Multicomponent Batch Distillation Column Research Articles

Solution of the maximum distillate on a batch distillation column by a Pseudo-Newton method

This paper presents a new algorithm for the solution of the maximum distillate problem based on Pontryagin's maximum principle. Four cases of study were analyzed with the algorithm. The first case is a literature problem where the column uses twenty trays to distillate ten components, the second case is a binary mixture with no ideal behavior, the third case is a quaternary mixture, and the last case is a reactive mixture. In all cases, the desired purity was settled as a final constraint. The solution algorithm found the optimal control faster than results reported in literature concerning the CPU time.The batch distillation process is modeled by using a rigorous model with no constant volatility. The proposed algorithm uses the Hamiltonian function to reformulate the maximum distillate problem. Then, the optimal control is solved by a Broyden–Fletcher–Goldfarb–Shanno algorithm. The solution procedure of the indirect approach required the forward integration of the states, the integration of the co-state equations backward in time, and the control input is the distillate flow rate which is parameterized. The binary batch distillation column uses six stages, and the maximum recovery is 95% of the light component with a 95% mol percent on the accumulator. The multicomponent batch distillation column uses 17 stages, and the recovery of the lightest component in the product is 90% mol percent. The reactive case reached 80% conversion.

Comparative Control Study of a High-Purity Ternary Batch Distillation

This paper presents a comparative closed-loop performance study on a multicomponent batch distillation column that produces high-purity distillate product. Initially, the distillation model representing a ternary system of cyclohexane-toluene-chlorobenzene has been simulated to observe the open-loop dynamics at the start-up as well as production phase. The next three control schemes, namely classical proportional integral (PI) controller, nonlinear proportional integral (NLPI) control strategy and gain-scheduled proportional integral (GSPI) law, have been designed and applied on the simulated distillation column. Numerical experiments based on servo and regulatory tests show that the GSPI algorithm provides relatively better results than the other two PIs.

Nonlinear adaptive control algorithm for a multicomponent batch distillation column

In this article, a nonlinear adaptive control strategy is proposed for a multicomponent batch distillation column. The hybrid control scheme consists of a generic model controller (GMC) and a nonlinear adaptive state estimator (ASE). In the first part of the study, an adaptive observer is designed aiming to estimate the partially known parameters based on the measured compositions in the presence of process/predictor mismatch. The open-loop dynamic behavior of the developed ASE estimator is investigated under initialization error, disturbance, and uncertain parameters. In the subsequent part, the adaptive GMC–ASE controller (GMC control structure in conjunction with ASE estimator) has been synthesized for the example distillation column. A simulation-based comparative study has been conducted between the derived nonlinear GMC–ASE control algorithm and a gain-scheduled proportional integral (GSPI) law in terms of constant composition control. The proposed adaptive control scheme is shown to be quite promising due to the exponential error convergence capability of the ASE estimator in addition to the high-quality performance of the GMC controller.

State Estimator Design for Multicomponent Batch Distillation Columns

In the control of batch distillation columns, one of the problems is the difficulty in monitoring the compositions. This problem can be handled by estimating the compositions from readily available online temperature measurements using a state estimator. In this study, a state estimator that infers the product composition in a multicomponent batch distillation column (MBDC) from the temperature measurements is designed and tested using a batch column simulation. An extended Kalman filter (EKF) is designed as the state estimator and is implemented for performance investigation on the case column with eight trays separating the mixture of cyclo-hexane, n-heptane and toluene. EKF parameters of the diagonal terms of process noise covariance matrix and those of measurement model noise covariance matrix are tuned in the range where the estimator is stable and selected basing on the least IAE score. Although NC-1 temperature measurements is sufficient considering observability criteria, using NC measurements spread through out the column homogeneously improves the performance of EKF estimator. The designed EKF estimator is successfully used in the composition—feedback inferential control of MBDC operated under variable reflux-ratio policy with an acceptable deviation of 0.5–3% from the desired purity level of the products.

