out under operating conditions of the real unit. The experience obtained in implementing the state control system is described. It was found that, with regard to dynamic column behaviour during disturbances, the state control system was superior to conventional PI-control concepts.

Probleme und Erfahrungen bei großtechnischen Packungskolonnen

AbstractProblems and experience with industrial scale packed columns. Apart from column plates, random and structured packings are being used increasingly as internal components of distillation columns. The advantage of structured packings lies in an enhanced specific separation performance at significantly lower pressure drops than in the case of classical plate columns. In contrast to column plates, there is no defined liquid pathway in random and structured packings; in particular, the dependence upon the initial distribution in columns of large diameter proves to be problematical. Recent theoretical model calculations and laboratory scale studies have shown that the liquid distribution in structured packings is of paramount importance, above all in columns having diameters in excess of 1 m. The present article reports problems and experience gained with industrial scale distillation columns by considering four examples. In addition, the authors also provide an in‐depth account of the factors and problems relating to the assessment of separation performance of industrial columns.

Control of a binary sidestream distillation column

We present results of a comprehensive study of the dynamics and control of a large industrial distillation column that separates a binary mixture of propylene and propane into three products: polymer-grade propylene distillate, chemical-grade propylene liquid sidestream, and propane bottoms

Model Based Observation and Control of Distillation Columns

Two applications of mathematical process modeling to industrial scale distillation columns are discussed. In the first part the stripping section of a methanol-water separation column is described with the help of the location of a temperature front. A simple linear state space model is used to design an observer and state controller for the reboiler duty of the column. Its application is compared with experimental data obtained from an industrial distillation column with a PID-controller.In the second part an analytically reduced mathematical model for the estimation of the product composition in multicomponent distillation is presented. It is applied successfully to a fractionation plant consisting of three interlinked columns and is used for the purpose of diagnosis.

Multivariable internal model control for a full-scale industrial distillation column

A multivariable internal model control system was developed for a full-scale distillation column. The basis for the design of the control is a two-input/two-output matrix of linear transfer functions describing column dynamics. The control system is designed to perform dual composition control of the overhead and bottom products. Hardware constraints dictate multirate sampling of the product concentrations. In addition, the column exhibits inverse response to changes in reflux flow. The multirate sampling is addressed by a unique implementation of a feedforward decoupling control. A reduced-order controller design technique is developed to handle the non-minimum-phase behavior of part of the column. Simulations demonstrate the improvement in control obtained from this approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

RGA ANALYSIS FOR DISTILLATION CONTROL

This paper presents the relative gain analysis of two industrial distillation columns. Both columns involve multicomponent separation and the purpose of the relative gain analysis has been to find proper pairing of manipulated and controlled variables. The matrix oriented method of Wang and Henke has been employed in the study, The study has investigated the effects of single-precision versus double-precision programming, step-size, and tightness of convergence, upon the relative gain array. The results with single-precision programming and double-precision programming have yielded significantly different results. The results confirm that a considerable reduction in the step-size of the manipulated variables may be necessary in some cases to achieve meaningful results. They also indicate that tight convergence may be required for some columns at a considerable expense in terms of CPU time while for others, loose convergence and moderate step-sizes may be adequate, The results of this study will be useful to those who are interested in the design of distillation control systems.

Self-Tuning Control Applied to an Industrial Distillation Column

The control of industrial distillation columns usually involves the implementation of dead-time compensation techniques. These compensators make use of a model of the process to eliminate the effects of the dead-time inherent in the process. Under most conditions, the implementation of such techniques brings about a noticeable improvement in the overall performance of the closed loop system. However, distillation columns are subject to changes in feed compositions, feed flow rates and various disturbances and, as a result, are forced to run under variety of operating conditions. Hence, the process characteristics change and the dead-time compensator which employs a fixed parameter model can no longer cope and a degradation in control performance is usually experienced. Therefore, the opportunity exists for employing self-tuning control strategy to ensure tight control under all operating conditions.

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.

The Computer as an Aid for the Implementation of Advanced Control Algorithms on Physical Processes

Previous to the application of advanced control algorithms to an industrial process, it is desirable to get some experience on simple processes (e.g. a pilot plant) or on simulated processes. All the described algorithms were fully tested on computer simulations, some were also applied to simple processes. Later on they were implemented on complicated, multivariable processes such as a semi-industrial cracking furnace and an industrial distillation column. It is shown that many results were predictable by the computer simulation.

Identification of a Model in Concentration of an Industrial Distillation at Low Pressure: On-line Application in View of a Control

This paper gives the results of an identification of a particular industrial distillation column with some constraining contitions. In spite of that, the models obtained by an off-line identification appear to be acceptable and the ones obtained on-line have allowed to realize a satisfying control.

Hausen and Murphree efficiencies in binary and multicomponent distillation

The design of industrial distillation columns is normally based on estimated values of plate efficiencies. Several different plate efficiency models have been proposed in the literature and among them the one presented by Murphree is widely used in spite of its limitations. However the difficulties involved in the use of Murphree's model are not present if Hausen's model is considered. In the present paper a comparative study of the two models considering both binary and multicomponent systems is presented. A graphical relationship be Experimental composition profiles obtained in small laboratory columns with binary and ternary systems are interpreted in terms of Hausen efficiencies. It is argued that the use of the Hausen efficiency model should be wider as it overcomes limitations of Murphree's model and is in agreement with physi

Deducing multicomponent distillation efficiencies from industrial data

This paper describes a study of data taken from an industrial distillation column producing benzene from a feed containing benzene, toluene and C8 arom