Batch Distillation Process Research Articles

Optimization of a Semibatch Distillation Process with Model Validation on the Industrial Site

An industrial semibatch distillation process with a chemical reaction in the reboiler is optimized to minimize the batch operation time. A detailed dynamic model is employed to describe the process and incorporated in the optimization problem. This model is validated with the measured data from the experiment directly on the industrial site. The optimal reflux ratio and the feed rate policies of the process are developed with an efficient optimization approach. It can be shown that up to 30% of the operation time can be saved with the optimal policies developed in comparison to the conventional operation. The modeling and optimization approach proposed can be readily applied to the optimization of general batch distillation processes.

Interactive supervision of batch distillation with advanced control capabilities

Industrial interest in batch distillation has increased significantly in recent years as more batch processing is being used for low-volume and high-value fine chemicals, but only a few studies of such a process has been reported in the literature concerned with advanced control. This work presents an interactive software that can be used for both simulation and control studies of a batch distillation column. The package uses a rigorous model and a suitable numerical integrator to integrate the stiff DAE system; the phase equilibria can be calculated using several thermodynamic models according to the nature of the system. Three control strategies were investigated to properly regulate the batch distillation process, namely, PID, predictive and adaptive control. Simulation results for closed loop operation are shown as well as a discussion about the recovery of more than one component in the batch column. The software shown here can be easily used to evaluate changes in all the process conditions, as well as in the controller settings, in order to minimise difficulties in the operation of such process.

Optimal operation of dynamic processes under process-model mismatches: Application to batch distillation

Optimal operation policy of dynamic process can be significantly different with and without due consideration to the process-model mismatches. In this work, a general optimisation framework is developed to obtain efficiently the optimal operation policy of dynamic processes under process-model mismatches. Neural network techniques have been used to predict the dynamic non-linear process-model mismatches. An important feature of the optimisation framework is that it allows the use of discrete process data in a continuous model to predict discrete and/or continuous mismatch profiles. The method is applied to an inherently dynamic batch distillation process and is demonstrated with an example. Neural network technique is found to predict dynamic mismatch profiles for this process with sufficient accuracy. Optimal operation policy using a simple model with mismatches, predicted by the neural network, is found to be very close to that of the actual process.

Synthesis of ETBE: Residue curve maps for the heterogeneously catalysed reactive distillation process

The liquid phase synthesis of octane-enhancing ethers is increasingly realized as a reactive distillation process, catalysed by ion exchange resins. To study the physical and chemical phenomena occurring in these systems, the present paper considers a reactive batch distillation process in a heated still. Because of its increasing technical importance, the synthesis of ETBE (ethyl tertiary butyl ether) from ethanol and isobutene is investigated as an example.

Residue curve maps for heterogeneously catalysed reactive distillation of fuel ethers MTBE and TAME

The liquid-phase synthesis of octane enhancing ethers like methyl tertiary butyl ether (MTBE) or tertiary amyl methyl ether (TAME) is increasingly realized as a reactive distillation process catalysed by ion exchange resins. To study the occurring physical and chemical phenomena of those systems, the present paper deals with a reactive batch distillation process in a heated still. The model is based on phase equilibrium between the liquid and the vapour phase and an adequate kinetic formulation of the heterogeneously catalysed etherification by application of the generalized Langmuir-Hinshelwood rate expressions. To describe the non-ideal mixture behaviour, liquid-phase activities are introduced. Simulation results show that the shape of residue curves depends on two essential parameters, the Damköhler number Da and the operating pressure p. The values of these parameters influence the existence and the position of stable nodes, saddles and separatrices in the residue curve map. The evaluated trajectories deviate quantitatively from those recently reported for homogeneous catalysis. The most interesting result lies in the fact that the lightest boiling component can be enriched in the still.

Batch Distillation of Multicomponent Systems with Constant Relative Volatilities

A method is proposed for the shortcut simulation of multicomponent batch distillation operations. The method relies on the assumption that a given batch column can be approximated with one having an infinite number of stages, so that the Underwood equations developed for the design of continuous columns can be applied to evaluate the evolution of product compositions during the batch. The results obtained represent the limiting fractionation that can be obtained when the number of stages becomes large. A rigorous, computationally efficient model is also developed within the assumptions of constant relative volatilities, constant molal overflows, and negligible stage holdup. Three operating modes are considered: constant reflux ratio, constant composition of one component in the overhead product, and total reflux. Examples are presented showing that the shortcut model allows close approximation to the results given by the rigorous model. The computational demand of the shortcut model is very low, so that it can be profitably used as a tool for preliminary batch distillation process design, simulation, and optimization.

Evolution of Pinch-Point Zones in Multicomponent Distillation Columns. 1. Rectifying Section

The principles concerning the evolution of pinch-point zones with variation of the reflux ratio in the rectifying section of a multicomponent distillation column with an infinite number of stages are presented in this work. Analytical formulas are obtained for calculating the pinch-point zones as well as the distillate exactly. It has been found that the evolution of pinch-point zones in the stripping section is much similar to the evolution of pinch-point zones in the rectifying section. Based on these new findings, a new method for calculating the minimum reflux ratio of multicomponent continuous distillation, as well as a new shortcut method for the design calculation of a batch distillation process, can be developed.