EKF and ANFIS Estimator Design in Multicomponent Batch Distillation Columns

In the control of batch distillation columns, one of the problems is the difficulty of monitoring the compositions. This problem can be handled by estimating the compositions from readily available online temperature measurements using a state estimator. In this study, an extended Kalman Filter (EKF) and an Adaptive Neuro-Fuzzy Inference System (ANFIS) state estimators that infer the product composition in a multi component batch distillation column (MBDC) from the temperature measurements are designed and tested using a batch column simulation. The designed EKF and ANFIS estimators are successfully used in the composition – feedback inferential control of MBDC operated under variable reflux-ratio policy with an acceptable deviation from the desired purity level of the products

Optimal programming of ideal and extractive batch distillation: single vessel operations

This work addresses the problem of optimal programming of multi-component batch distillation columns with a single vessel (batch rectifier, batch stripper, middle vessel and extractive middle vessel) so as to maximize an annualized profit function. A smooth price function is formulated for product valuation, allowing to release traditional purity constraints. The solution is the optimal batch policy of top/bottom withdrawals. A simplified cascade model is developed for separation calculations, offering several operational patterns. Ideal and non-ideal mixtures can be handled with this model that is proposed as a substitute for traditionally used Fenske–Underwood–Gilliland cascades. Batch separations of ideal quaternary feeds are optimally programmed for the first three operations aforementioned. The extractive middle vessel column was optimally programmed for production of anhydrous ethanol from hydrated, nearly azeotropic, alcohol with ethylene–glycol as entrainer. All applications considered fixed number of stages, heat duty, and, in the extractive system, fixed pump-around rate of entrainer.

Inferential Control of High-Purity Multicomponent Batch Distillation Columns Using an Extended Kalman Filter

To control the sequencing of the batch distillation steps and to guarantee that all products will meet their purity specifications, this work has proposed an inferential control system for high-purity multicomponent batch distillation columns, that is able to cope with difficulties commonly encountered in practice, including lack of on-line composition analyzers, plant/model mismatch, uncertainty in the initial system state, and measurement noise. An extended Kalman filter has been implemented to provide updated composition estimates from temperature measurements, and globally linearizing controllers have been designed to control the distillate composition. The choice of the number and location of temperature sensors, as well as the sensitivity of the controller settings to changes in the operating conditions, has also been discussed. Tight composition control was achieved, and the proposed inferential control scheme was shown to be robust and suitable for practical implementation.

Simulation of a Multicomponent Batch Distillation Column with Total Reflux through the Distillate Receiver

A shortcut procedure applicable to a multicomponent distillation in a batch column with a distillate receiver under total reflux condition was developed. It is based on the assumptions of constant molar overflow, constant vapor boilup rate, and constant relative volatilities. The effect of liquid holdup in each stage and condenser is taken into consideration in modeling the dynamic behavior of the batch column. Estimates of the volume of the distillate receiver, changes in compositions in the receiver and still, concentration profiles of the column, and total distillation time required to complete the separation can be made in the proposed model. Illustrative calculations were performed for the separation of a quaternary system for two cases: an initially empty distillate receiver and an initially filled-up distillate receiver.

Rigorous simulation of conventional and unconventional multicomponent batch distillation behavior for startup and production periods

A comparative study applied to multicomponent batch distillation using, for the reactive cases, conventional and unconventional column configurations is presented. Many other works in the literature have shown similar studies but much of them did not compare with experimental data nor use a rigorous software package either. Here the program called (ctive istillation namic imulator) is used for rigorous simulation purposes. This package permits the solution of a wide range of distillation problems accounting for simultaneous design, operation and control analysis, for single and multiple duties. Four example problems, two of them involving a reactive batch distillation column for the ethyl acetate production and its inverse configuration respectively. This last case was specially developed for this work in order to study such a system starting from the experimental data of the first case. The other two examples correspond to conventional multicomponent batch distillation columns, one of them using an optimal reflux ratio profile and operation conditions. The data employed for three examples are taken from experimental cases published in the literature. In addition the predicted dynamic behavior of a batch distillation column for separating a ternary mixture, obtained by, is compared with the results given by two well-known commercial software in order to evaluate its performance for implementing them in an inferential control structure inspired in the extended Luenberger observer design philosophy.

Simultaneous optimization of design and operation of multicomponent batch distillation column—single and multiple separation duties

A method is presented for the simultaneous optimization of a batch distillation column design and its operation, for single and multiple separation duties, each involving different multicomponent mixtures and complex operations with intermediate cuts. For operation structures selected a priori, the formulation presented permits the use of general distillation design and cost models. The objective function and constraints include capital and operating cost. In particular, the number of internal plates is optimized along with the most significant operating variables (recoveries in various cuts and reflux ratio profiles and times). The multiple duty formulation presented accounts for the different importance of each duty and setup time between batches. Application of the method to single duty multicomponent separation from the literature shows that significant profit improvements can be achieved within acceptable computing times. For multiple separation duties (two binary mixtures), the method clearly shows the importance of including allocation time to each duty and setup time for each batch in the objective function.

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

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.

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.