Günter Wozny

Experimental and theoretical studies of the dynamics of startup and product switchover operations of distillation columns

Abstract Experimental studies have been made with the help of laboratory-scale distillation columns of the startup and product switchover operations of distillation columns. The object of these studies was to minimize the time necessary from initial startup or product switchover for steady-state operations to be attained. It has been shown that the time needed can be clearly reduced by a specific mode of operation. Theoretical studies support the experimental findings. Dynamic simulation has proved to be a suitable aid for the preparation and planning of experimental studies. As a result, the time needed to reach steady state can be considerably reduced, and consequently the costs.

Experimental and theoretical studies of the steady-state and dynamic behaviour of packed columns

Abstract Experimental studies were made with the help of laboratory-scale distillation column. Concentration and temperature profiles were obtained at the steady-state operating point, and transition behaviour was observed after specific changes were made to relevant process variables. These results were compared with results obtained by means of simulation calculations. The mathematical model is explained in detail, as is the study method employed. The aim of this study was to obtain experimental verification of steady-state and dynamic calculation methods. It was found that the simulation results agreed closely with those obtained experimentally. The experimental findings thus confirmed the accuracy of the model and its underlying assumptions.

Model Based Observation and Control of Distillation Columns

Abstract 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.

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

Abstract 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.

An Analytical Approach to Modelling in Distillation Control

Abstract The development of an appropriate low order dynamic process model of a distillation column is the most important prerequisite for the design of a successful control concept. In this paper we present a second order linear process model for a distillation column that can be treated fully analytically. It gives a steady- state exact representation of the column for any control configuration in the time as well as in the frequency domain and preserves the physical significance of all parameters. Because of the low computational effort and the consistency of the modelling information it is an effective tool for control structure analysis and controller design. A systematic comparison with related work of other authors reveals the analytical strength of our unified approach. A comparison to simulation results shows the very satisfactory reproduction of the column behaviour in the low to mid frequency range as well as the high frequency deficiencies of the model. These can be attributed to the fact that higher frequency effects such as level control and hydrodynamics have been neglected in its derivation in order to ensure its analytical tractability.