Understanding batch distillation process principles with MultiBatchDS

This article describes the MultiBatch Distillation Systems MultiBatchDS for simulation, optimal design, and control of batch distillation columns with multiple configurations, multiple operating modes, and multiple fractions with multiple levels of models. The use of this package as a teaching aid for explaining batch distillation fundamentals is presented. © 1996 John Wiley & Sons, Inc.

Understanding batch distillation process principles with MultiBatchDS

This article describes the MultiBatch Distillation Systems (MultiBatchDS) for simulation, optimal design, and control of batch distillation columns with multiple configurations, multiple operating modes, and multiple fractions with multiple levels of models. The use of this package as a teaching aid for explaining batch distillation fundamentals is presented. © 1996 John Wiley & Sons, Inc.

Separation of azeotropic mixtures by batch distillation using an entrainer

Batch Distillation is an efficient unit operation which allows the separation of a multicomponent mixture into its components in a single column. However, the separation of azeotropic mixtures via distillation is quite complex because at the azeotrope liquid and gas have the same composition and, therefore, the driving force for distillation disappears. A systematical presentation of batch distillation processes for separating binary azeotropic mixtures using an entrainer is given.

Dynamic optimization of multicomponent batch distillation processes using continuous and discontinuous collocation polynomial policies

Optimization of batch distillation has been studied extensively over the last 30 years. Previously, the solution methods were basically derived or computed using short-cut models due to the lack of suitable computation techniques. In this study, a modified approach based on the work of Biegler and coworkers (L. T. Biegler, Comput. Chem. Eng., 8 (1984) 243; J. E. Cuthrell and L. T. Biegler, AIChE J., 8 (1987) 1257) was implemented to determine optimal constrained solutions for a ternary system with various objective functions, such as maximum product, minimum energy required and mininum end time, using a rigorous model. Unlike previous investigations, the optimal control solutions derived in this study were independent of the process model implemented. Therefore, no limitation on the distillation models exists, i.e. any rigorous model can be used to find solutions. The optimal control problem for the batch distillation of mixtures of benzene, toluene and o-xylene was solved. The solutions were assumed to be continuous or discontinuous polynomials. It was found that a discontinuous solution is superior to continuous results because of the discontinuous nature of the system itself.

Comparison of Several Startup Models for Binary and Ternary Batch Distillation with Holdups

In batch distillation processes, the startup operation is one of die important operations which affect the overall separation performance. There are different startup models which were utilized when analyzing batch distillation operation. In this research, four different models (Models A, B, C, and D) representing the dynamic behavior of startup operation for binary and ternary batch distillation have been simulated and investigated. The effect of operation and design parameters such as the tray and reflux drum holdups, amount of feed, product specification, number of trays, and relative volatility on startup time were studied and analyzed for all the above models. Linear correlations governing the startup time were obtained in terms of the holdups of trays and reflux drum. These correlations could be used to determine startup time for different combinations of these holdups. The effect of the startup time on the overall separation performance was also analyzed. For most of the cases, it was found that startup time and the composition profile through the column at the end of startup for simple Model A and complicated Models Cand D are quite the same. The overall separation performance is a function of the startup time and the column's profile. Thus, the simulation result means that simple Model A is sufficient in representing the startup operation of batch distillation.

Combining Adaptive and Neural Control for Distillation Control

Abstract Although developments in the computer industry have moved towards highly integrated parallel processing, the control industry generally only makes use of the computer as a digital numerical manipulation tool for controlling the plant with a monitoring ability for failure detections. However it seems sensible to suggest a controller design which makes much better usage of the parallel processing capabilities of the computer. Different types of control algorithms with a certain degree of intelligence can work in parallel, leading to an intelligent controller that can adapt to environmental and parameter changes. This gives the possibility of better control performance under increased uncertainty, learning abilities and the possibility of intelligent fault tolerant design. In this paper, a simple parallel control scheme is presented tor the control of the reflux, reboiler and condenser in a batch distillation process.

Inferential model-based control of multicomponent batch distillation

Industrial interest in batch distillation has increased significantly in recent years as more batch processing is being used for low-volume high-value specialty chemicals. Most studies have concentrated on the determination of optimum operating strategies: optimum trajectories of reflux ratio and pressure during the batch and processing of the slop cuts that are produced. Little attention has been paid to the problems of control. If instantaneous and perfect analyzers were available, the control of batch distillation would be straightforward once the optimum policies are available. Switching from total-reflux operation to producing product and from this to slop-cut production could be performed when compositions in the reflux drum or in product tankage reached the desired values. However, in most industrial applications of batch distillation, perfect composition measurements are not available. This means that an inferential control system that relies on temperature and flow measurements must be used. Models of the batch distillation process can be used to provide estimates of the required compositions. This paper presents the results of a study of two types of model-based inferential control systems for multicomponent batch distillation. The results showed that both steady-state and dynamic estimators provide good estimation of the distillate compositions using only one temperature measurement.

