Design and operating targets for nonideal multicomponent batch distillation

Batch distillation for separating the acetone and n-heptane binary azeotrope mixture: Optimization and simulation

Chapter 11 - Distillation

Inferential model-based control of multicomponent batch distillation

This article presents a unified approach to simultaneous solution of optimization and optimal control problems in batch distillation, operating under different modes of operation: variable, constant, or optimal reflux. The simplified, computationally efficient short‐cut method and a novel algorithm to solve the optimal control problems in batch distillation is the basis of this unified approach. The short‐cut method identifies the feasible region of operation essential for optimization and optimal control problems, and provides analytical partial derivatives of the model parameters crucial to the solution.The new algorithm for the solution of optimal combination of the maximum principle and NLP optimization techniques. It circumvents the problems associated with the maximum principle approach (iterative solution of a two‐point boundary value problem, undounded control variables, and inability to handle the simultaneous optimization and optimal control problem), and the coupled ODE discretization‐NLP optimization scheme for nonlinear models (higher system nonlinearities, multiplicity of solutions, sensitivity of convergence to initial guesses). This algorithm reduces the dimensionality of the problem, and the nature of the algorithm allows a common platform to optimal solutions of different operating conditions. This article also shows that different categories of the optimal control problems in batch distillation essentially involve the solution of the maximum distillate problem.

ABSTRACTUnlike the past work, the optimal operation policy, which minimizes the total batch time is derived for multivessel batch distillation (MVBD) for separation of binary components under constant total reflux. In this article, both the distribution of vessels along the MVBD column and the holdup in each vessel are optimized to minimize the total batch time. Furthermore, the time consumption of the optimal operation policy is also compared with that of the regular constant reflux operation theoretically and experimentally. The results show that the novel operation mode has great advantages in time saving and easy operation by adopting the optimal operation policy. Thus, for a given separation task, MVBD column reveals significant potential for separation with higher efficiency. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Synthesis, experiments and simulation of heterogeneous batch distillation processes

The distillation-based separation of ideal liquid mixtures has been comprehensively studied. The optimization of the different separation structures has allowed the development of general heuristic rules to aid the designers in finding good solutions quickly for the type of problem at hand. The separation of nonideal mixtures is also an exhaustively studied area, but because of the complexity of the vapor−liquid−liquid behavior of such mixtures, it is more difficult to suggest guidelines for synthesis in separation sequences. On the other hand, recently several special so-called hybrid separation tools have also been involved in that kind of synthesis task, complicating further the synthesis problem. To obtain some general conclusions for the separation structure synthesis of such mixtures, in this study the separation of two nonideal quaternary mixtures containing one nonazeotropic-forming component (most volatile or least volatile) is studied based on optimization of the separation structures. The separation schemes involve the so-called extractive heterogeneous azeotropic distillation, which is a novel hybrid separation process. The economic optimization of the different separation structures results in the conclusion that the heuristic rule for ideal mixtures, that is, “easy separation first should be done and the complicated one should be made last”, is valid also for such nonideal mixtures.

Optimisation of design and operation policies of binary batch distillation with fixed product demand

A multiple-input and multiple-output (MIMO) model, namely Recursive Orthogonal Least Square (ROLS) based radial basis function (RBF) is developed to estimate product compositions in a batch distillation process from temperature measurements. The process data is generated by simulating the differential equations of the batch distillation process, changing the initial feed composition and boiluprate from batch to batch. Moreover, the reflux ratio is also randomly varied within each batch to represent the exact dynamics of the batch distillation. Temperature and distillate composition is correlated by the RBF trained by ROLS algorithm. A Single RBF network estimate the quality of products in real-time. The results show that ROLS based estimator give correct composition estimations for a batch distillation process. The robustness of the ROLS algorithm and low computational requirement makes the estimator attractive for on-line use.

Neural-Network Approach to Dynamic Optimization of Batch Distillation: Application to a Middle-vessel Column

Patterns of composition change in multicomponent batch distillation

This study focuses on determining the feasibility of obtaining maximum mole percentage of acetone (99 mole%) in the distillate stream from a 3 mole% acetone waste stream using batch distillation. The device which is used in this work has eight trays that will act as the stages of the batch distillation. The effects of varying reflux ratio and heat load (power) on acetone concentration were studied. Moreover, the operating conditions for the bath distillation column such as flooding and weeping with the extreme limits of operation were considered. The temperatures were also be recorded at each tray. The McCabe-Thiele method was used to determine the theoretical number of trays and compared with actual trays (column efficiency). For a chemical analysis of acetone/water compositions a refractometer was used for a chemical analysis, known acetone/water concentrations were analysed and used to construct a calibration curve. The results obtained showed that, the acetone concentration increases with increasing reflux ratio until a highest concentration was reached. Then, the concentration gradually decreases with increasing reflux ratio. However, the distillate stream with 99 mole % acetone was achieved at a reflux ratio of R=3 and at both powers 0.5 kw and 0.7 kw. Finally, the highest overall column efficiency reached by this work was about 75%.

An optimization module for batch distillation with intermediate cuts

Integrating product and process design with optimal control: A case study of solvent recycling

Conventional batch distillation and middle-vessel batch distillation were studied for the separation of the ternary system of cyclohexane/n-heptane/toluene, which has low relative volatilities. The modified variable and constant reflux operations were applied in the conventional batch distillation. Two control structures were used: one of which was referred to as the composition control structure with a modified level-set point, and the other was referred to as the flowrate-limiting control structure. Thus, the middle-vessel batch distillation was able to simultaneously separate the components of the ternary mixture. Comparing the two control structures showed that the flowrate-limiting control structure was better than the composition control structure with a modified level-set point in terms of their applicability. Disturbances were introduced to assess the controllability of the flowrate-limiting control structure. The dynamic responses demonstrated that the control structure performed well. The results showed that the modified conventional batch distillation and middle-vessel batch distillation increased the purity of the separated components compared to previous studies.