Feed Flow Rate Disturbances Research Articles

Nonlinear State Control of Distillation Columns

Nonlinear state control is applied to a binary high-purity distillation column. Feedback rules are derived from the balance equations of the column to provide set-points for the inner control loops of a cascaded control scheme. For experimental implementation, the knowledge of flow and composition profiles in the column must be estimated by a suitable observer. Experiments show excellent results even for large disturbances in feed flowrate and concentration.

Linearized dynamic model of an industrial low density polyethylene plant

The dynamics of an industrial low-density polyethylene (LDP) plant are studied with the purpose of minimizing the transients generated during normal operation. The plant dynamic model allows the user to analyze the profiles for the key components when disturbances in feed flowrate, purge, ethylene conversion and/or LDP production enter the process. A block structure was implemented so as to reduce the computer time required for the dynamic simulation. All the process units and pipeling were represented by means of first or second order differential equations with dead times. Finally the model parameters were tuned on the basis of actual plan dynamic behaviour.

On‐line multivariable adaptive control of a binary distillation column

AbstractAn experimental evaluation of the simultaneous control of top and bottom product compositions of a binary distillation column utilizing multi‐variable self‐tuning control algorithms is presented. The study was carried out using an 8‐tray, 22.86 cm diameter methanol–water pilot scale column with continuous capacitance analysis of top product composition and bottom composition analyzed on a 3 minute cycle, by a gas chromatograph. Column control is studied for ±25% step disturbances in feed flow rate. Terminal composition regulation using both ‘positional’ and ‘incremental’ forms of a generalized minimum variance self‐tuning control algorithm is compared with that achieved using a conventional digital PI/PID multiloop control strategy.

Multivariable and multirate self-tuning control: a distillation column case study

This paper is concerned with the evaluation of self-tuning control algorithms for the multivariable control of distillation columns. Effective distillation control remains a key concern of industry because of the high energy consumption associated with distillation processes. The results presented here are taken from a continuing programme of investigations aimed at improving distillation column control performance. The performance of several multi-variable self-tuning strategies is evaluated by online application to a pilot-scale binary distillation column which is subjected to disturbances of ±25% step changes in feed flow rate. The performance of the multivariable algorithms is compared with that achieved using conventional digital multiloop PI/PID control. The results have demonstrated that use of multivariable self-tuning control, in particular multirate-multivariable self-tuning control, can provide better regulatory performance for feed flow rate disturbances than can be achieved using a multiloop PI/PID strategy.

Multivariable Self-tuning Control of a Binary Distillation Column

Control of distillation columns remains a key concern of industry because of the high energy consumption associated with distillation separations. The reported results, from a continuing program of experimental studies directed to improved distillation column control, are concerned with the evaluation of multivariable self-tuning control algorithms for the simultaneous control of both top and bottom product compositions. Evaluation of the performance of multivariable self-tuning control algorithms has been performed by experimental testing using a 8-tray, 30.5 cm diameter methanol-water pilot scale column. The column is controlled using a DLC LSI 11/03 microcomputer with continuous capacitance analysis of top product composition with bottom composition analyzed on a 3 min cycle, by gas chromatograph. Column control is studied for 25% step increases and decreases in feed flow rate. The performance of the multivariable algorithms is compared with that achieved using conventional digital PI/PH) control algorithms. The results have demonstrated that use of self-tuning control will provide better control performance for feed flow rate disturbances than can be achieved using well-tuned conventional multiloop PI/PTD control.

Distillation Columns—A Class of Dynamic Systems With Multiplicative Inputs

Distillation columns can be described by nonlinear state space equations but which are linear with respect to the inputs for a large domain of working conditions. For adiabatic distillation columns, these state space equations are also homogeneous with respect to the inputs and in this case the inputs act multiplicatively. Three important properties are derived from this structure concerning: 1. The equilibrium points; 2. The time scale around an equilibrium point; 3. The gain around an equilibrium point. These properties depend on the direction and the modulus of the input vector. They have been verified experimentally on the pilot distillation column of Laboratoire d’Automatique de Grenoble. The properties derived from the multiplicative effect of the inputs allow: 1) To implement a simple feedforward control technique for the compensation of the feed flow rate disturbances by maintaining the direction of the input vector. 2) To implement an open loop adaptive feedback control by taking in account the effect of the magnitude of the input vector upon the system dynamics.

Terminal composition control of a binary distillation column

Terminal composition control of a pilot scale binary distillation column operated under the control of an IBM 1800 digital computer has been studied for disturbances in feed flow rate. Conventional two point control, whereby the overhead composition is controlled by reflux flow rate and bottom composition by means of steam rate, was demonstrated to be unsatisfactory. Two alternate control systems, namely a noninteracting control system and a ratio control system were evaluated. The noninteracting control system was constructed from a transfer function representation of the distillation column dynamics, determined from a series of on-line pulse tests. The results show that a very significant improvement in the control of both compositions is achieved by using noninteracting control or the ratio control scheme suggested by Rijnsdorp compared to the behavior that results using conventional two point feedback control. However, the control performance obtained using noninteracting control was only marginally better than that using the ratio control scheme.