Modeling of multicomponent batch distillation processes with chemical reaction and their control systems

In this paper a process model will be presented which is based on nonideal stages, takes account of chemical reactions, and incorporates simulation of the process controllers. A combination of the two-point implicit method and the 2N+1 Newton-Raphson Method as described by Wozny . (1987) for the simulation of continuous distillation processes and their control systems is used.

Simulation of multicomponent batch distillation processes

A procedure has been developed to simulate the operation of multistage, multicomponent batch distillation operations. The unsteady state is simulated as a succession of a finite number of stationary states of short duration. For each time interval, the solution is carried out using a mathematical model corresponding to continuous distillation. Holdup is taken into account. The robustness of the procedure is the same as for a continuous distillation model (UNIDIST) and is not influenced by the time integration procedure. The computational efficiency of the method is found to compare very favourably with traditional methods using rigorous algorithms for the integration o Comparison between predicted distillation-time profiles and experimental values shows good agreement.

Fuel-Composition Effects on High-Temperature Corrosion in Industrial/Commercial Boilers and Furnaces: A Review

In this review, literature relevant to the problems of deposits and corrosion in industrial/commercial furnaces and boilers is analyzed, and the facts are synthesized into a picture that addresses corrosion problems expected with the use of unconventional fuels. Corrosion is found to depend greatly on the phenomena occurring during the combustion of fuel-oil sprays introduced into the furnace. In a first step, the drops that form the spray heat up and evaporate in a way that closely resembles a batch distillation process. Eventually, ignition and combustion occur with the subsequent change of the liquid fuel drops into carbonaceous, porous, sphere-like particles called cenospheres. In a second step, these cenospheres burn and the products of this combustion step determine the majority of the deposits on metal surfaces. This observation is very important since nonvolatile, non-combustible, corrosive trace compounds existing in the initial fuel-oil drop will have a much higher concentration in the cenosphere than in the original fuel. Accordingly, it is recommended that the theoretical and experimental study of oil spray combustion, cenosphere formation, and cenosphere combustion in a cloud of cenospheres receive a very high priority. Corrosion by gases is found to be unimportant. Deposits are found to be much more corrosive when in liquid form, although corrosion by solid deposits is by no means negligible. As a result, it is suggested in the study that corrosion on highly polished metal surfaces should be studied in order to evaluate the potential of this method of inhibiting deposition and thus hindering corrosion. Recent advances in the theory of deposition from combustion gases are also outlined in this study. The literature survey shows that the main corrosion-causing fuel constituents present in unconventional fuels are sulfur, alkali, vanadium, carbon and carbon monoxide, iron, and chloride. It is found that sometimes one of these compounds might act as a catalyst in corrosive reactions initiated by another compound, and therefore great care must be taken to identify the corrosion-causing compound in the deposits on metal surfaces. It is also found that in some cases a corrosive compound will inhibit the corrosive action of another corrosive compound. It is recommended that such situations be studied further so as to investigate the possibility of an optimum concentration of two such corrosive compounds that would minimize metal wastage. The problem of performing meaningful corrosion experiments is also addressed in this report and specific recommendations are made to achieve this goal. Finally, the effects of additives and the furnace operating conditions are discussed, and potential problems with both additives and new operating conditions are mentioned. The recommendations at the end of this study present a comprehensive set of areas to be investigated in order to better understand and be able to mitigate corrosion problems associated with unconventional fuels. High-priority experimental and theoretical studies are also outlined.

On the dynamics of distillation processes—VI. batch distillation

We have developed a simple model which explains the behavior of azeotropic batch distillations. The model is in agreement with known experimental results and explains features of the distillation process which have previously been considered anomalous. The model can be used to design batch distillation processes operating at either infinite or finite reflux ratios.

On the profit of optimum control in batch distillation

Using a profit function, in which the start-up time and several cost factors are taken into account, optimum reflux policies for binary batch distillation processes with negligible hold-up are calculated. The optimum in controlling is compared with the conventional constant-overheads composition and constant reflux policies. Calculations are made for a wide variety of cases. It is possible to systemise the results by introducing two dimensionless numbers. The first number, containing only process parameters, is a measure of the difficulty of a separation. The preference for one of the three reflux policies considered will be found to depend strongly on this number. The second dimensionless number combines the influences of the cost factors and the start-up time. By means of these numbers a simple rule of thumb is formulated, which predicts when optimum control is worth while.

The optimal control of an industrial batch distillation column

Reflux policies were calculated for a batch distillation process in which a fixed quantity and purity of a multicomponent product was required. The policies calculated, neglecting hold-up, were the constant reflux, constant overhead purity and minimum time methods of operation, the latter were similar and predicted that the constant reflux ratio time of 12·35 hr could be reduced by 3 hr using either of these variable reflux schemes. Experiments on a 30 theoretical stage industrial batch still processing a 10 component turpentine mixture showed that hold-up could not be ignored, even though this totalled less than 4 per cent of the initial still charge. A sub-optimal control scheme was therefore found which took hold-up into account. Using this policy the plant produced the required product in 10 hr 40 min compared with 12 hr 20 min using a constant reflux, a saving of 13·5 per cent. ln both cases the product was the same.